|Title of Invention||
"A PROCESS FOR THE PURIFICATION OF LIQUID SULPHUR"
|Abstract||The present invention provides a process for the purification of liquid sulphur by removing gaseous elements such as hydrogen sulfides and hydrogen poiysulfides therefrom. For this purpose a novel catalyst system comprising a synergistic mixture of a non-ammonia heteroaromatic nitrogen bearing compound and an alkyl amine is used. The residence times are low and the product obtained is of high purity. The present invention also relates to the novel catalyst system and a process for the preparation thereof.|
|Full Text||PROCESS FOR PURIFICATION BY DEGASSING OF LIQUID SULPHUR Field of the invention
The present invention relates to a process for degassing liquid sulphur. More particularly, the present invention relates to a process for purifying liquid sulphur by degassing the liquid sulphur using a non-ammonia degassing agent to remove hydrogen sulphide and hydrogen polysulphides therefrom. The present invention also relates to a composition for use in the degassing of liquid sulphur to remove hydrogen sulphide and hydrogen polysulphide impurities therefrom comprising a synthetic synergistic composition comprising of non-ammonia heteroaromatic nitrogen bearing compounds and alkyl amines. Background of the invention
The Claus process is a well-known process for producing elemental sulphur from hydrogen sulphide by the reaction of hydrogen sulphide and sulphur dioxide to produce elemental sulphur and water. Typically, hydrogen sulphide contained in product gas from petroleum refinery operations is partially combusted in a thermal zone to produce sulphur dioxide, which then reacts with the unburned hydrogen sulphide to yield sulphur and water. The sulphur is then condensed and recovered. One or more catalytic zones are also provided in which the same reaction is further promoted by means of a suitable catalyst, causing additional sulphur to be recovered.
In Claus plants the hydrogen sulphide is converted to elementary sulphur vapor by oxidation with sulphur dioxide. The sulphur vapor is condensed in condensers and the liquid sulphur is stored temporarily in sulphur pits. During condensation of the sulphur vapor in the condensers, the liquid sulphur absorbs a
considerable amount of hydrogen sulphide from the vapour phase. A part of the
hydrogen sulphide reacts with liquid sulphur and forms hydrogen poly sulphides.
The concentration of the latter increases with the increase in the liquid sulphur
Unfortunately, the transportation and handling of degassed liquid sulphur is
extremely difficult. Explosions and fires have been reported due to release of
hydrogen sulphide to the atmosphere during handling of the undegassed liquid
sulphur. It is reported that hydrogen sulphide is lethal at 600 ppm in air and
explosive at 3.5% volume in air at 150°C.
Apart from the problem of explosion and toxicity, another problem of
hydrogen sulphide contamination in liquid sulphur is that of odor. The stench due to
hydrogen sulphide is a nuisance. It is therefore essential that in installations
producing or processing sulphur, the amount of hydrogen sulphide and
polysulphides must be reduced to below 10 ppm by weight.
While it is relatively easy to remove dissolved hydrogen sulphide from liquid
sulphur by physical processes such as stirring, spraying, pumping or by passing gas
or air through it, removal of the hydrogen polysulphides formed is a difficult
problem. In order to remove the polysulphides, it is first essential that they be
decomposed to hydrogen sulphide and elemental sulphur according to the following
before the hydrogen sulphide thus formed can be removed from the liquid sulphur
It is known to accelerate the decomposition of polysulphides by adding nitrogenous compounds such as ammonia, ammonium salts, organic nitrogen compounds (such as alkyl amines, alkanol amines or aromatic nitrogen compounds) or urea. These nitrogen compounds function as a catalyst and thus shorten the decomposition time and hence the time required for degassing.
The SNEA sulphur degassing process [developed by Societe Nationale des Petroles d' Aquitaine (SNPA) now known as SNEA] involves pumping round and spraying of sulphur, with ammonia being added as catalyst (French Patent No. 1,435,788). This process was subsequently improved from non-continuous mode to continuous mode where the sulphur is circulated over two compartments and sprayed with the addition of ammonia as a catalyst. Further modifications of this process involve using liquid catalyst [The process is known as Aquisulph (Oil and Gas Journal Jul. 17,1989, pp. 65-69)].
