Method and system for extracting long chain dicarboxylic acid

A method for extracting long chain dicarboxylic acid, comprising:

• (1) subjecting a long chain dicarboxylic acid fermentation broth to a primary membrane filtration treatment to give a first filtrate;
• and subjecting the first filtrate to decolorization, acidification/crystallization, and solid-liquid separation treatments to give a first solid;
• (2) mixing the first solid, a base, and water to form a solution;
• subjecting the solution to a secondary membrane filtration treatment to give a second filtrate;
• and subjecting the second filtrate to decolorization, acidification/crystallization, and solid-liquid separation treatments to give a second solid;
• and
• (3) mixing the second solid and water to form a mixture;
• and subjecting the mixture to a thermostatic treatment, followed by cooling for crystallization and solid-liquid separation treatment,
• wherein the secondary membrane filtration treatment is an ultrafiltration membrane filtration using an ultrafiltration membrane with the cut-off molecular weight of 2000-50000 Da;
• and
• wherein the concentration of the second filtrate after the secondary membrane filtration is controlled at 2-10 wt % calculated as the long chain dicarboxylic acid.