(575c) Algae Derived Bio-Oil Separation By Supercritical Fluid Fractionation

Bio-oils produced by thermal processes, such as fast pyrolysis, catalytic pyrolysis or hydrothermal liquefaction, are a promising source of sustainable, low greenhouse gas (GHG) alternative fuels. These thermal treatment processes are also well suited to decentralized energy production due to low capital and operating costs. However, pyrolysis bio-oils from algae have complex chemical compositions, including large concentrations of water, carboxylic acids, carbohydrates, and protein-derived substances. The oils are viscous, reactive, and thermally unstable. Due to the occurrence of decomposition products together with water and an abundance of compounds of many classes, range of polarities, and the large fraction of oxygenated compounds the mixture is difficult to fractionate by distillation, chromatography, or membrane based processes.

Several methods have been explored to separate bio-oils into stable fractions. By far the most effective separation and stabilization method has been solvent extraction. Although effective, solvent extraction poses two main obstacles to commercialization: (1) the significant amounts of energy required to remove the solvent from the product and (2) the propensity of the solvent to be contaminated with minerals from the char or ash. Separation of thermally produced bio-oils using supercritical fluids offers the advantages of liquid solvent extraction while drastically reducing energy demands and the predisposition to carry over solids into the extracted phase.

Scenedesmus dimorphus was pyrolized at 350, 400, and 450°C with and without a catalyst. Near critical and supercritical carbon dioxide and propane were evaluated for the extraction and fractionation of algae pyrolysis oils into stable fractions. Extractions were carried out at 25, 40, 65 and 110°C at a reduced pressure of 2.0. The effect of pyrolysis conditions and extraction conditions on product composition and stability will be discussed.