Title of Invention	AN IMPROVED PROCESS FOR THE PRODUCTION OF NITRIC ACID
Abstract	Process for the production of a nitric acid having a concentration of 75 to 99.9% from a more diluted, optionally impure nitric acid, wherein a nitric acid of a concentration of about 45 to 70% is rectified at a pressure from 100 mbar absolute to 5 bar absolute by contacting it with a liquid extraction medium for preventing the formation of a nitric acid-water azeotropic mixture, the vapors of the concentrated nitric acid is obtained, and wherein, additionally, the extraction medium is recovered by re concentration at a pressure in the range from 50 mbar absolute to 4 bar absolute and returned to the extractive rectification, characterized in partially or substantially utilizing the heat contents of the available process streams of the entire process and feeding the nitric acid to be concentrated in the form of a boiling liquid or partially vaporized or separated into vapor and liquid into the extractive rectification, utilizing the heat contents available in the entire process (Wl, W2, W5), and enriching at least 50% of the amount of extraction medium before feeding it at a temperature in the range from 80°C to 160°C into the extractive rectification in an amount of 0.1 to 60% of the nitric acid to be concentrated with nitric acid, preferably a nitric acid in the concentration range of the nitric acid to be concentrated, and supplying the energy required for the extractive rectification exclusively, or to a substantial proportion thereof by indirect heating (W4, W8) and supplying the extraction medium to the extractive rectification in a form as concentrated as possible, such that when at the same time the extraction medium leaving the extractive distillation is as diluted as possible, the circulating amount of extraction medium is minimized.

Title of Invention

AN IMPROVED PROCESS FOR THE PRODUCTION OF NITRIC ACID

Abstract

Process for the production of a nitric acid having a concentration of 75 to 99.9% from a more diluted, optionally impure nitric acid, wherein a nitric acid of a concentration of about 45 to 70% is rectified at a pressure from 100 mbar absolute to 5 bar absolute by contacting it with a liquid extraction medium for preventing the formation of a nitric acid-water azeotropic mixture, the vapors of the concentrated nitric acid is obtained, and wherein, additionally, the extraction medium is recovered by re concentration at a pressure in the range from 50 mbar absolute to 4 bar absolute and returned to the extractive rectification, characterized in partially or substantially utilizing the heat contents of the available process streams of the entire process and feeding the nitric acid to be concentrated in the form of a boiling liquid or partially vaporized or separated into vapor and liquid into the extractive rectification, utilizing the heat contents available in the entire process (Wl, W2, W5), and enriching at least 50% of the amount of extraction medium before feeding it at a temperature in the range from 80°C to 160°C into the extractive rectification in an amount of 0.1 to 60% of the nitric acid to be concentrated with nitric acid, preferably a nitric acid in the concentration range of the nitric acid to be concentrated, and supplying the energy required for the extractive rectification exclusively, or to a substantial proportion thereof by indirect heating (W4, W8) and supplying the extraction medium to the extractive rectification in a form as concentrated as possible, such that when at the same time the extraction medium leaving the extractive distillation is as diluted as possible, the circulating amount of extraction medium is minimized.

