The present disclosure relates to a process to reduce total acid number (TAN) of a heat transfer fluid. The process comprises contacting the heat transfer fluid with an adsorbent composition at a temperature in the range of 50° C. to 350° C. and a pressure in the range of 1 bar to 10 bar to obtain a treated heat transfer fluid having total acid number (TAN) in the range of 0.003 to 0.03 and pH in the range of 6 to 7.5, wherein the adsorbent composition is provided in a fixed bed and the heat transfer fluid is passed through the fixed bed comprising the adsorbent composition at a liquid hourly space velocity (LHSV) in the range of 0.5 per hour to 10 per hour.