Mass Transfer of CO 2 into Water and Surfactant Solutions

Transcription

1 Mass Transfer of CO 2 nto Water and Surfactant Solutons Rouhollah Farajzadeh, Al Barat, Harm A. Dell, Johannes Brunng, Pacell L.J. Ztha Delft Unversty of Technology, Department of Geotechnology, Mjnbouwstraat 20, 2628 RX Delft, The Netherlands To whom correspondence should be addressed: Emal: p.l.j.ztha@ctg.tudelft.nl, Tel.: 3 (0) Fax.: 3 (0) R. Farajzadeh, SPE, H. Salm, SPE, P.L.J. Ztha, SPE, and J. Brunng, SPE and Delft Unversty of Technology Copyrght 2007, Delft Unversty of Technology Ths paper had been accepted for publcaton n Journal of Petroleum Scence and Technology n January Abstract The mass-transfer of CO 2 nto water and aqueous solutons of Sodum Dodecyl Sulphate (SDS) s expermentally studed usng a PVT cell at dfferent ntal pressures and a constant temperature (T=25ºC). It s observed that ntally the transfer rate s much larger than expected from a dffuson process alone. The model equatons descrbng the experments are based on Fck s law and Henry s law. The experments are nterpreted n terms of two effectve dffuson coeffcents, one for the early-stages of the experments and the other one for the later stages. The results show that at the early stages the effectve dffuson coeffcents are one order of magntude larger than the molecular dffusvty of CO 2 n water. Nevertheless, n the later stages the extracted dffuson coeffcents are close to lterature values. It s asserted that at the early stages densty drven natural convecton enhances the mass transfer. A smlar mass transfer enhancement was observed for the mass transfer between gaseous CO 2 rch phase wth an ol (n-decane) phase. It s also found that at the expermental condtons studed addton of pure SDS does not have a sgnfcant effect on the mass transfer rate of CO 2 n water. Keywords: Mass Transfer, CO 2, Natural Convecton, Effectve Dffuson Coeffcent, Surfactant. Introducton The mass transfer of a gas through a gas-lqud nterface (wth and wthout monolayers of surfactant) s of great mportance n many felds of scence and engneerng. Examples nclude CO 2 sequestraton, to reduce global heatng effects (Holt et. al., 994; Lndeberg and Wessel- Berg, 997; Bachu and Adams, 2003; Yang and Gu, 2006), ol recovery (Zhang et. al, 2000; Nguyen et. al., 2002) and gas absorpton (Vazquez et. al., 2000). There s a vast lterature on the mass transfer between gas and lquds. We confne our nterest to the expermental determnaton of the mass transfer rate of CO 2 nto water n a PVT cell. It has been suggested n the lterature that natural convecton enhances the mass transfer (Lndeberg and Wessel-Berg, 997; Yang and Gu, 2006). Lndeberg and Wessel-Berg (997) studed the condtons under whch natural convecton occurs as a result of CO 2 njecton n salne aqufers. They found the followng sequence of events: ntally the njected CO 2 accumulates under the cap rock. Then, CO 2 dssolves nto the reservor brne by molecular dffuson. As a result, the densty of brne ncreases, and therefore, natural convecton occurs. Nevertheless, Lndeberg and Wessel-Berg (997) dd not quantfy the effects of the natural convecton n terms of enhanced mass transfer of CO 2 nto the reservor brne. Yang and Gu (2006) studed the mass transfer of CO 2 nto water at hgh pressures and temperatures. They nterpreted the expermental results n terms of a modfed dffuson equaton and found an effectve dffuson coeffcent for each experment. The effectve dffuson coeffcents were two orders of magntude larger than the molecular dffuson coeffcent. However the duraton of ther experments were short (3-4 hours) and they dd not study the long tme behavor of the CO 2 mass transfer nto water. When surfactants are added to a quescent lqud the total resstance to the transfer of gas molecules s the sum of the lqud phase resstance, the gas resstance and the nterfacal resstance whch arses from the adsorpton of surfactant molecules to the nterface. It has been shown that the presence of soluble surfactants has no measurable effect on the passage of gas molecules through the gaslqud nterface (Sprnger and Pgford, 979; Caskey and Barlage, 972; Hanwght et. al., 2005); however, nsoluble surfactants can offer resstance to mass transfer (Kode and Orto, 974; La Mer et. al., 963; Blank, 962; Barnes and Hunter, 987; Barnes, 997). To our knowledge the reported experments n ths area are conducted under atmospherc pressure and the effect of surfactants on mass

