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Oxidative dehydrogenation of ethane in short contact time reactors

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Chapter 1 Introduction 1 Chapter 1 Introduction 1.1 Ethylene production Ethylene (C 2 H 4 ) is an organic molecule where the 2 carbon atoms are connected by a double bond, which causes the molecule to be highly reactive towards the reactions of halogen addition, hydration and polymerization (Solomons, 1976). Ethylene is the largest-volume petrochemical produced worldwide, but has no direct end uses. Half of the ethylene produced is polymerized to polyethylene, through high or low pressure processes. The remaining half is transformed into chemicals, such as ethylene glycol, oxirane, styrene, ethanol, 1,2-dichloro ethane, acetaldehyde and vinyl acetate. The extremely high versatility of ethylene, due to the chemical properties determined by its double bond, puts such molecule as building block in a large range of products, above all in the field of the fine chemicals. Currently, ethylene is produced by steam cracking in furnace reactors, accordingly to a well established technology, which was constantly improved since the 1940s, when U.S. oil and chemical company began to produce it from ethane obtained from refinery by-product streams and from natural gas. Today, various feedstocks are employed for ethylene production, from ethane to naphta, to LPG, to fuel oil, according to the convenience of the locations and the cost of the raw materials. For instance, in the U.S. ethane is the main feedstock, since it is largely available, while in Europe and Japan, where natural gas is more expensive, the fuel feeds are mainly constituted by light naphtas (Kirk-Othmer, 1978). Ethylene is produced by steam cracking, as sketched in Fig. 1.1. As reported in the Kirk-Othmer Encyclopedia, a hydrocarbon stream is heated and mixed with steam to incipient cracking temperature (500-650°C) before entering a fired tubular reactor (radiant tube or coil), where under controlled residence time, temperature profile and partial pressure is heated to 750-875°C. Saturated hydrocarbons crack into smaller molecules, amongst which ethylene, other olefins and diolefins are the major products. The steam cracking of saturated hydrocarbons to olefins is highly endothermic and requires high energy input rates. On leaving the fired tubular reactor, the products are cooled immediately to 550-650°C to prevent degradation by secondary reactions. These gases are then separated into the desired products. Large ethylene yields require high temperature, short residence times and low hydrocarbon pressure in the reactor. Fast and efficient heat transfer is achieved in the furnace,

Anteprima della Tesi di Francesco Donsì

Anteprima della tesi: Oxidative dehydrogenation of ethane in short contact time reactors, Pagina 1

Tesi di Dottorato

Dipartimento: Ingegneria Chimica

Autore: Francesco Donsì Contatta »

Composta da 194 pagine.

 

Questa tesi ha raggiunto 1055 click dal 04/11/2004.

 

Consultata integralmente 5 volte.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.