No description available.

Ce travail de Thèse est consacré à la caractérisation de la structure thermique des fronts de flammelaminaire de prémélange H2/CH4/Air et H2/CO/Air pauvres. L’étude a été réalisée sur un brûleur à jets opposés, permettant de stabiliser des flammes planes stationnaires, dans des conditions quasi-adiabatiques, pour différentes conditions d’étirement. Un diagnostic de Vélocimétrie par Imagerie de Particule (PIV) et un diagnostic bidimensionnel de diffusion Rayleigh induite par laser ont été utilisés successivement pour étudier l’influence de la richesse, de la concentration en hydrogène dans le combustible et de l’étirement sur le profil de température normal au front de flamme. Trois grandeurs fondamentales ont été étudiées : la température des gaz brûlés, le gradient maximum de température et l’épaisseur de flamme au sens de Spalding. Une attention particulière a été portée à l’interprétation du signal Rayleigh. Ce dernier dépendant notamment de la composition du gaz qui évolue à travers le front de flamme. Dans ce travaille de thèse, cette évolution a été évaluée numériquement (simulations 1D : CANTERA et OPPDIF) puis prise en compte pour améliorer le traitement des données expérimentales. Les résultats expérimentaux couvrent une gamme de richesses s’étalant pour H2/CH4/Air et H2/CO/Air, respectivement de 0.6 à 0.8 et de 0.4 à 0.6. Les concentrations en hydrogène dans le combustible s’étalent respectivement de 0 à 50% et de 10 à 50%. Une comparaison systématique a été faite avec les résultats de simulation numérique 1D (OPPDIF). / This Thesis is devoted to the characterization of the thermal structure of H2/CH4/Air and H2/CO/Air laminar flames. Counterflow flame setup has been used to study planar flames in steady and near-adiabatic conditions. Particle Image Velocimetry and laser induced Rayleigh scattering diagnostics has been successively applied to characterize the influence of equivalent ratio, hydrogen concentration in fuel and stretch on the temperature profile normal to the flame front. Three fundamental characteristics have been studied: the burned gas temperature, the maximum temperature gradient and the flame thickness defined by Spalding. Particular attention has been brought to the interpretation of the Rayleigh signal. Indeed, Rayleigh scattering depends on the gas composition which evolves across the flame front. This evolution has been numerical evaluated in this work (1D simulation: CANTERA and OPPDIF) and taken into account to improve Rayleigh data processing. Experimental results have been obtained for lean flames: equivalent ratio spreads from 0.6 to 0.8 and from 0.4 to 0.6 respectively for H2/CH4/Air and H2/CO/Air flames. A wide range of hydrogen concentration has been studied: from 0 to 50% of hydrogen in fuel for H2/CH4/Air flames and from 10 to 50% of hydrogen in fuel for H2/CO/Air flames. Experimental and numerical (OPPDIF) results have been systematically confronted.

Biomass-derived hydrocarbons that include gasoline, diesel, and jet fuel will help replace finite fossil fuel hydrocarbons of the same range. This study showed that temperature could be controlled in a scaled-up reactor system using three types of syngas. The CO conversion, selectivity and amount of product created from each type of syngas were examined. Clean syngas composed of 40% H2, 20% CO, 12% CO2, 2% CH4, and 26 % N2 was used to test ideal stoichiometric molar values. Clean syngas composed of 19% H2, 20% CO, 12% CO2, 2% CH4, and 47 % N2 was used to test an ideal contaminateree synthesis gas situation to mimic our particular downdraft gasifier. Gasifier wood syngas composed of 19% H2, 20% CO, 12% CO2, 2% CH4, 46 % N2, and 1% O2 was used in this study to determine the feasibility of using gasified biomass syngas to produce gasolinerange hydrocarbons.

