As far as I am aware, the Yuan (essentially a unit quantity of currency) is fully convertible and can be traded, but the Renminbi (the currency itself) is not. It's a bit weird that these are not the same thing. It may not be possible to use the Yuan for everything you need without also moving some Renminbi around. However, you can use the Yuan as the unit on which the trade balance of a country is counted - $1 billion Yuan of oil against $1 billion of silicon chip for example - without any Renminbi changing hands.