Process for preparing alkanesulfonic acids

Abstract

The present invention relates to a process for preparing alkanesulfonic acids from dialkyl disulfides with nitric acid and oxygen.

Claims

1. A process for preparing an alkanesulfonic acid of the formula RSO.sub.3H, comprising: oxidizing a symmetrical dialkyl disulfide of the formula RS.sub.2R, in solution in an alkanesulfonic acid, in the presence of a catalytic amount of nitric acid, with R denoting a C.sub.1-C.sub.12 alkyl radical and the alkanesulfonic acid used as solvent being identical with the alkanesulfonic acid obtained from the oxidation of the dialkyl disulfide, wherein the concentration of the dialkyl disulfide in the solution is not more than 20 weight percent, the ratio of dialkyl disulfide to nitric acid ranges from 2000:1 (mol/mol) to 1:1 (mol/mol), and the concentration of the alkanesulfonic acid used as solvent is more than 70 weight percent.

2. The process according to claim 1, wherein the dialkyl disulfide is dimethyl disulfide and the alkanesulfonic acid is methanesulfonic acid.

3. The process according to claim 1, wherein the ratio of dialkyl disulfide to nitric acid ranges from 500:1 (mol/mol) to 1:1 (mol/mol).

4. The process according to claim 1, wherein the ratio of dialkyl disulfide to nitric acid ranges from 500:1 (mol/mol) to 2:1 (mol/mol).

5. The process according to claim 1, wherein the concentration of the dialkyl disulfide in the alkanesulfonic acid is up to about 10 weight percent.

6. The process according to claim 1, wherein the process is carried out at temperatures of not more than about 90? C.

7. The process according to claim 6, wherein the process is carried out at temperatures of about 70? C. to about 90? C.

8. The process according to claim 1, wherein the concentration of the alkanesulfonic acid used as solvent is at least 80 weight percent.

9. The process according to claim 8, wherein the concentration of the alkanesulfonic acid used as solvent is at least about 90 weight percent.

10. The process according to claim 1, wherein, for the oxidation, air, a gas stream enriched with oxygen in free form, and/or pure oxygen in free form is fed in.

11. The process according to claim 10, wherein, for the oxidation, a gas stream comprising oxygen, containing more than 21 vol.-% of oxygen in free form, is fed in.

12. The process according to claim 1, wherein the process is carried out at a pressure of more than 1 bara to about 20 bara.

13. The process according to claim 12, wherein the process is carried out at a pressure of more than 2 bara to about 15 bara.

14. The process according to claim 1, wherein a solubilizer between the dialkyl disulfide and the alkanesulfonic acid is used.

15. The process according to claim 14, wherein alkanesulfonic acid S-alkyl ester of the formula RSO.sub.2SR is used as solubilizer between the dialkyl disulfide and the alkanesulfonic acid, with the alkyl radicals of the alkanesulfonic acid S-alkyl ester being identical with the alkyl radicals of the dialkyl disulfide to be converted and with the alkyl radical of the alkanesulfonic acid.

16. A process for preparing an alkanesulfonic acid of the formula RSO.sub.3H, comprising: oxidizing a symmetrical dialkyl disulfide of the formula RS.sub.2R, in solution in an alkanesulfonic acid, in the presence of a catalytic amount of nitric acid, with R denoting a C.sub.1-C.sub.12 alkyl radical and the alkanesulfonic acid used as solvent being identical with the alkanesulfonic acid obtained from the oxidation of the dialkyl disulfide, wherein the concentration of the dialkyl disulfide in the solution is not more than 20 weight percent, the ratio of dialkyl disulfide to nitric acid ranges from 2000:1 (mol/mol) to 1:1 (mol/mol), and the concentration of the alkanesulfonic acid used as solvent is more than 70 weight percent; wherein a solubilizer between the dialkyl disulfide and the alkanesulfonic acid is used; wherein alkanesulfonic acid S-alkyl ester of the formula RSO.sub.2SR is used as solubilizer between the dialkyl disulfide and the alkanesulfonic acid, with the alkyl radicals of the alkanesulfonic acid S-alkyl ester being identical with the alkyl radicals of the dialkyl disulfide to be converted and with the alkyl radical of the alkanesulfonic acid.

Description

FIGURES

(1) FIG. 1 shows the sample temperature in ? C. as a function of the time in seconds in a pressure/heat accumulation test (experiment 23) in an adiabatic calorimeter (Phi-TEC II). Sample composition: 79.2 g methanesulfonic acid/21.38 g dimethyl disulfide/5 g H.sub.2O/1.1 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Hastelloy C 276 with a volume of 115 ml Total sample volume: about 80 ml Sample container fill level: about 70%

(2) FIG. 2 shows the pressure in bara as a function of the time in seconds in a pressure/heat accumulation test (experiment 23) in an adiabatic calorimeter (Phi-TEC II). Sample composition: 79.2 g methanesulfonic acid/21.38 g dimethyl disulfide/5 g H.sub.2O/1.1 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Hastelloy C 276 with a volume of 115 ml Total sample volume: about 80 ml Sample container fill level: about 70%

(3) FIG. 3 shows the pressure in bara as a function of the sample temperature in ? C. in a pressure/heat accumulation test (experiment 23) in an adiabatic calorimeter (Phi-TEC II). Sample composition: 79.2 g methanesulfonic acid/21.38 g dimethyl disulfide/5 g H.sub.2O/1.1 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Hastelloy C 276 with a volume of 115 ml Total sample volume: about 80 ml Sample container fill level: about 70%

(4) FIG. 4 shows the time-dependent change in temperature in K/min as a function of the sample temperature in ? C. in a pressure/heat accumulation test (experiment 23) in an adiabatic calorimeter (Phi-TEC II). Sample composition: 79.2 g methanesulfonic acid/21.38 g dimethyl disulfide/5 g H.sub.2O/1.1 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Hastelloy C 276 with a volume of 115 ml Total sample volume: about 80 ml Sample container fill level: about 70%

