Catalysts for the Isomerization of C7 Paraffins

Catalysts having similar chemical compositions were tested for the isomerization of C7 paraffins, mainly branching of n-heptane. The principal objective was to maximize isomerization at minimal hydrocracking levels. Catalysts were prepared using commercially available zeolites with some modifications. Metals (mainly platinum) were incorporated in the conventional way (dispersed metal) but also as organometallic complexes. Initial activity tests used a stirred batch autoclave while time on stream tests used an automated continuous flow tubular microreactor. Products were analyzed by gas chromatography. Model compounds included other C7 hydrocarbons such as 2,4-dimethylpentane, methylcyclohexane, and toluene. A prototype catalyst provided 66% n-heptane isomerization with only 4% cracking per pass at high space velocities (LHSV = 5). Its selectivity was similar to that of a highly active commercial alumina-based catalyst while showing an improved tolerance for aromatic hydrocarbons and a longer catalyst life. Simple kinetic models were examined and used to simulate the sequence of events on the catalyst surface.