Formulated absorbent for fine desulfurization and carbon capture of blast furnace gas based on alcohol amine solution

He Jian; Gou Haobo; Geng Liyu; Shu Hao; Liu Yuling; Zhang Lei

doi:10.4491/eer.2024.648

Environ Eng Res > Volume 30(5); 2025 > Article

Jian, Haobo, Liyu, Hao, Yuling, and Lei: Formulated absorbent for fine desulfurization and carbon capture of blast furnace gas based on alcohol amine solution

Research

Environmental Engineering Research 2025; 30(5): 240648.

Published online: February 28, 2025

DOI: https://doi.org/10.4491/eer.2024.648

Formulated absorbent for fine desulfurization and carbon capture of blast furnace gas based on alcohol amine solution

He Jian¹, Gou Haobo¹, Geng Liyu¹, Shu Hao¹, Liu Yuling^1,^†

, Zhang Lei²

¹State Key Laboratory of Eco-hydraulics in Northwest Arid Region, Xi’an University of Technology, Xi’an, China

²China National Heavy Machinery Research Institute co., Ltd, Xi’an, 710018, China

^†Corresponding author: E-mail: lyl29992359@163.com, Tel: +86-185-9199-9882, ORCID: 0000-0001-6935-7399

Received November 19, 2024 Revised February 22, 2025 Accepted February 26, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The development of deep desulfurization of blast furnace gas combined with carbon capture is the key implementation point of pollution reduction and carbon reduction in the steel industry. Combined with the current situation of immature deep desulfurization technology and urgent demand for carbon capture, a CO₂/COS (carbon oxysulfide) /H₂S integrated high-efficiency removal formula absorbent was designed and developed. The main conclusions of this paper are as follows: The absorbent system for simultaneous deep removal of CO₂, H₂S and COS from blast furnace gas was constructed, and the formula absorbent composed of 1.5 mol/L MDEA + 0.5 mol/L MEA + 6% MOR + 4% DBU + 3% DDBAC was obtained. The total sulfur in the purified gas is less than 20 mg/Nm³, with a CO₂ capture efficiency greater than 90%, and the regeneration rate of the formulated absorbent is above 80%, exhibiting excellent anti-corrosion and thermal stability performance. This research lays the foundation for the practical implementation of collaborative pollution reduction and carbon reduction in the steel industry. It integrates the achievement of ultra-low emissions and carbon reduction, providing significant environmental and economic benefits, and demonstrates important practical value and research significance.

Keywords: Blast furnace gas, Carbon capture, Deep desulfurization, Formulated absorbent

Graphical Abstract

Keywords: Blast furnace gas, Carbon capture, Deep desulfurization, Formulated absorbent

1 Introduction

Blast Furnace Gas (BFG) is a combustible gas co-produced during the iron-making process in the steel industry. It is characterized by low calorific value and large volume, making it the largest source of gas fuel in steel enterprises. The main components of this gas mixture include N₂ (53%~57%), CO (21%~26%), CO₂ (16%~22%), H₂ (1%~4%), with small amounts of hydrocarbons, O₂, and sulfur compounds. The total sulfur content is approximately 100–300 mg/m³, primarily consisting of COS and H₂S, with COS accounting for 60%~70% and H₂S for 30%~40% [1]. As the world ‘s largest steel producer, China ‘s crude steel production will reach 1.019 billion tons in 2023, accounting for 54.0% of global crude steel production. The output of blast furnace gas produced by long process iron-making is huge, and 1700–2500 m³ blast furnace gas produced per ton of iron smelted [2].

With China proposing the goals of “carbon peak and carbon neutrality” at the seventy-fifth session of the United Nations General Assembly, carbon emission reduction has become a hot topic in the field of domestic environmental protection in recent years. As the non-electric industry with the highest carbon emissions, China ‘s iron and steel industry have a huge annual carbon dioxide emission, accounting for 15% to 18% of the country ‘s total carbon emissions. Among these, the blast furnace iron-making process is the most concentrated link of carbon dioxide emissions, accounting for about 70% to 90% of the total carbon dioxide emissions of the entire steel production process. The carbon emission reduction of the blast furnace process has also become a key link in the implementation of the “ 3060 “ target task of the steel industry [2]. Commonly used carbon capture technologies include chemical absorption method, solid adsorption method, membrane separation method, etc. The chemical absorption method has high decarbonization efficiency, mature process and good flue gas adaptability. It is the main technical path for capturing CO₂ from large fixed emission sources such as coal-fired and gas-fired power plants. However, the conventional organic alcohol amine solvent is gradually eliminated by the market due to its low absorption capacity and high regeneration energy consumption. Therefore, the addition of high-efficiency absorption components to the alcohol amine solution to form a formula absorbent is the focus of current carbon capture technology research.

The Opinions on Promoting the Implementation of Ultra-Low Emissions in the Iron and Steel Industry jointly issued by the Ministry of Ecology and Environment and other five ministries and commissions in 2019 clearly requires that the hourly average emission concentrations of particulate matter, SO₂, and NOx in the flue gas of blast furnace hot blast stoves are not exceed 10, 50, and 200 mg/m³, respectively. It is proposed that source control should be strengthened, and blast furnace gas and coke oven gas should be deeply desulfurized [3, 4]. The total amount of sulfur components in blast furnace gas ranges from 100–300 mg/m³, mainly hydrogen sulfide (H₂S) and carbonyl sulfur (COS). The flue gas after combustion is large in volume and high in temperature. If the end treatment equipment is used, the investment is large, the operation cost is high, and the desulfurization by-products are difficult to deal with. According to the weak acidity of COS and H₂S, the absorption methods are typically classified into dry and wet desulfurization techniques. The commonly used dry desulfurization methods include adsorption, hydrolysis and hydrogenation reduction. The traditional adsorption method is difficult to achieve precise desulfurization, and the adsorbent is easy to plug and poison; the hydrogenation reduction method has the problems of shortage of hydrogen source and high operating cost. The catalytic hydrolysis method is only suitable for small-scale and low-concentration H₂S removal or desulfurization under medium and high temperature conditions. Wet desulfurization mainly uses solvent absorption method to absorb COS and H₂S. Because of its strong acid gas load, fast and efficient absorption, controllable reaction conditions and simple equipment, it is often used in large-scale industrial gas desulfurization.

