Final Pyrolysis Temperature Research Articles

Comparative study of the composition and microstructural properties of semi-coke from microwave and conventional pyrolysis of low rank coal

Microwave pyrolysis technology can effectively realize the clean and quality improvement of coal. In order to study the changes of each component of coal in the process of microwave pyrolysis, the d002, La, Lc, combustion reactivity and conductivity of semi-coke after pyrolysis were analyzed by using XRD, TG, conductivity meter and other testing instruments, and the infrared spectra of semi-coke after pyrolysis were finely resolved by using Origin peak-splitting technique, and the composition of the coal gas in the process of pyrolysis and its percentage content were analyzed. The composition and percentage content of gas in the pyrolysis process were analyzed and compared with conventional pyrolysis. The results showed that compared with conventional pyrolysis, microwave pyrolysis can be completed at a lower temperature and microwave pyrolysis is more favorable to the release of volatile components, in which the content of CO and H2 in the gas fraction increased significantly compared with conventional pyrolysis. At the same pyrolysis temperature, the microwave semi-coke has a higher maximum combustion rate temperature than the conventional semi-coke, which is conducive to improving the thermal stability of semi-coke. The orderliness of the semi-coke increased with the increase of pyrolysis final temperature, resulting in the phenomenon of "similar graphitization". The increase in the number of carbon microcrystalline structures generates off-domain electrons, leading to a significant increase in conductivity. Meanwhile, FT-IR peak fitting analysis revealed that the R value inflection point temperature of microwave semi-coke was much lower than that of conventional semi-coke, which further proved that microwave pyrolysis could be accomplished at lower temperatures, and the C value showed a decreasing tendency with the increase of the final temperature of pyrolysis, which indicated that pyrolysis was an effective method to improve the quality of coal. The above analysis shows that compared with conventional pyrolysis, microwave can prepare high stability and high conductivity semi-coke at lower temperature.

Thermochemical Valorization of Plastic Waste Containing Low Density Polyethylene, Polyvinyl Chloride and Polyvinyl Butyral into Thermal and Fuel Energy

Pyrolysis is a promising technology for transforming waste plastics (WPs) into high-value products. In the near future it will play a key role in the circular economy, as a sustainable and environmentally friendly method of managing this waste. Although the literature reports on the pyrolysis of plastics, it is focused on pure polymers. On the other hand, the state-of-the-art knowledge about the pyrolysis of mixed and contaminated WPs is still scarce. Industrial waste processing usually uses polymer mixtures containing various impurities that influence the pyrolysis process during chemical WPs recycling. In the paper the pyrolysis of three types of WPs: low density polyethylene (LDPE), polyvinyl chloride (PVC) and polyvinyl butyral (PVB) from repeated mechanical recycling of plastics, as well as their binary and ternary mixtures, is considered. The influence of particular components on the pyrolysis process is analyzed. The aim is to determine synergistic behavior of the mixtures during the pyrolysis process, which is important for increasing the efficiency and quality of the obtained bioproducts. Methods such as thermogravimetric (TG/DTG) analysis coupled with Fourier transform infrared spectroscopy (FTIR) and mass spectroscopy (MS) are used. The variations in the initial and final temperature of pyrolysis, mass loss and mass loss rate are determined. The content of PVC significantly lowers the initial temperature and mass loss and increases the final temperature. The pyrolysis of the considered mixtures shows a noticeable synergism—in the initial stage of pyrolysis up to a temperature around 450 °C, the mass loss is accelerated compared to what is predicted by simple superposition. The inhomogeneity of the mixtures as well as the waste origin causes a significant variation in the activation energy. Three main conclusions are obtained: (i) if the waste does not contain PVC, the pyrolysis is nearly complete at a temperature around 500 °C at a heating rate of 10 °C/min, whereas PVC is not fully processed even at 995 °C; (ii) the synergistic effects affect significantly the pyrolysis process by accelerating some steps and lowering the activation energy; and (iii) the presence of PVC noticeably lowers the temperature of the first stage of PVB pyrolysis. The investigation results prove that chemical recycling of mixed LDPE, PVC and PVB waste can be an effective method of plastic waste management.

