Heat Stable Salts Research Articles

Analytical tools for monitoring glycol degradation

This paper aims to develop new methods for monitoring oxidative and thermal glycol degradation through solvent analysis. Methods for quantifying TEG, and for quantifying some degradation products (small glycols and acids), were successfully developed. The results were validated by applying two independent analytical methods for each compound monitored. The glycols were successfully quantified with gas chromatography coupled with flame ionization detection (GC-FID) and with quantitative carbon-13 nuclear magnetic resonance (13C NMR) spectroscopy. The acidic degradation compounds were successfully quantified with high-performance liquid chromatography coupled with ultraviolet detection (HPLC-UV) and heat-stable salt (HSS) analysis. The thermal stability of TEG decreased with the addition of impurities, especially formic acid. Some color changes were observed during the degradation, but they were not linked with the amount of TEG degraded. Finally, it was found that TEG samples have limited stability, even if stored cold.

Corrosion Investigation of Carbon Steel in Different Amine-Based CO2 Removal System

The steel industry is a major source of CO2 emissions, which is affecting the corrosion behavior of carbon steel. The corrosion behavior of carbon steel (C1018) absorbed for CO2 removal is examined in different blends of amine solution by adding a heat-stable salt neutralizer and increasing amine concentration. Corrosion of carbon steel using different methyldiethanolamine (MDEA)/ (5% piperazine amine solution) which had 26% amine solution that contained heat stable amine salts treated with neutralizer at 80 °C and CO2 loading was investigated. The effect of the treated solutions on the corrosion behavior was observed using either the K2CO3 treatment solution to reach 30% amine or increasing the concentration to 33% amine solution using weight loss, potentiodynamic polarization, cyclic voltammetry, and impedance measurements. A visual examination of the corroded samples of the different amine solutions was performed. XRD for phase identification and SEM for microstructure examination were used to describe the corroded surfaces and analyze the corrosion products on the specimen surfaces under different conditions. After nine days in the 30% amine solution, these analyses showed the formation of the FeCO3 protective layer. The carbon steel in 30% amine solution provides better protection, and the lowest corrosion resistance (39.9 µm/Y).

Corrosion performance of carbon/stainless steel in amine‐based solvents under different conditions for CO2 chemical absorption process

AbstractThe overall corrosion behavior of S304 stainless steel and A3 carbon steel in 30 wt.% MEA (monoethanolamine) and AMP/MEA (2‐amino‐2‐methyl‐1‐propanol / monoethanolamine) blended amine solutions at 40–100°C was investigated. The characterization analysis of the corroded material surfaces was performed, and the changes in the properties of both solvents after long‐term immersion corrosion were measured, including the accumulation of heat stable salts (HSS) and viscosity changes. The results of the long‐term immersion corrosion experiments showed that the corrosion rate of S304 stainless steel was significantly lower than that of A3 carbon steel in both amine solutions. However, the corrosion rate of both materials exhibited a similar trend, initially decreasing and then stabilizing over time. Due to the higher concentration of carbonate ions in the AMP/MEA system, it exhibited better overall corrosion resistance and degradation resistance compared to the MEA system. The main component of the corrosion product on carbon steel was identified as Fe2(OH)2CO3. The electrochemical test results showed that the corrosion current of S304 stainless steel was much smaller than that of A3 carbon steel, and its charge transfer resistance was much higher, indicating that it was less prone to electron loss in the organic amine solutions. Additionally, the AMP/MEA system exhibited superior corrosion resistance. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd.

