Ignition of CO2 methanation using DBD-plasma catalysis in an adiabatic reactor

In this work, a novel strategy of the use of dielectric barrier discharge (DBD) plasma-catalysis for exothermic reactions is presented. DBD-plasma is used as reaction ignitor, rather than the classical approach of continuous operation, by taking advantage of the synergy between catalytic plasma activation from room temperature and a self-sustained exothermic reaction. CO2 methanation reaction was performed in a thermal insulated reactor using an active nickel-based catalyst loaded in two catalytic bed sections, with electrodes implemented solely in the first section. DBD plasma was employed to activate the reaction from cold conditions with the subsequent increase in reactor temperature and, finally, reaction was self-sustained by thermal-catalysis. The experimental results pointed out the sensitive dependence of the reactor temperature on the gas flow rate during the plasma operation. Low-energy conditions were found in which the reaction could operate in autothermal mode, after plasma shut-off. Power and start-up time were optimized, obtaining a considerable low start-up time from cold conditions (25 ◦C) of only 3 min. Besides, the autothermal operation mode was maintained for 8 h without any energy input. This proof-of-concept work demonstrates that plasma can be implemented as initial power ignition in exothermic reactions using proper reactor design and conditions, and then, the reactor can operate in autothermal mode

Design of a Multi-Tubular Catalytic Reactor Assisted by CFD Based on Free-Convection Heat-Management for Decentralised Synthetic Methane Production

A simple reactor design for the conversion of CO2 methanation into synthetic methane based on free convection is an interesting option for small-scale, decentralised locations. In this work, we present a heat-management design of a multi-tubular reactor assisted by CFD (Ansys Fluent®) as an interesting tool for scaling-up laboratory reactor designs. The simulation results pointed out that the scale-up of an individual reactive channel (d = 1/4′, H = 300 mm) through a hexagonal-shaped distribution of 23 reactive channels separated by 40 mm allows to obtain a suitable decreasing temperature profile (T = 487-230 °C) for the reaction using natural convection cooling. The resulting heat-management configuration was composed of three zones: (i) preheating of the reactants up to 230 °C, followed by (ii) a free-convection zone (1 m/s air flow) in the first reactor section (0-25 mm) to limit overheating and, thus, catalyst deactivation, followed by (iii) an isolation zone in the main reactor section (25-300 mm) to guarantee a proper reactor temperature and favourable kinetics. The evaluation of the geometry, reactive channel separation, and a simple heat-management strategy by CFD indicated that the implementation of an intensive reactor cooling system could be omitted with natural air circulation

Environmental impact assessment of synthetic natural gas of renewable origin from pilot plant

There is currently a lot of pressure on the transition to fuels with less impact on the environment. The European Commission is applying different directives in order to establish a clear route to greener fuels. The present work is devoted to study the environmental impact of the production of this synthetic gas and to compare it with fossil natural gas. The method used in this study is by the life cycle assessment with the support of an experimental data from a pilot. The work presents different scenarios of possible cases and feasible improvements, studying the different environmental impacts of the cases

Fischer-Tropsch synthesis: Towards a highly-selective catalyst by lanthanide promotion under relevant CO2 syngas mixtures

The role of lanthanides as promoters on cobalt-based catalysts for Fischer-Tropsch synthesis was evaluated under relevant biomass-derived syngas mixtures. Cerium, lanthanum and a combination of them were impregnated on an industrial cobalt-based micro-catalyst. Lanthanide incorporation did not affect significantly the morphology of the catalyst, although it reduced the available surface cobalt. Catalytic tests revealed that both the presence of carbon dioxide in the feed and lanthanides in the catalyst led to similar outcomes; higher selectivity to long-chain hydrocarbons, at the expense of reactivity. Reaction experiments were well aligned with in-situ DRIFTS measurements, which evidenced the modification of the initial reaction mechanism, CO2 conversion and the presence of lower CO-cobalt coverages. This work reports two relevant findings for FTS development. Firstly, the presence of carbon dioxide is beneficial for long-chain hydrocarbon production. Secondly, the incorporation of lanthanides increases the production of gasoline, kerosene and diesel fractions

