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Shaping adsorption properties of nano-porous molecular sieves for solar thermal energy storage and heat pump applications
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ScienceDirect Solar Energy 104 (2014) 16–18 www.elsevier.com/locate/solener
Shaping adsorption properties of nano-porous molecular sieves for solar thermal energy storage and heat pump applications J. Ja¨nchen a,⇑, H. Stach b a
Technical University of Applied Sciences Wildau, Bahnhofstr.1, 15745 Wildau, Germany b ZeoSolar e.V., Volmerstr. 13, 12489 Berlin-Adlershof, Germany Available online 13 August 2013 Communicated by: Associate Editor Jane Davidson
Abstract The water adsorption properties of modified porous sorbents for solar thermal energy storage and heat transformation have been investigated by measurements of water adsorption isotherms, microcalorimetry and storage tests. A chabazite type SAPO, a dealuminated faujasite type zeolite, and a mesostructured aluminosilicate, have been synthesized and compared with common zeolites NaX, NaY and silica gel. It has been found that optimized lattice composition and pore architecture contribute to well adapt hydrophilic properties and a beneficial steep isotherm. Ó 2013 Elsevier Ltd. All rights reserved. Keywords: Water adsorption; Microcalorimetry; Thermal adsorption storage; Zeolites; SAPO-34; MCM-41
1. Introduction The development of porous materials with optimized hydrophilic properties are needed in compact thermal adsorption storage technologies and advanced heat pump application for significant contributions to energy savings and a “greener” energy supply by advanced solar energy utilization. In recent years the need for solid porous sorption materials with tailored adsorption properties became obvious which range in between the highly hydrophilic conventional zeolites on one hand and the weak hydrophilic silica gel on the other hand (Ja¨nchen et al., 2002; Kakiuchi et al., 2002). The chemical composition and the pore structure of the porous materials determine the strength and strength distribution of the adsorption sites for the water interaction and thereby the position and the shape of the adsorption isotherms. These factors are ⇑ Corresponding author. Address: TH Wildau (UAS Wildau), c/o ZeoSolar e.V., Volmerstr. 13, 12489 Berlin, Germany. Tel.: +49 30 63922573. E-mail address: [email protected] (J. Ja¨nchen).
0038-092X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.solener.2013.07.018
important for the application of solid sorbents in solar driven systems if certain limits are given for the temperature level of heat sources for charging or vaporisation and the heat sink for condensation of the working agent, respectively. Some efforts have been achieved in the last decade by using silicoaluminophosphates (SAPO’s) Ja¨nchen et al., 2005; Bauer et al., 2009) or composites with a hygroscopic salts (Levitskij et al., 1996; Glaznev et al., 2011) offering better adapted adsorption properties for heat pumps or solar applications. But these materials are still costly (SAPO’s) or may be less stable (composites) and other options might be welcome. Those options are dealuminated conventional zeolites (Ja¨nchen et al., 2008) or mesostructured molecular sieves (Ja¨nchen et al., 1997; Ristic´ et al., 2012). The dealumination and an alternative synthesis of mesoporous zeolites allow to tailor the hydrophilic character and the pore architecture. The aim of this paper is, therefore, to compare the water adsorption behaviour and the shape of the isotherms of modified faujasite- and chabazite type zeolites as well as mesostructured molecular
J. Ja¨nchen, H. Stach / Solar Energy 104 (2014) 16–18
sieve with those of common sorbents such as NaX, NaY and silica gel.
17
120 100
3. Results and discussions The results of the thermogravimetric measurements show in the DTG plot (not displayed) a downshift of the maximum desorption temperature of more than 200° from 550–400 K to about 370 K for the change from conventional zeolites NaX and NaY via the dealuminated NaY 7 and SAPO-34 to the mesostructured alumosilicate MCM-41. This result indicates already weakened interaction forces with varying structure type and composition of the materials. The structure- and composition influence
80 60 40 20 0 0
0.05
0.1
0.15
0.2
0.25
0.3
adsorbed amount in g/g Fig. 1. Differential molar heats of adsorption of water, Q, for: NaX (squares, 303 K), NaY (diamonds, 313 K), SAPO-34 (triangles, 303 K), and NaY (7) (circles, 303 K). The dashed line denotes the heat of condensation of the water.
