METHOD FOR THE PRODUCTION OF ALKANE SULFONIC ACIDS

Abstract

The present invention relates to methods for the production of alkane sulfonic acids, especially methane sulfonic acid, from alkane, especially methane, in which a carbocation, particularly a carbenium ion, is formed, as well as to the use of carbocations, particularly carbenium ions, for the production of alkane sulfonic acids, especially methane sulfonic acid.

Claims

1. A method for the production of alkane sulfonic acids from an alkane and sulfur trioxide, comprising a step of reacting a carbocation of the alkane with sulfur trioxide such that the alkane sulfonic acid is formed.

2. The method according to claim 1, wherein the carbocation is a carbenium ion.

3. The method according to claim 2, wherein the step of reacting the carbocation of the alkane with sulfur trioxide comprises the steps of i) reacting the carbenium ion with the sulfur trioxide to form an alkyl sulfite cation, and ii) reacting the alkyl sulfite cation with the alkane to form the alkane sulfonic acid and regenerate the carbenium ion.

4. The method according to claim 3, wherein the carbenium ion is obtained by reacting the alkane with an activated pre-catalyst, wherein the pre-catalyst comprises a hydrogen peroxide derivative and wherein the pre-catalyst is activated by reacting the pre-catalyst with a super acid.

5. The method according to claim 4, wherein the pre-catalyst corresponds to the formula ##STR00006## wherein R.sub.1 and R.sub.2 may be the same or different and are independently selected from the group of H, OH, CH.sub.3, OCH.sub.3, F, Cl, Br, C.sub.2H.sub.5 or higher alkanes, and OC.sub.2H.sub.5 or higher alkanes.

6. The method according to claim 4, wherein the pre-catalyst corresponds to the formula R.sub.1OOR.sub.2, wherein R.sub.1 and R.sub.2 are different and optionally the peroxo bond in the pre-catalyst is polarized.

7. The method according to claim 4, wherein the pre-catalyst is obtainable by reacting hydrogen peroxide with a sulfonic acid.

8. The method according to claim 1, wherein the sulfur trioxide is employed in pure form or in a solution of sulfur trioxide in oleum.

9. The method according to claim 1, wherein reacting a carbocation of the alkanewith sulfur trioxide is performed at a temperature within a range of from 0 to 100 C.

10. The method according to claim 9, wherein reacting a carbocation of the alkanewith sulfur trioxide is performed at a pressure within a range of from 10 to 150 bar.

11-12. (canceled)

13. A method for the production of alkane sulfonic acids comprising the following steps i. Providing sulfur trioxide ii. Providing an alkane iii. Providing a pre-catalyst, wherein the pre-catalyst comprises a hydrogen peroxide derivative iv. Activating the pre-catalyst by reaction with a super acid v. Reacting the pre-catalyst, the sulfur trioxide and the alkane in a reactor at a temperature of 50 C. or below vi. Separating alkane sulfonic acid from the reaction mixture

14. The method according to claim 13, wherein the pre-catalyst corresponds to the formula R.sub.1OOR.sub.2, wherein R.sub.1 and R.sub.2 are different and optionally the peroxo bond in the pre-catalyst is polarized.

15. The method according to claim 13, wherein the pre-catalyst corresponds to the formula ##STR00007## wherein R.sub.1 and R.sub.2 may be the same or different and are selected from the group of H, OH, CH.sub.3, OCH.sub.3, F, Cl, Br, C.sub.2H.sub.5 or higher alkanes, and OC.sub.2H.sub.5 or higher alkanes.

16. The method according to claim 15, wherein the pre-catalyst is provided in step iii) by providing a mixture of hydrogen peroxide, an alkane sulfonic acid, and sulfuric acid.

17. The method according to claim 13, wherein the temperature in step v) is 40 C. or below.

18. The method according to claim 17, wherein the pressure in step v) is within a range of from 10 to 150 bar

19. The method according to claim 13, wherein the sulfur trioxide is employed in pure form or in a solution of sulfur trioxide in oleum.

20. The method of claim 1 wherein the alkane comprises methane, the alkane sulfonic acid comprises methanesulfonic acid, and the carbocation of the alkane is a carbocation of methane.

21. The method of claim 13 wherein the alkane comprises methane, the alkane sulfonic acid comprises methanesulfonic acid, the carbocation of the alkane is a carbocation of methane and the superacid comprises SO.sub.3 in H.sub.2SO.sub.4.

