Py–FTIR–GC/MS Analysis of Volatile Products of Automobile Shredder Residue Pyrolysis

Abstract

Automobile shredder residue (ASR) pyrolysis produces solid, liquid, and gaseous products, particularly pyrolysis oil and gas, which could be used as renewable alternative energy resources. Due to the primary pyrolysis reaction not being complete, the yield of gaseous product is low. The pyrolysis tar comprises chemically unstable volatiles before condensing into liquid. Understanding the characteristics of volatile products will aid the design and improvement of subsequent processes. In order to accurately analyze the chemical characteristics and yields of volatile products of ASR primary pyrolysis, TG–FTIR–GC/MS analysis technology was used. According to the analysis results of the Gram–Schmidt profiles, the 3D stack plots, and GC/MS chromatograms of MixASR, ASR, and its main components, the major pyrolytic products of ASR included alkanes, olefins, and alcohols, and both had dense and indistinguishable weak peaks in the wavenumber range of 1900–1400 cm⁻¹. Many of these products have unstable or weaker chemical bonds, such as =CH–, =CH2, –C=C–, and –C=CH2. Hence, more syngas with higher heating values can be obtained with further catalytic pyrolysis gasification, steam gasification, or higher temperature pyrolysis.

1. Introduction

The dismantling and recycling of end-of-life vehicles (ELVs) is not only an important way to save resources and realize sustainable development but also bears huge social and environmental responsibility. As of the end of 2019, China’s car ownership exceeded 260 million. According to the international scrap ratio of 4–6%, the quantity of ELVs in China will be large in the future. Automobile shredder residue (ASR) accounts for about 20–25% of a vehicle’s weight [1,2,3,4,5,6] and consists of plastic, textile, leather, rubber, foam, wood, paper, glass, sand, metals, and other materials [3,4,5,6,7,8]. Organic components account for about 60–85% of ASR [9,10], for which thermal conversion technology represents a viable resource recovery process. Pyrolysis and gasification have gradually become the main means to dispose of ASR, since they can reduce the volume and quality of landfill with lower cost, while energy recovery can be carried out simultaneously [11,12,13]. ASR pyrolysis produces solid, liquid, and gaseous products, particularly pyrolysis oil and gas, which could be used as renewable alternative energy resources.

The yields and characteristics of ASR pyrolytic products depend on the feed (e.g., fractions of organic versus inorganic), temperature, residence time, and carrier gases used [12]. There is a great range of variations possible, and the values used in a given process design must be chosen depending on which products are the process targets. Harder and Forton analyzed the variations in the physical characteristics of ASR, provided a review of the current technical developments in pyrolysis processes, and emphasized that the energy content of ASR is crucial to the design of a thermal process [14]. Zolezzi et al. evaluated the performance and product yields of conversional and fast pyrolysis of ASR at different temperatures [12]. It proved that the gas yield in conventional pyrolysis was higher than in fast pyrolysis, and higher heating values (HHVs) of gas increased with increasing temperature. HHV gas is also the optimal pyrolytic product of our research project funded by the National Natural Science Foundation of China No. 51675343. Extensive experimental research into ASR pyrolysis by other authors [15,16,17,18,19,20] has shown CO, CO₂, H₂, and light hydrocarbons (C1–C4, such as CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆) as the dominant constituents of HHV gas. We also studied the pyrolytic product yields and characterizations of gaseous products (H₂, CO, CO₂, CH₄, C₂H₄, C₂H₆, C₃H₆ and C₃H₈), which were analyzed in laboratory-scale non-isothermal pyrolysis experiments at finished temperatures of 500, 600, and 700 °C [21]. Moreover, we found that the pyrolytic reaction was insufficient in primary ASR pyrolysis, and the yield and calorific value of HHV gas are limited. Since the yield of gaseous product is low, however, the yield of tar and char are always higher. Our previous results show that tar and gas accounted for 39.68 and 19.76% of the pyrolysis product when the pyrolysis temperature was set to 600 °C [21].

