DOI: 10.3303/CET25117089 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Paper Received: 29 December 2024; Revised: 24 February 2025; Accepted: 2 May 2025 
Please cite this article as: Spatolisano E., Restelli F., Leoni S., Pellegrini L.A., 2025, Exploring the Viability of Green Formic Acid as H2 Carrier, 
Chemical Engineering Transactions, 117, 529-534  DOI:10.3303/CET25117089 
  

 CHEMICAL ENGINEERING TRANSACTIONS  
 

VOL. 117, 2025 

A publication of 

 

The Italian Association 
of Chemical Engineering 
Online at www.cetjournal.it 

Guest Editors: Fabrizio Bezzo, Flavio Manenti, Gabriele Pannocchia, Almerinda di Benedetto 

Copyright © 2025, AIDIC Servizi S.r.l. 

ISBN 979-12-81206-17-5; ISSN 2283-9216 

Exploring the Viability of Green Formic Acid as H2 Carrier 

Elvira Spatolisano, Federica Restelli, Sofia Leoni, Laura A. Pellegrini 

GASP - Group on Advanced Separation Processes & GAS Processing, Dipartimento di Chimica, Materiali e Ingegneria 

Chimica “G. Natta”, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy 

elvira.spatolisano@polimi.it  

To favour the implementation of hydrogen energy, H2 carriers are regarded as a reliable alternative for hydrogen 

transport. Common hydrogen carriers include liquid organic compounds (as toluene, dibenzyltoluene or N-

ethylcarbazole), ammonia, methanol, formic acid and chemical hydrides. These substances can release H2 

upon demand through dehydrogenation or electrochemical reactions, offering a flexible way to integrate 

hydrogen into energy infrastructure. Among them, formic acid (HCOOH) is an attractive candidate due to its 

hydrogen content (4.4 wt.%) and straightforward dehydrogenation process. To explore the viability of green 

formic acid as H2 carrier, this work analyses all its possible production pathways from renewable energy, with a 

focus on the synthesis from captured CO2 as raw material. Advantages and disadvantages of this new process 

are presented, assessing its potential by means of the equivalent hydrogen methodology. The H2 delivery 

performance of formic acid, strictly related to its synthesis stage, is analyzed and then compared to other carriers 

(liquefied H2, ammonia, toluene, dibenzyltoluene), to discuss its practicality for industrial-scale implementation. 

1. Introduction 

While gaseous hydrogen low density and high volatility hinders its cost-effective transport, hydrogen carriers 

offer an attractive solution to connect green H2 production and utilization hubs (Restelli et al., 2023). These 

carriers are molecules, typically in liquid state at ambient temperature and pressure, in which hydrogen is 

chemically bonded and can be released upon need (Spatolisano and Restelli, 2024). A variety of hydrogen 

storage compounds have been proposed in literature: organic liquids derived from fossil feedstock, biomass-

based substances or synthetic products obtained from captured CO2. The latter are of particular interest in the 

research panorama since they are able to conjugate CO2 utilization and H2 transport. Formic acid (HCOOH) is 

one of them. The physico-chemical properties of interest for its implementation as H2 carrier are listed in Table 

1.  

Table 1: Main physico-chemical properties of formic acid. 

Property Value Reference 

H2 density [gH2/L] 53 Gao et al., 2024 

Melting temperature [°C] 8.4 NIST Chemistry WebBook 

Boiling temperature [°C] 101 American Chemical Society 

Cost [$/ton] 800 chemanalyst.com 

Dehydrogenation enthalpy [kJ/mol] 31.2 Patra et al., 2023 

 

Formic acid, a colorless liquid with a pungent odor, is a simple carboxylic acid. It finds applications across 

various industries, thanks to its versatile properties: it is commonly used as a chemical precursor to produce a 

variety of substances, including formamide, esters and other derivatives, in turn used in the manufacture of 

plastics, textiles, pharmaceuticals and agrochemicals. It is a non-volatile liquid (normal boiling point around 

