How does technology pathway choice influence economic viability and environmental impacts of lignocellulosic biorefineries?

Background: The need for liquid fuels in the transportation sector is increasing, and it is essential to develop industrially sustainable processes that simultaneously address the tri-fold sustainability metrics of technological feasibility, economic viability, and environmental impacts. Biorefineries based on lignocellulosic feedstocks could yield high-value products such as ethyl acetate, dodecane, ethylene, and hexane. This work focuses on assessing biochemical and biomass to electricity platforms for conversion of Banagrass and Energycane into valuable fuels and chemicals using the tri-fold sustainability metrics. Results: The production cost of various products produced from Banagrass was $1.19/kg ethanol,$1.00/kg ethyl acetate, $3.01/kg dodecane (jet fuel equivalent),$2.34/kg ethylene and $0.32/kW-h electricity. The production cost of different products using Energycane as a feedstock was$1.31/kg ethanol, $1.11/kg ethyl acetate,$3.35/kg dodecane, and $2.62/kg ethylene. The sensitivity analysis revealed that the price of the main product, feedstock cost and cost of ethanol affected the profitability the overall process. Banagrass yielded 11% higher ethanol compared to Energycane, which could be attributed to the differences in the composition of these lignocellulosic biomass sources. Acidification potential was highest when ethylene was produced at the rate of 2.56 × 10−2 and 1.71 × 10−2 kg SO2 eq. for Banagrass and Energycane, respectively. Ethanol production from Banagrass and Energycane resulted in a global warming potential of − 12.3 and − 40.0 g CO2 eq./kg ethanol. Conclusions: Utilizing hexoses and pentoses from Banagrass to produce ethyl acetate was the most economical scenario with a payback period of 11.2 years and an ROI of 8.93%, respectively. Electricity production was the most unprofitable scenario with an ROI of − 29.6% using Banagrass/Energycane as a feedstock that could be attributed to high feedstock moisture content. Producing ethylene or dodecane from either of the feedstocks was not economical. The moisture content and composition of biomasses affected overall economics of the various pathways studied. Producing ethanol and ethyl acetate from Energycane had a global warming potential of − 3.01 kg CO2 eq./kg ethyl acetate

Life cycle assessment of energy and GHG emissions during ethanol production from grass straws using various pretreatment processes

Background, aim and scope: The aim of this study was to perform a well-to-pump life cycle assessment (LCA) to investigate the overall net energy balance and environmental impact of bioethanol production using Tall Fescue grass straw as feedstock. The energy requirements and green house gas (GHG) emissions were compared to those of gasoline to explore the potential of bioethanol as sustainable fuel. Methods: The functional unit used in the study was 10000 MJ of energy. The data for grass seed production were collected from the farmers in Oregon and published reports. The compositions of straw, pretreatment and hydrolysis yields were obtained from laboratory experiments. Process models were developed for ethanol production using different pretreatment technologies in SuperPro Designer, to calculate the process energy, raw materials, utilities use and emissions related. The Greenhouse Gases Regulated Emissions and Energy use in Transportation (GREET) model and other literature studies were used to obtain additional data. Systematic boundary identification was performed using relative mass, energy, and economic value (RMEE) method using a 5% cutoff value. Results and discussions: Ethanol yields from grass straw were estimated 256.62, 255.8, 255.3 and 230.2 L/dry metric ton of biomass using dilute acid, dilute alkali, hot water and steam explosion pretreatments respectively. Fossil energy required to produce one functional unit was in the range of -1507 to 3940 MJ for different ethanol production techniques. GHG emissions from ethanol LCA models were in the range of -131 to -555.4 kg CO₂ eq. per 10000 MJ of ethanol. Fossil energy use and GHG emissions during ethanol production were found to be lowest for steam explosion pretreatment among all pretreatment processes evaluated. Change in coproduct allocation from economic to mass basis during agricultural production resulted in 62.4% and 133.1% increase in fossil energy use and GHG 34 emissions respectively. Conclusions: Technologies used for ethanol production process had major impact on the fossil energy use and GHG emissions. N₂O emissions from the nitrogen fertilizers were major contributor (77%) of total GHG emissions produced during agricultural activities. There was 57.43 to 112.67% reduction in fossil energy use to produce 10000 MJ of ethanol compared to gasoline, however about 0.35 hectare of land is also required to produce this energy.Keywords: Greenhouse gases, Grass straw, Net energy, Process model, E85, Lignocellulosic ethano

