氮气分析用高准确度微量混合气体标准物质研制

介绍了氮气分析用高准确度氮中微量混合气体标准物质的研制过程,主要包括称量法制备技术、稀释气定量分析及混合气体的均匀性检验、稳定性考察等.混合气体含有氢、氧、甲烷、二氧化碳和一氧化碳5种组分,标称浓度均为2 μmol/mol,F检验和回归曲线法实验结果表明,5组分微量混合气体标准物质在压力1～ 10 MPa内,具有良好的...     

城市有机生活垃圾的资源化利用

城市每天产生大量的生活垃圾,一直以来,人们往往通过填埋法和焚烧法对这些垃圾进行处理。然而随着环境问题日渐成为焦点,这些方法造成的二次污染越来越不容忽视。本文在评述填埋法和焚烧法基础上,着重介绍了新兴的城市垃圾甲烷化技术。从目前的研究来看,甲烷化技术具有投资少、运行费用低,工艺简单等特点。如果所得生物质气再通过甲烷-二氧化碳重整技术转化为合成气,该法完全可以避免二次污染且能源化效率更高。因此,最后简单介绍了发展中的甲烷-二氧化碳重整技术最新进展。     

氮中一氧化氮、二氧化碳气体标准物质的研制

本研究以氮气、一氧化氮、二氧化碳为原料,制备了低浓度氮中一氧化氮、二氧化碳(300×10~(-6) mol/mol,2%),高浓度氮中一氧化氮、二氧化碳气体标准物质(0.3%,12%)。主要介绍了标准物质的制备方法、均匀性检验、稳定性考察。研究结果表明,该气体标准物质具有良好的均匀性和稳定性,一氧化氮相对扩展不确定度Urel为2.0%(k=2),二氧化碳相对扩展不确定度Urel为1.0%(k=2),可进一步应用于汽车尾气分析仪等相关仪器的标定和检测。     

机动车排放监测用四元气体标准物质的研制

随着我国第六阶段机动车污染物排放标准的出台，对机动车的排放要求更加严格，其尾气检测需要有合适的标准物质作为测量依据。通过开展一种四元气体标准物质的研制，将气体逐步充装至气瓶中混合制备，采用称量法定值。该标准物质包含二氧化碳(100～18.0×10⁴)μmol/mol、一氧化碳(100～10.0×10⁴)μmol/mol、丙烷(50.0～1.20×10⁴)μmol/mol、一氧化氮(50.0～0.400×10⁴)μmol/mol,氮气为平衡气。对4种主要组分的分析方法进行了开发，方法精密度较好。对标准气体特性量值的均匀性、稳定性、不确定度进行了评价。结果显示：该气体标准物质在12个月内稳定性良好，特性量值的相对扩展不确定度为1%(k=2)。     

提高城市生活垃圾填埋场使用效率的研究

文章从城市垃圾填埋场甲烷逃逸的问题入手,探讨了填埋气体的产生过程及受影响因素,对甲烷菌的影响因素包括温度、水分、pH值等。文章接着以广州兴丰垃圾填埋场为例讨论了填埋气的收集及利用。最后研究如何更好的收集填埋气体,减少逃逸以及延长垃圾填埋场的使用寿命。     

一种新型汽车排气标准物质的研制

介绍了一种新型汽车排气标准物质的研制方法。该标准物质是将一氧化碳、二氧化碳、1,3-丁二烯和氮气充装到气瓶中制备而成,采用称量法定值。对原料气体中的杂质进行了测量,对分析检测方法进行了比较研究,对标准物质的稳定性进行了考查。结果显示:该气体标准物质在12个月内的稳定性良好,浓度的相对扩展不确定度为0.5%(k=2)。该标准物质中,一氧化碳的浓度范围为2.000%～8.000%mol/mol,二氧化碳的浓度范围为9.400%～13.60%mol/mol,1,3-丁二烯的浓度范围为40.00×10~(-6)～160.0×10~(-6) mol/mol,氮气为平衡气。     

基于称量法制备标准气体配气装置的研制与应用

介绍了称量法制备标准气体的原理、方法和制备过程中需要考虑的因素,并在此基础上研制了一种基于称量法制备标准气体的配气装置。用气相色谱仪对用该新型装置配制的标准气体进行压力均匀性和稳定性考察,其定值及不确定度均符合要求,该装置能提高配气效率达30%以上。     

