Pyrolysis Product Distribution Research Articles

Experimental investigation on the pyrolysis process and product distribution characteristics of organic-rich shale via supercritical water

Low-medium maturity organic-rich shale reservoirs have garnered increasing attention due to their enormous oil and gas generation potential. In this study, the pyrolysis conversion process and product distribution characteristics of shale core samples via supercritical water (SCW) were investigated. The yield of shale oil increased from 4.5 wt% at 385 °C to 15.13 wt% at 425 °C, with the maximum formation rate of shale oil ranging from temperatures of 405 °C to 425 °C. The thermal bitumen reached 15.11 wt% at 405 °C before rapidly decreasing to 3.2 wt% at 425 °C. In the pyrolysis process of shale cores via SCW, the intermediate thermal bitumen produced by thermal cracking of kerogen was retained in the cores and continued to be decomposed into shale oil and gas with the increase of SCW temperature. Simultaneously, a large number of pores were formed in the core matrix due to the massive decomposition of kerogen and thermal bitumen. The increase in SCW temperature greatly decreased the heavy components as well as increased the light components in shale oil. Additionally, aliphatic hydrocarbon cracking or Diels-Alder type aromatization reactions resulted in an increase in aromatic hydrocarbons and a decrease in the H/C atomic ratio of shale oil. Raising SCW temperature increased the content of C2-C5 hydrocarbon gases and the alkenes/alkanes ratio, which was related to the secondary cracking. The important findings of the pyrolysis conversion process and product distribution characteristics of shale cores via SCW not only enrich the theoretical basis in this area, but also provide strong support for the use of SCW in the in-situ conversion of low-medium maturity organic-rich shale reservoirs.

Production and physico-chemical characteristics of pyrolyzed bio-oil derived from cow hooves

Pyrolysis is becoming increasingly popular as a method of producing liquid yield from biomass. It has the potential to help build a sustainable renewable fuel market while simultaneously maintaining environmental sustainability. In the present study, cow hooves are pyrolyzed in a fixed-bed batch reactor to investigate product dispersion and determine optimal temperature parameters for optimizing pyrolysis oil yield. Temperature effects on the distribution, elemental content, and physical qualities of major pyrolysis products, such as pyrolysis oil and bio-char, are investigated. At a pyrolysis temperature of 500 °C, the maximum pyrolysis oil production was found to be 50.50 wt%, with the amount of bio-char excluding the gas being 27.20 wt%. A CHNS analyzer, Gas chromatography-mass spectrometry (GC-MS), and Fourier-transform infrared (FTIR) spectroscopy are used to investigate the chemical composition of pyrolysis oil generated under optimal conditions. The fuel properties of the pyrolysis oil are also determined, and it was discovered that it has a favourable fire point, flash point, and pour point. The density of the pyrolysis oil was 1.03 kg/L, the viscosity was 10.2 cSt, and the heating value was 22.7 MJ/kg. The FTIR analysis of the pyrolysis oil reveals that it contains functional groups, such as alkene, carboxylic acid, alcohol, ether, and ketone. According to the GC-MS analysis, the principal components are ester (40%), fatty acids (31%), phenol (3.8%) and p-Cresol (2.9%). Unsaturated fatty acids are abundant in the pyrolysis oil from cow hooves, while saturated fatty acids are in short supply. According to the findings of this study, cow hoof pyrolysis oil has the potential to be used as a source of biodiesel.

Valorisation of Waste Tyre via Pyrolysis: Advances and Perspectives

This paper first reviews the serious environmental concerns and waste management due to the rapid increase in the vast quantity of waste tyre globally. It then articulates the importance of pyrolysis as an attractive technical route for valorising waste tyre. A systematic summarisation on pyrolysis reaction chemistry is presented, including those for both waste tyre and its individual components. The key factors, including feedstock properties, reactor configurations, and reaction conditions that influence the properties and distribution of pyrolysis products and transformation and fate of impurities, are discussed. Such knowledge is essential to selecting operating parameters for optimal pyrolysis products and process performance. Potential applications of waste tyre pyrolysis products (i.e., char, oil, and gas) are subsequently surveyed and summarised. The important roles of key impurities (especially sulfur) and their derivatives, which are major constraints for commercialisation of waste tyre pyrolysis technologies, are also discussed. Remediation strategies of these impurities in pyrolysis products are summarised, compared, and benchmarked. The recent progress in process development, techno-economic analysis, and life cycle analysis of waste tyre pyrolysis processes is also covered. In closing, the remaining challenges and research gaps in the field of waste tyre pyrolysis are identified and future research perspectives are outlined.

