Eight different commercial catalysts, nickel based, for steam reforming of naphthas and of natural gas are tested in biomass gasification for hot gas cleanup and conditioning. They were manufactured by BASF AG, ICI−Katalco, UCI, and Haldor Topsøe a/s. The catalysts were tested in a slip flow after a biomass gasifier of fluidized bed type at small pilot-plant scale (10−20 kg of biomass/h). The gasifying agent used is steam-oxygen mixtures. A guard bed containing a calcined dolomite is used to decrease the tar content in the gas at the inlet of the catalytic bed. Main variables studied are catalyst type, bed temperature, H2O + O2 to biomass feed ratio, and time-on-stream. All catalysts for reforming of naphthas show to be very active and useful for tar removal and gas conditioning (in biomass gasification). 98% tar removal is easily obtained with space velocities of 14 000 h-1 (n.c.). No catalysts deactivation is found in 48 h-on-stream tests when the catalyst temperature is relatively high (780−830 °C). Using a simple first-order kinetic model for the overall tar removal reaction, apparent energies of activation (of around 58 kJ/mol) and preexponential factors are obtained for the most active catalysts.

Phenolic metabolites are frequently implicated in chemical defense mechanisms against pathogens in woody plants. However, tree breeding programmes for resistance to pathogens and practical tree-protection applications based on these compounds seem to be scarce. To identify gaps in our current knowledge of this subject, we explored some of the recent literature on the involvement of phenolic metabolites in the resistance of northern forest trees (Pinus, Picea, Betula, Populus, and Salix spp.) to pathogens. Although it is evident that the phenolic metabolism of trees is often activated by pathogen attacks, few studies have convincingly established that this induction is due to a specific defense response that is capable of stopping the invading pathogen. The role of constitutive phenolics in the resistance of trees to pathogens has also remained unclear. In future studies, the importance of phenolics in oxidative stress, cell homeostasis and tolerance, and the spatial and temporal localization of phenolics in relation to invading pathogens should be more carefully acknowledged. Possibilities for future studies using advanced methods (e.g., metabolic profiling, confocal laser scanning microscopy, and use of modified tree genotypes) are discussed.Résumé : Les métabolites phénoliques sont souvent impliqués dans les mécanismes de défense chimiques contre les agents pathogènes chez les plantes ligneuses. Cependant, il semble y avoir peu de programmes d'amélioration des arbres pour la résistance aux agents pathogènes ou de mesures pratiques de protection des arbres qui sont basés sur ces composés. Dans le but d'identifier les lacunes dans nos connaissances actuelles sur ce sujet, nous avons exploré une partie de la littérature récente traitant du rôle des métabolites phénoliques dans la résistance des espèces forestières nordiques (Pinus, Picea, Betula, Populus et Salix spp.) aux agents pathogènes. Bien qu'il soit évident que le métabolisme des composés phénoliques chez les arbres est souvent déclenché par les attaques des agents pathogènes, il a rarement été établi de façon convaincante que cette induction est due à une réaction de défense spécifique capable d'enrayer l'invasion de l'agent pathogène. De plus, on n'est toujours pas certain du rôle que jouent les composés phénoliques constitutifs dans la résistance des arbres face aux agents pathogènes. Dans les études ultérieures, on devrait accorder plus d'attention à l'importance des composés phénoliques en lien avec le stress oxydatif, l'homéostasie et la tolérance des cellules ainsi qu'à la localisation spatiale et temporelle des composés phénoliques en relation avec l'invasion des agents pathogènes. La discussion porte sur la possibilité que les études futures utilisent des méthodes de pointes telles que le profilage métabolique, le microscope confocal à balayage laser et aient recours à des arbres dont le génotype a été modifié.[Traduit par la Rédaction]

The performance of a biomass gasifier, fluidized-bed type, is improved by in-bed use of calcined dolomite. Tar contents in the raw flue gas below 1 g/m n 3 are obtained by using a bed with a percentage between 15 and 30 wt % of dolomite (the rest being silica sand). The work is carried out at small pilot-plant scale (10 kg of biomass/h) with equivalence ratios (ER) between 0.20 and 0.35 and temperatures of 800−840 °C in the gasifier bed. To replace the eroded and elutriated dolomite (from the gasifier bed), an amount of dolomite (0.40−0.63 mm) is continuously fed, mixed with the biomass at 3 wt %. When the results obtained with in-bed dolomite are compared to the ones gained in a gasifier bed without dolomite, change of the following variables is reported:  gas composition and its corresponding heating value, gas and char yields, apparent thermal efficiency, and tar contents. Once the usefulness of the in-bed use of dolomite is established, three main operation variables (ER and temperatures of the gasifier bed and freeboard) are studied in the improved gasifier. Carryover of solids from the gasifier also increases when calcined dolomite is used because of its softness. Elutriation rate constants are calculated for several operational parameters.

