A method for preparing a polyester polyol, comprising steps of:
- (1) processing an epoxy soybean oil and a small molecular alcohol with an organic acid catalyst to form an epoxy soybean oil polyol through an open-ring etherification reaction, which comprises specific steps of:
- adding a certain proportion of the organic acid catalyst into the small molecular alcohol in a reactor, then heating to 120-160° C.;
- stopping heating and adding the epoxy soybean oil to the reactor in batches to perform the open-ring etherification reaction until a required amount of the epoxy soybean oil is added;
- keeping a reaction solution at 180-200° C. for 1-3 hours and then cooling to obtain a yellow transparent viscous liquid, which is the epoxy soybean oil polyol, for subsequent use;
- wherein a molar ratio of the epoxy soybean oil and the small molecule alcohol is 1:4-1:7.5;
- an adding amount of the organic acid catalyst is 0.1-0.5% of a total mass of the small molecular alcohol and the organic acid catalyst;
- and
- (2) processing the epoxy soybean oil polyol and an organic acid with an esterification catalyst to form the polyester polyol, which comprises specific steps of:
- adding the epoxy soybean oil polyol prepared in the step (1) and the organic acid into the reactor according to a certain mass percentage, then adding the esterification catalyst and heating for a reflux reaction, keeping a temperature at 220-260° C. and checking an acid value;
- cooling to 180-220° C. when the acid value drops to below 5 mgKOH/g, and then performing vacuum distillation while controlling a relative vacuum degree at −0.065-0.095 MPa;
- cooling and discharging when the acid value of a rectification product drops to below 1.0 mgKOH/g and a mass fraction of a water content is less than 0.1%, so as to obtain the polyester polyol;
- wherein the certain mass percentage is:
- the organic acid 10-20%, and the epoxy soybean oil polyol 80-90%;
- an a adding amount of the esterification catalyst is 0.1-0.5% of the total reactant mass,
- wherein the obtained polyester polyol comprises a compound having an Ñ-type structure as shown in a formula (1) and a compound having an Ò-type structure as shown in a formula (2):
- wherein R is selected from a group consisting of, CH2CH2, CH2CH2OCH2CH2, CH2CH(CH3), CH2CH(CH3)OCH2CH(CH3), CH2CH2CH2CH2 and CH2CH(OH)CH2;
- R′ is selected from a group consisting of Ph, CH2CH2CHCH2, CH2CH2 and CH2(CH2)6CH2.