Title of Invention

AN IMPROVED PROCESS FOR THE HYDROGENATION OF NITROAROMATICS IN FIXED BED REACTORS

Abstract

The present invention discloses an improved process for the hydrogenatkm of nitroaromatics in fixed bed single tube reactors which results in reduction of peak reaction zone temperatures preventing thermal degradation thereby and improved catalyst performance, enhanced throughputs through the same reactor and better catalyst productivity. The process can be scaled up easily in similar industrial multi-tubular reactors.

Full Text

FORM 2 THE PATENT ACT, 1970 (39 of 1970) & THE PATENT RULES, 2003 COMPLETE SPECIFICATION (See Section 10, Rule 13) 1. TITLE OF THE INVENTION: AN IMPROVED PROCESS FOR THE HYDROGENATION OF NITROAROMATICS IN FIXED BED REACTORS. 2. APPLICANT® (a) Name: M/s. HINDUSTAN ORGANIC CHEMICALS LIMITED (b) Nationality (c) Address: Indian Mr. A. S.DWolkar.CMD 81, Maharshi Karve Road, MUMBAI - 400 002, Maharashtra, India. 3. PREAMBLE TO THE DESCRIPTION: COMPLETE SPECIFICATION The following speoftcation parttcutarty describes the invention and the manner in which it is to be performed: PRIOR ART Our previous went regarding hydrogenation of nitrobenzene to aniline (IN 197777 and Indian Patent Application Number 2010/MUM/2008 dated 18/09/2008) is concerned with vapor phase reaction in fixed beds involving a highly selective and active catalyst However many times, improvements in catalyst alone are not adequate enough to improve the reactor rjerformance* especially the productivity. Reaction engineering and catalyst layout aspects also assume significance in this respect Improved processes with respect to these factors can enhance me reactor throughput further, with better catalyst productivity. Exothermic reactions in fixed beds with heat removal arrangements for mamtaining isothermal conditions result in a peak/maximum temperature at a particular location (zone) akmg the length of the bed, which is much above me temperatures in me remaining part of the reactor. The catalyst in the peak temperature zone may degrade thermally. Sintering phenomenon may also occur in some cases, depending upon the magnitude of the temperature. High temperatures may also give rise to side-products formation, which may result in deposits etc. on the catalyst surface. This may result in decrease in catalyst life (productivity). Mixed catalyst beds without or with inerts, along with the regular catalysts, have already been successfully used for butynediol synthesis in liquid phase fixed bed bubble column reactors. Our Indian Patent Application Number 1523/MUM/2008 dated 18/07/2008 revealed mat the performance of a siHcagel based copper catalyst can be improved significantly, by mixing the same with magnesium oxide (MgOX in various proportions. However, MgO in this case was not an inert Our further work regarding the same (Indian Patent Application Number 1006/MUM/2009 dated 17/04/2009) for improving the performance of existing reactor, discovered mat by using inerts (porcelain inlelox saddles) in various proportions, the productivity of the catalyst mixed bed was enhanced significantly as compared to the reactor with normal catalyst bed. OBJECTIVE OF THE INVENTION The main objective of the invention is to eliminate file disadvantages of thermal degradation of catalysts (thereby sintering, loss m catalyst activity, formation of side products the main reaction etc.) in exothermic reactions in fixed bed reactors. Isothermal fixed bed reactor operations are accompanied by temperatnre peaks inside the reaction zone, with magnitude much more than the temperatures achieved in the remaining reaction zone. litis may result in lower capacity utilization of the reactor and lower catalyst productivity. Tins invention aims for better capacity utilization and better catalyst productivity from the existing fixed bed reactors, by an improved process of using merts m combination with the catalyst in optimum proportion, which enable lowering of me peak temperatures in the reaction zone, without decreasing die overall conversion through the catalyst bed SUMMARY OF THE INVENTION The present invention discloses an arrangement by which the performance of a fixed bed reactor can be improved significantly, by packing the catalyst along with suitable inerts in optimum proportion. In one embodiment of the present invention, the catalyst is mixed with inert ceramic raschig rings of suitable size, to form a mixed bed at the top (reactor entrance zone), with the bottom portion containing pure catalyst In another embodiment of mis invention, the said catalyst in two layers viz. mixed bed and pure bed, is employed for vapour phase hydrogenation of nitroaromatics to corresponding amines. In the most preferred embodiment of the present invention, the maximum (peak) temperature in the reaction zone is decreased significantly by using die catalyst arrangement disclosed in mis invention, thereby preventing the thermal degradation of the catalyst and various undesirable effects following the same. 3 in another preferred embodiment of the invention, it is possible to operate the same reactor in a better maimer, at increased throughputs (tower mole ratios of hydrogen to nitroaromatics) to achieve a much better productivity man the normal reactor, by the process of mis invention. DETAILED DESCRIPTION OF THE INVENTION The catalyst of the present invention is the same as mat referred to in our earlier work (Indian Patent Application Number 2010/MUM/2008 dated 18/09/2009), which is used in combination with standard ceramic raschig rums S mm diameter and 4 mm height, which act as inerts for the hydrogenation reaction. The combination is used in two layers, the top layer containing the catalyst mixed with the inert ceramic rings in a volumetric proportion from about 25% active catalyst to 70%, preferably 60%. The bottom layer contains me catalyst as such, without any inerts (pure catalyst). The volumetric proportion of the top layer in the total varies from 30% to 60% preferably 45%. The reactor for the present invention is similar to that used for our earner work (Indian Patent Application Number 2010/MUM/2008 dated 18/09/2009X comprising of a stainless steel single tube corresponding to a mum* tubular industrial reactor, with a jacketed arrangement for hot oil circulation and a multi point temperature measurement along its length. The catalyst activation procedure and the range of general parameters (pressure, temperature, space velocity, etc.) used is same as our earlier work referred above. Hydrogenation of nitroaromatics to corresponding