Gas-phase Products Research Articles

Flame retardant, heat insulating and hydrophobic chitosan-derived aerogels for the clean-up of hazardous chemicals

Leakage of hazardous chemicals often causes significant casualties, enormous economic losses, and negative social benefits. Presently, fire rescue personnel lack efficient and eco-friendly disposal materials for hazardous chemical leakage accidents. In this study, chitosan (CS) aerogels with excellent flame-retardant performance were prepared via cross-linking by two phosphorus-containing vanillin-based compounds (DV and TV). The as-prepared chitosan aerogels were lightweight and porous. The introduction of DV and TV greatly enhanced the residual char yields of CS at 700 °C and the flame-retardant performance of chitosan aerogels. TCS-5.0 possessed the best flame-retardant performance, indicating that TV was more effective than DV in enhancing the flame-retardant performance of chitosan aerogels. The greatly improved flame-retardant properties could be attributed to TV effectively promoting the residual char formation of chitosan aerogels and reducing the formation of combustible gas phase products. To improve the hydrophobicity of chitosan aerogels, TCS-5.0 was treated with solution immersion to load siloxane molecules on its surface. The water contact angle of HTCS-5.0 was 136.1°. HTCS-5.0 had a high oil absorption multiplicity, absorbing up to 31 times its own weight of chloroform. HTCS-5.0 could continuously absorb organic solvents on the water surface with the assistance of a vacuum pump, indicating that HTCS-5.0 could be used for the clean-up of hazardous chemical leakage accidents.

Investigating the gas-phase reaction mechanism of catechol with ozone: Product analysis and insights

Volatile aromatic compounds (VOCs) are ubiquitous in the environment, they can be emitted from biogenic and anthropogenic sources. They can contribute to the formation of many products leading to the formation of secondary organic aerosols (SOA). The products of the gas phase reaction of 1,2-benzenediol (catechol) with ozone were studied in a simulation chamber at atmospheric pressure and 294 ± 2 K in presence of different levels of relative humidity (0–60%). The gas phase products were monitored continuously by a PTR-ToF-MS for 2 h, whereas filters samples were collected directly from the reaction chamber and analyzed by thermo-desorption gas chromatography; TD-GC-MS. This study shows the different potential chemical pathways that catechol could follow to form a variety of products under dry, low and high humidity conditions. The molecular mass 98 was found to be distinctive and appears in the gas phase when humidity in the reaction chamber is between 20 and 60%. Other new masses (m/z) such as 176, 154, 116, 68, 72, 80, 96, 108, and 124 were also detected under different experimental conditions. Furthermore, the catechol concentration has been monitored continuously by a PTR-ToF-MS from low to high humidity conditions (RH = 7.5−78.8%). The purpose of the latter is to suggest that the formation of catechol-H2O clusters occurs in the gas phase of the reaction chamber causing a decrease in catechol reactivity towards ozone and other gases and subsequently a decrease in the rate constant.

Theoretical study on the potential environmental and ecological risk of 4-ethylphenol induced by hydroxyl radical

This study closely examines the environmental fate of 4-ethylphenol (4-EP), a significant byproduct of biomass combustion. We employed quantum chemical calculations to investigate the reaction mechanism, kinetics, and ecotoxicity of 4-EP initiated by OH radicals in various environments (aqueous, atmospheric liquid, atmospheric and inhomogeneous phases). Our findings highlight that solvent effects contribute to a higher OH-addition reaction branching ratio (Γadd) of 0.68 for 4-EP in an aqueous solution, compared to 0.26 in the gas-phase environment and 0.22 in the inhomogeneous environment at 298 K. We determined the rate constants for the liquid-phase, gas-phase, and nonhomogeneous phase to be 1.14 × 109 s−1 M−1, 3.09 × 109 s−1 M−1, and 6.19 × 1014 s−1 M−1, respectively. Notably, the adsorption of mineral particles considerably enhances the reaction rate of 4-EP with OH radicals. 4-ethylbenzene-1,2-diol, 4-hydroxycyclohexa-3,5-diene-1,2-dione, 1-ethyl-6-methyl-6H-benzo(c)chromene-4,9-diol, 5-ethyl-6'-(1-hydroxyethyl)-(1,1′-biphenyl)-2,3,3′-triol and 2-ethyl-4,6,9-trimethyl-6H-benzo(c) chromene are major products in both gas-phase and liquid-phase reactions, and (2Z, 4Z)-4-ethyl-6-oxohexa-2,4-dienoic acid is also one of the major products in gas-phase reactions. Toxicological predictions indicate that the ecotoxicity of 4-ethyl-6-methyl-6H-benzo(c)chromene-1,9-diol, 2-ethyl-6-methyl-6H-benzo(c)chromene-3,9-diol, and 2-ethyl-4,6,9-trimethyl-6H-benzo(c) chromene surpassed that of 4-EP. However, the toxicity of the reaction products is reduced in the presence of NOx. This investigation provides an exhaustive theoretical foundation for comprehending the degradation behavior of 4-EP and underscores the need to consider various environmental factors in assessing the potential risk of biomass combustion by products.

