Method for preparing acrylonitrile dimer

A method of preparing an acrylonitrile dimer, the method comprising:

• supplying an acrylonitrile monomer, a phosphorus-based catalyst, an alcohol solvent, and an ionic liquid to a reactor to perform a dimerization reaction to prepare a single-phase dimerization reaction product (S10);
• supplying a reactor discharge stream including the dimerization reaction product to a first distillation column, separating the alcohol solvent and an unreacted acrylonitrile monomer from an upper discharge stream, and supplying a lower discharge stream including an acrylonitrile dimer, the ionic liquid, and the phosphorus-based catalyst to a second distillation column (S20);
• and
• separating an upper discharge stream including the acrylonitrile dimer and separating a lower discharge stream including the ionic liquid and the phosphorus-based catalyst, from the second distillation column (S30),
• wherein the ionic liquid includes a cation and an anion, and the ionic liquid includes the pyridinium-based cation as the cation and the tetrafluoroborate anion as the anion, and
• wherein a moisture content in the ionic liquid is 50 ppm or less.