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Applied Thermal Engineering xxx (2011) 1e6

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Applied Thermal Engineering

journal homepage: www.elsevier .com/locate/apthermeng

Composites “binary salts in porous matrix” for adsorption heat transformation

Larisa Gordeeva a,*, Alexandra Grekova b, Tamara Krieger a, Yuri Aristov a

aBoreskov Institute of Catalysis, Lavrentiev av. 5, Novosibirsk 630090, RussiabNovosibirsk State University, Pirogova str. 2, Novosibirsk 630090, Russia

a r t i c l e i n f o

Article history:Received 14 March 2011Accepted 25 July 2011Available online xxx

Keywords:Adsorption heat transformationAdsorbent designComposite “salt inside porous matrix”WaterMethanolAmmonia

* Corresponding author. Tel.: þ7 383 3269454; fax:E-mail address: gordeeva@catalysis.ru (L. Gordeev

1359-4311/$ e see front matter � 2011 Elsevier Ltd.doi:10.1016/j.applthermaleng.2011.07.040

Please cite this article in press as: L. GordeeThermal Engineering (2011), doi:10.1016/j.a

a b s t r a c t

A family of Composites “Salt inside Porous Matrix” (CSPM) has been considered as promising foradsorption heat transformation (AHT) due to their high sorption capacity, steep sorption isobars andopportunity to harmonize CSPM properties with boundary conditions of the AHT cycle. In thiscommunication, we extend the harmonizing tools by confinement of one more salt to the matrix pores.Novel CSPMs based on a binary mixture of lithium, calcium, and barium halides inside various meso-porous matrices were synthesized with wide variation of the relative salts content. Their phasecomposition and sorption equilibrium with water, methanol and ammonia vapour were studied by XRDand TG techniques. It was shown that the formation of a homogeneous solid solution of the salts led tochanging the equilibrium temperature (pressure) of the solvation. Thus, the confinement of binary saltsystems to the matrix pores can be an effective tool for designing innovative materials with pre-determined sorption properties adapted to particular AHT cycles.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Solid sorption cycles can be energetically advantageous fortransformation of heat from various sources, e.g. solar energy,waste heat, etc [1e3]. However, improvement of the performance isobligatory to make AHT competitive with liquid absorption andcompression systems. The efficiency of AHT cycle is extremelysensitive to the sorption equilibrium of the working pair “adsor-benteadsorbate” [4e7]. It was shown that the Coefficient OfPerformance (COP) of adsorption chillers increases with the rise inthe amount of refrigerant, exchanged per cycle Dw, asymptoticallyapproaching to the ratio of latent heat to desorption heat DL/DH [8].Thus, fitting the adsorption equilibrium to requirements ofa particular AHT cycle is one of the encouraging ways to enhancethe cycle performance. For this reason many efforts have beendirected to selection [7,9,10] or synthesis [7,11] of new adsorbentmaterials suitable for AHT cycles.

The working conditions of AHT cycles depend on the number offactors, among which are a purpose of heat transformation (airconditioning, ice making, heating, deep freezing, etc.), temperatureof the external heat source used for the sorbent regeneration andclimatic conditions of the areawhere the cycle is used. The demandsof particular cycle to desirable properties of the working pair

þ7 383 3304573.a).

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va, et al., Composites “binarypplthermaleng.2011.07.040

“adsorbenteadsorbate” vary greatly in accordance with the workingconditions of the cycle [7]. Despite the wide variety of the require-ments imposed by different AHT cycles, only few working pairs aretraditionally used for AHT, namely, silica gels-water, zeolites-water,activated carbons-methanol and activated carbons-ammonia[1,2,7,12]. This conservative practice reflects two past tendencieswhich now are being overcome: (a) a poor understanding of whatadsorbent is optimal for a particular AHT cycle, and (b) a low level ofco-operation between materials scientists and thermal engineers.Both issues have been widely discussed in the IMPRES Symposiumsin Kyoto [13] and Singapore [14].

As a matter of fact, the modern materials science offers a hugechoice of novel porous solids which may be used for AHT. Originaland literature data on several classes of novel materials potentiallypromising for this important application, namely, metal-aluminophosphates (AlPOs, SAPOs, MeAPOs), metal-organicframeworks (MILs, ISEs, etc.), ordered porous solids (MCM, SBA,etc.), and various composites (SWSs, AlPO-Al foil) are reviewed in[1]. Moreover, the present-day level of material science allowsa target-oriented design of novel porous materials adapted to partic-ular application [7,15]. Tailoring the specific adsorbent in the frameof this approach is divided into two parts: (i) formulating thedemands of particular application to the necessary adsorbentproperties, and (ii) synthesis of the adsorbent which precisely ornearly fits these demands [7].

