The N-Acetylcysteine (NAC) is a thiol compound with a strong antioxidant effect and demonstrated preventive action as protector in chronic kidney disease, cancer, pulmonary insufficiency, in the treatment of AIDS and other systemic diseases. Experimental phase equilibrium data provide fundamental information for the micronization supercritical fluid SEDS technique, which is characterized by the reduction of the average particle size leads to changes in physical structure of the compounds processed. There are numerous advantages in particle size reduction and make narrower particle size distribution, the main one being the resulting increased bioavailability. Therefore, the aim of this work was to study the high pressure phase behavior of the ternary system {carbon dioxide (1) + dichloromethane (2) + acetone (3)} and for the quaternary system {carbon dioxide (1) + dichloromethane (2) + acetone (3) + NAC (4)} in order to assist the micronization process in supercritical media. The experiments were performed using a variable volume cell over the temperature range from 308 to 328 K, pressure from 4.7 to 9.87 MPa, and mass ratio dichlorometane/acetone of 1.5:1 for the ternary system. For the quaternary system, the same mass ratio of dichlorometane/acetone was adopted and an amount of 0.001 and 0.004 g cm(-3) of NAC was added to solution. Phase transitions of vapor-liquid type (bubble or dew points), in the presence or absence of solid phase were observed. The experimental results of the ternary system were modeled using the Peng-Robinson (PR) equation of state with the Wong-Sandler (PR-WS) mixing rule, providing a good representation of the experimental phase equilibrium data. (C) 2018 Elsevier B.V. All rights reserved.