Carbon dioxide as C1 building block in combination with amines : carbonylation and hydrogenation reactions

• Kohlenstoffdioxid als C1-Baustein in Gegenwart von Aminen : Carbonylierungs- und Hydrierungsreaktionen

Blas Molinos, Beatriz; Leitner, Walter (Thesis advisor); Liauw, Marcel (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2015)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2015

Abstract

CO2, due to its natural abundance, physico-chemical properties and non-toxicity, bears great potential as a source of carbon and as an energy vector. The aim of this research is to study the chemistry between amines and CO2 and to get some insight into control factors that influence the pathways and products. The work presented here is divided into two proyects: the first one is based on the incorporation of CO2 in primary amines towards carbamic salts, isocyanates and urea derivatives, and the second one describes different catalytic processes for the hydrogenation of CO2 to formic acid (-derivatives) in the presence of secondary or tertiary amines, principally. Chapter 2 outlines how the nucleophilic character of the primary amines leads to the formation of a carbon-element bond between the carbon atom of CO2 and the amine, building carbamates, isocyanates or urea (-derivatives). The formation and the properties of different carbamic salts and the effect of the addition on an extra base to the reaction with the primary amine are examined. In addition, the reactivity of these species and their behavior as intermediates are investigated. Previous publications, where carbamic salts were transformed into isocyanates using PCl3 as a dehydrating agent, are set as the starting point. Here, diverse dehydrating compounds, solvents and catalyst are tested. Moreover, the reaction conditions are also modified in order to optimize the reaction and reach high conversions and selectivities towards the desired products. Chapter 3 is based on the design and optimization of a catalytic system for the hydrogenation of CO2 to formic acid derivatives and their subsequent isolation. Previous results obtained by our group in the continuous hydrogenation of CO2 using a biphasic system, led to investigate further on this topic. This biphasic system is based on the immobilization of the catalyst in an amino-functionalized ionic liquid and the continuous separation of the product by solution in scCO2. In this research, secondary amines are used as bases in the production of formamides and formic acid adducts, but also the effect of tertiary and alcohol amines among other bases is investigated. Formamides are highly soluble in scCO2, but formic acid adducts cannot be separated using this solvent. Therefore, an alternative biphasic system with a different solvent has to be developed. The most widespread technique for the separation of CO2 from gas streams is based on the use of aqueous amine solutions. For this reason, water is tested as a mobile phase in the presence of several amines (dimethyl-, diethyl-, diisopropyl- and triethylamine) and two different stationary phases (an ionic liquid and an alcohol).