Continuous Monoisopropyl Amine Manufacturing: Sustainable Process Design and Plantwide Control

Abstract

Conceptual design, steady state economic optimization, and decentralized plantwide control of a conventional "reaction followed by separation" process for continuous manufacture of monoisopropyl amine (MIPA) via the catalytic amination of isopropyl alcohol (IPA) is studied. A unique feature of the design is the recycle to extinction of the diisopropyl amine (DIPA) side product for a sustainable zero DIPA discharge process. The reactor effluent mixture separation is complicated by the presence of DIPA−water, IPA−water, and IPA−DIPA minimum boiling binary azeotropes. Using the residue curve map tool, two alternative designs, without a decanter (FS1) and with a decanter (FS2), are devised and optimized with respect to the dominant design variables. A high single-pass reactor conversion is necessary so that the reactor effluent composition is in the appropriate distillation region to guarantee feasibility of the separation scheme. Also, reactor oversizing is needed to ensure operability for a moderately large throughput increase. FS2 is finally recommended as it consumes ∼8% less energy than FS1 and its total annualized cost (TAC) is approximately the same as that of FS1 post reactor oversizing. Effective rejection of large throughput and feed composition changes using decentralized plantwide control is demonstrated for FS2. In particular, the organic layer material balance control on the decanter is shown to significantly affect the overall plantwide response time. The case study is a categorical pitch for simultaneous design and operability studies. ■ INTRODUCTIONGreen engineering is universally recognized today as the bedrock of sustainable development. The continuous process industry has thus witnessed a concerted push toward significant material and energy integration for zero-discharge, green, and highly energy efficient processes. The flip side is that, unless due care is taken at the design stage, such highly integrated processes can suffer from poor operability with the several available recycle paths transforming "local" unit specific disturbances into large and undesirable plantwide transients. Realizing the sustainability benefits of process integration thus requires that plant controllability/ operability considerations be preferably addressed at the design stage.In view of the operability implications of process integration, the entire process design cycle, from conceptual flow sheet synthesis/screening to steady state economic optimization of the selected flow sheet(s) to evaluation of process operability via rigorous dynamic simulations, should ideally be done together by the same process engineering group and not sequentially by different groups, as has been the case traditionally. Such an integrated design cycle is possible with process/design engineers having ready access to extremely user-friendly modeling environments for conceptual flow sheet synthesis and heat integration, and rigorous steady-state/dynamic process simulations. Even as the need for an integrated process design cycle is well reco...

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