Composite materials based on zeolite 4A for adsorption heat pumps

Some additives and binders were chosen for the preparation of 4A-zeolite-based composites with high equivalent thermal conductivity for heat pumps application. Additives (SiC, Si₃N₄, graphite) and binders (PTFE, Al(OH)₃) were tested for their effectiveness in terms of equivalent thermal conductivity and maximum water adsorption capacity of the composites. The influence of the equivalent thermal conductivity of the composite adsorbents on the specific power of the heat pump was also calculated. Results show a significant improvement in the equivalent thermal conductivity of the composite samples which are prepared using aluminum hydroxide as binder, over that of zeolite pellet beds. Such composite materials could be used to build adsorption heat pumps with higher specific power and, consequently, with lower investment cost.     

水蒸气对高岭土高温吸附铅的影响

使用沉降炉开展了水蒸气对高岭土高温吸附铅影响的实验研究，其中铅的形态为PbO和PbCl₂两种。首先研究了0-20%水蒸气对高岭土吸附PbO（1100-1300 ℃）和PbCl₂（800-1300 ℃）的影响规律，然后基于XRD、SEM和残余羟基率等分析，掌握了水蒸气影响高岭土高温吸附的机理。结果表明，水蒸气可以减少高岭土表面羟基的高温脱落，从而阻碍了PbO吸附、促进了PbCl₂吸附。综合高温下惰性莫来石的出现和高岭土孔隙结构的坍塌等因素，PbO和PbCl₂的最佳吸附温度分别为1200和1000 ℃。     

Evaluation of energy distribution on a heterogeneous surface from heat of adsorption and its application to the ammonia/Na-Y zeolite system

The— function (energy level function) which represents surface heterogeneity was derived from theq— function (experimental heat function) in the case of reversible adsorption. The Langmuir equation was extended and applied to the procedure of calculations. An iterative calculation led to the most probable— function by setting theq— function and adsorption temperature. As an example for actual cases, the— function of Na-Y zeolite was calculated from theq— function obtained by the measurement of heats of adsorption of ammonia at 373 K. The— function thus derived seemed to be consistent with the positional distribution of sodium ions.     

用密度泛函理论研究NO在H-ZSM-5分子筛不同酸性位的吸附

利用密度泛函理论(DFT),基于7T簇模型,在B3LYP/6-31G(d,p)水平上研究了NO分子在H-ZSM-5分子筛孔道中α,β,γ酸性位的吸附.在计算过程中,首先对H-ZSM-5的α,β,γ酸性位进行优化计算,然后对NO分子η1-N和η1-O两种吸附模式的红外光谱和吸附能进行计算.计算结果表明,NO分子以η1-N模式吸附于H-ZSM-5分子筛酸性位上,不同酸性位对NO分子的吸附能力排序为:α酸性位>β酸性位>γ酸性位.此外,H-ZSM-5分子筛直型孔道更有利于NO分子的吸附和扩散,因而可更有效地促进NO分子催化分解反应的进行.     

The heat of adsorption of water on nonporous hydrophilic carbon adsorbents in the model of two-stage adsorption

The behavior of integral and differential heats of adsorption of water in the region of transition from the first stage of adsorption (formation of clusters) to the second stage (formation of a stretched liquid film) was considered. The curve of integral heat of adsorption has an inflection at the transition point, and the differential heat of adsorption changes jumpwise. The values of these effects were estimated by the simplest model of formation of one and two hydrogen bonds between a water molecule and an adsorption center on the surface of the carbon adsorbent. Curves of differential heat of adsorption with transition points for real systems are presented. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1479–1483, August, 1999.     

Enhancement of the heat and mass transfer in compact zeolite layers

Heat and mass transfer during the adsorption of water on zeolite has been studied both theoretically and experimentally. A dynamic simulation model of a zeolite layer has been developed to estimate the predominant transport resistances and calculations were carried out to assist the simultaneous experimental investigations. On one hand, a metallic matrix was added to the compact zeolite layer to improve the heat transfer. On the other hand, pore-forming materials such as melamine or tartaric acid were used. These organic components are removed during drying of the zeolite so that the mass transfer inside the zeolite is significantly enhanced compared to a granulated zeolite bed. The experimental investigations show that the theoretically deduced possibilities of improving the adsorption process can be realized in the manufactured zeolites.The investigations described here are of interest for the development of adsorption heat pumps. Due to the thermodynamic characteristics the adsorption system zeolite-water is a promising working pair for this application. The investigations show that the main shortcoming of these machines, the thermal output, can be increased significantly.     

