Sorption of nitrogen,oxygen, and argon in Cd (II) exchanged zeolite X: volumetric equilibrium adsorption and grand canonical Monte Carlo study

The adsorption of nitrogen, oxygen and argon has been studied in cadmium (II) cations exchanged zeolite X at 288.2 and 303.2 K. Experimentally measured adsorption isotherms are compared with theoretically calculated data using grand canonical Monte Carlo (GCMC) simulation. Nitrogen showed higher adsorption capacity and selectivity than oxygen and argon in these zeolite samples. The cadmium exchanged zeolite X was showed that increased adsorption capacity for nitrogen, oxygen, and argon with increase in Cd (II)-exchange levels, indicating as charge density increases adsorption capacity also increase. Isosteric heat of adsorption data showed stronger interactions of nitrogen molecules with cadmium cations in zeolite samples. These observations have been explained in terms of higher electrostatic interaction of nitrogen with extra framework zeolite cations. The selectivity of oxygen over argon is explained in terms of its higher interaction with Cd (II)-exchanged zeolites than argon molecules. The selectivity of N₂/O₂ of cadmium-exchanged zeolite X is better than only sodium containing zeolite-X. Heats of adsorption and adsorption isotherms were also calculated using GCMC simulation algorithm. Simulation studies expectedly show the proximity of nitrogen molecules to the locations of extra framework sodium and cadmium cations.     

Grand canonical Monte Carlo simulation and volumetric equilibrium studies for adsorption of nitrogen, oxygen, and argon in cadmium (II) exchanged zeolite A

The adsorption of nitrogen, oxygen and argon has been studied in cadmium (II) ions exchanged zeolite A at 288.0 and 303.0?K. Experimentally measured adsorption isotherms are compared with theoretically calculated data using grand canonical Monte Carlo (GCMC) simulation. Nitrogen showed higher adsorption capacity and selectivity than oxygen and argon in these zeolite samples. The cadmium exchanged zeolite A showed increased adsorption capacity for nitrogen, oxygen, and argon with increase in cadmium (II) exchange levels. Isosteric heat of adsorption data showed stronger interactions of nitrogen molecules with cadmium (II) cations in zeolite samples. These observations have been explained in terms of higher electrostatic interaction of nitrogen with extra framework zeolite cations. The selectivity of oxygen over argon is explained in terms of its higher interaction of oxygen with cadmium exchanged zeolites than argon molecules. Heats of adsorption and adsorption isotherms were also calculated using grand canonical Monte Carlo simulation algorithm. Simulation studies expectedly show the proximity of nitrogen molecules to the locations of extra framework sodium and cadmium cations.     

空分富氧沸石分子筛吸附剂的研究

介绍了国内外目前以PSA技术进行空气分离制备氧气所用沸石分子筛吸附剂的研究状况。从研究结果来看，N2吸附容量和N2／O2分离选择性的提高主要通过对沸石分子筛4A和13X进行离子交换，以对其表面进行改性，从而调整对N2、O2的吸附性能。另外，沸石分子筛制备过程中的硅铝比和成型条件等对N2和O2的吸附也有一定的影响。     

Clinoptilolites for nitrogen/methane separation

Clinoptilolites, naturally occurring zeolites, currently used by nuclear industry for ion exchange and drying, were evaluated for the nitrogen/methane separation. Ion exchange of purified clinoptilolite was carried out individually with the cations Na⁺, Mg²⁺, Ca²⁺, K⁺ and H⁺, and the adsorption isotherms and diffusion rates were measured. Purified and Mg-clinoptilolite show potential for nitrogen/methane separation and high-pressure adsorption isotherms were measured in a differential absorption bed. Pressure swing adsorption simulations were performed for purified clinoptilolite, Mg-clinoptilolite and the commercial sorbent ETS-4. Purified clinoptilolite shows slightly higher recovery and lower productivity than ETS-4 for similar product purity (∼95%). Mixed ion-exchanged clinoptilolites of Mg/Ca cations, K/Na cations and Mg/Na cations were also prepared and studied for the nitrogen/methane separation. Mg/Na (50/50) mixed ion-exchanged clinoptilolite exhibits very good equilibrium and kinetic selectivity in the low-pressure range, better than purified clinoptilolite. Mixed-exchange clinoptilolites were also found to show a wide range of adsorption characteristics with varying ratios of cation exchange, thereby making them suitable for further improvements in nitrogen/methane separation.     

