New insights to the use of ethanol in automotive fuels: a stable isotopic tracer for fossil- and bio-fuel combustion inputs to the atmosphere

The atmospheric relevance of primary alcohols and imidogen reactions

Organic alcohols as very volatile compounds play a crucial role in the air quality of the atmosphere. So, the removal processes of such compounds are an important atmospheric challenge. The main goal of this research is to discover the atmospheric relevance of degradation paths of linear alcohols by imidogen with the aid of simulation by quantum mechanical (QM) methods. To this end, we combine broad mechanistic and kinetic results to get more accurate information and to have a deeper insight into the behavior of the designed reactions. Thus, the main and necessary reaction pathways are explored by well-behaved QM methods for complete elucidation of the studying gaseous reactions. Moreover, the potential energy surfaces as  a main factor are computed for easier judging of the most probable pathways in the simulated reactions. Our attempt to find the occurrence of the considered reactions in the atmospheric conditions is completed by precisely evaluating the rate constants of all elementary reactions. All of the computed bimolecular rate constants have a positive dependency on both temperature and pressure. The kinetic results show that H-abstraction from the α carbon is dominant relative to the other sites. Finally, by the results of this study, we conclude that at moderate temperatures and pressures primary alcohols can degrade with imidogen, so they can get atmospheric relevance.

Short-term exposure to soils and sludge induce changes to plastic morphology and 13C stable isotopic composition

There is concern about the buildup of plastic waste in soil, their degradation into microplastics, and their potential to interfere with the natural processing of soil organic carbon and other nutrient cycling processes. Here we used scanning electron microscopy (SEM) and ¹³C isotope ratio mass spectrometry to determine if precut consumer plastics comprised of either high density polyethylene (HDPE), a blend of linear low density polyethylene and low density polyethylene (L/LDPE), or polyethylene terephthalate (PETE) would degrade or transform during a short-term, 32 day, exposure to soil or sludge in laboratory microcosms. SEM confirmed morphological changes occurred to all plastics, but the attachment of biofilm and presence of microorganisms mostly favored PETE and HDPE surfaces. These observations support the idea that abiotic and/or biotic processes may degrade plastics in soil; however distinguishable and significant changes in mean stable isotopic values (Δδ¹³C) of ~0.2-0.7‰ were only observed for exposed PETE and HDPE. This indicates that each plastic's degradation in soil may be dependent on their physical and chemical properties, with L/LDPE being more resistant and less prone to degradation compared to the others, and less dependent on the environmental conditions or properties of the soil or sludge. Our experiments were short-term and while the mechanisms of degradation are not clear, the results provide strong motivation for further studies of plastic fate and processing in soil systems. Direct mechanistic studies using stable isotopic approaches in combination with other characterizations and techniques are clearly warranted and may lead to a significant enhancement in our present understanding of the interactions and dynamics of plastics in the soil environment.

Principles and practice of designing microbial biocatalysts for fuel and chemical production

The finite nature of fossil fuels and the environmental impact of its use have raised interest in alternate renewable energy sources. Specifically, non-food carbohydrates, such as lignocellulosic biomass, can be used to produce next generation biofuels, including cellulosic ethanol and other non-ethanol fuels like butanol. However, currently there is no native microorganism that can ferment all lignocellulosic sugars to fuel molecules. Thus, research is focused on engineering improved microbial biocatalysts for production of liquid fuels at high productivity, titer and yield. A clear understanding and application of the basic principles of microbial physiology and biochemistry are crucial to achieve this goal. In this review, we present and discuss the construction of microbial biocatalysts that integrate these principles with ethanol-producing Escherichia coli as an example of metabolic engineering. These principles also apply to fermentation of lignocellulosic sugars to other chemicals that are currently produced from petroleum.

Porous Mn-based oxides for complete ethanol and toluene catalytic oxidation: the relationship between structure and performance

SmMn₂O₅ exhibited a higher catalytic activity for catalytic oxidation of ethanol and toluene than SmMnO₃, Mn₃O₄ and Mn₂O₃. Mn³⁺–Mn³⁺ dimers facilitate C–C bond cleavage.

An extra copy of the β-glucosidase gene improved the cellobiose fermentation capability of an engineered Saccharomyces cerevisiae strain

In a previously engineered Saccharomyces cerevisiae recombinant, the cellobiose fermentation rate was significantly lower than the glucose fermentation rate. Thus, we implemented a genome-wide perturbation library to find gene targets for improving the cellobiose fermentation capability of the yeast strain. Unexpectedly, we discovered a transformant that contained an additional β-glucosidase gene (gh1-1), possibly through homologous recombination between the plasmids. The additional β-glucosidase led to the fastest cellobiose fermentation activity among all the transformants evaluated, and the strain demonstrated significantly higher β-glucosidase activity than the control strain, especially during the initial exponential growth phase. The present work revealed the benefit of the extra gh1-1 copy for efficient cellobiose fermentation in the engineered S. cerevisiae strain.

Compound-Specific Carbon Isotopic Composition of Ethanol in Brazil and US Vehicle Emissions and Wet Deposition

Global atmospheric ethanol budget models include large uncertainties in the magnitude of ethanol emission sources and sinks. To apply stable isotope techniques to constrain ethanol emission sources, a headspace solid phase microextraction gas chromatograph-combustion-isotope ratio mass spectrometry method (HS-SPME-GC-C-IRMS) was developed to measure the carbon isotopic composition of aqueous phase ethanol at natural abundance levels (1-30 μM) with a precision of 0.4‰. The method was applied to determine the carbon isotope signatures (δ¹³C) of vehicle ethanol emission sources in Brazil (-12.8 ± 2.4‰) and the US (-9.8 ± 2.5‰), and to measure the carbon isotope composition of ethanol in wet deposition (-22.6 to -12.7‰). A two end-member isotope mixing model was developed using anthropogenic and biogenic end members and fractionation scenarios to estimate ethanol source contributions to wet deposition collected in Brazil and US. Mixing model results indicate anthropogenic sources contribute two and a half to four times more ethanol to the atmosphere than previously predicted in modeled global ethanol inventories. As established and developing countries continue to rapidly increase ethanol fuel consumption and subsequent emissions, understanding the magnitude of all ethanol sources and sinks will be essential for modeling future atmospheric chemistry and air quality impacts.

