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The demand for transportation fuels - gasoline (for cars), diesel (for trucks and cars), and kerosene (for aircraft) - is predicted to increase. The fastest growth will be observed for kerosene, in competition with diesel, inducing constraints on diesel. At the same time, all of these fuels are derived mainly from oil (more than 95 %), thus generating growing, uncontrolled CO2 emissions. Therefore, production of diesel derived from biomass (the so-called biodiesel) appears as a major objective. In this paper, we describe the existing industrial processes, discuss the possible improvements, and present the new routes (the "second-generation" processes) under development that will allow biodiesel to gain a significant percentage of the diesel (and maybe of middle distillates) pool.

In addition to developing its own C1-C6 alcohol production process and catalyst, the Institut Francais du Petrole has undertaken some fundamental studies on the genesis of mixed oxide precursors for CO hydrogenation. We present here some preliminary results on cobalt-containing heterogeneous catalysts for the selective synthesis of C1-C6 alcohols from carbon monoxide and hydrogen. The optimal composition range in the systems Cu/Co/Cr or Al/alkali cation is discussed. The preparation procedure is shown to have a determining effect on the final selectivity towards alcohols. Using coprecipitation of the metal nitrates by alkali carbonate, the different steps of catalyst preparation are examined and correlated to the catalyst activity. Stability of this type of catalyst is assessed by some duration tests. Finally, the role of the different components of the catalyst and some hypotheses on reaction mechanism are discussed.

Dans le cadre de la valorisation des coupes lourdes par vapocraquage, des distillats sous vide plus ou moins hydrotraites et des molecules modeles ont ete pyrolyses. Cette etude a ete realisee sur un micropilote dont la partie reactionnelle est chauffee entre 680 et 860°C, par induction electromagnetique haute frequence; le debit total peut varier de 60 a 800 g/h avec une perte de charge inferieure a 0,3 bar. Deux reacteurs tubulaires spirales de rapport surface/volume allant jusqu'a 2000 m-1 permettent d'atteindre des temps de sejour de 10 a 400 millisecondes. Un indice quantifiant l'aptitude de chaque molecule a produire de l'ethylene, du propylene et des composes lourds, a permis l'etablissement d'une echelle de potentialite de craquage, permettant d'orienter les performances d'un catalyseur de pretraitement : optimisation de la consommation d'hydrogene, meilleure valorisation des charges lourdes lors du vapocraquage. Grâce au profil de temperature rectangulaire du micropilote, des gains tres importants de rendements d'ethylene et une production tres faible d'asphaltenes ont ete mis en evidence par pyrolyse de distillats sous vide hydrotraites. L'importance primordiale de la temperature dans le couple temperature-temps de sejour a ete confirmee.

La decomposition thermique d'un melange de normales paraffines (nom commercial Solpar , provenance British Petroleum) a ete etudiee dans une unite micropilote entre 640 et 820 °C ; les produits principaux doses par chromatographie en phase gazeuse sont : hydrogene, methane, ethylene, propene, butene-1, pentene-1, hexene-1, heptene-1, octene-1 et nonene-1. Un des interets du travail est la description mecanistique de la pyrolyse d'un hydrocarbure lourd qui permet d'interpreter la formation primaire de ces produits principaux. On a aussi montre experimentalement l'interet du vapocraquage haute temperature et faible temps de sejour lorsque l'on veut produire selectivement des olefines legeres en minimisant la production d'aromatiques.

A general trend in the field of industrial supported catalysts has been to increase the dispersion of the catalytically active phase(s). Most of these systems can be described as very small particles (size less than 3 nm, very often below 1 nm) supported on a high area support, i.e. on small particles (2–10 nm) of (refractory) oxides or carbon. Their characterization requires elemental, chemical and structural analyses with a high spatial resolution. The use of X-ray emission microanalysis, electron energy loss spectroscopy and microdiffraction available in a dedicated high resolution STEM are described in the case of metallic and non-metallic catalytic particles deposited on high area supports. The required improvements of such instruments are presented. The adequacy of analytical electron microscopy as compared to other global methods is discussed, especially with respect to the determination of the surface composition and structure and the chemical state of the active phases.

Three hypotheses have been put forward in the literature to account for the differences between the sorption properties of Small Port (SPM) and Large Port (LPM) Mordenites: particular localization of Na cations, presence of amorphous material and stacking faults. Our study of some physico-chemical properties of Na SPM, Na LPM and of the H forms of variously modified SPM and LPM, accredits the hypothesis of structural defects. A schematic representation of an SPM crystal and a model of formation of these defects are proposed on the basis of the synthesis conditions.

The evolution with time of adsorbed species and reaction products formed from methanol decomposition on ThO 2 and Pd (0.1 wt %)/ThO 2 has been studied by FT-IR spectroscopy in transient and stationary states (P = 1 atm; T = 280°C). Besides the reaction products [CO, H 2 and (CH 3 ) 2 O], two kinds of formate and methoxy species have been observed and correlated to each other. The methoxy I and formate I species, bound to one surface Th 4+ ion, are formed on the (110) faces. They are very reactive and selectively lead to H 2 and CO. Type II species, bound to two Th 4+ ions on the (211) faces are less reactive. However it is found that methoxy II species can react with physisorbed methanol to produce dimethyl ether. Such results show evidence of a link between the structure of the exposed ThO 2 cristalline faces and their reactivity towards CH 3 OH decomposition.

