Thermogravimetric analysis of olive stones with sulphuric acid treatment

The thermal decomposition of olive stones, with different time-lengths of 72% sulfuric acid treatment (from olive stone to klason lignin), was studied by thermogravimetry (TG-DTG). The TG curves indicate that the isolation of lignin begins with the easy elimination of hemicellulose and some of the cellulose, while the lignin fractions remain practically unaltered. More intensive treatment produced the progressive removal of the cellulose, but the formation of volatiles at relatively low temperatures indicated that thermal resistance had decreased due probably to the breakdown of the three-dimensional structure of lignin. However, even with prolonged treatment, it is difficult to remove all the cellulose and even when this is removed, the lignin structure is greatly altered. A method based on the kinetic analysis of the thermal decomposition is proposed to characterize the isolation degree of klason lignin and to monitor alterations in its structure. (C) 1997 Elsevier Science B.V.