Removal of Char Particles From Bio-Oil by Liquid-Phase Microfiltration

Bio-oil formed by the fast pyrolysis of biomass has tremendous potential as a renewable feedstock to make liquid transportation fuels. However, the presence of char particles in the bio-oil causes problems in storage and end-use. Currently there is no well-established technology to remove char particles less than 10 microns in size. In this study we describe the application of a liquid-phase microfiltration (MF) process to remove char particles from bio-oil down to slightly sub-micron levels. Tubular ceramic membranes of nominal pore sizes 0.5 and 0.8 microns were employed to carry out the MF, which was conducted in the cross-flow mode at temperatures near 40 degrees Celsius and at different trans-membrane pressures varying from 1 to 3 bar. Microscopic and ash content analysis of the feed and permeate streams were conducted to determine the efficacy of the process. Our results demonstrated the removal of a large percentage of the char particles with a significant reduction in overall ash content of the bio-oil. Other than the removal of the suspended chars, the chemical composition of the liquid bio-oil was changed very little by the MF process. Results of fouling analysis obtained from longer runs of bio-oil through the membranes clearly showed that the cake formation mechanism of fouling is predominant in this process. A membrane cleaning protocol for the fouled membrane was also developed.