High-Performance Tubular Ultrafiltration for Precise Separation of Small Molecules

The tubular ultrafiltration membrane adopts a unique tubular design, which uses forced force to press the liquid into the ultrafiltration membrane tube, allowing water molecules to pass through the pores of the membrane and filter out impurities, bacteria, viruses, etc., thereby achieving the purpose of purification and filtration.

Definition and Principle:
Tubular ultrafiltration equipment is a membrane separation equipment based on the principle of ultrafiltration. The core of ultrafiltration is to use the screening characteristics of semipermeable membranes to make small molecular solutes (such as inorganic salts, small molecular organic matter, etc.) and solvents (water) in the solution pass through the membrane under a certain pressure, while large molecular solutes (such as proteins, colloids, bacteria, viruses, etc.) are retained.

The characteristic of tubular ultrafiltration equipment is that its membrane assembly is a tubular structure. Its working principle is that the raw liquid flows inside or outside the tubular membrane under pressure. When flowing through the surface of the ultrafiltration membrane, the solvent and small molecular substances pass through the micropores on the membrane wall into the other side of the membrane and are collected as permeate, while large molecular substances are retained on the feed side to form a concentrated solution.

Main components:
Tubular membrane assembly:
Structure of tubular membrane: Tubular ultrafiltration membranes are usually hollow fiber or tubular structures with a certain inner diameter and outer diameter. The membrane material is generally a high molecular polymer, such as polysulfone, polyethersulfone, polyacrylonitrile, etc. These materials have good chemical stability, mechanical strength and thermal stability, and can withstand certain pressure and chemical environment. There are many micropores distributed on the membrane wall, and the pore size determines the separation accuracy of ultrafiltration, which is generally between 0.001-0.1μm.

Form of membrane assembly:
Internal pressure membrane assembly:

The raw material liquid flows inside the tubular membrane. Under the action of pressure, small molecules and solvents permeate outward through the membrane wall and are collected outside the membrane tube. The advantage of this form is that the inner surface of the membrane is easy to clean, because the pollutants are mainly concentrated on the inner surface of the membrane, and the inside can be directly flushed or chemically cleaned during cleaning.

External pressure membrane assembly:

The raw material liquid flows outside the tubular membrane, and small molecules and solvents pass through the membrane wall into the inside of the membrane tube. The advantage of the external pressure membrane assembly is that it can handle raw material liquid containing larger suspended particles, because larger particles are not easy to block the channels inside the membrane tube.

Shell and support structure:
The shell is mainly used to protect the tubular membrane assembly and provide necessary mechanical support for the entire equipment. The shell material is usually stainless steel, fiberglass or high-strength plastic. These materials must be able to withstand the pressure during the operation of the equipment and have good corrosion resistance to prevent corrosion by chemicals in the raw liquid. The design of the shell must ensure that the raw liquid can be evenly distributed around or inside the membrane assembly to ensure that each membrane tube can fully exert its ultrafiltration effect.

Pump system:
Feed pump:

responsible for transporting the raw liquid to the tubular ultrafiltration equipment. The pressure and flow rate of the feed pump should be selected according to the properties of the raw liquid (such as viscosity, concentration, suspended matter content, etc.) and the requirements of the membrane assembly. Generally speaking, the feed pump needs to provide sufficient pressure to overcome the resistance of the membrane so that the raw liquid can pass through the membrane assembly smoothly for ultrafiltration.

Circulation pump (some equipment):

In some tubular ultrafiltration systems, a circulation pump is set to improve filtration efficiency and prevent membrane contamination. The circulation pump returns part of the concentrated liquid that has not passed through the membrane to the feed port, mixes it with the newly entered raw liquid, and then ultrafilters it again. This can increase the flow rate on the membrane surface and reduce the deposition of solutes on the membrane surface, thereby extending the service life of the membrane.

Valve and piping system:
Valves are used to control the flow direction, flow rate and pressure of the raw liquid, permeate and concentrate. It mainly includes feed valve, permeate outlet valve, concentrate outlet valve, cleaning liquid inlet valve, etc. By reasonably adjusting the opening of the valve, precise control of the ultrafiltration process can be achieved. The pipeline system is responsible for transporting various liquids between different parts of the equipment. The pipeline material is usually selected according to the properties of the raw material liquid. For example, for highly corrosive raw material liquid, stainless steel pipes or corrosion-resistant plastic pipes, such as UPVC pipes or PE pipes, may need to be used.

Cleaning system:
Since tubular ultrafiltration membranes will inevitably be contaminated during use, a cleaning system is essential. The cleaning system includes chemical cleaning devices and physical cleaning devices.

Chemical cleaning device:

used to inject specific chemical cleaning agents into the membrane assembly, such as acid (for removing inorganic scale such as calcium and magnesium), alkali (for removing organic matter and microorganisms), oxidants (for oxidative decomposition of organic pollutants), etc. The chemical cleaning process requires the selection of appropriate cleaning agents and cleaning time according to the type and degree of membrane contamination.

Physical cleaning device:

including water washing, backwashing and sponge ball scrubbing. Water flushing is the most basic physical cleaning method. By flushing the membrane surface with clean water, some loose dirt can be removed. Backwashing is to pass the permeate through the membrane in the reverse direction to wash away the contaminants on the membrane surface. Sponge ball scrubbing is to use a special sponge ball to roll inside or outside the membrane tube to wipe off the dirt on the membrane surface.

Workflow:
Pretreatment:

Before tubular ultrafiltration, the raw liquid usually needs to be pretreated, such as filtration, precipitation, centrifugation, etc., to remove larger particle impurities and suspended matter to prevent these substances from clogging the tubular ultrafiltration membrane. The pretreated raw liquid enters the feed port of the tubular ultrafiltration equipment.

