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.     

Separation of a Five-Component Gas Mixture by Pressure Swing Adsorption

Abstract

Bulk separation of a five-component mixture simulating coal gasification products was performed by pressure swing adsorption (PSA) using activated carbon. The PSA cycle consisted of four commercially used steps: (I) pressurization with H₂, (II) adsorption, (III) blowdown, and (IV) evacuation. Using this cycle, four products were obtained with a single PSA unit: H₂ (over 99.7% purity), CO, CH₄, and acid gas (CO₂ + H₂S). The first three products contained less than 0.001% H₂S, and the acid gas was suitable for sulfur recovery. A mathematical model incorporating equilibrium adsorption of mixture and mass transfer resistance (of CO₂) was found capable of simulating all steps of the PSA cycle. The model simulation results were in fair agreement with the experimental data. A fundamental understanding of the dynamics of the cyclic process was gained through the model.     

Simultaneous Production of Hydrogen and Carbon Dioxide from Steam Reformer Off-Gas by Pressure Swing Adsorption

Abstract

Pressure swing adsorption (PSA) processes are used for the production of ultrapure hydrogen from a crude hydrogen stream containing H₂O, CO₂, CO, CH₄, and N₂ impurities which is produced by steam reformation of natural gas or naphtha. Two commercial PSA processes designed for this purpose are reviewed and a new commercial PSA process which simultaneously produces ultrapure hydrogen and high purity carbon dioxide products from the crude hydrogen with high recoveries of both components is described. Performance data for the new process are reported.     

Equilibrium Analysis of Cyclic Adsorption Processes: CO2 Working Capacities with NaY

Abstract

The most common application of adsorption is via pressure swing adsorption. In this type of design, the feed and regeneration temperatures are kept approximately equal, whereas the feed pressure is higher than the regeneration pressure. By exploiting the difference in the amount adsorbed at a higher pressure to the amount adsorbed at a lower pressure, a working capacity is realized. Therefore, by examining the expected (ideal) working capacity of an adsorbent, a performance characteristic can be analyzed for a pressure swing adsorption process (PSA). For this work, feed pressures up to 2.0 atm CO₂ and feed temperatures from 20°C to 200°C were investigated. These limits were chosen due to the nature of the target process: CO₂ removal from flue gas.

Carbon dioxide adsorption isotherms were determined in a constant volume system at 23°C, 45°C, 65°C, 104°C, 146°C, and 198°C, for pressures between 0.001 and 2.5 atm CO₂ with NaY zeolite. These data were fit with the temperature dependent form of the Toth isotherm. Henry's Law constants and the heat of adsorption at the limit of zero coverage were also determined using the concentration pulse method. Comparison of the Henry's Law constants derived from the Toth isotherm, and those obtained with the concentration pulse method provided excellent agreement.

By using the Toth isotherm, expected working capacity contour plots were constructed for PSA (Pressure Swing Adsorption), TSA (Temperature Swing Adsorption), and PTSA (Pressure Temperature Swing Adsorption) cycles. The largest expected working capacities were obtained when the bed was operated under a high‐pressure gradient PSA cycle, or a high thermal and pressure gradient PTSA cycle. The results also showed that certain TSA and PSA cycle conditions would result with higher expected working capacities as the feed temperature increases.     

A New Composite Sorbent for Methane-Nitrogen Separation by Adsorption

Abstract

Composite sorbents were prepared by depositing molybdenum dioxide on Super A activated carbon. The adsorption isotherms of CH₄ and N₂ were measured. The adsorption capacities and BET surface areas of these adsorbents decreased with an increase in the amount of MoO₂; however, the equilibrium selectivity ratio (CH₄/N₂) increased significantly. Therefore, an optimum quantity of MoO₂ should be used to produce a sorbent with high adsorption capacity and selectivity ratio (CH₄/N₂). An adsorbent containing 18.2 wt% MoO₂ was found to be optimum which showed a CH₄/N₂ selectivity ratio of 4.25. The selectivity ratio decreased with pressure, and leveled off to about 3 at 12 atm. The separation of a CH₄/N₂ (50/50) mixture by pressure swing adsorption (PSA) was studied by using an equilibrium model. A new PSA cycle is described by which pipeline quality methane (>90% CH₄ purity) could be produced using the composite sorbent at a recovery of 73% and a throughput of 200 L STP/h/kg.     

