Preparation Method of Fly Ash-Based Ceramic Membrane Support

Abstract

The present disclosure provides a preparation method of a fly ash-based ceramic membrane support, including the following steps: 1) subjecting fly ash to alkali washing and acid washing to obtain pretreated fly ash; 2) blending a raw material including the pretreated fly ash, and then conducting aging and extrusion molding to obtain a green body; and 3) spraying a surface water-retaining agent (including glycerol, tung oil, a diol, and polyethylene glycol) on a surface of the green body to allow static curing in a constant-temperature and constant-humidity environment, and then conducting drying and sintering after the curing is completed. The preparation method can effectively improve molding and sintering performances of the fly ash to obtain a fly ash-based ceramic membrane support with a qualified performance.

Claims

1. A preparation method of a fly ash-based ceramic membrane support, comprising the following steps: 1) subjecting fly ash to alkali washing and acid washing to obtain pretreated fly ash; wherein the alkali washing is conducted using an alkali washing solution selected from the group consisting of 2 wt % to 4 wt % of a sodium hydroxide solution and 15 wt % to 25 wt % of a sodium carbonate solution, and a solid-to-liquid ratio of the alkali washing solution is in a range of 1 kg:1.5 L to 1 kg: 3 L; and the acid washing is conducted using an acid washing solution selected from the group consisting of 1 wt % to 3 wt % of a citric acid solution, 3 wt % to 7 wt % of a hydrochloric acid solution, 1 wt % to 5 wt % of a sulfuric acid solution, and 0.5 wt % to 3 wt % of a nitric acid solution, and at a solid-to-liquid ratio of the acid washing solution is in a range of 1 kg: 0.5 L to 1 kg: 2.5 L; 2) blending a raw material, and then conducting aging and extrusion molding to obtain a green body; the raw material comprises the following components in parts by mass: 80 parts to 95 parts of the pretreated fly ash, 6 parts to 9 parts of a plastic clay, 5 parts to 8 parts of a pore-forming agent, 2 parts to 4 parts of a binder, 20 parts to 28 parts of water, 1 part to 2 parts of a lubricant, 2 parts to 4 parts of a water-retaining agent, 0.5 parts to 1 part of a water-reducing agent, and 0.1 parts to 0.3 parts of a release agent; and 3) spraying a surface water-retaining agent on a surface of the green body to allow static curing in a constant-temperature and constant-humidity environment, and then conducting drying and sintering after the curing is completed; wherein the surface water-retaining agent is prepared from glycerol, tung oil, a diol, and polyethylene glycol at a mass ratio of (1-2.5):(2-4):(0.3-0.7):(0.5-1).

2. The preparation method of a fly ash-based ceramic membrane support according to claim 1, wherein the blending is performed in the following order: mixing the pretreated fly ash with the plastic clay, mixing with the water-reducing agent, mixing with the water-retaining agent and the lubricant, mixing with the pore-forming agent and the binder, and mixing with the release agent.

3. The preparation method of a fly ash-based ceramic membrane support according to claim 2, wherein the plastic clay is at least one selected from the group consisting of a Suzhou clay and a granite powder; the pore-forming agent is at least one selected from the group consisting of corn starch and saw dust; the binder comprises a cellulose; the lubricant comprises a long-chain fatty acid methyl ester (FAME); the water-reducing agent comprises a lignosulfonate; and the release agent comprises an emulsified silicone oil.

4. The preparation method of a fly ash-based ceramic membrane support according to claim 1, wherein the surface water-retaining agent is sprayed on the surface of the green body at (5-10) g/0.1 m.sup.2.

5. The preparation method of a fly ash-based ceramic membrane support according to claim 1, wherein the static curing is conducted at 20? C. to 25? C. with a relative humidity of 25%?5% for 8 h to 12 h; and the drying is microwave drying at 160? C. to 180? C. for 1 h to 3 h.

