(220l) Recovering a Liquid-Lignin Phase From Paper Mill Black Liquors

Recovering a Liquid-Lignin Phase from Paper Mill Black Liquors

Julian Velez and Mark C. Thies*

Department of Chemical and Biomolecular Engineering, Center for Advanced Engineering Fibers and Films, Clemson University, Clemson, SC, 29634-0909  USA.

* Corresponding author. E-mail: mcths@clemson.edu

In collaboration with Liquid Lignin Company, we have developed a process for recovering from paper mill black liquors a liquid-lignin phase of reduced ash content in the form of a low-viscosity, easy-to-process fluid.  The properties of this liquid lignin are such that a very low ash (< 1.0 wt %) lignin can readily be produced from it.

In this work, we investigated both hardwood and softwood black liquors under a wide range of conditions, including temperature, pressure, and pH, in order to determine the range over which this unique liquid-lignin phase forms.  Measurements of several fundamental lignin properties, including molecular weight, hydroxyl content, melting point, and sodium content, were carried out in order to relate precipitation conditions to characteristics of the lignins produced.

A semi-batch operating mode was used, with CO₂ being bubbled into a black-liquor charge in order to bring about the desired phase split.  Experiments were carried out in a stirred, 2-L Parr reactor setup especially modified for our work.  The CO₂ was fed to lower the pH of the black liquor from 13.5 to 9.5.  For each set of experimental conditions, a heavy, liquid-lignin phase  and a light, spent black liquor phase were generated, with samples of each phase being collected for further analysis.

Implications of the results obtained to date for the production of very low ash lignins for applications such as biofuels and value-added bioproducts will also be discussed.