PROCESS FOR THE SEPARATION OF SULPHURIC ACID FROM AQUEOUS MIXTURES THEREOF WITH PARAFFINSULPHONIC ACIDS

Abstract: Sulphuric acid is removed from aqueous mixtures thereof with (C₁₂-C₁₈) alkanesulfonic acids by extracting them with a solvent consisting of a halogenated (C₁-C₂) hydrocarbon.

Description: The present invention relates to a process for the separation of sulphuric acid from aqueous mixtures thereof with paraffin-sulphonic acids. The mixtures from which sulphuric acid must be separated according to the present invention are those which derive from the sulphoxidation of (C₁₂-C₁₈)-n-­ paraffins with SO₂ and O₂ in the presence of water and of U.V. light at a temperature comprised within the range of from 25 to 50°C, after the removal of n-paraffins, which separate spontaneously, and of the excess of SO₂, and after undergoing one of the following treatments: a) dehydration, by known systems, of the residual mixture, at least until said mixture becomes cloudy (due to the formation of a biphasic system), extraction of not-sulphoxidated paraffins from the dehydrated, cloudy mixture, or from the supernatant phase of the biphasic system, with supercritical CO₂ at a temperature comprised within the range of from 32°C to 80°C, under a pressure comprised within the range of from 75 to 350 bars, and with a CO₂/paraffin-­ sulphonic acids weight ratio of from 1/1 to 50/1. b) addition of H₂SO₄ to the residual mixture, at least until said mixture becomes cloudy (due to the formation of a biphasic system), extraction, with supercritical CO₂, from the cloudy mixture or from the supernatant phase of the biphasic system, of the residual paraffins under such conditions as shown under (a); c) addition to the residual mixture of an aliphatic alcohol containing a number of carbon atoms lower than, or equal to, 4, preferably isopropanol, until a biphasic mixture is formed, extraction from said biphasic mixture of the residual paraffins with supercritical CO₂ under such conditions as reported under (a). The mixture of paraffin-sulphonic acids free, or substantially free, from paraffins, obtained by means of the above disclosed treatments from (a) to (c) (the "refined mixture") still contains, besides the paraffin-­ sulphonic acids, a considerable amount of H₂SO₄. The purpose of the process of the present invention is to remove said excess of sulphuric acid. The compositions of the refined mixtures of paraffin-sulphonic acids obtained by means of the methods herein previously mentioned from (a) to (c) are the following: 1) (C₁₂-C₁₈)-Paraffin-sulphonic acids : from 3 to 83% by weight; 2) H₂O : from 79 to 8.5% by weight; 3) H₂SO₄ : from 18 to 8.5% by weight; 4) (C₁₂-C₁₈)-Paraffins: less than 1% relatively to (C₁₂-­ C₁₈)-paraffin-sulphonic acids. Obviously, the starting mixture, even if is obtained by the present Applicants in the above 3 ways, can be obtained in other ways too, so that the present invention should not be considered as being limited to the way in which the starting mixture with the above reported composition is obtained, in as much as the process of the invention can be applied to any mixtures, in whatever way they are obtained, having the above compositions. The process according to the present invention comprises mixing the refined mixture, having the above-­ said compositions, at a temperature comprised within the range of from 10 to 80°C, preferably of from 20 to 50°C, with one or more halogenated solvent(s) selected from those defined by the general formulae (1), (2), (3): wherein at least one of R₁, R₂, R₃, R₄, R₅, R₆ is a halogen, the other R radicals being H, the halogen being fluorine and/or chlorine and/or bromine and/or iodine, with a phase constituted by H₂SO₄ and water being separated from a phase containing the residual refined mixture, optionally mixing the residual refined mixture with H₂SO₄ (ranging from an aqueous H₂SO₄ having a minimum concentration of 70% by weight of H₂SO₄ to concentrated H₂SO₄, or oleum, or even SO₃), at a temperature comprised within the range of from 10°C to 80°C, preferably of from 20°C to 50°C, in such way a second phase, which is constituted by H₂SO₄ and H₂O, being separated from the residual refined mixture, submitting the residual refined mixture to a treatment of separation of the halogenated solvent and/or halogenated solvents, used, in particular by distillation at a temperature lower than 100°C, preferably lower than 50-­ 60°C, still more preferably at least partially under vacuum. The amount of halogenated solvent(s) added depends also on the type of the solvents, and on the composition of the refined mixture, and