Effect of solids loading on ethanol production: Experimental, Economic and Environmental analysis

This study explores the effect of high-solids loading for a fed batch enzymatic hydrolysis and fermentation. The solids loading considered was 19%, 30% and 45% using wheat straw and corn stover as a feedstock. Based on the experimental results, techno-economic analysis and life cycle assessments were performed. The experimental results showed that 205±25.8 g/L glucose could be obtained from corn stover at 45% solids loading after 96h which when fermented yielded 115.9±6.37 g/L ethanol after 60h of fermentation. Techno-economic analysis showed that corn stover at 45% loading yielded the highest ROI at 8% with a payback period less than 12 years. Similarly, the global warming potential was lowest for corn stover at 45% loading at -37.8 gCO2 eq./MJ ethanol produced

Economic and cradle-to-gate life cycle assessment of poly-3-hydroxybutyrate production from plastic producing, genetically modified hybrid poplar leaves

Poly-3-hydroxybutyrate (PHB) is a renewable, biodegradable biopolymer that has shown great promise to offset the use of hydrocarbon-derived plastics. The genes encoding the bacterial PHB production pathway have been engineered into several higher order plant species providing an opportunity to produce PHB as a co-product on an industrial, agricultural scale. This study investigates the economic feasibility and estimates the life-cycle greenhouse gas (GHG) emissions produced during the PHB production from hybrid poplar leaves. An established, bench scale extraction procedure was extrapolated upon using SuperPro designer to estimate the product cost, raw materials and energy used during extraction of PHB from poplar leaves on an industrial scale. Assuming an economically feasible concentration of PHB could be produced in the leaf material, a cradle-to-gate life cycle assessment was performed under two of the most likely poplar production scenarios for the Northwest United States where poplar is commonly grown for biomass applications. The cost of PHB production was found to vary greatly with the PHB content in the leaves; from $33.28 per kg at 0.5$1.72 per kg at 20% PHB content. Poplar production scenarios varied greatly in their emission of GHGs. An irrigated poplar production scenario is estimated to produce 248.8% more GHGs than production of the displaced polypropylene. An un-irrigated poplar production scenario produced 76.1% less GHGs. Both production scenarios produced significant amounts of volatile organic compounds (VOCs) associated with normal poplar growth that could prove detrimental to local air quality. PHB content of 15% in the poplar was required to bring the PHB production price to $2.26 per kg and make production competitive with petroleum-derived plastics

Optimization of surfactant addition in cellulosic ethanol process using integrated techno-economic and life cycle assessment for bioprocess design

Surfactants have been demonstrated to be effective in increasing the cellulase enzyme efficacy and overall enzymatic hydrolysis efficiency. However, the impact of the surfactant addition on the economic viability and environmental impacts of the bioethanol process has not been well-investigated. The objective of this study was to determine the economic and the environmental impacts of using five surfactant types—polyethylene glycol (PEG) 3000, PEG4000, PEG6000, PEG8000, and Tween80—at various concentrations (8%, 5%, 2%, 1%, 0.75%, 0.5%, 0.25%, and 0% (w/w)) during enzymatic hydrolysis and fermentation of pretreated Banagrass. We used an integrated techno-economic and life cycle assesment to guide the selection of optimal surfactant concentration in the bioethanol process. A surfactant concentration of >2% negatively affects the profitability of ethanol, even when there is a statistically significant increase in glucose and ethanol titers. Based on the overall performance indicators for final ethanol, economic viability and environmental impacts, the addition of PEG6000 at 2% (w/w) were determined to be the optimal option. Glucose and ethanol concentrations of 119.2 ± 5.4 g/L and 55.0 ± 5.8 g/L, respectively, with an 81.5% cellulose conversion rate, were observed for 2% (w/w) PEG6000. Techno-economic and life cycle analysis indicated that 2% w/w PEG6000 addition resulted in ROI of 3.29% and had reduced the global warming potential by 6 g CO2/MJ ethanol produced

