Characterization of derivatization reactions of conjugated dienes in plastic pyrolysis oils using 4-phenyl-1,2,4-triazoline-3,5-dione

Plastics, with their diverse characteristics and cheap production, have become an essential component to nearly all industrial and domestic processes and products; however, their production remains unsustainably fossil-based. To meet global climate and environmental targets, dependence on fossil naphtha must rapidly shift to more circular and sustainable alternatives. Circular alternatives in plastic production include bio-based naphtha, syngas-to-hydrocarbons, and waste plastic pyrolysis oils (PPOs). PPOs are currently limited in their commercial application because of their complexity and high level of contaminants, such as olefins, and more specifically conjugated dienes, which must be removed or transformed before these oils can be used to replace naphtha. Conjugated dienes (CDs) cause extensive fouling during the cracking of a hydrocarbon mixture and must first be saturated through hydrotreatment. To accurately design the hydrotreatment conditions, it is essential to quantify the CDs through analytical techniques. The current industrial standard method for quantification, titration using maleic anhydride, remains semi-quantitative, is highly labour intensive, has known interfering reactions with oxygenates and other hydrocarbon species, and is not adapted for use with PPOs. As a potential alternative to this method, the current study explores the use of derivatization agent, 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD), in reaction with conjugated diene standards and other species present in PPOs (mono-olefins, oxygenates, aromatics, and polyaromatic hydrocarbons). Standards of conjugated dienes and other analytes were individually derivatized with PTAD, and the resulting adducts were qualified using gas chromatography (GC) coupled with mass spectrometry (MS) and flame ionization detection (FID). It was observed that PTAD was not selective for CDs, forming undesired adducts with non-conjugated dienes, mono-olefins, and primary alcohols. In reaction with a PPO, PTAD formed many adducts with mono-olefins, non-conjugated dienes, and conjugated dienes which could not be distinguished simply using GC-MS. The results from the PTAD derivatization method were compared to the maleic anhydride titration method to determine if the undesired reaction products were the same or different between the two methods. This derivatization method, although not selective for CDs, could still be explored as an analytical technique coupled to GC-vacuum ultraviolet (VUV), once representative PTAD adducts of each different component class have been identified and added to the VUV spectral library. The quantification of CDs in hydrocarbon mixtures using PAD may not show an improvement over the existing maleic anhydride method, however, this study highlights the need for a faster and more precise technique for CD analysis.

Plastics, with their diverse characteristics and cheap production, have become an essential component to nearly all industrial and domestic processes and products; however, their production remains unsustainably fossil-based. To meet global climate and environmental targets, dependence on fossil naphtha must rapidly shift to more circular and sustainable alternatives. Circular alternatives in plastic production include bio-based naphtha, syngas-to-hydrocarbons, and waste plastic pyrolysis oils (PPOs). PPOs are currently limited in their commercial application because of their complexity and high level of contaminants, such as olefins, and more specifically conjugated dienes, which must be removed or transformed before these oils can be used to replace naphtha. Conjugated dienes (CDs) cause extensive fouling during the cracking of a hydrocarbon mixture and must first be saturated through hydrotreatment. To accurately design the hydrotreatment conditions, it is essential to quantify the CDs through analytical techniques. The current industrial standard method for quantification, titration using maleic anhydride, remains semi-quantitative, is highly labour intensive, has known interfering reactions with oxygenates and other hydrocarbon species, and is not adapted for use with PPOs. As a potential alternative to this method, the current study explores the use of derivatization agent, 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD), in reaction with conjugated diene standards and other species present in PPOs (mono-olefins, oxygenates, aromatics, and polyaromatic hydrocarbons). Standards of conjugated dienes and other analytes were individually derivatized with PTAD, and the resulting adducts were qualified using gas chromatography (GC) coupled with mass spectrometry (MS) and flame ionization detection (FID). It was observed that PTAD was not selective for CDs, forming undesired adducts with non-conjugated dienes, mono-olefins, and primary alcohols. In reaction with a PPO, PTAD formed many adducts with mono-olefins, non-conjugated dienes, and conjugated dienes which could not be distinguished simply using GC-MS. The results from the PTAD derivatization method were compared to the maleic anhydride titration method to determine if the undesired reaction products were the same or different between the two methods. This derivatisation method, although not selective for CDs, could still be explored as an analytical technique coupled to GC-vacuum ultraviolet (VUV), once representative PTAD adducts of each different component class have been identified and added to the VUV spectral library. The quantification of CDs in hydrocarbon mixtures using PAD may not show an improvement over the existing maleic anhydride method, however, this study highlights the need for a faster and more precise technique for CD analysis.