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The artificiality of the actual amount adsorbed (AAA) estimated from the experimentally measured Gibbsian surface excess (GSE) of a gas is discussed. The use of AAA for calculation of isosteric heat of adsorption or mixed gas adsorption isotherms using ideal adsorbed solution theory can be misleading and incorrect. The GSE, on the other hand, can be unambiguously used to describe all practical aspects of adsorption science and technology. [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

The uncertainty in the evaluation of the separation performance of a rapid pressure swing adsorption (RPSA) process for production of a high-purity product gas by using a numerical process model can be impractically high as a result of the theoretical or experimental uncertainty in the estimation of the high adsorbate mass transfer coefficient required by such a process. Actual experimental process performance data are required in order to judge the real value of the process. [ABSTRACT FROM AUTHOR]

The practical implications of replacing various individual transport resistances such as gas-solid mass and heat transfer, and gas phase axial dispersions of mass and heat in a numerical model of a pressure swing adsorption (PSA) process by a single, empirical, lumped, effective mass transport coefficient were evaluated. A non-isothermal, adiabatic, four-step Skarstrom-like PSA process for production of pure helium from a binary helium-nitrogen mixture using 5A zeolite adsorbent was considered. It was found that the above-described model simplification was adequate to describe key process performances such as the bed size factor and the product recovery vis-a-vis a detailed model where the effects of all individual resistances were explicitly included. [ABSTRACT FROM AUTHOR]

A concept of creating an ideal multicomponent-gas adsorbed phase by mixing pure gas adsorbed phases of the components at constant surface potential and temperature using the Gibbsian Surface Excess (GSE) framework of adsorption is proposed. The GSE provides the only unambiguously measured experimental quantity to describe the extent of adsorption. The actual amounts adsorbed can be estimated from the GSE only by making extraordinary assumptions about the volume and structure of the adsorbed phase. The correlations between the multicomponent and pure gas GSE isotherms generated by the proposed concept closely resemble those for the classic Ideal Adsorbed Solution Theory (IAST), which was developed by using the actual amounts adsorbed as the primary variables. The proposed correlations can be obtained by simply substituting the actual amount adsorbed of components in the corresponding IAST correlations by the GSE of the components. All pure and multicomponent gas adsorption data published in the literature are GSE, and they are directly used in the IAST by loosely assuming that they are actual amounts adsorbed. Thus, it appears that the proposed concept of this work has been inadvertently used in all past works which use IAST to estimate multicomponent adsorption isotherms from pure component isotherm data. [ABSTRACT FROM AUTHOR]

The effects of feed air pressure on the steady-state performance of a medical oxygen concentrator (MOC) were experimentally evaluated using a novel design of a MOC unit which produced a continuous stream of ∼90% O2 employing a rapid pressure swing adsorption (RPSA) process scheme. Dry, CO2 free air containing ∼1% Ar at different feed gas pressures was used in the tests in conjunction with a commercial sample of LiLSX zeolite as the N2 selective adsorbent in the process. The bed size factor (BSF) can be systematically reduced by increasing the feed air pressure for any given total cycle time. The effect of feed air pressure on the oxygen recovery (R) is, however, more complex; it increases with increasing feed pressure only at longer cycle times while the effect is marginal at shorter cycle times. The BSF cannot be indefinitely reduced by lowering total process cycle time at any pressure-a minimum is exhibited in the BSF-cycle time plot. The minimum value of the BSF decreases as the feed pressure is increased. The cycle time for the minimum BSF is, however, not significantly altered by the feed pressure in the data range of this work. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1212-1215, 2016 [ABSTRACT FROM AUTHOR]

A detailed numerical study of the individual and cumulative effects of various mass, heat, and momentum transfer resistances, which are generally present inside a practical adiabatic adsorber, on the overall separation performance of a rapid pressure swing adsorption (RPSA) process is performed for production of nearly pure helium gas from an equimolar binary (N2 +He) gas mixture using 5 A zeolite. Column bed size factor (BSF) and helium recovery (R) from the feed gas are used to characterize the separation performances. All practical impediments like column pressure drop, finite gas-solid mass and heat transfer resistances, mass and heat axial dispersions in the gas phase, and heats of ad(de)sorption causing nonisothermal operation have detrimental impacts on the overall process performance, which are significantly accentuated when the total cycle time of a RPSA process is small and the product gas helium purity is high. These impediments also prohibit indefinite lowering of BSF (desired performance) by decreasing process cycle time alone. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2008-2015, 2015 [ABSTRACT FROM AUTHOR]

