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
  • D21C5/00—Other processes for obtaining cellulose, e.g. cooking cotton linters ; Processes characterised by the choice of cellulose-containing starting materials
  • D21C5/02—Working-up waste paper
  • D21C5/025—De-inking
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
  • Y02W30/00—Technologies for solid waste management
  • Y02W30/50—Reuse, recycling or recovery technologies
  • Y02W30/64—Paper recycling

Definitions

• Paper Treatment of Cellulosic Material and Compositions for use in this invention relates to the de-inking of waste paper.
• paper we use the term "paper” to be generic to cellulosic sheet materials including filled and unfilled papers and paper board.
• waste paper It is standard practice to reclaim waste paper to allow the reclaimed paper fibres to be used as part or all of the stock of subsequent paper production.
• the waste paper needs to be de-inked and it is standard practice to achieve this by forming a pulp from the waste paper in an aqueous medium that includes de-inking chemicals, and separating the ink from the pulp. This separation may be by, for instance, washing and/or flotation.
• a typical de-inking process can comprise forming a pulp of the paper in the presence of the de-inking chemicals so as to disperse the ink into the pulp and then subjecting the resultant pulp to flotation to provide a Reject fraction that contains the floated ink components with a minimum of paper fibres, and an Accept fraction containing the paper fibres with a minimum of the ink components and the Accept fraction is then thickened to provide stock or other material that may be used for paper manufature, optionally after further conventinal treatments.
• the literature shows that the pH of the resultant pulp during the de-inking process is usually high, for instance above 9 and most usually above 10. Exposing the cellulosic fibres to this degree of alkalinity tends to cause yellowing of the fibres and so it is generally necessary to add a peroxide as a bleaching agent.
• a de-inking system which has been commercialised under the trade name Ennesco D is described in WO90/10749 and apparently consists solely of a mixture of sodium carbonate and sodium phosphate, optionally with hydrogen peroxide.
• the use of this can reduce some environmental problems but it introduces others, since the presence of large amounts of dissolved phosphate in the de-inking liquor is environmentally undesirable. It is possible to operate this system at a lower pH, for instance around pH 8.
• Various inks may be present in the paper that is to be de-inked and many of them comprise a binder and pigment.
• Many of the binders dissolve or soften sufficiently in the presence of the de-inking chemicals and/or during the pulping stage in order to release the pigment as a dispersion in the pulp.
• many binders are alkali-soluble or alkali-swellable and the alkaline conditions prevailing in a conventional de-inking pulp will be sufficient to release the ink from the paper fibres and to release the pigment from the binder.
• the pulp has finely dispersed pigment throughout it and a test of a good de-inking process is the whiteness of a sheet made from the Accept fraction, optionally after washing it.
• the finely dispersed pigment has a tendency to cause an overall grey colouration if the de-inking process is inefficient.
• overall greyness there is also a problem of visible specks in a sheet made from the Accept fraction.
• These specks arise when the ink particles on the paper that is to be de-inked are resistant to the de-inking chemicals and the pulping conditions as a result of the particles comprising a pigment and a binder that is sufficiently resistant to these conditions that ink particles retain their integrity and appear as specks in the Accept fraction (hereinafter referred to as a resistant binder) .
• a binder that is soluble or swellable at pH 9 sufficient to release pigment particles at that pH may not adequately release them when the pulping and de-inking process is conducted at a lower pH.
• de-inking at relatively neutral pH values can incur the disadvantage that ink binders that might release pigment during the pulping process in alkaline pulping are resistant during the neutral pulping such that they do not release the pigment.
• the ink particles may be resistant to dispersion of the pigment (hereinafter referred to as resistant ink particles) during neutral pulping even though they might swell and release the pigment during alkaline pulping.
• ink deposits bonded by the binders used in these processes have a tendency to be released from the pulp but to remain as dispersed particles of bonded pigment.
• Binders that are chemically cross linked are liable to promote this problem.
• the ink particles can be relatively large and so have a severe tendency to remain trapped by the fibres in the Accept fraction in preference to being floated with any dispersed pigment in the Reject fraction.
