EXPERIMENTAL AND THEORETICAL STUDIES OF BUBBLE-COLUMN SLURRY REACTORS USED FOR FISCHER-TROPSCH SYNTHESIS

A theoretical model of slurry reactors used for Fischer-Tropsch synthesis has been developed in an effort to understand the influence of synthesis gas composition and velocity, and catalyst loading and activity, on the rate of synthesis gas conversion and the composition of the products. The model takes into account axial mixing in the gas, liquid, and solid phases, as well as the existence of mass transfer resistances between the gas-liquid interface and the bulk liquid. It was found that in small diameter bubble column slurry reactors, axial mixing in the gas and liquid phases can be neglected. The predictions of this model are compared to experimental results obtained by other workers in bench and pilot plant scale reactors containing iron catalysts, as well as data obtained in this laboratory with a ruthenium-containing slurry reactor. The model accurately predicts the observed dependence of synthesis gas conversion and H(,2)/CO consumption ratio on the inlet composition and velocity of the synthesis gas. Our analysis of the dependence of conversion on gas velocity indicates that mass transfer has a significant influence on the reaction rate at low gas velocities (1-2 cm/s).; The model has also been used to predict the influence of process and design variables on the performance of large scale Fischer-Tropsch slurry reactors. The most effective use of the reactor volume occurs in small diameter reactors with high catalyst loading and high water-gas shift activity. The efficiency of the reactor does not depend strongly on the velocity of the feed gas. As the velocity increases, the rate of synthesis gas conversion goes through a weak maximum at 5 cm/s.; In addition to the work aimed at modeling the slurry reactor, experimental work has been carried out to understand the factors that influence the rate of carbon formation in iron-containing slurry reactors. High carbon formation rates are favored by high CO partial pressures, high temperature, and a high degree of catalyst reduction. Above 3 atm, the hydrogen partial pressure does not strongly influence the rate of carbon formation. At lower values of the hydrogen partial pressure, the carbon formation rate increases with increasing hydrogen partial pressure.