Copyrolysis characteristics of polyvinyl chloride, polyethylene and polypropylene based on ReaxFF molecular simulation

Reactive force field molecular dynamics (ReaxFF MD) simulation was used to study the copyrolysis behaviour of waste plastics i.e., polyvinyl chloride (PVC), polyethylene (PE), and polypropylene (PP) from three perspectives: (1) gas phase products, (2) reaction route, and (3) activation energy. The results demonstrate that the thermogravimetric (TG) experiment's findings and the weight loss characteristics of PVC/PE/PP copyrolysis obtained by ReaxFF MD simulation were consistent. Copyrolysis changed the amount of gas phase products generated, the direction of free radical movement, and the range of temperatures at which they were produced in considerable quantities. Due to the transfer of chloride (Cl) radicals, both PE and PP had a detrimental synergistic impact on the production of hydrogen chloride (HCl). Based on the first-order reaction kinetics model, the copyrolysis of waste plastics significantly lowered the total activation energy of the mixture, and the activation energy of PVC/PE/PP ternary blend system decreased most significantly.

Assessing the energy release characteristics during the middle detonation reaction stage of aluminized explosives

Afterburning behind the detonation front of an aluminized explosive releases energy on the millisecond timescale, which prolong the release of detonation energy and the energy release at different stages also shows significant differences. However, at present, there are few effective methods for evaluating the energy release characteristics of the middle reaction stage of such explosives, which can have a duration of tens to hundreds of microseconds. The present work demonstrates an approach to assessing the mid-stage of an aluminized explosive detonation based on a water push test employing a high degree of confinement. In this method, the explosive is contained in a steel cylinder having one end closed that is installed at the bottom of a transparent water tank. Upon detonation, the gaseous products expand in one direction while forcing water ahead of them. The resulting underwater shock wave and the interface between the gas phase products and the water are tracked using an ultra-high-speed framing and streak camera. The shock wave velocity in water and the expansion work performed by the gaseous detonation products were calculated to assess the energy release characteristics of aluminized explosives such as CL-20 and RDX in the middle stage of the detonation reaction. During the middle stage of the detonation process of these aluminized explosives, the aluminum reaction reduced the attenuation of shock waves and increased the work performed by gas phase products. A higher aluminum content increased the energy output while the presence of oxidants slowed the energy release rate. This work demonstrates an effective means of evaluating the performance of aluminized explosives.

Formation of nitrogen-containing gas phase products from the heterogeneous (photo)reaction of NO2 with gallic acid

