US20070062654A1

US20070062654A1 - Treatment of wood chips using enzymes

Info

Publication number: US20070062654A1
Application number: US11/228,623
Authority: US
Inventors: Xiang Wang; Jian Ma; Cheng Jiang; William Brown
Original assignee: Enzymatic Deinking Technologies LLC
Current assignee: Enzymatic Deinking Technologies LLC
Priority date: 2005-09-16
Filing date: 2005-09-16
Publication date: 2007-03-22
Also published as: CA2622699A1; WO2007035481A1

Abstract

A method of treating wood chips or saw dust with an enzyme formulation, prior to refining, in order to reduce the total extractives content of the wood chips or sawdust and to modify the wood structure is described herein. The wood chips or sawdust are treated with one or more enzymes such as lipases, esterases, pectinases, cellulases, laccases, hemicellulases and combinations thereof. The enzyme formulation can be applied to the surface of the wood chips or sawdust, e.g. by spraying, or can be impregnated into the wood chips. The enzyme formulation can further comprise one or more surface active agents which can enhance the effectiveness of the enzyme treatment by improving the diffusion or impregnation of the enzymes into the wood chips. The enzyme-based treatment can be applied at any of several different locations prior to the pulping process including chip piles, chip conveyors, chip silos, chips washers, chip washer water stream, impregnation liquor, or during chip storage. The enzyme-based treatment is quick and easy to apply in most commercial mill operations. The enzyme-based treatment is effective at temperatures from about 20° C. to about 100° C., preferably from about 35° C. to about 70° C. The wood chips or saw dust can be treated for a period of time from about 0.10 to about 200 hours, more preferably from about 10 to about 72 hours. The addition of the enzyme formulation into the wood chip or sawdust pile increases the concentration of pitch-degrading enzymes on the chip or dust surfaces which can significantly accelerate the degradation of pitch components inside the chips or sawdust. Decreasing the total extractives content of the wood chips and modifying the structure of the wood chips or sawdust leads to a decrease in the apparent pitch content during pulping and in reduced energy requirements, increased paper strength, improved paper machine runability, and lower costs associated with paper manufacturing.

Description

FIELD ON THE INVENTION

The present invention is generally in the field of managing wood pitch using enzyme treatments of wood chips prior to pulping.

BACKGROUND OF THE INVENTION

Wood extractives in wood chips, commonly known as pitch, have a significant impact on pulping and papermaking processes. Minimizing or preventing pitch deposits is critical to minimizing equipment fouling and down time, maximizing production efficiency, and improving paper product quality. Pitch is composed of low molecular weight olephilic materials (primarily triglycerides, resin acids, fatty acids, fatty esters, waxes, resin esters, fatty alcohols, sterols, and terpenes), which are released from wood fibers during chemical and mechanical pulping processes. These resinous substances may precipitate as aluminum, calcium and magnesium salts, causing problems on the paper machines and in the paper products. Generally, the amount of extractives in wood chips depends on the species of tree from which the chips are produced, the maturity of the tree, growing conditions, harvesting season, the debarking process, chip storage and the seasoning/aging of the chips.
Most chemical and mechanical pulp is produced from wood logs or from wood chips and saw dust, which are made from debarked stem wood. Wood chips typically have a thickness of 3-6 mm and a length of 10-30 mm. Wood chips go through a series of processing steps, such as the chip pile/tower, chip screening, chip conveyors, chip silos, chip washing and dewatering, and chip impregnation prior to the pulping process. The objective of these processing steps is to optimize the physical dimensions of the wood chips prior to pulping. During these processing steps, the extractives in the wood chips undergo dramatic changes not only in the total amount of extractives but also in terms of the chemical composition of the extractives.
When wood is stored, the living cells contained in the wood respire and release heat. The generated heat provides favorable conditions for the growth of natural airborne bacteria and fingi. The starches, simple sugars, and pitch extractives in the wood cells can be metabolized as a source of carbon and energy. This metabolism can lead to an overall decrease in the pitch content of the stored wood.
Seasoning has long been used for unbarked or barked round wood to reduce the formation of problematic pitch in wood pulp. Seasoning is typically only used for high pitch wood such as pine. The seasoning of wood chips is commonly done in an outdoor chip pile; however, it can also be done in specially designed chip silos in order to control the seasoning and aging conditions. Seasoning of some hardwoods and softwoods prior to pulping can lead to a decrease in wood extractives and removal of some of the unsaponifiable fractions, which can result in a decrease in digestion and wash times, particular in the summer or when the ambient temperature is high. However, storage of wood chips can result in excessive, undesirable microbiological growth which can result in decreased brightness which increases the amount of chemical bleaching required of the resulting pulp.
Microorganisms, such as fungi, have been added during the seasoning process to enhance the seasoning and/or aging process of wood. U.S. Pat. Nos. 5,476,789; 5,609,724; and 5,998,197 to Farrell et al.; U.S. Pat. No. 5,746,790 to Blanchette et al.; and U.S. Pat. No. 5,695,975 to Zimmerman et al. describe the use of ascospores of wood-penetrating, pitch-grading fungi of the class Ascomycotina and Deuteromycotina for pitch reduction of wood substrates such as logs and wood chips. Such methods, however, often require treatment times of about two weeks in order to be effective, significantly increasing the wood inventory and thus the space required for storage, thereby increasing production costs.
There is still a need for a method of treating wood chips or saw dust to quickly and effectively reduce the total amount of extractives in the wood chips prior to refining without a significant decrease in brightness.
Therefore, it is an object of the present invention to provide a method of treating wood chips or sawdust that decreases the total amount of extractives in the wood chips prior to refining.
It is further an object of the invention to provide a method of decreasing the total amount of extractives in wood chips or saw dust prior to refining which results in lower refining energy requirements, increased paper strength (burst strength), and better paper machine runability.
It is further an object of the invention to provide a method for decreasing the total amount of extractives in wood chips or saw dust prior to refining which is effective over relatively short treatment times without any significant decrease in brightness.