It is evident that wet alcohol amine absorption technology is used to remove sulfide and capture carbon dioxide in industry [5]. The absorption system can be divided into single alcohol amine system and compound alcohol amine system. The absorption method of single alcohol amine system mainly includes conventional alcohol amine, sterically hindered amine and heterocyclic amine, which has good removal and absorption selectivity for acidic gases [6].

Alkyl alcohol amines are conventional amine solvents formed by the combination of special organic materials and ammonia (NH₃). They can be classified based on nitrogen-related groups into primary amines represented by monoethanolamine (MEA), secondary amines represented by diethanolamine (DEA) and diisopropanolamine (DIPA), and tertiary amines represented by dimethylethanolamine (MDEA). Primary amine MEA has advantages such as highwater solubility, low viscosity, low cost, and high CO₂ loading capacity. It reacts more easily with both CO₂ and H₂S but lacks the ability to selectively remove H2S. It also tends to degrade at high temperatures, leading to reduced absorption, increased solvent consumption, foaming issues, and equipment corrosion. Secondary amines (DEA, DIPA) have lower heat of reaction with CO₂ compared to primary amines, resulting in lower regeneration energy consumption, but their lower absorption rates limit industrial applications. Tertiary amines (MDEA) have a lower CO₂ absorption rate and cannot directly react with CO₂. Instead, they act as basic substances to catalyze CO₂ hydration for carbon capture. However, their stable chemical structure and higher acid gas load make them widely used in natural gas streams to remove acidic gases like CO₂, H₂S, and COS. Representative sterically hindered amines, such as 2-amino-2-methyl-1-propanol (AMP), which is a recent extension of MEA, are obtained by replacing two hydrogen atoms on the carbon atom of the amino group in the MEA molecule with two methyl groups. In CO₂ absorption, the characteristic of sterically hindered amines is the introduction of large substituents near the amino group, which reduces the stability of carbamate formation during CO₂ absorption and increases the amount of free amine absorbent, promoting the formation of the absorption product. Compared with traditional MEA-based absorption, the energy consumption for regeneration is reduced by 20%. Mandal [7] studied the selective absorption of H₂S and CO₂ by AMP, investigating the effects of factors such as reaction time, acidic gas concentration, and temperature on absorption rates and selectivity. The results show that when the amine concentration increases, the absorption of CO₂ and H₂S increases, while the selectivity factor decreases. Common cyclic amines include morpholine (MOR) and 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU). Morpholine (MOR) is a cyclic amine that reacts rapidly with COS. It is also an under-researched amine for CO₂ capture, with good CO₂ capture characteristics, such as CO₂ absorption rate and CO₂ solubility. DBU and other cyclic amines have similar CO₂ absorption rates to MDEA aqueous solutions but exhibit an absorption rate for COS that is several times higher [8, 9].

A single alcohol amine solution is difficult to meet the requirements of simultaneous desulfurization and decarburization. Therefore, researchers at home and abroad have begun to explore absorbents that meet different gas purification requirements. Researchers have found that alkanolamines ( such as MDEA and AMP ) with large absorption capacity, low energy consumption, low corrosivity and large steric hindrance effect are mixed with primary amines/secondary amines with high reaction rate but small absorption capacity according to demand, and then a small amount of organic active substances (such as piperazine, MOR, quaternary ammonium salts, imidazoles) are added to form a formula solvent, which can make full use of the advantages of various absorbents, reduce regeneration energy consumption, improve absorption performance and absorption rate, and achieve good removal effect on sulfur-containing and carbonate-containing gases [10, 11]. At present, most of the formulated solvents used in industry are evolved from MDEA [12, 13]. Sema et al. [14] studied the mixing ratio, temperature, flow rate and CO₂ loading of MDEA and MEA amine mixtures, and found that they have superior mass transfer behavior compared to the single amine MEA.

Therefore, in order to achieve the simultaneous deep removal of CO₂, H₂S and COS in blast furnace gas, based on the existing research results at home and abroad, this paper focuses on the research of simultaneous desulfurization and decarburization formula absorbent system for blast furnace gas. From the problems of low absorption capacity, poor absorption and regeneration effect, high solvent loss and serious equipment corrosion of conventional wet absorbent, a new type of high-performance simultaneous desulfurization and decarburization double-effect absorbent is developed. Through the study of absorption and regeneration performance, foaming characteristics, corrosion characteristics and reaction mechanism of absorbent, it provides a basis for the large-scale popularization and application of deep desulfurization and carbon capture technology for blast furnace gas.

2 Experimental Methods and Equipment

2.1. Experimental Gases and Reagents

The raw gas used in the experiment is the standard gas distribution of simulated blast furnace gas (CO, 26.82%; CO₂, 17.35%; H₂S, 209 mg/m³; COS, 280.0 mg/m³; residual N₂). Diethanolamine (DEA), N-methyl diethanolamine (MDEA), 2-amino-2-methyl-1-propanol (AMP), morpholine (MOR) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; monoethanolamine (MEA), sulfolane (SF), 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU), dodecyl dimethyl benzyl ammonium chloride (DDBAC) was purchased from Shanghai McLean Biochemical Technology Co., Ltd.

