JPS58131156A - Dehydration due to vacuum filter accompanied by electric treatment - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vacuum filter using a known electrical process for dewatering aqueous suspensions.
This invention relates to improvements in the operation of augmented vacuum filters (hereinafter referred to as EAVFs). More specifically, the present invention relates to the use of membranes to limit the migration of certain ionic species and particulate solids in dewatering using EAVFs.

Slurry filtration by electrodynamic methods (electrophoresis, electrodialysis) has a long history.

US Pat. No. 1,229,203 to Schwerin discloses the dehydration of finely divided solid suspensions.

Nowadays, rather than dry powders, high solids contents (e.g. 70
%) slurry is increasingly required for unburned kaolin viscosity, etc. It is advantageous to be able to dry the dry powder and, if necessary, transport the solids content. Examples of industrially used dehydration methods include USP 4168222 and USP 41070.
26. These USPs disclose the operation of the EAVF. An electrodialysis/phoresis process for concentrating clays, etc. is disclosed in Kunkle et al., USP 4,110,189;
There is an electroflocculation cell in the kun.
Electrokinetic cells are disclosed in US Pat. No. 3,980,547 to Kle.

relatively dilute using an electrofilter, for example 4
A method for dewatering a slurry of dispersed kaolin, 0% solids content, to a level suitable for spray drying, such as 55-60%, is described in MiXOn US Application QQ1B9B.

Clays are typically processed by a wet process in which the crude clay is slurried in water with the aid of dispersants such as sodium silicate, sodium hexametaphosphate, sodium tripolyphosphate, and sodium birophosphate. Certain organic polymers may also be used alone or with inorganic dispersants. Clay slurry is mixed with water, separates large particles, disperses, bleaches,
Separate undesirable contaminants and improve properties needed for various other end uses. In many cases, clay is treated to remove impurities such as colored substances. After these treatments, it is dehydrated or filtered to give a solid filter cake of 50-60% clay.

This cake can then be redispersed and prepared by spray drying or other drying means into a dry product suitable for end use.

For a variety of reasons, clay manufacturers are increasingly desiring to transport slurries having a solids content of about 70 grams. Currently, 70% solids content slurry is used by adding 30 to 50 inches of spray-dried clay to a redispersed filter cake slurry with a solids content of 50 to 60 inches. Addition of spray-dried clay to this filter cake is highly impure due to the high cost of producing spray-dried clay. Therefore, it would be desirable to develop a technique to create a 70% solids slurry consistency without the addition of spray-dried clay. Similarly, it is highly desirable to have a high solids content of the f1 overfeed to the dryer when the clay needs to be fed dry.

The use of an electrofilter with vacuum treatment appears to be effective for delicately dehydrating suspensions. When an electrofilter is subjected to the action of an electric field (direct current), it becomes charged t.
The principle interest rate H that ~ particles move in the opposite polarity direction
” [7]. This movement of solid particles through a liquid based on the application of an electric field is called electrophoresis. Clay particles are normally negatively charged and move toward the anode (+). When this is applied to an aqueous suspension of clay, suspended clay particles are deposited on the filter membrane surrounding the anode. Commercially available EAVF devices have an anolyte chamber for each anode and means for supplying anolyte to and from that chamber. Vacuum at the anode is used to remove the anolyte and gaseous reaction products leaving the anolyte 0 Vacuum at the cathode is used to remove the 1 solution and gaseous reaction products at the cathode 0 Other ionic species, especially the dispersant Sodium cations, chloride, and hydroxyl anions, which primarily originate from the anolyte and the anolyte, also move within the electric field.

Reactions at the electrodes produce ionic compounds and gaseous products depending on the electrolyte used. For example in EA'VF the anode chamber is filled with an electrolyte such as a sodium chloride solution.

Under the action of an electric field, salt gas is generated at the anode, and sodium ions migrate from the anode and react (with electrons) at the cathode to produce sodium hydroxide and hydrogen gas. The negatively charged hydroxyl anions migrate from the cathode at a rate that depends on the strength of the electric field and the action of the P solution provided by the vacuum at the cathode.

