沸石吸附储氢研究进展

沸石类微孔材料作为储氢介质的研究已成为近年来储氢领域中备受关注的热点问题,但对于其储氢机理、储氢容量及其影响因素的文献报道不尽一致。本文从吸附实验测定和理论计算模拟方面综述了各种结构类型沸石的吸附储氢的研究结果。重点分析了沸石的结构类型、硅铝比、阳离子类型及吸附实验条件差异对储氢量的影响,并讨论了超临界吸附理论模型的发展状况,最后探讨了沸石作为储氢材料的可行性和发展方向。     

相转换法制备聚氨酯微孔膜过程中的非溶剂效应

利用湿法相转换的原理制备聚氨酯微孔薄膜,从实验和理论计算两方面研究了非溶剂组成对聚氨酯孔结构及相分离过程的影响.实验结果表明:与水体系相比,在醇类非溶剂体系中聚氨酯膜更易形成较均一形貌的多孔结构.用异丙醇作非溶剂可得到孔径均一、相互贯通的孔结构.而理论计算结果表明:这种非溶剂效应与水、甲醇、乙醇及异丙醇等非溶剂系统的Flory-Huggins 相互作用参数及扩散系数密切相关.     

小孔沸石微结构的CO_2吸附表征

以3种已知结构的小孔沸石3A、4A和5A为研究对象,以N2和CO2为吸附质,通过吸附数据测定,研究了小孔沸石微孔结构的吸附表征方法.结果表明,N2吸附无法检测4A沸石的孔,而CO2吸附可以检测.对于4A和5A沸石,在35s内CO2吸附就可以达到平衡.HK(Horvath-Kawazoe)柱状模型不能表征4A和5A沸石的孔结构,但是HK球形模型可以,基于最大吸附量、D-A(Dubinin-Astakhov)方程和Langmuir-Freundlich模型计算了4A和5A沸石的微孔孔容,其中根据最大吸附容量和D-A方程计算的微孔孔容与文献值最接近.     

用CO_2吸附法分析分子筛的孔结构

以NaA,NaY和NaZSM-5分子筛为研究对象,以CO2为吸附质,通过吸附数据测定,研究分子筛材料微孔结构的吸附表征方法.计算了NaA、NaY和NaZSM-5分子筛的微孔孔容,其中基于D-A方程的微孔孔容值与文献值一致.根据CO2吸附数据分析了3种分子筛的孔径分布.发现对于含有球形孔结构的NaA,NaY分子筛和NaA+NaY混合物,HK(Horvath-Kawazoe)球形模型(HKsphere)能够很好地描述其孔径分布,而HK柱状模型(HKcylinder)能够很好地表征具有柱状孔道结构的NaZSM-5分子筛.单一的HK方法不能表征同时含有柱状孔和球形孔的NaA+NaZSM-5混合物,使用HKcylinder只能得到混合物材料中柱状孔的分布情况,而使用HKsphere只能得到球形孔的分布情况.     

ZSM-5晶体内SnO_2团簇的热扩散法合成及表征

以ZSM-5晶体作为主体材料,采用热扩散方法于750和850℃在空气中分别制备了SnO2/ZSM-5主客体材料,通过一系列方法考察了该材料的化学组成、晶体形貌、晶相、光致发光等物理化学性质.采用基于密度泛函理论(DFT)的微孔吸附分析方法对该材料的孔结构进行详细研究,推断了该材料中SnO2的分布方式.结果表明:二氧化锡团簇负载到了分子筛孔道中而非分布在晶体表面,而且随着热扩散温度升高,样品中SnO2的含量增多;进入分子筛中的二氧化锡团簇主要分布在ZSM-5分子筛的微孔中;负载后的分子筛晶体在热扩散温度为750℃时保持了较好的晶体形貌而且具有较好的可见光通透性和良好的荧光发光性能,具有较大后续的器件化和功能化应用潜力.     

原位法合成Cu-BTC负载二氧化硅吸附材料的研究

采用溶剂热法,将均苯三甲酸(H3BTC)与硝酸铜进行反应合成了金属-有机骨架(Metal-Organic Frameworks,MOFs)微孔材料Cu-BTC;利用原位合成法,将Cu-BTC负载到介孔/大孔二氧化硅孔道中,获得介孔CuBTC-SiO2材料。通过静态吸附实验,测定了正己烷(n-C6)、环己烷(c-C6)和正癸烷(n-C10)在Cu-BTC及CuBTC-SiO2上的吸附速率曲线,结果表明,将微孔材料Cu-BTC负载在SiO2之后,CuBTC-SiO2中既有微孔又有一定量的介孔,适量的介孔结构可减小其对正己烷的静态饱和吸附量,但增加对环己烷和正癸烷的静态饱和吸附量。实验测得CuBTC-SiO2对c-C6和n-C10都具有更大的静态饱和吸附量。因此CuBTC-SiO2材料可望应用在烷烃的吸附分离上。     

