EP1994219A1

EP1994219A1 - Chemical pulp treatment compositions and methods

Info

Publication number: EP1994219A1
Application number: EP07717616A
Authority: EP
Inventors: Hui Xu; Kimberly Bloomfield; Stefanie Mccloskey; Kim Borch
Original assignee: Novozymes North America Inc
Current assignee: Novozymes North America Inc
Priority date: 2006-02-14
Filing date: 2007-02-14
Publication date: 2008-11-26
Also published as: WO2007095575A1; AU2007214449A1; BRPI0707656A2; JP2009526919A; CN101384769A; NO20083436L; CA2637691A1; US20090065159A1

Abstract

The present invention relates to compositions and methods for treating pitch problems in chemical pulp by treating chemical pulp process water with a combination of a lipase and a peroxide source. The present invention also relates to compositions and methods for treating pitch problems in chemical pulp by treating chemical pulp process water with a lipase, a peroxide source and organic acid(s).

Description

CHEMICAL PULP TREATMENT COMPOSITIONS AND METHODS

FIELD OF THE INVENTION

The present invention relates to enzymatic compositions and methods for treating pitch problems in chemical pulp,

BACKGROUND OF THE INVENTION

Wood contains about 1 to 10% of pitcn or extractives in addition to its main components cellulose, hemiculløse and lignin. Major components of pitch are fatty acids, triglycerdies, sterols, steryi esters and resirs adds, such as, for example, abietic acid. Pitch causes problems in paper machines by sticking to the rollers and causing spots or holes in the paper material.

Various enzymatic processes have been used to treat pitch problems. WO 00/53843 discloses steryl esterase enzyme preparations and their use in the manufacture of paper to hydroiyze the steryi ester part of pitch. U.S. Pat Ho. 6,066.486 discloses an enzyme preparation comprising a cholesteroi esterase derived from Pseudomoπas fragi_> and its use to hydrolyze pulp resin.

JP 2000080581 discloses the use of certain peroxidases for the decomposition of abietic acid during pulping or paper making processes.

X. 2hang; Pulp & Paper Canada. 101:3 (2000), page 5S-62, discloses studies of the ability of iaccase to remove dissolved and colloidal substances.

Karisson et at: Reactivity of Trametes iaccases with fatty and resin acids: Appl, Microbiol Biotechnoi. {2001} 55:317-320 discloses experiments in which iaccases were used to treat pitch. U.S. Patent application 20030124710 discloses a process for manufacturing a paper material by treating a papermakirsg pulp process water with a fatty acid oxidizing enzyme. U.S. Patent No. 5,356,517 discloses the use of lipases to hydroiyze tryglycerides during peroxy bleaching in the preparation of chemtthermomechanicai pulp.

SUMMARY OF THE INVENTION

The present invention relates to compositions and methods for treating pitch problems in chemical pulp by treating chemical pulp process water with a combination of a lipase and a peroxide source. Aimough not limited to any one theory of operation, it is believed that the addition of a lipase and peroxide leads to the formation of peracϊds which in turn oxidize unsaturated fatty acids and resin acids through an expoxidation reaction. The resuiting products are hydrophiiic and are readily washed from the pulp, thereby reducing pitch problems associated with chemical pulp. in another embodiment, the present invention relates to compositions and methods for treating pitch problems in chemical pulp by treating chemical pulp process water with a lipase, a peroxide source and an organic add.

DETAILED DESCRIPTION OF THE INVENTION A "paper-making process" refers to a process wherein a chemical pulp is suspended in water, mixed wrth various additives and then passed to equipment for further processing, e.g., in which frte paper, cardboard, tissue, towel etc. is formed, pressed and dried.

The term "paper material" refers to products which can be made out of pulp, such as pa- per, lirserboard, corrugated paperboard , tissue, towels, corrugated containers or boxes. The term "a papermaksng pulp" or "pulp" means any chemical pulp which can be used for the production of a paper materia).

A "chemical pulp" refers to chemical pulp (such as Kraft pulp or sulfite pulp) or seroichemical pulp (SCP). Chemicai pulp is usually manufactured by alkaline cooking whereby most of the lignin and some hemϊcelluloβe components are removed. Jn Kraft pulpmg or sulphate cooking, sodium sulphide or sαdrum hydroxide are generally used as principal cooking Chemicals. Jn such pulp, as a result of the alkaline cooking, the triglyceride part of pitch wfll be hydrolyzed ϊnto fatty acids and glycerol.

