Qualitative detection and source analysis of the organic chlorides in the byproducts of biodiesel prepared using swill-cooked dirty oil under sub-critical conditions

Abstract

This paper introduces a gas chromatography-mass spectrometry (GC-MS) qualitative detection method for organic chlorides in crude glycerol and distillated light components, which are the byproducts of biodiesel. Samples with a higher total chlorine content were obtained from the transesterification reaction between swill-cooked dirty oil and methanol under subcritical conditions. Before GC-MS analysis, n-hexane extraction was performed to remove the soluble lipid interfering components, such as methyl fatty acid ester and free fatty acids, from the samples. Moreover, the reference standards, 3-chlorinated glycerol and 2-chlorinated glycerol, and the degreased water phases of the samples were subjected to derivatization with phenylboronic acid (PBA), extraction with n-hexane, and concentration. After re-dissolution using n-hexane, GC-MS analysis was performed. The results showed that the organic chlorides in the biodiesel by-products mainly included 3-chlorinated glycerol and 2-chlorinated glycerol. The sources of the organic chlorides were discussed by considering previously reported results and the preparation process of the biodiesel. Therefore, we concluded that the presence of a large amount of inorganic chloride salts in the swill-cooked dirty oil is the main reason for the production of 3-chlorinated glycerol and 2-chlorinated glycerol.