*
1
Abstract
Carbon dioxide (CO2) is the most important greenhouse gas produced by
human activities, primarily through the combustion of fossil fuels; so that
we will discuss the main sources of the carbon dioxide and the amount of
CO2 emitted from these sources such as natural sources, thermal power
plants and refineries. Also to minimize the amount of CO2 and avoid the
negative effects of it we will present methods of capturing CO2 and use it
in petrochemical industries; these methods are:
1. Physical and chemical absorption.
2. Adsorption.
3. Others.
In Our project we will use the recovered carbon dioxide to produce Ethyl
alcohol (Ethanol).
2
Table of contents:
Contents
Abstract
Table of Content
List of Figure
List of Table
Introduction
Properties of Carbon Dioxide
Health Hazards of Carbon Dioxide
Sources of Carbon Dioxide
Capture of Carbon Dioxide
Types of Carbon Dioxide Capture Technology
Absorption
Adsorption
Cryogenic
Membranes
Uses of Carbon Dioxide
Some Reactions of Carbon Dioxide
Greenhouse
Ethyl Alcohol
Ethanol Properties
Types of Ethanol
Uses of Ethanol
Sources of Ethanol
Preparation of Ethanol
Ethanol Production Process
Reaction of Carbon Dioxide with Hydrogen to Produce
Ethanol
Ethanol storage
Advantages and Disadvantages of Ethanol
Ethanol Production from CO2
References
Page
2
3
4
5
6
7
10
11
16
20
21
29
31
32
33
35
40
44
44
49
49
51
51
52
56
58
58
59
64
3
List of Figures:
Figure
Fig.1 Sources of CO2 (2005)
Fig.2 Thermal Power Plant
Fig.3 Typical Breakdown of CO2 Emission in the Oil
Industry
Fig.4 Techniques of CO2 Capture
Fig.5 Post-Combustion Capture
Fig.6 Oxy-Fuel Combustion Capture
Fig.7 Pre-Combustion Capture
Fig.8 CO2 capture technologies
Fig.9 Schematic diagram of the amine separation process
Fig.10 Physical Absorption
Fig.11 Pressure swing adsorption
Fig.12 Temperature swing adsorption
Fig.12as Separation membrane
Fig.13Block Flow Diagram for DME
Fig.14Block Flow Diagram for Propylene
Fig.15Block Flow Diagram for Styrene
Fig.16Greenhouse Effect
Fig.17Global Warming
Fig.18A Ford Taurus "fueled by clean burning ethanol"
owned by New York City.
Fig.19thanol Production Process
Fig.20thanol plant in West Burlington, Iowa
Fig.21Ethanol plant in Sertãozinho, Brazil
Fig.22Block flow diagram for ethanol production
Fig.23 Hysys Flow Sheet for the Production of Ethanol
Fig.24 Hysys Flow Sheet for the Production of Ethanol
Page
12
13
16
17
17
18
19
21
24
26
30
31
33
37
38
39
41
43
50
52
53
54
57
60
62
4
List of Tables:
Table
Table 1 Physical Properties of Carbon Dioxide
Table 2 Amount of CO2 emitted from fuel combustion
Table 3 Amount of CO2 emitted from refineries in Kuwait
Table 4 Amount of CO2 emitted from EQUATE Plant
Table 5 Physical Properties of Ethanol
Table 6 Economic Result for the Hysys simulated Ethanol
Production
Table 7 Economic Result for the Hysys simulated Ethanol
Production
Page
8
14
15
15
45
61
63
5
1. Introduction:
Carbon dioxide is a chemical compound composed of one carbon and two
oxygen atoms with a chemical formula CO2. It is one of two oxides of
carbon which is gas at standard temperature and pressure and present in
the Earth's atmosphere at a low concentration which increases due to the
combustion of fossil fuels (hydrocarbons).
Carbon dioxide content in fresh air varies between 0.03% (300 ppm) and
0.06% (600 ppm), depending on the location. It acts as a greenhouse gas
because it transmits visible lights but absorbs strongly in the infrared. In
its solid state, it is called dry ice. It is a major component of the carbon
cycle.
The carbon dioxide which is present in the atmosphere is produced by
respiration and by combustion. However, it has a short residence time in
this phase as it is both consumed by plants during photosynthesis.
Carbon dioxide was one of the first gases to be described as a substance
distinct from air.
6
2. Properties of Carbon Dioxide:
2.1 Chemical Properties:
Chemical properties of matter describes its "potential" to undergo some
chemical change or reaction by virtue of its composition; What elements,
electrons, and bonding are present to give the potential for chemical
change.
The chemical properties of carbon dioxide that affect life on earth are:
1. Carbon dioxide dissolves very well in water.
2. After carbon dioxide dissolves in water, it rapidly forms a new
compound. This reaction is reversible.
3. The new compound formed from carbon dioxide and water is acidic
(Carbonic acid).
CO2 + H2O ==> H2CO3
4. Molecules of carbon dioxide can absorb heat from solar energy and
trap the heat in the atmosphere.
5. Carbon dioxide gas is very dense and will collect near ground level.
6. Carbon dioxide gas is not flammable and is used to put out fires.
7. Carbon dioxide is a linear covalent molecule.
8. Carbon dioxide reacts with alkalis to give carbonates and bicarbonates.
CO2 + NaOH ==> NaHCO3
Sodium
BiCarbonate
NaHCO3 + NaOH ==> Na2CO3 + H2O
7
Sodium Carbonate
A chemist would represent the first three properties with chemical
equations:
2.2 Physical Properties:
Physical properties can be observed or measured without changing the
composition of matter. Physical properties are used to observe and
describe matter. It includes appearance, texture, color, odor, melting
point, boiling point, density, solubility, polarity, and many others.
Carbon dioxide is a colorless odorless gas, which is soluble in water, in
ethanol and in acetone.
- Melting Point: -55.6 °C.
- Boiling Point: -78.5 °C.
Table (1): Physical Properties of Carbon Dioxide
Property
Value
IUPAC Name
Carbon Dioxide
Molecular Formula
CO2
Appearance
Colorless, Odorless
Molar Mass
44.0095 g/mol
Critical Temperature
31.1 °C
Critical Pressure
72.85 atm
8
Critical Density
468 Kg/ m3
Triple Point
-56.6 °C / 518 KPa abs
Gas Density @ 0°C & 1 atm
1.977 Kg/ m3
Liquid Density @ 0°C & 1 atm
929 Kg/ m3
Solid Density @ 0°C & 1 atm
1562 Kg/ m3
Specific Volume @ 21°C & 1 atm
0.546 m3/Kg
Viscosity @ 25°C & 1 atm
0.015 cp
Solubility of Gas in Water @ 0°C
& 1 atm
1.7 vol/vol
Vapor Pressure of Saturated Liquid
@ 0°C
3485 kPa abs
Latent Heat of Vaporization @ 0°C
234.5 kJ/kg
571.3 kJ/kg
Latent Heat of Fusion @ -56.6°C
(Triple Point)
Latent Heat of Sublimation @78.5°C (Dry Ice)
Specific Heat of Gas @ 25°C & 1
atm
Cp
Cv
Specific Heat of Liquid @ -17
(refrigerated liquid)
199.0 kJ/kg
0.850 kJ/kg°C
0.657 kJ/kg°C
2.048 kJ/kg°C
9
3. Health Hazards of Carbon Dioxide:
Carbon dioxide is dangerous when inhaled in high concentrations and it
causes the following effects on human health:
1. Affects respiratory function.
2. Causes excitation followed by depression of the central nervous
system.
3. High concentrations of CO2 can displace oxygen in the air, resulting in
lower oxygen concentrations for breathing.
4. Contact with liquefied CO2 can cause frostbite.
5. Exposure to very high concentrations of the gas may cause a stinging
sensation.
6. Direct contact with liquefied CO2 may cause freezing of the eye.
Permanent eye damage or blindness could result.
10
4. Sources of Carbon Dioxide:
4.1 Natural Sources:
The primary natural processes that release CO2 into the atmosphere are:
1. Animal and plant respiration, by which oxygen and nutrients are
converted into CO2and energy, and plant photosynthesis by which CO2 is
removed from the atmosphere and stored as carbon in plant biomass.
2. Ocean-atmosphere exchange, in which the oceans absorb and release
CO2 at the sea surface.
3. Volcanic eruptions, which release carbon from rocks deep in the
Earth’s crust (this source is very small).
4.2 Industrial Sources:
The largest source of CO2 emissions globally is the combustion of fossil
fuels such as coal, oil and gas in power plants, automobiles, industrial
facilities and other sources.
