Chemical Analysis and Characterization of Common Contaminants in LNG Hydrocarbons, Water, H2S, CO2, and Mercury


Liquefied Natural Gas (LNG) is a critical component of the global energy landscape, playing a pivotal role in meeting the growing demand for clean and efficient energy sources. LNG is formed by cooling natural gas to extremely low temperatures, transforming it into a liquid state for ease of storage and transportation. Chemical analysis is indispensable in the LNG industry to ensure the purity, safety, and adherence to quality standards. This article explores the various contaminants that can compromise LNG integrity and the vital role chemical analysis plays in mitigating these risks. Contaminants in LNG, such as hydrocarbons, water, hydrogen sulfide (H2S), carbon dioxide (CO2), and mercury, can have profound effects on both the quality of the product and the safety of the processes involved. Effective contaminant characterization is essential for maintaining the highest standards in LNG production, storage, and distribution.

Hydrocarbon Analysis in LNG

A. Types of Hydrocarbons Present in LNG

LNG is primarily composed of methane, but it may contain various hydrocarbons as impurities. These hydrocarbons include ethane, propane, butanes, and trace amounts of heavier hydrocarbons.

B. Analytical Techniques for Hydrocarbon Detection

Gas Chromatography (GC)

Gas Chromatography (GC) is a widely employed analytical technique for the detection and quantification of hydrocarbons. This method separates and analyzes individual components within a complex hydrocarbon mixture based on their differential affinities for a stationary phase and a mobile gas phase. In GC, the sample is vaporized and injected into a chromatograph, where it travels through a column filled with a stationary phase. As the components interact with the stationary phase, they undergo differential partitioning, resulting in their separation over time. The separated compounds are then detected by a detector, often a flame ionization detector (FID) for hydrocarbons. The resulting chromatogram provides a detailed profile of the hydrocarbon composition, allowing for precise identification and quantification of individual compounds. Gas Chromatography is known for its sensitivity, speed, and ability to analyze a wide range of hydrocarbons, making it an indispensable tool in various industries such as environmental monitoring, petrochemicals, and forensic analysis.

Fourier Transform Infrared Spectroscopy (FTIR)

Fourier Transform Infrared Spectroscopy (FTIR) stands as a powerful analytical technique for the detection and characterization of hydrocarbons. This method relies on the absorption of infrared radiation by molecular vibrations, offering valuable information about functional groups present in a sample. In FTIR, a broadband infrared light is passed through a sample, and the resulting spectrum is analyzed using a Fourier transform algorithm. Hydrocarbons exhibit characteristic absorption bands in the infrared region, allowing for their identification and quantification. FTIR excels in providing a comprehensive analysis of various hydrocarbon functionalities, aiding in the determination of compound structures and concentrations. Its non-destructive nature, high sensitivity, and rapid data acquisition make FTIR a versatile tool in industries such as petrochemicals, environmental monitoring, and quality control, contributing significantly to the understanding and control of hydrocarbon-related processes.

C. Quantitative Analysis and Identification Methods

Accurate quantitative analysis is achieved through calibration curves and standard reference materials. Identification methods involve spectral matching and comparison with known standards.

D. Impact of Hydrocarbon Contamination on LNG Quality and Safety

Hydrocarbon contamination can affect LNG quality by altering its heating value and combustion characteristics. Safety concerns arise due to the flammable nature of certain hydrocarbons, emphasizing the need for stringent analysis and control measures.

Water Content Analysis in LNG

A. Sources of Water Contamination in LNG

Water can enter LNG during the production, transportation, and storage processes. Sources include ambient humidity, condensation, and inadequate dehydration during production.

B. Measurement Techniques for Water Content

Karl Fischer Titration

Karl Fischer titration is a widely used method for determining water content in various substances, including liquefied natural gas (LNG). The principle behind Karl Fischer titration involves the reaction of water with iodine and sulfur dioxide in the presence of a suitable base. The reaction is typically performed in a titration cell with a Karl Fischer reagent, and the amount of titrant required to reach the endpoint is proportional to the water content in the sample.

Dew Point Analysis

Dew point analysis is another method used to determine the water content in liquefied natural gas (LNG). The dew point is the temperature at which air becomes saturated with moisture, leading to the formation of dew or condensation. In the context of LNG, the dew point analysis involves cooling a sample of LNG until water vapor begins to condense, and this temperature is then measured.

