Hierarchical Zeolites as Catalysts for Biodiesel Production from Waste Frying Oils to Overcome Mass Transfer Limitations

Hierarchical crystals with short diffusion path, conventional microcrystals and nanocrystals of ZSM-5 zeolites were used for biodiesel production from waste frying oils and were assessed for their catalytic activity in regard to their pore structure and acidic properties. Produced zeolites were characterized using XRD, nitrogen adsorption–desorption, SEM, TEM, X-ray fluorescence, and FTIR. Pore size effect on molecular diffusion limitation was assessed by Thiele modulus calculations and turnover frequencies (TOF) were used to discuss the correlation between acidic character and catalytic performance of the zeolites. Owing to the enhanced accessibility and mass transfer of triglycerides and free fatty acids to the elemental active zeolitic structure, the catalytic performance of nanosponge and nanosheet hierarchical zeolites was the highest. A maximum yield of 48.29% was reached for the transesterification of waste frying oils (WFOs) using HZSM-5 nanosheets at 12:1 methanol to WFOs molar ratio, 180 °C, 10 wt % catalyst loading, and 4 h reaction time. Although HZSM-5 nanosponges achieved high conversions, these more hydrophilic zeolites did not function according to their entire acidic strength in comparison to HZSM-5 nanosheets. NSh-HZSM5 catalytic performance was still high after 4 consecutive cycles as a result of the zeolite regeneration.

Conversion of no/low value waste frying oils into biodiesel and polyhydroxyalkanoates

A sustainable bioprocess was developed for the valorization of a no/low value substrate, i.e. waste frying oils (WFOs) with high content of free fatty acids (FFAs), otherwise unsuitable for biodiesel production. The bioprocess was verified using both recombinant (Escherichia coli) and native (Pseudomonas resinovorans) polyhydroxyalkanoates (PHAs) producing cell factories. Microbial fermentation of WFOs provided a 2-fold advantage: i) the reduction of FFAs content resulting into an upgrading of the “exhausted waste oils” and ii) the production of a bio-based microbial polymer. Proper strain designing and process optimization allowed to achieve up to 1.5 g L−1 of medium chain length, mcl-PHAs, together with an efficient conversion (80% yield) of the treated WFO into biodiesel.

VEGETABLE OILS DEGRADING CAPACITY BY BACILLUS SUBTILIS AND PHYSICOCHEMICAL CHARACTERIZATION OF WASTE FRYING OILS

Vegetable oils are considered important energy sources that provide essential fatty acids and vitamins indispensable for maintaining the physiological balance of the human body, besides emphasizing sensorial characteristics of foods such as texture, aroma and taste. The oxidation process that occurs in oils, fats and fatty foods is one of the main causes of deterioration of food causing the loss of organoleptic quality and the reduction of the nutritional properties. This process may be associated with heating, as occurs in the frying process, the presence of microorganisms, among other factors. The study aimed to analyze two samples of waste frying oils (WFO) by determination of physico-chemical and microbiological parameters. The methods used were Rancimat test, potentiometric titration, chromatography and UV-vis spectrophotometry. The results showed high acid value (1.77 and 1.17 mg KOH g-1) and low oxidative stability (OSI of 1.93 and 0.79 h). The iodine value found (95.81 and 106.21 g I2 100 g-1) is below the suggested by the Codex standard. The fatty acid composition indicated that the acids in greater amount in both samples were the oleic acid C18:1 and linoleic acid C18:2. Sample 1 showed 23.64% and 76.58% of saturated and unsaturated fatty acids, respectively, while sample 2 showed 18.38% of saturated and 81.51% of unsaturated fatty acids. Bacillus subtilis was isolated in samples of WFO, and its degrating capacity was proved for soybean and sunflower oils.