Lignin recovery from brewer’s spent grain black liquor Solange I. Mussatto * , Marcela Fernandes, Ine ˆs C. Roberto Departamento de Biotecnologia, Escola de Engenharia de Lorena, Universidade de Sa ˜o Paulo, Lorena/SP, Brazil Received 26 February 2007; received in revised form 23 March 2007; accepted 29 March 2007 Available online 14 April 2007 Abstract The present study describes the precipitation of lignin by acidification of a black liquor (pH 12.56 and 12.44 g/l soluble lignin) produced by soda pulping of brewer’s spent grain. Sulfuric acid was added to the liquor to decrease the pH, forming a lignin-rich precipitate. Ten pH values (varying from 12.56 to 2.15) were studied. The lignin mass precipitated for each pH condition was determined, and the obtained liquors were evaluated regarding the color and concentration of soluble lignin. Some phenolic acids (vanillic, syringic, p-hydroxybenzoic, ferulic and p-coumaric) were quantified in the liquors to verify their removal profiles as a function of the pH alteration. Significant lignin precipitation was only observed at pH < 7.7. At pH 2.15 the concentration of soluble lignin was reduced to 2.31 g/l (removal of 81.43%) and the color of the liquor was strongly modified from dark brown to pale yellow. The phenolic compounds concentration was reduced in different proportions (from 74.4% to 32.1%), suggesting that each lignin derived compound is differently affected by the pH alteration. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Acidification; Brewer’s spent grain; Black liquor; Lignin; Precipitation; Soda pulping 1. Introduction Lignocellulosics are the main raw material for pulp and paper industries. Among these, the woods are the most important, corresponding to 95% of all raw materials used by these industries (Jime ´nez, Ramos, Rodrı ´guez, de la Torre, & Ferrer, 2005). Nevertheless, some agricultural or agro-industrial residues such as brewer’s spent grain, maize stems, and some cereal straws can also be used for this pur- pose (Mussatto, Dragone, Rocha, & Roberto, 2006; Navaee-Ardeh, Mohammadi-Rovshandeh, & Pourjoozi, 2004; Xiao, Sun, & Sun, 2001). Developing countries, par- ticularly those in Asia, which do not have adequate wood supplies use straws and other non-wood materials as ligno- cellulosic fiber sources for pulp and paper production (Lawther & Sun, 1996). China, for example, has a long tra- dition for using non-wood raw materials for pulp and paper due to its limited forest resources and rich supply of agricultural residues, such as cereal straws of wheat, rice, and barley (Hammett, Youngs, Sun, & Chandra, 2001). The major constituents of lignocellulosics are cellulose, hemicellulose, and lignin, polymers that are associated with each other constituting the cellular complex of the vegetal biomass. Lignin is a three-dimensional polyphenolic mac- romolecule of very complex structure whose function is to provide rigidity and cohesion to the material cell wall, to confer water impermeability to xylem vessels, and to form a physic–chemical barrier against microbial attack (Fengel & Wegener, 1989). An example of structure pro- posed for the lignin is given in Fig. 1 (Adler, 1977). For the lignocellulosic materials be susceptible to the pulp and paper production, the separation of their cellu- losic fibers is necessary. Several processes have been used with this finality, and the soda pulping is one of the most relevant and most used for delignification of agricultural residues (Iglesias, Bao, Lamas, & Vega, 1996). During the pulping process, the lignin is dissolved from the raw mate- rial, being separated in the form of a liquor rich in phenolic compounds that represents the process effluent (Fengel & Wegener, 1989). This effluent is dark brown or black in 0144-8617/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2007.03.021 * Corresponding author. Tel.: +5512 3159 5027; fax: +5512 3153 3165. E-mail addresses: solange@debiq.eel.usp.br, solange@debiq.faenquil. br (S.I. Mussatto). www.elsevier.com/locate/carbpol Carbohydrate Polymers 70 (2007) 218–223