Pyrolysis Of High Density Polyethylene Research Articles

Study of the Synergetic Effect of Co-Pyrolysis of Lignite and High-Density Polyethylene Aiming to Improve Utilization of Low-Rank Coal.

The mutual impact of low-quality lignite and high-density polyethylene (HDPE) during open system pyrolysis was investigated, aiming to improve utilization of lignite with simultaneous treatment of HDPE waste. Pyrolysis of lignite, HDPE, and their mixture (mass ratio, 1:1) was performed at temperatures 400, 450, 500, 550, and 600 °C. Initial substrates and pyrolysis products were characterized by thermogravimetric analysis (TGA), gas chromatography–mass spectrometry (GC–MS), specific carbon isotope analysis of individual hydrocarbons (δ13C), Rock-Eval pyrolysis, and elemental analysis. The positive synergetic effect during co-pyrolysis of lignite/HDPE mixture was observed at temperatures ≥450 °C, with the greatest being at 500 °C. The highest yield of liquid co-pyrolysis products with a similar composition to that of crude oils is also noticed at 500 °C. The yields of liquid and gaseous products and quality of pyrolytic products obtained by co-pyrolysis of lignite/HDPE mixture are notably improved compared with pyrolysis of lignite alone. On the other hand, data obtained from pyrolysis of HDPE alone indicate that it cannot be concurrent to well-developed catalytic thermal processes for polymer recycling. However, concerning the huge amount of produced HDPE, at least part of this plastic material can be reused for advanced thermal treatment of lignite, particularly in countries where this low-rank coal represents the main source of energy.

Kinetics of polyethylene pyrolysis in the atmosphere of ethylene

Polyethylene is widely used due to its excellent properties. However, the growing demand and higher production of polyethylene have also brought new types of hazards. It is essential to study the pyrolysis of polyethylene for the polyethylene process conditions and the prevention of polyethylene dust explosion. In this paper, the pyrolysis of linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE) under different heating rates in N2 and different ethylene concentration was studied by the TG-DSC method. The pyrolysis kinetics of polyethylene was analyzed by using Li Chung-Hsiung thermal analysis method, and the pyrolysis characteristic and reaction kinetics parameters of LLDPE and HDPE were found. The research results show that the increase in the heating rate is beneficial to polyethylene pyrolysis in nitrogen. The temperature at the highest rate increases linearly with the heating rate. The rise of ethylene concentration has some inhibitory effect on the pyrolysis reaction of polyethylene, and ethylene has a significant impact on the polyethylene pyrolysis rate. We also found the most suitable mechanism function of polyethylene pyrolysis from the 12 considered mechanism functions. HDPE pyrolysis stability is higher than LLDPE in nitrogen, while LLDPE pyrolysis stability is higher than HDPE in ethylene.

Effect of Temperature on Pyrolysis Oil Using High-Density Polyethylene and Polyethylene Terephthalate Sources From Mobile Pyrolysis Plant

This research aims to study the effect of temperature, collecting time, and condensers on properties of pyrolysis oil. The research was done be analyzing viscosity, density, proportion of pyrolysis products and performance of each condenser towers for the pyrolysis of high-density polyethylene (HDPE) and polyethylene terephthalate (PET) in the mobile pyrolysis plant. Results showed that the main product of HDPE resin was liquid, and the main product of PET resin was solid. Since the pyrolysis of PET results in mostly solid which blocked up the pipe, the analysis of pyrolysis oil would be from the use of HDPE as a raw material. The pyrolysis of HDPE resin in the amount of 100 kg at 400, 425, and 450°C produced the amount of oil 22.5, 27, and 40.5 L, respectively. The study found that 450°C was the temperature that gives the highest amount of pyrolysis oil in the experiment. The viscosity was in the range of 3.287–4.850 cSt. The density was in the range of 0.668–0.740 kg/L. The viscosity and density were increased according to three factors: high pyrolysis temperature, number of condensers and longer sampling time. From the distillation at temperatures below 65, 65–170, 170–250, and above 250°C, all refined products in each temperature range had the carbon number according to their boiling points. The distillation of pyrolysis oil in this experiment provided high amount of kerosene, followed by gasoline and diesel.

