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Chromium containing slags from stainless steelmaking may be leached by acidic environments, therefore they should be treated before being stockpiled or land filled. In this work, synthetic slags were prepared and the effect of CaO/SiO2, Cr2O3, MgO and Al2O3 contents on the stability of the mineralogical species formed was analysed. The morphology and composition of the slags were determined by XRD and SEM‐EDS, whilst their chemical stability was evaluated by leaching with an aqueous acetic acid solution. It was found that CaCr2O4 and CaCrO4 are present in slags prepared with neither MgO nor Al2O3. The Al2O3‐based slags mainly produced Ca2Al2SiO7 and the Cr(VI)‐containing oxide complex Ca4Al6CrO16, whilst MgO‐based slags produced Mg Cr2O4 as main mineralogical species. Additionally, Eh‐pH diagrams for the Ca‐Cr‐H2O and Mg‐Cr‐H2O systems at 25°C were constructed. The results showed that the lowest chromium concentration levels in the leaching liquors corresponded to MgO‐based slags owing to the stable binding of chromium in spinel with MgO. It was also observed in the Al2O3‐based slags that when increasing the slag basicity from 1 to 2, the leachability of the slags was notably increased.

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Glycerol dehydration to acrolein was studied with three catalysts using zeolite-Y. This zeolite in its protonic form (HY), with La (LaY) and Pd with La (Pd/LaY), was characterized by X-ray diffraction (XRD), Fourier-transform-infrared spectroscopy (FTIR) with pyridine, BET, Scanning Electron Microscope (SEM)-Energy-Dispersive Spectroscopy X-ray (EDS) and the catalytic activity tests were carried out under H 2 atmosphere. It was found that La ions exchanged in the zeolite-Y resulted in the improvement of both glycerol conversion and yield to acrolein, also a relatively constant glycerol conversion was achieved up to three hours, due to the presence of Pd on the catalyst and H 2 in the feed. The comparison of the calculated and experimental yields obtained from the catalytic tests of the Pd/LaY catalyst indicates a greater activity for the reaction to acrolein than for the reaction to acetol. The calculated equilibrium yields of the dehydration reaction from glycerol to acrolein, acetol, ethanal, methanol, and water and the experimental yields of a Pd/LaY catalyst were compared. Thermodynamically, a complete conversion of glycerol can be achieved since the general system remains exothermic and promotes the path to acetol below 480 K. Above this temperature the system consumes energy and favors the production of acrolein, reaching its maximum concentration at 600 K.

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The objective of this study is to analyze the effect of MgO content and the slag basicity on the stability of the mineralogical species of the SiO 2 -CaO-MgO-Cr 2 O 3 system. Slag samples were prepared in equilibrium at 1600 °C under reducing conditions (pO 2 = 10 -9 atm). The MgO content ranged from 0 to 12 mass%, Cr 2 O 3 was 10 % and the slag basicity was held at 1 and 1. ResumenEl objetivo de este estudio es analizar el efecto del contenido de MgO y la basicidad de la escoria sobre la estabilidad de las especies mineralógicas del sistema de escoria SiO 2 -CaOMgO-Cr 2 O 3 . Se realizaron ensayos al equilibrio a 1600 °C bajo condiciones reductoras (pO 2 =10 -9 atm). El contenido de MgO fue de 0 a 12 % masa, el Cr 2 O 3 de 10% y la basicidad de 1 y 1,5. También se realizó un análisis termodinámico para determinar las fases mineralógicas más estables en la escoria. Los resultados experimentales y calculados muestran que el Cr 2 O 3 se encuentra principalmente ligado en una fase espinela MgCr 2 O 4 , incluso a bajos contenidos de MgO. Los resultados obtenidos por microscopia electrónica de barrido (MEB-EDS), muestran la evidencia de tres estructuras cristalinas: (A) Octaedros, los cuales corresponden a la espinela MgCr 2 O 4 , (B) Cristales alargados que corresponden a la formación de silicatos cálcicos y (C) Matriz de silicatos cálcicos con impurezas de Mg y Cr que no cristalizaron por completo.

The study of the deactivation of HY zeolites in the dehydration reaction of glycerol to acrolein has represented a challenge for the design of new catalysts. HY zeolites with SiO2/Al2O3 molar ratios between 3.5 and 80 were studied. The solids were characterized by XRD, N2 physisorption, SEM-EDXS, Raman and UV-vis spectroscopies, infrared spectroscopy of pyridine (FTIR-Py) and catalytic activity tests from 250 °C to 325 °C. It was found that the total amount of acid sites per unit area of catalyst decreased as the SiO2/Al2O3 molar ratio increased from 3.5 to 80, resulting in the decrease in the initial glycerol conversion. The initial acrolein selectivity was promoted with the increase of the Brønsted/Lewis acid sites ratio at any reaction temperature. The deactivation tests showed that the catalyst lifetime depended on the pore structure, improving with the presence of large surface areas as evidenced by the deactivation rate constants. The characterization of the deactivated catalysts by XRD, N2 physisorption and thermogravimetric analysis indicated that the deposition of coke resulted in the total obstruction of micropores and the partial blockage of mesopores. Moreover, the presence of large mesopores and surface areas allowed the amount of coke deposited at the catalyst surface to be reduced.