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IntroductionCoal fly ash (CFA) is generated in large amount by thermal power plants during coal combustion. Many attempts have been doing to CFA valorization in alternative to disposal leading to significant economic and environmental benefits, but its use in value added applications such as catalysts or catalyst supports is still a challenge [1]. Herein, we present, for the first time, the sulfonic acid-functionalization of CFA from different sources (Portugal, South Africa and Poland) in order to introduce acid sites in the CFA structure to improve its potential as solid acid catalysts for esterification reactions, important catalytic processes for bio-based molecules, free fatty acids methyl ester (FAMEs), also known as biodiesel and alkyl levulinates from levulinic acid (LA), building blocks for biofuels production [2,3].Materials and MethodsPreparation of aryl-sulfonic acid functionalized CFA: Benzylsulfonic acid CFA1,5,7-BnSO3H and CFA8_CSPTMS were prepared according to scheme 1 and procedures modified from the literature.[4, 5] The sulfonic acid functionalized CFAs were characterized by potentiometric titration, elemental analysis, x-ray powder diffraction (XRPD) and by 29Si, 13C and 1H solid state NMR.Scheme 1: Schematic representation of aryl-sulfonic acid CFAs functionalization by different methodologies.Esterification reactions: The catalytic performance as solid acid catalysts was evaluated in the esterification reaction of lauric acid (C12:0), linoleic acid (C18:2) or levulinic acid (LA) in the presence of an alcohol (methanol:FFA = 30 and ethanol:LA = 5) and the CFA sulfonic acid catalyst (10 % for FFA and 2.5 % for LA) under reflux for 3 hrs. Aliquots were collected periodically for control reaction and analysed by gas chromatography. Finally, the catalysts were separated by centrifugation, washed and dried for consequent reuse at same reaction conditions to evaluate the stability and reusability.Results and DiscussionThe EA and titration results are presented in Table 1 and shows differences in acid capacity and S content for CFAs functionalized with the same BnSO3H. The major acid capacity and S content was observed for CFA1_BnSO3H which allows complete conversion of FFA C12:0 and C18:2 after 120 min. The functionalized CFA8_CSPTMS although with lower acid capacity presents high sulfur content and excellent conversion of LA into ethyl levulinate with 100 % conversion after 120 min. reaction. This functionalized CFA (CFA8_CSPTMS) was also characterized by solid state 13C NMR which corroborate the success of the -SO3H functionalization, as shown in figure 2.All the catalytic results and characterizations of the sulfonic acid functionalized CFAs will be presented and discuss in details in this communication.ConclusionsNew solid catalysts were successfully developed based on sulfonic acid-functionalization of coal fly ashes derived from different sources. Differences on the acid capacity and sulfur content resulted from the sulfonic acid functionalization was observed by EA and potentiometric titration. The new CFA based solid acid catalysts were evaluated in the esterification reactions of C12:0 and C18:2 FFA and in LA and the catalysts CFA1_BnSO3H and CFA8_CSPTMS showed the best performance, stability and reusability.