Simulation of Methane Oxidation by Paddy Soils in a Closed System

Methane oxidation by paddy soils in a closed system could be simulsted by the equation where xo and x are the CH4 concentrations at time zero and t, respectively; k1 and k2 are constants related to the constant of first-order-kinetics. According to the equation the change of soil ability to oxidize CH4 could be estimated by the equstion The results showed that the soil ability to oxidize CH4 varied, depending on the initial CH4 concentration.High initial CH4 concentration stimulated soil ability to consume CH4, while low concentration depressed the ability. This characteristic of paddy soil seemed to be of considerable significance to self-adjusting CH4 emission from flooded rice fields if there exist oxic microsites in the soil.

Effects of Nitrogen Fertilizer,Soil Moisture and Temperature on Methane Oxidation in Paddy Soil

Effects of nitrogen fertilizer,soil moisture and temperature on methane oxidation in paddy soil were investigated under laboratory conditions. Addition of 0.05 g N kg-1 soil as NH4Cl strongly inhibited methane oxidation and addition of the same rate of KCl also inhibited the oxidation but with more slight effect,suggesting that the inhibitory effect was partly caused by increase in osmotic potential in microorganism cell.Not only NH but also NO greatly affected methane oxidation.Urea did not affect methane oxidation in paddy soil in the first two days of incubation,but strong inhibitory effect was observed afterwards.Methane was oxidized in the treated soil with an optimum moisture of 280 g kg-1, and air-drying inhibited methane oxidation entirely.The optimum temperature of methane oxidation was about 30℃in paddy soil,while no methane oxidation was observed at 5℃or 50℃

Application of the Clustering Method in Molecular Dynamics Simulation of the Diffusion Coefficient

Using molecular dynamics (MD) simulation, the diffusion of oxygen, methane, ammonia and carbon dioxide in water was simulated in the canonical NVT ensemble, and the diffusion coefficient was analyzed by the clustering method. By comparing to the conventional method (using the Einstein model) and the differentiation-interval variation method, we found that the results ob- tained by the clustering method used in this study are more close to the experimental values. This method proved to be more reason- able than the other two methods.

Measurements of Hydrate Equilibrium Conditions for CH4, CO2, and CH4＋C2H6＋C3H8 in Various Systems by Step-heating Method

Phase equilibrium conditions of gas hydrate in several systems were measured by the step-heating method using the cylindrical transparent sapphire cell device.The experimental data for pure CH4 or CO2+deionized water systems showed good agreement with those in the literatures.This kind of method was then applied to CH4/CO2+sodium dodecyl sulfate(SDS)aqueous solution,CH4/CO2+SDS aqueous solution+silica sand,and(CH4+C2H6+C3H8)gas mixture+SDS aqueous solution systems,where SDS was added to increase the hydrate formation rate without evident influence on the equilibrium conditions.The feasibility and reliability of the step-heating method,especially for porous media systems and gas mixtures systems were determined.The experimental data for CO2+silica sand data shows that the equilibrium pressure will change significantly when the particle size of silica sand is less than 96μm.The formation equilibrium pressure was also measured by the reformation of hydrate.

Conversion of Methane by Steam Reforming Using Dielectric-barrier Discharg

Conversion of methane by steam reforming was carried out by means of dielectric-barrier discharge.A systemic procedure was employed to determine the suitable experimental conditions.It was found that one of the plasma generators can match the system best.A higher power input can always bring a higher conversion,but the selectivity to C2H6 decreased from 52.48% to 39.43% as the power increased from 20W to 49W.When discharge distance was 4mm,selectivities to almost all main products reached the max.The inner electrode made of stainless steel and the outer electrode with aluminum foil were one of the best options which can obviously enhance the conversion of methane.A larger flow rate always resulted in a lower conversion of methane.In the most time,19.93% steam promoted conversion of methane.

ANALYSIS OF ABILITY FOR IGNITING METHANE OF WATER-CARRYING EXPLOSIVES

In this paper, the ability to ignite methane of water-carrying explosives is discussed in detail. The difference of the safety towards methane of water- carrying explosives and ammonite is analysed comparatively. lt is shown that the process of detonation reaction, the duration of fIame by combustible residues of detonation and the fineness of cooling salt in detonation products are important factors of the safety of explosive towards methane. Water-carrying explosives are safer than ammonite used in coal mines.

Steam reforming of methane over Ni catalysts prepared from hydrotalcite-type precursors: Catalytic activity and reaction kinetics

Ni/Mg–Al catalysts derived from hydrotalcite-type precursors were prepared by a co-precipitation technique and applied to steam reforming of methane. By comparison with Ni/γ-Al2O3 and Ni/α-Al2O3 catalysts prepared by incipient wetness impregnation, the Ni/Mg–Al catalyst presented much higher activity as a result of higher specific surface area and better Ni dispersion. The Ni/Mg–Al catalyst with a Ni/Mg/Al molar ratio of 0.5:2.5:1 exhibited the highest activity for steam methane reforming and was selected for kinetic investigation. With external and internal diffusion limitations eliminated, kinetic experiments were carried out at atmospheric pressure and over a temperature range of 823–973 K. The results demonstrated that the overall conversion of CH4 and the conversion of CH4 to CO2were strongly influenced by reaction temperature, residence time of reactants as well as molar ratio of steam to methane. A classical Langmuir–Hinshelwood kinetic model proposed by Xu and Froment(1989)fitted the experimental data with excellent agreement. The estimated adsorption parameters were consistent thermodynamically.

