Hydrocarbon reformation

Fired reactors contain tubes or coils in which an endothermic reaction within a stream of reac tants occurs. Examples include steam/ hydrocarbon reformers, catalvst-filled tubes in a combustion chamber pyrolyzers, coils in which alkanes (from ethane to gas oil) are cracked to olefins in both types of reac tor the temperature is maintained up to 1172 K (1650°F). 

Steps 1 through 9 constitute a model for heterogeneous catalysis in a fixed-bed reactor. There are many variations, particularly for Steps 4 through 6. For example, the Eley-Rideal mechanism described in Problem 10.4 envisions an adsorbed molecule reacting directly with a molecule in the gas phase. Other models contemplate a mixture of surface sites that can have different catalytic activity. For example, the platinum and the alumina used for hydrocarbon reforming may catalyze different reactions. Alternative models lead to rate expressions that differ in the details, but the functional forms for the rate expressions are usually similar. 

Electro-catalysts which have various metal contents have been applied to the polymer electrolyte membrane fuel cell(PEMFC). For the PEMFCs, Pt based noble metals have been widely used. In case the pure hydrogen is supplied as anode fuel, the platinum only electrocatalysts show the best activity in PEMFC. But the severe activity degradation can occur even by ppm level CO containing fuels, i.e. hydrocarbon reformates[l-3]. To enhance the resistivity to the CO poison of electro-catalysts, various kinds of alloy catalysts have been suggested. Among them, Pt-Ru alloy catalyst has been considered one of the best catalyst in the aspect of CO tolerance[l-3]. 

In technical hydrocarbon reforming processes using platinum catalysts, high hydrogen pressures are usually used to inhibit catalyst poisoning and coke formation as far as possible, for instance a total pressure of several atmospheres to several tens of atmospheres, with a several-fold excess of hydrogen in the reactant mixture. 

In hydrocarbon reforming processes the vapour of an alkane is passed over a supported metal catalyst such as platinum on silica or alumina. Dehydrocyclization, isomerization and cracking reactions all take place to... 

Preparation. Many reactions and processes are available for the preparation of hydrogen. Among the large-scale processes, the catalytic steam hydrocarbon reforming process can be mentioned. After de-sulphurization, natural gas (or oil-refinery feedstock) is mixed with steam and, at 700-1000°C, passed over a nickel-based catalyst. The irreversible reaction occurs ... 

For metal catalysts used for hydrogenations and, in combination with acid functions, in hydrocarbon reforming reactions, the advantage of nano-size metal particles has been well known. More recently it has been demonstrated that metals on... 

Four hydrogen production techniques are reviewed hydrocarbon reforming ammonia cracking and two other, less common, production techniques, pyrolysis and aqueous phase reforming. 

Few of the primary products of biomass pyrolysis are thermally stable at the typical temperatures of the hydrocarbon reformer. Hence there is significant competition between catalytic reforming reactions (Equation 6.3) and thermally induced cracking decomposition (Equation 6.4). 

It can be seen that the thermodynamic driving force for carbon formation decreases as temperature increases. Carbon formation from the Boudouard reaction is thermodynamically favored at lower temperatures because this reaction is exothermic. This kind of carbon formation usually dominates at the reactor inlet (or feed lines) where the temperature is lower. However, higher temperatures favor the cracking reaction (7). Therefore it is often desirable to conduct the hydrocarbon reforming at an intermediate temperature where the thermodynamic driving force for carbon formation is minimal. 

Solid oxide catalysts such as hexaaluminates and perovskites, in which an active metal catalyst is incorporated into a coke-resistant lattice, are effective for liquid hydrocarbon reforming due to their thermal stability over a broad-range of temperature. However, sulfur tolerance of those materials has yet to be demonstrated. 

Detailed knowledge of the reaction mechanisms and pathways of the reforming system can lead to optimization of reaction conditions, and catalyst design. Unfortunately, very meager information is available on the kinetics of liquid hydrocarbon reforming. Literature is limited mostly to kinetic studies of SR of single paraffinic components. 

In tlie steam-hydrocarbon reforming process, steam at temperatures up to 850°C and pressures up to 30 atmospheres reacts with the desulfurized hydrocarbon feed, in the presence of a nickel catalyst, to produce H2. CO, ( G CH4, and some undecomposed steam. In a second process stage, these product gases are further reformed. Air also is added at this stage to introduce nitrogen into the gas mixture. The exit gases from this stage are further puntied to provide the desired 3 parts H. to 1 part Nj which is the correct empirical ratio for NH3 synthesis. See also Ammonia. 

At present, hydrogen is produced mainly by the steam-hydrocarbon reforming process (Section 14.3). This method can contribute to global warming because it produces C02 as a by-product. It may be possible, however, to capture the C02 and sequester it in depleted gas wells or deep saline aquifers, thus avoiding addition of C02 to the atmosphere. 

Hydrocarbon-reforming catalysts, in Catalyst Handbook-with Special Reference to Unit Processes in Ammonia and Hydrogen Manufacture, Springer -Verlag, New York, Ch 5, pp. 63-96. 

Similar to the reforming of methane, the major product of aliphatic hydrocarbons reforming is syngas, although some dehydrogenated products such as olefins and alkynes may also be formed. Futamura et al. [49-51] reported the C02 reforming... 

Electrical heating requires power supply by an interim storage device, i.e. a battery. Even though batteries exist as buffer devices in most fuel cell system concepts, their size would need to increase considerably to meet the demands for start-up. Therefore, battery power is a less viable option especially for hydrocarbon reforming systems, where high operating temperatures of the reformer exceeding 600 °C need to be achieved. 

However, most fuel cell systems can tolerate methane concentrations up to at least 1% in the reformate, no special purification reactions are required. In contrast, hence, removing small residual amounts of carbon monoxide from pre-purifled reformate applying the methanation reaction may be considered as an alternative to the preferential oxidation of carbon monoxide, provided that the CO concentration is low enough to have no significant impact on the hydrogen yield. However, no applications of methanation for CO clean-up in micro structured devices appear to have been reported, hence the issue is not discussed in depth. Finally, during hydrocarbon reforming all hydrocarbon species (saturated and unsaturated) smaller than the feed molecule may be formed. 

Hydrocarbon Reforming 1 [HCR 1] Micro Structured Monoliths for Partial Methane Oxidation... 

Hydrocarbon Reforming 2 [HCR 2] Partial Methane Oxidation Heat Exchanger/Reactor... 

Hydrocarbon Reforming 3 [HCR 3] Micro Structured Autothermal Methane Reformer... 

Hydrocarbon Reforming 4 [HCR 4] Compact Membrane Reactor for Autothermal Methane Reforming... 

Hydrocarbon Reforming 5 [HCR 5] Sandwich Reactors Applied to Propane Steam Reforming... 

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