An Investigation of the Adsorption of C₅-C₁₂ Hydrocarbons in the ppmv and ppbv Ranges on Carbotrap B

Abstract

The effects of concentration and temperature on the breakthrough volumes (Vb) of 23 volatile organic compounds on Carbotrap B have been determined using the frontal chromatography method. From the measured Vb, original isotherms have been produced and adsorption parameters based on the Langmuir, Freundlich, and Dubinin-Polyani adsorption models have been calculated. The calculated adsorption parameters describe the behavior of these VOC on Carbotrap B under the experimental conditions and are useful data for VOC sampling applications including adsorption modeling of pumped and diffusive sampling. Each of the adsorption models give similar results and are in good agreement with the experimental data in the ppmv concentration range. It will be shown that contrary to previous assumptions the Langmuir adsorption parameters obtained at ppmv concentrations cannot be used to predict Vb at ppbv concentrations and the calculated parameter mmax does not represent the maximum adsorbent capacity. The Freundlich and Dubinin-Polyani models are shown to be more successful in describing the adsorption behavior of the VOC at ppbv levels where Vb is independent of concentration. The isosteric heats of adsorption (-delta Hst) for some of the compounds have been determined using the Van't Hoff equation which can be used to predict the effect of temperature on Vb.

Method to predict gas chromatographic response factors for the trace‐level analysis of volatile organic compounds based on the effective carbon number concept

“…Δ H ad = a *(CN) + b ) . The BTV is related to Δ H ad through the van't Hoff relationship, ln(BTV) ∝ (Δ H ad / RT ) + c , where T is the temperature in K, R is the gas constant, and c is an entropic term .…”

“…⌬H ad = a*(CN) + b) [34]. The BTV is related to ⌬H ad through the van't Hoff relationship, ln(BTV) ∝ (⌬H ad /RT) + c, where T is the temperature in K, R is the gas constant, and c is an entropic term [35]. In 2008, Pal and Kim [36] reported how the choice of sorbents used in a cold trap and dilution factors (DF) to prepare G-WS from PS influenced the experimentally observed RF values on an AS-TD-GC-FID apparatus.…”

Breakthrough characteristics of volatile organic compounds in the −10 to +170°C temperature range on Tenax TA determined by microtrap technology

“…Dependence of BTV on concentration of injected compounds is discussed in several works [12][13][14][15], although at lower concentrations BTVs can be independent of concentration [16]. With respect to temperature, typically Van't Hoff equations are proposed [7,16]. Another widely discussed parameter is the flow rate dependence of BTV [17].…”

Monte Carlo simulations of n-butane and n-octane adsorbed onto graphite and a molecular model of activated carbon

“…Alkane adsorption is particularly important to storage gases. In the last years there had been a great interest in the study of alkane adsorption on carbonaceous materials, mainly in activated carbons (Fletcher and Thomas 1999;Foley et al 2001;Fletcher et al 2006;Severson and Snurr 2007;Liu et al 2017).…”