This thesis deals with converting a mixture of H2 and CO, also referred to as syngas or producer gas, to higher or mixed alcohols and other fuels through a process called Fischer Tropsch Synthesis (FTS). It is a beneficial pathway that minimizes the dependence on oil and similar fossil fuels which contribute to rapid climate change by releasing harmful greenhouse gases. The syngas used in FTS, is generally obtained through gasification of biomass to make the entire process renewable and to make the resulting fuel carbon neutral. The products are pure due to prior cleaning of syngas mixture to remove oxides of nitrogen, sulphur and other particulate matter, before the process, thereby drastically reducing the net exhaust gas emissions. The major objective of this project is to design a novel catalyst system and subject it to a series of experimentation for testing its selectivity towards alcohols. This is because the present catalytic systems are either very expensive to assemble or confer to a low yield. Two cobalt (Co) based catalysts, one without a promoter and the other which is promoted by zirconium (Zr), are prepared. The activity and selectivity of Co catalysts are finally compared with the existing Swedish Biofuels AB’s Iron (Fe) based catalyst promoted by copper (Cu) and chromium (Cr) along with characterization of the optimum reaction parameters like temperature, pressure, GHSV and syngas ratio for FTS. Aqueous incipient impregnation approach was adopted wherein the Co active metal and Zr promoter (only in second catalyst) are introduced step-wise on a ϒ-alumina support to synthesize the catalyst after which it is heat treated through drying, calcination and reduction to obtain the active Co metal catalyst. A high temperature FTS, was employed for the yield of alcohols and other gasoline derivatives according to literature. Finally, the liquid and gaseous products are analyzed through GC or GC/MS analysis techniques. The unpromoted Co catalyst’s activity is regarded as a failure due to satisfactory results. There were a few problems associated with the catalyst alone like poor mechanical stability that could be attributed to the use of an incorrect binder. Other problems included methanation due to haphazard temperature variations and inefficient catalyst reduction. For the promoted Co catalyst, the yield of alcohols and hydrocarbons was significantly higher than the unpromoted Co catalyst. A temperature of 300 °C, a GHSV of 360 h-1 , a pressure of 10 bar and a H2:CO ratio of 1.3:1 were the optimal background conditions for FTS. Higher temperature caused methanation and reduced the chain growth probability factor, α, that resulted in the formation of lower hydrocarbons only. Any increase in gas ratio and GHSV, also increased the rate of methane formation and caused diffusion limitations. For a one-stage setup with the reversal of exhaust gases, the conversion rates of CO and H2 were quite promising. This success can be attributed to a higher calcination temperature that increased the degree of reduction of Co due to formation of promoter oxides thereby enabling CO hydrogenation and H2 insertion. It helped to reduce CO2 formation as well. Even for the Fe catalyst, a low temperature, a low GHSV and low syngas ratio were preferred. But unlike its Co counterpart, a higher pressure favored an increase in yield of alcohols and other long chain hydrocarbons. Fe’s ability to support WGS reaction disturbed the molar ratio of CO and also released more CO2 that could affect the rate of syngas conversion. But, on the whole, Fe catalyst was efficient than Co catalyst for alcohol synthesis. The overall yield of alcohols was just 5% of the liquid products. Nearly 86% of the alcohol fraction comprised of C1, C2 and C3 alcohols alone and very few C4, C5 and C6 alcohols were obtained. / Denna avhandling behandlar omvandling av en blandning av H2 och CO, även