Catalytic effects of NaOH and Na2CO3 additives on alkali lignin pyrolysis and gasification

The interest in utilization of alkali lignin in black liquor by pyrolysis and gasification is increasing due to the wish to produce bio-fuel and bio-chemical. Besides alkali lignin, the sodium salts are also the basic component of black liquor; they exist in two main forms: as phenolic sodium (CONa) and carboxylate sodium (COONa) groups forming a part of alkali lignin or as dissolved salts (NaOH and Na2CO3). In this paper, the influences of these dissolved salts on the pyrolysis and gasification characteristics of alkali lignin were discussed. Five lignin samples, including pure acid precipitated lignin, 10% and 60% NaOH-loaded lignin, 10% and 60% Na2CO3-loaded lignin, and black liquor solids were selected as the testing samples. Following experimental research on the evolution patterns of volatile products were carried out on a thermogravimetric analyzer coupled with Fourier transform infrared spectrometry. The experimental data indicated that the pyrolysis and gasification reaction of alkali lignin could be catalyzed by NaOH and Na2CO3. In the pyrolysis stage, the maximum mass loss rate decreased with increasing amount of NaOH and Na2CO3 additives, while in the gasification stage it increased. In the gasification stage, the temperature of the maximum mass loss rate shifted to lower value with increasing amount of NaOH and Na2CO3 additives, but did not significantly change in the pyrolysis stage. FTIR analysis showed that the influences of NaOH and Na2CO3 additives on the pyrolysis and gasification products mainly varied in amounts but not in species. FTIR results also suggested that the release time of the volatile was affected by increasing NaOH and Na2CO3 additives amount. Moreover, NaOH and Na2CO3 markedly improved the evolution of CO in the gasification stage.

► NaOH and Na2CO3 catalyzed alkali lignin pyrolysis and gasification.
► The thermogravimetric characteristics and product evolutions are affected by NaOH and Na2CO3 additives.
► The presence of NaOH and Na2CO3 moved the max mass loss rate to lower temperature side.
► The effect of NaOH and Na2CO3 additives on the pyrolysis products mainly varied in amounts but not in species.
► The addition of NaOH and Na2CO3 push back the time of alcohols and phenols release.