生物甲烷膜分离提纯系统的设计与优化

以厌氧发酵生物气为原料生产压缩天然气是大规模利用生物质资源的重要途径。首先,在过程模拟软件UniSim Design中基于有限元方法建立了中空纤维膜的离散数值计算模型,适合于模拟渗透切割比非常高的生物甲烷膜分离过程。以单级聚酰亚胺膜分离系统为例研究了关键操作条件--膜的进料压力对处理能力、甲烷收率及压缩天然气生产单耗的影响。目前的评估体系下,提高进料压力有利于提高处理能力和甲烷回收率,而压缩天然气生产单耗在2.70 MPa时最低,为0.46 kW·h·m^-3压缩天然气。通过分析渗透气的甲烷浓度变化趋势,开发了一级二段气体膜分离系统,兼具流程简单、设备投资低、甲烷收率高、产值高的优点。以处理1000 m³·h^-1生物气为例,甲烷收率达95.0%,压缩天然气产量500 m³·h^-1。对应地,装置总投资为3.8×10⁶ CNY,年运行费用及设备折旧为1.5×10⁶ CNY,年经济效益（毛利）超过2.50×10⁶ CNY。     

天然气非催化部分氧化技术在乙二醇项目上的应用

通过对比分析蒸汽转化法、自热重整法和非催化部分氧化法等天然气生产合成气的工艺技术，得出天然气非催化部分氧化法生产合成气装置工艺流程和设备结构简单，投资低，操作可靠，合成气中H₂/CO体积分数比接近于2，是乙二醇合成的理想原料气。介绍了某15万t/a天然气制乙二醇项目中天然气非催化部分氧化生产合成气的工艺流程，详述了转化炉、废热锅炉的设计要点和系统的控制方案及H₂/CO体积比调节方法。运行结果表明：天然气非催化部分氧化生产的合成气中H₂/CO体积分数比为1.99，比天然气消耗为368 m³/[1 000 m³(CO+H₂)]，比氧气消耗为258 m³/[1 000 m³(CO+H₂)]，合成气中甲烷体积分数为0.3%。     

HZSM5分子筛膜复合二氧化锡对甲烷的气敏性能研究

采用液相氧化法制备二氧化锡纳米颗粒,并利用浸渍法制备Pd负载二氧化锡纳米材料,通过丝网印刷得到气敏传感膜并在其表面印刷分子筛层。基于动态气敏测试系统探究传感器对甲烷气体的灵敏度及其在CO和乙醇干扰气体下的选择性。研究结果表明,在Pd-SnO₂敏感层表面印刷Pd-HZSM5层后,传感器对甲烷的响应能力显著提高,并且在体积分数为5×10^-4的CO存在时,对甲烷的选择性也得到明显的提升。同样,在质量分数为2×10^-5乙醇的存在下,传感器对甲烷的响应也没有受到干扰。通过对分子筛进行表征和催化分析,发现Pd-HZSM5对CO的催化效率可达100%,使得CO在扩散过程中被催化氧化,这可能是印刷Pd-HZSM5分子筛膜从而提高传感器选择性的主要原因。同时研究还表明,在敏感层表面印刷分子筛层并不会影响传感器的响应和恢复速率。     

重金属复合污染河道底泥淋洗动力学特征

文中以上海市崇明某河道底泥为研究对象，研究在不同pH、温度条件下，底泥中Cd、Cu、Pb的淋洗动力学特征(淋洗液为纯水),通过Tessier连续提取法分析底泥淋洗前后的重金属形态变化。结果表明：重金属淋洗量随时间增长呈上升趋势，且分为快反应、慢反应及淋洗平衡3个阶段，Elovich方程可以较好地描述该淋洗过程(R²=0.670～0.983,SE=3.296×10^-14～1.130×10^-6),略优于双常数方程(R²=0.653～0.982,SE=3.366×10^-14～1.381×10^-6),说明该淋洗过程为非均相扩散过程；pH降低(pH值=5～9)、温度升高(15～35℃),重金属淋洗量均有增加；淋洗脱除的重金属主要为不稳定形态，有机结合态重金属的去除与底泥中富里酸含量有较强相关性，淋洗脱除率表现为Cd>Pb>Cu,即31.34%>23.85%>22.86%,重金属的环境危害性有所下降。     

