(682a) Methanol Dehydration to Dimethyl Ether In An Autothermal Millisecond Residence Time Reactor

Methanol dehydration to dimethyl ether (DME) has been carried out in a two-stage autothermal millisecond residence time reactor in which top stage is noble metal coated monolith and bottom stage is zeolite catalyst. DME has attracted a lot of attention since it is a clean diesel substitute; it is environmental friendly with zero ozone depletion potential and it is a key intermediate for other important chemicals. The advantage of this reactor is: (1) external heat is not required since the reactor is autothermal; (2) The residence time of the reaction is on the order of milliseconds resulting in a smaller reactor and catalyst volume. The best result was obtained when methanol was fed from the side of the reactor between two stages in terms of maximizing the methanol conversion and DME selectivity. The experiment has been carried out using 1wt% Pt/α-Al₂O₃ catalyst on the top stage where heat is released by exothermic reactions and H-ZSM-5 (Si/Al=25) on the second stage where the heat is used to drive endothermic reactions. 1.2 g of H-ZSM-5 is used and the typical methanol dehydration temperature is between 523K and 603K. Different noble metal (Pt and Rh) coatings with different monolith lengths were tested to optimize the top stage of autothermal reactor. Two reactor configurations have been tested: (1) Methanol fed from the top of the reactor with hydrogen as sacrificial fuel and (2) methanol fed from the side of the reactor with methane as sacrificial fuel which is partially oxidized in the noble metal catalyst layer. For the first configuration, reaction temperature and product distribution of the second stage was adjusted by varying different fuel to oxygen ratio or varying distance between two stages. Second configuration results in higher methanol conversion and DME selectivity than those of the first one. The highest yield to DME is 76.11% at C/O ratio of 1.01.