Method for the preparation of 1,2-propanediol and dipropylene glycol
A method for preparing 1,2-propanediol and dipropylene glycol involves continuously reacting propene with hydrogen peroxide in the presence of a catalyst mixture, containing a phase transfer catalyst and a heteropolytungstate, in a liquid reaction mixture containing an aqueous phase with a maximum apparent pH of 6 and an organic phase, to obtain 1,2-propanediol and dipropylene glycol. The method then involves separating the reaction mixture into an aqueous phase (P a ) containing 1,2-propanediol and dipropylene glycol and an organic phase (P o ); recycling at least part of the separated organic phase (P o ) to the reaction; and recovering 1,2-propanediol and dipropylene glycol from the separated aqueous phase (P a ). The reaction heat generated is at least partially removed, and the ratio of 1,2 propanediol to dipropylene glycol is controlled by adjusting the weight ratio of hydrogen peroxide to water fed to the reaction.
1 . A method for the preparation of 1,2-propanediol and dipropylene glycol, the method comprising:
a) continuously reacting propene with hydrogen peroxide in the presence of a catalyst mixture, comprising a phase transfer catalyst and a heteropolytungstate, in a liquid reaction mixture comprising an aqueous phase with a maximum apparent pH of 6 and an organic phase, to obtain 1,2-propanediol and dipropylene glycol;
b) separating the liquid reaction mixture into an aqueous phase (P a ) comprising 1,2-propanediol and dipropylene glycol, and an organic phase (P o );
c) recycling at least a part of the separated organic phase (P o ) to a); and
d) recovering the 1,2-propanediol and the dipropylene glycol from the separated aqueous phase (P a );
wherein reaction heat generated in a) is at least partially removed,
adjusting a ratio of the 1,2-propanediol to the dipropylene glycol by adjusting a weight ratio of the hydrogen peroxide to water fed to a),
wherein the weight ratio of the hydrogen peroxide to water is varied within a range of from 0.05 to 1.5; and
wherein the ratio of 1,2-propanediol to dipropylene glycol is reduced by increasing the weight ratio of hydrogen peroxide to water fed to a) or the ratio of 1,2-propanediol to dipropylene glycol is increased by reducing the weight ratio of hydrogen peroxide to water fed to step a).
2 . The method of claim 1 , wherein the weight ratio of the hydrogen peroxide to water fed to a) is adjusted while maintaining a molar excess of the propene to the hydrogen peroxide fed to a).
3 . The method of claim 2 , wherein a molar ratio of the propene to the hydrogen peroxide fed to a) is from 1.1:1 to 10:1.
4 . The method of claim 1 , wherein the weight ratio of the hydrogen peroxide to water is varied within the range from 0.10 to 0.7.
5 . The method of claim 1 , wherein a concentration of the hydrogen peroxide in the aqueous phase of a) is from 0.1 to 5% by weight.
6 . The method of claim 1 , wherein a residence time of the liquid reaction mixture in a) is adjusted to maintain a hydrogen peroxide conversion in the range of from 80 to 99%.
7 . The method of claim 1 , wherein a) is conducted in a loop reactor, and the reaction heat generated in a) is at least partially removed by circulating the liquid reaction mixture through a heat exchanger.
8 . The method of claim 1 , wherein the aqueous phase (P a ) obtained in b) is further processed without recycling any part directly or indirectly to a).
9 . The method of claim 1 , wherein in d), the aqueous phase (P a ) is subjected to catalytic hydrogenation.
10 . The method of claim 1 , wherein a) is conducted in the presence of phosphoric acid, and wherein the heteropolytungstate is a polytungstophosphate.
11 . The method of claim 1 , wherein the organic phase in a) comprises an organic solvent having a boiling point of more than 100° C. at atmospheric pressure and a solubility in water at 20° C. of less than 250 mg/kg.
12 . The method of claim 1 , wherein the phase transfer catalyst comprises at least one selected from the group consisting of a tertiary amine, a tertiary ammonium salt, and a quaternary ammonium salt, and
wherein the tertiary amine, the tertiary ammonium salt, and the quaternary ammonium salt each comprises in total at least 12 carbon atoms.
13 . The method of claim 12 , wherein the phase transfer catalyst comprises a tertiary or quaternary ammonium ion having the structure R 1 R 2 R 3 NR 4+ ,
wherein R 1 , R 2 , and R 3 are the same or different and are each an alkyl group having from 8 to 10 carbon atoms, and
R 4 is hydrogen or methyl.
14 . The method of claim 1 , wherein b), c), and d) are carried out continuously.
15 . The method of claim 3 , wherein the molar ratio of the propene to the hydrogen peroxide fed to a) is from 1.2:1 to 4:1.
16 . The method of claim 4 , wherein the weight ratio of the hydrogen peroxide to water is varied within the range from 0.15 to 0.45.
17 . The method of claim 5 , wherein the concentration of the hydrogen peroxide in the aqueous phase of a) is from 0.12 to 1.0% by weight.
18 . The method of claim 11 , wherein the organic solvent is an alkylated aromatic hydrocarbon having 8 to 12 carbon atoms.