in Aqueous Single and Blended Amines

I am also grateful to my colleagues/friends from the research group at IIT Guwahati for their support and contribution. Madam. I would like to thank them all for their kind cooperation during my research work.

Publications Journal Papers

Papers in Conferences

INTRODUCTION, LITERATURE REVIEW AND OBJECTIVES

THERMOPHYSICAL PROPERTIES OF AQUEOUS SINGLE AND BLENDED AMINES

EQUILIBRIUM CO 2 SOLUBILITY IN AQUEOUS AEP AND ITS BLEND WITH MDEA / AMP

CONCLUSIONS AND DIRECTION FOR FUTURE WORK 221-224

88 Table 3.15 Comparison of the viscosities (μ) of aqueous MDEA solutions (mass . fraction, w) measured in the present work with literature values at pressure P= 0.1 MPa. 172 Table 5.1 Technical specification of the reagents used in the present work 198 Table 5.2 Modified KE model-based equilibrium constant parameters and.

INTRODUCTION, LITERATURE REVIEW AND OBJECTIVES

Background

However, major inequalities are observed worldwide when it comes to annual CO2 emissions per capita. In the category of the most populous countries, some of the largest emitters per capita can be observed in the case of Australia (17 tonnes), the US (16.2 tonnes) and Canada (15.6 tonnes). This figure appears to be more than 3. times higher than the global average, which was 4.8 tonnes in 2017.

Fig. 1.1 Global greenhouse gas emissions, per country and region [4].

Carbon capture and sequestration

Overview of CO 2 capture processes

Pre combustion
Oxy-fuel combustion
Post-combustion

Because this technology involves significant changes in power plant design, it is most feasible for newer plants. A large volume of gases must be treated because CO2 in the exhaust gas stream is diluted by the nitrogen from the combustion air.

Fig. 1.2 Schematic illustration of pre-combustion capture process

Post combustion carbon dioxide capture technologies

Chemical absorption

Alkanolamine based chemical absorption technology

Physical absorption
Physical adsorption
Cryogenic separation
Membrane technologies

Several separation techniques can be implemented, such as membrane separation, adsorption, physical absorption, and chemical absorption. The amount of dissolved gas absorbed in the system can be proportionally related to the partial pressure of the gas.

Fig. 1.6 Chemical structure of amines used in CO 2 capture application.

Literature review

Absorption of CO 2 in single amine solvent
Absorption of CO 2 in blended amine solvent

54], it can be observed that CO2 loading increases with increasing PZ concentration in mixed amine solvents of (PZ + MDEA) up to a loading of 1.0. 63] further applied the ENRTL model to explain the thermodynamics of CO2 adsorption in the mixed amine system of (AMP + PZ).

Table 1.1 Summary of the literature review about the CO 2 solubility measurement in different single amine solvents

Importance and objectives of present work

Increasing chain length results in a decrease in the initial absorption rate as the CO2 loading increases. Because of this rate-enhancing property, AEP can be considered a rate promoter in the CO2-amine reaction.

Thesis organization

Background of the work, comprehensive literature survey, objectives and outline of the thesis have been discussed in this chapter

Equilibrium solubility data are also modeled using modified KE and ANN models as discussed in the previous chapter. Finally, a comprehensive performance comparison of the studied mixture with the conventional solvent mixture used in PCC processes is presented in this chapter.

In an ending note, general conclusions of this work and the directions for future work have been discussed in this chapter

Along with these mixtures, the possibility of a second tertiary amine, 1-dimethylamino-2-propanol (1DMAP), was also evaluated for CO2 absorption.

Li, Equilibrium solubility of carbon dioxide in the amine solvent system of (triethanolamine + piperazine + water), J. Kundu, Solubility of CO2 in aqueous mixtures of (N-methyl-2-ethanolamine + N-methyldiethanolamine) and (N- methyl -2-ethanolamine + 2-amino- 2-methyl-1-propanol), J. Abbasi, Experimental modeling of carbon dioxide solubility in aqueous solution of monoethanolamine +1, 3-diaminopropane, J.

Javanmiri, Equilibrium solubility of carbon dioxide in aqueous mixture of monoethanolamine (MEA) and 2-1-piperazinylethylamine (PZEA) solutions: Experimental and optimization study, Process Saf.

