Vapor-Liquid Equilibria of the Binary n-Butane (HC-600) + Difluoromethane (HFC-32), + Pentafluoroethane (HFC-125), + 1,1,1,2-Tetrafluoroethane (HFC-134a) Systems Im, J.; Kim, M.; Lee, B.G.; Kim, H.; Journal of Chemical & Engineering Data 2005, 50, 359-363