Tandem hydropyrolysis–hydrogenolysis of polyolefin wastes over morphology‐tuned Co 3 O 4 for jet‐fuel hydrocarbons

Co-pyrolysis of waste polyolefins with waste motor oil

Degradation of polyethylene and polypropylene into fuel oil by using solid acid and non-acid catalysts

With ever-increasing plastic waste, a robust and sustainable methodology to valorize the waste and tweak, the composition of the value added product is the need of the hour. The present study describes the effect of different heterogeneous catalyst systems on the yield, composition and nature of the pyrolysis oil produced from various waste polyolefins like high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and polypropylene (PP). The waste polyolefins were subjected to thermal as well as catalytic pyrolysis. Liquid, gas, and solid products were obtained during the pyrolysis. Various catalysts such as activated alumina (AAL), ZSM-5, FCC catalyst, and halloysite clay (HNT) were used. Usage of catalysts has reduced the temperature of the pyrolysis reaction from 470 to 450°C with better liquid product yield. PP waste generated higher liquid yield compared to LLDPE and HDPE waste. The highest liquid yield of 70.0% was achieved with PP waste using AAL catalyst at 450°C. The sulfur and chloride content was found to be < 10 and < 20ppm respectively in all the pyrolysis liquid. Pyrolysis liquid products were analyzed using gas chromatography (GC), nuclear magnetic resonance (NMR) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, X-ray fluorescence (XRF) spectroscopy, and gas chromatography coupled with mass spectrophotometry (GC-MS). The obtained liquid products consist of paraffin, naphthene, olefin and aromatic components. Catalyst regeneration experiments with AAL showed that the product distribution profile remains the same up to three cycles of regeneration.

Thermal decomposition of individual and mixed plastics in the presence of CaO or Ca(OH)2

The need to find alternative liquid fuels more environmental friendly and with a more secure supply, has led to the idea of studying the conversion of carbonaceous wastes, like plastics, used tyres and biomass into liquid products to be used as fuels or as raw materials for several industries. As coal liquefaction is a well-known process to produce liquid products, coal blended with used tyres and plastic wastes was co-liquefied. Coal impregnated with 1 % wt. of molybdenum was used in co-liquefaction tests blended with 50 % wt. of used tyres or with the main plastics present in municipal solid wastes: PE (polyethylene), PP (polypropylene), PS (polystyrene) and a mixture of these plastics. The results obtained showed that all wastes promoted coal liquefaction. However, liquids yield and quality improved with the presence of plastics, while more solids were obtained when used tyres were used. Coal blends with PS wastes led to the highest liquid yield (74 % wt.) and conversion (88 % wt.) The presence of PE favoured the formation of linear alkanes, while PS promoted the formation of more aromatic compounds, which is in agreement with these plastics initial molecular structure. Some co-liquefaction tests were done in presence of tetralin, a hydrogen donor solvent that promoted the formation of liquids. Tetralin allowed increasing liquids yields obtained with plastics to values higher than 90 % wt., while in co-liquefaction of coal with used tyres led to liquids yields around 77 % wt.

Plastic waste is accumulated in landfills and the environment at an exponentially increasing rate. Currently, about 350 million tons of plastic waste is generated annually while only 9% is recycled. Plastic waste and its degradation products, microplastics, pose a severe threat to the ecosystem and eventually human health. Polyolefin (Polyethylene (PE) and Polypropylene (PP)) waste is 63% of the total plastic waste. Converting polyolefin waste into useful products including clean gasoline, diesel, wax, and monomers, via hydrothermal processing (HTP) can help reduce the plastic waste accumulation. In this study, sorted PE waste was converted via supercritical water liquefaction (SWL) into gasoline blendstock, No.1 ultra-low-sulfur diesel, and clean waxes with high yields and high purities. Comprehensive reaction pathways for PE conversion were proposed based on detailed GC×GC analyses. Furthermore, a new low-pressure (~2 MPa) hydrothermal processing (LP-HTP) method was developed to convert mixed polyolefin waste. This new LP-HTP method can save 90% of the capital cost and energy compared to SWL. The oil products were distilled into clean gasoline and No.1 ultra-low-sulfur diesel. The reaction pathways of PE and PP were independent while the synergistic effects improved the fuel qualities. With this LP-HTP method, polyolefin waste can be converted into up to 190 million tons of fuels globally, while 92% of the energy and 71% of the GHG emissions can be saved compared to conventional methods for producing fuels. Overall, this method is robust, flexible, energy-efficient, and environmental-friendly. It has a great potential for reducing the polyolefin waste accumulation in the environment and associated risks to human health.

