Monitoring Phase Behavior of Sub- and Supercritical CO2 Confined in Porous Fractal Silica with 85% Porosity

Journal Article · Fri Jan 01 00:00:00 EST 2010 · Langmuir

DOI:https://doi.org/10.1021/la904032p· OSTI ID:978818

Melnichenko, Yuri B ^[1]; Mayama, Dr Hiroyuki ^[2]; Cheng, Gang ^[1]; Cheng, Gang ^[3]; Blach, Tomasz P ^[1]

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1. ORNL
2. Hokkaido University, Japan
3. Joint Bioenergy Institute

Phase behavior of CO{sub 2} confined in porous fractal silica with volume fraction of SiO{sub 2} {phi}{sub 5} = 0.15 was investigated using small-angle neutron scattering (SANS) and ultrasmall-angle neutron scattering (USANS) techniques. The range of fluid densities (0 < ({rho}{sub CO{sub 2}}){sub bulk} < 0.977 g/cm{sup 3}) and temperatures (T = 22 C, 35 and 60 C) corresponded to gaseous, liquid, near critical and supercritical conditions of the bulk fluid. The results revealed formation of a dense adsorbed phase in small pores with sizes D < 40 {angstrom} at all temperatures. At low pressure (P < 55 bar, ({rho}{sub CO{sub 2}}){sub bulk} < 0.2 g/cm{sup 3}) the average fluid density in pores may exceed the density of bulk fluid by a factor up to 6.5 at T = 22 C. This 'enrichment factor' gradually decreases with temperature, however significant fluid densification in small pores still exists at temperature T = 60 C, i.e., far above the liquid?gas critical temperature of bulk CO{sub 2} (T{sub c} = 31.1 C). Larger pores are only partially filled with liquid-like adsorbed layer which coexists with unadsorbed fluid in the pore core. With increasing pressure, all pores become uniformly filled with the fluid, showing no measurable enrichment or depletion of the porous matrix with CO{sub 2}.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). High Flux Isotope Reactor (HFIR)
• Sponsoring Organization: USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 978818
• Journal Information: Langmuir, Vol. 26, Issue 9; ISSN 0743-7463
• Country of Publication: United States
• Language: English