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WO1999004087A1 - Produits de pate, de papier et absorbants presentant une concentration en poix reduite et procede d'obtention - Google Patents

Produits de pate, de papier et absorbants presentant une concentration en poix reduite et procede d'obtention Download PDF

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Publication number
WO1999004087A1
WO1999004087A1 PCT/US1997/012461 US9712461W WO9904087A1 WO 1999004087 A1 WO1999004087 A1 WO 1999004087A1 US 9712461 W US9712461 W US 9712461W WO 9904087 A1 WO9904087 A1 WO 9904087A1
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WO
WIPO (PCT)
Prior art keywords
wood
pitch
particulates
pulp
solvent
Prior art date
Application number
PCT/US1997/012461
Other languages
English (en)
Inventor
Jerry R. Speaks
Roger O. Campbell
Michael A. Veal
Original Assignee
North Pacific Paper Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by North Pacific Paper Corporation filed Critical North Pacific Paper Corporation
Priority to AU36692/97A priority Critical patent/AU3669297A/en
Priority to PCT/US1997/012461 priority patent/WO1999004087A1/fr
Publication of WO1999004087A1 publication Critical patent/WO1999004087A1/fr

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Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/08—Removal of fats, resins, pitch or waxes; Chemical or physical purification, i.e. refining, of crude cellulose by removing non-cellulosic contaminants, optionally combined with bleaching
    • D21C9/086—Removal of fats, resins, pitch or waxes; Chemical or physical purification, i.e. refining, of crude cellulose by removing non-cellulosic contaminants, optionally combined with bleaching with organic compounds or compositions comprising organic compounds
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C1/00—Pretreatment of the finely-divided materials before digesting
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
    • D21H27/16—Pure paper, i.e. paper lacking or having low content of contaminants

Definitions

  • the invention relates to a fibrous cellulosic pulp of reduced pitch and volatile organic compound content from which paper and absorbent products of reduced pitch content are produced. More particularly, according to the invention, wood particulates are subjected to a solvent extraction process that removes significant amounts of pitch and volatile organic compounds, as well as other wood extractives, from the wood particulates without significant dissolution of lignin and cellulosic components from the particulates. The particulates are then subjected to a pulping process to produce pulps of reduced pitch content.
  • the pulping process may be either chemical or mechanical. These pulps are processed into paper and absorbent products of reduced pitch content.
  • wood can be viewed as consisting of two major components, carbohydrates and lignin. Other components constitute a minor part of the wood and manifest as intercellular material, and extraneous substances that are related to the growth of the cells of the tree.
  • the cell walls of the wood are composed of polysaccharides, the chief of which is cellulose.
  • Lignin is an amorphous substance, partly aromatic in nature, that has been called a "cementing material” or an "encrusting substance.” It is insoluble in water and in most common organic solvents. It is also insoluble in acids, but undergoes condensation reactions in the presence of strong mineral acids. Lignin is partly soluble in alkaline solutions and is readily attacked and solubilized by oxidizing agents.
  • the extraneous substances of wood are deposited as cells grow, or after they reach maturity. Most of these substances are relatively simple compounds, having a low molecular weight. These low molecular weight substances include pectins, proteins, and like substances that are soluble in water or neutral organic solvents.
  • the extraneous substances also include "wood extractives" that include pitch and volatile organic compounds. These naturally-occurring wood extractives are found in both resin canals within the structure of the wood, as well as within the parenchyma cells of the wood. To produce pulp, paper and absorbent products, raw logs or wood fibrous material must be reduced to wood chips, flakes or sawdust.
  • wood particulates are then further processed by undergoing pulping and/or forming processes to produce a variety of papers and absorbent products.
  • processing of logs into wood particulates, and thence into finished products poses several challenges. Some of these arise from the nature of wood, namely, that it includes not only cellulosic fibers and lignin but also "wood extractives,” as discussed above. These naturally occurring wood extractives are found in both resin canals within the structure of the wood, as well as within the parenchyma cells of the wood.
  • wood extractives may be divided into a higher molecular weight, higher boiling point fraction, commonly known as "pitch", and a lower molecular weight, lower boiling point fraction that falls within the definition of "volatile organic compounds.”
  • VOCs volatile organic compounds
  • the United States Environmental Protection Agency (EPA) has determined that volatile organic compounds (VOCs) pose an environmental hazard when they are released into the atmosphere. These VOCs are defined in 40 CFR Part 51(s) as "any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate, which participates in atmospheric photochemical reactions.” Typically, these are volatile low molecular weight organic compounds.
  • the EPA has promulgated regulations limiting the quantity of VOCs that a manufacturing facility may release into the atmosphere.
  • pitch poses processing and product quality issues in the pulp and paper industry.
  • the pitch separates from the cellulosic fibers to form a colloid-like suspension that gradually deposits to build up a scale within the process equipment and ducting of the mill.
  • the pulp mill must be shut down so that this pitch scale may be manually removed.
  • pitch scale control chemicals such as sodium aluminate and alum, are added to the pulping process. While this strategy is partially successful in that it alleviates the equipment fouling problem, it does not eliminate all the problems caused by pitch. Indeed, the addition of scale control chemicals also poses a waste disposal problem since these chemicals are present in the process water. Although this water is recycled, a portion must be treated and disposed of. This, of course, entails additional operating costs for treatment chemicals, labor and facilities.
  • VOCs occur naturally in timber and the processing of timber into wood particulates facilitates the migration or diffusion of VOCs to particulate or chip surfaces from which the compounds vaporize into the surrounding atmosphere.
  • significant amounts of VOCs are released into the atmosphere from wood chip storage piles. Further, as illustrated in FIGURE 1, VOCs are also released into the atmosphere during the processing of the wood chips into paper and pulp products.
  • VWE volatile wood extractives
  • the cellulosic pulp produced may be bleached, such as by a chlorine or non chlorine based bleaching process, and is then formed into a continuous web and dried on a pulp drier or paper machine 14'. During these processes, a further significant amount of VOCs is released into the atmosphere.
  • the combined chipping, crushing, pulping, and paper or absorbent product making processes release about one-third of the total natural extractives in the wood into the atmosphere (shown by arrows 2', 4', 6', and 8') as VOCs, and another one-third into effluent water (arrows 20', 22' and 24').
  • the papermill product 15' such as newsprint, writing paper, or absorbent products, includes the residual of about one-third of the total amount of extractives, mainly pitch with low amounts of VOCs.
  • the amount of extractives, and VOCs, in wood varies depending upon several factors including wood species, age, and season of felling. However, chips may be expected to contain from 1 to 6 wt.% VOCs. While the percentage of VOCs released into the atmosphere may appear small, relative to wood particulate mass, the actual quantity is nevertheless very significant. For example, a facility may process about 1,000-6,000 tons of wood chips per day. A 6,000 ton per day facility could, therefore, emit as much as 120 tons of VOCs daily. The EPA proposes limiting the amount of VOCs that any wood chip processing facility releases into the atmosphere by regulations requiring permits.
  • Removing the gum can require shutting down the papermaking machine, chemical cleaning or removing the clothing, and cleaning all affected roll surfaces. This results not only in cleaning costs and paper wastage losses, but also in significant machine downtime with consequent economic loss.
  • Other methods of treatment include the use of continuous cleaning chemicals and equipment. Some of these chemicals may contribute to the release of VOCs and compositions with high biological oxygen demand (BOD) and/or high chemical oxygen demand (COD) into the environment.
  • BOD biological oxygen demand
  • COD chemical oxygen demand
  • a portion of the pitch vaporizes and later condenses to form a pitch scale that includes a gummy, sticky deposit that fouls the pulping equipment.
