CN111530295B - Inclined dipping preparation method of tubular ceramic membrane inner membrane - Google Patents
Inclined dipping preparation method of tubular ceramic membrane inner membrane Download PDFInfo
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Abstract
The invention discloses an inclined dipping preparation method of a tubular ceramic membrane inner membrane, which comprises the steps of enabling a ceramic coating liquid subjected to vacuum defoaming to enter a support body from a container through a pipeline, an inlet valve and an inlet end of a tubular support body in sequence, enabling the ceramic coating liquid to flow out of an outlet end of the tubular support body, and enabling the ceramic coating liquid to flow into a collection container through a connecting pipeline and an outlet flow limiting valve in sequence; before dipping and coating, the tubular support body is inclined upwards by 5-60 degrees on the horizontal plane, ceramic coating liquid enters the support body from the inlet end of the tubular support body and fills the inner hole of the tubular support body, after dipping for 5-100 seconds, the tubular support body pipe is inclined downwards by 5-60 degrees relative to the horizontal plane within 3 seconds, an inlet valve is closed, the inlet end of the tubular support body is communicated with the atmosphere, and the ceramic coating liquid naturally flows out from the outlet end of the tubular support body. Compared with the traditional vertical dip coating or grouting coating mode, the invention can ensure that the thicknesses of the two ends of the ceramic membrane are more uniform and improve the bonding strength of the ceramic membrane and the support body.
Description
Technical Field
The invention relates to an inclined dipping preparation method of a tubular ceramic membrane inner membrane, belonging to the field of high-performance ceramic membranes.
Background
A film is a three-dimensional structure material with dimensions in one dimension much smaller than the other two dimensions, as defined by the international union of theory and applied chemistry. The mass transfer is generated under the action of various driving forces such as pressure difference, concentration difference, chemical difference, potential difference and the like, wherein the pressure difference is mainly used as separation power, and the 'sieving principle' is utilized, so that (solid, liquid and gaseous) particles larger than the self-pore diameter are intercepted, and the purposes of multi-phase separation, purification and concentration are achieved.
The membrane material can be further classified into a solid membrane, a liquid membrane and a gaseous membrane according to the form, wherein the solid membrane is most commonly used in the industry. The solid film can be further divided into an organic film and an inorganic film according to different composition materials, at present, most of the active layers playing a role in separation in the organic film are organic high molecular materials such as cellulose acetate and polyfluoropolymer, and the active layers playing a role in separation in the inorganic film are inorganic non-metallic materials such as glass and ceramic. Among them, the most commonly used inorganic membrane is a ceramic membrane, which can be classified into a flat membrane, a tubular membrane, a hollow fiber membrane, etc. according to its shape.
Ceramic membranes can be classified into two types, namely symmetric membranes and asymmetric membranes according to different structures. A symmetric membrane refers to a membrane material whose physicochemical structure is uniform in all directions, while an asymmetric membrane refers to a membrane material consisting of an asymmetric structure, including a support layer providing mechanical strength, a filtration layer serving a sieving function, an intermediate transition layer bridging the support layer and the filtration layer.
The ceramic membrane has the advantages of high separation efficiency, acid and alkali resistance, organic solvent resistance, microorganism resistance, high temperature resistance, high mechanical strength, long service life and the like, and is widely applied to the fields of environmental protection, sewage treatment, gas separation, food processing and the like. The preparation method of the ceramic membrane mainly comprises a dip coating method, a chemical vapor deposition method, a spraying preparation method and the like. Chemical vapor deposition is a process of modifying the surface properties of a film by depositing a layer of the same or different compound on the surface of the material through a chemical reaction that occurs between components surrounded by a gaseous medium under certain temperature conditions. The spraying technique is to spray a layer of slurry on the surface of the support body pipe by a spray gun to obtain a filter layer. The dipping coating method comprises the steps of immersing the support body tube in the coating liquid for a plurality of times, then pulling out the support body tube at a certain speed to obtain a filter cake layer, and further sintering the filter cake layer to form a film. The dip coating method is suitable for large-scale industrial production due to the simple method and low cost.
In the process of coating the tubular ceramic membrane by using a dip coating method, the thickness of the filter layer of the ceramic membrane is mainly controlled by two processes, one is a capillary filtration process in the dipping process, the other is a film forming process in the pulling process, and the increase of the whole film thickness is equal to the linear superposition of the two processes; wherein the membrane thickness H during capillary filtrationcThe increase of (mum), the coating time t (S) and the viscosity eta (Pa S) of the coating liquid have the following mathematical relationship (Xunan Ping, ceramic membrane material design, preparation and application facing to the application process [ M)]Beijing scientific Press 2005.):
wherein the film thickness H in the film formation processmThe increase of (mum) and the solid content omega (wt.%), the viscosity eta (Pa S), the surface tension gamma (N/M) and the pulling speed mu (M/S) of the coating liquid have the following mathematical relations (Xunan plane, ceramic membrane material design, preparation and application facing to the application process [ M)]Beijing, science publishers, 2005.)：
Therefore, when the solid content ω (wt.%), the viscosity η (Pa S), the surface tension γ (N/m) of the coating solution, and the pulling speed μ (m/S) are fixed, the thickness of the filter layer of the ceramic membrane is only related to the coating time t (S). However, in order to increase the filtration flux of the ceramic membrane, it is desirable that the thickness of the ceramic membrane is as thin as possible, so the dipping time is not too long, and if the dipping time is too short, the thickness of the membrane is greatly affected by the dipping time.