(5) FIG. 5 shows the heat output in W/kg as a function of the sample temperature in ? C. in a pressure/heat accumulation test (experiment 23) in an adiabatic calorimeter (Phi-TEC II). Sample composition: 79.2 g methanesulfonic acid/21.38 g dimethyl disulfide/5 g H.sub.2O/1.1 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Hastelloy C 276 with a volume of 115 ml Total sample volume: about 80 ml Sample container fill level: about 70%

(6) FIG. 6 shows the sample temperature in ? C. as a function of the time in seconds in a pressure/heat accumulation test (experiment 24) in an adiabatic calorimeter (Phi-TEC II). The material investigated was the reaction effluent from experiment 23, with the following Sample composition: 79.2 g methanesulfonic acid/21.38 g dimethyl disulfide/5 g H.sub.2O/1.1 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Hastelloy C 276 with a volume of 115 ml Total sample volume: about 80 ml Sample container fill level: about 70%

(7) FIG. 7 shows the pressure in bara as a function of the time in seconds in a pressure/heat accumulation test (experiment 24) in an adiabatic calorimeter (Phi-TEC II). The material investigated was the reaction effluent from experiment 23, with the following Sample composition: 79.2 g methanesulfonic acid/21.38 g dimethyl disulfide/5 g H.sub.2O/1.1 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Hastelloy C 276 with a volume of 115 ml Total sample volume: about 80 ml Sample container fill level: about 70%

(8) FIG. 8 shows the pressure in bara as a function of the sample temperature in ? C. in a pressure/heat accumulation test (experiment 24) in an adiabatic calorimeter (Phi-TEC II). The material investigated was the reaction effluent from experiment 23, with the following Sample composition: 79.2 g methanesulfonic acid/21.38 g dimethyl disulfide/5 g H.sub.2O/1.1 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Hastelloy C 276 with a volume of 115 ml Total sample volume: about 80 ml Sample container fill level: about 70%

(9) FIG. 9 shows the sample temperature in ? C. as a function of the time in seconds in a pressure/heat accumulation test (experiment 25) in an adiabatic calorimeter (Phi-TEC II). Sample composition: 79.2 g methanesulfonic acid/21.38 g dimethyl disulfide/5 g H.sub.2O/1.1 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Hastelloy C 276 with a volume of 115 ml Total sample volume: about 80 ml Sample container fill level: about 70%

(10) FIG. 10 shows the pressure in bara as a function of the time in seconds in a pressure/heat accumulation test (experiment 25) in an adiabatic calorimeter (Phi-TEC II). Sample composition: 79.2 g methanesulfonic acid/21.38 g dimethyl disulfide/5 g H.sub.2O/1.1 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Hastelloy C 276 with a volume of 115 ml Total sample volume: about 80 ml Sample container fill level: about 70%

(11) FIG. 11 shows the pressure in bara as a function of the sample temperature in ? C. in a pressure/heat accumulation test (experiment 25) in an adiabatic calorimeter (Phi-TEC II). Sample composition: 79.2 g methanesulfonic acid/21.38 g dimethyl disulfide/5 g H.sub.2O/1.1 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Hastelloy C 276 with a volume of 115 ml Total sample volume: about 80 ml Sample container fill level: about 70%

(12) FIG. 12 shows the time-dependent change in temperature in K/min as a function of the sample temperature in ? C. in a pressure/heat accumulation test (experiment 25) in an adiabatic calorimeter (Phi-TEC II). Sample composition: 79.2 g methanesulfonic acid/21.38 g dimethyl disulfide/5 g H.sub.2O/1.1 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Hastelloy C 276 with a volume of 115 ml Total sample volume: about 80 ml Sample container fill level: about 70%

(13) FIG. 13 shows the heat output in W/kg as a function of the sample temperature in ? C. in a pressure/heat accumulation test (experiment 25) in an adiabatic calorimeter (Phi-TEC II). Sample composition: 79.2 g methanesulfonic acid/21.38 g dimethyl disulfide/5 g H.sub.2O/1.1 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Hastelloy C 276 with a volume of 115 ml Total sample volume: about 80 ml Sample container fill level: about 70%

(14) FIG. 14 shows the sample temperature in ? C. (continuous line) and the pressure in bara (interrupted line) as a function of the time in seconds in a pressure/heat accumulation test (experiment 26) in an adiabatic calorimeter (Phi-TEC II). Sample composition: 79.2 g methanesulfonic acid/21.38 g dimethyl disulfide/5 g H.sub.2O/1.1 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Stainless steel 1.4571 with a volume of 110 ml Total sample volume: about 80 ml Sample container fill level: about 73%

(15) FIG. 15 shows the time-dependent change in temperature in K/min as a function of the sample temperature in ? C. in a pressure/heat accumulation test (experiment 26) in an adiabatic calorimeter (Phi-TEC II). Sample composition: 79.2 g methanesulfonic acid/21.38 g dimethyl disulfide/5 g H.sub.2O/1.1 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Stainless steel 1.4571 with a volume of 110 ml Total sample volume: about 80 ml Sample container fill level: about 73%

(16) FIG. 16 shows the pressure in bara as a function of the sample temperature in ? C. in a pressure/heat accumulation test (experiment 26) in an adiabatic calorimeter (Phi-TEC II). Sample composition: 79.2 g methanesulfonic acid/21.38 g dimethyl disulfide/5 g H.sub.2O/1.1 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Stainless steel 1.4571 with a volume of 110 ml Total sample volume: about 80 ml Sample container fill level: about 73%

(17) FIG. 17 shows the sample temperature in ? C. as a function of the time in seconds in a pressure/heat accumulation test (experiment 27) in an adiabatic calorimeter (Phi-TEC II). Sample composition: 110.67 g methanesulfonic acid/11.0 g dimethyl disulfide/2.6 g H.sub.2O/0.57 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Hastelloy C276 with a volume of 115 ml Total sample volume: about 81 ml Sample container fill level: about 74%

