Hybrid Carbon Nanotubes/Gold Nanoparticles Composites for Trace Nitric Oxide Detection over a Wide Range of Humidity.

Composites of functionalized single walled carbon nanotubes (SWCNTs) and gold nanoparticles (Au NPs) of ≈15 nm diameter were drop-cast on a printed circuit board (PCB) substrate equipped with interdigitated electrodes to make a hybrid thin film. Addition of Au NPs decorated the surface of SWCNTs networked films and acted as catalysts which resulted into an enhanced sensitivity and low ppb concentration detection limit. The compositions of the film were characterized by scanning electron microscope (SEM). SWCNTs clusters were loaded with various amount of Au NPs ranging from 1-10% (by weight) and their effect on Nitric oxide (NO) sensitivity was studied and optimized. Further, the optimized composite films were tested in both air and nitrogen environments and as well as over a wide relative humidity range (0-97%). Sensors were also tested for the selectivity by exposing to various gases such as nitrous oxide, ammonia, carbon monoxide, sulfur dioxide and acetone. Sensitivity to NO was found much higher than the other tested gases. The advantage of this sensor is that it is sensitive to NO at low ppb level (10 ppb) with estimated response time within 10 s and recovery time around 1 min, and has excellent reproducibility from sensor to sensor and works within the wide range of relative humidity (0-97%).

Influence of early stages of triglyceride pyrolysis on the formation of PAHs as coke precursors.

Molecular beam (MB) time-of-flight mass spectrometry has been used to investigate thermal decomposition of triolein, to reveal the mechanisms of low temperature soot/coke formation characteristic for triglycerides (TGs). Mass detected pyrolysis products were observed at incremented temperatures using both VUV single photon ionization (general product detection) and REMPI based selective detection of aromatic products. To augment the simple mass characterizations, we have employed stoichiometric considerations; we have supplemented the analysis further by using the detailed information available from product analysis of batch reactor TG cracking. Both the VUV photoionization and batch reactor studies indicated that formation of C7-sized stable products is a marker of significant triolein decomposition that is coupled with PAH formation. A significant fraction of the C7 species observed likely formed as a result of a C-C bond scission at the allylic position to the ω-9 double bond of oleic acid. REMPI detection indicated a high specificity for PAH formation at three distinct molecular weight values, 276, 352 and 444 amu (the latter being a fullerene precursor). The stoichiometric analysis has shown that these PAHs likely arise from condensation reactions of either C7- or C8-sized fragments (three, four and five, respectively). The C8-sized intermediate would become essential whenever the PAH product of C7 fragment condensation contained an odd number of carbon atoms, resulting in a less stable aromatic structure with an incomplete double bond conjugation. MB experiments involving either addition or in situ generation of hydrogen resulted in an enhancement of lower molecular weight PAH formation, i.e., a decrease in the effective number of condensing fragments. In contrast, an increase in temperature yielded the opposite effect.

Biofiltration of gasoline and diesel aliphatic hydrocarbons.

The ability of a biofilm to switch between the mixtures of mostly aromatic and aliphatic hydrocarbons was investigated to assess biofiltration efficiency and potential substrate interactions. A switch from gasoline, which consisted of both aliphatic and aromatic hydrocarbons, to a mixture of volatile diesel n-alkanes resulted in a significant increase in biofiltration efficiency, despite the lack of readily biodegradable aromatic hydrocarbons in the diesel mixture. This improved biofilter performance was shown to be the result of the presence of larger size (C9-C(12)) linear alkanes in diesel, which turned out to be more degradable than their shorter-chain (C6-C8) homologues in gasoline. The evidence obtained from both biofiltration-based and independent microbiological tests indicated that the rate was limited by biochemical reactions, with the inhibition of shorter chain alkane biodegradation by their larger size homologues as corroborated by a significant substrate specialization along the biofilter bed. These observations were explained by the lack of specific enzymes designed for the oxidation of short-chain alkanes as opposed to their longer carbon chain homologues.

Evaluation of microbial triglyceride oil purification requirements for the CelTherm process: an efficient biochemical pathway to renewable fuels and chemicals.

