A total of 6 experiments were then conducted and observed to study the effectiveness of converting CO2 into formic acid using light, water and the RRR catalyst. The catalyst used for the experiments was made as a fulvic acid derivates by IOI Investment Zrt. The RRR catalyst is a silver complex as described in WO2021090038. Balint Analytics Engineering, Research and Service Provider Ltd determined the formic acid content of the aqueous solutions of the following samples: RK-X11, RK-X12, RK-X13, RK-X14, RK-X1, RK-X2, RK-X3, RK-X4.
Experiment #1
A Schott DURAN 1000 cm3glass bottle was filled with aqueous carbonic acid solution freshly prepared from 950 cm3 of distilled water. A SodaStream soda water automaton was used during the preparation of the aqueous carbonic acid solution.
Exactly 20.00 mg of RRR catalyst was added to the solution obtained, and after sealing the glass bottle, it was shaken until the dissolution of the catalyst. The initial pH of the solution was 4.2, the endpoint pH was 3.0. The pH of the reaction mixture was measured with a digital pH meter and a Dosatest pH indicator strip. The glass jar was exposed to natural sunlight. The reaction mixture was under the influence of full daylight for 14 days [end of experiment: 16.07.2019]. The onset of the reduction reaction is indicated by the appearance of a semicircular Tyndall phenomenon. The samples were identified as RK-X11 and RK-X12.
The progress of the reaction was monitored by measuring the pH of the reaction mixture and the amount of potassium permanganate and bromine used up by the sample of the reaction mixture.
Two observations were carried out to confirm that aqueous carbonic acid solution was converted to formic acid.
Potassium permanganate reacts with the formed formic acid according to form the below reaction equation: 5 HCOOH (aq) + 2 KMnO4 (aq) + 6 H+ (aq) →
2 K+ (aq) + 2 Mn2+ (aq) + 8 H2O (l) + 5 CO2 (g)
Observation: The reaction mixture decolorizes the potassium permanganate solution.
The bromine in the bromine water reacts with formic acid according to the below reaction equation: HCOOH (aq) + Br2 (aq) → + 2 Br– (aq) + 2 H+ (aq) + CO2 (g)
Observation: The reaction mixture decolourises the bromine water.
Test results for solutions RK-X11 and RK-X12 in [mg/L] units
Laboratory code
|
Sample code
|
Sample preparation commenced (test ended)
|
Quantity of formic acid
|
19-735/1
|
RK-X11
|
25.07.2019
|
11.1
|
19-735/2
|
RK-X12
|
25.07.2019
|
11.0
|
Table 1.
Experiment #2
Using 200 mg/L RRR catalyst and winter sunlight for 14 days [end of experiment: 01.01.2020], in a 50 litres LABFREEZ VGR-50DL PYREX 3.3 glass reactor. The samples were identified as RK-X13 and RK-X14.
Test results for solutions RK-X13 and RK-X14 in [mg/L] units
Laboratory code
|
Sample code
|
Sample preparation commenced
(test ended)
|
Quantity of formic acid
|
20-10/2
|
RK-X13
|
15.01.2020
|
179.0
|
20-10/3
|
RK-X14
|
15.01.2020
|
176.0
|
Table 2.
Experimental details in 2022 with the photoreactor (RK-X)
To determine the parameters for the very first CO2 – formic acid conversion, a photoreactor (RK-X) was used.
Reactor parameters (RK-X)
Height: 500 mm
Outer diameter: 100 mm
Inner diameter: 90 mm
Height (top and bottom fittings): 40 mm
Gross Volume: 2670 cm3
Net Volume: 2100 cm3
Volume (lighting fitting): 570 cm3
Volume (Gas): 400 cm3
Volume (Liquid): 1700 cm3
Lighting: LED 0.702 A (231 lux, 626 nm, 17 W – 48 W)
Experiment #3
The RK-X reactor was filled with 1700 cm3 of distilled water and RRR catalyst (300 mg/L) was dissolved. Fully saturated water with carbon-dioxide (CO2) was created in the reactor (constant pressure indicated that the water is fully saturated). The reactor was charged to 5 bar with carbon-dioxide (CO2) gas. Then the lights were switched on and left the reaction go until pressure in the reactor reduced to 1 bar. The sample was identified as RK-X1.
Amount of reacted CO2 (n) = 0.01613582 mol
Calculated concentration = 0.01613582 mol*46/1700 cm3 = 436.62 mg/L
Measured concentration (RK-X1): 301 mg/L
Experiment #4
Procedure was followed as described of Experiment #3. The sample was identified as RK-X2.
Amount of reacted CO2 (n) = 0.01613582 mol
Calculated concentration = 0.01613582 mol*46/1700 cm3 = 436.62 mg/L
Measured concentration (RK-X2): 313 mg/L
Experiment #5
Procedure was followed as decribed of Experiment #3. The sample was identified as RK-X3.
Amount of reacted CO2 (n) = 0.0645433 mol
Calculated concentration = 0.0645433 mol*46/1700 cm3 = 1746.46 mg/L
Measured concentration (RK-X3): 1650 mg/L
Experiment #6
In Experiment #6 the procedure of Experiment #3 was applied twice. The procedure of Experiment #3 was followed and when the pressure dropped to 1 bar, the reactor was recharged with carbon-dioxide to 5 bar and the reaction was carried on until the pressure dropped to 1 bar again. The sample was identified as RK-X4.
Pressure (∆p) = 8 bar (2x4 bar)
Amount of reacted CO2 (n) = 0.1290865 mol
Calculated concentration = 0.1290865 mol*46/1700 cm3 = 3492,93 mg/L
Measured concentration (RK-X4): 2600 mg/L
Test results for formic acid using RK-X photoreactor in [mg/L] units
Laboratory code
|
Sample code
|
Sample preparation commenced (test ended)
|
Quantity of formic acid
(mg/L)
|
22-68/4
|
RK-X1
|
03.02.2022
|
301
|
22-68/2
|
RK-X2
|
03.02.2022
|
313
|
22-68/6
|
RK-X3
|
07.02.2022
|
1650
|
22-68/8
|
RK-X4
|
11.02.2022
|
2600
|
Table 3.