Full Text	PROCESS FOR PRODUCING CONCENTRATED NITRIC ACID AND INSTALLATION TO CARRY OUT THE PROCESS [0001J The invention relates to a process for producing a nitric acid with the concentration of 75 to 99.9 % from a diluted, respectively an impure nitric acid, wherein a nitric acid of a concentration from about 45 to 70 % is brought into contact with a fluid extraction medium to prevent formation of a nitric acid-water-azeotropic mixture, which is rectified above normal pressure and/or normal pressure and/or vacuum and wherein the vapors of the concentrated nitric acid are condensed to thereby obtain a concentrated nitric acid, and wherein additionally, the extraction medium is regenerated and by means of reconcentration returned to the extractive rectification; as well as an installation for carrying out a preferred embodiment of such a process. [0002] Nitric acid of higher concentration, oftentimes more than 98 % by weight HNO3, is required for many organic reactions such as, for example nitrogenizations. [0003] Conventional production methods produce nitric acid of about 65 to 67 % by weight HNO3. Thus, an additional process is required in order to obtain highly concentrated nitric acid. The most suitable process for concentrating nitric acid beyond the azeotropic point is the extractive rectification. Thereby, liquid extraction media are used, in particular concentrated sulfuric acid or aqueous 1 solutions of magnesium nitrate solutions, wherein the extraction medium used is predominantly sulfuric acid. [0004] The thermodynamic bases of the extractive rectification utilizing an extraction medium are as follows: [0005] The component system, nitric acid/water exhibits at ambient pressure (1 bar absolute) a maximal azeotropic mixture with a boiling point temperature of 121.8°C at 69.2 % weight HNO3. For nitric acid concentrations below the azeotropic point, water is the more volatile component. Above the azeotropic point, HNO3 is contained in the vapor phase in higher concentration. For production of highly concentrated nitric acid, it is necessary to circumvent the azeotropic point or respectively to overcome it. It has been known for a long time that with the aid of extraction medium, such as for example sulfuric acid or aqueous magnesium nitrate solutions, the relative volatility of water can be reduced. For higher extraction medium concentrations, such as for example sulfuric acid concentrations of higher than 50 % by weight H2SO4, the formation of an azeotropic point is suppressed. Thus, concentrated nitric acid can be distilled therefrom. [0006] The basic process of concentrating nitric acid is by Pauling (DE 305553. DE 1056095). The process is industrially exploited on a large scale, in technically varying installations. A modern industrial method which is carried out 2 with the extraction medium sulfuric acid is described in the following paragraph for a better understanding of the invention (Schott Engineering GmbH, printed to 60014 D. 8895.0; Comp. Figure 1). The actual process is essentially carried out in a concentration column (RK in Figure 1), into which the concentrated sulfuric acid is supplied and somewhat below, the diluted nitric acid. By mixing the components, mixing-and condensation temperatures occur in the column. These amounts of heat are however not sufficient to cover the required energy requirement for the process. Thus, at the foot of the column, steam ("stripping steam") is directly blown into. Aside from its function as a heat carrier, this direct steam effects that the nitric acid is substantially stripped from the diluted sulfuric acid that is running off. The vapors of the concentrated nitric acid, which are given off at the head of the column CHNO3 exhaust vapors") also contain nitrogen oxides, which are formed by the thermal decomposition of nitric acid. These nitrogen oxides (essentially NO2) are at the same time condensed within the HNO3 exhaust vapors to red smoking nitric acid. In order to obtain the condensed highly concentrated nitric acid in colorless form, the nitric gases contained in the acid are stripped off by air in a countercurrent downstream column, a so-called bleaching column. The waste gases, which contain nitrogen oxides, are cleaned in a subsequent NO2 absorption step. [0007] A complete installation for producing highly concentrated nitric acid comprises aside from the installation for the nitric acid rectification, additionally an installation branch for the extraction medium reconcentration. The installation 3 parts for the afore-described bleaching of the smoking nitric acid, as well as the downstream NOx absorption are also added. It is also appropriate to provide a pre-concentration for the nitric acid to be concentrated ("feeding acid") having a concentration of less than about 58 % by weight HNO3. Beyond that, it could also be appropriate to purify the nitric acid through steaming. All parts of the entire installation have to be optimally designed in order to fulfill the required specification with respect to product quantity and wastewater purity with minimal use of resources. The resource consumption and specifically the heating energy requirement decidedly determine the operational cost of the process. [0008] In order to minimize the resources consumption, the required heating energy has to be supplied and utilized optimally in the process. In the classic process, the supply of heating energy is effected directly with steam, the stripping steam. Early on, it was tried to save on direct steam since it could be shown that thereby the requirement of extraction medium (sulfuric acid) can be minimized. [0009] In practice, several solutions have been carried out In the process where aqueous magnesium nitrate solutions is used as extraction medium, early on, a sump heater was utilized (cf. Ullman's Enzyclopedia of Technical Chemistry; 4th Edition, Volume 20, p. 325). In the process wherein sulfuric acid is used, a so-called intermediate heater, also called a column heater and has 4 being utilized for a long time (Uliman's Encyclopedia of Technical Chemistry; 4th Edition, Volume 20 p. 325). [0010] Furthermore, it is known that it is possible to save heating energy when reflux (internal and/or external) is reduced in the extraction rectification column. An internal reflux occurs for example, when the entry temperature of the extraction medium is lower than the boiling point temperature of the three component mixture, so that a certain amount of heat is first taken up by the extraction medium by partial condensation from the components of the vapor phase. [0011] In the conventional methods, where pure extraction medium is deposited at the head of the extractive rectification column, such as for example sulfuric acid, this extraction medium will first condense nitric acid so that the composition of the fluid mixture is moved into the direction of the equilibrium with the vapor phase. It follows, that the extraction medium has to be deposited in sufficiently cold condition to thereby effect an elevated internal reflux. This leads to an additional amount of heat which in turn can be supplied by means of additional heating energy to the extractive rectification. [0012] It is known that by supplying liquid nitric acid (for example, a partial amount of the nitric acid to be concentrated) to the extraction medium, the condensation behavior of the nitric acid in the column for the extractive 5 rectification can be influenced. Accordingly, EP 0330351 81 ("Gunkei") described an admixture of the nitric acid to be concentrated to a partial stream of the extraction medium. A disadvantage of the method described by Gunkei is how ever, that the mixture stream of nitric acid to be concentrated and extraction medium is first input below a further amount pure extraction medium already input at an upper location. Thus, the afore-described desired effect of reducing the internal reflux is not attained in the process described in EP 0 330 351. [0013] A further disadvantage of the process according to Gunkei is that the entire process comprising also the reconcentration of the extraction medium, the required energy has already been completely supplied to the extractive rectification, although the energy requirement of the extractive rectification is substantially lower than the energy requirement of the extraction medium-reconcentration. With an energy supply of this type, a high amount of extraction medium is necessary for circulation and a large minimum diameter of the extractive rectification column is required. [0014] In the process as described by Gunkei 51 to 99 % of the amount of nitric acid to be concentrated is fed into the extractive rectification in totally vaporized form. Through this type of input, the amount of steam in the column is substantially raised, so that in connection with the raised amount of extraction medium in circulation, columns of greater diameter are required for the extractive rectification. 6 [0015] A further disadvantage of the process described by GQnkel is that at the head of the column a substantially higher reflux amount of highly concentrated nitric acid is required in order to obtain highly concentrated nitric acid vapor containing 99 to 99.9 % by weight HNO3. [0016] Until now, in all installations that have been established for highly concentrating subazeotropic nitric acid (weak acid) to nitric acid having more than 90 % by weight, preferably more than 98 % by weight ("hico-acid") the energy requirement, such as for example, heating steam and cooling water determined the production costs substantially. Thus, in larger installations as they were commonly established in the immediate past, (with sump heater and/or intermediate heater) starting from an HNO3 of 67 % by weight, heating steam amounts of about 1.5 kg per kg produced 99 % by weight of nitric acid were required. [0017] Thus, it is an object of the invention, in particular in a generic process to substantially reduce the high operational costs as compared to the conventional methods, respectively installations, wherein possibly the same or even lower installation-operation costs can be realized. In particular, use of columns with large dimensions as they are required for high reflux ratios, respectively high circulation volume of extraction medium, should be avoided. 7 [0018] This object is attained with a method according to the principal features of claim 1. Preferred configurations of embodiments of such a method and additional features are reflected in the dependent claims to 2 to 19. [0019] An installation to carry out an especially preferred embodiment of the method according to the invention using a divided column for the concentration of nitric acid is reflected in the features of claims 20 and 21. [0020] The invention refers further to the commonly used principal method for separating azeotropic mixtures by extractive rectification as characterized in claim 22. [0021] Following, the invention is more closely described with reference to the Figures, which show the different variations of the preferred embodiments of the method according to the invention. [0022] In the figures it is shown: [0023] Figure 1 the flow diagram of a known industrial method for the production of concentrated nitric acid by extractive rectification by using sulfuric acid as extraction medium, with an extractive rectification branch and a branch for the reconcentration of the extraction medium, sulfuric acid, as described in general form in the introductory part of the description; 8 10024] Figure 2 the flow diagram of the extractive rectification branch of a first embodiment of the method according to the invention utilizing a divided extractive rectification column; [0025] Figure 3 the flow diagram of the branch for the reconcentration of the extraction medium, as the latter can be carried out in connection with an extraction rectification according to the embodiment of the method according to invention according to Figure 2; [0026] Figure 4 the flow diagram of the extractive rectification branch of an alternative embodiment of the method in accordance with the invention utilizing a divided extractive rectification column, wherein the second column is operated under pressure; [0027] Figure 5 the flow diagram of the branch for the preparation and reconcentration of an extraction medium which exhibits a relatively high portion of residual-nitric acid, as can be utilized in connection with the extractive rectification according to one of the embodiments of the process in accordance with the invention according to Figure 2 or 4. [00281 'n order to facilitate the understanding of explanations to the features and advantages of the method according to the invention in the various preferred embodiments and configurations, first, concrete embodiments of the 9 method, respectively the installation for carrying out the process with reference to the Figures are further explained. [0029] In describing the Figures it is assumed in exemplary manner that the process concerns the production of a highly concentrated nitric acid of about 99% by weight HNOa through concentration of a sub-azeotropic nitric acid of about 67 % by weight. It is further assumed that sulfuric acid is used as an extraction medium. Any limitations of the method according to the invention in the described conditions should not follow from such a concrete description, but modifications using other concentrations of the starting materials and end products and other extraction media are possible which are expressly comprised within the scope of the invention. The person skilled in the art can. without any problems, adjust any required conditions of the process on the basis of the present description and based on his/her own knowledge of the art. [0030] In Figures to 2 to 5, parts of the installation, which are functionally equivalent are referred to by the same reference numerals. The following embodiments refer foremost to Figure 2 in connection with Figure 3, however they are directly applicable to the embodiment according to Figure 4, aside from the obvious modifications, which apply to Figure 4 in that the second column, K. 1.1 is operated at below ambient-pressure and based thereon, is additionally supplemented through partial column K 1.3. 10 [0031] The process, as described in accordance with Figures 2 to 5, the concentration of the supplied, approximately azeotropic nitric acid (nitric acid to be concentrated) to 99 % by weight is carried out by means of extractive rectification. As an extraction medium, a possibly highly concentrated sulfuric acid, that is, one which is preferably 80 to 96 % by weight, is utilized, especially preferred is a sulfuric acid of 89 % by weight. [0032] In the most preferred embodiment, the extractive rectification is carried out in two separate columns K 1.0 and K 1.1, wherein the first of the two columns K 1.0 serves in the rectification of the nitric acid to be concentrated and yields of a vapor of concentrated nitric acid ("nitric acid exhaust vapors") and the second of the two columns K 1.1 utilized for separation of nitric acid from the sulfuric acid. [0033] The nitric acid to be concentrated is fed into the sump of the first column K 1.0 by heat exchanger or W5 as well as W1 and W2. The nitric acid to be concentrated is thereby pre-heated in heat exchanger W 5 by means of the exiting nitric acid vapors at the head to the column K 1.0, then further heated in heat exchanger W1 by means of the re-concentrated sulfuric acid and subsequently partially vaporized in heat exchanger W2, which is operated with heating steam condensate. 