Analysis of volatile species kinetics during typical medical waste materials pyrolysis using a distributed activation energy model

Dynamic pyrolytic reaction mechanisms, pathways, and products of medical masks and infusion tubes

Given the COVID-19 epidemic, the quantity of hazardous medical wastes has risen unprecedentedly. This study characterized and verified the pyrolysis mechanisms and volatiles products of medical mask belts (MB), mask faces (MF), and infusion tubes (IT) via thermogravimetric, infrared spectroscopy, thermogravimetric-Fourier transform infrared spectroscopy, and pyrolysis-gas chromatography/mass spectrometry analyses. Iso-conversional methods were employed to estimate activation energy, while the best-fit artificial neural network was adopted for the multi-objective optimization. MB and MF started their thermal weight losses at 375.8 °C and 414.7 °C, respectively, while IT started to degrade at 227.3 °C. The average activation energies were estimated at 171.77, 232.79, 105.14, and 205.76 kJ/mol for MB, MF, and the first and second IT stages, respectively. Nucleation growth for MF and MB and geometrical contraction for IT best described the pyrolysis behaviors. Their main gaseous products were classified, with a further proposal of their initial cracking mechanisms and secondary reaction pathways.

Valorisation of medical waste through pyrolysis for a cleaner environment: Progress and challenges

The COVID-19 pandemic has exerted great shocks and challenges to the environment, society and economy. Simultaneously, an intractable issue appeared: a considerable number of hazardous medical wastes have been generated from the hospitals, clinics, and other health care facilities, constituting a serious threat to public health and environmental sustainability without proper management. Traditional disposal methods like incineration, landfill and autoclaving are unable to reduce environmental burden due to the issues such as toxic gas release, large land occupation, and unsustainability. While the application of clean and safe pyrolysis technology on the medical wastes treatment to produce high-grade bioproducts has the potential to alleviate the situation. Besides, medical wastes are excellent and ideal raw materials, which possess high hydrogen, carbon content and heating value. Consequently, pyrolysis of medical wastes can deal with wastes and generate valuable products like bio-oil and biochar. Consequently, this paper presents a critical and comprehensive review of the pyrolysis of medical wastes. It demonstrates the feasibility of pyrolysis, which mainly includes pyrolysis characteristics, product properties, related problems, the prospects and future challenges of pyrolysis of medical wastes.

A comprehensive study on the oxidative pyrolysis of epoxy resin from fiber/epoxy composites: Product characteristics and kinetics

Thermal treatment has been the most feasible process to recycle valuable carbon fibers and obtain fuel and chemicals from waste fiber/epoxy composites. The present work studied the oxidative pyrolysis behaviors of epoxy resin from fiber/epoxy composites using a thermogravimetric apparatus and a fixed-bed reactor, respectively. The effects of various O₂ concentrations on the thermal behaviors of epoxy resin were investigated and the product characteristics were analyzed. Furthermore, a multi distributed activation energy model (multi-DAEM) was first developed to determine the oxidative pyrolysis kinetics of epoxy resin under various atmospheres. Results showed that the degradation behaviors of epoxy resin were largely altered by the O₂ concentrations. High O₂ concentrations accelerated the primary decomposition of epoxy resin and shifted the oxidation of resin residue into lower temperatures. High contents of methylcyclohexene and phenolic derivatives were detected in liquid products. In air atmosphere, high yields of CO and CO₂ were generated and distributed in several stages. The kinetic analysis indicated that the multi-DAEM method can well explain the oxidative pyrolysis behaviors of epoxy resin. A minimum six-reaction fitting process can perfectly simulate the oxidative pyrolysis of epoxy resin. The predictions for various O₂ concentrations were in good agreement with the experimental tests.

