WO2019158576A1 - Direct synthesis of alkane sulfonic acids from alkane and sulfur trioxide employing heterogeneous catalysis - Google Patents

Direct synthesis of alkane sulfonic acids from alkane and sulfur trioxide employing heterogeneous catalysis Download PDF

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Publication number
WO2019158576A1
WO2019158576A1 PCT/EP2019/053534 EP2019053534W WO2019158576A1 WO 2019158576 A1 WO2019158576 A1 WO 2019158576A1 EP 2019053534 W EP2019053534 W EP 2019053534W WO 2019158576 A1 WO2019158576 A1 WO 2019158576A1
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reaction vessel
alkane
sulfur trioxide
gaseous
process according
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PCT/EP2019/053534
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French (fr)
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Timo Ott
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Grillo-Werke Ag
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    • 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
    • C07C303/04—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 substitution of hydrogen atoms by sulfo or halosulfonyl groups
    • C07C303/06—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 substitution of hydrogen atoms by sulfo or halosulfonyl groups by reaction with sulfuric acid or sulfur trioxide
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/582—Recycling of unreacted starting or intermediate materials

Definitions

  • the present invention relates to a process for the direct synthesis of alkanesul- fonic acids, particularly methanesulfonic acid, from sulfur trioxide and alkanes employing heterogeneous catalysts, particularly transition metals such as rho- dium.
  • the synthesis is carried out in a tube furnace and the resultant product is isolated by quenching the resultant gas mixture in aqueous concen- trated sulfuric acid at room temperature.
  • Alkanesulfonic acids are organic acids that can reach a similar acid strength as that of inorganic mineral acids, for example, sulfuric acid.
  • inorganic mineral acids for example, sulfuric acid.
  • the sulfonic acids are non-oxidizing and do not give off vapors that are harmful to health, as can be observed with hydrochloric and nitric acids.
  • many sulfonic acids, for example, methanesulfonic acid are biologically degradable.
  • sulfonic acids are many, for example, in cleaning agents, surfactants, as catalysts, and in organic synthesis, pharmaceutical chemistry, for example, as protective groups.
  • the salts of sulfonic acids are employed, for example, as surfactants, for example, sodium dodecylsulfonate, or in the elec- troplating industry, especially as tin, zinc, silver, lead and indium, but also other metal, alkylsulfonates.
  • the very high solubility of alkyl sulfonates plays an im- portant role, in particular. Further, no harmful gases are formed in electrolysis, and the use of toxic compounds, for example, cyanide, which is common in many cases, is dispensed with.
  • the structurally simplest representative of alkanesulfonic acids is methanesul- fonic acid .
  • US 2,493,038 describes the preparation of methanesulfonic acid from SO3 and methane.
  • US 2005/0070614 describes further methods for preparing me thanesulfonic acid, and its application.
  • WO 2007/136425 A2 discloses the use of the compound di(methanesulfonyl) peroxide (DMSP), which must be prepared by a complex electrolysis and, in addition, is a crystallizable highly explosive solid, as an initiator in a reaction in which methanesulfonic acid is formed from sulfur trioxide and methane.
  • DMSP di(methanesulfonyl) peroxide
  • reaction conditions in conventional processes of alkanesulfonic acid produc- tion can result in undesirable side products, which even manifest themselves as disturbing inhibitors in the production of alkanesulfonic acids. This may lead to termination of the actual reaction for preparing the alkanesulfonic acid, but also to impurities, formation of side products and poor yields, based on sulfur trioxide and methane.
  • reaction vessel especially a tube fur- nace
  • the reaction vessel comprises a heterogeneous catalyst, such that the sulfur trioxide and the at least one gas- eous alkane are getting in contact with the heterogeneous cat- alyst
  • step iii) optionally recovering the not-reacted educt gases and feeding them back into step iii).
  • Figure 1 shows an exemplary mechanism of heterogeneous catalysis.
  • the inventive process provides a simple way to produce alkanesulfonic acids by direct reaction of sulfur trioxide and an alkane. No further educts or additives are required although their presence is not excluded by the invention, but pref- erably no further educts or additives are added in the method according to the present invention.
  • the reaction is assisted by a heterogeneous catalyst.
  • the product is then separated from the reaction mixture. Optionally the remaining educts can be recycled.
  • Sulfur trioxide is commercially available. It can be produced on a large scale for example by a contact process, wherein sulfur dioxide is oxidized with atmos- pheric oxygen to sulfur trioxide.
  • the alkane educts are also commercially available, for example from refining of natural gas and/or crude oil.
  • any alkane which can be brought into a gaseous state, can employed.
  • Particularly short-chained alkanes like methane, ethane, propane, butane, pentane, hexane, heptanes and so on can be used.
  • the alkanes can be branched or unbranched.
  • a single alkane compound can be employed in the inventive process leading to a single alkanesulfonic acid product.