Thermal Decomposition Kinetics of Basalt Fiber-Reinforced Wood Polymer Composites.

Thermogravimetric analysis (TGA) was used for the observation of the pyrolysis kinetics characteristics of high density polyethylene (HDPE)-based composites enhanced by a variety of basalt fibers (BFs) and wood flour (WF). The improved Coats-Redfern (C-R), Flynn-Wall-Ozawa (F-W-O), Friedman, and Kissinger methods were utilized to ascertain the specific apparent activation energy (Ea) of each component and composite material. The results indicate that BFs do not decompose under 800 °C, while the pyrolysis of WF and waste HDPE showed two significant weight loss zones (250–380 °C and 430–530 °C), relative to cellulose/hemicellulose and HDPE thermal degradation, respectively. The average Ea of WF/BF/HDPE composites over the entire pyrolysis process obtained by the modified C-R method fluctuated in a range of 145–204 kJ/mol and increased with the BF content, which was higher than that of WPC (115–171 kJ/mol). The value of Ea computed by the F-W-O method was significantly lower than that computed with the improved C-R method, which could validate the reliability of two methods by comparing with the literature. The Friedman and Kissinger methods were not applicable to this composite material reinforced by mixed fillers, so the obtained Ea values were quite different from the previous two methods. The changes in Ea showed that the addition of BFs could improve the average Ea and further enhance the thermal stability and flame resistance of the composites.

Application of Artificial Neural Networks to Predict the Catalytic Pyrolysis of HDPE Using Non-Isothermal TGA Data.

This paper presents a comprehensive kinetic study of the catalytic pyrolysis of high-density polyethylene (HDPE) utilizing thermogravimetric analysis (TGA) data. Nine runs with different catalyst (HZSM-5) to polymer mass ratios (0.5, 0.77, and 1.0) were performed at different heating rates (5, 10, and 15 K/min) under nitrogen over the temperature range 303–973 K. Thermograms showed clearly that there was only one main reaction region for the catalytic cracking of HDPE. In addition, while thermogravimetric analysis (TGA) data were shifted towards higher temperatures as the heating rate increased, they were shifted towards lower temperatures and polymer started to degrade at lower temperatures when the catalyst was used. Furthermore, the activation energy of the catalytic pyrolysis of HDPE was obtained using three isoconversional (model-free) models and two non-isoconversional (model-fitting) models. Moreover, a set of 900 input-output experimental TGA data has been predicted by a highly efficient developed artificial neural network (ANN) model. Results showed a very good agreement between the ANN-predicted and experimental values (R2 > 0.999). Besides, A highly-efficient performance of the developed model has been reported for new input data as well.

A catalytic reactive distillation approach to high density polyethylene pyrolysis – Part 2 – Middle olefin production

A catalytic reactive distillation reactor, previously described, was improved to increase the production of middle and heavy hydrocarbons, to be used as feedstock or fuel in the viewpoint of a Circular Economy of plastics. The thermal and catalytic pyrolysis experiments were run using high density polyethylene (HDPE) under several experimental conditions, with a 1 % (w/w) of HZSM-5 for catalytic pyrolysis. Three different temperatures were tested in each case and the influence of the reaction time was evaluated at 500 °C and 430 °C for thermal pyrolysis and catalytic pyrolysis, respectively. Thermal pyrolysis of HDPE produced the higher amount of solid products (80 %wt. or higher) under the form of a waxy cream-colored material (wax) for all the experimental sets. For catalytic pyrolysis, the major product fraction was always liquid. The analysis of the liquid products showed that, for both thermal and catalytic pyrolysis, the products obtained were within the range of C5 to C11, with a higher yield on C8 and C9 in the case of thermal pyrolysis and on C6 and C7 for catalytic pyrolysis. The aim of this study was the development of an integrated reactor/separation system to increase the middle olefin production. It is possible with this reactor design to direct the pyrolysis of HDPE to the production of middle olefins that can be reused in the petrochemistry industry, as chemical feedstock, including in the production of new plastics.