Gas Mixture Fractionation to Produce Two High Purity Products by Pressure Swing Adsorption

Abstract

Pressure swing adsorption processes have been traditionally used to produce one high purity gas stream from a gas mixture. One of the most common uses of this technology is in the production of ultrahigh purity hydrogen from various gas streams such as steam methane reformer (SMR) off-gas. However, many of these gas streams contain a second gas in sufficiently high concentrations, e.g., carbon dioxide in SMR off-gas, that the recovery of this secondary gas stream along with the primary product is extremely desirable. A new pressure swing adsorption (PSA) process, GEMINI-8, has been developed at Air Products and Chemicals, Inc., to achieve this goal. Process cycle steps for the GEMINI-8 PSA process are illustrated by SMR off-gas fractionation for the production of hydrogen and carbon dioxide. Capital and power savings of this process as well as other advantages compared with the previous technology are discussed.     

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.     

Separation of Gases by Pressure Swin

Abstract

The recent status of pressure swing adsorption (PSA) as a process for separating multicomponent gas mixtures is reviewed. The applications of a new generation of adsorbents, such as zeolites, carbon molecular sieves, and, more recently, pore engineered molecular sieves, are described in detail. The more important theories of adsorption from gas mixtures as well as those of the PSA process are described briefly. The commercial applications of PSA the process-present and potential-are discussed at length.     

Oxygen Production by Pressure Swing Adsorption

Abstract

The specific oxygen production capacity and the oxygen recovery of a pressure swing adsorption (PSA) process for the production of oxygen from ambient air by selective adsorption of nitrogen can be increased by operating the process at a superambient temperature. The higher temperature operation provides more efficient desorption of nitrogen from the adsorbent which more than off-sets the detrimental effects of the lower selectivity and capacity of adsorption of nitrogen from air at the elevated temperature. The concept is demonstrated by evaluating the performance of an eight-step PSA-oxygen process to produce a 90% oxygen product stream at different temperatures. It is shown that 10% higher oxygen production capacity and 14.5% larger oxygen recovery can be obtained by operating the PSA process at 60°C compared to its performance at 30°C. The PSA process and its performance data from a pilot plant are discussed.     

Process intensification in duplex pressure swing adsorption

As an alternative to the Pressure Swing Adsorption (PSA) based on the Skarstrom cycle or its variants, a novel two-bed PSA - called duplex PSA - has been proposed by Hirose and independently by Leavitt to get both products of high purities. A modified duplex PSA has been presented to achieve process intensification, that is, to enhance the product purities and productivities. Simulation studies were carried out to explore the attainable product purities and possible process intensification for CO₂ capture with the original and modified duplex PSA. The volume reduction of beds that can be realized with modified duplex PSA is about 100-50 times the original duplex PSA depending upon the product purities.     

非耦联吸附塔新变压吸附工艺的实验研究

通过提氢实验研究一种新的变压吸附工艺.变压吸附流程的主要特征是通过中间均压罐打开吸附塔之间由均压步骤形成的耦联,从而实现了各塔操作的独立性,并提供了降低吸附压力的可能性.以H₂/N₂/CH₄（60/10/30）混合气模拟石油炼厂干气,进行低吸附压力（≤1 MPa）条件下的提氢操作.针对已有变压吸附工艺的不足和新流程特征,确定了新流程的变压吸附循环时序.分别采用普通活性炭（OAC）和高比表面活性炭（SAC）与5A沸石分子筛（ZMS-5A）的组合吸附剂,研究了不同吸附压力下的变压吸附分离效果,证明此种变压吸附新工艺在1 MPa以下、甚至0.4 MPa的低吸附压力下运行,亦可在较高的回收率下达到99.99%的高氢气纯度,并且显示出更强的对偶然性故障的应变能力.     

Experiments of Improving the Performance of Disk Type PSA Columns in Oxygen Production

Abstract

Compact arrangement of the disk type PSA columns results in considerable reduction of the equipment size and the effect of adsorption heat on process performance. More effort has been made presently to improve the performance of the new design in producing oxygen. Considerable improvement is observed due to the replacement of adsorbent ZMS‐5A with ZMS‐VP800 and the adjustment of the operation plan. The feasibility of the compact arrangement of adsorption columns for a PSA process is further proven.     

