Reformate Production from LPG

The process under analysis comprises three major sections: (1) Dehydrocyclodimerization; and (2) Products Separation.

Dehydrocyclodimerization. Initially, an LPG stream is passed through fixed-bed adsorption systems, in which potential reforming catalyst poisons such as water, sulfur, and oxygen compounds are removed. The treated LPG stream is combined with recycle gas rich in unconverted paraffins and preheated by heat-exchange with effluent from the reactors. The first reactions are the dehydrogenation of propane and butane to mono-olefins, which quickly oligomerize forming large intermediates. Such intermediates, in turn, cyclize to naphthenes. All such reactions take place in the presence of bifunctionals catalyst based on a metal modified zeolite. Finally, the naphthenes formed are dehydrogenated to a mixture rich in benzene, toluene and xylene – Reformate. While all such reactions are endothermic, between each reaction stage the charge is reheated to reaction temperature. Coke tend to accumulate on the catalysts, deactivating them over time. Then, they are continually withdrawn from the bottom of the reactor, fed to a separate vessel to burn off the coke and lifted back to reactor,

Separation. The effluent from reactors is fed to a gas/liquid separator, in which it is split into vapor and liquid products. The vapor phase, rich in hydrogen produced from reforming, is split in two fractions: the first one is compressed and recycled to the charge heaters, while the remaining is compressed and sent to a PSA system, in which the hydrogen-rich gas is purified from unconverted paraffins. The liquid phase is also compressed and sent to a column, which strips off light hydrocarbons in the distillate. Reformate is withdrawn from bottom, cooled and stored.