Catalysis of the reactions: (R)-2-hydroxypropyl-CoM = H-S-CoM + (R)-1,2-epoxypropane, and (S)-2-hydroxypropyl-CoM = H-S-CoM + (S)-1,2-epoxypropane.
(R)-2-hydroxypropyl-CoM 2-mercaptoethanesulfonate lyase (cyclizing; epoxyalkane-ring-forming)