CO2 CH4 Gas Mixture Research Articles

Component fractionation of temporal evolution in adsorption–desorption for binary gas mixtures on coals from Haishiwan Coal Mine

Adsorption–desorption experiments on CO2–CH4 gas mixtures with varying compositions have been conducted to study the fractionation characteristics of CO2–CH4 on Haishiwan coal samples. These were carried out at constant temperature but different equilibrium pressure conditions. Based on these experimental results, the temporal evolution of component fractionation in the field was investigated. The results show that the CO2 concentration in the adsorbed phase is always greater than that in the original gas mixture during the desorption process, while CH4 shows the opposite characteristics. This has confirmed that CO2, with a greater adsorption ability has a predominant position in the competition with CH4 under different pressures. Where gas drainage is employed, the ratio of CO2 to CH4 varies with time and space in floor roadways used for gas drainage, and in the ventilation air in Nos.1 and 2 coal seams, which is consistent with laboratory results.

CO2 Removal from a CO2–CH4 Gas Mixture by Clathrate Hydrate Formation Using THF and SDS as Water-Soluble Hydrate Promoters

This study investigates the use of hydrate formation to separate the CO2 from a CO2–CH4 gas mixture in the presence of water-soluble additives—tetrahydrofuran (THF) and/or sodium dodecyl sulfate (SDS)—at low concentrations. The influence of additive concentration and process operating conditions on the gas enclathration kinetics, the quantity of gas removed, and the selectivity of the separation are studied under quiescent hydrate-forming conditions in a batch reactor. Gas consumption and enclathration occur at high rates only when the two additives are used in combination. Similarly to what has been observed with pure CO2, the proposed mechanism is that a mixed hydrate of structure sII containing THF forms first, which triggers the formation of CO2–CH4 binary gas hydrate of structure sI. However, the gas separation was found not to be selective enough to the CO2 for envisaging any practical application.

Deep eutectic assisted synthesis of carbon adsorbents highly suitable for low-pressure separation of CO2–CH4 gas mixtures

Ionic liquids and deep eutectic solvents (a new class of ionic liquids obtained by complexation of quaternary ammonium salts with hydrogen bond donors such as acids, amines, and alcohols among others) have been recently used as solvents and even as precursors in the synthesis of carbonaceous materials. The use of long-alkyl-chain derivatives of ionic liquids that, playing the role of structure directing agents, were capable of designing the mesoporous structure of the resulting carbons is of particular interest. Meanwhile, deep eutectic solvents proved efficient in tailoring the structure comprised between large mesopores and small macropores, but the control over the smaller ones (e.g. small mesopores and micropores) is still a challenge as compared to ILs. Herein, we have used deep eutectic solvents composed of resorcinol, 4-hexylresorcinol and tetraethylammonium bromide for the synthesis of carbon monoliths with a tailor-made narrow microporosity. Behaving as molecular sieves, these carbons exhibited not only good capacities for CO2 adsorption (up to 3 mmol g−1) but also an outstanding – especially at low pressures – CO2–CH4 selectivity.

Gas analyzer for continuous monitoring of carbon dioxide in gas streams

Abstract The construction and characterization of a simple and inexpensive gas analyzer setup for direct measurement of CO2 concentration in gas streams are presented. The analyzer was based on a hollow fiber membrane (HFM) contactor which served as a mean for continuous gas sampling and preconcentration of CO2 from the gas stream into a dilute buffer carrier solution. The resultant pH changes of the carrier solution were measured downstream by a pH flow-through detector. A Nernstian response of 55.5 mV/log[CO2] was obtained over a wide dynamic range of 0.1–100% CO2 in nitrogen. Moreover, the presented analyzer offered several favorable performance characteristics such as fast response (45 s) and recovery times (1–2 min), excellent signal stability and reproducibility (RSD = 1.2%) and intrinsic high selectivity in the presence of most common neutral gases (e.g., CH4, N2, O2, CO, etc.). H2S and SO2 which are potentially interfering acidic gases were efficiently removed by a simple prior in-line treatment using acidified potassium permanganate bubbler. The analyzer was applied successfully to monitor the treatment process of CO2 removal from CO2–CH4 gas mixtures. The merits of the developed analyzer suggest its reliable use in various applications requiring continuous carbon dioxide monitoring in gas streams for several hours.

