Isolation of lignin from wood

Abstract

The purpose of this bachelor’s thesis was to know well the different lignin isolation methods from various wood species and black liquor, and then the lignin obtained was identified by spectrophotometric methods which were UV and FTIR spectroscopy, to analyze and compare the physical and chemical properties of lignin, such as lignin content and color with different pH values, and their chemical structures, etc. The experimental part of this study was performed in the laboratory of Saimaa University of Applied Sciences, Imatra. Two different methods of lignin isolation were studied: one was isolation according to different pH values from the black liquor which was obtained from four wood species (pine, spruce, birch and aspen chips) in the batch digester by Kraft process, it was called Kraft lignin; another one was isolation from sawdust of four wood species in a flask reactor with reflux condenser, it was called Klason lignin. These lignins were characterized by UV and FTIR spectroscopy. According to the results, the lignin content and functional group were determined separately. The yields of lignin slightly increased with pH value decreasing, and the yields in softwood were higher than in hardwood. The UV absorption maximum of lignin revealed that lower pH value had a high purity level. In a comparison with Kraft and Klason lignin, they included different functional groups; there was a difference in chemical structure. In addition, the chemical structure was not similar between softwood and hardwood.