Biofuel Production Pathways Research Articles

Exergy-based performance analysis of a continuous stirred bioreactor for ethanol and acetate fermentation from syngas via Wood–Ljungdahl pathway

In this work, a thermodynamic framework was proposed to achieve improved process understanding of ethanol and acetate fermentation in a continuous stirred tank bioreactor from syngas through the Wood–Ljungdahl pathway. The bioreactor performance was evaluated using both conventional exergy and eco-exergy principles to identify the effect of different operational parameters i.e. agitation speeds and liquid media flow rates as well as syngas volume flow rates and its composition on the sustainability and renewability of the process. The exergy efficiency of the bioreactor was found to be in the range of 8.14–89.51% and 8.86–89.52% using the conventional exergy and eco-exergy concepts, respectively. The maximum exergetic productivity index was found to be 6.82 and 6.90 using the conventional exergy and eco-exergy concepts, respectively, at agitation speed of 450rpm, liquid media flow rate of 0.55ml/min, and syngas volume flow rate of 8ml/min containing 10% CO2, 15% Ar, 20% H2, and 55% CO. In general, the exergetic performance parameters computed using both concepts under the studied conditions did not display significant differences because of the low volume of the bioreactor and slow growth rate of the microorganisms. The results of the present study showed that exergy concept and its extensions could undoubtedly play a strategic role in assessing biofuel production pathways with respect to the issues currently of major interest in the renewable energy industry, i.e., sustainability and productively.

Performance analysis of a continuous bioreactor for ethanol and acetate synthesis from syngas via Clostridium ljungdahlii using exergy concept

In this paper, the exergetic performance of a continuous bioreactor for ethanol and acetate synthesis from syngas via a strictly anaerobic autotrophic bacterium Clostridium ljungdahlii was carried out for the first time. The fermentation process was evaluated using both conventional exergy and eco-exergy principles for measuring the productivity and renewability of the process at various liquid media flow rates. The microorganisms successfully upgraded the syngas into invaluable ethanol and acetate through the Wood–Ljungdahl pathway. The exergy efficiency was found to be in the range of 6.5–77.5 and 6.8–77.5 % during the fermentation using conventional exergy and eco-exergy concepts, respectively. The subtle differences observed in the exergetic parameters using the two exergetic concepts were ascribed to the slow growth rate of the microorganisms. Nevertheless, the eco-exergy concept would strongly be recommended for commercial bioreactor containing living organisms due to the inclusion of the information carried by microorganisms in the exergetic calculation. A desired liquid media flow rate of 0.55 mL/min was found according to a newly defined thermodynamic indictor namely exergetic productivity index. More specifically, the maximum exergetic productivity index of the fermentation process was found to be 8.0 using both approaches when the rate of inflow liquid was adjusted at the optimal value. The results of this study revealed that process yield alone cannot be a reliable performance metric for decision making on the productivity of various biofuel production pathways. Finally, the proposed exergetic framework could assist engineers and researchers to link biochemical and physical knowledge more robustly and to quantify and elucidate the general purpose of productivity and renewability.

Stochastic techno-economic evaluation of cellulosic biofuel pathways

This study evaluates the economic feasibility and stochastic dominance rank of eight cellulosic biofuel production pathways (including gasification, pyrolysis, liquefaction, and fermentation) under technological and economic uncertainty. A techno-economic assessment based financial analysis is employed to derive net present values and breakeven prices for each pathway. Uncertainty is investigated and incorporated into fuel prices and techno-economic variables: capital cost, conversion technology yield, hydrogen cost, natural gas price and feedstock cost using @Risk, a Palisade Corporation software. The results indicate that none of the eight pathways would be profitable at expected values under projected energy prices. Fast pyrolysis and hydroprocessing (FPH) has the lowest breakeven fuel price at 3.11$/gallon of gasoline equivalent (0.82$/liter of gasoline equivalent). With the projected energy prices, FPH investors could expect a 59% probability of loss. Stochastic dominance is done based on return on investment. Most risk-averse decision makers would prefer FPH to other pathways.

ChemInform Abstract: Recent Progress in Hydrocarbon Biofuel Synthesis: Pathways and Enzymes

AbstractReview: 37 refs.

