Edwin S. Olson

Mercury capture by native fly ash carbons in coal-fired power plants.

The control of mercury in the air emissions from coal-fired power plants is an on-going challenge. The native unburned carbons in fly ash can capture varying amounts of Hg depending upon the temperature and composition of the flue gas at the air pollution control device, with Hg capture increasing with a decrease in temperature; the amount of carbon in the fly ash, with Hg capture increasing with an increase in carbon; and the form of the carbon and the consequent surface area of the carbon, with Hg capture increasing with an increase in surface area. The latter is influenced by the rank of the feed coal, with carbons derived from the combustion of low-rank coals having a greater surface area than carbons from bituminous- and anthracite-rank coals. The chemistry of the feed coal and the resulting composition of the flue gas enhances Hg capture by fly ash carbons. This is particularly evident in the correlation of feed coal Cl content to Hg oxidation to HgCl2, enhancing Hg capture. Acid gases, including HCl and H2SO4 and the combination of HCl and NO2, in the flue gas can enhance the oxidation of Hg. In this presentation, we discuss the transport of Hg through the boiler and pollution control systems, the mechanisms of Hg oxidation, and the parameters controlling Hg capture by coal-derived fly ash carbons.

Flue gas effects on a carbon-based mercury sorbent

Coal is now the primary source of anthropogenic mercury emissions in the United States, accounting for 46%, or 72 tons/year, of the total U.S. Environmental Protection Agency (EPA) estimated 158 tons/year [U.S. Environmental Protection Agency, Mercury Study Report to Congress, EPA/600/P-94/002Aa, External Review Draft, Jan. 1995.]. Development of cost-effective mercury control for coal-fired boilers is a primary research need identified in the EPA Mercury Study Report to Congress [U.S. Environmental Protection Agency, Mercury Study Report to Congress, EPA/600/P-94/002Aa, External Review Draft, Jan. 1995.]. During combustion of mercury-containing fuels such as coal, the mercury is completely volatilized and is not controlled by conventional particulate control devices unless the solid material effectively traps the mercury through sorption mechanisms. Typically, this does not occur naturally to a significant degree by the collected ash material. However, a promising approach for mercury control is the injection of an effective sorbent upstream of the particulate control device. Since the amount of mercury in the gas stream from coal combustion is usually in the range of 5 to 10 μg/m3 (about 1 ppbv), only very small amounts of a sorbent may be necessary. A requirement is that the mercury be tightly bound in the sorbent, not desorbing upon exposure to ambient air or leaching under wet disposal conditions. On a worldwide basis, the projected increase in coal usage over the next two decades in China, India, and Indonesia will dwarf the current U.S. coal consumption of 1 billion tons/year [International Energy Outlook, U.S. Department of Energy, Energy Information Administration, Office of Integrated Analysis and Forecasting, Washington, DC, April 1998, DOE/EIA-0484(98).]. Therefore, in the United States, coal will be the dominant source of mercury emissions, and worldwide, coal may be the cause of significantly increased mercury emissions unless an effective control strategy is implemented. However, there is much uncertainty over the most technically sound and cost-effective approach for reducing mercury emissions from coal-fired boilers.

Surface compositions of carbon sorbents exposed to simulated low-rank coal flue gases

Abstract Bench-scale testing of elemental mercury (Hg0) sorption on selected activated carbon sorbents was conducted to develop a better understanding of the interaction among the sorbent, flue gas constituents, and Hg0. The results of the fixed-bed testing under simulated lignite combustion flue gas composition for activated carbons showed some initial breakthrough followed by increased mercury (Hg) capture for up to ∼4.8 hr. After breakthrough, the Hg in the effluent stream was primarily in an oxidized form (>90%). Aliquots of selected activated carbons were exposed to simulated flue gas containing Hg0 vapor for varying time intervals to explore surface chemistry changes as the initial breakthrough, Hg capture, and oxidation occurred. The samples were analyzed by X-ray photoelectron spectroscopy to determine changes in the abundance and forms of sulfur, chlorine, oxygen, and nitrogen moieties as a result of interactions of flue gas components on the activated carbon surface during the sorption process. The data are best explained by a competition between the bound hydrogen chloride (HCl) and increasing sulfur [S(VI)] for a basic carbon binding site. Because loss of HCl is also coincident with Hg breakthrough or loss of the divalent Hg ion (Hg2+), the competition of Hg2+ with S(VI) on the basic carbon site is also implied. Thus, the role of the acid gases in Hg capture and release can be explained.

Higher-alcohols biorefinery: improvement of catalyst for ethanol conversion.

The concept of a biorefinery for higher-alcohol production is to integrate ethanol and methanol formation via fermentation and biomass gasification, respectively, with, conversion of these simple alcohol intermediates into higher alcohols via the Guerbet reaction. 1-Butanol results from the selfcondensation of ethanol in this multistep reaction occurring on a single catalytic bed. Combining methanol with ethanol gives a mixture of propanol, isobutanol, and 2-methyl-1-butanol. All of these higher alcohols are usefulas solvents, chemical intermediates, and fuel additives and, consequently, have higher market values than the simple alcohol intermediates. Several new catalysts for the condensation of ethanol and alcohol mixtures to higher alcohols were designed and tested under a variety of conditions. Reactions of methanol ethanol mixtures gave as high as 100% conversion of the ethanol to form high yields of isobutanol with smaller amounts of 1-propanol, the amounts in the mixture depending on the starting mixture. The most successful catalysts are multifunctional with basic and hydrogen transfer components.