Co-pyrolysis Characteristics and Synergistic Interaction of Waste Polyethylene Terephthalate and Woody Biomass towards Bio-Oil Production

In this study, the impacts of co-pyrolyzing wood-based biomass from Ficus benghalensis with PET on liquid oil output, reactivity, and heating values were investigated. The effects of temperature on the product distribution of individual pyrolysis and the biomass-plastic ratio on co-pyrolysis were investigated. For individual pyrolysis, a maximum amount of 40.8 wt (%) liquid oil was obtained from biomass at 450°C. On the other hand, a maximum of 59.5 wt (%) liquid oil was obtained from PET at 500°C. The co-pyrolysis experiments were conducted by blending PET with biomass at different percentages, such as 20%, 40%, 60%, and 80%. At 60% addition of PET, a more positive synergistic effect was identified due to radical secondary reactions. In addition, the physical and chemical characterization studies conducted on pyrolysis oil showed that biomass and plastic materials could be used to make valuable chemicals.

Characterizing sludge pyrolysis by machine learning: Towards sustainable bioenergy production from wastes

Sludge pyrolysis has sparked the interest of researchers because of its capability to dispose of hazardous residues while producing valuable bioproducts. Numerous expensive and laborious experiments are conducted to understand sludge pyrolysis. Machine learning technology can eliminate the need for experimental measurements by systematically learning relationships between variables from historical data. This research aimed to propose a machine learning model to characterize sludge pyrolysis products. A comprehensive database covering various sludge types and pyrolysis reaction conditions was constructed from experimental data. The k-nearest neighbor algorithm was used to reconstruct the missing inputs of sludge composition. The principal component analysis method was then used to decrease dataset dimensionality and acquire relevant information. The obtained scores were normalized and introduced into three machine learning models. The input variables were the chemical properties of sludge and reaction conditions. The response parameters were the distribution and composition of pyrolysis products. Based on descriptive data analysis, the optimum bio-oil yield was obtained at temperatures between 500 and 600 °C. At higher temperatures (700–800 °C), a transition was observed in the product distribution towards more syngas. The random forest regression model showed the highest accuracy among the applied models, with a correlation coefficient higher than 0.813 and a relative mean squared error lower than 12.51. The SHAP analysis using the random forest algorithm was successfully conducted to understand the importance of input variables on output responses. The five top significant features affecting bio-oil yield were ash content, fixed carbon content, operating temperature, and volatile matter content.

Influence of particle characteristics, heating temperature and time on the pyrolysis product distributions of polystyrene micro- and nano-plastics

Pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) has been widely used for the detection of micro- and nanoplastics (MNPs) in the environment. However, there is a lack of thorough investigation on the effects of pyrolysis temperature and time, as well as the particle source, size and mass of MNPs on the pyrolysis efficiency and pyrolysis product distribution of MNPs. Herein, taking the common plastics polystyrene (PS) as a model, we systematically evaluated the influences of the above factors on the pyrolysis of PS MNPs. Results showed that pyrolysis temperature and time significantly affect the pyrolysis efficiency. By measuring the relative response values of the indicator compound styrene trimers to styrene monomer, the optimum condition was determined as the temperature of 510 ℃ and pyrolysis time longer than 18 s. Meanwhile, the mass of MNPs also affected the distribution of PS pyrolysis products. The proportions of styrene dimers and trimers increased slightly with PS MNP mass, while the source, particle size of MNPs have little effect on the pyrolysis product distribution. This work proposed a suitable pyrolysis temperature and time for the determination of PS by Py-GC/MS, which would contribute to the accurate analysis of PS MNPs in the environment.

Energy recovery of livestock manure and industrial sludge by co-hydrocarbonisation coupled to pyrolysis and gasification

Hydrothermal carbonization (HTC) of carbonaceous waste is an important way of energy recovery to obtain renewable fuels. Here, cow manure (CM) and industrial sludge (IS), two kinds of wastes with different properties, were pretreated by HTC at different temperatures. The elements migration and the physicochemical structural characteristics of hydrochar during HTC were evaluated. The pyrolysis and gasification performance of hydrochar was also studied. The results show that HTC treatment can significantly increase the carbon content and reduce the oxygen content of feedstocks, so as to obtain clean solid fuels with high energy densification and realize energy recovery from low value wastes. The distribution of pyrolysis products of co-hydrochar is close to that of IS due to the interaction between the components of CM and IS. The co-hydrochar has good gasification reactivity, showing obvious synergistic effect. There is multi-component interaction in the process of co-HTC due to the difference of feedstocks composition and properties between CM and IS. The abundant aliphatic and oxidized aliphatic hydrocarbons in IS may inhibit the polycondensation and aromatization of cellulose and hemicellulose hydrolysates in CM due to hydrogen supply or steric hindrance. Therefore, co-hydrochar has carbon structure and fuel properties close to that of IS hydrochar.