Recent progress in hydrocarbon biofuel synthesis: Pathways and enzymes

Biofuels derived from hydrocarbon biosynthetic pathways have attracted increasing attention. Routes to hydrocarbon biofuels are emerging and mainly fall into two categories based on the metabolic pathways utilized: Fatty acid pathway-based alkanes/alkenes and isoprenoid biosynthetic pathway based terpenes. The primary focus of this review is on recent progress in the application of hydrocarbon biosynthetic pathways for hydrocarbon biofuel production, together with studies on enzymes, including efforts to engineering them for improved performance.

Exergy Based Assessment of the Production and Conversion of Switchgrass, Equine Waste, and Forest Residue to Bio-Oil Using Fast Pyrolysis

The resource efficiency of biofuel production via biomass pyrolysis is evaluated using exergy as an assessment metric. Three feedstocks, important to various sectors of U.S. agriculture, switchgrass, forest residue, and equine waste, are considered for conversion to bio-oil (pyrolysis oil) via fast pyrolysis, a process that has been identified as adaptable to on- or near-farm application. Biomass and biofuel production pathways are defined, material flows are determined, and exergy in- and outflows associated with biomass production and conversion are computed, including the depletion of exergy from its natural state (cumulative exergy demand, CExD). Sources of exergy depletion are quantified and categorized by energy carriers, e.g., electricity and diesel fuel, and materials, e.g., fertilizer, as well as renewable and nonrenewable resources. Yields for biomass to bio-oil conversion by fast pyrolysis are determined experimentally. Breeding factors, a measure of exergy production (the ratio of the chemical exergy of the output product to process exergy inputs), are determined for the production of biomass and bio-oil. The quantification of exergy depletion for process pathways enables the possible identification of more sustainable (resource efficient) pathways for biomass and bio-oil production. It is shown, for example, that feedstocks grown primarily for biomass such as switchgrass may be less sustainable using the exergy measure compared to use of residue (e.g., forest thinnings) or waste biomass (e.g., equine waste). With regard to the pyrolysis process, there is substantial reduction in exergy depletion when the coproducts noncondensable gases and biochar are recycled and utilized as a source of heat. The sustainability of biomass production and conversion, as measured by exergy depletion, is strongly influenced by energy carriers. The study reveals that the method of electricity production, i.e., on-site generation or grid electricity, as well as the choice of grid electricity can have a significant impact on sustainability. The exergy content of the bio-oil produced varies from 24 to 27 MJ/kg bio-oil, which is much lower than traditional fuels. However, the cumulative exergy depletion for the production and conversion to bio-oil varies from approximately 4 to 11 MJ/kg bio-oil, which is also much lower than traditional fuels. Breeding factors for biomass production and conversion to bio-oil based on cumulative exergy depletion vary from approximately 2 to 5, demonstrating the potential exergy benefit of bio-oil production using fast pyrolysis.

Techno-economic comparisons of hydrogen and synthetic fuel production using forest residue feedstock

Mobile distributed pyrolysis facilities have been proposed for delivery of a forest residue resource to bio-fuel facilities. This study examines the costs of producing hydrogen or synthetic petrol (gasoline) and diesel from feedstock produced by mobile facilities (bio-oil, bio-slurry, torrefied wood). Results show that using these feedstock can provide fuels at costs competitive to conventional bio-fuel production methods using gasification of a woodchip feedstock. Using a bio-oil feedstock in combination with bio-oil steam reforming or bio-oil upgrading can produce hydrogen or petrol and diesel at costs of 3.25 $ kg−1 or 0.86 $ litre−1, respectively, for optimally sized bio-fuel facilities. When compared on an energy basis ($ GJ−1), hydrogen production costs tend to be lower than those for synthetic petrol or diesel production across a variety of bio-fuel production pathways.