kallad syngas eller producentgas, till högre eller blandade alkoholer och andra bränslen genom en process som kallas Fischer Tropsch Synthesis (FTS). Det är en bra väg som minimerar beroendet av olja och liknande fossila bränslen som bidrar till snabba klimatförändringar genom att släppa ut skadliga växthusgaser. Syngasen som används i FTS erhålls generellt genom förgasning av biomassa för att göra hela processen förnybar och för att göra det resulterande bränslet kolneutralt. Produkterna är rena på grund av föregående rengöring av syngasblandningen för att avlägsna kväveoxider, svavel och annat partikelformigt material före processen och därigenom drastiskt minska utsläppen av avgaserna. Huvudsyftet med detta projekt är att utforma ett nytt katalysatorsystem och utsätta det för en serie experiment för att testa dess selektivitet gentemot alkoholer. Detta beror på att de nuvarande katalytiska systemen antingen är mycket dyra att montera eller ge ett lågt utbyte. Två koboltbaserade (Co) -baserade katalysatorer, en utan en promotor och den andra som befordras av zirkonium (Zr), framställs. Aktiviteten och selektiviteten hos Co-katalysatorer jämförs slutligen med de befintliga Swedish Biofuels AB: s Iron (Fe) -baserade katalysator som främjas av koppar (Cu) och krom (Cr) tillsammans med karaktärisering av de optimala reaktionsparametrarna som temperatur, tryck, GHSV och syngasförhållande för FTS. Vattenhaltig begynnande impregneringsmetod användes där den Co-aktiva metallen och Zr-promotorn (endast i den andra katalysatorn) införs stegvis på ett ϒ-aluminiumoxidstöd för att syntetisera katalysatorn, varefter den värmebehandlas genom torkning, kalcering och reduktion för att erhålla aktiv Co-metallkatalysator. En hög temperatur FTS användes för utbytet av alkoholer och andra bensinderivat enligt litteratur. Slutligen analyseras de flytande och gasformiga produkterna genom GC- eller GC / MS-analystekniker. Den outpromoterade Co-katalysatorns aktivitet betraktas som ett misslyckande på grund av tillfredsställande resultat. Det fanns några problem associerade med katalysatorn ensam som dålig mekanisk stabilitet som kunde tillskrivas användningen av ett felaktigt bindemedel. Andra problem inkluderade metanering på grund av variationer i slumpmässiga temperaturer och ineffektiv katalysatorreduktion. För den befordrade Co-katalysatorn var utbytet av alkoholer och kolväten betydligt högre än den opromoterade Co-katalysatorn. En optimal temperatur på 300 ° C, en GHSV på 360 h-1, ett tryck av 10 bar och ett H2: CO-förhållande på 1,3: 1 var de optimala bakgrundsbetingelserna för FTS. Högre temperatur orsakade metanering och reducerade sannolikhetsfaktorn för kedjan tillväxt, a, vilket resulterade i bildandet av endast lägre kolväten. Varje ökning av gasförhållandet och GHSV, ökade också metanbildningshastigheten och orsakade diffusionsbegränsningar. För en inställning i ett steg med reversering av avgaser var omvandlingsgraden för CO och H2 ganska lovande. Denna framgång kan tillskrivas en högre kalcineringstemperatur som ökade graden av reduktion av Co på grund av bildning av promotoroxider och därigenom möjliggör CO-hydrering och H2-införing. Det hjälpte också till att minska koldioxidbildningen. Även för Fe-katalysatorn föredrog man en låg temperatur, ett lågt GHSV och lågt syngasförhållande. Men till skillnad från Co-motsvarigheten gynnade ett högre tryck en ökning av utbytet av alkoholer och andra långkedjiga kolväten. Fe: s förmåga att stödja WGS-reaktion störde det molära förhållandet CO och frigav också mer CO2 som kan påverka hastigheten på syngasomvandlingen. Men i stort sett var Fe-katalysator mer effektiv än Cokatalysator för alkoholsyntes. Det totala utbytet av alkoholer var bara 5% av de flytande produkterna. Nästan 86% av alkoholfraktionen bestod av C1-, C2- och C3-alkoholer enbart och mycket få C4-, C5- och C6-alkoholer erhölls.

No description available.

