Chapter 18 - Ethanol Economy: Environment, Demand, and Marketing

Global warming potential and energy analysis of second generation ethanol production from rice straw in India

BackgroundThe availability of feedstock options is a key to meeting the volumetric requirement of 136.3 billion liters of renewable fuels per year beginning in 2022, as required in the US 2007 Energy Independence and Security Act. Life-cycle greenhouse gas (GHG) emissions of sorghum-based ethanol need to be assessed for sorghum to play a role in meeting that requirement.ResultsMultiple sorghum-based ethanol production pathways show diverse well-to-wheels (WTW) energy use and GHG emissions due to differences in energy use and fertilizer use intensity associated with sorghum growth and differences in the ethanol conversion processes. All sorghum-based ethanol pathways can achieve significant fossil energy savings. Relative to GHG emissions from conventional gasoline, grain sorghum-based ethanol can reduce WTW GHG emissions by 35% or 23%, respectively, when wet or dried distillers grains with solubles (DGS) is the co-product and fossil natural gas (FNG) is consumed as the process fuel. The reduction increased to 56% or 55%, respectively, for wet or dried DGS co-production when renewable natural gas (RNG) from anaerobic digestion of animal waste is used as the process fuel. These results do not include land-use change (LUC) GHG emissions, which we take as negligible. If LUC GHG emissions for grain sorghum ethanol as estimated by the US Environmental Protection Agency (EPA) are included (26 g CO2e/MJ), these reductions when wet DGS is co-produced decrease to 7% or 29% when FNG or RNG is used as the process fuel. Sweet sorghum-based ethanol can reduce GHG emissions by 71% or 72% without or with use of co-produced vinasse as farm fertilizer, respectively, in ethanol plants using only sugar juice to produce ethanol. If both sugar and cellulosic bagasse were used in the future for ethanol production, an ethanol plant with a combined heat and power (CHP) system that supplies all process energy can achieve a GHG emission reduction of 70% or 72%, respectively, without or with vinasse fertigation. Forage sorghum-based ethanol can achieve a 49% WTW GHG emission reduction when ethanol plants meet process energy demands with CHP. In the case of forage sorghum and an integrated sweet sorghum pathway, the use of a portion of feedstock to fuel CHP systems significantly reduces fossil fuel consumption and GHG emissions.ConclusionsThis study provides new insight into life-cycle energy use and GHG emissions of multiple sorghum-based ethanol production pathways in the US. Our results show that adding sorghum feedstocks to the existing options for ethanol production could help in meeting the requirements for volumes of renewable, advanced and cellulosic bioethanol production in the US required by the EPA’s Renewable Fuel Standard program.

Economic and GHG emissions analyses for sugarcane ethanol in Brazil: Looking forward

A comparison of power generation and ethanol production using sugarcane bagasse from the perspective of mitigating GHG emissions

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 yields for PR and wheat straw were estimated 250.7 and 316.2 l/dry metric ton biomass, respectively, with annual ethanol production capacity of 58.3 and 73.5 × 106 l, respectively. 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 which was defined as 10 000 MJ of available energy in fuel at the pump. Fossil energies were calculated as 4282.9 and 2656.7 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 a potential to reduce ethanol production cost by making technological improvements in pentose fermentation and enzyme production. The 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.

Lowering cost will prompt the sustainable development of sugarcane‐based ethanol industry. In this work, we developed a low‐cost process for ethanol production from sugarcane by a genetically engineered Zymomonas mobilis. Fermentation media were first optimized, resulting in a 15.54% increase in ethanol fermentation efficiency as compared to control media. To further reduce the byproduct levan formation, a levansucrase‐encoding gene of Z. mobilis, sacB, was deleted through the type I‐F CRISPR‐Cas system, which resulted in a further elevation of both ethanol conversion ratio and productivity comparing with the starting strain ZMS912 (87.50% vs. 76.77%, 1.95 g/L/h vs. 1.71 g/L/h). Moreover, we conducted fed‐batch fermentation for ethanol production using sugarcane juice in 5 L bioreactors and employing the optimized media and engineered strain. The results showed that maximum ethanol titer of 81.59 g/L and productivity of 5.83 g/L/h were achieved. Finally, preliminary techno‐economic assessment demonstrated that our efforts to modify media and strain could reduce the processing cost of ethanol production from sugarcane juice, which provides the feasibility for economic ethanol production in the future.

The paper investigates the feasibility of integrating 1.5th and 2nd generation (G) conversion technology for ethanol production from sweet sorghum stalks, in terms of economic performance, energy consumption and greenhouse gas emissions (3E). To that end, discriminants were developed for economic analysis to determine the conditions under which the transition from pure 1.5thG to the integration technology takes place. The paper also developed equations to calculate energy output/input ratio and carbon emissions during ethanol production processes. The results indicate that the main barrier of the development of integration technology is the high cost of 2ndG ethanol production. The residues from 2ndG production should be burned to supply energy for the ethanol plant, which is important to enhance the energy output/input ratio and to cut down carbon emissions. Compared with 1.5thG technology, the integration pathway brings about higher energy output/input ratio, but with slightly less amount of carbon emission reduction. However, the absolute amount of carbon emission reduction is still considerable. The estimation shows that the integration technology is promising in long term but infeasible under current conditions.

