Dissertations / Theses on the topic 'Carbon dioxide Piperazine'

Estudou-se o processo de absorção e dessorção de CO2 em solução aquosa da mistura de metildietanolamina (MDEA) e piperazina (PZ). Os ensaios de absorção foram realizados numa coluna de parede molhada com promotor de película, e, os ensaios de dessorção num sistema de semibatelada, ambos em escala de laboratório. Os testes experimentais de absorção foram realizados a 298 K e pressão atmosférica, com vazão de gás (CO2 e ar atmosférico) de 2,2.10-4 m3 s-1 e as seguintes vazões de líquido: 1,0.10-6; 1,3.10-6 e 1,7.10-6 m3 s-1. O sistema de absorção foi caracterizado através da determinação da área interfacial, a, o coeficiente volumétrico de transferência de massa, kGa, e o coeficiente volumétrico global médio de transferência de massa, KGa. No caso dos ensaios de dessorção, estes foram realizados nas temperaturas de 353, 363 e 368 K, onde empregou-se uma solução carbonatada de 10% PZ-20% MDEA e uma corrente de ar atmosférico nas vazões de 1,1.10-5 m3 s-1 e 2,7.10-5 m3 s-1. Este sistema foi caracterizado através da determinação do coeficiente volumétrico global de transferência de massa, KLa. Os resultados experimentais da área interfacial mostram que este é função da vazão do líquido, sugerindo uma maior área de irrigação como o aumento desta, onde teve-se uma maior área de transferência de massa. O resultado do parâmetro, KGa, indica uma dependência da vazão de líquido, a qual está associada à variação da área interfacial e à dependência do parâmetro KG com o perfil das concentrações da MDEA e PZ ao longo da coluna. A partir da teoria do duplo filme e pelo conhecimento dos parâmetros KGa, a e kGa, estimou-se um parâmetro cinético-difusivo associado à fase líquida, (( ) ) . Os resultados experimentais mostram que esse parâmetro varia pouco com a vazão de líquido, indicando tratar-se de um processo independente da hidrodinâmica do líquido, característico de sistemas com reação rápida. A concentração das aminas e carbamatos, nos ensaios de absorção e dessorção, foi determinada através dos modelos de calibração obtidas pela técnica de espectroscopia no infravermelho. Nos ensaios de absorção, foram observados que a concentração de PZ teve uma variação considerável (4 a 5% massa massa-1), entanto que a de MDEA variou pouco (0,3 a 0,5% massa massa-1), sugerindo que o processo de absorção de CO2 na mistura MDEA-PZ é controlado principalmente pela PZ, e supõe-se que a MDEA tem um papel de receptor de prótons procedentes da reação entre a PZ e o CO2. Nos ensaios de dessorção, observou-se que esse processo é afetado pela temperatura, sendo que, em temperaturas perto da ebulição (372 K), a taxa de dessorção de CO2 é maior do que em temperaturas menores, em certa forma é devido à dependência da velocidade de reação química com a temperatura. Os resultados do parâmetro KLa indicam que este diminui em função da concentração de carbamato de PZ (por exemplo, na temperatura de 368 K, de 7,5.10-4 a 1,0.10-4 s-1), devido a que este componente é decomposto em altas temperaturas gerando o CO2 e as aminas, sugerindo uma diminuição na velocidade de dessorção de CO2. Assim também, os resultados experimentais do parâmetro KLa indicam que este aumenta ligeiramente com a vazão do gás.<br>The CO2 absorption and desorption process was studied in an aqueous mixture of methyldiethanolamine (MDEA) and piperazine (PZ). The absorption process was carried out in a wetted wall column with film promoter sized with inner diameter of 0,0184 m and height of 0,67 m. The desorption tests were carried out in semi batch system at laboratory scale. The absorption experimental tests were conducted at 298 K, atmospheric pressure, gas flow rate of 2,2.10-4 m3 s-1 and the following liquid flow rates: 1,0.10-6; 1,3.10-6 and 1,7.10-6 m3 s-1. The absorption process was characterized by the following mass transfer parameters: interfacial area, a, the volumetric mass-transfer coefficient of the gas phase, kGa, and the overall volumetric mass-transfer coefficient, KGa. In the case of desorption tests, these were carried out at temperatures of 353, 363 and 368 K, where was used a carbonated solution of 10% PZ-20% MDEA (% wt) and the air flow rates of 1,1.10-5 m3 s-1 and 2,7.10-5 m3 s-1. The desorption process was characterized by the overall volumetric mass-transfer coefficient of the