Wood Hydrolysis for Ethanol Production
As a rule, 1 to 3 tons of non-wood stems (straw, corn stover, bagasse) are produced by annual plants with every ton of harvested grain. Pound-for-pound, the stalk material contains as much fermentable sugars in the form of cellulose than available from starch in grains. Often, as is the case with sugarcane, the ethanol yield per acre can be tripled when the stem material is also processed. Cellulose conversion to fermentable sugars occurs by the process of acid hydrolysis, using aqueous mineral acids, enzymes or solvent assisted acid hydrolysis.
Wood and non-wood lignocellulosics are complex, renewable natural products consisting of cellulose (glucose), hemicelluloses (glucose, mannose, galactose the C6 sugars, and xylose, arabinose and rhamnose, the C5 sugars). Glucose, mannose and xylose make up 95-97% of the total wood sugars. Additionally, wood consists of lignin (5-30%), extractives (3-18%) and ash (0.3-12%). These components become sources of valuable coproducts (see diagram I) in the production of ethanol and allow significant reductions in production costs. Recovery of coproducts allows total closure of the water cycle in some conversion processes and makes them pollution- free.
Efficient recovery of the chemical components makes it mandatory that the lignocellulosic components be first dissolved and thereby refined to products of maximum value and highest market potential. Total dissolution of wood to fermentable sugars, lignin and extractives can be achieved only on simultaneous hydrolysis in a solvent system capable of solubilizing all the products in the hydrolysis liquor. Recovery of the organic solvent from the hydrolysate by distillation and flashing precipitates the water-insoluble lignin and extractives, leaving behind a concentrated, high-gravity solution of 25 to 38% sugar solids. These sugars become the feedstock for a multitude of fermentation products of which ethanol is just one.
The ACOS Process
The ACOS process (Acid Catalyzed Organosolv Saccharification) is the only known wood hydrolysis process capable of total (residue-free) dissolution of any wood or agricultural residue (see diagram II). The wood substance recovery after hydrolysis is 100% by the ACOS process. Solvent (acetone) recovery by distillation concentrates the sugars four times and cleanly co-precipitates the extractives with the lignin. Judicious fermentation of the C6 sugars (glucose and mannose, if any) produces 320 to 378 L/TOD (84.5 to 100 gal/TOD) ethanol. In addition, the process converts xylose (C5) to xylitol with an 88.5% overall yield (96-98 % purity). The lignin is recovered as a free-flowing powder and marketed as natural lignin or as ligosulphonate. Not only is the ACOS process largely water self-sufficient but the xylitol crystallization closes the water-cycle in providing an essentially effluent-free (MACT) plant
Due to the high value recovery by the ACOS process (ROI from 15 to 75 % in 150 to 350 t/day capacity plants) the process can be practised in relatively small scale (80 to 250 T/day feedstock capacity) plants. Larger plants (400 to 1000 T/day feedstock capacity) have substantially greater ROI returns. For details, see a summary of the economic calculations for cornstover conversion (1050 TOD/day) in the ACOS process along side of production of 40 million gal/yr grain ethanol. The much higher value recovery from the stover, as compared to the value of grain ethanol, is unmistakable.
The ACOS process is patented worldwide and an engineering feasibility study by Jaakko Poyry Fluor Daniel engineers in 1993 confirmed its commercial viability. The ACOS process uses established organosolv pulping technology and hardware, successfully upscaled in Germany in 1994 and the process is considered commercial-ready. Site-specific bankable engineering feasibility studies are usually conducted at the client’s expense.
The ACOS Technology
The ACOS technology distinguishes itself from all other wood hydrolysis processes in its ability to dissolve (refine) any lignocellulosic material to its chemical components and separate these components for further processing to a variety of value added products. Thereby, the value of the lignocellulose feedstock is maximized, irrespective of its source and origin, and credit-rated bioethanol can be produced at a competitive price with gasoline and other liquid fuels. The value recovery for cellulosic wastes allows bioethanol production at small economies of scale (as small as 50 T/day feedstock capacity) thus avoiding long transportation distances required for the larger (>1000 T/day) feedstock capacity plants of other technologies.
The ACOS technology is considered as a critical and strategic technology for the future for processing biomass. Bioethanol is a multipurpose fuel, suitable as a blending agent and a clean burning oxygenate additive to automotive gasoline and diesel fuels, as an affordable renewable hydrogen source for fuel cells for both automotive and stationary electricity generation, and a raw material supplier for production of renewable organic chemicals in the future. Much broader organic chemical markets can be developed based on fermentation of sugars. For these markets, quantitative refining of lignocellulosics to fermentable sugars is a first critical step and the small to medium scale capability (80-300 T/day feedstock capacity) an important economic aspect for this new industry. Currently, only the ACOS process provides high efficiency biomass refining capabilities for these new biomass-based industries without generating further wastes.
On a global scale, biomass refining and bioethanol production will become significant economic engines for sustainable development of developing countries and facilitate shifts from fossil to renewable energy in countries where large-scale biomass production (plantation forestry, high yield agriculture) is possible. Bioethanol becomes a tradable energy (fuel) currency. Thus biomass and bioethanol production become economic engines by providing significant employment, income to the poor and revenue in the hands of developing countries. It is estimated that for every 350 TOD/day capacity ACOS plant 50 full time jobs will be generated in growing the biomass and 125 in bioethanol production. This contrasts to wind and solar power generation which lack the job creating potential being fairly passive energy sources once installed.
For further information, please contact:
Dr. Laszlo Paszner; President, Paszner Technologies Inc., 2683 Parkway Drive, Surrey, BC, Canada, V4P 1C2
Tel: 604 538 1349; Fax: 604 538 5108
Email: paszner@interchg.ubc.ca
The company was incorporated in British Columbia, Canada in 1994 at the completion of an engineering and economic feasibility study by Fluor Daniel concerning the ACOS process. Paszner Technologies Inc. became the marketing arm for the ACOS technology. Active projects today include three in British Columbia, one each in Alaska, Hawaii, Dominican Republic, Philippines, two in Venezuela and two partnerships with
Mr Thornton - one in Brazil and one in California.