WO1997026404A1 - Pulping ligno-cellulosic material using high frequency radiation - Google Patents

Abstract

A method for treating ligno-cellulosic material with high frequency energy (18) or an electro-osmotic step (36) to enhance the removal of lignin from the material or improve the absorption characteristics of the material during pulp and paper manufacture.

Description

PULPING LIGNO-CELLULOSIC MATERIAL USING HIGH FREQUENCY RADIATION

Background of the Invention

The present invention relates to methods and systems for processing ligno-cellulosic material, and particularly to methods and systems for producing pulp and paper. As used herein, the term ligno-cellulosic material is intended to include logs, lumber, wood particles, wood chips, wood flakes, wood wafers, wood fibers, wood veneer and other wood products and parts thereof, as well as other lignin and cellulose containing matter, such as woody plants, foliage, roots, shells, nuts, husks, fibers, straw, vine, grass, bamboo, and reeds.

The processing of ligno-cellulosic material for the production of paper, pulp, cellulose, paperboard and similar products is a major part of the chemical wood products industry. Consequently, there are a number of well-developed and established industrial methods for producing paper and pulp, all of which include similar stages.

A conventional pulp and paper manufacturing plant includes extraordinarily expensive equipment to effectuate the cooking or pulping of ligno- cellulosic material. The main ingredient of the pulp manufacturing process are wood chips, which can be supplied to the pulp and paper plant or can be manufactured on site. The formation of the wood chips for the paper plant is important, since one key factor in obtaining the highest quality pulp possible with the most efficient use of pulping and bleaching chemicals, thus having the least environmental impact, is to have substantially uniformly sized chips. Chips are typically stored on site in large columnar chip silos. If the wood chips are manufactured on site, ligno-cellulosic material, such as logs of round wood, is first debarked using a barker device. The removal of bark from the logs is necessary as it has negligibly useful fiber content, tends to darken the resultant pulp, and requires extra chemical usage while introducing contaminants such as calcium, silica and aluminum into the chemical recovery system. One particular type of barker device commonly used in the industry is a drum barker device, which is essentially a large, rotating steel drum mounted with its exit disposed vertically lower than its entrance to promote the flow of logs therethrough. The drum rotates at about five revolutions per minute, and a dam located at the exit controls the log retention time, which is on the order of 20 to 30 minutes. Debarking of the round wood occurs by mechanical abrasion of the logs against each other. The debarked logs are then introduced into a chipper device to create the wood chips. One conventional chipper is a gravity feed, e.g., a drop-feed disk chipper, where the debarked wood enters through a spout mounted at the top of the chipper. As a result of this chipping process, the wood chips produced have varying sizes, and according to conventional chipping techniques, comprise about 85% accepted chips, 4% overthick chips, 2% overlength chips, 7% pin chips, and 2% fines.

The wood chips produced during the chipping process are then sorted according to size prior to introduction to a pulp digester. The sorting of the wood chips into selected sizes promotes uniform pulping, since large chips (e.g., particularly overthick chips during the kraft cooking process) undercook. leaving large amounts of shards, while small chips tend to clog the chemical circulation system, use large amounts of chemicals, and result in a relatively low and mechanically weak pulp yield. One particular classification for the wood chips sorts the chips according to selected thicknesses to remove overly thick chips. The wood chips formed by the chipping process are then subjected to a pulping process. The resultant pulp generated during the pulping process generally consists of ligno-cellulosic material that have been broken down physically and/or chemically such that more or less discrete fibers, e.g., such as cellulose and hemicellulose, are liberated and dispersed in a liquid, such as water, and then formed into a web. There are four broad categories of pulp and processor use, and include chemical pulping, semi-chemical pulping, semi-mechanical pulping and mechanical pulping. The foregoing are listed in the order of increasing mechanical energy required to separate fibers and decreasing reliance on chemical action. Therefore, chemical pulping methods rely on the effect of chemicals to separate fibers, whereas mechanical pulping methods rely completely on physical action. It is known that the more chemicals employed in the pulping process, the lower the pulp yield and lignin content since chemical action degrades and solubilizes selected components of the wood, especially lignin and hemi celluloses. On the other hand, chemical pulping yields individual fibers that are relatively free of abrasions and cuts, and thus are capable of fomώig mechanically strong paper since the lignin, which tends to interfere with the hydrogen bonding between adjacent fibers, is largely removed. The general chemical pulping techniques are the most widely used, and therefore will be described further.

Conventional chemical pulping processes delignify the ligno-cellulosic material, e.g., wood chips, by breaking down the chemical structure of lignin and rendering it soluble in a liquid, such as water. The amount of lignin present in the pulping liquor during the pulping process is designated by a selected measuring parameter, known as the kappa number. Hence, the higher the kappa number the higher the lignin content. The kappa number is typically used to monitor the amount of delignification of chemical pulps after pulping and between bleaching stages.

The wood chips generated by the chipper devices are introduced to a digester, which is a pressure vessel designed for cooking the wood chips into pulp. One particular digester used is a batch digester, which is typically between 70 and 359 cubic meters in size, and is filled with wood chips and cooking liquor. During this stage of the cooking process, the digester is first opened and then filled with wood chips, white liquor and black liquor. The liquor introduced to the digester during the pulping process is generally an aqueous solution of chemicals used for delignifying wood during this pulping process. The combined chips and liquor is then agitated, and additional chips are added as the contents within the digester settle.

The digester is then sealed and heated using steam. The steam can be introduced directly to the digester, or can be introduced indirectly where the steam is passed through the inside of tubes mounted within the digester. Conventional cooking times last between about 20 and 45 minutes in conventional kraft pulping processes. During this heating time, air and other non-condensable gases emitted during the digesting process are vented from the digester. There is generally sufficient force present within the digester during the chemical pulping process to cause fiber separation. When the chips are properly cooked, as determined by the kappa number of the pulp resident within the digester, the content of the digester is discharged to an attached blow tank located at the end of the cooking cycle. Below the tanks are typically large, cylindrical vessels that receive the hot pulp discharged from the digesters. The heat of the hot gases from the blow tank are recovered by a blow heat accumulator, which is generally a large heat exchanger. This delignification process which occurs during the pulping process is an important concept where it is desired to remove lignin while retaining as much of the cellulosic material as possible.

The chemical pulps are then generally refined after the cooking process to liberate individual wood fibers. During the chemical pulping process, this is relatively easily accomplished in the presence of the hot liquor, which is the basis of hot stock refining. The defiberating which occurs at this stage generally only separates the fibers for a thorough pulp washing, and the fibers must be further refined for paper making. The cooked wood stock is also generally screened to removed rejects, such as wood knots that do not sufficiently delignify during the cooking process. Coarse screens are generally used during chemical processing to remove such rejects. The resultant screened and cooked pulp is then washed to remove process chemicals, such as the liquor used during the pulping process. The pulp is generally washed in rotary vacuum type washers that consist of a wire mesh covered cylinder that rotates in a tub of pulp slurry with valve arrangements to apply vacuum during the washing process. As the drum rotates, the pulp is pushed past wash showers where the pulp is washed with relatively clean water to displace the black liquor used during the digesting process. After washing, the pulp is further screened to remove shives, dirt and other contaminants to protect processing equipment as well as the pulp product.

The washed pulp is then subjected to a bleaching process with chemical agents to increase the pulp brightness. Conventional bleaching of chemical pulps involves a much different strategy than bleaching of mechanical pulps. The bleaching of chemical pulps is achieved by lignin removal and chemical pulps leads to greater fiber to fiber bonding strength in paper, but the strong bleaching chemicals decrease the length of the cellulose molecules, resulting in weaker fibers. Chemical bleach pulping is typically accomplished with various compounds containing chlorine or oxygen and alkali extractions in several stages.

