Transformation of Dilute Ethylene at High Temperature on Micro- and Nano-Sized H-ZSM-5 Zeolites
Antoine BeuqueMathias BarreauÉlise BerrierJean‐François PaulNuno BatalhaAlexander SachseLudovic Pinard
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Ethylene dehydroaromatisation (EDA) was investigated at 700 °C under 1 bar of ethylene (5 mol% in N2) over a micro-(M) and a nano-sized (N) H-ZSM-5. On the M zeolite an induction period followed by deactivation was observed, which could be related to the presence of long diffusion path lengths in this sample, leading to mass transfer resistance. During the induction step, the aromatics yield increases, despite a significant loss of the acid site concentration as a result of coking. This induction period corresponds to the formation of an active hydrocarbon pool (HCP) composed of units of 2 to 5 aromatic rings with a molecular weight ranging from 130 to 220 g mol−1 (light coke). A kinetic study revealed that the developing HCP species is two times more active than Brønsted acid sites in the fresh zeolite. Diffusion limitations yet impact the product desorption by promoting coke growth and, therefore the deactivation of the HCP and hence of the catalyst. From MA-LDI/LDI-TOF MS (Matrix Assisted Laser Desorption Ionization—Time of Flight Mass Spectroscopy) characterisation was deduced that even after complete catalyst deactivation, the as-deposited coke continues growing at the external surface of the zeolite by condensation reactions, thus leading to heavy coke composed of more than 100 carbon atoms and a molar mass exceeding 1300 g mol−1. Unlike the micro-sized zeolite, the nano-scaled zeolite features a short diffusion path length and promotes fast formation of the active HCP. As a result, higher activity and selectivity into benzene were observed, whilst catalyst deactivation was significantly mitigated.Keywords:
Induction period
Abstract Methane dehydroaromatization (MDA) over Mo/HZSM‐5 has been hypothesized in literature to proceed via a two‐step mechanism: methane is first converted to ethylene on the molybdenum (Mo) functionality and then ethylene is oligomerized, cyclized and dehydrogenated on the Brønsted acid sites (BAS) of the HZSM‐5 support. This hypothesis is tested by studying the conversion of ethylene at the same conditions as used for MDA, namely 700 °C, atmospheric pressure, and by co‐feeding experiments with H 2 and CH 4 . Our results suggest that ethylene is not the main intermediate for MDA, because the aromatic selectivities obtained from methane conversion are higher than selectivities measured during ethylene conversion. Furthermore, carbonaceous deposits formed during MDA have a lower density, are more hydrogenated and more active than the ones formed during ethylene aromatization (EDA). Similarly as for MDA, an activation period in which Mo carburizes to its active phase and an induction period, in which aromatics formation rates increase to their maximum are observed for ethylene conversion. The induction period, which was explained by the buildup of a hydrocarbon pool (HCP) is much faster with methane than with ethylene. This period, is attributed to a slow buildup of hydrocarbons, strongly adsorbed on Mo sites, because it is only observed with catalysts containing Mo. Hydrogen co‐feeding with ethylene leads to the formation of more reactive coke species and a significantly prolonged lifetime of the catalyst, but not to a faster buildup of the HCP.
Aromatization
Induction period
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발 土壤에서 改良劑로써 Zeolite施用이 豌豆의 生育 및 窒素固定에 미치는 影響을 檢討고져 N.P.K 및 Zeolite 等 6個處理를 vinyl house內에서 pot試驗으로 遂行한 結果는 다음과 같다.
1. 乾物重은 窒素肥料 旅用區가 窒素 無施用區에 比하여 減少되는 傾向이나 Zeolite 施用區는 오히려 增加되었다.
2. 植物體中 窒素含量은 窒素와 Zeolite을 倂用함으로서 增加되었고 Zeolite施用量은 2% 施用이 1%보다 窒素含量이 낮았다. 그러나 土壤中의 窒素殘在量은 2%區에서 많았다.
3. 植物體中의 標識窒素(^(15)NH 肥料의 由來된 窒素量은 Zeolite를 倂用하는 편이 減少되는 傾向이며 이러한 傾向은 植物體 各 部位에서도 같은 樣相을 보였다.
4. 植物體中의 窒素固定에 由來된 窒素量은 Zeolite 施用區에서 많았다. 그러나 窒素肥料 施用區에서는 그 增加量이 적었다.
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This test has studied the influence of natural zeolite and modified zeolites on the adsorption and desorption characteristic of Cu2+.The adsorption isotherm of natural zeolite,modified zeolites to Cu2+ are conformed to the Langmuir equation,the Freundlich equation and the Temkin equation.As for natural zeolite and modified zoelites,the correlation coefficients of Freundlich equation is the highest.The adsorptive capacity order of four kinds of zeolites to the Cu2+ is NH4-zeolite K-zeolite Mg-zeolite Zeolite.The order related closely to the valences and hydrated radius of the coordinated cations.Desorption capacity and desoption rate order of zeolite and modified zeolite is zeolite Mg-zeolite K-zeolite NH4-zeolite.TheA-zeolite,K-zeolite and Mg-zeolite may not only enhance the adsorption of Cu2+,can but also reduce the desorption ratio of Cu2+.So modified zeolites has a broad application prospect in the agricultural practice,especially in soil contaminated by heavy metals.
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수중의 Sr과 Cs 이온을 제거하기 위하여 폴리술폰(polysulfone, PS)을 이용한 제올라이트 고정화로서 PS-zeolite 비드를 제조하였다. PS-zeolite는 SEM, XRD, FT-IR, TGA를 이용하여 특성 및 구조를 분석하였다. PS-zeolite 비드를 제조하기 위한 최적조건은 PS 1.25 g과 제올라이트 A 2 g이었다. 용액 pH의 증가에 따라 PS-zeolite 비드에 의한 Sr과 Cs 이온의 제거효율은 증가하였지만, pH 4 이상에서 일정하게 되었다. 본 연구에서 제조된 PS-zeolite 비드는 Na+, K+, Mg2+ 및 CA₂+와 같은 공존이온이 존재하더라도 Sr과 Cs 이온에 대한 높은 선택도를 나타내었다. 또한, 흡착과정에서 PS-zeolite 비드로부터 제올라이트 입자가 탈리되지 않았으며, PS-zeolite 비드는 SEM 이미지 상에서 구조가 유지되었다. PS-zeolite 비드에 의한 Sr과 Cs의 제거 효율은 5회 흡착-탈착 실험을 반복하여도 90% 이상 유지되었다. 본 연구에서는 이 결과로서 PS-zeolite 비드가 Sr과 Cs 이온의 흡착제로서 적용가능하다 것을 확인할 수 있었다. 또한, PS-zeolite는 산업폐수처리를 위한 방사성 이온 제거용 흡착제로서도 적용이 가능할 것이다.
Polysulfone
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國內産 天然 Zeolite를 利用하여 低廉한 重金屬吸着劑의 開發을 위해 이온 交換容量이 큰 Zeolite를 合成하고 이것의 重金屬 吸着能力을 調査하였다.
天然 Zeolite의 主 構成 粘土鑛物은 Clinoptilolite와 Mordenite였으나 合成 Zeolite는 Phillipsite였다.
試料에 依한 Cu와 Zn의 吸着反應은 1時間 以後에 吸着平衡에 到達하였다. 吸着量은 試料量 및 添加重金屬 이온들의 濃度가 增加할수록 增加하는 傾向이었으며 合成 Zeolite가 天然 Zeolite에 比해 高濃度에서 吸着率이 높았다.
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Clinoptilolite
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Induction period
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Thermal desorption spectroscopy
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