Kinetic study of CO hydrogenation over co-precipitated iron–nickel catalyst

The kinetic of the Fischer–Tropsch synthesis over a Fe–Ni/Al₂O₃ catalyst was investigated in a fixed bed micro reactor. Experimental conditions were varied as follow: reaction pressure 2–10 bar, H₂/CO feed ratio of 2/1 and space velocity of 96–450 cm³(STP)/h/gram_catalyst at the temperature range 523–573 K. On the basis of carbide-enol mechanism and Langmuir–Hinshelwood–Hougen–Watson (LHHW) type rate equations, seventeen kinetic expressions for CO consumption were tested and interaction between adsorption HCO and dissociated adsorption hydrogen as the controlling step gave the most plausible kinetic model. The activation energy was 46.5 kJ/mole for optimal kinetic model.     

Modeling and operating conditions optimization of Fischer–Tropsch synthesis in a fixed-bed reactor

The effect of a range of operation variables such as pressure, low temperature and H₂/CO molar feed ration the catalytic performance of 80%Co/20%Ni/30 wt% La₂O₃/1 wt% Cs catalyst was investigated. It was found that the optimum operating conditions is a H₂/CO = 2/1 molar feed ratio at 260 °C temperature and 2 bar pressure. Reaction rate equations were derived on the basis of the Langmuir–Hinshelwood–Hougen–Watson (LHHW) type models for the Fischer–Tropsch reactions. The activation energy obtained was 59.69 kJ/mol for optimal kinetic model.     

Sunflower oil hydrogenation on Pd in supercritical solvents: Kinetics and selectivities

The partial hydrogenation of sunflower oil on a few supported Pd catalysts in supercritical (SC) dimethyl ether (DME) as reaction solvent was studied to obtain hydrogenates with low trans C 18:1 and stearic contents.The kinetics was determined on eggshell 0.5% Pd/Al₂O₃ and uniform 2% Pd/C catalysts using a sequential experimental design in a continuous, radial-flow, internal recycle reactor. The operating variables were temperature (456–513 K), pressure (18–23 MPa) and the space-velocity (WHSV = 41–975 h⁻¹). The rotation frequency and the molar feed concentration (oil:H₂:DME) were held constant at 157 rad/s and 1:4:95 mol%, respectively. Kinetic scheme was based on that published before. Some reactor runs were simulated using mixed-flow assumption and the kinetics data for both systems with good results. A comparison was established between the eggshell 0.5% Pd/Al₂O₃ in DME and the data for 2% Pd/C in propane with respect to trans production and stearic formation. trans seems to be lower using 2% Pd/C in propane, while the undesired stearic formation is less on the eggshell 0.5% Pd/Al₂O₃ catalyst in DME. An overview is presented on the merits of the catalysts available for the SCF process in terms of linoleic selectivity and trans yield on a few vegetable fats.     

Low-pressure DME synthesis with Cu-based hybrid catalysts using temperature-gradient reactor

Dimethyl ether (DME), the target product of this study, has many advantages as diesel fuel. The aim of this study is to develop a catalytic process in which 90% CO conversion to DME and CO₂ from syngas (3CO+3H₂→DME+CO₂) is attained at 1–3 MPa. In such a process, both recycling loop and compression of syngas can be omitted resulting in an economic process based on unused, dispersed and small-scale carbon resources. To overcome the equilibrium conversion limit we designed temperature-gradient reactor (TGR). In TGR, the temperature of the catalyst bed decreases along with the down flow of reaction gas. The performance of the catalyst in TGR was much higher than that in a conventional isothermal fixed bed reactor. For example, 90% CO conversion and high STY (1.1 kg MeOH eqiv./kg cat./h) was attained at the same time in TGR at 550–510 K, 3 MPa.     

Filtration and loading characteristics of granular bed filters

The purpose of this study was to investigate the filtration and loading characteristics of granular bed filters. Stainless steel holders (diameter 71.6 mm, height 70 mm) were fabricated to accommodate 500 g of zirconium oxide (ZrO₂) beads, as the packed media of granular bed. Monodisperse ZrO₂ granules (0.3, 0.8, 2 and 4 mm in diameter) were used to demonstrate the effect of the granule size and packing geometry on both pressure drop and aerosol penetration. From the filter quality perspective, the selection of the ‘best” filter is complicated. Assuming a low face velocity (e.g., 0.58 cm/s), large granule size is more cost-effective because of the higher filter quality factor. The phenomenon implies that the gain in filtration efficiency due to larger surface area (of small granules in the filter) did not compensate for the increase in air resistance. After the cake formation point, the dust cake on glass fiber filter became compressed. This dust cake compaction caused the pressure to drop precipitously and intermittently. In contrast, the rate of increase in pressure drop of the dust cake formed on the granular bed filters decreased with time probably due to the pinhole channels in the increasing mass load. The size and density of the pinholes are determined by the granule size, the face velocity and the size of the challenge aerosols.     

