Recent years, the separation of organic liquid mixtures achieved by organic solvent nanofiltration (OSN), organic solvent reverse osmosis (OSRO), and organic solvent forward osmosis (OSFO) has gained a great momentum. In the methods, it is of particular importance to know the osmotic pressure of liquid mixtures for the correct process design. Although the Van’t Hoff law is frequently employed to estimate the osmotic pressure of such mixtures, unprecedented serious errors might be added to the results. In this study, the osmotic pressure of numerous binary liquid mixtures is predicted using the original definition of osmotic pressure along with the cubic plus association (CPA) equation of state (EoS) and the Van’t Hoff equation at various temperatures and compositions. CPA EoS considers hydrogen bonding effects in associating compounds (those with hydrogen bonds such as water and alcohols). The obtained results reveal that unlike the Van’t Hoff equation (the average deviation = 19.95 bar), the original definition of osmotic pressure with the aid of CPA EoS (the average deviation = 3.86 bar) can properly predict the osmotic pressure of the studied mixtures. Our findings are beneficial for various techniques utilized in the separation of organic liquid mixtures.

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