Selective phenol recovery via simultaneous hydrogenation/ dealkylation of isopropyl- and isopropenyl-phenols employing an H2 generator combined with tandem micro-reactor GC/MS

Abstract The pyrolysis of bisphenol A (BPA), an essential process ingredient used in industry and many everyday life products, helps produce low-industrial-demand chemicals such as isopropenyl- and isopropyl-phenols (IPP and iPrP). In this study, tandem micro-reactor gas chromatography/mass spectrometry combined with an H2 generator (H2-TR-GC/MS) was employed for the first time to investigate the selective recovery of phenol via simultaneous hydrogenation/dealkylation of IPP and iPrP. After investigating the iPrP dealkylation performances of several zeolites, we obtained full iPrP conversion with over 99% phenol selectivity using the Y-zeolite at 350 °C. In contrast, when applied to IPP, the zeolite acid centres caused IPP polymerisation and subsequent IPP-polymer cracking, resulting in many byproducts and reduced phenol selectivity. This challenge was overcome by the addition of 0.3 wt% Ni on the Y-zeolite (0.3Ni/Y), which enabled the hydrogenation of IPP into iPrP and subsequent dealkylation into phenol (full IPP conversion with 92% phenol selectivity). Moreover, the catalyst deactivation and product distribution over repetitive catalytic use were successfully monitored using the H2-TR-GC/MS system. We believe that the findings presented herein could allow the recovery of phenol-rich products from polymeric waste with BPA macro skeleton

Hydrogenation Reactions during Pyrolysis-Gas Chromatography/Mass Spectrometry Analysis of Polymer Samples Using Hydrogen Carrier Gas

Pyrolysis-gas chromatography/mass spectrometry of polymer samples is studied focusing on the effect of hydrogen (H₂) carrier gas on chromatographic and spectral data. The pyrograms and the related mass spectra of high density polyethylene (HDPE), low density polyethylene, and polystyrene (PS) serve to illustrate the differences between the species formed in H₂ and the helium environment. Differences in the pyrograms and the spectra are generally thought to be a result of the hydrogenation reaction of the pyrolyzates. From the peak intensity changes in the pyrograms of HDPE and PS, hydrogenation of unsaturated pyrolyzates is concluded to occur when the pyrolysis is done in H₂. Moreover, additional hydrogenation of the pyrolyzates occurs in the electron ionization source of a MS detector when H₂ is used as a carrier gas. Finally, the applicability of mass spectral libraries to characterize pyrograms obtained in H₂ is illustrated using 24 polymers. The effect of the hydrogenation reaction on the library search results is found to be negligible for most polymer samples with polar and nonpolar monomer units

Direct analysis of airborne microplastics collected on quartz filters by pyrolysis-gas chromatography/mass spectrometry

This paper reports the direct analysis of polymer components in the airborne particulates collected on quartz filters by pyrolysis (Py)-GC/MS. The airborne microplastics (AMPs) were collected with three classification stages depending on different aerodynamic diameters using a multi-nozzle cascade impact (MCI) sampler. The quartz filter holding AMPs was punched directly into several pieces without pretreatment procedures. Three pieces were introduced into a sample cup, and Py-GC/MS measurements were done to analyze AMPs. Evolved gas analysis (EGA) of AMPs showed the volatilization of phthalates, the generation of sulfur dioxide and nitrogen oxide, and the thermal decomposition of polymer components as the heating temperature increased. In thermal desorption (TD)-GC/MS prior to Py-GC/MS, polycyclic aromatic hydrocarbons were detected in addition to phthalates and some aliphatic carboxylic acids. The following Py-GC/MS results indicated the presence of polyethylene, polypropylene (PP), polystyrene (PS), styrene-butadiene rubber (SBR), and natural rubber in AMPs. Among these polymers, PS, PP, and SBR were quantified using the indicator ions of their characteristic pyrolysis products. The analytical results showed that PS and PP seem to accumulate in the smaller aerodynamic diameter stage, while SBR appears to collect in the larger one. The analytical method using Py-GC/MS described herein is a powerful one that requires no pretreatment of the AMP samples

Catalytic Copyrolysis of Cellulose and Thermoplastics over HZSM‑5 and HY

Catalytic pyrolysis with HZSM-5 is a promising method for the production of renewable aromatic hydrocarbons directly from biomass, even though the aromatic yields are still very low. Recent studies have shown that cofeeding of biomass with plastic significantly improves the aromatic yield due to high hydrogen content in plastic. In an effort to determine the influence of the zeolite pore size and the molecular diameter of cofeeding plastic on the aromatic production, catalytic copyrolysis of cellulose and thermoplastics, including random polypropylene (PP) and linear low density polyethylene (LLDPE) was conducted over HZSM-5 and HY catalysts. Thermogravimetric (TG) results showed that maximum decomposition temperature of PP was shifted to the higher temperature when PP was copyrolyzed with cellulose over HZSM-5 because the diffusion of PP molecules was hindered by the cellulose-derived coke and char. This hindering effect was attenuated by employing LLDPE as the cofeeding plastic due to its smaller molecular diameter than PP, and/or applying HY due to its larger pore size than HZSM-5. Heart-cut-evolved gas analysis (EGA)-GC/MS and flash pyrolysis-GC/FID were used to monitor the detailed product distribution and yields. The synergistic aromatic formation was easily achieved over HY catalyst for both PP and LLDPE, demonstrating the effectiveness of the larger pore zeolite for the catalytic copyrolysis. In contrast, HZSM-5 was very effective for the enhancement of aromatic production under severe reaction conditions, such as high catalyst to feed ratio (i.e., 10:1) or high pyrolysis temperature (i.e., 600 °C)