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Contribution à l’étude de la valorisation énergétique des résidus de plastique par craquage catalytique
Abstract
La consommation continue de matières plastiques a conduit, jusqu’à 2015, à l'accumulation de 6,3 milliards de tonnes de déchets plastiques. En Europe, le recyclage des plastiques ramassés ne dépasse pas les 30% pour des raisons logistiques et économiques liées à cette filière. La valorisation énergétique de ces déchets, non valables pour le recyclage, est alors préférée aux autres modes de gestion. L’incinération étant controversée pour son bilan énergétique et environnemental, d’autres moyens de valorisation tels que la pyrolyse sont privilégiés. Les travaux de recherche menés dans cette thèse ont été focalisés sur la pyrolyse des polyoléfines, le polyéthylène (PE) et le polypropylène (PP), en raison de leur forte présence dans les déchets plastiques municipaux. L’influence de la zéolithe Ultrastable Y (USY) sur la pyrolyse du PP et du PE, récupérés d’une déchèterie, a été étudiée par une analyse thermogravimétrique (ATG) puis sur un réacteur en batch à lit fixe et un réacteur continu. L’étude cinétique dedécomposition thermique des mélanges de PP et de PE a été réalisée, les paramètres cinétiques ont été déterminés et les interactions entre les différents composants du mélange ont été analysées. La quantité de zéolithe a été optimisée et le rapport catalyseur/plastique de 1:10 a été adopté durant les essais expérimentaux. L’utilisation de l’USY comme catalyseur a conduit à une distribution plus ciblée de composés et des temps de réaction plus courts. Les liquides de pyrolyse obtenus ont été séparés en différentes fractions de carburants compatibles avec les normes Européennes EN 590 et EN 228. Afin de réduire le coût de production de ces carburants, une étude de régénération du catalyseur a été menée et a montré que son niveau d’activité a diminué au bout de 14 cycles de régénération. A la fin de la thèse, un bilan d’énergie et de masse du procédé a été effectué puis les perspectives d’amélioration sont présentées afin de transposer l’étude à l’échelle industrielle.
... Le réacteur continu est conçu pour être un échangeur de chaleur multitubes à contre-courant chauffé par les gaz d'échappement, à 500 °C, d'un moteur diesel de 8 kW. Un travail antérieur, réalisé par (Kassargy, 2018) au GEPEA, visait à modéliser analytiquement ce réacteur continu en utilisant la méthode de différence de température moyenne logarithmique (LMTD). Cependant, dans cette étude, le travail se poursuit en modélisant numériquement le réacteur continu par la méthode des éléments finis et selon le modèle et les équations de pyrolyse validés précédents (à l'intérieur du réacteur semi-batch). ...
... Chantal Kassargy (Kassargy, 2018) in the IMT-Atlantique "Department of Energy and Environmental Systems (DSEE) in the GEPEA laboratory. The previous work focused on experimental studies for PE and PP pyrolytic and non-pyrolytic processes in a semi-batch reactor and making comparison between the oil byproducts and fossil fuels according to the international characteristic norm. ...
... Moreover, there exist some issues when using catalyst because of the high tendency of coke formation on the surface of catalyst, which reduces the catalyst efficiency over time and causes high residue in the byproducts. Besides that, it is also a challenge to separate the catalyst from the char residue at the end of the experiment (Kassargy, 2018). Furthermore, according to literature, batch and semi-batch reactors have been widely adopted as small-scale plastic pyrolysis reactors due to their simple design, high conversion, and feasibility of controlling operating parameters (Kassargy, 2018 Lee, 2008). ...
Nowadays, after the depletion of fossil energy reserves worldwide, the pursue for renewable energy became a crucial issue and subject for many researchers and academic institutions. Whereas, humanity is facing serious dilemma: the enormous growth of accumulated plastic wastes every year,due to the limitation of landfills and recycling processes. Therefore, a solution for plastic wastes accumulation and an alternative source of energy is pyrolysis process, which converts plastic wastes into a wide range of fuels and chemicals. Plastic pyrolysis consists of a thermal decomposition of large chain polymers in absence of oxygen. Different parameters affect this process like; Temperature,heating rate, feedstock material, catalyst, type of the reactor and pressure. However, many experimental studies are made so far regarding the influence of these parameters on the pyrolysis process and its by-products. On the other hand,modelling and simulating plastic pyrolysis process, at a lab scale or industrial scale, are rarely found in literature. Thus, the aim of this thesis is to model and upgrade a continuous pyrolysis reactor feasible at the industrial scale, heated by hot exhaust gases coming from 8 kW diesel engine, to convert plastic waste into heat and transportation fuels. But before crossing this step, plastic pyrolysis process for PP and HDPE is modelled and validated, as milli-particle scale, in a thermogravimetric analyzer coupled with differential scanning calorimeter (TGA-DSC), then in a laboratory scale semi-batch reactor (1 litter capacity) using Finite Element method and COMSOL-Multiphysics software. Finally, the calibrated models are used to conceive a continuous reactor and to study its behavior numerically.