  • a mixture of more than one alkanes can also be employed and a mixture of alkanesulfonic acid compounds is produced.
  • Both the at least one alkane and the sulfur trioxide need to be provided in gas- eous form. Said gases are then run through a reaction vessel. Any reaction vessel, which allows the flowing of gases therethrough, can be employed. Par- ticularly a tube furnace which may hold a quartz glass tube or ceramic tube may be employed. Within the reaction vessel a heterogeneous catalyst is contained. Any suitable catalyst can be employed. The catalyst may comprise a metal suit- able to catalyze the reaction of SO3 and the alkane to form the corresponding alkanesulfonic acid. The catalyst may be supported by an inorganic catalyst sup- port. Any catalyst support known from the prior art, such as for example silica, zirconia, alumina, or graphite may be employed. The support is preferably an inorganic support as this is stable even at higher reaction temperatures and does not lead to side-products by reacting with SO3 and/or the at least one alkane.
  • the reaction vessel needs to be operated at a temperature and pressure where the educt gases remain in gaseous form and the conditions allow for their de- sired reaction to alkanesulfonic acids.
  • the alkanesulfonic acids produced flow from the reaction vessel in a gaseous state along with not-reacted educt gases, i.e., not-reacted sulfur trioxide and not-reacted gaseous alkanes.
  • the separation of the product from said gas stream may be carried out by any suitable method known from the prior art to separate a mixture of gases, like absoption in a solvent, applying membrane technologie, condensation at lower temperatures, absorption on a solid carryier like alumina, zirconia, activated charcoal or silicon dioxide.
  • the not-reacted educt gases may be recovered by any suit- able method known from the prior art and fed back into step iii) of the inventive process. By recycling said gases, the overall yield of the inventive process can be increased significantly.
  • inventive process provides the formation of alkanesulfonic acids via the following reac- tions and mechanisms.
  • methanesulfonic acid is produced according to the following reaction
  • Figure 1 shows an exemplary mechanism of heterogeneous catalysis which is presumed to take place in the process according to the invention when methane is used as gaseous alkane.
  • the mechanism is shown for methane as an example. It is assumed to take place in a similar manner, when other alkanes are used according to the invention.
  • a methane molecule is bound to the catalyst.
  • one of the C-H bonds of the methane molecule is activated by the catalyst, wherein the carbon atom and the hydrogen atom of said C-H bond are bound to the catalyst.
  • a second step (II in Figure 1), sulfur trioxide is brought into contact with said activated methane molecule being bound to the catalyst.
  • Some form of coordi- native bond is formed between said hydrogen atom being bound to the catalyst and one of the oxygen atoms of the sulfur trioxide.
  • Another coordinative bond is formed between the central sulfur atom of the sulfur trioxide and said carbon atom being bound to the catalyst. Effectively, the sulfur trioxide is inserted into the aforementioned C-H bond of said methane molecule.
  • a third step (III in Figure 1), the formed methanesulfonic acid is desorbed from the catalyst and the catalyst is thus regenerated.
  • the alkanes provided in step ii) and employed in step iii) comprise methane.
  • methanesulfonic acid is produced as one particular product.
  • the alkanes consist of methane, i.e., only methane is employed as alkane compound.
  • the product of the inventive process is methanesulfonic acid.
  • the reaction vessel is operated at a temperature above room tem- perature. More preferably the reaction vessel is operated at a temperature in the range of 400 °C to 600 °C. Most preferably the reaction vessel is operated at a temperature in the range of 470 °C to 800 °C. Particularly the reaction vessel may be operated at a temperature of 600 °C.
  • the described temperatures are specifically suitable to carry out the inventive process. While a lower temperature leads to poor conversion, a higher temperature would destabilize the product gases and would lead to unwanted side-products.
  • the pressure of the reaction vessel is specifically controlled.
  • a pressure in the range of 0,1 to 50 bar is employed.
  • the reaction vessel is operated at a pressure in the range of 0,5 to 2 bar.
  • the heterogeneous catalyst comprises a metal.
  • the metal may be supported by an inorganic catalyst support.
  • the catalyst support corn- prises silica or alumina.
  • the catalyst may be supported by alumina.
  • the catalyst preferably has a specific surface (BET surface) in the range of 100 to 1000 m 2 More preferably, the specific surface (BET surface) is in the range of 180 to 500 m 2 , particularly 300m 2 .
  • the catalyst consists of one or more metals support by a catalyst support. More preferably, the catalyst consists of one or more metals supported by alumina.
  • the metal employed may comprise one or more metals selected from the group of transition metals.
  • the one or more metals are selected from the group consisting of rhodium, iridium, cobalt, copper, nickel, platinum, palla- dium, silver and gold.
  • the heterogeneous catalyst may consist solely of metals and inorganic catalyst supports. Particularly, the catalyst is free of any additional substances, espe- cially organic and/or polymeric substances.