is anyway such as to make it possible an as large as possible amount of H₂SO₄ to be separated. The optionally added amount of H₂SO₄ is, in case of H₂SO₄ at 96% of concentration, comprised within the range of from 0% to 200% by weight, preferably of from 50% to 150% by weight, relatively to the weight of the paraffin-­ sulphonic acids comprised in the mixture. According to a form of practical embodiment of the process according to the present invention, the halogenated solvent(s) and sulphuric acid can be simultaneously mixed with the refined mixture in a single processing step. Among the halogenated solvents, preferred are methylene chloride, chloroform, carbon tetrachloride and dichloroethane. Residual H₂SO₄, if any, or, partially, H₂SO₄ present before the application of the process according to the present invention, can be removed by being converted into an insoluble product by means of the addition of carbonates, hydroxides or oxides of alkaline-earth metals, in particular, by means of the addition of calcium carbonate, calcium hydroxide or calcium oxide. Some examples are now given for the purpose of better illustrating the invention, it being understood that the same invention has not to be considered as being limited to them or by them. Example 1 To a glass dropping funnel, tightly sealable, 20.47 g is charged of a mixture having the following composition: Paraffin-sulphonic acids : 59.95% by weight (C₁₂-C₁₈)-n-paraffins : 0.22% by weight Water : 28.72% by weight Sulphuric acid : 11.11% by weight which had been obtained by means of the extraction with supercritical CO₂ of the n-paraffins contained in the upper phase of a raw mixture (from which the decantable n-paraffins and SO₂ had been removed) of paraffin-­ sulphonic acids, obtained by means of the sulphoxidation of (C₁₂-C₁₈)-n-paraffins, having the following composition: Paraffin-sulphonic acids : 24.74% by weight (C₁₂-C₁₈)-n-paraffins : 26.46% by weight Water : 40.94% by weight Sulphuric acid : 7.86% by weight after the addition of 20% by weight of H₂SO₄ at 96% by weight, referred to the weight of said raw mixture, as reported under (c) (European Patent Application No.87201344.6) CO₂/paraffinsulphonic acids ratio = 15.5 Extraction pressure = 150 bar Extraction temperature = 45°C Extraction time = 1 hour To the dropping funnel, 30.69 g of CH₂Cl₂ is then added, the dropping funnel is thoroughly shaken for a few minutes, and the phases are allowed to separate. After 3 hours of standing at 22°C, the two separated phases are taken away from each other, and are analysed. The lower phase is constituted by water (55.44% by weight), sulphuric acid (44.02% by weight) and traces of CH₂Cl₂. In the upper phase, all charged paraffin-sulphonic acids are present, together with minor amounts of water, sulphuric acid, n-paraffins, besides CH₂Cl₂. In particular, the content of H₂SO₄ referred to the present paraffin-sulphonic acids, has decreased from 18.5% by weight (before the treatment with CH₂Cl₂) to 8.36% by weight. Also the water content, still referred to paraffin-sulphonic acids, has decreased from 47.9% by weight to 31.7% by weight. Aliquots of the upper phase, obtained by means of the treatment with CH₂Cl₂, as previously disclosed, having the composition: Paraffin-sulphonic acids : 25.92 % by weight (C₁₂-C₁₈)-n-paraffins : 0.094% by weight Water : 8.21 % by weight Sulphuric acid : 2.168% by weight CH₂Cl₂ : the balance to 100 are extracted, inside a dropping funnel, with different amounts of H₂SO₄ at 96% by weight. After the phase separation, at 22°C, the two phases formed are taken away from each other, and analysed. The obtained values are reported in Table 1. Example 2 To a glass dropping funnel, tightly sealable, 217.8 g is charged of the same mixture as used in Example 1. 652.9 g of CH₂Cl₂ is then added. The dropping funnel is thoroughly shaken and the phases are allowed to separate. After standing 24 hours at 22°C, the two separated phases are taken away from each other, and are analysed. The lower phase is constituted by water (50.73% by weight), sulphuric acid (44.03% by weight) and a small amount of CH₂Cl₂. In the upper phase, all charged paraffin-sulphonic acids are present, together with minor amounts of water, sulphuric acid, n-paraffins, besides CH₂Cl₂. In particular, the content of sulphuric acid, referred to the present paraffin-sulphonic acids, has decreased from 18.5% by weight (before the treatment with CH₂Cl₂) to 7.49% by weight. Also the water content, still referred to the present paraffin-sulphonic acids, has decreased from 47.9% by weight to 30% by weight. Aliquots of the upper phase, obtained by means of the treatment with CH₂Cl₂, as previously disclosed, having the composition: Paraffin-sulphonic acids : 16.535% by weight (C₁₂-C₁₈)-n-paraffins : 0.060% by weight Water : 4.96 % by weight Sulphuric acid : 1.238% by weight CH₂Cl₂ : the balance to 100 are extracted, inside a dropping funnel, with different amounts of H₂SO₄ at 96% by weight. After the phase separation, at 22°C, the two phases formed are separated from each other, and analysed. The obtained values are reported in Table 2. Example 3 To a dropping funnel, tightly sealable, 22.45 g is charged of the same mixture as used in Example 1. 