• sheets made from the Accept fraction may have very good whiteness (as a result of good removal of any dispersed pigment by the de-inking process) but may have a significant number of visible specks (as a result of resistant ink particles remaining in the Accept fraction) .
• neutral de-inking processes have advantages from an environmental point of view but have disadvantages in that binders that might swell in alkaline de-inking are resistant binders in neutral de-inking thereby leading to increased speck contamination, and speck contamination is additionally an increasing problem because of the increased amounts of laser or photocopier printed papers in paper waste.
• a process according to the invention for de-inking paper carrying ink particles comprising a binder, which is preferably resistant, and a pigment comprises forming a pulp of the paper and thereby dispersing the particles in the pulp often substantially without release of the pigmen from the particles, subjecting the pulp to flotation an thereby forming a Reject fraction containing the in particles and an Accept fraction, and thickening the Accep fraction, and in this process the pulping is conducted a a pH of from 6 to 8.5 in the presence of an anionic polyme formed fromwater-soluble ethylenically unsaturated monome or monomer blend comprising ethylenically unsaturate carboxylic acid and that promotes dispersion of the in particles in the pulp, and the flotation is conducted i the presence of a cationic surfactant that promote preferential flotation of the ink particles into the rejec fraction.
• the flotation step is optimise by the use of cationic surfactant so as to obtain optimu flotation of the resistant ink particles and we generall find that it is possible to do this without adversel affecting the whiteness due to dispersion of pigment in th pulp.
• th surfactant may be added to the Accept fraction from previous flotation stage so that dispersed pigment i primarily removed during the previous flotation stage an the resistant particles are primarily removed during th later flotation stage.
• the de-inking process of the invention is a substantially neutral de-inking process, that is to say the pulping is conducted at a pH which is substantially neutral, namely with a pH in the range of around 6 or 6.5 to 8 or 8.5. Often the pH is in the range of around 6.5 to 7.5 or 8.
• the pH value is the pH of the pulp during the pulping process, i.e., after the inclusion of any de-inking additives that are incorporated in the pulp in order to promote de-inking.
• Alkaline pulping is conducted in the presence of materials such as sodium phosphate, sodium hydroxide and/or sodium silicate and often with peroxide as a bleach. Although small quantities of such materials can be included, provided the pH stays within the substantially neutral range, in the invention the pulping is preferably conducted in the substantial absence of such alkaline materials.
• Some bleaching chemicals can be included if necessary, or a subsequent bleach step can be added, but preferably the pulping is conducted in the substantial absence of peroxide or other bleaches.
• the pulping is conducted in the presence of a buffer for providing the pulp with the desired pH, which is 6 to 8.5, often 6.5 to 8.
• the process is conducted utilising sodium carbonate and sodium phosphate with the anionic polymer, preferably the process is conducted in the substantial absence of phosphate.
• Conventional buffers such as sodium carbonate and/or sodium bicarbonate, for instance as described in PCT/GB93/00780, are preferably used.
• the proportions of buffer or other material and polymeric dispersing agent, on a dry weight basis are generally 1:5 to 5:1 by weight, most preferably 2:1 to 1:2.
• the anionic polymer that must be incorporated in the pulping composition may be an anionic dispersing agent or an anionic anti-redeposition aid. It must be a water soluble polymer.
• molecular weight (measured by gel permeation chromotography) should normally be above 1,000 and generally above 2,000. It is usually unnecessary for it to be above 200,000 or 150,000 and generally it is below 100,000. For instance it is often below 50,000. Best results are generally obtained when the molecular weight is in the range 2,000 to 20,000. However good results can also be obtained at higher values, e.g., 75,000 or higher.
• the molecular weight is sufficiently high to facilitate the formulation of the product as a solid, in which event the molecular weight is generally above 5,000 and frequently in the range 7,000 to 20,000. However when the de-inking chemicals are formulated as a solution the molecular weight can be lower. Best results are often obtained in the range 2,000 to 10,000, often around 2,500 to 6,000.
