Ensuring Chemical Compatibility in Sterlitech's Benchtops and Skids Systems: A Quick Guide to Material Selection

Sterlitech’s Skid Mounted Filtration Systems and Benchtop Filtration Systems are convenient solutions for testing membrane filtration processes for bench scale to small production scale. The material of construction is carefully selected to ensure high corrosion and deterioration resistance against the feed stream. This article serves as a quick guide for selecting materials to ensure long life and stable performance of the filtration setup. Please note that this article does not remove the user’s responsibility to ensure that materials are chemically compatible and to further assess the impact of their feed on the setup.

Key Materials used in Sterlitech’s Setups and Chemical Compatibility 

· 316 Stainless Steel (316 L): Commonly used in pumps, tubes, and fittings for its durability and resistance to corrosion against various feed streams including a wide range of organic solvents, and both strong and weak bases. However, it may not be compatible with some acids such as hydrochloric acid, acetic acid, hydrofluoric acid, and sulfuric acid. Also, 316L can be prone to corrosion when exposed to highly concentrated alkalis like sodium hydroxide and potassium hydroxide. 
· Hastelloy: known for its ultimate chemical resistance, Hastelloy is the ideal choice for applications involving highly corrosive chemicals and high salinity. It is used in pumps, tubes, and fittings to provide high chemical resistance where 316 L may suffer from corrosion. Hastelloy has great chemical resistance towards a wide range of acids and bases including sulfurous acid, acetic acid, formic acid, and strong oxidizing salts. However, it may not be well-suited for chromic acid, hydrobromic acid, sodium hydroxide, and nitrous acid. 

· Elastomers: used in gaskets, seals and O-rings, with common materials being Fluorine Kautschuk Material (FKM), Ethylene-Propylene Diene Monomer (EPDM), and Nitrile rubber. 
- FKM resists a wide range of chemicals and is used in various industries due to unique combinations of the strong nature of its structural chemistry and mechanical properties. It is resistant to Hydrocarbons, some acids and Ketones. However, it is not advisable to use FKM with acetone, esters, amines, organic acids, acetic acid, ethyl acetate, and highly polar chemicals. 
- EPDM is recommended water, dilute acids, dilute alkalis, ketones and alcohols. However, it is not advisable to use it with hydrocarbon environments such as oils, gasoline, kerosene, and mineral oil-based lubricants. 
- Nitrile rubber often known as Buna-N is resistant to water, hydraulic fluids, and most chemicals, making it a popular choice. However, Buna-N is not recommended for use in applications that involve exposure to aromatic hydrocarbons, ketones, or esters, as these chemicals can cause it to swell or degrade.

· Plastics: Used in components like fittings, tubing, O-rings. 
- Polypropylene (PP) is resistant to water, hydraulic fluids, and most chemicals, making it a popular choice. However, PP is not compatible with strong oxidants and nonpolar solvents such as xylene, tetralin, decalin, chloro-sulfonic acid, concentrated sulfuric acid, and hydrochloric acid especially at elevated temperatures. 
- Polyethylene (PE) offers excellent chemical compatibility, being highly resistant to strong acids, bases, mild oxidizing agents, and reducing agents. Polyethylene is not resistant to strong oxidizing agents such as nitric acid, fuming sulfuric acid or halogens. 
- Polyester exhibits excellent resistance to most chemicals, including acids, oxidizing agents like hydrogen peroxide, and most solvents. It also resists hydrocarbon fuels, oils, and lubricants effectively. However, it may not be suitable for strong alkalis, such as concentrated sodium hydroxide, calcium hydroxide, ammonia, trisodium phosphate, and sodium carbonate. 
- Nylon is chemically resistant to hydrocarbons, and some alcohols. However, it is not recommended to use it with ozone, most acids. 
- Polyvinyl chloride (PVC) is chemically resistant to many acids, salts, corrosives, bases, fats, and alcohols. However, it is not compatible with tetrahydrofuran or acetone, often incompatible with solvents. 
- Polyvinylidene fluoride (PVDF) offers excellent resistance to aggressive fluids, including inorganic and organic acids, hydrocarbons, and halogenated solvents. However, it is unsuitable for fuming sulfuric acid, concentrated alkalis (pH ≥ 12), and swells in polar solvents like acetone. 
- Polyetheretherketone (PEEK) may not be suitable for concentrated nitric acid and sulphuric acids. Also, Methylene chloride, dimethylsulfoxide (DMSO), and tetrahydrofuran (THF) may cause swelling in PEEK. 
- Polytetrafluoroethylene (PTFE) is resistant to most acids, alcohols, detergents and corrosive chemicals. PTFE is not compatible with certain alkali metals and fluorinating agents such as xenon difluoride and cobalt(III) fluoride.

Tips and Tricks to Consider When Evaluating Chemical Compatibility 

• Start by listing the feed stream and chemicals to be used in your experiment including concentration, temperature, and experimental time. List the material used to build the system including the main wettable material of construction and secondary part’s materials.
• Check the chemical compatibility of the primary wettable materials, like 316L or Hastelloy, ensuring they can withstand the feed stream to avoid costly damage to key components such as tubes, tanks, and pumps. The replacement of these parts could be very expensive and may require a complete setup rebuild.  
• Also, evaluate the compatibility of secondary wettable parts like O-rings, gaskets, and seals. Although these parts are more affordable compared to the main parts, the replacement can be difficult and require experience and working hours for replacement.
• If you have any doubts about the wettable parts provided or the chemical compatibility, do not hesitate to contact our experts for more details. 

Sterlitech's Benchtops solutions is an affordable solution with good chemical compatibility with various feed streams and chemicals. For enhanced customization and chemical resistance, consider using Sterlitech's Skids solutions which are compatible with wide variety of feed streams including water, organic solvents, acids, and alkalis. Sterlitech’s setups, using materials like 316L stainless steel, Hastelloy, and various elastomers and plastics, provide robust solutions, though careful attention to chemical compatibility is essential. Also, Sterlitech provides a wide range of membrane testing cells available in various sizes and materials. By thoroughly evaluating both primary and secondary components against the feed stream's chemical profile, users can avoid costly repairs and maintain system efficiency. 

Still have questions? Ask an Expert to learn more about our chemically resistant membrane testing options.