Use of Supercritical Fluids and Other Novel Methodologies for the Production of High-Value Compounds from Biomass

Grant: 04-01
Principal Investigator: Walter S. Trahanovsky
Organization: Department of Chemistry, Iowa State University
Technical Area: Renewable Energy

Background and Significance
Although plant biomass is abundant and renewable, relative little is converted to commercially useful low-molecular-weight compounds. We propose to explore novel approaches to convert biomass into small useful molecules. New practical methods for deriving economically useful chemicals from biomass would make it more possible to use biomass instead of petroleum as a source of chemicals.

Project Objectives
Our general objective is to develop methods to obtain significant yields of high-value compounds from biomass. We are especially interested in developing routes to enantiomerically pure (enantiopure) chiral compounds since the value of many of these is very high and plant biomass should be a good source of these compounds since most of plant biomass is composed of enantiopure chiral units.

We are also interested in developing practical methods to concentrate organic compounds from dilute aqueous solutions such as those that result from anaerobic digestion. Specific projects include the thermal decomposition of cellulose and lignocellulosic materials in high boiling solvents, the use of continuous liquid-liquid extraction as a means of extracting organic compounds from dilute aqueous solutions, and the conversion of isosorbide and isomannide (two enantipure compounds readily available from biomass) to novel chiral stationary phases that may have use in the separation of enantiomers of complex organic compounds. It is expect that this work will result in novel practical methods to convert biomass to high-value compounds.

Work to Date (Technical Report – March 2007)
We are continuing our effort to obtain alkyl glucosides from cellulose by heating cellulose in a supercritical alcohol. We have carried out a series of runs heating a mixture of cellulose and isopropyl alcohol in a high-pressure stainless steel reactor. The mixtures were stirred and heated above the supercritical temperature (Tc) of isopropyl alcohol (235°C) and enough isopropyl alcohol was used to generate pressures well above the supercritical pressure of isopropyl alcohol (705 pounds/in2).

The temperature of the runs ranged from 250 to 325°C and the pressures were in the 2000 psi range. At the end of each run the reaction mixture was allowed to cool and the solid phase was separated from the liquid phase. The liquid phase was concentrated by removing the isopropyl alcohol under reduced pressure. Analysis of the concentrated product mixture by 1H NMR spectroscopy showed that the α- and β- isopropyl glucosides and levoglucosan were the main products. Small amounts of furan aldehydes and levulinate products were also detected. Other compounds are produced and these are now under study. During this period we have initiated the study of related substances such as cellobiose and glucose. Heating these substances in a supercritical alcohol also leads to significant yields of low molecular weight products. These reactions are also now under study.

Several years ago we discovered a convenient method for the preparation of levoglucosenone from cellulose. The levoglucosenone is obtained in 5-10% yield and is relatively pure. Our method works reasonably well, but certain aspects of the procedure have not been fully investigated. During this period we have continued to study various aspects of the experimental procedure. Our main focus has been study of the pretreatment of the cellulose with salts derived from transition metals. This work has resulted in some improvement of the yield of levoglucosenone and we are continuing to study the effects of various
metal ions.