Trichlorosilane distillation
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What should be the difference between the top temperature and the reflux temperature in the distillation column for trichlorosilane?
It is best to keep the difference within 10 degrees
Theoretically, the “top of tower temperature and reflux temperature” should be equal. Because the heat transfer within the tower is driven by mass transfer, if the temperature difference between the two is large, a portion of the tower’s reflux section fails to perform mass transfer. It also increases energy consumption. We generally strive to use a reflux condition close to the bubble point; the material at the top of the tower first passes through a condenser, with part of the condensed material being recycled back while another part is taken out and then cooled.
I think the return temperature should be slightly below the bubble point, which is beneficial for mass transfer.
It should be controlled by the condensate water at the top of the tower!
When the vapor and liquid are in equilibrium, the temperature of the gas exiting the top of the tower should be the dew point temperature. The temperature of the liquid phase that returns to the tower via the condenser at the top should be slightly below the bubble point temperature, to ensure complete condensation; this facilitates heat and mass transfer upon return to the tower. If TCS and STC are separated, the purity of the gaseous TCS product obtained at the top of the tower is very close to 100%. Referring to the two-component vapor-liquid equilibrium diagram for TCS and STC, at a certain pressure, the bubble point temperature and the dew point temperature almost coincide at a single point
Our reflux temperature is very low in order to achieve high-purity TCS!
Theoretically, they should be roughly equal; I think the backflow temperature is slightly lower than the bubble point, which is beneficial for mass transfer.