Olefin oligomerization using surface modified molecular sieve catalyst

Abstract

In a process for the oligomerization of light olefins (e.g. propylene) to more valuable higher olefins (e.g. hexene), the use of a molecular sieve (e.g. SAPO-11) that has been acid washed has shown to provide superior selectivity to, and yield of, the desired product. These benefits are attributed to a reduction in non-selective acid sites as well as an increase in phosphorous content (in the case of SAPO molecular sieves) at the molecular sieve crystallite surface, a probable result of removing amorphous silicon aluminum phosphate acid, silicophosphorous acids, and/or phosphoric acids. Furthermore, this removal is likely accompanied by an increased accessibility of olefinic feed components to the so-called “selective” acid sites within the sieve pores. Post-synthesis acid washing of the molecular sieve has not only demonstrated a narrower carbon number distribution of olefin oligomers, but also improved the linearity of the oligomerized olefinic product slate in general. Such increases in linearity generally correspond to overall higher product values, when downstream applications such as plasticizer intermediates are considered.