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Removal of VOCs and Improvement of Indoor Air Quality Using Activated Carbon Air Filter

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Volatile Organic Compound (VOC) is one of the most common air pollutants emitted from industries like Chemical, Petrochemical industries, as well as when plastics are burned. It is very harmful to our environment which affects climate change, the life cycle of plants and the health of all living beings. So it is necessary to control its emission for improvement of air qualities which is beneficial to the indoor environment. The objective of the study is to review the performance of different activated carbon-based air filters. Various activated carbon-based techniques are the use of coconut shell, photocatalyst TiO 2, Polystyrene foam, sorption-type, and granular activated carbon. Several aldehydes and ketones have been removed effectively using activated coconut shell. Removal of nitrogen oxide was possible by using TiO 2 based activated carbon. It is observed from this study that activated carbon-based techniques are effective for removal of VOCs and enhancing the indoor air quality.
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1
Removal of VOCs and Improvement of Indoor Air Quality Using Activated
Carbon Air Filter
Sujon Mondal1, Soham De1 and Dr. Purnachandra Saha2* (ORCID-0000-0002-2722-1669)
1Students, School of Civil Engineering, KIIT Deemed to be University, Bhubaneswar
(Mail id: sujonmondal986@gmail.com, sohamde053@gmail.com)
2Senior Associate Professor, School of Civil Engineering, KIIT Deemed to be University,
Bhubaneswar, India
(Mail id: dr.purnasaha@gmail.com) * Corresponding Author
Abstract
Volatile Organic Compound (VOC) is one of the most common air pollutants emitted from industries like Chemical,
Petrochemical industries, as well as when plastics are burned. It is very harmful to our environment which affects
climate change, the life cycle of plants and the health of all living beings. So it is necessary to control its emission
for improvement of air qualities which is beneficial to the indoor environment. The objective of the study is to
review the performance of different activated carbon-based air filters. Various activated carbon-based techniques are
the use of coconut shell, photocatalyst TiO2, Polystyrene foam, sorption-type, and granular activated carbon. Several
aldehydes and ketones have been removed effectively using activated coconut shell. Removal of nitrogen oxide was
possible by using TiO2 based activated carbon. It is observed from this study that activated carbon-based techniques
are effective for removal of VOCs and enhancing the indoor air quality.
Keywords: VOCs, IAQ, Activated carbon filter, Coconut shell, photocatalyst TiO2, Polystyrene foam.
1. Introduction
Volatile organic component(VOC) is one the most harmful contaminant present in the air. Its boiling point lies
between 50oCto 260oC. It's consist of several components such as Acetaldehyde, Acetone, Benzene, Carbon
tetrachloride, Ethyl acetate, Ethylene glycol, Formaldehyde, Heptane, Hexane and several other [1]. There are
several detrimental effects that occur due to this such as serious health disorders which include irritation of nose and
eyes, damages liver, badly affect the nervous system [2]. It not only affects the human body but also affects the
change of climate, the temperature of the earth also reduces the plant growth. It is also responsible for the
photochemical smog which is hazardous in nature [3,2]. It reduces the indoor air quality (IAQ). IAQ is defined as
the air quality in and around the building. There are several factors that ./affect the IAQ such as temperature,
humidity, biological pollutants, air exchange rate, air movement, particle pollutants, and gaseous pollutants. One of
the major factors that affects the IAQ is the gaseous pollutants[4,5] For improvement of this IAQ and also outdoor
air quality there are several activated carbon-based filters are used which might be shell based such as coconut shell
based, pecan shell and almond shell based [6,7,8]or it might be activated charcoal, bamboo charcoal [9]. Another
type of activated carbon such as the granular activated carbon and the activated carbon fiber(AFC) [10,11] There are
several techniques that are used for the filtration process such as oxidation, catalysis, regeneration and reveres
reactor process [3,2,12].The main objective of the study is to study the different activated carbon-based filter and
comparing their
1) Removal Efficiency and Specific Surface area
2) Study the several filtration techniques that are available.
