Carbon Conversion Rate Research Articles

Study on mixing performance of atmospheric entrained flow gasification burner using fine ash as feedstock

A burner structure suitable for atmospheric entrained-flow gasifiers using fine ash as feedstock was proposed. The study investigates the impact of the burner structure on the mixing characteristics through 0.75:1 (geometry reduction) single-phase airflow experiments. Additionally, numerical simulations were conducted to study of the gasification process of fine ash in a 10,000 Nm3/h atmospheric entrained flow gasifier. The results indicate that a larger residual temperature near the burner outlet was observed when the diameter of the burner's gasification agents channel was 10 mm or 15 mm, approximately 0.7–0.8. Additionally, the mixing degree of the two airflows at the burner outlet was high, and the distance required for complete mixing was short. When the diameter of the gasification agent channel was 15 mm, the mixed syngas flow velocity was appropriate. This resulted in a maximum temperature of 2500 °C, an 80 % carbon conversion rate, and an outlet effective syngas (CO + H2) concentration of 62 %.

Optimization of coal chemical process parameters and energy saving and emission reduction based on genetic algorithm

Abstract Coal is an important energy resource. How to utilize it efficiently and cleanly is a hot topic nowadays. In the coal gasification process, the process parameter indexes have a significant impact, and the uncertainty of these factors will lead to a decrease in the quality of gas production. Therefore, in this paper, the uncertainty of process parameters is considered, and Aspen plus software with the Monte Carlo method is used to simulate the coal chemical process and measure the effect of uncertainty of process parameters on the yield of the coal gasification process. On this basis, in addition, coal flow rate, pressure, and steam/oxygen are taken as the process parameters and optimized, and three sets of multi-objective optimization models are established with gas calorific value, gasification efficiency, and gas yield, respectively, which are solved by improved multi-objective genetic algorithm based on crossover operator and variational operator to obtain Pareto curves, so as to adjust the parameter values according to the actual needs. The results show that the fluctuation of pressure has a big influence on the carbon conversion rate and gasification efficiency, and the carbon conversion rate and gasification efficiency can be made more stable by controlling the change of pressure. The improved genetic algorithm NSGA-II can reach the actual optimal objective function value in both high and low iteration times, providing the required parameters for the decision maker, and the optimal program results in TEC of 402,758 kW and CO2 content of 0.12%, which is effective in energy saving and emission reduction.

Study on the Co-gasification characteristics of biomass and municipal solid waste based on machine learning

Co-gasification of biomass and municipal solid waste (MSW) exhibits synergistic effects by improving the quality of syngas while reducing environmental pollution from MSW. In this study, Machine learning (ML) techniques were employed to investigate the co-gasification process of biomass and MSW. A comprehensive dataset was constructed using existing data, including different feedstock types and operating conditions, with 18 input features and 9 output features. Four advanced ML models were utilized to model and analyze the co-gasification process. By leveraging feedstock characteristics and operating parameters, key gasification parameters such as syngas composition, lower heating value (LHV) of syngas, tar yield, and carbon conversion efficiency were predicted. The results showed that all four models exhibited excellent predictive performance, with R2 values greater than 0.9 in both the training and testing stage. Specifically, Histogram-based gradient boosting regression (HGBR) exhibited the lowest root mean square error (RMSE) in predicting CO, while the gradient boosting regressor (GBR) achieved the best performance in H2 prediction with a RMSE of 1.6. The most influential input features for CO concentration were equivalence ratio (ER), oxygen content in biomass and hydrogen content in biomass. The key features affecting H2 concentration were steam/fuel and ER.