分子模拟研究微孔材料对光气吸附扩散性能的影响及材料筛选

利用分子模拟的方法研究了微量光气(COCl₂)在微孔材料中的吸附和扩散性能, 并分析了材料结构的影响. 结果表明, 光气在金属有机框架材料(MOF)和共价有机框架材料(COF)中的吸附等温线主要表现为第Ⅰ类型和第Ⅴ类型吸附. 当光气压力较低时, COF材料和含有开放金属位点的材料对其吸附性能较好. 通过对不同压力下吸附量的比较发现, 吸附达到饱和前, 随着压力和孔隙率(VF)的升高, 材料对光气的吸附量增大. 通过分子动力学模拟研究光气在微孔材料中的扩散性能发现, 较强吸附位点的存在不利于光气在孔道中的扩散. 通过气体分子在材料中的径向函数分布图及模拟轨迹分析发现, 分子协同效应和空间位阻效应相互竞争决定了扩散速率的快慢. 综合评价材料的吸附和扩散性能发现, COF-102, COF-300, ZnMOF-74, Zn-DOBDC和PCN-60是理想的吸附材料, 这些材料可以应用于环境中光气泄漏的防治.     

气体在纳孔分子材料中吸附的理论模拟研究进展

纳孔分子材料是由孤立分子通过非共价相互作用堆积形成的具有纳微孔道结构的材料.和传统共价网络孔材料相比,纳孔分子材料具有独特的溶解性,并兼具气体存储与分离,限域反应和催化等方面的潜在应用,已成为当前研究的新热点.通过着眼于新型纳孔分子材料的设计,对相关理论研究进行了综合评述,主要包括以下3个方面:(1)无论是气体吸附还是催化反应,纳孔分子材料的晶体结构预测都是先决条件,只有在纳孔分子材料的晶体结构得到准确预测的前提下,才能够定向、准确、系统地对其进行设计;(2)气体在纳孔分子材料中吸附的分子动力学研究有助于深刻理解气体吸附的微观传输扩散机制;(3)气体在纳孔分子材料中吸附的巨正则蒙特卡洛模拟有利于对设计材料的吸附性能进行直接预测,得到可以直接与实验吸附量、吸附热等信息进行比较的结果.最后,简述了理论设计新型纳孔分子材料存在的问题以及未来发展前景.     

分子筛材料在小分子吸附分离中的应用

吸附分离技术与工艺在工业上具有重要意义. 常见的吸附剂包括沸石分子筛、 金属有机框架材料、 活性炭等材料. 分子筛具有比表面积大、 稳定性高、 生产成本低等优势, 可以满足吸附分离技术中高效、 节能和环保的需求, 是一种非常有应用前景的小分子混合物分离吸附剂. 本文综合评述了吸附分离领域中常用的吸附剂材料的特点和吸附分离机理与评价方法, 总结了分子筛在空气分离、 烃类分离、 二氧化碳吸附、 芳香硫化物脱除、 一氧化碳吸附、 氮氧化物吸附、 氢气储存吸附及氢同位素分离等领域的应用, 并对基于分子筛膜的小分子混合物分离现状进行了介绍. 此外, 本文还系统分析了分子筛对不同混合物的吸附分离性能与其拓扑结构、 骨架组成及改性方法之间的关系, 并对未来的研究前景进行了展望.     

巨正则系综Monte Carlo模拟方法确定活性炭的微孔尺寸

根据299K下甲烷在活性炭中的吸附实验数据,通过调节狭缝微孔的孔宽参数,利用巨正则系综MonteCarlo(GCEMC)方法得到不同孔宽下流体的微观结构以及吸附等温线.比较并拟合模拟结果和实验数据,确定了活性炭微孔的平均孔宽,为下一步求解微孔尺寸分布以及为预测吸附剂在不同温度下吸附不同吸附质分子时的吸附性能提供了基础与指导.模拟中,甲烷分子采用单点Lennard-Jones球型分子模型,活性炭用狭缝孔来近似表征,流体分子与单个狭缝墙的相互作用采用著名的Steele的10－4-3势能模型.模拟表明,此方法为考察介孔材料的微孔分布以及微孔平均孔宽提供了新的思路.     

大孔吸附树脂的吸附机理

大孔吸附树脂(macroprous adsorption resin, MAR)是近几十年发展起来的一种具有多孔立体结构、人工合成的有机高分子聚合物。由于其特殊的理化性质和吸附性能,已被广泛应用于化学、医药、环保和食品等领域。本文介绍了近年来国内外对大孔吸附树脂在吸附机理研究方面的进展,重点介绍了不同温度条件下大孔吸附树脂对靶标分子的吸附热力学行为模式,靶标分子在大孔吸附树脂表面及孔内的吸附扩散行为模式。此外,大孔吸附树脂性能参数和靶标分子结构参数之间构效关系也对其吸附选择性规律具有重要的影响。因此,大孔吸附树脂与底物间构效关系的匹配程度及其对选择性的影响是大孔吸附树脂分离理论研究的核心。本文最后介绍了可以准确客观描述吸附过程并具有一定使用范围的大孔吸附树脂吸附模型的建立和评价。     

New method for the determination of adsorption space volume for sorbents with an arbitrary porous structure from excess gas adsorption isotherm measurements

A new method for the determination of adsorption space volume has been proposed, which is applicable to adsorbents with an arbitrary porous structure, including nonporous adsorbents with open surfaces. The method is based on the use of an experimental excess adsorption isotherm measured over a wide range of pressures in the equilibrium gaseous phase (as a rule up to 100–150 MPa) and the absolute adsorption isotherm equation with unspecified parameters in the most general form, given by statistical physics. The method has been tested for a number of adsorption systems, and it has been found that the result was always unambiguous, correct, and stable in the sense of input data.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2381–2385, December, 1995.     

