| 1. |
- Aguilera, Adriana Freites, et al.
(författare)
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Epoxidation of fatty acids and vegetable oils assisted by microwaves catalyzed by a cation exchange resin
- 2018
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Ingår i: Industrial & Engineering Chemistry Research. - Washington : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 57:11, s. 3876-3886
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Tidskriftsartikel (refereegranskat)abstract
- Epoxidation of oleic acid and cottonseed oil was conducted in a semibatch reactor with in-situ-formed percarboxylic acid (peracetic acid or perpropionic acid), using hydrogen peroxide as an oxidizing agent and carboxylic acid (acetic acid or propionic acid) as oxygen carriers. Amberlite IR-120 was implemented as the catalyst. The system was comprised of a loop reactor, where the mixture was pumped through a single-mode cavity in which microwave irradiation was introduced. A heat exchanger was integrated into the system to replace microwave heating, to compare the results obtained via microwave heating versus conventional heating. The catalyst loading effect was studied, as well as the influence of microwave irradiation and the implementation of the SpinChem rotating bed reactor (RBR), in hopes of decreasing the influence of the internal mass transfer. The application of microwave irradiation results in an improvement of the reaction yield in the absence of a catalyst.
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| 2. |
- Aguilera, Adriana Freites, et al.
(författare)
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Screening of ion exchange resin catalysts for epoxidation of oleic acid under the influence of conventional and microwave heating
- 2019
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Ingår i: Journal of chemical technology and biotechnology (1986). - : John Wiley & Sons. - 0268-2575 .- 1097-4660. ; 94:9, s. 3020-3031
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Tidskriftsartikel (refereegranskat)abstract
- Background: For many chemical systems, it is of great importance to find a durable, active and efficient catalyst that improves the process performance. Epoxidation of oleic acid with peracetic acid (Prilezhaev oxidation) was carried out in an isothermal loop reactor in the presence of heterogeneous catalysts. The kinetic experiments conducted under microwave heating (MW) were compared with identical experiments carried out under conventional (conductive/convective) heating. Extensive screening of heterogeneous catalysts was conducted and the influence of microwave irradiation on the reaction kinetics was studied. Several ion exchange resins were screened to explore their applicability and activity in the epoxidation of oleic acid. The perhydrolysis reaction (peracetic acid formed in situ from acetic acid and H2O2) was promoted with the use of various solid acid catalysts: Amberlite IR-120, Amberlyst 15, Smopex®, Dowex 50x8-100, Dowex 50x8-50, Dowex 50x2-100 and Nafion™.Results: From the selected group of catalysts, Dowex 50-x8100 and Dowex 50x8-50 produced the highest yield of epoxidized oil. Only minor differences in the reactant conversion and the product yield were found in the experiments carried out under microwave exposure compared to the conventionally heated experiments in the presence of several ion exchange resins.Conclusions: The catalytic effect was much more prominent than the microwave effect, because the solid acid catalysts enhanced the slow step of the process, the perhydrolysis of acetic acid. The catalytic effect was very dominant and a considerable improvement of the oleic acid conversion and the epoxide yield was observed in the presence of the top-performing catalysts.
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| 3. |
- Aldea, Steliana, et al.
(författare)
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Crystallization of Nano-Calcium Carbonate : The Influence of Process Parameters
- 2016
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Ingår i: Chemie Ingenieur Technik. - : Wiley-VCH Verlagsgesellschaft. - 0009-286X .- 1522-2640. ; 88:11, s. 1609-1616
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Tidskriftsartikel (refereegranskat)abstract
- Precipitated calcium carbonate was synthesized by carbonation of calcium hydroxide in the presence and absence of ultrasound (conventional stirring) at atmospheric as well as at elevated pressures and different initial concentrations of Ca(OH)2. Spherical morphology of the formed calcite was favored at high Ca(OH)2 concentrations and low CO2 pressures. The presence of ultrasound did not show any influence on the reaction rate in case of efficient mixing. A small increase of the reaction rate was observed at lower CO2 pressures. Elevated pressures in combination with ultrasound did not lead to notable changes of reaction rate or particle morphology.
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| 4. |
- Arve, Kalle, et al.
