Boudouard Reaction Research Articles

Experimental investigation of CO2 conversion in Boudouard reaction driven by an atmospheric-pressure microwave plasma torch

An atmospheric-pressure microwave plasma torch (APMPT) is employed to drive Boudouard reaction [C(s) + CO2(g) → 2CO(g)] to convert CO2 into CO with storable chemical energy. In this experiment, the solid carbon is placed in the downstream of the afterglow of carbon dioxide APMPT, which is enclosed in reaction chamber, thereby the reaction occurs in the environment with a plenty of the active species and the large enthalpy. The conversion and energy efficiency are experimentally determined by measuring the change of the gas composition, which is analyzed with a Fourier transformation infrared spectrometer and gas chromatograph. The variations of conversion and energy efficiency are investigated with respect to the plasma state, which is tuned by changing microwave power, gas flow rate, and Ar-CO2 mixture ratio, and the different forms of carbon material. And the high conversion efficiency is obtained with use of the herbaceous type of biomass as carbon material and by increasing microwave power, however, the large percentage of CO2 in carrier gas and increasing gas flow rate impose a negative influence on CO2 conversion.

The Effect of Bio-Coal Agglomeration and High-Fluidity Coking Coal on Bio-Coke Quality

Metallurgical coke with high strength and low reactivity is used in the ironmaking blast furnace. Replacement of some coking coal with bio-coal was shown to result in lower strength and higher reactivity of produced coke due to introduction of reactive bio-coal carbon and ash components catalyzing the Boudouard reaction, but also due to lowering of the coking coal blend fluidity, which influences coke strength and reactivity negatively. The current study aims to investigate the possibility to counteract negative impact from bio-coal addition on fluidity and coke reactivity by using high-fluidity coking coal and by agglomeration of bio-coal before addition. Original bio-coal and micro-agglomerate of bio-coal was added at 10%, 15% and 20% to the coking coal blend. The influence of bio-coals on the coke reactivity was measured by using CO2 in a thermogravimetric analyzer. Selected cokes and bio-cokes were produced in technical scale, and their reactivity and strength were measured in standard tests. The effect on dilatation of adding bio-coal or crushed agglomerates of bio-coal to the coking coal blends was measured in an optical dilatometer. The results show that by using a coking coal blend containing high-fluidity coal with agglomerated bio-coal, the max. contraction is increased, whereas the opposite occurs by using original bio-coal. The results show overlapping between contraction occurring before dilatation and during dilation, which affects max. dilatation. The bio-coke containing high-fluidity coal with agglomerated bio-coal has lower reactivity in comparison to bio-cokes with original bio-coal or bio-coke with agglomerated bio-coal produced from a coking coal blend without high-fluidity coal. The reactivity of coke produced in technical scale, as measured in CRI/CSR tests, shows a similar trend regarding reactivity, as measured by thermogravimetric analysis, on coke produced in laboratory scale.

Efficient Performance of the Methane-Carbon Dioxide Reform Process in a Fluidized Bed Reactor

The reforming of methane with CO2 was carried out efficiently in a fluidized bed reactor at 973 K under atmospheric pressure, taking advantage of the nickel catalyst efficiency achieved with a bed of particulate fines. The fluidization operation was characterized by determining a minimum velocity of 3.11 × 10−3 ms−1 and higher velocities. The reactor worked with surface speeds of up to 1.84 × 10−2 ms−1, providing conversions from 45% to 51% and a syngas yield of 97%. The control base of the operation focused on the use of CO2 was established through the reaction steps assumed for the process, including methane cracking, reverse Boudouard reaction, and RWGS (reverse reaction of water gas-shift). The reactor designed to operate in two zones was able to simultaneously process surface reactions and catalyst regeneration using feed with 50% excess CO2 in relation to methane. Predictions indicating the production of syngas of different compositions quantified with the H2/CO ratio from 2.30 to 0.91 decreasing with space-time were validated with the results available for process design.

