Preliminary results on optimising hydrothermal treatment used in co-production of biofuels

In December 2002, an EU-project for co-production of biofuels was started. The overall objective is to develop cost and energy effective production systems for co-production of bio ethanol and electricity based on integrated biomass utilization. Duringthe first 12 months period of the project, a pilot plan reactor for hydrothermal treatment (and other pre-treatments including wet oxidation) with a capacity of 100 kg/hour was constructed and tested for pre-treatment of wheat straw to be used for ethanoland/or electricity production. Pre-treatment by hydrothermal treatment (or wet oxidation) is performed to solubilize the hemicellulose fraction in straw, open the cellulose structure to increase accessibility of enzymes, and to remove the alkaline salts(e.g. potassium chloride). Alkaline salts cause corrosion problems in conventional boilers during incineration of straw for electricity production. The solubilised hemicellulose is in a second step converted by either enzymes or weak acid hydrolyses tomonomeric sugar compounds for ethanol production. The cellulose fraction containing the lignin will be burned for electricity or part of it may be used for ethanol production by means of SSF. By-products from the pre-treatment and fermentation processeswill be concentrated and used for animal feed. Several trials were made with varying parameters of water level, chemical addition and flow in the reactor. All experiments were performed at 190 C, except for a single experiment performed at 200 C. Theresults illustrates that it is possible to extract more than 95% of the alkaline salts (at 200 C) leaving a solid cellulose rich biofuel for combustion or for further treatment in the ethanol process. In the experiments performed at 190 C, the best totalglucose yield after pre-treatment and following enzymatic hydrolysis was found in the experiment with Na2CO3 addition (61% glucose yield), but improved conversion was found in the experiment at 200 C (97% glucose yield). Very good glucose recovery(80-100%) was found in all of these trials. The highest total yield of hemicellulose (67%) was found in the experiment with high flow. In this experiment the hemicellulose recovery was 87%. The highest hemicellulose recovery (91%) was found in theexperiment with Na2CO3 addition.