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The properties of lignocellulosic biomass, such as bulk physical, thermal, and mechanical properties, as well as the mobility of enzymes or catalysts, are largely affected by porosity, pore structures, and pore size distribution. While X-ray computed tomography (CT) has been introduced to effectively produce 3D volumetric images of material microstructure, a quantitative porosity analysis from the 3D images has never been done. This work introduces a first-of-its-kind X-ray CT-based quantitative porosity analysis method and applies the developed toolkit to characterize the internal porosity distribution of loblolly pine. A sample loblolly pine chip was scanned by a nano-resolution X-ray CT system and digitally reconstructed after a sequence of image processing operations. A comprehensive porosity analysis was then performed to quantify the envelope porosity, the spatial distribution of local porosity, and the directional porosity. Solutions to the various challenges in image processing, porosity calculation, and large data handling are provided.

This work presents an experiment-informed, semi-empirical, elasto-plastic bond model for the discrete element modeling of woody biomass particles. The model renders nonlinear plastic deformation of materials when subjected to compression/tension, bending, and twisting, essential for accurately simulating the behavior of biomass in comminution. The model is implemented in an open-source DEM package LIGGGHTS and is assessed in a number of verification tests. The model is applied to simulate the fracturing test of notched loblolly pine blocks. Reduced bond strength is prescribed to the weak planes along the growth rings. It is found that the square-root formulation for describing the elasto-plastic normal bond contact delivers the best agreement with the experimental data over its linear and quadratic counterparts. Furthermore, the model predicts a strong anisotropic behavior of wood blocks with regard to the grain orientations, indicating that the cutting angle should be an important attribute for the optimization of biomass comminution.

Biomass, as harvested, is composed of inorganic compounds both intrinsically and extrinsically and can be quite abrasive. The present study investigates the wear modes and mechanisms of two types of blades of hammer mills used in biomass size reduction (impacting particle size and distribution) and densification (impacting size, shape, and density). The dominant wear modes for the stage 1 steel blades are determined to be erosive and polishing wear. For the stage 2 blades with a carbide weld overlay, the main wear mechanisms are erosion and fracture. Partial replacement of Co by Fe in the outer layer of carbide grits, likely induced by diffusion during the high-temperature welding, has been correlated to the microcracking observed. The microcracking is believed to weaken the grit strength and fracture toughness and make the overlay prone to fracture and erosion due to repetitive contact with the inorganic contents in chopping biomass.

Here, we report on the effects of loblolly pine residue variability on material throughput, pilot plant uptime, operator intervention, product yield, and product quality for grinding, fast pyrolysi...

Early lignocellulosic biorefineries have been plagued with numerous issues that involve feedstock handling problems and variations in conversion efficacy that stem from feedstock variability and co...

The inorganic content of biomass impairs size reduction tool life and the conversion process. Conventional ash extraction relies on furnace combustion that inevitably alters the inorganic compounds due to oxidation and decomposition. This study developed composition-preserving methods for extracting and analyzing extrinsic and intrinsic inorganic compounds. Comprehensive characterization was carried out on selected biomass feedstocks, including corn stover, pine residue, and pine anatomical fractions, to reveal their inorganic species and morphology. The extrinsic inorganic compounds were found to be dominated by quartz, along with other minor minerals, such as albite, microcline, and gehlenite, and have particle sizes ranging from tens to hundreds of micrometers. Among the pine anatomical fractions, the needles contain the highest intrinsic silicon content while the bark trapped the most extrinsic minerals. By correlation of the total ash and extrinsic inorganic contents to the wear behavior, both the extrinsic and intrinsic inorganic compounds were concluded to have made significant contributions to the wear process. The results here validated a new approach to characterize inorganic compounds in biomass and provided fundamental insights for their potential impact on preprocessing tool wear.

This study applies design of experiments (DOE) methods in the conduct of a techno-economic assessment (TEA) on a newly developed rare-earth element (REE) recovery process. The goal of this effort is to identify main factors that affect the profitability of the process. We construct a factorial design with net profit as the response, where the experimental data are generated by simulation of different scenarios. The effects of different factors and their interactions are determined. Based on these results, a desirable recovery strategy is proposed. It is envisioned that the methods applied in the study can be utilized in other situations to promote the application of TEA in value recovery approaches.

