Carbon Dioxide Capture from Fuel Gas Streams under Elevated Pressures and Temperatures Using Novel Physical Solvents

The conventional processes for acid gas removal (AGR), including CO2 in the Integrated Gasification Combined Cycle (IGCC) power generation facilities are: a chemical process, using methyl-diethanolamine (MDEA); a physical process, using chilled methanol (Rectisol) or a physical process, using mixtures of dimethylethers of polyetheleneglycol (Selexol). These conventional processes require cooling of the fuel gas streams for CO2 capture and subsequent reheating before sending to turbines, which decreases the plant thermal efficiency and increases the overall cost. Thus, there is a pressing need for developing an economical process which can capture CO2 from the hot fuel gas stream without significant cooling. The overall objective of this study is to investigate the potential use of physical solvents for selective capture of CO2 from post water-gas-shift streams under relatively elevated pressures and temperatures. In order to achieve this objective, a comprehensive literature review was conducted to define an “ideal solvent” for CO2 capture and to identify six different physical solvents which should obey such a definition. The first physical solvents identified were perfluorocarbons (PFCs), which are known to have low reactivity, high chemical stability and relatively low vapor pressures. Three different PFCs, known as PP10, PP11, and PP25, were selected as potential candidates for CO2 capture. The equilibrium solubilities of CO2 and N2 were measured in these PFCs under different operating conditions up to 30 bar and 500 K. These PFCs have relatively low viscosity at 500 K, very good thermal and chemical stabilities and showed high CO2 solubilities; hence they were considered as “ideal solvents.” The CO2 solubilities in PP25 were found to be greater than in the other two PFCs. Due to its superior behavior, PP25 was selected for the development of a conceptual process for CO2 capture form Pittsburgh No. 8 shifted fuel gas mixture using Aspen Plus simulator. Unfortunately, during the pressure-swing option for solvent regeneration, the solvent loss was significant due to the fact that the boiling point of PP25 is 533 K which is close to the absorber temperature (500 K). Also, other drawbacks of PFCs include, high cost, and absorption of other gases (light hydrocarbons) along with CO2. It was then decided to seek different physical solvents, which have negligible vapor pressure, in addition to the other attractive properties of the “ideal solvent” in order to use in the Aspen Plus simulator. Extensive literature search led to Ionic Liquids (ILs), which are known to have unique properties in addition to extremely low vapor pressures, and therefore they were considered excellent candidates for the CO2 capture from fuel gas streams under elevated pressures and temperatures. Three ILs, namely TEGO IL K5, TEGO IL P9 and TEGO IL P51P, manufactured by Evonik Goldschmidt Chemical Corporation, were selected as potential solvents for CO2 capture. The solubilities of CO2, H2, H2S and N2 were measured in the TEGO IL K5 and the solubilities of CO2 and H2 were measured in the TEGO IL K5 at pressures up to 30 bar and temperatures from 300 to 500 K. Also, the density and viscosity of these three ILs were measured within the same pressure and temperature ranges, and the surface tension for TEGO IL K5 and TEGO IL P51P were measured from 296 to 369 K. Due to their superior performance for CO2 capture, the TEGO IL K5 and the TEGO IL P51P were selected to be used in the Aspen simulator for the conceptual process development. The density and surface tension data for the TEGO IL K5 and the TEGO IL P51P were used in Aspen Plus, employing the Peng-Robinson Equation of state (P-R EOS) to obtain the critical properties of the two ILs; and the measured solubility data were also used to obtain the binary interaction parameters between the shifted gas constituents and two ILs. The Aspen Plus simulator was employed to develop a conceptual process for CO2 capture from a shifted fuel gas stream (102.52 kg/s) generated using Pittsburgh # 8 coal for a 400 MWe power plant. The conceptual process developed consisted mainly of 4 adiabatic absorbers (2.4 m ID) arranged in parallel and packed with Plastic Pall Rings of 0.025 m for CO2 capture; 3 flash drums arranged in series for solvent regeneration using the pressure-swing option; and 2 pressure-intercooling systems for separating and pumping CO2 to the sequestration sites. The compositions of all process steams, CO2 capture efficiency, and net power were calculated using Aspen Plus for each solvent. The results indicated that, based on the composition of the inlet gas stream to the absorbers, 87.6 and 81.42 mol% of CO2 were captured and sent to sequestration sites; and 97.69 and 97. 86 mol% of H2 were separated and sent to turbines using the TEGO IL K5 and the TEGO IL P51P, respectively. Also, the two solvents exhibited minimum loss of 0.06 and 0.17 wt% with a net power balance of -26.44 and -14.72 MW for the TEGO IL K5 and the TEGO IL P51P, respectively. Thus, the TEGO IL K5 could be selected as a physical solvent for CO2 capture from shifted hot fuel gas streams since large quantities of CO2 are absorbed

Carbon dioxide capture and separation techniques for advanced power generation point sources

