Article pubs.acs.org/EF
CO2 Capture Using Phase-Changing Sorbents Robert J. Perry,*,† Benjamin R. Wood,† Sarah Genovese,† Michael J. O’Brien,† Tiffany Westendorf,† Matthew L. Meketa,† Rachel Farnum,† John McDermott,† Irina Sultanova,† Thomas M. Perry,‡ Ravi-Kumar Vipperla,§ Lisa A. Wichmann,§ Robert M. Enick,⊥ Lei Hong,⊥ and Deepak Tapriyal∥ †
GE Global Research, 1 Research Circle, Niskayuna, New York 12309, United States Physics Department, University of Wisconsin, 1150 University Avenue, Madison, Wisconsin 53706, United States § GE Energy, 300 Garlington Road, Greenville, South Carolina 29615, United States ⊥ Department of Chemical and Petroleum Engineering, University of Pittsburgh, 1249 Benedum Hall, 3700 O’Hara Street, Pittsburgh, Pennsylvania 15261, United States ∥ NETL, 626 Cochran Mill Road, Pittsburgh, Pennsylvania 15236, United States ‡
ABSTRACT: A novel method for the postcombustion capture of CO2 from coal-fired power plants has been described utilizing an aminosilicone absorbent. 1,3-Bis(3-aminopropyl)-1,1,3,3-tetramethyldsiloxane (GAP-0) rapidly transforms from a low viscosity liquid to a friable solid upon exposure to CO2 in simulated flue gas. This material has excellent thermal stability, low vapor pressure, high CO2 loading capability, and a large dynamic CO2 capacity between rich and lean solvent loadings. Preliminary plant and process models assembled from experimental data show a decrease in parasitic energy loss from 30% to 18% when compared to the benchmark monoethanolamine (MEA) process and a concomitant lowering of the cost of electricity (COE) from 74% to 44% increase versus a plant without carbon capture.
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INTRODUCTION Global concern over rising levels of CO2 in the atmosphere and its implication in global warming has spawned numerous efforts aimed at mitigating greenhouse gas emissions. The U.S. Department of Energy (DOE) has set a target for the capture and sequestration of 90% of the CO2 in flue gas generated from coal-fired power plants, with no more than a 35% increase in the cost of electricity.1 Organic materials known as alkanolamines have been the most heavily studied materials for postcombustion CO2 capture from flue gas.2−7 Of these materials, aqueous monoethanolamine (MEA) is the most widely used solvent having been used for over half a century for natural gas purification and foodgrade CO2 production,8−10 and more recently as a candidate for CO2 capture from flue gas.11−15 However, MEA-based systems have several negative attributes that have hindered their scaleup, including the huge parasitic energy demand required to heat and condense large quantities of water. This has resulted in an estimated increase in the cost of electricity (COE) of about 80% and a decrease in power plant efficiency of 30%.1 In addition, MEA is relatively volatile and corrosive16,17 and has poor thermo-oxidative stability.13,18,19 Our research has focused on the use of aminosilicones for the postcombustion capture of CO2. While a variety of siliconbased materials have been examined in the past as CO2-capture media,20−29 recent reports have shown that solutions of aminosilicones and glycol cosolvents are promising alternatives to the benchmark aqueous organic amine systems.30,31 Aminosilicones possess properties that offset some of the deficiencies found in the organic amines noted above, including lower vapor pressures, higher boiling points, greater thermal stability, and lower heat capacity. In addition, the replacement © 2012 American Chemical Society
of water with a nonvolatile cosolvent results in a substantial energy saving and significantly lowered the COE over that of the benchmark 30% aqueous MEA process. Additional calculations indicate that complete removal of a cosolvent would further reduce the parasitic energy loss and thereby decrease the COE even more. On the basis of observations from earlier work, it was noted that some liquid aminosilicones readily formed solid carbamate salts on exposure to CO2 and that these salts could subsequently be thermally decomposed to give pure CO2 and to regenerate the aminosilicone. Formation of a solid carbamate salt in this manner is incompatible with standard amine-based CO2 capture schemes. However, we wished to exploit the potential advantages of using neat aminosilicones and reported below is the general concept for a phase-changing CO2 capture sorbent process and the preliminary experimental results from such a design.