  • the fouling reaches a point that a shut down of the mill is required so that the pitch scale may be manually and/or chemically removed.
  • cellulosic fibers produced in a mechanical fiberizing step is combined with sufficient water to produce a pumpable slurry ("stock") of fibers that can then be transported to additional processing equipment (screens, cleaners, and bleaching facilities).
  • the stock is then formed into paper or other absorbent products or a useful pulp.
  • these fibers, and water used to transport the fibers contain pitch that was released from the wood chips during the fiberizing process. This pitch causes significant equipment fouling problems in papermaking machines where the stock is formed into a continuous web on high speed fabrics used to dewater the stock. The web is then dried to complete the papermaking process.
  • colloidal pitch carried in the slurry gradually deposits onto the rolls and machine "clothing" of the papermaking machine to form a tacky, gummy surface deposit.
  • This deposit ultimately results in reduced pulp or product quality and machine efficiency.
  • Removing the gummy deposit can require shutting down the papermaking machine, chemical cleaning of the clothing, often requiring removing of the clothing, and cleaning all other affected surfaces. This results not only in cleaning costs and paper wastage losses, but also in significant machine down time.
  • Other methods of treatment include the use of continuous cleaning chemicals and equipment. However, some of these chemicals may contribute to the release of VOCs and compositions with high biological oxygen demand (BOD) and/or high chemical oxygen demand (COD) into the environment.
  • BOD biological oxygen demand
  • COD chemical oxygen demand
  • the invention provides paper and absorbent products made from wood pulps that have reduced pitch content and a process for producing these products.
  • the invention provides a paper pulp of superior strength properties, brightness and optical properties, without loss of yield.
  • the invention includes a process that includes a wood pulping stage and a paper forming stage that have substantially reduced emissions of naturally-occurring volatile organic compounds from wood.
  • Pulps manufactured in accordance with the invention have a reduced pitch content. These reduced pitch content pulps substantially reduce or eliminate the formation of gummy, tacky deposits on pulp and papermaking equipment during the manufacturing of the pulps and the processing of the pulps into paper or absorbent products.
  • wood particulates are contacted with a solvent for pitch and VOCs.
  • the solvent extracts a substantial portion of both the pitch and VOCs from the particulates, and is separated as a "miscella" from the leached wood particulates.
  • the extraction removes from about 50 to about 100 wt.% of the VOCs present in the raw wood particulates. Further, the process also removes from about 40 to about 85 wt.% of the pitch.
  • the miscella including solvent, water, VOCs, and pitch, is subjected to a separation process that reclaims solvent for reuse in the extraction process.
  • the leached wood particulates, now having substantially reduced pitch and VOC contents, are then subjected to chemical or mechanical processes for the production of pulp, with significantly reduced emissions of VOCs and significantly reduced amounts of pitch. Pitch fouling of the equipment in the pulping process is reduced or substantially eliminated.
  • the pulps, having a reduced pitch content, are then formed into paper and absorbent products on forming and drying machines, without the attendant pitch deposits that occur in prior art.
  • the invention provides a superior paper product that is formed from a mass of cellulosic fibers and that has a pitch content at least about 40% less than an expected pitch content, based on the naturally-occurring pitch content of its wood of origin.
  • the product has superior burst index, tear index, tensile index, Scott Bond, Sheffield Smoothness, stiffness and stretch.
  • the removal of pitch from wood particulates provides brighter wood particulates that resist age-darkening. This allows the production of pulp of higher brightness, thereby reducing the demand for chemical bleaches.
  • the product is also of higher density and porosity (seconds/ 100ml).
  • the product is more oleophobic (i.e., less attractive to oils), but can be produced to a predictable degree of oleophobicity. This facilitates subsequent chemical treatment to control oleophilicity to a desired level for particular products.
  • Such products of specified oleophilicity are advantageous in certain printing applications, where the inks are oil-based or oleophilic.
  • the invention solves long-standing problems of VOC emissions and pitch fouling of equipment by removing pitch from the wood particulates before the pulping step.
  • the invention allows the virtual elimination of pitch scale formation in pulp mills, and on pulp and papermaking machines. This results in significant improvements in mill efficiencies and permits reduced use of pitch treatment chemicals, in pulp processes and process water, that pose a disposal problem.
  • wood- containing (commonly known as "mechanical") pulps of superior optical properties (i.e. appearance) the invention reduces the demand for chemical bleaches.
  • the invention reduces the BOD and COD of process water, alleviating the need for post environmental treatment.
  • the process also reduces the volume of black liquor produced per ton of pulp thereby debottlenecking liquor recovery systems, in particular the recovery boiler, while also allowing energy savings.
  • FIGURE 1 is a schematic block flow diagram of wood chip processing showing VOCs emissions in a papermaking process
  • FIGURE 2 is a schematic flow diagram of an embodiment of the process of the invention for pitch and VOC removal from wood chips;
  • FIGURE 3 A is a schematic diagram of an embodiment of a chip extractor of the invention.
  • FIGURE 3B is a schematic diagram of another embodiment of a chip extractor of the invention.
  • FIGURE 3C is a schematic diagram of another embodiment of a chip extractor of the invention.
  • FIGURE 3D is a schematic diagram of another embodiment of a chip extractor of the invention.
  • FIGURE 4 is a schematic flow-type diagram of an embodiment of a chemical pulping process of the invention.
  • FIGURE 5 is a schematic process flow-diagram of an embodiment of a mechanical pulp mill process of the invention.
  • FIGURE 6 is a schematic diagram of an exemplary papermaking machine for processing reduced pitch content pulp of the invention into paper or absorbent products, showing the paper forming, pressing and drying sections, in simplified form.
  • the invention provides pulp, paper and absorbent products of enhanced properties. Further, the invention provides a process for making these products that is virtually free of volatile organic compound emissions (or at least have substantially reduced emissions, depending upon the proportion of VOCs extracted) and that is substantially free of pitch-related operating problems.
  • the reduced pitch content pulps have enhanced brightness, bulk, tear, tensile and burst strength, and folding endurance.
  • the process of the invention uses an extractive solvent, that is either a single liquid chemical compound or a mixture of such compounds, for dissolving and removing wood extractives from wood particulates suitable for use as charge stock in pulp and paper operations before the pulping operation.
  • wood particulates refers to wood chips, shavings, sawdust, flakes, and other such solid wood in particulate form. It should be understood, that although the following descriptions may refer to “wood chips,” the process of the invention is equally applicable to other wood particulates.
  • wood extractives refers to VOCs and pitch, and is measured as the extractives removed from wood using an ether soxhlet extraction in accordance with TAPPI Standard Test No. T204 om-88, modified to use diethyl ether as a solvent. This test does not distinguish between VOCs and pitch but measures both as ether extractables of the wood.
  • the percent wood extractives removed by the extraction process of the invention is arrived at by measuring the difference between the ether wood extractables in samples of the wood particulates before and after undergoing the extraction process of the invention. At the outset, it should be understood that wood extractives form a continuum in the sense of ranging from lower to higher boiling point components.
  • VOCs volatile wood extractives
  • VOCs and volatilized wood extractives are removed by extraction from the wood particulates.
  • significantly reduced pitch content with reference to extracted wood particulates means that at least about 40% of the naturally-occurring pitch has been extracted from the wood. Preferably, 40 to 85%, and more preferably 45 to 75%, of the pitch is extracted.
  • the amount of pitch extracted is inferred from measurement of the wood extractives contents before and after extraction by the step of the process of the invention. While the difference between these two measurements is the total amount of ether extractable removed, compensating for the amount of VOCs removed (described below) provides an estimate of the pitch removed.
