Pyrolysis Reaction Research Articles

Investigation on steam co-gasification of torrefied biomass and coal: Thermal behavior, reactivity, product characteristic and synergy

The steam gasification of rice straw torrefied at 200–300 °C and its co-gasification with coal were examined in this study. The effect of torrefaction temperature on thermal behavior, reactivity, product characteristic, and synergy were investigated. The results showed that torrefaction temperature influenced the pyrolysis and char gasification stages by shifting them to higher temperature ranges. As torrefaction temperature increased, the H2 content increased while the CO and CH4 contents decreased, with H2/CO molar ratio increasing from 1.8 to 2.4. The total gas yield also increased from 0.95 to 1.30 Nm3/kg, especially with a large increase up to 27.4 %. As for the co-gasification, stages of biomass pyrolysis and coal pyrolysis overlapped at torrefaction temperature of 300 °C. The pyrolysis reactivity decreased while the char gasification reactivity increased with the torrefaction temperature increasing. The H2/CO molar ratio decreased slightly from 3.55 to 3.40, while the total gas yield increased from 1.87 to 1.96 Nm3/kg as well as the cold gas efficiency from 75 % to 77 %. The strongest synergistic effect on the reactivity occurred at torrefaction temperature of 250 °C. The increased torrefaction temperature enhanced the synergistic effect on the total gas yield but weakened it on the H2 yield.

Engineered Mg-modified biochar-based sorbent for arsenic separation and pre-concentration

The utilization of biochar as a relatively efficient sorbent or stationary phase for the separation and preconcentration of a wide range of analytes represents an innovative approach in current sample pretreatment methods. Appropriate pre- and post-pyrolysis modification of the input precursor and pyrolysis product, respectively, allows targeted design of the physicochemical properties and sorption characteristics of the resulting sorbent. The present work deals with the preparation of pyrolysis materials based on unmodified cattail leaf biomass (BC) and its Mg-modified analogue (MgBC) by a slow pyrolysis process at 500 °C and a residence time of 1 h in a pyrolysis reactor. Physicochemical characterization of BC and MgBC carried out by pH, total C, N, surface size analysis (SSA), 13C NMR, SEM-EDX and XRD confirmed significant morphological and mineralogical differences between the prepared sorbents. By performing sorption experiments using a model anionic analyte (As) and application of Langmuir isotherm, we found that the predicted maximum sorption capacity of MgBC for As is 13.5-fold higher than that of BC. The sorption process of As by both sorbents is best described by the Sips adsorption isotherm (R2 ≥ 0.995) and a pseudo-nth order kinetic model (R2 ≥ 0.997). The optimum pH for As sorption by BC and MgBC sorbents is in the interval 5–6. The presence of competitive phosphate anions (equimolar concentration of 1:1) in the solution significantly reduces the sorption capacity of MgBC for As by 40% for BC by 70%. The presence of Cl- ions showed no significant effect on the sorption capacity of Bc and MgBC for As. Both sorbents were best recovered using 0.1 mol/L NaOH solution when the desorption efficiency for both sorbents was more than 95%. The MgBC sorbent showed 35% retention of As from the real sample in the model SPE column at a flow rate of 0.12 mL/s. Based on the obtained knowledge, it is evident that biochar-based sorbent prepared from Mg-modified precursor represents an effective sorbent for anionic forms of analytes and opens the possibility of its use also in preconcentration and separation techniques.

Three-dimensional numerical simulation of coal and papermaking trash co-combustion in a circulating fluidized bed