6. The preparation method of a fly ash-based ceramic membrane support according to claim 1, wherein the sintering is conducted by burying sintering combined with low-temperature slow sintering; the burying sintering is conducted with a burying sintering sand comprising an alumina sand and/or a zirconia sand; and the low-temperature slow sintering comprises: heating from 25? C. to 180? C. at 0.5? C./min to 1.5? C./min, heating from 180? ? C. to 550? C. at 0.2? C./min to 0.8? C./min and holding the temperature of 550? ? C. for 30 min to 90 min, heating from 550? ? C. to 900? C. at 3? C./min to 4? C./min, and heating from 900? C. to 1,350? C. at 3? C./min to 5? C./min and holding the temperature of 1,350? C. for 1.5 h to 2.5 h.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 shows a ceramic mud of the fly ash-based ceramic membrane support prepared in Example 1; where the ceramic mud has moderate hardness and desirable plasticity;

[0043] FIG. 2 shows a green body of the fly ash-based ceramic membrane support prepared in Example 1;

[0044] FIG. 3 shows the fly ash-based ceramic membrane support prepared in Example 1;

[0045] FIG. 4 shows a green body of the fly ash-based ceramic membrane support prepared in Comparative Example 1, where a large number of transverse cracks appear after drying; FIG. 5 shows the fly ash-based ceramic membrane supports prepared in Example 2 and Comparative Example 2 (a: Comparative Example 2, and b: Example 2); where after sintering, the support cracks and has a darker appearance, indicating that there is poor discharge of organic matters inside, and a shrinkage rate of the support becomes higher; and

[0046] FIG. 6 shows a ceramic mud of the fly ash-based ceramic membrane support prepared in Comparative Example 3; where the ceramic mud is hard and loose, and has a low viscosity, which is not conducive to molding.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] The following examples are intended to further illustrate the protection content of the present disclosure and are not intended to limit the protection scope of the present disclosure.

[0048] All chemical raw materials used in the following examples are commercially available products, unless otherwise specified.

Example 1

[0049] Step 1: fly ash particles were ground and sieved through an airflow pulverizer and an airflow classifier to obtain a fly ash powder with a particle size of 9.5 ?m; alkali washing was conducted with 3 wt % NaOH solution, at powder:liquid=1:2; acid washing was conducted with 1.5 wt % citric acid, at powder:liquid=1:0.8.

[0050] Step 2: based on 10 g of each part, 80 parts of 9.5 ?m fly ash and 6 parts of Suzhou clay were mixed with a counter-flow mixer for 25 min; 0.7 parts of lignosulfonate was added and mixed for 5 min; 1 part of 99.9% pure FAME and 3 parts of glycerol were added and mixed for 5 min; 5.5 parts of corn starch and 2 parts of cellulose were mixed for 5 min; 22 parts of 75? C. water and 0.3 parts of an emulsified silicone oil were added and stirred for 25 min, and then mixed in a mixer for 7 min.

[0051] Step 3: a resulting mixed ceramic mud was aged for 24 h at 25? ? C., extrusion molding was conducted, first pugging was conducted at 3 MPa, vacuumizing was conducted to 0.1 atmospheric pressure to allow second pugging, aging was conducted for 5 h after the second pugging was completed, and then molding was conducted to obtain a green body.

[0052] Step 4: a surface water-retaining agent was prepared using glycerol, tung oil, a diol, and polyethylene glycol according to a mass ratio of 1:2:0.3:0.5, and stirred evenly before use; the green body was sprayed with the surface water-retaining agent at 6 g/0.1 m.sup.2 in a constant-temperature and constant-humidity environment at 24? ? C. with a relative humidity of 25%, cured for 10 h, and then dried in a microwave dryer at 170? ? C. for 2 h.

[0053] Step 5: an obtained dried green body was subjected to burying sintering using an alumina sand with a particle size of 30 ?m, where a sintering program included: heating from 25? C. to 180? ? C. at 1.2? C./min, heating from 180? C. to 550? C. at 0.4? C./min and holding the temperature of 550? C. for 60 min, heating from 550? C. to 900? C. at 3? C./min, and heating from 900? ? C. to 1,350? ? C. at 4? C./min and holding the temperature of 1,350? ? C. for 2 h, and then a resulting sintered support was taken out after natural cooling.

[0054] During the preparation of the fly ash-based ceramic membrane support in this example, the ceramic mud, green body, and sintered body were shown in FIG. 1 to FIG. 3, respectively. As shown in FIG. 1 to FIG. 3, the ceramic mud had moderate hardness and desirable plasticity, which were conducive to extrusion molding. The extruded green body had no cracking on its surface and showed high uniformity. The sintered support had a surface with no cracking.

Example 2

[0055] Step 1: fly ash particles were ground and sieved through an airflow pulverizer and an airflow classifier to obtain a fly ash powder with a particle size of 9.5 ?m; alkali washing was conducted with 16 wt % sodium carbonate solution, at powder:liquid=1:3; acid washing was conducted with 1.5 wt % nitric acid, at powder:liquid=1:1.5.