For the coating of the tubular membrane, the traditional vertical dip coating mode is to vertically place the ceramic support tube for coating, when the coating is started, the coating solution enters from the bottom end, and when the coating is finished, the coating solution flows out from the bottom end along the tube wall again under the action of gravity. Or a grouting film coating mode is used, the ceramic support body tube is vertically placed for film coating, when film coating is started, the bottom end of the support body tube is closed, the film coating liquid is filled from the top end, and after a certain period of time, the film coating liquid flows out from the bottom end under the action of gravity. For the support body tube with the length of more than 1m, the two coating methods can lead the time for the top end and the bottom end of the support body tube to contact with the coating liquid to be inconsistent, so that the problem of uneven coating thickness exists at the two ends of the support body tube, and further, the filtration precision and the service life of the ceramic membrane are greatly influenced. In order to solve the problem, in engineering, a support body tube is usually subjected to surface treatment or pre-wetting to remove capillary force, and then vertical dip coating is performed after the influence of coating time on the thickness of the ceramic film is eliminated.
Disclosure of Invention
The invention aims to improve the film coating uniformity and the film bonding strength of a longer tubular ceramic film and is realized by the following technical scheme.
The invention leads the time of contacting the coating liquid of each part of the support body tube to be consistent by the method of inclined coating. Compared with the traditional vertical dipping coating or grouting coating mode, the invention can ensure that the film thickness at two ends of the ceramic film is more uniform, thereby improving the filtering precision of the ceramic film. Compared with the traditional method of removing capillary force after the ceramic membrane is wetted and vertically dipping and coating, the method can improve the bonding strength of the ceramic membrane and the support body tube. Thereby improving the service life of the ceramic membrane.
The purpose of the invention is realized by the following technical scheme:
a method for preparing a tubular ceramic membrane inner membrane by inclined dipping comprises the following steps: the ceramic coating liquid after vacuum defoaming sequentially enters the support body from the container through the pipeline, the inlet valve and the inlet end of the tubular support body, flows out of the outlet end of the tubular support body, and sequentially flows into the collection container through the connecting pipeline and the outlet flow-limiting valve; the tubular support body is provided with at least one through inner hole to be coated; before dipping and coating, the tubular support body is inclined upwards by 5-60 degrees on a horizontal plane, after an inlet valve at a low position is opened, ceramic coating liquid enters the support body from the inlet end of the tubular support body and is filled with an inner hole of the tubular support body, after the tubular support body is dipped for 5-100 seconds, the inner hole of the support body to be coated is dipped by the ceramic coating liquid under the action of pressure or gravity, the tubular support body is inclined downwards by 5-60 degrees relative to the horizontal plane within 3 seconds, the inlet valve is closed, the inlet end of the tubular support body is communicated with the atmosphere, the ceramic coating liquid naturally flows out from the outlet end of the tubular support body, the outflow time and the inflow time of the ceramic coating liquid are controlled to be consistent through an outlet flow.
In order to further achieve the object of the present invention, preferably, the film-forming particles in the ceramic coating solution are one or more of alumina, titania, or zirconia.
Preferably, the viscosity of the ceramic coating liquid is 50-100 mPaS.
Preferably, the support is one or more of alumina, zirconia and silica.
Preferably, the number of the inner holes of the tubular support body is single hole, 7 holes or 19 holes; the outer diameter of the tubular supporting body is 12mm or 30mm respectively, and the inner diameter of the tubular supporting body is 10mm, 7mm or 4mm respectively.
Preferably, the thickness of the ceramic membrane layer is 10-20 μm.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1) compared with the traditional vertical dipping coating mode or grouting coating mode, the invention can ensure that the thicknesses of the two ends of the ceramic membrane are more uniform, thereby improving the filtering precision of the ceramic membrane.
2) Compared with the traditional method of removing the capillary force after the ceramic membrane is wetted and vertically dipping and coating, the method can obviously improve the bonding strength of the ceramic membrane and the support body tube, thereby prolonging the service life of the ceramic membrane.
Drawings
FIG. 1 is a scanning electron micrograph of an inlet end cross-section of the ceramic membrane prepared in example 1.
FIG. 2 is a scanning electron micrograph of an exit end cross-section of the ceramic membrane prepared in example 1.
FIG. 3 is a scanning electron micrograph of an inlet end cross-section of the ceramic membrane prepared in example 2.
FIG. 4 is a scanning electron micrograph of an exit end cross-section of the ceramic membrane prepared in example 2.
FIG. 5 is a scanning electron micrograph of an entrance end cross-section of the ceramic membrane prepared in example 3.
