▁ca ust ic ▁scr ub bing ▁tower . ▁ ▁Eth yl ene ▁product ▁gas ▁is ▁cont amin ated ▁with ▁( g ) ▁and ▁( g ), ▁and ▁those ▁cont amin ants ▁are ▁removed ▁by ▁absor ption ▁in ▁the ▁ca ust ic ▁scr ub bing ▁tower ▁to ▁produce ▁( a q ) ▁and ▁( a q ). ▁The ▁sod ium ▁hydro x ide ▁is ▁consum ed ▁and ▁the ▁resulting ▁waste water ▁( eth yl ene ▁spent ▁ca ust ic ) ▁is ▁cont amin ated ▁with ▁the ▁sul f ides ▁and ▁carbon ates ▁and ▁a ▁small ▁fraction ▁of ▁organ ic ▁comp ounds . ▁Re fin ery ▁spent ▁ca ust ic ▁comes ▁from ▁multiple ▁sources : ▁the ▁M ero x ▁processing ▁of ▁gas oline ; ▁the ▁M ero x ▁processing ▁of ▁k eros ene / jet ▁fuel ; ▁and ▁the ▁ca ust ic ▁scr ub bing / M ero x ▁processing ▁of ▁L PG . ▁In ▁these ▁streams ▁sul f ides ▁and ▁organ ic ▁ac ids ▁are ▁removed ▁from ▁the ▁product ▁streams ▁into ▁the ▁ca ust ic ▁phase . ▁The ▁sod ium ▁hydro x ide ▁is ▁consum ed ▁and ▁the ▁resulting ▁waste w aters ▁( c res y lic ▁for ▁gas oline ; ▁nap h then ic ▁for ▁k eros ene / jet ▁fuel ; ▁sul f id ic ▁for ▁L PG ▁- sp ent ▁ca ust ics ) ▁are ▁often ▁mixed ▁and ▁called ▁ref in ery ▁spent ▁ca ust ic . ▁This ▁spent ▁ca ust ic ▁is ▁cont amin ated ▁with ▁sul f ides ,