Lignin fractionation helps its valorization process and yields high-quality and -value products. In this study, cascading tangential flow filtration (TFF) was employed for the fractionation of lignin molecules. The lignin-rich stream was obtained from the pretreatment process of corn stover using alkali (NaOH) and cholinium lysinate ([Ch][Lys]) as the catalyst. The effect of TFF (microfiltration, ultrafiltration, and nanofiltration) on lignin molecular weight, sugar distribution, viscosity, and lignin functional groups was investigated. In general, the study concluded that the average molecular weight (MW) and polydispersity of the permeate stream decreased with the reduction of the membrane pore size. TFF was effective in separating the low-MW lignin (200-350 Da) from the aqueous stream. Approximately 2% of monomeric lignin and 10-20% of low-molecular-weight lignin were recovered from NaOH- and [Ch][Lys]-extracted streams. Techno-economic analysis (TEA) results show that a high percentage of the low-MW lignin extraction can be achieved via a cascade TFF membrane operating at high transmembrane pressures (TMPs) and cross membrane velocities. Additionally, a high initial concentration of lignin in the liquid stream plays a critical role in the lignin product yield and recovery cost.

This scale-up study demonstrated the feasibility of an ionic liquid (IL) pretreatment process at 40 kg scale, using the IL 1-ethyl-3-methylimidazolium acetate ([C2C1Im][OAc]) as the solvent. The pretreatment was followed by enzymatic hydrolysis through which the process efficiency for biomass conversion to monomeric sugars was determined. The results show that 43 wt% of switchgrass was dissolved in IL after 2 h of pretreatment at 160 °C with 15 wt% solid loading. A 120 h enzymatic hydrolysis of the pretreated switchgrass results in 96% glucan and 98% xylan conversion. [C2C1Im][OAc] pretreatment has been successfully scaled up to 40 kg with improved sugar titers and yields relative to bench scale (6 kg). The mass flow of the overall process was established and the major scale-up challenges of the process were identified.

Sixteen cellulose rich municipal solid waste (MSW) blends were developed and screened using an acid-assisted ionic liquid (IL) deconstruction process. Corn stover and switchgrass were chosen to represent herbaceous feedstocks; non-recyclable paper (NRP) and grass clippings (GC) collected from households were chosen as MSW candidates given their abundance in municipal waste streams. The most promising MSW blend: corn stover/non-recyclable paper (CS/NRP) at 80/20 ratio was identified in milliliter-scale screening based on the sugar yield, feedstock cost, and availability. A successful scale-up (600-fold) of the IL-acidolysis process on the identified CS/NRP blend has been achieved. The sugar and lignin streams were recovered and characterized. Mass and material energy flows of the optimized process were presented. Feedstock cost for MSW blends was also discussed. Results suggest the promising potential of using MSW as a feedstock blending agent for biorefineries while maintaining sufficient performance and low feedstock cost. The bench scale (6 L) study is an essential step in demonstrating the scalability of this IL technology.

Achieving low cost and high efficiency lignocellulose deconstruction is a critical step towards widespread adoption of lignocellulosic biofuels. Certain ionic liquid (IL)-based pretreatment processes effectively reduce recalcitrance of lignocellulose to enzymatic degradation but require either costly separations following pretreatment or novel IL compatible processes to mitigate downstream toxicity. Here we demonstrate at benchtop and pilot bioreactor scales a separation-free, intensified process for IL pretreatment, saccharification, and fermentation of sorghum biomass to produce the sesquiterpene bisabolene, a precursor to the renewable diesel and jet fuel bisabolane. The deconstruction process employs the IL cholinium lysinate ([Ch][Lys]), followed by enzymatic saccharification with the commercial enzyme cocktails Cellic CTec2 and HTec2. Glucose yields above 80% and xylose yields above 60% are observed at all scales tested. Unfiltered hydrolysate is fermented directly by Rhodosporidium toruloides-with glucose, xylose, acetate and lactate fully consumed during fermentation at all scales tested. Bisabolene titers improved with scale from 1.3 g L-1 in 30 mL shake flasks to 2.2 g L-1 in 20 L fermentation. The combined process enables conversion of saccharified IL-pretreated biomass directly to advanced biofuels with no separations or washing, minimal additions to facilitate fermentation, no loss of performance due to IL toxicity, and simplified fuel recovery via phase separation. This study is the first to demonstrate a separation-free IL based process for conversion of biomass to an advanced biofuel and is the first to demonstrate full consumption of glucose, xylose, acetate, and lactic acid in the presence of [Ch][Lys].

