CO2 Capture by Aqueous Absorption Summary of 1St Quarterly Progress Reports 2009 Supported by the Luminant Carbon Management Program and The
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1 CO2 Capture by Aqueous Absorption Summary of 1st Quarterly Progress Reports 2009 Supported by the Luminant Carbon Management Program and the Industrial Associates Program for CO2 Capture by Aqueous Absorption by Gary T. Rochelle Department of Chemical Engineering The University of Texas at Austin May 3, 2009 Introduction This research program is focused on the technical obstacles to the deployment of CO2 capture and sequestration from flue gas by alkanolamine absorption/stripping and on integrating the design of the capture process with the aquifer storage/enhanced oil recovery process. The objective is to develop and demonstrate evolutionary improvements to monoethanolamine (MEA) absorption/stripping for CO2 capture from coal-fired flue gas. The Luminant Carbon Management Program and the Industrial Associates Program for CO2 Capture by Aqueous Absorption support 14 graduate students. These students have prepared detailed quarterly progress reports for the period January 1, 2009 to March 31, 2009. Five original paper manuscripts are included; Cohen et al., Freeman et al., Plaza et al., and two by Sexton. Three Ph.D. research proposals are attached: Freeman, Van Wagener, and Plaza. We have also attached Powerpoint presentations made by Rochelle and Closmann at the semiannual meeting of the Process Science and Technology Center. Conclusions 7.7 m hydroxyethylpiperazine (HEP), 4.8 m aminomethylpropanol (AMP), and 8 m 2-piperidine ethanol provide a CO2 capacity of 0.7, 1.0, and 1.2 moles/mole (water+amine) and a normalized 2 CO2 flux (kg’) at rich conditions of 2.9e-10, 1.7e-10, and 2.0e-10 kmol/s.PA.m , respectively. These capacities are greater than 7 m MEA (0.5) and in the same range at 8 m PZ (0.8). The rates are less than MEA (3.1e-10) and piperazine (5.3e-10). The heat of CO2 desorption in the three new amines was 69, 73, and 73 kJ/mol, respectively compared to 70 for 8 m PZ and 82 for 7 m MEA. Structured packing M250X (60o flow) provided 40% less pressure drop and 20% greater capacity than M250Y (45o), but the mass transfer area was practically the same. Packing without surface texturing (M250YS) provided 20% less pressure drop and 10% less area than the comparable textured packing (M250X). The PZ thermodynamic model developed by Hilliard has been successfully modified to represent accurately the VLE by Dugas and the heat capacity data by Nguyen. It now provides stable predictions up to 150 oC. 1 2 With 8 m PZ in a three-stage heated flash at 150 oC, the equivalent work requirement was 35.0 kJ/mol CO2, compared to 36.3 kJ/mol CO2 and 40.3 kJ/mol CO2 for simple strippers using 8 m PZ and 7 m MEA, respectively. The activation energy for the thermal degradation of 7 m MDEA/2 m PZ is approximately 104 kJ/gmol. The thermal degradation rates of MDEA and PZ are 59 ± 25 and 66 ± 21 mmolal/day at 150 °C and 0.26 moles CO2/mole alkalinity. Analyses of solution from the pilot plant campaign in Fall 2008 with concentrated piperazine showed no signs of oxidation or thermal degradation. Nor did these samples have any significant foaming tendency. With 18 weeks at 150 oC, the degradation rate of 8 m PZ was 0.44%/week. The most prevalent degradation products identified were ethylenediamine (1.2 mM/wk), formate (0.9 mM /wk), and formamide (2.3 mM/wk). For 8 m PZ solution with 0.306 CO2 loading, the total pressure is 0.9 bar at 100 ºC. For 8 m PZ solution with 0.424 CO2 loading, the total pressure is 24 bars at 150 ºC. 7 m MEA is approximately twice as volatile as 8 m PZ and is roughly 2.5 times more volatile than the 7m MDEA/2 m PZ. 5 m AMP 1.5–3 times more volatile than 7 m MEA. In loaded PZ solutions the partial Cp for liquid PZ is approximately 2.33 J/g-K. The partial Cp of CO2 is only 0.76 J/g-K. The Cp of loaded 8 m PZ from 40 ºC–120 ºC varies from 3.1–3.6 J/g-K. Inhibitor B reduced the apparent degradation of MEA by about 50% at a variety of catalyst conditions. Thermal degradation of loaded MEA at anaerobic conditions in stainless steel bombs results in corrosion with production of up to 765 ppm Fe++, 400 ppm Ni++, and 300 ppm Cr+2. Accurate modeling of absorber performance may require a Gaussian distribution of stage packing height, with a finer grid at the top and bottom of the column. 1. Wetted Wall Column Rate Measurements p. 11 by Xi Chen The CO2 solubility and adsorption/desorption rate were measured in the wetted wall column for 7.7 m N-(2-hydroxyethyl)piperazine (HEP), 5 m 2-amino-2-methyl-1-propanol (AMP) and 8 m 2-piperidineethanol (2-PE). VLE models of CO2 were regressed from experimental data to calculate CO2 capacity and enthalpy of CO2 absorption (∆Habs). The liquid film mass transfer coefficients (kg’) and CO2 partial pressures (P*) obtained are compared to those of 8 m piperazine (PZ) and 7 m monoethanolamine (MEA). 