Bimetallic cobalt catalysts promoted by La2O3 for the production of high-calorie synthetic gas

A new catalytic route for the production of a high-calorie synthetic gas (40-60 MJ/Nm3), composed by C1-C4 hydrocarbons, has industrial interest for gas applications and locations with high heating requirements. In this work, a series of bimetallic Co-X (X = Ni, Pt and Fe) catalysts supported on La2O3 promoted Al2O3 micro-spheres were evaluated using both CO2 and CO carbon sources under mild temperature (T = 200-300 °C), moderate pressure (P = 10 bar·g) and relatively high gas hourly space velocity (40,000 N mL/gcat·h). Experimental results proved that the incorporation of nickel as a second metal is beneficial for high-calorie gas application. Besides, catalytic results showed that the utilization of CO as carbon source is beneficial in both conversion and C1-C4 hydrocarbon selectivities. Co-Ni presented the most interesting results, leading to a heating value of 57.9 MJ/Nm3 (40.01 % CH4 and 50.04 % C2-C4 hydrocarbon) at 250 °C through CO hydrogenation. The enhanced catalytic performance achieved over bimetallic Co-Ni was attributed to CoNi alloy catalytic activity, high reducibility (73.82 %), active metal content (9.65x10-4 mmol/g) and appropriate acid-basic sites for COx activation. In contrast, the conversion of CO2 to high-calorie gas was found to be more challenging and lower gas heating values were achieved (39.73 MJ/Nm3). In this case, an adapted reactor concept using a dual bimetallic catalyst and different reaction conditions is hereby proposed to shift selectivity towards the targeted products. This findings represent a step forwards in catalytic engineering for the development of high-calorie synthetic gas reactors

Passivation of Co/Al2O3 Catalyst by Atomic Layer Deposition to Reduce Deactivation in the Fischer-Tropsch Synthesis

The present work explores the technical feasibility of passivating a Co/γ-Al2O3catalyst byatomic layer deposition (ALD) to reduce deactivation rate during Fischer-Tropsch synthesis (FTS).Three samples of the reference catalyst were passivated using different numbers of ALD cycles (3, 6and 10). Characterization results revealed that a shell of the passivating agent (Al2O3) grew aroundcatalyst particles. This shell did not affect the properties of passivated samples below 10 cycles, inwhich catalyst reduction was hindered. Catalytic tests at 50% CO conversion evidenced that 3 and6 ALD cycles increased catalyst stability without significantly affecting the catalytic performance,whereas 10 cycles caused blockage of the active phase that led to a strong decrease of catalytic activity.Catalyst deactivation modelling and tests at 60% CO conversion served to conclude that 3 to 6 ALDcycles reduced Co/γ-Al2O3deactivation, so that the technical feasibility of this technique was provenin FTS

Facile integration of ordered nanowires in functional devices

The integration of one-dimensional (1D) nanostructures of non-industry-standard semiconductors infunctional devices following bottom-up approaches is still an open challenge that hampers the exploita-tion of all their potential. Here, we present a simple approach to integrate metal oxide nanowires inelectronic devices based on controlled dielectrophoretic positioning together with proof of conceptdevices that corroborate their functionality. The method is flexible enough to manipulate nanowiresof different sizes and compositions exclusively using macroscopic solution-based techniques in conven-tional electrode designs. Our results show that fully functional devices, which display all the advantagesof single-nanowire gas sensors, photodetectors, and even field-effect transistors, are thus obtained rightafter a direct assembly step without subsequent metallization processing. This paves the way to lowcost, high throughput manufacturing of general-purpose electronic devices based on non-conventionaland high quality 1D nanostructures driving up many options for high performance and new low energyconsumption devices

Ethyl octyl ether synthesis from 1-octanol and ethanol or diethyl carbonate on acidic ion-exchange resins