The bleached pulp is then further refined to develop its optimum paper making properties, which depend, of course, on the product being made. The refining of the pulp fibers before making paper increases the strength of fiber to fiber bonds by increasing the surface area of the fibers, and by making the fibers more pliable to conform to each other, which increases the bonding surface area and leads to a denser sheet or mat. Most strength properties of paper increase with pulp refining since they rely on fiber to fiber bonding. The tear strength, which depends highly on the strength of the individual fibers, actually decreases with refining. After a certain point the lirniting factor of strength is not fiber to fiber bonding, but the strength of the individual fibers themselves. Refining beyond this point begins to decrease other strength properties besides tear. Refining of pulp increases their flexibility and leads to denser paper. This means bulk, opacity and porosity values decrease with refining. The machines typically used during the refining process are called refiner devices and are typically machines that mechanically macerate and/or cut pulp fibers before they are made into paper.

The refined pulp is then converted into paper, which typically consists of a web of pulp fibers formed from an aqueous slurry on a wire or screen, and held together by hydrogen bonding. The fiber web formed on the screen is then drained to remove excess water and air dried over a hot surface. The pulp fibers must be properly slurried within the aqueous slurry and mixed with selected additives. Typically, the slurry is treated to remove contaminants in entrained air. The paper forming machine typically is a device for continuously forming, dewatering and pressing, and drying a web of paper fibers. The most common type of paper machine used is the Fourdrinier machine which processes a dilute suspension of fibers, typically having 0.3% to 0.6% consistency, which is applied to a wire screen or plastic fabric. The pulp is applied to the screen at relatively low consistencies to give good formation, that is, an even distribution of fibers so the paper has uniform thickness. Water is typically removed by gravity. The dried fiber mats are then cut to selected sizes and stacked to form paper.

A drawback of the foregoing pulp and paper manufacturing process (such as Kraft, Sulfite, TMP, CTMP, and Mechanical Pulping processes) is that it suffers from a number of significant disadvantages, which include high cost for each particular process stage, high energy consumption, use of environmentally destructive chemical solvents, such as bleaching agents and liquor, the required use of high volume apparatus to reduce the reduction cost per unit, significant duration of the process of delignification and bleaching, and the production of large quantities of waste liquor after pulp washing. Further shortcomings include the use of excessive and highly reactive and often dangerous chemical solvents during pulping and bleaching. These chemicals, however, are often essential to produce chemically stable cellulose, as well as removing significant amounts of lignin from the ligno-cellulosic material. Presently, during the production of bleached pulp, the kappa number of lignin is suppressed to decrease the consumption of bleaching reagents. Unfortunately, this also decreases the pulp yield of the pulp and paper process.

It is thus an object of the invention to provide a pulp and paper manufacturing system and method that cooks the ligno-cellulosic material in a relatively short period of time.

Another object of the invention is to provide a pulp and paper manufacturing system and method that is relatively cost-effective and reduces the amount of the chemicals necessary to cook the ligno-cellulosic material.

Other general and more specific objects of the invention will in part be obvious and will in part appear from the drawings and description which follow.

Summary of the invention

The present invention provides for systems and methods to introduce an additional stage for processing ligno-cellulosic material in the pulp and paper industry. The systems and methods include the electro-physical treatment of the ligno-cellulosic material, which can be followed by mechanical compression and/or chemical treatment and/or treatment by electro-osmosis. A significant advantage of the present invention is that this additional processing stage can be easily integrated with existing pulping plants. The additional processing stage can be performed either prior to or during the pulping process without altering commonly employed technologies, e.g., conventional pulp and paper methods, and leads to significant improvements in the quality and yield of the final pulp product.

The first method of the invention is based on a specific electrophysical treatment of raw materials. It includes exposing the material to an electromagnetic field with appropriately selected parameters (frequency, intensity, duration, etc.), or passing an electrical current through the material, or both, to induce destruction of lignin components for the easy removal and extraction of lignin during the pulping process. This relatively easy extraction significantly reduces the time required to prepare pulp, and increases pulp yield.

The ligno-cellulosic material can be treated at a remote location and then shipped to the pulp plant, or can be treated at the pulp plant and during the pulp making process.

Additionally, treatment of the ligno-cellulosic product has broad ramifications on the intensity and the effectiveness of (1) the process of impregnating the raw material with different solvents, (2) the delignification process (the process of lignin removal), as well as on (3) the bleaching process. These effects lead to significant improvement in the overall effectiveness of the process by increasing yield of pulp and decreasing the relative amounts of the necessary chemicals used during the pulping and bleaching processes, while minimizing energy consumption. The increasing of pulp yield has significant environmental advantages. Furthermore, there are associated with the present treatment systems significant time savings which further serve to reduce the time required to digest the wood.

Another preferred method of the invention is based on a combined electrophysical and mechanical treatment. This treatment utilizes the pretreatment of the ligno-cellulosic materials followed by mechanical deformation of the same, according to the following processes.

The present invention provides apparatus for changing the physical structure of a ligno-cellulosic work piece. The apparatus includes appropriate structure for subjecting the ligno-cellulosic work piece to a high frequency electromagnetic field to plasticize, e.g., soften, the lignin and hemicellulose components of the material. This softening of the lignin component of the wood severs the lignin-cellulose bond, which allows easy separation of the lignin from the ligno-cellulosic work piece in a relatively - 7 -

small amount of time. This device preferably includes two or more electrodes and a high frequency generator. An optional compressing element can compress the plasticized work piece, e.g., along an axis transverse to the grain of the work piece, to attain the second structural configuration of the work piece, e.g. the severing of the lignin-cellulose bond.

According to one aspect, the step of compressing the material further includes the step of maintaining the material in a selected condition of compression following treatment of the wood to delignify the same.

Brief Description of the Drawings

The foregoing and other objects, features and advantages of the invention will be apparent from the following description and apparent from the accompanying drawings, in which like reference characters refer to the same parts throughout the different views. The drawings illustrate principles of the invention and, although not to scale, show relative dimensions.

Figure 1 is a schematic flow chart depiction of the pulp and paper making process of the present invention, illustrating the integration of treatment stages for the ligno-cellulosic material at selected portion of the paper making process.

Figure 2 is a continuation of the schematic flow chart depiction of the pulp and paper making process of Figure 1.

Figure 3 A is a plan view of the electromagnetic treatment apparatus for treating ligno-cellulosic material with high frequency energy according to the teachings of the present invention.

Figure 3B is a plan view of the compressing treatment apparatus for compressing heated and plasticized ligno-cellulosic material according to the teachings of the present invention.

Figure 3C is an end view of the compressing apparatus of Figure 3B illustrating the pressing dies.

Figure 3D is a plan view of one embodiment of a treatment apparatus for treating wood chips with high frequency energy according to the teachings of the present invention.

Figure 3E is a plan view of another embodiment of a treatment apparatus for treating wood chips with high frequency energy according to the teachings of the present invention. Figure 3F is a diagrammatic cross-sectional view of one embodiment of a system for heating, plasticizing and compressing wood chips according to the teachings of the present invention.

Figure 3G is a diagrammatic cross-sectional view of another embodiment of a system for heating, plasticizing and compressing wood chips according to the teachings of the present invention.

Figures 4 A and 4B are schematic depictions of the electro-osmotic system of the present invention.

Figures 5 A and 5B illustrate the physical principles of the electro-osmotic system of Figures 4 A and 4B within the wood structure and pores.

Figure 6 is a tabular illustration of the affect of the treatment systems of the invention on selected parameters of the pulp and paper process and on the wood itself.

Description of Illustrated Embodiments

The present invention provides a method and system for producing pulp and/or paper from treated ligno-cellulosic material. The term "treated" is intended to include any ligno-cellulosic material that has been subjected to either a high frequency, high frequency and compression, electro-osmosis, or a combination of these methods during the pulping and paper process, as set forth below. The use of treated ligno- cellulosic material enhances the ability of the pulp and paper process to remove lignin from the material, while concomitantly reducing the amount of digesting or cooking time necessary to remove the lignin and the amount of cooking liquor uses or consumed by the process. The systems and methods for treating the material can be located off- site, e.g., not at the paper plant facility, or can be retrofitted with selected system components at the paper plant.

