Improved aromatic polyester polyol compositions

A process for making aromatic polyester polyol containing from 0.5 to 30 weight percent lignin comprising:

• a. contacting a reaction mixture comprising
• i. an aromatic acid source selected from the group consisting of terephthalic acid, isophthalic acid, phthalic anhydride, polyethylene terephthalate (PET) and mixtures thereof,
• ii. a glycol component selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol and their mixtures,
• iii. at least one selected from the group consisting of aliphatic diacids and hydroxyl-terminated aliphatic acids,
• iv. at least one functional reactant selected from glycerin, pentaerythritol, sorbitol, polyglycerin, tall oil fatty acids, vegetable oil triglycerides, monoester fatty acids, aliphatic diacids, hydroxyl aliphatic acids, and their mixtures at temperature from 230° C. to 240° C. in the absence of lignin to form an intermediate reaction product mixture;
• b. adding lignin, lignin incorporation catalyst and propylene carbonate to the reaction mixture of (a) and controlling the reaction temperature at 160° C. to 205° C.;
• and
• c. recovering lignin-containing aromatic polyester polyol from the reaction mixture.