CDFT的两种改进算法表征活性炭孔径分布的比较

为了提高经典密度泛函理论CDFT（classical density functional theory）在预测活性炭孔径分布时的准确性,比较了两种基于活性炭孔壁表面粗糙度影响的CDFT改进算法。结合狭缝孔壁上相同的碳原子密度分布,分别利用平滑密度近似（SDA）和基本测量理论（FMT）求解二元流体混合态的过剩自由能展开项,并预测氩气在非石墨化炭黑BP280上的吸附平衡。根据87.3 K下活性炭吸附氩气等温线,确定不同孔径的理论等温线核后,利用优化函数计算活性炭孔径在0.35~12 nm的分布。结果表明,MNLDFT算法预测孔径分布具有连续分布性,活性炭的比表面积为1252.63 m2/g;QSDFT算法测定的PSD(pore size distribution)在1 nm处具有断点,测定的活性炭比表面积为1431.64 m2/g,这一结果与通过BET方法确定的比表面积1445 m2/g接近。运用QSDFT来表征活性炭孔径分布更合理。     

基于Maxwell-Stefan双扩散模型的煤层气注气数值模拟

目前煤层气注气数值模拟软件中均以扩展Langmuir模型模拟多组分气体吸附/解吸,以拟稳态单孔扩散模型和Fick定律描述煤层基质中气体扩散,虽然简单,便于应用,但存在较大局限性。以试验数据为依据,评价扩展Langmuir、IAS和2D PR-EOS多组分气体吸附模型可靠性,并建立Maxwell-Stefan双扩散模型模拟气体扩散过程。最后,将双扩散模型与煤储层气水两相多组分渗流模型耦合,利用IMPES方法求解研究煤层气注气过程。研究表明:2D PR-EOS模型预测结果优于扩展Langmuir和IAS模型;注气初期基质中多组分气体吸附和甲烷解吸速率较快,之后逐渐变缓;该模拟方法可以较为准确地模拟煤层气衰竭和注气开发过程,预测煤基质中气体各组分浓度分布,为煤层气注气开发的研究及现场应用提供有效的技术手段。     

不同注源气体置换-驱替煤层甲烷突破时间的差异性分析

煤层注气促抽瓦斯是近年来逐步发展起来的强化抽采技术,注气突破时间是该技术的重要参数之一。突破时间是指注源气体从煤层一端注入到另一端检测出该组分所需的时间,它与注源气体的吸附性、渗透性有着密切的关系。为了研究渗透和吸附对注气突破时间的影响规律,利用含瓦斯煤层注气模拟实验装置,进行了煤层注He,N_2和CO_2置换-驱替CH_4的实验室模拟实验。实验结果表明,不考虑煤对气体吸附性的纯渗流条件下,N_2和CO_2纯渗流突破时间极短,仅为总突破时间的5.93%和0.28%,表明气体吸附性能是引起总突破时间差异的主要因素;另外,随着注源气体吸附性增强,其总突破时间大幅度增加,He,N_2和CO_2的总突破时间分别为0.92,14,246 min。实验结果结合理论模型计算分析得出:注源气体吸附性越强,总突破时间越长,注气初期的置换效应越明显,但随着注源气体的吸附不断趋于饱和,其驱替效应逐渐增强。     

Effects of calcination temperature on the structure and adsorption performance of Ce-Mn/AC materials

Activated carbon-supported bimetallic cerium-manganese (Ce-Mn/AC) materials were prepared by impregnation method to study the effect of calcination temperature on the structure and adsorption performance of absorbents. The obtained materials were characterized by using X-ray diffraction (XRD), scanning electron microscope (SEM), N₂ adsorption-desorption isotherm, Fourier transformed infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS). As the results showed, the diffraction peaks of CeO₂ decreased and even disappeared; Mn species were transformed from Mn₃O₄ to Mn₂O₃ on the surface of Ce-Mn/AC; the BET specific surface area increased first and then decreased on the elevating calcination temperature; the number of acid functions of AC was reduced after being modified by cerium and manganese. All these changes were directly attributed to the synergistic effects between MnO_x and CeO₂. AC800 exhibited the best phenol adsorption capacity. The adsorption mechanism of phenol on Ce-Mn/AC was discussed with hydrophilic (hydrophobic) interaction and hard and soft acid-base theory.     