A process was developed by Exxon for the degassing of sulphur which involved adding a liquid catalyst in the sulphur pit or tank (CEP October 1985, pp. 42-44 and in Hydrocarbon Processmg May 1981, pp. 102-103). In the Exxon process the sulphur is not circulated or agitated in any other way. While the process results in saving in terms of energy costs, the retention time is very high. To achieve substantial degassing, the retention time is from 3 to 4 days.
US Patents Nos. 3,807,141 and 3,920,424 to Texas Gulf disclose a sulphur degassing process wherein the liquid sulphur flows down a column over dishes and the sulphur is degassed countercurrently with air. The equipment modifications required are expensive in this process.
Dutch Patent 173,735 granted to Shell Internationale Research Maatschappij discloses a method consisting of a single process step in which air or a mixture of an inert gas and oxygen is passed through liquid sulphur in the presence of a catalyst, typically a nitrogen compound, in finely divided condition and thereafter the liquid sulphur and the used gas are separated from each other.
A comparable method is described in DD-A 292,635. According to this method, the treated sulphur, prior to the further processing, is subjected to a supplementary post-gassing. However, such a post-gassing has no effect or substantially no effect on the reduction of the sulphide content in the liquid sulphur. A proprietary sulphur degassing process known as "HySpec" (Procor) consists of a number of gas-liquid contact mixers arranged in series (presented at the Su?phur '94 conference at Tampa Fla., Nov. 6-9,1994; WO-A 95/06616). A catalyst is added to the contact mixers and finally in the last mixing stage the sulphur is stripped of the added catalyst by passing air through it. Such a gas-liquid contact mixer consists of a mixer driven by an electric motor, which circulates the sulphur with drawn-in air over a perforated cylinder. A disadvantage of this method is the use of moving parts such as an agitator, which comes into contact with the liquid sulphur. In systems with liquid sulphur, there is a great chance that moving parts will jam.
While the size of sulphur degassing plants can be reduced by using a catalyst, additional disadvantages of contamination of the sulphur arise. Another problem is of clogging due to the formation of ammonium sulphate salt where ammonia or ammoniacal compounds are used as a catalyst. The ammonium sulphate salts thus formed also lead to corrosion problems in the reactor thereby resulting in additional
costs of adaptation of sulphur degassing plants Another significant disadvantage is
that such a process requires a much longer degassing time, entailing higher investment and involving higher energy consumption.
British Patent No. 1,067,815 discloses a degasification process for removal of hydrogen sulphide by atomizing the liquid sulphur containing hydrogen sulphide by forcing it through a jet or nozzle and then directing the resulting spray against an obstacle, thus promoting the removal of the gaseous H2S. It is also disclosed that the presence of ammonia (100 ppm) promoted the removal of H2S. In the absence of the use of ammonia the H2S reduction is extremely slow, involving long time spans. However, the use of ammonia inherently results in a contaminated product.
Alternate methods for removal of H2S reminiscent of the Claus reaction have been reported in U.S. Patent No. 3,447,903 and Canadian Patent No. 964,040. In U.S. Patent No. 3,447,903 a catalytic process for producing elemental sulphur from H2S and SO2 in liquid sulphur is disclosed. The catalyst involved is described generically as a basic nitrogen compound having a KB value (in water) greater than 10"10 and a solubility in molten sulphur of at least one part per million. This process, as taught, can be practiced for the purpose of controlling purity of liquid sulphur containing small concentrations of H2S. Canadian Patent No. 964,040 involves injecting liquid SO2 and a nitrogen containing compound, which complexes with the SO2 to form an adduct, into the molten sulphur for the expressed purpose of having the SO2 -nitrogen adduct react with the xmdesirable poly sulphide dissolved in sulphur. Hence, it is known that certain nitrogen compounds in combination with SO2 will catalytically reduce the H2S and H2Sx concentration found in liquid sulphur. Such processes against inherently involve soluble nitrogen containing species being
present in the sulphur after degradation of the sulphide and polysulphides; i.e., the processes merely replace one contaminant for another contaminant.