The goal of this work was to establish the suitable and limiting concentrations of Zn, Cu and Mn compounds during syngas fermentation. The results showed that cells encased in polyvinylidene difluoride (PVDF) membranes had a faster accumulation of methane in reactors containing fermentation medium dosed with 5 mg/L of each heavy metal compared to free cells. It was also revealed that total inhibition of biohydrogen production occurred in medium containing 5 mg/L Cu, 30 mg/L Zn and 140 mg/L Mn while the most suitable metal concentration level was 0.1 mg/L Cu, 0.6 mg/L and 2.8 mg/L Mn. In addition, a comparison test showed that for the most suitable metal concentration in the medium, rate of performance at pH 6 and 7 was higher than at pH 5.

Catalysts are involved in a very large number of processes leading to the production of industrial chemicals, fuels, pharmaceutical, and to the avoidance, as well as the clean-up of environmental pollutants. In respect to the latter aspect, efforts are being made by different stake-holders (governments, researchers, industrials, etc) in order to prevent or to minimize pollution of our cities. A notably way to reduce pollution for a friendly environment is to make use of clean fuels. After years of research work, it is only recently that dimethyl ether alone or when combined with methanol has been identified as a potential alternative clean fuel. Nonetheless, the technology used for the methanol synthesis from syngas requires high pressure (>120 atm) to reach an acceptable CO conversion. The dimethyl ether production from methanol in a separate unit makes DME more expensive than methanol. However, the transformation of syngas directly into dimethyl ether can be used to relieve the thermodynamic constraints requiring operation at high pressure. If the synthesis of methanol and dimethyl ether takes place in the same reactor, the process should, in principle, be able to operate at a much lower pressure, making it a potentially cheaper process to produce methanol and dimethyl ether. The catalysts that need to be used for this coproduction have to be catalytically stable, selective and able to catalyze the main reactions (methanol and dimethyl ether synthesis) involved in this process at the same temperature. Unfortunately, existing commercial methanol/DME catalysts are not able to function efficiently in the presence of large concentrations of water or at high temperature. Thus, it is relevant to have a catalyst satisfying the above criteria. Recently, it has been reported that a supported gold catalyst could be used for methanol synthesis; accordingly this study has developed bifunctional gold-based catalysts for the methanol and DME synthesis. This study utilized process synthesis approach to determine the optimal operating conditions for methanol/dimethyl ether production that yielded results used to drive an experimental programme to get the most useful information for designing a process route. In a comparative way and by using the feed compressor work load per unit of valuable material generated as objective function, this study showed that the system where methanol is co-produced with DME is more efficient than the one involving the production of methanol alone and this is applicable for the operating reactor temperatures of 500-700K and the loop pressure ranging from 10 to 100 atm. The catalysts systems chosen in this study were consisted in the physical mixture of gold-based catalysts incorporating respectively gamma-alumina and zeolite-Y. The gold-based catalysts were prepared by a co-precipitation method, then characterized by XRD, Raman Spectrometry and Transmission Electron Microscopy and, afterwards tested using a 1/4 inch tubular fixed bed reactor between 573 and 673K at 25 atm. Amongst the catalysts tested at 673K, and 25 atm, 5%Au/ZnO/γ-Al2O3 produced both methanol and dimethyl ether with moderate yield, whereas 5%Au/ZnO/LZ Y-52 gave high dimethyl ether selectivity (75.7%) with a production rate of 252.3 μmol.h-1.g -1 cat . The presence of hydrocarbons detected by the GC-FID in the gas products requires that further investigations be done to determine the eventual source and optimize this new catalyst system based on gold for a large scale coproduction of methanol and dimethyl ether from syngas.