FIG. 6 is a scanning electron micrograph of an exit end cross-section of the ceramic membrane prepared in example 3.
Fig. 7 is a scanning electron microscope image of the bottom end cross section of the ceramic film prepared in comparative example 1.
Fig. 8 is a scanning electron microscope image of a top end cross section of the ceramic film prepared in comparative example 1.
Fig. 9 is a scanning electron microscope image of a bottom end cross section of the ceramic film prepared in comparative example 2.
Fig. 10 is a scanning electron microscope image of a top cross section of the ceramic film prepared in comparative example 2.
Fig. 11 is a scanning electron micrograph of a bottom cross section of the ceramic film prepared in comparative example 3.
Fig. 12 is a scanning electron microscope image of a top end cross section of the ceramic film prepared in comparative example 3.
Detailed Description
The present invention is described in detail below with reference to specific examples and comparative examples, but it should be noted that the following examples are only illustrative of the present invention, and are not intended to limit the scope of the present invention.
Example 1
The tubular ceramic membrane support body of the embodiment is a single-hole alumina support body tube with the outer diameter of 12mm, the inner diameter of 10mm and the length of 1m, is mainly applied to industrial sewage pretreatment, and has the principle of filtering fine-particle pollutants in sewage.
An inclined dipping preparation method of a tubular ceramic membrane inner membrane comprises the following steps:
(1) preparing a zirconium oxide ceramic coating solution: adding 10 wt.% of 520nm zirconia particles into 84.9 wt.% of water, adding 1 wt.% of polyacrylic acid serving as a dispersing agent and 0.1 wt.% of paraffin oil serving as a defoaming agent, fully ball-milling for 1h, uniformly dispersing, adding 4 wt.% of PVA solution, continuously ball-milling for 1h, uniformly dispersing to prepare a uniformly and stably dispersed zirconia ceramic coating solution, adding a proper amount of water, and uniformly stirring to control the viscosity of the zirconia ceramic coating solution to be 50 mPaS.
(2) Inclined dip coating: the ceramic coating liquid after vacuum defoaming sequentially enters the support body from the container through the pipeline, the inlet valve and the inlet end of the tubular support body, flows out of the outlet end of the tubular support body, and sequentially flows into the collection container through the connecting pipeline and the outlet flow-limiting valve; the whole circuit is connected by a plurality of quick connectors, and the ceramic coating liquid is impregnated into the support hole to be coated under the pressure of 5 bar. Before dipping and coating, the tubular support body is inclined upwards by 5 degrees on the horizontal plane, after an inlet valve at a low position is opened, the ceramic coating liquid enters the support body from the inlet end of the tubular support body and is filled with the inner hole of the tubular support body, after the tubular support body is dipped for 5 seconds, the tubular support body pipe is inclined downwards by 5 degrees relative to the horizontal plane within 3 seconds, the inlet valve is closed, the inlet end of the tubular support body is communicated with the atmosphere, the ceramic coating liquid naturally flows out from the outlet end of the tubular support body, and the outflow time and the inflow time of the ceramic coating liquid are controlled to be consistent.
(3) And (3) drying and sintering: and (3) putting the film-coated tubular support body tube into a high-low temperature test box for drying for 18h, and cooling along with a furnace after forming for 2h at 1400 ℃ to obtain the zirconia ceramic membrane.
Testing the average filtering aperture of the ceramic membrane by a bubble point pressure method according to the standard ASTM F316-03, testing the pure water flux of the ceramic membrane according to the standard HYT064-2002, and detecting the retention rate of the ceramic membrane by utilizing the retention proportion of graphite ink particles with equivalent filtering aperture of the ceramic membrane; testing the film thickness at two ends of the ceramic film by using a scanning electron microscope EVO 18; and testing the membrane bonding strength of the ceramic membrane by utilizing the average filtration pore diameter change of the ceramic membrane after the ceramic membrane is back flushed by pulse water flow with the time interval of 10s and the pressure of 0.8MPa for 2 h.
The average filtering pore diameter of the ceramic membrane is tested to obtain the filtering particle size range of the ceramic membrane, and the smaller the filtering pore diameter is, the finer the particles can be filtered; the sewage treatment capacity of the ceramic membrane can be obtained by testing the pure water flux of the ceramic membrane, and the larger the pure water flux is, the larger the sewage treatment capacity of the ceramic membrane is; the coating uniformity of the ceramic film can be obtained by measuring the thicknesses of the film layers at the two ends of the ceramic film, and the coating uniformity of the ceramic film is more uniform if the thicknesses of the film layers at the two ends of the ceramic film are consistent; the actual filtering precision of the ceramic membrane can be obtained by measuring the rejection rate of the ceramic membrane, and the high rejection rate reflects the high filtering precision of the ceramic membrane, so that the side surfaces prove that the thicknesses of the membrane layers at the two ends of the ceramic membrane are consistent, and the coating is more uniform; the bonding strength of the ceramic membrane can be obtained by changing the average pore diameter of the ceramic membrane after the back washing, and if the change of the average pore diameter of the ceramic membrane after the back washing is not large, the ceramic membrane has higher bonding strength. Scanning electron micrographs of both ends of the ceramic film prepared in example 1 are shown in fig. 1 and 2. The average thickness of the inlet end and the outlet end of the ceramic membrane measured by a scanning electron microscope EVO 18 is 11.0mm, which proves that the thickness of the membrane layers at the two ends of the ceramic membrane is consistent, and the coating of the ceramic membrane is more uniform compared with the coating of the ceramic membrane in the embodiment in the prior art. The ceramic membranes have an average filter pore size of 300nm, as determined according to the standard ASTM F316-03, according to the standard HYThe pure water flux of the ceramic membrane was 5866L h as measured by T064--1m-2bar-1The retention rate of the graphite ink with the particle size of 300nm reaches 98.0%, the graphite ink has high retention rate, the average filtering pore diameter of the ceramic membrane after backwashing is 300nm, and the average filtering pore diameter is unchanged compared with that before backwashing.
