Method of fractionating oxidic nanoparticles by crossflow membrane filtration

Abstract

A method of fractionating a dispersion of oxidic nanoparticles wherein at least one step of the method is a membrane crossflow filtration step, the flow of the dispersion over the membrane being brought about by means of driven rotating parts; and dispersions of oxidic nanoparticles that are obtainable by the method.

1 . A method of fractionating a dispersion of oxidic nanoparticles, wherein at least one step of the method is a membrane crossflow filtration step, which step comprises causing the dispersion to flow over the membrane by driven rotating parts. 
   
   
       2 . A method according to  claim 1 , wherein the dispersion is stirred directly over the membrane. 
   
   
       3 . A method according to  claim 1 , wherein the membrane has a pore diameter of between 0.01  82  m and 5 μm. 
   
   
       4 . A method according to  claim 1 , wherein the membrane has a pore diameter of between 0.1 μm and 1 μm. 
   
   
       5 . A method according to  claim 1 , wherein the dispersion is caused to flow over the membrane with an average flow rate of between 5 and 25 m/s. 
   
   
       6 . A method according to  claim 1 , wherein the dispersion is caused to flow over the membrane with an average flow rate of at least 8 m/s. 
   
   
       7 . A method according to  claim 1 , wherein the dispersion is caused to flow over the membrane with an average flow rate of at least 10 m/s. 
   
   
       8 . A method according to  claim 1 , wherein the oxidic nanoparticles are particles of at least one of titanium oxide, cerium oxide, aluminum oxide, silicon dioxide, zirconium dioxide, zinc oxide, indium tin oxide, antimony tin oxide, barium titanate. 
   
   
       9 . A method according to  claim 1 , wherein a grinding step is carried out after the filtration step. 
   
   
       10 . A method according to  claim 9 , wherein the grinding step is performed with a ball mill, stirred ball mill or wet-jet mill. 
   
   
       11 . A method according to  claim 1 , wherein the filtration step produces a retentate, which retentate is washed via a diafiltration. 
   
   
       12 . A method according to  claim 11 , wherein the retentate is returned to the grinding step. 
   
   
       13 . A method according to  claim 1 , wherein the filtration step produces a filtrate, which filtrate is concentrated in a subsequent separation step. 
   
   
       14 . A method according to  claim 13 , wherein the subsequent separation step is an ultrafiltration step. 
   
   
       15 . A method according to  claim 13 , wherein subsequent separation step produces a clear fraction, which clear fraction is returned to the filtration step. 
   
   
       16 . A method according to  claim 1 , wherein the filtration step takes place with periodic backwashing of the membrane. 
   
   
       17 . A method according to  claim 1 , wherein the dispersion has been diluted from a previous dispersion prior to the filtration step. 
   
   
       18 . A dispersion of oxidic nanoparticles obtainable by a method according to  claim 1 . 
   
   
       19 . A dispersion according to  claim 18 , wherein at least 50% of the nanoparticles have a particle diameter of less than or equal to 80 nm. 
   
   
       20 . A dispersion according to  claim 18 , wherein at least 50% of the nanoparticles have a particle diameter of less than or equal to 50 nm. 
   
   
       21 . A dispersion according to  claim 18 , wherein at least 50% of the nanoparticles have a particle diameter of less than or equal to 30 nm.