METHOD FOR AVOIDING PITCH TROUBLES BY USE OF THERMOSTABLE LIPASE

Abstract: More effective prevention of pitch troubles in a process for producing mechanical pulp or in a paper-making process using mechanical pulp. A paper-making process is conducted by addition of a fatty acid glyceride hydrolysing enzyme that is resistant to temperatures above 70 DEG C to paper-making raw material or white water that is exposed to temperatures above 70 DEG C.

Description: METHOD FOR AVOIDING PITCH TROUBLES BY USE OF THERMOSTABLE UPASE TECHNICAL FIELD This invention relates to a method for avoiding pitch troubles that arise in the production process for mechanical pulp such as ground wood pulp (in the following abbreviated as GP) or a paper-making process using mechanical pulp. BACKGROUND ART In a paper-making process, free-floating pitch or attached pitch causes pitch troubles such as cohesion in various places in the paper-making machinery, contamination of the equipment, paper contamination and paper breaks. Since mechanical pulp such as GP is produced by grinding wood mechanically, it is characteristic that the components of the wood remain almost unchanged in the pulp. Further, it is well-known that wood from coniferous trees which is a main raw material for mechanical pulp contains a large amount of pitch constituents such as fatty acids, resin acids and fatty acid glycerides. Therefore, pitch troubles are easily caused when a large amount of mechanical pulp is used. One method for avoiding pitch troubles that has been conducted in the past is the so-called seasoning, in which logs after felling are held outside for a long period. Other methods are e.g. adsorption by an inorganic filler such as talc or addition of a surfactant. Addition of a fatty acid glyceride hydrolysing enzyme (in the following called lipase) has also been tried, as disclosed in JP-A 2-160997 (equivalents AU-A-45822/89, EP-A-0 374 700). The pitch components in wood can be reduced by the above- mentioned seasoning, but this requires 3 to 6 months or even longer and a large piece of land for holding a large amount of logs; and other methods do not provide a fundamental solution to pitch troubles, either. The addition of lipase disclosed in JP-A 2-160997 causes a restriction of the place of addition in the pulp production process, since there is a risk of inactivation above 70°C. It is the object of this invention to provide a method for more effectively avoiding pitch troubles in a production process for mechanical pulp or in a paper - making process using mechanical pulp. SUMMARY OF THE INVENTION The present inventors noticed that in the production process for mechanical pulp the raw material for paper-making and/or the white water immediately after trituration of the logs or chips in a grinder or refiner reaches a high temperature above 70°C, and they discovered thermostable lipases that at this high temperature are able to hydrolyse triglycerides, which are a main component in causing pitch troubles; and they completed the invention. Accordingly, the above-mentioned object is achieved by a method for avoiding pitch troubles in a process for production of mechanical pulp and/or a paper-making process using mechanical pulp, characterized by removing pitch in paper-making raw material (pulp) and/or in white water by adding a lipase (fatty acid hydrolysing enzyme) resistant to temperatures higher than 70°Ctothe paper-making raw material and/or the white water that is exposed to temperature higher than 70°C. DETAILED DESCRIPTION OF THE INVENTION Any lipase (EC 3.1.1.3) can be used in this invention if it has a thermostability that enables it to hydrolyse triglyceride, a main component of pitch, at temperatures above 70°C; more particularly, the lipase should yield at least 80% hydrolysis of triglyceride at a dosage of 60-80 Olive Oil Units (defined below) in 4% pulp slurry during 2 hours with stirring at pH 4.5, 70°C. To obtain a high degree of hydrolysis, a positionally non-specific lipase is preferred. Such lipases can be found widely of animal, plant or microbial origin. Examples of microorganisms producing such thermostable lipases are strains of the genus Candida and Pseudomonas, particularly Candida antarctica, C. tsukubaensis, C. auriculariae, C. humicola, C. foliarum, P. cepacia, P. fluorescens and P. fragi. Lipases from strains of C. antarctica and P. cepacia are preferred, especially lipase A from C. antarctica strain DSM 3855. Such lipases and methods of producing are known from WO 88/02775 (equivalents JP-W 1 -501120, DK-C 159,882), US 4,876,024 and WO 89/01032. The strain DSM 3959 (mentioned in WO 89/01032) was deposited at Deutsche Sammlung von Mikroorganismen (DSM) in Germany on 30 January 1987 under the terms of the Budapest Treaty. The lipase to be used can be produced by the microorganism