  • the heterogeneous catalyst consists of a metal selected from the group consisting of rhodium, iridium, cobalt, copper, nickel, platinum, pal- lad ium, silver and gold and is supported by a catalyst support, particularly alu- mina. Most preferably the catalyst consists of rhodium supported by alumina.
  • the separation of the al- kanesulfonic acid product is conducted by running the gas stream flowing from the reaction vessel through one or more washing bottles. If more than one washing bottle is employed, the gas stream may be run through the washing bottles subsequently.
  • the one or more washing bottles may be filled with an aqueous solution, preferably a concentrated sulfuric acid solution. Said concen- trated sulfuric acid solution may have a sulfuric acid concentration of 98%.
  • the separation may be conducted at room temperature.
  • the inventive process can be carried out very effectively, if the products are separated from the gas stream by said washing bottles.
  • the methanesulfonic acid can very effectively be separated from the gas stream flowing from the reaction vessel by said washing bottles containing concentrated sulfuric acid solution.
  • the alkanesulfonic acid product is solved in an aqueous solution and thereby separated from the gas stream flowing from the reaction vessel
  • sulfur trioxide may also be solved in the aqueous solution whereby sulfuric acid may be formed. If the washing bottles contain sulfuric acid solution, the sulfur trioxide may be absorbed into said solution, wherein only the concentration of said solution is slightly changed. Operating the washing bottles at room temperature carries the particular ad- vantage of cooling the gas stream flowing from the reaction vessel.
  • the yield of the inventive process is increased, if the product gas mixture is cooled quickly after leaving the reaction vessel.
  • the reaction vessel is purged with an inert gas prior to running the educt gases through the vessel.
  • an inert gas Any suitable inert gas known from the prior art may be employed.
  • nitrogen gas is employed as inert gas.
  • Alterna- tively noble gases, such as helium or argon, can also be employed for example.
  • the reaction vessel is furthermore purged with the gaseous alkane to be employed in the inventive process before the sulfur trioxide is run through the reaction vessel alongside the alkane.
  • purging with the gaseous alkane is performed after the aforementioned purging with an inert gas.
  • the reaction vessel may be purged with methane gas, if methane is to be employed in the inventive process in order to produce methanesulfonic acid.
  • the heteroge- neous catalyst is preloaded with activated alkanes corresponding to the as- sumed catalytic mechanism illustrated above (step I in Figure 1). Furthermore it is believed that sulfur trioxide may bind to the catalyst and thereby deactivate it. If the catalyst is preloaded, such deactivation is prevented.
  • the molar ratio of sulfur trioxide and the alkane compounds run through the reaction vessel is less than 1, i.e., an excess of alkane compounds is employed. More preferably, the molar ratio of sulfur trioxide and alkane is in the range of 0.01 to 0.5, most preferably 0.05 to 0.25, especially 0.1. Particu- larly, an excess of methane with respect to sulfur trioxide may be employed. If the alkane compound is employed in an excess, i.e., if an excess of sulfur triox- ide is avoided, the aforementioned assumed deactivation of the catalyst is fur- ther prevented. Performing the inventive process with an excess of alkane corn- pounds assures that whenever the catalyst offers free sites, said sites are occu-pie with alkane molecules as shown in the mechanism of Figure 1.
  • the procedure of purging the reaction vessel with alkane corn- pound prior to the synthesis and employing the alkane compound in an excess during the synthesis can be combined. Surprisingly it has been found, that a particularly high catalyst activity can be achieved in this way. Without the in- tention of being bound by theory, it is believed that by said combination the catalyst is preloaded with activated alkane and the subsequent replacement by sulfur trioxide is prevented.
  • the provided gaseous sulfur trioxide and the provided alkane compound are mixed prior to running them through the reaction vessel.
  • the educt gases may also be mixed within the reaction vessel.
  • the object of the invention is solved by the use of the process described above for the production of alkanesulfonic acids.
  • said process is used for the production of methanesulfonic acid.
  • the object of the invention is solved by the use of transition metals in a heterogeneous catalyst for the direct syn- thesis of alkanesulfonic acids from sulfur trioxide and alkanes.
  • transition metals selected from the group consisting of rhodium, iridium, cobalt, platinum, palladium, silver and gold are used in said heterogeneous catalyst.
  • the aforementioned metals may be used in a heterogeneous cata- lyst for the direct synthesis of methanesulfonic acid from sulfur trioxide and methane.
  • a 20 quartz glass tube was filled with 5 g of a rhodium (5%) on alumina (support structure) catalyst. It was heated up to 600°C in a tubular furnace after it was purged with nitrogen gas. When it reached the temperature, a methane- gas-stream comprising 10% of gaseous sulfur trioxide was streamed over the cat- alyst. The reaction-gas was washed with a gas-washing-bottle containing sulfuric acid. After quenching the non-reacted sulfur trioxide with water, methanesulfonic acid was determined by NMR and ion chromatography. The yield was about 7% methanesulfonic acid, based on sulfur trioxide.

