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Treatment of wood chips using enzymesRelated Patent Categories: Paper Making And Fiber Liberation, Processes Of Chemical Liberation, Recovery Or Purification Of Natural Cellulose Or Fibrous Material, Treatment With Particular Chemical, OrganicTreatment of wood chips using enzymes description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070062654, Treatment of wood chips using enzymes. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD ON THE INVENTION [0001] 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 [0002] 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. [0003] 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. [0004] 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. [0005] 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. [0006] 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. [0007] 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. [0008] 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. [0009] 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. [0010] 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 [0011] 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.degree. C. to about 100.degree. C., preferably from about 35.degree. C. to about 70.degree. 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. BRIEF DESCRIPTION OF THE DRAWINGS [0012] 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.RTM. #1 and EnzOx.RTM. #2. [0013] 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.RTM. #1 and EnzOx.RTM. #2, at two different temperatures. [0014] 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.RTM.. [0015] 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.RTM.. [0016] 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.RTM.. [0017] FIG. 6 is a graph showing the increase in the burst strength of paper manufactured from wood chips treated with EnzOx.RTM.. [0018] FIG. 7 is a graph showing the decrease in average refining energy consumption for wood chips treated with EnzOx.RTM.. [0019] FIG. 8 is a schematic showing one possible application point for the enzyme treatment in a commercial pulping process. DETAILED DESCRIPTION OF THE INVENTION Continue reading about Treatment of wood chips using enzymes... Full patent description for Treatment of wood chips using enzymes Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Treatment of wood chips using enzymes patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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