Bio oil upgrading
Bio-oil upgrading refers to a set of techniques that can convert bio-oils produced via Cellulose Pyrolysis, Cellulose liquifaction, and other techniques. Upgrading improves the chemical stability of the bio-oil and converts it into forms compatible with existing fuel distribution and consumption infrastructure.
The major problem for bio-oil is the presence of acidic compounds, including acetic and propanoic acids and some alcohols, which compromise its chemical stability and long-term storability. Thus these techniques attempt to either remove the oxygen-containing components of the bio-oil or react them with other chemicals to render the acid inert.
Techniques for bio-oil upgrading include:
- Hydroxydeoxygenation, which reacts the bio-oil with hydrogen gas in the presence of catalysts to remove the acidic -OH substituents. The specific product mix is determined by the type of catalyst used. The result is a chemical mixture more similar to diesel fuel oil.[1] Bydroxydeoxygenation requires the use of high-pressure hydrogen. If this is brought in from the outside, it may constitute a significant added expense. It is possible, however, to produce the necessary hydrogen from biomass in an integrated processing facility.
- Zeolite conversion, in which the bio-oils are exposed to a zeolite substrate whose active sites have been tuned to react with the acidic or oxygen-containing substituents in the bio-oil chemical mix. The subsequent chemical reactions reduce the acidity level of the bio-oil and improve its fuel characteristics. It does not require the use of high-pressure hydrogen. However, zeolite catalysts are expensive and quickly poisoned by the coke and char byproducts of the reaction.
- Steam reforming of bio-oils uses high-temperature steam to induce chemical reactions which convert the bio-oil into syngas, which can then be further processed into a variety of fuels.
Each of these techniques has been proven to work. However, the economics of bio-oil fuels are presently not competitive with the cost of fuel derived from petrolum. Estimates of final production costs range from 2-10 times that of the equivalent fossil fuel, depending on the specific accounting method used and the choice of the representative fossil fuel cost.
References
- ↑ Furimsky, E. Appl. Catal. A 2000, 199, 147.; and Elliott, D. C.; Beckman, D.; Bridgwater, A. V.; Diebold, J. P.; Gevert, S. B.; Solantausta, Y. Energy Fuels 1991, 5, 399.