TCF mill trial on softwood pulp with Korsnaes thermostable and alkaline stable xylanase T6

Use of hemicellulases, including xylanases, for delignification in the paper industry has been slowed down by the lack of large-scale availability of enzymes which are active at a high pH (above 8) and a high temperature (above 60 degree C), conditions prevailing in many bleaching processes. During the past years, acidic or neutral hemicellulases, working at temperatures below 60 degree C, were used in most mill experiments. The Korsnaes T6 xylanase from Bacillus stearothermophilus, which is active at a pH above 9.0 and at a temperature above 65 degree C, was produced on a large scale in collaboration with Gist-brocades and was employed on a full scale mill trial to produce a Total Chlorine chemical-Free (TCF) pulp from softwood. The bleaching sequence used was (OO)BQQPP, where O stands for oxygen delignification, B for the enzymatic treatment, Q for the chelating agent step and P for the hydrogen peroxide step. The enzyme bleaching step was performed during a period of 4 h at 63 degree plus or minus 1 degree C and pH 8.7 plus or minus 0.1. The results of the mill trial show that the TCF pulp produced has a brightness of 78% ISO and, at the same time, it preserved the same strength properties as chlorine dioxide-bleached pulp. The saving of hydrogen peroxide was 20%. The results on brightness, strength and chemical saving of this first full scale trial with T6 xylanase indicate that, after optimization, a TCF bleaching sequence including an enzymatic step with a xylanase working at a high pH and a high temperature, such as T6 xylanase, can be used to produce a high-strength bleached pulp. The advantages of a high pH and a high temperature enzymatic bleaching step are discussed.