Figures 1 and 2 illustrate a schematic block diagram of the pulp and paper processing method and system 10 of the present invention employing at various stages one or more methods and systems for treating the ligno-cellulosic material at that stage. For the sake of simplicity, the term wood will be used herein in place of the term ligno- cellulosic material, and is not to be construed in a limiting sense. Other permutations of the aforementioned processing sequence are apparent to those of ordinary skill in the art. The illustrated system and method 10 includes an initial wood preparation stage designated generally as stage 12, and includes either the preparation of the wood on-site at the paper plant or off-site, such as at the sawmill supplying the wood for the paper plant. The main raw ligno-cellulosic material of the illustrated pulp manufacturing process 10 are wood chips, which can be supplied to the pulp and paper plant or can be manufactured on site. The formation of the wood chips for the paper plant is important, since one key factor in obtaining the highest quality pulp possible with the most efficient use of pulping and bleaching chemicals, thus having the least environmental impact, is to have substantially uniformly sized wood chips.

If the wood chips are manufactured at the sawmill 14, wood trees or wood logs are reduced to wood chips by conventional chippers. The operation and function of chippers and of selected other conventional hardware of the illustrated pulp and paper making process are well known in the art, and are described in Biermann, Christopher J., Essentials of Pulp and Papermaking. Academic Press, Inc., 1993, the teachings of which are hereby incorporated by reference, the wood chips can also be manufactured on-site 16 and stored in large columnar chip silos. The manufacture of wood chips typically requires that the wood first be debarked using a barker device. The removal of bark from the logs is necessary as it has negligibly useful fiber content, tends to darken the resultant pulp, and requires extra chemical usage while introducing contaminants such as calcium, silica and aluminum into the pulp processing system. One particular type of barker device commonly used in the industry is a drum barker device, which is essentially a large, rotating steel drum mounted with its exit disposed vertically lower than its entrance to promote the flow of logs therethrough. The drum has a dam located at the exit to control the log retention time within the device.

Debarking of the round wood occurs by mechanical abrasion of the logs against each other.

The debarked logs are then introduced into the foregoing chipper device (not shown) to create the wood chips. One conventional chipper is a gravity feed, e.g., a drop-feed disk chipper, where the debarked wood enters through a spout mounted at the top of the chipper. As a result of this chipping process, the wood chips produced have varying sizes. The chips are stored within the silo or are transported in a pile 22 to the digester 34 location.

The wood chips, whether manufactured on-site or at the sawmill, can be treated prior to introduction to the digester 34. The present invention contemplates those treatments that enhance the absoφtion characteristics of the wood chips, or enhance the severability of the lignin component of the chips from the remaining structure. According to one practice, the invention contemplates exposing the wood chips to a high frequency field in a radiation treatment stage 18 to plasticize the chips and to severe the chemical bonds between the lignin and cellulose/hemicellulose components of the wood. With reference to Figures 1 and 3A through 3F, the wood logs or chips are passed through an electromagnetic field having certain properly selected parameters, such as spectral composition, voltage potential, and spatial distribution, which are dependent upon the wood type, size and moisture content. The wood is treated in a high-frequency electromagnetic field created by either electric or magnetic type energy emitters. The basic principle of treatment with an electric type emitter is illustrated in Figures 3A-3E where the wood 4 is disposed between a pair of electrodes of opposite polarity 102, 104. The electrodes 102, 104 are connected to opposite terminals of an electric field generator 106 through appropriate electric leads. The configuration of the radiation treatment system 18, distribution and number of electrodes are selected to produce an electric field within the inter-electrode space having selected fixed parameters.

The illustrated radiation stage 18 heats the wood W by vaporizing moisture pockets within the wood, and is effected as follows. The wood W typically contains large pockets of moisture that are randomly dispersed throughout the wood structure, as well as other smaller moisture pockets. The size and number of moisture pockets is a function of the total moisture content of the wood, the ambient pressure and temperature, and other environmental factors. Wood used in the pulp and paper making industry are relatively wet and thus have moisture contents well in excess of the fiber saturation level of moisture. Typically, the moisture pockets are located towards the center of the wood since it dries from the outside towards the center thereof. When the wood article is placed between the electrodes 102, 104 and is exposed to a high frequency electric field, the field penetrates deep into the wood and transfers energy into the internal or interior portions of wood, and specifically to the water contained in the moisture pockets.

The quantity of heat generated within (and removed from) the wood during the heating portion of the radiation treatment stage 18 can be quantitated and is known as the specific absorption of wood , e.g., the heat power created per unit volume of medium, and can be determined by the following formula:

Po = 2 π ε εo fE2 tg δ

where Po is the specific heat absoφtion of wood, f is the frequency of the applied field, ε o is the absolute dielectric constant, ε is the dielectric permeability of wood, E is the intensity of the electric field, and tg δ is the tangent of the dielectric loss angle of the wood. Both ε and tg δ depend on the moisture content of the wood, and both increase in value when the moisture content of the wood increases. Hence, these values are relatively high. Consequently, those wood portions containing the most moisture, e.g., the large moisture pockets, experience more intensive heating than surrounding areas containing less moisture. Because of this phenomena, the core portions of the wood typically experience more intense heating and thus are disposed, at least initially, at a higher pressure.

The heat absoφtion of wood Po is also directly proportional to the frequency and the intensity of the applied electric field. The degree of heating and heating uniformity thus depends upon the frequency and voltage of the applied electric field. For example, the higher the frequency, the greater the amount of heat generated in the wood structure, and thus the greater the heat absoφtion. Additionally, the frequency can be selected or varied to provide for selected or optimum heating of the wood by initiating thermo-osmotic processes in the work piece.

According to one practice, the illustrated generator 106 produces an electric field between the electrodes 102, 104 having a frequency in the range between about 5 MHz and 2 GHz, and preferably in the radio-frequency range. The system of Figure 3 A can also include a control system having dedicated hardware with resident software that controls the frequency applied by the generator 106 to the wood based upon a number of specific parameters, including the temperature of the wood, the moisture content of the wood, the frequency produced by the generator, the size and volume of the wood, and the type of wood used. Thus, the control system can automatically vary the frequency, intensity, and/or duration based upon one or more of the foregoing parameters during processing of the wood, pulp, or paper.

According to a preferred practice, the generator produces radiation in the range between about 25 MHz and about 30 MHz, and preferably at about 27 MHz, when the moisture content in the wood exceeds 30%. Conversely, when the moisture content is below 30%, the generator produces radiation in the range between about 10 MHz and 15 MHz, and preferably about 13 MHz. The generator, as controlled by the dedicated hardware and software, preferably applies different frequencies to the wood to optimize the treatment process. The software can be constructed in accordance with principles known to those of ordinary skill in software design to instruct the dedicated hardware to control the generator and other components of the system as a function of one or more of the foregoing parameters.

The illustrated generator 106 is preferably a high frequency generator that generates a frequency in the foregoing ranges, and supplies a voltage to the electrodes 102, 104 in a range between about 0.4 KV and about 25 KV, and preferably about 4 KV. This frequency treatment stage 18 can be performed at the paper plant, e.g., on-site, or can be performed at the sawmill, e.g., off-site. Moreover, the original raw material, whether it be trees or logs can be treated prior to chipping, or the wood chips formed from the raw material can be treated. The wood material is plasticized by exposure to the electric field according to the following dynamics. Wood is a vascular material that is composed of, among other things, elongated cells having cell walls which surround an inner cell cavity. The cell wall is composed of a fibrous cellulose armature. The armature is typically a long chain polymer that comprises a plurality of linked monomers, up to 10,000 DP (degrees of polymerization) interspersed with amoφhous lignin and hemicellulose polymers . Hemicellulose and lignin are smaller, e.g., shorter, chained polymers, and thus have smaller molecular weights.

Lignin is a complex aromatic compound that contains methoxylated and nonmethoxylated phenyl propane chains, which are connected together by various types of bonds. The chemical structure of lignin varies between plant species, but it is believed that, in general, the monomer unit(s) of lignin includes a substituted styryl functionality, i.e., a substituted vinyl benzene unit, such as coniferyl alcohol, p-coumaryl alcohol, and sinapyl alcohol (See, e.g., S. Budavari, ed. (1989) "The Merck Index", 11th edition, Merck & Co., Rahway, New Jersey, p. 864, and references cited therein). It is presently understood that exposing wood to an electric field plasticizes the lignin and hemicellulose components. Additionally, the quantity of moisture present in the wood at the time of heating affects the transformation of lignin into a viscous or softened condition, i.e., plasticized state, and specifically affects the temperature at which this occurs. The type of wood used and the moisture content affects this temperature, which is in the range between about 60°C and about 150°C, and occurs at a pH between about 5.5-7.5. Lignin at temperatures within this temperature range are softened and thus diffuse more rapidly and exhibit increased mobility and tackiness.

