MXPA99006998A - Dimethylsulphide composition with masked odour - Google Patents

Abstract

Low odor dimethyldisulfide e.g. for sulfurisation of catalysts has very low content of methylmercaptan and dimethylsulfide impurities and contains at least one odor masking agent The normal strong aggressive odor of dimethyldisulfide is reduced by limiting the content of methylmercaptan to less than 500 ppm and of dimethylsulfide to less than 100 ppm, and incorporating up to 1%of at least one odor masking agent. A composition based on dimethyldisulfide CH3SSCH3 (DMDS) containing (by wt.) at least 95%DMDS, less than 500 ppm (preferably less than 200 ppm) methylmercaptan, less than 100 ppm (preferably less than 50 ppm) dimethylsulfide and up to 1%( preferably 0.1-0.5%and especially about 0.2%) of at least one odor masking agent.

Description

COMPOSITIONS BASED ON DIMETHYL DISULFIDE WITH ODOR Field of the Invention The present invention relates to the field of organic sulfides and, more particularly, to that of dimethyl disulfide. STATE OF THE ART Dimethyl disulfide (DMDS) has a strong and aggressive odor due in part to the presence of highly odorous impurities and partly to the smell of garlic and ether intrinsic to DMDS. This strong odor prevents the increased growth of this product in applications such as sulfurization of catalysts or as a filler additive for cracking with water vapor. In comparison with other products used in these applications, such as tere-alkyl polysulfides, DMDS exhibits numerous advantages, in particular a high sulfur content (68%) and non-coking degradation products (CEU, tfe). Furthermore, in these applications, the DMDS translates into generally superior behaviors with respect to other products, such as tere-alkyl polysulfides. However, these other products have markedly lower odor levels and, for this reason, they are easier to handle compared to the DMDS. A particularly efficient and economical method, among the methods of synthesis of DMDS, consists of the oxidation of methyl mercaptan by sulfur according to the reaction: 2CH3SH + S ^ CH catalyst, SSCH3 + H2S This oxidation of methyl mercaptan by sulfur, catalyzed by basic agents organic or inorganic, homogeneous or heterogeneous, under discontinuous or continuous conditions, is accompanied by the release of hydrogen sulfide and dimethyl polysulfides (CH3SXCH3) with a sulfur x greater than 2. In order to produce DMDS according to this process with high yields and with a limited production of DMPS (dimethyl polysulfides with a rank higher than 2), the European patent 0.446.109, whose content is incorporated herein for reference purposes only, describes a preparation process comprising two regions of reaction interrupted by an intermediate degassing region and followed by a distillation region. While it provides good performance in terms of performance and selectivity for DMDS, it can be seen that this process results in a non-negligible amount of methyl mercaptan (approximately 4000 ppm) and in a very small amount of dimethyl sulfide (approximately 300 ppm). ), the methyl mercaptan used or produced during the synthesis of DMDS remaining in the finished product. The result of these volatile impurities is that they make the odor of DMDS very unpleasant and aggressive, this strong odor being considered as a major cause of the discomfort that arises during the handling of this product by users. In order to mask the odor of organic polysulfides, US Patent 5,559,271 recommends the addition thereto of a certain amount of masking product such as, in particular, vanillin or ethyl vanillin. Although this general formula includes DMDS, said patent is directed more particularly to the treatment of heavy polysulfides such as, for example, di-t-nonyl pentasulfide. The application of this method to DMDS does not allow to mask its nauseating and highly unpleasant odor. It has now been found that, in the specific case of DMDS, the addition of an odor masking agent is only effective if the DMDS used exhibits a reduced content of highly odorous volatile impurities, such as methyl mercaptan and dimethyl sulfide and if it preferably comprises less than 200 ppm by weight of methyl mercaptan and less than 50 ppm by weight of dimethyl sulfide. It has also been found that the most effective odor masking agents are not those mentioned in the aforementioned US patent, but those chosen from the esters corresponding to the general formula: B ^ COaR2 (I) wherein R1 represents a hydrocarbon radical, linear or branched, optionally unsaturated, comprising from 1 to 4 carbon atoms and R2 represents a linear, branched or optionally unsaturated cyclic hydrocarbon radical, comprising from 2 to 8 carbon atoms. SUMMARY OF THE INVENTION Therefore, the object of this invention is a composition based on DMDS, characterized in that it comprises, by weight, at least 95% of dimethyl disulfide, less 500 ppm of methyl mercaptan (MM), less than 100 ppm of dimethyl sulfide (DMS) and up to 1% of at least one odor-masking agent, preferably an ester of general formula (I). DETAILED DESCRIPTION OF THE INVENTION In the context of the present invention, any method known to those skilled in the art can be employed for the production of a DMDS with lower volatile impurity contents, such as MM and DMS. However, in the case of a DMDS comprising high contents in MM and DMS, a particularly preferred method consists of a primary distillation. This method exhibits the advantage of simultaneously separating MM and DMS, while the usual methods for reducing odor, generally based on the separation of residual mercaptans by specific reaction of a mercaptan functional group with a separating agent, such as a base or an oxide of alkene in the presence of a base, have no effect on the DMS present in DMDS. The DMDS, thus separated by primary distillation, which preferably comprises less than 200 ppm of MM and less than 50 ppm of DMS, is used to prepare a composition according to the invention by the simple addition of at least one odor masking agent. Given that one of the main advantages of DMDS in its applications lies in its high sulfur content (68%), an excessively high content of odor-masking agent in the composition would result in a lower sulfur analysis and a lower this product in its main applications. Therefore, the maximum content of odor masking agents or agents should be set at 1%, preferably between 0.1 and 0.5% and more particularly at a value equal to approximately 0.2%. As illustrative but not limiting examples of esters of general formula (I), there can be mentioned butyl acetate, isoamyl acetate, benzyl acetate, ethyl butyrate, propyl butyrate, butyl butyrate, 2-methylbutyl butyrate or butyrate of isoamyl More particularly, isoamyl acetate, 2-methylbutyl butyrate, isoamyl butyrate, benzyl acetate and mixtures thereof are preferred. The esters (I) may or may not be used in combination with ortho-phthalates corresponding to the general formula: wherein the symbols R and R, which may be the same or different, each represent a linear, branched or cyclic hydrocarbon radical, optionally unsaturated, comprising from 1 to 8 carbon atoms. As a non-limiting example of the compound (II), diethyl ortho phthalate can be mentioned very particularly. A typical composition of the present invention comprises, by weight: Isoamyl acetate 0.1% Diethyl ortholate 0.1% DMDS separated by primary distillation 99.8% Another typical composition of the present invention comprises, by weight: Acetate isoamyl 0.05% 2-methylbutyl butyrate 0.03% Benzyl acetate 0.02% Ortho-diethyl phthalate 0.1% DMDS separated by primary distillation 99.85 The following examples illustrate the invention without limiting it.

