Mar 30, 2001 - Sorption of Propane, Ethane, Methane and. Carbon Dioxide on ... Sorption Thermodynamics of C3H8, C2H6, CH4, and CO2 on DAY Zeolite Crystals ............7 ..... For measurement of sorption isosteres, 5.0021 g (dry weight) of.
BOC-Degussa Petrox Sorbents. Sorption of Propane, Ethane, Methane and Carbon Dioxide on Crystals and Extrudates of Dealuminated Y-type Zeolite
by
Martin Bülow and Dongmin Shen
BOC Gases Technology Murray Hill, March 30, 2001
CONTENT
LIST OF FIGURES..........................................................................................................................3 LIST OF TABLES ...........................................................................................................................4 1. SUMMARY .................................................................................................................................5 2. INTRODUCTION 5 3. SORBENTS .................................................................................................................................6 4. EXPERIMENTAL METHOD .....................................................................................................7 5. RESULTS AND DISCUSSION ..................................................................................................7 5.1. Sorption Thermodynamics of C3H8, C2H6, CH4, and CO2 on DAY Zeolite Crystals ............7 5.1.1 Sorption Isosteres ...............................................................................................................7 5.1.2 Sorption Thermodynamic Functions ................................................................................16 5.1.3 Sorption Isotherms ...........................................................................................................18 5.2. Sorption Thermodynamics of C3H8, C2H6, CH4, and CO2 on DAY Zeolite Extrudates ......19 5.2.1 Sorption Isosteres .............................................................................................................19 5.2.2 Sorption Thermodynamic Functions ................................................................................27 5.2.3 Sorption Isotherms ...........................................................................................................31 5.3. Comparison between DAY Zeolite Crystals and Extrudates................................................31 5.3.1 Isosteric Heats of Sorption ...............................................................................................31 5.3.2 Sorption Isotherms ...........................................................................................................35 6. CONCLUSIONS ........................................................................................................................39 7. REFERENCES ..........................................................................................................................40
2
LIST OF FIGURES Figure 1. Sorption isosteres for propane on DAY zeolite crystals at loadings indicated. .............8 Figure 2. Sorption isosteres for ethane on DAY zeolite crystals at loadings indicated. ...............9 Figure 3. Sorption isosteres for methane on DAY zeolite crystals at loadings indicated. ..........10 Figure 4. Sorption isosteres for CO2 on DAY zeolite crystals at loadings indicated. .................11 Figure 5. Isosteric heats of sorption for C3H8, C2H6, CH4, and CO2 on DAY zeolite crystals. ........................................................................................................................16 Figure 6. Standard sorption entrolpies for C3H8, C2H6, CH4, and CO2 on DAY zeolite crystals. ........................................................................................................................17 Figure 7. Standard Gibbs free sorption energies for C3H8, C2H6, CH4, and CO2 on DAY zeolite crystals at 298 K. ..............................................................................................18 Figure 8. Sorption isotherms of C3H8, C2H6, CH4, and CO2 on DAY zeolite crystals at 298 K, calculated from sorption isosteres. ..........................................................................19 Figure 9. Sorption isosteres for propane on DAY zeolite extrudates at loadings indicated. .......20 Figure 10. Sorption isosteres for ethane on DAY zeolite extrudates at loadings indicated. ..........21 Figure 11. Sorption isosteres for methane on DAY zeolite extrudates at loadings indicated. .......22 Figure 12. Sorption isosteres for CO2 on DAY zeolite extrudates at loadings indicated. .............23 Figure 13. Isosteric heats of sorption for C3H8, C2H6, CH4, and CO2 on DAY zeolite extrudates. ....................................................................................................................28 Figure 14. Standard sorption entrolpies for C3H8, C2H6, CH4, and CO2 on DAY zeolite extrudates. ....................................................................................................................29 Figure 15. Standard Gibbs free sorption energies for C3H8, C2H6, CH4, and CO2 on DAY zeolite extrudates at 298 K. ..........................................................................................30 Figure 16. Sorption isotherms for C3H8, C2H6, CH4, and CO2 on DAY zeolite extrudates at 298 K............................................................................................................................31 Figure 17. Isosteric heats of sorption for C3H8 on DAY zeolite crystals and extrudates...............32 Figure 18. Isosteric heats of sorption for C2H6 on DAY zeolite crystals and extrudates...............33 Figure 19. Isosteric heats of sorption for CH4 on DAY zeolite crystals and extrudates. ...............34 Figure 20. sosteric heats of sorption for CO2 on DAY zeolite crystals and extrudates.................35 Figure 21. Sorption isotherms of C3H8 on DAY zeolite crystals and extrudates at 298 K. ...........36 Figure 22. Sorption isotherms of C2H6 on DAY zeolite crystals and extrudates at 298 K. ...........37 Figure 23. Sorption isotherms of CH4 on DAY zeolite crystals and extrudates at 298 K. ............38 Figure 24. Sorption isotherms of CO2 on DAY zeolite crystals and extrudates at 298 K. ............39