Adsorption separation of R134a,R125, and R143a fluorocarbon mixtures using 13X and surface modified 5A zeolites

We report a facile method for the adsorption separation of fluorocarbon blends containing tetrafluoroethane (R134a), pentafluoroethane (R125) and trifluoroethane (R143a) refrigerants into their pure components using commercial 13X zeolite and pore‐size modified 5A zeolite under ambient condition. Based on the measured R134a, R125, and R143a pure gas equilibrium adsorption isotherms, the adsorption capacity varies in the order of R134a > R143a > R125 on 13X zeolite. The mixed gas breakthrough experiments reveal that 13X zeolite selectively adsorbs R134a over R125 and R143a. By running two adsorption cycles, it is possible to obtain R134a with ultrahigh purity. Furthermore, through chemical modification of tetraethyl orthosilicate (TEOS), the pore size of 5A zeolite could be successfully narrowed to the extent to just adsorb R125 while excluding R143a. The modified 5A zeolite was utilized to separate refrigerant mixtures containing R125 and R143a into their pure components. © 2017 American Institute of Chemical Engineers AIChE J, 64: 640–648, 2018     

Air separation by pressure swing adsorption

The original pressure swing air separation process, developed almost simultaneously by Exxon and Air Liquide, uses a nitrogen selective zeolite adsorbent to produce a high purity oxygen product. The same basic process is still widely used in small scale units although, for larger scale units, many modifications to the cycle have been introduced in order to reduce power consumption. Although nitrogen can in principle be recovered from the blowdown stream of such systems, if high purity nitrogen is the required product, it is more economic to use an oxygen selective adsorbent. Most adsorbents show either no selectivity or preferential adsorption of nitrogen. However, in small pore carbon molecular sieves or 4A zeolite there is a substantial difference in diffusion rates so that an efficient kinetic separation is possible. Somewhat different cycles are generally used in such processes. Progress in modelling the dynamic behaviour of both types of PSA system is reviewed and comparisons between experimental performance and the model predictions are shown. A simple linear driving force model provides a good overall prediction of the effects of process variables but the computationally more cumbersome diffusion model gives better quantitative agreement with experiment. Comparisons are drawn between the performance achieved (in nitrogen production) with two different kinetically selective adsorbents; RS-10 (a modified 4A zeolite) and Bergbau Forschung carbon molecular sieve.     

Binary adsorption behaviour of methane and nitrogen gases

Separation of methane and nitrogen gases is critical in the upgrading of LFG (Landfill gas), natural gas and coal bed gas in order to have a commercial heating value for methane. From an environmental point of view, methane capture from landfill gas is essential to prevent greenhouse gas emissions. Adsorption could be a beneficial process to capture low purity methane from a landfill site that is nearing the end of its lifecycle and produce high purity methane. In this work, Ceca 13X zeolite and Alcan Activated Alumina AA 320-AP have been studied for their potential for this separation and compared with Silicalite in literature. Pure and mixture adsorption isotherms were determined at 40 and 100?°C for these adsorbents by constant volume method and concentration pulse chromatographic technique, respectively. Mixture adsorption isotherms for the binary system of methane and nitrogen gases at 40 and 100?°C and 1 atmosphere total pressure have been determined by VV?CCPM (Van der Vlist and Van der Meijden Concentration Pulse Method). The application of Extended Langmuir model for this binary system have also been discussed and compared to the experimental results. Results show that equilibrium separation factor for silicalite is larger than zeolite Ceca 13X and Alcan activated alumina AA320-AP. Both Silicalite and Ceca 13X find application in the bulk separation of methane from nitrogen when y _CH4?>?0.4, especially in LFG, coal bed gas and natural gas.     

