Microwave regeneration of zeolites in a 1 meter column

Abstract

Although sorption is a common method of removing volatile organic compounds (VOC's) from processes, the adsorbent must be regenerated to repeat the process. The use of microwaves to regenerate the bed of adsorbent can be more efficient than conventional heating methods. Desorption of methanol from a silicalite zeolite was studied by the use of microwaves in cylindrical column. Temperature probes at five axial and three radial positions monitored the temperature profile in time. A significant amount of microwave energy passed through the dry zeolite bed, whereas a strong attenuation occurs if methanol is adsorbed. The radial temperature distribution conforms to theoretical predictions; however, microwave reflections cause a distortion of the predictions in the axial direction. Irregularities during the saturation of the bed indicated a chemical reaction during the irradiation with microwaves. A fraction of the methanol reacted under microwave irradiation to form dimethylether and water, and to methoxylate the zeolite surface. V V C 2009 American Institute of Chemical Engineers AIChE J, 55: 1906AIChE J, 55: -1913AIChE J, 55: , 2009 Keywords: adsorption, isotherm, dielectric, heating, permittivity, methanol, silicalite IntroductionSorption is central to many industrial processes. Many manufacturing industries employ organic chemicals as solvents, cleaners, or reactants. To clear these pollutants from waste gas, adsorption of these VOC's (volatile organic compounds) on zeolites (molecular sieves) or on active carbons is widely used. The adsorbed species can be recycled and reused by heating the adsorbate to induce desorption. In a conventional desorption process, the energy used for desorption is introduced into the system via the gas phase or through the walls, and is distributed by heat transfer (convection and conduction). This is an indirect way of heating, since the entire system (the gas phase as well as the adsorbent bulk phase) has to be heated to the desorption regeneration temperature.Microwaves have the unique ability to heat materials selectively, depending on their dielectric properties. This makes microwaves interesting for use in sorption processes. With microwaves, energy can be delivered more efficiently to the actual sorption site, i.e., to an adsorbate on the surface of the adsorbent, provided that the adsorbate and/or the adsorbent surface can absorb microwave energy more efficiently than the adsorbent bulk phase. varying field intensity and penetration depth, become important. Mehdizadeh 3 discusses problems that have to be considered in scaling up processes involving microwave-induced reactions. This indicates a need to study the behavior of microwave propagation combined with desorption in larger scale systems.This study employs a pilot-scale cylindrical column (7.62 cm by 1 m) for desorption processes. It is intended to provide a basis to characterize the microwave propagation and sorption processes in a larger-scale system. A zeolite adsorbent was employed such that the adsorbent only we...

Microwave material processing—a review

“…The desorption process can be accomplished quickly with the help of using high microwave power or high flow rates. 241 Other industrial applications include microwave heating of a high volatile bituminous coal for rapid coke making 240 and pyrolysis of oil shale to enhance oil yield and oil quality by yielding oil containing less sulfur and nitrogen. 242 Use of microwave energy in mineral processing brings considerable benefits by reducing energy consumption and environmental pollution.…”

Adsorbents regeneration under microwave irradiation for dehydration and volatile organic compounds gas treatment

“…While the electric field is often considered homogeneously distributed in small cavities, microwave propagation in an industrial setting has to be taken into account and combined with the chemical and physical transformations of the process. A recent work on methanol desorption from a zeolite in a 1 m waveguide column [10] demonstrates the feasibility of this process. It also studies the instantaneous and transitory behaviour of temperature and the propagation of microwave energy.…”

Calculation of Critical Efficiency Factors of Microwave Energy Conversion into Heat

“…Meier et al [7] reported on microwave regeneration of silicalite zeolite from methanol in a circular waveguide, being also the 1-m desorption column. A stubbed tuner was utilized to minimize reflections of microwaves at the edges of the adsorbent bed, as these places were recognized being mostly responsible for reflections in the setup.…”