Experimental Study on Microwave Pyrolysis of Decommissioned Wind Turbine Blades Based on Silicon Carbide Absorbents

The rapid expansion of the scale of wind power has led to a wave of efforts to decommission wind turbine blades. The pyrolysis of decommissioned wind turbine blades (DWTBs) is a promising technological solution. Microwave pyrolysis offers the benefits of fast heating rates and uniform heat transfer, making it a widely used method in various heating applications. However, there are few studies on the microwave pyrolysis of DWTBs, and pyrolysis characteristics under different boundary conditions remain unclear. In this paper, we investigate the pyrolysis characteristics of DWTBs by utilizing silicon carbide (SiC) particles as a microwave absorbent. The results demonstrated that, when the microwave heating power increased from 400 W to 600 W, the heating rate and pyrolysis final temperature of the material increased, resulting in a reduction in pyrolysis residual solid yield from 88.30% to 84.40%. At 600 W, pyrolysis gas components included C2H4, CH4, and CO, while the tar components included phenol and toluene. The highest degree of pyrolysis was achieved under the condition of an SiC particle size of 0.85 mm, with better heating performance, and the calorific value of the pyrolysis gas generated was 36.95 MJ/Nm3. The DWTBs did not undergo pyrolysis when SiC was not added. However, when the mass ratio of SiC to DWTBs was 4, the tar yield was 4.7% and the pyrolysis gas yield was 17.0%, resulting in a faster heating rate and the highest degree of pyrolysis. Based on this, an optimal process for the microwave pyrolysis of DWTBs was proposed, providing a reference for its industrial application.

Oxygen bond cleavage and its migration mechanisms during pyrolysis of naomaohu sub-bituminous coal

Investigating the oxygen bond cleavage and its migration mechanisms during the pyrolysis process of sub-bituminous coals is essential for their classification utilization. The present study employed a fixed-bed pyrolysis technique (temperature range: 350–600 °C) to explore the cleavage of oxygen-containing bonds and subsequent behavior of oxygen migration and transformation during the pyrolysis process of Naomaohu sub-bituminous coal (NSBC). X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy results reveal that the organic oxygen in NSBC predominantly exists as the form of C–O bonds, accounting for 22.81 wt% of the total composition, mainly encompassing hydroxyl, carbonyl, ester, and ether groups. The organic oxygen in the light tar is mainly in the form of phenols, reaching 1.71 wt%, of which methyl substituted phenols is predominant at a final pyrolysis temperature of 600 °C. This can be attributed to the presence of more aryl ether bonds and hydroxyl groups in NSBC, which are prone to cleavage at higher temperatures, resulting in the formation of phenoxyl radicals. Additionally, the higher temperature facilitates the weakening of hydrogen bonds between phenolic hydroxyl groups, thereby enhancing the yield of phenolic compounds. The ester compounds present a decreasing trend with increasing temperature, primarily associated with the cleavage temperature of ester linkers being 350 °C, suggesting that an increase in temperature favors the cleavage of ester bonds. In addition, the cleavage of C–O bonds begins to accelerate significantly during the pyrolysis temperature range of 450–500 °C, subsequently accounting for the pronounced proliferation of phenols within this specific thermal interval. The oxygen content in semi-coke decreased with the increase of temperature, from 85.27 wt% at 350 °C to 37.17 wt% at 600 °C, while the oxygen content in the pyrolysis gas increases from 11.63 wt% at 350 °C to 47.53 wt% at 600 °C, indicating that a significant migration of organic oxygen to the pyrolysis gas during the pyrolysis of NSBC. This study can deepen the understanding of the transformation mechanism of oxygen-containing structure in NSBC pyrolysis process, and provide a theoretical basis for high-grade utilization of low-rank coals.

Liquid chromatographic fractionation of bio-oil from sugarcane bagasse: influence of heating rate on bio-oil yield and quality

Brazil stands out in the field of using biomass as a source of energy and biomaterials, due to its territorial extension, biodiversity and climatic conditions. In this sense, one can highlight the high potential of bio-products generated from biomass. This is the case of sugarcane bagasse, produced in large quantities allied to the sugar and alcohol industry. In Brazil, much research has been done to improve its amount of fiber, aiming at the production of alternative fuels and generating the so-called "energy cane". Thus, it was studied the use of sugarcane bagasse for the production of bio-oil through pyrolysis and the isolation of fractions for industrial application. A comparison was also made between two types of sugarcane, a commercial variety (Saccharum sp.) and a variety with some genetic improvement (Erianthus arundinaceus). The final pyrolysis temperature was set at 500 ° C by varying the heating rates (25, 45, and 65 ° C min-1). The bio-oils were fractionated using preparative liquid chromatography and their fractions were analyzed by gas chromatography coupled to mass spectrometry. The fractionation of bio-oils increased the number of compounds identified by about 50%, besides allowing the isolation of apolar compounds. In addition, it was found that the genetic improved sugarcane presented higher bio-oil content, with higher hydrocarbon content, when compared to commercial sugarcane, demonstrating that the improvement process was efficient. Among the compounds identified were phenols, furfural derivatives and hydrocarbons, which indicates the potential use of bio-oil not only as bio-fuels, but also for industrial purposes.