填埋气净化升级技术及研究进展

卫生填埋是当前中国主要的生活垃圾处置手段,同时也是第二大温室气体甲烷的重要人为排放源。对填埋气进行有效的管理是实现温室气体减排,缓解能源压力的途径之一。根据填埋气不同的利用途径,需要去除其中的杂质,包括硫化氢、水分、固体颗粒、氨气、甚至痕量有机物、氮气等等。其中,硫化氢是最主要的污染物质,必须得到去除。有时还需分离甲烷和二氧化碳,这是各环节中技术要求最高的一环。     

环境空气监测用氮气中多组分醛酮气体标准物质的研制

介绍了氮气中13组分醛酮气体标准物质的制备方法。气体标准物质的组分为甲醛、乙醛、丙烯醛、正丁醛、戊醛、2-丁酮、丙酮、丁烯醛、甲基丙烯醛、丙醛、己醛、间甲基苯甲醛和苯甲醛,标准值为1μmol/mol。根据组分的不同性质,经研究采用3步称量法来制备13组分醛酮标准气体,建立了气相色谱-质谱联用及选择扫描离子模式的分析方法,对研制的气体标准物质在气瓶中的均匀性和长期稳定性进行了考察。将研制的气体标准物质分别送至中国计量科学研究院(NIM)和中国环境监测总站(CNEMC)进行了对比测试,取得了良好的对比结果。结果表明,1μmol/mol氮气中13组分醛酮气体标准物质具有较好的均匀性和稳定性,其有效期为12个月,取得了国家二级标物证书,标物号GBW(E)083618。     

温室气体监测用4种氟氯烃混合标准气体的研制

介绍了氮气中三氯一氟甲烷、二氯二氟甲烷、1,1,2-三氯-1,2,2-三氟乙烷、一氯三氟甲烷4种氟氯烃混合标准气体的制备方法和定值方法。考察标准气体在气瓶内壁的吸附作用、制备重现性、均匀性和稳定性。浓度水平为5~9μmol/mol的4种氟氯烃混合标准气体采用称量法制备,采用气相色谱法测定。经瓶内均匀性考察,瓶内均匀性良好。经时间稳定性考察显示,4种氟氯烃混合标准气体使用有效期为1年。标准气体的不确定度包含样品定值不确定度、瓶内不均匀性和不稳定引起的不确定度,经评估和计算,其扩展相对不确定度为3%(置信度为95%)。4种氟氯烃混合标准气体可以为温室气体环境监测提供标准技术支持。     

Vacuum pressure swing adsorption process for coalbed methane enrichment

The enrichment of low concentration coalbed methane using adsorption process with activated carbon adsorbent was studied in this work.Adsorption isotherms of methane,nitrogen and carbon dioxide on activated carbon were measured by volumetric method,meanwhile a series of breakthrough tests with single component,binary components and three components feed mixture has been performed for exploring dynamic adsorption behaviors.Moreover,a rigorous mathematical model of adsorption bed containing mass,energy,and momentum conservation equation as well as dual-site Langmuir model with the Linear driving force model for gas-solid phase mass transfer has been proposed for numerical modeling and simulation of fixed bed breakthrough process and vacuum pressure swing adsorption process.Furthermore,the lumped mass transfer coefficient of methane,nitrogen and carbon dioxide on activated carbon adsorbent has been determined to be 0.3 s~(-1),1.0 s~(-1) and 0.06 s~(-1) by fitting the breakthrough curves using numerical calculation.Additionally,a six bed VPSA process with twelve step cycle sequence has been proposed and investigated for low concentration coalbed methane enrichment.Results demonstrated that the methane molar fraction in feed mixture ranged from 10% to 50% could be enriched to 32.15% to 88.75% methane in heavy product gas with a methane recovery higher than 83%under the adsorption pressure of 3 bar(1 bar=10~5 Pa) and desorption pressure of 0.1 bar.Energy consumption of this VPSA process was varied from 0.165 kW·h·m~(-3) CH_4 to 0.649 kW·h·m~(-3) CH_4.Finally,a dual-stage VPSA process has been successfully developed to upgrade a low concentration coalbed methane containing 20% methane to a target product gas with methane purity higher than 90%,meanwhile the total methane recovery was up to 98.71% with a total energy consumption of 0.504 kW·h·m~(-3) CH_4.     