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2. DIFFERENT TECHNIQUES OF ACTIVATED CARBON BASED AIR FILTER
Activated carbon-based air filter (ACBAF) are mainly used for the removal of different harmful contaminant and
impurities in the air which includes VOCs, CO2, NO2, SO2 etc. This filtration process mainly differs based on the
activated carbon used and process.[10] There are two types of techniques namely, adsorption and filter based are
used to improve the indoor air quality. In the adsorption process, increasing surface area with more pore
development should be used to improves the performance. [2]This types of techniques are mainly used for the
purification of the indoor as well as outdoor air. Filter based techniques mainly contain several activated carbon-
based filters which purify the air using oxidation, catalysis, regeneration and reveres reactor process[1].
2.1 ADSORPTION TYPE
Adsorption is a surface phenomenon in which solid surface attracts gas molecule or liquid solution. The adsorbing
solid is called adsorbent (activated carbon) and the adsorbed particle is called adsorbate (air contaminants).
When gas or vapor comes in contact with solid particles, a portion of the gas-composition is absorbed by the solid.
The gas The contact-solid surface is called adsorbate. Many organic and inorganic contaminants removed either
from the gaseous or liquid solutions by the natural process of adsorption on the very porous medium solid phase
with large internal surfaces. Adsorbates can attach themselves onto the surfaces in two ways a) physisorption b)
chemisorptions. In physisorption, adsorbents attach themselves to the solid medium by weak van der Waals
forces. But in case of chemisorptions, the absorbates sticks to the solid medium by forming (a) chemical bond
between the absorbates and the solid medium. The above-scripted steps of adsorption can be summarized as per
the following: solute diffuses near the solid surface, diffuses into the pores of the particle, then moves through the
pore wall and adsorbs to the pore wall surface. To increase the adsorption capacity of activated carbon a large
specific surface is favored [13].
2.2 ADSORPTION PROCESS
Activated carbons are mainly used as a filter material for removal of contaminant gases present in air, Porous
carbon-based materials have high thermal and chemical stability as well as good adsorption capabilities [14]
Coconut shell, Activated charcoals, Fiber rejects and commercial fibers of Polymetaphenylene is ophthalamide
,Fiber of Polyparaphenylene terephthalamide and bamboo carbon and anthracite activated carbon were used as raw
materials for activated carbon and Samples were milled inside planetary ball mill for 30 hours with the speed of 300
rpm to reduce the size, Hydrogen (H2) was used as adsorbate gas. The granular coconut shell charcoals used here in
the granulated form[15] The average diameter of the fibers was around 10 micrometer(pm)[11].
Different types of carbonaceous material for ex-plant, mineral origin which consists of carbon with more
concentration which can be converted to activated carbon using different types of a method such as chemical and
physical activation method, which affects the quality of the AC. For this reason, performed a pretreatment that
involved cutting, removing all of the pulp and some of the fibers, and air-drying the remaining shell. For uniform
quality in carbonization and activation, the water content of the shells was maintained at between 13% and 16%
[14]
Fig: 1 VOC removal process
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2.2.1 Carbonization/ activation
Activated carbons can be produced by two different processes one is Physical or gas activation process and other
process is the Chemical activation. The choice of activation method solely depends upon the material used which
can have either a low or high-density carbon [13] After pretreatment the samples are placed in a high-temperature
kiln for carbonization by electric heating ,During carbonization, heating rate of 10 C/min and held for 2 hours [16]
Five activation temperatures 600, 700, 800, 900, and 1000C [14] After carbonization, the samples were cooled to
room temperature under N2 flow (100cm3/min).[16] carbon is oxidized usually with the help of carbon dioxide or
steam at 800-1000 oC or and with low-temperature air flow, carbonization of primary raw material is followed by
the oxidation process [13].
