Abstract:
Process for the purification of a hydrocarbon stream by removing contaminating compounds contained in the hydrocarbon stream by contact with a solid adsorbent material and withdrawing a purified hydrocarbon stream, the improvement of which comprises passing the hydrocarbon stream through a first zone of the adsorbent material having supported thereon a fluorinated sulphonic acid and subsequently through zone of the adsorbent material.

Description:
FIELD OF INVENTION 
     The present invention relates to a process for the purification of a hydrocarbon stream by contacting the stream in presence of an acid with a solid adsorbent material and adsorbing impurities in the hydrocarbon stream on the adsorbent material. 
     BACKGROUND OF THE INVENTION 
     It is known that impurities can be removed from different media by adsorption treatment in a fixed bed of solid adsorbents (U.S. Pat. No. 5,360,547, U.S. Pat. No. 5,220,099, U.S. Pat. No. 4,677,231). Use of sulphonic acid containing activated carbon in the removal of organic cations from polar liquids is, furthermore, disclosed in U.S. Pat. No. 4,968,433. 
     SUMMARY OF THE INVENTION 
     It has now been found that impurities can be removed efficiently from a non-polar hydrocarbon stream by contacting the stream with solid adsorbent material having supported thereon a fluorinated sulphonic acid. 
     Based on the above finding, this invention provides an improved process for the purification of a hydrocarbon stream by removing contaminants contained in the hydrocarbon stream by contact with a solid adsorbent material and withdrawing a purified hydrocarbon stream, the improvement of which comprises passing the hydrocarbon stream through a first zone of the adsorbent material having supported thereon a fluorinated sulphonic acid and subsequently through a second zone of the adsorbent material without adsorbed fluorinated sulphonic acid. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention is, in particular, useful in the removal of impurities being present in an effluent stream from acid catalyzed alkylation of hydrocarbons. Thereby, sulphur compounds such as thiophene, benzothiophene and dibenzothiophene contained in the effluent stream are substantially removed by passing the stream through a bed of preferably silica gel material having supported in a zone of the material trifluoromethanesulphonic acid. 
     The advantage compared to the known sulphuric acid sweetening process is an effective contact between the supported acid and the hydrocarbon stream without the need for agitation. Higher acidity of the fluorinated sulphonic acid enhances adsorption of less polar impurities and thus renders the adsorption process more versatile and effective. 
     Spent adsorbent material may be regenerated in several ways. A zone of fresh added acid is passed through the bed whereby impurities adsorbed on the adsorbent are desorbed from the bed by dissolution into the acid. After the acid zone has passed through the bed, the remaining acid is removed by flushing the bed with a hydrocarbon stream optionally containing olefinic hydrocarbons and optionally at elevated temperature (50°-200° C.). After regeneration of the adsorbent, acid is added to the adsorbent for use in a subsequent purification cycle. 
     Alternatively, the adsorbent is washed with water followed by drying and calcination at elevated temperature. After cooling, acid is added to the adsorbent, prior to being used in a subsequent purification cycle. 
    
    
     EXAMPLES 
     Comparison Example 1 
     Removal of Coloured Impurities from Alkylate Using Activated Carbon 
     155 ml of yellowish alkylate (UV/VIS absorbents at 400 nm=1.01) were passed through a column containing 4.8 ml of activated carbon (Darco, granular, 20-40 mesh). The flow rate was 3.9 ml/min. Different samples of the purified alkylate were collected. In Table 1 the amounts of alkylate samples are expressed as volume per column volume. The colour intensity of each sample was measured by UV/VIS absorption at 400 nm. The results of the purification are summarized in Table 1. 
     
