Kinetic Modeling of Sorbitol Aqueous-Phase Reforming over Pt/Al₂O₃

Aqueous-phase reforming of polyols was investigated in the current work by mathematical modeling using sorbitol, which represents a C₆-polyol originating from biomass processing. The reaction was studied in the presence of Pt/Al₂O₃ catalyst at 498 K and 29.3 bar in a continuous fixed-bed reactor under kinetic control. The feasible scheme describing main pathways of sorbitol transformation was proposed considering experimental and literature data. The kinetic model was compared with experimental data through numerical data fitting showing good correspondence

Oxidation of Starch by H₂O₂ in the Presence of Iron Tetrasulfophthalocyanine Catalyst: The Effect of Catalyst Concentration, pH, Solid–Liquid Ratio, and Origin of Starch

Several types of starches were oxidized by H₂O₂ in the presence of iron tetrasulfophthalocyanine catalyst (FePcS) in batch mode, and the kinetics of the H₂O₂ decomposition was followed when varying the catalyst concentration and solid to liquid ratio of the starch and aqueous phase. Mainly, waxy corn starch with high content of amylopectin and potato starch were used, but also high amylose starch was studied. The COOH content was determined for the final oxidized starch. It was found that, with 40 mg of catalyst and the starch present in a larger amount, the H₂O₂ decomposition followed a first order kinetics with an initial decomposition rate in the range of 0.10 mol/L·h. Significantly less starch slowed down the decomposition rate to 0.05 mol/L·h; however, when no starch was present, the decomposition increased to a maximum of 0.14 mol/L. On the contrary, absence of catalyst resulted in a linear H₂O₂ decomposition profile. The FePcS catalyst concentration had a large impact on the decomposition of H₂O₂ regardless of the starch amount or the starch origin. When using very low starch amounts in relation to the catalyst amount, brown solid residues were observed on the reactor wall, indicating that iron was defragmented from the catalyst

Esterification of Fatty Acids and Short-Chain Carboxylic Acids with Stearyl Alcohol and Sterols

Esterification of tall oil fatty acids by neutral components, such as stearyl alcohol and sterols, is an undesired reaction; a potential solution is to eliminate the neutral components by a competing esterification with short-chain carboxylic acids. Esterification of fatty acids and short-chain carboxylic acids with stearyl alcohol and sterols was studied in a laboratory-scale glass reactor in the temperature range of 60–140 °C. Linoleic acid (LA) was used as a model component for fatty acid esterification with stearyl alcohol (StOH) and sitosterol (SitOH). Linoleic acid underwent esterification with stearyl alcohol and sitosterol. In the presence of short-chain carboxylic acids, such as formic and acetic acid, the esterification of linoleic acid by stearyl alcohol was efficiently suppressed because stearyl alcohol reacted with the short-chain carboxylic acid. Formic acid catalyzed the formation of dienes from sitosterol and campesterol. The esterification and dehydration processes were verified by gas chromatographic analysis and extensive kinetic studies. Mathematical models for esterification and dehydration were developed and successfully applied to a selected part of experimental data

Kinetics of the One-Pot Transformation of Citronellal to Menthols on Ru/H-BEA Catalysts

Temperature, pressure, and concentration variation experiments were conducted in the one-pot-transformation of citronellal to menthol with 1%Ru/H-BEA-25 as bifunctional catalyst. This reaction requires a combination of a cyclization and hydrogenation step, therefore the product distribution strongly depends on reaction conditions, especially on the reaction temperature. At lower temperatures the consecutive hydrogenation of citronellal prevails, whereas at high temperatures defunctionalization of menthols is favored leading to a maximum menthol yield at 373 K. A kinetic model was proposed based on a Langmuir–Hinshelwood mechanism and different active sites for cyclization and hydrogenation reactions. Kinetic parameters (reaction constants, activation energies, and adsorption coefficients) were estimated by using nonlinear regression

Kinetics of Catalytic Wet Peroxide Oxidation of Phenolics in Olive Oil Mill Wastewaters over Copper Catalysts

During olive oil extraction, large amounts of phenolics are generated in the corresponding wastewaters (up to 10 g dm^–3). This makes olive oil mill wastewater toxic and conventional biological treatment challenging. The catalytic wet peroxide oxidation process can reduce toxicity without significant energy consumption. Hydrogen peroxide oxidation of phenolics present in industrial wastewaters was studied in this work over copper catalysts focusing on understanding the impact of mass transfer and establishing the reaction kinetics. A range of physicochemical methods were used for catalyst characterization. The optimal reaction conditions were identified as 353 K and atmospheric pressure, giving complete conversion of total phenols and over 50% conversion of total organic carbon content. Influence of mass transfer on the observed reaction rate and kinetics was investigated, and parameters of the advanced kinetic model and activation energies for hydrogen peroxide decomposition and polyphenol oxidation were estimated

Sibunit-Supported Mono- and Bimetallic Catalysts Used in Aqueous-Phase Reforming of Xylitol