2 2 SPE 0738 transfer at hgher pressures apparently has not been reported n the lterature. In ths report we study the mass transfer of CO 2 nto bulk water and surfactant solutons expermentally to avod the complex adsorpton mechansm between surfactants and the porous medum. The emphass of the paper s on the expermental results and procedure. In order to quantfy the results we nterpret the results n terms of two effectve dffuson coeffcents usng a modfed dffuson equaton and leave a more complcated nterpretaton ncludng natural convecton for future work. Ths paper adds three contrbutons to the expermental knowledge base: Frstly, by extendng the duraton of the experments we nvestgate the long term behavor of CO 2 mass transfer and nvestgate whether enhanced transfer perssts over tme or whether t des out. Secondly, we perform the experments wth ol phase (n ths paper n- decane) and show expermentally the enhancement of CO 2 mass transfer to the ol phase. Thrdly, ths paper reports the effect of surfactants at hgh pressures. In secton 2 we descrbe the expermental setup, materals and expermental procedure. In secton 3 we defne a model to nterpret the experments and n secton 4 the obtaned expermental data are ncorporated nto a physcal model. Ths allows us to obtan two dffuson coeffcents for the mass transfer process of CO 2 through a ar-lqud nterface; one for the early stages of the experments and one for the late stages of the experments. The possble mechansms for the observed phenomena are dscussed n secton 5. We end our paper wth some remarks and conclusons. 2. Experments 2.. Expermental setup The expermental apparatus s shown n Fg.. It conssts of a transparent scaled glass tube wth an nner dameter of 7.0 mm, an outer dameter of.0 mm and a length of 45.0 cm. The tube was embedded n Teflon at the top and bottom and was sealed wth o-rngs and ftted nsde a stanless steel cylnder. The glass tube has the capablty of wthstandng pressures up to 50 bar. To assure that the lqud s stagnant the stanless steel cylnder was mounted nto a heavy (0 kg) steel holder. The bottom of the cell was equpped wth a valve and a pston pump, whch permtted njecton of lqud nto the cell. The top of the cell was connected to a hgh pressure gas cylnder. The gas pressure was measured wth a calbrated pressure transducer wth an accuracy of 5 mbar. Moreover, a safety valve was placed at the top part of the setup. A calbrated data acquston system was provded to record the pressure and temperature n the cell durng the experment. The expermental data were recorded every 0 seconds by the computer. To avod thermal fluctuatons the cell was located nsde a lqud bath. In all experments the bath was kept at 25±0. C. Fgure : Schematc of the setup: The setup conssts of a long tube n whch the lqud phase and gas phase are brought n contact wth each other at a certan pressure. The setup s held n a lqud bath wth a constant temperature. The pressure of the gas n top part s montored by a pressure transducer Materals and methods Gas: The gas used to carry out the experments was 99.98% pure carbon doxde. CO 2 s hghly soluble n water (Fogg and Gerrard, 99),.e., the Henry constant s Pa/mol/m³ (Sander, 997). The dffuson coeffcent of CO 2 n water s (.97±0.0) 0-9 m²/s (Gertz et al., 954). Ntrogen (N 2) was used to detect possble leakages n the setup. Surfactant: The surfactant used to perform the experments was Sodum Dodecyl Sulfate (SDS) wth the chemcal formula of C 2H 25SO 4Na and a molecular weght of 288 g/mol. It was dssolved n dstlled water ( ph = 5.5 ± 0. ). Before startng the experments the Crtcal Mcelle Concentraton (CMC) of the surfactant was measured. To that end, solutons of SDS and dstlled water wth the concentratons of 2, 2.5, 3, 3.5, 4, 5 and 6 mmol/l were prepared. The surface tenson of these solutons was measured by the DuNouy Rng method at room temperature. The apparatus was frst calbrated wth dstlled water (the surface tenson of dstlled water at the