• the monomeric material from which the polymeric dispersing agent is formed preferably comprises ethylenically unsaturated carboxylic acid.
• This can be methacrylic acid, maleic acid, crotonic acid, itaconic acid or any of the other polymerisable carboxylic acids, but preferably it is acrylic acid or a mixture of acrylic (or sometimes methacrylic) acid with maleic acid (frequently including anhydride) .
• the acrylic acid or other carboxylic monomeric material can be polymerised alone or with sulphonic monomer such as 2-acrylamido methyl propane sulphonate (AMPS, U.S. trade mark), vinyl sulphonate or (meth) allyl sulphonate, and/or it can be copolymerised with non-ionic monomer, especially acrylamide.
• AMPS 2-acrylamido methyl propane sulphonate
• vinyl sulphonate or (meth) allyl sulphonate and/or it can be copolymerised with non-ionic monomer, especially acrylamide.
• the carboxylic monomer constitutes at least 50% by weight of the monomers and preferably the polymer is formed from carboxylic monomer alone or a blend consisting of carboxylic and sulphonic monomers.
• Suitable polymers include polyacrylic acid, copolymers of this with maleic anhydride, and copolymers of acrylic acid with 10-50% by weight AMPS.
• the polymer preferably has polydispersity below 2, preferably below 1.8 and most preferably below 1.5, and generally above 1.1, for instance as described in EP 129,329.
• dispersing agents can be included in the pulping process in order to improve results.
• Suitable dispersing agents include cellulosic derivatives, polyphosphonates, bentonites, and sequestering agents.
• Suitable cellulosic derivatives include cellulose ethers, such as methyl cellulose, and carboxy methyl cellulose.
• Suitable bentonites include the various swelling clays that are referred to colloquially as bentonites, including true bentonite. Fuller's Earth, hectorite and various swelling montmorillonites, such as activated calcium montmorillonite.
• Suitable sequestering agents are amino carboxylic acid sequestering agents, such as ethylene diamine tetro acetic acid and nitrilo tri acetic acid.
• Suitable mixtures of two or more of the dispersing agents include mixtures of one of the described polymeric dispersing agents, especially polyacrylic acid or a copolymer of acrylic acid with maleic acid (including anhydride) or AMPS, with a polyphosphonate or sequestering agent or CMC or methyl cellulose.
• the components in such mixtures typically are present in proportions ranging from 1:3 to 3:1 by weight.
• the amount of dispersing agent that is required for optimum performance can be selected by routine experimentation and is normally in the range 0.01 to 1% by weight based on the dry weight of the pulp, generally 0.05 to 0.5%.
• the cationic surfactant is preferably added to the pulp after the pulping process so as to promote preferential flotation in the pulp.
• the cationic surfactant may be included in the pulping process. For instance it may be included initially in the water into which the waste paper is pulped or it may be added with the polycarboxylic acid and any other de-inking chemicals during the pulping process.
• the cationic surfactant that is used in the invention can either be a true cationic surfactant (in the sense that it is cationically charged at the time it is added to the pulp) or it can be a free base surfactant which we believe can become cationically charged by interaction with the polycarboxylic or other dispersing agent or other component of the pulp.
• Suitable materials that can be used include ethoxylated fatty amines and fatty diamines and quaternary fatty ammonium compounds (i.e., quaternary ammonium compounds including at least one fatty group) .
• the fatty groups can be naturally occurring or synthetic fatty groups, generally containing 6 to 24, often 8 to 18, carbon atoms. The fatty group is often alkyl. Ethoxylate fatty amines are preferred.
• the cationic surfactant can be a surfactant that includes both cationic and anionic groups (i.e., amphoteric) but preferably it is wholly cationic.
• the formation of the pulp may be conducted in the presence of additional materials but a particular advantage of the invention is that the chemicals used for it can consist essentially only of the dispersing agent, buffering alkali, optional surfactant and optional flotation aids and collectors. Peroxide or other bleach can be included if desired, but an advantage of the invention is that it is usually unnecessary. Accordingly the liquor resulting from the de-inking is relatively free of materials that would create environmental problems during disposal.
