Conversion of waste rubber to the mixture of hydrocarbons in the reactor with molten metal

Energy Conversion and Management 50 (2009) 1739–1745

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Conversion of waste rubber to the mixture of hydrocarbons in the reactor with molten metal Marek Stelmachowski * Faculty of Process and Environmental Engineering, Technical University of Lodz, Wolczanska 213, 90-924 Lodz, Poland

a r t i c l e

i n f o

Article history: Received 23 May 2008 Received in revised form 23 February 2009 Accepted 14 March 2009 Available online 10 April 2009 Keywords: Thermal degradation Waste rubber Scrap tires

a b s t r a c t Scrap tires are the source of renewable energy and raw chemical products for the refinery, petrochemical and rubber industry. The results of thermal degradation of waste rubber performed in a new type of a tubular reactor with the molten metal bed are presented in the paper. The melting and degradation processes were carried out in one apparatus at the temperature 390–420 °C. The time of the described conversion process is shorter than the time of catalytic cracking or pyrolysis performed in classical batch or continuous flow reactors. The process was carried out in the inside of the molten metal bed and on its surface. The problems encountered with: the disintegration of wastes, the heat transfer from the wall to the particles, cooking at the walls of the reactor, and mixing of the molten volume of wastes are significantly reduced. Three products: the gaseous (below 14 wt.%), liquid (over 41 wt.%) product and solid residue were obtained during the degradation of waste rubber. The streams of gaseous and liquid products were analyzed by gas chromatography. The gaseous stream contained hydrocarbons from C2 to C8 and the liquid product consisted of hydrocarbons C4–C24. Over 75 mol% of liquid hydrocarbons mixture was the fraction C4–C10. The obtained liquid product may be used in petrochemical and refinery industry for fuel production. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction Scrap rubber (particularly scrap tires) presents an enormous environmental and economical problem. A typical used automobile tire weighs 9–10 kg. Recoverable rubber (about 5.4–5.9 kg) consists of natural (about 35 wt.%) rubber and synthetic rubber (about 65 wt.%). A typical scrap truck tire weighs 18–20 and also contains 50–60% of recoverable rubber. The remaining part consists mainly of carbon black, zinc oxide, sulfur, and steel cord. These components may be also recovered (sulfur compounds have to be removed from gas product). At the beginning of XX century natural rubber cost nearly as much as silver [1]. Therefore, the rubber recycling industry was as old as the rubber production industry and over 50% of used rubber products were reclaimed. However, in 1960s and 1970s only 20% of scrap rubber was recycled and at the end of XX century about 40– 70% of used tires were dumped in many countries. The scrap tire generation in industrialized countries is approximately one passenger car tire equivalent (9 kg) per population and year. It is estimated that 2–3 billion scrap tires are stockpiled in illegal or abandoned piles throughout the United States. However, the statistical data of waste rubber or scrap tires are sometimes incoherent. Their fraction in municipal wastes amounted to 2% in terms of mass in 2000. * Tel.: +48 42 6313721; fax: +48 42 6368133. E-mail address: [email protected] 0196-8904/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2009.03.014

At the end of XX century, rubber production was about 34 million tons in the world [2–4]. A huge amount of produced rubber is used in tires production. It is estimated that 20% of tires have to be recycled every year [5]. Scrap tires dumped in massive stockpiles provide ideal breeding grounds for diseases and may also cause a fire hazard (e.g. in California 1999, in Poland 2003). Dumping and land filling of used tires are the worst method of their utilization but, simultaneously, the most popular one [2,4,6,7] not long ago. The other alternative methods that have been used in tire recycling such as retreating, reclaiming, incineration, grinding have also significant drawbacks and/or limitations but they influence the environment to a lesser extent than dumping [4–6]. The percentage fraction of different utilization methods in recycling of used tires in the USA and the UE are presented in Table 1. The thermodynamic, ecological and economical analysis of different thermal processes points out that the most profitable methods are: gasification, cracking (pyrolysis) and, finally, incineration [4]. Therefore, gasification, pyrolysis and cracking can be considered as viable recycling methods to treat the scrap tires [2–4,8–10] to obtain valuable raw materials and energy. The scientific investigations are generally focused on the pyrolysis of rubber [2–4,11–13]. All the obtained products may be used in other processes or recycled to the degradation process: the pyrolysis gas as a fuel for reactor heating, a solid residue for producing low-grade carbon black and the liquid product – a mixture of hydrocarbons as a stock in petrochemical and refinery industry or rubber industry.