Development of a nanostructured filter for pyrolysis wax purification: Effects of particulate filter aids

Wax obtained from the pyrolysis of polyethylene waste can contain inorganic contaminants and must be purified before application. We evaluated different filter aids (perlite, sand, and rice husk ash) for the filtration of a crude wax and a pyrolysis wax through a filter medium that was coated with nylon 6 nanofibers to improve filtration efficiency. We first examined the performance of the filter aids in improving crude wax filtration, with the filtration time, temperature, and pressure held constant at 1h, 170°C, and 2.5bar, respectively. Oily wax was then produced by pyrolysis of high-density polyethylene (HDPE) waste in the temperature range 425⿿475°C. The best filter aid was perlite, which had a filtrate production rate of 5.47ÿ10⿿5m3/h. The highest oily wax yield (87.8%) was achieved at a pyrolysis temperature of 425°C. The assembly comprising the filter medium coated with nylon 6 nanofibers plus perlite as a filter aid was most suitable for removing impurities from the oily wax generated by the HDPE pyrolysis as it achieved a purification efficiency of 99.9%.

Catalytic Cracking of High Density Polyethylene Pyrolysis Vapor over Zeolite ZSM-5 towards Production of Diesel

The upsurge in the amount of plastic pollution has drawn the attention of various researchers in finding the best solution for plastic waste treatment. Pyrolysis of high density polyethylene using ZSM-5 catalyst has been investigated using two-staged reactors consisting of a pyrolysis reactor and a catalytic fixed bed reactor. The effect of the heating rate (2 °C/min, 6 °C/min, 10 °C/min, 14 °C/min, 18 °C/min) of the pyrolysis reactor and reaction time (75 min, 90 min, 105 min) were studied on the yield of products and the quality of pyrolytic oil products. The quality of pyrolytic oil produced was evaluated based on the gross calorific values (GCV) and the paraffin, olefin, naphthenic and aromatic (PONA) compounds distribution, which were used to compare with conventional fuel. The highest yield of oil product was obtained at a reaction time of 75 minutes, where it was 61.05 wt.%, with solid product yield of 0.41wt.% and gas product yield of 38.54wt.%, at a heating rate of 2°C/min. The GCV of oil products were within the range of that of conventional diesel (44 – 45 MJ/kg). The pyrolytic oil products contained mainly C10 to C24 hydrocarbon compounds, which were diesel range hydrocarbon. In terms of the PONA distribution, the composition of paraffin was larger for most of the products, while the composition of naphthenes and aromatic were relatively small with respect to the range for conventional diesel.

Towards waste refinery: Co-feeding HDPE pyrolysis waxes with VGO into the catalytic cracking unit

The co-feeding of high-density polyethylene pyrolysis waxes (HDPE waxes) with vacuum gasoil (VGO) on the catalytic cracking has been investigated. Runs have been conducted by feeding a blend of HDPE waxes/VGO (1/4 in mass) to a laboratory-scale reactor that mimics the behavior of the riser reactor of the industrial FCC unit. Tested operating conditions have been the following: 500–560 °C; catalyst to oil mass ratio (C/O), 3–7 gcat gfeed−1; and, contact time, 6 s. The comparison of obtained results, i.e., yield and composition of the fractions, in the cracking of the blend with those obtained in the cracking of the VGO and HDPE waxes separately, has exposed the existence of synergetic mechanisms. This way, the cracking of the blend produces a more olefinic gaseous fraction and a naphtha with higher content of iso-paraffins and olefins and lower of aromatics, together with a comparable yield of coke.