Circulating fluidized bed (CFB) combustion is a important method of waste treatment with the benefits of harmlessness, recycling, and energy recovery. Using the existing co-firing CFB boiler to dispose of waste can reduce investment in boilers and environmental protection equipment. However, there is currently limited research available on the co-combustion of coal and waste (especially for papermaking trash), and the mechanism of pollutant emissions during unit operation remains unclear. In this work, the co-combustion of coal and papermaking trash in a three-dimensional industrial-scale CFB are investigated by using the Dense Discrete Phase Model (DDPM) method. Both homogeneous reactions (such as fuel particle pyrolysis, combustion, and surface reaction) and non-homogeneous reactions (such as gas combustion and pollutant generation) are considered. The co-combustion characteristics are comprehensively analyzed in terms of gas distribution, chemical reaction rates, and bed temperature under various operating conditions, including fuel mixing ratio, secondary air arrangement, and excess air coefficient. The results are obtained by comparing the distribution profile along the height. By reducing the mixing ratio of papermaking trash, the excess air coefficient, and adjusting the secondary air arrangement in the lower region, an expanding, reducing atmosphere is observed in the vicinity of the fuel feeding point. This, in turn, leads to an increase in CO concentration and a decrease in NO emissions, which is attributable to the interplay of gas distribution, chemical reaction rates, and bed temperature. A reduction in NO gas emissions was achieved by adjusting the secondary air arrangement and the excess air coefficient. Overall, this work provides valuable insights into the co-combustion characteristics of coal and papermaking trash in an industrial-scale circulating fluidized bed boilers.

A Carbon Capture and Utilization Process for the Production of Solid Carbon Materials from Atmospheric CO2 - Part 2: Carbon Characterization.

This article is the second part of a study reporting the results of a novel carbon capture and utilization (CCU) process, which converts atmospheric CO2 into solid carbon materials. The CCU process combines direct air capture (DAC) with catalytic methanation, which is then followed by methane pyrolysis in a reactor filled with liquid tin. While Part 1 discussed the performance of the overall process and individual process steps regarding conversions and yields, Part 2 characterizes the solid carbon products obtained under various synthesis conditions. The effects of the pyrolysis temperature and the composition of the gas mixture from the methanation step on the solid carbon product are analyzed. Carbon powder is synthesized from methane with either N2, H2 or CO2 as most important impurity. Carbon samples are characterized using SEM, TEM, Raman spectroscopy, XPS and XRD analysis. Very thin, disordered carbon flakes, soot aggregates and large carbon onions are identified as the main solid products of the process. Their formation mechanisms in the liquid metal-filled pyrolysis reactor are discussed.

A comprehensively experimental and kinetic modeling investigation of tetrahydropyran pyrolysis and oxidation in a jet-stirred reactor

Tetrahydropyran (THP), a kind of promising green cyclic-ether fuel derived from biomass, exhibits excellent resistance to autoignition characteristics and can be used as an alternative fuel or fuel additive to improve combustion efficiency as well as reduce harmful emissions. To further reveal insights into its high-temperature decomposition and low-and intermediate temperature oxidation behaviors closely related the deflagration to detonation in spark ignition engines, the comprehensive investigation of experiments and detailed kinetic modeling of THP were performed in the present work. The experiments at two equivalence ratios, i.e. ϕ = ∞ (pyrolysis) and ϕ = 1.0, were carried out in a jet-stirred quartz reactor at 1.0 atm and 733–1148 K. More than ten substances were identified and quantified by GC and GC/MS, including small hydrocarbons, oxygenated and stable products. A detailed kinetic model of THP pyrolysis and oxidation was developed by incorporating the O2 additions of fuel radicals and updating the rate constants of key reactions, and validated and showed the slight an improvement for the speciation profiles newly reported in this work and those available in the previous literature over a wide experimental range of 450–1260 K and 1.0–10.0 atm. Rate of production analysis indicated that the H-abstractions by H attacking are the important pathways governing THP reactivity with a minor contribution from C-C and C-O dissociations of ring-opening reactions in high-temperature pyrolysis, whereas the H-abstractions triggered by OH and HO2 largely control fuel consumption in low- and intermediate temperature oxidation. The formed three tetrahydropyranyls, especially α-tetrahydropyranyl, will proceed to decompose into acyclic C5H9O radicals via C-O and C-C β-scissions or C5H9OO2-2 intermediates via O2 addition in THP pyrolysis and oxidation, as the main source of small species. For the unique aromatics detected during the pyrolysis, the combination reactions of C2 + C4 unsaturated hydrocarbons predominantly determinate their generation. This work provides new experimental data and further analyses for understanding the pyrolysis and oxidation chemistry of THP and sheds light on directions for future practical application.