Swelling and softening behavior of iron ore-spent mushroom substrate composite pellets during carbothermal reduction

In the present day, we have reached close to an optimum condition of CO2 emission when using coal or coke for iron making process. Carbon neutrality is achieved during carbothermal reduction by employing biomass as a reducing agent in composite pellets. The swelling behavior of composite pellets during reduction has detrimental effects, and catastrophic swelling leads to subsequent disintegration of pellets, which causes low gas permeability through packed beds in the industry. In this study, we used coal, spent mushroom substrate, torrefied mushroom substrate (300 °C), and de-ashed torrefied mushroom substrate as reducing agents in our iron-ore composite pellets. Volume change of the composite was investigated with heating profile (15 °C/min until 1350 °C), reduction time is 70min, the maximum swelling observed in torrefied mushroom pellets is +158%, the pellets experienced swelling in between (700°C–1000 °C) and started to soften from 825 °C. However, no swelling is observed in the coal and de-ashed torrefied pellet. On the other hand, de-ashed torrefied pellets with the addition of alkali metal oxides and soda lime glass had significant swelling and decrease in softening temperature. With the presence of Na2O and K2O in pellets ash, during reduction in some localized areas, they form low melting slags like Soda-lime (∼1000 °C) and Potash-lime (∼1200 °C) compositions. These slags start to soften at a low temperature ∼700 °C for soda-lime composition. As the temperature increases, viscosity decreases, which causes pellets to soften more, and parallelly gas evolving from the pellet during reduction (mainly CO product of the Boudouard reaction) causes these slags to expand, like a glass blowing mechanism.

Investigation of the Pyrolysis of Animal Manure in a Laboratory-Scale Tubular Reactor: The Effect of the Process Temperature and Residence Time

This paper focuses on the pyrolysis of animal manure in a laboratory-scale tubular reactor between 300 and 900°C at nitrogen flow rates of 1 and 5 dm3/h. During the experiments, it was found that both the temperature and nitrogen flow rate had significant effects on the product yields and compositions. The highest gas yield and syngas content were observed at 900°C at a nitrogen flow rate of 1 dm3/h. In this case, since the gaseous product was characterized by a H2/CO ratio of 0:5, its quality must be improved prior to being used for synthesis. The composition of the solid residue was also affected by the pyrolysis parameters. Based on the hydrogen/carbon and oxygen/carbon ratios, it was concluded that both the water-gas shift and Boudouard reactions were the most critical.

Assessment of Greenhouse Gas Emissions from Hydrogen Production Processes: Turquoise Hydrogen vs. Steam Methane Reforming

Hydrogen has received substantial attention because of its diverse application in the energy sector. Steam methane reforming (SMR) dominates the current hydrogen production and is the least expensive endothermic reaction to produce grey hydrogen. This technology provides the advantages of low cost and high energy efficiency; however, it emits an enormous amount of CO2. Carbon capture storage (CCS) technology helps reduce these emissions by 47% to 53%, producing blue hydrogen. Methane pyrolysis is an alternative to SMR that produces (ideally) CO2-free turquoise hydrogen. In practice, methane pyrolysis reduces CO2 emissions by 71% compared to grey hydrogen and 46% compared to blue hydrogen. While carbon dioxide emissions decrease with CCS, fugitive methane emissions (FMEs) for blue and turquoise hydrogen are higher than those for grey hydrogen because of the increased use of natural gas to power carbon capture. We undertake FMEs of 3.6% of natural gas consumption for individual processes. In this study, we also explore the utilization of biogas as a feedstock and additional Boudouard reactions for efficient utilization of solid carbon from methane pyrolysis and carbon dioxide from biogas. The present study focuses on possible ways to reduce overall emissions from turquoise hydrogen to provide solutions for a sustainable low-CO2 energy source.

Chemical Looping Reforming with Perovskite-Based Catalysts for Thermochemical Energy Storage

The performance of a perovskite-based oxygen carrier for the partial oxidation of methane in thermochemical energy storage applications has been investigated. A synthetic perovskite with formula La0.6Sr0.4FeO3 has been scrutinized for Chemical Looping Reforming (CLR) of CH4 under fixed-bed and fluidized-bed conditions. Temperature-programmed reduction and oxidation steps were carried out under fixed-bed conditions, together with isothermal reduction/oxidation cycles, to evaluate long-term perovskite performance. Under fluidized-bed conditions, isothermal reduction/oxidation cycles were carried out as well. Results obtained under fixed-bed and fluidized-bed conditions were compared in terms of oxygen carrier reactivity and stability. The oxygen carrier showed good reactivity and stability in the range 800–1000 °C. An overall yield of 0.6 Nm3 of syngas per kg of perovskite can be reached per cycle. The decomposition of CH4 catalyzed by the reduced oxide can also occur during the reduction step. However, deposited carbon is easily re-gasified through the Boudouard reaction, without affecting the reactivity of the material. Fluidized-bed tests showed higher conversion rates compared to fixed-bed conditions and allowed better control of CH4 decomposition, with a H2:CO ratio of around 2 and CO selectivity of around 0.8. However, particle attrition was observed and might be responsible for a loss of the inventory of up to 9%w.

