Method for the preparation of 1,2-propanediol, dipropylene glycol and tripropylene glycol
A method can be used for preparing 1,2-propanediol, dipropylene glycol, and tripropylene glycol. The method involves reacting propene with hydrogen peroxide containing nitrate, 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. The method then involves separating the reaction mixture into an aqueous phase containing 1,2-propanediol, dipropylene glycol, tripropylene glycol, and nitrate and an organic phase. The method further involves recycling at least part of the separated organic phase to the reaction; hydrogenating the separated aqueous phase using a heterogeneous hydrogenation catalyst to provide a hydrogenated aqueous phase with a reduced nitrate content; and recovering 1,2-propanediol, dipropylene glycol, and tripropylene glycol from the hydrogenated aqueous phase by a sequential multiple-step distillation.
1 . A method for the preparation of 1,2-propanediol, dipropylene glycol, and tripropylene glycol, the method comprising:
a reacting propene with hydrogen peroxide containing nitrate 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, wherein apparent pH is a value determined by measurement with a glass electrode employing a commercial pH meter calibrated with aqueous buffer solutions of known pH for measuring dilute aqueous solutions forming a liquid reaction mixture comprising an aqueous phase comprising 1,2-propanediol, dipropylene glycol, tripropylene glycol, and nitrate and an organic phase;
b) separating the liquid reaction mixture into a separated aqueous phase (P a ) comprising 1,2 propanediol, dipropylene glycol, tripropylene glycol, and nitrate, and a separated organic phase (P o );
c) recycling at least a part of the separated organic phase (P o ) to a);
d) hydrogenating the separated aqueous phase (P a ) with a heterogeneous hydrogenation catalyst thereby converting nitrate and nitric acid present in said aqueous phase (P a ) to molecular nitrogen and volatile nitrogen oxides, to provide a hydrogenated aqueous phase; and
e) recovering the 1,2-propanediol, the dipropylene glycol, and the tripropylene glycol from the hydrogenated aqueous phase by a sequential multiple step distillation, comprising
a first water distillation step and optionally further water distillation steps, each providing an overhead product comprising water and a bottoms product which is passed to a subsequent first glycols distillation step,
the subsequent first glycols distillation step, providing a first overhead product comprising the 1,2 propanediol and a first bottoms product which is passed to a subsequent second glycols distillation step,
the subsequent second glycols distillation step, providing a second overhead product comprising the dipropylene glycol and a second bottoms product which is passed to a subsequent third glycols distillation step, and
the subsequent third glycols distillation step, providing a third overhead product comprising the tripropylene glycol and a residuals bottoms product.
2 . The method of claim 1 , wherein the heterogeneous hydrogenation catalyst comprises ruthenium.
3 . The method of claim 1 , wherein the hydrogenation is conducted at a temperature in a range of from 50 to 200° C.
4 . The method of claim 1 , wherein the separated aqueous phase (P a ) is further processed without recycling any part of it directly or indirectly to a).
5 . The method of claim 1 , wherein a) is carried out continuously, and
wherein a concentration of hydrogen peroxide in the aqueous phase of a) is from 0.1 to 5% by weight.
6 . The method of claim 1 , wherein a) is carried out continuously in a loop reactor comprising internals in a tubular section, and wherein the liquid reaction mixture is passed through the loop reactor at a flow rate sufficient to provide turbulent flow at said internals.
7 . The method of claim 1 , wherein a) is conducted in the presence of phosphoric acid.
8 . The method of claim 1 , wherein the heteropolytungstate is a polytungstophosphate.
9 . 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.
10 . 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 comprises in total at least 12 carbon atoms.
11 . The method of claim 10 , 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.
12 . The method of claim 1 , wherein the hydrogenated aqueous phase has a reduced nitrate content compared to the separated aqueous phase (P a ).
13 . The method of claim 3 , wherein the hydrogenation is conducted at a temperature in a range of from 80 to 140° C.
14 . The method of claim 9 , wherein the organic solvent is an alkylated aromatic hydrocarbon having 8 to 12 carbon atoms.