We offer a wide variety of filtration and coalescing products designed specifically for the chemical, refining, petrochemical, and polymer industries. These products remove liquid and solid contaminants from product streams, feedstocks, waste streams, and utilities. With capabilities spanning the full filtration spectrum—from coalescing through reverse osmosis—these products can treat liquids and gases at high temperatures and viscosities in regenerable and disposable configurations.

Our products can be used in the following applications to improve efficiency.

• Purifying final product streams in refineries as well as chemical, petrochemical, and polymer plants
• Removing corrosion products and liquid contaminants, such as water and caustic
• Treating high temperature and high viscosity melt polymers
• Recovering expensive catalyst for reuse
• Removing liquid aerosols to protect turbines, compressors, and other process equipment
• Preparing feedstocks and utilities for use in production of intermediate and final products
  

Common liquid aerosols include the condensed hydrocarbons and water in natural gas streams, condensed product in product streams, and entrained liquids, such as amine and lubricating oils. Presence of these liquid aerosols can: 

• Negatively impact compressors and other rotating equipment
• Foul burner nozzles
• Cause foaming in liquid/gas contactors, such as amine systems
• Poison catalysts
• Corrode process piping
• Shorten the life and reduce performance of membrane devices
  

There are three primary mechanisms for the formation of liquid aerosols: condensation from a saturated vapor, atomization (spray effect through a flow restriction), and liquid reentrainment. Tests have shown that condensation from a saturated vapor forms the smallest droplet, ranging from 0.1mm to 5mm. Atomization produces droplets of approximately 9mm to 200mm, and droplets formed by liquid reentrainment are approximately 400mm to 3000mm in size. When choosing a liquid/gas separation device, the anticipated droplet size should be taken into consideration. It is recommended that a high efficiency coalescer be used when the size of the droplet is less than 10mm.

A number of technologies are available to remove liquid aerosols from gas streams. These include knock-out pots, mist eliminators, filters, separators, and high efficiency liquid/gas coalescers. Since each device has a specified range of operation, proper selection depends on the application requirements and the characteristics of the feed gas and liquid aerosol.

The size of the smallest droplet efficiently removed by each device is provided below.

Pall SepraSol™ liquid/gas coalescer <0.1 µm
Mist eliminator  5 µm
Vane separator  10 µm
Cyclonic separator 10 µm
Knock-out drum 300 µm

The nature and composition of a liquid aerosol are important to consider when selecting and sizing separation equipment. These depend on the characteristics of the gas, such as composition, temperature range, pressure range, density, and viscosity impact. Another factor to consider is how difficult it is to separate a liquid and a gas. Condensed hydrocarbons are the most difficult to separate, since they tend to be the lightest, smallest droplets. Liquid density and surface tension must also be taken into account, since they affect droplet size and character, which in turn affects separation requirements. Another important factor is liquid aerosol concentration. Knowing the amount of liquid present enables a vendor to better size the equipment.

Many of the separation devices available are adequate when the primary requirement is for bulk removal of liquids and/or the downstream equipment and processes are immune to the presence of liquids. If further liquid/gas separation will be performed downstream, a bulk separation device can be used. In general, a cyclone or knock-out drum is recommended if waxy or coking materials are present.

High efficiency liquid/gas coalescers such as Pall’s SepraSol™ and SepraSol Plus coalescers are highly recommended for the protection of reciprocating compressors, furnace burner nozzles, and contactor towers; the recovery of carried-over amine, compressor lube oil, and ammonia; and the protection of sensitive catalysts and membrane devices.

Free water or other dispersed contaminants cause haze and process equipment fouling, poison catalysts, and lead to off-specification product. Removal of these contaminants can result in a more economical plant operation and the assurance that on-specification product is shipped every time.

A surfactant (surface active agent, also known as a wetting agent) is a substance that contains both hydrophilic (water loving) and hydrophobic (water fearing) components at the molecular level. This dual nature promotes emulsion formation and enables the surfactant to reduce interfacial tension between two liquids by adsorbing at their interface.

