Method for cyclically preparing polyether polyol by using DMC catalyst

A method of cyclically preparing a polyether polyol as a target polymer, the method comprising:

• polymerizing a low molecular-weight alcohol with an alkylene oxide to obtain a low molecular-weight polymer;
• obtaining an intermediate-target polymer by a first process in a reactor, the first process facilitating a first reaction of the low molecular-weight polymer with the alkylene oxide while a first amount of the low molecular-weight alcohol is introduced into the reactor;
• and
• obtaining the target polymer by a second process in the reactor using a first portion of the intermediate-target polymer,
• wherein:
• a second portion of the intermediate-target polymer is recycled for reproduction of the intermediate-target polymer,
• a double metal cyanide (DMC) catalyst is used as a catalyst of the first reaction,
• an acid is used as a promoter of the first reaction,
• the intermediate-target polymer and the low molecular-weight polymer have a same average molecular weight,
• the DMC catalyst is a double metal cyanide complex catalyst for ring opening in polymerization of epoxy,
• the acid is one of a nitric acid, a phosphoric acid, and a sulfuric acid, or a mixture of any two or three thereof,
• the alkylene oxide is one of a propylene oxide, a butylene oxide, a mixture of ethylene oxide and the propylene oxide, a mixture of an ethylene oxide and a butylene oxide, a mixture of the propylene oxide and the butylene oxide, and a mixture of the ethylene oxide, the propylene oxide and the butylene oxide,
• the low molecular-weight alcohol is a monohydric alcohol or a polyhydric alcohol, the monohydric alcohol being one of an allyl alcohol or a butanol, the polyhydric alcohol being one of an ethylene glycol, a propylene glycol, a butylene glycol, and a glycerol, and
• the first process comprises the following steps:
• 1a) introducing the low molecular-weight polymer into the reactor, the low molecular-weight polymer having been pre-added with the DMC catalyst and the acid;
• 1b) dewatering by a bubbling nitrogen for at least 10 minutes at a first temperature range of 100-175° C. under vacuum at a first pressure not higher than −0.085 MPa;
• 1c) turning off the bubbling nitrogen and further vacuuming for at least 10 minutes;
• 2) introducing into the reactor the alkylene oxide in an amount that is no more than 20% by weight (wt %) of the low molecular-weight polymer;
• 3a) simultaneously and continuously introducing the alkylene oxide and the first amount of the low molecular-weight alcohol into the reactor, the reactor maintained at a second temperature range of 120-180° C. and at a second pressure not higher than 0.2 MPa;
• 3b) introducing at least 10 wt % of the alkylene oxide into the reactor after the introducing of the first amount of the low molecular-weight alcohol is completed;
• 3c) waiting until no substantial pressure drop is observed in the reactor;
• and
• 3d) discharging the reactor to obtain the intermediate-target polymer.