Description

[0044] FIG. 1 shows the inventive method in its preferred embodiment for the activation and functionalization of CH.sub.4 to MSA (see Part A of FIG. 1). Part B shows how continuous reactors (1, 2 and nth) in a pilot plant can produce up to 20 ton/year, the enriched mixture is then distilled in column D to obtain pure MSA. No by-products are observed and the H.sub.2SO.sub.4/MSA stream is recycled back to reactor 1.

[0045] FIG. 2 shows the formation of a hydrogen peroxonium ion and the decomposition of methanol to MBS under superacid conditions.

[0046] FIG. 3 (top) shows a reaction profile of the synthesis of MSA measured as pressure of CH.sub.4 (bar) versus time (h); inset: close-up of region A. (bottom) shows a comparison of the reaction profile between the standard reaction and with the addition of traces of SO.sub.2 as a deactivating agent.

[0047] FIG. 4 shows the assumed cationic mechanism for the activation and functionalization of methane: A) pre-catalyst activation through the protonation of the peroxide 1 and; B) productive catalytic cycle where the methenium ion 5 is regenerated by the dehydrogenation of methane.

[0048] FIG. 5 shows how the disproportionation of methyl hydrogen sulfite at different temperatures affords MSA (50 C.) or MBS (120 C.).

[0049] A particular embodiment of the invention comprises the activation of methane at a pressure of circa 100 bar in a solution of fuming sulfuric acid (SO.sub.3/H.sub.2SO.sub.4) of different concentrations (15 to 60%) with circa 1 mol % pre-catalyst comprising a hydrogen peroxide derivative (FIG. 1A). For production in a pilot plant, the reaction may be carried out in continuous reactors (FIG. 1B). Pure SO.sub.3 and CH.sub.4 are fed at the first reactor and then the reaction mixture is passed to the next one increasing the concentration of MSA until the nth reactor where the distillation takes place. The distillate consists of pure MSA with over 99% yield (based on the initial amount of SO.sub.3) and 99% selectivity. The remaining solution comprising a mixture of H.sub.2SO.sub.4 and a small amount of MSA is fed back to the first reactor allowing for the desired oleum concentration at the beginning of the reaction. This configuration will allow scaling up the process to a major industrial production of around 10,000 metric tons of MSA/year.

[0050] 400 mL batch reactors were used to carry out a detailed investigation of the reaction mechanism and the reaction optimization (Table 1). Diffusion of methane into the mixture is key in the conversions to MSA, propellers with gas diffusion must be used. Table 1 shows the yield of MSA under different conditions (for example temperature, pressure, et cetera) using 0.9 mol % pre-catalyst MMSP formed in-situ. The most common experiment is carried out with oleum 34% affording 60% yield of MSA in 16 h at 50 C. The yield of MSA is largely increased up to 99% using large reactors. Entry 3 depicts a reaction using an UV radiation (vidae infra) with no significant yield of MSA. The influence of SO.sub.2 as deactivating agent is shown in Entry 4, where the total yield of MSA is 23%.

TABLE-US-00001 TABLE 1 Synthesis of MSA in a 400 mL batch reactor. Yield Entry SO.sub.3 (%) T ( C.) P.sub.CH4 (bar) MSA (%).sup.a 1 34 50 97 60 2 24 50 97 83 3 24 25 96 0.sup.b 4 34 50 95 23.sup.c 5 36 50 const..sup.d 97 6 36 40 96 26.sup.e .sup.apercentage yield of MSA (analyzed by ion chromatography) based on initial amount of SO.sub.3; .sup.bwith UV light; .sup.cwith addition of SO.sub.2; .sup.dconstant pressure of methane; .sup.econversion based on the reacted amount of methane.

[0051] Particularly entry 3 of the above table shows that the reaction occurs via an ionic pathway. A radical chain reaction would be triggered by the UV light even at a temperature of 25 C. The UV light is capable of homolytically splitting peroxo bonds leading to the formation of radicals. Without the intention of being bound by theory it is assumed that said homolytic splitting in fact does take place and disables the ionic pathway, which presumably involves the heterolytic splitting of R.sub.1OOR.sub.2 as discussed above.

[0052] Different compositions of pre-catalysts were studied. For example, solely H.sub.2O.sub.2 (60%) in H.sub.2SO.sub.4 (98%) does not trigger the formation of MSA in significant yields. Under superacid conditions H.sub.2O.sub.2 forms a hydrogen peroxonium ion H.sub.3O.sub.2.sup.+ that reacts with CH.sub.4 that subsequently affords methanol (FIG. 2). A mixture of H.sub.2O.sub.2, MSA and H.sub.2SO.sub.4 exhibits the best performance towards the synthesis of MSA. The asymmetric monomethyl sulfonyl peroxide (MMSP) was identified in the pre-catalyst mixture. It is known in the prior art that symmetric dimethyl sulfonyl peroxide (DMSP) is capable of producing significant yields of MSA, however, selectivity and rates outperform with this pre-catalyst.

