Method and plant for purifying unsaturated compounds

1. A process for purifying an unsaturated compound, comprising:

feeding a mixture of the unsaturated compound and at least one of a compound of higher volatility than the unsaturated compound, a catlyst and a compound of lower volatility than the unsaturated compound to a first evaporator;

vaporizing a portion of the unsaturated compound and any compound of higher volatility at a pressure of from 0.1 mbar to 20 mbar in the first evaporator;

removing the vapor phase from the first evaporator and isolating the unsaturated compound from the vapor phase;

transferring a portion of the nonvaporized mixture from a bottom of the first evaporator to a second evaporator having a pressure of from 0.1 mbar to 20 mbar;

vaporizing a portion of the unsaturated compound in the second evaporator;

condensing the unsaturated compound vapor from the second evaporator and returning the condensate to the first evaporator;

wherein

a mass flow of condensed vapor from the first evaporator is less than the mass flow of condensate from the second evaporator to the first evaporator, and

a purity of the isolated unsaturated compound is 99% or more.

2. The process according to claim 1 , wherein the unsaturated compound is a glycol ester.

3. The process according to claim 2 , wherein the glycol ester is a hydroxyalkyl (meth)acrylate.

4. The process according to claim 1 , wherein a ratio of a mass flow of the vapor phase from the first evaporator to a mass flow of the condensate from the second evaporator into the first evaporator is from 0.4 to 0.8.

5. The process according to claim 4 , wherein the ratio of the mass flow of the vapor phase from the first evaporator to the mass flow of the condensate from the second evaporator into the first evaporator is from 0.5 to 0.8.

6. The process according to claim 1 , wherein a portion of the mixture to be purified is first introduced into the second evaporator.

7. The process according to claim 6 , wherein a quantitative ratio of the portion of the mixture to be purified introduced into the first evaporator to the portion of the mixture to be purified introduced into the second evaporator is from 9:1 to 0.1:1.

8. The process according to claim 1 , wherein the unsaturated compound is converted to a gas phase at a pressure from 0.1 mbar to 20 mbar.

9. The process according to claim 8 , wherein a temperature of the conversion to the gas phase is from 40° C. to 120° C.

10. The process according to claim 9 , wherein a gas loading factor is from 0.8 to 3.0 Pa 0.5 .