Factors driving refinery CO<Subscript>2</Subscript> intensity,with allocation into products

Background and scope  

Attempts to develop adequate allocation methods for CO₂ emissions from petroleum products have been reported in the literature. The common features in those studies are the use of energy, mass, and/or market prices as parameters to allocate the emissions to individual products. The crude barrel is changing, as are refinery complexities and the severity of conversion to gasoline or diesel leading to changes in the emissions intensity of refining. This paper estimates the consequences for CO₂ emissions at refineries of allowing these parameters to vary.     

Mass and energy allocation method analysis for an oil refinery characterization using multi-scale modeling

Purpose

The goal of this study is to characterize a single oil refinery using a mass and energy multi-scale allocation method for 13 different fossil fuel-based products. This method structures a rigorous modeling and data collection approach to fill the gap that exists in traditional methods of life cycle assessment (LCA).

Methods

The refinery system’s information is used to subdivide a main process at different sub-process levels and obtain multi-scale information using calculated factors for the main process system’s raw material inputs and outputs. The analysis was performed using derived sub-models from an overall technological model that individually simulate the production of each final refinery product. Based on the technological models of the individual product refineries, the same environmental indicators identified for mass and energy allocation were calculated.

Results and discussion

With this approach, it was possible to build a mass and energy LCA model of a fully parameterized refinery capable to accurately describe up to 98% the analyzed system. Incoming raw materials and effluents are weighted by specific factors calculated from the total of each principal process refining amount and the percentage outputs of the intermediate products. From a bottom-up approach, a primary data questionnaire was obtained with the total raw materials and waste quantities for each of the five key processes and their auxiliary processes. Information that previously appeared at the system (global refinery) and processes (main processes) level can now be accounted for in sub-process terms, thus allowing the monitoring information and environmental performance of the product and intermediate products to be found in a multiproduct system.

Conclusions

The refining sub-process’ environmental impact with regard to specific and intermediate products within the refinery processing steps was accurately estimated. This resulted not only in improvement of the property allocation but also in the identification of critical points in the processing steps, thus enabling optimization and innovation with regard to the processing lines and the refining process and producing a more efficient environmental impact analysis with great quality. The obtained formulations can be extended to more complex refining systems and other manufacturing processes.

     

Customizing CO<Subscript>2</Subscript> allocation using a new non-iterative method to reflect operational constraints in complex EU refineries

Purpose

Developing a robust method for CO₂ allocation in oil refineries is an ongoing debate within the life cycle assessment (LCA) community. Several methodologies reported in the literature, mostly performing sequential and iterative calculations, tend to be biased toward diesel at the expense of gasoline, failing to properly consider the role played by hydrogen. This paper develops a new non-iterative refinery CO₂ allocation method to explore the concept of customized allocation to overcome the inherent bias in standard methods.

Methods

The allocation methodology is based on a system of linear equations built around the material and energy balances of a refinery. After describing the process of building such system, it is shown that the carbon allocation values of all final products and intermediate streams are directly obtained by solving it. A numerical example of CO₂ emission allocation to major refinery products is provided from an optimized refinery linear programming (LP) case for the European refining industry, based on literature projections for 2020.

Results and discussion

The paper presents the key emission sources in the European refinery sector, and by using a standard mass-based allocation technique, we show that the carbon intensities of refined petroleum products derived using the non-iterative method are consistent with other studies. We confirm the findings that the standard allocation typically used in attributional refinery LCA tends to reward diesel to the detriment of gasoline. We attempted reconciling this by applying a reallocation factor to customize the CO₂ allocation to represent the “real” economic purposes of process units reflecting the constraints European refineries face today. This moderated the octane production effects given the important role the reformer plays in hydrogen co-production, where the emission burden of highly knock-resistant reformate is redistributed to hydrogen and carried through to diesel.

Conclusions

By customizing the allocation of CO₂, we demonstrated that the differences between a consequential and an attributional approach in refinery LCA can partly be reconciled. We now run into the risk of increasing the subjectivity of the attributional method by using “judgment calls” to decide on the choice of weightage to be applied. We invite the wider LCA practitioners to further investigate the use of this new non-iterative method for allocating CO₂ and explore the concept of reallocation factors as means to customize emission allocation.