The figure below displays a breakdown of sources of CO2 emissions in
the U.S. in 2005. By far the largest source is fossil fuel combustion.
11
Figure (1): Sources of CO2 (2005)
Carbon dioxide is manufactured mainly from six processes:
1. As a byproduct in ammonia and hydrogen plants, where methane is
converted to CO2.
2. From combustion of wood and fossil fuels.
3. As a byproduct of fermentation of sugar in the brewing of beer, whisky
and other alcoholic beverages.
4. From thermal decomposition of limestone, CaCO3, in the manufacture
of lime, CaO.
5. As a byproduct of sodium phosphate manufacture.
12
6. Directly from natural carbon dioxide springs, where it is produced by
the action of acidified water on limestone or dolomite.
4.2.1 Fossil Fuel Combustion:
When fossil fuels are burned to produce energy the carbon stored in them
is emitted almost entirely as CO2. The main fossil fuels burned by
humans are petroleum (oil), natural gas and coal. CO2 is emitted by the
burning of fossil fuels for electricity generation, industrial uses,
transportation, as well as in homes and commercial buildings.
4.2.2 Thermal power plant:
In a thermal power plant, steam is produced and used to spin a turbine
that operates a generator. Shown here is a diagram of a conventional
thermal power plant, which uses coal, oil, or natural gas as fuel to boil
water to produce the steam. The electricity generated at the plant is sent
to consumers through high-voltage power lines.
As a result of fuel combustion (coal, oil, or natural gas) CO2 produced.
Figure (2): Thermal Power Plant
13
In Kuwait there are six thermal power plants they are Shuwaikh station,
Shuaiba station, Doha east station, Doha west station, Al-Zour station and
Sabiya station.
Table (2): Amount of CO2 emitted from fuel combustion.
Station/Fuel
Natural Gas (ton/yr)
Crude or heavy Oil
(ton/yr)
Shwaikh
1185.039
-
Shuaiba
5462.154
-
2250.827
4999927
Doha east
1962.23
8578588
Doha west
4378.936
14632306.5
Al-Zour
490.825
9613916.5
Sobiya
4.2.3 Refineries:
The Kuwait National Petroleum Company is the national oil refining
company of Kuwait. Established in October 1960, KNPC handles the
responsibility of oil refining. There are three refineries:
1. Mina Abdullah refinery: Built in 1958 by the American Independent
Oil Company, Mina Abdullah was passed to the Kuwaiti state in 1975and
transferred to KNPC in 1978. Spanning 7,835,000 m², and located 46km
south of Kuwait City, Mina Abdullah is capable of refining 240,000
Barrels-per-day (BPD).
2. Mina Al-Ahmadi refinery: Initially built in 1949, the refinery was
handed over to KNPC in 1980. Spanning 10,534,000 m², it is located
45km south of Kuwait City with a production rate exceeding 415,000
BPD.
3. Shuaiba Refinery: Built in 1966, Shuaiba Refinery was the first
refinery in the region to be built by a national company. The refinery
14
spans 1,332,000 m² and is located 50km south of Kuwait City within the
Shuaiba Industrial Area. The refinery has a capacity of 195,000 BPD.
Table (3): Amount of CO2 emitted from refineries in Kuwait
Hydrogen plant
Combustion units
(ton/day)
(ton/day)
AL-Ahmadi
2150
11666
Mina Abdullah
2000
6666
Shuaiba
1670
6666
Refinery
4.2.4 Other Industrial Sources:
A variety of other chemical operations have been used to produce carbon
dioxide. For example, the processing of phosphate rocks can release
carbon dioxide.
In Kuwait EQUATE is other source of CO2.
Table (4): Amount of CO2 emitted from EQUATE Plant
Ethylene Glycol Unit (ton/yr)
201480
Fuel Gas Consumption (ton/yr)
419375
Total (ton/yr)
620855
15
Figure (3): Typical Breakdown of CO2 Emission in the Oil Industry
5. Capture of Carbon Dioxide:
The objective of carbon dioxide capture is to produce concentrated stream
of carbon dioxide which can be transported and sequestered underground
or in deep oceans.
To capture carbon dioxide it first separated from the other gases resulting
from combustion or industrial.
There are three main techniques to capture carbon dioxide from the flue
gas of a power plant: post-combustion capture, oxyfuel combustion and
pre-combustion capture.
Post-combustion capture and oxyfuel combustion are technologies that
are well suited for retrofit, while pre-combustion capture is not. This last
technology does not build on a simple combustion of coal or other fuels,
but on the gasification of the fuel. This gasification results in synthetic
gas: a mixture of carbon monoxide and hydrogen. The carbon monoxide
and water are converted to hydrogen and carbon dioxide through the
water-gas-shift reaction. The capture of carbon dioxide takes in this
technology place before the hydrogen is combusted in a gas turbine.
16
Figure (4): Techniques of CO2 Capture
5.1. Post-Combustion Capture:
Post-combustion capture is the simplest capture technology in the sense
that it does not affect the power plant combustion process.
In post-combustion, the flue gas produced by combustion of the fuel with
air only contains a small fraction of CO2. It is captured by injecting the
flue gases in a liquid that selectively absorbs the CO2. Nearly pure CO2
can then be released from the liquid, typically by heating it or releasing
the pressure.
Figure (5): Post-Combustion Capture
17
Advantages:
- Applicable to power generation technologies currently in general use.
- Experience > 60 years, bears no risk.
Disadvantages:
- Low concentration of CO2 in a multi component mixture available at
high temperature and low pressure.
5.2. Oxy-Fuel Combustion Capture:
In oxyfuel combustion, the fuel is burned in oxygen instead of air. To
limit the resulting flame temperatures to levels common during
conventional combustion, cooled flue gas is recirculated and injected into
the combustion chamber. The flue gas consists of mainly carbon dioxide
and water vapor, the latter of which is condensed through cooling. The
result is an almost pure carbon dioxide stream that can be transported to
the sequestration site and stored. Power plant processes based on oxyfuel
combustion are sometimes referred to as "zero emission" cycles because
the CO2 stored is not a fraction removed from the flue gas stream but the
flue gas stream it self.
Figure (6): Oxy-Fuel Combustion Capture
18
Advantages:
- Combustors would be fairly conventional.
- May be able to avoid FGD.
-Store the SOx and NO2 along with the CO2.
Disadvantages:
-High cost of oxygen production.
-Need to recycle large quantities of flue gas.
-Not needed for circulating fluidised bed combustors.
-Potential for advanced oxygen separation membranes with lower energy
consumption.
5.3. Pre-Combustion Capture:
The technology for pre-combustion is widely applied in fertilizer,
chemical, gaseous fuel (H2, CH4), and power production, in these cases,
the fossil fuel is partially oxidized, for instance in a gasifier.
In a pre-combustion system, the primary fuel is first converted into gas by
heating it with steam and air or oxygen. This conversion produces a gas
containing mainly hydrogen and CO2, which can be quite easily separated
out. The hydrogen can then be used for energy or heat production.
Figure (7): Pre-Combustion Capture
19
Advantages:
-Generally higher CO2 concentration than for post-combustion capture.
-Higher pressure.
-More compact equipment.
-Higher driving force for CO2 separation.
Disadvantages:
-Fuel processing is needed.
-Partially oxidation.
-Needed anyway for coal and oil to remove impurities.
-Shift conversion of fuel gas to H2 and CO2.
5.4. Types of carbon dioxide capture technology:
Chemical solvents were developed to remove CO2 from impure natural
gas. In addition several power plants and other industrial plants use the
same or similar solvents to recover CO2 from flue gases for application in
the food processing and chemical industries. Finally, a variety of
alternative methods are used to separate CO2 from gas mixture during the
production of hydrogen for petroleum refining, ammonia production and
in other industries.
The selection of a technology for a given capture application depends on
many factors i.e. partial pressure of CO2 in the gas stream, extent of CO2
recovery required, sensitivity to impurities, such as acid gases,
particulates, purity of desired CO2 product, capital and operating costs of
the process, the cost of additives necessary to overcome fouling and
corrosion where applicable the environmental impacts.
Based upon the method of CO2 removal, capture technologies can be
broadly classified into the following categories:
1. Absorption.
2. Adsorption.
3. Cryogenic.
4. Membranes.
20
Figure (8): CO2 capture technologies
5.4.1. Absorption:
Chemical and physical absorption processes are widely used in the
petroleum, natural gas and chemical industries for separation of CO. The
solvent capacity of an absorbed gas is a function of its partial pressure in
the absorption unit. In physical absorption, the solvent capacity or
loading, which initially follows Henry's law, assumes an almost linear
dependence on the gas partial pressure. In chemical absorption, the
solvent loading assumes a non-linear dependence on partial pressure and
is higher at low partial pressure. At the concentration approaching the
saturation loading of the solvent, chemical absorption decreases sharply.
