Abstract

Biodiesel consists of various fatty acid methyl esters (FAMEs) that are mainly produced through transesterification of plant oil or animal fat. It is essential for biodiesel to be purified utmostly to meet its product standard before being traded, while the universal purification method has been water washing. However, water washing inevitably causes the residual of FAMEs in wastewater, which represents a loss of industrial profits. For the purpose of determination and monitoring of the FAME profile in wastewater, there is a necessity to develop a fast and reliable approach with small volume of sample in need. Hence, in this study, a combination of dispersive liquid–liquid microextraction (DLLME) and microwave demulsification is applied for the enrichment of residual FAMEs in water, followed by qualitative and quantitative analyses using gas chromatography–mass spectrometry. The results indicate that the optimal extractant in DLLME approach is toluene. And the optimal parameters are 20 mL of water sample, 80 μL of toluene as the extractant, 60 s of ultrasonic irradiation duration, 200 W of microwave power and 2 min of microwave irradiation duration. The standard curves and linear equations obtained with these conditions are used for the quantitative analysis of biodiesel wastewater, which reveals that there was 50.35 mg·L⁻¹ of the total FAME residuals in wastewater. To the best of our knowledge, it is for the first time that the combined technique of DLLME and microwave demulsification is applied in determination of residual FAMEs in water samples. The proposed method corresponds to small volumes of sample and extractant and short analytical period. It also has the potential to be extended to the analysis of other water pollutants.

中文翻译：

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分散液-液微萃取结合微波乳化法测定生物柴油废水中的FAME残留

摘要

生物柴油由各种脂肪酸甲酯（FAME）组成，这些脂肪酸甲酯主要是通过植物油或动物脂肪的酯交换反应产生的。对于生物柴油，必须进行最大程度的纯化以使其达到商品标准，然后才能进行交易，而通用的纯化方法是水洗。但是，水洗不可避免地导致废水中的FAME残留，这代表了工业利润的损失。为了确定和监测废水中的FAME曲线，有必要开发一种需要少量样品的快速可靠的方法。因此，在这项研究中，将分散液-液微萃取（DLLME）和微波破乳技术结合起来用于富集水中的残留FAME，然后使用气相色谱-质谱法进行定性和定量分析。结果表明，DLLME法中最佳的萃取剂是甲苯。最佳参数为20 mL水样，80μL甲苯作为萃取剂，60 s的超声波照射时间，200 W的微波功率和2 min的微波照射时间。在这些条件下获得的标准曲线和线性方程式用于生物柴油废水的定量分析，结果表明存在50.35 mg·L废水中FAME总残留量的^-1。据我们所知，这是第一次将DLLME与微波破乳技术相结合，用于测定水样中的残留FAME。所提出的方法对应于少量的样品和萃取剂，并且分析周期短。它还有可能扩展到其他水污染物的分析。