Etienne Laurent

Study of the Hydrodeoxygenation of Carbonyl, Carboxylic and Guaiacyl Groups Over Sulfided Como/gamma-al2o3 and Nimo/gamma-al2o3 Catalysts .1. Catalytic Reaction Schemes

The elimination of specific oxygenated groups of biomass-derived pyrolysis oils (bio-oils) is necessary for improving their stability. These are mainly unsaturated groups like alkene, carbonyl and carboxylic functions, as well as guaiacyl groups. For practical applications, it is desirable that the reactions are performed selectively in order to avoid excessive hydrogen consumption. The reactions must be done at relatively low temperature in order to limit competitive thermal condensation reactions. In this study, model oxygenated compounds were used, namely 4-methylacetophenone, diethyldecanedioate and guaiacol. They were tested simultaneously in one reaction test in the presence of sulfided cobalt-molybdenum and nickel-molybdenum supported on gamma-alumina catalysts in a batch system. Their reactivity and conversion scheme were determined. The ketonic group is easily and selectively hydrogenated into a methylene group at temperatures higher than 200 degrees C. Carboxylic groups are also hydrogenated to methyl groups, but a parallel decarboxylation occurs at comparable rates. A temperature around 300 degrees C is required for the conversion of carboxylic groups as well as for the conversion of the guaiacyl groups. The main reaction scheme of guaiacol is its transformation in hydroxyphenol which is subsequently converted to phenol. But in batch reactor conditions, guaiacol gives a high proportion of heavy products. CoMo and NiMo catalysts have comparable activities and selectivities. However, the NiMo catalyst has a higher decarboxylating activity than CoMo and also leads to a higher proportion of heavy products during the conversion of guaiacol.

Influence of Water in the Deactivation of a Sulfided Nimo Gamma-al2o3 Catalyst During Hydrodeoxygenation

Water and oxygenated compounds are generally viewed as highly detrimental to the stability of sulfided hydrotreating catalysts. In this paper, a sulfided NiMo/gamma-Al2O3 catalyst was treated in a batch reactor under typical hydrotreating conditions with or without water vapor. Changes of the HDO activity, composition, and texture of the various catalyst samples were further evaluated. Catalyst samples used in the HDO of organic oxygenated compounds were also characterized by XPS for modifications of the chemical surface composition. Water caused a decrease of the catalytic activity to one-third the activity of the fresh catalyst but did not change the hydrogenation-hydrogenolysis selectivity. Water was also the cause of a small loss of the specific surface area conjugated to some crystallization of the gamma-alumina support in a hydrated boehmite phase. On the other hand, the metal content, the dispersion, and the sulfidation state were not specifically affected by water. The deactivation would rather be related to the appearance of oxidized nickel species. The observations can be interpreted as resulting from the formation of an inactive nickel sulfate layer covering the active sulfide phases or from the formation of nickel aluminate. Otherwise, the oxidation of the molybdenum sulfide phase by water or oxygenated compounds in reaction conditions is very limited

Study of the Hydrodeoxygenation of Carbonyl, Carboxylic and Guaiacyl Groups Over Sulfided Como/gamma-al2o3 and Nimo/gamma-al2o3 Catalyst .2. Influence of Water, Ammonia and Hydrogen-sulfide

The hydrotreatment of various oxygenated groups (ketonic, carboxylic, methoxyphenol) present in bio-oils in the presence of CoMo and NiMo catalysts was studied in a batch reactor using a mixture of model compounds mimicking the real feed. The influence of potential poisons or inhibitors of the reactions (water, ammonia and hydrogen sulfide) was determined. High quantities of water had only a very slight inhibiting effect on the reactions. Ammonia strongly inhibited the conversion of carboxylic esters and the removal of the methoxy group of guaiacol, but, surprisingly, the hydrogenation of the ketonic group was not affected. Hydrogen sulfide depressed the activity of the NiMo catalyst for the conversion of the ketonic group but not that of the CoMo catalyst. It had an enhancing effect on the conversion of the carboxylic ester group and no effect on the removal of the methoxy group of guaiacol. The evolution of activities and selectivities as a function of the concentration of potential inhibitors provided an indication of the catalytic sites responsible for the various reactions. The absence of the influence of ammonia on the hydrogenation of the ketonic group was interpreted as resulting from the participation of nucleophilic sites and hydridic species in the reaction mechanism. Carboxylic esters seem to react on electrophilic sites. Bronsted acids were thought to be responsible for decarboxylation, while uncoordinated metal atoms and sulfhydryl groups could be responsible for the hydrogenation of carboxylic groups. On the other hand, the surface of the alumina support catalyzes the hydrolysis of carboxylic esters into acids. The demethylation of guaiacol occurs for a large part on the Lewis acid-base sites of the gamma-alumina support. The use of hydrogen sulfide and ammonia shows a high potential for controlling the selectivity of reactions occurring in bio-oils hydrotreatment. The present results give hope that the deoxygenation of carboxylic groups could be selectively performed through decarboxylation thanks to catalyst selection and control of the hydrogen sulfide pressure. Ketonic groups and aldehydic groups could be selectively eliminated from complex feeds by applying a pressure of ammonia which would inhibit all reactions but hydrogenation.

Hydrotreatment of pyrolysis oils from biomass : reactivity of the various categories of oxygenated compounds and preliminary techno-economical study

This paper describes essential aspects of the hydrotreatment of pyrolytic oils in the light of results obtained until now at the Universite Catholique de Louvain. Stability of pyrolysis oils necessitates a two-step processing. A low temperature hydrotreatment enables stabilization through reactions like olefin, carbonyl and carboxylic groups reduction. Further hydrotreatment aims at hydrodeoxygenation of phenols and hydrocracking of larger molecules. Results about catalysts, reaction conditions and parameters enabling or influencing the control of the reaction are summarized. Based on these laboratory data, a preliminary techno-economical evaluation is made. 50 wt.-% yields in hydrocarbons for deep hydrorefining of pyrolysis oils can be expected. Nevertheless, a moderate hydroconversion with partial elimination of oxygen would be, economically, more advantageous.

Hydrodeoxygenation of Oxygenated Model Compounds: Simulation of the Hydro-Purification of Bio-Oils

Oils produced by liquefaction of biomass contain a high quantity of oxygenated molecules which determines unwanted properties. Oxygen can be eliminated by catalytic hydrotreatment. Hydrocarbons and water are then produced The present work deals with the catalytic aspects of hydrodeoxygenation (HDO) of oxygenated model compounds representative of the composition of pyrolysis oils. The reaction schemes of the conversion of phenolic, ketonic, carboxylic and methoxy groups over sulfided catalysts are proposed and their reactivity compared. Two typical hydrotreating catalysts (NiMoS and CoMoS) are compared. The influence of hydrogen sulfide and water partial pressure on the efficiency of the catalysts is presented. The results indicate that the CoMoS catalyst is preferred because of its lower sensitivity to water. The hydrogen sulfide partial pressure has to be finely controlled because it influences strongly and diversely the catalytic functions of the catalysts. The results are discussed and interpreted in view of the multifunctional character of hydrotreating catalysts. Conclusions about the hydrotreating of pyrolysis oils are presented.