Untersuchung der porösen Materialien auf ihre Sorptionseigenschaften für die Adsorptionswärmeanwendung

Sedelnikova, Olesya; Palkovits, Regina (Thesis advisor); Rose, Marcus (Thesis advisor)

Aachen : RWTH Aachen University (2021)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2021

Abstract

This thesis is devoted to a general study of the water sorption properties of three classes of porous materials, namely zeolite, silica gel and hydrocarbon materials, according their structural and chemical features. The obtained water sorption characteristics may have useful applications to thermal energy storage (TES). The first part of the thesis concerns the investigation of the sorption properties of commercial silica gel B123 samples before and after treatment with a piranha solution (H2O2:H2SO4) by varying of contact times (5, 60, 120 min.). The hydroxylation of the silica gel surface led to an increase in the hydrophilicity of its external surface, at which point the material demonstrated improved water loading at low relative pressures P/P0. The second part of the thesis is about the sorption properties of hydrocarbons: active carbon, porous carbon cuboids (PCCs), and carbon nanotubes (CNTs). A commercial sample of active carbon Norit A Supra EUR from CABOT showed the highest specific surface values but also the lowest water loading values in the low pressure region. The porous carbon cuboids described in previous research as being promising materials due to their high water sorption capacities were synthesized according to the work of Hao and Mondin (2014). Both samples (PCC-1 and PCC-2), demonstrated a high reproducibility as well as high values for specific surface and water loading characteristics. The carbon nanotubes with excellent mechanical properties and hydrothermal stability have been studied as composite material in a combination with a polymer polyacrylonitrile (PAN), which has a high concentration of hydrophilic nitrile groups (-CΞN). The PAN-CNT based materials showed high values of water loading in the low relative pressure region. The CNT content increase in the PAN-CNT composite leads to a higher total pore volume, but meanwhile its polarity decreases as the concentration PAN polymer reduces. However, its polarity decreases as the concentration of the PAN polymer reduces. Lastly, the sorption features of zeolite materials of the FAU, MFI, LTA and GIS types were investigated according to several factors such as Si/Al module, type of counterion, pore size and their distribution. Both commercial samples and newly synthesized samples were used for this part of the study. The zeolites of FAU and GIS types were, according to their high hydrophilic properties, further treated with post-synthetic methods, including desilification with an NaOH solution, and wet impregnation with Mg- and La- containing solutions. The last two zeolite types showed the highest values of water loading.