Petroleum naphtha “reforming reaction

Interest in carbon deposition cm platinum surfaces has been driven by the fact that this metal and its alloys are used extensively in the reforming of petroleum naphthas. This reaction is carried out over bi-functional catalysts which consist of a single metal (e.g. Pt) or a combination of metals (e.g. Pt/Ir, Pt/Re, Pt/Sn) dispersed on an acidic support such as alumina, on which the acidity is controlled by addition of... 

The objective of the process is to convert saturated hydrocarbons (alkanes and cycloalkanes) in petroleum naphtha fractions to aromatic hydrocarbons as selectively as possible, since the latter have excellent antiknock ratings (1,2). Naphtha fractions are composed of hydrocarbons with boiling points in the approximate range of 50-200°C. Reaction temperatures of 425-525°C and pressures of 10-35 atm are employed in the process. Reforming catalysts commonly contain platinum (3-5) or a combination of platinum and a second metallic element such as rhenium (6) or iridium (2,7). 

Dehydrogenation is a key reaction in the production of commodity chemicals such as butadiene, styrene and formaldehyde and in the catalytic reforming of petroleum naphtha [1-3], In the fine chemical industry, however, dehydrogenation is used less than the numerous hydrogenation reactions which are available. Dehydrogenation is usually an endothermic reaction which requires high temperatures. For such conditions the chemical stability of many fine chemicals is often insufficient. Most of the dehydrogenation reactions used in fine chemistry yield aromatic or heteroaromatic compounds and aldehydes or ketones. 

The manufacture of gas mixtures of carbon monoxide and hydrogen has been an important part of chemical technology for about a century. Originally, such mixtures were obtained by the reaction of steam with incandescent coke and were known as water gas. Eventually, steam reforming processes, in which steam is reacted with natural gas (methane) or petroleum naphtha over a nickel catalyst, found wide application for the production of synthesis gas. 

An important commercial example of an endothermic reaction that is carried out adiabatically is the catalytic reforming of petroleum naphtha to produce high-octane gasoline. In this process, the naphtha is mixed with hydrogen and passed over a heterogeneous catalyst that contains platinum, and perhaps other metals such as rhenium or tin, on a ceramic support such as alumina. The temperature is in the region of 800-900 °F. 

Fuel Hydrogen for PAFC power plants will typically be produced from conversion of a wide variety of primary fuels such as CH4 (e.g., natural gas), petroleum products (e.g., naphtha), coal liquids (e.g., CH3OH) or coal gases. Besides H2, CO and CO2 are also produced during conversion of these fuels (unreacted hydrocarbons are also present). These reformed fuels contain low levels of CO (after steam reforming and shift conversion reactions in the fuel processor) which cause anode poisoning in PAFCs. The CO2 and unreacted hydrocarbons (e.g., CH4) are electrochemically inert and act as diluents. Because the anode reaction is nearly reversible, the fuel... 

Endothermic reactions can also be run with interstage heating. An example we have considered previously is the catalytic reforming of naphtha in petroleum refining, which is strongly endothermic. These reactors are adiabatic packed beds or moving beds (more on these in the next chapter) in which the reactant is preheated before each reactor stage. 

Hydrocarbons react with steam in an endothermic reaction to form carbon monoxide and hydrogen. The most important feedstock for the catalytic steam reforming process is natural gas. Other feedstocks are associated gas, propane, butane, liquefied petroleum gas, and some naphtha fractions (q.v.). The choice is usually made on the availability and the price of the raw material. 

A catalyst consisting of platinum dispersed on an acidic alumina is a very effective dual function catalyst, used in petroleum reforming of naphtha and also for paraffin isomerization. The conversion of naphtha constituents such as methylcyclopentane, MCP, to benzene, B, is desired in order to increase octane rating. The reaction pathway for conversion of MCP to B is illustrated in Fig. 3 . MCP is first dehydrogenated on a platinum site to the olefin of the same structure. The olefin then transfers to an acidic site where it is isomerized to cyclohexene. This olefin proceeds to a platinum site where it is dehydrogenated to B and H2. In the diagram, vertical movement represents hydrogen subtraction or addition and horizontal movement represents isomerization. 

Desulfurization of petroleum feedstock (FBR), catalytic cracking (MBR or FI BR), hydrodewaxing (FBR), steam reforming of methane or naphtha (FBR), water-gas shift (CO conversion) reaction (FBR-A), ammonia synthesis (FBR-A), methanol from synthesis gas (FBR), oxidation of sulfur dioxide (FBR-A), isomerization of xylenes (FBR-A), catalytic reforming of naphtha (FBR-A), reduction of nitrobenzene to aniline (FBR), butadiene from n-butanes (FBR-A), ethylbenzene by alkylation of benzene (FBR), dehydrogenation of ethylbenzene to styrene (FBR), methyl ethyl ketone from sec-butyl alcohol (by dehydrogenation) (FBR), formaldehyde from methanol (FBR), disproportionation of toluene (FBR-A), dehydration of ethanol (FBR-A), dimethylaniline from aniline and methanol (FBR), vinyl chloride from acetone (FBR), vinyl acetate from acetylene and acetic acid (FBR), phosgene from carbon monoxide (FBR), dichloroethane by oxichlorination of ethylene (FBR), oxidation of ethylene to ethylene oxide (FBR), oxidation of benzene to maleic anhydride (FBR), oxidation of toluene to benzaldehyde (FBR), phthalic anhydride from o-xylene (FBR), furane from butadiene (FBR), acrylonitrile by ammoxidation of propylene (FI BR)... 

The objectives of the catalytic reforming of naphtha are to increase the naphtha octane number (petroleum refination) or to produce aromatic hydrocarbons (petrochemistry). Bifunctional catalysts that promote hydrocarbon dehydrogenation, isomerization, cracking and dehydrocyclization are used to accomplish such purposes. Together with these reactions, a carbon deposition which deactivates the catalyst takes place. This deactivation limits the industrial operation to a time which depends on the operational conditions. As this time may be very long, to study catalyst stability in laboratory, accelerated deactivation tests are required. The knowledge of the influence of operational conditions on coke deposition and on its nature, may help in the efforts to avoid its formation. 

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