DE102007029686A1 - Process for forming calcium carbonate in a pulp suspension - Google Patents

Abstract

The method is used to load fibers with filler, especially calcium carbonate. This calcium hydroxide z. B. in lime (MOL) with gaseous carbon dioxide (CO <SUB> 2 </ SUB>) in combination, which is formed in a chemical reaction calcium carbonate. Prior to this reaction, the penetration of the fibers with calcium hydroxide is promoted by adding anionic substances, in particular salts, polyamides, retention aids or starch particles or a mixture of these substances.

Description

The The invention relates to a method according to the preamble of claim 1.

Of the Use of calcium carbonate as a mineral filler in paper and board making has long been known. He serves u. a. to the visual quality of graphic Decisively improve papers. There are already procedures where the calcium carbonate in an aqueous liquid is precipitated by z. For example, a reaction between calcium hydroxide and gaseous carbon dioxide is brought about. The fillers produced in this way can then be used in the Paper mill to the pulp. A newer development lies therein, the process of precipitation in the presence of the pulp trigger in a mixture in which the for the paper production certain fibers are already included. Such Procedures are called fiber loading procedures.

Several methods of fiber loading technology for loading pulp fibers with calcium carbonate are already known. In the US 5,223,090 For example, there is described a method of using fiber material having elongated fibers with a cell wall surrounding a cavity, the fibers having a humidity sufficient to form a dewatered pulp slurry. The fibers have a moisture content corresponding to a proportion of 40 to 50% of the weight of the fibers. The water is essentially present inside the fibers and inside the fiber walls. Subsequently, alternatively calcium oxide or calcium hydroxide is added to the pulp so that at least part of the incorporated calcium oxide or calcium hydroxide is associated with the water present in the pulp. Subsequently, the fibrous cellulosic material is contacted with carbon dioxide while being subjected to a shear mixing process to produce a fibrous material having a substantial amount of calcium carbonate on the fiber surface in the hollow interior and within the fibrous walls of the cellulosic fibers.

From the US 5,665,205 A method of loading a waste paper suspension is known, which serves in particular to increase the whiteness of the - deinked or non-deinked - waste paper. In this method, a waste paper suspension is preferably introduced at a consistency of between 0.1 and 5% in a gas / liquid reactor. Downstream of this point of introduction then takes place the supply of a basic salt-containing liquid, in particular of calcium hydroxide, wherein the thus mixed components are brought into contact with a reaction gas, in particular carbon dioxide, thereby to precipitate the filler. The thus loaded waste paper suspension is then used for paper or board production. As a particularly suitable gas / liquid reactor, a mixing container is proposed in which gas bubbles are distributed in a liquid. Apparently, an unusually high degree of filling of the pulp (filler content several hundred percent of the fiber weight) is required to achieve the desired whiteness.

From the DE 102 04 254 A1 Another method for loading a pulp suspension is known. The process comprises the following steps: introduction of calcium hydroxide in liquid or dry form or of calcium oxide into the pulp suspension, thickening and heating of the pulp suspension, feeding of gaseous carbon dioxide in a crystallizer, precipitation of calcium carbonate by the carbon dioxide.

By Process of this kind is possible with calcium carbonate loaded fiber (FLPCC = fiber loaded precipitate calcium carbonate) manufacture, in particular for pulp production or for pulp use in papermaking. The fiber raw material to be loaded is made, for example, from recycled paper, of DIP (= Deinked Paper), of secondary pulp, bleached or unbleached kraft cell fuel or wood pulp any Type, bleached or unbleached sulphite / sulphate pulp, pulp, Linen, cotton and / or hemp fibers and / or any other Paper stock made using in a paper machine place.

The Field of application of the invention extends to the paper and Pulp production and process technology including of the prepared filler and includes applications all types of paper including those in their production resulting committees that have a filler content between 1% and 60%. Preferably, the filler content between 5% and 50%.

Across from conventional processes for producing a pulp suspension can by loading (in lumens, fiber walls and / or Fiber surface) in a paper or board web the same strengths energetically cheaper be achieved; In particular, grinding energy can be saved in this way.

Loading has a positive effect on the processes in stock preparation, paper machine and / or further processing. Thus, a paper web made of loaded fibers can drain more easily, which is why z. B. increased the machine speed and / or the press section can be operated with lower pressure. It would also be possible to use less energy (eg steam) in the dryer section.

