Pyrolysis Of High Density Polyethylene Research Articles

Kinetics of Thermal Pyrolysis of High-Density Polyethylene

Thermal pyrolysis kinetics of virgin high-density polyethylene (HDPE) was investigated. Thermal pyrolysis of HDPE was performed using a thermogravimetric analyzer in nitrogen atmosphere under non-isothermal conditions at different heating rates 4, 7, 10 °C/min. First-order decomposition reaction was assumed, and for the kinetic analysis Kissinger-Akahira-Sunose(KAS), Flynn-Wall-Ozawa(FWO) and Coats and Redfern(CR) method were used. The obtained values of average activation energy by the KAS and FWO methods were equal to137.43 and 141.52 kJ/mol respectively, these values were considered in good agreement, where the average activation energy value obtained by CR equation methods was slightly different which equal to 153.16 kJ/mol.

Study of pyrolysis of high density polyethylene in the open system and estimation of its capability for co-pyrolysis with lignite

Pyrolysis of high density polyethylene (HDPE) in the open system was studied. A plastic bag for food packing was used as a source of HDPE. Pyrolysis was performed at temperatures of 400, 450 and 500?C, which were chosen based on thermogravimetric analysis. The HDPE pyrolysis yielded liquid, gaseous and solid products. Temperature rise resulted in the increase of conversion of HDPE into liquid and gaseous products. The main constituents of liquid pyrolysates are 1-n-alkenes, n-alkanes and terminal n-dienes. The composition of liquid products indicates that the performed pyrolysis of HDPE could not serve as a standalone operation for the production of gasoline or diesel, but preferably as a pre-treatment to yield a product to be blended into a refinery or petrochemical feed stream. The advantage of a liquid pyrolysate in comparison to crude oil is the extremely low content of aromatic hydrocarbons and the absence of polar compounds. The gaseous products have desirable composition and consist mainly of methane and ethene. The solid residues do not produce ash by combustion and have high calorific values. Co-pyrolysis of HDPE with mineral-rich lignite indicated positive synergetic effect at 450 and 500?C, which is reflected through the increased experimental yields of liquid and gaseous products in comparison to theoretical ones.

Experimental Investigation on the Reduction of Catalyst Costs in the Polyethylene Pyrolysis Process

In our earlier works, the catalyst USY zeolite was tested for the pyrolysis of High density polyethylene (HDPE). It yielded 71% liquid oil that could be separated into diesel and gasoline-like fractions [3]. However, the high cost of this catalyst led to the present study where the effects of different low-cost catalysts on catalytic cracking of HDPE were investigated. GC-MS analysis were performed to check the carbon distribution of each sample and to make theoretical gasoline/diesel quantification in the pyrolysis liquids. Products where compared by studying carbon distribution, condensable range, branching degrees and reaction speeds. According to all those parameters, none of them outperformed USY zeolite. The Second Part has been conducted to observe the regeneration of USY Zeolite and monitor its performance for its economic value. The regeneration was done 10 times and the performance was monitored after every experiment with respect to % of heavier compound yields, carbon distribution range, char deposition range and gasoline and diesel yields. It was found that the regenerated catalyst loses its capability very slowly and even after 10 regenerations products characteristics were not sensibly altered.

Comparison of catalytic performance of an iron-alumina pillared montmorillonite and HZSM-5 zeolite on a spouted bed reactor

Catalytic pyrolysis of high density polyethylene (HDPE) on HZSM-5 catalyst and an iron-alumina pillared montmorillonite, prepared in laboratory (FAMO), was performed by means of a conical spouted bed reactor. This type of reactor is a suitable technology for plastic pyrolysis due to its high heat and mass transfer rates and excellent performance in the handling of sticky solid materials. The pyrolytic process carried out on HZSM-5 catalyst gave significant yield of gaseous products (above 74 wt%), while FAMO catalyst gave high yields of waxes, particularly rich in diesel hydrocarbon range (C11–C21). Waxes obtained by subjecting HDPE to thermal pyrolysis had a higher range of molecular weight. Waxes have been characterised using different techniques, such as gel permeation chromatography (GPC), polidispersity (PD), Fourier transform infrared (FTIR) spectroscopy, Simulated Distillation, and TDP.

