TY - JOUR

T1 - Phase Transformation of Hydrothermally Stressed Adsorbents

AU - Buhl, Josef Christian

AU - Herzog, Thomas

AU - Lutz, Wolfgang

AU - Wieprecht, Wolfgang

N1 - Funding Information: The authors gratefully acknowledge Dr. M. Fechtelkord from Ruhr-Universität Bochum for performing the 29Si MAS NMR measurements. The authors are grateful to Clariant Produkte (Deutschland) GmbH for supply of AlPO-5 and SAPO-34 samples and to Invensor GmbH, Berlin for experimental support. The financial support by the German Federal Ministry of Education and Research, grant number FKZ 01 LY 11 60 9C, is acknowledged. The authors gratefully acknowledge the very helpful recommendations of the two anonymous reviewers.

PY - 2018/9/18

Y1 - 2018/9/18

N2 - Inorganic materials of zeolite type, silica gel or related materials are used as adsorbents in air conditioning machines. The cooling effect is obtained by evaporation of water thereby the adsorbent acts as pump system. After itôs saturation, the storage must be regenerated by heating. The hydrothermal stress may generate decomposition of their structure accompanied by a loss of sorption capacity. This work describes the hydrothermal stability of AlPO-5, SAPO-34, and silica gel in comparison with a newly developed dealuminated Y zeolite DAY. DAY (Si/Al = 3.1) and AlPO-5 zeolites are hydrothermally stable over a wide temperature range even under harsh condition of maximum water loading of their pore system. DAY exhibits a higher water sorption capacity but becomes amorphous with increasing temperature, whereas AlPO-5 transforms into a tridymite analogous crystalline phase with an intermediate state at 140 °C. But, both phase transformation processes are not relevant for the application of the compounds in low-temperature driven heat pumps due to less hydrothermal stressing there. SAPO-34 decomposes already under mild hydrothermal conditions. In analogy to AlPO-5 it forms the tridymite analogous structure at high temperature. The silica gel looses the sorption capacity systematically because of the healing of its structure by condensation of free silanol groups, whereby Q2 and Q3 groups change into Q4 groups.

AB - Inorganic materials of zeolite type, silica gel or related materials are used as adsorbents in air conditioning machines. The cooling effect is obtained by evaporation of water thereby the adsorbent acts as pump system. After itôs saturation, the storage must be regenerated by heating. The hydrothermal stress may generate decomposition of their structure accompanied by a loss of sorption capacity. This work describes the hydrothermal stability of AlPO-5, SAPO-34, and silica gel in comparison with a newly developed dealuminated Y zeolite DAY. DAY (Si/Al = 3.1) and AlPO-5 zeolites are hydrothermally stable over a wide temperature range even under harsh condition of maximum water loading of their pore system. DAY exhibits a higher water sorption capacity but becomes amorphous with increasing temperature, whereas AlPO-5 transforms into a tridymite analogous crystalline phase with an intermediate state at 140 °C. But, both phase transformation processes are not relevant for the application of the compounds in low-temperature driven heat pumps due to less hydrothermal stressing there. SAPO-34 decomposes already under mild hydrothermal conditions. In analogy to AlPO-5 it forms the tridymite analogous structure at high temperature. The silica gel looses the sorption capacity systematically because of the healing of its structure by condensation of free silanol groups, whereby Q2 and Q3 groups change into Q4 groups.

KW - Cooling technique

KW - Hydrothermal stability

KW - Phase transformation

KW - Silica gel

KW - Zeolites

UR - http://www.scopus.com/inward/record.url?scp=85053055919&partnerID=8YFLogxK

U2 - 10.1002/zaac.201800203

DO - 10.1002/zaac.201800203

M3 - Article

AN - SCOPUS:85053055919

VL - 644

SP - 1078

EP - 1083

JO - Zeitschrift fur Anorganische und Allgemeine Chemie

JF - Zeitschrift fur Anorganische und Allgemeine Chemie

SN - 0044-2313

IS - 18

ER -