Process for the Production of Specialty Mercaptans From the C4 Oligomerization Product

Abstract

The present invention relates to a process for the production of specialty mercaptans from C.sub.4 oligomerization product. The oligomer product from the commercial C.sub.4 oligomerization process is separated in desired fractions of C.sub.8 and C.sub.12 olefins and these streams are further used as feed stock for the production of the specialty mercaptans such as tert octyl mercaptan (TOM) & tert dodecyl mercaptan (TDM). These fractionated oligomer stream (C.sub.8 and C.sub.12) from the C.sub.4 oligomerization process reacts with hydrogen sulfide in presence of pretreated cation exchange resin catalyst using appropriate inhibitors such as amine precursors, nitriles and metals to produce respective sulfur compounds tert-octyl mercaptan (TOM) and tert dodecyl mercaptan (TDM).

Claims

1. A process for producing specialty mercaptans from C.sub.4 oligomerization product, the process comprising: fractionating C.sub.4 oligomerization product to selectively recover desired oligomer fractions; loading a cation exchange resin catalyst into a reactor; pretreating the loaded cation exchange resin catalyst with an inhibitor in the reactor; feeding the recovered desired oligomer fractions and hydrogen sulfide (H.sub.2S) into the reactor to obtain a reaction product mixture; and separating the reaction product mixture into an un-converted oligomer and a final product, wherein the final product comprises specialty mercaptans.

2. The process as claimed in claim 1, wherein the cation exchange resin catalyst is pretreated with 2-10 wt % of the inhibitor, followed by heating at a temperature in a range of 50 to 90 C. for 3 to 4 hours, and further followed by drying at a temperature in a range of 100 to 120 C. for 5 to 10 hours in presence of nitrogen (N.sub.2).

3. The process as claimed in claim 1, wherein the recovered desired oligomer fractions and hydrogen sulfide (H.sub.2S) are mixed and reacted in the reactor at a temperature in a range of 50 to 110 C., and at a pressure in a range of 1 to 15 bar.

4. The process as claimed in claim 1, wherein the recovered desired oligomer fractions comprise di-isobutene, and tri-isobutene.

5. The process as claimed in claim 1, wherein the final product comprises tert octyl mercaptan when the oligomer fraction is di-isobutene, and wherein the final product comprises tert dodecyl mercaptan when the oligomer fraction is tri-isobutene.

6. The process as claimed in claim 4, wherein H.sub.2S and di-isobutylene are fed in a mole ratio of 1:1 to 10:1.

7. The process as claimed in claim 4, wherein H.sub.2S and tri-isobutylene are fed in a mole ratio of 1:1 to 10:1.

8. The process as claimed in claim 1, wherein the inhibitor is selected from the group consisting of an amine precursor, a nitrile precursor and a metal precursor.

9. The process as claimed in claim 8, wherein the amine precursor is methyl ethanol amine or methyl di ethanol amine, the nitrile precursor is acetonitrile, and the metal precursor is iron or sodium.

10. The process as claimed in claim 9, wherein methyl di ethanol amine yielded 94.33% conversion of di-isobutylene, and a selectivity of 98.30% tert octyl mercaptan.

11. The process as claimed in claim 1, wherein the cation exchange resin catalyst is an acidic cation exchange resin.

12. The process as claimed in claim 11, wherein the acidic cation exchange resin is sulfonated polystyrene divinyl benzene resin.

13. The process as claimed in claim 1, wherein the pretreated cation exchange resin catalyst has an active site concentration in a range of 3 to 4.5 eq/kg.

14. The process as claimed in claim 5, wherein the di-isobutene conversion to tert octyl mercaptan is in a range of 45% to 98%, and wherein the pretreated cation exchange resin catalyst has a selectivity for tert octyl mercaptan in a range of to 75% to 99%.

15. The process as claimed in claim 5, wherein the tri-isobutene conversion to tert dodecyl mercaptan is in a range of 5% to 10%, and wherein the pretreated cation exchange resin catalyst has a selectivity for tert dodecyl mercaptan in a range of to 75% to 99%.

