MDEA

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Overview: MDEA, also known as N-methyldiethanolamine, is used in the MDEA-based decarbonization process to absorb carbon dioxide (CO2) from natural gas or syngas under high pressure and normal temperature conditions, using an activated MDEA aqueous solution. Under reduced pressure and increased temperature, the carbon dioxide (CO2) is desorbed from the solution, thereby regenerating it. In addition to building MDEA-based decarbonization units in China, our company has also successfully entered overseas markets, constructing similar units in Indonesia as well. Typical installations: CNOOC’s natural gas CO2 removal system using the MDEA method; Pertamina provides natural gas decarbonization systems using the MDEA method. The MDEA technology for removing acidic gases is primarily applied in the following areas: removal of carbon dioxide (CO2) from natural gas, used in conjunction with natural gas or LNG purification systems; removal of hydrogen sulfide (H2S) from natural gas, also used in conjunction with natural gas or LNG purification systems; selective removal of hydrogen sulfide (H2S) from natural gas, for use in natural gas transportation; removal of carbon dioxide (CO2) from syngas, used in conjunction with ammonia synthesis, methanol production, or deep cryogenic separation systems; removal of carbon dioxide (CO2) from syngas, again used in conjunction with ammonia synthesis, methanol production, or deep cryogenic separation systems; removal of both carbon dioxide (CO2) and hydrogen sulfide (H2S) from coal gas, used in conjunction with ammonia synthesis, methanol production, or deep cryogenic separation systems; production of food-grade carbon dioxide (CO2) to meet international beverage industry standards.

Device characteristics: Processing capacity: 1,000–500,000 m3/h of natural gas or syngas. Decarbonization accuracy: CO2 concentration of 10 PPM–3%. Desulfurization accuracy: H2S concentration of 0.1–20 mg/m3. Operating pressure: Appropriate pressure range is 0.5–15 MPa. Application areas: Natural gas processing and refinement, purification of methanol feedstocks, purification of ammonia synthesis feedstocks, etc.

Technical features: The MDEA process for removing acidic gases can employ either single-stage absorption using lean solution or two-stage absorption using both lean solution and semi-lean solution. The single-stage absorption approach requires less investment, generates lower electricity consumption, but higher heat consumption ； Two-stage absorption using lean liquid and semi-lean liquid involves high investment, high electricity consumption, and low heat consumption; different processes are employed depending on the scale of carbon dioxide to be removed. The solubility of natural gas in MDEA solution is lower than its solubility in pure water; therefore, very little natural gas is lost during the removal of acidic gases using MDEA. The MDEA solution exhibits both physical and chemical absorption properties, with a high capacity of the solvent to absorb carbon dioxide. MDEA has good stability and rarely degrades during use; it causes almost no corrosion to carbon steel equipment. High hydrocarbon recovery rate and high precision in carbon dioxide removal. It features a high carbon dioxide recovery rate and high purity; after simple post-treatment, it can meet food-grade standards. Technical principle: MDEA, or N-Methyldiethanolamine, has the molecular formula CH3-N(CH2CH2OH)2. Its molecular weight is 119.2, boiling point is 246–248°C, flash point is 260°C, freezing point is -21°C, and the latent heat of vaporization is 519.16 KJ/Kg. It is miscible with water and alcohols, and slightly soluble in ethers. Under certain conditions, it has a strong absorption capacity for acidic gases such as carbon dioxide; it also has low reaction heat, a low desorption temperature, stable chemical properties, and is non-toxic and non-degradable. String 6: A pure MDEA solution does not react with CO2, but its aqueous solution can react with CO2 according to the following equations: CO2 + H2O == H+ + HCO3- (1) H+ + R2NCH3 == R2NCH3H+ (2) Equation (1) is governed by the liquid film effect, resulting in a very slow reaction rate; whereas equation (2) is an instantaneously reversible reaction. Therefore, equation (1) represents the key step in MDEA’s absorption of CO2. To increase the absorption rate, 1–5% of the activator DEA (R2/NH) is added to the MDEA solution, and the reaction proceeds as follows: R2/NH + CO2 == R2/NCOOH (3) String 2: R2/NCOOH + R2NCH3 + H2O == R2/NH + R2CH3NH+HCO3- (4) (3) + (4): R2NCH3 + CO2 + H2O == R2CH3NH+HCO3- (5) From equations (3) to (5), it can be seen that the activator absorbs CO2 and transfers it to the liquid phase, thereby accelerating the reaction rate, while MDEA is regenerated in the process. The MDEA molecule contains a tertiary amine group; upon absorbing CO2, it forms bicarbonate, and significantly less heat is required for its regeneration by heating compared to that needed for the carbamates formed by primary and secondary amines. MDEA formula solutions: The SD-3A, SD-3B, and SD-AS formula solutions developed by our company consist of MDEA solution, an activator, and a corrosion inhibitor. SD-3A is suitable for use in the removal of carbon dioxide (CO2) from natural gas, effectively addressing the issue of the accumulation of higher hydrocarbons in the natural gas at the middle section of the absorption tower. The lean liquid has a high capacity to absorb acidic gases, while the rich liquid flashes rapidly when its pressure is reduced, requiring little stripping steam. String 7: The use of this SM-3A formulation in the natural gas decarbonization unit at the Dongfang 1-1 facility shows that, based on the corrosion rate measured by probes installed in the semi-poor solution, the corrosion rate is below 0.006 mm/year, which is far lower than the specified corrosion rate; this indicates that this solvent does not cause corrosion to carbon steel. The SD-3B is suitable for the removal of carbon dioxide (CO2) from syngas or reformate gas; it features a fast absorption rate and high removal precision, enabling CO2 levels to be reduced to below 10 ppm. SD-AS is a MDEA solution for selective desulfurization, equipped with sterically hindered amines; it enables **reduction of carbon dioxide absorption and lower regeneration energy consumption, while maintaining precision in hydrogen sulfide removal.