Thesis (M.Sc.)--Chulalongkorn University, 2007

The objectives of this study were to understand and quantify the relationship of factors affecting lignin recovery and to study the optimal condition for separation of lignin from black liquor by electrochemical process using 2³ factorial design where current density, time, and initial solids were varied. From the result, it was found that optimum pH for lignin recovery is at pH 6 where highest recovery of lignin using aluminum electrodes was 82.86% where 14.89% was the result of electrochemical process. The highest recovery of lignin using iron electrodes was 78% where 10.03% was as the result of electrochemical process. The conditions of highest recovery were considered to be the optimum lignin recovery conditions for aluminum and iron electrodes yielded from this 2³ factorial design experiments while to recovery at pH 8 and 7 were not accomplished. The models of lignin recovery at pH 6 were constructed was found that among all factors, initial solids content had the highest positive effect on lignin recovery then current density and time. But, the ability of models are limited due to other factors that have major impact on lignin recovery, which had not included in the model. However, lignin recovery with electrochemical process alone has several advantages over acidification alone. These advantages included less amount of caustic chemical used to gain the same recovery, control of pH of remaining black liquor, and no production of corrosive gas such as sulfur like in acidification process. In ecnomics aspect, recovery by aluminum electrode is about 1.2 times more efficient than iron electrodes.