11 [0034] The re-concentrated sulfuric acid from container B3 (Fig. 3; Fig. 5), which exhibits approximately boiling point temperature is transferred via the heat exchanger W1 and the further heat exchanger W3, which essentially acts as a coolant for the further temperature control of the sulfuric acid, and transported to the head of column K 1.0. A partial stream of the nitric acid to be concentrated is admixed to the sulfuric acid stream via a mixer, which is shown in the Figures 2 and 4 in front of the heat exchanger W1. The energy supply to columns K 1.0 and K 1.1, in addition to the partial vaporization in W2, is realized by means of the vaporizer W8 of column K 1.0 and vaporizer W4 (sump heater) disposed at column K. 1.1. The direct supply of a very small amount of stripping steam in W4, respectively the second column K 1. for start and control of the operation serves predominantly to lower the residual nitric acid of sulfuric acid which runs from the vaporizer W4. The nitric acid vapors exiting at the head of the column K 1.0 are partially condensed by means of the heat exchanger W5 and W6 and deposited to the bleaching column K 2 which operates with stripping air. The gas mixture emerging from the bleaching column is subjected to post condensation by a heat exchanger W7. The waste gas containing NOX is led to NOX absorption. [0035] The sulfuric acid, which has been conducted at the sump of column K 1.1 via the sump heater W4 is collected in the container B1 (Fig. 3) and conveyed to a vaporizer W10 operated under vacuum for concentrating the acid. A partial stream is conducted via the flash container B2 and subjected there to release vaporization, so that in container B1 a'temperature reduction is carried 12 out. The exhaust vapors rising from W10 (mostly steam) are conducted via separation column K 4 into condenser W11 wherein also simultaneously the vapors from the flash container are precipitated. The condensate reaches the container B4 through introduction via a barometrically submerged pipe. The reconcentrated sulfuric acid having a relatively high temperature, slightly under the boiling point, is brought back from the container B3 into the first column 1.0. [0036] In this afore-described example, the nitric acid concentration is operated at an absolute pressure of about 950 mbar and the reconcentration range for the sulfuric acid operated at an absolute pressure of about 80 mbar. [0037] For specific requirements/purposes, the process can be correspondingly varied in accordance with Figure 4 and Figure 5. Thereby, the column K 1.1 is operated at below ambient pressure which additionally requires partial column K 1.3 and if applicable, requires an adjustment of the branch for the sulfuric acid reconcentration. [0038] The process according to the invention, as described above with reference to the Figures shows a series of advantages, respectively modifications as compared to the conventional process, which is described in more detail herein in connection with the installation parts wherein the process according to the invention respectively the preferred embodiments of the process, are described in more detail. 13 [0039] The process according to the invention is carried out so that at the head of column K 1.0, a boiling equilibrium is established between nitric acid, sulfuric acid and water. For this purpose, sufficient nitric acid must be contained in the liquid phase, so that in the vapor phase the desired high percentage of nitric acid, up to 99.9 % weight HNO^can be realized. Surprisingly, it has been found, that if prior to inputting the extraction medium into column K 1.0, nitric acid, preferably 55 to 69 % by weight nitric acid, is added to the extraction medium, or at least 50 % of the extraction medium amount, in an amount of 0.1 to 60 % of the entire nitric acid to be concentrated, the boiling equilibrium of the liquid-/vapor mixture at the head of the column K 1.0 is more easily realized. With this input, a reduction of the column-internal nitric acid condensation in the sulfuric acid and thereby a reduction of the required heating energy is realized. Thus, what is desired and controlled is a target volume ratio in accordance with the equilibrium conditions for each of the compositions of the partial streams present (the nitric acid to be concentrated and the reconcentrated sulfuric acid). [0040] Based upon the afore-described measures, the strong cooling of the extraction medium that was heretofore required, for example, in the case of sulfuric acid to under 80° C, can be eliminated and the extraction medium can be supplied in warmer condition, for example, sulfuric acid of a temperature of 90 to 160° C can be supplied to column K1.0. 14 [0041] Furthermore, in most of the conventionally constructed installations, the nitric acid to be concentrated is supplied as liquid supplied into the extractive rectification. According to the present invention, the heat content of the heating steam condensation stream available in the entire process, which comprises the extractive rectification and the extraction medium-reconcentration is utilized as far as possible, and the nitric acid to be concentrated is partially vaporized and fed to the extractive rectification. [0042] The following amounts of heat that are available in this context and are preferably used as follows: a) the condensation enthalpy of the nitric acid vapor emerging from the head of column K1.0 (for example by means of the heat exchanger W5). b) the difference in enthalpy of the reconcentrated extraction medium, for example the sulfuric acid, between exiting from the reconcentration approximately in boiling condition and the entry condition into the column K1.0 (for example, by heat exchanger W1). c) the difference in enthalpy of the hightensioned heating steam condensate having a pressure in the range of 6 to 40 baru and/or the release steam from the heating steam condensate and/or of a released heat steam/condensate mixture having a pressure in the range from 1 to 15 16 baru (for example, by means of heat exchanger W2 through heating steam condensate utilization). Preferably, the heating steam condensate which is generated from the installation, from one, or from several, or from all heaters (for example from the heater of vaporizer W4 for the column K 1.1 and/or from the heater W10 of the vaporizer from the reconcentration). d.) the condensation enthalpy of the exhaust vapors, such as for example, the normal or above normal pressure level of a two or more step reconcentration of the extraction medium, for example the sulfuric acid, at simultaneous vacuum operation of column K 1.1. [0043] When utilizing the amounts of heat according to the afore-stated description under consideration of the admixture of nitric acid to the extraction medium, the nitric acid to be concentrated is fed to column K1.0 in an amount from 40 to 99.9 % of the entire amount of nitric acid to be concentrated, below the deposit location of the extraction medium, respectively the extraction medium-/nitric acid mixture in form of a vapoMiquid mixture or divided into steam and liquid. [0044] The extractive rectification is carried out according to an especially preferred embodiment in two separate columns (K 1.0 and K 1.1) or, which is comparable to a separation into two single columns (K 1.0 and K 1.1), wherein the first one of the two columns (K 1.0) serves the rectification of the nitric acid to 16 be concentrated and obtaining a vapor of concentrated nitric acid, whereas the second of the two columns (K 1.1) serves to separate the nitric acid from the extraction medium. The division into two columns (K 1.0, K 1.1) is realized approximately at the location of the input for the nitric acid to be concentrated. With the aid of corresponding devices, preferably an intimate mixing of the extraction medium, for example the sulfuric acid that trickles down from the upper column K 1.0 with the pre-reheated and partially vaporized nitric acid to be concentrated, is realized. [0045] In order to keep the heating energy requirement for the reconcentration of the extraction medium (e. g. sulfuric acid or also aqueous magnesium nitrate solutions) as low as possible and the amount of water which must be vaporized in the reconcentration should be kept as low as possible. Since in the conventional process, the direct steam which is blown in dilutes the sulfuric acid which is running off, according to the invention, a possibly complete indirect heating of the nitric acid-rectification is desirable, for which purpose the column for extractive rectification is equipped with sump heaters and/or intermediate heaters. [0046] These steps are actually already known. However, the novelty resides in that the configuration of the recumbent vaporizer W4, below the column K1.1, is preferably such that it is supplemented by additional separation steps thereby effecting a reduction of the column height and/or a reduction of the 17 heat supply into the sump of column K 1.1 and/or a reduction of their residual nitric acid content is reached in the extraction medium that is running off. Preferably, a suitable recumbent vaporizer is utilized with W4, wherein resistances are built into the bottom area transverse to the flow direction that form cascade-type system of chambers of distillation bubbles. A suitable vaporizer of the type for the acid concentration is shown, e. g. in a company pamphlet of the applicant herein. [0047] When blowing a certain volume of air and/or water vapor steam into the recumbent vaporizer W4 (Figs. 2 and 4), preferably into the extraction medium and preferably into the rear area, respectively at the end of the recumbent vaporizer W4, the concentration of the nitric acid in the extraction medium running off can be additionally reduced and/or under retention of the elevated residual nitric acid content in the extraction medium running off, the amount of energy to be supplied and/or the required height of column K 1.1 can be reduced. Preferably, release steam from the heating steam heaters of the entire installation is additionally blown in (stripping steam). [0048] When carrying out the extractive rectification, a single column K 1 (alternatives not shown in the Figures) can also be utilized, when the partially vaporized nitric acid to be concentrated is separated in a side container into a liquid and a vapor phase and the liquid stream is fed into the single column K 1 above the vapor stream. 18 [0049] Independent of the extractive rectification carried out in a single column K 1, or in two separate columns or column portions K 1.0 and K 1.1, a definite novelty of the process according to the invention is that the substantial portion of the steam which is contained in the nitric acid to be concentrated, which has been fed to the system and partially vaporized condition is condensed in a material exchange with the vaporized nitric acid. Due to this exchange, the reflux is reduced, thereby lowering the amount of heat required. [0050] When intimately mixing the extraction medium dripping down with the entering feed stream, the afore-described devices K 1.0 is configured in such a manner that a heater disposed interiorly and/or disposed exteriorly its utilized thereby amplifying the intimate mixing condition. [0051] In addition, a reduction of the required heating energy can be realized, so that according to one of the preferred embodiments an elevated residual content of nitric acid of up to about 5 % by weight HNO3 in the extraction medium (e. g. sulfuric acid) is permissible which exits from the recumbent vaporizer W4. To avoid an elevated nitric acid content in the exhaust vapor condensate of the extraction medium reconcentration, the extraction medium running off, which has up to about 5 % by weight HNO3 e. g. the sulfuric acid, is released in an vacuum step B2 upstream (Fig. 5) and the nitric acid contained in the exhaust vapor of this step is retained by a downstream rectification column K 5 and returned as an azeotropic nitric acid to the column K. 1.0 (Fig. 5). 19 [0052] Furthermore, in an additional energy saving, the columns K 1.0 and K 1.1 are operated at different pressures. Operational pressures for the extractive rectification are at 100 mbar absolute to about 5 bar absolute, preferably between 200 mbar absolute and 1.3 bar absolute. For the extraction medium- reconcentration, e. g. sulfuric acid, to about 4 bar absolute. By exploiting suitable operational pressures in each one of the areas, heat utilization (release vaporization, heating with exhaust vapors) is realized. [0053]- Within the scope of the process according to the invention, optionally the following further energy utilization measures are possible: a) the column K 1.1 is operated with a substantially smaller pressure as the column K 1.0 (Fig. 4). Thereby, the latent heat of the nitric acid- extraction medium mixture between the sump temperature of column K 1.0 and the boiling point temperature of the mixture at the head of column K 1.1 can be utilized and therefore less steam is required for expelling the residual nitric acid in the sump of column K 1.1. b) alternatively, or supplementary, the reconcentration of the extraction medium, e. g. the sulfuric acid is carried out in one or more pressure steps, preferably in the range of 50 mbar absolute to 4 bar absolute, wherein the exhaust vapors from the step(s) with the higher pressure for heating the extractive rectification can be utilized, as afore- stated. 20 c) alternatively, or supplementary, the exhaust vapors from the higher pressure step(s) of the extraction medium reconcentration (Fig. 3; Fig. 5), before or after heating the extractive rectification in one or several separate columns in mostly water with a concentration greater than 90 % by weight, preferably 99 to 99.99 % by weight; and sump azeotropic nitric acid, are separated, preferably with a concentration off 30 to 69 % by weight, whereby the subazeotropic nitric acid is preferably returned to column K 1.0. [0054] To reduce costs in the installation assembly, and if suitable on the basis of space, it is furthermore preferred that a partial stream of nitric acid exhaust vapors which exit from the head of column K 1.0 is condensed in heat exchanger W5 and/or by means of a further condenser W6t before inputting into the bleaching column K 2, and the so obtained condensate is introduced to the head of the bleaching column K 2. The part of the nitric acid exhaust vapors which are not condensed but are required for heating the bleaching column K 2 is conducted into the mid-portion of the bleaching column K 2. As a result, it is possible to substantially reduce the diameter of the bleaching column as compared with those utilized in the conventional process. [0055] In summary, the following advantages of the invention are highlighted: 21 [0056] With the process according to the invention, a reduction of the reflux in the extractive rectification column is realized. [0057] In order to further reduce the internal reflux, the extraction medium can be supplied in warmer condition. [0058] Utilizing the heat content of the various available process streams for a partial vaporization of the nitric acid to be concentrated, requires a smaller amount of heat energy. [0059] Purification of the extraction medium can be realized more easily through the utilization with a recumbent vaporizer (W 4) of suitable configuration. [0060] in the conventional installations for nitric acid concentration, heating steam amounts of about 1.8 kg per 1.0 kg produced highly concentrated nitric acid are required. If, as already known, a sump and/or an intermediate heater is utilized, the specific heating steam requirement is reduced to about 1.5 kg per kg highly concentrated HNO3. In the process according to the invention, the specific heating steam requirement can be reduced to under 1.1 kg per kg highly concentrated HNO3. The evidence for the specific heat energy requirement are applicable for about 67 % by weight nitric acid to be concentrated in producing a nitric acid of approximately 99 % by weight. 