A Robust Process to Produce Lignocellulosic Nanofibers from Corn Stover, Reed Canary Grass, and Industrial Hemp.

The use of agricultural waste biomass for nanocellulose production has gained interest due to its environmental and economic benefits compared to conventional bleached pulp feedstock. However, there is still a need to establish robust process technologies that can accommodate the variability of waste feedstocks and to understand the effects of feedstock characteristics on the final nanofiber properties. Here, lignocellulosic nanofibers with unique properties are produced from various waste biomass based on a simple and low-cost process using mild operating conditions. The process robustness is demonstrated by diversifying the feedstock, ranging from food crop waste (corn stover) to invasive grass species (reed canary grass) and industrial lignocellulosic residues (industrial hemp). This comprehensive study provides a thorough examination of the influence of the feedstocks' physico-chemical characteristics on the conversion treatment, including process yield, degree of delignification, effectiveness of nanofibrillation, fiber morphology, surface charge, and density. Results show that nanofibers have been successfully produced from all feedstocks, with minor to no adjustments to process conditions. This work provides a framework for future studies to engineer nanocellulose with specific properties by taking advantage of biomass feedstocks' intrinsic characteristics to enable versatile applications.

Lignocellulosic nanomaterials production from wheat straw via peracetic acid pretreatment and their application in plastic composites.

Cellulose nanofibrils are typically prepared from high-purity bleached pulp through harsh chemical treatments (e.g., TEMPO oxidation), resulting in high costs and environmental impact. In this work, we utilize inexpensive wheat straw feedstock and alkaline peroxide pulping followed by mild peracetic acid (PAA) pretreatment to produce lignocellulosic nanomaterials (nano and microfibrils) with potential bioplastics applications. PAA was chosen due to its biodegradability, non-toxicity, and high reaction selectivity. As-synthesized lignocellulosic nanomaterials were thoroughly characterized and compared to nanofibrils produced via TEMPO oxidation pretreatment and then applied as reinforcing agents in plastic composites. A remarkable case of simultaneous strengthening and toughening of the polymer nanocomposite was achieved with high specific tensile strength (up to 59.5 MPa g-1 cm3), elastic modulus (up to 2.6 GPa g-1 cm3), and fracture strain (up to 138 %). This work is a comprehensive investigation of all process steps involved in lignocellulosic nanomaterials production, from original residue feedstock to final product application.

Novel ethanol production using biomass preprocessing to increase ethanol yield and reduce overall costs.

BACKGROUND: Ethanol biorefineries need to lower their overall production costs to become economically feasible. Two strategies to achieve this are to reduce costs using cheaper feedstocks or to increase the ethanol production yield. Low-cost feedstocks usually have high non-structural components (NSC) content; therefore, a new process is necessary to accommodate these feedstocks and overcome the negative effects of NSC. This study developed a novel ethanol biorefinery process including a biomass preprocessing step that enabled the use of lower-cost feedstocks while improving ethanol production without detoxification (overliming). Two types of poplar feedstocks were used, low-quality whole-tree chips (WTC) and high-quality clean pulp chips (CPC), to determine if the proposed process is effective while using feedstocks with different NSC contents. RESULTS: Technical assessment showed that acidic preprocessing increased the monomeric sugar recovery of WTC from 73.2% (untreated) to 87.5% due to reduced buffering capacity of poplar, improved sugar solubilization during pretreatment, and better enzymatic hydrolysis conversion. Preprocessing alone significantly improved the fermentability of the liquid fraction from 1-2% to 49-56% for both feedstocks while overliming improved it to 45%. Consequently, it was proposed that preprocessing can substitute for the detoxification step. The economic assessment revealed that using poplar WTC via the new process increased annual ethanol production of 10.5 million liters when compared to using CPC via overliming (base case scenario). Also, savings in total operating costs were about $10 million per year when using cheaper poplar WTC instead of CPC, and using recycled water for preprocessing lowered its total operating costs by 45-fold. CONCLUSIONS: The novel process developed in this study was successful in increasing ethanol production while decreasing overall costs, thus facilitating the feasibility of lignocellulosic ethanol biorefineries. Key factors to achieving this outcome included substituting overliming by preprocessing, enabling the use of lower-quality feedstock, increasing monomeric sugar recovery and ethanol fermentation yield, and using recycled water for preprocessing. In addition, preprocessing enabled the implementation of an evaporator-combustor downstream design, resulting in a low-loading waste stream that can be treated in a wastewater treatment plant with a simple configuration.

Production routes to bio-acetic acid: life cycle assessment.

