H2S-CO2 gas separation with ionic liquids on low ratio of H2S/CO2.

Acid gas removal, especially H2S and CO2, is an essential process in natural gas processing. In this research, 1-butyl-3-methylimidazolium bromide [bmim][Br] ionic liquid was analyzed as a hydrophobic solvent with has high selectivity to H2S as an environmentally friendly solvent to absorb acid gas from natural gas with low H2S/CO2 concentration in ambient temperature and pressure. The absorption performance of pure [bmim][Br] ionic liquid was compared with various amine solutions, such as monoethanolamine (MEA), triethanolamine (TEA), and methyldiethanolamine (MDEA), as well as the mixture of [bmim][Br]-MDEA with various concentration. As a result, pure [bmim][Br] ionic liquid had high selectivity to H2S compared with conventional amine solutions. In addition, the mixture of [bmim][Br]-MDEA with the mass ratio of 1:3 provided the highest H2S/CO2 selectivity of 6.2 in certain absorption conditions due to free tertiary amine attached in the cations of ionic liquids that can attract more H2S to its functional site.

Introduction

Even though fossil fuels have been predicted to decline, they have remained the primary energy source for years. Natural gas is ranked the third most consumed fossil fuel after oil and coal, with 24% of world consumption in 2015. Its production is moderately projected to peak at 140–217 EJ/y between 2025 and 2066 [1]. Based on current production and consumption trends, the energy consumption share from natural gas is predicted to increase to 25% of global fossil fuels consumption in 2035 compared with the share of 22% in 2015, making natural gas a substantial energy source [2].

Generally, in natural gas processing, hydrogen sulfide (H2S) and carbon dioxide (CO2) are produced during operation in different concentrations based on location and underground soil characterization of the natural gas sources. CO2 is a significant greenhouse gas (GHG) that has the most considerable involvement in climate change, and it is typically released from hydrocarbon combustion. In processed streams, CO2 is categorized as acid gas that can form acids that corrode pipelines, reactors, and other equipment in the presence of water. Furthermore, CO2 provides no heating value, so it must be removed to meet gas quality specifications. The level of CO2 in commercial natural gas is typically limited to be less than 3% [3].

Meanwhile, H2S is a toxic, colorless, highly flammable gas and has an odor that is described similarly as a rotten egg. The acid property of this gas also makes it corrosive to the pipeline and could potentially poison the catalyst. From an environmental standpoint, the combustion of fuels containing H2S will cause the release of toxic sulfur oxides to the atmosphere, causing acid rain which has adverse impacts on human health [4]. Therefore, removing unacceptable amounts of H2S and CO2 from fossil fuel streams early before their further treatment is essential.

Conventional natural gas processing requires H2S and CO2 to be removed in an acid gas removal unit (AGRU) using aqueous amine absorption processes. In the operations with steam reformer units such as in ammonia production and methanol synthesis processes, H2S has to be separated early before the reformer because it will harm the reforming catalyst. Meanwhile, CO2 that will be more produced by water gas shift reaction in the reformer is separated before ammonia production since high purity of hydrogen is required [5]. Several groups of alkanolamines include monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), and methyldiethanolamine (MDEA) are commonly used for the natural gas sweetening process. However, the amine process application has some disadvantages, especially the loss of amine solution during regeneration, the degradation of amine to form corrosive byproduct, the high pressure for absorption, and the high temperature for desorption lead to expensive process [6].

For H2S removal, other processes can be applied, such as physical adsorption, chemical process, biological method, and electrochemical. Physical adsorption is appropriate to remove H2S even at low concentrations using common adsorbents, such as activated carbon, alumina, silica, zeolites, and metal oxides (Zn, Cu, Fe, etc.). The chemical process like the Fe3O4 involving reaction can be applied for H2S removal at high temperature and high concentration of H2S with the reaction occurs as follow:

The biological method was used to convert dissolved H2S to elemental sulfur using sulfur-oxidizing bacteria such as Thiobacillus. A similar concept was applied in liquid redox system that applying chemicals instead of microorganism [7,8]. In comparison, the indirect electrolysis method can be a very promising method that converts H2S in gas streams to produce both sulfur and hydrogen simultaneously using vanadium dioxide in acidic aqueous media [9].