Electricity,methane and liquid carbon dioxide production from landfill gas

Landfill gas, which has a typical composition of 40–60% methane, 40–50% carbon dioxide, and a wide range of impurities, has historically been recovered solely for its heating value. After only minor impurity removal, landfill gas has been used as medium Btu industrial fuel or to generate electricity; after significant impurity and carbon dioxide removal, landfill gas has been used as a source of pipeline quality methane. For both cases, the value of the substantial amount of contained carbon dioxide has not been realized. This has been due to the impurities which present a significant obstacle to the economic production of merchant grade carbon dioxide.This paper presents two processes¹ which make use of an oxygen fed combustion step to reduce both the quantity and variety of impurities which must be removed to meet carbon dioxide product specifications. The two processes produce carbon dioxide and electricity or carbon dioxide and pipeline quality methane, respectively. In both oxygen based coproduction processes, the combustion step is integrated into the overall process to maximize energy efficiency. The two processes are described and anticipated net liquid carbon dioxide manufacturing costs are presented.     

生活垃圾填埋场中恶臭气体的季节变化特点

通过对生活垃圾填埋场中恶臭气体（硫化氢、氨、氮氧化物、甲烷等）,在不同季节（春、夏、冬季）的监测,分析其随季节的变化特点。得出夏季垃圾填埋场恶臭气体的浓度高于冬季,和恶臭气体并不是由单个恶臭气体浓度简单加和而成,而是有明显的协同作用两个结论。从而为生活垃圾填埋场的恶臭污染控制提供参考依据。     

Molecular dynamics study on growth of carbon dioxide and methane hydrate from a seed crystal

In the current work, molecular dynamics simulation is employed to understand the intrinsic growth of carbon dioxide and methane hydrate starting from a seed crystal of methane and carbon dioxide respectively. This comparison was carried out because it has relevance to the recovery of methane gas from natural gas hydrate reservoirs by simultaneously sequestering a greenhouse gas like CO₂. The seed crystal of carbon dioxide and methane hydrate was allowed to grow from a super-saturated mixture of carbon dioxide or methane molecules in water respectively. Two different concentrations (1:6 and 1:8.5) of CO₂/CH₄ molecules per water molecule were chosen based on gas–water composition in hydrate phase. The molecular level growth as a function of time was investigated by all atomistic molecular dynamics simulation under suitable temperature and pressure range which was well above the hydrate stability zone to ensure significantly faster growth kinetics. The concentration of CO₂ molecules in water played a significant role in growth kinetics, and it was observed that maximizing the CO₂ concentration in the aqueous phase may not result in faster growth of CO₂ hydrate. On the contrary, methane hydrate growth was independent of methane molecule concentration in the aqueous phase. We have validated our results by performing experimental work on carbon dioxide hydrate where it was seen that under conditions appropriate for liquid CO₂, the growth for carbon dioxide hydrate was very slow in the beginning.     

Methane and carbon dioxide in dual-porosity organic matter: Molecular simulations of adsorption and diffusion

Shale gas, which predominantly consists of methane, is an important unconventional energy resource that has had a potential game-changing effect on natural gas supplies worldwide in recent years. Shale is comprised of two distinct components: organic material and clay minerals, the former providing storage for hydrocarbons and the latter minimizing hydrocarbon transport. The injection of carbon dioxide in the exchange of methane within shale formations improves the shale gas recovery, and simultaneously sequesters carbon dioxide to reduce greenhouse gas emissions. Understanding the properties of fluids such as methane and methane/carbon dioxide mixtures in narrow pores found within shale formations is critical for identifying ways to deploy shale gas technology with reduced environmental impact. In this work, we apply molecular-level simulations to explore adsorption and diffusion behavior of methane, as a proxy of shale gas, and methane/carbon dioxide mixtures in realistic models of organic materials. We first use molecular dynamics simulations to generate the porous structures of mature and overmature type-II organic matter with both micro- and mesoporosity, and systematically characterize the resulting dual-porosity organic-matter structures. We then employ the grand canonical Monte Carlo technique to study the adsorption of methane and the competing adsorption of methane/carbon dioxide mixtures in the organic-matter porous structures. We complement the adsorption studies by simulating the diffusion of adsorbed methane, and adsorbed methane/carbon dioxide mixtures in the organic-matter structures using molecular dynamics.     