Pyrolysis dynamics of two medical plastic wastes: Drivers, behaviors, evolved gases, reaction mechanisms, and pathways

The public has started to increasingly scrutinize the proper disposal and treatment of rapidly growing medical wastes, in particular, given the COVID-19 pandemic, raised awareness, and the advances in the health sector. This research aimed to characterize pyrolysis drivers, behaviors, products, reaction mechanisms, and pathways via TG-FTIR and Py-GC/MS analyses as a function of the two medical plastic wastes of syringes (SY) and medical bottles (MB), conversion degree, degradation stage, and the four heating rates (5,10, 20, and 40 °C/min). SY and MB pyrolysis ranged from 394.4 to 501 and from 417.9 to 517 °C, respectively. The average activation energy was 246.5 and 268.51 kJ/mol for the SY and MB devolatilization, respectively. MB appeared to exhibit a better pyrolysis performance with a higher degradation rate and less residues. The most suitable reaction mechanisms belonged to a geometrical contraction model (R₂) for the SY pyrolysis and to a nucleation growth model (A_1.2) for the MB pyrolysis. The main evolved gases were C₄-C₂₄ alkenes and dienes for SY and C₆-C₄₁ alkanes and C₈-C₄₁ alkenes for MB. The pyrolysis dynamics and reaction pathways of the medical plastic wastes have important implications for waste stream reduction, pollution control, and reactor optimization.

Insights into Thermal Degradation Behaviors and Reaction Kinetics of Medical Waste Infusion Bag and Nasal Oxygen Cannula

The thermal degradation behaviors and reaction kinetics of medical waste infusion bag (IB) and nasal oxygen cannula (NOC) were investigated under inert atmosphere with the heating rates of 5, 10, 15, and 25 K·min−1. Ozawa–Flynn–Wall (OFW), Kissinger–Akahira–Sunose (KAS), and Friedman were employed to estimate the activation energy. Coats–Redfern and Kennedy–Clark methods were adopted to predict the possible reaction mechanism. The results suggested that the reaction mechanism of IB pyrolysis was zero-order, and that of NOC pyrolysis was concluded that zero-order for the first stage and three-dimensional diffusion Jander equation for the second stage. Based on the kinetic compensation effect, the reconstructed reaction models for IB and NOC pyrolysis were elaborated by introducing adjustment functions. The results indicated that the reconstructed model fitted well with the experimental data. The results are helpful as a reference and provide guidance for the determination of IB and NOC degradation behaviors and the simulation of parameters.

Kinetic study of biomass pellet pyrolysis by using distributed activation energy model and Coats Redfern methods and their comparison

In this study, the pyrolysis behavior and kinetics of raw biomasses and their pellets were studied by Coats Redfern and DAEM methods. The results demonstrated that the similar activation energies obtained by both methods confirmed accuracy of the kinetics calculation. The activation energy of the pellets was 132.49-232.44 kJ mol^-1, slightly higher than those of raw biomasses, which was 120.58-210.55 kJ mol^-1. The results from Coats Redfern method showed that the pyrolysis of all the samples were controlled by mass and heat diffusion. DAEM revealed that the activation energies of the pellets were higher than those of raw biomasses during hemicellulose and cellulose decomposition stages, and was opposite for the lignin decomposition stage. Physical structure characterization indicated that the pellets had smaller surface area and more compact surface than those of their raw biomasses. Hence, the mass and heat diffusion were suppressed and more cross-linking reactions occurred during pellets pyrolysis.

