From waste tire to high value-added chemicals: an analytical Py-GC/TOF-MS study

Identification and quantification of microplastics in salts by complementary approaches using pyrolysis-gas chromatography/quadrupole-time of flight mass spectrometry (Py-GC/QTOFMS) and laser direct infrared (LDIR) chemical imaging analysis

Microplastics (MPs) and nanoplastics (NPs) have been suspected as contaminants in various foodstuffs, including salts, all over the world. Regarding the different sizes and polymer types, the mass concentrations of actual plastic particles in salt are not very clear. The purpose of this study is to develop a scalable method for qualitative and quantitative analysis of MPs and NPs by using Pyrolysis Gas Chromatography Quadrupole-Time of Flight mass spectrometry (Py-GC/QTOFMS) to detect their mass concentrations in salt samples. The targeted and suspected lists of polymers in salts were compiled based on the combined results of the high-resolution mass spectrometry (HRMS) full scanning with auxiliary MS dataset and the laser direct infrared (LDIR) chemical imaging analysis. The seven targeted MPs with polymer standards, i.e., polyvinyl chloride (PVC), polymethyl methacrylate (PMMA), polypropylene (PP), polystyrene (PS), polyethylene (PE), polyethylene terephthalate (PET), and polycarbonate (PC), were first subjected to a full MS scanning mode of the Py-GC/QTOFMS analysis. Subsequently, the parental masses of their pyrolysis compounds were used as the seeds to generate the related daughter masses. This process established both retention time and mass-pairs matching for the target MS/MS mode for enabling the identification and quantification of the particles. The suspected MPs with a matching degree >0.65 in the LDIR list were explored either by the full scan MS. Only PVC was identified, and PET was suspected. The Py-GC/QTOFMS result is complementary and comparable to the LDIR detection with the matching degree >0.85. We identified that PVC and PET (suspected) can be measured in both commercial and bulk sea salts, and their concentrations in sea salts are much higher than in rock salts, implying heavy contamination of the seawater.

Nickel and Cobalt Ilmenites-Based Catalysts for Upgrading Pyrolytic Oil during Pyrolysis of Waste Tires

Pyrolysis as a waste treatment method has gained relevance because it can generate higher value-added products in addition to reducing the environment’s secondary pollution. In this study, the catalytic pyrolysis of waste tires was evaluated using NiTiO3 and CoTiO3 ilmenites as catalysts and precursors of metal catalysts with the aim to produce an oil enriched in high-value hydrocarbons, such as benzene, toluene, a xylenes mixture, and products less-reported, such as p-cymene and p-cymenene. The experiments were performed in an analytical pyrolyzer coupled to GC/MS. The effect of the nature of the catalysts on the product distribution was compared with the uncatalyzed reaction. The main products of uncatalyzed pyrolysis were D, L-limonene (~60%), and isoprene (~25%) due to the depolymerization of natural rubber. Meanwhile, Ni-ilmenites-based catalysts favored the formation of target compounds to expense D, L-limonene. Moreover, the presence of metal in reduced-ilmenite sharply enhanced the selectivity by ~50% concerning oxidized ilmenite and above 80% compared to the uncatalyzed reaction for p-cymene and p-cymenene. By contrast, the Co-ilmenites-based catalysts showed a marginal effect on secondary reactions. Finally, the feasibility of forming the aromatic terpenes, p-cymene, and p-cymenene from limonene in the non-catalytic pyrolysis was evaluated.