BRIEF SUMMARY OF THE INVENTION

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the total amount of extractives released in the filtrate, in ppm, as a function of treatment time with two different enzyme formulations: EnzOx® #1 and EnzOx® #2.
FIG. 2 is a graph showing the total amount of extractives released in the filtrate, in ppm, as a function of treatment time with two different enzyme formulations, EnzOx® #1 and EnzOx® #2, at two different temperatures.
FIG. 3 is a graph showing the apparent pitch content (“APC”), or percent of surface or colloidal triglycerides based on dry fiber at the decker accept sample point before, during, and after treatment with EnzOx®.
FIG. 4 is a graph showing the organic acid content in the washing filtrate and at the decker accept sample point before and during treatment with EnzOx®.
FIG. 5 is a graph showing the apparent pitch content (“APC”) in the washing filtrate and at the decker accept sample point before and during the treatment with EnzOx®.
FIG. 6 is a graph showing the increase in the burst strength of paper manufactured from wood chips treated with EnzOx®.
FIG. 7 is a graph showing the decrease in average refining energy consumption for wood chips treated with EnzOx®.
FIG. 8 is a schematic showing one possible application point for the enzyme treatment in a commercial pulping process.

DETAILED DESCRIPTION OF THE INVENTION

I. Definitions
“Pitch” as used herein refers to a composition composed of low molecular weight olephilic materials (primarily triglycerides, resin acids, fatty acids, waxes, resin esters, fatty alcohols, sterols, and terpenes), which are released from wood fibers during chemical and mechanical pulping processes. These resinous substances usually precipitate as aluminum, calcium and magnesium salts, causing problems with the wet end components of paper machines.
“Apparent pitch” or “depositable pitch”, as used herein, refers to pitch which is located on the surface of the wood chips or sawdust or is suspended in the wash water as dissolved colloidal particles. Apparent pitch content is distinguished from total pitch content or total wood extractives, which includes pitch located on the surface of the wood chips or sawdust as well as pitch encapsulated or trapped within the wood fibers.
“Stone ground wood pulp” as used herein refers to pulp which is produced by grinding wood into relatively short fibers with stone grounding. This pulp is used mainly in newsprint and wood-containing papers, such as lightweight coated (LWC) and super-calendered (SC) papers.
“Thermomechanical pulp” or “TMP” as used herein refers to pulp that is produced in a thermo-mechanical process where wood chips or sawdust are softened by steam before entering a pressurized refiner. TMP generally has the same end-uses as stone groundwood pulp.
“Semi-chemical pulp” as used herein refers to pulp produced in a manner similar to TMP but the wood chips or sawdust are chemically treated before entering the refiner. This pulp has properties suited to tissue manufacture.
“Chemical pulp”, as used herein, refers to pulp produced by the treatment of wood chips or sawdust with chemicals to liberate the cellulose fibers by removing the binding agents such as lignin resins and gums. Sulphite and Sulphate or Kraft are two types of chemical pulping. Kraft is the predominant pulping process in chemical pulp production.
“Burst strength”, as used herein, refers to the resistance of paper to rupture as measured by the hydrostatic pressure required to burst the sheet when a uniformly distributed and increasing pressure is applied to one of its sides.
“Treated wood chips”, as used herein, refers to wood chips or sawdust which have been treated with one or more enzymes, optionally, in combination with one or more surface active agents.
“Untreated wood chips”, as used herein, refers to wood chips or sawdust which have not been treated with one or more enzymes, optionally, in combination with one or more surface active agents.
“Average refining energy consumption” as used herein refers to the average amount of energy (often measured as horsepower-days/ton) consumed by the TMP mill's equipment (refiners, screw presses, screens, etc.) during the processing of wood chips or sawdust to produce pulp.
II. Materials for Enzymatic Treatment of Wood Chips
