Molecular reconstruction of naphtha steam cracking feedstocks based on commercial indices

• Published in: Computers & chemical engineering 2007-09, Vol.31 (9), p.1020-1034
• Main Authors: Van Geem, Kevin M., Hudebine, Damien, Reyniers, Marie Françoise, Wahl, François, Verstraete, Jan J., Marin, Guy B.
• Format: Article
• Language: English
• Subjects: Molecular reconstruction; Naphtha; Optimization; Simulation; Steam cracking
• ISSN: 0098-1354; 1873-4375
• DOI: 10.1016/j.compchemeng.2006.09.001

A new method for feedstock reconstruction of industrially important hydrocarbon fractions is developed using as input the analytically determined commercial indices such as the average molecular weight, the specific density, the H/ C-ratio, the paraffin, isoparaffin, olefins, naphthenes, aromatics (PIONA) weight fractions and a set of ASTM boiling points. The method is based on Shannon's entropy criterion and allows generating a molecular composition of a naphtha fraction that meets all the boundary conditions set by the industrially available commercial indices. The most important components present in a naphtha fraction are selected as possible feedstock components. This approach is very fast because the optimization function can be transformed from a nonlinear equation in the N mole fractions ( N ∼ 10 2) into a nonlinear equation in maximally 14 parameters, making it very attractive for the petrochemical industry. A good correspondence exists between the simulated weight fractions and the actual analytically determined ones provided that the specified commercial indices are sufficiently accurate. The feedstock module is implemented in a simulation package for steam cracking but can be used as a stand-alone tool too. The combination of these two simulation tools makes it possible to obtain a good agreement between the simulated and experimentally determined product yields for a set of 50 pilot plant experiments with different naphtha feedstocks under widely varying operating conditions.