Sequential hydrothermal carbonization and CO2 gasification of sewage sludge for improved syngas production with mitigated emissions of NOx precursors

Due to high moisture and protein contents in sewage sludge (SS), conventional thermal treatment of SS is energy-intensive and a large amount of harmful nitrogen-containing gases are emitted. In this study, a sequential hydrothermal carbonization (HTC) and CO2 gasification system has been proposed to effectively improve the gasification efficiency and considerably reduce the emissions of NOx precursors (i.e., NH3 and HCN) in SS treatment. Yield and quality of syngas were comprehensively investigated during CO2 gasification in terms of various temperatures with different dosages of CaO additive in HTC, and varied reaction temperature and CO2 percentage in gasification process. On the whole, CO2 gasification of SS derived hydrochar (HC) demonstrated obvious reduction of tar formation from 10.9 to 6.8 % and enhancement of calorific value of formed syngas from 14.1 to 15.7 MJ/Nm3. Production of NOx precursors was greatly reduced due to formed non-active quaternary-N in HC, while HTC with CaO favored the mitigated NOx precursors in syngas owing to enriched pyrrole-N and quaternary-N therein. Catalytic tar decomposition and Boudouard reaction in CO2 gasification were responsible for the distinct reduction of tar formation, and notable increase of carbon conversion ratio and syngas yield. Although facilitated catalytic gasification in CO2 atmosphere can maximize syngas yield, lower portion of CO2 (ca. 20 %) was more beneficial to drastically mitigate emissions of NOx precursors, especially the reinforced transformation of NH3 to N2. The fundamental knowledge could ultimately help to achieve significant abatement of NOx precursors during CO2 gasification for improved syngas production.

A Self-Forming CO2/O2 Co-Transport Dual-Phase Membrane for Oxidative Coupling of Methane

Direct methane conversion (DMC) has garnered considerable interest from both industries and academia in recent years due to its great economic potential created by significantly increased price differential between low-cost natural gas (NG) and the derived value-added chemicals. Oxidative coupling of methane (OCM), which transforms CH4 into ethylene (C2H4) with molecular O2 as the oxidant in a single step, is one of the most studied DMCs. However, a major technical challenge for the OCM process is the difficulty to achieve high CH4 conversion at high C2 (ethane or ethylene) selectivity. The rudimentary cause for this “tradeoff” behavior is that the products (C2H6 or C2H4) are chemically more reactive than the reactant (CH4). To overcome this thermodynamic hurdle, minimizing the oxidizing power of the oxidant or lowering the local oxygen partial pressure is key. In this presentation, we show a CO2/O2 co-transport membrane reactor for OCM conversion. The results explicitly show that the permeated O2 can react preferably with CH4 as in the conventional OCM to form C2H6; the latter then undergoes thermal cracking into C2H4 and H2. The roles of the permeated CO2 are assumed to be reacting with H2 via reverse water gas shift (RWGS) reaction to shift the C2H6 thermal cracking; another role of CO2 is assumed to be mitigating coke formation via Boudouard (RB) reaction.