Example 2
The tubular ceramic membrane support body is a 7-hole alumina support body tube with the outer diameter of 30mm, the inner diameter of 7mm and the length of 1m, is mainly applied to industrial sewage pretreatment, and has the principle of filtering fine-particle pollutants in sewage.
(1) Preparing coating liquid: adding 10 wt.% of 520nm aluminum oxide particles into 84.9 wt.% of water, adding 1 wt.% of polyacrylic acid serving as a dispersing agent and 0.1 wt.% of paraffin oil serving as a defoaming agent, fully ball-milling for 1h, uniformly dispersing, adding 4 wt.% of PVA solution, continuously ball-milling for 1h, uniformly dispersing to prepare uniform and stably-dispersed aluminum oxide ceramic coating liquid, adding a proper amount of water, and uniformly stirring to control the viscosity of the aluminum oxide ceramic coating liquid to be 70 mPaS.
(2) Inclined dip coating: the ceramic coating liquid after vacuum defoaming sequentially enters the support body from the container through the pipeline, the inlet valve and the inlet end of the tubular support body, flows out of the outlet end of the tubular support body, and sequentially flows into the collection container through the connecting pipeline and the outlet flow-limiting valve; the whole circuit is connected through a plurality of quick connectors, the inner hole of the support body to be coated is soaked by the ceramic coating liquid under the action of gravity, and the tubular support body is provided with at least one through inner hole to be coated; before dipping and coating, the tubular support body is inclined upwards by 30 degrees on the horizontal plane, after an inlet valve at a low position is opened, the ceramic coating liquid enters the support body from the inlet end of the tubular support body and is filled in the inner hole of the tubular support body, after the tubular support body is dipped for 50s, the tubular support body pipe is inclined downwards by 30 degrees relative to the horizontal plane within 3s, the inlet valve is closed, the inlet end of the tubular support body is communicated with the atmosphere, the ceramic coating liquid naturally flows out from the outlet end of the tubular support body, and the outflow time and the inflow time of the ceramic coating liquid are controlled to be consistent.
(3) And (3) drying and sintering: and (3) putting the film-coated tubular support body tube into a high-low temperature test box for drying for 18h, and cooling along with a furnace after forming for 2h at 1300 ℃ to obtain the alumina ceramic membrane.
The average filtration pore size of the ceramic membrane is tested by a bubble point pressure method according to the standard ASTM F316-03, the pure water flux of the ceramic membrane is tested according to the standard HYT064-2002, and the retention rate of the ceramic membrane is measured by utilizing the retention ratio of graphite ink particles corresponding to the filtration pore size of the ceramic membrane; testing the film thickness at two ends of the ceramic film by using a scanning electron microscope EVO 18; and testing the membrane bonding strength of the ceramic membrane by utilizing the average filtration pore diameter change of the ceramic membrane after the ceramic membrane is back flushed by pulse water flow with the time interval of 10s and the pressure of 0.8MPa for 2 h. Scanning electron micrographs of both ends of the ceramic film prepared in this example are shown in fig. 3 and 4. The average thickness of the ceramic membrane at the inlet end and the outlet end was 18.0mm, both measured by scanning electron microscopy EVO 18. The ceramic membranes had an average filter pore size of 200nm, as measured according to the standard ASTM F316-03, and a pure water flux of 4155L h, as measured according to the standard HYT064-2002-1m-2bar-1The retention rate of the graphite ink with the particle size of 200nm reaches 98.0%, the average filtering aperture of the ceramic membrane after backwashing is 200m, and the average filtering aperture is unchanged from that before backwashing.
Example 3
The tubular ceramic membrane support body of the embodiment is a 19-hole alumina support body tube with the outer diameter of 30mm, the inner diameter of 4mm and the length of 1m, is mainly applied to industrial sewage pretreatment, and has the principle of filtering fine-particle pollutants in sewage.
