Chlorine Speciation by GC-XSD for the Characterization of Plastic Pyrolysis Oil as a Cracker Feedstock

Abstract

Chemical recycling via pyrolysis of plastic is one of the emerging areas to bring valuable used plastic resources into the chemical industry value chain. However, one of the major concerns is the large amount of heteroatom-containing compounds in plastic-derived pyrolysis oil (pyoil), hindering the effective utilization of pyoil as a viable cracker feedstock. Chlorine (Cl) is one such highly unwanted chemical class in pyoil. It can cause critical damage to the cracker and related installations, such as hydrotreaters, due to corrosion. Hence, monitoring the Cl-species in pyoil is critical for understanding the distribution of Cl-species to effectively decontaminate pyoil and protect crackers and hydrotreaters. Therefore, a robust gas chromatography-halogen-specific detector (GC-XSD) method was developed to detect and quantify Cl-species in pyoil. Identification of the Cl-species was corroborated by GC × GC-TOFMS, retention indices, and standards. Validation of 32 Cl-compounds was done for linearity (R2), limit of detection (LOD), limit of quantification (LOQ), repeatability, reproducibility, and recovery. The detection limits of the majority of the Cl-species were at a ppm level, which is fit for the purpose of such a characterization of complex pyoil. Recovery studies revealed satisfactory results for the majority of the Cl-classes (>90% recovery). Certain Cl-classes including Cl-alcohols and Cl-acids were found to be reactive to native pyoil species, resulting in poor recovery. Major sources of detected Cl-species in diverse pyoils were Cl-containing polymers like PVC, PCP, and Cl-additives. This Cl-monitoring method is a key enabler for determining the dechlorination success and, therefore, the effective integration of cracker and refinery with plastic-derived pyoils as the feedstock.