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
• • 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
  • D21C9/10—Bleaching ; Apparatus therefor
• • 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
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/1026—Other features in bleaching processes
  • D21C9/1042—Use of chelating agents

Definitions

• the present invention is related to a process for the bleaching of paper pulp with one or more peroxide oxidizing agents, in which the paper pulp is pretreated with a chelating agent.
• chelating agents are those of the aminocarboxylic type, such as ethylene diamine tetra-acetic acid and its salts (EDTA) or diethylene triamine pentaacetic acid and its salts (DTPA). Nevertheless, these chelating agents are poorly biodegradable and will thus be released in the environment where they will accumulate. Although their toxicity is not really an issue, their accumulation in lakes and rivers will lead to the mobilization of heavy metals that are present in the soil and that will become soluble in water. These heavy metals will then be assimilated by living organisms like fishes, therefore entering in the food chain.
• EDTA ethylene diamine tetra-acetic acid and its salts
• DTPA diethylene triamine pentaacetic acid and its salts
• biodegradable chelating agents such as aspartic acid and its derivatives, substituted on the nitrogen, is described in the international application WO 97/30209.
• Such products include ethylenediamine-N,N′-disuccinic acid (EDDS) and 2,2′-imino-disuccinic acid (IDS).
• EDDS ethylenediamine-N,N′-disuccinic acid
• IDS 2,2′-imino-disuccinic acid
• the pretreatment step must be conducted at a pH from 4 to 8 while EDDS and IDS perform best at a high pH, especially pH 8 for EDDS and 10 for IDS. Thus, this process does not lead to an optimal brightness of the paper pulp.
• the international application WO 99/46441 describes a process for the bleaching of mechanical paper pulp with one or more peroxide oxidizing agents in which the pulp is pretreated with one or more chelating agents chosen from aspartic acid and its derivatives, substituted on the nitrogen, at a pH above 8.
• the natural pH of the paper pulp being usually between 5 and 6, such process implies the measurement and the control of the pH during the whole pretreatment step, by the addition of a base such as caustic soda.
• This has the drawback of lowering the brightness of the paper pulp fed to the subsequent bleaching step, due to a yellowing effect of the paper pulp during the pretreatment step.
• the addition of caustic soda during the pretreatment step increases the amount of extractives leading to a reduced yield in pulp and a higher chemical oxygen demand (COD) charge in the effluent treatment plant.
• COD chemical oxygen demand
• a further drawback of the use of EDDS and IDS as chelating agents is the higher operating costs resulting from the higher price or the higher concentration required and of the additional use of a base to maintain the pH above 8 during the pretreatment step.
• the purpose of the present invention is to provide a simple and environmentally friendly bleaching process, avoiding the measurement and control of the pH during the pretreatment step and still conducting to an optimal brightness of the paper pulp.
• the present invention therefore relates to a process for the bleaching of paper pulp with one or more peroxide oxidizing agents, in which the pulp is first treated in a pretreatment step with one or more chelating agents chosen from the group consisting of:
• One of the essential features of the present invention resides in the use, during the pretreatment step, of an inorganic magnesium derivative combined with a carboxylic acid or its salt (i), or of a magnesium salt of a carboxylic acid (ii), the carboxylic acid being substituted by at least one electrodonating group or comprising at least one carbon-carbon double bond.