Example 1: Synthesis of dimethyl disulfide according to the process described in EP 0 446 109 a) Installation: The attached figure 1 is a diagram of the plant used where two reactors are combined (primary reactor 1 and finishing reactor 3) . The primary reactor is a stirred reactor and the finishing reactor is a stationary bed tubular reactor. A degassing system is located between these two reactors, this system being constituted by a jacketed receptacle 2 equipped with an agitator and topped by a cooled column that allows the methyl mercaptan, which can be transported with the hydrogen sulfide, to be recondensed before being separated. This plant is completed by a pump, located between the outlet of the degasser 2 and the inlet of the finishing reactor 3, whose pump makes it possible to feed this reactor with treated liquid product in the degasser. The degassing column 4 serves to completely separate the H2S dissolved in the liquid leaving the reactor 3. The distillation column 5 makes it possible to remove most of the excess methyl mercaptan in order to recycle it via line 22 to the reactor 1 Column 6 makes it possible to separate the residual dimethyl polysulphides (DMPS) in order to recycle them to reactor 3 or reactor 1. b) Procedure: Methyl mercaptan (MM) is introduced into reactor 1 under pressure via line Ia flow rate of 960 g / h. Liquid sulfur is introduced into reactor 1 via line 10 at a flow rate of 160 g / h (MM7S = 4 molar). Reactor 1 (reaction volume: 300 ml) contains 20 g of dried Amberlyst A21 resin. The operating pressure is maintained at 5.5 bar relative and the temperature at 40 ° C. The reaction mixture at the outlet of the reactor 1 has the following composition by weight, excluding the excess of methyl mercaptan and excluding H2S: DMDS 85%, DMPS 15%. This reaction mixture is then conducted to the degasser 2 via line 14 in order to carry out its treatment. After the treatment, the mixture, liberated from H2S, is conducted through the duct 17 into the finishing reactor 3, which contains a load of 94 grams of dried A21 resin. The pressure in the reactor is 5.5 bar relative and the temperature 40 ° C. At the outlet of the reactor 3, the mixture has the following composition by weight, excluding the H2S and excluding the excess of methyl mercaptan: DMDS 98.5%, DMPS 1.5%. The mixture is then introduced through the conduit 18 into the degasser 4, in order to separate the H2S that has formed in the reactor 3 during the retrogression of the dimethyl polysulfides by methyl mercaptan to give DMDS. At the outlet of the degassing column 4, the mixture is introduced through the conduit 21 into the first distillation column 5, in order to remove practically all of the excess of methyl mercaptan. This methyl mercaptan can be recycled through the conduit 22 to the introduction of the reactants in the reactor 1. At the outlet of the column 5, the mixture is conducted through the conduit 23 into the second distillation column 6, where the DMPSs are separated in the tail of the column via conduit 25, to be optionally recycled to reactor 3, or via conduit 26 to be optionally recycled to reactor 1. The DMDS, finally collected at the head of column 6 via line 24 and known as Ao for the olfactory tests described in the following examples have the following composition by weight: DMDS: 99.3% DMPS: 3000 ppm MM: 4000 ppm DMS: 300 ppm Example 2: Purification of the dimethyl disulfide prepared according to the process described in the EP patent 0.446.109 The synthesis procedure is the same as that described in example 1, except that the DMDS leaving column 6 through line 24 is introduced into a third distillation column 7 (see diagram in figure 2 attached) , wherein the volatile impurities, such as methyl mercaptan and dimethyl sulfide, are separated at the top of the column via line 27. The DMDS collected at the bottom of the column by line 28 has the following composition in weight. or: - DMDS: 99.7% - DMPS: 3000 ppm - MM: <; 10G ppm - DMS: < 50 ppm This purified DMDS, referred to below as Bo, and a sample Ao of DMDS prepared in Example 1, were subjected to an olfactory test. The eight people invited to this trial unanimously recognized a marked improvement in the odor of the Bo DMDS compared to the Ao, DMDS, but all of them also recognized that a smell of garlic and ether persisted in the Bo DMDS. EXAMPLE 3 2000 ppm by weight vanillin (4-hydroxy-3-methoxybenzaldehyde) was added to 100 g of B0 DMDS prepared in example 2. Complete dissolution of vanillin was observed after one hour at 25 ° C. The resulting sample was named Bi. EXAMPLE 4 The vaniline used in example 3 was replaced by 2000 ppm ethyl vanillin (3-ethoxy-4-hydroxybenzaldehyde). Its dissolution was observed after one hour at 25 ° C. The resulting sample was designated B2. Examples 5 and 6 illustrate the preparation of DMDS-based compositions with the odor masked by the preferred products of the present invention.

