The invention relates to a conversion method that is fed with a diol feedstock that comprises at least 90% by weight of diol and a carboxylic acid feedstock that comprises at least 80% by weight of carboxylic acid. The method comprising at least: An esterification step which is fed with at least the diol feedstock and at least the carboxylic acid feedstock, wherein the carboxylic acid/diol molar ratio at the inlet of the esterification step is between 2 and 6, the esterification step comprises at least one reactive distillation column that has a mixed reaction/separation zone located between two separation zones; and A water elimination step that is fed with distillate from the esterification step that comprises water and producing at least one water effluent.