Rubber waste pyrolysis

Likewise, another company whose technology may be based on a patent described in this chapter is T.R. Environtech Co. Ltd (www.trrecycling.co.kr). A Korea-based firm, their website mentions that their technology is based on the work performed by the person who some years earfier invented Patent US 4,118,282. However, even though the company claims to have a process for the low temperature pyrolysis for tyre waste and rubber waste , the website does not mention microwaves as the heat somce for the process. 

Thermal processes are mainly used for the feedstock recycling of addition polymers whereas, as stated in Chapter 2, condensation polymers are preferably depolymerized by reaction with certain chemical agents. The present chapter will deal with the thermal decomposition of polyethylene, polypropylene, polystyrene and polyvinyl chloride, which are the main components of the plastic waste stream (see Chapter 1). Nevertheless, the thermal degradation of some condensation polymers will also be mentioned, because they can appear mixed with polyolefins and other addition polymers in the plastic waste stream. Both the thermal decomposition of individual plastics and of plastic mixtures will be discussed. Likewise, the thermal coprocessing of plastic wastes with other materials (e.g. coal and biomass) will be considered in this chapter. Finally, the thermal degradation of rubber wastes will also be reviewed because in recent years much research effort has been devoted to the recovery of valuable products by the pyrolysis of used tyres. 

While many studies have been carried out aimed at the feedstock recycling of rubber wastes by pyrolysis and hydrogenation processes (see Chapters 5 and 7), little information is found on the catalytic cracking and reforming of rubber alone. Larsen35 has disclosed that waste rubber, such as used tyres, can be degraded in the presence of molten salt catalysts with properties as Lewis acids, such as zinc chloride, tin chloride and antimony iodide. The decomposition proceeds at temperatures between 380 and 500 °C to yield gases, oil and a residue, in proportions similar to those obtained by simple thermal decomposition. 

The most commonly used rubber in tyre manufacture is styrene-butadiene copolymer containing about 25 wt% of styrene. The presence of a high concentration of double bonds in the rubber backbone makes the alternative of degrading rubber wastes by treatment in hydrogen atmospheres very attractive. Moreover, because used tyres contain significant amounts of sulfur, hydrogenation also favours the removal of this undesired element as H2S, which allows oils to be produced with lower S content than those derived from tyre pyrolysis. 

Enerco, Inc. (Yardley, Pennsylvania) has a 600 tire/d demonstration pyrolysis plant located in Indiana, Pennsylvania. The facility operated 8 h/d, 5 d/wk for six months. The process involves pyrolysis in a 5.41/d batch-operated retort chamber. The heated tires are broken down to cmde oil, noncondensable gases, pyrolytic filter, steel (qv), and fabric waste. In this process, hot gases are fed direcdy to the rubber rather than using indirect heating as in most other pyrolyses. The pyrolysis plant was not operating as of eady 1996. 

R. Cypres and B. Bettens, Production of benzoles and active carbon from waste rubber and plastic materials by means of pyrolysis with simnltaneous post-cracking. In G. L. Ferrero, K. Maniatis, A. Buekens and Bridgwater A. V. (eds), Pyrolysis and Gasification, Elsevier Applied Science, London, 1989. 

A considerable number of reports regarding the formation of compounds that may represent a health hazard are related to the formation of polycyclic aromatic hydrocarbons (PAHs) during industrial pyrolysis processes (recycling of waste, incineration, etc.). This interest is particularly geared toward the study of polyolefins pyrolysis and synthetic and natural rubber pyrolysis. The formation of PAHs during polyethylene pyrolysis has been reported frequently in literature [6, 12] and is further discussed in Section 6.1. The formation of PAHs during tire pyrolysis is also of considerable concern. The concentrations of some components in the oils generated from the pyrolysis of used tires as a function of temperature are indicated in Table 5.3 1 [13]. 

Pyrolysis processes generate oil or a limited quantity of a rather rich gas (Table II), which can be purified, stored and conveyed over a large distance. Co-disposal of plastics, rubber and waste oil is often possible. On the other hand the condensa-ting liquors are grossly polluted and the pyrolysis coke is difficult to valorize. The pyrolysis process is complicated by the necessity of indirect heat transfer and the condensation of tar often leads to operating problems. 

If the PVC content of the plastic waste is low, the hydrogen chloride produced can be absorbed either directly in the fluidized bed to which calcium oxide or magnesium oxide is added, or in a separately connected fluidized bed. This method has proved satisfactory, at least for the absorption of hydrogen fluoride in the pyrolysis of PTFE-containing plastic wastes and for hydrogen sulfide in the pyrolysis of rubber. 

A pyrolysis system has been developed to recover useful material from scrap tires. An actual plant was constructed in 1979 The plant will be on a trial for a year to demonstrate that the equipment of the plant satisfies the test specifications and that the recovered carbon black has the quality demanded by the rubber industry. After passing one year tests, it will be put into commercial operation. This project is a full scale recycling for scrap tires supported by public agencies which also supported the pulverizing plant in Osaka. It is expected that the completion of the project will open a new course for recycling and disposal of waste. 

