WO2003055807A1

WO2003055807A1 - The fast harvest of agglomerate-free nano-particles/ultra-fine-particles from their sols/dispersions through ordinary filtration

Info

Publication number: WO2003055807A1
Application number: PCT/CA2002/000011
Authority: WO
Inventors: Weijie Zhou
Original assignee: Weijie Zhou
Priority date: 2002-01-03
Filing date: 2002-01-03
Publication date: 2003-07-10

Abstract

This invention presents a method for separating nano-particles/ultra-fine-particles from their sols/dispersions by using conventional filters with conventional industrial filter cloth on the filter board to filtrate the sols/dispersions and then wash the cake formed by the deposition of nano-particles/ultra-fine-particles on the filter cloth. During the filtrating process, the filtrate can pass through the cake and the filter cloth rapidly. Moreover, during the washing process, the water can pass through the cake and the filter cloth rapidly. Therefore, most of the dissolvable impurities that may cause agglomerations among nano-particles/ultra-fine-particles can be removed from the nano-particles/ultra-fine-particles. There are almost no nano-particles leaking through the filter cloth during both the filtrating and the washing processes. This invention provides a method for fast harvesting agglomerate-free nano-particles/ultra-fine-particles from their sols/dispersions by ordinary filtration.

Description

Title

The fast harvest of agglomerate-free nano-particles/ultra-fine-particles from their sols/dispersions through ordinary filtration

Description

In order to harvest the nano-particles/ultra-fine-particles, the sols/dispersions that contain the wanted nano-particles/ultra-fine-particles should be prepared firstly. Secondly, alkaline solutions should be prepared. Third, the formic acid, or acetic acid, or the solutions of oxalic acid should be prepared. Fourth, under the agitating condition, put the alkaline solutions into the prepared sols/dispersions at the temperature of 20 degree C to 100 degree C until the pH value of the said sols/dispersions increases to 9 to 11. Then, under the agitating condition, put formic acid, or acetic acid, or the solutions of oxalic acid, or any combinations of the three organic acids into the alkaline-treated sols/dispersions at the temperature of 20 degree to 100 degree C until the pH value of the alkaline-treated sols/dispersions decreases to 5 to 7. The order of adding alkaline solutions and the solutions of formic acid, or acetic acid, or oxalic acid, or any combinations of the three organic acids does not affect the performances of both the filtrating and water-washing processes in harvesting the nano-particles/dispersions from their sols/dispersions. Fifth, filtrate the treated sols/dispersions by using the conventional filters with the conventional industrial filter cloth on the hole-distributed filter board. During the filtrating process, the filtrate can pass through the cake and the filter cloth rapidly, and there are almost no nano-particles/ultra-fine-particles leaking through the filter cloth. After finishing filtration, pour hot distilled water over the cake formed by the deposition of the nano-particles/ultra-fine particles on the filter cloth in the filter to wash the cake for removing the dissolvable impurities from the nano-particles/ultra-fine particles. During the washing process, the washing water can pass through the cake and the filter cloth rapidly, and there are almost no nano-particles/ultra-fine-particles leaking through the filter cloth. The washing-cake operations should be repeated as many times as possible until the contents of some impurities in the washing water decrease to certain low level. Finally, took out the cake from the filter. Example 1: Put 0.500 liter of sols that contains about 20%w nano-titanium-dioxide particles into a glass beaker equipped with a class stirrer in the laboratory. At the temperature of about 85 Degree C and under agitating condition, add 40%Na.sub.2.CO.sub.3 solution into the said sols until the pH value of the sols increases to 9 to 11. Then, add acetic acid into the said alkaline-treated sols until the pH value of the sols decreases to 5 to 7. Pour the said alkaline-and-acetic-acid-solution-treated sols into a vacuum filter with two layers of conventional industrial filter cloth on the hole-distributed filter board. During the filtrating process, the filtrate passed through the cake and the filter cloth rapidly, and there were almost no nano-particles leaking through the filter cloth. After finishing filtration, pour hot distilled water over the cake formed by the deposition of the nano- particles on the filter cloth in the filter to wash the cake for removing the dissolvable impurities from the nano-particles. The washing- cake operations should be repeated as many times as possible until the content of Cl. Super, -l.in the washing water decreases to certain low level. During the washing process, the water passed through the cake and the filter cloth rapidly, and there were almost no nano-particles leaking through the filter cloth. Finally, took out the cake from the filter. Heat the cake at temperature of 100 Degree C until it became dry. The average crystal size of the nano-particles in the cake is 6.7 nm by Scherrer Method based on the data obtained by measuring the sample of the cake with Rigaku(Japan)'s D MAX - 3B Type X - Ray Diffraction Meter. Calcine the dried sample in the calciner at temperature of 500 Degree C for one hour to obtain nano- titanium-dioxide. The average crystal size of the nano-titanium-dioxide is 13.0 nm by Scherrer Method based on the data obtained by measuring the sample from the nano- titanium-dioxide with Rigaku(Japan)'s D/MAX - 3B Type X - Ray Diffraction Meter. The TEM photo of the said nano-titanium-dioxide from the sample prepared in the laboratory is shown in FIG. 1 , which was taken by using HITACHI (Japan)' s H - 600 Type Transmission Electron Microscope (TEM). It can be seen from GIG. I that the average crystal size of the said nano-titanium-dioxide is about 13 nm, and there are no agglomerations in the sample of the said nano-titanium-dioxide.