A family of composites “salt in porousmatrix”was developed forsorption of water, methanol and ammonia for various applications,

salts in porous matrix” for adsorption heat transformation, Applied

Fig. 1. XRD patterns of composites (LiClþLiBr)/vermiculite. nLiCl/nLiBr¼ 1:3 (1), 1:1 (2)and 3:1 (3).

L. Gordeeva et al. / Applied Thermal Engineering xxx (2011) 1e62

including adsorption heat transformation and storage. CSPMs arefound promising for AHT because of their high sorption capacityand steep sorption isobars [7]. The comprehensive study of CSPMshas revealed a dominant contribution of the confined salt to thecomposite sorption properties. The salt reacts with vapour thatresults in the formation of salt solvates. This shows itself as a sharpuptake rise on the sorption isobars. Finally the salt-sorbate solutionforms inside the pores and sorption increases gradually with thedecrease in temperature. The sorption equilibrium of CSPMs can beintently modified by proper choice of the active salt and the hostmatrix, matrix porous structure, the salt content and synthesisconditions [16,17].

Embedding two salts affecting each other into thematrix’s poresgives one more “tool” for intentional managing of the CSPMssorption properties [18]. The formation of the solid solutions (SSs)of LiCl and LiBr inside the pores of silica gel results in shifting theequilibrium temperature (or pressure) of the salt solvation. Due tolow mutual solubility of the lithium halides the shift of solvationtemperature did not exceed 5e15 K thus restricting the possibilityto vary the sorption equilibrium of the composites. The main goalsof this work are (a) to extend this approach to other binary saltsystems (LiClþ LiBr, CaCl2þ CaBr2 and BaCl2þ BaBr2), hostmatrices (mesoporous silica gel and macroporous expandedvermiculite) and sorbates (water and ammonia) and to preparenovel CSPMs; (b) to investigate their phase composition andsorption equilibrium with a special emphasis on changing thesolvation temperature; and (c) to assess the merit of applying thenew sorbents for several adsorption cooling cycles. Appropriatesingle salt composites have been studied before and demonstratedhigh sorption capacity to water, methanol and ammonia undertypical conditions of AHT cycles [8,19e24].

2. Experimetal

2.1. Materials and synthesis

A commercial silica gel Davisil gr. 646 (the average pore diam-eter dav¼ 15 nm (BET), the specific surface area Ssp¼ 293 m2/g(BET), the pore volume Vp¼ 1.18 cm3/g) and an expanded vermic-ulite (dav¼ 6.5 mm (BET), Ssp¼ 2.0 m2/g (BET), Vp¼ 2.7 cm3/g) wereused as host matrices. The composites were synthesized by a dryimpregnation of thematrices with the aqueous solution of two salts(MeClmþMeBrm) followed by the thermal drying at 433 K [18]. Anumber of composites were prepared with different molar ratio ofthe metal chloride to the metal bromide nMeClm:nMeBrm¼ 6:1, 3:1,1:1, 1:3, 1:6, indicated parenthetically as follows: (MeClmþMeBrm(nMeCl:nMeBr))/matrix. The total molar content of the saltsnS¼ nMeClmþ nMeBrm was equal for each raw of the samplesnS¼ 5.6, 2.0 and 1.4 mmole per gram of the composite for(LiClþ LiBr)/vermiculite, (CaCl2 þ CaBr2)/SiO2 and (BaCl2þ BaBr2)/SiO2, respectively.

2.2. Characterization

Phase composition of the newmaterials was characterized by anX-ray diffraction (XRD) using a Siemens D-500 diffractometer withCu Ka radiation and a graphite monochromator on the diffractionbeam. High temperature experiments were conducted using an X-ray reactor chamber installed at the diffractometer. The sample wasplaced in the reactor, heated up to T¼ 383e433 K in a heliumenvironment, and a diffraction pattern of the dry sample wasrecorded. The diffraction patterns were recorded by 0.05� stepscanning at the 2q angle range from 25� to 65�.

