Approaches to conditioning of vegetable oil feedstock for hydrotreating to produce renewable diesel

The hydrotreating (HDT) process is increasingly implemented due to its versatility in producing renewable diesel and its flexibility with various raw materials. Impurities in vegetable oils can disrupt the HDT process, necessitating a pretreatment stage to ensure optimal performance, catalyst and equipment preservation, and achieve high yields. While laboratory-scale studies often overlook pretreatment due to minimal impacts on production costs and the use of pre-refined oils, industrial processes are designed and tailored to optimize the purification step for efficiency and cost-effectiveness. This study discusses the effect of impurities such as phospholipids, metals, and free fatty acids (FFA) on HDT and outlines effective pretreatment methods. Removing impurities is critical as they can deactivate sulfur-based catalysts, promote coke formation, and initiate oligomerization. The introduction of dimethyl disulfide (DMDS) and co-processing with sulfur-containing petroleum fractions are examined for their effectiveness in mitigating catalyst deactivation. The two-stage HDT, or pre-HDT, which is emphasized for lowering coke formation and increasing hydrogen availability, is also covered. The study emphasizes the importance of tailored pretreatment strategies for different raw material, including used cooking oil (UCO), to enhance HDT efficiency and extend catalyst life.