liquid phase, KLa. The experimental results of the interfacial area indicate that this parameter increases in function of the liquid flow rate, this effect is due to an larger irrigation on the inner wall of the column, and hence an available larger contact surface for the mass transfer. The overall volumetric mass-transfer coefficient, KGa, is influenced by the liquid flow rate, which is associated with a change in the interfacial area and the dependence of the parameter KG of the concentration profile of MDEA and PZ along the column. From the two-film theory and by knowledge of the parameters \"kGa\", \"a\" and \"KGa\", it was estimated the kinetic-diffusive parameter, (( ) ) . The experimental results show that this parameter varies slightly in function of the liquid flow rate, and this behavior is characteristic of systems with rapid reaction. Furthermore, this behavior suggests that the absorption process is independent of liquid hydrodynamic occurring in the column. The concentrations of MDEA, PZ and PZ carbamate, in the absorption and desorption tests, were determined by multivariate calibration models based on mid-infrared spectroscopy. In the absorption test, it was observed that the PZ concentration had a considerable variation (4 to 5% w w-1), whereas MDEA varied slightly along the column (0,3 to 0,5% w w-1), suggesting that the CO2 absorption process in the MDEA/PZ blend is mainly controlled by PZ, and it is supposed that MDEA participates as a proton receptor coming from reaction between CO2 and PZ. The results of the desorption tests shown that this process is affected by desorption temperature, and at temperatures near the boiling point (372 K), the CO2 desorption rate is higher than at lower temperatures, a certain shape is due to the dependence chemical reaction rate with temperature. The results of parameter KLa indicated that this decreases in function of the concentration of PZ carbamate (for instance, at the temperature of 368 K, from 7,5.10-4 to 1,0.10-4 s-1), because this component is decomposed at high temperatures generating CO2 and amines, suggesting a decrease in the CO2 desorption rate. Likewise, experimental results of the parameter KLa indicated that this increased slightly with the gas flow rate.

Rigorous thermodynamic and kinetic models were developed in Aspen Plus® Rate SepTM for 8 m PZ, 5 m PZ, 7 m MDEA/2 m PZ, and 5 m MDEA/5 m PZ. Thermodynamic data was regressed using a sequential regression methodology, and incorporated data for all amine, amine/water, and amine/water/CO₂ systems. The sensitivity of CO₂ absorption rate was determined in a wetted wall column simulation in Aspen Plus®, and the results were used in Microsoft Excel to determine the optimum reaction rates, activation energies, and binary diffusivities. Density, viscosity, and binary diffusivity are calculated using user-supplied FORTRAN subroutines rather than built-in Aspen Plus® correlations. Three absorber configurations were tested: adiabatic, in-and-out intercooling, and pump-around intercooling. The two intercooled configurations demonstrated comparable improvement in capacity and packing area, with the greatest improvement in 8 m PZ occurring between lean loadings of 0.20 and 0.25 mol CO₂/mol alkalinity. The effects of absorber temperature and CO₂ removal were tested in the adiabatic and in-and-out intercooled configurations. For 7 m MDEA/2 m PZ at a lean loading of 0.13 mol CO₂/mol alkalinity reducing the absorber temperature from 40 °C to 20 °C increases capacity by 64% without an appreciable increase in packing area. Increasing CO₂ removal from 90% to 99% does not double the packing area due to favorable reaction rates at the lean end of the absorber. Two stripper configurations were tested: the simple stripper and the advanced flash stripper. For all amines, absorber configurations, and lean loadings the advanced flash stripper demonstrated the better energy performance, with the greatest benefit occurring at low lean loadings. An economic estimation method was developed that converts purchased equipment cost and equivalent work to $/MT CO₂. The method is based on economic factors proposed by DOE-NETL and IEAGHG. The total cost of CO₂ decreases as lean loading decreases for all amines and configurations. Increasing CO₂ removal from 90% to 99% results in a 1% increase in the total cost of CO₂ capture. Decreasing absorber temperature for 7 m MDEA/2 m PZ from 40 °C to 20 °C decreases total cost of CO₂ capture by up to 9.3%.<br>text

