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| Titel |
Leaching of organic acids from macromolecular organic matter by non-supercritical CO2 |
| VerfasserIn |
P. Sauer, C. Glombitza, J. Kallmeyer |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250066337
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| Zusammenfassung |
| The storage of CO2 in underground reservoirs is discussed controversly in the scientific
literature. The worldwide search for suitable storage formations also considers coal-bearing
strata. CO2 is already injected into seams for enhanced recovery of coal bed methane.
However, the effects of increased CO2 concentration, especially on organic matter rich
formations, are rarely investigated.
The injected CO2 will dissolve in the pore water, causing a decrease in pH and resulting
in acidic formation waters. Huge amounts of low molecular weight organic acids (LMWOAs)
are chemically bound to the macromolecular matrix of sedimentary organic matter and may
be liberated by hydrolysis, which is enhanced by the acidic porewater. Recent investigations
outlined the importance of LMWOAs as a feedstock for microbial life in the subsurface [1].
Therefore, injection of CO2 into coal formations may result in enhanced nutrient supply for
subsurface microbes.
To investigate the effect of high concentrations of dissolved CO2 on the release of
LMWOAs from coal we developed an inexpensive high-pressure high temperature system
that allows manipulating the partial pressure of dissolved gases at pressures and temperatures
up to 60 MPa and 120Ë C, respectively. In a reservoir vessel, gases are added to saturate the
extraction medium to the desired level. Inside the extraction vessel hangs a flexible and inert
PVDF sleeve (polyvinylidene fluoride, almost impermeable for gases), holding the sample
and separating it from the pressure fluid. The flexibility of the sleeve allows for subsampling
without loss of pressure.
Coal samples from the DEBITS-1 well, Waikato Basin, NZ (R0 = 0.29, TOC = 30%).
were extracted at 90Ë C and 5 MPa, either with pure or CO2-saturated water. Subsamples
were taken at different time points during the extraction. The extracted LMWOAs such as
formate, acetate and oxalate were analysed by ion chromatography. Yields of LMWOAs were
higher with pure water than with CO2-saturated water, revealing a suppressing effect of
CO2. Both extractions had higher yields than those reported for soxhlet extraction
[2].
LMWOAs found in the extraction fluid may not just result from hydrolysis but also from
different secondary reactions. It was suggested that oxalate in aqueous extracts of coals is a
result of the decomposition of 1,2-dihydroxy-carboxylic acids [3]. We assume that for oxalate
(and maybe for other LMWOAs as well) the extraction yield is not only affected by
hydrolysis but also by secondary reactions, which may be inhibited or suppressed in the
presence of CO2 in the extraction medium. During soxhlet extraction the sample only gets
into contact with freshly distilled water, not with an acidic fluid. This may explain the lower
yields.
REFERENCES
[1] Glombitza et al. (2009). Org. Geochem., 40, 175-183.
[2] Vieth et al. (2008). Org. Geochem., 39, 985-991.
[3] Bou Radd et al. (2000). Fuel, 79, 1185-1193. |
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