Effect of mixing hydrodynamics on the particle and filtration properties of precipitated lignin

• Effects of hydrodynamics on the acid precipitation process is studied.
• Lignin floc properties and filtration resistance were measured.
• The turbulent shear rate primarily controlled the properties of lignin flocs.
• Compact and large flocs showed better filtration and washing behavior.

The effects of mixing hydrodynamics on the particle and filtration properties of precipitated lignin from black liquor has been investigated. The hydrodynamics were varied in terms of turbulent shear rate and impeller flow pattern in the stirred tank. The precipitated lignin flocs were characterized in terms of particle size, size distribution, and particle shape. Our findings showed that the effect of hydrodynamics on the size and shape of primary lignin particles were negligible. However, the aggregation of primary particles into lignin flocs were affected by the hydrodynamics of the stirred tank. The size distribution and shape of the final lignin flocs could be controlled mainly through the manipulation of turbulent shear rate. Lignin flocs with higher compactness and size showed better filtration and washing properties. Optimal hydrodynamic conditions led to production of lignin with good filtration and washing properties at 1.83E + 09 m/kg specific filtration resistance, 243 kg/h m2 lignin filtration rate, generating high purity lignin at 0.09% ash content. The reproducibility of the findings was validated using three other black liquor samples.

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