This behavior is caused by an effect akin to weak physical absorption and
usually arises from gas absorption in the aqueous component of the
solvent used in the process. The primary method of regeneration in
physical absorption occurs by a simple pressure reduction in the system.
21
5.4.1.1. Chemical Absorption:
The majority of chemical solvents are organic amine based.
Stoichiometric manipulation of this group has lead to the development of
sterically hindered amines, which enhances the absorption capacity of the
solvent. Alternative inorganic solvent systems are Na/K carbonates and
aqueous ammonia processes.
Prior to CO2 removal the CO2 containing stream is cooled and particulates
and other impurities are removed as far as possible. It is then passed into
an absorption vassel where it comes into contact with the chemical
solvent, which absorbs must of the CO2 by chemically reacting with it to
form a loosely bound compound. The CO2 rich solvent from the bottom
of the absorber is passed into another vessel (stripper column) where it is
heated with steam to reverse the CO2 absorption reactions. CO2 released
in the stripper is compressed for transport and storage and the CO2 free
solvent is recycled to the absorption vessel. CO2 recovery rates of 98%
can be achieved, and product purity can be in excess of 99%.
5.4.1.1.1. Organic solvents:
- Amines:
Three classes of amines, basically primary, secondary and tertiary, are
generally used as organic chemical solvents. Mono ethanol amines
(MEA) are more reactive than secondary amines and hence dominate the
CO2 capture market.
Amine scrubbing technology has been established for removal of
hydrogen sulphide and CO2 from gas streams. There are several facilities
in which amines are used to capture CO2 from flue gas streams today.
The main concerns with MEA and other amine solvents are corrosion in
the presence of O2 and other impurities, high solvent degradation rates
from reaction with SO2 and NO2 and the large amounts of energy required
for regeneration. As much as 80% of the total energy consumption in an
alkanolamine absorption process occurs during solvent regeneration.
These factors generally contribute to large equipment, high solvent
consumption and large energy losses. New or improved solvents with
22
higher CO2 absorption capacities, faster CO2 absorption rates, high
degradation resistance and low corrosiveness and energy use for
regeneration are needed to reduce equipment sizes and capital and
operating costs.
There are many amine compounds being studied that exhibit this
binding.Menoethanolamine (MEA), diethanolamine (DEA),
diisopropanolamine (DIPA) ,triethanolamine (TEA) , and nmethyldiethanolamine (MDEA) are common carbon dioxide adsorbing
materials that have been extensively studied in previous work. MDEA
and TEA are actually tertiary amines ,but they are not used as commonly
as other compounds. Usually they are used as the base in mixed amine
systems. Mixed amine systems have been used in liquid amine
systems.These mixed amine systems typically consist of a primary or
secondary amine with a tertiary amine. Mixed amine systems are used to
take advantage of properties uniqueto each type of amine used. Tertiary
amines react more slowly with carbon dioxide than the primary or
secondary amine system. These mixtures are useful because the tertiary
amines assist in carbon dioxide binding while regenerating faster during
the desorption process. Primary and secondary amines in the mixture help
increase the reaction rate.
- hindered amines
Sterically hindered amines are amines in which a bulky alkyl group is
attached on the amino group. As a consequence the reactivity is different
from the alkalanolamines. Sterically hindered amines currently used in
absorption processes are 2-amino-2-methyl-1-propanol (AMP).
The advantage of sterically hindered amines over alkanol amines is that
only 1 mole of the sterically hindered amine, instead of 2 mole of alkanol
amine, is required to react with 1 mole of CO2 . Thermal degradation
occurs at temperatures higher than 478 K. Sterically hindered amine
systems can have lower heats of absorption/ regeneration as compared
with MEA. This makes these types of amines potential candidates for
CO2 removal in power generation systems.
23
Figure (9): Schematic diagram of the amine separation process.
-Caustic Soda:
Caustic soda, typically sold by Dow as a 50% solution in water, is an
odorless and colorless liquid. Sodium chloride, sodium carbonate, and
sodium sulfate are impurities that can be found in caustic soda.
It is used to react with the CO2 to produce the sodium carbonate. That
will minimize the amount of carbon dioxide.
2NaOH(ag) + CO2(g) → Na2CO3(aq)+ H2O(l)
-Hot potassium Carbonate:
Hot potassium carbonate (HPC) or "Hot Pot" is effectively used in many
ammonia, hydrogen, ethylene oxide and natural gas plants. To improve
CO2 absorption mass transfer and to inhibit corrosion, proprietary
activators and inhibitors are added. These systems are known as
"activated hot potassium carbonate" (AHPC) systems.
K 2 CO3  CO2  H 2 O  2KHCO3
24
- Sodium Carbonate:
Sodium carbonate was used as a sorbent to capture CO 2 from a gaseous
stream of carbon dioxide, nitrogen, and moisture. The breakthrough data
of CO 2 were measured in a fixed bed to observe the reaction kinetics of
CO 2 carbonate reaction. Several models such as the shrinking core
model, the homogeneous model, and the deactivation model in the non
catalytic heterogeneous reaction systems were used to explain the kinetics
of reaction among CO 2 , Na 2 CO 3 , and moisture using analysis of the
experimental breakthrough data. Good agreement of the deactivation
model was obtained with the experimental breakthrough data. The
sorption rate constant and the deactivation rate constant were evaluated
by analysis of the experimental breakthrough data using a nonlinear least
squares technique and described as Arrhenius form.
5.4.1.1.2. Inorganic Solvents:
The non-organic based chemical solvents include potassium, sodium
carbonate and aqueous ammonia. The potassium carbonate process can be
used in various configurations.
-Ammonia:
Most recently ammonia has been tested as a sorbent for CO2. It has been
observed that the maximum CO2 removal efficiency by NH3 absorbent
can reach 99%. On the other hand, the maximum CO2 removal efficiency
and loading capacity by MEA absorbent were 94%.
However, the concerns with this technology include the highly volatile
nature of ammonia. Also this technology lacks in the regeneration of
ammonia from its carbonate salts. Capability of anion-exchange resins to
regenerate ammonia from ammonium bicarbonate as well as the
feasibility for the regeneration of resin by heated water and collection of
CO2 are being tested. Released ammonia will react with the remaining
ammonium bicarbonate to form ammonium carbonate, which results in
the resin's inability to completely regenerate ammonia. A new scrubbing
system has been proposed where CO2 in flue gas, along with the acid gas
pollutants, SO2, NOx, HCl and HF, could be removed in a regenerable
25
scheme. The key advantage to the process is that the thermal energy
consumption for the CO2 regeneration is expected to be significantly less
than the MEA process.
5.4.1.2. Physical Absorption:
The physical solvents are ideally suited for the removal of CO2 from fuel
gases with high vapor pressure. These physical solvents combine less
strongly with CO2. The advantage of such solvents is that CO2 can be
separated from them in the stripper mainly by reducing the pressure,
resulting in much lower energy consumption. Physical solvent scru bbing
of CO2 is well established, e.g. in ammonia production plants. Majority of
physical absorption solvents are based on organic solvents with high
boiling points and low vapor pressures. Other than methanol, most of
these solvents can be used at ambient temperatures without appreciable
vaporization losses, but may require special water washing stages to
mitigate solvent losses.
In general, all physical solvents must have an equilibrium capacity for
absorbing CO2 several times that of water and a lower capacity for
removing other primary constituents of the gas stream. They must have
low viscosity, low or moderate hygroscopicity, and low vapor pressure at
ambient temperature. Key must be non corrosive to common metals as
well as non reactive with all components in the gas stream.
Figure (10): Physical Absorption
26
5.4.1.2.1 Flour process:
This process based on removal of CO2 using flour solvent at high
pressure.
5.4.1.2.2 Purisol process:
This process uses n-methyl-2-pyrrolidone. The solvent removes CO2 and
hydrocarbons.
5.4.1.2.3 Selexol process:
Selexol is the trade name for an acid gas removal solvent that can
separate acid gases such as hydrogen sulfide and carbon dioxide from
feed gas streams such as synthesis gas produced by gasification of coal,
coke, or heavy hydrocarbon oils. By doing so, the feed gas is made more
suitable for combustion and/or further processing.