Water catalysis of the reaction between hydroxyl radicals and linear saturated alcohols (ethanol and n-propanol) at 294 K

Water accelerates the title reaction by lowering the energy barrier and increasing the dipole moments of the reactants.

The influence of different referencing methods on the accuracy of δ(13) C value measurement of ethanol fuel by gas chromatography/combustion/isotope ratio mass spectrometry

RATIONALE

Brazil is the largest producer of sugar cane bioethanol in the world. Isotope ratio mass spectrometry (IRMS) is the technique of choice to certify the origin/raw materials for ethanol production, but the lack of certified reference materials (CRMs) for accurate measurements of δ(13) C values traceable to Vienna Pee Dee Belemnite (VPDB), the international zero point for (13) C/(12) C measurements, certified and compatible with gas chromatography (GC)/IRMS instruments may compromise the accuracy of δ(13) C determinations.

METHODS

We evaluated the influence of methods for the calibration and normalization of raw δ(13) C values of ethanol samples. Samples were analyzed by GC/C/IRMS using two different GC columns. Different substances were used as isotopic standards for the working gas calibration. The δ(13) C values obtained with the three methods of normalization were statistically compared with those obtained with elemental analyzer (EA)/IRMS, since the δ(13) C results obtained using EA are traceable to VPDB via the NBS 22 reference material.

RESULTS

It was observed that both the isotopic reference material for CO2 calibration and the GC column have a major effect on the δ(13) C measurements, leading to a bias of almost 2-3 ‰ in the δ(13) C values. All three methods of normalization were equivalent in performance, enabling an improvement in the GC/C/IRMS accuracy, compared with the EA/IRMS reference values for the samples.

CONCLUSIONS

All the methods of CO2 calibration, chromatography and normalization presented in this work demonstrated several sources of traceability and accuracy loss for the determination of δ(13) C values in ethanol fuel samples by GC/C/IRMS. This work has also shown the importance of using proper CRMs traceable to VPBD that should be compatible and certified using GC/C/IRMS, ideally in a wide range of δ(13) C values. This is important not only for bioethanol fuel samples, but also for many analytes commonly analyzed by IRMS.

Combined source apportionment and degradation quantification of organic pollutants with CSIA: 1. Model derivation

Compound-specific stable isotope analysis (CSIA) serves as a tool for source apportionment (SA) and for the quantification of the extent of degradation (QED) of organic pollutants. However, simultaneous occurrence of mixing of sources and degradation is generally believed to hamper both SA and QED. On the basis of the linear stable isotope mixing model and the Rayleigh equation, we developed the stable isotope sources and sinks model, which allows for simultaneous SA and QED of a pollutant that is emitted by two sources and degrades via one transformation process. It was shown that the model necessitates at least dual-element CSIA for unequivocal SA in the presence of degradation-induced isotope fractionation, as illustrated for perchlorate in groundwater. The model also enables QED, provided degradation follows instantaneous mixing of two sources. If mixing occurs after two sources have degraded separately, the model can still provide a conservative estimate of the overall extent of degradation. The model can be extended to a larger number of sources and sinks as outlined. It may aid in forensics and natural attenuation assessment of soil, groundwater, surface water, or atmospheric pollution.

Natural and anthropogenic ethanol sources inNorth America and potential atmospheric impacts of ethanol fuel use

We used an ensemble of aircraft measurements with the GEOS-Chem chemical transport model to constrain present-day North American ethanol sources, and gauge potential long-range impacts of increased ethanol fuel use. We find that current ethanol emissions are underestimated by 50% in Western North America, and overestimated by a factor of 2 in the east. Our best estimate for year-2005 North American ethanol emissions is 670 GgC/y, with 440 GgC/y from the continental U.S. We apply these optimized source estimates to investigate two scenarios for increased ethanol fuel use in the U.S.: one that assumes a complete transition from gasoline to E85 fuel, and one tied to the biofuel requirements of the U.S. Energy Indepence and Security Act (EISA). For both scenarios, increased ethanol emissions lead to higher atmospheric acetaldehyde concentrations (by up to 14% during winter for the All-E85 scenario and 2% for the EISA scenario) and an associated shift in reactive nitrogen partitioning reflected by an increase in the peroxyacetyl nitrate (PAN) to NO(y) ratio. The largest relative impacts occur during fall, winter, and spring because of large natural emissions of ethanol and other organic compounds during summer. Projected changes in atmospheric PAN reflect a balance between an increased supply of peroxyacetyl radicals from acetaldehyde oxidation, and the lower NO(x) emissions for E85 relative to gasoline vehicles. The net effect is a general PAN increase in fall through spring, and a weak decrease over the U.S. Southeast and the Atlantic Ocean during summer. Predicted NO(x) concentrations decrease in surface air over North America (by as much 5% in the All-E85 scenario). Downwind of North America this effect is counteracted by higher NO(x) export efficiency driven by increased PAN production and transport. From the point of view of NO(x) export from North America, the increased PAN formation associated with E85 fuel use thus acts to offset the associated lower NO(x) emissions.