2.2.1.1 Coconut shell, activated charcoal, Bamboo charcoal
The rapid development of industrial technologies increased the concentration of greenhouse gases such as VOCs,
CO2, NO2, N2, CH4, HFCs and because of this increasing global warming, raises ocean water levels,[14] Porous
carbon-based materials such as coconut shell, activated charcoal, bamboo charcoal, pecan shell and almond shell
based activated carbon has high thermal and chemical stability as well as good adsorption capabilities for such
harmful gases.
Phosphoric acid activated carbon almond shell having a surface area of 1340 m2/g and absorption of 347ppb.
coal based activated has the surface area 835m2/g and absorption is 476ppb whereas the steam-based activated
pecan shell has a surface of 917m2/g and absorption of 506ppb [7] coconut shell charcoal has least surface area
of about 36.5 m2/g. when chemically activated Coconut shell based activated carbon surface area increases up to
1768.8 m2/g [6] It can absorption is about 516ppb [7] but when modified or synthesis with tio2 nanoparticle
removal/absorption efficiency increase than the unmodified coconut shell based activated carbon [8] the removal
efficiency of the bamboo charcoal and activated carbon is 10% more than coconut shell based activated
carbon[9]
2.2.1.2 Granular activated carbon Fiber of polyparaphenylene terephthalamide and Fibers of
polymetaphenylene isophthalamide
Granular activated carbon is mainly used for the removal of harmful contaminants. It has a specific surface
area of 900 1200(m2/g) depending on the activation [10] In case of activated carbon fiber which may be of
different type of pitch-based activated, cellulose-based, pan-based ACF [17] The specific surface area varies
700-2500(m2/g) due to this the absorption of ACFs is more than that of the granular activated carbon. some
other derived of ACFs such as Nomex and Kevlar which have also specific area more than 1000(m2/g) [11] but
PAN has more surface area about 2400m2/g [17] also the so2 retention capacity of 266mgso2/gc which is more
than the Nomex (165.5 mgso2/g)and kevlar (192.5 mgso2/gc) making the PAN most efficient [11]
2.3 Filter based
Filter means to remove unwanted impurities from air or liquid. Filtration is the process by which the air or
liquid is getting filtered. Filtration can be done by several techniques such as using oxidation, catalysis,
regeneration and reveres reactor process. These techniques are mainly for the removal of impurities such as
VOCS , NO2 ,SO2, etc. filters mainly contain several activated carbons that is mention above such as ACF,
charcoal based activated carbon, granular activated carbon etc.
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Fig 2 Simple process of filtration
3. Different types of filtering technique
Thermal oxidation is one of the techniques used for VOC removal and other contaminants in the air. Generally, the
temperature at which the oxidation takes place is 1300-1800ocF.the temperature also depends on the material used
and the destruction and removal efficiency.
Of higher removal efficiency value required more elevated temperature is required and also longer retention time
within the reactor.
The process mainly proceeds with the inflow of the air which is injected in the filter then it is heated to a certain
temperature. The thermal oxidizer is used for oxidation of the air so the VOC can be removed. Also, the heat is
recovered either in the cyclic process or it is stored in the heat storage system. The removal efficiency of this filter is
about 99% if the temperature lies between 1400o F to 2000o F [3]
Another major technique that is used is the catalysis for oxidation. The catalyst is mainly provided increases the
surface area for reaction and also for the reduction for the activation temperature. The are various process by which
the catalyst is used for the filtration process
The first common step is that the injection of impure air heated to a temperature of about 303 oF. Then its taken to
the heat exchanger for the for the further heating process it then is passed through the catalysis bed which is mainly
a honeycombed shaped which is coated with the catalyst this lead to the catalytic oxidation. another process where
the air is directly sent to the catalysis bed which is honeycombed shape and coated with tio2 then this is subjected to
UV light with help in photocatalysis and removal of harmful contaminant. The other process where the air and the
catalyst are directly injected into the filter where the photocatalysis takes place due to absorption of the light energy
of the catalyst particle where the temperature is also controlled according to the catalyst size. This reaction mainly
takes place in the solid-gas phase where the optimal particle size is about
12mm. The other techniques used is the where the catalyst is in a fluidized bed and there also photo catalysis takes
place at first the air is injected into the reactor where the fluidized base is present it is subjected to UV light for the
photocatalysis for the removal of the contaminant. The fluidized catalyst bed is mainly obtained by the impregnation
of the silica gel with sol-gel which makes the bed more fluidized which improves the removal efficiency [18]. There
are several another catalyst which is also used for the removal such as the Carbon Chem bituminous coal, envirotrol
bituminous coal, envirotrol coconut shell etc are some of the add-on the catalyst that is also used for the removal
contaminants from the air [12].