on the sorption behaviour will be investigated in more detail by microcalorimetry. Fig. 1 shows the heat curves of some of the above mentioned molecular sieves. The faujasite NaX (uppermost curve) shows the strongest interaction of water with the zeolitic framework. The differential molar heats of adsorption are the highest due to the low Si/Al-ratio of 1.2 causing in this case the highest possible number of charges (Na+) per unit cell. Thus the number of strong bonded water molecules amounts to about 0.07 g water per g dry zeolite. Because of the high concentration of charges in the pores the general level of the adsorption heat remains higher compared with the other zeolites. So NaY (Si/Al = 2.3) and NaY 7 (Si/Al = 7) contain fewer Al and correspondingly less charge compensating cations per unit cell resulting in a lower concentration of charges as well as strong adsorption sites in the cavities. Consequently, less water is less strong bonded (about 0.04 g/g) and the entire heat curves are downshifted by 0.80
adsorbed amount in g/g
The samples used for this study were SAPO-34 (chabazite type zeolite, 3 Si/u.c.), a dealuminated faujasite type zeolite, NaY 7 (Si/Al ratio 7, dealumination by steaming, cf. McDaniel and Maher, 1968) and MCM-41 a mesostructured aluminosilicate with Si/Al = 25 (cf. Kresge et al., 1992). All these samples have been selected with the aim to reduce the interaction forces of water and to generate a steep water isotherm by changing the lattice composition and pore architecture. For comparison standard zeolites of type NaX and NaY (CWK Bad Ko¨stritz, Germany) have been included in our study. The adsorption properties of these materials have been investigated by thermogravimetry and differential thermogravimetry (TG/DTG) as well as by microcalorimetry and gravimetric isotherm measurements. For the isotherm measurements a McBain-Bakr balance (McBain and Bakr, 1926) was used measuring isotherms between T = 293– 353 K and p = 0.001–30 mbar. The Setaram C 80 microcalorimeter of Calvet-type connected with an adsorption apparatus served for the determination of the differential molar heats of adsorption Q. The measuring error of the Q-values amounts to ±2–3%. Prior to the isotherm and calorimetric measurements the samples (ca. 150 mg for isotherms and ca. 700 mg for calorimetric measurements) were calcined for at least 2 h at 623 K (isotherms) and 573 K over night (calorimetry) in high vacuum (p < 10 5 mbar). Our comparative study includes also tests of the storage properties of selected samples in a closed lab-scaled storage of 1.5 L volume. In charging mode (desorption of water) the storage material was heated up to 473 K while the minimum temperature in the condenser amounted 274 K (corresponds to 7 mbar). For discharging of the storage (adsorption of water) the temperature of the evaporator was kept at 293 K (23 mbar). The adsorption heat during discharging of the storage was transferred via heat exchanger into a water reservoir of 7 L volume. By determining the temperature difference of this amount of water and the heat capacity the energy generated was calculated. Further experimental details can be found in Ja¨nchen et al., 2005, 2004.
Q in kJ/mol
2. Materials and methods
0.60
0.40
0.20
0.00 0.001
0.01
0.1
1
10
100
RH in % Fig. 2. Water adsorption isotherms as function of the relative humidity, RH, for (from left to right): NaX (squares), NaY (diamonds), at 298 K as well as SAPO-34 (triangles), NaY(7) (bars) and the aluminosilicate MCM-41 (circles) at 293 K. Filled symbols and dashed lines denote desorption. NaX and NaY are reversible.
