Density of alkyl esters and its mixtures

Biodiesel density is a key parameter in biodiesel simulations and process development. In this work we selected, evaluated and improved two density models, one theoretical (Rackett-Soave) and one empirical (Lapuerta's method) for methanol based biodiesels (FAME) and ethanol based biodiesel (FAEE). For this purpose, biodiesel was produced from vegetable oils (sunflower, rapeseed, soybean, olive, safflower and other two commercial mixtures of vegetable oils) and animal fats (edible and crude pork fat and beef tallow) using both methanol and ethanol for the transesterification reactions, and blended to get 21 FAME and 21 FAEE, reporting their density and detailed composition. Bibliographic data have also been used. The Rackett-Soave method has been improved by the use of a new acentric factor correlation, whereas the parameters of the empirical one are improved by considering a bigger density data bank. Results show that the evaluated models could be used to estimate the biodiesel density with a good grade of accuracy but the performed modifications improve the accuracy of the models: ARD (%) for FAME; 0.33, and FAEE; 0.26, both calculated with the modification of Rackett-Soave method and ARD (%) for FAME; 0.40 calculated with the modification of the Lapuerta's method).

生物柴油密度是生物柴油模拟与工艺开发中的核心参数。本研究选取、评估并改进了两类密度模型：一类为理论模型（Rackett-Soave），另一类为经验模型（拉普埃塔法，Lapuerta's method），分别适配甲醇基生物柴油（脂肪酸甲酯，FAME）与乙醇基生物柴油（脂肪酸乙酯，FAEE）。为此，本研究以植物油（向日葵油、菜籽油、大豆油、橄榄油、红花油，以及另外两种商用植物油混合物）与动物油脂（可食用及粗制猪脂、牛脂）为原料，采用甲醇与乙醇分别进行酯交换反应制备生物柴油，并共混得到21组FAME样品与21组FAEE样品，同时测定并报告了其密度与详细组分组成。本研究同时采用了已公开的文献数据。本研究通过引入新的偏心因子关联式对Rackett-Soave模型进行了改进；针对经验模型，则通过扩充密度数据库优化其参数。研究结果表明，经评估的原始模型即可较为准确地估算生物柴油密度，而本研究提出的改进方法进一步提升了模型精度：采用改进版Rackett-Soave模型时，FAME样品的平均相对偏差（ARD，%）为0.33，FAEE样品为0.26；采用改进版拉普埃塔法时，FAME样品的平均相对偏差为0.40。