The use of enzyme formulations to treat wood chips or sawdust prior to pulping in order to lower the total extractive content of the wood chips or sawdust is described herein. The enzyme formulations are preferably used for mechanical pulping processes such as stone ground wood (“SGW”) or thermomechanical pulps (“TMP”). However, the formulations can also be used in the production of semi-chemical or chemical pulps. The effectiveness of the enzyme treatment can be determined by measuring the apparent pitch content (“APC”) in a wood pulp sample at various points in the pulping process. Decreasing the total wood extractives in the wood chips or sawdust can result in a decrease in the apparent pitch content of the pulp. A decrease in the apparent pitch content can result in reduced refining energy requirements, increased pulp and paper strength, improved paper machine runability, and lower costs associated with paper manufacturing.
A. Enzymes
The enzyme formulations comprise one or more enzymes selected from the group consisting of esterases, lipases, pectinases, cellulases, hemicellulases, laccases and mixtures thereof. Examples of commercially available cellulases are those derived from Trichoderma viride and Aspergillus niger. The enzyme formulations are active over a broad range of temperatures and pHs, preferably from about 20° C. to about 100° C., more preferably from about 35° C. to about 70° C. and a pH of about 3 to about 9. The concentration of the enzyme formulation is from about 0.001% to 5% by weight of oven dried wood chips, preferably 0.01% to about 1.0% by weight of oven dried wood chips. The specific enzymes and their concentrations can be varied based on the species of the tree and the nature of the wood chips or sawdust. The enzyme formulations can further comprise one or more surface active agents. The use of surface active agents can enhance the diffusion or penetration of the enzymes into certain types of wood chips or sawdust. In one embodiment, the enzyme formulation is EnzOx® #1, which contains 30% lipase by weight of the formulation, 30% pectinase by weight of the formulation, 10% C₁₂-C₁₆ethoxylated alcohol by weight of the formulation, and 30% water by weight of the formulation. In another embodiment, the enzyme formulation is EnzOx® #2, which contains 30% lipase by weight of the formulation, 20% pectinase by weight of the formulation, 5% cellulase by weight of the formulation, 5% hemicellulase by weight of the formulation, 20% C₁₂-C₁₆ethoxylated alcohol by weight of the formulation, and 20% water by weight of the formulation. The addition of the enzyme formulations can expedite the reaction of the natural microorganisms, which are present on the wood chips or sawdust, with the pitch without causing any significant decrease in wood chip brightness.
B. Surface Active Agents
The enzyme formulations may further comprise one or more surface active agents. The surface active agents can enhance the effectiveness of the enzyme treatment by improving the diffusion or impregnation of the enzymes into the wood chips or sawdust as well as improving the efficiency of the chip washing. Suitable surface active agents include, but are not limited to, primary and branched alkoxylates, fatty acid alkoxylates, phosphate esters and their alkoxylates, alkylphenol alkoxylates, block copolymers of ethylene and propylene oxide, alkanesulfonates, olefinsulfonates, fatty amine alkoxylates, glyceride alkoxylates, glycerol ester alkoxylates, sorbitan ester alkoxylates, polyethylene glycol esters, polyalkylene glycols, and combinations thereof. The concentration of the surface active agent(s) is from about 2% to about 50% by weight of the formulation, more preferably from about 5% to about 20% by weight of the formulation.
III. Methods of Treatment
The enzyme-based treatment can be applied at any of various points prior to pulping. Suitable locations include chip piles, chip conveyors, chip silos, chip washers, the chip washer water stream, the impregnation liquor, or in chip storage containers.
In one embodiment, the enzymes are sprayed onto the wood chips or sawdust immediately after the wood chipper. The ambient temperature of the chip or dust pile can affect the rate of reaction of the enzyme formulation. In general, the higher the chip pile temperature, the faster the rate of reaction is between the enzyme formulation and the pitch as well as the reaction between naturally present fungi and pitch components. For example, treatment times during the summer tend to be shorter than treatment times during the winter.