Example 2: Put 300 liter of sols that contain about 20%w nano-titanium-dioxide particles into an enameled steel tank equipped with a stirrer in the pilot workshop. At the temperature of about 85 Degree C and under agitating condition, add 40%Na.sub.2.CO.sub.3 solution into the said sols until the pH value of the sols increases to 9 to 11. Then, add industrial grade formic acid into the said alkaline-treated sols until the pH value of the sols decreases to 5 to 7. Pour the said alkaline-and-for ic-acid-treated sols into a centrifugal filter with three layers of conventional industrial filter cloth on the hole-distributed filter board. During the filtrating process, the filtrate passed through the filter cloth rapidly, and there were almost no nano-particles leaking through the filter cloth. After finishing filtration, pour distilled hot water over the cake formed by the deposition of the nano- particles on the filter cloth in the filter to wash the cake for removing the dissolvable impurities from the nano-particles. The washing-cake operations should be repeated as many times as possible until the content of Cl. Super. -1.in the washing water decreases to certain low level. During the washing process, the water passed through the cake and the filter cloth rapidly, and there were almost no nano-particles leaking through the filter cloth. Finally, took out the cake from the filter. Heat the cake at temperature of 100 Degree C until it became dry. The average crystal size of the nano-particles in the cake is 6.7 nm by Scherrer Method based on the data obtained by measuring the sample of the cake with Rigaku(Japan)'s D/MAX - 3B Type X - Ray Diffraction Meter. Calcine the dried sample from the cake in the calciner at temperature of 500 Degree C for one hour to obtain nano-titanium-dioxide. The average crystal size of the nano-titanium-dioxide is 13.0 nm by Scherrer Method based on the data obtained by measuring the sample the nano-titanium-dioxide with Rigaku( Japan)' s D/MAX - 3B Type X - Ray Diffraction Meter. The TEM photo of the said nano-titanium-dioxide from the sample prepared in the workshop is shown in FIG. 2, which was taken by using HITACHI (Japan)' s H - 600 Type Transmission Electron Microscope (TEM). It can be seen from GIG.2 that the average crystal size of the said nano-titanium-dioxide is about 13 nm, and there are no agglomerations in the sample of the said nano-titanium-dioxide.

Claims

Claims I claim:

1. After treating the sols/dispersions which contain the nano-particles/ultra-fine-particles with the methods I claimed bellow, the nano-particles/ultra-fine-particles can be harvested from their sols/dispersions by using conventional filters and conventional industrial filter cloth to filtrate the treated sols/dispersions and then wash the cake formed by the deposition of the nano-particles/ultra-fine-particles on the filter cloth:

(a). Add alkaline solutions and the solutions of formic acid HCOOH, or acetic acid CH. sub.3. COOH, or oxalic acid HOOC-COOH into the sols/dispersions that contain the wanted nano-particles/ultra-fine-particles.

(b). Or only add the solutions of formic acid HCOOH, or acetic acid CH. sub.3. COOH, or oxalic acid HOOC-COOH into the sols/dispersions that contain the wanted nano- particles/ultra-fine-particles.

2. The process of claim 1 wherein the base is selected from any one or any combinations of the following base:

NaOH,

Na.sub.2.CO.sub.3, KOH, NKsubAOH

3. The process of claim 1 wherein the adding amount of the base should be able to change the original pH value of the said sols/dispersions to about 9 to 11.

4. In the process of claim 1, any one or any combinations of the following organic acids can be used for the treatment of the sols/dispersions for the purpose of improving the performances of both the filtrating and washing processes in harvesting the nano- particles/dispersions from their sols/dispersions:

Formic acid HCOOH, Acetic acid CH.sub.3. COOH, Oxalic acid HOOC-COOH.

5. The process of claim 1 wherein the adding amount of formic acid, or acetic acid, or oxalic acid, or any combination of the above three organic acids should be able to decrease the pH value of the precipitates obtained by adding the base into the said sols/dispersions from about 9 to 11 to about 5 to 7.

6. The process of claim 1 wherein the order of adding alkaline solutions and the solutions of formic acid, or acetic acid, or oxalic acid, or any combinations of the three organic acids does not affect the performances of both the filtrating and water- washing processes in harvesting the nano-particles/dispersions from their sols/dispersions.

7. The process of claim 1 wherein the temperature of the said sols/dispersions can be kept at 1 to 100 degree C during adding the said alkaline solutions and the solutions of formic acid, or acetic acid, or oxalic acid or any combinations of the three organic acids.

8. The process of claim 1 wherein the said sols/dispersions should be agitated for 1 to 30 minutes after adding alkaline solutions and the solutions of formic acid, or acetic acid, or oxalic acid.

9. The process of claim 1 wherein the conventional filters can be any one of the following filters:

(a). Centrifugal filter, (b). Vacuum filter, (c). Pressing filter.