蒸餘曲線圖與沸點排序在反應蒸餾程序設計上的應用

Abstract

蒸餘曲線圖與沸點排序在有關反應蒸餾的程序設計與操作上相當重要。為了進一步瞭解它們所扮演的角色，本文以多項酯化製程的設計與操作加以呈現並予討論。 首先，本研究針對type II乙酸乙酯反應性蒸餾 [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] 試驗工廠為對像，利用蒸餘曲線圖說明起始填充組成的重要性並提出開車流程，確保得到高純度產品。透過多次的開車測試，提出此系統開車程序，並透過蒸餘曲線圖說明起始填充組成的重要性。 觀察到type II乙酸乙酯與乙酸異丙酯反應性蒸餾設計[Tang et al,. 2003, 2005 and Lai et al., 2007] ，其組成分布中具有再混合效應，把組成分佈進行座標轉換投影在四成份蒸餘曲線圖，其曲線皆為彎曲。利用蒸餘曲線圖，針對原有的乙酸乙酯與乙酸異丙酯反應性蒸餾架構設計，提出反應性分隔內壁蒸餾塔熱整合設計，消除再混合效應，達到省能目的。故在此大膽假設，若組成軌跡可以盡可能縮短，便能節能。故利用反應性分隔內壁蒸餾塔熱整合設計應用於乙酸乙酯與乙酸異丙酯酯化反應系統。所有塔板結構、進料條件與產品規格皆與先前共沸進料反應性蒸餾系統相同，且最適化能源消耗，比較先前共沸進料反應性蒸餾系統，進一步可分別節省11.8%與24%能源消耗。並結果利用蒸餘曲線圖驗證假設。 延續甲醇與己二酸酯化反應性蒸餾設計，針對甲醇與戊二酸兩階段酯化反應性蒸餾進行設計，利用沸點排序做為設計基礎，並提出與己二酸甲酯系統不同點，製程上稍與己二酸二甲酯系統不同。 為了回收己內醯胺製程中的廢酸，包含二元酸(己二酸與戊二酸)與羥基己酸，利用反應性蒸餾系統進行甲醇與混合酸酯化系統設計，其產物己二酸二甲以及羥基己酸甲酯為己二醇氫化反應之反應物，而戊二酸二甲酯為戊二醇氫化反應之反應物。以戊二酸酯化反應性蒸餾設計設計基礎，應用於真實工廠設計，由於羥基己酸於80°C以上將會裂解，故此設計將採低溫製程，最後針對動態控制進行進料流料擾動測試。

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.