Continuous process for the production of disulfides

Abstract: Process and apparatus for continuous production of disulfides by reacting at least one mercaptan and oxygen in the presence of a suitable catalyst selected from the group consisting of an alkaline earth metal oxide alone or in combination with an alkali metal oxide, on a refractory support, or a basic form of macroreticular polystyrene-divinyl benzene copolymer.

Description: This invention relates to a new and useful method for the continuous production of disulfides. Disulfide compounds are used in the manufacture of pesticides, rodent repellants, insecticides, and in pharmaceutical synthesis. They are also used as additives in greases and diesel fuels. The production of disulfides is well known in the art. The goal in producing disulfides is to obtain products of high purity in high yields, at the most economical cost. From US 2,028,303 a process for the production of organic disulfides by reacting mercaptan with oxygen is disclosed. It is taught that the process can be carried out with or without catalysts. As catalyst, charcoal but also metal oxide, especially iron- and copper oxide, are mentioned and yields in the range of 50% are reported. It is also desired that the methods and/or processes employed in such production be unhazardous and environmentally safe. Unfortunately, the prior art methods do not satisfy these goals to the extent that either safety, purity, yield, and/or cost is compromised when any of the known methods is used. This invention by avoiding and/or substantially minimizing the aforementioned problems of the prior art, represents a new, useful, and improved continuous process for producing disulfides using various catalysts. SUMMARY OF THE INVENTION It is an object of this invention, to provide for the continuous production of disulfides. It is also an object of this invention to provide for the continuous production of disulfides using a catalyst system comprising an alkaline earth metal oxide and alkali metal oxide impregnated on a refractory metal oxide support. It is another object of this invention to provide for the continuous production of disulfides using an alkaline earth metal oxide catalyst on a refractory metal oxide support. It is a further object of this invention to provide for the continuous production of disulfides using basic macroreticular polystyrene-divinyl benzene copolymer, such as those made and sold by Rohm and Haas under the trademark "AMBERLYST A-2I" as catalyst. In accordance with this invention, a continuous process is provided for the production of disulfides by contacting at least one mercaptan and oxygen in the presence of a catalyst as defined in claim 1. In Figure 1, there is illustrated schematically a process embodying the invention. DETAILED DESCRIPTION OF THE INVENTION The ingredients useful in carrying out this invention comprise mercaptans, an inert diluent, oxygen, and suitable catalyst(s). The process of the invention is further illustrated by Figure 1 and the accompanying description thereof. Broadly speaking, there are, at least, three separate embodiments of this invention. These embodiments use different catalysts selected from the group consisting of an alkaline earth metal oxide alone or in combination with an alkali metal oxide on a refractory metal oxide support, and a basic form of macroreticular polystyrene-divinyl benzene copolymer such as "AMBERLYST A-21" catalyst. However, these embodiments are practiced by utilizing the same general process. In very simplified terms, this process essentially involves contacting air or oxygen diluted with an inert gas, with mercaptan, in the presence of a suitable catalyst. Special features of this process include but are not limited to, introducing the air or oxygen/nitrogen in a manner countercurrent to the mercaptan flow, and recycling the nitrogen, unreacted oxygen, and unreacted mercaptans. The mercaptans useful in this invention broadly include those with 1 to 18 carbons in which the mercaptan can be located on a primary, secondary, tertiary or aromatic carbon. Examples of this group of mercaptans include but are not limited to, t-butyl mercaptan, t-dodecyl mercaptan, t-octyl mercaptan, t-hexadecyl mercaptan, isopropyl mercaptan, sec-butyl mercaptan, sec-dodecyl mercaptan, methyl mercaptan, n-propyl mercaptan, n-butyl mercaptan, n-amyl mercaptan, n-hexyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, n-octadecyl mercaptan, thiophenol, benzyl mercaptan, cyclohexyl mercaptan, and cyclopentyl mercaptan. However, the preferred mercaptans for purposes of this invention are those with the mercaptan still attached to a primary, secondary, or aromatic carbon, and having 1 to 12 carbon atoms. Examples of this class of compounds are isopropyl mercaptan, sec-butyl mercaptan, sec-dodecyl mercaptan, methyl mercaptan, n-propyl mercaptan, n-butyl mercaptan, n-amyl mercaptan, n-hexyl mercaptan, n-oxtyl mercaptan, n-dodecyl mercaptan, n-octadecyl mercaptan, thiophenol, benzyl mercaptan, cyclohexyl mercaptan, cyclopentyl mercaptan, and like compounds. Most