It is believed that the lignin components do not condense until the wood attains a selected temperature within the same range of temperatures as defined above, e.g., between about 60°C and 150°C. Consequently, heating the wood to within this range results in softening of the lignin, as well as removing of lignin with the help of a pulping liquor.

The heating of the wood to within this temperature range and the application of high frequency energy softens the lignin components and severs the lignin-cellulose, lignin-hemicellulose, and lignin-lignin bonds. The severing of the lignin bonds allows for rapid and relatively easy removal of the lignin from the wood using conventional techniques, such as solubilizing the lignin with conventional liquors to reduce the lignin to relatively low molecular weight compounds. It is also believed that the softening of the lignin components also improves the absoφtion characteristics of the wood, thus enabling the treated wood to rapidly attain its saturation point when immersed in fluid in significantly short periods of time, since the cleavage of the bonds effectively increases the size of the pore passageway through which the fluid migrates. This greater effective size of the softened material thus presents a smaller impedance to the migration of water into the inner regions of the wood. The cleaved lignin components of the wood are also more easily solubilized and thus removed by conventional liquors, thus increasing the wood solubilization rate, and the fluid absoφtion rate of the wood. The enhanced absoφtion characteristics of the treated wood hence allows it to be more quickly digested within the digester 34 of the illustrated system and method. The heating of relatively dry ligno-cellulosic materials, e.g., wood having a moisture content less than 30%, requires the application of greater amounts of energy in order to plasticize the wood components. This occurs since much of the bound moisture is believed to be trapped by hydrogen bonding of the water molecules to the hydroxyl groups of the lignin and other wood components. The additional energy absorbed by the wood breaks these bonds. In operation, the wood is exposed to the high frequency field generated by generator 106 for a selected period of time, such as between about 0.5 min. and about 10 min. Those of ordinary skill will recognize that the selected time period can differ according to the type of ligno-cellulosic material, moisture content, parameters of the applied electromagnetic field, and volume of material. According to another practice, the power supplied by the generator can be varied during the heating process in accordance with the exigencies of the particular situation. For example, the amplitude of the voltage can be automatically varied by the control system in a selected range, such as about 30% during the plasticizing stage, to attain the appropriate softening temperatures. A significant advantage of the plasticizing stage of the invention is that temperatures in the range between about 55°C and about 150°C. and preferably between about 60°C and about 100°C, are sufficient to heat the ligno-cellulosic material to plasticize the lignin and hemicellulose components.

The wood can be further heated by other known methods, such as by the application of steam, since steam is readily available as a by product of the pulp and paper process. Hence, to decrease the energy consumed by the high frequency generator, the wood can be preheated with steam to a selected temperature, such as around 100°C, which is within the lignin softening temperature range. Additionally, the wood is treated for a relatively short period of time, e.g., from about 2 seconds to about 5 minutes, with a high frequency electromagnetic field. This period of time is shorter than the foregoing method which heats the wood using only the high frequency field. Such treatment provides a sufficient amount of energy to sever or cleave the lignin- carbohydrate linkage (bonds), thus achieving easier delignification and beating of cellulose containing materials.

The process can further include an optional compression stage 20 for compressing the heated wood to reduce the volume thereof. The objective of this stage is to improve the parameters identified in Figure 6. As illustrated in Figure 3C, the plasticized wood is transferred to a compressing mechanism for compressing the wood. The mechanical deformation of the plasticized wood ensures compression of the pores in the wood. This can be achieved through various mechanical means, some of which are illustrated. The compression stage 20 includes a hydraulic pressing machine 108 that includes two pairs of matched mechanical dies 110, 112 that compress the wood 4 in a direction illustrated by the arrows and, according to one practice, in a direction transverse to the grain of the wood. The compression of the wood can be controlled by controlling the hydraulic pressure applied to the wood work piece. The dies 1102, 112 are preferably in registration with one another and are hydraulically coupled to a hydraulic press (not shown). A power supply supplies the operating power to the press, and thus to the dies.. The plasticized wood article can be positioned between the matched dies by any suitable method, such as by hand or by known automated assembly techniques. Those of ordinary skill will recognize that any conventional pressing machine can be used in the practice of the present invention. Additionally, although a two-dimensional press is shown, those of ordinary skill will recognize that other types of pressing machines can be employed, including one-dimensional presses, and can include the illustrated roll-type press assembly 120 of Figure 3 A to mechanically compress the wood. Figure 3B illustrates the roll-type pressing assembly 120 that includes a hydraulic pressing machine that includes a pair of opposed rollers 122, 124 for compressing the wood in a direction illustrated by the arrows. The rollers are preferably in registration with one another and are hydraulically coupled to a hydraulic press (not shown). A power supply supplies the operating power to the press, and thus to the dies.. The plasticized wood article can be positioned between the matched dies by any suitable method, such as by hand or by known automated assembly techniques. The compression of the plasticized wood reduces the voluminous mass and intercellular space thereof. This reduction in wood air mass compresses together the microstructure of the wood. When the compressed and plasticized wood is disposed within fluid, the expansion of the wood draws the fluid into the pores of the wood, thus significantly increasing the absoφtion characteristics of the wood. This enables the wood to become saturated in a short period of time compared with untreated wood. Another advantage of treating the wood either prior to or during the treatment process is that it enhances the overall pulp yield since it allows for easier and more rapid removal of lignin from the wood. The foregoing heating/plasticizing and compression stages 18, 20 can also be performed on wood chips, as illustrated in Figures 3D through 3G. With reference to Figures 3D and 3E, two methods of subjecting the wood chips 6 to an electromagnetic field are illustrated. According to a first practice, the chips 6 are fed onto a moving conveyor or transport 130 by a feed bin 132. The chips pass between a pair of vertically extending electrodes 134, 136 that are connected to a high frequency generator 138 by suitable electrical leads. The electric field generated between the electrodes 134, 136 heat and plasticize the wood in accordance with the principles previously discussed.

According to an alternate practice, as illustrated in Figure 3E, the chips 6 supplied by a feed bin 132 are fed onto the transport 130 and pass beneath an electrode 140 supported above the belt 142 of the conveyor 130. In this embodiment, the transport belt is formed of a conductive dielectric material, i.e. graphite impregnated rubber, to form a second electrode. The electrodes 142, 140 are connected to a high frequency generator 138 by suitable electrical leads. With reference to Figure 3F, the electromagnetically treated wood chips 6 can then be transported to a compression stage 20. This stage can be realized by the use of various technological means, one of which includes a worm-type press 150 that has a second feed bin 152 that is positioned to receive the wood chips from the treatment stage 18. The heated and plasticized wood chips that exit the treatment stage 18 are fed into the feed bin 152, which captures the processed wood chips and introduces them into the worm press 150. The worm press 150 compresses the wood chips 6 by a rotating shaft 157 and then discharges them at an exit end 154 opposite the entrance 156. The compressed chips 6 are then fed onto a second transport assembly 160. In an alternate embodiment, as illustrated in Figure 3G, the worm press 150 is in fluid communication with the second feed bin and a pulping vessel or digester 160 that contains pulping liquor 162. The treated wood chips can be compressed in the presence of the liquor in - 16 -

the worm press 150, and then conveyed directly to the pulping vessel 160. Hence, this embodiment, which provides for the compression of the chips in the boiling liquor solution, ensures a faster and more efficient saturation of the chips.