• the de-inking process can be carried out in broadly conventional manner, except for the choice of the de-inking chemicals, as described above.
• the de-inking chemicals can be included in the aqueous liquor into which the waste paper is initially pulped, or the waste paper can be pulped to form an aqueous pulp into which the de-inking chemicals are then incorporated.
• the waste paper preferably includes photocopy (xerographic) and/or laser ink printed paper, for instance in an amount of 10 to 100%, often 50 to 100%, of the waste paper.
• the process is of particular value for de-inking office waste.
• the overall de-inking process generally comprises a series of stages, typically consisting of an initial maceration or pulping stage (preferably conducted under very high shear) , a screening stage to remove grit and oversized particles, one or more flotation stages, and a thickening stage to form a clean pulp that can either be used as such or that may be drained to form a dried pulp.
• stages typically consisting of an initial maceration or pulping stage (preferably conducted under very high shear) , a screening stage to remove grit and oversized particles, one or more flotation stages, and a thickening stage to form a clean pulp that can either be used as such or that may be drained to form a dried pulp.
• Typical de-inking processes are described in more detail in, for instance. Handbook for Pulp and Paper Technologists by G.A.Smook.
• Thickening can be conducted on thickening drums in conventional manner, for instance to raise the solids content of the pulp from a concentration suitable for flotation to a concentration suitable for recycling to paper manufacture, for instance 5 to 15% dry weight.
• the Accept fraction from flotation may be subjected to washing with water or an aqueous solution of surfactant before or after thickening.
• the amphoteric cationic surfactant gives a low speck value on the laser paper but is not so efficient on the xerographic paper.
• the pulping is conducted at a pH of 6 to 8.5 in the presence of an anionic polymer as desribed above, and non-ionic surfactant is then added to the pulp in order to promote preferential flotation of the resistant ink particles into the reject fraction.
• the cationic surfactant can be omitted.
• the pulping is conducted in the presence of an anionic polymer as described above and the flotation is conducted in the presence of a cationic or non-ionic surfactant that promotes preferential flotation of the resistant ink particles into the reject fraction, but in this process the pulping is conducted at an alkaline pH, for instance up to 9 or 9.5.
• the pulping can be conducted in the presence of an alkali, optionally with a bleach.
• the alkali is typically selected from sodium silicate and sodium hydroxide and sodium phosphate.
• the bleach is typically hydrogen peroxide.
• the pulping is conducted at a pH of 6 to 8.5 as described above and the flotation is conducted in the presence of a cationic or non-ionic surfactant as described above, and the pulping is conducted in the presence of a blend of sodium carbonate and sodium phosphate instead of or in addition to the anionic polymer.

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• Paper (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Processing Of Solid Wastes (AREA)

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Citations (3)

• 1993
  • 1993-10-27 GB GB9322118A patent/GB9322118D0/en active Pending
• 1994
  • 1994-10-26 BR BR9406216A patent/BR9406216A/pt not_active Application Discontinuation
  • 1994-10-26 AU AU79978/94A patent/AU673782B2/en not_active Withdrawn - After Issue
  • 1994-10-26 WO PCT/GB1994/002350 patent/WO1995012026A1/en not_active Application Discontinuation
  • 1994-10-26 PL PL30962694A patent/PL309626A1/xx unknown
  • 1994-10-26 CA CA 2152782 patent/CA2152782A1/en not_active Abandoned
  • 1994-10-26 JP JP51247895A patent/JPH08505444A/ja active Pending
  • 1994-10-26 EP EP19940931095 patent/EP0680530A1/en not_active Withdrawn
  • 1994-10-26 NZ NZ274880A patent/NZ274880A/en unknown
  • 1994-10-27 ZA ZA948463A patent/ZA948463B/xx unknown
• 1995
  • 1995-06-21 FI FI953087A patent/FI953087A/fi not_active Application Discontinuation
  • 1995-06-26 NO NO952568A patent/NO952568L/no unknown

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