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Hydrofluoric acid concentration measurement:
Safe, precise, inline

HF concentration measurement with ±0.05 wt% accuracy and HF-resistant special materials.

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Real-time measurement

Continuous monitoring without delay

Maintenance-free

No moving parts or wear components

Highest accuracy

Precise measurement even under difficult conditions

Reduced operating costs

Cost-efficient solution with a short payback period

Hydrofluoric acid (HF) is the aqueous solution of hydrogen fluoride and occupies a special position in chemistry: although it is considered a moderately strong acid, its extreme toxicity and ability to dissolve glass and silicate materials make it one of the most dangerous industrial chemicals of all. At the same time, hydrofluoric acid is indispensable in certain key industries, for example in semiconductor production, in petrochemical alkylation plants, or in metal treatment. Exact monitoring of HF concentration is therefore not an option, but a prerequisite for process safety, product quality, and plant protection. LiquiSonic® was developed for these requirements, with special coatings and a measuring principle that withstand hydrofluoric acid.

  • HF attacks glass, quartz, and silicates - conventional sensors and electrodes are unusable!
  • Even small amounts pose an acute danger to life - manual sampling is a safety risk!
  • The concentration changes during the process - without measurement, no stable process!

How LiquiSonic® measures HF concentration

LiquiSonic® was developed, among other things, for safe use in hydrofluoric acid processes. All wetted parts are optionally made of PFA, ETFE, or other HF-resistant materials. Standard materials that would not withstand the acid are not used.

For example, in petrochemical alkylation plants, the system simultaneously measures HF concentration, water content, and ASO content, the three decisive parameters for process control and safety. Predefinable limit values ensure that the system triggers an immediate alarm in the event of critical deviations. In addition, LiquiSonic® can be seamlessly integrated into existing process control systems.

Our measuring system measures continuously and fully automatically. This means that manual sampling is completely eliminated. At the same time, the precise concentration data enable targeted, demand-based dosing of hydrofluoric acid, which noticeably reduces consumption and operating costs.

Typical challenges

  • Extreme material corrosiveness – standard materials fail
  • Toxicity and personnel protection – manual sampling is highly risky
  • Concentration drift – composition changes regularly
  • Safety-critical reactions – e.g. acid runaway
  • Leakage risk – potential HF ingress into secondary circuits

Our solution

  • All wetted components made of HF-resistant materials
  • Fully automatic inline measurement
  • Continuous real-time measurement
  • Definable limit values and direct integration into process control systems
  • Even the smallest concentration changes are detected

Application examples

Hydrofluoric acid is indispensable in some of the world's most demanding industrial processes. This is precisely what makes accurate monitoring critical. In petrochemical alkylation plants, HF acts as a catalyst in the production of high-octane fuels; even small changes in water content can lead to uncontrollable acid reactions. In semiconductor manufacturing, the exact HF concentration in the etching bath determines the quality of every single wafer. And wherever HF is carried in pipelines and heat exchangers, an undetected leak in the secondary circuit can cause serious damage within a short time. What all these applications have in common: Exact monitoring of HF concentration is not an option, but a prerequisite for process safety, product quality, and plant protection.

Semiconductor industry

HF is the standard etchant for SiO₂ layers on silicon wafers. Wet chemical cleaning and etching processes (wafer cleaning, BOE solutions) are inconceivable without HF.

Petrochemical alkylation

HF serves as a catalyst in alkylation plants for producing high-octane fuels (isoalkylates) from butane and olefins.

Surface treatment

Matting, engraving, and cleaning of glass, crystal, and quartz. Also surface treatment of titanium, tantalum, and other special metals.

Fluoride production

Intermediate product for sodium fluoride, aluminum fluoride, fluorspar derivatives, and fluorinated polymers (PTFE precursors).

Solar industry

Etching and cleaning of silicon surfaces in photovoltaic production.

Over 35 years of experience in concentration measurement

Since 1990, SensoTech has been a leading provider of inline measurement technology and has established itself as a specialist in precise concentration and density measurements.