Generally, it is more effective to subject kaolin slurry etc. to filtration accompanied by electrical treatment because the energy cost is lower than other methods. It is also desirable that the filter cake effluent can be sold without further processing. However, there are several problems with the operation of the EAVF. The movement of ions in the electrokinetic cell can result in the presence of unfavorable anions in the filter cake. For example, the presence of OH- ions in the filter cake will cause the slurry to become excessively dispersed, resulting in an abnormally high slurry viscosity, making optimal dispersion of the cake impossible. KAVF
Ionic contamination of the filter cake in can cause the viscosity of the clay slurry product to become too high and the resistivity to be too low. This is the EA' of clay for paper coatings and paints.
This is a major drawback when using VF. Furthermore, the pressure condition of vacuum (including reduced pressure) is practically used.
This increases the risk of fine particles leaking through the fabric and contaminating the anolyte at the anode and the P solution at the cathode.

The present invention relates to a tank capable of receiving and discharging a suspension to be subjected to filtration, and an anode and a cathode provided in the tank so as to be immersed in the suspension in the tank. a structure, the anode structure deposits a filter cake;
An electrical process comprising an anode element, a housing surrounded by a filter medium, and means for supplying an anolyte to the housing, the cathode structure having a cathode element and quadrupled with filter elements. In the method of dewatering a particulate solid aqueous suspension using a vacuum filter with It is intended to permit and substantially prevent the passage of anions and gaseous electrochemical reaction products from the anolyte to the filter cake deposited on the anode structure.

We dehydrate aqueous suspensions of particulate solids, such as hydrous kaolin viscosity, using an EAVF with an anode structure (as disclosed in US Pat. No. 4,168,222) that provides a means for circulating anolyte therein. We have found an improved method and method.

According to the invention, a permselective membrane is provided on the anode structure.

This j-shape allows cations to pass freely through it, but prevents the passage of anions and gaseous reaction products from the anolyte. As a result, anions such as chloride ions generated at the anode do not contaminate the filter cake deposited on the anode. In addition, the film-like permselective membrane supported on the grid prevents fine kaolin particles from contaminating the electrode solution (anolyte) in the anode chamber, and at the same time prevents anions from coming out of the anolyte through the membrane and forming a filter cake. It also prevents contamination. In a preferred embodiment, a selectively permeable membrane is provided between a grid and filter medium that is typically integral with the anode structure of an EAVF operated with circulating anolyte.

Preferably, the cathode structure of the EAVF is
In the structure described in the USP of AN, a selectively permeable membrane that selectively passes only the catholyte is provided in the cathode structure, and a chamber for the catholyte and a means for supplying and discharging the catholyte are incorporated. It is possible to do this. This selectively permeable membrane has a reaction product (
Prevent contamination with (mainly hydroxyl ions). In this embodiment, the cathode support structure is both conductive and an electrode. The catholyte can be made in situ and typically contains OR- and Na+. In this embodiment, the above F
, Reeman, USF', with a selectively permeable membrane on its internal cathode support structure (cathode), a filter medium supported on a second non-conducting external support grid, and an anode. Similar to the chamber, it is necessary to modify the electrolyte (catholyte) and recirculation means within the cathode support structure. This structure prevents anions such as hydroxyl ions generated at the cathode from migrating under the influence of the electric field and contaminating the feed TM, suspension and filter cake.

In a particularly preferred embodiment, the EAVF system of the present invention has a plurality of alternating anodes and cathodes with a selectively permeable membrane disposed around each anode and each cathode support structure. perm-selective membrane used in the present invention
mbrane) is the above-mentioned Kunkle and Kunkle.
This is different from the semipermeable membrane described in the USP. The membrane used in the known examples is just a piece of cloth, Kunkle and Kuncl.
USI such as e.

This will be explained below with reference to the drawings. The figures are all in the form of simple flow sheets, and corresponding known structures are also shown for comparison. Only the anode and cathode structures of the removed EAVF are shown. Portions that are not essential to understanding the present invention are omitted. For example, it should be understood that in all figures the anode and cathode structures are immersed in a slurry that is dehydrated in the EAVF. Means for lifting the anode 14 structure to remove the precipitated filter cake are known and the drawing does not show the lifting of the anode and the scraping of the filter cake therefrom and placing the anode structure back into the slurry.

Similarly, vacuum means provided on the anode and cathode structures, such as pumps, are not shown.

