Study on CH4 dry reforming process by high power inductively coupled plasma torch at atmospheric pressure

CO₂ dissociation and CH₄ dry reforming, by high power inductively coupled plasma (ICP) torch at atmospheric pressure, have been studied. At a frequency of 400 kHz and power of 30 kW, the ICP torch source dissociates CO₂ gas directly, causing CH₄ dry reforming. The resulting products are composed of syngas, C₂H₆, C₂H₄, and C₂H₂. The results show conversion efficiencies (CE) for both CO₂ and CH₄ of 95%. At an input power of 22 kW, a CO₂ flow rate of 30 SLM, and a CH₄ flow rate of 36 SLM, the energy conversion efficiency (ECE) is 57%. As input CH₄ flow rate increases, the selectivity of CO and H₂ decreases and that of C₂ hydrocarbons increases. In this condition, ECE increases. As a result, the high CE of CO₂ and CH₄, the large amount of products, and the high selectivity of C₂ hydrocarbons can be seen as important factors for achieving higher energy conversion efficiency in the CH₄ dry reforming process. The associated chemical reactions are simulated using CHEMKIN-PRO tool, and the results illustrate the tendency of CE to vary with variations in selected parameters, and syngas and C₂ hydrocarbons production trends achieved in the simulation agree with experimental results.     

Conversion of tar in a counter flow of supercritical water at a temperature varying along the reactor axis

The article reports the conversion of tar (empirical formula CH_1.47N_0.01S_0.007) continuously introduced into a counter flow of supercritical water (SCW) at 30 MPa in a tubular reactor with a temperature gradient along its vertical axis (450°C at the top and 650°C at the bottom). The yields of liquid products and volatile (C₁–C₉) hydrocarbons are 41.4 and 28.4%, respectively, relative to the weight of tar supplied into the reactor. Methane is the major component (40.5 mol %) of the volatile products, and the liquid products are dominated by oils (74.4 wt %). Deasphaltization and desulfurization of tar conversion products are observed. The average rate of water decomposition calculated from the quantity of O atoms in the conversion products is 0.24 g/min. Use of counter flows of the reactants in combination with a temperature gradient along the reactor axis affords a higher yield of low-boiling hydrocarbons than in the case of SCW pumping through a tar layer.     

生物质气经由二甲醚两步法制备低碳烯烃

制备出NiSAPO-34及NiSAPO-34/HZSM-5催化剂,考察了其对二甲醚催化转化制备低碳烯烃的性能．利用Cu/Zn/Al/HZSM-5和筛选出的2%NiSAPO-34/HZSM-5催化剂进行生物质气经由二甲醚两步法制备低碳烯烃的实验, 结果表明在SAPO-34上添加2%的Ni不改变其结构, 但降低了酸中心数量, 并生成了较强的酸中心． 添加少量具有稳定酸中心的HZSM-5, 该催化剂的活性提高到3 h以上, 反应进行2 h获得了最高的低碳烯烃选择性为90.8%． 当把该催化剂应用到两步催化转化过程的第二个反应器中, 其高催化活性可达5 h以上． 当以低氢碳比生物质气(H₂/CO/CO₂/N₂/CH₄=41.5/26.9/14.2/14.6/2.89)作为原料时,经两步转化,低碳烯烃的收率达到84.6 g/m³_syngas．     

利用双段床反应器从生物油重整合成气合成甲醇

一种组合了合成气在线调整和甲醇合成的双段床反应器,成功应用于由生物油重整得到的富CO₂合成气的高效合成甲醇．在前段催化床反应器内,富含CO2的原始生物质合成气在CuZnAlZr催化剂的催化作用下可以有效地转化为含CO的合成气．经过450 oC的合成气在线调整之后,CO₂/CO的比率由6.3大幅降至1.2．经过调整后的生物质基合成气在后段催化床反应器内由工业CuZnAl催化剂催化合成甲醇,当反应条件为260 oC 和5.5 MPa时得到每小时每kg催化剂的最大甲醇     

