Multifuel Catalytic Combustion in the Presence of Carbon Dioxide over

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Multi-fuel catalytic combustion in the presence of carbon dioxide over fully and partially perovskite-coated monoliths Gianluca Landi, Paola Sabrina Barbato, Valeria Di Sarli, and Almerinda Di Benedetto Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b00439 • Publication Date (Web): 05 Apr 2017 Downloaded from http://pubs.acs.org on April 6, 2017

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Industrial & Engineering Chemistry Research

Multi-fuel catalytic combustion in the presence of carbon dioxide over fully and partially perovskite-coated monoliths

Gianluca Landi*1, Paola Sabrina Barbato1, Valeria Di Sarli1, Almerinda Di Benedetto2 1 2

Institute for Research on Combustion - CNR, P.le Tecchio 80, 80125, Naples, Italy

Department of Chemical, Materials and Production Engineering, University of Naples Federico II, P.le Tecchio 80, 80125, Naples, Italy *corresponding author: [email protected]

Abstract In this work, we have investigated the opportunity to use fully and partially coated monoliths as catalytic combustors for syngas/methane mixtures in the presence of significant CO2 partial pressure. In particular, the effects of syngas-to-methane ratio and CO2 content were studied on perovskite-based monoliths to verify the ability of CO to sustain methane combustion also in the presence of CO2. Results have shown that syngas substitution to methane is effective in improving the resistance to the inhibiting effect of carbon dioxide. A novel light-off strategy has been proposed: regardless of the partial pressure of CO2, the catalytic combustor is first ignited with a syngas-rich fuel and, after ignition, syngas is partially replaced by methane. It has been found that the operative window of the reactor is dependent on the coating degree, the fuel composition and the partial pressure of CO2.

Keywords: methane, syngas, monolith, perovskite, carbon dioxide, catalytic combustion.

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1. Introduction Catalytic combustors have been widely studied as a possible alternative approach to homogeneous combustors for power generation with near-zero emissions1. However, several issues, mainly related to catalyst durability, cost and maximum operating temperature2, have limited the use of catalytic reactors to the field of abatement of volatile organic compounds (VOCs)3–6. Accordingly, catalytic combustion has been mainly studied at atmospheric pressure. However, the behavior of a catalytic combustor is significantly affected by the operating pressure and, consequently, studies at atmospheric pressure do not provide accurate information. On the other hand, the literature works dealing with high pressure catalytic combustion7–19 are mainly focused on noble metals12–19. Perovskite-based catalysts, which are less expensive than noble metals, have demonstrated good activity and stability at atmospheric pressure20–32 and, thus, we have chosen LaMnO3 to study catalytic combustion under pressure7–11. As recently reviewed by Royer et al.33, performance of perovskites towards oxidation reaction appears very interesting especially if high surface areas are obtained by supporting the active phase on other oxides. Catalytic combustion can be regarded with a renewed interest among the flameless distributed combustion technologies34 not only for economic reasons, as in the case of small size gas turbines35, but also when novel technologies, such as oxy-fuel combustion and/or syngas combustion, are considered. This is due to the occurrence of a specific phenomenon, called Combustion-induced Rapid Phase Transition36 (in the case of oxy-fuel combustion), and/or to specific features, such as the low heating value of syngas generally requiring lower dilution37. However, the above drawbacks should be overcome to make commercialization of catalytic combustors possible for these novel applications. To this end, we have proposed “core-shell” partially coated monoliths8. We have studied such configurations for methane combustion both experimentally11 and through a CFD model8,38,39, showing that reaction in the coated channels of the monolith allows reaction

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to be sustained in the uncoated channels8,11. Such configuration ensures complete combustion of methane with reduced catalyst load and also with reduced thermal stress of the catalyst surface8. The main limiting factor for catalytic combustion of CH4/CO2/O2/N2 mixtures over fully perovskitecoated monolithic reactors at high pressure (up to 10 bar) is the presence of CO2 itself. Indeed, we built the operating maps showing that the content of CO2 significantly reduces the operating window9. However, we have found that, when mixing methane with syngas, the presence of CO enhances CH4 reactivity10, thus enlarging the operating window of fully perovskite-coated monolithic reactors. In this work, we have investigated the opportunity to reduce the impact of CO2 on reactivity of CH4/O2/N2/CO2 mixtures by adding syngas. We performed tests at different syngas-to-methane ratios and CO2 contents to verify the ability of CO to sustain methane combustion also in the presence of CO2. Catalytic combustion was studied over 20 wt % LaMnO3/Al2O3 catalyst deposited onto cordierite monoliths. The effect of partial coating was addressed by comparing the behavior of a “core-shell” monolith to that of a fully coated configuration. The final aim was at demonstrating the opportunity to use a partially coated reactor as an effective pilot for homogeneous combustion in the presence of high CO2 contents.