For CO2 removal, there are two most favorable routes, i.e., chemical and physical absorption. The most popular one is chemical absorption using amine solutions with high operating costs. While physical absorption, that uses a solvent such as methanol (Rectisol), polyethylene glycol-dimethyl ether/PEG-DME (Selexol), n-methyl-2-pyrrolidone/NMP (Purisol), and propylene carbonate/PC (Fluor) are available at low capital and operating cost. This method applies the solubility of CO2 in the solvent as the driving force. Generally, the solubility increases with the increase of pressure and the decrease of temperature of the absorption process. Thus, the optimum condition for the CO2 absorption process occurs at high pressure and low temperature [10,11].

In addition, polymeric membranes and pressure swing adsorption (PSA) have also been proven as suitable methods for CO2 removal. Moreover, solid adsorbent like calcium is being investigated for the CO2 removal method. However, high-temperature operations for adsorption (600–800 °C) and desorption (over 900 °C) make this method hardly applied as a CO2 removal method. Moreover, the primary challenge of this method is the deactivation of CaO after the regeneration process due to the increased thickness of CaCO3 on CaO leads to the decrease of available surface area for carbonation [12,13].

Recently, room temperature ionic liquids (RTILs) have been introduced as attractive materials for CO2 and H2S removal due to their unique properties such as good thermal stability, high polarity, and considerably low vapor pressure. In the natural gas case, the separation of low concentration ratio of H2S/CO2 requires ionic solvents such as RTILs with high selectivity to H2S. Ionic liquids have a melting point below 100 °C, so it has a high potential to be used as a solvent for the gas separation process and sulfur recovery due to their unique physic-chemistry properties produced by cation and anion modification [14]. Ionic liquids are proposed as a strong solution to absorb H2S regarding CO2 presence due to the strong bond between H2S and RTILs. This specific bond increases gas solubility that promotes H2S separation from low soluble molecules such as hydrocarbons and CO2. It also encourages H2S gas to be released during the regeneration phase to achieve lower energy consumption [15].

Previously, Jalili et al. [16] investigated the comparison of H2S and CO2 solubility in three different 1-butyl-3-methylimidazolium [bmim] ionic liquids, including [bmim][PF6], [bmim][BF4], and [bmim][Tf2N], at temperatures ranging from 30 °C to 70 °C and pressures up to 10 bar. It was found that H2S solubility was always higher than CO2 solubility in those three ionic liquids. Zhang et al. [17] measured the selective separation of H2S and CH4 or H2S and CO2 in neutral and basic ionic liquids. It was found that neutral ionic liquids such as [bmim][TfO] and [bmim][CF3SO3] can remove H2S and CO2 from natural gas simultaneously. In contrast, basic ionic liquid such as [bmim][Ac] can be potentially used for selective removal of H2S from natural gas. Akhmetshina et al. synthesized [bmim][doc] ionic liquid that has H2S solubility about 4–5 times higher than conventional ionic liquids [18]. Recently, Zhang et al. [19] developed novel azole-based protic ionic liquids (PILs) 1,5-diazabicyclo [4,3,0] non-5-ene 1,2,4-1H-imidazolide [DBNH][1,-2,4-triaz] that has H2S solubility 20–30 times higher those in conventional ILs. Our previous work [15] proved that [bmim][Br] ionic liquid could selectively separate H2S from CO2 from H2S/CO2 mixture compared with n-methyldiethanolamine (MDEA-1) and the commercial mixture of MDEA and activator (MDEA-2) at ambient temperature and pressure. Table 1 shows H2S selectivity of [bmim][Br] ionic liquid compared with MDEA-1 and MDEA-2.

Table 1

Solubility and selectivity of H2S and CO2 in ambient temperature and pressure [15].

Solvent	H2S (mole/mole)	CO2 (mole/mole)	SelectivityH2S/CO2
MDEA-1	0.0183	0.0481	0.38
MDEA-2	0.0206	0.1392	0.15
[bmim][Br]	0.0313	0.0090	3.48

The imidazole-halide based ionic liquids are a complex structure carrying several sites that can specifically respond and interact with a guest molecule. As such, the [bmim][Br] ionic liquid is selected in this study because it is easy to prepare, stable, and has a basic anion [15]. In this research, the selectivity of H2S to CO2 absorption performance using [bmim][Br] ionic liquid was analyzed, especially for natural gas with a low concentration of H2S/CO2. The amine solutions, such as MEA, TEA, and MDEA, as well as water and the mixture of [bmim][Br]-MDEA solution with the mass ratio of 1:1, 1:3, and 3:1, were also used to compare the absorption performance of [bmim][Br] ionic liquid.

