A synergistic effect of carbon dioxide in supercritical state (scCO2) and NiO solid-state heterogeneous catalyst was investigated during the hydrothermal liquefaction of alkali lignin in the temperature range from 200 to 4000 C and constant pressure P=3200 psi. Matching the catalytic activity of scCO2 with the NiO as heterogeneous catalyst resulted in selectivity increase toward selective formation of phenolic monomers, such as 4-hydroxy-3-methoxybenzaldehyde, 3-hydroxy-4-methoxybenzaldehyde, methyl-(2-hydoxy-3-ethoxy-benzyl) ether, 2,4-bis(1,1-dimethylethyl) phenol, 1-(4-hydroxy-3-methoxyphenyl), 2-Methoxy-4-methylphenol, benzaldehyde, and 4'-Hydroxy-3'-methoxy-acetophenone. In equivalent conditions and in comparison to scN2-NiO, the hydrothermal liquefaction of alkali lignin in presence of scCO2-NiO was much more selective toward formation of phenolic monomers. For example, the corresponding relative yield of 4-hydroxy-3-methoxybenzaldehyde was increased from 0% to 54%. In case of 4'-Hydroxy-3'-methoxyacetophenone the relative yield increased from 5% to 10% at 2000 C. In presence of NiO at 2000 C the catalytic activity of the system containing scCO2 toward selective production of the 4-hydroxy-3-methoxybenzaldehyde was significantly higher and the total relative yield of phenolics was increased from 12 % to 64 %. Strong temperature dependence of the yield of the major phenolic compound, 4-hydroxy-3-methoxybenzaldehyde, was detected being the highest at 2000C (54%) and the lowest at 4000C. The gas chromatography-mass spectroscopy (GCMS), pyrolysis GCMS, temperature programmed reduction (TPR), and total carbon (TCA) analysis confirm the synergistic effect of the two catalysts: homogeneous carbon dioxide in supercritical state and the heterogeneous NiO catalyst. Described for the first time this approach has a potential for commercialization in regard to the selective synthesis of value-added phenolic monomers from biomass/lignocellulosic recovery for “green” polymer synthesis and sustainable utilization of the organic waste. The support from the NSF EPSCOR Cooperative Agreement #IIA-1330842 BIOCON is gratefully acknowledged.

Synergistic catalytic effect of supercritical carbon dioxide and nickel oxide as a heterogeneous catalyst for lignin liquefaction and selective synthesis of phenolics

251st National Meeting (2016)

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