Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Patent
1995-08-14
1997-02-11
Nutter, Nathan M.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
210670, 210681, 210683, D01F 1302, B01J 3922, B01J 4116
Patent
active
056022476
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates generally to a process for the purification of aqueous solutions of tertiary amine-oxides.
The viscose process is presently widely used to produce cellulose molded bodies. For some decades, scientists have searched for a replacement process for the production of cellulose molded bodies. An interesting replacement process having reduced environmental impact has been discovered. In this method, cellulose is dissolved without derivatization in an organic solvent, and this solution is extruded to form molded bodies, e.g. fibers and films. Such extruded fibers have been given the generic name Lyocell by BISFA (The International Bureau for the Standardization of man made fibers). BISFA defines a mixture of an organic chemical substance and water as an organic solvent.
It has been shown that a mixture of a tertiary amine-oxide and water is particularly useful as an organic solvent for the production of cellulose molded bodies. N-methylmorpholine-N-oxide (NMMO) is typically used as the amine-oxide. Other suitable amine-oxides are described e.g. in EP-A 0 533 070. A method for the production of moldable cellulose solutions is known e.g. from EP-A-0 356 419.
In this process, cellulose is precipitated from a molded cellulose solution in an aqueous precipitation bath. During this process, amine-oxide builds up in the precipitation bath. To render this method economical it is of decisive importance to recover and reuse nearly all of the amine-oxide. Thus the amine-oxide process has the following 3 main steps:
(A) dissolving cellulose in an aqueous solution of a tertiary amine-oxide, preferably N-methylmorpholine-N-oxide (NMMO), to produce a moldable cellulose solution,
(B) molding said cellulose solution and conducting said molded cellulose solution into an aqueous precipitation bath wherein the cellulose is precipitated, thus producing a molded body and a spent precipitation bath,
(C) regenerating (i.e. purifying and concentrating) the spent precipitation bath, thus producing a regenerated aqueous amine-oxide solution which is reused in step (A) as a cellulose solvent.
During this process, amine-oxide and degradation products of cellulose and the amine-oxide build up in the precipitation bath. These products may be heavily colored. If the colored products are not removed from the precipitation bath, the quality of the produced molded bodies will be impaired. Metal traces may also build up in the precipitation bath, which reduces process safety.
There are some proposals in the literature for removing these degradation products before using the amine-oxide solution again in step (A). Specifically, DD-A 254 199 describes a known process for purifying aqueous solutions of NMMO, wherein the solution passes through anion exchangers. In the first step of this process, the anion exchanger contains an exchange resin comprising a styrene-divinylbenzene copolymerizate carrying tertiary amine-groups of the --CH.sub.2 N(CH.sub.3).sub.2 type. In the second step of this process, quaternary ammonium groups of the --CH.sub.2 N(CH.sub.3).sub.3 OH type act as functional groups. According to DD-A 254 199, NMMO solutions treated according to the process are dark at the beginning of the purification, brown to yellow after the first process step and bright yellow to transparent after the second process step.
A disadvantage of this process is that the treated solutions have a high pH value, which subsequently requires more complex purification. Additionally, this process does not remove alkali and alkali-earth cations from the solution. The metal ions, alkali metal ions and alkali-earth metal ions lead to undesired precipitations and incrustation, unwanted insoluble substances in the solution, and reduced process safety. Although it is possible to remove these salts by adding a precipitation agent and subsequently filtering or through the use of other separating agents, these operations are disadvantageous because they introduce additional chemicals or require additional processing.
REFERENCES:
patent: 4577013 (1986-03-01), Merz
patent: 4724207 (1988-02-01), Hou et al.
patent: 5053138 (1991-10-01), Korger et al.
patent: 5157055 (1992-10-01), Akagi et al.
patent: 5409532 (1995-04-01), Astegger et al.
patent: 5441689 (1995-08-01), Laity
English language abstract of DD 254,199.
English language abstract of EP 356,419.
English language abstract of EP 427,701.
English language abstract of EP 553,070.
Rogowin und Galbraich, "Die chemische Behandlung und Modifizierung der Zellulose", Georg Thieme Verlag, p. 97-(1983).
Ullman, Encyclopedia of Industrial Chemistry, vol. A14, p. 396.
Firgo Heinrich
M ulleder Eduard
Lenzing Aktiengesellschaft
Nutter Nathan M.
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