How Does PTFE Compare to PEEK for Heat Exchanger Tubing in Mixed Acid Environments?

PTFE is the gold standard for universal chemical resistance, but PEEK-a high-performance thermoplastic-is increasingly being explored for heat exchanger tubing where higher mechanical strength or temperature capacity is required. However, PEEK is less chemically resistant and should be selected considering the unique environmental conditions.

PTFE Vs PEEK
Both PTFE and PEEK are common materials for heat exchanger tubing but the relative importance of chemical resistance, thermal performance and mechanical strength will decide which is more suitable for mixed acid situations.

PTFE (Polytetraflouroethylene)
One of the most attractive features of the PTFE is its almost universal chemical resistance. It is a perfect choice in situations where chemical compatibility is paramount. It is resistant to most acids, bases and solvents, except for molten alkali metals and some fluorinating agents. PTFE generally performs well in heat exchanger service up to 110°C.

One of the key advantages of PTFE is its flexibility and low strength that enables it to absorb mechanical stress without splitting or breaking. This means it is suited for applications where flexibility and resistance to harsh chemicals are needed. However, the downside is that PTFE has relatively poor mechanical strength compared to other materials such as PEEK and may not function as well in high-pressure settings.

PEEK (Polyetheretherketone) 
PEEK has a smaller range of chemical resistance than PTFE but has higher mechanical strength and can endure higher temperatures. Maximum service temperature can be up to 250°C. It is resistant to a lot of organic solvents and a broad spectrum of acids such as sulphuric acid, hydrochloric acid and phosphoric acid. However, PEEK is attacked by concentrated nitric acid, sulphuric acid (over 80°C) and halogens, therefore the chemical resistance of PEEK is not as general as PTFE.

PEEK has a high tensile strength, making it usable in high pressure applications. PEEK is a very stiff material and not as flexible as PTFE. This can be a hindrance in some applications. Furthermore, the thermal conductivity of PEEK is roughly 0.25 W/m·K, comparable to PTFE, suggesting that the benefit of PEEK rests more in its mechanical and thermal characteristics rather than in its ability to transport heat efficiently.

How PTFE and PEEK are Used
PTFE is often chosen for applications where chemical resistance to a variety of materials is needed. This is the case for environments with different acids, solvents and bases, where there can be no danger of incompatibility. Due to its capacity to work at low temperatures (up to 110°C) it is ideally suited for corrosive conditions at moderate temperatures.

On the other side, PEEK is preferred for applications where high temperature, high pressure are required and process chemistry is more known and can be consistently controlled. At temperatures of 150°C or above, PEEK heat exchanger tubing becomes a critical option. This is particularly true when the system must deliver mechanical strength to handle high pressure or aggressive fluid dynamics.

A fundamental difference is that PEEK is more expensive than PTFE as it has higher performance attributes and a more sophisticated manufacturing process. Therefore the choice is a compromise between performance needs and the cost of the material.

Technical Comparison of PTFE and PEEK Heat Exchange Tubing
The following table summarises the key distinctions between PTFE and PEEK in terms of their use in heat exchanger tubing applications:

Property PTFE PEEK 
Chemical Resistance Near universal (excluding molten alkali metals and certain fluorinating agents)Resistant to most acids (excluding intense nitric and sulphuric acids above 80°C, halogens) 
Max Service Temperature ~110°C To 250°C
Mechanical Strength Low strength, high flexiblityHigh tensile strength stiff
Thermal Conductivity ~0.25 W/m·K ~0.25 W/m·K CostLess expensive Generally higher
Summary
PEEK enhances the pool of materials available for corrosion resistant heat exchangers, especially for high temperature and pressure applications. It does not, however, replace the universal chemical inertness of PTFE . PTFE is still the material of choice for chemical resistance in a wide variety of conditions. PEEK is appropriate for specialised applications where strength, temperature resistance and chemical compatibility are more carefully defined.

In practice, the material selection for heat exchanger tubing should be based on the process chemistry, operating temperature and mechanical requirements of the particular system. Knowing the subtleties between PTFE vs PEEK heat exchanger tube guarantees the best material is chosen to satisfy the chemical and physical demands of the application.