(1) Preparing coating liquid: adding 15 wt.% of 1.1nm titanium oxide particles into 79.9 wt.% of water, adding 1 wt.% of polyacrylic acid serving as a dispersing agent and 0.1 wt.% of paraffin oil serving as a defoaming agent, fully ball-milling for 1h, uniformly dispersing, adding 4 wt.% of PVA solution, continuously ball-milling for 1h, uniformly dispersing to prepare a uniformly and stably dispersed titanium oxide ceramic coating solution, adding a proper amount of water, and uniformly stirring to control the viscosity of the titanium oxide ceramic coating solution to be 100 mPaS.
(2) Inclined dip coating: the ceramic coating liquid after vacuum defoaming sequentially enters the support body from the container through the pipeline, the inlet valve and the inlet end of the tubular support body, flows out of the outlet end of the tubular support body, and sequentially flows into the collection container through the connecting pipeline and the outlet flow-limiting valve; the whole circuit is connected through a plurality of quick connectors, the inner hole of the support body to be coated is soaked by the ceramic coating liquid under the pressure of 8bar, and the tubular support body is provided with at least one through inner hole to be coated; before dipping and coating, the tubular support body is inclined upwards by 60 degrees on the horizontal plane, after an inlet valve at a low position is opened, the ceramic coating liquid enters the support body from the inlet end of the tubular support body and is filled in the inner hole of the tubular support body, after the tubular support body is dipped for 100s, the tubular support body pipe is inclined downwards by 60 degrees relative to the horizontal plane within 3s, the inlet valve is closed, the inlet end of the tubular support body is communicated with the atmosphere, the ceramic coating liquid naturally flows out from the outlet end of the tubular support body, and the outflow time and the inflow time of the ceramic coating liquid are controlled to be consistent.
(3) And (3) drying and sintering: and (3) putting the film-coated tubular support body tube into a high-low temperature test box for drying for 18h, and cooling along with a furnace after forming for 2h at 1300 ℃ to obtain the titanium oxide ceramic film.
The average filtration pore size of the ceramic membrane is tested by a bubble point pressure method according to the standard ASTM F316-03, the pure water flux of the ceramic membrane is tested according to the standard HYT064-2002, and the retention rate of the ceramic membrane is measured by utilizing the retention ratio of graphite ink particles corresponding to the filtration pore size of the ceramic membrane; testing the film thickness at two ends of the ceramic film by using a scanning electron microscope EVO 18; and testing the membrane bonding strength of the ceramic membrane by utilizing the average filtration pore diameter change of the ceramic membrane after the ceramic membrane is back flushed by pulse water flow with the time interval of 10s and the pressure of 0.8MPa for 2 h. Scanning electron micrographs of both ends of the ceramic film prepared in this example are shown in fig. 5 and 6. The average thickness of the ceramic membrane at the inlet end and the outlet end was 20.0mm, both measured by scanning electron microscopy EVO 18. The ceramic membranes had an average filter pore size of 190nm, as measured according to the standard ASTM F316-03, and a pure water flux of 3685L h, as measured according to the standard HYT064-2002-1m-2bar-1The retention rate of the graphite ink with the particle size of 200nm reaches 98.6%, the average filtering aperture of the ceramic membrane after backwashing is 190nm, and the average filtering aperture is unchanged compared with that before backwashing.
Comparative example 1
Compared with the example 2, the thickness consistency of the film layers at the two ends of the ceramic film proves that the inclined dipping method has better film coating uniformity compared with the vertical dipping film coating method. The side of the ceramic membrane for the retention rate of graphite ink of 200nm proves that the inclined dipping method has better coating uniformity compared with the vertical dipping coating method.
The tubular ceramic membrane support body of the comparative example is a 7-hole alumina support body tube with the outer diameter of 30mm, the inner diameter of 7mm and the length of 3m, is mainly applied to the pretreatment of industrial sewage, and has the principle of filtering fine-particle pollutants in the sewage.
(1) Preparing coating liquid: adding 10 wt.% of 520nm aluminum oxide particles into 84.9 wt.% of water, adding 1 wt.% of polyacrylic acid serving as a dispersing agent and 0.1 wt.% of paraffin oil serving as a defoaming agent, fully ball-milling for 1h, uniformly dispersing, adding 4 wt.% of PVA solution, continuously ball-milling for 1h, uniformly dispersing to prepare uniformly and stably dispersed aluminum oxide ceramic coating liquid, adding a proper amount of water, and uniformly stirring to control the viscosity of the aluminum oxide ceramic coating liquid to 70 mPaS.
(2) Vertical dip coating: the ceramic coating liquid after vacuum defoaming sequentially enters the support body from the container through the pipeline, the inlet valve and the inlet end of the tubular support body, flows out of the outlet end of the tubular support body, and sequentially flows into the collection container through the connecting pipeline and the outlet flow-limiting valve; the tubular support is provided with a through bore to be coated. The whole circuit is connected through a plurality of quick connectors, and the ceramic coating liquid is impregnated in the holes of the support to be coated under the action of gravity. At the beginning stage of coating, the support body is vertically placed, after an inlet valve is opened, the coating liquid enters the inner hole of the support body pipe from the inlet end of the support body at the bottom, and then is led out from the outlet end of the support body at the top. And after soaking for 50s, disconnecting the inlet end of the support body from the pipeline within 3s, and connecting the coating liquid outlet at the top with the atmosphere to allow the ceramic coating liquid to naturally flow out from the inlet end of the support body at the bottom.
