Using CO 2 to mitigate evolution of harmful chemical compounds during thermal degradation of printed circuit boards

Recovery of non-metallic useable materials from e-waste

Tremendous amounts of electric and electronic wastes (e-waste) are generated daily, and their indiscriminate disposal may cause serious environmental pollution. The recovery of non-metallic materials from e-waste is a strategy to not only reduce the volume of e-waste but also avoid pollutant emissions produced by indiscriminate disposal of e-waste. Pyrolysis, sub/supercritical water treatment, chemical dissolution, and physical treatment (e.g., ball milling, flotation, and electrostatic separation) are available methods to recover useable non-metallic materials (e.g., resins, fibers, and various kinds of polymers) from e-waste. The e-waste-derived materials can be used to manufacture a large variety of industrial and consumer products. In this regard, this work attempts to compile relevant knowledge on the technologies that derive utilizable materials from different classes of e-waste. Moreover, this work highlights the potential of the e-waste-derived materials for various applications. Current challenges and perspectives on e-waste upcycling to useable materials are also discussed.

Micropollutants in biochar produced from sewage sludge: A systematic review on the impact of pyrolysis operating conditions

Biochar obtained from sewage sludge serves as a valuable soil amendment in agriculture, enhancing soil properties by increasing the nutrient content, cation exchange capacity, water retention, and oxygen transmission. However, its utilisation is hampered by the presence of micropollutants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and volatile organic compounds (VOCs). Previous studies indicate that the type and amount of micropollutants can be significantly adjusted by selecting the right process parameters. This literature review provides an overview of how (1) pyrolysis temperature, (2) carrier gas flow and type, (3) heating rate, and (4) residence time affect the concentration of micropollutants in biochar produced from sewage sludge. The micropollutants targeted are those listed by the European Biochar Certificate (EBC) and by the International Biochar Institution (IBI), including PAHs, PCDD/Fs, PCBs and VOCs. In addition, per- and poly-fluoroalkyl substances (PFAS) are also considered due to their presence in sewage sludge. The findings suggest that higher pyrolysis temperatures reduce micropollutant levels. Moreover, the injection of a carrier gas (N2 or CO2) during the pyrolysis and cooling processes effectively lowers PAHs and PCDD/Fs, by reducing the contact of biochar with oxygen, which is crucial in mitigating micropollutants. Nevertheless, limited available data impedes an assessment of the impact of these parameters on PFAS in biochar. In addition, further research is essential to understand the effects of carrier gas type, heating rate, and residence time in order to determine the optimal pyrolysis process parameters for generating clean biochar.

Achievements in pyrolysis process in E-waste management sector

Many aspects of modern life of our civilization are associated with using electrical and electronic devices (EEE). Ever-increasing demand for high-performance EEE and accelerated technological development make the replacement of EEE become frequent. This leads to the generation of a tremendous amount of electronic waste (E-waste). Challenges of the management of E-waste have recently arisen out of a dearth of proper technologies to treat E-waste. Pyrolysis process can thermochemically treat waste materials that have a complicated nature and inhomogeneity. This article gives a systematic review as an effort to tackle the challenges in the context of achievements in pyrolysis process in E-waste management sector. Pyrolysis mechanism and types of pyrolysis processes and pyrolysis reactors are first discussed. Various pyrolysis technologies applied to the E-waste treatment are then summarized and compared to each other. Points to be considered for further research and pending challenges of E-waste pyrolysis are also discussed. The pyrolysis treatment of E-waste is not yet fully industrialized mostly because of high costs. However, there should be much room for further developing the E-waste pyrolysis; hence, its industrialization and commercialization is just a matter of time.

