- 學位論文
甲醇與混合酸之平行酯化反應性蒸餾系統設計與控制
Design and Control of Reactive Distillation for Parallel Reactions System--Methanol and Mixed Acids
摘要
本研究提出完整的程序，將混合酸(乙酸、丙酸)與甲醇反應生成較具經濟價值的酯類(乙酸甲酯與丙酸甲酯)。上述反應使用異相觸媒Amberlyst 36 作為催化劑。由中國石油化學發展公司所提供的混合廢酸 (88 mol% 乙酸 and 12 mol% 丙酸)與純甲醇當作進料。在汽液平衡的計算上，用UNIQUAC model 來預測此系統之五個共沸點的溫度及其組成。考慮乙酸與丙酸於氣相因結合作用在氣相形成二聚體及三聚體。藉由系統中的沸點排序，提出一個完整的架構。包括一座反應蒸餾塔，其後接著一座傳統蒸餾塔。從反應蒸餾塔塔底可以分離出98mol%副產品-水。傳統蒸餾塔之目的在用來純化乙酸甲酯至98 wt%、丙酸甲酯至99 mol%以符合工業界的規範。由於在丙酸甲酯-乙酸甲酯-水之RCM路徑上，存在乙酸甲酯-水的共沸點，因此利用反應蒸餾來獲取更高純度的乙酸甲酯有一定的困難。根據最小年總成本(TAC)，利用系統化的設計步驟來做最適化設計。最後針對整廠的設計架構提出可行的控制設計。兩個可能的控制架構---三點溫度控制及四點溫度控制。動態的模擬結果顯示利用三點溫度及四點溫度控制可以有合理的控制效果。而溫度控制所造成的濃度偏差，可用前饋控制及串級控制來獲得改善。
並列摘要
This work presents a complete design for converting mixed acetic (HAc) and propionic (HPr) acids, into methyl acetate (MeAc) and methyl propionate (MePr) esters. The two esters are produced via a reactive distillation process using Amberlyst 36 as heterogeneous catalyst. Methanol (100 mol% MeOH) and mixed Acids (88 mol% HAc and 12 mol% HPr) are used as feeds, which are waste acids from a plant of China Petrochemical Development Corporation (CPDC). In the VLE calculations, UNIQUAC model is used to predict the compositions and temperatures for the five azeotropes in the system. The vapor association of acetic acid and propionic acid due to dimerization and trimerization has been considered as well. By the boiling point ranking of the system, a complete flowrsheet is proposed. It includes one reactive distillation column followed by a conventional distillation column. In the reactive distillation column, the by-product water (98 mole%) can be separated from the bottoms. To reach industrial specification, the conventional distillation column is used to purify the MeAc to 98 wt% and the MePr to 99 mol%. It is difficult to procure higher purity of MeAc by using this reactive distillation process, because of the existence of MeAc-H2O azeotrope on the MePr-MeAc-H2O RCM path. A systematic design procedure to optimize the flowsheet based on the total annual cost (TAC) is conducted. Finally, the control structure design for plant-wide control is proposed. Two possible quality control structures are considered---three-point temperature control, and four-point temperature control. Dynamic simulation results show that reasonable control can be achieved using these two control schemes. Moreover, steady-state composition offset can be mitigated using feedforward and cascade compensation for temperature set points.