(630v) A Comparative Investigation of Micro- and Mesoporous Materials On the Pressure Swing Adsorption Behaviors for N2 and CH4 Separation

A comparative investigation of micro- and mesoporous
materials on the pressure swing adsorption behaviors for N₂ and CH₄
separation

Fengjuan Shi ^a, Hongxing Dai ^a,*,
Lei Zhang ^a, Jiguang Deng ^a, Hong He ^a, Jian
Li ^b, Yingshu
Liu ^c, Kai Wang ^d

^aDepartment of Chemistry and Chemical
Engineering, College of Environmental and Energy Engineering, Beijing
University of Technology, Beijing 100124, China. Email: hxdai@bjut.edu.cn

^bInstitute of Environmental Engineering,
College of Environmental and Energy Engineering, Beijing University of
Technology, Beijing 100124, China

^cSchool of Mechanical Engineering, University of Science and Technology
Beijing, Beijing 100083, China

^dSchool of Resource and Safety Engineering, China University of Mining
& Technology Beijing, Beijing 100083, China

There are
mainly O₂, N₂, and CH₄ in natural gas or ventilation
air methane (VAM), in which the concentrations of O₂ and CH₄
must be strictly controlled so as to avoid the explosion limit range. Hence, the
separation of O₂/CH₄ and/or N₂/CH₄ is
of significance in the utilization of natural gas or VAM. Pressure swing
adsorption (PSA) is one of the important strategies for the purification and
bulk separation of such a gas mixture. The key issue is the availability of
effective adsorbents with sufficiently high selectivity and adsorption capacity.
Micro- and mesoporous materials¹ are
good candidates for the separation of O₂/CH₄ and/or N₂/CH₄.
We herein report the adsorption behaviors of micro- or mesoporous materials for
N₂ and CH₄ separation using the PSA technique. It is
found that the rod-like SBA-15 and MCM-41 mesoporous
materials showed exceptional performance of the separation of N₂
and CH₄.

All of
the micro- or mesoporous materials were synthesized according to the procedures
described in the literature^1a,1b,2.
Their surface areas and pore structures were determined by the BET method. The isotherms of N₂ or
CH₄ adsorption-desorption on the porous samples were recorded on the
static PSA apparatus (Micromeritics ASAP 2050). Before measurement, 0.2 g of the sample was pretreated at -0.1
MPa and 150^oC for 2 h. The purity of N₂ and CH₄
was 99.99%. The adsorption temperature and pressure range was 25^oC
and 0~6000 mmHg, respectively.

Table 1 summarizes
the surface areas, N₂ and CH₄ amounts adsorbed at 380 or 1140 mmHg,
and N₂/CH₄ separation factor (Alfa_N2/CH4) of the porous samples. The N₂ or
CH₄ adsorption isotherm for each of the samples was Langmuir type (it
obeys the equation: 1/q = q_m + (1/Bq_m) (1/p),
where B is the Langmuir adsorption constant), the saturated adsorption amount (q_m) can be calculated
according to the intercept and slope of the plot 1/q versus 1/p. For the
two-component (x and y) gas mixture, the separation factor (Alfa_x/y) can be defined as Alfa_x/y = ((q_m)_xB_x)/((q_m)_yB_y).
From Table 1, one can see that (i) there was no clear relationship of the Alfa_N2/CH4 value and N₂ or
CH₄ adsorption amount with the surface area of the porous sample; (ii) among the 4 microporous
samples, ZSM-5 showed the highest N₂ and CH₄
adsorption capacities and Alfa_N2/CH4 value (4.51); (iii) in the
6 mesoporous silica samples, the rod-like SBA-15 and MCM-41 gave unusually high
Alfa_N2/CH4 vales (9.38 and 6.59, respectively) although their N₂ and CH₄
adsorption capacities were lower; and (iv) as for the two mesoporous carbon
materials fabricated from differently morphological SBA-16, the polyhedral SBA-16-derived
mesoporous carbon sample was superior in N₂/CH₄
separation to the spherical
SBA-16-derived counterpart. The far discrepancy in N₂/CH₄ separation performance and their adsorption
capacity of these micro-
or mesoporous materials might be associated with their pore structure as well
as the possibly residual impurities. Detailed investigations are in progress.

Table 1.
Surface areas, N₂ and CH₄
amounts, and Alfa_N2/CH4 values of the porous samples.

References

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