Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
2001-02-16
2003-01-21
Jones, Dwayne C. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S127000, C536S128000, C536S084000, C536S090000
Reexamination Certificate
active
06509461
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the production of particulate water-soluble cellulose derivatives, preferably those with a thermal flocculation point.
BACKGROUND OF THE INVENTION
After the reaction and optionally after removing the byproducts formed in the reaction, cellulose derivatives, in particular cellulose ethers, are present in friable, particulate or wad-like form. In this form the cellulose derivatives still have the predetermined structures imparted by the raw materials. Thus for example cellulose ethers generally still exhibit the fiber-like structure of the initial cellulose. These cellulose derivatives are thus unsuitable for their intended use, for example as products soluble in organic and/or aqueous media.
It is typically also necessary to adjust specific grain size distributions, bulk densities, degree of dryness and viscosity values for the various areas of use.
In principle almost all cellulose derivatives therefore have to be compacted, ground and dried in order to make them suitable for use.
The industrially important cellulose derivatives include in particular the cellulose ethers, whose production, properties and applications are described for example in:
Ullmann's Encyclopaedia of Industrial Chemistry, 5th Edition (1986), Volume A5, pages 461-488, VCH Verlagsgesellschaft, Weinheim; and
Methoden der organischen Chemie, 4th Edition (1987), Volume E20, Makromolekulare Stoffe, (Methods of Organic Chemistry) (Macromolecular Substances) Part-Volume 3, pages 2048-2076, Georg Thieme Verlag Stuttgart.
U.S. Pat. No. 2,331,864 describes a process in which a water-moist cellulose ether is adjusted at temperatures of >50° C. to a water content of 72-88 wt. %. The cellulose ether is then cooled to temperatures of <50° C. The gel that is thus obtained is dried at temperatures >50° C. and the dried material is ground.
GB-A 804 306 describes a process for dissolving cellulose ethers soluble in cold water by cooling a hot mixture of the fibrous cellulose ether and water (98-65 wt. %). The cellulose ether is precipitated by renewed heating, and dried. The dried product is ground.
DE-A 952 264 discloses a three-stage process for converting moist, fibrous methyl celluloses into powders that dissolve rapidly. In this case the product, which contains 50-70 wt. % of water, is first of all homogenized to a plastic mass and cooled to 10° to 20° C., a cooled screw press being used for this purpose; the product is then ground with a hammer mill and dried in a circulating air dryer.
EP-A 0 049 815 (which is equivalent to U.S. Pat. No. 4,415,124) describes a two-stage process for the production of micronised powders of cellulose ethers or cellulose, in which the products, which have a fine fibrous or woolly structure, are first of all converted into a brittle solidified form, and the thus treated material is subjected to a grinding operation until a grain size distribution of at least 90% below 0.125 mm is achieved. Vibratory mills or ball mills, preferably cooled, or pellet presses are used in the embrittlement stage, and jet mills, pinned disc mills or impact disc mills are used in the grinding stage.
DE-A 30 32 778 discloses a two-stage process for the continuous homogenization of moist cellulose ethers, in which the moist cellulose ether is subjected to cutting, impact and shear forces generated by circulating rotating bodies having various jacket profiles, optionally with the simultaneous pelletising of the comminuted cellulose ethers with the addition of water, followed by drying of the resultant pellets.
EP-A-0 370 447 describes a process for the gentle grinding and simultaneous drying of moist cellulose ethers, in which a cellulose ether having an initial moisture content of 20 to 70 wt. % is conveyed by means of a carrier gas and at the same time is friction comminuted to an impact comminution size and is dried by the grinding energy to a residual moisture content of 1 to 10 wt. %.
EP-A-0 384 046 describes a process for the production of cellulose ether particles, comprising the comminution in a high rotational speed, air jet rotary impact mill to a particle size of 0.4 to 0.035 mm of cellulose ethers with a viscosity of greater than 100 Pa·s, measured as a 2% aqueous solution at 20° C. using an Ubbelohde tube.
WO 96/00748 discloses a process for the comminution of cellulose ethers, comprising the extrusion of a hydrated cellulose ether through openings with a cross-sectional area of 0.0075 mm
2
to 1 mm
2
(7.5×10
−9
m
2
to 1×10
−6
m
2
) and cutting the resultant extruded material to the desired length.
EP-A-0 835 881 describes a process for the production of methyl cellulose powders with a special particle-size distribution curve by adjusting a methylhydroxyalkyl cellulose granular material to a moisture content of 30 to 70 wt. % with water, followed by grinding in a rotary mill, the product being simultaneously dried by the imparted grinding energy. A special particle-size distribution curve is established by size classification.
U.S. Pat. No. 4,044,198 describes a process for the cold grinding of cellulose derivatives, in which the cellulose derivative with a water content of 40-150 wt. % of water, referred to its dry weight, is cooled with liquid nitrogen and subjected to cold grinding.
U.S. Pat. No. 4,044,198 describes a process in which crude products obtained by the etherification of cellulose are washed almost salt-free with hot water and are then separated at high temperatures by centrifugation to a water content of 50 wt. % referred to the total mass, and are next adjusted by mixing with water to a water content of 60 to 70 wt. % referred to the total mass. These mixtures are compacted, granulated, dried and ground.
The known processes according to the prior art are for the most part multi-stage processes involving a preliminary drier or preliminary embrittlement and/or compaction. Furthermore, in all the known processes the chemical and/or thermal stress on the macromolecules, particularly when processing extremely viscous, highly substituted products, is always also so intense that during the grinding the macromolecules are decomposed in the form of a chain scission, which is noticeable in particular by the more or less large decrease in viscosity compared to the starting products. Also the surfaces of the products treated by the preliminary embrittlement and/or preliminary drying steps become rough. Furthermore, a common feature of all the processes is the large amount of energy expended in grinding the cellulose derivatives after the preliminary drying, embrittlement or compaction.
Processes are already known that avoid one or more of the aforementioned disadvantages. For example, GB-A 2 262 527 describes a process for the comminution of cellulose derivatives by gelling a cellulose ether with a water content of 30 to 80 wt. % by cooling to a temperature of −10° to 60° C. followed by mill drying of the gel (preferably in an impact mill). Unfortunately GB-A 2 262 527 does not give any indication of how to proceed with hydroxyethylated mixed ethers of methyl cellulose (such as for example methylhydroxyethyl cellulose or methylhydroxypropylhydroxyethyl cellulose) in order to obtain a product having a bulk density of greater than 300 g/l. If a methylhydroxyethyl cellulose is processed as described in GB-A 2 262 527 for the case of methylhydroxypropyl cellulose, then wad-like products having a bulk density of <250 g/l are obtained. Also, the product from the-mill drying of methyl cellulose (Example 3) with a bulk density of 270 g/l is not satisfactory.
WO 98/31710 describes a process for the production of finely particulate polysaccharide derivatives by gelling or dissolving a cellulose ether with 35 to 99 wt. % (preferably 60 to 80 wt. %) of water referred to the total weight, followed by mill drying, wherein superheated steam is used to transport and dry the ground material.
Thus for example MHEC gels that have a dry substance content of 20 wt. % referred to the total mass ar
Kiesewetter Rene
Lelgemann Rudolf
Morning Martin
Schlesiger Hartwig
Weber Gunter
Franks James R.
Gil Joseph C.
Jones Dwayne C.
Wolff Walsrode AG
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