Classifications

• • 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
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/63—Inorganic compounds
  • D21H17/67—Water-insoluble compounds, e.g. fillers, pigments
  • D21H17/675—Oxides, hydroxides or carbonates
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F11/00—Compounds of calcium, strontium, or barium
  • C01F11/18—Carbonates
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F11/00—Compounds of calcium, strontium, or barium
  • C01F11/18—Carbonates
  • C01F11/181—Preparation of calcium carbonate by carbonation of aqueous solutions and characterised by control of the carbonation conditions
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F11/00—Compounds of calcium, strontium, or barium
  • C01F11/18—Carbonates
  • C01F11/182—Preparation of calcium carbonate by carbonation of aqueous solutions and characterised by an additive other than CaCO3-seeds
• • 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
  • D21C9/001—Modification of pulp properties
  • D21C9/002—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives
  • D21C9/004—Modification of pulp properties by chemical means; preparation of dewatered pulp, e.g. in sheet or bulk form, containing special additives inorganic compounds
• • 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
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/63—Inorganic compounds
  • D21H17/70—Inorganic compounds forming new compounds in situ, e.g. within the pulp or paper, by chemical reaction with other substances added separately
• • 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
  • D21H23/00—Processes or apparatus for adding material to the pulp or to the paper
  • D21H23/02—Processes or apparatus for adding material to the pulp or to the paper characterised by the manner in which substances are added
  • D21H23/04—Addition to the pulp; After-treatment of added substances in the pulp
  • D21H23/06—Controlling the addition
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/01—Particle morphology depicted by an image
  • C01P2004/03—Particle morphology depicted by an image obtained by SEM
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
  • C01P2004/00—Particle morphology
  • C01P2004/60—Particles characterised by their size
  • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer

Definitions

• the invention relates to a method and a system for precipitating calcium carbonate.
• the invention relates to a product comprising calcium carbonate. Background of the invention
• PCC is precipitated calcium carbonate.
• it is typically produced by allowing calcium hydroxide Ca(OH) 2 to react with a precipitating agent, such as, for example, carbon dioxide C0 2 , wherein the resulting product is precipitated calcium carbonate (PCC).
• the calcium hydroxide Ca(OH) 2 used in the reaction may be produced, for example, by slaking burnt lime CaO with water, wherein the reaction produces calcium hydroxide.
• calcium carbonate CaC0 3 is precipitated in industry by introducing gas containing carbon dioxide into a suspension of calcium hydroxide in water, which is also known as milk of lime. Calcium carbonate precipitated in such a manner may be used, for example, as paper filler or coating pigment. By changing process conditions it is possible to influence the crystalline and granular form of precipitated calcium carbonate and its properties.
• a purpose of the present invention is to provide a solution for the problem presented above for increasing the filler content.
• a new method and system for precipitating calcium carbonate is provided.
• paper, fibre composite construction and paperboard comprising calcium carbonate is provided.
• the invention is based on a new method, where calcium carbonate is precipitated from a mixture of fibre material and calcium hydroxide so that at least a part of calcium carbonate precipitates directly onto the surface of fibres.
• a purpose of the method according to the invention is to facilitate the production of a fibrous product so that increasing the filler content in a fibrous product in comparison to papers manufactured by conventional methods may be possible.
• the wet strength properties of the product being produced do not decrease by the addition of filler as much when producing paper or paperboard by the method according to the invention as when producing paper or paperboard according to prior art.
• the opacity of the product being produced improves in comparison to products according to prior art. Therefore, for example, the opacity of a product produced of birch pulpwood may be nearly as good as the opacity of a product manufactured from eucalyptus or acacia pulpwood by a conventional method.
• the method according to the invention is presented in claim 1.
• the system according to the invention is presented in claim 9.
• the product according to the invention is presented in claim 11.
• the method for precipitating calcium carbonate according to the invention is primarily characterized in that the method comprises at least the following steps:
• - calcium hydroxide for example aqueous suspension of calcium hydroxide, is introduced to a fibre suspension comprising cellulose- containing fibres,
• the product according to the invention is primarily characterized in that it is a fibrous product comprising calcium carbonate and produced by the method according to the invention.
• the product according to the invention is paper, fibre composite construction or paperboard, which is produced by some method according to the invention.
• the filler content of the product according to the invention is at least 15 %.
• calcium hydroxide is allowed to attach onto the surfaces of fibres for long enough before calcium hydroxide is precipitated to calcium carbonate by carbon dioxide. Therefore, carbon dioxide is introduced to the main flow typically only after a certain delay time from introducing calcium hydroxide.