Experimental

Ionic liquids synthesis

The [bmim][Br] ionic liquid is synthesized in two steps processes include preparation and separation. In the preparation step, about 32 mL of 1-bromobutane and 48 mL of toluene are mixed in a dropping funnel. Later, the mixed solution is weighted and cooled for 2 h. Meanwhile, another mixed solution contains about 14 mL the 1-methylimidazole and 21 mL of toluene are prepared in a three-neck flask. The mass of the solution is measured by weighing the three-neck flask before and after mixing. After the dropping funnel has cooled down, the apparatus is then assembled as visualized in Figure 1.

Figure 1

The experimental setup of ionic liquids synthesizing apparatus.

The mixture of 1-bromobutane and toluene in the dropping funnel is dropped to the three-neck flask while the solution is stirred at 300 rpm for 2.5 h until the dropping funnel is empty. After the mixing process, the three-neck flask is heated to 80 °C while the solution is continued to be stirred at 300 rpm for 12 h. The water bath is filled with ice and oil to keep the temperature stable. The cooling water from the water bath is introduced to the condenser part to condense evaporated liquid. At last, the two-phase solution is formed inside the three-neck-flask containing the ionic liquids at the bottom (yellowish color) and impurities consisting of excess toluene and bromobutane at the top.

In the separation step, a rotary evaporator uses to separate [bmim][Br] ionic liquid from toluene impurities by evaporating the toluene at vacuum pressure so that [bmim][Br] ionic liquid is separated from the two-phase solution. This separation is conducted at 82 °C and 0.27 bar with a mixing speed of 75 rpm. The produced ionic liquid is then characterized by 13C-NMR and 1H-NMR.

Gas absorption

In this step, the selectivity and absorption capacity of H2S and CO2 in [bmim][Br] ionic liquid and other solvents are determined. The experiment is done at both ambient temperature and pressure. The feeds are 100%-v of CO2 gas and 1%-v (CH4 99%-v) of H2S gas in 10,000 ppm-v. The CO2 gas absorption is done by introducing 6 mL/min CO2 gas to a vial that contains 5 mL of absorbent. The excess CO2 gas is then released into the atmosphere. The same procedure applies to H2S gas absorption. However, after going through the absorbent vial, excess H2S gas goes to a vial containing NaOH before being released to the acid chamber. The absorbents used in the gas absorption experiment are (1) pure water, (2) amine solutions, which are MDEA, TEA, and MEA, (3) [bmim][Br] ionic liquid with a range of water content of 0 wt%, 25 wt%, 50 wt%, and 75 wt%, and (4) [bmim][Br]-MDEA mixture with the mass ratio of 1:3, 1:1, and 3:1.

The gravimetry analysis is used to analyze the absorption capacity of H2S and CO2 by weighting solvent mass every 5 min for 60 min for every run. Herein, the solubility of each gas is represented by the total gas mole absorbed every mole solvent and calculated as follows:where Mr is the molecular weight for each gas and i represents CO2 or H2S. Meanwhile, the selectivity of H2S/CO2 is calculated by dividing H2S solubility with CO2 solubility in the same solvent as follows:

Results and discussion

Ionic liquids characterization

13C-NMR analysis

Figure 2 shows the spectrum of 13C-NMR result for [bmim [Br] ionic liquid, which determines how many carbon atoms are present in the molecule. The spectrum shows there were eight carbon atoms in the molecule that were represented by eight peaks. The peaks with carbon chemical shift (δC) more than 90 ppm (peak 1–3) represented sp2 hybridization that illustrates double-bonded carbon. Meanwhile, other peaks with δC less than 90 ppm (peak 5–9) represented sp3 hybridization that characterizes single-bonded carbon. The results were matched with the chemical structure of [bmim][Br], which has eight carbon atoms with the exact number of hybridizations as shown by Figure 3. Herein, the structure of [bmim][Br] ionic liquid was illustrated to have three double-bonded carbon atoms (sp2) shown by the bond numbers 2, 3, and 4. In comparison, five single-bonded carbon atoms (sp3) were indicated by the bond numbers 1, 5, 6, 7, and 8. Thus, characterization using 13C-NMR matched the [bmim][Br] structure, and the synthesized product could be confirmed as [bmim][Br] ionic liquid.

Figure 2

13C-NMR spectrum result of [bmim][Br] ionic liquid.

Figure 3

[bmim][Br] chemical structure.

1H-NMR analysis

This characterization was used to determine how many protons (H atoms) and their position inside the molecule. The 1H-NMR spectrometer could detect the proton chemical shift that represents the spin of the core molecule. The proton chemical shifts were represented by δH with ppm (part per million) unit. The multiplicity concept (n-1) as part of 1H-NMR characterization could determine how many hydrogen atoms are present in the neighboring cluster.