Catalytic pyrolysis gasification [22,23,24], steam gasification [25,26], and higher temperature pyrolysis [27] are effective methods of increasing HHV gas production. Aiming to improve the yields of syngas and hydrogen, a two-stage pyrolysis process with catalysts was designed in our research project. Before the polymer organic mixtures pyrolyzed in the first-stage reactor condensed into tar, secondary pyrolysis was expected to continue under the action of catalysts. Lin et al. [28] presented an analysis of the catalytic gasification of ASR for the generation of high-purity hydrogen in a lab-scale fixed-bed downdraft gasifier using 15 wt.% NiO/Al₂O₃ catalysts at 760–900 K. They verified that the NiO/Al₂O₃ catalysts can increase the output of hydrogen and CO, but did not explain how the catalyst affects the secondary reaction of pyrolysis intermediate products. The main challenges of implementing and improving catalytic gasification technology were to select or develop suitable catalysts for enhancing synthesis gas yield. Most pyrolysis tar is also volatile before condensing into liquid, and its chemical state is very unstable. Understanding the characteristics of volatile products will aid the design and improvement of subsequent processes. Thus, the purpose of this study was to analyze the chemical compositions and yields of volatile products of primary ASR pyrolysis.

Thermogravimetric analysis (TGA), coupled with Fourier transform infrared spectrometry (FTIR) and gas chromatography–mass spectrometry (GC/MS), is a good means by which to explore not only the weight loss characteristics and kinetics parameters of the thermal pyrolysis process but also identify the gaseous byproduct generated in real time. Kai et al. [29] investigated the effects of the interaction between rice straw (RS) and high-density polyethylene (HDPE) on the evolution of volatile species and their distributions during the co-pyrolysis of RS and HDPE by TG–FTIR–MS. Wu et al. [30] analyzed the pyrolysis and co-pyrolysis behaviors of polyethylene (PE), polystyrene (PS), and polyvinyl chloride (PVC) under N₂ atmosphere by TG–FTIR. Zhang et al. [31] investigated the thermal decomposition of six representative components of municipal solid waste (MSW, including lignin, printing paper, cotton, rubber, PVC, and cabbage). Surjit Singh et al. [32] reported the characterization and assessment of the volatile species evolved during the thermal degradation of several waste materials, biomass wood waste, refuse derived fuel (RDF), waste plastic, and tire by use of TGA–FTIR and TGA–MS. Guo et al. [33] analyzed gas emissions from the thermo-oxidative process of plastic ASR under different N₂/O₂ volume ratios using TG–MS analysis, but only the production changes of small molecular gases under different reaction conditions were considered, such as H₂, CH₄, NH₃, HCN, NO, NO₂, CO₂, and SO₂. Mayyas et al. [34] studied the effect of the TiO₂ catalyst on the pyrolyzed byproducts of industrial plastic waste (i.e., automotive shredder residue, ASR) with TG–FTIR–GC/MS. In our study, in the TGA experiments for ASR, each main component (plastic, textile, leather, rubber, foam) and artificial mixture was examined with a thermogravimetric analyzer under non-isothermal conditions. Simultaneously, the chemical compositions of volatile products of the primary ASR pyrolysis and its main components were detected and identified by TG–FTIR–GC/MS.

2. Experimental Procedure and Specimens

2.1. Experimental Specimens

The ASR specimens studied in this work were obtained from the Zhangjiagang Huaren Resources Recycling Co., Ltd. (Zhangjiagang, Jiangsu Province, China), a domestic automobile dismantling enterprise. Reusable components with market value and particularly valuable material fractions such as batteries, air bags, tires, and catalytic converters are usually removed from ELVs. The remaining parts and the hulks are reduced to small pieces, most of the metal fraction is sorted using magnetic separation and eddy current separation, and the remaining fraction is called ASR, which amounts to ~20–25% of the average input ELV weight. ASR initial specimens were continuously obtained over one week from a crushing and sorting production line for ELVs. Visible bulks of metal to the human eye were sought out from the ASR initial specimens. The characteristics of the ASR specimens were determined by manual sorting and with a Mettler Toledo analytical balance (Changzhou, Jiangsu Province, China), and the results are shown in

Table 1. Material compositions of the experimental specimens.

