soak up vs mop up

soak up is not a noun while mop up is a noun.

Word	Noun	Adjective	Verb	Adverb
soak up	No	No	Yes	No
mop up	Yes	No	Yes	No

As verbs, mop up is a hyponym of soak up; that is, mop up is a word with a more specific, narrower meaning than soak up:

Other hyponyms of soak up include mop, wipe up, blot, sponge up.

soak up (noun)	mop up (noun)
	a concluding action

soak up (verb)	mop up (verb)
devote (oneself) fully to	finish a task completely
take in, also metaphorically	defeat thoroughly
	to wash or wipe with or as if with a mop