David R. Shonnard

Green Diesel: A Second Generation Biofuel

Environmentally-conscious design of processes and products is increasingly viewed as an important strategy in the sustainable development of new refining and chemical processes. This paper discusses a new process technology developed by UOP and Eni S.p.A; the UOP/Eni EcofiningTM process to produce green diesel from vegetable oil. This novel process utilizes catalytic saturation, hydrodeoxygenation, decarboxylation and hydroisomerization reactions to produce an isoparaffin-rich diesel fuel from renewable feedstock containing triglycerides and fatty acids. The resultant biofuel product has a high cetane value, a lower gravity, good cold flow properties and excellent storage stability. Green diesel is completely compatible for blending with the standard mix of petroleum-derived diesel fuels, thus providing significant value to the refiner. The process for producing green diesel operates at mild operating conditions and integrates well within existing petroleum refineries. In contrast to fatty acid methyl esters, where fuel properties depend on feed origin and process configuration, green diesel product is independent of feed origin and the fully deoxygenated biofuel is readily blended with conventional diesel fuel. A life cycle assessment (LCA) of this promising new biofuel production technology has been undertaken to quantify the intrinsic benefits of green diesel production over the current practice of converting various forms of lipids to fatty acid methyl esters. This paper will describe the technology, discuss the results of the LCA study and summarize the advantages this new technology can offer over other processing routes.

Effects of dilute acid pretreatment conditions on enzymatic hydrolysis monomer and oligomer sugar yields for aspen, balsam, and switchgrass

The effects of dilute acid hydrolysis conditions were investigated on total sugar (glucose and xylose) yields after enzymatic hydrolysis with additional analyses on glucose and xylose monomer and oligomer yields from the individual hydrolysis steps for aspen (a hardwood), balsam (a softwood), and switchgrass (a herbaceous energy crop). The results of this study, in the form of measured versus theoretical yields and a severity analysis, show that for aspen and balsam, high dilute acid hydrolysis xylose yields were obtainable at all acid concentrations (0.25-0.75 wt.%) and temperatures (150-175 degrees C) studied as long as reaction time was optimized. Switchgrass shows a relatively stronger dependence on dilute acid hydrolysis acid concentration due to its higher neutralizing mineral content. Maximum total sugar (xylose and glucose; monomer plus oligomer) yields post-enzymatic hydrolysis for aspen, balsam, and switchgrass, were 88.3%, 21.2%, and 97.6%, respectively. In general, highest yields of total sugars (xylose and glucose; monomer plus oligomer) were achieved at combined severity parameter values (log CS) between 2.20 and 2.40 for the biomass species studied.

Comparative life-cycle assessments for biomass-to-ethanol production from different regional feedstocks.

This study compares life‐cycle (cradle‐to‐gate) energy consumption and environmental impacts for producing ethanol via fermentation‐based processes starting with two lignocellulosic feedstocks: virgin timber resources or recycled newsprint from an urban area. The life‐cycle assessment in this study employed a novel combination of computer‐aided tools. These tools include fermentation process simulation coupled with an impact assessment software tool for the manufacturing process life‐cycle stage impacts. The process simulation file was provided by the National Renewable Energy Laboratory (NREL) and was modified slightly to accommodate these different feedstocks. For the premanufacturing process life‐cycle stage impacts, such as the fuels and process chemicals used, transportation, and some preparatory steps (wood chipping, etc.), a life‐cycle inventory database (the Boustead Model) coupled with an impact assessment software tool were used (the Environmental Fate and Risk Assessment Tool). The Newsprint process has a slightly lower overall composite environmental index (created from eight impact categories) compared to the Timber process. However, the Timber process consumes less electricity, produces fewer emissions in total, and has less of a human health impact. The amount of life‐cycle fossil energy required to produce ethanol is 14% of the energy content of the product, making the overall efficiency 86%. Process improvement strategies were evaluated for both feedstock processes, including recycle of reactor vent air and heat integration. Heat integration has the greatest potential to reduce fossil‐derived energy consumption, to an extent that fossil‐derived energy over the life cycle is actually saved per unit of ethanol produced. These energy efficiency values are superior to those observed in conventional fossil‐based transportation fuels.

