Method for producing polybutylene terephthalate

A method for producing polybutylene terephthalate, the method comprising:

• (a) subjecting a diol component comprising a biomass-derived raw material 1,4-butanediol having a nitrogen content of from 0.01 to 20 ppm by mass and a dicarboxylic acid component comprising terephthalic acid or an alkyl terephthalate to an esterification reaction or ester-exchange reaction,
• (b) subjecting the reactant obtained in (a) to a polycondensation reaction, thereby obtaining polybutylene terephthalate, and
• further comprising directly producing the biomass-derived raw material 1,4-butanediol or a biomass-derived crude 1,4-butanediol from at least one carbon source selected from the group consisting of glucose, fructose, xylose, and saccharose by a fermentation method, and
• obtaining the biomass-derived raw material 1,4-butanediol by purifying the biomass-derived crude 1,4-butanediol before the subjecting (a),
• wherein a content of gamma butyrolactone in the biomass-derived raw material 1,4-butanediol is from 1 to 100 ppm by mass.