A high-performance direct carbon solid oxide fuel cell powered by barium-based catalyst-loaded biochar derived from sunflower seed shell

Direct carbon solid oxide fuel cell (DC-SOFC) is one of the most attractive thesises for clean and efficient utilization of solid carbon to produce electricity. According to the operating principle, DC-SOFC performance is closely associated with the carbon sources and catalysts of the reverse Boudouard reaction. Here, we report a high-performance DC-SOFC powered by the biochar derived from sunflower seed shell (SSS) with barium-based catalyst loaded. The physicochemical properties of the SSS biochar are characterized and analyzed detailly. The electrolyte-supported symmetrical SOFC fueled with the SSS biochar gives an output of 216 mW cm−2 at 850 °C, indicating a great potential of the SSS biochar for DC-SOFCs. More importantly, the best output of 265 mW cm−2 and open circuit voltage of 1.03 V are obtained from DC-SOFC operated on 5 wt% barium-loaded SSS biochar, which is comparable to the output of 273 mW cm−2 from the hydrogen-fueled SOFC at 850 °C with the identical configuration. The superiorities of the SSS biochar and barium-based catalyst are also reflected in the operation stability and fuel utilization of DC-SOFCs. The discharge platforms are stable and the longest lifetime is up to 28.0 h under 50 mA with the fuel utilization of 31.3%, which is very excellent and competitive. This work provides a new idea for the effective utilization of the SSS biochar and other biomass for DC-SOFCs.

Air-CO2 and oxygen-enriched air-CO2 biomass gasification in an autothermal downdraft gasifier: Experimental studies

The mounting CO2 emission and rapid depletion of fossil fuels are two significant challenges for sustaining growing energy requirements and keeping the environment clean. Biomass gasification using CO2 as a gasifying agent may be one of the alternative techniques to tackle such emerging problems. CO2 behaves as an inert gas at low temperatures and can be converted to CO at high temperatures. In the present study, air-CO2 and oxygen-enriched air-CO2 biomass gasification are successfully conducted in the autothermal reactor. The impacts of varying concentrations of CO2 and oxygen in the gasifying agent on the performance of the gasifier are analyzed. The CO2 content in the gasifying agent is varied from 0 to 45 vol% at two different oxygen concentrations (21 and 35 vol%). The reactor used is an Imbert-type downdraft gasifier with a thermal capacity of approximately 10 kW. The results reveal that the yield of CO in the producer gas increases compared to air gasification resulting in a higher heating value of the producer gas. However, the average temperature in the gasifier reduces with increasing CO2 percentage in the gasifying agent. Upon increasing the O2 fraction from 21 to 35 vol%, while keeping 30 vol% CO2 content constant, CO content is found to upsurge from 23.96 to 31.37 vol%. The inclusion of CO2 inside the gasifier promotes the endothermic Boudouard reaction that causes the conversion of CO2 into CO.

Prereduction Behavior of Manganese Ores With Solid Carbon and in CO/CO2 Gas Atmosphere

The prereduction reactions in the submerged arc furnace (SAF) are highly decisive of the total carbon, and energy consumption of the ferromanganese process. Therefore, understanding the dependency of prereduction behavior on ore characteristics and furnace conditions is of paramount importance. Prereduction behavior of Comilog, Nchwaning and UMK ores with solid carbon was studied in an open 75 kVA induction furnace set up simulating the conditions of an industrial SAF. In addition, the ores were thermogravimetrically studied with non-isothermal heating to 1000 °C in a flowing 70/30 CO/CO2 atmosphere. Gasification of carbon according to Boudouard reaction was considered significant for carbonate ores in induction furnace setup. UMK had a greater extent of prereduction compared to Nchwaning which is low in carbonates and Comilog which is known to have a higher CO reactivity at similar CO contents. TGA rate curves shows that prereduction of UMK ore occurred with two major distinctive steps. The first one was a combination of prereduction reactions and decomposition of carbonates with a peak temperature of 700 °C, and the second peak was the decomposition of calcite at 900 °C. The O/Mn ratio for UMK shows that prereduction is already completed prior to the second decomposition peak at 900 °C. In addition to prereduction reactions, Nchwaning is also characterized by an endothermic step which is decomposition of carbonates at 900 °C. Comilog ore produced the most fines followed by Nchwaning and lastly UMK on decrepitation.

