7 research outputs found
Adsorption of butanol and water vapors in silicalite-1 films with a low defect density
Pure silica zeolites are potentially hydrophobic and have therefore been considered to be interesting candidates for separating alcohols, e.g., 1-butanol, from water. Zeolites are traditionally synthesized at high pH, leading to the formation of intracrystalline defects in the form of silanol defects in the framework. These silanol groups introduce polar adsorption sites into the framework, potentially reducing the adsorption selectivity toward alcohols in alcohol/water mixtures. In contrast, zeolites prepared at neutral pH using the fluoride route contain significantly fewer defects. Such crystals should show a much higher butanol/water selectivity than crystals prepared in traditional hydroxide (OH–) media. Moreover, silanol groups are present at the external surface of the zeolite crystals; therefore, minimizing the external surface of the studied adsorbent is important. In this work, we determine adsorption isotherms of 1-butanol and water in silicalite-1 films prepared in a fluoride (F–) medium using in situ attenuated total reflectance–Fourier transform infrared (ATR–FTIR) spectroscopy. This film was composed of well intergrown, plate-shaped b-oriented crystals, resulting in a low external area. Single-component adsorption isotherms of 1-butanol and water were determined in the temperature range of 35–80 °C. The 1-butanol isotherms were typical for an adsorbate showing a high affinity for a microporous material and a large increase in the amount adsorbed at low partial pressures of 1-butanol. The Langmuir–Freundlich model was successfully fitted to the 1-butanol isotherms, and the heat of adsorption was determined. Water showed a very low affinity for the adsorbent, and the amounts adsorbed were very similar to previous reports for large silicalite-1 crystals prepared in a fluoride medium. The sample also adsorbed much less water than did a reference silicalite-1(OH–) film containing a high density of internal defects.The results show that silicalite-1 films prepared in a F– medium with a low density of defects and external area are very promising for the selective recovery of 1-butanol from aqueous solutions
Adsorption Properties of MFI-Type Zeolite Films for Upgrading of Biofuels
With the depleting reservoirs of fossil fuels, increasing environmental concerns for flue-gas emissions from fossil-fuel combustion and growing world population, the need for the development of new sustainable fuels is higher than ever. However, to be able to compete with today’s mature technologies for production of fuels from fossil sources, new efficient processing alternatives for upgrading of biofuels must be developed.   Bio-fuels produced by e.g. fermentative processes are promising alternatives to traditional chemicals and fuels produced from fossil sources. Recovery of biofuels by selective membranes and adsorbents has been identified as promising energy efficient recovery routes. In this work, adsorption properties of MFI-type zeolite films were studied using in situ ATR-FTIR spectroscopy in order to understand the adsorption properties of these zeolites.   Single component adsorption isotherms of butanol and water vapor were determined at different temperatures using ATR-FTIR spectroscopy. The Langmuir and Sips model were successfully fitted to experimental data, and the fitted parameters obtained in this work were in very good agreement with values reported in the literature. Adsorbed amounts of butanol and water from binary vapor mixtures were extracted from the infrared spectra as well as the adsorption selectivities. The silicalite-1 film prepared in fluoride medium found to be significantly more butanol selective due to the exceptionally low density of defects in the structure.   Biogas (methane) is another promising biofuel that is commonly produced by anaerobic degradation of biomass. However, before it may be used, contaminants have to be removed from the gas; two of the most abundant contaminants in biogas are carbon dioxide and water vapor. Adsorption of a ternary mixture of methane, carbon dioxide and water vapor in zeolite Na-ZSM-5 has been studied at various compositions and temperatures using ATR–FTIR spectroscopy. The amount adsorbed determined from experimental data were compared to predictions by the Ideal Adsorbed Solution Theory (IAST). This result confirms that Na-ZSM-5 could be a promising membrane material for upgrading of biogas
A Kinetic Study of CO2 and Steam Gasification of Char from Lignin Produced in the SEW Process
The reaction kinetics of gasification are important for the design of gasifiers using biomass feedstocks, such as lignin, produced in biorefinery processes. Condensed and uncondensed lignin samples used in the present study were prepared using the SEW (SO2-ethanol-water) fractionation process applied to spruce wood chips: the dissolved lignin is precipitated during the recovery of SO2 and ethanol from the spent fractionation liquor. The gasification of char made from condensed and uncondensed SEW lignin was investigated using thermogravimetric analysis (TGA) at atmospheric pressure using either CO2 or steam. The main aim of this study was to quantify the reaction rate during the gasification process, which was found to be best described as zero-order. All experiments were performed at constant temperatures between 700 and 1050 °C to obtain the necessary information for describing the reaction rate equation in an Arrhenius form; the heating rate was 20 °C/min for both samples. The experiments led to almost similar results for both samples. The activation energies of CO2 gasification were approximately 160 kJ/mol and 170 kJ/mol for uncondensed and condensed lignin char, respectively. The activation energies of steam gasification were approximately 90 kJ/mol and 100 kJ/mol for uncondensed and condensed lignin char, respectively
Ternary Adsorption of Methane, Water, and Carbon Dioxide in Zeolite Na-ZSM‑5 Studied Using in Situ ATR-FTIR Spectroscopy
The main component
in biogas and natural gas is methane, but these
gases also contain water and carbon dioxide that often have to be
removed in order to increase the calorific value of the gas. Membrane
and adsorbent-based technologies using zeolites are interesting alternatives
for efficient separation of these components. To develop efficient
processes, it is essential to know the adsorption properties of the
zeolite. In the present work, adsorption of methane, carbon dioxide,
and water from ternary mixtures in high silica zeolite Na-ZSM-5 was
studied using in situ ATR (attenuated total reflection)–FTIR
(Fourier transform infrared) spectroscopy. Adsorbed concentrations
were extracted from the infrared spectra, and the obtained loadings
were compared to values predicted by the ideal adsorbed solution theory
(IAST). The IAST could not fully capture the adsorption behavior of
this ternary mixture, indicating that the adsorbed phase is not behaving
as an ideal mixture. The CO<sub>2</sub>/CH<sub>4</sub> adsorption
selectivities determined for the ternary mixtures were compared to
selectivities determined for binary mixtures in our previous work,
indicating that the presence of water slightly improves the CO<sub>2</sub>/CH<sub>4</sub> adsorption selectivity at lower temperatures.