[cat] La utilització de bioetanol per produir compostos diesel seria una forma d’incrementar la producció de diesel (deficitària a Europa), i tan ho més important, de millorar-ne la qualitat i així reduir les emissions nocives de material particulat, òxids de nitrogen, sofre i compostos volàtils. Un èter derivat del bioetanol que té excel·lents propietats com a combustible diesel és l’etil octil èter. L’objectiu d’aquesta tesis és l’estudi de la producció d’etil octil èter en fase líquida mitjançant catalitzadors heterogenis. Això implica la selecció dels reactius i catalitzadors més adequats des d’un punt de vista de rendiment i selectivitat. A més, l’estudi termodinàmic i cinètic de la reacció en permeten tan el disseny com la optimització del procés. Els assajos catalítics s’han realitzat en un reactor de tanc agitat operant en discontinu i en un reactor tubular operant en continu utilitzant resines àcides de bescanivi iònic com a catalitzadors (P=25 bars, T=130-190ºC). Els resultats experimentals han mostrat que el compost etil octil èter es pot formar mitjançant l’etilació de 1-octanol a partir de dos reactius provinents d’origen renovable, l’etanol i el dietil carbonat. La comparació de dos agents etilants, etanol i dietil carbonat, ha revelat que es poden obtenir similars selectivitats i rendiments en temps de reacció elevats mitjançant resines àcides de bescanvi iònic, preferiblement de baix contingut de divinil benzè. Tanmateix, l’ús de dietil carbonat és menys competitiu en temps de reacció curts. A més, la formació de CO2 via dietil carbonat i la més alta disponibilitat d’etanol suggereix que l’ús de l’alcohol és preferit des d’un punts de vista tan industrial com ambiental. L’estudi termodinàmic ha revelat que els valors relativament alts de la constant termodinàmica d’equilibri químic en la formació de l’etil octil èter asseguren alts nivells de conversió en un procés industrial. Finalment, un exhaustiu estudi cinètic ha revelat que la velocitat de formació d’etil octil èter a partir d’etanol i 1-octanol és altament inhibit per l’adsorció de l’aigua en els centres actius de les resines. Finalment, s’ha observat que les velocitats de reacció són optimitzades utilitzant una raó molar 1-octanol / etanol de 1.4, un diàmetre de partícula menor a 0.63 mm d’Amberlyst 70 i una temperatura de reactor de 190ºC.[eng] Ethyl octyl ether is a bioethanol-derived component that has excellent properties as diesel fuel. This work proved that ethyl octyl ether can be produced successfully in liquid-phase at the temperature range of 130-190ºC by using acidic ion-exchange resins, as suitable and economic catalysts. The use of two promising reactants that can be a renewable compound source, ethanol and diethyl carbonate, have been explored. Both reactants are able to ethylate 1-octanol and form the desired product. However, an identical industrial drawback is observed on both reactants, the loss of ethyl groups to form diethyl ether, which is not suitable as diesel compound. In order to minimize the diethyl ether formation, and in this way, to maximize the ethyl octyl ether production; several commercial acidic resins were tested, or else, prepared and subsequently tested. The best catalysts are those allowing 1-octanol to access to most sulfonic groups of the catalyst. Such desired properties can be achieved by decreasing the amount of crosslinking agent of resins, as a result, the resin has a high capacity to swell and at the same time a low gel-phase density. Another tailoring technique that lets 1-octanol to access to the vast majority of sulfonic groups is by locating them only in the least crosslinked domains of the gel-phase. Both tailoring techniques involve higher selectivity to ethyl octyl ether, which can be extrapolated to other bulky molecules. However, the former involves a reduction of the catalytic activity per volume unit of the catalyst bed, and the latter, per mass unit. Interestingly for the resin designers and exploiters, it is proved that the Inverse Steric Exclusion Chromatography characterization technique allows predicting the catalyst performance in polar environments with high accuracy. In such a manner that polymeric catalysts having high specific volume of the swollen gel-phase and predominant domains with low polymer density are desired to enhance selectivity and yield to ethyl octyl ether formation. The comparison between both ethylating agents, ethanol and diethyl carbonate, revealed that similar selectivity and yield can be potentially obtained over acidic resins. Nevertheless, diethyl carbonate is less competitive at shorter reaction times in a batch reactor, or at lower catalyst mass in continuous units, as a result of the slow decomposition of the required intermediate, ethyl octyl carbonate. On the other hand, the production of CO2 via diethyl carbonate and the availability of ethanol nowadays suggest that use of the alcohol to form ethyl octyl ether is preferred. Reaction rates to form ethyl octyl ether from ethanol and 1-octanol showed similar, or slightly higher, dependency on the temperature than that to form the main side product, diethyl ether. Thus, an enhancement of the reactor temperature clearly increases the feasibility of an ethyl octyl ether production unit. Accordingly, the use of chlorinated resins, which proved to be thermally stable up to 190ºC in the ethyl octyl ether production, is desired. Among the commercial ones, Amberlyst 70 is the most suitable catalyst in terms of selectivity to ethyl octyl ether due to its low polymer density in aqueous swollen state. Such polymeric expansion should be taken into account to not block the liquid flow when fixed-bed reactors are employed. That is to say, Amberlyst 70 must be loaded to the reactor in a swollen state. The relatively large values found of the thermodynamic equilibrium constant of ethyl octyl ether formation assure high conversion levels in an industrial etherification process. Interestingly, the equilibrium values of the formation of diethyl ether are around a half than those of ethyl octyl ether (150-190ºC). A comprehensive kinetic analysis enlightened that reaction rates to form ethyl octyl ether on Amberlyst 70 are strongly inhibited by the presence of water. Thus, reaction rates would be enhanced if most water is removed from bioethanol