Promotion of medium-chain fatty acids and long-chain alcohols production by zero-valent iron: Effect of particle sizes

The effect of zero-valent iron (ZVI) particle size on biological chain elongation (CE) was explored. The addition of ZVI particles with diameters of 50 nm-1000 µm stimulated both medium-chain fatty acids (MCFAs) and long-chain alcohols (LCAs) production, and increased carbon conversion rate of CE process by 2.8–12.2 times. ZVI particle size of 75 µm exhibited the best performance in promoting MCFAs production, achieved the highest MCFAs production of 2164.2 mg/L, which was 11.9 times of control group. ZVI particle size of 1000 µm showed the best performance in stimulating LCAs production, obtained the highest LCAs production of 434.0 mg/L, which was 33.4 times of the control group. Microbial community analysis suggested that different ZVI particle sizes significantly affected genus Clostridium_sensu_stricto_12 and Clostridium_sensu_stricto_7. Functional enzyme analysis revealed that 75 µm ZVI particles induced the strengthened reverse β oxidation pathway, while 1000 µm ZVI particles enhanced the fatty acid biosynthesis pathway.

Experimental and numerical investigation of medical waste disposal via plasma gasification

The COVID-19 pandemic has increased global awareness of proper medical waste disposal. Conventional methods like incineration and gasification are insufficient due to low energy efficiency and harmful emissions. Plasma gasification, however, offers significant advantages, including economical benefits, higher efficiency, lower emissions, and greater hydrogen production potential. Hence, plasma gasification can be an influential alternative to conventional methods with further developments. In this study, gasification characteristics of medical waste are investigated in a novel laboratory-scale updraft plasma gasifier. The gasifier utilizes a DC arc plasma torch with a maximum capacity of 5 kWh. Medical waste samples are prepared by mixing various consumables like face masks and cotton bandages, whereas waste capacity of the gasifier is estimated to be 7.0 kg/h for an equivalence ratio (ER) of 0.2. Simulations are conducted for ER values of 0.1, 0.2, 0.3, and 0.4 using ANSYS Fluent software, and the plasma jet is modeled as hot gas. Results demonstrate that integrating the throat configuration to the updraft plasma gasifier and increasing the ER value enhance H2 production and reduce CO content in the syngas. The minimum H2 content is found as 48.5% for ER = 0.1 with 24.1% CO, while the maximum H2 content is 54.7% for ER = 0.4 with 17.1% CO. The gasifier configuration achieves a carbon conversion rate (CCR) of 29.1% and a cold gas efficiency (CGE) of 28.5%.

Experimental investigation and chemometric analysis of gasification and co-gasification of olive pomace and Sida Hermaphrodita blends with sewage sludge to hydrogen-rich gas

In the paper the results of the systematic study on oxygen/steam co-gasification of sewage sludge blends with biomass waste such as olive pomace or energy crops such as Sida Hermaphrodita to hydrogen rich gas were presented. In the first part of the experimental campaign the oxygen/steam gasification of sewage sludge, Sida Hermaphrodita and olive pomace, respectively, at 700, 800 and 900 °C were gasified. Only small amount of the total gas was produced in the oxygen/steam gasification of analyzed sewage sludge in all studied temperatures. The carbon conversion rate varied between 64% at 700 °C to 66% at 900 °C. The hydrogen amount in the total gas produced in the sewage sludge gasification was 28%vol. at all studied temperatures. The main conclusion from this part of experiments was that gasification of sewage sludge is ineffective. Different conclusions were drawn on the basis of Sida Hermaphrodita and olive pomace gasification tests at all studied temperatures. Therefore in the second part of the experimental campaign the co-gasification experiments of Sida Hermaphrodita/olive pomace blends with 10%w/w and 20%w/w of sewage sludge. The co-gasification experimental campaign covered series of tests at temperatures of 700, 800 and 900 °C, respectively. The comprehensive analysis of the experimental results of co-gasification and the physical and chemical parameters important for the co-gasification process performance were also conducted with the application of chemometric methods, such as hierarchical clustering analysis and principal component analysis. Based on the experimental results the optimal fuel blends as well as the optimal conditions of co-gasification were determined. It was proven that steam co-gasification of sewage sludge with selected biomass is beneficial in terms of the total gas produced and its composition.

