Butane/butene mixtures, dehydrogenation

Butadiene could also be produced by the catalytic dehydrogenation of butanes or a butane/butene mixture. 

During World War II, production of butadiene (qv) from ethanol was of great importance. About 60% of the butadiene produced in the United States during that time was obtained by a two-step process utilizing a 3 1 mixture of ethanol and acetaldehyde at atmospheric pressure and a catalyst of tantalum oxide and siHca gel at 325—350°C (393—397). Extensive catalytic studies were reported (398—401) including a fluidized process (402). However, because of later developments in the manufacture of butadiene by the dehydrogenation of butane and butenes, and by naphtha cracking, the use of ethanol as a raw material for this purpose has all but disappeared. 

Butane is primarily used as a fuel gas within the LPG mixture. Like ethane and propane, the main chemical use of butane is as feedstock for steam cracking units for olefin production. Dehydrogenation of n-butane to butenes and to butadiene is an important route for the production of synthetic rubber. n-Butane is also a starting material for acetic acid and maleic anhydride production (Chapter 6). 

The first step involves dehydrogenation of the butanes to a mixture of butenes which are then separated, recycled, and converted to butadiene. Figure 3-16 is the Lummus fixed-bed dehydrogenation of C4 mixture to butadiene. The process may also be used for the dehydrogenation of mixed amylenes to isoprene. In the process, the hot reactor effluent is quenched, compressed, and cooled. The product mixture is extracted unreacted butanes are separated and recycled, and butadiene is recovered. 

Much higher butadiene yields may be obtained in a two-step process developed by Phillips in which butane is first converted to butenes with the chromia-alumina catalyst, and the butenes are then further dehydrogenated to 1,3-butadiene.144 173 The butene selectivity in the first step is about 80-85% (600°C, atmospheric pressure). The butenes recovered from the reaction mixture undergo further dehydrogenation in the presence of excess steam (10-20 mol) over a mixed... 

Other catalysts for alkane oxidative dehydrogenation have also been reported in the patent literature. For example, it was claimed that a Na and Li phosphomolybdate produced 17% butadiene and 5% butenes at 600°C with a 1 1 mixture of butane and oxygen (13). 

Butenes are only obtained in mixtures (23 to 45 weight per cent) in cuts containing n-butenes, isobutene, n-butane and isobutane (see Tables 2.11 and 2.28 in Section 2). To achieve a satisfactory return from dehydrogenation operations, the n-butenes concen ... 

Let us examine the case of straightforward dehydrogenation of n-butane. It was assumed that the reaction produces an equilibrium mixture of butenes. The reaction is described by... 

This process was formerly the most widely used for the manufacture of butadiene by dehydrogenation. Using a feed containing 95 per cent or more n-C. it produces a mixture of butenes and butadiene in a single step. The butadiene is separated, and the unconverted butenes and butane are recycled. The catalyst, activated alumina containing 18 to 20 per cent weight of chromium oxide, has a life of more than six months. It is placed in a series of horizontal reactors lined with refractory bricks. The inert alumina is mixed with the catalyst to achieve the uniform distribution of the heat required for the reaction and a high heat capacity of the catalyst bed. 

The major end-use of iodine is in catalysis (e.g., the Monsanto process for producing acetic acid). Titanium tetraiodide and aluminum iodide are also significant in the dehydrogenation of butane and butene to butadiene, and in the preparation of stereoregular polymers. The second major end-use of iodine is as a stabilizer in the manufacture of nylon, for converting resins, tall oil and other wood products to more stable forms, while the third major use is as additives for animal and human food (iodization of salt and mineral mixtures). 

Dehydrogenation of hydrocarbons is a most important industrial process. Rubber production from inorganic matter is one of the related examples to which the isotopic kinetic method has been applied . " C-labelled butane and butene used in this studyhave been obtained according to equation 155. Various labelled 1 1 mixtures of... 

After isobutene removal, n-butenes in the mixture with butanes may be converted to 2-butanol by the old two-stage sulphuric acid process or by using an acidic ion-exchange resin catalyst. Essentially all 2-butanol so produced is converted to 2-butanone by dehydrogenation (cf. isopropanol... 

The best olefin yields were observed over Pt-coated monoliths. In the case of ethane/02 mixtures, selectivities to ethylene up to 65% at 70% ethane conversion and complete O2 conversion were reported." The oxidative dehydrogenation of propane and -butane produced total olefin select vies of about 60% (mixtures of ethylene and propylene) with high paraffin conversions." " Mixtures of ethylene, propylene and 1-butene were observed by the partial oxidation of -pentane and n-hexane ethylene, cyclohexene, butadiene and propylene were the most abundant products of the partial oxidation of cyclohexane." ... 

Dehydrogenation of butane to a mixture of butenes given by the rate constant ka is first order in butane and independent of the oxygen concentration. Since higher yields of MA are obtained from c/5-butene-2 than the mixture of cis and trans isomers, the stereochemistry of the butene formation may be important in determining kb vs... 

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