Marc Frère

Automated determination of high-temperature and high-pressure gas adsorption isotherms using a magnetic suspension balance

A gravimetric experimental device allowing the measurement of pure gas adsorption isotherms is presented. The mass measurement is performed by a Rubotherm magnetic suspension balance instrumented in such a way to allow completely automated adsorption isotherm measurements for pressures ranging from 0 to 10 000 kPa and for temperatures from 303 to 423 K. Its main originality is that, although it works at high temperature, all the components in contact with the adsorbate are at the experimental temperature so that it is possible to study adsorbates which condensate at high-pressure and ambient temperature. This paper provides a detailed experimental procedure, the measurement accuracy and some comments on the advantages and drawbacks of the method. As examples of experimental results, adsorption isotherms of nitrogen and butane on activated carbon (F30-470, Chemviron Carbon) at five temperatures (303, 323, 343, 363 and 383 K) are presented. As a first step of a general study devoted to the comparison of high-pressure adsorption measurement techniques, the 303 K nitrogen adsorption isotherm is compared to data obtained for the same system but with a volumetric apparatus working in narrower ranges of temperature and pressure.

High-pressure adsorption measurements. A comparative study of the volumetric and gravimetric methods

In this paper, we propose a comparative study between a volumetric apparatus and a gravimetric one, which were developed for the acquisition of high-pressure adsorption isotherms. The volumetric apparatus is able to perform measurements in the temperature range 278?323 K and in the pressure range 0?4000 kPa. We provide a complete report on the experimental errors due to the mass balance calculation based on pressure?volume?temperature measurements. The same analytical study has been achieved for a gravimetric apparatus (temperature range: 223?393 K, pressure range: 0?10?000 kPa). The comparison comments are based on experimental data obtained for the system: activated carbon (CENTAUR Chemviron Carbon)?nitrogen. It appears that for such a system exhibiting quite low adsorbed quantities, important discrepancies may appear if the measurements are not properly achieved. Minimizing the experimental errors for the two experimental techniques leads to an average observed deviation (relative error) between the two methods equal to 3% in the whole measurement range.

Characterization of Porous Carbonaceous Sorbents Using High Pressure CO2 Adsorption Data

In this paper we present adsorption isotherms of carbon dioxide on five different activated carbons from CHEMVIRON CARBON Belgium (Centaur HSV, BPL 410, F30-470, WS 42, Reactivated) and on a carbon molecular sieve from BERGBAU FORSCHUNG Gmbh (CMS II). The temperature is 303 K and the pressure ranges from 100 kPa up to 4000 kPa. Such conditions correspond to relative pressures ranging from 0.01 to 0.5. We also provide, for the same six sorbents, the nitrogen isotherms at 77 K (pressure: 0.001 to 100 kPa, relative pressure: 10-5 to 1). A theoretical treatment based on the Dubinin-Radushkevich and Stoeckli concept is presented and applied to the experimental results in order to obtain the micropore size distribution function (considered as Gaussian) of each sorbent. Using the CO2 data, it is possible to point out important structural differences between the six carbons. The theoretical treatment provides micropore size distribution functions in agreement with what is physically expected. Using N2 data, the structural differences are not so well marked. As a consequence, the structural parameters provided by the theoretical treatment are not reliable: except for the total micropore volume, they fluctuate strongly when changing the relative pressure domain of the used data.

Design of salt–metal organic framework composites for seasonal heat storage applications

Porous materials are recognized as very promising materials for water-sorption-based energy storage and transformation. This study presents the first attempt to use Metal Organic Frameworks (MOFs) as host matrices of salts for the preparation of composite sorbents for seasonal heat storage. We have considered six water stable MOFs (i.e. MIL-127(Fe), MIL-100(Fe), MIL-101(Cr), UiO-66(Zr)–NH2, MIL-125(Ti)–NH2 and MIL-160(Al)) differing in their crystalline structure, hydrophilic–hydrophobic balance, pore size/shape and pore volume. The successful encapsulation of CaCl2 in the pores of MOFs leads to two series of MOFs–CaCl2 composites whose salt content could be finely tuned depending on the pore volume of MOFs and the synthesis conditions. These materials were fully characterized by combining multiple techniques (i.e. powder X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, X-ray energy-dispersive spectrometry elemental mapping, N2 sorption and elemental analysis). The water sorption properties of these composites were studied under conditions of a solar heat storage system (i.e. adsorption at 30 °C, desorption at 80 °C, both steps at a water vapour pressure of 12.5 mbar) in comparison to the parent MOFs. We analyze how the physico-chemical and structural properties of these host matrices impact the energy density of composite sorbents. We show that two mesoporous MOFs–CaCl2 composites (i.e. MIL-100(Fe)/CaCl2 and MIL-101(Cr)/CaCl2) with the highest salt loading (46 and 62 wt% respectively) exhibit very high energy storage capacities (up to 310 kW h m−3 (485 W h kg−1)) outperforming the best composites or physical sorbents reported so far together with very little loss upon adsorption–desorption cycling and high chemical stability upon ageing (up to 18 months).

