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Synthesis of propylene glycol

- Oct 29, 2018 -

1. direct hydration of propylene oxide is a pressurized non catalytic hydrolysis method. Propylene oxide was synthesized by direct hydration of propylene oxide with water at 150-160 C and 0.78-0.98 MPa pressure. The product was obtained by evaporation and distillation.

2. indirect hydration of propylene oxide was prepared by indirect hydration of propylene oxide and water sulphuric acid as catalyst.

3. direct catalytic oxidation of propylene.

4. use 1,2- two chloropropane as raw material.

There are two processes for this method:

First, two chloropropane is directly hydrolyzed into propylene glycol in weak alkaline aqueous solution.

The two is the reaction of two chloropropane and carboxylate, and the ester is then hydrolyzed to propylene glycol.

(1) Directly hydrolyzing 1,2-dichloropropane, water, sodium bicarbonate and hexadecyl tributyl phosphonium bromide were added into the reactor and reacted for 18 hours under partial pressure of carbon dioxide at 100 C for 1.0 MPa to obtain 80% propylene glycol. To control the feeding speed of two chloropropane, that is to say, the feeding speed is fast at low temperature and slow at low temperature. Example: 60 g calcium carbonate and 150 g water were added into 300 ml autoclave, stirred to 230 C, and dichloropropane was added at 0.03 g / (min 100 g H2O) for 11.5 h continuously; stirred at this temperature for 30 min, then quenched to room temperature, the yield of propylene glycol was about 95%. The yield of propylene glycol can reach more than 95% if the feeding rate of dichloropropane is changed correspondingly in the temperature range of 130-300 C.

(2) In the two-step hydrolysis process, the raw material is reacted in a kettle reactor. After the conversion of dichloropropane reaches a certain level, the material is fed into a piston flow reactor to continue the reaction, and finally hydrolyzed to propylene glycol. Example: 606 kg dichloropropane was added into 2 cubic meters reactor, 800 kg sodium acetate, 556 kg 1,2-propanediol, 10 kg acetic acid and 1 kg water were added, stirred up to 180 C, cooled to 120 C after 4 hours, the material was extracted, heated to 180 C by preheater, and passed through a piston flow reversal reactor with a length of 400 m, an inner diameter of 25 mm and a volume of 230 L at a speed of 500 L. In the reactor, the products were collected in the second stirred tank and cooled to room temperature. The products were 44 kg dichloropropane, 334 kg propylene glycol, 32 kg sodium acetate, 44 kg acetic acid, 234 kg 1,2-diacetoxypropane, 693 kg propylene glycol monoacetate, 45 kg 1-chloropropylene, 547 kg NACL and 1 kg water.

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