Abstract
The saturation loadings for subcritical adsorption of n-, iso- and neo alkanes C1–C8 in 13X zeolite are modeled using the modified Rackett model of Spencer and Danner (J Chem Eng Data 17:236–240, 1972) for the saturated liquid densities combined with crystallographic data for the 13X zeolite. For validation of this model, alkane adsorption data in the literature is first critically evaluated and then compared to the model. The saturation loading of each isotherm that approaches saturation is extracted from the data. Log–log plots are used to determine whether each isotherm is near saturation; isotherms that exhibit a \(({{\partial \text{ \ ln \ } q)} \mathord{\left/ ({\vphantom {{\partial { \ ln \ } q} {\partial { \ ln \ }p}}} \right. \kern-0pt} {\partial \text { \ ln \ }p}})\) slope of zero at their maximum pressure point are assumed to be saturated. Isotherms not fulfilling this criterion are deemed unsaturated and not considered further. The theoretical equation satisfactorily models the available experimental data for the n- alkanes. However, steric factors are required for the model to fit iso alkanes and neo-pentane. For supercritical temperatures, no model presently exists to explain the data. However, the data are satisfactorily modeled with an equation of the form qmax = 8.5 ± 2.5 g/100 g.
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Abbreviations
- MW:
-
Molecular weight (g/mol)
- Pc :
-
Critical pressure (kPa)
- Pr :
-
Reduced pressure
- q:
-
Zeolite loading (g/100 g zeolite crystal)
- qmax :
-
Maximum zeolite loading (g/100 g zeolite crystal)
- qmax,c :
-
Theoretical maximum zeolite loading at the critical temperature, defined by Eq. 5 (g/100 g zeolite crystal)
- R:
-
Gas constant (8314 kPa-cm3/gmol.K)
- Tc :
-
Critical temperature (K)
- TCAR :
-
Critical adsorbate reduced temperature (K)
- Tr :
-
Reduced temperature
- Vsat :
-
Saturated liquid volume (cm3/g)
- ZRA :
-
Rackett parameter
- Γ:
-
Normalized loading, dimensionless, calculated in Eqs. 6 and 7
- εZ :
-
Crystallographic 13X zeolite void fraction, 0.428 (Breck 1974, p. 133)
- λ:
-
Steric factor, used in Eq. 8
- ρsat :
-
Sorbate liquid density, g adsorbate/cm3)
- ρZ :
-
Zeolite 13X crystallographic density, 1.43 g/cm3, (Breck 1974, p. 133)
References
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Acknowledgments
This is a detailed manuscript of a paper presented at the Fall 2011 conference of AICHE. The authors wish to acknowledge the support of the American University of Sharjah and the California State University at Bakersfield during this study. The authors also wish to acknowledge anonymous reviewers for their comments on steric factors.
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Kevin F. Loughlin—American University of Sharjah (retired).
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Fig. S1
qmax calculated from Rackett’s equation and crystal properties for n-alkanes C1 through C8 as a function of reduced temperature. A dashed line is used when Tr is above the TCAR for 5A zeolite (Loughlin and Abouelnasr 2009) for the given species. (TIF 90 kb)
Fig. S2a
Methane isotherms before screening. Labels are reduced temperatures. Isotherms in grey are inconsistent with others, and so are screened out. Deleted points are in grey. (TIF 104 kb)
Fig. S2b
Methane isotherms after screening. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. Isotherms that are not near saturation have a dotted line. (TIF 106 kb)
Fig. S2c
Log-log plot of methane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. Isotherms that are not near saturation have a dotted line. (TIF 93 kb)
Fig. S3a
Ethane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. Isotherms that are not near saturation have a dotted line. (TIF 113 kb)
Fig. S3b
Log–log plot of ethane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. Isotherms that are not near saturation have a dotted line. (TIF 111 kb)
Fig. S4a
Propane isotherms before screening. Labels are reduced temperatures. Isotherms in grey are inconsistent with others and so are screened out. Deleted points are in grey. Isotherms that attain saturation have a solid line. Isotherms that are not near saturation have a dotted line. (TIF 150 kb)
Fig. S4b
Log–log plot of propane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. Isotherms that are not near saturation have a dotted line. (TIF 122 kb)
Fig. S5a
n Butane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. (TIF 47 kb)
Fig. S5b
Log–log plot of n butane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. (TIF 42 kb)
Fig. S6a
Butane isotherms. Labels are reduced temperatures. Isotherms in grey are inconsistent with others, and so are screened out. Isotherms that attain saturation have a solid line. (TIF 113 kb)
Fig. S6b
Log–log plot of iso butane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. (TIF 99 kb)
Fig. S7a
n Pentane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. (TIF 49 kb)
Fig. S7b
Log–log plot of n pentane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. (TIF 42 kb)
Fig. S8a
iso Pentane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. (TIF 49 kb)
Fig. S8b
Log–log plot of iso pentane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. (TIF 43 kb)
Fig. S9a
neo Pentane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. (TIF 50 kb)
Fig. S9b
Log–log plot of neo pentane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. (TIF 47 kb)
Fig. S10a
n Hexane isotherms. Labels are reduced temperatures. Isotherms that are deleted are in grey. Isotherms that attain saturation have a solid line. (TIF 53 kb)
Fig. S10b
Log–llog plot of n hexane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. (TIF 48 kb)
Fig. S11a
n Heptane isotherms. Labels are reduced temperatures. Deleted points are in grey. Isotherms that attain saturation have a solid line. (TIF 93 kb)
Fig. S11b
Log–log plot of n heptane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. (TIF 85 kb)
Fig. S12a
n Octane isotherms before screening. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. Data points in grey are deleted. (TIF 41 kb)
Fig. S12b
Log–log plot of n octane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. (TIF 39 kb)
Fig. S13a
iso Octane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. Data points in grey are deleted. (TIF 45 kb)
Fig. S13b
Log–log plot of iso octane isotherms. Labels are reduced temperatures. Isotherms that attain saturation have a solid line. (TIF 43 kb)
Fig. S14
qmax vs. Tr for all alkanes. Bounding-lines for supercritical are at 6 and 11 g/100 g. (TIF 73 kb)
Fig. S15b
Same as Figure 15a, but with Barrer and Sutherland data removed. (TIF 63 kb)
Fig. S16
The model and observed qmax for all three isomers of pentane. The model for neo pentane with a steric factor of 0.8 is indicated by a dotted line. (TIF 69 kb)
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Al Mousa, A., Abouelnasr, D. & Loughlin, K.F. Saturation loadings on 13X (faujasite) zeolite above and below the critical conditions. Part I: alkane data evaluation and modeling. Adsorption 21, 307–320 (2015). https://doi.org/10.1007/s10450-015-9672-x
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DOI: https://doi.org/10.1007/s10450-015-9672-x