separate vs differentiate

separate is a noun but differentiate is not a noun.

Word	Noun	Adjective	Verb	Adverb
separate	Yes	Yes	Yes	No
differentiate	No	No	Yes	No

As verbs, separate and differentiate are synonyms defined as:

Other synonyms of separate include distinguish, secern, secernate, severalise, severalize, tell, tell apart.

As verbs, differentiate is a hypernym of separate; that is, differentiate is a word with a broader meaning than separate:

Other hypernyms of separate include distinguish, secern, secernate, separate, severalise, severalize, tell, tell apart.

separate (noun)	differentiate (noun)
a garment that can be purchased separately and worn in combinations with other garments
a separately printed article that originally appeared in a larger publication

separate (adjective)	differentiate (adjective)
independent; not united or joint
standing apart; not attached to or supported by anything
separated according to race, sex, class, or religion
have the connection undone; having become separate

separate (verb)	differentiate (verb)
become separated into pieces or fragments	become distinct and acquire a different character
divide into two or more branches so as to form a fork	become different during development
arrange or order by classes or categories	evolve so as to lead to a new species or develop in a way most suited to the environment
mark as different	calculate a derivative; take the derivative
move or break apart	mark as different
force, take, or pull apart	be a distinctive feature, attribute, or trait; sometimes in a very positive sense
divide into components or constituents
go one's own way; move apart
make a division or separation
treat differently on the basis of sex or race
separate into parts or portions
discontinue an association or relation; go different ways
act as a barrier between; stand between