Hi, the method of preparing a eutectic ionic liquid from Choline is similar in principle to the method that I used in my publications to prepare ammonium and phosphonium eutectic ionic liquids. Refer to my publications and read the experimental section to have a general idea of the procedure. Good Luck.
We did it with electrodialysis (Separation and Purification Technology 97 (2012) 90–95), but there 's still quite some NaCl remaining. The easiest way to get pure choline acetate is neutralization of choline hydroxide (which is a strong base) with acetic acid, but you 'll need fresh choline hydroxide as it deteriorates quite fast. Actually, you 'll have to synthezise it yourself or eventually purify commercial product as it is often deteriorated to a large extent during transport.