Claims
- 1. In a method of forming a solution of cellulose in a tertiary amine N-oxide which comprises the steps of:
- (a) forming a premix of a tertiary amine N-oxide, water and cellulose,
- (b) heating the premix under a pressure lower than atmospheric in a vertically mounted thin-film evaporator having a heated inner surface and a central shaft with paddle blades disposed along the shaft so that, on rotation of the shaft, material in the evaporator will be contacted by a plurality of blades annularly spaced around the shaft,
- (c) evaporating the water from the premix to a level such that the cellulose forms a solution in the amine oxide and
- (d) removing the solution form the thin-film evaporator,
- wherein the improvement consists essentially of using a heated inner surface with an area in the range of 1 m.sup.2 to 125 m.sup.2, rotating a rotor such that the tips of the blades have a linear speed of 2.5 m/sec to 8 m/sec, ensuring a circumferential spacing between the tips of adjacent blades in the range of 65 mm to 175 mm, applying a vacuum in the range 25 millibars to 100 millibars and heating the heated inner surface to a temperature such that, under the conditions of applied vacuum, the solution is removed at a temperature in the range 90.degree. to 135.degree. C.
- 2. A method as claimed in claim 1 wherein the surface area is in the range 10 m.sup.2 to 125 m.sup.2, the circumferential spacing between the tips of adjacent blades is in the range of 75 mm to 150 mm, and the blades are rotated to have a linear speed at their tips in the range 2.5 m/sec to 5 m/sec.
- 3. A method as claimed in claim 1 wherein the tips of the blades have a linear speed in the range 2.5 to 4.7 m/sec.
- 4. A method as claimed in claim 1 wherein the solution is formed at an exit temperature in the range 100.degree. C. to 115.degree. C.
- 5. A method as claimed in claim 1 in which the premix is fed into the thin film evaporator at a temperature between ambient and 95.degree. C.
- 6. A method as claimed in claim 1 wherein the rotor has blades located at intervals of 5.degree. to 15.degree. or 5.degree. to 10.degree. around the circumference of the rotor.
- 7. A method as claimed in claim 1 in which the solution contains 7% to 35% by weight cellulose, 15% to 4% water and the balance amine oxide.
- 8. A method as claimed in claim 1 in which the blades are spirally arranged about the shaft with adjacent blades being angularly and axially spaced from one another.
- 9. A method as claimed in claim 1 in which some of the plurality of blades are inclined so as to force material downwards through the thin-film evaporator.
Priority Claims (1)
Number |
Date |
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9219693 |
Sep 1992 |
GBX |
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Parent Case Info
This is a continuation of U.S. patent application Ser. No. 08/121,308, filed Sep. 14, 1993, now abandoned.
US Referenced Citations (15)
Foreign Referenced Citations (1)
Number |
Date |
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1619737 |
Jan 1971 |
DEX |
Continuations (1)
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Number |
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121308 |
Sep 1993 |
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