Simulation of pressure swing adsorption modules having laminated structure

A mathematical model was formulated for the bulk separation of binary gas mixtures in micro-structured pressure swing adsorption (PSA) modules consisting of parallel channels lined with adsorbent. Axial and radial dispersion in the gas phase and mass transfer resistance in the adsorbent phase were taken into consideration. The partial differential equations governing the concentration profiles in the gas and adsorbent phases were solved by orthogonal collocation. The model enabled the prediction of the concentration profiles in both the gas and adsorbent phases (as a function of location and time), the product purity and the separation efficiency. The effects of model parameters and operating conditions on the module performance were investigated. Simulation of oxygen enrichment from air by molecular sieve 13X indicated that long modules with thin layers of adsorbent, narrow gas flow channel heights and large numbers of flow channels give the best separation.     

Numerical simulation of rapid pressurization and depressurization of a zeolite column using nitrogen

The required durations of pressurization and depressurization steps of a rapid pressure swing adsorption process are primarily governed by adsorbent particle size, adsorption kinetics, column pressure drop, column length to diameter ratio, and the valve constant of the gas inlet and outlet control valve attached to the adsorbent column. A numerical model study of the influence of these variables for an adiabatic LiX zeolite column is presented using pure N₂ as an adsorbate gas. An adsorbent particle size range of 200–350 μm was found to minimize (<1 s) the times required for the pressurization and depressurization steps.     

Hydrogen separation by multi-bed pressure swing adsorption of synthesis gas

The performance of multi-bed pressure swing adsorption (PSA) process for producing high purity hydrogen from synthesis gas was studied experimentally and theoretically using layered beds of activated carbon and zeolite 5A. Nonisothermal and nonadiabatic models, considering linear driving force model and Dual-site Langmuir adsorption isotherm model, were used. The effects of the following PSA variables on separation process were investigated: linear velocity of feed, adsorption time and purge gas quantity. As a result, we recovered a high purity H₂ product (99.999%) with a recovery of 66% from synthesis gas when the pressure was cycled between 1 and 8 atm at ambient temperature.     

Determination of absolute gas adsorption isotherms: simple method based on the potential theory for buoyancy effect correction of pure gas and gas mixtures adsorption

The absolute adsorption isotherms are necessary to correctly evaluate the selectivity of the adsorbent material or to design adsorption processes at high pressure (e.g., H₂ purification from syngas processes, removal of acid gas from natural gas,…). The aim of this work is thus to propose an easy method to correct the buoyancy effect of the bulk phase on the adsorbed phase volume during both pure gas and gas mixtures adsorption for pressures up to 10 MPa. The potential theory of adsorption and the Dubinin–Radushkevich relation are adapted by introducing mixing parameters based on simple Berthelot rules. The concept of internal pressure used to characterize the adsorbed phase is also adapted for mixtures. The method is then improved on a commercial activated carbon (AC), when adsorbing pure H₂S and CH₄, and their mixtures up to 5 MPa. The study points out the importance to carefully consider the buoyancy effect of the bulk phase on the adsorbed phase volume. Its impact on the adsorbent material selectivity at high pressures could affect the design and the performances of PSA or TSA processes. For example, only considering the excess adsorption data leads to an apparent selectivity 13 % greater than the absolute one for a concentration of 6 ppm of H₂S in a CH₄ matrix at 5 MPa (298 K) on the AC.     

Piston-driven ultra rapid pressure swing adsorption

The piston-driven ultra rapid pressure swing adsorption (URPSA) equipment was developed and oxygen enrichment from air was examined as an example. The adsorbent bed is directly connected to the cylinder where a piston moves at high frequency. Thus pressurization and depressurization in the bed are driven by mechanical piston motion, which can achieve far more rapid cycles compared with the conventional pressure swing operation using valves. The cycle time is usually on the order of seconds or sub seconds. Oxygen enrichment from air up to about 60% or higher of oxygen concentration was achieved by small-scale equipment using zeolite 5A with a oxygen production capacity of 100 Nm³-product gas/m³-zeolite/hr, which is about ten times larger than those of commercialized PSAs for this purpose.A simplified numerical model describing the mass transfer taking place in URPSA was developed. The model could simulate fairly well the air separation characteristics in terms of oxygen concentration, oxygen production capacity and oxygen yield. The proposed model helps in the understanding of the basic nature of URPSA and possible applications. This novel PSA is promising as a compact yet high-capacity PSA to be utilized in a wide variety of applications.     