3
LIST OF TABLES Table 1. List of sorbents. ..................................................................................................................6 Table 2. Sorption isosteres and thermodynamic data for C3H8 on DAY zeolite crystals. .............12 Table 3. Sorption isosteres and thermodynamic data for C2H6 on DAY zeolite crystals. .............13 Table 4. Sorption isosteres and thermodynamic data for CH4 on DAY zeolite crystals................14 Table 5. Sorption isosteres and thermodynamic data for CO2 on DAY zeolite crystals................15 Table 6. Sorption isosteres and thermodynamic data for C3H8 on DAY zeolite extrudates. .........24 Table 7. Sorption isosteres and thermodynamic data for C2H6 on DAY zeolite extrudats............25 Table 8. Sorption isosteres and thermodynamic data for CH4 on DAY zeolite extrudates. ..........26 Table 9. Sorption isosteres and thermodynamic data for CO2 on DAY zeolite extrudates. ..........27
4
1. SUMMARY Sorption thermodynamics of propane, ethane, methane and carbon dioxide on BOC proprietary Petrox sorbents, DEGUSSA DAY (dealuminated Y-type) zeolite crystals and extrudates of those, evaluated using the Sorption Isosteric technique, to provide fundamental guides to develop next generation sorbents for Petrox applications. The isosteric heats of sorption at nearly zero coverage on DAY zeolite crystals are ca. 28, 24, 16 and 35 kJ/mol, respectively for propane, ethane, methane and carbon dioxide, while the corresponding values on DAY extrudates are 28, 21, 14 and 28 kJ/mol. The isosteric heats of sorption for CO2 on both crystal and extrudates decrease substantially as loading increases, compared to moderate decreases for hydrocarbons. Although the initial isosteric heats of sorption for CO2 are similar or higher than those for propane, at the half coverage the isosteric heats of sorption for CO2 are about 5 kJ/mol lower than those for propane, and become similar to those for ethane. The isosteric heats of sorption for CO2 on both crystals and extrudates are about 10 kJ/mol higher than those of methane at the half coverage. In most of the cases, the isosteric heats of sorption for all sorbates on extrudates are slightly lower than those on zeolite crystals, but the concentration dependence patterns are nearly similar. The sorption isotherms obtained from sorption isosteres show that at high loadings propane and ethane are preferably sorbed over CO2, which is preferably sorbed over methane. Comparing the sorption isotherms of these measured sorbates on DAY zeolite crystals and extrudates, it can be concluded that making the extrudates from the crystals has little effect on hydrocarbons’ sorption capacities, but significantly reduces CO2 sorption capacity. Such a change is desirable in Petrox applications, which improves sorption separation selectivity of hydrocarbons, e.g., propane and n-butane over CO2.
2. INTRODUCTION Over the last few years, there were discussions between one of the authors of this report, MB, and Dr. E. Sextl (ES), Degussa AG (Degussa-Hüls) (DAG) of Germany, under terms of confidentiality agreements (between BOC and DAG), on ensuring delivery of shaped DAY-type compositions at low cost for purposes of various BOC R&D projects. (DAY stands for dealuminated Y-type, i.e., faujasite sub-type zeolite.) Regarding many sorbents that were checked at BOC for various PSA process-related purposes in the past, a series of compositions were discussed as potential sorbents for BOC Petrox processes, specifically between MB (BOC) and ES (DAG), over the last four (to five) years. Based upon a detailed sorption characterization at BOC of three extruded test samples prepared by DAG in accordance with suggestions made by MB (DAG lot numbers: VP 108, VP 110, VP 102), it was concluded that one of those samples, viz., DAV-F20, exceeds significantly both sorption capacity and selectivity of a UOP material, HiSiv3000 [1], the hitherto considered BOC Petrox process sorbent-elect. Following teachings of these experiments, two additional specific DAY extrudates (VP 161 and VP 185) were prepared. These samples were shipped by DAG to GTC on February 9, 1998. For two of the compositions (coded DAV-F20, 2 mm pellet diameter; and DAV-F30, 3 mm diameter), successful MA (Maleic Anhydride) and AN (Acrylonitrile) Petrox bench-scale tests were performed by Dr. C.J. Guo and P. Balaraman (Chemicals Group; director: Dr. R. Ramachandran). These experiments were 5
followed by successful tests in the MA Petrox PAVSA pilot plant (purge-assisted vacuum swing adsorption), which was run as an intregrated part of the MA production process at Mitsubishi, Japan. This test gave additional and crucial proof of evidence for superiority of the BOC-DAG material over UOP’s HiSiv3000 [2]. It had also been considered by the authors of this report that one of the ways to a further performance improvement of Petrox processes consists in replacing quite an irregular extrudate shape of the novel BOC-DAG Petrox sorbent by that of beads of appropriate dimension. This idea had been reduced into practice independently, and results will be reported separately. As to both extrudates and beads of the BOC-DAG Petrox sorbent, a detailed description of sorption thermodynamic properties of the underlying Degussa DAY zeolite powder with regard to gases relevant in Petrox processes is necessary, and they will be reported here.
3. SORBENTS Original DAY zeolite crystals, DAV-P, were obtained from DAG, Germany, for a comparison of their basic sorption properties with those of the shaped material, DAY extrudates, DAV-F20, with 40 wt.-% of DAY crystals and 60 wt.-% binder. This composition resulted from technical suggestions made by MB [3], BOC, which were accepted by ES, DAG, to meet BOC’s expectations regarding a price of the final sorbent material, which had to be lower than that of the UOP HiSiv3000 sorbent. 1 The DAY crystals have a module of about 100. Table 1 lists further details of these two materials. Table 1. List of sorbents Sorbent
Lot No.