A large-scale pilot plant (0.43 m ID) was extensively modified and converted into an absorber/stripper system to demonstrate CO₂ capture technology using aqueous piperazine promoted potassium carbonate for coalfired power plants. Four pilot plant campaigns were completed. Three campaigns were conducted using 5 m K⁺/2.5 m PZ and 6.4 m K⁺/1.6 m PZ. Flexipac 1Y and Flexipac AQ Style 20 structured packing were used in the absorber. The stripper was tested with 14 sieve trays, IMTP #40 random packing, and Flexipac AQ Style 20 packing. Monoethanolamine (7 m) was tested in the third campaign to establish a base case. An approximate rate analysis showed that 5 m K⁺/2.5 m PZ is two times faster than 7 m MEA and three times faster than 6.4 m K⁺/1.6 m PZ. The location of the temperature bulge moves from the top of the column to bottom as the liquid to gas flow rate ratio is increased. Foaming occurred in the absorber in the first two campaigns and occurred in the stripper in the fourth campaign. Data from the pilot plant was used to develop a K⁺/PZ absorber model in Aspen Plus® RateSep[trademark]. The Hilliard (2005) Aspen Plus® VLE model and the kinetics developed by Cullinane (2005) were incorporated in the model. Data-Fit was simultaneously used to reconcile pilot plant data and perform a regression of the interfacial area and heat loss parameters for the RateSep[trademark] absorber model. The lean loading for the pilot plant data was shifted down by 10% to account for a discrepancy with the Cullinane vapor-liquid equilibrium data. The Data-Fit results showed that the average interfacial area for Flexipac 1Y was 80% of the value measure by the air-water column. The average interfacial area for Flexipac AQ Style 20 for 5 m K⁺/2.5 m PZ was 56% of the air-water measurement. The CO₂ heat of absorption may not have been adequately predicted by the RateSep[trademark] absorber model because the regressed values of heat loss were consistent with forced convection.

This work includes wetted wall column experiments that measure the CO₂ equilibrium partial pressure and liquid film mass transfer coefficient (kg') in 7, 9, 11, and 13 m MEA and 2, 5, 8, and 12 m PZ solutions. A 7 m MEA/2 m PZ blend was also examined. Absorption and desorption experiments were performed at 40, 60, 80, and 100°C over a range of CO₂ loading. Diaphragm diffusion cell experiments were performed with CO₂ loaded MEA and PZ solutions to characterize diffusion behavior. All experimental results have been compared to available literature data and match well. MEA and PZ spreadsheet models were created to explain observed rate behavior using the wetted wall column rate data and available literature data. The resulting liquid film mass transfer coefficient expressions use termolecular (base catalysis) kinetics and activity-based rate expressions. The kg' expressions accurately represent rate behavior over the very wide range of experimental conditions. The models fully explain rate effects with changes in amine concentration, temperature, and CO₂ loading. These models allow for rate behavior to be predicted at any set of conditions as long as the parameters in the kg' expressions can be accurately estimated. An Aspen Plus® RateSep™ model for MEA was created to model CO₂ flux in the wetted wall column. The model accurately calculated CO₂ flux over the wide range of experimental conditions but included a systematic error with MEA concentration. The systematic error resulted from an inability to represent the activity coefficient of MEA properly. Due to this limitation, the RateSep™ model will be most accurate when finetuned to one specific amine concentration. This Aspen Plus® RateSep™ model allows for scale up to industrial conditions to examine absorber or stripper performance.<br>text