Agricultural waste was used as substrate for fermentation by Gluconobacter oxydans to produce lixiviant for rare earth element (REE) recovery from industrial waste materials, i.e., spent fluid cata...

The environmental and economic impacts of implementing a circular economy in plastic waste supply chains are not well understood. The proposed systems analysis framework assesses environmental, social, and economic impacts of plastic waste supply chains in a circular economy. The first objective of this article is to identify data sets, models, and knowledge gaps associated with waste plastic supply chain processes, mainly in the U.S. Our literature review indicated that the best data sets exist for virgin plastic resin production, mechanical recycling, landfilling, and incineration, with the materials recovery facility being intermediate, and with chemical recycling the lowest. The second objective of this perspective is to develop an illustrative application of the framework by conducting a preliminary systems analysis of PET bottles with closed-loop recycling. The preliminary systems analysis of polyethylene terephthalate (PET) bottles utilized a linear programming optimization method. Our optimization model indicated that both chemical and mechanical recycling processes are needed to achieve a true circular economy of PET bottles with the least greenhouse gas emissions, specifically reductions of 24% when compared with the linear economy. Good quality and standardized life cycle assessment and techno-economic analysis studies are needed to better understand the environmental, economic, and social impacts of advanced sorting and chemical recycling technologies.

A bioleaching process to extract rare-earth elements (REE) from fluidized catalytic cracking (FCC) catalysts was optimized using a heterotrophic bacterium Gluconobacter oxydans to produce organic acids from glucose. Parameters optimized included agitation intensity, oxygen levels, glucose concentrations, and nutrient additions. Biolixiviants from the optimized batch process demonstrated REE leaching efficiencies up to 56%. A continuous bioreactor system was subsequently developed to feed a leach process and demonstrated leaching efficiencies of 51%. A techno-economic analysis showed glucose to be the single largest expense for the bioleach process, constituting 44% of the total cost. The bioleaching plant described here was found profitable, although the margin was small. Lower cost carbon and energy sources for producing the biolixiviant, sourcing FCC catalysts with higher total REE content (>1.5% by mass), and improved leaching efficiencies would significantly increase the overall profit. A life cycle a...

Biomass cost, supply, and quality are critical parameters to consider when choosing feedstocks and locations for biorefineries. Biomass cost is dependent upon feedstock type, location, quantities available, logistics costs, and the quality specifications required by the biorefinery. Biomass quality depends upon feedstock type, growth conditions, weather, harvesting methods, storage conditions, and any preprocessing methods used to improve quality. Biomass quantity depends on location as well as growth conditions, weather, harvesting methods, and storage conditions. This study examines the interdependencies of these parameters and how they affect the biomass blends required by biomass depots and/or biorefineries to achieve the lowest cost feedstock with sufficient quality at the quantities needed for biorefinery operation. Four biomass depots were proposed in South Carolina to each produce 200,000 t of feedstock per year. These depots supply a centrally located 800,000 t biorefinery that converts the feedstocks to bio-oil using either catalyzed or uncatalyzed fast pyrolysis. The four depots utilize biomass based upon availability, but the feedstock or feedstock blend still met the minimum quality requirements for the biorefinery. Costs were minimized by using waste biomass resources such as construction and demolition waste, logging residues, and forest residuals. As necessary, preprocessing methods such as air classification and acid leaching were used to upgrade biomass quality. For both uncatalyzed and catalyzed fast pyrolysis, all four depots could produce biomass blends that met quality and quantity specifications at a cost lower than using a single feedstock.

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.

Microbial cultures were evaluated for organic acid production and their potential utility for leaching of rare earth elements (REE) from retorted phosphor powder (RPP) and spent fluid catalytic cracking (FCC) catalyst. Two bacterial and one fungal strain were isolated from environmental and industrial materials known to contain REE and compared to the industrially important bacterium Gluconobacter oxydans. Gluconic acid was the predominant organic acid product identified in all of the cultures. Maximum REE leaching (49% of the total REE) from the FCC material was observed using cell-free culture supernatants of G. oxydans, with preferential recovery of lanthanum over cerium. The phosphor powder was more difficult to leach; only about 2% of the total REE was leached with G. oxydans. Leaching experiments with the RPP material indicated that the extent of REE solubilization was similar whether whole cell cultures or cell-free supernatants were used. Abiotic control experiments showed that increasing gluconic acid concentrations increased leaching efficiency; for example, total REE leaching from FCC catalyst increased from 24% to 45% when gluconic acid was increased from 10 mM to 90 mM. However, G. oxydans cell-free culture supernatants containing 10–15 mM gluconic acid were more effective than abiotically prepared leaching solutions with higher gluconic acid concentrations, suggesting that other exudate components were important too. Our results indicate that microorganisms producing gluconic and other organic acids can induce effective leaching of REE from waste materials, and that increasing organic acid production will improve recovery.

