Isobutene with improved catalyst

Many studies have been devoted to the hydroamination of isobutene with NH, since BASF started the production of FBuNHj in Antwerp in 1986 (6000 t/yr) [60, 61]. These studies were aimed mainly at improving conversion, selectivity, catalyst lifetime and space time yields, using less expensive catalysts than zeolites, decreasing the NHj/isobutene ratio to nearly 1/1, and recycHng of the NHj/isobutene mixtures. 

Heteropolyacids are much more active than mineral acids for several types of homogeneous reactions in both organic solvents and aqueous solution [4, 8]. The enhancement is generally greater in organic solvents. For the hydration of isobutene in a concentrated aqueous HPA solution (above 1.5 mol dm-3), the reaction rate is about 10 times greater than for mineral acids [21]. This rate enhancement is attributed to the combination of stronger acidity, stabilization of protonated intermediates, and increased solubility of alkenes [21]. In this case, the selectivity is also much improved with HPA catalysts. 

Conversion of n-butane into isobutene over theta-1 and ferrierite zeolites was studied in a continuous flow microreactor at 530°C and 100% n-butane as a feed. The zeolites were used as catalysts in the H- and Ga-forms. Insertion of Ga into the zeolites resulted in improved isobutene selectivities due (i) to an increase in the dehydrogenation activities and (ii) to a decrease in the cracking activities of the catalysts. The highest selectivities to isobutene (-27%) and butenes (-70%) were obtained with the Ga-theta-1 catalyst at n-butane conversions around 10%. These selectivities decreased with increasing conversion due to olefin aromatisation, which was enhanced considerably by the Ga species present in the catalysts. 

Use of Halide Ions to Improve Selectivity. Earlier work has claimed that enhanced selectivities for alkene oxidation can be achieved by the inclusion of electronegative elements such as S, Se, or halogens. This has been reviewed elsewhere. " More recent work has demonstrated substantial improvements in selectivity for propene (25—70%) and isobutene (35—80%) oxidation when either chloride or bromide is present. Both elements are added to the catalyst in the form of trace levels of organo-halide in the process gas stream. The selectivity increase is the result of a decrease in the rate of complete oxidation rather than an increase in the partial oxidation rate. Since the reaction is first order in oxygen pressure and zero order with respect to alkene in the presence and absence of halide, the reaction mechanism is probably similar in both cases. In the light of Anshits recent work, the effect of the halide is presumably to reduce the relative number and/or reactivity of surface lattice oxygen species and thus reduce the amount of irreversibly adsorbed alkene. 

The oxidative coupling of isobutene can be performed in two separate steps, coimected with reduction of catalyst and reoxidation of the reduced catalyst afterwards. The two step process leads to an improvement of DMH selectivity as compared to the conventional process. The formation of carbon dioxide requires surface lattice oxygen from tbe catalyst, while formation of DMH occurs by abstraction of protons and electrons at the catalyst surface. They are absorbed on the catalyst bulk and, finally, react to water there. Thus, the rate of carbon dioxide formation is more affected by catalyst reduction than the rate of DMH formation. 

Alkylation with Alkenes. The alkylation of phenols by olefins and cyclo-olefins has been reviewed, in Russia Several papers on the alkylation of phenols have appeared. Thus, p-t-butyiphenol has been prepared with good selectivity by treatment of phenol with isobutene and a Lewis acid catalyst followed by HCIO4 as an isomerization catalyst. The ort/io-alkylation of phenol by alkenes can be improved by using Al(OPh)3 and an aluminosilicate catalyst.Much greater ortho-selectivity in the alkylation of phenol with 4-bromostyrene is obtained if aluminium diphenylphosphorodithioate rather than BF3-OEt2 or BF3-H3P04 is used as catalyst. Relative reactivities of the various ring positions towards... 

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