The Drop Coalescence and Settling in Liquid/Liquid Systems Containing Electrolytes

• Main Authors: Chao-Tai Chen, 陳兆泰
• Other Authors: Jer-Ru Maa
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/92829885856559845789

博士 === 國立成功大學 === 化學工程學系 === 89 === Liquid/liquid separation or demulsification of dispersions is important in the petroleum industry. Molecular diffusion (Ostwald ripening), (reverse) sedimentation, flocculation and coalescence are involved in the breakdown processes of L/L dispersions, which may occur simultaneously as well as sequentially. The presence of various third components in one or both of the phases, such as surfactants, fine solid particles or electrolytes, may affect the drop behaviors. Studies of the effects of surfactants and fine solid particles had been carried out and reported in the literatures by various authors. But the effects of electrolytes dissolved in aqueous phase on these drop behaviors have not been investigated as extensively as that of surfactants and fine solid particles. In this thesis, the effects of electrolytes on the coalescence and settling of liquid drops were studied experimentally. Because flat tip nozzles which are usually used in the distributor of spray columns and packing columns in various industrial operations, were used for the formation of liquid drops of adequate sizes in the above studies, drop formation from flat tip nozzles in L/L systems were also investigated. In the first section of this thesis, the coalescence rate of aqueous drops containing electrolytes in organic media was studied experimentally, and the results were compared with coalescence rate data of organic drops in aqueous media of previous authors. The effects of electrolytes with cations and anions of various valencies, and organic liquids of different polarities were also investigated. It was found that for the cases of polar organic liquids, the effects of dissolved electrolytes on the coalescence of aqueous drops in organic media was just the opposite to that of organic drops in aqueous media. The coalescence rates of aqueous drops increase and those of organic drops decrease with the increase of electrolyte concentrations, but in the case of methyl isobutyl ketone (MIBK), electrolytes of trivalent cations or anions, such as AlCl3, LaCl3, FeCl3 and Na3PO4, increase the coalescence rates of aqueous drops and reduce those of organic drops strongly only within certain concentration ranges. Their effects are not nearly as pronounced outside these ranges. For the case of nonpolar organic liquids, dissolved electrolytes give no significant effect on the coalescence rates of either aqueous or organic drops. The effects of electrolytes on the coalescence processes of liquid drops is not significantly related to the bulk viscosity of the film liquids and the interfacial properties between the phases such as the interfacial tension gradient, and the mobility, viscosity, electroviscosity and electric charge of the interface. It is suggested that these phenomena are caused by salt effects and capillary nucleation through the change of intermolecular forces in the case of polar organic phases due to the addition of the electrolytes. The work in section 2 is an experimental study of the hydrodynamic behaviors of drops of aqueous solutions of electrolytes falling through an immiscible organic liquid. It includes the terminal descending velocities, the onset of drop oscillation and the drop shape after injection, followed by an examination of the deviations between the experimental data and some existing semi-empirical correlations which are formulated based on the experimental data of systems of dispersed organic phase and continuous aqueous phase using pure and nearly pure liquids. The effects of electrolytes on the motion of aqueous drops were then discussed and the applicability of existing empirical correlations to the reversed systems of continuous organic phase and dispersed aqueous phase was also examined. Dissolved electrolytes have the effect of causing the terminal velocities and their peak velocities at the onset of drop oscillation to become faster and the drop sizes at the peak velocities to become smaller when their concentrations are high enough to cause sufficient changes of physical properties. The existing correlations for drop terminal velocity in pure systems can be applied to the reversed systems of aqueous dispersed phase and organic continuous phase and are shown to be adequate in the presence of electrolytes. The mean absolute deviations of the correlations of Hu-Kintner, Grace, and Klee-Treybal used to estimate the terminal velocities of drops of aqueous solutions of electrolytes of various concentrations are within 3.5%, 4.2%, and 6.7% respectively. For high interfacial tension systems, the Hu-Kintner correlation predicts the terminal