(267e) Maximizing Production of Premium Distillate Fuels through Selective Hydroisomerization of Normal Paraffins

As the demand for clean distillate fuels grows around the world refiners are looking to optimize their refineries to produce these premium products while minimizing production of lower value products such as motor gasoline. Cetane number and cold-flow properties are critical performance specifications for distillate products, however due to the chemical nature of distillate range process streams it can be challenging to achieve both specifications without either using additive packages or blending with other product streams downstream of processing units. Both of these specifications are closely linked to paraffin concentration: cetane number benefits from high paraffin concentrations while cold-flow properties are adversely affected by high n-paraffin concentrations. Hydroisomerization is one process chemistry solution that can be employed to mitigate this dilemma through selective hydroisomerization of n-paraffins to i-paraffins which both preserves cetane number and improves cold-flow performance.

 

Selective hydroisomerization requires a bifunctional catalyst containing both a metal function to perform hydrogenation and dehydrogenation, and a shape-selective acid function to perform the skeletal isomerization of the olefin intermediate. These bifunctional catalysts need to be carefully designed to balance kinetics and molecular transport in order to maximize hydroisomerization selectivity. Through continuous research and development efforts over the last 25 years, ExxonMobil has developed and deployed multiple generations of MIDW^TM technology for production of premium distillate fuels via hydroisomerization.  In addition to maintaining cetane number and improving cold-flow properties, the MIDW^TM technology also demonstrates high distillate selectivity through the minimization of cracking reactions that produce lower value naphtha. Recent advances in catalyst formulations and process configurations have expanded the versatility of MIDW^TM technology enabling refiners to process difficult feeds, including sour feedstocks.

 

This paper will provide the audience an industrial perspective on catalyst development; specifically, catalyst formulation considerations will be described in light of competing process chemistries, feed contaminants, and equipment constraints.