Phase behavior measurement for poly(isobornyl acrylate) + cosolvent systems in supercritical solvents at high pressure

We have conducted experiments to obtain cloud-point data of binary and ternary mixtures for poly(isobornyl acrylate) [P(IBnA)] (Mw = 100,000) + isobornyl acrylate(IBnA) in supercritical carbon dioxide (CO₂), P(IBnA) (Mw = 100,000) + dimethyl ether (DME) in CO₂, P(IBnA) (Mw = 100,000) in propane and butane, and P(IBnA) (Mw = 1,000,000) in propane, propylene, butane and 1-butene at high pressure conditions. Phase behaviors for these systems were measured at a temperature range from 323.4 K to 474.1 K and pressure up to 296.7 MPa. The cloud-point curves of P(IBnA) (Mw = 100,000) + IBnA and DME in CO₂ change from upper critical solution temperature (UCST) behavior to lower critical solution temperature (LCST) behavior as IBnA and DME concentration increases, and liquid–liquid–vapor phase behavior appears for the P(IBnA) (Mw = 100,000) + CO₂ + 80.3 wt.% IBnA system. Phase behaviors of P(IBnA) and 50 wt.% IBnA in CO₂ and P(IBnA) in propane and butane show the pressure difference in accordance with Mw = 1,000,000 and Mw = 100,000 of P(IBnA). Also, the solubility curves for IBnA in supercritical CO₂ were measured at a temperature range of (313.2–393.2) K and pressure up to 22.86 MPa. The experimental results were modeled with the Peng–Robinson equation of state (PR-EOS) using a mixing rule including two adjustable parameters. The critical property of IBnA is estimated with the Joback–Lyderson method.     

Effect of the hybrid catalysts preparation method upon direct synthesis of dimethyl ether from synthesis gas

Direct synthesis of DME from synthesis gas attains more attention recently due to higher conversion and lower cost in comparison to dehydration of the methanol. In this work Synthesis gas To Dimethylether (STD) conversion was examined on various hybrid catalysts prepared by seven different methods. These catalysts had the same general form as CuO/ZnO/Al₂O₃ with theoretical weight ratio 31/16/53, respectively. A novel preparation method for hybrid catalyst namely sol–gel impregnation has also been developed which showed better performance in comparison with the other methods. Also, in order to find out the effect of various alumina contents at a fixed CuO/ZnO ratio on the performance of the hybrid catalyst, a series of catalysts with different contents of alumina have been prepared by sol–gel impregnation method. The optimum weight ratio for CuO/ZnO/Al₂O₃ catalyst has been found to be about 2:1:5, respectively. These catalysts characterized by TPR, XRD, XRF, BET, TGA, N₂O absorption. The catalysts performance were tested at 240 °C, 40 bar and space velocity 1000 ml/g_cat.h, with the inlet gas composition H₂/CO/N₂ = 64/32/4 in a micro slurry reactor.     

Methane steam reforming in large pore catalyst

In this work we have studied the performance of catalyst extrudates of Ni-Al₂O₃ promoted with potassium for steam methane reforming. The most interesting property of this catalyst is the presence of large pores (average diameter of 8×10^?4 m) to reduce diffusional limitations. We have determined the true kinetics using catalyst powder in the temperature range covering 757–804 K. Furthermore, experiments using a fixed bed filled with extrudates were performed in the temperature range covering 701–800 K at constant methane/steam ratio for different feed flowrates.In the true kinetic experiments using catalyst powder it was observed that this catalyst has a very high CO₂ selectivity against CO. The conversion of the catalyst is smaller than other commercial materials due to the smaller content of Ni (10%).Experiments using catalyst extrudates showed that the reaction suffers from strong mass and heat limitations: diffusion of reactants/products and heat transfer in the gas/solid interface. The presence of large pores has an important contribution in decreasing the resistance to mass transfer in particles with 1.1×10^?2 m diameter. At 800 K and 2 bar the effectiveness factor was about 0.43 for the steam methane reforming reaction and 0.41 for the global reaction.     