Our systems are used worldwide, including in critical applications.

35+

Years of experience

1000+

Installed systems

50+

Countries worldwide

ISO 9001

certified quality

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Frequently asked questions

How can hydrofluoric acid be measured inline?

LiquiSonic® measures HF concentration using the speed of sound in the process liquid. An ultrasonic pulse passes through the liquid between transmitter and receiver; the concentration is calculated in real time from the transit time. The method is independent of the liquid's color, turbidity, or conductivity and works directly in the process without sampling.

Which sensor can be used to measure HF concentration?

The LiquiSonic® measuring system is used for HF applications. It consists of a sensor and controller and is installed directly in the plant's main line.

How accurate is concentration measurement with LiquiSonic®?

The measurement accuracy is ± 0.05 wt%. This precision is achieved through direct sound velocity measurement, combined with integrated temperature compensation that balances fluctuations in process temperature.

Which materials are resistant to hydrofluoric acid?

Depending on the application, SensoTech sensors are made with corrosion-resistant special materials tailored to the respective process chemistry. HF-resistant materials are used for all wetted components to ensure long-term stability even with aggressive media.

How can laboratory samples of hydrofluoric acid be avoided?

By using inline measurement with LiquiSonic® directly in the process line, manual sampling is completely eliminated. This not only reduces labor, but above all the safety risk for personnel who would otherwise come into direct contact with the HF-containing process liquid.

Can HF concentration be measured continuously?

Yes, LiquiSonic® provides continuously updated measured values several times per second, which can be displayed online, stored, and evaluated. In contrast, laboratory analyses only provide selective snapshots.

How complex is commissioning the measurement system?

The sensors are integrated directly into the existing main line. This significantly reduces the installation effort compared to alternative analysis methods.

How high is the maintenance effort for hydrofluoric acid measurement?

Thanks to their robust, wear-free design, the sensors operate largely maintenance-free and without consumables. In addition, all wetted components are made from HF-resistant materials. This eliminates the need for regular recalibration as required with conventional measurement methods.

Can LiquiSonic® be integrated into existing control and safety systems?

Yes, the LiquiSonic® measurement system provides measurement data digitally and can be connected to higher-level control systems. Exceeding or falling below limit values is signaled immediately so that this information can be incorporated into existing safety procedures.

What happens when there are concentration fluctuations in the hydrofluoric acid bath?

Fluctuations in HF concentration change the reaction conditions in the process and can impair both product quality and plant safety, for example through increased hydrofluoric acid consumption, intensified corrosion, or a rising risk of leaks. Continuous measurement makes such deviations immediately visible and helps prevent risks.

How can acid runaways be prevented?

Continuous inline measurement with LiquiSonic® detects changes in material composition immediately before they become critical. This makes it possible to take corrective action at an early stage and significantly reduce the risk of an uncontrolled reaction progression ("acid runaway").

How can you prevent hydrofluoric acid from entering secondary circuits?

Through permanent concentration and phase monitoring with LiquiSonic®, deviations and leaks can be detected at an early stage before hydrofluoric acid passes unnoticed into downstream circuits. Complete online data recording also supports traceability in the event of a malfunction.

How is HF monitored in alkylation units?

The LiquiSonic® sensors are installed directly in the main line of the alkylation unit and simultaneously measure the concentration of hydrofluoric acid, water, and acid-soluble oils with an accuracy of ± 0.05 wt%. This enables optimal product quality with minimal hydrofluoric acid consumption and reduces the risk of acid runaways, corrosion, and leaks.

How can hydrofluoric acid be controlled in etching baths in semiconductor manufacturing?

In semiconductor manufacturing, LiquiSonic® monitors the HF concentration in etching and cleaning processes such as SC1, SC2, or BOE/BHF in real time with temperature compensation. This allows the etching solution to be replenished precisely and kept within the optimal concentration range, avoiding over-etching or under-etching of the wafer.

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