1.

Definition
A carbon dioxide scrubber is a device which absorbs carbon dioxide (CO2). It is used to treat
exhaust gases from industrial plants or from exhaust air in life support systems such as
rebreathers or in spacecrafts, submersible crafts or airtight chambers. Carbon dioxide scrubbers
are also used in controlled atmosphere (CA) storage. They have also been researched for carbon
capture.

Carbon dioxide

Carbon dioxide (chemical formula CO2) is a colorless and odorless gas that is vital to life on
earth. This naturally occurring chemical compound is made up of a carbon atom covalently
double bounded to two oxygen atoms. Carbon dioxide exists in earth’s atmosphere as a trace at a
concentration of about 0.04 percent (400 ppm) by volume. Natural sources include volcanoes,
hot springs and geysers, and it is freed from carbonate rocks by dissolution in water and acids.
Because carbon dioxide is soluble in water, it occurs naturally in groundwater, rivers and lakes,
in ice caps and glaciers and also in seawater. It is present in deposits of petroleum and natural
gas.

Carbon dioxide (CO2) is produced by all aerobic organism when they metabolize carbohydrate
and lipids to produce energy by respiration. Carbon dioxide is produced during the processes of
decay of organic materials and the fermentation of sugars in bread, beer and winemaking. It is
produced by combustion of wood and other organic materials and fossil fuels such as coal, peat,
petroleum and natural gas.

When a fossil fuel is burned, carbon dioxide – CO2 for short – is inevitably produced as well. This is

as true of coal as it is of natural gas and mineral oil. CO2 is a natural component in the atmosphere.
Humans and animals emit it every time they exhale. Carbon dioxide, just like water vapour, shares
the responsibility for the natural greenhouse-gas effect and brings Earth its moderate temperatures.
The CO2 ensures that some of the solar radiation does not escape back into space immediately, but

remains in the atmosphere to warm the Earth‘s surface. Plants and sea algae need CO2 to survive:
they absorb it and, as a waste product, return the oxygen on which

1
humans and animals, in their turn, depend. One thing is clear: CO2 is indispensable for life on
Earth. But that does not mean that humans can release as much as they like into the atmosphere.
So, if we are not to unduly inflate the natural greenhouse-gas effect and the observed rise in
global temperatures, it makes sense to curb man-made carbon dioxide emissions. Besides
industry, traffic and private households, we find that the energy sector, as operator of coal- and
gas-fired power plants, accounts for a large share of CO2 emissions. So it is especially duty-

bound to lower its CO2 emissions perceptibly.

Applications of Carbon dioxide:-

Carbon dioxide is used by the food industry, the oil industry, and the chemical industry. The
compound has varied commercial uses but one of its greatest use as a chemical is in the
production of carbonated beverages; it provide the sparkles in carbonated beverages such as soda
water.

Despite of many applications of Carbon dioxide (CO2) makes up the largest share of greenhouse
gases. The addition of man-made greenhouse gases to the Atmosphere disturbs the earth’s
radiative balance. This is leading to an increase in the earth’s surface temperature and to related
effects on climate, sea level rise and world agriculture.

What is Carbon Emission

Carbon emission is the release of carbon into the atmosphere and this is the main contributors to
climate change. Since greenhouse gas emission are often carbon dioxide equivalents, they are
often referred calculated as carbon dioxide equivalents, they are often referred to as “carbon
emission”. Since the industrial revolution the burning of fossil fuels has increased, which directly
correlates to the increase of carbon dioxide levels in our atmosphere and thus the rapid increase
of global warning.

