Moderate Heating Rates Research Articles

RECYCLING OF PLASTIC WASTE BY THE PYROLYSIS METHOD

Chemical recycling of plastic waste can be a useful complement to mechanical recycling to achieve the required rate of plastics recycling and create a climate-neutral and resource-saving circular economy. Various mixed plastic wastes to be recycled in the future are investigated under fully uniform intermediate pyrolysis conditions characterized by moderate heating rates and pyrolysis temperatures. The distribution of the product and the selected properties of the product are determined, and the mass and energy balance of the process is obtained. Product yield and composition are highly dependent on pyrolyzed residues. All results indicate that pyrolysis is a suitable process for obtaining chemical feedstocks from various complex mixed plastic wastes. The main mass and energy balances for chemical recycling of mixed plastic waste by pyrolysis method were determined. Products for recycling raw materials can be obtained from all investigated plastic waste. Product quality often depends on raw materials. The energy requirement for heating, melting, pyrolysis and evaporation is about 5% of the calorific value of the raw material. It has been demonstrated that 50 to 75% of the raw carbon can be recovered in the condensate and reintroduced into the value chain in the chemical industry.

Enhancing carbon fibre recovery through optimised thermal recycling: Kinetic analysis and operational parameter investigation

Thermal recycling is an attractive method for recovering carbon fibre from carbon fibre-reinforced polymer (CFRP) composite waste. The main drawbacks of the thermal recycling approach are its high operational cost resulting from significant energy requirements and the risk of fibre surface damage caused by overheating. In this research, we will establish an optimal heating temperature and operating parameters (such as atmosphere, heating rates and isothermal dwelling time) through an analysis of the kinetic behaviour of CFRP thermal degradation to obtain clean and undamaged recycled fibres, while minimising energy requirements. The results show that a higher conversion fraction can be reached by applying a lower nitrogen flow rate, moderate heating rate and cap temperature of 425 °C. To ensure the complete removal of any residual matrix and pyrolytic carbon, and to obtain clean recycled carbon fibres, an additional recycling step is employed. In this case, oxidation is conducted with a 45-min isothermal period following pyrolysis. Using the proposed method, it was possible to retain 87.6 % of the fibre's tensile modulus and 80.3 % of its strength after the recycling process. The outcomes of this research will contribute to production of high-grade recycled carbon fibres with controlled mechanical performance and physical characteristics.

Effect of heating rate on the kinetics of limestone calcination

This paper reports on the effect of heating rates between 0.1 °C/s and 205.0 °C/s on the thermodynamics and kinetics of limestone calcination in air. These heating rates are orders of magnitude higher than those used in the thermogravimetric analysers that have been reported previously (0.1 °C/s to 0.8 °C/s). It was found that the activation energy, E, is reduced by 59%, from 205.0 kJmol−1 to 84.5 kJmol −1, when the heating rate is increased from a low heating rate regime (<1 °C/s) to a moderate heating rate regime (99.2––205.0 °C/s). Additionally, the average reaction rate constant K¯ increases with an increase in the heating rate. As an example, for 205 °C/s, K¯ is 18.7 times higher than that for 0.2 °C/s, when approaching the same asymptotic temperature. It is also found that a higher heating rate increases the specific surface area (SSA), for the same Tas. This is caused by microfractures which are associated with decreased activation energy, and in turn increases the surface-to-volume ratios and speeds up conversion. The results highlight the importance of accounting for both heating rate and calcination time in the modelling of the calcination of limestone.Specific surface area measurements also revealed that the prolongation of calcination under moderate heating rate reduces the SSA, typically by a factor of 1.6 from 15.8 m2/g to 9.6 m2/g when the residence time tr is increased from 120 s to 240 s. Therefore, to maximize the SSA, the residence time should not be longer than that required for complete conversion.

