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Reusability and regeneration of solid catalysts used in ultrasound assisted biodiesel production

Reusability of two heterogeneous catalysts in ultrasound (US) assisted biodiesel production was investigated in comparison to each other. An ultrasound (US) generator (200 W, 20 kHz) equipped with a horn type probe (19 mm) was used. Regeneration experiments were planned according to second order central composite design (CCD) method. After the eighth use of the catalysts, biodiesel yield decreased from 99.1% to 90.4% for calcined calcite (CaO) and from 98.8% to 89.8% for calcined dolomite (CaO.MgO). Furthermore, regeneration of spent catalysts by calcination was investigated; optimum temperature and time were found as 750 °C and 90 min, lower than fresh catalyst preparation conditions. | Turkish Journal of Chemistry Turk J Chem 2021 45 342-347 http journals.tubitak.gov.tr chem TÜBİTAK Research Article doi 10.3906 kim-2008-33 Reusability and regeneration of solid catalysts used in ultrasound assisted biodiesel production 1 2 1 Mahmut BAYRAMOĞLU İbrahim KORKUT Başak TEMUR ERGAN 1 Chemical Engineering Department Gebze Technical University Gebze Turkey 2 Chemical Engineering Department Sivas University of Science and Technology Sivas Turkey Received 20.08.2020 Accepted Published Online 08.12.2020 Final Version 28.04.2021 Abstract Reusability of two heterogeneous catalysts in ultrasound US assisted biodiesel production was investigated in comparison to each other. An ultrasound US generator 200 W 20 kHz equipped with a horn type probe 19 mm was used. Regeneration experiments were planned according to second order central composite design CCD method. After the eighth use of the catalysts biodiesel yield decreased from 99.1 to 90.4 for calcined calcite CaO and from 98.8 to 89.8 for calcined dolomite CaO.MgO . Furthermore regeneration of spent catalysts by calcination was investigated optimum temperature and time were found as 750 C and 90 min lower than fresh catalyst preparation conditions. The regenerated catalysts were reused in a second process cycle biodiesel yield was calculated as 97.2 for CaO and 96.5 for CaO.MgO. Finally the process showed that calcination is an energetically favorable regeneration process of spent catalysts. Key words Biodiesel ultrasound assisted transesterification calcium oxide calcined dolomite heterogeneous catalyst regeneration 1. Introduction Transesterification reaction transforms oil or fats with methanol CH3OH into biodiesel in presence of a catalyst with glycerol as a by-product 1 2 . Usually homogeneous basic catalysts such as potassium hydroxide KOH or homogeneous acidic catalysts such as sulfuric acid H2SO4 are used 3 . However the homogeneously catalyzed transesterification process has some drawbacks such as the