Preparation of Core-Shell SAPO-34 Adsorbent on Ceramic Particles; Improvement of CO2 Separation from Natural Gas

Fine crystals of SAPO-34 were synthesized by preparation of sol-gel precursor and hydrothermal process. The produced crystalline phase and the crystal shapes were analyzed by XRD patterns and SEM images. The core-shell adsorbent was prepared by the formation of the fine layer of SAPO-34 on the surface of the inert ceramic particles using the same synthesis parameters and hydrothermal conditions by in situ crystallization. The prepared core-shell SAPO particles were tested in dynamic adsorption experiments of a mixture of 5% CO₂ and 95% CH₄ at 298 K and 0.1 MPa, and their performance was compared with pure powders of SAPO-34 in the same adsorption operational conditions. The longer breakthrough time, sharper breakthrough curves, and higher CO₂ adsorbed amount were observed using core-shell SAPO-34 particles as adsorbent rather than using pure particles of SAPO-34. It is concluded that the production of a thin layer of SAPO-34 on cheap and inert porous ceramic particles is preferred rather than using higher amounts of SAPO-34 powders pelleted or binded with inert material in dynamic adsorption processes for the separation of CO₂ from natural gas.     

Integrated adsorbent‐process optimization for carbon capture and concentration using vacuum swing adsorption cycles

A novel approach for integrated adsorbent and process design is proposed. The traditional pressure or vacuum swing adsorption (PSA) / vacuum swing adsorption (VSA) process optimization for chosen objectives, where operating conditions are the decision variables, and CO₂ purity and recovery are constraints, is expanded to include adsorbent isotherm characteristics as additional decision variables. Two VSA cycles, namely a four‐step process¹, currently known to have the lowest energy consumption for CO₂ capture and concentration (CCC), and a six‐step process², recently proven to have a wider operating window for the evacuation pressure, have been investigated in the current study. The integrated optimization results simultaneously provide the lower bound of minimum energy and upper bound of maximum productivity for CCC achievable from the two VSA processes along with the operating conditions and the corresponding isotherm shapes necessary to achieve them. It may be viewed as an enabler for adsorbent design or expedient adsorbent search by process inversion. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2987–2995, 2017     

Improving SAPO-34 performance for CO2/CH4 separation and optimization of adsorption conditions using central composite design

ABSTRACT

SAPO-34 molecular sieves have a high adsorption capacity in separation of CO₂ from CO₂/CH₄ mixture. In this study, SAPO-34 was modified by different solutions at various operating conditions to enhance the removal of carbon dioxide from the methane gas. Modifications can change pore size and also Si/Al ratio in SAPO-34 and make changes in the acidity of the adsorbent via the ion exchange process. The effects of temperature and pressure on the separation were studied using the design of experiments. Finally, based on the results of the experimental optimization process applying central composite design (CCD) method, the highest yield of CO₂ separation from the methane gas (95%) was obtained when using P-SAPO-34 sample at 17.4°C and 4.6 bar.     

Effect of Si/Al Ratio on CO2 – CH4 Adsorption and Selectivity in Synthesized SAPO-34

Impact of Si/Al ratio on the adsorption capacity and separation selectivity of CO₂/CH₄ in SAPO-34 has been investigated. SAPO-34 samples were synthesized with two Si/Al ratios (0.2 and 0.3). A batch adsorption volumetric apparatus was used to measure the adsorption equilibrium capacity and derive the equilibrium isotherms. The tests were performed in a wide range of pressure from normal to 3000 kPa and three levels of temperatures from 277 to 298 K. Results proved decreasing Si/Al ratio, from 0.3 to 0.2, improved CO₂ separation from CH₄.     

Cycle synthesis and optimization of a VSA process for postcombustion CO2 capture

A systematic analysis of several vacuum swing adsorption (VSA) cycles with Zeochem zeolite 13X as the adsorbent to capture CO₂ from dry, flue gas containing 15% CO₂ in N₂ is reported. Full optimization of the analyzed VSA cycles using genetic algorithm has been performed to obtain purity‐recovery and energy‐productivity Pareto fronts. These cycles are assessed for their ability to produce high‐purity CO₂ at high recovery. Configurations satisfying 90% purity‐recovery constraints are ranked according to their energy‐productivity Pareto fronts. It is shown that a 4‐step VSA cycle with light product pressurization gives the minimum energy penalty of 131 kWh/tonne CO₂ captured at a productivity of 0.57 mol CO₂/m³ adsorbent/s. The minimum energy consumption required to achieve 95 and 97% purities, both at 90% recoveries, are 154 and 186 kWh/tonne CO₂ captured, respectively. For the proposed cycle, it is shown that significant increase in productivity can be achieved with a marginal increase in energy consumption. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4735–4748, 2013     

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.     