Brown coal gasification in combustion in supercritical water

The yield and composition of conversion products are investigated in a layout that provides countersupply of reagents (brown coal, supercritical water (SCW), and O₂) into a vertical tubular reactor and drain of reactants into replaceable collectors under isobaric conditions (30 MPa). The coal (gross formula CH_0.96N_0.01S_0.002O_0.31) incorporated into coal-water slurry (CWS) stabilized by starch addition (1 wt.%), was supplied through the top end of the reactor, while SCW and SCW/O₂ fluids were supplied through the bottom end. Based on the results of elemental analysis of liquid products and solid residue of conversion, and mass spectrometric analysis of volatile products, we obtained gross reactions of brown coal conversion in SCW and SCW/O₂ fluids. It was found that addition of O₂ to SCW leads to autothermal conversion conditions and an increase in the contribution from heterogeneous reactions between carbon and water, which provides additional yield of H₂ and CH₄.     

Sonochemical conversion of CO2 into hydrocarbons: The Sabatier reaction at ambient conditions

In this study, we investigated an alternative method for the chemical CO₂ reduction reaction in which power ultrasound (488 kHz ultrasonic plate transducer) was applied to CO₂-saturated (up to 3%) pure water, NaCl and synthetic seawater solutions. Under ultrasonic conditions, the converted CO₂ products were found to be mainly CH₄, C₂H₄ and C₂H₆ including large amount of CO which was subsequently converted into CH₄. We have found that introducing molecular H₂ plays a crucial role in the CO₂ conversion process and that increasing hydrogen concentration increased the yields of hydrocarbons. However, it was observed that at higher hydrogen concentrations, the overall conversion decreased since hydrogen, a diatomic gas, is known to decrease cavitational activity in liquids. It was also found that 1.0 M NaCl solutions saturated with 2% CO₂ + 98% H₂ led to maximum hydrocarbon yields (close to 5%) and increasing the salt concentrations further decreased the yield of hydrocarbons due to the combined physical and chemical effects of ultrasound. It was shown that CO₂ present in a synthetic industrial flue gas (86.74% N₂, 13% CO₂, 0.2% O₂ and 600 ppm of CO) could be converted into hydrocarbons through this method by diluting the flue gas with hydrogen. Moreover, it was observed that in addition to pure water, synthetic seawater can also be used as an ultrasonicating media for the sonochemical process where the presence of NaCl improves the yields of hydrocarbons by ca. 40%. We have also shown that by using low frequency high-power ultrasound in the absence of catalysts, it is possible to carry out the conversion process at ambient conditions i.e., at room temperature and pressure. We are postulating that each cavitation bubble formed during ultrasonication act as a “micro-reactor” where the so-called Sabatier reaction -$C{O}_2+4H_2\stackrel{\mathit{Ultrasonication}}{\to }C{H}_4+2H_{2}O$ - takes place upon collapse of the bubble. We are naming this novel approach as the “Islam-Pollet-Hihn process”.     

Monolithic electrochemically promoted reactors: A step for the practical utilization of electrochemical promotion

A novel dismantlable monolithic-type electrochemically promoted catalytic reactor and “smart” sensor-catalytic reactor unit has been constructed and tested for hydrocarbon oxidation and NO reduction by C₂H₄ in the presence of O₂. In this novel reactor, thin (∼ 40 nm) porous catalyst films made of two different materials are sputter-deposited on opposing surfaces of thin (0.25 mm) parallel solid electrolyte plates supported in the grooves of a ceramic monolithic holder and serve as sensor or electropromoted catalyst elements. The catalyst dispersion was higher than 10%. A 22 flat plate reactor operated with apparent Faradaic efficiency up to 100, at near complete reactants conversion, at gas flow rates up to 30 l/min. The novel design has only two external electrical connections and thus significantly facilitates the practical utilization of electrochemical promotion of catalysis.     

