Formic acid is demonstrated as a hydrogen source in a solid reaction system by first stabilizing the acid as a calcium salt which then decomposes at temperatures of relevance in pyrolytic reactions. High yields of deoxygenated hydrocarbons are produced by thermal decomposition of formic and levulinic acid mixtures where the optimum feed stoichiometry is consistent with that of cellulose hydrolysis and dehydration. The method promises a high-yield, robust, low-pressure, non-catalytic route for converting biomass hydrolyzates to hydrocarbon mixtures which are similar to petroleum crude oils.

The present study examines the effect of calcium pretreatment on pyrolysis of individual lignocellulosic compounds. Previous work has demonstrated that the incorporation of calcium compounds with the feedstock prior to pyrolysis has a significant effect on the oxygen content and stability of the resulting oil. The aim of this work was to further explore the chemistry of calcium-catalyzed pyrolysis. Bench-scale pyrolysis of biomass constituents, including lignin, cellulose and xylan is performed and compared to the oils produced from pyrolysis of the same components after calcium pretreatment. The resulting oils were analyzed by quantitative GC-MS and SEC. These analyses, together with data collected from previous work provide evidence which was used to develop proposed reaction pathways for pyrolysis of calcium-pretreatment biomass.

Pine sawdust was pretreated with several calcium compounds and then pyrolyzed in a fluidized bed pyrolysis reactor at 500 °C. The catalytic action of the calcium compounds varies depending on the anion. Analysis of pyrolysis gas, liquid and char yields and compositions demonstrates that calcium sulfate is inert during pyrolysis while calcium formate, carbonate, hydroxide and oxide show significant deoxygenation activity. Of the salts which showed deoxygenation activity, calcium formate had the highest relative yield. This effect is likely attributable to the activity of calcium formate as a hydrogen donor at the pyrolysis temperature.

Instability of pyrolysis oil during aging is a significant issue for commercialization of pyrolysis technologies on an industrial scale. Hot gas filtration of pyrolysis vapors before condensation has been shown to dramatically improve the stability of pyrolysis oils. Detailed chemical analysis of oils produced under various hot gas filter temperatures and vapor residence times shows that the chemical composition of pyrolysis oil changes significantly when hot gas filtration is employed. Compounds that are known to cause instability are eliminated and more stable compounds are formed. This information provides insight into the mechanisms responsible for the stabilization of pyrolysis oils when hot gas filtration is employed.

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