Jan-Chan Huang

Gas-Solid Chromatography of Methane-Helium Mixtures: Transmission of a Step Increase in the Concentration of Methane through an Activated Carbon Adsorber Bed at 25°C

Abstract Time-dependent transmission or “breakthrough” curves of methane in helium flowing through an activated carbon adsorber bed were measured for methane concentrations between 34 and 105 ppm, and for mixture flow rates between 0.69 and 6.64 cm/s. The transmission is the ratio of the outlet concentration to the inlet concentration. The experimental transmission curves for a step-function increase in the methane concentration are compared with the predictions from a model which assumes a linear adsorption isotherm and equilibrium between the gas and solid phases. These two basic assumptions are discussed in detail. The data show that the two assumptions hold within the concentration and flow rate regions of this study. Effective diffusion coefficients of methane were calculated from the transmission data and found to increase with increasing flow rates.

Correlation of adsorption isotherms of hydrocarbon gases on activated carbon

A single curve of the adsorbate volume W in the adsorbed phase versus the reduced adsorption potential φ correlates adsorption isotherms of saturated hydrocarbons of low molecular weight (viz. ethane, propane, and n-butane) at pressures from 0.034 to 10 mm Hg on Columbia 4LXC 1228 activated carbon at 25 and 30°C. This correlation is based on the Polanyi-Dubinin adsorption potential theory and the use of the Peng. Robinson equation of state to calculate thermodynamic properties. This correlation can be represented analytically by expanding the logarithm of W in terms of a quadratic polynomial in φ.

Gas-solid chromatography of ethane on activated carbon at 25 C

Abstract The adsorption and diffusion of ethane in a chromatographic column packed with activated carbon were investigated for different concentrations and flow-rates. The adsorption isotherm of ethane can be represented by a three-parameter equation. The experimental data and theoretical asymptotic concentration profiles agree at high inlet concentrations and deviate at low inlet concentrations. The longitudinal diffusion coefficients were extracted from fitting the experimental data. Analytic criteria presented here for achieving an asymptotic concentration profile predict that the best result occurs at the flow-rate corresponding to the minimum of the height equivalent to a theoretical plate.

Linear non-equilibrium chromatographic reactor with a first-order chemical reaction

Abstract A model is presented for a linear chromatographic reactor with a first-order reaction and three non-equilibrium processes. The following three conclusions are derived based on the Laplace transform of the reactant concentration: (1) the input-output ratio of the reactant is a function of longitudinal diffusion and interfacial diffusion in addition to the reaction rate constant; (2) moment analysis indicates that six parameters pertinent to the linear chromatographic reactor can be determined from the area ratio (or zeroth moment), and the second-order central moment as a function of flow-rate; (3) an approximation to describe the solid-phase concentration by a first-order ordinary differential equation needs a rate coefficient which depends on other parameters of the system besides the solid-phase diffusion coefficient.

Gas-solid chromatography of methane-helium mixtures: moment analysis of breakthrough curves

A moment analysis method is suggested for calculating parameters of a breakthrough curve generated from a step change of concentration of an adsorbate. The longitudinal diffusion coefficient and the solid-phase diffusion coefficient are determined from the calculated moment. A criterion is given for assessing the relative importance of the longitudinal diffusion coefficient and the solid-phase diffusion coefficient. This criterion also serves as a guide for choosing experimental parameters to determine the solid-phase diffusion coefficients.

Adsorption of n-butane and 1,3-butadiene on cross-linked polystyrene

Abstract Adsorption isotherms of n -butane and 1,3-butadiene and their mixtures on cross-linked polystyrene at 25°C were measured by the frontal analysis method. Single-component isotherms appear to be of the Freundlich type. A binary Freundlich isotherm is adopted for discussing binary data and a method for calculating binary parameters is presented. Another binary Freundlich isotherm, which fails to agree with our data, was examined also.

Adsorption of binary mixtures of ethane and acetylene on activated carbon

Abstract Dynamic measurements of the adsorption of binary mixtures of ethane and acetylene (and also of each gas alone) in a helium carrier gas were made on an (Columbia 4LXC 12/28) activated carbon adsorber bed at 25°C. The adsorption capacities of the activated carbon for the pure gases and for each component in the mixtures are extracted from the transmission curves by the use of a mass balance equation. Transmission is the ratio of the concentration at the outlet of the adsorber bed to that at the inlet. The adsorption isotherms for pure ethane and acetylene can be represented by a modified Langmuir isotherm known as the Chakravarti-Dhar isotherm at gas concentrations up to at least 4.2 ± 10−7 mol/cm3 (viz., 7.8 mmHg). The gas-adsorbate equilibrium composition and the adsorption capacity of each component in the binary mixture of ethane and acetylene are estimated from the corresponding single-component isotherms by applying ideal adsorbed solution theory (IAST). The fact that the estimated values of ...

Study of frontal analysis by characteristic point

Abstract An analytical solution is derived for the desorption of an adsorbate that obeys a Langmuir isotherm and diffuses at a finite rate. The solution is integrated to give the adsorption isotherm by the technique of frontal analysis by characteristic point. The results indicate that the integration procedure does not yield the real isotherm for a system with a finite diffusion rate. The ratio of the equilibrium speed to the elution speed is given as a criterion for deviation from the real isotherm. An experimental result is given to show the deviation of the measurement of the adsorption isotherm of ethane on activated carbon.

Gas—solid chromatography of propane on cross-linked polystyrene at 25°C

Abstract Breakthrough curves of propane in a chromatograpic column packed with cross-linke polysterene were measured for different concentrations and flow-rates The adsorption isotherm, as determined from a mass-balance equation, was found to be a Freundlich-type isotherm. A theoretical model for the asymptotic concentration profile is discussed in order to examine the longitudinal diffusion coefficient and the lumped mass-transfer coefficient. Slopes of breakthrough curves at the inflection points were applied to calculate these two parameters for different input concentrations. The imperfection of the model is disclosed in this result because the data deviate from the theoretical prediction at high flow-rates, and the longitudinal diffusion coefficient and the lumped mass-transfer coefficient depend on the input concentration which contradicts the assumption of the model.

A Separation Factor Method for the Analysis of Ideal Binary Mixtures in Gas-Solid Adsorption

Abstract A correlation formula based on the separation factor is proposed for the mixture concentration in the adsorbed phase of an ideal binary solution in gas-solid adsorption. This formula is shown to apply to two binary systems (viz., 1,3-butadiene and n-butane on cross-linked polystyrene at 25°C, and acetylene and ethane on activated carbon at 25°C) with similar molecular and thermodynamic properties in the two components for each system. Comparison between the calculated and experimental values of the separation factor showed that the assumption of an ideal mixture is justified for each of these two binary systems. Mixture isotherms for the two ideal binary systems are calculated by the proposed correlation formula from the corresponding single-component isotherms. Good agreement between the calculated and experimental mixture isotherm data confirms that a binary system of two components with similar molecular properties (viz., molecular weight, normal boiling point, vapor pressure, number of carbon...