amines is carried out to almost completion in the fixed bed reactor, under varying mole ratios of hydrogen to nitroaromatics from 25 to 5, preferably 20 to 10 and hot oil inlet teinperatures 120° to 200°C, preferably 160° to 180°C. Hie various mole ratios correspond to me variation in reactors throughput, since hydrogen input is maintained constant Maximum reaction zone temperature for each set is recorded. The same is compared with the reactor under similar conditions, where only catalyst without inerts is used This invention covers hydrogenation of mtroaromatics in general, preferably nitrobenzene and nUrotohienes. The process of this invention using mixed catalyst bed, lowers die maximum reaction zone temperatures achieved in fixed bed reactors, thereby avoiding thermal degradation of die catalyst and achieving better rjroductivhy, as well as enhanced throughput from the existing reactors using catalyst packed in conventional manner* The present invention is described below by way of examples. However, the following examples are illustrative and should not be construed as limiting die scope of the invention. EXAMPLE 1 Vapour phase hydrogenation of nitrobenzene to aniline was carried out in a stainless steel single tube corresponding to a multi-tubular industrial reactor with mum' point temperature recorder along its length and a hot oil arrangement for heat removal The fixed bed catalyst used was the same and activated in the same manner, as described in our earlier work (Indian Patent Application # 2O10/MUM/2O08 dated 18/09/2008). The reaction was also carried out under the same range of space velocities and other parameters as therein. Almost complete conversion of nitrobenzene was ensured from the reactor outlet, with aniline content more man 99.5% w and un-reacted nitrobenzene content less man 10 ppm. Runs were carried out at different mole ratios of hydrogen to nitrobenzene under constant feed of hydrogen gas. Two sets of hot oil temperatures were taken and maximum (peak) temperature achieved in die reactor was recorded in each case. The results are described in Tables 1 and 2. Table 1 Runs at 160 #C hot oil inlet temperature Mole ratio (Hydrogen; Nitrobenzene) 20 15.3 1X5 10 Maximum reactor temperature, °C 260 280 295 310 Table 2 Rons at 180 9C hot oil inlet temperature Mole ratio (Hydrogen : Nitrobenzene) 20 15.3 12.5 10.22 Maximum reactor temperature, °C 280 300 315 325 EXAMPLE 2 The same fixed bed stamless steel reactor, as described in Example 1, was used for these studies, using the same catalyst, as before. However, the catalyst was mixed with inert ceramic raschig rings 5 mm diameter and 4 mm height in volumetric proportion of 60% active catalyst and charged as mixed bed at the top of the (down flow) reactor. Remaining part of the reactor was packed with the same catalyst as before, however without any inerts added to the same (pure bed). The vohimelric proportion of mixed catalyst bed (top) in the total reactor was 45% Reaction runs were carried out with this arrangement under the same parameters and space velocities as mentioned in Example 1, up to almost complete conversion of nitrobenzene. Peak reactor temperatures were noted each time with varying mole ratios of hydrogen to nitrobenzene. Two sets of hot oil inlet temperatures were taken similar to those given in Example 1. The results are described in Tables 3 and 4. Table 3 Runs at 160 *C hot oil inlet temperature Mole ratio (Hydrogen: Nitrobenzene) 20 12.5 10 8.33 Maximum reactor temperature, °C 200 245 270 290 Table 4 Runs at 180*C hot oil inlet temperature Mole ratio (Hydrogen: Nitrobenzene) 20 12.5 10 8.33 Maximum reactor temperature, °C 220 265 290 315 EXAMPLE 3 The same reactor and the same catalyst arrangement of mixed bed and pure bed, as described in detail in Example 2 was used for the hydrogenation of nitrotoluenes to corresponding tohndines (ortho and meta isomers). Reaction runs were carried out up to almost complete conversion of nitroaromatics at two sets of hot oil inlet temperatures at the same mole ratio of hydrogen to nitroaromatics. The results are summarized in Table 5. Peak reactor temperatures were noted and compared with those obtained under similar conditions to pure catalyst bed operation (described in Example 1). It clearly showed a decrease of about 50 °C in peak temperature, by using mixed beds. Moreover, peak temperatures achieved for ortho and meta tohndines were observed to be much below those for aniline, under similar conditions. Table 5 Runs at a 12.5:1 Mole Ratio of Hydrogen: Nitroaromatics We claim: 1. An improved process for the bydrogenation of nitroaromatics in fixed bed single tube reactors, which comprises of : mixing the catalyst with suitable inerts in optimum proportions and using the same as mixed bed in the top layer (near the entrance of the reactor), while the remaining part of the reactor contains normal catalyst, thereby preventing the thermal degradation of the catalyst, by lowering the peak reaction zone temperatures, enabling the rector to be operated at higher throughputs compared to a normal catalyst packed throughout the reactor, at complete conversion of nitroaromatics. 2. A process as claimed in Claim 1, wherein the nitroaromatics may be nitrobenzene or mtrotohsenes. 3. A process as claimed in Claim 1, which is preferably vapour phase using standard copper oxide based catalyst, with or without any additives, promoters or surface modifiers. 4. A process as claimed in Claim 1, wherein the inerts may be suitable as per the reactor size and their material may be preferably ceramic raschig rings. 5. A process as claimed in Claim 1, wherein the volumetric proportion of active catalyst in the top mixed layer varies from 25 to 70%, preferably 60%. 6. A process as aimed in Claim 1, wherein the volumetric proportion of the top mixed layer in the total reactor varies from 30 to 60%, preferably 45%. 7. A process as claimed in Claim 1, wherein the lowering of peak reaction zone temperatures increases wim increasing proportion of inerts, typically in the range of 0 to 80 °C. 8. A process as claimed in Claim 1, wherein the throughput is enhanced wim decreasing mole ratio of hydrogen to nifroaromatics, in the range of 25 to 5, preferably 20 to 10. 9. A process as claimed in Claims 1 to 8 which can be scaled up nearly 5000 times from the said single tube reactor to similar multi-tabular industrial scale reactors, substantially as herein described wim reference to Examples 1 to 3 in the specification. Dated this , day of 2009. For and on behalf of HINDUSTAN ORGANIC CHEMICALS LIMITED