Quantifying spatial dependencies, trade‐offs and uncertainty in bioenergy costs: An Australian case study (1) – least cost production scale

AbstractThis paper analyzes costs of several biofuel production pathways in Australia from crop residues (stubble), a lignocellulosic feedstock. As well as land (and sea) transport suitable biofuels, we also consider electricity, and aviation biofuels. Some biofuel cost calculations assume a minimum processing plant scale, often based on contemporary fossil fuels production scales. The more theoretical approach here minimizes production cost by trading off processing and transport costs. Optimal scales and process component costs depend on feedstock spatial concentration; however total costs are less strongly dependent. Lower concentrations correspond to smaller processing plant and greater collection areas and costs. Processing costs are added to feedstock production and transport costs to derive biofuel supply cost ranges as a function of feedstock concentration in an Australian context. Sensitivity analysis then identifies significant parameters and confidence interval estimates. A companion paper generates Australian nationally aggregated supply cost curves. © 2014 Society of Chemical Industry and John Wiley & Sons, Ltd

Quantifying spatial dependencies, trade‐offs and uncertainty in bioenergy costs: an Australian case study (2) – National supply curves

AbstractA biophysically constrained economic analysis of several alternative biofuel production pathways develops upper and lower bounds on national supply cost curves, taking into account implicit spatial dependencies and trade‐offs. As well as land (and sea) transport suitable biofuels, we also consider electricity and aviation biofuels. One feedstock (crop residues from grains) and five bioenergy pathways illustrate this approach for Australia. The methods are, however, applicable to any feedstock, bioenergy technology, region, or scale. Biofuel production costs, dependent on the spatial concentration of available feedstock, are derived in a companion paper by selecting a cost minimizing production scale. Lower concentrations imply smaller processing plants and greater collection areas and costs. Any candidate production plant location can have a collection area that approximates the least cost for its average spatial concentration, because feedstock concentration varies only modestly within cost minimizing area scales. A set of plant locations, scales, and near to least‐cost collection areas, is found that collectively service all the available residue feedstock using Australian data. This generates upper and lower bounds on nationally aggregated supply cost curves. The sizing of biofuel facilities will be also affected by investment scale commercial considerations, including the reliability of feedstock and investor appetite for risk: these are discussed qualitatively. © 2014 Society of Chemical Industry and John Wiley & Sons, Ltd

A comparison of on-site nutrient and energy recycling technologies in algal oil production

Research on biofuel production pathways from algae continues because among other potential advantages they avoid key consequential effects of terrestrial oil crops, such as competition for cropland. However, the economics, energetic balance, and climate change emissions from algal biofuels pathways do not always show great potential, due in part to high fertilizer demand. Nutrient recycling from algal biomass residue is likely to be essential for reducing the environmental impacts and cost associated with algae-derived fuels. After a review of available technologies, anaerobic digestion (AD) and hydrothermal liquefaction (HTL) were selected and compared on their nutrient recycling and energy recovery potential for lipid-extracted algal biomass using the microalgae strain Scenedesmus dimorphus. For 1kg (dry weight) of algae cultivated in an open raceway pond, 40.7gN and 3.8gP can be recycled through AD, while 26.0gN and 6.8gP can be recycled through HTL. In terms of energy production, 2.49MJ heat and 2.61MJ electricity are generated from AD biogas combustion to meet production system demands, while 3.30MJ heat and 0.95MJ electricity from HTL products are generated and used within the production system.Assuming recycled nutrient products from AD or HTL technologies displace demand for synthetic fertilizers, and energy products displace natural gas and electricity, the life cycle greenhouse gas reduction achieved by adding AD to the simulated algal oil production system is between 622 and 808gcarbon dioxide equivalent (CO2e)/kg biomass depending on substitution assumptions, while the life cycle GHG reduction achieved by HTL is between 513 and 535gCO2e/kg biomass depending on substitution assumptions. Based on the effectiveness of nutrient recycling and energy recovery, as well as technology maturity, AD appears to perform better than HTL as a nutrient and energy recycling technology in algae oil production systems.