BACKGROUND: Similar to biofuels, numerous chemicals produced from petroleum resources can also be made from biomass. In this research we investigate cradle to biorefinery exit gate life cycle impacts of producing acetic acid from poplar biomass using a bioconversion process. A key step in developing acetic acid for commercial markets is producing a product with 99.8% purity. This process has been shown to be potentially energy intensive and in this work two distillation and liquid-liquid extraction methods are evaluated to produce glacial bio-acetic acid. Method one uses ethyl acetate for extraction. Method two uses alamine and diisobutyl ketone. Additionally two different options for meeting energy demands at the biorefinery are modeled. Option one involves burning lignin and natural gas onsite to meet heat/steam and electricity demands. Option two uses only natural gas onsite to meet heat/steam demands, purchases electricity from the grid to meet biorefinery needs, and sells lignin from the poplar biomass as a co-product to a coal burning power plant to be co-fired with coal. System expansion is used to account for by-products and co-products for the main life cycle assessment. Allocation assessments are also performed to compare the life cycle tradeoffs of using system expansion, mass allocation, or economic allocation for bio-acetic acid production. Finally, a sensitivity analysis is conducted to determine potential effects of a decrease in the fermentation of glucose to acetic acid. RESULTS: Global warming potential (GWP) and fossil fuel use (FFU) for ethyl acetate extraction range from 1000-2500 kg CO2 eq. and 32-56 GJ per tonne of acetic acid, respectively. Alamine and diisobutyl ketone extraction method GWP and FFU ranges from -370-180 kg CO2 eq. and 15-25 GJ per tonne of acetic acid, respectively. CONCLUSIONS: Overall the alamine/diisobutyl ketone extraction method results in lower GWP and FFU values compared to the ethyl acetate extraction method. Only the alamine/diisobutyl extraction method finds GWP and FFU values lower than those of petroleum based acetic acid. For both extraction methods, exporting lignin as a co-product produced larger GWPs and FFU values compared to burning the lignin at the biorefinery.

Techno-Economic Analysis of Producing Glacial Acetic Acid from Poplar Biomass via Bioconversion.

Most of the current commercial production of glacial acetic acid (GAA) is by petrochemical routes, primarily methanol carbonylation. GAA is an intermediate in the production of plastics, textiles, dyes, and paints. GAA production from biomass might be an economically viable and sustainable alternative to petroleum-derived routes. Separation of acetic acid from water is a major expense and requires considerable energy. This study evaluates and compares the technical and economic feasibility of GAA production via bioconversion using either ethyl acetate or alamine in diisobutylkerosene (DIBK) as organic solvents for purification. Models of a GAA biorefinery with a production of 120,650 tons/year were simulated in Aspen software. This biorefinery follows the path of pretreatment, enzymatic hydrolysis, acetogen fermentation, and acid purification. Estimated capital costs for different scenarios ranged from USD 186 to 245 million. Recovery of GGA using alamine/DIBK was a more economical process and consumed 64% less energy, due to lower steam demand in the recovery distillation columns. The estimated average minimum selling prices of GGA were USD 756 and 877/ton for alamine/DIBK and ethyl acetate scenarios, respectively. This work establishes a feasible and sustainable approach to produce GGA from poplar biomass via fermentation.

Integration of wastewater treatment into process design of lignocellulosic biorefineries for improved economic viability.

BACKGROUND: Production and use of bio-based products offer advantages over conventional petrochemicals, yet the relatively high cost of production has restricted their mainstream adoption. Optimization of wastewater treatment processes could reduce capital expenditures, lowering the barrier to market entry for lignocellulosic biorefineries. This paper characterizes wastewater associated with lignocellulosic ethanol production and evaluates potential wastewater treatment operations. RESULTS: It is found that organic material is intrinsic to bioconversion wastewater, representing up to 260 kg of biological oxygen demand per tonne of feedstock processed. Inorganics in the wastewater largely originate from additions during pretreatment and pH adjustments, which increase the inorganic loading by 44 kg per tonne of feedstock processed. Adjusting the ethanol production process to decrease addition of inorganic material could reduce the demands and therefore cost of waste treatment. Various waste treatment technologies-including those that take advantage of ecosystem services provided by feedstock production-were compared in terms of capital and operating costs, as well as technical feasibility. CONCLUSIONS: It is concluded that wastewater treatment technologies should be better integrated with conversion process design and feedstock production. Efforts to recycle resources throughout the biofuel supply chain through application of ecosystem services provided by adjacent feedstock plantations and recovery of resources from the waste stream to reduce overall capital and operating costs of bioconversion facilities.

Removal of non-structural components from poplar whole-tree chips to enhance hydrolysis and fermentation performance.