(3) And (3) drying and sintering: and (3) putting the film-coated support body tube into a high-low temperature test box for drying for 18h, and cooling along with a furnace after forming for 2h at 1300 ℃ to obtain the alumina ceramic film.
The average filter pore size, root, of the ceramic membranes was measured by the bubble point pressure method according to the standard ASTM F316-03Testing the pure water flux of the ceramic membrane according to the standard HYT064-2002, and measuring the retention rate of the ceramic membrane by utilizing the retention ratio of graphite ink particles with equivalent filter aperture of the ceramic membrane; testing the film thickness at two ends of the ceramic film by using a scanning electron microscope EVO 18; and testing the membrane bonding strength of the ceramic membrane by utilizing the average filtration pore diameter change of the ceramic membrane after the ceramic membrane is back flushed by pulse water flow with the time interval of 10s and the pressure of 0.8MPa for 2 h. Scanning electron micrographs of both ends of the ceramic film prepared in comparative example 1 are shown in fig. 7 and 8. The thickness of the inlet end and the outlet end of the ceramic membrane is respectively 18.5mm and 16.0mm measured according to a scanning electron microscope EVO 18; the ceramic membrane has an average filter pore size of 200nm, as measured according to the standard ASTM F316-03, and a pure water flux of 4244L h, as measured according to the standard HYT064-2002-1m-2bar-1The retention rate of the graphite ink with the particle size of 200nm reaches 92.0%, and the average filtering pore diameter of the ceramic membrane after backwashing is 200nm and is unchanged from that before backwashing.
As is clear from comparison with example 2, the thickness of both ends of the ceramic film obtained by the oblique dip coating method was 18mm, while the thickness of both ends of the ceramic film obtained by the vertical dip coating method was 18.5mm and 16mm, respectively, thus demonstrating that the oblique dip coating method can achieve better coating film uniformity. Meanwhile, the rejection rate of the ceramic membrane obtained by the inclined dipping coating method to the graphite ink with the thickness of 200nm reaches 98.0%, and the rejection rate of the ceramic membrane obtained by the vertical dipping coating method to the graphite ink with the thickness of 200nm only reaches 92.0%, so that the inclined dipping coating method is proved to be capable of obtaining better coating uniformity from the side.
Comparative example 2
Compared with the example 2, the thickness consistency of the film layers at the two ends of the ceramic film proves that the inclined dipping method has better film coating uniformity compared with a grouting dipping film coating method. The side of the ceramic membrane for the retention rate of graphite ink of 200nm proves that the inclined dipping method has better coating uniformity compared with a grouting dipping coating method.
The tubular ceramic membrane support body of the comparative example is a 7-hole alumina support body tube with the outer diameter of 30mm, the inner diameter of 7mm and the length of 1m, is mainly applied to the pretreatment of industrial sewage, and has the principle of filtering fine-particle pollutants in the sewage. The average filtering aperture of the ceramic membrane is tested by a bubble point pressure method according to the standard ASTM F316-03, the pure water flux of the ceramic membrane is respectively tested according to the standard HYT064-2002, and the retention rate of the ceramic membrane is measured by utilizing the retention ratio of graphite ink particles corresponding to the filtering aperture of the ceramic membrane; testing the film thickness at two ends of the ceramic film by using a scanning electron microscope EVO 18; and testing the membrane bonding strength of the ceramic membrane by utilizing the average filtration pore diameter change of the ceramic membrane after the ceramic membrane is back flushed by pulse water flow with the time interval of 10s and the pressure of 0.8MPa for 2 h.
(1) Preparing coating liquid: adding 10 wt.% of 520nm aluminum oxide particles into 84.9 wt.% of water, adding 1 wt.% of polyacrylic acid serving as a dispersing agent and 0.1 wt.% of paraffin oil serving as a defoaming agent, fully ball-milling for 1h, uniformly dispersing, adding 4 wt.% of PVA solution, continuously ball-milling for 1h, uniformly dispersing to prepare uniformly and stably dispersed aluminum oxide ceramic coating liquid, adding a proper amount of water, and uniformly stirring to control the viscosity of the aluminum oxide ceramic coating liquid to 70 mPaS.
(2) Grouting, dipping and coating: the ceramic coating liquid after vacuum defoaming sequentially enters the support body from the container through the pipeline, the inlet valve and the inlet end of the tubular support body, flows out of the outlet end of the tubular support body, and sequentially flows into the collection container through the connecting pipeline and the outlet flow-limiting valve; the tubular support is provided with a through bore to be coated. The whole circuit is connected through a plurality of quick connectors, and the ceramic coating liquid is impregnated in the holes of the support to be coated under the action of gravity. In the initial stage of coating, the support body pipe is vertically placed, after the inlet valve is opened, the coating liquid enters the inner hole of the support body pipe from the inlet end of the support body at the top, and then is led out from the outlet end of the support body at the bottom. After the dipping and maintaining for 50s, the coating liquid outlet at the bottom is quickly cut off, the coating liquid inlet at the top is communicated with the atmosphere, and the ceramic coating liquid naturally flows out from the bottom outlet.
