Abstract
Vegetable oils are a vast triglyceride source for biodiesel production; i.e. fatty acid methyl esters (FAME), with methanol and a catalyst via transesterification reaction. The aim of this work was to study heterogeneously catalysed biodiesel production with solid oxides such as mayenite (Ca12Al14O33) and alumina (Al2O3) as catalyst carriers using edible rapeseed oil as feedstock. These oxides were impregnated to have Li2O and MgO concentrations of 5–10 and 5–30 wt% on each carrier, respectively. The catalysts were characterized using N2-physisorption (BET/BJH), scanning electron microscopy (SEM), and X-ray diffraction (XRD) analyses. The synthesized catalysts were mesoporous ranging from 119 to 401 Å and their chemical phase composition was confirmed by the XRD. The catalyst coating (MgO/Li2O) was studied, along with the catalyst amount in the reactor and the assessment of the transesterification reaction kinetics. The reaction was studied at 60 °C, atmospheric pressure, agitation rate of 180 rpm, and a reaction time of 2 h in a 6:1 molar ratio of methanol to oil. For each catalyst, loadings of 2.5, 5, and 10 wt% relative to the oil weight were evaluated. The highest biodiesel yield was obtained by 5 wt% (relative to oil weight) impregnated mayenite catalyst coated with 10 wt% of Li2O. The kinetic data fits to a pseudo-first-order model having a reaction rate constant equal to 0.045 min−1 under these mild reaction conditions.
Highlights
Vegetable oils feedstock and market are affected by several factors; e.g. population growth expressed through supply and demand, biodiesel access rate and production, and fossil oil price fluctuations
In addition to a larger surface area, Li2O impregnation increases pore diameter and pore volume of the mayenite-derived catalysts compared to bare mayenite
The impregnation of MgO on mayenite increases the surface areas and pore volume (M3 and M4) but the increase of the pore diameter is smaller compared to the Li2O impregnation case, which may alter the accessibility to the active sites
Summary
Vegetable oils (triglycerides) feedstock and market are affected by several factors; e.g. population growth expressed through supply and demand, biodiesel access rate and production, and fossil oil price fluctuations. Among the adversities of biodiesel production are the lower prices of petroleum barrel, which reduces the biodiesel production cost advantage (no competitive cost) and the food security policies that disregard integrated foodbiofuel policies to boost biofuel production [1, 2]. Despite such adversities, worldwide biodiesel production from vegetable oils is constantly growing [3, 4]. Even though vegetable oil production is increasing [8], the driving force towards eco-friendly biofuels has changed the attention towards second and third generation feedstocks; i.e. non-edible oils, waste cooking oil, animal fats and algae. Oil yield of algae is higher than soybean oil and rapeseed oil by 130 times and 50 times, respectively [9,10,11]
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