Biological delignification of pulp

[SEIFERTK at NCCCOT.AGR.CA]

The recent post on the use of white rot fungi to delignify
pulp lead me to contact a 'ringer' to get a good answer...

    Delignification of pulps with enzymes is an active research area,
lying somewhere between a scientific curiosity and a practical
process.  The use of xylanase to aid delignification and decrease (by
ca. 25%) the amounts of chemicals required for bleaching is well
established in Scandinavian and Canadian mills.  Several large enzyme
suppliers produce xylanase for the pulp bleaching market, often from
Trichoderma, and competition to improve enzyme properties and lower
price is intense.  The use of oxidative enzymes from white-rot fungi 
that can directly attack lignin is a second generation approach,
which could produce larger chemical savings than xylanase, but has not
yet been developed to the mill scale.  It is being studied at the
Pulp and Paper Research Institute of Canada, several laboratories in
Japan, and at Lignozym, a private research company in Germany.
Enzyme and chemical suppliers are keenly interested, and there is
likely more research going on but not yet publicized.  Certain white-
rot fungi can delignify kraft pulps, increasing their brightness and
their responsiveness to brightening with chemicals.  The fungal
treatments are too slow, but the enzymes manganese peroxidase and
laccase can also delignify pulps, and enzymatic processes are likely
to be easier to optimize and apply than the fungal treatments.
Progress up to 1993 was reviewed by Reid and Paice (FEMS Microbiology
Reviews 13 (1994) 369-376).  Pulp delignification with laccase is
enhanced by the presence of a compound named ABTS, by an unknown
mechanism.  In the spring of 1994, Hans-Peter Call of Lignozym
announced the discovery of a superior, but unnamed, "mediator" that
also enhanced the action of laccase on pulp, allowing 66% lignin
removal.  For the rest of 1994, the grapevine buzzed with
speculations about the identity of Call's mediator.  His patent
application has just been published (WO 94/29510), and we now know
that the mediator is hydroxybenztriazole (HBT).  Call has reported
successful pilot plant trials, but there are concerns that HBT is too
expensive for an economical process.  Development work on laccase-
mediator systems and on manganese peroxidase continues; further
advances will probably be reported at the International Conference on
Biotechnology in the Pulp and Paper Industry in Vienna this June.
 
Ian D. Reid,
Pulp and Paper Research Institute of Canada (PAPRICAN)
REID at paprican.ca