(271c) A Two-Stripper/Decanter Flowsheet for Methanol Recovery in the TAME Reactive-Distillation Process

The C5 feed stream to the Ter-Amyl Methyl Ether (TAME) process contains about 24 mol% reactive isoamylenes: 2M1B (2-methyl-1-butene) and 2M2B (2-methyl-2-butene). The remaining components are pentanes and pentenes (largely isopentane, iC5), which are inert in the TAME reaction. TAME is the highest boiling component, so it leaves in the bottoms stream from the reactive distillation column. The inert lighter C5 components leave in the distillate stream along with a significant amount of methanol because of the presence of C5/methanol azeotropes. A methanol recovery system is needed to be designed so that this reactant can be recycled back to the reactive section of the TAME process. The use of pressure-swing azeotropic distillation to break the azeotropes was studied in a previous paper in which both the steady-state design and the plantwide control of the entire process were developed. This paper considers another alternative flowsheet for the separation of the C5/methanol azeotropes that takes advantage of the heterogeneity of the azeotrope. A proposed flowsheet containing two stripping columns and a decanter is developed to obtain high-purity methanol and C5 products. The total annual cost of this flowsheet is a factor of four less than that of the pressure-swing distillation system. This flowsheet is demonstrated to be easy to control by controlling a tray temperature in each stripping column. Disturbances from feed composition variations and also throughput changes were introduced to test the proposed control strategy.

References:

Subawalla, H., Fair, J. R., Design guidelines for solid-catalyzed reactive distillation systems, Ind. Eng. Chem. Research 1999, 38, 3693.

Al-Arfaj, M. A., Luyben, W. L. Plantwide control for TAME production using reactive distillation, AIChE Journal 2004, 50, 7, 1462.