2.2. Experimental Methods

2.2.1. Acid gas absorption experiment

In this paper, a bubbling absorption device is used, as shown in Fig. 1 the configured 100 mL absorbent is placed in a three-neck flask, the water bath is turned on and stirred to preheat to 40°C, with the magnetic stirrer set at a rotation speed is 800 r/min, the gas standard gas cylinder valve is opened, the gas inlet flow is controlled to 100 mL/min through the mass flow meter on the front side, and the three-neck flask is passed into the three-neck flask for reaction with the absorbent, and the unreacted gas is emptied after being treated by the tail gas absorption device, and the outlet gas flow rate is determined by an electronic soap film flowmeter. The inlet and outlet gas concentrations are determined by a gas chromatograph. When the difference between the inlet and outlet gas flow rates is less than 1%, the absorption reaction is considered to have reached a saturated state, and the next experiment is carried out.

2.2.2. Acid gas desorption experiment

The absorption rich liquid obtained in the absorption experiment was placed in a three-neck flask, the oil bath was turned on and heated and kept at 120°C, the flow rate of N₂ into the experiment was controlled at 100 mL/min, the regenerated gas was condensed through the condenser tube and entered the anhydrous CaCl₂ drying flask to dry the residual water impurities, and finally the outlet gas flow rate of the regenerated gas was determined by an electronic soap film flowmeter. When the outlet gas flow rate is greater than the N₂ flow rate measured by the electronic soap film flowmeter, the absorbent regeneration process occurs. When the outlet gas flow rate is equal to the inlet N₂ flow rate, the primary absorbent regeneration process is considered complete. Finally, the absorbent was removed and the absorption-desorption process was repeated several times to test its regenerative cycle performance.

2.2.3. Calculation method

Acid gas removal efficiency:

(1)

η = \frac{C_{0} - C_{i}}{C_{0}} \times 100 %

Eq. (1) is the acid gas removal efficiency, and the absorption agent calculates the removal efficiency of each acid gas by the concentration of the import and export gases COS, H₂S and CO₂. Where:η Indicates the removal efficiency of COS, H₂S and CO₂ at a certain time; C₀ and C₁ is the concentration of COS, H₂S and CO₂ at the gas inlet and outlet at a certain time, mg/m³.

Acid gas absorption amount:

(2)

α = \sum \frac{C_{0} (η_{i} + η_{i + 1}) Δ t \times q}{2 V}

Eq. (2) denotes the amount of acid gas absorbed, Where:α indicates the amount of COS, H₂S and CO₂ absorbed by the amine solution per unit mass during the reaction time, g/L; η_i is the removal rate of COS, H₂S and CO₂ at t_i time; η_i+1 the removal rate of COS, H₂S and CO₂ at η_i+1 —— t_i+1; Δt is the time interval between t_i+1 and t_i time, min; q is the volume flow rate of the feed gas inlet, mL/min,; V is the volume of absorbed fluid, ml.

The instantaneous absorption rate of acid gas:

(3)

r_{abs} (t) = \frac{\partial α_{abs} (t)}{\partial t}

Eq. (3) the instantaneous absorption rate of acid gas: is the instantaneous absorption rate of COS, H₂S and CO₂ at any time; represents the instantaneous absorption of COS, H₂S and CO₂ at any time, g/L.

Acid gas instantaneous absorption rate and acid gas regeneration rate:

(4)

r_{abs} (t) = \frac{\partial α_{abs} (t)}{\partial t}

(5)

r_{reg} (t) = \frac{q_{i}}{1000 \times V_{0}} \times \frac{273.15}{22.4 (T + 273.15)}

Eq. (4) the instantaneous absorption rate of sour gas and EEq. (5) the regeneration rate of sour gas, where: represents the total regeneration capacity of sour gas (COS, H₂S, CO₂), g/L; is the total absorption capacity of acid gas (COS, H₂S, CO₂), g/L; and can be calculated from the mass difference of the system before and after each desorption, regeneration and absorption. r_reg(t) represents the instantaneous acid regeneration rate at any time;is the reading of the soap film flowmeter at the desorption outlet, mL/min; -rich liquid volume, L; t is the ambient temperature, °C.

2.3. Measurement of Physical Property Parameters and Product Characterization

The viscosity of the formulated absorbent was measured by a digital viscometer (NDJ-5S, Zhejiang Lichen Instrument Technology Co., Ltd.). Firstly, the uniformly stirred absorbent to be tested is poured into the viscosity test barrel and placed in a constant temperature heating water bath. Secondly, the corresponding viscometer is selected to test the rotor, after the solution is stable at the set temperature, the viscometer is used to measure and record the data.

The thermal stability of the solvent before and after the absorption by the formulated absorbent was analyzed using a thermogravimetric analyzer (Discovery TGA 550). The thermal stability of the solution in the temperature range of 30–600°C was measured at a heating rate of 10°C/min in a nitrogen atmosphere.

Fourier transform infrared spectroscopy FTIR (Thermo Scientific Nicolet iS50, wave number range 400–4000 cm⁻¹), nuclear magnetic resonance spectroscopy ¹H-NMR, ¹³C-NMR (German Bruker 600 MHz) were used to characterize and analyze the composition and structure of the pre-absorption and absorption products of the formulated absorbent system.