Commercial steam reforming (nickel-based) catalysts are used for hot gas cleaning and upgrading in biomass gasification with steam−oxygen mixtures. The gasifier used was an atmospheric and bubbling fluidized bed with an internal diameter of 15 cm and a total height of 3.2 m and was continuously fed with 5−20 kg of biomass/h. Eight different catalysts from four different manufacturers (BASF AG, TOPSOE A/S, ICI, and UCI) have been tested. They were located in a downflow fixed-bed reactor of 4 cm i.d. placed in a slip flow after the gasifier. A guard bed with a calcined dolomite was also used before the catalytic bed to decrease the tar content in the raw gas below the limit of 2 g of tar/m3 n, thus avoiding the catalyst deactivation by coke formation. The main variables studied were the temperature of the catalytic bed and the gas composition in the bed. Effects concerning tar elimination will be reported in part 2 of this work. This paper is mainly devoted to characterization of catalysts and to upgrading of the flue gas. H2 and CO contents increased by 4−14 and 1−8 vol %, dry basis, respectively. CO2, CH4, and steam contents decreased by 0−14, 87−99, and 2−6 vol %, dry basis, respectively. Other parameters varied in the following ways:  the lower heating value decreased by 0.3−1.7 MJ/m3 n, gas yield increased by 0.1−0.4 m3 n/kg of biomass daf, and apparent thermal efficiency increased by 1−20%. The results presented allow screening of the best catalysts to get an upgraded and useful gas in biomass gasification with steam−oxygen mixtures.

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Elms (Ulmus spp.) were once dominant trees in mixed broadleaf forests of many European territories, mainly distributed near rivers and streams or on floodplains. Since ancient times they have provided important services to humans, and several selected genotypes have been massively propagated and planted. Today elm populations are severely degraded due to the negative impact of human-induced changes in riparian ecosystems and the emergence of the highly aggressive Dutch elm disease pathogens. Despite the death of most large elm specimens, there is no evidence of genetic diversity loss in elm populations, probably due to their ability to resprout after disease. The recovery of elm populations from the remaining diversity should build from genomic tools that facilitate achievement of resistant elm clones. Research works to date have discerned the genetic diversity of elms and are well on the way to deciphering the genetic clues of elm resistance and pathogen virulence, key findings for addressing recovery of elm populations. Several tolerant clones suitable for use in urban and landscape planting have been obtained through traditional species hybridization with Asian elms, and various native clones have been selected and used in pilot forest restoration projects. Successful reintroduction of elms should also rely on a deeper understanding of elm ecology, in particular their resilience to abiotic and biotic disturbances. However, all these efforts would be in vain without the final acceptance of elm reintroduction by the social actors involved, making it necessary to evaluate and publicize the ecosystem services elms can provide for today's society.

Cleaning and upgrading of the hot raw gas from a biomass gasifier, bubbling fluidized bed type, is studied at small pilot plant scale (10 kg biomass fed/h) using a calcined dolomite located downstream from the gasifier. Gasification is made with steam−oxygen mixtures at 800−850 °C and atmospheric pressure. Main variables studied are the gas residence time in the bed of dolomite and the gas atmosphere composition, which depends on the gasifying agent (H2O + O2)-to-biomass and H2O/O2 ratios. H2 and CO content in the flue gas increases by 16−23 vol % and decreases by 15−22 vol % (dry basis), respectively. Although CH4 conversion (elimination) higher than 30 vol % has never been reached, tar conversion (elimination) of 90−95 vol % are obtained with space times of 0.06−0.15 kg calcined dolomite h-1 m-3. A detailed study is here presented on how the calcined dolomite significantly cleans and upgrades the flue gas, increasing also the gas yield by 0.15−0.40 m3(STP)/kg daf biomass fed.

Efforts to introduce pathogen resistance into landscape tree species by breeding may have unintended consequences for fungal diversity. To address this issue, we compared the frequency and diversity of endophytic fungi and defensive phenolic metabolites in elm (Ulmus spp.) trees with genotypes known to differ in resistance to Dutch elm disease. Our results indicate that resistant U. minor and U. pumila genotypes exhibit a lower frequency and diversity of fungal endophytes in the xylem than susceptible U. minor genotypes. However, resistant and susceptible genotypes showed a similar frequency and diversity of endophytes in the leaves and bark. The resistant and susceptible genotypes could be discriminated on the basis of the phenolic profile of the xylem, but not on basis of phenolics in the leaves or bark. As the Dutch elm disease pathogen develops within xylem tissues, the defensive chemistry of resistant elm genotypes thus appears to be one of the factors that may limit colonization by both the pathogen and endophytes. We discuss a potential trade-off between the benefits of breeding resistance into tree species, versus concomitant losses of fungal endophytes and the ecosystem services they provide.