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 and a cosolvent consisting of an alcohol or ether.

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 being submitted to 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 complying with 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 two phases being formed, one of which is essentially organic, and the other is constituted by H₂SO₄ and H₂O; to the two phases, together with each other, at least one cosolvent is added, which is selected from the class of the lower, saturated, linear or branched alcohols with from 1 to 6 carbon atoms, or of the lower, linear, branched or cyclic or possibly substituted aliphatic ethers with a number of carbon atoms comprised within the range of from 2 to 10, with the separation being obtained of a phase which is constituted by H₂SO₄ and H₂O, which is removed. The residual organic phase, practically free from H₂SO₄, is submitted to the removal of the solvents and cosolvents, 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. Relatively to the refined mixture, the amount of solvent is in a weight ratio comprised within the range of from 0.5/1 to 5/1, and the amount of cosolvent is, relatively to the refined mixture, in a weight ratio comprised within the range of from 0.3/1 to 2/1. The temperature at which the cosolvent is added is comprised within the range of from 10 to 80°C, preferably of from 20 to 50°C. According to a form of practical embodiment of the process according to the present invention, the halogenated solvent(s) and the cosolvent can be simultaneously mixed with the refined mixture in a single step. Among the halogenated solvents preferred are methylene chloride, chloroform, carbon tetrachloride and dichloroethane. Among alcohols, preferred are methanol, ethanol, propanol, isopropanol, butanols, pentanols, and among ethers, preferred are dimethyl-ether, diethyl-ether, dipropyl-ether, diisopropyl-ether, methyl-tert.-butyl-­ ether, tetrahydrofuran and mono-, di-, tri- and tetra-­ methyl-hydrofurans. 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 the addition of calcium carbonate, hydroxide or oxide. Some examples are now given for the purpose of better illustrating the invention, it being understood that it has not to be considered as being limited to them or by them. Example 1 To a large glass test tube, tightly sealable, 2.1012 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 It 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 extraction with 20% by weight of H₂SO₄ at 96% by weight, referred to the weight of said raw mixture, as reported in European Patent Application No. 87 201 344.6. The above-said mixture, having an H₂SO₄/paraffin-­ sulphonic acids weight ratio of 18.5%, is treated, at room temperature (20-22°C) with 1.9013 g of H₂O, and subsequently, with 6.4562 g of methylene chloride. The mixture is intensely shaken for a few minutes, and is left standing for half an hour. Thus, two phases separate from each other, the upper of which contains all of the paraffin-sulphonic acids together with water, sulphuric acid, the initially present n-paraffins and methylene chloride; and the lower phase contains a few methylene chloride, water and sulphuric acid. In particular, the content of sulphuric acid, referred to the paraffin-sulphonic acids in the upper phase, is reduced from 18.5% to 11%. Subsequently, without separating the phases, 1,3401 g of ethyl alcohol is added, the test tube is intensely shaken and is left standing for half an hour. The lower phase contains all of the paraffin-­ sulphonic acids together with a few water, the initially present n-paraffins, methylene chloride and ethyl alcohol, and the upper phase contains sulphuric acid, water and ethyl alcohol. From the analyses, the weight ratio of sulphuric acid/paraffin-sulphonic acids, in the organic phase, results to have been reduced from 11% to 1.5%. Example 2 1.9173 g of a mixture having the same composition as used in Example 1, is treated, at room temperature (20-­ 22°C) with 1.7349 g of H₂O, and subsequently, with 8.6370 g of a (3:1 by weight) methylene chloride/ethyl alcohol mixture. The whole mixture is intensely shaken and is centrifuged for 15 minutes. The lower phase contains all of the paraffin-sulphonic acids together with a few water, the initially present n-paraffins, methylene chloride and ethyl alcohol; and the upper phase contains sulphuric acid, water and ethyl