3 Results and Discussion

3.1. Characteristics of the Absorption and Regeneration Properties of the Formula Absorbent

3.1.1. The desulfurization and decarbonization performance of the formulated absorbent

Taking 1.5 mol/L MDEA and 0.5 mol/L MEA as base amine solution, selecting MOR, DBU and DDBAC mass concentrations of 6%, 4% and 3% respectively [15–17], the absorption effect of MDEA-MEA mixed amine system on CO₂/H₂S/COS in blast furnace gas after adding active additives was studied. The results are shown in Fig. 2.

As shown in Fig. 2, the removal efficiency of H₂S by the formulated absorbent remains above 95% with increasing time, and the removal rates of COS and H₂S decreased over time, more than 90% within 80 and 150 min, demonstrating a high removal rate for a long time. After 150 min, the CO₂ removal rate began to decrease rapidly due to the large consumption of amine concentration in the absorbent. The absorption of COS/H₂S/CO₂ by the formulated absorbent with active components increased with the reaction time, and the absorption amounts were 47.2852 × 10⁻³ g/L, 42.1737 × 10⁻³ g/L and 46.0734 g/L respectively at 240 min, showing a high absorption capacity. This is mainly due to the addition of different concentrations of active components (MOR, DBU, and DDBA) that preferentially react rapidly with H₂S in the solution, making the H₂S removal rate very stable, the strong alkalinity of DBU promotes the removal of CO₂ from the solution, and the addition of a cyclic structure MOR with secondary amine properties forms a carbamate bond with stronger bond energy when reacting with CO₂, resulting in a higher CO₂ absorption rate of the formulated absorbent [18, 19]. The cationic surface activity of both DBU with steric hindrance effect and DDBAC, a quaternary ammonium salt, promotes the hydrolysis of COS, thereby achieving deep removal of COS [20].

3.1.2. Research on the regeneration performance of formula-based absorbents

According to Fig. 3(a), when the regeneration temperature is 100°C, 110°C, 120°C and 130°C, the acid gas regeneration rates are 72.92%, 85.19%, 92.12% and 94.56%. The acid gas regeneration rate shows an increasing trend with the increase of regeneration temperature, and the value-added is the largest in the regeneration temperature range of 100°C to 110°C, which indicates that the desorption effect of the absorbent system is the best at this stage. After 110°C, the increment of acid gas regeneration rate decreases, especially in the 120°C to 130°C range, where the regeneration rate only increases by 2.44%, indicating that the increase of temperature has little contribution to the improvement of acid gas regeneration rate of the absorbent system. As shown in Fig. 3(b), under different constant regeneration temperature conditions, with the increase of constant regeneration temperature, the time of rich liquid entering the regeneration section is shortened and the acid gas regeneration rate is increased. When the temperature exceeds 110°C, the time to reach the regeneration section changes very little, remaining around 14 minutes of heating. At 110°C, 120°C and 130°C, the regeneration rates of rich liquid can reach 13.9410⁻³, 15.6510⁻³ and 16.3710⁻³, and the regeneration rate increases slowly after 120°C. Therefore, from the kinetic point of view, 120°C is the suitable regeneration temperature for the absorbent system.

As shown in Fig. 3(c) and (d), the absorption-desorption cycle performance of 1.5 mol/L MDEA + 0.5 mol/L MEA + 6% MOR + 4% DBU + 3% DDBAC formula absorbent at 120°C regeneration temperature was studied. As shown in Fig. 3(c), in the five cycle experiments, the removal efficiency of the three gases by the formula absorbent gradually decreased, but with the increase of the number of cycle absorption, the removal rate tended to be stable. In general, the multiple cycles of the formula absorbent have little effect on the absorption performance of CO₂, H₂S and COS, and the removal efficiency remains above 85%. As shown in Fig. 3(d), the acid gas regeneration rate decreased with an increasing number of regenerations, and the fifth regeneration rate is 83.82%. Therefore, considering the removal efficiencies of CO₂, H₂S and COS and the regeneration rate of acid gas under multiple cyclic absorption-desorption of formula type absorbent, the absorbent system developed in this paper shows good cyclic regeneration stability.

3.2. Performance Characteristics of the Formulation Absorbent

3.2.1. Analysis of viscosity characteristics

As shown in Fig. 4, at the same temperature, the viscosity of the rich liquid of the formulated absorbent is always higher than that of the lean liquid, mainly because the various salt compounds generated by the absorption reaction form more hydrogen bond structures, which increases the intermolecular force of the solvent and leads to the increase of the viscosity of the system. On the other hand, the viscosity of the lean and rich liquid of the formulated absorbent system decreases with the increase of temperature. Based on related studies [21–23], the viscosity of the absorbent used in this paper is not higher than 10 mPa· S, which has little impact on heat and mass transfer in the system.

3.2.2. Thermal stability analysis

As shown in Fig. 5, thermogravimetric analysis shows that the formula absorbent has good thermal stability in the temperature range of 30°C to 600°C. The extrapolated onset temperatures before and after desulfurization and decarburization were about 171.21°C and 168.42°C, the fastest weightless change temperatures were about 218.34°C and 220.29°C. After desulfurization and decarburization, the values of the TG and DTG curves decreased in the temperature range of 100°C to 160°C, which may be the desorption of acid gas components and the decomposition of reaction products. These results indicate that the formulated absorbent has good thermal stability and regeneration cycle performance.

3.2.3. Study on foaming characteristics

The foaming performance of the desulfurization and decarbonization solution was evaluated using the testing method recommended in the industry standard of “Formulated Selective Desulfurization Solvent” (SY/T6538-2016), and the foaming characteristics of the lean and rich solution of the formula absorbent under different inlet flow rates were measured.

