Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Patent
1997-04-15
1998-06-30
Raymond, Richard L.
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
564297, 210638, 210651, 210663, 210669, 210670, 210681, 210683, C07C29104, D01F 1302
Patent
active
057736553
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/AT96/00148, filed Aug. 16, 1996. The present invention is concerned with a process for the purification of an aqueous solution of a tertiary amine-oxide, which solution contains impurities partially present in a dissolved state and partially in a non-dissolved, colloidal state. In particular, the present invention is concerned with a process for the purification of precipitation baths of the amine-oxide process.
For some decades there has been searched for processes for the production of cellulose moulded bodies able to substitute the viscose process, today widely employed. As an alternative which is interesting among other reasons for its reduced environmental impact, it has been found to dissolve cellulose without derivatisation in an organic solvent and extrude from this solution moulded bodies, e.g. fibres, films and other moulded bodies. Fibres thus extruded have received by BISFA (The International Bureau for the Standardization of man made fibers) the generic name Lyocell. By an organic solvent, BISFA understands a mixture of an organic chemical and water.
It has turned out that as an organic solvent, a mixture of a tertiary amine-oxide and water is particularly appropriate for the production of cellulose moulded bodies. As the amine-oxide, primarily N-methylmorpholine-N-oxide (NMMO) is used. Other amine-oxides are described e.g. in EP-A - 0 553 070. A process for the production of mouldable cellulose solutions is known e.g. from EP-A - 0 356 419. For the purposes of the present specification and the present claims, the production of cellulose moulded bodies using tertiary amine-oxides generally is referred to as amine-oxide process.
In EP-A - 0 356 419, an amine-oxide process for the production of spinnable cellulose solutions is described, wherein as a starting material among other substances a suspension of cellulose in liquid, aqueous N-methylmorpholine-N-oxide (NMMO) is used. This process consists in transforming the suspension in a thin-film treatment apparatus in one single step and continuously into a mouldable solution. Finally, the mouldable solution is spun into filaments by a forming tool such as a spinneret and the filaments are passed through a precipitation bath.
The cellulose is precipitated from the solution in an aqueous spinning bath. The amine-oxide is accumulated in the spinning bath. The process liquids produced in this process may contain up to 30 weight % of amine-oxide. For the economy of the amine-oxide process it is of vital importance to recover the amine-oxide nearly completely and reuse it for the production of a mouldable cellulose solution.
In addition to the amine-oxide, colourless to intensively coloured degradation products of the amine-oxide process are also accumulated in the spinning bath. On the one hand, these may deteriorate the quality of the moulded bodies produced and on the other they may represent a safety risk, since under certain conditions the amine-oxide tends to show highly exothermic decomposition reactions. These substances have to be removed from the aqueous solution of the amine-oxide before it is concentrated.
The solutions of amine-oxide frequently contain inorganic cations and anions such as sodium, calcium and magnesium cations and chloride, sulfate etc. respectively, derived partly from the pulp employed in the process for the production of cellulose moulded bodies and partly from other substances used and formed in the process. When the solutions are evaporated and processed to concentrated aqueous solutions of the amine-oxide which may be reused in the process, these ions will be accumulated and will consequently cause deposits and incrustations in the evaporation plant.
Metal ions and metal particles which also may be derived from the pulp used or from metallic equipment parts employed in the process are also accumulated in the solution. It is known that in solutions of cellulose in aqueous amine-oxides, precisely theses metallic particles and ions may initiate frequently strong degradation reactions of t
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Mangeng Bruno
Manner Johann
Mulleder Eduard
Schwenninger Franz
Lenzing Aktiengesellschaft
Raymond Richard L.
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