Effects of carbon emission:-

 Sea level rise - densely settled coastal plains would become uninhabitable with just a
small rise in sea level, which would result from melting of the ice caps


  Impacts on agriculture - Global warming could have major effects on agricultural
productivity

 Reduction of the ozone layer - Warming would result in increase high cloud cover in
winter, giving chemical reactions a platform in the atmosphere, which could result in
depletion of the ozone layer

 Increased extreme weather - A warmer climate could change the weather systems of
the earth, meaning there would be more droughts and floods, and more frequent and
stronger storms

 Spread of diseases - Diseases would be able to spread to areas which were previously
too cold for them to survive in

 Ecosystem change - As with the diseases, the range of plants and animals would change,
with the net effect of most organisms moving towards the North and South Poles

As we can see, the effects of carbon dioxide emissions could be extremely far reaching and cause
major problems. Even a small reduction in household emissions could help to alleviate the
problems future generations are likely to face.

What is Scrubbers

Scrubber systems are a diverse group of air pollution control devices that can be used to remove
some particulates and/or gases from industrial exhaust streams. The first air scrubber was
designed to remove carbon dioxide from the air of an early submarine, a role for which they
continue to be used till today .Traditionally, the term "scrubber" has referred to pollution control
devices that use liquid to wash unwanted pollutants from a gas stream. Recently, the term has
also been used to describe systems that inject a dry reagent or slurry into a dirty exhaust stream
to "wash out" acid gases. Scrubbers are one of the primary devices that control gaseous
emissions, especially acid gases. Scrubbers can also be used for heat recovery from hot gases by
flue-gas condensation. They are also used for the high flows in solar, PV, or LED processes.

There are several methods to remove toxic or corrosive compounds from exhaust gas and
neutralize it.

 Combustion

3
  Wet scrubbing

 Dry scrubbing

 Absorber

 Mercury removal

 Scrubber waste products

 Bacteria spread

4
 2. Introduction

The economic stakes in dealing with climate change are big and costs could escalate
dramatically, if the transition to a zero emission economy would have to happen fast.
Abandoning existing infrastructure is prohibitively expensive and as long as new technology is
not yet ready to be phased in, improvements and additions to the existing infrastructure will tend
to perpetuate the problem. For this reason alone it is important to consider the possibility of
capturing carbon dioxide directly from the air, which need to be developed further

Figure 1 shows fossil fuel burning is the largest source of CO2 in the atmosphere.

5
Perhaps one day we will be able to scrub out CO2 just about anywhere. However at present, CO2
scrubbing is feasible primarily at stationary carbon dioxide sources like fossil fuel-burning power
plants. Don’t think that target area seems limited, though, think again. Fossil fuel combustion is
the single largest source of CO2 in the atmosphere; Power plants alone emit more than one-third

of total CO2 emissions worldwide. Only the most stubborn person would dispute the fact that
fossil fuels aren’t going away soon. Because despite the two-pronged push to reduce energy
consumption and switch to alternative sources of energy, people aren’t that inclined to change
their ways. And although we now have the knowledge to built cleaner, more efficient plants, the
newer plants won’t be able to replace the existing plants. Research indicates that by 2030, two-
thirds of CO2 emissions will come from existing plants.

Approaches to mitigate global climate change:-

Different approaches are considered and adopted by various countries to reduce their CO2
emissions including –

 Improve energy efficiency


 Promote energy conservation

 Increase usage of low carbon fuels including natural gas

  Deploy renewable energy such as solar, wind, hydro power and bio energy
 CO2 capture and storage

6
 3. Carbon dioxide scrubbers

It is the equipment which includes the process of removing carbon dioxide from entering the
atmosphere and storing it. Most of the technologies focus on removing the gas where it is
developed in high quantities, for example in the exhaust gases produced by coal power stations.

Carbon dioxide is found in the air everywhere though; so why just concentrate on where the gas
is emitted in higher quantities?

For the existence of human, aquatic, plants and animals CO2 plays an ambient role so our main
aim is to focus on higher quantities of carbon dioxide; so that doesn’t leads to greenhouse
effects.

It is possible to scrub CO2 from the air anywhere; the technology has been around for decades
and used on Submarines and Spacecraft, to name but a couple of examples. So the potential is
there to research and built on this technology, scaling it up so it can be positioned to effectively
scrub the air in any location.

