Invented by Vincenzo Vassarotti, Colin Lanyi, Christopher Biddell, Sartorius Stedim Biotech GmbH
TFF is a type of filtration that uses a porous membrane to separate particles from a liquid. The liquid is passed through the membrane at an angle, which creates a tangential flow. This flow helps to reduce the build-up of particles on the membrane, which can clog it and reduce its effectiveness.
Filtering cells are used in TFF systems to remove particles from the liquid before it is passed through the membrane. These cells can be made from a variety of materials, including ceramic, glass, and polymer. They are designed to remove particles of a specific size and shape, which makes them ideal for use in TFF systems.
The biopharmaceutical industry is one of the largest users of TFF systems. These systems are used to purify proteins, antibodies, and other biological molecules. TFF systems are also used in the production of vaccines and gene therapies. The demand for TFF systems in the biopharmaceutical industry is expected to grow rapidly in the coming years, as new therapies are developed and more companies enter the market.
The food and beverage industry is another major user of TFF systems. These systems are used to remove impurities from liquids, such as juice and beer. TFF systems can also be used to concentrate liquids, which can help to reduce transportation costs. The demand for TFF systems in the food and beverage industry is expected to grow as companies look for ways to improve the quality and safety of their products.
The water treatment industry is also a major user of TFF systems. These systems are used to remove impurities from water, such as bacteria and viruses. TFF systems can also be used to remove heavy metals and other contaminants from water. The demand for TFF systems in the water treatment industry is expected to grow as governments and companies look for ways to improve the quality of drinking water.
In conclusion, the market for filtration systems using TFF cells and filtering cells is growing rapidly. These systems are used in a variety of industries, including biopharmaceuticals, food and beverage, and water treatment. The demand for TFF systems is expected to grow in the coming years, as companies look for ways to improve the quality and safety of their products.
The Sartorius Stedim Biotech GmbH invention works as follows
A filtration element for tangential flow filtering of a liquid sample contains at least 2 blocks with at least 2 filtration elements between each pair. Each filtration element consists of an outlet for filtrate and a sheet supporting material, as well as two ultrafiltration or microfiltration flat membranes arranged in sandwich construction on either side. Each block, on the side opposite the membranes is equipped with a channel to feed a sample liquid tangentially across the membranes. The channels are connected parallel with each other and the inlet of the sample liquid flow. Each channel has a longitudinal section divided by transitional zones. It is designed and arranged so that the flow direction changes abruptly at the transitional zone.
Background for Filtration system using such a cell and filtering cell for tangential flow.
Many industrial, food and Biotechnology companies use micro and ultrafiltration methods and equipment in the processing and preparation of solutions. Filtration is used in a variety of ways, including as a sterilising process to remove bacteria, a clarification method to remove suspended particles and contaminants, a concentration for macromolecules like proteins, or a purification method to remove unwanted micromolecules, such as salts. “A variety of membranes with different porosities and applications are available to meet specific process and application requirements.
For larger volumes, the crossflow or tangential Flow technique is used.
Membranes (e.g. spiral wound, hollow fibre or flat type) are used as filter elements in this type of filtration. The spiral wound, hollow fiber or flat types are mounted into pressure-resistant housings to form filtration cells or modules. A pump is used in a filtration unit that includes such cells to feed the solution through the cell, tangentially. The rate of solute filtering is determined by several parameters, such as the general membrane characteristics, porosity and pressure.
The development of ultrafiltration has been hindered by problems related to gel polarisation and fouling the membrane, which reduce the speed of filtration. The most common causes of these problems are the formation and accumulation of particles on the surface of the membrane, which leads to a partial blocking of membrane pores. This phenomenon can result in a tenfold reduction or more in the membrane’s hydraulic permeability compared to its original rate of pure water permeation. These problems result in a need for significantly higher operating pressures and membrane areas for a given filtering capacity. This increases hold-up losses within the system. Losses of concentrated sample that cannot be drained out of the cell. This adds cost, and makes filtration less competitive with alternative processing techniques.