Pyrolysis characteristics and product distribution of oil sludge based on radiant heating.

It needs to be improved the conversion efficiency and stable operation of conventional pyrolysis with high-temperature flue gas heating (HFH). Herein, a new radiative heating (RH) pyrolysis method is proposed. Experimental studies are carried out on a self-made radiation pyrolysis pilot plant to investigate the effects of different factors (pyrolysis final temperature, residence time, and carrier gas volume) on product distribution. The results show that with the increase of pyrolysis temperature, the yield of the gas phase consistently increases, and the proportion of CH4 and H2 in the pyrolysis gas reaches 62.31% at 700°C. The yield of the liquid phase increases and then decreases. The recovery rate of pyrolysis oil achieves 68.07% when the pyrolysis temperature is 600°C with main components of ketones and unsaturated hydrocarbon compounds. The yield of the solid phase consistently decreases. The RH in this work generates more pyrolysis gas in the pyrolysis process and alleviates the effects of fouling layers on the continuous operation of the equipment which has guiding significance for the efficient resource utilization of oil sludge.

Experimental investigation on pyrolysis products and pore structure characteristics of organic-rich shale heated by supercritical carbon dioxide

The efficient pyrolysis and conversion of organic matter in organic-rich shale, as well as the effective recovery of pyrolysis shale oil and gas, play a vital role in alleviating energy pressure. The state of carbon dioxide (CO2) in the pyrolysis environment of shale reservoirs is the supercritical state. Its unique supercritical fluid properties not only effectively heat organic matter, displace pyrolysis products and change shale pore structure, but also achieve carbon storage to a certain extent. Shale samples were made into powder and three sizes of cores, and nitrogen (N2) and supercritical carbon dioxide (ScCO2) pyrolysis experiments were performed at different final pyrolysis temperatures. The properties and mineral characteristics of the pyrolysis products were studied based on gas chromatography analysis, X-ray diffraction tests, and mass spectrometry analysis. Besides, the pore structure characteristics at different regions of cores before and after pyrolysis were analyzed using N2 adsorption tests to clarify the impact of fracturing degree on the pyrolysis effect. The results indicate that the optimal pyrolysis temperature of Longkou shale is about 430 °C. Compared with N2, the oil yield of ScCO2 pyrolysis is higher. The pyrolysis oil obtained by ScCO2 extraction has more intermediate fractions and higher relative molecular weight. The ScCO2 can effectively improve the pore diameter of shale and its effect is better than that of N2. The micropores are produced in shale after pyrolysis, and the macropores only are generated in ScCO2 pyrolysis environments with temperatures greater than 430 °C. The pore structure has different development characteristics at different pyrolysis temperatures, which are mainly affected by the pressure holding of volatile matter and products blocking. Compared to the surface of the core, the pore development effect inside the core is better. With the decrease in core size, the pore diameter, specific surface area, and pore volume of cores all increase after pyrolysis.

High temperature viscoelastic behaviour of sugarcane bagasse char and coal blends: Role of oxygen and porosity of char on fluidity reduction