Likewise, Orr et al.29,30 have explored the possible use of tyre pyrolysis oil as a solvent for coal liquefaction. The potential of this alternative was demonstrated by the fact that coal-TPO mixtures were transformed with higher conversion than when coal was reacted directly with ground waste rubber tyres. It is proposed that the polyaromatic compounds present in the TPO favour coal dissolution during liquefaction. Treatment of coal-TPO mixtures (50/50%) at 430 °C under 68 atm of cold-hydrogen pressure in the presence of a Mo catalyst led to a high coal conversion in just 10 min of reaction. From electron probe microanalysis of the coal particles after the reaction, the authors conclude that TPO favours the catalyst dispersion and its contact with coal, which results in enhanced coal conversion. 

Silica particles were prepared by the pyrolysis-cum-water vapor treatment of waste green tires and used as a filler in fresh SBR rubber blends (Ivanov and Mihaylov, 2011). Pyrolysis was carried out by gradually heating tires between 300°C and 1000°C and continuously purging air, smoke gases, carbon dioxide, and nitrogen with the addition of vapor from 0% to 100%. The final product was... 

A number of methods [11,13-17] have been applied in an attempt to solve the problem and to find more effective ways of tire rubber recycling and waste rubber utilization. These methods include retreading, reclaiming, grinding, pulverization, microwave and ultrasonic processes, pyrolysis, and incineration. Processes for utilization of recycled rubber are also being developed, including the use of reclaimed rubber to manufacture rubber products and thermoplastic-rubber blends and the use of GRT to modify asphalt and cement. 

Computational Results Equilibrium thermochemical calculations (using STANJAN [35] and SOLGASMIX [36] codes) of a mixture of nonplastic and plastic surrogate solids were carried out under conditions of pyrolysis and combustion see Table 15.9. A large thermodynamic data file compiled from JANAF tables is used in these codes [37]. The nonplastic material is assumed to be cellulose while the plastic material may contain any or all of the following plastics polyethylene, polyvinyl chloride, polystyrene, polypropylene, polyethylene ter-aphathalic, nylon, latex in the form of rubber, polyurethane, and acetate. Cellulose represents the organic portion of the waste such as paper and cardboard. 

Recycl Blacks. The pyrolysis of carbon black containing rubber goods has been promoted as a solution to the accumulation of waste tires. In the processes in question, tires are pyrolyzed in the absence of oxygen, usually in indirect fired rotary kiln-type units. The mbber and extender oils are cracked to hydrocarbons which are collected and sold as fuels or petrochemical feedstocks. The gaseous pyrolysis products are burned as fuel for the process. Steel tire cord is removed magnetically and the remainder of the residue is milled into a pyrolysis black. This contains the carbon black, silica, and other metal oxides from the rubber and some newly created char. Typically these materials have 8-10% ash, and contain... 

Microwave heating is an appropriate tool for recycling polymer waste. For example, it can be applied to separate metal from polymer/metal laminates by pyrolysis, to depolymerize polyamide and poly(ethylene terephthalate) by solvolysis, or to devulcanize rubber (see Table 1.6). Detailed information on this topic is available in Ref. [19]. 

At pyrolysis temperatures (e.g., 800-1,200 °C) waste rubber (usually tyres that are either whole or shredded) can be reduced down to gas, oil, char, metal and inorganic fractions that, with further processing, can then be used as energy sources, or additives and starting materials for other products. 

Some studies have looked at producing useful products, effectively fillers, from waste rubber by using methods that use a partial pyrolysis approach. Silica is being used as a part replacement for carbon black as a filler in the production of green tyres . As this practice increases, there will be a corresponding increase in the total recoverable inorganic fraction from waste tyres, and so this recycling route could become more attractive. Examples of partial pyrolysis processes are described below. 

Scrap butyl rubber inner tubes represent a source of waste rubber that is easily identified and segregated. Workers in Pakistan [19] have subjected these items to a batch non-oxidative pyrolysis process under both uncatalysed and catalysed conditions. In both cases atmospheric pressure was used, with zinc oxide being used as the catalyst in the catalysed version. The resultant product in both cases consisted of a hydrocarbon mixture and carbon black. The effects of temperature, amount of zinc oxide and reaction time on the yield of the products were studied. The hydrocarbon fraction was assessed as a fuel by carrying out tests such as flash point and aniline point. 

This type of recycling process to generate valuable by-products is not exclusive to waste rubber and can be applied to any hydrocarbon-based polymers. These processes have some similarities to the pyrolysis routes in that they result in the formation of low-molecular-weight molecules. The main difference is often that the pyrolysis process takes place in the absence of oxygen, whereas it can be present in these processes. 

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