16. The process as claimed in claim 1, wherein the tert octyl mercaptan has a purity in a range of 75% to 99%.

17. The process as claimed in claim 1, wherein the tert dodecyl mercaptan has a purity in a range of 90% to 95%.

Description

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0031] The following figures form part of the present specification and are included to further illustrate aspects of the present disclosure. The disclosure may be better understood by reference to the figures in combination with the detailed description of the specific embodiments presented herein.

[0032] FIG. 1 illustrates schematic representation of process to produce TOM/TDM, according to an embodiment of the present disclosure.

[0033] FIG. 2 illustrates schematic representation of catalyst activity for longer life in terms of TOM yield.

DETAILED DESCRIPTION OF THE INVENTION

[0034] For convenience, before further description of the present disclosure, certain terms employed in the specification, and examples are delineated here. These definitions should be read in light of the remainder of the disclosure and understood as by a person of skill in the art.

[0035] The terms used herein have the meanings recognized and known to those of skill in the art, however, for convenience and completeness, particular terms and their meanings are set forth below. The articles a, an and the are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

[0036] The terms comprise and comprising are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as consists of only. The term at least one is used to mean one or more and thus includes individual components as well as mixtures/combinations. Throughout this specification, unless the context requires otherwise the word comprise, and variations such as comprises and comprising, will be understood to imply the inclusion of a stated element or step or group of elements or steps but not the exclusion of any other element or step or group of element or steps. The term including is used to mean including but not limited to. including and including but not limited to are used interchangeably.

[0037] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods and materials are now described.

[0038] The present disclosure is not to be limited in scope by the specific embodiments described herein, which are intended for the purposes of exemplification only. Functionally equivalent products, compositions, and methods are clearly within the scope of the disclosure, as described herein.

[0039] The present invention provides the process to produce high purity tert octyl mercaptan & tert dodecyl mercaptan using cation exchange resin catalyst. The invention also provides a process scheme for valorization of C.sub.4 streams to value added products such as tert dodecyl mercaptan & tert octyl mercaptans. These can be used in styrene butadiene polymerization process as chain modifiers and it can be used in synthetic lubricants for the production of high wear & tear lubricants.

[0040] In the present invention the cation exchange resin catalyst activity is optimized by pretreatment of the catalyst using inhibitors such as amine precursor, nitrile and metals etc. The pretreatment of catalyst reduces the formation of undesired heavier oligomers and enhances the yield and selectivity of the product. The undesired heavier oligomer generally deposits on the catalyst surface and deteriorates the catalyst performance. The technical advantage of pretreatment of catalyst are as follows: [0041] The formation of heavier oligomers was suppressed by 10-30% for TOM/TDM synthesis [0042] Less undesired products increase product selectivity and purity. Additionally, it will reduce the load on the product purification.

[0043] No catalyst activity deterioration takes place due to less formation of undesired by-products.

[0044] In an aspect, the present invention provides a process for production of mercaptans from C.sub.4 oligomerization product, the process comprising: [0045] a. fractionating C.sub.4 oligomerization product to obtain oligomer products di-isobutene (DIB) and tri-isobutene (TIB); [0046] b. loading a cation exchange resin catalyst into a reactor; [0047] c. pretreating the loaded cation exchange resin catalyst with an inhibitor in the reactor; [0048] d. feeding the oligomer products di-isobutene or tri-isobutene and hydrogen sulfide (H.sub.2S) into the reactor loaded with the pretreated cation exchange resin catalyst to obtain a reaction product mixture; and [0049] e. separating the reaction product mixture to obtain un-converted oligomer and tert octyl mercaptan or tert dodecyl mercaptan.

[0050] In an embodiment of the present invention, there is provided a process, wherein the cation exchange resin catalyst is pretreated with 2 to 10 wt % of the inhibitor, followed by heating at a temperature in a range of 50 to 90 C. for 3 to 4 hours and drying of catalyst at a temperature in a range of 100 to 120 C. for at least 5 to 10 hours in the presence of nitrogen (N2).

