Integration of catalytic cracking and hydrotreating technology for triglyceride deoxygenation

Abstract

Waste cooking oil (WCO) blended in dodecane was hydrotreated over a sulfided CoMo (CoMoS) supported catalyst. Hydrogenation, hydrodeoxygenation (HDO), and hydrodecarbonoxide (HDC) were the dominant reactions at low temperatures (275-325°C), whereas cracking, cyclization, and aromatization were dominant at high temperatures (365°C). The HDO reaction pathway was more dominant than the HDC at all investigated conditions. The optimal conditions for deoxygenation (DO) and hydrogenation included a relatively low temperature (275°C), a low pressure (500 psi), a low volume ratio of H2/oil (H/O, 100 ml/ml), a low blend ratio (20 wt%), and a low liquid hourly space velocity (LHSV, 2 h-1). Hydrogenation activity was strongly improved by the introduction of catalyst support and an increase in temperature. Compared to unsupported CoMoS, supported CoMoS not only exhibits higher hydrogenation and HDO abilities at low temperatures, but also exhibits higher dehydrogenation activity at high temperatures. The deactivation of the CoMoS catalyst started with a decrease in hydrogenation capability followed by HDO capability; however, there were no impacts on the cracking, polymerization, and HDC activities. The main factors contributing to catalyst deactivation are coke deposition, byproduct water, and the loss of sulfur. Coke formation significantly increased due to a high operating temperature (365°C). By-product water could be partially eliminated by in-situ drying. Loss of sulfur occurred due to the loss of MoS2 layers. In catalytic cracking, high oxygen removal rates (>97.7 %) were obtained by using CaO, MgO, and titania. Even though this rate was 73.0 %, the light oil yield was the highest obtained by using alumina for all investigated metal oxide upgrading liquid products. The aromatic contents were lower than 4 % in all liquid products. Decarbonylation (DC) was the major DO reaction among all catalysts. Decarbonylation (DCO) was the primarily DO mechanism for the acidic catalysts, whereas decarboxylation (DCO2) for the alkaline catalysts. Higher catalyst acidity was beneficial towards DO but secondary cracking as well. The CaO catalyst exhibited a higher dehydrogenation capability. Acid treated kaolin (ATK) was very effective in the DO of WCO, contributing to the liquid production of high yield and high quality. Both kaolin-based and petroleum commercial catalysts (CC) eliminated more oxygen by dehydration than by DC; DCO was favoured over DCO2. The catalytic cracking/hydrotreating integrated technology presented in this work was successfully applied for the DO of triglycerides: the result was with a high oxygen removal rate, high liquid yield, and low levels of hydrogen consumption.