2. Experimental 2.1. Preparation of monolithic reactor Lean methane-syngas combustion under self-sustained conditions was performed over 20 wt % LaMnO3/La-γ-Al2O3 catalyst supported on 900 cpsi honeycomb cordierite monoliths (NGK) in shape of cylinder (length, 50 mm; diameter, 12 mm). The behavior of a “core-shell” configuration, with two different coating degrees, was compared to that of a fully coated monolith. All monolithic reactors were prepared by using a dipping procedure, reported in more detail in Barbato et al.40. In the case of the monoliths with the “core-shell” partially coated configuration, the dip-coating procedure was applied 3



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only to the external annulus, while the internal core was left blank as detailed in Barbato el al.11. Figure 1 shows some pictures of substrates (figure 1a and figure 1c (middle)), partially coated (figure 1b) and fully coated (figure 1c (left and right)) monoliths. Catalysts were aged according to the procedure described in Barbato et al.40, thus assuring stable performance. Repeated tests showed catalytic performance differing within the experimental error. Geometrical features, coating degree (i.e., ratio between the number of coated channels and the total number of channels) and catalyst load of the prepared monoliths along with the used abbreviations are detailed in table 1. 2.2. High pressure test rig Experimental tests were run in a lab-scale rig designed to work at pressures up to 12 bar and described in more details in Barbato et al.7. Briefly, high purity gases (CH4, O2, N2, CO2) or certified mixtures (15 vol. % H2/N2, 5 vol. % CO/N2) were separately fed and controlled by means of mass flow controllers (Brooks SLA5850). A pressure transducer (ABB 261G) was placed just downstream the feed mixing point. A system of three electron valves was used to send the reacting gases alternately or to the analysis system (in order to check the feed composition) or to the stainless steel reactor, which was provided with a second pressure transducer (ABB 261G) placed just upstream. The operating pressure was set by means of a back-pressure regulator (Brooks SLA5820). A co-axial tube condenser was used to separate most of the water vapor produced by combustion. A fraction of the outlet stream was further dried by a CaCl2 trap before entering the analysis system (ABB AO2000), which was equipped with three modules for the online and continuous analysis of the main gaseous species (CH4, CO2, and CO by infrared detectors; O2 by a paramagnetic detector; H2 by a thermal conductivity (TC) detector) and with a cross-sensitivity correction.

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2.3. Catalytic tests The prepared monoliths were stacked between two ceramic foams (acting as thermal shields) and wrapped into ceramic wool. Several thermocouples were inserted both in the thermal shields and in the catalytic reactor thanks to multi-hole ceramic glands (Conax Buffalo). In particular, their tips were placed i) at 5 mm upstream of the catalytic monolith (inside the front thermal shield), ii) at 5 mm and 25 mm starting from the entrance of the catalytic monolith, and iii) at 5 mm downstream of the catalytic monolith (inside the back thermal shield). As previously reported41, due to the typical size of the thermocouples (0.5 mm OD), which significantly reduces the flow rate inside the measuring channel, and the position of their tips in close contact with the solid wall, the measured temperatures are believed to be more indicative of the surface temperatures, although, in general, they are weighted-averages with the gas temperatures. Moreover, temperatures are measured at fixed positions and no information can be provided on the trend between two measuring points. As a consequence, the measured maxima do not necessarily correspond to actual maxima. The thermal profiles reported in the following are to be considered semi-quantitative measurements in the central channel. Their comparison is useful in order to estimate the shift of the reaction fronts. The operating pressure was increased from approximately 1 to 12 bar. The mass flow rate was kept constant (i.e., the volumetric flow rate was decreased with increasing pressure). Four syngas/methane volumetric ratios (100/0, 70/30, 50/50 and 0/100) and three CO2 concentrations (0, 5 and 30 vol %) were investigated at fixed H2/CO ratio (1.5 v/v) and pre-heating temperature (520°C). The effect of fuel composition was investigated at fixed fuel heating value (16 Wth). The oxygen concentration was set equal to 10 vol %; the total flow rate was set equal to 60 dm3/h at room temperature and pressure. Some tests were repeated and gave results differing within the experimental error. Mass balances were closed within ±4 %. Table 2 summarizes the compositions of the investigated mixtures.

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3. Results 3.1. Effect of fuel composition and CO2 concentration: fully coated monolith In figure 2, the fuel conversion is shown as a function of the operating pressure for mixtures obtained by increasing the content of CH4 up to pure CH4 (Mix2, Mix3 and Mix4 of table 2). CO and H2 conversions obtained when feeding Mix1 are not shown, being always complete even at atmospheric pressure. Even after substitution of syngas with CH4, CO and H2 are extremely reactive over the perovskite catalyst. When substituting syngas with CH4, the ignition pressure almost linearly increases from 1 bar for Mix1 to 4 bar for pure methane (Figure 2d). The easier ignition of methane when syngas is fed can be addressed to the activation of methane catalytic combustion that is facilitated by the increase in surface temperature due to the heat produced by CO and H2 combustion. It is worth noting that the conversion scale under not ignited conditions, i.e., under kinetic rather than mass transfer limitation, is equal to that obtained in a previous kinetic study on single fuel combustion42. According to those results, combustion of CO, H2 and CH4 occurs via Mars-Van Krevelen mechanism. On the other hand, CO and CH4 adsorption on the catalyst surface is significant, whereas H2 surface coverage is very low, suggesting a weak interaction with the catalytic surface, in agreement with results on the CO-PROX activity of perovskites43,44. Furthermore, catalytic combustion of CO and CH4 can be described by the same kinetic model, corresponding reaction rates differing for the required availability of oxygen (four times higher for CH4 combustion). In conclusion, CO reacts more rapidly than CH4 and H2, because i) it requires lower oxygen transfer than CH4 and ii) it interacts with the perovskite active centers more strongly than H2. When decreasing the operating pressure from ignited conditions, complete fuel conversion is attained and no quenching phenomenon occurs for all the mixtures investigated. In figure 3, the axial thermal profiles are shown as obtained at 6 bar for Mix1, Mix2, Mix3 and Mix4. In the front thermal shield and in the rector zone close to the inlet section, temperatures decrease with increasing methane content. Conversely, in the middle of the reactor and close to the exit section, the 6


