Calcium-carbide residue: A precursor for the synthesis of CaO–Al2O3–SiO2–CaSO4 solid acid catalyst for biodiesel production using waste lard

Abstract

Calcium-carbide residue (CCR) was used as a precursor to synthesise CaO–Al2O3–SiO2–CaSO4 heterogeneous acid catalyst for biodiesel production. The synthesis was through a two-step process of thermal treatment of the CCR at 500, 700, and 900 °C and sulphonation, to produce anhydrite-based solid-acid catalysts (ASACs) as ASAC500, ASAC700, and ASAC900 respectively. The CCR and ASACs were characterised using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Brunauer–Emmet–Teller (BET). The ASACs were tested for biodiesel production using high free fatty acid waste lard. The XRD analyses show that the three catalysts consist of CaSO4 in addition to each containing Ca2.62Al9.8Si26.2O72H4.56 (ASAC500), carbon atom and Ca2.62Al9.8Si26.2O72H4.56 (ASAC700), Ca2.62Al9.8Si26.2O72H4.56 and Ca2Al4Si14O36•14H2O (ASAC900). The SEM images of the ASACs show the formation of different surface morphology with active sites and improved porosity based on calcination temperatures. The BET analysis presents a surface area of 94.48 (ASAC500), 90.28 (ASAC700), and 98.22 m2/g (ASAC900). The biodiesel yields obtained using 5% (w/w) catalyst, 12:1 of MeOH: Lard molar ratio, 120 min reaction time and 60 °C reaction temperature are 94.8% (ASAC500), 89.2% (ASAC700) and 98.9% (ASAC900). The excellent performance of CaO–Al2O3–SiO2–CaSO4 catalyst with the high yields of biodiesel and recyclability of seven cycles are attributed to the synergy among the calcium, aluminium, and silicon. Therefore, the CCR is a suitable precursor to synthesise a novel heterogeneous acid catalyst that is highly effective for biodiesel production.