Abstract:
Compositions and processed for their use as additives for reducing the sulfur content of FCC gasoline employ a support material having deposited on its surface (a) a first metal component from Group IIB of the Periodic Table and (b) a second metal component from Group III or Group IV of the Periodic Table. The additive composition is preferably made of a montmorillonite clay support containing zinc and gallium, zinc and zirconium. Alternatively, the additive composition includes support material having deposited on its surface a metal component from Group III of the Periodic Table, preferably a montmorillonite clay support containing gallium. The clay is impregnated with the metal(s) using the known incipient wetness method and the dried powdered additive composition is preferably formed into shapes suitable for use in the FCC unit.

Description:
RELATED APPLICATIONS 
     This application is a national phase application under 35 U.S.C. §371 of PCT/US2009/004433 filed on Jul. 30, 2009 which claims priority from United Stated Provisional Patent Application Ser. No. 61/137,471 filed on Jul. 30, 2008, which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the reduction of sulfur in gasoline produced in a fluid catalytic cracking process and, more particularly, to a method and composition for use in the fluid catalytic cracking process using a sulfur reduction additive composition. 
     2. Description of Related Art 
     Fluid catalytic cracking (FCC) is the largest refining process used for gasoline production with global capacity of more than 14.2 million barrels per day. The process converts heavy feedstocks such as vacuum distillates, residues, and deasphalted oil into lighter products, which are rich in olefins and aromatics. FCC catalysts are typically solid acids of fine-particles especially zeolites (synthetic Y-faujasite), aluminum silicate, treated clay (kaolin), bauxite, and silica-alumina. The zeolite content in commercial FCC catalysts is generally in the range of 5-40 weight %, or greater, while the balance is silica-alumina amorphous matrix. Additives to the FCC process usually amount to no more than 10% of the catalyst, and they are basically used to enhance octane, as metal passivators, SO x  reducing agents, CO oxidation and, recently, for gasoline sulfur reduction. 
     Stringent environmental regulations that target the reduction of the sulfur content of automobile gasoline and tailpipe emissions are being enforced worldwide. Sulfur in gasoline increases SO x  emissions in combustion gases, reduces the activity of vehicle catalytic converters, and promotes corrosion of engine parts. The upper limit of sulfur in gasoline in the United States and the European Union has been set at 10 parts per million (ppm) as a refinery average, and many other countries have also decreased the permitted sulfur specifications in transportation fuels. 
     A number of options are available for the reduction of sulfur in gasoline. The main options are hydrotreating the FCC feed, hydrotreating product naphtha, lowering the end boiling point of FCC gasoline, and the use of sulfur-reducing additives in FCC catalysts. The first two options are highly capital intensive. A disadvantage regarding the third option is that the lowering of end boiling point will also reduce the octane number, in addition to reducing the yield of gasoline. From an economic point of view, the last option is the most desirable since this will selectively desulfurize the gasoline fraction without the need for additional treatment. It has been reported that sulfur reduction by FCC additives or catalysts offers economic advantages over the standard solution-selective gasoline hydrotreating or hydrodesulfurization methods. 
     Various catalytic materials for effecting a sulfur reduction have been developed for use during the FCC process. The sulfur reduction component may be a separate additive to the FCC catalyst or part of an FCC sulfur reduction catalyst. However, the levels of sulfur in gasoline are still not low enough to meet current and proposed regulatory requirements and, accordingly, are unacceptable. 
     Catalyst additives for the reduction of sulfur in FCC gasoline products were proposed by Wormbecher in U.S. Pat. No. 5,376,608 and Kim in U.S. Pat. No. 5,525,210, the disclosures of which are incorporated by reference, using a cracking catalyst additive of an alumina-supported Lewis acid for the production of reduced-sulfur gasoline. It was also disclosed that the Lewis acid may comprise components and compounds including Zn, Cu, Ni, Ag, Cd and Ga deposited on aluminum oxide. However, this system has not achieved significant commercial success. 