Sample	Material Composition (wt.%)
	Metals	Plastics	Textiles	Leather	Rubber	Foam	Others
ASR	3.0	39.7	28.1	3.3	2.2	2.1	21.6
MixASR	0	53	37	3	4	3	0

.

All specimens were combined and mixed well to ensure a representative sample for the determination, and the uniformity of all specimens regarding the particle size (approximately ≤0.1 mm) was achieved. The reaction mechanism of ASR was unknown, so keeping the initial mass of each sample at a fixed constant for all measurements was safe [35]. Thus, the mass of all samples for the TG experiments was 100 ± 0.1 mg, considering the size of the sample pan and the accuracy of balance in the thermogravimetric analyzer.

2.2. Experimental Procedure

The TG–FTIR–GC/MS coupling technique is widely used in the analysis of organic pyrolysis behaviors. Therefore, we studied the pyrosis behaviors of ASR and its five main components with the TG–FTIR–GC/MS coupling technique. As shown in Figure 1, GC/MS (Perkin-Elmer SQ 8, Waltham, MA, USA) and FTIR (Perkin-Elmer TL 9000, Waltham, MA, USA) equipment was connected with a TG analyzer (Perkin-Elmer TGA 8000, Waltham, MA, USA), and all transmission lines were heated and maintained at 270 °C to prevent the condensation of any volatile disintegration products. Pyris-Manager software was used to analyze the TG and derivate TG (DTG) data, TimeBase Version 3.1.0 (Perkin-Elmer, Waltham, MA, USA) and Spectrum Version 10.5.3 (Perkin-Elmer, Waltham, MA, USA) were applied for the analysis of FTIR spectra data, and the mass spectra data were analyzed using TurboMass Ver 6.0.0 (Perkin-Elmer, Waltham, MA, USA).

The reaction evolution of plastic, textiles, rubber, leather, foam, ASR, and MixASR was recorded for a full range of temperatures from 30 to 800 °C at a constant heating rate of 10 °C/min under atmospheric control with high-purity (99.99%) nitrogen at a rate of 20.0 mL/min. The pressures of pneumatic gas and balance gas were set to 0.1 and 0.2 MPa, respectively. This nitrogen flow rate ensures an inert atmosphere for the sample during the run, whereas a small sample and slow heating rate ensures that the heat transfer limitations can be ignored. Gaseous products from the TG analyzer were directly collected in the gas cell and determined instantaneously using the Fourier transform infrared spectrometer. The resolution in FTIR was 4 cm⁻¹, and the scan range was from 4000 to 450 cm⁻¹. The FTIR spectra of the gaseous products were obtained continuously with the baseline modified. After the FTIR measurements, the gas products were instantaneously swept to the mass spectrometer. The oven temperature was heated and maintained at 270 °C, and the ionization energy under the electron-impact (EI) of gas volatiles was analyzed at 70 eV. The mass-to-ion ratio (m/z) ranged from 45 to 400 and was scanned 200 times per minute.

