R. Maggi

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.

CoMo/carbon hydrodeoxygenation catalysts: influence of the hydrogen sulfide partial pressure and of the sulfidation temperature

This work concerns the influence of the hydrogen sulfide partial pressure and the sulfidation temperature on the hydrodeoxygenation activity and selectivity of a CoMo catalyst supported on activated carbon. An attempt is made to identify the active sites involved in the reaction of different oxygenated molecules: guaiacol demethylation and dehydroxylation, ethyldecanoate hydrogenation and decarboxylation, 4-methylacetophenone hydrogenation

Characterization and Upgrading of Big-oils Produced By Rapid Thermal-processing

Flash pyrolysis oils have a high oxygen content. The presence of numerous and various oxygenated functions give these oils unwanted characteristics that may be improved by the elimination of oxygen by catalytic hydrotreating. This paper deals with the chemical characterization of RTP oils by liquid-liquid fractionation followed by mass spectrometric determination of the individual compounds. In a second part, the hydrodeoxygenation reactions were approached using model compounds selected on the basis of the characterization. The CH2Cl2 acidic fractions of the oils are mainly composed of phenolic structures. Nevertheless, the phenolic molecules are differently substituted depending on the pyrolysis conditions: carboxyl and carbonyl groups for short residence times and methoxy groups for long residence times. All the main chemical groups present in pyrolysis oils can be eliminated using nickel-molybdenum and cobalt-molybdenum traditional hydrotreating catalysts. The reactivity, the activation energies and the products of the hydrodeoxygenation conversion of the various oxygenated groups were determined.

A review of catalytic hydrotreating processes for the upgrading of liquids produced by flash pyrolysis

Abstract Liquids produced by flash pyrolysis of biomass and solid wastes are intendedto be used in direct combustion but they contain a high quantity of oxygenated molecules which causes unwanted characteristics such as thermal instability, tendency to polymerise, corrosion and low heating value. These properties can be improved by partial or total elimination of oxygen atoms by catalytic hydrotreating with production of hydrocarbons and water. This paper reviews the development of this process from the first empirical tests using real oils and industrial sulphided cobalt-molybdenum and nickel-molybdenum supported on alumina catalysts to the development of a specially dedicated catalytic system. Special attention is given to the catalytic aspects: the reaction schemes, the identification of the different catalytic functions and the control of the reaction. finally, we discuss the utilisation of activated carbon as a new support.

Use of noble metals in hydrodeoxygenation reactions

Two series of catalysts supported on active carbon containing noble metals (NM) Pt, Pd, Ru and Rh were prepared (bimetallic NM-Mo/C and trimetallic NM-CoMo/C catalysts) and tested in their sulphided form in hydrodeoxygenation (HDO) reactions of model molecules containing carbonyl, carboxyl, hydroxyl and methoxy groups. Results show that hydrogenation reactions of the carbonyl and carboxyl groups are favoured by the presence of NM in the case of the bimetallic catalysts. The influence of cobalt in the decarboxylation reaction was confirmed. Bimetallic catalysts without cobalt have no decarboxylation activity. A mutual interaction between noble metal sulphides and cobalt sulphide was observed for trimetallic catalysts. Effects of this interaction are different for each metal, which indicates that the noble metal nature is implicated in this phenomenon.

Epoxidation of cyclohexene by iron and cobalt phthalocyanines, study of the side reactions

This paper investigates the existence of side reactions involving oxygen donors in the epoxidation of cyclohexene in the presence of iron and cobalt phthalocyanines. An evaluation of the catalytic role of fragments coming from the degradation of phthalocyanines in the overall reactions has been undertaken, It is shown that neither tert-butyl-hydroperoxide (t-BHP) nor iodosylbenzene (PhIO), two commonly used donors, are convenient for evaluating the catalytic performances of phthalocyanines in the epoxidation of olefins, With t-BHP, the oxidation reaction is, at least partially, violently triggered by fragments from phthalocyanine decomposition; the reaction involves homogeneous radical pathways, and mainly leads to oxidized derivatives different than the epoxide. Its use necessitates precautions to preclude this decomposition. in the case of PhIO, the oxygen donor oxidizes the substrate even in the absence of catalyst. By contrast, hydrogen peroxide does not give way to major side reaction; it is efficient and selective for the heterogeneously catalyzed epoxidation of cyclohexene. It is therefore suitable, without special procedure, for studying the activity of phthalocyanines. Due to some spontaneous decomposition of H2O2, some precautions are nevertheless necessary to evaluate correctly the kinetics of the reaction.

Influence of the hydrogen sulfide partial pressure on the hydrodeoxygenation reactions over sulfided CoMo/Carbon catalysts

This work concerns the influence of the hydrogen sulfide partial pressure on the activity in hydrodeoxygenation and associated reactions of a CoMo/Carbon catalyst for the transformation of guaiacol, ethyldecanoate and 4-methylacetophenone. This has been studied over a wide range of hydrogen sulfide partial pressures, from 10 to 150 kPa, under a total pressure of 7 MPa, at reaction temperatures of 270 and 200 degrees C. An inhibition effect is observed in the hydrogenolysis pathway in guaiacol conversion and in ethyldecanoate dehydroxylation. The conversion of 4-methylacetophenone is also inhibited by hydrogen sulfide. The results have been interpreted on the basis of the existence of different active sites responsible for hydrogenolysis, hydrogenation and acid catalysed reactions. The increase in hydrogen sulfide partial pressure would decrease the average degree of reduction of the active sites and inhibit the hydrogenolysis pathway, more than the hydrogenation one. The results are compared to those observed with alumina supported catalysts in hydrodeoxygenation and hydrodesulfurisation.

Characterization of Bio-Oils Produced by Pyrolysis

This paper presents the results obtained in the characterization of two different pyrolysis oils, the first one produced by carbonization and the second by flash pyrolysis. Chemical and physical properties such as density, viscosity, elemental composition, char content, water content, solubility and heating value were first determined, then an in-depth chemical characterization was carried out by liquid-liquid fractionation. We present a diagram indicating the separation procedure to provide four fractions (acids, bases, polars and hydrocarbons). We also recuperated very polar molecules which were retained in the aqueous layer (“aqueous” fraction). Each fraction was subsequently analyzed by GC-MS and FTIR.

Influence of the impregnation order of molybdenum and cobalt in carbon supported catalysts for hydrodeoxygenation reactions

This work concerns the role of the impregnation order of molybdenum and cobalt in carbon supported catalysts. Four activated carbons have been used as supports and the effect of the impregnation order (either cobalt or molybdenum at first) has been considered. The samples were characterized by N-2 physisorption, XPS and SEM. The sulfided catalysts have been tested in hydrodeoxygenation, using a model mixture containing: 4-methylacetophenone, ethyldecanoate and guaiacol. Both series of samples exhibit a low dispersion of the active phase, but CoMo is more uniformly distributed than MoCo. This result was interpreted to be consequence of the position occupied by the metal impregnated at first and of the strong interactions existing between cobalt and molybdenum. In the samples containing only one metal, cobalt is mainly impregnated at the exterior of the grains, while molybdenum is impregnated at the interior of the grains, causing micropore blocking. When the second metal is added, cobalt seems to bring about the remobilization of molybdenum outside the grains in CoMo catalysts and the formation of molybdenum oxide on the external grain surface in MoCo. Concerning catalytic activity, CoMo catalysts show higher hydrogenation properties for the conversion of ketonic groups and higher decarboxylation selectivity in the conversion of the ester.