Heterogeneous reaction of gas phase NO2 with atmospheric humic-like substances (HULIS) is potentially an important source of volatile organic compounds (VOCs) including nitrogen (N)-containing compounds, a class of brown carbon of emerging importance. However, the role of ubiquitous water-soluble aerosol components in this multiphase chemistry, namely nitrate and iron ions, remains largely unexplored. Here, we used secondary electrospray ionization ultrahigh-resolution mass spectrometry for real-time measurements of VOCs formed during the heterogeneous reaction of gas phase NO2 with a solution containing gallic acid (GA) as a proxy of HULIS at pH 5 relevant for moderately acidic aerosol particles. Results showed that the number of detected N-containing organic compounds largely increased from 4 during the NO2 reaction with GA in the absence of nitrate and iron ions to 55 in the presence of nitrate and iron ions. The N-containing compounds have reduced nitrogen functional groups, namely amines, imines and imides. These results suggest that the number of N-containing compounds is significantly higher in deliquescent aerosol particles due to the influence of relatively higher ionic strength from nitrate ions and complexation/redox reactivity of iron cations compared to that in the dilute aqueous phase representative of cloud, fog, and rain water.

Methane-assisted selective bio-oil deoxygenation for high-quality renewable fuel production: A rational catalyst design and mechanistic study

Methane is the main component of naturally abundant natural gas resources and is under-utilized. Bio-oil is a promising energy source with lower economic and environmental costs compared to fossil fuels. However, pyrolysis-derived bio-oil obtained from lipid sources is hindered by high oxygen content and unsaturated species. In this work, an Ir-Ga-Ce/TiO2-A catalyst is theorized and subsequently tailored to optimize deoxygenation product oil quality. After synthesis, 2-hexyl-1-decanol is employed as a model compound to understand the mechanism of deoxygenation under different atmospheres and rationalize the assistance of methane compared to inerts. It is found that methane significantly facilitates the deoxygenation and chain growth reactions by direct incorporation into the paraffinic and naphthenic liquid-phase products. In the gas-phase products, isotopic labeling studies reveal that methane is directly involved with deoxygenation as a major contributor to CO2, and potentially CO. The role of each catalyst component (Ir, Ga, Ce, and TiO2-A) is elucidated, resulting in a sophisticated network tailored for deoxygenation of alcohols with the assistance of methane. The Ir-Ga-Ce/TiO2-A catalyst is then subject to testing on a real pyrolysis-derived bio-oil and shows 84.7% deoxygenation, 0.07% water content by weight, 0.2 (mg KOH g−1) TAN and greater than 1.5% methane conversion, while maintaining the product oil’s structural integrity as a renewable fuel. This work illustrates the potential of a methane-assisted deoxygenation process and explains multiple roles methane can play in achieving better reaction performance and product quality. The effective utilization of methane for bio-oil deoxygenation demonstrates unique benefits for the natural gas and fatty waste industries.

Pyrolysis behavior, properties and mechanism of high-energy oxidizer 2,3-bis(hydroxymethyl)-2,3-dinitro-1,4-butanediol tetranitrate

To evaluate the thermal properties and promote the application of 2,3-bis(hydroxymethyl)-2,3-dinitro-1,4-butanediol tetranitrate (BHDBT), thermal behavior of BHDBT was studied systematically using differential scanning calorimetry (DSC), thermogravimetric analysis (TG/DTG) and thermogravimetric-infrared-mass spectrometry (TG-IR-MS) techniques. The results show that the thermal behavior of BHDBT presents two stages, one is an obvious endothermic melting process, the other is a big exothermic decomposition process with mass loss of about 81 %, and the peak temperatures (Tp) of two processes are 86.5 °C and 186.9 °C at the heating rate of 10 °C min−1, respectively. In high-pressure sealed crucible, BHDBT presents similar thermal behavior to that in common open crucible. Non-isothermal decomposition kinetics equation of BHDBT was obtained, and the possible thermal decomposition mechanism for BHDBT was proposed based on the main gas-phase products, including H2O, HCN, CO, CO2, NO, N2O and NO2, which are proved by TG-IR-MS testing results. Finally, the combustion heat and standard molar enthalpy of formation of BHDBT were measured and calculated. All results will provide a theoretical support for the application of BHDBT.

Direct Synthesis of Formamide from CO2 and H2O with Nickel-Iron Nitride Heterostructures under Mild Hydrothermal Conditions.