With reference to Figure 1, the wood chips produced by the chipping process are then sorted by the screening stage 24. The wood chips are screened prior to introduction to the digester 34 to ensure that only ships of a selected size are digested. Conventional screening apparatus includes oscillating screens having a pass-through aperture of a selected size to aid in the sorting of chips by thickness. According to the conventional kraft cooking process, wood chips are sorted by thickness to remove overthick chips. The screening of the wood chips into selected sizes promotes uniform pulping, since large chips (e.g., particularly overthick chips) tend to undercook relative to the thinner chips, leaving large amounts of shards, while small chips tend to clog the chemical circulation system of the digesting process, use large amounts of chemicals, and result in a relatively low and mechanically weak pulp yield. The screened and sorted chips can then be subjected to either the high frequency treatment stage 18 or a combination of the high frequency stage 18 and the compression stage 20. The sorted chips can also be exposed to an additional electro- osmotic treatment stage 36 for treating the chips to enhance the absoφtion characteristics of the wood, as described below. Figures 4A and 4B illustrate another ligno-cellulosic treatment stage according to the invention. This method is preferably composed of two consecutive stages. The first stage consists of the electromagnetic processing of the chips by the previously described methods. The objective of this method is not only to improve the system parameters set forth in Figure 6, but also to create the proper conditions necessary for the electro-osmotic processing. The illustrated electro-osmotic system 36 is conducted in a channel or chamber 200 with insulated walls, on which electrodes 202, 204 are connected, the electrodes are connected to opposite poles of a high frequency generator 206. A pump 210 is coupled to the chamber 200 by suitable fluid conduits 212, 214, all connected as shown, the chamber can be divided into one or more subchambers by a partitioning wall 220. One or more valves 208 are coupled to the wall to allow fluid to pass between the subchambers.

The arrangement, shape and connecting scheme of the electrodes 202, 204 are chosen to ensure that the intensity of the electric field in the plane of the chips when in the chamber 200 always suφasses, in absolute value, some certain predetermined value, regardless of the direction of the intensity vector of the electric field in the plane. For example, alongside the axis of each element of the chips an electric field develops, which creates a flow of permanent cuπent of certain fixed density, and sufficiently strong to initiate the electro-osmotic processes within each element of the chips.

The physical nature of the electro-osmotic processing is schematically illustrated in Figure 5A and 5B, which show, in a somewhat simplified form, the ion electric double layer that exists on any inter-phase boundary, including the one between the solid base of the wood skeleton 240 and its pores 250, which in the original state of the wood is filled with various natural liquids (wood saps), and after exposure to this treatment with the solution 211. This electric double layer represents a system of oppositely charged ions, a portion of which are rigidly affixed to the skeleton, while the rest are distributed through the liquid and are mobile within the pore 250. A basic scheme of the oppositely-charged ions distribution inside the pores is illustrated in Figure 5B. The cuπent density (J) vector is also illustrated. The intensity of the electric field (E), which forms within the pores, characterizes the force acting upon the ions. Since the intensity of the electric field is in direct proportion to the current density (J), with the increment of the current's force (and consequently its density), the intensity of the field also increases and becomes sufficient to reallocate or move the ions at a certain speed V within the pores 250, as illustrated in Figure 5B. The moving ions attract the moisture or water located within the pore 250, thus moving the moisture with a certain speed V i < V. This movement of the pore moisture leads to the selected migration conditions where fluid, such as fluid 211 is drawn into the wood. For example, if the fluid 11 is a liquor solution, then the liquor is drawn into the pores of the wood. This process thus provides for a more intensive and deep saturation of the wood chips with the solution than with the use of the other methods.

Hence, the chips can be pre-processed in a particular solution bath to pre- soak the chips, or the electro-osmosis system can be integrated with the digester 34 by mounting appropriate electrode structure within a conventional digester, and then insulating the digester to prevent accidentally energizing the outer surface of the digester, other permutations of this apparatus would be readily recognized to the skilled artisan and is contemplated by the present invention.

With fiirther reference to Figure 1, the sorted wood chips formed by the chipping process are then cooked in the digester stage 34. The resultant pulp generated during the digesting or pulping stage 34 generally consists of ligno-cellulosic material that has been chemically broken down such that more or less discrete fibers, e.g., such as cellulose and hemicellulose, are liberated and dispersed in a liquid, such as water, and then formed into a web. The illustrated processing system is a chemical processing system, but the teachings are generally applicable to other processing methods, such as by mechanical paper processing systems. It is known that the more chemicals employed in the pulping process, the lower the pulp yield and lignin content since chemical action degrades and solubilizes selected components of the wood, especially lignin and hemicelluloses. On the other hand, chemical pulping yields individual fibers that are relatively free of abrasions and cuts (formed during mechanical pulping), and thus are capable of forming mechanically strong paper since the lignin, which tends to interfere with the hydrogen bonding between adjacent fibers, is largely removed. The illustrated digester 34 is filled with wood chips and cooking liquor

40 from a liquor supply source. The liquor can include fresh liquor, known as white liquor having active pulping species such as NaOH and Na2S, and black liquor, which is spent liquor from the digester which is recirculated via a waste liquor recovery system 48 into the digester 34. The digester 34 delignifies the ligno-cellulosic material, e.g., wood chips, by breaking down the chemical structure of lignin and rendering it soluble in a liquid, such as water. The prior treatment of the wood chips with the high frequency energy to sever the lignin-cellulose bonds simplifies the lignin removal process by reducing the need for prolonged digesting of the wood in the liquor. Additionally, the compression of the plasticized wood chips promotes the migration of solution into the wood chip, thus reducing the time it takes to saturate the chip and thus solubilize the lignin, resulting in time and cost savings. The wood chips can also be partially or completely saturated with the liquor through an electro-osmotic process to decrease the time it takes to saturate the wood chips.

According to one processing sequence, the digester is filled with wood chips, white liquor and black liquor. The liquor introduced to the digester during the pulping process is generally an aqueous solution of chemicals used for delignifying wood during this pulping process. The combined chips and liquor is then agitated, and additional chips are added as the contents within the digester settle. The digester is then sealed and heated using steam 41. The steam can be introduced directly to the digester, or can be introduced indirectly where the steam is passed through the inside of tubes mounted within the digester. Conventional cooking times last between about 20 and 45 minutes in conventional kraft pulping processes. During this heating time, air and other non-condensable gases emitted during the digesting process are vented from the digester. There is generally sufficient force present within the digester during the chemical pulping process to cause fiber separation. When the chips are properly cooked, as determined by the kappa number of the pulp resident within the digester, the content of the digester is discharged to an attached blow tank typically located at the end of the cooking cycle. Below the tanks are typically large, cylindrical vessels that receive the hot pulp discharged from the digesters. The heat of the hot gases from the blow tank are recovered by a blow heat accumulator, which is generally a large heat exchanger. This delignification process which occurs during the pulping process is an important stage since it removes lignin while retaining as much of the cellulosic material as possible. By treatment processes of the present invention enhance this fiber separation or reduce the time it takes to perform this fiber separation.

The pulp produced during digesting is then screened 42 to remove rejects 44, such as wood knots that do not sufficiently delignify during the cooking process and other improperly digested wood portions. Coarse screens are generally used during chemical processing to remove the rejects. The wood reject can be recycled fort further processing or can be removed from the system and destroyed or used as land fill. The treatment of the wood chips by the high frequency radiation, high frequency radiation and compression, or electro-osmosis reduces the amount of reject produced.

Specifically, treating the wood with radiation severs lignin- cellulose/hemicellulose bonds of the wood, thus enabling the lignin content to be more easily solubilized. Treating the wood with the electro-osmotic system of the invention enables the wood to be saturated faster and more easily. The chemical pulps are then generally refined after the cooking process to liberate individual wood fibers. During the illustrated chemical pulping process, this is relatively easily accomplished in the presence of the hot liquor, which is the basis of hot stock refining. The defiberating which occurs at this stage generally only separates the fibers for a thorough pulp washing, and the fibers must be further refined for paper making.

