ICCU-RWGS reaction system and ICCU methods

Fixed bed reactors are normally used for ICCU-RWGS. CO₂, N₂ and H₂ are used to provide the CO₂ source, purge gas and reduction agent. Gas concentrations are usually detected by an online gas analyser. In some cases, GC is used for gas analysis; however, using GC is inconvenient.

The following content provides some examples of ICCU-RWGS reaction system and reaction procedures.

Copied from (https://doi.org/10.1016/j.jcou.2022.102049) – “Fig. 2 shows a schematic of the experimental apparatus. It consists of mass flow controllers for gas supply, an electric furnace, a stainless-steel reactor (i.d. 9 mm, length 400 mm), a thermoelectric cooler, and a continuous gas analyzer. One gram of DFM was packed in the fixed-bed reactor, and the bed height was approximately 20 mm. Thermocouples covered by a stainless-steel tube was inserted into the reactor to monitor the reaction temperatures at the top, middle, and bottom part of the packed bed.” “The ICCC experiments were composed of four steps. In step 1, 5 vol% CO₂/N₂ was supplied to the reactor at a flow rate of 500 mL/min for 3 min to capture CO₂. In step 2, the gas stream was switched to N₂ to purge the CO₂. In step 3, H₂ was fed to the reactor at a predetermined flow rate to convert the captured CO₂. Finally, in step 4, N₂ was supplied in the same manner as in step 2 to purge H₂ and the converted products remaining in the reactor. Upon completion of step 4, the experimental operation was repeated from step 1. The reaction temperature was varied in the range of 350–500 °C between runs, although each individual run was isothermal. In addition, the H₂ flow rate in step 3 was regulated in the range of 25–500 mL/min, which corresponds to a weight hourly space velocity (WHSV) of 1.5–30 L/(h·g). During that time, the H₂ supply time was changed to maintain a constant total H₂ input.”

“Fig. 2. Schematic diagram of experimental apparatus.” (https://doi.org/10.1016/j.jcou.2022.102049)

Copied from (https://doi.org/10.1016/j.seppur.2022.121604) – “The ICCU-RWGS evaluations of Ni/support-CaO were carried out in a fixed-bed reactor and monitored by an online gas analyser (Kane Autoplus 5). The stainless-steel reaction tube (length: 500 mm, inner diameter: 64 mm) was placed in the middle of the tube furnace (Elite TSH-2416CG). Briefly, 0.30 g Ni/support-CaO bifunctional combined materials (BCMs) were placed in the middle of the reaction tube and fixed in place by quartz wool. Two thermocouples were placed in the reaction tube and inside the tube furnace to monitor the temperature of the BCMs and tube furnace, respectively. In a typical evaluation test, the BCMs were reduced at 550 °C in 5% H₂/N₂ for 2 h, and then the gas was switched to 100 ml min⁻¹ 20% CO₂/N₂ for ∼28 mins. 100 ml min⁻¹ 5% H₂/N₂ was then introduced for ∼28 mins for the RWGS. Then the flowing gas was switched to N₂ and equilibrated the temperature for the following test. The baseline of carbonation and hydrogenation steps was monitored using 0.3 g SiO₂ to eliminate the analyser signal delay. ”

“The cyclic performance of isothermal CaL was evaluated using a thermo-gravimetric analyzer (Hi-Res TGA 2950). A small amount (~20 mg) of calcined CaCO₃ was placed in a Platinum sample pan and heated up to 850 ˚C at a rate of 50 ˚C /min and keep isothermal for 10 mins to fully decompose CaCO₃ under a flow of 100 ml/min N₂. Additionally, the microbalance was protected by 100 ml/min N₂. Once the decomposition step is finished, equilibrate temperature to 600 ˚C, 650 ˚C or 700 ˚C and introduce a 15% CO₂/N₂ flow at 100 ml/min for 32 mins adsorption. Then switch gas from CO₂ to a 5% H₂/N₂ flow at 100 ml/min for 32 mins calcination (one cycle: 32 mins adsorption and 32 mins calcination). The capacity of CO₂ capture was calculated from continuously recorded weight changes and the weight after 10 mins calcination at 850 ˚C was applied as the weight of CaO. The non-isothermal CaL was evaluated using the same adsorption process under 650 ˚C. The calcination step was operated by raising the temperature to 850 ˚C at a rate of 50 ˚C /min and keep isothermal for 10 mins in 100 ml/min 5% H₂/N₂ or 15% CO₂/N₂. And then, equilibrate temperature to 650 ˚C for the next cycle test. Fig. S3 shows an example to measure the carbonation/regeneration rate and time of the adsorption and desorption process.” (https://doi.org/10.1016/j.seppur.2022.121604)