Oxidative Coupling of Methane (OCM) is a reaction for converting methane, as the main component of natural gas, directly to ethylene. The importance of OCM is based on the economic interest of ethylene which can be used widely in different chemical processes. Currently about 150 billion cubic meters of methane are flared or vented annually which leads to production of about 400 million tonnes of carbon dioxide each year. This makes OCM of great environmental benefit as well because of the current non-sustainable use of natural gas. However, OCM research has not found its industrial application till now after almost three decades of research, due to low yields of ethylene production. This work is focused on applicability of the fluidized-bed reactor (FBR) concept for OCM and testing the novel idea of fluidized-bed membrane reactor (FBMR) for the first time on OCM. In the course of this work, two FBRs and one FBMR have been tested in pilot-plant scale. All reactors are installed in the UniCat OCM mini-plant based in Technische Universität Berlin. FBRs have the advantage of providing an isothermal catalyst bed to prevent hot-spot formation, which is one of the main problems of OCM due to highly exothermic reactions. The FeCrAlloy reactor is designed for studying the material influence on OCM FBRs and to see if this material can provide better results in contrast with OCM stainless steel reactors. The reactor of the same dimensions was designed using quartz glass as the reactor material, as it is an inert material to have a base of comparison. Different reaction temperatures and reactant compositions have been tested for both reactors and the highest C2 yield achieved from FeCrAlloy FBR was 20% (methane conversion of 49%) at low nitrogen content of 40%. The maximum C2 yield achieved from the quartz glass reactor in the same conditions was 23% (methane conversion of 47%). The results showed the applicability of FeCrAlloy for OCM although it shows lower performance in comparison with quartz glass because of material reactivity at high temperatures, however, the difference is not so significant and it can be even lower in larger scales where the effect of the reactor wall material decreases. The scale of FBRs used in this work is one of the largest OCM FBRs reported in accessible literature and the C2 yield obtained is the highest as well. The FeCrAlloy FBR was modified by installing two membranes in order to study the novel concept of OCM FBMR, resulting in a performance enhancement achieved by dosing oxygen inside the fluidized-bed through the membranes. In this case, the fluidized-bed provides an isothermal catalyst bed and the membranes provide distributed dosage of oxygen, supplying the advantages of both fluidized-bed and membrane reactors in one reactor. The highest C2 yield achieved from this reactor was 19.5% with a gas flow containing 55% nitrogen dilution, which is a 2% improvement of C2 yield in comparison with the result from the FeCrAlloy FBR without membranes at the same conditions (17.5% C2 yield). The catalyst used for most of the experiments was 2.2%Na2WO4-2%Mn/SiO2, prepared by incipient wetness impregnation. Two other catalysts were prepared, by coating in a fluidized bed granulator, as well as a catalyst prepared on a monolithic ordered mesoporous silica support. However, the performance of these two catalysts was not as promising as the conventional catalyst prepared by incipient wetness impregnation. The second chapter of this work is a detailed explanation of experimental set-up used in this work. The experimental results from fluidized-bed reactors and fluidized-bed membrane reactor are discussed in chapter 3 and 4. The last chapter is about conclusion and the new ideas for the future work.


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    Title :

    Analysis of fluidized-bed and fluidized-bed-membrane reactor concepts for oxidative coupling of methane


    Additional title:

    Die Analyse der Wirbelschicht- und Wirbelschicht-Membranereaktor Konzepte für oxidative Kopplung von Methan


    Contributors:

    Publication date :

    2016



    Type of media :

    Miscellaneous


    Type of material :

    Electronic Resource


    Language :

    English



    Classification :

    DDC:    629





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