Figure 4 shows the result of 1H-NMR characterization on [bmim][Br] ionic liquid. The result shows that the peak number 4 with δH of 10.1403 ppm was H atom situated at the aromatic cluster and bonded with two N atoms. Meanwhile, the peak number 1 with δH of 4.0275 ppm was a methyl cluster with a direct bond to an aromatic cluster and the peak number 5 with δH around 4.2 ppm represented a carbon atom with a bond with the N atom. Moreover, carbon atoms in the structure of ionic liquids were characterized by the peak number 6 with δH around 1.8 ppm, the peak number 7 with δH around 1.3 ppm, and the peak number 8 with δH around 0.8 ppm.

Figure 4

1H-NMR characterization result of [bmim][Br] ionic liquid.

The peak number 4 is situated on the left because the carbon atom is bonded with two nitrogen atoms with high electronegativity. This phenomenon caused a lack of electrons in carbon number 4 and moved further from δH = 0. Using the multiplicity concept (n-1), the carbon number 8 had three peaks that show two neighboring protons corresponding with H atoms bonded with the carbon number 7. Besides those results, the peak at δH = 2.53 ppm was suspected of belonging to DMSO as impurities. The results of 1H-NMR characterization were consistent with [bmim][Br] structure. Thus, it could be concluded that the [bmim][Br] was successfully synthesized with the appropriate form.

Gas absorption in water and amine solution

Figure 5 shows the CO2 gas absorption using water and amine solutions that includes pure water/aqua DM, MDEA (7.6 wt% H2O), TEA (75.43 wt% H2O), and MEA (75.88 wt% H2O). The result indicated that all the solutions could absorb CO2 gas except pure water in an ambient condition showing the weak bond between CO2 and water caused difficulties in absorbing the gas. Specifically, CO2 has poor solubility in water at low operating pressure, leading to a high amount of water required to absorb a small amount of CO2. It is well known that the solubility of CO2 in water increases by increasing the operating pressure and lowering the operating temperature [20,21].

Figure 5

CO2 gas absorption in water and amine solutions.

In comparison, TEA and MEA also have poor CO2 absorption performance since they could not react directly with CO2. Their chemical structure forces the CO2 to react firstly with water and form carbonic acid before reacting with the alkanolamine group. In contrast, the chemical structure of MDEA enables it to react directly with CO2 so it has an exponential absorption profile in absorbing CO2 in 60 min compared with other amine solutions. Moreover, the low water content of MDEA did not interfere with the gas absorption significantly [22]. In addition, Kim et al. [23] said that at varied temperatures, CO2 mole/MEA mole is much higher than CO2 mole/TEA mole, making CO2 have a higher solubility in MEA than with TEA.

Meanwhile, H2S absorption using pure water, MDEA (7.6 wt% H2O), TEA (75.43 wt% H2O), and MEA (75.88 wt% H2O) are shown in Figure 6. It can be seen that H2S is only absorbed by amine solution because the instant reaction occurs between H2S and the primary, secondary, and tertiary amine solutions [24]. However, the hydroxyl cluster in amine solutions tends to pull electrons that inhibit nitrogen in the amine cluster from binding with H2S [25]. As a result, TEA with the highest hydroxyl cluster absorbed the least H2S compared to the other amine solutions. From Figure 6, it can be seen that MDEA had the best H2S absorption performance that increases with linear profile compared with TEA and MEA. Herein, as stated above, this might have been caused by the low water content of MDEA that resulted in optimal gas absorption.

Figure 6

H2S absorption in water and amine solution.

Gas absorption in mixture of water and [bmim][Br] ionic liquid

Figure 7 compares the solubility of CO2 in [bmim][Br] ionic liquid with the concentration of 100 wt%, 75 wt%, 50 wt%, and 25 wt% in the mixture with water. One can see that the total CO2 mole absorbed in [bmim][Br] ionic liquid was increased with the decrease of water content increment in [bmim][Br], and the pure ionic liquid solution absorbed the most of CO2 in 60 min of the absorption process. Even though the absorbed CO2 slightly decreased at 40 min of absorption time for pure [bmim][Br] ionic liquid, the absorption did not reach the saturated point until 60 min absorption time. The same trend could also be observed in H2S absorption for the same duration as shown in Figure 8. The pure [bmim][Br] solution had the best H2S absorption performance while there was no H2S absorbed in [bmim][Br] 75 wt% and 50% wt% solutions.