3 SPE room temperature s 72.6 mn/m). The crtcal mcelle concentraton of the SDS was measured to be 0.6 mm at our expermental condtons Expermental procedure In the pressure depleton experments, the lqud phase was ether pure dstlled water or surfactant solutons wth dfferent surfactant concentratons. The concentraton of the surfactant n some experments was above the CMC and n some experments below the CMC. For ths purpose an approprate amount of SDS was weghed and dssolved n dstlled water. Orgnally some foam s formed at the surface, whch collapses after leavng t undsturbed for a few mnutes. Before performng the experments, the dry cell was flled wth ntrogen to a certan pressure to assure that there s no leakage n the system. Fg. 2 shows the pressure versus tme plot for a leakage test. The small fluctuatons n the frst part of the plot are due to small fluctuatons n the temperature and the dfference between the temperature of the gas cylnder and the lqud bath. The expermental procedure s as follows: Frst, the lqud was njected from the bottom va an accurate pston pump nto the cell untl t reached the desred level. After that, pumpng of the lqud was stopped and the valve at the bottom of the cell was closed. Next CO 2 was slowly njected nto the cell from the top, for about 30 seconds. When the CO 2 pressure reached the desred value, the valve was closed and the cell was solated. Ths was the startng tme of the experment. Each experment was run for several days. All the experments were repeated to show the reproducblty. (z=0 at the gas-lqud nterface) and assume that dffuson coeffcent does not change sgnfcantly wth concentraton. Snce the lqud column s large the concentraton s taken zero at the bottom of the vessel. The gas nsde the vessel follows the real gas law and the gas pressure can be calculated by PV = ZRT. Fgure 2: Leakage test: The setup was checked for any possble leakage by njectng ntrogen. The pressure should be constant wth tme n the range of accuracy of the pressure transducer. 3. Physcal model 3.. Formulaton A physcal model has been developed to descrbe the mass transfer based on Fck s law takng nto account the solublty of the gas by Henry s law. The geometry of the problem under scrutny s depcted n Fg. 3. The vessel conssts of an upper column flled wth gas and a lower column flled wth a stagnant lqud layer. The model dsregards convecton and capllary effects. Moreover, t s assumed that the densty of CO 2 n the gas phase only depends on tme. We dsregard both water evaporaton (the contrbuton of water vapor to the gas pressure s 0.03 bar at 25 C (Greenwood and Earnshaw, 997)) and water swellng due to CO 2 dssoluton. Consequently we assume that the boundary remans fxed. The CO 2 concentraton at the lqud surface s related to the gas pressure by assumng nstantaneous thermodynamc equlbrum at the nterface. We assert that the transfer of gas molecules through the gas-lqud nterface can be descrbed as a one dmensonal unsteady-state dffuson process,.e., by Fck s law. We take z postve n the downward drecton Fgure 3: Schematc outlay of the process: The total length of the tube s L, the heght of water s L 2 and the heght of the gas s L. There s no gas flowng out at the end of the tube. The gas-lqud nterface s fxed. The lqud concentraton at the nterface s related to the gas pressure through Henry s law and changes wth tme.

