Membrane separation is a process used to filter substances from a mixture through a porous membrane. It has practical applications in water filtration and creating concentrated solutions. The main types of membrane separation are reverse osmosis, nanofiltration, ultrafiltration, and microfiltration. The texture and chemical composition of the membrane determine which materials pass through it. Membrane separation is used in many industries, including water processing and chemical recovery.
Membrane separation is a technique used in science and industry to separate substances from a mixture by filtering that mixture through a porous membrane. The substance being filtered can be a liquid or a gas. Membrane separation has many practical applications, including water filtration and creating concentrated solutions. The main types of membrane separation processes are reverse osmosis, nanofiltration, ultrafiltration and microfiltration.
When a feed solution or gas is passed through a porous membrane at high pressure, some substances in that mixture will permeate the membrane into the lower pressure area, but other substances will not be able to. The texture and chemical composition of the membrane determines which materials pass through it. For example, a membrane that has larger pores will tend to admit large and small particles, and a membrane that has smaller pores will exclude larger particles. Similarly, a membrane that has a particular chemical composition could be designed to chemically filter certain compounds.
In reverse osmosis, two solutions are contained on opposite sides of the membrane: one more concentrated and the other more aqueous or less concentrated. The natural tendency of water to spread from an area of low concentration to an area of high concentration is reversed by the pressure applied to the highly concentrated solution. This causes water to flow out of the highly concentrated solution through the membrane, making that solution even more concentrated by removing the water. Evaporated milk and other condensed products can be produced through this process.
Nanofiltration is typically used in water processing to remove its salty taste or unwanted mineral content. This method removes salts, such as sodium and potassium, from the liquid. The membranes used in nanofiltration have a slightly larger pore size than those used in reverse osmosis.
Ultrafiltration and microfiltration are used to separate larger particles while allowing smaller particles to pass through the membrane. Viruses, bacteria and suspended solid matter are excluded by these larger pore membranes. Often, ultrafiltration or microfiltration will be used in conjunction with a finer filtration method as part of an overall industrial process.
Many industries use membrane separation as part of their routine operations. For example, removing harmful salts and minerals that could create scale or corrosion in source water is important in boiler operation. Membrane separation can also be used to recover chemicals from a waste stream. Desalination is another method where membrane separation is used extensively to produce high quality drinking water.
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