Oral Presentation 5-04
Integrating Chemical Catalysis into the Biorefinery: Hydrogenation of Pure and Partially-Refined Bio-based Feedstocks
Dennis J. Miller* and James E. Jackson1
Department of Chemical Engineering and Materials Science
2527 Engineering Building
Michigan State University
East Lansing, Michigan 48824
Phone: #9; (517) 353-3928
Fax: (517) 432-1105
Email: millerd@egr.msu.edu
1
Department of ChemistryMichigan State University
The successful biorefinery will require integration of biological and chemical conversions to produce a diverse, value-added product slate. The use of heterogeneous catalysts will play a major role, as catalysis offers a wide variety of reaction pathways and high throughputs. Unfortunately, catalytic reaction rates can be adversely affected by species present in reactor feedstocks; the deactivating effects range from mild inhibition caused by product adsorption to rapid and complete catalyst poisoning by feed impurities.
The effect of process and feed impurities on aqueous-phase catalytic reaction rates is primarily illustrated here by hydrogenation of lactic acid to propylene glycol over carbon-supported ruthenium catalyst. A number of impurities are present in the raw product stream from lactic acid fermentation, including residual carbohydrates, inorganic salts, organic acid byproducts, and protein fragments. Via reactions with actual partially-refined lactic acid and model "spiked" feed materials, three modes of catalyst deactivation are observed: 1) pore blocking by protein fragments and color bodies; 2) irreversible poisoning from sulfur-containing amino acids, and 3) reversible deactivation attributed to competitive adsorption of process impurities and products onto the catalyst metal surface. Of these, competitive adsorption provides interesting insights into the nature of substrate-catalyst interactions and other factors that dictate catalyst activity. Examples from several reaction systems in addition to lactic acid are given to further illustrate the importance of competitive adsorption in elucidating aqueous phase catalytic reaction pathways.
Understanding the deleterious effects of biogenic impurities on downstream catalytic reactions is important for biorefinery development, particularly regarding integration of biological and chemical conversions. Not only does this work define potential requirements for purification of intermediates, it may lead to more careful choices of fermentation media and catalyst properties that altogether avoid the effects of impurities present.