This review presents a comprehensive description of the current pathways for recycling of polymers, via both mechanical and chemical recycling. The principles of these recycling pathways are framed against current-day industrial reality, by discussing predominant industrial technologies, design strategies and recycling examples of specific waste streams. Starting with an overview on types of solid plastic waste (SPW) and their origins, the manuscript continues with a discussion on the different valorisation options for SPW. The section on mechanical recycling contains an overview of current sorting technologies, specific challenges for mechanical recycling such as thermo-mechanical or lifetime degradation and the immiscibility of polymer blends. It also includes some industrial examples such as polyethylene terephthalate (PET) recycling, and SPW from post-consumer packaging, end-of-life vehicles or electr(on)ic devices. A separate section is dedicated to the relationship between design and recycling, emphasizing the role of concepts such as Design from Recycling. The section on chemical recycling collects a state-of-the-art on techniques such as chemolysis, pyrolysis, fluid catalytic cracking, hydrogen techniques and gasification. Additionally, this review discusses the main challenges (and some potential remedies) to these recycling strategies and ground them in the relevant polymer science, thus providing an academic angle as well as an applied one.
The fundamentals of pyrolysis, its latest developments, the different conditions of the process and its residues are of great importance in evaluating the applicability of the pyrolysis process within the waste management sector and in waste treatment. In particular the types of residue and their further use or treatment is of extreme interest as they could become the source of secondary raw materials or be used for energy generation in waste treatments. The main area of focus of this paper is the investigation of the link between the pyrolysis conditions, the chemical and mineralogical composition of their products and the benefits of pyrolysis in the waste management sector. More specifically the paper covers the fast, intermediate and slow pyrolysis of organic waste and mixtures of inorganic and organic waste from households. The influence of catalysts during fast pyrolysis on the product yield and composition is not being considered in this review.
Energy is extracted recently from the waste products. Environmental pollutions are being minimized along with the addition of considerable amount of energy beside the conventional sources. The energy extracted from the waste leads a hope of alternative fuel for internal combustion engines as well as to meet other requirement. Common energy conversion method uses tire, wood, rubber to derived energy through pyrolysis. About 9.25% gaseous, 43% liquid, and 47% solid product are obtained from tire pyrolysis process at around 450°C temperature. The liquid fuel is directly used in the engines and that phase is a mixture of complex hydrocarbon. In this work Fractional Distillation, oxidative desulfurization and de-colorization for upgrading liquid product has been conducted. In fractional distillation 30%, 20%, 6.35%, 6%, 4.5%, and 1.3% by volume oils are obtained at over the temperature ranges-121-180°C, 211-260°C, 71-120°C, 191-210°C, 181-190°C, and 40-70°C. Then by desulfurization around 54-58% sulphur was removed. For desulfurization hydrogen peroxide and formic acid (2:1 ratio) are used at constant temperature and magnetic stirring rate. The obtained fraction was characterized by elemental analyses, FT-IR techniques and compared with conventional diesel fuel. Sludge oil parts may be used as furnace oil which has higher calorific value than that of other conventional furnace oils. The rest of 40-70°C and 71-120°C oil parts may be used as alternative fuel like kerosene. Thus, the aim of the present study is to investigate the suitability of pyrolysis oil as an alternative fuel for IC engine.
Depletion of oil resources and increase in energy demand have driven the researchers to seek ways to convert the waste products into high quality oils that could replace fossil fuels. Plastic waste is in abundance and can be converted into high quality oil through the pyrolysis process. In this study, pyrolysis oils were produced from polyethylene (LDPE700), the most common used plastic, and ethylene–vinyl acetate (EVA900) at pyrolysis temperatures of 700 °C and 900 °C respectively. The oils were then tested in a four cylinder diesel engine, and the performance, combustion and emission characteristics were analysed in comparison with mineral diesel. It was found that the engine could operate on both oils without the addition of diesel. LDPE700 exhibited almost identical combustion characteristics and brake thermal efficiency to that of diesel operation, with lower NOX, CO and CO2 emissions but higher unburned hydrocarbons (UHC). On the contrary, EVA900 presented longer ignition delay period, lower efficiency (1.5–2%), higher NOX and UHC emissions and lower CO and CO2 in comparison to diesel. The addition of diesel to the EVA900 did not significantly improve the overall engine performance.
The two-stage pyrolysis-catalysis of high density polyethylene has been investigated with pyrolysis of the plastic in the first stage followed by catalysis of the evolved hydrocarbon pyrolysis gases in the second stage using solid acid catalysts to produce gasoline range hydrocarbon oil (C8–C12). The catalytic process involved staged catalysis, where a mesoporous catalyst was layered on top of a microporous catalyst with the aim of maximising the conversion of the waste plastic to gasoline range hydrocarbons. The catalysts used were mesoporous MCM-41 followed by microporous ZSM-5, and different MCM-41:zeolite ZSM-5 catalyst ratios were investigated. The MCM-41 and zeolite ZSM-5 were also used alone for comparison. The results showed that using the staged catalysis a high yield of oil product (83.15 wt.%) was obtained from high density polyethylene at a MCM-41:ZSM-5 ratio of 1:1 in the staged pyrolysis-catalysis process. The main gases produced were C2 (mainly ethene), C3 (mainly propene), and C4 (mainly butene and butadiene) gases. In addition, the oil product was highly aromatic (95.85 wt.% of oil) consisting of 97.72 wt.% of gasoline range hydrocarbons.
In addition, pyrolysis-staged catalysis using a 1:1 ratio of MCM-41: zeolite ZSM-5 was investigated for the pyrolysis–catalysis of several real-world waste plastic samples from various industrial sectors. The real world samples were, agricultural waste plastics, building reconstruction plastics, mineral water container plastics and household food packaging waste plastics. The results showed that effective conversion of the real-world waste plastics could be achieved with significant concentrations of gasoline range hydrocarbons obtained.