In a particular embodiment of the use and the process of the invention, the chemical pulp is a Kraft pulp or a sulfite pulp, In particular embodiments, the Kraft pulp is bleached Kraft pulp, for example softwood bleached Kraft (SWBK. also called NSKP (Nadef Note Bleached Kraft PuIp)), hardwood bleached Kraft (HWBK, also called LBKP (Laub HoIz Bleached Kraft Pulp and)) or a mixture thereof.

The Kraft pulp to be tmaieά may be a bleached Kraft pulp, which may consist of softwood bleached Kraft (SWBK₁ also called NBKP (Nadel HoIz Bleached Kraft PuIp)), hardwood bleached Kraft (HWSK, also called LBKP (Laub HoIz Bleached Kraft Pulp and)) or a mixture of these

The pulp to be used in the process of the invention is a suspension of chemical pulp. The pulp to be used in the process of the invention may comprise at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least S0%, at least 90%, at least 95%, or 100% of chemical pulp (such as Kraft pulp or sulfite pulp), The percentage of chemical pulp lies within the range of 1 -100%. in particular embodiments, the percentage of chemical pulp (such as Kraft pulp or sυime pulp) lies within the range of 1-99%, 2-98%, 3-97%, 4-96%, 5-85%, 8- 94%, 7-93%. 8-92%. 9-91%, 10-90%, 15-85%, 20-80%, 25-75%, 30-70%, 40-60%, or 45-55%.

In accordance with the present invention, chemical pulp process water is treated with a combination of a lipase and a peroxide source. Such chemical pulp process water contains pitch causing components, such as, fatty acids, triglycerdies.. sterols, steryl esters and/or resin acids (for example, abietic acid). The process of the invention is particularly applicable to the reduction of compounds constituting the pitch during a pulping or paper-making process, e.g. to avoid pitch troubles.

Any suitable lipase may be used. Lipases include the enzymes classified by EC 3.1.1 ,3, Ref- erence is made to the Recommendations (1992) of the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology, Academic Press Inc., 1992

In a preferred embodiment of the present invention, the lipase is preferably of microbial ori- gin, in particular of bacterial, fungal or yeast origin, The iipase may be derived from any source, in- cluding, for example, a strain of Absidia, in particular Absidia blakesleena and Absidia corymbifera, a strain of Achromobacter, in particular Achromobacter iophagus, a strain of Aeromonas, a strain of Altemaria, in particular Altemaria brassiciola, a strain of Aspergillus, in particular Aspergillus niger and Aspergillus flavus, a strain of Achromobrcter, in particular Achromobacter iophagus, a strain of Aureobasidium, in particular Aureobasidium pυllulans, a strain of Bacillus, in particular Bacillus pumilus, Bacillus sttearothermophilus and Bacillus subtilis, a strain of Beauveria, a strain of Bro- chothrix, in particular Brochothrix thermosonata, a strain of Candida, in particular Candida GyI- indracea (Candida rugαsa), Candida paratipolytica, and Candida antarcfica, a strain of Chromobac- ter, in particular Chromobacter viscosum, a strain of Coprinus, in particular Copnnus cinerius, a strain of Fusarfυm, in particular Fusarium oxysporum, Fusarium sotani, Fusarium solani pisi, and Fusanum roseum Gufmorum, a strain of Geotricum, in particular Geotricum penicillatum, a strain of Hansenula, in particular Hansenuiθ anomala. a strain of HumiGola. in particular Humicola brevispora. Humicola brevls var. thermoidea, and Humicola insofens, a strain of Hyphozyma, a strain of Lactobacillus, in particular Lactobacillus curvatυs, a strain of Metarhizium, a strain Mυcor, a strain of Paecilomyces, a strain of Penscilttum. in particular Penicϊllium cydopium, Penicillium crustosum and Penidliium ex- pansum, a strain of Pseudomonas in particular Pseudomonas aeruginosa, Pseudomonas afc&li- genes, Pseudomonas Gapaάa (syrt. Burkboldeiia cepacia), Pseudomonas ftυorescens, Pseudomo- nas tragi. Pseudomonas maltophilia, Pseudomonas mendocina, Pseudomonas mephitica lipolyfica, Pseudomonas alcaligenes, Pseudomonas plantari. Pseudomonas pseudoalcaligenes. Pseudomonas putida, Pseudomonas stutzeri, and Pseudomonas wisconsinensis, a strain of Rhizoctonia, in particu- lar Rhizoctonia soiani, a strain of Rhlzomucor, in particular Rhizomucor miehei, a strain of Rhizopus, in particular Rhizopus japonicus, Rhizopus microsporus and Rhizopus nodosus, a strain of Rhodosporidium, in particular Rhodosporidlum torυloides, a strain of Rhodotorula, in particular Rhodotorula glutinis, a strain of Sporobolomyces, in particular Sporobobmyces shibatanus, a strain of Themomyces, in particular Viermomyces lanuglnosus (formerly Humicoia lanuginosa), a strain of Thiamsporella, in particular Thiarosporeila phaseolina, a strain of Trichoderma, in particular Tricho- derma harzianum, and Trichoderma reeseϊ, and/or a strain of Vecticilliurn. in a preferred embodiment, the lipase is derived from a strain of Aspergillus, a strain of Achromohacter, a strain of Bacillus, a strain of Candida, a strain of Chromobacter, a strain of Fusa- rium, a strain of Humicola, a strain of Hyphozyma, a strain of Pseυdomonas, a strain of Rhizomucor, 3 strain of Rhizopus, or a strain of Thermomyces. Preferred lipases indude the upases described in U.S. Patent No, 6,074.863 and WO

