氣體驅動往復式震盪雙尺寸結晶管內之氯化鉀晶體成長動力學研究

Abstract

結晶是常用於純化和分離化合物的單元操作。透過控制溶液的過飽和度、溫度、濃度、攪拌和冷卻條件，可以使結晶析出，達到目標化合物的純化和分離。本實驗使用氣體驅動往復式震盪結晶器進行氯化鉀的結晶實驗。調整溶液濃度、冷卻溫度及震盪頻率參數，觀察參數對結晶產物產率、粒徑和形貌的影響。氯化鉀在農業、生醫業、食品加工產業皆有其商業應用，本論文即利用氯化鉀結晶進行觀察。 本研究之結果顯示，低濃度和高溫度下的產率較低，而隨著震盪頻率增加，有越容易達成理論產率的趨勢。在研究中最佳的操作條件可達到70 %之理論產率。結晶平均粒徑隨溶液濃度降低和冷卻溫度提升而增大，且較低震盪頻率的結晶平均粒徑較大，晶體粒徑在不同條件下，粒徑大小為200-900 μm等不同尺寸，符合不同產業之應用。 本研究也以結晶粒徑與時間曲線分析氯化鉀結晶成長動力學。利用不同溶液濃度和氣體震盪頻率的成長速率，分析不同過飽和指數和冷卻溫度對晶體成長速率的影響，並計算不同條件下的結晶活化能和成長速率常數。結果顯示，氯化鉀結晶成長動力式呈現為：G=10^22 exp⁡(-90/RT)S^3。過飽和S指數大約為3，而成長速率常數kg約為1022 m/s、活化能Ea約為90 KJ/mol。 總上所述，利用氣體驅動式往復震盪結晶器進行結晶操作時，最大優勢在於其來回震盪模式和球型雙尺寸管的設計，可以確保容器內部混合均勻，結晶粒徑分布較均勻。結晶器內部沒有死角且熱傳阻力低，使得結晶過程更高效和晶粒更均勻，比起利用攪拌槽的情況達到相同產率的時間短40%，而顆粒大小均勻程度在跨度上大約小75%。

Crystallization is a common unit operation used for the purification and separation of compounds. By controlling the supersaturation, temperature, concentration, stirring, and cooling conditions of the solution, crystals can precipitate, achieving the purification and separation of target compounds. In this experiment, a gas-driven reciprocating oscillatory crystallizer was used to conduct crystallization experiments on potassium chloride (KCl). Potassium chloride has wide applications in agriculture, biomedicine, and food processing industries. The effects of adjusting solution concentration, cooling temperature, and oscillation frequency parameters on the yield, particle size, and morphology of the crystalline product were observed. The results of this study showed that the yield was lower at low concentrations and high temperatures, while an increase in oscillation frequency made it easier to achieve the theoretical yield. At the optimal operating conditions, up to 70% of the theoretical yield could be achieved. The average crystal particle size increased with decreasing solution concentration and increasing cooling temperature. Additionally, crystals formed at lower oscillation frequencies had larger average particle sizes, with particle sizes ranging from 200 to 900 μm, making them suitable for various industrial applications. This study also analyzed the crystal growth kinetics of KCl by examining the particle size over time. The growth rates at different solution concentrations and gas oscillation frequencies were used to analyze the effects of different supersaturation indices and cooling temperatures on the crystal growth rate. Activation energy and growth rate constants were calculated under various conditions. The results indicated that the crystal growth kinetics of KCl could be expressed as: G=10^22 exp⁡(-90/RT) S^3.The growth rate is proportional to the supersaturation S of power 3; the growth rate constant kg was about 1022 m/s, and the activation energy Ea was about 90 KJ/mol. In summary, the main advantage of using a gas-driven reciprocating oscillatory crystallizer for crystallization operations lies in its reciprocating oscillation mode and the design of the dual-diameter-module tube. This ensures uniform mixing within the vessel, resulting in a more uniform crystal size distribution. The crystallizer has no dead zones and offers low thermal resistance, making the crystallization process more efficient and producing more uniform crystals. Compared to using a stirred tank as a crystallizer, the new crystallization process which reached the same yield 40% faster, and the particle size distribution is approximately 75% narrower.