Kinetics and Mechanism of NaOH-Impregnated Calcined Oyster Shell-Catalyzed Transesterification of Soybean Oil

Abstract

Abstract:The objective of this research is to develop a kinetic model to describe the transesterification of soybean oil with methanol using NaOH-impregnated calcined oyster shell (Na-COS). Batch experiments were performed via a two-factor randomized complete block design using a molar ratio of methanol to oil (MR) of 6, 12, and 18 and catalyst loadings (CL) (mass of catalyst/mass of oil in %) of 2%, 4%, 6%, and 8% to obtain fatty acid methyl ester yields. In addition, the catalyst was studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion spectrometry (TOF-SIMS) to elucidate the role of the catalyst in the transesterification reaction. XRD and XPS analyses suggested that the formation of sodium peroxide (Na 2 O 2 ) on the surface contributed to catalytic activity. The TOF-SIMS analysis suggested that the transesterification occurred between adsorbed triglyceride and free methanol, similar to the Eley-Rideal mechanism. The transesterification of adsorbed triglyceride to adsorbed diglyceride was found to be the rate-determining step with a rate constant of 0.0059 ± 0.0002 L mol −1 min −1 .

Effect of Preparation Conditions on Structure and Activity of Sodium-Impregnated Oyster Shell Catalysts for Transesterification

“…This doublet feature indicated that some of the surface oxygen had been shifted to lower BE for both catalysts, when compared to control (calcined oyster shell), acquiring a higher effective negative charge. As was also observed in our recent research [16], the shift in oxygen would have enhanced the electron donating ability, suggesting that the surface oxygen was more basic [30]. As a result, the increased electron donating ability may have allowed triglyceride and methanol to form a tetrahedral intermediate that may have resulted in FAME after structural rearrangement [2].…”

“…The specific surface area of the catalyst synthesized was determined using Quantachrome Monosorb Surface Area Analyzer (Quantachrome Instruments, Boynton Beach, FL, USA) based on the Brunauer-Emmett-Teller (BET) nitrogen adsorption method [16]. Prior to the measurement, all catalysts were degassed at 120 • C for 8 h.…”

“…X-ray powder diffraction (XRD) analyses were performed via a PANalytical Empyrean X-ray diffractometer (Malvern Panalytical Ltd., Almelo, Netherlands) with Cu Kα radiation (λ = 0.15418 nm) in the 2θ range of 5 • -90 • . The data were collected as described previously [16].…”

“…Our results indicated that impregnation of NaOH on oyster shell increased the FAME yield from 71% (3 h reaction time) (control) to 87% (1 h reaction time). In addition, the analysis of the surface of the catalyst revealed that impregnation of NaOH followed by calcination resulted in the formation of sodium peroxide species that significantly enhanced the activity of the calcined oyster shells [16].…”

Liquid Lipase-Catalyzed Esterification of Oleic Acid with Methanol for Biodiesel Production in the Presence of Superabsorbent Polymer: Optimization by Using Response Surface Methodology

“…Biodiesel is commonly produced from edible feedstocks such as soybean, sunflower, and rapeseed oils [5][6][7][8]; however, the use of these feedstocks for biodiesel production is restricted because of their high cost (which accounts for 75% of the production cost) and competition with demand for the food supply [9][10][11]. Therefore, inedible and waste oils have been developed as potential feedstocks for biodiesel production [12][13][14][15].…”