Magnetic field effect on mechanism and syngas products of microalgae pyrolysis with activated carbon catalysts

H2-rich syngas has various applications, but it is primarily produced from fossil fuels, contributing to greenhouse gas emissions. Its conversion from renewable sources, such as biomass, can bring environmental benefits and help achieve a reduction in global temperatures below 2 °C. Biomass conversion through the thermal process offers a promising solution for syngas generation. Pyrolysis is appealing as it is more cost-effective than other thermal conversion technologies. The objective of this study is to investigate the conversion of Spirulina microalgae (SP) into syngas (CH4, H2, and CO2) using activated carbon (AC) as a catalyst under the influence of a magnetic field, employing a fixed-bed pyrolysis reactor. Characterization on raw and char SP reveals those biomasses’s main component affecting volatile population, CH4 and H2 correlated with protein and lipid decomposition; on the other hand, CO2 product depends on carbohydrates degradation. An investigation of fresh and spent AC indicates that the main catalytic interaction between pyrolysis vapor and AC is through the Van der Waals force. The magnetic field helps prevent pore blocking on AC, which is proved by specific surface analysis results indicating in a positive synergistic effect between the magnetic field and AC. Activated carbon and magnetic field affected syngas production through a series of pyrolysis vapor cracking, deoxygenation, and hydrocarbon declustering, enhancing CH4 and H2 production by 28.66 and 8.4 %, respectively, and suppressing CO2 by 28.64 % compared to SP pyrolysis alone.

Research on Deoxygenation Pyrolysis of Larch Based on Microwave Heating

Aiming at problems such as low energy utilization efficiency and the high oxygen content of liquid products in the process of conventional biomass conversion to prepare liquid fuels, the deoxygenation pyrolysis technology route of larch based on microwave heating was proposed in this paper. Two kinds of calcium–iron composite oxygen carriers, including Ca2Fe2O5 with iron ore structure and CaFe2O4 with spinel structure, were successfully synthesized. The results showed that the selectivity of ideal products was improved under the action of single iron-based oxygen carriers; however, the deoxygenation effect was undesirable. Under the action of CaFe2O4, the selectivity of aromatics was increased to 27.17% and the selectivity of phenols was decreased to 36.46%, which mainly existed in the form of O1P with low oxygen content. The oxygen content of bio-oil was reduced to 27.70% and the calorific value was increased to 29.05 MJ/kg, thus leading to a great improvement in the quality of liquid products. After the pyrolysis reaction, the Fe2P3/2 XPS peak of CaFe2O4 shifted to a higher binding energy and was characterized as higher valence of iron oxide, which proved its “oxygen grabbing” capacity in microwave pyrolysis. The deoxygenation conversion of larch without an external hydrogen supply was achieved.

Co-pyrolysis of rubber seed oil and industrial hemp stem: Asym2sig deconvolution, thermal behavior, synergistic reaction and kinetic

Evaluation of Kinetic triplets and thermodynamics of the co-pyrolysis of industrial hemp stem (IHS) and rubber seed oil (RSO) contributes to the efficient utilization of agricultural waste. The thermodynamics and kinetics of four pseudo components from mixture (RSO: IHS=1: 1) are investigated using Asym2sig deconvolution. The results show that the Eα of pseudo hemicellulose, pseudo cellulose, pseudo triglyceride and pseudo lignin are 76.019, 193.587, 231.764 and 408.552 kJ/mol. The average differences in Eα and ΔH for the four pseudo-fractions also are 4.439, 4.929, 5.576 and 6.018 kJ/mol. Lower energy barrier favors the reaction. The frequency factor values for four pseudo-components pyrolysis are 1.07 × 108 s−1 for pseudo hemicellulose, 1.78 × 1019 s−1 for pseudo cellulose, 6.04 × 1018 s−1 for pseudo triglyceride, and 6.96 × 1031 s−1 for pseudo lignin. The four pseudo-components have different pyrolysis reaction mechanisms. The synergistic effect calculations show a significant interaction between RSO and IHS. According to thermodynamic analysis, the pyrolysis of the four pseudo components requires the provision of external energy. FT-IR results indicate that RSO can significantly increase the release of C2H2, C2H4, C2H6 and CH4 during the co-pyrolysis of RSO and IHS. The co-pyrolysis of IHS and RSO can increase the content of alkene, alkane and MAHs, which improve the quality of bio-oil significantly. Besides, it can reduce the content of PAHs, which reduces the viscosity of the bio-oil. The results can provide new insights into the synergistic and efficient disposal of triglycerides and lignocellulosic biomass.

