Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08H—DERIVATIVES OF NATURAL MACROMOLECULAR COMPOUNDS
  • C08H6/00—Macromolecular compounds derived from lignin, e.g. tannins, humic acids
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
  • C08B37/00—Preparation of polysaccharides not provided for in groups C08B1/00 - C08B35/00; Derivatives thereof
  • C08B37/0006—Homoglycans, i.e. polysaccharides having a main chain consisting of one single sugar, e.g. colominic acid
  • C08B37/0057—Homoglycans, i.e. polysaccharides having a main chain consisting of one single sugar, e.g. colominic acid beta-D-Xylans, i.e. xylosaccharide, e.g. arabinoxylan, arabinofuronan, pentosans; (beta-1,3)(beta-1,4)-D-Xylans, e.g. rhodymenans; Hemicellulose; Derivatives thereof
• • 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
  • D21C11/00—Regeneration of pulp liquors or effluent waste waters
  • D21C11/0007—Recovery of by-products, i.e. compounds other than those necessary for pulping, for multiple uses or not otherwise provided for

Definitions

• the present invention refers to a method for recovering non-fibrous substances from fibrous wood material processed in a mechanical pulping process, such as a TMP process or a groundwood process, as defined in the preamble of appending independent claim 1.
• Mechanical pulping of wood to produce fibers for paper and board is performed at elevated temperatures, typically above 80°C. High temperature is needed in order to soften the lignin binding the fibers together. The increased temperature facilitates separation of fairly undamaged fibers.
• Mechanical pulping is usually performed by processing wood chips in disc refiners, or by grinding logs on a rotating stone with appropriate grits at the stone surface. Refining of chips produces so called thermomechanical pulp (TMP).
• TMP thermomechanical pulp
• Chemical treatment of the wood chips prior to the refining typically with alkaline sulfite or alkali alone, can give even more selective fiber separation. Such chemimechanical pulps are used mainly in tissue products and paperboard.
• the disc refining is typically performed in two stages in separate refiners.
• This dissolved and colloidal (DisCo) material is mainly composed of hemicelluloses, lignin, lipophilic extractives (wood resin) and lignans.
• DisCo substances dissolved and colloidal substances
• the wood resin also called pitch, can form sticky deposits on the papermaking equipment and can also dramatically reduce the paper strength.
• the dissolved lignins consume bleaching chemicals and cause decreased brightness of the produced paper.
• the lignans and other hydrophilic extractives also consume bleaching chemicals, and can thus reduce the paper brightness when they are oxidized.
• Inorganic salts are also dissolved in mechanical pulping.
• the salts can disturb pulp bleaching processes using hydrogen peroxides, by catalyzing the degradation of hydroperoxide ions.
• the salts can also promote undesirable growth of bacteria in the process waters. It is thus obvious that the removal of DisCo substances released in mechanical pulping prior to pulp bleaching and papermaking would give many economically important advantages.
• the present invention thereby provides a method, for recovering non-fibrous substances from wood material being processed in a mechanical pulping process, as disclosed in the characterizing portion of enclosed independent claim 1.
• the method according to the present invention can advantageously be used for recovering valuable non-fibrous substances from wood material, for later use.
• the invention thereby provides a means to isolate certain valuable components and component groups, such as bio-active compounds and glucomannans, from wood material by separate extraction or from process liquids, such as washing waters, dilution waters and white water, into which these compounds have been extracted.
• the method can also be used for decreasing the concentration of non-desired non-fibrous substances, detrimental to the pulping and papermaking processes, present in process waters.
• the present invention provides a means to reduce the concentration of dissolved and colloidal components particularly in mechanical pulping and papermaking process liquids.
• different valuable non-fibrous components may be easily recovered from wood material in mechanical pulping and paper making processes and be separated into relatively pure fractions for further utilization. Upon isolation, these pure fractions may be returned back to the papermaking process or be used for other purposes, e.g. in pharmaceutical industry.
• Components or component groups that can be obtained as relatively pure fractions by using the invention are wood resins, aromatic substances, such as lignans, lignin, stilbenes, flavonoids, wood polysaccharides and salts.
