Father works with non-drinker in Illinois on purification process (12)
I believe the answer is:
distillation
'process' is the definition.
(distillation is a kind of process)
'father works with non-drinker in illinois on purification' is the wordplay.
I cannot quite see how this works, but
'works' could be 'is' ('be' can be a synonym of 'work') and 'is' is found within the answer.
'illinois' could be 'il' (I've seen this in other clues) and 'il' is present in the answer.
'on' could be 'at' (I've seen this in other clues) and 'at' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for distillation that I've seen before include "Whisky-making process" , "Process for producing spirits" , "Process of making, eg, whisky" , "Spirit-making process" .)