Abstract:
A process for the removal of oxygenated sulfur compounds from a hydrocarbon stream, especially the effluent from a sulfuric acid alkylation reactor, in which the hydrocarbon stream is first subjected to deentrainment of any carryover liquid sulfuric acid and then passed over a sorbent which removes the oxygenated sulfur compounds.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to the treatment of alkylate product from a process wherein normal olefins are reacted with isoalkanes in the presence of sulfuric acid to produce alkylate product. More particularly the invention relates to a process wherein sulfuric acid is mechanically removed from the effluent from the alkylation reactor and subsequently treated to remove residual oxygenated sulfur compounds. More particularly the invention relates to a process wherein the oxygenated sulfur compounds are removed by sorption.  
         [0003]     2. Related Information  
         [0004]     In the petroleum refining industry, acid catalyzed alkylation of aliphatic hydrocarbons with olefinic hydrocarbons is a well known process. Alkylation is the reaction of a paraffin, usually isoparaffins, with an olefin in the presence of a strong acid which produces paraffins, e.g., of higher octane number than the starting materials and which boil in range of gasolines. In petroleum refining the reaction is generally the reaction of a C 2  to C 5  olefin with isobutane.  
         [0005]     In refining alkylations, hydrofluoric or sulfuric acid catalysts are most widely used under low temperature conditions. Low temperature or cold acid processes are favored because side reactions are minimized. In the traditional process the reaction is carried out in a reactor where the hydrocarbon reactants are dispersed into a continuous acid phase.  
         [0006]     Although this process has not been environmentally friendly and is hazardous to operate, no other process has been as efficient and it continues to be the major method of alkylation for octane enhancement throughout the world. In view of the fact that the cold acid process will continue to be the process of choice, various proposals have been made to improve and enhance the reaction and to some extent moderate the undesirable effects.  
         [0007]     In the past the alkylate product has been washed with water or treated with caustic to remove or neutralize any carryover sulfuric acid. Both methods of treatment have drawbacks. When a water wash is used, there is some carryover of water to the distillation columns used to separate the alkylate from unreacted materials. This water dilutes any acid left or dissolves any sulfonates or sulfonic esters which cause corrosion problems. The caustic tends to produce salts which can foul downstream heat exchangers, especially the reboiler in the recovery columns. Various solutions have been proposed for this problem. U.S. Pat. No. 5,220,095 disclosed the use of particulate polar contact material and fluorinated sulfuric acid for the alkylation.  
         [0008]     U.S. Pat. Nos. 5,420,093 and 5,444,175 sought to combine the particulate contact material and the catalyst by impregnating a mineral or organic support particulate with sulfuric acid.  
         [0009]     Various static systems have been proposed for contacting liquid/liquid reactants, for example U.S. Pat. Nos. 3,496,996; 3,839,487; 2,091,917; and 2,472,578. However, the most widely used method of mixing catalyst and reactants is the use of various arrangements of blades, paddles, impellers and the like that vigorously agitate and blend the components together, for example, see U.S. Pat. Nos. 3,759,318; 4,075,258 and 5,785,933.  
       SUMMARY OF THE INVENTION  
       [0010]     In the present process oxygenated sulfur compounds are removed from a hydrocarbon stream comprising passing said hydrocarbon stream over a supported sorbent comprising a component selected from the group consisting of copper, zinc and mixtures thereof. Preferably the oxygenated sulfur compounds are present as a residual amount in the hydrocarbon stream, such as that present in a hydrocarbon stream separated and recovered from a sulfuric acid catalyzed paraffin alkylation. The residual amount is preferably less than 1000 wppm. Preferably the sorbent is regenerable.  
         [0011]     In a preferred embodiment the invention comprises removing the sulfuric acid from the alkylate by mechanical means instead of water wash or caustic treatment product prior to treatment to remove oxygenated compounds by absorption. The preferred mechanical means comprises a vessel containing a coalescer material upon which the sulfuric acid impinges. The sulfuric acid, being much heavier than the hydrocarbon, falls out and may be removed by gravity. The alkylate product may then be treated to remove the oxygenated sulfur compounds by adsorption in any of several points in the process after the mechanical deentrainment. The adsorber may contain regenerable or nonregenerable sorbents and may be located directly after the coalescer to treat the entire stream or downstream on any of the other product streams. The sorbents may remove the oxygenated sulfur compounds from light (C 4  and lighter) and heavier (C 5  and heavier) components separately if desired. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a simplified flow diagram of one embodiment of the invention.  
