Measuring water adsorption processes of metal-organic frameworks for heat pump applications via optical calorimetry

Optical calorimetry (broadband IR-detection of the released heat of adsorption, “InfraSORP”) during water adsorption processes is used for an accelerated assessment of porous materials performance in heat pump applications. Metal-organic frameworks (MOFs) are screened as a highly promising class of materials for water adsorption driven heat exchangers with high water adsorption capacities. Based on a proper calibration, optical calorimetry is demonstrated to allow for rapid estimation of the total water adsorption capacity at a given relative humidity. In a dynamic mode, full water adsorption isotherms can be measured using a step-wise increase of the relative humidity. As cycling stability is among the most critical issues for the integration of new porous materials into systems, the InfraSORP methodology provides a valuable and inexpensive tool for accelerated cycling and stability testing. The InfraSORP technique is demonstrated to provide a significantly accelerated automated and easy-to-acquire alternative as compared to conventional characterization methods

Verfahren zur Bestimmung der Porengrößenverteilung eines porösen Materials

Die Erfindung betrifft ein Verfahren zur Bestimmung der Porengrössenverteilung eines porösen Materials, insbesondere Aktivkohle, bei dem eine Probe desselben Materials innerhalb einer Kammer, die für elektromagnetische Strahlung im Wellenlängenbereich zwischen 150 nm bis 25 μm nicht transparent ist, jeweils mit einem gasförmigen Adsorptiv, dessen kinetischer Durchmesser und/oder Porenzugänglichkeitsbereich bekannt ist, beaufschlagt wird. Dabei wird das jeweilige Adsorptiv an der Oberfläche der jeweiligen Probe adsorbiert und mit mindestens einem optischen Detektor, der zumindest in einem Bereich des Wellenlängenbereichs zwischen 150 nm und 25 μm sensitiv ist, wird die in Folge der Adsorption von der jeweiligen Probe emittierte elektromagnetische Strahlung detektiert.; Die Messsignale des/der Detektors/Detektoren werden zeitaufgelöst erfasst und innerhalb eines vorgebbaren Zeitintervalls zur Bestimmung der durch die Adsorption sich ändernden Oberflächentemperatur und/oder der Adsorptionswärme der jeweiligen Probe ausgewertet. Die Porengrössenverteilung wird dann mit mindestens zwei unterschiedlichen Adsorptiven an mindestens zwei Proben, die aus demselben Material gebildet sind, anhand der so ermittelten spezifischen Peakflächen A/m, der Adsorptionskapazitäten und/oder der Adsorptionsenthalpien ΔHads für die jeweils eingesetzten Adsorptive ermittelt wird

Estimating pore size distributions of activated carbons via optical calorimetry

Optical calorimetry is a powerful technique for the characterization of porous materials within only a few minutes (e.g. specific surface area, adsorption capacity). In the current work, optical calorimetry is presented to be a versatile tool for the pore size characterization of activated carbons. Therefore, measurements were performed with six different test gases (N2O, C2H6, C3H8, n-C4H10, i-C4H10, SF6) in the optical calorimeter InfraSORP at ambient conditions. By combining the results of optical calorimetric measurement for each adsorptive, a pore size distribution (PSD) can be estimated in the range of 0.4–6 nm which is in accurate accordance with the PSD of reference CO2 (273 K) and N2 (77 K) physisorption experiments. While common physisorption experiments can easily take a few days, the PSD by using the optical calorimetric screening is obtained within roughly 1 h

Adsorption and detection of hazardous trace gases by metal-organic frameworks

The quest for advanced designer adsorbents for air filtration and monitoring hazardous trace gases has recently been more and more driven by the need to ensure clean air in indoor, outdoor, and industrial environments. How to increase safety with regard to personal protection in the event of hazardous gas exposure is a critical question for an ever‐growing population spending most of their lifetime indoors, but is also crucial for the chemical industry in order to protect future generations of employees from potential hazards. Metal–organic frameworks (MOFs) are already quite advanced and promising in terms of capacity and specific affinity to overcome limitations of current adsorbent materials for trace and toxic gas adsorption. Due to their advantageous features (e.g., high specific surface area, catalytic activity, tailorable pore sizes, structural diversity, and range of chemical and physical properties), MOFs offer a high potential as adsorbents for air filtration and monitoring of hazardous trace gases. Three advanced topics are considered here, in applying MOFs for selective adsorption: (i) toxic gas adsorption toward filtration for respiratory protection as well as indoor and cabin air, (ii) enrichment of hazardous gases using MOFs, and (iii) MOFs as sensors for toxic trace gases and explosives

Insights into the water adsorption mechanism in the chemically stable zirconium-based MOF DUT-67 - a prospective material for adsorption-driven heat transformations

A chemically and thermally stable MOF with composition Zr 6 O 4 (OH) 4 (tdc) 4 (CH 3 COO) 4 (tdc, 2,5-thiophenedicarboxylate), also known as DUT-67(Zr), was synthesised at the multigram scale using a green synthesis protocol as a potential material for adsorption heat pumps. A series of vapour physisorption experiments at 298 K identified water as the most promising working fluid, showing the desired S-shaped reversible physisorption isotherms with adsorption steps within the desired relative pressure range of p/p 0 = 0.1-0.4. An enhanced long-term chemical stability of the MOF was proved in liquid water and mineral acid and thermal stability was confirmed in temperature dependent PXRD experiments. Stable performance of the material under working conditions was confirmed in 20 adsorption/desorption cycles under conditions typical for an adsorption pump. The mechanism of water adsorption was further studied by neutron powder diffraction, suggesting that the preferable adsorption sites for water are near the μ 3 -O and μ 3 -OH groups of the Zr 6 O 8 cluster and the triangular window of the octahedral micropore, and the order of pore filling starts from the smallest pore, progressing to the middle and largest pore

Speeding up chemisorption analysis by direct IR-heat-release measurements (infrasorp technology): A screening alternative to breakthrough measurements

In this study, a new innovative adsorption screening method, Infrasorp technology, is presented as a quick and efficient measurement tool for the determination of H2S adsorption capacity and compared to breakthrough measurements. Using zinc oxide nanoparticles and metal–organic framework materials, a clear correlation between those two techniques was found, showing the broad applicability of the method for different classes of materials and the potential of Infrasorp to be used as an alternative or preliminary analysis to breakthrough measurements. This tool saves time and costs and speeds up characterization of new materials thanks to the feasibility of a quick and easy wide screening using a small amount of adsorbent

Improving component cleanliness during laser remote ablation processes with high-power lasers by optimized emission blower and suction strategies

Laser remote processing with high-performance laser sources enables materials such as metals or fiber composites to be cut, welded or ablated flexibly and quickly. All these manufacturing processes produce process and material specific particulate as well as gaseous emissions. This must be recorded quantitatively and qualitatively in order to implement appropriate protective measures with regard to occupational health and safety as well as to minimize the crosscontamination of the component to be treated. Ideally, an additional cleaning step should be avoided by optimizing the arrangement of the process suction and blower. Particle distributions as well as gas phase analyses during the remote ablation process were recorded during ablation tests on metals or carbon-based composites. The structure quality and the contamination of the sample surface after laser material processing as well as after the additional cleaning process were determined. Subsequently, the samples were thermally joined to evaluate the influences