The parameters half-life, z value, enthalpy, entropy, and free energy were evaluated in the temperature range of 40 to 55 degrees C for a Bacillus sp. P45 protease present in a medium composed of ionic liquid (IL) and organic solvent. The protease was previously treated in IL [Emim][Tf2N] and increased activity was observed in four out of five organic solvents tested. The reaction medium containing acetone and IL (1:1 v/v ratio) was more stable than the buffer medium. with half-life of 2.4 h at 55 degrees C. Thermodynamic parameters values showed there was probably less rupture of non-covalent bonds that stabilize the protein structure, which promoted the protease P45 stabilization. According to this study it was concluded that the protease P45 in a medium composed of [Emim][Tf2N] and acetone may be used at higher temperatures than those employed in buffer or medium containing organic solvent. (C) 2018 American Institute of Chemical Engineers