Iowa State University and Chevron U.S.A are partnering to develop an advanced biorenewables technology called solvent liquefaction.
The process of solvent liquefaction converts biomass such as quarter-inch wood chips into a bio-oil that can be processed into fuels or chemicals and a “biochar” that can enrich soils.
The Chevron-Iowa State collaboration began in 2013 when the company moved its $1.4 million small continuous liquefaction unit from Houston, Texas, to the BioCentury Research Farm, a biofuels pilot plant, just west of Ames, Iowa.
As part of the agreement, Chevron has donated the pilot plant to Iowa State.
“Our modular approach to the plant design allowed for a fair amount of prototyping and proof-of-concept experiments along the way,” says Martin Haverly, a doctoral student in mechanical engineering and the lead design engineer for the project.
“The system is a blend of commercially available products and custom solutions, all tied together at an industrially relevant scale. All of these efforts helped us end up where we are now, with a safe and functioning pilot plant.”
How it works. The solvent liquefaction process used in the pilot plant, initially developed by Chevron, begins with a proprietary solvent that is mixed with wood chips or other solid biomass.
The mixture is processed under moderate temperatures and pressures and the resulting slurry is extruded into a reactor.
After heating in the reactor, production is split into two processing streams, the upper stream handling gases and vapours while the lower handles liquids and small amounts of solids.
A series of filters and separators along both streams recovers bio-oil, small amounts of biochar, and solvent for recycling.
The process produces a bio-oil that is low in oxygen and therefore more stable than other bio-oils.
“With the work Chevron did, this looked like it could be a very cost-effective method for producing biofuels,” says Ryan Smith, the deputy director of the Bioeconomy Institute’s Thermochemical Research Group.
“But many of the unit operations hadn’t been tested, so the team has been working to design and optimise these operations,” Smith adds.
Lysle Whitmer, the senior thermochemical research engineer for Iowa State’s Bioeconomy Institute, says the engineers have now demonstrated the viability of every one of the pilot plant’s operations.
The pilot plant operates about once a week for up to 18 hours at a time and it can process about a pound of biomass every hour.
Brown says the project’s next steps could include working with new feedstocks to create high-value, biorenewable chemicals.