  • substantially reduced VOC content referring to the extracted wood particulates or the wood particulates used for mechanical or chemical pulping, means that at least about 40 wt% of naturally occurring VOCs have been removed by extraction, preferably from about 50% to 100%, and most preferably from about 75% to about 95%.
  • the percentage of VOCs extracted from wood particulates is estimated by subjecting the extracted wood particulates to an oven-heating procedure at 105°C for 24 hours.
  • the loss of weight of the wood particulates corresponds to the residual VOCs remaining in the extracted particulates.
  • the quantity of VOCs in the raw particulates, before extraction may be estimated by heating the particulates to 105°C for 24 hours.
  • the proportion of VOCs extracted may readily be estimated from the measured amounts of VOCs before and after extraction.
  • the amount of pitch extracted may be found by difference, since the total amount of wood extractives before and after extraction are determined by the TAPPI method.
  • the solvent used in the extraction process of the invention is of a type that can be recycled for reuse in the process.
  • the extractive solvent either does not form an azeotrope with water, or forms only a minimal azeotrope.
  • the solvent is applied to raw wood particulates that have not undergone a drying treatment to remove water, and consequently commingles with water. This process is preferred since it avoids costly drying processes.
  • the extractive solvent should have a high affinity for wood, i.e., the solvent should readily diffuse or enter into spaces between cellulosic fibers to leach out wood extractives.
  • the solvent should preferably have a physical property that allows ready separation from water, for example, a preferred solvent boils in the temperature range from about 40° to about 75°C under atmospheric pressure conditions, to facilitate separation by distillation using steam as a heating medium.
  • a preferred solvent boils in the temperature range from about 40° to about 75°C under atmospheric pressure conditions, to facilitate separation by distillation using steam as a heating medium.
  • the solvent could boil at a temperature higher than water, although this is undesirable from an energy usage standpoint.
  • the solvent could be immiscible with water, as long as it is able to leach out VOCs or pitch, or both from wood particulates.
  • the extractive solvent may include a mixture of solvents.
  • the mixture may include a first solvent that has a particularly high affinity for saponifiable (also known as “hydrophilic") components, and a second solvent that has a high affinity for unsaponifiable (also known as "hydrophobic") components.
  • the wood particulates may be sequentially subjected to one extractive process using a solvent for the removal of saponifiables, and another extractive process using a different solvent for the removal of unsaponifiables. The order of these two extraction processes is not important.
  • the extraction process is intended to remove wood extractives such as VOCs and pitch, and not lignin.
  • process parameters should be controlled to minimize lignin extraction or chemical attack of cellulosic wood components. Both lignin extraction and attack of cellulosic components adversely affect the ultimate yield of pulp from the wood particulates. It is an objective of the invention to maintain yield while removing VOCs and pitch. Consequently, temperature, pressure and time of extraction are controlled to avoid lignin extraction and cellulose attack. Such conditions are referred to, in the specification, as mild conditions.
  • the extraction process is carried out under as mild conditions of temperature and pressure as would require an extraction time of from about two hours to about 10 minutes, or less, to minimize equipment size for a particular rate of chips treated, in tons per hour.
  • the time of extraction is about 30 minutes, or less, and up to about one hour for economical extraction equipment sizing.
  • Extraction time, and hence size of equipment is also solvent dependent. Certain solvents are better at extracting out the extractives and their leaching or solvent capability is not as strongly adversely affected by increasing concentrations of extractives in the solvent. Such solvents potentially minimize solvent recovery costs because of the lower volumes needed.
  • the mass ratio of solvent to wood particulates is in the range of from about 6:1 to about 1:1, more preferably about 4: 1 to about 1 :1, and most preferably about 2:1.
  • solven wood ratio also depends on extraction time and temperature and pressure conditions. In some cases, depending upon extractor design, solvent will at least be present in sufficient quantity to fill void spaces between wood chips. This may provide a sufficient solvent to wood ratio. In general, longer extraction times require a lower solven wood ratio for the same degree of extraction for a particular solvent. Also, higher temperatures and pressures allow reduced extraction time and solvent:wood ratios.
  • the mass ratio of solven wood is measured as the total mass of solvent that a particular mass of wood will encounter in a typical extractor of the invention.
  • the solvent:mass ratio refers to the total mass of pure make-up solvent and the mass of solvent in the dirty recycled solvent, relative to the mass of wood chips in the extractor.
  • Temperature and pressure conditions also impose constraints on the selection of the solvent or solvents. Those solvents that are able to effectively remove wood extractives from wood particulates, under mild conditions of temperature and pressure, i.e., conditions that do not cause significant dissolution of lignin or attack of wood cellulosic components, are useful.
  • the extraction process operate at a temperature in the range of from about 10° to about 150°C, more preferably from about 20° to about 130°C.
  • Preferred pressure conditions range from about atmospheric pressure (14.7 psi) to about 50 psi, most preferably from about 15 to about 25 psi (about 103.5 to about 172.5 kPa).
  • the preferred solvent for the extraction of VOCs is exemplified by the group consisting of methylene chloride, 1,1,1-trichloroethane, 1 , 1 ,2-trichloro- 1 ,2,2-trifluoroethane, trichlorofluoromethane, dichlorodifluoromethane, chlorodifluoromethane, trifluoromethane, 1 ,2-dichloro- 1 , 1 ,2,2-tetrafluoroethane, chloropentafluoroethane, l,l,l-trifluoro-2.2-dichloroethane, 1,1,1,2-tetrafluoroethane, 1,1-dichloro-l-fluoroethane, l-chloro-l,l-difluoroethane, 2-chloro-
  • Acetone is the most preferred solvent since it is miscible with water, forms a minimal azeotrope with water, boils at about 55°C, and has a high affinity for wood, while also being an excellent solvent for VOCs.
  • wood particulates are extracted by the method of the invention without predrying of the particulates.
  • a polar solvent or mixture of solvents or a hydrophilic solvent is preferred.
  • a hydrophilic solvent which may also remove some wood extractives
  • a hydrophobic solvent may be used to remove any remaining wood extractives. Such a hydrophobic solvent may more effectively dissolve and leach out certain of the wood extractives.
  • the extractor solvent may include a mixture of solvents.
  • the mixture may include a first solvent that has a particularly high affinity for saponifiable ("hydrophilic") components of the extractives, and a second solvent that has a high affinity for the unsaponifiable (“hydrophobic") components.
  • the wood particulates may be sequentially subjected to one extractive process using a solvent for the removal of saponifiable components, and another extractive process using a different solvent for the removal of unsaponifiable components. The order of these two extraction processes is not important.
  • Pitch is of higher molecular weight and more hydrophobic than VOCs.
  • Such higher molecular weight extractives are best extracted with a less polar solvent or solvent mixture.
  • the solvent or solvent mixture is hydrophobic in nature, for example, kerosene, straight or cyclic alkanes, aromatics such as benzene, toluene and xylene, and the like.
  • the solvent is acetone, in which case a single solvent may be used for the extraction of both VOCs and pitch. This facilitates recovery of the solvent by eliminating any requirement for duplication of solvent recovery apparatus. Extraction operating conditions should be controlled to prevent significant attack of lignin or cellulosic components of the wood.
  • FIGURE 2 For ease of understanding the process of the invention, an embodiment of the invention is illustrated in FIGURE 2.
  • raw logs 250 are charged to a chipper 252 and then optionally a chip crusher 253 for crushing to increase internal surface area.
  • the chips are typically then stored in large piles.
  • VOCs are released and emitted into the surrounding environment.
  • the EPA has set stringent standards on the amount of VOCs that may be emitted.