itself, or it can be produced by a transformant wherein the structural gene for the lipase has been inserted. Particularly preferred lipases are SP 341 (lipase from Pseudomonas cepacia) and SP 344 (lipase from Candida antarctica), products of Novo Nordisk A/S, Denmark. When SP 341 is added to a slurry of raw material for paper-making containing mechanical pulp obtained by trituration in a grinder or refiner, the optimum temperature for triglyceride hydrolysis activity is 60-70°C, and even at 80°C it shows 57.5% hydrolytic activity. The optimum temperature for SP 344 in the above-mentioned reaction is 70°C, and even at 80°C it shows 84% hydrolytic activity. Adequate hydrolysis can be obtained even above or below the optimum temperature by increasing the enzyme dosage. Both of the above- mentioned two enzymes show good hydrolytic activity in a broad pH range, so in a process for producing mechanical pulp or a paper-making process using mechanical pulp, triglycerides in paper-making raw material and/or in white water can be removed by addition of these enzymes. When adding heat-resistant lipase to paper-making raw material and/or white water, it is generally preferred to add it to an aqueous slurry of the paper- making raw material or to white water at 10-80°C. The lipase can be used at a temperature up to 90°C, most preferably at 70-80°C. The lipase can be used at pH in the range 4.5-8, especially 4.5-7, normally found in mechanical pulp. The lipase treatment can be made at any convenient consistency, e.g. from 0.5% to 30%. The holding time for the lipase treatment can be between 10 minutes and 5 hours, especially 0.5-2 hours. The dosage of the thermostable lipase is preferably in the range 1-50 Olive Oil Units (units defined below) per g dry substance in the pulp or white water, particularly 5-25 Units per g. On weight basis the preferred dosage is 1-10,000 ppm based on the pulp weight in a slurry of paper-making raw material, or 0.01 -1000 ppm based on white water. 1 olive oil unit is the amount of enzyme that liberates 1 μmole of oleic acid per minute from an emulsion of olive oil at 30°C and pH 9.0. The enzyme hydrolysis of the olive oil is measured at pH-stat by recording the consumption of NaOH needed to titrate the liberated acid as a function of time. According to the invention, it becomes possible to add lipase even directly after tritur ation in a grinder or refiner which is the initial step in a process for producing mechanical pulp or a paper-making process using mechanical pulp, and it can be allowed to react for a longer time with the substrate triglycerides in the paper-making raw material and/or white water, so pitch is removed effectively. In plants equipped with a latency tank (generally held above 70°C), the lipase treatment can conveniently be made in this tank. Accordingly, pitch troubles can be avoided in a simple manner without any negative effect on the product quality or on the operation. Further, most of the water in the pulping or paper-making process is recycled and re-used, but enzyme having high thermostability retains its hydrolytic activity even during recycling, and therefore the enzyme dosage can be reduced, so it is economical compared to lipase without thermostability. EXAMPLES Below, the invention will be explained in more detail by way of examples. In each example, the blank is without enzyme treatment. EXAMPLE 1 The water content of a slurry of paper-making raw material containing mechanical pulp obtained by trituration in a grinder or refiner (in the following called "pulp slurry") was determined by a device for determining water content (Moisture Balance EB 330MOC, product of Shimadzu Seisakusho), and after adjusting to pH 4.5 with 1/10 N sulphuric acid, the concentration of the pulp slurry was adjusted to 4%. Samples of 500 g each of this pulp slurry were measured out and set in an incubator. Until each pulp slurry reached the fixed temperature, it was stirred at 300 rpm using a Three-One Motor (product of Shinto Kagaku). While continuing the stirring, a fixed amount of enzyme was added and was allowed to react for 2 hours. The amount of enzyme for 500 g of 4% slurry was 78 Olive Oil Units for SP 341 and 67 Olive Oil Units for SP 344. 1 Olive Oil Unit is the amount of enzyme that liberates 1 μM of fatty acid per minute with olive oil as substrate, determined by the JIS method for lipase enzyme activity. Immediately after completion of the reaction, 150 g from each sample was taken into a 500 cc beaker, and after adding 350 cc deionized water it was extracted with 200 cc of a 1 :1 chloroform:methanol solution. 