Título da Dissertação: Concentração de α-tocoferol do destilado dadesodorização do óleo de soja usando separação  por membrana modificada

Orientadora: Profa. Dra. Angélica Marquetotti Salcedo Vieira

Data da Defesa: 29/01/2020

INTRODUCTION. There is a large production of soybean oil in Brazil, with an abundant number of by-products available during the refining stage such as the soybean oil deodorization distillate (SODD). Due to its high concentration of tocopherols, SODD is indicated for obtaining vitamin E which has antioxidant activity and several health benefits. α-tocopherol is the constituent isomer of vitamin E with greater biological activity and added value in the food industry. This compound is considered thermolabile, so it is important that the technique used in its concentration does not require high temperatures, as is the case of membrane separation processes. However, oil is a fouling compound which can reduce the use of this process. Therefore, the membrane can be superficially modified which in addition to cheapening its cost, provides better membrane performance especially in terms of reducing fouling and increasing selectivity.
AIMS. The present study aims to concentrate SODD α-tocopherol from commercially modified polyethersulfone (PES) microfiltration membrane with sulfonation reaction, grafting of the polyethyleneimine (PEI) and graphene oxide nanoparticles functionalized with tannic acid.
MATERIAL AND METHODS. SODD was provided by the Cocamar Cooperativa Agroindustrial industry located in Maringá – PR. Physicochemical characterizations, quantification of esters and glycerides, composition and quantification of acylglycerides and tocopherols from SODD were performed. The pre-concentration of α-tocopherol occurred from the saponification reaction at room temperature. The feed solution was prepared from unsaponifiable matter diluted in hexane. The modification of the PES microfiltration membrane was done through perpendicular filtration of sulfuric acid, PEI and different masses of graphene oxide (GO) previously prepared functionalized with tannic acid (TA), with four modified membranes at the end. Tannic acid functionalized graphene oxide (TA-GO) was evaluated with dynamic light scattering (DLS) and transmission electron microscopy (TEM). All filtrations were realized at room temperature and under pressure of 6 bar. The performance parameters (fouling and total resistance) were determined from the calculation of the initial water, feed solution and final water flows. Physical hydraulic cleaning of the membrane was carried out between the filtrations. All modified and unmodified membranes were evaluated for permeability. The quantification of α-tocopherol was performed using the highperformance liquid chromatography technique and from the results obtained, the mass of α-tocopherol in the feed, permeate and concentrate solutions was calculated. All analyses were performed in triplicate. The characterization of the modified membranes was analyzed by the contact angle, spectroscopy in the infrared region with Fourier transform (ATR-FTIR), morphology through scanning electron microscopy (SEM) and zeta potential of the modifying solutions and the membrane surface.
RESULTS AND DISCUSSION. The results of the physical and chemical characteristics of the SODD under study showed an iodine index of 94.85 ± 0.28 g I2/100g indicating a high degree of unsaturation, since linoleic and oleic acid are its major constituents. The relative density was 0.913 g/cm3, this parameter being considered specific for each raw material, as well as the dynamic viscosity (65.56 mPa.s). The humidity was 0.96 ± 0.04%, which is important to be evaluated due to the probability of oxidative rancidity. The acidity index of 31.56 ± 0.5 mg KOH/g suggests that the content of free fatty acids is derived from the composition of the original oil according to its refining process. The saponification index was 124.98 ± 15.04 mg KOH/g, indicating that it may have a
higher presence of high molecular weight fatty acids. In the results obtained from the TEM it can be observed that there was functionalization of the GO by the TA and that there was an increase in the average hydrodynamic diameter and polydispersity index comparing the solution containing only GO. There was an increase in the contact angle for all modified membranes (100.33-126.67°) compared to the pure membrane (60.00°). This result is explained by the crosslinking of the PEI and the polymerization reaction of the TA which reduce the oxygen functional groups of the GO, which are hydrophilic. Likewise, there are low permeability values for the modified membranes (12.90-16.81 L.h-1.m-2.bar-1) when compared to pure (19451.00 L.h-1.m-2.bar-1), because, as the mass of GO-TA increases, the nanoparticles reduce porosity, making the permeate flow difficult. Regarding the performance of the modified membranes, there was an increase in the flow recovery rate for the M1, M2 and M3 membranes, proving the anti-fouling action of the GO. From the results obtained, it was found that the M3 membrane had the smallest irreversible fouling (37.20% ± 1.75) and the greatest flow recovery (62.81% ± 1.75). A previous step in the SODD saponification made it possible to increase the pre-concentration of α-tocopherol by approximately 28 times. The modified M3 membrane containing 1.12 mg of graphene oxide and 4.50 mg of tannic acid allowed 82.00% of α-tocopherol to be recovered in the concentrate (14.16% by weight of α-tocopherol). The modified membrane showed hydrophobic characteristics, which can be reused in two filtration cycles with a flow recovery rate of 64.39% and recovery of α-tocopherol of 71.96%. The characterization of the membrane can be proven through the functional groups obtained through the analysis of ATR-FTIR, which showed the differences between the pure membrane and the modified M3 membrane. In addition, the membrane spectrum after filtration showed exclusive functional groups that may be the result of lipid compounds adsorbed on the membrane surface. In the morphology obtained by SEM, it is also possible to prove the modification, with the rough surface characteristic of membranes modified with GO-TA. The GO-TA solution showed a negative zeta potential, - 50.63 mV, as expected. In contrast, the surface charge of the membrane was + 9.12 mV, suggesting that the GO-TA solution had gaps between the nanofoils, which interacted with the PEI (+ 6.41 mV) making the surface positively charged.
CONCLUSIONS. The modification of the PES microfiltration membrane through the reaction of sulfonation, polyethyleneimine and graphene oxide nanoparticles functionalized with PEI can be carried out and confirmed by characterization analyzes. The modified M3 membrane demonstrated better performance and recovery of 82.00% α-tocopherol, reaching the proposed objective. The results showed that the membrane modification technology with graphene oxide is an attractive methodology (low energy and environmentally friendly) for the recovery and purification of SODD α-tocopherol.
Key words: Vitamin E. Modification of membranes. Distillate from deodorization of soy oil. α-tocopherol. Concentration. Fouling.

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