The activities of Na,H-ZSM—5 catalysts for o-xylene isomerization and for dimethylether conversion into hydrocarbons are shown to be proportional to their protonic exchange rate, This indicates that all the active acid centres of ZSM—5 are identical.

Two procedures for the preparation of HM forms from both small-port mordenite (SPM) and large-port mordenite (LPM) have been studied. The procedures are acid attack of the NaM form and calcination of the NH4M form. The solids were characterized by chemical analysis, benzene adsorption, X-ray diffraction and precise measurements of the Al Kβ X-ray fluorescence line shifts. The conditions under which SPM can acquire LPM adsorption properties were determined: first, SPHM forms have been proved to exist, thus ruling out the hypothesis of pore blocking by cations; secondly, SPM pore unblocking occurs only when > ca. 20% of AlIV atoms are extracted from the framework. This result can be achieved either by severe acid attack of SPNaM or calcination of SPNH4M under deep-bed conditions. In addition, depending on the calcination procedure, the porosity of LPM itself can be blocked by AlVI species from framework dealumination.

Hydrogen adsorption on thoria activated at 973 K (ThO2-973) leads to weak bands at 1115 and 860 cm–1 and a shoulder at 910 cm–1 due to partially reversibly adsorbed bridged species Th—H—Th. The uptake is very small. The adsorption of CO on ThO2-973 turns the disc orange-yellow and gives rise to a large number of species, some of which are reversibly adsorbed. These species are characterized by a band at 2171 cm–1 and are coordinated to Lewis-acid sites. In addition to the carbonate and formate species, at least four types of irreversibly adsorbed species are formed. Three of them are characterized by bands in the 1200–1000 cm–1 frequency range and can be assigned to v(CO) vibrations of –O—CC—O– species; another possibility is the formation of CO2–2 species because of the strong basicity of thoria. The irreversibly adsorbed species are very sensitive to O2 and H2O but are not reduced by H2. Irreversibly adsorbed hydrogen species react with reversibly adsorbed CO species or CO gas, leading to species similar to those formed on adsorption of HCHO.

Depending on the calcinations procedure, the HM (M = mordenite) forms derived from small-port NH4M can be of the large-port or small-port type, thus ruling out the hypothesis of pore blocking by cations.

Adsorption of CO2, C5H5N, CH3OCH3 and CD3OCD2H on ThO2 has been studied by Fourier-transform infrared spectroscopy. CO2 adsorption gives rise to several types of species: polydentate carbonates, bidentate carboxylates, bidentate carbonates, hydrogenocarbonates, monodentate carbonates and linear CO2 species. The carbonate species have been identified on the basis of the splitting of the v3 vibration and of thermal-stability considerations. These results show that thorium dioxide is a basic oxide. Considering the va(CO2) mode of linear CO2 species, the v8a mode of pyridine, the v(CH) band of CD3OCD2H and the v(COC) modes of CH3OCH3, it is concluded that some Th4+ ions are very weak Lewis-acid sites. The OH groups giving rise to the 3740 cm–1 band are basic (some are involved in the formation of hydrogenocarbonate species), while some of the OH groups corresponding to the 3655 cm–1 band are very weak proton donors.

A study of the adsorption sites of thoria has been made using scanning transmission electronic microscopy (STEM) and Fourier-transform infrared spectroscopy (FTIR). The STEM study showed that the thoria surface was composed mainly of (110)(211) and (111) faces in about equal proportions. The infrared study of activated ThO2 at 873 K indicated the existence of two remaining hydroxyl groups at 3660 and 3510 cm–1. With water adsorption, a third one appeared at 3745 cm–1 which was thermally less stable. Methanol adsorption gave rise to three kinds of species: (i) one reversibly adsorbed at room temperature and linked by hydrogen bonds in which thoria acts as a proton receiver; (ii) two methoxy species characterized by ν(CO) bands at 1127 cm–1(species I) and 1060 cm–1(species II). Species I desorption bands led to methanol whilst species II, much more thermally stable, gave methanol, dimethyl ether and carbon monoxide. Species I, which corresponds to the hydroxyl species at 3745 cm–1, are of the Th—OMe (Th—OH) type, and are formed on the (110) faces. Species II, which correspond to hydroxyl species at 3660 cm–1, are of the [graphic omitted] type, and are formed on the (211) faces. The third hydroxyl species, characterized by the ν(OH) band at 3510 cm–1, is probably due to species of the [graphic omitted] type appearing on (111) faces. The stability and reactivity of the methoxy species are shown to depend on their structure, and therefore on the local arrangement of the surface.

Traduction de : Production d'hydrogène par photo(électro)lyse de l'eau Beauger C., Achard P. Dans L'Hydrogène, carburant de l'après-pétrole, coordonné par Edouard Freund et Paul Luchese (Ed.) (2012) pages 224-231 - http://hal-ensmp.archives-ouvertes.fr/hal-00800351; International audience

Une collaboration IFP Energies nouvelles - CEA; National audience

International audience