particularly preferred are those mercaptans with 1 to 8 carbon atoms, with the mercaptan attached to either a primary or an aromatic carbon atom. Examples of this class of compound are methyl mercaptan, n-propyl mercaptan, n-butyl mercaptan, n-amyl mercaptan, n-hexyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, n-octadecyl mercaptan, thiophenol, benzyl mercaptan, and similar compounds. Generally, any inert gas is useful as a diluent in this process. Examples of such inert gases are helium, argon, neon, and other Group VIII members of the periodic table. Particularly preferred, though, is nitrogen. The oxygen useful in this invention can be atmospheric oxygen. Preferred, however, is elemental oxygen. Various catalysts are useful in this invention. Such catalysts include alkaline earth metal oxides alone or in combination with alkali metal oxides, or mixtures of these oxides, on a suitable refractory metal oxide support. Of the alkaline earth metals, magnesium is the most preferred. Likewise sodium is the most preferred of the alkali metals. These metal oxide catalysts can be either commercially obtained or prepared by conventional methods known in the art. One such method is by calcining the carbonate, acetate, nitrate, hydroxide, or other suitable salts of the desired metal. Refractory metal oxide supports typically useful in carrying out this invention include but are not limited to alumina, silica, silica-alumina, titania, and the like. Alumina, however, is the preferred support. It is noted that the catalyst combination of MgO/Na 2 O on alumina support is the most preferred catalyst for carrying out this invention. Also preferred is MgO catalyst on a refractory metal oxide support. Another suitable catalyst for this invention is the class of basic macroreticular polystyrene-divinyl benzene copolymers, such as those manufactured by Rohm and Haas, and sold under the trademark "AMBERLYST A-21". There are, in general, at least, three separate preferred embodiments of this invention. In the first embodiment, a process is provided for the continuous production of disulfides using a catalyst comprising of magnesium oxide and sodium oxide impregnated on alumina support. In the second embodiment, a process is provided for the continuous production of disulfides using magnesium oxide catalyst on alumina support. In the third embodiment, a process is provided for the continuous production of disulfides using "AMBERLYST A-21" catalyst. These various embodiments, however, use the same general process in which the desired catalyst is contained in a reactor. The mercaptan is introduced through the top portion of the reactor. Air or oxygen diluted with an inert gas, preferably introgen, is introduced into the reactor in a manner countercurrent to the mercaptan flow. The oxygen can be introduced at various points as a means of distributing the heat of reaction throughout the reaction bed. This countercurrent flow maximizes contact between the oxygen, catalyst, and mercaptan. It is desirable that the oxygen be continuously diluted with nitrogen as a means of controlling reaction temperatures. It is also desirable that both the nitrogen and any unreacted oxygen be continuously recycled. Typically, this recycling is facilitated by means of a compressor, blower, or other suitable device, which is conveniently attached to the reactor. The general ranges of ingredients and reaction conditions suitable for carrying out the invention are as follows: mercaptan feed velocities are in the range of about 0.01 to about 10 g feed/g catalyst-hr Weight Hour Space Velocity (WHSV) with a preferred range of 0.1 to 1/hr. Oxygen feed velocities are generally in the range of from about 0.01 to about 100 ml oxygen/g catalyst hour Gas Hourly Space Velocity (GHSV) and more preferably in the range from about 0.1 to about 10 ml/g-hr GHSV. The midbed temperature for this reaction generally ranges from about 20°C to about 150°C. However, a temperature range of from about 80°C to about 120°C is preferred. The pressure in the packed reactor bed generally ranges from about 1 to about 35 atm (about 0 to about 500 psig), but more preferably in the range from about 1 to about 11 atm (about 0 to about 150 psig). The reaction of the invention usually proceeds at a fast rate and is a more complete reaction relative to those disclosed in the prior art. This improved reaction is attributable to the catalysts and process used. The products of the reaction which include disulfides, unreacted mercaptans, and water are conducted to a separating device. At this point, these products are separated into an oil phase and a water phase. The oil phase is further conducted to a mercaptan distillation device from which unreacted mercaptans are recycled overhead back into the reactor. The disulfide product is conducted to a distillation column where the "heavies" consisting of polysulfides and other undesirable by-products with greater molecular weights than the desired disulfide are separated out and the purified disulfide product is collected. The collected disulfide product can be analyzed