Accurate gas – Zeolite interaction measurements by using high pressure gravimetric volumetric adsorption method

international journal of hydrogen energy 34 (2009) 3191–3196

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Accurate gas – Zeolite interaction measurements by using high pressure gravimetric volumetric adsorption method B. Weinbergera,*, F. Darkrim Lamaria, A. Veziroglub, S. Beyazc, M. Beauvergera a

LIMHP, Universite´ Paris 13, CNRS UPR1311 Institut Galile´e, 99 avenue Jean-Baptiste Cle´ment, 93430 Villetaneuse, France International Association for Hydrogen Energy, 5783 SW 40 Street 303, Coral Gables, FL, USA c University of Kocaeli, Umuttepe Yerleskesi, Department of Chemistry, 41380 Izmit, Turkey b

article info

abstract

Article history:

In this work, we discuss the purification of hydrogen by physical adsorption on zeolites Li–

Received 7 November 2008

LSX exchanged 78%, 83% and 99%. A newly developed adsorption device is applied to the

Received in revised form

gas–solid adsorption measurements. Isotherms of hydrogen adsorption are gravimetric

28 January 2009

volumetrically measured at 293.15 K up to 5 MPa. The accuracy of this new device is

Accepted 30 January 2009

compared to NIST gas density data’s of hydrogen and nitrogen at 293.15 K. Further the real

Available online 26 February 2009

density of the zeolites is obtained by helium skeleton density measurements at high temperature (650 K). The paper provides an interpretation of hydrogen adsorption capac-

Keywords:

ities according to the gas-surface interaction. Further the isosteric heat of adsorption is

PSA process

obtained for the studied materials and analysed in relation to the zeolite cations exchange

Hydrogen

rate. Moreover, we discuss the influence of the ratio of cation exchange on hydrogen gas

Adsorption

adsorption.

Zeolite

ª 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights

High pressure

reserved.

Accurate device Excess adsorption

1.

Introduction

Generally hydrogen is produced by reforming or partially oxidation of hydrocarbons, then purified by Pressure Swing Adsorption process (PSA). This latter requires the knowledge of thermodynamic parameters of the used adsorbents like excess adsorption, gas–gas selectivity and heat of adsorption, which are basic data for the efficiency design of the process. Now the cheapest hydrogen production method is natural gas reforming process followed by purification via PSA. The main advantage of PSA in comparison to cryogenic and membrane processes is a high product purity up to 99.9999% [16,20]. This outcome is important for the application of hydrogen as future energy source because proton exchange membrane

fuel cells need high purity hydrogen to prevent the degradation of cell membrane efficiency. Indeed, current global production of hydrogen has risen to approximately 500 billions Nm3 per year and only 4.2% of this production is marketed; the majority of hydrogen produced is used for the synthesis of ammonia. In addition, with 14.4  1012 kJ per year, the share of hydrogen is negligible compared to the consumption of total primary energy (4  1018 kJ in 2000). Thus, investigating the optimisation of technologies like PSA to get clean and cheap hydrogen from natural gas or biomass in large amounts becomes a valuable undertaking. The performance of an adsorbent is determined by the measurement of its thermodynamic equilibrium with the considered gases at a fixed temperature and various

* Corresponding author. Tel.: þ33 1 49 40 34 56; fax: þ33 1 49 40 34 14. E-mail address: [email protected] (B. Weinberger). 0360-3199/$ – see front matter ª 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2009.01.092

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international journal of hydrogen energy 34 (2009) 3191–3196

pressures. Further the heat of adsorption is an important parameter which influences the thermal effects during the adsorption cycles [10]. The interactions between hydrogen and adsorbent surface area are generally weak [5] which implicate some difficulties for accurate measurements. Regarding the high volatility of hydrogen and the mostly low adsorption, leaks during the measurement can lead to important errors. Consequently, we chose a procedure which makes it possible to detect leaks in the adsorption system and where systematic errors are negligible. In this work, we describe the adapted device designed and built for this experiment. Also, we consider new aluminosilicate-based materials which may be able to lower the price of hydrogen production by PSA process. The significant criteria of the performance of an adsorbent for application in hydrogen purification process are: the adsorption capacity of the components in the mixture containing H2, CO2, CO, N2 and H2O, the adsorption selectivity between hydrogen and the impurities, the heat of adsorption and the desorption capacity of the components in the given range of pressure. Despite the price of the adsorbent is an important criteria, it will not be discussed in this study.

2.

