RECOVERY OF WATER-FREE METHANESULFONIC ACID FROM THE BOTTOM STREAM OF A DISTILLATION COLUMN

Abstract

Process for separating anhydrous methanesulfonic acid from a reaction mixture comprising methanesulfonic acid and sulfuric acid by distillation with at least three functional steps and the use of said methanesulfonic acid.

Claims

1. A process for separating anhydrous methanesulfonic acid from a reaction mixture comprising methanesulfonic acid and sulfuric acid by distillation, comprising feeding the reaction mixture into a first column K1 and producing a top stream and a bottom stream in column K1, transferring the top stream of column K1 to a second column K2, in which purified anhydrous methanesulfonic acid is obtained from its bottom stream, and transferring the bottom stream of column K1 to either a third column K3 or an evaporator W3-1, in which the top stream is recycled back into column K1, and in which the bottom stream is separated from the distillation process.

2. The process according to claim 1, wherein, in addition to evaporator W3-1, further (n−1) evaporators W3-2, W3-3, . . . , W3-n, n being an integer from 2 to 10, are used, wherein the bottom stream of each evaporator W3-k, k being an integer from 1 to (n−1)) is transferred to each evaporator W3-(k+1), and wherein the top stream of each evaporator W3-(k+1) is transferred back to each evaporator W3-k, while the bottom stream of evaporator W3-n is separated from the distillation process.

3. The process according to claim 1, wherein the reaction mixture comprises 55 to 95 wt.-% methanesulfonic acid, 5 to 45 wt.-% sulfuric acid, 0 to 5 wt.-% methanesulfonic acid anhydride, 0 to 1 wt.-% side products, 0 to 5% SO.sub.3, 0 to 5 wt.-% of water and traces of methane, wherein the sum of all components sums up to 100 wt.-%, and wherein the side products comprise methylmethanesulfonate and/or methylbisulfate and/or methanedisulfonic acid, and wherein the amount of components other than methanesulfonic acid and sulfuric acid is in the range of 0 to 10 wt.-%.

4. The process according to claim 1, wherein columns K1, K2 and optionally K3 can each be set-up as one column K1 and K2 and optionally K3, or as several columns with same functionalities K1, K2 and optionally K3 operated in parallel.

5. The process according to claim 1, wherein the bottom residue of column K3 or evaporator or cascade of evaporators W3-n contains at least 60 wt. % of sulfuric acid.

6. The process according to claim 1, wherein the pressure at the head of the columns and optionally evaporators ranges from 0.1 to 50 mbar, for all distillation columns K1, K2 and optionally K3 and evaporators W3-n.

7. The process according to claim 1, wherein the temperature at the bottom of the columns and optionally evaporators ranges from 140 to 220° C., in all distillation columns K1, K2 and optionally K3 and evaporators W3-n.

8. The process according to claim 1, wherein purified MSA leaves the distillation at bottom of K2 with a specification of <500 ppm sulfuric acid, <1000 ppm MMS, 0.5 wt.-% water.

9. The process according to claim 1, wherein MSA leaves the distillation with a purity of at least 98 wt-%.

10. The process according to claim 1, wherein the process is a batch or a continuous process.

11. The process according to claim 1, wherein the MSA recovery rate in the distillation is at least 80%.

12. The process according to claim 1, wherein at least a part of the bottom fraction of the MSA distillation column K3 is not purged from the system but at least partially recycled to the synthesis step of the starter solution or to the synthesis step of the MSA synthesis with methane and SO3.

13. The process according to claim 1, wherein the residence time in each distillation column and optionally evaporators W3-n is below 5 h.

14. The process according to claim 1, wherein the ratio of the inner column diameter in the sump and the inner column diameter of the column directly above the sump for each column is in the range from 0.20 to 0.99.

