Hydroamination zeolites catalyst

Despite the industrial importance of amines and imines, hydroamination, i.e. the direct reaction of alkenes or alkynes with primary or secondary amines, is only used in one commercial process where isobutene and ammonia are converted in the presence of a zeolite catalyst to /-butylaminc. Turnover frequencies are generally very low and consequently, high catalyst loadings are necessary, which in turn demands efficient recycling. 

The production of tert-hutylamine is interesting for the fact that this amine has been used to demonstrate the technical potential of hydroamination in commercial amine production [route (b) in Topic 5.3.4]. BASF introduced in the early 1990s the first process that operates vith a zeolite catalyst and converts isobutene directly with ammonia. The reaction is carried out by contacting the supercritical reaction mixture with the catalyst at temperatures between 250 and 300 °C and at pressures between 200 and 350 bar. Under equilibrium conversion conditions tert-butylamine forms in 95% selectivity. 

The hydroamination of alkenes has been performed in the presence of heterogeneous acidic catalysts such as zeolites, amorphous aluminosilicates, phosphates, mesoporous oxides, pillared interlayered clays (PILCs), amorphous oxides, acid-treated sheet silicates or NafioN-H resins. They can be used either under batch conditions or in continuous operation at high temperature (above 200°C) under high pressure (above 100 bar). 

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. 

Small to medium pore size zeolites, such as H-clinoptilolite, H-of6etite or H-eri-onite, are efficient for the hydroamination of ethylene [51-54]. Ethylene and NH3 react at 360°C and 50 bar over H-clinoptilolite to give EtNHi only (11.4% conversion). There is a clear shape selectivity since propene and 1-butene as well as higher amines give rise to extremely low conversions [52]. In contrast to H-cIinoptilolite or H-erionite, H-offretite is effective for proprene hydroamination with NH, (7.2% conversion, 90% i-PrNH -i- 8% i-Pr2NH) [55]. Small pore size H-erionite is the best catalyst in terms of lifetime, conversion and selectivity for the synthesis of ethyl-amine [56]. The efficiency of H-clinoptilolite can be improved by acid or base plus acid treatment of natural clinoptilolite (18% conversion, EtNH2/Et2NH>20) [57]. 

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