The removal efficiency of these photo catalysis techniques is about 95%. where the other techniques the efficiency
is about 90%. Another technique that is generally used is the reveres reactor. At first, the VOC leaden air enters the
filter then it is dried and is taken to a pressure regulated chamber then to adiabatically packed bed reactor where the
filtration process takes place. The feed flow direction is periodically changed. The main problem with the reactor is
that heat insulation which needs to be more than the packed bed. So in order to make it insulated it is vacuum
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jacketed. There are several factors that affect the performance of RFR a)cycle period b)gas velocity c)adiabatic
temperature d)different component e)pressure etc. the main advantage of the reactor that no external heat/thermal
energy is required for the reactor to function.
Regeneration is another technique which is also used for the filtration process. This process is carried out by the
release of the N2 gas from the cylinder it gets purified by the gas purifier which contains silica gel and mol. Sieves
which is mainly used for moisture removal a d hydrocarbon. Then it is bubbled through VOC to bottle the gas is
then passed to the chamber containing the shell on one side and activated carbon fiber wrapped Teflon on other side
and a device was used to maintain the bed temperature also gas chromatography with FID was used for the test for
purification. Now this AFC can be can be regenerated completely by electrical heating in the presence of the
nitrogen gas which is the biggest advantage of this filter absorption of VOC or other contaminant doesn’t decree
With the regeneration process [2].
Table 1 Adsorption Efficiency of different activated carbon materials:
Material Adsorption Efficiency
Coconut shell charcoal 51.6%
Bamboo activated carbon 70.9%
Bamboo charcoal 72.3%
Phosphoric acid activated carbon 34.7%
Charcoal based 47.6%
Pecan shell 50.6%
Table 2 Effective size of carbon:
Material SURFACE AREA Table 1
Table 1
Phosphoric acid activated carbon 1340 m2/g
Granular activated carbon 1050 m2/g
Charcoal based 835 m2/g
pecan shell 917 m2/g
activated carbon fiber 1600 m2/g
coconut shell charcoal 36.5 m2/g
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Fig 3 Adsorption efficiency (%)
Fig 4 Effective surface area (m2/g)
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
80.00%
Coconut shell
charcoal
Bamboo
activated carbon
Bamboo charcoal Phosphoric acid
activated carbon
Charcoal based Pecan shell
Adsorption efficiency(%)
Material
0
200
400
600
800
1000
1200
1400
1600
1800
Effective size (m2/g)
Activated carbon materials
coconut shell charcoal
Phosphoric acid activated
carbon
Granular activated carbon
Charcoal based
pecan shell
activated carbon fiber
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CONCLUSION
Different Techniques of Activated Carbon Based Air Filters have been discussed in this study. Adsorption and
commercially available filters using activated carbon are efficient methods of air purification. Based on the study
following observations can be made-
1. Bamboo Based Activated Carbons Have Highest Adsorption Efficiency.
2. Activated Carbon Fibers Have Better Effective Surface Area Than Other Materials.
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