• the carboxylic acids or the salts thereof, useful as chelating agents during the pretreatment step are usually substituted by at least one electrodonating group and/or comprise at least one carbon-carbon double bond within the skeleton of the molecule.
• Suitable electrodonating group are usually selected from the group consisting of amines, especially alkylamines or dialkylamines, alcohols, thiols, O-alkyl and 5-alkyl.
• Preferred electrodonating groups are the amino group (—NH 2 ), the alkylamino group (—NRH) or the dialkylamino group (—NRR′) or the hydroxyl group (—OH), in particular the dialkylamino group (—NRR′) or the hydroxyl group (—OH).
• suitable carboxylic acids are those of the following general formula (I)
• C n H m is linear or branched and saturated or unsaturated; n is an integer from 1 to 8, especially from 1 to 4; m is an integer from 0 to 2n; p is an integer from 0 to n; q is an integer from 0 to n; r is an integer from 0 to n; s is an integer from 0 to n; p+q+r+s is an integer from 0 to 2n, preferably at most n, and if p+q+r+s is 0, m is ⁇ 2n ⁇ 2; R′ is selected from —H, —CH 2 OH, —COOH; and R 1 , R 2 , R 3 , R 4 are the same or different and are selected from —H and linear or branched groups of formula —C n′ H m′ —R′′, wherein n′ is an integer from 1 to 8, m′ is an integer from 0 to 2n and R′′ has the same definition as R′ above; preferably R
• the carboxylic acids used in the process of the present invention are typically linear. They can also be branched. Usually they are staturated. They can also be unsaturated. Preferably, the carboxylic acids are not cyclic. In particular, they are not aromatic compounds.
• the carboxylic acids or the salts thereof comprise at least one carboxylic acid or carboxylate group, preferably at least two carboxylic acid or carboxylate groups, for example two, three or even four carboxylic acid or carboxylate groups.
• carboxylic acids are those of the formula (II), (III), (IV) or (V) below:
• n is an integer from 2 to 8, preferably from 2 to 4 and m is an integer from 0 to 2n ⁇ 2, preferably from n to 2n ⁇ 2;
• n is an integer from 2 to 8, preferably from 2 to 4, and m is an integer from 0 to 2n ⁇ p ⁇ s, p is an integer from 1 to n, s is an integer from 1 to n; and
• n is an integer from 1 to 8, preferably from 1 to 4, in particular 1 or 2
• m is an integer from 1 to 2n ⁇ 1
• R 1 and R 2 are the same or different and are selected from —H, —CH 2 —CH 2 OH, —CH 2 —COOH and —CH(CH 3 )—COOH, in particular from —CH 2 —COOH and —CH(CH 3 )—COOH.
• carboxylic acids, or salts thereof, useful in the present invention are lactic acid, citric acid, tartaric acid, glucaric acid, maleic acid, nitrilotriacetic acid (NTA), methylglycine diacetic acid (MGDA), their salts and mixtures thereof.
• Citric acid, maleic acid, nitrilotriacetic acid (NTA), methylglycine diacetic acid (MGDA), their salts and mixtures thereof are preferred.
• the most preferred carboxylic acids, or salts thereof are citric acid, nitrilotriacetic acid (NTA), methylglycine diacetic acid (MGDA), their salts and mixtures thereof.
• carboxylic acid or salt thereof substituted by at least one electrodonating group and/or comprise at least one carbon-carbon double bond within the skeleton of the molecule.
• more than one carboxylic acid or salt thereof according to the invention can be used.
• several carboxylic acids and/or salts thereof according to the invention can be combined.
• a carboxylic acid or a salt thereof according to the invention can also be combined with one or more conventional chelating agents such as ethylene diamine tetra-acetic acid and its salts (EDTA) or diethylene triamine pentaacetic acid and its salts (DTPA).
• EDTA ethylene diamine tetra-acetic acid and its salts
• DTPA diethylene triamine pentaacetic acid and its salts
• the present invention preferably, there is no peroxide oxidizing agent present during the pretreatment step of the paper pulp with the chelating agents.
• carboxylic acids which are biodegradable products.