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.     

Effects of Synthesis Temperature and Support Material on CO2 and CH4 Permeation through SAPO-34 Membranes

In this research, continuous SAPO-34 membranes were synthesized via secondary growth method onto both α-Al₂O₃ and mullite supports at three levels of synthesis temperature: 185, 195, and 220°C for 24 h. The synthesized membranes were characterized using XRD and SEM analysis and single gas permeation experiments. It was found out that support material and synthesis temperature both have significant effects on the membrane performance. At higher synthesis temperature, SAPO-34 crystals grown over the mullite support become more uniform and smaller in size but those grown on the α-Al₂O₃ support become larger. Effect of synthesis temperature on single gas permeation properties of the synthesized SAPO-34 membranes was also studied. For the mullite supported membranes, the CH₄ and CO₂ permeances decrease as synthesis temperature increases; but in the case of the alumina supported membranes, by increasing synthesis temperature, CH₄ and CO₂ permeances first decrease up to 195°C and then increase up to 220°C. Even in equal membrane thicknesses, the mullite supported membrane shows lower gas permenaces. Increasing synthesis temperature decreases CO₂/CH₄ ideal selectivity for the α-Al₂O₃ supported membranes, while increases for the mullite supported membranes. Under optimum synthesis conditions, at room temperature and 2 bar feed pressure, the CO₂ permeance through the α-Al₂O₃ and the mullite supported SAPO-34 membranes are 8.2 × 10^?7 and 8.5 × 10^?8 (mol/m² · s · Pa), respectively, and CO₂/CH₄ ideal selectivities are 51 and 61, respectively.     

Adsorption of Off‐Gases from Steam Methane Reforming (H2, CO2, CH4, CO and N2) on Activated Carbon

Abstract

Hydrogen is the energy carrier of the future and could be employed in stationary sources for energy production. Commercial sources of hydrogen are actually operating employing the steam reforming of hydrocarbons, normally methane. Separation of hydrogen from other gases is performed by Pressure Swing Adsorption (PSA) units where recovery of high‐purity hydrogen does not exceed 80%.

In this work we report adsorption equilibrium and kinetics of five pure gases present in off‐gases from steam reforming of methane for hydrogen production (H₂, CO₂, CH₄, CO and N₂). Adsorption equilibrium data were collected in activated carbon at 303, 323, and 343 K between 0‐22 bar and was fitted to a Virial isotherm model. Carbon dioxide is the most adsorbed gas followed by methane, carbon monoxide, nitrogen, and hydrogen. This adsorbent is suitable for selective removal of CO₂ and CH₄. Diffusion of all the gases studied was controlled by micropore resistances. Binary (H₂‐CO₂) and ternary (H₂‐CO₂‐CH₄) breakthrough curves are also reported to describe the behavior of the mixtures in a fixed‐bed column. With the data reported it is possible to completely design a PSA unit for hydrogen purification from steam reforming natural gas in a wide range of pressures.     

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.     

On thermodynamic separation efficiency: Adsorption processes

A simplified thermodynamic analysis of adsorption processes in temperature swing adsorption (TSA) and pressure swing adsorption (PSA) modes as a function of adsorbate concentration and the adsorbent–adsorbate interaction strength is presented in this article. The thermodynamic separation efficiency of a TSA process is optimal at dilute feed conditions, and becomes more thermodynamically efficient with increasing adsorbate affinity even though the energy of separation increases. The adsorption process is spontaneous, and for a strong isotherm, the energy required to reverse the adsorption is nearly independent of the adsorbate concentration as adsorbate loading in nearly‐saturated materials is essentially constant with feed concentration. PSA units are efficient thermodynamically and the efficiency increases with the concentration of the desired adsorbate. This thermodynamic treatment has implications for separation processes that address carbon emissions. TSA systems operate more efficiently (thermodynamically) in the “air capture” case because they apply work to the concentrated product rather than the dilute feed. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3699–3705, 2016     

Integrated Adsorbent Process Optimization for Minimum Cost of Electricity Including Carbon Capture by a VSA Process