  • the chipping and optional chip crushing processes are optionally enclosed within substantially airtight equipment from which air containing VOCs is continuously removed through ducts. This VOC-containing air stream may be purified by passage through air scrubbers, and then optionally activated charcoal filters, or through activated charcoal filters only.
  • the wood chips produced in crusher 253 are charged to an extraction operation 256 that removes pitch and VOCs from the wood chips.
  • this process is carried out in a counter current operation, as shown in FIGURES 3A, 3B, 3C, and 3D.
  • countercurrent it is meant that the freshest solvent entering the extractor contacts chips that have already flowed through most of the extractive volume, and fresh chips entering the extractor first contact solvent that has already flowed through the extractor.
  • influent solvent containing the lowest concentration of extractable material contacts chips from which a proportion of the extractives have already been removed, so that the highest driving force for extraction is maintained.
  • the extractor has a cylindrical housing 300, preferably having a length-to-diameter ratio of about 4:1.
  • Wood chips enter the compression screw feeder 302 that includes a progressively tapering screw thread 304 within a sleeve 306.
  • This type of feeder is favored because it can express some water from the chips, facilitating subsequent solvent recovery. Any water expressed in the screw feeder is drained and removed in conduit 303 and routed to VOC, pitch and solvent recovery processes.
  • the compressed chips enter the extractor near its top and flow downward under gravitational force, and the mass of chips continuously added to the extractor.
  • the base of the extractor is supplied with a plurality of screw feeders 304 aligned with the longitudinal axes parallel to the base of the extractor. As these screw feeders 302 rotate about the axes, they convey the chips towards the outlet compression screw feeder 306. During compression of the chips in this outlet screw feeder, residual solvent is removed from the chips. This solvent drains into conduit 307 and is routed to a used solvent storage tank 308.
  • solvent is added in at least two points in the extractor.
  • fresh solvent is injected near the base of the extractor; and "dirty" solvent that has already passed through the extractor, and that contains water and wood extractives, is injected nearer the middle or upper section of the extractor.
  • dirty solvent is controlledly pumped from the used solvent storage tank 308 through an outer concentric conduit 310 into the extractor at a location about midway along the length of the extractor.
  • Fresh solvent is injected in an inner concentric conduit 312 that terminates in a distributor near the base of the extractor.
  • flow of solvent in the extractor is of a plug-flow type.
  • the fresh solvent rises in the extractor as a "front” until it meets with upwardly rising dirty solvent.
  • commingling takes place and the combined solvent mass, including extracted wood extractives, rises upward through the extractor while leaching wood extractives from chips, until the solvent exits the extractor in conduit 314 and is routed to used solvent storage 308.
  • a portion of this solvent is continuously removed and charged through a conduit 60 to a solvent reclamation process, described above.
  • the extractor 320 has a cylindrical body inclined at an angle of about 60° to the horizontal.
  • the extractor is supplied with an internal screw 322 that has a longitudinal axis extending along the central longitudinal axis of the extractor and that is rotated by a drive motor 323 to move chips held up between the screw threads from inlet to outlet. Threads of the screw extend outward from the root of the screw at a screw pitch angle, toward the inner surface of the extractor body 320, without touching the inner surface.
  • the inclined screw 322 is free to rotate, under mechanical power, within the extractor.
  • Chips are fed into the solvent-filled extractor at an inlet near the extractor base by means of a compression screw feeder 324. These chips are captured between the helical threads of the rotating inclined screw of the extractor and conveyed upward until they are expelled from the extractor through a chip outlet 325 near the upper end of the extractor into an outlet compression screw feeder 326. As explained before, the outlet compression screw feeder compresses the chips and expresses residual solvent from the chips.
  • acetone is injected into the inclined extractor through a conduit 327 near the top of the extractor, and removed from the extractor in an outlet conduit 328, near its base, that is covered by a chip screen 329.
  • the extractor 330 is inclined at an angle of about 60°, and is supplied with an internal pan conveyor 332.
  • the pan conveyor includes an endless belt extending substantially along the central axis of the extractor.
  • Containers, or “pans,” for carrying chips are formed along the belt by planar sheets, typically of metal, mounted on, and extending at right angles from, the belt at spaced intervals. The sheets extend toward, but do not touch the internal wall of the extractor. Thus, chips are captured in the spaces between the plates and are carried in the direction of movement of the belt.
  • Chips are fed into the extractor inlet 335 by a compression screw feeder 334, located near the top of the extractor, on one side of the pan conveyor belt, and exit from the extractor through an outlet 336 on the opposite side of the pan conveyor belt, near the top of the extractor.
  • the chips are carried away in a compression screw feeder 337.
  • Solvent enters into the extractor through a conduit 338 near the outlet of the chips, and exits from the extractor through a conduit 340, equipped with a chip filter 339, near the chip inlet 335.
  • the flow through the extractor is not completely countercurrent, but approximates countercurrent conditions for at least the partially-extracted chips on the exiting side of the pan conveyor.
  • the extractor is enclosed in a housing 350 that that is cylindrical and has a cone-shaped bottom for drainage of solvent and an exit chute 360 at an end opposite the chip feed inlet 352.
  • Chips enter the extractor through a rotary feeder 356 above chip inlet 352.
  • This type of feed may be used substituted for the screw feeders shown as the chip inlets of the extractors shown in FIGURES 3 A, B and C.
  • the chips fall from inlet 352 onto an internal pan conveyor 358 that is disposed longitudinally within the housing 350 to carry the chips to the other end of the housing where the chips are spilled into the chute 360 for removal.
  • a solvent distributor 362 extends above and along the entire length of the internal pan conveyor 358.
  • the solvent distributor is supplied with a plurality of holes to allow solvent distribution across the entire mass of chips conveyed on the pan conveyor.
  • the solvent extracts wood extractives from the chips, while percolating through the chip mass.
  • Solvent containing leached extractives falls towards the cone-shaped bottom of the extractor and is removed through solvent outlet pipe 366, located at the apex of the cone-shaped housing bottom, that is covered with a chip screen 365.
  • the extracted chips as explained above, fall off the far end of the pan conveyor into chute 360 and are then removed through exit screw press 364.
  • the screw press by compression, removes residual solvent from the chips.
  • wood chips may be achieved with a variety of extractor designs of the invention.
  • the nature of wood chips, and wood particulates, impose certain limitations on the nature of the equipment.
  • Wood chips tend to interlock and form stable packed structures when placed within a container, such as an extractor, or a silo.
  • the above- described designs overcome this tendency by providing either inclined screws, pan conveyors, or screws near the base of the extractor to facilitate chip movement in the extractor and chip removal from the extractor.
  • the designs, especially those of FIGURES 3B, 3C and 3D also reduce channeling of wood chips from inlet to outlet of the extractor and facilitate control of chip residence time in the extractors.
  • the wood chips are immersed in the extraction solvent supplied in conduit 248 from solvent storage 276. Mild agitation, while preferred, is not necessary.
  • solvent surrounds and penetrates the wood chips dissolving and leaching wood extractives, including VOCs and pitch, from the structure of the wood chip.
  • the solvent penetrates to and removes extractives from the resin canals of the wood as well as the parenchyma cells of the wood. This removal or "leaching" of extractives from the wood takes place under conditions of temperature and pressure that do not cause substantial attack of the lignin or cellulosic component of the wood.
  • leaching can take place at either ambient conditions of temperature and at about atmospheric pressure conditions, or at slightly elevated temperature and pressure to increase extraction rate.
  • the extracted wood chips are separated from solvent in the extractor(s) and transported to optional chip pressing operations 262 for removal of residual solvent and extractives, for instance in screw presses.
