Use hollow fiber to wash and filter, realize automatic liquid exchange

Washing refers to the use of tangential flow filtration (TFF) techniques to "rinse" or remove certain smaller molecules (such as impurities, salt ions, solvents, small molecule proteins) from solution. Compared with the dialysis membrane tube, the washing operation is faster and the processing amount is larger. Buffer displacement, adjustment of particle size distribution, change of salt ion concentration, and maximum possible increase in clarification operations can also be achieved by selecting a suitable membrane. Buffer replacement, which uses ultrafiltration membranes to rapidly and gently change the protein solution, is one of the most common applications for the filtration of filtration using the Spectrum hollow fiber membrane module.

The success of the Fractionation operation by washing and filtering depends on whether the selected membrane is suitable. The membrane pore size must be large enough to allow passage of small molecular species (when performing fractionation applications) while the membrane pore size must also be small enough to retain macromolecular species. Spectrum offers a wide range of membranes for ultrafiltration and microfiltration under optimal conditions.

Tangential flow filtration achieves the purpose of treatment by circulating a feed liquid within the hollow fiber membrane. The pores in the fiber tube wall allow small molecules to pass through, while the macromolecular material is trapped in the circulating feed (Figure 1). The filtration can be achieved by supplementing the circulating fluid with a displacement buffer or a cleaning solution. The added buffer may be the same as the flow rate of the filtrate (continuous washing), or may be added intermittently after a certain concentration level (non-continuous washing). During the washing process, the components of the solution are gradually transferred from the original solution to the supplemental buffer.

A typical TFF system includes a pump, a pressure monitoring device, a flow monitoring device, a sample container, a buffer container, and a hollow fiber membrane module. The pump circulates the feed fluid in the process flow with a certain flow rate and shear force. In order to control the driving force of the filtration - transmembrane pressure, it is necessary to monitor the pressure at the inlet, outlet and filtrate outlet of the membrane module. Monitoring the filtration flow rate is a prerequisite for process amplification and process optimization.

There are many ways to perform a filter wash. The use of hollow fiber membrane modules, hoses and sealed containers is an effective method for continuous filtration. In the continuous wash mode, the filtrate discharge creates a negative pressure in the sample container, and the wash buffer is replenished to the sample container (or process loop) at the same rate as the filtrate discharge under negative pressure. Figure 2 shows a typical wash flow path setup.

Concentrate before washing

The volume of the feed liquid is proportional to the amount of buffer required to complete the wash.

To reduce buffer usage and operating time and increase efficiency, the sample can be concentrated prior to washing. In the tangential flow filtration operation, if the filtrate is not collected by adding the buffer to the sample container, the concentration can be achieved. As the macromolecular envelope is retained, the concentration will increase accordingly. The concentration of small molecules (salt ions or solvents) that can pass through the membrane remains unchanged. Figure 3 shows a schematic of the concentration, with the sample volume reduced to half of the starting volume and the concentration of the trapped macromolecules doubled.

An increase in macromolecular concentration can affect the filtration flow rate and the permeability of small molecules. As the concentration of the trapped molecules on the surface of the membrane increases, the resistance of the filtrate through the membrane will become larger, resulting in a decrease in the flow rate of the filtrate, that is, a decrease in the process flow J (see Equation 1).

J, (L/M ² /hr) = filtrate flow / membrane area (Equation 1)

In some applications, as the concentration of entrapped molecules on the surface of the membrane increases, the resistance of the permeable small molecule through the membrane increases. The relative concentration of the small molecule in the filtrate and the injection can be expressed as the transmittance (%T), and the transmittance can also be calculated by measuring the concentration of the small molecule in the injection and the filtrate during the concentration process.

T=C _filtrate /C _injection (2a)

T (%) = C _filtrate / C _injection × 100 (2b)

Equation 2: Transmission coefficient (2a) and % transmittance (2b)

Understanding the effect of concentration on filtration flow rate and transmission rate is helpful in optimizing the filtration and fractionation processes.

Washing (buffer replacement)

Washing the filter means adding a washing buffer to the sample container to rinse out small molecules that are permeable to the membrane. In the continuous washing process, the buffer is continuously replenished into the feed liquid at the same flow rate as the filtrate flowing out of the hollow fiber membrane module. See Figure 4.

Continuous washing is shown in Figure 2. It is carried out in a sealed system. The amount of buffer added can be adjusted automatically to keep the total volume of the liquid constant.

[Note: It is also possible to use an additional dual pump head to simultaneously adjust the flow of supplemental buffer and filtrate, both of which can add buffer to the sample container and withdraw filtrate (usually used for tangential flow microfiltration) at the same flow rate].

It is important to understand the concept of the filter volume VD. The washing volume is the sum of the volume of the liquid in the container and the volume of the liquid in the circulation loop.

The total volume of the buffer required for the washing treatment is usually expressed by the number of washings or the volume multiple n:

Buffer volume = n × V sample volume Equation 3

The wash filter volume required to "rinse off" a small molecule is estimated using Figure 5 and can also be calculated from Equation 4 shown below the graph.

If the transmission coefficient T is known and the wash filter volume used is used, the percentage of cleared osmotic molecules can be calculated.

Formula 4

to sum up

Washing, or concentration/washing, is a fast, gentle, process-enhanced tangential flow filtration process (ultrafiltration or microfiltration) for rinsing small molecules or salt ions that are permeable to the membrane. The small molecule may be a low molecular weight impurity, a buffer salt ion, a non-reactive component or a desired product (MF TFF, microporous tangential flow filtration). By selecting the correct membrane pore size and determining the relationship between concentration and transmission, the filtration process can be optimized to achieve a stable, repeatable purification process, which in turn ensures a consistent product for each operation.

Scan the QR code and pay attention to the official version of the WeChat public account to get more application information!

Speed Bumps & Cable Protectors

When the car passes, Speed Bumps can be remind the driver to slow down the speed. To avoid accidents.

Some deceleration belts are also inlaid with reflective light, which will reflect bright red or green light at night, which can attract drivers' attention, reduce speed and improve safety.

Cable Protectors is a special kind of Speed Bumps, when the Cable need through the road, it can be through cable Protectors, no need to put the Cable buried underground, it prevent car crush Cable. This is an ingenious solution.

Rubber Car Speed Humps,Wavy Speed Bumps,Rubber Speed Hump,Traffic Speed Hump

Greateagle Safety Products Co., Ltd. , https://www.greateaglesafety.com