(3) And (3) drying and sintering: and (3) putting the film-coated support body tube into a high-low temperature test box for drying for 18h, and cooling along with a furnace after forming for 2h at 1300 ℃ to obtain the alumina ceramic film.
The average filtering pore diameter of the ceramic membrane is tested to obtain the filtering particle size range of the ceramic membrane, and the smaller the filtering pore diameter is, the finer the particles can be filtered; the sewage treatment capacity of the ceramic membrane can be obtained by testing the pure water flux of the ceramic membrane, and the larger the pure water flux is, the larger the sewage treatment capacity of the ceramic membrane is; the coating uniformity of the ceramic film can be obtained by measuring the thicknesses of the film layers at the two ends of the ceramic film, and the coating uniformity of the ceramic film is more uniform if the thicknesses of the film layers at the two ends of the ceramic film are consistent; the actual filtering precision of the ceramic membrane can be obtained by measuring the rejection rate of the ceramic membrane, and the high rejection rate reflects the high filtering precision of the ceramic membrane, so that the side surfaces prove that the thicknesses of the membrane layers at the two ends of the ceramic membrane are consistent, and the coating is more uniform; the bonding strength of the ceramic membrane can be obtained by changing the average pore diameter of the ceramic membrane after the back washing, and if the change of the average pore diameter of the ceramic membrane after the back washing is not large, the ceramic membrane has higher bonding strength.
Scanning electron micrographs of both ends of the ceramic film prepared in comparative example 2 are shown in fig. 9 and 10. The thickness of the inlet end and the outlet end of the ceramic membrane is respectively 14.1mm and 17.1mm according to the EVO 18 of a scanning electron microscope; the average filter pore size of the ceramic membrane was 220nm as measured according to the standard ASTM F316-03, and the pure water flux of the ceramic membrane was 4769L h as measured according to the standard HYT064-2002-1m-2bar-1The retention rate of the graphite ink with the particle size of 200nm reaches 87.0%, and the average filtering pore diameter of the ceramic membrane after backwashing is 200nm and is unchanged from that before backwashing.
As is clear from comparison with example 2, the thickness of both ends of the ceramic film obtained by the oblique dip coating method was 18mm, while the thickness of both ends of the ceramic film obtained by the grout dip coating method was 14.1mm and 17.1mm, respectively, thereby proving that the oblique dip coating method can obtain better coating film uniformity. Meanwhile, the rejection rate of the ceramic membrane obtained by the inclined dipping coating method to the graphite ink with the thickness of 200nm reaches 98.0%, and the rejection rate of the ceramic membrane obtained by the vertical dipping coating method to the graphite ink with the thickness of 200nm only reaches 87.0%, so that the inclined dipping coating method is proved to obtain better coating uniformity from the side.
Comparative example 3
In comparison with example 2, the film bonding strength of the ceramic film proves that the inclined dipping method has better film bonding strength compared with the prewetting vertical dipping coating method.
The tubular ceramic membrane support body of the comparative example is a 7-hole alumina support body tube with the outer diameter of 30mm, the inner diameter of 7mm and the length of 1m, is mainly applied to the pretreatment of industrial sewage, and has the principle of filtering fine-particle pollutants in the sewage.
(1) Preparing coating liquid: adding 10 wt.% of 520nm aluminum oxide particles into 84.9 wt.% of water, adding 1 wt.% of polyacrylic acid serving as a dispersing agent and 0.1 wt.% of paraffin oil serving as a defoaming agent, fully ball-milling for 1h, uniformly dispersing, adding 4 wt.% of PVA solution, continuously ball-milling for 1h, uniformly dispersing to prepare uniformly and stably dispersed aluminum oxide ceramic coating liquid, adding a proper amount of water, and uniformly stirring to control the viscosity of the aluminum oxide ceramic coating liquid to 70 mPaS.
(2) Prewetting vertical dip coating: the ceramic coating liquid after vacuum defoaming sequentially enters the support body from the container through the pipeline, the inlet valve and the inlet end of the tubular support body, flows out of the outlet end of the tubular support body, and sequentially flows into the collection container through the connecting pipeline and the outlet flow-limiting valve; the tubular support is provided with a through bore to be coated. The whole circuit is connected through a plurality of quick connectors, and the ceramic coating liquid is impregnated in the holes of the support to be coated under the action of gravity. At the beginning stage of coating, the support body pipe is pre-wetted by deionized water and then vertically placed, after the inlet valve is opened, the coating liquid enters the inner hole of the support body pipe from the inlet end of the support body at the bottom, and then is led out from the outlet end of the support body at the top. And after soaking for 50s, disconnecting the inlet end of the support body from the pipeline within 3s, and connecting the coating liquid outlet at the top with the atmosphere to allow the ceramic coating liquid to naturally flow out from the inlet end of the support body at the bottom.