Solvent degradation and emissions from a CO2 capture pilot at a waste-to-energy plant

Degradation and emissions of amine-containing solvents from CO2 capture plants are important to address as we are getting closer to full-scale deployment. Solvent degradation and air emissions from CO2 capture with 30 wt% monoethanolamine (MEA) were monitored at a mobile capture pilot, treating flue gas from a waste-to-energy facility in Denmark. The release of nitrosamines and nitramines was shown to be below the detection limit. Preliminary results showed that the installation of an acid wash removes gaseous degradation products from the depleted flue gas by up to 83% for MEA. However, a more in-depth investigation of the acid wash performance is needed to fully make any conclusions. The release of CO, NO, NO2, SO2, NH3, and HCl was monitored over several days. Results showed that the release of these components in the depleted flue gas is affected by both the temperature in the wash tower and the process configurations. The emissions of CO, NO, NO2, SO2, NH3 and HCl in the CO2 product stream were below 5 mg/m3. Heat stable salts accumulate over time in 30 wt% MEA with formate and acetate being the main degradation products. Accumulation of iron in the solvent did not exceed 10 mg/L during the 4 month campaign. The solvent degradation and emission results obtained in this study create a solid basis for understanding potential solvent emissions to the environment from waste-to-energy plants. Currently, the accumulation of heat stable salts in amine-based solvent seems to be the main challenge. SynopsisThese results are important to control solvent based emissions and waste products in CO2 capture technology.

Handling heat‐stable salts in post‐combustion CO2 capture: A detailed survey

AbstractThe generation of heat‐stable salts (HSSs) in alkanolamine solutions for CO2 capture processes, which is adapted for power plant technologies, exists irrespective of the class of amine solution used for the capture process. Their presence do not only trigger decrements in the CO2 absorption capacities of the solvents and contribute to further alkanolamine degradation, but also result in foaming and loss of solvents, which impacts system economics and threatens the environment. HSSs also promote the corrosiveness of the metallic structures of capture systems by lowering the pH and increasing the conductivity of the absorbent solutions. Overall, these effects substantially subvert the reliability and integrity of CO2 capture units. This survey affords sufficient background on the existence of HSSs by unraveling the flow process in a typical alkanolamine‐based CO2 capture unit with respect to their formation points and potential threats. Furthermore, the major HSSs removal and alkanolamine reclamation methodologies (electrodialysis, distillation, ion exchange, electromagnetic separation, and solvent extraction) were comprehensively explored. We believe that this review paper will benefit researchers across disciplines as we continue to explore new and complex solvent formulations to minimize the cost of CO2 capture while maximizing efficiency. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd.

Removal of heat stable salts from degraded amine solvent by “BMED+ED” two-stage electrodialysis unit

Due to the degradation reaction and the presence of acidic impurities (HCl, SO2, etc.) in the flue gas, heat stable salts (HSS) are widely present in the aqueous amine solvent for post-combustion CO2 capture. Accumulation of HSS in the solvent can lead to decreased absorption capacity and even corrosion of equipment in post-combustion capture (PCC) pilot plants. This study presents a novel “BMED+ED” two-stage electrodialysis unit for the efficient removal of HSS, including glycolate, formate, Cl−, and SO42−, from degraded amine solvent with an initial loading of approximately 0.38 mol/mol taken from the solvent loop of a PCC pilot plant after over 1000 hours of operation at real conditions. Experimental results showed that 94.93% of HSSs were removed with an initial HSS concentration of approximately 1920 ppm. The amine loss rate in the two-stage electrodialysis unit was much lower than that in a conventional ED unit, as protonated amine is further converted to organic amines by bipolar membrane electrodialysis. The energy consumption of the two-stage electrodialysis unit was 0.1643 kWh/L amine solvent, and the total cost for amine reclaiming was 1.8145 $/kg amine. This method effectively addressed the challenges of high amine loss rate in the traditional ED treatment process and hazardous wastewater disposal.

Stability of Porous Polymeric Membranes in Amine Solvents for Membrane Contactor Applications.