• the preferred carboxylic acids according the present invention as well as their salts have the main advantage to be readily biodegradable products.
• the pretreatment step is conducted in the presence of at least one inorganic magnesium derivative and of at least one carboxylic acid or its salt, except its magnesium salt (i), as defined above, namely substituted by at least one electrodonating group and/or comprising at least one carbon-carbon double bond within the skeleton of the molecule.
• the salt of the at least one carboxylic acid may be selected from, for example, the sodium salt, the potassium salt, the lithium salt of the carboxylic acid.
• the inorganic magnesium derivative is preferably selected from magnesium oxide, magnesium hydroxide, magnesium chloride, magnesium nitrate and magnesium sulphate.
• Magnesium sulphate may be in its anhydrous form or in its hydrated form, for example in its heptahydrated form (Epsom salt).
• An especially preferred inorganic magnesium derivative according to this first embodiment is the magnesium sulphate heptahydrate or Epsom salt.
• the amount of the inorganic magnesium derivative must be optimized depending on the paper pulp to be pretreated and on the paper mill.
• the amount of the inorganic magnesium derivative, expressed as Mg 2+ ions is usually less than or equal to 1% by weight of the dry paper pulp, preferably less than or equal to 0.5%, more preferably lower than or equal to 0.1%, advantageously less than or equal to 0.08%.
• the amount of the inorganic magnesium derivative, expressed as Mg 2+ ions is generally more than or equal to 0.01% by weight of the dry paper pulp, preferably more than or equal to 0.02%, advantageously more than or equal to 0.04%.
• the concentration of the carboxylic acid or its salt (i) is typically less than or equal to 1% by weight of the dry pulp, preferably less than or equal to 0.8% of dry pulp.
• the concentration of the carboxylic acid or its salt (i) is usually more than or equal to 0.2% by weight of the dry pulp, preferably more than or equal to 0.3% by weight of dry pulp, for example more than or equal to 0.4% by weight of dry pulp.
• the pretreatment step is conducted in the presence of at least one carboxylic acid at least partially saponified with Mg 2+ (ii) as defined above, namely substituted by at least one electrodonating group and/or comprising at least one carbon-carbon double bond within the skeleton of the molecule.
• Said magnesium salt of carboxylic acid can be purchased as such to an industrial manufacturer or can be prepared before use by reacting a magnesium derivative such as magnesium oxide, magnesium hydroxide or magnesium carbonate, with the corresponding carboxylic acid to form the at least partial magnesium salt of the carboxylic acid, according to any method known in the art.
• the at least partial magnesium salt of the carboxylic acid (ii) is generally less than or equal to 1% by weight of the dry pulp, especially less than or equal to 0.8%.
• the concentration of the magnesium salt of the at least partial magnesium salt of the carboxylic acid (ii) is in general more than or equal to 0.2% by weight of the dry pulp, preferably more than or equal to 0.4%.
• the at least partial magnesium salt of the carboxylic acid (ii) may be in the form of the stoechiometric magnesium salt or of a partial magnesium salt. Indeed, all the carboxylic groups of all the carboxylic acid molecules may be saponified, or only a part of the carboxylic groups and/or a part of the carboxylic acid molecules may be saponified.
• Examples of stoechiometric salts of the carboxylic acids of the present invention are magnesium citrate, magnesium maleate and the magnesium salt of nitrilotriacetic acid.
• Magnesium citrate results from the stoechiometric reaction of two equivalents of citric acid with 3 equivalents of Mg(OH) 2 and can be written as Citrate 2 Mg 3 .
• Magnesium maleate results from the stoechiometric reaction of one equivalent of maleic acid with one equivalent of Mg(OH) 2 .
