C4H10 oxidation

The conversion of a chemical with a given molecular formula to another compound with the same molecular formula but a different molecular structure, such as from a straight-chain to a branched-chain hydrocarbon or an alicyclic to an aromatic hydrocarbon. Examples include the isomerization of ethylene oxide to acetaldehyde (both C2H40) and butane to isobutane (both C4H10). 

This Reppe process using acetylene for 1,4 butanediol is currently being replaced with processes that start with propylene oxide (C3H60), butadiene (C4H(.), or butane (C4H10). 

Experimental solid-oxide fuel cells that use butane (C4H10) as the fuel have been reported recently. These cells contain composite metal/metal oxide electrodes and a solid metal oxide electrolyte. The cell half-reactions are... 

Echols and Pease found that the reaction is partially inhibited by nitric oxide, and a similar result was obtained by Rice and Polly with propene. Evidence against the hypothesis that the uninhibitable reaction is a molecular process was obtained by Steacie and Folkins , who found that small amounts of ethylene oxide could sensitize the maximally-inhibited reaction. They also found that the products of the inhibited reaction were identical with those of the uninhibited reaction. The fact that the maximally-inhibited pyrolysis is not molecular has been firmly established by Kuppermann and Larson, who pyrolyzed a mixture of C4H10 and C4D10. They found that the ratio of CD3H to CD4 in the products was independent of the amount of nitric oxide. They also found that whereas the... 

A synthesis gas is made by partial oxidation of butane (C4H10) in the presence of steam and air. The product synthesis gas has the percent composition 3.5% CO2,... 

Figure 4 Selectivity, /C4H10 conversion, and reaction temperature for the oxidative dehydrogenation of (C4Hio over Pt/a-Al203 in a Pd membrane reactor as a function of time on stream. The reaction side contained 10% N2 dilution, had a total flow rate of 1 slpm, and was maintained at a pressure of 2 psig. The sweep side (N2) had a total flow rate of 4 slpm and was maintained at a pressure of 1 psig. Data is shown for (C4Hio 02 ratios of 1.0 and 1.45.

Sources of previous work on hydrocarbon cracking can be found in Ref.52. Cracking of CH4 and of C4H10 has also been studied in the presence of C02 and H20 vapor53, s4 The interesting observation is that the rupture of a C—H bond remains the slow step which occurs at rates very close to those measured in mixtures with hydrogen. Further oxidation to CO follows via C2 species. In the presence of 0252>, conversion to CO occurs through self-accelerated radical chain reactions. 

Yamazoe and Teraoka (1990) summarized the results from several researchers who reported rates for oxidation of hydrocarbons over Co- and Fe-perovskite-type oxides that tend to be maximum at smaller x values (0.1-0.4) than Mn perovskites (0.6-0.8). Figure 16 shows the amount of desorbed oxygen and the catalytic activity, expressed in terms of the temperature at which the conversion of C4H10 was 50% (T5o%), as a function of the Sr content, x in Lai vSr[Coo.4Fe(j(-)03. The amount of desorbed O2 increased monotonically with La substitution up to x = 0.8 while T50% had a maximum at x = 0.2, in agreement with the results mentioned above. 

Figure 4 The deactivation of a PdK Al20 + Th02) catalytic bead by HMDS and the subsequent recovery of catalytic activity. Temperature 800K. o—o, Oxidation of methane (composition of reactant mixture 2.5 mol% CH4, 20.5 mol% O2, together with 2.5 x lOr moP/o HMDS during deactivation experiments, balance N2). —, Oxidation of butane (composition of reactant mixture 0.75 moP/o C4H10,20.9 moP/o O2, together with 2.5 x 10" nwl% HMDS during deactivation experiments, balance N2)...

Tetra - ethylphosphonium carbonate, [(C2H5)4P]2C03, forms highly deliquescent, needle-shaped crystals. These at 2-10° to 250° C. are decomposed with formation of triethylphosphine, triethylphosphine oxide, diethyl ketone, carbon dioxide and a gaseous hydrocarbon (C4H10 ). An acid carbonate is known, and this gives a similar result W hen decomposed by heat. 

Figure 10. Galvanostatic oxidation curves for hydrocarbons adsorbed on platinum black electrodes at 25°C from 5N H2SO4 (1) C2H4, (2) C4H10, (3) C3H8, (4) C2H6, (5) CH4, (6) H2 [from Niedrach, J. Electrochem. Soc. Ill...

Almost all studies regarding direct hydrocarbon SOFCs show comparatively poor performance (lower OCP and higher polarization resistance) with hydrocarbon fuels when compared to H2 fuel, Fig. 3.2. Since most of these tests are performed by switching fuel on the same cell, the drop in performance must be linked to the anode. It is possible that the increased polarization resistance may be due to lower diffusivity of the hydrocarbon fuels, but the electrodes are typically highly porous and the current density per unit area is relatively low. In addition, the oxidation of 1 mole of hydrocarbon fuel yields a significantly greater number of electrons than 1 mole of H2 fuel (H2, CH4, and C4H10 total oxidation yield 2, 8, and 26 moles of electrons, respectively). Furthermore, the cell OCP is an equilibrium, zero current, measurement and is therefore not directly influenced by gas diffusivity. Therefore, it is unlikely that gas diffusivity limits the performance for pure fuels at low conversion. The conclusion must then be that the anode electrocatalytic activity toward hydrocarbon oxidation is the primary factor in reduced SOFC performance. 

While Cu can be utilized as a catalyst, it does not contribute significantly to the overall catalytic activity of the anode. This was verified by the low performance of Cu-only anodes, particularly in hydrocarbon fuels [22], and the identical performance achieved when Cu is replaced with catalytically inert bulk Au [41]. The role of Ce02 as electrocatalyst for fuel oxidation was confirmed by replacing Ce02 with other lanthanide oxides and comparing SOFC performance with the activity of the lanthanide toward fuel oxidation [22]. The ceU performance tracked well with the M-C4H10 light-off temperature of the lanthanide. 

While these results are interesting, SOFC with LSCM anodes show significantly lower power outputs in C4H10 and CH4, when compared with H2 fuel [6]. Since the change in fuel only influences anode conditions, the anode activity toward oxidation of hydrocarbons appears to be a performance-limiting process for these anodes. This was further illustrated by electrochemical measurements on SOFCs with dense LSCM films [18]. The OCP values measured for these SOFCs with CH4 on the anode were comparable to the values measured in inert gas (He), 0.06 V. It was suggested that the kinetics for CH4 oxidation are slow, and that the contact time of the fuel on the relatively smooth surface was too short to set the CH4 reaction equilibrium. The addition of small amounts of Pd as a catalyst to the anode resulted in reasonable OCP values, 0.87 V, proving that the catalytic performance of LSCM toward CH4 is low and must be improved. 

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