During condensation, the vapor, known as the overhead product, is passed through a cooling system called a condenser where the vapor is condensed to a liquid product. The remaining material in the still, referred to as the still bottoms, must be disposed of as hazardous waste. Batch process distillation involves feeding the waste to the still in a batch. No additional solvent waste can be added to the system until the original batch is completed. Continuous systems are those which continuously are fed waste solvent and likewise continuously produce the recovered solvent.
Continuous stills are able to recover large amounts of solvent faster than batch stills.
However, continuous stills require that large amounts of solvent waste be fed to it in order to be cost effective. The following list of equipment purchasing considerations was developed by the Wisconsin Department of Natural Resources to help Wisconsin businesses identify and evaluate current hazardous waste minimization opportunities. Although it is not possible to cover every aspect of equipment selection, the list covers some of the more important points and provides considerations for evaluating solvent recovery stills. The DNR would like to thank MnTAP for its contribution. The list should not be considered to be complete in its listing of manufacturers or suppliers.