确定多孔介质孔结构参数的渗流网络分析法

According to the simulation of nitrogen sorption process in porous media with three-dimensional network model, and the analysis for such a process with percolation theory, a new method is proposed to determine a pore structure parameter--mean coordination number of pore network, which represents the connectivity among a great number of pores. Here the “chamber-throat“ model and the Weibull distribution are used to describe the pore geometry and the pore size distribution respectively. This method is based on the scaling law of percolation theory after both effects of sorption thermodynamics and pore size on the sorption hysteresis loops are considered. The results show that it is an effective procedure to calculate the mean coordination number for micro- and meso-porous media.     

介孔材料低温氮气吸脱附的孔道网络模型

介孔结构的表征和分析对于介孔材料的开发至关重要,其中低温氮气吸脱附法是最常用的介孔表征方法之一。然而,目前氮气吸脱附法采用的分析模型仍基于平行孔假设,无法描述脱附过程堵孔现象,以及获取孔道连通性等重要孔结构信息。本文建立了低温氮气吸脱附的孔道网络模型,用于分析介孔结构对氮气等温吸脱附行为的影响。通过对比氧化铝材料的氮气吸脱附实验数据和模拟结果,证实了建立的孔道网络模型能很好地描述介孔材料中低温氮气吸脱附行为。模拟结果表明平均孔径较小时,毛细凝聚分压低,液氮堵孔效应显著,氮气吸脱附曲线回滞环的范围和面积较大;孔径分布较宽时,小孔和大孔数量均较多,毛细凝聚和堵孔效应显著,回滞环面积较大;孔道连通性不会影响吸附过程,但会通过改变堵孔效应显著影响脱附过程,连通性越差,堵孔效应越强。证实了堵孔效应对氮气脱附过程影响显著,因而氮气吸脱附法需要考虑堵孔效应,建立的孔道网络模型也可为介孔结构分析提供合理的模型工具。     

Analysis of the evolution of the pore size distribution and the pore network connectivity of a porous carbon during activation

The development of the microporosity, pore size distribution and pore network connectivity has been studied in the production of activated carbons from lignite char. Grand Canonical Monte Carlo simulation of adsorption was applied to the characterisation of a set of activated carbons produced at a sequence of times. The pore size distributions obtained from nitrogen at 77 K and ethane at 264 K were used as inputs to a method based on percolation theory to study the changing connectivity of the system. The incorporation of percolation concepts in the study of the porosity development gives an insight into the processes involved. The analysis is applied to a particular environmental application, the adsorption of phenanthrene.     

Evaluation of the pore size distribution in mercury porosimetry using computer simulations of porous media

The pore size distribution calculated using the Washburn equation was evaluated. The pore-sphere network was selected as a model for porous media since this model could qualitatively describe hysteresis and retention phenomena. 3-Dimensional lattices of square configuration were considered with normal, skewed and bimodal pore size distributions. The calculated pore size distribution was accurate up to the average size pores, but significantly different for larger pores. The fraction of average size pores was always exaggerated. Pore connectivity had larger influence on the pore size distribution than the lattice structures.     

Determination of the effects of the pore size distribution and pore connectivity distribution on the pore tortuosity and diffusive transport in model porous networks

An efficient computation method to study flow and transport process of small molecules in porous media using a dual site-bond lattice model, DBSM, is described. The microscopic properties of the porous network take into account the influence of local heterogeneities during the simulations. The numerical experiments demonstrated the combined effect of pore size distribution and connectivity distribution on the mass transport properties and the structural tortuosity. The results indicate that the pore size distribution and percolation phenomena related with pore shielding effects, influence significantly the tortuosity and the effective diffusivity of the porous network. Also, the simulations raise the important role of the connectivity distribution among the various pores in the gas diffusive properties of the poorly connected networks.     

Influence of catalyst pore network structure on the hysteresis of multiphase reactions

The effects of the catalyst pore network structure on multiphase reactions in catalyst pellets are investigated by using the experimentally validated pore network model proposed in our recent work (AIChE J, 62 , 451, 2016). The simulations display hysteresis loops of the effectiveness factor. The hysteresis loop area becomes significantly larger, when having small volume‐averaged pore radius, wide pore‐size distribution, and low pore connectivity; however, the loop area is insensitive to pellet size, even though it affects the value of the effectiveness factor. The hysteresis loop area is also strongly affected by the spatial distribution of the pore size, in particular for a bimodal pore‐size distribution. The pore network structure directly influences mass transfer, capillary condensation, and pore blocking, and subsequently passes these influences on to the hysteresis loop of the effectiveness factor. Recognizing these effects is essential when designing porous catalysts for multiphase reaction processes. © 2016 American Institute of Chemical Engineers AIChE J, 63: 78–86, 2017     

Effects of sample size on capillary pressures in porous media

Capillary pressure curves and their hystereses depend not only upon the geometry and wetting properties of the individual pores of a porous sample, but also upon the accessibility of these pores from the surface of the sample. Dependence of accessibility on distance from the surface of the sample implies that capillary pressure curves are sensitive to sample size. This sensitivity is investigated by measuring capillary pressure curves for porous samples of varying thickness. A theoretical investigation of sample thickness effects is made through application of the concepts of percolation theory of chaotic media. In the theory presented here, functions describing accessibility and pore size distribution appear in integral equations which account for all prominent features of drainage and imhibition, including threshold pressure, hystereses, residual saturations and dependence of residual saturation on initial saturation. The character and magnitude of sample thickness effects predicted by percolation theory are generally consistent with experimental results.     