Regional carbon footprint analysis of dairy feeds for milk production in the USA

PurposeA greenhouse gas emissions analysis (carbon footprint) was conducted for cultivation, harvesting, and production of common dairy feeds used for the production of dairy milk in the USA. The goal was to determine the carbon footprint (grams CO2 equivalents (gCO2e)/kg of dry feed) in the USA on a regional basis, identify key inputs, and make recommendations for emissions reduction.MethodsCommonly used dairy feeds in the USA, such as soybeans, alfalfa, corn, and others, were identified based on a recent literature review and information from dairy farm surveys. The following input data for the cultivation and harvesting of dairy feeds were collected for five US regions: crop production data, energy input, soil amendments, and crop protection chemicals. Life cycle inventory input data were mainly collected from the US Department of Agriculture National Agricultural Statistical Service on a state-by-state basis as well as from state extension services forage crop budget estimates. In addition to consulting other life cycle assessment studies and published articles and reports, this cradle-to-farm gate carbon footprint analysis was conducted using the Ecoinvent™ unit processes in SimaPro version 7.1© (PRé Consultants 2009).ResultsThe final carbon footprint results (gCO2e/kg of dry dairy feed) varied regionally depending on a number of factors such as lime and fertilizer application rates. The average national US carbon footprint results of the main feeds were: corn grain (390), corn silage (200), dried distillers grains with solubles (910 dry mill, 670 wet mill), oats (850), soybeans (390), soybean meal (410), winter wheat (430), alfalfa hay (170), and forage mix (160).Conclusions and recommendationsThe southeast dairy region generally showed a relatively high level of carbon footprint for most feeds, and this is attributable to the higher application rates of both synthetic fertilizers and lime. The highest contributor to carbon footprint for most regions (apart from soybeans and soybean meal) was due to the application of inorganic nitrogen fertilizer. Efficient transfer of knowledge to farmers with regards to fertilizer best management practices such as precision application of farm nutrients may contribute significantly to reducing regional crop carbon footprints.

Development and evaluation of an environmental multimedia fate model CHEMGL for the Great Lakes region

This paper describes the development of a multimedia compartmental model--CHEMGL--which predicts the fate and transport of chemicals in the Great Lakes region and can be used for risk assessment. CHEMGL includes 10 compartments that describe a given region: air boundary layer, free troposphere, lower stratosphere, surface water, sediment, surface soil, vadose soil, groundwater zone, plant foliage and plant root. The model assumes that the compartments are completely mixed and chemical equilibrium between the phases within each compartment is assumed (e.g., suspended solids and biota in water). The attenuation mechanisms include advection, transformation reactions, and diffusive and nondiffusive intermedia transport between compartments. Input parameters include a description of each environmental media, emission rates, and chemical-specific properties and reaction rates. The numerical model results are in good agreement with the analytical solution for an example that examines the fate of benzene. Accordingly, the mathematical and computational components of the model were verified. CHEMGL predicted the concentration of four representative chemicals (atrazine, benzo[a]pyrene, benzene and hexachlorobenzene) in all five basins: Superior, Michigan, Huron, Erie and Ontario. The predicted concentrations fell within one to two orders of magnitude of data reported in the literature. These results suggest that the model is appropriate for estimating the fate and exposure of chemicals for a screening level risk assessment.

Assessment of the Automobile Assembly Paint Process for Energy, Environmental, and Economic Improvement

A coat of paint adds considerable value to an automobile. In addition to consuming up to 60% of the energy needed by automobile assembly plants, however, the painting process also creates both economic and environmental impacts. This study investigated the degree of cost and environmental impact improvement that can be expected when modifications are considered for existing paint processes through heat integration. In order to accomplish this goal, a mathematical model was created to describe the energy use, costs, and environmental impacts from energy consumption in an automobile assembly painting facility. The model agrees with measured energy consumption data for process heating and electricity demand to within about 15% for one Michigan truck facility from which model input parameters were obtained. Thermal pinch analysis determined an energy conservation target of 58% of paint process energy demand. A heat exchanger network optimization study was conducted in order to determine how closely the network design could achieve this target. The resulting heat exchanger network design was profitable based on a discounted cash flow analysis and may achieve reductions in total corporate energy consumption of up to 16% if implemented corporatewide at a major automobile manufacturer.

