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  • 學位論文

於超重力系統中製備氫氧化鎂及其於二氧化碳/環氧丙烷之環加成反應之應用

Synthesis of Magnesium Hydroxide in Spinning Disk Reactor for Carbon Dioxide/Propylene Oxide Cycloaddition Reaction

指導教授 : 陳昱劭 林義峯

摘要


溫室效應為近年來氣候變遷的主因,溫室氣體中以二氧化碳的影響為最大宗,在國際能源局(International Energy Agency,IEA)對二氧化碳的減排技術當中,以「碳捕獲與封存技術(Carbon dioxide capture and storage,CCS)」最可降低目前大氣中之二氧化碳濃度,然而將捕獲之二氧化碳除了進行地底封存以外,更能轉變成為綠色化學品,其中以二氧化碳與環氧化物之環加成反應研究最為多元,因其產物可作為多項高分子材料之中間體,但由於其為一催化反應,所以觸媒的選用相當重要,為了能夠簡化反應後之分離程序,本研究將以開發異相觸媒為首要考量。於過去研究中,若觸媒與環氧化物間有氫鍵的產生,將有助於觸媒之效能,因此本實驗以旋轉盤反應器製備氫氧化鎂,希望其可與環氧化物間產生氫鍵,有助於環加成反應。超重力系統在製備奈米材料的研究上已發展多年,其設備特性為體積小、反應時間短,在高重力場下增加了質傳效率且能運用於連續操作程序,與水熱法、溶膠凝膠法等高耗能、耗時的批次實驗方法相比,較易於工業上發展。 本研究以旋轉盤反應器,利用氯化鎂與氫氧化鈉水溶液製備氫氧化鎂粒子,將實驗參數固定為:氯化鎂與氫氧化鈉莫耳比1:2、旋轉盤轉速2500rpm、液體流率0.28L/min,探討氯化鎂水溶液濃度改變對氫氧化鎂粒子的影響,並將氫氧化鎂粒子作為二氧化碳與環氧丙烷之環加成反應觸媒,研究反應溫度、反應壓力、反應時間對環加成反應之影響。其實驗結果顯示,以0.5M之氯化鎂水溶液所製備而成的氫氧化鎂粒子有著293.1m2/g的高比表面積,且其粒子之凝聚情況較其他二者少。在環加成反應的部分,反應溫度為180℃、反應壓力10kg/cm2、反應時間15小時,為最佳之操作條件,將所製備之氫氧化鎂在該條件下,且不添加共催化劑或溶劑的狀況,進行二氧化碳與環氧丙烷之環加成反應,可到達91.5%之產率,由此可證明氫氧化鎂粒子有著良好的催化效果。 最後將本實驗之氫氧化鎂經鍛燒程序後生成之氧化鎂,在反應溫度為180℃、反應壓力10kg/cm2、反應時間15小時下,進行環加成反應,其結果顯示,氫氧化鎂的催化效果優於氧化鎂,推測主要原因為氫氧化鎂可與環氧化物產生氫鍵,有利於開環反應,造成氫氧化鎂之優異效能表現。

並列摘要


CO2 is the primary greenhouse gas which causes global warming in recent decade. According to the International Energy Agency’s report, carbon capture and storage is the key method for reduction of the global CO2 emissions. The captured CO2 can not only be stored which knows as carbon sequestration but also be applied for many other economic utilization. Cyclic carbonate synthesis from CO2 and epoxide can be used as intermediates in the production of polymer. Catalyst plays an important role in cycloaddition reaction. Current research has found that hydrogen bond donors can activate the epoxides and enhance the reaction. Using the heterogeneous catalysts can decrease the difficulty of separation of the catalyst and product, making the process suitable for industrial operation. High-gravity system has been developed for many years. In the field of crystal engineering, high-gravity technique can be used to produce nanoparticles. The characteristics of high–gravity system are small equipment size, short reaction time, high mass–transfer rate and capable for continuous operation. High-gravity system has higher commercial potential than hydrothermal method and sol-gel method, which are time-consuming, expensive and difficult to scale up. The purpose of this research is to synthesize magnesium hydroxide in spinning disk reactor and investigate the efficiency of magnesium hydroxide as a catalyst in cycloaddition reaction. Magnesium hydroxide is prepared by mixing MgCl2 solution and Na(OH)2 solution in spinning disk reactor. The molar ratio of MgCl2 to Na(OH)2 is 1:2 and the rotational speed is 2500rpm. The liquid flow of two reactants are 0.28L/min. The effect of MgCl2 concentration on the particle size and catalytic property of Mg(OH)2 is investigated. In the cycloaddition reaction of CO2 and propylene oxide, the effect of temperature, pressure and reaction time on the cycloaddition efficiency is investigated. According to the results, Mg(OH)2 particles having a high surface area of 293.1 m2/g, are produced from 0.5M MgCl2 solution. Using the Mg(OH)2 particles in the cycloaddition reaction, a propylene carbonate yield of 91.5% is obtained at P = 10kg/cm2, T = 180℃ and time = 15hr, while no co-catalysts or solvents are required. Furthermore, the cycloaddition reaction using MgO, which is produced by calcination of Mg(OH)2 is performed. Accordion to the results, the catalytic efficiency of Mg(OH)2 is better than that of MgO. The reason is that Mg(OH)2 has hydrogen bond donors that can activate the epoxides and make the cycloaddition reaction more easier.

參考文獻


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