(562d) Triboelectric Particulate Matter Purifier Using Electrospun Ethyl Cellulose

Triboelectric
Particulate Matter Purifier Using Electrospun Ethyl Cellulose

Min Hee Cho, Jeong Gil Seo*

Department
of Energy Science and Technology, Myongji University, 116, Myongji-ro,
Cheoin-gu, Yongin-si, Gyeonggi-do 17058, Republic of Korea

*E-mail: jgseo@mju.ac.kr

As
a result of ever-increasing demand for transportation, industrial production,
and power plants, air pollution has become one of the most serious
environmental problems. One of the major pollutants, particulate matter (PM),
has attracted much attention because of its catastrophic effect on human health
such as cardiovascular and respiratory diseases. PMs are categorized by their
aerodynamic diameter; PM10 and PM2.5 are defined as a particulate matter with
an aerodynamic diameter less than 10 ¥ìm and 2.5 ¥ìm, respectively. Very recently,
South Korea has suffered from PMs especially during winter and spring seasons.
Although the main source of PMs is still controversial, it is urgent to protect
human health from the highly concentrated PMs. There are typical ways to remove
PMs such as electrical precipitation and filtration. However, in the case of
the electrical precipitation, it needs a very high voltage requiring a lot of
energy consumptions and O₃ which is very hazardous to a human being
is generated during the operation. In the case of filtration, it usually uses a
High-Efficiency Particulate Absorber (HEPA) filter. However, it also requires
high maintenance and administrative cost for exchanging and discarding. Furthermore,
in a high concentration of PMs, life time of the filter is drastically decreased.
Therefore, the reusable, economical and high-efficiency technology that
minimizes the energy consumption and maintains the high PM particles removal
efficiency is needed. In this study, a new method that utilized the
electrostatic effect induced by triboelectrification was developed in order to
make better PM purifier more than former ways. Triboelectrification is a
phenomenon that material surface becomes electrically charged as a result of
contact or collision between different materials. This phenomenon can be applied
in the PM purifying process. Our previous experiments demonstrated the
triboelectrification effect in PM capture process using the electrification
between PTFE and aluminum (Figure 1) and the electrification between PTFE and
nylon (Figure 2). Generally, PTFE has a very high electronegativity so its
surface can receive the electrons when it contacts aluminum or nylon.
Consequently, PTFE becomes negatively charged and the opposite material becomes
positively charged. So when polluted air flow into these materials, PM
particles can be captured on their surface. This mechanism is based on the
electrostatic filtration induced by triboelectrification. And there is also
another mechanism of capturing PM particles. That is mechanical filtration such
as interception, inertial impaction, diffusion and gravitational settling
because of its structural characteristics. In other words, electrostatic
filtration and mechanical filtration are accompanied and make a synergy effect
in the PMs capture process (Figure 1 and 2). On the basis of previous studies, ethyl
cellulose was selected as the replaced material to be positively charged
instead of nylon or aluminum. Ethyl cellulose is one of the cellulose
derivatives called cellulose ether. Cellulose is the most abundant natural
polymer and it is easily accessible, biodegradable and economical cost.
According to the triboelectric series, ethyl cellulose has a big tendency to be
positively charged much more than cellulose and even bigger than nylon. The
main components of Triboelectric PM Purifier (TPP) is a triboelectric layer
(TL) consisting of ethyl cellulose and PTFE spheres. In order to induce
electrification effectively on the surface of ethyl cellulose and PTFE sphere,
the structure of ethyl cellulose should be non-woven structure so it was
conducted by using electrospinning. Ethyl cellulose non-woven was placed in the
top and bottom of the triboelectric layer and PTFE spheres got into between top
and bottom space. Under some of the mechanical movement, PTFE spheres contact
and collide with the ethyl cellulose surface. As a result, PTFE becomes
negatively charged and in turn ethyl cellulose becomes positively charged. In
this state of the TL, PM particles can be effectively captured by the synergy
of mechanical filtration and electrostatic filtration induced by
triboelectrification. In order to test its capacity to remove PM
particles in the indoor environment, the indoor environment was simulated by an
acrylic box (W: 800mm, D: 550mm, H: 500mm, thickness: 10 mm). The mass
concentrations (¥ìg m^-3) of PM1, PM2.5, and PM10 were observed in
real time by the measurement instrument (Y09-PM handheld air quality monitor,
Sujing Group automation instrument equip CO, Ltd). And Rocker 3D digital shaker
(IKA) was used as a mechanical movement source (Figure 3). PMs were generated
by incense burning as it produces PMs much more than cigarettes and also
generates gas products such as CO, CO₂, NO₂ and SO₂
and organic compounds such as benzene, toluene, xylene, aldehydes and
polycyclic aromatic hydrocarbons. The performance of the TPP was tested by the
various ways to demonstrate its capacity to remove PMs. In order to verify the
effect of triboelectrification in the PMs capture process, the comparison test between
the TL and other TL without PTFE spheres was conducted. In the case without
PTFE spheres, it needed more time to reduce PMs. And from this result, the synergy
of mechanical filtration and electrostatic filtration induced by
triboelectrification was verified. And for the purpose of estimating its
ability, comparison with a commercial air purifier using HEPA filter was conducted
and the cycle test (> 30 cycles) of TPP was also conducted to investigate its
durability. In addition, the reusability test was conducted by just washing the
TL with water. After washing, it was dried in the room temperature and then the
PMs removal test was conducted again. Through the screening of surface
condition of ethyl cellulose and PTFE by using FE-SEM, the surface difference
before and after the capturing of PMs and the surface after washing were
observed in detail. The captured PMs could be found easily on its surface and particle
size distributions were from 1 nm to several micrometers. From the images of
washed TL components, it showed that the captured PMs were removed well by washing
with water. This work proves that the TPP is the reusable, economical, and
high-efficiency technology in the air purification field.

Keywords: triboelectrification, ethyl cellulose,
particulate matter

Figure 1. PM removal of prototype
TPP consisting of PTFE sphere and aluminum plate. In the graph, the frame means
that PTFE and aluminum are removed from the device.

(A) PM1 concentration graph. (B) PM2.5 concentration graph. (C) PM10
concentration graph.

Figure 2. PM removal of improved TPP
consisting of PTFE sphere and Nylon mesh. In the graph, the frame means that
PTFE and nylon are removed from the device. It was compared with a commercial
purifier using HEPA filter.

(A) PM1 concentration graph. (B) PM2.5 concentration graph. (C) PM10
concentration graph.

Figure 3. Simulated system for PM
removal test.