  • the solvent, containing water, pitch and VOCs, now called a "miscella" is removed in conduit 260 for processing to recover solvent for reuse, and pitch and VOCs for sale or combustion.
  • the extracted wood chips are subjected to mechanical pressure causing squeezing and compression of the chips.
  • residual solvent containing pitch and VOCs is expressed from the chips.
  • This liquid is conveyed in a conduit 263 to the solvent and pitch recovery processes, as will be described later.
  • the compressed wood chips, still containing residual solvent are charged to a solvent removal stage 266.
  • Solvent removal may be effected by conventional means, such as charging to a rotary drum dryer, or continuous dryers that comprise a multiplicity of drying stages enclosed in a housing and subjected to hot air and direct steam that removes solvent from a substrate to be dried. To facilitate drying, the air should be preheated to at least the boiling point of the solvent.
  • Solvent vapors removed during this stage are carried by conduit 268 to processes for solvent recovery.
  • the substantially solvent-free leached chips, with reduced VOC and pitch content, are charged to a pulping process, generally designated by the numeral 272.
  • VOC emissions during the pulping operations are significantly reduced.
  • pulp, paper and absorbent product manufacturing processes are enhanced, by the virtual elimination of pitch that causes fouling of equipment and related loss in efficiency and production.
  • the quality of paper and pulp products is also improved, as explained above.
  • the extractive solvent used in the VOC and pitch extraction stage is recovered and recycled for reuse.
  • streams 260, 263 and 268 containing solvent, from extractor(s) 256, optional chip pressing 262, and solvent removal 266, respectively, are gathered in header 270 which charges the solvent-containing fluids to a solvent reclamation stage 274.
  • solvent reclamation stage solvent is separated from a VOC product and a pitch product.
  • the solvent is routed to solvent storage 276 for reuse in the extraction process 256.
  • the VOCs are routed to VOC storage 280 for sale or use as a fuel.
  • pitch is routed to pitch storage 278 for sale or use as a fuel.
  • Solvent reclamation can be carried out by distillation or by other separation processes. Preferably, from about 95 to 98%, or more of the solvent is recovered. It is important to note that the volatile organic compound product produced, and the pitch product produced, are not necessarily "pure.” Rather, the VOC product may contain at least some, although minimal, amount of solvent, as well as water. The pitch product will contain pitch as well as water.
  • Pitch by itself solidifies at room temperature and is difficult to handle. While the pitch may be spray-dried into pellets for handling, it is preferred that the pitch product contain less than about 50 wt.% solids so that it may be maintained in a liquid state, either at ambient temperature or with the addition of economically minor amounts of heat or waste heat. This liquid pitch product is more readily pumped into heated tank cars for sale. The extracted chips, after drying to remove any residue or solvent, are then either stored, or charged directly to a pulp mill for the production of wood pulp. Any of several available commercial processes may be used to produce wood pulp from the extracted wood particulates, according to the invention.
  • mechanical including “thermomechanical”
  • kraft sulfite, or any other process
  • kraft sulfite
  • any other process may be used to produce an aqueous slurry containing a suspension of wood fibers that may be charged to a papermaking machine to make paper or absorbent products.
  • Chemical pulping encompasses all those wood pulping processes that incorporate the use of chemicals to dissolve lignin and thereby cause physical separation between wood fibers held together in a wood particulate, sometimes with the aid of mechanical forces.
  • the chemical pulping processes include, for example, the sulfite (or acid) process, the kraft process, and the alkaline or soda process.
  • the sulfide ion is the active reactant
  • the acid process the bisulfite ion is the active reactant.
  • the process of the invention is applicable to any chemical pulping processes.
  • a reactant or reactants
  • solvent-extracted wood particulates of reduced VOC and reduced pitch content in a digester, under controlled conditions of temperature and pressure, for a time sufficient to solubilize and remove lignin, a component that holds fibers of the wood together in a unitary structure.
  • individual wood or cellulosic fibers are separated from each other in an aqueous liquid medium, to form a pulp or slurry.
  • water is then added to this pulp to form a stock slurry of weak black liquor to facilitate pumping.
  • the fibers are washed to remove lignin and other impurities.
  • FIGURE 4 is a schematic that is illustrative of the major process operations in a typical chemical pulping process.
  • the various chemical pulping process are well- known in the art and the following explanation more clearly points out the benefits of the invention as applied to any of the chemical pulping processes.
  • reduced VOC and pitch-content chips 404 are charged to a digester 400 along with black liquor in conduit 402, and a predetermined amount of white liquor in conduit 406 to provide the appropriate liquor to chip ratio.
  • the liquor-to-oven dry chip ratio in the digester is from about 3.5 to about 4.5.
  • the cooking liquor is maintained at cooking temperatures ranging from about 160° to about 175°C and digestion time may vary from about 30 minutes to about 150 minutes depending upon the degree of complete separation required between individual cellulose fibers, or the degree of delignification required.
  • the pulp mass contents of the digester are blown through conduit 408 into a blow tank 410 of cyclone-type design so that steam and noncondensable gases are emitted through a central pipe 412.
  • VOC emissions through this central pipe 412 are significantly reduced.
  • the digested pulp mass, leaving the bottom of the blow tank, is charged to a screen 414 for removal of any large undigested wood particulates.
  • the pulp flowing through the screen is charged through conduit 416 to a pulp washing stage 420.
  • the pulp, or "brown stock” washing is carried out on a series of rotary drum filters.
  • the washing process produces a washed or cleaned pulp that is then charged to a pulp bleaching stage 430. At this point, bleaching chemicals are added to the pulp to achieve the required pulp brightness.
  • the bleached pulp is then charged through conduit 432 to a screen 434 and the screened pulp is finally charged to a cyclone-type cleaner 440 that removes fine, broken cellulosic particles through conduit 442 while charging the separated longer-fibered pulp to pulp storage 462.
  • This pulp may then be charged to processes for making paper and absorbent products.
  • VOCs are emitted during the pulp washing stages at the blow tank 410, on the rotary drums of the pulp washing stage 420, and in the bleaching step.
  • VOC emissions are also significantly reduced.
  • the removal of VOCs and pitch reduces the requirement for chemicals supplied in the white liquor since pitch and VOCs would consume some of the chemicals in the digester. This savings in chemicals provides a significant cost saving.
  • the pitch content of the pulp is significantly lower than in the prior art, less energy is required in the recovery stage 430, as explained below. Also, pitch fouling of equipment is significantly reduced allowing higher process equipment utilization rates.
  • the pulp washing stage 420 also produces a wash black liquor that is routed to a chemical recovery system 430.
  • White liquor is regenerated from the black liquor and may be recycled, as shown, in conduit 406 to the digester.
  • the quantity of heavy black liquor that is charged to the recovery boilers, process units in the recovery section 430 is reduced for a given amount of pulp production. Consequently, it is estimated that pulp production may be increased, typically from about 2 to about 3%, until the boiler solids limit is once again reached. This provides an effective debottlenecking of the chemical recovery operation, without the requirement of any further capital investment.
  • the invention provides significant advantages in any of the chemical pulping processes, ranging from significantly reducing potentially harmful emissions of VOCs, to the reduction in chemical consumption and reduction in energy consumption for a given tonnage of pulp production. Moreover, the reduced pitch content pulp produced has significantly enhanced properties that allow the production of superior quality products.
  • the extracted wood chips now having a substantially reduced pitch content, and substantially free of volatile organic compounds, are either placed in storage for subsequent processing, or charged directly to a pulp mill.
  • the chips are first subjected to steam heating and then also subjected to mechanical fiberizing forces and heat generated by these forces.
  • the mechanical forces cause the wood chips to cleave or delaminate along longitudinal boundaries between wood fibers to produce separate wood fibers.