As shown in Fig. 6, the foaming height of the lean/rich solution of the formula absorbent increases with the increase of the inlet flow rate. This is because increasing the N₂ inlet flow rate enhances the gas-liquid contact frequency, resulting in continuous generation of bubbles. Compared with other absorbents, the formulated absorbent exhibits a higher foaming height and longer defoaming time for the rich phase. This is because the products formed by absorbing CO₂, H₂S and COS increase the viscosity of the absorbent system, slowing down the bubble rupture speed, enhancing the elasticity of the liquid film, and enhance the foam stability. The results show that the foaming height and defoaming time of the lean/rich solution of the formula absorbent meet the industry requirements in the range of 100 mL/min to 150 mL/min. Therefore, the formulated absorbent has good anti-foaming performance and has industrial application conditions [23, 24].

3.2.4. Corrosion characteristics study

In this paper, the weight loss method of hanging pieces was used to study the corrosive properties of the formulated absorbent system on the corrosive specimens. The corrosion rate of the 304 stainless steel hanging sheets was measured after the poor/rich liquid of the formula absorbent was placed at an ambienttemperatures of 40°C and 120°C for 10 days.

As shown in Fig. S1, at the same temperature, the corrosion rate of the lean solution of the formula-type absorbent to the 304 stainless steel coupon is slower than that of the rich solution to the 304 stainless steel coupons. Under the low-temperature condition of 40°C, the corrosion rates of the stainless-steel hanging piece by the lean/rich solution of the formula type absorbent showed an ultra-low corrosion rate, which was 0.00069 mm/a and 0.00188 mm/a, respectively. Under the condition of high temperature 120°C, the corrosion rate of the lean/rich solution of the formula absorbent to the stainless-steel coupon increased, which was 0.00106 mm/a and 0.02314 mm/a, respectively. This is due to the accumulation of carbamate salts, HCO₃/CO₃²⁻ concentrations and high heat-stable salts in the rich liquid, as well as the addition of DDBAC cationic surfactant, which increase the corrosion rate of the steel. Compared with traditional alcohol amine MEA aqueous solution and UDS absorbent, the formula absorbent in this paper shows better corrosion resistance [25–27].

3.3. Possible Reaction Mechanism Analysis

3.3.1. FTIR before and after the reaction

Fig. 7 shows the FTIR spectra of the formulated absorbent before and after desulfurization and decarbonization. It is observed that the infrared spectrum of the absorbent after desulfurization and decarburization is similar to that before desulfurization and decarburization, indicating that the desulfurization and decarburization process has little effect on the infrared structure of the absorbent. However, several peak positions have changed, such as the OH stretching vibration peak moved from 3302 cm⁻¹ to 3261 cm⁻¹, the C-H bond stretching vibration peak and the C = N bond stretching vibration peak have a small offset and stretching. These changes indicate that the alkalinity of the solution in the formulated absorbent is continuously consumed and reacts with CO₂/H₂S/COS. In addition, the changes of other peak positions also indicate that there are components such as MEA, MDEA, DDBAC and MOR in the formula absorbent [28].

3.3.2. Characterization of 1H NMR and 13C NMR before and after formulation reaction

As shown in Fig. 8(a, b), the ¹H NMR spectra of the formulation-type absorbent before and after absorption of H₂S were detected by ¹H NMR. It was found that compared with the ¹H spectrum of the solvent before absorption, different degrees of displacement occurred after absorption of H₂S. Combining with Fig. 8(e), the chemical shifts of H1, H2, H3 and H4 in MEA structure are shifted from 1.98 ppm, 2.53 ppm, 3.40 ppm and 3.72 ppm to 2.18 ppm, 3.03 ppm, 3.31 ppm and 3.70 ppm; The chemical shifts of H5, 6, H7, H8, 9, H10, 11 on the MDEA structure were shifted from 2.42 ppm, 2.20 ppm, 3.50 ppm, 4.31 ppm to 2.64 ppm, 2.38 ppm, 3.48 ppm, 4.14 ppm. The chemical shifts of H12, H13, 14, 15, H16, H17, H18 and H19 in the DBU structure are shifted from 3.03 ppm, 3.33 ppm, 1.81 ppm, 2.32 ppm, 1.46 ppm and 1.54 ppm to 3.12 ppm, 3.31 ppm, 1.67 ppm, 2.75 ppm, 1.57 ppm and 1.67 ppm; The chemical shifts of H21, 22, H20, 23 and H24 in the MOR structure are shifted from 3.20 ppm, 2.90 ppm and 2.62 ppm to 3.25 ppm, 2.70 ppm and 2.75 ppm; The hydrogen atom displacement on the benzene ring of the DDBAC structure moves from 7.29 ppm-7.33 ppm to 7.17 ppm-7.10 ppm. In addition, the displacement of other H atoms adjacent to the benzene ring also changes to varying degrees, from 3.12 ppm, 2.09 ppm, 1.06 ppm to 3.18 ppm, 2.27 ppm, 1.29 ppm. In summary, the change of H atom displacement before and after the reaction in the ¹HNMR spectrum indicates that H₂S gas can react with the formula absorbent component through the proton transfer process to form positively charged amine ions and HS⁻, resulting in the change of hydrogen atom displacement of each component [29–31].

