Catalytic transfer hydrogenation for stabilization of bio-oil oxygenates: reduction of p-cresol and furfural over bimetallic Ni-Cu catalysts using isopropanol

Authors: KANNAPU, HARI - Korean Advanced Institute Of Science And Technology (KAIST); Mullen, Charles; Elkasabi, Yaseen; Boateng, Akwasi

Submitted to: Fuel Processing Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2015
Publication Date: 5/1/2015
Publication URL: http://handle.nal.usda.gov/10113/60881
Citation: Kannapu, H.P., Mullen, C.A., Elkasabi, Y.M., Boateng, A.A. 2015. Catalytic transfer hydrogenation for stabilization of bio-oil oxygenates: reduction of p-cresol and furfural over bimetallic Ni-Cu catalysts using isopropanol. Fuel Processing Technology. 137:220-228.

Interpretive Summary: Fast pyrolysis is the rapid heating of a material in the absence of oxygen. It is a method for producing a liquid product from biomass called bio-oil. Bio-oil can be used as intermediate to produce renewable biofuels and chemicals that can displace use of those produced from fossil sources. However, the bio-oil must be upgraded before using as fuel or refinery feedstock due to undesirable properties such as instability, high acidity and low heating value. This process usually involves treatment with hydrogen in multiple steps under extreme conditions including high pressures and temperatures, adding expense to the process. Furthermore, this hydrogen is usually fossil sourced. One potential alternative process for upgrading bio oil is transfer hydrogenation (TH), in which a hydrogen rich liquid chemical is used as a hydrogen source in place of gaseous hydrogen using much milder temperatures and pressures. This hydrogen rich chemical could be potentially be renewably sourced, perhaps even a lower value component of the bio-oil itself. We studied the TH with the two chemicals that are model systems for bio-oil (p-cresol and furfural) to optimize a transfer hydrogen process and the catalyst that promotes the reaction. We found that using a catalyst containing nickel and copper maximized the transformation of these compounds into more hydrogen rich compounds. Isopropyl alcohol was found to be a good hydrogen donating chemical. Then these conditions were applied to bio oils produced from two different pyrolysis processes and two different biomass feedstocks (switchgrass and oak). The results showed that the properties of bio oils were improved in terms of lower acidity, higher heating value when using this process. This information will be useful to those considering alternative processes to refine pyrolysis bio-oils into fuels and chemicals.

Technical Abstract: Transfer hydrogenation and hydrodeoxygenation of model bio-oil compounds (p-cresol and furfural) and bio-oils derived from biomass via traditional pyrolysis and tail-gas reactive pyrolysis (TGRP) were conducted. Mild batch reaction conditions were employed, using isopropanol as a hydrogen donor over alumina and carbon-supported Ni, Cu and Ni-Cu bimetallic catalysts. The main product from the upgrading of p-cresol was a result of the hydrogenation of the aromatic ring to yield 4-methylcyclohexanol while that from the reaction of furfural was a reduction of the aldehyde functional group to furfuryl alcohol. Of the catalysts tested the bimetallic Ni-Cu/Al2O3 proved to be the most active for transfer hydrogenation. The best reaction conditions obtained from the study of the model compounds were applied to real biomass fast pyrolysis bio-oils. Characterization of the upgraded products indicated that transfer hydrogenation of these bio-oils successfully increased their H/C ratio and in some cases lowered their O/C ratio. The acidity of the bio-oils was also reduced, and calorific value increased. The catalysts used were characterized pre- and post-reactions using XRD, TPR, TEM and TGA and their characteristics were interrelated to the conversion of the model compounds (p-cresol and furfural) as well as the bio-oils.