5.4.1.2.4 Sulfinol processes:
Sulfolane is a clear, colorless liquid commonly used in the chemical
industry as an extractive distillation solvent or reaction solvent.
Sulfolane is widely used as an industrial solvent, especially in the
extraction of aromatic hydrocarbons from hydrocarbon mixtures and to
purify natural gas. The sulfinol process purifies natural gas by removing
H2S, CO2, COS and mercaptans from natural gas with a mixture of
alkanolamine and sulfolane.
27
5.4.1.2.5 Rectisol:
Rectisol is the trade name for an acid gas removal process that uses
methanol as a solvent to separate acid gases such as hydrogen sulfide and
carbon dioxide from valuable feed gas streams. By doing so, the feed gas
is made more suitable for combustion and/or further processing. Rectisol
is used most often to treat synthesis gas (primarily hydrogen and carbon
monoxide) produced by gasification of coal or heavy hydrocarbons, as
the methanol solvent is well able to remove trace contaminants such as
ammonia usually found in these gases.
In the Rectisol process cold methanol at approximately –40 °F (–40 °C)
dissolves (absorbs) the acid gases from the feed gas at relatively high
pressure, usually 400 to 1000 psia The rich solvent containing the acid
gases is then let down in pressure and/or steam stripped to release and
recover the acid gases. The Rectisol process can operate selectively to
recover hydrogen sulfide and carbon dioxide as separate streams, so that
the hydrogen sulfide can be sent to a Claus unit for conversion to
elemental sulfur, while at the same time the carbon dioxide can be
sequestered or used for enhanced oil recovery.
5.4.1.3. Hybrid absorption processes:
Hybrid absorption processes use solvents which offer a combination of
chemical and physical absorption processes. Currently used with coal
syngas for removal of CO2 and sulphur compounds are the shell Sufinol
process and Amisol process developed by Lurgi.
In its original from the shell Sufinol process uses Sufolan (tetra hydro
ehiophene dioxide) as the organic solvent and an amine solvent, DIPA
(di-isopropanolamine) with 15% water shell has also developed M
Sufinol in which the amine solvent is MDEA instead of DIPA.
The Amisol process is based on a mixture of methanol and either MEA or
DEA as the chemical component and a small percentage of water.
Another version which is particularly suited for the removal of large
quantities of CO2 uses MDEA as the chemical solvent component.
28
5.4.2. Adsorption:
The intermolecular forces between gases such as CO2 and the surface of
certain solid materials permit separation by adsorption. Selective
adsorption of the gases depends on temperature, partial pressures, surface
forces and adsorbent pore size. The solid adsorbents, such as activated
carbon and molecular sieves are normally arranged as packed beds of
spherical particles. The process operates on a repeated cycle with the
basic steps being adsorption and regeneration. In the adsorption step, gas
is fed to a bed of solids that adsorbs CO2 and allows the other gases to
pass through. When a bed becomes fully loaded with CO2, the feed gas is
switched to another clean adsorption bed and the fully loaded bed is
regenerated to remove the CO2. In pressure swing adsorption (PSA), the
adsorbent is regenerated by reducing pressure. In temperature swing
adsorption (TSA), the adsorbent is regenerated by raising its temperature
and in electric swing adsorption (ESA) regeneration takes place by
passing a low-voltage electric current through the adsorbent.
Both PSA and TSA are commercially available technologies and are used
in commercial H2 production, bulk separation of O2 and in the removal
of CO2 from natural gas.
ESA which is commercially not ready holds promise as a possible
advanced CO2 separation technology that uses less energy than other
processes.
Adsorption is not yet considered attractive for large-scale separation of
CO2 from flue gas because the capacity and CO2 selectivity of available
adsorbents is low. However, it may be successful in combination with
another capture technology. Adsorbents that can operate at higher
temperatures in the presence of steam with increased capacity and
improved selectivity are needed.
5.4.2.1 Pressure swing adsorption:
Pressure Swing Adsorption (PSA) is a technology used to separate some
gas species from a mixture of gases under pressure according to the
species' molecular characteristics and affinity for an adsorbent material. It
operates at near-ambient temperatures and so differs from cryogenic
distillation techniques of gas separation. Special adsorptive materials are
29
used as a molecular sieve, preferentially adsorbing the target gas species
at high pressure. The process then swings to low pressure to desorb the
adsorbent material.
One of the primary applications of PSA is in the removal of carbon
dioxide (CO2) as the final step in the large-scale commercial synthesis of
hydrogen (H2) for use in oil refineries and in the production of ammonia
(NH3). Another application of PSA is the separation of carbon dioxide
from biogas to increase the methane (CH4) content. Through PSA the
biogas can be upgraded to a quality similar to natural gas.
Figure (11): Pressure swing adsorption
30
5.4.2.2Temperature swing adsorption:
Temperature swing adsorption to remove CO2 from a gas stream is
conducted using alumina to adsorb all the water and at least most of the
carbon dioxide from the gas stream. Optionally a downstream zone of
zeolite may be provided to remove further carbon dioxide and
hydrocarbons.
Figure (12): Temperature swing adsorption
5.4.3. Cryogenic:
Cryogenic separation is widely used commercially for purification of
CO2 from streams that already have high CO2 concentrations (typically >
50%). It is not normally used for dilute CO2 streams such as flue gas
from coal/natural gas fired boilers as the amount of energy required for
refrigeration is uneconomic for the plant. Cryogenic separation has the
advantage that it enables direct production of liquid CO2, which is
needed for economic transport, such as transport by ship or pipeline. The
most promising applications for cryogenics are expected to be for
separation of CO2 from high pressure gases, such as in pre-combustion
capture processes, or oxyfuel combustion in which the input gas contains
a high concentration.
31
5.4.4. Membranes:
A membrane is a barrier film that allows selective and specific
permeation under conditions appropriate to its function. With regards to
CO2 capture, two types of membranes systems are considered.
5.4.4.1. Gas separation membranes:
Gas separation membranes rely on differences in physical or chemical
interactions between gases and a membrane material, causing one
component to pass through the membrane faster than another. Various
types of gas separation membranes are currently available, including
ceramic, polymeric and a combination of two hybrid. The separation of
the gases rely on solubility or diffusivity of the gas molecules in the
membrane differences in the partial pressure from one side of the
membrane to other acts as driving force for gas separation .
5.4.4.2. Gas absorption membranes:
Gas absorption membranes are micro-porous solid membranes that are
used as contacting devices between gas flow and liquid flow. The CO2
diffuses through the membrane and is removed by the absorption liquid,
which selectivity removes certain components from a gas stream on the
other side of the membrane.
Several membranes with different characteristics may be required to
separate high-purity CO2. Membranes could be used to separate CO2 at
various locations in power generation processes, for example from fuel
gas in IGCC or during combustion in a gas turbine. However membranes
have not been optimized for the large volume of gas separation that is
required for CO2 capture. Membranes cannot usually achieve high
degrees of separation, so multiple stages and/or recycle of one of the
streams is necessary. This leads to increased complexity, energy
consumption and costs. Much development is required before membranes
could be used on a large scale for capture of CO2 in power stations.
32
Figure (12): Gas Separation membrane
6. Uses of Carbon Dioxide:
Large quantities of solid carbon dioxide are used in processes requiring
large scale refrigeration. Carbon dioxide is also used in fire extinguishers
as a desirable alternative to water for most fires. It is a constituent of
medical gases as it promotes exhalation. It is also used in carbonated soft
drinks and soda water.
Carbon dioxide is used by the food industry, the oil industry, and the
chemical industry. It is used in many consumer products that require
pressurized gas because it is inexpensive and nonflammable, and because
it undergoes a phase transition from gas to liquid at room temperature.
Carbon dioxide is the most commonly used compressed gas for
pneumatic systems in portable pressure tools and combat robots. It is used
as a welding gas primarily because it is much less expensive than more
inert gases such as argon or helium. Liquid carbon dioxide is a good
solvent for many organic compounds, and is used to remove caffeine
from coffee. Carbon dioxide can also be combined with limonene oxide
from orange peels to create polymers and plastics. Carbon dioxide is used
in enhanced oil recovery where it is injected into or adjacent to producing
oil wells. In the chemical industry, carbon dioxide is used for the
production of urea, carbonates and bicarbonates, Liquid and solid carbon
dioxide are important refrigerants, especially in the food industry, where
they are employed during the transportation and storage of ice cream and
33
other frozen foods. Solid carbon dioxide is called "dry ice" and is used for
small shipments where refrigeration equipment is not practical.
