REFINING OF VEGETABLE OIL AND FATTY ACID METHYL ESTERS WITH ELECTROSTATIC FIELDS AND NANO-ADSORBENTS
Traditional vegetable oil and fatty acid esters (FAE) refining strategies are energy-intensive, time-consuming, involve multiple operations, generate waste, and cause substantial loss of neutral oils. In metalworking and machine shops, electrostatic “oil cleaner” devices are used to remove particulate materials (e.g., wear particles, soot, vanish, and dust) from non-polar working fluids with low dielectric constants (e.g., lubricating and hydraulic oils). Pure vegetable oils and FAE are also non-polar fluids. However, polar contaminants, including phospholipids (P-lipid), free fatty acids (FFA), peroxides and soaps, moisture, glycerol, alcohol, and mono-/di- glycerides, can be present in unrefined vegetable oils and FAE, respectively. Therefore, electrostatic “oil cleaner” is a potential means for the separation of polar particulate substances from non-polar vegetable oils and FAE. Nano-adsorbents are widely employed in purification of contaminated industrial solutions due to their unique properties, including large specific surface area, and abundant adsorption sites. Oil refining efficiency could be greatly improved if nano-size adsorbents are properly utilized. The separation of nano-adsorbents from solutions is challenging, primarily due to their microscopic size. An electrostatic field (E-field) could affect the movement of oil-insoluble particulates regardless of their size. Theoretically speaking, E-field could be employed for the removal of the oil-insoluble spent nano-size adsorbents from oils in the post-adsorption stage. The main studies are as below. The effects of an E-field applied using a commercial electrostatic “oil cleaner” on crude canola oil were studied. In particular, E-field treatments of crude canola oil reduced over 50 wt. % of P-lipid, FFA, and peroxide. These treatments did not significantly alter carotenoid content, phytosterol content, or canola oil fatty acid composition. Furthermore, neutral oil loss (0.37 wt. %) was negligible during E-field treatments. Subsequently, the effects of E-field on crude canola oil-based fatty acid methyl ester (FAME) were also tested using the commercial electrostatic “oil cleaner”. An immediate reduction in FAME soap content was observed after a single pass through the E-field. However, the total glyceride content remained unchanged. When nano-adsorbents were introduced to enhance the refining efficiency of FAME, soap contents were reduced to below 66 mg/kg, meeting the ASTM D6751 and EN 14214 standards using adsorption treatment by three types of nano-adsorbents (Al2O3, SiO2, and TiO2), under mild adsorption conditions (e.g., low adsorbent dosage, short adsorption time, low agitation speed, and ambient temperature), while FAME total glyceride content reduction was less than that of soap content. After adsorption, the FAME and nano-adsorbent mixtures were treated with an E-field. Over 75 wt. % removal rates were observed in Al2O3 and SiO2 nano-adsorbents from the FAME. These nano-adsorbents did not hydrolyze the FAME and minimized FAME loss (< 3.0 wt. %) during refining. Finally, these nano-adsorbents were recyclable and retained 90% adsorption efficiency over multiple uses. The effects of three types of nano-adsorbents (Al2O3, SiO2, TiO2) on canola oil refining were determined. E-field as an alternative for the removal of the spent nano-adsorbents from canola oil in the post-adsorption stage was tested. Aluminum oxide nano-adsorbent effectively removed FFA from crude canola oil under moderate operating conditions (e.g., low dosage, short adsorption time, low agitation speeds, ambient temperature), while also contributing to moderate neutral oil loss (4.38 wt. %). The ratio of Al2O3 nano-adsorbents to oil played a critical role in the efficiency of acid removal. The Al2O3 nano-adsorbent treatment did not hydrolyze triacylglycerol in the canola oil. After treatment of crude oil with Al2O3 nano-adsorbents, E-field treatment removed 75.3 wt. % of absorbent from canola oil. Altogether, E-field treatment displayed strong applicability (e.g., removal of P-lipid, FFA and peroxide from canola oil, and soap from FAE) and high efficiency (e.g., the major portions of removed contaminants were observed at the first sampling/pass) in cleaning vegetable oil and vegetable oil-based fatty acid esters without consumption of water, chemicals, and no generation of waste, compared to the conventional refining methods. Besides, nano-adsorbents illustrated applicability in refining vegetable oil and vegetable oil-based FAE. Finally, E-field treatment demonstrated applicability in the removal of the spent nano-adsorbents from vegetable oil and vegetable oil-based FAE in the post-adsorption stage.
Vegetable oil, Fatty acid methyl esters, Electrostatic field, Nano-adsorbents, Refining
Doctor of Philosophy (Ph.D.)
Chemical and Biological Engineering