Thermal degradation of sulphuric acid lignins of hard wood

Abstract

The process of thermal degradation of lignins of hard wood (birch, aspen, oak), obtained under the wood treatment with 66 % sulphuric acid in the form of acid-insoluble and soluble fractions, has been investigated by thermal methods. Activation energy values of lignin pyrolysis have been determined at the stage of increasing rate of weight loss. It has been established that the difference in their thermal properties is conditioned by the structural changes in the process of isolation from wood. It has been suggested that acid-soluble lignins have a higher density than acid-insoluble ones. Sulphuric acid lignins of birch, in particular acid-soluble lignin, are assumed to possess a more homogeneous structure than sulphuric acid lignins of other species Lignin, which goes into acid solution during wood treatment with concentrated acids and is precipitated by water from the acid solution, has been little investigated. Some time ago even its carbohydrate character was under consideration. However, at present the aromatic nature of this lignin is fully proved, but there is very little information in the literature on the structure of acid-soluble lignins.As is known, the thermal properties of polymer materials are directly related to their stereochemistry and even slight changes of atomic arrangement in the basic and side chains of a macromolecule affect its thermal stability, mechanism and kinetics of degradation. We have used this thesis for establishing whether there are differences in the structures in acid-soluble lignins and lignins insoluble in sulphuric acid. A derivatographic technique was used in the present work, as this is one of the most sensitive methods for indicating structural changes in a substance, lignin in particular, as was shown in our recent investigation [1 ]. The kinetics of lignin degradation was studied at the definite stages of the process on the basis of DTA data.Various kinds of hard woods were used to yield lignin preparations, since they provide a considerable yield of acid-soluble lignin as compared with coniferous woods.

Modeling of Lignin Thermolysis

“…First, many complex phenols in the tar fraction are not experimentally identified, and second, our simulation did not consider the condensation and polymerization reactions, which might lower the yield of single-ring phenols in practice. In regard to individual phenols, the present simulation predicts most of the 30 phenols that have been detected in the literature. – In most cases, the simulated yields of individual phenols agree with experimental values to within a half an order of magnitude. It is also worth pointing out that deviations between the present simulation and experiments are no greater than deviations among experiments.…”

“…The matrix has six columns, representing our model predictions and five sets of literature references. The latter includes the collected reports of several authors as summarized in ref , the data of Iatridis and Gavalas, Kirshbaum, and Domburg. , In each matrix element, a numerical value or comment indicates that information relevant to that row was reported, whereas an “×” implies that it was not. The present simulation, column 1, provided entries for each row, save the CO 2 yield.…”

“…Kirshbaum provided overall gas, phenolics, and carbonaceous residue yields; detailed phenolic product spectra were also provided. Domburg , gives detailed descriptions of phenolic product spectra as well as DTA/DTG weight loss data. We now proceed to a discussion of Table by row, that is, product fraction; all yield references are in weight percent of the original lignin substrate.…”

Materials produced from plant biomass: part III: degradation kinetics and hydrogen bonding in lignin

“…On the other hand, it is interesting to compare the activation energy obtained in this study with the values found in the literature. In this study the activation energy values for the Klason lignin were in the range of 158-166 kJ/mol, while the values found in the literature for the Klason lignin varied from 12.5-89 kJ/mol [16][17][18] . This great difference may be caused by erroneous assumptions of the first order reaction by other authors.…”

Thermoanalysis of ancient, fresh and waterlogged woods

“…The application of thermal analysis to woods has been recently developed [5,6], especially due to H. G. Wiedemann who studied some egyptian ancient woods [3].…”