(18) FIG. 18 shows the pressure in bara as a function of the time in seconds in a pressure/heat accumulation test (experiment 27) in an adiabatic calorimeter (Phi-TEC II). Sample composition: 110.67 g methanesulfonic acid/11.0 g dimethyl disulfide/2.6 g H.sub.2O/0.57 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Hastelloy C276 with a volume of 115 ml Total sample volume: about 81 ml Sample container fill level: about 74%

(19) FIG. 19 shows the pressure in bara as a function of the sample temperature in ? C. in a pressure/heat accumulation test (experiment 27) in an adiabatic calorimeter (Phi-TEC II). Sample composition: 110.67 g methanesulfonic acid/11.0 g dimethyl disulfide/2.6 g H.sub.2O/0.57 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Hastelloy C276 with a volume of 115 ml Total sample volume: about 81 ml Sample container fill level: about 74%

(20) FIG. 20 shows the time-dependent change in temperature in K/min as a function of the sample temperature in ? C. in a pressure/heat accumulation test (experiment 27) in an adiabatic calorimeter (Phi-TEC II). Sample composition: 110.67 g methanesulfonic acid/11.0 g dimethyl disulfide/2.6 g H.sub.2O/0.57 g HNO.sub.3 (65%)/O.sub.2 Closed sample container: Hastelloy C276 with a volume of 115 ml Total sample volume: about 81 ml Sample container fill level: about 74%

(21) TABLE-US-00001 TABLE 1 Summary of the various diagrams of FIGS. 1 to 20. FIG. Experiment No. Representation 1 23 Sample temperature in ? C. as function of time in seconds 2 23 Pressure in bara as function of time in seconds 3 23 Pressure in bara as function of the sample temperature in ? C. 4 23 Time-dependent change in temperature in K/min as function of the sample temperature in ? C. 5 23 Heat output in W/kg as function of the sample temperature in ? C. 6 24 Sample temperature in ? C. as function of time in seconds 7 24 Pressure in bara as function of time in seconds 8 24 Pressure in bara as function of the sample temperature in ? C. 9 25 Sample temperature in ? C. as function of time in seconds 10 25 Pressure in bara as function of time in seconds 11 25 Pressure in bara as function of the sample temperature in ? C. 12 25 Time-dependent change in temperature in K/min as function of the sample temperature in ? C. 13 25 Heat output in W/kg as function of the sample temperature in ? C. 14 26 Sample temperature in ? C. (unbroken line) and pressure in bara (broken line) as function of time in seconds 15 26 Time-dependent change in temperature in K/min as function of the sample temperature in ? C. 16 26 Pressure in bara as function of the sample temperature in ? C. 17 27 Sample temperature in ? C. as function of time in seconds 18 27 Pressure in bara as function of time in seconds 19 27 Pressure in bara as function of the sample temperature in ? C. 20 27 Time-dependent change in temperature in K/min as function of the sample temperature in ? C.

EXAMPLES

A) Suitability of Methanesulfonic Acid as Solvent in the Oxidation of Dimethyl Disulfide

(22) Methanesulfonic acid was investigated in 10 experiments for its suitability as a solvent in the preparation of methanesulfonic acid by oxidation of dimethyl disulfide. This was done by preparing solutions of different amounts of dimethyl disulfide in methanesulfonic acid, nitric acid (65 wt.-%) and small amounts of water and transferring them to an autoclave. The conversion of the dimethyl disulfide to the methanesulfonic acid took place at temperatures of 50? C. to 90? C. and at pressures of 3 bara up to 12 bara oxygen. For this purpose, oxygen was introduced into each of the samples via an immersion tube, and a stirrer was used to ensure optimum distribution in the reaction mixture. The individual compositions of the reaction mixtures in experiments 1 to 10, and the specific reaction conditions in these reactions, are summarized in Table 2.

(23) The experimental results reproduced in Table 2 show that methanesulfonic acid (MSA) is suitable in principle as a solvent in the oxidation of dimethyl disulfide (DMDS) to methanesulfonic acid. Depending on the selected reaction conditions (pressure, temperature and time), however, yields of methanesulfonic acid that differ sharply from one another are obtained. The methanesulfonic acid yield, for instance, fluctuates between 78.0% (experiment 1) and >99.0% (experiments 5, 6 and 10).

B) Productivity Optimization of the Reaction Parameters

(24) In further experiments 11 to 22 in an autoclave, the reaction parameters were optimized with a view to maximum productivity (high methanesulfonic acid yield and low reaction time or residence time).

(25) The individual compositions of reaction mixtures 11 to 22 and the specific reaction conditions in these experiments are summarized in Table 3. Depending on the particular reaction temperature, for ratios of dimethyl disulfide to nitric acid in the range from 100:1 (mol/mol) to 1:1 (mol/mol), virtually complete conversion of the dimethyl disulfide is obtained within just an hour. In experiment 21, indeed, complete conversion of the dialkyl disulfide is achieved within half an hour.

(26) TABLE-US-00002 TABLE 2 Overview of experiments 1 to 10 on the suitability of MSA as solvent in the preparation of MSA from DMDS. Reaction mixture MSA DMDS H.sub.2O HNO.sub.3 (65%) MMTS p T t Yield of MSA No. [wt.-%]/[mmol] [wt.-%]/[mmol] [wt.-%]/[mmol] [wt.-%]/[mmol] [wt.-%]/[mmol] [bara] [? C.] [h] [%] 1 88.0/2665.0 9.8/301 1.7/307 0.51/15.47 6 50 3 78.0 2 88.0/2665.0 9.8/301 1.7/307 0.51/15.47 6 60 3 88.5 3 82.3/2050.0 13.7/347 3.2/464 0.71/17.54 3 70 3 96.3 4 82.3/2050.0 13.7/347 3.2/464 0.71/17.54 6 70 3 97.6 5 82.3/2050.0 13.7/347 3.2/464 0.71/17.54 9 70 3 >99.0 6 82.3/2050.0 13.7/347 3.2/464 0.71/17.54 12 70 3 >99.0 7 82.5/2050.0 13.8/347 3.3/460 0.46/11.35 6 70 3 89.7 8 82.0/2050.0 13.8/347 3.0/463 1.41/35.07 6 70 3 90.6 9 87.7/2050.0 13.6/347 4.0/575 0.70/17.54 6 70 3 88.2 10 81.8/2050.0 6.8/174 1.6/250 0.70/17.54 9.0/174 6 70 3 >99.0