This paper focuses on the introduction of sugarcane bagasse, an agricultural byproduct, as a renewable carbon-based additive to metallurgical coal to produce biocoke for the steel industry. Through subjecting pelletized sugarcane bagasse samples to various pyrolysis conditions, chars with varying properties were generated. With increasing final pyrolysis temperature (200, 400, 600, and 800 °C), a rise in carbon content and decline in oxygen, nitrogen and hydrogen levels in the chars were observed. The presence of an inert purge gas during pyrolysis prompted abundant micropore formation between 400 and 600 °C, yielding high specific surface area (SSA > 300 m2/g) chars at 600 °C and 800 °C. Conversely, chars produced in a fixed (unpurged) nitrogen environment exhibited minimal porosity and consequently low SSAs (<5m2/g). These various chars were then blended (at 10 % addition) with a medium-volatile bituminous coal to evaluate their impact on the viscoelastic properties of the coal. Chars pyrolyzed to lower final temperatures had the greatest detrimental effect on blend fluidity due to (1) their continued devolatilization which introduced void spaces in the blend creating pathways for the exhaust of coal volatiles, and (2) their elevated oxygen content, which scavenged essential mobile hydrogen needed to facilitate viscoelastic behaviour. Furthermore, chars with similar oxygen content but substantially different (by over two orders of magnitude) SSAs generated comparable coal-char blend viscosity profiles, indicating that the presence or absence of micropores in an additive does not significantly influence the viscoelastic behaviour of the coal. The reduction in blend fluidity for the addition of chars pyrolyzed to 800 °C was comparable to the modelled addition of inertinite macerals, implying that these high-temperature chars predominantly serve as inert solid additives. Comparison to a blend with 10 % mesoporous activated charcoal as the additive confirmed that it is mesopores that destroy fluidity, while micropores do not play a significant role. Mesopores were identified to adsorb/trap the relatively large tar-like compounds that are responsible for coal plasticity. Collectively, this research identifies three key factors contributing to fluidity reduction in coal-additive blends: void creation, oxygen content, and mesoporosity. These findings offer insights into optimizing biocoke production processes.

Enhanced microwave assisted pyrolysis of waste rice straw through lipid extraction with supercritical carbon dioxide.

A combination of supercritical carbon dioxide (scCO2) extraction and microwave-assisted pyrolysis (MAP) have been investigated for the valorisation of waste rice straw. ScCO2 extraction of rice straw led to a 0.7% dry weight yield of lipophilic molecules, at elevated temperatures of 65 °C and pressures of 400 bar. Lipid compositions (fatty acids, fatty alcohol, fatty aldehydes, steroid ketones, phytosterols, n-alkanes and wax esters) of the waxes obtained by scCO2 were comparable to those obtained Soxhlet extraction using the potentially toxic solvent n-hexane. ScCO2 extraction positively influenced the pyrolysis heating rate, with a rate of 420 K min-1 for particles of 500-2000 μm, compared to 240 K min-1 for the same particle size of untreated straw. Particle size significantly affected cellulose decomposition and the distribution of pyrolysis products (gaseous, liquid and char), highlighting the importance of selecting an adequate physical pre-treatment. TG and DTG of the original rice straw and resulting biochar produced indicated that cellulose was completely decomposed during the MAP. While a rapid pressure change occurred at ∼120 °C (size > 2000 μm) and ∼130 °C (size 500-2000 μm) during MAP and was associated with the production of incondensable gas during cellulose decomposition, this takes place at significantly lower temperatures than those observed with conventional pyrolysis, 320 °C. Wax removal by scCO2 influences the dielectric properties of the straw, enhancing microwave absorption with rapid heating rates and elevated final pyrolysis temperatures, illustrating the benefits of combining these sustainable technologies within a holistic rice straw biorefinery.

Boosting Oxygen Reduction Reaction with Fe-Based Single-Atom Catalysts: The Role of Cluster Interactions

