Effect of Calcium Formate on Hydrodeoxygenation of Biomass Model Compounds

Abstract

Hydrothermal liquefaction of biomass model compounds (cellulose, xylan, and lignin) was carried out between 350 and 400 °C using calcium formate (Ca­(HCOO)2) as the in situ hydrogen source. In this study, high temperatures have been adopted for liquefaction as calcium formate acts as a hydrogen donor in that range. Ca­(HCOO)2 catalyzes lignin degradation toward liquefaction and, consequently, increases the biocrude yields by about 80%. Conversely, cellulose biocrude yields decreased when Ca­(HCOO)2 was introduced due to pronounced gasification. It was also observed that Ca­(HCOO)2 did not have any effect on xylan biocrude yield which remained almost the same. The maximum biocrude yields of cellulose, xylan, and lignin in the presence of Ca­(HCOO)2 were 7, 13, and 32 wt %, respectively. The excess hydrogen from Ca­(HCOO)2 was successful in upgrading the biocrude by removing oxygen which was confirmed by a significant decrease in atomic O/C ratio and increase in heating values (by 34.6%). The formate salt slightly upgraded the quality of cellulose and xylan biocrude through an increase in H/C ratio which in turn improved the heating values by 15.6 and 8.8%, respectively. The gas chromatography mass spectroscopy chromatograms of biocrudes with and without the hydrogen donor were compared, and reaction mechanisms were postulated to better explain the deoxygenation of biocrude by Ca­(HCOO)2. With excess hydrogen, the biocrude from lignin was rich in alkylated phenols, whereas aromatics were the major components in cellulose biocrude. The formate salt resulted in the formation of alkylated phenols and cyclic ketones in xylan biocrude via aldol condensation reactions.

Kinetic Study of Noncatalytic Dissolution of Cellulose Biochar in Hydrogen Donor Solvent

“…Levulinic acid was produced from 5-HMF by dehydration followed by hydrogenation. 4 Above 250 °C, the concentrations of 5-HMF and levulinic acid decreased because they underwent decomposition to form products such as as γ-butyrolactone. 31 Although it has been reported in the literature that levulinic acid can readily cyclize to form valerolactone, the GC-MS analysis of the products did not show the presence of valerolactone.…”

“…Simultaneously, the concentration of levulinic acid also increased from 0 mg/g at 225 °C to 2.3 mg/g at 250 °C. Levulinic acid was produced from 5-HMF by dehydration followed by hydrogenation . Above 250 °C, the concentrations of 5-HMF and levulinic acid decreased because they underwent decomposition to form products such as as γ-butyrolactone .…”

“…Direct liquefaction of biomass occurs at 250–550 °C under a high pressure of 5–25 MPa to produce a water-insoluble bio-oil. Water has been widely used as a solvent because it is environmentally friendly and because of the ease of bio-oil separation. , Biofuel has also been produced by biomass liquefaction or dissolution using organic solvents such as acetone, ethanol, etc. , The production of fuel from carbon-based solids such as coal was first demonstrated by Fedrick Bergius in 1914 by the direct liquefaction of coal (DCL) in a hydrogen donor solvent . Liquefaction (dissolution) of coal in tetralin has been widely explored by various researchers. − Renewable carbon-based solids, such as biomass model compounds like cellulose, lignin, and lignocellulose biomass, have also been used as feeds to produce biofuel by liquefaction using tetralin.…”

“…Water has been widely used as a solvent because it is environmentally friendly and because of the ease of bio-oil separation. 4,5 Biofuel has also been produced by biomass liquefaction or dissolution using organic solvents such as acetone, ethanol, etc. 6,7 The production of fuel from carbonbased solids such as coal was first demonstrated by Fedrick Bergius in 1914 by the direct liquefaction of coal (DCL) in a hydrogen donor solvent.…”