Process for extracting paraffins from their mixtures with paraffinsulfonic acids
This invention relates to a process for extracting n-paraffins from their mixtures with paraffinsulfonic acids. 
     Paraffinsulfonic acids containing between 12 and 18 carbon atoms are generally prepared by sulfoxidation of C 12  -C 18  paraffins with sulfur dioxide (SO 2 ) and oxygen (O 2 ) in the presence of water (H 2  O), using ultraviolet (UV) radiation for reaction initiation. 
     The reaction product obtained from the sulfoxidation reaction consists of a mixture containing small percentages of paraffinsulfonic acids, H 2  O and sulfuric acid (H 2  SO 4 ), but mostly unreacted n-paraffins. 
     Most of the n-paraffins can be easily separated from said mixture, but a substantial fraction of them will remain together with the H 2  SO 4 , the H 2  O and the paraffinsulfonic acids. It is important to note that the n-paraffins must be separated to the maximum possible extent not only for obvious economic reasons, but also because their presence in paraffinsulfonic acids is undesirable. 
     The known art gives suggestions for separating n-paraffins from the rest of the H 2  SO 4 , paraffinsulfonic acid and H 2  O mixture. One of these suggestions is contained in European patent application No. 131913, in particular in Example 1. In No. 131913, Example 1, the mixture containing paraffinsulfonic acids, unreacted n-paraffins, H 2  O and H 2  SO 4  is treated with isopropanol in a quantity of 15%, to separate the mixture into three distinct phases; the upper one essentially consisting of n-paraffins, the lower one consisting of H 2  O, H 2  SO 4  and isopropanol, and the intermediate one containing paraffinsulfonic acids, H 2  SO 4 , H 2  O, n-paraffins and isopropanol. 
     The intermediate phase is then mixed with methylene chloride to separate an aqueous H 2  SO 4  phase containing isopropanol and a little methylene chloride from a phase containing paraffinsulfonic acids, n-paraffins, H 2  O, methylene chloride and H 2  SO 4 . It is neutralized with soda and concentrated. Finally it is heated to a temperature of 200° C. to distill off the n-paraffins. 
     This procedure for removing the n-paraffins is obviously complicated, and notwithstanding its various extraction stages it is still necessary to use high-temperature vaporization at the end, which in all cases damages the product obtained. 
     With the known process it is therefore not possible to prepare free paraffinsulfonic acids or their salts with weak bases, as these are unstable at high temperature. 
     It has been surprisingly found that the previously described drawbacks of the known art regarding the separation of n-paraffins can be obviated in a simple manner by adding H 2  SO 4  to the mixture of paraffinsulfonic acids, H 2  SO 4 , H 2  O and paraffins until a two-phase system forms or at least until the mixture becomes turbid. Then the turbid mixture or the supernatant phase of the two-phase system is extracted with carbon dioxide (CO 2 ) under supercritical conditions. 
     The present invention provides a process for removing n-paraffins containing between 12 and 18 carbon atoms from mixtures of said n-paraffins with paraffinsulfonic acids having the same number of carbon atoms, H 2  O and H 2  SO 4 . The mixtures are obtained by sulfoxidation of C 12  -C 18  n-paraffin mixtures at a temperature of between 25° and 50° C. with SO 2  and O 2  in the presence of H 2  O and UV radiation. Excess SO 2 , is removed if present, from the reaction mixture originating from the paraffinsulfonic acid synthesis reaction. The mixture is decanted to remove most of the C 12  -C 18  n-paraffins. The characteristic of the process is that the residual mixture obtained after removing the SO 2  and the decanted paraffins is fed with H 2  SO 4  until a two-phase system forms, or at least until the residual mixture becomes turbid. The turbid mixture or the supernatant phase of the two-phase system is then extracted with supercritical CO 2 . 
     With regard to the quality of H 2  SO 4  used according to the invention to form the two-phase system, this can be oleum, concentrated H 2  SO 4  or H 2  SO 4  diluted with H 2  O to a minimum H 2  SO 4  concentration of 20% by weight. With regard to the formation of the two-phase system due to the addition of H 2  SO 4 , it commences with the mixture becoming turbid and proceeds as further H 2  SO 4  is added, to give sharp separation of a heavy phase consisting of H 2  O and H 2  SO 4  from a supernatant phase. 
     The mixture to be subjected to extraction with supercritical CO 2  is either the turbid mixture formed by adding the minimum quantity of H 2  SO 4  or the supernatant mixture after separation from the heavy mixture of H 2  SO 4  and H 2  O obtained by adding H 2  SO 4  in a quantity exceeding the minimum, this latter as stated being that required to cause mixture turbidity. With 96% H 2  SO 4 , the weight ratio of H 2  SO 4  to residual mixture can attain a value of 1:1 or higher. 
     With regard to the conditions under which the turbid or aforesaid supernatant mixture is extracted with supercritical CO 2 , these are as follows: 
     
