Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C321/00—Thiols, sulfides, hydropolysulfides or polysulfides
  • C07C321/12—Sulfides, hydropolysulfides, or polysulfides having thio groups bound to acyclic carbon atoms
  • C07C321/14—Sulfides, hydropolysulfides, or polysulfides having thio groups bound to acyclic carbon atoms of an acyclic saturated carbon skeleton
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C303/00—Preparation of esters or amides of sulfuric acids; Preparation of sulfonic acids or of their esters, halides, anhydrides or amides
  • C07C303/02—Preparation of esters or amides of sulfuric acids; Preparation of sulfonic acids or of their esters, halides, anhydrides or amides of sulfonic acids or halides thereof
  • C07C303/16—Preparation of esters or amides of sulfuric acids; Preparation of sulfonic acids or of their esters, halides, anhydrides or amides of sulfonic acids or halides thereof by oxidation of thiols, sulfides, hydropolysulfides, or polysulfides with formation of sulfo or halosulfonyl groups
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C309/00—Sulfonic acids; Halides, esters, or anhydrides thereof
  • C07C309/01—Sulfonic acids
  • C07C309/02—Sulfonic acids having sulfo groups bound to acyclic carbon atoms
  • C07C309/03—Sulfonic acids having sulfo groups bound to acyclic carbon atoms of an acyclic saturated carbon skeleton
  • C07C309/04—Sulfonic acids having sulfo groups bound to acyclic carbon atoms of an acyclic saturated carbon skeleton containing only one sulfo group
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C319/00—Preparation of thiols, sulfides, hydropolysulfides or polysulfides
  • C07C319/14—Preparation of thiols, sulfides, hydropolysulfides or polysulfides of sulfides
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C319/00—Preparation of thiols, sulfides, hydropolysulfides or polysulfides
  • C07C319/22—Preparation of thiols, sulfides, hydropolysulfides or polysulfides of hydropolysulfides or polysulfides
  • C07C319/24—Preparation of thiols, sulfides, hydropolysulfides or polysulfides of hydropolysulfides or polysulfides by reactions involving the formation of sulfur-to-sulfur bonds

Definitions

• Dimethyl disulphide derived at least partially from renewable materials
• the invention relates to disulphides, and in particular dimethyldisulphide (DMDS), and its process for preparing from renewable raw materials.
• DMDS dimethyldisulphide
• the invention also relates to the use of such a DMDS for the preparation of methanesulfonic acid.
• DMDS Dimethyldisulphide of the formula H3C-S-S-CH3, hereinafter referred to as DMDS, which may also be called dimethyl disulphide or methyl dithiomethane, is used in a large number of applications.
• DMDS is used as a sulphurizing or pre-sulphurizing agent in refineries to activate hydrotreatment catalysts.
• DMDS is also used in the petrochemical industry to protect steam cracking systems from coke and carbon monoxide formation. It can also be used as a synthesis intermediate in fine chemistry or metallurgy for its anti-corrosion properties. It can also be used as a pesticide, and as a fumigant for agriculture.
• DMDS Dimethyl disulphide
• DMDS is synthesized from conventional hydrocarbon compounds, namely from the petroleum industry. If the DMDS is not dangerous for the ozone layer, the ecological balance of its production is not perfect, especially the CO2 balance, and the current DMDS manufacturing processes still contribute to global warming.
• the invention therefore aims to reduce global warming during the manufacture of DMDS, by reducing the greenhouse gas emissions associated with their manufacture.
• the invention therefore aims to improve the carbon footprint (cumulative greenhouse gas emissions related to the production of raw materials and the production process) polysulfides.
• the subject of the invention is a dimethyldisulphide of formula CH 3 -SS-CH 3 , the bio-carbon content of which is at least 1%.