Why Carbon dioxide scrubbers

Since the beginning of the industrial revolution, we are burning roughly 551 billion tons of
carbon. Regardless of what country we live in, the electricity powering our home is most likely
coming from a power plant. To produce energy, most power plants burn coal (or another fossil
fuel) in air to create stream. The stream turns a turbine, which generates electricity. Apart from
stream, various flue gases are also created and released into the atmosphere. Many of those
extraneous emissions are greenhouse gases that contribute to the greenhouse effect. As we
already know coke is a solidified form of carbon and CO2 scrubbing is a particular form of
carbon capture that takes place after fossil fuel has been combusted, but before the exhaust is
released into the air. It is one of the easiest way to reduce carbon dioxide emission since it
doesn’t require any lifestyle changes. No solar panels to set up or wind farms to connect to; no
guilt trips about accidentally leaving the lights on all day. Simply keep on burning that midnight
oil and let the scrubber handle the rest.

7
The figure 2 is the evidence that the air is becoming more polluted with greenhouse gases.

Using processes like CO2 scrubbing, it could also be possible in future to avoid an additional 90% or

so of CO2 emissions in coal-fired power generation. This method, referred to by specialists as PCC
(post-combustion capture), is downstream of a power plant‘s combustion process. So, the process
starts with CO2 capture before the flue gas – cleaned of dust, nitrogen oxides and sulphur dioxide –
reaches the atmosphere via a power station‘s cooling towers or stacks. The advantages of such a low-
CO2 power plant technology are obvious: the modern coal-fired power stations being built today can

be retrofitted with such a CO2-capture system, because it does not interfere with a power plant‘s
actual combustion process. Even in a possible failure of

8
the CO2-scrubbing system, electricity can still go on being produced reliably, i.e. the availability
of the power plant is guaranteed at all times. This being so, all new coal-fired power stations are
in principle being built “capture-ready“, i.e. they can be retrofitted with CO2-scrubbing systems.
Imported fossil fuels are becoming scarcer and more expensive – because their geological
deposits will be running out in the foreseeable future, and because they are used at times as
instruments of power in economic and foreign policy.

Challenges of CO2 Scrubbing:-

As with many relatively new technologies, CO2 Scrubbing faces its share of challenges.
Obstacles depend on the particular process used to remove carbon dioxide and may include

 degradation of the solvent by other flue gases,


 corrosion of membranes,

 increased energy costs and needs.

At present cost tend to be the most problematic. Some analyses estimate that current capture
technologies cost around $150 per ton of carbon captured, electric bill also gets add up.

How does CO2 scrubbing works

Despite several different designs currently being in development, they all are based on a
common chemical reaction. Air is sucked into the machinery where it is bought into contact with
a sorbent material which chemically binds with the Carbon dioxide. A sorbent material is one
that simply absorbs a gas or liquid (e.g. sponge is sorbent as it absorbs many times its own
weight in water).

The greater the surface area of the sorbent, the more efficiently it will absorb the gas or liquid,
therefore different mechanism have been suggested to maximize exposure of the sorbent to the
Carbon dioxide, thereby maximizing it’s scrubbing ability.

There are 2 approach to deal with Carbon dioxide:-

 First approach has proposed to draw the CO2 through a fine mist of liquid sorbent.
Housing this technology in towers that are several meters high, the mist would react with

9
 the gas and be collected in a chamber where they would once again be separated. The
pure CO2 could be compressed into liquid form and removed, while the sorbent would be
recycled and used again to collect more of the gas.

 Second approach has proposed to maximize the surface area of the sorbent, and this to
apply solid sorbent to thin sheets and allow the Carbon dioxide to react with it. Once the

 initial reaction has taken place, liquid chemicals are wasted over the sheets that create a
stronger bond with the CO2 than the sorbent. The liquid can then be collected (as it now
is bound to the CO2), and this can be heated which will allow the CO2 to be stripped
from the liquid, and so once again the pure CO2 could be compressed into liquid form
and removed, while the liquid can be recycled and used again to wash future CO2 from
the sheets.

