I dont know about isoproponol (sorry) but usually (in a lab) ethanol is added benzene because you then can have 99.6 ( i think it is) % pure ethanol. Without benzene ethanol would "capture" water from the air and the consentration would end around 96% (the azetrope)
Theoretical chemically, there is no residue. MortenA's first comment is right, depends on the purity. If there is a residue, it is because, as he further explains, NOTHING is pure 100%.