Catalytic Degradation Of Polyethylene Research Articles

A Cooperative OSDA Blueprint for Highly Siliceous Faujasite Zeolite Catalysts with Enhanced Acidity Accessibility

AbstractA cooperative OSDA strategy is demonstrated, leading to novel high‐silica FAU zeolites with a large potential for disruptive acid catalysis. In bottom‐up synthesis, the symbiosis of choline ion (Ch+) and 15‐crown‐5 (CE) was evidenced, in a form of full occupation of the sodalite (sod) cages with the trans Ch+ conformer, induced by the CE presence. CE itself occupied the supercages along with additional gauche Ch+, but in synthesis without CE, no trans was found. The cooperation, and thus the fraction of trans Ch+, was closely related to the Si/Al ratio, a key measure for FAU stability and acidity. As such, a bottom‐up handle for lowering the Al‐content of FAU and tuning its acid site distribution is shown. A mechanistic study demonstrated that forming sod cages with trans Ch+ is key to the nucleation of high‐silica FAU zeolites. The materials showed superior performances to commercial FAU zeolites and those synthesized without cooperation, in the catalytic degradation of polyethylene.

A Cooperative OSDA Blueprint for Highly Siliceous Faujasite Zeolite Catalysts with Enhanced Acidity Accessibility

A cooperative OSDA strategy is demonstrated, leading to novel high-silica FAU zeolites with a large potential for disruptive acid catalysis. In bottom-up synthesis, the symbiosis of choline ion (Ch+ ) and 15-crown-5 (CE) was evidenced, in a form of full occupation of the sodalite (sod) cages with the trans Ch+ conformer, induced by the CE presence. CE itself occupied the supercages along with additional gauche Ch+ , but in synthesis without CE, no trans was found. The cooperation, and thus the fraction of trans Ch+ , was closely related to the Si/Al ratio, a key measure for FAU stability and acidity. As such, a bottom-up handle for lowering the Al-content of FAU and tuning its acid site distribution is shown. A mechanistic study demonstrated that forming sod cages with trans Ch+ is key to the nucleation of high-silica FAU zeolites. The materials showed superior performances to commercial FAU zeolites and those synthesized without cooperation, in the catalytic degradation of polyethylene.

Experimental study of catalytic pyrolysis of polyethylene and polypropylene over USY zeolite and separation to gasoline and diesel-like fuels

Thermal catalytic and non catalytic degradation of polyethylene (PE) and polypropylene (PP) were carried out in a batch reactor at 450°C. The major product obtained from the non-catalytic pyrolysis of PE was 80wt% of wax, while the degradation of PP without any catalyst produced 85.5% of liquid. In catalytic degradation, ultra-stable Y (USY) zeolite was used in a ratio of 1:10, with respect to PE and PP. In both cases, polymers were converted to liquid products with high yields (71 and 82wt% respectively) and a low amount of coke deposit has appeared. The liquid fraction derived from the catalytic pyrolysis of PE was a mixture of C5-C39 compounds and that of PP was a mixture of C5-C30. This wide range of components suggests the separation of liquids into two phases in order to use them as diesel-like and gasoline-like fuels. Three temperatures of separation (130, 150, 170°C) were tested and the physical properties were compared. Among the tested temperatures, 170°C was the optimal temperature of separation where the distillation curves and physical properties of the light and heavy phases fitted completely those of gasoline and diesel fuels, respectively. After separation, the gasoline-like fuel which represents 60.6% of the total oil of PP and 57% of that of PE had high octane numbers (RON=96 and RON=97, respectively), while the diesel-like fuel which accounts for 36.5% of the total oil of PP and 35.3% of that of PE have high calculated cetane numbers (52 and 53, respectively).