The flue gas coming from the power station has a temperature of approx. 65°C after
desulphurization. It first reaches a wet scrubber where it is cooled and freed from any residual
traces of sulphur dioxide (SO2) that might impair CO2 scrubbing. A fan then transports the flue
gas to the absorber, through which it flows bottom-up. This is where it meets the scrubbing
solution, an aqueous solution of amines (a group of organic substances), which is added at the
head of the absorber and, in a counter current flow, takes up the CO2 from the flue gas. The low-
CO2 flue gas is scrubbed with water before leaving the absorber to remove any residues of the
scrubbing agent, and finally reaches the atmosphere by the normal route via the stack or cooling
tower. The scrubbing solution saturated with CO2 is conducted to a so-called desorber and
heated there to approx. 120°C, which strips the CO2 from the liquid and makes it available in a
high purity. The hot scrubbing agent freed from CO2 is cooled and then pumped back to the
absorber, where the scrubbing cycle can start again. The captured CO2 is to be compressed in
future largescale plants for transportation to the storage sites through pipelines for injection into
suitable geological structures, like deep saline formations or depleted natural-gas reserves. In the
chemical industry, CO2 scrubbing is a proven process used to separate carbon dioxide from
natural gas, for example, for use in the beverage or fertilizer sector. The application in CO 2
capture from flue gases is new, and the scrubbing technique must be adapted to the conditions of
a power plant. For instance, the flue-gas streams of a coal-based power station contain three to
five percent oxygen, while the gas streams usual in the chemical industry hold next to no oxygen.

10
What is more, today‘s plant engineering for CO2 scrubbing has higher energy needs than RWE is
aiming at for deployment in power stations. This makes it necessary in a first step to trial the
CO2-scrubbing technique optimized for power-plant conditions in a pilot and to gain experience
in new, improved scrubbing solutions that require less energy for CO2 capture. At the core of a
CO2-scrubbing system is an absorber in which a scrubbing solution takes up the carbon dioxide
from the power plant‘s flue gas at low temperatures. Absorber Heat exchanger Desorber Low-
CO2 flue gas Scrubbing solution Scrubbing solution Scrubbing solution and CO2 Flue gas
Heating steam CO2 CO2 flue-gas scrubbing

11
 4. Scrubber Technologies

Technologies used for Carbon dioxide Scrubbing:-

1. Amine scrubbing :-
The dominant application for CO2 scrubbing is for removal of
CO2 from the exhaust of coal- and gas- fired power plants. Virtually the only technology
being seriously evaluated involves the use of various amines, E.g. monoethanolamine.
Cold solutions of these organic compounds bind CO2 but the binding is reversed at
higher temperatures:

CO2 + 2 HOCH2CH2NH2 ↔ HOCH2CH2NH3+ + HOCH2CH2NH(CO2−)

But this technology has only been lightly implemented because of capital costs of
installing the facility and the operating costs of utilizing it.

2. Minerals and Zeolites:-

Several minerals and mineral-like materials reversibly bind
CO2. Most often, these minerals are oxides, and often the CO2 is bound as carbonate.
Carbon dioxide reacts with quicklime (calcium oxide) to form limestone (calcium
carbonate) in a process called looping.

3. Activated Carbon:-
Activated Carbon can be used as a carbon dioxide scrubber. Air with
high carbon dioxide content, such as air from fruit storage locations, can be blown
through beds of activated carbon and the carbon dioxide will adsorb onto the activated
carbon Once the bed is saturated it must then be “regenerated” by blowing low carbon
dioxide air, such as ambient air, through the bed. This will release the carbon dioxide
from the bed, and it can then be used to scrub again, leaving the net amount of carbon
dioxide in the air the same as when the process was started.

