▁to ▁be ▁greater ▁in ▁pilot ▁plant ▁tests ▁than ▁at ▁a ▁ben ch ▁scale . ▁ ▁Sul f ation ▁ ▁Sul f ation ▁is ▁a ▁relatively ▁slow ▁reaction ▁( se ver al ▁hours ) ▁compared ▁with ▁carbon ation ▁( < 1 0 ▁minutes ); ▁thus ▁it ▁is ▁more ▁likely ▁that ▁SO 2 ▁will ▁come ▁into ▁contact ▁with ▁Ca CO 3 ▁than ▁Ca O . ▁However , ▁both ▁re actions ▁are ▁possible , ▁and ▁are ▁shown ▁below . ▁ ▁Ind irect ▁sul f ation : ▁ ▁Ca O ▁+ ▁SO 2 ▁+ ▁ 1 / 2 ▁O 2 ▁-> ▁Ca SO 4 ▁ ▁Direct ▁sul f ation : ▁ ▁Ca CO 3 ▁+ ▁SO 2 ▁+ ▁ 1 / 2 ▁O 2 ▁-> ▁Ca SO 4 ▁+ ▁CO 2 ▁▁ ▁Because ▁calci um ▁sul f ate ▁has ▁a ▁greater ▁mol ar ▁volume ▁than ▁either ▁Ca O ▁or ▁Ca CO 3 ▁a ▁sul f ated ▁layer ▁will ▁form ▁on ▁the ▁outside ▁of ▁the ▁particle , ▁which ▁can ▁prevent ▁the ▁u pt ake ▁of ▁CO 2 ▁by ▁the ▁Ca O ▁further ▁inside ▁the ▁particle . ▁Furthermore , ▁the ▁temperature ▁at ▁which ▁calci um ▁sul f ate ▁dis soci ates ▁to ▁Ca O ▁and ▁SO 2 ▁is ▁relatively ▁high , ▁pre cluding ▁sul f ation ' s ▁revers ibility ▁at ▁the ▁conditions ▁present ▁in ▁Ca L . ▁ ▁Techn ical ▁imp lications ▁ ▁Cal ci um ▁looping ▁technology ▁offers ▁several ▁technical ▁advantages ▁over ▁am ine ▁scr ub bing ▁for ▁carbon ▁capture . ▁First ly , ▁both ▁carbon ator