# Effect of Nano-Sized Cavities in SAPO-34 Zeolite on Thermodynamics of Adsorbed Gas Mixtures

^{1}

^{2}

^{*}

^{†}

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

^{2}/g, 0.297 cc/g and 0.552 nm. The particle sizes were 1–2 μm. The acid site density was calculated from SEM-EDS and NH

_{3}-TPD data to be 1.0 mmol/g.

## 3. Results and Discussion

^{3}, indicate that the size difference would not be significant unless the adsorbates are densely packed, but which would not occur at the pressures used in this work. Note: Due to the absence of data, the kinetic diameter of DME was estimated from the kinetic diameter of methanol, by assuming that DME is 5% larger than methanol which is based on their molecular structures and that their diffusion coefficient in SAPO-34 are of the same order of magnitude.

_{i}

^{0}is the gas pressure of component i that gives it the spreading pressure π, that is, P

_{i}

^{0}is basically the virtual pressure of component i. Using the Langmuir isotherm in Equation (1) for the surface concentrations C

_{1}and C

_{2}gives

_{i}is the adsorption equilibrium constant of component i, “ln” denotes the natural logarithm, and P

_{i}

^{0}is not known and it has to be solved for. Equation (2) shows that the solution requires the Langmuir isotherm adsorption constants (b

_{i}) to satisfy

_{i}is the Henry (adsorption) constant of component i and the superscript “sat” denotes saturation. In our work, in Equation (4), the second site used Henry’s law because the adsorption on it is not strong and it would need a very high pressure to saturate it. In summary, the use of Equation (4) in Equation (1) will give

_{i}

^{0}, the virtual gas pressure of component i, is obtained, which would then be used with just the acid site isotherm equation to get the adsorbate concentration on the acid sites.

^{sat}= 1.0 mmol/g, b

_{1}= 0.50 kPa

^{−1}, K

_{1}= 0.001 mmol/g/kPa; for adsorbate B, C

^{sat}= 1.0 mmol/g, b

_{2}= 0.038 kPa

^{−1}, K

_{2}= 0.010 mmol/g/kPa. These parameters roughly describe the case where adsorbate A is a small, polar molecule and adsorbate B is a longer, non-polar molecule, e.g., methanol and propene, respectively.

## 4. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 1.**Heat of adsorption as a function of surface concentration of dimethyl ether on SAPO-34 zeolite at 25 °C (▲), 60 °C (●) and 100 °C (■). The arrow indicates the acid site density, which is 1 mmol/g.

**Figure 2.**Adsorption isotherms of dimethyl ether on SAPO-34 zeolite at 25 °C (●), 60 °C (▲) and 100 °C (□). The lines show the best fit curves calculated as the sum of the component Langmuir and Henry isotherms shown in the inset.

**Figure 3.**Heat of adsorption as a function of surface concentration of ethene on SAPO-34 zeolite at 25 °C. The inset shows the corresponding isotherm and the best fit curve and its components of Langmuir and Henry isotherms. The arrows indicate the acid site density, which is 1 mmol/g.

**Figure 4.**Heat of adsorption as a function of total surface concentration of a 57:43 mol% DME-ethene gas mixture at 25 °C. The inset shows the corresponding total adsorption isotherm. The arrows indicate the acid site density, which is 1 mmol/g.

**Figure 5.**Surface concentration of ethene by adsorption from a 57:43 mol% DME-ethene gas mixture. The curves show the concentrations calculated using the multicomponent Langmuir isotherm and the IAST. The inset shows the corresponding surface concentration of DME. The arrow indicates the acid site density, which is 1 mmol/g.

**Figure 6.**Type 1 site surface concentrations in a mixture as a function of the gas phase composition calculated by the multicomponent Langmuir isotherm and the IAST for adsorption on Type 1 and Type 2 dual sites.

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**MDPI and ACS Style**

Wang, F.; Kobayashi, Y.; Li, Y.; Wang, D.; Wang, Y. Effect of Nano-Sized Cavities in SAPO-34 Zeolite on Thermodynamics of Adsorbed Gas Mixtures. *Nanomaterials* **2018**, *8*, 672.
https://doi.org/10.3390/nano8090672

**AMA Style**

Wang F, Kobayashi Y, Li Y, Wang D, Wang Y. Effect of Nano-Sized Cavities in SAPO-34 Zeolite on Thermodynamics of Adsorbed Gas Mixtures. *Nanomaterials*. 2018; 8(9):672.
https://doi.org/10.3390/nano8090672

**Chicago/Turabian Style**

Wang, Fei, Yasukazu Kobayashi, Yuxin Li, Dezheng Wang, and Yao Wang. 2018. "Effect of Nano-Sized Cavities in SAPO-34 Zeolite on Thermodynamics of Adsorbed Gas Mixtures" *Nanomaterials* 8, no. 9: 672.
https://doi.org/10.3390/nano8090672