Kinetic study of CO hydrogenation on the MgO supported Fe–Co–Mn sol–gel catalyst

The kinetic of the Fischer–Tropsch synthesis over the MgO supported Fe–Co–Mn catalyst prepared using sol–gel procedure, was investigated in a fixed bed micro-reactor. Experimental conditions were varied as follow: reaction pressure 5–20 bar, reaction temperature 220–250 °C, H₂/CO feed molar ratio of 0.67–2 and space velocity range of 2400–3600 h^?1. 18 models according to the Langmuir–Hinshelwood–Hougen–Watson (LHHW) type rate equation were derived, and the reaction rate is fitted fairly well by one kinetic expressions based on LHWW mechanism. The kinetic parameters were estimated with non-linear regression method. The activation energy was obtained 110.9 kJ/mol for the best-fitted model.     

Preparation and characterization of Al2O3/TiC micro–nano-composite ceramic tool materials

An Al₂O₃-based composite ceramic tool material reinforced with micro-scale and nano-scale TiC particles was fabricated by a hot-pressing technology with cobalt additive in different sintering processes. The microstructure, indention cracks and phase composition of composites were characterized with scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The experimental results showed that Al₂O₃/TiC_μ/TiC_n micro–nano-composite containing 6 vol% nano-scale TiC and 35 vol% micro-scale TiC, which were sintered under a pressure of 32 MPa at a temperature of 1650 °C in vacuum for 20 min, had optimum mechanical properties. The addition of both nano-scale TiC and Co contributed to the microstructure evolution and the improvement of mechanical properties. Effects of nano-scale TiC on mechanical properties were investigated. The toughening and strengthening mechanisms of micro–nano-composites were discussed.     

Outstanding efficiency of indium in bimetallic catalysts for hydroconversion of bioacids to bioalcohols

Step by step reduction of acetic acid (AA) to ethanol was investigated over novel bimetallic catalysts (PtIn/Al₂O₃) for the processing of VFAs (volatile fatty acids) that can be produced simply by thermochemical or biological biomass degradation. A fixed bed flow-through reactor was applied with hydrogen stream at 21 bar total pressure in the temperature range of 220–380 °C. AA hydroconversion activity of the parent alumina supported Pt catalyst and the yield of selectively produced alcohol can be increased drastically by In₂O₃ addition. Appearance of metallic indium creating a bimetallic catalyst can direct the consecutive catalytic reduction to ethanol formation inhibiting hydrodecarbonylation. Comparing the In-containing bimetallic catalysts studied recently, NiIn-catalyst showing similar activity to that of the PtIn-catalyst can be a cheap substitute for the expensive Pt catalysts in the reduction carboxylic acids.     

Optimization of the supercritical fluid coextraction of oil and diterpenes from spent coffee grounds using experimental design and response surface methodology

The reported work aimed at the optimization of operating conditions of the supercritical fluid extraction (SFE) of spent coffee grounds (SCG) using pure or modified CO₂, with particular emphasis on oil enrichment with diterpenes like kahweol, cafestol and 16-O-methylcafestol. The analysis comprised the application of Box–Behnken design of experiments and response surface methodology, and involved three operating variables: pressure (140–190 bar), temperature (40–70 °C) and cosolvent (ethanol) addition (0–5 wt.%). The best conditions to maximize total extraction yield are 190 bar/55 °C/5 wt.% EtOH, leading to 11.97% (g_oil/100 g_SCG). In terms of the concentration of diterpenic compounds in the supercritical extracts, the best operating conditions are 140 bar/40 °C/0 wt.% EtOH, providing 102.90 mg g⁻¹_oil. The measurement of extraction curves near optimized conditions (140 bar/55 °C/0 wt.% EtOH and 190 bar/55 °C/0 wt.% EtOH) confirmed the trends of the statistical analysis and revealed that SFE enhances diterpenes concentration by 212–410% at the expenses of reducing the extraction yield between 39% and 79% in comparison to n-hexane extraction.     

Dynamic behaviour of sewage sludge incineration in a large-scale bubbling fluidised bed in relation to feeding-rate variations

In this paper, a mathematical model is developed for the simulation of a large-scale sewage sludge incineration plant. The model assumes the bed to consist of a fast gas phase, an emulsion phase and a fuel particle phase with specific consideration for thermally-thick fuel particles. The developed model is employed to predict the dynamic response of the bed combustion to fluctuations in sludge feeding-rate. Calculation results indicate that the bed combustion is sensitive to fluctuations with response times greater than 30 min, but severe delays exist for both outlet oxygen level and bed temperatures; from 6 to 13 min for O₂ and 22–45 min for temperatures. Depending on the fluctuation frequency, the corresponding phase shifts are 39–96° for outlet O₂, 138–336° for bed temperature and 80–336° for freeboard temperature.     

