| 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. |
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