Abstract
Amphiphilic phosphotungstic acid (A-PTA) and Ni2P/SBA-15 catalysts were prepared to apply for selective oxidation of refractory sulfur compounds in light cycle oils and hydrotreating of the oxidized S compounds, respectively. Physical properties of the catalyst samples were analyzed by BET, CO uptake chemisorption, and TEM. Structural properties for the supported Ni2P catalysts were analyzed by X-ray diffraction (XRD) and extended X-ray absorption fine structure (XAFS) spectroscopy. The selective oxidation of S compounds in the LCO feed was conducted in a batch reactor at H2O2/S ratio of 10, atmospheric pressure and 353 K and then the products were fed to a continuous flow fixed-bed reactor for hydrotreating at 623 K, 3.0 MPa, and LHSV’s of 0.5–2.0 h−1. A-PTA catalyst showed a high oxidation conversion of 95% for a real LCO feed. The following hydrotreating led to a hydrodesulfurization (HDS) conversion of 99.6% and a hydrodenitrogenation (HDN) conversion of 94.7% over Ni2P/SBA-15, which were much higher than those of direct hydrotreating results which gave an HDS conversion of 63.5% and an HDN conversion of 17.5% based on the same LHSV of 2.0 h−1. It was revealed that the reduction in refractory nitrogen compounds after oxidative treatment contributed to the increase of the following HDS activity.
Highlights
Light cycle oil (LCO) is a liquid residue of fluidized catalytic cracking process (FCC) in the petroleum industry and has been used as a blend stock for industrial fuel oil or diesel fuels
The spent samples showed a partial reduction in the surface area and CO uptake amount compared with the fresh samples, due to the remained reaction products on the catalysts
For Ni2 P/SBA-15 the sulfur content in the product was found was very low at 14 ppm S and most refractory sulfur compounds except 4,6-DMDBT were removed during the OX-HT process, while for Ni-Mo-S catalyst alkyl-DBTs and 4,6-DMDBT remained in the product
Summary
Light cycle oil (LCO) is a liquid residue of fluidized catalytic cracking process (FCC) in the petroleum industry and has been used as a blend stock for industrial fuel oil or diesel fuels. Hydrodesulfurization (HDS) belongs to the hydrotreatment process that needs hydrogen and a catalyst to decompose the sulfur-containing compounds [1,3,4]. Previous studies on the HDS revealed that alkyl-dibenzithiophenes (DBT) with alkyl substitutions at four- and/or six-position are hard to completely eliminate due to a steric hindrance. These compounds are inferior in HDS reactivity and are classified as refractory S compounds in the conventional. The high contents of polyaromatic compounds in LCO lead to a loss of feedstock during the extraction of sulfones [2,19]. The amphiphilic phosphotungstic acid catalyst (A-PTA) and the Ni2 P/SBA-15 catalysts were used for selective oxidation (OX) and the following hydrodesulfurization (HDS), respectively
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