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Desilicated ZSM-5 zeolite as catalyst for the dehydration of ethanol.

机译：脱硅的ZSM-5沸石作为乙醇脱水的催化剂。

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摘要

The new desilicated forms of the zeolites X, Y and ZSM-5 were prepared by the selective removal of silicon atoms from the parent zeolites in an aqueous solution of base. This treatment, which decreases the Si/Al ratio while keeping the zeolite framework almost unmodified, enhanced the ion exchange capacities of all the zeolites, a property which can be exploited industrially for the X and Y zeolites since the desilicated forms had higher total ion removal rates of calcium and magnesium ions from hard water.;Similarly, desilication results in a higher density of acid sites as shown in the following. ;In catalytic testing studies, the desilicated ZSM-5 zeolite was found to display a higher total conversion in the dehydration of absolute ethanol into ethylene, however the selectivity for ethylene was higher for the parent zeolite at lower reaction temperatures. This was a direct consequence of the higher density of acid sites on the desilicated zeolite, which is comprised of BAS II in the presence of "unusual" Lewis acid sites of type II (LAS II). These Lewis acid sites were also detected by ;Upon steam treatment of the desilicated zeolite, both the total conversion and selectivity for ethylene improved significantly in the dehydration of absolute ethanol. Steaming was capable of rehydrating the LAS II into BAS II, a reconversion which was previously too demanding to be achieved under the conditions of catalytic testing, hence the low selectivity for ethylene at lower reaction temperatures. Further evidence of this reconversion is provided by catalytic testing with aqueous ethanol for which the desilicated zeolite achieved higher total conversions and selectivities for ethylene than the parent at all reaction temperatures, and the selectivity for ethylene was always significantly higher than was achieved with absolute ethanol. This has important implications for the Bioethanol to Ethylene Process.;A cut off temperature was also confirmed for the dehydration of ethanol, at which the reaction mechanism changed from the two step conversion into diethyl ether and ethylene, into the one step, direct conversion to ethylene. These temperature ranges were determined to be 200-225
机译：通过在碱水溶液中从母体沸石中选择性除去硅原子来制备沸石X，Y和ZSM-5的新的脱硅形式。这种处理降低了Si / Al的比例，同时保持沸石骨架几乎未改性，从而提高了所有沸石的离子交换能力，该特性可用于X和Y沸石的工业生产，因为脱硅形式具有较高的总离子去除率硬水中钙离子和镁离子的比率较高；类似地，脱硅作用会导致较高的酸位密度，如下所示。 ；在催化测试研究中，发现无硅ZSM-5沸石在无水乙醇脱水成乙烯中显示出更高的总转化率，但是在较低的反应温度下，母体沸石对乙烯的选择性更高。这是脱硅沸石上酸性位点密度较高的直接结果，该沸石由BAS II组成，且存在II型“异常”路易斯酸性位点（LAS II）。这些路易斯酸位点也可以通过脱硅沸石的蒸汽处理来检测，在无水乙醇脱水中，乙烯的总转化率和选择性均显着提高。汽蒸能够将LAS II重新水合为BAS II，这是以前在催化测试条件下太过需要实现的转化，因此在较低的反应温度下对乙烯的选择性低。通过用乙醇水溶液进行的催化试验提供了这种再转化的进一步证据，在该试验中，脱硅沸石在所有反应温度下对乙烯的总转化率和对乙烯的选择性均高于母体，并且对乙烯的选择性始终明显高于用无水乙醇获得的乙烯。这对于生物乙醇制乙烯工艺具有重要意义。还确定了乙醇脱水的临界温度，在该温度下，反应机理从两步转化为二乙醚和乙烯，转变为一步，直接转化为乙醇。乙烯。这些温度范围确定为200-225

著录项

  • 作者

    Ramsaran, Arlene Ruth.;

  • 作者单位

    Concordia University (Canada).;

  • 授予单位 Concordia University (Canada).;
  • 学科 Chemistry Inorganic.;Chemistry Organic.
  • 学位 Ph.D.
  • 年度 1996
  • 页码 292 p.
  • 总页数 292
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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