Catalytic partial oxidation of ethane to ethylene and syngas over Rh and Pt coated monoliths: Spatial profiles of temperature and composition

Michael, Brian C.; Nare, David N.; Schmidt, L.D.

doi:10.1016/j.ces.2010.03.033

Cited by 47 publications

(35 citation statements)

References 33 publications

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“…The cellulose flow rate was varied to obtain the desired C/O ratio ( Figure 3 in a catalytic partial oxidation system to increase the yield of olefin products. [19] This effect is attributed to the higher sticking coefficient on noble metal catalysts and the higher diffusion coefficient of H 2 than alkanes in a mass transfer limited system. These experiments demonstrate that a fixed-bed catalytic pyrolysis reactor can run autothermally to produce high yields of pyrolysis oil from cellulose with no observable char formation.…”

Section: à2mentioning

confidence: 98%

Rapid Ablative Pyrolysis of Cellulose in an Autothermal Fixed‐Bed Catalytic Reactor

et al. 2010

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Many biological, chemical, and thermal pathways have been investigated as potentially efficient processing methods to utilize biomass as a renewable feedstock. Pyrolysis of biomass has been investigated as a process to produce gas and liquid products by using, amongst others, fluidized-bed, rotary kiln, and plate-ablative reactors. [1,2] However, many pyrolysis reactors are hindered by char production, resulting from limited heat transfer rates to the reactor. As a result, reactors are difficult to scale up due to the large heat inputs required to maintain operation, causing lower pyrolysis oil yields.Heat transfer rates to feed particles should be sufficiently high to prohibit char formation within pyrolysis reactors. Previous research has demonstrated the volatilization of cellulose particles on the front face of a Rh-Ce/a-Al 2 O 3 catalyst bed.[3]High-speed photography was used to image 300 mm cellulose particles impacting the 700 8C catalyst, pyrolyzing to liquid intermediate compounds that were then volatilized and convected into the catalyst bed and further reacted to synthesis gas. High heat transfer rates to the particles (3.4 MW m À2) resulted in the complete conversion of cellulose particles without char formation.An ideal pyrolysis reactor should operate continuously, efficiently, and char-free to maximize the yield of pyrolysis. Graham et al. demonstrated an ultrafast pyrolysis process that converted cellulose to more than 80 wt % gases at temperatures between 750 and 900 8C on millisecond timescales.[4] Wei et al. examined the fast pyrolysis of different biomass feedstocks by using a free-fall reactor with a residence time < 2 s. [5] Particles (300-450 mm) pyrolyzed at 700-800 8C yielded up to 80 wt % gases and 20 wt % char. Similar to these pyrolysis processes, the reactor presented here operates at millisecond residence times and high temperatures (700-900 8C); however, it is able to select for larger hydrocarbon liquid products, rather than gas products. A fraction of the cellulose pyrolysis vapors (10-40 %, Table 1) are sacrificially oxidized to CO 2 and H 2 O to provide heat to the front face for pyrolysis allowing for autothermal and char-free operation.Reactions were carried out in a quartz reactor tube (internal diameter 19 mm) over a fixed catalyst bed (1 cm), as shown in Figure 1. Two types of supports were used: a cylindrical monolith [16 mm diameter, 10 mm long, 65 ppi (pores per linear inch) a-Al 2 O 3 , 5 wt% g-Al 2 O 3 washcoat] and spheres (1 cm bed, 1.3 mm diameter a-Al 2 O 3 ). Metals were impregnated onto the supports by using the incipient wetness technique, described previously.[6] Rh-Ce catalysts contained 2.5 wt % of each metal, Pt was applied to the support at 2.5 wt %. Mass flow controllers fed N 2 , O 2 , CH 4 , and H 2 into the reactor. Methane (0

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Section: à2mentioning

confidence: 98%

Rapid Ablative Pyrolysis of Cellulose in an Autothermal Fixed‐Bed Catalytic Reactor

et al. 2010

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“…[4][5][6] Conversely, the SCT-ODH of short alkanes over platinum proceeds mainly in the gas phase, thus giving rise to the production of olefins and other hydrocarbon species. [7,8] On the basis of these examples, we could conclude that either catalytic or gas-phase chemistry governs the SCT conversion of hydrocarbons, depending only on the stability of the CÀH bond in the gas phase.Herein, by using novel techniques for collecting spatially resolved temperature and concentration profiles, we show that the partial oxidation of short-chain alkanes over rhodium breaks the paradigmatic compartments of heterogeneous processes and gas-phase processes, revealing the real complexity of these "flame-like" processes.Specifically, we examine the reaction of C 3 H 8 CPO (C 3 H 8 + 3/2 O 2 !3 CO + 4 H 2 ) as a case study, and we apply novel techniques for collecting spatially resolved gas-phase and solid temperature and concentration profiles within a rhodium-coated honeycomb monolith to monitor the evolution of a propane/air mixture fed at high flow rate. The temperature and the composition of the reacting system were monitored from the inlet reactor section where the mixture was fed to the outlet section of the catalytic unit where the syngas stream was delivered.…”

mentioning

confidence: 97%

Synergy of Homogeneous and Heterogeneous Chemistry Probed by In Situ Spatially Resolved Measurements of Temperature and Composition