According to the results of Fig. 8(c, d, f) and Table S1, the following conclusions can be drawn: the displacement at about 164.23 ppm is the carbon atom displacement of MEACOO⁻/MEACOS⁻ generated by MEA, indicating that the formulation-type reaction products contain an ester group structure [32]. The shift at approximately 162.29 ppm is the peak of HCO₃⁻ ion, indicating that MDEA reacts with CO₂/COS to form bicarbonate[33, 34]. The shift at approximately 167.70 ppm is the displacement of the carbon atom of the DBU formation product DBU + COO⁻/DBU + COS⁻, indicating that the carbon atom on the CO₂/COS reacts with the nitrogen atom on the C=N bond in the DBU structure to form a product with a C=O group. The shift at approximately 161.10 ppm is the carbon atom shift of the products of MOR: carbamate MOR + COO⁻ and thiocarbamate MOR + COS⁻ [30]. In addition, the displacement of C atoms before and after the reaction of DDBAC moved from high field to low field, which is speculated to be due to the phase transfer catalytic effect of DDBAC, accelerating the hydrolysis rate of CO₂/COS.

4 Conclusions

This paper developed a simultaneous decarbonization absorber of blast furnace gas, the removal rate of CO₂, H₂S and COS is kept above 90% for a long time, acid gas regeneration rate after desorption, viscosity is less than 10 mPa· S, initial weight loss temperature is 171.21°C, foam height is less than 5cm, defoaming time is less than 10 s, poor/rich liquid corrosion rate is 0.00069 mm/a, 0.00188 mm/a respectively, viscosity and foaming characteristics meet the requirements of the industry, and showed excellent corrosion resistance and thermal stability. Through mechanistic analysis, it was found that the formula absorber reacts with H₂S to form amine ions and HS⁻, and reacts with CO₂ and COS to form carbamate ion, thiocarcarbamate ion and bicarbonate. As a catalyst and activator, DDBAC accelerated the reaction rate and improved the hydrolysis efficiency of CO₂/COS. The main conclusions are as follows:

A blast furnace gas desulfurization and decarbonization absorbent composed of 1.5 mol/L MDEA + 0.5 mol/L MEA + 6% MOR + 4% DBU + 3% DDBAC was developed, with CO₂, H₂S, and COS removal rates remaining above 90% for an extended period. The reaction rate and absorption capacity of CO₂, H₂S and COS were improved, and the simultaneous deep removal of CO₂, H₂S and COS was realized.
The viscosity of the lean/rich solution of the formula type absorbent decreases with the increase of temperature, and the viscosity of the absorbent is not high 10 mPa·S, which is beneficial to the heat and mass transfer between the gas and liquid phases. The initial weight loss temperature is 171.21°C, indicating good thermal stability of the system.
The acid gas regeneration rate and regeneration rate of the formula type absorbent increased with the increase of regeneration temperature. The optimum regeneration temperature range was 110°C to 120°C. After 5 cycles of absorption-desorption, the removal rate of CO₂, H₂S and COS remained above 80%, and the acid gas regeneration rate was 80%, allowing for multiple cycles of use.
The foaming height and defoaming time of the lean/rich solution of the formulated absorbent increase with the increase of the inlet flow rate. The foam height h < 5 cm, the defoaming time < 10 s, and the absorbent system at 40°C, 0.00069 mm/a, 0.00188 mm/a; the corrosion rate of lean/rich liquid at 120°C is 0.00106 mm/a and 0.02314 mm/a, respectively. The viscosity and foaming characteristics meet the industry requirements.
Combined with FTIR, ¹HNMR, ¹³CNMR spectrum analysis, the formula absorbent reacts with H₂S to form amino ions and HS⁻, and reacts with CO₂ and COS to form carbamate ions, thiocarbamate ions and bicarbonate. As a catalyst and activator, DDBAC accelerated the reaction rate and improved the hydrolysis efficiency of CO₂/COS.

Supplementary Information

eer-2024-648-supplementary.pdf

Notes

Acknowledgments

This work is supported by Natural Science Basic Research Program of Shaanxi [Program No. 2024JC-YBQN-0413]; Shaanxi Province Postdoctoral Science Foundation [grant number 2023BSHEDZZ 252]; Xianyang Key Research and Development Project [grant number L2023-ZDYF-SF-009]; Key Research and Development Program of Shaanxi [2023-YBSF-282]; Open Fund of State Key Laboratory of Green and Low-carbon Development of Tar-rich Coal in Western China [grant number SKLCRKF23-06]; Xi’an Science and Technology Plan Project [grant number 24SFSF0006].

Conflict-of-Interest Statement

The authors declared that they have no conflicts of interest to this work. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.

Author Contributions

G.H.B. (Graduate student) conducts experiment, collects and analyzes data, writes originals and finalizes them. G.L.Y. (Graduate student) assisted in the experiment. S.H. (Lecturer) conducted a software calculation. Z.L. (Senior Engineer) assisted in the collation of experimental data. L.Y.L. (Professor) provided laboratory resources and methodological guidance. H.J. (Lecturer) oversees and funds experiments, manuscript writing and revision.

