Cellulosic Ethanol Biorefinery Research Articles

Ultraclean hybrid poplar lignins via liquid–liquid fractionation using ethanol–water solutions

As recovered from the byproducts stream of a cellulosic ethanol biorefinery, the renewable biopolymer lignin is too impure and polydisperse for many proposed applications. By mixing a hybrid poplar lignin with hot ethanol–water solutions, two liquid phases, one polymer-rich and one solvent-rich, are created. This liquid–liquid equilibrium phenomenon was used to generate solvated (and thus liquefied) lignin fractions of controlled molecular weight for which the impurities analyses for sugars and ash were near or below the limits of detection. Additionally, those carbohydrates and metals impurities end up highly concentrated in a single process stream also having potential value.

Lipid production from non-sugar compounds in pretreated lignocellulose hydrolysates by Rhodococcus jostii RHA1

The non-sugar compounds such as lignin derived phenolic compounds, furans, and organic acids generated from biomass pretreatment are often inhibitors to microbial growth and function, leading to lower ethanol yield in cellulosic ethanol biorefinery. In this study, phenols (vanillin, vanillate), furans (furfural, 5-hydroxymethylfurfural), and organic acids (acetate), which mimic the complex components of the non-sugar compounds in pretreated biomass hydrolysate, were either mixed with benzoate or used individually as carbon sources to investigate their effects on the growth and lipid accumulation of Rhodococcus jostii RHA1. Higher consumption rates of benzoate than that of vanillate, as well as different lipid yields from them, suggested that the strain preferred to employ the catechol branch of the β-ketoadipate pathway to catabolize benzoate and plausibly distinctly routed carbon to lipid biosynthesis when fed on different aromatics. Compared to benzoate, acetate was less favorable by R. jostii RHA1 for lipid synthesis, again emphasizing that carbon contribution to either lipid synthesis or cell biomass was selective, using different compounds as carbon sources. Among the five selected non-sugar compounds, the presence of 5-hydroxymethylfurfural (5-HMF) promoted the highest lipid yield at 0.46 g lipid g−1 CDW by using benzoate as the main carbon source. Furthermore, the oxidation pathway of furfural and 5-HMF was predicted for the first time in R. jostii RHA1 based on the characterization of the products by NMR.

Lignocellulosic Biomass Mild Alkaline Fractionation and Resulting Extract Purification Processes: Conditions, Yields, and Purities

Fractionation of lignocellulose is a fundamental step in the valorization of cellulose, hemicelluloses, and lignin to produce various sustainable fuels, materials and chemicals. Strong alkaline fractionation is one of the most applied processes since the paper industry has been using it for more than a century, and the mineral acid fractionation process is currently the most applied for the production of cellulosic ethanol. However, in the last decade, mild alkaline fractionation has been becoming increasingly widespread in the frame of cellulosic ethanol biorefineries. It leads to the solubilization of hemicelluloses and lignin at various extent depending on the conditions of the extraction, whereas the cellulose remains insoluble. Some studies showed that the cellulose saccharification and fermentation into ethanol gave higher yields than the mineral acid fractionation process. Besides, contrary to the acid fractionation process, the mild alkaline fractionation process does not hydrolyze the sugar polymers, which can be of interest for different applications. Lignocellulosic mild alkaline extracts contain hemicelluloses, lignin oligomers, phenolic monomers, acetic acid, and inorganic salts. In order to optimize the economic efficiency of the biorefineries using a mild alkaline fractionation process, the purification of the alkaline extract to valorize its different components is of major importance. This review details the conditions used for the mild alkaline fractionation process and the purification techniques that have been carried out on the obtained hydrolysates, with a focus on the yields and purities of the different compounds.