Experimental Design

The elaborated gravimetric–volumetric setup has several advantages. First there is no buoyancy due to the adsorption vessel since the cell is located in constant pressure and temperature conditions. This problem occurs primarily during high pressure measurement, such as in gravimetric measurements [4,6,7,11,15]. Additionally, there is no accumulation of error like in the case of the volumetric measurements [9,17,21]. Further with gravimetric–volumetric measurements a leak can be easily observed as a negative change of mass, contrary to volumetric systems where a decrease of pressure can be interpreted as adsorption phenomena. A scheme of our experimental setup is shown in Fig. 1. The principle based on the dynamically measuring of the mass of gas present in the adsorption vessel subtracted with the quantity of gas in the bulk, in order to calculate the excess of adsorption. After each state of equilibrium, the gas is re-injected to the system. As illustrated in Fig. 1, the gas in the adsorption vessel is weighed directly and is injected via a capillary tube. To avoid systematic errors during the mass measurement, the adsorption vessel must be symmetrical and its axis has to be in vertical position. The vertical alignment of the system is obtained using a counterweight. This compensates for the turning movement due to the capillary tube with a length (x). At its left the capillary tube is connected to the balance and on its right to the micrometric table. The micrometric table enables a precise adjustment for the verticality of the adsorption vessel. The axial deviation ( y) of the balance is slightly influenced by elasticity (E ) of the capillary tube. We used a capillary tube (stainless 316L, 200 GPa) with a length of 1520 mm, where a load of 0.1 mg at the free end induces a deviation of the capillary tube equal to 0.02 mm. The axial deviation is given by:

MC ma p

MT

CP

E S

C

MV

F Pt 100

R

V2

BG

SCR F V1

SC

20 °C RE

V3

TC

450 °C RCC

Fig. 1 – MC, mass comparator (Mettler Toledo, PR2004); E, climatic chamber (S.P.A.M.E.); C, Unichiller (Huber, 7006AH); SC, heating system; Pt 100, platinum temperature sensor; R, pressure vessel; SCR, heating system of the pressure vessel; F, micro-filters; v, valves (Autoclave); RE, climatic chamber regulation (Eurotherm 2404); RCC, regulation of the SCR (Watlow Se´rie 93); MT, micrometric table (Micro Controle); CP, pressure gauge of reference (DH Budenberg DPM1); S, security valve (Air Liquide); MV, micrometric valve (Autoclave); BG, gas bottle (Air Liquide); TC, turbo pump (Pfeiffer Vacuum TSH 071).

y¼

F ,x3 G  4 4 p De  di 3E 64

(1)

where De is the external diameter, di the internal diameter of the capillary tube and FG is the gravimetric force.

2.1.

Measurement Procedure

The procedure for measuring adsorption capacity can be subdivided into several stages and is illustrated on hand of the pressure and temperature evaluation in Fig. 2. 1. The cleaned and evacuated adsorption vessel is weighted. 2. The adsorption vessel volume (35 cm3) is filled with the adsorbent and sealed. 3. In order to prevent heating of the high pressure valve, the thermostatic chamber is stabilized to 273.15 K. 4. The system is evacuated gradually. 5. The heat jacket of the adsorption vessel heats up (2 K/min) until 373.15 K. 6. A stage at 373.15 K enables to eliminate water in the adsorbent cell. 7. Once the second vacuum is reached, the heating process continues until the final temperature is reached (depending on the adsorbent temperature decomposition). 8. The activation process is obtained at high temperature and secondary vacuum. 9. The adsorption cell is then cooled down to ambient temperature.

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international journal of hydrogen energy 34 (2009) 3191–3196

8

4

350 300

5

1,0E+04 1,0E+03

Temperature

1,0E+02

Pressure

1,0E+01 1,0E+00 1,0E-01

200

1,0E-02

6

150

1,0E-03

p [mbar]

250

T [°C]

9

7

400

1,0E-04

100

1,0E-05

50

1,0E-06

0 0,01

0,1

1

1,0E-07 100

10

t [h] Fig. 2 – Evolution of the pressure and the temperature during the regeneration.

10. The high pressure valve is closed and the vacuum pump is stopped and the desorbed adsorbent mass is determined. 11. The adsorption vessel is connected to the capillary gas inlet tube and the procedure (steps 3–8) is repeated. 12. The acquisition of measurement data starts. 13. The pressure is preset via the mano-pressure reducer. 14. The gas is then controlled injected by the micro-valve. 15. At thermodynamic equilibrium, the procedure (step 12) is repeated until reaching the maximal pressure.

