https://doi.org/10.3390/su14084750
“Mesoporous silicas were first introduced by scientists at the Mobil Oil company and Kuroda and co-workers, in the early 1990s, as a way to extend the utilization of zeolites [135,136,137,138]. These new synthesized materials ranged from 2–10 nm in width and were designed due to large molecules not being able to react effectively in existing zeolites [135]. The utilization of MCM-41 was reported in 2011, where it acted as a Lewis acid catalyst in the solvent regeneration process [76]. MCM-41 was already widely used but not in the CO2 absorption process as the catalyst had a high specific surface area [139]. The study on the utilization of this catalyst should branch out into the desorption process since previous study on this area is limited. depicts the summary for past commercially available mesoporous silica employed in the regeneration of solvent.”
Table 8. Summary of past studies using mesoporous silica in the regeneration of solvent.
| Solvent |
Quantity |
Temperature
°C |
Remarks |
Ref. |
| MEA |
25 g |
98 |
|
[129] |
| MEA |
25 g |
98 |
|
[140] |
| DEAPA |
25 g |
90 |
-
MCM-41 and SAPO-34
-
Catalyst was tested on DEAPA solvent in comparison to MEA
-
B/L ratio of MCM-41 is 0.75
-
MSA of MCM-41 is 171.50 m2/g
-
MCM-41 performed best after zeolite
|
[78] |
| MEA |
6.25 ± 0.01 g catalyst |
98.5 |
|
[107] |
”
The MCM-41 catalyst was compared with zeolite (HZSM-5) and sulfated metal oxide (SO
42−/ZrO) at 98 °C in 5 M MEA. The CO
2 desorption performance was better than the blank test and sulfated metal oxide, yet inferior to HZSM-5. The heat duty also displayed the same result with the MCM-41 catalyst, having a heat duty of 16.9 MJ/Kg CO
2, whereas HZSM-5 was reported to have 15.6 MJ/Kg CO
2. The MSA was reported to be larger than HZSM-5, yet the B/L ratio was smaller. This implies that the Bronsted acid sites relative to the Lewis acid sites was relatively small, despite having a large MSA. Therefore, its performance was inferior to HZSM-5, which has both a large MSA and an even larger B/L. This trend also shows similar results to Zhang et al. [
140].
The employment of the same catalyst was reported in a different study but in a different amine solvent; 3-(diethylamino)propylamine (DEAPA) [
78]. The results from comparing SAPO-34 zeolite and the blank amine solvent similar to previous studies, where the MCM-41 benefited over the blank test and SO
42−/TiO
2 but was poorer in comparison to the zeolite catalyst. Another material is SBA-15 that was compared with sulfated SBA-15 materials [
107]. The CO
2 desorption performance of the non-optimized SBA-15 was reported to be lower than the blank MEA test and the employment of HZSM-5. The heat duty of SBA-15 was 49.92, followed by 51.92 and 61.60 MJ/kg CO
2 for HZSM-5 and the blank MEA test.
Mesoporous silica was reported to aggregate, which affected its long term stability [
141]. It has lower hydrothermal stability in comparison to zeolite [
142,
143]; although, its stability is high enough to be heated to at least 850 °C [
143], which indicates it is suitable to undergo the temperature for the regeneration of solvent in a CO
2 capture process. The morphology of MCM-41 and SBA-15 was also reported to be intact after five cycles of the CO
2 capture process, which indicates good regeneration and reuse of the nanoparticle [
144].
depicts the type of mesoporous silica previously studied for the regeneration of solvent along with their respected heat duties (MJ/kg CO2). MCM-41 has a significantly lower heat duty in comparison to SBA-15, yet when it was compared to zeolite, it was found to be inferior.
“
