Methanol titanium silicalite

In the second step, a dilute H P-methanol solution is introduced in a fixed-bed epoxidation reactor. Make-up propene, recycled propene and HP from the product purification stage are fed into the reactor. The reaction is catalyzed by titanium silicalite, and takes place at 40-50 °C and 300 psi. HP per-pass conversion is initially 96% but drops down to 63% after 400 hours. PO selectivity is 95 mol.% propene per-pass conversion is 39.8%. This technology gives capital savings compared to conventional hydroperoxidation technologies however, it is likely that the operating costs of such a plant are higher than that of the latter. 

Titanium siliealites TS-1 and TS-2 catalyze hydroxylation in the aromatic ring of the monoalkylbenzenes studied to corresponding alkylphenols, using hydrogen peroxide as oxidant. Para-isomers are mainly formed in methanol or ethanol as solvents. In the case of ethyl- and 1-propylbenzenes, the first carbon atom of the aliphatic chain is also oxidised both to alcohols and ketones. As expected, the terminal methyl groups in all hydrocarbons are not oxidised. The probable reasons for this behaviour of titanium silicalites are discussed. 

Clerici and Bellussi" have shown that hexane in methanol can be selectively oxidized to 2-hexanol, 3-hexanol, 2-hexanone and 3-hexanone using a mixture of oxygen and hydrogen at 25 - 30 . The reactions were run in the presence of HCl for 20 - 24 hours. Several titanium silicalite catalysts containing Pd (0.01 mol ratio to Ti02) were prepared and used in these reactions. Presumably, hydrogen plays the role of an electron-donor activating the Ti catalyst. However, no explanations were offered. 

In the oxyfunctionalization of n-hexane by H2O2 (30 wt %) over titanium silicalites in methanol as a solvent [49a], the parallel-sequential reaction scheme was selected for transformation of the hydrocarbon into hexanol and hexanone ... 

A newer technology based on metal-peroxo chemistry, without most of the drawbacks just outlined, and usable in the above cases, employs the titanium silicalite (TS-1) heterogeneous catalyst. This works with aqueous hydrogen peroxide, with methanol as a co-solvent if required by the substrate, under relatively mild conditions. The epoxidation of a range of olefins has been demonstrated [72] some are oxidised to other products, such as styrene to phenylacetaldehyde. The system is powerful enough to oxidise terminal olefins and, e.g., allyl chloride. Its main limitation is upon the size of the substrate and products, which must pass down zeolite channels 5.5 A in diameter. 

A different type of chemistry has been realized in the process commercialized by EniChem in 1986, which is based on employment of and the titanium-silicalite TS-1 as heterogeneous catalyst [106, 111]. The hydroxy lation mechanism involves activation of hydrogen peroxide via the formation of a titanium hydroperoxo complex, TiOOH, followed by electrophilic oxygen atom transfer to phenol. Methanol and acetone are the solvents of choice to achieve high selectivity. The nature of solvent, phenol concentration, reaction time, and size of catalyst particles affect the CAT/ HQ ratio. The TS-l-based process offers clear advantages in terms of conversion, selectivity, efficiency (see Table 14.1), catalyst separation/recycling, and, hence, environmental impact. 

The oxidation of methanol with oxygen has been used to characterize titanium-containing catalysts. Pure silicalite is inactive, and TS-1 catalyzes the oxidation of methanol to give a mixture of products ... 

In the literature there has been much debate regarding the role of the lattice or extralattice Ti in Ti silicalite for a variety of oxidation reactions. In order to have a more precise idea of the role of the lattice or surface Ti and more specifically of the role of the coordination sphere of Ti, a series of monopodal and tripodal titanium surface complexes (i. e., =SiOTi(OR)3 and ( SiOIsTiOR) were derived by the reaction of the Ti alkyl (Structure 1) and hydride species with water, oxygen, methanol, and tert-butanol. The resulting complexes were then used in the epoxidation of 1-octene by tert-butyl hydroperoxide. Tripodal complexes, especially (=SiO)3Ti( Bu), were found to be significantly more active and more selective for the epoxidation of 1-octene than their monopodal counterparts [22]. 

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