The production of biofuels from lignocellulosic feedstock is attracting considerable attention in the United States and globally as a strategy to diversify energy resources, spur regional economic development and reduce greenhouse gas emissions. Because of the wide variation in feedstock types, compositions and content of convertible organics, there is a growing need to better understand correlations among feedstock quality attributes and conversion performance. Knowledge of the feedstock impact on conversion is essential to supply quality controlled, uniform and on-spec feedstocks to biorefineries. This review paper informs the development of meaningful feedstock quality specifications for different conversion processes. Discussions are focused on how compositional properties of feedstocks affect various unit operations in biochemical conversion processes, fast pyrolysis and hydrothermal liquefaction. In addition, future perspectives are discussed that focus on the challenges and prospects of addressing compositionally intrinsic inhibitors through feedstock preprocessing at regionally distributed depots. Such preprocessing depots may allow for the commoditization of lignocellulosic feedstock and realization of stable, cost-effective and quality controlled biomass supply systems.

Biomass feedstock costs remain one of the largest impediments to biofuel production economics. Municipal solid waste (MSW) represents an attractive feedstock with year-round availability, an established collection infrastructure paid for by waste generators, low cost, and the potential to be blended with higher cost feedstocks to reduce overall feedstock costs. Paper waste, yard waste, and construction and demolition waste (CD yard waste consisted of grass clippings, and C&D wastes consisted of engineered wood products obtained from a construction waste landfill. The waste materials were tested for thermochemical conversion potential using a bench scale fast micropyrolysis process. Bio-oil yields were the highest for the C&D materials and lowest for the paper waste. The C&D wastes had the...

Biomass such as agricultural residues, energy crops and yard waste has significant potential to be used as renewable feedstocks for production of fuels, chemicals and energy. However, in a given location, biomass availability, cost and quality can vary markedly. Strategies to manage these traits must be identified and implemented so that consistent low-cost and high-quality feedstocks can be delivered to biorefineries year round. In this study, we examine air classification as a method to mitigate high ash concentrations in corn stover, switchgrass, and grass clippings. Formulation techniques were then used to produce blends that met ash quality and biomass quantity specifications at the lowest possible cost for biopower and biochemical conversion applications. It was found that air classification can separate the biomass into light fractions which contain concentrated amounts of elemental ash components introduced through soil contamination such as sodium, alumina, silica, iron and titania; and heavy fractions that are depleted in these components and have relatively lower total ash content. Light fractions of corn stover and grass clippings were found to be suitable for combustion applications since they had less propensity to slag than the whole biomass material. The remaining heavy fractions of corn stover or grass clippings could then be blended with switchgrass to produce blends that met the 5% total ash specifications suggested for biochemical conversions. However, ternary blends of the three feedstocks were not possible due to the high ash content of grass clippings. It was determined that air classification by itself was not suitable to prepare these feedstocks for pyrolysis due to high ash content.

Polyethylene terephthalate (PET #1) and polyolefin plastics such polyethylene (HDPE #2, LDPE #4) and polypropylene (PP #5) are major products from the chemical industry, and they comprise a significant fraction of municipal solid waste that ends up in landfills or as litter and marine debris. The reuse of these polymeric materials can be optimized through systems analysis with a view on materials flow analysis, techno-economics, environmental life cycle assessment, and consequential societal impacts. This contribution will present the overall research approach for this exploratory project within the DOE- and industry-funded REMADE Institute and end with a proposed systems analysis framework.