6.1. Multi-Industry Uses for Carbon Dioxide (CO2):
Carbon dioxide in solid and in liquid form is used for refrigeration and
cooling. It is used as an inert gas in chemical processes, in the storage of
carbon powder and in fire extinguishers.
6.2. Chemicals, Pharmaceuticals and Petroleum Industry Uses:
Large quantities are used as a raw material in the chemical process
industry, especially for methanol and urea production. Carbon dioxide is
used in oil wells for oil extraction and maintain pressure within a
formation.
6.3. Food and Beverages Uses for Carbon Dioxide:
Liquid or solid carbon dioxide is used for quick freezing, surface
freezing, chilling and refrigeration in the transport of foods. Liquid
carbon dioxide is used to de-caffeinate coffee. It is used as an inert
“blanket”, as a product-dispensing propellant and an extraction agent. It
can also be used to displace air during canning. Supercritical CO2
extraction coupled with a fractional separation technique is used by
producers of flavors and fragrances to separate and purify volatile flavor
and fragrances concentrates.
34
7. Some reaction of CO2:
Hydrogenation
Methanol
CO2  3H 2  CH 3OH  H 2
Ethanol
2CO2  6H 2  C2 H 5OH  3H 2O
Dimethyl Ether
CO2  H 2  CH 3  O  CH3
Hydrocarbon
Methanen
CO2  4H 2  CH4  2H 2O
Synthesis
Ethylene
2CO2  6H 2  C2 H 4  4H 2O
Carboxylic Acid
Formic acid
CO2  H 2  HC  O  OH
Synthesis
Acetic acid
CO2  CH 4  CH 3  C  O  OH
Graphite
Synthesis
CO2  H 2  C  H 2O
CH4  C  H 2
CO2  4H 2  CH4  2H 2O
CO2  2 H 2O  CH 3OH  O2
Hydrolysis and
Photocatalytic
Other Reaction
CO2  H 2O  HC  O  OH  1 O2
2
CO2  2 H 2O  CH 4  2O2
CO2  eythylbenzene  styrene
CO2  C3 H 8  C3 H 6  H 2O  CO
CO2  3H 2  CH 3OH  H 2
35
7.1. Methanol:
CO2  3H 2  CH 3OH  H 2
Methanol has been proposed as a fuel for internal combustion and other
engines, mainly in combination with gasoline. Methanol fuel has received
less attention than ethanol fuel as an alternative to hydrocarbon fuel. Both
methanol and ethanol burn at lower temperatures than gasoline, and both
are less volatile, making engine starting in cold weather difficult. Using
methanol as a fuel in spark ignition engines it can offer an increased
thermal efficiency and increased power output compared with gasoline
due to its high octane rating and high heat of vaporisation. Methanol is
extremely poisonous. Since methanol vapour is heavier than air, it will
linger close to the ground or in a pit unless there is good ventilation, and
if the concentration of methanol is above 6.7% in air it can be lit by a
spark, and will explode above 54 F / 12 C.
7.2. Dimethyl ether:
CO2  H 2  CH 3  O  CH3
Dimethyl ether, also known as methoxymethane, oxybismethane, methyl
ether, wood ether, and DME, is a colorless gaseous ether with an ethereal
odor. Dimethyl ether gas is water soluble. It has the formula CH3OCH3 or
as its empirical formula C2H6O. Dimethyl ether is used as an aerosol
spray propellant, and is used in conjunction with propane to give a
thermic expansion that lowers temperature to -60°C. This property is
useful in cryogenic freezing of common warts found on the human body.
Dimethyl ether is also a clean-burning alternative to liquified petroleum
gas, liquified natural gas, diesel and gasoline. It can be made from natural
gas, coal, or biomass.
DME is used as:




A refrigerant
A (co-)blowing agent for foam
A propellant for aerosol products
A solvent
36




An extraction agent
A chemical reaction medium
A fuel for welding cutting and brazing
A multi-purpose fuel
Figure (13): Block Flow Diagram for DME
7.3. Methane:
CO2  4H 2  CH4  2H 2O
Methane is a chemical compound with a chemical formula CH4. It is the
simplest alkane, and the principal component of natural gas.
Methane is the major component of natural gas, it is a colorless, odorless
gas. Methane is important for electric generation by burning it as a fuel
in a gas turbine or steam biler. Methane is used in industrial chemical
processes and may be transported as a refrigerated liquid.
37
7.4. Ethylene:
2CO2  6H 2  C2 H 4  4H 2O
Ethylene (or IUPAC name ethene) is the chemical compound with the
formula C2H4. It is the simplest alkene . Because it contains a double
bond, ethylene is called an unsaturated hydrocarbon or an olefin.
Ethylene is produced in the petrochemical industry by steam cracking.
7.5. Propylene:
CO2  C3 H 8  CO  C3 H 6  H 2O
Propene, also known as propylene, is an organic compound having the
chemical formula C3H6 It is the second simplest member of the alkene
class of hydrocarbons At room temperature and pressure, propene is a
gas. It is colorless with an odor similar to garlic and highly flammable.
Figure (14): Block Flow Diagram for Propylene
38
7.6. Styrene:
CO2  eythylbenzene  styrene
Styrene, also known as vinyl benzene as well as many other names is an
organic compound with the chemical formula C6H5CH=CH2. Under
normal conditions, this aromatic hydrocarbon is an oily liquid. It
evaporates easily and has a sweet smell.
It's used in rubber, plastic, insulation, fiberglass, pipes, automobile parts,
food containers, and carpet backing.
Figure (15): Block Flow Diagram for Styrene
39
7.7. Formic acid:
CO2  H 2  HC  O  OH
Formic acid (systematically called methanoic acid) is the simplest
carboxylic acid. Its formula is HCOOH or CH2O2. It is an important
intermediate in chemical synthesis and occurs naturally, most famously in
the venom of bee and ant stings.
Formic acid is miscible with water and most polar organic solvents, and
somewhat soluble in hydrocarbons. The principal use of formic acid is as
a preservative and antibacterial agent in livestock feed. The principal
danger from formic acid is from skin or eye contact with liquid formic
acid or with the concentrated vapors.
7.8. Acetic acid:
CO2  CH 4  CH 3  C  O  OH
Acetic acid, also known as ethanoic acid, is an organic chemical
compound best recognized for giving vinegar its sour taste and pungent
smell. Its structural formula is represented as CH3COOH. Acetic acid is
one of the simplest carboxylic acids. It is an important chemical reagent
and industrial chemical that is used in the production of polyethylene
terephthalate mainly used in soft drink bottles.
8. Greenhouse Gases:
Many chemical compounds present in Earth's atmosphere behave as
'greenhouse gases'. These are gases which allow direct sunlight to reach
the Earth's surface unimpeded. As the shortwave energy heats the surface,
longer-wave (infrared) energy (heat) is reradiated to the atmosphere.
Greenhouse gases absorb this energy, thereby allowing less heat to escape
back to space, and 'trapping' it in the lower atmosphere. Many greenhouse
40
gases occur naturally in the atmosphere, such as carbon dioxide, methane,
water vapor, and nitrous oxide, while others are synthetic. Those that are
man- made include the the chlorofluorocarbons (CFCs),
hydrofluorocarbons (HFCs) and Perfluorocarbons (PFCs), as well as
sulfur hexafluoride (SF6). Atmospheric concentrations of both the natural
and man-made gases have been rising over the last few centuries due to
the industrial revolution. As the global population has increased and our
reliance on fossil fuels (such as coal, oil and natural gas) has been firmly
solidified, so emissions of these gases have risen. While gases such as
carbon dioxide occur naturally in the atmosphere, through our
interference with the carbon cycle (through burning forest lands, or
mining and burning coal), we artificially move carbon from solid storage
to its gaseous state, thereby increasing atmospheric concentrations.
8.1. Greenhouse Effect:
The troposphere is the lower part of the atmosphere, of about 10-15
kilometres thick. Within the troposphere there are gasses called
greenhouse gasses. When sunlight reaches the earth, some of it is
converted to heat. Greenhouse gasses absorb some of the heat and trap it
near the earth's surface, so that the earth is warmed up, this process
commonly known as the greenhouse effect.
Figure (16): Greenhouse Effect
41
A schematic representation of the exchanges of energy between outer
space, the Earth's atmosphere, and the Earth surface. The ability of the
atmosphere to capture and recycle energy emitted by the Earth surface is
the defining characteristic of the greenhouse effect. The greenhouse effect
means that the climate is affected by the concentrations of greenhouse
gasses on earth.