• the bio-carbon content is greater than 5%, preferably greater than 10%, preferably greater than 25%, preferably greater than 50%, preferably greater than 75%, preferably greater than 90%, preferably greater than 95%, preferably greater than 98%, preferably greater than 99%, advantageously substantially equal to 100%.
• the subject of the invention is also a method for preparing dimethyldisulphide according to the invention, comprising the step of providing one or more carbon chains comprising one or more carbon atoms having a biocarbon content of at least 1%, and the transformation by synthesis into DMDS.
• the supply step comprises a step of producing methanol.
• the step of producing methanol is by fermentation of biomass.
• the step of producing methanol comprises the following substeps: (i) production of methane from biomass, (ii) steam reforming thereof into a synthesis gas or production of synthesis gas by direct gasification of biomass and (iii) production of methanol from this synthesis gas.
• the methanol production step comprises the following substeps: (i) production of methane from biomass, (ii) direct oxidation of methane to methanol.
• the synthesis comprises at least one step of converting methanol to methyl mercaptan by reacting methanol with hydrogen sulfide and a step of converting methyl mercaptan to dimethyl disulphide by oxidation of methyl mercaptan with sulfur.
• the synthesis of methyl mercaptan can also be carried out using synthesis gas derived from biomass by direct reaction of the synthesis gas with hydrogen sulfide in a catalytic process without passing through methanol.
• the overall reaction is written in this case as follows: CO + 2H 2 + H 2 S -> CH 3 SH + H 2 O
• said supplying step comprises at least one methylmercaptan production step.
• the methyl mercaptan production step comprises the following sub-steps: (i) production of methane from biomass, (ii) steam reforming thereof into a synthesis gas and (iii) direct production of methyl mercaptan from this synthesis gas, by reaction of said synthesis gas with hydrogen sulfide.
• said synthesis step comprises at least one step of converting methyl mercaptan to dimethyl disulphide by oxidation of methyl mercaptan with sulfur.
• the subject of the present invention is also a composition based on dimethyl disulphide as defined above, containing by weight at least 95% of dimethyl disulphide, less than 500 ppm of methyl mercaptan, less than 100 ppm of dimethyl sulphide and from 0 to 1% of dimethyl disulphide. at least one odor masking agent selected from vanillin, ethyl vanillin and esters.
• the present invention also relates to the use of dimethyl disulphide as defined above for the preparation of methanesulphonic acid. Also, the present invention aims to methanesulfonic acid synthesized from dimethyl disulphide as defined above, and wherein the bio-carbon content is at least 1%.
• the present invention further relates to a process as defined above further comprising a methanesulfonic acid synthesis step, wherein the dimethyl disulfide according to that defined above is oxidized in the presence of chlorine and hydrolyzed in the presence of water.
• the subject of the present invention is also a process as defined above further comprising a step of synthesis of methanesulphonic acid, in which an alcoholic solution of dimethyl disulphide conforming to that defined above is subjected to irradiation, in the presence of oxygen, by light radiation of wavelength between 200 and 320 nm.
• the present invention also relates to the use of dimethyldisulphide according to that defined above, as sulphurizing agent, as anti-knock agent, as synthesis intermediate, as anti-corrosion agent, as a pesticide agent, as a fumigant.
• the invention uses products of natural origin as starting materials.
• the carbon of a biomaterial comes from the photosynthesis of plants and therefore atmospheric CO2.
• the degradation (by degradation, one will also hear the combustion / incineration at the end of life) of these materials in CO2 does not therefore contribute to the warming since there is no increase of the carbon emitted into the atmosphere.
• the CO2 balance of biomaterials is therefore much better and contributes to reducing the carbon footprint of the products obtained (only energy for manufacturing is to be taken into account).
• a material of fossil origin that is also degraded to CO2 will contribute to the increase of the CO2 level and therefore to global warming.
• the compounds according to the invention will therefore have a carbon footprint that will be better than that of compounds obtained from a fossil source.
• the invention therefore also improves the ecological balance during the manufacture of the DMDS.