22 [0061] The cooling water requirement is reduced by about the same ratio as the heating steam requirement. [0062] Finally, apparatuses can be configured partially in a smaller scale and/or when using the same size apparatus, a higher operational capacity can be realized as compared with the conventional method. [0063] The core of the process according to the invention refers to an optimization of energy use in separating azeotropic mixtures and was developed in connection with production of a highly concentrated nitric acid, however, the process can be, of course, under guidance of the skilled artisan, adapted to other process parameters without any problems, in that it can be utilized as a process for separating other technical azeotropic material mixtures, where a concentrated product fraction of one of the starting mixture components is to be produced, when, by addition a suitable extraction medium, the azeotropic point can be avoided/overcome in such a process. Typical examples for such material mixtures are halogen- hydrogen/water, in particular chloro-or fluorocarbon/water; alcohol/water in particular ethanol/water or isopropanol/water; ether/water, for example tertahydrofuran/water or mixtures or organic compounds, for example benzol/cyclohexan. The process according to the invention can be also applied successfully and in an economically feasible manner to mixtures of this type. The invention refers also to a process for azeotropic separation in a more general form, with the basic features reflected in claim 22. The advantageous 23 embodiment of the general process correspond to the advantageous embodiments according to patent claims to 2 to 19 as it relates to the features therein, such as most of the concrete temperature data, are not exclusively material-related and are applicable in its form not only in the concentration of nitric acid respectively the use of the extraction medium suifuric acid outputs. 24 We Claim: 1. Process for the production of a nitric acid having a concentration of 75 to 99,9% from a more diluted, optionally impure nitric acid, wherein a nitric acid of a concentration of about 45 to 70% is rectified at a pressure from 100 mbar absolute to 5 bar absolute by contacting it with a liquid extraction medium for preventing the formation of a nitric acid-water azeotropic mixture, the vapors of the concentrated nitric acid is obtained, and wherein, additionally, the extraction medium is recovered by reconcentration at a pressure in the range from 50 rabar absolute to 4 bar absolute and returned to the extractive rectification, characterized in - partially or substantially utilizing the heat contents of the available process streams of the entire process and - feeding the nitric acid to be concentrated in the form of a boiling liquid or partially vaporized or separated into vapor and liquid into the extractive rectification, utilizing the heat contents available in the entire process (Wl, W2, W5), and - enriching at least 50% of the amount of extraction medium before feeding it at a temperature in the range from 80°C to 160°C into the extractive rectification in an amount of 0.1 to 60% of the nitric acid to be concentrated with nitric acid, preferably a nitric acid in the concentration range of the nitric acid to be concentrated, and - supplying the energy required for the extractive rectification exclusively, or to a substantial proportion thereof by indirect heating (W4, W8) and - supplying the extraction medium to the extractive rectification in a form as concentrated as possible, such that when at the same time the LJ - extraction medium leaving the extractive distillation is as diluted as possible, the circulating amount of extraction medium is minimized. 2. Process as claimed in claim 1, wherein the extractive rectification is carried out in two separate columns (K1.0, Kl.l) or in one concentration column which is partitioned into two column portions (K1.0, Kl.l), wherein the first of the two columns (K1.0) is utilized for the rectification of the nitric acid to be concentrated and for obtaining a concentrated nitric acid vapor, and the second of the two columns (Kl.l) is utilized for the separation of the nitric acid from the extraction medium, the portioning into two columns (K1.0, Kl.l) being defined by the feeding location for the nitric acid to be concentrated. 3. Process according to claim 1 and 2, wherein - the nitric acid to be concentrated is introduced into a lower part of the first of the two columns (K1.0) in preheated form as a boiling liquid or as a vapor-liquid mixture or separated into vapor and liquid utilizing the heat content of process streams, heating steam and/or steam condensate from the entire process for pre-heating, and rectified in the first column (K1.0) in countercurrent flow with a fluid extraction medium, which prior to its introduction into the first column (K1.0) was enriched with nitric acid to such a point that when vapors of the concentrated nitric acid are contacted with the extraction medium the condensation of nitric acid is minimized, - the extraction medium from the lower part of the first column (K1.0) is drawn off and supplied to the head of the second of the two columns (Kl.l) and separated therein into an extraction medium fluid having a reduced residual content of nitric acid and into a nitric acid vapor, 26 - the extraction medium liquid being collected in an indirectly heated bottom of the second column (Kl.l) and drawn off therefrom for recovering and reconcentration and - the nitric acid vapor driven off from the extraction medium being returned from the head of the second column (Kl.l) into the lower part of the first column (K1.0). 4. Process as claimed in claim ls 2 or 3, wherein the nitric acid to be concentrated in preheated and/or partially vaporized by heat exchange with the concentrated nitric acid vapor (W5) from the first column (K1.0) and and/or the hot reconcentrated extraction medium (Wl) and/or a heating steam condensate and/or a flash vapor of a heating steam condensate (W2) from the indirectly heated vaporizers (W4> W10) of the extractive rectification and/or the extraction medium concentration and/or the vapor fractions of extraction medium obtained at its reconcentration. 5. Process as claimed in claim 1 to 4, wherein the concentration steps in the two columns (K1.0 and Kl.l) are operated at the same or different system pressures in the range of 100 mbar absolute to 5 bar absolute, preferably between 200 mbar absolute and 1.3 bar absolute. 6. Process as claimed in claim 1 to 5, wherein the second column (Kl.l) is operated at a lower pressure than the first column (K1.0). 7. Process as claimed in any one of claims 1 to 6, wherein as extraction medium sulfuric acid is utilized and that prior to feeding it at a temperature in the range from 80°C to 160°C into the first column (K1.0), at least 50% of the amount of sulfuric acid is enriched in an amount from 0.1 to 60% of the nitric acid is enriched in an amount from 0.1 to 60% of the nitric acid to be concentrated with a nitric acid in a concentration 27 range of the nitric acid in a concentration range of the nitric acid to be concentrated. 8. Process as claimed in any one of claims 1 to 7, wherein the extraction medium collected in the bottom of the second column (Kl.l) is heated in a horizontal vaporizer (W4), which is heated indirectly and in its bottom portion transversely to the flow direction of the acid is provided with weirs forming a cascading-type chamber system of single distillation vessels, so that the vaporizer provides additional separation steps, by which a reduction of the height of the second column (Kl.l) and/or a reduction of the heating energy requirements for the horizontal vaporizer (W4) and/or an adjustment of reduced residual nitric acid concentrations in the extraction medium flowing out off the horizontal vaporizer are achievable. 9. Process as claimed in claim 8, wherein for a further reduction of the residual content of nitric acid in the extraction medium leaving the second column (Kl.l), air and/or water steam is blown into the horizontal vaporizer (W4). 10. Process as claimed in any one of claims 1 to 10, wherein the introduction of the partially vaporized nitric acid into the first and/or second column (K1.0, Kl.l) of the concentration is effected in such a manner that an intimate mixture of the vapor portion of the partially vaporized nitric acid to be concentrated and the introduced extraction medium and/or a mixture of the extraction medium and the liquid portion of the partially vaporized liquid nitric acid to be concentrated is provided, whereby the intimate mixing can be amplified by suitable aggregates and devices 28 respectively which are disposed interiorly and/or exteriorly of the columns (K1, 0,K1.1). 11. Process as claimed in one of the claims 1 to 11, wherein the extraction medium drawn off from the horizontal vaporizer (W4) of the second column (K1.0) has a residual nitric acid content of up to 5% by weight. 12. Process as claimed in claim 12, wherein the extraction medium having a content of residual nitric acid in the range of 0.1 to 5% by weight is subjected to a flash vaporization in a vacuum step and the nitric acid from the vapor so obtained is retained as a diluted nitric acid and returned to an upstream process step, preferably to the first column (K1.0), while the liquid extraction medium depleted with respect to its nitric acid portion is subjected to a further processing for its reconcentration. 13. Process as claimed in one of claims 1 to 13, wherein the reconcentration of the extraction medium is carried out in two or more steps at varying pressures in the range from 50 mbar absolute to 4 bar absolute and the vapor fractions of this reconcentration with the higher pressure are utilized to heat the nitric acid to be concentrated and/or the extractive rectification column (Kl.l) indirectly (W4). 14. Process as claimed in claim 14, wherein before or after utilizing the vapor fractions for preheating the nitric acid to be concentrated they are separated in one or several additional columns into a fraction preferably consisting of water, preferably 99 to 99.99% by weight water, and into a sub-azeotropic nitric acid, which is returned into an upstream process step, preferably to the first column (Kl,)). 15. Process as claimed in one of claims 1 to 15, wherein the vapor of concentrated nitric acid obtained from the first column (K1.0) is at least 29 partially condensed by heat exchange with the nitric acid to be concentrated (W5) and that the liquid concentrated nitric acid obtained, optionally after passing further condensers (W6), is supplied to the head of a bleaching column (K2), while the required residual nitric acid vapor is returned to the mid-portion of this bleaching column (K2). 16. Process as claimed in claim 3, wherein the steam condensate utilized in the preheating of the nitric acid to be concentrated is a high pressure heating steam condensate of steam previously utilized for indirect heating, in particular from the indirect heating of the two columns (K1.0, Kl.l), having a pressure of 6 to 40 bar hyperbaric pressure, and/or the flash vapor of such a heating steam condensate and/or a mixture of heating steam condensate and flash vapor having a pressure in the range of from 1 to 16 bar hyperbaric pressure. 17. Process as claimed in claim 9, wherein the steam supplied to the horizontal vaporizer (W4) and/or into the second column (Kl.l) as stripping vapor is a steam obtained from flashing a heating steam condensate. 18. Process as claimed in claim 1 or 2, wherein the extractive rectification is carried out in a single column, wherein the partially vaporized nitric acid to be concentrated is fed into the column separated into the vapor phase and the liquid phase, the vapor phase being introduced below the feeding point for the liquid phase. 19. Installation for carrying out a process for producing a concentrated nitric acid as claimed in any one of claims 1 to 19, wherein the concentration column is divided into two columns (K0" Kl), which are provided in the form of two separate columns or as one single column portioned into two separate portions, wherein 2^ the first of the two columns (K1.0) is provided with at least one feeding line for the nitric acid to be concentrated as well as at least one feeding line disposed above in the head portion of the column (K1.0) for extraction medium liquid, to which preferably apart of the nitric acid to be concentrated was admixed, and a line for drawing off diluted liquid extraction medium mixture from the bottom portion of the column (K1.0) and the head of the second column (Kl.l) is connected with the line for the diluted liquid extraction medium mixture drawn off from the first column, and the second column (Kl.l) further is provided at a lower end thereof with a horizontal vaporizer (W4) which is indirectly heated and from which the extraction medium is transferred for regenerating to a reconcentration unit, while at the head of the second column (1.1) there is further provided an effluent line for returning nitric acid vapors driven off in the second column (Kl.l) from the diluted extraction medium mixture into the first column (K1.0). 20. Installation as claimed in claim 20, wherein the feeding line for the nitric acid to be concentrated is conducted through at least one heat exchanger (W5) in which a heat exchange with at least one hot product stream of the process, preferably the stream of the vaporized concentrated nitric acid from the first column, is effected, and that a mixer is provided in which to the extraction medium supplied to the first column (K1.0) a controlled amount of the nitric acid to be concentrated is admixed. Process for the production of a nitric acid having a concentration of 75 to 99.9% from a more diluted, optionally impure nitric acid, wherein a nitric acid of a concentration of about 45 to 70% is rectified at a pressure from 100 mbar absolute to 5 bar absolute by contacting it with a liquid extraction medium for preventing the formation of a nitric acid-water azeotropic mixture, the vapors of the concentrated nitric acid is obtained, and wherein, additionally, the extraction medium is recovered by re concentration at a pressure in the range from 50 mbar absolute to 4 bar absolute and returned to the extractive rectification, characterized in partially or substantially utilizing the heat contents of the available process streams of the entire process and feeding the nitric acid to be concentrated in the form of a boiling liquid or partially vaporized or separated into vapor and liquid into the extractive rectification, utilizing the heat contents available in the entire process (Wl, W2, W5), and enriching at least 50% of the amount of extraction medium before feeding it at a temperature in the range from 80°C to 160°C into the extractive rectification in an amount of 0.1 to 60% of the nitric acid to be concentrated with nitric acid, preferably a nitric acid in the concentration range of the nitric acid to be concentrated, and supplying the energy required for the extractive rectification exclusively, or to a substantial proportion thereof by indirect heating (W4, W8) and supplying the extraction medium to the extractive rectification in a form as concentrated as possible, such that when at the same time the extraction medium leaving the extractive distillation is as diluted as possible, the circulating amount of extraction medium is minimized.