The kinetics of typical medical waste pyrolysis based on gaseous evolution behaviour in a micro-fluidised bed reactor

In order to obtain the kinetic parameters during typical medical waste pyrolysis, the typical medical waste is pyrolysed in a micro-fluidised bed reactor. The gases evolved from the typical medical waste pyrolysis are analysed by a mass spectrometer, and only H₂, CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆, C₃H₈ and C₄H₄ are observed. According to the gaseous product concentration profiles, the activation energies of gaseous formation are calculated based on the Friedman approach, and the average activation energies of H₂, CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆, C₃H₈ and C₄H₄ formation during typical medical waste pyrolysis are in sequence as 65.10, 39.98, 35.17, 38.71, 40.75, 41.79, 58.57 and 63.95 kJ mol^-1. Moreover, the activation energy with respect to the gases mixture formation is 52.70 kJ mol^-1. Hence, it is concluded that the activation energy of typical medical waste pyrolysis is 52.70 kJ mol^-1. The model-fitting method is used to determine the mechanism model of medical waste pyrolysis. The results indicate that the chemical reaction ( n = 1) model (G(x) = -ln(1-x)) is the optimum.

The emission of fluorine gas during incineration of fluoroborate residue

The emission behaviors of wastes from fluorine chemical industry during incineration have raised concerns because multiple fluorine products might danger human health. In this study, fluorine emission from a two-stage incineration system during the combustion of fluoroborate residue was examined. In a TG-FTIR analysis BF3, SiF4 and HF were identified as the initial fluorine forms to be released, while fluorine gases of greenhouse effect such as CF4 and SF6 were not found. Below 700 °C, NaBF4 in the sample decomposed to generate BF3. Then part of BF3 reacted with SiO2 in the system to form SiF4 or hydrolyzed to HF. At higher temperatures, the NaF left in the sample was gradually hydrolyzed to form HF. A lab-scale two-stage tube furnace is established to simulate the typical two-stage combustion chamber in China. Experimental tests proved that HF was the only fluorine gas in the flue gas, and emissions of BF3 and SiF4 can be negligible. Thermodynamic equilibrium model predicted that all SiF4 would be hydrolyzed at 1100 °C in the secondary-chamber, which agreed well with the experimental results.

Healthcare waste management research: A structured analysis and review (2005-2014)

The importance of healthcare waste management in preserving the environment and protecting the public cannot be denied. Past research has dealt with various issues in healthcare waste management and disposal, which spreads over various journals, pipeline research disciplines and research communities. Hence, this article analyses this scattered knowledge in a systematic manner, considering the period between January 2005 and July 2014. The purpose of this study is to: (i) identify the trends in healthcare waste management literature regarding journals published; (ii) main topics of research in healthcare waste management; (iii) methodologies used in healthcare waste management research; (iv) areas most frequently researched by researchers; and (v) determine the scope of future research in healthcare waste management. To this end, the authors conducted a systematic review of 176 articles on healthcare waste management taken from the following eight esteemed journals: International Journal of Environmental Health Research, International Journal of Healthcare Quality Assurance, Journal of Environmental Management, Journal of Hazardous Material, Journal of Material Cycles and Waste Management, Resources, Conservations and Recycling, Waste Management, and Waste Management & Research. The authors have applied both quantitative and qualitative approaches for analysis, and results will be useful in the following ways: (i) results will show importance of healthcare waste management in healthcare operations; (ii) findings will give a comparative view of the various publications; (c) study will shed light on future research areas.

Pyrolysis kinetics and thermal characteristics of microalgae Nannochloropsis oculata and Tetraselmis sp

In this study non-isothermal thermogravimetric analysis were used to investigate pyrolysis behavior and kinetics of microalgae Nannochloropsis oculata (NO) and Tetraselmis sp. (TS). TG/DTG experiments at different heating rates were carried out. Heating rates had slight effect on the decomposition trend, however the maximum temperature and peak of weight loss rate in the DTG curves shifted towards higher temperature with the increase in heating rate. The average activation energy and pre-exponential factor for pyrolysis of NO and TS were estimated by distributed activation energy model. The highest activation energies were observed as 152.20 and 334kJ/mol for NO and TS, respectively, at various conversions. The pre-exponential factors for the corresponding activation energies were observed to be in the order of 10(8)-10(13) and 10(12)-10(25)s(-1) for NO and TS, respectively. Calculated kinetic parameters were used to predict devolatilization curves and results were in well agreement with experimental data.

