Linear driving force approximation in cyclic adsorption processes: Simple results from system dynamics based on frequency response analysis

The linear driving force (LDF) approximation for cyclic adsorptive processes is discussed on the basis of model equivalence with the homogeneous diffusion model (HDM), the pore diffusion model (PDM) and the intraparticle diffusion and convection model (IDCM). Model equivalence is based on the frequency response of the adsorbent particle, namely on the equality of the amplitude ratio and the phase-lag functions. The analysis of the continuous stirred tank adsorber (CSTA) and of the plug flow adsorber (PFA) is addressed.     

Novel design and performance of a medical oxygen concentrator using a rapid pressure swing adsorption concept

A novel design of a compact rapid pressure swing adsorption system consisting of a single adsorber enclosed inside a product storage tank is proposed for application as a medical oxygen concentrator (MOC). A self‐contained test unit for the process is constructed which is capable of directly and continuously producing 1–3 sl/m of 90% O₂ from compressed air. Pelletized LiLSX zeolite is used as the air separation adsorbent. Steady state process performance data [bed size factor (BSF) and O₂ recovery (R) as functions of total cycle time (t_c)], as well as transient, cyclic, adsorber pressure, and temperature profiles are presented. A four‐step Skarstrom‐like pressure swing adsorption cycle was used. Two options for column pressurization, (a) using compressed feed air cocurrently or (b) using a part of the oxygen‐enriched product gas counter‐currently were evaluated. Option (b) exhibited superior performance. The optimum total cycle time for option (b) was 5–6 s where the BSF was lowest (～45 kgs/TPD O₂) and the corresponding R was ～29.3%. These numbers indicate that the adsorbent inventory of a MOC can be potentially reduced by a factor of three while offering a ～10–20% higher O₂ recovery compared to a typical commercial unit. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3330–3335, 2014     

变压吸附法分离H_2－CO_2气体混合物

采用变压吸附法进行Ｈ２－ＣＯ２气体混合物的分离研究。通过对不同吸附剂的吸附性能比较试验，选取１３ｘ分子筛为本研究体系的吸附剂。在３塔变压吸附装置上进行了变压吸附过程试验；对不同的原料气组成，在不同的吸附压力、原料气量、再生压力、再生气量以及再生时间条件下，分别测定了变压吸附的动态吸附能参数；考察了这些参数对吸附分离过程的影响；得到了一些较为实用的工艺参数。用线性推动力模型对变压吸附的全过程进行了模拟，采用正交配置法对模型求数值解，较好地预测了实验结果。     

Analysis of Gas Purification by Pressure Swing Adsorption: Priming the Parametric Pump

Abstract

The transients during start-up of a pressure-swing adsorber lead to material and energy losses. A dynamic mathematical model is developed to analyze the PSA process to elucidate the conditions under which losses may be minimized. It is based on an ideal binary mixture comprised of components that have linear isotherms.

A processing alternative that virtually eliminates losses is suggested. The alternative is formulated by considering the PSA process as a specific type of parametric pump. It follows intuively that, as in an ordinary pump, the parametric pump will commence operation at steady-state if it is primed. In the case of PSA, that amounts to purging the initial adsorber contents with the less strongly adsorbed component.

Illustrations are provided of both single-bed and dual-bed processes. For a specific gas mixture and adsorbent, the effect of varying the ratio of the high and low pressures that occur in a cycle is examined. Results indicate that there is a significant advantage in priming the single-bed version because of the surge tank, which promotes backmixing. There is still an advantage in priming the dual-bed version, however, despite the absence of back-mixing.     

Modeling of solid—liquid adsorption: Effects of adsorbent loads on model parameters

The adsorption of cobalt phthalocyanine dye onto activated carbon in a continuous stirred tank adsorber was studied. The variables investigated were: adsorbent mass, adsorbent particle size and fluid flowrate. Several models based on film, pore and surface diffusion were constructed and fitted to the experimental data. Experimental results showed: (i) the increasing importance of the film mass transfer resistance for increasing adsorbent loads; (ii) the increasing importance of the surface diffusion mechanism for increasing adsorbent loads; and (iii) the better discrimination among different models for higher adsorbent loads and lower flowrate.     