4 4 SPE Equatons For ths system Fck's second law can be wrtten as 2 c c = D 0 z L, 0 t 2 2 t z where, D s the effectve dffuson coeffcent and c s the concentraton of CO 2 n the lqud phase. Intally there s no gas nsde the lqud,.e. ( ) c0 c z, t = 0 = = 0. (2) Snce the dffuson process s slow and the lqud column s large, we can assume that the concentraton of the gas s zero at the end of the tube (L 2 ). The second boundary condton s gven by Henry s law whch states that the pressure of a gas above a soluton s proportonal to the mole fracton (concentraton) of the gas n the soluton,.e., ( ) Hc ( t) P t =, (3) where H s taken as Henry's law proportonalty constant. An addtonal condton to the present problem can be wrtten n accordance wth the fact that the change of the total moles of gas n the system s due to dffuson nto the lqud. The mass flux of the gas at the nterface for real gas can be wrtten as dng V dpg c = = DS dt ZRT dt z = z= 0 z= 0 z 0 (), (4) where V and S are the gas volume and the cross-sectonal area of the cell respectvely, R s the unversal gas constant and Z s the compressblty factor. V s also assumed to be constant (no movng boundary). By substtutng Henry's law for the gas pressure n Eq. (4) we obtan c VH c DS = z ZRT t z= 0 z= 0. (5) 3.3. Analytcal soluton Eq. () has a tme dependent boundary condton and can be solved by Laplace transform method. Laplace form of Eq. () s C z s C D 2 = 0 2. (6) The fnal soluton of Eq. (6) wth the gven boundary condtons s C ( s) = exp H ZRT D s s P L P s z. (7) D Applyng Laplace transform to Eq. (4) and usng Eq. (7) yelds L ZRT ( spg P ) = H P D from whch we can obtan P g ( s) P = s LH s ZRT D 3/2, (8) ZRT s PL. (9) s The gas pressure as a functon of tme s found by Laplace nverson as 2 ( ) = 2 exp( κ ) ( κ ) Pg t P t erfc t, (0) where ZRT D κ =. () L H Due to our boundary condton that the concentraton s zero at the bottom of the cell ( z = L2 ) we fnd as long tme behavor that the pressure s declnng ndefntely. However, that occurs for tmes much longer than relevant for the experment. It should be also mentoned that the soluton of Fck s second law assumng a constant concentraton at the gaslqud nterface suggests that after a long tme the concentraton at the nterface s lnearly proportonal to the square root of tme,.e., the plot of gas pressure versus the square root of tme wll be a straght lne (Coulson and Rchardson, 977). 4. Results and Dscusson 4.. Pressure declne In ths study, the quantfcaton of the mass transfer rate s based on the measurement of the gas pressure n a closed volume contanng a column of lqud below a gas column. The changes n the gas pressure are assumed to be only due to transfer of gas nto the lqud phase. The measured gas pressure versus tme for both dstlled water and the surfactant soluton are plotted for all experments. The general trends of the curves for dfferent ntal pressures were smlar. Thus due to these smlartes only the curves of Exp2 wll be presented n ths paper.

5 SPE It becomes clear from Fg. 4 that the gas pressure declnes sgnfcantly at the ntal stages of the experment,.e., has a steep slope at the early tmes of the experment. However, the slope of the curve becomes less steep wth tme, meanng that also the mass transfer rate decreases wth tme. Fg. 5 shows the comparson between the measured pressures and the model usng the known dffuson coeffcent of CO 2 n water (n ths curve chosen to be D= m²/s). The curve shows sgnfcant dscrepancy between expermental and predcted values. Fgure 4: Reproducblty test: All of the experments were repeated to assure that the observed pressure declne s only due to the mass transfer of CO 2 nto water and the obtaned data are reproducble. Fgure 5: Comparson between experment and model: Ths curve shows the comparson between the model whch s based on the modfed Fck s second law and the expermental data. At the ntal stages of the experments the rate of mass transfer of CO 2 nto water s hgher than the predcted values by the physcal model. However, the extracted data wll be reported for all experments (Table -2). Fg. 4 shows normalzed CO 2 pressure versus tme durng pressure declne measurements for Exp2. It shows that the gas pressure decreases wth tme due to the transfer of the CO 2 molecules nto water. Comparson between the sold and dashed lnes n the fgure shows the reproducblty of the experment. The small dfference between these two curves s due to the dffcultes n settng the ntal pressure to the same value for the two experments 4.2. Devaton from the square root