Filtration of flowing material
Separation systems that combine classic solutions with advanced technology

Separation is a core process step and often one of the most expensive in the biotechnology, pharmaceutical and traditional chemical industries. PROCESS had a look at what some producers have to offer.

The selection and configuration of separation systems is one of the factors which can decide whether producers are able to achieve the quality they need at an acceptable price.
Filtering, distillation, solvent extraction and precipitation are the classic separation techniques. Even though filtration is a mature technology, its potential has not yet been exhausted. Filter process technology continues to evolve, and demand for filtration products remains srong. The US and Western European filtration and separation markets are the largest in the world and expected to see strong growth in during the next few years.

Cold pressed: sinter elements
Sika brand filter elements from GKN Sinter Metals are classic products which can be used for catalyst recovery, gas and fluid filtration and various refinery applications. Cold isostatic press technology is used to manufacture these filter elements. The metal powder is placed into the steel and elastomer press tool for molding and compression. Pressure applied from all sides by a fluid creates uniform porosity in the pressed piece, and this guarantees homogeneous physical properties throughout the entire part. Using this method, it is possible
to make seamless filter elements up to 1200 mm long and 320 mm in diameter with various wall thicknesses. Flanges and threads can also be molded into the parts with the isostatic press process. This in turn makes it easy to design filter cartridges and tubes. The manufacturer claims that even small lots can be produced at an acceptable cost.
Membranes: a technology with significant potential
The membrane has now virtually become a classic technology as well, and the membrane market continues to offer good growth potential. Microdyn-Nadir, which claims to be a membrane technology pioneer, offers a wide range of membranes with different polymers, molecular weight cutoffs and geometries (flat sheet, roll stock, tubular and capillary membranes). These membranes are used, for example, in biotechnology fermentation processes to sterilize the feed. Following fermentation, microfiltration membranes separate the cells and cell fragments in the upstream process to isolate the target products such as enzymes, proteins, vaccines or other pharmaceutical substances which have a low molecular weight. Ultra and nano membranes are normally used in the downstream process to concentrate products or to isolate them prior to final purification. The company has a new membrane module for submerged systems called Bio Cell, which was developed for use in membrane bioreactors. Microdyn-Nadir claims that the modular design featuring large, self supporting membrane pockets combines the advantages of conventional capillary modules and flat sheet modules.
Thin film filtration: thin cakes
BHS-Sonthofen offers filters for solid/liquid separation in batch and continuous production. All of the products have a relatively thin filter (2–25 mm). Filtration is heavily dependent on cake thickness. Doubling the thickness increases the filtration time by a factor of four. The company cites other advantages of thin film filtration:
-A thinner cake makes washing out the filter cake more efficient.
-A low differential pressure is sufficient for formation of a thinner cake.
-The moisture can be removed better and more easily from a thinner cake.
To cite a practical example, the BHS Autopress can be used to efficiently separate suspensions that are difficult to filter. It will also reliably separate media that have to be processed in a sterile environment or which need to be processed in closed apparatus to meet workplace hygiene requirements or because the substances are toxic.
Depending on process requirements, washing, extraction, pressing, blowing off and drying can be used in downstream processing. A thin cake, complete filtration with no residue and exceptionally low residual moisture in the pre-dried cake increase throughput performance.
Separation of water and waste water treatment
Waste water and process water in the chemical and pharmaceutical industry often contain high concentrations of a small number of contaminants, for example tensides or dyes. Enviro-Chemie supplies customized high-performance systems for cleaning partial flows prior to mixing. This process-integrated technology has the advantage that valuable substances can be recovered. To cite one example, AVR-Bedrijven, which runs one of Europe’s largest waste disposal operations, is located in the industrial zone at Rotterdam harbor. The plant treats waste from two neighboring petrochemical complexes. Dilute caustic soda, which is contaminated with molybdenum, high amounts of organic compounds and traces of heavy metals, is generated during the plastics production. When this waste byproduct is burned, the organic compounds are broken down mainly into carbon dioxide and water. Following the burning process, the residual solution is fed into a waste water treatment system. This system, which was supplied by Enviro-Chemie, contains two lines with a hydraulic throughput capacity of 30 m3/h. The first line is broken down into the process stages waste water cooling, solid separation, neutralization and selective ion exchange for molybdenum. Up to 6,000 kg of sodium molybdate is recovered daily and recycled. The second line is for heavy metals and contains the process stages solid separation, neutralization and selective ion exchange. This line can be used to separate out zinc, copper, nickel and lead ions among others.
Filters in aluminum production
Specialization can be the key to capturing significant market share, as the following example illustrates. The Bayer process to extract aluminum hydroxide from bauxite (followed by the Hall-Heroult process to produce aluminum metal) is one of the major target markets for Dorr-Oliver Eimco’s filtration and sedimentation technology. The following filters made by this manufacturer are used in the Bayer process:
-rotary drum vacuum filters for filtration of red mud;
-Kelly leaf filters for filtration and polishing of aluminate liquor;
-rotary drum vacuum filters for washing out the oxalate;
-high performance disc filters for seed hydrate filtration;
-flat filters for product hydrate filtration.
Dorr-Oliver Eimco filters are now used at plants that produce more than 90 percent of the total worldwide output of aluminum hydroxide. In recent years, the company has also become the market leader in vacuum belt filters for flue gas desulfurization systems which are used in power stations. Dorr-Oliver Eimco has installed more than 190 vacuum belt filters at more than 80 facilities world wide.
High precision for CPI and Pharma
High value products require top quality filter media. The filtration division at Sefar AG supplies high-precision fabrics for a wide range of filtration and separation applications ranging from process technology to blood filtration. The product line includes ready-to-use filter belts for vacuum belt filters, centrifuge filter bags, filter press cloths, leaf filter covers, rotary disc filter segments and covers and belts with sealing profiles for rotary drum filters. The major production steps are performed in house including weaving and fabrication of the filter media to guarantee quality and traceability for customers in the pharmaceutical industry. The in-house laboratory is available to handle engineering issues and clarify questions relating to the filter products.
Test and monitoring equipment
Palas has developed a range of equipment for testing hot gas filters. Temperature and humidity have a significant impact on the cleaning characteristics and filtration properties of a filter medium. This means that temperature and moisture settings are an essential feature of any test station which is used to test filters under simulated field conditions. The VDI 3926-compliant MMTC-2000 test station for washable filter media offers special advantages in hot gas applications up to 250°C.
The test rig is small, compact and modular. It can be used for a variety of tasks, and is designed to handle a range of filter test particles. A welas white light aerosol spectrometer is available for hot gas particle measurement. This modular device, which is used to measure particle size and quantities, can be heated up to 120°C. There is a special welas particle measurement system which can detect particles in hot gas up to 800°C.
High-speed characterization of demixing and consolidation phenomena and calculation of the particle size distribution make the Lumisizer (made by L.U.M.) the ideal tool for R&D and process control. The Lumisizer simultaneously analyzes demixing in 12 different dilute or concentrated dispersions. The system can measure different sample cell types and standards at the same time.