Kinetic Modeling of the Adsorption Rate of a Gaseous Adsorbate on a Granular Adsorbent by Ultra-Rapid-Scanning Fourier Transform Infrared Spectrometry

Abstract

A novel method for determining the rates of adsorption of gaseous adsorbates on granular adsorbents in the millisecond time regime is described. Mixtures of the adsorbate and nitrogen are passed through a solenoid valve and 100 mg of the adsorbent for periods of (typically) 100 ms. The concentration of the adsorbate passing into a low-volume, long path length gas cell is measured with an ultra-rapid-scanning Fourier transform infrared spectrometer capable of gathering 200 mid-infrared spectra per second with 6-cm(-1) resolution. The pressure of the gas entering the cell is measured simultaneously with a capacitance manometer. A dynamic mathematical model was developed to analyze and describe the results in terms of a Langmuir isotherm. The success of this approach is demonstrated by the estimation of the rate of adsorption of vapor-phase acetaldehyde on aminopropylsilylated granular silica gel.

Time-Resolved Infrared Spectroscopic Studies of Poly(ethylene terephthalate) Deformation

“…Indeed, a time resolution of 5 ms per spectrum has been recently demonstrated for gas adsorption studies. 13 In this work, we have used both PM-IRLD and URS-FTIR to study the evolution of molecular orientation and microstructure during and following the irreversible deformation of thin films of amorphous poly(ethylene terephthalate) (PET), a ubiquitous engineering polymer. The possibilities and limitations of these techniques for such studies will be contrasted.…”

Kinetic Modeling of Aldehyde Adsorption Rates on Bare and Aminopropylsilyl-Modified Silica Gels by Ultra-Rapid-Scanning Fourier Transform Infrared Spectrometry

“…In a companion paper, we described a kinetic model that was used to determine the adsorption coefficient ( k a ), the desorption coefficient ( k d ), and the total number of adsorption sites ( N t ) for the adsorption of a gas mixture of 4.0 Torr acetaldehyde in 196.0 Torr of nitrogen on 100 mg of type 1 APS silica gel. If the k a , k d , and N t values found by the model are correct, then the k a and k d values should not change when the amount of adsorbent is changed.…”

“…A Manning Applied Technology (Troy, ID) URS/FT-IR spectrometer , was coupled to a custom-built system for creating 100-ms exposures of granular adsorbent samples to gaseous formaldehyde or acetaldehyde in nitrogen. , Exposure times were controlled with the use of a fast-acting solenoid valve (series 9, Parker Instrumentation, Fairfield, NJ). The gases passing through the adsorbent enter a 2.40-m, 20-reflection multipass IR gas cell (Infrared Analysis, Anaheim, CA) through which interferograms are measured at 5-ms intervals.…”

“…To determine the kinetics of the rates of adsorption of aldehyde gases on siliceous adsorbents in the duration of about 100 ms, conditions analogous to a cigarette "puff" required the development of a new method of data acquisition and a new way to model the resulting data. The basis of this method was described in a previous report by Weinstock et al 2 In that paper, it was shown that the amount of acetaldehyde passing through a granular adsorbent and into a long-path infrared gas cell could be measured at 5-ms intervals by an ultra-rapid-scanning Fourier transform infrared (URS/FT-IR) spectrometer provided that the combined pressure of the acetaldehyde and nitrogen fill gas entering the cell could be measured simultaneously. In this paper, we describe a more detailed and precise model and apply it to the determination of the adsorption rates in terms of a Langmuir isotherm.…”