Ethane, steam reforming

Similar expressions have been found to be applicable to the steam reforming of higher hydrocarbons. For example, it has been shown that if it is assumed that ethane, CaHg is adsorbed on two neighbouring sites, the overall reaction rate can be expressed by the equation... 

The reaction shown above for the steam reforming of methatie led to die formation of a mixture of CO and H2, die so-called synthesis gas. The mixture was given this name since it can be used for the preparation of a large number of organic species with the use of an appropriate catalyst. The simplest example of this is the coupling reaction in which medrane is converted to ethane. The process occurs by the dissociative adsorption of methane on the catalyst, followed by the coupling of two methyl radicals to form ethane, which is then desorbed into the gas phase. 

As the molecular weight of the hydrocarbon increases (lower H/C feed ratio), the H2/CO product ratio decreases. The H2/CO product ratio is approximately 3 for methane, 2.5 for ethane, 2.1 for heptane, and less than 2 for heavier hydrocarbons. Noncatalytic partial oxidation of hydrocarbons is also used to produce synthesis gas, but the H2/CO ratio is lower than from steam reforming ... 

Dehydrogenations, e.g., ethane to ethene, ethylbenzene to styrene, methanol to formaldehyde Methane steam reforming Water-gas shift reaction... 

Rostrup-Nielsen48 has given the following results for the order of specific activities of a series of catalysts for the steam reforming of ethane ... 

This hypothesis is confirmed by the data of Rostrup-Nielsen (237, 238) listed in Table XXI, showing the effects of sulfur poisoning on the specific activity of 25 wt. % Ni/Mg0Al203 in steam reforming of ethane at 775 K. 

Influence of Sulfur Poisoning on Specific Activity in Steam Reforming of Ethane on 25% Ni/Al203 MgOa h... 

Rare earth oxides are useful for partial oxidation of natural gas to ethane and ethylene. Samarium oxide doped with alkali metal halides is the most effective catalyst for producing predominantly ethylene. In syngas chemistry, addition of rare earths has proven to be useful to catalyst activity and selectivity. Formerly thorium oxide was used in the Fisher-Tropsch process. Recently ruthenium supported on rare earth oxides was found selective for lower olefin production. Also praseodymium-iron/alumina catalysts produce hydrocarbons in the middle distillate range. Further unusual catalytic properties have been found for lanthanide intermetallics like CeCo2, CeNi2, ThNis- Rare earth compounds (Ce, La) are effective promoters in alcohol synthesis, steam reforming of hydrocarbons, alcohol carbonylation and selective oxidation of olefins. 

Ethane, propane, and butane, usually present in smaller concentrations in addition to methane in most natural gases, react in the steam reforming in similar way, with the overall reaction corresponding to Equation (35). With higher hydrocarbons, as contained in naphtha, the reaction is more complex. Higher paraffins in naphtha feed will be first completely cracked down in a methane-forming reaction, which proceeds between 400 and 600 °C and could be described, for example, as follows (Eq. 56) ... 

Figure 6. Intrinsic reaction rate in dependence of sulphur poisoning for a) normal catalysts ( ), b) gum deactivated catalysts (A). The dotted line represents the ideal relation for the average intrinsic activity of a normal shell poisoned catalyst, 0 = 0.9. Steam reforming of ethane, H2O/C = 4.0, P = 1 bar. Activities normalized with activity of unpoisoned catalyst.

Steam reforming is the reaction of steam with hydrocarbons to make a manufactured gas containing mostly methane with trace amounts of ethylene, ethane, and hydrogen. For the manufacture of this gas, a representative catalyst composition contains 13 wt % Ni, 12.1 wt % U, and 0.3 wt % K it is particularly resistant to poisoning by sulfur. To make hydrogen, the catalyst contains oxides of Ni, Ca, Si, Al, Mg, and K. Specific formulations are given by Satterfield (1980). 

Steam reforming reaction of ethane, propane, and n-butane are represented by Equations 2.21-2.23, while the thermodynamic data for these reactions are summarized in Tables 2.1-2.9, respectively ... 

Table 2.7. Thermodynamic Data for the Steam Reforming of Ethane C2H6(g) + 2H20(g) -> 5H2(g) + 2CO(g)...

Graf et al.108 performed a comparative study of steam reforming of methane, ethane and ethylene on Pt, Rh, and Pd supported on YSZ. They observed that the reactivity and product distribution depends on the type of noble metal loaded. Over Rh/YSZ catalyst, the reactivity decreased in the order C2H6 > CdE > CH4. On the other hand, over Pt/YSZ, methane reacted much faster than the C2 hydrocarbons and the order of reactivity is CH4 > C2H4 > C2H6 (Fig. 2.8). The higher reactivity of Rh... 

Figure 2.8. Conversion of methane, ethane, and ethylene in steam reforming reaction over (a) Rh/YSZ and (b) Pt/YSZ. Adapted from Graf et al.108...

Wang and Gorte144 measured the differential rates of steam reforming of methane, ethane, n-butanc, n-hexane, 2-4-dimethylhexane, n-octane, cyclohexane,... 

Figure 2.12. Arrhenius plots for the steam reforming of methane, ethane, n-butane, /t-hexane, and benzene over Pd/Ce02 catalyst. Water partial pressure is lOOtorr. Adapted from Wang and Gorte.144...

Graf, P.O., Mojet, B.L., van Ommen, J.G., and Lefferts, L. Comparative study of steam reforming of methane, ethane and ethylene on Pt, Rh and Pd supported on yttrium-stabilized zirconia. Applied Catalysis. A, General, 2007, 332 (2), 310. 

Laosiripojana, N., Sangtongkitcharoen, W., and Assabumrungrat, S. Catalytic steam reforming of ethane and propane over Ce02-doped Ni/Al203 at SOFC temperature Improvement... 

Natural gas constituents heavier than methane are also excellent petrochemical feedstocks [1]. Ethane is the most desirable starting material for producing ethylene whenever a minimum amount of byproducts is desired. Propane and butane can also be dehydrogenated to olefins, propylene, and butene, and butene can be further dehydrogenated to butadiene. The naphtha fraction, which is also known as natural gasoline, has a low octane number, but is an excellent feedstock for cracking to olefins and/or steam reforming. 

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