Sour crude natural gas is a highly corrosive form of natural gas containing increased levels of hydrogen sulfide and carbon dioxide, which can damage pipework and equipment. These impurities must be neutralized by a process known as amine gas treatment (also known as amine scrubbing or gas sweetening), before it can be sold as fuel. This process involves passing the gas through amine-rich scrubber solutions. Alkanolamines, such as ethanolamine, triethanolamine, and methyldiethanolamine, are the most commonly used amines for this purpose.
When the neutralizing capacity of these solutions is no longer efficient, the amine solutions are regenerated and stripped of elemental sulfur. However, this process leaves behind corrosive heat-stable amine salts, which can build up over time. To minimize equipment damage and reduce maintenance costs, it is essential to accurately and precisely determine the concentrations of alkanolamines and their salts in scrubber solutions.
Advanced ion chromatography technologies enable more cost-effective amine gas treatment
Ion chromatography with suppressed conductivity detection is a highly effective technique for the separation of ionic components and is widely used for quantitative analysis across a broad range of industrial applications. However, determining alkanolamines and degradation products in scrubber solutions has traditionally proven challenging due to the extreme variability in the component composition.
New columns optimized specifically for the separation of hydrophilic amines are supporting impressive improvements in alkanolamine determination. Unlike traditional cation-exchange columns, which typically contain only carboxylated functional groups, the Thermo Scientific™ Dionex™ IonPac™ CS20 cation-exchange column has an innovative stationary phase containing additional phosphorylated and sulfonated functional groups, resulting in enhanced selectivity for monovalent cations. This creates a wider separation window for alkanolamine peaks between the elution of monovalent cations and divalent cations, leading to more accurate analyses.
Innovative cation-exchange columns for highly selective alkanolamine separations
We put this advanced column chemistry to the test in a recent performance study, which you can read more about this application note.
Method optimization was undertaken using a standard solution containing four cations and six alkanolamines. The elution gradient used in our analysis consisted of a low methanesulfonic acid (MSA) starting concentration, a shallow gradient slope in the alkanolamine elution window, followed by a steep gradient for the rapid elution of magnesium and calcium ions. Given the high concentration of amine in the scrubber solution, a 4-port injection valve containing a 0.4 μL internal injection loop was used to reduce sample preparation time, and more importantly to reduce potential dilution errors from multiple serial dilutions.Figure 1 shows the excellent resolution achieved for the mixed cation-alkanolamine standard solution using this method. All ions of interest were baseline resolved, with the exception of the triethanolamine and methylaminoethanolamine peaks.
Figure 1. Separation of four cations and six alkanolamines using a Thermo™ Scientific™ Dionex™ IonPac™ CS20 cation-exchange column.
To test the stability of the column and method, the combined mixed standard solution was analyzed continuously over a period of five days. The relative standard deviations (RSDs) of the retention times were all less than 0.4% over the five days, and those of the peak areas averaged 0.9% to 2.3%, highlighting the reproducibility of the method.
Robust, reliable and reproducible cation and alkanolamine determination
We then used this method to analyze three alkanolamine-based neutralizing amine samples, diluted 1,000-fold. The concentrations of the (diluted) primary alkanolamines in the ethanolamine, triethanolamine, and methyldiethanolamine samples ranged from 900 mg/L to 2,300 mg/L.
Analyte recoveries were determined by measuring the diluted sample against an equivalent sample with an added reference standard. To remain in the calibration ranges for the method, the 1,000-fold samples were further diluted three-fold for the ethanolamine- and methyldiethanolamine-based samples, and five-fold for the triethanolamine-based sample. Sample recoveries ranged from 90% to 110%, demonstrating the strong performance of this method for alkanolamine determination.
Enhancing accuracy and consistency with advanced cation-exchange columns
Advanced ion chromatography columns offering enhanced selectivity for monovalent cations are resulting in significant improvements in alkanolamine determination. By creating a wider elution window for alkanolamine analysis, these technologies are achieving more reliable, accurate, and reproducible results, helping industry ensure the quality and safety of natural gas products.
Download the application note to learn more about this ion chromatography method for alkanolamine determination.