Influence of the Process Conditions on Yield, Composition, and

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Influence of the Process Conditions on Yield, Composition, and Properties of the Products Derived from the Thermolysis of Scrap Tire and Used Engine Oil Blends Arunas Jonusas* and Linas Miknius Department of Organic Chemistry, Kaunas University of Technology, Radvilėnų pl. 19, LT-50254 Kaunas, Lithuania ABSTRACT: The thermolysis of waste blends, consisting of shredded scrap tires and used motor oil, was carried out in a semicontinuous distillation reactor. The aim of this research was to investigate the influence of mixture composition, feedstock chopping degree, and pressure on the yield, composition, and properties of thermolysis products, i.e., oil, char, and gas. The distribution of the thermolysis products derived from Tire/Oil (T/O) mixtures was 44.8−60.2% (w/w) of liquid, 22.1−31.6% (w/w) of char, and 17.6−24.6% (w/w) of gas. The highest yield, 60.2% (w/w), of desired product (oil) was obtained from the finer feedstock (Type 1), which was mixed with engine oil in the ratio of 2:2 and thermolyzed at elevated pressure (40 bar). The results of the chemical composition of liquid thermolysis products revealed three dominant classes of hydrocarbons: arenes (21.84−34.48%, w/w), alkenes (21.06−34.54%, w/w), and alkanes (18.36−38.66%, w/w). The liquid products derived from Tire/Oil mixtures can be used as liquid fuels due to their high heating value (41−45 MJ/kg), low ash (0.01−0.11%, w/w), and sulfur (0.58−0.90%, w/w) content. Besides, 19.0−48.0% (w/w) of such liquids are in easily distillable fractions with a boiling range of 50−200 °C that comprise commercial gasoline, and 41.0−52.0% (w/w) boil at a temperature of 200−360 °C that is a typical range of a diesel fraction. The gaseous thermolysis product of the Tire/Oil mixture is composed of the lightest alkanes (over 41%, v/v), hydrogen (11.84−14.72%, v/v), carbon oxides (over 3.5%, v/v), and butenes (about 4%, v/v) as the main alkenes. The elemental analysis of residual char showed carbon as the main element; however, a significant share (13.4−19.8%, w/w) is taken by inorganic impurities. The average calorific value of the thermolysis char is 31 MJ/kg. This work could be considered as a contribution for strengthening and encouraging the blends of waste tires and used oil thermolysis for the production of liquid fuels, which could be used in industrial furnaces or can be refined as a crude oil for manufacture of conventional petroleum fuels and chemicals.

1. INTRODUCTION The increasing number of motor vehicles in the world is a major concern, because, every year, servicing this type of transport leaves a huge amount of various waste materials. Some of these are nonbiodegradable waste products and have a detrimental impact on humans and the environment. Therefore, waste utilization is a major issue to maintain a cleaner and healthier environment.1−3 According to the recent statistics, each year a worldwide accumulation of waste tires exceeds 20.2 million tons (over 1 billion units) and over 24 million tons of used engine oils are collected.2,4 The U.S. Rubber Manufacturers Association estimated that the U.S. is one of the largest producer of ELTs (end of life tires) in the World and generated about 3.824 million tons of the tire waste in 2013.5 Statistical data also shows that the U.S. is one of the leaders not only by the amount of the ELTs, but also because of a pool of more than 6.3 million tons of waste engine oil.6 During this period in the European Union (EU), the quantity of worn out tires and used motor oil was lower than in the U.S. and comprised a little more than 3.4 and 5.2 million tons, respectively.7,8 The ever growing amount of end-of-life tires and used oil is caused by an expansion of the vehicle manufacture industry, which, in turn, is dependent upon world population and economic growth as well as social welfare.9 A tire is a complex structure of a number of materials, such as various types of synthetic and natural rubber, carbon black, © XXXX American Chemical Society

steel, polyester, nylon, silica, and over 40 more different kinds of chemicals, such as waxes, oils, and pigments, that make the waste virtually nonbiodegradable.4,9,10 Waste automotive engine oil (WAO), such as scrap tires, is environmentally hazardous, because it may contaminate groundwater and soil, if discharged to the environment, and cause air pollution, if burnt as a low-grade fuel.1,11,12 Besides, it is a high-volume waste that is difficult to regenerate and dispose of because of a number of undesirable components: soot, polycyclic aromatic hydrocarbons (PAHs), and chlorinated paraffins, polychlorinated biphenyls (PCBs), and metal containing compounds that are incorporated as oil additives.13−17 There are a number of studies related to scrap tire and waste oil treatment methods. Some alternative solutions how to manage used tires are retreading, recycling, incineration, or reuse in civil engineering applications (i.e., playground surfaces, rubber roofs, etc.).18 Conventional treatment processes for waste engine oil are incineration, combustion, solvent refining, and hydro-refining; however, they are becoming less practicable as concerns over environmental pollution and additional sludge disposal are recognized.13,19,20 However, a more attractive method of tire, motor oil, or T/O mixture reprocessing is their thermal decomposition to lower molecular weight products that Received: July 6, 2015 Revised: September 24, 2015

A

DOI: 10.1021/acs.energyfuels.5b01540 Energy Fuels XXXX, XXX, XXX−XXX

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Energy & Fuels have energetic value or other potential application.15 There are several known tire rubber depolymerization, waste oil, and T/O blends thermal cracking methods (low/high-temperature pyrolysis/thermolysis, steam reforming, microwave destruction, gasification, and etc.), which are not worldwide spread for a number of reasons.3,9,21,22 The thermolysis techniques have recently shown great promise as an economic and environmentally friendly disposal method for waste tires and oils.23,24 During the low temperature thermolysis process, the waste material is thermally cracked at a temperature lower than 600 °C and decomposed to three different products, i.e. thermolysis oil and gas, which can be used directly as fuels or can be refined as a crude oil for manufacture of conventional petroleum fuels and chemicals,21,25,26 and the char that can be used as a substitute for activated carbon.27,28 Most interest is devoted to the liquid product because of its convenient handling, transportation, high energy density, and possibility to upgrade it by petroleum refining processes. A number of technologies have been proposed for tire and oil thermolysis. Most of them are operated at atmospheric pressure and only few under vacuum or elevated pressure.29−31 Previous our research showed that the higher pressure and chopping degree had a positive effect on the yield of liquid product from tire thermolysis.9 Copyrolysis with waste lubricant oil (WLO) produced more oil than pyrolysis of tires alone. Although the researchers concluded that the addition of WLO did not enhance the degradation of tires during pyrolysis, copyrolysis oils contained a higher amount of lighter fractions than that of commercial diesel. They concluded that the addition of scrap tires into WLO increased the degradation of heavy fractions in WLO.3,32 The objective of the present work is to investigate the effect of the composition of T/O blends mixed in different ratios, chopping degree (fineness of raw material), and pressure on yield as well as the properties and composition of thermolysis products. In the present investigation, the mixtures of two fractions of scrap tires with waste engine oil, which also acted as a heat conductor and distributor in the reactor, were thermolyzed under atmospheric and elevated pressure. For comparison, scrap tires and waste engine oil were thermolyzed individually under the same conditions.