REACTION MECHANISM AND MODELING APPROACHES FOR CO 2 -AQEOUS AMINE SYSTEM

Introduction

Along with the reliable solubility measurement techniques, appropriate mathematical models are also very necessary to predict the gas solubility over a varied range of operating conditions of temperature and acid gas load. Equilibrium thermodynamics prevailing in the aqueous amine system can be expressed as the fusion of physical equilibrium prevailing in the gas-liquid phase and the reaction equilibrium corresponding to various intermediate reactions existing in aqueous alkanolamine systems. The thermodynamic framework as well as the development of accurate process model development with respect to non-rigorous modified Kent Eisenberg models are discussed in the subsequent sections.

The chapter also discusses the development of ANN model, model architecture as well as optimization of the ANN network.

Reaction mechanism of CO 2 -aqueous alkanolamine system

Zwitterion mechanism

In the above reaction, the component b can be the species ranging from an amine group, hydroxyl ion or water molecule. Since the presence of OH-ion in the aqueous reaction phase is much less compared to the dominant species such as amine and H2O molecule. As a result, the net contribution of OH- to the overall reaction rate can be neglected.

The steady state principle for the intermediate zwitterionic species can be used to estimate the reaction rate that exists in the CO2-aqueous amine solutions.

Case 1

Base catalyzed hydration mechanism
Modeling of CO 2 solubility data

Modified Kent-Eisenberg model
Artificial neural network model

CO2 solubility data, or VLE, in aqueous amine systems is generally expressed as the total CO2 concentration prevailing in the aqueous amine solution versus the total gas phase partial pressure at equilibrium conditions. 20] expressed the equilibrium constant in terms of CO2 partial pressure, temperature and CO2 concentration in the solvent phase in order to predict solubility. Yi is the normalized value of the input and output variables in the range (0-1).

Furst, The effect of including speciation data in modeling the CO2–DEA–H2O system, Fluid Phase Equilib.

THERMOPHYSICAL PROPERTIES OF AQUEOUS SINGLE AND BLENDED AMINES

Introduction

The detailed summary of the corresponding literature review is shown in Tables I.1 – I.6 of Annex I. The present work focuses on the determination of the density, viscosity and surface tension of aqueous solutions of 1-(2-aminoethyl)piperazine (AEP) and N-(3-aminopropyl)-1,3-propanediamine (APDA) as well as various aqueous mixtures of (AEP + MDEA), (AEP + AMP), (APDA + MDEA) and (APDA + AMP) at atmospheric conditions and within the wide temperature range of (303.2 to 343.2) K. The concentrations of the aqueous binary mixture are varied from 0.10 to 0.40 mass fractions, while the AEP and APDA activated aqueous ternary mixtures are studied for a mass fraction of 0.40 and 0.30, respectively.

Experimental

Materials
Measurement of density
Measurement of viscosity and surface tension

Each reported experimental density value in this study is taken as the mean of three measurements. The viscosities of amine solutions were obtained using U-tube Ostwald viscometer [9], which uses a capillary flow method to measure viscosity and surface tension of the solution simultaneously. Each viscosity and surface tension data reported is taken as the average of at least three measurements.

Similarly, the estimated uncertainty in the measured surface tension data was estimated to be within 0.3 mN.m-1.

Results and discussion

Measurement and correlation of density
Measurement and correlation of viscosity

Thermodynamic property estimation

Measurement and correlation of surface tension

Furthermore, the experimentally measured density is used to determine the excess volume of the amine solution. The Grunberg and Nissan model was used to correlate the experimental viscosity of the ternary system [5, 44]. The experimental results show that the surface tension of the binary mixture decreases with temperature and concentration.

Where, ϒ is the measured surface tension of the aqueous amine solution and T stands for the temperature of the solution.

Fig. 3.1 Density of aqueous AEP system at various temperatures and composition (mass fraction)

Conclusions

Bandyopadhyay, Density and viscosity of aqueous solutions of (N-methyldiethanolamine + monoethanolamine), (N-methyldiethanolamine + diethanolamine), (2-amino-2-methyl-1-propanol + monoethanolamine) and (2-amino-2- methyl -1- propanol + diethanolamine), J. Romero, Surface tension of binary mixtures of water + monoethanolamine and water + 2-amino-2-methyl-1-propanol and tertiary mixtures of these amines with water from 25 °C to 50 °C C, J. Navaza, Surface tension of binary mixtures of water + N-methyldiethanolamine and ternary mixtures of this amine and water with monoethanolamine, diethanolamine and 2-amino-2-methyl-1-propanol from 25 to 50 °C, J .