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opposite trend is found: temperatures increase with increasing methane content. This is probably due to the fact that the reaction front shifts downstream when the mixture reactivity is decreased (i.e., when CH4 content is increased). In figure 4, the effect of CO2 addition to CH4/H2/CO/O2/N2 mixtures is shown at fixed syngas/methane ratio (50:50). The ignition pressure slightly increases from 2.5 to 4 bar, with increasing CO2 concentration from 0 to 30 vol. % (Figure 4d). The presence of carbon dioxide in the mixture has a different impact on the fuel conversion: the most sensitive is CH4 followed by H2, while CO is only slightly affected by CO2 content. In our previous paper9, we have found a much stronger inhibiting effect of CO2 on CH4 conversion, thus highlighting that the presence of CO and H2 in the mixture reduces the inhibiting effect. The effect of CO2 on CH4 conversion in the absence of syngas was addressed to the competitive adsorption of CH4 and CO2 on the same perovskite sites, CO2 being favored at temperatures below 600°C and forming surface carbonates. So, CO can successfully compete with CO2 in the adsorption on the catalyst active sites. Another possible explanation for this behavior can be related to the different amount of oxygen required by CO and CH4 combustion, affecting the reaction rates42, as reported above. As a matter of fact, carbonates formed on the surface when CO2 is added to the feed can limit transfer and availability of oxygen for the active centers. It is known that two oxygen species can participate in perovskite-catalyzed combustion, αoxygen (Oads) formed from the dissociative adsorption of molecular O2, active at low temperature, and β-oxygen (Olat), active at high temperature22,26. The concentrations of these two species are linked by the relative velocity of dissociative adsorption and oxygen transfer into the lattice structure: 1 2

↔

↔

While CO (and H2) oxidation can occur with only one oxygen atom, and thus with α-oxygen adsorbed onto the active site, methane combustion requires four oxygen atoms, thus benefiting from β-oxygen 7



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transfer from the surroundings. The formation of carbonates can make the β-oxygen transfer slower. For this reason, the CO2 addition affects more significantly methane combustion. During the syngas-methane co-feeding, CO combustion leads to the increase in surface temperature, thus shifting CO2 adsorption (i.e., favoring decomposition of carbonates) and allowing CH4 ignition, due to both higher temperatures and availability of β-oxygen. In figure 5, the axial temperature profiles obtained under ignited conditions at P = 6 bar are shown for different CO2 contents and syngas/methane ratio equal to 50:50 (Mix3, Mix7 and Mix11). In the front thermal shield and in the rector zone close to the inlet section, temperature decreases as CO2 content in the feed is increased. This behavior has to be addressed to the decrease in reaction rate that pushes the reaction front downstream, thus leading to higher temperature at the center of the channel. In the zone close to the exit section, temperatures are quite unaffected by CO2 concentration. This suggests that, at 6 bar, the reaction fronts are far enough from the exit section, whereas heat losses to the surroundings are substantially the same. The map of figure 6 summarizes the effect of CO2 addition and methane content on ignition of CO/H2/O2/N2 mixtures. Two surfaces are shown, the quenching surface (blue) and the ignition surface (red/yellow). Thus, three regions are identified: the ignited region (above the ignition surface), the steady state multiplicity region (between the ignition surface and the quenching surface), and the not ignited region (below the quenching surface). At high CO2 content (30 vol. %), ignition can occur even at atmospheric pressure for the syngas mixture. The ignition pressure increases with increasing CH4 and CO2 contents. It is also worth noting that the sensitivity of the ignition pressure to CO2 content significantly increases with increasing CH4 content. Conversely, the quenching pressure is slightly affected by the fuel composition and CO2 concentration. This result confirms that CO2 has a major kinetic effect on CH4/CO/H2 conversion, which is relevant only at low temperature and, thus, at and below ignition. 8


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The steady state multiplicity region is enlarged when increasing methane substitution and CO2 concentration. From this map, an ignition strategy for methane-enriched syngas mixtures can be identified: fuel can be ignited without methane, even under high CO2 concentrations. CH4 can be added later, when the temperature inside the catalytic reactor is high enough to limit the detrimental effect of CO2 adsorption. 3.2. Effect of partial coating The performances of the monoliths at different coating degrees are shown in figures 7 a-c for Mix3 (syngas/methane = 1, CO2 = 0 vol. %). At pressures lower than the ignition pressure, the fuel conversion decreases with decreasing coating degree. In order to get global ignition of the monolith, also homogeneous reactions should be activated in the uncoated channels. Ignition occurs if fuel conversion provides a fixed thermal power mainly determined by the heat exchange with the surroundings8,10,45. As a consequence, ignition is obtained at higher pressure for the P1 monolith, while no ignition is attained for the P2 monolith (Figure 7d). By decreasing the operating pressure starting from ignited conditions, quenching is observed on the P1 monolith at 2 bar, while complete fuel conversion is obtained on the fully coated monolith even at atmospheric pressure. Thus, the operative window of a partially coated monolith is narrower even if a highly reactive fuel, such as the synthesis gas, is used, as it occurs with methane fueled systems11. In figures 7 a-c, the theoretical fuel conversion (dashed line) that can be obtained if complete fuel conversion is attained only in the coated channels is also shown. In the partially coated monoliths (P1 and P2), CO conversion is always higher than the theoretical value, suggesting that CO combustion is also activated in the uncoated channels. Hydrogen conversion overcomes the theoretical conversion at pressure higher than 2 bar, suggesting that H2 homogeneous combustion is activated at 2 bar. In figure 8, the temperature profiles measured in the central uncoated channel of the P1 monolith are reported as a function of the operating pressure. Temperatures measured in the front thermal shield and 9