Influence of the conditions for reforming HDPE pyrolysis volatiles on the catalyst deactivation by coke

Pyrolysis of high density polyethylene (HDPE) has been carried out in a conical spouted bed reactor (500°C) and the volatiles have been reformed in-line over a Ni commercial catalyst in a fluidized bed reactor. The evolution of reaction indices (conversion, H2 yield and other gaseous product yields) with time on stream has been studied under the following operating conditions: temperature, 600–700°C; space-time, 8.3–20.8gcatmingHDPE−1, and steam/plastic ratio, 3–5. High initial conversion (>94.5%) and H2 yields (>76.7%) are attained under all the operating conditions studied, with HDPE conversion and H2 yield increasing when the three variables are increased, which is explained by the enhancement of the reforming reaction. However, a significant effect of operating conditions on catalyst stability has been observed. Thus, an increase in temperature, space-time and steam/plastic ratio decreases catalyst deactivation as a consequence of a lower rate of coke deposition on the catalyst due to both a lower C5+ coke precursor amount in the reaction medium and a higher gasification rate of the coke deposited.

Valorisation of different waste plastics by pyrolysis and in-line catalytic steam reforming for hydrogen production

The performance of an original two-step reaction system (pyrolysis and in-line reforming) was assessed in the hydrogen production from different plastics (polyethylene, polypropylene, polyethylene terephthalate and polystyrene) and their mixture. The pyrolysis step was performed in a conical spouted bed reactor at 500 °C, whereas the reforming of pyrolysis volatiles was carried out in a fluidized bed reactor at 700 °C. This two in-line reactor configuration was initially developed for the reforming of high density polyethylene pyrolysis volatiles, and this paper describes the influence composition of pyrolysis products derived from different plastics has on the reforming step, conversion, product yields and deactivation behavior. The products formed in both the pyrolysis and the reforming steps were analysed by on-line gas chromatography and micro-gas chromatography. Significant differences in the reforming behaviour of the plastics were observed, with hydrogen productions being higher in the case of polyolefins (from 34.8 to 37.3 wt% ) followed by polystyrene (29.1 wt%) and remarkably lower for polyethylene terephthalate (18.2 wt%). Furthermore, the evolution of conversion and product distribution with time on stream was assessed for the different plastics studied and the catalyst deactivation rate was related to the amount and morphology of the coke deposited on the reforming catalyst. It was proven that the features of the reactors used in the pyrolysis and reforming steps are suitable for minimizing operational problems, and therefore operating in continuous regime.

Kinetic Modeling of the Catalytic Steam Reforming of High-Density Polyethylene Pyrolysis Volatiles

The kinetics of the steam reforming of HDPE pyrolysis volatiles is studied on a Ni commercial catalyst in a fluidized bed reactor in-line with the pyrolysis reactor (a conical spouted bed reactor at 500 oC). Steam reforming reactions have been carried out under the following conditions: 600-700 oC and space time 0-16.7 gcat min gHDPE-1. Based on the composition of HDPE pyrolysis volatiles, a kinetic scheme is assumed with four reactions (C5+ hydrocarbon reforming, C2-C4 hydrocarbon reforming, CH4 reforming and WGS reaction). Moreover, the kinetics of the deactivation has been quantified with an expression dependant on C5+ hydrocarbon concentration (coke precursors). Calculation of the kinetic parameters is conducted by nonlinear multiple regression, fitting the experimental data to those calculated by the mass conservation equations for each component in the reaction medium. The overall kinetic model proposed describes accurately the evolution of the main products (H2, CO2, CO) with time on stream in the ...

