Lignin – a by-product from pulp and paper mills – is extracted from black liquor and processed in multiple steps to a depolymerized lignin-rich oil. The SunCarbon process can be divided to three different parts – all situated in the pulp and paper mills.
Lignin is separated from the black liquor using a membrane separation step. The membrane plant will fractionate the lignin in a retentate and a permeate stream. The lignin-rich retentate stream will then be processed further in the hydrothermal treatment. Approximately 10-25 % of all the lignin produced in the pulp and paper mill can be recovered without impacting the chemical recovery boiler operation!
Hydrothermal treatment & purification
The lignin-rich retentate stream is treated in a thermal catalytic cracker at sub-critical conditions. The catalytic cracker uses a catalyst internal to the pulp and paper mill. After hydrothermal treatment the resulting lignin mixture is processed with additional steps including acid wash and solvents to remove ash and residues. After additional desalting the resulting product is a depolymerized lignin-oil, ready for transport to a petroleum refinery for final hydrogenation!
The lignin is extracted with several major benefits such as increased pulp capacity and the possibility to fully or partly recycle the permeate stream from the membrane separation and use it in the green liquor preparation step. Through careful understanding of the pulp and paper industry, the material and energy efficiency achieved is high without compromising the delicate chemical balance of the mill!