Separation of organic and inorganic compounds from black liquor was investigated. Black liquor from the pulp and paper industry contains hundreds of different compounds and several high-value organic chemicals are formed during alkaline pulping. These organic compounds can be used in the fine chemicals, pharmaceutical and food industries. The main aim of this study was to recover and purify high value-added organic compounds (organic acids) from lignin and inorganic compounds by combining membrane filtration, acid precipitation and cooling crystallization. The effect of membrane filtration on the efficiency of precipitation and crystallization was also studied. A number of separation methods were studied under a variety of operating conditions. The results showed that a combination of membrane separation and crystallization is an efficient method for recovering and purifying valuable organic compounds in black liquor. The amount of major impurities in black liquor could be reduced significantly.