Cracking Of Polyethylene Research Articles

Exploring the Morphological Effect of Zeolite Beta on Catalytic Cracking of Polyethylene

Exploring the Morphological Effect of Zeolite Beta on Catalytic Cracking of Polyethylene

Micelles Cascade Assembly to Tandem Porous Catalyst for Waste Plastics Upcycling

AbstractCatalytic upcycling of polyolefins into high‐value chemicals represents the direction in end‐of‐life plastics valorization, but poses great challenges. Here, we report the synthesis of a tandem porous catalyst via a micelle cascade assembly strategy for selectively catalytic cracking of polyethylene into olefins at a low temperature. A hierarchically porous silica layer from mesopore to macropore is constructed on the surface of microporous ZSM‐5 nanosheets through cascade assembly of dynamic micelles. The outer macropore arrays can adsorb bulky polyolefins quickly by the capillary and hydrophobic effects, enhancing the diffusion and access to active sites. The middle mesopores present a nanoconfinement space, pre‐cracking polyolefins into intermediates by weak acid sites, which then transport into zeolites micropores for further cracking by strong Brønsted acid sites. The hierarchically porous and acidic structures, mimicking biomimetic protease catalytic clefts, ideally match the tandem cracking steps of polyolefins, thus suppressing coke formation and facilitating product escape. As a result, light hydrocarbons (C1‐C7) are produced with a yield of 443 mmol gZSM‐5−1, where 74.3 % of them are C3‐C6 olefins, much superior to ZSM‐5 and porous silica catalysts. This tandem porous catalyst exemplifies a superstructure design of catalytic cracking catalysts for industrial and economical upcycling of plastic wastes.

Micelles Cascade Assembly to Tandem Porous Catalyst for Waste Plastics Upcycling.

Catalytic upcycling of polyolefins into high-value chemicals represents the direction in end-of-life plastics valorization, but poses great challenges. Here, we report the synthesis of a tandem porous catalyst via a micelle cascade assembly strategy for selectively catalytic cracking of polyethylene into olefins at a low temperature. A hierarchically porous silica layer from mesopore to macropore is constructed on the surface of microporous ZSM-5 nanosheets through cascade assembly of dynamic micelles. The outer macropore arrays can adsorb bulky polyolefins quickly by the capillary and hydrophobic effects, enhancing the diffusion and access to active sites. The middle mesopores present a nanoconfinement space, pre-cracking polyolefins into intermediates by weak acid sites, which then transport into zeolites micropores for further cracking by strong Brønsted acid sites. The hierarchically porous and acidic structures, mimicking biomimetic protease catalytic clefts, ideally match the tandem cracking steps of polyolefins, thus suppressing coke formation and facilitating product escape. As a result, light hydrocarbons (C1-C7) are produced with a yield of 443 mmol gZSM-5 -1, where 74.3 % of them are C3-C6 olefins, much superior to ZSM-5 and porous silica catalysts. This tandem porous catalyst exemplifies a superstructure design of catalytic cracking catalysts for industrial and economical upcycling of plastic wastes.

Catalytic upcycling of waste polyethylene to fuels over a nanosized beta zeolite under mild conditions.

We herein report that a nanosized beta zeolite can achieve the upcycling of waste polyethylene into gasoline-range fuels under mild conditions. High accessibility to rich acidic sites intrinsic to the nanosized beta zeolite is crucial to the cracking of polyethylene, leading to a high fuel yield of over 90% at 250 °C for 3 h.

Synthesis of straight-chain C49H100 alkane using a modular splicing strategy

Ultra-long n-alkanes are highly valuable in both scientific research and as major constituents of specialty high-melting-point waxes. Unlike conventional methods (e.g., Fischer–Tropsch (FT), ethylene oligomerization, and polyethylene cracking) typically resulting in wide n-alkane distributions, the elaborate design strategy presented herein allows the direct synthesis of pure, long n-alkanes using a modular splicing method with acetone, furfural, and fatty acid anhydrides or acyl chlorides as bio-blocks. The herein approach is based on a simple four-step catalytic reaction scheme involving C–C chain elongation and C–O bond activation. The synthesized pure n-alkanes had a carbon chain length as high as C49 (total yield of 49%). The synthesis approach also allows to selectively prepare n-alkanes with even and odd carbon numbers ranging from C15 to C49. This process represents a great breakthrough in the synthesis of long-chain pure n-alkanes, surpassing the carbon number limitations reported in previous methodologies.

