Abstract:
The invention is directed to a process for the hydrogenation of hydrocarbon resins in the presence of a precious metal catalyst, wherein the hydrogenation is performed in the additional presence of at least one metal oxide, capable of reacting with sulfide and/or halogen.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of U.S. Ser. No. 10/129,156 filed Aug. 6, 2002, entitled HYDROGENATION OF HYDROCARBON RESINS and claims priority to PCT/NL00/00785 filed Nov. 1, 2000, entitled HYDROGENATION OF HYDROCARBON RESINS and to European application No. 99203611.1 filed Nov. 2, 1999, entitled HYDROGENATION OF HYDROCARBON RESINS, which are incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     N/A  
       BACKGROUND OF THE INVENTION  
       [0003]     The invention relates to a process for hydrogenating hydrocarbon resins containing sulfur impurities. Hydrocarbon resins are produced by polymerisation of hydrocarbon fractions, typically originating from the (catalytic) cracking of crude, including petroleum distillates and fractions from naphtha crackers, and tend to contain large amounts of impurities, such as sulfur compounds, nitrogen compounds, chlorine compounds and/or fluorine compounds. In order to give the resins the required properties they are usually hydrogenated using conventional hydrogenation catalysts, such as nickel or precious metal catalysts.  
         [0004]     In hydrogenation often a problem presents itself in that sulfur and/or sulfur components in the feedstock affect the lifetime of nickel catalysts negatively and affects the activity of precious metal catalysts negatively. To avoid this problem much attention has been paid to the development of sulfur-resistant catalyst systems for the hydrogenation and/or dehydrogenation.  
         [0005]     In general sulfur impurities are present in feedstocks as mercaptans or thiophenic compounds, which can be converted to H 2 S using a sulfided hydrogenation catalyst, such as a Co—Mo, a Ni—Mo or a Ni—W catalyst. This method is also known as hydrodesulfurization (HDS). The H 2 S formed may then be removed by reaction with zinc oxide, or, after separation and concentration in an organic stripper, be processed to elemental sulfur in a conventional Claus process.  
         [0006]     In EP-A 398,446 it has been proposed to use a hydrogenation or dehydrogenation catalyst based on at least one hydrogenation component and a metal oxide component, whereby the two components are present on a support as separate particles, preferably in absence of any direct contact between the metal oxide particles and the hydrogenation component particles.  
         [0007]     This catalyst provides a good basis for the hydrogenation of various sulfur containing feedstocks. However, there is a need for further improvement, especially in the area of resin hydrogenation in slurry phase, as the catalysts still deactivate rapidly, when hydrogenating hydrocarbon resins. In one embodiment of a hydrogenation process, wherein the sulfur containing resin was recirculated over a monolith catalyst, deactivation of the catalyst was considerable, thereby effectively making it impossible to carry out such a process.  
         [0008]     Accordingly it is a first object of the invention to provide a process for the hydrogenation of sulfur and/or halogen containing hydrocarbon resins, wherein the deactivation of the catalyst system is retarded considerably. It is a further object to provide such a process having a further improved tolerance for sulfur in the resin.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     The invention provides a process for the hydrogenation of hydrocarbon resins, said process comprising hydrogenating the said resins in the presence of a precious metal catalyst, wherein the hydrogenation is performed in the additional presence of at least one metal oxide, capable of reacting with sulfide and/or halogen.  
         [0010]     In the present invention the hydrogenation results in the breakdown of halogen and/or sulfur containing impurities. By the additional presence of the metal oxide component, either in admixture with the precious metal catalyst, or separately, the breakdown products are removed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0011]     The FIGURE is a graph showing the results of practicing the method of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]     In a preferred embodiment, the present invention comprises at least two steps, namely a first step wherein the resin is hydrogenated in the presence of a precious metal catalyst and a second step in which the hydrogen sulfide (or halogenide) produced in the hydrogenated resin is absorbed on a metal oxide based absorbent. These steps may be carried out simultaneously, wherein the metal oxide component and the precious metal component are present together in the reaction mixture. It is also possible to carry out the adsorption after the precious metal and the reaction mixture have been separated from each other. Optionally the reaction mixture is recirculated, i.e. contacted again with the precious metal.  
         [0013]     More in particular, as embodiments of the one step process, it is possible to have the metal oxide and the precious metal component slurried together in a reaction mixture, have both components present in the reactor in a fixed bed, or recirculate a reaction mixture having the metal oxide component slurried therein, over a bed of precious metal catalyst, for example a structured catalyst, such as a monolith, containing the precious metal catalyst, or recirculate the reaction mixture having the precious metal slurried therein, over a fixed bed of metal oxide.  