42
Figure (17): Global Warming
43
9. Ethyl alcohol:
Ethanol (ethyl alcohol, grain alcohol) is a clear, colorless liquid with a
characteristic, agreeable odor. In dilute aqueous solution, it has a
somewhat sweet flavor, but in more concentrated solutions it has a
burning taste. Ethanol, CH3CH2OH, is an alcohol, a group of chemical
compounds whose molecules contain a hydroxyl group, OH, bonded to a
carbon atom. The word alcohol derives from Arabic al-kuhul, which
denotes a fine powder of antimony used as an eye makeup. Alcohol
originally referred to any fine powder, but medieval alchemists later
applied the term to the refined products of distillation, and this led to the
current usage.
Ethanol was first prepared synthetically in 1826, through the independent
efforts of Henry Hennel in Great Britain and S.G. Sérullas in France.
Michael Faraday prepared ethanol by the acid-catalyzed hydration of
ethylene in 1828, in a process similar to that used for industrial ethanol
synthesis today. all the ethanol used industrially is a mixture of 95%
ethanol and 5% water, which is known simply as 95% alcohol. Although
pure ethyl alcohol (known as absolute alcohol) is available, it is much
more expensive and is used only when definitely required.
Ethanol fuel is ethanol (ethyl alcohol), the same type of alcohol found in
alcoholic beverages. It can be used as a fuel, mainly as a biofuel
alternative to gasoline, and is widely used in cars in Brazil. Because it is
easy to manufacture and process, and can be made from very common
materials, such as sugar cane, it is steadily becoming a promising
alternative to gasoline throughout much of the world.
9.1. Ethanol Properties:
Ethanol is a monohydric primary alcohol. It melts at -117.3°C and boils
at 78.5°C. It is miscible (i.e., mixes without separation) with water in all
proportions and is separated from water only with difficulty; ethanol that
is completely free of water is called absolute ethanol. Ethanol forms a
constant-boiling mixture, or azeotrope, with water that contains 95%
ethanol and 5% water and that boils at 78.15°C; since the boiling point of
this binary azeotrope is below that of pure ethanol, absolute ethanol
cannot be obtained by simple distillation. However, if benzene is added to
95% ethanol, a ternary azeotrope of benzene, ethanol, and water, with
boiling point 64.9°C, can form; since the proportion of water to ethanol in
this azeotrope is greater than that in 95% ethanol, the water can be
44
removed from 95% ethanol by adding benzene and distilling off this
azeotrope. Because small amounts of benzene may remain, absolute
ethanol prepared by this process is poisonous.
9.1.1. Physical properties:
Chemical structure of ethanol
The properties of ethanol stem primarily from the presence of its
hydroxyl group and the shortness of its carbon chain. Ethanol's hydroxyl
group is able to participate in hydrogen bonding, rendering it more
viscous and less volatile than less polar organic compounds of similar
molecular weight. Ethanol, like most short-chain alcohols, is flammable,
has a strong odor, volatile and a colorless liquid with a pleasant smell. It
is completely miscible with water and organic solvents and is very
hydroscopic.
Table (5): Physical Properties of Ethanol
Property
Value
IUPAC Name
Ethanol
Other Name
Ethyl Alcohol
Molecular Formula
C2H5OH
45
Appearance
colorless clear liquid
Molar Mass
46.06844 g/mol
Density (Liquid)
0.789 g/cm³
Melting Point
−114.3 °C
Boiling Point
78.4 °C
Solubility in water
Fully miscible
Viscosity
1.200 cp @ 20 °C
9.1.2. Chemical Properties:
9.1.2.1. Combustion of Ethanol
Ethanol burns with a pale blue, non luminous flame to form carbon
dioxide and steam.
C2H5OH + 3O2 ==>
Ethanol
2CO2 + 3H2O
9.1.2.2. Oxidation of Ethanol
Ethanol is oxidised
- with acidified Potassium Dichromate, K2Cr2O7, or
- with acidified Sodium Dichromate, Na2Cr2O7, or
- with acidified potassium permanganate, KMnO4,
to form ethanal, (i.e. acetaldehyde).
46
[O]
C2H5OH ==> CH3CHO + H2O
Ethanol
Ethanal
9.1.2.3. Chlorination
When exposed to chlorine, ethanol is both oxidized and its alpha carbon
chlorinated to form the compound, chloral.
4Cl2 + C2H5OH → CCl3CHO + 5HCl
9.1.2.4. Dehydration of Ethanol
When ethanol is mixed with concentrated sulphuric acid with the acid in
excess and heated to 170 degC, ethylene is formed. (One mole of ethanol
loses one mole of water)
H2SO4
C2H5OH
170 degC
==>
C2H4 + H2O
When ethanol is mixed with concentrated sulphuric acid with the alcohol
in excess and heated to 140 degC, diethyl ether distils over (two moles of
ethanol loses one mole of water) .
2 C2H5OH
==>
H2SO4
C2H5OC2H5 + H2O
140deg
9.1.2.5. Reaction of Ethanol with Sodium
Sodium reacts with ethanol at room temp to liberate hydrogen. The
hydrogen atom of the hydroxyl group is replaced by a sodium atom,
forming sodium ethoxide.
C2H5OH + Na ==> C2H5ONa + H2
47
9.1.2.6. Dehydrogenation of Ethanol
Ethanol can also be oxidised to ethanal (i.e. acetaldehyde) by passing its
vapour over copper heated to 300 degC. Two atoms of hydrogen are
eliminated from each molecule to form hydrogen gas and hence this
process is termed dehydrogenation.
C2H5OH
==>
CH3CHO + H2
Ethanol
Ethanal
9.1.2.7. Halogenation
Ethanol reacts with hydrogen halides to produce ethyl halides such as
ethyl chloride and ethyl bromide:
CH3CH2OH + HCl → CH3CH2Cl + H2O
HCl reaction requires a catalyst such as zinc chloride. Hydrogen chloride
in the presence of their respective zinc chloride is known as Lucas
reagent.
CH3CH2OH + HBr → CH3CH2Br + H2O
9.1.2.8. Ester formation
Under acid-catalyzed conditions, ethanol reacts with carboxylic acids to
produce ethyl esters and water:
RCOOH + HOCH2CH3 → RCOOCH2CH3 + H2O
48
9.2. Types of ethanol:
9.2.1. Denatured alcohol
Pure ethanol and alcoholic beverages are heavily taxed. Ethanol has many
applications that do not involve human consumption. To relieve the tax
burden on these applications, most jurisdictions waive the tax when
agents have been added to the ethanol to render it unfit for human
consumption. These include bittering agents such as denatonium
benzoate, as well as toxins such as methanol, naphtha, and pyridine.
9.2.2. Absolute ethanol
Absolute or anhydrous alcohol generally refers to purified ethanol,
containing no more than one percent water. Absolute alcohol not intended
for human consumption often contains trace amounts of toxic benzene
(used to remove water by azeotropic distillation). Generally this kind of
ethanol is used as solvents for lab and industrial settings where water will
disrupt a desired reaction.
9.3. Uses of Ethanol:
Ethanol is used extensively as a solvent in the manufacture of varnishes
and perfumes; as a preservative for biological specimens; in the
preparation of essences and flavorings; in many medicines and drugs; as a
disinfectant and in tinctures; and as a fuel and gasoline additive. Many
U.S. automobiles manufactured since 1998 have been equipped to enable
them to run on gasoline, a mixture of 85% ethanol and 15% gasoline.
however, is not yet widely available. Denatured, or industrial, alcohol is
ethanol to which poisonous or nauseating substances have been added to
prevent its use as a beverage; a beverage tax is not charged on such
alcohol, so its cost is quite low. Medically, ethanol is a soporific, i.e.,
sleep-producing; although it is less toxic than the other alcohols, death
usually occurs if the concentration of ethanol in the bloodstream exceeds
about 5%. Behavioral changes, impairment of vision, or unconsciousness
occur at lower concentrations.
49
Ethanol is used:
- In the manufacture of alcoholic drinks.
- As a widely used solvent for paint, varnish and drugs.
- In the manufacture of ethanal, (i.e. acetaldehyde), and ethanoic acid,
(i.e. acetic acid).
- As a fuel (e.g. in Gasahol).
- As the fluid in thermometers.
- In preserving biological specimens.
Other uses


Ethanol is easily miscible in water and is a good solvent. Ethanol is
less polar than water and used in perfumes, paints and tinctures.
Ethanol is also used in design and sketch art markers.
Use as fuel :
The largest single use of ethanol is as a motor fuel and fuel additive. The
largest national fuel ethanol industries exist in Brazil.
