Influence of Copper and Metallic Alloys on the Oxidation Reaction of Commercial Biodiesel in Mixture with Natural Antioxidant

The purpose of this research was to evaluate the influence of metallic alloys and copper in the degradation of biodiesel in mixture with blackberry extract. Biodiesel is formed by unsaturated esters highly susceptible to the oxidation reaction. The initial induction period (IP) of the control sample was 9.53 h and, after 208 days, the IP reduced to 5.74 h. However, with the addition of the antioxidant, the final IP was 6.27 h. The assays involving carbon steel, stainless steel, silver steel and copper showed final IP of 3.78, 4.43, 1.59 and 0.09 h, respectively. This behavior indicates that the reaction was catalyzed in the presence of metal. The addition of the blackberries extract favored the increase of the induction period and the decrease of the reaction rate constant values, aside from the carbon steel that presented a final IP of 1.22 h. The highest rate constant was 7.41 h obtained for biodiesel in contact with copper, as well as the highest IP. The acid number ranged from 0.34 to 0.60 mgKOH g-1. It was possible to observe in the oxidation reactions the presence of the linearity deviation proposed by Arrhenius.

本研究旨在评估金属合金与铜对混有黑莓提取物的生物柴油降解过程的影响。生物柴油由极易发生氧化反应的不饱和酯类构成。对照组样品的初始诱导期（Induction Period, IP）为9.53 h，208天后其诱导期降至5.74 h。然而添加抗氧化剂后，最终诱导期为6.27 h。针对碳钢、不锈钢、银钢及铜的实验组，其最终诱导期分别为3.78、4.43、1.59与0.09 h。该结果表明，金属的存在会催化该氧化反应。添加黑莓提取物可延长诱导期并降低反应速率常数值，但碳钢组除外，其最终诱导期为1.22 h。与铜接触的生物柴油样本的反应速率常数最高，达7.41 h⁻¹，同时其诱导期也最高。酸值范围为0.34至0.60 mgKOH·g⁻¹。在氧化反应中可观察到阿伦尼乌斯（Arrhenius）提出的线性偏离现象。