Synthesis of poly (oxymethylene) dimethy ethers catalyzed by acidic functionalized ionic liquids

Poly (oxymethylene) dimethyl ethers (PODEn, n > 1) were synthesized by the condensation of trioxymethylene (TR) and methanol (MeOH) over the functionalized ionic liquids like [Hnmp] HSO4, [Hnmp] H2PO4, [Hnmp] PTSA and [PyN (CH2)3SO3H] HSO4; the effects of the catalyst amount, raw materials ratio, temperature, pressure and time on the reaction behaviors were investigated. The results showed that the catalytic activity of ionic liquid is related to its acidity. [PyN (CH2)3SO3H] HSO4 exhibits the highest catalytic activity; under the optimum reaction conditions, i. e. [PyN (CH2)3SO3H] HSO4 amount of 2.0%, molar ratio of MeOH to TR of 2.0, 110°C, 2.0 MPa and reaction time of 6 h, the conversion of TR and selectivity to PODE3~8 reach 97.69% and 32.54%, respectively. Moreover, the ionic liquid [PyN (CH2)3SO3H] HSO4 can be spontaneously separated from product phase after the reaction.