Navaza, Density, speed of sound, viscosity and surface tension of dimethylethylenediamine + water and (ethanolamine + dimethylethanolamine) + water from T = (293.15 to 323.15) K, J. Tian, Experiments and model for surface tension DEAE- PZ and DEAE-MEA aqueous solutions, J. Fadrique, Surface tension of aqueous solutions of alkanolamines: single amines, mixed amines and systems with nonionic surfactants, Fluid phase Equilib.

Table 3.1 Provenance and purity of reagent

Introduction

Therefore, it is desirable to add a rate activator to said solvent to increase the rate of CO2 absorption [2]. The CO2 absorption properties of AEP can be explained by its molecular structure which consists of all three different types of amino groups, viz. These desirable characteristics as well as the lack of literature data on the measurement of CO2 solubility of the aqueous system AEP and (AEP + MDEA/AMP) convince us to investigate the following mixtures for PCC applications.

In addition to the KE model, an advanced artificial neural network (ANN) model was also used to model CO2 solubility data in single and mixed amine systems.

Experimental section

Materials
Experimental methodology

Equilibrium solubility measurement
Standard uncertainty in the solubility measurement

The balance cell is equipped with a pressure transmitter (0-100 psia, Rosemount 2051T, Emerson Process Management, USA) and has an accuracy of ±0.065% of full scale. A certain amount of CO2 gas from the buffer cell was then transferred to the equilibrium cell by operating the needle valve between them. Vapor and liquid phase equilibrium of CO2 gas was reached when no change of total pressure was observed in the equilibrium cell for at least 1 hour.

Where, Vg and ZCO2 represent the gas phase volume and the compressibility factor of CO2 in the equilibrium cell, respectively.

Fig. 4.1 Experimental arrangement for CO 2 solubility measurement: 1- CO 2 Cylinder, 2- Buffer Cell, 3- Equilibrium Cell, 4- Magnetic stirrer, 5- Vacuum Pump, 6- Temperature sensor, 7- Pressure Transducer, 8- Temperature sensor for wa

Modified Kent-Eisenberg model
Artificial neural network

The standard uncertainty in measuring CO2 loading can be considered a function of uncertainty in temperature, reactor volume, pressure and composition of the inlet solution. However, the protonation constant of the tertiary amine group present in the AEP molecule is very small and therefore the overall contribution to the reaction can be neglected [7–8]. Where the terms in the third parenthesis relate to the concentration of ionic species in the reaction medium.

In the present work, K4 and K5 are expressed in terms of temperature, CO2 partial pressure and amine concentration [18].

Fig. 4.2 Algorithm for regression of equilibrium constants from experimental data Begin

Results and discussion

Equilibrium solubility of CO 2 in aqueous amine system
Effect of reaction parameters on the equilibrium CO 2 solubility
Correlation of equilibrium CO 2 solubility
Liquid phase speciation profile, pH, solvent capacity
FTIR-ATR and NMR study
Comparison of solubility with other conventional single and blended amines

It can be predicted from the figure that the measurement of the present work agrees well with the solubility data reported in the literature for aqueous MDEA at the same experimental conditions. The promoting effect of AEP in the aqueous mixture can be inferred from the fact that there is a significant increase in CO2 loading by increasing the concentration of AEP in the mixed amine solvent system (Fig. In addition to this, the best ANN architecture developed in the current work for aqueous AEP system is presented in fig.

The increased solubility may be the result of the steric hindrance effect of the AMP molecule in addition to the substitution of the amine group in the saturated cyclic diamine ring of PZ.

Fig. 4.3 Comparison of solubility data of CO 2 in 0.30 mass fraction aqueous MDEA solution at 313.2 K with literature

Conclusions

On the other hand, the CO2 solubility in concentrated mixed system (0.40 w) obtained in this study is comparable at higher pressure and load to the benchmarked system (0.05w PZ + 0.35w AMP) [3]. This further facilitates the formation of free amine species and bicarbonate ions due to the gradual hydrolysis of unstable intermediate carbamates.