催化裂化汽油吸附脱硫工艺研究

在固定床吸附装置上对催化裂化汽油进行吸附脱硫实验,考察了吸附脱硫工艺条件对催化裂化汽油硫质量分数、辛烷值及吸附剂单程寿命的影响。实验结果表明,吸附脱硫适宜的工艺条件为:吸附温度360℃,吸附压力0.3 MPa,氢气流量300 mL/m in,体积空速1.0 h-1。通过对吸附脱硫实验过程中的尾气分析,对催化裂化汽油吸附脱硫的机理进行了探讨。     

π型向心径向流吸附器变质量流动特性研究

对径向流吸附器内变压吸附(PSA)制氧的变质量流动规律进行研究,有助于准确掌握吸附过程及床层内的变量因素对制氧性能的影响。对π型向心径向流吸附器建立气固耦合的两相吸附模型,并对其PSA制氧过程进行了数值模拟研究,得到了床层内氧气浓度分布、温度分布以及产品气浓度的变化规律。结果表明：首次循环结束时床层内氧气最高摩尔分数可达66.02%,回收率29.2%。非稳定循环期间,氧气摩尔分数从66.02%升高至 97.5%,回收率从29.2%提高至38.5%。循环达到稳定后,床层内氧气摩尔分数最高可达98.6%,回收率38.9%左右,且达到稳定状态后床层内气固两相温差减小,逐渐达到热平衡。获得了吸附器内部气体与吸附剂两相间的传质、传热过程,为π型向心径向流吸附器用于PSA制氧提供技术支持。     

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.     

载金属离子的氧化铝吸附净化汽油中硫醇

采用载金属离子的氧化铝吸附净化汽油中硫醇。在微波条件下负载不同离子 ,从净化效果和吸附速率等方面选择了适宜的金属离子 ,实验测定了静态吸附平衡数据和动态吸附透过曲线 ,在本文所测的浓度范围内 ,静态吸附平衡数据符合线性关系 ,研究结果表明 :吸附剂具有净化汽油中硫醇和总硫的双重效果 ,可以为吸附过程的设计提供基础数据     

Comparative performance of an adiabatic and a nonadiabatic PSA process for bulk gas separation—a numerical simulation

A detailed numerical model of a Skarstrom‐like PSA process is used to investigate the separation performance of an adiabatic and a nonadiabatic process for removal of bulk CO₂ impurity from inert He. The complexity of the gas phase adsorbate composition, adsorbate loading, and the adsorbent temperature profiles as functions of positions inside an adsorber at the start and end of each step of the PSA process are discussed. The separation performance of a nonadiabatic PSA process is generally inferior to that of the corresponding adiabatic process. Smaller adsorbent column diameter accentuates nonadiabatic operation and hence lower separation efficiency. Furthermore, the separation efficiency decreases more rapidly at short cycle times and smaller column diameters. Insulation of PSA columns of a process development unit operated under these conditions is recommended for reliable data analysis. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4066–4078, 2017     

吸附反应器的动态特性—非瞬时竞争吸附的影响

针对可逆催化反应Ａ－Ｂ＋Ｃ、各组分非瞬时Ｌａｎｇｍｕｉｒ吸附的情况，研究了固定床吸附反应器的动态特性，着重分析多组分非时竞争吸附的影响。对反应物阶跃输入时，吸附反应器的出口浓度响应进行了模拟分析，模拟结果预示，在一定的参数条件下，动态操作的吸附反应器有较高的反应转化率、高的产物和反应物分离度、而且产物Ｂ和Ｃ之间也能同时得到高度分离。另外，给出了Ｂ和Ｃ分离的条件及定性评价其分离程度的判据。     

Breakthrough analysis of carbon dioxide adsorption on zeolite synthesized from fly ash

Zeolite (FAZ) was synthesized by the fusion method using coal fly ash to adsorb carbon dioxide. The experimental adsorption was operated batchwise in a laboratory-scale packed-bed adsorber to obtain the breakthrough curves of CO₂ under conditions such as adsorption temperatures (20–80 °C), flow rates of gaseous mixture of carbon dioxide and nitrogen (40–100 cm³/min), and concentration of CO₂ (3000–10000 ppmv) at atmospheric pressure of 101.3 kPa. The influence of the experimental conditions, such as the gas flow rate, concentration of CO₂ and adsorption temperature on adsorption behavior, was discussed. The deactivation model, combined the adsorption with the deactivation of adsorbent, was used to analyze the physicochemical properties, such as the adsorption kinetics, capacity and heat of adsorption, by fitting the experimental data of the breakthrough curves to this model. The adsorptive activity and capacity of FAZ were as almost same as those of the commercial zeolite of Wako 4A.     