Valorization of swine manure biochar as a catalyst for transesterifying waste cooking oil into biodiesel

As demand of proteins from meats has significantly increased with economy growth, the population of livestock proliferates. Thus, heavy amount of livestock byproducts released from livestock industries will become more problematic if they are handled in an unsatisfactory manner. In this study, swine manure (SM) waste was directly valorized to be used as a reaction catalyst for biodiesel production. Pyrolysis was adapted to produce swine manure biochars at 500 (SMB@500) and 650 °C (SMB@650), and the materials were used for conversion of waste cooking oil into biodiesels (i.e., fatty acid methyl esters: FAMEs). The properties of SMBs and resulting pyrolytic gases (i.e., H₂, CO, and C_1-2 hydrocarbons (HCs)) and liquids during pyrolysis were also characterized. SMBs used in this study included a large quantity of metallic contents that significantly contributed to the rapid reaction for biodiesel production. In detail, SMB@500 and SMB@650 showed higher than 96% of FAME yield at 305 and 210 °C of reaction temperature, while non-catalytic reaction using SiO₂ showed similar FAME yield at 330 °C. Thus, this work offers a sustainable way to recycle organic and inorganic materials in livestock manures for energy (biodiesel, pyrolytic oil, H₂, and C_1-2 HCs) production.

Slow pyrolysis of municipal solid waste (MSW): A review

In recent years, extensive studies have been carried out to improve our knowledge of the reactor operations and system performance in thermal pyrolysis of municipal solid wastes (MSW). However, the fundamentals of MSW pyrolysis and their engineering applications remain unsatisfactorily explored. This paper is a review of the pyrolysis of MSW and synergistic co-pyrolysis of the constituents of MSW with reference to pyrolytic performance, the distribution and energy content of the end products, and the mechanisms of the synergistic effects. The prospects for, and challenges of, the MSW pyrolysis process are provided. A MSW pyrolytic process with maximal energy recovery and minimal carbon footprint is proposed.

Consequence of replacing nitrogen with carbon dioxide as atmosphere on suppressing the formation of polycyclic aromatic hydrocarbons in catalytic pyrolysis of sawdust

This study evaluates the effect of replacement of N₂ with CO₂ as atmosphere in catalytic pyrolysis of waste lignocellulosics with acidic and metal-modified zeolites, respectively, on the 16 EPA priority pollutant polycyclic aromatic hydrocarbons (PAHs) in bio-oils. By coupling solid phase extraction pretreatment with single ion monitoring detection, it is found that the replacement alleviates PAHs in bio-oil concerning synchronously abating the 16 PAHs with low, medium and high molecular weights, and the benzo[a]pyrene equivalent toxicity of bio-oil decreases. Meanwhile, CO₂ decreases the content of small oxygenates, e.g. furans, ketones, acids, and increases phenolics and aromatics affording more stable and valuable bio-oils. Moreover, CO₂ enhances carbon conversion efficiency, especially in combination with Fe-modified zeolite, which presents a synergistic effect. This study indicates the practical application of CO₂ as an atmosphere in catalytic pyrolysis to improve the bio-oil quality by suppressing PAHs formation and adjusting compound constituent.

Debrominated high quality oil production by the two-step catalytic pyrolysis of phenolic printed circuit boards (PPCB) using natural clays and HY

The two-step catalytic pyrolysis (CP) of a phenolic-printed circuit board (PPCB) over in-situ natural clays (dolomite, bentonite, and olivine) and ex-situ HY(30, SiO₂/Al₂O₃: 30) was investigated by tandem micro reactor-gas chromatography/mass spectrometry. The non-catalytic pyrolysis (NCP) of PPCB produced oxygenated, phosphorous, and brominated compounds due to the presence of paper, tetrabromo bisphenol A (TBBA), phosphorous flame retardants, and phenol resin in the PPCB. Among the natural clays, dolomite showed the highest debromination and aromatics formation efficiency during the in-situ CP of PPCB followed by bentonite and olivine owing to the different catalyst properties. Two-step CP of PPCB over in-situ natural clays and ex-situ HY(30) achieved higher efficiency on the formation of higher quality oil (mono-phenol and aromatic hydrocarbons) with a lower Br content than the one-step CP of PPCB. Among the two-step catalysts, the combination of in-situ dolomite and ex-situ HY(30) provided the highest quality oil production due to the high acidity and sufficiently large pore size of dolomite. Two-step CP of PPCB over in-situ dolomite and ex-situ HY(30) also revealed a longer lifetime than the one-step CP of PPCB over ex-situ HY(30), not only for the formation of aromatic hydrocarbons and mono-phenols, but also for debromination.