Description

EXAMPLES

[0056] The examples were carried out under the condition that the below product specifications are met: [0057] a) Specifications of MSA-product stream: [0058] MSA purity>=99.9% wt. MSA [0059] H.sub.2SO.sub.4=<20 ppm (wt.) [0060] H.sub.2O=<50 ppm or 30 ppm (wt.) [0061] MMS=<100 ppm or 20 ppm (wt.) [0062] b) Specifications of the reactor recycle: equal to 30% wt. MSA in the H.sub.2SO.sub.4 recycle stream.

[0063] In cases, where the target specification is not achieved, the results are marked with a star symbol (*) (see Table 2).

[0064] It will be easily understood for the person skilled in the art that the set-up also can handle product specifications with higher amounts of side products. While the general set-up of the system will not change, namely three columns with MSA leaving the system via bottom outlet, especially the energy demand and yield may vary when the stream to the distillation displays different compositions and and/or in case other specifications than above for MSA are targeted. The necessary fine-tuning of operating conditions will be easy to do for a person skilled in the art.

[0065] All examples are based on the following process parameters: [0066] a) Capacity: product stream mass flow of 2000 kg/h [0067] b) Feed preheating by a temperature of 120° C. [0068] c) Reactions: Due to thermal degradation of MSA, MMS and other decomposition products may form in the columns.

[0069] To evaluate and compare the results the following performance indicators were chosen: [0070] MSA product specification [0071] Specific energy demand (reboiler duty in MW/t MSA product) [0072] MSA recovery rate in kg/kg. Here, the MSA recovery rate is defined as the fraction of MSA product mass flow to the MSA mass flow in the fresh feed.

[00001]$\begin{array}{cc}\mathrm{recovery}\mathrm{rate}=\frac{{\stackrel{.}{m}}_{\mathrm{MSA},\mathrm{product}}}{\stackrel{.}{m_{\mathrm{MSA},\mathrm{fee}d}}}& \mathrm{Eq}.1\end{array}$ [0073] MMS formation in kg/h due to thermal degradation.

[0074] The feeds used in the below examples are obtainable in the processes described above e.g. in WO 2015/071455, Kappenthuler et al. [Journal of Cleaner Production, 202, 2018] or in EP Appl. No. 19190499.4.

[0075] Comparative Example 1: Performance of designs with up to two functional distillation columns and purified MSA being delivered as liquid side-draw of the first column. The distillation setups considered for this example are shown in FIG. 3. The composition of the feed to the MSA-purification section is given in

[0076] Table 1.

TABLE-US-00001 TABLE 1 Composition of the feed to the MSA-purification section Component Mass fraction (wt.-%) SO.sub.3 .sup. 0% H.sub.2O 1.0% MBS 0.3% MMS 0.4% MSAA .sup. 0% MSA  73% MDSA 0.3% H.sub.2SO.sub.4  25%

[0077] The purified MSA product stream was leaving K1 as liquid side-discharge above the feed stage of column K1. Water and light boiling side-products of the reaction (e.g. MBS, MMS) were separated from MSA in K1 and left the column at the top. Sulfuric acid was delivered as bottoms stream of K1 in a mixture with MSA and high boiling side-products of the reaction (e.g. MDSA). To reduce losses of MSA product, the sulfuric acid-rich stream which is meant to be recycled to the reactor, was conditioned to 30 wt.-% MSA.

[0078] Due to the pressure loss over the column, the MSA target specification given above cannot be reached in a single column (Type C1-1). For this reason, the bottoms stream of K1 (with an MSA content higher than 30 wt.-%) was directed to a subsequent distillation column K2 (Design C1-2) or a cascade of evaporators W2-N (Design C1-3), where the stream was enriched further with sulfuric acid. The MSA-rich stream from the top of K2 or from W2 was returned to K1. The sulfuric acid-rich stream (“heavies”) was leaving the set-up at the bottom of K2 or of W2 with 30 wt.-% MSA.

