The Application of Residue Curve Map and Boiling Point Ranking to the Design of Reactive Distillation Processes
Date Issued
2010
Date
2010
Author(s)
Lai, I-KUAN
Abstract
The residue curve map and boiling point ranking are the starting points of systematic methods for design of reactive distillation processes. In this study, we develop the esterification systems’ design and operation to know more about the role which the residue curve map and boiling point ranking play.
Ethyl and isopropyl acetates are important organic solvents which have been widely used in the production of varnishes, ink, synthetic resins and adhesive agents. In this study, the production of high-purity ethyl acetate (EtAc) using reactive distillation (RD) is studied experimentally in a pilot-scale plant. The objectives are two folds: (1) to realize the type-II RD process [Y.T. Tang, Y.W. Chen, H.P. Huang, C.C.Yu, S.B. Huang, M.J. Lee, Design of reactive distillations for acetic acid esterification with different alcohols, AIChE J. 51 (2005) 1683–1699] for EtAc production with a pilot plant, a complex two-column configuration with liquid phase split, (2) to study the initial charges to the column holdups and a start-up procedure for continuous production via residue curve map.
According to type II system [Tang et al., 2003, 2005 and Lai et al., 2007] studies, the rectifying section of both RD columns has prominent remixing phenomenon. Observing the transformation of composition profile projected on quaternary residue curve map, the composition trajectory is crooked. Based on their results, designs incorporating reactive divided wall column (RDWC) is proposed. In this work, we make a hypothesis that when the turning disappears or the composition trajectory becomes shorter, it would save energy. To find out the benefit in term of energy saving, the feed conditions, throughput, product specification and column tray setup are all the same with conventional reactive distillation design. The final simulation result shows that the energy savings for EtAc and IPAc systems are 11.8% and 24%, respectively. Furthermore, the residue curve maps (RCM) in the two systems show that the composition trajectory is shorter than those of the conventional RD designs. In these EtAc and IPAc systems, we also demonstrate beneficial and successful RDWC designs to deal with conventional design consisting of RD with a decanter.
Follow the design of adipic acid (AA) esterication (Hung, S. B. Design and Control of Reactive Distillation Systems: One-Stage and Two-Stage Esterification. Ph.D. Thesis, National Taiwan University of Science and Technology, Taipei, Taiwan, 2006.), a new complete reactive distillation process for two-stage reaction systems (glutaric acid (GA) esterifications with methanol) is explored. Similarities and differences between these two flowsheets have been identified. Both the acid esterification reactions are catalyzed heterogeneously by acidic ionexchange resin and reaction kinetics can be described using quasihomogeneous model. The UNIFAC group contribution method predicts suitable NRTL parameters for calculating liquid activity coefficients. Results show that the plantwide flowsheets need a large recycle ratio for the light key reactants and ester products could be achieved with a purity of 99 mol %. A systematic design procedure for the complete flowsheets is presented, and the optimum operating conditions of the overall systems are studied to minimize the total annual cost while meeting the product specifications.
Then, follow above design experience; there is an extension to acid mixture (glutaric acid (GA), adipic acid (AA) and 6-hydroxyhexanoic acid (HHA)) esterification with inert. The acid mixture is the byproduct of caprolactam production. The esterification products of acid mixture are the raw material of pentanediol and haxanediol. Due to thermal limitation of HHA, the acid mixture esterification system design should be based on FSA, a lower temperature process, to prevent the decomposition of HHA. Finally, dynamic control is proposed.
Subjects
reactive distillation
residue curve map
optimization
TAC
ethyl acetate
diacid
pilot plant
reactive divided wall column
Type
thesis
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