[0056] Step 2: based on 10 g of each part, 95 parts of 9.5 ?m fly ash and 9 parts of Suzhou clay were mixed with a counter-flow mixer for 25 min; 0.7 parts of lignosulfonate was added and mixed for 5 min; 1 part of 99.9% pure FAME and 4 parts of glycerol were added and mixed for 5 min; 5.5 parts of corn starch and 2 parts of cellulose were mixed for 5 min; 22 parts of 75? C. water and 0.3 parts of an emulsified silicone oil were added and stirred for 25 min, and then mixed in a mixer for 7 min.

[0057] Step 3: a resulting mixed ceramic mud was aged for 30 h at 25? C., extrusion molding was conducted, first pugging was conducted at 3 MPa, vacuumizing was conducted to 0.1 atmospheric a reagent pressure to allow second pugging, aging was conducted for 5 h after the second pugging was completed, and then molding was conducted to obtain a green body.

[0058] Step 4: a surface water-retaining agent was prepared using glycerol, tung oil, a diol, and polyethylene glycol according to a mass ratio of 2:3:0.6:0.7, and stirred evenly before use; the green body was sprayed with the surface water-retaining agent at 6 g/0.1 m.sup.2 in a constant-temperature and constant-humidity environment at 24? C. with a relative humidity of 25%, cured for 10 h, and then dried in a microwave dryer at 170? C. for 2 h.

[0059] Step 5: an obtained dried green body was subjected to burying sintering using an alumina sand with a particle size of 30 ?m, where a sintering program included: heating from 25? ? C. to 180? C. at 1? C./min, heating from 180? C. to 550? C. at 0.5? C./min and holding the temperature of 550? ? C. for 60 min, heating from 550? C. to 900? C. at 4? C./min, and heating from 900? ? C. to 1,350? C. at 5? C./min and holding the temperature of 1,350? C. for 1.5 h, and then a resulting sintered support was taken out after natural cooling.

[0060] The fly ash-based ceramic membrane support prepared in this example had no cracks on its surface, uniform size and color, and no shrinkage or deformation, and was a qualified fly ash-based ceramic membrane support product, as shown in b in FIG. 5.

Comparative Example 1

[0061] Step 1: fly ash particles were ground and sieved through an airflow pulverizer and an airflow classifier to obtain a fly ash powder with a particle size of 9.5 ?m; alkali washing was conducted with 3 wt % NaOH solution, at powder:liquid=1:2; acid washing was conducted with 1.5 wt % citric acid, at powder:liquid=1:0.8.

[0062] Step 2: based on 10 g of each part, 80 parts of 9.5 ?m fly ash and 6 parts of Suzhou clay were mixed with a counter-flow mixer for 25 min; 0.7 parts of lignosulfonate was added and mixed for 5 min; 1 part of 99.9% pure FAME and 3 parts of glycerol were added and mixed for 5 min; 5.5 parts of corn starch and 2 parts of cellulose were mixed for 5 min; 22 parts of 75? C. water and 0.3 parts of an emulsified silicone oil were added and stirred for 25 min, and then mixed in a mixer for 7 min.

[0063] Step 3: a resulting mixed ceramic mud was aged for 24 h at 25? C., extrusion molding was conducted, first pugging was conducted at 3 MPa, vacuumizing was conducted to 0.1 atmospheric pressure to allow second pugging, aging was conducted for 5 h after the second pugging was completed, and then molding was conducted to obtain a green body.

[0064] Step 4: The green body was cured in a constant-temperature and constant-humidity environment at 24? C. with a relative humidity of 25% for 10 h and allowed to stand for 2 h, and then dried in a microwave dryer at 170? C. for 2 h.

[0065] In this comparative example, no surface water-retaining agent was sprayed on the surface of the fly ash-based ceramic membrane support, and a large number of transverse cracks appeared in the green body after drying, as shown in FIG. 4. It was impossible to obtain a fly ash-based ceramic membrane support with no surface cracks through further sintering.

Comparative Example 2

[0066] Step 1: fly ash particles were ground and sieved through an airflow pulverizer and an airflow classifier to obtain a fly ash powder with a particle size of 9.5 ?m; alkali washing was conducted with 16 wt % sodium carbonate solution, at powder:liquid=1:3; and acid washing was conducted with 1.5 wt % nitric acid, at powder:liquid=1:1.5.