The thermogravimetric and calorimetric characteristics during pyrolysis of wood, paper, textile and polyethylene terephthalate (PET) plastic in municipal solid wastes (MSW), and co-pyrolysis of biomass-derived and plastic components with and without torrefaction were investigated. The active pyrolysis of the PET plastic occurred at a much higher temperature range between 360°C and 480°C than 220-380°C for the biomass derived components. The plastic pyrolyzed at a heating rate of 10°C/min had the highest maximum weight loss rate of 18.5wt%/min occurred at 420°C, followed by 10.8wt%/min at 340°C for both paper and textile, and 9.9wt%/min at 360°C for wood. At the end of the active pyrolysis stage, the final mass of paper, wood, textile and PET was 28.77%, 26.78%, 21.62% and 18.31%, respectively. During pyrolysis of individual MSW components at 500°C, the wood required the least amount of heat at 665.2J/g, compared to 2483.2J/g for textile, 2059.4J/g for paper and 2256.1J/g for PET plastic. The PET plastic had much higher activation energy of 181.86kJ/mol, compared to 41.47kJ/mol for wood, 50.01kJ/mol for paper and 36.65kJ/mol for textile during pyrolysis at a heating rate of 10°C/min. H2O and H2 peaks were observed on the MS curves for the pyrolysis of three biomass-derived materials but there was no obvious H2O and H2 peaks on the MS curves of PET plastic. There was a significant interaction between biomass and PET plastic during co-pyrolysis if the biomass fraction was dominant. The amount of heat required for the co-pyrolysis of the biomass and plastic mixture increased with the increase of plastic mass fraction in the mixture. Torrefaction at a proper temperature and time could improve the grindability of PET plastic. The increase of torrefaction temperature and time did not affect the temperature where the maximum pyrolytic rates occurred for both biomass and plastic but decreased the maximum pyrolysis rate of biomass and increased the maximum pyrolysis rate of PET plastic. The amount of heat for the pyrolysis of biomass and PET mixture co-torrefied at 280°C for 30min was 4365J/g at 500°C, compared to 1138J/g for the pyrolysis of raw 50% wood and 50% PET mixture at the same condition.
Co-pyrolysis of red oak and high density polyethylene (HDPE) was conducted in a laboratory-scale, continuous fluidized bed reactor in a temperature range from 525 to 675 °C. Pyrolysis products, including two fractions of pyrolysis-oil, non-condensable gases and char were analyzed to assess the influence of pyrolysis temperature and co-feeding of biomass with HDPE. It was found that increasing pyrolysis temperature up to 625 °C promoted the production of pyrolysis-oil and its yield reached 57.6 wt%. Further increase in pyrolysis temperature caused the cracking of pyrolysis-oil to form light gases rich in hydrocarbons. Organic phase of pyrolysis-oil produced from plastic-biomass mixture (PBM) had a higher heating value (HHV) up to 36.6 MJ/kg contributed by the additive effect of HDPE-derived aliphatic hydrocarbons. A significant synergetic effect was also observed during co-pyrolysis. Co-pyrolysis with HDPE increased the production of furan, acids and water from red oak. Co-presence of HDPE also inhibited char formation from red oak and improved the HHV of the resulting char. The char produced from co-pyrolysis had a significantly lower BET surface area than red oak biochar. Not only did HDPE-derived particulate matter blocks the pores, the synergetic interaction also resulted in the formation of large and shallow micro-pores on the char surface.
The thermal behavior of plastics (PS and HDPE) and their blends with biomass (bamboo, empty fruit bunch and sawdust) was investigated in this paper. The individual devolatilization behavior of each of the fuels obtained separately was compared with the behavior of the biomass blends with plastics at various blends. The result shows that the thermal decomposition of the materials can be characterized by one single reaction stage while that of the blends can be characterized by two decomposition reaction stages. The results of the analyses suggested that the co-pyrolysis characteristics of the blends are quite different to the combination of the individual materials and therefore the possible synergic effect points to the existence of chemical interactions during co-pyrolysis between the plastic and biomass fractions of the blends. While up to 25% deviation was observed between the experimental and calculated TGA for HDPE/biomass blends, up to 40% was observed for PS/biomass blends. The examination of the kinetic of the blends indicated that an increase in plastic percentage in the blends leads to decrease of activation energy for the first decomposition stage reaction and subsequently increases the activation energy for the second decomposition stage reaction.
Pyrolysis of polypropylene (PP) and high density polyethylene (HDPE) into fuel like products was investigated over temperature range of 250 to 400 °C. The product yields as a function of temperature were studied. Total conversion as high as 98.66 % (liquid; 69.82%, gas; 28.84%, and residue; 1.34 %) was achieved at 300 °C in case of PP and 98.12 % (liquid; 80.88 %, gas; 17.24 %, and residue; 1.88 %) in case of HDPE at 350 °C. The liquid fractions were analyzed by FTIR and GC-MS. The results showed that the liquid fractions consisted of a wide range of hydrocarbons mainly distributed within the C6–C16. The liquid product obtained in case of PP is enriched in the naphtha range hydrocarbons. Similarly, the liquid product obtained in case of HDPE is also enriched in naphtha range hydrocarbons with preponderance in gasoline and diesel range hydrocarbons. The % distribution of paraffinic, olefinic, and naphthenic hydrocarbons in liquid product derived from PP is 66.55, 25.7, and 7.58 %, respectively, whereas in case HDPE, the % distribution is 59.70, 31.90, and 8.40 %, respectively. Upon comparing the hydrocarbon group type yields, PP gave high yield of paraffinic hydrocarbons while HDPE gave high yields of olefins and naphthenes. The whole liquid fractions and their corresponding distillates fractions were also analyzed for fuel properties. The results indicated that the derived liquid fractions were fuel-like meeting the fuel grade criteria.
