THERMOGRAVIMETRIC ANALYSIS OF OLIVE STONES WITH SULFURIC-ACID TREATMENT

The thermal decomposition of olive stones, with different time-lengths of 72% sulfuric acid treatment (from olive stone to klason lignin), w as studied by thermogravimetry (TG-DTG). The TG curves indicate that t he isolation of lignin begins with the easy elimination of hemicellulo se and some of the cellulose, while the lignin fractions remain practi cally unaltered. More intensive treatment produced the progressive rem oval of the cellulose, but the formation of volatiles at relatively lo w temperatures indicated that thermal resistance had decreased due pro bably to the breakdown of the three-dimensional structure of lignin. H owever, even with prolonged treatment, it is difficult to remove all t he cellulose and even when this is removed, the lignin structure is gr eatly altered. A method based on the kinetic analysis of the thermal d ecomposition is proposed to characterize the isolation degree of klaso n lignin and to monitor alterations in its structure. (C) 1997 Elsevie r Science B.V.