et al. 2011

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The interaction between heterogeneous and homogeneous chemistries is a crucial issue for high-temperature catalytic processes. In particular, the assessment of the main routes that control the selectivity to the desired products is essential for the design and safe operation of reaction units. This assessment is particularly true for the ultrafast conversion of hydrocarbons in short-contact-time (SCT) reactors that play a pivotal role in the effort to cope with the worldwide growing demand for more efficient exploitation of energy and material resources. Examples are the catalytically assisted combustion for gas turbines with ultralow emissions, the catalytic partial oxidation (CPO) of hydrocarbons to H 2 or CO/H 2 mixtures (i.e., syngas), [1] and the oxidative dehydrogenation (ODH) of light alkanes to olefins. [2,3] As a common feature, these processes operate in autothermal and compact reactors, with noble-metal catalysts (palladium, rhodium, and platinum). An enormous energy intensity is peculiar to the SCT autothermal conversion of hydrocarbons over noble metals. Strongly exothermic and endothermic reactions proceed on the catalyst surface at extremely high rates. As a consequence, sharp gradients of temperature (up to 200 8C mm À1 ) and concentration are established within the small reactor volumes. Temperatures ranging from 250 to 1100 8C are generally experienced within a few millimeters. Such a level of severity-in terms of power density and extent of temperature and concentration gradients-is typical of flames and gas-phase oxidation processes in general. For a catalytic process, however, these conditions represent a thoroughly unconventional kinetic regime. To best grasp the intensity and the speed of the involved phenomena, we need to think of SCT conversion of light alkanes as the catalytic equivalent of a flame. This analogy can clearly depict the complexity of the process and emphasize the related scientific issues: To what extent does a catalytic process "stick" to the catalyst surface at these very high temperatures, where the adsorption of species is thermodynamically unfavored? Can the gas-phase activation of C À H bonds (e.g., the formation and propagation of radicals) cooperate or compete with the catalytic process?In this respect, it is largely accepted that in the case of CH 4 CPO over rhodium the gas-phase paths are negligible at atmospheric pressure and the catalytic route dominates. [4][5][6] Conversely, the SCT-ODH of short alkanes over platinum proceeds mainly in the gas phase, thus giving rise to the production of olefins and other hydrocarbon species. [7,8] On the basis of these examples, we could conclude that either catalytic or gas-phase chemistry governs the SCT conversion of hydrocarbons, depending only on the stability of the CÀH bond in the gas phase.Herein, by using novel techniques for collecting spatially resolved temperature and concentration profiles, we show that the partial oxidation of short-chain alkanes over rhodium breaks the paradigmatic compartments of heterogeneou...

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“…Therefore it can be argued that H2 is rapidly and preferentially oxidized instead of the hydrocarbon in the first part of the catalytic reactor due to its higher reactivity and diffusivity, causing a marked increase of the catalyst temperature in this zone [13]. Further downstream the reactor H2 is produced again via methane steam reforming [13]. The final composition of the syn-gas emerging from the CPO reactor at =4.2 is shown in Fig.…”

Section: Fig 2 Methane Conversion Catalyst Temperature and Yieldsmentioning

confidence: 99%

“…3a). This effect is due to the larger heat of combustion of H2 per mole of oxygen [13,14]. Methane conversion (Fig.…”

Section: Fig 2 Methane Conversion Catalyst Temperature and Yieldsmentioning

confidence: 99%

“…By increasing the H2 content in the fuel, the temperature peak progressively moved closer to the inlet section of the catalytic monolith: however we never observed a flashback. Therefore it can be argued that H2 is rapidly and preferentially oxidized instead of the hydrocarbon in the first part of the catalytic reactor due to its higher reactivity and diffusivity, causing a marked increase of the catalyst temperature in this zone [13]. Further downstream the reactor H2 is produced again via methane steam reforming [13].…”

Section: Fig 2 Methane Conversion Catalyst Temperature and Yieldsmentioning

confidence: 99%

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Combustion characterization of hybrid catalytic fuelled with methane and hydrogen mixtures

Allouis¹,

Cimino²,

Nigro³

2014

Proceedings of the 2014 International Conference on Quantitative InfraRed Thermography

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The novel concept of hybrid catalytic combustion based on Catalytic Partial Oxidation + homogeneous flame combustion was tested for the first time with fuel mixtures of methane and hydrogen. CPO experiments were run to elucidate the effect of the progressive substitution of CH4 with H2 in the fuel feed. Furthermore a prototype radiant hybrid burner was safely operated and characterized with up to 80% vol. of H2 in the fuel and a primary equivalence ratio in the range 2.4 -4.0. Outstanding NOx emission levels were attained due to the effective reduction of both thermal and prompt NOx formation.

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Catalytic partial oxidation of ethane to ethylene and syngas over Rh and Pt coated monoliths: Spatial profiles of temperature and composition

Cited by 47 publications

References 33 publications

Rapid Ablative Pyrolysis of Cellulose in an Autothermal Fixed‐Bed Catalytic Reactor

Rapid Ablative Pyrolysis of Cellulose in an Autothermal Fixed‐Bed Catalytic Reactor

Synergy of Homogeneous and Heterogeneous Chemistry Probed by In Situ Spatially Resolved Measurements of Temperature and Composition

Combustion characterization of hybrid catalytic fuelled with methane and hydrogen mixtures

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