Study of obtaining cellulosic pulps of coffee husks by organosolv process and enzymatic bleaching by laccase

Currently, there is a growing interest in the efficient use of agroindustrial residues for the production of chemical species with higher added value as ethanol, enzymes and organic acid. Thus, the work aimed to study the best condition for the organosolv pulping (ethanol / water) on coffee husks at acid and alkaline media and to evaluate the action of laccase in the bleaching process. The pulping was performed with a solution of ethanol/water 1:1 (v/v), under solid/liquid ratio of 1/10 (w/v), time of 1 and 1.5 hours, at 80°C, using as a catalyst NaOH and H₂SO₄. The obtained pulps were chemically characterized and it was determinated kappa number and viscosity. The best results were found when the catalyst was NaOH which is justified by the fact that lignin has higher affinity with sodium hydroxide (low kappa number). However, the viscosity was decreased in alkaline medium, which can be evidenced by the low values obtained (around 1.6 cP). The pulps were treated with commercial laccase under the following conditions: 30 UI/g, consistency around 5 % (w/v), for 2 hours at 45 °C and HBT as a mediator. After enzymatic treatment, the best result of viscosity was found in the pulps obtained in an alkaline medium (2.0 cP). However, the values of viscosity are still underwhelming. To better understand the action of the enzyme in the pulp, analysis by X-ray diffraction and Scanning Electron Microscopy (SEM) are underway.

[Acknowledgments: FAPESP, CAPES and CNPq, Brazilian agencies]