Study Of Preparing Nesquehonite In Micro-reactor

The reserves of magnesite in China are the first in the world,and its main component is magnesium carbonate.At the same time,China has a large amount of bittern produced each year.Using bittern and magnesium carbonate for the preparation of nesquehonite can not only create value,but also protect the environment.Using microreactors to adjust the degree of mixing can further improve the quality of nesquehonite.How to optimize the design of microreactors and select the appropriate parameters are the key issues.Based on the above background,the main research contents of this paper are as follows:?1?Explore the crystallization process of nesquehonite by detecting the concentration of Mg²⁺in the solution.Using numerical simulation to examine the mixing characteristics in the microchannels with different geometries.Based on above results,serpentine micro-reactor with a section of 1mm*1mm and a length of 3000mm was determined for experiments.?2?The Na₂CO₃ and MgCl₂ solution(0.2mol?L^-1)is used to prepare nesquehonite in the micro-reactor.The effects of the feed flow rate and residence time on the crystal quality are characterized using XRD and SEM.The results show that both nucleation surface area and supersaturation of the reaction solution which dramatically affect the growth of the crystal will decrease as the feed flow rate is too low or too high.With the flow rate at 4mL·min^-1,the product is highly crystallized and less shattered.As the residence time of the material in the channel increases,the product quality will first decrease and then increase.At the flow rate of 4 mL·min^-1 and residence time of 9s,the best crystal was obtained,the crystal cell distortion was small,and the crystal rod size distribution was uniform?average 150?m?,which was in accordance with the normal distribution.?3?For the case where the product crystallinity is low and the crystal shape is incomplete for a specific residence time,mixing is controlled by introducing a third phase gas,nitrogen.At the same time,high-speed video is used to investigate the fluid mixing in the channel,and a simplified normalized equation is used to calculate the degree of mixing at different cross sections in the channel.Visual observation results show that the introduction of the third phase significantly enhances the mixing,and at the same time separates the liquid phase to control the gas-liquid flow ratio,allowing the solution and nitrogen in the channel to flow in a slug-like manner.When the ratio of gas velocity to liquid velocity is 1:4 and the flow rate of liquid phase is 4 mL?min^-1,the product with a residence time of 6s was highly crystallinitzesThe experimental results show that by changing the length of the serpentine channel,the degree of mixing of the solution in the channel can be adjusted,and the crystal quality of the product can be effectively regulated;at the same time,it is also indicated that the microreactor has greater flexibility than fully-mixing flow reactor.