Pyrolysis has been examined as an attractive alternative to incineration for municipal solid waste (MSW) disposal that allows energy and resource recovery; however, it has seldom been applied independently with the output of pyrolysis products as end products. This review addresses the state-of-the-art of MSW pyrolysis in regards to its technologies and reactors, products and environmental impacts. In this review, first, the influence of important operating parameters such as final temperature, heating rate (HR) and residence time in the reaction zone on the pyrolysis behaviours and products is reviewed; then the pyrolysis technologies and reactors adopted in literatures and scale-up plants are evaluated. Third, the yields and main properties of the pyrolytic products from individual MSW components, refuse-derived fuel (RDF) made from MSW, and MSW are summarised. In the fourth section, in addition to emissions from pyrolysis processes, such as HCl, SO2 and NH3, contaminants in the products, including PCDD/F and heavy metals, are also reviewed, and available measures for improving the environmental impacts of pyrolysis are surveyed. It can be concluded that the single pyrolysis process is an effective waste-to-energy convertor but is not a guaranteed clean solution for MSW disposal. Based on this information, the prospects of applying pyrolysis technologies to dealing with MSW are evaluated and suggested.
Copyright © 2015 Elsevier Ltd. All rights reserved.
Waste plastics contribute to serious environmental and social problems, such as the loss of natural resources, environmental pollution, and depletion of landfill space, but they also create demands on the environmentally-oriented part of the society. Feedstock recycling of scrap polymers by thermal and chemical methods is well known and environmentally accepted. The paper presents the results of thermodynamic analysis of the conversion of polyolefins in a fuel-like mixture of hydrocarbons using thermal cracking in a new type of tubular reactor with molten metal. Evaluation of the efficiency of the process was based on exergy calculations. Calculated exergy efficiency was ca. 79.5 %. It means that feedstock recycling of waste is better from an energetic and environmental point of view than other processes, particularly incineration.
Pyrolysis of HDPE waste grocery bags followed by distillation resulted in a liquid hydrocarbon mixture with average structure consisting of saturated aliphatic paraffinic hydrogens (96.8%), aliphatic olefinic hydrogens (2.6%) and aromatic hydrogens (0.6%) that corresponded to the boiling range of conventional petroleum diesel fuel (#1 diesel 190-290 degrees C and #2 diesel 290-340 degrees C). Characterization of the liquid hydrocarbon mixture was accomplished with gas chromatography-mass spectroscopy, infrared and nuclear magnetic resonance spectroscopies, size exclusion chromatography, and simulated distillation. No oxygenated species such as carboxylic acids, aldehydes, ethers, ketones, or alcohols were detected. Comparison of the fuel properties to the petrodiesel fuel standards ASTM D975 and EN 590 revealed that the synthetic product was within all specifications after addition of antioxidants with the exception of density (802 kg/m(3)). Notably, the derived cetane number (73.4) and lubricity (198 mu m, 60 degrees C, ASTM D6890) represented significant enhancements over those of conventional petroleum diesel fuel. Other fuel properties included a kinematic viscosity (40 degrees C) of 2.96 mm(2)/s, cloud point of 4.7 degrees C. flash point of 81.5 degrees C, and energy content of 46.16 MJ/kg. In summary, liquid hydrocarbons with appropriate boiling range produced from pyrolysis of waste plastic appear suitable as blend components for conventional petroleum diesel fuel.
The aim of this research was to study fuel oil production from municipal plastic wastes by sequential pyrolysis and catalytic reforming processes. Three kinds of municipal plastic wastes were collected from the final disposal site and the small recycling company in Yogyakarta city, Indonesia. Commercial Y-zeolite and natural zeolite catalysts were used in this study. The results show that the feedstock types strongly affect the product yields and the quality of liquid and solid products. HDPE waste produced the highest liquid fraction. The catalyst presences reduced the liquid fraction and increased the gaseous fraction. Furthermore, municipal plastic wastes pyrolysis produced higher heating value solid products than those of biomass and low rank coal.
The yield as well as molecular weight and composition of the condensed product generated from the HDPE was studied to gain insight into the role of temperature, equilibrium FCC catalyst, agitator speed and carrier gas on the pyrolysis products. Pyrolysis was done in a suite stirred bucchi stainless-steel autoclave reactor. The effect of process parameters such as degradation temperature, catalyst/polymer ratio (%), carrier gas type and stirrer rate on the condensed product yield and composition was determined. Reaction products were determined by GC analysis and shown to contain naphthenes (cycloalkanes), paraffins (alkanes), olefins (alkenes) and aromatics.The maximum “fuel like” condensed product yields were at 450 °C and 10% catalyst, respectively.The influence of different types of carrier gasses with varied molecular weights and reactivity was studied. Hydrogen as a reactive carrier gas increased the condensed and paraffinic product yield. Appropriate heat transfer – by stirring – can increase the catalyst efficiency in a stirred reactor. It is demonstrated that the use of equilibrium FCC commercial catalyst under appropriate reaction conditions can have the ability to control both the condensed yield and carbon number distribution from HDPE degradation, and thus potentially decrease the process cost with more valuable hydrocarbons.