C. Implications of Excessive Water in LNG

Excessive water in LNG can lead to ice formation, pipeline corrosion, and compromised combustion efficiency. Addressing these implications requires accurate water content analysis and effective control strategies.

D. Strategies for Water Content Control and Prevention

Preventive measures include proper dehydration during LNG production, robust storage conditions, and regular monitoring. Control strategies involve adjusting dehydration units and implementing water removal technologies.

Hydrogen Sulfide (H2S) Analysis in LNG

A. Occurrence and Sources of H2S in LNG

Hydrogen sulfide can be present in LNG due to natural gas impurities, microbial activity, or chemical reactions during production and transportation.

B. Analytical Methods for H2S Detection

Gas Chromatography with Sulfur Specific Detection

This method involves separating the components of a LNG sample based on their chemical properties using a gas chromatograph. The sulfur-specific detector, often a flame photometric detector (FPD) or a pulsed flame photometric detector (PFPD), selectively responds to sulfur-containing compounds, such as H2S, with high sensitivity and specificity. As the LNG sample passes through the chromatograph, the H2S present is identified and quantified by the sulfur-specific detector, providing accurate and reliable measurements of H2S concentration in the LNG, which is crucial for ensuring compliance with safety and environmental regulations.

Electrochemical Sensors

These sensors operate by leveraging the electrochemical reactions that occur when H2S interacts with specific electrodes within the sensor. In the context of LNG analysis, an electrochemical H2S sensor can be integrated into a monitoring system. As H2S is present in the LNG sample, it reacts at the sensor’s electrodes, generating a measurable electrical signal proportional to the H2S concentration. This real-time detection method is advantageous for its simplicity, rapid response, and suitability for continuous monitoring applications. However, calibration and sensitivity considerations are essential to ensure accurate and reliable results, making electrochemical sensors a practical choice for on-site H2S detection in LNG facilities.

C. Safety Concerns and Regulatory Compliance

H2S is highly toxic, and its presence poses serious health risks to personnel. Stringent regulatory compliance is essential to safeguard against exposure and ensure a safe working environment.

D. Mitigation Strategies for H2S in LNG

Mitigation involves preventive measures, such as treating the natural gas feedstock, as well as reactive measures, including the use of scavengers and gas sweetening units.

Carbon Dioxide (CO2) Analysis in LNG

A. Impact of CO2 Contamination on LNG Properties

CO2 can affect LNG properties, including heating value, density, and combustion characteristics. Controlling CO2 levels is crucial for meeting quality standards and ensuring efficient energy production.

B. Analytical Techniques for CO2 Measurement

Infrared Spectroscopy

Infrared spectroscopy is a powerful analytical technique for measuring carbon dioxide (CO2) concentrations in liquefied natural gas (LNG). This method relies on the characteristic absorption of infrared light by CO2 molecules, which results in distinct peaks in the infrared spectrum. In LNG analysis, an infrared spectrometer is employed to transmit infrared light through the LNG sample. The CO2 molecules present absorb specific wavelengths of this light, and the degree of absorption is proportional to the concentration of CO2. By analyzing the changes in the transmitted light spectrum, the infrared spectrometer can accurately quantify CO2 levels in the LNG sample. Infrared spectroscopy offers high sensitivity, precision, and speed, making it a reliable and widely utilized technique for monitoring CO2 content in LNG, a crucial parameter for quality control and compliance with environmental standards.

Gas Chromatography

Gas Chromatography (GC) is a well-established analytical technique for measuring carbon dioxide (CO2) concentrations in liquefied natural gas (LNG). In this method, LNG samples are vaporized and injected into a chromatograph, where individual gas components are separated based on their chemical properties. The separated components, including CO2, pass through a detector, such as a thermal conductivity detector (TCD) or flame ionization detector (FID), which responds to their presence. The amount of CO2 is quantified by comparing the detector response to that of known standards. GC provides accurate and precise measurements of CO2 levels in LNG, allowing for quality control assessments and compliance with environmental regulations. The versatility of GC makes it suitable for both routine monitoring and detailed compositional analysis of LNG, contributing to the overall safety and quality assurance of LNG handling and transport.