木质素生物炭磺酸对水中阳离子染料的吸附性能与机制

以木质素磺酸钠(LS)为原料,采用浓硫酸一步氧化碳化的方法在60℃和210℃下分别制备了木质素生物炭磺酸SLBC-60和SLBC-210。SLBC-60磺酸基、羧基和酚羟基含量分别为1.66,1.40,4.41 mmol/g,而SLBC-210磺酸基、羧基和酚羟基含量分别为0.34,3.22,5.41 mmol/g。对比评价了它们对亚甲基蓝(MB)的吸附效果,结果显示,在pH=1～10溶液中,SLBC-60对MB保持高吸附量(>463.9 mg/g)和高去除率(>91.9%),而SLBC-210对MB吸附量<231.5 mg/g、去除率<45.8%,结合生物炭结构和Zeta电位分析,这可能与SLBC-60富含磺酸基官能团及其在pH=1～10溶液中表面均富集负电荷有关;优化pH、吸附剂加入量、吸附时间等参数,得到SLBC-60对MB、罗丹明B和孔雀石绿饱和吸附量分别为755.1,926.1,1 008.2 mg/g,且吸附性能不受一价金属离子影响。此外,SLBC-60对MB的吸附等温线符合Langmuir模型(R²=0.998 9),吸附动力学符合准二级动力学方程(R2=0.998 9),吸附动力学符合准二级动力学方程(R²=0.999 5),说明该吸附以单层化学吸附为主。因此,改性制备的木质素生物炭磺酸可作为高效的阳离子染料吸附剂,有望应用于印染废水治理。     

基于紫外吸光度的生物柴油氧化降解程度分析

为快速检测出生物柴油的氧化降解程度,利用小桐子生物柴油在氧化过程中共轭二烯以及共轭三烯的变化致使230nm处吸光度随氧化时间延长逐渐增强、270nm处吸光度逐渐减弱的现象,建立了生物柴油酸值与紫外吸光度的线性、指数、对数和乘幂这4种模型。留一法交叉验证显示线型模型的预测均方根误差最小,预测值与实测值的相关性最高。利用最小二乘法建立酸值与吸光度线性方程,并对模型进行了验证。结果表明：该拟合方程的拟合优度R²为0.987,表明该预测模型的拟合效果较好;模型验证中实测值与预测值的拟合优度R²为0.980;样本的最大相对误差为5.27%,该模型具有较高的准确度与精确度,可以用该方法代替滴定法快速准确地预测出酸值来表征氧化降解程度。     

基于径向力平衡的鼓泡塔二维流体力学模型

提出了一种鼓泡塔二维轴对称流体力学模型,模型中将气泡所受的升力以及湍动扩散力作为形成塔内气含率稳定分布的主要机制.采用Fluent 6.3流体力学软件求解模型,能得到稳定的二维流场,气含率与液速分布与实验值吻合良好,模型能准确反映表观气速(0.12～0.62 m·s^-1)以及塔径(ø200 mm、ø500 mm、ø800 mm)对流型的影响.利用该模型对更大直径鼓泡塔的流动参数进行了预测,结果与文献给出的经验关联式相符.     

利用元胞自动机模拟CO2或水蒸气在液态甲烷中的凝华行为

利用热质传输方程、流体动力学方程、连续性方程和生长动力学规律分析了晶体生长的物理机制,同时利用元胞自动机法建立了凝华相变的模型,通过计算机模拟了水蒸气以及CO₂在低温液态甲烷中凝华形成晶体的过程,得到了冰晶的二维模拟结果以及CO₂晶体的二维和三维模拟结果。结果显示该模型能够模拟出指定温度和过饱和度下的冰晶以及CO₂晶体生长过程。冰晶以及CO₂晶体生长过程中具有一定的各向异性。该模型可以用于分析LNG中冰晶以及CO₂晶体的形成,有利于改善LNG储存运输使用等过程中的技术流程。     

中药通草渣对水中亚甲基蓝吸附效能与机理的研究

选择中药通草残渣作为生物吸附剂,对水中亚甲基蓝染料(MB)进行吸附,探究其吸附效能和吸附机理。采用响应面法中Box-Behnken Design,考察吸附剂投加量、pH、MB溶液初始质量浓度和吸附时间对通草残渣去除MB的影响,并对实验参数进行优化。在最优参数组合条件下,通过实验验证其预测值和实验值符合度一致。吸附等温线与动力学模型拟合结果显示：通草残渣对水中亚甲基蓝的吸附过程符合Langmuir模型(R²=0.997)和准二级动力学模型(R²=0.999 8),其吸附量为115.72 mg/g,表明该吸附过程以均匀的单层吸附为主,对亚甲基蓝的吸附速率受膜扩散和颗粒内扩散共同控制。同时,该吸附过程存在Na⁺、K⁺、Ca²⁺的交换情况,对Cl^-、SO₄^2-的影响不明显。表征结果显示,通草残渣吸附水溶液中的亚甲基蓝后,出现比表面积增大、孔容加深、孔径缩小、电荷强度变小、红外基团变化不大的特点,提示通草残渣对水中亚甲基蓝...     

