Improved ODE integrator and mass transfer approach for simulating a cyclic adsorption process

The linear driving force (LDF) model is applied to predict the service life of activated carbon cartridges. It is compared with the currently used Wheeler-Jonas equation, which results from a model of chemical reaction kinetics. The LDF model is based on a mass transfer model of adsorbate into the particle. The two models are studied in constant-pattern conditions. The properties of the two models are first clarified and then compared. It is shown that the Wheeler-Jonas equation leads to symmetrical breakthrough curves, whereas the constant-pattern LDF equation results in asymmetrical curves. Thus, the curvature of the isotherm has no influence on the shape of the Wheeler-Jonas curve. For the LDF breakthrough curve, it is shown that the asymmetry increases with the curvature of the isotherm. Wheeler-Jonas can be used with a Dubinin-Raduskevitch isotherm, whereas the LDF model analytical solution is valid for a Langmuir isotherm only. The LDF model can be used with the DR isotherm, but a numerical solution is required. At very low concentrations where the isotherm is linear, the constant pattern no longer exists and both models fail. The Dubinin-Raduskevitch isotherm must be fitted with a Langmuir isotherm to use the analytical solution of the LDF model.

An equilibrium model for pressure swing adsorption (PSA) process with equalization step is developed by using the method of characteristics. The concentration profiles at the cyclic steady state are obtained by tracking the movement of wave fronts derived from the characteristic lines during the transient cycles. The results of this model compare quite well with the conventional finite difference method, but with less computational effort. Multiple waves in PSA processes are clearly demonstrated by this model. Effects of equalization step on PSA process performances are also analyzed using this model.

Adsorptive separations have gained considerable importance in process industry. A generic simulator has been developed in this work for Pressure Swing Adsorption (PSA) processes. Several simple and complex, conventional and unconventional PSA cycles have been studied using this simulator. Distinction has been made between PSA processes where a raffinate stream richer in the weakly adsorbed component as compared to the feed is the desired product as against processes where extract stream richer in the strongly adsorbed component is the desired product. These are termed as raffinate PSA and extract PSA respectively. Extract PSA is an unconventional process variation. The studies include several simple and complex PSA cycles for raffinate and extract PSA of industrial importance. The studies are aided by a generic simulator for all PSA process variations developed for the purpose. The simulator is equally applicable to Vacuum Swing Adsorption (VSA), Pressure Vacuum Swing Adsorption (PVSA), rapid cycle PSA processes, etc.

Correlations for the mass transfer coefficient in desiccant matrices when using linear driving force and pseudo-gas-side-controlled models

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.

Selecting an optimum kinetic model for gas–solid adsorption based on statistical approaches and a model selection criterion

Design and experiment of high-productivity two-stage vacuum pressure swing adsorption process for carbon capturing from dry flue gas

It has been reported that the CO2 adsorption capacity of the N-enriched activated carbon can increase or decrease. In this study a commercial activated carbon was functionalized with 3-chloropropylamine hydrochloride and its adsorption characteristics in a fixed-bed column were investigated. The N-enriched activated carbon presented lower BET surface area than the original activated carbon suggesting that the nitrogen incorporation partially blocks the access of N2 to the small pores. Although the surface basicity has increased it is not accomplished by an increase of the capacity of the adsorption of the N-enriched activated carbon. The breakthrough curves in a fixed bed column were obtained at different temperatures (301 K, 323 K, 373 K, and 423 K) and a total pressure of 1.01 bar using CO2 diluted in helium at two feed concentrations—10% and 20% (v/v). A model based on the Linear Driving Force (LDF) model for mass transfer was used to estimate the overall mass transfer coefficient and reproduced the breakthrough curves satisfactorily.

Approximation of a PSA process based on an equivalent continuous countercurrent flow process: Blow-up and blow-down representation

Design and performance evaluation of a multilayer fixed-bed binder-free desiccant dehumidifier for hybrid air-conditioning systems: Part II – Theoretical analysis

A pilot scale adsorber apparatus was designed and constructed to investigate water and ethanol adsorption/desorption kinetics on 3A zeolite for the design purposes of a fuel ethanol dehydration pressure swing adsorption (PSA) process. Equilibrium studies have shown that 3A zeolite adsorbed a significant amount of water while very weak ethanol adsorption was observed. The breakthrough curves were utilized to study the effects of column pressure, temperature, flow rate, pellet size, and adsorbate concentration on the overall mass transfer resistance. Based on experimentally observed trends, both macropore and micropore diffusion were identified as relevant mass transfer mechanisms. A mathematical model for a bench scale adsorption bed included the linear driving force (LDF) adsorption rate model and the variation of axial velocity. A detailed heat transfer model was a necessity since the bed dynamics was affected by heat transfer in the bed wall. The model was used to analyze the experimental data and extract values of pertaining diffusion coefficients.