CelTherm is a biochemical process to produce renewable fuels and chemicals from lignocellulosic biomass. The present study's objective was to determine the level of treatment/purity of the microbial triacylglyceride oil (TAG) necessary to facilitate fuel production. After a unique microbe aerobically synthesizes TAG from biomass-derived sugars, the microbes were harvested and dried then crude TAG was chemically extracted from the residual biomass. Some TAGs were further purified to hydrotreating process requirements. Both grades were then noncatalytically cracked into a petroleum-like intermediate characterized by gas chromatography. Experiments were repeated using refined soybean oil for comparison to previous studies. The products from crude microbial TAG cracking were then further refined into a jet fuel product. Fuel tests indicate that this jet fuel corresponds to specifications for JP-8 military turbine fuel. It was thus concluded that the crude microbial TAG is a suitable feedstock with no further purification required, demonstrating CelTherm's commercial potential.

A Comprehensive Study of Techniques to Optimize the Extraction of Lipids from the Autotrophic Strain of the Microalgae Chlorella vulgaris.

Microalgae represent a promising source of triglycerides and free fatty acids, synthesized in the form of lipids, for use in renewable fuels and chemicals. One challenge is the ability to efficiently recover the lipids from within the microalgae cell. Although various techniques have been studied individually, a comprehensive study of extraction techniques using consistent experimental and analytical methodology is missing. This study aims to provide this unifying comparison using the common microalgae strain Chlorella vulgaris. The factors that were surveyed and then optimized to achieve maximum extraction efficiency included the solvent type; mechanical pre-treatment using a ball mill at a variety of grinding speeds; microalgae-to-solvent ratio; extraction facilitated by microwave; extraction facilitated by sonication; extraction facilitated using increased temperature; and extraction facilitated by in situ transesterification to convert the lipids into esters prior to extraction. The optimum conditions determined during these studies were utilizing methanol as the solvent, with ball mill pretreatment at a grinding speed of 500 rpm, and a 1:9 microalgae to solvent ratio. When used in combination with microwave-assisted extraction at a temperature of 140 °C, approximately 24 wt% of the initial lipids were recovered. Recoveries of over 70 wt% were obtained without a microwave at extraction temperatures of over 200 °C.

Chemistry of Trace Inorganic Elements in Coal Combustion Systems: A Century of Discovery.

Coal fueled the Industrial Revolution and the global expansion of electrification in the 20th century. In the 21st century, coal use has declined in North America and Europe, but continues to increase in Asia. Coal contains many of the elements of the Periodic Table, in percent-levels or in trace amounts (ppm, ppb). The impact of many of these elements on the environment via air and water discharges from coal-fired plants has been studied with decades of research on their chemical transformations within combustion systems and on their fates upon reintroduction into the environment. The transformations of the trace elements present in coal burned during combustion can be categorized as thermal volatilizations from the coal in the furnace; thermal decomposition of trace element compounds inside the coal; encapsulation inside ash structures through high-temperature vitrification; oxidation of the trace elements with the myriad species contained in flue gas through gas phase (homogeneous) reactions or catalytic (gas-solid) reactions; adsorption and/or reactions with active sites on entrained fly ash particulates contained in the flue gas; and absorption into solutions. These transformations can, in many cases, impact the fraction of these trace elements that are removed by various pollution control devices compared to the fraction released into the environment. The sampling and measurement of trace elements, in the inlet coal, outlet flue gas, aqueous scrubber solutions, and ash matrices, represents a significant challenge. This review focuses on the behavior of trace elements in industrial coal combustion systems with an emphasis on what has been learned over the past century uniquely related to the use of coal in boilers for electricity and heat production. Key accomplishments in measurement, modeling and control of trace element emissions in coal-fired systems are highlighted.

Simultaneous high-temperature gas chromatography with flame ionization and mass spectrometric analysis of monocarboxylic acids and acylglycerols in biofuels and biofuel intermediate products.

