修正的硬球三参数状态方程(Ⅰ)计算流体的饱和性质

对硬球三参数状态方程(CSPT)引力参数的温度校正系数α和拟临界压缩因子(?)提出了新的温度关系式.用修正的CSPT方程(MCSPT)计算了105种纯物质的饱和性质.结果表明,新的方程改善了原CSPT方程在低对比温度下物质的饱和性质,以及临界区域内热力学性质的计算精度.并用于计算超临界状态下物质的热力学性质,有良好的外推性.     

修正的硬球三参数状态方程(Ⅰ)计算流体的饱和性质

对硬球三参数状态方程(CSPT)引力参数的温度校正系数α和拟临界压缩因子(?)提出了新的温度关系式.用修正的CSPT方程(MCSPT)计算了105种纯物质的饱和性质.结果表明,新的方程改善了原CSPT方程在低对比温度下物质的饱和性质,以及临界区域内热力学性质的计算精度.并用于计算超临界状态下物质的热力学性质,有良好的外推性.     

气体溶解度的分子热力学(I)——气体在非极性溶剂中的Henry常数

本文介绍一个气体在非极性溶剂中溶解度的分子热力学模型.混合物的Helmholtz自由能分三步计算:首先将处于标准态的纯组分等温混合成理想气体混合物;然后将每个分子膨胀成具有直径σ的硬球,相应的Helmholtz自由能变化用Mansoori-Carnahan-Starling-Leland方程计算;最后按LJ12-6位能函数给分子充以位能,形成实际流体混合物.在这最后一步中,引入一个近似的径向分布函数:g_(ij)(γ)=H(γ-γ_(ij))+βδ(γ-γ_(ij)).Henry常数则通过剩余化学位求得.与计算机模拟实验数据比较的结果表明:在使用同样的LJ参数的条件下,本模型的预测结果显著优于常用的Pierotti理论.对于实际系统,本模型一般只用一个可调参数便可在较大的温度范围内很好地关联各种气体在C_1—C_(20)的正烷烃及其异构体、环烷烃、芳香烃和一些液化气体中的Henry常数.计算的△(?)_(s1),△(?)_(s1)及(?)_1亦令人满意.     

二元无机水溶液的(火用)值计算法

本文探讨了有关二元无机水溶液的蒸汽压、溶质与溶剂的偏摩尔(?),溶液总(?)值的工程计算方法。提出了能关联全浓度范围内溶液蒸汽压数据的经验式和计算无机水溶液中水的偏摩尔(?)的半经验式。根据Gibbs-Duhem方程,推导出计算二元无机水溶液(?)值的通用式。     

多孔催化剂有效因子的近似分析解(Ⅱ)近似分析解与数值解的比较

根据本文第Ⅰ部分所提出的多孔催化剂有效因子近似计算式,针对不同形式的幂函数型动力学方程和双曲型动力学方程,计算了等温下Thiele模数不同时非一级反应的有效因子,并且用数值方法求出相应条件下的有效因子以作比较.大量的计算结果证明所提出的近似计算式较之文献上已有的近似式,不但精度高,而且适用范围广.同时近似式中参数估值简便,克服了以往研究者所提出的式子中这方面所存在的困难.     

从统计力学推导流体状态方程(Ⅲ)——关于马丁-侯状态方程等的统计力学证明与解释

本文从多方阱非球形势硬粒子微扰理论出发,通过适当的近似与化简,导出了马丁-侯状态方程,从而使这个由经验提出的状态方程得到了统计力学的证明与解释.从多方阱非球形势硬粒子微扰理论出发,通过更粗略的近似也能得到范德华状态方程以及Barner与Adler改进的(?)offie状态方程.由理论分析,马丁-侯方程较为全面,不仅有高级微扰项,保留了多级密度展开式,同时取用了较精确的多级参考流体状态方程.     

从统计力学推导流体状态方程(Ⅲ)——关于马丁-侯状态方程等的统计力学证明与解释

本文从多方阱非球形势硬粒子微扰理论出发,通过适当的近似与化简,导出了马丁-侯状态方程,从而使这个由经验提出的状态方程得到了统计力学的证明与解释.从多方阱非球形势硬粒子微扰理论出发,通过更粗略的近似也能得到范德华状态方程以及Barner与Adler改进的(?)offie状态方程.由理论分析,马丁-侯方程较为全面,不仅有高级微扰项,保留了多级密度展开式,同时取用了较精确的多级参考流体状态方程.     

