Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C5/00—Other processes for obtaining cellulose, e.g. cooking cotton linters ; Processes characterised by the choice of cellulose-containing starting materials
  • D21C5/005—Treatment of cellulose-containing material with microorganisms or enzymes
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/001—Modification of pulp properties

Definitions

• the present invention concerns a method according to the preamble of claim 1 for
• the material to be treated is contacted with enzymes containing hemicellulase, cellulase and/or lignin degrading activities to hydrolyze 10 hemicellulose, cellulose and/or lignin.
• Ratt ⁇ M Bacterial hemicellulases. Licentiate's Thesis, University of Helsinki, Department of Forestry and Agriculture. 1990.
• the hemicellulases act primarily on the xylan located on the surface of the fibres [2].
• This xylan has been solubilized under alkaline pulping conditions and thereafter reprecipitated on the fibre surface in a chemically and structurally modified form.
• This xylan is the target for hemicellulase treatments carried out prior to bleaching or between different chemical delignification steps.
• the chemical structure of hemicelluloses varies according to the wood species and pulping method used.
• the xylan in birch sulphate (kraft) pulps contains mainly xylose units with some methylglucuronic acid side groups
• xylan in pine sulphate pulp contains in addition to methyl glucuronic acid groups also arabinose side groups [3]
• Pulp contains various ionizable groups. Of these groups only the carboxyl groups are ionized in neutral or slightly acidic conditions. The majority of the carboxyl groups in kraft pulps are methylglucuronic acid groups present on the xylan backbone [4], although the peeling reaction of the polysaccharide is stopped by the formation of metasaccharinic acid or other alkali-stable carboxyl groups. The counter-ions of the carboxylic ions influence the polyelectrolytic behavior, the extent of swelling and even the optical properties, such as the brightness stability.
• the present invention aims at eliminating the drawbacks of the prior art enzymatic methods by providing a new method for the treatment of lignocellulose materials, in particular cellulose pulps.
• the method according to the present invention is mainly characterized by what is stated in the characterizing part of claim 1.
• the invention provides several important advantages. Thus, it is particularly important that, using the invented method, the extractability of lignin due to hemicellulase action can be greatly improved.
• the type and amount of chemicals and enzyme dosages used for pretreatment of industrial lignocellulosic, in particular cellulose pulps can be optimized. This allows for the use of environmentally suitable totally chlorine-free or low-chlorine bleaching methods.
• the invention also essentially improves the possibilities to employ said methods.
• the enzyme action and thus the brightness of the pulps is improved.
• Another essential advantage resides in the fact that the loss of pulp yield, usually observed after the enzymatic treatment, can be remarkably decreased due to the site-directed, limited hydrolysis of pulp.
• the accessibility of lignocellulose degrading enzymes and the overall hydrolysis yield of lignocellulosic materials can be improved.
• the present invention provides a method for promoting the action of enzymes on essentially metal free pulps or other lignocellulosic materials.
• the enzymatic treatment is carried out before the metal removal or the steps of enzymatic treatment and metal removal are carried out at the same time.
• the action of the enzymatic treatment is enhanced by substituting the (monovalent) counter-ions present in the pulp by bi- or trivalent counter-ions. This may be achieved by adding salts or other compounds containg bivalent or trivalent metal ions to the pulp. The metal cations may also be added to the pulp in the enzyme preparation.
• the pulp counter- ions are converted to magnesium-form prior to the enzymatic hydrolysis in order to improve the enzyme action and the peroxide bleaching.
• the method of invention is used for modification of the fibre counter-ions for enhancement of the hydrolysis of lignocellulosic materials or for improving the enzymatic treatment prior to totally chlorine free bleaching sequences wherein i.e. peroxide, ozone or oxygen is used. It is noteworthy, however, that the method of invention can also be applied to other lignocellulosic raw materials, such as mechanical pulps. The method can also be utilized in connection with enzymatic treatment of lignocellulosic materials employing two or more enzymes selected from the group comprising hemicellulases, cellulases and ligninases. Although different pulp bleaching applications are particularly interesting, the invention generally may be used for enhancing the hydrolytic action of the above-mentioned enzymes.