XPS, XRD and SEM characterization of a thin ceria layer deposited onto graphite electrode for application in lithium-ion batteries

Thin ceria layer deposited by electro-precipitation onto graphite was synthesised and characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electro-precipitated ceria has a cubic structure with nanocrystallites of about 6 nm. The SEM analyses shows that the ceria layer reflects the morphology of the graphite electrode, exhibits small cracks usually found on the electro-precipitated films but covers almost completely the surface of the graphite. The ceria layer is composed of 75% Ce(IV) and 25% Ce(III) oxides as indicated by the XPS analyses. Cyclic voltammetry and galvanostatic charge-discharge tests in ethylene carbonate/dimethyl carbonate (1/1) (wt/wt) in the presence of 1 M LiPF₆ show that reversible lithium insertion and deinsertion occurs in the graphite/ceria electrode and that the ceria layer on the graphite electrode prevents from the loss of capacity during the first four cycles. The reduction of the electrolyte occurs at about 0.7 V vs Li/Li⁺ on both electrodes but XPS and SEM analyses show that the SEI layer is thin and not as homogenous on the graphite as on the graphite/ceria electrode. The composition of the SEI layer on the graphite/ceria electrode, mainly composed of Li₂CO₃, ROCO₂Li, R-CH₂OLi and LiF, is different than those obtained on the graphite.     

Carbon nanotubes supported Cu-Ni bimetallic catalysts and their properties for the direct synthesis of dimethyl carbonate from methanol and carbon dioxide

Multi-walled carbon nanotubes (MWCNTs) supported Cu-Ni bimetallic catalysts for the direct synthesis of dimethyl carbonate (DMC) from CH₃OH and CO₂ were synthesized and investigated. The supporting materials and the synthesized catalysts were fully characterized using FTIR, scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), X-ray diffraction (XRD) and X-ray photoelectron spectrum (XPS) techniques. The catalytic activities were investigated by performing micro-reactions. The experimental results showed that the metal phase and Cu-Ni alloy phase in the catalyst were partially formed during the calcination and activation step. Active metal particles were dispersed homogeneously on the surface of the MWCNTs. Cu-Ni/MWCNTs catalysts were efficient for the direct synthesis of DMC. The highest conversion of CH₃OH was higher than 4.3% and the selectivity of DMC was higher than 85.0% under the optimal catalytic conditions of 120 °C and around 1.2 MPa. The high catalytic activity of Cu-Ni/MWCNTs in DMC synthesis can be attributed to the synergetic effects of metal Cu, Ni and Cu-Ni alloy in the activation of CH₃OH and CO₂, the unique structure of MWCNTs and the interaction between the metal particles and the supports.     

Superparamagnetic behaviour of cement clinker and its ferrite phase doped with different impurities

Two oxide mixtures of clinker and its ferrite phase of compositions (66.5 wt.% CaO+24.5 wt.% SiO₂+6.0 wt.% Al₂O₃+3.0 wt.% Fe₂O₃) and (60.4 wt.% CaO+15.4 wt.% Al₂O₃+24.2 wt.% Fe₂O₃) respectively were divided into protions and were mixed individually with 0.5, 1, 1.5 or 3 wt.% of LiF, MgF₂, CaF₂, CaCl₂ or ZnO. Each portion of clinker was fired at 1450°C and each portion of ferrite was fired at 1350°C for 30 min. then quenched in air. Mössbauer effect and X-ray diffraction measurements were performed on each sample. The impurities doping produced small particle size. The LiF doping gave the smallest particle size and the highest blocking temperature. The ferrite with LiF exhibited two Fe³⁺ sites while the other used impurities gave one site only. The superparamagnetic relaxation appeared only in the spectra of ferrite with impurities, which means that the impurities in clinker have a tendency to combine with the calcium silicate phases not with C₄AF.     

Lean or ultra-lean stretched planar methane/air flames

Lean premixed combustion has potential advantages of reducing pollutants and improving fuel economy. In some lean engine concepts, the fuel is directly injected into the combustion chamber resulting in a distribution of lean fuel/air mixtures. In this case, very lean mixtures can burn when supported by hot products from more strongly burning flames. This study examines the downstream interaction of opposed jets of a lean-limit CH₄/air mixture vs. a lean H₂/air flame. The CH₄ mixtures are near or below the lean flammability limit. The flame composition is measured by laser-induced Raman scattering and is compared to numerical simulations with detailed chemistry and molecular transport including the Soret effect. Several sub-limit lean CH₄/air flames supported by the products from the lean H₂/air flame are studied, and a small amount of CO₂ product (around 1% mole fraction) is formed in a “negative flame speed” flame where the weak CH₄/air mixture diffuses across the stagnation plane into the hot products from the H₂/air flame. Raman scattering measurements of temperature and species concentration are compared to detailed simulations using GRI-3.0, C₁, and C₂ chemical kinetic mechanisms, with good agreement obtained in the lean-limit or sub-limit flames. Stronger self-propagating CH₄/air mixtures result in a much higher concentration of product (around 6% CO₂ mole fraction), and the simulation results are sensitive to the specific chemical mechanism. These model-data comparisons for stronger CH₄/air flames improve when using either the C₂ or the Williams mechanisms.     