[0051] In an embodiment of the present invention, there is provided a process, wherein oligomer products di-isobutene or tri-isobutene and hydrogen sulfide (H.sub.2S) are mixed and reacted into the reactor loaded with the pretreated catalyst at a temperature in a range of 50 to 110 C., pressure of 1 to 15 bar and H2S to di-isobutylene/tri-isobutylene mole ratio of 1:1 to 10:1.

[0052] In an embodiment of the present invention, there is provided a process, wherein the cation exchange resin catalyst is selected from strongly acidic cation exchange resins, wherein the acidic cation exchange resin is sulfonated polystyrene divinyl benzene resin.

[0053] In an embodiment of the present invention, there is provided a process, wherein the inhibitor is selected from amine precursor, nitrile precursor and metal precursor, particularly amine precursor is methyl ethanol amine or methyl di-ethanol amine, more particularly methyl di-ethanol amine (MDEA).

[0054] In an embodiment of the present invention, there is provided a process, wherein the nitrile precursor is acetonitrile and metal precursor are iron or sodium.

[0055] In an embodiment of the present invention, there is provided a process, wherein the pretreated cation exchange catalyst has an active site concentration in a range of 3 to 4.5 eq/kg.

[0056] In an embodiment of the present invention, there is provided a process, wherein the pretreated cation exchange catalyst has selectivity for tert octyl mercaptan or tert dodecyl mercaptan in a range of 75% to 95%.

[0057] In an embodiment of the present invention, there is provided a process, wherein the di-isobutene conversion to tert octyl mercaptan is in a range of 45% to 98%.

[0058] In an embodiment of the present invention, there is provided a process, wherein the tri-isobutene conversion to tert dodecyl mercaptan is in a range of 5% to 10%.

[0059] In an embodiment of the present invention, there is provided a process, wherein the tert octyl mercaptan has purity in a range of 75% to 99%, wherein the tert dodecyl mercaptan has purity in a range of 90% to 95%.

[0060] The production of TOM and TDM involves reacting their respective olefinic streams (C.sub.8 for TOM and C.sub.12 for TDM) with hydrogen sulfide (H.sub.2S) gas. H.sub.2S, a low-value byproduct of the petroleum refining industry, is typically produced from various desulfurization processes, such as hydrocracking, hydrotreating, and amine absorption.

[0061] The proposed method not only provides a sustainable use for low-value hydrogen sulfide but also effectively valorizes the heavier, undesired oligomers from the C.sub.4 oligomerization process. This dual approach offers significant value addition and profitability while broadening the scope of the process to produce specialty chemicals.

[0062] C.sub.4 oligomerization is well known process for the production of di-isobutylene which is a high octane gasoline additive. In the oligomerization process formation of higher oligomers such as tri-isobutene (10-15 wt %) also takes place which is highly undesired product. The oligomer product reacts with hydrogen sulfide in the presence of cation exchange resin catalyst. Synthesis/process conditions are given in Table-1. During the synthesis of these specialty mercaptans, formation of higher oligomer also takes place which gets deposited on the catalyst surface and reduces the catalyst activity.

TABLE-US-00001 TABLE 1 Operating Conditions S. No Parameter Temp( C.) 50-110 Pressure (bar) 1-15 H.sub.2S/Oligomer Product Mole Ratio 10-1

[0063] In the present invention the catalyst is pretreated prior to use. The pretreatment will reduce the catalyst activity and reduce the heavy oligomers formation during the TOM/TDM synthesis, which increases the product selectivity and also reduces the catalyst deactivation rate. The pretreatment conditions are given in Table 2. High selectivity and purity of product streams reduces the additional load on separation process in purification section.

TABLE-US-00002 TABLE 2 Catalyst Pretreatment S. No Parameter Inhibitor concentration 2-10 wt % Pre-treatment Temperature 70-90 C. Pretreatment Time At least 3 hours, preferably 4-8 hours Drying temperature 100-120 C. post pretreatment Drying Time At least 8 hours in presence of N.sub.2