卤代苯对呆头鱼、发光菌急性毒性的构效关系研究

基于分子拓扑邻接矩阵,计算了11种卤代苯的分子形状指数（K_m）。通过最佳变量子集回归方法,建立了11种上述化合物对发光菌和呆头鱼等急性毒性(pC₅₀:pEC₅₀,pLC₅₀)的QSAR模型。对于发光菌的pEC₅₀模型的判定系数（R²）和校正判定系数R_adj²依次为0.884和0.855,相应呆头鱼pLC₅₀模型为0.897和0.871。经R²,R_adj²等检验,上述模型具有令人满意的稳健性和预测能力。     

Oxygen permeation in Ag/YSZ air cathodes

Potential-step chronoamperometry of Ag/YSZ (YSZ = yttria stabilized zirconia) air cathodes was measured at 350–500°C in air. A decay equation was derived by solving Fick's diffusion equation assuming a diffusion mechanism in which oxygen diffuses through the solid silver and is reduced to oxide ion at the Ag-YSZ. The theoretical decay curves calculated from the decay equation were fitted to the experimental data by optimizing the equation parameters. The diffusion constant calculated from the time constant, which was obtained as one of the optimized parameters, agreed with the known values. This agreement suggests that the silver electrode shows bulk oxygen permeation.     

Factors controlling diel patterns of methane emission via rice

Methane emissions from flooded rice grown under greenhouse conditions were monitored using a closed chamber technique. The three rice cultivars showed similar diel emission patterns though the amplitudes differed. Variation in emissions (maximum emission rate) from the different cultivars ranged from 0.164–0.241 mg/pot/h at tillering stage, 0.714–2.334 mg/pot/h at heading stage, 0.399–1.393 mg/pot/h at ripening stage. The methane emissions increased in the morning at accelerating rates, reached a maximum in the early afternoon, then decreased rapidly to constant rates during the night. The diel emission pattern was modeled using a Gaussian equation for daytime, and a constant for nocturnal emissions. Applying an Arrhenius equation, more than 90% of the diel variation of methane emissions could be predicted from soil temperature fluctuations. The predictions improved by using a diffusion model based on soil temperature and dissolved methane concentrations in soil solution. Soil temperature and methane concentration in soil solution are the two major factors controlling diel methane emissions.     

Evaluation of methane oxidation in rice plant-soil system

Mechanisms of methane oxidation in the plant-soil system of rice were studied in a pot experiment using two cultivars (PSBRc-30 and IR72) at two growth stages (flowering and heading). Methane emission was measured by chambers, while methane oxidation was determined through propylene amendment as an alternative substrate to be propylene oxide (PPO) and acetylene as an inhibitor for methane oxidizing (methanotrophic) bacteria. Cell numbers (methanotrophic and methanogenic bacteria) were determined by the most probable number method. The cultivar PSBRc-30 consistently showed higher methane emission rates than IR72. Methane flux clearly decreased from flowering to heading stages in both cultivars. This observation was largely reflected by trends in the mechanisms involved: either methanogenic cell numbers or activities decreased with plant age while methanotrophic cell numbers or activities generally showed an increasing trend. The methanogenic population was in the order of 10⁵ g^–1 dry soil, while the population of methanotrophs ranged from 10⁴ to nearly 10⁶ g^–1 dry soil. Methanotrophic activity followed the order; root (1.7–2.8 nL PPO g^–1 DM h^–1) > shoot (0.7–2.0) > soil (0–0.4) when the consumption of alternative substrate was related to dry matter. Derived from the estimated amounts of soil and plant biomass in the pot experiment, however, the soil generally accounted for more than 90% of the total methane oxidation. Within the plant segments, methane oxidation activities in the root exceeded those of the shoot by factor of approximately 10.     

Biocatalytic methane oxidation

The kinetics of biocatalytic methane oxidation should be known to make use of this process in environmental biotechnology. Here, biocatalytic methane oxidation is described using multisubstrate kinetic models (studies were performed at 30°C). The dependence of the specific growth rate of microorganisms (biomass buildup per unit time divided by the amount of biomass) on the methane and oxygen concentrations in the culture liquid is best describable in terms of the Moser-Moser multisubstrate kinetic model. The methane and oxygen consumption coefficients and the carbon dioxide yield coefficient have been determined. These data are used to construct a mathematical model for heterogeneous biocatalytic methane oxidation. With this model, it is possible to predict the behavior of the biocatalytic system under given conditions.     

