CO2 Utilization to Formic Acid

Abstract

CO2 emissions rate is increasing with an alarming pace during the last decades. Carbon capture and storage could be an effective methodology for reducing CO2 emission on a short term due to its relatively mature status. Moreover, carbon utilisation, as a closing the carbon cycle approach, is gaining significant attention on a scientific level and on a public level. A large amount of technical possible directions for CO2 utilisation have been identified and examined. However, the majority of these reaction pathways are focused on the use of pure CO2, leading to a relatively high overall cost for commodity chemicals. It would be beneficial from a cost perspective to integrate the capturing of CO2 with the utilisation and this is the focus of this thesis.

The research described in this thesis is centred around the novel methodology to capture CO2 from flue gases using an aqueous ammonia based solution. Instead of a conventional thermal swing process, hydrogen is used to convert the captured CO2 (in the form of ammonium bicarbonate) towards formate. A distillation process has been developed to basically split the ammonium formate solution in an ammonia solution and a concentrated formic acid solution. This formic acid solution can be used as such or even further converted via hydrogen towards formaldehyde.

It is of importance to note that this pathway has been selected based on in principal known chemical steps but combined in an innovative manner. A theoretical (modelling) approach is combined with an experimental part to achieve proof of principle of all the key steps, leading towards a detailed techno-economic evaluation. A design has been made for a 100 kton of flue gas captured and utilised system. Starting point is the capturing of CO2 from a 6 v/v \% flue gas concentration with a capture efficiency of 90\%. Depending on the methodology used this can lead, after hydrogenation and distillation, to a formic acid product with a concentration between 32 - 37 \% wt. It can be stated that the above described process could be economically feasible, with payback time of 9.3 years and an interest of 8\%. A final production price of formic acid at 400 \euro/tn making the process attractive compared to the market price of formic acid.

Sensitivity analysis is been conducted towards various parameters that may affect and influence these production costs, such as electricity price, capital cost of the electrolyzer and lifetime of the capture plant. The market for formic acid is relatively small, however, this thesis discusses as well the possibility of converting the formic acid to formaldehyde, which is a very important commodity chemical. A concentrated formaldehyde is produced, comparable to the 37 \% wt commercial product. Recommendations are discussed for process options which can in principal lead to significant improvement towards the basic design of the integrated capture and conversion method.