Triacyl-, diacyl- and monoacylglycerols (TAGs, DAGs, MAGs) along with monocarboxylic acids (MCAs) are intermediate products in many triacylglycerol oil-to-biofuel conversion pathways. Accumulation of these compounds leads to poor biofuel characteristics and may result in fuel system damage. We developed a method for simultaneous identification and quantification of a wide range of MCAs (C4-C18), MAGs, DAGs, and TAGs. The method is based on trimethylsilylation followed by high temperature GC with programmed temperature vaporizer (PTV) injection coupled to parallel FID and MS detectors (HTGC-FID/MS). To minimize the discrimination of both low and high molecular weight species typically occurring on the injector, we optimized injection conditions using a central composite design. The critical variables were the time at initial temperature (40 °C), splitless time, and the interaction between these two parameters. Among three tested electron ionization source/quadrupole analyzer temperatures, a 350/200 °C setting provided the highest response and signal-to-noise ratio for TAGs and did not have an effect on MAGs and DAGs. Similar results were obtained when quantifying target analytes in intermediate products of soybean oil cracking with FID and MS (using specific acylglycerol fragmentation ions). The instrumental FID limits of detection (LODs) were 0.07-0.27 ng for most of the target analytes. Selected ion monitoring (SIM) LODs were 0.01-0.05 ng for MCAs and 0.03-0.14 ng for acylglycerols. For the total ion current (TIC), LODs observed increased with acyl chain length and degree of unsaturation, resulting in an increase from 0.05 to 0.18 ng for MCAs (C5 to C18) and from 0.03 to 1.8 ng for acylglycerols (TAGs C8 to C22). Deviations in the repeatability of sample preparation, intra- and inter-day analyses, including sample stability over an eight-day time period, did not exceed 10% variance. These results demonstrate that the developed method is accurate and robust for the determination of acylglycerols and MCAs produced during the processing of TAGs into biofuels.

Impacts of biodiesel on pollutant emissions of a JP-8-fueled turbine engine.

The impacts of biodiesel on gaseous and particulate matter (PM) emissions of a JP-8-fueled T63 engine were investigated. Jet fuel was blended with the soybean oil-derived methyl ester biofuel at various concentrations and combusted in the turbine engine. The engine was operated at three power settings, namely ground idle, cruise, and takeoff power, to study the impact of the biodiesel at significantly different pressure and temperature conditions. Particulate emissions were characterized by measuring the particle number density (PND; particulate concentration), the particle size distribution, and the total particulate mass. PM samples were collected for offline analysis to obtain information about the effect of the biodiesel on the polycyclic aromatic hydrocarbon (PAH) content. In addition, temperature-programmed oxidation was performed on the collected soot samples to obtain information about the carbonaceous content (elemental or organic). Major and minor gaseous emissions were quantified using a total hydrocarbon analyzer, an oxygen analyzer, and a Fourier Transform IR analyzer. Test results showed the potential of biodiesel to reduce soot emissions in the jet-fueled turbine engine without negatively impacting the engine performance. These reductions, however, were observed only at the higher power settings with relatively high concentrations of biodiesel. Specifically, reductions of approximately 15% in the PND were observed at cruise and takeoff conditions with 20% biodiesel in the jet fuel. At the idle condition, slight increases in PND were observed; however, evidence shows this increase to be the result of condensed uncombusted biodiesel. Most of the gaseous emissions were unaffected under all of the conditions. The biodiesel was observed to have minimal effect on the formation of polycyclic aromatic hydrocarbons during this study. In addition to the combustion results, discussion of the physical and chemical characteristics of the blended fuels obtained using standard American Society for Testing and Materials (ASTM) fuel specifications methods are presented.

Method development for the characterization of biofuel intermediate products using gas chromatography with simultaneous mass spectrometric and flame ionization detections.