of tme Fg. 6 shows the plot of the measured gas pressure versus the square root of tme for Exp2. It shows that the ntal behavor of ths curve s faster than the square root of tme. Ths s an ndcaton of the hgher mass transfer of CO 2 nto water, whch cannot be explaned by a dffuson lke process. Interestngly, after about one day the pressure vs. square root of tme curve becomes lnear. It can be expected that at longer tmes the mass transfer of CO 2 nto water s determned by molecular dffuson Estmated dffuson coeffcents In ths paper two effectve dffuson coeffcents are extracted from the expermental data descrbng the ntal and long-tme behavor of the CO 2 mass transfer nto water and surfactant solutons. The procedure s as follows: In the plots of pressure versus square root of tme (for example Fg. 6 for Exp2), the late-stage expermental data are ftted to a straght lne. The ntercept of the ftted lne n Fg. 6 s the ntal pressure wth whch the mass transfer process would have started f dffuson had been the only responsble mechansm for mass transfer of CO 2 nto the lqud (no convecton case). Therefore, to obtan the late-stage dffuson coeffcent ths pressure s put as ntal pressure n the physcal model, for whch the model equaton s Fck s second law wth a tme dependent boundary condton. The lower sold curve n Fg. 7 s the predcted gas pressure by Eq. (0) usng the ntal pressure obtaned from Fg. 6 and choosng D 9 = m 2 /s and nsertng the lterature value of 3 Henry s coeffcent ( H = Pa/mole/m ). The dashed lne shows the expermentally measured pressure data versus tme. Wth a dffuson coeffcent close to the molecular dffuson coeffcent of CO 2 nto the water the predcted values by the model are n excellent agreement wth the measured pressure values. To obtan the effectve coeffcents for early stages of the experments the expermental ntal pressure was put n the model and the effectve dffuson coeffcent was obtaned wth the help of the data. The upper sold curve n Fg. 7 s the predcted gas pressure by Eq. (0) choosng D = m 2 /s and H = Pa/mole/m 3. Alternatvely we can use

6 6 SPE = m 2 /s the later stage dffuson coeffcent but then the Henry s coeffcent needs to be modfed to H = Pa/mole/m 3. Such a small value has not been reported n the lterature for CO 2 solublty n water. Therefore, we have chosen to use the lterature value of Henry s coeffcent n the nterpretaton of the experments. Fgure 6: Measured pressure data plotted versus the square root of tme. The long tme part of the experment can be ftted to a straght lne. D The extracted effectve dffuson coeffcents for dfferent experments are shown n Table 3. The obtaned effectve dffuson coeffcents for the early stages of the experments are one order of magntude larger than the actual molecular dffuson of CO 2 nto water, agan ndcatng the faster mass transfer rate of CO 2 nto water at the early stages of the experment. However, the obtaned effectve dffuson coeffcents for the later stages of the experments mply that after a certan tme, the mass transfer of CO 2 nto aqueous solutons becomes slower compared to the ntal stages. The early-stage dffuson coeffcents ncrease wth ncreasng ntal pressure provng the fact that even at slghtly hgh pressures for CO 2-water system the dffuson coeffcent s a strong functon of the ntal pressure,.e., the ntal concentraton of CO 2 n the system. Ths means that at hgher pressures the effectve dffuson coeffcents wll be even hgher. Ths observaton s also supported by the expermental results n Yang and Gu (2006) n whch the authors found dffuson coeffcents whch were two orders of magntude larger than the molecular dffuson coeffcent of CO 2 nto water at hgher pressures. In addton, that regardless of the ntal pressure, after a certan tme, dffuson becomes the domnant mechansm for mass transfer of CO 2 nto water. The dffuson coeffcent extracted from the long tme behavor turns out to be ndependent of the ntal expermental pressure. Fgure 7: Extracton of dffuson coeffcents, usng Eq. (0): the data are ftted to two curves of the form suggested by Eq. (0). The lower sold lne shows the predcted pressure values usng the vrtual ntal 9 = m 2 /s. pressure obtaned from Fg. 8 and The dashed lne s the measured pressure data. The left sold lne shows the predcted pressure values usng the real pressure obtaned from Fg. 8 and D = m 2 /s. D Fgure 8: Comparson of measured pressure data for pure water, soluton of water and SDS and soluton of water and surfactant wth NaCl versus tme Influence of surfactant To study the nfluence of the soluble surfactants on the nterfacal mass transfer some of the experments were done usng surfactant solutons of SDS as lqud phase. Fg. 8 shows the normalzed pressure declne curve for the experments wth surfactant soluton together wth the