• bio-carbon indicates that the carbon is of natural origin and comes from a biomaterial, as indicated below.
• the biocarbon content and the biomaterial content are expressions designating the same value.
• a renewable source material also called a biomaterial, is an organic material in which carbon is derived from recently-fixed CO2 (on a human scale) by photosynthesis from the atmosphere. On land, this CO2 is captured or fixed by plants. At sea, CO2 is captured or fixed by bacteria or plankton carrying out photosynthesis.
• a biomaterial (100% carbon naturally occurring) has an isotopic ratio 14 C / 12 C higher than 10 ⁇ 12, typically of the order of 1.2 x 10 "12, while a fossil material has a void ratio.
• the isotope 14 C is formed in the atmosphere and is then integrated by photosynthesis, according to a time scale of a few tens of years at most.
• the half-life of 14 C is 5730 years. from photosynthesis, namely plants in general, necessarily have a maximum content of 14 C isotope.
• ASTM D 6866 (ASTM D 6866-06) and ASTM D 7026 (ASTM D 7026-04).
• ASTM D 6866 is “Determining the Biobased Content of Natural Range Materials Using Radiocarbon and Isotope Ratio Mass Spectrometry Analysis”
• ASTM D 7026 relates to "Sampling and Reporting of Results for Determination of Biobased Content of Materials”. via Carbon Isotope Analysis ".
• the second standard refers in its first paragraph to the first.
• the first standard describes a test of the ratio 14 CV 12 C of a sample and compares it with the ratio 14 C / 12 C of a reference sample of origin 100% renewable, to give a relative percentage of C of renewable origin in the sample.
• the standard is based on the same concepts as 14 C dating, but without applying the dating equations.
• the calculated ratio is referred to as the "pMC"
• ASTM D 6866 proposes three techniques for measuring the 14 C isotope content: - Liquid Scintillation Counting (LSC).
• LSC Liquid Scintillation Counting
• This technique consists of counting "Beta” particles from the decay of 14 C.
• the beta radiation from a sample of known mass (number of known C atoms) is measured for a certain time.
• This "radioactivity” is proportional to the number of 14 C atoms, which can be determined.
• the 14 C present in the sample emits ⁇ radiation, which in contact with the scintillating liquid (scintillator) give rise to photons. These photons have different energies (between 0 and 156 keV) and form what is called a spectrum of 14 C.
• the analysis relates to the CO2 previously produced by the carbon sample. in absorbent solution, or on benzene after prior conversion of the carbon sample to benzene.
• ASTM D 6866 thus gives two methods A and C, based on this LSC method.
• - AMS / IRMS Accelerated Mass Spectrometry coupled with Isotope Radio Mass Spectrometry.
• This technique is based on mass spectrometry. The sample is reduced to graphite or gaseous CO2, analyzed in a mass spectrometer.
• This technique uses an accelerator and a mass spectrometer to separate 14 C ions and 12 C and thus determine the ratio of the two isotopes.
• the compounds according to the invention come at least in part from biomaterial and therefore have a biomaterial content of at least 1%. This content is advantageously higher, especially up to 100%.
• the compounds according to the invention can therefore comprise 100% bio-carbon or on the contrary result from a mixture with a fossil origin.
• the compounds according to the invention are, as indicated above, dimethyldisulfides derived at least partially from raw materials of renewable origin.
• a non-sulfur-containing carbon compound is first produced: methanol.
• this non-sulfurized compound is subjected to sulfurization reactions to form a methyl mercaptan.
• the methyl mercaptan from this methanol is oxidized with sulfur to give the DMDS according to the invention.
• Biogas methane results from anaerobic digestion or anaerobic digestion of fermentable waste. Common sources are landfills, selective collection of putrescible waste (possibly through the use of digesters), sewage sludge, livestock manure, effluents from food industries, or from a lake (eg Lake Kivu), etc. Biogas contains a major proportion of methane.