Molecular Dynamics Investigation of the Gasification and Hydrogen Production Mechanism of Phenol in Supercritical Water

Supercritical water gasification is an efficient and clean method for converting biomass into hydrogen-rich gas. Phenol plays a crucial role as an intermediate product in biomass supercritical water gasification, and studying its reaction pathway in supercritical water is essential for understanding the chemical reaction mechanism and optimizing biomass energy conversion processes. In this paper, we investigated the conversion mechanism of phenol gasification and hydrogen production in supercritical water using a combined approach of reactive force field (ReaxFF) and density functional theory (DFT). We determined the decomposition pathways and product distribution of phenol in supercritical water. The calculation results demonstrate that in the supercritical water system, the efficiency of phenol conversion for hydrogen production is approximately 27 times higher than that of hydrogen production through gasification in the pyrolysis state. Moreover, both the carbon conversion rate and hydrogenation rate in the supercritical water system are significantly higher compared to those in the pyrolysis system. Furthermore, we found that the energy in the supercritical system is approximately half that of the pyrolysis system, favoring the ring-opening reactions of phenol and promoting hydrogen production. In contrast, the pyrolysis system produces a greater quantity of aromatic compounds, leading to tar formation and having significant implications for both the reaction process and reactor design. Additionally, we conducted comparative experiments between the supercritical water gasification process and the pyrolysis process to explore the advantages of supercritical water gasification.

Alkali and alkaline earth metals catalytic steam gasification of ashless lignin: Influence of the catalyst type and loading amount

This work studies the effects of alkali and alkaline earth metallic species (AAEMs) (Na2CO3, K2CO3, and CaCO3), Na+ impregnation amount (2, 5, and 7 mmol) and sodium salts (NaHCO3, Na2SO4, and NaAlO2) on the gasification characteristics and product distribution of G-type lignin in a fixed-bed system for continuous gasification. The results showed that six catalysts all could improve lignin gasification performance by increasing total gas yields, syngas yields, H2/CO ratios, and carbon conversion rates. Na2CO3 had the strongest catalytic ability, followed by NaHCO3 and K2CO3, while CaCO3, Na2SO4 and NaAlO2 had poor catalytic abilities. Gaseous AAEMs, especially NaOH and KOH, could enhance tar cracking, volatiles reforming, coke gasification, the water-gas shift reaction, and methane steam reforming. The high melting points of CaO and NaAlO2 greatly reduced the catalytic capacities of CaCO3 and NaAlO2. AAEMs could combine with the carbon matrices to form carboxylate structures or phenol/aldehyde structures which might volatilize to catalyze homogeneous reactions. Moderately increasing Na+ impregnation amount to 5 mmol was beneficial to lignin gasification, but excessive impregnation reduced the gasification parameters. In addition, all six catalysts had effects on the tar composition, especially K2CO3 and NaAlO2, which could effectively catalyze tar cracking and reduce heavy compounds.

Research on co-gasification of polyethylene and cellulose via reactive molecular dynamics simulation

Co-gasification of waste plastic and biomass is an effective way for waste disposal and renewable energy utilization. In this paper, the co-gasification of polyethylene and cellulose was explored. The reaction mechanism and thermochemical characteristics of co-gasification were comprehensively analyzed. Results showed that the co-gasification reduced the initial decomposition temperature of polyethylene but delayed its later decomposition, and also delayed the decomposition of cellulose. Polyethylene acted as a hydrogen donor in co-gasification to provided free radicals conductive to hydrogen and hydrocarbon generation. Cellulose as an oxygenated compound contributed to CO production. Compared with the separate gasification of cellulose, the separate gasification of polyethylene and the co-gasification of the two produced more hydrogen and hydrocarbons but less CO. The synergistic effect of co-gasification increased the lower heating value of gas product and carbon conversion rate and reduced the activation energy, but decreased the combustible gas yield. The gas product composition of co-gasification could be regulated by adjusting the blending ratio. This work sheds lights on the co-gasification characteristics of polyethylene and biomass, which would be helpful for the application of this technology to produce high-quality syngas.