     

Solving the multifunctionality dilemma in biorefineries with a novel hybrid mass–energy allocation method

Processing biomass into multifunctional products can contribute to food, feed, and energy security while also mitigating climate change. However, biorefinery products nevertheless impact the environment, and this influence needs to be properly assessed to minimize the burden. Life cycle assessment (LCA) is often used to calculate environmental footprints of products, but distributing the burdens among the different biorefinery products is a challenge. A particular complexity arises when the outputs are a combination of energy carrying no mass, and mass carrying no energy, where neither an allocation based on mass nor on energy would be appropriate. A novel hybrid mass–energy (HMEN) allocation scheme for dealing with multifunctionality problems in biorefineries was developed and applied to five biorefinery concepts. The results were compared to results of other allocation methods in LCA. The reductions in energy use and GHG emissions from using the biorefinery's biofuels were also quantified. HMEN fairly distributed impacts among biorefinery products and did not change the order of the products in terms of the level of the pollution caused. The allocation factors for HMEN fell between mass and economic allocation factors and were comparable to energy allocation factors. Where the mass or the energy allocation failed to attribute burdens, HMEN addressed this shortcoming by assigning impacts to nonmass or to nonenergy products. Under the partitioning methods and regardless of the feedstock used, bioethanol reduced GHG by 72–98% relative to gasoline. The GHG savings were 196% under the substitution method, but no GHG savings occurred for sugar beet bioethanol under the surplus method. Bioethanol from cellulosic crops had lower energy use and GHG emissions than from sugar beet, regardless of the allocation method used. HMEN solves multifunctional problems in biorefineries and can be applied to other complex refinery systems. LCA practitioners are encouraged to further test this method in other case studies.     

Predicting carcinogenicity of petroleum distillation fractions using a modified Salmonella mutagenicity assay

The Ames Salmonella/microsomal activation mutagenesis assay has been modified to improve sensitivity and reproducibility to complex mixtures derived from the refining and processing of petroleum. Oil samples were dissolved in cyclohexane and subsequently extracted with dimethyl sulfoxide to produce aqueous compatible solutions which readily interact with tester bacteria. Also, the liver homogenate (S-9) and NADP cofactor concentrations were increased and hamster rather than rat liver S-9 was used. The initial slope of the dose response curve relating mutagenicity (revertants per plate) to the dose of extract added was used as an index of mutagenic activity, this slope was obtained through a computerized curve fitting procedure. The modified assay was used to rank 18 oil samples for mutagenic activity, this ranking correlates highly (r = 0.92) with potency rankings of the same samples previously determined from dermal carcinogenicity bioassays. Sensitivity and reproducibility of the assay are sufficient to permit routine use for detecting potential carcinogenic activity of individual refinery streams and blends which contain components boiling above 500°F.Abbreviations API American Petroleum Institute - B[a]P benzo[a]pyrene - DMSO dimethyl sulfoxide - NADP nicotinamide adenine dinucleotide phosphate - PAH polycyclic aromatic hydrocarbon - S-9 microsomal fraction from rat liver     

Biotechnology in the petroleum industry: An overview

A significant quantum of crude oil is trapped in reservoirs and often unrecoverable by conventional oil recovery methods. Further downstream, the petroleum industry is facing challenges to remove sulfur, metal, nitrogen as well as undesirable organic compounds from the crude.Conventional secondary recovery methods such as water and gas injections helped to increase the productivity of the well, while chemical and physical refinery processes such as hydrodesulfurization, desalting, and high-pressure high-temperature hydrotreating remove most inorganic impurities. The increasing demand for oil in the world coupled with very stringent environmental laws piled economical and technical pressure upon the refinery industry to further improve crude oil recovery as well as reduce sulfur, metal and nitrogen concentration to the low ppm levels.In the search for economical and environmentally friendly solutions, growing attention has been given to biotechnology such as the use of microbial enhanced oil recovery (MEOR). MEOR is an alternate recovery method that uses microorganisms and their metabolic products. In addition, the emerging field of crude oil refining and associated industrial processes such as biodesulfurization, biodemetallation, biodenitrogenation and biotransformation are also covered.This review aims to provide an overview on MEOR and biorefining relevant to the petroleum industry and highlights challenges that need to be overcome to become commercially successful. Literature pertaining to laboratory experiments, field trials and patents are included in view of industrial applications and further developments.     