[0079] However, for all distillation designs of Type C1 with the MSA-product delivery as a liquid side-discharge above the feed stage and the formation of thermal degradation products like MMS, the product specification regarding MMS were not achieved (Table 2). In addition, the specific energy demand was higher than in the inventive examples 1 to 4.

[0080] Compared to WO2018/219726, which discloses distillation set-ups of Type C1, the composition of the feed summarized in

[0081] Table 1 was more complex with a higher amount of side product. This comparative example showed, that with a complex feed composition a robust and economic separation of light boilers from MSA is not possible with a liquid side discharge and up to two columns.

[0082] Even for low concentration of sulfuric acid in the feed (e.g. 15 wt.-%) the MMS concentration in the MSA purified stream was above the specified limit of 100 ppm-wt. A variation of the sulfuric acid concentration in the feed from 15 to 47%-wt showed concentrations of MMS in the purified MSA stream from 104 to 120 ppm-wt and concentrations of water for 72 to 90 ppm-wt. The required specific energy demand for 15 wt.-% sulfuric acid in feed was 1.2 MW/tMSA product, while for 47%-wt sulfuric acid in the feed, the required energy demand was much higher, equal to 2.6 MW/tMSA product.

TABLE-US-00002 TABLE 2 Key parameters and performance of a distillation set-up with up to two columns and a liquid side discharge Design C1-1 Separation One distillation column (K1) for both product set-up recovery and conditioning of the reactor recycle. MSA-product as liquid side-draw of K1 above feed stage. Theoretical stages 8 9 Pressure (mbar) 7 for K1 7 for K1 Performance Product quality 99.96 wt.-% MSA 99.96 wt.-% MSA 20 ppm wt. H.sub.2SO.sub.4 20 ppm wt. H.sub.2SO.sub.4 110 ppm wt. H.sub.2O * 126 ppm wt. H.sub.2O * 228 ppm wt. MMS * 180 ppm wt. MMS * MSA- MSA: 54.1 wt.-% * MSA: 30 wt.-% * concentration in bottom stream Bottom T.sub.sump K1: 185° C. T.sub.sump K1: 195° C.* Temperature F-Factor F-Factor = 2.0 F-Factor = 1.9 MMS formation 18.3 26.8 (kg/h) Specific energy 1.110 1.126 demand (MW/ tMSA Product) MSA recovery 0.590 0.541 rate (kg/kg) Design C1-2 Design C1-3 Separation First distillation column (K1) for Distillation column (K1) for set-up product recovery and second product recovery, followed by a distillation column (K2) for cascade of two evaporators (W3-1, conditioning of the reactor recycle. W3-2) for conditioning of the Distillate of K2 returns to K1 bottoms. reactor recycle. Distillates of W3-1 MSA-product as liquid side-draw and W3-2 return to K1 bottoms. of K1 above feed stage. MSA-product as liquid side-draw of K1 above feed stage Theoretical stages 8 for K1, 2 for K2 8 for K1 Pressure (mbar) 7 for K1, 8 for K2 7 for K1, 6 for W3-1, W3-2 Performance Product quality 99.98 wt.-% MSA 99.97 wt.-% MSA 20 ppm wt. H.sub.2SO.sub.4 20 ppm wt. H.sub.2SO.sub.4 75 ppm wt. H.sub.2O 97 ppm wt. H.sub.2O 118 ppm wt. MMS * 113 ppm wt. MMS * MSA-concentration MSA 30 wt.-% MSA 30 wt.-% in bottom stream Bottom T.sub.sump K1: 185° C., T.sub.sump K1 182° C.; Temperature T.sub.sump K2: 183° C. T.sub.out W3-1: 171° C.; T.sub.out W3-2: 175° C.; F-Factor F-Factor K1 = 2.0 F-Factor K1 = 2.0 F-Factor K2 = 1.0 MMS formation 23.2 11.5 (kg/h) Specific energy 1.301 1.333 demand (MW/ tMSA Product) MSA recovery 0.768 0.820 rate (kg/kg)

[0083] Comparative Example 2: Performance of a design with three functional distillation columns, where the MSA product was delivered as liquid side-discharge of the second column, for an MSA-rich feed. This distillation set-up is depicted in FIG. 4. The feed had the same composition as in Comparative Example 1.