2. Influence of Liquid Properties on Effective Mass Transfer Area of Structured Packing p. 22 by Robert Tsai (also supported by the Separations Research Program) Two Sulzer structured packings were evaluated: an untextured (smooth) version of Mellapak 250Y (M250YS) and Mellapak 250X (M250X). 2 3 M250YS exhibited 15–20% lower pressure drop and hold-up than standard (textured) Mellapak 250Y (M250Y). Baseline (0.1 M NaOH) mass transfer tests revealed texture to have only a minor impact on effective area; measured area for M250YS was at most 10% lower than for M250Y. A reduction in surface tension to 30 dynes/cm appeared to impact both packings in the same manner, marginally increasing effective area (10%). M250X displayed drastically better hydraulic performance than M250Y. Pressure drop was 40% that of M250Y, and capacity was 20% greater, although hold-up was only around 10% lower. Interestingly, mass transfer area did not suffer as a consequence of the improved hydraulics. While the measured area for M250X was observed to be lower than for M250Y, this was by a very small margin (less than 5%) – essentially indistinct relative to the experimental noise. The mass transfer area database was updated, and the current global (ae/ap) correlation, able to represent the entire database within limits of ±15%, is as follows: 116.0 a − 1 e 3 = 327.1 []()()FrWe LL ap 3. Modeling Stripper Performance for CO2 Removal p. 35 by David Van Wagener Since Hilliard developed thermodynamic models for various amine solvents, additional experimental data has been collected at new conditions. The data primarily of interest has been for concentrated piperazine (PZ). The Hilliard model predicted well for low concentrations, 0.9 m–5 m, but 8 m PZ will be used in future simulations. VLE data collected by Dugas as well as heat capacity data collected by Nguyen for concentrated piperazine was incorporated into previous parameter regression files. The parameters to be regressed were reconsidered, and more focus was put on the heat capacity parameters of the dominant species at relevant loadings. The predictions by the newly regressed model were near-perfect for the relevant loading range, 0.3–0.4, and only had a maximum deviation of 5% at a loading of 0.2. The accuracy of the VLE predictions was not significantly compromised at these loadings with the new parameter values. The performance of multi-stage flash configurations with concentrated PZ was also assessed. Compressing to 150 atm, a three-stage flash operated with 8 m PZ had an equivalent work of 35.0 kJ/mol CO2 compared to the 40.3 kJ/mol CO2 required for a simple stripper using 7 m MEA. 4. Solvent Management of MDEA/Piperazine p. 50 by Fred Closmann (also supported by the Process Science & Technology Center) Thermal degradation experiments were conducted on 7 m MDEA/2 m PZ in the past quarter. The compounds dimethylaminoethanol (DMAE), diethanolamine (DEA), methylaminoethanol (MAE), ethylenediamine (EDA), methyl piperazine, dimethyl piperazine, and N,N- diethylethanolamine were identified in degraded solvent samples through ion chromatography mass spectrometry (IC-MS). MDEA and PZ degrade with a stoichiometric one-to-one relationship and a mechanism that may be first order in both amines, until the PZ has approached zero concentration. Thereafter, the loss of MDEA slows. Our findings are consistent with the literature which indicates that MDEA degrades through disproportionation processes, and can then react with piperazine (PZ) to form diamine compounds through arm-switching processes 3 4 when both MDEA and PZ are present in the solvent. The activation energy for the degradation of MDEA and PZ is approximately 104 kJ/gmol, and rates of degradation of MDEA and PZ are 59 ± 25 and 66 ± 21 mmolal/day at 150 °C and α=0.26. 5. Solvent Management of Concentrated Piperazine p. 59 by Stephanie Freeman The solution analysis of the pilot plant was completed this quarter and all the measured values are reported. There is slight disagreement between the measurements taken at the pilot plant during the actual campaign and those completed afterward in the laboratory. There was not a significant production of degradation products with the highest concentrations of anions below 0.5 mM. A small amount of ethylenediamine (EDA) was detected with the samples ranging from 0.61 mM, well below the baseline detection limit of the cation IC, to 9.79 mM. A foaming test of the final campaign solution indicated that very little foaming occurred during the test.