Liquid nitrogen evaporative cooling

Update:12 Jan 2019
Summary:

Directly introducing liquid nitrogen into the reaction […]

Directly introducing liquid nitrogen into the reaction solution can also achieve the purpose of cooling. However, the following defects exist in the process of liquid nitrogen cooling:
1.1.1 In the process of cooling, liquid nitrogen is in direct contact with the material. The boiling point of liquid nitrogen at normal pressure is -196 °C. When the liquid nitrogen mesh distributor is sprayed, the instantaneous temperature difference is as high as 160 °C ~ -200 °C. Far from the process control temperature, resulting in a strong supercooling zone. The deviation of the local process control points must result in an unbalanced reaction process, which ultimately leads to a decline in product quality:
Liquid nitrogen absorbs heat and vaporizes during use. It is discharged into the atmosphere in the form of a gaseous state, and will carry some materials during the intense discharge process, thus causing a decrease in product yield and an increase in the consumption of the solvent:
Liquid nitrogen cooling is not easy to carry out with other materials. Because in the process of using liquid nitrogen to cool down. Due to the vaporization and expansion of liquid nitrogen, the pressure inside the reaction vessel is positive and the pressure is difficult to control. At this time, other materials must be added to participate in the reaction. The liquid nitrogen must be stopped first, which will cause the reaction temperature control to be interrupted and the process control to be biased;
 Liquid nitrogen cannot be recycled after use, resulting in an increase in production costs;
The cooling process is unstable and the controllability is poor. High operational requirements. The expansion ratio of liquid nitrogen is as high as 600, and the evaporation temperature is low. In the course of use, it is easy to cause explosion due to improper operation, running materials, solidification of materials to block pipes and even personal accidents.

https://www.chinacoldroom.com/