The most common methods currently used for the removal of waste glycerol, monoglycerides and diglycerides remaining after phase separation during biodiesel production involve wet processes. These procedures are not environmentally viable because they require large volumes of water and thus generate significant quantities of effluent. In this study, adsorption was employed to replace this purification step. Some commercial activated carbons were tested along with adsorbents chemically modified with HNO3. A kinetics study was conducted at 30°C and adsorption isotherms were obtained at 20°C, 30°C and 40°C. The results indicated that the adsorption of glycerol increased with the use of chemically-modified activated carbon, showing that pH has a strong influence on glycerol adsorption. The pseudo-first-order kinetic model provided the best fit with the experimental data for the monoglycerides while the pseudo-second-order model showed a better fit for the glycerol and diglycerides. The Freundlich model had the best fit with experimental data on the adsorption equilibrium for all temperatures. The thermodynamic study indicated that the adsorption process is endothermic and thus adsorption is favoured by increasing the temperature. The adsorption process using chemically-modified activated carbon was therefore very effective for the removal of waste glycerol resulting from biodiesel production, which is of considerable significance given the legal limits imposed.

中文翻译：

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吸附由大豆油生产的生物柴油中存在的甘油、甘油单酯和甘油二酯

目前用于去除生物柴油生产过程中相分离后残留的废甘油、甘油单酯和甘油二酯的最常用方法涉及湿法工艺。这些程序在环境上是不可行的，因为它们需要大量的水并因此产生大量的污水。在这项研究中，吸附被用来代替这个纯化步骤。一些商业活性炭与用 HNO3 化学改性的吸附剂一起进行了测试。在 30°C 下进行动力学研究，并在 20°C、30°C 和 40°C 下获得吸附等温线。结果表明，甘油的吸附随着化学改性活性炭的使用而增加，表明pH对甘油吸附有很大影响。伪一级动力学模型为甘油单酯的实验数据提供了最佳拟合，而伪二级动力学模型显示出对甘油和甘油二酯的更好拟合。Freundlich 模型最适合所有温度下吸附平衡的实验数据。热力学研究表明吸附过程是吸热的，因此升高温度有利于吸附。因此，使用化学改性活性炭的吸附过程对于去除生物柴油生产中产生的废甘油非常有效，鉴于施加的法律限制，这具有相当大的意义。Freundlich 模型最适合所有温度下吸附平衡的实验数据。热力学研究表明吸附过程是吸热的，因此升高温度有利于吸附。因此，使用化学改性活性炭的吸附过程对于去除生物柴油生产中产生的废甘油非常有效，鉴于施加的法律限制，这具有相当大的意义。Freundlich 模型最适合所有温度下吸附平衡的实验数据。热力学研究表明吸附过程是吸热的，因此升高温度有利于吸附。因此，使用化学改性活性炭的吸附过程对于去除生物柴油生产中产生的废甘油非常有效，鉴于施加的法律限制，这具有相当大的意义。