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Extraction temperature:                                                   
                   between 32 and 80° C.                           
Extraction pressure:                                                      
                   between 75 and 350 bar                                 
Weight ratio of CO.sub.2 used for extraction to                           
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     The paraffinsulfonic acid mixture resulting from the process according to the present invention is then generally neutralized in known manner using chosen bases to thus obtain paraffin sulfonates of any desired type. 
     The H 2  SO 4  contained in the mixture resulting from the process of the present invention, in the case of extraction of the supernatant phase with supercritical CO 2 , is less in quantity than that present before the treatment and can be separated, if required, by methods known in the art, such as mixing with suitable substances or precipitation to form insoluble salts. Some examples are given hereinafter to better illustrate the invention, but without intending to limit it thereto or thereby. 
    
    
     EXAMPLE 1 
     A laboratory extraction apparatus was used consisting essentially of an extraction vessel into which the mixture containing the product to be extracted with supercritical CO 2  was fed, and a separator from which the CO 2 , separated from the extracted substance, was recycled to the extractor by a metering pump after condensation. 
     401.0 g of crude mixture (with decantable n-paraffins and SO 2  removed) of paraffinsulfonic acids obtained by sulfoxidation of C 12  -C 18  n-paraffins, and having the following composition: 
     
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paraffinsulfonic acids                                                    
                    24.74% by weight                                      
C.sub.12 -C.sub.18 n-paraffins                                            
                    26.46% by weight                                      
H.sub.2 O           40.94% by weight                                      
H.sub.2 SO.sub.4     7.86% by weight                                      
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     were treated with 80.0 g of 96 wt % H 2  SO 4  at ambient temperature in a separator funnel. 
     After decantation, two phases were separated. The lower phase (213.5 g) consisted of H 2  O and H 2  SO 4  ; the upper phase (267.5 g) contained all the n-paraffins and paraffinsulfonic acids present in the feed, together with H 2  O and H 2  SO 4 . 
     105.8 g of the upper phase product were extracted with supercritical CO 2 . 
     The extraction was effected at 45° C. at 150 bar; the CO 2  throughput was maintained constant at 1.72 kg/h. After one hour, the CO 2  feed was interrupted and the refined product contained in the extractor was discharged. 
     Analysis of this product gave the following results: 
     
