Sep-2024

Formic acid production using heterogenised iridium catalyst through the ICCC process (RI 2024)

Production and use of intermediates such as formic acid with a significantly lower product carbon footprint (PCF) are becoming important for a net-zero future.

Raj Kumar Das, Supriyo Majumder, Shivanand Pai, Chanchal Samanta, Chiranjeevi Thota and BharatNewalkar
BPCL – Corporate Research & Development Centre

Article Summary

Conventional formic acid production relies on fossil-based feedstocks. It goes through a series of steps, such as methanol production, methanol formulation, and hydrolysis of methyl formate intermediate to formic acid, making formic acid production highly carbon-intensive. On the other hand, the utilisation of CO₂ as a feedstock is considered an accelerated path towards a circular economy.

Conventional CO₂ utilisation strategies involve the capture of CO₂ from the source, followed by desorption, compression, and then the storage of CO₂. This process is known as the carbon capture and storage (CCS) route. When utilised for the production of value-added products, it is referred to as carbon capture and utilisation (CCU). However, such a utilisation process is energy- and cost-intensive as it requires additional steps for desorption, compression, and transportation.

On the other hand, the integrated CO₂ capture and conversion (ICCC) process offers an alternative energy-efficient solution and is considered an important research field in the CCU area. Additionally, this process operates in a reduced (hydrogen) atmosphere rather than the usual CO₂-rich environment, requiring a lower sorbent regeneration temperature than conventional desorption temperatures. This allows the ICCC process to operate at isothermal conditions, leading to lower energy consumption.

The key features of this process are:
· Does not require a desorption process, significantly reducing the cost and area footprint. It also avoids storage and compression steps, which require additional space and utility costs.  
· Reduces the energy penalty for CO₂ desorption. Thus, the integrated CO₂ capture and conversion can attain high energy efficiency or shrink the heat release in the CO₂ conversion stage by integrating the enthalpies of absorption, desorption, and conversion.
· Captured CO₂ remains an activated form owing to its bent structure. Thus, it avoids additional activation energy required for activating the kinetically inert-linear form of CO₂; therefore, it promotes the subsequent conversion under mild conditions.
· The integrated system offers improved thermodynamic efficiency and the ability to change or bypass limited chemical equilibria, which is more economical due to the reduction of redundancy.

Two broad concepts of CO₂ capture and in-situ conversion have been identified (Figure 1). In the first concept, CO₂ is captured using a suitable sorbent, followed by conversion of the captured CO₂ into various chemicals in the presence of a suitable catalyst. In the second concept, a dual functional material is used for CO₂ capture and conversion to valuable chemicals. The first concept is a little more robust as it can reduce the unwanted exposure of gases (such as SOx, NOx and moisture, nitrogen, and oxygen) into the catalyst system, which is unavoidable for the second concept of dual-functional material. Thus, sustaining catalyst life for the second concept is challenging.

Among all the CO₂ conversion processes, the hydrogenation of CO₂ to formate is considered an effective way to store hydrogen and attracts much attention these days. Additionally, formic acid is used as an intermediate in the manufacturing of essential drugs, plant protection agents, pesticides, vulcanisation accelerators, antioxidants, cleaning agents, and many other applications.

The commercial production of formic acid involves a two-step process. First, methanol is carbonylated with carbon monoxide to form methyl formate. In the second step, methyl formate is hydrolysed in the presence of a base to obtain formic acid. The other methods include oxidation of methanol, oxidation of methane, hydrolysis of formamide, and preparation from formats.

Although, at present, 80% of formic acid produced worldwide is based on the hydrolysis of methyl formate process, developed by BASF, significant efforts have been made in recent decades to develop a suitable formic acid production process that uses CO₂ as a feedstock, as the current formic acid production is highly carbon intensive.

The current formic acid production process relies on natural gas as a primary feedstock for syngas production, which generates a significant amount of CO₂ as a by-product. In contrast, formic acid production using CO₂ as feedstock could provide a carbon-neutral solution. However, to drive the activation of thermodynamically stable CO₂ molecules, there is a need to develop a highly-active and selective catalyst system for the hydrogenation of captured CO₂ to formic acid:

Step 1: Methanol carbonylation: CH₃OH + CO _HCOOCH

Step 2: Methyl formate hydrolysis: HCOOCH₃ + H₂O _ CH₃OH + HCOOH

Towards this goal, BPCL has developed integrated CO₂ capture and conversion to formic acid using first concept, where heat-stable amine is used as a sorbent to capture CO₂. An iridium-based catalyst system is employed that offers a TON value of more than 8,000 for formic acid production at 150°C and 40 bar of hydrogen pressure for 0.8 mol/mol of CO₂ loaded amine solution. A continuous stirred tank reactor (CSTR) system is utilised, where heat-stable (1M solution) amine is used for CO₂ absorption, and an iridium complex under a hydrogen atmosphere is used to regenerate the amine and produce formic acid (Figure 2).

The process offers more than 97% formic acid selectivity and more than 0.5M formic acid concentration for every 0.8M CO₂ captured amine (Figure 3). It is a promising alternative that avoids the utilisation of highly pure CO (>99.5%) as a feedstock, which is used in the commercial formic acid process.

References
1 Acc. Chem. Res. 2019, 52, 10, 2892–2903.
2  J. Am. Chem. Soc. 2024, 146, 19.271-19,278.
3 ACS Catalysis 2024, 14, 8541-8,548.
4 Langmuir 2024, 40 (10) , 5,401-5,408.

This short article originally appeared in the 2024 Refining India Newspaper, which you can VIEW HERE