US Patent No. 6149887 discloses a method for removing hydrogen sulphide and hydrogen polysulphide compounds out of liquid sulphur by stripping with a gas, such as air. The method is conducted in an apparatus equipped with at least two degassing compartments and a sulphur collection pit wherein the degassing compartments are separated from each other by a first partition wall, the last degassing compartment is separated from the sulphur collection pit by a second partition wall. Each degassing compartment contains at least a first, and second sub-compartments separated from each other by a third partition wall and are open to each other at the top and the bottom. At least one first sub-compartment in each said degassing compartment is provided at the bottom with a plurality of stripping gas inlet nozzles and at least one second sub-compartment in each said degassing compartment is not provided with stripping gas inlet nozzles. The one first sub-compartment is constructed to allow flow of liquid sulphur over or through the first partition wall to a subsequent degassing compartment. The last degassing compartment is constructed to allow flow of liquid sulphur to the sulphur collection pit over the second partition wall and the apparatus is also provided with a provision for discharging gas comprising hydrogen sulphide. The apparatus is expensive.
US Patent No. 5080695 discloses a process for the degasification of liquid sulphur produced by the Claus process to remove hydrogen sulphide. The liquid sulphur is caused to flow continuously through a vessel where it is contacted by a
counter-flowing inert gas such as nitrogen or air thereby stripping hydrogen
sulphide from the sulphur. However the disadvantage of this process is that the
portion of the conduit which is common to the flow of both liquid sulphur and gas
should be long enough to ensure sufficient intimate contact between the gas and the
liquid sulphur so that adequate stripping of hydrogen sulphide takes place. Further,
the annular space between the gas tubing and the conduit should be large enough so
as not to restrict the flow of sulphur through the vessel as required by the output of
the manufacturing process, but small enough to allow the desired intimate contact.
The pressure of the stripping gas must be sufficient to overcome the pressure of the
liquid sulphur and the pressure head at the bottom of the tube in order to escape
from the tube. These physical parameters render the process equipment expensive.
Another disadvantage is that the reduction in ppm level of hydrogen sulphide is
only to the level of 50%. The efficiency of the process also depends on the residence
time which in turn depends on the above-mentioned physical equipment
requirements of tube length.
US Patent No. 5935548 discloses a process where hydrogen sulphide is
removed from a molten sulphur steam containing at least one of hydrogen sulphide
and hydrogen polysulphides by mixing the molten sulphur stream with a degassed
molten sulphur in an eductor to form a mixture, contacting the mixture with a finely
dispersed gaseous oxidant such as sulphur dioxide, oxygen enriched air or air,
separating hydrogen sulphide from the mixture and recovering molten sulphur
having a reduced hydrogen sulphide content. The process suffers from a singular
disadvantage that the level of removal of hydrogen sulphide is dependant on the
residence time and therefore for higher level of removal of hydrogen sulphide,
longer tubes, have to be provided to increase the residence time.
US Patent No. 4844720 discloses a process for catalytic degradation of hydrogen polysulphide to hydrogen sulphide in liquid sulphur and removal of hydrogen sulphide from the liquid sulphur by contacting the liquid sulphur containing the hydrogen sulphide and hydrogen polysulphide with a solid degradation catalyst selected from alumina and alumina impregnated with a cobalt-molybdenum desulphurization catalyst at a temperature of from 250°F to 320°F and simultaneously purging the liquid sulphur in contact with solid catalyst with a gas selected from air or oxygen enriched air. It is claimed that this removes the hydrogen sulphide and hydrogen polysulphide from the liquid sulphur at a rate greater than previously achieved. However, again the residence times are still not suitable for large scale commercial operations. Additionally, the use of a solid catalyst apart from the use of air or oxygen enriched air results in a complex and expensive process.