224.35 g of CH₂Cl₂ is added. The dropping funnel is thoroughly shaken and the phases are allowed to separate. After standing 24 hours at 22°C, the two separated phases are taken away from each other, and are analysed. The lower phase is constituted by water (53.51% by weight), sulphuric acid (42.48% by weight) and minor amounts of CH₂Cl₂. In the upper phase, all charged paraffin-sulphonic acids are present, together with minor amounts of water, sulphuric acid, n-paraffins, besides CH₂Cl₂. In particular, the content of sulphuric acid, referred to the present paraffin-sulphonic acids, has decreased from 18.5% by weight (before the treatment with CH₂Cl₂) to 6.36% by weight. Also the water content, still referred to the present paraffin-sulphonic acids, has decreased from 47.9% by weight to 33.0% by weight. Aliquots of the upper phase, obtained by means of the treatment with CH₂Cl₂, having the composition: Paraffin-sulphonic acids : 5.584% by weight (C₁₂-C₁₈)-n-paraffins : 0.020% by weight Water : 1.840% by weight Sulphuric acid : 0.355% by weight CH₂Cl₂ : the balance to 100 are extracted, inside a dropping funnel, with different amounts of H₂SO₄ at 96% by weight. After the phase separation, at 22°C, the two phases formed are separated from each other, and analysed. The obtained values are reported in Table 3. Example 4 To a dropping funnel, tightly sealable, withstanding moderate pressures, 16.1 g is charged of the same mixture as used in Example 1. 48.6 g of CH₂Cl₂ is added. The dropping funnel is thoroughly shaken and is placed inside an oven maintained at the controlled temperature of 40°C. After 30 minutes, the dropping funnel is thoroughly shaken once more inside the oven. The phases are allowed to separate. After standing 16 hours at 40°C, the lower phase is removed, with the dropping funnel being kept inside the oven. The funnel containing the upper phase is removed from the oven, and is cooled to room temperature. The two phases are analysed. The lower phase is constituted by water (53.47% by weight), sulphuric acid (42.90% by weight) and minor amounts of CH₂Cl₂. In the upper phase, all charged paraffin-sulphonic acids are present, together with minor amounts of water, sulphuric acid, n-paraffins, besides CH₂Cl₂. In particular, the content of sulphuric acid, referred to the present paraffin-sulphonic acids, has decreased from 18.5% by weight (before the treatment with CH₂Cl₂) to 5.58% by weight. Also the water content, still referred to the present paraffin-sulphonic acids, has decreased from 47.9% by weight to 27.22% by weight. Aliquots of the upper phase, obtained by means of the treatment with CH₂Cl₂, having the composition: Paraffin-sulphonic acids : 15.98 % by weight (C₁₂-C₁₈)-n-paraffins : 0.058% by weight Water : 4.35 % by weight Sulphuric acid : 0.892% by weight CH₂Cl₂ : the balance to 100 are extracted, inside a tightly sealable dropping funnel withstanding moderate pressures, with different amounts of H₂SO₄ at 96% by weight, by operating at 40°C inside an oven. After the phase separation, at 40°C, the lower phase is removed, by operating inside the oven. The funnel is then removed from the oven, and is made cool to room temperature. The two phases are analysed. The obtained values are reported in Table 4. Example 5 To a dropping funnel, tightly sealable, withstanding moderate pressures, 23.0 g is charged of the same mixture of paraffin-sulphonic acids as used in Example 1. 