The effect of triethyl citrate on the dispersibility and water vapor sorption behavior of polylactic acid/zeolite composites

The aim of this study was to investigate the water vapor adsorption behavior and mechanical properties of poly (lactic acid) (PLA)/zeolite (5, 10, or 15 phr) composites prepared with triethyl citrate (TEC; 20 phr) via a melting process. TEC was used to improve the flexibility of the PLA and the dispersibility of the zeolite in TEC-zeolite suspensions that were ultra-sonicated. It was found that zeolite was uniformly dispersed in the PLA matrix, and the interfacial adhesion between the PLA matrix and zeolite was enhanced by TEC. In addition, the tensile strengths and Young's modulus of the composites improved with increasing zeolite content. The PLA/zeolite composites prepared with TEC had increased water vapor permeability and contact angles compared to neat PLA and standard PLA/zeolite due to the presence of TEC. In particular, TEC accelerated the hydrolysis of the PLA surface in a high humidity environment, resulting in an improvement in water vapor sorption capacity. At the same zeolite content of 15 phr, the equilibrium moisture content (EMC) values of PLA/zeolite films prepared with TEC increased by up to 39.25 mg/g whereas those prepared without TEC only increased by up to 24.33 mg/g. The results suggest the possibility of applying PLA/zeolite films prepared with TEC as a flexible active packaging material.     

Thermal behavior and water adsorption of natural and modified sepiolite having dolomite from Turkey

The water adsorption properties of sepiolite having dolomite supplied from Eskisehir region and their exchanged forms (K⁺, Na⁺, Mg²⁺ and Ca²⁺) were investigated. The sepiolite samples were characterized using XRD, TG-DTA, DSC and nitrogen adsorption methods. The temperature ranges were determined for the dehydrations of hydroscopic and zeolitic water as 30–200°C, for the dehydration of the bound water as 250–750°C and for the dehydroxylation of hydroxyls as 810–850°C in the sample. It was observed that the value of percent mass loss for natural and modified samples varied in the range from 36.70 to 39.05%. Two mass loss steps for all samples were observed using a differential scanning calorimetry (DSC) in the range of 30–550°C. Adsorption isotherms for water on natural and modified forms were obtained at pressures up to 2.39 kPa. Uptake of water increased as K-SEP.<Na-SEP.<Mg-SEP.<Ca-SEP. for sepiolite samples at 293 K.     

CuNaY分子筛的有效吸附位与其脱硫性能的关联性研究

以液相离子交换法制备了一系列不同Cu负载量的CuNaY分子筛;采用XRD及N₂吸附-脱附表征分子筛的微观结构和织构性质,采用动态吸附法考察其对噻吩模拟油的吸附脱硫性能,结合NH₃-TPD和Py-FTIR方法对CuNaY分子筛的酸量和有效Cu⁺物种进行定量分析,研究了CuNaY分子筛的表面酸性和铜物种形态结构对其吸附脱硫性能的影响机制。结果表明,通过改变铜负载量可有效调控改性Y分子筛的表面酸性以及铜物种化学形态;适量铜物种的引入可以最大限度的形成有效吸附位,从而获得最优吸附脱硫性能,而过量的Cu物种会在Y分子筛笼内形成多核铜物种结构,导致有效吸附位点的减少,影响其对噻吩的吸附能力。     

内蒙胜利褐煤腐殖酸对煤平衡复吸水的影响

研究了褐煤中重要的成分腐殖酸对褐煤水分的影响。测定了内蒙胜利褐煤中腐殖酸含氧官能团的含量,并分析了褐煤、棕黑腐殖酸和残余煤的等温吸附和脱附曲线。通过Dent吸附等温模型研究了褐煤和棕黑腐殖酸第一层吸附和第二层吸附。结果表明,胜利褐煤2/5羧基和1/5羟基是由腐殖酸提供的。棕黑腐殖酸相对褐煤孔径和孔容较小,不利于水簇的形成。腐殖酸对褐煤的复吸水是不利的     

Validity of energy distribution derived from heat of adsorption in an ammonia/cation-exchanged Y zeolite system

The validity of- functions (energy level functions) which were derived from experimentalq- functions (heat functions) was examined in an ammonia/cation-exchanged Y zeolite system. The- functions of Na-Y zeolite and Cs-Na-Y zeolite were respectively calculated from theirq- functions measured by ammonia adsorption at 373 K. The heat of adsorption of ammonia was also measured on a mixture of these two zeolites at a certain mixing ratio at 373 K. The- function of the mixture was likewise calculated on the basis of this measurement. The- function thus calculated was in good agreement with the synthesized- function derived by linearly combining two- functions of each zeolite mentioned above. The- function derived from experimental- function thus proved to be valid in an actual adsorption system.     