Abstract

The present invention relates to a process for the direct synthesis of alkanesulfonic acids, particularly methanesulfonic acid, from sulfur trioxide and alkanes employing heterogeneous catalysts, particularly transition metals such as rhodium. Particularly the synthesis is carried out in a tube furnace and the resultant product is isolated by quenching the resultant gas mixture in aqueous concentrated sulfuric acid at room temperature.

Description

Direct synthesis of alkane sulfonic acids from alkane and sulfur trioxide employing heterogeneous catalysis
The present invention relates to a process for the direct synthesis of alkanesul- fonic acids, particularly methanesulfonic acid, from sulfur trioxide and alkanes employing heterogeneous catalysts, particularly transition metals such as rho- dium. Particularly the synthesis is carried out in a tube furnace and the resultant product is isolated by quenching the resultant gas mixture in aqueous concen- trated sulfuric acid at room temperature.
Alkanesulfonic acids are organic acids that can reach a similar acid strength as that of inorganic mineral acids, for example, sulfuric acid. However, in contrast to usual mineral acids such as sulfuric and nitric acids, the sulfonic acids are non-oxidizing and do not give off vapors that are harmful to health, as can be observed with hydrochloric and nitric acids. Further, many sulfonic acids, for example, methanesulfonic acid, are biologically degradable.
The applications of sulfonic acids are many, for example, in cleaning agents, surfactants, as catalysts, and in organic synthesis, pharmaceutical chemistry, for example, as protective groups. The salts of sulfonic acids are employed, for example, as surfactants, for example, sodium dodecylsulfonate, or in the elec- troplating industry, especially as tin, zinc, silver, lead and indium, but also other metal, alkylsulfonates. The very high solubility of alkyl sulfonates plays an im- portant role, in particular. Further, no harmful gases are formed in electrolysis, and the use of toxic compounds, for example, cyanide, which is common in many cases, is dispensed with. The structurally simplest representative of alkanesulfonic acids is methanesul- fonic acid .
US 2,493,038 describes the preparation of methanesulfonic acid from SO3 and methane. US 2005/0070614 describes further methods for preparing me thanesulfonic acid, and its application. WO 2007/136425 A2 discloses the use of the compound di(methanesulfonyl) peroxide (DMSP), which must be prepared by a complex electrolysis and, in addition, is a crystallizable highly explosive solid, as an initiator in a reaction in which methanesulfonic acid is formed from sulfur trioxide and methane.
The reaction conditions in conventional processes of alkanesulfonic acid produc- tion can result in undesirable side products, which even manifest themselves as disturbing inhibitors in the production of alkanesulfonic acids. This may lead to termination of the actual reaction for preparing the alkanesulfonic acid, but also to impurities, formation of side products and poor yields, based on sulfur trioxide and methane.
The methods known in the prior art are in part complicated, cost-intensive, and lead to undesirable products.
It is thus the object of the present invention to provide a process for the direct synthesis of alkanesulfonic acids, particularly methanesulfonic acid, from sulfur trioxide and alkanes employing heterogeneous catalysts. Particularly it is the object of the invention to provide a convenient and simple process which can be employed using standard equipment and which is cost-effective.
In a first aspect of the invention the problem is solved by a process for manu- facturing alkanesulfonic acids comprising the steps of
i) providing sulfur trioxide in a gaseous state,
ii) providing at least one alkane in a gaseous state, iii) running said gaseous sulfur trioxide and said at least one gas- eous alkane through a reaction vessel, especially a tube fur- nace, wherein the reaction vessel comprises a heterogeneous catalyst, such that the sulfur trioxide and the at least one gas- eous alkane are getting in contact with the heterogeneous cat- alyst,
iv) separating the resultant at least one alkanesulfonic acid from the gas stream flowing from said reaction vessel and
v) optionally recovering the not-reacted educt gases and feeding them back into step iii).
Brief description of drawing
Figure 1 shows an exemplary mechanism of heterogeneous catalysis.