Taguchi method approach on catalytic degradation of polyethylene and polypropylene into gasoline

Plastics have become indispensable materials in the world. They are non-biodegradable polymers of mostly containing carbon, hydrogen. Due to their non-biodegradability and low life, HDPE, LDPE, and PP contribute significantly to the problem of Municipal Waste Management. Thermal and Catalytic converting of these materials into the valuable liquids like gasoline and diesel would be a promising method of waste management. Current paper focuses on catalytic cracking of the mixed polyethylene and Polypropylene in the presence of silica alumina catalyst in a semi batch reactor operating isothermally at ambient pressure with a statistical approach. The parameters affecting degradation of polymer mixture studied in this paper include the temperature (410–450 °C), catalyst (10–50 wt%), and feed composition (1–5). The statistical Taguchi experimental design method has been used to optimize the reaction condition in degradation process in order to maximize the gasoline production. The liquid and gas products were analyzed by GC/FID to find out their composition. Using more catalyst leads the reaction to produce more aromatic components. The result of experiments discussed in this work compared with empirical data shows that the use of Taguchi as a DOE method has an appropriate approach to the optimum condition. Arrhenius law as a kinetic model at optimum reaction condition has been developed and the activation energy determined. The model gives a suitable representation of the experimental results.

Low-Temperature Thermocatalytic Degradation of Polyethene Films by Nano-Titanium Dioxide in Water

nanoTiO2powders were utilized as thermocatalyst for catalytic degradation of polyethylene in water. LDPE/TiO2composite films were prepared by the method of melt blending. The aging experiments were conducted in ovens under temperatures of 30 °C, 40 °C and 50 °C, respectively. The thermocatalytic degradation behavior towards the composite films was characterized by fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TG) and scanning electron microscopy (SEM). Results show that both pure LDPE films and LDPE /TiO2composite films can be degraded even under low temperatures in water. After thermal degradation for 90 days at 50 °C, the composite film with 2wt% nanoTiO2was oxidized the most acutely: the quantity of branched chains decreased to some extent and lots of small molecules were detected, the decomposition temperature was also reduced by 28.2 °C. Besides, the surface of the films became rougher than that of the film before degradation.

Catalytic degradation of polyethylene over SBA-16

The performance of SBA-16 catalysts toward the degradation of two kinds of polyethylenes, high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE), was evaluated by using a thermogravimetric analyzer and batch reactor. The effect of the acidity of SBA-16 upon degradation efficiency was investigated. Quantitative analyses of the products were conducted by GC/MS and GC. The Al-SBA-16 led to a higher catalytic conversion than SBA-16. Hydrocarbons (C7–C10) were mainly produced by Al-SBA-16, whereas a much broader distribution of oil products (C7–C14) was obtained by SBA-16. The Al-SBA-16 also showed high catalytic stability. The results of this study suggest that Al-SBA-16 has a high potential as a catalyst for degradation of waste plastics.

Catalytic degradation of polyethylene using nanosized ZSM-2 zeolite

Nanosized ZSM-2 zeolite with crystal size of ∼100 nm was synthesized and ion exchanged in order to characterize its behaviour in the catalytic degradation of polyethylene (PE) in a semi-batch reactor. The starting ZSM-2 allowed a reduction in the PE degradation temperature of more than 80 °C as quantified by dynamic thermogravimetric analysis (TGA). By either proton or Lanthanum exchanges, the nanozeolite increased the acidity improving even more these degradation processes. The starting nanometric catalyst was dramatically more active than a micrometric Y-zeolite displaying lower onset temperatures of PE degradation due to its higher external surface area. These differences nevertheless were reduced by ion-exchanging the Y-catalysts. Our results confirm the relevance of both the zeolite acidity and other parameters, such as crystal size and crystallinity of the zeolite framework, on the catalytic efficiency. Regarding the degradation products during the catalytic process, both zeolites increased the production of low boiling compounds being more efficient the ZSM-2 based catalysts reaching a yield about 90%. Higher amount of accessible sites active for cracking on the external surface of the nanosized crystals would be responsible of this high gas yield. Furthermore, ZSM-2-based zeolites were highly selective to propylene and C4 compounds compared with Y-based zeolites. These results open up the use of nanosized ZSM-2 zeolites in the catalytic degradation of PE with relevant energetic applications.