using conventional methods known in the art. Referring now to Figure 1, there is schematically illustrated an apparatus useful in the practice of the invention. A packed catalyst bed reactor 10 has operably attached thereto: (a) a mercaptan feed conduit 12 for feeding mercaptan into the packed reactor 10; (b) an oxygen conduit 14 in communication with a suitable oxygen source; (c) a nitrogen conduit 16 in communication with a suitable nitrogen source; (d) a conduit means 18 for oxygen and nitrogen circulation to and from the reactor 10; and (e) a pressure regulating and/or maintenance device such as a blower or compressor 20 operably associated with the conduit means 18 to form a gas recycling means 19. The reactor 10 is linked by means of a product conduit 22 to a separator device 24. The separator device 24 has a water phase outlet conduit 26 operably attached to its bottom portion, and an oil phase conducting conduit 28 operably attached to or near its top portion to provide communication with a mercaptan distillation device 30. Attached to the top of the mercaptan distillation column 30 and leading to the top of the reactor 10, is a recycle mercaptan conduit 32 for recycling unreacted mercaptans to the reactor 10. Attached to the bottom portion of the mercaptan distillation column 30 is a product conduit 34, for unpurified disulfide products, in communication with a disulfide distillation device 36. Operably attached to the bottom portion of the disulfide distillation device is a conduit 38 for separating out the heavies. In communication with the disulfide distillation device 36, is a collecting device 40 for the purified disulfide product. In operation, the desired catalyst is first introduced into the reactor 10. Mercaptan is then fed into the reactor 10, via the mercaptan feed conduit 12. Oxygen is fed into the reactor 10 via the oxygen conduit 14 while nitrogen is fed into the reactor via the nitrogen conduit 16. Feeding these ingredients in the manner described above and illustrated in Figure 1 facilitates countercurrent contacting of mercaptan and oxygen. Recycling of nitrogen and unreacted oxygen is accomplished via the joint effort of the circulation conduit 18 and the blower or compressor 20. The remnants of the oil phase containing impure disulfide are conducted via the impure disulfide conduit 34 to the disulfide distillation device 36. Purified disulfide is collected with the aid of the disulfide collecting device 40, while the heavies are separated out of the disulfide distillation device via the separation conduit 38. The following illustrative examples further detail the various aspects of this invention. EXAMPLE I Preparation of Catalyst A catalyst suitable for use in the process of the present invention was prepared by mixing 300g alumina with 225g magnesium nitrate and 12g sodium nitrate in 370ml water. The mixture was allowed to soak followed by calcination for 3 hours at 400°C. The process resulted in magnesium oxide and sodium oxide impregnated onto alumina support for use in the invention. EXAMPLE II To a water cooled stainless steel tubular reactor, 93.7g of the catalyst prepared as described in Example I was added. The feedstock methyl mercaptan (MeSH) was continuously fed to the reactor at weight hourly space velocities (WHSV) and flow rates indicated in Table I. Oxygen was introduced into the reactor at various gas hourly space velocities and flow rates shown in Table I. Nitrogen was also introduced into the reactor. The temperature of the reactor was controlled by cooling water to about 80°C at the midbed of the reactor. The reaction pressure was maintained at about 6,6 atm (94 psig). The product stream discharged at the bottom of the reactor contained dimethyl disulfide and unreacted methyl mercaptan. The impure dimethyl disulfide was purified by using a distillation column, and the purified product was collected. The percent conversion of the starting mercaptans was as shown in Table I and was determined on the basis of oxygen utilized in each run. Continuous Production of Dimethyl Disulfide Catalyzed by MgO/Na 2 O Feedstock Methyl mercaptan Oxygen Run Flow rate (moles/min) WHSV (hr -1 ) Flow rate (moles/min) GHSV (m1/g-hr) Mole ratio (MeSH/O 2 ) Conversion (%) 1 0.0231 0.71 0.0044 62.4 5.25 4.9 2 0.0342 1.05 0.0044 62.4 7.77 41.9 3 0.0200 0.61 0.0022 31.2 9.09 42.0 4 0.0229 0.708 0.0022 31.2 10.42 62.3 5 0.0298 0.915 0.0009 11.8 33.10 76.0 6 0.0204 0.628 0.0009 11.8 22.67 92.1 7 0.0134 0.413 0.0009 11.8 14.89 82.5 The results shown in Table I above indicate that a molar ratio of MeSH to O 2 of at least greater than 5.25, preferably at least about 7, is required in order to obtain s high conversion. Runs 4-7 of Table I, further indicate that an MeSH to O 2 molar ratio of from about 15 to 33 is the optimal range for carrying out this invention. In Run 7, with a molar ratio (MeSH/O 2 ) of 14.98, the yield was 82.5% which was increased to 92.1% by an increased MeSH/O 2 ratio of 22.67 as sbown in Run 6. EXAMPLE III This comparative example illustrates how dimethyl disulfide can be prepared using