How can benzene and naphthalene in coke oven gas be accurately analyzed? The Corei chromatography solution addresses the analytical challenges posed by naphthalene’s tendency to condense, crystallize, and adsorb.

In the processes of coke oven gas purification and hydrogen production, the benzene and naphthalene contents serve as critical indicators for assessing the efficiency of benzene washing and naphthalene removal, as well as the operational status of downstream purification steps. Traditional manual sampling and analysis suffer from issues such as complex sampling procedures, sample distortion, long analytical turnaround times, and insufficient data continuity. Compared with benzene, naphthalene is a high-boiling‑point compound that is more prone to condensation, crystallization, or adsorption at lower‑temperature locations—such as the sampling probe, filters, transfer lines, fittings, and injection valves. If naphthalene is lost prior to entering the analytical instrument, even a highly sensitive detection system may yield results that underestimate its actual concentration in the process gas.

Therefore ， The key to analyzing benzene and naphthalene in coal gas is not merely… “Whether it can be detected,” but rather:

How can we ensure that naphthalene is lost as little as possible during its transport from the sampling point to the analytical system, thereby yielding accurate and stable measurement results?

In view of naphthalene’s high boiling point, Core Chromatography The sampling and sample pretreatment procedures were specifically designed, and an absorption solution was employed to process the samples, thereby minimizing the risks of naphthalene condensation, crystallization, and adsorption during gas transport. On this basis, combined with… KR-PGS 2032  R5 An online gas chromatograph enables automated analysis and continuous monitoring of benzene and naphthalene.

Practical application of the plan The results show: the limit of detection for benzene is: 0.0034 pp m ( 3.4ppb ) ； Limit of detection for naphthalene: 0.065 pp m ； Continuous 7 Repeatability of quantitative analysis for the next injection RSD ： 0.296% and 0.261% ； Quantitative repeatability RSD All are less than: 0.3% 。

I. Why is naphthalene more difficult to analyze accurately than benzene?

1. High boiling point, easily condensed.

When the sampling and delivery system includes sections at lower temperatures, naphthalene readily condenses out of the coal gas and deposits on the inner walls of the sampling probe, filters, and piping.

2. It tends to crystallize upon cooling.

If the temperature of the tubing or valve components drops further, naphthalene may crystallize, leading to blockage of the sample pathway or underestimation of the analytical results.

3. It is easily adsorbed and exhibits a memory effect.

Naphthalene may also adsorb onto the surfaces of filters, pipelines, and valve bodies, leading to slower response times, sample carryover, and cross-contamination between successive samples.

4. Coke oven gas has a complex composition.

Coke oven gas contains hydrogen, methane, carbon monoxide, carbon dioxide, nitrogen, and various hydrocarbon components; it may also contain moisture, particulate matter, and tar. These constituents further complicate sample pretreatment and chromatographic separation.

Therefore, online analysis of benzene and naphthalene in coal gas requires not only attention to detector performance but also a thorough evaluation of the overall effectiveness of sampling, sample pretreatment, sample transport, and chromatographic separation.

II. Kerry Chromatography How can sample loss during naphthalene transport be minimized?

 

Kerry Chromatography It is not merely a matter of enhancing detector sensitivity; rather, it involves a systematic design of the entire sample pathway, from the sampling point to the detector.

The plan primarily includes:

Sample collection and pretreatment;

Filtration, pressure reduction, and flow stabilization;

Sample heat tracing and temperature control;

Absorption treatment unit;

Automatic valve injection;

Chromatographic separation specifically for benzene and naphthalene;

FID Testing;

Automatic quantification and data processing;

Industrial communication and data upload.

 

The system analysis process can be summarized as follows:

Gas sampling →Sample pretreatment → Auto-sampling → Chromatographic separation → FID Detection → Quantitative Calculation → Data Upload

During sample transfer, the following areas require particular attention:

Sampling probe →Filter→Pressure-reducing and flow-stabilizing component→Delivery pipeline→Fitting→Valve→Injection port

Only by minimizing low-temperature cold spots and sample adsorption at these stages can we ensure that the samples entering the analytical system are as representative as possible.

