Recovery of volatile organic compounds by microwave regeneration of adsorbents

The topic of this dissertation is the development of a process for using microwave heating to regenerate adsorbent beds as a means for solvent recovery and the assessment of the technical and economic feasibility of the process. As a case study, emission streams typical of industrial coating and printing operations were considered.;A series of bench-scale microwave regeneration experiments was conducted to determine desorption kinetics and to study the effects of key process variables (electric field intensity, regeneration pressure, etc.). These tests were conducted under vacuum at pressures ranging from 25 to 150 torr in a 2450 MHz multimode cavity. Water and three common industrial solvents were desorbed from molecular sieves, high-silica zeolites, and polymeric adsorbents. The results show that the dielectrically-enhanced mass transfer characteristics result in a quasi-equilibrium process consistent with the manufacturer sorption equilibrium data; accordingly, desorption increases with temperature and decreasing system pressure. Heat-up and desorption rates were found to be proportional to the power density for a given adsorbent/solvent combination.;Process models were developed based on these lab results to simulate the adsorption and regeneration bed dynamics and to determine key operating variables, such as microwave power consumption, for batch and continuous microwave regeneration systems. Parametric studies were conducted to examine the effects of adsorbent selection, column flow configuration, regeneration purge method, regeneration system pressure, and final regeneration coverage.;Based on these designs, the economic feasibility of microwave-regenerated adsorption systems was evaluated by systematically comparing the capital and operating costs of the proposed system with ten conventional VOC control systems. It was found that the microwave systems have similar capital and operating costs to conventional systems, and may present an attractive solvent recovery alternative to steam regeneration for industries using water-miscible solvents.;A laboratory pilot desorption column and recovery unit were designed and constructed to demonstrate the technical feasibility of a continuous flow microwave desorber. A systematic design methodology is presented and practical guidelines for the implementation of this new technology are enumerated. This system processes up to 45 kg/h of saturated adsorbent (10 kg/h of solvent).