Fuel cells (FCs) have emerged as a promising alternative for efficient electricity production in the future [1]. However, their widespread commercialization is hindered by their prohibitive cost due to the large amount of platinum used in these electrochemical systems [2]. Platinum is used to accelerate the unfavorable kinetics of the cathodic oxygen reduction reaction (ORR) [3]. To achieve large-scale and cost-effective development of FCs, it is essential to find high-performance platinum-free catalysts. Two solutions are mainly reported in the literature: the development of non-precious metal-based carbon catalysts and metal-free carbon catalysts. However, the work reported on these two types of carbon catalysts is sometimes contradictory regarding the actual nature of the active sites and the mechanisms of reduction of oxygen molecules on the catalyst [4].Pyrolyzed metal-nitrogen-carbon (M-N-C) catalysts for the ORR, especially single-atom catalysts (SACs), have been widely studied because they exhibit excellent electrocatalytic performance, thanks to the high content of metal atoms anchored on a carbon support [5]. Recent research has indicated that the combination of single-atom active sites with metal nanoclusters can further improve the catalytic activity, but the underlying mechanism remains unclear [6]. Therefore, it is necessary to develop model catalysts based on both single-atoms and nanoclusters to better understand their catalytic activity.In this work, we prepared nitrogen-doped and iron-doped carbon catalysts (called Fe-NC below) with precise control of the type of iron in the material. First, the functionalization of an activated carbon was performed by carbonizing it under air in the presence of urea. Then, the sample was placed in an autoclave for hydrothermal treatment in the presence of FeCl3.6H2O to allow the incorporation of iron, and thermal post-treatment was applied to synthesize model catalysts (Fig. 1a). The precursor ratio and final pyrolysis temperature were adjusted and optimized to produce either iron-based single atoms (SA) (here referred to as FeSA-NC) or atomic clusters (AC) associated with single atoms (here referred to as FeSA+AC-NC). The results show that the iron-based catalysts exhibit outstanding catalytic activity (Fig. 1b) and durability (Fig. 1c) in alkaline medium for the ORR, even better than commercial Pt (20 wt.%)/C in the case of FeSA+AC-NC. The analysis provided insight into the development of highly efficient multifunctional electrocatalysts, where the presence of iron nanoclusters was found to be a crucial determinant of the catalytic activity for the ORR.[1] M.K. Debe, Electrocatalyst approaches and challenges for automotive fuel cells, Nature. 486 (2012) 43–51. https://doi.org/10.1038/nature11115.[2] C. Sealy, The problem with platinum, Mater. Today. 11 (2008) 65–68. https://doi.org/10.1016/S1369-7021(08)70254-2.[3] M. Borghei, J. Lehtonen, L. Liu, O.J. Rojas, Advanced Biomass-Derived Electrocatalysts for the Oxygen Reduction Reaction, Adv. Mater. 30 (2018) 1703691. https://doi.org/10.1002/adma.201703691.[4] A. Dessalle, J. Quílez-Bermejo, V. Fierro, F. Xu, A. Celzard, Recent progress in the development of efficient biomass-based ORR electrocatalysts, Carbon. 203 (2023) 237–260. https://doi.org/10.1016/j.carbon.2022.11.073.[5] K. Liu, J. Fu, Y. Lin, T. Luo, G. Ni, H. Li, et al., Insights into the activity of single-atom Fe-N-C catalysts for oxygen reduction reaction, Nat. Commun. 13 (2022) 2075. https://doi.org/10.1038/s41467-022-29797-1.[6] X. Wan, Q. Liu, J. Liu, S. Liu, X. Liu, L. Zheng, et al., Iron atom–cluster interactions increase activity and improve durability in Fe–N–C fuel cells, Nat. Commun. 13 (2022) 2963. https://doi.org/10.1038/s41467-022-30702-z. Figure 1

Effects of circulating ash and dolomite on mercury transition during coal step conversion of pyrolysis and combustion

In aim to study the influence of circulating ash used as heat carrier and dolomite used as catalyst on mercury transition during the step conversion of coal pyrolysis and combustion, five experiments with different operating conditions were conducted in this study, including four pyrolysis experiments of raw coal, coal/ash, coal/dolomite, coal and ash/dolomite, and combustion experiment of pyrolysis solid product. By changing the experimental conditions including final pyrolysis temperature, heating rate, coal-ash ratio and dolomite type, the transition path and final mercury distribution in the step conversion process were comprehensively analyzed. Experiments results indicated that mercury completely released out from coal when the final pyrolysis temperature was 600 °C. The individual addition of ash could promote the mercury release from coal at lower temperature. Dolomite could catalyze the oxidation of Hg0 in gas phase, and the modified dolomite had better catalytic capacity for Hg0 oxidation than natural dolomite. The addition of circulating ash and natural dolomite both had a certain catalytic effect on Hg0 emission peaks during the coal pyrolysis. Increasing the coal-ash ratio was conducive to the oxidation of Hg0 in pyrolysis gas. During the direct combustion of coal, the content of Hg0 released into the gas phase could reach to 69.97%. By adding ash, ash/natural dolomite and ash/modified dolomite to the coal pyrolysis process, the content of Hg0 in pyrolysis gas decreased to 58.99%, 34.77% and 31.30%, respectively. The research is able to offer the theoretical foundation for mercury contaminants’ removal and process optimization of the step conversion technology.