3. Results and Discussion

3.1. FTIR Analysis of Volatile Products

FTIR is an effective analytical instrument for detecting functional groups and characterizing covalent bonding information. In this study, the Fourier transform infrared spectra of pyrolytic product of plastic, textile, rubber, leather, foam, ASR, and MixASR were recorded to certify the basic chemical group of thermal decomposition product. As shown in Figure 2, Gram–Schmidt profiles of plastic, textile, MixASR, and ASR had only one significant peak, while the Gram–Schmidt profiles of rubber, leather, and foam had two peaks. Below 300 °C, the pyrolysis reactions of ASR, MixASR, or its main components were slow or nonexistent. Over 300 °C, the pyrolysis reactions of rubber, leather, and foam were rapid; the first peak appeared at 346, 322, and 371 °C, respectively, while the second peak appeared at 536, 533, and 452 °C, respectively. Pyrolysis reactions of plastic and textile mainly occurred in the temperature range of 400 to 600 °C, and the only peak appeared at 525 and 515 °C, respectively. Reaching 620 °C, the pyrolysis reaction of plastic, rubber, leather, textile and foam was basically completed, and the curve dropped sharply. The pyrolysis reaction of MixASR mainly occurred in the range of 400–600 °C, and the peak temperature was 526 °C. In addition to the five major organic components, ASR contains 24.6% of other substances in this study, so Gram–Schmidt profiles of ASR and MixASR were very different, but peaks both appeared at 526 °C. The reason is that plastics and fibers accounted for a high proportion of ASR and MixASR, which were the main substances affecting pyrolytic products.

According to the 3D stack plots of MixASR and ASR in Figure 3, the wavenumber ranges of absorption peaks are different. The main absorption peaks in the 3D stack plots of plastic and textiles also appear in the same wavenumber ranges in the 3D stack plots of ASR and MixASR. However, the intensity of the absorption peak at a certain position of MixASR or ASR is not the linear superposition result of the intensities of the absorption peaks at the same position of the five components. In short, the pyrolysis product of ASR is not a simple superposition of the pyrolysis products of its components, but the pyrolysis characteristics of the main components have the greatest influence on the product distribution, especially plastic and textiles.

With TimeBase and Spectrum software (Perkin-Elmer, Waltham, MA, USA), the Gram–Schmidt profiles of samples were analyzed, and the FTIR spectra of ASR, MixASR, its main components at 200, 300, 400, 500, 600, 700 °C, and temperatures of peaks of Gram–Schmidt profiles are shown in Figure 4 and Figure 5. These functional groups are useful for distinguishing some specific chemical compounds, like CO₂, alkanes, olefins, benzene, alcohols, and other organic components. According to Figure 4a–e and Figure 5, it can be observed that the locations of the absorption bands were almost the same for the same sample, but the absorbance intensities were different After pyrolysis, the temperature was higher than 300 °C. This indicated that the major categories of volatile products were not affected by the pyrolysis temperature, but the yield of each main product was still affected by the pyrolysis temperature. Strong absorption peaks appeared at 3100–2700, 1700–1550, and 1500–1250 cm⁻¹ for ASR and its main components, which were assigned to the stretching of =CH₂, –CH₃, –CH₂, –CH–, and C=C bonds. Furthermore, the absorption intensity of the corresponding macromolecules such as alkanes, aldehydes, and alcohols increased with pyrolysis temperatures and increased sharply at the peak temperatures of the Gram–Schmidt profiles, then sharply decreased. The bands of stretching of =CH–, stretching of –C=C–, and plane –CH– bending –C=CH₂ were assigned to the alkenes. The strong absorption peaks of 2930, 2850, and 1460 cm⁻¹ certify the existence of the methylene (–CH₂–) group. The formation mechanisms of–CH– and C=C bonds were cleavage of alkyl side chains and β bond scission of alkenes. CO₂ is represented by the peak between 2395 and 2250 cm⁻¹ for ASR and its main components, and the production of CO₂ increased with temperature, peaked at the first pyrolysis peak temperature, and then decreased sharply. After exceeding 500 °C, peaks appeared between 720–570 and 1050–1150 cm⁻¹, which were assigned to the symmetric stretching of C–O. Meanwhile, the CO at 2109–2173 cm⁻¹ can also be detected in the entire pyrolysis process. In addition to these substances, each component of ASR had relatively independent functional groups, but which eventually appeared in the mixture FTIR spectrum.