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Table 1 Recycling methods of scrap tires in 2004. Integrated and estimated data from different sources. Method

UE

USA

6

10 Mg Thermal (incineration: in municipal and industrial plants, in the cement kilns, in pulp and paper industry) Dumping, land filling Civil engineering (for example road building) Direct recycling (for example vulcanization) Other methods (for example pyrolysis, cracking and other chemical methods) and export Total

Numerous scientific papers present the results of investigation of pyrolysis and other thermal decomposition methods. Scientists have been dealing with the yield, productivity, and kinetics of the processes. They proposed and investigated a different type of a catalyst and methods of decomposition. Several types of the reactors were invented and patented. The laboratory scale apparatus, pilot and industrial plants are generally based on tubular reactors to perform thermal pyrolysis [2–4,8–12] or fluidized-bed reactors that, as it is considered, have many advantages [12,13]. However, the industrial applications of the invented reactors are rare. It means that the patented solutions are probably technically imperfect and/or their profitability is weak. The main weakness that should be overcome concerns the heat transfer from a heating medium to the particle of disintegrated rubber, because rubber has very low value of thermal conductivity [14]. However, thermal conversion will be profitable only if all components of tires are recycled and the gas product of pyrolysis is desulfurized. The methods of desulfurization of gases are well known and there are also methods of utilization of carbon black [10,15] and zinc oxide [16]. The problem of bad conditions of the heat transfer from a heating medium to the particle of disintegrated scrap tire may be solved by a new technology based on the thermal decomposition of waste in the molten metal bed reactor. This method is known as ‘‘Clementi Process” [17] and several patents are based on this process for the degradation of organic wastes [18–20] and scrap plastics. The paper presents the preliminary results of the investigations of thermal rubber decomposition in the molten metal.

%

6

10 Mg

Japan and China %

0.75

30.7

1.10

43.4

0.95 0.28 0.15 0.31 2.44

38.9 11.5 6.1 12.7 100.0

0.87 0.29 0.14 0.14 2.54

34.3 11.4 5.5 5.3 100.0

106 Mg Data not available

2.2–2.6

tors that have been patented until now [18–20]. It was built from two tubes of different diameters. The new type of the tubular reactor has been patented [21]. The inner (input) tube was placed coaxially in the external (outflow) tube. A mobile piston was located inside the inner pipe for transporting wastes into the molten metal bed. The hold-up time of waste rubber in volume of the liquid metal bed depends on the piston’s speed of shifting. The scheme of the reactor is presented in Fig. 1 and the scheme of the experimental set-up is shown in Fig. 2. 2.3. Measurements and analytical procedures The liquid and gas product samples were analyzed by gas chromatography. The GC analytical conditions are presented in Table 3. The internal normalization method was applied for calculating of concentrations of all components (olefin and paraffin). The Eq. (1) was used to determine the mole fraction of the component ‘‘i”: Ai  fi nC xi ¼ P i A N j j¼1 nC j

fi ¼

Ai nC i AR nC R

 xi  xR

 fj



ð1Þ

ð2Þ

2. Experimental 2.1. Materials Disintegrated waste bicycle tires and flat rubber boards were the stock for the thermal decomposition in the laboratory reactor. The size of the particles was about 5–15 mm depending on the experiment. Thirteen kilograms of the alloy of tin and lead was used to create the molten metal bed. The properties of the alloy are presented in Table 2. 2.2. Experimental set-up The degradation of rubber was carried out in a new type of a tubular reactor with molten metal called ‘‘the tube in the tube”. The construction of the reactor differs from the known basin reac-

Table 2 The composition of the alloy used in the reactor. Fraction of tin (wt.%) Fraction of lead (wt.%) Fraction of impurities (wt.%) Specific gravity (g/cm3) Melting temperature (°C)

59–61 38–40 1 8.5 183–185

Fig. 1. The vertical section of the tubular reactor ‘‘the tub in the tube” for thermal cracking of polymers. (1) The external (outflow) pipe, (2) the inner (input) pipe, (3) the loading port, (4) the device for wastes transporting, (5) the outlet of vapors (total product), (6) the bed of molten metal, (7) the thermocouple (gas phase temperature), (8) the thermocouple (molten metal), and (9) electrical heating.