Microwave susceptor positional configuration for palm empty fruit bunch and waste tire co-pyrolytic oil yield and selectivity of value-added chemicals

The co-pyrolysis of the palm empty fruit bunch (EFB) and waste tire (WT) was conducted at a constant microwave power of 600 W, a reaction temperature of 500 °C, and EFB-to-WT ratio of 65:35 using activated carbon as a carbonaceous microwave susceptor (CMS). The study investigated the effect of CMS positional configuration on heating rates, pyrolytic oil yield, and chemical selectivity. Nine CMS positions were tested, and the results showed that the CMS located at the bottom of the feedstock (P1) produced the highest average heating rate (80.45 °C.min−1) with the fewest hotspots. In contrast, the feedstock sandwiching the CMS (P3) had the lowest average heating rate (45.86 °C.min−1), leading to an inconsistent heating profile due to hotspot formation. The study also found that faster heating rates (>70 °C.min−1) significantly affected pyrolytic oil yield, with position P1 producing a higher yield (39.53 wt%). The properties of the pyrolytic oil were characterised using GCMS, which revealed that higher average heating rates favoured the formation of d-limonene, with position P1 containing a higher fraction of this compound (35.24%). Slower average heating rates (<60 °C.min−1) favoured phenolic selectivity. Surprisingly, the CMS position with significant hotspots promoted the formation of monoaromatic hydrocarbons, resulting in a higher relative content of these compounds. Furthermore, moderate average heating rates (60–70 °C.min−1) favoured benzene, toluene, ethylene, and xylene (BTEX) selectivity, with toluene and xylene being the most prevalent compounds. Notably, CMS positions had no discernible effect on the heating value (HHV) of the pyrolytic oil produced, which had an average value of 42.00 MJ.kg−1 ± 1.0.

Thermo-catalytic reforming (TCR) of waste solid grade laminate

Thermo-catalytic reforming (TCR) is defined as intermediate pyrolysis at moderate temperatures and heating rates with subsequent reforming at elevated temperatures using biochar as a catalyst. TCR experiments were carried out to pyrolyze and subsequently reform Solid Grade Laminate (SGL) waste. SGL is a Kraft paper-derived product and as it is widely used in many applications, high volumes of waste laminate must be disposed of at end of life. To assess TCR for SGL waste treatment, the characterisation of the initial feedstock was accomplished, and it concluded that SGL is suitable to be processed via TCR. The main energy carrier products (char, oil and syngas) were generated by TCR in a 2 kg/h pilot-scale reactor under a pyrolysis temperature of 500 °C and reforming temperature of 650 °C, respectively. The mass balance analysis demonstrated that 50 wt% of the initial feedstock was comprehensively converted to syngas, 28 wt% to char and 22 wt% to a liquid fraction containing both water (17 wt%) and organics (5 wt%). The oil showed good properties as its HHV reached a value of 32.72 MJ/kg, with low oxygen and sulphur contents. However further processing is required for the fuels to be within suitable limits for use as drop-in fuels for vehicles. The syngas was found to be rich in hydrogen especially when pyrolysis temperature reaches its maximum. Lastly, char revealed a calorific value of 25.94 MJ/kg and was of a stable form of carbon, exhibiting potential as a feedstock for gasification or as a carbon capture and storage medium. TCR of SGL represents novelty as this feedstock has not been tested before in a pyrolysis/reforming system and it is a promising route in an optic of circularity. In waste valorisation, TCR oil has a great opportunity to be used as a fuel or blended with other conventional fuels, thus supporting the shift towards more sustainable mobility.

Crystallization and Texturing of SrxBa1–xNb2O6 Thin Films Prepared by Aqueous Solution Deposition─An In Situ X-ray Diffraction Study

Aqueous chemical solution deposition (CSD) is an environmentally friendly and highly flexible fabrication route to prepare oxide thin films. Here, we present an aqueous CSD process for ferroelectric SrxBa1–xNb2O6 (SBN) thin films on SrTiO3 (STO) single-crystal substrates. In situ synchrotron X-ray diffraction was employed to study the crystallization of the films during thermal processing with heating rates in the range 0.04–20 °C/s. Three different crystal orientations of SBN were observed based on the heating rate and the orientation of the STO substrates. SBN(001) and SBN(310) orientations were observed on STO(100), while only the SBN(311) orientation was observed on STO(110). The SBN(001) orientation was favored by an ultraslow heating rate of 0.04 °C/s, suggesting that this is the thermodynamic stable orientation. The SBN(310) orientation was kinetically favored at moderate heating rates and also promoted by increasing the Sr content in the film. A high heating rate of 20 °C/s rendered polycrystalline SBN films. It was revealed that nucleation and growth occurred via a classical Volmer–Weber (VW) growth mode and that the SBN grains preferably grow along the c-axis. The present findings demonstrate that control of nucleation and growth is a prerequisite to deposit films with different orientations and textures, which is detrimental for the film properties.