Figure (18) : A Ford Taurus "fueled by clean burning ethanol" owned by
New York City.
50
9.4. Sources of Ethanol:
Ethanol can be made from products other than corn. Corn is the
predominant feed stock today because of chronic corn surpluses, low
prices and wide availability. Other grains, plus sugar beets, potato wastes
and cheese whey are currently being used where they are available and
competitively priced. It is also possible to convert cellulose materials to
ethanol. Cellulosic materials include grasses, trees, crop residues,
wastepaper and even municipal solid waste. Cellulose to ethanol is
currently too expensive to compete with corn as a feed stock but new
technologies might make it a commercial reality within the next decade.
Newly developed enzymes are being researched that will convert
cellulose to sugars which can then be fermented into ethanol This would
mean not only having a greater supply of clean burning, renewable
ethanol but would also reduce the volume of waste entering our landfills.
9.5. Preparation
Ethanol can be prepared by the fermentation of sugar (e.g., from
molasses), which requires an enzyme catalyst that is present in yeast; or it
can be prepared by the fermentation of starch (e.g., from corn, rice, rye,
or potatoes), which requires, in addition to the yeast enzyme, an enzyme
present in an extract of malt. The concentration of ethanol obtained by
fermentation is limited to about 10% since at higher concentrations
ethanol inhibits the catalytic effect of the yeast enzyme. For non-beverage
uses ethanol is more commonly prepared by passing ethylene gas at high
pressure into concentrated sulfuric or phosphoric acid to form the
corresponding ester; the acid-ester mixture is diluted with water and
heated, forming ethanol by hydrolysis, and the alcohol is then removed
from the mixture by distillation, usually with steam.
51
9.6. Ethanol Production Process:
Figure (19) : Ethanol Production Process
Ethanol is commercially produced in one of two ways, using either the
wet mill or dry mill process. Wet milling involves separating the grain
kernel into its component parts (germ, fiber, protein, and starch) prior to
fermentation.
Ethanol is produced both as a petrochemical, through the hydration of
ethylene, and biologically, by fermenting sugars with yeast. Which
process is more economical is dependent upon the prevailing prices of
petroleum and of grain feed stocks.
52
9.6.1. Ethylene hydration
Ethanol for use as industrial feedstock is most often made from
petrochemical feed stocks, typically by the acid-catalyzed hydration of
ethylene, represented by the chemical equation
C2H4(g) + H2O(g) → CH3CH2OH(l)
The catalyst is most commonly phosphoric acid, adsorbed onto a porous
support such as diatomaceous earth or charcoal.
9.6.2. Fermentation
Ethanol for use in alcoholic beverages, and the vast majority of ethanol
for use as fuel, is produced by fermentation. When certain species of
yeast, most importantly, metabolize sugar in the absence of oxygen, they
produce ethanol and carbon dioxide. The chemical equation below
summarizes the conversion:
C6H12O6 → 2 CH3CH2OH + 2 CO2
Ethanol has been made since ancient times by the fermentation of sugars.
All beverage ethanol and more than half of industrial ethanol is still made
by this process. Simple sugars are the raw material. An enzyme from
yeast, changes the simple sugars into ethanol and carbon dioxide.
9.6.3. Cellulosic ethanol
Sugars for ethanol fermentation can be obtained from cellulose.
9.6.4. Distillation
Figure (20) : Ethanol plant in West Burlington, Iowa
53
Figure (21) : Ethanol plant in Sertãozinho, Brazil.
For the ethanol to be usable as a fuel, water must be removed. Most of the
water is removed by distillation, but the purity is limited to 95-96% due
to the formation of a low-boiling water-ethanol azeotrope. The 95.6%
m/m (96.5% v/v) ethanol, 4.4% m/m (3.5% v/v) water mixture may be
used as a fuel alone, but unlike anhydrous ethanol, is immiscible in
gasoline, so the water fraction is typically removed in further treatment in
order to burn with in combination with gasoline in gasoline engines.
How ethanol is currently produced from corn?
Ethanol is produced primarily from starch in corn kernels. Ethanol
production from corn grain involves one of two different processes: Wet
milling or dry milling. In wet milling, the corn is soaked in water or dilute
acid to separate the grain into its component parts (e.g., starch, protein,
germ, oil, kernel fibers) before converting the starch to sugars that are
then fermented to ethanol. In dry milling, the kernels are ground into a
fine powder and processed without fractionating the grain into its
component parts. Most ethanol comes from dry milling. Key steps in the
dry mill ethanol-production process include:
1. Milling. Corn kernels are ground into a fine powder called "meal."
2. Liquefying and Heating the Cornmeal. Liquid is added to the
meal to produce a mash, and the temperature is increased to get the
starch into a liquid solution and remove bacteria present in the
mash.
3. Enzyme Hydrolysis. Enzymes are added to break down the long
carbohydrate chains making up starch into short chains of glucose
(a simple 6-carbon sugar) and eventually to individual glucose
molecules.
4. Yeast Fermentation. The hydrolyzed mash is transferred to a
fermentation tank where microbes (yeast) are added to convert
glucose to ethanol and carbon dioxide (CO2). Large quantities of
CO2 generated during fermentation are collected with a CO2
54
scrubber, compressed, and marketed to other industries (e.g.,
carbonating beverages, making dry ice).
5. Distillation. The broth or "beer" produced in the fermentation step
is a dilute ethanol solution containing solids from the mash and
yeast cells. The beer is pumped through many columns in the
distillation chamber to remove ethanol from the solids and water.
After distillation, the ethanol is about 96% pure. The solids are
pumped out of the bottom of the tank and processed into proteinrich co products used in livestock feed.
6. Dehydration. The small amount of water in the distilled ethanol is
removed using molecular sieves. A molecular sieve contains a
series of small beads that absorb all remaining water. Ethanol
molecules are too large to enter the sieve, so the dehydration step
produces pure ethanol . Prior to shipping the ethanol to gasoline
distribution hubs for blending, a small amount of gasoline (~5%) is
added to denature the ethanol making it undrinkable.
How is ethanol produced from cellulosic biomass?
Conversion of cellulosic biomass to ethanol is less productive and more
expensive than the conversion of corn grain to ethanol. More efficient
processing is needed to take advantage of this plentiful and renewable
resource. The structural complexity of cellulosic biomass is what makes
this an illustrated description of key steps in the conversion process.
1. Mechanical Preprocessing. Dirt and debris are removed from
incoming biomass (e.g., bales of corn stover, wheat straw, or
grasses), which is shred into small particles.
2. Pretreatment. Heat, pressure, or acid treatments are applied to
release cellulose, hemicellulose, and lignin and to make cellulose
more accessible to enzymatic breakdown (hydrolysis).
Hemicellulose is hydrolyzed into a soluble mix of 5- and 6-carbon
sugars. A small portion of cellulose may be converted to glucose. If
acid treatments are used, toxic by-products are neutralized by the
addition of lime. Since cellulose biomass can come from many
different sources (e.g., grasses, wheat straw, corn stover, paper
products, hardwood, softwood), a single pretreatment process
suitable for all forms of biomass does not exist.
3. Solid-Liquid Separation. The liquefied syrup of hemicellulose
sugars is separated from the solid fibers containing crystalline
cellulose and lignin.
55
4. Fermentation of Hemicellulosic Sugars. Through a series of
biochemical reactions, bacteria convert xylose and other
hemicellulose sugars to ethanol.
5. Enzyme Production. Some of the biomass solids are used to
produce cellulase enzymes that break down crystalline cellulose.
The enzymes are harvested from cultured microbes. Purchasing
enzymes from a commercial supplier would eliminate this step.
6. Cellulose Hydrolysis. The fiber residues containing cellulose and
lignin are transferred to a fermentation tank where cellulase
enzymes are applied. A cocktail of different cellulases work
together to attack crystalline cellulose, pull cellulose chains away
from the crystal, and ultimately break each cellulose chain into
individual glucose molecules.
7. Fermentation of Cellulosic Sugars (Glucose). Yeast or other
microorganisms consume glucose and generate ethanol and carbon
dioxide as products of the glucose fermentation pathway.
8. Distillation. Dilute ethanol broth produced during the fermentation
of hemicellulosic and cellulosic sugars is distilled to remove water
and concentrate the ethanol. Solid residues containing lignin and
microbial cells can be burned to produce heat or used to generate
electricity consumed by the ethanol-production process.
Alternately, the solids could be converted to coproducts (e.g.,
animal feed, nutrients for crops).
9. Dehydration. The last remaining water is removed from the distilled
ethanol.