Simulation on coal combustion and calcium carbonate decomposition in a 5500 t/d full scale cement calciner

With the continuous growth of global cement production, the increasing coal consumption in the cement industry has been drawing great attention, thus adopting advanced technologies to reduce energy consumption has become an important issue. To address this problem, this study carried out 3D Eulerian-Lagrangian simulations of the coupling process of pulverized coal combustion and CaCO3 decomposition in a 5500 t/d full-scale cement calciner. On the basis of the multiphase particle-in-cell (MP-PIC) approach, reaction models including devolatilization, combustion of char and volatiles, and CaCO3 decomposition are incorporated into the scheme. Detailed combustion characteristics including temperature distribution, carbon exhaust rate, and gas emission characteristics, as well as decomposition characteristics are comprehensively analyzed. Besides, effects of different operating performances including O2 content in bottom flue gas on carbon exhaust rate, CaCO3 decomposition rate, and NOx emission are also investigated. Results show that under the typical working condition with O2 concentration in the flue gas of 1.7 %, the CaCO3 decomposition rate can reach around 96.42 %, the carbon conversion rate is up to 98.65 %, and the NOx can be controlled at around 105 ppm. The increase of O2 content promotes higher carbon conversion rates with excessive O2 leading to higher NOx emission. Appropriately increasing the proportion of raw material flow rate in upper tubes can facilitate a more complete CaCO3 decomposition.

Thermodynamic and economic analysis of a hydrogen production process from medical waste by plasma gasification

To reduce the environmental pollution caused by pathogens and radioactive substances carried by medical waste, and alleviate the shortage of non-renewable energy, this work proposes a novel overall process for hydrogen production from medical waste by plasma gasification coupled with ionic liquid-based CO2 capture. The validity of the model is verified by the experimental data. Based on the simulation results, the effects of medical waste types, different gasification agents and carbon conversion rate on the syngas compositions, H2/CO ratio, carbon conversion rate, higher heating value and exergy efficiency are explored. The results show that the rate of hydrogen production from surgical masks is more than twice that of the other two types of medical waste. Steam is the best gasification agent. At this time, the higher heating value of syngas is 26.72 MJ/kg and the exergy efficiency is 78.25%. A comprehensive analysis of the thermodynamic efficiency and technical economy of the overall process shows that the total exergy efficiency is 70.84%. The production cost is 2115.74 USD and the raw material consumption is 2.61 t/t H2. This study can provide a promising theoretical guidance for the resource treatment of medical waste.

Effect of Steam on Carbonation of CaO in Ca-Looping.

Ca-looping is an effective way to capture CO2 from coal-fired power plants. However, there are still issues that require further study. One of these issues is the effect of steam on the Ca-looping process. In this paper, a self-madethermogravimetric analyzer that can achieve rapid heating and cooling is used to measure the change of sample weight under constant temperature conditions. The parameters of the Ca-looping are studied in detail, including the addition of water vapor alone in the calcination or carbonation stage and the calcination/carbonation reaction temperatures for both calcination and carbonation stages with water vapor. Steam has a positive overall effect on CO2 capture in the Ca-looping process. When steam is present in both calcination and carbonation processes, it increases the decomposition rate of CaCO3 and enhances the subsequent carbonation conversion of CaO. However, when steam was present only in the calcination process, there was lower CaO carbonation conversion in the following carbonation process. In contrast, when steam was present in the carbonation stage, CO2 capture was improved. Sample characterizations after the reaction showed that although water vapor had a negative effect on the pore structure, adding water vapor increased the diffusion coefficient of CO2 and the carbonation conversion rate of CaO.

Ultralight FeSiAl micro-flake flying with propylene to favor fast growth of carbon nanotube arrays at 99 % high-efficient conversion

The efficiency of catalyst-gas contact and the selectivity of catalyzing carbon source cracking determine the yield of highly oriented carbon nanotube arrays (CNTAs). Herein, the flying FeSiAl (FSA) micro sheets were in full contact with propylene (C3H6), effectively catalyzing propylene gas cracking with an astonishing 99 % carbon conversion rate. The propylene with more carbon atoms and high safety grew carbon nanotube arrays faster. The growth kinetics of the CNTAs were studied, and the apparent activation energy of the CNTAs was 49.04 kJ/mol. This indicated that there were two diffusion modes: the surface diffusion of the catalyst and the step-edge diffusion of the graphene-catalyst interface. The well-dispersed linear CNTAs (1D) and a point-like carbon black (0D) conductive agent form a 1D/0D conductive network, which was used as a conductive additive for lithium/fluorocarbon (CFx) primary cells. Effective electron conduction improved the rate performance of the battery, which was increased from 1229.22 Wh/kg at 2 C to 1358.35 Wh/kg at 4 C. The high catalytic efficiency of propylene molecules with high carbon content and FeSiAl (FSA) alloy provides a new method for large-scale and efficient production of CNTAs. High-orientation CNTAs have potential application prospects in the field of energy storage.