Hidrocarburos C6−C10 a partir de polietileno residual

En este trabajo de investigación se obtienen hidrocarburos liquidos combustibles (gasolina) con rendimiento del 90% por medio de pirólisis del polietileno de alta densidad (PEAD) a 390 ± 5 °C sobre el catalizador α−PbO. La masa catalítica se varía en 10, 15, 20 y 40% p/p utilizando 10 g de PEAD por cada experimento. El α−PbO se sintetizó a 550 °C en atmósfera de aire durante 1 hora. Los productos líquidos son caracterizados por espectroscopia infrarroja con transformada de Fourier (FT-IR) y cromatografía de gases y espectrometría de masas (GC/MS). La relación óptima experimental de PEAD/α−PbO para la conversión del polietileno residual es 20% α−PbO. Los análisis por FT-IR y GC/MS, permiten corroborar que los líquidos obtenidos corresponden a hidrocarburos con cadenas en un intervalo de 6 a 10 carbonos (C6–C10) y contienen un calor de combustión promedio de 10.9492 kcal/g con potencial aplicación como combustibles alternativos.

High-Precision Monitoring of Average Molecular Weight of Polyethylene Wax from Waste High-Density Polyethylene.

High-density polyethylene (HDPE) is a major component of polyethylene waste, yet only under 29.9% of waste HDPE is recycled. As an important additive, polyethylene wax (PEW) is increasingly used in many industries such as plastics, dyes, and paints. The preparation of PEW has received considerable interest because recycling and precisely controllable production can bring huge economic benefits. In this study, to recycle waste HDPE, a single screw extruder was innovatively combined with a connecting pipe to prepare PEW from the pyrolysis of waste HDPE. Using a test platform, PEWs were prepared under different pyrolysis temperatures and screw speeds, and corresponding number-average molecular weights (NAMWs) of PEWs were measured. To precisely monitor NAMW of PEW, a program was developed in MATLAB. First, the relationship between NAMW and pyrolysis ratio was obtained, and a measure-point-independence verification was conducted. Then, modified Arrhenius equations and time-dependent pyrolysis temperature were for the first time introduced into the HDPE pyrolysis model. Furthermore, the screw-speed-dependent inverse method was proposed and validated for high-precision monitoring of NAMW of PEW from the pyrolysis of waste HDPE by extrusion. PEW of desired molecular weight was able to be precisely obtained from waste HDPE.

Mathematical Modeling of the Catalytic Pyrolysis of High-Density Polyethylene in a Plug-Flow Tubular Reactor

A detailed mathematical model for the catalytic pyrolysis of high-density polyethylene is presented. The model is based on the known kinetic mechanism of the catalytic cracking of hydrocarbons, whi...

A catalytic reactive distillation approach to high density polyethylene pyrolysis – Part 1 – Light olefin production

An integrated reactor/separation semi-batch catalytic pyrolysis reactor system, based on a distillation approach, was developed to produce gaseous hydrocarbons, to be used as feedstock or fuel in the perspective of a Circular Economy approach. This work intends to be a proof of concept and to test the operating conditions and performance of the reactor to control the molecular weight of the products. For that purpose, thermal and catalytic pyrolysis experiments were run using high density polyethylene (HDPE) under several experimental conditions. Different temperatures were used (400, 450 and 500 °C) for both thermal and catalytic pyrolysis, with 1% (w/w) of HZSM-5. The influence of the temperature of the coolant at the outlet of the reactor was also investigated for the catalytic degradation of the HDPE at 450 °C, providing a way to control the average molecular weight of the recovered products, which increased with increasing coolant temperature. The focus of the study was to develop an integrated reactor/separation system where only the lighter compounds produced could leave the reactor and thus direct the production to chemical feedstock to be reused in petrochemistry, including in the production of new plastics. The analysis of the volatile products indicated that, for both thermal and catalytic pyrolysis, the products obtained were within the range of C2 to C8. Higher amounts of C3 to C5 were formed, with a particular emphasis on olefins, with very high yields in the case of catalytic pyrolysis. The activity of the catalysts after use was also checked through the ARDT index (Ability to Reduce the Decomposition Temperature), with values for this index above 50% which indicate a good possibility for reuse of the catalyst.