[0064] The schematic representation of the present invention for the production of specialty mercaptans from the C.sub.4 oligomerization process is given in FIG. 1. FIG. 1 shows commercial C.sub.4 oligomerization process which consists of a hydration reactor (101) along with the oligomer reactor (102). The C.sub.4 stream (210) and unconverted recycle C.sub.4 stream (217) is mixed up and partially sent to hydration reactor (101) & oligomerization reactor where tert-butyl alcohol (TBA) & C.sub.4 oligomerization takes place respectively. The product from the hydration reactors which consists of tert-butanol is sent to the oligomerization reactor (102) via stream (214). TBA acts as additive to restrict formation of higher oligomers of C.sub.4 mainly trimers and tetramers formation. Further, the product stream (216) from the oligomer reactor is fractionated in fraction column (103) where unconverted C.sub.4 (217) is separated from the top recycled back. The di-isobutene (DIB) rich stream (218) is separated in the middle stream and it is rooted to the gasoline pool. Tri-isobutene (TIB) rich oligomer product stream (219) is separated from the bottom which is further taken in the reactor for synthesis of specialty mercaptans. These DIB & TIB rich streams are further used as feed for the production of tert octyl mercaptan (TOM) or tert dodecyl mercaptan (TDM) based on the requirement in a separate reactor (104) where pretreated catalyst is used for the reaction. Before proceeding for TOM/TDM synthesis the catalyst is pretreated with appropriate inhibitors such as amine precursors, nitriles and various metals from the inhibitor storage tank (106) via stream (226). In this process catalyst bed is soaked in inhibitor solution for at least 3 hours as per the pretreatment conditions. After completion of the catalyst soaking, inhibitor solution is drained, and catalyst is dried as per disclosed conditions. Further pretreated dried catalyst is used for the synthesis of the TDM/TOM as per disclosed process conditions. The oligomer products from fractionators (103) and hydrogen sulfide (H.sub.2S) via stream (221) is taken to the reactor (104). Product stream (223) from reactor is routed to commercial fractionator (105) at vacuum conditions where un-converted oligomers (225) are separated and recycled back to the reactor to optimize the conversion. The bottom stream (224) from fractionator column (105) contains high purity TOM/TDM which is further routed to a storage tank.

EXAMPLES

[0065] The present disclosure is further illustrated by reference to the following examples which is for illustrative purposes only and does not limit the scope of the disclosure in any way. These examples are not intended to be inclusive of all aspects of the subject matter disclosed herein, but rather to illustrate representative features, methods, compositions, and results. These examples are not intended to exclude equivalents and variations of the present disclosure, which are apparent to one skilled in the art.

Example 1

[0066] In this example, the cation exchange resin catalyst is pretreated with different inhibitors and the pretreated catalyst performance has been evaluated for the synthesis of tert-octyl mercaptan. Pre-treatment has been carried out at 70-90 C., 2% by weight of inhibitor solutions used for the catalyst pretreatment. After the pretreatment of the catalyst, synthesis of tert-octyl mercaptan was carried out in the fixed bed process at 60-80 C. and 5-15 bar pressure conditions. Di-isobutylene (DIB) with a purity of 98% and hydrogen sulfide (H.sub.2S) with a purity of 99.9% were employed as the feedstocks. H.sub.2S and DIB were introduced in the reactor after proper mixing, ensuring a mole ratio of H.sub.2S to DIB of 2:1. The outcome of the experiments has been given in Table-3. With using the different precursor for the catalyst treatment, it is observed that only treatment with the methyl di-ethanol amine shows the catalyst activity, no conversion is observed using other precursors, this may be attributed either deactivation of the catalyst activity or the clogging of the pore size of the catalyst.

TABLE-US-00003 TABLE 3 Effect of catalyst pretreatment using different precursors on TOM synthesis Inhibitor Pretreated % Tert Precursor used Catalyst % Conversion Octyl S. for catalyst Activity (Acid of di- mercaptan NO pretreatment Capacity), meq/g isobutylene selectivity 1. Methyl Ethanol 3.31 No conversion Amine 2. Methyl Di ethanol 4.40 94.33 98.30 Amine 3. Acetonitrile 4.91 No conversion 4. Ferrous sulfate 4.79 No conversion heptahydrate