Characterization of NOM and THM formation potential in eutrophic reservoir water

Resin adsorption technique with XAD-8 and XAD-4 was used to characterize the raw water from Erlong reservoir in Jilin province of China. The NOM chemical composition sequences of four organic fractions in the raw water, from high to low, are fulvic acid （FA） fraction, hydrophilic non-acid （HPINA） fraction, hydrophilic acid （HPIA） fraction, and humic acid （HA） fraction. Experimental results show that FA is the main precursor of THMFP among the four organic fractions. However, HA or hydrophobie acid exhibits the highest chlorination activity in forming THMs. It is also found that the value of FI/DOC or SUVA and the specific THMFP have better positive correlation. It is implied that certain source water has unique nature of NOM and DBPs.

人类的未来燃料——海底甲烷

正当温室效应日趋恶化,人们对清洁能源的渴求越来越迫切的时候,媒体陆续传来美国、日本在各自海域发现新能源的消息。 所谓新能源实际上就是冷藏在海底的甲烷,学名为甲烷水合物或水化甲烷,是气体甲烷在海底低温、高压下形成的结晶体,外表被水分子包围起来看上去如冰雪般晶莹透明。甲烷是可燃气体,即便结“冰”也会神奇地被点燃,因此有人称它为“可燃冰”。 可喜的是前不久,我国也在南海、东海海域发现海底甲烷,据报道,其蕴藏量相当于目前全国能源总量的50％。尤为可喜的是,这是一种燃烧后不会产生任何污染物的清洁能源,所以在环保呼声日益高涨的今天更被世人看好。

天然气水化物的非凡前景与挑战

本文介绍甲烷水化物作为一种潜在资源愈加引起人们兴趣的基本原因 ,讨论何为水化物 ,其形成和被发现的方式、地点及其易碎特征所产生的地理危险性。作者进一步讨论目前世界对之关注、勘探和地缘政治影响的情况。

气体水合物研究进展

本书是2003年春季美国化学工程协会召开的“气体水合物讨论会”的论文集，共收录16篇论文。气体水合物是一种非常特殊的化学组成，它是由水分子（主体分子）包裹着气体分子（客体分子）在低温高压条件下形成的一种无化学键的晶体物质。通常的气体水合物是甲烷水合物，在常温常压下，甲烷水合物中包含的甲烷气体是甲烷水化物本身的180倍。作为一种替补能源，气体水合物的研究已经越来越受到人们的重视。

Pre-activation based stereoselective glycosylations: Stereochemical control by additives and solvent

Stereochemical control is an important issue in carbohydrate synthesis.Glycosyl donors with participating acyl protective groups on 2-O have been shown to give 1,2-trans glycosides reliably under the pre-activation based reaction condition.In this work,the effects of additives and reaction solvents on stereoselectivity were examined using donors without participating protective groups on 2-O.While several triflate salt additives did not have major effects,the amount of AgOTf was found to significantly impact the reaction outcome.Excess AgOTf led to lower stereochemical control presumably due to its coordination with the glycosyl triflate intermediate and a more SN1 like reaction pathway.In contrast,the stereoselectivity could be directed by reaction solvents,with diethyl ether favoring the formation of glycosides and dichloromethane leading to β isomers.The trend of stereochemical dependence on reaction solvent was applicable to a variety of building blocks including the selective formation of β-mannosides.

Protective effects of methane-rich saline on mice with allergic asthma by inhibiting inflammatory response, oxidative stress and apoptosis

Background:Asthma is a common cause of breathing difficulty in children and adults,and is characterized by chronic airway inflammation that is poorly controlled by available treatments.This results in severe disability and applies a huge burden to the public health system.Methane has been demonstrated to function as a therapeutic agent in many diseases.The aim of the present study was to explore the effect of methane-rich saline(MRS)on the pathophysiology of a mouse model of asthma and its underlying mechanism.Methods:A murine model of ovalbumin(OVA)-induced allergic asthma was applied in this study.Mice were divided into three groups:a control group,an OVA group,and OVA-induced asthmatic mice treated with MRS as the third group.Lung resistance index(RI)and dynamic compliance(Cdyn)were measured to determine airway hyper-responsiveness(AHR).Haematoxylin and eosin(H&E)staining was performed and scored to show histopathological changes.Cell counts of bronchoalveolar lavage fluid(BALF)were recorded.Cytokines interleukin(IL)-4,IL-5,IL-13,tumor necrosis factorα(TNF-α),and C-X-C motif chemokine ligand 15(CXCL15)from BALF and serum were measured by enzyme-linked immunosorbent assay(ELISA).The oxidative stress indexes,including malondialdehyde(MDA),superoxide dismutase(SOD),catalase(CAT),glutathione(GSH),myeloperoxidase(MPO),and 8-hydroxydeoxyguanosine(8-OHdG),were determined using commercial kits.Apoptosis was evaluated by western blot,quantitative real-time polymerase chain reaction(qRT-PCR),and biochemical examination.Results:MRS administration reversed the OVA-induced AHR,attenuated the pathological inflammatory infiltration,and decreased the cytokines IL-4,IL-5,IL-13,TNF-α,and CXCL15 in serum and BALF.Moreover,following MRS administration,the oxidative stress was alleviated as indicated by decreased MDA,MPO,and 8-OHdG,and elevated SOD and GSH.In addition,MRS exhibited an anti-apoptotic effect in this model,protecting epithelial cells from damage.Conclusions:Methane improves pulmonary function and decreases infiltrative inflammatory cells in the allergic asthmatic mouse model.This may be associated with its anti-inflammatory,antioxidative,and anti-apoptotic properties.

