Two-stage catalytic up-grading of vacuum residue of a Wandoan coal liquid

A successive two-stage hydrotreatment using a commercial Ni-Mo/Al₂O₃ catalyst (HDN-30) was applied to the vacuum residue of a Wandoan coal liquid to achieve high levels of hydrocracking, hydrodenitrogenation and hydrodeoxygenation. Two-stage hydrotreatment in 1-methylnaphthalene containing 20wt% fluoranthene as a solvent at solvent/coal liquid ratio of unity removed 83% (overall) of nitrogen and 90% (overall) of oxygen in the asphaltene (benzene-soluble fraction) at 380 °C for 3 h and at 420 °C for 3 under hydrogen pressure of 15 MPa and 14 MPa, respectively, while the single stage treatment at 420 °C for 3 h removed only 41% and 46%, respectively. The same two-stage treatment allowed the overall denitrogenation of 51% and the overall deoxygenation of 67% from a mixture of asphaltene and preasphaltene (THF-soluble fraction). Addition of the catalyst prior to the second stage reaction increased the removal of nitrogen and oxygen to 75 and 82%, respectively, indicating significant catalyst deactivation by the preasphaltene fraction in the first stage. Increasing the solvent/coal liquid ratio to 2 or addition of tetrahydrofluoranthene as a component of the solvent increased the removal of nitrogen and oxygen to 70 and 80%, respectively. Such two-stage hydrotreatment was also effective in refining the whole residue, allowing denitrogenations and deoxygenations of 68 and 75%, respectively using tetrahydrofluoranthene. The coke, unreacted coal and minerals in the residue may not cause acute catalyst deactivation. High dissolving ability of the reaction solvent is very effective to decrease catalyst deactivation by carbon deposition. The successive two-stage hydrotreatment also enhanced hydrocracking of polar and resin fractions in the residue into oils (conversion, 65%). The extensive hydrogenation of the former fractions in the first stage may allow more easy cracking and may suppress with the aid of solvents their irreversible adsorption on the catalyst which leads to their coking into the catalyst poisons.