Quality and environmental impacts of oil production through pyrolysis of waste tyres

Highlights

• Quality of tyre pyrolysis oil and pollution generated via pyrolysis investigated.

• The density of heavy oil was lower as compared to light oil.

• Tyre Pyrolysis Units are badly affecting the surrounding environment.

• Sulphate, TSS, TDS, Copper, and Manganese were found above the allowable limit.

Abstract

The quality of tyre pyrolysis oil (TPO) and the pollution generated through tyre pyrolysis units were investigated. Two oil types are generally produced, known as light TPO and heavy TPO, exhibiting a pungent smell. Gross calorific value (GCV) of TPO varies from 18275.5 Btu/lb to 18641.8 Btu/lb. GCV shows TPO can be used as fuel oil in industries for energy recovery purposes. The density of heavy oil was lower as compared to light oil. Values of density for both oils were higher than the furnace oil and petroleum, which are 0.96 g/cm³ for local furnace oil and 0.98 g/cm³ for imported furnace oil and 0.88 for petroleum. Results showed that tyre pyrolysis units are badly affecting the surrounding environment. The emission level of CO was 2608 ± 1442.3 mg/Nm³ at site 1, NOx was 826.16 ± 645.52 mg/Nm³ at site 2, SO₂ was 997 ± 1164 at site 2 and emission of PM was 1629 ± 311.6 mg/Nm³ at site 2. The emission level of all these pollutants was above permissible limits. The effluents results show that the concentration of sulphate, TSS, TDS, copper (Cu${}^{+2}$), and manganese was above the allowable limit. COD was very high; it varied from 31809 mg/L to 42144 mg/L.

Introduction

Currently, waste-to-energy is receiving additional significance to deal with economic and environmental problems (Uyumaz et al., 2019). At the global level, removing desecrate tyres is emerging as the most important ecological problem; population growth, increased vehicle usage, and rapid industrialization are major causes of this problem (Cheung et al., 2011). Waste tyres are not decomposed naturally and, if not properly handled, can last for numerous years (Suhanya et al., 2013).

Approximately 1.5 billions tyres are sold annually worldwide, and consequently, a similar quantity of waste tyres are discarded. This will finally go into the waste stream producing a major potential waste and environmental problem (Williams et al., 1998). Apart from this, 15%–20% of these waste tyres are recognized for reuse (Chen et al., 2019). It means that the remaining 75%–80% of waste tyres persist in the environment as waste. As a result, the disposal of garbage and tyres is regarded as a serious pollution problem. In tyres, rubber contains a high calorific value that makes them ideal feedstock for fuel protection (Song et al., 2018). Energy and material recovery are considered as a good use from waste tyres (Li et al., 2018). The waste tyre’s life span is 80–100 years in landfills because of the thermostat polymer structure that neither melts nor distributed into its chemical constituents (Murugan et al., 2008). Tyre waste is bulky and their disposal in landfill cause eruption of fire and toxicity because of accumulation of harmful gases or habitat of disease-causing vectors, flies and rodents. The utilization of pyrolysis oil of waste tyres as an alternative to petroleum-based fuels is a good choice to minimize natural resource utilization. It is reported by various researchers that pyrolysis of waste tyre produced tyre pyrolysis oil, pyrolytic gas, and char. It is also revealed that waste tyre pyrolysis oil has near diesel fuel characteristics (Czajczyńska et al., 2017).

Pyrolysis is a thermochemical tertiary recycling method in which organic polymers are converted into liquid oil at high temperatures (400–600 °C) in the absence of oxygen (O${}_2$). Pyrolysis allows the dissolution of the waste, and it also produces useful by-products. In this process, gas, liquid, and solid phases are formed. Pyrolytic gases have a high heating value, about 30–40 MJ/Nm³. The energy obtained from the combustion of the pyrolytic gas is enough to perform the pyrolysis process and be utilized for other applications (Czajczyńska et al., 2017). Since the 1990’s sustainable development has transferred the world’s attention from poor technologies and simple growth towards​ environment-friendly development, sustainable development could not catch the attention of policy developers (Nasir and Rehman, 2011).

The import of used tyres is permitted with the terms to fulfil environmental requirements for using scrap tyres as a source of direct fuel approved in Pakistan by the federal government, according to the Pakistan Import Policy Order 2013 (IPO-2013). In the case of tyre pyrolysis plants, second-hand tyres are used to extort oil and not directly used as fuel. Therefore, the importation of second-hand tyres for extraction oil through pyrolysis is not under the IPO-2013. In Pakistan’s case, the tyre pyrolysis technique used for the generation of pro-oil, carbon black, and hydrocarbon gas is incomplete and unsuccessful. It results in low-quality pyro-oil production, which causes major environmental problems such as liquid waste and gaseous emissions. Water is used for cooling purposes. The wastewater of cooling tanks is discharged after 3–4 batches and contains some oil, carbon particles, and dirt. Wastewater from wet scrubbers is drained after 2–3 batches and contained particulate matter, oil, and carbon. Fluid effluent is discharged into the surrounding without any treatment (Szklo and Schaeffer, 2007). Pyrolysis has been addressed as an attractive thermochemical process to tackle the waste tyre disposal problem while allowing energy recovery (Martínez et al., 2013). Different chemical compositions and the cross-linked structures of rubber in tyres are the main cause due to extremely resistant to biodegradation, photochemical decomposition, chemical reagents, and high temperatures. Therefore, the increasing numbers of used tyres constitute a serious threat to the natural environment (Sienkiewicz et al., 2012).

Tyre management strongly affects environmental protection and involves the maintenance of the resource since problems linked with reducing resources, energy demand, and waste management are severely associated and necessary combined method (Antoniou and Zabaniotou, 2013). The properties of the TPOs showed their potential to replace conventional fuels. However, some of them need to be improved, i.e., by reducing the sulphur, nitrogen, and aromatic content (Alvarez et al., 2017). This study focuses on monitoring the environmental pollution produced by tyre pyrolysis plants in terms of air emissions and wastewater. Qualitative analysis of pyro-oil made through tyre pyrolysis has also been carried to check the oil’s quality.