7 SPE experment wth pure water. It s evdent from Fg. 8 that at our expermental condtons the addton of soluble surfactant (SDS) has no sgnfcant effect on mass transfer rate of CO 2 nto water. However, t seems that addton of salt slghtly retards the mass transfer. Several parameters can be responsble for ths behavor: (a) the addton of NaCl ncreases the vscosty of the soluton and therefore the effectve dffuson coeffcent decrease by addng NaCl, (b) the addton of NaCl decreases the solublty of CO 2 n water. Therefore, less CO 2 s dssolved n water n the experment wth NaCl compared to experments wthout NaCl and (c) the addton of salt ncreases the adsorpton of the surfactant molecules at the nterface (Santanu and Pak, 2006) and the nterface becomes more packed whch could be another possble reason for the dfferences of the curves n Fg. 8. Our results are consstent wth the results of other researchers (La Mer et al., 963; Molder et al., 998; Raymond and Zemnsk, 97),.e., the surface resstance for soluble surfactants s very small. However, the nsoluble surfactants do have a sgnfcant effect on the transfer rates of gas through the gas-lqud nterface. The same procedure as dscussed above was also followed to extract the effectve dffuson coeffcents for surfactant solutons. Indeed, the obtaned dffuson coeffcent values for surfactant solutons are about the same as for the experments wth water and are presented n Table 3. Fgure 9: Pressure declne curve n the experment wth n-decane. The pressure behavor s smlar to the water case, ndcatng an enhancement of mass transfer n the ntal stages of the experment. In long tme the conventonal dffuson behavor s observed Experment wth n-decane We carred out a few experments to study the mass transfer of CO 2 nto hydrocarbons from whch we report the obtaned pressure curve from a experment wth n- decane. The dssoluton of CO 2 ncreases the densty of the hydrocarbons (Ashcroft and Ben Isa, 997). The expermental procedure and condtons were the same as explaned n secton 2. The ntal pressure of the experment was.85 bar. Fg. 9 shows that ntally the mass transfer of CO 2 s faster than at the later stages. We beleve that ths result has mplcatons for enhanced ol recovery for CO 2 floodng and mproved ol recovery n fractured ol reservors. 5. Possble mechansms As an explanaton for the observed dscrepancy between the physcal model and the expermental data n Fg. 5 the followng possbltes have been consdered. a) CO 2 may be adsorbed to the water attached to the gas flled part of the glass tube. Ths explanaton s however unlkely because t requres a water layer thckness of 2mm. b) Other possbltes are related to the valdty of Henry s law n relatng the surface concentraton of the flud to the gas pressure. Even f we consder these possbltes less lkely, they have to be nvestgated. c) When CO 2 s brought nto contact wth water, the dssoluton and dffuson of CO 2 leads to a concentraton gradent n the water and also a densty gradent (Gmeln, 973). As the densty ncreases wth ncreasng dssoluton of CO 2 at the nterface, the flud on top of the water near the nterface becomes denser. Ths densty gradent nduces natural convecton to the system whch speeds up the transfer of CO 2 nto water and results n hgher flux of CO 2 at the nterface. However, the densty gradent and therefore natural convecton effects, decreases wth tme and after a certan tme the densty gradent s not large enough to sustan convecton to the system. In addton to the natural convecton, the tmedependency of the boundary condton n Eq. (4) can be another reason why the early pressure hstory s not proportonal to the square root of tme. However, as we can see from Fg. 6 the pressure declne s slow at the later stages and then the gas pressure can be consdered constant for the boundary condton. The observatons mentoned above can be quantfed n terms of the effectve dffuson coeffcents. It s seen that regardless of the ntal pressure, after a certan tme, the enhancement effects wll be less and dffuson becomes the domnant mechansm for CO 2 mass transfer CO 2 nto water. Furthermore, as can be seen from Fg. 9 t appears that natural convecton s also responsble for the mass transfer of CO 2 nto n-decane (ol phase). Once more, at the later stages the effect of natural convecton becomes less sgnfcant.