9.7. Reaction of Carbon dioxide with Hydrogen to produce Ethanol:
As a result of fuel combustion CO2 and H2O is produced, this outputs
inter the separator, where CO2 will separate from H2O. CO2 will react
with hydrogen in the reactor to produce ethanol and water according to
the following reaction:
2CO2  6H 2  C2 H 5OH  3H 2O
The products will be separated in the separator , the water can be re-used
in many industrial processes , and ethanol will recycle to iner the fuel
stream .
56
57
9.8. Ethanol storage:
Before ethanol is sent to storage tanks, a small amount of denaturant is
added , making it unfit to human consumption. Most ethanol plants
storage tnaks are sized to allow storage of 7-10 days production capacity.
9.9. Advantages and Disadvantages of Ethanol :
9.9.1 Advantages of Ethanol
1- Reduces CO emissions.
2- Ethanol reduces greenhouse gas (CO2) emissions.
3- Adding ethanol dilutes the concentration of aromatics in gasoline –
reducing emissions of some air toxics such as benzene .
9.9.2 Disadvantages of Ethanol
1- Lower fuel economy (2-5% for a 10% blend, ~20-30% for E85)
2- At 2-10 vol%, ethanol increases gasoline Reid Vapor Pressure by 1 psi
.
3- Leads to greater evaporative emissions.
4- Increases the permeation of fuel hydrocarbons through the fuel storage
and delivery systems of motor vehicles – contributing to the inventory
of atmospheric ozone precursors.
5- EtOH increases emissions of some air toxics.
6- In some areas, the use of 10% EtOH blends may actually increase
ozone due to the local atmospheric conditions.
58
9.10. Ethanol Production from CO2 :
Two potentially new processes for the production of ethanol were
selected and simulated by HYSYS. The results of these simulations are
given below. Ethanol and water form a minimum boiling azeotrope at a
temperature of 351K, where the mixture contains 89 mol% ethanol.
Starting with a mixture containing a lower proportion of ethanol, it is not
possible to obtain a product richer in ethanol than 89%. The mixture
could be separated with azeotropic distillation, where benzene is added to
form a ternary azeotrope. Using HYSYS flow sheet, it was observed that
the separation of ethanol and water mixture beyond 90 mol% ethanol is
energy intensive. Such a process requires high capital investment to meet
the energy demands. Based on the value added economic analysis, a
profit could not be obtained if ethanol was produced with purity greater
than 90 mol%. Thus, the ethanol produced in these simulations was 90
mol% pure.
9.10.1 Ethanol from CO2 Hydrogenation over Cu-Zn-Fe-K catalyst
The experimental study by Inui, for the production of ethanol by CO2
hydrogenation over a Cu-Zn-Fe-K catalyst was simulated using HYSYS.
The HYSYS flow sheet for this process is shown in Figure. The
conversion of CO2 per single pass was 21.2% . The unreacted CO2 and
H2 were recycled, as shown in Figure. Thus, a total conversion of CO2
was obtained. The following reaction occurs in this study.
2CO2 + 6H2 → C2H5OH + 3H2O ΔHº = -173 kJ/mol, ΔGº = -65 kJ/mol
The ethanol production capacity of the simulated plant was selected to be
104,700 metric tons per year (11, 950 kg/hr). This production capacity
was based on Shepherd Oil, and the production capacity of this plant is 36
million gallons of ethanol per year (107,500 metric tons/year). The
ethanol produced in this process was 88% pure.
Using HYSYS flow sheet, the energy required for this process was 276 x
106 kJ/hr. The HP steam required to supply this energy was 166 x 103
kg/hr, as shown in Table. The energy liberated from this process was 373
x 106 kJ/hr, and the cooling water required to absorb this heat was 446 x
104 kg/hr. Using the HYSYS flow sheet, the amount of CO2 that can be
utilized in this process was estimated to be 215,640 metric tons per year.
59
Figure (23) : Hysys flow sheet for the production of ethanol
The economic model for this process gave a profit of 31.6 cents per kg
ethanol. The value added economic model was based on a selling price of
67 cents per kg of ethanol. The economic data used in this evaluation is
listed in the Table .
60
Table(6) : Economic Results for the HYSYS Simulated Ethanol
Production
9.10.2 Ethanol from CO2 Hydrogenation over K/Cu-Zn-Fe-Cr oxide
catalyst:
The experimental study described by Higuchi, for the production of
ethanol by CO2 hydrogenation over a K/Cu-Zn-Fe-Cr oxide catalyst was
simulated using HYSYS. The conversion of CO2 per pass was 35% . As
shown in Figure, the unreacted CO2 and H2 were recycled, and a total
conversion of CO2 was obtained. The HYSYS flow sheet for this study
is shown in Figure. The following reaction occurs in the reactor.
2CO2 + 6H2 → C2H5OH + 3H2O ΔHº = -173 kJ/mol, ΔGº = -65 kJ/mol
The ethanol production capacity of the simulated plant was selected to be
103,700 metric tons of ethanol per year (11,830 kg/hr). This production
capacity was based on Shepherd Oil, and the production capacity of this
plant is 36 million gallons of ethanol per year (107,500 metric tons/year).
The ethanol produced in this process was 88% pure.
Using HYSYS flow sheet, the energy required for this potentially new
process was 259 x 106 kJ/hr. The HP steam required to supply this energy
was 156 x 103 kg/hr. The energy liberated from this process was 352 x
106 kJ/hr. The cooling water required to absorb this heat was 421 x 104
kg/hr, as shown in the Table . Using HYSYS flow sheet, the amount of
CO2 that can be consumed by this process was estimated to be 205,640
metric tons per year.
61
A value added economic analysis was evaluated, and the model gave a
profit of 33.1 cents per kg ethanol. This profit was based on a selling
price of 67 cents per kg of ethanol, as shown in Table. The data used for
this economic evaluation is listed in Table.
Figure (24) : Hysys flow sheet for the production of ethanol
62
Table(7): Economic Results for the HYSYS Simulated Ethanol
Production Process
9.10.3 Comparison of Ethanol Processes
The two processes simulated for ethanol production were similar to each
other, and only one process was selected to integrate into the chemical
complex. The value added economic model for the experimental study
described by Inui, gave a profit of 31.6 cents per kg of ethanol. The
economic model for the study described by Higuchi, gave a profit of 33.1
cents per kg of ethanol. The best process based on the value added
economic profit was selected. Thus, the potentially new process described
by Higuchi, was included in the chemical complex.
63
References :
- http://en.wikipedia.org/wiki/carbon_dioxide
- Martin M. Halmann Ph. D., "Chemical fixation of carbon dioxide methods for
recycling CO2 in to useful products".
-http://www.epa.gov/chemfact/styre-sd.txt
-www.cetc.nrcan.gc.ca
-www.ieagreen.org.uk
-http://www.infoplease.com/ce6/sci/A0817769.html
-http://www.lenntech.com
-http://genomicsgtl.energy.gov/biofuels/ethanolproduction.shtml#corn
http://www.ccohs.ca/oshanswers/chemicals/chem_profiles/carbon_dioxid
e/health_cd.html
-http://www.uigi.com/carbondioxide.html
-http://en.wikipedia.org/wiki/global_warming
-Joshuah K. Stolaroff, “Capturing CO2 from ambient air: a feasibility
assessment “, Carnegie Mellon University Pittsburgh, PA, 2006.
-Whorf, T.P., Keeling, CD (2005). "Atmospheric CO2 records from sites in the SIO air
sampling network.. Period of record: 1958-2004.
-Pierantozzi, Ronald (2001). "Carbon Dioxide". Kirk-Othmer Encyclopedia of Chemical
Technology. Wiley.
-Austell, J Michael (2005). "CO2 for Enhanced Oil Recovery Needs - Enhanced Fiscal
Incentives". Exploration & Production: The Oil & Gas Review -. Retrieved on 2007-09-28.
-http://www. Ethanol Sources Not Just Corn Alone - - SEARCH - Flash Player
Installation.htm
-Jotaro Itoh, (Chemical & Physical Absorption of CO2”, January 14.2005.
64
-New York Times, Biofuels Deemed a Greenhouse Threat Biofuels Deemed a
Greenhouse Threat by Rosenthal, Feb. 8, 2008
-http://www.ethanol.org/ Ethanol Can Contribute to Energy and Environmental Goals
-http://www.icminc.com/ethanol/
-Climate Change: Basic Information. United States Environmental Protection Agency (200612-14). Retrieved on 2007-02-09. “In common usage, 'global warming' often refers to the
warming that can occur as a result of increased emissions of greenhouse gases from human
activities.”
65