Membrane gas-liquid contactors have great potential to meet the challenges of amine CO2 capture. In this case, the most effective approach is the use of composite membranes. However, to obtain these, it is necessary to take into account the chemical and morphological resistance of membrane supports to long-term exposure to amine absorbents and their oxidative degradation products. In this work, we studied the chemical and morphological stability of a number of commercial porous polymeric membranes exposed to various types of alkanolamines with the addition of heat-stable salt anions as a model of real industrial CO2 amine solvents. The results of the physicochemical analysis of the chemical and morphological stability of porous polymer membranes after exposure to alkanolamines, their oxidative degradation products, and oxygen scavengers were presented. According to the results of studies by FTIR spectroscopy and AFM, a significant destruction of porous membranes based on polypropylene (PP), polyvinylidenefluoride (PVDF), polyethersulfone (PES) and polyamide (nylon, PA) was revealed. At the same time, the polytetrafluoroethylene (PTFE) membranes had relatively high stability. On the basis of these results, composite membranes with porous supports that are stable in amine solvents can be successfully obtained to create liquid-liquid and gas-liquid membrane contactors for membrane deoxygenation.

Degradation behaviour of fresh and pre-used ethanolamine

The oxidative degradation of previously used ethanolamine from three different CO2 capture pilot plants was studied in a laboratory-scale degradation setup. Different solvents behave differently under the same experimental conditions, indicating that different solvent contaminants, resulting from different operational conditions, can act either stabilising or destabilising under oxidising conditions. Some ionic compounds in the solvent seem beneficial to amine stability under oxidising conditions, while the presence of some inorganic compounds appears to have a negative effect on the stability of the solvent. The most stable pre-used ethanolamine solutions were those that contained the highest total concentrations of heat-stable salts, calcium, sodium, sulphur, potassium, and silicon. These solutions were previously used for CO2 capture from a lignite-fired power plant and a waste-to-energy plant. The least stable amine solution had a higher concentration of metal ions like chromium, magnesium, and zinc, making these suspects of deteriorating solvent stability.

Reclaiming of Amine CO2 Solvent Using Extraction of Heat Stable Salts in Liquid-Liquid Membrane Contactor

Amine CO2 solvents undergo oxidative degradation with the formation of heat stable salts (HSS). These HSS reduce the sorption capacity of amines and lead to intense corrosion of the equipment. In our work, we propose a membrane-supported liquid-liquid extraction of the HSS from alkanolamines. For this purpose, a hollow fiber membrane contactor was used for the first time. A lab-scale extraction system on the basis of a hollow-fiber liquid-liquid membrane contactor with hollow fiber ultrafiltration polyvinylidenefluoride and polysulfone membranes has been studied. The extraction of the HSS-ions from a 30 wt.% solution of monoethanolamine was carried out using a 0.25-1 M solution of OH-modified methyltrioctylammonium chloride in 1-octanol as an extractant. It has been shown that >90% of HSS ions can be extracted from the alkanolamine solvent within 8 h after extraction. The results obtained confirm the possibility of using membrane extraction with a liquid-liquid membrane contactor for the reclaiming of amine CO2 solvents to increase the general efficiency of carbon dioxide capture.

Box-Behnken Response Surface Method to Optimize Amine Liquid Purification Process Based on Ion Exchange

In the process of recycling MDEA (N-methyldiethanolamine) solution in a terminal decarburization system of CNOOC, the quality of MDEA solution was deteriorated due to the generation and accumulation of impurities such as solid suspended solids and heat stable salts, which led to blockage and unstable operation of pipeline equipment in the decarburization system, thus affecting the CO₂ removal effect of the solution, the Box-Behnken effect surface method was used to design the three main factors of the ion exchange-based amine purification process: the continuous adsorption time of the amine solution, the resin regeneration temperature and the resin regeneration time. Taking the conductivity of the MDEA solution after purification as the response function, a corresponding mathematical model was established to optimize the test method, and the correlation coefficient R² (R²=0.9418) of the regression equation obtained was greater than 0.9, indicating that the predicted value had a high correlation with the experimental value, and the test method was optimized accordingly. The best test conditions obtained were: the continuous adsorption time of amine solution was 50 min, the resin regeneration temperature was 40°C, and the resin regeneration time was 30 min. Under this condition, the conductivity of the purified MDEA solution was 1.56 ms/cm, and the salt content was 0.8%. The experiment was repeated 3 times according to this method, and the salt content of the MDEA solution after purification was ≯0.8%, which met the technological requirements. The Box-Behnken experimental design method was feasible for amine solution purification process optimization screening based on ion exchange, and the predicted value of the mathematical model was consistent with the experimental observation value.