III. Measured data: Low detection limits for benzene and naphthalene, with excellent repeatability in continuous injection.

1. FID Baseline Test Results

Test Items	Measured value (unit: pA)	Enterprise Standard (Unit: pA)	Whether it is qualified
FID baseline noise (/min)	0.012	0.02	Is
FID baseline drift (/30 min)	0.04	0.1	Is

Both the FID baseline noise and baseline drift meet the project’s test specifications, laying the groundwork for the stable detection of low-concentration benzene and naphthalene.

 

2. Test Results for the Detection Limits of Benzene and Naphthalene

Limit of detection = 3 × baseline noise × span gas concentration ÷ component peak height

Substance name	Limit of detection (unit: ppm)
Benzene	0.0034
Naphthalene	0.065

 

The above data demonstrate that the system is capable of detecting low concentrations of benzene and naphthalene, thereby providing reliable data support for the monitoring of coke oven gas purification and hydrogen production processes.

 

3. Repeatability results from seven consecutive injections

The system performs continuous injection of standard samples. Seven times, the test results are as follows:

Indicator Type	RSD value 1	RSD value 2
Qualitative repeatability	0.045%	0.099%
Quantitative repeatability	0.296%	0.261%

Both the qualitative and quantitative repeatabilities for benzene and naphthalene were excellent. In particular, the quantitative repeatability… The RSDs were all less than 0.3%, indicating that the system exhibited highly stable performance in sample injection, separation, and detection under the conditions of this test.

 

IV. What problems can online monitoring of benzene and naphthalene address?

 

Continuous online analysis of benzene and naphthalene in coal gas can provide data support for the following tasks:

- Evaluate the operational performance of the benzene washing and naphthalene removal units.

- Promptly detect when the adsorbent is approaching saturation or when purification efficiency declines;

- Monitor changes in benzene and naphthalene levels within the gas transmission pipeline network.

- Early warning of the risk of pipeline and valve blockage caused by naphthalene precipitation;

- Determine the regeneration or replacement cycle of the adsorbent.

- Optimize temperature, pressure, flow rate, and purification cycle;

- Reduce manual sampling and laboratory analysis efforts.

5. In which applications can the online benzene–naphthalene analysis system for coal gas be used?

 

Core Chromatography The online analytical method for benzene and naphthalene in coal gas can be applied to:

- Monitoring of the coke oven gas purification process;

- Analysis of the feed gas for hydrogen production from coke oven gas;

- Monitoring of the inlet and outlet of the benzene washing unit;

- Monitoring of the inlet and outlet of the naphthalene removal unit;

- Gas pipeline network monitoring;

- Adsorbent breakthrough and determination of replacement cycle;

- Gas analysis in steelmaking, coking, and coal chemical processes.

The composition of samples and operating conditions vary significantly across different sites; therefore, the analytical scheme must be tailored to account for pressure, temperature, dew point, moisture content, particulate matter, tar, and the target concentration range, with specific design considerations for sample pretreatment, heated‑line temperature, chromatographic column, measurement range, and analysis cycle.

 

VI. Conclusion: Naphthalene detection must not only be capable of accurate quantification but also ensure that the sample remains free from distortion.

 

The challenges in detecting benzene and naphthalene in coal gas extend beyond chromatographic separation and detection; they also lie in ensuring that the sample remains free from distortion throughout its entire journey—from the process pipeline to the analytical instrument. In particular, naphthalene is prone to condensation, crystallization, and adsorption. Only by designing sampling, heat tracing, injection, separation, detection, and data processing as an integrated system can stable and reliable analytical results be achieved.

 

Liaoning Kerui Chromatography Technology Co., Ltd. is based on KR-PGS 2032 R5 Centered around an online gas chromatograph, it is integrated with heated sampling, sample pretreatment, automated valve injection, and dedicated chromatographic separation, FID By leveraging technologies such as sensing, automated data processing, and industrial communication, an online analytical system for benzene and naphthalene in coal gas has been developed, enabling continuous and stable monitoring of target constituents. This provides reliable data support for process control, equipment protection, and the evaluation of purification performance in coal‑chemical enterprises.