Supplier
DAV-P (powder)
VP 1
Degussa AG ~(2-5) m
DAY-F25 VP 161
Size
Shape
Zeolite
intergrown DAY-crystals
DAY (FAU)
Degussa AG ~2.5 mm (diameter) extrudates
DAY (+60 wt-% silica as binder)
DAY zeolite crystals, coded as DAV-P, were agglomerated without binder and sieved into a fraction, ca. (1.5~2.0) mm. For measurement of sorption isosteres, 5.0021 g (dry weight) of these DAY-P agglomerates were used. For measurements on the extrudates, DAY-F25, 8.4600 g (dry weight) of the sorbent was used. Activation of the sorbent within the sample holder attached 1
Regarding BOC Petrox processes, cf., US Patents Nos. 4,987,239 (1991); 5,126,463 (1992); 5,262,547 (1993); and 5,278,319 (1994) granted to R. Ramachandran, et al.; and for sorbents claimed for those processes, cf., US Patent No. 6,002,019 (1999), “Process for the production of petrochemicals”, granted to S.S. Tamhankar, D.R. Acharya and S.S. Stern. In the latter, there were claimed various types of hydrophobic sorbents. No quantitative statements on binder contents in those materials were made or expressed by related claims. As to binding and shaping DAY zeolites, cf., US Patent No. 5,316,993 (1994), “Molded bodies containing dealuminated zeolite Y and the process of their production”, granted to E. Sextl, E. Roland, P. Kleinschmit, and A. Kiss, (Degussa). In this patent, there are claimed and/or described (i) a clay mineral binder content that ranges from 2 to 40 wt. % and (ii) a mixture of clay minerals and one or more sources of SiO2 in quantities amounting to a total of 5 to 70 wt. % of the primary silicic acid esters to be transformed into SiO2.
6
to the isosteric rig was performed in vacuo by slowly elevating the sample temperature to 400 oC during a period of 48 hours, and keeping it at 400 oC for ca. 24 hours.
4. EXPERIMENTAL METHOD The principle of the isosteric method [4,5] for a gas-solid sorption system is to measure subsequently equilibrium pressure as function of temperature at (nearly) constant sorption phase concentration. By measuring sorption isosteres at various concentrations, one can obtain full sets of sorption thermodynamic quantities as functions of concentration, i.e., a full description of sorption equilibria for the gas-solid system. According to fundamentals of physical sorption, sorption isosteres are straight lines at constant sorbate concentration, n, in plots of the ClausiusClapeyron equation, ln p vs. 1/T, as long as no sorption phase transition takes place. Therefore, sorption thermodynamic functions, e.g., isosteric molar sorption enthalpy, H (n) , i.e., isosteric sorption heat, q st (n) = - H (n) , standard sorption entropy, S°, and standard Gibbs free sorption energy, G°, can be calculated by basic formulas, cf., [4-7]. Therein, S° and G° are referred to the gas pressure, 760 torr, as standard state.
5. RESULTS AND DISCUSSION 5.1. Sorption Thermodynamics of C3H8, C2H6, CH4, and CO2 on DAY Zeolite Crystals 5.1.1 Sorption Isosteres Sorption isosteres for C3H8, C2H6, CH4, and CO2 on DAY zeolite crystals, DAY-P, were directly measured by the sorption isosteric apparatus. Figures 1-4 plot, respectively, all the sorption isosteres for the four sorbates measured at different sorption phase concentrations indicated. The isosteric heats of sorption, cf. Figure 5, were calculated from the slopes of these isosteres, which were obtained by fitting the highest slope fraction of an straight isostere, and the standard sorption entrolpies, cf. Figure 6, were calculated from the interceptions of the linear fits. Using these concentration dependences of the sorption thermodynamic quantities, standard Gibbs free sorption energies, cf. Figure 7, and sorption isotherms, cf. Figure 8, could be calculated for any temperature physically meaningful. The sorption phase concentrations, isosteric heats of sorption, standard entropies of sorption and Gibbs free sorption energies of 298.15 K, corresponding to each isostere, are listed in Tables 2-5, respectively, for propane, ethane, methane and CO2.
