The product yields and selectivity from fast pyrolysis of biomass are highly dependent on the physicochemical properties of the biomass feedstock and the process conditions. The objective of this study was to compare the product yields and selectivity from fast pyrolysis of pinewood using three different reactors systems typically used in research laboratory settings for studying biomass pyrolysis: a micropyrolyzer coupled to a GC/MS system, a batch tubular reactor, and a fluidized-bed (FB) continuous reactor. The pyrolysis of pinewood using the three reactors gave different bio oil yields, altered the amounts and compositions of the non-condensable gases, and gave rise to variations in the amount and types of chemicals in bio-oil produced. The variability in residence times of the three reactors and mechanical factors within the FB altered the degree of secondary reactions of the primary pyrolysis vapor leading to the observed changes in composition. Lower yields of carbohydrates were also found to be a consequence of these same intrinsic reactor design constraints. These findings shed significant light on how residence time and the mechanical properties of a reactor configuration affect the products of pyrolysis through the alteration of secondary pyrolytic reactions.
A newly developed two-step pyrolysis process for the fractionation of lignocellulosic biomass components into sugar-rich and lignin-derived rich bio-oils by using pinewood as the feedstock has been studied. In the first step, biomass is pyrolyzed between 300°C and 350 o C decomposing cellulose and hemicellulose fibers to produce bio-oil having significantly higher selectivities towards sugars and lower selectivities towards low molecular weight oxygenated compounds, such as organic acids, aldehydes, and ketones than those of bio-oil produced from the conventional one-step pyrolysis at 500 o C. In the second step, the lignin-rich biomass remaining was pyrolyzed in the presence of HZSM-5 catalyst to produce aromatic-rich bio-oil with low selectivity towards oxygenated compounds. Comparison with the conventional one-step 500°C catalytic pyrolysis showed the advantage of biomass "heat pretreatment" in the first-step pyrolysis, which promoted the decomposition of lignin to monomeric phenolic compounds which were more easily converted to aromatics. Application of catalytic pyrolysis to both steps produced two bio-oil fractions, combined, having significantly higher selectivity towards aromatics and lower selectivity towards oxygenated compounds. Over the conventional one-step pyrolysis, by decomposing biomass components separately at different pyrolysis temperature levels, the developed two-step pyrolysis process allows more flexibility for producing bio-oils with specific composition of chemical moieties that meet the requirements for their desired end uses.
This study investigates the use of spent mushroom compost (SMC) as a potential feedstock for the production of bio-oil via fast pyrolysis process. It was found that, although SMC can be converted to bio-oil, due to its high moisture and ash contents, fast pyrolysis of SMC results in low yield and quality of bio-oil. Reduction of the moisture and ash contents in SMC is the key element to make SMC a desirable feedstock for biomass conversion. This investigation has revealed that pyrolysis of SMC that has been treated by a combination of hydrolysis and torrefaction processes results in a higher yield of bio-oil production. The biomass that was only pretreated with torrefaction produces a lower yield of bio-oil compared to those that have been hydrolyzed or hydrolyzed then torrefied.
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