G. De Weireld

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.

Strategies for the production of high-content fructo-oligosaccharides through the removal of small saccharides by co-culture or successive fermentation with yeast

Fructo-oligosaccharides (FOS) obtained by fermentation of sucrose may be purified at large-scale by continuous chromatography (Simulated Moving Bed: SMB). In order to improve the efficiency of the subsequent SMB purification, the optimization of the fermentative broth composition in salts and sugars was investigated. Fermentations conducted at reduced amount of salts, using Aureobasidium pullulans whole cells, yielded 0.63 ± 0.03 g of FOS per gram of initial sucrose. Additionally, a microbial treatment was proposed to reduce the amount of small saccharides in the mixture. Two approaches were evaluated, namely a co-culture of A. pullulans with Saccharomyces cerevisiae; and a two-step fermentation in which FOS were first synthesized by A. pullulans and then the small saccharides were metabolized by S. cerevisiae. Assays were performed in 100mL shaken flasks and further scaled-up to a 3 L working volume bioreactor. Fermentations in two-step were found to be more efficient than the co-culture ones. FOS were obtained with a purity of 81.6 ± 0.8% (w/w), on a dry weight basis, after the second-step fermentation with S. cerevisiae. The sucrose amount was reduced from 13.5 to 5.4% in total sugars, which suggests that FOS from this culture broth will be more efficiently separated by SMB.

Evaluation of commercial resins for fructo-oligosaccharide separation.

Fructo-oligosaccharides (FOS) produced by fermentative processes are obtained in mixtures containing significant amounts of salts and other non-prebiotic sugars. A demineralisation process using a mixture of a cationic and an anionic resin was proposed. The separation of FOS from a mixture of fructose, glucose and sucrose was evaluated. Experiments were conducted with several commercial cationic exchange resins in calcium, sodium and potassium forms packed in preparative columns (7cm×2.2cm length×diameter). Resins in potassium form obtained the higher retention factor values for sugars when compared to the other ionic forms. However, when compared to calcium and sodium ones, resins in potassium cationic forms were shown to be the less efficient separating sugar mixtures. The resin with best separation performance was the Diaion UBK535Ca. A recovery yield of 92% (w/w) of FOS with 90% (w/w) of purity was obtained from batch experiments conducted in a single column loaded with the Diaion UBK535Ca resin at 25°C. The temperature shown did not influence the separation performance significantly. By increasing the column length, the purity of FOS increased to 92% (w/w), however the recovery yield decreased to 88% (w/w).

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.

Structural characterization of porous carbonaceous materials using high-pressure adsorption measurements

The aim of this work is to present a new method for porous carbonaceous solids characterization: the pore size distribution function (PSDF) of the adsorbent is determined by a theoretical treatment applied to adsorption data. The measurements are performed with different adsorbates at different temperatures in a wide pressure range. The theoretical model is based on the concept of integral adsorption equation (IAE). The main assumptions of the model are: (1) The PSDF is considered as an intrinsic property of the adsorbent. (2) The slit shaped pore model is used to describe the geometric configuration of the porous structure. (3) The adsorbent-adsorbate interactions are described by a Lennard-Jones potential model. (4) The pore wall surface is considered to be energetically homogeneous and the adsorbed phase is monolayer. (5) Both the gas phase and the adsorbed phase are supposed to be efficiently described by a Redlich-Kwong type equation of state. (6) We assumed a priori the analytical form of the pore size distribution function. We used adsorption isotherms of nitrogen, oxygen, argon and methane on different carbonaceous solids (four activated carbons and one molecular sieve) at 283 K, 303 K and 323 K and for pressures up to 2200 kPa.

Correction to: A reference high-pressure CO2 adsorption isotherm for ammonium ZSM-5 zeolite: results of an interlaboratory study

The original version of this article was published open access. Unfortunately, due to a technical issue, the copyright holder name in the online version (HTML and XML) is incorrectly published as “Springer Science+Business Media, LLC, part of Springer Nature 2018”. Instead, it should be “The Author(s) 2018”.