Crossflow membrane filtration is a pressure-driven separation process. Application: Industrial, food, water, chemical, and biotechnology markets, as well as for those providing environmental protection.
Membranes serve as highly-engineered, physical barriers that permit the passage of materials only up to a certain size, shape or character. Aquacheme offers reverse osmosis membranes in a variety of configurations, materials and sizes; each designed to meet specific application needs.
There are four main membrane separation processes currently employed for liquid/liquid and liquid/solid separation: microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO).
Spiral wound products have become the most commonly used membranes for industrial water applications such as boiler make-up water, brackish water treatment, seawater desalination, microelectronics and pharmaceutical water applications. These membranes are available as UF, NF and RO.
Membranes are thin films of porous material which can be used for a number of chemical separations. Although many membranes are made from polymer films, membranes can be formed from ceramics, carbon fiber, and porous metal substrates. The pores can range from atomic dimensions (< 10 angstroms) to 100+ microns.
What is Semi-permeable Membrane?
Semi-permeable membrane refers to a membrane that selectively allows certain species to pass through it while retaining others. In actuality, many species will pass through the membrane, but at significantly different rates. In RO, the solvent (water) passes through the membrane at a much faster rate than the dissolved solids (salts). The net effect is that a solute-solvent separation occurs, with pure water being the product. (In some cases, dewatering is desired to concentrate the salts).
What is Osmosis?
Osmosis is a natural process involving the fluid flow of across a semi-permeable membrane barrier. Consider a tank of pure water with a semi-permeable membrane dividing it into two sides. Pure water in contact with both sides of an ideal semi-permeable membrane at equal pressure and temperature has no net flow across the membrane because the chemical potential is equal on both sides. If a soluble salt is added on one side, the chemical potential of this salt solution is reduced. Osmotic flow from the pure water side across the membrane to the salt solution side will occur until the equilibrium of chemical potential is restored. In scientific terms, the two sides of the tank have a difference in their “chemical potentials,” and the solution equalizes, by osmosis, its chemical potential throughout the system. Equilibrium occurs when the hydrostatic pressure differential resulting from the volume changes on both sides is equal to the osmotic pressure. The osmotic pressure is a solution property proportional to the salt concentration and independent of the membrane.
How are membranes used?
The small pores of the membranes can serve as a physical barrier, preventing passage of certain materials such as salt, bacteria and viruses while allowing the free passage of water and air. The desalination of water using reverse osmosis is a well known use of membranes as a filter.
Recently, recovery of water from sewage and recovery of whey protein from waste streams during cheese making have been carried out with ultrafiltration and microfiltation membranes which require much less pressure than reverse osmosis. While pressure is be used to drive filtration, electrical current, osmotic pressure, and temperature can also be used to preferentially allow one component in a mixture to pass freely through the membrane while retaining the rest. The membrane structure and chemistry can also serve to carry out other separations.
Membranes provide a high surface area material where chemical reactions or diffusion can take place. For example, bundles of hollow fiber membranes (membranes in a thin tubular form) are used in dialysis to purify the blood by removing certain toxins. Membranes can also be used to carry out solvent extraction and catalysis while also serving to separate the reactants.
Hydrophobic membranes can be used to prevent passage of liquid water but allow vapor to pass (like Goretex). This property has been exploited in membrane distillation where brackish water is heated using solar power and the pure water vapor passes through the membrane and condensed to produce very high quality water. This uses less energy than boiling and utilizes bountiful but low value energy in remote areas.
Aquacheme Co., Ltd. is a wholesalers’ of the reverse osmosis membranes. To find out more about how Aquacheme can help you with your special water quality needs, contact Aquacheme for further assistance with all your Membrane needs. We will be happy to assist you.
To find out more about how Aquacheme can help you with your special water quality needs, contact Aquacheme for further assistance with all your Membrane needs. We will be happy to assist you.