German Patent No. 15 67 791 discloses a process where the liquid sulphur is sprayed into a chamber at a temperature of 125 to 145°C. Ammonia (used as a degasification accelerator) is added to the sulphur before it is sprayed. The degasification accelerator serves mainly to convert the polysulphide to liquid hydrogen sulphide. British Patent No. 1,433,822 teaches the use of air or diethanolamine as a degasification accelerator. The process in accordance with the British patent uses a vessel having two chambers and an overflow over which the treated sulphur flows from the first chamber into the second.
US Patent No. 4612020 discloses a process wherein the liquid sulphur containing the H2S is sprayed in a steel vessel and the liberated gases which are rich
in H2S are withdrawn. A degasification accelerator comprising 40 - 100% nitrogen is
added to the liquid sulphur. The steel vessel contains at least two chambers, which communicate with each other and are connected in series. Sulphur at temperatures in the range from 140 to 160°C is supplied to the first chamber. Sulphur is withdrawn from the second chamber and is cooled to temperatures of 120 to 135°C outside the vessel. The liquid sulphur, which has been cooled, is sprayed in the gas space of the first chamber. The sulphur is caused to remain in the steel vessel for a dwelling time of 12 to 32 hours. The gas spaces of the chambers are scavenged with an oxygen-free inert gas. The sulphur is withdrawn from the vessel and sprayed in the gas space of one of the chambers about 30 to 50 times until the dwelling time of the sulphur in the vessel has expired. The disadvantage of this process is that the residence time is too long rendering the process unsuitable for large-scale commercial operations.
US Patent 5030438 discloses a process for the degassification of liquid sulphur using a catalyst system comprising of a heterocyclic compound. Examples of the heterocyclic compound include quinoline, isoquinoline, acridine, benzacridine, benzoquinoline, quinoxaline and the like. However, the commercial viability of the process on commercial scale have not been demonstrated.
US Patent 5004591 discloses an improved catalytic process for removing H2S
and sulfanes from liquid sulfur and a catalyst system for carrying out the process.
The catalyst comprises a basic component and optionally a surfactant component
The surfactant when employed comprises at least one compound selected from the
group consisting of fatty amines, fatty alkylene diamines, salts of fatty amines, salts
of fatty diamines, oxyalkylated derivatives of fatty amines, oxyalkylated derivatives
of fatty diamines, salts of oxyalkylated fatty amines, salts of oxyalkylated fatty
diamines, fatty quaternary ammonium compounds and benzalconium salts. The
base used comprises heterocyclic compounds such as quinoline, isoquinoline,
benzoquinoline, acridine, benzacridine, quinoxaline, quinazoline, phenazine,
phenantridine, phenantrolines, naphthyridines, bipyridyls. As used in this
disclosure, the catalyst system can also be monocomponent comprising a single
compound having both basic and surfactant properties. As such, in the two
component system, the purpose of the surfactant is only to ease the operation of the
As disclosed above, it is known in the art to remove the hydrogen sulphide
and hydrogen polysulphides by physical separation. The release of hydrogen
sulphide from the liquid sulphur accelerates the rate of decomposition of tne
hydrogen polysulphides to hydrogen sulphide and elemental sulphur. However, the
major disadvantage of modern commercial degassing processes is that they require
large, complex and expensive equipment. For example, the Shell process takes place
in a sulphur pit or storage tank where liquid sulphur is vigorously agitated by
bubbling air at atmospheric pressure. The stripping columns are open at the top and
bottom in order to allow the sulphur to circulate along with the sweep air to displace
the hydrogen sulphide produced from vapour phase.
Another disadvantage of the prior art processes is that a large retention time
is required in the sulphur pit. For example, the Shell process requires the liquid
sulphur to be circulated through the stripping column for about 20 - 24 hour, and
the SNEA process typically requires 24 - 32 hours.
There is therefore a definite need for a liquid sulphur degassing process that
not only efficiently reduces the hydrogen sulphide concentration in the liquid
sulphtir but also requires a relatively short residence time to achieve the desired liquid sulphur degassing, a minimum space area and reduced cost. Objects of the invention
It is the principal object of the present invention to degassify the liquid sulphur reliably at low cost while precluding the risk of explosion or fire.
Another object is to effect the method such that an undesired temperature rise of the liquid sulphur to be treated is avoided.