With further reference to Figure 1 , the screened chemical pulp is then washed 46 to recover excess chemicals, such as liquor, to recycle the liquor and to reduce the amount of potentially harmful waste that otherwise may reside in the pulp. The resultant screened and cooked pulp is then washed to remove process chemicals, such as the liquor used during the pulping process. The pulp is generally washed in rotary vacuum type washers that consist of a wire mesh covered cylinder that rotates in a tub of pulp slurry with valve aπangements to apply vacuum during the washing process. As the drum rotates, the pulp is pushed past wash showers where the pulp is washed with relatively clean water to displace the black liquor used during the digesting process. After washing, the pulp is further screened to remove shives, dirt and other contaminants to protect processing equipment as well as the pulp product. The liquor used during the pulping process is then recovered according to a chemical recovery process, illustrated by the waste liquor recovery stage 48. This process typically results in the recovery of the inorganic cooking chemicals, the generation of large amounts of heat energy by burning the organic materials derived from the wood, and the reduction of air and water pollution by converting the waste products into useful or at least harmless materials. The recovery process for conventional kraft pulping plants typically includes concentrating the black liquor by evaporation, and then combusting the evaporated black liquor to recover inorganic chemicals in the form of smelts. The smelt is then dissolved in water to form a green liquor, from which the white cooking liquor is prepared. This is typically done by converting the smelt, such as Na2CO3 to NaOH using Ca(OH)2, which is recovered as CaCoβ. Any byproducts from this process are then recovered, and typically include tall oil, energy and twpentine.

The washed pulp can also be subjected to one of the treatment stages 18, 20, 36 prior to introduction to the pulp bleaching stage 50 to either further sever bonds or to enhance the saturation of the pulp fibers.

The washed pulp is then subjected to the illustrated bleaching stage 50, where the pulp is mixed with bleaching chemical agents 52 to increase the pulp brightness. It is also known that enhancing the amount of lignin removed also increases the brightness of the pulp. Hence, the treatment stages 18, 20, 36 of the invention can enhance the brightness, if desired, by assisting in the further removal of lignin from the pulp, according to the methods set forth above. The use of strong bleaching chemicals, however, also decreases the length of the cellulose molecules, resulting in weaker fibers, hence, reducing the pulps exposure to these chemicals is desired. The treatment processes 18, 20, 36 facilitate this end since they provide for easier removal of lignin from the wood chips, thus reducing the overall lignin removal time and the amount of time the pulp has to be exposed to the bleaching chemicals.

Chemical bleach pulping is typically accomplished with various compounds containing chlorine or oxygen and alkali extractions in several stages. The use of 3 to 7 stages increases the efficiency of bleaching by reducing the amount of overall bleaching chemicals. This is due to the complex nature of lignin, and especially because each bleaching chemical reacts differently with lignin. Since lignin is a complex molecule with different types of linkages, the use of different chemicals break various types of bonds. For example, a large increase in brightness is achieved by using relatively small amounts of CIO2 in a later stage that could only be achieved using massive amounts of additional CI2 in an initial stage. The bleached pulp is then further refined in a refinishing stage 56 to develop its optimum paper making properties, which depend, of course, on the product being made. The refining of the pulp fibers before making paper increases the strength of the fiber to fiber bonds by increasing the surface area of the fibers, and by making the fibers more pliable to conform to each other, which increases the bonding surface area (to promote hydrogen bonding between the cellulose fibers of the mat) and leads to a denser sheet or mat. Most strength properties of paper increase with pulp refining since they rely on fiber to fiber bonding. The refining of pulp increases also increases the flexibility and density of the fibers and thus leads to denser paper. This means bulk, opacity and porosity values decrease with refining. The machines typically used during the refining process are called refiner devices and are typically machines that mechanically macerate and/or cut pulp fibers before they are made into paper, other machines include beaters which pass the pulp slurry through an oval tank around a midsection and passes between a revolving roll with bars. During the refining stage, the fibers are dried by removing water therefrom, the ability of remove water from the fibers is known as the freeness of the fibers, and increased freeness is generally desired. Pulp fibers generally low in lignin and high in cellulose/hemicellulose are relatively easy to refine, and thus the treatment of the pulp by stages 18, 20, 36 prior to the refining stage enhances this feature. With reference to Figure 2, the refined pulp is then converted into paper in a paper forming stage designated generally as stage 58. The refined pulp, which typically consists of a web of pulp fibers formed from an aqueous slurry on a wire or screen, are held together by hydrogen bonding. The fiber web formed on the screen is then drained to remove excess water and air dried over a hot surface. The pulp fibers are slurried within the aqueous slurry and mixed with selected additives. Typically, the slurry is treated to remove contaminants in any entrained air. The paper forming machine 60 typically is a device for continuously forming, dewatering and pressing, and drying a web of paper fibers. The most common type of paper machine used is the Fourdrinier machine which processes a dilute suspension of fibers, typically having 0.3% to 0.6% consistency, which is applied to a wire screen or plastic fabric. The pulp is applied to the screen at relatively low consistencies to give good formation, that is, an even distribution of fibers so the paper has uniform thickness. Water is typically removed by gravity.

The fiber web can also undergo one or more selected treatments, such as treatment stages 18,20 prior to coating, impregnating or laminating the fiber web, e.g., paper. The treatment dates convert the fiber into a more highly reactive form, thereby enhancing each fibers ability to bond with an adjacent fiber. The dried fiber mats are then trimmed as by trimming stage 64, or formed into the desired paper product.

As shown in Figure 1 , there are a number of different stages during the paper making process for treating the ligno-cellulosic product using various methods. The effects of all these treatments on the physical and chemical properties of the wood are summarized in Figure 6. Preferably, the treatment stages 18, 20, 36 are in the first two columns and coπespond to the treatment stages prior to or immediately after the chipping of the wood logs. Columns 3-5 coπespond to treatment systems 18, 20 and 36 that may occur immediately before digesting. The treatment stages 18, 20, 36 coπespond to columns 6-8 which may occur immediately after the washing stage 46. The last two columns coπespond to the treatment stages 18, 20 that may occur during the paper formation stage 58.

As a result of testing performed on raw materials by the foregoing methods, a significant improvement in the parameters set forth in Figure 6 have been observed.

The foregoing treatment methods can also be realized by using other specialized electromagnetic generators, such as ones that generate a propagating or modulated propagating field within the ligno-cellulosic material.

The effects on the ligno-cellulosic material when subjected to one or more of the following methods are set forth below in the following non-limiting examples.

EXAMPLES

Example 1 Water Absoφtion Characteristics Of Treated Wood

The effects of the preliminary treatment of wood according to the teachings of the present invention, such as by high frequency energy and high frequency/compression, on the water absoφtion behavior of the wood were evaluated.

Two wood samples were prepared starting from a single piece of air dried Douglas Fir. The first sample was untreated and used as a reference. The second sample was subjected to electromagnetic treatment followed by mechanical deformation. Both samples were then soaked in a water bath maintained at 36°C.

As can be seen in Table 1 below, the wood treated with high frequency energy, such as by an electromagnetic field at 27 MHz and compressed under pressure at 80 kg/cm^ exhibits rapid absoφtion of water compared to the untreated reference wood.

The heating of the wood by the high frequency energy softens the lignin components and severs the lignin-cellulose, lignin-hemicellulose, and lignin-lignin bonds. It is believed that the softening of the lignin components improves the absoφtion characteristics of the wood since the cleavage of the bonds effectively increases the size of the pore passageway through which the water migrates. This greater effective size of the softened material thus presents a smaller impedance to the migration of water into the inner regions of the wood. Hence, the water is more easily absorbed by the treated wood, thus enabling it to rapidly attain its saturation point when immersed in water in significantly shorter periods of time.

Table 1 Influence of preliminary treatment of wood by high frequency electromagnetic field and mechanical compression on its water absoφtion qualities.