velocity of organic drops in water and aqueous drops in organics equally well, irrespective of the presence of electrolytes. Since most of the existing correlations tend to under estimate the terminal velocities of aqueous electrolytic drops of moderate to larger sizes slightly. A probable mechanism based on the negative adsorption of the electrolytes on the interfaces was proposed to demonstrate the effect of dissolved electrolytes on the drop terminal velocities. In this mechanism, the effect of dissolved electrolytes on the internal circulation of the drops is just opposite to the effect of surfactants. The criteria of Hu-Kintner can be used to estimate the peak velocities and drop sizes at the onset of oscillation within a deviation of 3.7%. The database of the existing correlations for the terminal velocity of drops are extended to a wider range of physical properties of continuous phase of density less than 1g/cm3 and viscosity larger than 1cp. In section 3, the formation of drops of aqueous solutions of electrolytes from flat tip nozzles of various dimensions into a pool of n-dodecane was studied experimentally. Since most of the existing correlations for the estimation of the size of drops formed by nozzles at low flow rate are based on experimental data using sharp-edged nozzles, an evaluation of the deviation of some widely accepted empirical correlations for drop size predication to the cases of flat tip metallic nozzles was examined. A simple rule of thumb was then developed to modify these correlations in order to be applied to the flat tip nozzles. It was found that the correlation of Scheele-Meister gives slightly less deviation from the experimental data than that of Kagan. The correlations of Scheele-Meister and Kagan usually underestimate the drop size by as much as 55%. The deviations of the estimated values are not affected by the dissolved salts within the range of concentrations studied. And most importantly, the mean deviation of the correlation of Scheele and Meister can be reduced to a few percents if different characteristic diameters, dn, are used in the computation: dn=O.D. for the cases of relatively large nozzles of about 1cm O.D. with wall thickness between 0.098 and 0.170cm; dn=1.15×O.D. for small thin wall nozzles of O.D.<0.35cm with wall thickness < 0.036cm. 頁次 摘要(中文)……………………………………………………………I 摘要(英文)……………………………………………………………V 誌謝 ………………………………………………………………… IX 目錄 ………………………………………………………………… XI 表目錄 ……………………………………………………………… XVI 圖目錄 ……………………………………………………………… XVIII 符號說明 …………………………………………………………… XXIII 第一章 緒論 ……………………………………………………… 1 1.1 前言…………………………………………………………… 1 1.2 液／液分散系統中的分離機制……………………………… 2 1.3 工業上常用的去乳化方法…………………………………… 7 1.4 原油的脫鹽程序……………………………………………… 10 1.5 液／液分散系統中的各種液滴現象………………………… 12 1.6 研究主題及論文架構………………………………………… 14 1.7 研究方法……………………………………………………… 15 第二章 液滴的合併現象 ………………………………………… 16 2.1 液滴合併的過程及影響因素………………………………… 16 2.2 液膜減薄的驅動力…………………………………………… 18 2.3 單一液滴在平面液／液界面處的併入時間及其關係式…… 21 2.4 界面活性劑及微細固體顆粒對液滴合併的影響…………… 25 2.5 液滴合併的理論模式………………………………………… 31 第三章 電解質與有機相的極性對液滴在平面液／液界面處 併入現象的影響 ………………………………………… 36 3.1 文獻回顧……………………………………………………… 36 3.2 研究內容……………………………………………………… 37 3.3 實驗部份……………………………………………………… 37 3.3.1 實驗裝置…………………………………………………… 37 3.3.2 實驗材料…………………………………………………… 40 3.3.3 實驗方法與步驟…………………………………………… 41 3.4 實驗裝置的驗證……………………………………………… 43 3.5 結果與討論…………………………………………………… 45 3.5.1 實驗數據…………………………………………………… 45 3.5.1.1 有機相為極性 ………………………………………… 45 3.5.1.2 有機相為非極性 ……………………………………… 51 3.5.1.3 酸、鹼電解質 ………………………………………… 56 3.5.2 合併時間分佈關係式的應用……………………………… 56 3.5.3 現有液滴合併理論的檢討………………………………… 63 3.6 結論…………………………………………………………… 72 第四章 液滴的沉降(或上浮)運動………………………………… 74 4.1 前言…………………………………………………………… 74 4.2 單一液滴的流體力學………………………………………… 74 4.2.1 內循環……………………………………………………… 75 4.2.2 液滴沉降時的形狀………………………………………… 77 4.2.3 液滴的振盪………………………………………………… 79 4.2.4 界面活性劑及微細固體顆粒的影響……………………… 79 4.3 液滴的沉降(或上浮)速度 …………………………………… 80 4.3.1 單一液滴的終端速度……………………………………… 80 4.3.2 影響液滴終端速度的因素………………………………… 82 4.3.3 理論分析及現有的關係式………………………………… 84 4.3.3.1 終端速度的關係式 …………………………………… 86 4.3.3.2 振盪起始的關係式 …………………………………… 88 第五章 電解質對單一水滴在不互溶有機相中沉降運動的 影響 ……………………………………………………… 90 5.1 文獻回顧……………………………………………………… 90 5.2 研究目的及內容……………………………………………… 92 5.3 實驗裝置與步驟……………………………………………… 92 5.3.1 實驗槽及終端速度的測量………………………………… 92 5.3.2 液滴的形成………………………………………………… 96 5.3.3 系統的物性………………………………………………… 98 5.4 結果與討論…………………………………………………… 100 5.4.1 終端速度…………………………………………………… 100 5.4.2 液滴的形狀………………………………………………… 116 5.4.3液滴振盪的起始…………………………………………… 118 5.5 結論…………………………………………………………… 120 第六章 液滴的形成 ……………………………………………… 123 6.1 流經噴嘴所形成的液滴……………………………………… 123 6.2 低流速系統液滴的體積……………………………………… 127 6.3 沾濕性對液滴形成的影響…………………………………… 131 第七章 在液／液系統中以平口型噴嘴形成液滴之研究 ……… 136 7.1 研究目的……………………………………………………… 136 7.2 實驗裝置及步驟……………………………………………… 137 7.3 結果與討論…………………………………………………… 137 7.4 結論…………………………………………………………… 148 第八章 總結與後續工作建議 …………………………………… 149 參考文獻 ………………………………………………………… 156 自述 ……………………………………………………………… 169 本論文發表的文章 ……………………………………………… 170