Assessing vacuum swing adsorption (VSA) technology for postcombustion CO₂ capture and concentration (CCC) using energy and productivity indicators are useful, but its ultimate test must be the cost of electricity from a power plant including CCC. Here, our integrated optimization platform (Khurana and Farooq, AlChE J. 2017;63:2987–2995) developed earlier to simultaneously obtain the optimum adsorbent and process conditions is extended to include a comprehensive costing framework. The framework is complete with scale-up design and column scheduling, and compliant with National Energy Technology Laboratory costing guidelines for carbon capture. This is the ultimate tool that enables integrated optimization to minimize the cost of electricity. The Shell Cansolv CO₂ capture system is used as the benchmark for evaluating the best performance of two VSA cycles for two adsorbents. The operating conditions and isotherm shapes necessary to achieve the lowest possible cost of electricity for the two VSA cycles are also presented to facilitate designing or searching the best adsorbent for CCC. © 2018 American Institute of Chemical Engineers AIChE J, 65: 184–195, 2019     

Screening Supported Amine Sorbents in the Context of Post-combustion Carbon Capture by Vacuum Swing Adsorption

The aim of this work was to evaluate the performance of three different supported amine sorbents in a 6-step vacuum swing adsorption (VSA) cycle through process simulation and optimization for a representative post-combustion CO₂ capture system. Detailed process optimization revealed that all the adsorbents were able to achieve the desired purity-recovery targets. The best performing adsorbent in terms of productivity was Lewatit with a productivity of 0.48 mol m⁻³ ads s⁻¹. All the adsorbents exhibited similar minimum specific energy value of around 1 MJ kg⁻¹ on an electric basis.     

Numerical analysis of CO2 concentration and recovery from flue gas by a novel vacuum swing adsorption cycle

The objective of this work is to study the feasibility of carbon dioxide concentration and recovery from flue gases using a novel VSA cycle without rinse step with the aid of mathematical modeling. A theoretical model based on conservation equations (following the one proposed by Da Silva and Rodrigues (2001)) is used for an initial evaluation of the process performance. Activated carbon is the adsorbent considered, simulating adsorption equilibrium and kinetics with the equations proposed by Kikkinides, Yang, and Cho (1993). According to the simulated results, it is possible to recover carbon dioxide with high purity (>93%) from a mixture with 13% carbon dioxide at 40 °C, with higher recovery (>90%) and a lower power consumption (<0.12 kWh/kgCO₂) than other processes with rinse step reaching the same purity. Although these results are theoretical, they show the potential advantages of this process for CO₂ capture.     

CO2 recovery from flue gas by PSA process using activated carbon

An experimental study was performed for the recovery of CO₂ from flue gas of the electric power plant by pressure swing adsorption process. Activated carbon was used as an adsorbent. The equilibrium adsorption isotherms of pure component and breakthrough curves of their mixture (CO₂ : N₂ : O₂=17 : 79 : 4 vol%) were measured. Pressure equalization step and product purge step were added to basic 4-step PSA for the recovery of strong adsorbates. Through investigation of the effects of each step and total feed rate, highly concentrated CO₂ could be obtained by increasing the adsorption time, product purge time, and evacuation time simultaneously with full pressure-equalization. Based on the basic results, the 3-bed, 8-step PSA cycle with the pressure equalization and product purge step was organized. Maximum product purity of CO₂ was 99.8% and recovery was 34%.     

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.     

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     

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。     

Preparation and characterization of SAPO-34 – Matrimid 5218 mixed matrix membranes for CO2/CH4 separation

Different SAPO-34 zeolite loaded Matrimid^® 5218 mixed matrix membranes (MMMs) were prepared by solution casting method and characterized using XRD and SEM analysis. Findings showed that semi crystalline neat polymer becomes more crystalline after thermal treatment at higher temperatures close to Matrimid^® 5218 glass transition temperature. Furthermore, incorporation of crystalline filler particles of SAPO-34 zeolite resulted in more and more crystallinity of the MMMs. SEM images also exhibited acceptable contacts between the filler particles and the polymer chains. Permeation measurement showed that CO₂ permeabilities and CO₂/CH₄ selectivities of the MMM with 20 wt% loading of SAPO-34 zeolite particles up to 6.9 (Barrer) and 67, respectively. This can be attributed to size discrimination of SAPO-34 pores that falls between CO₂ and CH₄ kinetic diameters.     

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.