columns with side columns, and re-using waste heat for the system. After combining distillation columns, the amount of energy used is only that of one separated column rather than both columns combined. In addition, using side columns saves energy by preventing different columns from carrying out the same separation of mixtures. Combining main and side columns saves equipment costs by reducing the number of heat exchangers in the system. Re-using waste heat requires the amount of heat and temperature levels of the waste to match that of the heat needed. Thus, using waste heat requires changing the pressure inside evaporators and condensers of the distillation system in order to control the temperatures needed. Controlling the temperature levels in a part of a system is possible with Pinch Technology. These energy-saving techniques have a wide application in industrial distillation of zeotropic mixtures: side columns have been used to refine crude oil, and combining main and side columns is increasingly used. Examples of zeotropic mixtures Examples of distillation for zeotropic mixtures can be found in industry. Refining crude oil is an example of multi-component distillation in industry that has been used for more than 75 years. Crude oil is separated into five components with main and side columns in a sharp split configuration. In addition, ethylene is separated from methane and ethane for industrial purposes using multi-component distillation. Separating aromatic substances requires extractive distillation, for example, distilling a zeotropic mixture of benzene, toluene, and p-xylene. Refrigeration Zeotropic mixtures that are used in refrigeration are assigned a number in the 400 series to help identify its component and their proportions as a part of nomenclature. Whereas for azeotropic mixtures they are assigned a number in the 500 series. According to ASHRAE, refrigerants names start with 'R' followed by a series of numbers—400 series if it is zeotropic or 500 if it is azeotropic—followed by uppercase letters that denote the composition. Research has proposed using zeotropic mixtures as substitutes to halogenated refrigerants due to the harmful effects that hydrochlorofluorocarbons (HCFC) and chlorofluorocarbons (CFC) have on the ozone layer and global warming. Researchers have focused on using new mixtures that have the same properties as past refrigerants to phase out harmful halogenated substances, in accordance to the Montreal Protocol and Kyoto Protocol. For example, researchers found that zeotropic mixture R-404A can replace R-12, a CFC, in household refrigerators. However, there are some technical difficulties for