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paraffinsulfonic acids                                                    
                    62.29% by weight                                      
C.sub.12 -C.sub.18 n-paraffins                                            
                     0.11% by weight                                      
H.sub.2 O           26.47% by weight                                      
H.sub.2 SO.sub.4    11.13% by weight                                      
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     The extracted n-paraffins are practically pure and can be recycled to the sulfoxidation reaction without any treatment. 
     EXAMPLE 2 
     3149.7 g of a crude mixture (as heretofore defined) of paraffinsulfonic acids having the composition indicated in Example 1 were treated with 158.1 g of 96 wt % H 2  SO 4 . After separating the lower phase (92.6 g) consisting of H 2  O and H 2  SO 4 , the upper phase was again treated with 96 wt % H 2  SO 4  (161.1 g). A lower phase was separated (827.2 g) consisting of H 2  O and H 2  SO 4 , and the upper phase was again treated with 160.3 g of 96 wt % H 2  SO 4 . A lower phase was separated (392.4 g) consisting of H 2  O and H 2  SO 4  sulphuric acid. The resultant upper phase (1918.1 g) was extracted with supercritical CO 2 . Fifteen extraction tests were carried out, feeding about 120 g of product into the extractor for each test. 
     Extraction was effected at 45° C., 150 bar, with a CO 2  throughput of 1.72 kg/h and an extraction time of 2 hours. After each test the refined product and the extracted paraffins are discharged, and the extractor was fed with a new charge of material to be extracted. 
     The refined products and extracts of all the 15 tests were pooled and analysed. 
     Analysis of the refined product gave the following values: 
     
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paraffinsulfonic acids                                                    
                    69.73% by weight                                      
C.sub.12 -C.sub.18 n-paraffins                                            
                     0.55% by weight                                      
H.sub.2 O           19.58% by weight                                      
H.sub.2 SO.sub.4    10.14% by weight                                      
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     EXAMPLE 3 
     200.2 g of a crude mixture (as heretofore defined) of paraffinsulfonic acids having the composition indicated in Example 1 were treated at ambient temperature with 32.2 g of 96 wt % H 2  SO 4 . 
     After separating the lower phase (88.8 g), a fraction of the upper phase (102.5 g) was extracted with supercritical CO 2  under the conditions described in Example 2. 
     Analysis of the refined product gave the following values: 
     
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paraffinsulfonic acids                                                    
                    60.55% by weight                                      
C.sub.12 -C.sub.18 paraffins                                              
                     0.09% by weight                                      
H.sub.2 O           27.77% by weight                                      
H.sub.2 SO.sub.4    11.59% by weight                                      
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     EXAMPLE 4 
     199.9 g of a crude mixture (as heretofore defined) of paraffinsulfonic acids having the composition indicated in Example 1 were treated at ambient temperature with 16.75 g of 96 wt % H 2  SO 4 . 
     A lower phase was separated (45.4 g) consisting of H 2  O and H 2  SO 4 , and the upper phase containing all the paraffinsulfonic acids and paraffins present in the initial crude mixture was extracted with supercritical CO 2  under the conditions described in Example 2. 
     Analysis of the refined product gave the following values: 
     
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paraffinsulfonic acids                                                    
                    43.98% by weight                                      
C.sub.12 -C.sub.18 paraffins                                              
                     0.07% by weight                                      
H.sub.2 O           39.89% by weight                                      
H.sub.2 SO.sub.4    16.06% by weight                                      
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     EXAMPLE 5 
     96 wt % H 2  SO 4  was added to 200.3 g of a crude mixture (as heretofore defined) of paraffinsulfonic acids having the composition indicated in Example 1 and kept under efficient agitation at 22° C., until persistent turbidity was obtained at 22° C. 
     The quantity of H 2  SO 4  added was 9.65 g. 114.6 g of this mixture were extracted with supercritical CO 2  under the conditions described in Example 2. 
     Analysis of the refined product gave the following values: 
     
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paraffinsulfonic acids                                                    
                    33.72% by weight                                      
C.sub.12 -C.sub.18 n-paraffins                                            
                     0.28% by weight                                      
H.sub.2 O           50.12% by weight                                      
H.sub.2 SO.sub.4    15.88% by weight                                      
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     EXAMPLE 6 
     96 wt % H 2  SO 4  was added to 200.5 g of a crude mixture (as heretofore defined) of paraffinsulfonic acids having the composition indicated in Example 1 and kept under efficient agitation at 45° C., until persistent turbidity was obtained at 45° C. 
     The quantity of H 2  SO 4  added was 6.10 g. 119.25 g of this mixture were extracted with supercritical CO 2   under the conditions described in Example 2. 
     Analysis of the refined product gave the following values: 
     
