Olefins, catalytic dehydrogenation

Olefin—Paraffin Separation. The catalytic dehydrogenation of / -paraffins offers a route to the commercial production of linear olefins. Because of limitations imposed by equiUbrium and side reactions, conversion is incomplete. Therefore, to obtain a concentrated olefin product, the olefins must be separated from the reactor effluent (81—85), and the unreacted / -paraffins must be recycled to the catalytic reactor for further conversion. 

Butadiene is obtained mainly as a coproduct with other light olefins from steam cracking units for ethylene production. Other sources of butadiene are the catalytic dehydrogenation of butanes and butenes, and dehydration of 1,4-butanediol. Butadiene is a colorless gas with a mild aromatic odor. Its specific gravity is 0.6211 at 20°C and its boiling temperature is -4.4°C. The U.S. production of butadiene reached 4.1 billion pounds in 1997 and it was the 36th highest-volume chemical. ... 

Not only the linear Cl0-Cl8 a-olefins but also the linear C10-Cl8 olefins with internal double bonds, the so-called -v /-olefins, are of great importance in surfactant chemistry, n-a-Olefins and n-y-olefins have the same suitability for the manufacture of linear alkylbenzenes, the most important synthetic anionic surfactants, by alkylation of benzene. Nowadays medium molecular weight n- /-olefins are industrially produced by two processes the catalytic dehydrogenation of the corresponding n-alkanes [4,28] and the cometathesis of low and high molecular weight n-v /-olefins, obtained by double-bond isomerization of the isomeric n-a-olefins [29]. 

The LAB production process (process 1) is mainly developed and licensed by UOP. The N-paraffins are partially converted to internal /z-olefins by a catalytic dehydrogenation. The resulting mixture of /z-paraffins and n-olefins is selectively hydrogenated to reduce diolefins and then fed into an alkylation reactor, together with an excess benzene and with concentrated hydrofluoric acid (HF) which acts as the catalyst in a Friedel-Crafts reaction. In successive sections of the plant the HF, benzene, and unconverted /z-paraffins are recovered and recycled to the previous reaction stages. In the final stage of distillation, the LAB is separated from the heavy alkylates. 

CATOFIN [CATalytic OleFIN] A version of the Houdry process for converting mixtures of C3 - C5 saturated hydrocarbons into olefins by catalytic dehydrogenation. The catalyst is chromia on alumina in a fixed bed. Developed by Air Products Chemicals owned by United Catalysts, which makes the catalyst, and licensed through ABB Lummus Crest. Nineteen plants were operating worldwide in 1991. In 1994, seven units were used for converting isobutane to isobutylene for making methyl /-butyl ether for use as a gasoline additive. 

Another area of high research intensity is the catalytic dehydrogenation of alkanes to yield industrially important olefin derivatives by a formally endothermic (ca. 35 kcal mol-1) loss of H2. Recent results have concentrated on pincer iridium complexes, which catalytically dehydrogenate cycloalkanes, in the presence of a hydrogen accepting (sacrificial) olefin, with turnover numbers (TONs) of >1000 (Equation (23)) (see, e.g., Ref 33,... 

As chemical companies rely more heavily on ethane and propane feeds to their olefins plants to generate their ethylene and propylene supplies, the coproduction of butadiene in olefins plants has not kept up with demand. Industry has resorted to building plants that make on-purpose or swing supply butadiene. The processes involve catalytically dehydrogenating (removing hydrogen from) butane or butylene. 

Another route to ethylbenzene is available for those remote places where olefin plants or refinery crackers are not nearby but a supply of ethane is— catalytic dehydrogenation of ethane to ethylene followed by its reaction with benzene to produce EB. The first of two steps in Figure 8-4 use a gallium zinc zeolyte catalyst that promotes ethane dehydrogenation to ethylerie at 86% selectivity and up to 50% conversion per pass. 

The stream from the cryogenic unit which is rich in C /C-olefins can be fractionated and selectively hydrogenated (to remov traces of dienes) to yield the pure olefins. Common uses of propene are the production of polypropylene, acrylonitrile, cumene etc. Butene can be catalytically dehydrogenated to butadiene which is used in the production of synthetic rubbers. 

Substrates which can undergo partial oxidation are characterized by a 7T-electron system or unshared electrons olefins and aromatics contain the first, methanol, ammonia and sulphur dioxide the second. Alkanes do not contain such electrons. Their selective oxidation appears to demand (thermal or catalytic) dehydrogenation to alkenes as the initial process. 

The continuous increase in world consumption of MTBE has created a strong incentive to increase the production of isobutylene. Isobutylene can be produced by catalytic dehydrogenation of isobutane. However, the largest production of C4 olefins comes from the thermal cracking processes for the manufacture of ethylene which generate as by-products C4 mixtures containing C4 olefins and C4 alkanes plus butadiene. Isobutylene is also a product of fluid bed catalytic cracking units. 

Paraffin dehydrogenation for the production of olefins has been in use since the late 1930s. During World War II, catalytic dehydrogenation of butanes over a chro-mia-alumina catalyst was done for the production of butenes that were then dimerized to octenes and hydrogenated to octanes to yield high-octane aviation fuel. 

A different approach to catalytic dehydrogenation was first introduced in the mid-1960s for the supply of long-chain linear olefins for the production of biodegradable detergents. 

Production of light olefins by the catalytic dehydrogenation of light paraffins must be able to maintain reasonable per-pass conversion levels and high olefin selectivity. Very importantly, it must be able to produce olefins in high yields over long periods of time without shutdowns. 

The processes discussed above are for the direct catalytic dehydrogenation of paraffins to the corresponding olefins or of olefins to diolefins. Other methods have also been considered, although none has reached the level of commercialization. Some of the most notable are ... 

Catalytic dehydrogenation of paraffins and of ethylbenzene is a commercial reality in numerous applications, from the production of light olefins, heavy olefins, to that of alkenylaromatics. Oxydehydrogenation, on the other hand, is still in the developmental stage, but, if successful, holds great promise on account of its potential energy savings. 

The most common route to LAB involves HF alkylation to produce LAB from linear mono-olefins and benzene. In this route, linear mono-olefins are produced by catalytic dehydrogenation of linear paraffins. The mono-olefins may then be enriched, by selective hydrogenation of diolefins (formed because of the side reactions in the dehydrogenation step). In the final step, olefins and benzene are fed to the alkylation unit to produce LAB. There are over 30 operating plants worldwide producing LAB by this manufacturing route. 

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