Numerical investigation of the reaction kinetics of dry reforming of methane over the yolk–shell and single-atom alloy catalysts

Dry reforming of methane (DRM) over Ni-based supported catalysts has been widely studied due to Ni's low cost and high activity. Despite their excellent performance, side reactions such as methane decomposition and Boudouard reaction can cause severe coke formation leading to catalyst deactivation. Our recent work reported that both yolk–shell morphology and Pt-Ni interaction in single-atom-alloy (SAA) structures could maintain the DRM activity. However, the effect of morphology and Pt-Ni interaction could not be elucidated. In this work, we studied the reaction kinetics of DRM by proposing a detailed elementary reaction mechanism with 12 surface species and 17 elementary steps over the Ptx-NiCe@SiO2 and Pt0.25-NiCe/SiO2WI catalysts. Due to the different DRM activity over the wet-impregnated and yolk–shell structures, we examined multiple reaction models to explain the effect of morphology and Pt-Ni interaction on the DRM activity. Our results show that the reverse Boudouard reaction and dissociative adsorption of CO2 and CH4 are the rate-limiting steps. The desorption of CO* and H* is also critical to products yield and selectivity. Compared with Pt0.25-NiCe/SiO2WI catalyst, the C* removal followed by the fast CO* desorption is more favored on Pt0.25-NiCe@SiO2 SAA, suggesting the reverse Boudouard reaction prevents the catalyst deactivation by coking. The high O* and low H* coverages are observed on Pt0.25-NiCe@SiO2 SAA due to the confined yolk–shell morphology and enhanced Pt-Ni interaction in SAA structures, respectively. Both these effects can lead to facile C* removal in the Pt0.25-NiCe@SiO2 SAA catalyst leading to a stable DRM activity.

Thermal conductivity of porous refractory material after aging in service with carbon pick-up

Medium Density Insulating Boards, based on vermiculite, are used for the insulating lining of ladles in steel production. In service, carbon monoxide is generated from oxidation of neighbouring Magnesia – Carbon bricks and diffuses through the refractory brick lining to deposit carbon in the colder insulating lining via the Boudouard reaction. Characterization by laser flash and hot disk measurements of original and post-mortem samples reveals an approximate increase by 26% in the overall thermal conductivity of the board to 0.34 W m−1 K−1 at room temperature following 15 months service. This is attributed to carbon and chloride phases detected by X-ray fluorescence and energy dispersive X-ray spectroscopy in the outermost zone of the board, cut into three zones for analysis along the heat flow direction. The increase in thermal conductivity is reduced to 17% when the thermal gradient in service conditions is considered.

Transient Behavior of CO and CO2 Hydrogenation on Fe@SiO2 Core–Shell Model Catalysts—A Stoichiometric Analysis of Experimental Data

The hydrogenation of CO and CO2 from industrial exhaust gases into CH4 represents a promising method for sustainable chemical energy storage. While iron-based catalysts are in principle suitable for that purpose, the active metal Fe undergoes a complex transformation during the chemical reaction process. However, only little is known about the change in catalytically active species under reaction conditions, primarily caused by structural changes in the catalyst material, so far. By using core–shell model materials, factors that alter the catalyst structure can be excluded, making it possible to observe the direct influence of the reactants on the activity in the present work. Furthermore, stoichiometric analysis was used as a key tool for the evaluation of individual key reactions in the complex reaction network purely from experimental data, thus making it possible to draw conclusions about the catalyst state. In the case of CO hydrogenation, the presumed Boudouard reaction and the associated carburization of the catalyst can be quantified and the main reaction (CO methanation) can be determined. The results of the CO2 hydrogenation showed that the reverse water–gas shift reaction mainly took place, but under an ongoing change in the catalytic active iron phase. Due to the systematic exchange between CO and CO2 in the reactant gas stream, a mutual influence could also be observed. The results from the stoichiometric analysis provide the basis for the development of kinetic models for the key reactions in future work.

Parameters to estimate the metal dusting attack in different gases

The relation between the experimentally observed metal dusting attack and parameters calculated from the test conditions is analysed. Commercial alloys were exposed for nearly 1000 h at elevated pressure in four gas mixtures. The gases had a constant carbon activity regarding the synthesis gas and the Boudouard reaction. However, these parameters did not correlate properly with the observed aggressivity. Alternative descriptions by the CO/H2 ratio, the carbon activity after water gas shift reaction and at metastable equilibrium are discussed. The results show that the whole set of reactions between gas and solid needs to be considered to describe the complex system.