[0084] The light boiling components were separated from the main MSA stream in a first distillation column K1. In the second distillation column K2 the rest of the light components were separated from the MSA stream from the top of the column. The MSA product stream was a liquid side-discharge from K2 above feed stage. The remaining MSA and sulfuric acid at the bottom of K2 were fed to distillation column K3. A MSA-rich stream was generated at the top of K3 and returned to the bottoms of K2. The heavies left the distillation set-up at the bottoms discharge of K3.

[0085] For this design all specifications for the product stream and the sulfuric acid recycle could be achieved (Table 3). Also a high product recovery rate could be reached, however, the specific energy demand was still too high.

TABLE-US-00003 TABLE 3 Key parameters and performance of a distillation set-up with three distillation columns and a liquid side discharge Design C2 Separation First distillation column (K1) for separation of light set-up boiling components, second distillation column (K2) for product recovery and third distillation column (K3) for conditioning of the reactor recycle. Distillate of K3 returns to K2 bottoms. MSA-product as side-draw of K2 above feed stage. Theoretical stages 7 for K1, 9 for K2, 3 for K3 Pressure (mbar) 9 for K1, 8 for K2, 7 for K3 Product quality 99.99 wt.-% MSA 20 ppm wt. H.sub.2SO.sub.4 1 ppb wt. H.sub.2O 100 ppm wt. MMS MSA MSA 30 wt.-% Concentration Bottom stream Bottom T.sub.sump K1 181° C. Temperature T.sub.sump K2 185° C. T.sub.sump K3 183° C. F-Factor F-factor K1 = 0.9 F-factor K2 = 1.2 F-factor K3 = 1.7 MMS formation 15.1 (kg/h) Specific energy 0.853 demand (MW/ tMSA Product) MSA recovery 0.820 rate (kg/kg)

[0086] Example 1: Performance of the proposed design Type 1 according to the present invention for MSA-rich feed as shown in FIG. 2. The feed had the same composition as in Comparative Example 1 (see Table 1).

[0087] Sulfuric acid and heavy boiling side-products of the reaction were separated from the main MSA stream in a first distillation column K1. In the second distillation column K2 remaining light components were separated from the MSA stream. The MSA product stream was delivered as bottoms liquid discharge of K2. The remaining MSA and sulfuric acid from column K1 were fed to distillation column K3 (Design 1-1) or to a cascade of evaporators (Design 1-2). A MSA-rich stream was delivered from the top of K3 and returned to the bottoms of K1. The bottoms discharge of K3 left the distillation system.

[0088] All specifications for the product stream and the sulfuric acid recycle were fulfilled. Compared to the distillation design of type C1 and C2 a high product recovery rate could be achieved with a significant reduction of the specific energy demand.

