Bioconversion of heterogeneous lignocellulosic biomass for sugar production

Abstract

In order to accomplish large scale utilization of lignocellulosic feedstocks to produce fuels and chemicals, a consistent, inexpensive and stable supply of biomass from a variety of sources will be required. These biomass will be heterogeneous and will change as a function of time and price, and will most likely be available to the biorefinery in a mixed input stream with diverse physico chemical properties. Consequently a potential biomass processing facility must be able to convert these diverse feedstock without significantly altering the overall performance, sugar yields and fuel production. Currently, most bioconversion research has been carried out with high quality raw material such as clean wood chips and agricultural residues and little attention has been paid to the efficiency of converting diverse feedstocks into fermentable sugars and fuels. Since particle size reduction is expensive and energy intensive but a critical operation for preparing the biomass for pretreatment, initial particle size heterogeneity was studied during the bioconversion of hybrid poplar. Different particles sizes, ranging from 0.2x0.2 cm to 2.0x1.5 cm, plus an equal mixture of all the particles, were used to determine the influence of initial particle size heterogeneity during sugar production of hybrid poplar (HP) via bioconversion. It was found that there is essentially no effect of particle size heterogeneity on saccharification after steam pretreatment. The overall sugar recovery from all the samples ranged from 87-90% and 61-64% for glucose and xylose respectively and was not influenced by particle size. Alongside showing that bioconversion of HP managed different particles size, and considering the availability of wheat straw (WS) as potential feedstock for a biorefinery. The influence of mixing these two feedstock during the bioconversion for sugar production were investigated. Despite that raw HP and WS have different physico-chemical properties, mixing both types of biomass positively affects the bioconversion process. In fact, mixed biomass exhibited on average 20% more sugar production than either single biomass. Since it was showed that is technically feasible the utilization of different combinations HP and WS as a feedstock for sugar production, a techno-economics analysis was performed to determine and compare the economic feasibility of processing simultaneously mixed biomass (HP and WS) vs. using single HP and WS in a campaign processing plan for ethanol production. The ethanol yields from process simulations estimated that mixed biomass yield 10 more gallons of ethanol per ton of biomass than using single HP and WS in a campaign system. Mixed biomass generate almost twice as much income per year than using single biomass in campaign plan processing, which is equivalent to extra 13.5 million per year. Techno-economic analysis indicated that production of ethanol using mixed biomass is more competitive vs. using single HP and WS in campaign design processing to ethanol production.