Liquid biofuels can be produced from a variety of feedstocks and processes. Ethanol and biodiesel production processes based on conventional raw materials are already commercial, but subject to further improvement and optimization. Biofuels production processes using lignocellulosic feedstocks are still in the demonstration phase and require further R&D to increase their production efficiency. Exergy analysis is a primary tool to assess the efficiency and renewability of biofuels production processes from an integrated point of view. In this chapter, an exergy-based comparative analysis of four biofuels production routes are described and discussed. The selected feedstocks are glucose and sugarcane syrups, the fruit and flower stalk of banana tree and palm oil. For each production route, the effect of process variables on the exergy efficiency and the renewability exergy index (presented in Chap. 2) are determined allowing the identification of possible ways to optimize the production of such biofuels. According to the values of the renewability exergy index, ethanol production process using sucrose, amilaceous, or lignocellulosic material cannot be considered renewable, while biodiesel production from palm oil can be considering renewable. The main reason for these conclusions is due to the irreversibilities that take place along the energy conversion processes of these biofuels production routes. These unexpected conclusions highlight that although renewable raw materials are used as feedstocks, the biofuel itself cannot be considered renewable due especially to the exergy destruction of its production process.KeywordsEthanol ProductionLignocellulosic MaterialExergy AnalysisExergy EfficiencyBanana FruitThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Optimization of food-fuel-fibre in biorefinery based on environmental and economic assessment: The case of sugarcane utilization in Thailand

Fuel ethanol produced from sugar and starch is to be complemented and eventually even replaced by ethanol produced from lignocellulose, in order to mitigate possible competition with the food sector. A first step towards this goal may be a combination of both feedstocks in one plant. This is topic of the presented study, whether synergies in lowering the production costs and greenhouse gas (GHG) emissions can be reached through combined processing was topic of the presented study. A greenfield straw ethanol plant, a wheat ethanol plant and an integrated plant, processing both wheat grain and straw were developed and compared regarding the resulting GHG emissions and production costs. Despite showing the best results with regard to greenhouse gas emissions, greenfield straw ethanol production is related to relatively high production costs. The wheat based ethanol plant again is associated with higher GHG emissions, but low production costs. By combining straw and wheat processing, resulting production costs of EUR651/m3 ethanol are at a level close to market prices, but the same mitigation potential as separate straw based ethanol cannot be reached. The low level of 16.1 g CO2-eq/MJ of straw based ethanol results mainly from the use of the agricultural residue as feedstock and the use of the internally produced lignin to ensure the steam supply. In the assessment of the production costs, feedstock costs are one of the most relevant parameters. Since straw prices are not available from market statistics, an assessment of Germany’s sustainable straw potential in a high spatial resolution has served to calculate straw supply costs. Depending on the exact location of the plant, a range of EUR50/t to EUR90/t (fresh matter) was found to be the cost for straw provision.

Energy assessment and heat integration of biofuel production from bio-oil produced through fast pyrolysis of sugarcane straw, and its upgrading via hydrotreatment

Life cycle greenhouse gas (GHG) impacts of a novel process for converting food waste to ethanol and co-products

The interaction between nanostructures and yeast cells, as well as the description of the effect of nanoparticles in ethanol production are open questions in the development of this nanobiotechnological process. The objective of the present study was to evaluate the ethanol production by Saccharomyces cerevisiae in the free and immobilized state on chitosan-coated manganese ferrite, using cane molasses as a carbon source. To obtain the chitosan-coated manganese ferrite, the one-step coprecipitation method was used. The nanoparticles were characterized by X-ray diffraction obtaining the typical diffraction pattern. The crystal size was calculated by the Scherrer equation as 15.2 nm. The kinetics of sugar consumption and ethanol production were evaluated by HPLC. With the immobilized system, it was possible to obtain an ethanol concentration of 56.15 g/L, as well as the total sugar consumption at 24 h of fermentation. Productivity and yield in this case were 2.3 ± 0.2 g/(L * h) and 0.28 ± 0.03, respectively. However, at the same time in the fermentation with free yeast, 39.1 g/L were obtained. The total consumption of fermentable sugar was observed only after 42 h, reaching an ethanol titer of 50.7 ± 3.1, productivity and yield of 1.4 ± 0.3 g/(L * h) and 0.25 ± 0.4, respectively. Therefore, a reduction in fermentation time, higher ethanol titer and productivity were demonstrated in the presence of nanoparticles. The application of manganese ferrite nanoparticles shows a beneficial effect on ethanol production. Research focused on the task of defining the mechanism of their action and evaluation of the reuse of biomass immobilized on manganese ferrite in the ethanol production process should be carried out in the future.

Comparative environmental performance of lignocellulosic ethanol from different feedstocks

Greenhouse gas emissions from sugar cane ethanol: Estimate considering current different production scenarios in Minas Gerais, Brazil