TABLE-US-00004 TABLE 4 Key parameters and performance of the distillation set-up according to the present invention (Design 1) Design 1-1 Design 1-2 Separation First distillation column First distillation column set-up (K1) for separation of (K1) for separation of heavy boiling components, heavy boiling components, second distillation column second distillation (K2) for product recovery column (K2) for product and third distillation column recovery and a cascade (K3) for conditioning of the of two evaporators (W3-1, reactor recycle. Distillate of W3-2) for conditioning K3 returns to K1 bottoms. of the reactor recycle. MSA-product as liquid or MSA-rich condensate of gaseous bottoms residue W3-1 returns to K1 bottoms of K2. and of W3-2 returns to W3-1. MSA-product as liquid or gaseous bottoms residue of K2. Theoretical stages 8 for K1, 4 for K2, 3 for K3 8 for K1, 4 for K2 Pressure (mbar) 7 for K1, 10 for K2, 7 for K3 7 for K1, 10 for K2, 7 for W3-1, 7 for W3-2 Product quality 99.98% wt. MSA 99.98% wt. MSA 20 ppm wt. H.sub.2SO.sub.4 20 ppm wt. H.sub.2SO.sub.4 33 ppm wt. H.sub.2O 38 ppm wt. H.sub.2O 100 ppm wt. MMS 100 ppm wt. MMS MSA MSA 30% wt. MSA 30% wt. Concentration Bottom stream Bottom T.sub.sump K1 185° C. T.sub.sump K1 184° C. Temperature T.sub.sumpK2 169° C. T.sub.sump K2 169° C. T.sub.sump K3 186° C. T W3-1 172° C. T W3-2 175° C. F-Factor F-factor K1 = 1.6 F-factor K1 = 1.5 F-factor K2 = 0.5 F-factor K2 = 0.5 F-factor K3 = 2.0 MMS formation 10.7 7.6 (kg/h) Specific energy 0.627 0.767 demand (MW/ tMSA Product) MSA recovery 0.850 0.851 rate (kg/kg)

[0089] The choice of the number of theoretical stages for K1 (and therefore the height of the packing) was a trade-off between the reduction of specific energy demand and requirements on the thermal stability of the equipment material. On the one hand, higher number of stages results to lower energy demand for column K1. On the other hand, a higher number of stages corresponds to higher pressure drop along the packing and therefore higher temperature in the sump and the reboiler of K1, having the disadvantage of higher MMS formation. Thereafter, the thermal stability of equipment material defines the maximum operating temperature allowed for the reboiler and the maximum number of the theoretical stages for K1.

[0090] FIG. 5 illustrates the trade-off between reduction of the specific energy demand and temperature increase in the sump/reboiler for varying number of theoretical stages of K1. The specific energy demand for Design 1-1 could be further reduced to 0.593 MW/tMSA product, if temperatures of up to 194° C. were allowed in the sump of K1. For all cases shown in FIG. 5, the product specifications were achieved, namely with mass fraction of sulfuric acid by 20 ppm, mass fraction of MMS by 100 ppm and mass fraction of water varying between 30 and 36 ppm.

[0091] The energy demand of the designs of type 1 is approximately 26% lower than the energy demand of designs of type C2 and of approximately 52% lower than the energy demand by the designs of type C1, which were both given above in the comparative examples.

[0092] Example 2: In example 2 the operation of the same distillation design as in Example 1 was used, except with a higher H.sub.2SO.sub.4-concentration in the feed. Thus, the H.sub.2SO.sub.4-concentration was varied between 15 and 47 wt.-%. Proposed design according to the present invention operated with a sulfuric-acid rich feed and variation of feed composition regarding sulfuric acid.

TABLE-US-00005 TABLE 5 Composition of sulfuric-acid rich feed to the MSA-purification section Component Mass fraction (wt. %) SO.sub.3 .sup. 0% H.sub.2O 1.0% MBS 0.3% MMS 0.4% MSAA .sup. 0% MSA  53% MDSA 0.3% H.sub.2SO.sub.4 45

[0093] In this example, Design 1-1 was used with sulfuric acid concentration in the feed from 15 to 45 wt.-%. With the designs of type 1 the product specifications could be achieved. FIG. 6 and FIG. 7 show the impact of a variation in the sulfuric acid concentration in the feed on the specific energy demand, the recovery rate of MSA and the product specifications. The energy demand for a concentration of 45 wt.-% sulfuric acid in the feed was approximately 50% higher than for a concentration of 25 wt.-% sulfuric acid in the feed. To obtain a constant production rate of MSA a higher feed rate was used and the reboiler duty was increased. Although with higher sulfuric acid concentrations in the feed the product recovery rate was reduced, but designs of type 1 proved to be robust and the product specifications were achieved in all cases: sulfuric acid 20 ppm-wt, MMS 100 ppm-wt and water from 28 to 46 ppm-wt in the MSA product stream (FIG. 7). Comparing these findings with Eq. 1, it is obvious that the reduction of the recovery rate, was also caused by a dilution of the feed. The current inventive example also showed, that a high MSA concentration in the feed to the distillation was beneficial.