Ratio of the

Time for amount of water water absorbed by the absorption Weight of the Amount of absorbed water, original and the

(min.) samples, g g (g/min.) pretreated wood samples

Original Pretreat Original Pretreated wood ed wood wood wood

0 29.0 29.4 - - -

2 32.0 41.8 3.0 (1.5) 12.4 (6.2) 1: 4.1 (1:4.1)

8 33.2 55.0 4.2 (0.2) 25.6 (2.2) 1 :6.1 (1:11)

17 34.1 59.8 5.1 (0.1) 30.4 (0.55) 1:6.0 (1:5.5)

The wood samples were not completely dried, and had an original moisture saturation of about 54%, noting that the calculations account for the original moisture content of the samples at 6%, close to full saturation. The above information set forth in Table 1 illustrates that the untreated, reference piece of wood did not absorb any appreciable amounts of water. For example, after 17 minutes, the pretreated wood absorbed 30.4 grams of water in 17 minutes compared to 5.1 grams for the reference piece of wood. Hence, the treated wood is nearly saturated with water, while the sample in the original form will be absorbing water for many more hours, and possibly for more than 24 hours

Also, columns 4 and 5 of Table 1 show the difference in speed, designated by the values in parentheses in g/min, of the water absorbed by the treated and untreated wood samples. The values in these columns illustrates that the initial rate of water absoφtion is over 4 times faster than the untreated sample after 2 minutes. The rate of absoφtion of the treated sample is reduced only because the pre-treated sample is nearly saturated and is incapable of absorbing water at the original speed.

On the other hand, the speed of absoφtion by the original sample

(column 4) is continuously decreasing, though the wood remains well below full saturation. This situation is caused by air entrapped in the porous structure of the original wood, whereas in the pretreated and compressed wood this air has been removed.

The values within parentheses in column 6 represent the ratio of the values in parentheses in columns 4 and 5. This example illustrates the marked reduction in time that the treated wood takes to reach full saturation, e.g., significantly increased water absoφtion characteristics, as compared to an untreated wood sample.

The method and system of the invention when employed prior to common chemical treatments (in the production of pulp & paper, cellulose for chemical processing, paperboard, etc.) increases the pulp yield, and lowers the amount of chemicals and energy consumed by the delignification and bleaching processes, without degrading the quality of the final products. The present invention also results in a notable decrease in the use of harmful reactants in various stages of the production of paper and paperboard, which leads to lower concentrations of harmful chemicals in the environment and to lower environmental costs.

Example 2 Pulping Douglas Fir

This example illustrates the benefits and advantages of the treatment of wood according to the teachings of the present invention on a laboratory scale. Three pieces of air dried Douglas Fir were treated as follows:

A first wood sample (A) is the reference piece and was subjected to any of the treatment processes of the present invention. The second sample (B) was exposed to a high frequency electromagnetic field (27 MHz, 4.0 kV) for 3-5 minutes. The third sample (C) was exposed to a high frequency electromagnetic field (27 MHz, 4.0 kV) for 3-5 minutes and then compressed at a pressure of 80kg/cm .

For the puφose of this example, wood chips were produced on site and were cut with a guillotine knife to the following size: a length of about 20 mm, a width of about 15 mm, and a thickness of about 2-3 mm. The samples were then stored in polyethylene sacks to allow equilibration of moisture content to between about 9-11%. All three samples were then pulped under strictly identical conditions. The wood chips were weighted, allowing for moisture content. Then they were placed into an autoclave having a volume of about 350 ml, a white sulfate liquor was added having an effective alkali (EA) content of 100 g/l and sulfidity of 25% (Na2θ units). Wood-to-Liquor ratio was 1 :4. The EA was 18% in units of Na2θ, based on the weight of oven dried (O.D.) wood. The autoclaves were placed directly in a glycerol bath with temperature 170°C without preliminary heating. This temperature was maintained throughout the cooking. The bath had systems for circulating and heating the glycerol, and the autoclaves were rotated to ensure uniform temperature and liquor concentration inside of autoclaves. Every 30 minutes a subsample of A, B, and C was removed for analysis.

The results of this example are set forth below in Table 2. As is illustrated by the acquired data, the treatment of wood sample B and especially wood sample C considerably increased the delignification rate, decreased the quantity of reject, and provided a more uniform cooked pulp.

The wood treatment, e.g., application of high frequency energy and compression resulted in increased amounts of pulp with significantly fewer amounts of reject. This thus illustrates that the delignification process was substantially enhanced, since the high frequency energy severed the lignin bonds within the wood sample.

Table 2 also illustrates that despite the resultant lower kappa numbers (lignin content of the pulp) of the pulp from the treated wood, the pulp viscosity, which is a measure of the average chain length (polymerization) of the cellulose fiber, is within acceptable industry defined limits. Those of ordinary skill will recognize that a higher viscosity value indicates a stronger fiber, and thus by maintaining the viscosity within industry defines limits ensures relatively strong pulp and paper. The kappa number can be varied according to known techniques and the present invention contemplates variations in the kappa number (higher or lower) depending upon the exigencies of the situation.

In the last column, the active alkali content indicates that larger mounts of active alkali remain in the liquor after cooking of the wood, which indicates that the lignin was more easily removed from the treated wood than from the untreated wood. This is significant since the amount of liquor used during the cooking or digesting process can be reduced, or more of the liquor can be recycled, thus reducing the costs of the pulp and paper process. Table 2. Influence of Pretreatment of Douglas Fir on the Results of Cooking.

n Pulp

Duration of Viscosity in Active Alkali

Cooking at Yield of Quantity of Copper- in the Black

I70°C Sciecnccl Wood Reject Total Yield Ammonia Liquor

Wood (minutes) Pulp (%) (col 2 +3)% Kappa Solution, (g Na₂0)

Sample (%) Number (mPasec)

1 30 0 632 632 115 - 17.2

Λ 60 294 307 601 66 54.5 127

(Reference) 90 33.5 211 54.6 45 57.0 115

120 39.1 11.5 50.6 41 55.9 8.2

2 30 0 - - 108 - 14.3 I M σ>

B 60 328 243 57.1 61 - 10.9 I

90 348 169 517 44 545 94

120 382 100 482 405 51.8 7.8

3 30 0 - - 8 - 12.1

C 60 459 25 484 58 69.1 11.2

90 452 04 456 41 582 108

120 44.5 00 445 36 513 10.5

Note: Kappa Number determined in screened pulp

Table 3. Influence of Pretreatment on Douglas Fir on the Properties of Pulp.

Factors A B C

(Reference)

Pulp yield (%) from O.D. wood 43.0 43.1 41.7

Reject (%) 2.8 3.0 0.1

Kappa Number 29.9 31 22.2

Brightness 14.5 14.9 16.6

Freeness 58 58 60

Beating Time (minutes) 52 37 34.5

In another experiment, the same 3 samples of chips, A, B, C, the same autoclaves, the same glycerol bath, and the same cooking temperature (170°C) as above were used, but the duration of pulping was increased to 150 minutes and the consumption of effective alkali was increased by 20% based on the mass of oven dried wood. The results of are set forth above in Table 3. The data in Table 3 show the pulps obtained from samples B and C are significantly easier to beat and therefore consume considerably less energy for this process. The amount of reject for sample C is significantly less than (almost 28 times) the reject produce from the reference wood sample, without significantly affecting the brightness or freeness of the pulp. Those of ordinary skill will recognize that freeness is the rate at which water drains through the pulp. If this rate is relatively slow, then the pulp takes longer to dry, thus slowing the papermaking process. ln a last portion of this example, the same 3 samples of chips (A, B, C), the same autoclaves, the same glycerol bath, and the same cooking temperature (170°C) as in the first two experiments were used, but the temperature was increased from room temperature to 170°C was accomplished over a period of 90 minutes. The alkali charge (EA) was the same 20% based on O.D. wood. Subsamples were taken and analyzed after 80,120, and 150 minutes of pulping. The resultants are set forth below in Table 4. Table 4. Influence of Pretreatment on Pulp Quality.

Number of Cooking time, Total yield/ Kappa Number Pulp viscosity., sample minutes reject, % mPasec

80 44.8/2.9 32.9 66.3

A 120 42.7/0.7 25.5 53.6

150 41.9/0.6 24.4 49.1

80 44.1/1.7 32.2 73.6

B 120 42.0/0.9 - -

150 41.9/0.4 23.5 48.2

80 42.9/ - 28.4 60.0

C 120 41.4/ - 22.2 42.7

150 41.3/ - 21.3 41.8

The data in Table 4 shows that pretreatments B and C accelerate the pulping process, e.g., decrease the pulping time, decrease the quantity of reject produced during cooking, while pulp viscosity remains at an industry acceptable level.

