CH4/N2 Adsorptive Separation on Zeolite X/AC Composites

Cai Long Xue,Rui Feng Li,Wen Ping Cheng,Wen Ming Hao,Jing Hong Ma

doi:10.1155/2019/2078360

Abstract

A series of zeolite X/activated carbon (AC) composites were prepared from the same starting materials at various activation time. The corresponding modified samples were obtained by being treated with diluted NH4Cl solution. The relationship between porosity development, surface properties, and CH4/N2 adsorption performance was investigated. The increase of micropore volume is beneficial to the improvement of CH4 and N2 adsorption capacity, but more sensitive for CH4. In addition, the polar functional groups of zeolite X/AC composites may enhance CH4 adsorption capacity. More importantly, both developing micropore structure and surface modification contributed to enhance the adsorption selectivity αCH4/N2. As the optimum sample of these studies, HZAC(24) showed CH4 adsorption capacity of 17.3 cm3/g and the highest adsorption selectivity αCH4/N2 of 3.4. The CH4 and N2 adsorption isotherms of all samples can be well fitted by the Langmuir–Freundlich model. HZAC(24) showed an excellent cyclability of adsorption/desorption of CH4 with a neglectable capacity loss after subsequent cycles. Moreover, HZAC(24) displayed relatively rapid adsorption kinetics. These properties of zeolite X/AC composites are essential for the adsorptive separation of CH4 from N2 in the pressure swing adsorption (PSA) process.

Highlights

E main aim in this work is to introduce amine modifications in a series of zeolite X/activated carbon (AC) composites with different activation time in order to increase the interactions with CH4 without improving those with gases. is strategy will improve the potential of these materials to separate CH4/N2 mixtures, making these materials candidates for natural gas upgrading. e effect of pore texture and surface properties of the adsorbents on the adsorption performance of CH4 and N2 was investigated in detail
It can be seen that, as far as ta ≤ 24 h, the SBET, Smic, Vtotal, and Vmic of ZAC(ta) samples presented a significant rising trend, and it occurred sharply decrease thereafter, while the Sext was increasing with lengthening the activated time. is means that extending the activation time when ta ≤ 24 h mainly induces the creation of new pores, while widening of pores becomes the main mechanism of porosity development with longer activation time [25]
Zeolite X/AC composites with different pore textures were prepared and treated by diluted NH4Cl solution

Summary

Introduction

Activated carbons have higher equilibrium selectivity for CH4 over N2 but smaller adsorption capacities for CH4 than zeolites. It can be seen that, as far as ta ≤ 24 h, the SBET, Smic, Vtotal, and Vmic of ZAC(ta) samples presented a significant rising trend, and it occurred sharply decrease thereafter, while the Sext was increasing with lengthening the activated time. In comparison with ZAC(ta), the pore structure parameters of HZAC(ta) decrease except Sext, due to the partially collapse of the crystalline structure in the composites during surface modification [32].

Results

Conclusion