TABLE-US-00006 TABLE 6 Key parameters and performance of the distillation set-up according to the present invention (Design 1) with a variation of the sulfuric acid concentration in the feed to 47 wt.-% Design 1-1 high sulfuric acid concentration (47 wt.-%) Separation First distillation column (K1) for separation of set-up heavy boiling components, second distillation column (K2) for product recovery and third distillation column (K3) for conditioning of the reactor recycle. Distillate of K3 returns to K1 bottoms. MSA-product as liquid or gaseous bottoms residue of K2. Theoretical stages 8 for K1, 4 for K2, 3 for K3 Pressure (mbar) 7 for K1, 10 for K2, 7 for K3 Product quality 99.98% wt. MSA 20 ppm wt. H.sub.2SO.sub.4 43 ppm wt. H.sub.2O 100 ppm wt. MMS MSA MSA 30 wt.-% Concentration bottom stream Bottom T.sub.sump K1 189° C. Temperature T.sub.sump K2 169° C. T.sub.sump K3 186° C. F-Factor F-factor K1 = 2.0 F-factor K2 = 0.6 F-factor K3 = 2.0 MMS formation 19.6 (kg/h) Specific energy 0.991 demand (MW/ tMSA Product) MSA recovery 0.600 rate (kg/kg)

[0094] Example 3: Example 3 shows the performance of the proposed design with a variation of the MMS-concentration in the feed.

TABLE-US-00007 TABLE 7 Composition of feed to the MSA-purification section for variation of the MMS concentration Component Mass fraction (wt. %) SO.sub.3 .sup. 0% H.sub.2O 0.01%  MBS 0.3% MMS 0 to 1%  MSAA .sup. 0% MSA 73.4 to 72.4%    .sup.   MDSA 0.3% H.sub.2SO.sub.4  25%

[0095] The same design of type 1-1, which is shown in FIG. 2 was used in this example and the MMS-concentration in the feed was varied from 0 to 1 wt.-%. It was found that the design according to this invention was robust towards variation of the MMS content in the feed. The separation task and the product specifications were fulfilled over the whole concentration range (Table 8). Furthermore, the specific energy demand and the MSA recovery rate were only slightly changed with the concentration of MMS (FIG. 8).

TABLE-US-00008 TABLE 8 Key parameters and performance of the distillation set-up according to the present invention (Design 1) with a variation of the MMS-concentration in the feed. Design 1-1 Variation MMS-concentration Separation First distillation column (K1) for separation of set-up heavy boiling components, second distillation column (K2) for product recovery and third distillation column (K3) for conditioning of the reactor recycle. Distillate of K3 returns to K1 bottoms. MSA-product as liquid or gaseous bottoms residue of K2. Theoretical stages 8 for K1, 4 for K2, 3 for K3 Design 1-1 Variation MMS-concentration Pressure (mbar) 7 for K1, 10 for K2, 7 for K3 Product quality 99.98 wt.-% MSA 20 ppm wt. H.sub.2SO.sub.4 35 ppm wt. H.sub.2O 100 ppm wt. MMS MSA Concentration MSA 30 wt.-%. bottom stream Bottom T.sub.sump K1 185° C. Temperature T.sub.sump K2 169° C. T.sub.sump K3 186° C. F-Factor F-factor K1 = 1.6 F-factor K2 = 0.5 to 0.6 F-factor K3 = 2.0 MMS formation 10.7 (kg/h) Specific energy 0.622 to 0.633 demand (MW/ tMSA Product) MSA recovery 0.851 to 0.849 rate (kg/kg)

[0096] Example 4: Performance of the proposed design 1-1 according to the present invention (FIG. 2) for a water-free feed with small amounts of SO.sub.3.