A dynamic flux balance model and bottleneck identification of glucose, xylose, xylulose co-fermentation in Saccharomyces cerevisiae

A combination of batch fermentations and genome scale flux balance analysis were used to identify and quantify the rate limiting reactions in the xylulose transport and utilization pathway. Xylulose phosphorylation by xylulokinase was identified as limiting in wild type Saccharomyces cerevisiae, but transport became limiting when xylulokinase was upregulated. Further experiments showed xylulose transport through the HXT family of non-specific glucose transporters. A genome scale flux balance model was developed which included an improved variable sugar uptake constraint controlled by HXT expression. Model predictions closely matched experimental xylulose utilization rates suggesting the combination of transport and xylulokinase constraints is sufficient to explain xylulose utilization limitation in S. cerevisiae

Economic feasibility and environmental life cycle assessment of ethanol production from lignocellulosic feedstock in Pacific Northwest U.S.

Bioethanol produced from the lignocellulosic feedstock is a potential alternative to fossil fuels in transportation sector and can help in reducing environmental burdens. Straw produced from perennial ryegrass (PR) and wheat is a non-food, cellulosic biomass resource available in abundance in the Pacific Northwest U.S. The aim of this study was to evaluate the economic viability and to estimate the energy use and greenhouse gas (GHG) emissions during life cycle of ethanol production from PR and wheat straw. Economic analysis of ethanol production on commercial scale was performed using engineering process model of ethanol production plant with processing capacity of 250,000 metric tons of feedstock/year, simulated in SuperPro designer. Ethanol production yields for PR and wheat straw were estimated 250.7 and 316.2 L/dry metric ton biomass respectively, with total production capacity of 58.3 and 73.5 million liters of ethanol annually. Corresponding production costs of ethanol from PR and wheat straw were projected to be $0.86 and$0.71/L ethanol. Energy and emissions were calculated per functional unit of 10,000 MJ. Fossil energies were calculated as 4,282.9 and 2,656.7 MJ to produce one functional unit of ethanol from PR and wheat straw respectively. The GHG emissions during life cycle of ethanol production from PR and wheat straw were found to be 227.6 and 284.3 % less than those produced for 10,000 MJ of gasoline. Results from sensitivity analysis indicated that there is potential to reduce ethanol production cost by making technological improvements in pentose fermentation and enzyme production. These integrated economic and ecological assessment analyses are helpful in determining long-term sustainability of a product and can be used to drive energy policies in an environmentally sustainable direction.Keywords: fossil energy, bioethanol, greenhouse gases, life cycle assessment, ethanol production cost, grass straw, wheat strawKeywords: fossil energy, bioethanol, greenhouse gases, life cycle assessment, ethanol production cost, grass straw, wheat stra

Effects of Environmental Factors and Nutrient Availability on the Biochemical Composition of Algae for Biofuels Production: A Review