• calcium hydroxide is allowed to attach onto the surfaces of fibres for the time period it takes for fibre pulp to travel from refining feeding tank through refiners to the actual pulp feeding tank.
• One advantage of the method and system according to the invention is the simplicity of the method. It is possible to implement the method and the system mainly with existing process devices, wherein only relatively small additional investments are needed.
• calcium carbonate may be precipitated either in a batch process or in a continuous process.
• the precipitation according to the invention is carried out in a continuous process.
• Fig. shows a method for precipitating calcium carbonate according to prior art in a schematic view
• Fig. 2 shows a continuous method for precipitating calcium carbonate according to the present invention in a schematic view
• Fig. 3a shows calcium carbonate precipitated among fibres by a method according to prior art
• Fig. 3b shows calcium carbonate precipitated among birch pulpwood by a method according to the present invention
• Fig. 3c shows calcium carbonate precipitated among pine pulpwood by a method according to the present invention
• Figs. 4a and 4b show some test run results.
• the product according to the invention is preferably a fibrous product, such as, for example, paper, paperboard or fibre composite construction.
• a product produced by the method according to the invention is fine paper, which preferably comprises birch pulpwood.
• a reactive mineral substance used is calcium hydroxide, advantageously an aqueous suspension of calcium hydroxide.
• An aqueous suspension of calcium hydroxide is also called milk of lime.
• a precipitating chemical used is preferably carbon dioxide, such as, for example, gas containing carbon dioxide.
• the precipitation of calcium hydroxide Ca(OH) 2 according to the invention at least partly onto the surface of fibres as PCC for creating a fibrous product may be carried out either in a batch process or in a continuous process.
• aqueous suspension of calcium hydroxide is first introduced to a fibrous pulp suspension.
• the calcium hydroxide is allowed to attach for a pre-determined delay time onto the surface of fibres.
• carbon dioxide CO 2 is led to the aqueous suspension of fibre and calcium hydroxide.
• calcium hydroxide precipitates to calcium carbonate so that calcium carbonate attaches onto the surfaces of fibres.
• Carbon dioxide is led to the reactor advantageously as long as substantially all milk of lime has precipitated.
• continuous precipitations is used in the method (Continuous Precipitated Calcium Carbonate, CPCC).
• CPCC Continuous Precipitated Calcium Carbonate
• calcium carbonate can be precipitated by using the method according to the invention so that it attaches at least partly onto the surface of fibres.
• calcium hydroxide as, for example, aqueous suspension is first introduced to the fibrous pulp suspension. After this the calcium hydroxide is allowed to attach for a pre-determined delay time onto the surface of fibres. After a pre-determined time carbon dioxide is introduced to this mixture containing at least milk of lime and fibres, advantageously to the flow of said mixture. Carbon dioxide is advantageously introduced by injecting.
• calcium hydroxide may react chemically with carboxyl groups on the surface of a fibre, thus forming a strong attachment between the fibre and precipitated calcium hydroxide.
• calcium hydroxide is precipitated to calcium carbonate especially onto the surfaces of fibres when calcium hydroxide is allowed to react with carbon dioxide.
• the natural pH of about 11-12 of calcium hydroxide is suitable for the reaction, and therefore it is typically not necessary to add special pH adjustment chemicals in the mixture.
• the fibres and calcium hydroxide should be in the same space for at least a minute before carbon dioxide is led to the reactor. According to an advantageous embodiment the fibres and calcium hydroxide should be in the same space for at least 00 seconds or at least 1.5 minutes, preferably at least 5 minutes before the introduction of carbon dioxide. According to an advantageous embodiment the above- identified delay time is approximately 15 minutes.
• the average size of produced crystals is approximately 1.5 pm, while the average size of crystals produced by a prior art method in corresponding conditions is around 2.2 pm. It is also substantial that the slope of the size distribution of calcium carbonate crystals produced by the method according to the invention is small; the d30/d70 value of a product produced by a method according to the invention may be reduced even to 28 while the corresponding value of a product produced according to a prior art method is 47. In other words, a part of the produced crystals may be normal-sized PCC, but correspondingly, the crystals may also include very small crystals, approximately of size 1 pm.
• the fibre is covered at least partly, preferably mostly, by PCC by the effect of the formed small calcium carbonate crystals bound onto the surface of a fibre.
• a calcium carbonate layer precipitated by the method according to the invention so to say, coats the fibre.
• the invention is characterized in that calcium hydroxide Ca(OH) 2 reacts with the surface of the fibre by attaching onto it.
• carbon dioxide CO 2 is introduced to the mixture, especially small crystals are formed because the crystal size of the crystals being formed cannot increase as the calcium hydroxide is attached onto the surface of the fibre.