• the magnesium salt of nitrilotriacetic acid results from the stoechiometric reaction of two equivalents of nitrilotriacetic acid (NTA) with three equivalents of Mg(OH) 2 and can be written NTA 2 Mg 3 .
• the magnesium salt of methylglycine diacetic acid results from the stoechiometric reaction of two equivalents of methylglycine diacetic acid (MGDA) with three equivalents of Mg(OH) 2 and can be written MGDA 2 Mg 3 .
• An example of a partial magnesium salt of the carboxylic acids of the present invention is the compound Citrate 2 Mg 1.5 resulting from the reaction of two equivalents of citric acid with 1.5 equivalents of Mg(OH) 2 , said formula being actually an average one and the resulting product being in reality a mixture of compounds, i.e. a mixture of the acid and of the mono-, di- and tri-saponified molecules.
• the stoechiometric compound Citrate 2 Mg 3 has a solubility in water of maximum 10% by weight at room temperature, while the solubility of the partial magnesium salt Citrate 2 Mg 1.5 is of at least 30% by weight in water at room temperature.
• the solubility in water at room temperature of the stoechiometric magnesium salt of maleic acid is of maximum 20% by weight and of the stoechiometric magnesium salt of nitrilotriacetic acid (NTA 2 Mg 3 ) is of at least 30% by weight.
• the pretreatment step of the process of the present invention is typically performed at a neutral pH or at a weakly acidic pH, in particular at the natural pH of the paper pulp.
• the pretreatment step is conducted at a pH equal to or above 4, particularly at a pH equal to or above 5.
• the pH during the pretreatment step is usually equal to or below 8, in many cases equal to or below 7, especially equal to or below 6.5, values equal to or below 6 being common. Suitable ranges for the pH during the pretreatment step are for example from 4 to 8, preferably from 5 to 7, and even more preferably from 5 to 6.
• the pH of the paper pulp may be adjusted to preferred values by means of pH modifying compounds.
• pH modifying compounds are sodium hydroxide or suitable alternative bases and sulfuric acid or chlorhydric acid or suitable alternative acids.
• the pretreatment step is usually carried out in the presence of water in order to reach a final consistency of at least 1% by weight of dry paper pulp.
• final consistency is meant the amount of paper pulp present into the paper pulp slurry after the addition of the chelating agents needed for the pretreatment step.
• the final consistency of the paper pulp is usually less than or equal to 20% by weight, particularly less than or equal to 15%, more particularly less than or equal to 10%. In the majority of the cases, a final consistency of 1 to 20% by weight of dry pulp will be suitable, preferably from 3 to 15%, especially from 5 to 10%.
• the pretreatment step is usually carried out at the temperature generated by the mechanical treatment of the wood.
• the temperature can vary widely and is usually of at least 40° C.
• the temperature is generally less than or equal to 95° C.
• the duration of the pretreatment step is usually from 5 to 180 minutes, varying from mill to mill. In general, good results are obtained provided that the duration of the pretreatment step is of at least 5 minutes. Preferably, the duration of the pretreatment step is equal to or higher than 30 minutes.
• the pretreatment step may be applied to a mechanical paper pulp, a chemical pulp or a waste paper pulp, preferably to a mechanical paper pulp.
• mechanical paper pulp are meant paper pulps obtained by mechanical treatment. Examples of such paper pulps are pressure groundwood (PGW), stone groundwood (SGW), thermomechanical pulp (TMP), refiner mechanical pulp (RMP), chemithermomechanical pulp (CTMP) and alkaline peroxide mechanical pulp (APMP or APP).
• the present invention relates to a process for the bleaching of paper pulp with one or more peroxide oxidizing agent, comprising the steps of
