Improved lignin pyrolysis for phenolics production in a bubbling bed reactor – Effect of bed materials

• A bed of activated lignin char is superior to a sand bed for bubbling pyrolysis of Kraft lignin.
• A bed of activated lignin char provides a non-contaminated char product.
• A bed of activated lignin char provides a higher dry bio-oil yield (relative increase by 43%).
• A bed of activated lignin char helps produce more simple phenols and less pyrolytic lignin.

Lignin pyrolysis was studied in a bubbling fluidized bed reactor equipped with a fractional condensation train, using nitrogen as the fluidization gas. The effect of different bed materials (silica sand, lignin char, activated lignin char, birch bark char, and foamed glass beads) on bio-oil yield and quality was investigated for a pyrolysis temperature of 550 °C.Results how that a bed of activated lignin char is preferable to the commonly used silica sand: pyrolysis of Kraft lignin with a bed of activated lignin char not only provides a pure char product, but also a higher dry bio-oil yield (with a relative increase of 43%), lower pyrolytic water production, and better bio-oil quality. The bio-oil obtained from Kraft lignin pyrolysis with a bed of activated lignin char has a lower average molecular weight, less tar, more phenolics, and less acidity than when sand is used as bed material.