Effects of Sulfur Dioxide and Nitric Oxide on Mercury Oxidation and Reduction under Homogeneous Conditions

Abstract This paper is particularly related to elemental mercury (Hg0) oxidation and divalent mercury (Hg2+) reduction under simulated flue gas conditions in the presence of nitric oxide (NO) and sulfur dioxide (SO2). As a powerful oxidant and chlorinating reagent, Cl2 has the potential for Hg oxidation. However, the detailed mechanism for the interactions, especially among chlorine (Cl)-containing species, SO2, NO, as well as H2O, remains ambiguous. Research described in this paper therefore focused on the impacts of SO2 and NO on Hg0 oxidation and Hg2+ reduction with the intent of unraveling unrecognized interactions among Cl species, SO2, and NO most importantly in the presence of H2O. The experimental results demonstrated that SO2 and NO had pronounced inhibitory effects on Hg0 oxidation at high temperatures when H2O was also present in the gas blend. Such a demonstration was further confirmed by the reduction of Hg2+ back into its elemental form. Data revealed that SO2 and NO were capable of promoting homogeneous reduction of Hg2+ to Hg0 with H2O being present. However, the above inhibition or promotion disappeared under homogeneous conditions when H2O was removed from the gas blend.

Evaluating mercury transformation mechanisms in a laboratory - scale combustion system

Mercury speciation measurements during injections of 10 microg/m3 Hg0(g) into a 42-MJ/h combustion system containing gaseous O2-Ar- and O2-N2-rich mixtures indicate that 43 and 55% of the Hg (g) spike was transformed rapidly (< 0.1 s) to Hg2+X(g) within a refractory-lined heat exchanger where gas temperatures decrease from approximately 620 to 200 degrees C. O2(g) is the probable Hg0(g) oxidant (i.e. X = O2-). The apparent formation of HgO(g) involves a heterogeneous reaction with adsorbed Hg0 or O2 on refractory surfaces or a Hg0(g)-O2(g) reaction catalyzed by corundum (Al2O3) and/or rutile (TiO2) components of the refractory. The potential catalytic effects of Al2O3 and TiO2 on Hg0(g) oxidation were investigated by injecting Al2O3 and TiO2 powders into approximately 650 degrees C subbituminous coal (Powder River Basin, Montana, USA) combustion flue gas. On-line Hg0(g) and total mercury measurements indicate, however, that Al2O3 and TiO2 injections were ineffective in promoting the formation of additional Hg2+X(g). Apparently, either the chemically complex flue gas hindered the catalytic effects of Al2O3 and TiO2, or these compounds are simply not Hg0(g) oxidation catalysts.

Elucidation of aliphatic structures in low-rank coals with ruthenium tetroxide oxidations☆

Abstract The oxidation of low-rank coals with ruthenium tetroxide was investigated with the objective of elucidating the aliphatic bridging groups and hydroaromatic groups present in the organic structure. The reaction was carried out in a two-phase system with a phase transfer catalyst. An accurate quantitative method was developed for the analysis of the carboxylic acid products. Six of the products were determined by isotope dilution with standard acids followed by gas chromatography-mass spectrometry of methyl esters prepared from the acid mixture. A suite of low-rank coals were oxidized in this system and product yields were compared. Higher yields of the aliphatic acids were obtained from the higher-rank subbituminous coals. A series of lithotypes of Beulah lignite were oxidized. The yields of the aliphatic acids obtained from lithotypes were in the order: vitrain > durain > fusain, and aromatic acids were obtained from the lithotypes in the opposite order. A method was developed to distinguish whether the aliphatic acids originated from hydroaromatic or bridging groups. A prior-dehydrogenation experiment resulted in a 50% change in the amount of succinic acid obtained in the oxidation but very little change in the amount of adipic acid. This finding implies that half of the succinic acid originates from hydroaromatics and half from bridging groups, whereas very little of the adipic acid results from hydroaromatic groups.

Molecular weights of solubilized lignite macromolecules

Abstract The determination of molecular weights and molecular weight distributions in humic acids derived from lignite by base extraction has been successfully carried out by low-angle laser light scattering (LALLS) photometry and by coupling size exclusion chromatography (SEC) with LALLS photometry. Since light scattering techniques give absolute molecular weight values, no error-prone calibrations of the size exclusion column were necessary. Reduction of soluble derivatives of the humic acids with zinc in acetic anhydride was required to reduce the optical absorbance so that a linear scattering response was observable. Weight average molecular weights of ≈ 1.3 × 10 6 and low polydispersity ratios were obtained for humic acid derivatives of Beulah, ND, lignite. Extension of this technique to the study of the more highly crosslinked humin which comprises the major portion of the lignite was investigated by treatment of the lignite with sodium hydroxide solution in a blender. This treatment converted up to 90% of the lignite into humic acids, which could be derivatized and studied by the LALLS techniques. The molecular weights of the products from lowtemperature solubilization of the lignite are inversely proportional to the per cent conversion.

Ester fuels and chemicals from biomass

Bench-scale research demonstrated that using an efficient esterification step to integrate an ethanol with a carboxylic acid fermentation stream offers potential for producing valuable ester feedstocks and fuels. Polar organic acids from bacterial fermentations are difficult to extract and purify, but formation of the ammonium salts and their conversion to esters facilitates the purifications. An improved esterification procedure gave high yields of esters, and this method will lower the cost of ester production. Fuel characteristics have been determined for a number of ester-gasoline blends with promising results for lowering Reid vapor pressure and raising octane numbers.

Size exclusion chromatography-low angle laser light scattering photometry of lignite macromolecules

Abstract The determination of molecular weight distribution in humic acids, derived from lignite, has been successfully carried out by the application of size-exclusion chromatography, coupled with low-angle laser light-scattering photometry. Reduction of soluble derivatives with zinc in acetic anhydride was required to reduce the absorbance so that a linear scattering response was obtained. A benzyl derivative and a methyl derivative exhibited the best chromatographic results, giving weight average molecular weights of about 1 500 000.