Table 1. Parameters of Solid Feedstock Feedstock designation by different chopping degree Type 1

Parameter Tire type Length, mm Width, mm Height, mm Weight of specimena, g Length × width, mm2 Specimen surface areab, mm2 Specific surface area, mm2/g

Type 2

Passenger car tires 50 50 25 50 10−15 10−15 9.6302 18.4820 1250 2500 4375 7500 454.31 405.80

a

Average weight of 10 specimens. bA specimen surface area was calculated as the average area of the biggest and the smallest specimens., i.e. 10 and 15 mm.

Table 2. Composition of the T/O Mixtures T/O mass ratio

Solid feedstock Type 1 Type 2 a

2:0 2:0

2:1a 2:1

2:2 2:2

0:2 0:2

Value of one part is 0.5 kg.

Table 3. Proximate Analysis of Scrap Tires and Waste Engine Oil Feedstock designation Fraction of tire Property Moisture (mg/kg) Volatile substancesa (%, w/w) Fixed carbon (%, w/w) Heating value (MJ/kg) C (%) H (%) N (%) Ob (%) S (%) Ash (%, w/w) Metal (mg/kg) Cd Cr Cu Pb Zn Ni Fe

2. MATERIALS AND METHODOLOGY In this research, the feedstock was mixtures of waste car tires and used engine oil, which have been made by mixing tires of two different fractions (Table 1) with an appropriate amount of oil (Table 2). Both fractions of tire were obtained by chopping passenger car tires, which were randomly taken, into 50 × 25 × 10/15 and 50 × 50 × 10/15 mm pieces, respectively. Then each fraction of different brands of tires was mixed in equal parts by mass such that the chemical composition of both fractions would be the same. The mixing procedure of solid fractions was performed in a rotating drum machine for 30 min. Their designations are shown in Table 1. For the mixtures, ultrahigh quality synthetic oil Q8 T 860 SAE 10W40 was collected from the locomotive diesel engine at intervals of approximately 23000 km. Before mixing, the oil samples were filtered through 100 μm pore filter. The oil sample and tire pieces were dried before thermolysis by heating at 110 °C for 24 h. The properties of the feedstocks are shown in Table 3. The thermolysis process of shredded tires and oil was conducted in a 3000 cm3 capacity semicontinuous vertical reactor, which was connected to a cooling and condensation system of the reaction products and the equipment for the separation of liquid and gaseous products (Figure 1).

a,b

Type 1

Type 2

Waste engine oil

230 65.15 34.83 37.65 84.7 6.6 0.4 1.4 1.6 5.3

218 66.11 33.87 37.72 85.0 6.5 0.4 1.3 1.5 5.3

153 98.94 1.45 45.13 87.0 9.8 0.3 0.8 0.7 1.4

0.09 2.4 81.4 55.2 11260 7.4 745

0.13 2.4 81.5 55.0 11250 7.5 735

0.32 2.5 18.6 80.1 840 39.7 91.4

Calculated by difference.

In all thermolysis experiments, a hermetically sealed reactor, loaded with the appropriate amount of feedstock under nitrogen gas, was heated by an electrical muffle furnace, raising the temperature from 20 to 550 °C at a heating rate of 2.5 °C/min. The destruction process was carried out at both atmospheric and elevated (40 bar) pressures. Throughout the process, the furnace was transferring heat to the reactor at a constant 3 kW power. During the T/O mixtures thermolysis processes, the gaseous and liquid products were separated in the separator. The thermolysis oil accumulated in a tank, and noncondensable thermolysis components flowed through the gas meter to the torch or gas sample branch pipe. The solid-phase product remained in the reactor, which was discarded after the system cooled. B

DOI: 10.1021/acs.energyfuels.5b01540 Energy Fuels XXXX, XXX, XXX−XXX

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Energy & Fuels

temperature program was 30 °C for 3 min, followed by a 2 °C/min heating rate to 200 °C, followed by a 3 °C/min heating rate to a final temperature of 260 °C, and held at 260 °C for 2 min. The quadrupole mass spectrometer was set at the standard ionizing voltage of 70 eV with a mass range of m/z 10−500 and a scan speed of 2500 amu/s. The identification of the compounds was accomplished using a library search in a National Institute of Standards and Technology (NIST) database in combination with evaluation of the mass fragmentation pattern. Quantitative analyses were accomplished by the results of qualitative analysis; that is, all chromatograms of samples were integrated under equal conditions, and the percentage amounts of the components were calculated according to the peak areas. The data were presented as the average of two chromatograms. Elemental analyses were conducted using Elemental Analyzers CE440 (Exeter Analytical, Inc.) and Rigaku NEX QC. The metals were analyzed by atomic-absorption spectrometry (AAS). Water content was measured with a Dean and Stark apparatus by the ASTM D95 standard method. The heat of combustion values were determined with an IKA C2000 control calorimeter by the ASTM D240 standard method. The distillation characteristics of thermolysis oils were analyzed under atmospheric pressure according to the ASTM D86 (EN ISO 3405) standard method. The density, coke, and ash contents were determined by standards ASTM D4052, ASTM D4530, and ASTM D482, respectively. All results were presented as the average of three measurements.

