RU2031891C1 - Method of making of ceramic filter member - Google Patents

Abstract

FIELD: chemical technology. SUBSTANCE: membrane material is precipitated from aqueous suspension on the ceramic porous backing. Dispersion of mono- or polycrystalline fibers of oxides or carbides suspended in water is used as a source of suspension. This dispersion is prepared by their dispersing in water by ultrasonic treatment for 15-30 min at ultrasonic oscillation intensity 2-10 Wt/сm² following by sedimentation for 0.5-20 h and decantation to separate part of liquid containing thin-fibrous fractions with fiber diameter 0.05-0.5 mcm. Fiber concentration in suspension at dispersing is 5-40 g/l and fiber concentration in suspension where membrane is precipitated is 0.05-1 g/l. After drying treatment with 2-8% aqueous solution of aluminium salts or 3-10% colloidal aqueous solution of silicon oxide is carried out following by calcination of material. Properties: average pore diameter is 0.05-0.5 mcm, output by water is 5000-15000 l/m²p·atm. Material is used for sewage treatment. EFFECT: improved method of material making. 10 cl

Description

 The invention relates to the manufacture of a ceramic filter element for ultra- and microfiltration on a membrane.

 In modern technologies, filtration in the range of 0.2-1 microns occupies a significant place in the medical, biological, chemical and food industries, in solving problems associated with wastewater treatment and water treatment. These industries place high demands on filter elements in terms of performance and holding capacity, corrosion resistance in various chemical media, mechanical strength and regeneration ability.

 Ceramic membranes can best meet the above industry demands.

для ультрафильтрации. В основе изготовления керамических мембран лежит использование фракционных порошков оксида алюминия, оксида циркония, карбида кремния, с диаметром частиц 0,2-2,5 мкм для изготовления водных суспензий, которые наносят на пористые подложки. Завершают процесс изготовления сушка и обжиг изделий.Ceramic filter elements, as a rule, consist of a ceramic substrate with an average pore size of 15 μm and a membrane deposited on this base with a thickness of several tens of microns with an average pore diameter of 0.2-1 μm for microfiltration and 40-1000

for ultrafiltration. The basis for the manufacture of ceramic membranes is the use of fractional powders of alumina, zirconia, silicon carbide, with a particle diameter of 0.2-2.5 microns for the manufacture of aqueous suspensions that are applied to porous substrates. Complete the manufacturing process of drying and firing products.

 The formation of a ceramic membrane from powder components is complicated by difficulties in obtaining a defect-free uniform porous layer structure. The membrane coating is often affected by microcracks due to shrinkage during drying and sintering.

 A known method of manufacturing a membrane, consisting in the preparation of an aqueous suspension from a set of fractions of a fine powder of aluminum oxide with the addition of an organic component. The suspension is in contact with the horizontal upper surface of the porous ceramic substrate for a certain period of time. Due to the different deposition rates of particles of different diameters, the dropping powder forms a membrane in which the pore sizes in the layer in contact with the substrate were 1-5 μm, and in the upper layer of the membrane, 0.1-0.5 μm. Excess liquid is forcibly removed, and the filter element is dried and fired. The application of this method is limited by the fact that the substrate should have a strictly horizontal surface, the possibility of manufacturing tubular single-channel and multi-channel filter elements is excluded.

 There is also a known method of manufacturing a filter element of a tubular shape, consisting of several stages.

Initially, a ceramic mass is prepared from alumina powders of various sizes and a binder, which is extruded into tubes. The tubes, after drying and firing at 1800 ^{° C} is used as the porous substrate.

At the next stage, a membrane with a thickness of 30-40 μm is formed, which is applied to the substrate in two steps. An aqueous suspension of alumina powders with various additives is prepared. Powders with an average particle diameter of 2.5 μm are introduced into the suspension for the first layer of the membrane, and 0.2 μm for the second layer. The suspension fills the internal volume of the tube, after which a porous layer of 20-30 μm after the first application and 10 μm after the second remains on the surface. The first layer is calcined at 1550 ^C, the second at 1000 ^C. The open porosity in the two layers is approximately the same and is 30-40%, average diameter of pores in the first layer of 1.2 m in the second - 0.2 microns. The productivity of the filter element obtained in this way is 3000 l / m ² ˙h˙ atm, holding capacity 0.2 μm.

