Oxidation Of Lignite Research Articles

Hydrogen peroxide oxidation of humic acids and lignite

The H2O2 degradation of humic acids and lignite from Mír mine (South Moravian region, Czech Republic) resulted in oxidation of aromatic structures and cleavage of aromatic units. The hydrophilic fraction largely dominated the oxidation digest in both parental materials. The presence of polycyclic biomarkers α-Phyllocladane, De-A-lupane confirms the high plant contribution. Hopanoid structures and branched C15 and C17 (iso and anteiso) fatty acids show slight bacterial inputs. Short chain n-fatty acids (<C20) are ubiquitous in living kingdom, whereas long chain homologs are probably derived from higher plants. Phosphoric acid production through the H2O2 oxidation probably results from hydrolyses of pyrophosphate. From hydrophilic fractions of lignite and humic acids, malonic acid and succinic acid are dominant compounds and could indicate that methylene and ethylene chains are main bridge bonds connecting between the aromatic rings in the structure. The H2O2 oxidation of lignite was very selective for producing malonic acid and succinic acid in high yields and the oxidation degradation method appears to be a suitable new way for utilizing South Moravian lignite. For production of malonic acid and succinic acid, the results indicated that the appropriate condition especially was at 50°C for 4h and 40°C for 4h, respectively. But oxidation followed by reoxidation of lignite at 30°C for 1h could be also a reasonable way to produce that kind of molecules (particularly malonic acid). Lipophilic compounds represented the minor GC-amenable fraction of the total products obtained by oxidation of lignite.

Changes in active functional groups during low-temperature oxidation of coal

Using Fourier Transform Infrared (FTIR) combined with an adiabatic oxidation test, temperature-programmed oxidation and gas analysis, we studied the changes of active functional groups during low-temperature oxidation of lignite, gas coal, fat coal and anthracite. During slow low-temperature heat accumulation, aliphatic hydrocarbons, such as methyl and methylene, are attacked by oxygen atoms absorbed by pores on coal surfaces, generating unstable solid intermediate carbon-oxygen complexes, which then decompose into gaseous products (CO, CO 2) and stable solid complexes. At the accelerated oxidation stage, the stable complexes begin to decompose in large amounts and provided new active sites for further oxidation, while the aliphatic structures gained energy and fell from the benzene rings to produce C x H y and H 2.

Effects of Pretreatment of Coal by CO2 on Nitric Oxide Emission and Unburned Carbon in Various Combustion Environments

Polar solvents are known to swell coal, break hydrogen bonds in the macromolecular structure, and enhance coal liquefaction efficiencies. The effects of the pretreatment of coal using supercritical CO{sub 2} on its physical structure and combustion properties have been studied at the bench-scale level. Emphasis has been placed on NO reburning, NO emissions during air-fired and oxy-fired combustion, and loss on ignition (LOI). Pretreatment was found to increase porosity and to significantly alter the fuel nitrogen reaction pathways. Consequently, NO reduction during reburning using bituminous coal increased, and NO emissions during oxidation of lignite decreased. These two benefits were achieved without negative impacts on LOI.

Lignite degradation and mineralization in lignite-containing mine sediment as revealed by 14C activity measurements and molecular analysis