Ash in biomass is believed to damage biorefinery equipment due to its abrasive properties, and is undesirable in thermal and biological conversion reactions as it cannot be converted into fuels, can catalyze undesirable side reactions, and poisons catalysts. All biomass contains at least some ash, or inorganic content, as a result of normal physiological processes. The concentration of biogenic ash in biomass is largely species dependent; however it can also be affected by weather patterns, irrigation, soil type, and fertilizer applications. Ash concentrations in harvested biomass can also be elevated due to the incorporation of soil and dust during the harvest and collection processes. While ash concentration in biomass is important, so also is the mineral form of the ash. Certain mineral forms of ash can be much harder than the steels used to construct biorefinery equipment and cause excessive wear. In this perspective, the relative concentrations of ash elements, mineral forms of ash, and the hardness of these minerals are considered to identify ash components of concern to biorefinery operators. Strategies are suggested to remove ash from harvested biomass to reduce the risk of excessive wear on biomass processing equipment.

Alicyclobacillus acidocaldarius, a thermoacidophilic bacterium, has a repertoire of thermo- and acid-stable enzymes that deconstruct lignocellulosic compounds. The work presented here describes the ability of A. acidocaldarius to reduce the concentration of the phenolic compounds: phenol, ferulic acid, ρ-coumaric acid and sinapinic acid during growth conditions. The extent and rate of the removal of these compounds were significantly increased by the presence of micro-molar copper concentrations, suggesting activity by copper oxidases that have been identified in the genome of A. acidocaldarius. Substrate removal kinetics was first order for phenol, ferulic acid, ρ-coumaric acid and sinapinic acid in the presence of 50 μM copper sulfate. In addition, laccase enzyme assays of cellular protein fractions suggested significant activity on a lignin analog between the temperatures of 45 and 90 °C. This work shows the potential for A. acidocaldarius to degrade phenolic compounds, demonstrating potential relevance to biofuel production and other industrial processes.

Lignocellulosic biorefineries have tonnage and throughput requirements that must be met year round, and there is no single feedstock available in any given region that is capable of meeting the price and availability demands of the biorefineries. Ionic liquid (IL) pretreatment with certain ILs is receiving significant attentions as a potential process that enables fractionation of a wide range of feedstocks and produces high yields of fermentable sugars suitable for biofuel production. Building on the large-scale demonstration of a single herbaceous feedstock (switchgrass), this work extends scale-up of IL pretreatment to woody (eucalyptus) and mixed feedstock (mixtures of two) by 30-fold, relative to the bench scale (6 vs 0.2 L) at 10 % solid loading. The mixed feedstock recovered similar yields of glucan (99.7 %), xylan (62.8 %), and lignin (59.9 %) as switchgrass and eucalyptus at 6-L scale operation, and results of all three feedstocks are better than those obtained from small-scale studies. By integrating the process of IL pretreatment with efficient and scalable homogenization, washing, and product recovery system, IL contents in the recovered materials were decreased to 0.2 %, mitigating the risk to downstream enzymatic saccharification and microbial fermentation. Results indicate that mixed feedstock are viable and valuable resource to consider when assessing biomass availability and affordability for lignocellulosic biorefineries. This scale-up evaluation demonstrates that IL pretreatment technology is feedstock agnostic and can be effectively scaled to larger operations.