Comparing bed materials for fluidized bed steam cracking of high-density polyethylene: Olivine, bauxite, silica-sand, and feldspar

Steam cracking in fluidized beds is an alternative method for producing valuable petrochemicals from plastic waste. Previous studies on the conversion of plastics in fluidized beds have revolved around non-catalytic cracking using silica sand as the bed material. On the other hand, studies on catalytic cracking have focused on the use of active materials such as olivine, bauxite, feldspar, and zeolites. The potential influence of the above-mentioned materials, in their natural or inactive state, on fluidized bed hydrocarbon cracking, is not well-documented in the literature. In this paper, steam cracking of polyethylene in a bubbling fluidized bed at 750 °C is investigated in the presence of four different natural ores: olivine, bauxite, silica sand, and feldspar. The paper compares the performance of the steam cracking process in terms of cracking severity, conversion, and product distribution among different hydrocarbon groups. The results show that there is only a marginal difference in cracking severity among the different bed materials, while the conversion remain relatively consistent, ranging from 93% to 95% (carbon.%). The yields of paraffins and carbon oxides are narrow, ranging from 15% to 16% and 3–4%, respectively, while the yields of light olefins and aromatics show a slightly wider range. The yield of olefins is in the range of 52–57%, and for aromatics, it ranges from 16% to 21%. The paper also discusses the potential impact of these bed materials on the cracking reactions, including their thermal and reactive interactions.

Catalytic Depolymerization of Polyolefinic Plastic Waste

AbstractIn a circular economy, processes such as the pyrolysis of polyolefin plastic waste must be established for naphtha cracker feedstock production. However, the composition of the plastic waste used has a strong influence on the conversion process and the heteroatom content, and thus on the quality of the pyrolysis oils. In this work, the influence of critical plastic components (e.g., polyamide 6) on the catalytic cracking of polyethylene (PE‐HD) in a batch rotary kiln reactor was investigated and a cost‐effective concept for integrating chemical recycling into a steam cracking plant was proposed.

High-Silica Layer-like Zeolites Y from Seeding-Free Synthesis and Their Catalytic Performance in Low-Density Polyethylene Cracking.

Layer-like FAU-type zeolite Y was synthesized by an organosilane-assisted low-temperature hydrothermal method and its catalytic activity was verified in the low-density polyethylene (LDPE) cracking process. The synthesis procedure of high-silica layer-like zeolite Y was based on organosilane as a growth modifier, and for the first time, the seeding step was successfully avoided. The X-ray diffraction and electron microscopy studies, scanning electron microscopy and transmission electron microscopy confirmed the formation of pure FAU structure and zeolite particles of plate-like morphology arranged in the manner of the skeleton of a cuboctahedron. The in situ Fourier transform infrared (FT-IR) spectroscopic studies, low-temperature nitrogen sorption, and electron microscopy results provided detailed information on the obtained layer-like zeolite Y. The acidic and textural properties of layer-like zeolites Y were faced with the catalytic activity and selectivity in the cracking of LDPE. The quantitative assessment of catalyst selectivity performed in FT-IR/GC–MS operando studies pointed out that LDPE cracking over the layer-like material yielded value-added C3–C4 gases and C5–C6 liquid fraction at the expense of C7+ fraction. The detailed analysis of coke residue on the catalyst was also performed by means of FT-IR spectroscopy, thermogravimetric analysis, and thermoprogrammed oxidation coupled with mass spectrometry for the detection of oxidation products. The acidic and textural properties gave a foundation for the catalytic performance and coking of catalysts.