The first [2] is a plan view of the cathode structure of the current EAVF.

FIG. 2 is a partial side view of the cathode chamber showing the flow of the basic catholyte components (H2, Na+ and OH-) of the f-liquid. A front view of this cathode structure is shown in FIG. 7 of US Pat. No. 4,168,222.

FIG. 3 is a side view of a current anode structure with an anode chamber. A front view of this structure is shown in Figure 5 of US Pat. No. 4,168,222. Figure 3 shows the slurry, the precipitation of filter cake, and the flow of gas and ions when the anolyte is chlorinated.

FIG. 4 is a plan view showing the cathode-anode arrangement of the preferred electrofilter of the present invention. Contrast with Figure 1.

FIG. 5 is a partial side view showing an example of the anode chamber of the present invention, showing changes in the flow of ions caused by providing a selectively permeable membrane on the anode structure. Figure 5 shows an example in which the anolyte is a sodium chloride aqueous solution (the front view of the modified anode structure is U
(See Figure 5 of SP4168222).

FIG. 6 is a partial front view of the cathode structure of the present invention, showing the cathode chamber and catholyte circulation. The flow of fPe is also shown 1
There are 7. FIG. 7 is a front view of the structure of FIG. 6.

FIG. 8 is a partial side view of the cathode structure of the present invention, showing the features of the catholyte chamber and the selectively permeable membrane. Figure 8 shows the cathodic reaction and the resulting reaction products () (2, Na+ and 0
The flow of 1-(-) is shown, showing how the shunted selectively permeable membrane and cathode chamber prevent the OH- produced in the cathodic reaction from migrating to the slurry. Contrast with Figure 2. Of course, the hydrated kaolin clay dehydrated according to the present invention may be pretreated and formulated to be suitable for the final use. For example, when the dehydrated suspension (slurry) is used as a paper coating or paint component, the kaolin clay particles typically contain approximately 80% of particles smaller than 2 microns.
~100%, with an average particle size of 03-0.9 microns e, s, d, (equivaleutsph
It is preferable to adjust the size to a certain size (erical diameter). Clay products that have undergone the treatment of the present invention can be used to make fired clay pigments.

Dehydration of these slurries can be achieved using anionic inorganic and/or organic dispersants such as TSPP (tetrasodium birophosphate), Cal gon (sodium hexametaphosphate), and/or ammonium or sodium polyacrylates. It is preferable to carry out the process in this (dispersed) state.

Dispersants promote negative charging around clay particles and enhance their aerophoretic properties. In one embodiment of the EAVF described in USP 4,168,222, a series of parallel alternating cathodes and anodes are immersed in a circulating slurry of clay solids suspended in a liquid in a tank. A direct current is applied to the electrode to deposit a solid as a filter cake on the wall soil of the anode support structure. Each anode is a hollow structure with a flat surface;
It has an anode (+), an electrolyte (anolyte) circulation means, a support grid, a filter medium and a protective cage. When the anolyte is sodium chloride, an electrochemical reaction produces field gas at the anode. Although the extent of the reaction depends on the current density, the vacuum (also referred to as reduced pressure) applied to the anode and circulating anolyte is effective in removing gaseous components from the anode chamber.

Preferably, the cathode has a fluid-permeable wall, in particular a fluid-permeable fabric (substantially impermeable to clay) covering the support grid or grid-like structure. The same 18-like fabric used on the anode support structure can also be used as a filter medium. A vacuum source connected to the hollow, flat cathode causes the liquid phase of the slurry (1" I liquid) to fill the hollow interior of each cathode between the electrode and the support structure. The f liquid fills with the P liquid at a controlled rate. The pump is operated from a hollow cathode that has been heated up.By passing an electric current through the f-liquid, a reaction occurs at the cathode, producing mainly hydrogen gas and a sodium hydroxide solution.

The apparatus of the present invention may include a moving means with a pulley for raising the anode vertically from the slurry. Preferably, the moving means is equipped with a doctor blade to scrape off clay filter cake from the flat surface of the anode while it is returning to the tank. The scraped clay is collected on a conveyor belt. It is also preferred to be able to pump the slurry into and out of the tank so that the electrode remains immersed during the dewatering operation. Current density and vacuum are adjusted to balance the movement of clay to the anode and the removal of r-liquid through the cathode.