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.     

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.     

Pure and binary adsorption of CO2, H2, and N2 on activated carbon

A new developing field of application for pressure swing adsorption (PSA) processes is the capture of CO₂ to mitigate climate change, especially the separation of CO₂ and H₂ in a pre-combustion context. In this process scheme the conditions of the feed to the separation step, namely a pressure of 3.5 to 4.5 MPa and a CO₂ fraction of around 40% are favorable for an adsorption based separation process and make PSA a promising technology. Among the commercial adsorbent materials, activated carbon is most suitable for this application. To evaluate the potential, to benchmark new materials, and for process development a sound basis of the activated carbon thermodynamic data is required, namely equilibrium adsorption isotherms of the relevant pure components and mixtures, Henry’s constants and isosteric heats.     

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.     

Advanced adsorbents for the separation of the ortho- and para-hydrogen spin isomers at cryogenic temperatures

Improved adsorbent types and compositions have been developed for the challenging separation of the ortho- and para-hydrogen spin isomers at 77 K. From a systematic study of commercially available adsorbent types, it has been found that zeolites of type X offer the largest capacity and selectivity towards ortho-hydrogen and that performance is significantly impacted by the cation type and the number of cations present in the zeolite. For the present separation improved performance was obtained with larger Group I cations, especially K and Cs. Another key property of the adsorbents addressed in the present work is the need to control the adsorbent composition to avoid unwanted catalytic conversion of the para- to ortho-hydrogen. A common source of unwanted catalytic activity in many adsorbent compositions was identified as the presence of unwanted transition metal impurities, especially iron associated with the natural clays, commonly employed as binding agents in the commercial agglomerated zeolite products. To avoid this, equivalent adsorbent compositions were agglomerated instead using colloidal silica binding agents which successfully minimize back conversion of the para- to ortho-hydrogen and produced adsorbents with higher capacities and selectivities for the ortho component at the test temperature of 77 K. These advanced adsorbents can be applied in more efficient hydrogen liquefaction processes.     

Kinetic separation of carbon dioxide and methane on a copper metal-organic framework

Separation of carbon dioxide and methane is an important issue in upgrading low-quality natural gas. Adsorption equilibria and kinetics of CO(2) and CH(4) on a copper metal-organic framework (MOF), Cu(hfipbb)(H(2)hfipbb)(0.5) [H(2)hfipbb=4,4'-(hexafluoroisopropylidene) bis(benzoic acid)], were investigated to evaluate the feasibility of removing CO(2) from CH(4) in a pressure swing adsorption process using this new MOF adsorbent. The heat of adsorption of CO(2) on the Cu-MOF at zero-coverage (29.7 kJ/mol) is much lower than those on a carbon molecular sieve and a zeolite 5A adsorbent; and the heat of adsorption of CH(4) on the Cu-MOF (21.4 kJ/mol) is similar to that on the zeolite 5A adsorbent and smaller than that on a carbon molecular sieve. The Cu-MOF being investigated has apertures of (~3.5 × 3.5 ?), which favors the kinetically controlled separation of CO(2) and CH(4). The kinetic selectivity is found to be 26 at 298 K, and the overall selectivity (combining the equilibrium and kinetic effects) is about 25 for an adsorption separation process. These results suggest that the Cu-MOF adsorbent is an attractive alternative adsorbent for the CO(2)/CH(4) separation.     

Production of oxygen enriched air by rapid pressure swing adsorption

A novel rapid pressure swing adsorption (RPSA) process is described for production of 25–50% oxygen enriched air. The embodiment consists of one or more pairs of adsorbent layers contained in a single adsorption vessel. The layers undergo simultaneous pressurization-adsorption and simultaneous depressurization-purge steps. A total cycle time of 6–20 seconds is used. The process yields a very large specific oxygen production rate and a reasonable oxygen recovery for production of 20–50 mole% oxygen enriched gas.It is demonstrated by a simple mathematical model of isothermal single adsorbate pressure swing ad(de)sorption concept on a single adsorbent particle that the specific production rate of a PSA process cannot be indefinitely increased by reducing the cycle time of operation when adsorbate mass transfer resistances are finite.     