[0053] MMSP was identified via NMR, IR and MS. The following signals were obtained: [0054] .sup.1H NMR (neat H.sub.2SO.sub.4, capillary CDCl.sub.3): 12.23 (ov s), 5.38 (ov s). [0055] FT-IR (ATR cm.sup.1): 1693 (SO), 1334 (SO). [0056] ESI-MS (m/z): 192.86 (MH)

[0057] The reaction profile of the standard reaction (oleum 30%, 0.9 mol % of MMPS prepared in-situ, circa 100 bar of methane heating the reactor to 50 C.) shows a particular period of up to 2 h after the addition of the pre-catalyst where the pressure drop is almost linear (FIG. 3A). Afterwards, the decrease in pressure resembles a rapid decay (FIG. 3B) followed by a plateau after 10 h (FIG. 3C). The calculated yield of MSA based on the pressure drop, and supported by ion chromatography analysis, showed that equimolar amounts of product are formed relatively to the moles of H.sub.2O.sub.2 in the induction period (FIG. 3A). Moreover, the decomposition of the pre-catalyst at 50 C. and atmospheric pressure, measured by redox titration, rapidly occurs in the first 70 min with 40% decomposition of the peroxide. This indicates that the aforementioned period could be indeed the catalytic activation (FIG. 3A).

[0058] The reaction is highly sensitive to the temperature affording several product distributions and considerably affecting the rates. Low temperatures (below 50 C.) afford selectivities higher than 99% of MSA, however, at higher temperatures (above 100 C.) the reaction starts exhibiting more complex product mixtures with MBS and SO.sub.2 as major components. Yields of MSA up to 85% can be obtained at 20 C. after seven days of reaction time. On the other hand, the concentration of SO.sub.3 has important effects on the selectivity of MSA similar to those observed with change of temperature. At concentrations up to 60% of SO.sub.3 the yields of MSA are quantitative, in contrast higher concentrations of SO.sub.3 (>60%) promote the formation of MBS and SO.sub.2, decreasing the yield and selectivity for MSA. Ethane, SO.sub.2 and O.sub.2, have also important effects as deactivating agents. For example, concentration of 1.29% and 0.44% (based on the total amount of SO.sub.3) of SO.sub.2 and C.sub.2H.sub.6, respectively, completely quenched the synthesis of MSA. The Hammett acidity values H.sub.0 of different oleums increases with the amount of SO.sub.3. For example, oleums of 35 mol % have H.sub.0 values of 13.94, while the increase in acidity is consisted with the concentration of SO.sub.3, however, at higher values over 50 mol % SO.sub.3 the increase in acidity is very small (for example, for 75 mol % H.sub.0=14.96). This trend is in agreement with the observations in the synthesis of MSA where at higher SO.sub.3 content the selectivity decreases with formation of high quantities of MBS and SO.sub.2 at expenses of MSA.

[0059] Olah and co-workers (Olah, Prakash, Sommer, Molnar, Superacid Chemistry, Wiley-Interscience, 2.Auflage 2009) have extensively shown that under superacid conditions (for example, oleums of H.sub.2SO.sub.4) dissolved methane is protonated to a 2e-3c CH.sub.5.sup.+ pentacoordinate cation. Similarly, H.sub.2O.sub.2 is protonated to generate a highly active hydrogen peroxonium ion H.sub.3O.sub.2.sup.+ which has been invoked in a large number of transformations. The rapid H/D exchange of CH.sub.4 in D.sub.2SO.sub.4 at atmospheric pressure also demonstrates the facile CH activation of CH.sub.4 in a borderline superacid. The potential involvement of radicals in the formation of MSA under superacid conditions was tested. The irradiation of UV light with a broad wavelength Hg lamp is not sufficient to trigger the formation of MSA at 98 bar of CH.sub.4 at room temperature with and without added pre-catalyst. On the other hand, control experiments showed that 0.9 mol % MMSP pre-catalyst prepared in-situ is capable to polymerize styrene at 25 C. under UV irradiation. In contrast, the polymerization of styrene is not observed in absence of UV light using the same pre-catalyst mixture.

[0060] Based on the described observations a cationic activation of methane followed by functionalization to MSA in superacid conditions is achieved, as depicted in FIG. 4.