                       TABLE 1______________________________________Portion of purified           UV/VIS Ab-alkylate        sorbentsvol./column vol.           400 nm______________________________________  0-4.2         0.034.2-9.4         0.09 9.4-15.2       0.1415.2-20.8       0.2220.8-26.9       0.2626.9-32.3       0.32______________________________________ 
    
     Comparison Example 2 
     Removal of Coloured Impurities from Alkylate Using Silica Gel 
     134 ml of yellowish alkylate (UV/VIS absorbents at 400 nm=1.28) was passed through a column containing 4.8 ml silica gel (Merck 100, 0.2-0.5 mm). The flow rate was 0.73 ml/min. and samples of the purified alkylate were collected. The colour intensity of each sample was measured by UV/VIS absorption at 400 nm. The results of the purification are summarized in Table 2. 
     
                       TABLE 2______________________________________Portion of purified           UV/VIS Ab-alkylate        sorbentsvol./column volume           400 nm______________________________________  0-2.9         0.032.9-5.2         0.185.2-8.3         0.34 8.3-12.7       0.4212.7-16.9       0.4616.9-19.8       0.4819.8-24.2       0.5024.2-27.9       0.52______________________________________ 
    
     Example 3 
     Removal of Coloured Impurities from Alkylate on Silica Gel Supporting Trifluoromethanesulphonic Acid 
     2300 ml of yellowish alkylate (UV/VIS absorbents at 400 nm) were passed through a column containing 25 ml silica gel (Merck 100, 0.2-0.5 mm). The gel was wetted with 10 ml trifluoromethanesulphonic acid in a first zone. Beneath the first zone, 125 ml silica gel (Merck 100, 0.2-0.5 mm) were placed in a second zone. In order to reduce alkylate cracking, the inlet temperature was kept at -15° C. The flow rate was 7.1 ml/min. The decolorized alkylate was collected in samples. The colour intensity of each sample was measured by UV/VIS absorption at 400 nm. In Table 3 the amount of alkylate samples is expressed as volume per column volumes. The results of the purification are summarized in Table 3. 
     
                       TABLE 3______________________________________Portion of purifiedalkylate         UV/VIS Absor-Vol./column volumes            bents 400 nm______________________________________  0-1.3          0.001.3-2.7          0.002.7-4.0          0.004.0-5.3          0.005.3-6.7          0.006.7-9.3          0.01 9.3-15.3        0.04______________________________________ 
    
     Example 4 
     For the adsorption of thiophene derivatives a solution of 0.77% thiophene (T), 0.96% benzothiophene (BT) and 0.80% dibenzothiophene (DBT) in hexane was passed through a column with 17 ml silica gel on which 3.0 ml trifluoromethanesulphonic acid were placed. The feedflow was 4.5 ml/min. at a temperature of 20-25° C. 
     The composition of the effluent stream was determined by GC in samples collected after passage of varying amounts of the above solution through the column. The first effluent sample from the column contained no detectable concentrations of the sulphur compounds in the feed stream. A sample taken after 12 ml of the solution had passed through the column showed no thiophene, no benzothiophene, and 0.05% dibenzothiophene. After passage of 25 ml solution, the DBT content in the effluent had increased to 0.58%, whereas none of the other sulphur compounds had been detected. After passage of 40 ml solution the DBT content in the effluent stream reached a level of 0.72% whereas the content of T and BT remained below the detection limit (30 ppm). A sample taken after the passage of 146 ml solution had almost essentially the same composition as the sample taken after 40 ml. However, after passage of 170 ml solution, T and BT appeared in the product at a concentration of 0.18% and 0.34% respectively, whereas the content of DBT was the same as in the feed 0.80% (all percentages are w/w). 
     Example 5 
     Decolouration of diesel oil. 
     20 ml hydrotreated diesel oil (yellow colour, a blue/green fluorescence and a sulphur content of 206 ppm including 41 ppm 4,6-dimethyl-dibenzothiophene) were stirred with 6 ml trifluoromethanesulphonic acid at 0° C. After 2 min. a 10 ml sample was removed and washed with water. The sample was colourless without any fluorescence. The sulphur content was measured to be 137 ppm including 10 ppm 4,6-dimethyl-dibenzothiophene.