7
100
n, m ol/kg 0.0393 0.0772 0.1535 0.2640 0.4141 0.6333 0.9581 1.3171 1.7413 2.2293 2.8102 3.3331 3.7809 4.2194 4.5929
p, torr
10
1
0.1 2
4
6
8
10
1000/(T, K) Fig. 1. Sorption isosteres for propane on DAY zeolite crystals at loadings indicated
8
100
n, m ol/kg 0.0446 0.0852 0.1740 0.2610 0.3923 0.6734 0.9965 1.3827 1.8098 2.2677 2.8436 3.2597 3.6843
p, torr
10
1
0.1 3
4
5
6
7
8
1000/(T, K) Fig. 2. Sorption isosteres for ethane on DAY zeolite crystals at loadings indicated
9
n, m ol/kg 0.0396 0.0798 0.1581 0.3973 0.6060 0.9109 1.2593 1.6088 2.0488 2.4337 2.7816 3.3386 3.8249 4.2508 4.6227 4.9503 5.4927
100
p, torr
10
1
0.1 6
8
10
12
1000/(T, K) Fig. 3. Sorption isosteres for methane on DAY zeolite crystals at loadings indicated
10
n, m ol/kg 0.0718 0.1506 0.3260 0.5409 0.7498 0.8494 1.2184 1.4648 1.6841 2.1595 2.6186 3.1626 4.1163 4.9103 5.6842 6.4267 7.1424 7.8874
100
p, torr
10
1
0.1 3
4
5
6
7
8
9
1000/(T, K) Fig. 4. Sorption isosteres for CO2 on DAY zeolite crystals at loadings indicated
11
Table 2. Sorption isosteres and thermodynamic data for C3H8 on DAY zeolite crystals Related Symbol
Concentration of
Sorption Enthalpy
Standard Sorption
Stand. Sorpt. Free
Entropy
Energy at 293 K
in Fig. 1
C3H8 Sorbed
-,-
n, mol/kg
-H, kJ/mol
So, J/mol K
Go, kJ/mol
0.0393
28.173
-42.057
-15.634
0.0772
27.974
-48.366
-13.554
0.1535
27.539
-53.479
-11.594
0.2640
27.135
-57.050
-10.126
0.4141
27.207
-61.398
-8.901
0.6333
27.476
-65.973
-7.806
0.9581
27.586
-69.760
-6.787
1.3171
28.054
-74.380
-5.878
1.7413
28.986
-81.270
-4.755
2.2293
31.508
-97.784
-2.354
2.8102
33.001
-118.163
2.229
+
3.3331
29.465
-118.345
5.820
x
3.7809
26.544
-117.080
8.363
4.2194
20.524
-89.490
6.157
4.5929
20.916
-90.000
5.917
*
12
Table 3. Sorption isosteres and thermodynamic data for C2H6 on DAY zeolite crystals Related Symbols
Concentration of
in Fig. 2
C2H6 Sorbed
-,-
n, mol/kg
Sorption Enthalpy
Standard Sorption
Stand. Sorpt. Free
Entropy
Energy at 298 K
-H, kJ/mol
So, J/mol K
Go, kJ/mol
0.0446
23.537
-43.628
-10.529
0.0852
22.936
-48.199
-8.565
0.1740
22.186
-52.968
-6.394
0.2610
21.221
-52.754
-5.492
0.3923
20.748
-54.573
-4.477
0.6734
20.343
-57.656
-3.153
0.9965
20.514
-61.530
-2.169
1.3827
20.698
-64.378
-1.504
1.8098
20.905
-67.512
-0.776
2.2677
21.791
-73.276
0.056
2.8436
20.526
-69.086
0.072
+
3.2597
17.766
-56.510
-0.918
x
3.6843
14.522
-45.128
-1.067
13
Table 4. Sorption isosteres and thermodynamic data for CH4 on DAY zeolite crystals Related Symbols
Concentration of
Sorption Enthalpy
Standard Sorption Stand. Sorpt. Free
in Fig. 3
CH4 Sorbed
-,-
n, mol/kg
0.0396
15.720
-37.542
-4.527
0.0798
15.257
-42.777
-2.503
0.1581
14.738
-47.407
-0.604
0.3973
13.663
-51.554
1.708
0.6060
13.418
-53.961
2.670
0.9109
13.273
-57.166
3.771
1.2593
13.292
-60.181
4.651
1.6088
13.385
-62.944
5.382
2.0488
13.501
-65.879
6.141
2.4337
13.527
-67.731
6.667
2.7816
13.458
-68.694
7.023
+
3.3386
13.259
-69.655
7.509
x
3.8249
12.628
-68.181
7.700
*
4.2508
12.289
-68.607
8.166
4.6227
11.626
-66.600
8.231
4.9503
11.563
-66.980
8.407
5.4927
11.833
-75.399
10.647
Entropy -H, kJ/mol
So, J/mol K
Energy at 298 K Go, kJ/mol
14
Table 5. Sorption isosteres and thermodynamic data for CO2 on DAY zeolite crystals Related Symbol
Concentration of Sorption Enthalpy
Standard Sorption
Stand. Sorpt. Free
Entropy
Energy at 298 K
-H, kJ/mol
So, J/mol K
Go, kJ/mol
in Fig. 4
CO2 Sorbed
-,-
n, mol/kg
0.0718
34.319
-76.894
-11.393
0.1506
31.201
-77.135
-8.203
0.3260
27.985
-77.613
-4.845
0.5409
26.088
-78.238
-2.761
0.7498
24.244
-77.200
-1.227
0.8494
23.915
-76.387
-1.140
1.2184
22.526
-75.299
-0.076
1.4648
22.602
-77.634
0.545
1.6841
21.940
-76.884
0.983
2.1595
22.056
-80.461
1.933
2.6186
21.656
-80.172
2.247
+
3.1626
22.117
-83.996
2.926
x
4.1163
22.991
-91.418
4.265
*
4.9103
22.495
-91.351
4.741
5.6842
23.227
-96.779
5.628
6.4267
23.819
-105.347
7.590
7.1424
24.391
-116.357
10.301
7.8874
24.887
-125.535
12.541
15
5.1.2 Sorption Thermodynamic Functions Figure 5 shows the concentration dependences of the isosteric heats of sorption for C3H8, C2H6, CH4, and CO2 on DAY zeolite crystals. The initial heats of sorption, i.e. at zero concentrations, are ca. 28, 23, 16 and over 35, respectively for C3H8, C2H6, CH4, and CO2. These initial heats are slightly lower than those on NaX and NaY zeolites [8,9], because number of cations in DAY zeolite supercages are much less than those in NaX after de-alumination. Furthermore, as concentration increases, the isosteric heat of CO2 on DAY zeolite decreases significantly, while that of propane increases. This change is desirable for Petrox sorbents, enhancing thus sorption separation selectivity for propane over CO2. The isosteric heat of sorption for n-butane on DAY zeolite is expected to have a similar pattern like that of propane, but with even higher heat of sorption. Therefore, sorption separation selectivity for n-butane over CO2 is expected to be more favourable on DAY zeolite. 40 35
-H, kJ/mol
30 25 20 15
C 3H 8 C 2H 6 CH 4 CO 2
10 5 0 0
2
4
6
8
n, mol/kg Fig. 5. Isosteric heats of sorption for C3H8, C2H6, CH4, and CO2 on DAY zeolite crystals The isosteric heats of sorption also show that propane and ethane have stronger intermolecular interactions than methane and CO2 at high concentrations. The isosteric sorption heats of ethane and methane are lower than those for CO2 over the entire concentration range. The
16
concentration dependences of the isosteric sorption heats for propane and ethane on DAY zeolite agree well with those on NaY zeolite [8], but with values lower by 1~4 kJ/mol over their entire concentration ranges. The Gibbs free sorption energies, cf. Figure 7, and the derived sorption isotherms at 298 K, cf. Figure 8, show that the DAY zeolite sorbs propane and ethane preferably over CO2, which is, in turn, preferably sorbed over methane.
