Co-cracking of bio-oil distillate bottoms with vacuum gas oil for enhanced production of light compounds

Abstract

Seamless co-processing of pyrolysis bio-oil within existing petroleum refineries is the most synergistic and economic way to improve biorefinery output. Coprocessing bio-oil with vacuum gas oil (VGO) is one logical pathway. Bio-oil has a viscosity and molecular weight range similar to that of VGO, and the hydrogen-rich nature of VGO can chemically complement the bio-oil hydrogen deficiency. Distillation of biomass pyrolysis oils produces solid residues with a significant fraction of fixed carbon and heavy volatiles. Maximization of yields of light compounds like olefins and gasoline-range aromatics are crucial for both attainment of desired product output levels as well as to follow methods that mimic petroleum-based methods and chemistries. Herein we discuss a systematic study on the additive coprocessing of specific bio-oil distillation bottoms with VGO. Tail-gas reactive pyrolysis (TGRP) bio-oils from spirulina, switchgrass, and guayule biomasses were distilled, and their bottoms were subject to analytical experiments in mixtures with VGO over different zeolite catalysts (no catalyst, HZSM-5, Y-zeolite). Switchgrass-based bottoms exhibit greater hydrogen deficiency and higher oxygen content compared with that of spirulina or guayule. Switchgrass-based bottoms, with or without VGO, produced more aromatics and less olefins and alkanes, compared with spirulina or guayule bottoms. When compared across different mixing ratios, thermal cracking of a 10:1 guayule/VGO mixture resulted in higher aromatics yields than even the VGO by itself. Addition of more VGO up to a 1:1 ratio of VGO/switchgrass bottoms nearly tripled the production of BTEX compounds. For hydrogen-rich bottoms spirulina and guayule, LPG-range olefins yields increased nearly 50% for 1:1 VGO/bottoms blends, compared with theoretical yields.