TExt temperature of the capillary, VCap the volume of capillary ~ Gas is the tube, mAds mass of the degassed adsorbent and M molar mass of the gas. The bulk density of the gas rGas is evaluated by an algorithm, which is based on the data of the IUPAC. In order to determine with accuracy the volumes, the thermal dilation of the adsorption vessel and the adsorbent are taken in account. The factor 0.5 is due to the fact that the capillary tube is supported at equal height on the micrometric table side and the mass comparator side.

The excess adsorption ma is expressed in mole per gram. The following equation applies to the adsorption of pure gases used in this study. The excess adsorption of these gases obtained by volumetric–gravimetric measurement is:

2.2.

Validation of the Experimental Setup

where mGas is the total mass of gas in the adsorption vessel, rGas the bulk density, TInt the adsorbent temperature, p the gas pressure, VC volume of the adsorption vessel, VAds volume of the adsorbent, TInt is the temperature in the climatic chamber;

With the gravimetric–volumetric device described above, it is possible to determine the gas density. The gas density measurement enables to verify the accuracy of the gravimetric–volumetric setup in the considered range of pressure and temperature. A comparison between the results measured with nitrogen and hydrogen gases and those tabled by the NIST at 293.15 K gives a maximum difference of 0.78% and 0.51% respectively (Tables 1 and 2). The uncertainty in density enables us to conclude that the results are very satisfying in the considered range of pressure and

Table 1 – Nitrogen density at 293.15 K. p pressure (105 Pa), N2 3 rN2 m measured density of nitrogen (g/cm ), rNIST density of nitrogen referenced by NIST (g/cm3), s difference of rN2 m 3 and rN2 NIST (g/cm ), G relative error (%).

Table 2 – Hydrogen density at 293.15 K. p pressure H2 3 (105 Pa), rH2 m measured density of hydrogen (g/cm ), rNIST 3 density of hydrogen referenced by NIST (g/cm ), s H2 3 difference of rH2 m and rNIST (g/cm ), G relative error (%).

h h i ma ¼ mGas  rGas ðTInt ; pÞ, VC ðTInt Þ  VAds ðTInt Þ i.  ~ Gas mAds ,M  rGas ðTExt ; pÞ,VCap ðTExt Þ,0:5

p 6.3735 10.2001 15.2077 20.1327 25.2321 29.8906 35.0630 40.0676 44.8992 51.3801

(2)

rN2 m

rN2 NIST

s

G

7.308E-03 1.172E-02 1.748E-02 2.304E-02 2.909E-02 3.450E-02 4.051E-02 4.634E-02 5.198E-02 5.954E-02

7.335E-03 1.175E-02 1.753E-02 2.322E-02 2.912E-02 3.451E-02 4.049E-02 4.628E-02 5.186E-02 5.934E-02

2.73E-05 2.85E-05 4.43E-05 1.80E-04 2.40E-05 5.51E-06 1.51E-05 5.66E-05 1.15E-04 2.08E-04

0.37 0.24 0.25 0.78 0.08 0.02 0.04 0.12 0.22 0.35

p 7.4212 10.5127 15.1488 19.9134 25.6137 31.1254 36.5314 40.5274 45.1244 51.2539

rH2 m

rH2 NIST

s

G

6.103E-04 8.662E-04 1.242E-03 1.624E-03 2.085E-03 2.526E-03 2.946E-03 3.256E-03 3.627E-03 4.103E-03

6.110E-04 8.640E-04 1.242E-03 1.628E-03 2.086E-03 2.527E-03 2.957E-03 3.272E-03 3.634E-03 4.112E-03

6.88E-07 2.21E-06 1.62E-07 3.15E-06 1.94E-06 1.38E-06 1.07E-05 1.65E-05 6.92E-06 9.06E-06

0.11 0.26 0.01 0.19 0.09 0.05 0.36 0.51 0.19 0.22

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international journal of hydrogen energy 34 (2009) 3191–3196

3,5

1 Li-LSX 78%

0,9 3

ma [mmol/g]

ma [mmol/g]

Li-LSX 83%

0,7

2,5

2

1,5 AL 40,3 °C

1

0,5 0,4

0,2

AL 60,6°C

0,1

LIMHP 20°C

0,5

0,6

0,3

AL 20°C

LIMHP 40°C

0

LIMHP 60°C

0

Li-LSX 99%

0,8

0

10

20

30

40

50

p [105 Pa] 0

10

20

30

40

50

p [105 Pa]

Fig. 4 – Hydrogen adsorption equilibrium of the zeolites Li– LSX exchanged 78%, 83% and 99% at 293.15 K.

