Certain tin compounds are known to be used to treat those cracking catalysts conventionally employed in the catalytic cracking of hydrocarbons for the production of gasoline, motor fuel, blending components and light distillates. These conventional cracking catalysts generally contain silica, or silica-alumina. Such materials are frequently associated with zeolitic materials. These zeolitic materials can be used as naturally occurring, or they can be modified by conventional ion exchange methods to attach metallic ions which improve the activity of the catalyst.
While the presence on the catalyst of certain metals can be beneficial, the presence of others is detrimental. It is well known that varying amounts of metals such as nickel, vanadium and iron cause deterioration of the cracking catalyst during the cracking process. In fact, some oils contain these metals in such a high concentration that they cannot be economically catalytically cracked into gasoline and other fuels. The metals accumulate on the cracking catalyst and cause increased hydrogen production and coke laydown on the cracking catalyst, thereby adversely affecting the yield of desired products.
It has heretofore been proposed to passivate those deleterious metals by treating the contaminated catalyst with compounds containing antimony, tin, indium or bismuth (see U.S. Pat. No. 4,257,919). Tin compounds are particularly useful as passivating agents for vanadium. Among the organic tin compounds proposed are tin dicarboxylates such as tin didodecanoate, tin dioctadecanoate, tin tetradodecanoate and tin tetraoctadecanoate.
Prior art processes for tin carboxylate preparation involve direct reactions between tin hydroxides and carboxylic acids (see U.S. Pat. No. 2,684,973) or between alkyl tin oxides and acetic anhydride (see U.S. Pat. No. 2,838,554).
The production of tin carboxylates by the direct reaction between alkyl tin oxides and the desired higher carboxylic acids or acid anhydrides is generally less satisfactory for producing higher carboxylates because of the difficulty of the reaction and the low yield obtained. Accordingly, it is an object of the present invention to provide a process for preparation of higher carboxylates of tin which uses readily available reactants and affords high yields of the desired carboxylate. It is another object of the invention to provide a method of preparation wherein the tin carboxylate produced is substantially free of deletrious impurities and has a high level of thermal stability. These and other objects, aspects and advantages of the present invention will become apparent to those skilled in the art from the following description of the invention.