Impact of surrogate selection on risk assessment for total petroleum hydrocarbons

Environmental contamination involving total petroleum hydrocarbons (TPH) is being investigated and remediated at underground storage tanks, tank farms, pipelines, and refineries across the country. Human health and environmental risk play a significant role in decision making at these sites. However, risk assessment for sites contaminated with petroleum products typically is complicated by inadequate information about the composition of TPH present at the site and the physical and chemical properties and toxicity of the components. To address these data gaps, risk assessors can select surrogate compounds to represent the movement of TPH in the environment at the site and toxicity of TPH present at the site. This article illustrates the potential impact of choice of surrogates on risk estimates, which in turn affect remediation costs.     

Allocation issues in LCA methodology: a case study of corn stover-based fuel ethanol

Background, aim, and scope

Facing the threat of oil depletion and climate change, a shift from fossil resources to renewables is ongoing to secure long-term low carbon energy supplies. In view of the carbon dioxide reduction targets agreed upon in the Kyoto protocol, bioethanol has become an attractive option for one energy application, as transport fuel. Many studies on the LCA of fuel ethanol have been conducted, and the results vary to a large extent. In most of these studies, only one type of allocation is applied. However, the effect of allocation on outcomes is of crucial importance to LCA as a decision supporting tool. This is only addressed in a few studies to a limited extent. Moreover, most of the studies mainly focus on fossil energy use and GHG emissions. In this paper, a case study is presented wherein a more complete set of impact categories is used. Land use has been left out of account as only hectare data would be given which is obviously dominated by agriculture. Moreover, different allocation methods are applied to assess the sensitivity of the outcomes for allocation choices.

Materials and methods

This study focuses on the comparison of LCA results from the application of different allocation methods by presenting an LCA of gasoline and ethanol as fuels and with two types of blends of gasoline with ethanol, all used in a midsize car. As a main second-generation application growing fast in the USA, corn stover-based ethanol is chosen as a case study. The life cycles of the fuels include gasoline production, corn and stover agriculture, cellulosic ethanol production, blending ethanol with gasoline to produce E10 (10% of ethanol) and E85 (85% of ethanol), and finally the use of gasoline, E10, E85, and ethanol. In this study, a substantially broader set of eight environmental impacts is covered.

Results

LCA results appear to be largely dependent on the allocation methods rendered. The level of abiotic depletion and ozone layer depletion decrease when replacing gasoline by ethanol fuels, irrespective of the allocation method applied, while the rest of the impacts except global warming potential are larger. The results show a reduction of global warming potential when mass/energy allocation is applied; in the case of economic allocation, it gives contrary results. In the expanded systems, global warming potential is significantly reduced comparing to the ones from the allocated systems. A contribution analysis shows that car driving, electricity use for cellulase enzyme production, and ethanol conversion contribute largely to global warming potential from the life cycle of ethanol fuels.

Discussion

The reason why the results of global warming potential show a reverse trend is that the corn/stover allocation ratio shifts from 7.5 to 1.7 when shifting from economic allocation to mass/energy allocation. When mass/energy allocation is applied, both more credits (CO₂ uptake) and more penalties (N₂O emission) in agriculture are allocated to stover compared to the case of economic allocation. However, more CO₂ is taken up than N₂O (in CO₂ eq.) emitted. Hence, the smaller the allocation ratio is between corn and stover, the lower the share of the overall global warming emissions being allocated to ethanol will be. In the system expansion approach, global warming potentials are significantly reduced, resulting in the negative values in all cases. This implies that the system expansion results are comparable to one another because they make the same cutoffs but not really to the results related to mass, energy, and economic value-based allocated systems.

