Hydrogenation of carbon disulfide to methyl mercaptan in presence of hydrogen sulfide
United States Patent 1191 Kubicek 1 3,880,933 Apr. 29, 1975 HYDROGENATION OF CARBON DISULFlDE TO METHYL MERCAPTAN lN PRESENCE OF HYDROGEN SULFlDE [75] Inventor: Donald ll. Kubicek, Bartlesville,  
 Okla.  
 [73] Assignee: Phillips Petroleum Company,  
 Bartlesville, Okla.  
 [22] Filed: May 2,1973  
 [211 Appl. No.: 356,414  
 [56] References Cited UNITED STATES PATENTS 3,488.73) l/l970 van Vcnroog 260/609 R Primary Examiner-Lewis Gotts Assistant Examiner-D. R. Phillips [57] ABSTRACT The conversion of carbon disulfide by hydrogenation in presence of a sulfactive hydrogenation catalyst to methyl mercaptan is conducted in presence of hydrogen sulfide added in an amount effective to permit an increase in space velocity such that increased conversion of carbon disulfide to methyl mercaptan at the expense of dimethyl sulfide is obtained. Dimethyl sulfide, also produced, is reduced, higher space velocities are attained ,over a broad range with increase in conversion of CS the H 5 moderating the reaction or modifying same to yield the obtained results. Generally. very considerable increase in mol ratio of CH SH/(CH S is obtained.  
 3 Claims, No Drawings HYDROGENATION OF CARBON DISULFIDE TO METHYL MERCAPTAN IN PRESENCE OF HYDROGEN SULFIDE This invention relates to the hydrogenation of carbon disulfide to convert the same to methyl mercaptan or methyl thiol. In one of its aspects, the hydrogenation is effected in the presence of a sulfactive hydrogenation catalyst. In another of its aspects, the invention makes use of hydrogen sulfide.  
  In one of its concepts, the invention provides a process for the conversion of carbon disulfide to methyl thiol by hydrogenation employing hydrogen, hydrogen sulfide and a sulfactive hydrogenation catalyst, the H S being present in an amount effective to permit substantially increased space velocities, e.g. the H 5 to C5 ratio being of the order of at least about 0.5/1 on a molar basis.  
  I have found that the inclusion of H 5 in the feed to the reaction zone, as noted above, during hydrogenation of carbon disulfide to produce methyl thiol, unavoidably obtaining also dimethyl sulfide, permits very considerably to increase the space velocity of the feed stream. Carbon disulfide conversion surprisingly is increased over a broad range of increased space velocities which are possible even while the ratio of methyl mercaptan to dimethyl sulfide is considerably increased.  
  It is an object of this invention to provide a process for the conversion of carbon disulfide to methyl thiol. lt is another object of the invention to provide an improved process for the conversion of carbon disulfide by hydrogenation in the presence of sulfactive hydrogenation catalysts. It is a further object of the invention to provide a modified process for the hydrogenation of carbon disulfide to methyl thiol.  
  Other aspects, concepts, objects, and the several advantages of the invention are apparent from a study of this disclosure and the appended claims.  
  According to the present invention, the conversion of or hydrogenation of carbon disulfide to form methyl thiol is conducted in presence of hydrogen sulfide in an amount with respect to the carbon disulfide effective to permit substantially over a broad range an increase in space velocity with concomitant increase in conversion of carbon disulfide to methyl mercaptan at the expense of dimethyl sulfide.  
  U.S. Pat. No. 3,488,739, issued Jan. 6, 1970, which deals with preparation of methyl mercaptan and dimethyl sulfide, shows the reaction which comprises passing carbon disulfide and an excess of hydrogen in the gaseous or vapor state over a sulfactive hydrogenation catalyst at an elevated temperature and a pressure of from about atmospheric to about 1,000 psi to prepare methyl mercaptanand/or dimethyl sulfide. The patent also states that by recycling the dimethyl sulfide with H S, methyl mercaptan is produced at the expense of dimethyl sulfide. By recycling methyl mercaptan, dimethyl sulfide is produced at the expense of the methyl mercaptan. The relative amounts of the primary products can be accordingly controlled to a high degree according to the patent. The patent also shows among equations therein given the conversion of methyl mercaptan to dimethyl sulfide and hydrogen sulfide. It is also stated that this reaction is a reversible catalyzed disproportionation which permits the control of the relative amounts of dimethyl sulfide and methyl mercaptan being formed.  
  According to the present invention, by operating as herein described, it has been found unexpectedly that as more and more hydrogen sulfide was added to a constant carbon disulfide-hydrogen feed the per-pass conversion of carbon disulfide remained nearly constant even though the space velocity had been increased by almost three-fold. Thus, it was strange and unexpected to be able to operate at increased space velocities yet without loss of conversion. This increase in space velocity result could not be duplicated using nitrogen, as shown by tabular data herein. Indeed there appears to be an effect of the H 5 to CS ratio as space velocity is increased, which I have discovered which does not appear to have been fathomable based upon available knowledge of the chemistry of this kind of reaction.  