18
J. Ja¨nchen, H. Stach / Solar Energy 104 (2014) 16–18
Table 1 Comparison of the adsorbed amount of water, a, in g/g taken from isotherms at p/ps = 0.3, the relative pressure interval of the main isotherm upraise, and the storage density. Molecular sievea
a in g/g (from isotherms at 293 K)
p/ps at upraise of isothermsc
Storage density in (W h/kg)
NaX (1.2) NaY (2.3) NaY (7) SAPO-34 MCM-41 (25) Silica gel
0.28 0.29 0.20 0.28 0.6b 0.23
0.0002–0.02 0.0004–0.04 0.01–0.2 0.043 0.48 0.004–0.4
156 156 155 133 – 123
a b c
Numbers in brackets denote Si/Al ratio of the lattice. a in g/g at p/ps = 0.6. Upraise from a = 0.05 g/g to about a = 75–80% of the max. loading.
approximately 15 or 20 kJ/mol, respectively. The SAPO-34 is in between pointing to a similar low concentration of charges in its cavities as NaY shows. However, in this case the number of isomorphously substituted Al into the aluminophosphate lattice determines the number of charges which seems to be comparable with this in NaY 7. Fig. 2 illustrates the adsorption isotherms of another selection of samples (NaX, NaY, SAPO-34 and MCM-41) to illustrate the possible shift of the isotherms towards higher relative pressure (here plotted as relative humidity). This shift is a result of the decreasing strength of the water-surface-interaction as described above. Important to note is, beside the considerable shift of more than three orders of magnitude, the steep shape of the isotherms for SAPO-34 and MCM-41 compared to the common zeolites NaX and NaY. A similar shape as for the SAPO-34 has been found for the dealuminated faujasite (not shown). The steep profile of the isotherms is due to a narrower distribution of the adsorption site strength. Table 1 presents a comparison of the value of the relative pressure at what the isotherms show upraise for the samples investigated. Obvious is the broad p/ps-range of the conventional sorbents (NaX, silica gel) and the big difference in the absolute values between them. The modified sorbents, however, show relative pressure values ranging in between the two others, offering beneficial adsorption properties for solar applications because of the individual tight p/ps-ranges. Another advantage is the tailored adsorption range possible by comparably simple material modifications. The storage densities (cf. Table 1, column 4) are similar but it has to be taken into account that with raising relative pressure (column 3) the temperature lift diminishes. Consequently, a compromise has to be found between charging temperature, storage density, temperature lift, and performance of the system. 4. Conclusions A new approach of solid sorbent modification offers an extended range of tailored porous materials with medium hydrophilic character for solar thermal adsorption storage
and solar driven heat transformation. The chemical composition of the framework and thus the concentration of charges in the pore structure as well as the pore architecture of the materials determine the adsorption equilibrium of water that has a strong dipole. Controlling these parameters offers the possibility to modify materials for solar driven thermal adsorption storage applications. Acknowledgements We thank H. Toufar (Clariant, former Su¨d-Chemie Inc.) for supply of the SAPO-34 and A. Brandt (CWK Bad Ko¨stritz) for his contribution to this paper. References Bauer, J., Herrmann, R., Mittelbach, W., Schwieger, W., 2009. Zeolite/ aluminum composite adsorbents in adsorption refrigeration. International Journal of Energy Research 33, 1233. Glaznev, I., Ponomarenko, I., Kirik, S., Aristov, Y., 2011. Composites CaCl2/SBA-15 for adsorptive transformation of low temperature heat: Pore size effect. International Journal of Refrigeration 34 (5), 1244– 1250. Ja¨nchen, J., Busio, M., Hintze, M., Stach, H., Von Hooff, JHC., 1997. Adsorption studies on ordered mesoporous materials (MCM-41). In: Chon, H., Ihm, S-K., Uh, Y.S. (Eds.), . In: Progress in Zeolite and Microporous Materials, vol. 105. Studies in Surface Science and Catalysis, Elsevier, pp. 1731–1738. Ja¨nchen, J., Ackermann, D., Stach, H., 2002. Adsorption properties of aluminophosphate molecular sieves – potential applications for low temperature heat utilization, In: Proceedings of the International Sorption Heat Pump Conference (ISHPC) 2002, Shanghai, PR China. In: Wang, R.Z., Lu, Z., Wang, W., Huang, X. (Eds.). Science Press New York Ltd., pp. 635–638. (24–27 September) Ja¨nchen, J., Ackermann, D., Stach, H., Bro¨sicke, W., 2004. Studies of the water adsorption on zeolites and modified mesoporous materials for seasonal storage of solar heat. Solar Energy 76, 339–344. Ja¨nchen, J., Ackermann, D., Weiler, E., Stach, H., Bro¨sicke, W., 2005. Calorimetric Investigation on Zeolites, AlPO4’s and CaCl2 impregnated attapulgite for thermochemical storage of heat. Thermochimica Acta 434, 37–41. Ja¨nchen, J., Stach, H., Hellwig, U., 2008. Water sorption in faujasite- and chabazite type zeolites of varying lattice composition for heat storage applications. In: Ge´de´on, A., Massiani, P.F., Babonneau. F., (Eds.). Proceedings of 4th International FEZA Conference on Zeolites and Related Materials, vol. 174., Studies in Surface Science and Catalysis, Elsevier, Paris, France, pp. 599–602. (2–6 September) Kakiuchi, H., Takewaki, T., et al., 2002. Adsorption heat pump and use of adsorption material as adsorption material for adsorption heat pump. European Patent Application 44, 219–235. Kresge, C.T., Leonowicz, M.E., Roth, W.J., Vartuli, J.C., Beck, J.S., 1992. Ordered mesoporous molecular sieves synthesized by a liquid-crystal template mechanism. Nature 359, 710. Levitskij, E.A., Aristov, Yu.I., Tokarev, M.M., Parmon, V.N., 1996. Chemical heat accumulators: a new approach to accumulating low potential heat. Solar Energy and Solar Cells 44, 219–235. McBain, J.W., Bakr, A.M., 1926. A new sorption balance. Journal of the American Chemical Society 48, 690. McDaniel, C.W., Maher, P.K., 1968. New Ultrastable form of Faujasite. Molecular Sieves, Society of Chemicals Industrial, London, pp. 186– 194. Ristic´, A., Darja Maucˇec, D., Henninger, S.K., Kaucˇicˇ, V., 2012. New two-component water sorbend CaCl2–KIL2 for solar thermal energy storage. Microporous and Mesoporous Materials 164, 266–272.
ScienceDirect Solar Energy 104 (2014) 16–18 www.elsevier.com/locate/solener
Shaping adsorption properties of nano-porous molecular sieves for solar thermal energy storage and heat pump applications J. Ja¨nchen a,⇑, H. Stach b a
Technical University of Applied Sciences Wildau, Bahnhofstr.1, 15745 Wildau, Germany b ZeoSolar e.V., Volmerstr. 13, 12489 Berlin-Adlershof, Germany Available online 13 August 2013 Communicated by: Associate Editor Jane Davidson
Abstract The water adsorption properties of modified porous sorbents for solar thermal energy storage and heat transformation have been investigated by measurements of water adsorption isotherms, microcalorimetry and storage tests. A chabazite type SAPO, a dealuminated faujasite type zeolite, and a mesostructured aluminosilicate, have been synthesized and compared with common zeolites NaX, NaY and silica gel. It has been found that optimized lattice composition and pore architecture contribute to well adapt hydrophilic properties and a beneficial steep isotherm. Ó 2013 Elsevier Ltd. All rights reserved. Keywords: Water adsorption; Microcalorimetry; Thermal adsorption storage; Zeolites; SAPO-34; MCM-41
1. Introduction The development of porous materials with optimized hydrophilic properties are needed in compact thermal adsorption storage technologies and advanced heat pump application for significant contributions to energy savings and a “greener” energy supply by advanced solar energy utilization. In recent years the need for solid porous sorption materials with tailored adsorption properties became obvious which range in between the highly hydrophilic conventional zeolites on one hand and the weak hydrophilic silica gel on the other hand (Ja¨nchen et al., 2002; Kakiuchi et al., 2002). The chemical composition and the pore structure of the porous materials determine the strength and strength distribution of the adsorption sites for the water interaction and thereby the position and the shape of the adsorption isotherms. These factors are ⇑ Corresponding author. Address: TH Wildau (UAS Wildau), c/o ZeoSolar e.V., Volmerstr. 13, 12489 Berlin, Germany. Tel.: +49 30 63922573. E-mail address: [email protected] (J. Ja¨nchen).