With a diverse and widely distributed global resource base, woody biomass is a compelling organic feedstock for conversion to renewable liquid fuels. In California, woody biomass comprises the largest fraction of underutilized biomass available for biofuel production, but conversion to fuels is challenged both by recalcitrance to deconstruction and by toxicity toward downstream saccharification and fermentation due to organic acids and phenolic compounds generated during pretreatment. In this study, we optimize pretreatment and scale-up of an integrated one-pot process for deconstruction of California woody biomass using the ionic liquid (IL) cholinium lysinate [Ch][Lys] as a pretreatment solvent. By evaluating the impact of solid loading, solid removal, yeast acclimatization, fermentation temperature, fermentation pH, and nutrient supplementation on final ethanol yields and titers, we achieve nearly full conversion of both glucose and xylose to ethanol with commercial C5-utilizing Saccharomyces cerevisiae. We then demonstrate process scalability in 680 L pilot-scale fermentation, achieving >80% deconstruction efficiency, >90% fermentation efficiency, 27.7 g/L ethanol titer, and >80% ethanol distillation efficiency from the IL-containing hydrolysate post fermentation. This fully integrated process requires no intermediate separations and no intermediate detoxification of the hydrolysate. Using an integrated biorefinery model, current performance results in a minimum ethanol selling price of $8.8/gge. Reducing enzyme loading along with other minor process improvements can reduce the ethanol selling price to $3/gge. This study is the largest scale demonstration of IL pretreatment and biofuel conversion known to date, and the overall biomass-to-ethanol efficiencies are the highest reported to date for any IL-based biomass-to-biofuel conversion.

Feedstock variability that originates from biomass production and field conditions propagates through the value chain, posing a significant challenge to the emerging biorefinery industry. Variability in feedstock properties impacts feeding, handling, equipment operations, and conversion performance. Feedstock quality attributes, and their variations, are often overlooked in assessing feedstock value and utilization for conversion to fuels, chemicals, and products. This study developed and employed a multiscale analytical characterization approach coupled with data analytic methods to better understand the sources and distribution of feedstock quality variability through evaluation of 24 corn stover bales collected in 4 counties of Iowa. In total, 216 core samples were generated by sampling nine positions on each bale using a reliable bale coring process. The samples were characterized for a broad suite of physicochemical properties ranging across field and bale, macro, micro, and molecular scales. Results demonstrated that feedstock quality attributes can vary at all spatial scales and that multiple sources of variability must be considered in order to establish and manage biomass quality for conversion processes.

Lignin is an abundant renewable resource that is a promising substrate for upgrading to fuels and chemicals. However, lignin-rich biorefinery streams are often physically and chemically complex, and could benefit substantially from fractionation. In this work, a membrane process was developed to fractionate low molecular weight (LMW) lignin-related compounds (molecular weight (MW) < 1000 Da) from a ligninrich, alkaline pretreated liquor (APL) prepared from pretreatment of corn stover with NaOH. The developed membrane process exhibits up to 98.5% rejection of high molecular weight (HMW) (MW > 1000 Da) species and generates a permeate stream with >80% recovery of LMW lignin-related compounds including aromatic species such as p-coumarate and ferulate, resulting in a 6-fold enrichment in LMW organic compounds relative to the crude APL. Experimental batch data were used to develop a detailed process model of an industrial scale, continuous membrane filtration system. The open-source model has several independent process inputs, such as the concentration of target compounds, feed flow rate, volume recovery, and membrane selectivity. This process model was used to show that the system has a low estimated energy demand (0.75 kW h m-3 permeate) and was used to identify primary cost drivers, including the membrane material cost. These results offer a key step towards a scalable, low energy, and costeffective lignin MW fractionation method with implications for both improving product isolation from lignin and improving carbon yields across the biorefinery.