High resolution,quasi-equilibrium sorption studies of molecular sieves

Argon, nitrogen, and neopentane adsorption isotherms from molecular sieves are recorded at 87 K, 77 K, and 273 K, respectively, by a quasi-equilibrium, high resolution gas sorption technique. The molecular sieves used in this study are alkali exchanged zeolite X, AlPO₄-11, AlPO₄-5, VPI-5, KL, CaA, ZSM-5, and ZSM-11. Little relation is observed between the transition pressure for microporous nitrogen adsorption and pore size. Small changes in the effective pore size resulting from variations in cation size are detected in the transition pressure for argon adsorption. Large shifts in the transition pressure for argon adsorption are found for the 10-, 12-, and 18-membered ring pores of AlPO₄-11, AlPO₄-5, and VPI-5, respectively. Argon adsorption combined with neopentane adsorption on microporous materials provides additional information regarding transitions in the isotherm that result from dual pore systems and effects that may be due to adsorbate packing. The step in the nitrogen isotherm atP/P ₀> 0.1 from ZSM-5 is not observed in the nitrogen isotherm from ZSM-11.     

AC/X-G吸附剂的制备及CH4/N2吸附分离性能

采用浓度为0.2g·ml^-1的葡萄糖溶液对13X沸石/活性炭复合材料(AC/X)进行碳沉积,研究沉积次数对复合吸附剂(AC/X-G)孔结构、表面性质和CH₄/N₂吸附分离性能的影响。通过X射线衍射,77K下的N₂吸附/脱附,扫描电镜,CO₂-TPD以及红外光谱表征样品的晶型、孔结构和表面性质,在298K、100kPa下对其CH₄和N₂吸附等温线进行测定,并将吸附结果与文献中碳材料和13X沸石的吸附性能进行比较。结果表明:随着沉积次数的增加,AC/X-G吸附剂中X型沸石的相对含量降低,微孔比表面积和微孔体积减少。AC/X-G的表面被碳膜覆盖,碱量降低,但出现强碱位和含氧基团C-O键。AC/X-G的CH₄和N₂吸附量下降,但吸附分离系数提高,沉积3次的样品AC/X-G-3的CH₄/N₂吸附分离系数达到3.0,表面的含氧基团有利于提高复合材料的CH₄/N₂吸附分离性能。     

Sr2+ Exchanged Zeolite X as an Adsorbent Material for Chromatographic Separation of Argon-Oxygen Gaseous Mixture

The separation of argon and oxygen from their gaseous mixture is very difficult to accomplish by the adsorption process using zeolite adsorbents due to the closeness of their molecular properties and adsorption behavior in the zeolites. Strontium exchanged zeolite X (SrX) showed the adsorption selectivity for oxygen over argon at ambient temperature and demonstrated its potential as a column–packing material for the gas chromatographic analysis of argon-oxygen mixtures. The adsorption capacities and Henry's law constants for oxygen and argon increased in SrX compared to NaX at ambient temperature. Activation of the SrX adsorbent is shown to play a highly significant role in the separation of argon-oxygen mixture due to the low hydrothermal stability of SrX.     

Fractionated Vacuum Swing Adsorption Process for Air Separation

Abstract

A novel adsorptive process for air separation using a zeolitic adsorbent is described. The process essentially consists of three simple cyclic steps, and it can be used for simultaneous production of an 80—90% oxygen-enriched gas and a 98 + % nitrogen-enriched gas from ambient air. Successful operation of the process requires the use of a zeolite which exhibits high nitrogen adsorption capacity and selectivity from air. The role of nitrogen adsorption selectivity of the zeolite in the vacuum desorption process is examined, and experimental performance data for the air separation process are reported.     