Formamide can serve as a key building block for the synthesis of organic molecules relevant to premetabolic processes. Natural pathways for its synthesis from CO2 under early earth conditions are lacking. Here, we report the thermocatalytic conversion of CO2 and H2O to formate and formamide over Ni-Fe nitride heterostructures in the absence of synthetic H2 and N2 under mild hydrothermal conditions. While water molecules act as both a solvent and hydrogen source, metal nitrides serve as nitrogen sources to produce formamide in the temperature range of 25-100 °C under 5-50 bar. Longer reaction times promote the C-C bond coupling and formation of acetate and acetamide as additional products. Besides liquid products, methane and ethane are also produced as gas-phase products. Postreaction characterization of Ni-Fe nitride particles reveals structural alteration and provides insights into the potential reaction mechanism. The findings indicate that gaseous CO2 can serve as a carbon source for the formation of C-N bonds in formamide and acetamide over the Ni-Fe nitride heterostructure under simulated hydrothermal vent conditions.

Construction of hollow heterogeneous microspheres containing energy storage fibers by electric spray to promote combustion of nano aluminum

To solve the problem of nano-aluminum (nAl) powder easy agglomeration and improve its thermal reaction, nAl was combined with adhesive (Viton A, F2602) and oxidizer (Ammonium perchlorate, AP) forming microspheres by electrostatic spray method. The morphology and structure were analyzed by SEM, EDS and XPS. The results showed that the microspheres (diameter≈Φ10–15 μm) were hollow structures formed by winding of fluoropolymer fibers, while AP and nano aluminum particles were embedded on the fibers. By controlling the electric spray process, the well-dispersed AP and nAl nanocrystals were assembled on the fiber. Thermal analysis indicated that the gas phase products decomposed by AP were absorbed by porous microspheres, and part of the heat was stored in polymer fibers, thus promoting the breakdown of the alumina shell and accelerating the pre-ignition reaction. The combustion and laser ignition experiments proved hollow heterogeneous microspheres have excellent thermodynamic properties. The assembled microspheres not only solved the problem of poor rheology caused by the agglomeration of nAl, but also improved the insufficient combustion of nAl and the condensation of products.

(Invited) Photoelectrode Membrane Assemblies with Transparent Conductive Gas Diffusion Layers for Solar Fuel Production

Gas diffusion electrodes are essential components of common fuel and electrolysis cells that use gas phase reactants and products, but are typically made from graphitic carbon or metallic materials, which do not allow light transmittance, and thus limit the development of photoelectrode membrane assemblies for gas-phase solar fuel production. In this presentation, the application of solar H2 production from humid air is motivated and the simple and scalable preparation of transparent gas-diffusion layers using F-doped SnO2 (FTO) coated SiO2 interconnected fiber felt substrates is introduced. The resulting substrates have a porosity of 90 %, a roughness factor of 15.8 and a Young’s Modulus of 0.2 GPa. A sheet resistivity of 20 ± 3 Ω sq−1 and a loss of incident light of 41% at an illumination wavelength of 550 nm is found with FTO coating. The application of various semiconductors on the substrates was established including Fe2O3 (chemical bath deposition), CuSCN and Cu2O (electrodeposition), and semiconducting polymers (dip coating) and the liquid-phase photoelectrochemical performance commensurate with flat FTO substrates was confirmed. Finally, gas phase H2 production was demonstrated with a polymer semiconductor photocathode membrane assembly at 1-Sun photocurrent density on the order of 1 mA cm–2 and Faradaic efficiency of 40%.

Electrochemical CO2 Reduction Using a Free-Standing Porous Cu Framework as Catalyst

