Polymer
membranes

Polymer membranes are also often referred to as organic membranes. They are a family of membranes produced of polymers. The alternative to polymer membranes is ceramic membranes, also referred to as inorganic membranes. A polymer membrane is a semi-permeable filter media produced of polymers used for pressure-driven water treatment. The polymeric materials can, among others, be polysulfone, polyethersulfone, polycarbonate, polyvinylidene fluoride, polyamide, or cellulose acetate.

Polymer membrane technology is employed in large-scale industrial applications to treat water and wastewater in order to separate micron-sized particles. The membranes have a semi-permeable surface. This means that some particles can pass through the membrane while others are rejected. It is the membrane's pore size that defines the size of the rejected particles. The membrane pore size is defined in microns. One micron is one-millionth of a meter. Thus, membranes can separate even the smallest particles such as bacteria, viruses, protozoa, and salts.

Organic membranes can operate within microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. Microfiltration separates suspended solids, while reverse osmosis separates salts.

Membrane technology is highly alike regardless of the materials utilized for the membranes. Thus, polymer membrane technology is generally the same technology as that of its ceramic counterpart. A pressure generated by a feed pump will force the liquid purification process by forcing the liquid to pass through the porous semi-permeable membrane barrier.

A feed stream enters the membrane, and pressure is applied. This will separate the feed stream into two new streams, which are the permeate and the retentate. The permeate consists of the filtered liquid, which can pass through the porous membrane barrier. The retentate consists of the particles that are retained by the membrane barrier.

Polymer membranes can operate within all four filtration technologies. They are used for microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. They can be used for water and wastewater treatment. They are, among others, used within dairy, bakeries, wine distilleries, alcohol distilleries, and cosmetics.

The material and the preparation process highly affect the membrane's chemical, thermal, and mechanical strength.

Sintering is a well-known membrane preparation method. It is both used for polymer and ceramic membranes. For this technique, membranes are prepared by sintering powders of organic materials for polymer membranes and inorganic materials for ceramic membranes. While polymer membranes are produced of organic materials such as polysulfone, cellulose acetate, polycarbonate, or polyimide, ceramic membranes are made of inorganic materials such as alumina, titania, zirconia, or silicon carbide. The advantage of organic membranes is that they can be sintered at lower temperatures than inorganic membranes, lowering the production costs.

Organic membranes are used in many industries. The main advantage of organic membranes is the low capital expenditure due to low manufacturing costs and easy scalability. Therefore, these membranes have been used for many industrial water treatment applications. Polymer membrane technology is especially suitable for water desalination processes through reverse osmosis. The polymeric material cellulose acetate is often employed for water treatment due to its high chlorine tolerance.

However, due to the polymeric membrane properties, the balance flips towards ceramic membranes within several industries and water treatment applications.   

Polymer membranes suffer from a low degree of mechanical, thermal, and chemical stability. Contrary, ceramic membranes possess a high degree of these exact attributes. This makes polymer membrane technology an inadequate technology for harsh industries, ultimately calling for ceramic membranes with stronger properties.

Ceramic membranes have the advantage of being able to withstand harsh chemical cleaning, high temperatures, and aggressive fluids with acids or strong solvents. Thus, ceramic membranes can be used in harsh environments, such as corrosive and high-temperature environments, where polymer membranes are inadequate. These industries can be:

• Power plants
• Oil and gas
• Marine
• Mining

With the current focus on sustainability and the rapid implementation of environmental regulations and discharge limits for various industries to obtain cleaner industrial processes, it becomes more and more essential to have durable and cost-effective filtration solutions that can withstand arduous industries.

Moreover, ceramic membranes can withstand harsh chemical cleaning for sterilization and frequent backwash, which is crucial for several industries in order to maintain superior hygiene standards. Any compromises on cleaning and sterilization can contaminate the operation and result in operational downtime. Industries with extensive hygiene needs can be:

• Pharmaceutical
• Cosmetics
• Biotech
• Food and beverage
• Dairy

As ceramic membranes are more expensive to produce, they are linked with higher capital expenditure. Yet, this is compensated by an efficient membrane with a long lifetime, ensuring a low cost of ownership. The durable and hard inorganic material delivers a robust and stable membrane, which provides efficient and reliable operation and can withstand strong pressure and the stress it causes. As organic membranes are not as durable, they have a shorter lifetime and generally require more frequent replacement.