Two-phase flow effect on methane conversion in pyrolysis reactors embedding molten salts or metals

In this work, we numerically investigate the impact of flowrate, sparger and reactor geometry on methane conversion in lab-scale cylindrical pyrolysis reactors embedding molten salts or metals. A multiscale approach is enforced, where a diffusion-reaction model yielding the conversion vs time within a single rising bubble is combined with the average residence time of gas bubbles obtained through the two-phase turbulent bubbly flow model. We find that the relative size of the sparger and the height-to-diameter ratio of the molten medium are key parameters for controlling the average residence time of the bubbles, which always results lower than that predicted by the terminal velocity of a single bubble rising in an overall static melt. The highest relative discrepancy (order 300%) between the single-bubble estimate and the CFD-based residence time is found in the case of molten salts in low-aspect ratio reactors fed by small spargers. The physical mechanism underpinning the influence of geometric parameters on the overall conversion is addressed in detail, together with the impact of two-phase flow effects on the estimation of bubble size in laboratory scale bubble reactors.

Investigating the potential of plastic pyrolysis oil-diesel blends in diesel engine: Performance, emissions, thermodynamics and sustainability analysis

The abrupt rise in demand for conventional fuels has become a major cause for concern despite their increasing depletion. That's why the pyrolysis process to make plastic pyrolysis oil (PPO), can be used to prepare fuel as an alternative fuel. The batch pyrolysis reactor was fabricated to produce plastic pyrolysis oil (PPO) from locally sourced grocery bags made of high-density polyethylene (HDPE). The purpose of this study was to thoroughly analyze the performance and emission characteristics of an engine running on up to 15 % PPO-diesel blended fuel. Then, the experimental data obtained from a single-cylinder, four-stroke engine with five distinct speeds ranging from 1000 to 3500 rpm were utilized to undertake energy, exergy, and sustainability assessments. The results showed that DPO5 had a maximum brake power of 1.92 kW at 2500 rpm. At 3500 rpm, the engine achieved a thermal efficiency of 47.44 % for diesel and 51.6 % for DPO5 blended fuel. Furthermore, DPO15 produced the least quantity of CO2 at all engine speeds. DPO5 has the highest sustainability index, 1.52 at 2500 rpm. As a result, our research found that a low-level PPO-diesel fuel blend may be effectively injected into diesel engines without requiring any modifications.

Reaction kinetics dominated by melt decomposition mechanism: Intrinsic pyrolysis of insensitive HTPE polyurethane and the efficient inter-reaction with AP

The novel insensitive HTPE (hydroxyl terminated polyether) adhesive holds a great potential application to develop the insensitive solid propellants. However, the pyrolysis kinetics and reaction mechanism of HTPE polyurethane are remained unclear. In this experimental investigation, the DTG curve of HTPE polyurethane was effectively deconvoluted into two main reaction stages via Gaussian peak fitting method, and the kinetic parameters for each pyrolysis stage were calculated. The calculation of the reaction mechanism functions indicated that both reaction stages follow an n-order reaction model with a very close n value. The overall pyrolysis process can be expressed as f(α) = (1 - α)ⁿ (n = 1.8 or 1.9). The TG-FTIR-GCMS results of online-collected gaseous products demonstrated that the pyrolysis of HTPE polyurethane is gradually decomposed from the outer layer to the inner layer, rather than being completely dominated by the kinetics of different functional groups. Localized melting of HTPE polyurethane was observed at 150 °C, moreover, it would almost completely transform into the liquid phase before the decomposition reaction occurred. Thus, it is suggested that the distinctive melt decomposition process of HTPE polyurethane alters the chemical environment even turns heat and mass transfer models of internal molecules, ultimately leading to its unique pyrolysis kinetics and reaction mechanisms. Furthermore, HTPE polyurethane could delay the first-stage pyrolysis of ammonium perchlorate (AP), but significantly promote its second-stage pyrolysis process. Therefore, HTPE polyurethane is beneficial in reducing the sensitivity of AP under thermal stimulation as well as promoting its concentrated heat release process.

