Reforming ethane

R, = a k4 [CHolCCoHglg., where R, is the rate of formation of ethane in reaction 3, and a = k5/(k5 + k4 [CH4]), the fraction of ethyl radicals formed in reaction 4 which decompose via reaction 5 if reaction 4R is negligible, a = 1. The concentration of methyl radicals will be given by [CH3] = ((R3 + k3 [C2Hg]55)/k3). Note that while reaction 3R, the reverse of reaction 3, must be taken into account in calculating the radical concentration and in fact becomes the dominant source of radicals, it does not enter directly into the steady-state equation for ethane because it does not lead to a net consumption of methyl radicals, since these ultimately can only recombine to reform ethane in the present system. 

Mulla et al. [17] proposed the following mechanism for the oxidative steam reforming. Ethane is activated by molecular oxygen leading to the formation of ethyl radicals and their subsequent decomposition to ethylene [Reactions 1.6 and 1.7], the conversion of ethane pmely by its thermal eracking is drastically increased. 

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). 

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. 

Natural gas and crude oils are the main sources for hydrocarbon intermediates or secondary raw materials for the production of petrochemicals. From natural gas, ethane and LPG are recovered for use as intermediates in the production of olefins and diolefms. Important chemicals such as methanol and ammonia are also based on methane via synthesis gas. On the other hand, refinery gases from different crude oil processing schemes are important sources for olefins and LPG. Crude oil distillates and residues are precursors for olefins and aromatics via cracking and reforming processes. This chapter reviews the properties of the different hydrocarbon intermediates—paraffins, olefins, diolefms, and aromatics. Petroleum fractions and residues as mixtures of different hydrocarbon classes and hydrocarbon derivatives are discussed separately at the end of the chapter. 

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 ... 

The first step in the production of synthesis gas is to treat natural gas to remove hydrogen sulfide. The purified gas is then mixed with steam and introduced to the first reactor (primary reformer). The reactor is constructed from vertical stainless steel tubes lined in a refractory furnace. The steam to natural gas ratio varies from 4-5 depending on natural gas composition (natural gas may contain ethane and heavier hydrocarbons) and the pressure used. 

Alkanes and Alkenes. For this study, C150-1-01 and C150-1-03 were tested under primary wet gas conditions with ethylene, ethane, propylene, and propane being added to the feed gas. This study was made in order to determine whether these hydrocarbons would deposit carbon on the catalyst, would reform, or would pass through without reaction. The test was conducted using the dual-reactor heat sink unit with a water pump and vaporizer as the source of steam. All gas analyses were performed by gas chromatography. The test was stopped with the poisons still in the feed gas in order to preserve any carbon buildup which may have occurred on the catalysts. 

It can also be prepd by the catalytic reforming of other low-boiling hydrocarbons (ethane to butane) (Ref 3)... 

Hydrogenolysis of butane was used to study the catalysis of the RhPt particles in mesoporous silica. This is a test reaction of reforming of alkanes in oil refinery, and methane, ethane, and propane are formed by the cleavage of terminal or central C-C bond (Scheme 1). 

Alkane metathesis can also formally appear as the breaking and reformation of one C-H and one C-C bonds. Scheme 3.7 shows, for example, the case of ethane where methane and propane are produced ... 

The study of archetype molecules. This method has been proposed and widely used by Rooney, Burwell, Anderson, and others (see, for review, 155,156,160). In this method a molecule is used which can form an archetype of chemisorbed complex ( caged molecules as derivatives of ada-mantane or ethane in its hydrogenolysis, neopentane in exchange with D2 or in reforming reactions, etc.) or which can form several complexes, but the contribution of these complexes to the overall mechanism is easily derived from the product spectrum [as is the case, for example, with neohexane (167, 168). ... 

The first suggestions concerning the mechanism of catalytic reforming were based on studies with hydrocarbon mixtures that permitted only observation of composition changes.91,98,120 It was observed, for example, that about 30% of the Ci—C4 product consisted of methane and ethane. These, however, are not common products in catalytic cracking processes. In fact, when n-heptane was hydrocracked, less methane and ethane were formed than expected, according to the stoichiometry of Eqs. (2.15) and (2.16). Therefore, C5 and C6 hydrocarbons were not considered... 

All these derivations assume that radical R is converted to oxidation products and that it does not reform the hydrocarbon. The relations are summarized in Table II, which also includes the experimental results for methane and ethane. 

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

The reactor impregnated with nickel showed inferior performance again. Deactivation was observed, which was assumed to originate from coking, sintering, oxidation of the nickel or even losses of volatile nickel species. With increasing temperature, enhanced formation of by-products, namely methane and ethane, was observed in the reformate both under partial oxidation conditions and in the autothermal mode, which was attributed to thermal cracking. 

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

Intermediate Duty catalysts are for feeds with a significant content of components from ethanes up to liquid petroleum gas (LPG). The heavier feedstock increases the tendency for catalyst deactivation through carbon laydown and requires a special catalyst in the top 30% to 50% of the reformer tubes. This tendency also occurs when light feeds are run at low steam-to-carbon ratios and/or at a high heat flux. 

Cyclam)Ni(II) complexes react readily with methyl radicals [12]. The resulting (cyclam)Ni(III)-CH3 intermediates transform with excess radiolytically generated methyl radicals to ethane and reform the initial Ni(II) complex. The kinetics was determined. 

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... 

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