Sol-gel (solution-gelation) method was used to prepare Ni-Ti and Ni-Ti-Al catalysts for reforming of methane with carbon dioxide. This method, after optimizing the parameters such as hydrolysis and acid/alkoxide ratio, is able to make a Ni-Ti catalyst with a surface area as high as 426m2/g when calcined at 473K; but calcination at higher temperature lead to dramatic decrease in surface area. XRD, XPS, TEM and SEM were used to understand this change. Using a packed bed reactor, the catalysts were evaluated with the reforming reaction. It was found that the activity of the Ni-Ti catalyst increases with the Ni loading in the range of 1-10wt%. The reduction temperature has strong effect on activity of the reduced catalyst. Up to 973K, the activity increases with the reduction temperature; but after 973K, the activity decreases and become 0 when the temperature is over 1023K. The Ni-Ti catalyst also deactivated as 15% after 4h of time on stream. The XRD analysis shows that Ti3O5 formed in the catalyst after higher-temperature reduction as well as after the reaction for a period of time. The formation of Ti3O5 may render the catalyst to loss its activity. However, further study is expected to understand the mechanism. TG/DTA analysis shows that both Ni-Ti and Ni-Ti-Al catalysts had carbon deposition; but the latter maintained higher activity in a longer period of time.

A novel catalytic process for producing high-purity, elevated-pressure hydrogen from synthesis gas was proposed and investigated. The process combines the advantages of low investment and operating costs with the flexibility to adapt to a small-scale operation. The process consists of a loop containing two complementary reactions: ethanol dehydrogenation and acetaldehyde hydrogenation. In one part of the loop, hydrogen is produced by dehydrogenation of ethanol to acetaldehyde. Since acetaldehyde is a liquid under standard conditions, it can be easily separated and pure hydrogen is obtained. In the other part of the loop, hydrogen contained in synthesis gas is reacted with acetaldehyde to produce ethanol and purified carbon monoxide. Ethanol, also a liquid under standard conditions, is easily removed and purified carbon monoxide is obtained, which can be further water-gas shifted to produce more hydrogen. Various dimensionless criteria were evaluated to confirm there was no significant effect of heat and mass transfer limitations and thus the experimental results represent true kinetics. Furthermore, a thermodynamic study was conducted using a Gibbs free energy minimization model to identify the effect of reaction conditions on ethanol/acetaldehyde conversion and determine the thermodynamically favourable operating conditions. Various catalysts were synthesized, characterized and screened for each reaction in a down-flow, fixed-bed quartz reactor. A novel gas chromatography analysis method allowing for an on-line detection of all products was also developed. Unsupported copper in the form of copper foam and copper supported on three different high surface supports were evaluated in ethanol dehydrogenation. Copper foam provided the lowest activity, because of its low surface area. Cu/SiO2 was the most active catalyst for ethanol dehydrogenation. The effects of temperature, pressure, residence time, and feed composition on ethanol conversion and product composition were determined. While increasing temperature or residence time resulted in increased ethanol conversion, elevated pressure and water content in the feed had no effect on ethanol conversion. On the other hand, acetaldehyde selectivity decreased with increasing temperature, pressure and residence time, as acetaldehyde participated in undesirable transformations to secondary products, out of which the most dominant was ethyl acetate. The maximum operating temperature was limited by the stability of the copper catalyst, which deactivated by sintering at temperatures higher than 300°C. The range of temperatures investigated was from 200°C to 350°C, while pressures ranged from atmospheric to 0.5 MPa. For ethanol:water ratios <1, the addition of water to the ethanol feed improved the catalyst stability and acetaldehyde selectivity, but a detrimental effect was observed at higher ratios. The introduction of acetaldehyde into the feed always lowered the conversion, thus indicating a need for stream purification within the loop. An empirical kinetic model was used to determine the activation energy, the order of reaction and the frequency factor. Unsupported and SiO2-supported copper catalysts were compared in acetaldehyde hydrogenation. Pure copper was identified as the best catalyst. Effects of temperature, pressure, residence time, feed composition and catalyst promoter on acetaldehyde conversion and product composition were evaluated. The acetaldehyde hydrogenation was enhanced by increased temperature, pressure and residence time and suppressed in presence of Fe or Zn promoters. Once again, at elevated temperature and residence time, ethanol combined with acetaldehyde to produce undesired ethyl acetate. CO acted as an inert when testing with the pure copper catalyst, but slightly decreased conversion with the supported catalyst. A decrease in conversion was also observed with the introduction of water and ethanol in the feed, once again indicating a requirement for feed purity within the loop. A temperature range of 150-300°C was investigated with catalysts deactivating at temperatures exceeding 250°C. A pressure range identical to ethanol dehydrogenation was used: 0.1-0.5 MPa. Again, an empirical kinetic model allowed determination of the activation energy, the order of reaction and the frequency factor.