Due to fossil fuel combustion, the CO2 concentration in the atmosphere has reached around 410 ppm, causing major climate change on our planet. It thus becomes increasingly important to limit CO2 emissions or even remove CO2 from our atmosphere. One promising pathway to transform CO2 into useful chemicals is electrochemical reduction. However, electrochemical CO2 reduction is a challenging process that requires robust, low cost and stable catalysts. Copper is a promising candidate, at which CO2 can be reduced to several types of hydrocarbons.In this contribution, CO2 reduction was performed with a free-standing porous copper catalyst that was prepared using an inexpensive hydrogen assisted electroplating process [1]. The porous copper framework has good mechanical stability and a large internal surface area. Furthermore, it can easily be manufactured on a large scale. Due to its porous nature with tunable pore sizes this copper framework is at the same time gas diffusion layer and catalyst. A porous sample with a 10 cm2 geometric surface area was assembled in a custom-made electrochemical cell consisting of an open cell anode compartment, a closed compact cell for the cathode, separated by a cation-exchange membrane. CO2 mixed with water vapor is transported to the free-standing porous Cu in the closed compact cell for the CO2 reduction process. The electrochemical cell is connected to a gas chromatograph (GC) for further gas phase product analysis. The experiments were performed in the potential range between -0.3 V vs RHE and -1.7 V vs RHE in 0.5 M KHCO3 as the anolyte. GC measurements show a considerable amount of methane (CH4), ethylene (C2H4), ethane (C2H6), and propane (C3H8) which indicates a successful reduction reaction of the CO2 on the porous copper framework surface.[1] M. Kurniawan, M. Stich, M. Marimon, M. Camargo, R. Peipmann, T. Hannappel, A. Bund: "Electrodeposition of cuprous oxide on a porous copper framework for an improved photoelectrochemical performance." J. Mater Sci. 56 (2021) 11866-11880

Probing the Stability of Lithium Carbonate in the Lithium-Metal Solid Electrolyte Interphase

The chemical composition and structure of the solid electrolyte interphase (SEI) are two of the key factors that determine the reversibility of lithium-metal (Li) anodes for next-generation batteries. As a result, much of the research aimed at enabling practical Li-metal batteries emphasizes tuning SEI composition, either via electrolyte formulation1–5 or synthesis of artificial SEIs.6–8 Ideally, the lithium SEI should minimize parasitic side reactions by effectively passivating Li while also promoting facile conduction of lithium ions (Li+). To do this, SEI materials must have high (electro)chemical stability, be ionically conductive, and be sufficiently mechanically robust to accommodate substantial volume changes. However, studying these properties in bulk-scale materials often yields values that diverge by orders of magnitude from those observed in SEIs. For example, typical SEI ionic conductivities lie in the range of 10-7-10-9 S cm-1, yet bulk ionic conductivity measurements of relevant materials such as lithium carbonate, lithium fluoride, and lithium oxide ranges from 10-18 and 10-10 S cm-1.9 Our group has developed a technique to directly study these materials at realistic length scales by synthesizing model interphases through the reaction of gases with Li.10,11 Our previous work on Li2O and LiF revealed that Li2O is a better Li+ conductor than LiF (~1 x 10-9 S cm-1 vs ~5.2 x 10-10 S cm-1),11 and that these species’ chemical stability varies substantially in different electrolytes.12 One of the remaining key SEI materials is lithium carbonate, which has been proposed to act as a metastable phase in the outer portion of the SEI.13 In this work, we have developed a technique to synthesize Li2CO3 films via sequential reaction of oxygen and carbon dioxide with clean lithium surfaces. Using scanning electron microscopy and air-exposure tests, we can confirm that these films are conformal and generally pinhole-free. Titration gas chromatography (TGC)14 was used to quantify relative proportions of lithium carbonate, metallic lithium, and lithium carbide, and X-ray photoelectron spectroscopy (XPS) offers insights into how composition changes across the depth of the film. These films were then used as a platform to further investigate the reactivity of Li2CO3 with different electrolytes, comparing carbonates versus ethers and varying the lithium salt used. Electrochemical impedance spectroscopy (EIS) offers insights into the evolution of transport properties at these interphases, while electrolyte soak tests coupled with gas chromatography of gas-phase products and TGC of solid-phase products can track their chemical evolution. Taken together, this work illuminates how lithium carbonate may evolve during battery cycling, offering perspective that can help guide future design of Li-metal SEIs.References Liu, Y. et al. Solubility-mediated sustained release enabling nitrate additive in carbonate electrolytes for stable lithium metal anode. Nat. Commun. 1–10 (2018).Suo, L. et al. Fluorine-donating electrolytes enable highly reversible 5-V-class Li metal batteries. Proc. Natl. Acad. Sci. 115, 1156–1161 (2018).Chae, O. B., Adiraju, V. A. K. & Lucht, B. L. Lithium Cyano Tris(2,2,2-trifluoroethyl) Borate as a Multifunctional Electrolyte Additive for High-Performance Lithium Metal Batteries. ACS Energy Lett. 6, 3851–3857 (2021).Li, Y. et al. Correlating Structure and Function of Battery Interphases at Atomic Resolution Using Cryoelectron Microscopy. Joule 2, 2167–2177 (2018).Zhao, Q. et al. Upgrading Carbonate Electrolytes for Ultra‐stable Practical Lithium Metal Batteries. Angew. Chemie Int. Ed. 61, e2021162 (2021).Zhao, J. et al. Surface Fluorination of Reactive Battery Anode Materials for Enhanced Stability. J. Am. Chem. Soc. 139, 11550–11558 (2017).Li, Y. et al. Robust Pinhole-free Li3N solid electrolyte grown from molten lithium. ACS Cent. Sci. 4, 97–104 (2018).Kozen, A. C. et al. Next-Generation Lithium Metal Anode Engineering via Atomic Layer Deposition. ACS Nano 9, 5884–5892 (2015).Lorger, S., Narita, K., Usiskin, R. & Maier Films of Li, J. Enhanced ion transport in Li2O and Li2S films. Chem. Commun 57, 6503–6506 (2021).He, M., Guo, R., Hobold, G. M., Gao, H. & Gallant, B. M. The intrinsic behavior of lithium fluoride in solid electrolyte interphases on lithium. PNAS 117, 73–79 (2020).Guo, R. & Gallant, B. M. Li 2 O Solid Electrolyte Interphase: Probing Transport Properties at the Chemical Potential of Lithium. Chem. Mater 32, 5525–5533 (2020).Guo, R., Wang, D., Zuin, L. & Gallant, B. M. Reactivity and Evolution of Ionic Phases in the Lithium Solid−Electrolyte Interphase. ACS Energy Lett. 877–885 (2021) doi:10.1021/acsenergylett.1c00117.Han, B. et al. Poor Stability of Li2CO3 in the Solid Electrolyte Interphase of a Lithium-Metal Anode Revealed by Cryo-Electron Microscopy. Adv. Mater. 33, 2100404 (2021).Hobold, G. M. & Gallant, B. M. Quantifying Capacity Loss Mechanisms of Li Metal Anodes beyond Inactive Li0. ACS Energy Lett. 4, 3458–3466 (2022).