Figure 1. Schematic diagram of the T/O mixtures thermolysis unit: 1, heating furnace; 2, reactor; 3, pressure transducer; 4, thermocouple; 5, valve; 6, air condenser; 7, safety valve; 8, separator; 9, liquid product tank; 10, water reflux condenser; 11, gas meter; 12, gas sample branch pipe; 13, torch. During the thermolysis process, the pressure and temperature were recorded with the valve (Figure 1, position 5) opened. For pressurized experiments, the valve was kept closed until the pressure in the reactor reached 40 bar (gauge). Afterward, the valve was opened, and vaporphase products were released from the reactor for further processing. The process was terminated when the gas ceased to flow from the reactor and the temperature in it reached 550 °C. The reprocessing time of T/O mixtures, intermediates, and end products depends upon the chosen pressure, and the whole buildup rate was affected by the thermochemical processes taking place in the reactor. The T/O mixtures thermolysis results are the mean of at least two thermolysis experiments conducted under identical process conditions: load of the feedstock, heating rate, and highest pressure and temperature. The gas produced from the thermolysis experiments was analyzed on a Varian CP 3800 gas chromatograph consisting of three channels that were equipped with two thermal conductivity detectors (TCDs) and a flame ionization detector (FID). The sample of a process gas was investigated in all channels of the chromatograph at the same time. The first channel that consists of three columns, CP81522 (13 m × 0.32 mm), CP7568 (50 m × 0.53 mm), and CP735732 (10 m × 0.32 mm), was used to separate the light hydrocarbons in a range of C1− C4. The second channel, which consists of two molecular sieves, CP81069 (1.0 m × 1/8 in. SS Hayesep Q, 80−100 mesh) and CP81025 (1.0 m × 1/8 in. SS Molsieve 5A, 80−100 mesh), was used for determination of hydrogen, which was detected by TCD. The third channel of the gas chromatograph, which consists of three molecular sieves, CP81072 (0.5 m × 1/8 in. Ultimetal Hayesep T, 80−100 mesh), CP81073 (0.5 m × 1/8 in. Ultimetal Hayesep Q, 80−100 mesh), and CP81071 (1.5 m × 1/8 in. SS Molsieve 13X, 80−100 mesh), was used to separate O2, N2, CO, CO2, and H2S (an explanation of the analysis: the gas sample is injected by means of a gas sampling valve onto a series of Hayesep columns; the fraction containing O2, N2, and CO is flushed onto a molecular sieve column and parked; CO2 and H2S are eluted to the TCD, by passing the molecular sieve column; after the elution of H2S, the molecular sieve column is set to flow again, giving the separation of O2, N2, and CO). The first channel was maintained at 50 °C for 9 min and then heated to 180 °C at a rate of 8 °C/min. The second channel was held at 50 °C throughout the experiment. The third channel was maintained at 50 °C for 9 min and then heated up to 90 °C at a rate of 8 °C/min. Hydrogen was used as a carrier gas, and the temperature of the detectors was maintained at 175 °C. Quantification was carried out using blends of gases of known composition. Samples of used oil (Q8 T 860 SAE 10W40) and obtained liquid products were dissolved in methanol and analyzed using a Shimadzu GCMS-QP2010 Ultra gas chromatograph, equipped with a Rtx-1 PONA capillary fused silica column (100 m × 0.25 mm inner diameter, with a film thickness of 0.5 μm), flame ionization and mass selective detectors, and helium as the carrier gas. The column

3. RESULTS AND DISCUSSION 3.1. Product Yield. Figure 2 presents the yield distribution of gaseous, liquid (oil), and solid (fixed carbon) products,

Figure 2. Yield distribution of thermolysis products with respect to the shredding degree of raw material and tire to oil ratio.

which were obtained under different thermolysis process pressure, shredding degree of tires, and T/O ratio. As the results show that the composition of a mixture had a significant effect on the yield of the three thermolysis products. During the thermolysis of T/O blends, regardless of the process pressure C

DOI: 10.1021/acs.energyfuels.5b01540 Energy Fuels XXXX, XXX, XXX−XXX

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Energy & Fuels Table 4. Composition of Thermolysis Gas Derived from T/O Mixtures Components of Gaseous Thermolysis Products

Feedstock type; Pressure and T/O ratio Type 1

Type 2

Used Engine Oil

1 atm and 2:0 1 atm and 2:1 1 atm and 2:2 40 bar and 2:0 40 bar and 2:1 40 bar and 2:2 1 atm and 2:0 1 atm and 2:1 1 atm and 2:2 40 bar and 2:0 40 bar and 2:1 40 bar and 2:2 1 atm and 2:2 40 bar and 2:0

CH4

C2H6

C2H4

C3H8

C3H6

n-C4H10

i-C4H10

C4H8

H2

CO2

CO

H2S

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

30.55 29.11 27.72 30.53 29.54 29.36 30.06 29.79 29.88 30.20 29.41 28.48 25.32 26.41

14.62 13.48 13.36 15.03 14.75 14.57 14.42 14.19 14.32 14.80 14.11 13.77 12.86 13.42

0.90 1.10 0.95 0.73 2.36 1.23 0.88 1.04 1.24 0.82 1.05 1.12 1.54 1.52

11.51 12.64 12.41 12.89 13.05 14.31 11.68 12.33 13.51 12.96 13.16 13.47 15.18 15.21

1.86 2.61 2.42 1.45 2.33 2.07 1.85 1.91 2.08 1.50 1.78 1.87 1.98 2.86

2.99 2.53 3.27 4.73 2.84 2.97 2.78 2.89 3.02 4.61 4.78 5.04 8.77 8.47

12.56 12.32 12.26 12.50 12.42 12.66 12.54 12.74 12.04 12.96 12.01 11.13 8.55 8.32

4.25 5.39 6.41 3.72 3.25 3.37 4.18 4.35 4.22 3.60 3.84 3.54 4.94 5.27

14.65 14.01 13.77 11.60 12.04 11.84 15.82 14.72 14.26 11.80 12.36 12.92 9.47 9.06

3.96 4.02 5.03 3.35 4.08 3.98 3.80 3.81 3.55 3.40 3.94 4.21 5.74 5.21

2.05 2.55 2.18 3.36 3.19 3.55 1.88 2.10 1.74 3.20 3.48 4.31 5.47 4.08

0.10 0.24 0.22 0.11 0.15 0.09 0.11 0.13 0.14 0.15 0.08 0.14 0.18 0.17

Figure 3. GC/MS TIC of the thermolysis oil derived from (a) pure used tire; (b) mixture of used tire and waste engine oil mixed in a ratio of 2:1; (c) mixture in a ratio of 2:2; (d) pure waste engine oil.

