Conversion of ethane

Fig. 7. Equihbrium conversion of ethane versus temperature at 210 kPa in a membrane reactor. The effect of hydrogen removal on ethane conversion is...

The process achieves about 90% conversion of ethane to VC. With the elimination of so many intermediate steps compared to the traditional EDC route, this process could achieve VC production cost savings of up to 35% anywhere an adequate supply of ethane can be found. That could even include the recycle stream from a heavy liquids olefins plant. If these killer economics persevere, this technology could grab all the growth in VC capacity and even replace most of the conventional VC capacity in a couple of decades. That s what happened to the acetylene-based route to VC when the ethylene-based route came on stream in the mid-20th century. 

Figure 2. The conversion of ethane and the yields of acetaldehyde and ethylene in the C2H6 + N2O reaction on silica supported M0O3 and metal molybdates at 823 K.

Rb2Mo04 This catalyst was found to be much more active and selective than the divalent metal molybdates. As shown in Figure 2, very little decay was obsei ved in the conversion of ethane. In contrast with the previous catalysts, acetaldehyde was the main product of partial oxidation at 823 K it was fornied with a selectivity of 23-24%. The selectivity for ethylene was 10-13%. As it appears from Figure 2, the yield of acetaldehyde formation was about 5 times higher than on Mo03/Si02... 

Divalent Metal Molybdates. Except for the first point, the conversion of ethane did not change in the conditioning period at 823 K and it lay in the same range as for the N2O as oxidant. The main product was ethylene the selectivity of its foimation mai kedly exceeded that obtained with N2O as oxidant. Acetaldehyde was formed with 4.8% and 6.8% selectivity on the Mg and Zn salts. As a result, the yields for ethylene and acetaldehyde were much higher than in the case of N2O oxidation (Figure 5). Other hydrocarbons and alcohols were also detected in very small concentrations, with less than 1% selectivity. 

With decrease of the reaction temperature, no change was experienced in the selectivity for ethylene, but there was an increase in the selectivity of acetaldehyde formation. The oxidation of ethane has been also investigated on Mo03/Si02. Under these conditions, this catalyst was found to be very active for the total oxidation of ethane. At 510 K, the conversion of ethane was 21%, the products of partial oxidation were formed only in trace amount. 

Oxidation with N2O. In the evaluation of the catalytic data, we first compare the catalytic behavior of the metal molybdates with that of Mo03/Si02. Data obtained for this catalyst eailier (7) under the present conditions aie also included in Figure 2 and the appropriate tables. The conversion of ethane on Mo03/Si02 at 823 K was... 

The dependence of ethene selectivity on the conversion of ethane for the better catalysts shown in Fig. 1 shows that the selectivity is high at low conversions and decreases as the conversion increases. This trend is consistent with a reaction pathway that consists of mostly sequential reactions [Eq. (3)]. Depending on the reaction temperature, the reaction network may involve two parallel reaction pathways shown below, which is modified from... 

Consequently the overall reaction is of order 0.5 in [C2H6]. Equation 13.42 only holds for a low conversion at higher conversions of ethane into ethylene and hydrogen, subsequent reactions of these components would have to be considered. Ethane pyrolysis is another example that global parameters can be inferred from knowledge of the detailed chemistry. Global rate measurements can then be used to verify the proposed mechanism. 

Significant amounts of CH4 and C2H2 are also formed but will be ignored for the purposes of this example. The ethane is diluted with steam and passed through a tubular furnace. Steam is used for reasons very similar to those in the case of ethylbenzene pyrolysis (Section 1.3.2., Example 1.1) in particular it reduces the amounts of undesired byproducts. The economic optimum proportion of steam is, however, rather less than in the case of ethylbenzene. We will suppose that the reaction is to be carried out in an isothermal tubular reactor which will be maintained at 900°C. Ethane will be supplied to the reactor at a rate of 20 tonne/h it will be diluted with steam in the ratio 0.3 mole steam 1 mole ethane. The required fractional conversion of ethane is 0.6 (the conversion per pass is relatively low to reduce byproduct formation unconverted ethane is separated and recycled). The operating pressure is 1.4 bar total, and will be assumed constant, i.e. the pressure drop through the reactor will be neglected. 

Calculation with reversible reaction. At 900°C the equilibrium constant Kr for ethane decomposition FoHtfWPciH, is 3.2 bar using the method described in Example 1.1 the equilibrium conversion of ethane under the conditions above (i.e. 1.4 bar, 0.5 kmol steam added) is 0.86. This shows that the influence of the reverse reaction is appreciable. 

A prototype study for this issue was performed for the conversion of ethane to acetic acid [71] and the same group highlighted in an earlier comparative study of C3 oxidation [54] that, although initial propane activation is a difficult step, subsequent reactions associated with either excessive residence times of intermediates or with branching of reaction sequences into total oxidation may interfere with the overall selectivity to partial oxidation products. 

Ni-Ta-Nb oxide catalysts also show high activity for the conversion of ethane to ethylene in primary screening tests. For further optimization bulk catalysts were prepared to perform secondary screening in an 48-channel fixed-bed reactor at 300 °C (see Table 3.4).The highest selectivity (86%) for ethylene was achieved with an Nio.62Tao.ioNbo.28°x catalyst [7]. 

The dehydrogenation of other hydrocarbons has also been studied in CMRs, generally with porous membranes. Conversions of ethane [47], propane [48], butane [49], and ethylbenzene [50] have been reported to be higher when membrane reactors were used. In the case of ethylbenzene dehydrogenation, the undesirable hydrodealkylation side reaction is slowed down due to the removal of H2, i.e. the membrane enables an increase in selectivity as well [50]. 

Note that in radical chain processes, ethylene is produced by a series of reactions. The direct conversion of ethane to ethylene and hydrogen is absent from the seheme ... 

Oxidation is not a well-defined concept in organic chemistiy. It hardly ever involves simply the removal of electrons, and when covalent bonds are being made and broken some arbitrary choices must be made. When a C—bond is converted to a C—OH bond, we say that the C—bond has been oxidized. Similarly, the conversion of ethane to ethylene is generally considered to be an oxidation, and hydrogenation of an alkene is generally considered a reduction. However, if these conversions are indirect we must specify in which step the oxidation or reduction occurred. 

To establish the apparent (power-law) reaction order at low conversion, eqn 9.41 without the second numerator term must be integrated. For this purpose, pcc and pc=c are expressed in terms of the fractional conversion of ethane at constant volume ... 

If the fractional conversion of ethane is 0.501, the fraction unconverted (and hence leaving the reactor) must be (1 - 0.501). 

Li et al compare different approaches, in the study of the conversion of ethane to methanol. They employ a X weighted histogram analysis method (WFIAM) in order to improve statistics. Minh uses WHAM to develop a multi-dimensional potential of mean force. 

Determine Che plug-flow reactor volume necessary to produce 300 millioa pounds of ethylene a year from cracking a feed stream of pure ethane, The reaction is irreversible and follows an elementary rate law. We want to achieve 80% conversion of ethane, operating the reactor isothermally at 1100 K at a pressiu e of 6 atm. 

The catalytic activity for the conversion of ethane on V and/or Mg containing aiuminophosphates are shown in Table 1. VAPO-5 and MgVAPO-5 samples show an reaction rate higher than the corresponding ALPO4-5 and MgAPO-5. For this reason, it can be concluded that vanadium species are the active sites for the alkane conversion. This has also been proposed in supported vanadium catalysts [1,2,14]. 

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