• the method according to the invention is used to form not only cubic calcium carbonate crystals but also prismatic calcium carbonate crystals.
• Prismatic crystals may be formed because calcium hydroxide is attached onto the surface of fibres by precipitating substantially to its attaching point.
• Calcium carbonate precipitated by a conventional method comprises substantially only cubic crystals, because then calcium hydroxide and carbon dioxide are available in excess and carbon dioxide is not attached onto the surfaces of fibres.
• a mixture of fibre and calcium carbonate produced by the method according to the invention typically has better wet strength values with a specific PCC filler amount in comparison to a mixture of fibre and calcium carbonate produced in a conventional manner.
• the substantial wet tensile strength has increased substantially when producing paper or paperboard according to the invention in comparison to conventional production methods. Due to the improvement of wet tensile strength it is possible to introduce into the pulp suspension substantially larger amounts of fillers than previously, which typically has the effect of lowering paper and paperboard manufacturing costs.
• the improved wet strength is especially useful when using birch or some other fibre material comprising a relatively poor wet strength as the main pulp raw material in, for example, fine paper manufacture.
• the properties of the product according to the present invention may change in the manner described above, because in a product produced by the method according to the invention the particle size of PCC is on average smaller than in a product produced by a method according to prior art.
• the wet strength of the product being produced typically improves when e.g. the friction between fibres increases. Scattering of light and opacity also improve, because there are more light scattering surfaces.
• the dry strength of the product being produced typically weakens, because the fibres cannot form hydrogen bonds in the same manner as in production methods according to prior art, as the surface of fibres has, so to say, been coated by PCC. The decrease in dry strength does not, however, typically become problematic in production.
• FIGS 4a and 4b show some examples of test run results.
• the figures show the effect of processing according to an embodiment of the invention in specific properties of the product being produced.
• Both pulps i.e. the reference pulp “REF” and test point “TP11” are substantially the same birch pulpwood pulp.
• REF the precipitated calcium carbonate
• TP11 the precipitated calcium carbonate
• the precipitated calcium carbonate (PCC) is, in turn, formed by a method according to the invention, where calcium hydroxide is first introduced among the fibres and the delay time according to the invention is used between the calcium hydroxide introduction and carbon dioxide introduction.
• the wet tension strength of a product produced by a method according to the invention has already been on almost the same level in an approximately 10 % lower dry matter content as the wet tension strength of the reference point produced by a method according to prior art.
• the wet tension strength of a product produced by a method according to the invention has been approximately 100 % higher than that of a product produced by a prior art method.
• Figure 4b shows in table format some test run results of the properties of test point TP11 in comparison to the properties of a reference point product REF produced by a prior art method.
• the product TP11 produced by the method according to the invention has, in addition to the wet tension strength seen in figure 4a, also an improved light scattering coefficient and opacity in comparison to the reference product REF.
• the dry strength has, as expected, weakened in comparison to the reference point.
• the crystals formed during precipitation are typically divided substantially all over the surface of the fibre. This prevents the formation of too large, unadvantageous crystals and attaches the formed crystals better onto the surface of the fibre.
• the method according to the present invention may be implemented, for example, in connection with existing paper and paperboard mills relatively cost-effectively.
• new structural parts in the method according to the present invention may include, for example, a tank for the relatively long mixing time of lime of milk and fibre suspension, as well as an feeding solutions for carbon dioxide (for example the so-called TrumpJet®).
• the delay in, for example, the refining line may be sufficient for attaching calcium hydroxide onto the surfaces of fibres before the precipitation taking place by the effect of carbon dioxide.
• the refining phase in the solution according to this example may boost the chemical reaction between the calcium hydroxide and the fibre.
• the fibre mixture used in the method according to the present invention may be normal pulp suspension, where the fibre portion is mainly formed of hardwood.
• the fibre portion of the fibre suspension comprises mainly birch.
• the fibre portion of the pulp suspension may comprises also softwood instead of, or in addition to, hardwood. In such a case, the fibre portion may be even entirely softwood.
• the portion of hardwood is not more than 40 wt-%, preferably not more that 30 wt-% of fibres, because thus the benefit from the present invention, especially the benefit of increased wet strength is typically emphasized. Irrespective of the wood type the degree of refining of the fibre suspension being used may vary from slightly refined fibre suspension to a very refined fibre suspension.
• Example 1 show test runs where the method according to the invention has been used, as well as test results from a product produced by the method according to the present invention, in this case paper sheets.
• Example 1 show test runs where the method according to the invention has been used, as well as test results from a product produced by the method according to the present invention, in this case paper sheets.