100°C), less hazardous compared to some other hydrogen carriers like NH3, which is highly toxic, but corrosive 

in the concentrated form. Formic acid high H2 density allows, in principle, for an efficient storage and transport 

of hydrogen. As confirmed by the dehydrogenation enthalpy, it can undergo catalytic dehydrogenation at mild 

529



conditions (around 200°C), to release CO₂ and H₂. Dehydrogenation is less energy-intensive compared to other 

hydrogen carriers, such as NH3 or toluene, which often require more complex and energy-consuming processes. 

Since CO2 is released during the dehydrogenation stage, in view of improving the carrier carbon footprint, 

research efforts are devoted to enable the synthesis reaction from renewable sources, such as biomass or CO₂ 

itself, through catalytic hydrogenation. This makes formic acid a sustainable option for hydrogen storage, unlike 

fossil fuel-derived hydrogen carriers. The H2 value chain with formic acid as hydrogen carrier, synthetized from 

captured CO2, is depicted in Figure 1.  

 

Figure 1: H2 value chain considering formic acid as H2 carrier. Long distance harbour-to-harbour scenario.  

Due to the straightforward nature of dehydrogenation stage, the tiebreaker of formic acid implementation at 

large scale is the effectiveness of the synthesis stage, which is deepened in section 1.1. 

1.1 Formic acid production 

The state-of-the-art production method at industrial-scale is the well-established carbonylation of methanol, 

which is a two-stage process occurring via reactions (1) and (2) (Bulushev and Ross, 2018).  

Reaction (1) is operated at high pressure (4 MPa), but at relatively low temperatures (80°C), with a selectivity 

of 96% in the presence of a strong base (sodium methoxide). The second step is the hydrolysis of methyl formate 

to produce formic acid at high concentration (up to 98%) and methanol, which can be recycled back to stage 

(1). 

CH3OH + CO → HCOOCH3 (1) 

HCOOCH3 + H2O → HCOOH + CH3OH (2) 

Despite the good process performance, formic acid production through methanol carbonylation is not a good 

choice for its implementation as H2 carrier. Since CH3OH is required as raw material, it would be more practical 

to consider CH3OH itself as H2 carrier, rather than HCOOH.  

More sustainable approaches for HCOOH synthesis are being explored and summarized in Table 2, together 

with the related technology readiness level (TRL).  

Table 2: Proposed formic acid production pathway and related TRL. 

Production pathway TRL Reference 

catalytic CO2 hydrogenation 
homogeneous 3-5 Perez-Fortes et al., 2016 

heterogeneous 3-5 Chen et al., 2020 

electrochemical CO₂ reduction 3-5 Perez-Fortes et al., 2016 

biological  1-3 Schwarz et al., 2022 

direct oxidation of biomass 1-3 Chen et al., 2020 

 

The CO₂ hydrogenation methods can be broadly classified into homogeneous and heterogeneous catalytic 

processes. Álvarez et al. (2017) reviewed the state-of-the-art for the catalytic hydrogenation reaction, offering a 

summary of many catalytic complexes explored in literature.  

As far as the homogeneous catalysis is concerned, transition metal complexes are typically used, as Rh, Ir, and 

Pd. Rh catalysts show high activity and good selectivity towards formic acid and typically operate at low to 

moderate temperatures (50–150°C) and moderate pressures (20–50 bar) with phosphine or carboxylate ligands. 

Similar concepts have been explored for Ir-based catalytic systems.  

Pd-based catalysts, on the other hand, are known to be less effective than Ir or Rh-based: their activity and 

stability need improvement compared to Rh and Ir catalysts. Also, they often require higher temperatures and 

pressures than Rh and Ir systems. 