The capture/separation step for carbon dioxide (CO2) from large-point sources is a critical one with respect to the technical feasibility and cost of the overall carbon sequestration scenario. For large-point sources, such as those found in power generation, the carbon dioxide capture techniques being investigated by the in-house research area of the National Energy Technology Laboratory possess the potential for improved efficiency and costs as compared to more conventional technologies. The investigated techniques can have wide applications, but the research has focused on capture/separation of carbon dioxide from flue gas (postcombustion from fossil fuel-fired combustors) and from fuel gas (precombustion, such as integrated gasification combined cycle – IGCC). With respect to fuel gas applications, novel concepts are being developed in wet scrubbing with physical absorption; chemical absorption with solid sorbents; and separation by membranes. In one concept, a wet scrubbing technique is being investigated that uses a physical solvent process to remove CO2 from fuel gas of an IGCC system at elevated temperature and pressure. The need to define an ideal solvent has led to the study of the solubility and mass transfer properties of various solvents. Fabrication techniques and mechanistic studies for hybrid membranes separating CO2 from the fuel gas produced by coal gasification are also being performed. Membranes that consist of CO2-philic silanes incorporated into an alumina support or ionic liquids encapsulated into a polymeric substrate have been investigated for permeability and selectivity. An overview of two novel techniques is presented along with a research progress status of each technology

Phospholipid Scramblase-1-Induced Lipid Reorganization Regulates Compensatory Endocytosis in Neuroendocrine Cells

Calcium-regulated exocytosis in neuroendocrine cells and neurons is accompanied by the redistribution of phosphatidylserine (PS) to the extracellular space, leading to a disruption of plasma membrane asymmetry. How and why outward translocation of PS occurs during secretion are currently unknown. Immunogold labeling on plasma membrane sheets coupled with hierarchical clustering analysis demonstrate that PS translocation occurs at the vicinity of the secretory granule fusion sites. We found that altering the function of the phospholipid scramblase-1 (PLSCR-1) by expressing a PLSCR-1 calcium-insensitive mutant or by using chromaffin cells from PLSCR-1−/−mice prevents outward translocation of PS in cells stimulated for exocytosis. Remarkably, whereas transmitter release was not affected, secretory granule membrane recapture after exocytosis was impaired, indicating that PLSCR-1 is required for compensatory endocytosis but not for exocytosis. Our results provide the first evidence for a role of specific lipid reorganization and calcium-dependent PLSCR-1 activity in neuroendocrine compensatory endocytosis

Novel Physical Solvents for Selective CO₂ Capture from Fuel Gas Streams at Elevated Pressures and Temperatures

Three perfluorinated compounds (PFCs), PP10, PP11, and PP25, manufactured by F2 Chemicals Ltd., U.K., were investigated as physical solvents for selective CO₂ capture from synthesis gas or syngas streams at elevated pressures and temperatures. The equilibrium solubility, the hydrodynamic, and the mass-transfer parameters of CO₂ in the solvents were measured in a 4-L ZipperClave agitated reactor under wide ranges of operating conditions: pressures (6−30 bar), temperatures (300−500 K), mixing speeds (10−20 Hz), and liquid heights (0.14−0.22 m). The CO₂ solubilities in the three solvents decreased with an increasing temperature at constant pressure and followed Henry’s law. The CO₂ solubilities in PP25 were greater than those in PP10 and PP11. The volumetric liquid-side mass-transfer coefficients (<i>k</i>_L<i>a</i>) of CO₂ in the PFCs increased with mixing speed, pressure, and temperature. Also, the gas−liquid interfacial areas of CO₂ in the three PFCs appeared to control the behavior of <i>k</i>_L<i>a</i>. This study proved the thermal and chemical stability and the ability of the PFCs to selectively absorb CO₂ at temperatures up to 500 K and pressures as high as 30 bar. A preliminary conceptual process design using PP25 for selective CO₂ capture from hot-shifted gas with pressure-swing and pressure−temperature-swing regeneration options was devised [a temperature-swing option was also examined but is not reported here because it is outside the context of the present study, which involves a physical solvent process benchmark (Selexol) for which temperature-swing regeneration is not a viable option]. The pressure−temperature-swing option led to greater PP25 solvent loss but a more favorable (more negative) net enthalpy than the pressure-swing option. However, for either regeneration option to be economically viable, the PP25 solvent must be completely recovered from the process

Development of a Conceptual Process for Selective Capture of CO₂ from Fuel Gas Streams Using Two TEGO Ionic Liquids as Physical Solvents

Two ionic liquids (ILs), TEGO IL K5 and TEGO IL P51P, were used as physical solvents to develop a conceptual process for CO₂ capture from a shifted warm fuel gas stream produced from Pittsburgh no. 8 coal for a 400 MWe power plant. The physical properties of the two ILs and the solubilities of CO₂, H₂, N₂, and H₂S in the TEGO IL K5 solvent, as well as those of CO₂ and H₂ in the TEGO IL P51P solvent, were measured in our laboratories at pressures up to 30 bar and temperatures from 300 to 500 K. The Peng–Robinson equation-of-state (P-R EOS) with Boston–Mathias (BM) α function and standard mixing rules was used in the development of the process, and the solubility data were used to obtain the binary interaction parameters (δ_<i>ij</i> and <i>l</i>_<i>ij</i>) between the shifted gas constituents and the two ILs. The binary interaction parameters were then correlated as functions of temperature. The conceptual process consists of four identical adiabatic packed-bed absorbers (4.5 m i.d., 27 m height, packed with 0.0254 m plastic Pall Rings) arranged in parallel for CO₂ capture, three flash drums arranged in series for solvent regeneration,and two pressure/intercooling systems for separating and pumping CO₂ to sequestration sites. The compositions of all process streams, CO₂ capture efficiency, and net power were calculated using Aspen Plus for the two solvents. The results showed that TEGO IL K5 and TEGO IL P51P were able to capture 91.28% and 90.59% of CO₂ in the fuel gas stream, respectively