On the direct hydrogenation of CO2 towards formic acid
Nowadays, the global energy demands have skyrocketed caused by mass industrialization. In order to prevent further human induced climate change, future emissions need to be drastically reduced and the urge for more renewable fuels is urgent. A potential solution to this problem, would be to switch to hydrogen instead of fossil fuels such as oil.
However, such a switch in every day fuels does not come straightforward. For example, the amount of energy that hydrogen contains per volume is much lower than is the case for every day fuels such as gasoline and diesel. This translates to the need of very large, and thus expensive storage vessels. One solution could be to store the hydrogen in the form of an organic liquid instead of a gas, for example through the chemical transformation of hydrogen into formic acid, which is much easier and safer to store than gaseous hydrogen. Formic acid is a chemical naturally produced by ants and on an industrial scale it is synthetically made from carbon monoxide produced from fossil fuels.
The work in this dissertation was focused on the sustainable production of formic acid using CO2 and hydrogen. By using CO2 instead of fossil fuels, a major advantage can be achieved. The CO2 filtered from the atmosphere can be used to create valuable materials, instead of expensive storage of this harmful gas. However, CO2 is a very stable molecule, making chemical conversion of it challenging.
As CO2 is such a stable molecule, additional ‘tricks’ are required to allow for the chemical conversion of it. Within this work, two approaches were used: the design of novel catalytic materials, and the addition of additional chemicals known as amines. A catalyst is a material that accelerates the reaction, without being consumed in it. Such materials are often based on expensive noble metals such as gold, making that it is very important to use them to their full potential. Here, the formulation of the catalyst and conditions within the reactor were optimized to ensure no expensive metals are wasted.
Secondly, the reaction proposed within this work is very unfavorable to perform due to large stability of the CO2, making it almost inactive. One way to ‘force’ the CO2 into formic acid is by adding amines. Amines are organic molecules with a nitrogen center. These molecules are very basic, and thus very reactive with acids. An every day example of such a reaction is the removal of limescale with cleaning agents, in which a violent reaction occurs that produces heat and sometimes even foam. The energy released in this second reaction was tuned such that enough heat is released to transform the CO2 into formic acid.
As is important for any novel technology, a key question that arises is how expensive will the new process be compared to the old one. To answer this question, the process was design at a large scale, comparable to the well-known chemical sites in Geleen and Rotterdam. Here, it was found that the proposed process is still too expensive, despite the progress achieved during this work. More research is needed before this process can be applied, especially on the usage of the expensive metal catalysts.
Title of PhD-thesis: . Supervisors: prof.dr.ir. John van der Schaaf (TUe), Prof.Dr.Eng. Fausto Gallucci (TUe), dr. Larissa Brito (Engie Biomass Lab, CRIGEN) and dr. Adeline Miquelot (Engie Hydrogen Lab, CRIGEN). This research was funded by the European Horizon 2020 and .