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M. Stelmachowski / Energy Conversion and Management 50 (2009) 1739–1745 Table 4 The detailed specification of all measurements accuracy.

Fig. 2. The scheme and the photograph of the experimental set-up. (1) The tubular reactor with molten metal, (2) the loading port, (3) the injection piston, (4) the outlet of vapors, (5) the basic cooler of the liquid product, (6) receivers of liquid products, (7) the final cooler, (8) the thermostats, (9) computer system of acquisition data, (10) thermocouples for gas phase and molten metal bed, and (11) electrical heating, A – polymers, B, C – vapor products, D – non-condensable gases to bubble flow meter and to GC, E – cooling water, F – temperature signal to the acquisition system.

Table 3 Gas chromatography analytical conditions. Liquid samples Gas chromatograph Column

Detector Injector Temperature program

Detector temperature Injector temperature Gases

Syringe Sample

Gas samples

GC autosystem XL Perkin–Elmer PE – volatile N931-6393, Supelco SPB-1 25349 L = 75 m L = 60 m ID = 0, 52 mm ID = 0, 53 lm Film 5 lm Film 2, 55 lm FID FID For capillary columns; split 1:50 60 °C, 3 min 35 °C, 5 min 20 °C/min to 100 °C 23 °C/min to 150 °C 100 °C, 5 min 150 °C, 12 min 40 °C/min to 240° 30 °C/min to 210 °C 240 °C, 120 min 210 °C, 15 min 260 °C 240 °C 260 °C 210 °C Hel 2 ml/min Hel 2 ml/min Hydrogen 45 ml/min Hydrogen 45 ml/min Air 450 ml/min Air 450 ml/min 100 lL 10 lL 5 lL 50 lL

where Aj – the peak area, xj – mol fraction, nCj – Carbon number and fj – relative response factor of the component j. The subscript R represents reference component in all the mixtures (heptane). The relative response factors were calculated from the Eq. (2) based on the analysis of the reference mixtures (of 11 components) that were composed from pure hydrocarbons (olefins and paraffins (Fluka) standards). Each mixture was analyzed three times. The estimated error of factors determination was below 0.1%. Nevertheless, the error of gas sample analysis was estimated at 0.5–2% depends on the component; the error of liquid sample analysis for hydrocarbons C5–C10 was below 0.5%, for C11–C16 1.5% and for other below 3.0%. The factors of isomers are nearly the same. The factors for other components, not included to the reference mixtures, were extrapolated because it was impossible to determine experimentally factors for all components (over 200) present in genuine liquid mixtures derived in the runs. The gas flow was measured by bubble flow meter that was calibrated for air at 20 °C. The error of calibration was 0.05%. However, the error of the measure of the gas flow is greater due to

Measurement parameter

Device

Measurement accuracy

Gas flow Liquid samples weight Temperature Gas sample analysis Liquid sample analysis C5–C10 Liquid sample analysis C11–C16 Liquid sample analysis C17–C24

Bubble flowmeter Balance (Metler) K-type thermocouple GC Autosystem XL PE GC Autosystem XL PE GC Autosystem XL PE GC Autosystem XL PE

