Identification and thermochemical analysis of high-lignin feedstocks for biofuel and biochemical production

Abstract

BackgroundLignin is a highly abundant biopolymer synthesized by plants as a complex component of plant secondary cell walls. Efforts to utilize lignin-based bioproducts are needed.ResultsHerein we identify and characterize the composition and pyrolytic deconstruction characteristics of high-lignin feedstocks. Feedstocks displaying the highest levels of lignin were identified as drupe endocarp biomass arising as agricultural waste from horticultural crops. By performing pyrolysis coupled to gas chromatography-mass spectrometry, we characterized lignin-derived deconstruction products from endocarp biomass and compared these with switchgrass. By comparing individual pyrolytic products, we document higher amounts of acetic acid, 1-hydroxy-2-propanone, acetone and furfural in switchgrass compared to endocarp tissue, which is consistent with high holocellulose relative to lignin. By contrast, greater yields of lignin-based pyrolytic products such as phenol, 2-methoxyphenol, 2-methylphenol, 2-methoxy-4-methylphenol and 4-ethyl-2-methoxyphenol arising from drupe endocarp tissue are documented.ConclusionsDifferences in product yield, thermal decomposition rates and molecular species distribution among the feedstocks illustrate the potential of high-lignin endocarp feedstocks to generate valuable chemicals by thermochemical deconstruction.

Global bioenergy potential from high-lignin agricultural residue

“…The endocarp of a drupe fruit is the hardened inedible portion of the fruit that encases the seed and is discarded, whereas the flesh (mesocarp) is edible. The hardened drupe endocarp represents the highest lignin content of any woody biomass source produced in appreciable amounts, commonly up to 50% wt/wt (13,14). As a biofuel, lignin has much higher energy density (approximately double) than cellulose (15,16).…”

Engineering Plant Biomass Lignin Content and Composition for Biofuels and Bioproducts

“…Of all the plant cell wall polymers, lignin is highly reduced and energy dense with a high heating value [16,83]. The high lignin biomass can be used for the production of high-energy dense jet fuels, bioenergy and bioelectricity by thermochemical conversion methods [10,84].…”

“…The composition of lignocellulosic material varies between different species, varieties, plant parts and environmental conditions (Table 1, [16,18]). This is particularly noticed between angiosperm (hardwoods) and gymnosperm (softwoods) plants [18,19].…”

“…Though this type of agricultural waste represents a great source of lignocellulosic material, pelleting and transportation are major concerns. High density feedstocks such as the drupe fruit endocarps (shells) of olives, eastern black walnut and coconut have the highest lignin content of all known plant organs, and the energy derived from the endocarp is comparable to coal [16]. The endocarp is an inedible portion of an edible fruit, and therefore, can be considered for dual purposes: food and fuel.…”

“…The fruit endocarp material has high energy density due to its high-lignin content and can be an excellent feedstock for the production of bioelectricity by gasification or high-energy dense biooil via pyrolysis. There are about 24 to 31 million tons of drupe endocarp biomass available in the world [10], which is highly underutilized, and a recent assessment suggests that proper utilization could benefit the countries with energy scarcity [16]. Additionally, other forms of agricultural (forest thinnings, cotton linters) and industrial wastes (sugarcane bagasse, paper and pulping waste) could be used as lignocellulosic feedstocks.…”