Comparing different methods for olefin quantification in pygas and plastic pyrolysis oils: Gas chromatography-vacuum ultraviolet detection versus comprehensive gas chromatography versus bromine number titration

Abstract

In steam cracking, upstream pyrolysis oil hydroprocessing, and in many downstream processes, olefinic content is key to assess process performance and process safety risk associated with highly exothermic reactions. When looking to plastic pyrolysis oils as a potential feedstock, as well as downstream products such as pyrolysis gasoline (pygas), these materials contain unsaturated hydrocarbons which are not present in fossil feedstocks. Pygas is a product of pyrolysis and exhibits a large number of chemical structural similarities with plastic pyrolysis oils, especially in terms of olefins structure. Quantification of the unsaturation content (olefins and di-olefins) is extremely important in industry, hence the focus of this manuscript. Detailed hydrocarbon analysis with flame ionization detection is inadequate to fully characterize the hydrocarbon composition of such samples, especially when peaks are closely eluting, or even co-eluting. In this study, the gas chromatography coupled to vacuum ultraviolet (GC-VUV) detection method previously described for the analysis of liquid hydrocarbon streams11M.N. Dunkle, P. Pijcke, B. Winniford, G. Bellos. Journal of Chromatography A, 1587 (2019) 239-246. https://doi.org/10.1016/j.chroma.2018.12.026. and plastic pyrolysis oils22M.N. Dunkle, P. Pijcke, W.L. Winniford, M. Ruitenbeek, G. Bellos. Journal of Chromatography A, 1637 (2021) 461837. https://doi.org/10.1016/j.chroma.2020.461837. has been compared with comprehensive gas chromatography (GC × GC) and the industry standard for olefin quantification (i.e., bromine number titration). Although based on different methodologies, a correlation between the olefin content obtained from GC-VUV and the bromine number titration method is hereby presented.