Hydroxyl Group Stabilization for Increased Yields of Low-Molecular-Weight Products in the Copyrolysis of Cellulose and Thermoplastics

Biomass is a promising renewable and sustainable resource to produce energy and value-added chemicals. Fast pyrolysis is one of the simplest thermochemical methods to convert biomass into high yields of liquid products that can be upgraded into drop-in fuels or platform chemicals; however, its diverse product distributions and low product selectivity incur significant cost due to subsequent upgrading and separation operations. In this work, a strategy to promote yields of low-molecular-weight products (LMWPs) from cellulose pyrolysis via hydroxyl group stabilization using molten polymers (MPs) is presented. Three types of thermoplastics, high-density polyethylene (HDPE), polyethylene glycol (PEG), and polystyrene (PS), were copyrolyzed with cellulose to investigate the possible hydroxyl group stabilization effects caused by the ether and aromatic moieties in MPs during cellulose pyrolysis. A custom-made batch pyrolysis reactor was employed for the copyrolysis experiments. Our results showed that the combined yields of levoglucosan (LG) and LMWPs significantly increased in the presence of MPs due to the physical inhibition of anhydrosugar oligomer evaporation. The product distributions were varied dependent on the MPs used. In particular, both ether groups in PEG and aromatic groups in PS were found to stabilize the cellulosic hydroxyl groups during glycosidic bond cleavage, inhibiting the formation of LG. Aromatic moieties in MPs were observed to create a stronger inhibition effect on the glycosidic bond cleavage than ether moieties. Our experiments also suggest that both ether and aromatic groups in MPs stabilize the hydroxyl groups during dehydration, leading to increased yields of products from retro-Diels–Alder fragmentation. Ether moieties were found to be more effective at inhibiting dehydration than aromatic moieties. Yields of the HDPE-derived products increased during copyrolysis, suggesting a possible catalytic effect in HDPE pyrolysis caused by the LMWPs produced from carbohydrate pyrolysis. Yields of the PEG-derived products increased only in the presence of cellulose and glucose, whereas yields of the PS-derived products were unaffected in all copyrolysis experiments. A possible reaction mechanism accounting for the hydroxyl group stabilization effects is proposed based on our experimental findings.

Fuel production by cracking of polyolefins pyrolysis waxes under fluid catalytic cracking (FCC) operating conditions

The catalytic cracking of high–density polyethylene pyrolysis waxes under fluidized catalytic cracking conditions has been investigated with the aim of producing fuels at large–scale from waxes obtained in pyrolysis plants located nearby collection and segregation points. Additionally, preliminary information about the capacity of these units to valorize waste polyolefins has been obtained. The catalytic cracking runs have been performed in a riser simulator reactor under industrial conditions: 500–560 °C; catalyst to oil mass ratio, 3, 5 and 7 gcat goil−1; and, contact time, 6 s. The product distribution has been quantified determining the yields of different fractions, which have been defined according to their boiling point range: dry gas, liquefied petroleum gas, naphtha, light cycle oil, heavy cycle oil and coke. The concentration of the families of compounds has been also determined, which are n–paraffins, iso–paraffins, olefins, naphthenes and aromatics. For the shake of comparison, the results of catalytic cracking of a common stream fed to the industrial units, i.e., vacuum gasoil, have been included. Globally, promising results have been obtained in the valorization of waste polyolefins by means of this combination of pyrolysis–cracking stages that expose, at the same time, the capacity of this unit to manage waste plastics.

Effect of the FCC Equilibrium Catalyst Properties and of the Cracking Temperature on the Production of Fuel from HDPE Pyrolysis Waxes

The catalytic cracking of high-density polyethylene pyrolysis waxes has been investigated with the aim of promoting the production of fuels. The runs have been conducted in a CREC riser simulator r...

Thermal pyrolysis of high density polyethylene (HDPE) in a novel fixed bed reactor system for the production of high value gasoline range hydrocarbons (HC)