• the pH level in the entire mechanical pulping process is preferably to be maintained at pH ⁇ 7, preferably at pH 4 to 6, up to the extraction and recovery of the lignans.
• the present invention is particularly suitable for separating non-fibrous substances from wood material being processed in thermomechanical pulping (TMP) processes.
• TMP thermomechanical pulping
• the recovery of dissolved and colloidal (DisCo) substances is especially facile in TMP processes as the DisCo substances can be washed out from the wood material, at relatively low preferred pH levels in the range of pH 5 and at preferred temperatures below 90°C. Momentarily the temperature may be higher in the actual pulping process. Further the valuable substances may be recovered using relatively small amounts of water, leading to high concentrations of recoverable substances in the liquid fraction.
• non-fibrous substances may be
• the valuable substances may be
• pH levels particularly at pH levels >6, lower temperatures should be used.
• Extraction of non-fibrous substances from wood material according to the present invention preferably takes place in an extractor, in which non-fibrous substances from wood material are dissolved and dispersed into a water fraction during mixing of pulp with water.
• Pulp material should preferably be processed in the extractor at a rather diluted state. This will often necessitate dilution of pulp material before the extraction process.
• Dilution liquid typically water, may be introduced directly into the extractor or may be mixed into the pulp material before its introduction into the extractor.
• TMP pulp taken from a refiner stage of a papermaking process and having a typical dry matter content of about 5 - 50 %, typically 20 - 40 %, more typically 30 - 40 %, should preferably be diluted by addition of water to a dry matter content of about 0,5 - 20 %, typically to 0,5 - 15 %, more typically to 0,5 - 10 %, before processing in the extractor.
• non-fibrous substances such as small particles including wood resins and water-soluble components including aromatic compounds, salts and polysaccharides, are dispersed and dissolved into the liquid fraction of the diluted pulp material.
• the portion of the liquid fraction, from which dissolved and colloidal non- fibrous substances are to be separated and recovered, is preferably separated from the rest of the pulp material by pressing, but may in some processes be separated by gravity, e.g. by sedimentation or centrifugation, or even by coarse material filtration.
• extraction of water soluble aromatic compounds should preferably take place at pH ⁇ 7, more preferably at pH 4 - 6.
• the pH level of the pulp suspension is higher, the pH level should be lowered to provide a suitable pH level for the extraction process.
• Suitable acid may be introduced into the pulp suspension to provide the desired pH level.
• the main component groups in wood resins i.e. the fatty acids, resin acids and sterols, are commercially produced chemicals that until now have been recovered only at kraft pulp mills in the form of tall oil soap.
• the tall oil soap is acidified and distilled to give a pure fraction of fatty acids and resin acids.
• the sterols have been recovered either from the tall oil soap or from the tall oil pitch, which is formed as a residue in tall oil distillation.
• the lignans are potentially valuable bio-active components for pharmaceutical or functional food applications due to their antioxidative and anticarcinogenic properties. This is especially true for lignans from softwood species, such as Norway spruce, containing the very bioactive substance hydroxymatairesinol (HMR) as the major component.
• HMR hydroxymatairesinol
• the separation and isolation of the HMR in industrial scale is made possible by the present invention. Particularly the isolation at a pH level below pH 7, preferably between pH 4 - 6, improves the yield.
• the low molar-mass lignin present in mechanical pulping hquors is a pure, sulfur-free and reactive lignin, which may be a valuable complement to presently produced lignin products.
• Non-fibrous components may, according to a typical embodiment of the present invention, be extracted from the wood material in mechanical pulping processes in a separate extraction stage, in which non-fibrous components are extracted as dissolved and colloidal components into a washing liquor, typically water.
• the washing liquor separated from the fibrous wood material may be concentrated before recovery of the different components therefrom.
• the washing liquor, from the extraction stage is then typically first treated to recover dispersed fine particles, such as wood resins, therefrom.
• Wood resins may be separated from the liquor by a microfilter, by ultra-filtration or by microflotation. After removal of wood resins and other fine particles possibly present in the washing liquor the remaining hquid consist primarily of water and water soluble components.