Direct conversion of syngas to DME as a green fuel in a high pressure microreactor: Influence of slurry solid content on characteristics and reactivity of washcoated CuO–ZnO–Al2O3/HZSM-5 nanocatalyst

Microchannels of a stainless steel microreactor were successfully washcoated with slurry of Cu–ZnO–Al₂O₃/HZSM-5 (CZAZ) nanocatalyst with different concentrations (10, 20 and 30 wt.%). The properties of nanocatalyst and the washcoated microchannels were investigated by XRD, FESEM, N₂ physisorption, FTIR, EDX-Dot mapping and EDX-Line mapping analysis. The best adherence was observed for 20 wt.% catalyst which has a uniform coating, almost no cracks and homogenous dispersion of copper and zinc. Trend of weight gain during 10 soaks in catalyst slurry was very slow for 10 wt.% but faster for 20 and 30 wt.%. Low amount of weight gain was observed for the last soaks of catalyst slurry in the case of 30 wt.% washcoating. The performance of microreactor with different slurry concentrations were evaluated in direct synthesis of DME at 200–300 °C, 60–150 cm³/min and 40 bar. Regardless of slurry concentration, the microreactor exhibited a better reactivity in comparison to fixed-bed reactor performance. Among three different slurry concentrations, 20 wt.% catalyst slurry revealed the best reactivity in direct DME synthesis. The reduction in reactor performance at higher flow rates was significant in the fixed-bed reactor while microreactor, particularly 20 wt.% washcoated channels, revealed less drastic reduction.     

Extraction of lipids from fermentation biomass using near-critical dimethylether

The extraction of lipids from both wet and dry biomass produced by fermentation has been carried out using near-critical dimethylether (DME) as the extraction solvent. Fermentations were carried out from a shake flask up to a 300 L scale using the microorganism Mortierella alpina, and up to a 20 L scale for Phaffia rhodozyma and Agrobacterium tumefaciens. The lipids extracted at a laboratory and pilot scale from the biomasses were enriched in arachidonic acid, astaxanthin, and co-enzyme Q10 respectively. Extractions were also performed on marine microalgae, produced by a proprietary fermentation process, to obtain lipids rich in EPA. Lipids were extracted from wet biomass using DME, which removes the need to dry the biomass. Water is also co-extracted, which has to be separated from the lipid. The biomass shrunk considerably during packed bed extraction of wet biomass, leading to channelling. Repacking and re-extraction of the packed bed enabled full lipid yields to be obtained. The extraction of lipids from biomass suspended in fermentation broth showed considerable promise, and lipid yields were improved due to the recovery of lipids that had been exuded into the broth from the microorganism. In contrast, the extraction of lipids from freeze-dried biomass using DME was routine, yields were substantially higher than using CO₂ or CO₂ + ethanol, but were lower than from wet biomass. DME also extracted polar lipids from both wet and dry biomass, leading to the higher total lipid yields compared to CO₂. Separate extraction of non-polar and polar lipids was possible by sequential extraction of dry biomass using initially CO₂ followed optionally with ethanol co-solvent; and then DME.     

Sintering,microstructure and electricity properties of ITO targets with Bi2O3–Nb2O5 addition

High density and low electrical resistivity ITO targets were prepared by normal pressure sintering in oxygen with Bi₂O₃–Nb₂O₅ addition. The relative density, microstructure and electrical properties of the ITO targets can be adjusted by changing the sintering temperature (1350 °C~1550 °C) and the content of Bi₂O₃–Nb₂O₅. The results show that the sintering temperature of ITO targets with Bi₂O₃–Nb₂O₅ decreased from 1550 °C to 1450 °C, and the maximum relative density (99.6%) and the lowest electrical resistivity (1.78×10⁻⁴ Ω cm) were reached when the sintering temperature was 1450 °C with 5 wt% Bi₂O₃–Nb₂O₅. The carrier concentration increased as the increase of the contents of Bi₂O₃–Nb₂O₅ and sintering temperature. The mobility first increased, and then decreased above 1450 °C as the sintering temperature increased.     