Generating Self-Shaped 2D Aluminum Oxide Nanopowders.

The thermal-assisted exfoliation phenomena of boehmite particles under moderate heating rates were examined. The exfoliation that generated flakes of 5–6 nm in thickness can be achieved because of the perfect cleavage on the boehmite particles that are stripped when thermal treatments bring about dehydration and γ-Al2O3 formation in sequential phase transformation of boehmite. Examinations of the exfoliation effects were carried out on calcined boehmite single crystal particles, which were about 500 nm in diameter, and obtained at three heating rates 0.5, 1.0, and 2.0 °C/min with the heating schedules. The TEM techniques, BET-N2 measurements, XRD-Scherrer equation, and AFM images were employed in the examination. That the BET values increased as increasing of exfoliated flakes reflected two stages of exfoliation. In the beginning stage, during which the BET values were <40 m2/g, the exfoliation resulted from the stress produced by dehydration. In the second stage, the increased rate of surface area was due to the additional force, which originated from the γ-Al2O3 formation. Exfoliation occurred on the cleavage planes {010}, the side pinacoid of the boehmite particle. The generation of flakes resulted in the thinning of boehmite particles. Some of the flakes preserved the external form of boehmite crystals. From the surface energy evaluations of boehmite and γ-Al2O3, it can be inferred that exfoliation is a natural way of thermal treatment.

Facile and General Method to Synthesize Pt-Based High-Entropy-Alloy Nanoparticles.

Pt-based high-entropy-alloy nanoparticles (HEA-NPs) have excellent physical and chemical properties due to the diversity of composition, complexity of surface structure, high mixing entropy, and properties of nanoscale, and they are used in a wide range of catalytic applications such as catalytic ammoxidation, the electrolysis of water to produce hydrogen, CO2/CO reduction, and ethanol/methanol oxidation reaction. However, offering a facile, low-cost, and large-scale method for preparing Pt-based HEA-NPs still faces great challenges. In this study, we employed a spray drying technique combined with thermal decomposition reduction (SD-TDR) method to synthesize a single-phase solid solution from binary nanoparticles to denary Pt-based HEA-NPs containing 10 dissimilar elements loaded on carbon supports in an H2 atmosphere with a moderate heating rate (3 °C/min), thermal decomposition temperature (300-850 °C), duration time (30 min), and low cooling rate (5-10 °C/min). The Pt autocatalytic behavior was found and investigated, confirming that Pt element could decrease the reduction temperature of other metals via autocatalytic behavior. Therefore, using the feature of Pt autocatalytic behavior, we have achieved Pt-based HEA-NPs at a minimum temperature of 300 °C. We not only prepared a series of Pt-based HEA-NPs with targetable ingredient, size, and phase using the SD-TDR method but also proved the expandability of the SD-TDR technique by synthesizing Pt-based HEA-NPs loaded on different supports. Moreover, we investigated methanol oxidation reaction (MOR) on as-synthesized senary PtCoCuRuFeNi HEA-NPs, which presented superior electrocatalytic performance over commercial Pt/C catalyst.

Microstructure and ignition mechanisms of reactive aluminum–zirconium ball milled composite metal powders as a function of particle size

Al:Zr composite powders are synthesized via arrested reactive ball milling (ARM) and contain small inclusions of Zr within an Al matrix. We characterize the microstructure and ignition temperatures of the powders as a function of size using the following size ranges: 0–10, 10–32, 32–53, 53–75, and > 75 µm. We observe uniformity in density for all size ranges but the largest (> 75 µm), implying consistent elemental composition, and we observe elongation of Zr inclusions within particles of the larger three size ranges. Williamson–Hall analyses of Zr XRD patterns indicate similar Zr grain sizes across all powder size ranges and negligible residual strain and interfacial energies within the composite powders. TGA shows an increase in oxidation as particle size decreases, which we attribute to surface oxidation through comparison to an analogous Zr-rich composite powder. The onset of ZrO2 formation is compared to that of Al–Zr intermixing and intermetallic formation, and we find that the latter corresponds well to the measured ignition temperature. Unlike pure metal fuels, where ignition is governed by the onset of oxidation and ignition temperatures typically increase with particle size, these particles ignite at much lower temperatures (< 350 °C) with no dependence on size for particles less than 75 µm. Atomic intermixing and the formation of intermetallic and Zr compounds are the primary drivers for ignition in this system at slow to moderate heating rates, and we attribute the similar ignition temperatures across multiple particle sizes to the shortest diffusional intermixing distances being comparable in each size range.