(27) TABLE-US-00003 TABLE 3 Productivity optimization of the reaction parameters (.sup.a MSA used as solvent, .sup.b total amount of MSA, inclusive of solvent) Reaction mixture DMDS HNO.sub.3 MSA/ DMDS/ Reaction conditions Product MSA.sup.a [g]/ (65%) H.sub.2O DMDS HNO.sub.3 O.sub.2 p T t MSA.sup.b DMDS MMTS No. [g]/[wt.-%] [wt.-%] [g]/[wt.-%] [wt.-%] [mol/mol] [mol/mol] [g] [bara] [? C.] [min] [wt.-%] [wt.-%] [wt.-%] 11a 201.1/92.9 13.07/6.0 0.22/0.0020 1.146 15.2 2000 1.8 6 70 15 92.5 3.1 1.3 11b 201.1/92.9 13.07/6.0 0.22/0.0020 1.146 15.2 2000 3.4 6 70 45 92.6 3.0 1.8 11c 201.1/92.9 13.07/6.0 0.22/0.0020 1.146 15.2 2000 4.1 6 70 95 93.3 2.6 1.3 11d 201.1/92.9 13.07/6.0 0.22/0.0020 1.146 15.2 2000 4.4 6 70 280 94.3 1.0 0.2 12a 201.1/92.9 13.07/6.0 0.0040 1.145 15.2 1000 1.5 6 70 10 93.3 3.4 1.5 12b 201.1/92.9 13.07/6.0 0.0040 1.145 15.2 1000 2.6 6 70 20 93.4 3.0 1.6 12c 201.1/92.9 13.07/6.0 0.0040 1.145 15.2 1000 3.0 6 70 30 93.5 2.7 1.6 12d 201.1/92.9 13.07/6.0 0.0040 1.145 15.2 1000 3.5 6 70 60 93.9 2.4 1.4 12e 201.1/92.9 13.07/6.0 0.0040 1.145 15.2 1000 3.9 6 70 120 94.4 2.0 0.8 12f 201.1/92.9 13.07/6.0 0.0040 1.145 15.2 1000 4.2 6 70 194 94.5 1.7 0.5 13a 201.1/92.8 13.07/6.0 0.0080 1.143 15.2 500 4.3 6 70 15 93.9 1.1 0.3 13b 201.1/92.8 13.07/6.0 0.0080 1.143 15.2 500 7.7 6 70 30 95.9 1.6 0.7 13c 201.1/92.8 13.07/6.0 0.0080 1.143 15.2 500 9.3 6 70 45 97.5 0.7 0.4 13d 201.1/92.8 13.07/6.0 0.0080 1.143 15.2 500 10.6 6 70 60 97.8 0.1 0.1 13e 201.1/92.8 13.07/6.0 0.0080 1.143 15.2 500 11.1 6 70 90 98.6 0.0 0.05 14a 201.1/92.8 13.07/6.0 0.0201 1.137 15.2 200 2.4 6 70 10 94.2 3.1 1.1 14b 201.1/92.8 13.07/6.0 0.0201 1.137 15.2 200 4.0 6 70 15 94.5 2.5 1.0 14c 201.1/92.8 13.07/6.0 0.0201 1.137 15.2 200 5.1 6 70 20 96.0 2.0 0.8 14d 201.1/92.8 13.07/6.0 0.0201 1.137 15.2 200 7.1 6 70 30 96.9 1.1 0.5 14e 201.1/92.8 13.07/6.0 0.0201 1.137 15.2 200 9.1 6 70 45 97.9 0.3 0.3 14f 201.1/92.8 13.07/6.0 0.0201 1.137 15.2 200 10.2 6 70 60 98.5 0.0 0.05 15a 201.1/92.8 13.07/6.0 0.0401 1.125 15.2 100 3.1 6 70 10 94.2 3.0 1.0 15b 201.1/92.8 13.07/6.0 0.0401 1.125 15.2 100 4.5 6 70 15 95.1 2.4 0.8 15c 201.1/92.8 13.07/6.0 0.0401 1.125 15.2 100 6.0 6 70 20 97.1 1.9 0.6 15d 201.1/92.8 13.07/6.0 0.0401 1.125 15.2 100 8.1 6 70 30 97.7 0.8 0.3 15e 201.1/92.8 13.07/6.0 0.0401 1.125 15.2 100 9.7 6 70 45 98.8 0.05 0.05 15f 201.1/92.8 13.07/6.0 0.0401 1.125 15.2 100 10.2 6 70 60 99.8 0.01 0.01 16a 201.1/92.8 13.07/6.0 0.0502 1.120 15.2 80 3.2 6 70 10 94.4 3.2 1.0 16b 201.1/92.8 13.07/6.0 0.0502 1.120 15.2 80 4.8 6 70 15 95.5 2.5 0.8 16c 201.1/92.8 13.07/6.0 0.0502 1.120 15.2 80 6.2 6 70 20 96.0 1.7 0.6 16d 201.1/92.8 13.07/6.0 0.0502 1.120 15.2 80 8.6 6 70 30 97.3 0.7 0.3 16e 201.1/92.8 13.07/6.0 0.0502 1.120 15.2 80 10.5 6 70 45 98.7 0.05 0.05 17a 201.1/92.8 13.07/6.0 0.0669 1.111 15.2 60 4.8 6 70 10 95.1 2.5 0.8 17b 201.1/92.8 13.07/6.0 0.0669 1.111 15.2 60 6.7 6 70 15 96.3 1.7 0.5 17c 201.1/92.8 13.07/6.0 0.0669 1.111 15.2 60 8.2 6 70 20 97.6 0.9 0.4 17d 201.1/92.8 13.07/6.0 0.0669 1.111 15.2 60 10 6 70 30 98.5 0.1 0.1 17e 201.1/92.8 13.07/6.0 0.0669 1.111 15.2 60 10.6 6 70 45 98.7 0.05 0.05 18a 201.1/92.8 13.07/6.0 0.143 1.1 15.2 40 3.3 6 70 10 94.3 3.1 0.9 18b 201.1/92.8 13.07/6.0 0.143 1.1 15.2 40 4.6 6 70 15 95.1 2.4 0.7 18c 201.1/92.8 13.07/6.0 0.143 1.1 15.2 40 6.2 6 70 20 96.6 1.7 0.5 18d 201.1/92.8 13.07/6.0 0.143 1.1 15.2 40 7.5 6 70 25 97.6 1.1 0.3 18e 201.1/92.8 13.07/6.0 0.143 1.1 15.2 40 8.6 6 70 30 97.4 0.5 0.2 18f 201.1/92.8 13.07/6.0 0.143 1.1 15.2 40 9.7 6 70 45 98.6 0 0 18g 201.1/92.8 13.07/6.0 0.143 1.1 15.2 40 10.6 6 70 60 99.1 0 0 19a 201.1/92.8 13.07/6.0 0.2 1.0 15.1 20 3.9 6 70 10 95.3 2.7 0.7 19b 201.1/92.8 13.07/6.0 0.2 1.0 15.1 20 7.1 6 70 20 96.7 1.2 0.4 19c 201.1/92.8 13.07/6.0 0.2 1.0 15.1 20 8.4 6 70 30 98.4 0.1 0.1 19d 201.1/92.8 13.07/6.0 0.2 1.0 15.1 20 10.6 6 70 50 99.1 0 0 20a 201.1/92.7 13.07/6.0 0.4022 0.9313 15.1 10 5.2 6 70 10 95.0 2.4 0.6 20b 201.1/92.7 13.07/6.0 0.4022 0.9313 15.1 10 7.0 6 70 15 97.2 1.3 0.4 20c 201.1/92.7 13.07/6.0 0.4022 0.9313 15.1 10 9.3 6 70 20 97.8 0.5 0.2 20d 201.1/92.7 13.07/6.0 0.4022 0.9313 15.1 10 10.9 6 70 30 98.4 0 0.0 21a 201.1/91.8 13.07/6.0 2.029 0.0669 14.8 2 2.4 6 70 10 95.7 2.3 0.8 21b 201.1/91.8 13.07/6.0 2.029 0.0669 14.8 2 4.9 6 70 15 97.6 1.6 0.6 21c 201.1/91.8 13.07/6.0 2.029 0.0669 14.8 2 6.7 6 70 20 97.9 1.0 0.3 21d 201.1/91.8 13.07/6.0 2.029 0.0669 14.8 2 10.3 6 70 30 98.0 0.0 0.0 22a 201.1/90.8 13.07/6.0 4.102 0 14.5 1 6.4 6 70 10 96.4 0.6 0.3 22b 201.1/90.8 13.07/6.0 4.102 0 14.5 1 10.0 6 70 15 96.4 0 0