Interfacial tension (IFT) is the excess energy per area (erg/cm^2) or the force per distance (dyne/cm) required to stretch an interfacial film. IFT results from the difference in energy between the molecules near a hydrocarbon-liquid/aqueous-liquid interface and the molecules of the liquid that is present in the bulk phase. As a surfactant is added to a two-phase system, the IFT decreases, allowing for the formation of an emulsion (either water drops in hydrocarbon or hydrocarbon drops in water). At low interfacial tension (<20 dyne/cm), this emulsion can be very stable, requiring a high efficiency polymeric liquid/liquid coalescer—such as a Pall AquaSep® coalescer or PhaseSep® coalescer—to separate the two phases.

Surfactants in petroleum and chemical streams may occur as natural byproducts of the process or as performance enhancing additives. Some of the surfactants that may be present are sodium naphthasulfonates, cresylic acids, naphthenic acids, corrosion inhibitors, biocides, metal scavengers, and emulsion breakers.

The following conditions should be taken into account.

Viscosity:	The higher the viscosity, the more difficult the separation.
Suspended solids:	Fine solids can stabilize emulsions or plug the separating device.
Liquid/liquid density differences:	The narrower the difference between the continuous phase and the dispersed phase, the more difficult the separation.
Temperature:	The solubility of the dispersed phase is affected by temperature. Significant temperature reductions downstream of the coalescer can lead to condensation of dissolved liquid contaminant.

Earlier methods of chlor-alkali production involved the use of mercury cells or asbestos diaphragms. In the early 1970s, operators of the mercury cell process began to experience pressures to address environmental concerns because of the emergence in Japan of a disease called Minimata. Similar pressures developed in regard to asbestos use.

The membrane cell process is the newest technology for chlor-alkali production. It is environmentally friendly and more energy efficient than earlier methods used. New plants are adopting this technology, and older production facilities have been converting to it.

Pall provides the critical filtration needed to keep the brine free of particulates in order to better protect the expensive electrolysis cell membrane separators.

Pall Corporation has a line of Septra™ filters made specifically for the chlor-alkali market. These filters are constructed of all polymeric materials to prevent brine from being contaminated by metals. One key feature of Pall Septra filters is the patented crescent shape pleat design of the filtration media, which provides maximum filtration surface in compact systems. This design enables the build-up of a uniform cake thickness because of the uniform flow channel. This allows all of the medium area to be used, which enhances recovery. Because of their unique pleat design, Septra filters can withstand the mechanical stress required to effectively dislodge the cake during filter regeneration. Filters designed with a standard pleat configuration will break at the top of the pleat.

Nylon salt solutions can contain hard particulate (corrosion products) as well as softer gel material (polymer). For the removal of gel contaminants, depth filtration is best. Gels get deposited in the depth of the filter medium, providing optimized utilization of filter area and, consequently, longer filter life. The extra depth also provides a more effective barrier against gels pushing through the filter media. Pleated filters are better suited for the removal of hard particulate matter. They are typically constructed of a thin layer of media and contain a higher surface area than depth filters.

A balanced filtration approach is recommended: deployment of the optimum filter across various polymer feed streams, including monomers, solvents, slurry additives, and polymer precursors, to achieve the highest quality polymer at the lowest cost. As an example, the filtration of slurry additives has been found to significantly extend the life of melt filters by removing contaminants that can accelerate polymer degradation in the high-melt temperature zone. Degraded polymer is removed by melt filters before it reaches the extruder. Melt filtration typically has the highest operating costs for cleaning and servicing between cycles, so extending the life of these filters is worth the additional step of filtering slurry additives.

Gels can form when the polymer melt is exposed to high temperatures for extended periods of time. By reducing residence time during filtration unit operation, excessive localized heating of the polymer melt at any stagnation zones in the flow path can be reduced. For this purpose, stacked segment filters are superior over pleated candle filters. Since segments are not all alike, the use of advanced flow channel spacers in the segment filter has proven beneficial by reducing polymer residence time in the filtration step. The removal of contaminants, such as iron oxides, in upstream processes can reduce both the formation of gels and polymer degradation in the heated zones.

Particles and gels can significantly interfere with production in polymer manufacturing operations. During the production of polymer films, defects can be caused by contaminant particles and gels, which may cause tears in the film. Such circumstances will force a shutdown. Film quality is also critical for high-tech applications in the microelectric industries, where low conductivity is required. In fiber production, contaminant particles or gels can negatively impact the production process by causing breaks in the fiber or reducing fiber strength. Particulates and gels can also change the polymer’s optical properties, reducing its value as a component for the manufacture of CDs and DVDs.