• This methane then undergoes a steam reforming reaction or SMR (Steam Methane Reforming).
• SMR Steam Methane Reforming
• a mixture of CO and hydrogen is obtained according to a variable ratio (typically about 2), also called synthesis gas or syngas.
• This syngas is used, for example, for the production of hydrocarbons by the Fischer-Tropsch reaction, hydrocarbons which can then be converted into various products, especially olefins, by conventional upgrading reactions, so-called upgrading in English.
• This syngas can also, depending on the ratio H 2 : CO, and / or depending on the catalysts used, be converted into methanol or higher alcohols. So in the case of transformation into methanol:
• the starting biomass can be a lignocellulosic biomass (wood, sugar cane, straw, etc.) or a biomass with carbohydrates (cereals, sugar beet, etc.) easily hydrolysable.
• the methanol thus obtained is used in the preparation of methyl mercaptan
• FR7343539 and FR2477538 which is to achieve the synthesis of methyl mercaptan by vapor phase reaction between methanol and hydrogen sulfide at a temperature, in all point of the reaction mass between 280 and 450 ° C., preferably 320 ° and 370 ° C., under a pressure of between 2.5 and 25 bar, preferably between 7 and 12 bar, the reaction being carried out by passing the reagents over at least three successive catalyst beds, all of the hydrogen sulphide being introduced at the first bed and a fraction of the total methanol being introduced at each bed, and the overall molar ratio of hydrogen sulphide to total methanol being between 1 , 10 and 2.5.
• a precondensation and settling operation is advantageously carried out at the outlet of the last reactor so as to obtain an organic phase consisting mainly of products containing sulfur and an aqueous phase consisting of products containing no sulfur which are separated. one from the other.
• the organic phase is then distilled, under pressure, so as to eliminate the hydrogen sulfide at the top, then the mixture is subjected to a relaxation in the foot, which is subjected to a new distillation, the mercaptan being collected at the head of this second distillation .
• the bottom product which contains dimethylsulphide may advantageously be recycled at the level of the reaction after extraction of unreacted residual alcohol.
• the hydrogen sulphide collected at the top of the first distillation can be returned to the top of the reaction.
• the aqueous phase resulting from the precondensation and decantation step is subjected to distillation with optional recycling to the reaction of the alcohol thus collected.
• the vapors from the reaction mixture can be washed with methanol in order to release the mercaptan from its hydrates.
• methanol is injected in fractions at the inlet of each catalyst zone. Fractions can be equally or unevenly distributed across all beds. It is also possible to distribute all of the methanol feed over all the beds minus a few units in order to use these as finishers of the reaction. For example, it is decided to divide the catalytic mass into ten successive beds, the charge of methanol being divided into nine equal parts each introduced at the level of the first nine beds, the last to complete the reaction.
• the device for introducing methanol is chosen so as to be able to inject it partly in liquid form and partly in gaseous form.
• the heat of evaporation of the methanol thus makes it possible to absorb all or some of the calories released by the reaction. It is also possible, by controlling the proportion of methanol introduced in liquid form at the inlet temperature of the reagents in the catalytic bed. concerned to control the temperature of the reaction very efficiently.
• Another characteristic consists in choosing an overall H 2 S / CH 3 OH molar ratio of between 1.10 and 2.5. Thanks to the multi-injection technique described above, it is possible to obtain a high selectivity in favor of methyl mercaptan despite the low molar ratio chosen. But this characteristic is important from the economic point of view because it reduces the size of reactors, pipes, pumps, etc.
• Another characteristic consists in choosing as catalyst an activated alumina having a specific surface area of between 100 and 350 m 2 / g.
• promoter in order to further improve the selectivity of the reaction, it is possible to use a promoter. All promoters proposed in the literature are suitable for the implementation of the invention. However, it is advantageous to choose the most effective, including metal sulphides such as cadmium sulphide or potassium salts and oxides such as carbonate and tungstate.