• the present invention also relates to a process for the bleaching of paper pulp with one or more peroxide oxidizing agent in which the pulp is first treated in a pretreatment step as described above, and comprising the additional steps of:
• the paper pulp is submitted to only one pretreatment step before the bleaching with one or more peroxide oxidizing agent.
• a washing step may also be conducted between the pretreatment step and the bleaching step.
• Other steps such as additional bleaching steps, can also be added to the process. Nevertheless, only one pretreatment step, one pressing step, one washing step and one bleaching step with one or more peroxide oxidizing agents is usually sufficient for the bleaching of mechanical paper pulp.
• the peroxide oxidizing agent is usually chosen from the group consisting of hydrogen peroxide, organic peracids such as peracetic acid and/or a combination thereof.
• the oxidizing agent is preferably hydrogen peroxide, which is advantageously used in an alkaline medium.
• Hydrogen peroxide is thus preferably used in combination with an alkaline compound, especially with at least alkaline earth hydroxide such as sodium hydroxide, potassium hydroxide, calcium hydroxide and magnesium hydroxide.
• the bleaching step is conducted using hydrogen peroxide, an alkaline compound and a stabilizer, such as sodium silicate or an organic stabilizer such as a polyacrylate and/or a polyhydroxyacrylate salt.
• the present invention also relates to the use as chelating agents of
• the brightness of paper pulp was measured using a Datacolor Elrepho spectrophotometer (SF450) according to ISO standard 2470.
• the percentages of chelating agents are expressed as the amount of pure product by weight of dry pulp.
• Examples conducted in the absence of a chelating agent are the result of a pretreatment step performed with demineralised water only.
• the bleaching step was conducted in the same conditions as the other examples of the series.
• DTPA means diethylene triamine pentaacetic acid.
• DTPA was used as a commercial solution of 40% DTPA by weight of water.
• Citrate 2 Mg 1.5 is a partially saponified magnesium salt of citric acid. This product results from the reaction of two equivalents of citric acid with 1.5 equivalents of Mg(OH) 2 , said formula being actually an average one and the resulting product being in reality a mixture of compounds.
• Maleic Mg means the magnesium salt of maleic acid. It results from the stoechiometric reaction of 1 equivalent of maleic acid with one equivalent of Mg(OH) 2 .
• NTA means nitrilotriacetic acid.
• NTA is commercially available, for instance as TRILON AS® from BASF.
• NTA Na 3 means the tri sodium salt of nitrilotriacetic acid. This product is commercially available, for example as TRILON A® sold by BASF.
• NTA 2 Mg 3 means the magnesium salt of the nitrilotriacetic acid (NTA).
• NTA 2 Mg 3 was prepared by reacting 2 equivalents of NTA (commercially available as TRILON AS® from BASF) with 3 equivalents of Mg(OH) 2 .
• NTA, NTA Na 3 and NTA 2 Mg 3 were used as aqueous solutions (40 wt %).
• MGDA means methylglycine diacetic acid.
• MGDA Na 3 means the trisodium salt of methylglycine diacetic acid. This product is commercially available, for example as TRILON M® from BASF. MGDA and MGDA Na 3 were used as aqueous solutions (40 wt %).
• MGDA Na 3 /NTA means a mixture of the trisodium salt of methylglycine diacetic acid (MGDA Na 3 ) and of nitrilotriacetic acid (NTA).
• This product was prepared by adding 1.6 g of NTA stepwise (by 0.4 g) to 10 g of MGDA Na 3 .
• the resulting mixture was diluted with water in order to obtain a concentration of active product of 40% by weight.
• This solution contained 72% by weight of MGDA Na 3 and 28% by weight of NTA, both being partially saponified and present under the form of their partial sodium salt.
• the pH of this solution was about 5.0.
• RMP refiner mechanical pulp
• the pretreatment step was carried out at 60° C. during 30 minutes on pulp samples at a final consistency in water of 10 wt %, at the natural pH of the paper pulp. After said pretreatment, the pulp was pressed up to a consistency of 30 wt %.