  In studies made to determine what effect space velocity would have on the reaction of hydrogen with carbon disulfide, in the absence of hydrogen sulfide, at a given temperature and pressure the space velocity was changed in several different ways. In one procedure this was done by increasing both the carbon disulfide and hydrogen feed rates keeping them at the same ratio. In another procedure, the space velocity was also increased by adding a diluent to the carbon disulfidehydrogen feed kept constant in both rate and ratio.  
  As space velocity was increased by increasing the feed rates of the carbon disulfide and hydrogen, the per-pass conversion of the carbon disulfide decreased as expected. There appeared to be little effect on the ratio of products methyl mercaptan to methyl sulfide caused by this change in space velocity.  
  Further, a similar result was obtained when the space velocity was increased by adding a nitrogen diluent keeping the carbon disulfidehydrogen feed constant in both rate and ratio. Here, too, the per-pass conversion of carbon disulfide decreased with the increased space velocity caused by the addition of nitrogen and the ratio of products was not affected to any extent by the addition of the nitrogen.  
  Accordingly, it appears that it must be accepted as unexpected that the per-pass conversion of carbon disulfide could remain nearly constant, in presence of added hydrogen sulfide, even though the space velocity has been increased by almost three-fold.  
  Catalysts Catalysts suitable for use in the instant invention can be defined as sulfactive hydrogenation catalysts and are broadly described. By sulfactive hydrogenation catalyst, it is meant the sulfides of Group VI and Group VIII metals either alone or in combination. For example, the sulfides of cobalt, nickel, molybdenum, iron, tungsten, chromium, platinum, etc. Usually the catalytic material is deposited on a support such as activated carbon, alumina, zirconia, thoria, pumice, silica and silica-aluminum compositions. Combinations of nickel or cobalt with molybdenum are generally among the most preferred of such catalysts. Quite effective catalysts of the foregoing preferred combinations but in the oxide form are available commercially. One such catalyst is available under the designation Aero HDS-3A; Aero HDS-3A comprises NiO (3 weight percent), M00, (15 weight percent). and small amounts of Na (about 0.02 percent) and phosphorus (about 1.5 percent), the remainder being alumina. It is easily sulfided using well-known and conventional sulfiding conditions, conventional techniques 3 and equipment. For example, using H 5 and hydrogen at about 350 to 650 F and pressures of about atmospheric to 300 psi. Since many of the suitable catalysts are commercially available in the oxide form they can l5,000. preferably from 5002,200 in the units just described.  
  The effluent from the reaction zone can be subjected to conventional separation processes such as fractional be sblilded Prior to use 0h P yemployed distillation to recover the desired methyl mercaptan, rectly in the oxide form since sulfiding appears to CHQSH f time-acted 5 H and H 5 as we&#34; as readily occur in situ in the instant invention. One such product (CH3)2S Any or ll f h above compounds commercially available catalyst that is preferred for use can be recycled t0 the rcactitm Zone. However, if d in the process of this invention is designated Aero sired ((341025 and 5 (in excess f that ngeded in the HDS2 and has the following Composition: COO 6-4 i0 reaction zone) can be recovered as valuable separate Percent y weight) 1: 546%) N320 (04% Fe by-product streams since they have well-known utility (0.05%), the remainder being alumina. This catalyst is in other chemical apphcationsv commonly referred to as cobalt molybdate on alumina. Methyl mercaptah i a h i l hi h i One skilled in the art in possession of this disclosure employed in large quantities in the preparation f i having Studied the Same will recognize thilt the lhvehl5 secticides, herbicides, and methionine, an amino acid tion l&#39;lOt limited, necessarily, t0 catalysts here deused in feed supplements for poultry and livestock scribed. Having the concept Of the invention before Although CS2 from any source can be employed as a himtiie will be able to Select catalysts with which to reactant in the process of this invention, the instant in tain the advantag s 0f th nti vention has particular utility in those instances wherein Mol Ratio 2 to 2 The mOl ratio of a to 2 the reaction of methane (CH with sulfur or a mixture employed in the feedstream for this invention is of sulfur and H S is employed to produce CS In such broadly ithin th ang of fr m .5/1 o 20/1 and pre instances there is a net production of H 8 along with erably within the range of from 1.5/1 to lO/l. It is rec- CS both of which are needed in the process of the inognized that ratios greater than 20/1 would be operastant invention. Thus, the instant invention provides ble. However, these higher ratios would tend to unneC- opportunity for a well-integrated process for producing essarily burden the product separation facilities and CH SH starting from CH It is noted that a one-step rewould require the uneconomical recycling of large volaction for the conversion of CH and sulfur to CH SH umes of H 3 to the reaction zone. has apparently not been successfully developed be- Mol Ratio H to CS The mol ratio of H to CS cause of the extreme difficulty in stopping the reaction employed in the feedstream for this invention is at the CH SH stage. broadly in the range of from 0.1/1 to 10/1, preferably Of runs made, those which are presented in the folfrom 0.25/1 to 5/1. lowing examples are representative of the invention.  