0038-092X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.solener.2013.07.018
important for the application of solid sorbents in solar driven systems if certain limits are given for the temperature level of heat sources for charging or vaporisation and the heat sink for condensation of the working agent, respectively. Some efforts have been achieved in the last decade by using silicoaluminophosphates (SAPO’s) Ja¨nchen et al., 2005; Bauer et al., 2009) or composites with a hygroscopic salts (Levitskij et al., 1996; Glaznev et al., 2011) offering better adapted adsorption properties for heat pumps or solar applications. But these materials are still costly (SAPO’s) or may be less stable (composites) and other options might be welcome. Those options are dealuminated conventional zeolites (Ja¨nchen et al., 2008) or mesostructured molecular sieves (Ja¨nchen et al., 1997; Ristic´ et al., 2012). The dealumination and an alternative synthesis of mesoporous zeolites allow to tailor the hydrophilic character and the pore architecture. The aim of this paper is, therefore, to compare the water adsorption behaviour and the shape of the isotherms of modified faujasite- and chabazite type zeolites as well as mesostructured molecular
J. Ja¨nchen, H. Stach / Solar Energy 104 (2014) 16–18
sieve with those of common sorbents such as NaX, NaY and silica gel.
17
120 100
3. Results and discussions The results of the thermogravimetric measurements show in the DTG plot (not displayed) a downshift of the maximum desorption temperature of more than 200° from 550–400 K to about 370 K for the change from conventional zeolites NaX and NaY via the dealuminated NaY 7 and SAPO-34 to the mesostructured alumosilicate MCM-41. This result indicates already weakened interaction forces with varying structure type and composition of the materials. The structure- and composition influence
80 60 40 20 0 0
0.05
0.1
0.15
0.2
0.25
0.3
adsorbed amount in g/g Fig. 1. Differential molar heats of adsorption of water, Q, for: NaX (squares, 303 K), NaY (diamonds, 313 K), SAPO-34 (triangles, 303 K), and NaY (7) (circles, 303 K). The dashed line denotes the heat of condensation of the water.
on the sorption behaviour will be investigated in more detail by microcalorimetry. Fig. 1 shows the heat curves of some of the above mentioned molecular sieves. The faujasite NaX (uppermost curve) shows the strongest interaction of water with the zeolitic framework. The differential molar heats of adsorption are the highest due to the low Si/Al-ratio of 1.2 causing in this case the highest possible number of charges (Na+) per unit cell. Thus the number of strong bonded water molecules amounts to about 0.07 g water per g dry zeolite. Because of the high concentration of charges in the pores the general level of the adsorption heat remains higher compared with the other zeolites. So NaY (Si/Al = 2.3) and NaY 7 (Si/Al = 7) contain fewer Al and correspondingly less charge compensating cations per unit cell resulting in a lower concentration of charges as well as strong adsorption sites in the cavities. Consequently, less water is less strong bonded (about 0.04 g/g) and the entire heat curves are downshifted by 0.80
adsorbed amount in g/g
The samples used for this study were SAPO-34 (chabazite type zeolite, 3 Si/u.c.), a dealuminated faujasite type zeolite, NaY 7 (Si/Al ratio 7, dealumination by steaming, cf. McDaniel and Maher, 1968) and MCM-41 a mesostructured aluminosilicate with Si/Al = 25 (cf. Kresge et al., 1992). All these samples have been selected with the aim to reduce the interaction forces of water and to generate a steep water isotherm by changing the lattice composition and pore architecture. For comparison standard zeolites of type NaX and NaY (CWK Bad Ko¨stritz, Germany) have been included in our study. The adsorption properties of these materials have been investigated by thermogravimetry and differential thermogravimetry (TG/DTG) as well as by microcalorimetry and gravimetric isotherm measurements. For the isotherm measurements a McBain-Bakr balance (McBain and Bakr, 1926) was used measuring isotherms between T = 293– 353 K and p = 0.001–30 mbar. The Setaram C 80 microcalorimeter of Calvet-type connected with an adsorption apparatus served for the determination of the differential molar heats of adsorption Q. The measuring error of the Q-values amounts to ±2–3%. Prior to the isotherm and calorimetric measurements the samples (ca. 150 mg for isotherms and ca. 700 mg for calorimetric measurements) were calcined for at least 2 h at 623 K (isotherms) and 573 K over night (calorimetry) in high vacuum (p < 10 5 mbar). Our comparative study includes also tests of the storage properties of selected samples in a closed lab-scaled storage of 1.5 L volume. In charging mode (desorption of water) the storage material was heated up to 473 K while the minimum temperature in the condenser amounted 274 K (corresponds to 7 mbar). For discharging of the storage (adsorption of water) the temperature of the evaporator was kept at 293 K (23 mbar). The adsorption heat during discharging of the storage was transferred via heat exchanger into a water reservoir of 7 L volume. By determining the temperature difference of this amount of water and the heat capacity the energy generated was calculated. Further experimental details can be found in Ja¨nchen et al., 2005, 2004.