Full Text

PROCESS FOR PRODUCING CONCENTRATED NITRIC ACID AND INSTALLATION TO CARRY OUT THE PROCESS
[0001J The invention relates to a process for producing a nitric acid with
the concentration of 75 to 99.9 % from a diluted, respectively an impure nitric acid, wherein a nitric acid of a concentration from about 45 to 70 % is brought into contact with a fluid extraction medium to prevent formation of a nitric acid-water-azeotropic mixture, which is rectified above normal pressure and/or normal pressure and/or vacuum and wherein the vapors of the concentrated nitric acid are condensed to thereby obtain a concentrated nitric acid, and wherein additionally, the extraction medium is regenerated and by means of reconcentration returned to the extractive rectification; as well as an installation for carrying out a preferred embodiment of such a process.
[0002] Nitric acid of higher concentration, oftentimes more than 98 % by
weight HNO3, is required for many organic reactions such as, for example nitrogenizations.
[0003] Conventional production methods produce nitric acid of about 65 to
67 % by weight HNO3. Thus, an additional process is required in order to obtain highly concentrated nitric acid. The most suitable process for concentrating nitric acid beyond the azeotropic point is the extractive rectification. Thereby, liquid extraction media are used, in particular concentrated sulfuric acid or aqueous
1

solutions of magnesium nitrate solutions, wherein the extraction medium used is predominantly sulfuric acid.
[0004] The thermodynamic bases of the extractive rectification utilizing an
extraction medium are as follows:
[0005] The component system, nitric acid/water exhibits at ambient
pressure (1 bar absolute) a maximal azeotropic mixture with a boiling point temperature of 121.8°C at 69.2 % weight HNO3. For nitric acid concentrations below the azeotropic point, water is the more volatile component. Above the azeotropic point, HNO3 is contained in the vapor phase in higher concentration. For production of highly concentrated nitric acid, it is necessary to circumvent the azeotropic point or respectively to overcome it. It has been known for a long time that with the aid of extraction medium, such as for example sulfuric acid or aqueous magnesium nitrate solutions, the relative volatility of water can be reduced. For higher extraction medium concentrations, such as for example sulfuric acid concentrations of higher than 50 % by weight H2SO4, the formation of an azeotropic point is suppressed. Thus, concentrated nitric acid can be distilled therefrom.
[0006] The basic process of concentrating nitric acid is by Pauling (DE
305553. DE 1056095). The process is industrially exploited on a large scale, in technically varying installations. A modern industrial method which is carried out
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with the extraction medium sulfuric acid is described in the following paragraph for a better understanding of the invention (Schott Engineering GmbH, printed to 60014 D. 8895.0; Comp. Figure 1). The actual process is essentially carried out in a concentration column (RK in Figure 1), into which the concentrated sulfuric acid is supplied and somewhat below, the diluted nitric acid. By mixing the components, mixing-and condensation temperatures occur in the column. These amounts of heat are however not sufficient to cover the required energy requirement for the process. Thus, at the foot of the column, steam ("stripping steam") is directly blown into. Aside from its function as a heat carrier, this direct steam effects that the nitric acid is substantially stripped from the diluted sulfuric acid that is running off. The vapors of the concentrated nitric acid, which are given off at the head of the column CHNO3 exhaust vapors") also contain nitrogen oxides, which are formed by the thermal decomposition of nitric acid. These nitrogen oxides (essentially NO2) are at the same time condensed within the HNO3 exhaust vapors to red smoking nitric acid. In order to obtain the condensed highly concentrated nitric acid in colorless form, the nitric gases contained in the acid are stripped off by air in a countercurrent downstream column, a so-called bleaching column. The waste gases, which contain nitrogen oxides, are cleaned in a subsequent NO2 absorption step.
[0007] A complete installation for producing highly concentrated nitric acid
comprises aside from the installation for the nitric acid rectification, additionally an installation branch for the extraction medium reconcentration. The installation
3

parts for the afore-described bleaching of the smoking nitric acid, as well as the downstream NOx absorption are also added. It is also appropriate to provide a pre-concentration for the nitric acid to be concentrated ("feeding acid") having a concentration of less than about 58 % by weight HNO3. Beyond that, it could also be appropriate to purify the nitric acid through steaming. All parts of the entire installation have to be optimally designed in order to fulfill the required specification with respect to product quantity and wastewater purity with minimal use of resources. The resource consumption and specifically the heating energy requirement decidedly determine the operational cost of the process.
[0008] In order to minimize the resources consumption, the required
heating energy has to be supplied and utilized optimally in the process. In the classic process, the supply of heating energy is effected directly with steam, the stripping steam. Early on, it was tried to save on direct steam since it could be shown that thereby the requirement of extraction medium (sulfuric acid) can be minimized.
[0009] In practice, several solutions have been carried out In the process
where aqueous magnesium nitrate solutions is used as extraction medium, early on, a sump heater was utilized (cf. Ullman's Enzyclopedia of Technical Chemistry; 4th Edition, Volume 20, p. 325). In the process wherein sulfuric acid is used, a so-called intermediate heater, also called a column heater and has
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being utilized for a long time (Uliman's Encyclopedia of Technical Chemistry; 4th Edition, Volume 20 p. 325).
[0010] Furthermore, it is known that it is possible to save heating energy
when reflux (internal and/or external) is reduced in the extraction rectification column. An internal reflux occurs for example, when the entry temperature of the extraction medium is lower than the boiling point temperature of the three component mixture, so that a certain amount of heat is first taken up by the extraction medium by partial condensation from the components of the vapor phase.
[0011] In the conventional methods, where pure extraction medium is
deposited at the head of the extractive rectification column, such as for example sulfuric acid, this extraction medium will first condense nitric acid so that the composition of the fluid mixture is moved into the direction of the equilibrium with the vapor phase. It follows, that the extraction medium has to be deposited in sufficiently cold condition to thereby effect an elevated internal reflux. This leads to an additional amount of heat which in turn can be supplied by means of additional heating energy to the extractive rectification.
[0012] It is known that by supplying liquid nitric acid (for example, a partial
amount of the nitric acid to be concentrated) to the extraction medium, the condensation behavior of the nitric acid in the column for the extractive
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rectification can be influenced. Accordingly, EP 0330351 81 ("Gunkei") described an admixture of the nitric acid to be concentrated to a partial stream of the extraction medium. A disadvantage of the method described by Gunkei is how ever, that the mixture stream of nitric acid to be concentrated and extraction medium is first input below a further amount pure extraction medium already input at an upper location. Thus, the afore-described desired effect of reducing the internal reflux is not attained in the process described in EP 0 330 351.
[0013] A further disadvantage of the process according to Gunkei is that
the entire process comprising also the reconcentration of the extraction medium, the required energy has already been completely supplied to the extractive rectification, although the energy requirement of the extractive rectification is substantially lower than the energy requirement of the extraction medium-reconcentration. With an energy supply of this type, a high amount of extraction medium is necessary for circulation and a large minimum diameter of the extractive rectification column is required.
[0014] In the process as described by Gunkei 51 to 99 % of the amount of
nitric acid to be concentrated is fed into the extractive rectification in totally vaporized form. Through this type of input, the amount of steam in the column is substantially raised, so that in connection with the raised amount of extraction medium in circulation, columns of greater diameter are required for the extractive rectification.
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[0015] A further disadvantage of the process described by GQnkel is that
at the head of the column a substantially higher reflux amount of highly concentrated nitric acid is required in order to obtain highly concentrated nitric acid vapor containing 99 to 99.9 % by weight HNO3.
[0016] Until now, in all installations that have been established for highly
concentrating subazeotropic nitric acid (weak acid) to nitric acid having more than 90 % by weight, preferably more than 98 % by weight ("hico-acid") the energy requirement, such as for example, heating steam and cooling water determined the production costs substantially. Thus, in larger installations as they were commonly established in the immediate past, (with sump heater and/or intermediate heater) starting from an HNO3 of 67 % by weight, heating steam amounts of about 1.5 kg per kg produced 99 % by weight of nitric acid were required.
[0017] Thus, it is an object of the invention, in particular in a generic
process to substantially reduce the high operational costs as compared to the conventional methods, respectively installations, wherein possibly the same or even lower installation-operation costs can be realized. In particular, use of columns with large dimensions as they are required for high reflux ratios, respectively high circulation volume of extraction medium, should be avoided.
7

[0018] This object is attained with a method according to the principal
features of claim 1. Preferred configurations of embodiments of such a method and additional features are reflected in the dependent claims to 2 to 19.
[0019] An installation to carry out an especially preferred embodiment of
the method according to the invention using a divided column for the concentration of nitric acid is reflected in the features of claims 20 and 21.
[0020] The invention refers further to the commonly used principal method
for separating azeotropic mixtures by extractive rectification as characterized in claim 22.
[0021] Following, the invention is more closely described with reference to
the Figures, which show the different variations of the preferred embodiments of the method according to the invention.
[0022] In the figures it is shown:
[0023] Figure 1 the flow diagram of a known industrial method for the
production of concentrated nitric acid by extractive rectification by using sulfuric acid as extraction medium, with an extractive rectification branch and a branch for the reconcentration of the extraction medium, sulfuric acid, as described in general form in the introductory part of the description;
8

