Polyoxymethylene dimethyl ethers (PODEn) are promising diesel additive which can be synthesized from aqueous formaldehyde solutions and methanol. Formaldehyde+methanol has been found as an economical and feasible way for the production of PODEn due to the cheap raw materials. In this study the extraction process is chosen to obtain PODEn from aqueous solution. A reliable thermodynamic model for a good system description is important for extraction equipment modeling

development and design. Liquid-liquid equilibria(LLE) data are valuable in studies of the applicability of thermodynamic model. In this work

LLE was analytically determined at 293.15 K for the following four systems:(PODE1+water+n-hexane)

(PODE2+water+n-hexane)

(PODE3+water+n-hexane) and (PODE4+water+n-hexane)

respectively. Based on high selectivity of PODE1-4 over water and the PODEn mass fraction in the organic phase was much larger than that in aqueous phase

it was found that washing with n-hexane was an effective way of extracting PODEn from the aqueous phase without losing any significant amount of PODEn to the extract phase. The isothermal experimental data were shown a good linear fit in Hand plots with R2 being approximately unity. The well-known NRTL and UNIQUAC thermodynamic models were applied to correlate the experimental data

and the results of root mean square deviation calculation (RMSD) and ternary phase diagram analysis indicated that NRTL and UNIQUAC models all shown good predictive capabilities.