Numerical simulation of a reactor for heterogeneous pyrolysis of hydrocarbon gases over biochar granules

Numerical simulation of a reactor for heterogeneous pyrolysis of hydrocarbon gases over biochar granules

Exergy Analysis of Hydrogen-Rich Syngas Production System Utilizing Palm Oil Empty Fruit Bunch using Pyrolysis Connected with Steam Methane Reformer

Fossil fuel consumption on a large scale continues to increase yearly, causing a shortage of energy sources. Hydrogen can help to overcome the shortage of energy sources. It can be produced from renewable energy sources, such as oil palm Empty Fruit Bunch (EFB) as biomass using pyrolysis processes equipped with steam methane reformer and water gas shift reactions. This research was conducted to determine the amount of hydrogen that can be produced and to analyze the exergy of the existing systems in the hydrogen production process. Aspen Plus has been used to design and analyze pyrolysis processes, steam methane reform, and water gas shift reactions. The results showed that when 6.54 kg Empty Fruit Bunch was used as raw material in a pyrolysis reactor, hydrogen could be produced in the amounts of 0.435 kg. The exergy values of raw materials and fuels are relatively high because the chemical exergy values of the compounds contained therein are also high. Based on the calculations, it is found that the combustion process is the process that experiences the most significant exergy destruction. The exergy efficiency of this hydrogen production process system is 22.77%.

Study on common amino acid pyrolysis products and analysis of pyrolysis products from interaction with aspartic acid

Nitrogen in nitrogen-rich biomass can be converted into high-value nitrogen-containing chemicals such as pyrroles, pyridines and indoles by pyrolysis. Understanding the nitrogen transport mechanism and reaction pathways is important for the utilization of nitrogen-rich biomass. In this study, the pyrolytic reaction pathways of 16 amino acids and interaction between others with aspartic acid were analyzed by pyrolysis in a closed U-tube reactor followed by gas chromatography/mass spectrometry (GC/MS) measurements. It was found that amino acids with lighter molecular tended to produce more gases during the pyrolysis, while amino acids with heavier molecular tended to produce more liquids and solids. The gaseous products of amino acid pyrolysis mainly consisted of CO2 and some CO, of which the content of CO2 reached 86.21 % of glycine and 70.97 % of aspartic acid, respectively. Liquid oils contain a large number of nitrogen-containing heterocyclic compounds, which are mainly produced by four types of reactions: cyclisation, R group removal, polymerization, and fragmentation reforming. And it was found that aspartic acid was able to promote the changes of the three phases of pyrolysis products and the formation of characteristic products.

Co‐Pyrolytic Recycling of Bakelite and Polymethyl Methacrylate: Kinetic, Synergistic, and Thermodynamic Analysis