10024] Figure 2 the flow diagram of the extractive rectification branch
of a first embodiment of the method according to the invention utilizing a divided extractive rectification column;
[0025] Figure 3 the flow diagram of the branch for the reconcentration
of the extraction medium, as the latter can be carried out in connection with an extraction rectification according to the embodiment of the method according to invention according to Figure 2;
[0026] Figure 4 the flow diagram of the extractive rectification branch
of an alternative embodiment of the method in accordance with the invention utilizing a divided extractive rectification column, wherein the second column is operated under pressure;
[0027] Figure 5 the flow diagram of the branch for the preparation and
reconcentration of an extraction medium which exhibits a relatively high portion of residual-nitric acid, as can be utilized in connection with the extractive rectification according to one of the embodiments of the process in accordance with the invention according to Figure 2 or 4.
[00281 'n order to facilitate the understanding of explanations to the
features and advantages of the method according to the invention in the various preferred embodiments and configurations, first, concrete embodiments of the
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method, respectively the installation for carrying out the process with reference to the Figures are further explained.
[0029] In describing the Figures it is assumed in exemplary manner that
the process concerns the production of a highly concentrated nitric acid of about 99% by weight HNOa through concentration of a sub-azeotropic nitric acid of about 67 % by weight. It is further assumed that sulfuric acid is used as an extraction medium. Any limitations of the method according to the invention in the described conditions should not follow from such a concrete description, but modifications using other concentrations of the starting materials and end products and other extraction media are possible which are expressly comprised within the scope of the invention. The person skilled in the art can. without any problems, adjust any required conditions of the process on the basis of the present description and based on his/her own knowledge of the art.
[0030] In Figures to 2 to 5, parts of the installation, which are functionally
equivalent are referred to by the same reference numerals. The following embodiments refer foremost to Figure 2 in connection with Figure 3, however they are directly applicable to the embodiment according to Figure 4, aside from the obvious modifications, which apply to Figure 4 in that the second column, K. 1.1 is operated at below ambient-pressure and based thereon, is additionally supplemented through partial column K 1.3.
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[0031] The process, as described in accordance with Figures 2 to 5, the
concentration of the supplied, approximately azeotropic nitric acid (nitric acid to be concentrated) to 99 % by weight is carried out by means of extractive rectification. As an extraction medium, a possibly highly concentrated sulfuric acid, that is, one which is preferably 80 to 96 % by weight, is utilized, especially preferred is a sulfuric acid of 89 % by weight.
[0032] In the most preferred embodiment, the extractive rectification is
carried out in two separate columns K 1.0 and K 1.1, wherein the first of the two columns K 1.0 serves in the rectification of the nitric acid to be concentrated and yields of a vapor of concentrated nitric acid ("nitric acid exhaust vapors") and the second of the two columns K 1.1 utilized for separation of nitric acid from the sulfuric acid.
[0033] The nitric acid to be concentrated is fed into the sump of the first
column K 1.0 by heat exchanger or W5 as well as W1 and W2. The nitric acid to be concentrated is thereby pre-heated in heat exchanger W 5 by means of the exiting nitric acid vapors at the head to the column K 1.0, then further heated in heat exchanger W1 by means of the re-concentrated sulfuric acid and subsequently partially vaporized in heat exchanger W2, which is operated with heating steam condensate.
11

[0034] The re-concentrated sulfuric acid from container B3 (Fig. 3; Fig. 5),
which exhibits approximately boiling point temperature is transferred via the heat exchanger W1 and the further heat exchanger W3, which essentially acts as a coolant for the further temperature control of the sulfuric acid, and transported to the head of column K 1.0. A partial stream of the nitric acid to be concentrated is admixed to the sulfuric acid stream via a mixer, which is shown in the Figures 2 and 4 in front of the heat exchanger W1. The energy supply to columns K 1.0 and K 1.1, in addition to the partial vaporization in W2, is realized by means of the vaporizer W8 of column K 1.0 and vaporizer W4 (sump heater) disposed at column K. 1.1. The direct supply of a very small amount of stripping steam in W4, respectively the second column K 1. for start and control of the operation serves predominantly to lower the residual nitric acid of sulfuric acid which runs from the vaporizer W4. The nitric acid vapors exiting at the head of the column K 1.0 are partially condensed by means of the heat exchanger W5 and W6 and deposited to the bleaching column K 2 which operates with stripping air. The gas mixture emerging from the bleaching column is subjected to post condensation by a heat exchanger W7. The waste gas containing NOX is led to NOX absorption.
[0035] The sulfuric acid, which has been conducted at the sump of column
K 1.1 via the sump heater W4 is collected in the container B1 (Fig. 3) and conveyed to a vaporizer W10 operated under vacuum for concentrating the acid. A partial stream is conducted via the flash container B2 and subjected there to release vaporization, so that in container B1 a'temperature reduction is carried
12

out. The exhaust vapors rising from W10 (mostly steam) are conducted via separation column K 4 into condenser W11 wherein also simultaneously the vapors from the flash container are precipitated. The condensate reaches the container B4 through introduction via a barometrically submerged pipe. The reconcentrated sulfuric acid having a relatively high temperature, slightly under the boiling point, is brought back from the container B3 into the first column 1.0.
[0036] In this afore-described example, the nitric acid concentration is
operated at an absolute pressure of about 950 mbar and the reconcentration range for the sulfuric acid operated at an absolute pressure of about 80 mbar.
[0037] For specific requirements/purposes, the process can be
correspondingly varied in accordance with Figure 4 and Figure 5. Thereby, the column K 1.1 is operated at below ambient pressure which additionally requires partial column K 1.3 and if applicable, requires an adjustment of the branch for the sulfuric acid reconcentration.
[0038] The process according to the invention, as described above with
reference to the Figures shows a series of advantages, respectively modifications as compared to the conventional process, which is described in more detail herein in connection with the installation parts wherein the process according to the invention respectively the preferred embodiments of the process, are described in more detail.
13

[0039] The process according to the invention is carried out so that at the
head of column K 1.0, a boiling equilibrium is established between nitric acid, sulfuric acid and water. For this purpose, sufficient nitric acid must be contained in the liquid phase, so that in the vapor phase the desired high percentage of nitric acid, up to 99.9 % weight HNO^can be realized. Surprisingly, it has been found, that if prior to inputting the extraction medium into column K 1.0, nitric acid, preferably 55 to 69 % by weight nitric acid, is added to the extraction medium, or at least 50 % of the extraction medium amount, in an amount of 0.1 to 60 % of the entire nitric acid to be concentrated, the boiling equilibrium of the liquid-/vapor mixture at the head of the column K 1.0 is more easily realized. With this input, a reduction of the column-internal nitric acid condensation in the sulfuric acid and thereby a reduction of the required heating energy is realized. Thus, what is desired and controlled is a target volume ratio in accordance with the equilibrium conditions for each of the compositions of the partial streams present (the nitric acid to be concentrated and the reconcentrated sulfuric acid).
[0040] Based upon the afore-described measures, the strong cooling of
the extraction medium that was heretofore required, for example, in the case of sulfuric acid to under 80° C, can be eliminated and the extraction medium can be supplied in warmer condition, for example, sulfuric acid of a temperature of 90 to 160° C can be supplied to column K1.0.
14

[0041] Furthermore, in most of the conventionally constructed installations,
the nitric acid to be concentrated is supplied as liquid supplied into the extractive rectification. According to the present invention, the heat content of the heating steam condensation stream available in the entire process, which comprises the extractive rectification and the extraction medium-reconcentration is utilized as far as possible, and the nitric acid to be concentrated is partially vaporized and fed to the extractive rectification.
[0042] The following amounts of heat that are available in this context and
are preferably used as follows:
a) the condensation enthalpy of the nitric acid vapor emerging from
the head of column K1.0 (for example by means of the heat exchanger
W5).
b) the difference in enthalpy of the reconcentrated extraction medium,
for example the sulfuric acid, between exiting from the reconcentration
approximately in boiling condition and the entry condition into the column
K1.0 (for example, by heat exchanger W1).
c) the difference in enthalpy of the hightensioned heating steam
condensate having a pressure in the range of 6 to 40 baru and/or the
release steam from the heating steam condensate and/or of a released
heat steam/condensate mixture having a pressure in the range from 1 to
15

16 baru (for example, by means of heat exchanger W2 through heating steam condensate utilization). Preferably, the heating steam condensate which is generated from the installation, from one, or from several, or from all heaters (for example from the heater of vaporizer W4 for the column K 1.1 and/or from the heater W10 of the vaporizer from the reconcentration).
d.) the condensation enthalpy of the exhaust vapors, such as for example, the normal or above normal pressure level of a two or more step reconcentration of the extraction medium, for example the sulfuric acid, at simultaneous vacuum operation of column K 1.1.
[0043] When utilizing the amounts of heat according to the afore-stated
description under consideration of the admixture of nitric acid to the extraction medium, the nitric acid to be concentrated is fed to column K1.0 in an amount from 40 to 99.9 % of the entire amount of nitric acid to be concentrated, below the deposit location of the extraction medium, respectively the extraction medium-/nitric acid mixture in form of a vapoMiquid mixture or divided into steam and liquid.
[0044] The extractive rectification is carried out according to an especially
preferred embodiment in two separate columns (K 1.0 and K 1.1) or, which is comparable to a separation into two single columns (K 1.0 and K 1.1), wherein the first one of the two columns (K 1.0) serves the rectification of the nitric acid to
16

be concentrated and obtaining a vapor of concentrated nitric acid, whereas the second of the two columns (K 1.1) serves to separate the nitric acid from the extraction medium. The division into two columns (K 1.0, K 1.1) is realized approximately at the location of the input for the nitric acid to be concentrated. With the aid of corresponding devices, preferably an intimate mixing of the extraction medium, for example the sulfuric acid that trickles down from the upper column K 1.0 with the pre-reheated and partially vaporized nitric acid to be concentrated, is realized.
[0045] In order to keep the heating energy requirement for the
reconcentration of the extraction medium (e. g. sulfuric acid or also aqueous magnesium nitrate solutions) as low as possible and the amount of water which must be vaporized in the reconcentration should be kept as low as possible. Since in the conventional process, the direct steam which is blown in dilutes the sulfuric acid which is running off, according to the invention, a possibly complete indirect heating of the nitric acid-rectification is desirable, for which purpose the column for extractive rectification is equipped with sump heaters and/or intermediate heaters.
[0046] These steps are actually already known. However, the novelty
resides in that the configuration of the recumbent vaporizer W4, below the column K1.1, is preferably such that it is supplemented by additional separation steps thereby effecting a reduction of the column height and/or a reduction of the
17

heat supply into the sump of column K 1.1 and/or a reduction of their residual nitric acid content is reached in the extraction medium that is running off. Preferably, a suitable recumbent vaporizer is utilized with W4, wherein resistances are built into the bottom area transverse to the flow direction that form cascade-type system of chambers of distillation bubbles. A suitable vaporizer of the type for the acid concentration is shown, e. g. in a company pamphlet of the applicant herein.
[0047] When blowing a certain volume of air and/or water vapor steam into
the recumbent vaporizer W4 (Figs. 2 and 4), preferably into the extraction medium and preferably into the rear area, respectively at the end of the recumbent vaporizer W4, the concentration of the nitric acid in the extraction medium running off can be additionally reduced and/or under retention of the elevated residual nitric acid content in the extraction medium running off, the amount of energy to be supplied and/or the required height of column K 1.1 can be reduced. Preferably, release steam from the heating steam heaters of the entire installation is additionally blown in (stripping steam).
[0048] When carrying out the extractive rectification, a single column K 1
(alternatives not shown in the Figures) can also be utilized, when the partially vaporized nitric acid to be concentrated is separated in a side container into a liquid and a vapor phase and the liquid stream is fed into the single column K 1 above the vapor stream.
18