Adsorption of CO2 on Zeolite 13X and Activated Carbon with Higher Surface Area

In this work, adsorption isotherms and adsorption kinetics of CO₂ on zeolite 13X and activated carbon with high surface area (AC-h) were studied. The adsorption isotherms and kinetic curves of CO₂ on the adsorbents were separately measured at 328 K, 318 K, 308 K, and 298 K and with a pressure range of 0–30 bar by means of the gravimetric adsorption method. The mass transfer constants and adsorption activation energy E_a of CO₂ on the adsorbents were estimated separately. Results showed that at very low pressure the amounts adsorbed of CO₂ on the zeolite 13X was higher than that on the AC-h, while at higher pressure, the amounts adsorbed of CO₂ on the AC-h was higher than that on the zeolite 13X since the AC-h has a larger surface area and a larger total pore volume compared to the zeolite 13X. The adsorption kinetics of CO₂ can be well described by the linear driving force (LDF) model. With the increase of temperature, the mass transfer constants of CO₂ adsorption on both samples increased. The adsorption activation energy E_a for CO₂ on the two adsorbents decreased with the increase of pressure. Furthermore, at low pressure the E_a for CO₂ adsorption on the zeolite 13X was slightly lower than that on the AC-h, while at higher pressure the E_a for CO₂ adsorption on the zeolite 13X was higher than that on the AC-h.     

Adsorption of Carbon Dioxide on High-Silica Zeolites with Different Framework Topology

Adsorption isotherms of carbon dioxide were measured on six high-silica zeolites TNU-9, IM-5, SSZ-74, ferrierite, ZSM-5 and ZSM-11 comprising three-dimensional 10-ring (8-ring for ferrierite) at 273, 293, 313 and 333 K. Based on the known temperature dependence of CO₂ adsorption, isosteric heats of adsorption were calculated. The obtained adsorption capacities and isosteric adsorption heats related to the amount of CO₂ adsorbed have provided detailed insight into the carbon dioxide interaction with zeolites of different framework topology. The zeolites TNU-9 and ferrierite are characterized by pronounced energetic heterogeneity whereas due to the location of Na⁺ cations in the same positions the isosteric adsorption heats of CO₂ adsorption on IM-5, ZSM-5 and ZSM-11 zeolites are rather constant for molecular ratio CO₂/Na⁺ < 1. As IM-5 zeolite has a maximum adsorption capacity, it appears to have optimum properties for carbon dioxide separation.     

干气中烷烃、烯烃新型分离吸附剂的研究进展

综述了二十年来烯烃烷烃新型分离吸附剂的研究进展,与传统的π络合吸附剂相比,优先吸附烯烃的吸附剂包括金属有机材料（MOF）、Engelhard Titanosilicate （ETS）、高硅分子筛和介孔分子筛,主要是利用氢键作用、孔径大小、分子扩散速率差异或π络合作用,将烷烃烯烃分离;而优先吸附烷烃的吸附剂包括AlMePO-α、ZIF-7和凹凸棒黏土,主要利用吸附剂上甲基与烷烃的相互作用。MOF对烯烃吸附量大,但选择性较差;高硅分子筛对烯烃的动力学分离效果良好;介孔分子筛经过渡金属改性后,对烯烃有优良的选择性;ETS类对烯烃有较高的吸附量和选择性,且稳定性强,有很好的应用前景。     

应用Wilson方程和均相溶液理论计算固液吸附平衡

固液吸附平衡计算对于吸附分离设计具有重要意义。采用吸附质固体溶液理论并用Wilson方程描述各组分之间的相互作用,计算了6个烃类二元液体混合物在分子筛NaX和KBaY、硅凝胶和活性炭上的吸附平衡数据,进一步考察了该理论的适用性和计算精度。结果表明,该理论模型可以较好地关联二元液相混合物在固体表面的吸附等温线,关联结果的总平均相对偏差为5.0%,而且该模型可以预测其他温度下的吸附平衡,预测精度也在5%之内。     

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.     

