Dehydrocondensation of 1-hexanol to di-n-nhexyl ether (DNHE) on Amberlyst 70
Advancing the chemical engineering fundamentals
Catalysis (T2-13P)
Keywords: 1-hexanol, DNHE, Amberlyst 70, liquid phase reaction
Dehydrocondensation of 1-hexanol to di-n-hexyl ether (DNHE) on Amberlyst 70
Medina, E.; Bringué, R.; Tejero, J.; Iborra, M.; Fité, C.; Izquierdo, J. F. and Cunill, F
Chemical Engineering Department. University of Barcelona. C/ Martí i Franquès, 1. 08028-Barcelona. Spain.
The number of diesel fuelled cars in EU is nowadays larger than gasoline fuelled ones. As health concern on pollutant emissions from diesel engines is increasing, new regulations point towards more strict limits of standards emissions combustion of CO, NOx, hydrocarbons and smog. Due to higher demand in processing of heavier oils, refiners are blending in diesel fuels streams with high length chain compounds, usually aromatics, with boiling points ranging from 200 to 390ºC. On the other hand, thermal efficiency of diesel engines has been improved by raising the compression ratio about 20:1 and the combustion temperature in the chamber. As a result, higher energy efficiency is gained, but also emissions raise, especially NOx and smog.
A clean burning diesel fuel composition may be attained by using alkyl ethers with 6 to 24 carbon atoms. Linear ethers are preferred since they can be blended with all kind of diesel fuel streams. In all cases, diesel cetane number is improved, and self-ignition problems and emissions are reduced due to enhancing cold weather operability. Di-n-hexyl ether (DNHE, blending cetane number 118) may be a reliable option to produce quality diesel fuels. It can be obtained by dehydration of 1-hexanol, a product of the hydroformylation, and subsequent hydrogenation, of 1-pentene from C5 cuts.
The dehydration reaction of 1-hexanol to DNHE has been studied at 150-190ºC in a stainless steel 100 cc batch reactor on macroporous resin Amberlyst 70 [A70] (max. operation temperature 200ºC, exchange capacity 3 eq/kg, surface area 36 m2/g). To keep reacting mixture in the liquid phase pressure was set at 20 bars by using N2 as inert gas. Catalyst was dried at 110ºC and 1 bar for 15 h, and then at vacuum for 2 h. Runs lasted 6 h. and liquid samples were analyzed online in an HP-GLC apparatus.
Preliminary experiments performed at 190ºC by using catalyst mass from 0.5 to 5 g, stirring rates from 50 to 900 rpm, and up to six A70 fractions of bead size ranging 0.45-0.8 mm, showed that diffusion and external mass transfer influence on reaction rate is negligible within the limits of the experimental error, operating at 200-700 rpm, with 0.45-0.8 mm beads, and less of 3 g of catalyst.
Kinetic runs were performed at 150-190ºC by using 1 g of catalyst, at 500 rpm and 20 bars. Reaction rate is fairly temperature-sensitive. In this way, runs carried out with pure 1-hexanol showed at 190ºC and 6 h reaction time, alcohol conversion of 67% with selectivities to DNHE 90%, 8% to C6 olefins and about 1.5% to other ethers. At 150ºC, alcohol conversion was 17%, with selectivities to DHNE 97%, 2.6% to C6 olefins, and about 0.35 % to other ethers. In addition, initial reaction rates varied from 145 ± 8 mol (h kg)-1 at 190ºC to 9 ± 1 mol (h kg)-1 at 150ºC.
Additional series of experiments were carried out by adding DNHE or water to 1-hexanol fed at 190, 180 and 160ºC. It was observed that reaction rate hardly changed when DNHE was initially added, but with water it highly decreased, what shows the high inhibitor effect of water. A kinetic model stemming from an Eley-Rideal mechanism wherein a 1-hexanol molecule from the liquid phase reacts with a second alcohol molecule adsorbed on the catalyst surface, the surface reaction being the rate-limiting step, represented appropriately rate data. The inhibitor effect of water was accounted for by introducing a like-deactivation function that modifies the apparent rate constant. Activation energy was estimated as 114 ± 3 kJ/mol.
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Presented Wednesday 19, 13:30 to 15:00, in session Catalysis (T2-13P).