The influence of sediment pH and redox conditions on the oxidation of lignite and sediment organic carbon was studied using a series of laboratory microcosms. The experiment was conducted over 450 d in reducing sediment suspensions maintained at four redox potentials (−170, 0, +350 and +500 mV) and two pH values (3.2 and 5.3). Carbon and lignite mineralization were determined over time using 14C analysis, DOC carbon production, solid state 13C NMR (nuclear magnetic resonance spectroscopy) and pyrolysis–gas chromatography/mass spectrometry (GC/MS). More than 50% of measured carbon mineralization occurred during the first 200 d. Maximum mineralization occurred under the more oxidizing conditions. The amount of CO 2 produced was greater at pH 5.3 than at pH 3.2, indicating that low pH reduces organic matter mineralization regardless of sediment redox potential. The 14C analysis showed that lignite carbon was mineralized at each redox potential level. Under the lowest redox level (−170 mV) mineralization was minimal as compared to the other redox levels. Pyrolysis–GC/MS showed that the dissolved aromatic fraction accumulated in solution. Solid state 13C NMR spectroscopy analysis showed that lignite, although generally recalcitrant in nature, was structurally diverse, including containing easily decomposable components. The 14C measurements of plant material sampled in the field provided evidence that lignite carbon mineralization occurs under field conditions. From the data, it can be concluded that the lignite in mine sediments is susceptible to oxidation or degradation and therefore must be considered at least as a semi-reactive compartment in the sediment carbon cycle.

Combustion characteristics of lignite and oil shale samples by thermal analysis techniques

Abstract In this research thermal analysis and kinetics of ten lignite's and two oil shale samples of different origin were performed using a TA 2960 thermal analysis system with thermogravimetry (TG/DTG) and differential al analysis (DTA) modules. Experiments were performed with a sample size of ~10 mg, heating rate of 10C min-1. Flow rate was kept constant (10 L h-1) in the temperature range of 20-900C. Mainly three different reaction regions were observed in most of the samples studied. The first region was due to the evaporation of moisture in the sample. The second region was due to the release of volatile matter and burning of carbon and called as primary reaction region. Third region was due to the decomposition of mineral matter in samples studied. In kinetic calculations, oxidation of lignite and oil shale is described by first-order kinetics. Depending on the characteristics of the samples, the activation energy values are varied and the results are discussed.

Application of high-performance liquid chromatography/electrospray mass/spectrometry for identification of carboxylic acids containing several carboxyl groups from aqueous solutions

A high-performance liquid chromatography/electrospray ionization mass spectrometry (HPLC/ESI-MS) method has been developed for the separation and detection of a series of carboxylic acids with one or more carboxyl groups, which can be formed during air oxidation of lignite. Chromatographic separation used an RP-C18 column with a gradient of water [containing 0.01% (v/v) formic acid] and acetonitrile, at a flow rate of 0.3 mL min−1. Detection by means of megaflow electrospray-MS was performed in the negative-ion mode [ESI(–)] at different cone voltages. The ESI(–) mass spectra of the carboxylic acids at a cone voltage of −20 V are characterized by the formation of [M – H]− anions together with fragmentation by loss of CO2 and sometimes H2O. Increasing the cone voltage effects enhanced fragmentation and leads to further structural hints. Lignite-derived analytes used for these HPLC/ESI-MS investigations were enriched from aqueous solution by solid-phase extraction on ISOLUTE ENV+, a polystyrene copolymer. F...

Desulphurization of Bolu-Göynük lignite using cupric chloride

Cupric chloride oxidation of Bolu-Göynük lignite was studied using a four-level factorial design with four process variables: temperature, time, cupric chloride concentration and particle size of the lignite. The main aim was to remove the organic sulphur from the lignite. Maximum organic sulphur removal was achieved by the oxidation of lignite with a particle size of 0.3mm at 150 °C for 210min using 50g CuCl 2 per 100ml of solution.