         [0014]     It is also possible to carry out the process in a two step manner, wherein the resin is first hydrogenated over a precious metal component and subsequently treated with the metal oxide component. This can be done in two subsequent reactor beds, preferably in two subsequent reactors, wherein first the resin is hydrogenated over the precious metal catalyst and subsequently the hydrogen sulfide produced therein is absorbed in a second bed (reactor). In another embodiment it is also possible that the precious metal component and/or the metal oxide component are slurried in the reaction mixture in each step. This means that first a precious metal is slurried in the reaction mixture, the metal is subsequently separated after the hydrogenation, the metal oxide is slurried in the mixture and separated again after adsorption, optionally followed by recirculation, as above.  
         [0015]     In this process it is also possible to recirculate part of the resin over the system, thereby increasing the removal of contaminants.  
         [0016]     It has been found that the present approach to hydrogenating hydrocarbon resin that contain amounts of sulfur impurities, provides a further improvement of the known systems. More in particular it has been found that this process has a high resistance against catalyst deactivation.  
         [0017]     In the present invention various hydrocarbon resin feedstocks may be used. A general definition of hydrocarbon resins has been given in ISO 472, namely products produced by polymerization from coal tar, petroleum and turpentine feedstocks. Preferred are petroleum distillates, resins, and the like. It is possible to use these feedstocks directly, but it is also possible to use the product from a previous hydrodesulfurisation process, i.e a feedstock having a reduced sulfur content, for example in the range of up to 500 ppm, preferably up to 300 ppm.  
         [0018]     The feedstock is first hydrogenated over a conventional precious metal catalyst. Generally these are supported precious metal catalysts, containing from 0.0001 to 5 wt. %, more in particular 0.01 to 5 wt. % precious metal calculated on the weight of the catalyst. Preferred amounts are between 0.1 and 2 wt %. The precious metals that may be used are platinum, palladium, rhodium, ruthenium, and alloys thereof, such as platinum-palladium.  
         [0019]     As support suitable supports for precious metal catalysts may be used, such as ceramic materials. Examples are silica, alumina, silica-alumina, titania, zirconia, zeolites, clay materials, combinations thereof and the like.  
         [0020]     The metal of the metal oxide component will generally be selected from those metals that react with hydrogen sulfide to give stable metal sulfides. An enumeration of suitable metals has been given in the cited EP-A 398,446. Examples are silver, lanthanum, antimony, nickel, bismuth, cadmium, lead, tin, vanadium, calcium, strontium, barium, cobalt, copper, tungsten, zinc, molybdenum, manganese and iron. Preferred metals are zinc and iron.  
         [0021]     As indicated above, there are various possibilities for carrying out the present invention. In a first embodiment the feedstock is first hydrogenated over a bed of precious metal catalyst. The hydrogenated feedstock is subsequently treated in an absorbing bed of metal oxide particles. This can either be a second bed in the same reactor as the bed of the precious metal catalyst or in a separate reactor. From the point of view of ease of recovery and regeneration of catalyst, the latter embodiment is preferred.  
         [0022]     According to another embodiment it is possible to carry out the hydrogenation in the presence of the metal oxide particles. This can be done by mixing the metal oxide particles and the precious metal catalyst in one bed. However, for the reasons given above this is not preferred.  
         [0023]     The present invention may suitably be carried out in a slurry reactor, wherein the precious metal catalyst is slurried in the resin to be hydrogenated, optionally together with the metal oxide component.  
         [0024]     The hydrogenation conditions will depend on the type of resin to be hydrogenated. Generally lighter resins require less severe conditions. In general the temperature will be between 125 and 350° C., with hydrogen pressures of between 2 and 250 bar.  
       EXAMPLES  
       [0025]     Two experiments were done on polymerised hydrocarbon resins, containing 25 ppm of sulfur, mainly in the form of thiophenic compounds, whereby in the first experiment a precious metal catalyst (0.5 wt. % of platinum on silica-alumina spheres) was slurried in the resin, in an amount of 23 g catalyst/kg of resin. At a temperature of 250° C. hydrogen, at a pressure of 100 bar was bubbled through the resin. In the attached FIGURE the reaction rate (consumption of hydrogen) is plotted against the degree of conversion.  
         [0026]     In the second experiment additionally zinc oxide powder was slurried in the resin in an amount of 10 g/kg of resin. The FIGURE also gives the plot of rate versus conversion of this experiment. It is clear from a comparison of the two plots, that the activity of the precious metal is strongly enhanced in the system of the invention.