Method for the preparation of polymer polyols
The present invention refers to the use of hydrofoil impellers for the preparation of polymer polyols and to a method for preparing a polymer polyol, which comprises reacting a base polyol, at least one ethylenically unsaturated monomer and a macromer or a preformed stabilizer in the presence of a free-radical initiator and optionally a chain transfer agent in a reactor, wherein said reactor is stirred by means of a stirring system comprising a shaft rotatable about its longitudinal axis, and a plurality of radially extending hydrofoil impellers mounted on the shaft and respectively axially spaced apart and wherein the reactor does not contain baffles.
1. A method for preparing a polymer polyol, comprising reacting a base polyol, at least one ethylenically unsaturated monomer, and a macromer or a preformed stabilizer, in the presence of a free-radical initiator and optionally a chain transfer agent in a reactor ( 1 ), wherein said reactor ( 1 ) is stirred by means of a stirring system comprising a shaft ( 2 ) rotatable about its longitudinal axis ( 3 ), and a plurality of radially extending hydrofoil impellers ( 4 ) mounted on the shaft ( 2 ) and respectively axially spaced apart and wherein the reactor ( 1 ) does not contain baffles.
2. The method according to claim 1 , wherein the stirring system comprises 3-6 radially extending hydrofoil impellers ( 4 ) mounted on the shaft ( 2 ).
3. The method according to claim 1 , wherein each hydrofoil impeller ( 4 ) comprises 2, 3, 4, 5 or 6 blades ( 5 ).
4. The method according to claim 1 , wherein the shaft ( 2 ) is placed centrally and vertically in the reactor ( 1 ).
5. The method according to claim 1 , wherein all the hydrofoil impellers ( 4 ) are identical.
6. The method according to claim 1 , wherein the ratio of the internal diameter of the reactor ( 1 ) to the diameter of the hydrofoil impellers ( 4 ) is 1.2-4.0.
7. The method according to claim 1 , wherein the ratio of the axial distance between each hydrofoil impeller ( 4 ) and the diameter of the hydrofoil impellers ( 4 ) is 0.5-1.5.
8. The method according to claim 1 , wherein the reactor is a cylindrical reactor.
9. The method according to claim 1 , wherein:
the ratio of the blade length to blade height in each hydrofoil impeller ( 4 ) is 1.0-3.0; and/or
the ratio of the hydrofoil impeller diameter to the blade height is 2.5-6.5; and/or
the ratio of the hydrofoil impeller diameter to the blade length is 2.0-5.0; and/or
the ratio between the distance from the bottom hydrofoil impeller ( 4 ) to the internal bottom of the reactor ( 1 ) and the hydrofoil impeller diameter is 0.08-1.8.
10. The method according to claim 1 , wherein the tip speed of the hydrofoil impellers ( 4 ) is between 2.5 and 10.0 m/s.
11. The method according to claim 1 , wherein the method is performed as a semi-batch process or as a continuous process.
12. The method according to claim 1 , wherein at least part of the base polyol, the at least one ethylenically unsaturated monomer, the free-radical initiator and the optional chain transfer agent are fed to the reactor through an inlet port at the bottom of the reactor.
13. The method according to claim 1 , wherein:
the base polyol is a polyether polyol; and/or
the at least one ethylenically unsaturated monomer is a mixture of styrene and acrylonitrile.
14. A method for preparing a polyurethane which comprises preparing a polymer polyol by a method as defined in claim 1 and reacting the resulting polymer polyol with a polyisocyanate.
15. The method according to claim 1 , wherein the stirring system comprises 3-5 radially extending hydrofoil impellers ( 4 ) mounted on the shaft ( 2 ).
16. The method according to claim 1 , wherein each hydrofoil impeller ( 4 ) comprises 3, 4 or 5 blades ( 5 ).
17. The method according to claim 1 , wherein the ratio of the internal diameter of the reactor ( 1 ) to the diameter of the hydrofoil impellers ( 4 ) is 1.5-3.5.
18. The method according to claim 1 , wherein the ratio of the axial distance between each hydrofoil impeller ( 4 ) and the diameter of the hydrofoil impellers ( 4 ) is 0.5-1.2.
19. The method according to claim 1 , wherein the base polyol is a polyether polyol with a number average molecular weight of from 1,500 to 12,000 Da.
20. The method according to claim 1 , wherein the base polyol is a polyether polyol built up of propylene oxide and ethylene oxide units, with a hydroxyl functionality from 2 to 6 and with a number average molecular weight of from 1,500 to 12,000 Da.