(412e) Post-Combustion CO2 Capture Using Hexamethylenediamine Activated Aqueous Sodium Glycinate Solvent

One of the most serious problems facing the world today is global warming and consequential climate change. Prevention of the catastrophic global worming requires an effective implementation of CO₂ capture strategy to the major point sources of the CO₂ emission. Among the major point sources, fossil fuel based power plants contributes almost 40% of the anthropogenic discharge. So the main target for implementing the CO₂ emission-reducing strategy is pointed towards this sector. Aqueous amine based absorption-regeneration process for removing CO₂ is a mature technology. Monoethanolamine (MEA), diethhanolamine (DEA) are the conventional solvents for rapid capture of CO₂. However, implementation of the conventional amine solvent for capturing CO₂ from power plant flue gas stream leads to high energy requirement, large solvent circulation rate and high solvent degradation rate, all of which in turn increases the operating and capital cost of carbon capture. These drawbacks are the main motivation for the investigation of the alternative solvents.

CO₂ absorption property of hexamethylenediamine (HMDA) activated aqueous sodium glycinate (SG) solvent is investigated in this work to explore its potential as an efficient alternative solvent for CO₂ capture. The ionic nature of aqueous SG makes it more resistant to oxidative and thermal degradation which is a desired property for the CO₂ capture from the oxygen rich power plant flue gas. It also provides certain other desirable physical properties such as low volatility, higher surface tension, etc. On the other, HMDA, a straight chain diamine (Mondal et al., 2017, 2015) will enhance the solvent characteristics due to its high kinetic and absorption capacity. All these characteristics of the component solvents motivated us to investigate aqueous (HMDA+SG) hybrid solvent.

In this work, the physico-chemical properties (density, viscosity, physical solubility), vapour-liquid equilibrium (VLE) and kinetics of CO₂ absorption in (5 mass% HMDA+ 25 mass% SG+ 70 mass% H₂O) solvent as well as (30 mass% SG+70 mass% H₂O) solvent are measured in the temperature range of 313-333K. These properties are required for the design of absorber-regenerator system for CO₂ capture from power plant flue gas. VLE of CO₂ is measured in a custom made stirred equilibrium cell set up using the method of Park and Sandall (2001). VLE data obtained in this work is presented in terms of CO₂ loading (mole CO₂ absorbed per mole total amine). The experimental VLE data shows a general trend of increasing CO₂ loading with the increase in CO₂ partial pressure. For both the solvent systems, loading capacity decreases with the increase in the temperature which indicate the exothermic nature of the chemical absorption. At 10kPa CO₂partial pressure and 313K temperature, comparison of the hybrid solvent (CO₂ loading = 0.616) with the 30% SG (CO₂ loading = 0.471) shows 20% enhancement of the loading capacity (due to addition of HMDA).

For the kinetic study, a reaction calorimeter (Model: RC1e, Mettler Toledo) set-up is used. Kinetics of CO₂ absorption is explored assuming pseudo-first-order reaction condition. Seconds order rate constant for CO₂ absorption in aqueous 30 mass% SG (592 m³mol^-1s^-1) is estimated using zwitterion mechanism with fast deprotonation step and compared with the existing literature data (Lee et al., 2007) . For both the solvent systems, overall reaction rate constant is found to increase with the temperature. Overall reaction rate constant for the aqueous 30 mass% SG (2080s^-1) and (5mass% HMDA+25mass% SG) (10410 s^-1) are compared which shows 5 times enhancement of the absorption rate of the hybrid solvent compared to 30% SG solvent.

So, from the investigation of absorption properties, (HMDA+SG+H₂O) hybrid solvent appears to be a potential solvent with high CO₂ absorption rate and capacity which can be used for the CO_2 capture from the power plant flue gas.

References:

Lee, S., Song, H., Maken, S., Park, J., 2007. Kinetics of CO2 Absorption in Aqueous Sodium Glycinate Solutions. Ind. Eng. Chem. Res. 46, 1578–1583. doi:10.1021/ie061270e

Mondal, B.K., Bandyopadhyay, S.S., Samanta, A.N., 2017. Kinetics of CO2 absorption in aqueous hexamethylenediamine. Int. J. Greenh. Gas Control 56, 116–125. doi:10.1016/j.ijggc.2016.11.023

Mondal, B.K., Bandyopadhyay, S.S., Samanta, A.N., 2015. Vapor–liquid equilibrium measurement and ENRTL modeling of CO2 absorption in aqueous hexamethylenediamine. Fluid Phase Equilib. 402, 102–112. doi:10.1016/j.fluid.2015.05.033

Park, M.K., Sandall, O.C., 2001. Solubility of Carbon Dioxide and Nitrous Oxide in 50 mass % Methyldiethanolamine. J. Chem. Eng. Data 46, 166–168. doi:10.1021/je000190t