<![CDATA[The effects of designed protection conditions such as different antioxidant (propyl gallate, PG and Pyrogallol, PY), antioxidant concentration (30 – 600 ppm), temperature (30˚C -120˚C) and storage period (3 – 5 days) on the oxidation stability of castor biodiesel were investigated. Using the American Standard for Testing Materials (ASTM) recommended protocols to determine the changes in the physicochemical properties (acid value, p-anisidine value, peroxide value, totox value, density, kinematic viscosity and refractive index ) of the castor biodiesel were measured and protection conditions optimized using the Response Surface Methodology (RSM) according to the Box–Behnken Design (Design Expert version 11 Statistical Software). The analysis of variance (ANOVA) showed results indicated the nature of antioxidants; concentration levels and temperature were the most important factors in the biodiesel oxidation, whereas the day of storage was one of the lowest factors. The changes in some important physicochemical values are indication of degradation occurring in the biodiesel under the set storage condition. The optimal conditions for better protection against biodiesel degradation were propyl gallate with the concentration of 316.634 ppm, temperature of 57.874 oC for 4.166 days produced refractive index of 1.515 oC, acid value of 1.423, p-anisidine value of 21.068 and Totox was 1.842 with the overall desirability of 1.000. The overall results showed that castor biodiesel could comply with the standard with PY being more effective than PG. The combined use of these antioxidants did not show, especially at low concentrations, a synergic or additive effect, which makes the mixture of these antioxidants unsuitable to improve the oxidative stability.]]>
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