Homogeneous catalysis can also involve bimetallic systems, where two metals (such as Rh/Ir or Rh/Pd) are 

combined to enhance the reactivity and selectivity for CO₂ hydrogenation. Different patents have been filed by 

Green H2

H2 utilization

HCOOH

synthesis
Storage Marine 

transport

Storage and 

distribution

FAFA FA

FA

deH2-ation

CO2 CO2

530



BP and BASF. Anderson et al. (1989) proposed a process which occurs into different stages. In the first stage, 

CO2 reacts with H2 in the presence of a transition metal catalyst, with a high boiling solvent (e.g., polyethylene 

glycol, 1-phenyl-1-propanol, 3-phenyl-1-propanol, sulpholane) to produce a formate salt. Next, the catalyst is 

removed from the formate salt. The latter undergoes futher treatments in order to be thermally decomposed to 

formic acid.  

Hladiy et al. (2004) patented a process comprising the following steps: a) hydrolysis of methyl formate to give a 

mixture of water, formic acid, methanol and excess methyl formate; b) removal of the methanol and excess 

methyl formate from the mixture of water, formic acid, methanol and excess methyl formate by distillation to give 

aqueous formic acid; c) extraction of the aqueous formic acid with at least one formic acid ester; d) separation 

of formic acid ester and formic acid by distillation.  

The most recent invention is the one by Schaub et al. (2014), which proposed CO2 hydrogenation in the 

presence of a catalyst comprising an element of group 8, 9 or 10, a tertiary amine comprising at least 12 carbon 

atoms per molecule and a polar solvent as methanol, ethanol, propanols or butanols. Despite the promising 

catalytic performance, the major drawback of these homogeneous catalysts is their separation from the product, 

to be recycled back to the reaction stage. 

As regards the heterogeneous catalysis, different alternatives have been proposed in literature. Transition and 

noble metals such as Ru (Park et al., 2020), Pd, Pt, Rh, Ni, Cu are commonly used (Chen et al., 2020).  

However, lower selectivity is demonstrated for heterogeneous catalytic systems and complex reaction pathways 

are found in this case. 

With reference to Table 2, other sustainable formic acid production pathways include: 

• electrochemical reduction of CO₂, applying an electric current to CO₂ dissolved in an electrolyte, 

typically water, in the presence of a catalyst (often metals like silver, copper or tin). The reaction 

produces formic acid along with oxygen at the anode; 

• thermochemical conversion of biomass, where lignocellulosic materials (such as wood, straw, or 

agricultural waste) are subjected to high temperatures in the presence of chemicals or steam. This 

can produce formic acid as a by-product, often as part of a broader bio-refinery process; 

• microbial fermentation, that utilizes renewable biomass feedstocks like sugars (glucose or fructose) 

derived from agricultural waste, food scraps or algae. In this process, specific microorganisms are 

used to ferment these substrates into formic acid as a metabolic by-product under anaerobic 

conditions.  

Despite these methods could seem viable at the laboratory level, they suffer from poor scalability.  

The only realistic alternative for the green acid formic production, in view of its application as H2 carrier, is the 

catalytic hydrogenation of CO2. Although continuous homogeneous catalytic processes have been proposed at 

the laboratory scale, still the incomplete catalyst recovery from the reaction mixture hinders its scale-up. As for 

the heterogeneous catalysis, many studies in literature are focused on the tuning of the catalytic complex few 

of them delve into the evaluation of process aspects of CO2 hydrogenation, also discussing the separations 

downstream the reaction section. After a preliminary literature analysis, the work of Park et al. (2020) is assumed 

as the reference. The authors tested the Ru-based heterogeneous catalytic complex in a continuous fashion 

and proposed a process flow diagram for formic acid synthesis stage. 

With reference to the work of Park et al. (2020), Figure 2 shows the block flow diagram (BFD) of the formic acid 

production stage.  

 

Figure 2: Block flow diagram (BFD) of the formic acid production stage, according to Park et al. (2020).  