Microwave effect on kinetics of paper cups pyrolysis

AbstractNot only are microwaves notorious in food heating, but they exhibit interesting properties in different domains including chemical engineering. Their ability to concentrate heat transfer inside dielectric materials enhances process efficiency and permits high heating rates. Nonetheless, their effect on reactions is still controversial. While some researchers believe in non‐thermal effects due to the efficient conversion of microwave energy to enhance reactions without heat dissipation, others assert that microwave frequencies are not high enough to excite molecular bonds. In this study, paper cups pyrolysis is achieved in electrical and microwave TGA using two heating modes. The effect of microwaves on the kinetics of paper cups pyrolysis is shown to depend on the heating regime: at a moderate heating rate, microwave pyrolysis started at a lower temperature, while the pyrolysis in the electrical and microwave TGA have similar kinetic parameters at high heating conditions. This difference is linked with reaction mechanisms. At moderate heating conditions, cellulose decomposes first to an intermediate compound then to final products. The intermediate has a short reaction time and interacts with the microwave. Hence, hot spots at the molecular scale are generated in a short amount of time below the detectable limits of existing temperature measurements media. At a high heating rate, the decomposition of cellulose is direct and no effect is observed.

Comparison of pyrolysis of live wildland fuels heated by radiation vs. convection

During wildland fires, which include both planned (prescribed fire) and unplanned (wildfire) fires, live and dead plants may be subject to both radiative and convective heat transfer mechanisms. In this study, the pyrolysis of 14 live plant species native to the forests of the southern United States was investigated using a flat-flame burner (FFB) apparatus under three heating modes in order to mimic pyrolysis of plants during wildland fires. The heating modes were: (1) radiation-only, where the plants were pyrolyzed under a moderate heating rate of 4 °C s−1 (radiative flux of 50 kW m−2); (2) convection-only, where the FFB apparatus was operated at a high heating rate of 180 °C s−1 (convective heat flux of 100 kW m−2); and (3) a combination of convection and radiation, where the plants were exposed to both convective and radiative heat transfer mechanisms. Data were also compared with slow heating experiments (0.5 °C s−1). During the experiments, the pyrolysis products were collected and analyzed using GC–MS for the analysis of tars and GC-TCD for the analysis of light gases. The results indicate that the highest light gas and tar yields were obtained from the combined mode, which was performed at a higher pyrolysis temperature and heating rate. CO, CO2, CH4, and H2 were the major light gas species in all three heating modes. The radiation-only mode led to formation of primary tars and a few secondary tars consisting of aliphatic and 1–2 ring aromatic compounds with 1 to 3 attachments, including alkyl, hydroxyl, and methoxy groups.

Effect of latent heat during primary crystallization on the nanostructural formation process in nanocrystalline soft magnetic materials

Nanocrystalline soft magnetic materials are known to be prepared by primary crystallization of Fe-based amorphous precursors. Since the crystallization reaction is exothermic, the amorphous precursor may experience a temporary rise in its temperature relative to its surroundings during the process of nanocrystallization. Given the typical latent heat of primary crystallization (∼ 100 kJ/kg), this temperature rise may exceed hundreds of degrees if not adequately controlled and thus, lead to the formation of unwanted magnetically hard compounds. This effect is generally small for isolated ribbons annealed with a moderate heating rate. However, the recent adoption of high heating rates and short annealing times has caused the self-heating effect to become relevant even for small sample sizes. In this work, the effect of self-heating on the microstructure and magnetic properties of nanocrystalline Fe86B14 is investigated. It is found that magnetically hard Fe-B compounds cannot be avoided when annealing under vacuum in an infrared furnace with a heating rate ≥3 K/s due to the self-heating effect. However, the high thermal conductivity of the copper blocks used by the ultra-rapid annealing process can successfully prevent a self-heating induced temperature rise during annealing, avoiding unwanted compound formation. Finite Element Analysis is also used for predicting the extent of self-heating during infrared annealing.