A novel design of a compact rapid pressure swing adsorption system consisting of a single adsorber enclosed inside a product storage tank is proposed for application as a medical oxygen concentrator (MOC). A self-contained test unit for the process is constructed which is capable of directly and continuously producing 1-3 sl/m of 90% O2 from compressed air. Pelletized LiLSX zeolite is used as the air separation adsorbent. Steady state process performance data [bed size factor (BSF) and O2 recovery (R) as functions of total cycle time (tc)], as well as transient, cyclic, adsorber pressure, and temperature profiles are presented. A four-step Skarstrom-like pressure swing adsorption cycle was used. Two options for column pressurization, (a) using compressed feed air cocurrently or (b) using a part of the oxygen-enriched product gas counter-currently were evaluated. Option (b) exhibited superior performance. The optimum total cycle time for option (b) was 5-6 s where the BSF was lowest (∼45 kgs/TPD O2) and the corresponding R was ∼29.3%. These numbers indicate that the adsorbent inventory of a MOC can be potentially reduced by a factor of three while offering a ∼10-20% higher O2 recovery compared to a typical commercial unit. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3330-3335, 2014 [ABSTRACT FROM AUTHOR]

Significance A nonequilibrium, nonisothermal, nonisobaric model was used for numerical simulation of the efficiency of N2 desorption from a LiX zeolite column by rapid purge with O2 in a pancake adsorber. The key parameters included desorption time, adsorbent particle size, and the adsorber length to diameter ratio. The efficiency was found to be a complex function of these variables. [ABSTRACT FROM AUTHOR]

The effects of gas-phase axial thermal dispersion andsolid-phasethermal conduction on gas–solid heat transfer in a packed bedof solid particles was numerically studied using a simplified conduction–dispersionmodel for heat transfer in conjunction with a realistic set of boundaryconditions. It is reconfirmed that the exclusion of gas-phase thermalaxial dispersion in the model analysis of gas–solid heat transfercoefficients can result in misleading interpretation of heat transferin packed beds, particularly in the low Reynolds number gas flow region. [ABSTRACT FROM AUTHOR]

A high pressure condenser is considered to remove water vapor as well as recover heat from the desorbed steam-CO2 gas mixture in a novel sorption enhanced reaction process. It is possible to have water condensation at the gas side as well as water evaporation at the coolant water side because of large temperature difference between the hot and cold side. A model of heat and mass transfer and phase change was developed to understand the complex phenomena associated with the simultaneous condensation and evaporation taking place in the unit. A finite difference method was used to solve the boundary value problem. Additional insight was obtained by describing the operating lines and equilibrium condition in an enthalpy diagram. The model was used to explore the performance in terms of the heat recovery. The heat recovery was best at the beginning of the process when the superheated steam was generated. © 2011 American Institute of Chemical Engineers AIChE J, 2012 [ABSTRACT FROM AUTHOR]

The effects of the sorption and the regeneration temperatures on the performance of a novel rapid thermal swing chemisorption (RTSC) process (Lee and Sircar in AIChE J. 54:2293–2302, ) for removal and recovery of CO2 from an industrial flue gas without pre-compression, pre-drying, or pre-cooling of the gas were mathematically simulated. The process directly produced a nearly pure, compressed CO2 by-product stream which will facilitate its subsequent sequestration. Na2O promoted alumina was used as the CO2 selective chemisorbent, and the preferred temperatures were found to be, respectively, 150 and 450 °C for the sorption and regeneration steps of the process. The specific cyclic CO2 production capacity of the process and the pressure of the by-product CO2 gas were substantially increased over those previously achieved by using the sorption and regeneration temperature of, respectively, 200 and 500 °C (Lee and Sircar in AIChE J. 54:2293–2302, ). The net compressed CO2 recovery from the flue gas (∼92%) did not change. However, substantially different amounts of high and low pressure steam purges were necessary for comparable degree of desorption of CO2. A first pass estimation of the capital and the operating costs of the RTSC process was carried out for a relatively moderate size application (flue gas clean up and CO2 recovery from a ∼80 MW coal fired power plant). Both costs were substantially lower than those for a conventional absorption process using MEA as the CO2 solvent (Desideri and Paolucci in Energy Convers. Manag. 40:1899–1915, ). [ABSTRACT FROM AUTHOR]