Showing papers by "Ralph T. Yang published in 1986"

Bulk separation of multicomponent gas mixtures by pressure swing adsorption: Pore/surface diffusion and equilibrium models

Abstract: A theoretical and experimental study is performed for the bulk separation of a ternary mixture by pressure swing adsorption. Three concentrated products can be obtained by cycling the pressure in the adsorber. Three models are formulated for the cyclic process: equilibrium, Knudsen diffusion, and Knudsen plus surface diffusion. The latter model provides the best results when compared with the experimental data, due to the important contribution of surface flux to the total flux in the sorbent pores.

Bulk Gas Separation by Pressure Swing Adsorption

Abstract: Etude theorique et experimentale de la separation d'un melange H 2 /CO, 50/50 sur charbon actif, en deux produits. Comparaison d'un modele d'equilibre et d'un modele de force motrice lineaire. Dans ces deux modeles on tient compte de l'adsorption a partir des deux composants du melange et du bilan energie

Analytic solution for adsorber breakthrough curves with bidisperse sorbents (zeolites)

Abstract: A time-domain solution in the form of infinite series for the break-through curves is derived for zeolite adsorbers. Three diffusion steps are accounted for in the solution: external film, macropore, and micropore. The solution is based on the assumption that the concentration profiles in micropores and macropores are both parabolic. Based on the analytic solution, a simple criterion is given for the relative importance of the three individual mass transfer resistances. The adsorber behavior is determined by four independent dimensionless parameters. For the commercial zeolite sorbents, the bed behavior is dominated by two parameters: Henry's law constant (K) and the parameter M2, which is the product of the stoichiometric time (L/v) and the time constant for macropore diffusion (Dp/Ro2). The analytic solution is in good agreement with experimental data for the breakthrough curves of nitrogen and methane carried in helium in 5A zeolite beds. When reduced to monodisperse pores, the solution is also in good agreement with Rosen's exact solution.

Improved pressure swing adsorption processes for gas separation: by heat exchange between adsorbers and by using high-heat-capacity inert additives

Abstract: Two new pressure swing adsorption processes for bulk gas separation are proposed. The first one is by allowing heat exchange between the adsorber columns, for example, by using a shell-and-tube type heat exchanger, where the shell and the tube are two beds. By model simulations, it is shown that the new process offers substantial improvements in both product purities and recoveries over the adiabatic process, which resembles the industrial operations using large beds. A fundamental understanding for the improvements is given through model simulations. A peculiar high-temperature plateau and cold ends in the bed are predicted for the adiabatic process. In the second process, an inert material with a high heat capacity is added into the adsorbent bed. The inert additive serves to store heat during adsorption and release it during desorption, hence reducing the magnitudes of the temperature excursions during pressure swing cycle and improving the separations. Model simulation results are presented for bulk separation of H/sub 2//CH/sub 4/ and H/sub 2//CO mixtures with various amounts of iron particles added in a bed of activated carbon. The results show substantial improvements in both product purities and recoveries by the inert additive. A fundamental understanding of the role played bymore » the inert additive is gained through a comparison of the temperature profiles in the bed and its variation with time during a steady-state cycle.« less

Parametric study of the pressure swing adsorption process for gas separation: a criterion for pore diffusion limitation

Abstract: The performance for gas separation by pressure swing adsorption is determined by four dimensionless parameters, pore diffusion (Detc/a2 ); bed utilization (uctc/L); purge-to-feed ratio (γ): and feed composition (yA0 ) The unique dependence of the product purities on these parameters are shown for binary-mixture separation on activated carbon The importance of pore diffusion in PSA separation for binary mixtures may be assessed by the threshold value of Detc/a2 = 43, above which pore diffusion is not important

Separation of binary gas mixture into two high-purity products by a new pressure swing adsorption cycle

Abstract: Binary mixtures can be separated into two high-purity products by a new pressure swing adsorption (PSA) cycle. The product purity depends on the purge/feed ratio of the respective gases in the PSA cycle. The process characteristics of the new PSA cycle, using activated carbon as the sorbent, can be adequately predicted by an equilibrium model.

Adsorption of mixtures of water vapor and hydrocarbons by activated carbon beds: Thermodynamic model for equilibrium adsorption and adsorber dynamics

Abstract: A simple thermodynamic model is developed for predicting the equilibrium adsorption of water vapor mixed with hydrocarbons on activated carbon. The model is simple to use and compares favorably with experimental data. This model is used to predict the adsorber bed behaviours during adsorption and desorption of a binary (water-benzene) mixture. During adsorption, a long leading wavefront followed by a shock wave for water vapor exists due to the S-shaped isotherm, and a significant amount of water condensation can occur.