processing tire rubber with half as much used oil (2:1) generated about 1.4−7.8% (w/w) more gaseous products than thermolysis of the tires alone. However, in the case of 2:2 mixtures the changes in gas yield were practically negligible. The yield varied in the range from 16.5 to 18% (w/w). On the other hand, the oil addition reduced the yield of solid phase. As seen from the conversion processes (Figure 2) of 2:1 and 2:2 mixtures, the yield of the solid phase decreased by 6.45−11.8% (w/w) and 14.3−17.4% (w/w), respectively, in comparison with the thermolysis of pure tire. Previously we reported that the highest yield of liquid product derived from a pure tire thermolysis was 43.1% (w/w), when the thermolysis process was carried out at a pressure of 40 bar and the size of tire specimen was 50 × 25 × 10/15 mm (Type 1).9 In the present research, blends of used tires and

and chopping degree of the rubber feedstock, it was revealed that the oil additive in thermal destruction processes of a tire has a positive effect on the yield of the target product, i.e. the yield of the liquid product increased approximately from 39.4 to 60.2% (w/w). The tire, being as a mixture component, is treated with hot oil, so/thus/hence the entire surface of the rubber specimens are heated more evenly than in the case of sole tire thermolysis. For this reason, the beginning of the destruction processes for the whole volume of T/O mixtures had to start almost at the same time. Hence, more molecules of raw materials could participate in the decomposition and secondary reactions, which gave a higher amount of liquid hydrocarbons in the thermolysis process. On the other hand, these conditions required longer residence times that allowed formation of more gaseous products. It was found that D

DOI: 10.1021/acs.energyfuels.5b01540 Energy Fuels XXXX, XXX, XXX−XXX

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Energy & Fuels Table 5. Amount of Compounds of Different Hydrocarbon Classes in Thermolysis Oil Feedstock type; Pressure and T/O mass ratio Type 1 Organic compd class Alkanes Alkenes Alkynes Dienes Trienes Alcohols Aromatic HCs Other Total

Type 2

Used Engine Oil

1 atm and 2:0 (%)

1 atm and 2:1 (%)

1 atm and 2:2 (%)

40 bar and 2:0 (%)

40 bar and 2:1 (%)

40 bar and 2:2 (%)

1 atm and 2:0 (%)

1 atm and 2:1 (%)

1 atm and 2:2 (%)

40 bar and 2:0 (%)

40 bar and 2:1 (%)

40 bar and 2:2 (%)

1 atm and 0:2 (%)

40 bar and 0:2 (%)

22.23 22.35 0.24 8.52 0.65 0.02 41.31

19.53 30.95 0.00 7.50 0.00 2.48 34.40

18.36 33.80 2.45 6.16 0.78 1.53 28.33

28.13 26.83 0.31 2.70 0.13 2.35 36.54

34.24 21.06 1.01 1.97 0.07 2.29 34.48

29.61 32.24 0.00 1.37 0.00 2.02 29.80

15.53 23.39 0.22 10.20 1.47 0.18 41.81

26.98 26.14 0.26 3.70 1.45 4.53 29.96

29.42 34.54 2.83 1.93 1.39 2.08 23.45

30.49 26.23 0.33 2.94 1.00 0.39 35.28

37.25 24.71 1.27 1.98 0.92 1.39 31.56

38.66 30.46 0.43 1.84 0.87 2.57 21.84

40.74 39.04 1.32 5.26 0.00 3.53 5.91

57.51 28.95 0.00 2.49 0.00 0.09 8.55

4.68 100.00

5.14 100.00

8.59 100.00

3.01 100.00

4.88 100.00

4.96 100.00

7.20 100.00

6.98 100.00

4.36 100.00

3.34 100.00

0.92 100.00

3.33 100.00

4.20 100.00

2.41 100.00

3.3. Analysis of Thermolysis Oil by Gas Chromatography/Mass Spectrometry (GC/MS). Figure 3 shows the total ion chromatograms (TIC) for the gas chromatographic/ mass spectrometric analysis of the oils derived from the thermolysis of T/O mixtures, which were composed of Type 1 feedstock and waste engine in different ratios, reprocessing under atmospheric pressure. The results of CG-MS analysis are presented in Table 5, where components are grouped into distinct organic compound classes. The data of gas chromatography revealed that the thermolysis oil is a very complex mixture comprised of all classes of hydrocarbons.35−37 Investigation of the liquid product derived from a pure tire thermolysis under atmospheric pressure showed the main hydrocarbons were arenes (41−42%), alkenes (22−24%), and alkanes (15−23%), whereas the liquid product obtained from a pure oil was composed predominantly of alkanes (41%) and olefins (40%).13,20,38 Aromatic hydrocarbons in thermolysis oils were formed mainly from the degradation of scrap tires whereas liquid product from engine oil contained mainly paraffinic species. Meanwhile, the target product obtained from the thermolysis of the mixtures of Type 1 feedstock and motor oil in a ratio of 2:1 and 2:2 contained an increased amount of alkenes (8.6− 11.45%), alkynes (2.2%), and alcohols (1.5−2.5%), as well as a decreased quantity of saturated alkanes (2.7−3.9%), dienes (1.0−2.4%), and aromatic hydrocarbons (6.9−13.0%). When the T/O mixture was prepared from the Type 2 feedstock and processed under atmospheric pressure, the yield of saturated alkanes in the main product was significantly higher (11.4− 14.0%) in comparison with the liquid product obtained from the thermal cracking of pure tire. It should be noted that the mixtures with a lower degree of chopping of solid raw material (Type 2) generated a significantly lower quantity of dienes (6.5−8.3%) and aromatic hydrocarbons (11.85−18.4%). As can be seen from the results in Table 5, the thermolysis process at elevated pressure generated less dienes and trienes, whereas the yield of more stable alkanes increased with pressure and the quantity of the waste oil in the T/O mixture. Production of dienes and trienes was accompanied by hydrogen separation, which was an unfavorable phenomenon under elevated pressure, as was discussed in chapter 3.2. The quantity of aromatic hydrocarbons in the liquid products was influenced by the feedstock origin rather than the process pressure; thus, the quantity of arenes increased with tire share rise in the feedstock. The highest yield of alkanes (38.66%) was achieved