多组分气体吸附平衡理论研究进展*

关于多组分气体吸附平衡理论的研究之所以重要,一是因为其在分离技术中的应用前景,二是因为其尚不成熟。本文对临界温度以下多组分气体吸附平衡理论研究的进展、各种数学模型的特点及适用范围作了评述,并探讨了含超临界值组分的气体吸附平衡理论所面临的问题及其研究方向。     

Expressiveness of Adsorption Measurements for Characterization of Zeolitic Materials—A Review

This critical review concerns the author's results and experience in adsorption studies on molecular sieves comprising crystalline microporous aluminosilicates and aluminophosphates as well as amorphous mesoporous aluminosilicates. The discussion is mainly based on three distinctly different standard adsorbates: nitrogen, benzene, and water. The highlights or advantages and the shortcomings or limitations are considered from the points of view of the experimental procedures and expressiveness or concluding. The results are compared to several other zeolitic materials and adsorbates. Adsorption technique is a valuable tool for characterization of the molecular sieves. Since the measurements are very sensitive to modification of the materials, the investigations require sufficiently thorough procedures and the results a careful interpretation. A comparison between the results for larger series of materials yields valuable conclusions that are much more expressive than those from a single measurement or material. Dedicated to the memory of Professor Wolfgang Schirmer.     

Adsorption of Nitrogen on Silica Gel Over a Large Range of Temperatures

To study the mechanism of physical adsorption of supercritical gases, the adsorption equilibria of N₂ on silica gel for 103–298 K using 20 K increments and pressures up to 10 MPa were measured. A transition of the adsorption mechanism was proven on crossing the critical temperature, but the transition way observed is different from that observed with activated carbon. This causes a difference in the locations of the linear section of the n- _g isotherm at the near-critical temperature. Although the isotherm type is different on silica gel and on activated carbon in the sub-critical region, all isotherms in the supercritical region can be well modeled by a single model. It leads to the argument that the adsorption mechanism of supercritical gases is identical no matter what kind of adsorbent is used.     

Thermodynamic parameters of adsorption described by the logarithmic Temkin isotherm

Thermodynamic analysis of the adsorption Temkin isotherm was performed. The equations that describe the dependence of the thermodynamic functions on the amount adsorbed were obtained. A relationship between the excess differential and mean molar thermodynamic functions was found. The thermodynamic approach does not contradict the molecular statistical theory and appears to be more general.     

Description of NaX zeolite deformation during adsorption of xenon

The equation describing the experimental data of NaX zeolite deformation during adsorption of xenon at pressures of 0.001–7 MPa and temperatures of 252–333 K was obtained on the basis of the generalized Lennard-Jones pair interaction potential. The temperature dependences of the constants in the equation were determined. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1887–1890, October, 1999.     

Mesoporous Carbons of Well-Organized Structure in the Removal of Dyes from Aqueous Solutions

Mesoporous carbons with differentiated properties were synthesized by using the method of impregnation of mesoporous well-organized silicas. The obtained carbonaceous materials and microporous activated carbon were investigated by applying different methods in order to determine their structural, surface and adsorption properties towards selected dyes from aqueous solutions. In order to verify applicability of adsorbents for removing dyes the equilibrium and kinetic experimental data were measured and analyzed by applying various equations and models. The structural and acid-base properties of the investigated carbons were evaluated by Small-Angle X-ray Scattering (SAXS) technique, adsorption/desorption of nitrogen, potentiometric titration, and Transmission Electron Microscopy (TEM). The results of these techniques are complementary, indicating the type of porosity and structural ordering, e.g., the pore sizes determined from the SAXS data are in good agreement with those obtained from nitrogen sorption data. The SAXS and TEM data confirm the regularity of mesoporous carbon structure. The adsorption experiment, especially kinetic measurements, reveals the utility of mesoporous carbons in dye removing, taking into account not only the adsorption uptake but also the adsorption rate.     

Thermodynamic characteristics of hydrocarbon and chloroalkane adsorption by polymethylsilsesquioxane

Adsorption of n-alkanes (C₇H₁₆–C₁₁H₂₄), cyclohexane, benzene, CHCl₃, CCl₄, and ClCH₂CH₂Cl by polymethylsilsesquioxane [MeSi(OH)_0.4O_1.3] _n was investigated by inverse gas chromatography in the Henry region. The adsorption isotherms are linear for all adsorbates. The standard changes in the thermodynamic parameters of adsorption were determined. The absence of specific selectivity with respect to aliphatic, cyclic, or aromatic hydrocarbons or chloroalkanes indicates that the adsorbent is chemically homogeneous.