纳米碳酸钙制备新工艺的研究及其数学模型的建立

【作者】 赵春霞；

【导师】 满瑞林；

【作者基本信息】 中南大学 ， 化学工艺， 2003， 硕士

【摘要】 纳米碳酸钙是一种新兴的功能性填充材料，广泛的应用于橡胶、塑料、造纸、涂料、油墨等行业，它不仅可以起到增容降价的作用，而且也具有优良的补强性。尤其是近年来，随着纳米技术的发展和橡胶、塑料、造纸等行业的发展，对纳米碳酸钙的需求量迅速增加，对其粒度、晶形和性能提出了更高的要求。因此，纳米活性碳酸钙制备技术的研究具有重要意义。 目前，国内外普遍采用碳化法制备纳米CaCO₃。在合成过程中，碳化反应是最为关键的一个步骤。本论文将超声波引入碳化过程，发现超声波可以在一定程度上强化碳化反应，缩短碳化时间，使纳米CaCO₃粒径更加细小。为了从根本上强化碳化反应，本文开发了一种新的碳化工艺——自吸式搅拌碳化法，并作为本文研究的重点。试验中用pH计和电导率仪跟踪碳化反应的全过程，研究了碳化过程的特点。结果表明：这种带有高速搅拌的自吸式反应器，可以极大地强化碳化反应，可以使CO₂的平均吸收率提高到75％左右，而且使反应时间缩短了4倍多（和传统的鼓泡搅拌法相比），制备的纳米碳酸钙粒径为30—50nm，粒度分布更窄。文中还以CO₂的吸收率和沉降体积为参数，对温度、CO₂浓度和Ca（OH）₂浓度进行了单因素和正交试验研究，最终确定了制备纳米碳酸钙的最佳工艺条件：温度为20—30℃，Ca（OH）₂浓度为8—12％，CO₂浓度为50—80％。 为了满足不同行业对不同晶形碳酸钙的需求，本论文以自吸式搅拌反应器为主体设备，通过添加不同的添加剂，得到了立方形、链形、片形、球形和棒形五种超细碳酸钙产品。并以晶体生长动力学为基础，从添加剂的种类、用量及添加时间三个角度出发，研究了其对CaCO₃产品的粒度和晶形的影响。 基于粘胶工业的需求以及实际生产中存在的问题，本文从纳米碳酸钙的活化机理出发，研究了粘胶专用低吸油量纳米活性碳酸钙的工艺条件和主要影响因素。工艺条件选择活化温度为50—60℃，活化时间为1小时。研究表明，活化剂、添加剂、碳化工艺对吸油值都有较显著的影响。最终选择了两种较好的复合活化剂和相应的添加剂，活化产品能达到国家优等品，吸油值也可明显降低。 最后，本文以自吸式搅拌碳化法为研究对象，研究了碳化反应的宏观动力学规律，并拟合了试验数据，进行了模型验证，得到了具有令人满意的预测效果的宏观动力学分段模型，并对鼓泡搅拌反应器的传质特性进行研究，与自吸式搅拌反应器进行比较，结果表明自吸式搅拌反应器可以使液相体积传质系数kt.a和气液相界接触面积a提高一个数量级，从理论上证明了新型反应器可以极大强化吸收传质，提高相界接触面积，从而极大强化碳化反应，缩短碳化反应时间。同时也充分说明了新工艺选择的科学性和可靠性，也为纳米碳酸钙的生产提供了一定的理论依据。更多还原

【Abstract】 Nanometer calcium carbonate is a kind of new functional filler, widely used in rubber, plastic, paper, paint, printing ink, and so on. Nanometer CaCO3 not only has the function of increasing volume and decreasing cost, but also has the function of reinforcing. Especially in recent years, with the development of nanometer technology, nanometer calcium carbonate demand of different trades such as rubber, plastic and paper is highly increased; at the same time, those trades also make more requirements for particle size, crystal shape and performance. So the study of active nanometer calcium carbonate has important significance.Presently, carbonization method is widely adopted to prepare nanometer CaCO3 in home and abroad. During the synthesis process, carbonization reaction is the key step. Initially taking sonochemistry in carbonization, the influence of ultrasound on the carbonation process of the synthesis of nanometer calcium carbonate was studied. The result showed that under the ultrasound, nanometer calcium carbonate with uniform fine particle size could be obtained, and carbonization time could be shortened. Carbonization reaction was strengthened in some degree. Inorder to strengthen carbonization fundamentally, a new technology --self-suction stirred carbonization method was developed in this article.Taking the new reactor -- self-suction stirred reactor as main researchobject, using pH meter and conductivity meter to trace the whole process, carbonization characters of new technology were studied. The results showed that self-suction stirred reactor, with high-speed stirring, could strengthen carbonization effectively, obviously raise the average absorptivity of CO2 to 75%, shorten the carbonization time fourfold or so (comparing to the traditional bubbling method), and prepare 30-50 nanometer calcium carbonate with mean particle size. Taking CO2 absorptivity and sedimentation volume as parameters, and based on the single factor and orthogonal experiments of temperature, CO2 concentration and Ca(OH)2 concentration, the optimum technology conditions were determined. The temperature was 20 to 30 C, CO2 concentration was about 50% to 80% and Ca(OH)2 concentration was 8%to 12%.To meet the demands of different trades for CaCO3 of various crystal shapes, using self-suction stirred reactor as main equipment, through adding different additives, ultrafine CaCO3 with five different shapes (including cube, chain, plate, sphere and stick) were synthesized in this article. Based on the crystal growing kinetics, the influences of additives on CaCO3 were studied. From the sorts, the amount, and the adding time, the influences of additives on particle size and crystal shape were studied.Based on the mechanism of surface modification, the technology conditions and main influence factors of nanometer calcium carbonate using in viscose with low oil absorption were studied. The modification temperature was 50 to 60 C, and modification time was about 1 hour. The carbonation technology, modification temperature, time, composition and additive had notably influence on oil absorption. In the end, two better compound activators and some additives were selected. Under the condition, modifying products could reach the national standard of high quality products, and oil absorption could be decreased sharply.In the end, using self-suction stirred carbonization as research object, macrokinetics law of carbonization was explored. Macrokinetics sectioned model with favorable prediction effect was obtained. Comparing to bubbling stirred reactor, new reactor could raise liquid volume mass transfer coefficient kL-a and gas-liquid contact area a an order of magnitude. It showed theoretically that new technology could make gas and liquid mixing completely, make bubble little, strengthen gas-liquid reaction effectively, and shorten carbonization time. It also fully illustrated reliability and scientific quality of the new technology. Moreover, it provided theory reference for producing nanometer calcium carbonate.更多还原