Cleaning and liquid contact with solids – Processes – Hollow work – internal surface treatment
Patent
1996-02-26
1998-07-14
Scheiner, Laurie
Cleaning and liquid contact with solids
Processes
Hollow work, internal surface treatment
134 21, 134 23, 134 30, 134 33, 134 37, 134 40, 21050023, 2103218, 210634, 264 41, B08B 900
Patent
active
057798150
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The invention relates to the removal of a lumen filler and/or other soluble residues from hollow filaments.
The production of hollow filaments, especially of hollow filament membranes, from various organic and synthetic polymers is well known. During the extrusion of the spinning solution necessary for the production of hollow filaments, a liquid (lumen filler) is generally extruded into the spinning solution which is expressed from a ring spinneret, in order to guarantee the lumen (cavity) in the hollow filament. Only liquids which do not modify the polymer of the hollow filament or react with the means necessary for the production of the hollow filament are suited for the lumen filler.
For instance in the production of cellulosic hollow filament membranes isopropyl myristate is used as a lumen filler. This lumen filler can be removed from the membrane using chlorofluorocarbons (CFCs), but the problem arises in this case that the cleaning agent as well must then be completely removed from the membrane, for instance by flushing with a gas. In addition the usage of CFCs should be avoided if possible because of the very negative environmental impact.
For other polymers as well, such as polyamides, polyacrylonitrile or poly(ether sulfone), specific lumen fillers are necessary, which can only be removed from the membrane by means of specific solvents. Likewise in this case, solvents must frequently be employed which pose a considerable burden on the environment, and/or their removal requires a great deal of effort.
Various processes are known for removing lumen fillers from hollow filaments. For instance, highly volatile lumen fillers are used for the production of hollow filaments and can easily be removed from the hollow filaments by means of gassing under pressure. However up to now, a highly volatile lumen filler has not been found for the production of cellulosic hollow filaments. In the case too of other hollow filaments where higher-boiling lumen fillers must be employed, a direct removal of the lumen filler by means of gas (if necessary under the influence of heat) is not possible at all or only with a very high expenditure of time.
An apparatus for removal of lumen fillers from hollow filaments has been disclosed by DD-A-224 343, whereby hollow filament bundles are situated radially in a centrifuge in order to first spin out most of the lumen filler. Then the drain end of the hollow filament bundles is closed and the hollow filament bundles are flooded with solvent in such a way that they are completely submerged in the solvent. The solvent, which contains lumen filler, is then spun out (rough cleaning). Then a fine cleaning is carried out by constantly feeding new solvent and spinning it off. Subsequently the solvent is evaporated by means of a gas while the centrifuge continues to operate. The described operating process using the known apparatus requires considerable amounts of solvent and flushing gas, so that this process must therefore be described as uneconomical.
In addition, DD-A-219 804 describes a process for removal of lumen fillers from hollow filaments whereby the lumen filler is first roughly removed, the bundles are cleaned in two steps by means of end flooding with a flushing agent which is a solvent for the lumen filler, and the solvent is subsequently removed by means of a gas. This process is used for rolled-up hollow filament mats. Huge amounts of solvent and gas are also consumed in this case.
The two latter processes must therefore also be described as uneconomical because considerable energy is necessary to recover the lumen filler, the solvent and the gas from the considerable quantities of solvent and gas which emerge from the centrifuge. The problem upon which the present invention is based consists in providing a process for removal of a lumen filler and/or other soluble residues from hollow filaments, whereby the lumen filler is first roughly removed through centrifuging, the bundles are cleaned with a solvent by end feeding of flushing agent and centrifuging,
REFERENCES:
patent: 4263053 (1981-04-01), McKinnon, Jr.
patent: 5470474 (1995-11-01), Ansorge et al.
Breidohr Hans-Gunter
Konig Martin
Krautwurst Bernhard
Martin Manfred
Akzo Nobel nv
Morris Louis A.
Noto Joseph M.
Scheiner Laurie
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