| Scope and Method of Study. A trickle-bed reactor system equipped with adequate temperature, pressure and flow controls was designed, constructed and operated for hydrotreatment of a coal-derived liquid. Two commercial Ni-Mo-Al(,2)O(,3) catalysts of similar chemical but significantly different physical properties were used separately and in combination as composite catalyst beds. Four experimental runs were conducted using temperatures in the range of 260 to 400(DEGREES)C, and liquid volume hourly space times in the range of 0.94 to 1.87 hours; hydrogen gas pressure and flow rate were held constant at 11.6 MPa and 1781 std.m('3)/m('3) of oil, respectively. The product liquid samples were analyzed for elemental nitrogen and hydrogen content; some selected liquid samples were subjected to 454 C('+) distillation and solvent residue analysis. The used catalyst samples were separated into six sections, extensively extracted with tetrahydrofuran, and dried in a vacuum oven. These catalysts were characterized in terms of coke content, surface area, pore volume, pore size distribution and deposited metal content.;Findings and Conclusions. Both the small and the large pore catalysts lost significant hydrodenitrogenation activity over the 240 hours of oil-catalyst contact, the deactivation being severe during the first 12-36 hours. Small pore diameter catalyst (KF-153S) was observed to have consistently higher hydrogenitrogenation, 454 C('+) distillation and solvent residue reduction activity. Under the conditions of this study, the composite catalyst bed combination of small and large pore diameter catalysts did not offer any significant advantage for hydrodenitrogenation and residue reduction of an SRC liquid over single catalyst beds. The two temperature reactor zone experiment revealed significant removal of feedstock inorganic constituents in the top reactor at relatively mild operating temperatures (260(DEGREES)C). Based on the experimental hydrodenitrogenation data, a mathematical model was developed to represent the catalyst hydrodenitrogenation activity as a function of catalyst pore diameter and diffusing species molecular diameter. Optimum catalyst activity was predicted to occur for catalyst pore diameter five times the diameter of the diffusing molecule. |