ChemInform Abstract: New Pathways in Plastics Recycling

The catalytic degradation of polyethylene to short-chain hydrocarbons is possible with zirconium hydride compounds (see picture), and represents the first step in the reversal of Ziegler - Natta polymerization. Thus, even in the case of polyolefins the important target of plastics recycling, the recovery of reusable monomers from polymer waste, may be achieved.

The effect of PVC on thermal and catalytic degradation of polyethylene, polypropylene and polystyrene by a continuous flow reactor

A continuous flow reactor was operated at atmospheric pressure and feed rate of 0–1.5 kg h −1 for degradation of PE, PP and PS in presence of 1–2 wt% PVC. The degradation temperatures were between 360 and 440 °C depending on the feeding material. The influence of PVC, temperature and silica-alumina catalysts on degradation behavior and on the properties of the products was studied and discussed. Different effects were observed for binary PE/PVC, PP/PVC, PS/PVC and complex PE/PP/PS/PVC mixtures due to specific interactions between PVC and each hydrocarbon polyolefin. Silica-alumina catalysts decreased the Cl concentration in oils but it seems to generate high amounts of Cl-containing organic compounds in gases.

Catalytic degradation of polyethylene in the presence of synthetic aluminosilicates

Degradation of polyethylene in the presence of synthetic amorphous aluminosilicates as catalysts to form petroleum-like hydrocarbons was studied.

Catalytic degradation of polyethylene: An evaluation of the effect of dealuminated Y zeolites using thermal analysis

Commercial samples of high density polyethylene were degraded over Y zeolites with different Si/Al: ultrastable Y zeolite (USY) and three dealuminated Y zeolites (HY(4), HY(12) and HY(20)). Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) was used aiming to evaluate the apparent activation energy of polymer cracking. The results obtained show that the efficiency of different zeolites was due to their acidity. A high Si/Al ratio gave a greater acidity to zeolites and the onset degradation temperature of the polymer and related activation energy decreased. The sample residues obtained after an isothermic TGA, were analysed by DSC and it was observed that the crystallinity decreases with the acidity of zeolites. HY(20) zeolite was the most active catalyst due to the isolation of the residual Brønsted acid sites which promote their strong acidity.

The effect of acidity behaviour of Y zeolites on the catalytic degradation of polyethylene

Thermogravimetric (TGA) and differential scanning calorimetric (DSC) analyses were used to investigate the effect of the acidity behaviour of Y zeolites on the catalytic degradation of polyethylene (PE). The acidity behaviour of these zeolites was modified by ion exchange treatments. Two Y zeolites with similar Si/Al atomic ratios were subjected to an ion exchange treatment using NaNO 3 for H-form (HY) and NH 4NO 3 for Na-form (NaY). The activity and the deactivation behaviour of the Y zeolites were determined in the samples by TGA measurements, using a polymer/catalyst ratio of 9:1. The sample residues obtained after an isothermic TGA, were analysed by DSC, in order to evaluate the crystallinity of each mixture. The HY zeolite, which has the strongest acidity, reduced the onset temperature resulting in more rapid degradation of the polymer. It is shown that the ion exchange treatment over Y zeolites enhances the selective catalytic degradation of polymer in detriment of the rapid deactivation.

Catalytic degradation of plastic waste to liquid fuel over commercial cracking catalysts: Effect of polymer to catalyst ratio/acidity content

The catalytic degradation of polyethylene over two commercial cracking catalysts, containing 20% and 40% ultrastable Y zeolite, respectively, was studied in a semi-batch reactor. More specifically, the effect of the polymer to catalyst ratio – expressed as the acidity content of the polymer/catalyst system – was studied on the formation of liquid hydrocarbons. After a sharp increase at small values, the liquid yield seemed to have a negative correlation to the acidity content, showing a maximum at acidity values around 7% of pure US-Y. Regarding the boiling point distribution of the liquid fraction in systems with higher content of active catalyst, a shift was generally observed towards lighter products. Comparing liquid samples during the same experiment, later samples contained heavier components with the exception of the system with the smallest US-Y content of this study.