Homogeneous ignition of CH4/air and H2O and CO2-diluted CH4/O2 mixtures over Pt; an experimental and numerical investigation at pressures up to 16 bar

The homogeneous ignition of CH₄/air, CH₄/O₂/H₂O/N₂, and CH₄/O₂/CO₂/N₂ mixtures over platinum was investigated experimentally and numerically at pressures 4 bar p 16 bar, temperatures 1120 K T 1420 K, and fuel-to-oxygen equivalence ratios 0.30 0.40. Experiments have been performed in an optically accessible catalytic channel-flow reactor and included planar laser induced fluorescence (LIF) of the OH radical for the determination of homogeneous (gas-phase) ignition and one-dimensional Raman measurements of major species concentrations across the reactor boundary layer for the assessment of the heterogeneous (catalytic) processes preceding homogeneous ignition. Numerical predictions were carried out with a 2D elliptic CFD code that included elementary heterogeneous and homogeneous chemical reaction schemes and detailed transport. The employed heterogeneous reaction scheme accurately captured the catalytic methane conversion upstream of the gaseous combustion zone. Two well-known gas-phase reaction mechanisms were tested for their capacity to reproduce measured homogeneous ignition characteristics. There were substantial differences in the performance of the two schemes, which were ascribed to their ability to correctly capture the p–T– parameter range of the self-inhibited ignition behavior of methane. Comparisons between measured and predicted homogeneous ignition distances have led to the validation of a gaseous reaction scheme at 6 bar p 16 bar, a pressure range of particular interest to gas-turbine catalytically stabilized combustion (CST) applications. The presence of heterogeneously produced water chemically promoted the onset of homogeneous ignition. Experiments and predictions with CH₄/O₂/H₂O/N₂ mixtures containing 57% per volume H₂O have shown that the validated gaseous scheme was able to capture the chemical impact of water in the induction zone. Experiments with CO₂ addition (30% per volume) were in good agreement with the numerical simulations and have indicated that CO₂ had only a minor chemical impact on homogeneous ignition.     

Oxidation of H2/CO2 mixtures and effect of hydrogen initial concentration on the combustion of CH4 and CH4/CO2 mixtures: Experiments and modeling

An experimental investigation of the oxidation of hydrogen diluted by nitrogen in presence of CO₂ was performed in a fused silica jet-stirred reactor (JSR) over the temperature range 800-1050 K, from fuel-lean to fuel-rich conditions and at atmospheric pressure. The mean residence time was kept constant in the experiments: 120 ms at 1 atm and 250 ms at 10 atm. The effect of variable initial concentrations of hydrogen on the combustion of methane and methane/carbon dioxide mixtures diluted by nitrogen was also experimentally studied. Concentration profiles for O₂, H₂, H₂O, CO, CO₂, CH₂O, CH₄, C₂H₆, C₂H₄, and C₂H₂ were measured by sonic probe sampling followed by chemical analyses (FT-IR, gas chromatography). A detailed chemical kinetic modeling of the present experiments and of the literature data (flame speed and ignition delays) was performed using a recently proposed kinetic scheme showing good agreement between the data and this modeling, and providing further validation of the kinetic model (128 species and 924 reversible reactions). Sensitivity and reaction paths analyses were used to delineate the important reactions influencing the kinetic of oxidation of the fuels in absence and in presence of additives (CO₂ and H₂). The kinetic reaction scheme proposed helps understanding the inhibiting effect of CO₂ on the oxidation of hydrogen and methane and should be useful for gas turbine modeling.     