• Fig. 2 shows the method being used in a schematic vied.
• the pulp which was normally refined birch pulp, remained in the tank in an aqueous suspension of calcium hydroxide for about 100 minutes. Carbon dioxide was introduced after this to the mixture by using TrumpJet® equipment.
• the temperature of the process was about 50°C and the pressure in the reactor was about 4.1 bar.
• the flow rate of the main process flow in the tube reactor was about 2 l/s.
• INJ refers to the introduction of a component, which in the test runs took place by injection.
• Fig. 1 shows the method used in the reference samples in a schematic view.
• the particle size of the PCC formed in the test point according to the invention was very small in comparison to reference samples and the particles covered the surface of fibres substantially entirely.
• the median particle size was only about 1.5 ⁇ for the PCC produced by the method according to the invention, while in the reference point the median particle size was about 2.2 ⁇ .
• Paper sheets were made from the produced pulps.
• the properties of paper sheets produced by the method according to the invention differed from the properties of paper sheets produced from fibre suspension consisting of PCC precipitated in connection with fibre according to prior art in that the paper produced from the fibres suspension implemented by the method according to the invention had in at least one reference line a substantially better wet tension strength (317 N/m vs. 143 N/m in dry matter 50 %).
• the paper produced from fibre suspension implemented by the method according to the invention also had a clearly better light scattering coefficient (75 m 2 /kg vs. 61 m 2 /kg), as well as a better opacity (91.2 % vs. 88.9 %).
• the dewatering properties were substantially the same when using both production methods.
• the realized differences in properties were mainly due to a chemical reaction between fibres and calcium hydroxide.
• test run was performed with a total of ten test points, four test points 1-4 of which were reference points, where the fibres did not have a delay with milk of lime, or the delay was short.
• test points 5- 10 there were six actual test run test points according to the method according to the invention, i.e. test points 5- 10, where the method according to figure 2 was used.
• test points 1 to 4 were birch cellulose fibres. Carbon dioxide and milk of lime were dispensed in the test points 1 to 4 (reference points)listed below in the following manner:
• test points 5 to 10 were used, and in three, pine cellulose fibres (test points 8 to10). Milk of lime was dispensed into the fibres, after which carbon dioxide was introduced with a 15 to125 min dispensing delay to the test points in the manner described below, where test points 5 to 7 comprise birch pulp and test points 8 to 10 pine pulp:
• the properties of pulp and a product produced from the pulp were substantially the same in all reference points 1-4. In other words, when introducing milk of lime substantially simultaneously with carbon dioxide or even about 30 seconds before carbon dioxide, the pulp properties were almost the same. The properties of pulp and the product, however, changed notably when moving on to the actual test points 5-10.
• Figures 3a-c show precipitated calcium carbonate particles in scanning electron microscope (SEM) images both in the first reference point 1 and in the first birch-containing test point 5 and in the first pine-containing test point 8.
• Figure 3a shows a fibre-PCC-mixture taken from reference point 1.
• Figure 3b shows a fibre-PCC-mixture taken from test point 5.
• Figure 3c shows a fibre-PCC-mixture taken from test point 8.
• Test sheets were produced from all test points 1 -10 with a grammage of about 80 g/m 2 . Only CPCC produced by a method according to each test point was used as filler in the test point sheets. Pulp ration was always adjusted to 50 % / 50 % birch/pine, i.e. pine or birch without PCC precipitation was introduced in the mixture in the end so that the pulp composition of the sheet was always constant. In other words, the difference was mainly in whether the PCC was introduced with birch pulp or pine pulp.
• the light scattering and opacity properties of the product being produced were significantly better in test points 5-10 than in reference points 1-4.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Geology (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)
• Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)

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• 2010
  • 2010-08-20 FI FI20105868A patent/FI125278B/fi active IP Right Grant
• 2011
  • 2011-08-16 US US13/814,413 patent/US9051689B2/en not_active Expired - Fee Related
  • 2011-08-16 JP JP2013525331A patent/JP2013536329A/ja active Pending
  • 2011-08-16 WO PCT/FI2011/050716 patent/WO2012022836A1/en not_active Ceased
  • 2011-08-16 EP EP11817817.7A patent/EP2606181B1/en not_active Revoked
  • 2011-08-16 CN CN201180040335.0A patent/CN103154369B/zh active Active
  • 2011-08-16 BR BR112013002379A patent/BR112013002379A2/pt not_active IP Right Cessation
  • 2011-08-16 RU RU2013112360/12A patent/RU2013112360A/ru not_active Application Discontinuation
• 2015
  • 2015-02-24 US US14/630,295 patent/US20150167244A1/en not_active Abandoned

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