CO2 separation

The urea solution leaving the stripper bottom contains about 12 wt% of NH and is further purified in the 1.8 MPa (18 bar) and 0.2 MPa (2 bar) recovery sections of the plant. The resultant NH and CO2 separated in the decomposers is absorbed and returned to the synthesis section by the high pressure centrifugal carbamate pump. 

Here, we first discuss whether such semi-closure (which is introduced so that CO2 separation can be undertaken more easily) is likely to lead to higher or lower thermal efficiency, and in this discussion it is helpful to consider recirculation in relation to an air standard cycle (see Fig. 8.4). Fig. 8.4a shows a closed air standard cycle with unit air flow Fig. 8.4b shows an open cycle similarly with unit air flow and an air heater rather than a combustion chamber. The cycles are identical in every respect except that in the former the turbine exhaust air from the turbine is cooled before it re-enters the compressor. In the latter, the turbine exhaust air is discharged to atmosphere and a fresh charge of air is taken in by the compressor. The quantities of heat supplied and the work output are the same for each of the two cycles, so that the thermal efficiencies are identical. 

We have been studying the novel process for CO2 separation named membrane/absorption hybrid method. The advantages of this process are that high gas permeance and selectivity were obtained. The concept of this process is shown in Fig. 1. Both feed gas and absorbent solution are supplied to the inside of hollow fibers. While Ae liquid flows upward inside the hollow fibers, absorbent solution absorbs CO2 selectively and it becomes a rich solution. Most of rich solution permeates the membrane to the permeate side maintained at reduced pressure, where it liberated CO2 to become a lean solution. Compared to a conventional gas absorption... 

CO2 Separation Using a Thermally Optimised Membrane. This project aims to manufacture a high-temperature polymer membrane with better separation capabilities than current polymer membranes. The project focuses on the separation of CO2, methane, and nitrogen gases in the range of 100 to 400°C. 

Develop technologies, components and innovative systems for hydrogen production from renewable sources or from fossil fuels with CO2 separation. 

Table 9.2 Capital cost and % cost of CO2 separation unit for different power plants with C02 capture, after [13].

Figure 48 (a) H-bonded assembly of the carbamate 41. (b) Interlinking H-bonds with contiguous cell units, (c) Side view of the assembly, (d) Pleated-sheet staircase-like H-bonded core with bifurcated H-bonds. (e) Single strand of diamine 29 and CO2 separated from the triple-stranded helicate for viewing purposes. Note right-handed helicity [51]. 

Investigations carried out for the NMFS Charleston process indicated that chain length (i.e., molecular size) was a dominant factor observed in research on supercritical CO2 separations of ethyl esters of marine oil fatty acids (93). The initial... 

FIGURE 7.2 Caffeine rejection rate (o) and permeability constant ( ) obtained during caffeine/SC CO2 separation on a nanofilter having a thin layer of Zr02-Ti02 ( = 308 K, transmembrane pressure = 0.2 MPa). Values of estimated cluster size for each experimental point are indicated. (Adapted from Chiu, Y.-W. and Tan, C.-S., J. Supercrit. Fluids, 21, 81, 2001.)... 

Meldon JH and Dutta A. Analysis of ultimate permselectivity for H2S over CO2 in alkaline solutions. Chem Eng Sci, 1994 49(5) 689-697. Saha S and Chakma A. Selective CO2 separation from CO2/C2H6 mixtures by immobilized diethanolamine/PEG membranes. J Mem... 

Feron PHM and Jansen AE. CO2 separation with polyolefin membrane contactors and dedicated absorption liquids Performances and prospects. Sep. Purif. Technol. 2002 27 231-242. 

Chen H, Ohuskovic G, Majumdar S, and Sirkar KK. Immobilized glycerol-based liquid membranes in hollow fibers for selective CO2 separation from CO2-N2 mixtures. J. Mem. Sci. 2001 183 75-88. 

Membrane-based separation processes to capture either H2 or CO2 from the gasifier are new and less studied methods of CO2 separation and capture. Membranes separate the desired gas component without requiring phase changes or chemical or physical sorption. The cost of membrane separation is generally dictated by the overall pressure drop. Membranes made of various types of materials such as polymers, metals, and rubber composites have been investigated. Palladium and molecular sieves are currently under study. ° ... 

Leithner, R. Energy conversion processes with intrinsic CO2 separation. Proceedings of SME, Denver, CO, Feb. 2004. 

SILP systems have proven to be interesting not only for catalysis but also in separation technologies [128]. In particular, the use of supported ionic liquids can facilitate selective transport of substrates across membranes. Supported liquid membranes (SLMs) have the advantage of liquid phase diffusivities, which are higher than those observed in polymers and grant proportionally higher permeabilities. The use of a supported ionic liquid, due to their stability and negligible vapor pressure, allow us to overcome the lack of stability caused by volatilization of the transport liquid. SLMs have been applied, for example, in the selective separation of aromatic hydrocarbons [129] and CO2 separation [130, 131]. 

Figure 3. Ratios of and CO2 in the reaction products when CH4 and CH4 reacted with CO2 separately over Pt/Ce-ZrO2 at 800 "C, 1 12 feed ratio and 14 atm...

Hanioka, S., Maruyama, T., Sotani, T., Teramoto, M., Matsuyama, H., Nakashima, K., Hanaki, M., Kubota, F., Goto, M. (2008). CO2 separation facilitated by task-specific ionic hquids using a supported hquid membrane. J. Membr. Sci., 314, 1-4. 

Saha S, Chakma A. Selective CO2 separation from CO2/C2H, mixtures by immobilized diethanolamine/PEG membranes. J Membr Sci 1995 98 157-171. 

SILMs have been also employed for the separation of CO2/N2 and CO/ CH4 mixtures. Scovazzo et al. [54] used common ionic liquids such as imidazohum [emim] + and different water stable anions such as bis(trifluor-omethanesulfonyl)amide [T N] , trifluoromethanesulfone [CFsSOj] , and dicianamide dca in polyethersulfone as polymer substrate. It was observed an interesting increase in CO2 permeability (up to 50%) decreasing the gas phase pressure from 19 to 1.5 kPa with an ideal selectivity (CO2/N2) ranging from 15 (for CI ) up to 61 (for [dca] ) and permeabilities of 350 barrer (for CI ) to 1000 barrer (for [T N] ). In the case of CO2 separation from CH4, the ideal selectivity was ranging from 4 (for [Cl ) to 20 (for dca ) which are above the upper-bound for the CO2/CH4 Robson plot. 

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