[0049] Independent of the extractive rectification carried out in a single
column K 1, or in two separate columns or column portions K 1.0 and K 1.1, a definite novelty of the process according to the invention is that the substantial portion of the steam which is contained in the nitric acid to be concentrated, which has been fed to the system and partially vaporized condition is condensed in a material exchange with the vaporized nitric acid. Due to this exchange, the reflux is reduced, thereby lowering the amount of heat required.
[0050] When intimately mixing the extraction medium dripping down with
the entering feed stream, the afore-described devices K 1.0 is configured in such a manner that a heater disposed interiorly and/or disposed exteriorly its utilized thereby amplifying the intimate mixing condition.
[0051] In addition, a reduction of the required heating energy can be
realized, so that according to one of the preferred embodiments an elevated residual content of nitric acid of up to about 5 % by weight HNO3 in the extraction medium (e. g. sulfuric acid) is permissible which exits from the recumbent vaporizer W4. To avoid an elevated nitric acid content in the exhaust vapor condensate of the extraction medium reconcentration, the extraction medium running off, which has up to about 5 % by weight HNO3 e. g. the sulfuric acid, is released in an vacuum step B2 upstream (Fig. 5) and the nitric acid contained in the exhaust vapor of this step is retained by a downstream rectification column K 5 and returned as an azeotropic nitric acid to the column K. 1.0 (Fig. 5).
19

[0052] Furthermore, in an additional energy saving, the columns K 1.0 and
K 1.1 are operated at different pressures. Operational pressures for the extractive rectification are at 100 mbar absolute to about 5 bar absolute, preferably between 200 mbar absolute and 1.3 bar absolute. For the extraction medium- reconcentration, e. g. sulfuric acid, to about 4 bar absolute. By exploiting suitable operational pressures in each one of the areas, heat utilization (release vaporization, heating with exhaust vapors) is realized.
[0053]- Within the scope of the process according to the invention,
optionally the following further energy utilization measures are possible:
a) the column K 1.1 is operated with a substantially smaller pressure
as the column K 1.0 (Fig. 4). Thereby, the latent heat of the nitric acid-
extraction medium mixture between the sump temperature of column K
1.0 and the boiling point temperature of the mixture at the head of column
K 1.1 can be utilized and therefore less steam is required for expelling the
residual nitric acid in the sump of column K 1.1.
b) alternatively, or supplementary, the reconcentration of the
extraction medium, e. g. the sulfuric acid is carried out in one or more
pressure steps, preferably in the range of 50 mbar absolute to 4 bar
absolute, wherein the exhaust vapors from the step(s) with the higher
pressure for heating the extractive rectification can be utilized, as afore-
stated.
20

c) alternatively, or supplementary, the exhaust vapors from the higher pressure step(s) of the extraction medium reconcentration (Fig. 3; Fig. 5), before or after heating the extractive rectification in one or several separate columns in mostly water with a concentration greater than 90 % by weight, preferably 99 to 99.99 % by weight; and sump azeotropic nitric acid, are separated, preferably with a concentration off 30 to 69 % by weight, whereby the subazeotropic nitric acid is preferably returned to column K 1.0.
[0054] To reduce costs in the installation assembly, and if suitable on the
basis of space, it is furthermore preferred that a partial stream of nitric acid exhaust vapors which exit from the head of column K 1.0 is condensed in heat exchanger W5 and/or by means of a further condenser W6t before inputting into the bleaching column K 2, and the so obtained condensate is introduced to the head of the bleaching column K 2. The part of the nitric acid exhaust vapors which are not condensed but are required for heating the bleaching column K 2 is conducted into the mid-portion of the bleaching column K 2. As a result, it is possible to substantially reduce the diameter of the bleaching column as compared with those utilized in the conventional process.
[0055] In summary, the following advantages of the invention are
highlighted:
21

[0056] With the process according to the invention, a reduction of the
reflux in the extractive rectification column is realized.
[0057] In order to further reduce the internal reflux, the extraction medium
can be supplied in warmer condition.
[0058] Utilizing the heat content of the various available process streams
for a partial vaporization of the nitric acid to be concentrated, requires a smaller amount of heat energy.
[0059] Purification of the extraction medium can be realized more easily
through the utilization with a recumbent vaporizer (W 4) of suitable configuration.
[0060] in the conventional installations for nitric acid concentration, heating
steam amounts of about 1.8 kg per 1.0 kg produced highly concentrated nitric acid are required. If, as already known, a sump and/or an intermediate heater is utilized, the specific heating steam requirement is reduced to about 1.5 kg per kg highly concentrated HNO3. In the process according to the invention, the specific heating steam requirement can be reduced to under 1.1 kg per kg highly concentrated HNO3. The evidence for the specific heat energy requirement are applicable for about 67 % by weight nitric acid to be concentrated in producing a nitric acid of approximately 99 % by weight.
22

[0061] The cooling water requirement is reduced by about the same ratio
as the heating steam requirement.
[0062] Finally, apparatuses can be configured partially in a smaller scale
and/or when using the same size apparatus, a higher operational capacity can be realized as compared with the conventional method.
[0063] The core of the process according to the invention refers to an
optimization of energy use in separating azeotropic mixtures and was developed in connection with production of a highly concentrated nitric acid, however, the process can be, of course, under guidance of the skilled artisan, adapted to other process parameters without any problems, in that it can be utilized as a process for separating other technical azeotropic material mixtures, where a concentrated product fraction of one of the starting mixture components is to be produced, when, by addition a suitable extraction medium, the azeotropic point can be avoided/overcome in such a process. Typical examples for such material mixtures are halogen- hydrogen/water, in particular chloro-or fluorocarbon/water; alcohol/water in particular ethanol/water or isopropanol/water; ether/water, for example tertahydrofuran/water or mixtures or organic compounds, for example benzol/cyclohexan. The process according to the invention can be also applied successfully and in an economically feasible manner to mixtures of this type. The invention refers also to a process for azeotropic separation in a more general form, with the basic features reflected in claim 22. The advantageous
23

embodiment of the general process correspond to the advantageous embodiments according to patent claims to 2 to 19 as it relates to the features therein, such as most of the concrete temperature data, are not exclusively material-related and are applicable in its form not only in the concentration of nitric acid respectively the use of the extraction medium suifuric acid outputs.
24

We Claim:
1. Process for the production of a nitric acid having a concentration of 75 to 99,9% from a more diluted, optionally impure nitric acid, wherein a nitric acid of a concentration of about 45 to 70% is rectified at a pressure from 100 mbar absolute to 5 bar absolute by contacting it with a liquid extraction medium for preventing the formation of a nitric acid-water azeotropic mixture, the vapors of the concentrated nitric acid is obtained, and wherein, additionally, the extraction medium is recovered by reconcentration at a pressure in the range from 50 rabar absolute to 4 bar absolute and returned to the extractive rectification, characterized in
- partially or substantially utilizing the heat contents of the available
process streams of the entire process and
- feeding the nitric acid to be concentrated in the form of a boiling
liquid or partially vaporized or separated into vapor and liquid into the
extractive rectification, utilizing the heat contents available in the
entire process (Wl, W2, W5), and
- enriching at least 50% of the amount of extraction medium before
feeding it at a temperature in the range from 80°C to 160°C into the
extractive rectification in an amount of 0.1 to 60% of the nitric acid to
be concentrated with nitric acid, preferably a nitric acid in the
concentration range of the nitric acid to be concentrated, and
- supplying the energy required for the extractive rectification
exclusively, or to a substantial proportion thereof by indirect heating
(W4, W8) and
- supplying the extraction medium to the extractive rectification in a
form as concentrated as possible, such that when at the same time the
LJ

- extraction medium leaving the extractive distillation is as diluted as
possible, the circulating amount of extraction medium is minimized.
2. Process as claimed in claim 1, wherein the extractive rectification is
carried out in two separate columns (K1.0, Kl.l) or in one concentration
column which is partitioned into two column portions (K1.0, Kl.l),
wherein the first of the two columns (K1.0) is utilized for the rectification
of the nitric acid to be concentrated and for obtaining a concentrated
nitric acid vapor, and the second of the two columns (Kl.l) is utilized for
the separation of the nitric acid from the extraction medium, the
portioning into two columns (K1.0, Kl.l) being defined by the feeding
location for the nitric acid to be concentrated.
3. Process according to claim 1 and 2, wherein

- the nitric acid to be concentrated is introduced into a lower part of the
first of the two columns (K1.0) in preheated form as a boiling liquid
or as a vapor-liquid mixture or separated into vapor and liquid
utilizing the heat content of process streams, heating steam and/or
steam condensate from the entire process for pre-heating, and rectified
in the first column (K1.0) in countercurrent flow with a fluid
extraction medium, which prior to its introduction into the first
column (K1.0) was enriched with nitric acid to such a point that when
vapors of the concentrated nitric acid are contacted with the extraction
medium the condensation of nitric acid is minimized,
- the extraction medium from the lower part of the first column (K1.0)
is drawn off and supplied to the head of the second of the two
columns (Kl.l) and separated therein into an extraction medium fluid
having a reduced residual content of nitric acid and into a nitric acid
vapor,
26

- the extraction medium liquid being collected in an indirectly heated
bottom of the second column (Kl.l) and drawn off therefrom for
recovering and reconcentration and
- the nitric acid vapor driven off from the extraction medium being
returned from the head of the second column (Kl.l) into the lower
part of the first column (K1.0).