Electrochemical oxidation of lignite in basic media

Electrolysis of lignite slurries in 1N NaOH at Pt electrodes produced humic acids, CO 2, H 2, relatively small amounts of O 2 and traces of CH 4 and C 2H 2. The amount of humic acids that could be precipitated from the electrolyte increased with the applied potential, reached a maximum at E = 2.7 V, SCE and then declined with further increase in electrode potential. The rates of reaction increased with increasing temperature and activation energies computed from limiting currents and overall rates of reaction indicate that the reaction pathway is complex and involves more than one reaction. The current efficiencies for H 2 production were in the range 80–90% and > 50% of the lignite could be reacted at E = 2.0 V (SCE) in 48 h with 4 cm 2 Pt gauze electrodes. Although a graphite anode is itself electrochemically oxidized when used in this process, it increases reaction rates, ≈ 2–3 times higher with graphite than with Pt. Many aromatic organic compounds can be extracted from the residual reacted coal into suitable solvents. A significant amount of oxygenated organic compounds can also be recovered from the electrolyte as a precipitate after neutralization and by solvent extraction of the filtrate. Various products were characterized by elemental analysis, and gas chromatography-mass spectrometry. Data are also presented to show the influence of electrode potential on the rate of gas production and on the composition of the organic products. Various reaction pathways are hypothesized for the processes which lead to the products observed.

Geochemistry of Groundwater in Cretaceous Sediments of the Southeastern Coastal Plain of Eastern Mississippi and Western Alabama

Geochemical samples of waters along two hydrologic flow paths in four Upper Cretaceous aquifers of northeastern Mississippi and western Alabama indicate similar geochemical evolution of their respective waters. The waters of the Coker, Gordo, and Eutaw‐McShan aquifers, noncalcareous sands, increase downgradient in dissolved solids and pH, and are dominated by sodium and bicarbonate ions, which generally result from a calcite dissolution‐cation exchange process. Increases in dissolved iron from oxidation reduction reactions followed by decreases in total inorganic carbon from siderite precipitation occur along the flow paths. As the total inorganic carbon increases, carbon 13 (δ13C) generally is enriched in the moving waters, indicating the addition of a predominantly heavy source of carbon, most likely dissolving calcite. In the Coker aquifer δ13C values in the waters become more negative downgradient, resulting from lignite oxidation, followed by δ13C values becoming more positive, resulting from dissolving calcite and perhaps some mixing with brines. In northeastern Mississippi the Ripley aquifer, a calcareous sand, initially contains calcium‐bicarbonate dominated water that evolves to a sodium‐ bicarbonate dominated water downgradient, primarily from the calcite dissolution‐cation exchange process. Feldspar hydrolysis to kaolinite dominates aluminosilicate reactions in the upgradient parts of the aquifers. Authigenesis of smectite clay may be occurring in the deeper, downgradient parts of the aquifers.

13CO2 and 14CO2 Measurements on Soil Atmosphere Sampled in the Sub-Surface Unsaturated Zone in the Western Great Plains of the US

Soil gas samples were obtained from the unsaturated zone at eight sites in the Great Plains. Three of these sites were sampled extensively for gas composition and carbon isotopes. Sampling equipment consisted of a nest of gas probes vertically spaced by roughly 3m at most sites, generally approaching the water table. Water wells, 10cm in diameter, were screened in the topmost layer groundwater. Inverted cattle tanks were used to collect CO2 samples from the soil surface. The major gas components were analyzed with emphasis on CO2, δ 13C, and 14C measurements. The same components were studied in groundwater samples. Higher than atmospheric CO2 concentrations were found in all soil samples. Root respiration and oxidation of organic matter were sources for the additional CO2. When lignite was present in the unsaturated zone, gaseous oxygen reacted almost completely, and CO2 levels rose to 19%. Near the surface, annual cycles in total CO2, δ 13C, and 14C were observed. 14C activities were close to present post-bomb levels at the surface and generally declined with depth. At some sites, oxidation of lignite caused decline of 14C levels to 1 or 2% of their surface value at 8m depth. Without lignite, the 14C activity remained above 50% at all depths. Concentrations of total carbon and its isotopes in ground water remained very stable throughout the study. This implies that geochemical processes in the aquifer vary on time scales longer than the seasonal effects observed in the near-surface unsaturated zone.

