Processing Pyrolysis Oil: Pilot Plant Scale Centrifugal Filtration and Stability Testing
Wynne, P. Zachary
Pyrolysis oil is known to be unstable due to polycondensation reactions that negatively affect properties, such as increased viscosity and water content, lower heating values, and phase separation. Filtration of particulates and solid content out of the pyrolysis oil has been proven to increase stability, thus a filtration system was designed for pilot scale testing for the Mississippi State University Sustainable Energy Research Center (SERC). A literature review was conducted to determine potentially effective methods and eliminate methods likely to not improve the pyrolysis oil properties and stability. An in-line centrifuge system was identified as a useful and cost effective way to remove solids from the pyrolysis oil with an added benefit of potentially removing water content through a three-phase separation configuration. Lab-scale testing of centrifugation on pyrolysis oil indicated both two phase (solid + oil phases) and three phase (solid + aqueous phase + oil phases) separations could be obtained depending on feedstock and pyrolysis oil characteristics, and that centrifugation was a viable option for the removal of solid content. KiOR, Inc. pine clear wood derived pyrolysis oil (formerly known as ReCrude™) was characterized to determine physicochemical properties in comparison to literature results. Aging tests were also performed to investigate stability. In comparison with literature data, the properties for the KiOR product indicated significantly lower water content, particulate matter loading, and viscosity coupled with higher heating and pH values, indicating a product much closer in composition to fossil fuel oils than other pyrolysis oils. The KiOR ReCrudeM™ oil also demonstrated a much higher degree of stability versus other pyrolysis oils; however, there are still some stability issues with the aged samples resulting in slightly higher water content and viscosity values and lower heating and pH values. It is recommended that stability testing (aging) be performed on aliquots separated using a method such as rotary evaporation to more accurately determine what mechanisms are resulting in the properties changes observed over time in response to elevated temperature and/or pressure.