  • These fibers are then combined with sufficient water to produce a pumpable aqueous pulp that may be processed into paper and other absorbent products.
  • the process of the invention is applicable in a range of mechanical wood pulping processes.
  • processes include, but are not limited to, the stone ground wood process (SGW), the pressurized ground wood process (PGW), the refiner mechanical pulp process (RMP), the thermo-refiner mechanical pulp process (TRMP), the pressure refined mechanical pulping process (PRMP), the thermomechanical pulp process (TMP), the pressure/pressure thermomechanical pulping process (PPTMP), the chemi-refiner-mechanical pulping process (CRMP), the chemi-thermo-mechanical pulping process (CTMP), the thermo-chemi-mechanical pulping process (TCMP), the thermo-mechanical-chemi pulping or OPCO pulping process (TMCP), the long fiber chemi-mechanical pulping process (LFCMP) and the chemically treated long fiber process (CTLF).
  • SGW stone ground wood process
  • PGW pressurized ground wood process
  • RMP refiner mechanical pulp process
  • TRMP thermo-refiner mechanical pulp process
  • PRMP pressure refined mechanical pulping process
  • TMP thermomechanical pulp process
  • PTMP pressure/pressure thermomechanical pulping process
  • FIGURE 5 An embodiment of an exemplary mechanical pulping process of the invention, using reduced pitch content, substantially VOC-free wood particulates as a reduced chargestock, is shown in FIGURE 5, it being understood that the process of the invention is also applicable to other mechanical wood pulping processes.
  • the extracted chips are charged through conduit 502 from chip silo 500 to a chip washing process 504 to remove sand and other debris.
  • the cleaned chips are then conveyed to a surge hopper 506 from which they are charged to a steam unit 510 where the chips are exposed to low-pressure steam, typically at about 35-65 psig, charged through conduit 508.
  • the heated chips are then charged through line 512 into the first of a series of from about 2 to about 4 mechanical refiners.
  • the first refiner 514 is operated under a slightly elevated pressure.
  • the chips are charged to the spacing between two opposing grinding surfaces in the refiner that are rotated in opposite directions by their respective drive motors.
  • the chips, caught between the grinding surfaces are delaminated or cleaved, usually along interfiber boundaries, to produce individual fibers.
  • Fibers and unfiberized chips exit from the refiner through conduit 516 and pressure let-down valve 518 to enter a separator 520.
  • steam exits through a central pipe 522.
  • this exiting steam is substantially free of VOCs and volatile wood extractives.
  • the fibers and any unfiberized chips continue through conduit 524 to a second refiner, atmospheric refiner 526.
  • Wood fibers are carried from the refiner through conduit 528 to a bleaching unit 530, where the fibers are chemically treated to a desired level of brightness than in the prior art processes.
  • a bleaching unit 530 where the fibers are chemically treated to a desired level of brightness than in the prior art processes.
  • the bleached wood pulp is then charged to a screen 532.
  • the oversized fraction, representing incompletely fiberized wood particulates, are returned in conduit 534 to one of the refiners.
  • the screen undersize passes through to a cleaning stage 536 and thence to a thickener 538, while any oversize is recycled for re- refining.
  • the thickener typically a rotary drum filter, forms a filter cake of pulp on its filter surface that is removed by a doctor blade 540.
  • the caked pulp 542 is then transported to pulp storage 544. This pulp may then be used for the manufacture of paper and absorbent products. More typically, mechanical pulps are utilized for the manufacture of newsprint.
  • the burst index increases by from about 10 to about 60%, preferably about 50%.
  • the tear index increases by from about 10 to about 35%, preferably about 28%.
  • the tensile index increases by from about 10 to about 40%, preferably around 35%.
  • the Scott Bond increases by from about 10 to about 30%, preferably about 25%.
  • the density of the products increases by from about 2 to about 10%, typically around 5%.
  • Sheffield Smoothness increases by from about 10 to about 25%, preferably around 18%. Stiffness increases by from about 5 to about 15%, preferably around 10%.
  • the stretch of the products of the invention increases by from about 5 to about 15%, preferably around 12%.
  • Papermaking and absorbent products Papermaking machines include at least three sequential sections, each performing a separate primary function and each in operating communication with any prior or subsequent sections in the sense of receiving a continuous unfinished paper web from a prior section, or conveying the web to the next section, for further processing.
  • the "forming section” an aqueous suspension or slurry containing about 0.5 to 1.0 wt.% paper pulp fiber of reduced pitch content, made in accordance with the invention, is formed onto an endless wire mesh belt to form a wet fibrous mat on the belt.
  • this endless belt permits rapid drainage of water from the fibrous mat under gravity and applied suction to produce a web containing about 20 wt.% solids that is conveyed to the next section, the "press section.”
  • the paper web is supported on a series of air and water- permeable felts that convey the web through a series of press nips between horizontal, cylindrical rollers to mechanically express and remove water from the web.
  • the web is transferred to the next section of the papermaking machine, the "drying section.”
  • the partially dried web is contacted with a series of heated drums or cylinders to evaporate water from the web and produce a finished product having a dryness of about 90 to 95%.
  • the web is conventionally unsupported at certain points in the process as it travels between press nips and heated drums in the drying section. Web strength is therefore a factor in determining the rate of papermaking. Continuous high speed operation is not feasible when the web is weak, and subject to breaking.
  • FIGURE 6 illustrates schematically a typical papermaking machine 600.
  • a slurry of 0.5-1.0 wt.% reduced pitch content pulp fiber enters one of a plurality of header boxes 602 that form a wet web 610 onto a continuous, endless wire mesh belt 612.
  • Belt 612 is supported and transported by rollers exemplified by rolls 608 and 609.
  • web 610 While on the belt, web 610 is dewatered by natural gravity flow of water from the web as well as by vacuum suction applied by several suction conduits 604 located beneath mesh 612 and in fluid communication with web 610.
  • the web Upon exiting the forming section, the web enters the press section. In this section, the web 610 is urged against an endless pickup felt 614 that is supported by a cylindrical pickup roll 620 having a rotatable outer perforated shell 616 and an internal stationary vacuum compartment 618, in fluid communication with the felt through perforations in the outer shell 616.
  • the continuous web 610 is continuously transferred by vacuum assist onto the pickup felt 614.
  • the web is then sandwiched between pickup felt 414 and a bottom felt 630.
  • This bottom felt is guided around roller 632 into contact with the other surface of the wet paper web 610.
  • This layered arrangement of felts with an intermediate wet paper web is then fed into a press nip between a suction roll 650 and a circumferentially grooved roll 640 where pressure is applied on the lateral surfaces of the felts and web, as shown by the arrows in FIGURE 6, to express water from the wet paper web.
  • the bottom felt 630 is conventionally separated from the paper web, guided around roll 634, and returned continuously back to roller 632.
  • the paper web 610, carried on pickup felt 614 proceeds to a second nip press between a grooved roll 682 on the felt side, and a smooth roll, such as a granite roll 680, on the paper side.
  • a smooth roll such as a granite roll 680
  • the adhered paper web on roll 680 is carried by rotation of the roll into a nip between a second felt 692 and a supporting perforated roll 690 to further express water from the web.
  • the second felt 692 separates from the paper and is continuously guided to a return to the perforated roll 690.
  • the paper web, now unsupported, is transferred to the drying section of the paper machine.
  • the drying section of the papermaking machine conventionally also consists of a series of rolls, heated and/or supplied with hot air to remove moisture from the paper web to produce a continuous dried roll of paper.
  • web 610 is drawn onto felt 696 and is carried around a series of heated rollers 694 before separating from the felt.