A superstructure‐based optimal synthesis of PSA cycles for post‐combustion CO2 capture

Recent developments have shown pressure/vacuum swing adsorption (PSA/VSA) to be a promising option to effectively capture CO₂ from flue gas streams. In most commercial PSA cycles, the weakly adsorbed component in the mixture is the desired product, and enriching the strongly adsorbed CO₂ is not a concern. On the other hand, it is necessary to concentrate CO₂ to high purity to reduce CO₂ sequestration costs and minimize safety and environmental risks. Thus, it is necessary to develop PSA processes specifically targeted to obtain pure strongly adsorbed component. A multitude of PSA/VSA cycles have been developed in the literature for CO₂ capture from feedstocks low in CO₂ concentration. However, no systematic methodology has been suggested to develop, evaluate, and optimize PSA cycles for high purity CO₂ capture. This study presents a systematic optimization‐based formulation to synthesize novel PSA cycles for a given application. In particular, a novel PSA superstructure is presented to design optimal PSA cycle configurations and evaluate CO₂ capture strategies. The superstructure is rich enough to predict a number of different PSA operating steps. The bed connections in the superstructure are governed by time‐dependent control variables, which can be varied to realize most PSA operating steps. An optimal sequence of operating steps is achieved through the formulation of an optimal control problem with the partial differential and algebraic equations of the PSA system and the cyclic steady state condition. Large‐scale optimization capabilities have enabled us to adopt a complete discretization methodology to solve the optimal control problem as a large‐scale nonlinear program, using the nonlinear optimization solver IPOPT. The superstructure approach is demonstrated for case studies related to post‐combustion CO₂ capture. In particular, optimal PSA cycles were synthesized, which maximize CO₂ recovery for a given purity, and minimize overall power consumption. The results show the potential of the superstructure to predict PSA cycles with up to 98% purity and recovery of CO₂. Moreover, for recovery of around 85% and purity of over 90%, these cycles can recover CO₂ from atmospheric flue gas with a low power consumption of 465 k Wh tonne^?1 CO₂. The approach presented is, therefore, very promising and quite useful for evaluating the suitability of different adsorbents, feedstocks, and operating strategies for PSA, and assessing its usefulness for CO₂ capture. Published 2009 American Institute of Chemical Engineers AIChE J, 2010     

2-Ethylhexyl acrylate/4-acryloyloxy benzophenone copolymers as UV-crosslinkable pressure-sensitive adhesives

Summary It has been previously shown that copolymer of 2-ethylhexyl acrylate with an 4-acryloyloxy benzophenone can be used as PSA. This paper presents synthesis and application of solvent-based polymer system for the preparation of acrylic pressure-sensitive adhesives (PSA). 2-Ethylhexyl acrylate benzophenone copolymers, having molecular mass in the range of 120 000 to 380 000 Dalton were prepared by free-radical solution polymerization. These copolymers were tacky but possessed insufficient cohesive strength after UV-crosslinking to be useful as PSAs. These copolymers resulted in materials having a balance of cohesive and adhesive characteristics required of a good PSA. Some of the parameters affecting the pressure-sensitive adhesive properties of the copolymer are: amount of the 4-acryloyloxy, molecular mass of the polymeric components, UV-reactivity and such properties like tack, peel adhesion and cohesion.     

Pressure swing adsorption processes to purify oxygen using a carbon molecular sieve

Four different pressure swing adsorption (PSA) cycles using CMS for oxygen purification were developed to produce high-purity oxygen of over 99% with a high level of productivity. The cyclic performances such as purity, recovery, and productivity of the four different PSA cycles were experimentally and theoretically compared under non-isothermal conditions. In addition, one binary (O₂/Ar; 95:5 vol%) and two ternary (O₂/Ar/N₂; 95:4:1 and 90:4:6 vol%) mixtures were used to study the effects of feed composition. The PSA cycles with two consecutive blowdown steps produced oxygen with 98.0-99.9% purity and 56-66% recovery. The PSA cycle with oxygen generation in the second blowdown step produced oxygen with a higher level of purity and productivity. Also, the cycle introducing a pressure equalization step instead of a pure step produced oxygen with about 99.8% purity and 78% recovery. The period for the cyclic steady state of the ternary feed with 1% N₂ was slightly longer than that of the binary feed, while the PSA performance of the ternary feed was similar to that of the binary feed without nitrogen. However, in the ternary feed with 6% N₂, the purity of the O₂ in the purification cycles decreased by up to 97.3%. Therefore, nitrogen played a key role in producing high-purity oxygen in the CMS PSA instead of argon.     