02/055679, Preferred commercial lipases include Resinase A2X and Resinase HT (Novozymes A/S). In another preferred embodiment, the lipase is the Candida antarctioa lipase A (CALA) or the Candida antarctica lipase 8 (CALB) (available from Novozymes A/S)

As used herein, a "peroxide source" or "hydrogen peroxide source" refers to hydrogen per- oxide itseif or components which can generate peroxide. The hydrogen peroxide source may be added at the beginning or during the lipase treatment process, e.g., at a concentration of about 0.001-100 mM, particularly 0,01-50 mM. One source of hydrogen peroxide includes precursors of hydrogen peroxide, such as, e.g., a perborate or a percarbonate. Another source of hydrogen peroxide includes enzymes which are able to convert molecular oxygen and an organic or inor- ganic substrate into hydrogen peroxide and the oxidized substrate, respectively. These enzymes produce only low levels of hydrogen peroxide, Examples of enzymes which are capable of produc- ing hydrogen peroxide include, but are not limited to, glucose oxidase, urate oxidase, galactose oxidase, alcohol oxidase, amine oxidase, amino acid oxidase and cholesterol oxidase.

Although not limited to any one theory of operation, it is believed that the addition of a Ii- pase and peroxide leads to the formation of peracids which in turn oxidize unsaturated fatty acids, resin acids and other pitch components through an epoxidation reaction. The resulting products are hydrophillic and are readily washed from the pulp, thereby reducing or eliminating pitch prob- lems.

Organic acid{s) may aiso be added to the pulp, e.g., to enhance the pitch treatment. Or- ganic acids refer to any organic substance which contains at least one acidic group. Examples of organic acids are acetic acid, butyric acid, and linoieic acid. The concentration of organic acid is preferably between 0.001-500 mM.

Sn the case of paper and puip processing, the process according to the invention can be carried out at any pulp production stage. The enzyme can be added to any holding tank, e.g, to a puip storing container (storage chest), storage tower, mixing chest or metering chest. The enzyme treatment is preferably applied before or after pulp bleach process or in between the pulp bleaching stages. The enzyme can be added to the circulated process water (white water) originating from bleaching. In a particular embodiment of a Kraft pulping process, the enzyme is added during the brown-stock washing. in the present context, the term "process water" can include water added as a raw material to the paper manufacturing process; intermediate water products resulting from any step of the process for manufacturing the paper material: as well as waste water as an output or by-product of the process, In a particular embodiment, the process water is, has keen, is being, or is intended for being circulated or re-circulated, i.e., re~used in another step of the process. The term "water" in turn means any aqueous medium, solution, suspension, e.g., ordinary tap water, and tap water in admixture with various additives and adjuvants commonly used in paper manufacturing processes, in a particular embodiment the process water has a low content of solid (dry) matter, e.g,, below 20%, 18%, 16%_: 14%, 12%, 10%, 8%, 7%, 6%, S%, 4%, 3%. 20% or below 1% dry matter.

The process of tπe invention may be carried out at conventional conditions in the paper and puSp processing. The process conditions wiii be a function of the enzyrne(s) applied, the reaction time and the conditions given.