The enzyme-based treatment can also be sprayed onto the wood chips or sawdust during the chipping process, on the conveyor belts, in the silos, and/or in the washer water. Alternatively, the wood chips or sawdust can be impregnated with the enzyme formulation in the impregnation liquor. If the enzyme-based treatment is applied to the chip washing water, it is preferred that a portion of the chip washing water be removed prior to pulping. In one embodiment, the washing water can be diverted to a water treatment facility or pumped directly into the sewer system. The chip washing water often contains large amounts of pitch-based materials and removal of a portion of this stream will minimize the introduction of these contaminants into the pulping process.
The enzyme-based treatment can be performed at a temperature from 20° C. to about 100° C., preferably from about 35° C. to about 70° C. for a period of about 0.10 to about 200 hours, preferably about 10 to about 72 hours. The effectiveness of the enzyme treatment can be determined by measuring the apparent pitch content (“APC”) in a wood pulp sample at various points in the pulping process.
IV. Methods for Analyzing the Apparent Pitch Content
The apparent pitch content (“APC”) can be measured using the triglyceride assay methods described in U.S. Patent Application Publication No. 2003/0046984 by Jiang et al. A wide variety of methods that have been developed to assay for triglycerides in biological applications also can be adapted for use in assaying for pulp triglycerides.
A. Wood Pulp and Sample Points
Triglyceride analytical methods can be applied to essentially any wood pulp sample. As used herein, the term “wood pulp sample” includes wood pulp suspensions, wood pulp fibers, and process water taken from essentially any sampling point in the chip wash water, pulp mill whitewater or paper mill whitewater. Representative examples of sample points include the low density (“LD”) chest, which is a storage chest for pulp; the high density (“HD”) chest, which is another storage chest for pulp; the decker, which thickens the pulp; the whitewater sample, which is a sample of the water inside the system loop; the blend chest; the headbox, which is the location just before the paper machine where the stock is prepared for the paper making process; and the paper machine (“PM”) itself where the paper is actually made.
These methods are particularly useful in paper mills that use a mechanical pulp. The methods are also useful with other pulps, such as Kraft and other chemical pulps.
B. Enzymatic Hydrolysis of the Triglycerides
The apparent pitch in a wood pulp sample is reduced (i.e. hydrolyzed) in the presence of a lipolytic enzyme to form glycerol and fatty acids. Preferably, the lipolytic enzyme is a triacylglycerol lipase. Suitable lipases for the hydrolysis of triglycerides can be derived from plant, animal, or preferably microbial sources. Representative examples of sources for microbial lipases include Candida rugosa, Rhizopus arrhizus, and Chromobacterium viscosum. Other suitable lipolytic enzymes belong to the family of carboxylic ester hydrolases. Representative examples of these include phospholipases, lipoprotein lipase, and acylglycerol lipase.
Alternatively, the lipolytic enzyme can be a non-lipase enzyme. For example, the lipolytic enzyme could be a carboxylesterase, such as acetyl esterase or aceyl esterase, which hydrolyze lower fatty acid esters. Examples of other suitable lipolytic enzymes include cholesterol esterase, which hydrolyses steroid esters, which can be used in combination with the lipase.
C. Detection of Change in Glycerol or Fatty Acid Concentration
In one embodiment, the method of detection of changes in the fatty acid concentration is an enzyme-based colorimetric method that uses a spectrophotometer for detection. It generally takes only between about 20 and 30 minutes to assay a set of samples using such a method. The results are accurate and reproducible, and the method advantageously does not require the use of volatile organic compounds and solvents which are required for extraction-based methods. The method also measures surface triglyceride content in the pulp and in the water, which correlates directly with the surface pitch content, which in turn directly relates to pitch deposition problems.
In other embodiments, non-colorimetric methods are used to determine the apparent pitch content in a wood pulp sample. Representative examples of non-colorimetric methods employ tests based on turbidities, titrations, impacts of electrical current arrays, or spectroscopic methods such as GC, HPLC, and NMR.
The present invention will be further understood by reference to the following non-limiting examples.