Figure 7

Solubility of CO2 in [bmim][Br] ionic liquid for various concentration.

Figure 8

Solubility of H2S in [bmim][Br] ionic liquid for various concentration.

As stated above, pure water had inferior performance in absorbing CO2 and H2S. In the mixture with ionic liquid, water addition to [bmim][Br] would create bonds with anion and cation in ionic liquid to create clusters and upset the structure of the ionic liquid. Previous research found that CO2 and H2S absorptions are influenced by anion and cation interaction in ionic liquids structure with the acid gas. In the mixture of ionic liquids and water, the presence of hydrogen bonds in the water structure can significantly affect the properties of ionic liquids. In addition, the bond competitions between water–water, cation-anion, and water–ionic liquids interactions in the mixture of [bmim][Br]-water hinder the interaction of the solvent with the gas. Hence, those reasons diminish the capability of mixture [bmim][Br]-water to absorb gases [15,26]. Therefore, the pure [bmim][Br] ionic liquid was the optimum solvent to absorb CO2 and H2S gas.

Gas absorption in mixture of [bmim][Br] ionic liquid and MDEA

Figure 9 and Figure 10 show the gas absorption results in the mixture of [bmim][Br] ionic liquid and MDEA with the mass ratio of 1:1, 1:3, and 3:1 for CO2 and H2S at a constant flow rate of 6 mL/min, respectively. As shown by Figure 9, the CO2 gas absorption profile by three of the mixture increased exponentially during 60 min absorption time with the mixture of [bmim][Br]-MDEA with 1:3 mass ratio has the best performance. Yu et al. [27] indicated that higher amine concentration in the mixture with ionic liquids is favorable for CO2 absorption. While Figure 10 shows that the mixture of [bmim][Br]-MDEA with 1:3 mass ratio absorbed the most H2S as well compared with other mixing proportions with relatively constant absorption profiles. Haghtalab and Afsharpour [28] confirmed that high ionic liquids concentration in the mixture with amine solution leads to lower H2S absorption, especially at high temperatures. Both results show that the mixture of [bmim][Br]-MDEA with a 1:3 mass ratio absorbed more H2S than CO2 during 60 min absorption time. In the CO2 absorption case, the CO2 absorbed in the mixture solvents increases in 60 min. However, in the H2S absorption case, the absorbed H2S reaches its saturated point at the beginning of the absorption process. Huang et al. [29] confirmed that H2S absorption has a higher rate than CO2 absorption in the mixture of ionic liquids-amine solvent.

Figure 9

CO2 absorption in the mixture of [bmim][Br] and MDEA.

Figure 10

H2S absorption in the mixture of [bmim][Br] and MDEA.

The idea of mixing ionic liquids with amine solutions provides relatively lower cost and lower partial pressures compared with the conventional acid gas removal process using amine solutions [30]. The mixture of [bmim][Br] and MDEA creates functionalized ionic liquids with a free tertiary amine group tethered on the cations of the ionic liquids. As a result, increasing MDEA amount increases free tertiary amine group base properties on the solvent mixture as a functional site for CO2 and H2S absorption [29]. Hence, it enhances the solubility of CO2 and H2S in the solvent mixture compared with those solvents in pure conditions.

H2S/CO2 selectivity in various solvents

Table 2 shows H2S/CO2 selectivity in MDEA, [bmim][Br], and their mixture at various proportions that only applied to CO2 gas feed with 100%-v purity and H2S gas feed with 1%-v purity at ambient condition. It should be noted that the solubility of CO2 and H2S in amine solutions decreases by the decrease of partial pressure and the increase of operating temperature [31]. Thus, the very low H2S/CO2 feed ratio used in this research might be why commercial MDEA solution is poorly selective to H2S compared with synthesized [bmim][Br] ionic liquid at room temperature. In comparison, the high H2S/CO2 selectivity by pure [bmim][Br] ionic liquid is determined by the interaction of hydrogen bond in H2S with [bmim][Br] ionic liquid cation that generates stronger bonding than the interaction between CO2 and the ionic liquid. The interaction between the anion atom, Br, and S atom of H2S is dominantly affected by the affinity of [bmim][Br] ionic liquid to H2S as well [15].

Table 2

H2S/CO2 selectivity at 60 min of absorption in ambient temperature and pressure.

