Hydrotropic fractionation of birch wood into cellulose and lignin: a new step towards green biorefinery

Hydrotropic treatment is an attractive process that uses water-soluble and environmentally friendly chemicals. Currently, this method is practically unexploited on a large scale due to the long treatment times required. In this study, the hydrotropic process was modified by the addition of hydrogen peroxide, formic acid, or both. The modified treatments were more selective than the reference, and the pulps obtained using the modified treatments had lower lignin contents. After bleaching, the resultant pulps were comparable to dissolving pulps with respect to the content of hemicelluloses and viscosity. Cellulose solutions were successfully obtained in a 7% NaOH/12% urea aqueous solvent after pretreating the bleached pulp with a HCl/EtOH mixture. Hydrotropic lignin was recovered from the spent solution by precipitation in water. The lignin had very low contents of carbohydrates and sulphur. The preliminary results show that a hydrotropic process can be used for such biorefinery applications as fractionation of fibres, cellulose polymer, and lignin from birch wood. The green cellulose and lignin biopolymers can potentially be used for shaping biomaterials or production of bio-based chemicals.