Polymer degradation to fuels over microporous catalysts as a novel tertiary plastic recycling method

The catalytic degradation of polyethylene over various microporous materials—zeolites, zeolite-based commercial cracking catalysts as well as clays and their pillared analogues—was studied in a semi-batch reactor. Over all catalysts the liquid products formed had a boiling point distribution in the range of motor engine fuels, which increases considerably the viability of the method as a commercial recycling process. From the zeolites, ZSM-5 resulted mostly in gaseous products and almost no coking due to its shape selectivity properties. Commercial cracking catalysts fully degraded the polymer resulting in higher liquid yield and lower coke content than their parent ultrastable Y zeolite. This confirmed the suitability of such catalysts for a polymer recycling process and its commercialisation potential, as it confirmed the potential of plastic waste being co-fed into a refinery cracking unit. Clays, saponite and Zenith-N, a montmorillonite, and their pillared analogues were less active than zeolites, but could fully degrade the polymer. They showed enhanced liquid formation, due to their mild acidity, and lower coke formation. Regenerated pillared clays offered practically the same performance as fresh samples, but their original clays' performance deteriorated after removal of the formed coke. Although performance of the regenerated saponite was satisfactory, with the regenerated Zenith the structural damage was so extensive that plastic was only partly degraded.

Investigations on polyethylene degradation into fuel oil over tungstophosphoric acid supported on MCM-41 mesoporous silica

The catalytic degradation of polyethylene (PE) was carried out at atmospheric pressure under batch conditions at 420 °C using mesoporous MCM-41 material, tungestophosphoric acid (H 3PW 12O 40), water and methanol impregnated H 3PW 12O 40 (HPW) over MCM-41 material, (HPW/MCM-41). It has been found that the pore size of MCM-41 plays an important role in PE degradation. While smaller pore-size promote degradation into lower molecular weight, larger pore-size produce a product distribution similar to that of thermal degradation. However, the larger size was used in this work to support HPW acid. The MCM-41 and HPW acid had negligible effects on PE degradation and did not show any catalytic behavior. However, the water-impregnated HPW/MCM-41 promoted the degradation of PE into lower molecular weight products and showed catalytic cracking roots as evidenced by the liquid product carbon number distribution and the production of large quantities of isobutane in the gaseous products. Isobutane was absent in the thermal degradation and when MCM-41 and HPW acid were used as catalysts. It was concluded from a detailed analysis of gaseous products that the methanol-impregnated HPW/MCM-41 showed a very similar catalytic behavior to the water-impregnated HPW/MCM-41 catalyst. However, the liquid product distribution was similar to the thermal one.

Product distribution from catalytic degradation of polyethylene over H-gallosilicate

For developing a novel technology to reuse plastic waste chemically, the degradation of low-density polyethylene into aromatic hydrocarbons was investigated with H-gallosilicate as a catalyst at 375–550°C. The gallosilicate produced valuable aromatic hydrocarbons, mainly benzene, toluene and xylenes (BTX). The BTX yield increased with reaction temperature and went up to over 58 wt.% at 500°C. The liquid products obtained at temperatures above 500°C consisted of aromatics only. For this simplified liquid composition and the high BTX yield, the catalytic degradation of polyethylene using H-gallosilicate is highly promising as a new technology for chemical recycling of polyolefins. The polyethylene degradation occurring at temperatures below 450°C involved aromatization by direct cyclization of the decomposed fragments that correspond to the liquid products with six or more carbon atoms. In addition to this, above that temperature, the aromatization also proceeded through the oligomerization of the C 4 and C 5 fractions formed in the degradation steps and subsequent cyclization. The latter mechanism contributed more to the formation of aromatics with increasing reaction temperature.