Phase behavior and hydrocarbons distribution in shale oil during EOR with nano-confinement effect

The pore structure of shale reservoirs leads to the complex phase behavior of shale reservoir fluids, which is aggravated due to changes in fluid composition during reservoir development. Effective prediction of changes in the phase behavior of fluids in shale reservoirs is important. This paper proposes a pore-size-dependent Peng-Robinson equation of state (PR-EOS) to describe phase behavior in nanopores. The approach considers the shift of critical parameters and the gas-liquid capillary pressure and compiles by MATLAB. The verification of the model is satisfying by matching the result with Tnavigator PVTi using the published date. The results show that fluids in nanoscale pores are more likely to exhibit near-critical or condensate states. We also compare the changes in phase behavior when fluids dissolve CO2 and CH4 and observe the phase transition (from gaseous to liquid phase) of the lighter crude oil sample that dissolved more gas during the differential liberation experiment (DL). Finally, we use CO2 pre-pad energized fracturing of a shale oil reservoir in northern China as an example to explain abnormal production performances, such as a majority of light hydrocarbons in the produced fluid of the well during the flow back stage, single gas phase production in the early production stage, and stable gas/oil ratio (GOR) in the process of development. Our novel methodology and phase behavior change mechanism can enhance our understanding of the phase behavior of fluids in shale oil reservoirs during enhanced oil recovery.