The enzyme mό peroxide should be added sn an effective amount. By the term "effective amount" is meant the amount sufficient to achieve the desired effect of reducing or inhibiting pitch components, such as, by degrading or converting such components into a form which can be more readily removed from the pulp or pulp process water. in a particular embodiment, the dosage of the lipase enzyme Is from about 0,1 mg enzyme protein to about 100.000 mg enzyme protein (of each enzyme) per ton of paper pulp.

The enzymatic treatment can be done at consistency, e.g._t 0,5-10 % dry substance, in particular embodiments, the consistency is within the range of 0.5-45; 0.540; 0,5-35; 0.5-30; 0.5- 25; 0.5-20; 0,5-15; 0.5-10; 0,5-8: 0.5-6; or 0.5-5% dry substance.

The enzymatic treatment may be carried out at a temperature of from about 10 to about

100⁰C. Further examples of temperature ranges (ail trorn about" an<S "to abouf) are the following;

20-100, 30-100, 35-10O₁ 37-100, 40-100, 60-100, 60-100, 70-100, 10-90, 10-SO, 10-70, 10-60, and

30-δ0^c'C, as well as any combination of the upper and lower values hem indicated. The temperature may be from about 20 to 9G¹⁵C, or 20 to 95⁰C. preferably from about 40 to 7O⁰C₁ or 40 to 75°C.

The enzymatic treatment may be carried out at a pH of from about 2 to about 12. Further examples of pH ranges (all "from about" and "to about") are the following: 3-12, 4-12, 5-12, 6-12, 1-

12, 8-12, 9-12, 2-11, 2~10_s 2-9, 2-8, 4-10, 5-8 as well as any combination of the upper and lower values here indicated. The pH range may be from about 2 to 11 , preferably within the range from about 3-δ.

A suitable duration of the enzymatic treatment may be in the range from a few seconds to several hours, e.g. from about 30 seconds to about 48 hours, or from about 1 minute to about 24 hours, or from about 1 minute to about 16 hours, or from about 1 minute to about 12 hours, or from Bboui 1 minute to S hours, or from about 1 minute to about 2 hours, or from about 1 minute to about 1 hour, or from about 1 minute to about 30 minutes. The reaction time may be from about 10 minutes to 3 hours, 10 minutes to 10 hours, preferably 15 minutes to 1 hour, or 15 minutes to 2 hours,

Various additives over and above the enzyme and peroxide treatment can be used in the process or use of the invention. Surfactants and/or dispersants are often present in, and/or added to a papermaking pυip. Thus the process and use of the present invention may be carried out in the presence of an anionic, non-ionic, cationic and/or zwilterionic surfactant and/or dispersant conventionally used m a papermaking pulp. Examples of anionic surfactants are carboxyiates, sulphates, suiphonates or phosphates of alkyl, substituted alkyl or aryl. Fatty acids are examples of alkykarboxyiates. Examples of non-ionic surfactants are poiyoxyethyiene compounds, such as alcohol ethoxyiates, propoxylates or mixed ethoxy-/propoxy Sates, poly-giyeerois and other polyols, as weil as certain block-copolymers. Examples of cafionic surfactants are wafer-soluble cationic polymers, such as quartenary ammonium sulphates and certain amines, e.g. epichlorohydrin/dimethylamine polymers (EPI-DMA) and cross-linked solutions thereof, polydiallyl dimethyl ammonium chioride (DADMAO), DADMAC/Acrylamide co-polymers, and ionene polymers, such as those disclosed in US patents nos. 5,681,862; and 5,575.993. Examples of zwitterionic or amphoteric surfactants are Detains, glycinaies, amino propionates, imino propionates and various imidazolin-derivatives. Also the polymers disclosed in US patent no. 5,256,252 may be used.

Also according to the invention, surfactants such as the above, including any combination thereof may be used in a paper making process. The amount of each surfactant in such composition may amount io from about 8 to about 40% (w/w) of the composition, in particular embodiments the amount of each surfactant is from about 10 to about 38, or from about 12 to about 36, or from about 14 to about 34, or from about 16 to about 34, or from about 18 to about 34, or from about 20 to about 34, or from about 22 to about 34, or from about 24 to about 34, or from about 26 to about 34, or from about 23 to about 32% {w/w}-

It is to be understood that the term enzyme, as well as the various enzymes and enzyme classes mentioned herein, encompass wild-type enzymes, as well as any variant thereof that re- tains the activity in question. Such variants may be produced by recombinant techniques. The wild-type enzymes may also be produced by recombinant techniques, or by isolation and purifica- tion from the natural source.