For plastic, the major pyrolytic products were alkanes and olefins, such as styrene, 3-ethyl-3-methyl heptane, and 2,4-dimethyl-1heptene, since the bonds of stretching =CH2, –CH₃, –CH₂, –CH– and bending RHC=CH₂ were assigned. The major pyrolytic products of textiles were CO₂, alkanes, olefins, benzene, and alcohols, e.g., 2,6-dimethylnonane, styrene, and 2-methyl-1-pentene. Except for CO₂, alkanes, olefins, and benzene series, the major pyrolytic products of rubber and leather also included alcohols, since the bands of stretching of alcoholic C–OH were assigned to the alcohols, e.g., 1-phenyl-2-propanol. The major pyrolytic products of foam were different; ketones were identified by the bonds of stretching keto C=O, e.g., 1-isopropoxy-propan-2-one. Compared with other components, there are more alkanes and alcohols in foam pyrolysis products.

The major pyrolytic products of ASR and MixASR were much the same, which included alkanes, olefins, and alcohols, and both had dense and indistinguishable weak peaks in the wavenumber range of 1900–1400 cm⁻¹. Obviously, many of these products have unstable or weaker chemical bonds, which can be further pyrolyzed under further high-temperature (>800 °C) or catalytic pyrolysis.

3.2. GC/MS Analysis of Volatile Products of ASR Pyrolysis

In the accurate identification of complicated volatile species, MS analysis is a useful complementary technique for TG–FTIR because TG–FTIR cannot measure homodiatomic species. In order to further accurately analyze the compound types and yields of volatile products of ASR pyrolysis, GC–MS analysis technology was used. The detectable compound was that with a concentration above the detection limit of GC–MS, while the identifiable compound by the NIST library was that with a comparatively large peak area. Since there is no distinguishable peak after 15 min, the chromatogram for the range from 0 to 15 min is shown in Figure 6. Moreover, during the identification of chemical compounds of volatile products, the radicals and functional groups evolved at peaks were based on the results of FTIR analysis. The identification results including compound names and yields of volatile pyrolytic products of ASR and its main components were summarized and are provided in

Table 2. GC–MS analysis results of the original ASR pyrolysis volatiles.

No.	Peaks	Formula	Compound	CAS Number	Yield/%
1	2.226	C8H16O	1-prop-2-enoxypentane	23186-70-1	2.8681
2	2.445	C3H9NO	1-aminopropan-2-ol	78-96-6	0.4912
3	2.544	C6H12	1-hexene	592-41-6	0.8056
		C6H12	4-methyl-1-Pentene	691-37-2
		C6H13Cl	2-chlorohexane	638-28-8
4	2.771	C4H8O	tetrahydrofuran	109-99-9	0.2440
		C5H10O2	4-ethyl-1,3-dioxolane	29921-38-8
5	3.037	C6H11ClO	α-chlorohexanal	762-39-0	2.6292
6	3.508	C7H12O3	2-methylacrylic acid 3-hydroxypropyl ester	2761-09-3	0.8626
		C7H12O3	2-hydroxypropyl methacrylate	923-26-2
7	4.364	C7H8	toluene	108-88-3	4.1164
8	4.798	C8H18O	2,3-dimethylhexan-3-ol	4166-46-5	0.2205
		C6H14O	4-Methyl-2-pentanol	108-11-2
9	5.147	C6H12O2	1-isopropoxy-propan-2-one	42781-12-4	0.3793
10	5.623	C9H18	2,4-dimethyl-1heptene	19549-87-2	1.6540
11	6.026	C8H10	ethylbenzene	100-41-4	1.2742
			o-Xylene	95-47-6
12	6.593	C8H8	annulene	629-20-9	20.6849
			benzocyclobutene	694-87-1
			styrene	100-42-5
13	7.205	C9H12	cumene	98-82-8	0.0749
14	7.614	C9H10	prop-2-enylbenzene	300-57-2	0.1990
15	8.127	C6H6O	phenol	108-95-2	0.3113
16	8.181	C8H14O2	butyl methacrylate	97-88-1	0.2616
17	8.274	C9H10	2-phenyl-1-propene	98-83-9	3.0575
18	8.717	C14H30	7-methyltridecane	26730-14-3	0.0597
		C10H22	3-ethyl-3-methyl heptane	17302-01-1
19	9.06	C8H18O	2-ethylhexan-1-ol	104-76-7	0.8311
			2-propylpentan-1-ol	58175-57-8
20	9.142	C8H16	3,4,4-trimethyl-2-pentene	598-96-9	0.2199
			2,4,4-trimethyl-2-pentene	107-40-4
21	9.36	C10H12	4-phenyl-1-butene	768-56-9	0.1319
22	9.601	C10H12	alpha,p-dimethylstyrene	1195-32-0	0.2256
23	9.754	C8H8O	acetophenone	98-86-2	0.0718
24	9.907	C13H28O	11-methyl-1-dodecanol	85763-57-1	0.2098