Kinetic Parameters of Polyethylene Degradation by the Natural Zeolite Chabazite

High-density polyethylene (PE) was subjected to thermal degradation alone and in the presence of an ammonium-exchanged zeolite chabazite (CHA/PE). The processes were carried out in a reactor connected online to a gas chromatograph/mass spectrometer in order to analyse the evolved products. Polymer degradation was also evaluated by thermogravimetry, from room temperature up to 800°C, under a dynamic nitrogen atmosphere, with multiple heating rates. From the TG curves, the activation energy relating to the degradation process was calculated by using the Flynn and Wall multiple heating rate kinetic model for pure PE and for CHA/PE. The exchanged chabazite exhibited good selectivity for the catalytic degradation of PE to low molecular mass hydrocarbons.

Catalytic degradation of polyethylene and polypropylene to fuel oil

AbstractThermal and catalytic degradation of plastic polymers, polyethylene and polypropylene to fuel oil were carried out in batch operations. The catalysts employed were acid silica‐alumina (SA‐1, SA‐2) and zeolite ZSM‐5, and non‐acidic mesoporous silica FSM (folded sheet material). The yields of product gas, liquid and residues, recovery rate of liquid products, and boiling point ranges of liquid products due to degradation were compared with those of non‐catalytic thermal degradation. Both the effect of catalytic contact mode and of catalyst type on the degradation were studied.In liquid‐phase degradation of PP over SA‐1, liquid hydrocarbon products were obtained in a yield of 69 wt.‐% with a boiling point range 36‐270°C, equivalent to the boiling point of normal paraffins C6 ‐ C15. The liquid products from catalytic degradation have a carbon‐number distribution very similar to commercial motor gasoline. In vapor‐phase contact, the yield of liquid products was much lower (54%) and the rate of liquid recovery was much slower.With FSM, the initial rate of degradation of PP and PE to liquid products was as fast as that over acid catalyst SA‐1, but the yield of liquid products was higher. The liquid products from catalytic degradation over FSM have a carbon‐number distribution similar to kerosene and diesel oil. In repeated use, SA‐1 deactivated very rapidly due to coke deposition on the catalyst, whereas FSM deactivated much more slowly. These findings suggest that mesopores surrounded by the silica sheet may act as reservoir for radical species, which accelerate the degradation of plastic melt.

Catalytic degradation of polyethylene and polypropylene into liquid hydrocarbons with mesoporous silica

The catalytic degradation of polyolefinic polymers such as polyethylene (PE) and polypropylene (PP) was carried out at atmospheric pressure by batch operation at 430 °C and 380 °C using non-acidic mesoporous silica catalyst (FSM). A comparison with non-catalytic thermal degradation and catalytic degradation using solid acid catalysis (silica-alumina, zeolite ZSM-5), silicalite, and silica-gel was made. Compared with thermal degradation, non-acidic FSM catalyst accelerated the initial rate of degradation, increased the liquid product yield and promoted degradation into lower molecular weight products. Silicalite and silica-gel had very negligible effects on polymer degradation. When the batch reaction was repeated four times using the same FSM catalyst, the extent of the decline in the degradation rate was lower for PE than PP. Compared with the solid acid catalyst, which turned completely black in the cases of both PE and PP, the deposition of coke on the used FSM catalyst was extremely slight. It seems likely that the catalytic effect of FSM for polyolefinic polymer degradation is related more to the hexagonal pore structure system of FSM.

Catalytic degradation of polyethylene into fuel oil over mesoporous silica (KFS-16) catalyst

The thermal degradation of plastic polymers into fuel oil over mesoporous silica (KFS-16) catalyst has been investigated. The product yields, composition and degradation rate of polyethylene over KFS-16 were compared with those over solid acid catalyst (silica–alumina and zeolite) and non-catalytic thermal degradation. The initial rate of degradation of PE over KFS-16, which possesses no acid sites was as fast as that over silica–alumina (SA-1) and the yield of liquid products was higher. The composition of the liquid products of degradation over KFS-16 was different from that over SA-1 and similar to that of non-catalytic thermal degradation. SA-1 catalyst deactivated very rapidly due to coke deposition, whereas KFS-16 deactivated much more slowly. These findings over mesoporous silica suggest that the mesopores surrounded by the silica sheet may act as a flask for storing radical species for a long time and then long-lived radicals accelerate the degradation of plastics.