Conclusions

The choice of the allocation methods is essential for the outcomes, especially for global warming potential in this case. The application of economic allocation leads to increased GWP when replacing gasoline by ethanol fuels, while reduction of GWP is achieved when mass/energy allocation is used as well as in the system where biogenic CO₂ is excluded. Ethanol fuels are better options than gasoline when abiotic depletion and ozone layer depletion are concerned. In terms of other environmental impacts, gasoline is a better option, mainly due to the emissions of nutrients and toxic substances connected with agriculture. A clear shift of problems can be detected: saving fossil fuels at the expense of emissions related to agriculture, with GHG benefits depending on allocation choices. The overall evaluation of these fuel options, therefore, depends very much on the importance attached to each impact category.

Recommendations and perspectives

This study focuses only on corn stover-based ethanol as one case. Further studies may include other types of cellulosic feedstocks (i.e., switchgrass or wood), which require less intensive agricultural practice and may lead to better environmental performance of fuel ethanol. Furthermore, this study shows that widely used but different allocation methods determine outcomes of LCA studies on biofuels. This is an unacceptable situation from a societal point of view and a challenge from a scientific point of view. The results from applying just one allocation method are not sufficient for decision making. Comparison of different allocation methods is certainly of crucial importance. A broader approach beyond LCA for the analysis of biorefinery systems with regard to energy conservation, environmental impact, and cost–benefit will provide general indications on the sustainability of bio-based productions.     

Photochemical processes and the environmental impact of petroleum spills

A review of the photochemical processes involved in the degradation of petroleum,its products, and some model compounds found in petroleum. Emphasis is given to processes which affect emulsification, water solubility, and toxicity. Waterphase photodegradation is also treated. The interaction of these processes withbiodegradation is discussed. Areas requiring further work are indicated. 96references.     

Recombinant carbazole-degrading strains for enhanced petroleum processing

Biotechnological upgrading of fossil fuels is of increasing interest as remaining stocks of petroleum show increasing levels of contaminants such as heavy metals, sulfur and nitrogen-containing heteroaromatic compounds. Carbazole is of particular interest as a major petroleum component known to reduce refining yields through catalyst poisoning. In this study, the biotransformation of carbazole was successfully demonstrated in a liquid two-phase system, when solubilized in either 1-methylnaphthalene or in diesel fuel. The effects of solvent toxicity were investigated by expressing the carbazole-transformation genes from MB1332, a rifampicin-resistant derivative of Pseudomonas sp. LD2, in a solvent-resistant heterologous host, P. putida Idaho [1]. This solvent-resistant strain successfully degraded carbazole solubilized in 1-methylnaphthalene and in the presence of 10 vol% xylenes similar to the non-recombinant strain Pseudomonas sp. LD2. Identification of a suitable recombinant host, however, was essential for further investigations of partial pathway transformations. Recombinant P. putida Idaho expressing only the initial dioxygenase enzymes transformed carbazole to an intermediate well retained in the oil phase. Partial carbazole transformation converts carbazole to non-aromatic species; their effect is unknown on refinery catalyst poisoning, but would allow almost complete retention of carbon content and fuel value. Electronic Publication     

2014生物质炼制专刊序言

生物质是自然界最丰富的含碳有机大分子功能体,它有望通过"生物炼制"实现"石油炼制"的辉煌。但是由于生物质资源本身及其转化过程的复杂性,生物质产业虽备受关注,却被认为是遥远的未来产业。传统的生物质资源化利用思路都是先耗费一定的能量破坏生物质结构,然后再进行转化,不仅没有考虑到产品的功能需求,而且过程的原子经济性不高。如何实现化学键更加复杂的固相木质纤维素生物质炼制是实现生物质产业的关键和难点。理想的生物质炼制的目的是以最大得率分离木质纤维原料中各个组分,以尽可能地保持分子的完整性,最大可能地优化利用和最终实现最大价值。这就要求生物质炼制应当是基于原料结构、过程转化和产品特点三者的关联,面向原料、面向过程、面向产品的炼制过程。本期专刊报道了我国生物质炼制技术领域专家学者在原料炼制、炼制技术、组分转化等领域取得的最新研究进展。     