Gas hydrate formation in fine sand

Gas hydrate formation from two types of dissolved gas (methane and mixed gas) was studied under varying thermodynamic conditions in a novel apparatus containing two different natural media from the South China Sea. The testing media consisted of silica sand particles with diameters of 150-250 μm and 250-380 μm. Hydrate was formed (as in nature) in salt water that occupies the interstitial space of the partially water-saturated silica sand bed. The experiments demonstrate that the rate of hydrate formation is a function of particle diameter, gas source, water salinity, and thermodynamic conditions. The initiation time of hydrate formation was very short and pressure decreased rapidly in the initial stage. The process of mixed gas hydrate formation can be divided into three stages for each type of sediment. Sand particle diameter and water salinity also can influence the formation process of hydrate. The conversion rate of water to hydrate was different under varying thermodynamic conditions, although the formation processes were similar. The conversion rate of methane hydrate in the 250-380 μm sediment was greater than that in the 150-250μm sediment. However, the sediment grain size has no significant influence on the conversion rate of mixed gas hydrate.

Theoretical limiting concentration for mineralization of trichloromethane and dichloromethane in aqueous solutions by AOPs

It is widely stated that most organic contaminants could be completely mineralized by Advanced Oxidation Processes(AOPs). This statement means that the concentration of the organic contaminant at equilibrium(limiting concentration,LC)is low enough to be neglected.However,for environmental safety,especially drinking water safety,this statement needs to be verified from chemical engineering thermodynamic analysis.In this paper,trichloromethane(CHCl3)and dichloromethane(CH2Cl2) are selected as the model systems,and the equilibrium concentration(theoretical limiting concentration,TLC)for the mineralization of chlorinated methanes in aqueous solutions at the different initial concentrations of chlorinated methanes,pH values and·OH concentrations by AOPs are investigated by thermodynamic analysis.The results in this paper show that the TLC for the mineralization of CHCl3 and CH2Cl2 with·OH increases with increasing initial concentrations of CHCl3 and CH2Cl2,decreases with increasing concentration of·OH,and the TLC for the mineralization of CHCl3 decreases with increasing pH values except that the pH value changes from 3.0 to 3.5.For the mineralization of CH2Cl2 with·OH,at the concentrations of·OH obtained from the literature,there is no obvious change of the TLC with pH values,while as the concentrations of·OH increase by 10 and 100 times,the TLC decreases with the increasing pH values from 2.0 to 3.0 and from 3.5 to 4.5,and increases with the increasing pH values from 3.0 to 3.5 and from 4.5 to 5.0.The investigations in this paper imply that high concentration of·OH,a bit higher pH values(4.0–5.0)in acid environment and low initial concentrations of the organic contaminants are beneficial for the complete mineralization of chlorinated methanes by AOPs.

Factors influencing the formation of chlorination brominated trihalomethanes in drinking water

The formation of brominated trihalomethanes (THMs-Br) which is proved more carcinogenic than their chlorinated analogues reported was very different at various water qualities.This study was performed to assess the effects of water quality parameters (bromide concentration,pH value and ammonia concentration),chlorination conditions (chlorine dose,reaction time) and ratios of Br-/DOC and Br-/Cl2 consumption on the formation and distribution of THMs-Br in chlorination.The results showed good correlation between the bromine incorporation factor (BIF) n(Br) and Br-/Cl2 consumption ratio.The formation of total THM (TTHM) was found to decrease with increasing ammonia concentration but to increase with bromide concentration and pH value.The n(Br) trends were significantly affected by the presence of bromide concentration.The effects on the molar yields of THMs were more strongly influenced by bromide concentration and dissolved organic carbon (DOC) concentration than pH value and natural organic matter (NOM) source.High Br-/DOC and Br-/Cl2 favor the formation of THMs-Br over chlorinated THMs (THMs-Cl).The experimental data including the main parameters such as bromide,DOC,ammonia,pH and reaction time were used for developing the predictive model for THMs-Br.