Supercritical Fluids Processing of Biomass to Chemicals and Fuels

Principal Investigator: Norman Olson
Organization: Iowa Energy Center,
Iowa State University
Technical Area: Renewable Energy

Project Objectives
The main objective of this project is to develop and/or enhance cost-effective methodologies for converting biomass into a wide variety of chemicals, fuels, and products using supercritical fluids. Supercritical fluids will be used both to perform reactions of biomass to chemicals and products as well as to perform extractions/separations of bio-based chemicals from non-homogeneous mixtures.

This work supports the Biomass Program’s Thermochemical Platforms Goals. Supercritical fluids are a thermochemical approach to processing that, while aligned with the Biomass Program’s interests in gasification and pyrolysis, offer the potential for more precise and controllable reactions. Indeed, the literature with respect to the use of water as a supercritical fluid frequently refers to “supercritical water gasification” or “supercritical water pyrolysis”.

Project Scope
There are numerous proposed means of converting biomass into valuable chemicals. Enzymatic hydrolysis of cellulose to sugars has recently received much attention. Thermochemical processes such as biomass gasification combined with Fischer-Tropsch chemistry and fast pyrolysis have also benefited from significant research efforts. Supercritical fluids processing of biomass to chemicals represents a path in the thermo-chemical processing platform of the DOE Program and also relates directly to the Biorefinery concept.

Supercritical fluids processing of biomass represents a very versatile and diverse path to the production of chemicals. Supercritical water can be used under a variety of conditions to quickly convert cellulose to sugar or to convert biomass into a mixture of oils, organic acids, alcohols and methane. Using supercritical water to convert biomass to chemicals is analogous to the “deep hole” (i.e. high pressure, high temperature) geological conditions originally thought to have, long ago, produced existing petroleum and natural gas deposits from ancient biomass.

Carbon dioxide can also be used as a supercritical fluid. It is currently used in its supercritical state to extract caffeine from coffee beans. At supercritical conditions, the characteristics of carbon dioxide radically change and it exhibits the characteristics of a solvent similar to hexane. The main advantages of using carbon dioxide are its low-cost and that it is environmentally benign. Supercritical carbon dioxide can also be used to extract oil from plant seeds and enhances esterification and polymerization reactions.

The potential for using supercritical fluids for reactions and separations is just starting to be realized and offers promise for huge breakthroughs in the cost-effective conversion of chemicals from biomass. Fluids such as propane, alcohols, ketones and other (not to mention combinations of supercritical fluids) have not been fully explored regarding their potential to convert biomass to chemicals. A concentrated effort in the supercritical fluids processing area could potentially yield significant breakthroughs in the cost-effective conversion of biomass to chemicals.

A thorough understanding of the scientific principles behind the chemistry of supercritical fluids does not exist. Through this project we hope not only to empirically develop new paths for the conversion of biomass to chemicals but also to enhance the understanding of the science behind the nature of supercritical fluids.