Fast pyrolysis of muconic acid and formic acid salt mixtures

Lignocellulosic feedstocks are a potential renewable resource for the production of liquid fuels and chemicals. As a major by-product of the pulping industry, lignin is an underutilized source of organic carbon in lignocellulosic biomass. Residual lignin remaining in pulp after cooking of lignocellulosic biomass is typically removed during the bleaching stage of a pulping operation. This stage is composed of a sequence of steps including oxidation and alkaline extraction. Given that muconic acid and formic acid are formed during oxygen treatment of alkaline solutions of lignin, fast pyrolysis coupled with gas chromatography-mass spectrometry (Py-GC/MS) of alkali/alkaline earth salt mixtures of muconic acid and formic acid was employed to produce significantly deoxygenated products, such as cyclic ketones, hydrocarbons, aromatics, and phenolics. The cations investigated in this study were sodium, calcium, and magnesium to observe the difference in product distribution, volatile formation, and the formation of carbonaceous residue. The compounds observed after pyrolysis of the various salts suggest that along with the expected intramolecular condensation reactions, free radical reactions are likely occurring at the temperatures investigated explaining the observed alkylation and hydrogenation of the vapor products beyond deoxygenation which can be expected from reactive hydrogen formed by formate decomposition. Hydrogenation may also be occurring as a result of catalytic effects of the metal cations on the pyrolysis vapors. Pyrolysis of calcium muconate favors cyclic ketone formation almost exclusively, and when formate is added a 61 wt% reduction in carbonaceous residue formation is observed at 550 °C in a thermogravimetric analyzer (TGA) equipped with an evolved gas analyzer furnace (EGA). The highest yields of gaseous species were observed for the magnesium muconate-formate mixture, approximately 47 wt%, while the least amount of carbonaceous residue was formed upon pyrolysis of the sodium muconate-formate mixture, both at 550 °C in a TGA. The data suggests that pyrolysis at 550 °C of sodium formate and oxidized lignin mixtures may be of interest for the production of aromatic compounds.