Determination of Acetate, Formate, Chloride, Sulfate, and Thiocyanate in Lean Amine by Wayeal Ion Chromatograph

Organic amine absorption solutions are a class of weakly alkaline organic amine solvents commonly used in chemical processes such as petroleum refining, natural gas processing, coal chemical industry, and ammonia synthesis, for capturing carbon dioxide from flue gases, as well as for adsorbing and removing impurities such as hydrogen sulfide or carbon dioxide from raw feed gases. After absorbing impurities, the amine solution is regenerated by heating and distillation to remove the absorbed components, and the resulting regenerated amine solution is referred to as "lean amine solution."

Commonly used organic amine absorbent solvents include monoethanolamine (MEA), diethanolamine (DEA), diisopropanolamine (DIPA), N-methyldiethanolamine (MDEA), and their mixtures. Under the synergistic effect of oxygen and acidic gases, these alkanolamine compounds undergo complex chemical reactions, initially forming aldehydes, which are further converted into acidic substances such as formic acid and acetic acid. These acidic species can exacerbate equipment corrosion, alter the surface tension and viscosity of the amine solution, cause severe foaming in the absorption tower, and impair gas–liquid contact efficiency. Chloride and thiocyanate ions are the anionic components of heat-stable salts (HSS) present in organic amine absorption solutions. If they accumulate continuously, they can cause severe corrosion to metallic materials of the equipment and adversely affect the desulfurization and decarbonization performance of the amine solution. Sulfate ions are generally introduced into the amine solution by external substances such as sulfur trioxide, which enter the system and react with the organic amines. Therefore, monitoring the concentrations of these salts is of great significance for determining when the amine solution requires purification or replacement, optimizing the regeneration process, and verifying whether the upstream desulfurization unit is operating effectively, as well as detecting any potential gas leakage or carryover of acidic gases in the system.

In this study, a Wayeal IC6200 ion chromatograph equipped with a conductivity detector and a NovaChrom HS-5A-P3 chromatographic column was employed to determine the concentrations of acetate, formate, chloride, sulfate, and thiocyanate ions in the samples. This method features a simple pretreatment procedure, high sensitivity, and good linearity, providing a valuable reference for the determination of various acid radical ions in the chemical industry.

Keywords: Ion chromatograph, Conductivity detector, Acetate, Formic acid, Chloride, Sulfate, Thiocyanate.

1. Instrument and Reagents

1.1 Ion Chromatograph Configuration List

Table 1 Instrument Configuration List

1.2 Reagents and Standards

1.3 Experiment Material and Auxiliary Equipment

Analytical balance (0.0001 g precision);

RP pretreatment cartridg;

H pretreatment cartridge;

Aqueous polyethersulfone (PES) membrane filter (0.45µm);

Disposable syringe (5mL);

Ultrapure water.

2. Experiment Method

2.1 Sample Pretreatment

Transfer 100μL of the sample into a 10mL volumetric flask, and dilute to the mark with ultrapure water to obtain a 100-fold diluted sample solution. Pass both the original sample solution and the 100-fold diluted sample solution successively through an RP pretreatment cartridge, an H pretreatment cartridge, and a 0.45μm aqueous membrane filter prior to instrumental analysis. Prior to use, the RP pretreatment cartridge was successively conditioned by passing through 20mL of methanol and 15mL of water, and then allowed to equilibrate for 30min. Prior to use, the H pretreatment cartridge was conditioned by passing 15mL of water through it, and then allowed to equilibrate for 30min.

2.2 Experiment Conditions

2.2.1 Ion Chromatographic Conditions

Table 3 Gradient Elution Program

3. Experiment Result

3.1 Standards Chromatogram

The determination was completed within 65 minutes. All peaks exhibited satisfactory peak shapes, and each analyte showed good response and resolution, meeting the requirements for experimental analysis.

Fig 1 Chromatogram of Mixed Anion Standard Solution

3.2 Linear Range

Appropriate volumes of mixed standard working solutions at various concentrations were injected for analysis. The deviations between the linear calibration results and the known concentrations were within the maximum permissible deviation limits. The correlation coefficients (R²) were all above 0.999, indicating good linearity for all analyte components.

Table 4 Linear Ranges for the Target Compounds

Fig 2 Linearity Results for Various Anions

3.3 Sample Test Result

Results of sample repeatability tests:

Fig 3 Overlaid Chromatograms of a 100-fold Diluted Sample Solution in Six Consecutive Injections for Repeatability Testing

Table 5 Test Results of Acetate Ion in the Sample

Table 6 Test Results of Formate Ion in the Sample

Table 7 Test Results of Chloride Ion in the Sample

The test results are as follows:

Actual Content = Average Measured Concentration × Dilution Factor

Fig 4 Overlay Chromatograms of the Original Sample Solution in Six Consecutive Injections for Repeatability Testing

Table 8 Test Results of Sulfate Ion in the Sample

Table 9 Test Results of Thiocyanate Ion in the Sample

The test results are as follows:

4. Conclusion

This method employs the Wayeal IC6200 ion chromatography system equipped with a conductivity detector for the determination of linearity, sample repeatability, and sample content of acetate, formate, chloride, sulfate, and thiocyanate ions. The chromatograms and data obtained demonstrate that the method exhibits well-shaped peaks without tailing for all target analytes, with sensitivity meeting the requirements of the national standard. The linear correlation coefficients (R²) for all analytes exceeded 0.999, and the sample repeatability was satisfactory. These results confirm that the Wayeal ion chromatography system used in this method fulfills the requirements for the qualitative and quantitative analysis of acetate, formate, chloride, sulfate, and thiocyanate ions in lean amine samples, providing a valuable reference for the quality assessment of lean amine solutions in the chemical industry.