Preparation of titania and cobalt aluminate catalyst supports and their use in Fischer-Tropsch synthesis

#This invention relates to titania and cobalt aluminate containing catalyst supports. It also relates to use of the supports and a catalytic component in Fischer-Tropsch hydrocarbon synthesis whereby the alpha is improved and the selectivity of the process to higher hydrocarbons is enhanced.

#The Fischer-Tropsch process was developed in the 1920's as a way of producing hydrocarbons from synthesis gas, i.e., hydrogen and carbon monoxide. Initially, the process was centered on producing gasoline range hydrocarbons as automotive fuels. Today, however, the Fischer-Tropsch process is increasingly viewed as a method for preparing heavier hydrocarbons such as diesel fuels, and more preferably waxy molecules for conversion to clean, efficient lubricants. Thus, the importance of catalysts for producing higher boiling hydrocarbons, i.e. a product slate containing a higher carbon number distribution, is ever increasing. A measure of the carbon number distribution is the Schulz-Flory alpha value, which represents the probability of making the next higher carbon number from a given carbon number. The Schulz-Flory distribution is expressed mathematically by the Schulz-Flory equation: Wi=(1−α)2iαi-1 Where i represents carbon number, α is the Schulz-Flory distribution factor which represents the ratio of the rate of chain propagation to the rate of chain propagation plus the rate of chain termination, and Wi represents the weight fraction of product of carbon number i. Alpha numbers above about 0.9 are, in general, representative of wax producing processes and the higher the alpha number—as it approaches 1.0—the more selective the process is for producing wax molecules.

#The catalysts usually employed in the Fischer-Tropsch process are iron and cobalt; ruthenium has the requisite catalytic activity for use in the process but is expensive and is in relatively short supply. Promoters, like rhenium, zirconium, manganese, and the like, are commonly used, especially with cobalt, to improve various aspects of catalytic performance.

#FIGS. 1, 2 and 3 are graphs of data presented in the Examples which illustrate various aspects of the present invention.

#The support of the present invention is a particulate material comprising oxides of elemental titanium, aluminum, and cobalt. These oxides may be simple oxides, i.e., oxides of a single element such as TiO2, Al2O3, CoO, and Co3O4 and oxides of more than one element such as CoTiO3 and CoAl2O4. In any event, the support comprises primarily titania (TiO2) and a minor amount of cobalt aluminate. In general the support will contain at least 50 wt % titania and preferably from 80 to about 97 wt % titania based on the total weight of the support. About 20 to 100 wt %, and preferably 60 to 98 wt % of the titania of the support is in the rutile crystalline phase with the balance being the anatase crystalline phase or amorphous phases. The amount of cobalt aluminate in the binder is dependent upon the amount of cobalt and aluminum compounds used in forming the support. Suffice it to say that sufficient cobalt is present in the support to provide a cobalt/aluminum atomic ratio greater than 0.25, preferably from 0.5 to 2, and more preferably about 1. Thus, at a Co/Al ratio of 0.25 about half the aluminum oxide is present as cobalt aluminate. At a Co/Al ratio of 0.5 substantially all the alumina oxide present is present as cobalt aluminate. At Co/Al ratios above 0.5 the support will contain cobalt titanate in addition to cobalt aluminate and be essentially free of alumina.

#As previously stated the binder may also include alumina and optionally silica. In general, the binder is less than about 30 wt % of the support and preferably less than about 15 wt % of the support. Typically the binder is greater than about 3 wt % of the support. The amount of silica is less than 50 wt % of the total amount of binder, preferably 35 wt % of the binder.

#Typically the support will have a surface area in the range of from about 5 m2/g to about 40 m2/g and preferably from 10 m2/g to 30 m2/g. Pore volumes range from about 0.2 cc/g to about 0.5 cc/g and preferably from 0.3 cc/g to 0.4 cc/g.