Ultrafiltration process:

The feed pump delivers the pretreated raw liquid to the tubular membrane assembly. Under pressure, the raw liquid flows inside or outside the membrane tube, and small molecular solutes and solvents pass through the membrane wall to form a permeate, which is collected on the other side of the membrane; large molecular solutes are retained on the feed side to form a concentrate. The permeate is output through the pipeline system and can be used as a product or enter the next processing link; the concentrate is further processed as needed, such as recirculating ultrafiltration, recovery after concentration, etc.

Cleaning and maintenance:

As the ultrafiltration process proceeds, the membrane flux will gradually decrease, which is due to the contamination of the membrane surface. When the membrane flux drops to a certain level, the tubular ultrafiltration membrane needs to be cleaned. First, physical cleaning is performed, such as rinsing or backwashing with clean water to remove loose dirt on the surface. If the physical cleaning effect is not good, chemical cleaning is performed, and appropriate chemical cleaning agents are selected according to the type of contamination, such as using citric acid to clean inorganic scale, and using a mixed solution of sodium hydroxide and sodium hypochlorite to clean organic matter and microorganisms. After cleaning, the performance of the tubular ultrafiltration equipment can be restored.

Performance characteristics:
High separation accuracy:

The tubular ultrafiltration equipment can effectively intercept substances with a relative molecular mass greater than the membrane cut-off molecular weight, and the molecular weight cut-off range is generally between 1000-1000000Da. It can accurately separate macromolecules and small molecules in the solution. For example, in the biopharmaceutical industry, macromolecular drug components such as proteins can be effectively separated from small molecular impurities.

Strong anti-pollution ability:

Compared with some other membrane component forms (such as hollow fiber membrane components), tubular ultrafiltration equipment has relatively good anti-pollution ability. This is because the channels of tubular membranes are relatively large and are not easily blocked by macromolecules or suspended matter. Moreover, the internal channels of internal pressure membrane components and the external channels of external pressure membrane components are relatively easy to clean, and both physical cleaning and chemical cleaning can effectively remove pollutants.

Stable flux:

Under appropriate operating conditions, the filtration flux of tubular ultrafiltration equipment is relatively stable. The flux is generally between 30-300L/(m²・h) and is relatively less affected by suspended matter and macromolecules in the raw material solution. Through reasonable operation, such as controlling parameters such as pressure, flow rate and temperature, a high and stable flux can be maintained, thereby ensuring the processing efficiency of the equipment.

Wide range of applications:

It can treat raw material liquids of various properties, including solutions containing high concentrations of suspended solids, macromolecular organic matter, colloids, etc. It has a wide range of applications in water treatment, food processing, chemical industry, pharmaceuticals and other fields. For example, in sewage treatment, industrial wastewater containing a large amount of suspended solids and organic matter can be treated, and in food processing, raw materials containing macromolecular nutrients such as juice and milk can be treated.

Easy to maintain and clean:

Due to the structural characteristics of the tubular membrane assembly, the maintenance and cleaning of the equipment are relatively easy. Whether it is an internal pressure or external pressure membrane assembly, the membrane surface can be easily physically and chemically cleaned. Moreover, the damaged part of the tubular membrane assembly is relatively easy to detect and replace, unlike some other membrane assemblies with complex structures, where one damage requires the replacement of the entire assembly.

Application field:
Water treatment field:
Drinking water purification:

As a link in the deep purification of drinking water, tubular ultrafiltration equipment can remove impurities such as bacteria, viruses, colloids, macromolecular organic matter, etc. in water, and improve the quality and safety of drinking water. Especially for some areas where water sources are polluted, such as surface water or groundwater containing pollutants such as microorganisms and algae, tubular ultrafiltration can effectively purify water quality.

Industrial wastewater treatment:

For industrial wastewater containing macromolecular organic matter, colloids, suspended solids, etc., tubular ultrafiltration equipment can be used as a pretreatment or deep treatment unit. In the treatment of printing and dyeing wastewater, it can remove dye macromolecules and fiber impurities in the wastewater; in the treatment of papermaking wastewater, it can remove macromolecular substances such as lignin and cellulose, creating good conditions for subsequent biological treatment or deep treatment.

Food industry:
Juice clarification and sterilization:

During the juice processing process, tubular ultrafiltration equipment can remove impurities such as pectin, protein, bacteria, etc. in the juice, making the juice clear and transparent, while retaining the flavor and nutrients of the juice. For example, in the processing of apple juice, orange juice and other juices, the quality and stability of the juice have been improved after tubular ultrafiltration treatment.

Milk sterilization and concentration:

used for sterilization and partial concentration of milk. It can remove bacteria, somatic cells and other impurities in milk, while retaining nutrients such as protein and lactose in milk. When producing dairy products such as cheese, tubular ultrafiltration equipment can also be used for pre-concentration of milk to improve production efficiency.

Pharmaceutical industry:
Drug extract refining:

During the drug extraction process, tubular ultrafiltration equipment can remove macromolecular impurities (such as polysaccharides, proteins, etc.) in the extract to improve the purity of the drug. For example, in the refining process of Chinese medicine extracts, tubular ultrafiltration can effectively separate the active ingredients of the drug and impurities, and improve the quality of Chinese medicine preparations.

Injection sterilization filtration:

As a sterilization filtration link in the production process of injections, tubular ultrafiltration equipment can effectively remove pathogens such as bacteria and viruses to ensure the sterility of injections. Compared with traditional sterilization filtration methods, tubular ultrafiltration has higher safety and reliability.