乙酸酐复合催化法制备无水氯化镁的研究

发布时间：2018-03-16 05:36

  本文选题：水卤镁石　切入点：二水氯化镁　出处：《青海师范大学》2015年硕士论文　论文类型：学位论文

【摘要】：我国镁资源丰富,尤其是青藏高原蕴藏着巨大的镁盐资源。以青海察尔汗盐湖为例,开发钠盐和钾盐之后的废料老卤,其主要成分为六水氯化镁。对老卤中的镁进行利用不仅能解决盐湖中废物污染的问题,而且有利于盐湖中微量元素的开发,达到“变废为宝”的目的。由六水氯化镁制备无水氯化镁,是电解法冶炼金属镁的关键技术。现有的无水氯化镁制备工艺,一类是通入酸性保护性气体(如氯气和氯化氢)除水,此工艺对设备的腐蚀严重;另一类在水溶液中通入氨气,氨气的络合能力强于水的络合能力,替代结晶水,形成六氨氯化镁,再进一步脱氨制备无水氯化镁,此工艺在水体系中进行,产物中残余水较多。本论文使用有机体系,避免水体系中残余水分的问题,采用乙酸酐法除去六水氯化镁中的结晶水。六水氯化镁中的结晶水分为两类,四个分子间的结晶水和两个分子内的结晶水,分子间的结晶水较易脱去,分子内的结晶水较难脱去,按照脱去结晶水的难易程度,本论文的主要内容分为两个部分。第一部分,使用乙酸和乙酸酐体系,利用乙酸酐除去六水氯化镁中分子间的四个结晶水,制备二水氯化镁。实验结果显示:氯化镁和乙酸酐的物质的量之比为1:9,回流时间为4h,旋蒸油浴温度105℃,旋蒸时间为2h,产物中氯化镁和结晶水的物质的量之比为1:2.0031。第二部分,采用乙酸、乙酸酐和N,N-二甲基甲酰胺体系。首先,加大回流时间,发现产物中结晶水在逐渐减少,但是,回流时间过长,没有现实意义。其次,采用具有络合作用的物质做催化剂,降低乙酸酐法除去六水氯化镁分子内结晶水的难度,制备无水氯化镁。按照催化剂的性质不同,催化剂分为碱性、中性和酸性。碱性催化剂为三乙胺和乙二胺四乙酸二钠,中性催化剂为乙酸铵和氯化铵,酸性催化剂为柠檬酸、琥珀酸和草酸。实验结果显示:试验选取乙酸酐和草酸作为混合催化剂,二者的物质的量之比为1:1,回流24h,滴加乙酸酐的速度为1mL/20min,旋蒸油浴温度为105℃,旋蒸时间为2h,得到产品。与无水氯化镁对比,产物中的氯化镁和结晶水的物质的量之比为1:0.0177,水的质量分数为3.3‰。
[Abstract]:China is rich in magnesium resources, especially in the Qinghai-Tibet Plateau, where there is a huge amount of magnesium salt. Taking the Qarhan Salt Lake in Qinghai as an example, the waste materials after the development of sodium salt and potassium salt are old brine. The main component is magnesium chloride hexahydrate. The utilization of magnesium in the old brine can not only solve the problem of waste pollution in salt lake, but also benefit the development of trace elements in salt lake. The preparation of anhydrous magnesium chloride from magnesium chloride hexahydrate is the key technology of smelting magnesium metal by electrolysis. One is the removal of water through acidic protective gases (such as chlorine and hydrogen chloride), which corrodes the equipment seriously; and the other is the introduction of ammonia in aqueous solution, which has a stronger complexing capacity than water, replacing crystalline water. Magnesium hexamethylammonium chloride is formed and anhydrous magnesium chloride is prepared by further deamination. This process is carried out in water system, and the residual water in the product is more. In this paper, organic system is used to avoid the problem of residual water in water system. The crystalline water in magnesium chloride hexahydrate is removed by acetic anhydride method. The crystalline water in magnesium chloride hexahydrate is divided into two categories: four intermolecular crystalline water and two intramolecular crystalline water, and the intermolecular crystalline water is easy to be removed. The intramolecular crystalline water is difficult to be removed. According to the degree of difficulty in removing the crystalline water, the main content of this paper is divided into two parts: the first part, using acetic acid and acetic anhydride system, Magnesium chloride dihydrate was prepared by removing four crystalline water between molecules in magnesium chloride hexahydrate by acetic anhydride. The experimental results showed that the ratio of magnesium chloride to acetic anhydride was 1: 9, the reflux time was 4 h, and the spinning oil bath temperature was 105 鈩，

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