Piezo-elasticity and stability limits of monocrystal methane gas hydrates: Atomistic-continuum characterization

Gas hydrates are guest-host crystalline materials formed by water cages and guest gases such as methane and carbon dioxide under simultaneously relative high-pressure and low-temperature conditions. With this unique guest-host structural feature, gas hydrates can be used for gas storage and carbon dioxide (CO₂) sequestration, creating challenges such as flow assurance and geological stability. Some of these challenges are related to material instabilities caused by changing external conditions. Thus, this paper aims to determine the theoretical pressure stability limits of monocrystal defect-free sI methane gas hydrates at 0 K using accurate density functional theory to simulate the hydrate's thermodynamic and elastic responses under varying pressures. The pressure stability limits are determined by Born stability criteria and piezo sensitivity factors. The important brittle-to-ductile transitions of gas hydrates are established. Also, polycrystalline mechanical properties, including the Poisson ratio and Young modulus, are calculated from the second-order elastic constants obtained from the monocrystal sI methane hydrates, which provide the upper bounds. Taken together, the piezo-sensitivity of a complete set of elastic properties of sI methane gas hydrates and material stability limits determined by atomistic calculations provide new data and fundamental understanding for technological applications.     

Kinetic separation of carbon dioxide from hydrocarbons using carbon molecular sieve

Experimental results are reported on a pressure swing adsorption (PSA) process using carbon molecular sieve (CMS) for the separation of a gas mixture containing carbon dioxide, hydrocarbons (methane, ethane, propane, etc.) and nitrogen. This PSA process has direct applications in carbon dioxide removal or purification from landfill gas, natural gas processing plants and tertiary oil recovery effluent streams. The CMS-based PSA process separates the carbon dioxide in a single stage by using the differences in component diffusivities. This approach, therefore, provides a significant advantage compared to conventional equilibrium adsorption processes which require one separation stage for removing components such as ethane and propane that are more strongly adsorbed than carbon dioxide and another separation stage for removing components such as methane and nitrogen that are less strongly adsorbed than carbon dioxide. The CMS-based PSA process operates between a feed pressure of 20 to 40 bars and a regeneration pressure of 1.5 bars at ambient temperature and produces a 98+% carbon dioxide product. The PSA process can be integrated with a liquid carbon dioxide plant to produce food grade product.     

Investigation of carbon dioxide photoreduction process in a laboratory-scale photoreactor by computational fluid dynamic and reaction kinetic modeling

The production of solar fuels via the photoreduction of carbon dioxide to methane by titanium oxide is a promising process to control greenhouse gas emissions and provide alternative renewable fuels. Although several reaction mechanisms have been proposed, the detailed steps are still ambiguous, and the limiting factors are not well defined. To improve our understanding of the mechanisms of carbon dioxide photoreduction, a multiphysics model was developed using COMSOL. The novelty of this work is the computational fluid dynamic model combined with the novel carbon dioxide photoreduction intrinsic reaction kinetic model, which was built based on three-steps, namely gas adsorption, surface reactions and desorption, while the ultraviolet light intensity distribution was simulated by the Gaussian distribution model and Beer-Lambert model. The carbon dioxide photoreduction process conducted in a laboratory-scale reactor under different carbon dioxide and water moisture partial pressures was then modeled based on the intrinsic kinetic model. It was found that the simulation results for methane, carbon monoxide and hydrogen yield match the experiments in the concentration range of 10⁻⁴ mol·m^–3 at the low carbon dioxide and water moisture partial pressure. Finally, the factors of adsorption site concentration, adsorption equilibrium constant, ultraviolet light intensity and temperature were evaluated.     

SOFC中低浓度干甲烷在Ni/YSZ阳极上的反应

固体氧化物燃料电池(SOFC)趋向于直接使用甲烷天然气为燃料,确定甲烷在固体氧化物燃料电池阳极发生的化学与电化学反应非常重要.以Ni/YSZ为阳极、YSZ板做电解质、LSM为阴极,用涂浆法制作电解质支撑的电池,研究低浓度干甲烷在固体氧化物燃料电池中的反应.改变甲烷浓度、电池工作温度、电解质厚度,用在线色谱测量不同电流密度下,阳极出口气体产生速率.根据阳极出口气体产生速率变化,分析干甲烷在阳极的反应变化.通过氧消耗计算和转移电子数的分析,说明甲烷在电池阳极发生不同类型的反应.电流密度小时,甲烷发生部分氧化反应.电流密度大时,发生氢氧化和CO氧化,部分甲烷发生总反应为完全氧化的反应.部分甲烷发生完全氧化反应的同时,部分甲烷仍发生部分氧化反应,但其反应速率随电流密度增加逐渐降低.甲烷浓度和试验温度增加,甲烷开始发生完全氧化的电流密度增加.