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paraffinsulfonic acids                                                    
                    33.53% by weight                                      
C.sub.12 -C.sub.18 n-paraffins                                            
                     1.49% by weight                                      
H.sub.2 O           49.38% by weight                                      
H.sub.2 SO.sub.4    15.60% by weight                                      
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     EXAMPLE 7 
     200.1 g of a crude mixture (as heretofore defined) of paraffinsulfonic acids having the composition indicated in Example 1 were treated at ambient temperature with 54.6 g of 70% H 2  SO 4  (aqueous solution). A lower phase was separated (107.5 g) consisting of H 2  O and H 2  SO 4 . 
     127.2 g of the upper phase were extracted with supercritical CO 2  under the conditions described in Example 2. 
     Analysis of the refined product gave the following values: 
     
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paraffinsulfonic acids                                                    
                    58.185% by weight                                     
C.sub.12 -C.sub.18 n-paraffins                                            
                     0.025% by weight                                     
H.sub.2 O           29.680% by weight                                     
H.sub.2 SO.sub.4    12.110% by weight                                     
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     EXAMPLE 8 (Comparative example without H 2  SO 4  addition) 
     76.1 g of a crude mixture (as heretofore defined) of paraffinsulfonic acids having the composition indicated in Example 1 were extracted with supercritical CO 2  under the conditions described in Example 2. 
     Analysis of the refined product gave the following values: 
     
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paraffinsulfonic acids                                                    
                    33.33% by weight                                      
C.sub.12 -C.sub.18 paraffins                                              
                     8.99% by weight                                      
H.sub.2 O           47.11% by weight                                      
H.sub.2 SO.sub.4    10.60% by weight                                      
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     In this case the paraffin extraction was found to be totally insufficient. 
     EXAMPLES 9-16 (Comparative examples without H 2  SO 4  addition) 
     The crude mixture (as heretofore defined) of paraffinsulfonic acids having the composition indicated in Example 1 was extracted with supercritical CO 2  under various operating conditions. The operating conditions used and the results of the analyses carried out on the refined products are given in Table 1. 
     
                                           TABLE 1                                 
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                                         ANALYSIS OF REFINED              
MIX-                                     PRODUCT % WT                     
EXAM-                                                                     
     TURE                                                                 
         EXTRACTION                                                       
                  EXTRACTION                                              
                           EXTRACTION                                     
                                    CO.sub.2                              
                                         PARAFFIN-        SUL-            
PLE  FED TEMP.    PRESSURE TIME     RATE SULFONIC                         
                                                PARAF-    FURIC           
No.  g   °C.                                                       
                  bar      hours    kg/h ACIDS  FINS WATER                
                                                          ACID            
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 9   124.1                                                                
         33       300      1        1.07 28.74  18.56                     
                                                     43.79                
                                                           8.91           
10   125.2                                                                
         35       150      1        1.80 27.80  14.84                     
                                                     46.84                
                                                          10.52           
11   125.9                                                                
         40       150      1        1.80 28.65  11.55                     
                                                     49.70                
                                                          10.10           
12   124.2                                                                
         40       150      3        1.80 31.99  11.37                     
                                                     45.94                
                                                          10.70           
13   124.3                                                                
         40       300      2        1.40 29.50  11.22                     
                                                     48.67                
                                                          10.61           
14   123.9                                                                
         45       200      1        1.46 31.40  11.95                     
                                                     46.78                
                                                           9.87           
15   124.3                                                                
         50       350      1        1.11 32.82   8.20                     
                                                     48.50                
                                                          10.48           
16   124.2                                                                
         86       300      2        1.07 43.80   2.21                     
                                                     45.18                
                                                           8.81           
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