Removal of CO from process gas with Sn–activated carbon in pressure swing adsorption

A pressure swing adsorption (PSA) system using activated carbon impregnated with SnCl ₂·2H ₂ O and pure activated carbon was used to remove CO from a model H ₂/CO mixture representing the steam reformer process gas. On comparing PSA results for both carbons, the CO adsorptive capacity of impregnated carbon was found to be superior to that of the pure carbon. This was confirmed by the fact that the concentration of CO, initially at 1000 ppm, was successfully reduced to 4.02% and 1.04% of its initial concentration by the pure and the impregnated activated carbons respectively in the PSA system. The species in the impregnated carbon responsible for the improved gas phase CO adsorption was found to be SnO ₂. Simulation results at a cyclic time of 600 s in the PSA operating at 10 atmospheres gave a product recovery and purity of 99.99% and 57.48%, respectively. At 6 atmospheres, the product recovery and purity were 92.17% and 77.12%, respectively. © 2000 Society of Chemical Industry     

Predictive equations in gas adsorption kinetics

The experimental method of determining the operative parameters of adsorptive capacity and rate in the gas adsorption kinetics of packed bed sorbents relies upon the linear relationship between gas breakthrough time and sorbent weight. The slope and intercept of the straight line, resulting from such a plot, yields values for the gas saturation capacity and adsorption rate constant of the adsorbent. This relationship is shown in the modified Wheeler adsorption equation, originally derived from a continuity equation of mass balance between the gas entering an adsorbent bed and the sum of the gas adsorbed by plus that penetrating through the bed. We have found that for wellpacked adsorbent beds, the Dubinin-Polanyi equations for predicting adsorption space at equilibrium, based upon prior characterization of an adsorbent with a reference gas, could also be applied to gas flow conditions, and the kinetic capacity of the adsorbent predicted within close limits. Although no theoretical relationship exists for prediction of the adsorption rate constant, recent gas tests at high linear flow velocities have shown experimental evidence of the mass transfer limiting value for the rate constant. The functionalities of the kinetic saturation capacity and the mass transfer limited value for the adsorption rate constant have been incorporated into the modified Wheeler adsorption equation to provide an expanded equation permitting prediction by calculation of the breakthrough time of a gas through a well-packed bed of adsorbent granules.     

Ultra-deep desulfurization and denitrogenation of diesel fuel by selective adsorption over three different adsorbents: A study on adsorptive selectivity and mechanism

Adsorptive desulfurization and denitrogenation were studied using a model diesel fuel, which contains sulfur, nitrogen and aromatic compounds, over three typical adsorbents (activated carbon, activated alumina and nickel-based adsorbent) in a fixed-bed adsorption system. The adsorptive capacity and selectivity for the various compounds were examined and compared on the basis of the breakthrough curves. The electronic properties of the adsorbates were calculated by a semi-empirical quantum chemical method and compared with their adsorption selectivity. Different adsorptive selectivities in correlation with the electronic properties of the compounds provided new insight into the fundamental understanding of the adsorption mechanism over different adsorbents. For the supported nickel adsorbent, the direct interaction between the heteroatom in the adsorbates and the surface nickel plays an important role. The adsorption selectivity on the activated alumina depends dominantly on the molecular electrostatic potential and the acidic–basic interaction. The activated carbon shows higher adsorptive capacity and selectivity for both sulfur and nitrogen compounds, especially for the sulfur compounds with methyl substituents, such as 4,6-methyldibenzothiophene. Hydrogen bond interaction might play an important role in adsorptive desulfurization and denitrogenation over the activated carbon. Different adsorbents may be suitable for separating different sulfur compounds from different hydrocarbon streams.     