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.     

Large‐scale optimization strategies for pressure swing adsorption cycle synthesis

Pressure swing adsorption (PSA) is an efficient method for gas separation and is a potential candidate for carbon dioxide (CO₂) capture from power plants. However, few PSA cycles have been designed for this purpose; the optimal design and operation of PSA cycles for CO₂ capture, as well as other systems, remains a very challenging task. In this study, we present a systematic optimization‐based formulation for the synthesis and design of novel PSA cycles for CO₂ capture in IGCC power plants, which can simultaneously produce hydrogen (H₂) and CO₂ at high purity and high recovery. Here, we apply a superstructure‐based approach to simultaneously determine optimal cycle configurations and design parameters for PSA units. This approach combines automatic differentiation, efficient ODE solvers for the state and sensitivity equations of the PSA model, and state of the art nonlinear programming solvers. Three optimization models are proposed, and two PSA case studies are considered. The first case study considers a binary separation of H₂ and CO₂ at high purity, where specific energy is minimized, whereas the second case study considers a larger five component separation. © 2012 American Institute of Chemical Engineers AIChE J, 58: 3777–3791, 2012     

Bulk Separation and Purification of CH4/CO2 Mixtures on 4A/13X Molecular Sieves by Using Pressure Swing Adsorption

Abstract

Results of bulk gas separation and purification of a CH₄/CO₂ mixture by pressure swing adsorption (PSA) are reported. Bulk gas separation and purification of CH₄/CO₂ mixture have direct application in landfill gases and tertiary oil recovery and effluent separations. ZMS-13X/4A with calculated kinetic selectivities equal to 0.604 and 0.601, respectively, were used as sorbents. The step times corresponding to various flow rates and compositions were chosen to allow sorption of CO₂ but preclude penetration of CH₄ into the micropores. By using a simulated biogas mixture (66% CH₄ and 34% CO₂) as a feed, the results for bulk gas separation for a PSA cycle between 1.2–36.0 P_H/P_L ratios over ZMS-13X adsorbent was 95% or more CH₄ in the raffinate, whereas with a 10/90 CH₄/CO₂ feed, purification over ZMS-4A at P_H/P_L ratios of 10–304 gave 85–90% CH₄ at 900 and 1800 mL/min flow rates.     

An Evaluation of Acrylic Pressure Sensitive Adhesive Tapes for Bonding Wood in Building Construction Applications

Abstract

Wood connections made with high-performance pressure sensitive adhesive (PSA) tapes have significant promise for mitigating damage in buildings under high wind or seismic conditions. Benefits may include improved joint ductility and sealing protection from water-intrusion damage from hurricanes. In this work a series of connection tests were performed primarily on acrylic PSA tapes in accordance with ASTM D 1761-88 (2000). Performance results for PSA tape/wood joints are presented and trends examined for comparisons of commercial PSA tapes from three manufacturers. The results also provided implementation data on required application pressure levels and time duration, and comparisons with adhesive connection types. Specific parameters were discussed and examined using statistical methods to quantitatively determine performance gains or losses. The variables investigated included the use of oriented strand board (OSB) versus plywood sheathing, the effect of priming and surface sanding on adhesion, and a comparison of connections involving mechanical fasteners with those that utilized only adhesive tape or a combination of the two. Properly bonded OSB and plywood connections provided fairly ductile failure modes. The overall results of the study suggest that the International Building Code (IBC) ban on construction adhesives for shear walls in high seismic zones could be lifted for high-performance acrylic PSA tapes.     

Feed Purge Cycles in Pressure Swing Adsorption

Abstract

Three new pressure swing adsorption cycles for the production of oxygen-enriched air at very high recoveries are developed. The cycles involve a purge step using low-pressure feed gas. Local equilibrium theory is used to predict purities and recoveries for air separation with 5A zeolite. Novel methods for drying the inlet air are developed. For low product purities these processes are predicted to have very high recoveries and adsorbent productivities. A simple new method for determining the location of a curved shock wave is illustrated. Other possible applications of PSA feed purge cycles are briefly discussed.