Household Determinants of Liquified Petroleum Gas (LPG) as a Cooking Fuel in SW Cameroon

Currently 70% of the population in Cameroon are reliant on solid fuel for cooking (90% in rural communities) and the associated household air pollution contributes to significant mortality and morbidity in the country. To address the problems of energy security, deforestation and pollution the government has developed a strategy (Masterplan) to increase use of liquified petroleum gas (LPG) as a cooking fuel from 12% to 58% by 2030. As a clean fuel scaled adoption of LPG has the potential to make significant positive impacts on population health. The LPG Adoption in Cameroon Evaluation (LACE) studies are assessing in the community (i) barriers and enablers for and (ii) local interventions to support, adoption and sustained use of LPG. A census survey conducted for LACE in rural and peri-urban regions of SW Cameroon provided an opportunity to investigate current fuel use patterns and factors associated with primary and exclusive use of LPG. A cross-sectional survey of 1577 households (1334 peri-urban and 243 rural) was conducted in March 2016 using standardised fuel use and household socio-demographic questions, administered by trained fieldworkers. Wood (40.7%) and LPG (51.1%) were the most frequently reported fuels, although the dominant fuels in rural and peri-urban communities were wood (81%) and LPG (58%) respectively. Fuel stacking was observed for the majority of LPG using households (91% of peri-urban and 99% of rural households). In rural homes, a higher level of education, access to sanitation and piped water and household wealth (income and asset ownership) were all significantly associated with LPG use (p < 0.05). In peri-urban homes, younger age, access to sanitation and piped water and increasing education were significantly associated with both any and exclusive use of LPG (p < 0.05). However, whilst household wealth was related to any LPG use, there was no relationship with exclusive use. Results from this census survey of a relatively well-established LPG market with lower levels of poverty and high levels of education than Cameroon as a whole, find LPG usage well below target levels set by the Cameroon government (58% by 2030). Fuel stacking is an issue for the majority of LPG using households. Whilst, as observed here, education, household wealth and socio-economic status are well recognised predictors of adoption and sustained use of clean modern fuels, it is important to consider factors across the whole LPG eco-system when developing policies to support their scaled expansion. A comprehensive approach is therefore required to ensure implementation of the Cameroon LPG Masterplan achieves its aspirational adoption target within its stated timeframe.     

Investigation of the sublethal effects of some petroleum refinery effluents

In Canada, environmental regulations for protection of the biota from the adverse effects of effluents from petroleum refineries have tended to focus on acute toxicity. There is concern those effluents may have other subtle, but still deleterious, long-term effects on aquatic ecosystems. We have used a battery of toxicity tests to assess the acute toxicity, genotoxicity, and chronic toxicity of effluent samples from two Ontario refineries. The test organisms included representatives of the bacterial, algal, plant, cladoceran, and fish communities. The results of our preliminary study indicate that the effluent samples had little acute toxicity to the test organisms. There were indications of some sublethal toxicity to Ceriodaphnia dubia, Panagrellus redivivus, and Pimephales promelas. One of the effluents inhibited the growth of Selanastrum capricornutum (IC₅₀ of 59.9%) and Lemna gibba (IC₂₅ of 73.3%) and also caused a 15 percent reduction in the germination of Lactuca sativa seeds. The SOS-Chromotest, a commercially available test that measures the activity of a bacterial DNA repair system, detected genotoxic effects in a single effluent that had been concentrated ten fold. There was no apparent relationship between several chemical parameters and the observed sublethal effects. Further research is needed to establish whether or not the observed toxic effects are typical of effluents from Ontario refineries.     