(3) And (3) drying and sintering: and (3) putting the film-coated support body tube into a high-low temperature test box for drying for 18h, and cooling along with a furnace after forming for 2h at 1300 ℃ to obtain the alumina ceramic film.
The average filtration pore size of the ceramic membrane is tested by a bubble point pressure method according to the standard ASTM F316-03, the pure water flux of the ceramic membrane is tested according to the standard HYT064-2002, and the retention rate of the ceramic membrane is measured by utilizing the retention ratio of graphite ink particles corresponding to the filtration pore size of the ceramic membrane; testing the film thickness at two ends of the ceramic film by using a scanning electron microscope EVO 18; and testing the membrane bonding strength of the ceramic membrane by utilizing the average filtration pore diameter change of the ceramic membrane after the ceramic membrane is back flushed by pulse water flow with the time interval of 10s and the pressure of 0.8MPa for 2 h.
Scanning electron micrographs of both ends of the ceramic film prepared in comparative example 3 are shown in fig. 11 and 12. The thickness of the inlet end and the outlet end of the ceramic membrane is respectively 10.2mm and 10.1mm measured according to an EVO 18 of a scanning electron microscope; the ceramic membranes had an average filter pore size of 230nm, as measured according to the standard ASTM F316-03, and a pure water flux of 5847L h, as measured according to the standard HYT064--1m-2bar-1The retention rate of the graphite ink with the particle size of 200nm reaches 95.0%, the average filtering aperture of the ceramic membrane after backwashing is changed to 2 mu m, and the change is huge compared with that before backwashing, which indicates that the membrane layer is broken.
Compared with the embodiment 2, the average pore diameter of the ceramic membrane obtained by the inclined dipping coating method after back washing is not changed greatly, and the binding strength of the membrane layer is higher; the film layer is broken after the ceramic film obtained by the pre-wetting vertical dipping film coating method is back washed, and the bonding strength of the film layer is low. Thus demonstrating that the oblique dip coating process can achieve better film bond strength.
In summary, as can be seen from comparison between comparative examples 1 and 2 and example 2, compared with the conventional vertical dip coating or grouting coating method, the inclined dip coating method can make the film thickness at both ends of the ceramic support tube having a length of 1m or more uniform, thereby improving the filtering accuracy of the ceramic membrane. As can be seen from the comparison between the comparative example 3 and the example 2, compared with the conventional method of pre-wetting with water and then vertically dip-coating, the inclined dip-coating method can make the prepared ceramic membrane and the support tube be more tightly combined, thereby improving the service life of the ceramic membrane. Therefore, the inclined dip coating method can obtain better membrane uniformity and membrane quality for coating the inner wall of the traditional tubular ceramic membrane.
The embodiments of the present invention are not limited to the above-described embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents and are included in the scope of the present invention.
Claims (6)
1. A method for preparing a tubular ceramic membrane inner membrane by inclined dipping is characterized by comprising the following steps: the ceramic coating liquid after vacuum defoaming sequentially enters the support body from the container through the pipeline, the inlet valve and the inlet end of the tubular support body, flows out of the outlet end of the tubular support body, and sequentially flows into the collection container through the connecting pipeline and the outlet flow-limiting valve; the tubular support body is provided with at least one through inner hole to be coated; before dipping and coating, the tubular support body is inclined upwards by 5-60 degrees on a horizontal plane, after an inlet valve at a low position is opened, ceramic coating liquid enters the support body from the inlet end of the tubular support body and is filled with an inner hole of the tubular support body, after the tubular support body is dipped for 5-100 seconds, the inner hole of the support body to be coated is dipped by the ceramic coating liquid under the action of pressure or gravity, the tubular support body is inclined downwards by 5-60 degrees relative to the horizontal plane within 3 seconds, the inlet valve is closed, the inlet end of the tubular support body is communicated with the atmosphere, the ceramic coating liquid naturally flows out from the outlet end of the tubular support body, the outflow time and the inflow time of the ceramic coating liquid are controlled to be consistent through an outlet flow.
2. The method for preparing a tubular ceramic membrane inner film by inclined dipping according to claim 1, wherein the membrane forming particles in the ceramic coating solution are one or more of alumina, titania or zirconia.
3. The method for preparing a tubular ceramic membrane inner film by inclined dipping according to claim 1, wherein the viscosity of the ceramic coating liquid is 50-100 mPaS.
4. The method according to claim 1, wherein the support is one or more of alumina, zirconia and silica.
5. The method for preparing a tubular ceramic membrane inner membrane by inclined dipping according to claim 1, wherein the number of inner holes of the tubular support body is single hole, 7 holes or 19 holes; the outer diameter of the tubular supporting body is 12mm or 30mm respectively, and the inner diameter of the tubular supporting body is 10mm, 7mm or 4mm respectively.
6. The method for preparing a tubular ceramic membrane inner film by inclined dipping according to claim 1, wherein the thickness of the ceramic membrane layer is 10-20 μm.
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