A novel catalytic process for producing high-purity, elevated-pressure hydrogen from synthesis gas was proposed and investigated. The process combines the advantages of low investment and operating costs with the flexibility to adapt to a small-scale operation. The process consists of a loop containing two complementary reactions: ethanol dehydrogenation and acetaldehyde hydrogenation. In one part of the loop, hydrogen is produced by dehydrogenation of ethanol to acetaldehyde. Since acetaldehyde is a liquid under standard conditions, it can be easily separated and pure hydrogen is obtained. In the other part of the loop, hydrogen contained in synthesis gas is reacted with acetaldehyde to produce ethanol and purified carbon monoxide. Ethanol, also a liquid under standard conditions, is easily removed and purified carbon monoxide is obtained, which can be further water-gas shifted to produce more hydrogen. Various dimensionless criteria were evaluated to confirm there was no significant effect of heat and mass transfer limitations and thus the experimental results represent true kinetics. Furthermore, a thermodynamic study was conducted using a Gibbs free energy minimization model to identify the effect of reaction conditions on ethanol/acetaldehyde conversion and determine the thermodynamically favourable operating conditions. Various catalysts were synthesized, characterized and screened for each reaction in a down-flow, fixed-bed quartz reactor. A novel gas chromatography analysis method allowing for an on-line detection of all products was also developed. Unsupported copper in the form of copper foam and copper supported on three different high surface supports were evaluated in ethanol dehydrogenation. Copper foam provided the lowest activity, because of its low surface area. Cu/SiO2 was the most active catalyst for ethanol dehydrogenation. The effects of temperature, pressure, residence time, and feed composition on ethanol conversion and product composition were determined. While increasing temperature or residence time resulted in increased ethanol conversion, elevated pressure and water content in the feed had no effect on ethanol conversion. On the other hand, acetaldehyde selectivity decreased with increasing temperature, pressure and residence time, as acetaldehyde participated in undesirable transformations to secondary products, out of which the most dominant was ethyl acetate. The maximum operating temperature was limited by the stability of the copper catalyst, which deactivated by sintering at temperatures higher than 300°C. The range of temperatures investigated was from 200°C to 350°C, while pressures ranged from atmospheric to 0.5 MPa. For ethanol:water ratios <1, the addition of water to the ethanol feed improved the catalyst stability and acetaldehyde selectivity, but a detrimental effect was observed at higher ratios. The introduction of acetaldehyde into the feed always lowered the conversion, thus indicating a need for stream purification within the loop. An empirical kinetic model was used to determine the activation energy, the order of reaction and the frequency factor. Unsupported and SiO2-supported copper catalysts were compared in acetaldehyde hydrogenation. Pure copper was identified as the best catalyst. Effects of temperature, pressure, residence time, feed composition and catalyst promoter on acetaldehyde conversion and product composition were evaluated. The acetaldehyde hydrogenation was enhanced by increased temperature, pressure and residence time and suppressed in presence of Fe or Zn promoters. Once again, at elevated temperature and residence time, ethanol combined with acetaldehyde to produce undesired ethyl acetate. CO acted as an inert when testing with the pure copper catalyst, but slightly decreased conversion with the supported catalyst. A decrease in conversion was also observed with the introduction of water and ethanol in the feed, once again indicating a requirement for feed purity within the loop. A temperature range of 150-300°C was investigated with catalysts deactivating at temperatures exceeding 250°C. A pressure range identical to ethanol dehydrogenation was used: 0.1-0.5 MPa. Again, an empirical kinetic model allowed determination of the activation energy, the order of reaction and the frequency factor.