• the fraction containing the dimethylsulfide may be recycled in whole or in part in the reaction step.
• the catalyst used for this reaction is preferably an activated alumina having a specific surface area of between 100 and 400 m 2 / g, such as in the form of beads 2 to 5 mm in diameter.
• the temperature is between 280 and 450 ° C. and preferably between 350 and 450 ° C. and under a pressure of between 2.5 and 25 bar.
• the pressure in the first distillation stage is between 5 and 30 bar, and preferably between 10 and 20 bar, whereas in the second distillation step is 1 to 5 bar and preferably between 1.5 and 3 bar.
• the synthesis of methyl mercaptan can also be carried out directly from the synthesis gas (syngas) produced according to the reactions described above from biomass.
• the synthesis of methyl mercaptan is carried out by direct reaction of the synthesis gas with hydrogen sulfide in a catalytic process, and without passing through methanol.
• the overall reaction is written in this case as follows:
• the mercaptan thus obtained is used in the manufacture of dimethyldisulphide.
• R-SS-R disulfide is generally accompanied by the formation of secondary products, namely polysulfides of disulfide-like structure but containing a larger number of sulfur atoms combined (R-Sn-R with n> 2).
• CH 3 -S 3 -CH 3 + 2CH 3 SH - ca has yseur ⁇ 2 CH 3 -S-CH 3 + H 2 S
• the present invention which relates to a process for producing dimethyl disulphide
• the presence of hydrogen sulphide in the reactants introduced into the retrogradation reactor has an adverse effect on the conversion yield of dimethylpolysulfides to dimethyl disulphide and the prior elimination of hydrogen sulphide makes it possible to achieve conversions to dimethyl disulphide substantially. Total.
• the process according to the invention for the manufacture of dimethyl disulphide from methyl mercaptan of at least partially renewable origin and of sulfur comprises two reaction zones and an intermediate degassing zone.
• the first reaction zone is supplied with reagents (methyl mercaptan and sulfur) which, in the presence of a catalyst (optionally introduced simultaneously with the reagents), react with each other to give dimethyl disulphide and dimethylpolysulfides.
• the degassing zone is situated downstream of the first reaction zone and serves to eliminate the hydrogen sulfide contained in the liquid raw products leaving the first reaction zone. While it is preferred to remove hydrogen sulfide as completely as possible, it is within the scope of the present invention to remove only a portion (at least 50%) of the hydrogen sulfide.
• This degassing operation can be performed, either by heating the products, or by driving with an inert gas optionally combined with heating, at a pressure above atmospheric pressure of up to 10 bar, preferably below 6 bar.
• the second reaction zone supplied with products from the degassing zone after removal of at least 50% of the hydrogen sulfide, is intended to convert dimethylpolysulfides to dimethyl disulphide by reaction with methyl mercaptan in the presence of catalyst.
• a schematic device comprising a first reactor 1 is used.
• the reagents: sulfur (liquid or solid) and methyl mercaptan (liquid) in excess of the stoichiometry, are introduced into the reactor 1 respectively by two pipes.
• the catalyst of the reaction is incorporated simultaneously, it is introduced by a single pipe.
• the gaseous effluents that can be formed in the reactor are optionally removed by another pipe, and the liquid reaction crude, withdrawn from the reactor 1, is fed through a pipeline into the degasser 2.
• the residence time in the reactor 1 is set to in a manner known per se so as to obtain at its output an almost total conversion of the sulfur initially introduced, that is to say a conversion equal to 100% or at least such that the unprocessed sulfur is solubilized in the liquid effluent .
• the degasser 2 is equipped to selectively remove hydrogen sulfide dissolved in the liquid that comes from the reactor 1, either by heating or by driving by means of an inert gas introduced through a pipe.
