Processing algal biomass to renewable fuel oil extraction and hydrothermal liquefaction

Date of Award

2012

Degree Name

M.S. in Bioengineering

Department

Department of Chemical and Materials Engineering

Advisor/Chair

Advisor: Sukh Sidhu

Abstract

Since the industrial revolution the world's reliance on fossil fuels has been increasing at an accelerated rate. The negative environmental effects of burning fossil fuels and the demand for energy security have increased interest in renewable fuels technology. Using biomass as a feedstock for energy generation has emerged as an area of interest, and the focus of this study is on the sustainable production of a crude oil from the algal species Chlorella vulgaris. The derived crude oil is to serve as a feedstock for renewable diesel production. The constituents of this algae derived oil must be similar in structure and low in impurities, especially nitrogen and sulfur content, to allow for the economical upgrade of this oil to renewable diesel. Two methods for the generation of the crude oil were explored: direct oil extraction from the algal biomass and hydrothermal liquefaction of the algal biomass. Total algal lipid extraction from both dry and wet algal biomass was studied and multiple solvents, procedures and cell pretreatment methods were compared; this includes solvents at ambient conditions, supercritical carbon dioxide, liquefied dimethyl ether, ultrasonication, mechanical disruption and steaming. It was determined that pretreatment of the Chlorella vulgaris biomass is not necessary for total oil extraction, that total oil extraction from dry algae can be achieved by using a 95 percent ethanol solvent and that total oil extraction from wet algae can be achieved by using a 6:77:17 w/w/w ratio of water to ethanol to hexane. The optimal oil extraction procedure was scaled up and a process was developed to fractionate the algal biomass and isolate the lipid fractions conducive to upgrading to renewable diesel. The crude oil produced through this method was analyzed and found to be suitable for economical upgrade to renewable diesel. However biomass conversion to oil was low; only about 13.5 percent of the biomass could be converted to oil due to the relatively low lipid content of the Chlorella vulgaris (about 18 percent lipids on a dry weight basis). The hydrothermal liquefaction of the Chlorella vulgaris biomass was capable of converting about 44 percent of the initial Chlorella vulgaris biomass to bio-crude. However, the quality of the oil produced was not ideal for upgrading to renewable diesel due to the high nitrogen and sulfur content of the oil and the diverse molecular structures of the oil constituents. In conclusion, it was recommended that a method to enhance Chlorella vulgaris lipid content, such as nitrogen starvation or the introduction of sugars in the growth media, should be adopted prior to harvest and that the developed oil extraction procedure should be used to produce a renewable upgradable crude oil.

Keywords

Algae products Research, Biomass energy Research, Energy crops Research, Renewable energy sources Research

Rights Statement

Copyright © 2012, author

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