(författare)
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Did Chemisorption Become an Obsolete Method With Advent of Tem? Comparison of Mean Particle Size and Distribution of Silver on Alumina
- 2011
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Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 141:5, s. 665-669
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Tidskriftsartikel (refereegranskat)abstract
- Silver particle size and dispersion on a Ag/Al2O3 for HC-SCR were examined by means of chemisorption and TEM. Experimental results showed that determination of the accurate mean particle size (mps) is challenging and that the both applied methods have specific characteristics increasing the inaccuracy in the results which has to be taken into account in evaluation of catalytic activity. The results from TEM imaging were found to depend highly on the mode in which the surface was scanned (bright field versus dark field). Generally the point resolution was higher in dark field but the obtained mps did not increased along with the increasing silver loading. The main limitation with the O-2-chemisorption was related to the choice of the stoichiometric factor between the adsorbent and silver atoms. However, together these techniques support each other and help to give a more realistic picture of the mean silver particle size, distribution and indications of the oxidation states on the alumina support.
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| 5. |
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| 6. |
- Behravesh, Erfan, et al.
(författare)
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Synthesis and characterization of Au nano particles supported catalysts for partial oxidation of ethanol : Influence of solution pH, Au nanoparticle size, support structure and acidity
- 2017
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Ingår i: Journal of Catalysis. - : Elsevier. - 0021-9517 .- 1090-2694. ; 353, s. 223-238
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Tidskriftsartikel (refereegranskat)abstract
- Partial oxidation of ethanol to acetaldehyde was carried out over gold catalysts supported on various oxides and zeolites by deposition precipitation. The special focus of this work was on the influence of H-Y zeolite surface charge on Au cluster size and loading linking it to activity and selectivity in ethanol oxidation and comparing with other studied catalysts. The catalysts were characterized by nitrogen physisorption, transmission electron microscopy (TEM), scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDXA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and zeta potential measurements. pH of the solution governed the Au NPs size within the range of 5.8–13.2 nm with less negatively charged surfaces leading to formation of smaller clusters. Au loading on H-Y zeolite with silica to alumina ratio of 80 was increased by raising the pH. In fact, H-Y-12 and H-Beta-25 were selective towards diethyl ether while acetaldehyde was the prevalent product on less acidic H-Y-80. The results demonstrated strong dependency of the catalytic activity on the Au cluster size. Namely turn over frequency (TOF) decreased with an increase in metal size from 6.3 to 9.3 nm on H-Y-80. Selectivity towards acetaldehyde and ethyl acetate did not change significantly on H-Y-80 within 6.3–9.3 nm Au particle size range. On Al2O3 support, however, selectivity towards acetaldehyde increased considerably upon diminishing Au average particle size from 3.7 to 2.1 nm.
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| 7. |
- de Araujo Filho, Cesar A., et al.
(författare)
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A comprehensive study on the kinetics, mass transfer and reaction engineering aspects of solvent-free glycerol hydrochlorination
- 2014
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 120, s. 88-104
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Tidskriftsartikel (refereegranskat)abstract
- The thorough kinetic study of the solvent-free hydrochlorination of glycerol using gaseous hydrogen chloride in a laboratory-scale semibatch reactor was carried out. A wide set of experiments was performed where reaction temperature (70–120 °C), catalyst concentration (0–50% by moles) and partial pressure (0.25, 0.5, 0.75 and 1.0 atm) were varied. Acetic acid was used as a homogenous catalyst. A more accurate approach was given to the semibatch reactor modeling since it was demonstrated that the liquid volume significantly increased along the reaction. The concentration of HCl was determined experimentally and it was possible to observe the influence of the reaction parameters on the HCl uptake. It was also evidenced that a non-catalytic hydrochlorination takes place in the system and its effect is non-negligible, especially at high temperatures. A new kinetic model was proposed and tested in order to explain the experimental observations. Non-linear regression analysis was successfully applied on the experimental data and the modeling results showed a satisfactory agreement. The model was able to estimate the activation energies for both catalyzed and non-catalyzed experiments. A new concept named Catalyst Modulus was derived from the kinetic equations and then verified with experimental data; the fit of this parameter was very high, thus, pointing out the validity of the model.
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| 8. |
- de Araujo Filho, Cesar A., et al.