Process design and economics for production of advanced biofuels from genetically modified lipid-producing sorghum

This study evaluates the potential for making advanced biofuels from genetically modified (GM) lipid–producing sorghum. A biodiesel coproduction process is developed to extract, purify, and upgrade lipids to diesel fuel while carbohydrates are utilized for making ethanol through acid thermal pretreatment, enzymatic hydrolysis, and fermentation. To assess the advantages of coproducing biodiesel from GM–sorghum, process economics are compared to a cellulosic ethanol biorefinery receiving non-GM sorghum. Minimum ethanol selling prices (MESP) that reach a breakeven point after 30 years of service life are calculated as an economic index to compare the two processes. Results indicate that biodiesel coproduction improves the economics by lowering the MESP from $3.08/gal for the ethanol-only process to $2.46/gal. Sensitivity analyses reveal that increasing sorghum’s lipid content, increasing the lipid extraction efficiency, and reducing the solvent-to-solids ratio in lipid extraction columns are the most important process parameters to further enhance technoeconomics. Analyses indicate that a lipid content above 13 wt% (dry basis) or a biomass price less than $65/Mg (dry basis) will result in a 2014 ethanol wholesale price of $2.25/gal for the coproduction process.

A comparative investigation of H2O2-involved pretreatments on lignocellulosic biomass for enzymatic hydrolysis

An effective pretreatment to improve cellulose accessibility and facilitate glucose release is crucial in a cellulosic ethanol biorefinery. This work comparatively assessed four H2O2-involved pretreatments, i.e., concentrated H3PO4 plus H2O2 (PHP), H2O2–CH3COOH (HPAC), alkaline-H2O2 (AHP), and Fenton chemistry (FC), for their pretreatment performances on wheat straw, poplar, and birch biomass. Substrate characteristics before and after pretreatment were assessed using SEM, XRD, and LSCM. The hydrolytic potentials of the pretreated substrates were compared by Simons’ stain and cellulose–glucose conversion assessment. The results showed that acidic H2O2-involved pretreatments (PHP and HPAC) were more efficient in biomass delignification compared to AHP and FC. PHP pretreatment is more promising for cellulosic ethanol production due to its corresponding high glucose yield (368.0 mg g−1) after enzymatic hydrolysis.

Co-metabolic substrates enhanced biological nitrogen removal from cellulosic ethanol biorefinery wastewater using aerobic granular sludges

ABSTRACTThe effect of different co-metabolic substrates (glucose, acetic acid and ethanol) on aerobic granular sludge treating cellulose ethanol wastewater was investigated using sequencing batch reactors. The efficiencies of the three substrates in removing chemical oxygen demand were respectively 18.87%, 28.88% and 27.99%, all of which were remarkably higher than without co-metabolic substrates, indicating that co-metabolic substrates can promote the degradation of the refractory substances. With acetic acid as the co-metabolic substrate, the removal amount of ammonium nitrogen and nitrate nitrogen was greater than glucose and ethanol used. The nitrogen removals by the three co-metabolic substrates were 53.18%, 72.15%, 69.36%, respectively, which were 1.4, 1.8, and 1.6 times the removal without co-metabolic substrates. Fluorescence in situ hybridization results showed that the proportion of ammonium-oxidizing bacteria in the granular sludge was greater than that of nitrite-oxidizing bacteria after adding co-metabolic substrates, and the order was acetic acid > ethanol > glucose.

High-resolution techno–ecological modelling of a bioenergy landscape to identify climate mitigation opportunities in cellulosic ethanol production

Although dedicated energy crops will probably be an important feedstock for future cellulosic bioenergy production, it is unknown how they can best be integrated into existing agricultural systems. Here we use the DayCent ecosystem model to simulate various scenarios for growing switchgrass in the heterogeneous landscape that surrounds a commercial-scale cellulosic ethanol biorefinery in southwestern Kansas, and quantify the associated fuel production costs and lifecycle greenhouse gas (GHG) emissions. We show that the GHG footprint of ethanol production can be reduced by up to 22 g of CO2 equivalent per megajoule (CO2e MJ–1) through careful optimization of the soils cultivated and corresponding fertilizer application rates (the US Renewable Fuel Standard requires a 56 gCO2e MJ−1 lifecycle emissions reduction for ‘cellulosic’ biofuels compared with conventional gasoline). This improved climate performance is realizable at modest additional costs, less than the current value of low-carbon fuel incentives. We also demonstrate that existing subsidized switchgrass plantings within this landscape probably achieve suboptimal GHG mitigation, as would landscape designs that strictly minimize the biomass collection radius or target certain marginal lands.