Absorption-stripping with aqueous, concentrated piperazine (PZ) is a viable retrofit technology for post-combustion CO2 capture from coal-fired power plants. The rate of thermal degradation and oxidation of PZ was investigated over a range of temperature, CO2 loading, and PZ concentration. At 135 to 175 °C, degradation is first order in PZ with an activation energy of 183.5 kJ/mole. At 150 °C, the first order rate constant, k1, for thermal degradation of 8 m PZ with 0.3 mol CO2/mol alkalinity is 6.12 × 10-9 s-1. After 20 weeks of degradation at 165 °C, 74% and 63%, respectively, of the nitrogen and carbon lost in the form of PZ and CO2 was recovered in quantifiable degradation products. N-formylpiperazine, ammonium, and N-(2-aminoethyl) piperazine account for 57% and 45% of nitrogen and carbon lost, respectively. Thermal degradation of PZ likely proceeds through SN2 substitution reactions. In the suspected first step of the mechanism, 1-[2-[(2-aminoethyl) amino]ethyl] PZ is formed from a ring opening SN2 reaction of PZ with H+PZ. Formate was found to be generated during thermal degradation from CO2 or CO2-containing molecules. An analysis of k1 values was applied to a variety of amines screened for thermal stability in order to predict a maximum recommended stripper temperature. Morpholine, piperidine, PZ, and PZ derivatives were found to be the most stable with an allowable stripper temperature above 160 °C. Long-chain alkyl amines or alkanolamines such as N-(2-hydroxyethyl)ethylenediamine and diethanolamine were found to be the most unstable with an allowable stripper temperature below 120 °C. Iron (Fe2+) and stainless steel metals (Fe2+, Ni2+, and Cr3+) were found to be only weak catalysts for oxidation of PZ, while oxidation was rapidly catalyzed by copper (Cu2+). In a system with Fe2+ or SSM, 5 kPa O2 in the inlet flue gas, a 55 °C absorber, and one-third residence time with O2, the maximum loss rate of PZ is expected to 0.23 mol PZ/kg solvent in one year of operation. Under the same conditions but with Cu2+ present, the loss rate of PZ is predicted to be 1.23 mole PZ/kg solvent in one year of operation. Inhibitor A was found to be effective at decreasing PZ loss catalyzed by Cu2+. Ethylenediamine, carboxylate ions, and amides were the only identified oxidation products. Total organic carbon analysis and overall mass balances indicate a large concentration of unidentified oxidation products.<br>text

碩士<br>中原大學<br>化學工程研究所<br>95<br>The objectives of this research are to study both experimentally and theoretically the absorption of carbon dioxide into aqueous blends of triethanolamine (TEA) and piperazine (PZ). The solution systems studied are CO2/PZ/H2O, and CO2/PZ/TEA/H2O. The concentration range are : 0.1, 0.2, 0.3, and 0.4 kmol m-3 PZ for CO2/PZ/H2O; and 0.1, 0.2, 0.3, and 0.4 kmol m-3 PZ was blended into 1.0 and 1.5 kmol m-3 TEA for CO2/PZ/TEA/H2O. The temperatures were from 30 to 40 °C. The experimental reaction kinetics data were represented by a combined mass transfer-reaction kinetics-equilibrium model which contains a set of differential-algebraic equations. A numerical method was applied to obtain the concentration of each species as functions of time and position. When integrating to the contact time, the average specific absorption rate was obtained and the reaction rate constants of carbon dioxide with TEA and PZ were determined. The period of the project is three years. For the second year, the program to perform the calculation of the combined mass transfer-reaction kinetics-equilibrium model was carried out and tested, the thermophysical properties such as density, viscosity, Henry’s constant, and diffusivity of PZ and water system were completed as planned. The specific CO2 absorption rate will be measured using a wetted-wall column apparatus. The physicochemical properties such as density, viscosity, Henry’s law constant and diffusivity of nitrous oxide in amines were also be measured. The N2O analogy was used to estimate the Henry’s law constant and diffusivity of CO2 in amines solutions. The mutual diffusivity of TEA and PZ in water were measured using the apparatus based on the Taylor dispersion method. A rigorous mathematical model applied to interpret the rate data is based on the principle of diffusional mass transfer accompanied with liquid-phase chemical reactions over the wetted-wall column. The kinetics data of CO2/PZ/TEA/H2O were used to determine the reaction rate constants for CO2/TEA, CO2/PZ. The determined reaction rate constants were consistent for both single amine and blend amine systems. the results of the proposed research can provide the fundamental kinetics data for the process design for the CO2 absorption using aqueous PZ/TEA solutions as absorbents.