Study on the pore evolution of Xinjiang oil shale under pyrolysis based on joint characterization of LNTA and MIP

During the in-situ exploitation of oil shale, the evolution of pore structure will affect the heat transfer medium and the transport capacity of products. In this study, using the oil shale from Jimsar region of Xinjiang, in combination with the low-temperature nitrogen adsorption experiment (LNTA) and high-pressure mercury injection experiment (MIP), the effect of temperature on evolution law of its pores during pyrolysis were analyzed according to the LNTA and MIP joint characterization results. The results show as follows: the change curve of oil shale porosity with pyrolysis final temperature in Xinjiang shows an “S” shape. The pore volume increases slightly before 300 °C, and it shows an increasing trend in the subsequent temperature range, with the mesopore volume change being the most noticeable. However, the increase slows down after 600 °C. The evolution of full-scale pores in the pyrolysis process of oil shale is reflected by the joint characterization of LNTA and MIP, which indicates that the temperature has a controlling effect on the evolution of pore, and provides basic theoretical support for how to improve the oil recovery rate of exploitation of oil shale.

Densified biochar capsules as an alternative to conventional seedings

The application of biochar in soil provides various benefits that can vary in intensity as the pyrolysis temperature increases. However, its low density makes this material easily transportable and prone to being removed from the system. The objective of this study was to investigate the pyrolysis temperatures and compression pressure of densified biochar carrier capsules on the physiological quality of Schizolobium parahyba var. amazonicum seeds. Produced at three final pyrolysis temperatures (300, 600, and 900 °C), the biochar was characterized through bulk and true density analyses, immediate composition, pH, electrical conductivity, cation exchange capacity, water-soluble carbon, characterization of organic structures by FTIR, and PAH analysis. Subsequently, the biochar was compacted by briquetting at two compression pressures (50 and 200 psi) with one seed per capsule, and germination, emergence, and quality of generated seedlings were evaluated. After verifying residue normality and variance homogeneity, analysis of variance was conducted following a completely randomized design in a 3 × 2 factorial arrangement, with four replications per treatment and two additional control treatments. Upon identifying significant differences, regression model adjustments were performed. Cluster-based multivariate analysis was used to identify similarities among the studied treatments, both for capsules and controls. Pyrolysis temperature and compression pressure influenced seed germination, emergence, and initial seedling growth. Lower pressure favored shoot development, while higher pressure favored root development and generated seedlings of higher quality. The benefits of biochar to soil, combined with the implementation of seeds, make the production of densified biochar capsules an alternative to conventional seedings, potentially reducing high energy and financial costs and enabling the recovery of degraded areas, even in difficult-to-access regions.

A Review of Pyrolysis Technologies and the Effect of Process Parameters on Biocarbon Properties

Biomass-based solutions have been discussed as having the potential to replace fossil-based solutions in the iron and steel industry. To produce the biocarbon required in these processes, thermochemical treatment, pyrolysis, typically takes place. There are various ways to produce biocarbon, alongside other products, which are called pyrolysis oil and pyrolysis gas. These conversion methods can be divided into conventional and non-conventional methods. In this paper, those techniques and technologies to produce biocarbon are summarized and reviewed. Additionally, the effect of different process parameters and their effect on biocarbon yield and properties are summarized. The process parameters considered were final pyrolysis temperature, heating rate, reaction atmosphere, pressure, catalyst, use of binders, and particle size. Finally, the effect of different reactor configurations is discussed. Understanding the combination of these methods, technology parameters, and reactor configurations will help to produce biocarbon with the desired quality and highest yield possible.

Evaluation of the content and degradation rates of PAHs in biochars, in terms of assessing the environmental risks of their application for soil remediation

The growing worldwide practice of biochar application as soil ameliorants, as well as adsorbents for remediation of soil contaminated with oil products and heavy metals, can lead to an increase the risk of environmental pollution by pyrolysis by-products. One of the most dangerous components of biochars is polycyclic aromatic hydrocarbons (PAHs), which are inevitably formed during the production of pyrogenic material. In this work, biochars obtained from various plant materials (millet, corn, willow, linden) under different pyrolysis temperatures were tested for the content of polycyclic aromatic hydrocarbons. The total content of PAHs in the studied samples ranged from 8.49 to 221.21 µg/kg, which does not exceed the limit concentrations established by the International Biochar Initiative. At the same time, polynuclear hydrocarbons with high carcinogenic and immunotoxic properties are found in the composition of biochars. A natural question arises about the effect of the final pyrolysis temperature on the total content and composition of PAHs in pyrolysis by-products. To study the degradation of polycyclic aromatic hydrocarbons in soil, linden biochar obtained by pyrolysis at 250 °C was used, from which the contaminants were extracted and applied to the soil so that the concentration of the marker was 20 and 40 µg/kg. The determination of the residual amount of polycyclic aromatic hydrocarbons was carried out after 1, 2, 6, and 11 months of incubation. Complete degradation of some 3–5-membered polycyclic aromatic hydrocarbons was found after 1–2 months of incubation. The most persistent pollutants were benzo(a)pyrene, benzo(b)fluoranthene, and pyrene, the concentration of which decreased to 31–71% on after 11 months of incubation. The slower degradation was found in the variant of the experiment with the high concentration level of polycyclic aromatic hydrocarbons. It was concluded that in soils selective accumulation of polynuclear PAHs, that most resistant to biodegradation, can occur.

