Abstract
In the present study, the performance of four biomass-derived physically activated biochars for dynamic CO2 capture was assessed. Biochars were first produced from vine shoots and wheat straw pellets through slow pyrolysis (at pressures of 0.1 and 0.5 MPa) and then activated with CO2 (at 0.1 MPa and 800 °C) up to different degrees of burn-off. Cyclic adsorption-desorption measurements were conducted under both dry and humid conditions using a packed-bed of adsorbent at relatively short residence times of the gas phase (12–13 s). The adsorbent prepared from the vine shoots-derived biochar obtained by atmospheric pyrolysis, which showed the most hierarchical pore size distribution, exhibited a good and stable performance under dry conditions and at an adsorption temperature of 50 °C, due to the enhanced CO2 adsorption and desorption rates. However, the presence of relatively high concentrations of water vapor in the feeding gas clearly interfered with the CO2 adsorption mechanism, leading to significantly shorter breakthrough times. In this case, the highest percentages of a used bed were achieved by one of the other activated biochars tested, which was prepared from the wheat straw-derived biochar obtained by pressurized pyrolysis.
Highlights
Global warming is gaining wider recognition in the world
The relatively poor results obtained in terms of regeneration efficiency for the rest of materials could be explained by an insufficient vacuum level during the regeneration step
Regarding the experimental CO2 -over-N2 selectivity at 25 ◦ C, all the samples showed a very good behavior with values in the range of 44.5 to 58.6. These values, which were calculated according to Equation (A5), were considerably higher than those reported by González et al, (20–30) [13] and Shahkarami et al, (17.4–29.3) [14] from multicomponent adsorption measurements
Summary
Global warming is gaining wider recognition in the world. Fossil fuel power plants are responsible for approximately one-third of global CO2 emissions to the atmosphere. Removing CO2 from low-pressure flue gas (i.e., CO2 capture in postcombustion) has been the focus of extensive research over the last few decades. As an alternative to the energy-intensive amine-based chemical absorption processes, CO2 capture via adsorption on renewable biomass-derived carbons has gained increased interest, since these adsorbents are relatively cheap, require low energy for regeneration, and show a relatively good tolerance to moisture existing in flue gas [1]. An increasing number of studies have focused on producing activated carbons (ACs) from different biomass precursors (through physical or chemical activation) and assessing their performance in terms of CO2 uptake at 10–15 kPa and selectivity towards CO2 over N2 [2,3,4,5,6,7,8,9,10]. Regarding the apparent CO2 /N2 selectivity, which is defined as the ratio of molar uptakes divided by the ratio of partial pressures, values in the range of 8–14 (deduced from single component adsorption data at 25–50 ◦ C)
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