<1.5% <0.05% ±1 °C 0.5–2.0% <0.5 % <1.5% <3.0%

difficulties in measuring of temperature and the flow in the reaction conditions that changed quickly. It was estimated at 1.5%. The liquid product was measured by taking small samples of condensed hydrocarbons mixture that was weighted. The error of measurement of liquid product mass was 0.05–0.1%. The detailed specification of all measurement accuracies is listed in Table 4. 2.4. The run description Disintegrated rubber particles were put through the loading port to the inner tube and then slowly transported by the piston into the liquid molten alloy to the end of the inner tube. Meanwhile, rubber was melted and decomposed. Products of degradation and un-decomposed components flowed out to the external tube and, next, to the surface of the bed. Further degradation was carried out in the molten metal bed in the external tube and on the surface to give final products – the mixture of hydrocarbons. The vapors flowed out from the reactor and were condensed in coolers. Liquid products were collected in the small receivers what allowed us to measure liquid stream during the time of the experiments. Gaseous product, the mixture of un-condensable hydrocarbons, flowed out from the reactor to the bubble flow meter and, next, through the sampling port to the ventilation system. Samples of liquid product and gaseous product were analyzed by gas chromatography. The temperatures: of the molten metal bed, the gas phase, and the liquid product in the coolers were measured and recorded by the acquisition data system. 3. Results and discussion Results of selected nine experiments performed in three runs (RM1, RM3 and RM4) were performed. The runs RM3 and RM4 consisted of four experiments each. The general profiles and mass balances of all of them are presented in Table 5. Disintegrated flat rubber board (plate) was decomposed in the first (RM1) run. Rubber was cut to particles by size about (5–15)  (2–4)  3 mm. Total mass of the loaded stock was 229.5 g and it was put into the reactor in three portions of 77.00, 100.01 and 120.72 g in very short intervals, one after another. The liquid product was received in the first cooler at the temperature 408 °C of the molten metal bed after 8 min after the time of loading of the first portion. The temperature of the gaseous phase in the reactor was kept between 228 °C and 226 °C during all the experiments. The temperature in the first, basic cooler of hydrocarbons was kept at 23 °C. The liquid product was collected to several small receivers. It enabled to calculate the liquid stream product in time. The distribution of product flow rate and the temperature distribution of molten metal for the run RM1 is presented in Fig. 3. The liquid samples weighted from 5 to 25 g. Non-condensed (in the first cooler) gaseous hydrocarbons were flowed to the second cooler (at T = 15–17 °C), where the light hydrocarbons were obtained. Ten liquid samples are taken for the run RM1 in time. They were analyzed by a gas chromatograph; the results of three of them are presented in Fig. 4

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Table 5 The profile and mass balance of all runs. Symbol of the run

RM1 RM3A RM3B RM3C RM3D RM4A RM4B RM4C RM4D

Mass of the stock (g)

Yield

Temperature of the process (°C)

Total volume of the gas product (Ndm3)

299.5

409–440

14.51 18.99

156.97 (51.43 + 30.19 + 39.33 + 36.02)

425–427 391–431 365–427 379–430

18.12

14.73

153.37 (38.02 + 38.38 + 38.39 + 38.58)

400–403 403 396–403 395–403

Gas product (wt.%)

Liquid product (wt.%)

Residue (wt.%)

5.79

41.04

53.17

14.72

41.28

44.00

43.63

41.64

Fig. 3. The distributions of product flows and temperature of molten metal bed in the run RM1.

Fig. 5. The distributions of temperature and product flows in the time for the run RM3 (a) and RM4 (b).

Fig. 4. The carbon number liquid products distribution for rubber decomposition in the run RM1.

which shows that the composition of liquid product is almost stable in time. Runs RM3 and RM4 consisted of four experiments each and were performed in different way than run RM1. Fig. 5 shows the distribution of temperatures measured in the reactor and distributions of product flows in these runs. The stock consisted of scrap bicycle’s tires. They were cut to particles of size between 5 and 10 mm. The total stock was divided

into four portions, in both runs. When the liquid metal obtained demanded temperature, the first small part of disintegrated rubber particles was put through the loading port into the reactor and, next, transported into molten metal by the piston. The gaseous product was obtained in a few minutes after loading. In further few minutes the liquid product (obtained only from each decomposed portion of rubber) was collected to one receiver for each experiment. When the flow of gas product was decreased and stopped, the temperature of the molten metal bed was changed and a new experiment started. When new conditions were achieved, another part of rubber waste was loaded to the reactor. The runs RM3 and RM4 were very similar. The method of performing of the runs and the amount of the stock material were

M. Stelmachowski / Energy Conversion and Management 50 (2009) 1739–1745

Fig. 6. Carbon number liquid (a) and gas (b) products distributions in the run RM3.