142.6 g of CH₂Cl₂ is added, and the dropping funnel is thoroughly shaken. The dropping funnel is then placed inside an oven maintained at the controlled temperature of 40°C. After 1 hour, the dropping funnel is thoroughly shaken once more, by operating inside the oven. The phases are allowed to separate. After standing 26 hours at 40°C, the lower phase is removed from the interior of the oven. The funnel containing the upper phase is removed from the oven, and is allowed to cool down to room temperature. The two phases are analysed. The lower phase (4.4391 g) is constituted by water (56.66% by weight), sulphuric acid (43.08% by weight) and minor amounts of CH₂Cl₂. In the upper phase (160.8172 g), all of the charged paraffin-sulphonic acids are present, together with minor amounts of water, sulphuric acid, n-paraffins, besides CH₂Cl₂. In particular, the content of sulphuric acid, referred to the present paraffin-sulphonic acids, has decreased from 18.5% by weight (before the treatment with CH₂Cl₂) to 4.84% by weight. Also the water content, still referred to the present paraffin-sulphonic acids, has decreased from 47.9% by weight to 28.11% by weight. To 148.1 g of the upper phase, inside a dropping funnel resistant to moderate pressures, 11.5 g of H₂SO₄ at 96% by weight is charged. The dropping funnel is thoroughly shaken, and is placed inside an oven maintained at the controlled temperature of 40°C. After 1 hour, the dropping funnel is thoroughly shaken once more and is then left standing 4 hours at 40°C. By operating inside the oven, the lower phase (15.2294 g) is removed. The funnel containing the upper phase (143.9 g) is removed from the oven, and is allowed to cool down to room temperature. The two phases are analysed. The lower phase contains water (25.5% by weight), sulphuric acid (73.6% by weight), together with minor amounts of CH₂Cl₂ (the balance to 100%), and does not contain paraffin-sulphonic acids. The upper phase has the following composition: Paraffin-sulphonic acids : 9.07 % by weight (C₁₂-C₁₈)-n-paraffins : 0.033% by weight Water : 0.230% by weight Sulphuric acid : 0.198% by weight CH₂Cl₂ : the balance to 100 The H₂SO₄/paraffin-sulphonic acids ratio results to be 2.18%; the water/paraffin-sulphonic acids ratio results to be 2.54%. 134 g of this upper phase is fed, in continuous mode, to a rotary evaporator operating under a slight vacuum (120-130 mm Hg ), and with the temperature of the heating bath being of 50-55°C. When all of the product has been fed, and approximately the total amount of CH₂Cl₂ has evaporated, the vacuum is increased up to 700 mm Hg . The whole process step lasts about 1 hour. The residual product remaining inside the kettle of the rotary evaporator is a thin liquid essentially constituted by paraffin-sulphonic acids, with 1.585% by weight of H₂O, 2.182% by weight of H₂SO₄ and 0.360% by weight of (C₁₂-C₁₈)-n-paraffins. The distribution of monosulphonic, disulphonic and trisulphonic acids found in the concentrated end product results to be the same as found in the raw mixture of paraffin-sulphonic acids downstream the sulphoxidation reactor. Example 6 By operating at 22°C, and using the same mixture of paraffin-sulphonic acids as used in Example 1, tests of purification of the paraffin-sulphonic acids from sulphuric acids, using different solvents, were carried out. The results obtained are shown in Table 5. It can be observed how only the halogenated solvents supply interesting results. Example 7 To a tightly sealable test tube, 7.4428 g is charged of the same mixture of paraffin-sulphonic acids as used in Example 1. 14.7382 g of CHCl₃ is added. The test tube is thoroughly shaken, and is then left standing at 23°C for 6.5 hours, and is then centrifuged, to favour the phase separation. The two phases are taken away from each other, and are analysed. The lower phase (1.3330 g) is essentially constituted by water (57.5% by weight) and sulphuric acid (42.46% by weight). In the upper phase (20.7284 g), all of the charged paraffin-sulphonic acids are present, together with minor amounts of water, sulphuric acid, n-paraffins, besides CHCl₃. In particular, the content of sulphuric acid, referred to the present paraffin-sulphonic acids, has decreased from 18.5% by weight (before the treatment with CHCl₃) to 5.74% by weight. Also the water content, still referred to the present paraffin-sulphonic acids, has decreased from 47.9% by weight to 29.35% by weight. To 10.5305 g of the beforehand separated upper phase, 2.0448 g of H₂SO₄ at 96% by weight is charged. The test tube is thoroughly shaken, and is left standing at 23°C. After 7 hours, the two phases are taken away from each other, and are analysed. The lower phase contains water (25.08% by weight), sulphuric acid (73.44% by weight), together with a small amount of CHCl₃, and does not contain paraffin-sulphonic acids. The upper phase has the following composition: Paraffin-sulphonic acids : 22.75 % by weight (C₁₂-C₁₈)-n-paraffins : 0.082% by weight Water : 0.80 % by weight Sulphuric acid : 0.686% by weight CH₂Cl₂ : the balance to 100 The H₂SO₄/paraffin-sulphonic acids ratio result to be 3.02%; the water/paraffin-sulphonic acids ratio results to be 3.52%.

