变压吸附技术的应用研究进展1

变压吸附(PSA)技术是近几十年来在工业上新崛起的气体分离技术,是物理化学渗流理论在工业上的具体应用。自上世纪70年代以来,变压吸附技术因其优势明显,在化工分离中占有重要地位,受到关注和发展。文章简要综述了变压吸附技术的发展里程、理论基础及其研究进展、分离过程的计算机模拟和在国内外工业领域中的应用情况,并对其应用前景进行了展望。     

Pressure Transients in Gas Phase Adsorptive Reactors

The role of pressure and flow transients caused by strong adsorption on the behavior of gas phase adsorptive reactors was studied using a staged model. The general gas phase reaction A + B C is considered for two cases: (1) the product C is adsorbed and (2) both reactants A and B are adsorbed. Strong adsorption of one or more components causes a decrease in the pressure(s) in the stage(s). The pressure decrease causes variations in the inlet and outlet flow rates and in the case of multiple stages, it causes variations in the flows between tanks. In accordance with Le Chatelier's principle, the pressure decrease aids or inhibits product formation depending on whether there is an increase or decrease in total moles by reaction. Reactant flow into the section where adsorption occurs increases because of increased pressure drop behind the adsorption front. However, the residence time of the reactants behind the adsorption front is lower because of the higher velocity. The flow variations can aid or hinder product formation depending on the specific conditions. Thus, the adsorption-caused pressure variations directly modify reaction rates and product concentrations and, also indirectly, by causing flow variations which affect reaction rates and product concentrations. This study highlights the need to include pressure variations when modeling gas phase adsorptive reactors if adsorption is strong irrespective of the net change in the total moles by reaction. It also demonstrates a method to incorporate axial pressure drop in staged models.     

Effect of Operation Symmetry on Pressure Swing Adsorption Process

In a multi-bed pressure swing adsorption (PSA) process, cycle steps with gas flow transferring from one bed to another such as equalization, purge, etc. are generally practiced to enhance the product recovery. However, if the flows for the connected beds in these steps are not balanced, the PSA process may not operate in a symmetrical manner. In the modeling of the PSA process, most of the simulations consider only one bed and assume that the rest of the beds would behave in a same way. In order to assess the impact of bed symmetry on the PSA performance, a new PSA model capable of studying bed symmetry in a two-bed system is developed. Experimental results from this paper show that uneven equalization flow can result in a lower product purity and a peculiar purity curve at different equalization levels. This phenomenon can be successfully predicted by this model. Simulation results also show that in large-scale PSA units, asymmetrical operation can cause drastically different temperature profiles in different adsorbers and hence a much lower performance. This paper demonstrates the importance of maintaining operation symmetry in PSA processes.     

Parametric Study of a Pressure Swing Adsorption Process

The performance of a pressure swing adsorption (PSA) process for production of high purity hydrogen from a binary methane-hydrogen mixture is simulated using a detailed, adiabatic PSA model. An activated carbon is used for selective adsorption of methane over hydrogen. The effects of various independent process variables (feed gas pressure and composition, purge gas pressure and quantity, configuration of process steps) on the key dependent process variables (hydrogen recovery at high purity, hydrogen production capacity) are evaluated. It is demonstrated that many different combinations of PSA process steps, their operating conditions, and the feed gas conditions can be chosen to produce an identical product gas with different hydrogen recovery and productivity.     

Focusing in Liquid Thermal Adsorption Systems

Focusing can be obtained in liquid thermal cycling zone adsorption by significantly increasing the temperature of the hot feed. To prevent boiling column pressure is raised. This method for concentrating dilute fluids was studied using the simulation package ADSIM. The systems studied were ethanol-water on silicalite and toluene-n-heptane on silica gel. Substantial concentration of dilute feeds while producing a pure solvent product were obtained. This research highlights the need for equilibrium data for liquid adsorption systems at elevated temperatures and pressures.     

Tuning of Pressure Swing Adsorption Systems Based on Differential Pressure Profile

A method for tuning a Pressure Swing Adsorption (PSA) system aimed to achieve symmetrical operating conditions based on pressure differential in the adsorption vessels is developed in this study. Simulation of an oxygen Pressure-Vacuum Swing Adsorption (PVSA) process indicates that the pressure drop inside the adsorption vessel is closely related to the nitrogen concentration and gas velocity. The technique is applied to the tuning of an oxygen PVSA process. Adsorbent vessels of the PSA system are monitored and tuned by making corrective adjustments in each of the steps in a PSA cycle in response to imbalances in the differential pressure profiles in each of the adsorbent vessels. The method developed in this study provides a faster, easier, and more effective way to bring a PSA plant to its symmetrical, optimal state than those based on other parameters such as concentration, temperature, and pressure profile. This paper is dedicated to the memory of Professor Wolfgang Schirmer.     

