Dehydrogenation of isobutane

Methyl /-Butyl Ether. MTBE is produced by reaction of isobutene and methanol on acid ion-exchange resins. The supply of isobutene, obtained from hydrocarbon cracking units or by dehydration of tert-huty alcohol, is limited relative to that of methanol. The cost to produce MTBE from by-product isobutene has been estimated to be between 0.13 to 0.16/L ( 0.50—0.60/gal) (90). Direct production of isobutene by dehydrogenation of isobutane or isomerization of mixed butenes are expensive processes that have seen less commercial use in the United States. 

Methyl tert-Butylluther Methyl /-butyl ether (MTBE) is an increasingly important fuel additive. Platinum—tin and other PGM catalysts are used for the dehydrogenation of isobutane to isobutene, an intermediate step in MTBE manufacture. 

Dehydrogenation of isobutane to isobutylene is highly endothermic and the reactions are conducted at high temperatures (535—650°C) so the fuel consumption is sizeable. Eor the catalytic processes, the product separation section requires a compressor to facHitate the separation of hydrogen, methane, and other light hydrocarbons from-the paraffinic raw material and the olefinic product. An exceHent overview of butylenes is avaHable (81). 

The concept of site isolation is important in catalysis. On metal particles one usually assumes that ensembles of metal atoms are necessary to activate bonds and to accommodate the fragments of molecules that tend to dissociate or to recombine. We present here three examples of such effects the dehydrogenation of decane into 1-decene, the dehydrogenation of isobutane into isobutene and the hydrogenolysis of acids or esters into aldehydes and alcohols. In most cases the effect of tin, present as a surface alloy, wiU be to dilute the active sites, reducing thereby the yield of competitive reactions. 

Another well-studied catalyst system is Cr203 loaded onto various supports used in almost exclusively in the oxidative dehydrogenation of isobutane to isobutylene.361-364 In the case of Cr203 on La2(C03)3, the surface active center was found to be a chromate species bound to the surface La carbonate.361 With optimum loadings between 10-15% selectivities exceed 95% below 250°C. Correlations between... 

In this paper, we will report the electronic and catalytic reactivities of the model VC/V(110) surface, and our attempt to extend them to VC powder catalysts. By using high-resolution electron energy loss spectroscopy (HREELS) and NEXAFS techniques, we observed that the surface properties of V(110) could be significantly modified by the formation of vanadium carbide some of the experimental results on these model surfaces were published previously.3-5 We will discuss the selective activation of the C-H bond of isobutane and the C=C bond of isobutene on V(110) and on VC/V(110) model systems. These results will be compared to the catalytic performances of vanadium and vanadium carbide powder materials in the dehydrogenation of isobutane. 

These electronic properties in turn give rise to some unique catalytic properties for vanadium carbide. Compared to metallic vanadium, vanadium carbide shows an enhancement in the activation of the C-H bond of alkanes and a reduction in the interaction with the C=C bond of alkenes. The surface reactivity of VC/V(110) can be generally described as similar to those of Pt group metals, although the VC/V(110) surface might have an even higher activity towards the activation of C-H bonds. The dehydrogenation of isobutane on VC powder catalysts will be compared to the reactivities of the VC/V(110) model surfaces. 

This paper covers primarily the spectroscopic characterization of the VC/ V(110) model surface and VC powder materials. These results are organized as follows section 24.3.1 uses the VC/V(110) surface as a model system to briefly describe the electronic properties of metallic vanadium and vanadium carbide. Section 24.3.2 extends the fundamental information obtained on the VC/V(110) model system to VC powder catalysts by comparing the NEXAFS results of these two types of materials. Finally, section 24.3.3 uses the dehydrogenation of isobutane as an example to compare the catalytic properties of the VC/V(110) surface and the VC powder catalysts. 

Commercial plants Two commercial plants using the STAR process for dehydrogenation of isobutane to isobutylene have been commissioned (in the US and Argentina). More than 60 Uhde reformers and 25 Uhde secondary reformers have been constructed worldwide. 

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