STUDY ON THE DECOMPOSITION OF ISOPROPYL ALCOHOL BY USING MICROWAVE/Fe3O4 CATALYTIC SYSTEM

Isopropyl alcohol (IPA) is the major organic emission in the semiconductor manufacturing industry. A microwave/Fe3O4 catalytic system was proposed for treatment of IPA. This system comprises a household microwave oven modified as the reaction chamber, which was fitted with a vertical, cylindrical quartz reactor comprising a catalytic packed column filled with granular Fe3O4. Experimental results showed that the destruction and removal efficiency of IPA by microwave alone was close to zero, but with the microwave/Fe3O4 system, the temperature of the catalytic packed column increased rapidly and reached thermal balance within 10-15 min. Analysis of the rear gas after combustion showed that most of IPA was thermally oxidized into CO2 and H2O. The successful application of the proposed microwave/Fe3O4 system to thermal destruction of IPA promises a new technology for treatment of volatile organic compounds. *Corresponding author Email: [email protected] INTRODUCTION The semiconductor industry is of the major economic interest in Taiwan, but it also brings significant amounts of pollutants. In the semiconductor manufacturing process, a large number of high concentrations of volatile organic solvents are used. The exhaust gas and wastewater containing more complex components are emitted by these processes. Isopropyl alcohol (IPA), acetone, propylene glycol monomethyl ether acetate, ethyl lactate, phenol, benzene and xylene are the common organic reagents present at high concentrations in the wastewater [1] and most of them are volatile organic compounds (VOCs). Most VOCs are not only volatile but also toxic. In view of their harmful effects on the environment and potential threat to human health, the U.S. Environmental Protection Agency enacted the Clean Air Act Amendment in 1990 and classified many VOCs as toxic air pollutants. Common control techniques for VOCs include combustion, adsorption, absorption, and condensation processes. While the conventional thermal treatment and some advanced oxidation processes have shown greater efficiency in removing VOCs and enhancing public safety, they require both larger capital investment and processing costs. Also, adsorption and absorption approaches only achieve phase transformation only, rather than reduction in quantity or toxicity of the VOCs [2-4]. Microwave was first applied to heating food. In 64 J. Environ. Eng. Manage., 20(2), 63-68 (2010) recent years, its applications have grown rapidly in diverse fields such as concentration, extraction and synthesis in chemistry [5-8]. This study focused on employing microwave as the source of energy radiating on the catalyst of Fe3O4 to treat VOCs such as IPA. Microwave processing technique not only saves time but also requires no additional fuel. Thus, it is more environmentally friendly and causes no secondary pollution. In this study, a high-temperature combustion system is established by applying microwave of 2450 MHz to a catalytic Fe3O4 packed column, which is then employed to destroy and remove VOCs in waste gas. Results of this research confirm the feasibility of this approach to removal of air pollutants [9] and the treatment system has already been granted a patent (No. M309457) in Taiwan [10]. EXPERIMENTAL METHODS AND MATERIALS 1. Design of Microwave Catalytic Packed Column Figure 1 is a schematic diagram showing the proposed continuous microwave radiation (CMWR) system. A household microwave oven (Panasonic Taiwan, NE-R30A) with frequency of 2450 MHz and continuous power output was modified as a reaction chamber. The rotating plate of a microwave oven was originally designed to overcome the potential problem of irregular microwave absorption due to geometric shapes. In this study, the rotating plate was replaced by a vertical, cylindrical reactor comprising quartz tubes of dimensions 50 mm I.D. × 53 mm O.D. × 27.5 cm L (Shan-Long Glass Co., Taiwan). These quartz tubes of the reactor were first filled with granular Fe3O4 (5 mm I.D. × 7 mm L, Osaka Co., Japan) to a height of 25 cm, serving as the catalytic packed column. The images of reactor in CMWR and the packed catalyst, Fe3O4, are illustrated in Fig. 2. The structure of granular Fe3O4 was rather uniform and the diameter was about 100 nm. The K-type thermocouples (KTS1320, Star Co., Taiwan) were then inserted into the packed column at a distance of 2.5 cm from the bottom of the reactor. Inflow gas was pumped from the outside air using an air compressor of 1.1 kW. With water, oil and suspended particles filtered and removed, the purified air then flowed through the mass flow meter (GFM17, AALBORG Co., Germany) for controlling the air flow. A simulative IPA (Aldrich) gas at fixed concentration was injected by the work bee controller (Bioanalytical Systems Inc., Indiana, USA) marked as “Syringe” in Fig. 1. Flowing along the heated pipes, the injected IPA became completely vaporized. It was then mixed with various proportions of inflow gas and flew through two buffering flasks into the reactor. To ensure complete mixing and reaching the designed concentration, the mixed gas was sampled by a gas chromatography equipped with 1. Air compressor