Documents:

1334-mum-2009-abstract.doc

1334-mum-2009-abstract.pdf

1334-MUM-2009-ANNEXURE B(SUBMISSION)-(17-7-2013).pdf

1334-MUM-2009-CLAIMS(AMENDED)-(17-7-2013).pdf

1334-MUM-2009-CLAIMS(AMENDED)-(22-2-2012).pdf

1334-mum-2009-claims.doc

1334-mum-2009-claims.pdf

1334-MUM-2009-CORRESPONDENCE(10-7-2009).pdf

1334-MUM-2009-CORRESPONDENCE(21-1-2013).pdf

1334-MUM-2009-CORRESPONDENCE(27-12-2012).pdf

1334-MUM-2009-CORRESPONDENCE(5-2-2013).pdf

1334-MUM-2009-CORRESPONDENCE(9-11-2012).pdf

1334-mum-2009-description(complete).doc

1334-mum-2009-description(complete).pdf

1334-mum-2009-form 1.pdf

1334-mum-2009-form 18.pdf

1334-mum-2009-form 2(title page).pdf

1334-mum-2009-form 2.doc

1334-mum-2009-form 2.pdf

1334-mum-2009-form 3.pdf

1334-mum-2009-form 5.pdf

1334-mum-2009-form 9.pdf

1334-MUM-2009-PUBLICATION REPORT(10-7-2009).pdf

1334-MUM-2009-REPLY TO EXAMINATION REPORT(22-2-2012).pdf

1334-MUM-2009-REPLY TO HEARING(17-7-2013).pdf