Production d'hydrogene en boucle chimique

This Ph.D. project focuses on applying the chemical looping technology to produce hydrogen. We developed a special experimental apparatus designed to mimic large scale operational conditions A micro reactor was coupled to an online MS to investigate transient gas-solid reactions. Originally, we intended to use a fixed bed reactor but changed to a fluidized configuration to reduce temperature gradients and improve gas-solid contact. The O-carrier was placed in a quartz tube and reacted by alternating different gas to simulate redox cycles.;The first article is entitled "Hydrogen production through chemical looping using NiO/NiAl2O4 as oxygen carrier." This paper presents experimental results obtained in the vicinity of 800 ºC regarding the production of hydrogen from partial oxidation of methane with nickel as oxygen carrier. The tests were carried out in our micro reactor operated in fixed bed at a GHSV of about 11 200 h--1. We demonstrated that by controlling the global oxidation state of the carrier, it was possible to choose between total and partial oxidation. When limiting the global oxidation state of the O-carrier to below 30 % of the total oxygen capacity, oxidation was partial and thus produced hydrogen.;The second article is "Steam carbon gasification of a nickel based oxygen carrier." This article presents coke-removing of an oxygen-carrier as a particular issue that has never been explained in the chemical looping literature. Ni-based catalysts are common to a number of processes including steam methane reforming, methane cracking or hydrogenation. However, like many metal based catalysts used in the oil/gas industry, fouling is often cited as a major industrial issue. Ni-based oxygen carriers are promising candidates for Chemical Looping Reforming (CLR i.e. H2 production) due to a combination of excellent methane conversion performance, mechanical stability and oxygen transfer capacity.;An additional chapter based on the experimental observations reported in both articles 1 and 2, investigates the transient kinetics of the NiO reduction by methane, for CLC or CLR applications. The study is divided into two sub-sections that look into the catalytic reactions on one hand and the transient NiO reduction on the other hand. In fact, metallic nickel is well known to be an active catalyst for steam methane reforming and water gas shift. Kinetic parameters are determined and included in a more general transient kinetic model that represents well the reduction of NiO by methane.;The third and last article is slightly different compared to the two other and is entitled "Kinetics of mixed copper-iron based oxygen carriers for hydrogen production by chemical looping water splitting". The article still focuses on H2 production through chemical looping, but in this case the source of H2 is not a fuel anymore, but water. The CLWS (chemical looping water splitting) process is based on two reactors, similar to those used in CLR or CLC. A fuel is reacted with an oxygen carrier in the fuel reactor to produce both H2O and CO2. The carrier is then transported to the steam reactor where it is re-oxidized using steam. Water splitting for hydrogen production through chemical looping was investigated in a micro fluidized bed reactor, at temperature ranging from 500 ºC to 800 ºC. Fewer oxygen carriers are suitable for CLWS than for CLR. Zinc, nickel, iron, manganese and copper based particles are among the very few carriers capable of reacting with steam. In our article, iron and copper based oxygen carriers were prepared by two methods and compared in terms of activity towards H2 production. CuO has the particularity among other metallic based O-carriers, of releasing heat during its reduction with methane to form Cu2O. Combined to another metal which reacts endothermically, the use of copper will limit the temperature drop in the fuel reactor. Analogously, the temperature increase will be moderated in the water splitter. Kinetic parameters were evaluated following classic gas-solid mechanisms determination. The activation energies (46-51 kJ/mol) for decomposition of water were determined using the Avrami model (nucleation) for the mixed Cu-Fe carrier prepared by coprecipitation and a shrinking core model for the powder prepared by incipient wetness impregnation. (Abstract shortened by UMI.).