waste oil were used as feedstock, which size as well as the process pressure had also a certain effect on the products yield. When the T/O mixtures were processed in ratio of 2:1 at elevated pressure (40 bar) (Figure 2b), the yield of the liquid product reduced by 3.3−3.7% (w/w), compared to the corresponding results of atmospheric thermolysis. The expense of a liquid product can be explained by the increased amount (by 1.2 to 3.1%, w/w) of the gas. In the case of thermolysis of the T/O mixtures in a ratio of 2:2, the process pressure virtually had no effect on products yield (Figure 2). Investigation of the influence of the solid feedstock particle size (Type 1 and Type 2) in T/O mixtures on the yield of liquid thermolysis product revealed that reprocessing of the finer solid feedstock (Type 1) gave more (up to 3%, w/w) liquid product at any process pressure. The faster heat transfer to the deepest layers of the finer rubber specimens caused shorter duration of the decomposition products in the reactor that decreased a possibility for the secondary gasification and coking reactions. 3.2. Composition of Process Gas. The data of the compositional analysis of the gases derived from the thermolysis of T/O mixtures under different process conditions are presented in Table 4. The main components in the gaseous phase are saturated hydrocarbons and hydrogen. The studies of the pure tire thermolysis under atmospheric pressure showed that the gas phase was predominantly composed of methane (30.0−30.6%, v/v), hydrogen (14.6−15.9%, v/v), ethane (14.4−14.7%, v/v), isobutane (12.5−12.6%, v/v), and propane (11.5−11.7%, v/v).15,33,34 Thermal destruction of used oil generated gaseous products with a higher content of saturated paraffins with a longer carbon chain such as propane, n-butane, and isobutane. The amount of non-hydrocarbon components was higher too, but the yield of hydrogen was, by 5.2% (v/v), lower than the one detected in the gaseous product from a scrap tire. Thermolysis of the mixtures of chopped tires and used engine oil under atmospheric pressure gave a higher quantity of olefins (ethylene, propylene, and butene), carbon monoxide, carbon dioxide, and hydrogen sulfide. The highest level of hydrogen sulfide (0.24%, v/v) was obtained when the mixture of Type 1 feedstock and engine oil in a ratio of 2:1 was processed under atmospheric pressure. In the case of Type 2, pressure had no influence on the quantity of hydrogen sulfide. The difference in hydrogen and olefins content in the gaseous products is a result partly of thermodynamically unfavorable dehydrogenation reactions at elevated pressure. E

DOI: 10.1021/acs.energyfuels.5b01540 Energy Fuels XXXX, XXX, XXX−XXX

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Energy & Fuels Table 6. Aromatic Compounds in Oils Derived from the T/O Mixture Thermolysis Feedstock type; Pressure and T/O mass ratio Type 1

Aromatic compds Benzene Toluene Ethylmethylbenzene Ethylbenzene Styrene Xylenes Other alkylated benzenes Total of alkylated benzenes Naphthalene Alkylated naphthalenes Indane Indene Alkylated indenes Phenol Alkylated phenols Thiophene Alkylated thiophenes Other aromatic compounds Total:

Type 2

1 atm and 2:0 (%)

1 atm and 2:1 (%)

1 atm and 2:2 (%)

40 bar and 2:0 (%)

40 bar 40 bar and 2:1 and 2:2 (%) (%)

11.79 10.26 0.25 2.14 0.38 5.13 6.45

6.67 10.17 0.30 1.98 0.39 5.51 6.53

6.85 8.56 0.00 1.43 0.00 3.69 5.79

6.87 9.34 0.29 2.40 0.23 4.61 8.91

4.35 5.66 0.31 1.93 0.00 4.19 13.19

24.61

24.88

19.47

25.78

0.31 0.05

0.19 0.62

0.20 0.00

0.25 0.34 1.04 0.13 0.20 0.00 0.94 1.65

0.30 0.00 0.00 0.35 0.84 0.00 0.55 0.00

41.31

34.40

Used Engine Oil

1 atm and 2:0 (%)

1 atm and 2:1 (%)

1 atm and 2:2 (%)

40 bar and 2:0 (%)

8.15 9.52 0.19 1.65 0.02 4.51 6.12

11.75 10.91 0.27 2.15 0.57 4.43 7.05

2.81 4.65 0.24 1.25 0.30 3.66 12.80

2.16 4.16 0.19 1.33 0.00 3.53 8.38

7.71 8.43 0.29 2.16 0.18 5.14 8.36

2.83 5.80 0.23 1.67 0.00 1.14 15.87

25.28

22.01

25.38

22.90

18.59

24.56

0.14 0.59

0.35 1.14

0.34 0.00

0.25 0.14

0.39 1.02

0.19 0.47

0.23 0.00 0.05 0.41 0.76 0.00 0.36 0.00

0.29 0.00 1.06 0.11 0.26 0.00 0.94 0.50

0.49 0.00 0.99 0.22 0.21 0.00 0.73 0.72

0.31 0.00 0.18 0.10 0.00 0.00 0.71 0.00

0.23 0.00 1.32 0.16 0.08 0.00 0.95 1.55

0.42 0.00 1.44 0.14 0.00 0.00 0.47 0.37

28.33

36.54

34.48

31.80

41.81

29.96

when Type 2 feedstock and engine oil were mixed in a ratio of 2:2 and reprocessed at 40 bar. Comparison of the quantities of saturated alkanes in the oil derived from thermolysis under elevated and atmospheric pressures revealed that the amount of these compounds increased by 11−15% and 9−10.5%, respectively (Table 5). In the case when pure waste engine oil was used, the content of the saturated hydrocarbons in liquid product increased almost by 17% in comparison with the results obtained under atmospheric thermolysis. As was discussed above, the particular amount of oil in the initial mixture reduces the content of aromatic hydrocarbons in the liquid product under atmospheric thermolysis. The data of experiments at elevated pressure (40 bar) showed that the influence of pressure on the quantity of aromatic hydrocarbons derived from the T/O mixtures in a ratio of 2:1 and 2:2 was insignificant; that is, the values fluctuated in the range of 1−2%. The more detailed analysis of the aromatic compounds of thermolysis oil is presented in Table 6. All identified aromatic hydrocarbons were divided into 5 groups: benzenes, naphthalenes, indenes, phenols, and thiophenes. The dominant aromatic compounds in the liquid product were benzenes (from 16.92 to 25.78%), indenes (from 0 to 1.44%), and thiophenes (from 0.16 to 0.95%), which were mostly prevalent in the liquid product derived from pure tires, irrespective of the particles size of the tire and process pressure. The analysis of the liquid product derived from thermolysis of used oil revealed benzene and its first two homologues as the main constituents of the aromatic part of the product. It should be noted that the liquid products obtained from the T/O mixtures contained a much lower quantity of benzene, toluene, ethylmethylbenzene, ethylbenzene, and alkylated thiophenes than the products derived from pure tires. For the mixtures of Type 1 feedstock with an increased amount of engine oil (2:2), the benzene

40 bar 40 bar and 2:1 and 2:2 (%) (%)

1 atm and 0:2 (%)

40 bar and 0:2 (%)