Kinetic study of solid waste pyrolysis using distributed activation energy model

The pyrolysis characteristics of municipal solid waste, agricultural residues such as ground nut shell, cotton husk and their blends are investigated using non-isothermal thermogravimetric analysis (TGA) with in a temperature range of 30-900 °C at different heating rates of 10 °C, 30 °C and 50 °C/min in inert atmosphere. From the thermograms obtained from TGA, it is observed that the maximum rate of degradation occurred in the second stage of the pyrolysis process for all the solid wastes. The distributed activation energy model (DAEM) is used to study the pyrolysis kinetics of the solid wastes. The kinetic parameters E (activation energy), k0 (frequency factor) are calculated from this model. It is found that the range of activation energies for agricultural residues are lower than the municipal solid waste. The activation energies for the municipal solid waste pyrolysis process drastically decreased with addition of agricultural residues. The proposed DAEM is successfully validated with TGA experimental data.

Pyrolysis characteristics of cattle manures using a discrete distributed activation energy model

The pyrolysis characteristics of cattle manures were conducted using a discrete distributed activation energy model (DAEM) coupled with the thermogravimetric analysis. The results showed that the pyrolysis process can be accurately characterized by 27 dominating reactions, and the dominating reactions form four groups to represent respectively the decomposition processes of the different constituents of cattle manures. Moreover, the devolatilization kinetics under the heating rate changing from 0.1Kmin(-1) to 10,000Kmin(-1) were predicted with the discrete DAEM. Prediction results demonstrated that with increasing the heating rate, the main decomposition regions of individual constituent become more and more concentration and their interactions are more and more complex. Particularly, it was interesting to discover that the peak decomposition rate is perfectly proportional to the heating rate, and the peak, starting and ending decomposition temperatures satisfy a relationship of quadratic function with the common logarithm of the heating rate.

Classification and comparison of municipal solid waste based on thermochemical characteristics

Municipal solid waste (MSW) has been normally sorted into six categories, namely, food residue, wood waste, paper textiles, plastics, and rubber In each category, materials could be classified further into subgroups. Based on proximate and ultimate analysis and heating value, statistical methods such as analysis of variance (ANOVA) and cluster analysis were applied to analyze the characteristics of MSW in every subgroup and to try to distinguish their relative properties. The chemical characteristics analysis of MSW showed that polyethylene (PE), polypropylene (PP), and polystyrene (PS) had the highest volatile matter content, with almost no ash and fixed carbon, while polyethylene terephthalate (PET) had high carbon content but low hydrogen content. Bones and vegetables had the highest ash content, while nutshells and rubber had the highest fixed carbon content. Paper and starch food had the highest oxygen content, and wool and bones had the highest nitrogen and sulfur content. Polyvinyl chloride (PVC) had the highest chlorine content at about 55%. PE, PP and PS had the highest heating value, followed by chemical products such as rubber and chemical fiber. Conversely, paper, vegetables and bones had the lowest heating value. The results of cluster analysis of MSW components showed that fruit peel, weeds, wood, bamboo, leaves and nutshells could be classified as the lignocellulose category; starch food, cotton, toilet paper, printing paper and cardboard could be classified as the glucose monomer category; wood and chemical fiber could be classified as the high nitrogen and sulfur category; and PE, PP, and PS could be cluster as the polyolefin category.

IMPLICATIONS

The yield of municipal solid waste (MSW) is constantly increasing and waste to energy (WTE) has been used extensively all over the world. During the processes of incineration, pyrolysis, or gasification, the impact of physical and chemical properties of MSW is of great significance. However, the traditional classification of MSW is too general to provide more detailed information in many investigations. It is necessary to perform the investigation of characteristics of combustible MSW to distinguish different categories of MSW and find out their subclassification.