Catalytic pyrolysis of bamboo residue and its extracted three main components over copper modified ZSM-5 for the production of aromatic hydrocarbons

In this study, the product distribution from the catalytic pyrolysis of bamboo residue and its three main extracted components (cellulose, hemicellulose, and lignin) over Copper (Cu) modified ZSM-5 with different loading rates was conducted using pyrolysis-gas chromatography/mass spectroscopy. The addition of Cu modified ZSM-5 reduced the relative content of phenols, while that of monocyclic aromatic hydrocarbons (MAHs) increased significantly. The relative content of MAHs for the bamboo residue without catalyst was 2.10%, which increased considerably by 66.67% over Cu(2)/ZSM-5. The MAHs yield in cellulose is 3.03 times as that of the bamboo residue during catalytic pyrolysis over Cu(2)/ZSM-5. Phenolic compounds are mainly produced by lignin, whereas cellulose and hemicellulose are the primary producers of ketones and aldehydes. This study is crucial for understanding the pyrolytic product distribution of the bamboo residue and its three main extracted components.

In-situ catalytic upgrading of Hami coal pyrolysis volatiles over acid-modified kaolin

Low-cost kaolin was modified by calcination at different temperatures, followed by HCl leaching, and used as catalyst for in-situ upgrading of Hami coal pyrolysis volatiles in a fixed-bed reactor. The catalyst characteristics, pyrolysis product distributions and tar properties were investigated by multiple methods to understand the relationship between catalyst properties and tar quality. The results indicated that calcination of kaolin promoted the formation of amorphous metakaolin, then the HCl leaching removed most metakaolin framework Al, leading to the production of abundant micro-/mesopores and acid sites. As the rising calcination temperature, the specific surface area and pore volume of acid-modified kaolin (AMK) showed a trend of increasing and then decreasing, and the Brønsted acid sites (BAS) displayed an increasing trend. Compared to non-catalytic pyrolysis, the high specific surface area and certain acid sites of AMKs enhanced the light tar fraction from 37.81 wt% to 43.00–48.45 wt%, and the relative content of aromatics in tar increased from 9.76% to 16.65–22.11%, with monocyclic aromatics, naphthalenes and polycyclic aromatics increasing to 3.5–4.2, 1.2–1.8 and 2.1–3.3 times higher, respectively. AMKs also reduced the content of element O in tar by 17.92–31.54% by promoting the deoxygenation reaction. The tar upgrading performance was determined by the BAS amount and the pore structure of AMKs together. Among all AMKs, AMK800 (calcined at 800 °C and treated by HCl) exhibited the optimum performance for heavy tar conversion, aromatics generation and oxygen removal due to its highest specific surface area and the maximum BAS except AMK900. The acid-modified kaolin has the potential to be an inexpensive and efficient catalyst for future practical applications of upgrading coal pyrolysis tar.

Co-pyrolysis of paper mill sludge and textile dyeing sludge with high calorific value solid waste: Pyrolysis kinetics, products distribution, and pollutants transformation

Paper mill sludge (PMS) and printing and textile dyeing sludge (TDS) are two typical industrial sludge with high calcium content, high ash content and low calorific value. To attain effective removal of industrial solid waste, in this study, PMS and TDS are first pyrolyzed independently to study their thermochemical behavior. Results show that 600 °C is the optimal pyrolysis temperature for both PMS and TDS from the perspective of organics degradation. However, the yield and quality of pyrolysis oil and gas are still at low level due to the characteristics of high ash content and low organic content, which is not suitable for fuel recovery. Two kinds of organic solid wastes with high calorific value, duckweed (DW) and waste tire (WT), are co-pyrolyzed with PMS and TDS, which can effectively reduce activation energy and increase the yield of liquid and gas products. The most prominent is P1D1 pyrolysis gas, the production of CH4 and C2-C3 increased from 10.80 L/kg and 3.89 L/kg to 20.16 L/kg and 15.58 L/kg respectively, and the high calorific value also increased to 230.93 kJ/kg. The quality of pyrolysis liquid has been improved significantly as the declined N and O-heteroatom content (especially for P1D1 and T1W1) due to the inhibition effect of co-pyrolysis on the N/O migration into pyrolytic liquid. The solid residue from the co-pyrolysis of PMS and DW contains rich N-functional groups and can promote the conversion of pyridinic-N and pyrrolic-N to quaternary-N. Compared with independent pyrolysis, co-pyrolysis can promote the degradation of harmful organic matter in sludge. The addition of DW and WT co-pyrolysis reduced the solid residue yield of PMS by 19.9 wt% and 14.9 wt% (13.4 wt% and 10.5 wt% for TDS). This work provides inspiration for further understanding the safe disposal of PMS and TDS by pyrolysis.