2.38 4.43 0.16 1.18 0.00 3.22 7.93

0.80 1.94 0.13 0.37 0.00 1.08 1.16

1.33 2.92 0.00 0.64 0.00 2.07 1.39

24.71

16.92

4.68

7.02

0.16 0.10

0.35 0.69

0.21 0.15

0.00 0.00

0.00 0.20

0.33 0.14 1.52 0.07 0.00 0.00 0.38 0.60

0.31 0.00 1.02 0.00 0.03 0.00 0.92 0.47

0.44 0.21 1.41 0.09 0.00 0.00 0.16 0.67

0.29 0.13 0.81 0.07 0.00 0.00 0.43 0.45

0.00 0.10 0.02 0.00 0.31 0.00 0.00 0.00

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

23.45

35.28

31.56

21.84

5.91

8.55

content in the liquid product reduced from 11.79 to 6.85%, and the one of toluene decreased from 10.26 to 8.56%. However, when Type 2 feedstock was used, the reduction of benzene and toluene was even greater, i.e, from 11.76 to 2.16% and from 10.91 to 4.16%, respectively. The quantity of ethylbenzene and alkylated thiophenes remained virtually unchanged in the case of both types of raw material. As can be seen from the data in Table 6, an increase of pressure in the reactor led to the reduction of the benzene amount by 5% (Type 1) and 4% (Type 2) as well as the one for toluene by 1% (Type 1) and 2.5% (Type 2), respectively. Meanwhile, when the mixtures of tires and oil were reprocessed at a pressure of 40 bar, the amount of benzene and toluene reduced only of the T/O mixture from the Type 1 feedstock in ratio of 2:1. In other cases the quantity of benzene (by 0− 1.3%) and toluene (by 0.2−1.2%) increased. The quantity of ethylmethylbenzene, ethylbenzene, xylenes, naththalene, indane, and phenol remained similar in the liquid product under different process conditions. Formation of toluene occurs via direct scission of beta C−C bonds with later benzyl radical neutralization, while production of benzene initially involves bimolecular addition reaction with hydrogen atom and then quick dealkylation of the formed active radical. Hence, benzene and its methyl homologues content in the product is highly dependent on the feedstock chemical composition, process temperature, atomic hydrogen availability, and duration of the intermediates in the reaction zone. Such a number of the process-affecting parameters at a time impedes the uniform and clear consistency of the lightest arenes distribution, so that becomes an attractive area for deeper investigations. 3.4. Properties of the Thermolysis Oil. The distillation characteristics of liquid products derived from the T/O mixtures in different ratios are presented in Figure 4. The F

DOI: 10.1021/acs.energyfuels.5b01540 Energy Fuels XXXX, XXX, XXX−XXX

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Energy & Fuels

(IBP−360 °C), which is suitable for production of engine fuels. Its maximum yield was 92% (v/v) (Table 7). When a small amount of used oil was added (2:1) to the Type 1 feedstock, the yield of the wide distillate fraction in the atmospheric thermolysis product increased by 3.5% (v/v). When the thermolysis process was performed at elevated pressure (40 bar), the quantity of this fraction raised up approximately by 2.1% (v/v). When the engine oil content in the mixture was increased to a ratio of 2:2, the opposite effect was observed; that is, the yield of the wide fraction decreased by 16.8% (v/v) under atmospheric thermolysis and by 8% (v/v) at a pressure of 40 bar. When the T/O mixtures prepared from bigger tire specimens (Type 2) and an appropriate amount of engine oil (ratio of 2:1 and 2:2) were processed, the yield of the wide distillate fraction increased in both cases, i.e. by 5 and 16% (v/ v), respectively, under atmospheric thermolysis, and by 8.5 and 1% (v/v), respectively, at 40 bar. As the pure oil was thermolyzed at 40 bar pressure (Figure 4c), the yield of the wide distillate fraction was approximately 2.24 times higher than the one obtained under atmospheric pressure. Distillation characteristics also indicate the presence of a naphtha fraction which boils in the temperature range of IBP− 200 °C and is suitable for gasoline production. The yield of the naphtha fraction in the thermolysis oil can be in the range of 12−48% (v/v). More compounds fall into the diesel fraction that boils in the temperature range of 200−360 °C. The yield of this fraction varies from 36 to 52% (v/v) and depends on the composition of primary components and the process conditions. The minimum yield of the diesel fraction (36%, v/v) was obtained, when the pure oil thermolysis was carried out under atmospheric pressure. The yield of naphtha and diesel fraction were influenced not only by the relative composition of the T/O mixture but also by the size of shredded tire specimen. In the case of T/O mixtures prepared from Type 1 feedstock and engine oil mixed in a ratio of 2:2, the yield of naphtha decreased almost twice in comparison with the yield of naphtha derived from the mixture in a ratio of 2:1. When these two types of mixtures were thermolyzed at elevated pressure (40 bar), the yields of naphtha and diesel fraction increased by 5.4% (v/v) and 1.3% (v/v), respectively (Table 7). The higher content of distillable components in the liquid product is the effect of prolonged duration of intermediates in the reactor and, consequently, the higher extent of compounds cleavage. In the case of Type 2 feedstock, the yield distribution of these two fractions was heavily influenced by the process pressure. When the Type 2 feedstock was mixed with oil in a ratio of 2:1 and thermolyzed under atmospheric pressure, a greater diesel fraction (52%, v/v) was obtained, whereas, when the ratio was 2:2, the obtained naphtha fraction (48%, v/v) was greater than the diesel fraction (44%, v/v). As the cracking process was

Figure 4. Distillation characteristics of thermolysis liquid products.

products are characterized by low initial boiling points (IBPs), which are in the range of 42−84 °C. The value of this parameter depends on the efficiency of the cooling-condensing system and the flow of thermolysis products from the reactor. The analysis data revealed that the composition of the feedstock and process conditions practically did not influence the IBP of the liquid products. In majority of the cases (Figure 4), the presence of engine oil in the T/O mixtures had a positive impact on the yield of the wide distillate fraction

Table 7. Fuel Fractions Separated from Liquid Thermolysis Product Feedstock type; Pressure and T/O mass ratio Type 1

Type 2

Used Engine Oil

1 atm and 2:0

1 atm and 2:1

1 atm and 2:2

40 bar and 2:0

40 bar and 2:1

40 bar and 2:2

1 atm and 2:0

1 atm and 2:1

1 atm and 2:2

40 bar and 2:0

40 bar and 2:1

40 bar and 2:2

1 atm and 0:2

40 bar and 0:2

Fraction

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

%, v/v

Naphtha Diesel total:

35.4 44.1 79.5

38.0 45.0 83.0

19.0 43.7 62.7

33.3 44.7 78.0

37.6 42.5 80.1

24.0 46.0 70.0

32.4 43.6 76.0

31.0 52.0 83.0

48.0 44.0 92.0

33.1 45.4 78.5

46.0 41.0 87.0

37.0 43.5 80.5

12.0 36.0 48.0

41.0 46.5 87.5

G

DOI: 10.1021/acs.energyfuels.5b01540 Energy Fuels XXXX, XXX, XXX−XXX

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Energy & Fuels Table 8. Properties of Thermolysis Oil Feedstock type; Pressure and T/O mass ratio Type 1 Properties Heating value (MJ/kg) Sulfur (%, w/ w) Density at 20 °C (kg/m3) Initial boiling point (°C) Water content (%, w/w) in primary liquid product in separated oil in emulsion Ash (%, w/w) Coke (%, w/w) Metals (mg/kg) Cd Cr Cu Pb Zn Ni Fe

