Negative pressure distillation of dichloromethane
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Hello everyone, in the synthesis of fine chemicals, there is a process involving vacuum distillation of dichloromethane (with a boiling point of 39°C at atmospheric pressure) using an enamel-lined reactor. The known parameters are as follows: the volume of the enamel-lined reactor is 3000 L, the temperature of the heat medium in the jacket is 40–50°C, the vacuum level inside the reactor is 35–25 kPa, the temperature of the liquid inside the reactor is 15–25°C (in a boiling state), and the temperature of the liquid after condensation is -5°C. There are currently 2 issues: 1. Is -5°C sufficient after the liquid material is condensed? What are the general requirements regarding the temperature to which the liquid material should be condensed? 2. Since this operation involves vacuum pump negative-pressure distillation, what is the exhaust volume of the vacuum pump in m3/h during the distillation process? What is the concentration of dichloromethane in that exhaust gas, and how is it calculated? Please please please
Chemical engineering problems are not mathematical problems; there is no right or wrong, only good or bad. Problems should be viewed systematically; it is necessary to understand the material balance and energy balance relationships involved, as well as the factors that affect the temperature after the condenser, in order to determine whether adjustments to the parameters are needed. Many parameters cannot be adjusted directly; indirect adjustment is required. The exhaust volume of a vacuum pump is influenced by both design and operation factors, and it cannot be set to whatever value you desire
To answer the above question, it is necessary to clarify: 1. What is the required evaporation rate of dichloromethane for the process? 2. Boiling point of dichloromethane at operating pressure (from literature or simulation?) 3. Air leakage rate of the reaction system (check relevant data). 4. As it is an extremely volatile organic compound, it is recommended to add a tail cooling gas after the vacuum pump; otherwise, significant losses of dichloromethane from the system will occur
1. During the design phase, the bubble point temperature of dichloromethane under this negative pressure condition was certainly calculated, that is, the temperature at which it will condense into a liquid. The lower the absolute pressure, the lower the temperature required to cool it to the point of condensation into a liquid. 2. The exhaust volume of a vacuum pump is generally determined by referring to the manual before making a selection. The question is not specific enough to answer.
Sigh. For the atmospheric distillation of dichloromethane, use two stages of chilled brine; the recovery rate is around 95%. If vacuum is required, then use two stages of chilled brine in front of the vacuum pump, and another two stages behind it.
This negative-pressure distillation of dichloromethane is confusing – is it due to thermosensitivity that negative-pressure distillation is required? In negative-pressure distillation of dichloromethane, there is significant material loss; the amount of material that can be condensed at -5 degrees is limited. Therefore, the vacuum pump required must be very powerful, as it is responsible for removing the material from the system. Additionally, a further condenser is needed after the vacuum pump to recover the material. The parameters you provided are also incomplete; the area of the condenser, the evaporation rate, and the composition of the material inside the reactor are all missing