A combined approach for the management of desalination reject brine and capture of CO2

Water desalination plants produce huge amounts of reject brine, which are usually sent back to the sea, where they could, in the long run, result in detrimental effects on the aquatic life as well as the quality of the seawater in the area. In this study, a new approach for the management of desalination reject brine and capture of CO2, where ammoniated brine is reacted with carbon dioxide, has been investigated. The effects of reaction temperature, reaction time, and excess ammonia were assessed. Carbon dioxide was used either as a pure gas or a mixture of 10% CO2 in methane. The experimental results indicated that the optimum reaction temperature was about 20°C and the optimum NH3/NaCl ratio was 2 for synthetic brine solutions and 3 for actual reject brine. The proposed process proved to be effective in reducing the CO2 concentration in a CO2–CH4 gas mixture by more than 90%. The solubility of sodium bicarbonate was found to play a key role in the removal of sodium. The results indicated that the new approach can reduce the salinity of reject brine and, at the same time, contribute to the reduction CO2 emissions.

Differential transport of CO2 and CH4 in coalbed aquifers: Implications for coalbed gas distribution and composition

Coalbed gas content and composition are critical for the successful exploration and production of coalbed methane. We investigated the differential transport of a preadsorbed CO2-CH4 gas mixture along a coalbed aquifer by groundwater flow or across a coal bed by upward diffusion through pore water. Consistent analytical approximations and numerical solutions were obtained for typical cases. The results suggest that differential transport of CH4 and CO2 in a water-saturated coal seam is mainly controlled by their adsorption equilibrium in coals and solubilities in water. Although CO2 is about 20 times more soluble than CH4 in water at temperatures lower than 50C, the transport of CO2 from a coal seam is only several times more efficient than that of CH4 because of the stronger adsorption of CO2 than CH4 in coals. Preferential transport of CO2 over CH4 by groundwater advection can substantially accumulate more gas rich in CO2 at downstream or near discharge zones if gas-trapping structures exist, and it may cause low total gas content of CH4 near recharge zones, which may explain the CO2 and CH4 distribution in the San Juan and Powder River basins and the undersaturation of gas in many other coals. The separation and redistribution of coalbed gas by transport processes may also be complicated by late-stage biogenic gas generation with infiltration of meteoric water with nutrients and gas-producing microbes into the coal beds as suggested for some basins. Overall, hydrogeologic systems strongly influence the distribution of coalbed gas content and composition in coal seams.

Nature of band-A cathodoluminescence inCVD diamond films

Several sets of diamond films have been grown by Microwave Plasma-Enhanced Chemical Vapor Deposition (MWPECVD) using CH4-H2 and CO2-CH4 gas mixtures. The growth conditions were systematically changed in order to obtain different film morphologies, preferential orientations and crystal qualities. In particular, the CH4 concentration in the gas mixture was varied in a wide range to obtain different preferential orientations. Substrate growth temperatures as high as 950 °C were used to intentionally obtain highly defective films. The resulting films were characterized by X-Ray Diffraction, Raman spectroscopy and Scanning Electron Microscopy. Cathodoluminescence has been investigated in the energy range 1.55-6.20 eV (200-800 nm). A strong dependence of the 2.85 eV (435 nm) band-A emission on the CH4 concentration is found. Moreover, this dependence does not substantially change with the growth conditions (substrate temperature, nucleation pretreatment, gas mixture etc.). The position of the diamond Raman peak is also correlated with the band-A emission. These results are discussed in terms of crystal defects and diamond film texturing induced by the growth process.