Pathways of lignocellulosic biomass conversion to renewable fuels

The increased worldwide demand for energy, particularly from petroleum-derived fuels has led to the search for a long-term solution of a reliable source of clean energy. Lignocellulosic biomasses appear to hold the key for a continuous supply of renewable fuels without compromising with the increasing energy needs. However, the major possible solutions to the current energy crisis include ethanol, bio-oils and synthesis gas (syngas) produced from lignocellulosic biomass. Recently, a great deal of research has been made in the fields of biomass conversion through biochemical, hydrothermal or thermochemical pathways to biofuels. However, a broad-spectrum assessment of the above pathways is rare in literature in terms of technology used, biofuel yields, potential challenges and possible outcomes. This review paper discusses different routes for biofuel production, particularly ethanol, bio-oil and syngas with the bio-oil upgrading techniques. This review highlights ethanol fermentation and available biomass pretreatment as the biochemical mode, not limiting to the pros and cons of the pretreatments. Supercritical water gasification (hydrothermal pathway) of biomass for syngas production followed by gas-to-liquid technologies (syngas fermentation and Fischer–Tropsch catalysis) has been discussed. In addition, thermochemical pathway dealing with biomass gasification for syngas and pyrolysis for bio-oils has been presented with compositional analysis of bio-oils and their upgrading technologies. The review focuses on various engineering limitations encountered during biomass conversion and bioprocessing with the potential solutions which do not restrict them to different biofuel production pathways.

Supply chain design and operational planning models for biomass to drop-in fuel production

Renewable fuel is playing an increasingly important role as a substitute for fossil based energy. The US Department of Energy (DOE) has identified pyrolysis based platforms as promising biofuel production pathways. In this paper, we present a general biofuel supply chain model with a Mixed Integer Linear Programming (MILP) methodology to investigate the biofuel supply chain facility location, facility capacity at strategic levels, and biofuel production decisions at operational levels. In the model, we accommodate different biomass supplies and biofuel demands with biofuel supply shortage penalty and storage cost. The model is then applied to corn stover fast pyrolysis pathway with upgrading to hydrocarbon fuel since corn stover is the main feedstock for second generation biofuel production in the US Midwestern states. Numerical results illustrate unit cost for biofuel production, biomass, and biofuel allocation. The case study demonstrates the economic feasibility of producing biofuel from biomass at a commercial scale in Iowa.

Metabolic engineering: Use of system-level approaches and application to fuel production in Escherichia coli

Metabolic engineering was formally defined more than two decades ago (Bailey, 1991) and it is now an established discipline. Metabolic engineering is generally defined as the directed improvement of product formation or cellular properties through the modification of specific biochemical reactions or the introduction of new ones with the use of recombinant DNA technology (Bailey, 1991; Stephanopoulos, 1998). Therefore, the analysis and engineering/synthesis of metabolic pathways is of central importance to metabolic engineering. The analytical part uses a number of experimental and modeling techniques for the systematic study of cellular responses (in terms of RNA, protein and metabolite levels, metabolic fluxes, etc.) to genetic and environmental perturbations. This facilitates a rational design of metabolic modifications, which are implemented using recombinant DNA technology. Both, the analysis and the synthesis of metabolic pathways will be covered in this review. Recent efforts on the engineering of fermentative and biosynthetic pathways for biofuel production in Escherichia coli , as well as those enabling the utilization of novel feedstocks, will be highlighted.

Comparison of various microalgae liquid biofuel production pathways based on energetic, economic and environmental criteria

In view of the increasing demand for bioenergy, in this study, the techno-economic viabilities for three emerging pathways to microalgal biofuel production have been evaluated. The three processes evaluated are the hydrothermal liquefaction (HTL), oil secretion and alkane secretion. These three routes differ in their lipid extraction procedure and the end-products produced. This analysis showed that these three processes showed various advantages: possibility to convert the defatted microalgae into bio-crude via HTL thus increasing the total biodiesel yield; better energetic and environmental performance for oil secretion and an even increased net energy ratio (NER) for alkane secretion. However, great technological breakthroughs are needed before planning any scale-up strategy such as continuous wet biomass processing and heat exchange optimization for the HTL pathway and effective and sustainable excretion for both secretion pathways.

Progression of lipid profile and cell structure in a research-scale production pathway for algal biocrude

Abstract Although there has been a large research effort associated with individual parts of various algal biofuel production pathways, few studies have tracked changes in product composition throughout an integrated biofuel production process. This study uses microscopy and chromatography to analyze the progression of lipid profile and cell structure of algal cells throughout a research-scale production pathway for biocrude. For the specific processing methods used in this pathway, it is shown that TAG content decreased, while DAG and FFA content increased during processing. The changes in the lipid content corresponded to cell degradation that was observed by SEM and TEM throughout processing. These results demonstrate the dynamic nature of lipid composition in an algal culture used for biofuel production and emphasize the need to monitor changes in lipid profile, as those changes can directly impact biofuel productivity.

