Catalytic upcycling of post-consumer multilayered plastic packaging wastes for the selective production of monoaromatic hydrocarbons.

In order to obtain extended storage life of food-grade materials and better barrier properties against environmental factors, a multilayer plastic packaging (MLP) is often used. The multilayer packaging plastics are labelled as "other" (SPI#7) category, and are manufactured with a combination of barrier plastics, rigid plastics and printing surface. Owing to their complex composition and difficulty in separating the layers of MLP, its mechanical recycling is challenging. In this study, MLP wastes (MLPWs) were collected from zero-waste garbage collection center of IIT Madras, India, and thoroughly characterized to determine their composition and plastic types. MLPWs were characterized using various physico-chemical methods such as thermogravimetric/differential scanning calorimetric analysis, Fourier transform infrared spectroscopy, bomb calorimetry, and proximate and ultimate analyses. The MLPWs were mainly made up of polyethylene (PE) and polyethylene terephthalate (PET). Further, the non-catalytic and zeolite-catalyzed fast pyrolysis of these MLPWs were studied using analytical pyrolysis coupled with gas chromatograph/mass spectrometer (Py-GC/MS). The non-catalytic fast pyrolysis of MLPWs primarily produced a mixture of aliphatic and alicyclic hydrocarbons, while zeolite catalyzed fast pyrolysis resulted in the formation of mono-aromatic hydrocarbons (MAHs). The activity of HZSM-5, zeolite Y (HY) and zeolite beta (Hß) catalysts were evaluated, and the salient products were quantified. The yields of MAHs like benzene, toluene, ethylbenzene and xylene using the zeolites followed the trend: HZSM-5 (14.9 wt%) > HY (8.1 wt%) > Hß (7.8 wt%), at 650 °C. The use of HZSM-5 resulted in highest yield of MAHs, viz. 16.1 wt%, at the optimum temperature of 550 °C and MLPW-to-catalyst ratio of 1:15 (w/w). The superior activity of HZSM-5 is due to its nominal acidity and larger pore size of 4.24 nm, as compared to HY and Hß. The MAHs yield from three other types of MLPWs varied in the range of 9-16 wt%. The present study demonstrates a promising pathway for the catalytic upcycling of highly heterogeneous MLPWs in the context of circular economy.

Distributed Activation Energy Modeling and Py-GC/MS Studies on Pyrolysis of Different Printed Circuit Boards for Resource Recovery.

Printed circuit boards (PCBs) constitute an important segment of electronic waste that can be effectively utilized to recover valuable metals and organics. The present work is focused on the kinetics and product distribution from pyrolysis of three different PCB samples, viz., television PCB (TV PCB), motherboard PCB (MB PCB), and hard disk PCB (HD PCB). The PCBs were pretreated to eliminate most of the metallic constituents. Kinetic analysis was performed using Vyazovkin's isoconversional method and distributed activation energy model (DAEM). The average apparent activation energies obtained from the Vyazovkin method were 207.2, 158.9, and 179.7 kJ mol-1 for the TV PCB, MB PCB, and HD PCB, respectively. The DAEM with five, four, and four pseudo-components was used to describe the decomposition kinetics of the TV PCB, MB PCB, and HD PCB, respectively. Importantly, two types of distributions, viz., Gaussian and Weibull, were utilized to effectively model the nonisothermal data obtained from thermogravimetric analysis at 10 and 20 °C min-1. The evolution of pyrolysates belonging to functional groups such as phenolics, aromatics, aliphatics, halogenated compounds, N-containing compounds, and oxygenates was studied at two different temperatures (500 and 700 °C) using analytical pyrolysis-gas chromatograph/mass spectrometry (Py-GC/MS). The Py-GC/MS results demonstrated an increase in selectivity to aromatics and straight-chain aliphatics at 700 °C with a concomitant decrease in selectivity to phenols and oxygenates.

Microwave-Assisted Catalytic Solvolysis of Lignin to Phenols: Kinetics and Product Characterization.

Lignin, a major component of lignocellulosic biomass, is a valuable source of phenolic and aromatic compounds. It is, therefore, vital to develop strategies to selectively deconstruct lignin to valuable chemicals. This study focuses on the kinetics of depolymerization of lignin and the production of phenols via a microwave-assisted catalytic process at mild conditions of 80 °C in dimethyl sulfoxide/water medium. Four different catalysts used in this study, viz., Fe2O3, LaFeO3, ZrO2, and zeolite-Y hydrogen (ZYH), were characterized for structure, specific surface area, and surface morphology. The molecular weight reduction of lignin and the evolution of phenolic monomers and oligomers were monitored using various techniques, and the rate constants of lignin degradation in the presence of different catalysts were determined using a continuous distribution kinetics model, assuming scission of the lignin macromolecule at any random position. The rate constants (min-1) followed the trend: ZYH (26 × 10-4) ≈ LaFeO3 (25 × 10-4) > ZrO2 (22 × 10-4) > Fe2O3 ≈ no catalyst (16 × 10-4). Vanillic acid (15 mg g-1) and methyl phenol (17 mg g-1) were the major phenolics obtained with LaFeO3, whereas coniferaldehyde (13 mg g-1) was the major phenolic compound with Fe2O3. Vanillin was produced at ca. 11 mg g-1 with both Fe2O3 and ZYH. LaFeO3 is shown to be a promising catalyst for both molecular weight reduction of lignin and the production of monomeric phenols, whereas the use of Fe2O3 results in the formation of only phenols, possibly via specific end-chain depolymerization. The selectivities of the monomeric phenols were higher with these two catalysts, whereas with ZYH and ZrO2, the selectivities of the oligomers were better. The reusability of the catalysts and the effect of catalyst loading on kinetics of lignin depolymerization were also evaluated.