TABLE-US-00009 TABLE 9 Composition of water-free feed to the MSA-purification section with small amounts of SO.sub.3. Component Mass fraction (wt. %) SO.sub.3 0.04%  H.sub.2O .sup. 0% MBS 0.3% MMS 0.4% MSAA .sup. 0% MSA  73% MDSA 0.3% H.sub.2SO.sub.4 25.96% 

[0097] In this example the feed comprised SO.sub.3 (assuming in the quenching step of FIG. 1 not all SO.sub.3 is completely converted with water to sulfuric acid). As sulfur trioxide has the highest vapor pressure of all components, it exited the system with the off-gas of distillation column K1. Consequently, the product specifications could be achieved too (Table 10). The product recovery rate was maintained, and design 1 proved to be robust as the separation task was achieved with the same energy demand.

TABLE-US-00010 TABLE 10 Key parameters and performance of the distillation set-up according to the present invention (Design 1) with a water-free feed containing SO.sub.3 Design 1-1 - Water-free feed containing SO.sub.3 Separation First distillation column (K1) for separation of set-up heavy boiling components, second distillation column (K2) for product recovery and third distillation column (K3) for conditioning of the reactor recycle. Distillate of K3 returns to K1 bottoms. MSA-product as liquid or gaseous bottoms residue of K2. Theoretical stages 8 for K1, 4 for K2, 3 for K3 Pressure (mbar) 7 for K1, 10 for K2, 7 for K3 Product quality 99.98 wt.-% MSA 20 ppm wt. H.sub.2SO.sub.4 100 ppm wt. MMS MSA Concentration MSA 30 wt.-% bottom stream Bottom T.sub.sump K1 182° C. Temperature T.sub.sump K2 169° C. T.sub.sump K3 186° C. F-Factor F-factor K1 = 1.5 F-factor K2 = 0.5 F-factor K3 = 2.0 MMS formation 10.7 (kg/h) Specific energy 0.625 demand (MW/ tMSA Product) MSA recovery 0.845 rate (kg/kg)

[0098] As a result, the inventive process leads to a reduction of the energy demand of up to 52%, compared to the designs where MSA product is delivered as a liquid side-discharge above the feed stage (comparative examples 1 and 2). For high side-product concentrations in feed and for a higher MMS formation due to thermal degradation of MSA at a larger hold-up and a residence time higher than 2 hours, designs with up to two functional distillation columns do not guarantee that the product specifications regarding MMS target spec can be achieved (Comparative Example 1). The inventive process is robust against variation of the feed composition, i.e. higher H.sub.2SO.sub.4 mass fraction (up to 47%) (Example 2) and higher concentrations of reaction side-products like MMS (Example 3). Moreover, it was shown, that lower mass fractions of sulfuric acid in the feed were beneficial as the energy demand for the process could be reduced. A high mass fraction of sulfuric acid and/or MMS in the feed to the distillation led to an increase in the specific energy demand and a reduction of the MSA recovery rate. With the invention on hand the formation of thermal degradation products, like MMS, could be limited by keeping the temperature in the bottoms of columns below 185° C. As shown in the examples all product specifications were achieved with this boundary condition. If the temperature in the bottom of the columns was higher, more side products were formed. As discussed above, the inventive process guarantees a stable operation even with higher amounts of side-products. Additionally, the residence time in bottom of the distillation columns could be limited to reduce the formation rate of degradation products, e.g. by reducing the inner diameter of sump of each column compared to the rest of the column.

[0099] Finally, a further object of the present invention is also the use of MSA, obtainable by the inventive process, for cleaning applications, for chemical synthesis or in an electroplating process.