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at the reactor inlet steadily increase with increasing pressure; on the contrary, in the middle of the reactor and at its exit, a non-monotonic behavior is detected. In previous works8,10,45, we have demonstrated that, when a partially coated monolith is fueled with methane alone, fuel ignition in uncoated channels occurs after fuel ignition in the coated section. Moreover, ignition occurs at the end of the reactor, thus a welldefined reaction front is formed that shifts towards the reactor inlet38,39,45. Taking these considerations into account and according to fuel conversions (figure 7b) and temperature profiles (figure 8), we can identify three different behaviors (sketched in figure 8). At low pressure (< 3 bar), the temperature increase along the reactor is mainly due to syngas combustion in both coated and uncoated channels, mostly occurring in the second section of the reactor. When increasing the pressure, a more defined syngas reaction front is formed, moving towards the reactor inlet; at the same time, the temperature close to the reactor exit is high enough to allow methane activation first in the coated channels and then in the uncoated ones. For this reason, we have detected both a significant temperature increase at the reactor inlet and the temperature maximum at the reactor center. When further increasing the pressure, both reaction fronts move upstream, probably merging at the highest pressures, thus explaining the maximum temperature at the entrance. In figure 9 a-c, the effect of CO2 addition is shown for the P1 monolith, while figure 9 d-e shows the operating maps for the F and P1 configurations as a function of the CO2 content. The impact of CO2 content on ignition is similar to that seen in the case of the fully coated monolith (figure 4): both ignition pressure and quenching pressure increase with increasing CO2 addition. However, the effect of CO2 content on the ignition pressure in the case of the P1 monolith is less significant than in the case of the F monolith, suggesting a peculiar behavior of the “core-shell” partially coated configuration. In the fully coated monolith, ignition and quenching occur only through catalytic reaction. Conversely, in the P1 configuration, they are also controlled by homogeneous reaction in the uncoated channels. Ignition is mainly controlled by the competition between reaction time and residence time. In the F 10


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configuration, the reaction time is limited by CO2. In the P1 configuration, due to the activation of homogenous reaction, ignition occurs at higher temperatures, which inhibit CO2 adsorption. As a result, the ignition pressure is slightly affected by CO2 content. On the contrary, the effect of CO2 concentration on quenching pressure is more evident in the case of the P1 monolith than in the case of the F monolith. Quenching is controlled by the competition between heat produced by reaction and heat transferred towards the external environment. In the P1 configuration, the heat produced by reaction comes from catalytic reaction and homogeneous reaction. The latter is sustained by the radial heat transferred from the catalytic channels through the walls. In the presence of CO2, the temperature level and then the heat transferred is reduced due to the high thermal capacity of CO2. As a result, when increasing the content of CO2, homogeneous reaction becomes less stable and, thus, it quenches earlier. The above considerations are also reflected in the temperature profiles measured in the central (uncoated) channel of the P1 monolith at 7 bar (figure 10). The pre-heating temperature decreases with the CO2 content, due to its higher specific heat with respect to N2. The peak temperature, detected close to the reactor inlet, decreases, while other temperatures increase. This behavior is related to the shift of the reaction fronts downstream, due to i) the corresponding shift of temperatures in the inlet section and ii) the negative effect of CO2 on gas phase reactions. From figure 9 d-e, it appears that the region of steady state multiplicity is reduced when reducing the coating degree. However, in the partially coated configuration, it is possible to operate even in the presence of a large amount of CO2 (30 vol. %). These results allow to conclude that more stable operation of a catalytic combustor fed with methane in the presence of CO2 can be achieved by partial substitution with syngas, also on a partially coated monolith. In particular, this configuration offers the advantage to operate with relatively low amounts of catalyst, acting as an effective (homogeneous) combustion igniter and stabilizer. 11