In a particular embodiment the enzyme in question is well-defined, meaning that only one major enzyme component is present. This can be inferred e.g. by fractionation on an appropriate Size-exclusion column. Such weii-deftned, or purified, or highly purified, enzyme can be obtained as is known in the art and/or described in publications relating to the specific enzyme in question.

The term "applied together with" (or "used together with") means that the additional enzyme may be applied in the same-, or in another step of the process of the invention. The other process step may be upstream or downstream in the paper manufacturing process, as compared to the step in which the papermaking, pulp or process water is treated with lipase and peroxide source, in particular embodiments the additional enzyme is an enzyme which has protease, xy- larsase, cutinase, oxidoreductase, cellulase, endogiucanase, amylase, mannartase, steryl es- terase, and/or cholesterol esterase activity. Examples of oxidoreductase enzymes are enzymes with Iaccase, and/or peroxidase activity.

The term "a step" of a process means at least one step, and it could be one, two, three, four, five or even more process steps. Thus, the lipase and peroxide source may be applied in at least one process step, and the additional enzyme(s) may also be applied in at least one process step, which may be the same or a different process step as compared to the step where the lipase anύ peroxide source is used.

The term "enzyme preparation" means a product containing at ieast one lipase enzyme. In addition to the enzymatic activity such a preparation preferably contains at least one adjuvant Examples of adjuvants, which are used in enzyme preparations for the paper and pulp industry, are buffers, polymers, surfactants and stabilizing agents.

Any enzyme having protease, xylanase, cutinase, oxidoreductase, cellulase endogiuca- nase, amylase, mannanase, steryl esterase, and/or cholesterol esterase activity can be used as additional enzymes in the use and process of the invention. Selow some non~iimiting examples are listed of sued additional enzymes. The enzymes written in capitals are commercial enzymes available from Novozymes A/S. KrogshoejveJ 36. DK-2880 Bagsvaerd, Denmark, The activity of any of those additional enzymes can be analyzed using any method known in the art for the en- zyme in question, including the methods mentioned in the references cited.

Examples of cutinases are those derived from Humicola insolens (US 5,627,71 S); from a strain of FuSBnUm₁ e.g. F. roseum cutmorum, or particularly F. sαlani pisi (WO 80/09446; WO 94/14964, WO 94/03578). The cutinase may also be derived from a strain of Fthizoctonia, e.g. R. solønh or a strain of Attemaria, e.g. A, hrassicicola (WO 94/03578), or variants thereof such as those described in WO 00/34450, or WO 01/92502,

Examples of proteases are the ALCALASE, ESPERASE, SAVINASE, NEUTRASE and DURAZYM proteases. Other proteases are derived from Nocardiopsis, Aspergillus, Rhlzopus, Ba- citkis afcafophiius, B. oereus, B. natto, B, vulgatus, B. myoolde, and subtHisins from Bacillus, es- pecially proteases from the species Nooardiopsis sp, and NocarΦ^'opsis dassonvillei such as those disclosed in WO 88/03947, and mutants thereof, e.g. those disclosed in WO 91/00345 and SP 415286.

Examples of amylases are the BAN, AQUAZYM, TERMAiVIYL, and AQUAZYM Ultra amy- fases. Art example of a xyianase is the PULPZYME HC hemscelluiase. Examples of endogluca- nases are the NOVOZYM 613, 342, and 476 enzyme products.

Examples of mannanases are the Tnchoderma reesei endo-foeta-mannanases described in Stδhlbrand et ai. J. Biotechnoi. 29 (1893), 229-242.

Examples of steryl esterases, peroxidases, laccases, and cholesterol esterases are dis- closed in the references mentioned in the background art section hereof. Further examples of oxi- doreducfases are the peroxidases and laccases disclosed In EP 730641; WO 01/98469; EF 719337; EP 765394; EP 767θ3Q; EP 763115; and EP 7S8547, in the present context, whenever an oxtdoreductase enzyme is mentioned that requires or benefits from the presence of acceptors, enhancers., mediators and/or activators, such compounds should foe considered to be included if not already present Examples of enhancers and mediators are disclosed in EP 705327; WQ 98/56899; EP 677102; SP 7S1326: and EP 707637. If desired a distinction couid be made by defining an αxidoreductase enzyme system {e.g. a laccase, or a peroxidase enzyme system) as the combination of the enzyme in question anά its acceptor, and optionally also an enhancer and/or mediator for the enzyme in question. These are particular embodiments of the present invention: Use of a lipase and peroxide source for reducing the deposition of pitch in the paper making process. A process for reducing deposition of pitch in the paper making process, wherein the process comprises treating the pulp and/or process water with a lipase and peroxide source. Use of a lipase, peroxide source and organic acid for reducing the deposition of pitch in the paper making process, A process for reducing deposition of pitch in tπe paper making process, wherein the process comprises treating the pulp and/or process water with a lipase, a peroxide source and organic acid.