基于核磁共振T2谱的页岩岩心孔隙分布量化表征方法

由于类固体信号的干扰,导致直接从流体饱和页岩的核磁共振T2谱（NMR-OS）中得到的孔隙分布结果不准确,通过采用Beta峰模型统一描述类固体和流体的横向弛豫峰分布,结合六阶导分析和最小二乘法,提出了一种简单、快速、准确分析页岩孔隙分布的核磁共振-反褶积方法（ND）,并对其验证和开展实例应用,分析结果表明：1)该方法可同时拟合对称峰和非对称峰,且峰的衰减速率高,能有效避免基线远离峰情况;2)无需洗油、烘干等复杂的样品预处理过程,可简单、快速得到峰的个数以及各峰参数的估计和约束条件,进而将类固体干扰信号分离出来;3)孔径小于10 nm时,ND方法得到的孔径分布与低温液氮吸附方法（LTNA）和洗油烘干后的T2谱曲线相减反演方法（NMR-O）的结果具有很好的一致性,当T2<1 ms时,ND方法测得的孔隙分布相对误差绝对值（<15%）明显小于通过NMR-OS方法得到的孔隙分布结果（>135%）。     

Synthesis of mesoporous polymeric carbon nitride exhibiting enhanced and durable visible light photocatalytic performance

A thiourea precursor was employed to synthesize mesoporous carbon nitride(C3 N4) by a thermal polycondensation process with high surface area SiO2 and nanosphere SiO2 as two types of hard templates. The resultant mesoporous C3 N4 samples have high surface areas(105–112 m2/g) and mesopores with narrow sizes distribution(9.3 nm). Photocatalytic performance was evaluated by removal of NO in air under visible light irradiation. The results showed that mesoporous C3 N4 samples exhibited significantly improved photocatalytic activity in comparison with bulk C3 N4, which also exceeded that of N-doped TiO2 and C-doped TiO2. The activity enhancement can be ascribed to the synergistic effects of large surface area and pore volume, enhanced light-harvesting ability, increased redox potential, and reduced recombination of charge carriers. In addition to the high activity, the mesoporous C3 N4 samples also showed high photochemical stability. The mesoporous C3 N4 photocatalysts with enhanced and durable activity could provide a new efficient material for environmental pollution control.     

FeCl3-CO2体系改性活性炭的研究

以FeCl₃为催化剂，用CO₂对原料炭（LAC）进行改性。用乙醇、亚甲基蓝和VB₁₂表征其吸附性能；氮气吸附（温度为77K）方法测定活性炭的孔结构，计算其BET比表面积；密度函数理论（DFT）表征其孔径分布。实验结果表明，改性后活性炭的BET比表面积和总孔容增加了1倍，使改性后活性炭对乙醇、亚甲基蓝和VB₁₂的吸附量都有显著提高，且改性后活性炭的孔径分布更趋均匀。     

Hydrogen Adsorption on Metal-Organic Framework MOF-177

This review summarizes the recent literature on the synthesis, characterization, and adsorption properties of meal-organic framework MOF-177. MOF-177 is a porous crystalline material that consists of Zn4O tetrahedrons connected with benzene tribenzoate (BTB) ligands. It is an ideal adsorbent with an exceptionally high specific surface area (BET4500 m2/g), a uniform micropore size distribution with a median pore diameter of 12.7 ?, a large pore volume (2.65 cm3/g), and very promising adsorption properties for hydrogen storage and other gas separation and purification applications. A hydrogen adsorption amount of 19.6 wt.% on MOF-177 at 77 K and 100 bar was observed, and a CO2 uptake of 35 mmol/g on MOF-177 was measured at 45 bar and an ambient temperature. Other hydrogen properties (kinetics and heat of adsorption) along with adsorption of other gases including CO2, CO, CH4, and N2O on MOF-177 were also be discussed. It was observed in experiments that MOF-177 adsorbent tends to degrade or decompose when it is exposed to moisture. Thermogravimetric analysis showed that the structure of MOF-177 remains intact at temperatures below 330℃ under a flow of oxygen, but decomposes to zinc oxide at 420℃.     

聚三嗪亚胺的合成及从水溶液中吸附铀

利用熔盐法合成了聚三嗪亚胺(polytriazineimide,PTI),并用来吸附水中的U(VI)。在常温下,PTI对铀的最大饱和吸附量达到了135.5 mg/g,与g-C₃N₄相比,是g-C₃N₄饱和吸附量的54.2倍。通过对动力学与吸附等温线模型的探究,发现PTI对U(VI)的吸附符合准一级动力学模型,说明PTI吸附U(VI)属于物理吸附。同时,Langmuir吸附等温线模型能更好地拟合PTI对U(VI)的吸附过程,说明U(VI)在PTI上属于单层吸附。通过对吸附铀后的材料进行XPS表征,发现铀在吸附后的价态没有改变,仍为U(VI)。     

Hydrotalcite-supported Pd-Cu catalyst for nitrate adsorption and reduction from water

With the rapid development of industry and agricul- ture, the nitrate contamination in groundwater becomes increasingly serious in many countries [1]. Therefore, the remediation of nitrate-contaminated groundwater is one of the targets urgently confronted…     