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4. Conclusions and outlook In this work, we have investigated the combined effects of partial substitution of syngas with methane and addition of carbon dioxide on combustion over partially and fully perovskite-coated monoliths, to demonstrate the ability of syngas to drive catalytic combustion of methane in the presence of CO2. Regardless of the coating degree, methane-poor fuel mixtures have shown resistance to the inhibiting effect of carbon dioxide even at low temperature, while a significant shift of ignition pressure at higher values has been detected for methane-rich fuel mixtures. Hence, a novel light-off strategy has been proposed: if syngas and methane come from different sources (such as in IGCC plants), the catalytic combustor can be ignited with a syngas-rich fuel and, after ignition, syngas can be partially substituted with methane, quite independently of the partial pressure of CO2. The reason for the marked mitigation of the inhibiting effect of carbon dioxide on ignition for low CH4 content in the syngas mixture is the high reactivity of carbon monoxide on LaMnO3 perovskite. In particular, CO successfully competes with CO2 in the adsorption on the catalyst surface and, through its combustion, enhances the surface temperature, thus reducing the surface CO2 coverage. Moreover, CO needs a significantly lower oxygen amount than methane to be burned and CO2 adsorption can limit oxygen availability. It has been demonstrated that partially perovskite-coated “core shell” monoliths can operate with different fuels (i.e., CH4, H2, CO) also in the presence of huge amounts of CO2. The operative window is dependent on the coating degree, the fuel composition, and the partial pressure of CO2. In addition, it should be considered that the ratio between produced thermal power and thermal power lost towards the surroundings affects the operative window as well. Indeed, the maximum thermal power is related to fuel flow rate, while the thermal power lost towards the surroundings is affected by the combustor size. As a consequence, the coating degree of a perovskite-based catalytic combustor can be optimized as a function of fuel type and composition, CO2 concentration, and combustor size. Partially coated monoliths are 12


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preferred at large size and large syngas concentration, the catalyst acting as igniter and stabilizer for homogeneous reaction. Conversely, at small scales (i.e., in the case of micro-combustors) and high methane and carbon dioxide concentrations, high coating degrees offer improved stability. Finally, we have definitively demonstrated that homogeneous combustion of fuels with different compositions (even with large amount of carbon dioxide) can be sustained and stabilized by a parallel catalytic combustion. To date, we have worked on a single reactor fed with the same gaseous flow and divided into a coated section and an uncoated section. However, the two sections are linked only by the radial heat exchange. As a consequence, partially coated catalytic combustors can be theoretically designed to be fed with two flows (one for the coated section, another one for the uncoated section) differing for flow rate, fuel composition, presence of poisons, etc.. In particular, the use of “cleaner” (and, thus, more expensive) fuels could be limited to the coated section.

Acknowledgements This work was financially supported by MiSE-CNR “CO2 capture- Carbone pulito” Project (Italy).

References (1)

Lee, J. H.; Trimm, D. L. Catalytic Combustion of Methane. Fuel Process. Technol. 1995, 42 (2– 3), 339.

(2)

Furuya, T.; Sasaki, K.; Hanakata, Y.; Ohhashi, T.; Yamada, M.; Tsuchiya, T.; Furuse, Y. Development of a Low NOₓ Catalytic Combustor for a Gas Turbine. Catal. Today 1995, 26 (3– 4), 351.

(3)

Du, P. P.; Wang, W. W.; Jia, C. J.; Song, Q. S.; Huang, Y. Y.; Si, R. Effect of Strongly Bound Copper Species in Copper-Ceria Catalyst for Preferential Oxidation of Carbon Monoxide. Appl. Catal. A Gen. 2016, 518, 87. 13



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 31

(4)

Răciulete, M.; Layrac, G.; Papa, F.; Negrilă, C.; Tichit, D.; Marcu, I.-C. Influence of Mn Content on the Catalytic Properties of Cu-(Mn)-Zn-Mg-Al Mixed Oxides Derived from LDH Precursors in the Total Oxidation of Methane. Catal. Today 2017, (in press), DOI: 10.1016/j.cattod.2017.01.013.

(5)

Hussain, M.; Deorsola, F. A.; Russo, N.; Fino, D.; Pirone, R. Abatement of CH4 Emitted by CNG Vehicles Using Pd-SBA-15 and Pd-KIT-6 Catalysts. Fuel 2015, 149, 2.

(6)

Bernardi, M.; Deorsola, F. A.; Fino, D.; Russo, N. Catalytic Wet Air Oxidation of Maleic Acid Over Lanthanum-Based Perovskites Synthesized by Solution Combustion Synthesis. Waste and Biomass Valorization 2014, 5 (5), 857.

(7)

Barbato, P. S.; Di Benedetto, A.; Di Sarli, V.; Landi, G.; Pirone, R. High-Pressure Methane Combustion over a Perovskyte Catalyst. Ind. Eng. Chem. Res. 2012, 51 (22), 7547.

(8)

Di Benedetto, A.; Landi, G.; Di Sarli, V.; Barbato, P. S.; Pirone, R.; Russo, G. Methane Catalytic Combustion under Pressure. Catal. Today 2012, 197 (1), 206.

(9)

Di Benedetto, A.; Barbato, P. S.; Landi, G. Effect of CO2 on the Methane Combustion over a Perovskyte Catalyst at High Pressure. Energy & Fuels 2013, 27 (10), 6017.