Background Pretreatment is necessary to reduce biomass recalcitrance and enhance the efficiency of enzymatic saccharification for biofuel production. Ionic liquid (IL) pretreatment has gained a significant interest as a pretreatment process that can reduce cellulose crystallinity and remove lignin, key factors that govern enzyme accessibility. There are several challenges that need to be addressed for IL pretreatment to become viable for commercialization, including IL cost and recyclability. In addition, it is unclear whether ILs can maintain process performance when utilizing low-cost, low-quality biomass feedstocks such as the paper fraction of municipal solid waste (MSW), which are readily available in high quantities. One approach to potentially reduce IL cost is to use a blend of ILs at different concentrations in aqueous mixtures. Herein, we describe 14 IL-water systems with mixtures of 1-ethyl-3-ethylimidazolium acetate ([C2C1Im][OAc]), 1-butyl-3-ethylimidazolium acetate ([C4C1Im][OAc]), and water that were used to pretreat MSW blended with agave bagasse (AGB). The detailed analysis of IL recycling in terms of sugar yields of pretreated biomass and IL stability was examined. Results Both biomass types (AGB and MSW) were efficiently disrupted by IL pretreatment. The pretreatment efficiency of [C2C1Im][OAc] and [C4C1Im][OAc] decreased when mixed with water above 40%. The AGB/MSW (1:1) blend demonstrated a glucan conversion of 94.1 and 83.0% using IL systems with ~10 and ~40% water content, respectively. Chemical structures of fresh ILs and recycle ILs presented strong similarities observed by FTIR and 1H-NMR spectroscopy. The glucan and xylan hydrolysis yields obtained from recycled IL exhibited a slight decrease in pretreatment efficiency (less than 10% in terms of hydrolysis yields compared to that of fresh IL), and a decrease in cellulose crystallinity was observed. Conclusions Our results demonstrated that mixing ILs such as [C2C1Im][OAc] and [C4C1Im][OAc] and blending the paper fraction of MSW with agricultural residues, such as AGB, may contribute to lower the production costs while maintaining high sugar yields. Recycled IL-water mixtures provided comparable results to that of fresh ILs. Both of these results offer the potential of reducing the production costs of sugars and biofuels at biorefineries as compared to more conventional IL conversion technologies.Graphical abstractSchematic of ionic liquid (IL) pretreatment of agave bagasse (AB) and paper-rich fraction of municipal solid waste (MSW) Electronic supplementary material The online version of this article (doi:10.1186/s13068-017-0758-4) contains supplementary material, which is available to authorized users.

© 2017 The Author(s). Background: Lignocellulosic biorefineries have tonnage and throughput requirements that must be met year round and there is no single feedstock available in any given region that is capable of meeting the price and availability demands of the biorefineries scheduled for deployment. Significant attention has been historically given to agriculturally derived feedstocks; however, a diverse range of wastes, including municipal solid wastes (MSW), also have the potential to serve as feedstocks for the production of advanced biofuels and have not been extensively studied. In addition, ionic liquid (IL) pretreatment with certain ILs is receiving great interest as a potential process that enables fractionation of a wide range of feedstocks. Acid catalysts have been used previously to hydrolyze polysaccharides into fermentable sugars following IL pretreatment, which could potentially provide a means of liberating fermentable sugars from lignocellulose without the use of costly enzymes. However, successful optimization and scale-up of the one-pot acid-assisted IL deconstruction for further commercialization involve challenges such as reactor compatibility, mixing at high solid loading, sugar recovery, and IL recycling, which have not been effectively resolved during the development stages at bench scale. Results: Here, we present the successful scale-up demonstration of the acid-assisted IL deconstruction on feedstock blends of municipal solid wastes and agricultural residues (corn stover) by 30-fold, relative to the bench scale (6 vs 0.2 L), at 10% solid loading. By integrating IL pretreatment and acid hydrolysis with subsequent centrifugation and extraction, the sugar and lignin products can be further recovered efficiently. This scale-up development at Advanced Biofuels/Bioproducts Process Demonstration Unit (ABPDU) will leverage the opportunity and synergistic efforts toward developing a cost-effective IL-based deconstruction technology by drastically eliminating enzyme, reducing water usage, and simplifying the downstream sugar/lignin recovery and IL recycling. Conclusion: Results indicate that MSW blends are viable and valuable resource to consider when assessing biomass availability and affordability for lignocellulosic biorefineries. This scale-up evaluation demonstrates that the acid-assisted IL deconstruction technology can be effectively scaled up to larger operations and the current study established the baseline of scaling parameters for this process.

Transforming renewable biomass into cost-competitive high-performance biofuels and bioproducts is key to the U.S. future energy and chemical needs. Butanol production by microbial fermentation for chemical conversion to polyolefins, elastomers, drop-in jet or diesel fuel, and other chemicals is a promising solution. A high temperature fermentation process could decrease energy costs, capital cost, give higher butanol production, and allow for continuous fermentation. In this paper, we describe our approach to genetically transform Geobacillus caldoxylosiliticus, using a pUCG18 plasmid, for potential insertion of a butanol production pathway. Transformation methods tested were electroporation of electrocompetent cells, ternary conjugation with E. coli donor and helper strains, and protoplast fusion. These methods have not been successful using the current plasmid. Growth controls show cells survive the various methods tested, suggesting the possibility of transformation inhibition from a DNA restriction modification system in G. caldoxylosiliticus, as reported in the literature.