2025-06-27
How Fast Is the Adsorption and Desorption Speed of Activated Carbon Fiber?
Activated carbon fiber is an efficient adsorption material, often used in environmental protection, industrial purification, medical health and other fields. The most obvious advantage of activated carbon fiber is its rapid adsorption and desorption speed as well as strong regeneration capacity, which is why it holds a certain position in traditional granular and powdered activated carbon.
How Fast Does Activated Carbon Fiber Capture Contaminants?
The structure of ACF determines its extremely fast adsorption capacity. It is composed of fibers with diameters ranging from 5 to 20μm, and its surface is densely covered with a large number of micropores of 1 to 2nm. These micropores are directly exposed, unlike granular activated carbon, which requires pollutants to pass through macropores and mesopores first before reaching the micropores. The adsorption rate of volatile organic compounds (VOCs) by ACF can reach 10 to 100 times that of traditional activated carbon
The ultra-high specific surface area (1500-2500 m²/g) provides sufficient adsorption sites. Observation through high-resolution transmission electron microscopy reveals that the surface of ACF presents a honeycomb-like porous structure, with pore size distribution concentrated in 1-2nm, which precisely matches the molecular size of most organic pollutants, generating a strong capillary coagulation effect.
The optimized fiber structure promotes mass transfer of the fluid. ACF can be processed into various forms, such as non-woven fabrics and honeycomb bodies. Its porosity is as high as over 90%, and the pressure drop is only 1/5 of that of GAC packed beds. This open structure avoids channel flow and short circuits, ensuring that the fluid is in full contact with the adsorbent. Computational fluid dynamics simulations show that in the ACF filter, the streamline distribution is uniform and there are no obvious dead areas.
The adsorption rate performance of different pollutants
In terms of gas-phase adsorption, the adsorption of benzene series substances is the most rapid. Experimental data show that under the conditions of an initial concentration of 200ppm and a space velocity of 10,000 H ⁻¹, ACF can reach 90% of the saturated adsorption capacity for benzene vapor within 10 seconds, while GAC requires more than 5 minutes. For formaldehyde (HCHO) with a larger molecular weight, ACF can also complete adsorption equilibrium within one minute, which is attributed to the specific interaction between the rich oxygen-containing functional groups on its surface and the formaldehyde molecule.
In the field of liquid-phase adsorption, the capture speed of heavy metal ions by ACF is impressive. The tracking test by inductively coupled plasma mass spectrometry (ICP-MS) revealed that the adsorption rate of Pb²⁺ by ACF exceeded 95% within 5 minutes, which was 15 times that of traditional activated carbon. For organic dyes, the adsorption rate constant of ACF for methylene blue reaches 2.5×10⁻³ g/(mg·min), and the adsorption can be completed within 20 minutes, while GAC requires more than 2 hours.
The key factors affecting the adsorption rate
The influence of temperature on the adsorption rate shows a dual effect. On the one hand, raising the temperature (50-150℃) will increase the molecular kinetic energy, enhance the diffusion rate, and accelerate the initial adsorption speed. For example, the adsorption rate constant k of toluene on ACF increases exponentially with the rise of temperature, and it is three times faster at 80℃ than at 25℃. On the other hand, excessively high temperatures can lead to a decrease in the equilibrium adsorption capacity, as adsorption is an exothermic process.
The concentration of pollutants is positively correlated with the adsorption rate. In the low concentration range (<100ppm), the adsorption rate is mainly controlled by diffusion. At high concentrations (>500ppm), the surface adsorption reaction becomes the rate-limiting step. Experiments show that when the concentration of toluene increases from 50 PPM to 500 PPM, the adsorption half-life t₁/₂ of ACF shortens from 30 seconds to 5 seconds.
The pore size distribution needs to match the molecular size of the target pollutant. Through the analysis of N₂ adsorption and desorption tests, it was found that when the mesoporous ratio of ACF (2-50nm) increased from 5% to 20%, the adsorption rate of macromolecular dyes increased by 50%, but the adsorption rate of small molecule benzene remained basically unchanged.