8 8 SPE Conclusons In ths paper t s shown that a relatvely smple PVT cell can be used to study the enhanced mass transfer between gases and lquds. A physcal model based on the Fck s second law and Henry s law can be used to nterpret the expermental data. We use the model to extract two dffuson coeffcents. The mass transfer process cannot be modeled wth a modfed Fck s second law wth a sngle effectve dffuson coeffcent. The ntal stages and later stages of the experments could be modeled ndvdually wth the descrbed model and two effectve dffuson coeffcents could be obtaned from the expermental data. The obtaned effectve dffuson coeffcent values for the ntal stages of the experments were one order of magntude larger than the molecular dffusvty. It was suggested that at the early stages of the experments densty-drven natural convecton enhances the mass transfer of CO 2 nto water. The effectve dffuson coeffcents for the ntal stages of the experments ncrease wth ncreasng pressure. The extracted dffuson coeffcents for the later stages of the experments agree wth the molecular dffusvty of CO 2 nto water. It was asserted that after a certan tme, the densty drven natural convecton becomes less mportant. At the later stages dffuson becomes the domnant mechansm for the mass transfer experments of CO 2 nto water and surfactant solutons. The same behavor was seen from the surfactant soluton experments. Moreover, the results of experments show that the addton of SDS to water has no measurable effect on the mass transfer rate n our expermental setup. A smlar mass transfer enhancement was observed for the mass transfer between gaseous CO 2 rch phase wth an ol (n-decane) phase. Ths has mplcatons for the ol recovery. 7. Acknowledgments Ths work was funded by a specal program of the TU Delft, Delft Earth Research. We thank the staff of Detz laboratory of our faculty, especally H. van der Meulen and P. de Vreede for ther techncal support. c = Gas concentraton [M] C = Laplace transform of c [M] D eff = Effectve dffuson coeffcent [m 2 /s] H = Henry s constant [Pa/ mol/m 3 ] L = Length of the expermental tube [m] L = Heght of the gas n the expermental tube [m] L 2 = Heght of the lqud n the expermental tube [m] P g = Gas pressure [Pa] P = Intal gas pressure [Pa] R = Unversal gas constant [J/mol/K] S = Cross sectonal area of the tube [m 2 ] t = tme [sec] T = Temperature [K] V = Volume of the gas n tube [m 3 ] Z = Gas compressblty factor [-] 9. References. Ashcroft S. and Ben Isa M., Effect of dssolved gases on the denstes of hydrocarbons, J. Chem. Eng. Data, 997, Bachu S., Adams J.J., Sequestraton of CO2 n geologcal meda n response to clmate change: capacty of deep salne aqufers to sequester CO2 n soluton, Energy Convers. Manage.,2003, 44, Barnes G.T., Hunter D.S., The evaporaton resstance of monolayers of cellulose decanoate, J. Collod Interface Sc., 989, 29, Barnes G.T., Permeaton through monolayers, Collods Surf. A, 997, 26, Blank M.J., Monolayer Permeablty and the Propertes of Natural Membranes, Phys. Chem., 962, 66, Caskey, J.A., Barlage W.B. Jr., A study of the effects of soluble surfactants on gas absorpton usng lqud lamnar jets, J. Collod Interface Sc., 972, 4, Coulson J.M., Rchardson J.F., Chemcal Engneerng, 3rd ed.,pergamon Press, Oxford, 977, Vol., pp Fogg P.G.T., Gerrard W., Solublty of gases n lquds, Wley, New York, 99, pp Nomenclature