多孔硅酮建筑密封胶的制备与机理研究

研究了多孔功能材料、表面改性剂种类和用量等对密封胶性能的影响。使用扫描电镜（SEM）、X射线衍射（XRD）、氮气吸附-脱附等温测试（BET）和脱附孔径测试（BJH）等对多孔功能材料的形貌、物相、比表面积、孔体积和孔径进行了表征。结果表明,多孔材料比表面积和孔体积均增大,平均孔径减小,有利于拉伸模量的提高。     

Simulation of nitrogen sorption processes in materials with cylindrical mesopores: Hysteresis as a thermodynamic and connectivity phenomenon

A numerical simulation of nitrogen sorption in materials with cylindrical mesopores is proposed. Multilayer formation and capillary condensation-evaporation processes are followed by using the Sonwane and Bhatia's molecular-continuum model, although an empirical expression is used to represent the potential interaction between the adsorbate and the adsorbent. The pore structure of the solid is generated by inscribing 3D cylindrical pores in a 2D square lattice. The connectivity effects on the nitrogen isotherms are studied by using percolation theory. The ability to predict the multilayer thickness and the relative pressure at which phase transition takes place is corroborated with data reported in literature, finding good fittings in this work. On the other hand, we report for the first time a study on the effect that both pore mean diameter and connectivity have on the extent of hysteresis.     

天然沸石的孔道效应在改善密封胶性能中的作用

天然沸石粉体的主要成分是铝硅酸盐,由硅氧四面体和铝氧四面体组成,其聚集态结构呈三维孔道结构。用扫描电镜（SEM）、X射线衍射（XRD）、氮气吸附—脱附等温测试（BET）和脱附孔径测试（BJH）方法对沸石的微观形貌、物相、比表面积、孔容和孔径进行了表征。详述了用天然沸石制备密封胶的工艺过程,研究了沸石及表面改性剂用量对密封胶的拉伸强度和断裂伸长率影响,分析了沸石的补强作用是多孔材料的孔道效应和锚固效应共同作用的结果。     

A new analysis method for the determination of the pore size distribution of porous carbons from nitrogen adsorption measurements

A new analysis method has been developed for the determination of the pore size distribution of porous carbons from nitrogen adsorption measurements. The method is based on a molecular model for the adsorption of nitrogen in porous carbon. It allows, for the first time, the distribution of pore sizes to be determined over both the micropore and mesopore size ranges using a single analysis method. In addition to carbons, this method is also applicable to a range of adsorbents, such as silicas and aluminas.     

Improving the interpretation of mercury porosimetry data using computerised X-ray tomography and mean-field DFT

Despite widespread use of the technique for a long time, the proper interpretation of mercury porosimetry data, particularly retraction curves, remains uncertain. In this work, the usefulness of two complementary techniques, mean-field density functional theory (MF-DFT) and micro-computerized X-ray tomography (micro-CXT), for aiding interpretation of ambiguous mercury porosimetry data has been explored. MF-DFT has been used to show that a specific, idiosyncratic form for the top of the mercury intrusion and extrusion curves is probably associated with a particular network structure where the smallest pores only form through connections between larger pores. CXT has been used to study the pore potential theory of hysteresis and entrapment directly using a model porous material with spatially varying pore wetting properties. CXT has also been used to directly study the percolation properties, and entrapment of mercury, within a macroporous pellet. Particular percolation pathways across the heart of the pellet have been directly mapped. The forms of entrapped mercury ganglia have been directly observed and related to retraction mechanisms. A combination of CXT and mercury porosimetry can be used to map spatial variation in pore neck sizes below the spatial resolution of imaging.     

低场核磁法测定凝胶过滤介质的孔径分布

凝胶过滤介质在蛋白质、多糖等生物大分子的分离纯化过程中具有非常重要的作用,其中介质的孔径分布是决定分离纯化效果的关键因素。由于绝大部分凝胶过滤介质是软凝胶,因此很难用常规的方法如压汞法、低温氮吸附法等测定其孔径分布。本文探索了利用低场核磁共振测定凝胶过滤介质的孔径分布的方法。首先通过抽滤、自制琼脂糖凝胶块等实验确定了峰的归属,明确了介质孔内水、介质间隙水和自由水在核磁共振横向弛豫时间(T₂)图谱上的分布范围;随后与逆体积排阻层析法(ISEC)测定的结果相对比,得出层析介质孔径和介质孔内水弛豫时间的关系;最后通过高斯正态拟合得到了介质的孔径分布。实验结果证实了低场核磁共振法测定凝胶过滤介质孔径分布的可行性。该法操作简单、测定迅速,并可以为其他层析介质孔径分布的测定提供参考。     