[0067] Step 2: based on 10 g of each part, 95 parts of 9.5 ?m fly ash and 9 parts of Suzhou clay were mixed with a counter-flow mixer for 25 min; 0.7 parts of lignosulfonate was added and mixed for 5 min; 1 part of 99.9% pure FAME and 4 parts of glycerol were added and mixed for 5 min; 5.5 parts of corn starch and 2 parts of cellulose were mixed for 5 min; and 22 parts of 75? C. water and 0.3 parts of an emulsified silicone oil were added and stirred for 25 min, and then mixed in a mixer for 7 min.

[0068] Step 3: a resulting mixed ceramic mud was aged for 30 h at 25? C., extrusion molding was conducted, first pugging was conducted at 3 MPa, vacuumizing was conducted to 0.1 atmospheric a reagent pressure to allow second pugging, aging was conducted for 5 h after the second pugging was completed, and then molding was conducted to obtain a green body.

[0069] Step 4: a surface water-retaining agent was prepared using glycerol, tung oil, a diol, and polyethylene glycol according to a mass ratio of 2:3:0.6:0.7, and stirred evenly before use; the green body was sprayed with the surface water-retaining agent at 6 g/0.1 m.sup.2 in a constant-temperature and constant-humidity environment at 24? C. with a relative humidity of 25%, cured for 10 h, and then dried in a microwave dryer at 170? C. for 2 h.

[0070] Step 5: an obtained dried green body was subjected to sintering as follows: heating from 25? ? C. to 550? ? C. at 2.5? C./min, heating from 550? C. to 900? C. at 5? C./min, and heating from 900? C. to 1,350? C. at 5? C./min and holding the temperature of 1,350? C. for 1.5 h, and then a resulting sintered support was taken out after natural cooling.

[0071] In this comparative example, the burying sintering was not conducted. It was clearly seen that the fly ash-based ceramic membrane support cracked after sintering, and the support was darker in color. This indicated that there was poor discharge of organic matters, as shown in a in FIG. 5. Moreover, a shrinkage rate of the support became larger, and its size was significantly different from a designed size.

Comparative Example 3

[0072] Step 1: based on 10 g of each part, 95 parts of 9.5 ?m fly ash and 9 parts of Suzhou clay were mixed with a counter-flow mixer for 25 min; 0.7 parts of lignosulfonate was added and mixed for 5 min; 1 part of 99.9% pure FAME and 4 parts of glycerol were added and mixed for 5 min; 5.5 parts of corn starch and 2 parts of cellulose were mixed for 5 min; and 22 parts of 75? C. water and 0.3 parts of an emulsified silicone oil were added and stirred for 25 min, and then mixed in a mixer for 7 min.

[0073] Step 2: a resulting mixed ceramic mud was aged for 30 h at 25? C., extrusion molding was conducted, first pugging was conducted at 3 MPa, vacuumizing was conducted to 0.1 atmospheric a reagent pressure to allow second pugging, aging was conducted for 5 h after the second pugging was completed, and then molding was conducted to obtain a green body.

[0074] Step 3: a surface water-retaining agent was prepared using glycerol, tung oil, a diol, and polyethylene glycol according to a mass ratio of 2:3:0.6:0.7, and stirred evenly before use; the green body was sprayed with the surface water-retaining agent in a constant-temperature and constant-humidity environment at 24? C. with a relative humidity of 25%, cured for 10 h, and then dried in a microwave dryer at 170? C. for 2 h.

[0075] Step 4: an obtained dried green body was subjected to burying sintering using an alumina sand with a particle size of 30 ?m, where a sintering program included: heating from 25? ? C. to 180? C. at 1? C./min, heating from 180? C. to 550? C. at 0.5? C./min and holding the temperature of 550? ? C. for 60 min, heating from 550? ? C. to 900? C. at 4? C./min, and heating from 900? ? C. to 1,350? C. at 5? C./min and holding the temperature of 1,350? C. for 1.5 h, and a resulting sintered support was taken out after natural cooling.

[0076] In this comparative example, the fly ash was not washed and pretreated, and there were differences in the batching methods. This resulted in the prepared ceramic mud being hard, loose, and low in viscosity, which was not conducive to molding. A specific ceramic mud state was shown in FIG. 6.