Addition of corn stover arabinoxylan into hardwood during pulping for improved physical properties

Agricultural residues, such as corn stover, are being considered for biofuels and bioproducts. They represent inexpensive, pentosan-rich feedstock that are available in abundance. These materials are typically pretreated to make them more amenable to biological processes such as fermentation. One such treatment involves extraction using alkali to remove the hemicellulose, leaving the cellulose more accessible for chemical or enzymatic hydrolysis. Extracted xylan hemicellulose may be considered for use in pulp and paper, or for providing a potential value stream from cellulosic ethanol biorefineries. To be useful, the extracted xylan should be concentrated and adsorbed into the pulp using existing equipment or a minimal number of new unit operations. In this work, we explored the concept of size-exclusion membrane-filtration to concentrate xylan that was extracted from corn stover in mild alkaline conditions. We examined hollow-fiber and tangential-flow filtration types and achieved a nearly two-fold increase in the xylan concentration using the former with a 50 kDa molecular weight cut-off (MWCO) membrane. Cassette-type tangential-flow filtration resulted in slightly greater xylan concentration with the use of a 10 kDa MWCO membrane. Hemicellulose extracts were then used as an additive during kraft pulping of hybrid poplar to show that the xylan could be adsorbed onto pulp fibers and retained even after washing. Pulp tensile strength improved after xylan addition following refining. An average of 33% of the xylan added in this method was retained, with xylan loading between 5 wt% and 20 wt%, compared with the control pulp sample that did not have added xylan. These results suggest potential for further exploration of biorefinery extracts use as additive feedstock for pulping. The study, being an evaluation of the proof-of-concept, aims to push research and optimization in this area that will lend well to scale-up and commercialization.

Syngas fermentation by Clostridium carboxidivorans P7 in a horizontal rotating packed bed biofilm reactor with enhanced ethanol production

Gasification of lignocellulosic biomass followed by syngas fermentation is a promising process for producing fuels and chemicals. Syngas fermentation, however, is commonly limited by low mass transfer rates. In this work, a horizontally oriented rotating packed bed (h-RPB) reactor was developed to improve mass transfer and enhance ethanol production. In the h-RPB reactor, cell attachment materials were packed in the reactor and half submerged in the liquid and half exposed to the headspace. With continuous rotation of the packing materials, the cells in biofilm were alternately in contact with liquid and headspace; thus, transport of syngas to the cells occurred in both the liquid phase and headspace. The volumetric mass transfer coefficient (kLa) of the h-RPB reactor was lower than that in a traditional continuous stirred tank reactor (CSTR), indicating the mass transfer in the liquid phase of h-PRB was lower than CSTR, and the mass transfer in the headspace phase played an important role in syngas fermentation. The syngas fermentation of Clostridium carboxidivorans P7 in h-RPB resulted in a 7.0g/L titer and 6.7g/L/day productivity of ethanol, respectively, 3.3 times higher than those obtained in a CSTR under the same operational conditions. The results demonstrate that the h-RPB reactor is an efficient system for syngas fermentation, making cellulosic ethanol biorefinery one step closer to technical and economic feasibility.

Bioethanol production from forestry residues: A comparative techno-economic analysis

A techno-economic analysis was conducted to assess the feasibility of using forestry residues with different bark contents for bioethanol production. A proposed cellulosic ethanol biorefinery in Sweden was simulated with Aspen Plus. The plant was assumed to convert different forestry assortments (sawdust and shavings, fuel logs, early thinnings, tops and branches, hog fuel and pulpwood) to ethanol, pellets, biogas and electricity. The intention was not to obtain absolute ethanol production costs for future facilities, but to assess and compare the future potential of utilizing different forestry residues for bioethanol production. The same plant design and operating conditions were assumed in all cases, and the effect of including bark on the whole conversion process, especially how it influenced the ethanol production cost, was studied. While the energy efficiency (not including district heating) obtained for the whole process was between 67 and 69% regardless of the raw material used, the ethanol production cost differed considerably; the minimum ethanol selling price ranging from 0.77 to 1.52USD/L. Under the basic assumptions, all the forestry residues apart from sawdust and shavings exhibited a negative net present value at current market prices. The profitability decreased with increasing bark content of the raw material. Sensitivity analyses showed that, at current market prices, the utilization of bark-containing forestry residues will not provide significant cost improvement compared with pulpwood unless the conversion of cellulose and hemicellulose to monomeric sugars is improved.