Adsorption of helium on zeolite NaA

Isotherms of helium adsorption on zeolite NaA were measured by the volumetric method under static conditions at 23–50 K and pressures from 1 Pa to 65 kPa. The Henry constants and the initial heat of helium adsorption were calculated; the isosteric heat was calculated, and its dependence on the adsorption was determined.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1291–1292, May, 1996.     

Effect of cobalt oxide on performance of Pd catalysts for lean-burn natural gas vehicles in the presence and absence of water vapor

Pd-based catalysts modified by cobalt were prepared by co-impregnation and sequential impregnation methods, and characterized by X-ray powder diffraction (XRD), N_2 adsorption/desorption (Brunauer-Emmet-Teller method), CO-chemisorption and X-ray photoelectron spec-troscopy (XPS). The activity of Pd catalysts was tested in the simulated exhaust gas from lean-burn natural gas vehicles. The effect of Co on the performance of water poisoning resistance for Pd catalysts was estimated in the simulated exhaust gas with and without the presence of water vapor. It was found that the effect of Co significantly depended on the preparation process. PdCo/La-Al_2O_3 catalyst prepared by co-impregnation exhibited better water-resistant performance. The results of XPS indicated that both CoAl_2O_4 and Co_3O_4 were present in the Pd catalysts modified by Co. For the catalyst prepared by sequential impregnation method, the ratio of CoAl_2O_4/Co_3O_4 was higher than that of the catalyst prepared by co-impregnation method. It could be concluded that Co_3O_4 played an important role in improving water-resistant performance.     

电厂废气中饱和水蒸气对活性炭变压吸附捕集CO2的影响

由于热电厂废气中含有高湿饱和水蒸气,选用疏水材料活性炭为吸附剂,利用真空变压吸附技术研究了活性炭分离电厂废气中水蒸气和二氧化碳的可行性和优越性,研究了水对CO₂捕集的影响。实验分析表明,水在活性炭上的“S”型等温吸附曲线有利于真空条件下被解吸。同时,圆锥模型描述了水蒸气在吸附床内的浓度分布。结果表明,即使水蒸气可以被活性炭吸附,但它的存在不影响CO₂的捕集。每个循环操作可在相对较短的解吸时间和较高的解吸压力下完成。实验中单床三步变压吸附工艺可以使CO₂回收率高达80%,CO₂纯度达43%。     

Experimental determination and prediction of the compressibility factor of high CO_2 content natural gas with and without water vapor

In order to study the effect of different CO2 contents on gas compressibility factor(Z-factor),the JEFRI-PVT apparatus has been used to measure the Z-factor of dry natural gas with CO2 content range from 10.74 to 70.42 mol%at the temperature range from 301.2 to 407.3 K and pressure range from 7 to 44 MPa.The results show that Z-factor decreases with increasing CO2 content in natural gas at constant temperature and increases with increasing temperature for natural gas with the same CO2 content.In addition,the Z-factor of water-saturated natural gas with high CO2 content has been measured.A comparison of the Z-factor between natural gas with and without saturated water vapor indicates that the former shows a higher Z-factor than the latter.Furthermore,Peng-Robinson,Hall-Yarborough,and Soave-Benedict-Webb- Rubin equations of state(EoS)are used for the calculation of Z-factor of high CO2 content natural gas with and without water vapor.The optimal binary interaction parameters(BIP)for PR EoS are presented.The measured Z-factor is compared with the calculated Z-factor based on three models,which shows that PR EoS combined with van der Waals mixing rule for gas without water and Huron-Vidal mixing rule for water-saturated gas,are in good agreement with the experimental data.     