The current review provides an assessment of the main waste plastics valorization routes to produce syngas and H2, thus covering different gasification strategies and other novel alternative processes, such as pyrolysis and in-line catalytic steam reforming. The studies dealing with plastics gasification are in general scarce. However, due to the knowledge acquired on biomass and coal gasification, the state of development of plastic gasification technologies is considerable and, in fact, several gasification studies have been performed at pilot scale units. Air gasification is the most studied and developed strategy and pursues the production of a syngas for energy purposes. In spite of the higher H2 content and heating value of the gas produced by steam gasification, this alternative faces significant challenges, such as the energy requirements of the process and the tar content in the syngas. Moreover, the co-gasification of plastics with coal and biomass appears to be a promising valorization route due to the positive impact on process performance and greater process flexibility. Other promising alternative is the pyrolysis and in-line reforming, which allows producing a syngas with high hydrogen content and totally free of tar.
This volume represents a continuation of the Polymer Science and Technology series edited by Dr. D. M. Brewis and Professor D. Briggs. The theme of the series is the production of a number of stand alone volumes on various areas of polymer science and technology. Each volume contains short articles by a variety of expert contributors outlining a particular topic and these articles are extensively cross referenced. References to related topics included in the volume are indicated by bold text in the articles, the bold text being the title of the relevant article. At the end of each article there is a list of bibliographic references where interested readers can obtain further detailed information on the subject of the article. This volume was produced at the invitation of Derek Brewis who asked me to edit a text which concentrated on the mechanical properties of polymers. There are already many excellent books on the mechanical properties of polymers, and a somewhat lesser number of volumes dealing with methods of carrying out mechanical tests on polymers. Some of these books are listed in Appendix 1. In this volume I have attempted to cover basic mechanical properties and test methods as well as the theory of polymer mechanical deformation and hope that the reader will find the approach useful.
The effectiveness of different experiments for the regeneration of a phosphorus poisoned 15 wt.% Ni/Al2O3 catalyst was investigated during the time on stream hydrogenation of octanal to octanol. The catalyst was deactivated after being exposed to feed contaminated with 500 ppm of triphenylphosphine. Regeneration of the catalyst was attempted by either treating the poisoned catalyst with hydrogen, washing the catalyst with octanol or conducting a combined octanol wash-hydrogen treatment experiment, all at elevated temperatures and at atmospheric pressure. The combined regeneration experiment was the most effective, since the conversion and octanol selectivity were recovered to a significant extent. Characterisation of the regenerated catalysts by ICP-OES, XRD, magnetic measurements and TEM showed that sintering also contributed to the deactivation of the catalysts, and that regeneration did not remove phosphorus from the catalyst, due to phosphorus having reacted with nickel. It was also established that some phosphorus was incorporated into the alumina support to generate strongly acidic sites.
Among alternative techniques to overcome the difficulties associated with thermal regeneration of coked zeolite, non-thermal plasma can be considered as one of the most promising technology. A complete regeneration of zeolite can be achieved at room temperature with a low energy consumption. The active species responsible for catalyst regeneration are the short-lived oxygenated species and not ozone. Based on EPR analysis, which allows the mapping of radicals, the active species generated by NTP are able to diffuse within zeolite eliminating coke molecules. The efficiency of regeneration is directly related to the number of active species present in gas phase. A simple way to increase their concentration consists to substitute N2 by a noble gas as He. In this case, coke is totally oxidized into CO2, 6 times faster than under air.
Removal of aliphatic and aromatic sulfur compounds from fuel by adsorption on zeolites, has been reviewed. Zeolites can be loaded with different metal ions such as Fe2 +, K⁺, Ag⁺, Cu⁺, Ni2 +, Zn2 +, and Ce 4 + and Pd2 + via ion-exchange or impregnation methods. Modified zeolites with these metal ions increase their adsorption capacity and selectivity. Specially, Ce4 + and Pd2 + shows a selectivity towards the sulfur compounds in the presence of the other compounds such as aromatics, O-containing fuel additives and nitrogen compounds. Three types of adsorptive desulfurization include reactive adsorption, selective adsorption, and π-complexation have been used by zeolites for the removal of sulfur compounds. Thermal and solvent regeneration of zeolites in adsorptive desulfurization process have been discussed in detail. Adsorption methods of the sulfur compounds on the zeolite, the charge of metal cations, texture properties of the zeolite, the numbers of active sites on the frameworks of zeolite, acid properties of zeolites, SiO2/Al2O3 ratio and the pore size have a significant impact on the adsorption of sulfur compounds. X and Y zeolites have been widely studied for adsorption of sulfur compounds, due to their tuneable selectivity regarding polar molecules and pore size. Zeolites have been shown good sulfur loading capacity, good regenerability and stable structure for removal of sulfur compounds.
Branched alkanes are important parts of naphtha, and their conversions are related to the adsorption stabilities in the pore of zeolites. In this work, the adsorption stabilities of C7–C10 mono-branched alkanes in the pores of HY (ca. 0.74 nm) and HZSM-5 (ca. 0.55 nm) zeolites are investigated using DFT calculation. After excluding the effect of Brønsted acid by subtracting the adsorption energy on 8T cluster from the total adsorption energy, it is found that confinement effect plays an essential role in stabilizing mono-branched alkanes. With the increase in the carbon number of alkanes, there is gradual increase of adsorption energy on both HZSM-5 and HY zeolites. Moreover, in the narrow channel of HZSM-5 zeolite, the change of adsorption energy (ethyl-alkane < methyl-alkane < n-alkane) is completely different from that in the pore of HY zeolite (ethyl-alkane > methyl-alkane > n-alkane), which is mainly due to confinement effect rather than effect of Brønsted acid. Methyl-alkanes prefer to stay in the pore of HZSM-5, while ethyl-alkanes and propyl-alkanes are more likely absorbed in the pore of HY zeolite. By analyzing the total electron densities of adsorbates, it is concluded that only when there is a certain distance between zeolite fragment and the adsorbate and low electron density region occupies the remaining space of the pore, the confinement effect is the strongest.