The isobars (or isotherms) of water, methanol or ammoniasorption on the new composites were measured by a TG method. A

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sample of 0.1e0.4 g weight was heated up to 443 K under contin-uous pumping for 3 h. Then the sample was cooled down to a fixedtemperature and put in contact with water, methanol or ammoniavapour that initiated sorption. The temperature of the sample wasmeasured with an accuracy of �0.2 K. The vapour pressure wasa saturated pressure of a liquid sorbate in an evaporator, whosetemperature was set by a thermostat with an accuracy of �0.1 K.The weight of the sample was recorded continuously during theadsorption until the constant value became settled that wasconsidered as the equilibrium one. The sorption was calculated asw¼m(P, T)/m0, or as the equilibrium number of sorbed moleculesrelated to one metal atom N(P, T)¼ [m(P,T)/Mv]/(m0Ns), where m(P,T) is the weight of vapour adsorbed, m0 is the dry weight of thesorbent, Mv is a molecular weight of the sorbate. Accuracy of theuptake measurements was �0.0001 g/g.

3. Results and discussion

3.1. The system (LiClþ LiBr)/vermiculite

The XRD patterns of composites (LiClþLiBr(1:3))/vermiculite(Fig. 1) exhibit symmetrical peaks, which can be assigned as (111),(200), (220), (311) and (222) reflections of a cubic LiBr (space groupFm-3m) (JCPDS No. 06-0319). These peaks are shifted towardslarger angles with respect to those of the reference salt (LiBr). Thisindicates a decrease of the lattice parameter due to the formation ofa homogeneous solid solution of LiCl in LiBr. The XRD patternsof composites (LiClþLiBr(1:1))/vermiculite and (LiClþLiBr(3:1))/vermiculite are quite different. The reflections (111) and (200)become asymmetrical or transform to two clearly separatedreflections. This indicates the formation of the mixture of two solidsolutions, one of which is enriched with LiCl (SSCl) and the other isenriched with LiBr (SSBr). Considering the linear dependencebetween the spacing parameters and the composition of solidsolutions, the approximate molar content of chloride nCl andbromide nBr ions in each solid solution are evaluated (Fig. 2). Thus,the SS formation is observed for all the composites (LiClþ LiBr)/vermiculite. For those with a dominant content of LiBr, the homo-geneous SSBr forms inside the pores. Further increase in the LiClcontent results in the transformation of this homogeneous solutionto the mixture of two solid solutions SSCl and SSBr.

A sharp increase in the sorption is observed on each isobar for thesingle-salt composite which can be attributed to the reactions [18]

LiBrþ CH3OH¼ LiBr$CH3OH, (1)

LiClþ 3CH3OH¼ LiCl$3CH3OH. (2)

LiBr has a higher affinity to methanol and sorbs it at highertemperature (348e353 K) than LiCl (308e313 K). Essential

salts in porous matrix” for adsorption heat transformation, Applied

Fig. 2. The parameter of cubic crystalline lattice of SSCl and SSBr for the composites(LiClþ LiBr)/vermiculite.

Fig. 3. Isobars of methanol sorption on the composites (LiClþ LiBr)/vermiculite withdifferent salts content (aec) as well as curves calculated as a linear combination of thesorption on the single-salt composites LiCl/vermiculite and LiBr/vermiculite.P¼ 10.7 kPa.

L. Gordeeva et al. / Applied Thermal Engineering xxx (2011) 1e6 3

distinctions are found between the experimental and curvescalculated as a sum of the sorption on the single-salt compositesNLiCl(P, T) and NLiBr(P, T) taken with the proper weight coefficients

N¼ (NLiCl(P,T)� nLiClþNLiBr(P,T)� nLiBr)/nS (3)

forall the composites. The experimental stepcorresponding to thetransition SSBreSSBr$CH3OH is shifted towards lower temperature bysome 15 K in the bromine enriched composite (LiClþLiBr(1:3))/vermiculite (Fig. 3a). That means the SSBr reacts with methanol atlower temperature than LiBr in the vermiculite pores. The reason ofthis shift is likely to be the formation of SSBr with smaller latticeparameter. The transition SSCleSSCl$CH3OH in (LiClþ LiBr(1:1))/vermiculite and (LiClþ LiBr(3:1))/vermiculite shifts towards highertemperature regarding LiCl (Fig. 3b, c). Contrary to (LiClþ LiBr(3:1))/SiO2 [18], the increase in the temperature of SSCl solvation in thecomposite (LiClþ LiBr(1:1))/vermiculite is quite large (10e15 and 5 Kfor vermiculite and silica gel based composites, respectively), prob-ably, due to higher LiCl content in the solid solution.