Quantification of Amines in Refinery Process Water via Surface-Enhanced Raman Spectroscopy

Amines are used in crude oil production, natural gas recovery, and hydrocarbon refining as hydrogen sulfide scavengers, corrosion inhibitors, and pH control neutralizers. Residual amines can be detrimental to the refining process, such as forming heat-stable salts that lead to corrosion-inducing deposits or causing nitrification of wastewater streams. Traditional methods for amine analysis such as ion chromatography are complex, time-consuming, and not adapted to field deployment. We present a new method using surface-enhanced Raman spectroscopy for amine quantification with a focus on two problem-causing tramp amines: monoethanolamine and methylamine. This method is calibration-free, accurate across spectrometers, stable over years in laboratory-standard solutions and in real-world process samples, and can be performed by minimally trained operators within less than 5 min.

Perstraction of Heat-Stable Salts from Aqueous Alkanolamine Solutions

Amine absorption processes designed to remove acid gases from gas streams generally face a major challenge of solvent degradation. This degradation leads to the formation of heat-stable salts (HSS), corrosive agents that irreversibly bind free alkanolamine. The present study proposes, for the first time, a method for HSS perstraction using a liquid–liquid membrane contactor that allows HSS to transfer through porous membranes from the solvent into a hydrophobic extractant represented by a methyltrioctylammonium solution in 1-octanol. The perstraction provides selective extraction of HSS anions without direct mixing of liquid phases or the formation of stable emulsions of the solvent and the extractant. For this purpose, a number of industrial and laboratory porous membrane samples fabricated from polyvinylidene fluoride, polypropylene, and polysulfone were investigated. Their chemical and morphological stability, surface properties, and transport properties were tested under prolonged (>600 h) contact with a model solvent (an aqueous monoethanolamine solution) and with the components of the selective extractant. The feasibility of HSS perstraction was demonstrated using the formic acid (as an HSS model) extraction from the model solvent. The most promising results were obtained for a system with a polyvinylidene fluoride membrane: up to 50% of formic acid was extracted over 18 h.

Removal of heat-stable salts from lean amine solution using bipolar membrane electrodialysis

Traditional resin exchange processes for the removal of heat-stable salt (HSS) from lean amine solutions have limited efficiency, and require large amount of alkali for regeneration, causing a serious negative impact on the sustainable environmental development. In this study, a new bipolar membrane electrodialysis (BMED) process was proposed to replace the original resin-based method for the removal of HSS from practical lean amine liquids (from a natural gas factory of PetroChina Company). The experimental conditions of current density, volumetric ratio, HSS concentration, and etc., were systematically investigated. It was found that a high HSS removal efficiency of up to 95.7% with an extremely low loss rate of the organic amine of down to 1.39% can be obtained, under the optimal current density of 60 mA/cm 2 . A continuous operation verified the long-term stability of BMED for a high-efficiency HSS removal rate of up to 80.3% after a 600-h duration. From the findings in this study, we develop a conceptual exploration describing the BMED process for the separation of HSS from practical desulfurization wastewater, beyond the lean amine liquids, offering a guidance for their potential industrial applications. • A zero-discharge process was proposed for the removal of heat-stable salt. • A variety of process conditions were explored for the impact of HSS separation. • The removal of HSS was over 95%, which is acceptable for industrial scale.