Valorization of sludge using microwave pyrolysis for green bio-energy: Combined effects of key parameters on the directional optimization of high-quality syngas

To directionally convert sludge into the high-quality syngas, the effects of various parameters on the biogas produced by the sludge microwave pyrolysis are explored, and the syngas generation mechanism under the synergistic effect of parameters is revealed. The results showed that the pyrolysis final temperature, reaction time, and the amount of the microwave absorber were the key factors that affected the biogas yield. A response surface analysis was used to explore the synergistic effect of each key parameter on the yield and the lower heating vale (LHV) of syngas. The pyrolysis temperature was the key to driving syngas generation. Properly prolonging the reaction time decreased the formation of tar by-products and increased the syngas yield. The addition of a microwave absorber increased the heating rate by enhancing the conversion efficiency of microwave energy, and this contributed to accelerating the dehydrogenation and the Boudouard reactions to promote the generation of H2 and CO. Under high temperature conditions (900 °C), a higher syngas yield (10.25–34.31 mol/kgDS) and LHV (4.85–14.53 MJ/kgDS) were obtained in a shorter period time by synergistically optimizing the amount of microwave absorbers (8–10 g) and the reaction time (28–40 min). As the pyrolysis temperature increased, the H2 content gradually rose to the peak, while the content of CO continued to increase. By analyzing the evolution of the specific pyrolysis products, the secondary pyrolysis of bio-oil at high temperatures and the Boudouard reaction were found to be the primary pathways that promoted syngas generation. This research provides strategic guidance for producing high-quality syngas using the microwave pyrolysis of waste biomass, thereby minimizing the exploration cost of basic experiments and providing directional control of the syngas quality.

CO-promoted low-temperature conversion of CH4 to hydrogen and carbon nanotubes on Nanocrystalline Cr-doped ferrite catalyst

Catalytic decomposition of methane (CDM) to H2 and multiwalled carbon nanotubes (MWCNTs) was achieved by a nanocrystalline Cr-doped ferrite (FeCr) catalyst at 500 °C and atmospheric pressure with minor cofed CO. The exothermic Boudouard reaction increased the temperature and H2 from CDM at catalyst surface that induced Fe2+ reduction to Fe0. The Fe0 clusters along with the CO-originated surface oxygens enabled transfer of C and H to sustain the surface CDM and CO reactions. The metallic Fe-enabled C transfer led to the formation of MWCNTs. The Cr6+/3+ dopants facilitated the Fe redox cycles and maintained surface oxygens for high catalytic activity.

Boudouard reaction under graphene cover on Ni(1 1 1)

We investigated the interaction of CO with graphene/Ni(111) and the Boudouard reaction at 3.7 mbar by Near Ambient Pressure X-Ray Photoemission Spectroscopy (NAPXPS), i.e. at one order of magnitude higher pressure than previously explored in-operando conditions. In this regime, CO intercalates under the graphene layer causing its partial detachment from the Ni substrate. The so-obtained high local CO coverage opens the way to CO2 formation via the Boudouard reaction. Its onset is witnessed by observing physisorbed CO2 accumulating below the graphene cover. The so-generated additional carbon atoms transform carbide into graphene, causing the expansion of the graphene islands. In addition, CO adsorption occurs on the strongly interacting areas of the graphene layer, confirming previous results obtained by some of us at low temperatures and in ultra-high vacuum conditions.

An advanced, comprehensive thermochemical equilibrium model of a downdraft biomass gasifier

A stoichiometric model is formulated for predicting the syngas yield from the reduction zone of a downdraft biomass gasifier. It incorporates the thermodynamic equilibrium of the global gasification reaction, predicts the concentration of the minor gasification products of hydrogen sulphide and ammonia as the sulphur-based and nitrogen-based contaminants, respectively, and implements a new empirical correlation, formulated using existing pertinent experimental data, to account for the mass tar yield. The governing set of model equations is solved in a fully coupled manner, with the boudouard reaction employed to predict char output and the ammonia synthesis reaction used to predict ammonia production. The model does not require the use of correction factors and satisfactorily predicts the concentration of methane, a shortcoming that has tended to plague existing equilibrium models. The syngas composition, tar and char yields, gasification temperature, cold gas efficiency and lower heating value are obtained for various biomass feedstock with a specific ultimate analysis, for different equivalence ratios and varying moisture content. Where possible, predictions are compared with corresponding experimental data and found to be in very good agreement.