The inventive process provides a simple way to produce alkanesulfonic acids by direct reaction of sulfur trioxide and an alkane. No further educts or additives are required although their presence is not excluded by the invention, but pref- erably no further educts or additives are added in the method according to the present invention. The reaction is assisted by a heterogeneous catalyst. The product is then separated from the reaction mixture. Optionally the remaining educts can be recycled.
Sulfur trioxide is commercially available. It can be produced on a large scale for example by a contact process, wherein sulfur dioxide is oxidized with atmos- pheric oxygen to sulfur trioxide.
The alkane educts are also commercially available, for example from refining of natural gas and/or crude oil. In principal any alkane, which can be brought into a gaseous state, can employed. Particularly short-chained alkanes like methane, ethane, propane, butane, pentane, hexane, heptanes and so on can be used. The alkanes can be branched or unbranched.
A single alkane compound can be employed in the inventive process leading to a single alkanesulfonic acid product. A mixture of more than one alkanes can also be employed and a mixture of alkanesulfonic acid compounds is produced. Preferably only one alkane is used and the preferred alkane is methane.
Both the at least one alkane and the sulfur trioxide need to be provided in gas- eous form. Said gases are then run through a reaction vessel. Any reaction vessel, which allows the flowing of gases therethrough, can be employed. Par- ticularly a tube furnace which may hold a quartz glass tube or ceramic tube may be employed. Within the reaction vessel a heterogeneous catalyst is contained. Any suitable catalyst can be employed. The catalyst may comprise a metal suit- able to catalyze the reaction of SO3 and the alkane to form the corresponding alkanesulfonic acid. The catalyst may be supported by an inorganic catalyst sup- port. Any catalyst support known from the prior art, such as for example silica, zirconia, alumina, or graphite may be employed. The support is preferably an inorganic support as this is stable even at higher reaction temperatures and does not lead to side-products by reacting with SO3 and/or the at least one alkane.
The reaction vessel needs to be operated at a temperature and pressure where the educt gases remain in gaseous form and the conditions allow for their de- sired reaction to alkanesulfonic acids.
The alkanesulfonic acids produced flow from the reaction vessel in a gaseous state along with not-reacted educt gases, i.e., not-reacted sulfur trioxide and not-reacted gaseous alkanes. The separation of the product from said gas stream may be carried out by any suitable method known from the prior art to separate a mixture of gases, like absoption in a solvent, applying membrane technologie, condensation at lower temperatures, absorption on a solid carryier like alumina, zirconia, activated charcoal or silicon dioxide.
As an optional step the not-reacted educt gases may be recovered by any suit- able method known from the prior art and fed back into step iii) of the inventive process. By recycling said gases, the overall yield of the inventive process can be increased significantly.
Without the intention of being bound by theory, it is believed that the inventive process provides the formation of alkanesulfonic acids via the following reac- tions and mechanisms.
When sulfur trioxide is brought into contact with an alkane the following reaction takes place
R-CH2-H(g) + S03(g) -» R-CH2-SO3H I
Specifically when methane is employed as gaseous alkane, methanesulfonic acid is produced according to the following reaction
CH4(g) + S03(g) -» HsC-SOsH II
Figure 1 shows an exemplary mechanism of heterogeneous catalysis which is presumed to take place in the process according to the invention when methane is used as gaseous alkane. The mechanism is shown for methane as an example. It is assumed to take place in a similar manner, when other alkanes are used according to the invention.
In a first step (I in Figure 1), a methane molecule is bound to the catalyst. In this step, one of the C-H bonds of the methane molecule is activated by the catalyst, wherein the carbon atom and the hydrogen atom of said C-H bond are bound to the catalyst.
In a second step (II in Figure 1), sulfur trioxide is brought into contact with said activated methane molecule being bound to the catalyst. Some form of coordi- native bond is formed between said hydrogen atom being bound to the catalyst and one of the oxygen atoms of the sulfur trioxide. Another coordinative bond is formed between the central sulfur atom of the sulfur trioxide and said carbon atom being bound to the catalyst. Effectively, the sulfur trioxide is inserted into the aforementioned C-H bond of said methane molecule.
In a third step (III in Figure 1), the formed methanesulfonic acid is desorbed from the catalyst and the catalyst is thus regenerated.