On the reaction mechanism of CO2 reforming of methane over a bed of coal char

CO₂ reforming of methane was studied over a bed of coal char in a fixed bed reactor at temperatures between 1073 and 1223 K and atmospheric pressure with a feed composition of CH₄/CO₂/N₂ in the ratio of 1:1:8. Experimental results showed that the char was an effective catalyst for the production of syngas with a maximum H₂/CO ratio of one. It was also found that high H₂/CO ratios were favoured by low pressures and moderate to high temperatures. These results are supported by thermodynamic calculations. A mechanism of seven overall reactions was studied and three catalytic reactions of CH₄ decomposition, char gasification and the Boudouard reaction was identified as being of major importance. The first reaction produces carbon and H₂, the second consumes carbon, and the third (the Boudouard reaction) converts CO₂ to CO while consuming carbon. Equilibrium calculations and experimental results showed that any water present reacts to form H₂ and carbon oxides in the range of temperatures and pressures studied. Carbon deposition over the char bed is the major cause of deactivation. The rate of carbon formation depends on the kinetic balance between the surface reaction of the adsorbed hydrocarbons with oxygen containing species and the further dissociation of the hydrocarbon.     

The Ca-looping process for CO<Subscript>2</Subscript> capture and energy storage: role of nanoparticle technology

The calcium looping (CaL) process, based on the cyclic carbonation/calcination of CaO, has come into scene in the last years with a high potential to be used in large-scale technologies aimed at mitigating global warming. In the CaL process for CO₂ capture, the CO₂-loaded flue gas is used to fluidize a bed of CaO particles at temperatures around ~?650 °C. The carbonated particles are then circulated into a calciner reactor wherein the CaO solids are regenerated at temperatures near ~?950 °C under high CO₂ concentration. Calcination at such harsh conditions causes a marked sintering and loss of reactivity of the regenerated CaO. This main drawback could be however compensated from the very low cost of natural CaO precursors such as limestone or dolomite. Another emerging application of the CaL process is thermochemical energy storage (TCES) in concentrated solar power (CSP) plants. Importantly, carbonation/calcination conditions to maximize the global CaL-CSP plant efficiency could differ radically from those used for CO₂ capture. Thus, carbonation could be carried out at high temperatures under high CO₂ partial pressure for maximum efficiency, whereas the solids could be calcined at relatively low temperatures in the absence of CO₂ to promote calcination. Our work highlights the critical role of carbonation/calcination conditions on the performance of CaO derived from natural precursors. While conditions in the CaL process for CO₂ capture lead to a severe CaO deactivation with the number of cycles, the same material may exhibit a high and stable conversion at optimum CaL-CSP conditions. Moreover, the type of CaL conditions influences critically the reaction kinetics, which plays a main role on the optimization of relevant operation parameters such as the residence time in the reactors. This paper is devoted to a brief review on the latest research activity in our group concerning these issues as well as the possible role of nanoparticle technology to enhance the activity of Ca-based materials at CaL conditions for CO₂ capture and energy storage.     

Temperature and carbon source effects on methane–air flame synthesis of CNTs

We have conducted experimental and numerical studies on flame synthesis of carbon nanotubes (CNTs) to investigate the effects of three key parameters – selective catalyst, temperature and available carbon sources – on CNT growth. Two different substrates were used to synthesize CNTs: Ni-alloy wire substrates to obtain curved and entangled CNTs and Si-substrates with porous anodic aluminum oxide (AAO) nanotemplates to grow well-aligned, self-assembled and size-controllable CNTs, each using two different types of laminar flames, co-flow and counter-flow methane–air diffusion flames. An appropriate temperature range in the synthesis region is essential for CNTs to grow on the substrates. Possible carbon sources for CNT growth were found to be the major species CO and those intermediate species C₂H₂, C₂H₄, C₂H₆, and methyl radical CH₃. The major species H₂, CO₂ and H₂O in the synthesis region are expected to activate the catalyst and help to promote catalyst reaction.     

