Separator for producing aromatic carboxylic acids

A separation system comprising:

• a distillation column into which a mixture of a first component mainly comprising water and a second component mainly comprising nonaqueous substances is supplied;
• an overhead vapor supply pipe connected to a top of said distillation column;
• first and second branch pipes branched from said overhead vapor supply pipe;
• a superheater connected to said first branch pipe;
• a first separator provided downstream of said superheater and including a first separation membrane for separating overhead vapor discharged from the top of said distillation column into a permeable vapor which mainly comprises said first component and a nonpermeable vapor which mainly comprises said second component by allowing only a selected portion of said overhead vapor to permeate said separation membrane;
• a second separator including a second separation membrane for separating said first permeable vapor into a second permeable vapor which mainly comprises said first component and is higher in the concentration of said first component than said first permeable vapor, and a second nonpermeable vapor which mainly comprises said second component, by allowing only a selected portion of said first permeable vapor to permeate said second separation membrane;
• and
• a reflux unit comprising a condenser connected to said second branch pipe for cooling a portion of said overhead vapor into a liquid, and a gas-liquid separator for separating gas from the liquid produced by cooling in said condenser, and returning the thus separated liquid into the top of said distillation column.