[0061] Referring to FIG. 4, MMSP 1 is initially protonated to a peroxonium ion 2 which subsequently generates oxygen- and sulfur-centered cations (4a or 4b), and the hydroxyperoxide 3 that forms another molecule of MMSP 1 upon reaction with excess SO.sub.3 (Scheme 1A). The species 4a or 4b activate CH.sub.4 by electrophilic hydride abstraction to form a methenium ion 5. It is important to notice that the catalytic amount of MMSP 1 may be approximately 0.9 mol % based on the total amount of SO.sub.3 and hence the amount of CH.sub.3.sup.+ that enters the productive catalytic cycle in FIG. 4B. Nucleophilic attack of SO.sub.3 on CH.sub.3.sup.+ generates sulfur- and oxygen-centered methyl sulfite cations (6a and 6b) that resemble those formed in the pre-catalyst activation cycle. The methyl sulfite cation 6b can react with CH.sub.4 to produce methyl hydrogen sulfite 7 that suffers a rapid rearrangement at 50 C. to MSA. Once the pre-catalyst MMSP 1 is completely consumed the productive catalytic cycle undergoes auto catalysis through the formation of CH.sub.3.sup.+ 5. The assumed catalytic cycle takes into account the reaction profile observed in FIG. 3 with three different distinctive periods (vide supra). FIG. 5 shows the rearrangements of methyl hydrogen sulfite at different temperatures. High temperatures trigger the isomerization to SO.sub.2 and methanol, the latter immediately reacts with free SO.sub.3 to generate MBS.

[0062] The separation of MSA from the reaction mixture is challenging. Vacuum distillation achieved high purity of MSA, however, high temperatures afford decomposition products such as methane sulfonic acid anhydrous and methane sulfonic ester. Under these conditions, MBS is not observed as a decomposition product of MSA. Upon incorporation of the distillation into the continuous reactors; the present invention provides a highly efficient process for the mass production of MSA from only two reactants: SO.sub.3 and CH.sub.4.

[0063] In a further embodiment, the object of the invention is solved by the use of a carbocation for the production of an alkane sulfonic acid, especially methanesulfonic acid. Preferably, the carbocation is a carbenium ion, especially methenium (CH.sub.3.sup.+). Particularly, the carbocation may be used for the production of methane sulfonic acid from methane and sulfur trioxide.

[0064] In a further embodiment, the object of the invention is solved by a method for the production of alkane sulfonic acids, especially methane sulfonic acid, comprising the following steps [0065] i) Providing sulfur trioxide [0066] ii) Providing an alkane, especially methane [0067] iii) Providing a pre-catalyst, wherein the pre-catalyst comprises a hydrogen peroxide derivative [0068] iv) Activating the pre-catalyst by reaction with a super acid, especially SO.sub.3 in H.sub.2SO.sub.4 [0069] v) Reacting the pre-catalyst, the sulfur trioxide and the alkane in a reactor at a temperature of 50 C. or below [0070] vi) Separating alkane sulfonic acid, especially methanesulfonic acid, from the reaction mixture.

[0071] Preferably, no substances promoting the formation of radicals or their stabilization are employed in the inventive process. Particularly, no metal salts are added to the reaction mixture.

[0072] Preferably, the pre-catalyst corresponds to the formula R.sub.1OOR.sub.2, wherein R.sub.1 and R.sub.2 are different and optionally the peroxo bond in the pre-catalyst is polarized.

[0073] More preferably, the pre-catalyst corresponds to the formula

##STR00005##

[0074] wherein R.sub.1 and R.sub.2 may be the same or different and are selected from the group of H, OH, CH.sub.3, OCH.sub.3, F, Cl, Br, C.sub.2H.sub.5 or higher alkanes, OC.sub.2H.sub.5 or higher alkanes.

[0075] The pre-catalyst may be provided in step iii) by providing a mixture of hydrogen peroxide, an alkane sulfonic acid, especially methane, and sulfuric acid.

[0076] Preferably, the temperature in step v) is 40 C. or below, especially 30 C. or below, particularly 25 C. or room temperature.

[0077] In a preferred embodiment of the inventive method the pressure in step v) is within a range of from 10 to 150 bar, especially within a range of from 50 to 120 bar.

[0078] The sulfur trioxide may be employed in pure form or in a solution of sulfur trioxide in oleum, especially in a solution of 15 to 60% sulfur trioxide in oleum.