almost the same. The compositions of obtained products at the time of the experiments are very similar too. Figs. 6 and 7 indicate that the carbon liquid (and gas) product distributions for the runs RM3 and RM4 were almost the same. The composition of average liquid product was also very similar in all experiments. It means that the obtained liquid product and the process of degradation were stable regardless of process condition. Fig. 8 presents compositions of average liquid products obtained in three runs. It may be also seen in Table 6. The products obtained from thermal decomposition of waste rubber in the molten metal contained above 95% mol of the most valuable, light fractions of hydrocarbons (called ‘‘gasoline” (C4–C10) and ‘‘diesel” (C11–C16) fraction). It is the great advantage for further usage of the product in petrochemical industry. The received products are generally the mixture of paraffins and olefins. The ratio of paraffins to olefins is presented in Table 6 for liquid products too. The amount of olefins is about 50% greater then paraffin. The products contain also a small amount of aromatic hydrocarbons; however below 5%. Their content was estimated approximately using an IR spectrophotometer (Fig. 9). The degradation process of waste rubber in molten metal is innovative and no detailed results have been published up to now for it. The comparison of obtained results with other published results for pyrolysis of disintegrated scrap tires in tubular or fluidized-bed reactors is very difficult due to completely

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Fig. 7. Carbon number liquid (a) and gas (b) products distributions in the run RM4.

Fig. 8. Carbon number average liquid products distributions in all runs.

different conditions for the considered processes. Nevertheless, the compositions of liquid products obtained in different processes and yields of the gas and liquid products may be compared. The basic difference between the liquid products lies in the fact that the

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Table 6 Fraction composition of the average liquid products. Run symbol

Fraction composition of the liquid product RM1

RM3

RM4

C4–C10 (mol%) C11–C16 (mol%) C17–C24 (mol%)

65.31 22.94 6.75

71.57–72.03 20.18–20.92 2.45–2.80

69.93–73.85 18.61–22.97 1.90–2.91

Total paraffins and olefinsa (mol%) Paraffins (mol%) Olefins (mol%)

>95 29.96 65.04

26.06–30.65 62.43–68.92

35.05–37.73 57.27–59.31

n-Paraffins (mol%) 1-Olefins (mol%) Iso-paraffins (mol%) iso-olefins (mol%)

12.96 21.39 17.01 43.64

18.45–23.71 55.58–63.78 7.63–8.85 5.14–7.89

15.59–21.55 36.80–41.91 15.00–20.10 17.39–20.46

Total aromatic hydrocarbons (mol%)

<5

a

With cycloalkanes.

Fig. 9. The representative FTIR analysis of the average (mixed) liquid product obtained from all the runs.

content of aromatic hydrocarbons is definitely lower for the process carried out in the molten metal than for processes performed in the fluidized-bed reactors or other types of tube reactors. Only

Williams and Brindle [12] reported that the content of aromatic hydrocarbons may be small for uncatalysed pyrolysis. However with presence of catalyst, (zeolites) they have observed an increase of the amount of aromatic hydrocarbons in liquid too. Other researches [2,3,11,12,22,23] usually notice a higher content of aromatic hydrocarbons in the pyrolysis oil; particularly, if the process was performed with the presence of zeolites as catalysts. The shorter reaction time (of rubber degradation) and intensive heat transfer to particle of waste from heating medium, lower temperature of gas phase and lower temperature of liquid phase and absence of catalyst are the cause of differences between the results. The yields of the gas and liquid products for processes performed at similar temperatures were almost the same for thermal pyrolysis of waste rubber. Zeolites and higher temperatures cause the increase of gas product yield. However, the liquid product is the most demanded one because it is more valuable and may be recycled to fuel or rubber production. Utilizing and storing (transporting) of great amount of the gas product obtained in large industrial plants may be more difficult. The comparison of the results received by different scientists for thermal and pyrolysis and catalytic cracking of waste rubber is showed in Table 7. The comparison of pyrolytic oil with crude oil is presented e.g. by Benallal et al. [24].

Table 7 Comparison of products yield and composition of liquid product derived from different pyrolysis processes of waste rubber. This work (mol%)

Rodriguez et. et. al. [3]b (% of GC peak area)

Wiliams and Brindle [11]c (wt.%)

Li et. al. [22]d (wt.%)

C4–C10

65.3–73.9

C11–C16

18.6–22.9

C17—C24 Total (alkanes and alkenes)

1.9–6.8 >95a

59.2–19.8

95–84

77–71

Aromatic hydrocarbons (total)

<5

34.7–75.6

4.2 7.5–6.3 15.6–7.1

23–29

Yield (wt.%) Gas product

Liquid product

a b c d e

5–15

41–44

8–18

5–38

6.1 15–19 16–23 56 43–35 39–34

With cycloalkanes. Thermal pyrolysis at 300 and 600 °C. Without catalyst at 500 °C, with zeolite ZSM-5 as a catalyst and Y-zeolite at 430 and 600 °C. Pyrolysis in rotary kiln at 450 and 600 °C. At 500: thermal pyrolysis, with HZMS-5 catalyst and with HY catalyst.

