Towards Photothermal Acid Catalysts Using Eco-Sustainable Sulfonated Carbon Nanoparticles—Part II: Thermal and Photothermal Catalysis of Biodiesel Synthesis

Abstract

The main goal of this work is to evaluate the abilityof sulfonated carbon nanoparticles (SCN) to induce photothermal catalysis ofthe biodiesel synthesis reaction (transesterification of natural triglycerides(TG) with alcohols). Carbon nanoparticles (CN) are produced by carbonization ofcross-linked resin nanoparticles (RN). The RN are made by condensation of aphenol (resorcinol or natural tannin) with formaldehyde, under ammoniacatalysis (Stober’s method). The method produces nanoparticles which arecarbonized to carbon nanoparticles (CN). The illumination of CN increases thetemperature, proportionally (linear) to nanoparticle concentration and to theexposure time (with saturation). The solid acid catalysts are made by heatingin concentrated sulfuric acid (SEAr sulfonation). The application of eitherlight or catalyst (SCN) (at 25 °C) induces low conversions (<10 %) for theesterification reaction of acetic acid with bioethanol. In contrast,illumination of the reaction medium containing SCN induces high conversions(> 75 %). In the case of biodiesel synthesis (transesterification ofsunflower oil with bioethanol), conversions larger than 40 % were observed onlywhen light and catalyst (SCN) are applied simultaneously. Therefore, it ispossible to use sulfonated carbon nanoparticles as photothermally activatedcatalysts for Fischer esterification and triglyceride transesterification(biodiesel synthesis).