Defect engineering to boost catalytic activity of Beta zeolite on low-density polyethylene cracking

Catalytic cracking is of considerable interest as a sustainable, renewable, efficient, and eco-friendly chemical conversion method of plastic wastes. In catalytic cracking, plastic wastes can be converted into valuable products such as monomers or petrochemical feedstock. Solid acid catalysts, especially zeolites, significantly lower the thermal decomposition temperature of plastics. However, the catalysts have not shown enough performance to be implemented in society. Therefore, major efforts have recently been devoted to solving this problem by appropriately designing zeolite catalysts. Herein, we report a new defect-rich Beta zeolite synthesized by a dry gel conversion method using methyltriethoxysilane. The obtained catalyst exhibited outstanding activity on low-density polyethylene cracking. We measured Fourier-transform infrared spectra using pyridine as a probe molecule and found that this high activity is contributed by the increase of the amount of Lewis acid sites. It probably arises from the ratios of extra-framework hexacoordinated aluminum and silanol groups higher than the conventional Beta zeolite shown in 27Al and 1H magic angle spinning nuclear magnetic resonance spectra. We can say that the increase of defects of zeolite Beta further accelerated polymer cracking. This work provides a new strategy to improve the catalytic activity of zeolites on polymer cracking.

Pyrolysis of long chain hydrocarbon-based plastics via self-exothermic effects: The origin and influential factors of exothermic processes

Converting plastic wastes into value-added products through energy-efficient pyrolysis is essential, and it requires lower pyrolysis temperatures and shorter processing times than that of other processes. An exothermic phenomenon was observed during the process high-pressure polyethylene pyrolysis. It was proven for the first time that the exotherm is caused by a pressure-induced phase transition, in which colossal heat release can be driven by relatively small pressures. A large temperature change (> 100 °C) leads to the deep cracking of polyethylene, although the set temperature is far lower than the required temperature for thermal cracking. Importantly, the heat input stops immediately when the set temperature is reached; thus, the external heating time is short. Polyethylene can be completely converted into liquid products in ~90 wt% yield and with a small number of gases. The self-exothermic phase transition only occurs within a certain range of material thickness, which is related to the corresponding phase behavior. In the self-exothermic pyrolysis process, with an increase in the thickness of polyethylene, the proportion of low-value olefins in oil products decreases gradually, while alkanes, isoalkanes and aromatics show an increasing trend, making the product composition closer to the fuel standard. This work provides a viable approach for plastic recycling at low pyrolysis temperatures and short external heating times with the help of a self-exothermic phase transition in the absence of a catalyst.

Conversion of HDPE into Value Products by Fast Pyrolysis Using FCC Spent Catalysts in a Fountain Confined Conical Spouted Bed Reactor.

Continuous catalytic cracking of polyethylene over a spent fluid catalytic cracking (FCC) catalyst was studied in a conical spouted bed reactor (CSBR) with fountain confiner and draft tube. The effect of temperature (475–600 °C) and space‐time (7–45 gcat min gHDPE −1) on product distribution was analyzed. The CSBR allows operating with continuous plastic feed without defluidization problems and is especially suitable for catalytic pyrolysis with high catalyst efficiency. Thus, high catalyst activity was observed, with waxes yield being negligible above 550 °C. The main product fraction obtained in the catalytic cracking was made up of C5−C11 hydrocarbons, with olefins being the main components. However, its yield decreased as temperature and residence time were increased, which was due to reactions involving cracking, hydrogen transfer, cyclization, and aromatization, leading to light hydrocarbons, paraffins, and aromatics. The proposed strategy is of great environmental relevance, as plastics are recycled using an industrial waste (spent FCC catalyst).

Catalytic thermochemical cracking of polyethylene over nanocomposite bentonite clay

Catalytic thermochemical cracking of polyethylene has been investigated in presence of a series of bentonite clay based nanocomposite with a view toward assessing their suitability in a process for converting plastic waste to fuel. Metal oxides such as manganese oxide (MnO), titanium oxide (TiO2) and zinc oxide (ZnO) were impregnated with sodium montomorillonite bentonite. The clay catalysts were characterized by x-ray diffraction (XRD), scan electron microscope (SEM), transmission electron microscope (TEM) and energy dispersive x-ray (EDX) spectrometers. The effect of different catalysts on the composition and the yield of gaseous was evaluated. ZnO nanocomposite bentonite clay achieved the highest methane gas formation around 93%. The superior catalytic performance of nanocomposites is probably attributed to their uniform dispersed of oxides particles on montmorillonite support.