碩士<br>中原大學<br>化學工程研究所<br>100<br>The reaction kinetics for the absorption of CO2 into aqueous solutions of Diethylenetriamine (DETA) and into mixed aqueous solutions of DETA and Piperazine (PZ) were investigated by a wetted wall column at 30, 35 and 40°C. The systems studied were: DETA (5, 10, 15, 20, 25, and 30 wt%) + H2O and DETA (26 wt%) + PZ (4 wt%) + H2O, DETA (22 wt%) + PZ (8 wt%) + H2O, DETA (18 wt%) + PZ (12 wt%) + H2O. The physical properties such as density, viscosity, Henry’s constant and diffusivity of the studied systems were also measured. Due to the reactivity of CO2 to the amine system, an N2O analogy was used to estimate the solubility and diffusivity of CO2 in the aqueous amine solutions. From the kinetics measurements, the absorption rates of CO2 in the aqueous blended DETA/PZ solutions were found to be significantly faster than in conventional amine systems. The reaction rate constants were calculated by applying a hybrid model which combines a pseudo-first-order model with a zwitterion mechanism. This model was found to satisfactorily represent the absorption of CO2 in both the aqueous DETA and aqueous blended DETA/PZ systems. It can be concluded that the results of this study can be used in the design of absorption processes which employ aqueous solutions of DETA or DETA/PZ as absorbents.

Rigorous CO₂ absorption models were developed for aqueous 4.5 m K+/4.5 m PZ, monoethanolamine (7m - 9m), and piperazine (8m) in Aspen Plus® RateSepTM. The 4.5 m K+/4.5 m PZ model uses the Hilliard thermodynamic representation and kinetics based on work by Chen. The MEA (Phoenix) and PZ (5deMayo) models incorporate new data for partial pressure of CO₂ vs. loading and kinetics from wetted wall column data. They use reduced reaction sets based on the more relevant species present at the expected operating loading. Kinetics were regressed to match reported carbon dioxide flux data using a wetted wall column (WWC). Density and viscosity were satisfactorily regressed to match newly obtained experimental data. The activity coefficient of CO₂ was also regressed to include newly obtained CO₂ solvent solubility data. The models were reconciled and validated using pilot plant data obtained from five campaigns conducted at the Pickle Research Center. Performance was matched within 10% of NTU for most runs. Temperature profiles are adequately represented in all campaigns. The calculated temperature profiles showed the effect of the L/G on the location and magnitude of the temperature bulge. As the L/G is increased the temperature bulge moves from near the top of the column towards the bottom and its magnitude decreases. Performance improvement due to intercooling was validated across the campaigns that evaluated this process option. Absorber intercooling was studied using various solvent rates (Lmin, 1.1 Lmin and 1.2 Lmin). It is most effective at the critical L/G where the temperature bulge without intercooling is in the middle of the column. In this case it will allow for higher absorption by reducing the magnitude of the bulge temperature. The volume of packing to get 90% removal with L/Lmin =1.1 at the critical L/G is reduced by 30% for 8m PZ. For MEA and a solvent flow rate of 1.1 Lmin packing volume is increased with intercooling at constant L/G. This increase is compensated by higher solvent loadings that suggest lower stripping energy requirements. The critical L/G is 4.3 for 8m PZ, 6.9 for 9m MEA and 4.1 for K+/PZ.<br>text

To screen amine solvents for application in CO2 capture from coal-fired power plants, the equilibrium CO2 partial pressure and liquid film mass transfer coefficient were characterized for CO2-loaded and highly concentrated aqueous amines at 40 – 100 °C over a range of CO2 loading with a Wetted Wall Column (WWC). The acyclic amines tested were ethylenediamine, 1,2-diaminopropane, diglycolamine®, methyldiethanolamine (MDEA)/Piperazine (PZ), 3-(methylamino)propylamine, 2-amino-2-methyl-1-propanol and 2-amino-2-methyl-1-propanol/PZ. The cyclic amines tested were piperazine derivatives including proline, 2-piperidineethanol, N-(2-hydroxyethyl)piperazine, 1-(2-aminoethyl)piperazine, N-methylpiperazine (NMPZ), 2-methylpiperazine (2MPZ), 2,5-trans-dimethylpiperazine, 2MPZ/PZ, and PZ/NMPZ/1,4-dimethylpiperazine (1,4-DMPZ). The cyclic CO2 capacity and heat of CO2 absorption were estimated with a semi-empirical vapor-liquid-equilibrium model. 