Example 2

[0067] In this example, the synthesis of tert-octyl mercaptan was carried out using both a pretreated cation exchange resin catalyst and a fresh cation exchange resin catalyst. A total of 2 grams of catalyst was utilized in a tubular reactor operated in continuous mode. The experiments were conducted at a temperature of 60-110 C. and a pressure of 5-15 bar. Di-isobutylene (DIB) with a purity of 98% and hydrogen sulfide (H.sub.2S) with a purity of 99.9% were employed as the feedstocks. DIB and H.sub.2S were introduced in the reactor after proper mixing, ensuring a mole ratio of H.sub.2S to DIB of 4:1. The experiments were performed over a duration of 24 hours for both the catalyst and the product samples analyzed using gas chromatography. The results of the experiments for both the fresh and pretreated catalysts are presented in Table-4.

TABLE-US-00004 TABLE 4 TOM synthesis using feed having 98% DIB % TOM % Heavier Exp % DIB Selec- oligomers in % purity No Catalyst Conversion tivity product of TOM 1 Fresh Catalyst 99.01 76.43 18.2 80.3 2 Pretreated 95.49 98.11 2.0 97.8 catalyst

Example 3

[0068] Similar to Example 1, the activity of both fresh and pretreated cation exchange resin catalysts was evaluated for the formation of tert-dodecyl mercaptan (TDM). The operating conditions were maintained consistent with those described in Example 1. Tri-isobutylene (TIB) with a purity of 90 wt % was used as the feedstock for TDM production. TIB and hydrogen sulfide (H.sub.2S) were fed to reactor maintaining an H.sub.2S to TIB mole ratio of 4:1. The experiments were conducted over a 24-hour period, with product samples analyzed thereafter in the Gas Chromatograph Mass Spectroscopy. The product analysis indicated a significantly lower conversion of TIB compared to DIB, which is attributed to the higher stability of TIB. The results of these experiments are presented in Table 5.

TABLE-US-00005 TABLE 5 TDM synthesis using feed having 90% TIB % TDM % Heavier Exp % TIB Selec- oligomers in % purity No Catalyst Conversion tivity product of TDM 3 Fresh Catalyst 10.41 93.12 31.0 92.1 4 Pretreated 7.22 94.88 7.26 94.4 Catalyst

Example 4

[0069] In experiments no. 5-9, the effect of different concentration of MDEA solution on the cation exchange resin active sites and catalyst performance in terms of TOM selectivity has been studied. The pretreatment on cation exchange resin catalyst is done as per the conditions given in Table 2. Experiments were performed with DIB having purity 98% as feed with each pretreated catalyst. The experimental conditions were fixed as per the previous examples. The product samples were analyzed in Gas Chromatograph after each experiment and results are given in Table-6.

TABLE-US-00006 TABLE 6 Effect of precursor concentration on Conversion and Selectivity MDEA concen- Catalyst Activity % TOM % Exp. tration (Acid Capacity), % DIB Selec- Heavier No (wt %) meq/g Conversion tivity oligomers 5 0 5.2 99.01 76.43 18.24 6 2 4.4 95.50 98.30 2.00 7 4 4.0 64.79 97.00 1.55 8 6 3.5 41.39 97.81 1.78 9 8 2.9 No conversion

Example 5

[0070] Longer duration experiments were performed to assess the performance of the pretreated catalyst. Experiment conditions were kept similar to previous examples. From the outcome of the results, no decrease in catalyst performance observed till 180 hours. The experimental results are shown in FIG. 2.

ADVANTAGES OF THE PRESENT INVENTION

[0071] The present invention provides a process for the production of high purity tert octyl mercaptan & tert dodecyl mercaptan. [0072] The present invention involves the pre-treatment of the cation exchange resin catalyst with appropriate inhibitors such as amine precursors, nitriles and various metals to optimize the catalyst activity so that less undesired by-product formation takes place. [0073] The present invention provides improved yield/selectivity of the desired products tert octyl mercaptan & tert dodecyl mercaptan.

[0074] The cation exchange resin catalyst is not deactivated due to less formation of undesired oligomers which generally get deposited on the catalyst surface and reduces the catalyst activity. There is less undesired byproducts formation, thus reducing the load on the product fractionation in purification section.