AbstractBakelite, a thermosetting plastic, has limited feasibility for thermal recycling processes such as pyrolysis, unlike thermoplastics, due to its inherent tendency to get charred upon heating and difficulty in being converted into valuable fuel and chemical compounds. In this study, the co‐pyrolysis of bakelite and poly methyl methacrylate is explored to improve the thermal degradation and thus recycling feasibility of bakelite by pyrolysis. The kinetics and thermodynamics of the co‐pyrolysis of blended samples are analyzed using different kinetics models. The thermal degradation experiments of the sample are conducted from ambient to 1000 °C at five various heating rates of 5, 10, 20, 30, and 50 °C/min in an inert N2 gas environment. The results showed that adding poly methyl methacrylate to bakelite changes the pyrolytic degradation temperature and weight loss trend. The kinetic analysis reveals that the thermal degradation at 220–345 °C follows an F2.5 order‐based model with an average activation energy of 181 kJ/mol, while the degradation at 345–475 °C follows an F2 order‐based model with an average activation energy of 318 kJ/mol. The enthalpy changes and free energy change associated with thermal degradation exhibit a positive trend while that of entropy change shows a negative trend. With blending the free energy change and entropy change decreased while enthalpy change increased. During batch pyrolysis at 450 °C, the PMMA‐Bakelite blend generates oil (49.17 %), wax (12.36 %), residue (15.36 %), and gas (23.11 %). According to FTIR and GC‐MS analyses, the pyrolytic oil produced by the co‐pyrolysis of the blended sample at 450 °C comprises 32.23 % saturated hydrocarbons (C9–40), 20.97 % unsaturated hydrocarbons (C6–24), and 46.80 % oxygenated material (C5–19). These findings can assist in the optimization of pyrolysis reactor design for the recycling of thermosetting plastics.

Applications of H2-Enriched syngas and slag products from plastic wastes via novel plasma dual-stage-arc pyrolysis

Sustainable plastic waste management in the prevailing ‘new-normal’ post-pandemic scenario calls for calorific waste plastic up-cycling into high-end product recovery pathways. The present work employed a novel dual-stage arc plasma pyrolysis reactor to recover syngas and slag products from mixed plastics and Low-Density Polyethylene and Polyethylene Terephthalate (LDPE-PET) plastic waste feeds. Syngas product yield decreased while the solid slag yield increased with rising arc current, attaining 75% and 25% for mixed plastic waste feed and 59% and 41% for LDPE-PET wastes, respectively, at 200A arc current. The resultant syngas composition showed 83% and 77% H2 while 1.7% and 2.7% CO for mixed plastic waste-feed and LDPE-PET wastes, respectively, with no significant presence of CO2. Slag characterization studies revealed the presence of scattered pores on the slag surface, graphitic nanostructures due to scraped carbon depositions from electrode tips and the absence of aromatic groups due to complete conversion. High carbon content was observed in the slag due to the dissociation of lighter hydrocarbon and carbon dioxide on dual-arc exposure in two stages, underscoring the higher efficiency. For holistic integrated circular onsite ‘plastic waste-to-resource’ recovery-cum-application, electricity was generated from the resultant syngas and the slag was used for the manufacture of tiles in the community platform. Techno-economic evaluation of an up-scaled plasma pyrolysis facility shows the power recovery of 3.5 kWh/kg of waste plastic, with a net annual profit of $2800 and a payback period of 1.7 years. The findings of the present work suggest that the proposed integrated dual-arc plasma pyrolysis based plastic waste-to-resource recovery in circular-economy model has a viable outcome.

Creating pyrolysis reactor for disposal of municipal solid waste

In order to utilize municipal solid waste (MSW), a prototype reactor for thermal processing was created using materials developed at the National Research Center “Kurchatov Institute” – Central Research Institute of Structural materials “Prometey”, the technology for decomposing MSW in the reactor was developed, and its tests were carried out. The test results allowed us to conclude that the use of pyrolysis reactors for recycling ensures the environmental safety of the process and produces high-temperature gas (1000–1200°C) suitable for further use in power plants. Technical requirements were determined for the development of an industrial reactor for the disposal of solid waste with a productivity of up to 10 t/h, taking into account the shortcomings identified during testing of the prototype.

The effect of temperature on the Emission Factor of air emissions from pyrolysis of used tyres

