Development of Process for Disposal of Plastic Waste Using Plasma Pyrolysis Technology and Option for Energy Recovery

Production of hydrogen-rich fuel gas from waste plastics using continuous plasma pyrolysis reactor

There is a serious concern about the large amount of accumulated plastic waste all around the world. Synthetic polymers such as polyethylene terephthalate (PET), polypropylene (PP), and polyethylene (HDPE, LDPE) are substantially present in the plastic waste generated. There are various methods reported to minimise such plastics waste with certain limitations. To overcome such limitations the present study have been carried out in which thermal decomposition of plastic waste of PET, PP, HDPE, and LDPE studied using a novel plasma pyrolysis reactor. The major objective of this work is to investigate the viability of the continuous plasma pyrolysis process for the treatment of various plastic wastes with respect to waste volume reduction and production of combustible hydrogen-rich fuel gas. The effect of temperature and feed flow rate on product gas yield, product gas efficiency, solid residue yield, and H2/CO ratio has been evaluated. The experiments have been carried out at different temperatures within the range of 700-1000 °C. Plasma pyrolysis system exhibited combustible hydrogen-rich gas as a product and solid residue. Liquid products have not been observed during plasma pyrolysis, unlike conventional pyrolysis. The reaction mechanism of plastic cracking has been discussed based on literature and products obtained in the present work. The effects of feed flow rate and temperature on exergy efficiency were studied using the response surface method. The mass, energy, and exergy analyses have also been carried out for all the experiments, which are in the range of 0.95-0.99, 0.48 to 0.77, and 0.30 to 0.69, respectively.

Progress and perspective for conversion of plastic wastes into valuable chemicals

Today, discarded plastics in nature have caused serious "white pollution", however these plastic wastes contain abundant carbon resources that could serve as the feedstock to produce commodities. Because of this, it is requisite to convert these plastic wastes into valuable chemicals. Herein, the state-of-the-art techniques for plastic conversion are divided into two categories, those performed under violent conditions and mild conditions, in which the conversion mechanisms are discussed. The strategies under violent conditions are closer to practical application thanks to their excellent conversion efficiencies, while the strategies under mild conditions are more environmentally friendly, showing enormous development potential in the future. We summarize in detail the pyrolysis, hydropyrolysis, solvolysis and microwave-initiated catalysis for bond cleavage in plastic wastes at temperatures ranging from 448 to 973 K. Also, we overview the photocatalysis, electrocatalysis and biocatalysis for bond cleavage in plastic wastes at near and even normal temperature and pressure. Finally, we present some suggestions and outlooks concerning the improvement of current techniques and in-depth mechanisms of investigation for conversion of plastics into valuable chemicals.

Overcoming challenges due to enhanced biomedical waste generation during COVID-19 pandemic

Biomedical wastes (BMWs) are potentially infectious to the environment and health. They are co-dependent and accumulative during the ongoing coronavirus disease-2019(COVID-19) pandemic. In India the standard treatment processes of BMWs are incineration, autoclaving, shredding, and deep burial; however, incineration and autoclaving are the leading techniques applied by many treatment providers. These conventional treatment methods have several drawbacks in terms of energy, cost, and emission. But the actual problem for the treatment providers is the huge and non-uniform flow of the BMWs during the pandemic. The existing treatment methods are lacking flexibility for the non-uniform flow. The Government of India has provisionally approved some new techniques like plasma pyrolysis, sharp/needle blaster, and PIWS-3000 technologies on a trial basis. But they are all found to be inadequate in the pandemic. Therefore, there is an absolute requirement to micromanage the BMWs based on certain parameters for the possible COVID-19 like pandemic in the future. Segregation is a major step of the BMW management. Its guideline may be shuffled as segregation at the entry points followed by collection instead of the existing system of the collection followed by segregation. Other steps like transportation, location of treatment facilities, upgradation of the existing treatment facilities, and new technologies can solve the challenges up to a certain extent. Technologies like microwave treatment, alkaline hydrolysis, steam sterilization, biological treatment, catalytic solar disinfection, and nanotechnology have a lot of scopes for the treatment of BMWs. Hi-tech approaches in handling and transportation are found to be fruitful in the initial steps of BMW management. End products of the treated BMWs can be potentially fabricated for the application in the built environment. Some policies need to be re-evaluated by the health care facilities or government administrations for efficient BMW management.