• the liquid, freed from hydrogen sulphide, is withdrawn at the bottom of the degasser and is led through a pipe into the finishing reactor 3 in which the dimethylpolysulfides formed in reactor 1 are converted to dimethyl disulphide in the presence of catalyst by reaction with excess methyl mercaptan. .
• the residence time in the reactor 3 is regulated in a manner known per se, depending on the content of dimethylpolysulfides accepted in the effluent, a longer residence time promoting the retrogradation of dimethylpolysulfides to dimethyl disulphide.
• the products leaving the reactor 3 are brought into the degassing column 4 for the complete elimination of the dissolved hydrogen sulphide, either by heating or by entrainment by means of an inert gas introduced via a pipe.
• the distillation section is fed with products leaving the degassing column 4 for the separation in the column 5 of the methyl mercaptan contained in the product for its recycling to the reactor 1.
• the product recovered at the bottom of the column 5 is fed through a pipe in column 6 at the top of which the dimethyl disulphide is recovered, while the column bottoms 6, consisting of dimethyl disulfide mixed dimethylpolysulfides mixed, are preferably recycled to the finishing reactor 3.
• a possible variant is to return the bottom of the column 6 in the reactor 1.
• the device described above corresponds to the simplest embodiment. Those skilled in the art will understand that it is not beyond the scope of the present invention by implementing a first reaction zone consisting of several reactors operating in parallel and connected to the same degasser or to a plurality of degassers constituting a degassing zone. intermediate. Likewise, it would not be departing from the scope of the present invention by implementing a second reaction zone consisting of several finishing reactors. For example, to improve the efficiency of dimethyldisulphide and avoid the recycling of dimethylpolysulfides, it is possible to implement several finishing reactors arranged in series, each preceded by an intermediate degasser for removing the hydrogen sulfide formed in the preceding reactor.
• This step of the process according to the invention can be carried out with different types of reactors, for example agitated and / or tubular, the choice of which may depend on the reaction conditions and the nature of the catalysts used.
• the methylmercaptan / sulfur molar ratio must be at least 2.
• a large excess of methyl mercaptan promoting the dimethyl disulfide selectivity, the molar ratio of methyl mercaptan / sulfur can be between 2 and 10, and preferably is included between 3 and 6 to minimize the amount of methyl mercaptan to separate and recycle.
• each of the reaction zones operating at pressures above atmospheric pressure.
• the pressure must at least be sufficient to maintain the methyl mercaptan in the liquid state and can be up to 50 bar.
• the process according to the invention can be carried out over a wide range of temperatures depending on the nature of the catalysts used.
• the temperature may be between 25 ° C. and 150 ° C. in the case of thermally stable catalysts.
• All the catalysts known in the prior art for the oxidation of mercaptans by sulfur can be used in the process according to the invention, whether it be organic or inorganic liquid or solid basic agents, such as alkaline bases, alkaline alkoxides, alkali mercaptides, combinations of alkaline bases with a mercaptan and an alkene oxide, amines in the free state or attached to organic carriers (organic anion exchange resins), or whether they are inorganic oxides of certain metals such as magnesium oxide or aluminosilicates such as zeolites. Catalysts can be identical in the two reaction zones or possibly different.
• the choice of catalyst can determine the type of primary reactor (reactor 1) to be used in the process according to the invention.
• the use of a stirred reactor as a primary reactor is to be avoided.
• the reaction temperature must in this case be greater than the sulfur melting temperature.
• the primary reactor can be either of the agitated type or of the tubular type.
• This type of catalyst is introduced simultaneously with the reagents methyl mercaptan and sulfur in the primary reactor and in this case it serves as a catalyst for the finishing reactor (reactor 3) of the process according to the invention, which can be either agitated type or type tubular.
• the finishing reactor reactor 3
• the solid catalyst used in the finishing reactor may be the same or different.
