Aging of Biomass Fast Pyrolysis-Oil and Process Strategies to Produce Stable Pyrolysis Oils
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Fast pyrolysis bio-oils are unstable due to a variety of factors, the most important being the high concentration of reactive oxygen-functionalized organic molecules, especially carbonyl containing compounds. Condensation and oligomerization reactions of these molecules lead to an increase in the average molecular weight and viscosity of the pyrolysis-oil. The focus of the pyrolysis research program at the Eastern Regional Research Center (ERRC) part of USDA’s Agricultural Research Service (ARS) is to develop methods that would allow for the production of stable and upgradable pyrolysis oil on a scale amenable to use at the farm. To this end, the aging of a variety of biomass fast pyrolysis oils was studied to better understand the sources of pyrolysis oil instability with the aim of using the information to improve the conversion process to produce higher quality pyrolysis oils. Therefore the effects of the concentration of several individual chemical components, such as water, acetic acid, furfural, and others on the rate of the molecular weight and viscosity increases of several pyrolysis oils were studied. The results of these experiments aided in the development of approaches to produce more stable pyrolysis oil. These strategies include the addition of in situ catalytic processing, selection of feedstocks with compositions amenable to production of stable pyrolysis oil, fractionation of the pyrolysis oil, and addition of co-reactants to the process with the main goal of efficiently producing partially deoxygenated, stable pyrolysis oils. The results of the stability studies along with experimental results on each of the above process changes will be presented and discussed. The discussion will focus on the differences in the chemical mechanisms for each process, the composition of the pyrolysis oils and its effect on their stability and other properties of the pyrolysis oil.