• the resulting paper pulp was then subsequently bleached at a final consistency of 15 wt % and at a temperature of 70° C. during 120 minutes in the presence of 5.0% of hydrogen peroxide, 3.1% of caustic soda and 3.5% of sodium silicate, all these percentages being expressed by weight of dry pulp.
• the amount of 0.69% of Citrate 2 Mg 1.5 by weight of dry pulp corresponds to an amount of 0.06% of Mg 2+ and of 0.63% of citric acid by weight of dry pulp.
• the amount of 0.31% of the magnesium salt of maleic acid (Maleic Mg) by weight of dry pulp corresponds to an amount of 0.06% of Mg 2+ and of 0.19% of maleic acid by weight of dry pulp.
• thermomechanical pulp (TMP) was pretreated with the chelating agents summarized in Table II below.
• the pretreatment step was carried out in the same conditions as in previous examples.
• the resulting paper pulp was then subsequently bleached at a final consistency of 15 wt % and at a temperature of 80° C. during 60 minutes in the presence of 3.9% of hydrogen peroxide, 1.9% of caustic soda and 1.5% of sodium silicate, all these percentages being expressed by weight of dry pulp.
• the amount of 0.5% of Citrate 2 Mg 1.5 by weight of dry pulp corresponds to an amount of 0.04% of Mg 2+ and of 0.46% of citric acid by weight of dry pulp.
• the amount of 0.75% of Citrate 2 Mg 1.5 by weight of dry pulp corresponds to an amount of 0.06% of Mg 2+ and of 0.69% of citric acid by weight of dry pulp.
• CTMP chemithermomechanical pulp
• the pretreatment step was carried out in the same conditions as in the previous examples.
• the resulting paper pulp was then subsequently bleached at a final consistency of 15 wt % and at a temperature of 65° C. during 120 minutes in the presence of 2.5% of hydrogen peroxide, 1.7% of caustic soda and 2.3% of sodium silicate, all these percentages being expressed by weight of dry pulp.
• the amount of 0.69% of Citrate 2 Mg 1.5 by weight of dry pulp corresponds to an amount of 0.06% of Mg 2+ and of 0.63% of citric acid by weight of dry pulp.
• the amount of 0.31% of the magnesium salt of maleic acid (Maleic Mg) by weight of dry pulp corresponds to an amount of 0.06% of Mg 2+ and of 0.19% of maleic acid by weight of dry pulp.
• the amount of 0.28% of NTA 2 Mg 3 by weight of dry pulp corresponds to an amount of 0.04% of Mg 2+ and of 0.24% of NTA by weight of dry pulp.
• SGW stone ground wood pulp
• the pretreatment step was carried out in the same conditions as in the previous examples.
• the resulting paper pulp was then subsequently bleached at a final consistency of 15 wt % and at a temperature of 80° C. during 180 minutes in the presence of 3.5% of hydrogen peroxide, 1.17% of Kaliol (magnesium hydroxide suspension) and 0.2% of DTPA, all these percentages being expressed by weight of dry pulp.
• the amount of 0.24% of NTA 2 Mg 3 by weight of dry pulp corresponds to an amount of 0.04% of Mg 2+ and of 0.28% of NTANa 3 by weight of dry pulp.

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=40822931

Family Applications (1)

Country Status (9)

Families Citing this family (1)

Citations (14)

Family Cites Families (7)

• 2010
  • 2010-05-28 PL PL10724373T patent/PL2435628T3/pl unknown
  • 2010-05-28 CN CN2010800236724A patent/CN102449234A/zh active Pending
  • 2010-05-28 WO PCT/EP2010/057372 patent/WO2010136550A1/en not_active Ceased
  • 2010-05-28 MY MYPI2011005702A patent/MY154626A/en unknown
  • 2010-05-28 US US13/321,256 patent/US20120061043A1/en not_active Abandoned
  • 2010-05-28 EP EP10724373.5A patent/EP2435628B1/en not_active Not-in-force
  • 2010-05-28 CN CN201510789210.8A patent/CN105442372A/zh active Pending
  • 2010-05-28 BR BRPI1016066A patent/BRPI1016066A2/pt not_active Application Discontinuation
  • 2010-05-28 CA CA2762712A patent/CA2762712C/en not_active Expired - Fee Related
• 2011
  • 2011-11-29 CL CL2011003017A patent/CL2011003017A1/es unknown

Patent Citations (14)

Also Published As

Similar Documents

Legal Events