Due to significant lipid and carbohydrate production as well as other useful properties such as high production of useful biomolecular substrates (e.g., lipids) and the ability to grow using non-potable water sources, algae are being explored as a potential high-yield feedstock for biofuels production. In both natural and engineered systems, algae can be exposed to a variety of environmental conditions that affect growth rate and cellular composition. With respect to the latter, the amount of carbon fixed in lipids and carbohydrates (e.g., starch) is highly influenced by environmental factors and nutrient availability. Understanding synergistic interactions between multiple environmental variables and nutritional factors is required to develop sustainable high productivity bioalgae systems, which are essential for commercial biofuel production. This article reviews the effects of environmental factors (i.e., temperature, light and pH) and nutrient availability (e.g., carbon, nitrogen, phosphorus, potassium, and trace metals) as well as cross-interactions on the biochemical composition of algae with a special focus on carbon fixation and partitioning of carbon from a biofuels perspective.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by MDPI. The published article can be found at: http://www.mdpi.com/journal/energies.Keywords: algae, biofuel production, biochemical composition, environmental effectKeywords: algae, biofuel production, biochemical composition, environmental effec

Life cycle assessment of ethanol production from tropical banagrass (Pennisetum purpureum) using green and dry processing technologies in Hawaii

This study conducted well-to-pump and well-to wheel life-cycle assessment of fossil energy use and greenhouse gas (GHG) emissions during ethanol production from tropical Banagrass (Pennisetum purpureum) using green-processing (with the use of fresh feedstocks) and dry or conventional processing (with the use of dried feedstocks) in the state of Hawaii. 10 000 MJ of energy was used as a functional unit with a systematic boundary drawn based on relative mass, energy, and economic value method using a 1% cutoff value, and the results were compared to those of conventional gasoline, and ethanol from corn and other ethanol lignocellulosic feedstocks. Detailed techno-economic model was built using the SuperPro designer. Ethanol yields were estimated at 0.27 l/kg (green processing with fungal co-product), 0.27 l/kg (green processing without co-product), and 0.29 l/kg (dry-processing) of feedstock, respectively. The well-to-pump analysis indicate that ethanol production consume 8200 MJ (green processing with co-product), 7600 MJ (green-processing without co-product) and 7200 MJ (dry-processing without co-product) of fossil energy and emit approximately 144 kg CO₂-eq., 90.6 kg CO₂-eq., and 59.1 kg CO₂-eq. per 10 000 MJ of ethanol produced, respectively; well-to-wheel analysis showed that 280 g of gCO₂-eq., 260 g CO₂-eq., and 250 g CO₂-eq. of emissions were produced per kilometer by driving Flex Fuel Vehicle. In summary, ethanol produced using the green-processing technology required greater amount of fossil energy and produced more GHG emissions compared to that of dry processing technology, due to additional energy needed for fungal growth and related processes. Process power, enzyme, and chemical production during ethanol processing were identified as emissions hot-spots for both green and dry processing

Potential for ethanol production from conservation reserve program lands in Oregon

Increase in energy demand has led towards considering lignocellulosic feedstocks as potential for ethanol production. Aim of this study was to estimate the potential of grass straws from conservation reserve program (CRP) lands as feedstocks for ethanol production. The CRP was initiated to ensure reduction in soil erosion with a concomitant improvement in water quality and aquatic habitats. Species and abundance of various grasses in CRP sites can vary substantially. Ethanol yield from biomass is directly correlated to sugar content among other factors. It therefore becomes important to study the variability in the biomass composition from different CRP sites to reliably estimate biofuel production potential. Grass samples were collected from five fields contracted to CRP in Umatilla County in Northeastern Oregon. Composition of these samples was experimentally determined and was statistically verified to be similar for most of the sites. Sugar content was highest (60.70%) and statistically different for only one site (CRA 8.2). Our results suggest that biomass harvested from different sites did not significantly vary in terms of their chemical composition and therefore could be used in a single integrated process to produce bioethanol. Total potential ethanol yield from various CRP lands in Oregon, assuming a 10 yr harvesting frequency, was estimated to be 40 x 10(6) 1 of ethanol (28.5-53.7 x 10(6) 1/yr) with current management practices subject to other constraints. (C) 2011 American Institute of Physics. [doi:10.1063/1.3658399]Keywords: Biomass, Hydrolysis, Pretreatment technologies, Lignocellulosic materials, Switchgrass, Corn stove