0
C 3H 8 C 2H 6 CH 4 CO 2
-20
o
S , J/mol K
-40
-60
-80
-100 -120
-140 0
2
4
6
8
n, mol/kg Fig. 6. Standard sorption entropies for C3H8, C2H6, CH4, and CO2 on DAY crystals
17
20
at 298 K
0
o
G , kJ/mol
10
C 3H 8 C 2H 6 CH 4 CO 2
-10
-20 0
2
4
6
8
n, mol/kg Fig. 7. Standard Gibbs free sorption energies for C3H8, C2H6, CH4, and CO2 on DAY crystals at 298 K
5.1.3 Sorption Isotherms Sorption isotherms for C3H8, C2H6, CH4, and CO2 on DAY zeolite crystals can be obtained from their sorption thermodynamic functions for any temperature and pressure physically meaningful. Figure 8 shows isotherms of these sorbates on DAY zeolite crystals at 298 K that were calculated from sorption isosteres.
18
4
at 298 K
n, mol/kg
3
C 3H 8 C 2H 6 CH 4 CO 2
2
1
0 0
500
1000
1500
2000
2500
3000
p, torr Fig. 8. Sorption isotherms of C3H8, C2H6, CH4, and CO2 on DAY zeolite crystals at 298 K
5.2. Sorption Thermodynamics of C3H8, C2H6, CH4, and CO2 on DAY Zeolite Extrudates 5.2.1 Sorption Isosteres Sorption isosteres for C3H8, C2H6, CH4, and CO2 on DAY zeolite extrudate, DAY-F25, were directly measured by the sorption isosteric apparatus. Figures 9-12 show, respectively, all sorption isosteres obtained for the four sorbates considered on DAY-F25 at different sorption phase concentrations indicated. The isosteric heats of sorption, cf. Figure 13, were calculated from the slopes of those isosteres, which were obtained by fitting the highest slope fractions of straight isosteres. The standard sorption entrolpies, cf. Figure 14, were calculated from the interceptions of the linear fits. Using these concentration dependences of the sorption thermodynamic quantities, standard Gibbs free sorption energies, cf., Figure 15, and sorption isotherms, cf., Figure 16, could be calculated for any temperature physically meaningful.
19
100
n, m ol/kg 0.0216 0.0449 0.0869 0.1458 0.2458 0.3627 0.5729 0.8279 1.2088 1.4803 1.7780 2.0515 2.3738
p, torr
10
1
0.1 2
4
6
8
10
1000/(T, K) Fig. 9. Sorption isosteres for propane on DAY zeolite extrudates at loadings indicated
20
100
n, m ol/kg 0.0234 0.0463 0.0939 0.1784 0.3138 0.4393 0.6752 0.9272 1.1888 1.4555 1.7239 2.0088 2.2988 2.5878
p, torr
10
1
0.1 2
4
6
8
10
12
1000/(T, K) Fig. 10. Sorption isosteres for ethane on DAY zeolite extrudates at loadings indicated.
21
100
n, m ol/kg 0.0222 0.0448 0.0918 0.1878 0.2961 0.4859 0.8287 1.2158 1.6188 1.9468 2.3054 2.5900 2.8612 3.1466 3.4651 3.8103
p, torr
10
1
0.1 4
6
8
10
12
14
16
18
20
1000/(T, K) Fig. 11. Sorption isosteres for methane on DAY zeolite extrudates at loadings indicated
22
100
n, m ol/kg 0.0711 0.1311 0.2137 0.3256 0.5920 0.9144 1.2598 1.6134 2.0663 2.4511 2.8851 3.2912 4.0606
p, torr
10
1
0.1 4
5
6
7
8
9
1000/(T, K) Fig. 12. Sorption isosteres for CO2 on DAY zeolite extrudates at loadings indicated The sorption phase concentration, isosteric heat of sorption, standard entropy of sorption and Gibbs free sorption energy at 298 K, corresponding to each isostere, are listed in Tables 6-9, respectively, for propane, ethane, methane and CO2.