Solvent	CO2 mole/solvent mole	H2S mole/solvent mole	H2S/CO2 selectivity
MDEA	0.228	0.009	0.038
[bmim][Br]	0.025	0.060	2.417
[bmim][Br]:MDEA = 1:3	0.173	1.075	6.222
[bmim][Br]:MDEA = 1:1	0.136	0.059	0.439
[bmim][Br]:MDEA = 3:1	0.040	0	0

Table 3 summarizes and compares the reported CO2 and H2S separation results using various ionic liquids as the solvent at a specific temperature and pressure [18,32,33,34]. It is suggested that pure synthesized [bmim][Br] ionic liquid had relatively good selectivity in H2S/CO2 separation compared with other pure ionic liquids. Herein, the mixture of [bmim][Br]-MDEA with a 1:3 mass ratio increased the selectivity towards H2S significantly compared to the separation performance of any other pure ionic liquids. It should be noted that hydrophobic protic ionic liquids formed by hydrophobic functionalized ionic liquids tethered with a free tertiary amine group on their cations were expected to have absorption selectivity of H2S from CO2. In addition, the reaction between CO2 with tertiary amine hardly occurred, both thermodynamically and kinetically. This phenomenon is due to the absence of active protons in the CO2 molecule [35]. Hence, a high amount of MDEA in the solvent mixture with [bmim][Br] prefers to absorb H2S more than CO2, even in the low H2S/CO2 feed ratio.

Table 3

Comparison of H2S/CO2 selectivity in this research with various reported ionic liquids.

Solvent	Temperature (K)	Pressure (kPa)	H2S/CO2 selectivity	Ref.
1-buthyl-3-methylimidazolium bis(2-ethylhexyl) sulfosuccinate [bmim][doc]	303.15	207.3	3.488	[18]
1-(2-Hydroxyethyl)-3-methylimidazolium Tetrafluoroborate [hemim][BF4]	303.15	175	2.167	[32]
1-ethyl-3-methylimidazolium ethylsulfate [emim][EtSO4]	303.15	122	1.667	[33]
1-octyl-3-methylimidazolium tetrafluoroborate [Omim][BF4]	303.15	1021	3.052	[34]
[bmim][Br]	303.15	101.3	2.417	This work
[bmim][Br]:MDEA = 1:3	303.15	101.3	6.222

Conclusions

The [bmim][Br] ionic liquid was successfully synthesized in this study. Its capacity and selectivity to separate CO2 and H2S from natural gas were investigated, especially for the low ratio of H2S/CO2 in ambient temperature and pressure. The absorption performance results were compared with amine solutions such as MEA, TEA, and MDEA, and water as benchmarking. The acid gas absorption in the mixture of [bmim][Br] ionic liquid and MDEA at various compositions were also observed. It is found that the pure [bmim][Br] solvent was more selective to H2S rather than pure MDEA with the selectivity of 2.417 and 0.038, respectively. Comparison of H2S/CO2 selectivity with some other reported ionic liquids shows that pure synthesized [bmim][Br] ionic liquid has relatively acceptable performance. In addition, the mixture of [bmim][Br]-MDEA with a 1:3 mass ratio increases the selectivity towards H2S significantly with the H2S/CO2 selectivity of 6.2. The free tertiary amine group tethered in the cations of ionic liquids in the mixture became a functional site that leans to absorb more H2S. However, H2S and CO2 gas absorption using [bmim][Br] and MDEA were hugely affected by water content. Thus, the water content in each solvent should be measured and minimized before operation. Even though the industrial applicability in the acid gas removal process still needs further investigation, this research proposed a promising idea for selective absorption of H2S/CO2 in natural gas treatment.

Declarations

Author contribution statement

Tri Partono Adhi: Conceived and designed the experiments; Analyzed and interpreted the data.

Yohanes Andre Situmorang: Analyzed and interpreted the data; Wrote the paper.

Haryo Pandu Winoto: Conceived and designed the experiments; Performed the experiments; Analyzed and interpreted the data.

Danu Ariono: Analyzed and interpreted the data; Contributed reagents, materials, analysis tools or data.

Diannisa Septiana & Patricia Imanuela: Performed the experiments; Wrote the paper.

Antonius Indarto: Conceived and designed the experiments; Analyzed and interpreted the data; Contributed reagents, materials, analysis tools or data; Wrote the paper.

Funding statement

This work was supported partially by the Korea Institute of Science and Technology (2020 KIST School Partnership Project).

Data availability statement

Data included in article/supp. material/referenced in article.

Declaration of interests statement

The authors declare no conflict of interest.

Additional information

No additional information is available for this paper.