Synthesis of organosilane-multiwalled carbon nanotube catalyst using supercritical CO2 and its catalytic performance for conversion of high FFA oil to biodiesel

• Main Author: Macawile, Maria Cristina A.
• Format: text
• Language: English
• Published: Animo Repository 2021
• Subjects: Fatty acids; Transesterification; Biodiesel fuels; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_doctoral/1413; https://animorepository.dlsu.edu.ph/cgi/viewcontent.cgi?article=2400&context=etd_doctoral
• Institution: De La Salle University

An environmentally friendly surface modification method was applied to synthesize heterogeneous acid, base, and bifunctional catalysts suitable for biodiesel production. The catalysts were prepared using a multiwalled carbon nanotube (MWCNT) as its catalyst support and organosilane compounds as sources of sulfonic and amine functional groups. The supercritical carbon dioxide (scCO2) with ethanol as cosolvent allows swift transportation and promotes uniform distribution of organosilane groups on randomly entangled and layered orientation of MWCNT. The catalysts were characterized by using Field emission scanning electron microscopy–energy dispersive x-ray (FESEM-EDX), Thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, X- ray powder diffraction (XRD), Brunauer–Emmett-Teller (BET) analysis, Time-of-Flight secondary ion mass spectrometry (TOF-SIMS) and Boehm titration method. The performance of the catalysts was tested using a high free fatty acid (FFA)-containing Hibiscus cannabinus oil (AV = 116.20 mg KOH/g), and the fatty acid methyl esters (FAME) products from simultaneous esterification and transesterification reactions were quantified. Among the three scCO2-functionalized catalysts, the acid catalyst has the highest kenaf oil conversion of 93.10% at the following transesterification conditions: temperature = 63oC, methanol:oil ratio = 14:1, 10 wt. % catalyst and time = 240 min. In the case of transesterification of kenaf oil using a base catalyst, FAME was not produced due to the formation of carboxylated salts. A low FFA oil was used in transesterification and resulted in a 95.76% conversion. On the other hand, the use of bifunctional catalyst in kenaf oil has resulted only in 2.79% conversion. This result indicates that although successful grafting of two incompatible functional groups on the same solid support surface was observed, the accessibility of acid active sites, larger surface area, and pore diameter of catalyst are important factors in converting high FFA oil to biodiesel.