Aplicação de ondas eletromagnéticas no tratamento térmico de diferentes materiais: uso de micro-ondas e infravermelho nas áreas ambiental e alimentar

Abstract

Electromagnetic heating techniques allow the direct transmission of wave energy to the absorbent materials, bringing the advantage of fast volumetric heating with minimal energy losses. These characteristics make these methods attractive to the industry when compared to other conventional thermal techniques. In this scope, the present work addresses two distinct themes: the first is the microwave remediation of drilling cuttings contaminated with polyaromatic hydrocarbons (PAHs), and the second is the combined microwave/infrared (IR) treatment of faba beans to improve their physical and nutritional properties. In the decontamination of cuttings containing PAHs (naphthalene, biphenyl, fluorene and phenanthrene) the bench-scale microwave oven NEOS-GR (Milestone) was used. A Central Composite Planning (CCP) was proposed considering three variables: total initial content of PAHs, power and time; the analyzed responses were the total residual content of PAHs and the removal percentage. The results showed that the cuttings can be decontaminated at levels lower than those required by environmental legislation, starting from a total contamination of 7 to 40 ppm and reaching residual levels lower than 2 ppm. Power and time had positive influence on both responses, while the initial contamination content had negative influence only on the total residual content response. The boiling temperature of the PAHs was reached, and it was observed that the percentage of removal was inversely proportional to the boiling temperature of each compound. The proposed removal mechanisms were thermal desorption vaporization and thermal decomposition. For the treatment of faba beans, the bench-scale Advantium™ oven (General Electric) was used. For the CCP, the following variables were considered: microwave power, IR power and time. The final starch profile was the main answer analyzed on the CCD. From a general point of view, a positive result was observed after the combined treatment of the CDC SSNS-1 bean variety, with reduced digestibility (lower glycemic indexes). In the region considered to be optimal for the response (at medium levels of IR and microwave power, and low levels of time), there was a decrease in the Rapidly Digestible Starch (RDS) content and in the Slowly Digestible Starch (SDS) content, and an increase in the Resistant Starch (RS) content. No significant losses were observed in the selected experimental range.