Pointless transforming it into refined fuel (6)
I believe the answer is:
futile
'pointless' is the definition.
(thesaurus)
'transforming it into refined fuel' is the wordplay.
'transforming' indicates anagramming the letters (I've seen this in other clues).
'into' indicates putting letters inside.
'refined' indicates an anagram.
'it' anagrammed gives 'ti'.
'fuel' is an anagram of 'fule'.
'ti' going into 'fule' is 'FUTILE'.
(Other definitions for futile that I've seen before include "Useless, a waste of effort" , "Pointless, a waste of effort" , "Ineffective" , "Useless, producing no results" , "Useless, pointless" .)