Distilling 90% ethanol

[hobojoe00]

Hi guys I use ethanol to extract essential oils from plants. After the extraction I need to place the solution into a boiler and recover it. My problem is since I'm at 90% ethanol. As it boils the cooling effect from evaporation drops the temperature of my boiler faster than I can raise it. Does anybody know the mathematical equation I would need to do in order to figure out how much energy will be required to maintain a boil?