Innovative processes for the production of acetaldehyde, ethyl acetate and pure hydrogen by ethanol
Carotenuto, Giuseppina (2011) Innovative processes for the production of acetaldehyde, ethyl acetate and pure hydrogen by ethanol. [Tesi di dottorato] (Inedito)
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In the recent years, the interest in the ethanol production from renewable natural sources, as a possible alternative energy vector, has strongly grown in the world. The low-cost ethanol availability has also favored the study of the production of different chemicals such as ethylene, ethyl ether, acetaldehyde and ethyl acetate starting from ethanol as raw material. In this research, ethanol oxidative dehydrogenation to acetaldehyde, dehydrogenation to ethyl Acetate and hydrogen, in one step reaction, has been studied by using three different copper and vanadia based catalysts. The ethanol oxidative dehydrogenation was studied in low range of residence time to favor the acetaldehyde production in mild operative condition of temperature (140-180°C) and pressure (1 bar). The ethanol dehydrogenation reaction has been conducted in a conventional packed bed tubular reactor, by exploring a temperature range of 200–260 ◦C and a pressure range of 10–30 bars. The best results have been found by using a commercial copper/copper chromite catalyst, supported on alumina and containing barium chromite as promoter, operating at 220–240 ◦C, 20 bars and 98 g h mol−1 of ethanol contact time. In these conditions, a conversion of 65% with a selectivity to ethyl acetate of 98–99% has been obtained. However, the effect of temperature, pressure and ethanol contact time on both conversion and selectivity to ethyl acetate has been investigated. Moreover, the best catalyst has also shown a good stability to deactivation. A kinetic study of the ethanol dehydrogenation to ethyl acetate on a copper/copper- chromite catalyst has been performed. The kinetic runs were carried out in a packed bed tubular reactor, alternatively filled with 2 or 50 g of catalyst, approximately isothermal, by feeding pure ethanol together with a mixture of nitrogen and hydrogen as carrier gas. A Langmuir-Hinshelwood-Hougen-Watson kinetic model has been used for interpreting all the experimental data collected. This model corresponds to a mechanism in which the first step is the dissociative adsorption of ethanol on the surface, giving an adsorbed ethoxy group. Then two other consecutive steps give place to respectively acetaldehyde as intermediate and ethyl acetate. This kinetic model allows a satisfactory fitting of all the performed experimental runs with a standard error below 15% for the runs performed with 2g of catalyst and less than 10% for the runs made with 50 g of catalyst. On the basis of the realized kinetic study, a process hypotesis was realized by using CHEMCAD. Moreover, the catalytic generation of hydrogen by ethanol decomposition and oxidative reforming over copper-chromite and copper-zinc catalyst supported on alumina has been investigated. The catalysts have been prepared by the innovative method of combustion synthesis, characterized by a fast heating rate and a short reaction time, leading to increase catalyst porosity and total surface area. The catalytic activity and selectivity have been investigated without O2 and under various O2 and C2H5OH molar ratio in the temperature range up to 500°C. It was found that copper chromite supported on alumina shows the best activity and hydrogen selectivity during ethanol decomposition. The selectivity decreased during oxidative reforming but with a low O2/EtOH=0.6 molar ratio at 300°C, a hydrogen rich mixture (35-40%) was obtained. The use of relatively low amount of oxygen is necessary to reduce the coke formation, which causes catalyst deactivation. The catalysts were characterized by ex-situ methods such as XRD, BET, XPS, and in-situ EXAFS and FTIR with the aim to evaluate their physic-chemical properties and to correlate them with the catalysts performance.
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