13–18 43–45

Olazar et. al. [23]e (wt.%) 47.0 38.8 11.1 12.5 8.7 2.8 59.5 47.5 13.9 21.3 38.5 77.3 2.5 19.3 2.3 Not specified

M. Stelmachowski / Energy Conversion and Management 50 (2009) 1739–1745 Table 8 The content of heavy metals in the mixed, average liquid product. Metal

Sn

Pb

Zn

Ni

Cr

Content (mg/kg) Error (mg/kg)

29.7 ±0.2

23.4 ±0.2

16.4 ±0.1

0.44 ±0.01

1.23 ±0.01

The conversion of waste rubber, described in this paper, was performed in the molten, liquid metal alloy (consisted of tin and lead) in the temperature 400–430 °C. Tires contain zinc oxide, too. Therefore, it is immensely essential to know the content of selected heavy metals in the liquid product. The content of zinc, tin, lead, chromium, and nickel was analyzed by AAS spectrometry (Perkin Elmer AAS). The results of their content in average liquid product and the accuracy of the analysis are presented in Table 8. As it can be seen, the content of heavy metals is not too high. No detailed results for this process have been published up to the present moment. Newborough et al. [17] reported that the product (monomers) of thermal PMMA (poly-methyl-methacrylate) depolymerisation in molten lead ‘‘had contained small but significant quantities of lead”. However, Clementi Process described by Newborough (based on Spanish patent [18]), had been carried out at the temperature of 550 °C, in basin reactor with large surface of molten metal what is extremely essential for lead evaporation. The process, described in this paper was carried out at 380– 430 °C and the temperature of gas phase flowing out of the reactor was kept between 220 and 250 °C. Furthermore, the surface of metals (lead and tin) evaporation is very small because the molten alloy bed is high (the reactor is vertical) and the diameter of the reactor is small. The derived liquid products are fluid in ambient conditions; however, black carbon is suspended in a liquid hydrocarbon mixture. Therefore, before further utilization of the liquid product has to be clarified. Solid (residue) product has not been analyzed yet. It was collected from the surface of the molten metal after experiments. Its yield of is about 42–52 wt.%. The recovering methods of char, zinc oxide and steel are known. It is vital for the industrial applications of all methods and processes based on thermal degradation of scrap rubber (tires). 4. Conclusions The results of the investigation of the new tubular reactor with molten metal bed are promising. The thermal decomposition of rubber wastes in molten metal has many advantages. The process is fast. The problems with the heat transfer resistance between the particles of wastes and the heating medium is overcome. Therefore, the cocking processes are minimized (no cock was observed on the walls of the reactor). The liquid product contains mainly gasoline fraction of hydrocarbons. The hold-up time of wastes in the reactor and the reaction time are shorter than in other tube reactors applied for rubber pyrolysis. No catalyst is used in the process. The temperature of the gas phase in the reactor is not too high (below 230 °C). Therefore the amount of the recombination reactions products is minimized and the fraction of aromatic hydrocarbons is very small. The content of heavy metals is small, too, that means that the process temperature and the surface of the liquid, molten alloy in the reactor were proper and the metal particles and metal ions have not been transferred to the liquid products. Nevertheless, thermal cracking processes of rubber in the reactor with molten metal bed (as other thermal processes) will be costeffective only if all of obtained products: not only hydrocarbons

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carbon black, zinc oxide and steal as well may be recycled and used for producing different semi-products. Up to 10% of recovered energy (gas product) may be used for the disintegration of waste rubber (heating reactors). It is supposed that, in the industrial-scale even whole scrap tires could be converted (without their disintegration) in the molten metal. No catalyst and no stirring of the reaction mixture is needed. Therefore the process performed in the molten metal bed may be probably more profitable than other methods due to energy saving. Acknowledgements This work was done as a part of the project ‘‘Thermo-catalytic degradation of waste plastics and rubber” supported by Ministry of Science and Higher Education: Project number 3 T09D 035 27.

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