and

Table 3. GC–MS analysis results of the MixASR pyrolysis volatiles.

No.	Peaks	Formula	Compound	CAS Number	Yield/%
1	2.229	C6H12O	1-prop-2-enoxypropane	1471-03-0	8.1671
2	2.431	C7H10O6	methanetricarboxylic acid, 1,1,1-trimethyl ester	1186-73-8	0.4723
3	2.521	C6H12	2-methyl-1-pentene	763-29-1	1.9019
			1-hexene	592-41-6
4	4.347	C9H12O	1-phenyl-2-propanol	698-87-3	2.0945
5	4.784	C6H14O	4-methyl-2-pentanol	108-11-2	0.8483
6	5.13	C6H12O2	1-isopropoxy-propan-2-one	42781-12-4	0.7124
7	5.609	C9H18	2,4-dimethyl-1heptene	19549-87-2	6.9013
8	6.0009	C8H10	ethylbenzene	100-41-4	0.2366
			o-xylene	95-47-6
9	6.579	C8H8	styrene	100-42-5	17.1758
10	8.266	C9H10	2-phenyl-1-propene	98-83-9	0.3269
11	8.702	C10H22	3-ethyl-3-methyl heptane	17302-01-1	0.4045
		C11H24	2,6-dimethylnonane	17302-28-2
		C14H30	dodecane,4,6-dimethyl	61141-72-8
12	9.136	C10H16	(3R)-(+)-isosylvestren	1461-27-4	0.2890
13	9.902	C13H28O	11-methyl-1-dodecanol	85763-57-1	0.7403

, and Appendix A. According to the GC–MS analysis results, several points were concluded as follows:

(1)

The identified gaseous pyrolytic products were both composed of alkanes, olefins, alcohols, and benzene series, which were consistent with the analysis results of FTIR. The gaseous pyrolytic products of MixASR and ASR were not the simple superposition of pyrolytic gaseous products of its components, but main compounds of MixASR and ASR also appeared in the pyrolytic products of its main components, especially plastic and textile, e.g., styrene, 1-hexene, toluene, ethylbenzene, 2,4-dimethyl-1heptene, and 11-methyl-1-dodecanol.

(2)

In the volatile products of the plastics, rubber, leather, textiles, and foam pyrolysis, the total proportions of detectable macromolecular substances were 26.2634, 34.9797, 39.0640, 54.1273, and 39.2296%, respectively. The pyrolysis product of plastic contains 6.0263% olefins, 2.5443% alcohols, 15.25114% benzene series, and very few alkanes. The pyrolysis product of the rubber component contains 13.3232% alkanes, 4.7653% olefins, and 4.6502% alcohols. The leather component pyrolysis product contains 3.3224% alkanes, 7.1102% alkenes, 6.4884% alcohols, and 7.4626% ethers. The pyrolysis products of textiles components contained 1.1139% alkanes, 20.4953% olefins, 7.5055% alcohols, and 15.9611% benzene series. The pyrolysis products of foam components contained 6.8049% alkanes, 12.4046% olefins, 2.4621% ethers, 1.8138% benzene series, and 13.4151% ketones.