Evaluation of bioenergy production and material flow in treating Japanese concentrated Johkasou sludge using high-solid anaerobic membrane bioreactor based on one-year operation

The treatment of waste sludge generated from on-site wastewater treatment facilities (Johkasou) applied extensively in Japan is a key concern. In this study, a high-solid anaerobic membrane bioreactor (AnMBR) was continuously operated throughout a year to investigate the bioenergy production, material flow and seasonal impacts of concentrated Johkasou sludge (CJoS). The CJoS has higher carbon-to-nitrogen ratio and lipid fraction, but less proteins than waste activated sludge (WAS). The biogas yield of CJoS by AnMBR ranged from 0.47 to 0.52 L/g-VSfed, which was higher than the anaerobic digestion of WAS and lower than mixed sewage sludge from centralized wastewater treatment facilities. The greatest biogas production rate was observed during summer (0.63 L/L/d), owing to the high total organic and solid content. However, winter CJoS had the highest biogas yield and carbon conversion rate owing to the conservation of soluble organic matter in low temperature and high digestibility. The material flow results revealed that 46.5–52.4% total COD and 50.2–58.0% carbon was converted to biogas. The energy recovery rates ranged from 8.69 to 9.96 kJ/g-VSfed and the system energy self-sufficiency rates ranged from 1.92 to 3.02. The optimal dewaterability of digested sludge was achieved when polyamidine flocculant dosage was 30 mg/g-MLSS and the corresponding sludge specific resistance to filtration was 2.26 × 1012 m/kg. The results demonstrated that AnMBR yielded high energy conversion efficiency without co-digestion and pretreatment processing.

Experimental Study on the Preparation of Hydrogen-Rich Gas by Gasifying of Traditional Chinese Medicine Residue in a DFB Based on Calcium Looping

Using traditional Chinese medicine residue biomass as the raw material and industrial limestone as a carbon absorbent, this paper investigates the production of hydrogen-rich synthesis gas in a pilot-scale calcium looping dual fluidized bed (DFB) system. The study focuses on analyzing the distribution characteristics of temperature and pressure, as well as the operation and control methods of the DFB system. The effects of reaction temperature, material layer height (residence time), water vapor/biomass ratio (S/B), and calcium/carbon molar ratio (Ca/C) on gasification products are examined. The experimental results demonstrate that as the temperature (600–700 °C), S/B ratio (0.5–1.5), Ca/C ratio (0–0.6), and other parameters increase, the gas composition shows a gradual increase in the volume content of H2, a gradual decrease in the volume content of CO, and an initial increase and subsequent decrease in the volume content of CH4. Within the range of operating conditions in this study, the optimal conditions for producing hydrogen-rich gas are 700 °C, an S/B ratio of 1.5, and a Ca/C ratio of 0.6. Furthermore, increasing the height of the material layer in the gasification furnace (residence time) enhances the absorption of CO2 by the calcium absorbents, thus promoting an increase in the volume content of H2 and the carbon conversion rate in the gas.