Thermochemical interaction of wood and polyethylene during co-oxidation in the conditions of thermogravimetric analysis

In this work, using the methods of thermal analysis, we investigated the features of the oxidative decomposition of mixtures of polyethylene and sawdust (in different mass ratios). The results show that during the mixtures decomposition, the effects of interaction between wood and polyethylene are observed, which, apparently, are associated with the chain nature of the oxidation reactions of both components. It was found that the oxidation of mixtures with a polyethylene fraction of 20% or less proceeds without the formation of a significant amount of products of incomplete decomposition of hydrocarbon chains. Thermogravimetric and calorimetric data are compared with data from mass spectrometric analysis of decomposition products. These data indicate competition between the oxidation and thermal cracking of polyethylene. The presence of biomass due to its high reactivity contributes to an increase in the proportion of oxidation in the total decomposition of polyethylene.

Cost-effective synthesis of hierarchical HZSM-5 with a high Si/TPA+ ratio for enhanced catalytic cracking of polyethylene

In this work, hierarchical HZSM-5 zeolites, with the high Si/TPA+ ratio of 34 and Si/Al ratios of 100 and 30, have been synthesized by the mesoporogen-free, Na+-free, and steam-assisted crystallization route using industrial silica sol as the silicon source. Highly crystalline HZSM-5 (30)-34 sample inherited the strong acidity of conventional HZSM-5 and exhibited the relatively large mesopore volume (0.08 ​cm3 ​g−1). With this structure, the accessibility of Brønsted acidity sites is increased from 6.25% of conventional HZSM-5 to 64.3% of HZSM-5 (30)-34, which enhanced the catalytic cracking performance of low-density polyethylene (LDPE). As a result, the decomposition temperature of LDPE was reduced to 420 ​°C, which is apparently lower than 482 ​°C when no catalyst was adopted. Moreover, the HZSM-5 (30)-34 sample showed good reusability and catalytic stability in the regeneration-recycle experiments.

Opening up ZSM-5 Hierarchical Zeolite's Porosity through Sequential Treatments for Improved Low-Density Polyethylene Cracking.

An adequately tuned acid wash of hierarchical ZSM-5 zeolites offers a levelling up in the catalytic cracking of low-density polyethylene. Identification of crucial and limiting factors governing the activity of the zeolite was extended with studies about the accessibility of acid sites, nature of the realuminated layer and role of Lewis acid sites. The sequential treatment of a ZSM-5 zeolite offered enhanced activity in low-density polyethylene (LDPE) cracking at low and high conversions, as confirmed by a decrease in the temperatures needed to reach 20% and 80% conversion (T20 and T80, respectively). A linear dependence of the T80 on the coupled IHF (indexed hierarchy factor) and AFB (accessibility factor) highlighted the importance of the textural and acidic parameters in the catalytic cracking of LDPE. Operando FT-IR-GC studies confirmed a higher fraction of short-chain hydrocarbons (C3–C5) in the product distribution of hierarchical catalysts resulting from the effective polymer cracking in easily accessible pores.

Highly efficient catalytic pyrolysis of polyethylene waste to derive fuel products by novel polyoxometalate/kaolin composites.

We report here alumina-substituted Keggin tungstoborate/kaolin clay composite materials (KAB/kaolin) as polyethylene cracking catalysts. KAB/kaolin composites with varying concentrations of KAB (10-50 wt.%) were synthesized by the wet impregnation method and successfully characterized by Fourier-transform infrared spectroscopy, powder X-ray diffraction, thermo-gravimetric analysis and scanning electron microscopy with energy dispersive X-ray spectroscopy analytical techniques. Use of KAB loaded kaolin composites as the catalyst for low-density polyethylene (LDPE) cracking exhibited a higher percentage of polymer conversion (99%), producing 84 wt.% of fuel oil and negligible amount (˂ 1 wt.%) of solid residue while thermal cracking produced ~22 wt.% residue. Furthermore, gas chromatography-mass spectrometry analysis of oil obtained by non-catalytic cracking exhibited a high selectivity to high molecular weight hydrocarbons (C13-C23) compared to the catalytic cracking where 70 mol.% of gasoline range hydrocarbons (C5-C12) were produced. We propose that higher cracking ability of our prepared catalysts might ensue from both Brønsted and Lewis acid sites (from KAB and kaolin respectively), which enhanced the yield of liquid fuel products and reduced the cracking temperature of LDPE. These findings suggest that the prepared composites were cost-effective and excellent cracking catalysts that could be recommended for highly efficient conversion of waste plastic materials to petrochemicals at an industrial scale.