A Review of Environmental Life Cycle Assessments of Liquid Transportation Biofuels in the Pan American Region

Life-cycle assessment (LCA) has been applied to many biofuel and bioenergy systems to determine potential environmental impacts, but the conclusions have varied. Different methodologies and processes for conducting LCA of biofuels make the results difficult to compare, in-turn making it difficult to make the best possible and informed decision. Of particular importance are the wide variability in country-specific conditions, modeling assumptions, data quality, chosen impact categories and indicators, scale of production, system boundaries, and co-product allocation. This study has a double purpose: conducting a critical evaluation comparing environmental LCA of biofuels from several conversion pathways and in several countries in the Pan American region using both qualitative and quantitative analyses, and making recommendations for harmonization with respect to biofuel LCA study features, such as study assumptions, inventory data, impact indicators, and reporting practices. The environmental management implications are discussed within the context of different national and international regulatory environments using a case study. The results from this study highlight LCA methodology choices that cause high variability in results and limit comparability among different studies, even among the same biofuel pathway, and recommendations are provided for improvement.

An inversion algorithm for determining area-source emissions from downwind concentration measurements

Measuring emissions from nonuniform area sources, such as waste repository sites, has been a difficult problem. A simple but reliable method is not available. An objective method of inverting downwind concentration measurements, utilizing an assumed form of atmospheric dispersion to reconstruct total emission rate and distribution, is described in this study. The Gaussian dispersion model is compared to a more realistic model based on K-theory and similarity expressions. A sensitivity analysis is presented indicating the atmospheric conditions under which a successful application of the method could be anticipated. Field releases of sulfur hexafluoride (SF6) from a simulated area source in flat terrain were conducted to check the method, ability to reconstruct source distribution, and total emission rate. The sensitivity analysis and the field study confirm that a few ground-level concentration measurements and a simple determination of the atmospheric dispersion characteristics are sufficient, under neutral to stable conditions, to obtain the total emission rate accurately. Reconstruction of the spatial pattern of the source is possible by utilizing concentration information from samplers located on two separate ground-level receptor lines, if a shift in the wind direction occurs and if it can be assumed that the total emission rate is time invariant. A method of cross-checking the accuracy of the reconstruction, using a simultaneous tracer release, is presented.

Environmental and economic assessments of heat exchanger networks for optimum minimum approach temperature

Abstract Heat exchanger networks (HENs) design for optimum minimum approach temperature (Δ T min,opt ) is presented using economic and environmental evaluations. The environmental assessment methodology includes seven environmental indices, based on the life-cycle impact assessment (LCIA) of both pre-manufacturing and manufacturing stages for equipment, fuel, and energy. A single normalized and weighted environmental index ( I PC ) is developed and then incorporated with the economic index using the analytic hierarchy process (AHP) method to identify Δ T min,opt . Three case studies of pinched problems are presented. It is found that Δ T min,opt using I PC as the objective is similar but not identical to Δ T min,opt using annualized cost as the objective. For some environmental categories, pre-manufacturing impacts are dominant, however, environmental impacts of the HEN are always less than without a HEN. A sensitivity analysis shows the effect of several parameters on Δ T min,opt .

Feedstock mixture effects on sugar monomer recovery following dilute acid pretreatment and enzymatic hydrolysis

This study seeks to investigate the effects of biomass mixtures on overall sugar recovery from the combined processes of dilute acid pretreatment and enzymatic hydrolysis. Aspen, a hardwood species well suited to biochemical processing, was chosen as the model species for this study. Balsam, a high-lignin softwood species, and switchgrass, an herbaceous energy crop with high ash content, were chosen as adjuncts. A matrix of three different dilute acid pretreatment severities and three different enzyme loading levels was used to characterize interactions between pretreatment and enzymatic hydrolysis. No synergism or antagonism was observed for any of the feedstock mixtures. Maximum glucose yield was 70% of theoretical for switchgrass and maximum xylose yield was 99.7% of theoretical for aspen. Supplemental β-glucosidase increased glucose yield from enzymatic hydrolysis by an average of 15%. Total sugar recoveries for mixtures could be predicted to within 4% by linear interpolation of the pure species results.