Determination of the heat of pyrolysis of HDPE via isothermal differential scanning calorimetry

Due to the complexity of solid state reactions such as cracking of polymers, it is very difficult to find the required heat of the involved reactions. In this study, using a differential scanning calorimetry (DSC) instrument, a new method is proposed to determine the heat of decomposition of polymers at constant temperatures. The integration of an isothermal DSC curve with respect to time gives the overall consumed heat by the process, which consists of two components: net heat of reaction and heat loss. Finding an effective solution to measure heat loss from DSC instrument is an important part of this new approach. The heat loss is determined as function of sample mass and operating temperature. The heat loss is employed to correct the DSC results and produce the net heat of decomposition reactions. This approach is new since, firstly, it uses high-certainty isothermal DSC measurements, and secondly, the heat loss values are calculated in the decomposition range. The procedure is employed to determine the required heat for pyrolysis of high-density polyethylene at constant temperatures of 400, 410, 420 and 430 °C, and the average value was calculated to be 1375 ± 233 kJ kg−1.

In-situ catalytic co-pyrolysis of yellow poplar and high-density polyethylene over mesoporous catalysts

Catalytic co-pyrolysis of biomass and hydrogen-rich materials is an effective approach for enhancing the production of bio-based hydrocarbons. In this work, mesoporous solid acid materials, such as hierarchical mesoporous MFI (meso MFI), hierarchical mesoporous Y (meso Y) and Al-SBA-15, were used as the catalysts for the catalytic co-pyrolysis of yellow poplar (YP) and high-density polyethylene (HDPE). Among three catalysts, meso MFI revealed the highest catalytic efficiency for the production of aromatic hydrocarbons from catalytic pyrolysis of YP or HDPE due to its effective pore structure, large channels, and high acidity. Moreover, meso MFI showed the highest synergistic formation of aromatic hydrocarbons during the catalytic co-pyrolysis of YP and HDPE as a result of hydrogen donating effect of HDPE and catalytic interactions between YP- and HDPE-derived pyrolyzates. The amounts of solid residue obtained from the catalytic co-pyrolysis of YP and HDPE over meso MFI were also much lower than their theoretical yields.

Pyrolysis of waste high density polyethylene (HDPE) and low density polyethylene (LDPE) plastics and production of epoxy composites with their pyrolysis chars

High density polyethylene (HDPE) and low density polyethylene (LDPE) plastic wastes were pyrolysed in the temperature range of 300–700 °C, liquid, gas and solid fractions (char) were quantified and pyrolysis char was used as additive in production of epoxy composite. Effects of pyrolysis temperature on products fractions, char quality and composite quality were investigated. In the composite composition, char was included as 10–50 wt% of epoxy to determine the effects of additive dosage on the composite quality. The char additives and produced composites were characterized by FTIR and SEM. Mechanical properties, namely tensile strength, surface hardness and electrical properties were determined for the epoxy composite materials. Epoxy composite materials produced with HDPE pyrolysis char additive obtained at 300 °C (ER300) showed the most ideal behavior in terms of elongation at break and tensile strength. With increasing pyrolysis temperature and char doses elongation at break and tensile strength of composites generally decreased. While tensile strength showed an increase by 32% at 10% wt% dose for composite (ER300) with HDPE char obtained at 300 °C, the increases were 21%, 14%, 14% and 13% for ER400-ER700 composites prepared with 10 wt% HDPE chars obtained at 400–700 °C pyrolysis temperatures, respectively. Despite this, LDPE chars a small decreased the tensile strength of epoxy. The hardness of neat epoxy was improved from 79.8 Shore D up to 86.3 and 87 Shore D by the LDPE and HDPE char additives, respectively. The study offers a new recovery approach for HDPE and LDPE type plastic wastes.