Gasification reactivity of char from dried sewage sludge in a fluidized bed

The gasification reactivity of char from dried sewage sludge (DSS) applicable to fluidized bed gasification (FBG) was determined. The char was generated by devolatilizing the DSS with nitrogen at the selected bed temperature and was subsequently gasified by switching the fluidization agent to mixtures of CO₂ and N₂ (CO₂ reactivity tests) and steam and N₂ (H₂O reactivity tests)._. The tests were conducted in the temperature range of 800–900 °C at atmospheric pressure, using partial pressure of the main reactant in the mixture (CO₂ or H₂O) in the range of 0.10–0.30 bar. Expressions for the intrinsic reactivity (free of diffusion effects) as a function of temperature, partial pressure of gas reactant (CO₂ or H₂O) and degree of conversion were obtained for each reaction. For the whole range of conversion it was found that the char reactivity in an H₂O–N₂ mixture was roughly three times higher than that in a mixture with the corresponding partial pressure of CO₂. The reactivity was only influenced by particle size greater than 1.2 mm in the tests with steam at 900 °C. It was demonstrated that the method of char preparation greatly influences the reactivity, highlighting the importance of generating the char in conditions similar to that in FBG.     

Catalytic decomposition of biomass tars with iron oxide catalysts

Catalytic gasification of wood (Cedar) biomass was carried out using a specially designed flow-type double beds micro reactor in a two step process: temperature programmed non-catalytic steam gasification of biomass was performed in the first (top) bed at 200–850 °C followed by catalytic decomposition gasification of volatile matters (including tars) in the second (bottom) bed at a constant temperature, mainly 600 °C. Iron oxide catalysts, which transformed to Fe₃O₄ after use possessed catalytic activity in biomass tar decomposition. Above 90% of the volatile matters was gasified by the use of iron oxide catalyst (prepared from FeCl₃ and NH_3aq) at SV of 4.5 × 10³ h^?1. Tar was decomposed over the iron oxide catalysts followed by water gas shift reaction. Surface area of the iron oxide seemed to be an important factor for the catalytic tar decomposition. The activity of the iron oxide catalysts for tar decomposition seemed stable with cyclic use but the activity of the catalysts for the water gas shift reaction decreased with repeated use.     

High pressure plant for heterogeneous catalytic CO2 hydrogenation reactions in a continuous flow microreactor

The CO₂ hydrogenation to methanol is favored by high pressure from the thermodynamic point of view. Mostly experimental work on this reaction is limited at 400 bar due to technical and safety reasons. In this work we present a high pressure plant able to conduct CO₂ hydrogenation reactions at pressures up to 950 bar in a capillary microreactor; we focus on the influence of pressure concerning process intensification.To validate the plant functionality the reverse water–gas shift (RWGS) reaction was conducted over a 1 wt% Pt/CeO₂ catalyst at 450 °C and between 200 and 950 bar. A mass flow controller for hydrogen was developed due to lack of commercial available hydrogen mass flow controller able to work in the micro liter per minute range and up to 1000 bar. Additional to the RWGS reaction two more reactions take place. The first is the CO disproportionation reaction which results in deposited carbon on the catalyst. The second is the subsequent hydrogenation of carbon to methane. The experimentally determined CO₂ conversion is clearly below the equilibrium of the entire reaction network, hence the reaction is kinetically limited. The reaction performance increases with pressure showing process intensification.     

High pressure phase behavior of poly[isopropyl acrylate] and poly[isopropyl methacrylate] in supercritical fluid (SCF) solvent and SCF solvent + cosolvent mixtures

Cloud-point data are reported for poly(isopropyl acrylate) [P(IPA)] in CO₂, propane, propylene, butane, 1-butene, and dimethyl ether (DME) and for poly(isopropyl methacrylate) [P(IPMA)] in CO₂. P(IPA) + alkene cloud-point curves are ∼100 °C lower than the P(IPA) + alkane curves, which are close to the P(IPA) + CO₂ curve located at temperatures greater than 130 °C and pressures of 2500 bar. P(IPA) dissolves in pure DME at conditions as mild as 50 °C and 200 bar. Since IPA and IPMA monomers are used as cosolvents with CO₂, binary IPA + CO₂ and IPMA + CO₂ data are reported to complement the ternary cloud-point data. Both monomer + CO₂ mixtures exhibit type-I behavior and both are adequately modeled with the Peng–Robinson equation of state. IPMA is a more effective cosolvent than IPA. The polymer + CO₂ + monomer phase behavior suggests that it is viable to polymerize IPA or IPMA in CO₂ at moderate operating conditions.