If I understand what you want correctly and assuming Row 1 contains the headers and your data starts on Row 2, put this formula in cell D2 and copy it down to the end of your data...

=IF(B2="","",IF(COUNTIF(B2:B$16,B2)=1,1,""))

The red highlighted number needs to be any number equal to or greater than the last row number containing your data (make sure you retain that $ sign that is in front of the number).