One further advantage when using the invention Technology for the types of paper listed above in that it can also be easily processed in a calender can be. By doing so when using the fiber-loading technology Fiber-loading particles are deposited in and around the fibers, blackening is reduced or avoided altogether.

comparing one this paper with conventionally produced papers, so show at the same and / or higher Füllstoffgehalten higher and / or equal strengths, porosity, specific volume (which optionally also deliberately lower can be adjusted), opacity and printability. By this type of fiber loading can be depending on the degree of loading of the pulp increase the productivity of the paper machine and / or make their production more cost-effective (eg by Commodity energy cost reduction).

It The object of the invention is a process for loading a pulp suspension in which the advantages of the loading process are increased in particular, that the amount of in the cavities the fiber is fixed fixed fillers.

According to the invention This object by the measures mentioned in claim 1 solved.

With Help of the new procedure is the Calciumhydroxidaufnahme of the Reinforced fibers. Due to the electrical effect of the added anionic substances can be a stronger compound to the Fibrous surfaces and / or better penetration into the cavities achieved and also the production of calcium carbonate within the Fibers ("lumen loading") are increased.

The Lumen loading can be further intensified if the anionic Substances after addition to the pulp suspension by a special process step, z. B. washing / thickening of the outer surfaces the fibers are removed again, so that is the charge setting different from lumens and fiber outer surfaces is.

In the following, typical process steps and parameters for the loading of a pulp suspension according to the invention are described:
The starting material for the loading process is an aqueous pulp suspension, in particular pulp suspension with 0.1 to 30% consistency. This is mixed with calcium oxide or hydroxide in liquid or solid form. The calcium hydroxide is suspended to a large extent in the form of fine solid particles and is brought into contact with the surface of the fibers. Since the fibers are in the form of elongated hollow bodies open on at least one side, the calcium hydroxide can also penetrate into the interior of the fibers, the so-called lumen.

In the direct or indirect subsequent chemical reaction to form the calcium carbonate gaseous CO ₂ is preferably initiated, it can be assumed that the distribution of CO ₂ in the aqueous suspension very quickly and easily progresses, so that wherever Calcium hydroxide is located, a Calciumcarbonatausfällung will take place. Depending on the process, it may be necessary to thicken the pulp suspension beforehand.

In particular embodiments, especially if several Reactors can also be used with additional calcium hydroxide or calcium oxide in aqueous and / or solid form in the Reactor mixed in, for. B. may be added as lime milk.

Preferably is the process temperature when producing the calcium carbonate between + 15 ° C and 130 ° C, especially between 20 ° and 60 ° C.

The Formation of the calcium carbonate is preferably in a pressure range between 0.1 and 6 bar, in particular between 1 and 4 bar performed. There are also higher pressures, z. B. up to 20 bar possible. The mean residence time of the substance in the reactor is between 60 Seconds and 15 minutes, especially between 5 and 10 minutes.

According to one further embodiment of the method according to the invention The solids concentration of the reaction with carbon dioxide provided pulp suspension in a range of about 0.1 to about 40%, and preferably in a range of about 0.5 chosen to 30%.

It For example, crystals may be derived from a rhombohedral Shape with a grain size fraction in one area from about 0.02 to about 5 microns. In particular It is also beneficial to crystals of a scalenohedral case Mold or agglomerates with a respective length in one Range from about 0.02 to about 5 microns and a respective Diameter in a range of about 0.02 to about 5 microns to create.

The The invention and its advantages are explained with reference to Drawings. Showing:

1 A plant scheme for illustrating the method according to the invention;

2 Plant schematic for a varied process.

In 1 is shown a favorable embodiment of the method according to the invention with the aid of a plant scheme. From the raw materials 9 is in the pulper 10 a pulp suspension 1 educated. The dissolution in the pulper 10 should be so complete that virtually all fibers are singular. Otherwise it would be the pulper 10 downstream deduster recommended. A mixing container 2 with stirrer 28 serves to the fiber suspension 1 Calcium oxide or calcium hydroxide, e.g. B. as here in the form of milk of lime MOL, mix and also to allow a defined residence time. The lime milk MOL is from a lime leaching equipment 3 provided and with a pump 11 promoted. The attachment of the added or formed calcium hydroxide to the fibers is favored by the addition of anionic substances, which results in a chemical container 22 and appropriate dosage is indicated. The anionic substances are preferably added before the calcium oxide or hydroxide. They are composed in particular of salts, polyamides, retention aids or starch particles.

The mixture thus treated 7 is then here with a consistency between 0.1 and 6% in a reactor 5 in which gaseous carbon dioxide CO _{2 is} added. It is provided in a CO ₂ supply facility 16 , with the possibility also exists in a CO ₂ heater 17 to warm up. A suitable reactor 5 is z. B. a closed container with a stirrer 27 is provided.