Example 5 To 100 g of Bo DMDS prepared in Example 2 was added 2000 ppm of a mixture composed by weight of 50% of isoamyl acetate and 50% of diethyl ortho phthalate. Since this mixture was liquid, the solution was immediate at 25 ° C. The resulting sample was referred to as B3. Example 6 The mixture used in Example 5 was replaced by 2000 ppm of a mixture having the following composition by weight: Isoamyl acetate 25% Diethyl ortho-phthalate 50% 2-methylbutyl butyrate 15% Benzyl acetate 10% La Dissolution of this mixture in Bo was immediate at 25 ° C. The resulting sample was referred to as B. The samples Bo, Bi, B2, B3 and B were subjected to a comparative olfactory test performed by the group of 8 people mentioned in example 2. These 8 people were asked to attribute to the samples a grade of 0 to 5. according to his preference with respect to the odor, attributing to the note 0 the less preferred odor, to the note 5 the most preferred odor and to the notes 1, 2, 3 and 4 values that allow to classify the intermediate levels. The results are offered in the following table: It will be appreciated that the odor of the compositions Bi, B2, B3 and B4 is always preferred to the odor of Bo and that the note obtained for B4 is very close to the maximum possible score (40). The members of the group further specified that they preferred the "ruined" note of the compositions B3 and B4 in relation to the "vanilla-garlic" note of the compositions Bi and B2. Comparative examples 7 to 11 illustrate the need to separate most of the volatile impurities from the DMDS in order to observe a significant odor masking effect. Example 7 Example 3 (masking agent: vanillin) was repeated but replacing 100 g of Bo DMDS per 100 g of DMDS A or not separated by primary distillation and prepared in example 1. The resulting sample was referred to as Ai. The 8 members of the group compared the smell of Ai with that of B0 and all of them preferred that of Bo (DMDS purified from their volatile impurities and without masking agent) with respect to composition Ai based on DMDS without purifying and vanillin. Example 8 The procedure of Example 7 was followed, vanillin being replaced by ethyl vanillin. The 8 people on the panel preferred the odor of the Bo sample to that of the resulting sample (A2). Example 9 The procedure of example 7 was followed, replacing vanillin with menthol. The smell of the Bo sample was still preferred over the resulting sample (Ace). Example 10 The procedure of example 7 was followed, replacing vanillin with the mixture of masking products mentioned in example 5. The resulting sample was referred to as A4. The 8 people in the group preferred the smell of B0 Example 11 The procedure of Example 7 was followed, vanillin being replaced by the mixture of masking products mentioned in Example 6. The resulting sample was referred to as A5. The 8 people in the group preferred the smell of Bo to that of A5.