C) Safety Optimization of the Reaction Parameters

(28) In experiments 23 to 27, the reaction behaviour of different mixtures of dimethyl disulfide, methanesulfonic acid, nitric acid and water was examined from the standpoint of plant safety, with addition of pure oxygen under largely adiabatic conditions. For this purpose, a number of experiments were conducted with different experimental conditions, using in each case a closed sample in an adiabatic calorimeter (Phitec II).

(29) 1. Samples

(30) 1.1 Methanesulfonic Acid

(31) 1.2 Dimethyl Disulfide

(32) 1.3 Nitric Acid, 65% Strength

(33) 1.4 DI Water (Deionized Water, i.e. Fully Demineralized Water)

(34) 2. Investigation of Reaction Behaviour Under Adiabatic Conditions

(35) 2.1 Measurements in the Adiabatic Calorimeter (Phi-TEC II)

(36) 2.1.1 Measurement Method

(37) The Phi-TEC II is a PC-controlled calorimeter which can be used to simulate the behaviour of a large reactor under conditions of an industrial plant even using relatively small quantities of sample, such as 10 to 100 ml, for example.

(38) With the PHITEC II calorimeter, a pressure/heat accumulation method is employed in which (depending on the mandated experimental conditions) a relatively high measurement accuracy is obtained, taking account of the detectable heat output in the reaction (typically about 2-5 W/kg when using a closed sample container). From the profile of the temperature and of the pressure, measured over time, reflecting the exothermicity of the reaction and the formation of decomposition gases, the thermal stability of the sample in question can be investigated.

(39) The experiments are carried out using an adiabatic calorimeter; the entire measurement apparatus is installed in a pressure-resistant autoclave.

(40) Inserted into the pressure vessel is a cylindrical sample container made from stainless steel of material number 1.457 (alternatively, a sample container made of Hastelloy) with a volume of 110 ml, insertion taking place into a heater system whose heating units, while fully surrounding the sample container, do not have any mechanical contact with it. Using a magnetic stirring rod (also referred to as magnetic flea or stirring bar), which is located on the base of the sample vessel, the sample is stirred.

(41) The sample container has very thin walls, with a wall thickness of typically only 0.15 mm. The pressure which comes about in the closed sample container in the course of a measurement, therefore, and which is composed of the vapour pressure and the partial pressure of decomposition gases, is also established, via a tracking control system, in the surrounding autoclave, in order to prevent deformation of the sample container.

(42) The ambient temperature of the sample container is adapted continually to the sample temperature, thereby largely preventing a flow of heat from the sample into the ambient environment. The ambient temperature is therefore regulated in such a way that at no point in time is the difference between the sample temperature and the ambient temperature 0 Kelvin, and so adiabatic conditions prevail.

