Modeling Effective Diffusivity of Volatile Organic Compounds in Activated Carbon Fiber

Abstract

Volatile organic compounds (VOCs) comprise 67% of total hazardous air pollutants (HAPs) that are emitted by major industrial point sources into the U.S. atmosphere (1). Adsorption by activated carbon fiber (ACF) has been recognized as one of the feasible regenerative control processes to separate and recover VOCs for reuse. Characteristics of VOCs transport in ACFs are required to efficiently design ACF sorption systems. However, extensive resources are spent experimentally obtaining transient sorption data to design adsorption systems. As an alternative, this work develops a new model that predicts effective diffusivities of VOCs into ACFs. The diffusion process is modeled as Knudsen transport into the ACF open pore spaces coupled with activated surface diffusion on the ACF's internal surface area. Temperature and Darken's factors are included in the surface diffusion model to provide corrections for thermodynamic state and deviation from Fick's Law, respectively. Depth of the adsorption potential well is considered as the product of the heat of adsorption of a reference VOC, an adsorption similarity factor, and a surface diffusion energy factor. Introduction of the adsorption similarity factor in the effective diffusivity model is a new concept providing a means to predict effective diffusivity of similar adsorption systems from a reference system. Experimental data from a short length column are used to determine effective diffusivity of acetone in ACF. Results from this diffusivity model are compared to experimental values for the acetone/ACF system to describe the degree of closure between modeled and experimental results.

Fabrication of Diatomite/Silicalite-1 Composites and Their Property for VOCs Adsorption

“…A number of studies have indicated the effectiveness of VOC removal by adsorption technology. The most frequently used materials for the capture of VOCs are porous substances with large surface areas and pore volume such as zeolites [4], resins [5] and activated carbons together with their derivatives [6,7,8,9]. It has been demonstrated that zeolites are desirable materials for the removal of hydrocarbons because of their “tailor-made” physico-chemical properties [10], together with their high thermal and chemical stability and renewable ability [11].…”

Adsorption and separation of linear and branched alkanes on carbon nanotube bundles from configurational-bias Monte Carlo simulation

“…For instance, many volatile organic compounds classified as atmospheric pollutants are directly or indirectly related to alkanes and their derivatives, and adsorption is currently one of the technically feasible and cost effective technologies to remove and recover these compounds. 1 The catalytic conversion and cracking of alkanes are major reactions in the petrochemical refinery industry, and the simultaneous alkane adsorption on catalysts or catalyst supports has been found to be important to interpret kinetic data. 2 Many industrial processes involve alkane mixtures, and how to separate them for particular use is an important topic.…”

Air oxidation effects on microporosity, surface property, and CH4 adsorptivity of pitch-based activated carbon fibers

“…The microporosity of ACFs enhances physisorption of vapors with the aid of the micropore field by overlapping solid-molecule interaction potentials from the opposite walls. These properties with high surface areas/pore volumes, enhanced adsorption dynamics due to the short molecular diffusion path inside the fiber, and operational advantages make ACFs excellent adsorbents for solvent recovery, high-grade water quality purification, and other industrial/environmental processes [4][5][6]. The uniform microporosity of ACFs in comparison with the traditional granular activated carbons is also likely * Corresponding author.…”