Upgrading mixed polyolefin waste with magnetic density separation

For the development of nickel oxide (NiO) as an oxidation catalyst, a fundamental understanding of the role of surface morphology and of nickel and oxygen vacancy defects is essential, since they govern the reactivity of the surface. Using density functional theory (DFT) calculations, we investigated the reactivity of two different crystal facets of NiO and reveal the contribution of the coordinatively unsaturated Ni–O pairs, nickel and oxygen vacancies, and low valent dopant Li in determining and altering the reactivity of the surfaces. The most stable surface, NiO(100), is relatively inactive for methane C–H activation with an activation barrier of 136.6 kJ mol–1. However, the relatively less stable NiO(110) surface is extremely active and can dissociate methane with an activation barrier of 57.1 kJ mol–1. The coordinative unsaturation and comparatively low binding strength of the four-coordinated surface lattice oxygen on the NiO(110) surface leads to strong chemisorption of the dissociated H, facilitating extremely low activation barriers for methane dissociation. The presence of a Ni vacancy on the inactive NiO(100) surface brings down the activation barrier for methane dissociation to 90 kJ mol–1. This is a result of weakening of the binding strength of the oxygen, allowing strong chemisorption of the dissociated H. In this work, we predict that an equivalent increase in the surface reactivity can be achieved by doping the inactive NiO(100) surface with low valent metals like Li, which also weakens the binding strength of surface oxygen. The hydrogen chemisorption energy on the oxygen site is identified as a descriptor for estimating the reactivity of surfaces.

Synergistic effects during co-pyrolysis of milled wood lignin and polyolefins at the gas phase and liquid/solid phase contacting modes

Thermochemical conversion of mixed plastics from car dismantling by pyrolysis and distillation and potential applications of the products.

Unraveling the catalytic activity of CaClOH-rich incineration fly ash in the pyrolysis of single-use plastics

Degradation of pure and waste polyolefins and PVC in the presence of modified porous catalysts

Multi-color polymer carbon dots synthesized from waste polyolefins through phenylenediamine-assisted hydrothermal processing

Polyolefin waste is among the most generated yet least recycled. Despite its potential as a feedstock of superhydrophobic membranes for organic solvent filtration, it remains a challenge to achieve high selectivity and permeability for viscous oils. In this study, we valorized polyolefin waste into trimodal water filtration membranes through acid-catalyzed oxidation and a void inducer. This approach enabled the creation of membranes with exceptional wettability and strength, characterized by a combination of micropores, macrovoids (30–70 µm), and cavities (150–200 µm). The acid-catalyzed oxidation introduced oxygen moieties into the membrane structure, resulting in a reduced water contact angle, improved hydrophilicity, and increased permeability. The micropores facilitated capillary action, macrovoids enabled efficient water passage, and cavities acted as oil reservoirs, for optimal oil–water separation. Various membranes were synthesized using low-density and high-density polyethylene (PE), polypropylene (PP), and their blend. The obtained results were compared with commercial membranes, revealing a flow rate of 43 ml/min, a retention capacity of 261 mg, and an oil removal efficiency ranging from 84–94 %. Furthermore, the membranes exhibited recyclability, demonstrating stability over at least 10 cycles. This hybrid process transforms plastic waste into trimodal water filtration membranes, achieving a balance between superoleophilicity and hydrophilicity.

Production of liquid hydrocarbons from rice crop wastes mixtures by co-pyrolysis and co-hydropyrolysis