1
Bioeconomy Institute TCS Conference, Raleigh NC November 1-4, 2016 Martin R. Haverly, Arpa Ghosh, Robert C. Brown Funding for this research was provided by the Gary and Donna Hoover Endowment in Mechanical Engineering at Iowa State University and the U.S. Department of Energy under contract #EE0005974. Effect of feedstock moisture on solvent liquefaction of biomass in non-aqueous solvents INTRODUCTION METHODOLOGY RESULTS & DISCUSSION CONCLUSIONS FUTURE WORK Please follow this link to learn more about research being done at the Bioeconomy Institute • Energy to dry biomass to 10 wt% moisture represents about 18% of the energy content of fresh biomass [1] • Fast pyrolysis typically requires feedstock with moisture content of less than 10 wt% to achieve necessary heating rates [2] • Solvent liquefaction performance is relatively independent of heating rates [3] • Since solvent liquefaction utilizes solvents other than water, excessive moisture in feedstock is expected to impact performance • Biomass decomposition reactions in water are expected to be different than those in non- aqueous solvents due to the unique properties of water at elevated temperatures • Some solvents such as tetralin are recognized to be hydrogen donors • Water can hydrolyze ether linkages • Ionic dissociation of water reaches its maximum around 280 °C – resulting in an increased concentration of H + and OH - ions • The objective of this work was to evaluate the effect of feedstock moisture on solvent liquefaction of biomass in tetralin • Experiments were performed in a modified Autoclave reactor with continuous pressure control and vapor condensation that allowed water and other low boiling point compounds to vaporize from the reactor • Solvent: Reagent Grade Tetralin • Feedstocks: • Loblolly Pine • Sigmacell Crystalline Cellulose • Hardwood Plantrose™ Lignin • Reaction Temperature: 280 °C • Reaction Pressure: 15 – 70 bar • Liquid Analyses: GC-FID, HPLC • Solid Analyses: FTIR, Elemental • Feedstock moisture was simulated by oven-drying the feedstock to <1 wt% moisture and then re-wetting with specific quantities of deionized water • Liquid Yields • Solid Yields • Liquid yields consistently decreased with increasing moisture for all 3 feedstocks • Increasing pressure generally improved liquid yields – most likely due to enhanced solvent penetration • Reduction in liquid yields resulted in very low levels of detectable products 0% 20% 40% 60% 80% 1% 33% 50% Liquid Yield (wt%) Feedstock Moisture (wt%) Loblolly Pine 29 bar 42 bar 70 bar 0% 10% 20% 30% 40% 50% 60% 1% 5% 33% 50% Liquid Yield (wt%) Feedstock Moisture (wt%) Cellulose 29 bar 42 bar 70 bar 0% 20% 40% 60% 80% 100% 1% 5% 33% 50% Liquid Yield (wt%) Feedstock Moisture (wt%) Lignin 29 bar 42 bar 70 bar 0% 10% 20% 30% 40% 50% 60% 1% 5% 33% 50% Solid Yield (wt%) Feedstock Moisture (wt%) Cellulose 29 bar 42 bar 70 bar 0% 10% 20% 30% 40% 50% 1% 33% 50% Solid Yield (wt%) Feedstock Moisture (wt%) Loblolly Pine 29 bar 42 bar 70 bar • Solid yields consistently increased with increasing moisture for all 3 feedstocks • Increasing pressure reduced solids yields • Cellulose residue congealed into a solid lump at 50 wt% moisture – below 50 wt% solids existed as a powder • Lignin residue agglomerated into larger particles and an acetone-insoluble sludge Feedstock Moisture (wt%) Pressure (bar) Yield (wt%) Monosaccharide Yield Feedstock Moisture (wt%) Pressure (bar) Yield (wt%) Phenolic Monomer Yield • Some moisture was required to result in appreciable monosaccharide yields • At constant pressure, increasing moisture beyond 5 wt% resulted in a reduction in monosaccharides – most likely due to polymerization of monosaccharides and their derivatives in the presence of water • Phenolic monomer yields were significantly reduced when moisture was increased • Increasing pressure improved phenolic monomer yields at all feedstock moisture levels • Water balance indicated a consumption of water during wet lignin liquefaction • Solids analysis (FTIR, Elemental) indicated formation of humins with increasing moisture contents • Humin formation is acid-catalyzed – likely hydrogen ions from the ionic dissociation of water at reaction conditions SEM of 50 wt% Moisture Cellulose Solid Residue 0 10 20 30 40 50 60 70 80 100 150 200 250 300 Pressure (bar) Temperature (°C) • Water had a deleterious effect on liquid yields for tetralin solvent liquefaction resulting in reduction in overall liquid yield as well as reduction in monomer yields • Solid yields increased at the expense of liquid yields when the feedstock moisture was increased • Humin formation from cellulose indicated acid behavior from water due to ionic dissociation at elevated temperatures and pressures • Despite only constituting up to 20 wt% of the solvent mixture, water introduced as feedstock moisture significantly reduced liquid yields and increased solid yields from the liquefaction of loblolly pine, cellulose, and lignin in tetralin • Explore the effect of feedstock moisture on alternative non-aqueous solvent systems (e.g. γ– valerolactone, phenol, etc.) • Determine the economic impact of fully drying feedstock versus feeding wet feedstock on product yields and quality • Investigate energy and economic impact of separating water from product streams (■) theoretical vapor pressure of pure water at 280 °C (●) theoretical boiling point of pure water at each operating pressure (✕) experimentally determined boiling points for water 0 2E-12 4E-12 6E-12 8E-12 0 100 200 300 400 Ionization Constant (Kw) Temperature (°C) Temperature Dependence of Water Ionic Dissociation Mass of Dry Feed (g) Mass of Water Added (g) Simulated Feed Moisture (wt%) 25.0 0.0 1 25.0 1.2 5 25.0 12.5 33 25.0 25.0 50 0% 10% 20% 30% 40% 50% 1% 5% 33% 50% Solid Yield (wt%) Feedstock Moisture (wt%) Lignin 29 bar 42 bar 70 bar • Moisture balance indicated increasing consumption of water with increasing feed moisture • FTIR solids analysis indicated formation of aryl ketone (1685 cm -1 ), aryl alkene (1510-1430 cm -1 ), and ether linkages (1208-1110 cm -1 ) in the presence of moisture – suggesting production of aromatic rings joined by ether linkages 1110 1208 1685 1510 b) 33% c) 50% % Transmittance 1800 750 Wavenumber (cm -1 ) a) 1% 1430 FTIR Analysis of Lignin Solids Proposed Humin Structure References: [1] Brown, R.C. and T.R. Brown, Biorenewable resources: engineering new products from agriculture. 2013: John Wiley & Sons. [2] Wright, M.M., et al., Techno-economic analysis of biomass fast pyrolysis to transportation fuels. Fuel, 2010. 89: p. S2-S10. [3] Kumar, S., et al., Liquefaction of Lignocellulose: Process Parameter Study To Minimize Heavy Ends. Industrial & Engineering Chemistry Research, 2014. 53(29): p. 11668-11676.
