N. A. Al-Qahtani, L. IBRAHIM and S. JALI, Saudi Aramco, Dhahran, Saudi Arabia; and Z. ALSHAHRANI, Saudi Aramco, Hawiyah, Saudi Arabia
This experimental investigation evaluates the role of activated carbon in foam behavior management for methyldiethanolamine (MDEA)-based solvents used in gas purification processes. Foam generation and stability in amine solutions are critical operational concerns, particularly influenced by parameters such as amine concentration, temperature and flow dynamics. This study explores the potential of activated carbon, a well-known adsorbent, to act synergistically in foam control by mitigating impurity-induced destabilization and augmenting antifoaming agent performance.
Laboratory-scale foam tests were conducted using aqueous MDEA solutions, with the addition of piperazine, under controlled temperature conditions [25°C (77°F)], and amine concentration (20 wt–40 wt). The foam volume and break time were quantified using a modified ASTM D892 method. The presence of contaminants, such as formaldehyde and formic acid, were found to significantly enhance foam stability, necessitating additional control measures.
The activated carbon, selected for its high surface area and microporous structure, demonstrated effective adsorption of these contaminants. This resulted in a measurable reduction in foam volume and an increase in foam break time. The surface tension analysis of the amine solution and activated carbon interaction revealed that the carbon particles altered interfacial properties, promoting foam film drainage and destabilization.
When used in conjunction with silicone-based antifoaming agents, activated carbon exhibited a synergistic effect. At a dosage of 0.1 wt% antifoam, the combined system showed a 40% increase in foam break time and a 15%–20% reduction in foam volume compared to antifoam alone. This suggests that activated carbon may reduce the required antifoam concentration while maintaining or improving foam control efficiency.
The study further examined the operational durability of activated carbon under lab conditions and impurity load. The results indicated that optimal performance could be achieved under moderate flowrates, with minimal fouling observed.
This laboratory-based analytical study demonstrates that activated carbon is technically sound, which can extend its operation by more than 6 mos if the feed contaminations and silicone antifoams injection are well-controlled for foam control in MDEA-based gas sweetening processes. Its dual function in impurity removal and foam destabilization positions it as a promising candidate for enhancing solvent performance in extended operations. Future work should focus on pilot-scale testing to validate these findings under dynamic process conditions.
Scope of the study. Amine-based gas sweetening units (FIG. 1) are essential in removing acidic components such as hydrogen sulfide (H₂S) and carbon dioxide (CO2) from sour gas streams. The efficiency and reliability of these units are significantly influenced by foam formation, which can lead to operational disruptions, reduced absorption efficiency and increased maintenance efforts. The efficient operation of amine-based gas sweetening units relies heavily on maintaining solvent purity and minimizing foam generation. Foam formation in amine systems can lead to operational disruptions, reduced absorption efficiency and increased maintenance costs.
This study investigated the effectiveness of activated carbon in foam control within the MDEA-based gas sweetening unit at the authors’ company’s gas plant GT-7. The focus was on evaluating the filtration system’s ability to enhance solvent performance by removing foam-stabilizing impurities and optimizing antifoam functionality. Samples were collected at key stages of the filtration system before the cartridge filter, before the carbon bed and before the polishing filter to assess contaminant removal efficiency and foam behavior across the treatment stages.
Analytical methods included MDEA composition analysis, quantification of heat stable salts (HSS), elemental profiling, hydrocarbon screening and foam testing. Additionally, solid particulates retained by the filtration system were characterized using x-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM) coupled with energy-dispersive x-ray spectroscopy (EDS) to identify their origin and potential impact on foam generation.
EXPERIMENTAL METHODOLOGY
HSS analysis. The mechanism of how HSS affects solvent foaming is detailed in FIG. 2. For the analysis, an ion chromatography systema, with a conductivity detector, was used to quantify HSS species such as acetate, formate, chloride, sulfate and thiosulfate. Samples were diluted and filtered before analysis using a proprietary ion chromatography columnb.
MDEA composition. MDEA and piperazine concentrations were analyzed using gas chromatography with thermal conductivity detection (GC-TCD). Degradation products were also monitored.
Elemental analysis. Optical emissions spectroscopy was employed to determine the concentrations of metals, including silicon, iron, sodium and potassium.
Hydrocarbon screening and foam testing. Foaming tendency was evaluated by purging samples with nitrogen and measuring foam volume and break time using a graduated cylinder. Gas chromatography-mass spectrometry (GC-MS) was used to detect hydrocarbons extracted from the samples using dichloromethane and analyzed via GC–MS using a non-polar column under programed temperature conditions.
XRD. To identify crystalline phases in the solid particulates, an x-ray diffractometer was used. Quantitative phase analysis was performed using proprietary softwarec.
ESEM-EDS analysis. Solid particulates were examined using an environmental scanning electron microscope equipped with an EDS detector for elemental composition mapping.