Q in kJ/mol
2. Materials and methods
0.60
0.40
0.20
0.00 0.001
0.01
0.1
1
10
100
RH in % Fig. 2. Water adsorption isotherms as function of the relative humidity, RH, for (from left to right): NaX (squares), NaY (diamonds), at 298 K as well as SAPO-34 (triangles), NaY(7) (bars) and the aluminosilicate MCM-41 (circles) at 293 K. Filled symbols and dashed lines denote desorption. NaX and NaY are reversible.
18
J. Ja¨nchen, H. Stach / Solar Energy 104 (2014) 16–18
Table 1 Comparison of the adsorbed amount of water, a, in g/g taken from isotherms at p/ps = 0.3, the relative pressure interval of the main isotherm upraise, and the storage density. Molecular sievea
a in g/g (from isotherms at 293 K)
p/ps at upraise of isothermsc
Storage density in (W h/kg)
NaX (1.2) NaY (2.3) NaY (7) SAPO-34 MCM-41 (25) Silica gel
0.28 0.29 0.20 0.28 0.6b 0.23
0.0002–0.02 0.0004–0.04 0.01–0.2 0.043 0.48 0.004–0.4
156 156 155 133 – 123
a b c
Numbers in brackets denote Si/Al ratio of the lattice. a in g/g at p/ps = 0.6. Upraise from a = 0.05 g/g to about a = 75–80% of the max. loading.
approximately 15 or 20 kJ/mol, respectively. The SAPO-34 is in between pointing to a similar low concentration of charges in its cavities as NaY shows. However, in this case the number of isomorphously substituted Al into the aluminophosphate lattice determines the number of charges which seems to be comparable with this in NaY 7. Fig. 2 illustrates the adsorption isotherms of another selection of samples (NaX, NaY, SAPO-34 and MCM-41) to illustrate the possible shift of the isotherms towards higher relative pressure (here plotted as relative humidity). This shift is a result of the decreasing strength of the water-surface-interaction as described above. Important to note is, beside the considerable shift of more than three orders of magnitude, the steep shape of the isotherms for SAPO-34 and MCM-41 compared to the common zeolites NaX and NaY. A similar shape as for the SAPO-34 has been found for the dealuminated faujasite (not shown). The steep profile of the isotherms is due to a narrower distribution of the adsorption site strength. Table 1 presents a comparison of the value of the relative pressure at what the isotherms show upraise for the samples investigated. Obvious is the broad p/ps-range of the conventional sorbents (NaX, silica gel) and the big difference in the absolute values between them. The modified sorbents, however, show relative pressure values ranging in between the two others, offering beneficial adsorption properties for solar applications because of the individual tight p/ps-ranges. Another advantage is the tailored adsorption range possible by comparably simple material modifications. The storage densities (cf. Table 1, column 4) are similar but it has to be taken into account that with raising relative pressure (column 3) the temperature lift diminishes. Consequently, a compromise has to be found between charging temperature, storage density, temperature lift, and performance of the system. 4. Conclusions A new approach of solid sorbent modification offers an extended range of tailored porous materials with medium hydrophilic character for solar thermal adsorption storage
