ABSTRACT
Today, Fischer-Tropsch (FT) synthesis is carried out in diverse reactor designs, such as fixed beds, bubble columns, or circulating fluid beds. If a fixed bed mode of operation is favored, the Fischer-Tropsch catalyst will generally consist of particles of a few millimeters in size in order to minimize the pressure drop. Unfortunately, for particle diameters of more than about 1 mm, the effective reaction rate decreases significantly due to pore filling of the catalyst with high molecular weight hydrocarbons formed during synthesis.1 As a result, a limited diffusion rate of dissolved hydrogen and carbon monoxide is produced. Furthermore, steam is formed that induces strong inhibiting effects on the reaction rate, especially in the rear part of a fixed bed reactor.2-5
Taking these effects into account, internal pore diffusion was modeled on the basis of a wax-filled cylindrical single catalyst pore by using experimental data. The modeling was accomplished by a three-dimensional finite element method as well as by a respective differential-algebraic system. Since the Fischer-Tropsch synthesis is a rather complex reaction, an evaluation of pore diffusion limitations
12.1 Introduction ..............................................................................................216 12.2 Fundamentals ............................................................................................216