50 mmHg
Tbottom = 145°C

Formate 
formation

reactor
Evaporator

Amine exchange
column

FA separation
column

96 mol% 
Formic acid

CO2

H2

Triethylamine

carbonate 

formation

Triethylamine

Unreacted
gas

120 °C, 12 MPa
cCO2= 48%

150 mmHg
Tbottom = 140°C

100 mmHg
Tbottom = 155°C

531



CO2 and H2 are fed to the formic acid formation reactor, together with the recycled gases, water and 

triethylamine. In the first stage, a carbonate complex is formed which is routed to the formate formation reactor, 

the latter operated at very high pressure (120 bar) and moderate temperature (120°C). The liquid product 

undergoes evaporation to concentrate the adduct formed in the reaction stage and, then, the latter is introduced 

into the amine exchange column. This unit makes the separation of the strongly non ideal mixture possible by 

replacing triethylamine with a heavier homologue. The triethylamine is routed back to the reaction stage, while 

the new amine formate complex is further processed in another separation unit, which allows the recovery of 

formic acid as the top product.  

Pressure and temperatures levels are specified in Figure 2, for each stage of the process. Considering the 

operating conditions of Figure 2, high energy consumptions are expected because of the low pressures but, 

mostly, because of the high temperatures needed in the separation downstream the reactor.  

Starting from Figure 2 and in view of preliminarily exploring formic acid viability as H2 carrier, its production stage 

is assessed by means of equivalent hydrogen methodology, described in section 2, and then compared with 

others H2 carrier. In this way, opportunities and weaknesses are pointed out, to understand whether further 

deepening is needed or not.  

2. Methodology 

The equivalent hydrogen methodology is useful to compare and assess different hydrogen carriers based on 

their ability to store, transport and release hydrogen. According to this concept, the H2 delivered at the utilization 

hub is evaluated by equation (2). 

�̇�𝐻2,𝑛𝑒𝑡
= �̇�𝐻2,𝑖𝑛

− �̇�𝐻2,𝑐𝑜𝑛𝑠𝑢𝑚𝑒𝑑
 (2) 

All the electric and thermal energy consumptions are expressed as equivalent H2 consumed which must be 

subtracted in equation (2) to account for the net H2 quantity delivered upon arrival.  

The following contributions are considered in the calculation. 

1. Cooling duty produced by a proper refrigeration cycle, for cooling down to temperatures lower than the 

ambient one (cooling above the ambient temperature is neglected in the present analysis).  

The theoretical Coefficient Of Performance (COP) of the refrigeration cycle is evaluated according to 

equation (3), where TH and TL are the two constant temperatures, respectively, of the condenser and of 

the evaporator in the refrigeration cycle. The temperature of the hot reservoir is set equal to 25°C, whereas 

the one of the cold reservoir is determined as the temperature of the process stream to be cooled down 

(from simulations) minus a temperature approach of 5°C.  

𝐶𝑂𝑃𝑅,𝐶𝑎𝑟𝑛𝑜𝑡 =
1

𝑇𝐻
𝑇𝐿

− 1
 

(3) 

From the ideal COP of equation (3), the real COP can be calculated through equation (4), taking into 

account the rational efficiency ηII and the amount of hydrogen equivalent to the cooling duty Q can be 

determined according to equation (5), from the value of the efficiency of the combined cycle ηCC. 

𝐶𝑂𝑃𝑅 = 𝐶𝑂𝑃𝑅,𝐶𝑎𝑟𝑛𝑜𝑡 ⋅ 𝜂𝐼𝐼 (4) 

�̇�𝐻2
=

𝑄

𝐶𝑂𝑃𝑅 ⋅ 𝜂𝐶𝐶 ⋅ 𝐿𝐻𝑉𝐻2

 (5) 

2. Mechanical work required by compressors, evaluated according to equation (6), recalling that the COPR 

represents the ratio of the provided cooling duty and the electrical energy consumed, WEL, by the cycle 

(equation (6)). 

