Predictive Dynamic Model of Air Separation by Pressure Swing Adsorption

A general dynamic model is developed for separation of air over a carbon molecular sieve and a zeolite adsorbent for production of nitrogen and oxygen. The proposed model is validated using experimental data from working laboratory scale N₂–PSA and laboratory scale O₂–PSA systems. Simulations studies are performed to investigate the effect of changing various process variables, such as the duration of PSA steps, bed length and feed inlet velocity.     

Carbon-based oxygen selective desiccants for use in nitrogen PSA

Techniques for the production of composite oxygen selective adsorbents are disclosed. These adsorbents are comprised of a carbon molecular sieve (CMS) which is kinetically selective for the adsorption of oxygen over nitrogen and an agent for the sorption of water such as LiCl or SiO₂. The adsorption properties of the composite adsorbents and results obtained from pressure swing adsorption (PSA) process testing are presented. The composite adsorbents improve the nitrogen PSA process performance (recovery and productivity) over the use of conventional desiccants which do not exhibit oxygen selectivity. Using a standard nitrogen PSA process cycle, replacement of conventional inorganic desiccants like alumina with the current CMS-based desiccants improved air recovery 2 to 4 percentage points and increased nitrogen productivity 15 to 20% at 70°F and a nitrogen purity of 99.5%.     

Adsorbent Evaluation Based on Experimental Breakthrough Curves: Separation of p‐Xylene from C8 Isomers

The search for new adsorbents with enhanced capacity and selectivity, suitable for application on large‐scale simulated moving‐bed units for separation of p‐xylene, requires efficient, reliable, and fast adsorbent characterization methods for this specific separation. Fixed‐bed experiments were carried out under the conditions of the Parex process to evaluate a faujasite‐type zeolite as adsorbent for the separation of p‐xylene from its isomers in the proportions of the real Parex feed stream. The experimental breakthrough curves were used to evaluate the selected adsorbent in terms of nonselective and selective volumes, adsorption capacity, selectivity, and productivity, which can be applied to identify the feasible separation region for different operating conditions.     

Air Fractionation by Adsorption

Abstract

Pressure swing adsorption (PSA) processes for air separation differ by the modes and conditions of operation of the adsorption, the desorption, and the complementary steps, as well as by the types of adsorbents used. Three commercial PSA processes for air separation are reviewed and compared. The first process uses a zeolitic adsorbent and produces only an oxygen-enriched product gas. The second process uses a carbon molecular sieve and produces only a nitrogen-enriched product gas. The third process uses a zeolite and simultaneously produces both oxygen-and nitrogen-enriched product gases. The performance and separation efficiency of the last process, called the ‘vacuum swing adsorption (VSA) process’, are reported to be superior to the others.     

丙烯丙烷吸附分离材料研究进展

在丙烯的生产过程中,因丙烯/丙烷的分子大小及挥发性较为接近而难以高效分离,其精馏分离过程能耗较高。变压吸附(PSA)技术作为一种高效的气体分离技术,其核心是高效吸附剂的开发。该文综述了近年来国内外关于丙烯/丙烷分离吸附剂的研究进展。重点介绍了分子筛、碳分子筛以及金属-有机骨架材料(MOFs)在丙烯/丙烷分离上的应用。详细阐述了影响多孔材料丙烯/丙烷吸附分离比的关键因素,并对比了几种吸附分离材料的优缺点。研究发现,应根据实际应用场合、原料气体的组成、丙烯/丙烷相对含量以及吸附材料的实际使用条件等来选择合适的吸附剂。最后,对丙烯/丙烷吸附分离材料的开发及其在实际中的应用进行了展望。     

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.     

氧和氮在炭分子筛上的吸附与扩散

用重量法研究了氧、氮在两种空分用炭分子筛上的吸附与扩散。结果表明,氧和氮在炭分子筛中的扩散是活化扩散,该过程可用双孔模型进行描述。求得了氧、氮的扩散系数。     

Adsorption and Desorption of Carbon Dioxide and Nitrogen on Zeolite 5A

The adsorption equilibrium data of CO₂ and N₂ at (303, 333, 363, 393, 423) K ranging 0-1 bar on zeolite 5A is reported. The pressure and temperature range covers the operating pressure in adsorption units for CO₂ capture from power plants. Experimental data were fitted by the multi-site Langmuir model. The adsorbent is much more selective to CO₂: loading at 303 K and 100 kPa is 3.38 mol/kg while loading of N₂ at the same pressure is 0.22 mol/kg. The Clausius-Clapeyron equation was employed to calculate the isosteric enthalpy of adsorption. The fixed-bed adsorption and desorption of carbon dioxide and nitrogen on zeolite 5A pellets has been studied. A model based on the bi-LDF approximation for the mass transfer, taking into account the energy and momentum balances, had been used to describe the adsorption kinetics of carbon dioxide and nitrogen. The model predicted satisfactorily the breakthrough curves obtained with carbon dioxide–nitrogen mixtures. Desorption process (consisting of depressurization, blowdown, and purge) was also performed. Following the feasibility of concentration and capture of carbon dioxide from flue gases by Pressure Swing Adsorption (PSA) process was simulated. A CO₂ recovery of 91.0% with 53.9% purity was obtained using a five-step Skarstrom-type PSA cycle.     