Type 2

Used Engine Oil

1 atm and 2:0

1 atm and 2:1

1 atm and 2:2

40 bar and 2:0

40 bar and 2:1

40 bar and 2:2

1 atm and 2:0

1 atm and 2:1

1 atm and 2:2

40 bar and 2:0

40 bar and 2:1

40 bar and 2:2

1 atm and 0:2

40 bar and 0:2

42.06

42.87

42.77

42.04

43.76

44.02

41.98

44.41

42.97

42.27

43.89

44.50

45.61

46.05

0.60

0.70

0.82

0.67

0.58

0.65

0.63

0.78

0.90

0.66

0.67

0.73

0.29

0.27

902

871

846

893

848

813

903

851

823

898

840

836

816

810

65

55

67

62

84

42

66

55

72

65

53

70

53

46

3.80

0.03

0.03

4.47

0.04

0.17

3.98

0.24

0.6

4.23

0.03

0.14

0.02

n.d.

0.15 24.8 0.03 9.44

0.03 n.a. 0.01 2.58

0.03 n.a. 0.05 0.64

0.1 15.6 0.07 7.09

0.04 n.a. 0.01 3.21

0.17 n.a. 0.09 0.81

0.03 38 0.02 9.18

0.24 n.a. 0.01 1.44

0.6 n.a. 0.08 2.31

0.03 35.2 0.05 8.32

0.03 n.a. 0.11 3.47

0.14 n.a. 0.11 2.52

0.02 n.a. 0.04 3.05

n.d n.a. 0.05 4.25

n.d. 1.9 5.2 2.9 1820 0.8 48.9

0.1 1.9 3.9 3.4 1300 1.4 32.0

0.1 1.8 3.2 3.6 985 1.9 27.6

n.d. 1.8 4.8 2.6 1480 0.6 46.6

n.d. 1.7 3.7 3.0 1130 1.5 33.2

n.d. 1.7 3.1 3.2 980 1.8 29.0

n.d. 2.1 5.4 3.2 1980 0.8 50.2

0.1 1.9 4.2 3.5 1360 1.4 36.0

0.2 2.0 3.3 3.8 1110 1.9 28.3

n.d. 1.8 4.7 2.5 1550 0.7 49.7

n.d. 1.6 3.6 3.0 1060 1.3 35.2

n.d. 1.7 3.3 3.2 900 1.8 28.0

0.1 1.9 1.2 4.3 150 3.0 6.3

0.1 1.5 1.3 3.8 120 2.9 6.3

Table 9. Properties of Tire Thermolysis Char Ash Feedstock type; Pressure and T/O mass ratio Type 1

Type 2

Used Engine Oil

1 atm and 2:0 1 atm and 2:1 1 atm and 2:2 40 bar and 2:0 40 bar and 2:1 40 bar and 2:2 1 atm and 2:0 1 atm and 2:1 1 atm and 2:2 40 bar and 2:0 40 bar and 2:1 40 bar and 2:2 1 atm and 0:2 40 bar and 0:2

Elemental composition, % (w/w)

Metal (mg/kg)

Calo-rific value, MJ/ kg

%, w/w

C

H

N

S

Cd

Cr

Cu

Pb

Zn

Ni

Fe

31.4 28.4 30.8 31.2 30.6 29.6 31.7 31.1 31.4 31.7 31.6 31.2 32.1 31.8

16.4 18.6 19.5 14.3 13.4 14.4 14.7 16.9 19.8 14.5 15.6 16.5 45.2 43.2

76.2 75.0 73.7 75.0 73.6 71.1 78.6 76.3 74.9 78.1 75.2 74.1 76.4 72.0

0.8 0.7 0.7 0.7 0.8 0.6 0.8 0.8 0.8 0.7 0.5 0.7 0.8 0.2

0.2 0.3 0.3 0.4 0.4 0.5 0.2 0.3 0.5 0.3 0.2 0.3 0.7 0.2

2.1 2.5 2.9 2.0 2.3 2.5 2.0 2.4 2.8 2.1 2.2 2.3 1.9 1.6

0.04 0.03 0.12 0.02 0.05 0.08 0.04 0.05 0.11 0.02 0.05 0.08 0.09 0.03

0.1 0.1 0.1 0.2 0.4 0.4 0.1 0.1 0.3 0.2 0.3 0.4 0.2 0.5

57.8 42.8 35.5 58.5 43.4 35.5 58.1 43.2 35.7 58.5 43.3 35.8 13.3 13.2

46.1 53.2 56.7 46.8 53.7 57.3 46.2 53.2 56.7 46.5 53.6 57.1 67.3 67.8

6126 4245 3245 6556 4545 3455 6279 4301 3367 6619 4471 3372 455 485

4.5 11.6 14.9 4.6 11.7 15.0 4.6 11.6 14.9 4.8 11.5 15.1 25.3 25.4

563 398 316 563 398 316 556 396 312 558 395 311 68.9 68.9

conditions and mixture compositions, water did not form in the liquid product. Just traces of water were detected. The sulfur content in the thermolysis oil derived from pure oil and tire under atmospheric pressure was found to be 0.29% (w/w) and 0.58−0.66% (w/w), respectively.13,36 Processing of the T/O mixtures (2:2) resulted in the increased sulfur content in the liquid product by 0.22−0.27% (w/w). When the thermolysis process was performed at elevated pressure (40 bar), the amount of oil in the T/O mixture had no influence on the sulfur content in the main product. In this case, the sulfur content was close to that of the liquid product from a pure tire, i.e. 0.6−0.67% (w/w).

performed at 40 bar pressure, the pattern of the fraction distribution was opposite. The data presented in Table 8 show that the gross calorific values of these thermolysis liquid products are quite similar and lie down in the range of 41.98−46.05 MJ/kg.39,40 The gross calorific value of liquids is closely related to the density of the material; therefore, decreased density of the product (Table 8) resulted in higher calorific values of thermolysis oil. The liquid product obtained from the tire thermolysis alongside the organic phase usually has the water phase, which accumulates at the bottom of the separator. However, it should be noted that, for the T/O mixtures under any thermolysis H

DOI: 10.1021/acs.energyfuels.5b01540 Energy Fuels XXXX, XXX, XXX−XXX

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higher amount of cadmium (from 0.02 to 0.04 mg/kg), lead (from 46.1 to 57.3 mg/kg), and nickel (from 4.5 to 15.1 mg/ kg) in the char. The gross calorific values of the solid products were obtained in the range from 28.4 to 32.1 MJ/kg. This parameter depends on the elemental composition of a char, particularly on carbon content because hydrogen, the main booster of calorific value, virtually has gone with liquid products. The solid products derived from the T/O mixtures are distinguished for a high content of ash, i.e. 13.4−19.8% (w/ w).13,33 The main reason for the phenomenon is that the char accumulates different metal based additives, which are incorporated during the production of brand new tires and fresh engine oils. The majority of these additives are not volatile, nor valuable, and they remain as ballast in a solid phase.