Comprehensive study on copper adsorption using an innovative graphene carbonate sand composite adsorbent: Batch, fixed-bed columns, and CFD modeling insights

In this study, a coupled Computational Fluid Dynamics (CFD) and Linear Driving Force (LDF) model was developed to simulate CO 2 adsorption onto activated carbon which is a promising approach for carbon capture and storage systems. The model captures the dynamic interplay between fluid flow, heat transfer, and adsorption within a packed bed, and was validated against experimental data. Parametric studies revealed that increasing bed porosity from 0.1 to 0.7 accelerated adsorption by up to 22%, but reduced total CO 2 uptake by over 66% due to lower adsorbent mass. An annular-shaped reactor with dual cooling surfaces reduced breakthrough time by 60% compared to the standard cylindrical reactor, with only a 10% increase in specific energy usage. Radial CO 2 injection also improved adsorption kinetics over standard reactor. Additionally, raising the inlet pressure from 3 bar to 5 bar increased CO 2 uptake by 35% with a 17% rise in energy consumption, while increasing the cooling temperature from 5 °C to 10 °C reduced uptake by 11% and lowered energy use by 15%. These results offer design-level insights for optimizing CO 2 capture systems under realistic process conditions.

Hollow fiber adsorbents have potential to overcome high pressure drop, adsorbent bed settling, and channeling problems in fixed bed adsorption systems. A coaxial spinning method was used for the synthesis of hollow fibers with an outer layer of electrically conducting polyvinylidene fluoride/carbon black composite with a positive temperature coefficient of resistivity and an inner layer of zeolite 13X/polyethersulphone adsorbent. The outer layer was optimized for self-limiting/regulating alternating current (AC) electrothermal regeneration. A fiber cartridge was constructed for studying the dynamic breakthrough and adsorbent regeneration characteristics. The breakthrough results for water vapor adsorption were analyzed by Wheeler–Jonas, Linear Driving Force (LDF) and Richards sigmoidal models. The isosteric enthalpy and kinetics for adsorption were determined for static vapor adsorption. The LDF adsorption kinetics observed at low surface coverage change to a stretched exponential kinetic model with increasing surface coverage. Intraparticle diffusion in the zeolite crystalline porous structure was rate-determining for water vapor breakthrough characteristics.

Efficient desorption of selectively adsorbed N2 from air in a packed column of LiX zeolite by rapidly purging the adsorbent with an O2 enriched gas is an important element of a rapid cyclic pressure swing adsorption (RPSA) process used in the design of many medical oxygen concentrators (MOC). The amount of O2 purge gas used in the desorption process is a sensitive variable in determining the overall separation performance of a MOC unit. Various resistances like (a) adsorption kinetics, (b) column pressure drop, (c) non-isothermal column operation, (d) gas phase mass and thermal axial dispersions, and (e) gas-solid heat transfer kinetics determine the amount of purge gas required for efficient desorption of N2. The impacts of these variables on the purge efficiency were numerically simulated using a detailed mathematical model of non-isothermal, non-isobaric, and non-equilibrium desorption process in an adiabatic column. The purge gas quantity required for a specific desorption duty (fraction of total N2 removed from a column) is minimum when the process is carried out under ideal, hypothetical conditions (isothermal, isobaric, and governed by local thermodynamic equilibrium). All above-listed non-idealities (a–e) can increase the purge gas quantity, thereby, lowering the efficiency of the desorption process compared to the ideal case. Items (a–c) are primarily responsible for inefficient desorption by purge, while gas phase mass and thermal axial dispersions do not affect the purge efficiency under the conditions of operation used in this study. Smaller adsorbent particles can be used to reduce the negative effects of adsorption kinetics, especially for a fast desorption process, but increased column pressure drop adds to purge inefficiency. A particle size range of ∼300–500 μm is found to require a minimum purge gas amount for a given desorption duty. The purge gas requirement can be further reduced by employing a pancake column design (length to diameter ratio, L/D<0.2) which lowers the column pressure drop, but hydrodynamic inefficiencies (gas mal-distribution, particle agglomeration) may be introduced. Lower L/D also leads to a smaller fraction of the column volume that is free of N2 at the purge inlet end, which is required for maintaining product gas purity. The simulated gas and solid temperature profiles inside the column at the end of the rapid desorption process show that a finite gas-solid heat transfer coefficient affects these profiles only in the purge gas entrance region of the column. The profiles in the balance of the column are nearly invariant to the values of that coefficient. Consequently, the gas-solid heat transfer resistance has a minimum influence on the overall integrated N2 desorption efficiency by O2 purge for the present application.