Compositions: coating or plastic – Coating or plastic compositions – Carbohydrate or derivative containing
Reexamination Certificate
1998-09-24
2001-01-16
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Carbohydrate or derivative containing
C106S163010, C106S166010, C106S166400, C106S166410, C106S166420, C106S166430, C106S166800, C106S167010, C106S200200, C106S200300, C106S200400, C106S204010, C264S180000, C264S181000, C264S349000
Reexamination Certificate
active
06174358
ABSTRACT:
This invention relates to a method for producing cellulose particles and to an apparatus for carrying out this method.
The invention is based on the problem of providing a method and apparatus for producing cellulose particles which permit cellulose particles to be produced easily and cost-effectively. In particular, it should be possible to produce a plurality of particle shapes and sizes, in particular small particles, and to change over from one size to another without great effort. Furthermore, the method should permit cellulose particles to be produced which have cationic groups in the inside. Finally, the method and apparatus should allow the use of a plurality of initial substances, in particular for producing cationized products.
The invention is based on the finding that this problem can be solved by a method for producing cellulose particles wherein a cellulose solution is dispersed in a regenerant and the cellulose is regenerated and precipitated in dispersed form into cellulose particles.
The subject of the invention is a method characterized in that a cationizing agent is added to a cellulose solution, the cellulose solution mixed with cationizing agent is dispersed in a regenerant, the dispersion taking place under shear load, and the cellulose is regenerated and precipitated directly in dispersed form into longitudinally oriented, fibrous, cationized cellulose particles.
Such a method makes it possible to produce small cellulose particles directly, thereby eliminating an additional method step of grinding large cellulose particles. Moreover, this method can ensure a uniform size of the produced particles. Finally, the particles produced by this method have an advantageous structure since they are made by production of a fine dispersion.
Longitudinally oriented cellulose solution dispersion drops are preferably formed in the regenerant. These longitudinally oriented drops have a large surface, i.e. interface with the regenerant, so that the precipitation or regeneration can take place quickly and the drop size and shape adjusted in the dispersion thus determines the particle size and shape of the final product.
According to a preferred embodiment, the regeneration and precipitation of the cellulose particles takes place under high shear load. This shear load is crucial for fast formation and maintenance of a fine dispersion of the cellulose solution. By adjusting the shear load to different values one can thus vary the size of the particles to be produced. By high shear load one can e.g. adjust the size of the particles to be produced to small values. At high shear load a fine dispersion is produced which ensures fast precipitation or regeneration out of the dispersion in the form of small particles.
The cellulose solution is preferably mixed with a cationizing agent before being dispersed in the regenerant. By adding such a cationizing agent to the cellulose one can produce cationized cellulose particles by the inventive method. One can preferably thus also produce cellulose particles which have cationized groups in the inside. These are of high importance in particular for application in the paper and waste-water industries.
The cationizing agent is preferably added shortly before the regenerant is added. This addition directly before dispersion also permits cationized cellulose solutions which are unstable with respect to the regenerant to be used in the inventive method.
The dispersion and regeneration or precipitation step is preferably performed at a temperature greater than room temperature. The working temperature is preferably 40 to 85° C. These elevated temperatures accelerate the reactions, e.g. the regeneration of the cellulose or the precipitation. The production time can thus be reduced and the total method improved by elevated temperatures.
The cellulose concentration in the cellulose solution is preferably lower than 10 wt %, it being particularly preferred for the concentration to be in the range of 4 to 8 wt %. A low concentration in the cellulose solution minimizes the particle size in the inventive method. At the same time, a deficient concentration of cellulose in the cellulose solution is unfavorable for the strength of the particles to be produced. Moreover, a deficient concentration of cellulose unnecessarily increases the effort for processing the mother liquor from the process.
Solvents to be used for the cellulose are e.g. N-methylmorpholine-N-oxide, lithium chloride-dimethylacetamide, tetraamminecopper-copper(II) hydroxide (cuen or cuoxam). Further, one can use sodium hydroxide solution and carbon disulfide as solvents.
In a preferred embodiment, the regenerated cellulose particles are supplied to a twin screw extruder for degassing.
Particularly in the viscose process, carbon disulfides and hydrogen sulfides arise during regeneration and must be removed before cleaning and dewatering of the cellulose particles. The use of a twin screw extruder for degassing ensures complete degassing, and this element can moreover be connected directly to the outflow pipe of the disperser.
For production one uses an apparatus wherein the disperser comprises a rotor and a stator each having a toothing, and wherein a mixing nozzle is disposed in the feed pipe for the cellulose to the disperser for passing in the regenerant or nonsolvent, the mixing nozzle comprising a plurality of pipes ending shortly before the gap formed between the toothing of the rotor and that of the stator. If the rotor runs in the stator, the toothing of the rotor is located on the outer circumference thereof and the toothing of the stator on the inner circumference thereof.
Between the toothings of the stator and rotor one can adjust a small gap causing a high shear force to be exerted on the cellulose solution and the regenerant or nonsolvent. Moreover, one can adjust the speed of the rotor and thus likewise influence the shear load in such an apparatus. In addition, this apparatus makes it possible to add the regenerant or nonsolvent directly before the disperser in which the dispersion is produced and the cellulose precipitated or regenerated. This permits the time between addition and dispersion to be kept to a minimum. This minimal time ensures that the cellulose is precipitated or regenerated in dispersed form. Finally, such an apparatus has the advantage that one can add before this disperser a mixing element in which the cellulose solution can optionally be provided with cationizing agent or the cellulose solution modified. This inventive apparatus also readily permits connection with degassing apparatuses or with devices for removing excess nonsolvent in the dissolved cellulose process.
The disperser is preferably a “pumping disperser”. Such a disperser has the advantage that one can exactly adjust the shear load it produces on the phase mixture of cellulose solution/regenerant or nonsolvent and achieve high values. The pumping disperser preferably has three rotors in three successive dispersing zones. Repeated treatment of the material to be dispersed within an extremely short time and a high shearing rate as well as shear stress minimize the particle size in the dispersion. One can thus ensure that the precipitated cellulose particles have a small particle size.
The cellulose particles produced with the inventive method preferably have a mean particle size of 0.001 to 10 mm, preferably 0.01 to 5 mm and in particular 0.1 to 1 mm. This small particle size permits the cellulose particles to be used advantageously in different applications. A small particle size is advantageous in particular for use of the cellulose particles in paper plants or waste-water plants. In the paper industry, for example, the particle size may not be thicker than the paper thickness. Additionally, a low particle size can rule out forming problems.
The cellulose particles are preferably so constituted that cationic groups are immobilized in the inside of the particles. Such cellulose particles are suitable in particular for use in papermaking. The cationized groups in the cellulose permit inter
Brandner Alexander
Oberkofler Jorg
Schmalhofer Anton
Spedding Jeffrey F.
Brunsman David
Cellcat GmbH
Fay Sharpe Fagan Minnich & McKee LLP
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