• the liquor may then be treated to separate the water soluble aromatic components therefrom.
• the water soluble components may be isolated, as relatively pure fractions, by optimizing pH and temperature of the liquid and by using suitable process steps for the removal of each specific component or component group.
• the process steps for separating desired components or component groups from extraction hquid or a liquid fraction, such as process water, washing water or white water, may according to a typical solution of the present invention, for recovering of non-fibrous substances from wood material being processed in a mechanical pulping process, include:
• the wood resin free liquor may according to a preferred embodiment of the present invention be mixed with macroreticular particles of acrylate or divinylbenzene- polystyrene resin to give sorption of aromatic substances, such as lignans, stilbenes, flavonoids and lignin, therein.
• aromatic substances such as lignans, stilbenes, flavonoids and lignin, therein.
• the acrylate or resin eluent including absorbed aromatic substances therein is separated from the hquor, which remaining hquor effluent mainly includes water soluble salts and polysaccharides, such as hemicelluloses.
• the aromatic substances are recovered from the acrylate or resin eluent with a polar solvent, such as acetone, ethanol or methanol.
• Aromatic substances may be separated from the eluent with a strong alkaline solution, if there is no need to recover lignans, without causing chemical transformation.
• the aromatic compounds may be further fractionated into fractions containing lignans and lignin respectively. This may be accomplished, for instance, by extraction with methyl-tert-butylether (MTBE), dialysis, reverse osmosis or using chromatographic methods.
• MTBE methyl-tert-butylether
• a pH between 4 and 6 is preferably maintained until the lignans have been separated. Outside this pH range, lignans undergo various chemical transformations.
• FIG. 1 shows an exemplary scheme of fractionation of dissolved and colloidal compounds present in mechanical pulp and paper making process liquids
• FIG. 2 shows amount and composition of dissolved lignans separated from process liquids at different pH levels at a temperature of 90°C
• FIG. 3 shows amount and composition of dissolved lignans separated from process liquids at different pH levels at a temperature of 60°C
• FIG. 4 shows amount and composition of lipophihc extractives at different pH levels
• FIG. 5 shows amount and composition of dissolved and dispersed hemicellulose at different pH levels
• FIG. 6 shows an exemplary schematic view of a system utilizing the present invention
• FIG. 7 shows schematically another system utilizing the present invention for recovering aromatic substances, particularly lignans, from wood material;
• FIG. 8 shows lignan and lignin concentration in effluent after sorption of aromatic compounds in the system shown in FIG. 7, and
• FIG. 9 shows sorption of different lignan components in the system shown in
• FIG. 1 shows an exemplary scheme of fractionation of dissolved and colloidal compounds present in process liquids 10 from pulp and paper making processes.
• process liquid 10 may be
• a fraction of fibers and larger particles are separated from the liquid by pressing, filtration or other suitable means.
• the fibers and larger particles 14 separated from the liquid may be returned to the pulp- and papermaking process.
• the remaining hquid fraction 16 still includes finely dispersed fiber material and colloidally dispersed wood extractives, such as wood resins (pitch).
• suitable separation means such as microfiltration, ultrafiltration, flotation, centrifugation or extraction.
• the solids in reject 20 may be disposed of or brought to further use.
• the accept fraction 22 from the second separation step 18 includes dissolved components from the pulping hquors, such as water-soluble aromatic compounds, salts and polysaccharides. These components or component groups may be fractionated based on their molecular characteristics, i.e. size, hydrophobicity, ionicity, volatility, etc.
• Aromatic compounds such as lignins and lignans, may be separated from the accept fraction 22 in a third separation step 24, utilizing absorbents, aromatic exchange resin, column- or liquid chromatography, dialysis, reverse osmosis, or membrane filtration to provide an eluent 26 from which lignins and lignans may be recovered e.g. by treating the eluent with a polar solvent.
• the effluent 28 of step 24 includes salts and polysaccharides.
• a dialysis or reverse osmosis separation step 30 may be used to separate hemicellulose from salts.
• the salts are separated into the permeate 32 of step 30.