重心插值配点法计算碳纳米管的振动频率

以碳纳米管的Euler-Bernoulli梁理论建立的四阶偏微分方程为计算模型,通过简谐振动假设得到碳纳米管的模态分析方程.采用重心Lagrange插值近似未知模态函数,将模态分析方程和边界条件离散为代数方程,施加边界条件求解代数特征值方程,得到碳纳米管在不同边界条件下的自由振动频率.数值计算结果与文献报道结果比较表明所提方法的有效性和计算精度.     

用近似Broekhoff方程(脱附)计算孔径分布

本文对用于脱附线的Broekhoff方程做了简化,得到一组仅以相对压力X为自变量的近似方程。用此方程计算孔径分布比B.J.H法和D.H法简单,很容易进行手算,其结果与用电子计算机按原Broekhoff方程计算结果很一致,而且计算所得之累计孔容与实测孔容之比值大都在0.93—1.05之间,累计孔壁面积与B.E.T比表面之比值大部分在0.90—1.12之间。这样的相符程度     

关于质子平衡方程应用的近似处理问题

在一定误差条件下,对质子平衡方程作近似处理,可以简化复杂酸碱平衡体系H 浓度的计算问题,由此导出H 浓度计算的近似式和最简式。该方法简便、实用、易于掌握。     

Simulation of nitrogen adsorption-desorption isotherms. Hysteresis as an effect of pore connectivity

The sorption mechanisms in porous materials have been of long standing interest and debate. Concretely, the involved hysteresis during nitrogen adsorption-desorption processes and its interpretation has represented an important challenge for experimentalists and theoreticians. Moreover, a better understanding of the different observed hysteretic behaviors and the elapsed are as is still remaining. Such a scenario has motivated us to study the pore connectivity and pore size distribution effects upon the hysteresis in nitrogen adsorption-desorption isotherms of a porous solid. Our simulation has been carried out over the entire range of connectivity assuming three-dimensional pores randomly inscribed in a two-dimensional lattice with different occupation probabilities, related with pore connectivity, including the percolation threshold. The adsorption and desorption curves as a function of pressure have been simulated taking into account the monolayer-multilayer formation process and the capillary condensation-evaporation phenomena by using the Broekhoff de Boer and Kelvin equations, respectively. Results show that the employed methodology allows reproducing different types of hysteresis experimentally observed where the hysteretic behavior is strongly dependent upon both connectivity and the broadening of the pore size distribution. Specifically, the hysteresis loop area exhibits a maximum at the percolation threshold and then it decreases monotonically above the threshold.     

Water adsorption equilibria on microporous carbons correlated using a modification to the Sircar isotherm

Water vapor adsorption equilibria are measured for several unimipregnated and impregnated microporous carbons, including BPL, ASC, ASC-TEDA and a polymeric beaded carbon. Both the shape of the isotherms and the presence of hysteresis are characteristics of the capillary condensation mechanism. Sircar's isotherm expression, which incorporates capillary condensation with the Kelvin equation, has been modified to correlate the data for both adsorption and desorption. Two gamma distribution functions are required to represent the pore size distribution for the activated carbons while only one gamma distribution function is required to represent the pore size distribution for the polymeric beaded carbon. The pore distributions that result from correlating the isotherm data are consistent with the known structure of these adsorbents.     

Improvement in the Pore Size Distribution for Ordered Mesoporous Materials with Cylindrical and Spherical Pores Using the Kelvin Equation

Ordered mesoporous materials such as MCM-41 and SBA-15, which exhibit cylindrical pores open at both ends and SBA-16 with spherical pores, show a strong influence on adsorption and catalytic processes, basically due to their defined pore sizes. In general, the textural characteristics of these materials are obtained by N₂ adsorption?Cdesorption isotherms at 77 K where, for the calculus of the mesopores size, the ??Kelvin equation?? is used. Thus, several authors have conducted studies on the pore size distribution (PSD) for these materials, applying diverse methods such as: Barret, Joyner and Halenda (BJH); Dollimore and Heal (DH); and Kruk, Jaroniec and Sayari (BJH-KJS) methods. To obtain the PSD, the BJH and DH methods were proposed for cylindrical pores, using the desorption branch data of the isotherm, meanwhile the BJH-KJS method uses the adsorption branch data, but assumes the mechanism corresponding to the desorption branch for cylindrical pores. Due to the diversity of methods to evaluate the PSD, all of them with different considerations, it is difficult to determine the most suitable. In this work, with the aim to improve the analysis, the PSD was evaluated from the N₂ adsorption?Cdesorption isotherms at 77 K for a series of materials, MCM-41, SBA-15 and SBA-16 type, synthesized in our laboratory. By a modification in the Kelvin equation with the addition of a correction term (f _c ) and assuming appropriate mechanisms of capillary condensation and capillary evaporation, an improved method is proposed to be used for cylindrical as well as spherical pore geometries based on the BJH algorithm. This term was obtained adjusting simulated isotherms with different values of f _c to the experimental isotherm. The results were compared to those obtained by traditional methods and by the Non-Local Density Functional Theory (NLDFT) model.     