BACKGROUND: Whole-tree chips will be a likely feedstock for future biorefineries because of their low cost. Non-structural components (NSC), however, represent a significant part of whole-tree chips. The NSC can account for more than 10% of whole-tree poplar mass when the trees are grown in short rotation cycles. The influence of NSC, however, on the production of fuels and chemicals is not well known. In this study, we assessed the impact of NSC removal from poplar whole-tree chips on pretreatment and enzymatic hydrolysis yields, overall sugar recovery, and fermentation yield. In addition, we evaluated the economics of preprocessing as a new unit operation in the biorefinery. RESULTS: Poplar whole-tree chips were preprocessed by neutral or acidic washing before steam pretreatment, enzymatic hydrolysis, and fermentation. Preprocessing of poplar reduced ash and extractives content as much as 70 and 50%, respectively. The overall sugar yield after pretreatment and hydrolysis was 18-22% higher when the biomass had been preprocessed, which was explained by higher sugar yields in liquid fraction and more efficient enzymatic hydrolysis of the solid fraction. The liquid fraction ethanol fermentation yield was 36-50% higher for the preprocessed biomass. CONCLUSIONS: It appears that preprocessing reduced the buffering capacity of the biomass due to ash removal, and thereby improved the enzymatic hydrolysis. Removal of extractives during preprocessing improved the fermentation yield. The economic modeling shows that a preprocessing unit could have significant economic benefits in a biorefinery, where poplar whole-tree chips are used as bioconversion feedstock.

Bridging the gap between feedstock growers and users: the study of a coppice poplar-based biorefinery.

BACKGROUND: In the biofuel industry, land productivity is important to feedstock growers and conversion process product yield is important to the biorefinery. The crop productivity, however, may not positively correlate with bioconversion yield. Therefore, it is important to evaluate sugar yield and biomass productivity. In this study, 2-year-old poplar trees harvested in the first coppice cycle, including one low-productivity hybrid and one high-productivity hybrid, were collected from two poplar tree farms. Through steam pretreatment and enzymatic hydrolysis, the bioconversion yields of low- and high-productivity poplar hybrids were compared for both sites. RESULTS: The low-productivity hybrids had 9-19% higher sugar yields than the high-productivity hybrids, although they have the similar chemical composition. Economic calculations show the impact on the plantation and biorefinery of using the two feedstocks. Growing a high-productivity hybrid means the land owner would use 11-26% less land (which could be used for other crops) or collect $2.53-$3.46 MM/year extra revenue from the surplus feedstock. On the other side, the biorefinery would receive 5-10% additional revenue using the low-productivity hybrid. CONCLUSION: We propose a business model based on the integration of the plantation and the biorefinery. In this model, different feedstocks are assessed using a metric of product tonnage per unit land per year. Use of this new economic metric bridges the gap between feedstock growers and users to maximize the overall production efficiency.

Can we use short rotation coppice poplar for sugar based biorefinery feedstock? Bioconversion of 2-year-old poplar grown as short rotation coppice.

BACKGROUND: Feedstock cost is a substantial barrier to the commercialization of lignocellulosic biorefineries. Poplar grown using a short rotation coppice (SRC) system has the potential to provide a low-cost feedstock and economically viable sugar yields for fuels and chemicals production. In the coppice management regime, poplars are harvested after 2 years' growth to develop the root system and establish the trees. The biomass from these 2-year-old trees is very heterogeneous, and includes components of leaf, bark, branch, and wood chip. This material is quite different than the samples that have been used in most poplar bioconversion research, which come from mature trees of short rotation forestry (SRF) plantations. If the coppice management regime is to be used, it is important that feedstock growers maximize their revenue from this initial harvest, but the heterogeneous nature of the biomass may be challenging for bioconversion. This work evaluates bioconversion of 2-year-old poplar coppice and compares its performance to whitewood chips from 12-year-old poplar. RESULTS: The 2-year-old whole tree coppice (WTC) is comprised of 37% leaf, 9% bark, 12% branch, and 42% wood chip. As expected, the chemical compositions of each component were markedly different. The leaf has a low sugar content but is high in phenolics, ash, and extractives. By removing the leaves, the sugar content of the biomass increased significantly, while the phenolic, ash, and extractives contents decreased. Leaf removal improved monomeric sugar yield by 147 kg/tonne of biomass following steam pretreatment and enzymatic hydrolysis. Bioconversion of the no-leaf coppice (NLC) achieved a 67% overall sugar recovery, showing no significant difference to mature whitewood from forestry plantation (WWF, 71%). The overall sugar yield of NLC was 135 kg/tonne less than that of WWF, due to the low inherent sugar content in original biomass. An economic analysis shows the minimum ethanol selling price required to cover the operating cost of NLC bioconversion was $1.69/gallon. CONCLUSIONS: Leaf removal resulted in significant improvement in overall monomeric sugar production from SRC biomass. Leaf removal is essential to achieve good yields in bioconversion of poplar. Economic analysis suggests the NLC could be a reasonable feedstock provided it can be obtained at a discounted price.