23
Table 6. Sorption isosteres and thermodynamic data for C3H8 on DAY zeolite extrudates Related Symbol
Concentration of
Sorption Enthalpy
Standard Sorption
Stand. Sorpt. Free
Entropy
Energy at 298 K
in Fig. 9
C3H8 Sorbed
-,-
n, mol/kg
-H, kJ/mol
So, J/mol K
Go, kJ/mol
0.02163
28.132
-47.462
-13.981
0.04488
27.076
-51.923
-11.595
0.08693
26.216
-54.742
-9.895
0.14576
26.008
-58.371
-8.605
0.24583
26.034
-62.039
-7.537
0.36268
26.187
-64.954
-6.821
0.57293
26.872
-70.889
-5.736
0.82786
26.893
-75.472
-4.391
1.20883
31.519
-113.116
2.207
1.48034
25.395
-102.248
5.090
1.77802
20.580
-87.315
5.453
+
2.05145
19.797
-85.033
5.556
x
2.3738
19.836
-85.382
5.621
24
Table 7. Sorption isosteres and thermodynamic data for C2H6 on DAY zeolite extrudats Related Symbol
Concentration of
Sorption Enthalpy
Standard Sorption
Stand. Sorpt. Free
Entropy
Energy at 298 K Go, kJ/mol
in Fig. 10
C2H6 Sorbed
-,-
n, mol/kg
-H, kJ/mol
So, J/mol K
0.0234
20.722
-39.104
-9.063
0.0463
20.059
-44.150
-6.896
0.0939
20.358
-52.512
-4.702
0.1784
20.454
-58.612
-2.979
0.3138
21.037
-65.130
-1.618
0.4393
21.577
-69.500
-0.856
0.6752
22.174
-74.323
-0.015
0.9272
22.081
-76.029
0.587
1.1888
21.844
-78.322
1.508
1.4555
20.493
-77.023
2.471
1.7239
20.121
-85.623
5.407
+
2.0088
15.343
-73.636
6.612
x
2.2988
14.900
-78.176
8.408
*
2.5878
15.094
-79.498
8.608
25
Table 8. Sorption isosteres and thermodynamic data for CH4 on DAY zeolite extrudates Related Symbol
Concentration of
Sorption Enthalpy
Standard Sorption
Stand. Sorpt. Free
Entropy
Energy at 298 K
So, J/mol K
Go, kJ/mol
in Fig. 11
CH4 Sorbed
-,-
n, mol/kg
0.0222
14.045
-34.959
-3.622
0.0448
13.885
-43.081
-1.040
0.0918
12.961
-44.933
0.436
0.1878
12.329
-47.854
1.939
0.2961
12.593
-53.872
3.469
0.4859
12.960
-60.186
4.984
0.8287
13.085
-64.440
6.128
1.2158
12.463
-63.528
6.478
1.6188
11.445
-61.928
7.019
1.9468
10.087
-56.731
6.827
2.3054
9.219
-57.159
7.823
+
2.5900
8.976
-62.160
9.557
x
2.8612
8.746
-66.497
11.080
*
3.1466
8.005
-63.937
11.058
3.4651
9.035
-79.775
14.750
3.8103
9.068
-80.457
14.920
-H, kJ/mol
26
Table 9. Sorption isosteres and thermodynamic data for CO2 on DAY zeolite extrudates Related Symbol
Concentration of
in Fig. 12
CO2 Sorbed
-,-
n, mol/kg
Sorption Enthalpy
Standard Sorption Stand. Sorpt. Free Entropy
Energy at 298 K
-H, kJ/mol
So, J/mol K
Go, kJ/mol
0.0711
27.982
-75.849
-5.368
0.1311
24.308
-71.521
-2.984
0.2137
21.720
-69.682
-0.944
0.3256
20.660
-69.226
-0.020
0.5920
22.480
-86.634
3.350
0.9144
23.447
-92.242
4.055
1.2598
23.168
-91.454
4.099
1.6134
22.440
-89.730
4.313
2.0663
21.479
-88.214
4.822
2.4511
20.065
-85.810
5.519
2.8851
25.030
-125.460
12.376
+
3.2912
25.273
-127.925
12.868
x
4.0606
25.304
-128.269
12.939
5.2.2 Sorption Thermodynamic Functions Figure 13 shows the concentration dependences of the isosteric heats of sorption for C3H8, C2H6, CH4, and CO2 on DAY zeolite extrudates. The initial heats of sorption, i.e. at the zero concentration, are c. 28, 21, 14 and over 28, respectively for C3H8, C2H6, CH4, and CO2. These initial heats are from slightly lower to similar, compare with those on DAY zeolite crystals, with nearly the same concentration dependences. Values of Gibbs free sorption energy, cf. Figure 15, and the derived sorption isotherms, cf. Figure 16, at 298 K show that the DAY zeolite material sorbs propane preferably over ethane and ethane preferably over CO2, which is sorbed preferably over methane.