alcohol. From the analyses, the weight ratio of sulphuric acid/paraffin-sulphonic acids, in the organic phase, results to have been decreased from 18.5% to 1.8%. Example 3 20.85 g of a mixture having the same composition as used in Example 1, is treated, at room temperature (23°C) with 18.85 g of H₂O, with 64.00 g of methylene chloride, and with 13.30 g of ethanol. The mixture is intensely shaken and is centrifuged for 15 minutes. The lower phase contains all of the paraffin-­ sulphonic acids together with a few water, the initially present n-paraffins, methylene chloride and ethyl alcohol; and the upper phase contains sulphuric acid, water and ethyl alcohol. The two phases are separated from each other. The lower phase is evaporated inside a rotary evaporator, so as to distill off all of the solvents, by operating with the heating bath being kept at 70°C (75°C during the last 5 minutes), and under a progressively increasing vacuum up to 750 mm Hg during the end step. The distillation residue is a thin liquid essentially constituted by paraffin-sulphonic acids, 4.91% by weight of H₂O, 1.84% by weight of H₂SO₄ and 0.337% by weight of (C₁₂-C₁₈)-n-paraffins. The distribution of monosulphonic, disulphonic and trisulphonic acids in the concentrated end product results to be the same as of the raw mixture of paraffin-­ sulphonic acids downstream the sulphoxidation reactor. Examples 4 to 21 By operating according to the same modalities as reported in the preceding Examples, different tests were carried out, with the solvent and the cosolvent being varied both in type and in amount. All the tests were carried out by using the mixture of paraffin-sulphonic acids as used in Example 1. The results obtained are shown in the following Table.

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 (C₁₂-­ C₁₈)-paraffin-sulphonic acids, characterized in that said mixtures, possibly diluted with water, 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 complying with 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 two phases being formed, one of which is essentially organic, and the other is constituted by H₂SO₄ and H₂O; to the two phases, together with each other, at least one cosolvent is added, which is selected from the class of the lower, saturated, linear or branched alcohols with from 1 to 6 carbon atoms, or of the lower, linear, branched or cyclic aliphatic, possibly substituted, ethers with a number of carbon atoms comprised within the range of from 2 to 10, with the separation being obtained of a phase which is constituted by H₂SO₄ and H₂O, which is removed, and the residual organic phase is submitted to the removal of the solvents and cosolvents. 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 cosolvent is selected from methanol, ethanol, 1-propanol, isopropanol, butanols, pentanols, dimethyl-­ ether, diethyl-ether, dipropyl-ether, diisopropyl-ether, methyl-tert.-butyl-ether, tetrahydrofuran and mono-, di-, tri- and tetra-methyl-hydrofurans. 4. Process according to claim 1, characterized in that the cosolvents are added to the mixture of paraffin-­ sulphonic acids and H₂SO₄ at a temperature comprised within the range of from 10 to 80°C. 5. Process according to claim 1, characterized in that the weight ratio of the solvent or solvents to the refined mixture is comprised within the range of from 0.5/1 to 5/1. 6. Process according to claim 1, characterized in that the weight ratio of the cosolvent to the refined mixture is comprised within the range of from 0.3/1 to 2/1. 7. Process according to claims 1 and 4 weherein the temperature is comprised within the range of from 20 to 50°C. 8. Process according to claim 1, characterized in that the removal of the solvents and cosolvents is carried out by distillation at a temperature lower than 100°C, preferably lower than 50-60°C. 9. Process according to claims 1 and 8, characterized in that the removal of the solvents and cosolvents is carried out under vacuum. 10. Process according to claim 1, characterized in that the halogenated solvent or solvents and the cosolvents are simultaneously admixed to the mixture of paraffin-sulphonic acids in one single step. 11. 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, FAGGIAN, LUCIO, FRANCO, COSIMO, PLATONE, EDOARDO
Applicants: ENICHEM AUGUSTA S.P.A., ENIRICERCHE S.P.A.
Application year: 1987
Main classification: C07C309
IPC codes: C07C309, C07C303, C07C301, B01D12, C07C67, B01D17, C01B17