By the movements of the content can be the reaction partners easily get in touch.

The loaded pulp then passes into a finishing unit, z. B. a storage tank 13 , From there it is pumped for further processing, ultimately for the production of paper or cardboard.

The plant scheme of 2 shows a variant of the method. The formation of the pulp suspension and its treatment with anionic substances can be carried out similarly as in the 1 described. As a possible variant is here (dashed lines) the addition of at least part of the milk of lime MOL in the pulper 10 specified. If the dissolution in batch mode, the milk of lime MOL can later than the anionic substances in the pulper 10 be registered. The mixture 7 gets into the press 4 , in which the consistency is set to a value that z. B. up to 30%. The pressed filtrate 14 flows into the press water tank 8th and can be via a filtrate pump 12 be promoted to the desired places. Since during pressing and a portion of the calcium hydroxide in the filtrate 14 goes, it is advantageous, this in the process upstream, z. B. in the pulper 10 feed again. The dewatered pulp S is then placed in a reactor at a consistency of between 6% and 30% 6 guided. Eventually there will be another addition of calcium hydroxide in the form of milk of lime (MOL). A rotating spiral 15 transports the substance through the reactor 6 , In addition, gaseous carbon dioxide CO _{2 is} added. It is provided here in a CO ₂ supply facility 16 , with the possibility also exists in a CO ₂ heater 17 to warm up. A suitable reactor 6 is z. B. a closed screw conveyor, which is preferably operated so that it is filled to a maximum of 80% -vol, preferably 50% -vol, with a moist solid, wherein the water volume of the pulp is included. The remaining volume in the reactor 6 is taken by gas or steam or spray liquid. Due to the movements of the contents, the reactants can easily come into contact.

In cases where the reactor 6 is operated at a pressure that differs from the ambient pressure, ie z. B. is between 1.1 and 5 bar, is usually a seal at the inlet 18 and spout 19 required, eg. B. in the form of known rotary valves. Of course, there are other options, such. B. a plug formation with the aid of a screw plug.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - US 5223090 [0003]
• - US 5665205 [0004]
• - DE 10204254 A1 [0005]

Claims (14)

Process for loading fibers with filler, in particular with calcium carbonate, in which calcium oxide or calcium hydroxide is introduced in liquid or dry form into an aqueous fiber material and this mixture thus formed ( 7 ) in at least one reactor ( 5 . 6 ) is mixed with carbon dioxide, in particular with gaseous carbon dioxide, wherein filler, in particular calcium carbonate is formed by chemical reaction with calcium hydroxide, characterized in that the pulp anionic substances are added, in particular salts, polyamides, retention or starch particles or a mixture of these substances. Method according to claim 1, characterized in that that the anionic substances are the pulp prior to introduction of the calcium oxide or calcium hydroxide. Method according to claim 1 or 2, characterized that the electric charge in the cavities of the fibers is set more negative than on the outer surfaces the fibers. Method according to claim 3, characterized that at least part of the anionic substances from the outer surfaces the fibers removed again, in particular washed off. Method according to one of the preceding claims, characterized in that the calcium hydroxide in the form of lime milk (MOL) is added to the pulp. Method according to claim 5, characterized in that that the milk of lime (MOL) is ground before addition to the pulp, that the average particle size (d 50) of the calcium hydroxide particles maximum 5 microns, preferably at most 1 micron. Method according to one of the preceding claims, characterized in that as a reactor ( 5 ) is used for the formation of calcium carbonate, a closed vessel is introduced into the gaseous carbon dioxide CO ₂ . Process according to Claim 7, characterized in that the pulp suspension in the reactor ( 5 ) is stirred by a mechanically driven rotor. Process according to claim 7 or 8, characterized in that the reactor ( 5 ) is operated at a pressure which corresponds to the ambient pressure with a maximum tolerance of 10% deviation. Process according to claim 7 or 8, characterized in that the reactor ( 5 ) is operated at a pressure which is between 1 and 6 bar, preferably 1 to 4 bar. Method according to one of the preceding claims, characterized in that the reactor ( 5 ) for the formation of calcium carbonate at a temperature between 15 ° and 130 ° C, preferably 20 ° to 60 ° C, is operated. Method according to one of the preceding claims, characterized in that the pulp suspension ( 1 ) by a dissolution process in a pulper ( 10 ) is formed with admixture of water (W) and that the addition of the anionic substances takes place in this dissolution process. Method according to one of the preceding claims, characterized in that the pulp suspension ( 1 ) is formed from fresh pulp. Method according to one of the preceding claims, characterized in that the pulp suspension after the calcium carbonate forming reaction is used for paper or board production.