Characterizing the olefin oligomerization products using two-dimensional gas chromatography-photoionization-time of flight mass spectrometry

Commercial dodecenes are the products of light olefin oligomerization in the petrochemical industry. It is a complex mixture of C8-18 olefins with C12 olefins dominantly. The dodecene products may consist of linear alkenes, branched alkenes, and cyclic hydrocarbons. The composition of the dodecene products and their properties are very different due to the different feedstocks and catalysts used in the production. Better understanding the composition of dodecene products can help tune the production process and select the appropriate products according to their end-use. In this study two-dimensional gas chromatography (GCGC) coupled photoionization (PI) - time of flight mass spectrometry (TOFMS) was applied to characterize the dodecene products. A conventional column combination (non-polar column as 1st dimension and mid-polar column as 2nd dimension) was selected. The GC condition was optimized using fractional factorial experimental design (DoE). Olefin congeners according to carbon chain length and double bond equivalent (DBE) can be separated based on the enhanced intensity of molecular ions by PI-TOFMS. The structural subgroups of dodecenes, namely linear, mono-branched, di- and tri-branched isomers, were separated based on branching index (BI). The dodecene isomers were identified by retention indices (RI) and confirmed by PI mass spectra. The global information of dodecene products enabled the multimodal characterization with statistical tools. The difference among seventeen dodecene products by different catalysts, solid phosphoric acid (SPA) and zeolite, and different feedstocks, with C4 and without C4 olefins, is explained by principal component analysis (PCA) and hierarchical clustering analysis (HCA).