Pyrolysis is a promising thermolysis technique to recover valuable oils and light hydrocarbons (HC) with high yields from plastic solid waste (PSW). In this work, thermal pyrolysis of high density polyethylene (HDPE) with the aim of producing gasoline range hydrocarbon oils, has been carried out in a novel fixed bed (batch) reactor. The pyrolysis of HDPE has been conducted between 500 to 800 °C in the presence of nitrogen as an inert carrier gas media to produce liquid fuel oil, gaseous products and solid char. The optimum temperature of obtaining maximum oil product yield (70%) was 550° C. A comprehensive gas chromatography (GC) analysis of the liquid and gaseous products was conducted to quantify high molecular weight individual HC components. Moreover, light molecular weight HC constituting the gaseous fraction were identified. A chemical kinetic analysis of the cracking reactions, was performed to investigate the reaction mechanism of yielding the maximum oil product. The oil product recovered had a high proportion of aliphatic HC especially in the range of C8 to C12, whilst aromatic HC were of lower proportion. The carbon number of the pyrolysis oil was noted to increase proportionally with the increasing operating temperature. The gaseous product had a high percentage (> 70%) of C2 to C4 HC, which was attributed to the high activity of carbon/carbon (C-C) chain scission reaction.

Use of Waste Polyethylene as a Source of Reducing Agent for Metal Oxide Reduction: A Case Study on NiO

This study introduces a novel way of using pyrolytic gas generated by the pyrolysis of waste high-density polyethylene (HDPE) for metal oxide reduction. A case study on NiO was carried out to reveal the feasibility of the method. Thermodynamic calculations were performed to guide and better understand the experiments. It was predicted that the pyrolytic gas mainly consisted of H2, CH4, and C6H6. HDPE pyrolysis and NiO reduction were simultaneously carried out during heating to the temperatures 550–900 K. NiO was reduced to Ni by the pyrolytic gas carried by Ar flow above 650 K. The conversion of HDPE to the pyrolytic gas increased as the temperature increased to 900 K. The extent of NiO reduction also increased with temperature due to enhanced HDPE pyrolysis. NiO reduction was completed at 900 K. It is feasible to use waste HDPE to reduce metal oxides such as NiO.

Urban mining of fuel gases via low temperature pyrolysis of post-consumer high density polyethylene wastes

Low temperature pyrolysis of high density polyethylene (HDPE) wastes was studied by adapting a cylindrical pressure cooking pot of height 30.00 cm with an internal diameter of 31.50 cm. The pyrolysis reaction was carried out with and without catalysts. The gases evolved during the pyrolysis were collected in Tedlar bags and analysis was done using a Buck 530 Gas chromatograph. Results when the pyrolysis was without catalyst, showed aliphatic hydrocarbons in the range of C 1 – C 10 with a total concentration of 87.0114 ppm and 93.9733 ppm at 200oC and 350oC respectively. The pyrolysis was repeated under catalytic influence of zeolite using catalyst/sample ratios of 1:8 and 1:16 at 150 oC and 250 oC. Results showed that the total yield of gases for HDPE under the zeolitic effect at temperatures of 150 oC and 250 oC using catalyst/sample ratio of 1:8 to be 159.4613 ppm and 394.4499 ppm respectively. The corresponding values obtained at 150 oC and 250 oC using catalyst/sample ratio of 1:16 were 595.8016 ppm and 724.0983 ppm respectively. The hydrocarbon gases revealed C 1 – C 10 aliphatic hydrocarbons which can be fractionated into fuel gases (C 1 – C 4 ), gasoline range gases (˃C 7 ) and organic solvents (C 5 – C 7 ). Keywords: Pyrolysis, high density polyethylene, zeolite, aliphatic hydrocarbon

Simulation of the HDPE Pyrolysis Process

Pyrolysis is a thermochemical decomposition of organic compounds such as High-density polyethylene (HDPE) plastics. The product of the HDPE pyrolysis is usually diesel with other wastes (such as carbon black, etc.). A pyrolysis reaction is essentially a decomposition reaction performed at elevated temperatures in the absence of oxygen. There are many other complex reactions taking place in pyrolysis, however, in this paper, the focus has been on three main reactions of HDPE pyrolysis, namely: 𝛽−scission, hydrogen abstraction and chain fission. Of these, 𝛽−scission is known to be most dominant reaction in HDPE pyrolysis reactions. In this work, the reaction equations and reaction constants were defined and solved in MATLAB® using the in-built ordinary differential equation (ODE) solver. The solution represents the rate of the reaction and the product yield.