Claims: 1. Process for the separation of sulphuric acid from aqueous mixtures thereof with (C₁₂-C₁₈)-paraffin-­ sulphonic acids, wherein said mixtures contain an amount of (C₁₂-C₁₈)-paraffin-sulphonic acids comprised within the range of from 3 to 83% by weight; an amount of water comprised within the range of from 8.5 to 79% by weight; an amount of H₂SO₄ comprised within the range of from 8.5 to 18% by weight; and an amount of (C₁₂-C₁₈)-n-­ paraffins smaller than 1% by weight, relatively to the weight of (C₁₂-C₁₈)-paraffin-sulphonic acids, characterized in that said mixtures are mixed, at a temperature comprised within the range of from 10 to 80°C, with one or more halogenated solvent(s) selected from those defined by the general formulae (1), (2), (3): wherein at least one of R₁, R₂, R₃, R₄, R₅ and R₆ is a halogen, the other R radicals being H, with a phase constituted by H₂SO₄ and H₂O being separated from a phase containing the residual mixture, the residual mixture is optionally mixed with H₂SO₄ in such way a second phase, which is constituted by H₂SO₄ and H₂O, being separated from the remainder of the mixture, the remainder of the mixture being submitted to a treatment of separation of the halogenated solvent and/or of the halogenated solvents used. 2. Process according to claim 1, characterized in that the halogenated solvent is selected from chloroform, methylene chloride, carbon tetrachloride and dichloroethane. 3. Process according to claim 1, characterized in that the H₂SO₄ used in the optional mixing is mixed at a temperature comprised within the range of from 10 to 80°C. 4. Process according to claim 3, characterized in that H₂SO₄ is aqueous H₂SO₄ having a minimum concentration of 70% of H₂SO₄. 5. Process according to claim 3, characterized in that H₂SO₄ is concentrated H₂SO₄ in particular H₂SO₄ at 96%. 6. Process according to claim 3, characterized in that H₂SO₄ is oleum. 7. Process according to claim 3, characterized in that H₂SO₄ is used in the form of SO₃. 8. Process according to claims 1 and 3, wherein the temperature is comprised within the range of from 20 to 50°C. 9. Process according to claim 1, characterized in that the treatment of separation, to remove the halogenated solvent, or solvents, is carried out by distillation at a temperature lower than 100°C, preferably lower than 50-60°C. 10. Process according to claims 1 and 9, characterized in that the treatment of removal of the halogenated solvent(s) is carried out under vacuum. 11. Process according to claim 1, characterized in that the halogenated solvent(s) and sulphuric acid are simultaneously admixed to the mixture of paraffin-­ sulphonic acids in one single step. 12. Process according to claim 1, characterized in that H₂SO₄ still present inside the end mixture of paraffin-sulphonic acids is removed by insolubilization, carried out by means of the addition of carbonates, hydroxides or oxides of alkaline-earth metals.

Inventors: BORGARELLO, ENRICO, CARRILLO, GERARDO, FAGGIAN, LUCIO, FRANCO, COSIMO
Applicants: ENICHEM AUGUSTA S.P.A., ENIRICERCHE S.P.A.
Application year: 1987
Main classification: C07C303
IPC codes: C07C309, B01D3, B01D11, C07C67, C01B17, C07C303, B01D12, C07C301