The present invention is not limited by the mechanism described above and depicted in Figure 1.
In what follows the invention is described in detail in its preferred embodiments. The description is meant to be exemplary and is not supposed to limit the scope of the invention. Further embodiments not showing the specific features of the preferred embodiments are possible and covered by the invention as well.
In a preferred embodiment of the invention, the alkanes provided in step ii) and employed in step iii) comprise methane. As a consequence, methanesulfonic acid is produced as one particular product. More preferably, the alkanes consist of methane, i.e., only methane is employed as alkane compound. In the latter case, the product of the inventive process is methanesulfonic acid.
Preferably the reaction vessel is operated at a temperature above room tem- perature. More preferably the reaction vessel is operated at a temperature in the range of 400 °C to 600 °C. Most preferably the reaction vessel is operated at a temperature in the range of 470 °C to 800 °C. Particularly the reaction vessel may be operated at a temperature of 600 °C. Surprisingly it has been found that the described temperatures are specifically suitable to carry out the inventive process. While a lower temperature leads to poor conversion, a higher temperature would destabilize the product gases and would lead to unwanted side-products.
In a preferred embodiment of the inventive process the pressure of the reaction vessel is specifically controlled. Preferably a pressure in the range of 0,1 to 50 bar is employed. More preferably the reaction vessel is operated at a pressure in the range of 0,5 to 2 bar.
Preferably, the heterogeneous catalyst comprises a metal. The metal may be supported by an inorganic catalyst support. Preferably the catalyst support corn- prises silica or alumina. Particularly, the catalyst may be supported by alumina. The catalyst preferably has a specific surface (BET surface) in the range of 100 to 1000 m2 More preferably, the specific surface (BET surface) is in the range of 180 to 500 m2, particularly 300m2.
In a preferred embodiment, the catalyst consists of one or more metals support by a catalyst support. More preferably, the catalyst consists of one or more metals supported by alumina.
The metal employed may comprise one or more metals selected from the group of transition metals. Preferably, the one or more metals are selected from the group consisting of rhodium, iridium, cobalt, copper, nickel, platinum, palla- dium, silver and gold. Surprisingly it has been found that the aforementioned group of metals shows particularly good performance as heterogeneous cata- lysts in the process according to the invention. The heterogeneous catalyst may consist solely of metals and inorganic catalyst supports. Particularly, the catalyst is free of any additional substances, espe- cially organic and/or polymeric substances.
More preferably, the heterogeneous catalyst consists of a metal selected from the group consisting of rhodium, iridium, cobalt, copper, nickel, platinum, pal- lad ium, silver and gold and is supported by a catalyst support, particularly alu- mina. Most preferably the catalyst consists of rhodium supported by alumina.
In a preferred embodiment of the inventive process, the separation of the al- kanesulfonic acid product is conducted by running the gas stream flowing from the reaction vessel through one or more washing bottles. If more than one washing bottle is employed, the gas stream may be run through the washing bottles subsequently. The one or more washing bottles may be filled with an aqueous solution, preferably a concentrated sulfuric acid solution. Said concen- trated sulfuric acid solution may have a sulfuric acid concentration of 98%. The separation may be conducted at room temperature.
Surprisingly it has been found that the inventive process can be carried out very effectively, if the products are separated from the gas stream by said washing bottles. Particularly, if methane is used as alkane and the product is thus me- thanesulfonic acid, the methanesulfonic acid can very effectively be separated from the gas stream flowing from the reaction vessel by said washing bottles containing concentrated sulfuric acid solution.
