Illini Algae - Hydrothermal Liquefaction
Waste Biomass to BioEnergy Conversion
Algae provide many potential routes for the conversion into biofuels, including hydrothermal liquefaction. During hydrothermal liquefaction, high moisture biomass is subjected to elevated temperatures (250-350 deg C) and pressures (10-20 MPa) in order to break down and reform the chemical building blocks into a bio-crude oil. At these temperatures and pressures, water becomes a highly reactive medium promoting the breakdown and cleavage of chemical bonds, allowing for the reformation of biological molecules. The conversion mimics the natural geological processes which produced our current fossil fuel reserves and allows for the conversion of a wide range of feedstocks. Tested feedstocks include low lipid algae, swine manure, sawdust, garbage, and even sewage sludge.
Water is also beneficial as a reaction medium since the newly formed bio-crude oil self-separates after conversion. The aqueous medium also eliminates the need dry the incoming feedstock, bypassing resource and energy intensive preprocessing steps . Depending on the feedstock, the resulting bio-crude oil can have a heating value comparable to bunker crude oil (30-40 MJ/kg) and can be burned in boilers or upgraded and refined into higher value fuel or chemical compounds.
Chemistry During Hydrothermal Liquefaction
The ability to convert such a wide range of feedstocks under hydrothermal conditions is due to the fundamental biological building blocks that are broken down and reformed during the process. Depending on the feedstock, waste biomass is composed of varying ratios of macromolecules including carbohydrates (cellulose and starch), lignin, lipids, and proteins. Initially, these macromolecules are broken down into their monomer units.
As the hydrothermal liquefaction process continues, the monomer units are further cleaved and broken into smaller fragment molecules. During fragmentation, the goal is to remove oxygen and other heteroatoms (e.g. nitrogen, sulphur, phosphorous), leaving behind the initial carbon and hydrogen atoms in the form of low molecular weight compounds. This process maximizes the energy content of the biocrude oil and increases the value and ability to refine the final product.
Synergistic Wastewater Treatment and BioEnergy Production
The robust reaction conditions and aqueous environment make hydrothermal liquefaction well suited for the conversion of low-lipid, fast-growing algae that proliferate in wastewater treatment facilities. Additionally, integrating algae cultivation into a wastewater treatment plant offers the synergetic benefit of providing nutrient remediation. Algae capture and utilize dissolved nitrogen and phosphorous present in wastewater to support growth. These plentiful nutrients would otherwise be released into the environment, creating harmful eutrophic zones as a result of prolific algal growth. By converting nutrient waste into a resource, we can reduce environmental pollution, produce bioenergy, and preserve our water resources.