Hydrocarbon bio-jet fuel from bioconversion of poplar biomass: life cycle assessment.

BACKGROUND: Bio-jet fuels compatible with current aviation infrastructure are needed as an alternative to petroleum-based jet fuel to lower greenhouse gas emissions and reduce dependence on fossil fuels. Cradle to grave life cycle analysis is used to investigate the global warming potential and fossil fuel use of converting poplar biomass to drop-in bio-jet fuel via a novel bioconversion platform. Unique to the biorefinery designs in this research is an acetogen fermentation step. Following dilute acid pretreatment and enzymatic hydrolysis, poplar biomass is fermented to acetic acid and then distilled, hydroprocessed, and oligomerized to jet fuel. Natural gas steam reforming and lignin gasification are proposed to meet hydrogen demands at the biorefineries. Separate well to wake simulations are performed using the hydrogen production processes to obtain life cycle data. Both biorefinery designs are assessed using natural gas and hog fuel to meet excess heat demands. RESULTS: Global warming potential of the natural gas steam reforming and lignin gasification bio-jet fuel scenarios range from CO2 equivalences of 60 to 66 and 32 to 73 g MJ(-1), respectively. Fossil fuel usage of the natural gas steam reforming and lignin gasification bio-jet fuel scenarios range from 0.78 to 0.84 and 0.71 to 1.0 MJ MJ(-1), respectively. Lower values for each impact category result from using hog fuel to meet excess heat/steam demands. Higher values result from using natural gas to meet the excess heat demands. CONCLUSION: Bio-jet fuels produced from the bioconversion of poplar biomass reduce the global warming potential and fossil fuel use compared with petroleum-based jet fuel. Production of hydrogen is identified as a major source of greenhouse gas emissions and fossil fuel use in both the natural gas steam reforming and lignin gasification bio-jet simulations. Using hog fuel instead of natural gas to meet heat demands can help lower the global warming potential and fossil fuel use at the biorefineries.

Kinetic modeling of Moorella thermoacetica growth on single and dual-substrate systems.

Acetic acid is an important chemical raw material that can be produced directly from sugars in lignocellulosic biomass. Development of kinetic models that capture the bioconversion dynamics of multiple sugar systems will be critical to optimization and process control in future lignocellulosic biorefinery processes. In this work, a kinetic model was developed for the single- and dual-substrate conversion of xylose and glucose to acetic acid using the acetogen Moorella thermoacetica. Batch fermentations were performed experimentally at 20 g L(-1) total sugar concentration using synthetic glucose, xylose, and a mixture of glucose and xylose at a 1:1 ratio. The product yield, calculated as total product formed divided by total sugars consumed, was 79.2, 69.9, and 69.7 % for conversion of glucose, xylose, and a mixture of glucose and xylose (1:1 ratio), respectively. During dual-substrate fermentation, M. thermoacetica demonstrated diauxic growth where xylose (the preferred substrate) was almost entirely consumed before consumption of glucose began. Kinetic parameters were similar for the single-substrate fermentations, and a strong linear correlation was determined between the maximum specific growth rate µ max and substrate inhibition constant, K s . Parameters estimated for the dual-substrate system demonstrated changes in the specific growth rate of both xylose and glucose consumption. In particular, the maximum growth rate related to glucose tripled compared to the single-substrate system. Kinetic growth is affected when multiple substrates are present in a fermentation system, and models should be developed to reflect these features.

Post-treatment mechanical refining as a method to improve overall sugar recovery of steam pretreated hybrid poplar.

This study investigates the effect of mechanical refining to improve the sugar yield from biomass processed under a wide range of steam pretreatment conditions. Hybrid poplar chips were steam pretreated using six different conditions with or without SO2. The resulting water insoluble fractions were subjected to mechanical refining. After refining, poplar pretreated at 205°C for 10min without SO2 obtained a 32% improvement in enzymatic hydrolysis and achieved similar overall monomeric sugar recovery (539kg/tonne) to samples pretreated with SO2. Refining did not improve hydrolyzability of samples pretreated at more severe conditions, nor did it improve the overall sugar recovery. By maximizing overall sugar recovery, refining could partially decouple the pretreatment from other unit operations, and enable the use of low temperature, non-sulfur pretreatment conditions. The study demonstrates the possibility of using post-treatment refining to accommodate potential pretreatment process upsets without sacrificing sugar yields.