The invention described and claimed herein is not to be limited in scope by the specific embodiments herein disclosed, since these embodiments are intended as illustrations of several aspects of the invention. Any equivalent embodiments are intended to be within the scope of this invention, indeed, various modifications of the invention in addition to those shown anά described herein wiii become apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims, In the case of conflict, the present disclosure including definitions will control.

Various references are cited herein, the disclosures of which are incorporated by refer- ence in their entireties.

εXAtøftiεs

Sample ,L Peresination of Kraft pulp pitch by Candida Antarctica lipase B (CALB)

Dammar resin was obtained from Fluka and used as a model pitch to simulate Kraft pulp pitch. TAED was also obtained from Fluka. Put 75 mg of Dammar resin in a flask and add 75 mL of Dl water. Add chemicals or enzymes according to the conditions shown in Table 1. Stir at ambient temperature overnight. Turbidity of the solutions was determined by UV-vis at 600 nm.

After mixing the samples overnight, it was observed that the lipase (CALB) and peroxide treated sample turned into milky emulsion whereas the control sample was stiil as clear as water with! the resins deposited either at the bottom on the wait of the of the fiask. The turbidity results clearly showed that a combination of peroxide with lipase couid iead to better emulsification of dammar resin. Peracetic acid generated In situ by peroxide and a bleach activator (TAED) was aiso fairly effective, but not as effective as peroxide and lipase combination.

Examate 2, Dereslnatlon of Kraft pulp pitch by Resinase A2X and Resinase HT. The experiment was carried out in tr$e same manner as iiiustrated in Example 1 except that the flasks were stirred ovemfgrtt at 4O⁰C. The lipases used in this study were Resinase® A2X and Resinase® HT (available from Novσzymes A/S).

it is evident that both Resinase® A2X and Resinase® HT worked to emulsify the Kraft model pitch.

Claims

CLAIMS:

1. A method for reducing pitch problems in a chemical pulp, comprising treating a chemical pulp with a lipase and a peroxide source in amount effective to reduce pitch problems.

2. Tne metnod of claim 1, wherein said treating is performed before, after or in between bleaching stages,

3. The method of ciaim 1 , wherein said cnsmicai pulp is a Kraft pulp.

4. The method of claim 1 , wherein said chemical pulp is a sulfite pulp,

5. The method of claim 1 , wherein said chemical pulp is bleached Kraft pulp.

6. The method of claim 1, further comprising the step of preparing paper, iirserboard, corrugated paperboard, tissue, towels, corrugated containers or boxes from said pulp.

7. The method of claim 1, wrterein said lipase is derived from a strain of Aspergillus, a strain of Achromobacter, a strain of Bacillus, a strain of Candida, a strain of Chromobacter, a strain of Fusa- ήum, a strain of Humicolβ, a strain of Hyphozyma, a strain of Pseudomonβs, a strain of Rhizomucor, a strain of Rhizopus, or a strain of Thertnomyces.

8. The method of ciaim 1 , wherein said lipase is derived from a strain of Candida,

9. The method of claim 1 , wherein said lipase is derived from a strain of Candida aαtaivtiαs lipase A or the Candida antarcfba lipase B.

10. The method of claim 1 , comprising treating a chemical pulp with a lipase, a peroxide source and an organic acid,

11. The method of ciaim 1 , wherein peroxide source is hydrogen peroxide.

12. The method of claim 1 , wherein peroxide source is a precursor of hydrogen peroxide,

13. The method of claim 12, wherein the precursor of hydrogen peroxide is perborate or a percarbonate.

14. The method of claim 1 , wherein the peroxide source is an enzyme that converts motecu- tar oxygen and an organic or inorganic substrate into hydrogen peroxide.

15. Use of a lipase and a peroxide source for reducing pitch problems,

18. Use of a lipase and a peroxide source for reducing pitch problems in chemical pulp.