| Nano-CaCO3 with its low price, no toxic, tasteless and little pollution is widely used in the field of rubber, plastics, paper-making, ink, paint and pharmaceuticals, etc. In industry, it is prepared generally by intermittent bubbling carbonation method, because of simply operation and less investment. Nano-CaCO3 which using in this way obtained has a larger particle size and wide particle size distribution. Therefore, it can only be used in the low-end products, which limits its application. The key technical problem of the preparation is the well mixing and a high degree of supersaturation. As a high performance mixing equipment, microreactor with lots of advantages such as mixing uniformity, low mixing scale is very suitable for the preparation of nano materials. But its disadvantages include low flux and plug easy restrict its application in industry. Therefore, it is great significance to develop a microreactor with high performance and flux to prepare nano-CaCO3.In this thesis, the main paper contents are as follows:1. Thesis carried on the optimization of structural parameters for a high-flux annular microreactor designed by tsinghua university Luo research group. Through analysis of the effect of the microreactor structural include membrane pore size, membrane material, ring gap channel height in preparing nano-CaCO3 to determine the best structural parameters. The results show that using 5 um organic polymer membrane is better while the height of annular channel is 2.5 mm, the length of the reaction chamber is 3.5 cm.2. Taking carbon dioxide as the dispersed phase and calcium hydroxide as the continuous phase, by using high-flux annular microreactor, we successfully prepared nano-CaCO3 with average diameters ranged from 40 to 80 nm. The reaction conditions were studied, including calcium hydroxide slurry place time, the different materials, disperse phase flow rate, continuous phase flow rate, the concentration of disperse phase, the concentration of continuous phase, reaction temperature, carbonization time and control agent. Then, compared with traditional bubbling of preparation. At the same time, the experimental slurry pH in the reaction process and the sedimentation rate of grout after reaction were tested. The optimal reaction conditions were as follows:the time of calcium hydroxide slurry placed is two days or more, analytical reagent, disperse phase flow rate is 3 m3·h-1, continuous phase flow rate is 5 m3·h-1, initial concentration of calcium hydroxide is 1.8%, carbon dioxide concentration is 30%, the reaction temperature between 10-20 ℃, add sodium hexametaphosphate is helpful to the production of catenary nano-CaCO3. The process of preparing nano-CaCO3 by microreactor do not appear re-alkali phenomenon. Characterization results show that the structure of nano-CaCO3 is calcite crystal. Its specific surface area reached 29 m2·g-1 with narrow size distributions.3. The nano-CaCO3 was modified by three modifier. By studying the impact of modifier types, modified time, modified temperature and dosage of modifier on activation degree and oil absorption value, we draw the following conclusions:sodium stearate has the best modification effect among the three kinds of modifiers; The activity degree of nano-CaCO3 increased with the amount of modifier, the modified temperature and the time of modification, and the oil absorption value decreased rapidly with the increase of the degree of activation, when the activation degree is close to 100%, the amplitude tends to be gentle. When dosage is 4%, temperature is 60 ℃, modified time is 45 min, sodium stearate get the best results. Modified nano-CaCO3 has the same crystal type and particle size,but the better dispersion. |
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