• the term "enzyme preparation” denotes any product containing at least one enzyme.
• the enzyme preparation may be a culture liquid containing one or several enzymes, an isolated or cloned enzyme or a mixture of two or several specific enzymes acting on hemicellulose, cellulose or lignin.
• Enzymatic bleaching means a bleaching process which comprises at least one treatment step, during which the material to be treated is subjected to the action of a hydrolytic enzyme. Typically the enzymatic treatment step is carried out before contacting the material with conventional bleaching chemicals.
• hydroxogen form and “acid form” are in the following used interchangeably to denote the carboxlic acid form of the carboxylic groups.
• the counter-ions of pulp carboxylic groups are converted before the enzymatic treatment to hydrogen form or to mono- bi- or trivalent metal cation form or to a known mixture thereof.
• Pulps in different metal forms can also be obtained by adjusting the cooking processes or by modifying the pulp counter-ions with known methods [5,6].
• the monovalent metal cations may be selected from the group comprising Na + , Li + and K +
• the bivalent cations may be selected from the group ft comprising Ca 2+ , Mg + , Ba 2+ and Fe (H)
• the trivalent cations may be selected from the group comprising Al 3+ and Fe(HT.).
• Pulps which are in the hydrogen-form are essentially lacking metal counter-ions (metal-free).
• Such metal-free hydrogen-form pulp can be obtained by acidifying the pulp to a sufficiently low pH, which causes the counter-ions to dissociate, and by subsequently washing the pulp, or by treating the pulp with known complexing agents (e.g. EDTA, DTP A).
• known complexing agents e.g. EDTA, DTP A
• the degree of dissociation and the type of the counter-ion affect the swelling of the fibres.
• the swelling of the fibres can also be modified by increasing the ionic strength by adding the salt corresponding to the counter-ion of the pulp.
• the pulps can be analyzed for metal counter-ions by conventional analytical methods used for determining metals.
• the amounts of carboxylic groups in pulp can be determined by titration (i.e. conductometric or potentiometric), and the swelling can be measured by the WRV method (SCAN-M 102 X, proposal).
• the zeta potential can be determined on basis of the microelectrophoresis principle.
• the enzymatic action in fibres or other lignicellulosic materials can be monitored by for instance, determining the amounts sugars released during the treatment or by extraction of lignin fragments or by determining the result of the bleaching carried out after the enzymatic treatment.
• the pulp brightness values were measured by ISO 2470, the kappa number by SCAN Cl: 1977 and the viscosity by SCAN-C15: 1988.
• the applicable hemicellulases, cellulases and lignin modifying enzymes are usually exemplified by using purified xylanases, mannanases and cellulases from the well-known fungus Trichoderma reesei and laccase from
• Birch kraft pulp from a pulp mill was modified by the method of Scallan and Grumble [5].
• the pulps were converted into acid (hydrogen) form at 2 % consistency in 0.1 M HC1 overnight at room temperature.
• the pulp was subsequently washed with distilled water until no chlorides were present in the washings.
• the acid pulp was converted to different metal forms in 0.1 M metal chloride solutions (NaCl, LiCl, KC1, CaCl 2 , BaCl 2 ) and the pH of the suspensions was adjusted to 9.5 with the corresponding metal hydroxides.
• the pulps were incubated at room temperature overnigth with occasional shaking.
• the WRV-values and zeta potentials were measured from the modified pulps before the enzyme addition.
• the modified pulps were used as subtrates which were hydrolyzed with Bacillus circulans VTT-E-87305 xylanase [16].
• the enzyme dose was 500 nkat/g and the hydrolysis time 1 h at 50 °C.
• the consistency of the hydrolyzation was 2 %.
• Birch kraft pulp was converted to sodium-form according to the procedure of Example 1.
• Sodium chloride was added to the pulp prior to enzymatic hydrolysis.
• the hydrolysis was carried out as described in Example 1.
• the hydrolysis time was 20 h and the hydrolysis temperature 50 °C.
• the results are presented in Table 2.
• the WRV was measured after one our incubation before the enzyme addition.
• Birch kraft pulp was converted to metal-free form as described in Example 1.
• the pul thus obtained was used as substrate for the hydrolytic actions of xylanase and mannanase enzymes isolated from Trichoderma reesei [18, 21].
• the enzyme dose was 500 nkat g and the consistency during hydrolysis was 5 %.
• the degree of hydrolysatio was determined on basis of the amounts of reducing sugars obtained after 1 h. Conventional pine kraft pulp was used as reference.
• the pH of the hydrolysis was 4.5 to 5.
• Trichoderma reesei xylanase and mannanase enzymes Trichoderma reesei xylanase and mannanase enzymes