Accurate analytical methods are required to develop and evaluate the quality of new renewable transportation fuels and intermediate organic liquid products (OLPs). Unfortunately, existing methods developed for the detailed characterization of petroleum products, are not accurate for many of the OLPs generated from non-petroleum feedstocks. In this study, a method was developed and applied to the detailed characterization of complex OLPs formed during triacylglyceride (TG) pyrolysis which is the basis for generating one class of emerging biofuels. This method uses gas chromatography coupled simultaneously with flame ionization and mass spectrometry detectors (GC-FID/MS). The FID provided accurate quantification of carbonaceous species while MS enabled identification of unknown compounds. A programed temperature vaporizer using a 25 °C, 0.1 min, 720 °C min(-1), 350 °C, 5 min temperature program is employed which minimizes compound discrimination better than the more commonly utilized split/splitless injector, as verified with injections at 250 and 350 °C. Two standard mixtures featuring over 150 components are used for accurate identification and a designed calibration standard accounts for compound discrimination at the injector and differing FID responses of various classes of compounds. This new method was used to identify and quantify over 250 species in OLPs generated from canola oil, soybean oil, and canola methyl ester (CME). In addition to hydrocarbons, the method was used to quantify polar (upon derivatization) and unidentified species, plus the unresolved complex mixture that has not typically been determined in previous studies. Repeatability of the analytical method was below 5% RSD for all individual components. Using this method, the mass balance was closed for samples derived from canola and soybean oil but only ca. 77 wt% of the OLP generated from CME could be characterized. The ability to close the mass balance depended on sample origin, demonstrating the need for an accurate quantification method for biofuels at various stages of production.

Mercury oxidation in flue gas using gold and palladium catalysts on fabric filters.

The feasibility of oxidizing elemental mercury in coal combustion flue gas using catalytic material impregnated onto fabric filters was explored. TiO2, Au/TiO2, and Pd/Al2O3 were studied based on promising results in previous research. Several fabric coating methods were investigated to determine the best way to load a filter. A spray coat method was found to have the highest initial loading and had the lowest losses after simulated pulse-jet cleaning. The oxidation performance of the catalyst-coated filters was tested using a simulated flue gas in a bench-scale reactor under conditions similar to those found in a baghouse. Au/TiO2 and Pd/Al2O3 were effective, yielding mercury oxidation ranges of 40-60% and 50-80%, respectively. A 19 kW research combustor equipped with a baghouse was used to fire a range of coals and further test the performance of Pd/Al2O3. Results obtained warrant further development of this technique as a means of mercury pollution control.

A study of fine particulate emissions from combustion of treated pulverized municipal sewage sludge.

Municipal sewage sludge (MSS) is formed during wastewater treatment and its processing and disposal represent one of the most environmentally challenging aspects of the wastewater treating process. One disposal option currently being considered is a process involving heat treatment (to render the sludge biologically inactive) followed by dewatering, drying, pulverizing, and combustion. This research focuses on fine particle emissions from the combustion of dried, treated, MSS, cofired with either natural gas or pulverized Ohio bituminous coal as a supplemental fuel. These fuels were burned at 13 kW in a downflow laboratory combustor designed to replicate time/temperature histories and particle concentrations typical of practical combustion units yet also sufficiently well defined aerodynamically to allow elucidation of mechanisms. Size-segregated particle size distributions were obtained by isokinetic sampling followed by dilution/quenching and passage into a Berner Low-Pressure Impactor. Major and trace elements were analyzed by flame and graphite furnace atomic absorption spectroscopy. Four particle size regions were identified: furnace vapor-phase material that formed ultrafine particles either in or just before the sampling probe, submicron-sized particles formed during the combustion process, micron-sized fine particles, and larger supermicron sized bulk fly ash particles. The fuel mix appears to influence trace metal partitioning routes and the composition of fine particulate matter in the exhaust. Cofiring of MSS with coal increases the ultrafine/submicron particle emission compared to firing coal alone. This increase in ultrafine/submicron particles is most likely due to an interaction between species derived from MSS (possibly alkali metals) and those from coal (possibly sulfur and/or chlorine). Vapor-to-solid phase partitioning of arsenic and selenium is controlled by surface reaction with active surface sites during MSS combustion with either gas or coal. Co-combustion of MSS with the Ohio bituminous coal allows the arsenic and selenium to be reactively scavenged by calcium, thus changing the speciation of the trace metal emitted. Ohio bituminous coal alone contained insufficient calcium to accomplish this same scavenging effect.