Process for producing cellulose derivatives of high bulk density, good flowability and improved dispersibility in cold water
View Patent ↗A particulate cellulose derivative is obtained in a process of grinding and drying a moist cellulose derivative which comprises the steps of A) providing a cellulose derivative having a moisture content of from 60 to 95 percent, based on the total weight of the moist cellulose derivative, B) grinding and partially drying the moist cellulose derivative in a gas-swept impact mill; and C) contacting the ground and partially dried cellulose derivative with an additional amount of a drying gas outside the gas-swept impact mill. The obtained particulate cellulose derivative has a high untapped bulk density and a good flowability.
1. A process for producing a particulate cellulose derivative comprising the steps of
A) providing a moist cellulose derivative having a moisture content of from 25 to 95 percent, based on the total weight of the moist cellulose derivative, with the proviso that no substantial amount of a surface-treatment additive is added to the cellulose derivative,
B) grinding and partially drying the moist cellulose derivative in a gas-swept impact mill wherein a gas fed into the impact mill has a temperature of 100° C. or less; and
C) contacting the ground and partially dried cellulose derivative with an additional amount of a drying gas outside the gas-swept impact mill, wherein the additional amount of drying gas outside the gas-swept impact mill has a higher temperature than the gas fed into the impact mill
to produce the particulate cellulose derivative.
2. The process of claim 1 wherein the additional amount of drying gas outside the gas-swept impact mill has a temperature that is at least 70° C. higher than the gas fed into the impact mill.
3. The process of claim 1 wherein the ratio of the gas flow in the gas-swept impact mill in step B) and the flow of the additional amount of drying gas in step C) is from 1:10 to 8:1.
4. The process of claim 1 wherein the circumferential speed of the gas-swept impact mill is not more than 100 m/s.
5. The process of claim 1 wherein in a step D) the ground and dried cellulose derivative is sieved through a sieve of from 125 to 400 micrometers mesh size and the cellulose derivative retained on the sieve is recovered.
6. The process of claim 1 wherein the cellulose derivative is a cellulose ether.
7. The process of claim 1 wherein the produced particulate cellulose derivative has an untapped bulk density of at least 370 g/l or a Carr Index of 20 or less or both.
8. A particulate cellulose derivative producible by the process of claim 1 .
9. A method of improving the flowability and/or the cold water dispersibility of a particulate cellulose derivative comprising the steps of
A) providing a moist cellulose derivative having a moisture content of from 25 to 95 percent, based on the total weight of the moist cellulose derivative, with the proviso that no substantial amount of a surface-treatment additive is added to the cellulose derivative,
B) grinding and partially drying the moist cellulose derivative in a gas-swept impact mill wherein a gas fed into the impact mill has a temperature of 100° C. or less; and
C) contacting the ground and partially dried cellulose derivative with an additional amount of a drying gas outside the gas-swept impact mill, wherein the additional amount of drying gas outside the gas-swept impact mill has a higher temperature than the gas fed into the impact mill.
10. A particulate cellulose derivative having an untapped bulk density of at least 370 g/l, a Carr Index of 20 or less, a median Equivalent Projected Circle Diameter (EQPC) of at least 200 micrometers and a viscosity of from 1.2 to 200 mPa·s, measured as a 2% by weight aqueous solution at 20° C., with the proviso that the particulate cellulose derivative does not comprise a substantial amount of a surface-treatement additive.
11. The particulate cellulose derivative of claim 10 having a Carr Index 13 or less.
12. The process of claim 2 wherein the circumferential speed of the gas-swept impact mill is not more than 100 m/s.