Air-Con Metal–Organic Frameworks in Binder Composites for Water Adsorption Heat Transformation Systems

Abstract

Metal–organic frameworks (MOFs) currently receive high interest for cycling water adsorption applications like adsorption heat transformation for air-conditioning purposes. For practical use in adsorption heat pumps (AHPs), the microcrystalline powders must be formulated such that their high porosity and pore accessibility are retained. In this work, the preparation of millimeter-scaled pellets of MIL-160­(Al), Al-fumarate (Basolite A520), UiO-66­(Zr), and Zr-fumarate (MOF-801) is reported by applying the freeze granulation method. The use of poly­(vinyl alcohol) (PVA) as a binder reproducibly resulted in highly stable, uniformly shaped PVA/MOF pellets with 80 wt % MOF loading, with essentially unchanged MOF porosity properties after shaping. The shaped pellets were analyzed for the application in AHPs by water adsorption isotherms, over 1000 water adsorption/desorption cycles, and thermal and mechanical stability tests. Furthermore, the Al-fum pellets were applied in a fixed-bed, full-scale heat exchanger, yielding specific cooling powers from 349 up to 431 W/kg (adsorbent), which outperforms the current commercially used silica gel grains in AHPs under comparable operating conditions.

Metal‐Organic Frameworks as Sorption Materials for Heat Transformation Processes

“…The pellets withstood mechanical loads of up to 79 N. The Al-fumarate/PVA pellets were placed between the lamellae of a pipe-lamella heat exchanger, Dynamic adsorption and cooling performance testing provided specific cooling powers (SCP) from 349 up to 431 W/kg(adsorbent), which is better than current commercially used silica gel grains in AHPs under comparable operating conditions. [31] Another promising shaping method for MOF/polymer monoliths was presented by Hastürk et al [119,120] based on Sun′s method of phase separation (Figure 13). [121] The Al-fum/PVA composites with a MOF loading of 50 to 80 wt.-% even exhib- Figure 13.…”

“…Bottom: pipe‐lamella heat exchanger unfilled (left) and filled (right) with pellets. [ 31 ] Reproduced from ref. [ 30 ] © (2019), with permission from the American Chemical Society.…”

“…The pellets withstood mechanical loads of up to 79 N. The Al‐fumarate/PVA pellets were placed between the lamellae of a pipe‐lamella heat exchanger, Dynamic adsorption and cooling performance testing provided specific cooling powers (SCP) from 349 up to 431 W/kg(adsorbent), which is better than current commercially used silica gel grains in AHPs under comparable operating conditions. [ 31 ]…”

“…This has opened up the potential application of cyclic water sorption with water‐stable MOFs in adsorption heat pumps (AHPs), including adsorption chillers. [ 31 ] Physical adsorption and desorption processes on inner surfaces of highly porous materials, can be used to convert heat in heat transformation processes. [ 32 ] Adsorption is a process of adhesion of atoms, molecules, or ions of a gas or liquid at the surface of a solid or liquid.…”

Aqueous Flow Reactor and Vapour‐Assisted Synthesis of Aluminium Dicarboxylate Metal–Organic Frameworks with Tuneable Water Sorption Properties

“…It exhibits high porosity and stability, even under hydrothermal stress, and therefore has sparked the interest of industrial researchers . In particular, the sigmoidal water ad‐/desorption curve without hysteresis demonstrated by Al‐MIL‐53‐Fum and other Al‐MOFs is attractive for applications in heat‐exchange devices . The patented synthesis of Al‐MIL‐53‐Fum is a hydrothermal batch process that makes use of inexpensive and readily available starting materials (fumaric acid, NaOH, aluminium sulfate) and avoids hazardous solvents such as dimethylformamide .…”