1. Dienst Chemische Ingenieurstechniek, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussel, Belgium, and Eni S.p.A., Divisione Refining & Marketing, Centro Ricerche di San Donato Milanese, Via Felice Maritano 26, I-20097 San Donato Milanese, Milano, Italy