  • the dried paper web is then conveniently wound onto a roll 698.
  • the foregoing typical papermaking process, and any other papermaking process is used to produce paper and absorbent products from the reduced pitch content pulps of the invention. This results in the production of paper and absorbent products of reduced pitch content, that have superior brightness, strength and optical properties.
  • due to the increased pulp strength there is also a possibility of increasing the rate of operation of the pape ⁇ naking machine due to the superior strength of the pulps of the invention, provided that the particular machine is not rate limited by its drying section.
  • the properties of products produced according to the invention are significantly enhanced relative to products made of comparable "raw" wood particulates, i.e. wood particulates that were not extracted by a solvent, as described above.
  • the burst index increases by from about 10 to about 60%, preferably about 50%.
  • the tear index increases by from about 10 to about 35%, preferably about 30%.
  • the tensile index increases by from about 10 to about 40%, preferably around 35%.
  • the Scott Bond increases by from about 10 to about 30%, preferably about 25%.
  • the density of the products increases by from about 2 to about 10%, typically around 5%. Sheffield Smoothness increases by from about 10 to about 25%, preferably around 20%. Stiffness increases by from about 5 to about 15%, preferably around 10%.
  • the stretch of the products of the invention increases by from about 5 to about 15%, preferably around 12%. While optical properties, as measured by brightness, decreases by around 10%, it has been found that less chlorine or non-chlorine bleach is required to achieve a desired brightness with pulps of the invention. That is, the pulps of the invention are markedly more responsive to bleaches and demonstrate a higher gain in brightness when undergoing bleaching. Significantly, since the pulp has reduced pitch content relative to pulp obtained from wood particulates that have not undergone the extraction process, fouling of the papermaking machine equipment with pitch is significantly reduced, or entirely eliminated, depending upon the proportion of pitch that is extracted. Consequently, papermaking machine down time caused by pitch fouling is either reduced or eliminated and product wastage caused by pitch deposits on the machine and the machine clothing is eliminated. Indeed, the pulps of reduced pitch content of the invention not only produce products of superior quality, but also reduce the operating costs of papermaking machines. Finally, and importantly, depending upon the level of VOC extraction, VOC emissions are substantially reduced or virtually completely eliminated from the papermaking process.
  • the batch of wood chips was subjected to a batch extraction process.
  • the wood chips were not predried, so that their condition approximated that of wood chips normally received for treatment in a wood pulping facility, or used in a composite wood product manufacturing facility.
  • the wood chips were preheated with atmospheric steam for 30 minutes. During this time, the wood chip temperature rose to about 95°C.
  • the wood chip batch was then immediately submerged in the extraction solvent. In each case, the solvent: wood ratio was 4.0 and the extraction time was 30 minutes.
  • solvent was drained from the chips, and the chips were subjected to a second heating cycle of 30 minutes with atmospheric steam. Thereafter, the chips were subjected to a second extraction cycle using the same solvent at the same solvent:wood ratio. After draining solvent from the chips, the chips were analyzed to determine the amount of residual wood extractives. The percent wood extractives removed was calculated for each batch and the results are reported in the accompanying Table 1.
  • acetone is the best solvent for the removal of wood extractives from Lodgepole Pine. Acetone has advantages over the use of an 80/20 acetone/water mixture, and is also superior to the other solvents tested.
  • oxidized acids or alkaline reagents
  • alkaline extractions have several disadvantages. These include the darkening of wood fibers which would result in higher fiber bleaching costs. Moreover, the nonselective nature of caustic treatments result in loss of yield. Also, caustic extracts are extremely toxic and costly to treat.
  • Example 2 Process Conditions for the Removal of Wood Extractives
  • a 50 gram batch of oven dried wood chips was treated in a solvent:wood ratio of 4.0.
  • the wood chip species evaluated were seven batches of Ponderosa Pine (PP) and four batches Douglas Fir (DF) along with a PP control.
  • steam preheating time, acetone extraction time, and post-steaming times were varied. Steam was supplied at ambient pressure, and the extractions were carried out at ambient temperatures and pressures.
  • the extracted wood chips were finally squeezed in a press at 1500psi (10,350 kPa) for 5 minutes.
  • presteaming steam #1
  • presteaming appears to reduce extraction.
  • multi-stage extractions show slight increases in overall extraction, this increase may not justify the additional equipment required in a commercial operation.
  • Increasing the extraction time, in a single- or multiple-stage extraction, is effective in increasing the percent wood extractives removed.
  • TAPPI T204 om-88 modified to use diethyl ether as a solvent, to ascertain the amount of wood extractives in the chips. Then, samples of the chips were each treated with acetone for 3, 5, 10, and 20 minutes, respectively. Each extracted chip sample was then air dried, ground to 1 mm size particulates, and extracted in the same modified
  • Example 4 Determination of the Effect of Wood Particle Size and Handling Conditions on Removal of Wood Extractives.
  • wood chips were treated in equipment that would either (1) reduce average particle size or, (2) cause fractures in the wood chips opening internal surfaces and reducing average chip thickness.
  • a batch of chips was treated with a Rader DynaYield Chip Conditioner, designed to squeeze those wood chips that have a thickness greater than 1.5mm.
  • this conditioner the greater the thickness of the charged wood chip, the more work is applied to the wood causing delamination along the wood grain. In effect, this reduces the apparent particle thickness without significantly decreasing chip size or integrity.
  • treating chips in a Rader conditioner allows some increase in the removal of wood extractives, especially for larger size wood chips. This is to be expected, since fracturing the larger wood chips allows better penetration of the solvent into the interior of the chip.
  • Two of the five chip batches were extracted using acetone as the extraction solvent in a 4:1 solvent.wood mass ratio.
  • the extraction process consisted of a first steaming cycle of 30 minutes with atmospheric steam, a 30 minute extraction with acetone under ambient conditions, a second 30 minute steam cycle with atmospheric steam, and a 5 minute pressing at 400 psi.
  • a third batch was extracted with acetone, but the chips were not pressed after extraction.
  • the solvent was drained and the sample was air dried.
  • a fourth chip batch was treated in the same manner as the first two, but the solvent was water. Finally, the fifth batch was not extracted and is a control.
  • the chips were remoisturized to simulate the chip moisture that would be encountered under commercial operating conditions.
  • the remoisturized chips were then refined in the 12 inch Sprout Waldron refiner.
  • Each batch (except batch No. 3) was passed through the refiner six times, in succession, to achieve a Canadian Standard Freeness (CSF) (TAPPI test T227 om-94) of about 150.
  • CSF Canadian Standard Freeness
  • the refiner plate gap was 0.012 on the first pass, 0.006 on the second pass, and 0.003 inches on all successive passes through the refiner.
  • the CSF, energy input to achieve the CSF, and characteristics of the resultant fibers are reported in Table 5B.
  • Standard TAPPI hand sheets were made (T205 om-88) with each of the pulps to conduct standard tests. Physical and optical properties of the pulps were tested and are reported in Table 5C below.
  • density and strength indicators such as burst index, tear index, tensile index, and Scott Bond increase significantly over the control.
  • porosity measured as the number of seconds for 100ml of air to pass through a measured area of paper, also increases significantly. This corroborates the increase in density. It is theorized, without being bound, that density and strength measurements increase due to better inter-fiber bonds as a result of the removal of a substantial proportion of the wood extractives (especially pitch and heavier components) that might interfere with inter-fiber bonding. Whereas opacity did not appear to change significantly, the scattering coefficient showed a reduction. However, calculation of the opacity, normalized for the same brightness, suggests a decrease in opacity.