Synthesis Optimization, Shaping, and Heat Reallocation Evaluation of the Hydrophilic Metal–Organic Framework MIL‐160(Al)

The energy-storage capacities of a series of water-stable porous metal-organic frameworks, based on high-valence metal cations (Al3+ , Fe3+ , Cr3+ , Ti4+ , Zr4+ ) and polycarboxylate linkers, were evaluated under the typical conditions of seasonal energy-storage devices. The results showed that the microporous hydrophilic Al-dicarboxylate MIL-160(Al) exhibited one of the best performances. To assess the properties of this material for space-heating applications on a laboratory pilot scale with an open reactor, a new synthetic route involving safer, greener conditions was developed. This led to the production of MIL-160(Al) on a 400 g scale, before the material was shaped into pellets through a wet-granulation method. The material exhibited a very high energy-storage capacity for a physical-sorption material (343 Wh kg-1 ), which is in full agreement with the predicted value.

Simultaneous determination of mass and calorimetric adsorption data of volatile organic compounds on microporous media in the low relative pressure range

In this paper, we present a new experimental procedure which aims at measuring adsorption isotherms and heats of adsorption of volatile organic compounds (VOCs) on porous media in the low relative pressure range for temperatures ranging from 303 to 573 K. The experimental set-up and the experimental dynamic procedure are presented as well as a complete report on the treatment of the rough experimental results to obtain the adsorption isotherms and the adsorption heat curves. Measurement accuracy and repeatability are given. The maximum measurement error is 3% on the adsorbed mass, 9% on the partial pressure of VOC and 15% on the adsorption heat. Results are provided for a toluene/NaY system (isotherm and adsorption heat curve at 423 K in the pressure range 0.4–2000 Pa).

Characterisation of new Pd / hierarchical macro-mesoporous ZrO2, TiO2 and ZrO2-TiO2 catalysts for toluene total oxidation

Amorphous (macro)-mesoporous ZrO 2 , TiO 2 and ZrO 2 -TiO 2 have been synthesised and characterised for volatile organic compounds (VOCs) catalytic oxidation. These solids used as catalytic supports present high surface areas. The stability of the porous structure after the calcination at 400°C is observed for ZrO 2 -TiO 2 and TiO 2 but partial breakdown of the structure occurred for ZrO 2 by the crystallisation to tetragonal phase. All these Pd impregnated solids are found to be powerful catalysts for total oxidation of toluene. Pd/TiO 2 presents the highest catalytic potential. The lowest toluene adsorption enthalpy, the low coke content observed after the catalytic test and the highest pore diameter leading to palladium particles more accessible and reducible should explain the interesting catalytic behaviour of Pd/TiO 2 .

Adsorption equilibria of single gas and gas mixture on homogeneous surfaces: a unified approach based on statistical thermodynamics developments. Part II: extension to gas mixture adsorption

Theoretical description of single gas and gas mixture adsorption equilibria can be achieved in many different ways depending on the kind of approach (microscopic or macroscopic). In this paper, we present a statistical thermodynamics approach for the calculation of mixed gas adsorption equilibrium data on uniform surfaces. The non-ideality of both the mixed gas phase and the adsorbed phase is considered by using the Redlich–Kwong EOS associated to the classic Lorentz–Berthelot mixing rules. This is an interesting way to extend the model presented in Part I and to predict multicomponent gas adsorption equilibria for highly non-ideal systems from parameters deduced from pure gas data. We present mixture adsorption isotherms and selectivity curves calculated using our model.

Comparative study of the dynamic gravimetric and pulse chromatographic methods for the determination of Henry constants of adsorption for VOC–zeolite systems

In this paper, we propose a comparative study between a gravimetric apparatus operating under dynamic conditions and a pulse chromatographic device developed for the determination of Henry constants of adsorption for VOC–zeolite systems. In both cases, we provide a description of the experimental set-up and procedure, as well as a complete report on the treatment of the rough experimental data. The experimental errors are also discussed. The comparison work is based on the study of the adsorption of toluene on a NaY zeolite (Si/Al 2.43) for temperatures ranging from 503 to 623 K. The maximal discrepancy found between the experimental Henry constants was 15.0%. The pulse chromatographic method is only dedicated to high-temperature measurements. For low-temperature experiments, the rough data cannot be treated in an efficient way, and it is not possible to obtain reliable Henry constant values. The dynamic gravimetric method is not temperature limited. It is however time-consuming, especially when low-temperature measurements (not presented in this paper) are concerned. Both methods are complementary if the determination of Henry constants is required in a wide temperature range.

Determination of the Porous Structure of Activated Carbons Using the IAE Concept. Influence of the Local Adsorption Model

In this paper we study a method for the determination of the micropore volume distribution function of activated carbons. This method is based on the Integral Adsorption Equation concept (IAE). The micropore volume distribution function is assumed to be a Gaussian of which the parameters are unknown. These parameters are determined using adsorption isotherms of carbon dioxide on a given activated carbon (F30/470 CHEMVIRON CARBON) at 278, 288, 298, 303, 308, 318 and 328 K and for pressures up to 100 kPa. Several local adsorption models are used (Langmuir, Volmer, Fowler-Guggenheim, Hill-de Boer). The influence of the choice of the local model on the pore volume distribution function is discussed. The physical validity of this function and the performances of the different models are presented. It appears that the effect of the temperature on the adsorption isotherms is difficult to model over a wide range of relative pressure. The Hill-de Boer and the Langmuir local models are the most efficient (average errors respectively equal to 3.53% and 2.80% in the studied range of temperature and pressure). They provide the most meaningful parameters for the pore volume distribution function.