The slurry is dispersed (M) as an aqueous suspension of EAVIi.
'Supplied to. Typically Ir:r, pH is 6-95. Poultices include, but are not limited to, sodium hydroxide, condensed sodium phosphate, sodium carbonate, and mixtures thereof. Organic dispersants may also be used. As a dispersing agent, the usual amount is added. for example,
The slurry may contain 3 to 6 bonds of commercially available sodium silicate solution, such as 0■ brand. Typical clay solids content in the feed slurry is as per US Application 00j, 898, US
P4168222 and USP4107206.

In FIG. 5, it is preferable to provide a selectively permeable membrane between the support directly connected to the anode chamber and the filter medium because there is less possibility of clay solids accumulating on the selectively permeable membrane. If the cathode structure is provided with a permselective membrane, the membrane should be provided on two internal support grids (which also constitute the cathode), thereby forming a central chamber containing the catholyte. It may be necessary to introduce electrolyte into the cathode chamber at the start of operation. During operation, the electrode reaction that occurs at the cathode forms an electrolyte in situ.

As shown in FIG. 8, an external, non-conducting filter medium support grid covered with filter methium is provided on each of the two operative sides of the cathode structure. An internal space is created between the membranes in which the e-liquid is collected. A catholyte recirculation mechanism is also provided.

Examples of preferred anolytes include sodium chloride, sodium carbonate and sodium hydroxide solutions. Of course, others can also be used. The use of a non-chloride anolyte eliminates the release of chlorine at the anode and eliminates the possibility of corrosive chloride and hypochlorite ions contacting metal components.

Using sodium carbonate produces oxygen gas and sodium hydroxide solution at the anode. The use of sodium hydroxide as the anolyte has the advantage of not producing corrosive reaction products yet providing high electrical conductivity.

The sodium cations move to the cathode and undergo an electrochemical reaction involving water. This reaction produces hydrogen gas and sodium hydroxide. Therefore, in conventional dehydration of kaolin slurry, the pH of the slough usually takes a high value of 10 to 13. Using a permselective membrane surrounding an external, non-conductive support structure with a filter medium, sodium ions migrate through the membrane and undergo a reaction at the cathode, releasing hydrogen which is dissolved in the catholyte. OH- ions are generated in the cathode chamber and can be transferred to the liquid by a selectively permeable membrane,
The result is a more neutral liquid. This prevents contamination of the filter cake with hydroxyl and other anions that would adversely affect slurry dispersion. In the case of kaolin slurry, contamination of the filter cake with anions increases the viscosity of the kaolin/water slurry, resulting in unfavorable uses of the kaolin.

Preferred membranes for the present invention are those that are permeable to cations and impermeable to anions, gases, water and other liquids. Preferred selectively permeable membranes include E, 1. du Pont de N
There is a perfluorosulfonic acid polymer sold by Emoura, Inc. under the trademark Nafion. Other membranes with permselectivity may of course be used.The functionality of Nafton depends on the number of sulfonic acid groups in the polymer. This membrane has superior chemical stability and toughness compared to other selectively permeable membranes, such as those in which sulfonic acid groups are replaced with carboxyl groups. Nafto
The n-membrane allows positively charged ions (cations) to pass through, but not negatively charged ions (anions).

[Brief explanation of the drawing]