4. Regenerative Carbon dioxide removal system:-

12
 The regenerative carbon dioxide removal
system (RCRS) on the space shuttle orbiter used a two-bed system that provided
continuous removal of carbon dioxide without expendable products. Regenerable systems
allowed a shuttle mission a longer stay in space without having to replenish its sorbent
canisters. Older lithium hydroxide (LiOH) based system, which are non-regenerable were
replaced by regenerable metal-oxide-based systems. A system based on metal oxide
primarily consisted of a metal oxide sorbent canister and a regenerator assembly. It
worked by removing carbon dioxide using a sorbent material and then regenerating the
sorbent material.

5. Metal-organic frameworks (MOFs) :-

Metal-organic frameworks are one of the most
promising new technologies for carbon dioxide capture via adsorption. Although no
large-scale commercial technology exists nowadays, several research studies have
indicated the great potential that MOFs have as a CO2 adsorbent. It’s characteristic, such

as pore structure functions can be easily tuned to improve CO2 selectivity over other
gases.

6. Lithium hydroxide
7. Sodium hydroxide

13
 5. Chemical Engineering and Carbon Dioxide

What Does Chemical Engineering have to do with Carbon dioxide Scrubbing

Although the Scrubber may sound like more of a piece of mechanical engineering equipment, it
is actually a great example of chemical engineering concepts. The scrubber is like one giant
fluids and thermodynamic problem, as pumps suck in air, fluids are heated to change their vapor
pressure and solubility and fluids pass through packed beds. Also, orifices, piotet tubes are used
to measure flow rates, and heat exchangers are used to transfer thermal energy. The reason why
the scrubber is such a simple, and relatively unchanged, piece of equipment is that these simple
engineering concepts are very effective

14
 6. Carbon Dioxide and its Concentration

If cleaning carbon dioxide from the atmosphere was easy, we'd already be doing it. But carbon
capture has proven to be a tough technology to feasibly roll out on a grand scale, and that means
all the things we do that produce carbon dioxide emissions--which seems to be just about
everything these days--are still roughly as bad for the planet as they were several years ago.
That's a problem in a warming world, and one that a team of researchers may have just found a
solution for via an inexpensive polymeric material.
Reporting their findings in the Journal of the American Chemical Society, the team (which
includes a Nobel laureate in chemistry) describes a new solid material based on
polyethylenimine that can be used to capture carbon dioxide at the source--be that an industrial
smokestack or a car's exhaust pipe--under real-world conditions where the air contains moisture.
That last part is important. Previous methods of scrubbing CO2 from the air have enjoyed
varying degrees of success (usually under controlled conditions), but none has been particularly
effective in the presence of humidity. The new material, which is inexpensive and readily
available, has shown some of the highest carbon dioxide removal rates of any material ever
tested in the presence of humidity.
It's also reusable. After capturing carbon, the material also gives it up easily so it can be
sequestered or recycled through the manufacture of other substances. The polyethylenimine
material can then also be reused over and over again to capture more carbon dioxide. Used to
line smokestacks or even out in the open atmosphere, the material could blunt the impact of all of
those things we humans do that are contributing to the carbon glut in the atmosphere.

Carbon Dioxide Required Concentration:-

In normal breathing, the concentration of oxygen in the breathing gas is reduced and the oxygen
is replaced by a nearly equal volume of carbon dioxide. If carbon dioxide is included in the
inhaled gas, the partial pressure of carbon dioxide in the blood increases and the respiratory
centre in the brain increases ventilation rate to restore normal carbon dioxide tension. Excessive
amounts of carbon dioxide in the breathing gas result in toxic effects, the severity of which
depend upon exposure time and the partial pressure of carbon dioxide.

15
Carbon dioxide is produced as oxygen is consumed at the rate of 0.8 to 1.0 litre CO2 per litre of
oxygen consumed. This ratio is called the respiratory quotient (RQ) and can be assumed to be
about 0.85 for purpose of canister design.

