In the membrane separation industry, materials drive the update and iteration of membrane separation products and the development of application technologies.Silicon carbide is a new generation of ceramic membrane separation material recognized in the industry, with significant performance advantages such as high flux, corrosion resistance, easy cleaning, long life and excellent oil-water separation.

Advantages of silicon carbide ceramic membranes:

high throughput

preservative

easy to clean

long life

一、Filtration principle

The silicon carbide ceramic membrane ultrafilter is driven by positive pressure, and the transmembrane pressure difference is within the optional range of 0.2-0.6bar to complete the solid-liquid separation process.

Silicon carbide ultra filters have the following advantages:

1. Ideal filtration accuracy, suitable for concentration of silica sol products with different particle sizes, 830, 1430 or larger particle size products;

2. The scale of treatment can be large or small, and can be carried out continuously or intermittently. Membrane modules can be used alone or in combination. The process is simple and the operation is simple.

Simple and easy to automate control.

3. Stable and lasting filtration performance and reliable service life, 3-year warranty, and 5-year service life.

二、Application of Silicon Carbide Ceramic Membrane in Silica Sol Concentration

As an important inorganic polymer material, silica sol has been widely used in chemical industry, precision casting, textile, papermaking, paint, food, electronics, mineral processing and other fields.

At present, the domestic production process of silica sol basically adopts dilute silica sol with a concentration of 2 to 5% after ion exchange and stabilization of sodium silicate. This solution needs to be concentrated to more than 30%. The multiple is large, and most of them are concentrated by ultra filtration. Jianmo has developed two silicon carbide tubular membrane ultra filters according to the working conditions of different silica sol manufacturers.

1.Multi-core series first generation silicon carbide tubular membrane ultrafilter

Features of the first generation silicon carbide ultrafilter:

1. The working capacity of a single silicon carbide ultrafilter is 1.5~2 times that of the traditional PVDF organic tubular membrane ultrafilter;

2. The occupied area is a quarter of that of the traditional PVDF organic tubular membrane ultrafilter;

3. Silicon carbide ultrafilter has almost no replacement cost of membrane elements;

4. The working project does not need to consider cooling, and can adapt to the working environment of 60 ℃ ~ 120 ℃.

2. Single-core parallel first-generation silicon carbide tubular membrane ultrafilter

Equipment main configuration:

Features of the second generation silicon carbide ultrafilter:

1. The working capacity of a single silicon carbide ultrafilter is 1.5~2 times that of the traditional PVDF organic tubular membrane ultrafilter;

2. The floor area is two-thirds of the traditional PVDF organic tubular membrane ultrafilter;

3. Silicon carbide ultrafilter has almost no replacement cost of membrane elements;

4. Compared with the first-generation silicon carbide ultrafilter, it is easy to replace a single membrane element after it is damaged; the first-generation silicon carbide ultrafilter needs to dismantle the 19-core membrane container to check the damaged membrane element, and the process is cumbersome.

5. The working project does not need to consider cooling, and can adapt to the working environment of 60°C~120°C.

Causes of Membrane Fouling

Low flow rate operation of feed liquid: Generally, the surface flow rate of ultrafiltration membrane is easily controlled at 2.5-3 M/S. If the flow rate is low and the flow rate is slow, the surface of ultrafiltration membrane will be attached

When the gel layer is applied, the permeation rate will decrease rapidly.

Incomplete replacement when the ultrafiltration is shut down: It is necessary to eject the silica sol in the membrane module and carry out protection or chemical cleaning when the ultrafiltration is shut down. if not

Complete replacement in time, silica sol will be deposited on the membrane surface, forming a layer of glue film, affecting the transmission rate.

The impact of the feed liquid itself: The reaction is not complete, the colloid stability is poor, and it is easy to cause the pollution of the ultrafiltration membrane.

Membrane Fouling Countermeasures

The need for cleaning:

After a period of ultrafiltration membrane operation, membrane clogging and concentration polarization often occur. Membrane clogging is caused by the deposition of certain components on the membrane surface and in the mesh, resulting in a change in the pore size of the membrane; concentration polarization refers to the formation of a concentration gradient on the membrane surface by the intercepted components that is opposite to the filtration direction. These two phenomena exist simultaneously during the silica sol concentration process, and lead to a significant decrease in the filtration capacity of the membrane. In order to ensure that the membrane has a high permeability (that is, the capacity of the membrane volume per unit surface to transfer solvent) and a significant rejection rate (that is, the membrane has the ability to intercept solutes above a fixed molecular mass), the ultrafiltration system operates for one cycle (usually Concentrate a tank of material) and then carry out a protective cleaning with permeated water. After running for a certain period of time or when the inlet flow rate is lower than the parameter range, chemical cleaning must be carried out in time.

The role of cleaning:

Remove the components that are deposited in the membrane mesh and affect the membrane permeability; remove low molecular weight salts in the membrane mesh; fail to form silica sol with sufficient particle size; remove product particles deposited in the ultrafiltration membrane tube; carry out pipeline Disinfect and control the growth and reproduction of bacteria; clean pipeline valves, pumps and other parts.

Cleaning method:

Each concentrated batch (one tank of feed liquid) is protected with permeated water for 15 minutes; continuous production runs for 50 hours, and chemical cleaning is performed once (generally 5% NaOH aqueous solution is used as the cleaning agent); intermittent production requires daily cleaning once. The cleaning agent can be used repeatedly many times.

Preventive measures to mitigate membrane fouling

1. Pay attention to the flow rate of the circulating pump, and the pressure meets the needs of the ultrafilter;

2. Pay attention to anti-corrosion and water sealing when the membrane is not used for a long time;

3. Establish ultrafilter operation files;

4. Equipped with a precision filtration system, regularly clean the filter bag;

5. Ensure that the silica sol passing through the ultrafilter has a normal pressure drop and membrane surface flow rate;

6. When shutting down for a period of time, it should be cleaned and water-sealed in time to ensure that the membrane surface is moist.