References

1. Jingshu Z, Jialin S, Lisong X, Qi Z. The CO2 emission reduction path towards carbon neutrality in the Chinese steel industry: A review . Environ. Impact Assess. Rev. 2023;99:107017. http://doi.org/10.1016/j.eiar.2022.107017

2. Hanlin W, Xuelai Z, Qing W. Research progress of carbon capture technology based on alcohol amine solution. Sep. Purif. Technol. 2024;333:125715. http://doi.org/10.1016/j.seppur.2023.125715

3. Jialin S, Qi Z, Lisong X, Shuoshuo T, Peng W. Future CO2 emission trends and radical decarbonization path of iron and steel industry in China. J. Clean Prod. 2021;326:129354. http://doi.org/10.1016/j.jclepro.2021.129354

4. Na L, Ping N, Xin S, Chi W, Xin S, Fei W, et al. Simultaneous catalytic hydrolysis of HCN, COS and CS2 over metal-modified microwave coal-based activated carbon. Sep. Purif. Technol. 2021;259:118205. http://doi.org/10.1016/j.seppur.2020.118205

5. Wang J, Huang L, Yang R, Zhang Z, Wu J, Gao Y, et al. Recent advances in solid sorbents for CO2 capture and new development trends. Energy Environ. Sci. 2014;7(11)3478–3518. http://doi.org/10.31224/osf.io/y654z

6. Pengfei L, Guangchun W, Yuan D, Yuqun Z, Yaming F. A Review on Desulfurization Technologies of Blast Furnace Gases. Curr. Pollut. Rep. 2022;8(2)189–200. http://doi.org/10.1007/s40726-022-00212-z

7. Mandal BP, Biswas A, Bandyopadhyay S. Selective absorption of H2S from gas streams containing H2S and CO2 into aqueous solutions of N-methyldiethanolamine and 2-amino-2-methyl-1-propanol. Sep. Purif. Technol. 2004;35(3)191–202. http://doi.org/10.1016/s1383-5866(03)00139-4

8. Robert C, Ewa K, Paweł W, Damian J, Jerzy S. Carbon Dioxide Separation Technologies. Arch. Min. Sci. 2019;64(3)487–498. http://doi.org/10.24425/ams.2019.129364

9. Pandey D, Mondal MK. Experimental Data and Modeling for Viscosity and Refractive Index of Aqueous Mixtures with 2-(Methylamino)ethanol (MAE) and Aminoethylethanolamine (AEEA). J. Chem. Eng. 2019;64(8)3346–3355. http://doi.org/10.1021/acs.jced.9b00171.s001

10. Fang M, Xie Y, Shao Y, Xu X, Xia Y, Mou M, et al. Development of carbon capture absorbents for top gas recycling-oxygen blast furnace in the steel industry. Sep. Purif. Technol. 2025;355(PB)129616. http://doi.org/10.1016/j.seppur.2024.12961

11. FS , KKL , BP , AMS . A review on the selection criteria for slow and medium kinetic solvents used in CO2 absorption for natural gas purification. J. Nat. Gas Sci. Eng. 2021;98:104390. http://doi.org/10.1016/j.jngse.2021.104390

12. Ali MS, Rashid A, Abdul WB, MSI , SAB , MJB , et al. Thermal degradation kinetics of morpholine for carbon dioxide capture. J. Environ. Chem. Eng. 2020;8(3)103814. http://doi.org/10.1016/j.jece.2020.103814

13. Fanzhi M, Yuan M, Tongyao J, Siyu H, Li L, Jianguo J. Research progress of aqueous amine solution for CO2 capture: A review. Renew. Sust. Energ. Rev. 2022;168:112902. http://doi.org/10.1016/j.rser.2022.112902

14. Sema T, Naami A, Fu K, Edali M, Liu H, Shi H, et al. Comprehensive mass transfer and reaction kinetics studies of CO 2 absorption into aqueous solutions of blended MDEA–MEA. Chem. Eng. J. 2012;209:501–512. http://doi.org/10.1016/j.cej.2012.08.016

15. Song Q, Zou Y, Zhang P, Xu S, Yang Y, Bao J, et al. Novel High-Efficiency Solid Particle Foam Stabilizer: Effects of Modified Fly Ash on Foam Properties and Foam Concrete. Cem Concr Compos. 2024;105818. http://doi.org/10.1016/j.cemconcomp.2024.105818

16. Ma D, Liu Q, Zhu C, Feng H, Ma Y. Volumetric and viscometric properties of ternary solution of (N-methyldiethanolamine + monoethanolamine + ethanol). Int. J. Greenh. Gas Control. 2019;134:5–19. http://doi.org/10.1016/j.jct.2019.02.019

17. Xiao M, Cui D, Yang Q, Liang Z, Puxty G, Yu H, et al. Role of mono- and diamines as kinetic promoters in mixed aqueous amine solution for CO 2 capture. Chem. Eng. Sci. 2021;229:116009. http://doi.org/10.1016/j.ces.2020.116009

18. Xie J, Zhang L, Fu D, Zhu H. CO2 Capture Process and Corrosion of Carbon Steel in [Bmim][Lys]-K2CO3 Aqueous Solutions. Int. J. Electrochem. 2019;14(1)634–650. http://doi.org/10.20964/2019.01.57

19. Wu K, Zhou X, Wu X, Lv B, Jing G, Zhou Z. Understanding the corrosion behavior of carbon steel in amino-functionalized ionic liquids for CO 2 capture assisted by weight loss and electrochemical techniques. Int. J. Greenh. Gas Control. 2019;83:216–227. http://doi.org/10.1016/j.ijggc.2019.01.010

20. Jiangsheng L, Juan Q, Yan H. Water-lean triethylenetetramine/N,N-diethylethanolamine/n-propanol biphasic solvents: Phase-separation performance and mechanism for CO2 capture. Sep. Purif. Technol. 2022;289:120740. http://doi.org/10.1016/j.seppur.2022.120740

21. Annanurov S, Mi Z, Hui H, Xueying Y, Li L, Hao H. Mechanism study on CO2 capture by ionic liquids made from TFA blended with MEA and MDEA. J. Greenh. Gas Control. 2022;119:103709. http://doi.org/10.1016/j.ijggc.2022.103709