Pilot-scale investigation on the treatment of cellulosic ethanol biorefinery wastewater

The treatment of wastewater from a cellulosic ethanol biorefinery presents special challenges. A pilot-scale process that utilized a continuous stirred tank reactor (CSTR), an internal circulation reactor (IC), and a sequencing batch reactor (SBR) with ozone oxidation enhancement was developed for the treatment of this challenging biorefinery wastewater. The CSTR and IC were used for COD removal through anaerobic treatment, and the SBR process was used for nitrogen removal through alternating aerobic nitrification and anaerobic denitrification. The combined process removed 85% of chemical oxygen demand (COD) and 80% of ammonium. The corresponding effluent concentrations of COD and ammonium were 1591±226mg/L and 61±8mg/L, respectively. Ozonation enhanced the biodegradability of the anaerobic effluent, the BOD5/COD ratio of which increased from 0.15±0.02 to 0.33±0.05. The BOD5/COD ratio of the effluent from the SBR was 0.07±0.01, which indicated the effluent was no longer treatable using a biological process. A total sulfate removal efficiency of 65% was obtained through an alternating anaerobic and aerobic process, and the final effluent sulfate concentration was 217±10mg/L.

Estimation of economic impacts of cellulosic biofuel production: a comparative analysis of three biofuel pathways

AbstractThe development of a cellulosic biofuel industry utilizing domestic biomass resources is expected to create opportunities for economic growth resulting from the construction and operation of new biorefineries. We applied an economic input‐output model to estimate potential economic impacts, particularly gross job growth, resulting from the construction and operation of biorefineries using three different technology pathways: (i) cellulosic ethanol via biochemical conversion in Iowa, (ii) renewable diesel blendstock via biological conversion in Georgia, and (iii) renewable diesel and gasoline blendstock via fast pyrolysis in Mississippi. Combining direct, indirect (revenue‐ and supply‐chain‐related), and induced effects, capital investment associated with the construction of a biorefinery processing 2000 dry metric tons of biomass per day (DMT/day) could yield between 5960 and 8470 full‐time equivalent (FTE) jobs during the construction period, depending on the biofuel pathways. Fast pyrolysis biorefineries produce the most jobs on a project level thanks to the highest capital requirement among the three pathways. Normalized on the scale of $1 million of capital investment, the fast pyrolysis biorefineries are estimated to yield slighter higher numbers of jobs (12.1 jobs) than the renewable diesel (11.8 jobs) and the cellulosic ethanol (11.6 jobs) biorefineries. While operating biorefineries is not labor‐intensive, the annual operation of a 2000 DMT/day biorefinery could support between 720 and 970 jobs when the direct, indirect, and induced effects are considered. The major factor, which results in the variations among the three pathways, is the type of biomass feedstock used for biofuels. Unlike construction jobs, these operation‐related jobs are necessary over the entire life of the biorefineries. Our results show that indirect effects stimulated by the operation of biorefineries are the primary contributor to job growth. The agriculture/forest, services, and trade industries are the primary sectors that will benefit from the ongoing operation of biorefineries. Copyright © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd

Life Cycle Carbon Footprint of Ethanol and Potassium Acetate Produced from a Forest Product Wastewater Stream by a Co-Located Biorefinery

Integrated production systems are designed on the concept of “minimum waste” to fully utilize natural resources by building industries next to each other when the waste of one is able to be the feedstock of another. A forest hardboard product wastewater stream contains wood extractives suspended in it that meet the input requirement of a cellulosic ethanol biorefinery facility. In addition, the biorefinery process partially substitutes for conventional wastewater treatment (WWT). A life cycle carbon footprint of fuel ethanol produced from a co-located biorefinery facility has been evaluated with a focus on greenhouse gas (GHG) emissions and compared with petroleum gasoline. The methodology takes into account changes to the original hardboard facility due to the presence of the integrated biorefinery. Three allocation methods (system expansion, mass allocation, and market value allocation) are applied in this study. Six scenarios are analyzed to evaluate the significance of several key variables. The basecase life cycle carbon footprint results show that ethanol produced from this biorefinery emits −27, 21, or 16 g of CO2 eq/MJ using system expansion, mass, or market value allocation, respectively. The sources of energy employed have significant influence on the life cycle GHG emissions for ethanol and potassium acetate.