Plastic plays an important role in our daily lives due to its versatility, light weight and low production cost. Plastics became essential in many sectors such as construction, medical, engineering applications, automotive, aerospace, etc. In addition, economic growth and development also increased our demand and dependency on plastics which leads to its accumulation in landfills imposing risk on human health, animals and cause environmental pollution problems such as ground water contamination, sanitary related issues, etc. Hence, a sustainable and an efficient plastic waste treatment is essential to avoid such issues. Pyrolysis is a thermo-chemical plastic waste treatment technique which can solve such pollution problems, as well as, recover valuable energy and products such as oil and gas. Pyrolysis of plastic solid waste (PSW) has gained importance due to having better advantages towards environmental pollution and reduction of carbon footprint of plastic products by minimizing the emissions of carbon monoxide and carbon dioxide compared to combustion and gasification. This paper presents the existing techniques of pyrolysis, the parameters which affect the products yield and selectivity and identify major research gaps in this technology. The influence of different catalysts on the process as well as review and comparative assessment of pyrolysis with other thermal and catalytic plastic treatment methods, is also presented.
Catalytic pyrolysis of mixed plastics including high density polyethylene (HDPE), polystyrene (PS), polypropylene (PP), and PET (polyethylene terephthalate) has been performed in presence of a series of modified pillared clays (PILC) and Al-PILC. The catalysts were well characterized by BET, FTIR of pyridine adsorption, XRD, SEM, TEM/EDX. The effect of different catalysts on the composition and amount of pyrolysis products including gas, liquid, and char residue was evaluated. With the introduction of Fe-PILC, the yields of oil product were enhanced, suggesting that secondary over-cracking of primary pyrolytic intermediate species was reduced in the presence of the catalyst. A high oil yield of 79.3 wt.% with excellent selectivity for diesel fraction (80.5%) and high yield of H2 gas (47.7 vol%) were obtained in the case of Fe-PILC. The superior catalytic performance of Fe-PILC is probably attributed to its moderate total acidity, relatively high BET surface area, and uniformly dispersed iron oxide particles on montmorillonite support. Accordingly, with the clay catalyst, an efficient and environmentally friendly process can be developed to produce valuable products (e.g. diesel, hydrogen) through pyrolysis of plastic waste.
This paper reviews the progress and challenges of the catalytic pyrolysis of plastic waste
along with future perspectives in comparison to thermal pyrolysis. The factors affecting the
catalytic pyrolysis process such as the temperature, retention time, feedstock composition
and the use of catalyst were evaluated in detail to improve the process of catalytic pyrolysis.
Pyrolysis can be carried out via thermal or catalytic routes. Thermal pyrolysis produces
low quality liquid oil and requires both a high temperature and retention time. In order
to overcome these issues, catalytic pyrolysis of plastic waste has emerged with the use of
a catalyst. It has the potential to convert 70–80% of plastic waste into liquid oil that has
similar characteristics to conventional diesel fuel; such as the high heating value (HHV) of
38–45.86 MJ/kg, a density of 0.77–0.84 g/cm3, a viscosity of 1.74–2.5 mm2/s, a kinematic viscosity
of 1.1–2.27 cSt, a pour point of (−9) to (−67) ◦C, a boiling point of 68–352 ◦C, and a flash
point of 26.1–48 ◦C. Thus the liquid oil from catalytic pyrolysis is of higher quality and can be
used in several energy-related applications such as electricity generation, transport fuel and
heating source. Moreover, process by-products such as char has the potential to be used as
an adsorbent material for the removal of heavy metals, pollutants and odor from wastewater
and polluted air, while the produced gases have the potential to be used as energy carriers.
Despite all the potential advantages of the catalytic pyrolysis, some limitations such as
high parasitic energy demand, catalyst costs and less reuse of catalyst are still remaining.
The recommended solutions for these challenges include exploration of cheaper catalysts,
catalyst regeneration and overall process optimization.
In this contribution, HZSM-5 zeolites were modified by ethylene diamine tetraacetic acid (EDTA) to selectively eliminate the strong external acid sites, and the modified catalysts were then used to conduct the microwave assisted catalytic fast pyrolysis (MACFP) of mushroom waste (MW). Experiment results showed that the modification of HZSM-5 with EDTA had no significant effect on topological structure, and the surface area and total acid sites decreased while the pore volume increased within the modification time regions. Among the modified catalysts, an EDTA treatment for 2 h (labeled as 2H-Z5) performed prominent promise for removing oxygenated chemicals and promoting the aromatic species as well as inhibiting the formation of coke. Simultaneously, the effects of various regeneration steps for deactivated 2H-Z5 catalysts on products distribution were studied, and the highest relative content of hydrocarbons (19.9%) and the lowest coke yield (3.48%) could be obtained under the third regeneration cycle condition.
