Hydrogen Purity Analysis in Industrial Chemical Processes

Hydrogen is utilized in several industrial chemical processes. For instance, hydrogen is employed as a carrier gas in the semiconductor industry for thin-film deposition and to safeguard semiconductor devices from damage through neutralizing residual oxygen. Ultra-high purity hydrogen, which is certified to >99.999%, is needed by these semiconductor processes.

Recently, hydrogen has attained momentum as a source of fuel for fuel cell electric vehicles (FCEV) that decrease air pollution, greenhouse gas emissions, and fossil fuels’ dependency when compared to typical combustion engines. Impurities like hydrogen fluoride, ammonia, formic acid, hydrogen chloride, and formaldehyde decrease the fuel cell’s performance even at low part-per-billion (ppb) levels.

This application needs hydrogen at a purity of 99.97% or above.

Purity Challenge

Instrumentation should have detection limits in the low ppb range to fulfill the complex purity necessities of hydrogen applications — like those in automotive and semiconductors described earlier. To offer an economical and fast solution, it must also be able to measure several gases at the same time.

Conventionally, when examining those impurities defined by the International Standard for Organization in ISO 14687 for fuel cell hydrogen, several analyzers are needed, usually employing a combination of gas chromatography (GC) and spectroscopic techniques.

GC techniques can fulfill the requirements of sensitivity; however, the maintenance charges are high and the time required for analysis is usually long owing to the required sample separation. Real-time precise examination for a cheaper ownership cost is provided by FTIR spectroscopy, but most FTIR devices on the market require a detector that is cooled with liquid nitrogen and cannot obtain the necessary detection limits for such complicated applications.

Solution

The complete IR spectral range (500–5000 cm-1) can be monitored by the Thermo Scientific™ MAX-iR™ FTIR Gas Analyzer using a deuterated triglycine sulfate (DTGS) detector without the need for liquid nitrogen.

With detection limits that are equal to or above cumbersome liquid nitrogen cooled mercury-cadmium-telluride (MCT) detectors, the MAX-iR analyzer enables the quick and precise measurement of most needed impurities — making the MAX-iR analyzer best-suited for use in the field at fueling stations.

Thermo Scientific™ StarBoost™ Technology — an optional sensitivity enhancement — lets the MAX-iR analyzer identify impurities with compact FTIR gas analysis at levels never achieved before, down to 1 ppb or below.

Hydrogen Purity Analysis in Industrial Chemical Processes

Image Credit: Thermo Fisher Scientific – Materials & Structural Analysis

Experimental

An array of 12 consecutive blank samples were studied to test the MAX-iR FTIR Gas Analyzer’s detection limits. Either research-grade hydrogen with 99.9999% purity or nitrogen without any detectable impurities is used as the blank sample.

The instrument detection limit (DL) was characterized as thrice the standard deviation of the 12 replicates. The MAX-iR analyzer configuration utilized in the assessment had a DTGS detector that could be operated 24/7 as it needs no liquid nitrogen and no maintenance.

Table 1. Detection limit assessment. Source: Thermo Fisher Scientific – Materials & Structural Analysis

Compounds Max allowable limit in ISO 14687 (ppm) MAX-iR DTGS DL (ppm)
Ammonia 0.1 0.020
Carbon dioxide 2 0.010
Carbon monoxide 0.2 0.020
Formaldehyde 0.2 0.030
Formic acid 0.2 0.010
Hydrogen chloride 50* 0.020
Hydrogen fluoride 50* 0.010
Water 5 0.100
Total hydrocarbon (C1-C5) 2 0.200
Non-methane hydrocarbon (C2-C5) 2 0.200
Methane 100 0.010
Ethane -- 0.020
Ethylene -- 0.050
Propane -- 0.040
Butane -- 0.080
Pentane -- 0.050

 

* Limit for total halogenated compounds is 50 ppm

Along with the gases listed in Table 1, the DTGS configuration can also be used to examine other halogenated species, which include, but are not limited to, dichlorodifluoromethane, chloromethane, vinyl chloride, and dichloromethane.

The MAX-iR analyzer’s StarBoost technology configuration has a narrower spectral range than the DTGS. However, it offers improved sensitivity for impurities like CO2, CO, and CH4. NIST traceable calibration standards were acquired with 5 ppm of CO, CO2, and CH4 in a balance of hydrogen to confirm the performance of the StarBoost configuration for the trace impurities’ analysis in hydrogen.

Using a gas blending system, this standard was diluted to concentrations as little as 10 ppb. For blank samples as well as dilution of the 5 ppm calibration blend, research-grade hydrogen was used.

Four concentration levels (10 ppb to 5 ppm), with a minimum of four replicates in each, were randomly examined by the MAX-iR analyzer with StarBoost configuration — every day for three days to identify accuracy, linearity, and method detection limit (MDL). A repeatability analysis was also performed to test precision, where a concentration of 10× the detection limit was examined 30 times (see Figure 1).

Concentration plot for 25 ppb repeatability study on StarBoost configured MAX-iR instrument.

Figure 1. Concentration plot for 25 ppb repeatability study on StarBoost configured MAX-iR instrument. Image Credit: Thermo Fisher Scientific – Materials & Structural Analysis

Table 2. Summary results of validation study on StarBoost configured MAX-iR system. Source: Thermo Fisher Scientific – Materials & Structural Analysis

  Accuracy Linearity Precision EPA 821-R-16-006
  % of Expected R2 RSD MDLS (ppb)
Carbon dioxide 1.25% 0.9999 0.70% 0.7
Carbon monoxide 2.91% 0.9999 2.43% 0.6
Methane 2.15% 0.9998 0.88% 1.1

 

Conclusion

For the real-time measurement of several trace level impurities present in bulk hydrogen, the MAX-iR analyzer is a sensitive and flexible analytical tool. The DTGS detector of the analyzer offers the most effective solution for quick, precise analysis of the several impurities outlined in ISO 14687 and for monitoring the quality of fuel cell grade hydrogen (99.97% purity).

To monitor ultra-high purity hydrogen for industries with strict demands like semiconductors, the StarBoost configuration offers improved sensitivity for a compact subset of impurities.

The validation study establishes that the StarBoost configured MAX-iR analyzer is an exceptionally accurate and dependable tool that attains detection limits down to 1 ppb. Both the MAX-iR system and the MAX-iR with StarBoost configuration are ideal for use in the field and can be used 24/7 as neither liquid nitrogen nor maintenance are required.

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific – Materials & Structural Analysis.

For more information on this source, please visit Thermo Fisher Scientific – Materials & Structural Analysis.

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