16
 7. Material Used
Material used for Carbon dioxide Scrubbers:-
The most natural solution to the CO2 dumping problem is reducing the use of fossil fuels but
practicality is a major issue. Renewable energy and nuclear energy are at rise but according to
international energy outlook 2014, 80% of the world energy through 2040 will be provided by
fossil fuels. By then, it is necessary to mitigate the condition raised by the use of fossil fuel by
reducing the amount of CO2 being dumped in the atmosphere. A conventional method of
absorbing CO2 by CaO is studied by using ASPEN Plus process simulator to understand-steady
state model of air–steam gasification of biomass. The model will analyze the effect of CaO
sorbent for in-situ CO2 capture.
There are many methods adopted for CO2 capturing like using physical adsorbent, catalytic
conversion and capturing CO2 using different solvents like Monoethanol Amine (MEA),
Ammonia, tetrahydrofuran, and tetra-n-butyl ammonium bromide. Among all, the solvent
scrubbing technique is considered to be the most advanced post-combustion capture technology.
Focusing on solvent based CO2 capturing.

MEA is one of the predominant solvents due to its

 commercial availability,

 relatively low cost,

 fast absorption rate and

 rich experience in industrial applications.

However, there are limitations of using MEA solution alone, i.e.

 degradation in the presence of O2


 SOx and

 NOx,

 corrosive nature of MEA

 high regeneration energy requirements
17
 To mitigate such limitations MEA is blended with other solvents like

 Triethanolamine (TEA),

 2-amino-2-methyl-1-propanol (AMP),

 benzylamine (BZA) and

 methyldiethanolamine (MDEA)

There are several advantages of blending these amines: viz.,

 Improved thermodynamic efficiency,


 Reduction in issues relating to degradation and operation of the solvent caused by
corrosion,

 Flexibility in the range of amines available to tailor and optimize the composition of the
solvent to achieve the highest absorption efficiency.

 High absorption rates observed in single amine solvents can often be maintained in
blends of the individual components.

 Energy requirement for solvent regeneration can be reduced

With significant CO2 loading capacity TEA shows great regeneration efficiency. Additionally,
with limited literature available on TEA blended MEA, there is wide scope of investigating the
potential of TEA as a blended amine. Moreover, MEA + TEA blended amines system was
suggested in order to capitalize the performance of TEA (tertiary) and MEA (primary) amines.
The low energy requirement for regeneration and high absorption capacity of tertiary amine
coupled with the fast reaction kinetics of primary amine are an ideal combination for CO2
scrubbing.

The present research was commenced primarily for:

Investigating the potential of TEA as a blend for MEA solution in the scrubbing of CO2 by a
continuous process

 Incorporating Recycle stream of solvent in the continuous scrubbing and observing
equilibrium of the process and

 Evaluating the influence of different parameters on the process with the help analysis.


 8. Experimental Set-up

A column of 1.15 m height and internal diameter of 0.285 m served as the scrubbing column as
given in Fig. The column was supported by the metal structure. An inlet for gas was set at the
bottom of the column through which the gas travels upstream. For better dispersion of gas
throughout the column perforated sprayer was used at the gas inlet. Similar mechanism was
introduced at the top of the column at the liquid inlet for proper distribution of liquid. Raschig
ring made of inert material with length 10 mm and diameter 2 mm was used as random packing
inside the column. The packing used enhanced surface area of mass transfer as well as increased
contact time between gas and liquid. Raschig ring is normally recommended for the liquid-gas
operations. An emergency valve was introduced at the top of the column as a safety precaution.
In case of increased pressure, the gas could be released from the column. A drain valve was
introduced at the bottom of the column for emptying the column after the process and collecting
the sample liquid. CO2sample for analysis could be taken from the gas outlet at the top.