Generation of an Industry-specific Physico-chemical Allocation Matrix. Application in the Dairy Industry and Implications for Systems Analysis (9 pp)

Background, Aims and Scope Allocation is required when quantifying environmental impacts of individual products from multi-product manufacturing plants. The International Organization for Standardization (ISO) recommends in ISO 14041 that allocation should reflect underlying physical relationships between inputs and outputs, or in the absence of such knowledge, allocation should reflect other relationships (e.g. economic value). Economic allocation is generally recommended if process specific information on the manufacturing process is lacking. In this paper, a physico-chemical allocation matrix, based on industry-specific data from the dairy industry, is developed and discussed as an alternative allocation method. Methods Operational data from 17 dairy manufacturing plants was used to develop an industry specific physico-chemical allocation matrix. Through an extensive process of substraction/substitution, it is possible to determine average resource use (e.g. electricity, thermal energy, water, etc) and wastewater emissions for individual dairy products within multi-product manufacturing plants. The average operational data for individual products were normalised to maintain industry confidentiality and then used as an industry specific allocation matrix. The quantity of raw milk required per product is based on the milk solids basis to account for dairy by-products that would otherwise be neglected. Results and Discussion Applying fixed type allocation methods (e.g. economic) for all input and outputs based on the quantity of product introduces order of magnitude sized deviations from physico-chemical allocation in some cases. The error associated with the quality of the whole of factory plant data or truncation error associated with setting system boundaries is insignificant in comparison. The profound effects of the results on systems analysis are discussed. The results raise concerns about using economic allocation as a default when allocating intra-industry sectoral flows (i.e. mass and process energy) in the absence of detailed technical information. It is recommended that economic allocation is better suited as a default for reflecting inter-industry sectoral flows. Conclusion The study highlights the importance of accurate causal allocation procedures that reflect industry-specific production methods. Generation of industry-specific allocation matrices is possible through a process of substitution/subtraction and optimisation. Allocation using such matrices overcomes the inherit bias of mass, process energy or price allocations for a multi-product manufacturing plant and gives a more realistic indication of resource use or emissions per product. The approach appears to be advantageous for resource use or emissions allocation if data is only available on a whole of factory basis for several plants with a similar level of technology. Recommendation and Perspective The industry specific allocation matrix approach will assist with allocation in multi-product LCAs where the level of technology in an industry is similar. The matrix will also benefit dairy manufacturing companies and help them more accurately allocate resources and impacts (i.e. costs) to different products within the one plant. It is recommended that similar physico-chemical allocation matrices be developed for other industry sectors with a view of ultimately coupling them with input-output analysis.     

Effects of petroleum refinery wastewater exposure on gill ATPase and selected blood parameters in the Pacific staghorn sculpin (leptocottus armatus)

1. The effects of in vivo exposure to various concentrations of petroleum refinery wastewater on gill ATPase, plasma protein, plasma osmolarity, and hematocrit were measured in the euryhaline fish, Leptocottus armatus. 2. The extent of the reduction in Na,K-ATPase activity resulting from the exposure to the two refineries wastewaters may be related to wastewater chemical composition. 3. Changes in the blood chemistry parameters did not follow a consistent or easily explainable pattern.     

Recent advances in petroleum microbiology.

Recent advances in molecular biology have extended our understanding of the metabolic processes related to microbial transformation of petroleum hydrocarbons. The physiological responses of microorganisms to the presence of hydrocarbons, including cell surface alterations and adaptive mechanisms for uptake and efflux of these substrates, have been characterized. New molecular techniques have enhanced our ability to investigate the dynamics of microbial communities in petroleum-impacted ecosystems. By establishing conditions which maximize rates and extents of microbial growth, hydrocarbon access, and transformation, highly accelerated and bioreactor-based petroleum waste degradation processes have been implemented. Biofilters capable of removing and biodegrading volatile petroleum contaminants in air streams with short substrate-microbe contact times (<60 s) are being used effectively. Microbes are being injected into partially spent petroleum reservoirs to enhance oil recovery. However, these microbial processes have not exhibited consistent and effective performance, primarily because of our inability to control conditions in the subsurface environment. Microbes may be exploited to break stable oilfield emulsions to produce pipeline quality oil. There is interest in replacing physical oil desulfurization processes with biodesulfurization methods through promotion of selective sulfur removal without degradation of associated carbon moieties. However, since microbes require an environment containing some water, a two-phase oil-water system must be established to optimize contact between the microbes and the hydrocarbon, and such an emulsion is not easily created with viscous crude oil. This challenge may be circumvented by application of the technology to more refined gasoline and diesel substrates, where aqueous-hydrocarbon emulsions are more easily generated. Molecular approaches are being used to broaden the substrate specificity and increase the rates and extents of desulfurization. Bacterial processes are being commercialized for removal of H(2)S and sulfoxides from petrochemical waste streams. Microbes also have potential for use in removal of nitrogen from crude oil leading to reduced nitric oxide emissions provided that technical problems similar to those experienced in biodesulfurization can be solved. Enzymes are being exploited to produce added-value products from petroleum substrates, and bacterial biosensors are being used to analyze petroleum-contaminated environments.     

