ABSTRACT

Many anthropogenic chemicals released into the atmosphere are toxic and can cause adverse effects on human health. Under the 1990 Clean Air Act Amendment (CAAA), the United States Environmental Protection Agency (USEPA established Maximum Achievable Control Technology (MACT) standards to reduce emissions of industrial toxic materials. These regulations have encouraged the development of new technologies to capture and recover toxic chemical vapors from industrial gas streams. In this research, a new activated carbon fiber cloth (ACFC) adsorber coupled with an electrothermal regenerator and a cryogenic condenser was designed and developed to efficiently capture and recover toxic volatile organic compounds (TVOCs) from simulated industrial gas streams. The system was characterized for adsorption by ACFC, electrothermal desorption, and cryogenic condensation to recover acetone and methyl ethyl ketone (MEK). Acetone was listed as a TVOC at the initiation of this project, has large emissions to the atmosphere, and is a good surrogate for other TVOCs. Results for research pertaining to acetone are also reported have. Results for research pertaining to acetone are also reported here. ACFC demonstrated good performance characteristics due to its high adsorption capacity, faster adsorption and desorption rates, zero ash content, and desirable electrical conductivity for an efficient electrothermal regeneration. The adsorption throughput ratios (TPRs) averaged from 65% to 86% for an effective bed length of 18 cm, a packing density of 94 mg/g and ACFC content of 27 g and 19 g. During electrothermal regeneration, supersaturated effluent vapor was produced in a very short time and low consumption energy (e.g. 63% by volume acetone was generated in 5.4 min with a consumption energy of 1 KJ/g-acetone/g-carbon) while heat loss to the carrier gas stream was not appreciable. Generating a concentrated vapor during a short time period by electrothermal regeneration reduces the size and operating cost of the cryogenic condenser. Cryogenic treatment of the effluent gas stream condensed TVOCs to concentrations to meet MACT standards. The Net Present Value analysis of the entire system including the adsorption, desorption and condensation processes indicated good prospects for economical recovery of the TVOCs. Sensitivity analysis showed the effect of component cost on the total break-even price of recovered acetone. Reducing the adsorption cycle time reduced the total cost and made the total cost less sensitive to changes in ACFC price. Experimental evaluation of the system and preliminary economic analysis provide encouraging results for developing a pilot-scale system for further analysis.