Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Treatment with particular chemical
Patent
1993-03-03
1994-08-16
Alvo, Steve
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Treatment with particular chemical
162 83, 435277, 435278, D21C 910
Patent
active
053384032
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a process for hydrolysis of resin in pulp.
BACKGROUND ART
Mechanical pulping, alone or combined with a gentle chemical treatment, is widely used in the manufacture of pulps. These processes occur at pH in the range 4-9, and the components of the wood undergo relatively small chemical changes. The pulp therefore has a considerable content of triglycerides, esters and waxes from resin.
Residual resin may cause problems during the subsequent use of the pulp. Thus, agglomerated resin may cause paper breakage during paper manufacture or during printing as well as lowering the paper quality. It is known that the hydrophobic part of resin contains considerable amounts of triglycerides and other esters. It would be desirable to hydrolyze these as the hydrolysis products are more easily removed in aqueous systems.
GB 1,189,604 discloses a process for removing resin constituents from wood chips by applying microorganisms to wood chips during storage. However, decomposition of resin by growth of microorganisms is very difficult to control; temperature, residence time, microbial flora etc. may fluctuate, and the microorganisms may secrete cellulase and hemicellulase that decreases fibre strength and yield.
It is the object of the invention to provide a controllable process for reducing the resin content of pulp with minimal changes of existing equipment and process conditions.
SUMMARY OF THE INVENTION
We have found that, surprisingly, resin can be hydrolyzed enzymatically during the reductive bleaching (e.g. with sodium dithionite) commonly used in pulp manufacture. The enzyme treatment necessitates little or no change of commonly used bleaching conditions.
Accordingly, the invention provides a process for hydrolysis of resin in pulp, characterized by carrying out enzymatic hydrolysis of resin simultaneously with reductive bleaching of the pulp.
BRIEF DESCRIPTION OF THE FIGURE
FIGURE 1 shows the stability of lipase towards sodium dithionite.
DETAILED DESCRIPTION OF THE INVENTION
The process of the invention may be applied to any resin-containing pulp, especially to pulps with a considerable content of triglycerides, esters and waxes from resin. Examples are pulps produced by mechanical pulping, alone or combined with a gentle chemical treatment, such as GW (Ground Wood), TMP (Thermo Mechanical Pulp) and CTMP (Chemical Thermo Mechanical Pulp).
The process of the invention uses an enzyme to hydrolyze the triglycerides and/or other esters in the resin, i.e. an enzyme with lipase and/or esterase activity. For obvious reasons, the enzyme to be used should be active and reasonably stable at the process conditions to be used; especially temperature, pH and the presence of reductive bleaching agents affect the enzyme stability. More specifically, enzyme and process conditions are preferably chosen such that at least 10% of the enzyme activity remains after the reaction, and preferably more than 50% activity remains after 40 minutes.
Examples of suitable enzymes are lipases derived from strains of Pseudomonas (especially Ps. cepacia, Ps. fluorescens, Ps. fragi and Ps. stutzeri) Humicola (especially H. brevispora), Candida (especially C. antarctica), H. lanuginosa, H. brevis var. thermoidea and H. insolens), Chromobacter (especially C. viscosum) and Aspergillus (especially A. niger). An example of a commercial lipase preparation is Resinase.TM.A, product of Novo Nordisk A/S.
The enzyme dosage required for significant resin hydrolysis depends on process conditions, but is generally above 0.1 KLU/kg of pulp dry matter (KLU=1000 Lipase Units, defined in WO 89/04361), preferably 0.5-150 KLU/kg.
To avoid break-down of the fibre structure in the pulp, cellulase side-activities should be essentially absent, preferably below 1000 EGU/kg of pulp dry matter (EGU unit for cellulase activity defined in WO 91/07542).
The process of the invention includes bleaching with a reductive bleaching agent which may be hydrosulfites; e.g. sodium- or zinc-dithionite, sodium borohydride or sodium b
REFERENCES:
patent: 3486969 (1969-12-01), Nilsson et al.
patent: 4922989 (1990-05-01), Backlund et al.
Alvo Steve
Lambiris Elias J.
Novo Nordisk A S
Zelson Steve T.
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