9 SPE Gertz Kh., Loeschcke Hh., Helv. Physol. Pharmacol. Acta., 954, 2(4) : C Gmeln L., Gmeln Handbuch der anorganschen Cheme, 8. Auflage. Kohlenstoff, Tel C3, Verbndungen., 973, pp Greenwood N.N. and Earnshaw A., Chemstry of the elements, 2nd Ed. Butterworth Henemann, Oxford, Hanwght J., Zhou J., Evans G.M., Galvn K.P., Influence of Surfactant on Gas Bubble Stablty, Langmur, 2005, 2, Holt T., Jensen J., Lendeberg E., Underground storage of CO 2 n aqufers and ol reservors, Energy Convers. Manage.,994, 36, Vazquez G., Antorrena G., Navaza J.M., Influence of Surfactant Concentraton and Chan Length on the Absorpton of CO2 by Aqueous Surfactant Solutons n the Presence and Absence of Induced Marangon Effect, Ind. Eng. Chem. Res., 2000, 39, Yang Ch., Gu Y., Accelerated mass transfer of CO 2 n reservor brne due to densty-drven natural convecton at hgh pressures and elevated temperatures, Ind. Eng. Chem. Res., 2006, 45, Zhang Y.P., Hyndman C.L., Man B.B., Measurement of gas dffusvty n heavy ols, J. Petroleum Sc. and Eng., 2000, 25, Kode K., Orto Y. and Hara Y., Mass transfer from sngle bubbles n Newtonan lquds, Chem Engng Sc. 974, 29, La Mer V.K., Aylmore L.A.G., Healy T.W., The deal surface behavor of mxed monolayers of long chan n- paraffnc alcohols, J. Phys. Chem., 963, 67, Lndeberg E., Wessel-Berg D., Vertcal convecton n an aqufer column under a gas cap of CO 2, Energy Convers. Manage.,997, 38, S229-S Molder E., Tenno T., Ngu P., The Influence of Surfactants on Oxygen Mass Transfer through Ar-Water Interface, Crtcal Rev. Anal. Chem., 998, 28, Nguyen P., Ztha P.L.J., Curre P.K., Effect of foam flms on gas dffuson, J. Collod and Int. Sc., 2002, 248, Raymond D.R. and Zemnsk S. A., Mass transfer and drag coeffcents of bubbles rsng n dlute aqueous solutons, A.I.Ch.E.J, 97,7, Sander R, Complaton of Henry s Law Constants for Inorganc and Organc Speces of Potental Importance n Envronmental Chemstry, Verson 3, 999, p57 2. Santanu Para and Pak K. Yuet, Effects of Chan Length and Electrolyte on the Adsorpton of n- Alkylpyrdnum Bromde Surfactants at Sand-Water Interfaces, Ind. Eng. Chem. Res., 2006, 45, Sprnger T.G., Pgford R.L., Influence of Surface Turbulence and Surfactants on Gas Transport through Lqud Interfaces, Ind. Eng. Chem. Fundam., 970, 9,

10 0 SPE 0738 Table : Lst of Experments wth water Experment Number Intal Pressure (bar) Temperature (ºC) Exp ±0. Exp ±0. Exp ±0. Experment Number Table 2: Lst of Experments wth SDS soluton Intal Pressure (bar) T (ºC) SDS Concentraton Exp ±0. C=30mM>CMC Exp ±0. C <CMC Exp ±0. C=30mM+NaCl Table 3: The late-stage and early stage effectve dffuson coeffcents extracted from expermental data. The effectve dffuson coeffcents n the thrd and fourth columns were extracted by choosng the lterature value of Henry s coeffcent, H= Pa/mol/m³ Experment Number D / H D eff for early stages (m 2 /s) D eff for later stages (m 2 /s) Exp Exp Exp Exp Exp Exp