4. Process as claimed in claim ls 2 or 3, wherein the nitric acid to be
concentrated in preheated and/or partially vaporized by heat exchange
with the concentrated nitric acid vapor (W5) from the first column (K1.0)
and and/or the hot reconcentrated extraction medium (Wl) and/or a
heating steam condensate and/or a flash vapor of a heating steam
condensate (W2) from the indirectly heated vaporizers (W4> W10) of the
extractive rectification and/or the extraction medium concentration and/or
the vapor fractions of extraction medium obtained at its reconcentration.
5. Process as claimed in claim 1 to 4, wherein the concentration steps in the
two columns (K1.0 and Kl.l) are operated at the same or different
system pressures in the range of 100 mbar absolute to 5 bar absolute,
preferably between 200 mbar absolute and 1.3 bar absolute.
6. Process as claimed in claim 1 to 5, wherein the second column (Kl.l) is
operated at a lower pressure than the first column (K1.0).
7. Process as claimed in any one of claims 1 to 6, wherein as extraction
medium sulfuric acid is utilized and that prior to feeding it at a
temperature in the range from 80°C to 160°C into the first column (K1.0),
at least 50% of the amount of sulfuric acid is enriched in an amount from
0.1 to 60% of the nitric acid is enriched in an amount from 0.1 to 60% of
the nitric acid to be concentrated with a nitric acid in a concentration
27

range of the nitric acid in a concentration range of the nitric acid to be concentrated.
8. Process as claimed in any one of claims 1 to 7, wherein the extraction
medium collected in the bottom of the second column (Kl.l) is heated in
a horizontal vaporizer (W4), which is heated indirectly and in its bottom
portion transversely to the flow direction of the acid is provided with
weirs forming a cascading-type chamber system of single distillation
vessels, so that the vaporizer provides additional separation steps, by
which a reduction of the height of the second column (Kl.l) and/or a
reduction of the heating energy requirements for the horizontal vaporizer
(W4) and/or an adjustment of reduced residual nitric acid concentrations
in the extraction medium flowing out off the horizontal vaporizer are
achievable.
9. Process as claimed in claim 8, wherein for a further reduction of the
residual content of nitric acid in the extraction medium leaving the
second column (Kl.l), air and/or water steam is blown into the
horizontal vaporizer (W4).
10. Process as claimed in any one of claims 1 to 10, wherein the introduction
of the partially vaporized nitric acid into the first and/or second column
(K1.0, Kl.l) of the concentration is effected in such a manner that an
intimate mixture of the vapor portion of the partially vaporized nitric acid
to be concentrated and the introduced extraction medium and/or a
mixture of the extraction medium and the liquid portion of the partially
vaporized liquid nitric acid to be concentrated is provided, whereby the
intimate mixing can be amplified by suitable aggregates and devices
28

respectively which are disposed interiorly and/or exteriorly of the columns (K1, 0,K1.1).
11. Process as claimed in one of the claims 1 to 11, wherein the extraction
medium drawn off from the horizontal vaporizer (W4) of the second
column (K1.0) has a residual nitric acid content of up to 5% by weight.
12. Process as claimed in claim 12, wherein the extraction medium having a
content of residual nitric acid in the range of 0.1 to 5% by weight is
subjected to a flash vaporization in a vacuum step and the nitric acid
from the vapor so obtained is retained as a diluted nitric acid and returned
to an upstream process step, preferably to the first column (K1.0), while
the liquid extraction medium depleted with respect to its nitric acid
portion is subjected to a further processing for its reconcentration.
13. Process as claimed in one of claims 1 to 13, wherein the reconcentration
of the extraction medium is carried out in two or more steps at varying
pressures in the range from 50 mbar absolute to 4 bar absolute and the
vapor fractions of this reconcentration with the higher pressure are
utilized to heat the nitric acid to be concentrated and/or the extractive
rectification column (Kl.l) indirectly (W4).
14. Process as claimed in claim 14, wherein before or after utilizing the
vapor fractions for preheating the nitric acid to be concentrated they are
separated in one or several additional columns into a fraction preferably
consisting of water, preferably 99 to 99.99% by weight water, and into a
sub-azeotropic nitric acid, which is returned into an upstream process
step, preferably to the first column (Kl,)).
15. Process as claimed in one of claims 1 to 15, wherein the vapor of
concentrated nitric acid obtained from the first column (K1.0) is at least
29

partially condensed by heat exchange with the nitric acid to be concentrated (W5) and that the liquid concentrated nitric acid obtained, optionally after passing further condensers (W6), is supplied to the head of a bleaching column (K2), while the required residual nitric acid vapor is returned to the mid-portion of this bleaching column (K2).
16. Process as claimed in claim 3, wherein the steam condensate utilized in
the preheating of the nitric acid to be concentrated is a high pressure
heating steam condensate of steam previously utilized for indirect
heating, in particular from the indirect heating of the two columns (K1.0,
Kl.l), having a pressure of 6 to 40 bar hyperbaric pressure, and/or the
flash vapor of such a heating steam condensate and/or a mixture of
heating steam condensate and flash vapor having a pressure in the range
of from 1 to 16 bar hyperbaric pressure.
17. Process as claimed in claim 9, wherein the steam supplied to the
horizontal vaporizer (W4) and/or into the second column (Kl.l) as
stripping vapor is a steam obtained from flashing a heating steam
condensate.
18. Process as claimed in claim 1 or 2, wherein the extractive rectification is
carried out in a single column, wherein the partially vaporized nitric acid
to be concentrated is fed into the column separated into the vapor phase
and the liquid phase, the vapor phase being introduced below the feeding
point for the liquid phase.
19. Installation for carrying out a process for producing a concentrated nitric
acid as claimed in any one of claims 1 to 19, wherein the concentration
column is divided into two columns (K0" Kl), which are provided in the
form of two separate columns or as one single column portioned into two
separate portions, wherein
2^

the first of the two columns (K1.0) is provided with at least one feeding line for the nitric acid to be concentrated as well as at least one feeding line disposed above in the head portion of the column (K1.0) for extraction medium liquid, to which preferably apart of the nitric acid to be concentrated was admixed, and a line for drawing off diluted liquid extraction medium mixture from the bottom portion of the column (K1.0) and
the head of the second column (Kl.l) is connected with the line for
the diluted liquid extraction medium mixture drawn off from the first
column, and the second column (Kl.l) further is provided at a lower
end thereof with a horizontal vaporizer (W4) which is indirectly
heated and from which the extraction medium is transferred for
regenerating to a reconcentration unit, while at the head of the second
column (1.1) there is further provided an effluent line for returning
nitric acid vapors driven off in the second column (Kl.l) from the
diluted extraction medium mixture into the first column (K1.0).
20. Installation as claimed in claim 20, wherein the feeding line for the nitric
acid to be concentrated is conducted through at least one heat exchanger
(W5) in which a heat exchange with at least one hot product stream of the
process, preferably the stream of the vaporized concentrated nitric acid
from the first column, is effected, and that a mixer is provided in which
to the extraction medium supplied to the first column (K1.0) a controlled
amount of the nitric acid to be concentrated is admixed.
Process for the production of a nitric acid having a concentration of 75 to 99.9% from a more diluted, optionally impure nitric acid, wherein a nitric acid of a concentration of about 45 to 70% is rectified at a pressure from 100 mbar absolute to 5 bar absolute by contacting it with a liquid extraction medium for preventing the formation of a nitric acid-water azeotropic mixture, the vapors of the concentrated nitric acid is obtained, and wherein, additionally, the extraction medium is recovered by re concentration at a pressure in the range from 50 mbar absolute to 4 bar absolute and returned to the extractive rectification, characterized in partially or substantially utilizing the heat contents of the available process streams of the entire process and feeding the nitric acid to be concentrated in the form of a boiling liquid or partially vaporized or separated into vapor and liquid into the extractive rectification, utilizing the heat contents available in the entire process (Wl, W2, W5), and enriching at least 50% of the amount of extraction medium before feeding it at a temperature in the range from 80°C to 160°C into the extractive rectification in an amount of 0.1 to 60% of the nitric acid to be concentrated with nitric acid, preferably a nitric acid in the concentration range of the nitric acid to be concentrated, and supplying the energy required for the extractive rectification exclusively, or to a substantial proportion thereof by indirect heating (W4, W8) and supplying the extraction medium to the extractive rectification in a form as concentrated as possible, such that when at the same time the extraction medium leaving the extractive distillation is as diluted as possible, the circulating amount of extraction medium is minimized.

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Patent Number

200932

Indian Patent Application Number

IN/PCT/2002/01473/KOL

PG Journal Number

N/A

Publication Date

19-Jan-2007

Grant Date

19-Jan-2007

Date of Filing

28-Nov-2002

Name of Patentee

QVF ENGINEERING GMBH

Applicant Address

HATTENBERGSTRASSE 36, D-55122 MAINZ

Inventors:

#	Inventor's Name	Inventor's Address
1	DICHTL, GOTTFRIED	FUSTSTRASSE 24, D-55268 NIEDER-OLM
2	DORSTEWITZ, FRANK	PAUL-GERHARDT-STRASSE 27, D-65199 WIESBADEN
3	SASSENBERG, MANFRED	FONTANESTRASSE 20, D-55127 MAINZ
4	WALTER, ULRICH	IM ALTEN HOF 4, D-65510 IDSTEIN

PCT International Classification Number

C01B 21/44

PCT International Application Number

PCT/EP00/04641

PCT International Filing date

2000-05-22

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	N/A	2002-11-28	Germany