Production of light hydrocarbons from pyrolysis of heavy gas oil and high density polyethylene using pillared clays as catalysts

Mesoporous catalysts are currently used in the petroleum and petrochemical industry to convert heavy hydrocarbons into light ones. There is a few papers on iron-pillared clays are available. In the catalytic pyrolysis, it was used a commercial clay fractionated to remove sand and silt and treated to remove soluble salts and the organic fraction. That clay was intercalated with iron or aluminum oligomers and calcined at specific temperatures to form pillars in the layers. The main advantage of the use of pillared clays in catalytic pyrolysis is that their cost is much more reduced than that of zeolite catalysts. All thermal pyrolysis at 500°C have high pyrolysis oil yield (>80%), except for the pyrolysis of high density polyethylene (HDPE) using zeolite as catalyst. It was observed significant difference in the catalytic pyrolysis of the HDPE at 450°C as the following: zeolite > Al-PILC–450≈Fe-PILC–450> Fe-PILC–300> Al-PILC-Fe-450. The presence of heavy gas oil (HGO) improves the oil yield from both thermal and catalytic pyrolysis of HDPE, which can be attributed to the solvency effect of HGO. Pyrolysis oils were analyzed by GCAR-MS and their profiles were compared to the standard diesel. The oil from the HGO/HDPE pyrolysis using the catalyst Fe-PILC-Fe-300 was the more similar to the GC–MS homologous series of standard diesel. That catalyst produced a light linear hydrocarbon content 63% higher than that produced with zeolite.

Catalytic cracking of heavy fractions from the pyrolysis of waste HDPE and PP

In the present paper, automotive waste plastics were considered as a potential source of fuels and chemicals. The feedstock in the experimental tests was represented by the heaviest fractions from the distillation of pyro-oil from the pyrolysis of high-density polyethylene (HDPE-wax) and polypropylene (PP-wax). Due to their very high viscosity both polymer-waxes were, prior to processing, diluted in atmospheric gas oil (GO). Mixtures with hydrotreated vacuum gas oil (HVGO) were also prepared and processed under simulated fluid catalytic cracking conditions via a MAT-test. The product distribution was similar to the one shown by the commercial FCC process: light gases (C1, C2), LPG, gasoline fraction, light and heavy cycle oil. To maintain optimal performance a commercial FCC equilibrium catalyst (FCC-ECAT) was used. When processing HDPE and PP waxes, high yields of profiling products – propylene and gasoline were obtained. In the case of the PP-wax feed without HVGO, the yield of gasoline was even higher than in case of pure HVGO. When cracking HDPE-wax feed mixtures the product distribution was oriented more towards the production of propylene. The composition of liquid products considering all types of feedstock consisted mainly of iso-alkanes and aromatics. The calculated values of microactivity for the HDPE-wax and PP-wax feedstock, with or without HVGO, were significantly higher than in the case of pure HVGO.

Thermo-catalytic pyrolysis of waste high-density polyethylene: Effect of γ-ray irradiation on degradation

ABSTRACTIn this work, the synergistic effect of the γ-ray irradiation and catalyst on the pyrolysis of High-Density Polyethylene (HDPE) waste was investigated in a batch reactor. Two catalysts, Zeolite Socony Mobil–5 (ZSM-5) and Ferric oxide, were used, and their loading was optimized. The results revealed that the degradation temperature significantly reduced with increasing dosage of irradiation. The complete pyrolysis of HDPE waste occurs at a temperature of 400°C and reaction time of 240 min (4 h), while in a case of irradiation-induced pyrolysis, there is higher yield and decrease in the residence time of pyrolysis. Irradiation with a higher dosage (2,000 kGy) increases the rate of thermo-catalytic pyrolysis for HDPE waste and gives maximum conversion.

Role of the Catalyst in the Pyrolysis of Polyolefin Mixtures and Used Tires

The role of polymeric structures and the presence of a catalyst in the pyrolysis of polyolefin mixtures and used tires was studied in a fixed bed reactor at 450 °C. Our results showed that while thermal pyrolysis of high density polyethylene (HDPE) produced 23.3%wt of condensable products, a mixture of polyolefins (HDPE, LDPE, and PP) showed an increase of more than 23%wt in this fraction. In both cases, a wide carbon number distribution was obtained for the condensable products, confirming that there was not any selectivity. By using HZSM-5 zeolites, the pyrolysis of pure HDPE was dramatically changed with both more gaseous products and a major selectivity toward C10–C16 hydrocarbons in the condensable fraction. It is noteworthy that, although the PP present in the mixture increases the production of lighter hydrocarbons as compared with pure HDPE, no major differences in product distribution were observed between HDPE and polyolefin mixture in catalytic pyrolysis. However, the zeolites used improved the...