27
35
-H, kJ/mol
30 25
C 3H 8 C 2H 6 CH 4 CO 2
20
15
10 5
0 0
1
2
3
4
5
n, mol/kg
Fig. 13. Isosteric sorption heats for C3H8, C2H6, CH4, and CO2 on DAY zeolite extrudates
28
0
C 3H 8 C 2H 6 CH 4 CO 2
-20
o
S , J/mol K
-40
-60
-80
-100 -120
-140 0
1
2
3
4
5
n, mol/kg Fig. 14. Standard sorption entrolpies for C3H8, C2H6, CH4, and CO2 on DAY zeolite extrudates
29
20
0
o
G , kJ/mol
10
C 3H 8 C 2H 6 CH 4 CO 2
-10
-20 0
1
2
3
4
5
n, mol/kg Fig. 15. Standard Gibbs free sorption energies for C3H8, C2H6, CH4, and CO2 on DAY zeolite extrudates at 298 K.
30
5.2.3 Sorption Isotherms Sorption isotherms for C3H8, C2H6, CH4, and CO2 on DAY zeolite extrudates, cf., Figure 16, were obtained from their sorption thermodynamic functions at 298 K. 2.0
at 298 K C 3H 8 C 2H 6 CH 4 CO 2
n, mol/kg
1.5
1.0
0.5
0.0 0
500
1000
1500
2000
2500
3000
3500
p, torr Fig. 16. Sorption isotherms for C3H8, C2H6, CH4, and CO2 on DAY zeolite extrudates at 298 K
5.3. Comparison between DAY Zeolite Crystals and Extrudates 5.3.1 Isosteric Heat of Sorption Figures 17-20 illustrate a comparison of isosteric sorption heats between DAY zeolite crystals, DAY-P, and extrudates, DAY-F25. The latter sample contains only ca. 40% of the native zeolite crystals. The comparison is shown for C3H8, C2H6, CH4, and CO2, respectively. In case of DAY-F25, both the sorption phase concentrations based on extrudates and on pure zeolite content were plotted for easy comparison with pure zeolite sample, DAY-P. For propane, the isosteric heats of sorption on both samples follow nearly the same pattern with slightly lower sorption heat on extrudates. For ethane, the initial heat of sorption on zeolite
31
crystals is higher than that for extrudates by ca. 3 kJ/mol, and the concentration dependences are also different from each other. The extruded sample has higher total capacity than the crystal sample. For methane, the isosteric heats on both samples have nearly the same pattern of concentration dependence, but the isosteric heat on zeolite crystals is about 1~2 kJ/mol higher than that on extrudates over the entire concentration range. A slightly higher capacity on the extrudate sample was also found. For CO2, the concentration dependences for both samples are more or less similar, and the change is more smoother on crystals than on extrudates. On both samples, the isosteric sorption heat decreases significantly as the sorption phase concentration increases. 40 35
-H, kJ/mol
30 25 20 15 10
C 3 H 8 / DAY-F25 C 3 H 8 / DAY-P C 3 H 8 / DAY-F25(Zeo)
5 0 0
1
2
3
4
5
6
7
n, mol/kg Fig. 17. Isosteric heats of sorption for C3H8 on DAY zeolite crystals and extrudates
32
30
-H, kJ/mol
25
20
15
10
C 2 H 6 / DAY-F25 C 2 H 6 / DAY-P C 2 H 6 / DAY-F25(Zeo)
5
0 0
1
2
3
4
5
6
7
n, mol/kg
Fig. 18. Isosteric heats of sorption for C2H6 on DAY zeolite crystals and extrudates
33
20
-H, kJ/mol
15
10
5
CH 4 / DAY-F25 CH 4 / DAY-P CH 4 / DAY-F25(Zeo)
0 0
2
4
6
8
10
n, mol/kg Fig. 19. Isosteric heats of sorption for CH4 on DAY zeolite crystals and extrudates
34
40 35
-H, kJ/mol
30 25 20 15
CO 2 / DAY-F25 CO 2 / DAY-P CO 2 / DAY-F25(Zeo)
10 5 0 0
2
4
6
8
10
n, mol/kg Fig. 20. Isosteric heats of sorption for CO2 on DAY zeolite crystals and extrudates
5.3.2 Sorption Isotherms Figures 21-24 show comparisons of sorption isotherms between DAY zeolite crystals, DAY-P, and extrudates, DAY-F25, the latter containing only 40% zeolite, for C3H8, C2H6, CH4, and CO2, respectively. In the case of DAY-F25, both the sorption phase concentrations based on extrudates and on pure zeolite content were plotted for easy comparison with the pure zeolite sample, DAY-P. For propane, the isotherm on DAY extrudates after correcting for the binder content coincides with that on Day zeolite crystals, indicating thus that the binder fraction of the sorbent did not change the sorption properties of the native DAY zeolite. This finding agrees well with that of similar isosteric heats of sorption obtained on both samples.
35
For ethane, like the isosteric heat curves, the sorption isotherm on zeolite crystals is initially higher than the binder-content corrected isotherm of the extrudates, but as equilibrium pressure increases, the isotherm on extrudates exceeds that on DAY zeolite crystals. For methane, the isotherm on DAY extrudates after correcting for the binder content coincides with that on DAY zeolite crystals in low pressure region, but exceeds slightly at high equilibrium pressures. This also agree well with similar information from the isosteric heats of sorption on both samples. For CO2, the concentration dependence for both samples is more or less similar, and the change is smoother on the crystals than on extrudates. On both samples, the isosteric sorption heat decreases significantly as the sorption phase concentration increases. By comparing the sorption isotherms of these measured sorbates on DAY zeolite crystals and extrudates, it can be concluded that the process of making extrudates from crystals has little effect on hydrocarbons’ sorption capacities, but significantly reduces CO2 sorption capacity. This change is desirable, which improves sorption separation selectivity of propane and n-butane over CO2 in Petrox applications.