(3)

The total proportions of detectable macromolecular substances in the volatile products of the original ASR and MixASR pyrolysis were 41.884% and 40.2709%, respectively. The specific detected substances are shown in Table 2 and Table 3. The ASR pyrolysis product contains 3.7385% alkanes, 26.5539% alkenes, and 9.3305% benzene series. The MixASR pyrolysis products contains 0.4045% alkanes, 2.1909% olefins, and 17.739% benzene series. From the comparison of the yield of various pyrolysis products, it can also be seen that the pyrolysis products of ASR or MixASR are not the linear superposition of the pyrolysis products of its main components. This shows once again that the main components of ASR have obvious interactions in the pyrolysis process, and this effect affects the product distribution.

(4)

Based on the GC–MS analysis results of ASR and its main components, it can be seen that the yields of olefin and benzene series are high in the pyrolytic products, especially styrene. In pyrolytic products of plastic, textiles, foam, ASR, and MixASR, styrene accounted for 13.62, 11.64, 11.93, 17.18, and 20.68%, respectively. However, these substances are chemically unstable and can be further reacted by improving the process to generate more CO and H₂.

3.3. Analysis, Summary, and Discussion

According to the Py–FTIR–GC–MS analysis, the pyrolysis process of ASR could be concluded as follows. Firstly, small molecule alkenes and cycloalkenes were generated from the degradation of ASR due to chain scission at low temperature. Then, the released alkenes and cycloalkenes underwent a series of reactions to form benzene and benzene derivatives as the pyrolysis temperature increased. The main pyrolysis products were concentrated in alkenes, olefins, alcohols, and aromatic hydrocarbons. The yields of volatile products of ASR pyrolysis varied greatly with changing pyrolysis temperature. Considering that plastic and textiles account for a high proportion of ASR, and other organic matter is affected by them during the pyrolysis process [21], the design of pyrolysis temperature can refer to the pyrolysis characteristics of plastics and fibers. Since most volatile products are chemically unstable, more syngas with a greater calorific value could be obtained by catalytic pyrolysis and gasification [36,37,38].

4. Conclusions

In this work, efforts were made to investigate the pyrolysis characteristics of ASR and its main components (i.e., plastic, textile, leather, rubber, and foam) through TG–FTIR-GC–MS. The mass variation of samples and the gaseous products were measured simultaneously. Comparing the results of FTIR and GC–MS analysis, good consistency between these two approaches was observed, and the main conclusions can be summarized as follows:

(1)

The main volatile products of ASR and its main components are alkanes, olefins, alcohols, and benzene series, and their proportions in the pyrolysis products are 3.7385, 26.5539, and 9.3305%, respectively. Many of these volatile products have unstable or weaker chemical bonds, such as =CH–, =CH₂, –C=C–, and –C=CH₂. Hence, more syngas can be obtained with further high-temperature (>800 °C) pyrolysis [39,40]. Catalytic pyrolysis and gasification are important research directions for obtaining syngas with a greater calorific value [36,37,38].

(2)

According to the Gram–Schmidt profiles and the 3D stack plots of MixASR, ASR, and its main components, the pyrolysis product of ASR is not a simple superposition of the pyrolysis products of its components, but the pyrolysis characteristics of the main components have the greatest influence on the product distribution, especially plastic and textiles. Some hazardous gas exists in pyrolytic products of ASR, such as benzene and toluene, which are harmful to the human body and environment. Therefore, the elimination of toxic and hazardous substances must be considered in the design of pyrolysis process.

In brief, the TG–FTIR–GC–MS coupling technique provided a deeper insight into the understanding of pyrolysis behaviors of ASR. This is helpful for the design of further pyrolysis processes for obtaining more syngas with higher heating value. It could also provide basic information for an industrial pilot or industrialization of the ASR or polymer pyrolysis process.