The shift of the solvation steps on the sorption isobars can beused for intent modification of sorption properties of CSPMs. Forinstance, a small additive of LiCl to the LiBr/SiO2 compositediminishes the temperature necessary for regeneration of thesorbent by some 15 K and consequently allows using a heat sourcewith lower temperature at the desorption stage of AHT cycle.

Fig. 4. XRD patterns of the (CaCl2þ CaBr2)/SiO2 composites.

3.2. The system (CaCl2þ CaBr2)/SiO2

XRD patterns of all the composites (CaCl2þ CaBr2)/SiO2 exhibitthe symmetrical reflexes (Fig. 4) which can be assigned to ortho-rhombic modification (space group Pnnm), typical of both CaCl2[JCPDF 74-0992] and CaBr2 [JCPDF 25-1034]. As the chloridecontent increases, the reflexes gradually move from those of CaBr2towards lower angles and progressively transform to the reflexes ofCaCl2. This indicates the successive reducing the lattice parametersdue to the formation of continuous set of homogeneous solidsolutions over the whole range of nCaCl2/nS from 0 to 1 that agreeswell with the data for the bulk system CaCl2eCaBr2 [25].

Water sorption on the single-salt composites CaCl2/SiO2 andCaBr2/SiO2 results in the formation of crystalline hydrates accord-ing to the following reactions

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CaCl2þ 2 H2O¼ CaCl2$2H2O (4)

CaCl2$2H2Oþ 2 H2O¼ CaCl2$4H2O (5)

CaBr2þH2O¼ CaBr2$H2O (6)

CaBr2$H2OþH2O¼ CaBr2$2H2O (7)

CaBr2$2H2Oþ 2 H2O¼ CaBr2$4H2O (8)

salts in porous matrix” for adsorption heat transformation, Applied

Fig. 6. Isotherms of methanol sorption on the (CaCl2þ CaBr2)/SiO2 composites.T¼ 308 K.

L. Gordeeva et al. / Applied Thermal Engineering xxx (2011) 1e64

which show themselves as steps on the water sorption isobars(Fig. 5a). As CaBr2 has higher affinity to water than CaCl2 theformation of its hydrates occurs at higher temperature.

The water sorption isobars of the composites (CaCl2þCaBr2)/SiO2 differ significantly from the curves calculated as a linearcombination of the sorption on the single-salt composites (Fig. 5b,c). The steps caused by the formation of the hydrates SSCl∙2H2O andSSCl∙4H2O in the CaCl2 rich composite (CaCl2þCaBr2(3:1))/SiO2 aresituated at higher temperature by 5e10 K as regards the formationof CaCl2∙2H2O and CaCl2∙4H2O. On the contrary, steps attributed tothe formation of hydrates SSBr∙2H2O and SSBr∙4H2O in thecomposite enriched with CaBr2, namely, (CaCl2þCaBr2(1:3))/SiO2,move towards lower temperature by 15e20 K with respect to thoseof CaBr2.

Isotherms of methanol sorption on the single-salt compositesCaCl2/SiO2 and CaBr2/SiO2 have two steps attributed to the forma-tion of crystalline methanolates (Fig. 6)

CaCl2þ 2CH3OH¼ CaCl2∙2CH3OH (9)

CaCl2∙2CH3OHþ 2CH3OH¼ CaCl2∙4CH3OH (10)

Fig. 5. Isobars of water sorption on the composites CaCl2/SiO2 and CaCl2/SiO2 (a) and(CaCl2þ CaBr2)/SiO2 (b, c) as well as a linear combination of the sorption on thecomposites CaCl2/SiO2 and CaBr2/SiO2. P¼ 1.3 kPa.

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CaBr2þ 2CH3OH¼ CaBr2∙2CH3OH (11)

CaBr2∙2CH3OHþ 2CH3OH¼ CaBr2∙4CH3OH (12)

CaBr2 demonstrates higher afinity to methanol vapour. Theformation of CaBr2∙2CH3OH occurs at very low pressurePCH3OH¼ 0.3e0.8 kPa approximate to the pressure of CaCl2∙2-CH3OH formation (0.7e1.2 Pa). The methanolate CaBr2∙4CH3OHforms at lower methanol pressure (3.1e4.0 kPa) than CaCl2∙4-CH3OH (11.5e13.7 kPa). Isotherms of methanol sorption on the(CaCl2þ CaBr2)/SiO2 composites are located at intermediate pres-sure range. As the chloride content increases the step corre-sponding to the formation of methanolate SS∙4CH3OH graduallymoves towards higher pressure due to the formation of continuoushomogeneous solid solution of the salts.