Multi-Scale Modeling of Plastic Waste Gasification: Opportunities and Challenges

Among the different thermo-chemical recycling routes for plastic waste valorization, gasification is one of the most promising, converting plastic waste into syngas (H₂+CO) and energy in the presence of an oxygen-rich gas. Plastic waste gasification is associated with many different complexities due to the multi-scale nature of the process, the feedstock complexity (mixed polyolefins with different contaminations), intricate reaction mechanisms, plastic properties (melting behavior and molecular weight distribution), and complex transport phenomena in a multi-phase flow system. Hence, creating a reliable model calls for an extensive understanding of the phenomena at all scales, and more advanced modeling approaches than those applied today are required. Indeed, modeling of plastic waste gasification (PWG) is still in its infancy today. Our review paper shows that the thermophysical properties are rarely properly defined. Challenges in this regard together with possible methodologies to decently define these properties have been elaborated. The complexities regarding the kinetic modeling of gasification are numerous, compared to, e.g., plastic waste pyrolysis, or coal and biomass gasification, which are elaborated in this work along with the possible solutions to overcome them. Moreover, transport limitations and phase transformations, which affect the apparent kinetics of the process, are not usually considered, while it is demonstrated in this review that they are crucial in the robust prediction of the outcome. Hence, possible approaches in implementing available models to consider these limitations are suggested. Finally, the reactor-scale phenomena of PWG, which are more intricate than the similar processes-due to the presence of molten plastic-are usually simplified to the gas-solid systems, which can result in unreliable modeling frameworks. In this regard, an opportunity lies in the increased computational power that helps improve the model's precision and allows us to include those complexities within the multi-scale PWG modeling. Using the more accurate modeling methodologies in combination with multi-scale modeling approaches will, in a decade, allow us to perform a rigorous optimization of the PWG process, improve existing and develop new gasifiers, and avoid fouling issues caused by tar.

A Journey from Processing to Recycling of Multilayer Waste Films: A Review of Main Challenges and Prospects

In a circular economy context with the dual problems of depletion of natural resources and the environmental impact of a growing volume of wastes, it is of great importance to focus on the recycling process of multilayered plastic films. This review is dedicated first to the general concepts and summary of plastic waste management in general, making emphasis on the multilayer films recycling process. Then, in the second part, the focus is dealing with multilayer films manufacturing process, including the most common materials used for agricultural applications, their processing, and the challenges of their recycling, recyclability, and reuse. Hitherto, some prospects are discussed from eco-design to mechanical or chemical recycling approaches.

Recycled (Bio)Plastics and (Bio)Plastic Composites: A Trade Opportunity in a Green Future

Today’s world is at the point where almost everyone realizes the usefulness of going green. Due to so-called global warming, there is an urgent need to find solutions to help the Earth and move towards a green future. Many worldwide events are focusing on the global technologies in plastics, bioplastic production, the recycling industry, and waste management where the goal is to turn plastic waste into a trade opportunity among the industrialists and manufacturers. The present work aims to review the recycling process via analyzing the recycling of thermoplastic, thermoset polymers, biopolymers, and their complex composite systems, such as fiber-reinforced polymers and nanocomposites. Moreover, it will be highlighted how the frame of the waste management, increasing the materials specificity, cleanliness, and a low level of collected material contamination will increase the potential recycling of plastics and bioplastics-based materials. At the same time, to have a real and approachable trade opportunity in recycling, it needs to implement an integrated single market for secondary raw materials.