and solar driven heat transformation. The chemical composition of the framework and thus the concentration of charges in the pore structure as well as the pore architecture of the materials determine the adsorption equilibrium of water that has a strong dipole. Controlling these parameters offers the possibility to modify materials for solar driven thermal adsorption storage applications. Acknowledgements We thank H. Toufar (Clariant, former Su¨d-Chemie Inc.) for supply of the SAPO-34 and A. Brandt (CWK Bad Ko¨stritz) for his contribution to this paper. References Bauer, J., Herrmann, R., Mittelbach, W., Schwieger, W., 2009. Zeolite/ aluminum composite adsorbents in adsorption refrigeration. International Journal of Energy Research 33, 1233. Glaznev, I., Ponomarenko, I., Kirik, S., Aristov, Y., 2011. Composites CaCl2/SBA-15 for adsorptive transformation of low temperature heat: Pore size effect. International Journal of Refrigeration 34 (5), 1244– 1250. Ja¨nchen, J., Busio, M., Hintze, M., Stach, H., Von Hooff, JHC., 1997. Adsorption studies on ordered mesoporous materials (MCM-41). In: Chon, H., Ihm, S-K., Uh, Y.S. (Eds.), . In: Progress in Zeolite and Microporous Materials, vol. 105. Studies in Surface Science and Catalysis, Elsevier, pp. 1731–1738. Ja¨nchen, J., Ackermann, D., Stach, H., 2002. Adsorption properties of aluminophosphate molecular sieves – potential applications for low temperature heat utilization, In: Proceedings of the International Sorption Heat Pump Conference (ISHPC) 2002, Shanghai, PR China. In: Wang, R.Z., Lu, Z., Wang, W., Huang, X. (Eds.). Science Press New York Ltd., pp. 635–638. (24–27 September) Ja¨nchen, J., Ackermann, D., Stach, H., Bro¨sicke, W., 2004. Studies of the water adsorption on zeolites and modified mesoporous materials for seasonal storage of solar heat. Solar Energy 76, 339–344. Ja¨nchen, J., Ackermann, D., Weiler, E., Stach, H., Bro¨sicke, W., 2005. Calorimetric Investigation on Zeolites, AlPO4’s and CaCl2 impregnated attapulgite for thermochemical storage of heat. Thermochimica Acta 434, 37–41. Ja¨nchen, J., Stach, H., Hellwig, U., 2008. Water sorption in faujasite- and chabazite type zeolites of varying lattice composition for heat storage applications. In: Ge´de´on, A., Massiani, P.F., Babonneau. F., (Eds.). Proceedings of 4th International FEZA Conference on Zeolites and Related Materials, vol. 174., Studies in Surface Science and Catalysis, Elsevier, Paris, France, pp. 599–602. (2–6 September) Kakiuchi, H., Takewaki, T., et al., 2002. Adsorption heat pump and use of adsorption material as adsorption material for adsorption heat pump. European Patent Application 44, 219–235. Kresge, C.T., Leonowicz, M.E., Roth, W.J., Vartuli, J.C., Beck, J.S., 1992. Ordered mesoporous molecular sieves synthesized by a liquid-crystal template mechanism. Nature 359, 710. Levitskij, E.A., Aristov, Yu.I., Tokarev, M.M., Parmon, V.N., 1996. Chemical heat accumulators: a new approach to accumulating low potential heat. Solar Energy and Solar Cells 44, 219–235. McBain, J.W., Bakr, A.M., 1926. A new sorption balance. Journal of the American Chemical Society 48, 690. McDaniel, C.W., Maher, P.K., 1968. New Ultrastable form of Faujasite. Molecular Sieves, Society of Chemicals Industrial, London, pp. 186– 194. Ristic´, A., Darja Maucˇec, D., Henninger, S.K., Kaucˇicˇ, V., 2012. New two-component water sorbend CaCl2–KIL2 for solar thermal energy storage. Microporous and Mesoporous Materials 164, 266–272.