Accumulation of lipid production in Chlorella minutissima by triacylglycerol biosynthesis-related genes cloned from Saccharomyces cerevisiae and Yarrowia lipolytica

Discovery of an alternative fuel is now an urgent matter because of the impending issue of oil depletion. Lipids synthesized in algal cells called triacylglycerols (TAGs) are thought to be of the most value as a potential biofuel source because they can use transesterification to manufacture biodiesel. Biodiesel is deemed as a good solution to overcoming the problem of oil depletion since it is capable of providing good performance similar to that of petroleum. Expression of several genomic sequences, including glycerol-3-phosphate dehydrogenase, glycerol-3-phosphate acyltransferase, lysophosphatidic acid acyltransferase, phosphatidic acid phosphatase, diacylglycerol acyltransferase, and phospholipid:diacylglycerol acyltransferase, can be useful for manipulating metabolic pathways for biofuel production. In this study, we found this approach indeed increased the storage lipid content of C. minutissima UTEX 2219 up to 2-fold over that of wild type. Thus, we conclude this approach can be used with the biodiesel production platform of C. minutissima UTEX 2219 for high lipid production that will, in turn, enhance productivity.

Genomic Analysis of the Hydrocarbon-Producing, Cellulolytic, Endophytic Fungus Ascocoryne sarcoides

The microbial conversion of solid cellulosic biomass to liquid biofuels may provide a renewable energy source for transportation fuels. Endophytes represent a promising group of organisms, as they are a mostly untapped reservoir of metabolic diversity. They are often able to degrade cellulose, and they can produce an extraordinary diversity of metabolites. The filamentous fungal endophyte Ascocoryne sarcoides was shown to produce potential-biofuel metabolites when grown on a cellulose-based medium; however, the genetic pathways needed for this production are unknown and the lack of genetic tools makes traditional reverse genetics difficult. We present the genomic characterization of A. sarcoides and use transcriptomic and metabolomic data to describe the genes involved in cellulose degradation and to provide hypotheses for the biofuel production pathways. In total, almost 80 biosynthetic clusters were identified, including several previously found only in plants. Additionally, many transcriptionally active regions outside of genes showed condition-specific expression, offering more evidence for the role of long non-coding RNA in gene regulation. This is one of the highest quality fungal genomes and, to our knowledge, the only thoroughly annotated and transcriptionally profiled fungal endophyte genome currently available. The analyses and datasets contribute to the study of cellulose degradation and biofuel production and provide the genomic foundation for the study of a model endophyte system.

Development of a decision support tool for the assessment of biofuels

Alternative fuels for the transport sector are gaining growing attention as a means against fossil fuel dependence and towards greener forms of energy. At the same time, however, they are surrounded with doubts concerning sustainability of their production. This work presents the basic framework for a decision support tool to evaluate biofuel production pathways, with the purpose of providing the decision maker with a structured methodology that will lead him to the final decision. The tool integrates the most important aspects along the entire value chain (i.e. from biomass production to biofuel end-use), namely the technical, economic, environmental and social aspect. The tool consists of a computational part, which can be combined with the personal preferences of the user. The analysis provides a score for the respective pathway that can be used to rank different options and select among them the optimal solution. The functionality of the tool has been tested for the case of biodiesel from rapeseed in Germany.

Engineering microbial biofuel tolerance and export using efflux pumps

Many compounds being considered as candidates for advanced biofuels are toxic to microorganisms. This introduces an undesirable trade-off when engineering metabolic pathways for biofuel production because the engineered microbes must balance production against survival. Cellular export systems, such as efflux pumps, provide a direct mechanism for reducing biofuel toxicity. To identify novel biofuel pumps, we used bioinformatics to generate a list of all efflux pumps from sequenced bacterial genomes and prioritized a subset of targets for cloning. The resulting library of 43 pumps was heterologously expressed in Escherichia coli, where we tested it against seven representative biofuels. By using a competitive growth assay, we efficiently distinguished pumps that improved survival. For two of the fuels (n-butanol and isopentanol), none of the pumps improved tolerance. For all other fuels, we identified pumps that restored growth in the presence of biofuel. We then tested a beneficial pump directly in a production strain and demonstrated that it improved biofuel yields. Our findings introduce new tools for engineering production strains and utilize the increasingly large database of sequenced genomes.