Further, the results show that water and carbon dioxide are adsorbed
preferentially over methane in high silica zeolite Na-ZSM-5
Effect of Water on the Adsorption of Methane and Carbon Dioxide in Zeolite Na-ZSM‑5 Studied Using <i>in Situ</i> ATR-FTIR Spectroscopy
Methane
is the main component in biogas and natural gas along with
contaminants such as water and carbon dioxide. Separation of methane
from these contaminants is therefore an important step in the upgrading
process. Zeolite adsorbents and zeolite membranes have great potential
to be cost-efficient candidates for upgrading biogas and natural gas,
and in both of these applications, knowing the nature of the competitive
adsorption is of great importance to further develop the properties
of the zeolite materials. The binary adsorption of methane and carbon
dioxide in zeolites has been studied to some extent, but the influence
of water has been much less studied. In the present work, <i>in situ</i> ATR (attenuated total reflection)–FTIR (Fourier
transform infrared) spectroscopy was used to study the adsorption
of water/methane and water/carbon dioxide from binary mixtures in
a high-silica Na-ZSM-5 zeolite film at various gas compositions and
temperatures. Adsorbed concentrations for all species were determined
from the recorded IR spectra, and the experimental values were compared
to values predicted using the ideal adsorbed solution theory (IAST).
At lower temperatures (35, 50, and 85 °C), the IAST was able
to predict the binary adsorption of water and methane, whereas the
values predicted by the IAST deviated from the experimental data at
the highest temperature (120 °C). For the binary adsorption of
water and carbon dioxide, the IAST could not predict the adsorption
values accurately. This discrepancy was assigned to the particular
adsorption behavior of water in high-silica MFI forming clusters at
hydrophilic sites. However, the predicted values did follow the same
trend as the experimental values. The adsorption selectivity was determined,
and it was found that the H<sub>2</sub>O/CH<sub>4</sub> adsorption
selectivity was decreasing with increasing water content in the gas
phase at low temperatures whereas the selectivity was increasing at
higher temperatures. The H<sub>2</sub>O/CO<sub>2</sub> adsorption
selectivity was increasing with increasing water content at all temperatures
Comparative Study of the Effect of Defects on Selective Adsorption of Butanol from Butanol/Water Binary Vapor Mixtures in Silicalite‑1 Films
A promising route for sustainable
1-butanol (butanol) production
is ABE (acetone, butanol, ethanol) fermentation. However, recovery
of the products is challenging because of the low concentrations obtained
in the aqueous solution, thus hampering large-scale production of
biobutanol. Membrane and adsorbent-based technologies using hydrophobic
zeolites are interesting alternatives to traditional separation techniques
(e.g., distillation) for energy-efficient separation of butanol from
aqueous mixtures. To maximize the butanol over water selectivity of
the material, it is important to reduce the number of hydrophilic
adsorption sites. This can, for instance, be achieved by reducing
the density of lattice defect sites where polar silanol groups are
found. The density of silanol defects can be reduced by preparing
the zeolite at neutral pH instead of using traditional synthesis solutions
with high pH. In this work, binary adsorption of butanol and water
in two silicalite-1 films was studied using in situ attenuated total
reflectance–Fourier transform infrared (ATR-FTIR) spectroscopy
under equal experimental conditions. One of the films was prepared
in fluoride medium, whereas the other one was prepared at high pH
using traditional synthesis conditions. The amounts of water and butanol
adsorbed from binary vapor mixtures of varying composition were determined
at 35 and 50 °C, and the corresponding adsorption selectivities
were also obtained. Both samples showed very high selectivities (100–23 000)
toward butanol under the conditions studied. The sample having low
density of defects, in general, showed ca. a factor 10 times higher
butanol selectivity than the sample having a higher density of defects
at the same experimental conditions. This difference was due to a
much lower adsorption of water in the sample with low density of internal
defects. Analysis of molecular simulation trajectories provides insights
on the local selectivities in the zeolite channel network and at the
film surface