Modified network kinetic model for coal pyrolysis with high-value products and low carbon emissions

Pyrolysis is a clean and efficient technology for the conversion of low-rank coal. Its key product is tar with high value. The complex composition of tar limits its further effective utilization. Although most kinetic models can provide the final distribution of three-phase products in coal pyrolysis, an effective prediction method for the specific composition of tar and gas has not yet been developed. Most numerical models serve to improve the total yield of volatile matter and cannot provide theoretical guidance for the improvement of tar quality or the reduction of carbon emission. Based on the basic assumptions of the CPD (Chemical Percolation Devolatilization) model for product molecules structure and generation mechanism, this paper proposed a more sophisticated method for dividing tar composition, which can achieve the division of light, medium, and heavy fractions of tar components according to boiling point. Light gas composition could be obtained with the combination of FG(Functional Group) submodel. The influence of pyrolysis final temperature, heating rate, and environmental pressure was explored for the yield and distribution of products of 18 coals. The simulation results showed that the total yield of tar was affected by both coal structure characteristics and operating parameters. Under conditions favorable for evaporation, such as low pressure and high temperature, the total yield of tar was positively correlated with the average aromatic core size in coal. Under other conditions, tar release was limited by its volatility. Coal with larger average aromatic core size corresponded to less tar yield instead. The pressure in the operating parameters had the most significant influence on the total yield of tar. The heavy fractions of tar are more sensitive to changes in operational parameters, making working conditions that increase the total yield of tar reduce tar quality. The overall carbon emission of pyrolysis is <1 kg CO2/kg tar, which is far lower than the 2–4 kg CO2/kg tar and 3–9 kg CO2/kg tar of direct and indirect liquefaction processes. Under the conditions of sufficient insulation time and no consideration of secondary reactions, the carbon emission of pyrolysis only depended on the content of carboxyl groups in the precursor functional groups. Therefore, the carbon emission intensity decreased with the increase of coal rank. For the optimization for total tar yield and tar quality, 1 atm pressure and 723–923 K temperature was optimal for low rank coals, while low temperature and heating rate with 10–20 atm pressure or high temperature and heating rate with 45–50 atm pressure were optimal for medium rank coals. For the optimization of light tar yield and tar quality, 6–9 atm pressure was optimal for low-rank coals, and 1–3 atm pressure was optimal for medium-rank coals.

Nanoscale MOF-catalyzed pyrolysis of oil shale and kinetic analysis

Oil shale is of increasing interest as it is considered an essential alternative to traditional energy sources due to its abundant reserves. In this research, nanoscale Co/MOF and Ni/MOF were prepared by modified methods, and the catalytic pyrolysis mechanism of oil shale was studied using structural characterization and pyrolysis experiments. The TG and DTG curves show that MOF catalysts increase the total weight loss rate of oil shale pyrolysis and decrease the temperature corresponding to the initial temperature, final temperature, and maximum weight loss rate of oil shale pyrolysis. Kinetic analysis shows that Co/MOF and Ni/MOF catalysts reduce the activation energy of oil shale pyrolysis reaction by 32 KJ/mol and 25 KJ/mol, respectively. The change in the yield and composition of the products before and after catalytic pyrolysis was compared through the dry distillation experiment. It was found that MOF had a good catalytic effect, and the shale oil output was significantly increased. The FT-IR and GC/MS analysis of the catalytic pyrolysis of shale oil shows that the addition of Co/MOF and Ni/MOF catalysts is conducive to the increase of aromatics, olefins, and alkanes and the decrease of oxygen-containing compounds. The effect of the catalysts on the nature of the products and on the yields suggests that the Lewis and Bronsted acid groups on the surfaces of the MOF catalysts and that these can induce positive charges on carbon atoms in alkanes, alkenes etc to promote pyrolysis generate more oil.