     Another composition is that disclosed in U.S. Pat. No. 6,036,847 to Ziebarth et al., the disclosure of which is incorporated herein by reference, used 10 weight % of a mixture including particles of Zn supported on alumina and titania particles as an additive in the cracking of 2.7 weight % sulfur vacuum gas oil (VGO) feed. The results indicated that the combination of alumina-supported Lewis acid component and titania-containing component resulted in greater sulfur reduction than the use of either component alone. 
     Myrstad et al. in U.S. Pat. No. 6,497,811, the disclosure of which is incorporated herein by reference, disclosed a composition of a hydrotalcite material impregnated with a Lewis acid, and optionally an FCC-catalyst, as a sulfur-reducing additive. The Lewis acid included transition metals elements and compounds, including Zn, Cu, Ni, Co, Fe and Mn. 
     Another additive disclosed by Roberie et al. in U.S. Pat. No. 6,482,315, the disclosure of which is incorporated herein by reference, discloses a composition comprising vanadium supported on a refractory inorganic oxide. When using 2 weight % vanadium-containing additive, a 33% reduction in gasoline sulfur was reported. 
     Various papers, published by Andersson, P. et al.,  Catalysis Today  53:565 (1991), Beltran F. et al,  Applied Catalysis Environmental  34:137 (2001) and 42: 145 (2003), relate in only a very general manner to the concept of the present invention. 
     Notwithstanding the reported sulfur-reducing catalysts, there remains a need for effective and economical catalysts for reducing sulfur from gasoline in a commercially sustainable manner. 
     Therefore, it is an object of the present invention to provide a sulfur-reducing composition and a method for the use of same which provides a gasoline with a significantly lower sulfur level, when compared to the sulfur reduction activity of a conventionally used FCC catalyst in the FCC process. 
     SUMMARY OF THE INVENTION 
     The present invention provides additive compositions for reducing the sulfur content of FCC gasoline and processes using the compositions. In one aspect of the present invention, the sulfur reduction additive composition comprises a support material having deposited on its surface (a) a first metal component from Group IIB of the Periodic Table and (b) a second metal component from Group IIIA or Group IVB of the Periodic Table. The composition is most preferably made of a montmorillonite clay support on which zinc and gallium or zinc and zirconium are impregnated. 
     In another aspect, the composition comprises a support material having deposited on its surface a metal component from Group IIIA of the Periodic Table. The composition is most preferably made of a montmorillonite clay support on which only gallium is impregnated. 
     Preferably, the support material is an amorphous or inorganic oxide such as, for example, Al 2 O 3 , clays, or mixtures thereof. In certain preferred embodiments, the support material is montmorillonite clay. 
     The metal or metals are impregnated or dispersed on the surface of the clay particles by any suitable conventional process, e.g., the incipient wetness method. 
     The sulfur reduction additive composition is used as a separate additive in combination with the conventional fluid catalytic cracking catalyst, which is normally a faujasite, such as zeolite Y, to crack hydrocarbon feeds in the FCC unit to produce low-sulfur gasoline and other liquid cracking products. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in further detail below and with reference to the attached drawings in which: 
         FIG. 1  is a plot of the sulfur content of product gasoline fractions obtained with a conventional FCC catalyst without any additive as a reference material, and a mixture of the FCC catalyst with a commercial additive, as a comparative material, versus percent conversion; 
         FIG. 2  is a plot of the sulfur content of product gasoline fractions obtained with the reference material and the comparative material of  FIG. 1 , and a base clay material used in additive compositions of the present invention, versus percent conversion; 
         FIG. 3  is a plot of the sulfur content of product gasoline fractions obtained with a zinc impregnated-base material, the reference material and the comparative material, versus percent conversion; 
         FIG. 4  is a plot of the sulfur content of product gasoline fractions obtained with the reference material and the comparative material of  FIG. 1 , and a zinc and zirconium impregnated base material, versus percent conversion; 
         FIG. 5  is a plot of the sulfur content of product gasoline fractions obtained with the reference material and the comparative material of  FIG. 1 , and a gallium impregnated base material, versus percent conversion; and 