(10) Barbato, P. S.; Landi, G.; Russo, G. Catalytic Combustion of CH4-H2-CO Mixtures at Pressure up to 10 Bar. Fuel Process. Technol. 2013, 107 (x), 147. (11) Barbato, P. S.; Di Sarli, V.; Landi, G.; Di Benedetto, A. High Pressure Methane Catalytic Combustion over Novel Partially Coated LaMnO3-Based Monoliths. Chem. Eng. J. 2015, 259, 381. (12) Ghermay, Y.; Mantzaras, J.; Bombach, R.; Boulouchos, K. Homogeneous Combustion of FuelLean H2/O2/N2 Mixtures over Platinum at Elevated Pressures and Preheats. Combust. Flame 2011, 158 (8), 1491. (13) Mantzaras, J.; Bombach, R.; Schaeren, R. Hetero-/Homogeneous Combustion of Hydrogen/Air 14


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Mixtures over Platinum at Pressures up to 10 bar. Proc. Combust. Inst. 2009, 32 (2), 1937. (14) Mantzaras, J. Catalytic Combustion of Syngas. Combust. Sci. Technol. 2008, 180 (6), 1137. (15) Andrae, J. C. G.; Johansson, D.; Bursell, M.; Fakhrai, R.; Jayasuriya, J.; Carrera, A. M. HighPressure Catalytic Combustion of Gasified Biomass in a Hybrid Combustor. Appl. Catal. A Gen. 2005, 293, 129. (16) Carroni, R.; Griffin, T.; Mantzaras, J.; Reinke, M. High-Pressure Experiments and Modeling of Methane/air Catalytic Combustion for Power-Generation Applications. Catal. Today 2003, 83 (1), 157. (17) Reinke, M.; Mantzaras, J.; Schaeren, R.; Bombach, R.; Inauen, A.; Schenker, S. High-Pressure Catalytic Combustion of Methane over Platinum: In Situ Experiments and Detailed Numerical Predictions. Combust. Flame 2004, 136 (1), 217. (18) Persson, K.; Ersson, A.; Carrera, A. M.; Jayasuriya, J.; Fakhrai, R.; Fransson, T.; Järås, S. Supported Palladium-Platinum Catalyst for Methane Combustion at High Pressure. Catal. Today 2005, 100 (3), 479. (19) Reinke, M.; Mantzaras, J.; Bombach, R.; Schenker, S.; Inauen, A. Gas Phase Chemistry in Catalytic Combustion of Methane/air Mixtures over Platinum at Pressures of 1 to 16 Bar. Combust. Flame 2005, 141 (4), 448. (20) Seiyama, T. Total Oxidation of Hydrocarbons on Perovskite Oxides. Catal. Rev. 1992, 34 (4), 281. (21) Alifanti, M.; Blangenois, N.; Florea, M.; Delmon, B. Supported Co-Based Perovskites as Catalysts for Total Oxidation of Methane. Appl. Catal. A Gen. 2005, 280 (2), 255. (22) Arai, H.; Yamada, T.; Eguchi, K.; Seiyama, T. Catalytic Combustion of Methane over Various Perovskite-Type Oxides. Appl. Catal. 1986, 26, 265. (23) Saracco, G.; Geobaldo, F.; Baldi, G. Methane Combustion on Mg-Doped LaMnO3 Perovskite 15



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Catalysts. Appl. Catal. B Environ. 1999, 20 (4), 277. (24) Cimino, S.; Lisi, L.; Pirone, R.; Russo, G.; Turco, M. Methane Combustion on PerovskitesBased Structured Catalysts. Catal. Today 2000, 59 (1), 19. (25) Marti, P. E.; Maciejewski, M.; Baiker, A. Methane Combustion over La0.8Sr0.2MnO3+x Supported on MAl2O4 (M = Mg, Ni and Co) Spinels. Appl. Catal. B Environ. 1994, 4 (2), 225. (26) Choudhary, T. .; Banerjee, S.; Choudhary, V. . Catalysts for Combustion of Methane and Lower Alkanes. Appl. Catal. A Gen. 2002, 234 (1), 1. (27) Cifà, F.; Dinka, P.; Viparelli, P.; Lancione, S.; Benedetti, G.; Villa, P. L.; Viviani, M.; Nanni, P. Catalysts Based on BaZrO3 with Different Elements Incorporated in the Structure I: BaZr(1−x)PdxO3 Systems for Total Oxidation. Appl. Catal. B Environ. 2003, 46 (3), 463. (28) Giebeler, L.; Kießling, D.; Wendt, G. LaMnO3 Perovskite Supported Noble Metal Catalysts for the Total Oxidation of Methane. Chem. Eng. Technol. 2007, 30 (7), 889. (29) Uenishi, M.; Taniguchi, M.; Tanaka, H.; Kimura, M.; Nishihata, Y.; Mizuki, J.; Kobayashi, T. Redox Behavior of Palladium at Start-up in the Perovskite-Type LaFePdOx Automotive Catalysts Showing a Self-Regenerative Function. Appl. Catal. B Environ. 2005, 57 (4), 267. (30) Kucharczyk, B.; Tylus, W. Effect of Pd or Ag Additive on the Activity and Stability of Monolithic LaCoO3 Perovskites for Catalytic Combustion of Methane. Catal. Today 2004, 90 (1), 121. (31) Scarpa, A.; Barbato, P. S.; Landi, G.; Pirone, R.; Russo, G. Combustion of Methane-Hydrogen Mixtures on Catalytic Tablets. Chem. Eng. J. 2009, 154 (1–3), 315. (32) Feng, X. B.; Qu, Z. G. Lean Methane Premixed Combustion over a Catalytically Stabilized Zirconia Foam Burner. Int. J. Green Energy 2016, 13 (14), 1451. (33) Royer, S.; Duprez, D.; Can, F.; Courtois, X.; Batiot-Dupeyrat, C.; Laassiri, S.; Alamdari, H. Perovskites as Substitutes of Noble Metals for Heterogeneous Catalysis: Dream or Reality. 16