EXAMPLES

Example 1

Measurement of the Apparent Pitch Content (“APC”) in a Wood Chip Sample Using Different Enzyme Formulations

Materials and Methods
Wood chip samples were treated with two different formulations, EnzOx® #1 and EnzOx®#2 and the apparent pitch content (“APC”) was measured. 800 grams of water was heated to 50° C. 200 grams of freshly cut wood chips were added to the water and mixed at 200 rpm using a standard mixer while maintaining the temperature of the water bath at 50° C. EnzOx® #1 or #2 was added in the desired amount of 0.20 grams, and the mixing was continued for 100 minutes at 50° C. The pH was 5.2 due to the natural pH of the wood chips.
Samples were taken at several different reaction times. The APCs in the filtrate and the organic acid content released from the wood chips were measured. The APC was measured using the same procedure described in U.S. Patent Application Publication No. 2003/0046984. The organic acid content was measured by extracting the filtrate with hexane and removing the hexane by evaporation. The organic residue remaining upon evaporation was dissolved in an isopropanol/water cosolvent and titrated with potassium hydroxide (“KOH”) using thymol blue as the pH indicator.
Results
The results are shown in FIG. 1. FIG. 1 shows that the APC in the filtrate increased with the EnzOx® treatment over the control, demonstrating that treatment of wood chips with the enzyme formulations resulted in a greater amount of extractives being released from the chips into the filtrate than for the control (untreated wood chips).

Example 2

Measurement of the Apparent Pitch Content (“APC”) in a Wood Chip Sample Using Different Enzyme Formulations at Different Temperatures

Materials and Methods
Wood chip samples were treated with two different EnzOx® formulations at 50° C. and 65° C. and the apparent pitch content (“APC”) was measured as described in Example 1.
Results
The results are shown in FIG. 2. Treatment of the wood chips with the enzyme formulation resulted in an increase in the APC of the filtrate. The increase was greater at 65° C. than at 50° C.

Example 3

Measurement of the Apparent Pitch Content (“APC”) at the Decker Accept Before, During and After Enzyme Treatment

Wood chips were treated with EnzOx® and the APC of the resulting pulp was measured at the decker accept sample point in the pulping process.
The results are shown in FIG. 3. The APC levels measured at the decker accept sample point were lower due to the fact that a greater amount of wood extractives were released from the wood chips upon treatment with the enzyme formulation. The wood extractives were removed in the chip washing filtrate prior to the pulp reaching the decker accept sample point.

Example 4

Measurement of the Fatty Acid Content in the Washing Filtrate and at the Decker Accept Before and During Enzyme Treatment

The fatty acid content was measured in the chip washing filtrate after treatment with EnzOx®.
The results are shown in FIG. 4. Treatment of the wood chips with EnzOx® converts the wood extractives into glycerol and fatty acids, which remain behind in the chip washing filtrate. As a result, analysis of the pulp at the decker accept showed a decrease in the fatty acid content after treatment with EnzOx®.

