Oil vapor coking kinetics over oxidized Colorado oil shale

A model for coking of shale oil vapors over porous oxidized recycle shale has been derived. This model includes mass transfer of the oil vapor through the gas film surrounding the shale particles with countercurrent flow of cracked low-molecular weight products, diffusion through the pore system, adsorption onto the internal surfaces, chemical reaction of the adsorbate, and desorption of oil and light gas. The intrinsic chemical coking rate has been determined in a fixed-bed reactor using a constant oil vapor feed. The kinetics of adsorption/desorption have been determined by analyzing responses of oxidized shale beds to inlet oil vapor pulses. The experimental results and corresponding model calculations show that particle size strongly influences coke yield. Mass transfer is particularly important initially when pure mineral surfaces are exposed. Once the surfaces have been covered by coke, the chemical coking rate declines substantially relative to the uncovered rate. High-boiling components adsorb selectively on the surface, and this explains the observed selectivity toward high-boiling components in the overall coking process.