SAPO-34上甲醇及二甲醚吸附等温线及吸附热测量与分析(英文)

在25,60和100°C下分别测定了甲醇及二甲醚在SAPO-34分子筛上的吸附等温线,同时用微量热法测定了微分吸附热与覆盖率的关系曲线(量热线),提出了吸附数据需要利用双吸附位Langmuir方程拟合,并获取了相应的吸附参数.对比测得的吸附等温线与量热线发现,在一定压力下,当甲醇及二甲醚在SAPO-34上达到一定吸附量后,随着吸附质分压增加,量热线快速下降,而吸附等温线显示出吸附量仍然继续增加.由此推断,在SAPO-34分子筛上存在两种吸附位——常规吸附位及弱吸附位,其中弱吸附位在高分压下继续吸附.如缺乏量热数据提供的常规吸附位饱和吸附量数据,对吸附等温线进行单吸附位拟合获取吸附参数极易导致错误结果,尤其是当吸附质分压较高时.建议采用双吸附位Langmuir方程,参照量热线提供的常规吸附位的饱和吸附量,通过拟合可以获得两种吸附位的吸附参数.     

Equilibrium adsorption of an oxygen-nitrogen mixture on zeolite NaX

Dependences of the Helmholtz energy, entropy, and internal energy in single micropores on the total number of guest molecules and the oxygen to nitrogen ratio were found by analysis of experimental data on adsorption of the binary oxygen-nitrogen mixture on zeolite NaX using the statistical model. A substantially non-ideal character of the adsorption phase, which exhibits negative deviations from Raout's law, can result from heterogeneity of the adsorption field inside single cavities. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1077–1082, June, 1999.     

Thermodynamics of CO<Subscript>2</Subscript> adsorption on zeolite NaX in wide intervals of pressures and temperatures

The dependences of the differential molar isosteric heat of adsorption and entropy of adsorption of CO₂ on zeolite NaX were determined in wide temperature (196–423 K) and pressure (0.1 Pa to 5.4 MPa) intervals. In the initial region of adsorption (a < 1 mmol g^–1), the differential molar heat of adsorption increases from 40 to 43 kJ mol^–1 and then decreases to 33 kJ mol^–1. The heat of adsorption remains virtually unchanged at 3 mmol g^–1< a < 6.5 mmol g^–1 and decreases sharply at high fillings of zeolite micropores (a > 7 mmol g^–1). The heat of adsorption was found to be temperature-dependent. The region with the constant heats shrinks with the temperature increase, and the heats begin to decrease at lower fillings of micro pores. The dependences of the change in the differential entropy of the adsorption system on the amount adsorbed were calculated at different temperatures. The specific features of the behavior of the thermodynamic functions of this adsorption system in the initial and medium region of fillings kre associated with interactions of adsorbate molecules with Na⁺ cations and walls of large cavities. For high fillings, an increase in repulsion forces between adsorbed molecules results in a sharp expansion of the adsorbent and a decrease in the heat of adsorption.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1570–1573, August, 2004.     

Comments on surface structure analysis by water and nitrogen adsorption

Specific surface area and pore size distribution are determined usually from adsorption isotherms at low temperatures using nitrogen or noble gases. These are not absolute parameters and the measuring methods are fraught with serious difficulties. General problems of sorption measurements and recent developments are discussed. To obtain information for practical purposes these measurements need to be supplemented by investigations of the sorbate/sorbent system used in practice. Results of the measurement of nitrogen and water vapour adsorption on different materials are compared. This revised version was published online in July 2006 with corrections to the Cover Date.     

Adsorption of water vapor on modified methacrylate polymeric sorbents

Adsorption of water vapor on methacrylate copolymers and terpolymers was studied. An increase in the content of the cross-linking agent gives rise to increase in the limiting adsorption of water vapor at the saturation pressure (a _s) and to decrease in the concentration of primary adsorption centers. Modification of the initial copolymer containing 60 % of 2,3-epoxypropyl methacrylate (EPMA) monomer and 40 % of cross-linking agent, ethylene dimethacrylate, with diethylenetriamine (DETA) results in an increase in thea _s value, while modification with C₁₂ and C₁₈ alkyl, benzyl, and phenyl groups gives rise to decrease in thea _s values for the copolymeric sorbents. The concentration of primary adsorption centers (a _m) increases considerably on modification of the copolymer with DETA and C₁₂ groups and decreases markedly on modification with benzyl and phenyl groups. For terpolymers, containing EPMA and styrene, an increase in the styrene/EPMA ratio reduces thea _s anda _m values. The copolymer modified with DETA groups possesses the most hydrophilic properties, while the copolymer modified with benzyl group exhibits the most hydrophobic properties. The mechanism of adsorption of water molecules on the polymers is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2163–2167, November, 1995.The work was financially supported by the Russian Foundation for Basic Research (Project No. 94-03-09550).