Optimizing fermentation process miscanthus-to-ethanol biorefinery scale under uncertain conditions

Ethanol produced from cellulosic feedstocks has garnered significant interest for greenhouse gas abatement and energy security promotion. One outstanding question in the development of a mature cellulosic ethanol industry is the optimal scale of biorefining activities. This question is important for companies and entrepreneurs seeking to construct and operate cellulosic ethanol biorefineries as it determines the size of investment needed and the amount of feedstock for which they must contract. The question also has important implications for the nature and location of lifecycle environmental impacts from cellulosic ethanol. We use an optimization framework similar to previous studies, but add richer details by treating many of these critical parameters as random variables and incorporating a stochastic sub-model for land conversion. We then use Monte Carlo simulation to obtain a probability distribution for the optimal scale of a biorefinery using a fermentation process and miscanthus feedstock. We find a bimodal distribution with a high peak at around 10–30 MMgal yr−1 (representing circumstances where a relatively low percentage of farmers elect to participate in miscanthus cultivation) and a lower and flatter peak between 150 and 250 MMgal yr−1 (representing more typically assumed land-conversion conditions). This distribution leads to useful insights; in particular, the asymmetry of the distribution—with significantly more mass on the low side—indicates that developers of cellulosic ethanol biorefineries may wish to exercise caution in scale-up.

Can Lignin Wastes Originating From Cellulosic Ethanol Biorefineries Act as Radical Scavenging Agents?

Lignin is a co-product from the biorefinery and paper industries. Its non-energetic valorisation remains a field of extensive research and development. In this perspective, this study was undertaken to evaluate the radical scavenging ability of selected herbaceous lignins. These lignins, extracted from either Miscanthus (Miscanthus × giganteus) or switchgrass (Panicum virgatum L.), were selected as benchmarks for this study based on their chemical structure and average molecular weight. These technical lignins, which are side-products in the bioethanol production process, displayed a moderate antioxidant activity as evaluated by the 1,1-diphenyl-2-picrylhydrazil free radical scavenging test system. A correlation between the radical scavenging properties and the molecular features is proposed and discussed. Infrared spectroscopy was employed as a straightforward qualitative prediction tool for assessing the radical scavenging capacity.

Pretreatment as the crucial step for a cellulosic ethanol biorefinery: Testing the efficiency of wet explosion on different types of biomass

The efficiency of wet explosion applied as modified dilute acid pretreatment at previously identified reference conditions (150°C, 0.3% H2SO4, 15min) was investigated on lucerne, ryegrass, fescue grass, cocksfoot grass, rye fescue, forage grass, and wheat straw in order to identify their potential as feedstock for cellulosic bioethanol production.After pretreatment, cellulose recovery was more than 95% for all biomass while enzymatic convertibility of cellulose ranged from 40% to 80%. Lower enzymatic conversion of cellulose was correlated with higher lignin content of the biomass. Hemicellulose recovery was 81–91% with a final pentose yield of 65–85%. Cocksfoot grass and wheat straw had the highest bioethanol potential of 292 and 308L/ton DM, respectively. Overall efficiencies were higher than 68% for cocksfoot grass harvested in August, fescue grass, wheat straw, and forage grass while efficiencies were lower than 61% for the other tested biomass resources, making further adjustment of the process parameters necessary.

Development of feedstocks for cellulosic biofuels.

The inclusion of cellulosic ethanol in the Energy Independence and Security Act (EISA) of 2007 and the revised Renewable Fuel Standard (RFS2) has spurred development of the first commercial scale cellulosic ethanol biorefineries. These efforts have also revived interest in the development of dedicated energy crops selected for biomass productivity and for properties that facilitate conversion of biomass to liquid fuels. While many aspects of developing these feedstocks are compatible with current agricultural activities, improving biomass productivity may provide opportunities to expand the potential for biofuel production beyond the classical research objectives associated with improving traditional food and feed crops.