Effects of the Residence Time in Four-Bed Pressure Swing Adsorption Process

Abstract

Hydrogen separation by the four-bed PSA process using layered beds of activated carbon and zeolite 5A was investigated experimentally and theoretically to recover high purity H₂ from steam methane reforming off-gas. The recovery increased with increasing the residence time at given product purity because of the contact time between the impurities and the adsorbents is increased. The difference of increasing the recovery became smaller with increasing the residence time and then the recovery was not increased after 43.6 seconds of the residence time. The minimum residence time exists to obtain the maximum recovery at desired product purity (99.999%+).     

变压吸附法回收高炉气中CO的研究

采用载铜吸附剂进行了变压吸附回收高炉气中CO的工业侧线试验 ,考察了载铜吸附剂与 5A分子筛分别用于回收高炉气中CO时的产品纯度和CO的回收率 ,试验结果表明 ,载铜吸附剂对高浓度N2 中的CO有很好的选择性 ,其性能优于 5A分子筛。从技术经济角度分析了两步变压吸附法应用于高炉气中CO回收的可行性、环境效应和经济效益。     

Gas separation by pulsed pressure swing adsorption

An experimental study of the separation of a binary mixture of methane and carbon dioxide by pulsed pressure swing adsorption in a single isothermal column packed with an activated carbon adsorbent revealed that a product containing 72% methane could be obtained from a feed mixture containing only 44% methane. When a 5A zeolite was used as adsorbent, the product contained more than 92% methane, the initial feed mixture being only 46% methane. A mathematical model of the process operation is shown to be in general agreement with the experimental results obtained.     

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。     

Carbon Di-Oxide Removal with Mesoporous Adsorbents in a Single Column Pressure Swing Adsorber

Abstract

A five-step PSA cycle was studied for CO₂ separation from CO₂-N₂ gas mixture in a single column at elevated temperatures using Poly-ethyleneimine (PEI) impregnated mesoporous silica SBA-15 as adsorbent. The PSA cycle study included a strong adsorptive rinse step in which the strongly adsorbed component, i.e., CO₂ was used for rinsing the adsorbent bed in order to increase the purity of CO₂ product. The study indicates that the adsorbent is regenerable under typical PSA conditions. The productivity of the adsorbent studied for CO₂ separation was found to be comparable with commercial zeolite adsorbents as reported in literature.     

沸石分子筛用于VOCs吸附脱除的应用研究进展

挥发性有机化合物（volatile organic compounds,VOCs）作为空气中有机污染物的主要成分,对环境与人类健康造成了严重的危害。吸附法可有效富集低浓度VOCs气体,成本低、易操作,是末端治理去除VOCs的主要技术。沸石分子筛具有高度有序、孔径可调的微孔孔道,可实现VOCs分子的选择性吸附,且热稳定性极佳,易于脱附再生,是一种优良的VOCs气体吸附剂。本文分别从沸石分子筛的结构性质、复合型分子筛吸附剂以及整体式分子筛吸附剂三方面详细介绍了沸石分子筛用于VOCs吸附脱除的研究进展。结果表明,变换骨架拓扑结构以及补偿阳离子类型,可实现对VOCs分子进行选择性吸附;提高结构疏水性可有效降低高湿度条件下水分子对VOCs的竞争吸附,增强分子筛吸附剂的环境适应性;通过孔道多级化或与其他介/大孔构建复合型吸附剂,可提高分子筛吸附剂的比表面积和孔容,增大对VOCs的吸附容量;沸石分子筛可构建为整体式吸附剂,相较于颗粒型吸附剂,其机械强度更高,应用性更强。文章还指出,作为整体式分子筛吸附剂的典型代表,分子筛转轮吸附技术在高通量、高压降等吸附工况条件下均表现出极佳的VOCs吸附脱除效率,已广泛应用于工业排放VOCs的有效治理。     