The analysis of metals (Table 8) showed that the liquid products derived from T/O mixtures accumulated heavy metals, such as Cd, Cr, Cu, Pb, and Zn. The main source of metals in the target product might be attributed to the engine oil and tire additives, which had been added during the manufacture processes.23 As the results showed the highest levels of heavy metals were obtained when the mixtures of Type 1 and Type 2 and engine oil in both ratios (2:1 and 2:2) were processed under atmospheric pressure, it should be noted that the concentration of these metals reduced when the T/O mixtures were thermolyzed under elevated pressure (40 bar). Prevalent metals in the liquid product were zinc (900−1360 mg/kg) and iron (27.6−36.0 mg/kg). High quantities of heavy metals in the thermolysis oil are a result either of an entrainment of some of the lubricant additives which are in organometallic forms, or these compounds could show significant vapor pressure at high temperature (up to 600 °C).1 Hence, the metallic compounds with gaseous thermolysis products escaped from the reactor, and the form condensed and remained in the final liquid product. Efforts are being made to incorporate additional processes such as hot gas cleaning and demetalization of waste materials in order to obtain free-from-ash liquid products.13 The liquid thermolysis oil derived from the T/O mixtures is characterized by high calorific value, low ash content (0.01− 0.11%, w/w), and moderate sulfur content. These properties make this energetically valuable product as a whole or partly suitable for manufacture of liquid fuel for industrial and domestic furnaces, foundries, or boilers in power plants, or suitable for upgrade to a high-quality automotive fuel. 3.5. Char Analysis. Table 9 presents data on the elemental composition of the solid phase obtained from T/O mixtures by the thermolysis process under different conditions. It should be noted that the distribution of hydrogen (0.5−0.8%, w/w) and nitrogen (0.2−0.5%, w/w) in all products was almost identical except the ones obtained from the pure oil thermolysis. As the engine oil was thermolyzed at a pressure of 40 bar, hydrogen in the solid product was observed of the smallest quantity (0.2%, w/w). The fixed carbon and sulfur distribution in the solid phase vary depending on the composition of the T/O mixture, the feedstock type, and the pressure in the reaction zone. The thermolysis experiments revealed that the higher amount of motor oil in the T/O mixture reduced the quantity of fixed carbon in the range from 2.5 to 3.7% (w/w) (2:2; 1 atm. pressure) and from 3.9 to 4% (w/w) (2:2; 40 bar) depending on the feedstock type and in the range from 2.5 to 3.9% (w/w) (2:2; Type 1) and from 3.7 to 4.0% (w/w) (2:2; Type 2) depending on the process pressure. On the other hand, the increased amount of motor oil in the T/O mixtures raised up a sulfur content in the solid phase by 0.8% (w/w) under atmospheric thermolysis and 0.2−0.5% (w/w) under 40 bar pressure. The metal analysis of the solid thermolysis product (Table 9) showed that the majority of metals accumulated in the char. Zinc, iron, copper, and lead appeared to be the predominant elements.33 The data revealed that the feedstock chopping degree and process pressure virtually did not influence the metals content of the solid product, except zinc. The quantity of the latter increased a little with a higher pressure of the process. The higher amount of engine oil in the T/O mixtures gave a lower copper (from 58.5 to 35.5 mg/kg), zinc (from 6619 to 3245 mg/kg), and iron (from 563 to 311 mg/kg) content in the char. In other cases the oil additives generated a

4. CONCLUSIONS This paper analyzes the mixtures of waste tires of passenger cars and used ultrahigh quality synthetic oil Q8 T 860 SAE 10W40 that was mixed in ratios of 2:0; 2:1; 2:2; 0:2 and thermolyzed in a semicontinuous distillation reactor to determine the influence of the mixture composition, feedstock shredding degree, and pressure on the yield, properties, and composition of the thermolysis products. The experimental data showed that the oil as an additive in the thermolysis processes of tire has a positive effect on the yield of the liquid product, which increased from 39.4 to 60.2% (w/w). Besides, the finer particles of a feedstock (Type 1) also increased the yield of the liquid by 3%, w/w; however, the higher pressure in the reaction zone reduced it. On the other hand, thermolysis of a smaller size specimen resulted in a higher amount of solid and gaseous products. GC-MS analysis revealed the complexity of the thermolysis oil composition, with arenes, olefins, and alkanes as dominating compounds in the oil products derived from the T/ O mixture thermolysis under atmospheric pressure. The process at the elevated pressure generated more stable alkanes but less olefins and aromatic compounds. The distillation characteristics revealed that the T/O mixtures, which consisted of smaller feedstock particles, produced more diesel fractions, whereas more naphtha cut in the liquid product was obtained when the specimen size of a feedstock increased. The calorific values and the elemental composition of chars derived from T/ O mixtures were very similar regardless of the thermolysis conditions. The majority of metal deposition was detected in the solid product that virtually was not influenced by the feedstock chopping degree and the process pressure. On the other hand increased process pressure and quantity of used engine oil in the T/O thermolysis gave a lower amount of metals in the liquid phase. As a final conclusion, the results obtained in this study showed that the thermolysis of T/O mixtures is an effective method of conversion of these problematic wastes into liquid fuels.

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AUTHOR INFORMATION

Corresponding Author

*E-mail address: [email protected] (A. Jonusas). Notes

The authors declare no competing financial interest. I

DOI: 10.1021/acs.energyfuels.5b01540 Energy Fuels XXXX, XXX, XXX−XXX

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Energy & Fuels

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ACKNOWLEDGMENTS The authors gratefully acknowledge refinery PC ORLEN Lietuva for the financial support.

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DOI: 10.1021/acs.energyfuels.5b01540 Energy Fuels XXXX, XXX, XXX−XXX