I don't know what that is, but if the younger leaves remain blemish-free, they will probably just end up replacing the damaged lower leaves. I don't think there's any benefit to trying to clean off those lower leaves, it looks like the brownish parts are embedded in the skin.
Black Prince is normally dark green to brownish black, more the latter in strong light. If your plant is Black Prince, it's got an unusual color pattern. The yellowish hue has me concerned. How much light has it been getting? Have there been any recent changes in its exposure or care? How much and how often are you watering?