Title

THERMAL AND CATALYTIC CONVERSION OF LIGNIN

Date of Completion

January 1983

Keywords

Engineering, Chemical

Degree

Ph.D.

Abstract

Pyrolysis of seven lignins has been studied in different pyrolysis apparatus in the temperature range of 0-1350(DEGREES)C. Effects of experimental parameters, such as temperature-time history, pressure, particle size, atmosphere of ambient gases and lignin source were investigated. The temperature dependence of the total weight loss was strongest between 350-500(DEGREES)C where tar evolution appear to have the strongest temperature dependence in both vacuum (0.1 torr) and atmospheric pressure pyrolysis.^ The lignins, its chars and tars were characterized using different analytical techniques in order to elucidate the relationship between the lignin and the products of thermal decomposition. The lignins' aliphatic and aromatic hydrogen absorptivities were determined by FTIR spectroscopy; the experimental hydrogen (total) concentration was in good agreement with the calculated values.^ The dynamic pyrolysis of Iotech lignin using a Thermogravimetric Analyzer was analyzed using a kinetic model in which the activation energy was a linear function of conversion in the conversion range of 0-40% (E' = 13.96 Kcal/mole +6.942X).^ Free radical formation in lignin char was studied using ESR. The spin concentration of the residual char was increased with static temperature to a maximum at 475(DEGREES)C and then decreased. A very similar and parallel trend was found for the rate of weight loss versus temperature measured by TGA. Changing the pyrolysis environment from N2 to H2 reduced the relative spin concentration observed in the 600-900(DEGREES)C temperature range.^ The pyrolysis of Iotech lignin was mathematically modelled using two different models. The first model successfully simulated the temperature-time dependent yield and evolution rate of lignin tar and specific gas species. The evolution rates of gas species and tar was found to be independent of the type of lignin or the method by which it was extracted. The second model (the tar model) successfully simulated the temperature, pressure and heating rate effect on the tar yield and its molecular weight distribution.^ The pyrolysis/catalysis process of lignin was studied with different catalysts. The H-ZSM5 catalyst was found to have the lowest coke yield and the highest yield of polynuclear aromatics in the tar fraction from the dawnstream catalytic reactor. Slow heating rate pyrolysis of lignin-H-ZSM5 mixture indicated the catalytic conversion of the methanol evolved during pyrolysis to ethelene. ^