Abstract
Hydrothermal liquefaction (HTL) of biomass such as lignin could contribute to finding replacements for petroleum, both as a fuel and production of chemicals. The organic phase produced in formic acid assisted HTL of lignin has been extensively analyzed previously. The solid phase is routinely analyzed by elemental analysis, and the gas phase has also been studied. The aqueous phase, on the other hand, has received little attention so far and this paper aims to identify and quantify the organic compounds that remain in the aqueous phase after the workup of the organic phase. Using NMR with water suppression, this is achieved with simple sample preparation. The major components are identified using 2D NMR (HSQC spectra) together with proton spectra and 13C spectra as well as verification with standard samples. Their concentrations are determined based on 1H spectra with an added internal standard. An initial evaluation of the effect of temperature and catalyst in the formic acid assisted HTL is given to demonstrate the relevance of the approach. Methanol, formic acid, acetic acid, acetone, phenol, catechol, and dimethyl ether have been identified and quantified in aqueous samples from six different HTL-experiments. 76 %–86 % of the peak area of the proton spectra have been accounted for.
Highlights
Finding replacements for petroleum products is important both because of the depletion of petroleum resources and the increased focus on the reduction of greenhouse gas emissions
There are studies that investigate the recycling of the aqueous phase for use as solvent in the continuous hydrothermal liquefaction (HTL) reaction, which report an increase in bio-oil yield in experiments with various whole biomasses [8,9,10]
NMR analysis has proven to be a good method for quantitative analysis of aqueous samples from hydrothermal conversion of lignin, and we have successfully quantified 76 % – 86 % of the total peak area of the proton spectra
Summary
Finding replacements for petroleum products is important both because of the depletion of petroleum resources and the increased focus on the reduction of greenhouse gas emissions. A promising process in this respect is the lignin to liquid solvolysis (LtL), which, in essence, is a formic acid assisted hydrothermal liquefaction (HTL) [1]. It is of interest to investigate the compounds that remain in the aqueous phase after liquid-liquid extraction, both qualitatively and quantitatively These compounds can play a role in the depolymeriza tion reactions of the lignin and conversion of carbohydrate residues in partially purified lignin feedstocks, as well as possibly providing an additional product if extracted and purified. There are studies that investigate the recycling of the aqueous phase for use as solvent in the continuous HTL reaction, which report an increase in bio-oil yield in experiments with various whole biomasses [8,9,10]. Knowledge of the precise composition of the organic compounds in the water phase are important for understanding the thermochemical re action pathways and optimizing the process conditions to give a maximum value product slate
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