Hydrotreating of oak wood bio-crude using heterogeneous hydrogen producer over Y zeolite catalyst synthesized from rice husk

Abstract

Hydrotreating is an effective method for bio-crude upgrading. However, the high cost of catalysts and gaseous hydrogen consumption limits its application. In this research, oak wood hydrothermal liquefaction bio-crude upgrading was conducted by using Zn as heterogeneous hydrogen producer and low-cost Ni supported Y zeolite synthesized from rice husk as catalyst. The Y zeolite was obtained by two-step synthetic route, using different Tetramethylammonium hydroxide (TMAOH)/silica mole ratios of 0, 0.03 and 0.08. Synthesized Y zeolite showed better performance than commercial one due to the higher total acid sites (24–28% higher). Compared with template-free Y zeolite, the introduction of TMAOH template brings more mesopore structure to the synthesized zeolite, improving its catalytic activity. The yield of upgraded oil increased from 65.5% of blank upgrading test to 80.0% of the synthesized 10%Ni/HY (0.08), and the coke amount reduced from 14.3% to 3.9%. The H/C ratio increased, and the O/C ratio decreased, consequently the higher heating value (HHV) raised from 30.04 to 33.13 MJ/kg. The area percentages of hydrogenation products: cyclopentanones and hydrogenated lignin-derived compounds increased in the catalytic upgraded oil samples consuming furan derivatives and lignin-derived compounds. Deactivation of the synthesized catalyst was observed due to the zeolite structure collapse, Ni active site oxidation, coke deposition and presence of ZnO impurity. The one-pot catalytic hydrothermal treatment of oak wood was also conducted with interesting result, bio-crude yield of 39.0% and HHV of 32.61 MJ/kg, which greatly simplified the process by combining the bio-crude production and upgrading steps together.