MDEA method for desulfurization

Generally, the temperature entering the tower is around 36°. As for the temperature at the top of the tower, it depends on the number of theoretical plates you have

For the desulfurization of refinery gases using N-methyldiethanolamine (MDEA), the alcohol amine method is primarily employed. Initially, ethanolamine (MEA) and diethanolamine (DEA) were used for this purpose, and later diisopropylamine (DIPA) was applied in Claus off-gas treatment systems. In the 1980s, China developed a new type of selective desulfurization solvent, N-methyldiethanolamine (MDEA), which began to be used in natural gas desulfurization units ； Entering the 1990s, MDEA also began to be used in desulfurization units for refinery gases; MDEA is a desulfurization solvent developed by Fluor in the early years. Currently, as a next-generation desulfurization solvent, it is widely used in natural gas desulfurization, coal gasification desulfurization, and refinery desulfurization. Due to its high selectivity for H2S and low energy consumption, MDEA is used in processes such as the concentration of raw gas in the Claus process, the treatment of off-gases from the Scott process, and the desulfurization of gases with low calorific value. Since 1993, due to increased processing capacity in the refineries under Sinopec, or the blending of high-sulfur crude oil, insufficient desulfurization of dry gas and liquid hydrocarbons has occurred. Under these conditions, the high-efficiency desulfurizer using MDEA as the main component fully demonstrates its advantages of high sulfur capacity and good selectivity. Since the usage concentration of this agent can reach up to 50%, its circulation volume can be **reduced**; it can absorb gases at high gas-liquid ratios or high liquid-liquid ratios. Moreover, the regeneration and desorption heat required for MDEA is lower than that of the three amines mentioned above, which in turn reduces the energy needed for regeneration. In summary, all these characteristics mean that using MDEA to remove acidity from gases can significantly reduce energy consumption and thus lower operational costs. The Nanjing Institute of Chemical Technology conducted comparative tests on five solvents, including diethanolamine; the test results are shown in Table 1, which explains why MDEA has become the primary component for efficient desulfurization. At the same time, Table 1 also shows that the various properties of polyethylene glycol dimethyl ether are on par with those of MDEA. It should be noted, however, that using it as a solvent is a physical absorption process; to achieve the same treatment capacity, more of it is required compared to MDEA, which increases the cost of desulfurization. Comparative test of five desulfurizing agents: Desulfurizing agent, H2S removal efficiency %, H2S content in the regenerated gas. Diethanolamine at 2.5 moles/liter: 40–50%, 8%. Diisopropanolamine at 2.5 moles/liter: 85–90%, 10–14%. Polyethylene glycol dimethyl ether: 95%, 25%, 65%. 65% polyethylene glycol dimethyl ether + 30% diisopropanolamine + 5% water: 80%, 5–8%. N-Methyldiethanolamine (MDEA): 94%, 33%. MDEA also has unique advantages in the carbon removal process in ammonia synthesis. MDEA has lower energy consumption for CO2 absorption and regeneration compared to monoethanolamine (MEA), and it has extremely low solubility for non-polar gases such as hydrogen, nitrogen, methanol, methane, and other higher hydrocarbon compounds, resulting in minimal self-loss. The reaction of MDEA with CO2 produces only bicarbonates, without the formation of urethanes; thus, it does not degrade during the absorption process, resulting in a **reduction in the amount required for daily supplementation. MDEA does not corrode carbon steel; it is weakly alkaline and does not produce thermal or chemical degradation products. The wet CO2 emerging from the regeneration and desorption stage has a low temperature (around 70°C), so its corrosive effect on carbon steel is minimal. Currently, there are five sets of MDEA decarburization equipment for ammonia synthesis in China, all of which are constructed from carbon steel. Due to certain chemical properties of MDEA itself, it enables **energy savings** in the CO2 removal process from syngas ； For new installations, the investment can be reduced since carbon steel equipment can be used for the decarbonization system. Furthermore, the purity of the recovered CO2 can reach up to 99.9%, which is advantageous whether for subsequent urea production or for further utilization of the CO2. N-Methyldiethanolamine (MDEA) is a type of tertiary amine. Its molecular formula is CH3N(CH2CH2OH)2, with a molecular weight of 119.16; its specific gravity is 1.0418, its boiling point is 247°C, its viscosity at 12°C is 101 cP, and its freezing point is –48°C. It is completely soluble in water. This production process utilizes the most advanced pipeline-based reaction technology available internationally: ethylene oxide reacts with pure monomethylamine in a tubular reactor at a pressure of 2.5 MPa, and through distillation and rectification, MDEA is obtained with a purity of over 97%. This process has the following significant advantages: 1. Good safety. Piped reactions can prevent runaway polymerization caused by local overheating, making them the safest process route for ethylene oxide. 2. Good quality with few by-products. By controlling the ratio of cycloethane to methylamine, the formation of high-boiling substances can be prevented; the product has an excellent color – it is almost colorless. Industrial testing has shown that the color quality of this product is far better than that obtained using batch reactors. 3. Extremely low energy consumption. Tubular reactions can use anhydrous methylamine, while batch processes employ a 40% aqueous methylamine solution; the latter requires significant energy for water evaporation and results in a higher water content in the product. 4. High yield. The continuous reaction process is easy to start and stop, and the output per hour can be adjusted. This process has been tested on an industrial scale of 600 tons per year and fully meets international standards. Research and development personnel have successfully developed a domestic production process for 10,000-ton-scale ethanolamine, bringing it to international standards; they have also accumulated extensive experience, which provides a solid foundation for the production process of MDEA. Process requirements include 1.0 MPa steam or hot oil boilers, a set of vacuum units, as well as utility systems such as cooling water. The total investment in the equipment is approximately 800,000 yuan, with a designed annual production capacity of 1,000 tons or more; the operation requires around 30 employees working in 4 shifts.

There are 27 theoretical plates; does the temperature inside the tower affect the desulfurization efficiency? What is the appropriate top temperature of the regeneration tower, and how is it controlled?