Pyrolysis characteristics of excavated waste and generation mechanism of gas products

The mining of landfills provides an important opportunity for waste resource recovery, and the excavated waste with potential useable value has attracted widely attention. In this work, the pyrolysis technique was used to analyze the properties of excavated waste, including the thermal characteristics and kinetics analysis, the distribution of pyrolysis products and the composition of pyrolysis gas. The pyrolysis of excavated waste was performed in a lab-scale reactor in the temperature range of 500–900 °C. The results show that the pyrolysis activation energy of wood and textile was lower than that of plastics and rubber, and it was easier for the pyrolysis reaction to proceed. With the increase of temperature, the pyrolysis gas yield increased and the tar showed a decreasing trend. The plastic has the highest yield of tar with 74.9% and the textile has the highest yield of gas with 61.8% at 900 °C. Wood and rubber tend to produce high yield char with 28.5% and 40.6%, respectively. The pyrolysis gas composition was determined by Micro GC, and the release pattern during pyrolysis was also monitored. High temperature favors the production of H2/CO, and hinders the CO2/CH4. Plastics and rubber were more likely to produce C2∼C3 gases than wood and textiles. In addition, the pyrolysis properties of excavated waste and raw waste was compared.

Effect of glycerol addition on the pyrolysis characteristics and pyrolytic product distribution of cigar tobacco

Effect of glycerol addition on the pyrolysis characteristics and pyrolytic product distribution of cigar tobacco

Tobacco fractionation and its effects on pyrolysis chemistry

Tobacco is a major cash crop in the world market. As a special biomass, it has relatively high extract content and particularity of mainly using its volatile components. The degrading of tobacco extractives may influence the reactant surface, the reaction energy and the product distribution during tobacco pyrolysis. However, the interplay among the tobacco extractive components and others during pyrolysis and its influence on the pyrolysis product distribution is not clear enough. Hence, the water-soluble tobacco fractionated component and ethanol-soluble tobacco fractionated component as well as the remaining solid phase component was obtained, followed by a comparative analysis of weighted product distribution (by weighted calculation of fractionated components, Weighted) and actual pyrolysis product distribution (Raw). Results indicates that polycondensation to 2,2'-methylenebis-phenol and volatilization of (S)− 3-(1-methyl-2-pyrrolidinyl) pyridine were both free from the interplay among components. The generation of CO2 was inhibited and the decomposition to produce furans, phenols and toluene was promoted to different degree by the interplay among components. Pyrolysis kinetic results showed that the conversion of 40% was a dividing line, below which the activation energy of Weighted was lower than Raw, above which, the activation energy of Weighted surpassed Raw, indicating that the synergistic pyrolysis between the components failed to play a significant role in promoting the devolatilization or the depolymerization, dehydration, and decarboxylation of small molecules, but could significantly promote the depolymerization of macromolecules and the subsequent decomposition reactions. Such results are critical to the advancement of tobacco utilization, improving reuse efficiency of tobacco extractives.

Preparation of low-nitrogen chlorella based on proteolysis technology and pyrolysis characteristics of the products

