Submitted to: Annual European Bioenergy Conference
Publication Type: Abstract Only
Publication Acceptance Date: May 8, 2012
Publication Date: June 20, 2012
Citation: Holser, R.A. 2012. Co-product recovery from biomass during ethanol production [abstract]. Annual European Bioenergy Conference. 2012 CDROM. Technical Abstract: The conversion of biomass to ethanol represents a sustainable alternative liquid fuel technology that does not need to compete with the supply of commodity crops such as corn and soybeans. Maintaining agricultural production of edible crops for the food supply and using agricultural waste or low input energy crops grown on marginal land for biofuel production is necessary although economically challenging. The separation and recovery of valuable co-products from biomass would improve the process economics of ethanol production. Available biomass is primarily lignocellulosic with minor components including waxes and other lipids that are potential co-products which could be separated and recovered from the biomass on-site prior to conversion using hot ethanol. Ethanol is not a traditional lipid solvent however at temperatures above 50°C ethanol can solubilize the waxes typically found on plant stems. Additionally, the lignin may also be separated from the cellulosic substrate and recovered for use in plastics and resins or decomposed into phenolic acid compounds such as the bioactive ferulic and coumaric acids. These phenolic acids have applications as antioxidant and antimicrobial agents, respectively. The process for the recovery of co-products was evaluated for a 70 T/day facility using Panicum virgatum (switchgrass) as the biomass feedstock. Switchgrass is a perennial North Amercian prairie grass with harvests of 5-11 tonnes/hectare. It was chosen for this investigation due to the amount of attention it has received as an energy crop rather than for the amount or unique co-products it contains. The amount of recoverable surface lipids was estimated at 0.1% dry weight and the lignin content was estimated at 5.5% in the leaf with 7.5% in the stem. The analysis assumed complete recovery of the lipids from the biomass with 0.5% residual lignin. The evaluation was facilitated with the simulation software SuperPro Designer 7.5 (Intelligen, Inc., Scotch Plains, New Jersey, USA). The initial process design did not include a co-product recovery section. This was modified by adding a section to separate the lipids from the biomass in a continuous solid/liquid extraction operation using 50°C ethanol generated on-site. The lipids were recovered from the ethanol by cooling and centrifugation with recycle of the ethanol stream. This scheme produced 70 kg/day of mixed lipid extract which could be marketed as a natural wax product. The recovery of a lignin as co-product was addressed by considering existing fermentation process designs where a de-lignified cellulosic substrate is used for saccharification and the lignin fraction is combusted as a heating fuel. This becomes an economic comparison of the market value for the lignin as co-product versus the heating value of some alternative fuel (ethanol). It is possible to change the operation of the facility in response to fluctuations in the market price. At a high value for lignin it could be recovered as co-product otherwise used as fuel with minimal interruption to bioethanol production. The results of this study suggest two paths to improve the process economics of bioethanol production.