Mechanistic analysis of post-combustion CO2 capture performance during amine degradation

Degradation of amine is often regarded as a major problem for amine-based post-combustion CO2 capture. However, the observed regeneration energy in long-term pilot plant operations does not necessarily increase, regardless of the accumulation of degradation compounds. This paper provides a mechanistic explanation for this seemingly paradoxical behavior by focusing on the influence of heat stable salts and the CO2 loading range on solution properties. Post-combustion CO2 capture using degraded amine solution was simulated in Aspen Plus®, and the influence of heat stable salts on CO2 loading, solution properties, and regeneration energy were analyzed. Results indicate that the alteration of the operational CO2 loading range and the physical properties of heat stable salts themselves cause changes in solution properties that dictate overall energy consumption, such as viscosity, vapor liquid equilibrium, and specific heat capacity. These effects often offset each other to some extent, thereby obscuring the influence of individual factors on regeneration energy. These counteracting effects can largely explain the seemingly paradoxical behavior of post-combustion capture maintaining relatively low energy consumption even when amine degradation proceeds.

Time- and temperature-dependence of the anticorrosion effect of sodium sulfide on Q235 steel for post-combustion CO2 capture system

As a heat stable salt, sodium sulfide remains thermally-unregenerable during the regeneration process for post-combustion capture. Therefore, it became important to undertake a full assessment of its potential presence in the system. The paper investigates the mechanism and influence of sodium sulfide on the corrosion behavior of Q235 steel in amine-based post-combustion CO2 capture technology with respect to exposure time and temperature. The inhibitive influence of sulfide in the system was first confirmed by electrochemical techniques, while gravimetry was used to evaluate the effect of time and temperature on the inhibitive actions. SEM/EDX and XPS were used to characterize the corrosion product films on the steel surface. The behavior of sulfide was largely dependent on its concentration as its inhibition ability decreased with increasing concentration, and this is credited to the presence of FeS corrosion film layer. Time-dependent corrosion studies of steel conducted at 50 °C for the solution with 0.05 M and 0.1 M sulfide showed that the inhibition efficiency decreased from 89.1% and 75.0% to 82.4% and 68.6%, respectively, after 7 and 14 days immersion. At 80 °C, the inhibition efficiency of 0.05 M sulfide decreased from 89.1% to 48.9% after 7 days immersion and 82.4% to 46.1% after 14 days immersion. Together with FeS layer, FeCO3, Fe2O3 were also confirmed on the steel surface by XPS measurement. The research provides practical information on the influence of sulfide in the absorber and rich-lean heat exchanger sections of a CO2 capture unit.

Removal of Heat Stable Salts from Degraded Amine Solvent by “Bmed+Ed” Two-Stage Electrodialysis Unit

Removal of Heat Stable Salts from Degraded Amine Solvent by “Bmed+Ed” Two-Stage Electrodialysis Unit

Applying intelligent approaches to estimate the removal efficiency of heat stable salts from lean amine via electrodialysis

Intelligent approaches based on radial basis function (RBF) neural networks and genetic programming (GP) were used to establish accurate models for estimating the removal efficiency of heat stable salts from lean amine via electrodialysis. The operating time, current intensity, membrane types, HSS concentration, and kind of concentrated solution were lumped into dimensionless groups. The groups with the most influence were selected based on the Pearson's correlation matrix for the models’ inputs. The RBF model showed an excellent agreement with real data with average absolute relative error (AARE) of 1.90% and R2 of 99.21%. Then, an explicit empirical correlation was developed for the removal efficiency using the GP technique, which yielded AARE and R2 values of 5.74% and 96.35%, respectively. The performance of the GP and RBF models for estimating the removal efficiency of different ions for different types of membranes and operating conditions were assessed and reasonable results were achieved. Finally, to identify the most effective dimensionless groups to describe the removal efficiency, a sensitivity analysis based on the developed GP and RBF models was accomplished.