3.0
T = 298 K C 3 H 8 DAY-F25 C 3 H 8 DAY-P C 3 H 8 DAY-F25(Zeo)
2.5
n, mol/kg
2.0
1.5
1.0
0.5
0.0 0
20
40
60
80
100
120
140
p, torr Fig. 21. Sorption isotherms of C3H8 on DAY zeolite crystals and extrudates at 298 K
36
5
T = 298 K C 2 H 6 DAY-F25 C 2 H 6 DAY-P C 2 H 6 DAY-F25(Zeo)
n, mol/kg
4
3
2
1
0 0
500
1000
1500
2000
2500
p, torr
Fig. 22. Sorption isotherms of C2H6 on DAY zeolite crystals and extrudates at 298 K
37
2.0
T = 298 K CH 4 DAY-F25 CH 4 DAY-P CH 4 DAY-F25(Zeo)
n, mol/kg
1.5
1.0
0.5
0.0 0
1000
2000
3000
4000
5000
6000
7000
p, torr Fig. 23. Sorption isotherms of CH4 on DAY zeolite crystals and extrudates at 298 K
38
5
T = 298 K CO 2 DAY-F25 CO 2 DAY-P CO 2 DAY-F25(Zeo)
n, mol/kg
4
3
2
1
0 0
1000
2000
3000
4000
5000
p, torr Fig. 24. Sorption isotherms of CO2 on DAY zeolite crystals and extrudates at 298 K
6. CONCLUSIONS Sorption thermodynamics of propane, ethane, methane and carbon dioxide on BOC Petrox sorbents, DEGUSSA DAY zeolite crystals and its extrudates, measured by the Sorption Isosteric Technique, provides fundamental information for developing next generation sorbents for Petrox applications. The isosteric heats of sorption at nearly zero coverage on DAY zeolite crystals amount to ca. 28, 24, 16 and 35 kJ/mol, respectively for propane, ethane, methane and carbon dioxide, while the corresponding values on DAY extrudates are 28, 21, 14 and 28 kJ/mol. The isosteric heats of sorption for CO2 on both sorbents decrease substantially as loading increases, compared to moderate decreases for hydrocarbons. Although the initial isosteric heats of sorption for CO2 are similar or higher than those for propane, at the half coverage the isosteric heats
39
of sorption for CO2 are about 5 kJ/mol lower than those for propane, and become close to those for ethane. The isosteric heats of sorption for CO2 on both sorbents are by about 10 kJ/mol higher than those for methane at the half coverage. In most of the cases, the isosteric heats of sorption for all sorbates on extrudates are slightly lower than those on zeolite crystals, but the concentration dependence patterns are nearly similar. The sorption isotherms obtained from the sorption isosteres show that at high loadings propane and ethane are preferably sorbed over CO2 that is preferably sorbed over methane. Comparing the sorption isotherms of these measured sorbates on DAY zeolite crystals and extrudates, it was found that making the extrudates from the crystals has little effect on hydrocarbons’ sorption capacities, but significantly reduces CO2 sorption capacity. This change is desirable for Petrox applications, which, thus, improves sorption separation selectivity of hydrocarbons, e.g., propane and n-butane, over CO2.
7. REFERENCES [1] D.M. Shen, M. Bülow, Sorption Equilibria and Kinetics of n-Butane, Propane, Carbon Dioxide and Water on Zeolites: UOP HiSiv3000 and DEGUSSA DAY Extrudates, The BOC Group, GTC, Technical Report, Murray Hill, May, 1999. [2] C.J. Guo, Private Communication to M.B. and D.S. [3] M. Bülow (BOC) and E. Sextl (DAG, Hanau, Germany), Correspondence during 1997-99. [4] M. Bülow, Stud. Surf. Sci. Catalysis, 83 (1994) 209. [5] D.M. Shen, M. Bülow, Micropor. Mesopor. Mater., 22 (1998) 237. [6] D.M. Shen, M. Bülow, Sorption Thermodynamics of Nitrogen and Oxygen on CaA Zeolite (Crystals), The BOC Group, GTC, Technical Report, RE-98-079, Murray Hill, December 22, 1998. D.M. Shen, S.R. Jale, M. Bülow, A.F. Ojo, Stud. Surf. Sci. Catalysis, 125 (1999) 667. [7] D.M. Shen, M. Bülow, F. Siperstein, M. Engelhard, and A.L. Myers, Adsorption, 6 (2000) 275. [8] J.A. Hampson and L.V.C. Rees, Zeolites and Microporous Crystals, Kodansha Ltd., 1994, p.197. [9] O.M. Dzhigit, A.V. Kiselev and T.A. Rachmanova, Zeolites, 4 (1984) 389.
ACKNOWLEDGEMENTS Thanks are due to Dr. Elfriede Sextl, previously with the DEGUSSA AG, for her ongoing support to this project. Fruitful discussions with Dr. R. Ramachandran on Petrox processes and related commercial issues are highly appreciated. The authors thank officials of the former BOC Group, Murray Hill, NJ, for permission to publish this report. Dierhagen, June 17, 2017
40