Deactivation dynamics of a Ni supported catalyst during the steam reforming of volatiles from waste polyethylene pyrolysis

The valorization of waste high density polyethylene (HDPE) for hydrogen production has been studied in a two-step process, comprising pyrolysis and subsequent steam reforming of the volatiles produced in the first step. Particularly, this work focuses on the deterioration mechanisms (sintering and coke deposition) of the Ni commercial catalyst used in the second step, as it conditions the overall process performance. Pyrolysis of HDPE has been performed in a conical spouted bed reactor at 500°C, and the catalytic steam reforming of the pyrolysis volatiles, in a fluidized bed reactor at 700°C. Deactivated catalyst samples were recovered at different values of time on stream, and characterized using XRD, N2 adsorption-desorption, SEM and TEM electronic microscopies, temperature programmed oxidation (TPO), Raman, FTIR and LDI-TOF MS spectroscopies. The results show that the deactivation is due to the sintering and encapsulation -by coke- of Ni. The former is inevitable within the current conditions, and the latter can be ascribed to the condensation of adsorbed precursors that evolve over time. Encapsulating coke is partially carbonized into filamentous coke with lower effect on catalytic deactivation and higher economic interest.

Pyrolysis of HDPE into fuel like products: Evaluating catalytic performance of plain and metal oxides impregnated waste brick kiln dust

The work explores the catalytic activities of plain and metal oxides (Fe2O3, CoO, ZnO, MnO2 and NiO) impregnated waste brick kiln dust (WBKD) for pyrolysis of high density polyethylene (HDPE) in order to get useful liquid oil that can be used as substitute to petro-fuels. The catalysts prepared in the laboratory were characterized by scanning electron microscopy (SEM), energy dispersive x-rays (EDX) analysis, surface area analysis (SAA) and x-ray diffractometry (XRD). The conversion of HDPE into liquid oil (LO) as a function of concentration of catalysts was studied. Based on the yielding results, ZnO- impregnated WBKD (5%) was found to be highly active. The liquid oils obtained in the thermal and ZnO-impregnated WBKD catalyzed runs were analyzed by using fourier transform infra-red spectroscopy (FTIR) and gas chromatographic-mass spectrometry (GC–MS). While comparing the results with the un-catalyzed thermal run, the ZnO-impregnated WBKD altered the liquid oil composition in terms of carbon range and hydrocarbon group type distributions. The fuel properties of the resultant liquid oils showed fuel values resembling to the generic petro-fuels.

Thermal and Catalytic Degradation Kinetics of High-Density Polyethylene Over NaX Nano-Zeolite

Thermal and catalytic pyrolysis of waste plastics in an inert atmosphere has been regarded as a creative method, since pyrolysis can convert plastics waste into hydrocarbons that can be used either as fuels or as a source of chemicals.
 Natural Iraqi kaolin clay was used to synthesis the NaX nano- zeolite by hydrothermal conditions with average particle size equal to 77.63nm.Thermal decomposition kinetics of high-density polyethylene (HDPE) in the absence and presence of catalysts nano NaX Zeolite was investigated. Thermal and catalytic degradation of HDPE was performed using a thermogravimetric analyzer in nitrogen atmosphere under non-isothermal conditions 4, 7 and 10 °C/min heating rates were employed in thermogravimetric analysis (TGA) experiments.
 First-order decomposition reaction was assumed, and for the kinetic analysis Coats and Redfern (CR) method was used. The apparent activation energy (Ea) was evaluated. Results showed that the NaX nano-zeolite decreases the activation energy (Ea) of HDPE pyrolysis further than the thermal pyrolysis.

