17:00
Unconventional activation/energy supply methods 1
Chair: Víctor Antonio de la Peña O'Shea
17:00
20 mins
#24
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CATALYST DESIGN FOR OXIDATIVE COUPLING OF METHANE IN A GAS-SOLID VORTEX REACTOR
Saashwath Swaminathan Tharakaraman, Guy Marin, Mark Saeys
(presenter: Mark Saeys)
Abstract: Oxidative coupling of methane (OCM) is a promising route for the direct synthesis of C2 hydrocarbons from methane according to the following reactions1.
2CH4 + O2 → C2H4 + 2H2O ΔHr0 = -282 kJ mol-1 ( 1 )
2CH4 + 0.5O2 → C2H6 + H2O ΔHr0 = -177 kJ mol-1 ( 2 )
The presence of O2 and the high reaction temperatures limit C2 yields to 25% for most catalysts2. In the gas-solid vortex reactor (GSVR), a rotating fluidized bed is obtained by tangential injection of gas at high velocities (Fig. 1)3, creating a dense bed and high gas-solid slip velocities, resulting in increased heat, mass and momentum transfer and a decrease in gas phase residence time. Recently, Vandewalle et al. showed that the good thermal back mixing combined with limited species back mixing in the GSVR can potentially improve C2 yields4. The high temperatures, the high solids velocity and the limited space times require the design of highly active, thermally and mechanically stable catalysts. This work focusses on the development of such a supported catalyst. Cold flow experiments show that a stable catalyst bed can be formed and less than 1% of the catalyst is entrained over a 1 hour experiment. Experiments with conventional Sr/La2O3 catalyst pellets show instantaneous pulverization and entrainment. Fixed bed experiments at GSVR conditions of temperature and space time show a reasonable methane conversion of 5-10% with 50% C2 selectivity under intrinsic kinetic regime. First proof-of-concept OCM experiments in the GSVR will be reported. Microkinetic simulations indicate a methane conversion of 10% and a C2 selectivity above 50%.
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17:20
20 mins
#70
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OPTIMAL CYCLIC OPERATION OF A MICROWAVE-ASSISTED REACTOR FOR METHANE VALORIZATION UNDER NON-OXIDATIVE CONDITIONS
Clemens Lindscheid, Ignacio Julian, Reinaldo Hernandez, Reyes Mallada, Jesus Santamaria, Sebastian Engell
(presenter: Clemens Lindscheid)
Abstract: During the valorization of methane under non-oxidative conditions (MNOC), a decrease in methane conversion over time due to the deposition of coke can be observed. Recently, the use of microwave-assisted heating was proposed as an alternative to conventional heating in order to reduce polyaromatics production and, thus, coking in the MNOC process. Although the gas-solid temperature gradient generated by the microwave radiation was effective for the reduction of catalyst deactivation, coking cannot be fully avoided1. In the MNOC process assisted by microwave-heating, the coke deposition on the catalyst causes the dielectric properties of the heated material to change leading to locally high temperatures, which again affect the coke deposition.
To restore methane conversion and therefore the economic profitability of the process, the MNOC operation has to be terminated and the catalyst must be regenerated by burning out the coke deposits. This cyclic operation raises two main questions: How to best operate the reactor during normal operation and when to switch to regeneration mode.
In this work, we show the methodology for optimizing the cyclic operation of the microwave reactor under operational constraints and how this operation can be realized in practice using industrial automation systems.
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17:40
20 mins
#33
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INVESTIGATION OF DIELECTRIC BARRIER DISCHARGE REACTOR FOR AMMONIA SYNTHESIS
sirui Li, Thijs van Raak, fausto Gallucci
(presenter: Sirui Li)
Abstract: Ammonia synthesis has been one of the most important topics in chemical engineering for more than a century. The conventional process for ammonia synthesis requires high temperature, high pressure and accompanied by a large amount of CO2 emission 1. Non-thermal plasma technology has been considered as a promising alternative due to its advantages of mild reaction condition, easy to be coupled with renewable energy and so on 2. Dielectric barrier discharge (DBD) plasma reactor has been widely applied in many fields such as ozone production and biomedical treatment 3. In this research, a coaxial DBD reactor was investigated for the synthesis of ammonia. Different discharge gap sizes and electrode materials including copper, stainless steel and aluminium were tested along with variations of process parameters such as residence time, the ratio of reactants, voltage and power supplied. Moreover, Ru/Al2O3 was packed inside the reactor, the energy efficiency and ammonia yield were investigated. In addition, the temperature profile of the packed and unpacked DBD reactor was analyzed regarding the thermal effect on ammonia production. The results presented in this research provides useful information for the design of the DBD reactor to achieve better performance in ammonia synthesis.
References
1. Li, S., Medrano Jimenez, J., Hessel, V. & Gallucci, F., Processes, 2018, 6, 248.
2. Hong, J., Prawer, S. & Murphy, A. B. , ACS Sustain. Chem. Eng. 2018, 6, 15–31.
3. Brandenburg, R., Plasma Sources Sci. Technol. 2017, 26, 53001.
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18:00
20 mins
#63
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LOW-TEMPERATURE PLASMA-CATALYTIC NITROGEN FIXATION
Nikolay cherkasov
(presenter: Nikolay Cherkasov)
Abstract: Ammonia is the second largest produced industrial chemical used as a raw material for numerous chemicals. Besides, there is a growing interest in applications of ammonia as electrical energy storage chemical, as fuel and in the selective catalytic reduction of NOx. These applications demand on-site distributed ammonia production under mild process conditions.
In the work, we investigated different transition metal and oxide catalysts supported on γ-Al2O3 for plasma-catalytic ammonia production in a dielectric barrier discharge (DBD) reactor. We studied the influence of the N2/H2 feed ratio, specific energy input, reaction temperature, metal loading, and gas flow rates onto the yield and energy efficiency of ammonia production.
The optimum N2/H2 feed flow ratio found was 1-2, depending on the catalyst – substantially above ammonia stoichiometry of 0.33. The concentration of ammonia formed was proportional to the specific energy input. A higher reaction temperature or lower gas flow rates resulted in a lower specific production due to accelerated ammonia decomposition. The most efficient catalysts were found to be 2wt% Rh/Al2O3. The combination of plasma doubled ammonia formation compared to plasma-only case showing a strong synergetic effect.
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