Results of Trial of Supercritical Fluid Process for Hydrolysis of Biomass for Cellulosic Ethanol Production
|Phase diagram for CO2. Source: Los Alamos National Lab|
Globex, a waste-to-cellulosic ethanol startup, announced that trials of its new supercritical fluid (SCF) technology have demonstrated a lignin removal of more than 50% at ambient temperatures into a SCF 4-liter pressure vessel. The material used in the trial was common wood chips.
The SCF-based pre-treatment process seems to be effective in converting an important part of hemicellulose to sugars and thereby leaves the cellulose ready to be treated by hydrolytic enzymes, according to the company.
Cellulosic biomass contains approximately 45% of cellulose (which can be converted to fermentable glucose), 30% hemicellulose (also convertible) and 15 to 20% of lignin (a non-fermentable phenyl-propene).
Before hydrolytic enzymes can access the cellulose inside the biomass, some form of pre-treatment is required. Steam explosion is an approach used by SunOpta, for example. (Earlier post.)
Globex’ approach uses highly pressurized CO2 as the chemical reagent, which is recovered at a high rate in a closed loop system. There is no use of acid or base chemical reagent and thus waste treatment costs are minimized.
Supercritical fluids (SCF) are liquids or gases used in a state above their critical temperature and pressure (critical point). In this state, the SCF has unique properties different from those of either gases or liquids, offering a combination of liquid-like density and solvency, with gas-like viscosity, diffusivity, compressibility and lack of surface tension.
As a result, supercritical fluids can rapidly penetrate porous and fibrous solids, offer good catalytic activity and can dissolve and extract a wide range of chemicals. Carbon dioxide is commonly used as a supercritical fluid.
The solvent properties are strongly pressure-dependent in the vicinity of the critical point, making supercritical fluids highly tunable, and giving them an important emerging role in new chemical processes.
For example, in 2004, Professors Charles Eckert and Charles Liotta at the Georgia Institute of Technology received a Green Chemistry Award from the EPA for their work on novel, benign, tunable solvents—especially supercritical CO2, nearcritical water and CO2-expanded liquids—to create a paradigm for sustainable development: benign solvents and improved performance.
Chemicals from Biomass with Novel Tunable Solvents (Georgia Tech)
Supercritical Fluid Processing for Renewable Energy (University of Iowa)