# Variation of the Chemical Composition of Waste Cooking Oils upon Bentonite Filtration
###### Abstract  
The chemical composition and the color of samples of waste cooking oils (WCOs) were determined prior to and after filtration on two different pads of bentonite differing in particle size. The volatile fraction was monitored by headspace solid-phase microextraction (HS-SPME) coupled with gas-chromotography, while the variation of the composition of the main components was analyzed by \({}^{1}\)H NMR. Both techniques allowed the detection of some decomposition products, such as polymers, terpenes, and derivatives of the Maillard process. The analysis of the chemical composition prior to and after bentonite treatment revealed a tendency for the clays to retain specific chemical groups (such as carboxylic acids or double bonds), independent of their particle size. A pair comparison test was conducted in order to detect the sensory differences of the intensity of aroma between the WCO treated with the two different bentonite. In addition, characterization of the bentonite by means of powder X-ray diffraction (XRD) and thermogravimetric measurements (TG) was performed. waste cooking oil; nuclear magnetic resonance; headspace solid-phase microextraction; thermogravimetry; principal components analysis; X-ray diffraction 122019  
and negatively affecting the characteristics of the oil. Most of the studies reported to date regarding cooking oils are focused on the consequences of the frying process on the food, and the variation of the chemical-physical properties of the oil is only discussed in terms of possible contamination of the cooked food [3; 4]. As waste cooking oils (WCOs) are becoming popular as green raw materials for bio-lubricant production, it would be useful to gain some knowledge about their chemical composition and the effect upon it caused by recycling procedures, such as, for instance, treatment with clays. In fact, during the past few years, interest in the composition of the edible oil at the end of its life cycle has grown exponentially as WCOs, previously considered a by-product of food production, have been revealed to be an important raw material for several industries [5; 6]. The increasing quantities of WCOs produced worldwide, as well as the environmental risk associated with their uncontrolled dispersion, forced local governments towards the implementation of specific regulations for enhancing its safe recycling or disposal [7]. The availability of WCOs is impressive despite the fact that recycling is compulsory in several countries, only around 0.6 of the estimated 4 Mt of WCOs produced per year is currently collected in Europe, meaning that about 3.4 Mt of accessible cheap raw material are available per year [8]. Many ways of reutilization have been explored and nowadays WCOs find applications in bio-lubricant production [9; 10], as an additive for animal feed [11; 12], and as the basis for eco-friendly biodegradable solvents [13]. WCOs can even be used as energy sources, through direct burning [14; 15; 16; 17] or as an ingredient for the biodiesel production [18; 19]. Important applications have been found in the construction sector, for example as an additive for bitumen binders [20; 21] or in environmental chemistry, such as mercury sorbent devices [22]. In Europe, WCOs are defined as \"municipal wastes\" by the European Waste Catalogue [23] and are collected through the urban waste systems or directly delivered by the final user to a recycling point. The main consequence of this procedure is the generation of a complex mixture composed of different kinds of exhausted vegetable oils, most of them previously employed for frying, with different origins and compositions. The general chemical profile of WCOs is mainly constituted of triacylglycerolgycerols, free fatty acids (FFAs), and several polymerization compounds. Physically, WCOs appear as dark and viscous, with a low smoking point.