The alkanesulfonic acid product, especially methanesulfonic acid, is solved in an aqueous solution and thereby separated from the gas stream flowing from the reaction vessel sulfur trioxide may also be solved in the aqueous solution whereby sulfuric acid may be formed. If the washing bottles contain sulfuric acid solution, the sulfur trioxide may be absorbed into said solution, wherein only the concentration of said solution is slightly changed. Operating the washing bottles at room temperature carries the particular ad- vantage of cooling the gas stream flowing from the reaction vessel. Since the product alkanesulfonic acids, especially methanesulfonic acid, show a low sta- bility at the temperatures at which the reaction vessel is preferably operated, the yield of the inventive process is increased, if the product gas mixture is cooled quickly after leaving the reaction vessel.
Preferably, the reaction vessel is purged with an inert gas prior to running the educt gases through the vessel. Any suitable inert gas known from the prior art may be employed. Preferably, nitrogen gas is employed as inert gas. Alterna- tively noble gases, such as helium or argon, can also be employed for example.
In a preferred embodiment of the invention the reaction vessel is furthermore purged with the gaseous alkane to be employed in the inventive process before the sulfur trioxide is run through the reaction vessel alongside the alkane. Op- tionally, purging with the gaseous alkane is performed after the aforementioned purging with an inert gas. Particularly, the reaction vessel may be purged with methane gas, if methane is to be employed in the inventive process in order to produce methanesulfonic acid.
Without the intention of being bound by theory, it is believed that by purging the reaction vessel with an alkane prior to running the synthesis, the heteroge- neous catalyst is preloaded with activated alkanes corresponding to the as- sumed catalytic mechanism illustrated above (step I in Figure 1). Furthermore it is believed that sulfur trioxide may bind to the catalyst and thereby deactivate it. If the catalyst is preloaded, such deactivation is prevented.
Preferably, the molar ratio of sulfur trioxide and the alkane compounds run through the reaction vessel is less than 1, i.e., an excess of alkane compounds is employed. More preferably, the molar ratio of sulfur trioxide and alkane is in the range of 0.01 to 0.5, most preferably 0.05 to 0.25, especially 0.1. Particu- larly, an excess of methane with respect to sulfur trioxide may be employed. If the alkane compound is employed in an excess, i.e., if an excess of sulfur triox- ide is avoided, the aforementioned assumed deactivation of the catalyst is fur- ther prevented. Performing the inventive process with an excess of alkane corn- pounds assures that whenever the catalyst offers free sites, said sites are occu- pied with alkane molecules as shown in the mechanism of Figure 1.
More preferably, the procedure of purging the reaction vessel with alkane corn- pound prior to the synthesis and employing the alkane compound in an excess during the synthesis can be combined. Surprisingly it has been found, that a particularly high catalyst activity can be achieved in this way. Without the in- tention of being bound by theory, it is believed that by said combination the catalyst is preloaded with activated alkane and the subsequent replacement by sulfur trioxide is prevented.
In a preferred embodiment of the invention, the provided gaseous sulfur trioxide and the provided alkane compound are mixed prior to running them through the reaction vessel. In an alternative embodiment, the educt gases may also be mixed within the reaction vessel.
In a further embodiment of the invention the object of the invention is solved by the use of the process described above for the production of alkanesulfonic acids. Preferably, said process is used for the production of methanesulfonic acid.
In yet another embodiment of the invention the object of the invention is solved by the use of transition metals in a heterogeneous catalyst for the direct syn- thesis of alkanesulfonic acids from sulfur trioxide and alkanes. Preferably tran- sition metals selected from the group consisting of rhodium, iridium, cobalt, platinum, palladium, silver and gold are used in said heterogeneous catalyst. Particularly, the aforementioned metals may be used in a heterogeneous cata- lyst for the direct synthesis of methanesulfonic acid from sulfur trioxide and methane.
Example
A 20 quartz glass tube was filled with 5 g of a rhodium (5%) on alumina (support structure) catalyst. It was heated up to 600°C in a tubular furnace after it was purged with nitrogen gas. When it reached the temperature, a methane- gas-stream comprising 10% of gaseous sulfur trioxide was streamed over the cat- alyst. The reaction-gas was washed with a gas-washing-bottle containing sulfuric acid. After quenching the non-reacted sulfur trioxide with water, methanesulfonic acid was determined by NMR and ion chromatography. The yield was about 7% methanesulfonic acid, based on sulfur trioxide.