�̇�𝐻2
=

𝑊𝐸𝐿

𝜂𝐶𝐶 ⋅ 𝐿𝐻𝑉𝐻2

 (6) 

3. Heating above the ambient temperature, calculated as in equation (7), where ηB is the boiler efficiency. 

�̇�𝐻2
=

𝑄

𝜂𝐵 ⋅ 𝐿𝐻𝑉𝐻2

 (7) 

This methodology provides a standardized way of comparing hydrogen carriers based on practical and efficiency 

metrics, not just theoretical hydrogen content. Thus, the comparison allows for conscious decision-making in 

selecting the most suitable hydrogen storage and transport solutions. 

532



3. Results and discussion 

Based on the methodology described in section 2, energy consumptions of the production stages of different H2 

carriers (liquefied H2 (LH2), ammonia (NH3), toluene (TOL), DBT (dibenzyltoluene), formic acid (FA)) are 

accounted for. The same H2 flow rate is considered for the synthesis of all these species, equal to 20000 Nm3/h, 

to take into account the land footprint of solar panels. 

As regards ammonia, toluene, dibenzyltoluene and liquefied hydrogen, their detailed technical (Pellegrini et al., 

2024) and economic assessment (Spatolisano et al., 2024) has been already published elsewhere and is not 

detailed in this work. For formic acid, the catalytic production process of Figure 2 is assumed. Energy 

consumptions have been evaluated from Park et al. (2020) and referred to the considered H2 capacity.  

 

Figure 3: Energy consumptions in terms of equivalent H2 for the production stage of different H2 carriers: 

liquefied H2 (LH2), ammonia (NH3), toluene (TOL), dibenzyltoluene (DBT), formic acid (FA).  

As can be observed in Figure 3, formic acid production stage is very energy intensive with respect to the other 

carriers, consuming even more H2 than the one needed by gaseous hydrogen liquefaction. Indeed, the 

production stage of Figure 2 is quite complex: it involves a huge quantity of amine diluted in water which act as 

the reaction medium. This amine undergoes a reactive distillation, in which it is substituted by a heavier 

homologue to enable the product separation. Also, the system is strongly non ideal: a heterogeneous ternary 

azeotrope is present, formed by water, formic acid complex and amine.  

Liquefied H2 (LH2), ammonia (NH3), toluene (TOL) and dibenzyltoluene (DBT) only require electric energy for 

their production stage. On the other hand, formic acid needs a huge amount of heat for the separation 

downstream the reaction section to occur. This is another drawback of the analyzed production stage, as heating 

by a hot utility as stream is associated with indirect CO2 emissions release.  

Due to the energy-intensive reaction and separation stages, green formic acid production of Figure 2 is far from 

the industrialization target. 

4. Conclusions 

This work discusses the potential of formic acid (FA) as green H2 carrier, focusing on its production stage from 

CO2 and H2. Referring to the studies reported in literature, FA catalytic synthesis is analysed by means of the 

equivalent hydrogen methodology described in section 2. Due to the low maturity of the synthesis stage from 

CO2, as well as the lack of effective heterogeneous catalysts, formic acid is proved to be an unrealistic alternative 

for hydrogen transport.  

Research efforts should be devoted to the identification of more active and selective catalysts, also considering 

the process design aspect. In the present case study, despite the good catalytic performances, product 

separation from the reaction medium is not straightforward and calls for energy-intensive unit operations.  

In addition, it must be pointed out that the HCOOH melting point is not very low (around 8°C). This is a practical 

drawback for its implementation as H2 carrier on a large scale: during winter, it must be stored in heated vessels 

to hinder solid deposits formation.  

0

500

1000

1500

2000

2500

3000

LH2 NH3 TOL DBT FA

H
2,

e
q

 [k
g/

h
]

Cooling

Power

Heating

533



By the way, green formic acid production, in view of its application as a chemical rather than energy vector, also 

from methanol, still could be an interesting topic to focus on. 

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