Extraction of ethane from natural gas by adsorption on modified ETS-10

Ethane was extracted from a synthetic natural gas mixture at 298 K and 101.3 kPa using modified ETS-10 as a packed bed adsorbent. Ethane was completely separated from the mixture for a prolonged period until the initial stages of breakthrough. The adsorptive properties of several cation-exchanged forms of ETS-10, a large-pored titanosilicate molecular sieve, were compared. Na-, Ba- and Ba/H-ETS-10 were all found to be selective for ethane over methane. Na-ETS-10 showed the highest Henry's selectivity (α=52) for ethane over methane of the three ETS-10 materials tested. Ideal Adsorbed Solution Theory (IAST) models indicate that significant selectivity should persist at high pressures. Ethane is commonly removed from raw natural gas by energy-intensive cryogenic methods and these results reflect the potential for an alternative and efficient separation process using cation-exchanged ETS-10 as an adsorbent.     

Dynamic simulation of pressure swing adsorption system with the electrical network

With the electrical network model and object-oriented programming technique, a pressure swing adsorption (PSA) system may be decomposed to four objects: adsorbent column, tank, pressure source, and pipeline. Various flowsheets and operating patterns of PSA may be constructed with different combinations of objects and their topology. The objects are represented by class inheritance and encapsulation. The classes encapsulate the methods of setting up and solving the state equations according to the topological constraints and elemental constraints of resistor, capacitor, inductor and voltage and current sources. A PSA flowsheet may be represented with a heterogeneous list that creates the instances of the classes. The state equations are solved numerically on the basis of the polymorphic mechanism via virtual member functions in C++. A four-bed PSA process, consisting of four adsorbent columns, eight tanks, two constant pressure sources, four variable pressure sources and 30 pipelines, are simulated with the electrical network model. The simulated results agree well with the experimental data, and only 7-20 outer cyclic iterations are required to reach the cyclic steady state. The effect of the dead volume and fluid resistances in pipelines on operating results is examined. Optimal searching for the valve coefficients and operating time can suggest the corresponding suitable values to increase the experimental recovery.     

Deep desulfurization of model gasoline by selective adsorption on Ag+/Al-MSU-S

The desulfurization of model gasoline containing 600 ppmw thiophene or dibenzothiophene (DBT) by selective adsorption over Ag⁺ exchanged mesoporous material Al-MSU-S was studied in a fixed adsorbent bed at ambient temperature and pressure. The results showed that the sulfur capacity increased with Al content incorporated in the silicate framework and Ag⁺ exchange can effectively improve the desulfurization performance. The best adsorbent, Ag⁺/20%Al-MSU-S, has adsorption capacity of 5 or 20 ml model gasoline containing thiophene or DBT per gram adsorbent, respectively, before the detection limit in our experiments, as a result of π-complexation. The adsorbent can be regenerated more than six times by simple calcination in air at 350 °C without obvious losing the sulfur adsorption capacity.     

连续循环式吸附空气取水系统

引　言随着社会的发展,人类的活动范围越来越大.在海岛、沙漠等缺少淡水资源的地区,解决饮用水成为人们在这些地区进行活动的先决条件.空气中的水蒸气含量大、不受空间的限制、可循环再生,因此空气取水是解决这些地区饮用水的渠道之一.空气取水可以采用吸附式空气取水方式,目前     

Thermal effects in dynamic storage of hydrogen by adsorption

Thermal effects in dynamic hydrogen storage by adsorption at room temperature and high pressure are studied theoretically and experimentally. The system of adsorbate–adsorbent used was hydrogen in granular activated carbon. The theoretical analysis was based on heat- and mass-transfer modeling in a packed-bed adsorber, with particular emphasis on the thermal effects occurring during charge and discharge steps. The influence of gas flow rate and storage pressure (up to 15 MPa) on the total amount stored or delivered was investigated. Operating conditions were compatible with practical application for onboard vehicle storage. The experimental study was carried out in cylindrical 2-L reservoirs filled with granular activated carbon in which the bed temperature was measured at various positions. The temperature changes during both charge and discharge agreed well with the model predictions.