• the polysaccharides are to be recovered from the concentrate 34 of step 30.
• thermomechanical pulp TMP
• samples of thermomechanical pulp were taken after the first refiner stage at a pulp and paper mill producing spruce TMP. These samples were used for the preparation of DisCo-hquors containing dissolved and colloidal (DisCo) substances by stirring the pulp at 1 % consistency in distilled water, followed by centrifugation to separate fibers therefrom. The stirring was performed at 90°C at pH 3, 4, 5, 6, 7 and 8 respectively for 10, 30, 60, and 180 minutes using a vibro mixer. After centrifugation at 500g (30 min), the resulting DisCo-hquors were analyzed for their contents of lignans, lipophilic extractives and polysaccharides by gas chromatography.
• DisCo DisCo-hquors containing dissolved and colloidal (DisCo) substances by stirring the pulp at 1 % consistency in distilled water, followed by centrifugation to separate fibers therefrom. The stirring was performed at 90°C at pH 3, 4, 5, 6, 7 and 8 respectively for 10, 30, 60, and 180 minutes using a vibr
• FIG. 3 shows the results of a similar experiment, in which the treatment was performed 5 at a temperature of 60°C. It can be seen that a higher concentration of HMR is received at this lower temperature. Also longer stirring time does not seem to have any major impact at pH 5 and 6.
• FIG. 4 shows that the composition of lipophilic extractives in the DisCo-hquors was 10 only slightly dependent on pH, but the amount extractives dispersed into the water phase was highly affected by pH. The solubility of extractives was increased by higher pH level. At pH 8 the amount of lipophilic extractives was about five times higher than at pH 3. This can probably be explained by the formation of fatty and resin acid soaps at higher pH, whereby the soaps can act as dispersants for the other lipophilic extractives. 15
• FIG. 5 shows that the amount of dissolved and dispersed hemicellulose were fairly constant throughout pH 3 to 7. However, at pH 8 the glucomannan amount decreased clearly, whereas an increase of dissolved pectin occurred. At alkaline conditions native glucomannans are deacetylated, rendering them less water soluble, which leads to 20 precipitation onto the pulp fibers. At the same conditions, pectins are demethylated resulting in higher solubility of the polygalacturonic acid sodium salts formed.
• a first portion of the DisCo-liquor was filtered through a 0.1 mm membrane filter at
• a second portion of the DisCo-liquor was treated in a microflotation apparatus.
• Bentonite and polyacrylamide (PAM) were used as flotation chemicals.
• a combination of bentonite and anionic PAM resulted in a 20 % decrease of wood resin removal. Practically no loss of lignans, lignin or polysaccharides occurred.
• the low flotation efficiency probably depends on the low concentration of wood resins in the DisCo- liquor tested. More concentrated DisCo-hquors would probably give higher removal rates also by flotation.
• Filtrate from the filtration of wood resins was passed through e.g. a column containing a hydrophobic interaction resin (XAD-7) at pH 5 in order to recover aromatic substances. Substances adsorbed onto the resin were eluted with acetone or methanol. The yield of lignans was over 95 % and the yield of lignin up to 80 %. The recovered lignans and lignins could be fractionated by extraction with methyl-tert-butylether (MTBE).
• MTBE methyl-tert-butylether
• Separation of hemicellulose was performed on DisCo-liquor after the removal of wood resin.
• the separation was performed with ultra-filtration through membranes having molar cut-offs of 3, 10 or 30 kD.
• the filtration was done employing centrifugal force.
• the 3 kD membrane gave the best yield, over 80 % of hemicellulose.
• the high wood resin content of the DisCo-liquor used in the ultra-filtration test resulted in slow filtration.
• Better resin removal by either micro-filtration or efficient flotation followed by a step of XAD-7 treatment for lignan and lignin removal, should result in a more efficient ultra-filtration of hemicelluloses.
• the size of wood chips has an impact on extraction of valuable lignans, such as HMR.
• Potentially valuable lignans particularly the hydroxymatairesinol (HMR) portion thereof, can be extracted into water and recovered with a high yield from rather coarse TMP in the pH range 4 to 6.