The unbleached pulps A, B, C after pulping for 150 minutes were then bleached according to known techniques. The pulps formed from the treated wood samples (B and C) were highly reactive with hydrogen peroxide and chlorine dioxide. Additional experiments showed that wood sample C produced wood chips with a low specific volume. This gives the possibility of filling the digester with 20-40% more wood. This last finding is very important for the more effective use of pulping equipment, especially when cooking soft wood with low specific density. Hence, the treatment processes of the invention significantly impact the cost- effectiveness of the pulp and paper processing method and system by reducing the costs associated with digesting (reducing digesting time and liquor waste), and increasing the ability of the digester to process more wood in the same amount of time.

Example 3 Additional Pulping of Douglas Fir. For this example, samples of air dry Douglas Fir 100 x 100 x 300 mm were used. The samples were treated for 3 minutes with a high frequency electromagnetic field (frequency 27 MHz and field Voltage 4 kV). Then the samples

2 were pressed at a pressure of about 80 kg/cm (samples TR). Chips were then cut from these samples. Chips were also cut from untreated pieces of Douglas Fir (untreated samples UTR). Both treated and untreated samples were cooked in 5 liter autoclaves that were rocked 20 times per minute through 270° to ensure mixing of the chips and kraft liquor. The Liquor-to- ood ratio was 4:1. Initial effective alkali (EA) charge was 19.2% NaOH. White liquor sulfidity was about 30%. EA consumption on wood was 14.0-14.7%; and H-factor was between about 1006-1042. The heating time to 110°C was 15 minutes. The temperature was maintained at 110°C for 30 minutes, then increased to 170°C over 30 minutes and maintained at 170°C to the target H-factor. The results of this example (averaged from two parallel cooks) are set forth below in Table 5.

Table 5. Influence pretreatment wood on the delignification process.

Name of index UTR Pulp TR Pulp

H-F actor 1020 1021

Total Yield, % 56.2 51.2

Reject, % 20.6 7.4

Screened Pulp, % 35.6 44.1

Kappa Number 50.7 50.2

Viscosity, mPa sec 55.8 63.6

UTR chips were presteamed before pulping. TR chips were not presteamed.

Table 5 shows that despite the elimination of presteaming before delignification, the pulp from the treated chips produced a much higher yield of screened pulp, 44.1% compare 35.6%, and a higher viscosity, 63.6 versus 55.8 mPasec, although both pulps were cooked to practically the same Kappa Number. This last result confirms that pulp from the treated wood samples has superior physical - mechanical properties when cooked to the same Kappa Number.

Example 4 Pretreatment of White Pine Chips

White Pine chips with 50% moisture content were used for this example. Chips were treated in a high frequency electromagnetic field having a frequency of 27 MHz and a voltage between about 1.7-2.0 kV for 22 minutes (TRI ); a voltage between about 3.8-3.9 kV for 3 minutes (TR2); a voltage between about 3.8-4.0 kV for 8 minutes (TR3); and a voltage between about 3.8-3.9 kV for 1.5 minutes (TR4). The cooking regime was the same as that set forth in Example 3. The conditions and results of theses experiments are presented below in Table 6. Table 6 The influence of the treatments of the invention on the delignification process and pulp properties of White Pine chips.

Name of index TR I TR 2 TR 3 TR 4 Reference

EA consumed, % 14.7 14.2 14.0; 14.1 14.1 ; 14.7 14.1; 14.2; 14.0; 14.0 on wood total

Residual EA g l 12.3 12.5 13.1. 12.7; 11.2 12.7; 12.5; 13.1; 12.9

NaOH end of cook 12.8

H-factor 1006 1014 1042; 1005; 1016 1027; 1005; 1027; 1007 1023

Kappa Number 45.7 50.1 47.7; 49.8 50.2; 53.0; 50.3; 49.1 ; 48.9; 50.6

Total Yield, % on 50.2 49.3 49.1 ; 49.6 49.3; 50.9 47.5; 47.7; 47.4; 48.1 wood

Rejects, % on 1.61 1.15 1.83; 1.13 0.50; 1.18 0.38; 0.83; 0.55; 0.72 wood

Screened Pulp 48.6 48.2 47.2; 48.5 48.8; 49.7 47.1 ; 46.8; 46.8; 47.4

Yield, % on wood

ISO Brightness, % 25.2 25.0 21.6; 21.1 21.0; 18.6 19.7: 20.8; 19.7; 19.6

Note: Two cooks of reference material were made with presteaming but all others were without presteaming.

Table 6 shows that for all variants of pretreatment the total yield of screened pulp is increased by an amount between about 1.5-2.0 % compared with the reference wood sample. This means an increase of pulp yield of between 3% - 4% relative to total pulp yield. It is also seen from Table 6 that the pulp obtained from chips treated according to any of the presses of the invention (HF, HF/compression, electro- osmosis) has an increased ISO Brightness between about 1.5-5.0%. The last result is very important as it suggests decreased bleaching of the pulp may be required, reducing the cost and the ecological problems of pulp production.

Example 6. Additional Treatments with White Pine Chips

White Pine chips (50% moisture content ) were utilized in this example. Part of the chips was treated with an HF electromagnetic field between electrodes with a frequency of 27 MHz for 3.0 minutes and a voltage of between 0.4-0.6 kV (TR 5); over 5 minutes with a voltage of 0.4-0.6 kV (TR 6); and over 3.5 minutes with a voltage of 1.2-1.5 kV (TR 7). All samples were cooked using the conditions described in Example 3 with H- factors of 1000-1020. All pulp samples after pretreatment had Kappa Numbers of 46-51 versus 55 for the reference. Total yield was 49-51% versus about 50% for the reference. These results confirmed the findings of increased yield and digesting and cooking speed after application electromagnetic field pretreatment.

It will thus be seen that the invention efficiently attains the objects set forth above, among those made apparent from the preceding description. Since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. It is also to be understood that the following claims are to cover all generic and specific features of the invention described herein, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described the invention, what is claimed as new and desired to be secured by Letters Patent is:

Claims

1. A method for producing pulp or paper from ligno-cellulosic material having a lignin component bonded to a cellulose component, comprising the steps of

exposing the ligno-cellulosic material to high frequency radiation for rendering the lignin component of the material to a selected plastic condition and to severe a substantial portion of the lignin-cellulose bonds of the material, and

digesting the plasticized ligno-cellulosic material in the presence of a liquor to separate the lignin component from the cellulose component of the material,

whereby the severing of the ligno-cellulosic bonds by the high frequency radiation enhances the separation of the lignin component from the cellulose component.

2. A method in accordance with claim 1 , further comprising the step of compressing the ligno-cellulosic material while in said plastic condition to reduce the volume of the material.

3. A method in accordance with claim 2, wherein said step of compressing comprises the step of compressing the material along at least one axis thereof.

4. A method in accordance with claim 2, further comprising the step of enhancing the absoφtion characteristics of the ligno-cellulosic material.

5. A method in accordance with claim 2, wherein said step of digesting further comprises the step of forming a pulp from the ligno-cellulosic material.

6. A method in accordance with claim 5, further comprising the step of screening the pulp to remove reject.

7. A method in accordance with claim 1 , further comprising the steps of forming a pulp from the ligno-cellulosic material, and washing the pulp to remove any excess liquor.

8. A method in accordance with claim 5, further comprising the steps of forming a pulp from the ligno-cellulosic material, and bleaching said cellulose fiber to a selected brightness.

9. A method in accordance with claim 8, further comprising the step of forming paper from said bleached cellulose fiber.

10. A method for producing pulp or paper from ligno-cellulosic material having a lignin component bonded to a cellulose component, comprising the steps of

digesting the ligno-cellulosic material in the presence of a liquor to separate the lignin component from the cellulose component of the material to form a pulp, and

exposing the pulp or paper to high frequency radiation for severing a substantial portion of the cellulose-containing bonds between any remaining cellulose- containing components of the material.

whereby the severing of the bonds of the cellulose-containing material by the high frequency radiation further enhances the separation of the lignin component from the cellulose component.