4 ml of 1% litocholic acid was added as internal standard. After suction filtration on filter paper, the solvent layer was analyzed by latroscan (product of latron). The developing system was as follows: First time: hexane. Second time: hexane:ether:ethanol:acetic acid = 90:8:2:2. The amount of triglycerides in the hydrolysed pulp slurry (in percent of the blank) was calculated from the internal standard and is shown in Table 1 as % hydrolysis = 100% - % residual triglyceride. Table 1 Hydrolysis of triglycerides by lipase (SP 341 and SP 344) at various temperatures EXAMPLE 2 In accordance with EΞxample 1, the reaction temperature was fixed at 80°C, and the hydrolysis of triglycerides at various enzyme concentrations was determined and is shown in Table 2. Table 2 Hydrolysis of triglycerides at various concentrations of SP 341 and SP 344 at βO^C 1) Olive Oil Units of each enzyme added to 500 g of 4% pulp slurry Comparative example Using Lipase OF of Meito Sangyo (a known lipase produced by Candida cylindracea), the degree of hydrolysis at various temperatures was determined in accordance with the method described in EΞxample 1. The results are shown in Table 3. The amount of enzyme was 184 Olive Oil Units for 500 g of 4% pulp slurry. Table 3 Degree of hydrolysis at various temperatures with Lipase OF As seen clearly from Table 3, Lipase OF was inactivated above 60°C and did not show the same heat resistance as the enzymes of this invention in the pulp slurry. EXAMPLE 3 Enzyme addition was conducted in a GP product line and a newsprint papermaking line shown in the Figure, and the pitch control effect was observed. Newsprint with a weight of 46 g/m 2 was made with a pulp raw-material composition of GP:DIP:NKP:TMP = 30:45:10:15 in a Bel-Barie II paper machine (Beloit Co., USA) with a width of 3,800 mm and a speed of 1000 m/min. The GP in this raw material was made from debarked red pine logs by trituration in a grinder. The pulp raw material made by trituration in this grinder was passed through a so-called Jόnsson screen, and after removing dust in a cleaner it was pressed in a filter. It was then diluted with white water of 30-40°C, adjusted to freeness 70-90 by post-refining, mixed with the other raw materials to prepare the finished pulp and sent to the paper-making machine. In this process, the temperature of the pulp raw material from the grinder to the filter was 60-80°C, and the holding time was about 30 minutes. The enzyme was added to the shower water in the grinder at a dosage of 1000 ppm relative to the pulp dry weight. Continuous addition was conducted for one month, and the amount of triglycerides (TG) and the frequency of attached pitch from the centre roll were followed to check the pitch control effect. The enzyme used was lipase from Candida antarctica with an activity of 6,100 Olive Oil Units per g. A ratio of 50 % seasoned red pine and 50 % unseasoned red pine were used. For comparison, the amount of TG and the frequency of pitch removal from the centre roll were followed without addition of enzyme. The results are shown in the Table below. By addition of enzyme, the amount of TG was reduced by 85% and the frequency of pitch removal was much reduced, thus clearly showing the pitch control effect of the thermostable lipase. International Application No: PCT/ . erm . CT/RO/1J (January 1M1)

Claims: CLAIMS 1. A method for avoiding pitch troubles in a process for production of mechanical pulp or a paper-making process using mechanical pulp, characterized by adding a lipase that is able to resist temperatures above 70°C to the pulp or to white water and holding at a temperature above 70°C to hydrolyse triglycerides in the pitch. 2. A method according to Claim 1 , wherein said thermostable lipase is derived from a strain of the genus Candida or the genus Pseudomonas. 3. A method according to Claim 2, wherein the lipase is derived from a strain of C. antarctica, C. tsukubaensis, C. auriculariae, C. humicola, C. foliarum, P. cepacia, P. fluorescens, or P. fragi. 4. A method according to Claim 3, wherein the lipase is derived from a strain of C. antarctica or P. cepacia, preferably C. antarctica lipase A. 5. A method according to any preceding claim, wherein the lipase dosage is in the range 1-50 (preferably 5-25) Olive Oil Units per g dry substance in the pulp or white water. 6. A method according to any preceding claim, wherein the holding temperature is in the range 70-90°C, preferably 70-80°C. 7. A method according to any preceding claim wherein the pH during said holding is in the range 4.5-8, preferably 4.5-7. 8. A method according to any preceding claim, wherein the holding time in the range from 10 minutes to 5 hours, preferably 0.5-2 hours.

Inventors: ABO MASANOBU, FUJITA YUKO, ITAMI RYOKO, MATSUKURA MOTOO, ABO, MASANOBU, FUJITA, YUKO, ITAMI, RYOKO, MATSUKURA, MOTOO
Applicants: JUJO PAPER CO LTD, NOVONORDISK AS, JUJO, PAPER, CO., LTD., NOVO NORDISK A/S
Application year: 1992
Main classification: D21C9
IPC codes: C02F3, C12S3, D21C5, D21C9, D21H17, D21H21