Monoethanolamine (MEA) is corrosive in nature and hence plastic container was used as feed
tank. All the piping and fittings used in the set-up are of Polyvinyl chloride material. Aqueous
solution of amines (MEA or MEA + TEA) was pumped to the top of the column. A by-pass
stream was arranged with the pump to decrease the load on the pump. CO 2 cylinder was used as
a source of CO2 to pump CO2 at 2.5 kg/cm2 pressure from the bottom of the column. A recycle
stream was arranged at the bottom of the column leading to the feed tank. Rotameters of the unit
Litre per minute (Lmin−1) were installed for controlling the liquid and gas flow rates. For gas,
the range of rotameter was 2–20 Lmin−1 and for liquid it was 1–10 Lmin−1. For collecting CO2
samples at regular time interval a stream was set at the top of the column.
Sample of CO2 was collected in the flask containing NaOH for 3 s at regular intervals. The flask
containing NaOH and CO2 was covered with rubber balloon for better contact time without
leakage of any CO2. The absorption cycle was continued till the equilibrium was achieved.
Equilibrium was assumed to have been established when a constant titer value was achieved.
After every operation, the set up was cleansed with water to remove any contaminants and
carbamates produced during the reaction in the column.

19
 9. Absorption parameters

 Absorption efficiency (E):-

The absorption efficiency of the packed column can be
expressed as follows: Ct and C0 are the estimated mass of CO2 at outlet and inlet,
respectively

 Absorption rate (AR):-

The absorption rate was calculated from the inlet–outlet
concentration difference or different positions at the steady-state condition, where G is
the molar flux of gas,

A B =G( y1 − y2 )

 Scrubbing factor (ϕ):-

The scrubbing factor is defined as shown below:

Where,
V is the volume of the scrubber.
Fg and Fl are gas molar flow rate and liquid molar flow rate respectively.
The scrubbing factor can be evaluated when E, V, and y1 are available.

 Pressure drop in a packed bed:-

20
For calculating pressure drop in a packed bed Ergun equation is used. The general form of Ergun
equation is

Where

ΔP – Pressure drop in a packed bed (Pa),

H – Height of the packed bed (m),
μ – Viscosity of the fluid flowing through the packed bed (Pa⋅s), U – Superficial Fluid Velocity (m/s),

ϵ – Bed voidage,
ρ – density of fluid flowing through packed bed (kg/m3),
x – equivalent diameter (m).

CO2 Utilization:-

After capture, the high CO2 content can be transported for CO2 utilization.
CO2 can be used in other areas such as

 food beverages,

  refrigerants and
 fire extinguishing gases. Current CO2 utilization accounts for only 2% of emissions,

 utilized through mineralization 

21
CHAPTER 10

Composition of PEI :

The monomer is easy to describe. It consists of a three-membered ring. Two corners of the
molecule consist of -CH2- linkages. The third corner is a secondary amine group, =NH. In the
presence of a catalyst this monomer is converted into a highly branched polymer with about 25%
primary amine groups, 50% secondary amine groups, and 25% tertiary amine groups. This
product is sometimes called "pure polyethyleneimine" in order to differentiate it from certain
copolymers of ethyleneimine and acrylamide. The latter mixture is copolymerized to produce so-
called "modified PEI," that has a molecular mass up to about 2 million grams per mole. Each of
these types of products is delivered to the mill in the form of viscous solutions. Solids contents
are the range of about 10 to 50%, depending on molecular mass.

Function of PEI :

Pure PEI is very effective for neutralization of excess anionic colloidal charge, especially under
acidic and neutral pH conditions. Modified PEI copolymers having relatively high molecular
mass can be effective for drainage and pitch control.

Synthesis of PEI :

24
CHAPTER 11
Result :
Maximum absorption of CO2
The inlet Carbon dioxide pressure during the operation was maintained at 2.4 atm. The bed
voidage was considered 0.4. The pressure drop for 1.15 m of packed bed was between 0.674 and
1.685 atm depending on the inlet flow rates. This pressure drop observed was due to the presence
of Raschig ring packing randomly packed in the packed bed column. The variation of the
measured CO2 outlet concentration with time for different experimental conditions is shown in

Fig.. As the solvent is recycled in the column, the outlet CO2 concentration initially decreases

(i.e. the ratio of Ct/C0 decreases) with time to reach maximum point (maximum efficiency) and
again starts increasing till no further absorption takes place. From the results it was observed that
the ratio of outlet Carbon dioxide concentration to inlet concentration reaches a constant value of
1 after 35–40 minutes of operation. The absorption efficiency (E), absorption rate (RA) and
scrubbing factor (ϕ) were calculated separately using.