Hydrocarbon bio-jet fuel from bioconversion of poplar biomass: techno-economic assessment.

BACKGROUND: Infrastructure compatible hydrocarbon biofuel proposed to qualify as renewable transportation fuel under the U.S. Energy Independence and Security Act of 2007 and Renewable Fuel Standard (RFS2) is evaluated. The process uses a hybrid poplar feedstock, which undergoes dilute acid pretreatment and enzymatic hydrolysis. Sugars are fermented to acetic acid, which undergoes conversion to ethyl acetate, ethanol, ethylene, and finally a saturated hydrocarbon end product. An unfermentable lignin stream may be burned for steam and electricity production, or gasified to produce hydrogen. During biofuel production, hydrogen gas is required and may be obtained by various methods including lignin gasification. RESULTS: Both technical and economic aspects of the biorefinery are analyzed, with different hydrogen sources considered including steam reforming of natural gas and gasification of lignin. Cash operating costs for jet fuel production are estimated to range from 0.67 to 0.86 USD L-1 depending on facility capacity. Minimum fuel selling prices with a 15 % discount rate are estimated to range from 1.14 to 1.79 USD L-1. Capacities of 76, 190, and 380 million liters of jet fuel per year are investigated. Capital investments range from 356 to 1026 million USD. CONCLUSIONS: A unique biorefinery is explored to produce a hydrocarbon biofuel with a high yield from bone dry wood of 330 L t-1. This yield is achieved chiefly due to the use of acetogenic bacteria that do not produce carbon dioxide as a co-product during fermentation. Capital investment is significant in the biorefinery in part because hydrogen is required to produce a fully de-oxygenated fuel. Minimum selling price to achieve reasonable returns on investment is sensitive to capital financing options because of high capital costs. Various strategies, such as producing alternative, intermediate products, are investigated with the intent to reduce risk in building the proposed facility. It appears that producing and selling these intermediates may be more profitable than converting all the biomass into aviation fuel. With variability in historical petroleum prices and environmental subsidies, a high internal rate of return would be required to attract investors.

Synergistic effects of mixing hybrid poplar and wheat straw biomass for bioconversion processes.

BACKGROUND: Low cost of raw materials and good process yields are necessary for future lignocellulosic biomass biorefineries to be sustainable and profitable. A low cost feedstock will be diverse, changing as a function of seasonality and price and will most likely be available from multiple sources to the biorefinery. The efficacy of the bioconversion process using mixed biomass, however, has not been thoroughly investigated. Considering the seasonal availability of wheat straw and the year round availability of hybrid poplar in the Pacific Northwest, this study aims to determine the impact of mixing wheat straw and hybrid poplar biomass on the overall sugar production via steam pretreatment and enzymatic saccharification. RESULTS: Steam pretreatment proved to be effective for processing different mixtures of hybrid poplar and wheat straw. Following SO2-catalyzed steam explosion pretreatment, on average 22 % more sugar monomers were recovered using mixed feedstock than either single biomass. Improved sugar recovery with mixtures of poplar and wheat straw continued through enzymatic hydrolysis. After steam pretreatment and saccharification, the mixtures showed 20 % higher sugar yields than that produced from hybrid poplar and wheat straw alone. CONCLUSIONS: Blending hybrid poplar and wheat straw resulted in more monomeric sugar recovery and less sugar degradation. This synergistic effect is attributable to interaction of hybrid poplar's high acetic acid content and the presence of ash supplied by wheat straw. As a consequence on average 20 % more sugar was yielded by using the different biomass mixtures. Combining hybrid poplar and wheat straw enables sourcing of the lowest cost biomass, reduces seasonal dependency, and results in increasing biofuels and chemicals productivity in a cellulosic biorefinery.

Converting lignocellulosic solid waste into ethanol for the State of Washington: an investigation of treatment technologies and environmental impacts.

There is little research literature on the conversion of lignocellulosic rich waste streams to ethanol, and even fewer have investigated both the technical aspects and environmental impacts together. This study assessed technical and environmental challenges of converting three lignocellulosic waste streams to ethanol: municipal solid waste (MSW), low grade mixed waste paper (MWP), and organic yard waste (YW). Experimental results showed high conversion yields for all three streams using suitable conversion methods. Environmental impacts are highly dependent on conversion technology, and process conditions used. Life cycle assessment results showed that both chemicals production and waste collection are important factors to be included within a waste-to-ethanol study.