Exploring the hydrogenation of furfural in the liquid phase by high-throughput screening of commercial catalysts: Effects of temperature, solvents, and promoters on the production of 2-methylfuran

2-methylfuran from the hydrogenation of furfural could be a viable green route to get synthetic gasoline or to be used as a blending fuel. However, it is currently produced as a by-product during the gas phase production of furfuryl alcohol using Cu catalysts, presenting fairly low productivities, while due to the complexity of the reaction, other more active metals lead mostly to by-products. Recently, solvents and promoters have been demonstrated to be useful for tuning the kinetics of the reaction. Here, to speed up the industrialization of 2-methylfuran, 48 commercial catalysts, involving the use of Cu, Ni, Co, Ir, Pt, Pd, Rh, Ru, and Re on several supports and different metallic loadings, were tested employing a high-throughput approach in the liquid phase at 60, 120 and 180 °C, using ethyl acetate, chlorobenzene, ethyl acetate, n-heptane and two mixed solvents involving a 0.5 w.t. % CHCl3/n-heptane and a 20 w.t. % isopropanol/n-heptane mixture. Among the selected catalysts, the top performing ones, in order of importance, were Ir/C, allowing up to 89 % 2-methylfuran yields, followed by Ni/Al2O3 in the presence of chlorine as a promoter, and Cu/ZnO/Al2O3. Besides relations between the achieved yields, active metal loadings, and support effects, useful correlations have been investigated between activity, selectivity, and solvents polarity.

Transformation mechanism of C and N during rapid devolatilization of pulverized coal particles under the pressurized atmospheres

Pressurized O2/CO2 combustion technology is a new power generation technology that can achieve CO2 capture efficiently. In this study, we investigated the pressurized devolatilization of Shenhua bituminous coal in a pressurized drop tube furnace experimental system at 1273 K. The evolution mechanism of carbon/nitrogen gas–solid products during the pressurized devolatilization process was analyzed using online measurements and offline analysis. We found that increasing the pressure from 0.3 to 1.2 MPa promoted the emission of CO and inhibited emission of NO. N2O emissions were insensitive to the change of pressure, and NO2 emissions were almost zero under the experimental conditions. The introduction of CO2 decreased the production of NOx and primary sources of nitrogen-containing gas-phase products were N-5 and N-6 active groups. Therefore, pressurized O2/CO2 combustion technology can effectively reduce NOx emissions in the devolatilization of pulverized coal and impact the subsequent char-combustion process.

Analysis of hydrogen-rich syngas generation in chemical looping gasification of lignite: Application of carbide slag as the oxygen carrier, hydrogen carrier, and in-situ carbon capture agent

Chemical looping gasification (CLG) has become a popular method for producing hydrogen-rich syngas due to its environment-friendliness. Recently, a method of using industrial solid waste carbide slag as an oxygen carrier, hydrogen carrier, and in-situ carbon capture agent in the CLG process has been proposed. However, the actual experiment was affected by heat and mass transfer, and the detailed reaction pathway of the carbide slag was not fully understood. In the present study, the process of the CLG process for producing hydrogen-rich syngas with lignite and carbide slag was analyzed using tube furnace experiments, FactSage calculations, and joint characteristic experiment of carbide slag. The result showed that to achieve a gas phase product with a hydrogen concentration exceeding 90 vol% (with dry N2 excluded), a molar ratio of lignite to carbide slag of greater than 1:5 and a reaction temperature of 923 K should be maintained. In terms of the reaction pathway of carbide slag in the CLG process, it was revealed that calcium hydroxide, the primary component of carbide slag, directly participated in the reaction at temperatures of less than 773 K. Overall, this work provides a novel idea for the preparation of hydrogen-rich syngas during CLG process.

