Analysis of equilibrium and dynamic adsorption of benzene vapor over unimodal and bimodal silica-based mixed-metal oxides
Analysis of equilibrium and dynamic adsorption of benzene vapor over unimodal and bimodal silica-based mixed-metal oxides
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DOI：
10.1016/j.cej.2020.125273
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发表时间：
2020-09-15
影响因子：
15.1
通讯作者：
Rezaei, Fateme
中科院分区：
文献类型：
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作者：
Adebayo, Busuyi O.;Lawson, Shane;Rezaei, Fateme
在这项研究中，为了了解二级金属氧化物和载体孔结构对吸附能力和动力学的影响，研究了单峰和双峰硅基混合金属氧化物对苯贫气流的净化。单峰二氧化硅落在微孔和介孔的交界处，即由大微孔和表面积大的小介孔组成，而双峰二氧化硅由大微孔、小介孔和大介孔组成，介孔体积大。二氧化钛和氧化锆混合金属氧化物的表面面积和孔体积由于孔隙的部分堵塞而减小，但相对于裸二氧化硅，它们表现出更好的吸附行为。平衡吸附实验表明，单峰吸附剂对苯的吸收率高于双峰吸附剂，在25℃和101 kPa条件下，对SiO2、TiO2/SiO2和ZrO2/SiO2样品的吸附量分别达到10.05、11.71和11.25 mmol/g。相比之下，当苯蒸汽浓度为465 ppm时，动态突破试验表明，相对于单峰材料，双峰吸附剂的吸附动力学更快，因为它们的孔隙较大，产生的颗粒内扩散阻力较小。研究还发现，二氧化钛或氧化锆的掺入提高了裸二氧化硅的平衡吸附能力，但降低了吸附速率。同样，所有吸附剂的分配系数都在0.31 ~ 1.75 mmol/g/ μ m之间。根据双峰SiO2、TiO2/SiO2和ZrO2/SiO2样品的浓度谱估计的传质系数分别为0.58、0.45和0.41 s（-1）。总的来说，本研究结果表明，在微孔-介孔二氧化硅结构中引入大介孔是开发混合金属氧化物吸附剂的一种简便方法，可以提高吸附能力和动力学，以减少苯蒸气的排放。
In this study, purification of a benzene-lean gas stream over unimodal and bimodal silica-based mixed-metal oxides was investigated for the purpose of understanding the effects of secondary metal oxide and support pore structure on the adsorption capacities and kinetics. The unimodal silica fell in the borderline of micropores and mesopores, i.e., they consisted of large micropores and small mesopores with large surface area, while the bimodal silica consisted of large micropores, small mesopores and large mesopores with large mesopore volume. The titania and zirconia mixed-metal oxides showed reduced surface area and pore volume as a result of partial blockage of the pores, however, they exhibited improved adsorption behavior relative to the bare silica. Equilibrium adsorption measurements revealed unimodal adsorbents are superior to their bimodal analogues by exhibiting higher benzene vapor uptake, with capacities reaching 10.05, 11.71 and 11.25 mmol/g for SiO2, TiO2/SiO2 and ZrO2/SiO2 samples at 25 degrees C and 101 kPa. In contrast, dynamic breakthrough tests with 465 ppm benzene vapor concentration indicated faster adsorption kinetics for bimodal adsorbents relative to unimodal materials as a result of their larger pores which produced lesser intraparticle diffusion resistance. It was also found that, while titania or zirconia incorporation enhances the equilibrium adsorption capacity of the bare silica, it deteriorates the adsorption rate. Similarly, all the adsorbents depicted partition coefficient in the range of 0.31-1.75 mmol/g/mu M. The mass transfer coefficients estimated from concentration profiles of bimodal SiO2, TiO2/SiO2 and ZrO2/SiO2 samples were 0.58 and 0.45, and 0.41 s(-1), respectively. Overall, the findings of this investigation indicated that the introduction of large mesopores in the structure of microporous-mesoporous silica is a facile approach in developing mixed-metal oxide adsorbents with improved adsorption capacity and kinetics for the abatement of benzene vapor emissions.