The most significant drawbacks of the known method are a consequence of the powder system used for the membrane, prone to cracking and the formation of defects. These include - low open porosity of the membrane (30-40%) and, accordingly, low permeability (≈3000 l / m ² ˙h˙ atm in water);
application of two layers separately with a double firing procedure;
the duration of the drying process to prevent the spread of cracking of the powder layer due to shrinkage phenomena;
complex and lengthy procedures for preparing powders for mixtures.

 As a result, the resulting filter elements have a very high cost without guarantees of the absence of large defects (1 μm).

Closest to the proposed is a method of manufacturing ceramic permeable porous membranes, comprising forming on a porous basis of ceramic or metal a thin membrane layer of simple or complex oxides or hydroxides, as well as metal fluorides or a mixture thereof from a suspension treated with ultrasound, followed by drying of the resulting membrane and its heat treatment at 400-1100 ^about C.

 Membranes obtained in a known manner have insufficient porosity and productivity.

 The purpose of the invention is to increase porosity and productivity.

 This goal is achieved in that the suspension used is obtained by dispersing the fibers in water using ultrasonic treatment, sedimentation, followed by decantation of a fine fraction of the fibers, and the membrane deposited from the suspension is fixed by binder treatment in the form of solutions of aluminum or zirconium salts or colloidal silicon dioxide.

When applying the membrane, the fibers must have certain geometric parameters, be uniformly distributed in the liquid component, and must not flocculate in suspension. For this, the dispersion of the fibers in the liquid component is carried out at a fiber concentration of 5-40 g / l by ultrasonic treatment of the suspension for 15-30 minutes with a radiation intensity of 2-10 W / cm ² .

 The specific values of the concentration of fibers in the suspension, the duration of sonication and the intensity of ultrasonic radiation are selected depending on the initial size of the fibers used and their composition. Reducing the concentration below the proposed level is not technologically advanced, exceeding the upper limit does not allow complete dispersion, the original conglomerates are preserved.

 Depending on the composition of the fibers, to prevent their flocculation, the pH of the suspension should be 7-11.

 At the end of the dispersion, the suspension is sedimented for 0.5-20 hours, after which a part of it, which is located above the visible interface, containing the finest fraction and free from coarse non-fibrous inclusions, is drained. The specific value of the duration of the sedimentation process is set depending on the type and diameter of the fibers.

 The decanted portion of the suspension is diluted with water to a fiber concentration of 0.05-1 g / l and is used to precipitate the membrane.

 The difference in concentration within the above range depending on the diameter of the fiber used. For thin fibers, the concentration is lower, for thick - more.

, где V_ж - объем суспензии, л;
С - концентрация волокна в суспензии, г/л;
h_м - толщина мембраны, см;
S - площадь покрываемой поверхности, см²;
Р - плотность волокна, г/см³;
θ - относительная плотность мембраны, %.The thickness of the membrane layer is set by the volume of the suspension, calculated by the formula:
V _W =

where V _W - suspension volume, l;
C is the concentration of fiber in suspension, g / l;
h _m - membrane thickness, cm;
S is the surface area, cm ² ;
P is the fiber density, g / cm ³ ;
θ is the relative density of the membrane,%.

 For applying the membrane using the method of forced impregnation. In this case, the suspension is fed to the coated surface of the substrate under a pressure of 1-2 atm, the liquid component is removed through the opposite.

 The operation is carried out in two steps, with the first half of the calculated volume of the suspension being supplied under a pressure of 2 atm, the second under a pressure of 1 atm. In the case of tubular elements of large length and multichannel, the suspension is supplied in two steps from the opposite ends of the tube. Such a membrane application scheme ensures its minimum defectiveness and uniformity of thickness on the surface of the substrate.