Impact of climatic and non-climatic stressors on ocean life and human health: A review

Ocean life forms are fundamentally well adapted to natural environmental variations, and they can even tolerate extreme conditions for a short time. However, several anthropogenic stressors are causing such drastic changes in the ocean ecosystem. First, the review attempts to outline the impact of climatic and non-climatic stressors on ocean life, and it also outlines the synergistic impact of both stressors. Then the impact on human health caused by the damage of the marine ecosystem has been discussed. Furthermore, the type of prior studies and current mitigation adaptation programs have been presented. Finally, some perspectives about future research and mitigation adaptation are offered.

Current Trends in Waste Plastics’ Liquefaction into Fuel Fraction: A Review

Polymers and plastics are crucial materials in many sectors of our economy, due to their numerous advantages. They also have some disadvantages, among the most important are problems with the recycling and disposal of used plastics. The recovery of waste plastics is increasing every year, but over 27% of plastics are landfilled. The rest is recycled, where, unfortunately, incineration is still the most common management method. From an economic perspective, waste management methods that lead to added-value products are most preferred—as in the case of material and chemical recycling. Since chemical recycling can be used for difficult wastes (poorly selected, contaminated), it seems to be the most effective way of managing these materials. Moreover, as a result this of kind of recycling, it is possible to obtain commercially valuable products, such as fractions for fuel composition and monomers for the reproduction of polymers. This review focuses on various liquefaction technologies as a prospective recycling method for three types of plastic waste: PE, PP and PS.

Plastic waste management: A road map to achieve circular economy and recent innovations in pyrolysis

The contemporary world is challenged by mounting of plastic waste on the environment due to increase in economy and population. Over 90% of virgin plastics are produced from fossil fuels, hence, recycling is the best solution to reduce extracting and exploiting fossil fuels, and grow towards a circular economy. The type of waste and its hierarchy offers a route to pick up proper waste recycling policies which get the most out of the available resources and its protection. Pyrolysis process offers more valuable ways to turn the plastic waste to useful products for fueling and raw materials for making new plastics, and acts as an environmentally sound alternative to incineration and inefficient landfilling. This study provides a basic insight into plastic pyrolysis technology with recent trends and innovations in various countries, and their path towards the achievement of a circular economy. Plastic manufacturers, waste managers and the public plays a vital role in the development of the recycling sector. Recycling will stay underdeveloped and borderline without specific regulations to increase its effectiveness. Sustainable development in managing the plastic would be possible only through significant policies to instruct the individual and social challenges. The current article also targets the readers without scientific knowledge to get a basic idea of pyrolysis and general awareness of proper plastic waste management in a closed loop system.

An Overview of Thermal Plasma Arc Systems for Treatment of Various Wastes in Recovery of Metals

Thermal plasma systems are being used for the recovery of metals from complex waste and minerals. The latter contain multiphase metals in various forms that are extremely tedious to separate. Thermal plasma arc melts the waste and minerals for qualitative plasma products for powder industries. In this overview, we briefly report a description of the various thermal plasma systems and their uses in recovering metal from metal-containing materials in the form of waste or minerals. Various plasma arc systems, such as transferred, nontransferred, and extended arc, have enabled the development of an efficient and environmentally friendly way to recover valuable metals from industrial wastes such as red mud and minerals such as ilmenite.

Thermal Plasma Treatment of Medical Waste

The harmless treatments of medical waste have significantly drawn people’s attention owing to their risks to health-care staff, the public, and the environment. The traditional thermal technology for processing medical waste may cause indispensable secondary pollution such as dioxin, furan, and heavy metals, and infectious materials that may remain in the solid residual. Thermal plasma technologies offer advantages of effectively treating medical waste due to its high temperature and energy density, lower pollutant emissions, rapid start-up and shut-down, and smaller size of the installation. These benefits play roles in the treatment of medical waste on-site or off-site, especially when somewhere encounters an abnormally sharp increase in medical waste. This paper mainly introduces the typical thermal plasma processes of medical waste and its central component, plasma furnace. Meanwhile, how process parameters influence the formed gaseous and solid products, the performances of mass and volume reduction, pathogen destruction, and energy recovery, are discussed in detail. Finally, the mechanism of the thermal plasma process is also analyzed.