magnesium oxide as catalyst. The feedstock methyl mercaptan and oxygen were continuously fed to the reactor using the same procedures and apparatus as in Example II except for the substitution of magnesium oxide as catalyst. The results are shown in Table II. Continuous Production of Dimethyl Disulfide Catalyzed by MgO Feedstock Methyl mercaptan Oxygen Run Flow rate (moles/min) WHSV (hr -1 ) Flow rate (moles/min) GHSV (ml/g-hr) Conversion for Digital (%) 8 0.0237 0.478 0.0005 6.6 8.20 9 0.0300 0.648 0.0047 66.9 9.74 10 0.0304 0.614 0.0047 66.9 19.29 The results shown in Table II demonstrate that MgO is useful as a catalyst for the continuous conversion of MeSH to dimethyl disulfide. A comparison of the results shown in Tables I and II suggests that MgO is less effective than MgO/Na 2 O on alumina as a catalyst useful in the practice of this invention. EXAMPLE IV To a water cooled stainless steel tubular reactor, 53,2 g of "AMBERLYST A-21" catalyst which had been washed with acetone and dried in a 40°C vacuum oven was added. N-butyl mercaptan liquid feed stock was then continuously fed to the reactor at a rate of 0.64/hr liquid hourly space velocity. Atmospheric oxygen (air) was also continuously introduced at 4.2/hr gas hourly spece velocity. The temperature of the reactor was controlled by water cooling to 62°C at the midbed of the reactor. The reaction pressure was maintained at about 50-60 psig (about 4 atmospheres). Reaction product, dibutyl mercaptan, was discharged at the bottom of the reactor. Analysis showed a 50.7% conversion, based on the utilization of n-butyl mercaptan. This example demonstrates that a dialkyl disulfide can also be made continuously employing a basic macroreticular polystyrene-divinyl benzene copolymer, "AMBERLYST A-21" catalyst.

Claims: A continuous process for preparing disulfides comprising continuously reacting at least one mercaptan and oxygen in the presence of a catalyst selected from an alkaline earth oxide alone or in combination with an alkali metal oxide on a refractory metal oxide support and a basic form of macroreticular polystyrene-divinyl benzene copolymer, to produce disulfides and continuously recovering the disulfide product. The process of claim 1 wherein said mercaptan has from 1 to 12 carbon atoms per molecule. The process of claim 1 wherein said mercaptan has from 1 to 8 carbon atoms per molecule. The process in accordance with claims 1-3, wherein said refractory metal oxide support is selected from alumina, silica, silica-alumina, and titania. The process of any of the preceding claims wherein said catalyst comprises a combination of an alkali metal oxide and an alkaline earth oxide on a refractory metal oxide support. The process of claims 5, wherein said catalyst comprises magnesium oxide and sodium oxide impregnated on a refractory metal oxide support. The process in accordance with claims 1-4, wherein said catalyst comprises magnesium oxide on a refractory metal oxide support. The process of any of the preceding claims, wherein: (a) the oxygen is contacted with the mercaptan by a countercurrent flow method; (b) the oxygen is continuously diluted with nitrogen gas; and (c) the unreacted oxygen and nitrogen gases are recycled. The process of claim 1, comprising: (a) continuously feeding a feedstream comprising of at least one mercaptan into a reactor containing said catalyst; (b) continuously feeding a stream comprising oxygen and nitrogen into the reactor so as to contact the said at least one mercaptan and said nitrogen and oxygen in a countercurrent manner; (c) continuously removing unreacted oxygen and nitrogen from said reactor and recycling them back into said reactor; (d) continuously recycling unreacted mercaptans back into said reactor; (e) continuously recovering a product stream comprising at least one disulfide from said reactor; (f) maintaining the reaction pressure in the range of 1 to 11 atmospheres. A continuous process for making disulphides comprising continuously reacting a mercaptan-based feedstream and an oxygen-bearing feedstream in the presence of a catalyst selected from (a) alkaline earth metal oxides on a refractory metal oxide support (b) alkaline earth metal oxides and alkali metal oxides in combination on a refractory metal oxide support, and (c) a polymer comprising a basic form of macroreticular polystyrene-divinyl benzene copolymer thereby producing a continuous disulfide product stream and a depleted oxygen-bearing stream. The process of claim 10 wherein said oxygen-bearing feedstream comprises oxygen and an inert gas, said oxygen-bearing feedstream is contacted countercurrently with said mercaptan-based feedstream, said process further comprising recycling said depleted oxygen-bearing stream by combining said depleted oxygen-bearing stream with said oxygen-bearing feedstream.

Inventors: DRAKE CHARLES ALFRED, HUNT HAROLD RAY, ROBERTS JOHN SCOTT, DRAKE, CHARLES ALFRED, HUNT, HAROLD RAY, ROBERTS, JOHN SCOTT
Applicants: PHILLIPS PETROLEUM CO, PHILLIPS PETROLEUM COMPANY
Application year: 1993
Main classification: C07C319
IPC codes: C07C321, C07C319