Factors driving refinery CO2 intensity,with allocation into products: comment

Purpose

Recently, using a long-run refinery simulation model, Bredeson et al. conclude that the light transportation fuels have roughly the same CO₂ footprint. And, any allocation scheme which shows substantial difference between gasoline and diesel CO₂ intensities must be seen with caution. The purpose of this paper is to highlight the inappropriate modeling assumptions which lead to these inapplicable conclusions into the current oil refining context.

Methods

From an economic point of view, optimization models are more suitable than simulation tools for providing decision policies. Therefore, we used a calibrated refinery linear programming model to evaluate the impact of varying the gasoline-to-diesel production ratio on the refinery's CO₂ emissions and the marginal CO₂ intensity of the automotive fuels.

Results and discussion

Contrary to Bredeson et al.'s conclusions, our results reveal that, within a calibrated optimization framework, total and per-product CO₂ emissions could be affected by the gasoline-to-diesel production ratio. More precisely, in a gasoline-oriented market, the marginal CO₂ footprint of gasoline is significantly higher than diesel, while the opposite result is observed within a diesel-oriented market. These two scenarios could reflect to some extent the American and the European oil refining industry for which policy makers should adopt a different per-product taxation policy.

Conclusions

Any relevant and economic ground CO₂ policies for automotive fuels should be sensitive to the environmental consequences associated with their marginal productions. This is especially true in disequilibrium markets where the average and marginal reactions could significantly differ. Optimization models, whose optimal solution is fully driven by marginal signals, show that the refinery's global and/or per-product CO₂ emissions could be affected by the gasoline-to-diesel production ratio.     

Life cycle assessment of switchgrass-derived ethanol as transport fuel

Background, aim, and scope  

The increasing gasoline price, the depletion of fossil resources, and the negative environmental consequences of driving with petroleum fuels have driven the development of alternative transport fuels. Bioethanol, which is converted from cellulosic feedstocks, has attracted increasing attention as one such alternative. This study assesses the environmental impact of using ethanol from switchgrass as transport fuel and compares the results with the ones of gasoline to analyze the potential of developing switchgrass ethanol as an environmentally sustainable transport fuel.     

Avoiding investment in fossil fuel assets

Reducing greenhouse gas emissions requires a transformation of capital assets in the economy, especially those for energy supply. This paper explores the hypothesis that economically efficient decarbonization occurs when the demand for fossil fuels declines at the same rate as their capital assets depreciate. In theory this means that new investments in fossil fuel assets are avoided, but without incurring stranded assets. We examine the practicality of this hypothesis using a biophysical economic model of the US energy supply system, with an example focused on impacts of electric vehicles on the petroleum supply chain. We specifically address two questions: (1) What rate of market penetration for electric vehicles is necessary to avoid investments in the petroleum-related assets? (2) How do the costs of upstream capital assets change with the transformation to electric vehicles? High annual depreciation rates for oil refineries (δ = 9.47%) and assets for crude oil extraction (δ = 8.23%) have important impacts on results. To avoid new investment in oil refining assets through widespread electrification of light-duty vehicles, the vehicle stock would need to be transformed in just 4 or 5 years. Under most scenarios, some petroleum pipelines will likely become stranded assets due to their low rate of depreciation (δ = 2.48%). In some scenarios, additional investments in wind and solar power generation surpass oil and gas extraction for about 5 years during the transformation to electric vehicles. Once built, however, wind and solar capital assets last longer, as shown by their low rate of depreciation (δ = 3.26%).