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Analysis of absorption rate (RA)

The absorption rate obtained here was in the range of 0.05–0.18 mol/m2 s. From the two film
models, higher liquid and gas flow rate attenuated the individual mass transfer resistance, and
hence increased the absorption rate

Analysis of scrubbing factor (ϕ)

The scrubbing factor obtained here was within the range of 0.17–0.63 mol-CO2/mol-MEA

Absorption efficiency

The Absorption efficiency obtained in these experiments was in the range of 51.11–92.22%,
depending on the operating conditions.

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CHAPTER 12

Future Development:-
A new method for taking carbon dioxide directly from the air and converting it to oxygen and
nanoscale fibers made of carbon could lead to an inexpensive way to make a valuable building
material.

The fibres in the above microscope image are made of carbon, produced via a new method that
also removes carbon dioxide from the air.

Carbon fibers are increasingly being used as a structural material on the aerospace, automotive,
and other industries, which value its strength and light weight. The useful attributes of carbon
fibers, which also include electrical conductivity, are enhanced at the nanoscale. The problem is
that it’s very expensive to make carbon fibers, much less nanofibers. Carbon fibres are doing
both captures the carbon dioxide from the air and employs an electrochemical process to convert
it to carbon nanofibers and oxygen, is more efficient and potentially a lot cheaper than existing
methods.
But it’s more than just a simpler, less expensive way of making a high-value product. It’s also a
“means of storing and sequestering carbon dioxide in a useful manner, a stable manner, and in a
compact manner,”. If the process is powered by renewable energy, the result is a net removal of
carbon dioxide from the atmosphere. In a recent demonstration, a group used a unique
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concentrated solar power system, which makes use of infrared sunlight as well as visible light to
generate the large amount of heat needed to run the desired reaction.
The process requires molten lithium carbonate, with another compound, lithium oxide, dissolved
in it. The lithium oxide combines with carbon dioxide in the air, forming more lithium carbonate.
When voltage is applied across two electrodes immersed in the molten carbonate, the resulting
reaction produces oxygen, carbon (which deposits on one of the electrodes), and lithium oxide,
which can be used to capture more carbon dioxide and start the process again.

The researchers demonstrated the ability to make a variety of different nanofiber shapes and
diameters by adjusting specific growth conditions, such as the amount of current applied at
specific points of time and the composition of the various ingredients used in the process. They
also showed they could make very uniform fibers.The mechanisms underlying the formation of
the fibers still need to be better understood.

As for the technology’s emissions-cutting potential, the researchers are optimistic. They
calculate that given an area less than 10 percent of the size of the Sahara Desert, the method
could remove enough carbon dioxide to make global atmospheric levels return to preindustrial
levels within 10 years, even if we keep emitting the greenhouse gas at a high rate during that
period.

Of course, this would require a huge increase in demand for carbon nanofibers. The material’s
properties, especially the fact that it is so lightweight and also very strong, will spur greater and
greater use as the cost comes down, and he thinks his new process can help with that. Imagine
that carbon fiber composites eventually replace steel, aluminum, and even concrete as a building
material. “At that point, there could be sufficient use of this that it’s actually acting as a
significant repository of carbon.”

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CHAPTER 13

Conclusion:-

MEA was better for absorption rate, while MEA + TEA (30%) was better for efficiency and
scrubbing factor. The best suitable operating conditions were obtained for the carbon dioxide
absorption in a packed bed column. By incorporating recycle stream, the amount of amine
solution required was reduced. Further the work can be extended for other amine blends of AMP
with MEA and for varied types of packing in the column under the influence of different process
temperatures.

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