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EXPERIMENTAL SECTION
General. 1H and 13C NMR spectra were obtained on a Bruker 400 MHz instrument. Fourier transform infrared (FTIR spectra) were recorded on a Perkin-Elmer Spectrum 100 spectrometer. Mass spectra were acquired on a JEOL AccuTofF JMS T100 LC-MS instrument retrofitted with an Ionsense DART (direct analysis in real time) ion source in place of the normal electrospray source used for liquid chromatography mass spectrometry (LCMS). Helium (2.4 L/min) was used as the DART gas. The gas heater (post glow discharge) of the DART source was set to 240 °C. The analytes experience temperatures far below this during analysis. Melting points were Received: January 14, 2012 Revised: March 12, 2012 Published: March 20, 2012 2528
dx.doi.org/10.1021/ef300079w | Energy Fuels 2012, 26, 2528−2538
Energy & Fuels
Article
spray chamber and in the cyclone. The CO2-depleted gas stream exited the system via the vortex finder of the cyclone separator. The two heating coils before the CO2 inlets can change the temperature of bulk and dispersion gases. The humidifier bubbler (Charles Ross & Son Company) allows us to change the water content in the bulk gas. The pressure in the spray reactor can be read by a manometer (Slack Tube, Dwyer Instruments, INC). The slight pressure in the spray assembly was determined to be 2.3 in. H2O (0.083 psi) with no CO2 flow in the chamber. With CO2 flow, the pressure is about 2 in. H2O (0.072 psi). Two flow controllers (Sierra Instruments, USA) were installed in the gas supply line. The mass of supply gas fed into the spray tank can be measured accurately. Desorption Isotherms. A 10 mL stainless steel pressure vessel capable of full immersion was equipped with a rupture disk, high pressure relief valve, an Omega PX-1004 high temperature pressure transducer having a 0−34.5 bara range, and a 2-way valve attached to a vacuum pump and heated in a thermostatted oil bath. The preformed carbamate salt was varied between 20 wt % in unreacted GAP-0 to 100 wt % to vary the loading of CO2 in the experiments. After the system was sealed, it was attached to a vacuum source and the system was evacuated. The 2-way valve was then closed, the vacuum source detached, and the system immersed in the oil bath. The temperature controller was programmed to ramp through the desired temperatures (100, 120, 140, and 160 °C), holding at each temperature for 3−5 h, depending the length of time required for the system to reach equilibrium. At the conclusion of each experiment, the data was analyzed to determine the average equilibrium pressure at each temperature. This pressure, along with the system volume and moles of CO2 in the system (from the carbamate salt), were then used to calculate the average CO2 in the liquid/solid phase in the reactor. By repeating this procedure at various carbamate/CO2 loadings, a chart of CO2 loading vs CO2 pressure was constructed. The highest pressure datum on the 120, 140, and 160 °C isotherms in Figure 9 was determined by heating a GAP-0 carbamate salt sample in a closed, fixed volume, high pressure, windowed cell and monitoring the increase in pressure associated with the release of CO2 as the sample was slowly heated. Materials. General. 1,3-Bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (GAP-0) and 1,3-bis(2-aminoethylamino-methyl)-1,1,3,3-tetramethyldisiloxane (GAP-AEAM) disiloxane starting materials were obtained from Gelest and used as received. 1,5-Bis(3-amino[propyl)1,1,3,3,5,5-hexamethyltrisiloxane (GAP1). A 20.0 g portion of GAP-0 (0.0805 mol) was mixed with 6.0 g octamethylcyclotetrasiloxane (0.0805 mol D) and 0.15 g of tetramethylammonium hydroxide pentahydrate. The mixture was heated to ca. 40 °C under vacuum for 1 h to remove some of the water from the catalyst. Next, a nitrogen atmosphere was established and the temperature was increased to 90−95 °C and allowed to react overnight. The reaction mixture was then heated to 150 °C for 30 min, and then, a vacuum was carefully applied (house vacuum). Heating was then continued to 165 °C, and the most volatile species were stripped off. After cooling, ca. 25 g (96%) of product was obtained as a light yellow oil with an average composition of M′DM′. 1H NMR (CDCl3) δ 2.60 (t, J = 6, 4H), 1.39 (m, 4H), 1.03 (br. s., 4H), 0.45 (m, 4H), 0.05 to −0.06 (m, 18.6H). 1,3,5-Tris(3-aminopropyl)-1,1,3,5,5-pentamethyltrisiloxane (M′D′M′). A 111.8 g portion of GAP-0 (0.404 mol) was mixed with 77.2 g 3-aminopropyl-methyldiethoxysilane (0.403 mol) and 1.5 g of tetramethylammonium hydroxide pentahydrate. Next, a nitrogen atmosphere was established and the mixture was heated using an oil bath. As the temperature reached approximately 60 °C, 17 mL water were added. Heating was continued and once the temperature reached ∼85−90 °C, 160 mL toluene were added. After 1 h, vacuum was carefully applied (ca. 40 Torr), and the toluene, excess water, and ethanol were distilled off. Once the volatiles had ceased coming over, the vacuum was broken with nitrogen and the reaction mixture was allowed to remain at 90−95 °C overnight. It was then heated to 150 °C for 30 min to decompose the catalyst, and then, vacuum was carefully applied. Heating was continued to an oil bath temperature of 170 °C, during which time volatiles were stripped off. After cooling, ca.
measured on an electrothermal melting point apparatus and are uncorrected. Gas chromatographic analyses were performed on an HP6890 instrument with a thermal conductivity dectector (TCD), using a 30 m, 0.31 mm inner diameter HP-5 column with 0.25 μm film thickness. The initial oven temperature was held at 40 °C for 2 min then ramped at 10 °C/minute. The final oven temperature was 280 °C, which was held for 5 min. X-ray diffraction (XRD). Data was collected with an Inel CPS 590 500 mm curved position sensitive detector with an angular area of detection of 90° 2θ. A Rigaku ultraX 18 high-frequency X-ray generator was used with Mo radiation at Kα1 λ = 0.7093 Å and Kα2 λ = 0.7136 Å. The slit was 3.6 mm wide × 0.5 mm tall. Samples were ground and loaded into glass capillaries and data was collected for 1 h. Differential Scanning Calorimetry/Thermogravimetric Analysis (DSC/TGA). The samples were analyzed as received in 150 μL alumina sample pans. The TGA analysis was carried out using a Mettler Toledo DSC/TGA1 serial number 5129474678 under a 50 mL/min nitrogen purge in the sample chamber per the temp program described within the graphs (25−200 at 5 °C/min). Instrument temperature and enthalpy calibration were verified with respect to gallium and indium and were found to be within 2 °C of the expected Tm onset and 1 mJ/g. A baseline check showed
