EFFECT OF WATER CONTENT OF SILICA-ALUMINA CATALYST ON 1-BUTENE ISOMERIZATION AND POLYMERIZATION

The effect of variations in water content of silica-alumina was investigated for the polymerization and isomerizations of 1-butene. The water contents of the catalysts were varied by heat treatments ranging from 150 to 800°. The effect of structural changes in the catalyst was eliminated by a preliminary heat treatment at 800° prior to rehydration and subsequent activation in the selected temperature range. Studies with 1-butene indicate that on all catalysts prepared here there was rapid formation of a residue (polymeric complex) which ceased after a few minutes. The results of ammonia-blocking studies imply that this complex is associated with isomerization activity. Both polymeric complex formation and isomerization showed maximum activity on catalysts activated at 300°. Catalysts activated at lower temperatures were less active presumably because of poisoning or blocking of active sites. For catalysts activated in the 400-600° range the reactions show different linear dependencies on water content. The presence of water above a certain threshold value, 0.45%, appears necessary for the isomerization reaction. The results of the studies with ammonia suggest either that the average degree of polymerization declines from 4 to 2 on dehydration of the catalyst from 400 to 800° or that it remains constant at about 4 by utilizing fewer active sites. The data here indicate that isomerization activity depends on both the presence of the polymeric complex and the degree of dehydration of the surface. It is concluded that the water serves as a cocatalyst with the polymeric complex to provide the protons necessary for carbonium ion formation and subsequent reaction.