(509t) Transport In Nanoporous Zeolites Used In Alkylation Processes

Alkylation of isobutane and n-butene to produce gasoline with a high octane number and low Reid vapor pressure has been carried out since World War II. Homogeneous catalysts such as hydrofluoric acid (HF) (Garwood, 1968) and sulfuric acid (H2SO4) (Chang, 2000) have been successfully used to catalyze these processes. These homogeneous catalyzed processes have matured over the years to give high product selectivity (~ 85 ? 90 %) at relatively safe and mild operating conditions (Rao and Vatcha, 1996). However, given the inherent toxicity and environmental hazards associated with these acid catalysts, scientists over the years have been looking for more environmentally benign replacements (Clark et al., 1998; Feller and Lercher, 2004).

Zeolites, in particular, have been studied in great detail over the last three decades (Sun Oil and Mobil in late 1960), as these show high product selectivity (~ 85 ? 95 %) but a rapid decrease in activity (Ramaswamy et al., 2005). Zeolites are crystalline nanoporous materials mainly composed of silicon and oxygen atoms whose composition is very similar to sand. Several necessarily important questions about alkylation processes catalyzed by zeolites still remain to be answered. How do organic molecules diffuse inside a nanoporous zeolite? How does the intra-crystalline channel network of a zeolite influence diffusion, adsorption/ desorption and reaction pathway of organic molecules?

The objectives of the current work are to understand and exploit different phenomena taking place during alkylation of iso-butane and n-butene on zeolites. Fundamental understanding and quantification of diffusion and adsorption/ desorption of the reactants, products and byproducts of alkylation reactions on the different zeolite morphologies, will help in determining the key features needed for catalyst design, process operation, and regeneration techniques for solid acid processes.

References:

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Huss. A.and Kennedy, C. R. US Patenet No. 4,935,577, Mobil Oil Corp, June 19, 1990

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