Deoxygenation of palm fatty acid distillate to green diesel over molybdenum nitride and carbide-based catalysts in a trickle-bed reactor

Abstract

In this present work, the deoxygenation of palm fatty acid distillate (PFAD) to green diesel over γ-Al2O3 supported bimetallic CoMo and NiMo carbide and nitride catalysts was conducted in a trickle bed reactor. The catalysts were prepared by a single-step decomposition method of mixture containing hexamethylenetetramine and corresponding metal salts in presence of hydrogen and nitrogen for carbide and nitride forms, respectively at 700 oC. The prepared catalysts were characterized by XRD, XPS, N2-sorption, SEM/EDX and TGA techniques. The catalyst performance was evaluated at a temperature of 330 °C, hydrogen pressure of 5 MPa, LHSV of 1 h−1, and H2/feed ratio of 1000 N(cm3·cm-3). It was found that the carbide catalysts exhibited the superior performance that those of nitride catalysts. The bimetallic CoMoC showed higher diesel yield than monometallic Mo carbide and bimetallic NiMoC catalysts. Thus, the CoMoC and NiMoC catalysts were selected for further investigations. The catalysts prepared by a single-step decomposition method exhibited higher catalytic activity than that of catalysts prepared by temperature-programmed reduction method due to higher catalyst surface area. In order to optimize the operating conditions, the operating temperatures were varied from 300 to 390 °C under 3-5 MPa of hydrogen pressure. The operating temperature of 330 °C and 5 MPa of hydrogen pressure was found to be a suitable condition for CoMoC and NiMoC catalysts. In the stability test, the CoMoC catalyst exhibited complete PFAD conversion with diesel yield 82.0% for 72 h. time on stream. However, the catalytic activity of CoMoC catalyst gradually decreased after 72 h. and PFAD conversion of 81% with diesel yield of 68.5% were obtained after 102 h. time on stream.