Page 17 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Chem. Rev. 2014, 114 (20), 10292. (34) Khidr, K. I.; Eldrainy, Y. A.; EL-Kassaby, M. M. Towards Lower Gas Turbine Emissions: Flameless Distributed Combustion. Renew. Sustain. Energy Rev. 2017, 67, 1237. (35) Major, B. Cost Analysis of NOx Control Alternatives for Stationary Gas Turbines. ONSITE SYCOM Energy Corp. 1999, No. Contract DE-FC02-97CHIO877. https://www1.eere.energy.gov/manufacturing/distributedenergy/pdfs/gas_turbines_nox_cost_ana lysis.pdf (accessed April 2017). (36) Di Benedetto, A.; Cammarota, F.; Di Sarli, V.; Salzano, E.; Russo, G. Effect of Diluents on Rapid Phase Transition of Water Induced by Combustion. AIChE J. 2012, 58 (9), 2810. (37) Yilmaz, I.; Ilbas, M. An Experimental Study on Hydrogen–methane Mixtured Fuels. Int. Commun. Heat Mass Transf. 2008, 35 (2), 178. (38) Landi, G.; Di Benedetto, A.; Barbato, P. S.; Russo, G.; Di Sarli, V. Transient Behavior of Structured LaMnO3 Catalyst during Methane Combustion at High Pressure. Chem. Eng. Sci. 2014, 116, 350. (39) Di Sarli, V.; Barbato, P. S.; Di Benedetto, A.; Landi, G. Start-up Behavior of a LaMnO3 Partially Coated Monolithic Combustor at High Pressure. Catal. Today 2015, 242 (Part A), 200. (40) Barbato, P. S.; Landi, G.; Pirone, R.; Russo, G.; Scarpa, A. Auto-Thermal Combustion of CH4 and CH4-H2 Mixtures over Bi-Functional Pt-LaMnO3 Catalytic Honeycomb. Catal. Today 2009, 147, 271. (41) Landi, G.; Barbato, P. S.; Cimino, S.; Lisi, L.; Russo, G. Fuel-Rich Methane Combustion over Rh-LaMnO3 Honeycomb Catalysts. Catal. Today 2010, 155 (1–2), 27. (42) Landi, G.; Barbato, P. S.; Di Benedetto, A.; Pirone, R.; Russo, G. High Pressure Kinetics of CH4, CO and H2 Combustion over LaMnO3 Catalyst. Appl. Catal. B Environ. 2013, 134–135, 110. 17



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(43) Maluf, S. S.; Assaf, E. M. CO Preferential Oxidation (CO-PROx) on La1−xCexNiO3 Perovskites. Catal. Commun. 2011, 12 (8), 703. (44) Gosavi, P. V.; Biniwale, R. B. Effective Cleanup of CO in Hydrogen by PROX over Perovskite and Mixed Oxides. Int. J. Hydrogen Energy 2012, 37 (4), 3958. (45) Barbato, P. S.; Di Benedetto, A.; Di Sarli, V.; Landi, G. Ignition and Quenching Behaviour of High Pressure CH4 Catalytic Combustion over a LaMnO3 Honeycomb. Chem. Eng. Trans. 2013, 32, 655.

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CAPTIONS Table captions Table 1. Features of the fully and partially coated monoliths. Table 2. Compositions of the gas mixtures used for combustion tests.

Figure captions Figure 1. Picture of the prepared monoliths. Figure 2. Hydrogen (▲), carbon monoxide (▼) and methane () conversion as obtained by increasing (full symbols) and decreasing (open symbols) the operating pressure for mixtures at different syngas/methane substitution degrees: 70/30 (a: Mix 2); 50/50 (b: Mix 3); 0/100 (c: Mix 4). d: Ignition pressure as a function of the CH4 fraction in the fuel. F monolith. Figure 3. Axial thermal profiles at fixed operating pressure (6 bar) for mixtures at different syngas/methane substitution degrees. Symbols:  100/0 (Mix 1);  70/30 (Mix 2); ▼ 50/50 (Mix 3); ▲ 0/100 (Mix 4). F monolith. Figure 4. Hydrogen (▲), carbon monoxide (▼) and methane () conversion as obtained by increasing (full symbols) and decreasing (open symbols) the operating pressure for mixtures at syngas/methane 50/50 and different CO2 content: 0 % vol. (a: Mix 3), 5 % vol. (b: Mix 7), 30 % vol. (c: Mix 11). d: Ignition (full symbols) and quenching (open symbols) pressure as a function of the CO2 concentration. F monolith. Figure 5. Axial thermal profiles at fixed operating pressure (6 bar) for mixtures at syngas/methane 50/50 and different CO2 content: 0 % vol. (Mix 3; circles), 5 % vol. (Mix 7; squares), 30 % vol. (Mix 11; triangles). F monolith. Figure 6. Operating map of F monolith.