Sintered glass-ceramics and foams by metallurgical slag with addition of CaF2

The possibilities for the production of self-glazed sintered glass-ceramics or/and glass-ceramic foams using metallurgical slag are discussed. The effect of CaF2 addition on the glass melting, the densification and the foaming is also studied.The sintering and the bloating trends are evaluated by hot stage microscopy and the phase formation is estimated by X-ray diffraction spectroscopy. The structure of the obtained samples is studied with scanning electron microscopy and with computed tomography.The results demonstrate a good sinter ability of the used glass powders in the interval 800–950 °C and a subsequent intensive bloating behaviour of the sintered samples in the range 1050–1150 °C.The addition of a certain amount of CaF2 in the glass batches leads to a noticeable decrease of both the melting and the sintering temperatures as well as to some increase of the crystallinity. As a result, self-glazed glass-ceramics with high percentage of CaF2 and with an improved micro-hardness and crystallinity can be obtained using finer glass powders, moderate heating rates and holding temperatures of 950–1000 °C.At the same time, glass-ceramic foams with closed porosity of about 80 vol % can be synthesized using glass powders with a modest addition of CaF2 by applying higher heating rates and holding temperatures of 1100–1150 °C.

Annealing of LiCoO2 films on flexible stainless steel for thin film lithium batteries

Abstract

Combustion behavior of large size coal over a wide range of heating rates in a concentrating photothermal reactor

Combustion behaviors of large size coal pellets were studied in a novel room temperature chamber type concentrating photothermal apparatus. 4 heating rates of 4.0 °C/s, 15.1 °C/s, 52.4 °C/s and 69.4 °C/s were realized by adjusting the voltage-up rates of the heating lamps. The temperature, image, gas emission, and mass loss were synchronously detected and the reliabilities of data were strictly verified. Coal pellets presented “heterogeneous” ignition mechanism at slow (4.0 °C/s) heating rate, “joint homo-heterogeneous” at moderate (15.1 °C/s) heating rate, and “homogeneous” at sub-fast (52.4 °C/s) and fast (69.4 °C/s) heating rates. High concentrations of CO and CH4 were evident at all heating rates. The increase of heating rate accelerated all gas generation rates and leaded to the gas yield reduction of CO but rising of CO2. Kinetics studies of the reactions around the maximum mass loss rate were carried out ultimately. 1-dimensional diffusion mechanism model (D1) showed best correlation coefficients with the reactions at slow, moderate and sub-fast heating rates and the apparent activation energies slightly decreased from 84.45 and 66.18 to 62.28 kJ/mol. The fitting curve of reactions at fast heating rate was two-stage-style and correlated best to the 3-dimensional diffusion mechanism model based on Jander equation (D3) with activation energies of 33.74 and 11.54 kJ/mol.

Dielectric properties, effect of geometry, and quality changes of whole, nonfat milk powder and their mixtures associated with radio frequency heating

Radio frequency (RF) heating is a promising pasteurization technique providing a fast and more uniform heat generation throughout a sample. In this paper, the effect of composition, frequency (1–30 MHz) and temperature (20–90 °C) on the dielectric properties of whole, nonfat milk powder and their mixtures were studied to develop an effective RF pasteurization. Moreover, the effect of the shape and dimension of the container on RF heating were evaluated. Milk powders were loaded into rectangular and cylindrical boxes with the same volume and different heights (3, 6 and 9 cm), and heated in a 6 kW, 27.12 MHz pilot scale free-running oscillator RF oven. The heating rate, temperature profile, penetration depth, and electric field strength were determined. The quality of the RF heated milk powders was evaluated by measuring moisture content, water activity, solubility, and color. Overall, heating milk powder in the 6 cm height cylindrical box showed a relatively more uniform temperature distribution than 6 cm height rectangular box, with moderate heating rate as well as improved quality in the finished product with less changes in moisture content, water activity, solubility and color. Electric field strength increased with the increase in the height of the container.