The design of filtration systems must also consider the following parameters: minimising the volume of liquid held up per unit membrane area, low pressure drop along the length of the flow, easy cleaning with minimal dead spaces, the ability to drain the cell completely, the ease of scaling to larger or smaller pilot systems, the minimum energy requirements, which means a high flow rate combined with low pressure drops across the cell, and the overall economy.
The use of long, thin, high-flow channels using membranes that are either flat plates or hollow fibre bundles has shown improvement in reducing fouling while achieving low energy and holdup requirements.
The present invention is directed towards a cell and system that uses flat membranes.
In an existing filtration cell, a thin, flat channel is spirally arranged on the one side of a membrane. The inlet and outlet ports for the filtrate are located at the cell’s outer and inner edges, respectively. The outlet port in the middle is perpendicular to both the membrane and the flat channel.
The main problem with this configuration is that the membrane’s available area is not used to its fullest extent when it is cut (circular), which increases the price of the membrane. This type of cell also isn’t suitable for large-scale process systems because of the central outlet, which prevents the stacking multiple cells. This configuration is mainly used in small laboratory systems.
The company MILLIPORE sells a filtration cell with membranes that are flat under the brand MINITAN. This cell is made up of a rectangular membrane that is swept with sample solution flowing in multiple parallel straight channels, from the inlet manifold on one side of the membrane to the outlet manifold on the opposite side.
The need to set the pump speed in conjunction with the back pressure of the cell’s recirculation outlet is another problem that exists with existing tangential-flow cells. This will create the transmembrane membrane pressure required within the cell.
In existing systems, the flow is restricted by a valve while pump speed is varied to achieve adequate pressure. A pinch valve, which is used in small laboratory systems to compress the outlet tubes, is usually used. Larger process systems are equipped with more sophisticated mechanical vales. Mechanical valves, while more precise and expensive than pinch valves, are easier to control but also less affordable. The interdependency of the valve and pump settings makes it difficult and time-consuming to control processes in both cases.
To achieve an adequate control of pressure, at least one gauge must be installed in the filtration system. This is usually located at the inlet and outlet of the filter cell. Diaphragms are often used to achieve this, but they can cause a large volume of liquid to enter the internal mechanism. This is problematic when sanitary operation and a high level of cleanliness is required. The sanitary designs developed to solve this problem can be expensive and are not usually justified in small laboratory systems. Due to the pulsation produced by most pumps and due to their high frequency, pressure readings are inaccurate.
Along with reducing the volume of the hold-up in the filter cell, it’s also important to reduce the volume and surface area within the recirculation system, including the feed reservoir and pump, and the connective tubing. This will allow for a higher level of final filtrate volume or concentration. The feed or sample tank must be located at a distance of a considerable amount from the pump and cell assembly, as initial volumes can often be large. It is necessary to add additional tubing to the system for recirculation, which increases the volume of the holding tank. Also, it can be difficult to pump the liquid from a large container completely.
When e.g. When processing small volumes and the retentate is of high value, it’s important to keep both the holding volume in the cell and the entire recirculation circuit at a minimum. This is a common situation in laboratories when working with samples. When the product being processed is the filtrate, the volume of hold-up is less important. When clarifying fruit drinks, the hold-up volume is not important.
BRIEF DESCRIPTION ABOUT THE INVENTION
The invention aims to develop a tangential-flow filtration cell with a high degree of cross-flow turbulent flow to reduce the problems associated with gel polarisation, and fouling on the membrane surface.
It is also an object of the invention to provide a tangential-flow filtration cell with a square or rectangular shape, or a trapezoidal one in order to maximize yields from rolls or sheets when cutting membrane material.
It is also an object of this invention, to provide a tangential-flow filtration cell that can be expanded simply by stacking successive filter cells in series. The entire assembly only requires pressure plates on each end.
The invention also aims to reduce the length of the recirculation tube by mounting the inlet and output ports on the same side of the housing.
It is also an object of the invention to provide a tangential-flow filtration cell with low liquid holdup per unit area.
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