After deposition of the membrane, the filter element is dried in air for 1-3 hours at 100-120 ^about C.

To fix the membrane on the surface of the substrate, the dried filter element is immersed in a solution containing aluminum, zirconium or colloidal silicon dioxide salts with concentrations in the range of 2-10 wt.%. The filter element is then dried for 1-3 hours at 120 ^C and calcined at 700-1100 ^C for 1 hour. These operations provide high strength of the membrane and its adhesion to the substrate without changing the nature of the fibrous structure of the membrane and decrease its filtering characteristics.

 The proposed method allows you to apply fibrous membranes on the external and internal surfaces of single-channel tubes, on the internal surfaces of multi-channel tubes, on the surface of porous substrates of any geometry, strictly controlling the thickness of the applied layer. An important advantage of the proposed method is the possibility of high heating and cooling rates during drying and firing, and the lack of the need for careful control thereof, which reduces the cost of filter elements by almost an order of magnitude in comparison with the known methods used for powder membranes.

EXAMPLE 1. For the manufacture of a ceramic filter element, single-channel porous alumina tubes (inner diameter 6 mm, outer diameter 10 mm, length 800 mm) are used as a substrate. The substrate tubes have a surface of 35–40%, an average pore diameter of 10 μm, and a water productivity of 60,000 l / s ² ˙ h˙ atm. Monocrystalline silicon carbide fibers with an average diameter of 0.1 μm are used for the membrane.

To apply the membrane, prepare 1 l of an aqueous (pH = 10-11) suspension with a fiber concentration of 10 g / l. The suspension is treated with ultrasound for 15 minutes at an ultrasonic intensity of 4 W / cm ² , which leads to uniform dispersion of the fibers in the liquid component.

 To separate non-fibrous inclusions and large fractions, sedimentation is carried out for 20 hours, after which the suspension is decanted, and the upper part of the suspension is drained, separating it from the settled fraction. The fused portion of the suspension, where the fiber concentration is 5 g / l, is diluted with water, the liquid volume is adjusted to 15 l, in which the fiber concentration is 0.3 g / l. This suspension is used for applying the membrane.

The required volume of suspension is determined by the above formula. For a membrane with a thickness of 40 μm, a coated surface of 150 cm ² , a fiber density of silicon carbide of 3.2 g / cm ² , a relative density of the membrane of 10%, it is 0.6 L. The calculated volume of the suspension is divided into two equal parts and fed into the tube, the first part under a pressure of 2 atm, and the second part under a pressure of 1 atm.

After application of the membrane tube was dried in air for 2 hours at 120 ^C. Then, at 2-3 was immersed in a container with a binder solution, which is used for a 0.25 molar aqueous zirconium nitrate. Then the tube is dried at 700 ^C. The resulting filter element has a capacity for water of 8000 l / m ² h ˙atm, average pore diameter - 0.2 microns.

 PRI me R 2. For the manufacture of a ceramic filter element using single-channel tubes of aluminum oxide (inner diameter 5 mm, outer 10 mm, length 500 mm). The properties of the substrate tubes are similar to those of the substrate tubes used in Example 1. A membrane of single crystal zinc oxide fibers is applied to the outer surface. The average fiber diameter of zinc oxide is 0.7 microns.

 A suspension is prepared from 1 liter of water (pH = 7), where the concentration of zinc oxide fibers is 5 g / l. The dispersion, sedimentation and decantation conditions of the suspension correspond to Example 1. In the merged portion of the suspension, the fiber concentration is 2.5 g / l, it is diluted with water, the liquid volume is adjusted to 2.5 l, where the zinc oxide fiber concentration is 1 g / l.

The required volume of the suspension is determined as in Example 1. For a membrane with a thickness of 30 μm, a coated surface of 157 cm ² , a fiber density of 5.6 g / cm ² , and a relative density of the membrane of 30%, the volume of the suspension is 0.8 L.