  Pressure The pressure employed in the process of the instant invention is broadly from atmospheric pressure up to 1,000 psig with a preferred range of from EXAMPLE I 150-700 psig. Product separation processes down- A tubular reaction chamber containing 80 ml of the stream are benefited by the application of pressure in Aero HDS-2 catalyst was employed as the reaction the reaction zone. Preferably, there should be selected zone in the runs described below. Each run was cona pressure that is insufficient to cause liquefaction of ducted at a pressure of 180 psig and a temperature of the reactants in the reaction zone. The pressure se- 450 F. The feed rate for H and CS in each run was lected then will be dependent somewhat on the temper- 1.1 and 0.4 mols/hour, respectively, except in run 3 of ature chosen and the composition of the feedstream. Table l in which the rate was 2.2 and 0.8, respectively. Temperature The hydrogenation of CS according The feed rate of H 8 was varied in this series of runs into the instant invention is generally conducted within cluding four control runs in which no H- S was added. a temperature range of from 300650 F, preferably The results obtained in this series of runs are shown in from 350-550 F. Table 1.  
 TABLE 1 Product. Mol 71 M01 Ratio HZS Space CHHSH (CH3)2S CS2 CH -,SH/(CH,,)2S CS2 Conv. mols/hr. Velocity 7? These runs conducted at 170 psig.  
  Space Velocity The process of this invention in which a mixture of CS- H 8. and H are contacted with a sulfactive hydrogenation catalyst under conditions described above is conducted under conditions such that the space velocity can be expressed in gaseous volumes of reactants per volume of catalyst per hour. Broadly, the space velocity employed is from The above results clearly demonstrate the beneficial effects on CH SH yield and ratio of CH SH/(CH S in the product mixture. Space velocity in the above table is in the units gaseous volumes of reactants per volume of catalyst per hour. The comparison of the second and third runs, in neither of which H 5 was present, shows a very large drop in CS conversion with increased space velocity, also, a substantial loss in CH SH/(CH S ratio. Values shown for product, mole percent are obtained by gas-liquid chromatography analysis and are normalized to exclude H 8 which does Reasonable variation and modification are possible within the scope of the foregoing disclosure and the appended claims to the invention the essence of which is that there can be the inclusion of hydrogen sulfide in appear in the Product mixlurc- 5 the manner and according to the conditions herein described which with increased space velocities thus ob- EXAMPLE tained, will yield increased carbon disulfide conver- To demonstrate that the above desirable results of 810118 and considerably mprove methyl mercaptan to Example I were not the result of a simple diluent effect, dimethyl sulfide ratios in the product. other runs were conducted in which N rather than H S l0 1 claim: was fed to the reaction zone. The results of these runs 1. A process for the conversion of carbon disulfide to are shown below in Table 11. The temperature, pressure methyl mercaptan and unavoidably to dimethyl sulfide and feed rates for the H and CS were the same as which comprises hydrogenating carbon disulfide in the those employed in Example I and the same reactor and presence of hydrogen and a sulfactive hydrogenation catalyst were also employed. catalyst and hydrogen sulfide added in an amount with TABLE 11 Product, Mol 7r Mol Ratio N2 Space CH;,SH (CH,,)2S CS2 CH;,SH/( CH S CS2 Conv. Mols/Hr Velocity 7r- EXAMPLE 111 Other runs were conducted according to the invention wherein the temperature and H feed rate were varied. The pressure was 180 psig in each run and the feed rates for H 8 and CS were 4.0 and 0.4 mols/hour, respectively. The same reactor and catalyst as previously employed in Examples 1 and 11 were also used in these runs. The results obtained in this series of runs are presented in Table 111 below.  
 respect to the carbon disulfide effective to permit substantially over a broad range an increase in space velocity with concomitant increase in conversion of carbon disulfide to methyl mercaptan at the expense of dimethyl sulfide wherein the mol ratio of H 8 to CS is in the approximate range of from about 0.5/1 to about 20/1, the mo] ratio of hydrogen to carbon disulfide is in the approximate range of from about 0.1/1 to about 10/ 1, the pressure is in the approximate range from about atmospheric to about 1,000 psig, the temperature is in the approximate range of from about 300 to about 650F, and the space velocity is in the approximate range of from about 100 to about 5,000 expressed as gaseous volumes of reactants per volume of catalyst per hour.  
  2. A process according to claim 1 wherein the catalyst is a sulfactive hydrogenation catalyst having approximately the following composition: CoO, 3-4 per- TABLE 111 Product, Mol 7:- Mol Ratio CS Conv. Temp. H Space CH,-,SH (CH; S CS CH,,SH/(CH S 7:  
 F mols/hour Velocity The above data demonstrate that good results can be achieved according to this invention over a range of temperatures and a range of H feed rates.  
  From the data and description of the invention herein it is evident that the H 8 considerably and unexpectedly improves or retains the CS conversion while permitting higher space velocities.  
 lyst per hour.