Liquid-liquid dispersion and mixing and mixing of mutual solution

1 Introduction The liquid-liquid dispersion operation is usually for the following purposes: (1) increasing the phase interface by liquid-liquid dispersion; (2) reducing the diffusion resistance outside the dispersed phase droplets; (3) generating turbulent flow to promote concentration and temperature uniformity. (4) The dispersed phase droplets are repeatedly crushed and coagulated to promote mass transfer between the dispersed phase droplets.
In liquid-liquid dispersion, agitation plays a key role in controlling the aggregation, rupture and suspension of droplets. Stirring affects the strength and direction of the liquid flow and thus the distribution and uniformity of the droplets.
2 Mixing and mixing of the mutual solution 2.1 Stirring and mixing of the low-viscosity liquid The mixing of the mixed solution is a process in which the concentration, density, temperature and other physical states of the two or more kinds of mutual solution are uniform at any point. Often referred to as the mixing process, it is the most basic process in the mixing process. Sometimes it is emphasized that it belongs to the characteristics of homogeneous mixing. Also known as blending or blending.
The main feature of the low viscosity inter-liquid agitation process is that there is no phase interface for the transfer process. For a purely physical mixing process, mixing of low viscosity inter-liquids is the easiest process to accomplish. However, if the mixing process is accompanied by a chemical reaction, it will often complicate the process, mainly in two aspects: First, there are strict requirements on the mixing time to avoid some undesired side reactions; second, most have The export of heat of reaction or the introduction of heat increases the control difficulty of the mixing process. The agitation of the low viscosity inter-liquid is generally carried out under turbulent conditions. Therefore, this process has strong bulk diffusion, turbulent diffusion and molecular diffusion, and the macro-mixing process is accompanied by a strong micro-mixing process.
In order to achieve a uniform mixing state of the agitating liquid, the agitation of the low-viscosity mutual solution first requires a sufficient circulation amount to avoid a dead zone in the apparatus, so that all the stirring liquid can generate a rapid convection circulating motion. Secondly, it is also required that the liquid turbulence intensity or shearing speed caused by the agitator is large, especially when the viscosity difference between the two liquids is relatively large, the presence of shearing will facilitate the dispersion of the high-viscosity liquid in the device, which is favorable for turbulent diffusion. Strengthening. In addition, when the amount of the two liquids to be mixed differs greatly, the feeding position of a small amount of liquid is very important. The ideal position is the impeller area or near the impeller suction port to ensure that the feed can pass through the impeller quickly. , the stirring liquid is quickly reached to achieve concentration homogenization.
The main performance indicators for evaluating the mixer mixing effect are mixing time, energy consumption and shear performance. The mixing time is the most important performance indicator for judging the mixing effect.
2.1 Stirring and mixing of highly viscous liquids The use of high viscosity fluids in industrial production is increasing. Many high molecular weight polymers are high viscosity fluids, many of which are non-Newtonian fluids. The viscosity also changes during the agitation process, so the requirements for the agitator are higher, and the agitator is required to adapt to the change in viscosity to complete the agitation operation. Stirring of highly viscous fluids is often referred to as mixing between miscible, highly viscous liquids. However, high viscosity fluid agitation also has various heterogeneous operations such as dispersion, solid dissolution, and chemical reaction in the industry.
In the stirring operation, it is not difficult to cause turbulence in the low-viscosity mutual solution by the agitator. However, after the viscosity reaches a high level, the laminar flow state can only occur due to the influence of the viscous force. Particularly difficult, this laminar flow can only occur in the vicinity of the agitator, and the highly viscous liquid that is slightly further away from the blade remains stationary. This makes it difficult to cause circulating flow of the liquid in the stirring device, that is, there is a dead zone in the device, which is disadvantageous for various mixing processes such as mixing, dispersion, heat transfer, and reaction. Therefore, the primary problem with high viscosity liquid agitation is to solve the problem of fluid flow and circulation. In this case, the stirring flow rate cannot be increased by increasing the stirring speed, because the flow rate of the agitator is small when the viscosity of the fluid is high, and the flow rate is too high, and the channel flow is formed in the high viscosity solution. The surrounding liquid is still dead. A more effective solution is to try to get the agitator to push a wider range of fluids. Therefore, the ratio of the diameter of the agitator of the high-viscosity liquid to the inner diameter of the device, the ratio of the width of the blade to the inner diameter of the device are relatively large, and it is sometimes required to increase the number of layers of the agitator to increase the agitation range.
From the viewpoint of the stirring mechanism, when the high-viscosity liquid is mixed in the laminar flow region, the liquid unit is subjected to the shearing and subdividing action to be elongated, drawn or divided, and the mixing is gradually achieved as the shearing time increases. At the same time, since the shearing field in the mixing device is not uniform, for example, the anchoring zone of the anchor agitator is a strong shear zone in the gap between the anchor and the wall of the kettle, the mixing rate of the liquid is faster, and the middle zone of the kettle is the low shear zone. The mixing rate is slower. Therefore, the liquid exchange rate between the high shear zone and the low shear zone or the circulation ability of the liquid in the kettle is also an important factor affecting the mixing. In addition, fluctuations in the velocity of the fluid within the device also promote mixing. In other words, the mixing rate of the high viscosity liquid mainly depends on the relative movement rate between the agitator and the surface of the kettle wall and the distance between them. For this purpose, a stirrer for the high viscosity fluid is also required, and the ratio of the diameter of the agitator to the inner diameter of the device is also required. They are quite large. In the actual production process, the commonly used viscous fluid agitator has an anchor stirrer, a ribbon stirrer, a frame stirrer and the like.
The main performance indicators for evaluating the mixing effect of the agitator are mixing time, mixing energy per unit volume, and the like. The mixing time is the most important performance indicator for judging the mixing effect.