(43) The favourable ratio of the heat capacity of the sample container to the heat capacity of the sample results in a relatively high sensitivity of measurement, which is quantified by the so-called phi factor ?, as given by the following equation:

(44) $?=\frac{\mathrm{Heat}\mathrm{capacity}\mathrm{of}\mathrm{sample}+\mathrm{heat}\mathrm{capacity}\mathrm{of}\mathrm{sample}\mathrm{container}}{\mathrm{Heat}\mathrm{capacity}\mathrm{of}\mathrm{sample}}$

(45) The value of the dimensionless phi factor is ideally not much more than 1.

(46) The maximum adiabatic temperature increase determined in each experiment is corrected by the phi factor, in order to take account of the energy needed to heat the container.

(47) 2.1.2 Experimental Procedure and Measurement Results

(48) 2.1.2.1 Experiment 23

(49) A closed sample container made from the nickel-chromium-molybdenum alloy Hastelloy C276 was used, with a volume of 115 ml, the container being equipped with an immersion tube for the feeding-in of molecular oxygen, and with a stirring bar.

(50) The composition of the sample for the experiment is summarized in the table below:

(51) TABLE-US-00004 [g] [%] Density [g/ml] [ml] [g] [%] [ml] Methanesulfonic acid 198 74.24 1.48 133.78 79.2 74.24 53.51 Nitric acid (65%) 2.75 1.03 1 2.75 1.1 1.03 1.10 Dimethyl disulfide 53.45 20.04 1.03 51.89 21.38 20.04 20.76 Water 12.5 4.69 1 12.50 5 4.69 5.00 Total: 266.7 100.00 200.93 106.68 100.00 80.37

(52) Under intrinsic vapour pressure, the sample container, which had been evacuated beforehand, was charged first with the methanesulfonic acid and also with the fractions of nitric acid and water, and then dimethyl disulfide was added. Thereafter the sample was heated to the setpoint temperature of 70? C. When the heater was switched off, a weakly exothermic reaction was apparent in the subsequent period, in which a temperature of 72? C. was reached up to the point of addition of the oxygen. This was followed by the addition of pure oxygen, with an initial pressure in the sample container of about 7.5 bara, with the objective of using the feeding-in of oxygen to set an overall pressure of 12 bara as rapidly as possible. For this purpose, the pressure reduction station of the oxygen flask was set to the target pressure and verified using a reference pressure manometer. A reverse flow preventer installed in the feed line prevented backward flow of the gas. Immediately after the introduction of the oxygen, a very strongly exothermic reaction began, in association with very rapid pressure rise.

(53) Owing to the very strongly exothermic reaction, the pressure in the sample container, in spite of pressure limitation and shut-off of the feed-line valve for the oxygen, rose well beyond the setpoint pressure, and reached a maximum of 20.4 bara. The sample temperature reached a maximum of 119? C. Since the tracking control system of the temperature was unable to follow the very rapid temperature rise, it is assumed that the achievable temperature maximum would be even higher. (Not included in the appraisal of the temperature increase and pressure increase are the effects of the rate of introduction of the oxygen and of a fraction of heat of compression resulting from the injection.)

(54) After the temperature and the pressure had dropped to about 84? C. and to about 11.2 bara, respectively, oxygen was injected again at up to 12 bara. This produced a further exothermic effect, although significantly weaker in extent by comparison with the first addition of oxygen.

(55) FIGS. 1 and 2 show the time-dependent profiles of the sample temperature and of the pressure, respectively, and FIG. 3 shows the temperature-dependent profile of the pressure. The uncertainty of results is ?1 K for the temperature and ?0.4 bar for the pressure. FIG. 4 shows the time-dependent change in temperature as a function of the sample temperature, and FIG. 5 represents the temperature relationship of the heat output. For the calculation of the exothermic heat output, the specific heat of the sample was estimated at constant pressure (c.sub.p) For this purpose, for the fraction of organic compounds, the assumption was made of a specific heat at constant pressure (c.sub.p) of 2 J/(g*K), and a (c.sub.p) of 4.1 J/(g*K) for the inorganic fraction.

(56) Owing to the concentration of dimethyl disulfide, there was a very rapid increase in temperature and pressure when this experiment was carried out. Under the experimental conditions, however, there was no damage, and certainly not any destruction, of the sample container. The temperature and pressure increase that occurred in this experiment was therefore non-critical. The concentration of 20 wt.-% therefore represents the marginal region in the process of the invention at which the oxidation of the dialkyl disulfide to the corresponding alkanesulfonic acid can still be carried out safely and readily. For a controllable implementation of the oxidation of the dialkyl disulfide to the alkanesulfonic acid, therefore, the concentration of the dialkyl disulfide in the reaction mixture ought to be not more than 20 wt.-%, preferably less than 20 wt.-%.

2.1.2.2 Experiment 24

(57) In this experiment, the reaction effluent from experiment 23 was used, and the effect of the addition of oxygen at different temperatures was investigated. For this purpose, the sample container was filled with the reaction effluent from experiment 23, and the sample was first heated to the setpoint temperature of 50? C. with the stirrer running. After the heater had been switched off, the pressure was about 0.7 bara and the temperature remained constant. Thereafter the pure oxygen was added via the immersion tube of the sample container, with the aim of achieving a final setpoint pressure of 12 bara. For this purpose, the pressure reduction station of the oxygen flask was set to this pressure and checked using a reference pressure manometer. A reverse flow preventer installed in the feed line prevented the gas from flowing back.