Modeling of the devolatilization kinetics during pyrolysis of grape residues

Thermo-gravimetric analysis (TGA) was performed on grape seeds, skins, stalks, marc, vine-branches, grape seed oil and grape seeds depleted of their oil. The TGA data was modeled through Gaussian, logistic and Miura-Maki distributed activation energy models (DAEMs) and a simpler two-parameter model. All DAEMs allowed an accurate prediction of the TGA data; however, the Miura-Maki model could not account for the complete range of conversion for some substrates, while the Gaussian and logistic DAEMs suffered from the interrelation between the pre-exponential factor k0 and the mean activation energy E0--an obstacle that can be overcome by fixing the value of k0 a priori. The results confirmed the capabilities of DAEMs but also highlighted some drawbacks in their application to certain thermodegradation experimental data.

Thermal removal of PCDD/Fs from medical waste incineration fly ash--effect of temperature and nitrogen flow rate

The fly ash used in this study was collected from a bag filter in a medical waste rotary kiln incineration system, using lime and activated carbon injection followed by their collection as mixed fly ash. Experiments were conducted on fly ash in a quartz tube, heated in a laboratory-scale horizontal tube furnace, in order to study the effect of temperature and nitrogen flow rate on the removal of PCDD/Fs. Results indicated that in this study PCDD/Fs in the fly ash mostly were removed and desorbed very little into the flue gas under thermal treatment especially when the heating temperature was higher than 350 °C, and dechlorination and destruction reactions took important part in the removal of PCDD/Fs. However, in terms of flow rate, when flow rate was higher than 4 cm s(-1), destruction efficiency of PCDD/Fs decreased dramatically and the main contributors were P(5)CDF, H(6)CDF and H(7)CDF desorbed to flue gas, the PCDD/Fs in the fly ash decreased with enhanced flow rate.

Logistic distributed activation energy model--Part 1: Derivation and numerical parametric study

A new distributed activation energy model is presented using the logistic distribution to mathematically represent the pyrolysis kinetics of complex solid fuels. A numerical parametric study of the logistic distributed activation energy model is conducted to evaluate the influences of the model parameters on the numerical results of the model. The parameters studied include the heating rate, reaction order, frequency factor, mean of the logistic activation energy distribution, standard deviation of the logistic activation energy distribution. The parametric study addresses the dependence on the forms of the calculated α-T and dα/dT-T curves (α: reaction conversion, T: temperature). The study results would be very helpful to the application of the logistic distributed activation energy model, which is the main subject of the next part of this series.

Combustion characteristics of particles of hazardous solid waste mixtures in a fixed bed

Hazardous waste disposal is vitally important as industrial production increases. Grate furnaces are a common means to incinerate hazardous waste. In this present work, a fixed bed assembly is used to experimentally model combustion within grate furnaces. Combustion characteristics are examined and the effects of primary air rate, moisture, bed height and particle size on burning rate, ignition-front speed and temperatures in the bed are also investigated. The results indicate that a rising temperature front descends through the bed while weight loss remains constant during the main combustion stage. Primary air rates and moisture content are shown to have significant effects on burning rates and average ignition-front speeds. Bed height has no effect on burning rates but does have an effect on average ignition-front speeds. Particle size is found to have slight effects on burning rates while having no effect on average ignition-front speeds.

TG-FTIR characterization of pyrolysis of waste mixtures of paint and tar slag

Safe disposal of hazardous waste is becoming generally more important as industrial production increases. The pyrolysis characteristics and gas evolution of mixtures of several wastes are discussed in this paper. Experiments are described for various heating rates, particle sizes and final temperatures using thermogravimetric analysis (TGA) and a Fourier transform infrared spectrometer. The results indicate that there are three stages in the pyrolysis process. The composition of evolved gas includes carbon monoxide, carbon dioxide, ammonia, methane, nitric oxide, hydrocyanic acid and a number of other light alkanes. Gas evolution temperatures and gas generation rates were significantly influenced by the factors identified.