Production of argon free oxygen by adsorptive air separation on Ag‐ETS‐10

The purification of different components of air, such as oxygen, nitrogen, and argon, is an important industrial process. Pressure swing adsorption (PSA) is surpassing the traditional cryogenic distillation for many air separation applications, because of its lower energy consumption. Unfortunately, the oxygen product purity in an industrial PSA process is typically limited to 95% due to the presence of argon which always shows the same adsorption equilibrium properties as oxygen on most molecular sieves. Recent work investigating the adsorption of nitrogen, oxygen and argon on the surface of silver‐exchanged Engelhard Titanosilicate‐10 (ETS‐10), indicates that this molecular sieve is promising as an adsorbent capable of producing high‐purity oxygen. High‐purity oxygen (99.7+%) was generated using a bed of Ag‐ETS‐10 granules to separate air (78% N₂, 21% O₂, 1% Ar) at 25°C and 100 kPa, with an O₂ recovery rate greater than 30%. © 2012 American Institute of Chemical Engineers AIChE J, 59: 982–987, 2013     

New cycle configuration to enhance performance of kinetic PSA processes

This work shows a new column arrangement to improve the utilization of the adsorbent in multi-column Pressure Swing Adsorption (PSA) processes. This cycle was specifically designed to increase the unit productivity for gas separations using adsorbents with slow diffusion kinetics where mass transfer zone (MTZ) inside the column is important. In this column arrangement, when the heavy (most adsorbed) gas breaks through one column, the exit of this column is connected to a second column (trim bed) where more heavy gas can be adsorbed. In this way, also more heavy gas will be adsorbed in the first (lead) column. The increase of process performance is directly related to the length of the MTZ: the larger the MTZ, the better will perform using the lead-trim beds concept. The cycle performance was tested for biogas upgrading to obtain high purity bio-methane (purity >98%) that can be used as renewable fuel. Two different adsorbents were employed in the process simulations: zeolites 13X (fast diffusion) and carbon molecular sieve (slow diffusion). Furthermore, the possibility of using less power in the purge step was considered. Using this process, it was possible to obtain unit productivity of 5.5 mol CH₄ per hour per kilogram of adsorbent.     

炭分子筛上氧、氮吸附特性的实验测定

针对BF型炭分子筛孔结构的特点,利用双分散孔结构吸附模型,采用色谱扰动-应答方法,对微孔扩散控制传质机理进行了实验认定,测定了O2的吸附平衡常数K、扩散时间常数Dc/rc2以及O2、N2两组分常温下的吸附等温线.     

CMS+ZMS二级变压吸附制纯氧的优化研究

文利用电路网络模型对变压吸附制氧工艺流程模拟并优化操作参数后,用碳分子筛吸附空气中大部分的Ar和N2,解吸出的大约70%左右的氧气作为沸石分子筛单元的进料气,在沸石分子筛中除去余下的N2,即可得到产品回收率为28.4%,浓度为99.06%的纯氧。通过模拟发现,在保证氧气纯度的前提下,通过筛选工艺流程,优化阀系数、操作时间、吸附和脱附的压力,从而提高氧气回收率,降低了制纯氧的成本。     

无机固体吸附剂在二氧化碳捕集应用中的研究进展

随着全球气候变暖,二氧化碳的捕集、利用和封存（CCUS）逐渐成为科学界和工业界的研究热点。CCUS的关键是选择性地从气体混合物中捕集二氧化碳。目前二氧化碳捕集技术包括化学吸收、膜分离、吸附和低温分离等。吸附法是利用吸附剂对不同气体的吸附能力差异来进行二氧化碳捕集。综述了分子筛、介孔二氧化硅、黏土及多孔碳等无机固体吸附剂在二氧化碳捕集应用中的研究进展。对比了不同改性方法对吸附剂吸附二氧化碳性能的影响。从应用角度来看,分子筛、介孔二氧化硅、黏土具有潜在的成本效益,但仍需在工程设计开发方面得以进一步发展,以适用于不同应用需求的二氧化碳捕集。     

改性沸石对气态汞吸附的实验研究

为了获得消耗量小、性能高效的燃煤烟气脱汞吸附剂,采用活性MnO2浸渍、FeCl3浸渍和不同温度下渗硫等方法,对沸石进行了改性,制得一系列改性沸石吸附剂。采用固定床吸附的方式,对吸附剂在不同条件下的吸附效果进行了测试,筛选出一种高效、廉价的MnO2浸渍沸石吸附剂,和原沸石吸附剂相比,改性沸石吸附剂对汞蒸气的吸附能力有较大提高,有效吸附时间大大增加,在有效吸附时间内,穿透率大大降低。改性后的沸石吸附能力大大提高的原因在于其吸附过程中,除了物理吸附,还发生了化学吸附。