Field to fuel: developing sustainable biorefineries

Life-cycle assessment (LCA) can be used as a scientific decision support technique to quantify the environmental implications of various biorefinery process, feedstock, and integration options. The goal of DuPont's integrated corn biorefinery (ICBR) project, a cost-share project with the United States Department of Energy, was to demonstrate the feasibility of a cellulosic ethanol biorefinery concept. DuPont used LCA to guide research and development to the most sustainable cellulosic ethanol biorefinery design in its ICBR project and will continue to apply LCA in support of its ongoing effort with joint venture partners. Cellulosic ethanol is a biofuel which has the potential to provide a sustainable solution to the nation's growing concerns around energy supply and climate change. A successful biorefinery begins with sustainable removal of biomass from the field. Michigan State University (MSU) used LCA to estimate the environmental performance of corn grain, corn stover, and the corn cob portion of the stover, grown under various farming practices for several corn growing locations in the United States Corn Belt. In order to benchmark the future technology options for producing cellulosic ethanol with existing technologies, LCA results for fossil energy consumption and greenhouse gas (GHG) emissions are compared to alternative ethanol processes and conventional gasoline. Preliminary results show that the DuPont ICBR outperforms gasoline and other ethanol technologies in the life-cycle impact categories considered here.

Biorefinery sustainability assessment

AbstractThis article presents a comparative sustainability assessment of three biorefineries that produce liquid fuels used in current infrastructure. The three options considered are biochemical production of ethanol from grain and from cellulosic feedstocks and thermochemical production of Fischer‐Tropsch diesel from biomass‐derived syngas. These biorefineries were compared using numerous environmental, economic, and social metrics, with numerical values derived from a thorough review of recent literature. For each of the three biorefinery options, the metrics were not determined from a specific process design, but from a variety of different designs reported in literature. Where necessary, corn was selected as the feedstock for grain ethanol and switchgrass was selected for cellulosic ethanol and Fischer‐Tropsch diesel. These sustainability metrics were used in an Analytic Hierarchy Process decision analysis to compare the sustainability of the different biorefineries. Thus, a new decision‐making tool has been created in which the user can assign different weights to each category and its metrics. This tool was used to explore the influence of different weights, different market conditions, and uncertainties in the values of the metrics on the relative sustainability of the different options. Based on the results of this assessment, cellulosic ethanol biorefineries are modestly more sustainable than grain ethanol and Fischer‐Tropsch diesel. Grain ethanol was favorable economically whereas Fischer‐Tropsch diesel had the highest score on the societal metrics. © 2010 American Institute of Chemical Engineers Environ Prog, 2010

Anaerobic digestion as final step of a cellulosic ethanol biorefinery: Biogas production from fermentation effluent in a UASB reactor—pilot‐scale results

In order to lower the costs for second generation bioethanol from lignocellulosic biomass anaerobic digestion of the effluent from ethanol fermentation was implemented using an upflow anaerobic sludge blanket (UASB) reactor system in a pilot-scale biorefinery plant. Both thermophilic (53 degrees C) and mesophilic (38 degrees C) operation of the UASB reactor was investigated. At an OLR of 3.5 kg-VS/(m(3) day) a methane yield of 340 L/kg-VS was achieved for thermophilic operation (53 degrees C) while 270 L/kg-VS was obtained under mesophilic conditions (38 degrees C). For loading rates higher than 5 kg-VS/(m(3) day) the methane yields were, however, higher under mesophilic conditions compared to thermophilic conditions. The conversion of dissolved organic matter (VS(diss)) was between 68% and 91%. The effluent from the ethanol fermentation showed no signs of toxicity to the anaerobic microorganisms. However, a high content of suspended matter reduced the degradation efficiency. The retention time of the anaerobic system could be reduced from 70 to 7 h by additional removal of suspended matter by clarification. Implementation of the biogas production from the fermentation effluent accounted for about 30% higher carbon utilization in the biorefinery compared to a system with only bioethanol production.