Fast activation of natural biomasses by microwave heating

Abstract

Microwave was effectively applied as a fast heating tool for activating two natural biomasses, pine wood and Arabica coffee residues. The heated biomasses were tested for removing four food dyes: Allura Red E129, Sunset Yellow E110, Tartrazine E102, and Brilliant Black E151 from solution. The biomasses were heated by 2.45GHz microwaves at different input powers 200–1000W for 8min. The results indicated that heating at high input powers is necessary to activate biomasses and to enhance dyes adsorption. Dielectrical properties (dielectric constant ɛ′, dielectric loss ɛ″, tangent loss tanδ, and penetration depth dp) indicated that Arabica coffee is a better microwave absorber leading to significant structural damage when heating at high input powers. Microwave-heated pine wood showed a better performance for dyes removal compare to coffee residue. Heating at 1000W is not recommended for both biomasses where oxidation reactions destroyed the structure of the materials. Moreover, microwave heating for long times had a bad influence on dyes removal. %Removal–adsorption capacity plot indicated that 0.8 and 1.0g/100mL is the optimum adsorbent dosage for E110 and E129, respectively. Analysis by Langmuir equation revealed that saturation values were 9.3 and 7.2mg/g for E110 and E129 at pH 2.0 and 25°C, receptively. Dyes removal by microwave-heated wood was a fast process and more than 90% of adsorbent's capacity was utilised within 30min.