Thermo-catalytic reforming of co-form® rejects (waste cleansing wipes)

Co-form® products are typically used for personal hygiene care (cleansing wipes), household cleaning (pads and mops) and absorbent applications. Co-form® is a thermo-bonded multilayer nonwoven composite and Kimberly-Clark patented its process in 2008. Co-form® rejects are composed of 30% plastic polypropylene and 70% wood pulp fibre. It is difficult to recycle and to-date no research articles explore pyrolytic valorisation for its energy recovery. This paper investigated pyrolytic valorisation of co-form® rejects into energy vectors. Pelletised co-form® rejects obtained from a secondary fibre paper mill were processed using a laboratory scale 2 kg/h Thermo-Catalytic Reforming (TCR®) reactor. The TCR® process combines intermediate pyrolysis, using an auger reactor to heat the material under moderate temperatures (350–450 °C) and moderate solid residence times (minutes) in the complete absence of Oxygen, with post catalytic reforming in a fixed bed reactor at 700 °C. Pelletised co-form® rejects were successfully converted into 12 wt% bio-oil, 9 wt% aqueous phase liquid, 8 wt% char and 71 wt% syngas products. The bio-oil higher heating value was found to be 39.36 MJ/kg, comparable to biodiesel. Naphthalene was found to be the most abundant aromatic compound within the oil, with a relative abundance of 15.22% measured by GC–MS. Oleic acid methyl ester (15.86%) was the most abundant long chain hydrocarbon detected. The higher heating value of produced gas was 11.02 MJ Nm3 and char 30.79 MJ/kg. TCR® conversion of co-form® rejects proved to be a feasible route for the valorisation of this waste stream into sustainable energy vectors. In previous works, gasification processes could not successfully convert organic waste streams with a high plastic content, without implications attributed to agglomeration and melting of plastics. The TCR® process overcome these issues with no evidence of agglomeration or melting of plastics present within the reactor. The success was believed to be through applying moderate heating rates (°C/min) and temperatures (max 700 °C), as well as the mechanical effect of continuous mixing of material within the reactor via the internal auger screw. Overall, TCR® is a promising future route for the valorisation of co-form® rejects to produce energy vectors.

Prediction of structure evolution and fragmentation phenomena during combustion of coal: Effects of heating rate

Literature models developed to predict evolution of coal particles over the very first instances of coal combustion/gasification processes only account for primary fragmentation, a phenomenon that can significantly modify the particle size distribution of a coal feed. In this paper, a model that goes beyond primary fragmentation and considers also the effects of combustion of both char and volatiles within the pores on the fragmentation propensity of particles is presented. The model is able to predict the evolution of temperature, pressure, porosity, and concentration of the main chemical species within the particle. Ultimately, the model calculates maps of internal stress and probability of rupture.A campaign of computational experiments is presented with reference to a medium rank coal undergoing different heating rates: when the heating rate is high, the effect of combustion is to augment the probability of fragmentation and to change the very mode of particle rupture; differently, at low and moderate heating rate, combustion plays a negligible effect on particle fragmentation phenomena.

Local supersaturation during melting in a temperature gradient

A homogeneous single-phase Al–Cu alloy was exposed to a steep temperature gradient for a short time interval, melting of the sample at the hot end was interrupted at intermediate stages. In the resolidified microstructure, the local supersaturation was determined by analysing concentration profiles across former liquid films at grain boundaries and adjacent zones in the grain interior. Already at moderate heating rates (3 K/s) significant supersaturations occurred and were quantified.

Effects of thermal activation conditions on the microstructure regulation of corncob-derived activated carbon for hydrogen storage

Activated carbons derived from corncob (CACs) were prepared by pyrolysis carbonization and KOH activation. Through modifying activation conditions, samples with large pore volume and ultrahigh BET specific surface area could be obtained. The sample achieved the highest hydrogen uptake capacity of 5.80 wt% at 40 bar and −196 °C. The as-obtained samples were characterized by N2-sorption, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Besides, thermogravimetric analysis was also employed to investigate the activation behavior of CACs. Detailed investigation on the activation parameters reveals that moderate activation temperature and heating rate are favorable for preparing CACs with high surface area, large pore volume and optimal pore size distribution. Meanwhile, the micropore volume between 0.65 nm and 0.85 nm along with BET surface area and total pore volume has great effects on hydrogen uptake capacities. The present results indicate that CACs are the most promising materials for hydrogen storage application.