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A simple and quantitatively reliable method for determination of amine speciation is introduced. The method employs three experimental methods that should be readily accessible. The results for CO 2 loaded aqueous solutions of 30 wt % monoethanolamine (MEA) are used for demonstration of the method and show promising agreement with the more complicated spectroscopic methods reported in the literature. The measurements were done at ambient temperature and atmospheric pressure, since theoretical calculations and experimental data from the open literature revealed no considerable difference in speciation at different temperatures. The procedure is based on acid and base titration of the CO 2 loaded amine solution along with the determination of total CO 2 loading. The quantitative results for the different species concentration in the example MEA solution is in agreement with other available spectroscopic methods, mainly NMR, particularly for the free amine, carbamate, and protonated amine concentrations. Aspen Plus was also used for further assessment of the experimental data. ■ INTRODUCTIONRemoval of acidic gases, particularly CO 2 , is a very important operation from an industrial and environmental point of view. Primary, secondary, and tertiary amines and their blends have found widespread application in the absorption and removal of carbon dioxide from process gases. 1,2 In the designing of absorption or desorption columns for a CO 2 capture process by amine or other reactive solvents, the precise knowledge of the reaction chemistry is crucial. In this regard, having an accurate determination of liquid phase species concentration is critical in CO 2 absorption processes modeling vapor−liquid equilibria data. The contribution of the protonated amine, carbamate, and bicarbonate formed in amine solvents to, for example, the CO 2 heat of absorption makes their quantities critical for thermodynamic understanding. 3 Furthermore, providing a good estimation of the free amine concentration is important for mass transfer study of the CO 2 absorption process, where the free amine concentration explicitly appears in the liquid film mass transfer coefficient. 4 Finally, with good understanding of the above concepts it is possible to better design new solvents and blends.Various thermodynamic models, mainly based on activity coefficients, have been proposed for the CO 2 −H 2 O−alkanolamine systems. 5−7 However, many of the models employ computational models, which are not readily accessible or require parameters not necessarily available for all solvents, making experimental methods of merit. 5 Furthermore, reliable experimental values for species concentration in the liquid phase can improve the thermodynamic models. The activity coefficient models and their parameters can be better evaluated by the available amine speciation data. 3 The NMR approach for speciation study of alkanolamine solutions containing dissolved CO 2 is one of the basic methods for this purpose. 8−10 As it was discussed by Boẗtinger et al., the quantif...

The amine assisted CO₂ capture process from coal fired power plants strives for the determination of degradation components and its consequences. Among them, nitrosamine formation and their emissions are of particular concern due to their environmental and health effects. The experiments were conducted using morpholine as a representative secondary amine as a potential CO₂ capture solvent with 100 ppm standard NO₂ gas to better understand the nitrosamine reaction pathways under scrubber and stripper conditions. The role of nitrite in the nitrosation reaction was probed at elevated temperatures. The effects of different concentrations of nitrite on morpholine were evaluated. Formation rate, decomposition rates, activation energy, and the possible reaction pathways are elaborated. Thermal stability tests at 135 °C indicated the decomposition of nitrosamines at the rate of 1 μg/(g h) with activation energy of 131 kJ/mol. The activation energy for the reaction of morpholine with sodium nitrite was found as 101 kJ/mol. Different reaction pathways were noted for lower temperature reactions with NO₂ gas and higher temperature reactions with nitrite.

Oxygen carrier (OC) development is an important topic in chemical looping combustion (CLC). Bimetal oxide OCs usually impart better performance than monometal oxide OCs; one example of which is the introduction of CeO2 as a partially reducible material capable of generating oxygen vacancies that lead to faster oxygen transfer inside OC particle. In this study, CeO2 was used as an additive to a Fe2O3-based OC and its effect on physical properties, such as morphology, surface area and crushing strength, was analyzed in detail. The reactivity of OCs during reduction and oxidation was studied using thermogravimetric analysis mass spectrometry and a bench scale CLC setup. The results showed that the reduction reaction at the OC surface was independent of whether CeO2 was present or not, but after the surface oxygen had been consumed during the oxidation of fuel, the OC with CeO2 additive provided faster oxygen transfer rates from the bulk to the surface to produce better average reaction rates. The OCs after reduction and oxidation cycles were characterized by using X-ray diffraction and Raman scattering techniques. The promotional role of the CeO2 additive is postulated that it enables the creation of oxygen vacancies in a solid solution. These vacancies were able to transfer oxygen from Fe2O3 quickly to the surface of the OC by vacancy diffusion or even through an oxygen tunnel formed by vacancies. The formation of a CeO2 and Fe2O3 solid solution provides the prerequisite for these short-range interactions.

An unpromoted ultrafine iron nano-particle catalyst was used for Fischer-Tropsch synthesis (FTS) in a CSTR at 270°C, 175 psig, H 2 /CO = 0.7, and a syngas space velocity of 3.0 sl/h/g Fe. Prior to FTS, the catalyst was activated in CO for 24 h which converted the initial hematite into a mixture of 85% v-Fe 5 C 2 and 15% magnetite, as found by Mössbauer measurement. The activated catalyst results in an initial high conversion (ca. 85%) of CO and H 2 ; however the conversions decreased to ca. 10% over about 400 h of synthesis time and after that remained nearly constant up to 600 h. Mössbauer and EELS measurement revealed that the catalyst deactivation was accompanied by gradual in situ re-oxidation of the catalyst from initial nearly pure v-Fe 5 C 2 phase to pure magnetite after 400 h of synthesis time. Experimental data indicates that the nucleation for carbide/oxide transformation may initiates at the center of the particle by water produced during FTS. Small amount of e¢-Fe 2.2 C phase was detected in some catalyst samples collected after 480 h of FTS which are believed to be generated by syngas during FTS.Particle size distribution (PSD) measurements indicate nano-scale growth of individual catalyst particle. Statistical average diameters were found to increase by a factor of 4 over 600 h of FTS. Large particles with the largest dimension larger than 150 nm were also observed. Chemical compositions of the larger particles were always found to be pure single crystal magnetite as revealed by EELS analysis. Small number of ultrafine carbide particles was identified in the catalyst samples collected during later period of FTS. The results suggest that carbide/oxide transformation and nano-scale growth of particles continues either in succession or at least simultaneously; but definitely not in the reverse order (in that case some larger carbide particles would have observed). EELS-STEM measurement reveals amorphous carbon rim of thickness 3-5 nm around some particles after activation and during FTS. Well ordered graphitic carbon layers on larger single crystal magnetite particles were found by EELS-STEM measurement. However the maximum thickness of the carbon (amorphous or graphitic) rim does not grow above 10 nm suggesting that the growths of particles are not due to carbon deposition.