Amine-based Solvent Characterization (Reaction Kinetics Measurement and Modeling)

  • Ahmed Sodiq

Student thesis: Master's Thesis

Abstract

The recent anthropogenic emissions of greenhouse gases (about 400 ppm atmospheric concentration of CO2) are the highest in history since record keeping began. These emissions would have widespread foreseeable impacts on human and environmental systems due to global warming engendered by high concentration of greenhouse gases in the atmosphere. This is an indication that human influence on the climate system is strong and it is only human effort that can be harnessed through mitigation strategies to save the planet from destruction. By 2050, it is proposed that carbon capture and storage (CCS), as one of the proposed mitigation strategies, will be responsible for the reduction of atmospheric CO2 emissions by19 percent if the current R&D in CCS persists. Post-combustion capture with chemical absorption remains the most mature and adequately researched technology that can be used to meet 2050 CO2 emission reduction target. However, this technology needs further improvement on the reduction of operational cost that is hampering its large scale deployment. One of the ways to reduce the operational cost and capital intensive nature of CCS is the development of solvent system that has high CO2 absorption capacity, low absorption enthalpy and fast reaction kinetics. The absorption capacity and absorption enthalpy of the solvents used in this work have been determined previously. Thus, this work focuses on the reaction kinetics measurement of selected solvents. These include aqueous solution of amines and salts of amino acid. The amines used in this work cover all classes of amine; such as primary amine (Monoethanolamine, MEA), secondary amine (Diethanolamine, DEA), tertiary amine (N-Methyldiethanolamine, MDEA), cyclic amine (Piperazine, PZ), sterically-hindered amine (2amino-2-methyl-1-propoanol, AMP) and cyclic monoamines (3-piperidinemethanol, 3PM). In addition, salts of amino acid such as sodium taurate (NaTau) and sodium prolinate (NaPr) were used. Stopped-flow equipment is used to measure the direct pseudo first-order reaction constants of the reaction between CO2 and aqueous amines or aqueous salts of amino acid. Proposed reaction mechanisms such as zwitterion, termolecular and base-catalysis mechanisms for the absorption of CO2 in aqueous amines are employed in this work to fit the experimental data. Zwitterion mechanism fits the experimental data of the aqueous reaction between CO2 and stand-alone MEA, DEA, AMP and PZ better while base-catalysis mechanism fits the experimental data of the reaction between CO2 and stand-alone MDEA better than other proposed mechanisms. None of the proposed mechanisms fits the experimental data of the reaction between CO2 and aqueous stand-alone 3PM. For the blend systems, hybrid of zwitterion mechanisms fit the experimental kinetic data of the reaction between CO2 and aqueous AMP/MEA, AMP/PZ, MEA/PZ, DEA/PZ better while hybrid of zwitterion and base-catalysis mechanisms fits the experimental kinetic data of the reaction between CO2 and aqueous MDEA/PZ blend better. The results obtained show stand-alone 3PM having the fastest reaction rate, followed by PZ. As expected, MDEA is the least reactive stand-alone amine being a tertiary amine. Of the two tested salts of amino, NaPr is more reactive than NaTau and shows a significant faster reaction with CO2 than the industrial standard MEA. For the blends, MEA/PZ is adjudged to be the blend that has the fastest kinetics. However, due to other parameters such as high absorption enthalpy reported previously, the blend cannot be taken as a novel sorbent. The next reactive blend is AMP/PZ; AMP shows a significant improvement upon being activated by PZ and displays a faster reaction kinetics than the corresponding DEA/PZ, though stand-alone DEA is more reactive than stand-alone AMP. AMP/PZ blend displays a faster reaction kinetics than the industrial standard MEA. When other parameters (such as absorption capacity and absorption enthalpy) are taken into consideration, AMP/PZ blend in this work is the novel solvent forecasted in the thesis prospectus.
Date of AwardMay 2015
Original languageAmerican English
SupervisorMohammad Abu Zahra (Supervisor)

Keywords

  • Climate Change
  • Carbon Capture
  • Reaction Kinetics
  • Stopped-Flow Technique
  • Amine Blends
  • Zwitterion Mechanism
  • Termolecular Mechanism
  • Base-Catalysis Mechanism.

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