Mathematical Modeling of Multicomponent Nonisothermal Adsorption in Sorbent Particles Under Pressure Swing Conditions

A detailed model for nonisothermal sorption of multicomponent mixtures in a single sorbent particle (monodisperse or bidisperse with negligible intracrystalline mass transport limitations) under pressure swing conditions is developed in this study. The dusty-gas model is used to describe the coupling of the molar fluxes, the temperature, the partial pressures and the partial pressure gradients of the components in the pore space of the particle. The variations of the temperature are described by an energy equation in which both convective and conductive modes of heat transport are accounted for. No limitations are imposed on the number of the components in the mixture and on the type of the adsorption isotherm. The model is applied in the investigation of the industrially important air-zeolite 5A system. Two cases with respect to the surrounding gas phase are examined: infinite environment, which is representative for single particle experiments, and finite environment, which is representative for the situation in packed bed adsorbers. It is found that in an infinite environment the external and internal temperature gradients are equally important while in a finite environment the external heat transport limitations are negligible. It is concluded that in modeling the nonisothermal operation of adsorption processes occurring in packed beds it is not necessary to allow for the temperature differences between the gas phase and the surface of the adsorbing particles. Furthermore, if the temperature gradients within the particles can be neglected, only a single temperature equation is needed to describe the energy transport in the bed.     

Simulation of a Combined Isomerization Reactor & Pressure Swing Adsorption Unit

The Total Isomerization Process developed by Union Carbide in 1970 (Gary, 1987) for the conversion of normal paraffin's to their isomers consists of a reactor followed by a PSA unit each operating at similar pressures and temperatures. The combination of these two operations in one unit in a Pressure Swing Adsorption Reactor (PSAR) process may provide an increased throughput and a significant cost saving in ancillary equipment.The simulation of a mathematical model linking the catalyst packed-bed and the adsorbent packed-bed is reported. The catalyst is a Pd/Y-zeolite and the adsorbent is 5A zeolite. The simulated feed consists of 17% each of n- and isopentane with the remainder being hydrogen. The mathematical model assumes dispersed plug-flow in both sections, constant velocity in the reactor section but varying in the adsorber, with mass transfer in the adsorber section due to external fluid film resistance and macropore diffusion in series. The fraction of the total column length occupied by the catalyst (denoted by ) is accounted for in the model by solving numerically using orthogonal collocation on finite elements. Parameters varied are the ratio of catalyst/column length (), temperature range (506–533 K), high pressure (15–20 bars), with the low pressure held constant at 2 bars. The catalyst/column ratio has a strong effect at low temperatures. The optimum catalyst/column length ratio appears to be controlled by the low pressure step and occurs at = 0.7 for the assumptions used in this work.     

Pressure Swing Adsorption Technologies for Carbon Dioxide Capture

The principles of pressure swing adsorption (PSA) for carbon dioxide capture are reviewed. Previous work on PSA, relevant modeling and experimental investigation for specifically carbon dioxide separation are also presented and significant findings highlighted. Simple rules for PSA process design based on analysis of the inherent properties of adsorbate-adsorbent systems encompassing equilibrium isotherm, adsorption kinetics, shape of breakthrough curves, screening and selection of adsorbent, bed porosity, adsorption time, purge to feed ratio, residence time, pressure equalization and rinse steps are provided to promote better understanding of the technology so that it gains wider acceptance in the future to address the global environmental concern, particularly in the removal of carbon dioxide as a greenhouse gas.     

吸附分离技术在现代工业中的应用

概括介绍了吸附分离技术的发展,详细评述了吸附分离技术的最新进展和在现代工业中的应用,并预测了吸附分离技术未来的发展方向。     

Comparison of Finite Difference Techniques for Simulating Pressure Swing Adsorption

Three different finite-difference routines were compared for solving the nonlinear, coupled, partial differential and algebraic equations that describe pressure swing adsorption processes. A successive substitution method (SS), a block LU decomposition procedure (BLUD), and the method of lines approach with adaptive time stepping (DASSL) were used to simulate and compare the computation times required to reach the periodic state for two different PSA systems: PSA-air drying and PSA-solvent vapor recovery. For both systems, the results showed that DASSL was nearly twice as fast as BLUD, whereas SS was nearly an order of magnitude slower than BLUD. DASSL and BLUD were also very robust and accurate, as nearly identical bed profiles were obtained from both methods under both transient and periodic state conditions.     

Experimental Determination and Analysis of High Pressure Adsorption Data of Pure Gases and Gas Mixtures

Adsorption data of the pure gases ethane, methane and their mixtures on zeolite 13X and the pure gases carbon dioxide, nitrogen and their mixtures on activated carbon Norit R1 were measured gravimetrically at a temperature of 298 K and pressures up to 15 MPa. From the total loads the partial loads were calculated by the modified van Ness approach. The calculated loads show a good agreement with the experimental data.     

Study on Pressure Swing Adsorption Removing C2^＋ from Natural Gas as Raw Material for Thermal Chlorination

The experimental investigation demonstrates that a setisfactory can be expected for pressure swing adsorption (PSA) purification of natural gas as raw material for thermal chlorination process.Using hh-4 molecular sieve as adsorbent for removing C2^ components,the suitable adsorption pressure is 0.4-0.45 MPa,desorption vacuum is 0.08-0.09 MPa and circulation time is 20-21 min.     