 This volume of the suspension is divided into two equal parts and, alternately, under a pressure of 2 atm, a container is filled inside which the coated tube-substrate is located. The suspension is fed to the outer surface, and the liquid component is removed through the inner channel of the tube, and a membrane 30 microns thick is obtained on the outer surface of the tube.

After drying according to the mode of Example 1, the filter element is immersed for 5 s in a binder solution, for which a 5% aqueous solution of colloidal silicon dioxide is used. After impregnation with a binder, the filter element is dried, as in example 1. Firing is carried out at 1100 ^about C for half an hour. The resulting filter element has a water capacity of 5000 l / m ² ˙ h ˙ atm, an average pore size of 0.05 μm.

 PRI me R 3. For the manufacture of a ceramic filter element, a seven-channel substrate tube with a diameter of 25 mm, a length of 300 mm, where the inner diameter of each channel is 4 mm, is used as a substrate. The properties of the substrate tubes are similar to the properties of the substrate tubes used in example 1.

 The membrane is applied to the inner surface of the channels using polycrystalline alumina fibers with an average diameter of 0.8 microns.

 Prepare in 1 l of water (pH 7) a suspension with a fiber concentration of 40 g / l. The dispersion conditions of the suspension are similar to the regime of example 1, and sedimentation is carried out for half an hour. After decantation in the merged portion of the suspension, the fiber concentration is 12 g / L. it is diluted with water, the liquid volume is adjusted to 20 l, where the concentration of alumina fibers is 0.6 g / l.

The required volume of the suspension is determined as in Example 1. For a membrane with a thickness of 100 μm, a coated surface of 264 cm ² , with an alumina fiber density of 3.9 g / cm ³ and a relative density of 40%, the volume of the suspension is 6.8 L.

 This volume is divided into two equal parts, half of it is supplied from one end of the tube under a pressure of 1 atm, and the second part is fed from the opposite end of the tube under a pressure of 1 atm.

 After drying according to the mode of example 1, the filter element is immersed in a binder solution for 5 s. For the binder, a 10% aqueous solution of colloidal silicon dioxide is used.

 Drying and firing of the filter element after impregnation is carried out according to the mode of example 2.

The resulting filter element has a water capacity of 15,000 l / m ² ˙ ˙h˙atm, the average pore diameter is 0.5 μm.

Claims (9)

 1. METHOD FOR PRODUCING A CERAMIC FILTER ELEMENT, consisting of a ceramic porous substrate and a ceramic porous membrane, comprising preparing an aqueous suspension by dispersing the ceramic material by ultrasonic treatment, forming a membrane on the substrate by deposition from the suspension, drying and calcining, characterized in that the suspension material is used ceramic fibers, after ultrasonic treatment of the suspension, it is subjected to sedimentation followed by decantation to obtain a suspension of fine fractions of fibers, and before firing, the membrane is fixed by treatment with solutions of aluminum salts, or zirconium, or colloidal silicon dioxide.  2. The method according to claim 1, characterized in that the dispersion is carried out in water at a pH of 7-11 and a concentration of the starting fibers of 5-40 g / L. 3. The method according to claim 1, characterized in that the dispersion is carried out at an intensity of ultrasonic radiation of 2 to 10 W / cm ² for 15 to 30 minutes  4. The method according to claim 1, characterized in that the sedimentation of the suspension is carried out for 0.5 to 20 hours  5. The method according to claim 1, characterized in that the suspension is decanted to separate a portion of the liquid containing the fine-fiber fraction with an average fiber diameter of 0.05 - 0.5 microns.  6. The method according to claims 1 and 5, characterized in that the decanted suspension is diluted to a fiber concentration of 0.05-1 g / l.  7. The method according to claim 1, characterized in that the precipitated membrane after drying is treated by immersing the filter element for 3-5 seconds in a solution of aluminum salt, or zirconium, or colloidal silicon dioxide.  8. The method according to claims 1 and 7, characterized in that for the processing of the membrane using a 2 - 8% solution of aluminum or zirconium salts.  9. The method according to claims 1 and 7, characterized in that for the processing of the membrane using a 3 - 10% solution of colloidal silicon dioxide.