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Dehydration of Si containing alcohol feedstocks Disclosure Number: IPCOM000022656D
Publication Date: 2004-Mar-24

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A method for dehydration of alcohols, typically linear alcohols from an alcohol feed stream, to high purity olefins, typically alpha-olefins, the method including the step of removing silicon species from the alcohol feed stream.

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THIS invention relates to the dehydration of alcohols to olefins.

The increasing global demand for co-monomer grade 1-hexene and 1-octene, which are used in the synthesis of linear low density polyethylene, has necessitated investigations into alternative processes for the production of these 1-alkenes, apart from the existing Fischer-Tropsch synthesis, ethylene trimerization or oligomerization routes.

An alternative route for the production of these alkenes is the dehydration of the corresponding alcohols, namely 1-hexanol and 1-octanol respectively. The alcohols in turn can be obtained from (i) Fischer-Tropsch synthesis, or (ii) from the Ziegler alcohol synthesis route (Alfol process), etc.

For such dehydration reactions, where the extent of the double-bond shift reaction has to be minimized, since the internal isomers are unwanted products, use is made of weak solid acid catalysts such as g-alumina. Catalysts of higher acid strength, such as silica-aluminas, molecular sieves, zeolites and resin catalysts, would result in higher isomerization activities, and also show higher activity for reactions such as skeletal isomerization and other olefin interconversion reactions, thereby minimizing the yield of the 1-alkene.

Whilst there are innumerable patents and publications on the dehydration reactions of the C1-C4 alcohols, the number of reports dealing with the higher alcohols is more limited.

Recently, the conversion of 1-hexanol was studied using zeolite Y-based catalysts and Nafion/SiO2 composites and reported in C. Park and M.A. Keane, J. Mol. Catal. A, General, 166 (2001) 303. High conversions were obtained, but due to the strongly acidic nature of the catalysts, extensive isomerization to the internal alkenes also took place. In Y.A. Kalvachev, C.P. Bezouhanova and H. Lechert, Collect. Czech. Chem. Commun., 57 (1992) 739, the conversion of 1-hexanol over the H-ZSM-5 zeolite and SAPO-5 resulted in both positional as well as skeletal isomerization.

1-Hexanol dehydration over alumina for the production of 1-hexene for co-monomer usage was the subject of a report by Russian workers (T.G. Minko and A.V. Timofeev, Khim. Prost-st, 10 (1986) 595). The alumina was treated with a 0.25% KOH solution and the selectivity to 1-hexene was between 90-95%. The temperatures employed ranged from 300 to 3200C. In a previous Russian publication (M.R. Musaev, I.K. Magamedov, S.N. Klychkova and Z.T. Imanov, Neftekhim Protsessov, Akad. Nauk Az. SSR, 9 (1977) 65) it was reported that the degree of isomerization increased with increasing reaction temperature, 280-5300C, but decreased on treating the catalyst with 1-2% alkali.

The dehydration of secondary alcohols over zirconia catalysts to produce a-olefins has been the subject of several patents and publications. It was reported that at a conversion of 14.7%, the selectivity to 1-hexene was 84.4% (S. Chokkaram and B.H. Davis, J. Mol. Catal. A, Chemical, 118 (1997) 89). Another family...