• the coarseness of TMP can be expressed as the Canadian Standard Freeness (CSF).
• CSF Canadian Standard Freeness
• the CSF value of TMP pulp after the first refiner stage is higher than 300. The coarseness of TMP pulp at this stage enables efficient pressing, i.e. separation of the liquor from the solid wood material.
• FIG. 6 shows a schematic view of an exemplary system, in which DisCo-liquor is taken from the first refiner stage in a TMP process.
• FIG. 6 shows in a TMP process a first and second refiner stage 40, 42.
• Coarse TMP at 35 % dry matter content is introduced from the first refiner stage 40 through line 44 to an extractor 46.
• Water 48 is introduced into the extractor to dilute the TMP to 5 % dry matter content.
• TMP processed in the extractor 46 is discharged through line 50 into a screw press 52, from which TMP at 35 % is fed through line 54 into the second refiner stage 42.
• DisCo-liquor separated from the TMP in the screw press is fed through hne 56 for further treatment, e.g.
• a significant advantage of extracting coarse TMP, e.g. from the first refiner stage, instead of final paper-grade TMP is that the extraction hquor can be pressed out more effectively, e.g. using a screw press.
• the present invention provides a method for separating different valuable non-fibrous components, such as the bioactive HMR, at desired form and high yield, allowing the components to be used in industrial scale.
• the pH and temperature levels play an important part in the recovery process. Also separation of resins from the DisCo liquors prior to separation of lignans and hemicellulose enhances the separation of the valuable components.
• the recovery process shown in FIG. 1 includes several process stages. It is e.g. suggested that finely dispersed material and colloidally dispersed wood extractives, such as wood resins (pitch), is separated in a first separation step by e.g. filtration, flotation or centrifugation. Thereafter, lignans and lignins may be separated in a second step by e.g. sorption onto a sorbent in a column.
• the first separation step i.e. filtration, flotation or centrifugation step, is performed in order to prevent colloidal or other finely dispersed material from plugging the sorbent column in the second separation step.
• FIG. 7 shows a process in which wood material 60, such as pulp from a TMP process, is stirred with water 62 in an extractor 64, at a pH between pH 3 and pH 6,6, preferably between pH 4 and pH 6.
• the hquid from the extractor is centrifuged in centrifuge 66 to separate - a liquid fraction, so called DisCo fluid 68, including dissolved aromatic substances, such as lignans and lignins, salts and polysaccharides, and colloidal substances, such as wood resins, and
• DisCo fluid 68 is introduced into a process vessel 72 together with a sorbent 74, preferably as coarse particles or ion exchange beads.
• the sorbent comprises e.g. macroreticular particles of acrylate or divinylbenzenepolystyrene resin, which provide sorption of aromatic substances, such as lignans and hgnins.
• the sorbent and the DisCo fluid are stirred so as to provide a close contact for effective sorption.
• the sorbent may be introduced as free particles or on a carrier.
• the size of the particles may preferably be up to 2 mm.
• FIG. 7 shows that sorbent material 76 is separated from the hquid fraction 78 in a separate step 80, but it could, of course, be discharged already from vessel 72.
• the aromatic substances such as lignans, may be separated from the sorbent material e.g. with a suitable solvent, such as acetone, ethanol or methanol.
• FIG. 8 shows that lignans may be quantitatively sorbed onto hydrophilic exchange resin XAD-4 used as sorbent material. This sorption of lignans is achieved with rather small amounts of sorbent material in the liquid, compared to amounts needed in columns. About e.g. 20 g/1, as shown in FIG. 8 and FIG. 9, may be sufficient. Lignins, on the other hand, are only partly sorbed.
• FIG. 9 shows that when different lignans, Hydroxymatairesinol of type 1 (HMR1),
• HMR2 Hydroxymatairesinol of type 2
• Conidendrin Conidendrin
• ConA Conidendric acid

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• Polysaccharides And Polysaccharide Derivatives (AREA)

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• 2000
  • 2000-11-16 FI FI20002519A patent/FI115978B/sv not_active IP Right Cessation
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