Defining reactions and mass transfer in part of the Floridan aquifer

This paper examines the observed changes in water chemistry down a hydraulic gradient in part of the Floridan aquifer. Through the use of mass balance relationships and mass transfer calculations several reactions are derived that simulate the observed water chemistry. The calculation of σ13C and 14C activity implied by these reactions limits the number of possible reactions and leads to the following conclusions. The waters of the recharge area near Polk City have an average age of 3200 yr and have formed by congruent solution of dolomite and calcite. Although the calculated isotopic composition of CO2 entering the groundwater, σ13C = −22.5, is near that measured for soil gas CO2 in the vicinity of the recharge area (Rightmire and Hanshaw, 1973(, the mechanism)s) by which soil CO2 enters the saturated zone is not well defined. Down the hydraulic gradient from the vicinity of Polk City, isotopically light dolomites (σ13C = − 3.9 to − 1.5‰) and gypsum dissolve. All reactions south of Polk City are incongruent to a low‐magnesium calcite. The reaction path between Polk City and Fort Meade is partially open to CO2, presumably soil zone CO2. Further south between Fort Meade and Wauchula the Floridan aquifer becomes essentially closed to CO2. Beyond Wauchula to Arcadia, oxidation of lignite via sulfate reduction adds additional carbon to the water composition. 14C ages, corrected for the derived mass transfer reactions, are slightly younger than was previously recognized owing to consideration of incongruent dissolution. The age of Arcadia water (at the farthest point down the gradient) is estimated to be 36,000 yr B.P. Flow velocities derived from 14C ages are in reasonable agreement with flow velocities estimated from hydrologie considerations. The corrected 14C ages and derived mass transfer reaction coefficients allow estimation of apparent rates of reaction in central Florida from field data. The results of this study point to a complex diagenetic history in central Florida in which the position of the freshwater‐saltwater interface appears to determine whether dolomite is a reactant or product mineral.

Oxidation of Lignite into Water-Soluble Organic Acids

Abstract A sample of North Dakota lignite is oxidized by an aqueous alkaline permanganate solution. Organic acids recovered account for 50% of the lignite used. In contrast to other coals or kerogens, practically no monocarboxylic acids, either normal or benzenoic, could be detected. On the other hand, normal dicar-boxylic acids and benzene di- and tricarboxylic acids have been found. These facts suggest that part of the lignite structure is composed of fused aromatic systems.

Sources of Dissolved Carbonate in an Aquifer Free of Carbonate Minerals

Water from 14 wells in the Magothy aquifer, Long Island, New York, was sampled for chemical analysis and C13/C12 ratio measurements of the dissolved carbonate. The Magothy is essentially free of carbonate minerals and contains water whose chemistry is controlled by the chemistry of the atmospheric precipitation that recharged the aquifer. Wells near the recharge area have δC13 values of −25‰ and total carbonate contents corresponding to a PCO2 of about 4×10−3 atmosphere, showing that the carbonate here is derived from the soil zone. Downgradient, the total carbonate doubles, but the δC13 values remain more negative than −18‰. The dissolved carbonate increase is due in part to carbonate mineral solution but results largely from oxidation of lignite in the aquifer by oxygen dissolved in the water.

Oxidation of Lignite to Chemicals by Nitric Acid(II)

前報に引続き亜炭の高度硝酸分解を行い, 特に一次分解生成物の分離法および生成物の二次的処理などについて検討し, アルカリ土類金属による分別沈澱ならびに溶剤抽出の併用は生成物を特性群に分離するのに適当であること, 温和な二次的酸化は生成物の炭水素比をさげるのに効果があることなどをしつた。また少量ながら4-ニトロ, 3-ナキシ, 1-ベソゼンカルボン酸を確認した。しかしながら本研究における最終収得物としての蒸溜生成物は量的に少く, また芳香族性にも乏しい。従つて所期の目的達成には友応残渣あるいは水溶性高分子分解生成物の再分解についてなお多くの研究がなされなければならない。

Oxidation of Lignite to Chemicals by Nitric Acid

Oxidation of Lignite to Chemicals by Nitric Acid