5 m MDEA/5 m PZ, 8 m 2MPZ, 4 m 2MPZ/4 m PZ and 3.75 m PZ/3.75 m NMPZ/0.5 m 1,4-DMPZ were identified as promising solvent candidates for their large CO2 capacity, fast mass transfer rate and moderately high heat of absorption. The speciation in 8 m 2MPZ and 4 m 2MPZ / 4 m PZ at 40 °C at varied CO2 loading was investigated using quantitative 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. In 8 m 2MPZ at 40 °C over the CO2 loading range of 0 – 0.37 mol CO2/mol alkalinity, more than 75% of the dissolved CO2 exists in the form of unhindered 2MPZ monocarbamate, and the rest is in the form of bicarbonate and dicarbamate; 19% - 56% of 2MPZ is converted to 2MPZ carbamate at 0.1 - 0.37 mol CO2/mol alkalinity. A rigorous thermodynamic model was developed for 8 m 2MPZ in the framework of the Electrolyte Nonrandom Two-Liquid (ENRTL) model. At 40 °C, the reaction stoichiometry for 2MPZ and CO2 is around 2 at lean loading but diminishes to 0 at rich loading. Bicarbonate becomes the major product at CO2 loading greater than 0.35 mol/mol alkalinity. The predicted heat of CO2 absorption is 75 kJ/mol at 140 °C and decreases with temperature when CO2 loading is above 0.25. The mass transfer rate data for 8 m 2MPZ was represented with a rate-based WWC model created in Aspen Plus®. The reaction rate was described with termolecular mechanism on an activity basis. With minor CO2 loading adjustment and regression of pre-exponential kinetic constants and diffusion activation energy, a majority of the measured CO2 fluxes in the WWC experiments were fitted by the model within ±20% over 40 – 100 °C and 0.1 – 0.37 mol CO2/mol alkalinity. The diffusion activation energy for 8 m 2MPZ at the rich loading is about 28 kJ/mol. The activity-based reaction rate constant at 40 °C for 2MPZ carbamate formation catalyzed by 2MPZ is 1.94×1010 kmol/m3•s. The calculated liquid film mass transfer coefficients are in close agreement with the experimental values. The liquid film mass transfer rate is dependent on the diffusion coefficients of amine and CO2 to the same extent at lean loading and 40 °C. The sum of the powers for the two diffusivities is approximately equal to 0.5 over the loading range of 0 – 0.4 mol CO2/mol alkalinity. The sum of the powers for the dependence of the liquid film mass transfer coefficient on the carbamate formation rate constants (k2MPZ-2MPZ and k2MPZCOO--2MPZ) approaches 0.5 at very lean loading at low temperature, but it decreases as CO2 loading and temperature is increased. At 100 °C, the physical liquid film mass transfer coefficient is the most important factor that determines the liquid mass transfer rate. The pseudo-first order region shifts to higher range of physical liquid film transfer coefficient as temperature increases.<br>text

The Electrolyte Nonrandom Two-Liquid Activity Coefficient model in Aspen PlusTM 2006.5 was used to develop a rigorous and consistent thermodynamic representation for the base sub-component systems associated with aqueous combinations of K₂CO₃, KHCO₃, MEA, and piperazine (PZ) in a mixed-solvent electrolyte system for the application of CO₂ absorption/stripping from coal fired power plants. We developed a new vapor-liquid equilibrium apparatus to measure CO₂, amine, and H2O vapor pressures at 40 and 60 oC. We found that the volatility of MEA and PZ can be approximated at 50 and 20 ppmv at 40°C for any solvent composition studied in this work, over the CO₂ partial pressure range from 0.01 to 0.1 kPa. Very few solvent compositions exhibited a greater differential capacity than 7 m MEA at 60°C; specifically 11 m MEA, 3.5 m MEA + 3.6 m PZ, 7 m MEA + 2 m PZ, 7 m MEA + 3.6 m PZ, and 5 m K+ + 7 m MEA + 3.6 m PZ. Piperazine exhibited a possible maximum differential capacity of 2.21 mole CO₂/kg-H₂O at a concentration of 7.3 m. At the Norwegian University of Science and Technology, Inna Kim determined the differential enthalpy of CO₂ absorption for