Fig. 3 – Reproducibility of the network of isotherms of adsorption of N2: LIMHP/AL at three temperatures.

temperature. Further we compared results obtained by a volumetric setup published [3, 22–24] where we obtained a maximum difference of 1.3% at 293.15 K, 2.1% at 313.15 K and 2.1% at 333.15 K for nitrogen adsorption on 13X (see Fig. 3).

3.

The Na–LSX sample was prepared hydrothermally according to the procedure described by Ku¨hl [8], from a gel with the molar composition: 1Al2O3:2SiO2:4.9Na2O:1.6K2O:110H2O. Ionic exchange of the zeolite by lithium is carried out by a percolation technique. Different structural characterization techniques were performed on similar crystals, including X-ray diffraction and scanning electronic microscopy, to discover the effect of the cation exchanges on crystal

Results and Discussion

In terms of potential for application in PSA engineering, we obtained promising results for different zeolites (type faujasite) exchanged at different degrees of cations. These materials are compared by their adsorption capacity, the heat of adsorption and pressure range applicability for hydrogen. Hydrogen adsorption selectivity of the Li–LSX exchanged molecular sieves at the rates of 78%, 83% and 99% have been performed up to a pressure of 5 MPa at a temperature of 293.15 K Adsorption properties of adsorbed species in faujasite zeolites are strongly correlated to the nature and amount of cations in the structure. Adsorption as well as diffusion is related to the location of the cations [1]. Therefore, the chemical nature of the zeolites was modified by exchanging the cations and as well the pore entry diameter, which influences gas diffusion inside the exchanged zeolites.

Table 3 – Real densities (g/cm3) of the zeolites Li–LSX 78%, Li–LSX 83% and Li–LSX 99% obtained by volumetric helium displacement measurements at 673.15 K. Li–LSX 99% Li–LSX 83% Li–LSX 78%

2.15  0.01 2.22  0.01 2.09  0.01

Table 4 – Hydrogen adsorption on Li–LSX exchanged 78%, 83% and 99%: p pressure (105 Pa), rB bulk density of hydrogen (mol/cm3), maV and mamol excess adsorption (N cm3/g) and (mmol/g). p

rB

mV a

mmol a

2.26 4.35 9.72 11.92 14.64 17.94

0.10 0.19 0.43 0.53 0.65 0.80

1.66 3.03 5.58 7.84 9.62 11.27

0.07 0.14 0.25 0.35 0.43 0.50

2.92 4.23 8.32 10.52 13.65 15.33

0.13 0.19 0.37 0.47 0.61 0.68

Li–LSX 78% at 293.15 K 5.053 2.07E-04 10.037 4.09E-04 24.464 9.89E-04 30.555 1.23E-03 38.913 1.56E-03 50.504 2.01E-03 Li–LSX 83% at 293.15 K 5.004 2.05E-04 10.147 4.14E-04 20.270 8.22E-04 30.410 1.23E-03 40.443 1.62E-03 50.639 2.02E-03 Li–LSX 99% at 293.15 K 7.375 3.01E-04 10.720 4.37E-04 23.157 9.37E-04 30.455 1.23E-03 43.017 1.72E-03 50.122 2.00E-03

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international journal of hydrogen energy 34 (2009) 3191–3196

Table 5 – Efficiency of Li–LSX 78%, Li–LSX 83% and Li–LSX 99% at 293.15 K. Component

Li-LSX 78%

Li–LSX

mR [mmol/g]

78%

83%

99%

0.76

0.48

0.64

morphology and structure and the influence of these adsorbent parameters on the PSA process [14]. First, we determined the real density of the zeolites using a volumetric setup at high temperature under helium equilibrium [12,18]. The results (Table 3) are varying between 2.22 and 2.09 g/cm3. We observe the absence of a linear relation between the exchanged cation ratio and the material density. By exchanging Na atom with a Li atom one can expect a reduction of the orthorhombic structure [2]. The adsorption isotherms of high purity hydrogen (99.9995%) at 293.15 K on the zeolites Li–LSX 78%, Li–LSX 83% and Li–LSX 99% are represented in Fig. 4 and in Table 4. The zeolite LSX 83% at 50  105 Pa adsorbs about 38% less hydrogen than the Li-SX 78% and 26% less than Li–LSX 99%. In the present pressure range the excess of adsorption of hydrogen increases with the pressure and there is no saturation. Furthermore we conclude that there is no simple relation between the exchanged cation ratio and the excess of hydrogen adsorption. Judging from these adsorption results, it is possible to characterize the efficiency mR of the adsorbent materials. This is, defined as the difference between the capacity of adsorption of gas at high pressure (50  105 Pa) and the capacity of adsorption obtained at low pressure (1  105 Pa):     mR ¼ ma 50  105 Pa; 293:15K  ma 1  105 Pa; 293:15K

