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首页> 外文期刊>Journal de Chimie Physique et de Physico-Chimie Biologique >Coke formation on HFAU and HEMT zeolites. lnfluence of the reaction temperature and propene pressure
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Coke formation on HFAU and HEMT zeolites. lnfluence of the reaction temperature and propene pressure

机译：在HFAU和HEMT沸石上形成焦炭。反应温度和丙烯压力的影响

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The formation of coke from propene (P_p = 1.3 kPa and 13 kPa) was investigated on HFAU and HEMT zeolites in a microbalance for temperatures ranging from 120 deg C to 450 deg C. For both zeolites, the greater the propene pressure and the lower the temperature the faster the initial coke formation. However for high propene pressure, initial coke formation is faster with MEMT zeolite. This can be related to the stronger acidity of the HEMT sample. For low propene pressure and after 420 minutes of coking, a minimum in coke is observed for T = 350 deg C, which can be related to the difference between the rate of formation and the rate of retention of coke molecules. At low temperature, due to their low volatility, oligomers are easily formed and retained in the zeolite pores. These molecules can be totally eliminated by an adequate thermal treatment in vacuum. At higher temperature, only aromatic or polyaromatic compounds which present a size larger than the pore apertures can be retained in the cavities of the zeolites. The greater the reaction time, the faster the retention. Whatever the reaction temperature, coke molecules are more homogeneously distributed in the HEMT crystallites than in those of HFAU samples. For this latter zeolite coke molecules are preferentially formed in the cavities located near the outer surface of the crystallites (shell coking).
机译：研究了在HFAU和HEMT沸石上在120℃至450℃温度范围内的微量天平上由丙烯形成的焦炭（P_p = 1.3 kPa和13 kPa）的情况。对于两种沸石，丙烯压力都越大，且温度越高，初始焦炭形成越快。但是，对于较高的丙烯压力，使用MEMT沸石可以更快地形成初始焦炭。这可能与HEMT样品的强酸性有关。对于低丙烯压力和焦化420分钟后，对于T = 350℃，观察到最低焦炭，这可能与焦炭分子的形成速率和保留速率之间的差异有关。在低温下，由于其低挥发性，容易形成低聚物并保留在沸石孔中。通过在真空中进行适当的热处理，可以完全消除这些分子。在较高的温度下，只有尺寸大于孔尺寸的芳族或多芳族化合物可以保留在沸石的空腔中。反应时间越长，保留速度越快。无论反应温度如何，与HFAU样品相比，焦炭分子在HEMT微晶中的分布更均匀。为此，后者的沸石焦分子优选在微晶外表面附近的腔中形成（壳焦化）。

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