(58) Even with a relatively quick injection of the oxygen, a rapid temperature rise was evident, initially up to about 60? C. At this point the pressure in the sample container, despite pressure limitation and shut-off of the oxygen feed-line valve, rose above the setpoint pressure and reached a value of about 13 bara. After a slight drop, the sample temperature rose without external supply of energy, solely as a result of the heat released during the exothermic reaction, up to about 105? C. This was paralleled by a drop in the pressure from 13 bara to 3 bara. After heating to 111? C. and a short run-in phase, oxygen was again injected to a setpoint pressure of 12 bara, with a pressure of 12.1 bara becoming established. Both during the injection and also thereafter, there was only a slight change in temperature observed, of about 1 K. This was followed by a further two heating steps to a final temperature of 121? C., but no exothermic reaction was observed. The experiment was therefore discontinued. After cooling to room temperature and release of pressure on the sample container, the remnant sample was removed.

(59) FIG. 6 shows the time-dependent profile of the sample temperature, and FIGS. 7 and 8 show the time-dependent and temperature-dependent profiles of the pressure, respectively. The measurement accuracy is ?1 K for the temperature and ?0.4 bar for the pressure.

(60) The profile of temperature and pressure as shown in FIGS. 6 and 7 indicates that in the subsequent reaction of the reaction effluent from experiment 23 there is still a certain conversion. In this subsequent reaction, however, both the development of temperature and the development of pressure are significantly lower than in the preceding conversion. The two experiments 23 and 24 show that the oxidation of dialkyl disulfide to the corresponding alkanesulfonic acid can be carried out controllably in two successive reactors.

(61) 2.1.2.3 Experiment 25

(62) In this experiment, the oxygen was added at 50? C. (in contrast to the corresponding temperature of 70? C. in experiment 23) and the setpoint pressure was 12 bara. For this purpose, a closed sample container made from the stainless steel alloy Hastelloy C276 was used, with a volume of 115 ml, this container being equipped with an immersion tube and a stirring rod or stirring flea.

(63) The composition of the sample for the experiment is as follows:

(64) TABLE-US-00005 [g] [%] Density [g/ml] [ml] [g] [%] [ml] Methanesulfonic acid 198 74.24 1.48 133.78 79.2 74.24 53.51 Nitric acid (65%) 2.75 1.03 1 2.75 1.1 1.03 1.10 Dimethyl disulfide 53.45 20.04 1.03 51.89 21.38 20.04 20.76 Water 12.5 4.69 1 12.50 5 4.69 5.00 Total: 266.7 100.00 200.93 106.68 100.00 80.37

(65) Under intrinsic vapour pressure, the sample container, which had been evacuated beforehand, was charged first with the methanesulfonic acid and also with the corresponding fractions of nitric acid and water. Subsequently the corresponding fraction of dimethyl disulfide was added to the sample container. Thereafter the sample was heated to the setpoint temperature of 50? C., with the stirrer running.

(66) When the heater was switched off, a very weakly exothermic reaction was apparent in the subsequent period, in which a temperature of 51.4? C. was reached up to the point of addition of the oxygen. At a pressure of about 6.7 bara, the addition of pure oxygen via the immersion tube in the sample container was commenced, in order to set a total pressure of 12 bara with the use of oxygen as rapidly as possible. For this purpose, the pressure reduction station of the oxygen flask was set to the corresponding pressure and verified using a reference pressure manometer. A reverse flow preventer installed in the feed line prevented backward flow of the gas stream. Immediately after the introduction of the oxygen, a very strongly exothermic reaction was apparent, in association with very rapid pressure rise. Despite pressure limitation on the oxygen supply flask and closing of the inlet valve, the pressure in the sample container rose to about 18.5 bara. The sample temperature reached a maximum of about 98? C. Since the tracking control system of the temperature was unable to follow the very rapid temperature rise, it is assumed that the achievable temperature maximum would be even higher. (Not included in the appraisal of the temperature increase and pressure increase are the effects of the rate of introduction of the oxygen and of a fraction of heat of compression resulting from the injection.) After the attainment of the temperature maximum and the shutting-off of the oxygen supply, and also a drop in pressure to about 8.9 bara, the experiment was ended.

(67) FIG. 9 shows the time-dependent profile of the sample temperature. FIGS. 10 and 11 represent the time-dependent and temperature-dependent profile of the pressure, respectively. The measurement accuracy is ?1 K for the temperature and ?0.4 bar for the pressure. FIG. 12 shows the time-dependent change in temperature as a function of the sample temperature, and FIG. 13 shows the heat output as a function of the sample temperature. For the calculation of the (exothermic) heat output, the specific heat of the sample at constant pressure (c.sub.p) is estimated. For this purpose, for the fraction of organic compounds, a specific heat at constant pressure (c.sub.p) of 2 J/(g*K) is assumed, and a (c.sub.p) of 4.1 J/(g*K) for the inorganic fraction.

(68) In experiment 25, the oxidation of the dimethyl disulfide to the corresponding methanesulfonic acid is initiated by feeding in oxygen at a temperature of 50? C., which is 20? C. lower than the corresponding temperature in experiment 23. Accordingly, the curve profiles for the time-dependent change in temperature and for the heat output of the reaction are also shifted by this temperature difference in experiment 25 by comparison with the corresponding curve profiles in experiment 23. Apart from this shift, the profile for the time-dependent change in temperature and the profile for the heat output in experiment 25 are parallel to those in experiment 23 (cf. FIGS. 4 to 5 and 12 to 13). Similar comments also apply in respect of the development of temperature and of pressure in experiments 23 and 25 (cf. FIGS. 1 to 2 and 9 to 11).

(69) The results of experiments 23 and 25 show that the oxidation of the dialkyl disulfide proceeds with a comparable exotherm in both experiments, independently of the respective starting temperature.

(70) 2.1.2.4 Experiment 26

(71) In contrast to experiments 23 to 25, which used a sample container made from the Hastelloy C276 alloy, and with an immersion tube, this experiment was conducted in a sample container made from a stainless steel with material number 1.4571. The closed sample container in this experiment has a volume of 110 ml and is equipped with a stirring bar or stirring flea, but not with an immersion tube.

(72) The initial setpoint temperature before the addition of oxygen was 50? C., and the setpoint pressure for the addition of oxygen was 12 bara.