Speciation of ultra-trace amounts of inorganic arsenic in water and rice samples by electrothermal atomic absorption spectrometry after solid-phase extraction with modified Fe3O4 nanoparticles

A new magnetic adsorbent, 3-mercaptopropionic acid coated 3-aminopropyl triethoxysilane modified Fe₃O₄ nanoparticle, was synthesised and used for the extraction and preconcentration of arsenic ions in aqueous solutions followed by electrothermal atomic absorption spectrometric determination. The adsorbent was characterised by TEM, SEM, XRD and FT-IR techniques and the method used the unique properties of magnetic nanoparticles, namely, high surface area and superparamagnetism which gave it the advantages of high extraction capacity, fast separation and low adsorbent consumption. Different parameters affecting extraction efficiency of the analyte including pH value, sample volume, adsorbent amount, extraction time and desorption conditions were investigated and optimised. Under the optimum conditions, wide linear range of 30–25,000 ng L^?1 and low detection limit of 10 ng L^?1 were obtained. The interday and intraday precisions (as RSD%) for five replicates determination of 50 and 25,000 ng L^?1 of arsenic ions were in the range of 2.3–3.2%. Furthermore, no significant interference was observed in the presence of coexisting ions and high preconcentration factor of 198 was obtained. The adsorption isotherm followed Langmuir model and its kinetic was second-order. The accuracy of the method was validated by analysing certi?ed reference materials for water and rice with satisfactory recoveries. Finally, the proposed method was successfully applied for the determination of ultra-trace amounts of arsenic in rice and water samples.     

High-rate and high-density gas separation adsorbents and manufacturing method

High-rate and high-density gas separation adsorbents used in vacuum pressure swing adsorption (VPSA) processes are described. Agglomerated zeolite Li–LSX compositions made using colloidal silica binding agents and having improved nitrogen pore diffusivity compared to like compositions prepared with traditional clay binders, are also described. Preparation methods for the colloidal silica-bound adsorbents are described together with their characterization by mercury (Hg) porosimetry, scanning electron microscopy (SEM) and low dead-volume breakthrough testing, from which the pore diffusivity is obtained. In this article, we show how the location and dispersion of the colloidal silica binding agent within the agglomerated zeolite particle yields pore-architectures that resemble “state-of-the-art” binderless adsorbents. In addition, we use VPSA process simulations to show that the best process performance is achieved by the combination of high-rate and high-density adsorbent properties.     

Adsorption of ethane, ethylene, propane, and propylene on a magnesium-based metal-organic framework

Separation of olefin/paraffin is an energy-intensive and difficult separation process in petrochemical industry. Energy-efficient adsorption process is considered as a promising alternative to the traditional cryogenic distillation for separating olefin/paraffin mixtures. In this work, we explored the feasibility of adsorptive separation of olefin/paraffin mixtures using a magnesium-based metal-organic framework, Mg-MOF-74. Adsorption equilibria and kinetics of ethane, ethylene, propane, and propylene on a Mg-MOF-74 adsorbent were determined at 278, 298, and 318 K and pressures up to 100 kPa. A dual-site Sips model was used to correlate the adsorption equilibrium data, and a micropore diffusion model was applied to extract the diffusivities from the adsorption kinetics data. A grand canonical Monte Carlo simulation was conducted to calculate the adsorption isotherms and to elucidate the adsorption mechanisms. The simulation results showed that all four adsorbate molecules are preferentially adsorbed on the open metal sites where each metal site binds one adsorbate molecule. Propylene and propane have a stronger affinity to the Mg-MOF-74 adsorbent than ethane and ethylene because of their significant dipole moments. Adsorption equilibrium selectivity, combined equilibrium and kinetic selectivity, and adsorbent selection parameter for pressure swing adsorption processes were estimated. The relatively high values of adsorption selectivity suggest that it is feasible to separate ethylene/ethane, propylene/propane, and propylene/ethylene pairs in a vacuum swing adsorption process using Mg-MOF-74 as an adsorbent.     