C. Quality Control Measures for CO2 in LNG

Quality control measures involve setting and monitoring acceptable CO2 concentration limits, ensuring compliance with industry standards and optimizing LNG performance.

D. Environmental and Economic Implications

Excessive CO2 in LNG can contribute to greenhouse gas emissions, necessitating a balance between economic considerations and environmental responsibility. Analytical methods play a crucial role in achieving this balance.

Mercury Analysis in LNG

A. Sources and Occurrence of Mercury in LNG

Mercury can enter LNG through natural gas deposits or external contamination during production and transportation.

B. Mercury Detection Methods

Cold Vapor Atomic Absorption Spectroscopy (CVAAS)

Cold Vapor Atomic Absorption Spectroscopy (CVAAS) is a highly effective analytical method for detecting mercury in liquefied natural gas (LNG). In this technique, LNG samples are first treated with reducing agents to convert mercury into its elemental form. The vaporized mercury is then carried into an atomic absorption spectrometer, where it absorbs light at a specific wavelength when exposed to ultraviolet radiation. The degree of absorption is directly proportional to the concentration of mercury in the sample. CVAAS provides excellent sensitivity and selectivity for mercury detection in complex matrices like LNG. This method is particularly crucial for ensuring compliance with stringent environmental regulations, as even trace amounts of mercury can be harmful. The precision and reliability of CVAAS make it a preferred choice for the accurate measurement of mercury levels in LNG, contributing to safety and quality control in the liquefied natural gas industry.

Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is a highly sensitive and precise analytical method for detecting mercury in liquefied natural gas (LNG). In this technique, LNG samples are introduced into an inductively coupled plasma, where they are atomized and ionized. The resulting ions are then directed into a mass spectrometer, which separates and quantifies them based on their mass-to-charge ratios. ICP-MS offers excellent sensitivity, capable of detecting extremely low levels of mercury in LNG. Its ability to provide accurate measurements across a wide dynamic range makes it well-suited for both routine monitoring and trace analysis. ICP-MS is a versatile and powerful tool for ensuring compliance with environmental regulations and maintaining the safety and quality of LNG, as even minute concentrations of mercury can have detrimental effects.

C. Health and Environmental Risks Associated with Mercury

Mercury poses health risks to humans, and its release into the environment can have long-term ecological consequences. Strict adherence to regulatory guidelines is crucial to minimize these risks.

D. Regulatory Guidelines and Mercury Limitations in LNG

International regulations set stringent limits on mercury content in LNG, requiring comprehensive monitoring and control measures to ensure compliance.

Integrated Approaches to Contaminant Analysis

A. Comprehensive Analytical Strategies for Multiple Contaminants

Integrating various analytical techniques allows for a holistic approach to contaminant analysis, ensuring a thorough understanding of LNG composition.

B. Challenges and Solutions in Simultaneous Analysis

Simultaneous analysis of multiple contaminants presents challenges, including method compatibility and instrument capabilities. Addressing these challenges requires innovative solutions and advancements in analytical technologies.

Future Trends and Technologies in LNG Contaminant Analysis

A. Emerging Analytical Techniques

Ongoing research and development continue to introduce cutting-edge analytical techniques, such as sensor arrays and advanced spectroscopy, for improved contaminant detection.

B. Advances in Real-time Monitoring

Real-time monitoring technologies enable continuous surveillance of LNG composition, allowing for prompt corrective actions and minimizing risks.

C. Industry Innovations for Enhanced Contaminant Characterization

Innovations in sampling methods, data analysis, and automation contribute to enhanced contaminant characterization, paving the way for safer and more efficient LNG production.


The significance of rigorous chemical analysis cannot be overstated when considering the preservation of LNG integrity and reliability. By acting as a safeguard against potential risks, thorough chemical analysis becomes instrumental in upholding industry standards, contributing to the overall sustainability of the LNG sector. As we conclude, a call to action emerges, urging the industry to prioritize ongoing research, development, and collaboration. Such initiatives are crucial for advancing analytical techniques, addressing emerging challenges, and ensuring the continual success of the LNG sector. This commitment to improvement is essential for keeping the industry at the forefront of safety, quality, and environmental responsibility.

– Kahan Sheth