It is another object of the invention to provide a method for the degasification of liquid sulphur where that is economical and efficient.
It is a further object of the invention to provide a process for the degasification of liquid sulphur by the removal of hydrogen sulphide impurities that is safe, requires less time and is easy to operate and results in a final pure product with minimal contamination. Summary of the invention
The present invention is based on the use of non-ammoniacal degassing agents for reducing the concentration of hydrogen sulphide and hydrogen polysulphide present in liquid sulphur. The invention is based on the surprising interaction and results obtained by the use of a synergistic composition comprising of a synthetic mixture of a nitrogen bearing heteroaromatic compound and an alkyl amine. It has been now surprisingly found that this combination of a non-ammonia heteroaromatic nitrogen bearing compound such as quinoline and an alkyl amine such as dibutylamine or diethylamine or propylamine when contacted with liquid sulphur containing hydrogen sulphide and hydrogen polysulphide as impurities
reduces the concentration of the contaminants to less than 10 ppm while requiring
less residence time. Another significant advantage of using the synergistic mixture of the invention in degassing of liquid sulphur is that the level of equipment modification is low thereby reducing the costs of the process. Thus, the process of the invention is suitable for large scale commercial operations. Since the components of the mixture are readily available, the net costs of the process are further reduced.
The synthetic mixture of non-ammonia heteroaromatic nitrogen bearing compound and alkyl amine is a synergistic composition showing improved and unexpected properties over the prior art and not an aggregate of properties of the individual ingredients.
Accordingly the present invention provides a process for the purification of liquid sulphur by the removal of hydrogen sulphide and hydrogen polysulphide present therein comprising adding an effective amount of a degassing agent comprising a non-ammonia heteroaromatic nitrogen bearing compound such as herein described and an alkyl amine to a solution of liquid sulphur in a degassing chamber, sweeping the vapor phase of hydrogen sulphide out of the degassing chamber, separating out the substantially pure liquid sulphur.
In one embodiment of the invention, the degassing agent is added to the liquid sulphur at the rate of 10 to 15 ppm by weight.
In another embodiment of the invention, the sweep to remove the hydrogen sulphide gas released from the liquid sulphur is carried out in vacuum of about 0.02 bar.
In yet another embodiment of the invention, the residence time for the liquid sulphur in the sulphur pit is in the range of 3 to 4 hours.
In a further embodiment of the invention, the temperature in the sulphur pit is maintained in the range of 125 to 140°C
In yet another embodiment of the invention, the temperature in the sulphur pit is maintained by means of LP steam coil.
In another embodiment of the invention, the concentration of the hydrogen sulphide and hydrogen polysulphides in the final product is between 4-10 ppm.
The invention also provides a degassing agent for use in degassing of liquid sulphur comprising a synthetic mixture of a non-ammonia heteroaromatic nitrogen bearing compound and an alkyl amine.
In one embodiment of the invention, the degassing agent composition comprises a synthetic mixture of a non-ammonia heteroaromatic nitrogen bearing compound and an alkyl amine in a ratio of nitrogen bearing compound to alkyl amine of 4:1 to 19:1.
In another embodiment of the invention, the non-ammonia heteroaromatic nitrogen bearing compound comprises quinoline.
In a further embodiment of the invention, the alkyl amine is selected from the group consisting of dibutyl amine, dipropyl amine and ethyl amine.
The invention also relates to a process for preparing a catalyst composition for use as a degassing agent which comprising mixing in any conventional manner a non-ammonia heteroaromatic nitrogen bearing compound and an alkyl amine in a ratio of 4:1 to 19:1.
In one embodiment of the invention, the non-ammonia heteroaromatic nitrogen bearing compound comprises quinoline.
In another embodiment of the invention, the alkyl amine is selected from the group consisting of ethylamine, dipropyl amine and dibutylamine.