aqueous combinations of K₂CO₃, KHCO₃, MEA, PZ, and CO₂, based on a consistent experimental method developed for MEA, from 40 to 120°C for use in this work. In addition, we developed a consistent method to measure the specific heat capacity for a number of similar solvent combinations. We found that the enthalpy of CO₂ absorption increased with temperature because the apparent partial heat capacity of CO₂ may be considered small. Finally, by using a differential scanning calorimeter, we determined the dissolution temperature for aqueous mixtures of unloaded piperazine, which inferred an effective operating range for solutions of concentrated piperazine, greater than 5 m PZ, over a loading range between 0.25 to 0.45 mole CO₂/2·mol PZ. Through unit cell x-ray diffraction, we were able to identify and characterize the presence of three solid phases (PZ·6H₂O, KHCO₃, and KvPZ(COO)₂) in aqueous mixture combinations of K₂CO₃, KHCO₃, PZ, and CO₂.<br>text

Amine degradation in aqueous amine scrubbing systems for capturing CO₂ from coal fired power plants is a major problem. Oxygen in the flue gas is the major cause of solvent deterioration, which increases the cost of CO₂ capture due to reduced capacity, reduced rates, increased corrosion, solvent makeup, foaming, and reclaiming. Degradation also produces environmentally hazardous materials: ammonia, amides, aldehydes, nitramines, and nitrosamines. Thus it is important to understand and mitigate amine oxidation in industrial CO₂ capture systems. A series of lab-scale experiments was conducted to better understand the causes of and solutions to amine oxidation. This work included determination of rates, products, catalysts, and inhibitors for various amines at various conditions. Special attention was paid to understanding monoethanolamine (MEA) oxidation, whereas oxidation of piperazine (PZ) and other amines was less thorough. The most important scientific contribution of this work has been to show that amine oxidation in real CO₂ capture systems is much more complex than previously believed, and cannot be explained by mass transfer or reaction kinetics in the absorber by itself, or by dissolved oxygen kinetics in the cross exchanger. An accurate representation of MEA oxidation in real systems must take into account catalysts present (especially Mn and Fe), enhanced oxygen mass transfer in the absorber as a function of various process conditions, and possibly oxygen carriers other than dissolved oxygen in the cross exchanger and stripper. Strategies for mitigating oxidative degradation at low temperature, proposed in this and previous work are less effective or ineffective with high temperature cycling, which is more representative of real systems. In order of effectiveness, these strategies are: selecting an amine resistant to oxidation, reduction of dissolved metals in the system, reduction of the stripper temperature, reduction of the absorber temperature, and addition of a chemical inhibitor to the system. Intercooling in the absorber can reduce amine oxidation and improve energy efficiency, whereas amine oxidation should be considered in choosing the optimal stripper temperature. In real systems, 2-amino-2-methyl-1-propanol (AMP) is expected to be the most resistant to oxidation, followed by PZ and PZ derivatives, then methyldiethanolamine (MDEA), and then MEA. MEA oxidation with high temperature cycling is increased 70% by raising the cycling temperature from 100 to 120 °C, the proposed operational temperature range of the stripper. PZ oxidation is increased 100% by cycling to 150 °C as opposed to 120 °C. Metals are expected to increase oxidation in MEA and PZ with high temperature cycling by 40 - 80%. Inhibitor A is not expected to be effective in real systems with MEA or with PZ. MDEA is also not effective as an inhibitor in MEA, and chelating agents diethylenetriamine penta (acetic acid) (DTPA) and 2,5-dimercapto-1,3,4-thiadiazole (DMcT) are only mildly effective in MEA. Although MEA oxidation in real systems cannot be significantly reduced by any known additives, it can be accurately monitored on a continuous basis by measuring ammonia production from the