         [0013]      FIG. 2  is a simplified flow diagram of the invention showing various placements of the sorber. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     The alkylate product to be treated may come from any cold acid alkylation process which uses sulfuric acid as the catalyst. Preferably, the fluid system comprises a liquid and is maintained at about its boiling point in the reaction zone.  
         [0015]     The coalescer is a conventional liquid-liquid coalescer of a type which is operative for coalescing vaporized liquids and comprises demisters and co-knit structures which are catalytically inert or active. Demisters and co-knit structures are typically used for liquid-liquid coalescers and coalescing of mists. They are known as “mist eliminators” or demisters and are composed of one or more materials which are knit together to form a mesh. The stitched mesh is then crimped, stretched, and folded or bundled to provide the desired amount of surface area per volume ratio, and are commonly known as “mist eliminators” or “demisters” used to coalesce condensible vapors in gaseous streams. A suitable coalescer comprises a mesh such as a co-knit wire and fiberglass mesh. For example, it has been found that a 90 needle tubular co-knit mesh of wire and fiberglass such as manufactured by Amistco Separation Products, Inc of Alvin, Tex. or ACS Industries LLC of Houston, Tex., can be effectively utilized, however, it will be understood that various other materials such as co-knit wire and teflon (Dupont ™), steel wool, polypropylene, PVDF, polyester or various other co-knit materials can also be effectively utilized in the apparatus. Various wire screen type packings may be employed where the screens are woven rather than knitted. Other acceptable coalescers include perforated sheets and expanded metals, open flow cross channel structures which are co-woven with fiberglass or other materials, such as polymers.  
         [0016]     Typically the alkylate from the alkylation process contains some sulfuric acid as well as sulfonates and sulfonic esters which must be removed. Referring now to  FIG. 1 a  simplified flow diagram of one embodiment is shown. The alkylate is taken from alkylation reactor  10  via flow line  101  and fed to deentrainment vessel  20 . Deentrainment vessel  20  contains a coalescer material upon which the sulfuric acid droplets impinge and fall out. The sulfuric acid and hydrocarbons in the alkylate product are practically insoluble in one another. The sulfuric acid droplets are collected and recycled to the alkylation reactor  10  via flow line  104 .  
         [0017]     The liquid from the deentrainment vessel is passed via flow line  102  to absorption vessel  50  containing a bed  52  of sorbent material. Any material that will sorb the oxygenated sulfur compounds will suffice. One typical sorbent is Engelhard Cu-0226 14×28, 10% Cu on alumina. Another is BASF R3-12, 40% Cu/40% Zn on alumina. Substantially all of the oxygenated sulfur compounds are sorbed by the sorbent. Hydrogen is fed to the sorber as required via flow line  108  during the regeneration step. The liquid from the sorber is then fed via flow line  110  to a deisobutanizer  30  containing standard distillation structure  32  such as sieve trays, bubble cap trays and the like, where iC 4  and C 3 &#39;s and lighter are taken as overheads via flow line  109 . The overheads containing the iC 4  and lighter material is then fed via flow line  109  to depropanizer  60  containing standard distillation structure  62  where C 3  and lighter is removed as overheads via flow line  111 . The iC 4  is recycled to the alkylation reactor via flow line  104 . The bottoms from the deisobutanizer containing the alkylate are fed via flow line  105  to debutanizer  40  containing standard distillation structure  42  where nC 4  is removed as overheads via flow line  106  and alkylate product is taken as bottoms via flow line  107 . When the efficiency of the sorbent declines to a determined level, the alkylate feed is ended and the sorbent regenerated with hydrogen at 125 psig and 650° F., the hydrogen ended, the sorbent cooled, the alkylate feed restated and the steps repeated.  
         [0018]      FIG. 2  shows alternate placements of the sorber  50  as indicated by the dashed lines and the reference numerals  50 A- 50 G. The remaining vessels are numbered as in  FIG. 1 . As seen the sorber may be placed to remove the oxygenated sulfur compounds from any of the streams downstream of the deentrainment vessel such as the nC 4  stream, the feed to the depropanizer, the C 3  product, the feed to the deisobutanizer, the feed to the debutanizer or the alkylate product stream.  
