Untersuchung von festen Basenkatalysatoren und Aufbau eines kontinuierlich betriebenen Festbettreaktors für heterogen katalysierte Aldolreaktionen von n- und i-Butyraldehyd
Aachen / Publikationsserver der RWTH Aachen University (2015) [Dissertation / PhD Thesis]
Page(s): X, 155 Bl. : Ill., graph. Darst.
The aldol reactions of n-butyraldehyde, and i-butyraldehyde with formaldehyde, respectively, are industrially important reactions which are currently being catalysed by homogeneous bases. In order to optimise the large-scale processes in terms of economy and ecology, heterogeneous catalysts were developed and investigated regarding structure-activity relationships. Furthermore, the aldol reactions were carried out in a continuously operated fixed bed reactor.In the catalytic aldol reaction of n-butyraldehyde, the condensation product 2-ethyl-2-hexenal was predominantly formed while the production of the addition product 2-ethyl-3-hydroxyhexanal turned out to be challenging due to the ready elimination of water. As catalysts, different metal oxides as well as MgO supported alkaline metal hydroxides were applied. Especially the degree of surface dehydration, i.e. the number of Brønsted basic hydroxyl groups, and the basic strength were observed to have an influence on the catalytic activity.The aldol addition of i-butyraldehyde with formaldehyde to produce hydroxypivaldehyde (HPA) was carried out using hydrotalcites, spinels, perovskites and metal nitrides as catalysts. The conversion and selectivity generally followed an opposing trend when varying the reaction conditions which was related to the increased formation of side products. A dependency of the catalytic activity on the concentration of Brønsted basic hydroxyl groups was observed. Amongst the metal nitrides, AlN, which was hydrolysed to the more basic boehmite during the reaction, was identified as the most promising catalyst.The application of selected catalysts in a continuously operated fixed bed rector led to very promising result with mostly very high selectivities in both the aldol reaction of n-butyraldehyde and that of i-butyraldehyde with formaldehyde. The formation of side products was mostly reduced due to shorter contact times.