Environmentally Friendly Catalysts For N-butyraldehyde Aldol Condensation And For The Reaction Integration Of The Condensation-hydrogenation

The aldol self-condensation of n-butyraldehyde to 2-ethyl-2-hexenal（2E2H） and the hydrogenation of 2E2 H are two important processes for industrial production of 2-ethylhexanol（2EHO）. The integration of the self-condensation of n-butyraldehyde and the hydrogenation of 2E2 H can simplify the technological process, decrease the energy consumption, and lower the capital of equipment. Therefore research on the environmentally friendly catalysts used in the self-condensation of n-butyraldehyde and the integration process has important academic and application value.First of all, several sulfonic acid-functionalized ionic liquids（SFILs） were synthesized. Their acid strength was determined by Hmmett method with UV-Vis spectroscopy and their catalytic performances in n-butyraldehyde self-condensation were investigated. The result showed that the conversion of n-butyraldehyde correlated well with the acid strength of the SFILs with the same cation. The SFILs with triethylammonium cation showed a better catalytic performance than those with imidazolium cation or pyridinium cation, and [HSO₃-b-N（Et）3]p-TSA exhibited the highest selectivity. Under the suitable reaction conditions of mass ratio of [HSO₃-b-N（Et）3]p-TSA to n-butyraldehyde = 0.1, reaction temperature = 120 °C and reaction time = 6 h, the conversion of n-butyraldehyde was 89.7% and selectivity to 2E2 H was 87.8%. [HSO₃-b-N（Et）3]p-TSA could be reused for four times without a significant loss in its catalytic performance. Furthermore, a possible reaction mechanism for n-butyraldehyde self-condensation catalyzed by [HSO₃-b-N（Et）3]p-TSA was proposed.Secondly, a kinetic analysis result showed that n-butyraldehyde self-condensation reaction catalyzed by [HSO₃-b-N（Et）3]p-TSA is a reversible second-order reaction. The activation energy is 60.29 ± 2.856 kJ/mol and the pre-exponential factor is 1.999×104 L/（mol·s） for the forward reaction while the activation energy is 62.94 ± 0.323 kJ/mol and the pre-exponential factor is 1.001×104 L/（mol·s） for the reverse reaction in the temperature range of 90¹20 °C. As compared with the kinetic parameters obtained from the reaction catalyzed by an aqueous base or acid catalyst, the pre-exponential factor is much lower due to the restriction of high viscosity of [HSO₃-b-N（Et）3]p-TSA.Thirdly, the effect of reaction conditions on the integration reaction catalyzed by Ni/CeAl₂O₃ prepared under suitable conditions was investigated and the suitable reaction conditions were obtained as follows: weight percentage of Ni/Ce-Al₂O₃ = 15%, reaction temperature = 170 °C, reaction pressure = 4.0 MPa and reaction time = 8 h. Under the above reaction conditions, the yield of 2EHO increased to 66.9%. The evaluation on the reusability of Ni/Ce-Al₂O₃ showed that the recovered Ni/Ce-Al₂O₃ catalyst lost its catalytic activity for C=O bond hydrogenation. The main reason for deactivation was that the Ni species were covered by the flaky boehmite formed from the hydration of γ-Al₂O₃ in the reaction process. Furthermore, introduction of some stabilizers onto the surface of γ-Al₂O₃ would change its textural property. The hydration of γ-Al₂O₃ was restrained to some extent while the catalytic activity for aldol condensation of n-butyraldehyde decreased slightly. The catalytic hydrogenation activity of Ni-Ce/Al₂O₃-C was strengthened and the evaluation on the reusability of Ni-Ce/Al₂O₃-C showed that the recovered catalyst presented catalytic activity for C=O bond hydrogenation as fresh.Finally, in order to study the catalytic activity of Ni/[HSO₃-b-N（Et）3]p-TSA for the nbutyraldehyde aldol condensation-hydrogenation integration reaction to 2EHO, the influence of metal nickel on the aldol condensation of n-butyraldehyde catalyzed by [HSO₃-b-N（Et）3]p-TSA was investigated. The result showed that the decreasing acidic sites weakened the catalytic activity of [HSO₃-b-N（Et）3]p-TSA for aldol condensation of nbutyraldehyde and the change of atmosphere in the reaction system altered the product distribution.