Claims (9)

NO LEAVE OF THE INVENTION Having described the present invention is considered as a novelty and, therefore, claimed as property contained in the following claims:

1. - Composition based on dimethyl disulfide (DMDS), characterized in that it comprises, by weight, at least 95% of DMDS, less than 500 ppm of methyl mercaptan, less than 100 ppm of dimethyl sulfide and up to 1% of at least one Odor masking agent.

2. Composition according to claim 1, characterized in that it comprises less than 200 ppm of methyl mercaptan and less than 50 ppm of dimethyl sulfide.

3. Composition according to claim 1 or 2, characterized in that it comprises from 0.1 to 0.5% of odor masking agent or agents, preferably around 0.2%.

4. Composition according to any of claims 1 to 3, characterized in that the odor masking agent is chosen from the esters corresponding to the general formula: RxC02R2 wherein R1 represents a hydrocarbon radical, linear or branched, optionally unsaturated, comprising 1 to 4 carbon atoms and R2 represents a linear, branched or optionally unsaturated cyclic hydrocarbon radical, comprising from 2 to 8 carbon atoms.

5. Composition according to claim 4, characterized in that the odor masking agent is selected from the group consisting of isoamyl acetate, 2-methybutyl butyrate, isoamyl butyrate, benzyl acetate and mixtures thereof.

6. Composition according to claim 4 or 5, characterized in that the ester of formula (I) is used in combination with an ortho-phthalate corresponding to the general formula: wherein the symbols R3 and R4, which may be the same or different, each represent a linear, branched or cyclic hydrocarbon radical, optionally unsaturated, comprising from 1 to 8 carbon atoms.

7. Composition according to claim 6, characterized in that the ortho-fialate is diethyl ortho-phthalate.

8. Composition according to claim 7, characterized in that it comprises 0.1% of isoamyl acetate and 0.1% of diethyl ortho-phthalate.

9. Composition according to claim 7, characterized in that it comprises 0.05% isoamyl acetate, 0.03% 2-methylbutyl butyrate, 0.02% benzyl acetate and 0.1% ortho-phthalate. diethyl