(författare)
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Dynamic modelling of homogeneously catalysed glycerol hydrochlorination in bubble column reactor
- 2016
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Ingår i: Chemical Engineering Science. - : Elsevier. - 0009-2509 .- 1873-4405. ; 149, s. 277-295
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Tidskriftsartikel (refereegranskat)abstract
- The homogeneously catalysed glycerol hydrochlorination was thoroughly investigated in a continuous isothermal co-current bubble column reactor over a wide range of reaction parameters, such as temperature (70–120 °C), catalyst concentration (3–12%), liquid flow rate (6–12 mL/min) and gas flow rate (0.4–1.0 L/min). The flow patterns inside the reactor were studied by means of step response residence time distribution experiments and by high-speed camera images. The fluid dynamics of the system presented an unusual behaviour due to the extremely high solubility of HCl in the reaction mixture. Interestingly, the fluid dynamics imposed severe limitations to the reaction conversion. The axial dispersion model was applied for describing the dynamic changes in concentrations of compounds. Kinetic and solubility data were collected from previous work on glycerol hydrochlorination in semi-batch reactor conducted by our research group. The bubble column model was able to successfully describe the dynamic behaviour of 29 experiments, as well as estimate hydrodynamics and mass transfer parameters.
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| 9. |
- Eta, Valerie, et al.
(författare)
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Loop vs. batch reactor setups in the fractionation of birch chips using switchable ionic liquids
- 2014
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Ingår i: Chemical Engineering Journal. - : Elsevier. - 1385-8947 .- 1873-3212. ; 238, s. 242-248
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Tidskriftsartikel (refereegranskat)abstract
- The fractionation of lignocellulosic feedstock into its major components with high purity represents an important commercialization milestone in the transformation of lignocellulosic forest derived products into fuels and commodity chemicals. A comparison between the traditionally used batch reactor and loop reactor systems demonstrates that improved dissolution of hemicelluloses and lignin are obtained using switchable ionic liquids in a loop reactor system which facilitates decreased heat and mass transfer restrictions. The treatment of birch chips using switchable ionic liquid (SIL) based on 1,8-diazabicyclo-[5.4.0]-undec-7-ene, CO2 and diethanolamine at 120 °C for 30 h in a loop reactor resulted in 24% loss of original weight of wood corresponding to dissolution of 52 wt.% of hemicelluloses and 42 wt.% of lignin, respectively, as opposed to 20% weight loss corresponding to 43 wt.% dissolution of hemicelluloses and 38 wt.% of lignin in the batch system. The non-dissolved material obtained from both reactors was efficiently fibrillated and softened cellulose fibres. The flow of switchable ionic liquid through the loop reactor and agitation of the chips enhanced the dissolution of hemicelluloses and lignin. The dissolved fractions recovered from spent SIL after treatment contained both hemicelluloses and lignin.
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| 10. |
- Hernandez Carucci, José R, et al.
(författare)
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Preparation and characterization of coated microchannels for the selective catalytic reduction of NOx
- 2012
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Ingår i: Focus on Catalysis Research. - New York : Nova Science Publishers. - 9781621004776 ; , s. 209-236
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Bokkapitel (refereegranskat)abstract
- Shallow microchannels (Ø= 460 m) were successfully coated with different catalytically active phases, e.g., Cu-ZSM-5, Cu/(ZSM-5+Al2O3), Au/Al2O3, Ag/(Al2O3+Ionic liquid) and Ag/Al2O3, and tested on the hydrocarbon-assisted selective catalytic reduction of NOx (HC-SCR) with different model bio-derived fuels, i.e., methyl- and ethyl laurate produced by transesterification and hexadecane, a paraffinic component that can be produced by decarboxylation and/or decarbonylation of natural oils and fats. Characterization of the washcoats was done by means of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDXA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), showing a dependence of the metal loading with the impregnation time and the precursor concentration. The Ag/Al2O3 catalysts exhibited, in general, the highest activities towards the NOx reduction. Optima in impregnation time and concentration of AgNO3 solution displaying the highest activity in HC-SCR among the prepared Ag/Al2O3 washcoats were established. A combination of Cu-ZSM-5 or Cu/(ZSM-5+Al2O3) and the optimum Ag/Al2O3 catalyst were tested in order to improve the low temperature reduction in SCR with hexadecane as a reducing agent. The enhancement of the activity at low temperatures (< 350 °C) was up to seven-fold compared to the case when only Ag/alumina was used. The effect of the hydrocarbon concentration (hexadecane) and the presence of water in the feed were also investigated.
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