EXAMPLES

Example 1: Procedure for the Synthesis of MSA

[0079] In a 400 mL stainless steel high-pressure reactor, 245.02 g of fuming sulfuric acid (34.1%) were added using a HPLC pump maintaining the temperature of the lines at 50 C. The re-actor was heated to 50 C. with constant stirring speed of 1000 rpm. The pre-catalyst was prepared by dropwise addition of 464 L of hydrogen peroxide (60%) over a cold mixture (0 C.) of 12 mL sulfuric acid (98%) and 1.38 mL MSA (99.5%). Once the reactor has reached a constant temperature of 50 C. the vessel is pressurized with 92.6 bar of methane (99.5%). The pre-catalyst was then injected into the rector using a HPLC pump raising the pressure inside the reactor to 97 bar. After 16 h the pressure dropped to 31.8 bar indicating that a large amount of methane was consumed. The reactor was then cooled down to room temperature, the excess pressure of methane was removed to a set of scrubbers and a sample consisting of a slightly colorless liquid was stored in a glass bottle weighing 279.57 g. The sample was subsequently analyzed using IC affording a 59.9% yield of MSA based on the total initial moles of SO.sub.3.

Example 2: Procedure for the Synthesis of MSA

[0080] In a 400 mL stainless steel high-pressure reactor, 288.07 g of fuming sulfuric acid 24% was added using a HPLC pump with constant heating of 50 C. The reactor was then heated to 50 C. and the stirrer was set to 1000 rpm. Once the temperature inside the reactor was constant at 50 C., 92.6 bar of methane were added. The pre-catalyst was prepared separately by dropwise addition of 464 L of hydrogen peroxide (60%) over a cold mixture (0 C.) of 12 mL sulfuric acid (98%) and 1.38 mL MSA (99.5%). The pre-catalyst was added into the reactor using a HPLC pump increasing the total pressure to 97.4 bar. After 20 h of reaction time, the pressure dropped to 26.1 bar. The reactor was then cooled down to room temperature and the excess methane was removed to a set of scrubbers. The entire content (264.2 g) of the reactor was transferred to a glass bottle and stored properly. IC analysis showed that the yield of MSA in this reaction was 83.3% based on the total amount of SO.sub.3 added.

Example 3: Procedure for the Attempted Synthesis of MSA Using UV Radiation (Comparison Example)

[0081] In a 400 mL stainless steel high-pressure reactor equipped with two oblong sapphire windows, 249.31 g of fuming sulfuric acid 24% was added using a HPLC pump maintained at 50 C. The reactor was then heated to 25 C., the stirrer set to 1000 rpm and pressurized with 91.7 bar of methane. A medium-pressure mercury vapour UV lamp (UV-Consulting Peschl, Germany), broad emission over 190 nm equipped with a quartz immersion tube and a cooling jacket was positioned at 4 cm away from the reactor window, both covered with aluminum foil. The heat produce by the UV lamp was not enough to change the temperature inside the reactor. The pre-catalyst was prepared by dropwise addition of 464 L of hydrogen peroxide (60%) over a cold mixture (0 C.) of 12 mL sulfuric acid (98%) and 1.38 mL MSA (99.5%). The pre-catalyst was then added into the reactor using a HPLC pump reaching a total pressure of 95.7 bar. After 2 h the temperature inside the reactor remained stable at 25 C. and the pressure was constant at 96 bar. At 4 h of reaction time the pressure still remained at 95.9 bar. The unchanged values in pressure indicate that the consumption of methane did not take place and MSA was not produced under these conditions.

Example 4: Procedure for the Synthesis of MSA

[0082] In a 4 L stainless steel high pressure-reactor, 1.943 kg of fuming sulfuric acid 36% were added via cannula transfer. The reactor was maintained at 40 C. with a stirring speed of 350 rpm. Once the temperature is constant, the reactor is charged with 95.6 bar of methane. Separately, the pre-catalyst is prepared by dropwise addition of 3.4 mL of H.sub.2O.sub.2 (70%) over a cold mixture (0 C.) of 90 mL sulfuric acid (98%) and 10 mL MSA. The pre-catalyst is added into the reactor employing a HPLC pump raising the total pressure up to 98.5 bar. The pressure was constantly monitored during the experiment. At 16 h of reaction time the pressure was 71.1 bar. After 67 h the pressure inside the reactor has dropped to 31.1 bar. At this point the reactor was cooled down, the excess pressure of methane was removed to a set of scrubbers filled with sulfuric acid and a sample was taken. The sample was stored in a glass bottle weighting 2.244 kg. The calculated conversion of methane at 16 h (based on the initial amount of SO.sub.3) was 26%. Ion chromatography showed that the yield of MSA after 67 h was 92% MSA.