Oxidative coupling of methane over chloride-modified magnesium oxide catalysts /
The oxidative coupling of methane, to produce ethane and ethylene, is catalyzed by a number of metal oxide systems. Of particular interest is lithium-doped magnesium oxide, Li-MgO, which has been extensively investigated as an oxidative coupling catalyst. The incorporation of chloride ions into Li-...
| Main Author: | |
|---|---|
| Format: | Thesis Book |
| Language: | English |
| Published: |
[Place of publication not identified] :
[publisher not identified] ;
1996.
|
| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=743266861&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | The oxidative coupling of methane, to produce ethane and ethylene, is catalyzed by a number of metal oxide systems. Of particular interest is lithium-doped magnesium oxide, Li-MgO, which has been extensively investigated as an oxidative coupling catalyst. The incorporation of chloride ions into Li-MgO results in a more active catalyst that gives ethylene-to-ethane product ratios that are significantly higher than for Li+MgO. High ethylene yields are desirable due to the value of ethylene as a feedstock for the chemical industry. Exceptionally large C2H4/C2H, ratios are obtained at Cl/Li ratios of near unity. These high C2H4/C2H6ratios are a result of the enhanced activity for the dehydrogenation of ethane over these Li'-MgO-Cl- catalysts. The enhancement by chloride is dependent on the Cl/Li ratio; not the absolute amount of chloride present. At CVLI ratios below unity, the promotional effect of chloride rapidly declines and the C2H4/C2H, product ratio drops to the level of the unpromoted Li-MgO catalyst. Chloride modifies the catalyst, reducing the basicity, so that C02 does not poison Li+MgO-Cl- as it does L@-MgO. This poisoning by C02has a major effect on the reaction kinetics, significantly reducing the intrinsic activity of Li+MgO. No such poisoning takes place over Li'-MgO-Cl-. Although the Cl/Li ratio is of primary importance for enhanced C2H4selectivity, long term catalyst stability depends on an excess of Li and Cl to provide a reservoir. Under typical reaction conditions at 650'C, both are slowly lost from the catalyst surface. It is possible to restore the activity and selectivity to a partially deactivated Li-MgO-Cl- catalyst by addition of HCI to the feed stream. |
|---|---|
| Item Description: | Vita. "Major Subject: Chemistry". |
| Physical Description: | xii, 122 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references. |