Both IBC and BCH codes apply to the chemical tanker.

Both these codes provide an international standard for the safe carriage in bulk by the sea of dangerous chemicals and noxious liquid substances.

Both these codes prescribe the design and construction standards of ships and the equipment they should carry, with due regard to the nature of the products involved

But the main difference between these codes lies in its applicability.

The BCH code is applicable to the chemical tankers built before 1 July 1986. The IBC code is applicable to the chemical tankers built after 1 July 1986. 

For further info, you can read my answer to this question.

Why was there a need for making a new IBC code?