Industrial & Engineering Chemistry Research, Vol.41, No.20, 4936-4940, 2002
The etherification of methanol and isobutene in a catalytic distillation column packed with zeolite-beta-coated catalytic packings
Zeolite-beta-coated catalytic packings were used to improve the etherification of methanol and isobutene in a catalytic distillation column. The steady-state composition profiles and the characteristics of the reaction in the catalytic distillation column were investigated. The zeolite-beta-coated packing has better characteristics and an activity that is comparable to that of the conventional resin catalyst in both catalysis and the separation of reactants from products. The optimal operating conditions for the catalytic distillation process are a pressure of 0.7 MPa, a methanol/isobutene feed molar ratio of 1, and a reflux ratio of more than 3. The effect of the strong nonlinearity in the vapor-liquid equilibrium of the reactive system on the conversion of isobutene was analyzed on the basis of the experimental results for both catalytic distillation and conventional distillation. There is a valley in the boiling-point temperature surface of the ternary mixture of methanol/isobutene/MTBE. This valley, as a separatrix, divides the boiling-point temperature surface into two regions. Although the conventional distillation profiles are restricted by the valley, the catalytic distillation system is not because the composition profiles in the reaction-separation section can cross the valley. A higher methanol/isobutene feed ratio can result in a lower conversion of isobutene and less MTBE obtained, which is different from what happens in a reactor. In this case, the product in the stripping section will run back up to the reaction zone so that the positive reaction is restrained. To obtain a high conversion of isobutene, a lower methanol/isobutene feed ratio should be used.