Feedstocks for Engine Fuels from Waste Polyolefins

Hydrogenation and hydroisomerization of kerosene fractions produced by thermal cracking of polyethylene, polypropylene and those mixtures were studied on Pt/SAPO-11 catalyst. Effects of the process parameters and the composition of the feedstocks on the isoparaffin contents, and the main performance properties of JET fuels (e.g. freezing point, smoke point) were examined. It was found that, practically sulphur- olefin- and aromatic free kerosene fractions having excellent burning properties (smoke point: 42.0 – 50. 0 mm) can be produced from the tested polyolefin cracked fractions. In the examined catalytic system JET fuel with adequate freezing point can only be produced from the clear cracked fraction of polypropylene. Due to the inadequate freezing point and density the products of the experiments cannot be used directly as engine fuel, just only as high value blending components.

Study of the effects of regeneration of USY zeolite on the catalytic cracking of polyethylene

In this work, a study of the deactivation and reuse of USY zeolite for the pyrolysis of polyethylene has been carried out in a batch reactor at 500 °C. From the different tested zeolite/plastic ratios, 1/10 is the optimal ratio which allows giving rise to a liquid product free of wax. Regeneration was established by heating at 500 °C for 3 h coked zeolite in presence of air. The liquid yield begins to increase from the 11th cycle of regeneration until reaching a maximum at the 14th cycle showing a lost in the zeolite activity producing a viscous product.The liquid fraction derived from the first eight cycles was a mixture of C4-C27 compounds with a maximum C5-C7 fraction. In the 14th cycle of regeneration, compounds having higher carbon number were obtained and the yield of linear compounds increases up to 29%. To explain the relative activity of the regenerated zeolite, the textural properties and the XRD patterns results of the zeolite recovered after the 1st and 14th cycles have been compared with those obtained with fresh catalyst. The study showed that after 14 cycles of regeneration, the zeolite is still active but its activity level has decreased.

Catalytic cracking of polyethylene plastic waste using synthesised zeolite Y from Nigerian kaolin deposit

The increasing rate of accumulation of plastic waste (PW) is quite disturbing to the world, particularly in developing nations due to its non-biodegradable nature and inadequate waste management practices. The need to properly manage this waste and utilize the potential and chemical energy value that can be derived from this waste justifies the encouragement and employment of newer and better recycling methods and technology of these wastes. Therefore, this has led us to explore the catalytic pyrolysis of plastic waste using zeolite Y synthesized from kaolin deposit in Covenant University, Sango Ota, Ogun state of Nigeria. A stainless steel packed bed reactor was used in the cracking of low-density polyethylene (LDPE) plastic wastes into liquid fuel components at a temperature of 300 ℃ using zeolite Y catalyst. The liquid fuel obtained from the catalytic pyrolysis was analyzed using GC–MS. Fifty compounds were identified, which revealed the presence of mostly alkenes and aromatics in the hydrocarbons range of C8–C29. This is made up of 56% of gasoline fractions range of C6–C12, 26% of diesel and kerosene fractions range C13–C18, and 10% of fuel oil range C18–C23, while 8% is residual fuel range greater than C24.

TG/DTA-FTIR Study on Total Resource Recovery from Tetra Pak Waste by Pyrolysis under a CO2 Environment

Pyrolysis of Tetra Pak waste under CO2 was investigated using a thermogravimetric/differential thermal analyser coupled with a Fourier transform infrared spectrometer. Experimental results showed that cellulose was decomposed between 270 and 390 °C, leading to the formation of aldehydes, ketones, carboxylic acids and levoglucosan. Thermal cracking of polyethylene occurred between 440 and 530 °C and the main products were aliphatic hydrocarbons. CO can be produced by the gasification of pyrolytic char by CO2 at temperatures ranging from 860–970 °C. Aluminium (Al) foil remained in a “thin layer shape” despite melting above 660 °C. CaO was generated from the decomposition of CaCO3 used as a paper filler at 722 °C. The reaction between CaO and the CO2 atmosphere during the cooling process led to the formation of new CaCO3 which was the main component of ash after gasification and was easy to separate from Al foil.