Simulation of gas-solid combustion characteristics in a 1000 MW CFB boiler for supercritical CO2 cycle

Supercritical CO2 (S-CO2) power cycle has become one of the most efficient and low-pollution cycle schemes to improve thermal power generation efficiency and reduce energy consumption around the world. In this study, the 3D physical model of a 1000 MW S-CO2 circulating fluidized bed (CFB) boiler with annular furnace is established to simulate the gas-solid combustion process based on the MP-PIC method under the Eulerian-Lagrangian framework. By comparing with the conventional water steam CFB boiler, the S-CO2 CFB boiler has a smooth and stable gas-solid flow pattern with good uniformity of the particle concentration and velocity distribution, indicating that the annular structure and the layout of the heating surfaces is conducive to the gas-solid flow uniformity. The gas-solid phase temperature distributes uniformly basically without sudden rise or sudden drop, and the temperature difference between the solid phase and the gas phase is not large, which reflects the good combustion uniformity of the S-CO2 CFB boiler. Compared with 300 MW and 600 MW S-CO2 CFB boilers, the 1000 MW one shows a higher carbon conversion rate, lower desulphurization effect, and lower nitrogen removal performance with the CO, NO, and SO2 outlet concentration of 0.002%, 5.8 mg/m3, and 125 mg/m3, respectively.

Insights into the Electron Transfer Behaviors of a Biocathode Regulated by Cathode Potentials in Microbial Electrosynthesis Cells for Biogas Upgrading.

Bioelectrochemical-based biogas upgrading is a promising technology for the storage of renewable energy and reduction of the global greenhouse gas emissions. Understanding the electron transfer behavior between the electrodes and biofilm is crucial for the development of this technology. Herein, the electron transfer pathway of the biofilm and its catalytic capability that responded to the cathode potential during the electromethanogenesis process were investigated. The result suggested that the dominant electron transfer pathway shifted from a direct (DET) to indirect (IDET) way when decreasing the cathode potential from -0.8 V (Bio-0.8 V) to -1.0 V (Bio-1.0 V) referred to Ag/AgCl. More IDET-related redox substances and high content of hydrogenotrophic methanogens (91.9%) were observed at Bio-1.0 V, while more DET-related redox substances and methanogens (82.3%) were detected at Bio-0.8 V. H2, as an important electron mediator, contributed to the electromethanogenesis up to 72.9% of total CH4 yield at Bio-1.0 V but only ∼17.3% at Bio-0.8 V. Much higher biogas upgrading performance in terms of CH4 production rate, final CH4 content, and carbon conversion rate was obtained with Bio-1.0 V. This study provides insight into the electron transfer pathway in the mixed culture constructed biofilm for biogas upgrading.

Effects of the construction of fertile and cultivated soil layer on soil fertility and maize yield in Albic soil.

We examined the effects of fertile soil layer construction technology on soil fertility and maize yield with a 3-year field experiment in Albic soil in Fujin, Heilongjiang Province. There were five treatments, including conventional tillage (T15, without organic matter return) and fertile soil layer construction methods [deep tillage (0-35 cm) with straw return, T35+S; deep tillage with organic manure, T35+M; deep tillage with straw and organic manure return, T35+S+M; deep tillage with straw, organic manure return and chemical fertilizer, T35+S+M+F]. The results showed that: 1) compared with the T15 treatment, maize yield was significantly increased by 15.4%-50.9% under fertile layer construction treatments. 2) There was no significant difference of soil pH among all treatments in the first two years, but fertile soil layer construction treatments significantly increased soil pH of topsoil (0-15 cm soil layer) in the third year. The pH of subsoil (15-35 cm soil layer) significantly increased under T35+S+M+F, T35+S+M, and T35+M treatments, while no significant difference was observed for T35+S treatment, compared with T15 treatment. 3) The fertile soil layer construction treatments could improve the nutrient contents of the topsoil and subsoil layer, especially in the subsoil layer, with the contents of organic matter, total nitrogen, available phosphorus, alkali-hydrolyzed nitrogen and available potassium being increased by 3.2%-46.6%, 9.1%-51.8%, 17.5%-130.1%, 4.4%-62.8%, 22.2%-68.7% under the subsoil layer, respectively. The fertility richness indices were increased in the subsoil layer, and nutrient contents of the subsoil layer were close to those of topsoil layer, indicating that 0-35 cm fertile soil layer had been constructed. 4) Soil organic matter contents in the 0-35 cm layer were increased by 8.8%-23.2% and 13.2%-30.1% in the second and third years of fertile soil layer construction, respectively. Soil organic carbon storage was also gradually increased under fertile soil layer construction treatments. 5) The carbon conversion rate of organic matter was 9.3%-20.9% under T35+S treatment, and 10.6%-24.6% under T35+M, T35+S+M, and T35+S+M+F treatments. The carbon sequestration rate was 815.7-3066.4 kg·hm-2·a-1 in fertile soil layer construction treatments. The carbon sequestration rate of T35+S treatment increased with experimental periods, and soil carbon content under T35+M, T35+S+M and T35+S+M+F treatments reached saturation point in the experimental second year. Construction of fertile soil layers could improve the fertility of topsoil and subsoil and maize yield. In term of economic benefits, combination application of maize straw, organic material and chemical fertilizer within 0-35 cm soil, cooperating with conservation tillage, is recommended for the Albic soil fertility improvement.

