Industrial & Engineering Chemistry Research, Vol.48, No.11, 5230-5238, 2009
Dehydration of C-5-C-12 Linear 1-Alcohols over eta-Alumina to Fuel Ethers
Naphtha from low temperature Fischer-Tropsch (LTFT) synthesis is rich in n-paraffins, but it also contains alcohols and olefins. These alcohols and olefins can be converted into linear fuel ethers and olefin dimers to improve the overall yield and quality of distillate from LTFT refining. The reaction network was studied for the conversion of 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, and 1-dodecanol over an eta-alumina catalyst in a fixed bed flow reactor at 250-350 degrees C, 0-4 MPa, and WHSV of 1-4 h(-1). The main products were the corresponding linear ethers and linear alpha-olefins. The highest ether yield (54%) was obtained at 300 degrees C, I MPa, and WHSV of 1 h(-1) (unoptimized conditions). The main side-products were aldehydes and olefin dimers. Dehydration occurred predominantly on Lewis acid sites, with acid-catalyzed side-reactions taking place over Bronsted acid sites and dehydrogenation taking place over basic and/or redox sites. Dehydration to produce 2-olefins was cis-selective and occurred mainly over Lewis acid sites by dehydration-hydration-dehydration. GC-FID response factors for di-n-butyl ether and heavier linear ethers were determined experimentally. The GC-FID response factors were expressed in terms of the equivalent carbon number (ECN) concept as an ECN of -0.6 +/- 0.1 for the linear ether oxygen atom, and this value could be mechanistically justified (literature ECN is -1.0).