HZSM-5分子筛的改性及其催化裂解废轮胎制备低碳烯烃

用不同浓度氢氧化钠溶液对硅铝比为200的商业HZSM-5分子筛进行了扩孔改性,利用粉末X射线衍射、扫描电镜、NH₃程序升温脱附和N₂吸脱附对改性分子筛的晶体结构、孔结构、形貌和酸性进行了表征,考察了改性HZSM-5分子筛在催化裂解废轮胎反应中的性能.结果表明,通过改变氢氧化钠溶液的浓度,可以一定程度调控分子筛晶体的孔结构和酸量.随着碱浓度增大,改性HZSM-5分子筛平均孔径增大,而介孔孔容和酸量先增加后减少.经0.4 mol/L氢氧化钠溶液改性处理后的HZSM-5分子筛催化剂,介孔孔容及酸量最大,其催化裂解废轮胎低碳烯烃选择性最高,达到了32.39%,远高于商业HZSM-5分子筛.      

Nb(100)表面吸附和解离氮气的密度泛函理论计算

【目的】研究多个氮气分子吸附于Nb(100)表面的问题.【方法】采用基于密度泛函理论的总能计算方法研究Nb(100)表面吸附多个氮气分子。【结果】得到0.25,0.50,0.75覆盖度(ML)下氮气分子吸附Nb(100)表面的结构,能量,振动频率以及表面功函数等性质,并进一步讨论了氮气分子在Nb(100)表面吸附与分解的物理机制。【结论】吸附在Nb(100)表面的氮气分子容易发生解离,部分氮气分子以分子态的形式吸附,而部分氮气分子则分解成原子吸附于铌表面。     

Carboxyl-modified hierarchical wrinkled mesoporous silica supported TiO2 nanocomposite particles with excellent photocatalytic performances

Titanium dioxide (TiO₂) is a common photocatalyst for organic pollutants degradation. However, in practical application, the poor adsorption capacity of pure TiO₂ seriously impeded its efficiency in the degradation of organic molecules. In this work, a series of hierarchical wrinkle mesoporous silica supported TiO₂ nano-composite particles (TiO₂ @WMS-COOH) were successfully prepared. Thanks to their high surface areas, large pore volumes and mesoporous structures, these materials showed high adsorption capacity and excellent photocatalytic performance towards dye molecules, which is comparable to or even better than commercial catalyst P25. Moreover, their photocatalytic efficiency can be further enhanced by increasing the calcination temperature during preparation process. Therefore it can be concluded that the TiO₂ @WMS-COOH particles may find promising applications in the photodegradation of organic pollutants.     

活性炭孔结构的混合碱改性

具有较大比表面积的且以微孔孔隙居多的活性炭对气体小分子具有较好的吸附性能,以椰壳活性炭为原料、KOH/NaOH为活化扩孔剂,考察了温度、时间以及KOH与NaOH的质量比对活性炭孔隙结构的影响,使用N2在77 K下对产品活性炭进行表征测试。表征结果表明,当m(KHO)∶m(NaOH)为4∶1、溶液浓度为50%时,活性炭在600℃下活化4 h所得的活性炭产品平均孔径最大。对比HK模型和DFT模型对微孔活性炭孔径分布的分析结果,表明DFT模型更符合实际情况。经过孔结构改性的活性炭对CH4与CO2吸附能力均有提高。     

化学修饰型PRB反应介质草炭土的制备及性能

选用11种化学试剂对渗透性反应墙(PRB)反应介质草炭土进行修饰, 并分析吸附前后草炭土的微观结构. 结果表明： 经HCl,NaOH,CH₃COOH,Mg²⁺,Na₃C₆ H₅O₇和PO^3-₄修饰后的草炭土吸附总石油烃(TPH)的能力降低; 经Ca²⁺ ,Fe³⁺,Cu²⁺,乙二胺四乙酸(EDTA)和腐植酸修饰后的草炭土吸附TPH的能力升高, 其中, 经0.100 mol/L Ca²⁺修饰后的草炭土去除地下水中TPH为92.26%, 其吸附规律符合Langmuir等温吸附方程, 理论最大吸附量为2.04 g/g; 吸附动力学规律遵循准二级动力学方程, 吸附60 min后达到动态平衡; 草炭土通过物理吸附和化学吸附去除石油污染物.     

