Preparation of alumina with different precipitants for the gas phase dehydration of glycerol and their characterization
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Preparation of alumina with different precipitants for the gas phase dehydration of glycerol and their characterization by thermal analysis Dirleia S. Lima1 · Oscar W. Perez‑Lopez1 Received: 12 September 2019 / Accepted: 9 January 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract Mesoporous aluminas were prepared using different precipitants at different pH of precipitation and evaluated in the gas phase dehydration of glycerol. Samples were characterized by thermal analysis techniques (TGA, N H3-TPD and TPO), specific surface area measurements, XRD and SEM. The gas phase dehydration of glycerol was performed in a fixed bed quartz tubular reactor at 773 K using a 10% glycerol aqueous solution. Thermogravimetric analysis has revealed the temperature regions of decomposition for the prepared alumina catalyst precursors. The specific surface area and the crystallinity of the samples were dependent on both the pH and the used precipitating agent. Samples precipitated with NaOH presented higher density of acid sites than the samples prepared with N a2CO3, regardless of precipitation pH. The catalytic properties of the prepared aluminas are mainly related to the specific surface area and to acidic characteristics. Conversions of glycerol above 85% were obtained for all samples. The selectivity for glycerol dehydration was strongly related to the amount and strength of acid sites. The best result for dehydration was obtained for samples prepared with NaOH and precipitated at pH = 5. These results are related to the higher specific surface area, greater amount of acid sites and the higher ratio of weak acid sites. TPO revealed the amount of carbon deposited on the catalysts. Samples that showed higher carbon formation also showed a higher production of light olefins, indicating that the formation of carbon is related to the formation of these byproducts. NH3-TPD has shown the ratio of different acid sites on the surface of alumina samples that makes possible to estimate the correlation between the acidity and the catalytic properties. Keywords Dehydration of glycerol · Acrolein · Alumina synthesis · Co-precipitation · Acid strength
Introduction Glycerol is an alcohol obtained as a byproduct of biodiesel production via the transesterification reaction of vegetable oils and animal fats [1]. One way of adding value to residual glycerol is through glycerochemistry, which studies the different chemical routes through which it is possible to recover this low-quality glycerol and transform it into other products. Among the existing catalytic chemical routes, dehydration, oxidation, hydrogenolysis, etherification, acetylation, halogenation and steam reforming of glycerol are the most important [2]. * Oscar W. Perez‑Lopez [email protected] 1
Laboratory of Catalytic Processes ‑ PROCAT, Department of Chemical Engineering, Federal University of Rio Grande do Sul (UFRGS), Ramiro Barcelos Street, 2777, Porto Alegre, RS CEP 90035‑007, Brazil
An interesting product that can be obtained through glycerol conversion is a
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