Chemical reaction between dichloromethane and solid carbon dioxide

Question

I studied heat transfer liquids with low melting point (coolants), and how fast their temperature decreases when they are contacting with solid carbon dioxide. Nearly all liquids (brines, glycols etc.) that I studied have similar behavior, except dichloromethane.

When I put solid carbon dioxide grains into dichloromethane, the temperature of the liquid dropped nearly immediately! At first, the temperature was $\pu{20^\circ C}$, and after just $\pu{5 s}$ the temperature of the liquid was $\pu{-70^\circ C}$! Do you know why is it possible? When I freezed $\ce{KCl}$-brine, the temperature had been decreasing from $\pu{20^\circ C}$ to $\pu{-40^\circ C}$ for more than $\pu{5 min}$!

This property of dichloromethane may be very useful. I think it is due to its low viscosity.

Can you help me and explain this phenomenon?

Answer 1

In brine cooling happens only on the surface of the solid carbon dioxide and causes the water to freeze there, forming an insulating layer (the same happens with ethylene glycol). In dichloromethane, which freezes below $-97$ degrees, no freezing occurs. Moreover, carbon dioxide is well soluble in dichloromethane, which makes the heat transfer more efficient. The latter property may cause you problems if you want to use your coolant in closed installations, because after warming the solution may release the excess of carbon dioxide.