absorber. Ammonia production was shown to account for two-thirds of nitrogen in degraded MEA at low temperature and with high temperature cycling, suggesting that it is a reliable indicator of MEA oxidation under a variety of process conditions. A proposed system, which minimizes amine oxidation while maintaining excellent rate and thermodynamic properties for CO₂ capture would involve use of 4 m AMP + 2 m PZ as a capture solvent with the stripper at 135 °C, intercooling in the absorber, and use of a corrosion inhibitor or continuous metals removal system. Reducing (anaerobic) conditions should be avoided to prevent excessive corrosion from occurring and minimize the amount of dissolved metals. This system is expected to reduce amine oxidation by 90-95% compared with the base case 7 m MEA with the stripper at 120 °C.<br>text

碩士<br>中原大學<br>化學工程研究所<br>92<br>The reaction kinetics of the absorption of CO2 into aqueous solutions of piperazine (PZ) and into mixed aqueous solutions of PZ and triethanolamine (TEA) and were investigated by a wetted wall column at 30 to 40 �aC. For CO2 + PZ + H2O, the systems studied are aqueous 0.23, 0.46, 0.69, and 0.92 (kmol•m-3 PZ) solutions; for CO2 + PZ + TEA + H2O, the systems considered are PZ (0.1, 0.2, 0.3, 0.4, and 0.5 kmol•m-3) + TEA (0.5 and 1.0 kmol•m-3) + H2O. The physical properties such as density, viscosity of the solutions and the solubility and diffusivity of nitrous oxide (N2O) in the aqueous alkanolamine solutions were also measured. The N2O analogy was applied to estimate the solubilities and diffusivities of CO2 in aqueous amine systems. Based on the pseudo-first-order for the CO2 absorption, the overall pseudo first-order reaction rate constants were determined from the kinetic measurements. For CO2 absorption into aqueous PZ solutions, the obtained second-order reaction rate constants for the reaction of CO2 with PZ are in a good agreement with the results of Bishnoi and Rochelle (2000). For CO2 absorption into mixed aqueous solutions of PZ and TEA, it was found that the addition of small amounts of PZ to aqueous TEA solutions has significantly effect on the enhancement of the CO2 absorption rate. A second-order reaction rate equation is applied to model the reaction of CO2 with PZ and the reaction of CO2 with TEA. The model is satisfactory to represent the CO2 absorption into mixed aqueous solutions of PZ and TEA. The result of this study can be used as a data base for calculating the gas absorption rate in the <a href="http://www.ntsearch.com/search.php?q=design&v=56">design</a> of the gas absorption apparatus using TEA + CO2 +H2O as absorbents.

碩士<br>中原大學<br>化學工程研究所<br>95<br>The objective of this research was to study both experimentally and theoretically the absorption of carbon dioxide into aqueous blends of piperazine (PZ) and 2-amino-2-methyl-1-propanol (AMP). The PZ with concentrations of 0.1, 0.2, 0.3, and 0.4 (kmol·m-3) were blended into 2.0 and 3.0 (kmol·m-3) aqueous AMP solutions. The temperature ranges from 30 to 40 oC. The experiment can estimate the effect of absorption rate of carbon dioxide for increasing PZ into AMP aqueous solution. The specific CO2 absorption rate was measured using a wetted-wall column apparatus. The physicochemical properties such as density, viscosity, Henry’s law constant and diffusivity of nitrous oxide in amines were also measured. The N2O analogy was used to estimate the Henry’s law constant and diffusivity of CO2 in amines solutions. The experimental reaction kinetics data were represented by two models：(1) Pseudo-first order reaction mechanism incorporated with the zwitterion mechanism for CO2-AMP reaction mechanism. (2) Simplified combined mass transfer reaction kinetics equilibrium. Both of these two methods can obtain the reaction rate constants of carbon dioxide with PZ and AMP. The kinetics data of CO2/PZ/AMP/H2O were used to determine the reaction rate constants for CO2/AMP, CO2/PZ. The determined reaction rate constants were consistent for single amines and blend amine systems. The result shows that increasing PZ in AMP aqueous solution can raising the absorption rate of carbon dioxide of blended amine solution.