Claims

Claims
1. Process for manufacturing alkanesulfonic acids comprising the steps of i) providing sulfur trioxide in a gaseous state, ii) providing at least one alkane in a gaseous state,
iii) running said gaseous sulfur trioxide and said at least one gaseous alkane through a reaction vessel, especially a tube furnace, wherein the reaction vessel comprises a heteroge- neous catalyst, such that the sulfur trioxide and the at least one gaseous alkane are getting in contact with the hetero- geneous catalyst,
iv) separating the resultant at least one alkanesulfonic acid from the gas stream flowing from said reaction vessel and v) optionally recovering the not-reacted educt gases and feed- ing them back into step iii)
2. Process according to claim 1, wherein the at least one alkane in steps ii) and iii) comprises methane and the resultant at least one alkanesulfonic acid in step iv) comprises methanesulfonic acid.
3. Process according to claim 1 or 2, wherein the reaction vessel is operated at a temperature in the range of 400 °C to 600 °C.
4. Process according to one or more of claims 1 to 3, wherein the reaction vessel is operated at a pressure of 0.1 to 50 bar.
5. Process according to one or more of claims 1 to 4, wherein the heteroge- neous catalyst comprises at least one metal, especially a metal supported by an inorganic catalyst support, particularly a metal supported by aluminum oxide.
6. Process according to claim 5, wherein the at least one metal is selected from the group of transition metals, especially from the group consisting of rho- dium, iridium, cobalt, copper, nickel, platinum, palladium, silver and gold.
7. Process according to one or more of claims 1 to 6, wherein the separation of the resultant at least one alkanesulfonic acid is conducted by running the gas stream flowing from the reaction vessel through a washing bottle or a series of at least two washing bottles, wherein said washing bottle(s) contain(s) an aque- ous solution, especially a concentrated (98%) sulfuric acid solution, and wherein the separation is preferably conducted at room temperature.
8. Process according to one or more of claims 1 to 7, wherein prior to run- ning said gaseous sulfur trioxide and said at least one gaseous alkane through said reaction vessel in step iii), the reaction vessel is purged with an inert gas, especially nitrogen gas.
9. Process according to one or more of claims 1 to 8, wherein prior to run- ning said gaseous sulfur trioxide and said at least one gaseous alkane through the reaction vessel in step iii), the reaction vessel is purged with at least one gaseous alkane, especially methane, optionally after purging said reaction ves- sel with an inert gas, especially nitrogen gas.
10. Process according to one or more of claims 1 to 9, wherein the molar ratio of gaseous sulfur trioxide and gaseous alkane run through the reaction vessel in step iii) is less than 1.
11. Process according to one or more of claims 1 to 10, wherein the gaseous sulfur trioxide and the at least one gaseous alkane are mixed prior to running them through the reaction vessel in step iii) or are mixed in step iii) within the reaction vessel.
12. Process according to one or more of claims 1 to 11, wherein the process is used for the production of alkanesulfonic acids, especially the production of methanesulfonic acid.
13. Use of transition metals, especially transition metals selected from the group consisting of rhodium, iridium, cobalt, copper, nickel, platinum, palla- dium, silver and gold, in a heterogeneous catalyst for the direct synthesis of alkanesulfonic acids from sulfur trioxide and alkanes, especially for the direct synthesis of methanesulfonic acid from sulfur trioxide and methane.
PCT/EP2019/053534 2018-02-16 2019-02-13 Direct synthesis of alkane sulfonic acids from alkane and sulfur trioxide employing heterogeneous catalysis WO2019158576A1 (en)

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Citations (4)

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Publication number Priority date Publication date Assignee Title
US2493038A (en) 1946-05-31 1950-01-03 Houdry Process Corp Reaction of methane with sulfur trioxide
US20050070614A1 (en) 2003-06-21 2005-03-31 Richards Alan K. Anhydrous processing of methane into methane-sulfonic acid, methanol, and other compounds
WO2007136425A2 (en) 2006-05-19 2007-11-29 Richards, Alan, K. Manufacture of dimethyl ether or olefins from methane, using di(methyl-sulfonyl) peroxide as radical initiator
WO2015071365A1 (en) * 2013-11-13 2015-05-21 Grillo Chemie Gmbh Process for preparing alkanesulfonic acids from sulfur trioxide and an alkane

Patent Citations (4)

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Publication number Priority date Publication date Assignee Title
US2493038A (en) 1946-05-31 1950-01-03 Houdry Process Corp Reaction of methane with sulfur trioxide
US20050070614A1 (en) 2003-06-21 2005-03-31 Richards Alan K. Anhydrous processing of methane into methane-sulfonic acid, methanol, and other compounds
WO2007136425A2 (en) 2006-05-19 2007-11-29 Richards, Alan, K. Manufacture of dimethyl ether or olefins from methane, using di(methyl-sulfonyl) peroxide as radical initiator
WO2015071365A1 (en) * 2013-11-13 2015-05-21 Grillo Chemie Gmbh Process for preparing alkanesulfonic acids from sulfur trioxide and an alkane

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Title
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