STEAM REFORMING AND OXIDATIVE STEAM REFORMING OF METHANE AND BIOGAS OVER STRUCTURED CATALYSTS
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AbstractIn 2006 the global demand for primary energy amounted to nearly 12 million tons of oil equivalent (Mtoe), to a large extent (over 80%) supplied by fossil fuels, i.e. coal, oil, and natural gas. According to the scenario suggested by the International Energy Agency (IEA), energy demand will rise in 2030 to about 17 Mtoe. Fossil fuels will remain largely dominant. Over 70% of the expected demand for the period 2008-2030 will be due to the developing countries (China, India, Middle East, Africa, Latin America). Approximately 50% of this energy demand will involve the generation of electricity, but a significant proportion (20%) will be linked to the transport sector, while the remaining 30% will be distributed between industry, services and residential use. Obviously, predictions of growth in energy demand suggested some problems: if the availability of primary sources, mainly fossil fuels, will be sufficient to meet the demand in quantity, quality and distribution; whether the progressive increase in the use of fossil sources will be compatible with environmentally sustainable development, what role other sources of energy such as nuclear and renewables can play in the future landscape and economical development?. In this scenario, the hydrogen plays a key role as an energy carrier. But the hydrogen is not available in its free form; hydrogen atoms are only available linked to other natural resources, and it must extracted somehow. Currently, most of the hydrogen on the planet is produced by steam reforming of methane, as it is the most abundant gas among the fossil fuels, at an acceptable cost and easily available through the dense network of distribution (pipelines). However, there are also other techniques of syngas production such as the partial oxidation (CPOX), the oxy steam reforming (OSR), which has the characteristic of being able to be made autothermal (ATR) and the dry reforming (DR). The dry reforming is particularly interesting because it uses as a reagent mixture methane and carbon dioxide, two gases with particular heavy greenhouse effect. In this regard the biogas (mixture of carbon dioxide and methane), produced by anaerobic digestion basically from biomass, is particularly suitable for this process since it allows avoiding the preventive separation of CO2 from methane in the production process of syngas. The main aim of this doctoral thesis is the study of the process of syngas production from methane and biogas on catalysts supported on ceramic monoliths made of cordierite, using the steam reforming (SR) process and oxy-steam reforming (OSR) process. The tests were carried out in collaboration with the Institute of Advanced Techniques for Energy "Nicola Giordano" (CNR -ITAE) in Messina (Italy). This thesis is constituted by an introductory part that covers topics related to the production and storage of hydrogen (Chapter 1, “Introduction”); a central part which describes the pilot plant used to carry on tests on steam reforming and oxy steam reforming of methane and biogas, and the preparation of the various tested structured catalysts (Chapter 2, “Experimental part”); and a final part which consists of four papers describing the various experimental works carried out (Chapters 3 to 6). Finally, conclusions on the work done are reported (Chapter 7, “Conclusions”). Chapter 3, “Methane oxy-steam reforming reaction: performances of Ru/γ-Al2O3 catalysts loaded on structured cordierite monoliths”, reports the process of production of syngas via oxy-steam reforming of methane on Ru structured catalyst supported on γ-Al2O3 as carrier. In particular, the influence of the catalyst loading, the influence of the O/C and S/C ratios, the influence of the reaction temperature and the space velocity, were specifically addressed. Chapter 4, “Syngas production by methane oxy-steam reforming: performance of Me/CeO2 (Me = Rh, Pt, Ni) catalyst lined on cordierite monoliths”, presents the process of production of syngas via oxy-steam reforming comparing the performances of three structured catalysts, based on noble and non-noble metals (Rh, Pt and Ni) supported on CeO2 as carrier, focusing on the comparison of the influence of reaction temperature and space velocity on the reactor performance. Chapter 5, “Comparative Study on Steam and Oxydative Steam Reforming of Methane with Ru and Rh Based Catalysts supported on Cordierite Monoliths”, shows the comparison between the processes of steam reforming and oxy-steam reforming of methane on two structured catalysts (Ru/γ-Al2O3 and Rh/CeO2). The two different processes on the two catalysts were studied separately, and then compared. Moreover, an energy requirement discussion on the two processes was addresses (with the support of a series of Aspen Plus® simulations), with specific reference to the energy required for the vaporization of water (the only liquid reagent), and the energy required by the reforming reaction with respect to the moles of methane fed to the process. Chapter 6, “Biogas Steam and Oxy-Steam Reforming processes over structured catalysts based on Me/CeO2 (Me = Rh, Pt, Ni) coated on cordierite monoliths”, describes the comparison between the processes of steam reforming and oxy-steam reforming of biogas on three structured catalysts, based on noble and non-noble metals (Rh, Pt and Ni) supported on CeO2 as carrier . At the time of the submission of the present doctoral thesis to the external Commission, December 2013, the first paper, presented on Chapter 3, has been submitted to the peer reviewed “International Journal of Hydrogen Energy” (manuscript nr. HE-S-13-04515-2), while the other three papers, Chapters 4 to 6, are almost ready for the submission to other international peer reviewed journals (“Applied Catalysis B: Environment”, “Applied Energy”, and “Industrial Engineering and Chemistry Research”).