The amount of plastic waste is growing every year and with that comes an environmental concern regarding this problem. Pyrolysis as a tertiary recycling process is presented as a solution. Pyrolysis can be thermal or catalytical and can be performed under different experimental conditions. These conditions affect the type and amount of product obtained. With the pyrolysis process, products can be obtained with high added value, such as fuel oils and feedstock for new products. Zeolites can be used as catalysts in catalytic pyrolysis and influence the final products obtained.
Thermal degradation of waste plastics in an inert atmosphere has been regarded as a productive method, because this process can convert waste plastics into hydrocarbons that can be used either as fuels or as a source of chemicals. In this work, waste high-density polyethylene (HDPE) plastic was chosen as the material for pyrolysis. A simple pyrolysis reactor system has been used to pyrolyse waste HDPE with the objective of optimizing the liquid product yield at a temperature range of 400°C to 550°C. Results of pyrolysis experiments showed that, at a temperature of 450°C and below, the major product of the pyrolysis was oily liquid which became a viscous liquid or waxy solid at temperatures above 475°C. The yield of the liquid fraction obtained increased with the residence time for waste HDPE. The liquid fractions obtained were analyzed for composition using FTIR and GC-MS. The physical properties of the pyrolytic oil show the presence of a mixture of different fuel fractions such as gasoline, kerosene and diesel in the oil.
The thermal and catalytic processes of converting waste plactics into fuels are promising techniques to eliminate the refuse which otherwise is harmful to the enivironment, and decrease the dependence on fossil fuels. Thermal degradation decomposes plastic into three fractions: gas, crude oil, and solid residue. Crude oil from non-catalytic pyrolysis is usually composed of higher boiling point hydrocarbons. The optimization of conversion parameters such as the choice of catalyst, reactor design, pyrolysis temperature, and plastic-to-catalyst ratio plays a very important role in the efficient generation of gasoline and diesel grade fuel. The use of a catalyst for thermal conversion lowers the energy required for conversion, and the catalyst choice is important for efficient fuel production. The suitable selection of catalysts can increase the yield of crude oil with lower hydrocarbon content. Co-pyrolysis of plastics with coal or shale oil improves crude oil quality by decreasing its viscosity. A large number of publications have appeared on various processes, and continued improvements and/or innovations are expected in the future. Further investigations on the catalytic systems are required in order to advance the field, particularly to enhance the added value of fuels and to minimize the use of energy. This review aims to provide both the highlights of the remarkable achievements of this field and the milestones that need to be achieved in the future.
Abstract An experimental investigation was carried out to assess the effects of using plastic oil in a DI diesel engine. Plastic oil was synthesized from plastic waste, collected from municipal landfill areas, by pyrolysis process. PO25 (25% plastic oil and 75% diesel in volume), PO 50 and PO75 blends were prepared using plastic oil and the reference diesel fuel. In this present work the combustion characteristics of a constant speed diesel engine were studied under variable loading conditions. The results indicate that the thermal efficiency of all blends and neat plastic oil is lower than diesel at all loading conditions. At full load, the peak cylinder pressure, heat release, combustion duration and ignition delay of plastic oil and its blends were higher than that of diesel. The peak pressure of the engine running on neat plastic oil was increased by about 6% but it showed poor thermal efficiency. Based on test results it can be noticed that the combustion characteristics are greatly affected by the physical properties of the fuel.
Due to the depleting fossil fuel sources such as crude oil, natural gas, and coal, the present rate of economic growth is unsustainable. Therefore, many sources of renewable energy have been exploited, but the potentials of some other sources such as plastics waste are yet to be fully developed as full scale economic activity. Development and modernization have brought about a huge increase in the production of all kinds of plastic commodities, which directly or indirectly generate waste due to their wide range of applications coupled with their versatility of types and relatively low cost. The current scenario of the plastic recycling technology is reviewed in this paper. The aim is to provide the reader with an in-depth analysis with respect to the pyrolysis of plastic waste as obtained in the current recycling technology. As the calorific value of the plastics is comparable to that of hydrocarbon fuel, production of fuel from plastic waste would provide a good opportunity to utilize the waste as a better alternative to dumpsites. Different techniques of converting plastics waste into fuel including thermal and catalytic pyrolysis, microwave-assisted pyrolysis and fluid catalytic cracking are discussed in detail. The co-pyrolysis of plastics waste with biomass is also highlighted. Thus, an attempt was made to address the problem of plastic waste disposal as a partial replacement of the depleting fossil fuel with the hope of promoting a sustainable environment.
Individual and mixed plastics consisting of polyethylene (PE), polypropylene (PP), polystyrene (PS), and poly(ethylene terephthalate) (PET) were decomposed at 600 °C in the presence and absence of either calcium oxide (CaO) or calcium hydroxide (Ca(OH)2) under a steam atmosphere. In the presence of CaO, steam cracking was enhanced, increasing gas and liquid yields and decreasing the wax content derived from PE and PP. The production of sublimating substances from PET was also reduced. However, the presence of CaO and steam had a negative influence on PS degradation, reducing the oil yield. In addition, synergistic effects were observed in plastic mixtures. PET enhanced gasification, PS and PET reduced wax production from PE and PP, and mixing all four plastics enhanced oil production in the presence of CaO and steam. Both CaO and Ca(OH)2 enhanced the total gas and oil yield of mixed plastics, achieving a maximum oil yield of 52.2 wt% in the presence of steam. Furthermore, solids were almost completely decomposed at 700 °C, with only 0.2 wt% of residue remaining.