Comparative study of temperature-programmed pyrolysis and two-step fast pyrolysis of oily sludge

Oily sludge (OS) is the main waste produced in the process of crude oil extraction, transportation, and refining. As a promising technology of OS treatment, pyrolysis can reduce pollutant emissions and fully recover resources. In this study, the pyrolysis characteristics and product quality of temperature-programmed pyrolysis (TPP) and two-step fast pyrolysis (TSFP) were investigated. For the TG analysis, the faster heating rate could promote the pyrolysis of OS and increase its weight loss rate. In TPP, the higher final pyrolysis temperature provided more energy, which made the CH bond and CC bond break, increased the gas yield and oil yield, and also increased the hydrogen component in the gas, but reduced the char yield. However, the lower final pyrolysis temperature could improve the calorific value of oil. In TSFP, the oil yield was mainly affected by the first step pyrolysis temperature (T1), and the oil yield was 30.9 % at T1 of 500 ℃. The gas yield was both affected by T1 and the second step pyrolysis temperature (T2), and the gas yield could reach a maximum of 32.5 % at 550 ℃ (T1) × 800 ℃ (T2), which was 46.9 % higher than that of TPP (700 ℃, 22.1 %). This was due to the fact that as the T2 rose, the macromolecular components broke down, promoting the generation of gas. In TSFP, the hydrogen component in the gas was the most at 500 ℃ (T1) × 800 ℃ (T2). Compared with TPP, the total calorific value of the available products (oil and hydrogen) could be increased by TSFP, which increased the energy utilization efficiency. This study is expected to provide a theoretical basis for the industrial application of TSFP.

Mechanism of sulfur migration and conversion in pyrolysis/combustion staged conversion process of high sulfur coal

To investigate the effects of circulating ash heat carriers and dolomite catalysts on sulfur migration in the coal pyrolysis/circulating fluidized bed combustion staged conversion process, five experiments of coal pyrolysis, ash/coal co-pyrolysis, coal pyrolysis catalyzed by dolomite, ash/coal co-pyrolysis catalyzed by dolomite and combustion of pyrolysis solid products were designed and carried out. By examining the effects of pyrolysis temperature, heating rate, coal-ash ratio and dolomite species on sulfur migration, the final distribution of sulfur-containing pollutants throughout the staged conversion process was systematically analyzed. The results showed that the separate mixing of ash heat carrier at final pyrolysis temperature of 600 °C increased the residual sulfur in solid phase from 79.29 % of raw coal pyrolysis to 90.00 %. When dolomite catalyst was added individually, the sulfur released into gas phase and tar was reduced from 18.28 % and 2.43 % of the raw coal to 13.14 % and 1.94 %, respectively. And Fe additive significantly improved sulfur resistance of the dolomite catalyst. The regeneration process has little effect on the sulfur fixation capacity of natural dolomite. When ash heat carrier and dolomite catalyst were simultaneously added to the system, the sulfur fixed in ash increased from 79.29 % of the raw coal to 91.27 %, and the sulfur fixed in natural dolomite and modified dolomite accounted for 4.32 % and 4.46 % of the total sulfur, respectively. In the combustion experiments of pyrolysis solid phase products, 43.57 %, 65.57 % and 61.44 % of sulfur was retained in the solid phase residue after combustion with circulating ash, circulating ash/natural dolomite and circulating ash/modified dolomite were added, respectively. Compared with direct combustion of coal, the staged conversion process resulted in a 55 % reduction of sulfur in the boiler flue gas. This study provides a theoretical basis for the purification of sulfur-containing pollutants in the staged conversion process.

Pyrolysis and Torrefaction-Thermal Treatment of Creosote-Impregnated Railroad Ties as a Method of Utilization.

A fundamental issue of waste management and the rail transport industry is the problem of utilizing used railroad ties. Wooden railroad ties are treated with a preservative, usually creosote. Due to their high toxicity, railroad ties are considered hazardous waste and must be utilized under various directives. It is proposed to utilize the troublesome waste by using the pyrolysis and torrefaction process. The research proves that the thermal method is effective for disposing of this type of waste. Torrefaction up to 250 °C gives high efficiency of impregnation removal, while pyrolysis up to 400 °C completely neutralizes waste. A series of experiments were conducted for various final pyrolysis temperatures to determine a minimum temperature for which the obtained solid products are free from creosote. Extraction with the use of the Soxhlet technique was performed for the raw materials and the obtained solid products-chars. The oil content for liquid fraction was also examined for each sample. As a result of the thermal treatment of the waste, fuel with combustion parameters better than wood was obtained. For a high final temperature of the process, the calorific value of char is close to that of hard coal.