CO2 capture performance of a CaO sorbent modified with fulvic acid for the calcium looping cycle

AbstractCapturing CO2 from fossil fuel combustion is of importance for mitigation of climate warming. Among the CO2 capture technologies, the calcium‐based sorbent method is promising. However, the most prominent problem of this method at present is that the activity of the sorbent decreases as the number of cycle reactions increases. It seriously affects the industrial application of the calcium‐based sorbent method in carbon capture technology. Fulvic acid (FA) is a biologically active and soluble component of humic acid. Compared with other humic acids, it contains more oxygen and heterocyclic rings. Also, the rings are connected by bridge bonds. Therefore, the ability of FA to chelate cations and its adsorption capacity is stronger than the other humic acids. Therefore, in this work, we first proposed using FA to modify CaO to improve CO2 capture from flue gas. The effects of calcination temperature, carbonation temperature, reaction time and the amount of doped FA on the carbonation conversion rate (CCR) of CaO modified with FA (FA/CaO) were studied in the calcining/carbonizing room at atmospheric pressure. The experiment showed that the first CCR (X1) of FA/CaO reached 0.872 under the optimal conditions, which was 31% higher than X1 of original CaO. The 20th CCR (X20) was still as high as 0.47, which was three times than X20 of original CaO. In addition, the sorbent was analyzed and characterized by XRD, SEM, BET and LPSA. Due to the doped FA, the microstructure of CaO became fluffy and open, which improved the specific surface area and pore size of CaO. It indicated that the addition of FA was beneficial to the diffusion and absorption of CO2 and delayed the appearance of sintering, which significantly enhanced the CO2 capture performance of CaO. Using FA to modify CaO to capture CO2 provides an idea for efficient carbon capture, and has practical application potential. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd.

Catalytic upcycling of waste polypropylene for gram-scale production of FeCo@N-doped carbon nanotubes toward efficient oxygen reduction electrocatalysis

Exploring novel low-cost and high-efficiency non-precious metal catalysts for use in oxygen reduction reactions (ORR) is of key importance. Based on catalytic pyrolysis of waste plastics, a facile method for preparing N-doped Fe/Co-encapsulated carbon nanotubes (FexCoy@NCNTs) was proposed. Particularly, gram-scale yield of the composite catalyst (3.87 g) was achieved in one pot with considerable atomic conversion rate of carbon (∼57.3 %) from waste polypropylene to high-quality CNTs, suggesting great potential for waste plastics valorization. The effects of Fe-to-Co ratios were studied by testing the ORR performance of each sample, indicating that as the Fe proportion increased, the ORR performance initially increased and then decreased. The Fe1Co1@NCNTs catalyst showed optimal performance which was comparable with commercial Pt/C catalyst: Particularly, an initial potential of 0.97 V vs RHE, a half-wave potential of 0.81 V vs RHE, and a limiting current density of –5.68 mA cm−2 were recorded. The encapsulated Fe and Co species in N-doped CNTs enhanced catalytic activity, while the porous carbon structure augmented the exposure of active sites. This strategy offers an auspicious platform for reusing waste plastics in the mass production of CNTs, and also provides an innovative approach for preparing low-cost, high-performance, and non-precious metal-based electrocatalysts for ORRs.