An insight into the heat-management for the CO2 methanation based on free convection

This article presents a novel heat-management approach for CO2 valorization to synthetic natural gas based on free convection to the environment, without requirements of heat-exchange services. With this aim, a reactor channel was built (d = 4.6 mm, L = 250 mm) and tested at different conditions of inlet temperatures, gas hourly space velocities and pressures using an active nickel/ceria-based catalyst. After experimentation, a CFD model was developed, validated and employed for an efficient sensitive analysis of the most suitable reaction conditions. The simulation criteria were obtaining high CO2 conversion level and restricting overheating to avoid catalyst and reactor degradation. Then, the optimal conditions found by CFD modelling were successfully validated at lab-scale. The CO2 conversion level experimentally obtained was 93%, by using a decreasing temperature profile in the range of 830-495 K, operating at a pressure of 5 atm and a gas hourly space velocity of 11,520 h−1. The proposed reactor configuration guarantees an efficient heat management along the reactor channel by using feasible conditions of pressure, temperature and flowrate for its implementation in small-scale applications, where the use of the exothermic heat is less profitable

Satisfactory catalyst stability in SNG production using real biogas despite sulfur poisoning evidences at different reactor zones

The performance of a nickel-ceria micro-catalyst in biogas methanation was evaluated in a complete pilot plant during 1,000 h. The core of the exothermic methanation process consisted in two micro-reactors using a decreasing temperature profile, intermediate water removal and moderate pressure. The obtained gas quality and the reactors temperature profile remained constant during operation, indicating no signs of catalyst deactivation. After the experimental campaign, catalyst samples from different reactors sections were withdrawn, collected and independently characterized. It has been demonstrated that the different reaction conditions, in which the catalyst operated, played a significant role on the different level of degradation of the catalyst samples. On one hand, various characterization techniques agreed that sintering of nickel and ceria nanoparticles (+10-30%) and loss of surface area (−20%) was restricted to the initial reactor zones, which is attributed to the higher operation temperatures. On the other hand, despite the cautions undertaken for biogas cleaning and gas monitoring, sulfur was detected along the entire reactor longitudinal profile (0.25-0.91%). Accordingly, a progressive diffuse flow poisoning mechanism is expected from very long operation times. In particular, higher amount of sulfur was detected in the latest reactor zones, which operated at lower temperatures and under more oxidizing conditions. Beneficially, sulfur was predominantly detected as Ce2O2S phase, confirming thereby the crucial sacrificial role of CeO2 that allows for maintaining the catalytic activity of nickel active sites. The overall outcome of this work is very promising and reveals a sufficient catalyst lifespan for industrial application