Compositions: coating or plastic – Coating or plastic compositions – Carbohydrate or derivative containing
Patent
1997-11-10
1999-03-30
Brunsman, David
Compositions: coating or plastic
Coating or plastic compositions
Carbohydrate or derivative containing
1062002, C08L 902
Patent
active
058882880
DESCRIPTION:
BRIEF SUMMARY
This invention relates to methods of forming solutions and has particular reference to methods of forming solutions of cellulose in aqueous tertiary amine oxide, particularly aqueous N-methylmorpholine N-oxide (NMMO).
It is well known that cellulose can be dissolved in aqueous solutions of NMMO. It is also well known that such solutions can conveniently be prepared by subjecting a mixture (hereafter referred to as a "premix") of cellulose, NMMO and excess water (which is a non-solvent for cellulose) to conditions of heat and reduced pressure so as to convert the premix into a solution of cellulose in aqueous NMMO by removal of excess water. Such a process is, in general terms, described in Franks and Varga U.S. Pat. No. 4,196,282.
The process of heating a premix under conditions of reduced pressure can be carried out in batches or in a continuous process. Both batch and continuous processes are described in McCorsley U.S. Pat. No. 4,246,221. In the continuous process, as described in McCorsley U.S. Pat. No. 4,246,221, and as also described in EP 356,419, and as further described in published International Application WO 94/06530, the process involves heating a premix by bringing it into contact with a heated surface whilst subjecting the premix to reduced pressure and simultaneously agitating the premix.
All of these processes will produce solutions of cellulose in aqueous NMMO.
Considering, however, the process in which the premix is heated under reduced pressure in a thin film evaporator such as a Filmtruder (Registered Trademark) thin film evaporator, available from Buss AG of Pratteln, Switzerland essentially there is provided a rotatable rotor within an externally heated cylinder which agitates the premix and then the solution as it is formed during its passage through the Filmtruder. The process of forming the cellulose solution is described in a schematic manner in EP-B-356,419, but there is no disclosure therein of the conditions for operating the process at the high production rates required for commercial operation. According to the description and as claimed in EP 356,419 it is of decisive importance to the continuous control of the process that the water vapour be drawn off in counterflow relative to the product transport.
In the process described in WO 94/06530 in which it is described how to operate a solution forming process on a large and practical scale, the Filmtruder is also described as operating in a countercurrent mode. When this process is operated in a large scale Filmtruder at an ever increasing throughput, to increase its productivity, it has now been found that lyocell fibre produced from cellulose solutions made at the higher rate can on occasions become discoloured.
A method and apparatus has now been developed which overcome these problems and the present invention requires the operation of a process and equipment in direct contradiction to the teachings of EP-B-356,419.
By the present invention there is provided a method of converting a mixture of cellulose, tertiary amine oxide and excess non-solvent, such as water, to a solution of cellulose in tertiary amine oxide containing a reduced amount of the non-solvent, wherein the improvement comprises in combination the steps of: heating the mixture to a temperature in excess of the boiling point of the non-solvent at a predetermined sub-atmospheric pressure; continuously feeding the thusly heated mixture into the introduction zone of a mixing chamber at the predetermined sub-atmospheric pressure so as to cause flash evaporation of some of the excess non-solvent so that some at least of the cellulose goes into solution in the tertiary amine oxide closely adjacent to the introduction zone of the mixing chamber; providing in the mixing chamber a rotor which agitates the thusly formed solution and the remaining mixture of cellulose, tertiary amine oxide and excess non-solvent; transporting the solution and the remaining mixture through the mixing chamber whilst continuing evaporation of excess non-solvent to form further solution; a
REFERENCES:
patent: 4196282 (1980-04-01), Franks et al.
patent: 4246221 (1981-01-01), McCorsley, III
patent: 5094690 (1992-03-01), Zikeli et al.
patent: 5330567 (1994-07-01), Zikeli et al.
patent: 5337776 (1994-08-01), Perry et al.
patent: 5413631 (1995-05-01), Gray et al.
patent: 5419810 (1995-05-01), Van Der Piepen et al.
Armistead Roger James Rees
Naef Rainer
Nussberger Werner
Quigley Michael
Ronchetti Andrew
Acordis Fibres (Holdings ) Limited
Akzo Nobel Faser AG
Brunsman David
Buss AG
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