Regeneration of Used Frying Oils by Selected Metal–Organic Frameworks as Adsorbents

Abstract

AbstractThe aim of this study was to utilize seven synthesized metal–organic frameworks (MOF) and three natural clays as adsorbents in regenerating used frying oil. First, surface and pore properties, and morphologies of the adsorbents were determined, and used frying oil was treated at 0.1% addition (w/w) level. Then, physicochemical properties, mineral, and fatty‐acid compositions of oil were analyzed. Finally, a recycling study was performed over five cycles with three selected adsorbents. Although there were only small improvements in oil color values, oil turbidity was significantly reduced with the adsorbents. Free fatty acidity values were reduced by 50.6% and 42.2% with Ti‐MOF and zeolitic‐MOF (ZIF‐8‐MOF) adsorbent treatments. Likewise, peroxide value reductions ranged from 43.6% with the Ti‐MOF to 18.1% with natural zeolite. Reductions in the total polar materials (TPM) were the highest (42.5%) with aluminum‐MOF (Al‐MOF) followed by the ZIF‐8‐MOF (40.4%). Contents of aluminum, zinc, phosphorous, chromium, magnesium, and potassium were measured in the control and adsorbent‐treated oil samples, and it was found that there was no leakage of minerals from the MOF into the oil, but rather some reductions due to adsorption. Furthermore, recycling studies with Ti‐MOF, Cr‐MOF, and sepiolite showed that the MOF can be used up to five times with only small activity losses compared with sepiolite. Overall, this study demonstrated the great potential of the MOF as adsorbents for frying oil regeneration, and pointed out that more research needed to design and synthesize new MOF structures for applying in the edible oil industry.