Equilibrium geometric structure and electronic properties of Cl and H2O co-adsorption on Fe (100) surface

Based on the first principles density functional theory, the equilibrium geometric structure and surface electronic properties of Cl and H₂O co-adsorption on the Fe (100) surface are investigated. The results indicate that the optimal adsorption site for Cl and H₂O co-adsorption on the Fe (100) surface is the location of Cl at the bridge site and H₂O at the top site. Compared with the Fe (100)/H₂O adsorption system, remarkable changes in geometric structure and electronic properties occur, owing to the presence of Cl in the Fe (100)/(H₂O+Cl) adsorption system. The analysis of equilibrium geometric structure and surface electronic properties shows that the presence of Cl in the Fe (100)/(H₂O+Cl) adsorption system unstablizes the Fe surface, making it easy to lose electrons. Supported by the National Natural Science Foundation of China (Grant Nos. 50675112, 50721004) and Research Fund for the Doctoral Program of Higher Education (Grant No. 20070003103)     

巨正则系综Monte Carlo模拟CO/H2在碳纳米狭缝孔内的吸附和分离

采用巨正则系综Monte Carlo（GCMC）方法研究了CO/H₂在碳纳米狭缝孔中的吸附和分离。H₂和CO均采用单点Lennard Jones（LJ）模型,孔壁作用势则用Steele 10-4-3模型描述。研究结果表明,混合物中H₂的吸附量高于与其分压相同压力下纯H₂的吸附量,而CO则与之相反。通过不同孔宽下的模拟,得到吸附分离的最佳孔宽为0.74nm,此时H₂和CO的吸附量分别为2.0和12.9mmol/g,CO对H₂的平衡分离因子达到6.5(温度为300K,压力为1.0MPa,等物质的量混合气体)。此外,还详细研究了压力、温度和混合气体组成对吸附量和平衡分离因子的影响,发现平衡分离因子随压力降低而提高,而低压下尤其明显,0.03MPa时平衡分离因子可超过9.0。随温度升高,平衡分离因子近乎线性下降;而随着体相混合气体中H₂组成的增加,平衡分离因子显著提高。     

Measurement of laminar burning velocities and analysis of flame stabilities for hydrogen-air-diluent premixed mixtures

The laminar burning velocities and Markstein lengths of the hydrogen-air-diluent mixtures were meas-ured at different equivalence ratios (0.4―1.5), different diluents (N2, CO2 and 15%CO2+85%N2) and di-lution ratios (0, 0.05, 0.10 and 0.15) by using the outwardly expanding flame. The influences of flame stretch rate on the flame propagation characteristics were analyzed. The results show that both the laminar burning velocities and the Markstein lengths of the hydrogen-air-diluent mixtures decrease with the ...     

吸附树脂对油气分子吸脱附性能实验研究*

吸附材料的性能对油气分子吸附过程起着关键性的作用。系统表征了三种吸附树脂材料(HX-1型、HX-2型和HX-3型)孔结构信息,计算了相应的标准特征吸附能,考察了其初次吸附钝化过程和动态吸附过程特性。实验结果表明,三种吸附树脂均具有丰富的微孔和介孔分布,其中HX-1型树脂的微孔孔容与微孔占有率最大,通过相应的标准吸附特征能可反映其微孔分布;三种吸附树脂的初次钝化吸附量和动态吸附量变化情况相似,均为HX-1型树脂最大,HX-2型树脂次之,HX-3型树脂最小。吸附树脂中的微孔分布决定了油气分子吸附过程,从而影响对应的吸附量。     

Experimental and kinetic study on ignition delay times of methane/hydrogen/oxygen/nitrogen mixtures by shock tube

Ignition delay times of methane/hydrogen/oxygen/nitrogen mixtures with hydrogen amount-of-substance fractions ranging from 0–20% were measured in a shock tube facility.The ambient temperature varied from 1422 to 1877 K and the pressure was maintained at 0.4 MPa behind the reflected shock wave.The experiments were conducted at an equivalence ratio of 2.0.The fuel mixtures were diluted with nitrogen gas so that the nitrogen amount-of-substance fraction was 95%.The experimental ignition delay time of the CH4/H2 mixture decreased as the hydrogen amount-of-substance fraction increased.The enhancement of ignition by hydrogen addition was weak when the ambient temperature was >1750 K,and strong when the temperature was <1725 K.The ignition delay time of 20% H2/80% CH4 was only one-third that of 100% CH4 at 1500 K.A modified model based on GRI-Mech 3.0 was proposed and used to calculate the ignition delay times of test mixtures.The calculated results agreed with the experimental ignition delay times.Normalized sensitivity analysis showed that HO·+H2 →H·+H2O was the main reaction for the formation of the H· at 1400 K.As the hydrogen amount-of-substance fraction increased,chain branching was enhanced through the reaction H·+O2→O·+HO·,and this reduced the ignition delay time.At 1800 K,the methyl radical (H3C·) became the key species that influenced the ignition of the CH4/H2/O2/N2 mixtures,and sensitivity coefficients of the chain termination reaction 2H3C·(+M)→C2H6(+M),and chain propagation reaction HO2+H3C·→HO·+CH3O decreased,which reduced the influence of hydrogen addition on the ignition of the CH4/H2 mixtures.