The catalyst system used in the invention is a synergistic admixture evincing enhanced properties over the prior art catalyst systems used in the degassing of liquid sulphur. The catalyst system of the invention is not a mere admixture with properties that are an aggregate of the properties of the individual components, neither is it a product of a chemical reaction. Brief description of the accompanying drawing
The present invention will now be described in greater detail with reference to the sole figure of the accompanying drawings which shows a schematic representation of the liquid sulphur degassing system for use in the process of the present invention. Detailed description of the invention
The present invention involves the use of a synthetic mixture of a non-ammonia heteroaromatic nitrogen bearing compound and an alkyl amine as a degassing agent for the degassing of liquid sulphur to reduce the concentration of hydrogen sulphide and hydrogen polysulphide. The solution of the degassing agent is metered into the sulphur pit of the Claus process by a chemical injection pump. In the process of the invention, the residence time of the liquid sulphur in the sulphur pit required to reduce the concentration of hydrogen sulphide and hydrogen polysulphide to less than 10 ppm is reduced to 3 - 4 hours. The process also involves the use of air sweep to remove the gaseous hydrogen sulphide released from the liquid sulphur, liquid sulphur circulation and spray in the sulphur pit.
In order to illustrate the invention better, reference is made to the accompanying drawing showing the process flow of the invention using the degassing agent of the invention.
The liquid sulphur of a conventional Claus unit is fed through a line (1) at a temperature of 125 - 140°C and at a positive pressure into the inspection compartment (2) of the sulphur pit (4). The temperature of the liquid sulphur in the pit (4) is maintained by LP steam using an LP steam coil (5). The sweep air is allowed to enter into the discharged compartment (3) of the pit (4) by line (6) through a window provided at the top section of the discharge compartment (3). The air flows to the inspection compartment (2) from the discharge compartment (3) and is finally fed to an incinerator by a line (7) using an ejector. The sweep air reduces the partial pressure of the hydrogen sulphide in the gas phase over the liquid sulphur in the pit (4) by removing the hydrogen sulphide gas. As a result, the hydrogen polysulphide decomposes according to the reaction H2Sx -> H2S+(x-l)S
The hydrogen sulphide thus formed in liquid phase is converted to gaseous phase and then swept out of the pit as described above. This accelerates the degassing of hydrogen sulphide and hydrogen polysulphide from the liquid sulphur.
Two liquid circulation pumps - pump (P-01) in inspection compartment (2)
and pump (P-02) in the discharge compartment (3) are engaged to draw the liquid
sulphur from the sumps of both compartments and then spray the liquid sulphur
into the opposite compartments. The circulation and spray level and speed is
maintained at a rate sufficient to ensure maximum mass transfer of the hydrogen
sulphide gas phase from the liquid sulphur.
The degassing agent comprising a synthetic mixture of a non-ammonia heteroaromatic nitrogen bearing compound and an alkyl amine is stored in a tank (8) and pumped into the sulphur pit (4) by means of a metering pump (P-03). Generally, the degassing agent is injected through a line (9) to the inspection compartment (2). If desired, the degassing agent may also be injected through a line (10) at the time of start up of the process to the discharge compartment (3). For both the degassing injection systems, the injection lines (9 and 10) are dipped into the liquid sulphur.
The sulphur pit (4) is provided with a partition (11) between two compartments. The two compartments are interlinked through a window in order to enable liquid circulation between two compartments. The bottom of each compartment is inclined from the partition window to the sump. For normal operation, a minimum liquid level (12) is maintained in each compartment so that the liquid sulphur can flow from one compartment to the other through the window. This is essential before injection of the degassing agent into the liquid sulphur.
Injection of the degassing agent can be done in either batch mode or in continuous mode. The continuous mode of injection is preferable if the accumulated amount of liquid sulphur in the sulphur pit (4) is high. The batch mode is carried out when the accumulated amount of liquid sulphur in the sulphur pit is considerably low. The residence time for the liquid sulphur in the sulphur pit irrespective of the mode of injection is from about 3 to 4 hours.
The rate at which the degassing agent is injected into the sulphur pit is
maintained at a rate of 10 to 15 ppm by weight with respect to the amount of liquid
sulphur in the pit (4). When the mode of injection used is the batch mode, the
amount of degassing agent is calculated based on the total amount of liquid sulphur
present in the pit and the concentration of the degassing agent at dosing time, the liquid sulphur inlet rate and the time between two successive doses. In the case of continuous mode of injection, the amount of degassing agent is calculated based on the liquid sulphur inlet rate into the pit.