         FIG. 6  is a plot of the sulfur content of product gasoline fractions obtained with the reference material and the comparative material of  FIG. 1 , and a zinc and gallium impregnated base material, versus percent conversion. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with the present invention, the sulfur content of an FCC gasoline is reduced to lower levels by the use of the additive composition of the invention mixed with a conventional FCC catalyst. The FCC catalyst is preferably made of powder and generally possesses an average particle size in the range of 50-100 microns and a bulk density in the range of 0.5-1.0 kg/L. It is preferred that the particle size, density, shape and mechanical strength of the catalyst additive composition of the present invention is the same as a conventional FCC catalyst in which the composition is to be physically mixed. 
     The support material of the additive compositions of the present invention is preferably a montmorillonite clay possessing a surface area in the range of 150-350 m 2 /g. Clay material itself possesses considerable capacity to reduce sulfur in gasoline fraction. However, the reduction in the benzothiophene fraction is typically minimal. It was observed that the impregnation of only a Lewis acid component onto the clay did not significantly increase either overall sulfur reduction capacity or the reduction of benzothiophene. 
     It was also observed that use of an additive composition of the clay material that was impregnated with zinc and a metal from Group IIIA of the Periodic Table, such as Ga, or Group IV, such as Zr, did further reduce the sulfur content of the gasoline fraction which was catalytically cracked in the FCC unit. The clay material undergoes a drying step to produce shaped bodies suitable for use in the reduction of sulfur from gasoline and it can also be used alone as the gasoline sulfur reduction additive composition. 
     It was further that use of an additive composition of the clay material that was impregnated with a metal from Group IIIA of the Periodic Table, such as Ga, reduced the sulfur content of the gasoline fraction that was catalytically cracked in an FCC unit. 
     In order to further illustrate the present invention and the advantages thereof, the following specific examples are presented. The examples are presented as specific embodiments of the claimed invention. It should be understood, however, that the invention is not limited to the specific details set forth in the examples. The examples illustrate the preparation and evaluation of the catalytic activity specific additive compositions for reducing sulfur content of a catalytically cracked gasoline fraction in a typical FCC unit. 
     The conventional cracking catalyst particles preferably contain at least one cracking catalyst component which is catalytically active for the cracking of hydrocarbons in the absence of added hydrogen. The cracking catalyst component can comprise a zeolite, a non-zeolite molecular sieve, a catalytically active amorphous silica alumina species, or a combination thereof. In certain embodiments, the cracking catalyst component is a Y-type zeolite selected from the group consisting of Y, USY, (described in U.S. Pat. No. 3,293,192, which is incorporated herein by reference), REY and RE-USY (described in U.S. Pat. Nos. 3,867,307 and 3,676,368, both of which are incorporated herein by reference) and mixtures thereof. The cracking catalyst particles can also contain one or more matrix components such as clays, modified clays, alumina, and the like. The cracking catalyst particles can also contain a binder such as an inorganic oxide sol or gel. The cracking catalyst particles generally contain at least 5 weight %, and in certain embodiments about 5 weight % to about 50 weight %, of the cracking catalyst component. 
     EXAMPLES 
     Micro activity test (MAT) evaluations of FCC catalyst/additive mixtures were carried out according to ASTM method D-3907, at a reaction temperature of 510° C. and a injection time of 30 seconds for a catalyst-to-oil ratio between 3 to 5, to obtain a conversion to gasoline of 55 to 75% of the original feed. The feed used was a vacuum gas oil of Arabian light crude origin. The sulfur content of this feed was 2.5 weight percent. Other properties of this feed are shown in Table 1. The sulfur content of the gasoline fraction was measured by GC-SCD. For comparison purposes, the sulfur content of the gasoline fraction was calculated at 71% conversion level. The montmorillonite clay was calcined in air at 550° C. to remove physically adsorbed water. Calcinations at 550° C. did not result in a significant increase in the surface area. 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Properties of vacuum gas oil (VGO). 
               
