9.2.4.1 Formic Acid, HCO 2
Market of ca. 800 kt/y and annual growth estimated at 4.95% by 2027 [13].
Has a utilization in sectors such as animal feed, rubber and leather production,
dyeing and finishing textiles, cleaning agents, goods preservatives. The use as H 2 -
carrier/storage may increase its market to tens Mt/y. Formic acid is currently made
through routes based on CO, produced via coal or methane reforming that cause
emission of CO 2 . Its direct synthesis from CO 2 and H 2 (Eq. 9.4a) is attempted since
long time as would be highly beneficial (reduction of CO 2 emission). Reaction 9.4a
has some thermodynamic limitations (DG° = +6 kcal/mol) due to the negative
entropic contribution (two gases are converted into a liquid). The equilibrium
concentration is low. If carried out in presence of a proton acceptor (amine or
water/Na(K)OH) the thermodynamics is much improved (DG° = ca. −30 kcal/mol)
and the reaction is shifted to the right, but producing salts more than the free acid
(Eq. 9.4b). The latter can be obtained by treating the salts with a strong acid
(Eq. 9.4c), increasing the complexity of the process and waste production.
H 2g þ CO 2g ! HCO 2 H l
ð9:4aÞ
H 2g þ CO 2g þ RR
0
NH Na K
ð ÞOH
½
!RR
0
NH
þ À
2 HCO 2 Na K
ð Þ
þ À HCO 2 þ H 2 O
Â
Ã
ð9:4bÞ
RR
0
NH
þ À
2 HCO 2 þ HX ! HCO 2 H þ RR
0
NH
þ À
2 X
ð9:4cÞ
Noteworthy, some catalysts have been developed so far for the synthesis of
formates (Eq. 9.4b) which could be considered for industrial application [14].
Should the ongoing attempts to their use in the synthesis of the free acid, instead of
salts, succeed (by using SC-CO 2 [15] or water as reaction solvents [16]), the direct
synthesis of formic acid from CO 2 and water (as source of H 2 ) will be ready for
exploitation. The interest in formic acid lays also in the fact that reaction 9.4a can
be easily catalytically reversed to CO 2 and H 2 making, thus, formic acid an
interesting liquid carrier (or storage) of hydrogen for fuel cells.
9.2 Carbon Dioxide Conversion (CCU)
153
Market of ca. 800 kt/y and annual growth estimated at 4.95% by 2027 [13].
Has a utilization in sectors such as animal feed, rubber and leather production,
dyeing and finishing textiles, cleaning agents, goods preservatives. The use as H 2 -
carrier/storage may increase its market to tens Mt/y. Formic acid is currently made
through routes based on CO, produced via coal or methane reforming that cause
emission of CO 2 . Its direct synthesis from CO 2 and H 2 (Eq. 9.4a) is attempted since
long time as would be highly beneficial (reduction of CO 2 emission). Reaction 9.4a
has some thermodynamic limitations (DG° = +6 kcal/mol) due to the negative
entropic contribution (two gases are converted into a liquid). The equilibrium
concentration is low. If carried out in presence of a proton acceptor (amine or
water/Na(K)OH) the thermodynamics is much improved (DG° = ca. −30 kcal/mol)
and the reaction is shifted to the right, but producing salts more than the free acid
(Eq. 9.4b). The latter can be obtained by treating the salts with a strong acid
(Eq. 9.4c), increasing the complexity of the process and waste production.
H 2g þ CO 2g ! HCO 2 H l
ð9:4aÞ
H 2g þ CO 2g þ RR
0
NH Na K
ð ÞOH
½
!RR
0
NH
þ À
2 HCO 2 Na K
ð Þ
þ À HCO 2 þ H 2 O
Â
Ã
ð9:4bÞ
RR
0
NH
þ À
2 HCO 2 þ HX ! HCO 2 H þ RR
0
NH
þ À
2 X
ð9:4cÞ
Noteworthy, some catalysts have been developed so far for the synthesis of
formates (Eq. 9.4b) which could be considered for industrial application [14].
Should the ongoing attempts to their use in the synthesis of the free acid, instead of
salts, succeed (by using SC-CO 2 [15] or water as reaction solvents [16]), the direct
synthesis of formic acid from CO 2 and water (as source of H 2 ) will be ready for
exploitation. The interest in formic acid lays also in the fact that reaction 9.4a can
be easily catalytically reversed to CO 2 and H 2 making, thus, formic acid an
interesting liquid carrier (or storage) of hydrogen for fuel cells.
9.2 Carbon Dioxide Conversion (CCU)
153