Fig. 1 is a plan view of the cathode structure of a conventional EAVF, Fig. 2 is a side view of the cathode chamber, Fig. 3 is a side view of the conventional anode structure, and Fig. 4 is a cathode-anode of the EAVF of the present invention. 5 is a side view of the anode structure of the present invention; FIG. 6 is a front view of the cathode structure of the present invention; FIG. 7 is a side view of the structure of FIG. 6; The figure is a side view of the cathode structure of the present invention. 1...Slurry, 2...Anolyte inlet, 5...Pg
Outlet, 4... Electrical terminal, 5... P liquid return, 6...
- Anolyte outlet, 7... P liquid, 8... Filter medium, 9... Support grid, 10... Anode, 11...
・Anolyte, 12...Protection cage, 16...Filter cake, 14...Catholyte outlet, 15...Catholyte inlet, 16...Cathode chamber, 17...Anode chamber, 18.・・・
selectively permeable membrane, 19... catholyte, 20... catholyte H
20 discharge (vacuum), 21... P liquid discharge (vacuum). JFF for patent 1 person Engelhard Corporation 71″ 25- Engraving of drawings (no changes in content) FIG, 1 FIG, 5 FIG, 6 FIG, 7 Procedural amendment (method) July 2, 1980 Commissioner of the Patent Office Wakasugi Mr. Kazuo 1, Indication of the case Patent Application No. 10790 of 1982, 2, Title of the invention: Electrical processing All cases Dehydration using a vacuum filter 3, Corrected Sound Connection with the case Patent applicant name Engelhard Corporation - '1.1 Name Patent attorney (6323) Ryoji Yose, 7....
':+(. 5. Date of dispatch of amended order
...Jig..."June 29, 1980 6, Drawing 7 attached to the application to be amended, Contents of amendment Procedure amendment c method) % formula % 1, Indication of case Showa 1 J 57 Patent Application No. 10790 No. 2, Name of the invention Dehydration using a vacuum filter accompanied by electrical processing 3, Basis for correction - Relationship to the case Name of patent applicant Engelhard Corporation Name Patent attorney (6323) Ryoji Kawase β''゛-35 , the subject of the amendment (゛・ “＼□−□ゞ (1) The column of the patent applicant in the petition and the proof of representation (2) The handwritten specification attached to the petition, the content of the amendment

Claims (1)

[Claims] A tank capable of receiving and discharging a suspension to be subjected to filtration, an anode provided in the tank so as to be immersed in the liquid in the tank, and the cathode structure is for depositing a filter cake and has an anode element, a housing surrounded by a filter medium, and means for supplying anolyte to the housing; In a vacuum filter involving electrical processing, the structure has a cathode surrounded by a filter element, and by attaching a selectively permeable membrane to the anode structure, filter cake and ρ are removed from the anolyte. % to allow the passage of canon into the turbid solution and actually prevent the overload of anions and gaseous electrochemical reaction products from the anolyte to the filter cake deposited on the 11i structure. Vacuum filter for dehydration of aqueous suspensions of granular solids. 2. The filter according to the first embodiment, wherein the anode structure contains filter methium for suppressing precipitation of particulate solids onto the membrane and/or protecting the membrane. 3. The filter according to item 1, wherein the anode structure contains filter methium, and the membrane is a film-like material having sufficient strength that no filter methium is required for protection. 4. A means for a cathode chamber integrated with the cathode element to circulate the catholyte and discharge the catholyte and reaction products; a means for discharging the tco-liquid from the 1-liquid chamber and the Pg chamber located outside the cathode chamber; A selectively permeable membrane is installed between the catholyte chamber and the P liquid chamber to allow cations to pass through, but virtually no anions or gases pass through, and a filter around the P liquid chamber is installed to prevent particulate solids from entering the f liquid chamber. 2. The filter according to claim 1, comprising methium. 5 The selectively permeable membrane is made of perfluorosulfonic acid polymer J
The filter according to paragraph 1.2.6 or 4. 6. A tank capable of receiving and discharging the suspension to be subjected to filtration, with an anode and a cathode structure provided in the tank so as to be immersed in the suspension in the tank, and a nuclear anode. The structure is for depositing a filter cake and has an anode element, a housing with four filter mediums, and a means for supplying anolyte to the housing.The cathode structure has a cathode element and a filter element. In a vacuum filter with electrical processing in a quadruple configuration, a selectively permeable membrane is attached to the anode structure to increase the transfer of cations from the anolyte to the filter cake and the suspended suspension. Dewatering the aqueous suspension of particulate solids using a vacuum filter that allows the passage and substantially prevents the passage of anions and gaseous electrochemical reaction products from the anolyte to the filter cake deposited on the anode structure. A dehydration method characterized by: 7. The method according to item 6, wherein the suspension is a clay suspension. & The method according to item 7, wherein the clay is hydrated kaolin clay. 9. The method of claim 6, wherein the anolyte meets sodium ions and the layer allows sodium ions to pass therethrough. 10. The method according to item 7, wherein the anolyte is a water bath solution of sodium chloride, sodium hydroxide, or sodium carbonate.