Technologies for chemical recycling of household plastics - A technical review and TRL assessment

Chemical recycling is considered an attractive technological pathway for reducing waste and greenhouse gas emissions, as well as promoting circular economy. In the EU, readiness to develop a full commercial plant is becoming increasingly important given the ambitious goal to recycle all plastics by 2030. Household packaging streams tend to be of lower quality and lower recycling performance compared to industrial and commercial waste streams, thus requiring particular attention. This paper assesses chemical recycling technologies available and identifies the most suitable for recycling of household plastic waste. We identify eight different technologies and compare them in terms of process temperature, sensitivity to feedstock contamination and level of polymer breakdown, three critical factors affecting the cost and attractiveness of a chemical process. In addition, we carry out a Technology Readiness Level (TRL) assessment for eight technologies based on the stage of their present development. The review is based on peer-reviewed scientific papers and information collected from technology developers and providers, as well as interviews with experts. Our analysis outlines advantages and disadvantages of technologies available for chemical plastic recycling and their TRL. The chemical recycling technologies with the highest TRL are pyrolysis, catalytic cracking and conventional gasification. However, the economic feasibility of these technologies is difficult to assess due to the low number of projects in operation and scarcity of data available for comparison. The results of this analysis provide timely information as policy makers and developers set targets for recycling, and contemplate investments on research and chemical plastic recovering plants.

Thermal degradation of waste plastics under non-sweeping atmosphere: Part 1: Effect of temperature, product optimization, and degradation mechanism

Continuous generation of plastic waste has prompted substantial research efforts in its utilization as a feedstock for energy generation. Pyrolysis has emerged as one of the best waste management technique for energy extraction from the plastic waste. The objective of this work is to investigate the effect of operating temperature on the liquid product yields in the pyrolysis process by non-isothermal heating. Non-catalytic thermal pyrolysis of waste polyethylene (PE) [high density polyethylene (HDPE)], waste polypropene (PP), waste polystyrene (PS), waste polyethylene terephthalate (PET) and mixed plastic waste (MPW) was carried out in a non-sweeping atmosphere in a semi-batch reactor at four different temperatures 450, 500, 550, and 600 °C. The minimum degradation temperature of the mixed and individual plastics was obtained using a thermogravimetric apparatus (TGA) at a heating rate of 20^°C/min. The TGA results show that all plastics degrade in a single step and the degradation temperatures of PS > PET > PP > HDPE, while mixed plastic degradation indicates two distinct degradation steps. Further, a waste polymer shows a lower degradation temperature than the virgin polymer. The degradation of HDPE is found to produce the maximum oil yield with minimum solid residue. The degradation of PET results in the highest amount of solid and benzoic acid as crystals and gas with no oil. Degradation of mixed plastic causes oil yield in the intermediate range of pyrolysis of individual plastic wastes. Overall, 500 °C is observed to be an optimum temperature for the recovery of low-density pyrolytic oil with the highest liquid yield. The degradation of PE and PP is found to be caused by random chain scission followed by inter and intramolecular hydrogen transfer. The degradation of PS occurs by side elimination or end chain scission followed by β-scission mechanism. The degradation of mix plastics results from random chain scission followed by β-scission mechanism. The effect of temperature on oil and gas recovery as well as recovery time was also assessed.

Towards the effective plastic waste management in Bangladesh: a review

The plastic-derived product, nowadays, becomes an indispensable commodity for different purposes. A huge amount of used plastic causes environmental hazards that turn in danger for marine life, reduces the fertility of soil, and contamination of ground water. Management of this enormous plastic waste is challenging in particular for developing countries like Bangladesh. Lack of facilities, infrastructure development, and insufficient budget for waste management are some of the prime causes of improper plastic management in Bangladesh. In this study, the route of plastic waste production and current plastic waste management system in Bangladesh have been reviewed extensively. It emerges that no technical and improved methods are adapted in the plastic management system. A set of the sustainable plastic management system has been proposed along with the challenges that would emerge during the implementation these strategies. Successful execution of the proposed systems would enhance the quality of plastic waste management in Bangladesh and offers enormous energy from waste.