dc.description.abstract | A composite nonwoven (CNW) material, activated carbon fiber enhanced microfibrous
entrapped sorbent (ACF-MFES) , was prepared by incorporating micro sized (100-500µm)
sorbent particulates into the blended microfiber (10-20µm bicomponent polymer fiber and ACF)
webs via wet-lay process. This novel fibrous sorbent media is characterized by its small
particulates, high voidage and uniform structure. The manufacturing process of ACF-MFES is
similar with the industrial nonwovens production and thereby it can be readily scaled up. The
application of ACF-MFES nonwovens materials in the air cleaning systems can provide
considerable advantages over traditional packed bed design; these advantages include higher
single pass removal efficiency, lower pressure drop, higher bed utilization and lightweight.
The first part of this work is the development of ACF-MFES, including the formation of
recipe and process optimization. For the recipe, self-bonding bicomponent fiber, activated carbon
fiber, sorbent particulates and various process additives was used. For the process optimization,
each process step, including the fiber selection, wet-end chemistry, web formation technology,
and web bonding technology, was optimized. In this study, for the first time, ACF was added to
create a blended fiber web; it was found that only small portion of ACF effectively improved the
nonwoven’s quality including the softness, strength, resilience, and the homogeneity of particle
distribution.
The second part is the performance test of ACF-MFES. Hexane adsorption is used to
demonstrate the media’s adsorption rate and capacity; the performance is compared with
traditional granular packed bed sorbent. Bench scale experiments were firstly conducted in a
2.54cm (1.0”) diameter stainless steel pipe setup, and then full scale tests were conducted in a
24x24” HVAC filter test rig. The hexane breakthrough curve showed that the ACF-MFES media
has much faster adsorption kinetics compared to packed bed sorbent. This enhancement in
adsorption rate is resulted from ACF-MFES media’s high contacting efficiency due to its small
particulates and high surface area.
The third part is the kinetics study of adsorption in ACF-MFES. Hexane adsorption onto
activated carbon is a strong physisorption process, which is usually in mass transfer control
rather than in intrinsic reaction control. Therefore, the kinetics study of adsorption is actually the
study of mass transport between fluid and solid. The mass transfer of hexane molecule from the
bulk of fluid to the specific adsorption site on the interior surface of activated carbon involves
two steps: external mass transport and internal mass transport. The external mass transport
mainly carried out through film diffusion, whereas the internal mass transport is more
complicated because some different mechanisms are involved in this step, including molecular
and Knudsen diffusion in the fluid phase, and surface diffusion in the solid phase. In this work,
these four mass transfer coefficients are lumped into one overall mass transfer coefficient kG by
analogy to the electrical resistance model. | en_US |