The efficient separation of CO2 from air remains
an
important and challenging goal for direct air capture (DAC). Herein,
iron-containing 13X zeolite (Fe@13X) with an efficient separation
of CO2 from the air was synthesized via a simple one-step
in situ crystallization method. The results demonstrate that Fe@13X
exhibited outstanding DAC performance (the CO2 capacity
of Fe@13X was 0.64 mmol/g, much higher than the 13X zeolite under
simulated air), which was attributed to the introduction of Fe atoms,
effectively narrowing the 13X micropore channel. Moreover, the DAC
adsorption performance of Fe@13X in the temperature range from 25
to 75 °C was explored by combined thermogravimetric analysis
and differential scanning calorimetry. The results revealed that low
temperatures were more favorable for the adsorption of CO2 with a high adsorption rate but less selectivity. Furthermore, Fe@13X
showed a 3 times higher CO2 production (0.003 kgCO2/kgads·h) and 3.6 times lower desorption energy (0.005
kW h/kgCO2
) than 13X zeolite in 400 ppm CO2 in N2. Finally, Fe@13X exhibited excellent cycle
stability in simulated air and maintained its initial CO2 uptake in 10 consecutive cycles, showing the broad application prospects
of materials in industrial adsorption and separation.
Biochar-based carbonaceous adsorbents are gaining interest due to their high availability, ease of modification, and low cost; however, they show limited adsorption of CO2 in flue gas due to common textural properties. In this study, TEPA-modified biochar was used to prepare a solid amine adsorbent for the efficient capture of CO2 in flue gas. First, the porous biochar was prepared with FeCl3, Mg(NO3)2, and H2O (g) as activators and walnut shells as carbon sources. Next, the biochar was modified with TEPA to obtain a solid amine adsorbent. Porous texture properties and sample surface functional groups were characterized, and we measured the adsorption CO2 of the amine-modified biochar in a breakthrough adsorption device. Results showed that biochar has a large specific surface area (744.38 m2 g−1), a total pore volume of 1.41 cm3 g−1, and a high mesoporous volume ratio (82.7%). The high pore volume provided a more efficient support space for loading tetraethylenepentamine (TEPA). The adsorbent had an excellent CO2 adsorption capacity, corresponding to 2.82 mmol g−1, which increased to 3.31 mmol g−1 and kept water resistance at 10% H2O (g) simulated flue gas (SFG). The FTIR analysis showed that H2O (g) inhibited urea production after cyclic adsorption. Therefore, solid amine adsorbent created by amine-modified biochar has potential advantages in its application for capturing CO2 in SFG.
For the problems of poor enhancement effect and long time consuming of the traditional algorithm, an adaptive smoothness constraint image multilevel fuzzy enhancement algorithm based on secondary color-to-grayscale conversion is proposed. By using fuzzy set theory and generalized fuzzy set theory, a new linear generalized fuzzy operator transformation is carried out to obtain a new linear generalized fuzzy operator. By using linear generalized membership transformation and inverse transformation, secondary color-to-grayscale conversion of adaptive smoothness constraint image is performed. Combined with generalized fuzzy operator, the region contrast fuzzy enhancement of adaptive smoothness constraint image is realized, and image multilevel fuzzy enhancement is realized. Experimental results show that the fuzzy degree of the image is reduced by the improved algorithm, and the clarity of the adaptive smoothness constraint image is improved effectively. The time consuming is short, and it has some advantages.
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