A comparison of nitrogen adsorption and thermogravimetric methods in the assessment of the pore size distribution of mesoporous silica gels

The pore dimensions are determined by using adsorption and thermogravimetry methods for unmodified silica gel Si-100 and silanized silica gel Lichrosorb RP-18. Thermal desorption measurements for various liquids were performed under quasi-isothermal conditions. Methanol, acetone, benzene and n-hexane were used as a wetting liquids. Pore size distributions and total pore volumes derived from thermal desorption compare reasonably well with results obtained from the analysis of adsorption isotherms of nitrogen. For different types of adsorbates the effects connected with the presence of the surface liquid film are discussed. The presence of long alkyl chains on the silica surface strongly influences the pore diameter calculated from thermogravimetric data.     

用氮气吸附法研究二甲醚催化剂表面分形维数

在77K下对四种二甲醚催化剂进行N2吸附—脱附等温线测定,得到了催化剂的孔结构参数,研究了其孔径分布、比表面积、等温线形态变化,并利用等温吸附数据计算其分形维数。结果表明,四种催化剂分形维数在2～3之间,将催化剂颗粒机械成型得到的片剂都具有分形特性,但其分形维数与比表面积和孔容积没有直接联系。     

碳化—活化条件对剑麻基活性炭纤维结构及性能的影响

对一系列剑麻基活性炭纤维的孔结构特征分析表明,这些活性炭纤维具有发达的微孔和高的比表面积,含有部分中孔。随活化温度升高,平均孔径不断增大,中孔体积也相应提高。ＤＲ曲线显示了ＳＡＣＦ吸附等温线由多段直线组成,揭示了活性炭纤维孔分布的多段性。此外,Ｘ－射线衍射数据的结果表明,随碳化活化温度升高,石墨片层间距增大,而微晶尺寸减少     

Surface area and pore structure of thorium dioxide

Water vapour isotherms at 35° were measured on two samples of thorium dioxide, one crystalline and the other an amorphous gel. Specific surface areas and pore size distributions were estimated and compared with those obtained from nitrogen adsorption at ?196°. The effect of thermal treatment on both samples was also investigated at 35–500°. It was shown that the adsorption of water vapour on thoria gel is purely physical in nature, and that the gel surface is characterised by the existence of pores of very particular sizes, namely of hydraulic radii 4–6 ǎ. On the other hand, water seems to interact chemically with the surface of the crystalline sample. In this case the specific surface area could not be evaluated from the adsorption branch of the isotherm, but was successfully evaluated through the application of the ‘corrected modelless’ method to the desorption branch of the water isotherms. This gave the surface area of the total pore system which was found to be in good agreement with the B.E.T.-nitrogen area.     

Modelling of a pressure swing adsorption process for oxygen enrichment with carbon molecular sieve

Adsorptive separation of oxygen from nitrogen and argon is carried out during the desorption steps of a pressure swing adsorption (PSA) process which uses carbon molecular sieves developed by Bergbau-Forschung GmbH. The adsorption isotherms of the three main components of air are very similar. On account of the pore size distribution of CMSN2, the diffusion coefficient of oxygen is more than eight times those of nitrogen and argon so that air separation occurs by adsorption kinetics. Experimental results for the individual steps and cyclic operation of the PSA process are presented and compared with the predictions of an isothermal plug-flow model. Adsorption rate is represented by a linear driving force equation. If the diffusion coefficients are adapted separately to every step, a good agreement is observed between the model calculations and experimental results.     

甲烷、乙烷、丙烷和丁烷在中孔活性炭上的吸附平衡

以活性炭AC1为吸附剂,在体积法实验装置上分别测定了其对甲烷、乙烷、丙烷和丁烷4种气体的吸附等温线,吸附温度分别为283、293、303和313 K。利用77 K吸附氮气数据表征AC1,得到其比表面积为956 m²·g^-1,孔体积为1.36 mL·g^-1,孔径分布在1~5 nm,中孔的比例达到了61%。AC1对4种气体的吸附等温线均为I型等温线,分别采用Langmuir方程和Langmuir-Freundlich方程(简称L-F方程)对吸附平衡数据进行拟合,结果表明,L-F方程具有更好的拟合效果,为后序的多组分吸附平衡研究提供了基础数据。AC1对乙烷/丙烷的吸附平衡选择性系数在1.7~2.5,吸附选择性随吸附压力的增大而减小,吸附温度对吸附选择性无明显影响。