Experimental Evaluation and Empirical Modeling of Cross-Flow Microfiltration for Solids and Ash Removal from Fast Pyrolysis Bio-Oil

Abstract

The presence of suspended char particulate and ash in fast pyrolysis bio-oil produced from the fast pyrolysis of high ash forestry materials poses a significant technical challenge for the direct utilization and/or catalytic upgrading of these low-carbon renewable fuels. Cross-flow microfiltration is a physical upgrading process strategy that can remove suspended solids and ash from the fast pyrolysis bio-oil. To develop data sets on operational characteristics of fast pyrolysis bio-oil cross-flow microfiltration, experimental research was undertaken. Using a variety of filtration media with nominal pore sizes between 1 and 40 μm, typical solids and ash rejection ranged from 80 to 95% and 4–45%, respectively. An empirical modeling procedure was developed to predict the throughput and resistance associated with cross-flow microfiltration of fast pyrolysis bio-oil, which demonstrated good agreement with generated experimental data. Key operating parameters were also studied, and it was found that transmembrane pressures less than 1 bar and fluid preheat temperatures up to 60 °C were ideal for maximizing the pseudo steady-state flux of the process. Furthermore, the use of low viscosity, miscible solvents, and/or initial solids reduction pathways prior to microfiltration offered additional routes to potentially improve the throughput of such a process.