(130b) Comparative Study of Vapor-Liquid Equilibrium during Hydroprocessing of Different Petroleum Feedstocks

Hydroprocessing is one of the most important upgrading and refining processes to produce clean and high quality transportation fuels. During commercial hydroprocessing, petroleum fractions (hydrocarbons) and hydrogen pass through trickle-bed catalytic reactors at relatively high temperatures and pressures (350-400°C and 50-100 atm.) to undergo various reactions. Under such conditions, the vapor and liquid phases in the reactors are at equilibrium (VLE) with both containing hydrogen and hydrocarbons. As temperature and treat-gas-to-oil ratio increase and pressure decreases, more oil is vaporized, resulting in a reduced liquid flow rate. This important issue is almost always ignored in reactor performance analysis, even though it could change the reactor behavior and performance. Industrial hydrotreater design and most modeling attempts assume that all the feed hydrocarbons remain in the liquid phase under operating conditions. The poor shape of research on this vapor-liquid equilibrium effect on hydroprocessing is probably due to difficulties in experimental measurements and the complexity of the resulting multi-phase modeling analysis. In this study, VLE experiments were conducted with real petroleum feedstocks in a continuous flow bench-scale unit at temperatures, pressures, and gas-to-oil ratios typically used for hydroprocessing. For comparison, two different types of feedstocks were used: one was highly aromatic light cycle oil (LCO) from fluid catalytic cracking and the other was highly paraffinic white oil. It was found that with the increase in temperature and the decrease in pressure, the amount of oil evaporated into the vapor phase increased significantly. Similar trends were observed for the total sulphur and individual sulphur compounds in the experiments with LCO feed. Although the averaged boiling point of white oil, as well as IBP and FBP, is higher than that of the LCO, under the same conditions white oil showed higher volatility than LCO. To predict the VLE behaviors of any hydroprocessing system under any conditions, a commercial flash calculation program has been used. The feedstocks were divided into 29 hydrocarbon pseudo-components and the flash model was fitted to our experimental data by adjusting the interaction coefficients between hydrogen and hydrocarbon pseudo-components. The interaction coefficients were subsequently correlated with the boiling point of the pseudo-components. Detailed discussion of the interaction coefficients and the quality of the predictions of the calibrated flash model will be given in the full paper and the associated presentation.