Dehydrogenation, butene ethane

The distributed-reactant membrane reactor has also been studied for several oxidative dehydrogenation reactions ethane to ethylene, propane to propylene and butane to butene. The results for these reactions have shown more promise, with higher yields for the membrane reactor when compared with a fixed bed, over certain ranges of the operating parameters. 

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). 

Because hydrogen can easily be removed from a reaction stream, many dehydrogenations have been studied. These include dehydrogenation of methane to carbon,326 ethane to ethene,327,328 propane to propene,329 n-butane to butenes,330 isobutane to isobutene,331,332 cyclohexane to benzene,332-334 meth-ylcyclohexane to toluene 335 n-heptane to toluene,336 methanol to formaldehyde,330 and ethanol to acetaldehyde.337... 

Cyclohexane is rly easily dehydrogenated into benzene, and even at very low extents of reaction, stoichiometry reaction (6) can be replaced by the secondary stoichiometry reaction (12). For cyclohexane, the constituents are (apart from cyclohexane) hydrogen, methane, ethane, ethylene, acetylene, propene, 1-butene, 1,3-butadiene, cydohexene, and benzene [3]. However, one can check that the equations written are independent, using the Jouguet [IS] criterion, (t.e., if/ = n-o)). In this criterion, the number of the independent constituents, 1//, for a chemical system is equal to the required constituents. n, (i e., H3, Cl, C3, CsHe, Q, C4, Cj. c-Q, CaJ, subtracting the number of independent stoichiometric equations. q>. 

In the first stage of this reaction, butane is converted to butenes and hydrogen, propylene and methane, and ethylene and ethane. In these primary products, methane and ethane are difficult to convert further. Therefore, for a high selectivity for aromatics formation, it is desirable for the primary reaction to be only the dehydrogenation of butane to produce butene and hydrogen. Figure 7 shows the effect of contact time (W/ F) over Ga(Imp)Cu(Ex)(66 %) catalyst. At a short contact time, the main product was butenes. Therefore, on this catalyst selectivity for aromatics formation from butane is high. 

Direct use of oxygen as a means of dehydrogenating, for example, ethane to ethylene. Oxydehydrogenation has successful commercial applications in the conversion of n-butenes to butadiene (e.g., as in the Oxo-D process referred to earlier), but not yet for the production of ethylene or propylene. 

Natural gas constituents heavier than methane are also excellent petrochemical feedstocks [1]. Ethane is the most desirable starting material for producing ethylene whenever a minimum amount of byproducts is desired. Propane and butane can also be dehydrogenated to olefins, propylene, and butene, and butene can be further dehydrogenated to butadiene. The naphtha fraction, which is also known as natural gasoline, has a low octane number, but is an excellent feedstock for cracking to olefins and/or steam reforming. 

Ethylene for polymerization to the most widely used polymer can be made by the dehydration of ethanol from fermentation (12.1).6 The ethanol used need not be anhydrous. Dehydration of 20% aqueous ethanol over HZSM-5 zeolite gave 76-83% ethylene, 2% ethane, 6.6% propylene, 2% propane, 4% butenes, and 3% /3-butane.7 Presumably, the paraffins could be dehydrogenated catalyti-cally after separation from the olefins.8 Ethylene can be dimerized to 1-butene with a nickel catalyst.9 It can be trimerized to 1-hexene with a chromium catalyst with 95% selectivity at 70% conversion.10 Ethylene is often copolymerized with 1-hexene to produce linear low-density polyethylene. Brookhart and co-workers have developed iron, cobalt, nickel, and palladium dimine catalysts that produce similar branched polyethylene from ethylene alone.11 Mixed higher olefins can be made by reaction of ethylene with triethylaluminum or by the Shell higher olefins process, which employs a nickel phosphine catalyst. 

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." ... 

---