Dehydrogenation of paraffins

For ethane dehydrogenation at 600 °C with bimetallic Pt-Sn nanoparticles (Pt/Sn = 3) supported on calcined hydrotalcite, a strong decrease in coke formation was reported in comparison with a monometallic platinum catalyst of the same particle size. Moreover, initial turnover frequency (TOF) and selectivity to ethene increased with tin addition, likely due to both geometric and electronic effects induced by tin on the surface of the platinum nanoparticles. 

Dehydrogenation of light paraffins is limited by thermodynamics and the process is highly endothermic so that high temperature ( 550 °C) and low pressure ( 0.5 MPa) are usually required to obtain reasonable olefin yields. Most of the industrial processes are based on supported bimetallic 

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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. 

Catalytic Reforming. Worldwide, approximately 30% of commercial benzene is produced by catalytic reforming, a process ia which aromatic molecules are produced from the dehydrogenation of cycloparaffins, dehydroisomerization of alkyl cyclopentanes, and the cycHzation and subsequent dehydrogenation of paraffins (36). The feed to the catalytic reformer may be a straight-mn, hydrocracked, or thermally cracked naphtha fraction ia the... 

Dehydrogenation. The dehydrogenation of paraffins is equihbrium-limited and hence requites high temperatures. Using this approach and conventional separation methods, both Houdry and UOP have commercialized the dehydrogenation of propane to propylene (92). A similar concept is possible for ethane dehydrogenation, but an economically attractive commercial reactor has not been built. 

Figure 7. Possible formation of Te dihydride during dehydrogenation of paraffins over Te-NaX zeolite.

The dehydrogenation of paraffins to olefins, while it does not take place to a large extent at typical reforming conditions (equilibrium conversion of n-hexane to 1-hexene is about 0.3% at 510°C. and 17 atm. hydrogen partial pressure), is nevertheless of considerable importance, since olefins appear to be intermediates in some of the reactions. This matter will be discussed in more detail in a subsequent section. The formation of olefins from paraffins, similar to the formation of aromatics, is favored by the combination of high temperature and low hydrogen partial pressure. The thermodynamics of olefin formation can play an important role in determining the rates of those reactions which proceed via olefin intermediates, since thermodynamics sets an upper limit on the attainable concentration of olefin in the system. 

These heterogeneous catalysts consist of muitimetallic clusters, containing metals, such as platinum, iridium, or rhenium, supported on porous acidic oxide supports, such as alumina. The catalysts are said to be bifunctional because both the metal and the oxide play a part in the reactions. The metal is believed to carry out reversible dehydrogenation of paraffins to olefins, while the oxide is believed to carry out isomerization. 

This question is discussed in detail in the book by Skarchenko [52], It is noted that dehydrogenation of paraffin hydrocarbons dominates by selectivity over thermal cracking in the presence of iodine or other halogens, sulfur-containing compounds, oxygen and nitrous oxide. For example, in the presence of iodine dehydration dominates in the system, whereas in the case of other additives, independently of their amounts—oxygen, ethylene oxide and nitric acid—the main shift of the process toward cracking is preserved. 

Cracking and dehydrogenation of //-paraffins is now the preferred method, giving very linear chains. 

Linear olefins are prepared by dehydrogenation of paraffins, by polymerization of ethylene to a-olefins using a triethyl aluminum catalyst (Ziegler-type catalyst), by cracking paraffin wax, or by dehydrohalogena-tion of alkyl halides. 

The dehydrogenation of //-paraffins yields detergent alkylates and //-olefins. The catalytic use of rhenium for selective dehydrogenation has increased in recent years since dehydrogenation is one of the most commonly practiced of the chemical unit processes. 

While many publications in the field of heat-integrated processes focus on specific processes such as dehydrogenation of paraffins or hydrogen production [3-5], this chapter is more focused on general conceptual trends in process and apparatus design. 

The PACOL process (paraffin conversion to olefin) produces n-olefins by dehydrogenation of paraffin over a heterogeneous platinum catalyst. The Pacol process is more selective than thermal cracking and produces smaller amounts of byproducts. 

Among the different method for manufacturing olefins discussed in Section 2, the dehydrogenation of paraffins and the dehydration of alcohols find a specific application in tte manufacture of isobutene. The following is one of the schemes propos ... 

In its literal form, this reaction is only of academic interest because a molecule is unlikely to break up or isomerize irreversibly in two or more different ways. However, situations frequently encountered in practice are those of multistep parallel first-order decomposition reactions and of parallel reactions that involve coreactants but are pseudo-first order in the reactant A. An example of the first kind is dehydrogenation of paraffins, examples of the second kind include hydration, hydrochlorination, hydroformylation, and hydrocyanation of olefins and some hydrocarbon oxidation reactions. All these reactions are multistep, but the great majority are first order in the respective hydrocarbon, and pseudo-first order if any co-reactant concentration is kept constant. 

LASs were found to possess interesting foaming characteristics, which are very significant for their application as detergents. However, LAS can be controlled by foam regulators. Also, the foam produced is stabilized by form stabilizers. The basic processes have been applied for the manufacture of LAS. The dehydrogenation of paraffins, followed by alkylation of benzene with a mixed olefin or paraffin feedstock, represents the most important route for the production of LAS. This process is catalyzed by hydrogen fluoride (HF) [1—4]. 

It is well known that the supported Pt catalyst show s a high activity for the dehydrogenation of paraffins whereas the supported palladium does not. The results shown in Table 1 suggest that the dehydrogenation activity of supported metals is not essential for the appearance of the paraffin isomerization activity, but the ability of hydrogen activation (dissociation) of the catalyst seems to be essential as well as the acidity. 

The dehydrogenation of paraffins to olefins over carbons with or without zirconium, vanadium, and titanium has also been reported by Shirasaki and Monoto. From the information given it is impossible to discover whether the reaction route is similar although this could, and possibly should, be the case. 

The consecutive reactions, the dehydrogenation of mono-olefins to diolefins and triolefins, are catalyzed on the same active sites as the dehydrogenation of paraffins to mono-olefins. The consecutive reactions that... 

Although the previous discussion had centered on the catalytic dehydrogenation of paraffins, a study on the subject would not be complete without analysis of the dehydrogenation of ethylbenzene to styrene. 

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 ... 

Use of halogens for the dehydrogenation of paraffins has been proposed in different ways. For example, heavy paraffins were first chlorinated and then dehydrochlorinated to heavy olefins commercially in... 

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 chief sources of olefins are cracking operations, especially catalytic cracking. However, olefins can be produced by the dehydrogenation of paraffins butanes are dehydrogenated commercially to provide feeds to alkylation. Isobutane is obtained from crude oils, cracking operations, catalytic reformers, and natural gas. To supplement these sources, n-butane is sometimes isomer-ized. Only small concentrations of diolefins are permissible in feeds to alkylation, particularly for sulfuric add catalyst. Diolefins increase the consumption of acid. 

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