Catalytic depolymerisation and conversion of Kraft lignin into liquid products using near-critical water

• We set up a continuous plant for the conversion of lignin in near-critical water.
• We used phenol (co-solvent) and ZrO2 + K2CO3 (catalysts), operating at 350 °C.
• LignoBoost Kraft lignin can be converted into bio-oil and water-soluble organics.
• Main 1-ring aromatic products are anisoles, alkylphenols, guaiacols and catechols.
• The yield of 1-ring aromatic products increases from 17% to 27% with K2CO3.

A high-pressure pilot plant was developed to study the conversion of LignoBoost Kraft lignin into bio-oil and chemicals in near-critical water (350 °C, 25 MPa). The conversion takes place in a continuous fixed-bed catalytic reactor (500 cm3) filled with ZrO2 pellets. Lignin (mass fraction of approximately 5.5%) is dispersed in an aqueous solution containing K2CO3 (from 0.4% to 2.2%) and phenol (approximately 4.1%). The feed flow rate is 1 kg/h (reactor residence time 11 min) and the reaction mixture is recirculated internally at a rate of approximately 10 kg/h. The products consist of an aqueous phase, containing phenolic chemicals, and a bio-oil, showing an increased heat value (32 MJ/kg) with respect to the lignin feed. The 1-ring aromatic compounds produced in the process are mainly anisoles, alkylphenols, guaiacols and catechols: their overall yield increases from 17% to 27% (dry lignin basis) as K2CO3 is increased.

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