(73) The composition of the sample for the experiment is summarized in the table below:

(74) TABLE-US-00006 [g] [%] Density [g/ml] [ml] [g] [%] [ml] Methanesulfonic acid 198 74.24 1.48 133.78 79.2 74.24 53.51 Nitric acid (65%) 2.75 1.03 1 2.75 1.1 1.03 1.10 Dimethyl disulfide 53.45 20.04 1.03 51.89 21.38 20.04 20.76 Water 12.5 4.69 1 12.50 5 4.69 5.00 Total: 266.7 100.00 200.93 106.68 100.00 80.37

(75) Under intrinsic vapour pressure, the sample container, which had been evacuated beforehand, was charged first of all with the methanesulfonic acid and with the fractions of nitric acid and water. Thereafter the fraction of dimethyl disulfide was added to the sample container, followed by the heating of the sample to the setpoint temperature of 50? C., with the stirrer running.

(76) The time-dependent profiles of the sample temperature (unbroken line) and of the pressure (broken line) are depicted jointly in FIG. 14. FIG. 15 shows the time-dependent change in the sample temperature as a function of the sample temperature, and FIG. 16 the temperature-dependent pressure profile.

(77) After the heater was switched off when the setpoint temperature of 50? C. was reached, a temperature of about 51.5? C. was established in the subsequent period, before commencement of addition of oxygen. This was followed by addition of pure oxygen at a pressure in the sample container of about 71.2 bara, with the objective of setting an overall pressure of 12 bara as rapidly as possible by the feeding-in of oxygen. For this purpose the pressure reduction station of the oxygen flask was set to the target pressure, and checked using a reference pressure manometer. A reverse flow preventer installed in the feed line prevented the gas from flowing back. With a certain delay, there was a very strongly exothermic reaction after the introduction of the oxygen, and a temperature maximum of about 350? C. was reached. The delay is attributed to the fact that in contrast to experiments 23 to 25, oxygen is not introduced into the sample container via an immersion tube, but instead is introduced from above onto the liquid phase.

(78) In the phase of the addition of the oxygen, a banging noise was heard from the autoclave box in which the calorimeter had been placed for the experiments. The experiment was subsequently ended by switching off the heating system. A real pressure increase of up to about 5.5 bara was still recorded, but the subsequent pressure/time profile was no longer recorded. This is attributable to the destruction of the pressure transducer, whose maximum permissible pressure is 100 bar.

(79) The vapours of dimethyl disulfide are able, with air or oxygen, to form an explosive mixture; the corresponding ignition temperature is 370? C. With regard to the ignition temperature of mixtures of flammable gases and vapours with air or oxidizing gas, it is known that the temperature decreases very sharply with increasing pressure (cf. e.g. Hirsch, W., Brandes, E., Z?ndtemperaturen bin?rer Gemische bei erh?hten Ausgangsdr?cken, Physikalisch Technische Bundesanstalt, Braunschweig, 2005). With the sharp increase in the temperature and the increased initial pressure on addition of oxygen, the preconditions for the obtainment of the ignition temperature were provided for dimethyl disulfide. Despite the free gas volume in the sample container being relatively small, it can therefore very probably be assumed that there was self-ignition of the gas phase containing oxygen and dimethyl disulfide.

(80) This experiment clearly shows that the formation of explosion hazard mixtures from ignitable dialkyl disulfides with oxygen must fundamentally be avoided.

(81) 2.1.2.5 Experiment 27

(82) A sample container made from the alloy Hastelloy C276 was used. This closed sample container has a volume of 115 ml and is equipped with an immersion tube and with a stirring bar or stirring flea.

(83) The initial setpoint temperature before the addition of oxygen was 50? C., and the setpoint pressure for the addition of oxygen was 12 bara.

(84) The composition of the sample for the experiment is summarized in the table below:

(85) TABLE-US-00007 [g] [%] Density [g/ml] [ml] [g] [%] [ml] Methanesulfonic acid 302 87.66 1.48 204.05 100.67 87.67 68.02 Nitric acid (65%) 1.7 0.49 1 1.70 0.57 0.49 0.57 Dimethyl disulfide 33 9.58 1.03 32.04 11.00 9.58 10.68 Water 7.8 2.26 1 7.80 2.60 2.26 2.60 Total: 344.5 100.00 245.59 114.83 100.00 81.86

(86) Under intrinsic vapour pressure, the sample container, which had been evacuated beforehand, was charged first of all with the methanesulfonic acid and with the fractions of nitric acid and water. Thereafter the fraction of dimethyl disulfide was added to the sample container, followed by the heating of the sample to the setpoint temperature of 70? C., with the stirrer running.

(87) The time-dependent profile of sample temperature and pressure is depicted in FIGS. 17 and 18, respectively. FIG. 19 shows the temperature-dependent pressure profile, and FIG. 20 shows the time-dependent change in the sample temperature as a function of the sample temperature.

(88) An exothermic reaction started immediately after the heater was switched off, when a temperature of 70? C. was reached. At about 71.3? C., oxygen was added rapidly with the aim of establishing a pressure of 12 bara. When this pressure had been reached and the inlet valve was closed for the first time, the sample temperature was about 93? C. Following the subsequent drop in pressure, oxygen was injected repeatedly in order to re-establish a pressure of 12 bara. The accompanying increase in temperature, however, was no longer spontaneous, but instead was relatively slow. Over a time of approximately 4900 seconds, with repeated further addition of oxygen, a maximum sample temperature of about 110? C. was attained.

(89) In this experiment, not only the development of temperature but also the development of pressure are much smaller than in experiments 23 and 25 (cf. FIGS. 17 and 18). In contrast to experiments 23 and 25, therefore, the starting concentration selected for the dimethyl disulfide in this experiment permits discontinuous addition of oxygen over a prolonged time period, without the setpoint pressure of 12 bara being markedly exceeded. The process parameters of experiment 27, especially the selected concentration of the dimethyl disulfide, therefore permit a corresponding process for the preparation of methanesulfonic acid to be operated with no safety problems.