RESULTS AND DISCUSSION
MDEA composition. All samples showed consistent MDEA content (33.48 wt%–36.71 wt%) and piperazine (5.11 wt%–5.42 wt.%). No MDEA or piperazine degradation products were detected, indicating stable solvent conditions.
The analytical results showed that the lean MDEA samples collected from gas plant GT-7 had similar amine strength measurements in the range of 33.48 wt%–36.71 wt%, whereas piperazine content was in the range of 5.11 wt%–5.42 wt% (TABLE 1). No MDEA degradation products including ethanolamine, diethanolamine or triethanolamine were detected in the samples. Additionally, the samples did not contain any glycol carryover from the dehydration processes, including ethylene glycol and triethylene glycol.
HSS. HSS analysis for acetate, formate, chloride, sulfate and thiosulfate (TABLE 2) showed similar results for all samples. Acetate had the highest concentration detected in the sample at the range of 991 parts per millions (ppm)–1,014 ppm. All samples had a chloride content below the chloride limit of 500 ppm, which is specified in Saudi Aramco’s Best Practices.
The acetate was the dominant HSS at ~1,000 ppm, while other salts such as chloride and sulfate were present at low levels, within acceptable operational thresholds.
Elemental analysis. Trace metal analysis for several metals, specifically iron, silicon, sodium, potassium, calcium, magnesium, copper, aluminum, manganese, nickel, chromium and molybdenum (TABLE 3) showed that all samples contained a minimal content of metals below the quantification limit of 10 ppm, except for silicon with a content of 9 ppm–10 ppm. This is likely due to the presence of the silicon-based antifoam chemical used to suppress foaming.
Hydrocarbon screening and foam testing. The samples were further assessed by following standard practice to find the foaming tendency. No foam was produced by the samples. The samples were also subjected to hydrocarbon screening, and similar results were obtained in all samples (FIG. 3). No dissolved paraffinic hydrocarbons were detected. However, derivatives of piperazine—including 1-methylpiperazine and 1- piperazinecarboxalydehyde—were detected. Additionally, butyl glycol and 1,2,5-trithiepane, which is a sulfur-containing compound, were present in the samples. The samples also contained other unidentified organic compounds.
No foam was observed in any of the samples, suggesting that current foam control strategies are effective under the tested conditions.
Solid particulates analysis. A black solid particulate was observed in the sample collected before the carbon bed. XRD analysis revealed a high silicon content, suggesting the presence of siliceous material. EDS analysis confirmed the presence of carbon, oxygen and fluoride, with minor contributions from magnesium, sulfur, calcium and iron.
These particulates may have originated from upstream sources or the degradation of system components. Their presence highlights the importance of activated carbon filtration in maintaining solvent purity.
With visual inspection of the samples received, it was noted that sample lean MDEA that was collected before the carbon bed contained black solid particulates (FIG. 4). These particulates were filtered and further analyzed.
Note: The samples did not contain sufficient particle concentration needed to measure particle size distribution. The XRD analysis showed that the crystalline part of the particulates primarily consisted of silicon, with possible deposits of elemental sulfur on the surface. The XRD pattern of the particulates is shown in FIG. 5. The XRD semi-quantitative phase analysis results are detailed in TABLE 4.
Further investigation of the solid particulates using EDS allowed the identification of the elements within the particulates. The EDS spectra was acquired from various regions of the sample. The analysis primarily identified carbon, oxygen and fluoride, along with varying levels of other elements, including magnesium, sulfur, calcium, silicon and iron. Representative images and spectrum of the sample are shown in FIGS. 6 and 7. Additionally, the semi-quantitative analysis of the detected elements is summarized in TABLE 5.
Takeaways. This study demonstrated that activated carbon plays a dual role in foam control within MDEA-based solvent systems by removing foam-promoting impurities and by enhancing the performance of antifoaming agents. Experimental results showed a measurable reduction in foam volume and an increase in foam break time when activated carbon was used in combination with antifoam additives.
Analytical testing of lean MDEA samples from a gas plant unit indicated that the solvent remains within acceptable quality parameters, with no evidence of degradation or contamination that could lead to foam formation. The black particulates found in one sample were identified as primarily silicon-based, likely originating from upstream processes or equipment wear.
Based on current findings, it was recommended that regular amine monitoring continue and that representative samples be collected during any future foaming events for root cause analysis. Activated carbon filtration remains a technically sound and operationally viable strategy for maintaining solvent performance and foam control in MDEA-based gas sweetening units.
Future work. Further validation under dynamic process conditions is recommended through pilot-scale testing. Long-term performance monitoring of activated carbon filters and antifoam dosing strategies will help optimize foam control and extend solvent life cycles. HP
ACKNOWLEDGMENTS
The authors would like to thank the HG Plant Engineering Division for initiating this investigation and providing access to operational data and samples.
NOTES
Thermo Fisher Scientific’s Dionex ICS 6000
Thermo Fisher Scientific’s Dionex IonPac AS25 column
MDI Jade Pro