Distillation and molecular — sieve absorption are used to recover ethanol from the raw fermentation beer. The flow sheet of this section is presented in Figure 12 and figure 13. Distillation itself is a two-way progress include heating and cooling. That could be possible to save much steam and cooling water if we take good advantage of the heat exchange in the system. Due to its energy-saving, so far negative pressure distillation system has been popular in China. Take molasses alcohol as an example, compare to air distillation system, negative pressure distillation system could save approximately 2t steam per ton 95% (v/ v) alcohol. The system showed in figure contains 3 columns, which is .fractioning column 1, fractioning column 2, and separating methanol column respectively. Making use of the different boiling points the alcohol in the fermented wine is separated from the main resting solid components. The remaining product is hydrated ethanol with a concentration of 95% (v/v). Further dehydration is normally done by molecular-sieve absorption, up to the specified 99.7°GL in order to produce anhydrous ethanol which is used for blending with pure gasoline to obtain the country’s E10 mandatory blend. The fermented mash which contains 10~13 %(v/ v) alcohol is preheated by the alcohol gas from the top of the first column and gas is cooled simultaneously. Then the gas stream is cooled by 3 heat exchangers, the cooler is water. Subsequently the liquid distillate which contains 30% (v/ v) alcohol is feeding on the middle tray of column 2. Wastewater of column 1 is heated by the alcohol gas from the top of column 2 in the reboiler, meanwhile the steam flash evaporated in the vacuum bottom. The waste goes to anaerobic jar and then aeration tank. Cooled alcohol is pumped back to the top trays of column 2. Fusel oil is extracted from the middle trays of the column 2. Liquid distillate contains 95 %( v/v) alcohol and exceeded methanol amount. In order to decrease the concentration of aldehyde and methanol, one more column is needed. The 96%v/v alcohol with 4% water is feeding on the molecular-sieve absorption systemFinally 99.5%v/v ethanol which could be added to the gas to make gasohol is achieved.

Fig. 13. Ethanol dehydration with molecular sieve bed