(3)

The selected pressures represent possible operation values for a pressure swing adsorption process. Table 5 shows the efficiency mR in the field of our measurements. The values of the excess adsorption for 1  105 Pa and 50  105 Pa are calculated from an interpolation based on a polynomial smoothing of the experimental results. The Li–LSX 83% has the lowest efficiency (0.48 mmol/g) and is therefore a material of interest in terms of hydrogen

Li-LSX 83%

Li-LSX 99%

0

Li-LSX 83%

Li-LSX 99%

0

1000

2000

3000

4000

5000

6000

7000

8000

ΔH [J/mol] Fig. 5 – Isosteric heat of adsorption of hydrogen on the zeolites Li–LSX 78%, Li–LSX 83% and Li–LSX 99% at 293.15 K.

2

3

4

5

6

ΔH [J/g] Fig. 6 – Mass specific heat of adsorption of hydrogen on the zeolites Li–LSX 78%, Li–LSX 83% and Li–LSX 99% at 293.15 K and 50 3 105 Pa.

purification trough PSA, because of a low cyclical loss of hydrogen. In order to draw a final conclusion, the efficiency of the adsorbent for the other gases in a process of hydrogen purification (CO2, CO, CH4 and N2), have also to be taken in account. To determine the isosteric heat of adsorption we used the isotherms obtained at three temperatures up to 50  105 Pa. The isosteric method is derived from the determination of the pressures which at different temperatures correspond to identical capacities of adsorption. With a given capacity of adsorption, these pressures form the isostere network. Then the heat of adsorption can be calculated by a Van’t Hoff equation. The average heat of adsorption varies between 5.5 kJ/mol and 7.5 kJ/mol, for the Li–LSX 78% up to the Li–LSX 99% (see Fig. 5). This represents a linear relation between the heat of adsorption and the exchanged ratio of cations, contrary to the case where the heat of adsorption is related to the adsorbent mass (see Fig. 6). At 50  105 Pa and 293.15 K, the lowest heat of adsorption is obtained with the Li–LSX 83% (3.3 J/g). The highest value (5.1 J/g) is obtained with the Li–LSX 99% zeolite. These results underline the interesting potential of the Li–LSX 78% because it represents in this study the adsorbent with the lowest efficiency as already discussed above.

4. Li-LSX 78%

1

Conclusion

A new gravimetric–volumetric setup was designed and constructed in order to obtain the weak adsorption of hydrogen and other gases on small quantity of framework materials in pellet or powder shape. An accuracy was calculated by comparing NIST PVT data [13] (uncertainty in density: 0.51% for hydrogen and 0.78% for nitrogen) and with a volumetric device from the company Air Liquide (difference up to 2.1% on a zeolite 13X with nitrogen). Accurate measurements of adsorption of hydrogen were performed up to pressures of 50  105 Pa on the zeolites Li–LSX 78%, Li–LSX 83% and Li–LSX 99% at 293.15 K. As a result of this comparison the Li–LSX 83% remains as the adsorbent with the lowest heat of adsorption at 50  105 Pa and 293.15 K alike the lowest efficiency mR at PSA process

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parameters of 1  105 Pa to 50  105 Pa. Nevertheless further co-adsorption measurements with gas mixture composition introduced in the PSA process are necessary because gas–gas interactions can modify strongly the excess adsorption results [19]. While exchanging the Li cations, their localization in the crystal-zeolite differs from that of Na cations. Moreover, the exchange can induce a structural deformation of the skeleton structure [14]. Isosteric heat results from the combined influence of the modification of the excluded effects of volume and the modification of the Coulomb interactions with the electric multipoles and the polarization of the adsorbed molecules. The former is dependant on the modification of the localization of the cations in zeolites, while the latter is depending on the change in the effective loads of the cations.

