薄膜輔助結晶之操作與動力式模擬

Abstract

薄膜輔助結晶相對於傳統蒸發結晶在節能方面具有極高的潛力及開發價值，本研究選定了兩種薄膜以建構薄膜輔助結晶之動力式參數研究，分別執行了實驗以及電腦模擬的探討。 實驗部分，分別以逆滲透薄膜對於己二酸及輸水性孔洞薄膜對於氯化鉀水溶液進行結晶實驗，利用回歸方法針對動力式參數施行研究。模擬部分，選定了五種物質利用文獻中已發表之結晶動力學參數，進行薄膜結晶的成核及成長模擬；分別為硝酸鉀、硫酸鉀、季戊四醇、丁二酸及鉀明礬。在結晶粒徑分布圖的探討中，於晶體完全均勻混合及分佈的假設下，我們考慮了兩種極端的結晶槽：清澈水溶液循環的理想結晶槽，以及晶體伴隨水溶液循環的結晶槽。在模擬研究中，我們也利用靈敏度分析探討了晶種重量以及晶種粒徑對於目標函數成核體積比率的關聯性。另外，為了探討薄膜除水量對於成核體積比率的影響，我們將除水量列為不同的時間函數軌跡作探討歸納出其對於產物粒徑的影響。

Membrane-assisted crystallization processes have the potential to reduce energy consumption and equipment size (footprint) compared to evaporative crystallization. In this thesis, reverse osmosis membranes and porous hydrophobic membranes are considered for the removal of water from solution to facilitate crystallization. Experiments using both types of membranes are performed and mathematical models of membrane-assisted crystallization processes are also constructed. Simulation of the process is also conducted to identify conditions that minimize the nucleated crystal volumetric ratio (μ_(3,n)⁄(μ_3)). Adipic acid and potassium chloride are used in the experimental work for the reverse osmosis membrane and the porous hydrophobic membrane respectively. Preliminary experimental work has been done including solubility measurements, data collection and regression for relation of temperature and conductivity measurements for online measurement of concentration, and salt rejection tests to measure membrane selectivity. Five substances are chosen for the membrane-assisted crystallization simulation: potassium nitrate, potassium sulfate, pentaerythritol, succinic acid, and potassium alum; the kinetic parameters from literature are used. Two limiting cases of crystallizer design are considered: one in which only clear solution is circulated from the crystallizer to the buffer tank, and one in which a crystal slurry is circulated. In the simulation, the effect of seed loading and seed size on the objective function is discussed. Furthermore, in order to understand the influence of membrane water removal rate on the product nucleation volumetric ratio, different water removal trajectories as function of time were considered.