R and D Note: Separation of a Nitrogen-Carbon Dioxide Mixture by Rapid Pressure Swing Adsorption

A N₂-CO₂ mixture is separated in a rapid pressure swing adsorption apparatus, which consists of single or double adsorbent beds filled with silica gel and operates in the sequence of adsorption, backflow and desorption. Nitrogen-rich gas is produced at the top of the bed, and carbon dioxide-rich gas at the bottom. Carbon dioxide purity of 89.5% and recovery of 70% were obtained in the single-bed apparatus, while purity of 93.5% and recovery of 72.3% were obtained in the double-bed apparatus. The feed in both cases consisted of 81% N₂ and 19% CO₂.     

捕集高湿烟气中CO2的变压吸附技术

变压吸附法在捕集烟气中的CO₂这一领域中显示出强大的优越性,但实际电厂烟气含有少量的水蒸气,这对利用常规吸附剂捕集CO₂造成很大挑战。为解决上述瓶颈问题,改进变压吸附工艺以及开发对湿度不敏感、高效的吸附剂成为最主要的途径。本文详细介绍了两种常用的变压吸附工艺,即多层变压吸附及微波辅助真空再生法分离高湿烟气的研究进展,综述了近年来研发的适于捕集高湿烟气的高效吸附剂,系统阐述了各种吸附剂的物理化学特性及其吸附CO₂、H₂O的机制,并在此基础上讨论了变压吸附技术捕集高湿烟气时存在的问题,提出了研究展望。相信随着人们对变压吸附工艺的改进以及对新型高效吸附剂的进一步研发,必将显著降低捕集高湿烟气中CO₂的成本,这将对燃煤电厂等高湿CO₂排放源的温室气体减排具有重要意义。     

Study on Pressure Swing Adsorption Removing C+2 from Natural Gas as Raw Material for Thermal Chlorination

The experimental investigation demonstrates that a satisfactory result can be expected for pressure swing adsorption (PSA) purification of natural gas as raw material for thermal chlorination process. Using hh-4 molecular sieve as adsorbent for removing C2 components, the suitable adsorption pressure is 0.4-0.45 MPa, desorption vacuum is 0.08-0.09 MPa and circulation time is 20-21 min.     

An Equilibrium Relation for Gas Adsorption Applications

A new multicomponent equilibrium relation is proposed for engineering applications. This relation is based on a lattice model for mixtures of unequally sized molecules. An approximation is introduced for loading-dependent enthalies of adsorption that simplifies the energy balance in fixed-bed models and allows efficient solution of the equation set in process simulations. Comparisons are made with nonideal binary data in the literature.     

63Ni在泥煤-水体系中的吸附动力学

应用同位素示踪技术,简要地研究了63Ni在泥煤中的静态吸附行为。结果表明,5 min后泥煤对63Ni的吸附率可达69%,60min后达到吸附平衡;第1吸附阶段内镍吸附量随时间的延长而增加,不易解吸;从泥煤-水液固体系中泥煤的电离平衡和镍离子-氢离子之间离子交换平衡,以及物料平衡关系推导出泥煤平衡时63Ni的吸附量和氢离子的浓度、平衡时镍离子的浓度有关。溶液的pH值对镍的吸附和解吸有很大影响,随着溶液pH值增大,63Ni由水分室向泥煤分室转移的速率常数也逐渐增大,而由泥煤分室向水分室转移的速率常数逐渐减小,二者比值逐渐增大,pH=4.624 6时,2种可逆传递速率常数相等,为2.51。即适宜pH值范围内的pH值升高吸附量增大,低pH值不利于吸附。63Ni在泥煤-水体系中的动态变化可用封闭二分室进行描述,经拟合后的理论值与实验数据点具有较好的一致性。     

Infrared Spectroscopic Study on Adsorption of Acetonitrile from Solution onto Several Oxide Surfaces at High Pressure

Adsorption of acetonitrile from toluene solution at a liquid-solid interface under pressures of up to 300 MPa was investigated by IR spectroscopy. The CN stretching vibration bands (v_CN) of adsorbed acetonitrile were observed at higher frequencies than those of the same species in the liquid phase. The shift on alumina-pillared montmorillonite (ALPM) was the largest (ca. 8 cm^-1) for the adsorbents studied. The v_CN intensities of adsorbed acetonitrile on ALPM and on alumina (Al₂O₃) considerably increased with increased pressure, indicating an increase acetonitrile adsorption due to compression. It was concluded that the total volume of the system was reduced by adsorption, and that the reduction was brought about not only by the formation of an adsorption bond but also by the change in the solvation of the adsorbate in the adsorbent pore.     

利用压差法测定高分辨率超低压吸附等温线的装置

 介绍了一种新型气体吸附测量装置. 该装置利用压差法测量,采用美国MKS高精度压差传感器来提高测量精度,通过微调泄漏阀控制极小进气量,并且采用间断法与连续法相结合. 实验证明,该装置具有很好的可重复性,能获得高分辨率及超低压吸附等温线.