3.3. The system (BaCl2þ BaBr2)/SiO2

The phase composition of both single-salt composites BaCl2/SiO2 and BaBr2/SiO2 is characterized by a mixture of the twomodifications of the salts, namely, orthorhombic and hexagonal.With the increase in bromine content, the reflexes on the XRDpatterns of the composites (BaCl2þ BaBr2)/SiO2 transform gradu-ally from those of BaCl2 to the reflexes of BaBr2 (Fig. 7). That showsthe formation of continuous row of homogeneous solid solutions inthe whole range of nBaCl2/nS¼ 0e1.

Two steps are observed on isotherms of the ammonia sorption onboth the single salt composites (Fig. 8). Firstly, at PNH3¼ 0e10 kPathe uptake w rises from 0 to 0.03e0.05 g/g due to the ammoniaadsorption on active centres of the silica gel. The second rise ofsorption from 0.05 to 0.20e0.23 g/g is attributed to the formation ofcomplexes due to the reactions

BaCl2þ 8NH3¼ BaCl2∙8NH3, (13)

BaBr2þ 8NH3¼ BaBr2∙8NH3. (14)

Again a bromide BaBr2 demonstrates higher affinity to ammoniaand the formation of BaBr2∙8NH3 occurs at lower ammonia pres-sure (70e160 and 550e650 kPa for BaBr2 and BaCl2, respectively,Fig. 8). Isotherms of ammonia sorption on the composites(BaCl2þ BaBr2)/SiO2 have a similar shape, and two steps areobserved (Fig. 8). As the chlorine content increases, the pressurecorresponding to the formation of ammonia complexes of the salts

salts in porous matrix” for adsorption heat transformation, Applied

Fig. 7. XRD patterns of the composites (BaCl2þ BaBr2)/SiO2.

L. Gordeeva et al. / Applied Thermal Engineering xxx (2011) 1e6 5

and their solid solution continuously moves from 70e160 to550e650 kPa.

Thus, the results obtained reveal some common features ofsorption equilibriumof the composites based on binary salt systemsconfined to porous matrices. The SS formation in such binarysystems leads todistortionof the crystalline lattice of the salts and tochange of the spacing parameter. That results in shifting the equi-librium temperature (pressure) of the complexes formationSSþNV¼ SS�NV regarding the solvation of pure salt SþNV¼ S�NV. The dissolution of a metal chloride MeClm in the lattice ofametal bromideMeBrm leads to the reducing the spacing parameterthat probably hinders the incorporation of the sorbate molecules inthe lattice. Therefore, the transition of SSBr to its solvates occurs atlower temperature (higher pressure) than the MeBrm solvation.Dissolution of the MeBrm in the lattice of the MeClm results in theopposite effect: expanding the crystalline lattice occurs thatpromotes the incorporation of the sorbate molecules in the latticeand raises the solvation temperature (reduces the pressure). Theshift of the temperature of the salt solvation due todissolution of theadditional salt can be used for the intent design of the compositesorbents for particular AHT cycles.

3.4. Tailoring the composites (BaCl2þBaBr2)/SiO2 for airconditioning, ice making and deep freezing cycles

The revealed gradual shift of adsorption isobars (isotherms) dueto the formation of solid solution of metal halides can be used for

Fig. 8. Isotherms of ammonia sorption on the silica gel and the composites(BaCl2þ BaBr2)/SiO2. T¼ 312 K.

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tailoring the composite which properties fit the demands ofparticular AHT cycle. Let us demonstrate this for three coolingcycles specified for air conditioning (AC), ice making (IM) and deepfreezing (DF).

Taking into account the data on ammonia sorption on thecomposites (BaCl2þ BaBr2)/SiO2 the pressure corresponding to theformation of the complexes SSBaClnBr(2-n)$8NH3 (wz 0.23 g/g) isplotted vs. the relative content of Br-ions nBaBr2/nS (Fig. 9). This graphallows a precise determination of the solvation pressure for thecomposite with a fixed ratio nBaBr2/nS. On the other hand, this graphis very convenient for predicting the composition of CSPM whichsorbs ammonia at the pre-determined conditions (PNH3 and T).

