Model-based Design of Product, Solvent and Process for Formic Acid Synthesis from CO2 and H2

Today humanity faces a challenge: Global warming that is caused by emissions of CO2. To reduce CO2 emissions, usage of CO2 as a renewable carbon source has gained attention. In particular, the CO2-based synthesis of formic acid has been intensively studied, since in addition to utilizingCO2, formic acid could also act as chemical storage of fluctuating renewable energy. Developing such storage is paramount for any renewable energy system due to the fluctuating occurrence of e.g. wind. However, for the CO2-based formic acid synthesis, only a few processes have been developed. Thus, novel formic acid synthesis processes are developed in this thesis. The development considers process structure and solvents, as well as formic acid derivatives due to the unfavorable equilibrium of the CO2-based formic acid synthesis.

Firstly, a process is developed for the formic acid synthesis with the widely investigated solvent dimethyl sulfoxide (DMSO). The work identifies that DMSO has an azeotrope with formic acid. To avoid the high energy demand that usually occurs in processes containing azeotropes, a novel process is developed that uses a co-solvent. Process simulations show that this novel process has an exergy demand on par with the existing state of the art CO2-based formic acid synthesis process.

Secondly, a process is developed where formic acid or a derivative is used to store fluctuating renewable energy before reforming to carbon monoxide. Here, more than 100,000 combinations of formic acid derivative, solvent and process are considered by a novel design method. For the developed process, process simulations show that the exergy demand is significantly lower than for the literature benchmark.

Thirdly, a novel process is developed for the synthesis of the formic acid derivative methyl formate. In this process, the supply of CO2 is integrated with the methyl formate synthesis. Usually, the CO2 supply and the synthesis are considered separate. By integrating these two steps, the energy demand and minimum selling price of methyl formate can be reduced.

Finally, the thesis shows that the highest reductions in CO2 emissions and in minimum selling price are achieved with the co-solvent and the integrated methyl formate processes. Since both these processes are developed in this work, this thesis contributes towards utilization of CO2 as a raw material in chemical industries.