• the finishing reactor 3 may be of agitated or tubular type; in the case of a solid catalyst with low attrition resistance, the reactor will preferably be tubular to a fixed bed.
• This oxidation of methyl mercaptan by sulfur, catalysed by organic or inorganic basic agents, homogeneous or heterogeneous, batch or continuous, is accompanied by a release of hydrogen sulphide and of dimethyl polysulphides (CH 3 S x CH 3) Sulfur x rank greater than 2.
• an odor masking agent is effective only if the DMDS used has reduced levels of highly odoriferous volatile impurities such as methyl mercaptan and dimethylsulfide and preferably contains less than 200 ppm by weight of methyl mercaptan and less 50 ppm by weight of dimethylsulfide.
• highly odoriferous volatile impurities such as methyl mercaptan and dimethylsulfide
• contains less than 200 ppm by weight of methyl mercaptan and less 50 ppm by weight of dimethylsulfide are described in EP0976726.
• odor-masking agents are selected from esters having the general formula (I): R 1 CC ⁇ R 2 wherein R 1 represents a hydrocarbon radical, linear or branched, containing from 1 to 4 carbon atoms, optionally unsaturated and R 2 represents a hydrocarbon radical containing from 2 to 8 carbon atoms, linear, branched or cyclic, optionally unsaturated.
• the invention therefore also relates to a composition based on DMDS manufactured at least partially based on raw materials of renewable origin, characterized in that it contains, by weight, at least 95% dimethyldisulphide, less than 500 ppm methylmercaptan (MM), less than 100 ppm of dimethylsulfide (DMS) and 0 to 1% of at least one odor-masking agent selected from vanillin, ethyl vanillin and, preferably, esters of the general formula ( I).
• MM ppm methylmercaptan
• DMS dimethylsulfide
• any method known to those skilled in the art to obtain a DMDS with reduced levels of volatile impurities such as MM and DMS may be used in the context of the present invention.
• a particularly preferred method is a distillation top. This method has the advantage of jointly removing the MM and the DMS while the usual methods of odor reduction, generally based on the elimination of residual mercaptans by specific reaction of the mercaptan function with an elimination agent such as base or an alkene oxide in the presence of a base, have no effect on the DMS present in the DMDS.
• the DMDS thus topped which preferably contains less than 200 ppm of MM and less than 50 ppm of DMS, is used to prepare a composition according to the invention.
• composition according to the invention comprises at least one odor-masking agent.
• DMDS DMDS in its applications
• the maximum content of odor-masking agent (s) is therefore set at 1%, but this content is preferably between 0.1 and 0.5% and more particularly equal to 0.2%.
• esters of general formula (I) mention may be made of butyl, isoamyl or benzyl acetates and butyrates of ethyl, propyl, butyl, 2-methylbutyl or isoamyl. Particularly preferred are isoamyl acetate, 2-methylbutyl butyrate, isoamyl butyrate, benzyl acetate and mixtures of these compounds.
• Esters (I) may or may not be associated with orthophthalates, such as
• composition according to the present invention comprises by weight: isoamyl acetate 0.1% diethyl orthophthalate 0.1%
• composition according to the present invention comprises by weight: isoamyl acetate 0.05% 2-methylbutyl butyrate 0.03% benzyl acetate 0.02% diethyl orthophthalate 0.1%
• the subject of the present invention is also the use of DMDS obtained according to the process of the invention for the synthesis of methanesulphonic acid.
• Alkanesulfonic acids such as methanesulfonic acid
• their salts have many industrial applications, especially as detergents, emulsifiers, esterification catalysts, hardeners for certain resins.
• the dimethyl disulphide of the invention according to that defined above is oxidized in the presence of chlorine and hydrolyzed in the presence of water under conditions known to those skilled in the art, and as described in patent US5583253.
• Methyl mercaptan reacts with chlorine in the presence of aqueous hydrochloric acid at an elevated temperature ranging from about 85 to 115 ° C, more preferably from about 95 to 105 ° C, and generally from about 98 ° C. ° C.