Influence of interface‐related parameters on some heat stable salts in the corrosion studies of carbon steel for post‐combustion CO2 capture

AbstractThe effect of flow and temperature on the corrosion behavior of carbon steel in an aqueous methyldiethanolamine solution containing different heat stable salts, such as sodium sulfate, sodium sulfite and sodium thiosulfate, has been studied. The introduction of flow and increase in temperature generally caused an increase in the corrosion rate of carbon steel but the presence of the heat stable salts affected the corrosion behavior to different extents. Sulfate increased the corrosivity of the aqueous methyldiethanolamine solution, thus showed accelerated corrosion behavior in the presence of flow and with increase in temperature when compared with the solution without heat stable salts. The presence of sulfite reduced the corrosivity of the methyldiethanolamine solution due to its oxygen scavenging ability. Although flow and temperature stimulated an increase in the corrosion rate of carbon steel, the corrosion inhibiting effects of sulfite ions increased with the salt concentration. Also, the presence of sodium thiosulfate caused a reduction in carbon steel corrosion. Its inhibition ability is largely the result of the formation of FeS product layer resulting from its disproportionation reaction. This layer offered a slight resistance to the influence of flow and increase in temperature when compared with the system without heat stable salts.

Transient H2S content rise in the effluent of a natural gas treating unit: Role of COS hydrolysis and heat stable amine salts

In response to expanding requests towards natural gas usage as a key energy source and vital feedstock, revamping current gas refineries to provide additional capacity and meet the sustainability limitations is considered a crucial essence. In this work, the behavior of a gas refinery after switching its amine solution from diethanolamine to methyldiethanolamine was evaluated. The plant's main goals by this change, i.e., increase sweetening capacity and lowering energy consumption intensity was fulfilled. However, after some overhaul services, the hydrogen sulfide content of final treated gas raised from permissible limit, i.e., 3 ppm at least for three initial months of operation, and then progressively reduced to around 2 ppm. Systematic investigation of plant data shows that carbonyl sulfide hydrolysis in the dehumidification section as downstream of the sweetening section would increase the hydrogen sulfide content of the treated stream. Meanwhile, the gradual formation of heat stable amine salts in amine solution promotes its absorption capacity, which can counterpoise the effect of further hydrogen sulfide generation due to carbonyl sulfide hydrolysis in the subsequent section. Monitoring heat stable amine salts concentration in amine solution suggests that there should be a minimum level of 0.25 wt.% of these compounds to achieve suitable hydrogen sulfide content in final treated gas.

Use of chicken feathers as potential adsorbent for the reclamation of industrial lean methyl diethanolamine solutions

ABSTRACT Sweetening units using methyl diethanolamine (MDEA) solvent are instrumental in removing hydrogen sulfide and carbon dioxide from natural gas. However, over time MDEA degrades and loses its scavenging efficiency due to the formation of heat-stable salts (HSS) that are hard to remove. Chicken feathers (CFs), a poultry waste by-product, are rich in functional groups that could help to remove HSS from alkanolamine solutions. CFs were characterized using XRD, SEM-EDX, TGA, DSC, and BET. FTIR spectroscopy analysis confirmed the presence of hydroxyl and amide groups that were responsible for the total organic acid (TOA) anions adsorption. The Freundlich model best fitted the equilibrium adsorption data with a maximum uptake capacity of 525 mg/g at 298 K. Kinetic analysis showed that the Pseudo-Second-Order model best fitted results with a rate constant of 0.0006 min−1. The equilibrium thermodynamic study showed that the biosorption process was spontaneous. CFs exhibited good recyclability and high TOA uptake capacity even after five cycles using absolute ethanol as the eluent, maintaining 88% of the adsorption ability. The results demonstrated that CFs could be employed as a low-cost alternative to commercial activated carbon absorbents that are currently used to clean industrial lean MDEA aqueous solutions from their HSS contaminants.