Used tyres pyrolysis is an efficient solid waste management strategy for used tyres and a growing method of fuel oil production. However, the impact of air emissions associated at different temperature on ambient air quality has not been determined. To solve this problem, a pyrolysis fixed bed reactor and a condensing unit for separating liquid from produced gas were designed and constructed. 0.20 kg of used tyres were pyrolysed in the reactor and air emissions from the reactor chamber was characterized for air pollutants using the E-instrument E8500. Using a combination of measured mass of pollutants, mass of tyre pyrolzed and time taken during pyrolysis, Emission Factors of the air pollutants were established from the study at 200 °C, 300 °C and 400 °C. The concentration measured between 200 °C - 400 °C were in the range of 15 -7497 mg/m3, 0 – 4680 mg/m3, 38.25 – 103, 277.76 mg/m3 and 2 – 293 mg/m3 for CO, NOx, HC and H2S respectively. The developed emission factors were in the range of 16.52 – 8370.04 g kg-1, 0 – 4470.26 g kg-1, 42.126 – 104,055.9 g kg-1 and 2.20 – 322.69 g kg-1. The designed and constructed pyrolysis reactor and condenser unit were effective for used tyre pyrolysis while the measured air pollutants concentration were higher for all pollutants except H2S using the Federal Ministry of Environment (FEPA, 1991) standard. Hence, it is necessary to carry out further studies on air pollution control from waste tyre pyrolysis at lower temperature.

Comprehensive evaluation of the physicochemical properties and pyrolysis mechanism of products from the slow pyrolysis of waste coffee shells

Slow pyrolysis is an efficient method for converting agricultural and forestry wastes into valuable resources, thereby addressing energy shortage and environmental pollution. In this study, a slow-pyrolysis experiment of coffee shells (CS) at 450–850 °C was conducted in a tube furnace. The resulting pyrolysis products were comprehensively characterized via FTIR, Raman spectroscopy, nitrogen adsorption analysis via BET theory, SEM, XPS, and PY-GC-MS. Moreover, the pyrolysis reaction mechanism and N transformation pathway of CS were proposed. The results showed that with the increase in pyrolysis temperature, the yield of biochar gradually decreased, and the yield of biogas gradually increased. At 850 °C, the yields of biochar, bio-oil and biogas of CS were 27.13, 35.16 and 37.71 %, respectively (on a dry, ash-free basis). The bio-oil yield was highest at 550 °C, reaching 35.7 %. Notably, biochar exhibited favorable characteristics such as high specific surface area and porosity, demonstrating its potential as both a biomass fuel and an adsorption material. Acetone (78.30 %) and caffeine (8.29 %) was the predominant substance in bio-oil. Biogas was predominantly composed of CO2, CO, CH4 and H2. The pyrolysis process of CS mainly involved the degradation of macromolecules into small molecules, the repyrolysis of small molecules, dehydrogenation, deoxygenation, alkylation, isomerization, and self-condensation. These results provide a theoretical basis for the recycling of waste biomass CS, which has environmental protection significance and economic value.

Enhancing oil shale pyrolysis using metal-doped carbon quantum dot catalysts: A comprehensive behavioral, kinetic, and mechanistic analysis

Current oil shale extraction technologies face significant challenges, including high heating costs, slow pyrolysis reaction rates, and low efficiency, which hinder effective resource exploitation. To address these issues, this study synthesized three types of metal-doped carbon quantum dot (M/CQD) catalysts—Co/CQDs, Ni/CQDs, and Mn/CQDs—and tested their effects on the pyrolysis of oil shale. The introduction of these catalysts resulted in a notable enhancement of the pyrolysis process, reducing the required activation energy by approximately 40 % and lowering the initiation temperatures for Co/CQDs, Ni/CQDs, and Mn/CQDs by 64 °C, 62 °C, and 94 °C, respectively. Consequently, the yield of shale oil increased significantly by 23.1 %, 13.3 %, and 19.8 % for each catalyst. Kinetic and product analyses indicate that these catalysts facilitate electron transfer from organic molecules, promoting the formation of free radicals and the cleavage of C–C bonds. This enhancement leads to an increased production of short-chain hydrocarbons and a reduction in oxygenates and esters, thereby improving the quality of the shale oil. Further insights from Density Functional Theory (DFT) calculations suggest that the catalysts enhance pyrolysis by promoting the formation of carbocations and synergizing with radicals released from the shale, intensifying the pyrolysis process. This study not only elucidates the catalytic mechanisms that enhance oil shale pyrolysis but also offers a promising approach to overcome technological challenges in shale resource recovery, such as high heating costs and low efficiency, paving the way for more efficient and cleaner shale oil production.