Pyrolysis of Polyethylene in a Fluidized Bed Reactor
TL;DR: In this paper, a fluidized sand bed reactor was used to study the production of gases from polyethylene (HDPE) at five nominal temperatures (ranging from 500 to 900°C).
Abstract: A fluidized sand bed reactor was used to study the production of gases from polyethylene (HDPE) at five nominal temperatures (ranging from 500 to 900°C). Both HDPE primary decomposition and wax cracking reactions take place inside the reactor. Yields of 13 pyrolysis products (methane, ethane, ethylene, propane, propylene, acetylene, butane, butylene, pentane, benzene, toluene, xylenes, and styrene) were analyzed as a function of the operating conditions. The results are compared with the data obtained by pyrolysis of HDPE in a Pyroprobe 1000, where secondary wax and tar cracking is small. Correlations between the products analyzed with those of methane are discussed.
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TL;DR: In this paper, the main thermochemical routes for the valorization of waste polyolefins to produce chemicals and fuels are analyzed for the purpose of producing more sustainable waste management policies.
Abstract: The continuous increase in the generation of waste plastics together with the need for developing more sustainable waste management policies have promoted a great research effort dealing with their valorization routes. In this review, the main thermochemical routes are analyzed for the valorization of waste polyolefins to produce chemicals and fuels. Amongst the different strategies, pyrolysis has received greater attention, but most studies are of preliminary character. Likewise, the studies pursuing the incorporation of waste plastics into refinery units (mainly fluid catalytic cracking and hydrocracking) have been carried out in batch laboratory-scale units. Other promising alternative to which great attention is being paid is the process based on two steps: pyrolysis and in-line intensification for olefin production by means of catalytic cracking or thermal cracking at high temperatures.
498 citations
TL;DR: In this article, the authors provide an in depth analysis regarding the recovery, treatment and recycling routes of plastic solid waste (PSW), as well as the main advantages and disadvantages associated with every route.
Abstract: Polymers are the most versatile material in our modern day and age. With certain chemicals and additives (pigments, concentrates, anti-blockers, light transformers (LTs), UV-stabilizers, etc.), they become what we know as plastics. The aim of this review is to provide the reader with an in depth analysis regarding the recovery, treatment and recycling routes of plastic solid waste (PSW), as well as the main advantages and disadvantages associated with every route. Recovery and recycling of PSW can be categorized by four main routes, i.e. re-extrusion, mechanical, chemical and energy recovery. Re-extrusion (primary recycling) utilizes scrap plastics by re-introducing the reminder of certain extruded thermoplastics (mainly poly-α-olefins) into heat cycles within a processing line. When plastic articles are discarded after a number of life cycles, mechanical recycling techniques present themselves as a candidate for utilizing a percentage of the waste as recyclate and/or fillers. Collectively, all technologies that convert polymers to either monomers (monomer recycling) or petrochemicals (feedstock recycling) are referred to as chemical recycling. The technology behind its success is the depolymerization processes (e.g. thermolysis) that can result in a very profitable and sustainable industrial scheme, providing a high product yield and a minimal waste. Nevertheless, due to their high calorific value and embodied energy, plastics are being incinerated solely or in combination with municipal solid waste (MSW) in many developed countries. This review also presents a number of application and technologies currently being used to incinerate plastics. Cement kilns and fluidized beds are the two most common units used to recover energy from PSW or MSW with high PSW content. It is concluded that, tertiary (chemical methods) and quaternary (energy recovery) are robust enough to be investigated and researched in the near future, for they provide a very sustainable solution to the PSW cycle.
384 citations
07 Jun 2006
TL;DR: In the pyrolysis process of PP the intramolecular radical transfer is preferred to the intermolecular one, thus the low oligomer formation predominates as discussed by the authors.
Abstract: hydrogen, transferring the radical site to a tertiary carbon atom of an other macromolecule or that of its own chain. The intermolecular radical transfer of 2 is followed by the β-scission reaction drawn in Scheme 12.3, resulting in a vinyl terminal group 3 and reproducing 2. This chain reaction produces n-propyl and 2-methylvinylene terminal groups in the fragments, which can be isoalkanes, 1-isoalkenes (oligomers) and α, ωisoalkadienes. The series of peaks above pentamer represent these fragment compounds in the pyrogram of PP in Figure 12.2. The considerably superior yield of trimer, tetramers and pentamers to that of the larger oligomers indicates the contribution of another reaction. Intramolecular radical transfer of a secondary macroradical to a tertiary carbon atom of its own chain leads to these oligomers, drawn in Scheme 12.5. The two possible directions of β-scission explain the occurrence of n-pentane among the wholly isoalkanoic products of PP. In the pyrolysis process of PP the intramolecular radical transfer is preferred to the intermolecular one, thus the low oligomer formation predominates. Consequently the pyrolysis oil of PP is much more volatile than that of PE, decomposing mainly through intermolecular radical transfer. The difference of the backbone structure of the products of these polymers is more important from the point of view of fuel properties. The isoalkanoic structure of PP is held in the thermal decomposition products, in this way the octane number of the pyrolysis oil might be high. In a batch reactor [26] the gasoline fraction (44–220◦C) of the pyrolysis oil obtained from 100 g PE and PP mixture at 440◦C has an octane number of 88.6 with 5.6 wt% aromatic content, and the diesel oil (151–347◦C boiling point range) had 56◦C ignition temperature, −4◦C cloud point and a cetane index of 59.5. Pyrolysing waste PP in an 1 L autoclave at 430◦C for 20 min
348 citations
Cites background or methods from "Pyrolysis of Polyethylene in a Flui..."