基于分形理论的油页岩有效扩散系数研究

以直径为1.6—2 mm柳树河油页岩为原料,采用扫描电镜法与氮吸附法得出油页岩吸附-脱附等温线,孔径分布曲线等;分析了油页岩内部孔隙结构,计算出孔道弯曲分形维数与孔隙面积分形维数,并研究油页岩内部的有效扩散系数。结果表明:油页岩吸附-脱附曲线属于Ⅲ型等温线,是一种典型的二端都开放的管状毛细孔型结构的多孔物质;其含有较发达孔隙,孔径分布为0.4—40 nm;油页岩孔道弯曲分形维数越小,孔道越平坦,孔隙面积分形维数为2.464;油页岩有效扩散系数与其内部结构和操作温度有关,温度越高,粒径越小,有效扩散系数越大。     

Activated carbon porosity tailoring by cyclic sorption/decomposition of molecular oxygen

Activated-carbon pore size tailoring is usually achieved by pore size reduction, pore size widening or more rarely by direct activation. Successive widening cycles composed of an initial molecular oxygen sorption step, followed by a carbonization step under nitrogen, have been applied to three different materials in order to study their gradual pore size modifications. For years, the whole microporosity obtained after several cycles is known to present better pore size distribution than those inherited from conventional activations. Moreover, as shown in the present paper, the gradual obtained microporosities cover a wide and valuable range of porous textures highly dependent on the initial material origin and initial activation. Gradual mean pore size evolutions of 1 or 2 Å per cycle were observed linked to a simultaneous increase in microporous specific volume in the case of pitch-based and coconut activated carbons, respectively. Comparatively, the microporous specific volume of a commercial coconut carbon molecular sieve was increased by 26% without modification of its mean pore size and therefore of its sieving effect. Those results have been used to test a simple textural model of activated carbon porosity proposed in the recent literature.     

沸石补强硅酮建筑密封胶的应用

考察了用沸石和焙烧沸石作为补强剂用于制备硅酮建筑密封胶的工艺过程,分析了粉体用量对密封胶热稳定性、拉伸强度、断裂伸长率、干燥时间的影响;用扫描电镜(SEM)、X射线衍射(XRD)、氮气吸-脱附等温测试(BET)和脱附孔径测试(BJH)方法对沸石和焙烧沸石的微观形貌、物相、比表面积、孔容和孔径进行了表征;研究结果表明,它们是一种具有多孔结构的铝硅酸盐矿物,主要成分分别为KNa2Ca2(Si29Al7)O72和K(Si3Al)O8,孔径分别为10.68 nm和14.02 nm,孔体积分别为0.465 5 mL/g和0.587 1 mL/g,比表面积分别为153.6 m2/g和191.4 m2/g,孔径分布宽、孔体积和比表面积大有利于补强,焙烧沸石的补强性优于沸石,揭示了它们的补强作用是硅烷偶联剂表面改性、孔道效应和锚固效应共同作用的结果。     

沸石补强硅酮建筑密封胶的应用研究

详述了用沸石和焙烧沸石作为补强剂用于制备硅酮建筑密封胶的工艺过程,分析了粉体用量对密封胶热稳定性、拉伸强度、断裂伸长率、干燥时间的影响;用扫描电镜（SEM）、X射线衍射（XRD）、氮气吸附—脱附等温测试（BET）和脱附孔径测试（BJH）方法对沸石和焙烧沸石的微观形貌、物相、比表面积、孔容和孔径进行了表征;研究结果表明它们是一种具有多孔结构的铝硅酸盐矿物,主要成分KNa2Ca2(Si29Al7)O72和K(Si3Al)O8,孔径分别为10nm和14nm,孔体积0.4655cc/g和0.5871cc/g,比表面积153.6m2/g和191.4m2/g,孔径分布宽、孔体积和比表面积大有利于补强,焙烧沸石的补强性优于沸石,揭示了它们的补强作用是硅烷偶联剂表面改性、孔道效应和锚固效应共同作用的结果。     

A comparison of nitrogen and mercury pore size distributions of silicas of varying pore volume

Although good correlation between the pore size distribution determined by nitrogen desorption isotherm and mercury penetration methods has been reported with low pore volume samples, large discrepancies in pore size distribution and in pore volume were found with high pore volume silicas and were shown to be a function of the pore volume of the silica. The mercury penetration method is believed-to compress these highly porous silicas and therefore reduces the pore volume and forms smaller pores.     

Gel Permeation Chromatography Using a Bio-Glas Substrate Having a Broad Pore Size Distribution

Abstract

Gel permeation chromatography has been performed using a porous glass of broad pore size distribution, which was subjected to hexamethyl-disilazane treatment. The elution volumes and peak widths of narrow molecular weight distribution polystyrenes using toluene as solvent have been determined. The physical characteristics of the porous glass have been studied by the methods of mercury porosimetry. nitrogen ad-sorption-desorption isotherms, and electron microscopy. The characteristics of this column packing material are compared with other packing materials in popular use.