         [0019]     Although not shown there would be typically two, preferably three, sorbers in parallel use. One sorber would be in use, a second would be a back up and the third would be undergoing regeneration.  
       EXAMPLES  
       [0020]     In the following examples hydrocarbon feeds treated to remove oxygenated sulfur compounds are simulated as C 4 =about 95% isobutane or C 8 =about 50% isooctane and 20% n-butane with sulfur esters added. In the initial run the sorber catalyst treatment was activation and in subsequent runs the treatment was regeneration. The sorbent unit was ⅜″ OD tubing containing 10 grams (11 ml) of the sorbent. The sorption took place at 125 psig and 150° F. to simulate conditions of the hydrocarbon stream entering a debutinizer column. The length of each run was determined by time to break through (Time to BT). Break through was defined as when the effluent from the sorber contained 15% of the sulfur of the feed stream.  
         [0021]     Catalyst activation and regeneration procedure was as follows: 
    1. Purged with nitrogen −40 ccm for 20 minutes at 125 psig and 300° F.     2. Started hydrogen −30 ccm, 125 psig and ramped temperature to 650° F. (10° F./min). Held for 3 hours then cooled to 150° F. while flowing hydrogen. (6 hrs total).    
 
         [0024]     The adsorption procedure was carried by the following procedure: 
    1. Purged with nitrogen (or He)—flowed 40 ccm for 30 min at 125 psig and kept temperature at 150° F. Shut off gas flow before starting hydrocarbons.     2. Hydrocarbon flow at 125 psig and 150° F.     3. After complete breakthrough occurred feed terminated.     4. Regenerated catalyst per procedure above.    
 
       Example 1  
       [0029]     Engelhard Cu-0226 S 14×28, 10% Cu on alumina was used as sorbent to treat sulfur ester containing hydrocarbon feeds as described. The conditions, residual sulfur compound content (wppm), and results are shown in TABLE I.  
                                                                                                 TABLE I                           Catalyst:   Engelhard Cu-0226 S 14 × 28, 10% Cu/Alumina                grams   10           ml   11                    SORBENT TREATMENT STEP                    Reduction   Run #1   Run #2   Run #3   Run #4   Run #5       H2 feed Ml/min   30   30   30   30   30       Temp ° F.   650   650   450   450   450       Pressure psig   100   100   100   100   100       Time hrs   4   4   4   4   4                    HYDROCARBON PROCESSING STEP                    Feed   C 4     C 4     C 4     C 8     C 8         Flow rate: ml/min   3   3   3   2   2       WHSV: 1/hr   10.026   10   10   8.436   8.436       Density: g/cm3   0.557   0.557   0.557   0.703   0.703       Temp ° F.   100   100   100   325   325       Pressure psig   100   100   100   200   200       Time to BT hr   44   50   &gt;70   24   29       S in Feed, wppm   14   14   7   23   18       Capacity gS/gcat   0.006176   0.007018   &gt;0.005   0.004608   0.004524       Productivity: grams   441.144   501.3   NA   202.464   244.644       feed/g cat                  
 
       Example 2  
       [0030]     BASF R3-12, 40% Cu/40 Zn on alumina was used as sorbent to treat sulfur ester containing hydrocarbon feeds as described. The conditions, residual sulfur compound content (wppm), and results are shown in TABLE II.  
                                                                                                         TABLE II                                       Catalyst:   BASF R3-12, 40% Cu, 40% Zn/alumina                    grams   10               ml   10.5                        SORBENT TREATMENT STEP                        Reduction       Run #1   Run #2   Run #2           H2 feed   ml/min   30   30   30           Temp   ° F.   450   450   450           Pressure   psig   100   100   100           Time   hrs   12   18   18                        HYDROCARBON PROCESSING STEP                    Feed       C 4     C 8     C 8         Flow rate:   ml/min   6   2   2       WHSV:   1/hr   20.052   8.436   8.436       Density:   g/cm3   0.557   0.703   0.703       Temp   ° F.   100   325   325       Pressure   psig   100   200   200       Time to BT   hr   74   23   14       S in Fd   wtppm   4.937163   16   23       Capacity   gS/gcat   0.007326   0.003036   0.002688       Productivity:   grams feed/   1483.848   194.028   118.104           g cat