• the aqueous methanesulfonic acid may contain significant amounts of stable intermediates such as DMDS, methane methyl thiosulfonate (hereinafter abbreviated MMTS) and chloride. of methanesulfonyl (hereinafter abbreviated MSC).
• DMDS methane methyl thiosulfonate
• MSC methanesulfonyl
• the total amount of DMDS and MMTS is referred to as oxidizable impurities in the product characteristics. These impurities can be reacted with hydrogen peroxide or ozone by post-treatment of the aqueous MSA product with these agents.
• the crude aqueous MSA containing the oxidizable impurities may be treated with sufficient chlorine to convert said oxidizable impurities to MSC, and the MSC containing aqueous MSA is subjected to heat sufficient to hydrolyze the MSC to MSA.
• the amount of chlorine used is adapted, as described in US Pat. No. 5,583,253, according to whether the treatment of raw MSA with chlorine is part of a continuous or batch process.
• the crude aqueous MSA is generally passed under a stream of steam or the like to remove residual impurities from the crude aqueous MSA. Chlorides, DMDS, MMTS, MSC, water and non-condensed chlorine having thus been removed, the product is recovered an aqueous MSA whose oxidizable impurities are substantially reduced. MSC, which is produced by the conversion of oxidizable impurities with chlorine, is hydrolyzed to MSA in the vapor stream.
• a finishing reactor submits the MSC found in the raw aqueous MSA at sufficient heat for a time sufficient to convert the MSC to MSA.
• the product of the finishing reactor may further be subjected to a vapor stream, if necessary.
• the chlorination of crude aqueous MSA is preferably carried out in the reactor discharge line or pipe as close as possible to the reactor, advantageous purification results can be obtained by injecting chlorine into the crude at any point in the process. after leaving the reactor provided that the chlorine is in appropriate contact with the oxidizable impurities to react and form MSC, so that the MSC can be hydrolyzed to MSA.
• Different alternative chlorine injection points in the aqueous MSA can therefore be used.
• the aqueous MSA thus purified is further treated to remove almost all water, for example, according to the evaporation procedures described in US4450047 or US4938846.
• alkanesulfonic acids are therefore most often made from alkanes by sulfoxidation or by sulfochlorination. These two synthesis routes can sometimes lead to the formation of sulfonated by-products on the different carbon atoms of the hydrocarbon chain.
• the hydrolysis of the alkanesulfochlorides can lead to more or less colored alkanesulphonic acids, requiring a final treatment of discoloration, for example by means of chlorine.
• the alcohol used may advantageously be chosen from primary, secondary or tertiary alcohols containing from 1 to 12 carbon atoms. It is however preferred to use a C1 to C4 alcohol, and more particularly methanol.
• the methanol used is advantageously that synthesized from renewable materials, as described above.
• the DMDS content of the alcoholic starting solution can vary within wide limits depending on the alcohol used. It can generally range from 0.1 to 90% by weight, but is preferably between 2 and 25%.
• the oxygen required for the reaction may be provided in pure form or diluted with an inert gas such as, for example, nitrogen.
• the oxygen is preferably introduced gradually into the alcoholic solution.
• the total amount of oxygen required is at least 4 moles per mole of DMDS present in the initial solution, but it is preferred to operate with an excess of oxygen of at least 50%.
• the photooxidation can be carried out at a temperature of between -20 ° C. and the boiling point of the alcohol, but the operation is preferably carried out between 18 and 45 ° C.
• the operation is advantageously carried out at atmospheric pressure, but it would not be outside the scope of the present invention working under slight pressure.
• This embodiment of the process according to the invention can be carried out batchwise or continuously in any photochemical reactor, for example in a immersion or falling film reactor, equipped with one or more low, medium or high pressure mercury vapor lamps, or ultraviolet emitting excimer lamps.

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