The degassed sulphur obtained by the process of the invention consists of a total of hydrogen sulphide and hydrogen polysulphide content of less than 10 ppm. Normally the liquid circulation pump (P-02) in the discharge compartment (3) is used to pump the liquid sulphur off from the pit (4). The minimum liquid sulphur level in the pit controls the amount of the liquid sulphur that is discharged.
The concentration of the hydrogen sulphide and hydrogen polysulphides is detennined analytically. The analytical method comprises of rapid cooling of molten sulphur in a closed vessel. The sulphur is dissolved in an organic solvent and the hydrogen sulphide reacted with excess of standard silver nitrate solution. The polysulphides decompose to hydrogen sulphide during the reaction. The balance amount of silver nitrate is titrated by a standard solution of sodium chloride.
The following examples illustrate the process of the invention, the composition used as a degassing agent and are not intended to restrict the scope of the invention in any manner. Variations are possible and are within the scope and spirit of the invention. Example 1:
The process of the invention was run in a commercial unit. Two liquid sulphur streams containing total concentration of the hydrogen, sulphide and hydrogen polysulphides before degassing of 117 ppm and 120 ppm respectively was
taken for this study. The sweep air flow and circulation and spray of the liquid
sulphur during the demonstration run were maintained to ensure maximum mass transfer of the hydrogen sulphide from the liquid sulphur to the gas phase. The concentration of the degassing agent of the invention was maintained between 10 to 15 ppm in both liquid sulphur streams. The degassed liquid sulphur on analysis showed a total concentration of hydrogen sulphide and hydrogen polysulphide of less than 10 ppm for both studies. The degassed liquid sulphur obtained was bright yellow and of good quality. The results of both studies are provided in Table 1 below:
Table 1: Results of demonstration run using liquid sulphur containing 170 and 120 ppm of hydrogen sulphide and hydrogen polysulphide before degassing
As can be seen from Table 1 above, the process of the invention results in the
reduction of the total hydrogen sulphide and hydrogen polysulphide concentration
in the degassed liquid sulphur to less than 10 ppm due to the addition of the
degassing agent of the invention. The residence time is also less (3-4 hours).
1. A process for the purification of liquid sulphur by the removal of hydrogen
sulphide and hydrogen polysulphide present therein comprising adding to said
liquid sulphur in a degassing chamber, a degassing agent characterised in that
said degassing agent comprises a non-ammonia heteroaromatic nitrogen
bearing compound and an alkyl amine, the ratio of the non-ammonia
heteroaromatic nitrogen bearing compound to the alkyl amine being in the
range of 4:1 to 19:1, sweeping the vapor phase of hydrogen sulphide out of the
degassing chamber, separating out the substantially pure liquid sulphur.
2. A process as claimed in claim 1, wherein the non-ammonia heteroaromatic
nitrogen bearing compound is quinoline.
3. A process as claimed in claim 1, wherein the alkyl amine is selected from the
group consisting of ethylamine, dipropylamine and butylamine.
4. A process as claimed in any preceding claim, wherein the degassing agent is
added to the liquid sulphur at the rate of 10 to 15 ppm by weight.
5. A process as claimed in claims 1 to 4, wherein the sweep to remove the
hydrogen sulphide gas released from the liquid sulphur is carried out in
vacuum at a pressure of about 0.02 bar.
6. A process for the purification of liquid sulphur substantially as hereinbefore
described and with reference to the foregoing example and the accompanying
|Indian Patent Application Number||944/DEL/2001|
|PG Journal Number||48/2010|
|Date of Filing||12-Sep-2001|
|Name of Patentee||ENGINEERS INDIA LIMITED|
|Applicant Address||ENGINEERS INDIA BHAVAN, 1, BHIKAJI CAMA PLACE, NEW DELHI-110 066, INDIA.|
|PCT International Classification Number||C01B 17/02|
|PCT International Application Number||N/A|
|PCT International Filing date|