The catalytic activity of a clay catalyst was studied through the degradation of high-density polyethylene (HDPE) using a thermogravimetric (TG) and fixed bed batch reactor and comparison of that with other catalysts (HZSM-5, all-silica MCM-41, Al 2 O 3 , and CaO). The results of TG experiments showed that clay had the same catalytic effects on degradation temperature as Al 2 O 3 and CaO, while HZSM-5 and MCM-41 were able to shift the degradation reaction to lower temperatures. The catalytic degradation results of HDPE with a fixed bed batch reactor showed that the major product over HZSM-5 was fuel gases, all-silica MCM-41 produced the highest fuel oil yield, and the clay catalyst produced the highest yield of liquid products, including wax and oil. Compared with the composition of the gaseous products and fuel oil, that of the clay catalyst was favorable to the formation of alkanes, which indicated that the intermolecular hydrogen transfer reaction was enhanced while the β-scission reaction of radicals was inhibited over a clay catalyst. The results further verified that the catalytic cracking performance of HDPE and the product distributions were related to the textural properties of clay. 1. INTRODUCTION The invention of plastics has brought convenience to people's lives. However, the consumption of plastics has caused great damage to environment because of their low biodegradability. Feedstock recycling, which turns plastic wastes into chemical raw materials or fuels by means of chemical reactions, has been considered the most economically viable and environmentally friendly method for mitigating the consequences of plastics.
USY zeolite was treated by the citric acid. The properties and catalysis of the USY zeolite were studied. The X-ray diffraction has been used to identify and quantify extra framework aluminum (EFAL) in USY zeolite by EFAL extraction using citric acid. The acid character changed depending on the EFAL concentration. The Lewis acid sites can be obtained from the Si/Al ratio. The removing of trace olefins was carried out over kinds USY zeolites with different amount of EFAL. The catalytic performance was correlated with the Lewis acid sites of USY.
Pyrolysis of polypropylene (PP) with an equilibrium fluid catalytic cracking (FCC) catalyst in a stirred reactor was studied to produce “fuel like” hydrocarbons. The effect of process parameters such as degradation temperature, catalyst/polymer ratio (%), carrier gas type and stirrer rate on the condensed product yield and composition were determined.
Reaction products were determined by GC analysis and shown to contain naphthenes, paraffins, olefins and aromatics.
Temperature was shown to influence PP cracking. The addition of the catalyst has improved the economic viability of the process to produce light hydrocarbons. PP pyrolysis showed the maximum condensed product yields at 450 °C and 10% catalyst respectively. Hydrogen as a reactive carrier gas increased the condensed and paraffinic product yield. The results showed that reactive carrier gases can affect on the product yield and composition patently.
Appropriate heat transfer - by stirring - can increase the catalyst efficiency in a stirred reactor.
Waste or contaminated polyolefins were disposed through microwave assisted pyrolysis (MAP) using tires or carbonaceous char as microwave (MW) absorber. High density polyethylene (HDPE) was converted into waxy products when standard heating was employed. However HDPE was converted into a low viscosity fraction by using a very lowMWpower, but a not completed conversion was achieved while PP was always converted into a liquid having a low viscosity. Using an oven containing a system able to fractionate the vapor formed, the residence time of the waxy products in the oven was improved together with the overall pyrolysis efficiency. However the time of the process was strongly reduced with respect to processes using a classical heating. The liquid fraction from HDPE contained linear alkanes and 1- alkenes with negligible formation of branched, cyclic, or aromatic hydrocarbons, while liquid from PP was formed by a mixture of methyl- branched alkane and alkenes, and sometimes aromatics as a function of pyrolysis conditions.
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.
Catalytic pyrolysis of plastic wastes is a promising recycling alternative to the disposal methods currently used for this type of residues (i.e. land filling or energetic valorisation). In order to optimize the yields of compounds obtained with this treatment, the knowledge of the parameters’ influence on the degradation process is of great interest.Pyrolysis temperature and volatiles residence time are the most influential variables in the process, since they affect the primary as well as the secondary reactions.In this work, the pyrolysis temperature effect on the primary and secondary reactions of the thermal and HZSM-5 catalyzed pyrolysis of HDPE is reported and evaluated, in the range 500–800 °C. For this purpose, two different equipments have been used, i.e. a flash coil pyrolyzer (pyroprobe 1000), that allows us to study the primary products, since the extent of secondary reactions can be neglected, and a fluidized bed reactor, where the extent of the secondary reactions is significant.The results of the present study show that 1-hexene is the major product obtained when primary thermal cracking reactions are mainly taking place. However, the major compounds obtained when thermal secondary reactions are present in larger extension are propene at low temperatures and ethene at high temperatures. In catalytic pyrolysis, the effect of HZSM-5 is clearly evident at all temperatures evaluated, increasing the volatile yields in both equipments used. The influence of this catalyst is more significant in the primary cracking reactions showing an increase of the volatile compounds with the degradation temperature. In this case, propene is the main volatile product obtained reaching a yield of 30.6% at the highest temperature evaluated. When the presence of the secondary reactions is evident, using a fluidized bed reactor, the combined effect of generation and possible cracking reactions leads to a low-dependent product distribution on the degradation temperature, propene being the main volatile compound in the range of temperatures studied. It has been observed that branched hydrocarbons are formed mainly from secondary reactions and are quickly destroyed by increasing the temperature. In the zeolite catalyzed pyrolysis the differences between the yields obtained in both equipments are lower than in the thermal case.