A comprehensive review on pyrolysis from the circular economy point of view and its environmental and social effects

Abstract

The rising volume of waste created worldwide due to industrialization and commercial activity necessitates a method of waste management that is both effective and efficient. However, waste management is linked to unsustainable patterns in a linear economic system. On the contrary, a circular economy (CE) is widely perceived to solve various issues, including resource scarcity and long-term economic benefits. Utilizing pyrolysis to convert waste to energy and valuable compounds is a potential method for reducing waste while producing valuable end products. The current article offers a thorough analysis of pyrolysis from a circular economy point of view. First, the nature of pyrolysis is briefly described to understand subsequent concepts better. In the following, the pyrolysis of three types of waste, including tire, plastic, and biomass, is deeply investigated from the CE aspect. Then, the social and environmental impacts of pyrolysis from the life cycle assessment (LCA) perspective in developed and developing countries are scrutinized. In the end, ongoing challenges and suggestions for future research are also discussed. Pyrolysis products have not yet been standardized for trade in the market. However, pyrolysis might be able to close the loop of energy and materials. Also, LCA results revealed that pyrolysis has acceptable environmental impacts and a low global warming potential (GWP).

Introduction

Today, the planet faces several grave concerns, including an ever-increasing world population and the resulting threats to water, energy, and food security (Amulya et al., 2016). Additionally, greenhouse gas (GHG) emissions and other contaminants pose a tremendous danger to humanity because of human-caused climate change (Ouda et al., 2016). Due to constrained funds, maintenance facilities, and infrastructure, sustainable waste management is still in its infancy in most developing nations (Tan et al., 2015). The actual rate of waste collection in the majority of cities in developing nations such as Pakistan, Bangladesh, and India is only around 60 percent, with the remaining waste accumulating on vacant lands, railway lines, street sides, sewers, and low-lying regions (Sadef et al., 2016). Hence, the gap between economic development and environmental sustainability is expanding (Nizami et al., 2017). The sustainable methods, policies, and legislation to overcome climate change and guarantee a consistent source of feed and energy have become essential to facilitating circular economies in developing nations (Guerrero et al., 2013).

Circular Economy (CE) became associated with offering an alternative to the current linear economic paradigm, often known as the “take, manufacture, and discard” model, during the past decade (Andersen, 2007). CE is projected to stimulate economic development by establishing new enterprises and employment opportunities, cutting the cost of products, reducing price volatility, and enhancing supply security while minimizing environmental consequences (Kalmykova et al., 2018). CE is based on the premise that the economy and environment might mutually reinforce environmental protection and develop and profit from new business models while offering creative employment prospects (Ghisellini et al., 2018).

Pyrolysis has recently received much attention from researchers. In this technique, organic molecules disintegrate thermochemically at temperatures between 300 and 1200 °C in an inert atmosphere (Foong et al., 2020). Pyrolysis, unlike combustion, is a thermochemical recycling process that allows for the recovery of energy and materials (Boateng, 2020). As a result, liquid and gaseous hydrocarbon compounds and a carbon-rich solid are produced. As will be discussed later, pyrolysis allows for separating the primary components of feedstock, creating ideal circumstances for a circular economy (Martínez, 2021). Furthermore, it can simultaneously address issues related to energy consumption, greenhouse gas (GHG) emissions, and waste management. When pyrolysis products are employed commercially as raw materials in other processes, ensuring social and environmental equality, pyrolysis is established as a tool for a CE. In this scenario, the waste cycle is closed, and natural resource consumption is reduced for the benefit of present and future generations (Kirchherr et al., 2017).

This review article first addresses the nature of pyrolysis. In the following, the pyrolysis of three types of waste, including biomass, plastic, and tire, is studied in depth from the CE perspective. Finally, in developed and developing countries, pyrolysis's environmental and social effects from the life cycle assessment (LCA) aspect are explored.