Monitoring tert-Butylhydroquinone Content and Its Effect on a Biolubricant during Oxidation

The use of biolubricants as a replacement for petroleum-based products is becoming more and more important, due to the current global energy and crude oil scenario. Thus, the production of biolubricants (which could take place in biorefineries) should be as efficient as possible, obtaining high-quality products with suitable viscosity or oxidation stability values to compete with oil refineries. One of the ways to produce biolubricants is through double transesterification from vegetable oils, where the role of catalysts (usually homogeneous) is vital, as they can improve the yield of the process. However, they should be removed after the chemical reaction, which is difficult once the biolubricant is obtained. Otherwise, they could act as catalysts during oxidation, contributing to a further decrease in oxidation stability and provoking significant changes. To avoid this, antioxidant addition could be an interesting choice. The aim of this work was to assess TBHQ addition in frying oil biolubricants, monitoring properties such as viscosity, acid number, absorbance or TBHQ content (through voltammetry) during oxidation. TBHQ addition (2114 mg·L^-1) kept the main quality parameters during oxidation compared to control samples. In contrast, TBHQ content decreased during oxidation (to 160 mg·L^-1), which proved its antioxidant effect.

Effect of synthetic and aromatic amine antioxidants on oxidation stability, performance, and emission analysis of waste cooking oil biodiesel

In the present study, an attempt was made to improve the oxidation stability of biodiesel by adding antioxidants to waste cooking oil biodiesel, and their impact on performance and emissions was analyzed. Two types of antioxidants were chosen for the analysis: an aromatic amine antioxidant, diphenylamine (DPA), and synthetic oxidants, tert-butylhydroxyquinone (TBHQ) and pyrogallol (PY). All the antioxidants were added to the biodiesel at doses of 200 ppm and 500 ppm to evaluate their effect. The oxidation stability was found as per the ASTM standard by mixing 500 ppm antioxidants for all three antioxidant-treated biodiesel blends. DPA yielded similar results as TBHQ, although PY had a better oxidation stability according to the Rancimat test. Gas chromatography and mass chromatography were also performed on the neat biodiesel. Performance and emission tests were performed on the antioxidant-treated biodiesel blends and diesel. The brake thermal efficiency of the tested fuel increased by 9.8%, 6.9%, and 15.88% when the DPA, TBHQ, and PY antioxidants were added to the test fuel compared to that of the test fuel without added antioxidant. The brake specific energy consumption of the test fuel decreased by 9.05% with DPA, 7.03% with TBHQ, and 14.08% with PY compared to that of the test fuel without antioxidant. The NOx emissions of the antioxidant-treated test fuels were reduced by 14.65% with DPA, 11.22% with TBHQ, and 23.10% with PY compared to those of the test fuel without antioxidants. Additionally, the aromatic amine antioxidant (DPA) was found to be effective in enhancing the performance and lowering the exhaust emissions compared to diesel for unmodified diesel engines.

Supercritical Fluid Extraction of Phenolic Compounds from Mango (Mangifera indica L.) Seed Kernels and Their Application as an Antioxidant in an Edible Oil

Phenolic compounds from mango (M. indica) seed kernels (MSK) var. Sugar were obtained using supercritical CO₂ and EtOH as an extraction solvent. For this purpose, a central composite design was carried out to evaluate the effect of extraction pressure (11–21 MPa), temperature (40–60 °C), and co-solvent contribution (5–15% w/w EtOH) on (i) extraction yield, (ii) oxidative stability (OS) of sunflower edible oil (SEO) with added extract using the Rancimat method, (iii) total phenolics content, (iv) total flavonoids content, and (v) DPPH radical assay. The most influential variable of the supercritical fluid extraction (SFE) process was the concentration of the co-solvent. The best OS of SEO was reached with the extract obtained at 21.0 MPa, 60 °C and 15% EtOH. Under these conditions, the extract increased the OS of SEO by up to 6.1 ± 0.2 h (OS of SEO without antioxidant, Control, was 3.5 h). The composition of the extract influenced the oxidative stability of the sunflower edible oil. By SFE it was possible to obtain extracts from mango seed kernels (MSK) var. Sugar that transfer OS to the SEO. These promissory extracts could be applied to foods and other products.

Comparison of the oxidative stability of linseed (Linum usitatissimum L.) oil by pressure differential scanning calorimetry and Rancimat measurements

The aim of this study was to compare the oxidative stability of linseed oil using the pressure differential scanning calorimetry (PDSC) and Rancimat methods, and to determine the kinetic parameters of linseed oil oxidation. Five cold pressed linseed oils were oxidized at different temperatures under PDSC (90-140 °C) and Rancimat (70-140 °C) test conditions. The oxidative stability of the linseed oils was calculated based on induction times (PDSCτ_max, Rancimat τ_on), the Arrhenius equation and activated complex theory, frequency factors (Z), the reaction rate coefficient (k) for all temperatures, activation energies (Ea), Q₁₀ numbers, activation enthalpies (∆H⁺⁺), and activation entropies (∆S⁺⁺). The PDSC method was more convenient for the determination of the induction time of linseed oils than the Rancimat method. During oxidation measurement by Rancimat method, the linseed oil polymerized, which affected the measurements. The reaction rate coefficient increased with rising temperature during measurement by both methods. The activation energy values of linseed oil oxidation using the PDSC and Rancimat methods ranged from 93.14 to 94.53 and 74.03 to 77.76 kJ mol^-1, respectively. The Q₁₀ , ∆H⁺⁺, and ∆S⁺⁺ values for the analyzed linseed oils were between 2.11-2.13, 90.54-91.30 kJ mol^-1, -33.20 to -30.90 J mol K^-1 calculated by PDSC measurements, and 2.23-2.32, 71.03-74.76, -59.42 to -49.08 J mol K^-1 by Rancimat measurements, respectively.