             
          
           
               
                   
                 Property 
                 Value 
               
               
                   
                   
               
             
          
           
               
                   
                 Density (g/cc) 
                 0.882 
               
               
                   
                 API 
                 29.1 
               
               
                   
                 Carbon (wt %) 
                 85.08 
               
               
                   
                 Hydrogen (wt %) 
                 12.08 
               
               
                   
                 Sulfur (wt %) 
                 2.46 
               
               
                   
                 Nitrogen (wt %) 
                 960 
               
               
                   
                 Initial Boiling Point (° C.) 
                 214 
               
               
                   
                 Final Boiling Point (° C.) 
                 588 
               
               
                   
                   
               
             
          
         
       
     
     Example 1 
     Sulfur Content of Gasoline Fraction Obtained with Use of a Conventional FCC Catalyst 
     A steamed, conventional, commercial FCC zeolite catalyst, a typical low RE-USY type available from any FCC catalyst supplier, was evaluated in the MAT according to ASTM D 3907.  FIG. 1  shows the plot of gasoline sulfur content versus percent conversion obtained with only the conventional catalyst without any additive composition. This sulfur content is taken as a reference. 
     Example 2 
     Sulfur Reduction with a Commercially Available Additive Composition 
     A commercial sulfur reduction additive composition generally available from a catalyst supplier, for example, Albemarle, CClC, Englehard, Grace Davison, or Intercat, labeled as comparative additive composition in the tables, was added (10 weight %) to the same steamed conventional FCC catalyst, namely, low RE-USY, as in Example 1 and was tested in MAT under the same conditions as in Example 1. The sulfur content of the gasoline fraction in this Example 2 is compared to the reference sulfur content in  FIG. 1 . At a conversion to gasoline of 71%, the overall sulfur reduction achieved, including benzothiophene, was 16%. Table 2 lists the sulfur content of the gasoline fraction for all the additive compositions. 
     Example 3 
     Sulfur Reduction of FCC Naphta with the Base Material of the Present Invention 
     To measure the sulfur reduction capability of the support material, montmorillonite clay itself was mixed with a conventional catalyst, a typical RE-USY type available from any FCC catalyst supplier, and evaluated in MAT. The results obtained, which are shown in  FIG. 2 , were compared with the reference. Montmorillonite demonstrated a significant sulfur reduction capability. As reported in Table 2, the sulfur content of the product gasoline fraction was reduced by 21%. 
     Example 4 
     Results Obtained by Use of Zinc-Impregnated Clay 
     An additive composition was prepared by impregnating 3 weight % Zn on montmorillonite clay by the incipient wetness method. A quantity of 10 weight % of this composition was mixed with the same commercial catalyst, a typical low RE-USY type, available from any FCC catalyst supplier, as in Example 1 and tested in MAT.  FIG. 3  compares the sulfur content of gasoline obtained by using the composition of Example 4 with that obtained with use of the reference catalyst and the composition of Example 3. It is seen that sulfur reduction capability of this composition of Example 4 is similar to the composition of Example 3. At 71% gasoline conversion, product gasoline sulfur was reduced by 21%, as reported in Table 2. 
     Example 5 
     Results Obtained by Use of Clay Impregnated with Zinc and Zirconium 
     An additive composition of the invention was prepared by impregnating 3 weight % Zn and 1 weight % Zr on montmorillonite clay by the incipient wetness method. A quantity of 10 weight % of this composition was mixed with the same commercial catalyst, a typical low RE-USY type, available from any FCC catalyst supplier, as in Example 1 and tested in MAT.  FIG. 4  compares the sulfur content of gasoline obtained using the composition of Example 5 with that obtained by use of the reference catalyst and the composition of Example 4. It is seen that sulfur reduction capability of this composition is higher than the composition of Example 4. At 71% conversion to gasoline, product gasoline sulfur was reduced by 40%, as reported in Table 2. 
     Example 6 
     Results Obtained by Use of Gallium-Impregnated Clay 
     An additive composition of the invention was prepared by impregnating 3 weight % Ga on montmorillonite clay by the incipient wetness method. A quantity of 10 weight % of this composition was mixed with the same commercial catalyst, a typical low RE-USY type, available from any FCC catalyst supplier, as in Example 1 and tested in MAT.  FIG. 6  compares the sulfur content of gasoline obtained using the composition of Example 6 with that obtained by use of the reference catalyst and the composition of Example 3. It is seen that sulfur reduction capability of this composition is superior to the composition of Example 4. At 71% conversion, product gasoline sulfur was reduced by 38%, as reported in Table 2. 
     Example 7 
     Results Obtained by Use of Clay Impregnated with Zinc and Gallium 
     An additive composition was prepared by impregnating 3 weight % Zn and 1 weight % Ga on montmorillonite clay by the incipient wetness method. A quantity of 10 weight % of this composition was mixed with the same commercial catalyst, a typical low RE-USY type, available from any FCC catalyst supplier, as in Example 1 and tested in MAT.  FIG. 5  compares the sulfur content of gasoline obtained using the additive composition of Example 7 with that obtained by use of the reference catalyst and the additive composition of Example 4. It is seen that sulfur reduction capability of this additive composition is higher than the additive composition of Example 4. At 71% gasoline conversion, product gasoline sulfur was reduced by 39%, as reported in Table 2. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Sulfur content of gasoline fraction and 
               
               
                 percent reduction in sulfur content 
               
             
          
           
               
                   
                   
                 Sulfur 
                   
               
               
                   
                 Additive Composition 
                 content 
                 % reduction 
               
               
                   
                   
               
             
          
           
               
                   
                 Reference Material 
                 659 
                 0 
               
               
                   
                 (no additive composition) 
               
               
                   
                 Comparative 
                 553 
                 16 
               
               
                   
                 Clay 
                 523 
                 21 
               
               
                   
                 Zn/Clay 
                 520 
                 21 
               
               
                   
                 Ga/Clay 
                 410 
                 38 
               
               
                   
                 Zn—Zr/Clay 
                 393 
                 40 
               
               
                   
                 Zn—Ga/Clay 
                 405 
                 39 
               
               
                   
                   
               
             
          
         
       
     
     The compositions of the present invention and their methods of use have been described above; however, modifications will be apparent to those of ordinary skill in the art and the scope of protection for the invention is to be defined by the claims that follow.