Acknowledgments The authors thank Air Liquide/Ministe`re de l’Industrie et des Finances for their capital grant in the frame of the ZEOMAT project.

references

[1] Beyaz Kayiran S, Lamari Darkrim F. Synthesis and ionic exchanges of zeolites for gas adsorption. Surf Interface Anal 2002;34:100–4. [2] Breck DW. Zeolite molecular sieves. Malbar, Florida: Krieger Publishing Company; 1974. [3] Chahine R, Bose TK. Low-pressure adsorption storage of hydrogen. Int J Hydrogen Energy 1994;19(2):161–4. [4] Darkrim F, Vermesse J, Malbrunot P, Levesque D. Monte Carlo simulations of nitrogen and hydrogen physisorption at high pressures and room temperature. Comparison with experiments. J Chem Phys 1999;110(8):4020–7. [5] Darkrim F, Aoufi A, Malbrunot P, Levesque D. Hydrogen adsorption in Na a zeolite: a comparison between numerical simulations and experiments. J Chem Phys 2000;112:5991–9. [6] De Weireld G, Fre`re M, Jadot R. Automated determination of high-temperature and high-pressure gas adsorption isotherms using a magnetic suspension balance. Meas Sci Technol 1999;10:117–26. [7] Dreisbach F, Seif R, Lo¨sch HW. Messmethoden fu¨r Gasphasen-Adsorptionsgleichgewichte. Chemie Ing Tech 2002;74:1353–66.

[8] Ku¨hl GH. Crystallization of low-silica faujasite (SiO2/ Al2O3w2.0). Zeolites 1987;7:451–7. [9] Kiyobayashi T, Takeshita HT, Tanaka H, Takeichi N, Zu¨ttel A, Schlapbach L, et al. Hydrogen adsorption in carbonaceous materials – how to determine the storage capacity accurately. J Alloys Compd 2002;330–332:666–9. [10] Lamari M, Aoufi A, Malbrunot P. Thermal effects in dynamic storage of hydrogen by adsorption. AIChE J 2000;46(3):632–46. [11] Li X, Zhua H, Xua C, Mao Z, Wu D. Measuring hydrogen storage capacity of carbon nanotubes by tangent-mass method. Int J Hydrogen Energy 2003;28:1251–3. [12] Malbrunot P, Vidal D, Vermesse J, Chahine R, Bose TK. Adsorbent helium density measurement and its effect on adsorption isotherms at high pressure. Langmuir 1997; 13:539. [13] NIST (National Institute of Standards and Technology) web page with gas densities database: http://webbook.nist.gov/ chemistry/fluid/2008. [14] Porcher F, Souhassou M, Dusausoy Y, Lecomte C. Structure cristalline sur monocristal de la ze´olithe LiA totalement e´change´e et de´shydrate´e. Comptes Rendus de l’Acade´mie des Sciences – Serie IIC-Chimie 1998;1:701. [15] Staudt R, Saller G, Tomalla M, Keller JU. A note on gravimetric measurement of gas-adsorption equilibria. Ber Bunsenges Phys Chem 1993;97:98–105. [16] Ruthven DM. Principles of adsorption and adsorption processes. New York: John Wiley; 1984. [17] Vidal D, Malbrunot P, Guengant L, Vermesse J, Bose TK, Chahine R. Measurement of physical adsorption of gases at high pressure. Rev Sci Instrum 1990;61:1314–8. [18] Weinberger B, Darkrim Lamari F, Beyaz Kayiran S, Gicquel A, Levesque D. Molecular modeling of H2 purification on Na–LSX zeolite and experimental validation. AIChE J 2005;51: 142–8. [19] Weinberger B, Darkrim Lamari F, Levesque D. Capillary condensation and adsorption of binary mixtures. J Chem Phys 2006;124:234712.1–9. [20] Yang RT. Gas separation by adsorption processes. London: Imperial College Press; 1999. [21] Zhang C, Lu X, Gu A. How to accurately determine the uptake of hydrogen in carbonaceous materials. Int J Hydrogen Energy 2004;29:1271–6. [22] Weinberger B, Universite´ Paris 13, PhD Thesis, Limhp CNRS; 2005. [23] Beyaz SK, Darkrim Lamari F, Weinberger B, Gadelle P, Firlej L, Bernier P. Herringbone nanofiber CVD synthesis and high pressure hydrogen adsorption performance analysis by molecular modelling. Int J Hydrogen Energy 2009;34(4): 1965–70. [24] Beyaz S, Darkrim Lamari F, Weinberger B, Veziroglu A. Nanoscale carbon material porosity effect on hydrogen adsorption at high pressure. Int J Hydrogen Energy 2009.