Solid phase extraction of hexavalent chromium by Mannich base polymer wrapped flower-like layered double hydroxide

In the present work, synthesis of polymer wrapped flower-like MgAl layered double hydroxide was done through condensation of 1,4 phenylenediamine and resorcinol by p-formaldehyde. The nanocomposite was characterised with X-ray diffraction analysis, fourier transform infrared spectroscopy, thermogravimetric analysis and field emission scanning electron microscopy techniques and employed for effective adsorption of Cr(VI) from aqueous solution prior to flame atomic absorption spectrometer determination. Optimum level of effective parameters (pH, reaction time and adsorbent dosage) and their interaction was determined by response surface methodology. To investigate applicability of method for trace heavy metal adsorption, the method was employed for preconcentration of Cr(VI) in water samples. At the optimum conditions, pH = 4.5, shaking time of 15 min and adsorbent dosage of 20 mg, analytical performance of the method was evaluated and results showed that calibration curve is linear in the concentration range of 2–100 μg L^?1. Moreover, limit of detection was 0.22 µg L^?1 and relative standard deviation of six replicate experiments at initial concentration of 0.1 mg L^?1 was 3.3%. Isotherm study showed that Freundlich model can better describe adsorption behaviour as well as the sorbent showed the adsorption capacity of 62.5 mg g^?1. Moreover, thermodynamic study revealed that chromate adsorption was spontaneous and followed the endothermic path. Regeneration of sorbent was performed using 1.0 mol L^?1 of NaOH solution. The sorbent was employed for Cr(VI) determination from food additives and seawater samples.     

Comparative study of adsorbents performance in ethylene/ethane separation

Some potential adsorbents for ethylene/ethane separation are ethylene selective while the others are ethane selective. Among different adsorbents, i.e., zeolites and metal organic frameworks (MOFs), a comparative study is critical to find the more suitable adsorbent for the separation. In this paper, binary ethylene/ethane adsorption performances of zeolites and MOFs, i.e., equilibrium selectivities and adsorption capacities are investigated utilizing ideal adsorbed solution theory (IAST). IAST model is applied at different gas compositions (0.1–0.9 ethylene mole fractions) and pressures up to 100 kPa. The results revealed that the most selective adsorbent toward ethylene is 5A zeolite while MOFs have higher equilibrium adsorption capacities. Among zeolites and MOFs, 5A and Fe₂(dobdc) have the highest selectivity (27.4 and 13.6) and capacity (≈2.8 and 5.8 mmol ethylene/g) at 100 kPa and 298 K for a 50/50 mixture. Among ethane selective adsorbents, Silicalite-1 zeolite and UTSA-33a (MOF) have the highest selectivity and capacity (≈2.9 and ≈1.5 mmol ethane/g) at 100 kPa and 298 K for a 50/50 mixture, respectively. Investigation showed that adsorption capacity of ethylene selective adsorbents is higher than that of ethane selective ones.     

Novel thionin-functionalised core shell magnetic nanoparticles for dispersive solid-phase extraction of Hg(II) in food and water samples

To develop an accurate and precise method for separation and pre-concentration of Hg(II), a novel thionin functionalised core shell structure magnetic material has been prepared and characterised. The extraction ability of the material was evaluated by magnetic solid-phase extraction coupled with inductively coupled plasma mass spectrometry determination of Hg(II) in food and water samples. Combining the advantages of magnetic separation with selective extraction of thionin towards Hg(II), the material exhibits enhanced enrich selectivity and efficiency for Hg(II). The experimental parameters influencing Hg(II) extraction efficiency, including pH of the aqueous solution, the dosage of the adsorbent, extraction time and sample volume, were systematically investigated. Under the optimised conditions, concentration of Hg(II) at 1.0 μg L^?1 can be successfully enriched by the material without the interference of the common co-existing ions. The enrichment factor and adsorption capacity were 250 and 75.2 mg g^?1, and precise of the method was confirmed by analysing the spiked food, water samples and standard water reference samples with the recoveries of 92.5–101.8%.     

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.     

Sol–gel synthesis,characterization and water vapor adsorption properties of 1,1′-(1,6-hexanediyl)-bis(imidazolium)dichloride-silica hybrid material

1,1′-(1,6-hexanediyl)-bis(imidazolium)dichloride-silica hybrid material was prepared in 90 % yield by ammonia catalyzed sol–gel condensation of 1,1′-(1,6-hexanediyl)-bis[3-(3-triethoxysilylpropyl)-imidazolium]dichloride in aqueous ethanol. This novel ionic liquid-silica hybrid material can adsorp 27 % w/w water vapor in 90 min at room temperature and atmospheric pressure. This is a higher water adsorption capacity and rate than commercial desiccant Drierite which showed only 16 % w/w of water vapor adsorption and required 10 h to reach the maximum adsorption under identical conditions. The new adsorbent could be reused for five cycles without any significant loss in activity after regeneration by heating at 110 °C, for 24 h.