Carbon-supported mono- and bimetallic catalysts prepared via incipient wetness impregnation were systematically studied in aqueous-phase reforming (APR) of xylitol aiming at hydrogen production from biomass. The catalytic performance of several VIII group metals and their combinations, such as Pt, Ni, Pt–Ni, Re, Pt–Re, Ru, Pt–Ru, and Pt–Co, was compared for xylitol APR in a fixed-bed reactor at 225 °C and 29.7 bar (N₂). Ni/C, Ru/C, and Re/C catalysts displayed significantly lower activity compared to others. Activity and selectivity to H₂ of bimetallic Pt–Ni/C, Pt–Co/C, and Pt–Ru/C catalysts were close to that of Pt/C. Pt–Re/C catalyst showed an outstanding performance which was accompanied by a shift of the reaction pathways to the alkane formation and thereby lower hydrogen selectivity. Addition of the second metal to Pt was not found to be beneficial for hydrogen production, thus leaving Pt/C as the optimum carbon-supported catalyst

Direct Amination of Dodecanol over Noble and Transition Metal Supported Silica Catalysts

Direct amination of 1-dodecanol with NH₃ and H₂ over Rh, Pt, Ir, Ru, Ni, Cu, and Co catalysts on SiO₂ has been studied. Catalyst synthesis was performed to allow high metal dispersion. The catalysts were characterized by TPO/TPR-MS, N₂ physisorption at 77 K, transmission electron microscopy, ICP analysis, and XPS. Through this characterization it was possible to relate the physical properties of the catalysts with activity and selectivity in 1-dodecanol amination. Iridium and ruthenium catalysts showed the highest conversion, about 77% after 24 h, and the selectivity of 78% and 81%, respectively, toward the desired product 1-dodecylamine. The Ru catalyst exhibited the highest yield of the desired product. In the conditions studied, the conversion increased in the order Cu < Ni < Rh < Pt < Co < Ir < Ru, and the selectivity was the highest for Ni and Co after 24 h. Both activity and selectivity of an oxidized Ir/SiO₂ catalyst increased considerably as the reaction progressed showing clearly that <i>in situ</i> catalyst reduction occurs being beneficial for dodecanol amination. High activity of Ir was also related to high metal dispersion

Catalytic Transformations of Birch Kraft Pulp

The goal of the work was to investigate hydrolysis and hydrogenation of a mixture of cellulose and hemicelluloses. Hydrolysis and hydrolytic hydrogenation of bleached birch (betula) kraft pulp from a Finnish pulping mill and microcrystalline cellulose (Aldrich) into sugars and sugar alcohols was carried out in the liquid phase in a batch mode under 20 bar of hydrogen at 458 K. Proton forms of different microporous and mesoporous materials, Pt modified MCM-48, MCM-41 mesoporous material, and Pt on Al₂O₃ were used in the catalytic experiments. The conversion of cellulose and hemicelluloses was dependent on the type of zeolite structure, strength of active sites, their number, and presence of metal. The ratio of formed monomers/dimers varied because of the pore size of the used catalyst. The yields of the main products, for example, sugars, sugar alcohols, and furfurals (xylose, glucose, xylitol, sorbitol, furfural, furfuryl alcohol, and 5-hydroxymethyl furfural), were shown to depend on the type of substrate as well as on the active sites, acidity, presence of metal, and structure of the zeolite and mesoporous material

One-Pot Synthesis of Menthol from Citral over Ni/H-β-38 Extrudates Containing Bentonite Clay Binder in Batch and Continuous Reactors

Optimization of bifunctional Ni catalysts was performed to enhance the catalytic performance in the one-pot synthesis of commercially valuable menthol from citral. The effect of nickel precursors (nitrate, chloride, acetate, and sulfate) and the addition of bentonite clay was investigated in citral transformations in a batch reactor at 70 °C and 10 bar hydrogen, demonstrating higher activity for the Ni-H-β-38-bentonite composite derived from a nickel nitrate precursor, which can be attributed to a higher surface area, optimal Brønsted to Lewis acidity and metal particle size, as well as the egg-shell distribution of Ni particles. H-β-38 impregnated with nickel nitrate, followed by calcination and reduction, was shaped with bentonite as a binder to give extrudates for exploring the citral transformations in the trickle-bed reactor at 50–70 °C and 10 bar hydrogen. The highest selectivity to the desired menthols of 45% was obtained with 70% stereoselectivity to the menthol isomer at 70 °C. The apparent activation energy for citral transformations to menthols of 18.6 kJ/mol indicated the presence of mass transfer limitations. Catalytic activity was linked with the physical-chemical properties, which were characterized by transmission electron microscopy, X-ray diffraction, temperature-programmed reduction, Fourier transform infrared spectroscopy with pyridine, N2 physisorption, and inductively coupled plasma–optical emission spectrometry methods

Extraction of Lipids from <i>Chlorella</i> Alga by Supercritical Hexane and Demonstration of Their Subsequent Catalytic Hydrodeoxygenation

Extraction of lipids from <i>Chlorella</i> algae with supercritical hexane resulted in the high lipids yield of approximately 10% obtained at optimum conditions in terms of extraction time and agitation compared to the total content of lipids being 12%. Furthermore, an easiness of hexane recovery may be considered as economically and ecologically attractive. For the first time, in the current work catalytic hydrodeoxygenation (HDO) of <i>Chlorella</i> algal lipids was studied over 5 wt % Ni/SiO₂ at 300 °C and under 30 bar total pressure in H₂. The conversion of lipids was about 15% as the catalyst was totally deactivated after 60 min. The transformation of lipids proceeded mostly via hydrogenation and hydrogenolysis with formation of free fatty acid (FFA). Lower activity might be attributed to deactivation of catalysts caused by chlorophylls and carotenoids. Even though the conversion is low, future studies in HDO of lipids extracted from other algae species having higher lipid content could be proposed. A coke resistant catalyst might be considered to improve catalytic activity