Let us consider the three working cycles specialized for airconditioning, ice making and deep freezing for hot climatic areas.Typical boundary conditions of these cycles are as follows:Tcon¼Tads¼ 313 K, Tev¼ 280, 270 and 250 K for AC, IM and DFcycles, respectively (Fig. 10). According to the data of Fig. 9, thecomposite BaBr2/SiO2 sorbs ammonia at PNH3¼ 220 kPa atTads¼ 312 K that allows estimating Tev¼ 255 K. This composite(CSPMeDF) can be considered as a proper one for DF cycle (Fig.10).The rich and weak isosters, which correspond to the ammoniauptakes w¼ 0.23 and 0.03 g/g, respectively, are schematically pre-sented in Fig. 10. An adsorbent for ice making (Tev¼ 270 K, Fig. 10)has to sorb ammonia at PNH3z 380 kPa, hence, its optimalcomposition should be nBaBr2/nSz 0.6 (Fig. 9). And finally, thecomposite with BaBr2 content nBaBr2/nS¼ 0.2 sorbs ammonia atPNH3¼ 550 kPa that corresponds to Tev¼ 280 K (Fig. 9). Thisadsorbent can be considered as optimal for air conditioning cycle(Fig. 10). Ammonia sorption on each of these sorbents reachwads¼ 0.23 g/g at the conditions of adsorption stage of the corre-sponding cycle.

Another point of primary importance is the temperature Tregnecessary for regeneration of the composite at methanol pressurecorresponding to Tcon¼ 113 K (Fig. 10). For accurate determinationof Treg the measurement of the set of adsorption/desorption isobarsfor each the composite is required. However some reasonableestimation can be done considering that ammonia sorption on thecomposite obeys the Polanyi principle of temperature invariance[8,26]. According to this principle, at different temperatures Ta andTb, an equal volume of adsorbed phase V can be achieved at thevapour pressures Pa and Pb, linked in the formula below:

Taln�PP0

�a¼ Tbln

�PP0

�b

(15)

where P/P0 is the relative pressure of adsorbate.

Fig. 9. Ammonia pressure, corresponding to the ammonia uptake wz 0.23 g/g vs. theBaBr2 content in the composites (BaCl2þ BaBr2)/SiO2 at T¼ 312 K.

salts in porous matrix” for adsorption heat transformation, Applied

Fig. 10. PeT diagram of the AC, IM and DF cycles as well as the rich (w¼ 0.23 g/g) andweak (w¼ 0.05 g/g) isosters of the sorbents CSPM-AC, CSPM-IM and CSPM-DF optimalfor these cycles.

L. Gordeeva et al. / Applied Thermal Engineering xxx (2011) 1e66

Taking into account this principle the following equation can bewritten

Tadsln�

PevP0ðTadsÞ

�¼ Tregln

�Pcon

P0�Treg

��

(16)

and regeneration temperature can be estimated as Treg¼ 378, 399and 431 K for AC, IM and DF cycles, respectively. Obviously, the riseof affinity of the composites to ammonia vapour due to higherbromine content results in the increase in the regenerationtemperature at fixed Pcon. However, even the composite CaBr2/SiO2specialized for DF cycle can be regenerated at temperature 431 Kwhich is quite available using the solar energy concentrated byparabolic collectors.

The amount of ammonia leaved after regeneration at thistemperature wreg¼ 0.05 g/g (Fig. 9) that gives a quite large varia-tion in the uptake per cycle Dw¼ 0.18 g/g. Thus, the selection ofproper composite composition allows an intentional adjustment ofthe composite properties to particular cooling cycle as well as anexchange of the large ammonia amount at the cycle.

4. Conclusions

Phase composition of CSPMs based on various binary saltssystems (LiClþ LiBr, CaCl2þ CaBr2 and BaCl2þ BaBr2) confined tothe silica and vermiculite pores, and their sorption equilibriumwith water, methanol and ammonia are studied. The formation ofthe salt solid solutions inside the pores results in shifting theequilibrium temperature (or pressure) of the salt solvation reac-tions. The dissolution of the metal bromides, which demonstratehigher affinity to water, methanol and ammonia than corre-sponding chlorides, leads to the increase in the equilibrium solva-tion temperature and appropriate pressure reduction. On thecontrary, the additive of chlorides decreases the equilibriumtemperature and increases the pressure of the solvation. Thistemperature tuning is a powerful tool for tailoring CSPMs withpredetermined sorption properties which fairly fit requirements ofthe particular AHT cycle.

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Acknowledgements

The authors thank the Russian Foundation for Basic Researches(projects09-03-00916aand10-08-91156) forpartialfinancial support.

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