Catalytic ignition of light hydrocarbons over Rh/Al2O3 studied in a stagnation-point flow reactor

The ignition (light-off) temperatures of catalytic oxidation reactions provide very useful information for understanding their surface reaction mechanism. In this study, the ignition behavior of the oxidation of hydrogen (H₂), carbon monoxide (CO), methane (CH₄), ethane (C₂H₆), and propane (C₃H₈) over Rh/alumina catalysts is examined in a stagnation-point flow reactor. The light-off temperatures are identified by means of the sudden increase of the catalyst temperature when linearly heating the catalyst for various fuel/oxygen ratios. For hydrogen and all hydrocarbons studied, the results show a rise of ignition temperature with increasing fuel/oxygen ratio, whereas the opposite trend is observed for the light-off of CO oxidation. Hydrogen oxidation, however, shows an opposite trend compared to previous investigations, performed on platinum [1], [2].     

Theoretical and experimental study of methane steam reforming reactions over nickel catalyst

In this work we perform DFT theoretical calculations of methane and steam interactions on Ni(1 1 1) surface. The calculations allow us to improve our understanding of the competition between these reactants by catalytic sites in methane steam reforming (MSR) process. For this purpose we compare theoretical results with kinetic measurements of MSR on a Ni(II)-Al(III) catalyst prepared from lamellar double hydroxides as precursor. This comparison shows that, for low H₂O/CH₄ ratios methane and water intermediate species adsorb on different catalytic sites. While CHO species adsorbs on top of Ni atom, OH one occupies preferentially a tri-coordinate surface site. On the other hand, for high H₂O/CH₄ ratios a competency between these species by Ni sites would establish, diminishing methane conversion. In addition competition between methane and steam for Ni sites would lead to a decrease in CO production. Nevertheless, intermediate species adsorbed on different active sites would produce CO₂, whatever the steam/methane ratio. Thus, it would be optimum steam concentration in hydrocarbon feed and active sites distribution on catalyst surface, which could maximize H₂ production and minimize CO selectivity. The theoretical findings agree with kinetic measurements, which show that maximum methane conversion depends on steam partial pressure in the feed; whereas always, selectivity to CO₂ increases and to CO diminishes.     

In-situ gasification chemical looping combustion of plastic waste in a semi-continuously operated fluidized bed reactor

Conventional air incineration of plastic waste has been considered as one of important sources of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) through de novo synthesis and precursor conversion. Chemical looping combustion (CLC) is an attractive technology for the conversion of plastic wastes to energy with the potential to drastically suppress the formation of PCDD/Fs. In this paper, the iG-CLC (in-situ gasification CLC) experiments of plastic waste were implemented in a semi-continuously operated fluidized bed reactor, which actually simulates the fuel reactor of a continuously-operated interconnected fluidized bed reactor. A kind of low-cost material, natural iron ore without/with 5 wt% CaO adsorbent through the ultrasonic impregnation method, was used as oxygen carrier (OC). Firstly, some key performances of the reactor system, such as the relevance of the bed inventory to the flow rate of fluidizing agent as well as the relationship between the feeding rate and overflow rate of OC, were calibrated. Then, 90 min of single experiment was conducted for each experimental case and an accumulative operation of more than 10 h was attained. Typically, the combustion efficiency can reach at about 98%, and both the carbon conversion and CO₂ yield can approach to 95% at 900 °C and input thermal power of 150 W with a mixture of 5 vol% H₂O and 95 vol% N₂ as the fluidizing agent (U_FR/U_mf = 3). Moreover, the results obtained in the semi-continuously operated fluidized bed reactor demonstrated that CaO decoration to iron ore is conductive to suppressing the formation of chlorobenzene (as a toxic matter and precursor/intermediate of PCDD/Fs) and does not obviously deteriorate the OC performance.     

A pyrolysis study on C4–C8 symmetric ethers

Pyrolysis of diethyl (C₄), di-n-propyl (C₆), di-isopropyl (C₆) and di-n-butyl (C₈) ethers were studied in a jet-stirred reactor between 720 and 1140 K, at 10 atm with an initial ether mole fraction of 0.1%. Major common pyrolysis products were observed to be CO, CH₄, H₂, and C₂H₄. All ethers produced the n/2 alcohol and olefin as products of molecular reaction to a small extent. Under pyrolysis conditions at 10 atm, hydrogen abstraction reactions by H atoms and CH₃ radicals were found to be important. Acetylene and benzene were formed for all ethers when T > 1000 K. A kinetic mechanism is used to represent these results. This study shows that there is need of systematic studies in determining site specific rate constants of important fuel related reactions of ethers.