...612 6 Results from Ateklab Free-Fall Reactor . . . . . . . . . . . . . . . 613 6.1 LDPE Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 613 6.1 Polystyrene Results . . . . . . . . . . . . . . . . . . . . . . . . . 617 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 621...
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...The catalytic mechanism over acidic catalysts has been reviewed by Bukens [16]....
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...Vrije Universiteit Brussel (V.U.B.), Brussels, Belgium ABBREVIATIONS ABS acrylonitrile–butadiene–styrene APP atactic polypropylene ASR automobile shredder residue EVA ethylene vinyl acetata HDPE high-density polyethylene HIPS high impact polystyrene LDPE low-density polyethylene Low (LD)PE low-molecular-weight polyethylene MSW municipal solid waste...
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...Generally over clays and pillared clays higher liquid yield values are reached than over zeolites [13, 16, 17]....
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...In the 1990s numerous studies have been carried out using as catalysts silica–alumina [5–7], zeolites [6–11], zeolite-based commercial cracking catalysts [12–14], MCM mesoporous materials [15] or clays and pillared clays [16, 17] Besides the direct catalytic conversion of plastic, the subsequent in situ catalytic conversion of products of noncatalytic thermal degradation was also researched [18, 19]....
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TL;DR: In this paper, the influence of pyrolysis temperature from 500 to 700°C on the yield and composition of derived products was analyzed for low density polyethylene (LDPE) derived oils and waxes.
Abstract: Pyrolysis of plastic waste has been proposed as a tertiary or feedstock recycling route where the plastic waste materials are processed back to produce basic petrochemicals that can be used as feedstock to make virgin plastic or refined fuels. The detailed analysis of the derived products from the pyrolysis of plastics provides data on the suitability of the process and the influence of process conditions on the compatibility of the feedstock produced with the conventional petroleum feedstock. Low density polyethylene (LDPE) is a major component of municipal solid waste and this paper describes the influence of pyrolysis temperature from 500 to 700°C on the yield and composition of the derived products. The main gases produced from the pyrolysis of LDPE were hydrogen, methane, ethane, ethene, propane, propene, butane and butene. There was a dramatic increase in gas yield with increasing temperature of pyrolysis. Analysis of the derived oils and waxes showed that the pyrolysis of LDPE gave a mainly aliphatic composition consisting of a series of alkanes, alkenes and alkadienes which showed a decrease in concentration as the pyrolysis temperature was increased. The oil showed an increase in aromatic composition with increasing temperature of pyrolysis and at 700°C significant concentrations of single ring aromatic compounds and polycyclic aromatic hydrocarbons were detected. The derived oil and wax have great potential to be recycled back into the petrochemicals industry as a feedstock for the production of new plastics or the production of refined fuels.
337 citations
Abstract: Plastics have become an indispensable ingredient of human life. They are non-biodegradable polymers of mostly containing carbon, hydrogen, and few other elements such as chlorine, nitrogen etc. Rapid growth of the world population led to increased demand of commodity plastics. High density poly ethylene is one of the largest used commodity plastics due to its vast applications in many fields. Due to its non bio degradability and low life, HDPE contributes significantly to the problem of Municipal Waste Management. To avert environment pollution of HDPE wastes, they must be recycled and recovered. On the other hand, steady depletion of fossil fuel and increased energy demand, motivated the researchers and technologists to search and develop different energy sources. Waste to energy has been a significant way to utilize the waste sustainably, simultaneously add to meet the energy demand. Plastics being petrochemical origin have inherently high calorific value. Thus they can be converted back to useful energy. Many researches have been carried out to convert the waste plastics into liquid fuel by thermal and catalytic pyrolysis and this has led to establishment of a number of successful firms converting waste plastics to liquid fuels. This paper reviews the production and consumption HDPE, different methods of recycling of plastic with special reference to chemical degradation of HDPE to fuel. This also focuses on different factors that affect these degradations, the kinetics and mechanism of this reaction.
318 citations