The high protein content in the microalgal biomass leads to the high relative content of nitrogen compounds in the pyrolysis oil, which hinders the efficient application of the microalgal pyrolysis oil. In this paper, a method for preparing low-nitrogen chlorella by using alkaline protease based on proteolysis technology was proposed to reduce the nitrogen content of chlorella, and its process conditions were optimized. The results showed that the maximum nitrogen removal rate and yield could reach 20.32% and 52.36 wt%, respectively. The thermal decomposition characteristics of Chlorella and low-nitrogen chlorella were analyzed by TG-DTG technology, and their main thermal decomposition were calculated by Coats-Redfern method. It was found that compared with Chlorella, the low-nitrogen Chlorella had a larger weight loss rate in main thermal decomposition stage and its average activation energy value reduced by 2.23 kJ/mol. The Py-GC-MS technology was further used to study the distribution of pyrolytic products of Chlorella and low-nitrogen Chlorella at 550 °C. It was found that the relative content of nitrogen compounds in pyrolytic products from low-nitrogen Chlorella was 43.02% lower than that of Chlorella. This is because that the proteolysis pretreatment has a significant effect on reducing the relative contents of some nitrogen compounds in bio-oil, such as pyridines, pyrroles and benzyl nitrile. Based on the above experimental results, a brief mechanism of proteolysis pretreatment on removing nitrogen compounds was proposed, mainly through the proteolytic process to reduce the relative content of various amino acids in Chlorella as precursors for the synthesis of nitrile and N-heterocyclic compounds in pyrolysis. In conclusion, proteolysis technology can effectively reduce the relative content of nitrogen compounds in pyrolysis components and improve the potential of microalgal pyrolysis oil as a high-quality alternative fuel.

Co-pyrolysis of neem wood bark and low-density polyethylene: influence of plastic on pyrolysis product distribution and bio-oil characterization.

In this study, the investigation on the effect of plastic during co-pyrolysis with biomass was carried out in a fixed reactor. Pyrolysis of neem wood bark (NB), low density polyethylene (LDPE) and their blends at different ratios was performed in order to evaluate the product distribution. The effects of reaction temperature and NB-to-LDPE blend ratio on product distribution and the chemical compositions of pyrolysis oil were examined. The co-pyrolysis of NB and LDPE increased the yield and quality of the bio-oil. The experiments were conducted under different LDPE addition percentages such as 20%, 40%, 50%, 60% and 80%. Under the optimum experimental condition of 60% addition of LDPE and a temperature of 450 °C, the maximum yield of bio-oil (64.8 wt%) and hydrocarbon (75.2%) was achieved with the lowest yield of oxygenated compounds. The calorific value of the co-pyrolysis oil was found to be higher than that of the NB pyrolysis oil. The relationship between NB and LDPE during co-pyrolysis was validated with the help of gas chromatography-mass spectrometry (GC-MS) analysis, which showed decreased oxygenated compounds.

Conversion of low-density polyethylene into monocyclic aromatic hydrocarbons by catalytic pyrolysis: Comparison of HZSM-5, Hβ, HY and MCM-41

The catalytic properties of different catalytic materials on the pyrolysis of plastics have been extensively investigated. In order to better understand the relevant mechanism of catalytic pyrolysis of plastic waste, the effect of different acidity and pore size of catalytic material on its pyrolysis kinetic parameters and the distribution of pyrolysis products needs to be studied to provide a stronger theoretical basis for its resource utilization. This study aims to study the effects of HZSM-5, Hβ, HY and MCM-41 on the thermodynamic properties , kinetic parameters and pyrolysis characteristics of low-density polyethylene (LDPE), analyze the relationship between the specific catalytic pyrolysis products and the properties of the catalyst. Among the four catalysts, HZSM-5 obtained the most concentrated product distribution and the highest yield of monocyclic aromatic hydrocarbons , and it was found that the cracking of LDPE mainly occurred in its pores. Due to the large pore size and low concentration of acid sites, the main product type obtained by MCM-41 was olefins . In addition, it was found that HY reduced the pyrolysis temperature of LDPE and the activation energy of the reaction to the greatest extent. The different catalytic effects were mainly caused by different pore structures and acid site concentration. Moreover, it was found that the addition of catalyst changed the cracking mechanism of LDPE. Under the comprehensive consideration with the goal of producing monocyclic aromatic hydrocarbons, HZSM-5 is the most suitable catalyst among them. • The catalytic effects of HZSM-5, Hβ, HY and MCM-41 were studied. • HZSM-5 is the most suitable catalyst for the production of MAHs from LDPE. • Different pore structures and acid sites cause the changes of catalytic effects. • Partial LDPE scission sites changed from random-chain to end-chain due to catalysis. • The cracking reaction of LDPE occurs in the pores of HZSM-5.