22. Liu H, Barzagli F, Luo L, Zhou X, Geng J, Li Ce, et al. CO2 gas-liquid equilibrium study and machine learning analysis in MEA-DMEA blended amine solutions. Sep. Purif. Technol. 2025;356(PB)130024. http://doi.org/10.1016/j.seppur.2024.130024

23. Cao E, Zheng Y, Zhang H, Wang J, Li Y, Zhu T, et al. In-situ regenerable Cu/Zeolite adsorbent with excellent H2S adsorption capacity for blast furnace gas. Sep. Purif. Technol. 2024;336:126305. http://doi.org/10.1016/j.seppur.2024.126305

24. Ghanbari T, Abnisa F, Daud WMAW. A review on production of metal organic frameworks (MOF) for CO 2 adsorption. Sci. Total Environ. 2020;707(C)135090. http://doi.org/10.1016/j.scitotenv.2019.135090

25. Zhang G, Qian J, Liu J, Yu T, Liu Q. Insight and assessment of CO2 capture using diethylenetriamine/2-(diethylamino) ethanol/n-propanol water-lean biphasic solvent: Experimental and quantum chemical calculation. Chem. Eng. J. 2024;500:156834. http://doi.org/10.1016/j.cej.2024.156834

26. Lin Y, Li Y, Wang B, Tian J, Liu H, Li Y, et al. Pilot-scale testing on catalytic hydrolysis of carbonyl sulfur combined with absorption-oxidation of H2S for blast furnace gas purification. J. Environ. Sci. 2025;151:360–372. http://doi.org/10.1016/j.jes.2024.03.027

27. Sukma MS, Zheng Y, Scott SA. Dicalcium ferrite: A chemical heat pump in integrated carbon capture and chemical looping combustion for the steel industry. Chem. Eng. J. 2024;488:150658. http://doi.org/10.1016/j.cej.2024.150658

28. Jia L, Zheng Y, Li Y, Zhu T, Cui Y. Physical mixing of K2CO3/Al2O3 and poly(divinylbenzene) to promote COS removal from blast furnace gas with high humidity at low temperature. Colloids Surf. Physicochem. Eng. Aspects. 2024;690:133854. http://doi.org/10.2139/ssrn.4720276

29. Guo Y, Li Y, Jiang H, Liao J, Chang L. Desulfurization performance and mechanism for H2S from blast furnace gas over FAU zeolite sorbent. Chem. Eng. Sci. 2024;291:119926. http://doi.org/10.1016/j.ces.2024.119926

30. Ying W, Xiaoqin W, Di W, Yue C, Jia Y, LvYou W. Research progress on adsorption and separation of carbonyl sulfide in blast furnace gas. RSC Adv. 2023;13(18)12618–12633. http://doi.org/10.1039/d2ra07409e

31. Yifan W, Long D, Hongming L, Junjun X, Lixin Q, Hongtao W, et al. Carbonyl sulfur removal from blast furnace gas: Recent progress, application status and future development. Chemosphere. 2022;307(P4)136090. http://doi.org/10.1016/j.chemosphere.2022.136090

32. Nie K, Shang R, Miao F, Wang L, Liu Y, Jiao W. An integrated technology for the absorption and utilization of CO2 in alkanolamine solution for the preparation of BaCO3 in a high-gravity environment. Chin. J. Chem. Eng. 2024;72:117–125. http://doi.org/10.1016/j.cjche.2024.04.012

33. Kim D, Han J. Techno-economic and climate impact analysis of carbon utilization process for methanol production from blast furnace gas over Cu/ZnO/Al 2 O 3 catalyst. Energy. 2020;198:117355. http://doi.org/10.1016/j.energy.2020.117355

34. Zhiwei Z, Suk-Hoon H, Chang-Ha L. Role and impact of wash columns on the performance of chemical absorption-based CO2 capture process for blast furnace gas in iron and steel industries. Energy. 2023;271:127020. http://doi.org/10.1016/j.energy.2023.127020

Fig. 1

Bubble absorption device diagram. 1. Gas cylinders; 2. Pressure reducing valve; 3. Mass flow controller; 4. Heat-collecting constant temperature magnetic stirring water (oil) bath pan; 5. Three-neck flasks; 6. Reflux condensation tube; 7. Digital display electronic thermometer; 8. Electronic soap film flowmeter; 9. Exhaust gas absorption device (ferric chloride); 10–11. Connecting pipe; 12. Gas chromatograph; 13. Computer.

Fig. 2

The purification rate and absorption amount of each component. (a) Purification rate of each component; (b) Acid gas absorption.

Fig. 3

Regeneration performance of absorbent. (a, b) The regeneration performance of formula absorbents at different regeneration temperatures; (c, d) The effect of multiple cycles of absorption-desorption of formula absorbents.

Fig. 4

The viscosity of the lean/rich solution of formulated absorbents at different temperatures

Fig. 5

Thermal stability analysis. (a) Thermogravimetric analysis curve; (b) Thermogravimetric analysis curve at 80–260°C.

Fig. 6

The effect of intake flow rate on the foaming height and defoaming time of the lean/rich solution of formulated absorbents.

Fig. 7

FTIR spectra of formula absorbents before and after desulfurization and decarburization.

Fig. 8

¹HNMR, ¹³CNMR and molecular structure. (a, b) ¹HNMR spectra of formula absorbent before and after reaction; (c, d) ¹³CNMR spectra of formula absorbent before and after reaction; (e) The molecular structure diagram of each component of the formula absorbent; (f) The predicted material structure of each component of the formula absorbent before and after the absorption of CO₂/COS reaction.