Experimental Investigation on Thermocatalytic Pyrolysis of HDPE Plastic Waste and the Effects of Its Liquid Yield over the Performance, Emission, and Combustion Characteristics of CI Engine

An experimental investigation was carried out to study two process parameters of thermocatalytic pyrolysis of high density polyethylene (HDPE) plastic waste, and the liquid yield of pyrolysis (plastic oil) was analyzed over its working characteristics in a direct injection compression ignition (DICI) engine. A series of pyrolysis experiments with four different heating rates (5, 10, 15, and 20 °C/min) were performed in identical environments with the objective of analyzing the heating rate and residence time on end products. It was found that the liquid yield was maximum at the heating rate of 10 °C/min and the residence time decreases with an increase in the heating rate due to variation of reaction kinetics at different heating rates. The characterization of the plastic oil revealed that the major constituents belong to alkene, alkane, and alcohol functional groups; totally 90 six fuel range hydrocarbons were present ranging from C5 to C28, and the other thermophysical properties were comparable with th...

Initial Stages of the Pyrolysis of Polyethylene.

An experimental study of the kinetics of the initial stages of the pyrolysis of high-density polyethylene (PE) was performed. Quantitative yields of gas-phase products (C1-C8 alkanes and alkenes) and functional groups within the remaining polyethylene melt (methyl, vinyl, vinylene, vinylidene, and branching sites) were obtained as a function of time (0-20 min) at five temperatures in the 400-440 °C range. Gas chromatography and NMR ((1)H and (13)C) were used to detect the gas- and condensed-phase products, respectively. Modeling of polyethylene pyrolysis was performed, with the primary purpose of determining the rate constants of several critical reaction types important at the initial pyrolysis stages. Detailed chemical mechanisms were created (short and extended mechanisms) and used with both the steady-state approximation and numerical integration of the differential kinetic equations. Rate constants of critical elementary reactions (C-C backbone scission, two kinds of H-atom transfer, radical addition to the double bond, and beta-scission of tertiary alkyl radicals) were adjusted, resulting in an agreement between the model and the experiment. The values of adjusted rate constants are in general agreement with those of cognate reactions of small molecules in the gas phase, with the exception of the rate constants of the backbone C-C scission, which is found to be approximately 1-2 orders of magnitude lower. This observation provides tentative support to the hypothesis that congested PE melt molecular environment impedes the tumbling motions of separating fragments in C-C bond scission, thus resulting in less "loose" transition state and lower rate constant values. Sensitivity of the calculations to selected uncertainties in model properties was studied. Values and estimated uncertainties of four combinations of rate constants are reported as derived from the experimental results via modeling. The dependence of the diffusion-limited rate constant for radical recombination on the changing molecular mass of polyethylene was explicitly quantified and included in the extended kinetic mechanism, which appears critical for the agreement between modeling and experiment, particularly the agreement between the experimental and the calculated activation energies for product formation rates. Calculations were performed to estimate the contribution to the overall rate of radical recombination of the "reaction diffusion" phenomenon, where recombination is driven not by the actual motion of the recombining radical sites but rather by the migration of the radical site through PE melt due to rapid hydrogen transfer; this contribution was shown to be negligible for the conditions of the current work.

HDPE pyrolysis-steam reforming in a tandem spouted bed-fixed bed reactor for H2 production

Steam pyrolysis (500°C) of high density polyethylene (HDPE) in a conical spouted bed reactor followed by a steam reforming (700°C) in a fixed bed reactor (Ni commercial catalyst) has been carried out for obtaining a syngas stream rich in H2. The product yields obtained in the pyrolysis of HDPE using steam are very similar to the previous ones with N2 as fluidizing agent. A comparison of the results obtained here with those for gasification-reforming strategy reveals that tar and C2+ hydrocarbons are not fully reformed using the pyrolysis-reforming strategy. Besides, although a high H2 yield is obtained (81.5% the stoichiometric value), it is slightly lower than the yield obtained in gasification-reforming. Coke yield is high (4.43wt.%), which causes fixed bed blockage and hinders a correct flow of the volatiles through the bed. SEM, TEM and TPO results show that two types of coke are deposited on the catalyst, with amorphous coke prevailing in the pyrolysis-reforming strategy and filamentous coke in gasification-reforming.