Process for the production of cellulose moulded bodies

Details Process for the production of cellulose moulded bodies Process for the production of cellulose moulded bodies

1995-06-05

1997-05-13

Tentoni, Leo B.

Plastic and nonmetallic article shaping or treating: processes

Recycling of reclaimed or purified process material

Of gaseous process material

264187, 564297, 564298, C07C29100, D01F 224, D01F 1302

Patent

active

056289413

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention is concerned with a process for the production of cellulose moulded bodies, and a regenerated, aqueous solution of an amine-oxide used for the production of a mouldable cellulose solution.
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, a method has been found for dissolving cellulose without derivatisation in an organic solvent and extruding from this solution moulded bodies, e.g. fibres and films. 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 been shown that as an organic solvent, a mixture of a tertiary amine-oxide and water is particularly useful for the production of cellulose moulded bodies. As amine-oxide, basically N-methylmorpholine-N-oxide (NMMO) is used. Other amine-oxides are described e.g. in EP-A - 0 553 070. A method for the production of mouldable cellulose solutions is known e.g. from EP-A-0 365 419.
The cellulose is precipitated from the cellulose solution in an aqueous precipitation bath. During this process, amine-oxide builds up in the precipitation bath. To render the method economical, it is of decisive importance to recover and reuse nearly all of the amine-oxide. Thus the amine-oxide process presents the following 3 main steps: in particular N-methylmorpholine-N-oxide (NMMO), to produce a mouldable cellulose solution, solution into an aqueous precipitation bath, wherein the cellulose is precipitated, thus being obtained a moulded body and a spent precipitation bath, bath, thus being obtained a regenerated aqueous amine-oxide solution which is used again in step (A) for dissolving cellulose.
The term "regenerating" is to be understood as any means capable of processing the precipitation bath so that an aqueous amine-oxide solution is produced, which can be used again in step (A). Such means include purification, treatment with ion exchangers, concentration, etc.
In the precipitation bath, not only amine-oxide but also degradation products of the cellulose and the amine-oxide build up. These may be heavily coloured, thus impairing the quality of the produced moulded bodies if they are not removed from the precipitation bath. Additionally, also metal traces may build up in the precipitation bath, leading to a reduced process safety.
In order to remove these degradation products, some proposals are known from the literature:
DD-A 254 199 describes a process for the purification of aqueous solutions of NMMO, according to which the solution passes through anion exchangers, wherein in a first step the anion exchanger contains an exchange resin of a styrene-divinylbenzene copolymerisate carrying tertiary amine groups of the -CH.sub.2 N(CH.sub.3).sub.2 type and in a second step quaternary ammonium groups of the -CH.sub.2 N(CH.sub.3).sub.3 OH type as functional groups. It is described that the NMMO solution to be purified is dark at the beginning of the purification, brown to yellow after the first step and bright yellow to transparent after the second step.
A disadvantage of this process consists in that the solutions thus treated exhibit a high pH value, which subsequently requires a more complex purification. Additionally, in this already known process alkali and earth alkali cations, as well as partially basic degradation products (morpholine, N-methylmorpholine and other compounds) are not removed from the solution. The metal ions and alkali and earth alkali metal ions respectively lead to undesired precipitations and incrustations, unwanted non-dissolved substances in the solution, and a reduced process safety. Although it is possible to remove these substances by adding a precipitation agent with subsequent filtration or other separating mean

REFERENCES:
patent: 4324593 (1982-04-01), Varga
English language absract of AT 399,519 (published May 26, 1995).
English language absract of DD 218,104 (published Jan. 30, 1985).
English language abstract of DD 254,199 (published Feb. 17, 1988).
English language abstract of DE 2,000,082 (published Jul. 15, 1971).
English language abstract of EP 47,929 (published Mar. 24, 1982).
English language abstract of EP 427,701 (published May 15, 1991).
English language abstract of EP 356,419 (published Feb. 28, 1990).
English language abstract of EP 553,070 (published Jul. 28, 1993).

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