甲烷常压非催化部分氧化制合成气研究

考察了常压下甲烷非催化部分氧化制合成气过程中,甲烷转化率、气体产物产率以及积炭率随反应器温度、进气配比、原料气流量变化的影响。通过考察反应器温度对制备合成气过程的影响结果,分析了甲烷非催化部分氧化制合成气过程的反应机理。     

Multiple linear equation of pore structure and coal–oxygen diffusion on low temperature oxidation process of lignite

This work aimed at studying the feasibility of calculating the coal–oxygen diffusion properties during the low temperature oxidation process of lignite so as to predict its spontaneous combustion process. Coal samples were oxidized in air ambient under different temperatures. Scanning Electron Microscope was used to indicate the surface morphology changes of oxidization. Then, based on fractal theory and flow characteristics, the fractal dimension of gas diffusion in the pore ways was calculated under different temperature. Considering pore size distribution, connectivity distribution and Fick diffusion mechanisms, the relationship between the gas diffusivity change with pore area fractal dimension and porosity was investigated, and multiple linear equation of the coal–oxygen diffusion coefficients and pore parameters was obtained. Comparison between the experimental data and model prediction verifies the validity of the model. The research provides a theoretical basis for the prediction model of coal–oxygen diffusion law.     

Anaerobic Digestion Process of Food Waste for Biogas Production: A Simulation Approach

Anaerobic digestion (AD) involves a series of biological processes in which organic material is broken down and transformed into biogas. A simulation model of the AD process in treating food waste to produce biogas was developed using Aspen Plus software. The components list, thermodynamic property package, reaction list, reactor model, and process condition were specified in Aspen Plus. Sensitivity analysis was performed to study the effect of hydraulic retention time and changes in food waste composition on the biogas production. The methane composition in biogas decreased when the hydraulic retention time was increased which is due to the reduction of substrate consumption during the AD process. The process model is able to represent the AD process and provides a good approximation on the production of biogas under various process operating conditions.     

Modelling of multicomponent gas separation with asymmetric hollow fibre membranes—methane enrichment from biogas

A mathematical model for the dynamic performance of gas separation with high flux, asymmetric hollow fibre membranes was developed considering the permeate pressure build‐up inside the fibre bore and cross flow pattern with respect to the membrane skin. The solution technique provides reliable examination of pressure and concentration profiles along the permeator length (both residue/permeate streams) with minimal effort. The proposed simulation model and scheme were validated with experimental data of gas separation from literature. The model and solution technique were applied to investigate dynamic performance of several membrane module configurations for methane recovery from biogas (landfill gas or digester gas), considering biogas as a mixture of CO₂, N₂ and CH₄. Recycle ratio plays a crucial role, and optimum recycle ratio vital for the retentate recycle to permeate and permeate recycle to feed operation was found. From the concept of two recycle operations, complexities involved in the design and operation of continuous membrane column were simplified. Membrane permselectivity required for a targeted separation to produce pipeline quality natural gas by methane‐selective or nitrogen‐selective membranes was calculated. © 2012 Canadian Society for Chemical Engineering     

Ultraviolet Lamp Output Measurement: A Concise Derivation of the Keitz Equation

An equation relating the measured irradiance and the output power of a fluorescent lamp was derived by Keitz. The equation forms the basis for a new protocol that has been proposed for quantifying the total flux from an ultraviolet lamp. There has been confusion in the literature regarding the spatial distribution of flux from lamp emitters, which has led to emission models that are similar to the Keitz model but are incorrect. The Keitz equation is derived here from first principles in an effort to eliminate the confusion and present a correct method of calculating total flux.     

Reduction kinetics of SrFeO3−δ/CaO∙MnO nanocomposite as effective oxygen carrier for chemical looping partial oxidation of methane

Chemical looping reforming of methane is a novel and effective approach to convert methane to syngas, in which oxygen transfer is achieved by a redox material. Although lots of efforts have been made to develop high-performance redox materials, a few studies have focused on the redox kinetics. In this work, the kinetics of SrFeO_3−δ–CaO∙MnO nanocomposite reduction by methane was investigated both on a thermo-gravimetric analyzer and in a packed-bed microreactor. During the methane reduction, combustion occurs before the partial oxidation and there exists a transition between them. The weight loss due to combustion increases, but the transition region becomes less inconspicuous as the reduction temperature increased. The weight loss associated with the partial oxidation is much larger than that with combustion. The rate of weight loss related to the partial oxidation is well fitted by the Avrami–Erofeyev equation with n = 3 (A3 model) with an activation energy of 59.8 kJ∙mol^‒1. The rate law for the partial oxidation includes a solid conversion term whose expression is given by the A3 model and a methane pressure-dependent term represented by a power law. The partial oxidation is half order with respect to methane pressure. The proposed rate law could well predict the reduction kinetics; thus, it may be used to design and/or analyze a chemical looping reforming reactor.