19



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Page 20 of 31

Figure 7. Hydrogen (▲), carbon monoxide (▼) and methane () conversion as obtained by increasing (full symbols) and decreasing (open symbols) the operating pressure for monoliths at different coating degree: 100 % (a: F), 79 % (b: P1) and 63 % (c: P2) fueled with Mix 3. d: Ignition (full symbols) and quenching (open symbols) pressure as a function of the coating degree; lines have been added to semiquantitatively divide the planes into different zones. Figure 8. Axial thermal profiles at different pressures for mixtures at syngas/methane 50/50 and sketch of the development of reaction fronts (S: syngas reaction front; M: methane reaction front) and their position inside the reactor. P1 monolith. Figure 9. Hydrogen (▲), carbon monoxide (▼) and methane () conversion as obtained by increasing (full symbols) and decreasing (open symbols) the operating pressure for mixtures at syngas/methane 50/50 and different CO2 content: 0 % vol. (a: Mix 3), 5 % vol. (b: Mix 7), 30 % vol. (c: Mix 11); P1 monolith. Operating maps of F (d) and P1 (e) monolith at 50/50 methane/syngas ratio. Figure 10. Axial thermal profiles at fixed operating pressure (7 bar) for mixtures at syngas/methane 50/50 and different CO2 content: 0 % vol. (Mix 3; circles), 5 % vol. (Mix 7; squares), 30 % vol. (Mix 11; triangles). P1 monolith.

20


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TABLES

Table 1. Monolith F P1 P2

D, mm

L, mm

Cell density, cpsi

12

50

900

Total Coated channels channels 172 172 136 108

Coated fraction 1 0.79 0.63

Catalyst weight, g 1.83 1.36 1.11

Table 2.

Mix1 Mix2 Mix3 Mix4 Mix5 Mix6 Mix7 Mix8 Mix9 Mix10 Mix11 Mix12 * vol.%

CH4*

H2*

CO*

1.71 2.27 3 1.71 2.27 3 1.71 2.27 3

5.6 2.4 1.36 5.6 2.4 1.36 5.6 2.4 1.36 -

3.73 1.6 0.9 3.73 1.6 0.9 3.73 1.6 0.9 -

CO2*

0

5

30

(H2+CO):CH4 100: 0 70:30 50:50 0:100 100: 0 70:30 50:50 0:100 100: 0 70:30 50:50 0:100

O 2* 10 10 10 10 10 10 10 10 10 10 10 10

21



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FIGURES

Figure 1.

22


Page 23 of 31

1.0

CO

CO H2

H2

0.8

Conversion

0.6 CH4

0.4

CH4 CH4

0.2 a: Mix 2

0.0 0

2

4

6

8

b: Mix 3

0

2

4

6

8

c: Mix 4 0

2

4

6

8

Pressure, bar 5

Pressure, bar

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47


4 3 2 d

1 0

20

40

60

80

100

CH4 in the fuel, % Figure 2. 23



650

Temperature, °C

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 31

600

550

500 -10

0

10

20

30

40

50

60

axial coordinate, mm Figure 3.

24


Page 25 of 31

1.0 CO 0.8

Conversion

CO H2

CO

H2

H2

0.6 0.4

CH4

CH4

CH4

0.2 a: Mix 3

0.0 0

2

4

6

8

b: Mix 7

0

2

4

6

8

c: Mix 11 0

2

4

6

8

Pressure, bar

5

Pressure, bar

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47


d Ignited region

4 3

Steady state multiplicity region

2

Not ignited region

1 0

5

10

15

20

25

30

35

CO2 in the feed, vol. % Figure 4. 25



700

Temperature, °C

650

600

550

500 -10

0

10

20

30

40

50

60


9 8 7

Pressure, bar

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 31

6 5

n regio d e t i Ign

4 3 2 1 30

co 20 nc CO 10 en tra 2 t io n, %

ta dy-s a e t S 0

0

20

te

40

re licity p i t l mu 60

gion

80

100

,% (CH4)/(CH4+H2+CO)

Figure 6. 26


Page 27 of 31

1.0 0.8

Conversion

CO H2

CO

0.6

CO H2

CH4

H2

CH4

0.4

CH4

0.2

a: F

0.0 0

2

4

6

8

c: P2

b: P1 0

2

4

6

8

0

Pressure, bar 5

Pressure, bar

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47


2

4

6

8

d Ignited region

4 3

Steady state multiplicity region

2

Not ignited region

1 0.5

0.6

0.7

0.8

0.9

1.0

Coating degree Figure 7. 27



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Page 28 of 31

Figure 8.

28


Page 29 of 31

1.0 0.8

Conversion

CO

CO

CO

H2 H2

0.6

H2 CH4

0.4

CH4

CH4

0.2 a: Mix 3

0.0 0

2

4

6

5

Pressure, bar

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47


8

b: Mix 7 0

2

4

Pressure, bar e

d

4

6

8

c: Mix 11

0

2

4

6

8

10

Ignited region

Ignited region Steady state multiplicity region

3 Steady state multiplicity region

2

Not ignited region Not ignited region

1 0

10

20

30 0

10

20

30

CO2 concentration, vol.% Figure 9. 29



750

Temperature, °C

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 31

700 650 600 550 500 -10

0

10

20

30

40

50

60


30


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FOR TABLE OF CONTENTS ONLY

31


Multifuel Catalytic Combustion in the Presence of Carbon Dioxide over

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