Accelerated synthesis of all-silica DD3R and its performance in the separation of propylene/propane mixtures

Synthesis of the all-silica Deca-Dodecasil 3 Rhombohedral (DD3R) zeolite was accelerated 10 times by seeding with small amount of crystals (0.02 wt%) with yields approaching 100%. The effects of other synthesis variables, like silica source, the presence of methanol or the synthesis pH on the final product distribution have been studied. The adsorption and separation of propylene and propane mixtures on this material are presented. The improved synthesis may form the basis to scale-up production of DD3R for selective separation processes. The single component adsorption isotherms could be well described with a dual-site Langmuir model. The binary mixture adsorption was determined from breakthrough/desorption experiments at 323, 358 and 383 K. By modelling the adsorptive column, diffusion coefficients at infinite dilution for single component and the effect of propane over propylene adsorption were determined. Cylindrical geometry describes the pore topology of DDR type materials well. Propane decreases the uptake rate of propylene by adsorption in the surface of the crystals. Propylene diffusion is best described by the “strong confinement” model inside the zeolite cages. Separation is due to only propylene adsorption with diffusion as rate determining step.Results revealed DD3R as a very effective molecular sieve for the separation or purification of propane–propylene mixtures.     

Diffusion of propane,propylene and isobutane in 13X zeolite by molecular dynamics

This paper presents single component diffusion data of propane, propylene and isobutane in zeolite 13X obtained by molecular dynamics (MD) simulations, especially its dependence on temperature and concentration. Our results are critically compared to experiments and previous simulation data, when available. One novelty of this work is that the diffusion coefficients are computed taking the framework cations of zeolite 13X into consideration. Furthermore, to our knowledge, we present the first simulation results for propylene diffusion in faujasite frameworks. From the mean squared displacements, self-diffusion coefficients of 7.5×10^?9, 9.1×10^?9, and 9.6×10^?10 m² s^?1 for 2 molecules/unit cell were calculated for propane, propylene, and isobutane at 373 K, respectively. The simulations show that the diffusivity decreases with increasing loadings for all adsorbates studied. Finally, transport diffusivities were estimated from the self-diffusion coefficient and the equilibrium adsorption isotherms by using the Darken equation.     

Concentration-Thermal Swing Adsorption Process for Separation of Bulk Liquid Mixtures

Abstract

A novel concentration-thermal swing adsorption process is described for separation of bulk binary liquid mixtures. The process is designed to produce essentially two pure products with high recoveries of both components. It is particularly suited for separation of azeotropic or close-boiling liquid mixtures which are difficult to separate by distillation. An example of the performance of the new process for separation of an azeotropic water-methyl acetate mixture is given. Experimental binary surface excess equilibrium isotherms, adsorptive mass transfer coefficients, and column dynamics for adsorption of water-methyl acetate mixtures on NaX zeolite are reported.     

Separation of fatty acid methyl esters from tall oil by selective adsorption

Fatty acid methyl esters (FAME) and resin acids (RA) were separated from tall oil by selective adsorption. Commercial nonmodified molecular sieve 13X was used as adsorbent. The adsorption isotherms of fatty acids (FA), FAME, and RA on molecular sieve 13X at 25°C were determined using various solvents. The solvents were methanol, ethanol, isopropanol, acetone, benzene, hexane, isooctane, petroleum ether (40–60°C), and petroleum naphtha (80–180°C). With each solvent, FA and RA were adsorbed to a greater extent than FAME. Adsorption isotherms for RA and FAME in binary adsorption systems were also determined using petroleum ether, petroleum naphtha, benzene, and isopropanol. For each component in the binary adsorption, the equilibrium amounts are lower than the values for pure component adsorption. The adsorption of FAME decreased in the presence of RA markedly in petroleum ether and petroleum naphtha. This fact may be the indication of the phenomenon of selective adsorption. Separation was accomplished by adding a solution of esterified tall oil in solvents used in the binary adsorption systems, through a column packed with molecular sieve 13X. With petroleum naphtha, FAME and RA were recovered in yields of 93 and 94%, respectively, from esterified tall oil. Petroleum naphtha gave the best results. The effects of particle size of adsorbent and flow rate of solvent on the efficiency of the separation were also investigated in fixed-bed column studies. The particle size of adsorbent did not apparently alter the results. Changes in the particle size should not significantly change the number of available adsorption sites in a microporous molecular sieve.