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Clays and Clay Minerals

, Volume 30, Issue 5, pp 347–352 | Cite as

Surface Properties of Sepiolite from Amboseli, Tanzania, and Its Catalytic Activity for Ethanol Decomposition

  • A. J. Dandy
  • M. S. Nadiye-Tabbiruka
Article

Abstract

The catalytic activity of sepiolite from Amboseli, Tanzania, for the dehydration and dehydrogenation of ethanol at 150°–300°C has been studied using a flow reactor. Both reactions occur, but the catalyst activity decreases with use. The products include water, carbon dioxide, ethene, ethanal (acetaldehyde), diethyl ether, but-1,3-diene, but-2-enal (crotonaldehyde), and an unidentified aromatic compound. The proportions change with temperature, the dehydrogenation reaction being favored at the higher temperatures. The BET surface areas of the sepiolite are 316 m2/g (nitrogen adsorption at — 197°C) and 212 m2/g (ethanol vapor adsorption at 25°C, assuming a molecular cross-sectional area of 24.6 Å2), indicating a possible greater penetration of pores and channels by nitrogen compared with ethanol vapor under these conditions. The pore-size distribution reveals that approximately 55% of the surface area measured by nitrogen adsorption is contributed by micropores.

Key Words

Adsorption Catalysis Ethanol Pore size Sepiolite Surface area 

Резюме

Резюме—Исследовалась каталитическая активность сепиолита из Амбосели, Танзания, на дегидра-тацию и дегидрирование этаноля при 150°–300°С при помощи проточного реактора. Обе реакции происходят, но активность катализатора уменьшается со временем его использования. Продукты включают: воду, углекислоту, этен, этаноль (ацетальдегид), двухэфир, бут-1,3-диен, бут-2-енал, и неопределенное ароматическое соединение. Пропорции изменяются с температурой, реакция деги-дрирования преобладает при больших температурах. Площади поверхности сепиолита, определен-ные методом БЭТ, равны 316 м2/г (адсорбция азота при–197°С) и 212 м2/г (адсорбция пара этаноля при 25°С), предполагая, что площадь молекулярного поперечного сечения равна 24,6 Å2. Это указывает на возможное большое проникание азота в поры и каналы сепиолита по сравнению с прониканием пара этаноля при таких же условиях. Распределение пор по размерам указывает на то, что приблизительно 55% площади поверхности, измеренной адсорбцией азота, принадлежит микропорам. [E.C.]

Resümee

Die katalytische Wirkung des Sepiolith von Amboseli, Tanzania, bei der Dehydratation und Dehydrierung von Äthanol bei 150°–300°C wurde unter Verwendung eines Durchflußreaktors untersucht. Beide Reaktionen treten ein, aber die katalytische Wirkung nahm mit der Zeit ab. Die Produkte waren Wasser, Kohlendioxid, Äthylen, Äthanal (Acetaldehyd), Diäthyläther, But-1,3-Dien, But-2-Enal (Crotonaldehyd), und eine unidentifizierte aromatische Verbindung. Die Mengenverhältnisse veränderten sich mit der Temperatur, die Dehydrierungsreaktion wurde bei höheren Temperaturen begünstigt. Die BET-Oberfiäche des Sepiolith beträgt 316 m2/g (Stickstoffadsorption bei -197°C) und 212 m2/g (Äthanoldampf-Adsorption bei 25°C), was auf eine molekulare Querschnittsfläche von 24,6 Å2 schließen läßt. Außerdem deutet dies daraufhin, daß unter den gegebenen Bedingungen Stickstoff weiter in Poren und Kanäle eindringen kann als Äthanoldampf. Die Verteilung der Porengröße zeigt, daß etwa 55% der durch Stickstoffadsorption gemessenen Oberfläche von Mikroporen stammt. [U.W.]

Résumé

On a étudié avec un réacteur à flot l’activité catalytique de la sepiolite d’Amboseli, Tanzanie, pour la déshydration et la déshydrogènation d’éthanol à 15°–30O°C. On observe les deux réactions, mais l’activité catalyste décroit avec l’emploi. Les produits comprennent l’eau, le carbone dioxide, l’éthène, l’éthanal (acétaldéhyde), l’éther diethyl, but-l,3-diène, but-2-énal (crotonaldéhyde), et un composé aromatique non-identifié. Les proportions changent avec la température, la réaction de déshydrogènation étant favorisée à de plus hautes températures. Les aires de surface de la sépiolite sont 316 m2/g (adsorption de nitrogène à — 197°C) et 212 m2/g adsorption (de vapeur d’éthanol) à 25°C, en supposant que l’aire moléculaire d’une section transversale est 24,6 Å2, indiquant possiblement une plus grande pénétration possible de nitrogène dans les pores et les canaux en comparaison avec la vapeur d’éthanol sous les mêmes conditions. La distribution de tailles de pores révèle qu’approximativement 55% de la surface mesurée par l’adsorption par le nitrogène est contribué par des micropores. [D.J.]

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Copyright information

© The Clay Minerals Society 1982

Authors and Affiliations

  • A. J. Dandy
    • 1
  • M. S. Nadiye-Tabbiruka
    • 2
  1. 1.School of Natural ResourcesUniversity of the South PacificSuvaFiji
  2. 2.Department of ChemistryMakerere UniversityKampalaUganda

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