Partial inhibition of acrylonitrile–butadiene–styrene dust explosion by sodium bicarbonate

During acrylonitrile–butadiene–styrene (ABS) plastic processing, dust explosions could occur in production and transportation. In this paper, the explosion properties and pyrolysis mechanism of ABS dust were studied. The inhibition effects of sodium bicarbonate (NaHCO3) on ABS dust were investigated using the 20-L explosion chamber, Hartmann tube, and G-G furnace. The results demonstrated that NaHCO3 effectively decreased both the ignition sensitivity and the explosion severity of ABS dust explosion by increasing the mass fraction of the inhibitor. Adding 50 wt% NaHCO3 could reduce the explosion hazard to an acceptable level. Combined with an analysis of gas phase products and thermal decomposition behaviour, it was discovered that incorporating NaHCO3 enhanced the heat stability of ABS dust. The decomposition of added NaHCO3 produced a substantial quantity of CO2, consuming many free radicals especially OH• and H•, which further reduced the decomposition temperature of ABS. The inhibitor effectively interrupted the combustion chain reaction and inhibited the propagation of the explosion. The results establish a scientific and operational basis for the prevention and management of dust explosion hazards in the ABS processing field.

Revealing Active Sites and Reaction Pathways in Methane Non-Oxidative Coupling over Iron-Containing Zeolites.

Non-oxidative coupling of methane is a promising route to obtain ethylene directly from natural gas. We synthesized siliceous [Fe]zeolites with MFI and CHA topologies and found that they display high selectivity (>90 % for MFI and >99 % for CHA) to ethylene and ethane among gas-phase products. Deactivated [Fe]zeolites can be regenerated by burning coke in air. In situ X-ray absorption spectroscopy demonstrates that the isolated Fe3+ centers in zeolite framework of fresh catalysts are reduced during the reaction to the active sites, including Fe2+ species and Fe (oxy)carbides dispersed in zeolite pores. Photoelectron photoion coincidence spectroscopy results show that methyl radicals are the reaction intermediates formed upon methane activation. Ethane is formed by methyl radical coupling, followed by its dehydrogenation to ethylene. Based on the observation of intermediates including allene, vinylacetylene, 1,3-butadiene, 2-butyne, and cyclopentadiene over [Fe]MFI, a reaction network is proposed leading to polyaromatic species. Such reaction intermediates are not observed over the small-pore [Fe]CHA, where ethylene and ethane are the only gas-phase products.

Understanding of the Fate of α-Fe2O3 in CO2 Hydrogenation through Combined Time-Resolved In Situ Characterization and Microkinetic Analysis

CO2 hydrogenation over Fe-based catalysts is a promising pathway to mitigate emissions of this greenhouse gas and provides a possibility for crude-oil-free production of chemicals and fuels. Understanding of (i) the role of crystalline phases or/and surface species in the working catalysts, (ii) the factors affecting their formation under reaction conditions, and (iii) the kind and reactivity of surface precursors of gas-phase products is vital for controlling the efficiency of CO2 hydrogenation. In this study, we applied time-resolved in situ characterization techniques for monitoring phase transformations during Fe2O3 reduction, starting of CO2 hydrogenation, steady-state operation, and finally catalyst deactivation. The obtained structural information after different times on stream was related to kinetic data obtained from temporal analysis of H2 and CO2 activation as well as from steady-state isotopic transient kinetic analysis (SSITKA). Fe2O3 is easily reduced to Fe3O4 and Fe in H2 above 300 °C. Fe5C2 and Fe3C, which are quickly formed from metallic Fe/Fe3O4 under CO2 hydrogenation conditions, do not undergo oxidation with rising time on the reaction stream under ambient-pressure conditions. Nevertheless, the catalyst loses its initial activity and, particularly, the selectivity to hydrocarbons in favor of CO. Thus, we do not confirm the well-recognized deactivation mechanism of CO/CO2 hydrogenation through oxidation of iron carbides. Instead, surface carbonaceous species identified by in situ Raman and pseudo in situ XPS measurements were concluded to cause catalyst deactivation and deselectivation due to hindering the catalyst ability to generate surface species from H2 and CO2. Specifically, the strength of CO2 adsorption and the catalyst activity to dissociate adsorbed CO2 to adsorbed CO decrease in the presence of carbon deposits. Kinetic evaluation of SSITKA tests revealed the presence of (i) only one kind of surface intermediate yielding gas-phase CO after 1.5 h on reaction stream but (ii) at least two kinds (short-lived and long-lived) of surface intermediates participating in CH4 formation in parallel. Carbon deposits seem to block the sites responsible for the formation of short-lived intermediates.