Example 5

Measurement of the Apparent Pitch Content (“APC”) in the Washing Filtrate and at the Decker Accept Before and During Enzyme Treatment

The apparent pitch content (“APC”) was measured at two different sample points: the washing filtrate and the decker accept. The APC was measured before and after enzyme treatment.
The results are shown in FIG. 5. The APC content decreased at both sample points due to the conversion of the wood extractives to glycerol and fatty acids which were subsequently removed in the chip washing filtrate.

Example 6

Measurement of the Burst Strength of a Thermomechanical Pulp (“TMP”) Following Enzyme Treatment

The burst strength of thermomechanical pulp (“TMP”), which was prepared from wood chips treated with EnzOx®, was measured. The results are shown in FIG. 6. The burst strength of the pulps prepared from wood chips treated with EnzOx® were higher than the burst strengths for pulps prepared from untreated wood chips.

Example 7

Measurement of TMP Energy Consumption for Wood Chips Treated with Enzyme Formulation

The average refining energy consumption required for the production of TMP from wood chips treated with EnzOx® was measured. The results are shown in FIG. 7. The average refining energy consumption for the production of TMP decreased after treatment with EnzOx®.
It is understood that the disclosed invention is not limited to the particular methodology, protocols, and reagents described as these may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention which will be limited only by the appended claims.

Claims

1. A method of treating wood chips or sawdust, prior to refining, the method comprising treating the wood chips or sawdust with a formulation comprising one or more enzymes at a concentration of at least about 0.001% by weight of the oven-dried wood chips or sawdust.

2. The method of claim 1 wherein the one or more enzymes is selected from the group consisting of lipases, esterases, pectinases, cellulases, hemicellulases, laccases and combinations thereof.

3. The method of claim 1 wherein the concentration of the one or more enzymes is from about 0.001% to about 5% by weight of the oven-dried wood chips.

4. The method of claim 3 wherein the concentration of the one or more enzymes is from about 0.01% to about 1% by weight of the oven-dried wood chips.

5. The composition of claim 1 further comprising one or more surface active agents.

6. The method of claim 1 wherein the one or more surface active agents is selected from the group consisting of primary and branched alkoxylates, fatty acid alkoxylates, phosphate esters and their alkoxylates, alkylphenol alkoxylates, block copolymers of ethylene and propylene oxide, alkanesulfonates, olefinsulfonates, fatty amine alkoxylates, glyceride alkoxylates, glycerol ester alkoxylates, sorbitan ester alkoxylates, polyethylene glycol esters, polyalkylene glycols, and combinations thereof.

7. The method of claim 6 wherein the concentration of the one or more surface active agents is from about 2% to about 50% by weight of the formulation.

8. The method of claim 7 wherein the concentration of the one or more surface active agents is from about 5% to about 20% by weight of the formulation.

9. The method of claim 1 wherein the wood chips or sawdust are treated with the one or more enzymes at a temperature from about 20 to about 100° C.

10. The method of claim 9 wherein the wood chips or sawdust are treated with the one or more enzymes at a temperature from about 35 to about 70° C.

11. The method of claim 1 wherein the wood chips or sawdust are treated with the one or more enzymes for a time ranging from about 0.10 to about 200 hours.

12. The method of claim 11 wherein the wood chips or sawdust are treated with the one or more enzymes for a time ranging from about 10 to about 72 hours.

13. The method of claim 1 wherein the wood chips or sawdust are treated in a location selected from the group consisting of chip piles, chip conveyors, chip silos, chip washers, chip washer water stream, impregnation liquor, and chip storage.

14. The method of claim 1 wherein the wood chips or sawdust are treated by spraying the one or more enzymes onto the wood chips.

15. The method of claim 1 wherein the wood chips or sawdust are treated by impregnating the wood chips with the one or more enzymes.

16. The method of claim 1 wherein the wood chips or sawdust are washed with water after treatment with the one or more enzymes.

17. The method of claim 1 wherein the wash water is removed after the wood chips or sawdust have been treated and washed.

18. The method of claim 1 wherein the woodchips or sawdust are treated with the one or more enzymes at a pH of between about 3 and about 9.

19. The method of claim 1 further comprising measuring the decrease in the total extractives content in the wood chips or sawdust by comparing the pitch content of a wood pulp sample prepared from wood chips or sawdust treated with a formulation comprising one or more enzymes with the pitch content of a wood pulp sample prepared from untreated wood chips or sawdust.