  • a pilot plant extractor designed and operated by Crown Iron Works of
  • the extractor was a Model 5 Crown Iron Works extractor with a capacity to process 1000 lbs (454 Kg.) per day of oven-dried wood.
  • This extractor uses the principle of solvent percolation to extract wood extractives from a bed of chips. Solvent is sprayed from above onto a 2 inch (5 cm.) thick bed of chips as the bed of chips moves through a series of sequential compartments of the housing of the extractor. The chip bed rests on a screen, thereby allowing solvent to drain from the chips for collection in each segregated compartment. The collected solvent is pumped from one compartment to the next, in a counter current flow direction relative to the chips.
  • the chips were sized so that approximately 60% by weight had an average size of 2.5 cm. by 6 mm. thick.
  • Two batches of wood chips were evaluated: (1) a 50/50 blend of Western Hemlock Lodgepole Pine, and (2) Douglas Fir. Each batch of chips was subjected to a 30 minute soak time (residence time in the extractor) at a 4:1 solvent to wood mass ratio. The extraction was carried out under ambient conditions, approximately 70°F (20°C). After extraction, the chips were passed through an indirect heated drier, where heat was applied with 180°F (82°C) steam. The temperature at the drier outlet was 150°F (65°C), and the wood was dried to an approximate 8% moisture (volatile liquid weight) content. No residual acetone was detected in the dried wood. The results of the solvent extraction are summarized in Table 6A.
  • thermomechanical pulping system The dried extracted chips were then refined in a thermomechanical pulping system.
  • the equipment included a Sprout-Bauer 36" Model CD 300 refiner.
  • the primary stage of the refiner was pressurized to 30 psi, and the secondary refiner was operated under atmospheric conditions.
  • the resulting thermomechanical pulps were evaluated for ether extractables. Based on this data, the overall VOC removal and emissions were estimated. These results are shown in Table 6B.
  • immersion extraction especially when combined with post pressing and drying, provides significant enhancement in extraction as compared to percolation extraction.
  • from about 70 to about 80% of the wood extractives can be removed.
  • VOCs As can be seen from the above, about 100% of the VOCs can be extracted from Lodgepole Pine, while about 92% of the VOCs can be removed from Hemlock, using the process of the invention. TAPPI hand sheets were made from each pulp produced. These pulps were tested for strength and optical properties. The results are summarized in Tables 7C-F, below.
  • Example 8 Reduction of VOC Emissions and Pitch Fouling from a Chemical Pulping Process
  • a chemical pulp mill is charged with control raw, unextracted, wood particulates to prepare a wood pulp, in accordance with the process explained above, with reference to FIGURE 4.
  • VOCs are emitted from a blow tank receiving a digested pulp mass from the digester, and also from the brown stock washing process.
  • the levels of VOC emissions are monitored and the total VOCs emitted per day is calculated.
  • the maximum output of the pulping process is achieved when the recovery boiler of the chemical reclaiming stage reaches a "solids limit". The maximum throughput of the pulping facility is recorded.
  • the quantity of defoaming chemicals added in the washing step to depress foaming and facilitate washing is recorded. Also recorded is the amount of bleaching chemicals needed to bleach the pulp to a specific brightness. The amount of chemical reactants consumed in the digestion process per ton of chips processed is also recorded. Wood chips, of the same species and containing the same quantity of naturally occurring pitch and VOCs are then subjected to an extraction procedure, as explained above, with reference to FIGURES 2 and 3 A, using acetone as the solvent. The extracted wood particulates have a significantly lower concentration of wood extractives. In particular, the VOC content is reduced to virtually zero, and the pitch content is reduced by about 50%.
  • the extracted wood chips are now charged to the same chemical pulping process as the control chips, while maintaining operating conditions of temperature and pressure at substantially the same levels as for the control raw wood particulates.
  • the pulp mass from the digester is debouched into the blow tank, except that the vapors emitted from the blow tank are substantially free of naturally-occurring VOCs.
  • the washing operation is also substantially free of naturally-occurring VOC emissions.

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Abstract

L'invention concerne des produits de pâte et de papier présentant une concentration en poix réduite et des propriétés améliorées, telles que l'augmentation de l'indice d'extensibilité, de l'indice de déchirement, de l'indice d'éclatement, de la cohésion Scott, du lissé et de la rigidité. En outre, les pâtes faisant l'objet de cette invention, bien qu'elles présentent un degré de blancheur légèrement réduit, réagissent plus aux agents de blanchiment, ce qui permet de réduire la quantité de produits chimiques utilisée pour obtenir un degré de blancheur spécifique. On obtient ces produits par le biais d'un processus qui consiste à extraire des particules de bois par solvant pour des composés organiques volatils et la poix d'origine végétale. Les particules de bois extraites sont ensuite écrasées et transformées en produits de papier et absorbants présentant des propriétés améliorées. En raison de l'extraction de composés organiques volatils, les étapes consistant à écraser et à fabriquer du papier sont sensiblement exemptes d'émissions de composés organiques volatils se trouvant normalement dans le bois. En outre, l'extraction de la poix réduit ou élimine l'encrassement de l'équipement dû à la poix et permet la production de produits de papier présentant des qualités améliorées.
PCT/US1997/012461 1997-07-17 1997-07-17 Produits de pate, de papier et absorbants presentant une concentration en poix reduite et procede d'obtention WO1999004087A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU36692/97A AU3669297A (en) 1997-07-17 1997-07-17 Pulp, paper and absorbent products of reduced pitch content and process
PCT/US1997/012461 WO1999004087A1 (fr) 1997-07-17 1997-07-17 Produits de pate, de papier et absorbants presentant une concentration en poix reduite et procede d'obtention

Applications Claiming Priority (1)

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PCT/US1997/012461 WO1999004087A1 (fr) 1997-07-17 1997-07-17 Produits de pate, de papier et absorbants presentant une concentration en poix reduite et procede d'obtention

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2307477A1 (de) * 1972-02-18 1973-08-23 Ahrel Per J I Verfahren zum herstellen von mechanischem faserstoff aus harzreichen holzarten, wie kiefernholz u. aehnlichen arten
CA1105660A (fr) * 1977-03-03 1981-07-28 Gordon Brown Traduction non-disponible
US4308200A (en) * 1980-07-10 1981-12-29 Champion International Corporation Extraction of coniferous woods with fluid carbon dioxide and other supercritical fluids
FR2619837A1 (fr) * 1987-08-25 1989-03-03 Isoroy Sa Procede pour preparer un support cellulosique activable et support obtenu par ce procede
WO1996036765A1 (fr) * 1995-05-11 1996-11-21 Clariant Finance (Bvi) Limited Procede pour traiter le bois a l'aide de bacteries

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2307477A1 (de) * 1972-02-18 1973-08-23 Ahrel Per J I Verfahren zum herstellen von mechanischem faserstoff aus harzreichen holzarten, wie kiefernholz u. aehnlichen arten
CA1105660A (fr) * 1977-03-03 1981-07-28 Gordon Brown Traduction non-disponible
US4308200A (en) * 1980-07-10 1981-12-29 Champion International Corporation Extraction of coniferous woods with fluid carbon dioxide and other supercritical fluids
FR2619837A1 (fr) * 1987-08-25 1989-03-03 Isoroy Sa Procede pour preparer un support cellulosique activable et support obtenu par ce procede
WO1996036765A1 (fr) * 1995-05-11 1996-11-21 Clariant Finance (Bvi) Limited Procede pour traiter le bois a l'aide de bacteries

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
"PAPER CHEMISTRY", BLACKIE ACADEMIC & INTERNATIONAL, GLASGOW, XP002053483 *

Also Published As

Publication number Publication date
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