• EDTA treatment Combination of metal removal (EDTA treatment) with enzymatic treatment
• metals contained in the pulp can be removed by lowering the pH or by complexing the metals with, for instance, EDTA or DTPA or similar complexing agents.
• pulp was treated with EDTA at 5 % consistency and at pH 5, the amount of EDTA being 0.2 % (of pulp d.w.).
• the treatment was carried out for 1 h.
• the peroxide delignification was carried out at 80 °C for 1 h.
• the chemical dosages were 3 % of H,O 2 , 1.5 % of NaOH, 0.5 % of MgSO 4 , and 0.2 % of EDTA.
• Washing was carried out after the enzymatic treatment as well as after the EDTA treatment. 200 nkat/g T. reesei xylanase was used for the enzymatic treatment. The hydrolysis time was 2 h and the consistency was 5 %.
• This example shows how metal-free pulps can be rendered more hydrolyzable by adding Al containing salts and how this affects the hydrolysis and bleachability of said pulps.
• Birch kraft pulp was converted to metal-free form as described in Example 1.
• the pulp in hydrogen-form was then converted to aluminium form by suspending it in a 0.25 M
• A1C1 3 solution at 1 % consistency without pH-adjustment The pulp was incubated at room temperature for 15 hours with occasional shaking. Thereafter the pulp was washed according to the procedure of Example 1.
• the aluminium-form and unmodified (reference) pulp were used as substrates for xylanase treatment.
• the xylanase dosage was 500 nkat/g, the consistency during hydrolysation being 2 %.
• the degree of hydrolysation was measured by determining the amounts of reducing sugars released after 1 h.
• the counter-ions of metal-free birch kraft pulp were modified by adjusting the pH to 5 with Mg(OH> 2 and MgCl, or mixtures of Mg(OH) 2 and MgSO 4 .
• the molalities of the solutions used were 0.25 M.
• Metal-free pulp whose pH had been adjusted with NaOH was used as a reference.
• the enzyme dosage (T. reesei xylanase) was 200 nkat/g and the hydrolysis time was 2 h.
• Table 6 Effect of magnesium salts on the hydrolyzability of metal-free birch kraft pulp.
• the hydrolyzability of metal-free pulp can be increased by adding Mg-salts to the pulp.
• Example 7 Improving the hydrolysis of metal-free pulps by adjusting the pulp pH with suitable hydroxides
• the effect of pH adjustment of metal-free birch kraft pulp was assassed by using different metal hydroxides.
• the metal-free hydrogen-form pulp was prepared as described in Example 1. The pulp was hydrolyzed with T. reesei xylanase for 2 h at 5 % consistency using an enzyme dosage of 200 nkat/g.
• the metal cations of the pulp were removed by acidifying the pulp as described in Example 1.
• the pH of the metal-free pulp was adjusted with a solution of A1C1, and with mixtures of LiOH and LiCl 2 , Ba(OH), and BaCl 2 , Ca(OH) 2 and CaCl,, and KOH and KCl, respectively, to pH 7.5, Then, the pulp was washed with distilled water and treated with T. reesei xylanase (pi 9).
• the enzyme dosage was 500 nkat/g and the hydrolysis time 2 h at 45 °C in 5 % consistency. Table 8. Effect of various cations on pulp bleachability
• Sulphite pulp (made by the acid Mg process) was used as a substrate for Trichoderma reesei xylanase, the enzyme dosage being 500 nkat/g and the hydrolysis time 2 h at 45 °C.
• the pH of the pulp was adjusted with NaOH to pH 5 and CaCl 2 was added to the mixture (0.5 % of pulp d.w.).
• Table 9 Effect of CaCl 2 addition on the action of xylanases on sulphite pulps
• xylanases on sulphite pulp can be increase by adding bi- or trivalent cations to the pulp.
• CaCl 2 is described but it is clear that Mg, Al and Ba containing compounds can be used, as well.
• Birch kraft pulp was converted to aluminium form by using the method described in Example 1. Then the pulp was subjected to enzymatic hydrolysis carried out at 2 % consistency for 24 h.
• the cellulase employed comprised a mixture of Trichoderma reesei cellulases (endoglucanase 1 and CBH I) .
• the enzyme dosages were 100,000 nkat/g of the endoglucanase and 50 mg/g of the cellobiohydrolase.
• Conventional birch kraft pulp which had been subjected to pH adjustment with NaOH to pH 5 was used as reference.

Priority Applications (5)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8533272

Family Applications (1)

Country Status (7)

Cited By (3)

Citations (3)

• 1991
  • 1991-10-10 FI FI914780A patent/FI914780A0/fi not_active Application Discontinuation
• 1992
  • 1992-10-12 CA CA002120949A patent/CA2120949A1/en not_active Abandoned
  • 1992-10-12 JP JP5506647A patent/JPH07500151A/ja active Pending
  • 1992-10-12 WO PCT/FI1992/000272 patent/WO1993007332A1/en not_active Application Discontinuation
  • 1992-10-12 AU AU27546/92A patent/AU2754692A/en not_active Abandoned
  • 1992-10-12 EP EP92921169A patent/EP0607243A1/en not_active Withdrawn
• 1994
  • 1994-04-08 NO NO941279A patent/NO941279L/no unknown
  • 1994-04-08 FI FI941615A patent/FI941615A/fi not_active Application Discontinuation

Patent Citations (3)

Also Published As

Similar Documents

Legal Events