Research on the pyrolysis characteristics and mechanisms of waste printed circuit boards at fast and slow heating rates

The pyrolysis treatment of waste printed circuit boards (WPCBs) shows great potential for sustainable treatment and hazard reduction. In this work, based on thermogravimetry (TG), pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS), and density functional theory (DFT), the thermal weight loss, product distribution, and kinetics of WPCBs pyrolysis were studied by single-step and multi-step pyrolysis at fast (600 °C/min) and slow (10 °C/min) heating rates. The heating rates of TG and Py-GC/MS were the same for each group of experiments. In addition, the bond dissociation energy (BDE) of WPCBs polymer monomers was calculated by DFT method. Compared with slow pyrolysis, the final weight loss of fast pyrolysis is reduced by 0.76 wt%. The kinetic analysis indicates that the activation energies of main pyrolysis stages range from 98.29 kJ/mol to 177.59 kJ/mol. The volatile products of fast pyrolysis are mainly phenols and aromatics. With the increase of multi-step pyrolysis temperature, the order of the escaping volatiles is phenols, hydrocarbyl phenols, aromatics, and benzene (or diphenyl phenol). The pyrolysis residue of WPCBs may contains phenolics and polymers. Based on the free radical reactions, the mechanism and reaction pathways of WPCBs pyrolysis were deduced by the DFT. Moreover, a large amount of benzene is produced by pyrolysis, and its formation mechanism was elaborated.

Product distribution from pyrolysis of large biomass particle: Effects of intraparticle secondary reactions

Thermochemical conversion provides promising approaches for utilization of agroforestry residues as energy sources in rural areas, such as decentralized biomass combustion and gasification. Understanding of the pyrolysis characteristics are crucial for the design of reactors and optimization of working conditions, but in these scenarios, utilization of centimeter-sized large fuel particles will bring challenges in predicting the evolution of pyrolytic products owing to the intraparticle secondary reactions. In this work, the product distribution of biomass pyrolysis was investigated in wide ranges of temperatures and particle sizes, and special attention was paid to the pyrolysis of centimeter-sized fuel particles under medium to high temperatures (500 °C – 900 °C). The yields of solid/liquid/gas-phase products were quantified, and the composition of tar and gas products were qualitatively and quantitatively evaluated, aiming at illustrating the effects of intraparticle secondary reactions. The results have shown that the differences between the product distribution of sawdust (<1 mm) and centimeter-sized wood cubes were significant over the whole temperature range, but the differences between wood cubes with varying sizes (1 cm, 1.5 cm and 2 cm) were dependent with the external temperature, indicating that the extent of intraparticle secondary reactions was simultaneously determined by external temperature and particle size. The evolution of tar composition indicated that the intraparticle secondary reactions could be divided into two distinctive steps. Increasing the particle size would firstly result in fast consumption of primary tar species and emergence of secondary tar species, while the second step would lead to the formation of simple phenols and aromatics, and large quantities of PAHs were released for centimeter-sized fuel particle under high temperatures (≥800 °C). Kinetic analysis further revealed that the first step was mainly transport controlled and sensitive to particle size, while the second step was jointly controlled by kinetics and transport, which appeared to be significant only if the particle size was large and simultaneously the temperature was sufficiently high.

Modifying pyrolysis behavior and products distribution of sewage sludge and water hyacinth by microwave pretreatment and subsequent calcium oxide catalytic co-pyrolysis

Modifying pyrolysis behavior and products distribution of sewage sludge and water hyacinth by microwave pretreatment and subsequent calcium oxide catalytic co-pyrolysis

Recovery of Rare-Earth Elements from Printed Circuit Boards by Vacuum Pyrolysis and Multiple Electrostatic Separation

The influence of the multi-stage electrostatic separation (ESS) of mechanically treated and magnetically separated waste electronic material and the pyrolysis of the selected ESS fraction on the distribution of metal elements (MEs), elements contained in refractory oxides (EROs), bromine (Br), and rare-earth elements (REEs) contained in waste electronic material was studied. The concentration of MEs, Br, and EROs in the tested samples was determined by X-ray fluorescence analysis, and the concentration of REEs and uranium was determined by inductively coupled plasma mass spectrometry (ICP-MS). The analysis of the distribution of elements during the multi-stage ESS showed that MEs were predominantly distributed in the conductive fraction and Br, EROs, and REEs were distributed in the nonconductive fraction. The nonconductive fraction (NC2) of the two-stage ESS was subjected to a low-temperature vacuum pyrolysis (T = 550 °C, p = 10 mbar). The distribution of pyrolysis products of the NC2 fraction was determined. The main products of the vacuum pyrolysis experiments were the solid residue phase (54.4 wt.%) and oils (35.4 wt.%). It has been proven that pyrolysis can significantly increase the concentration of MEs, EROs, and REEs in raw materials, thereby providing a method for cost-effectively obtaining of REEs from waste printed circuit boards.