CHAPTER -1.
Introduction
There
is an increasing the inclination of chemical industries toward new processes
that should meets requirement such as generation of nearly zero waste
chemicals, less energy, and sufficient uses of product chemicals in various
application. Hence the esterification is widely employed reaction in the
organic process industry. The reaction is carried out between acetic acid and
ethanol at with or without presence of different acid catalyst Under such
specific condition’s. Ethyl acetate was first prepared in 1859 by the French
Chemist; Charles Wurtz It was produced on a small scale during World War I as a
coolant and as an ingredient in explosives. Ethyl acetate is the
most popular ester from ethanol and acetic acid. It is manufactured on a large
scale for use as a solvent. Ethyl acetate is a moderately polar solvent that
has the advantages of being volatile, relatively non-toxic, and non-hygroscopic
.Ethyl Acetate is an organic compound which is also known as, ethyl ethanoate, commonly
abbreviated EtOAc or EA. Ethyl Acetate is primarily produced by direct
esterification of ethyl alcohol (e.g. ethanol) with acetic acid, a process
which involves mixing acetic acid with excess of ethyl alcohol and adding a
small amount of sulphuric acid. This mixture contains about 65% of ester (EA).
Then the EA is separated and purified by distillation in order to achieve
commercial specification. This process considers as exothermic where the heat
of reaction is -0.0114kJ/mole with no danger of Decomposition.
There
are 9 units in the organized sector engaged in making ethyl acetate with the
combined capacity of 5 lakh tons (see Table 1). Laxmi Organics, GNFC, Godavari
Bio Refineries, Jubilant Life Science and IOL Chemicals are the major players
having combined share of 73 percent of the total capacity.
Table 1: Installed Capacity for Ethyl Acetate in
India in Tons per annum
The global ethyl acetate market is
estimated to witness a CAGR of 5.8% during the forecast period. Asia-Pacific is
expected to lead the market in both production as well as consumption during
this period. Increasing investments and strong growth in the end-user
industries, such as food & beverage, paints & coatings, cosmetics,
pharmaceutical, plastics, packaging, etc. in the region is expected to drive
the market.
Figure 1.1--Consumption pattern of EA in word
Global Market Outlook on Ethyl Acetate
The global demand of ethyl acetate is
estimated at 3.7 MMT in 2016, expected to grow at a CAGR of 4.5 percent until
2021.Asia has excess capacity, whereas North America and Europe are dependent
on imports from Asia to cater the domestic Demand .Capacity–demand gap during
2016–2021 is expected to narrow down, as the capacity additions announced may
not cater to the expected increase in demand. Global capacity is 4.7 MMT in
2016 indicating capacity utilisation of 79%.
Figure.1.2-Global Capacity of EA in world
Uses of Ethyl acetate
·
Ethyl acetate is most commonly used as a
solvent (due to its dilution properties).
·
As a high purity solvent, it is used in
cleaning electric circuit boards and as a nail polish remover.
·
At a lower purity, it can be used as
in printing, pharmaceuticals, perfumes, food, decaffeination of tea/coffee and
a carrier solvent for herbicides.
·
Ethyl acetate is also used in coating
formulations for wood furniture, agricultural, construction equipment, mining
equipment and marine uses.
·
It is also naturally produced in
wine during the fermentation process.
·
The
main user end markets of these product are the electronics, cosmetic, printing,
food and coatings industries.
·
Ethyl acetate is an important component in extractants for
the concentration and purification of antibiotics. It is also used as an
intermediate in the manufacture of various drugs.
·
Flavours and essences: Ethyl acetate finds extensive use in
the preparation of synthetic fruit essences, flavours and perfumes.
·
Flexible packaging: Substantial quantities of ethyl acetate
are used in the manufacture of flexible packaging and in the manufacture of
polyester films. It is also used in the treatment of aluminium foils.
·
Miscellaneous: Ethyl acetate is used in the manufacture of
adhesives, cleaning fluids, inks, nail-polish removers and silk, coated papers,
explosives, artificial leather, photographic films & plates.
Figure 2--Consumption pattern of EA in India
CHAPTER No-2
Ester
The first thing that we need to
do is understand what is Ester? Well, to answer that question, according to the
common definition, It is basically a chemical compound that is derived from an
organic or inorganic acid in which at least hydroxyl (-OH) group is replaced by
an alkyl (-O-) group. To put it in simple terms, esters are the group of
chemical compounds which are formed by bonding of an alcohol group with a group
of organic acids, by losing water molecules
Esters are also usually derived
from carboxylic acids. It may also be obtained by
reaction of acid anhydrides or acid halides with alcohols or by
reaction of salts of carboxylic acids with alkyl halides.
Uses of Esters
It is a sweet-smelling substance. Some
of them are used as food flavorings and other esters are used as fragrances or
perfumes. Apart from that, they can be turned into polymers dubbed as
polyesters which can be used to make cans or plastic bottles.
Here are some of the other users of
esters:
- Esters that have
fragrant odours are used as a constituent of perfumes, essential oils,
food flavourings, cosmetics, etc
- It is used as an
organic solvent
- Natural esters are
found in pheromones.
- Naturally
occurring fats and oils are fatty acid esters of glycerol.
- Nitrate esters,
such as nitro-glycerin, are used in explosive materials.
- Polyesters can be
further converted into fibers to make clothing.
- It is used to make
surfactants E.g. soap, detergents
Esterification
Esterification is
a chemical reaction process between alcohol and carboxylic acid in the presence
of catalyst that formed ester. This mixture converts to ester about 65% at room
temperature. The commonly concentrated sulphuric acid is acting as a
esterification catalyst to enhance the reaction. The sulphuric acid removes
water to help shift the equilibrium towards forming more ester product. Water
is a by- product and must be removed in order to get the equilibrium in the
desired direction. This process is a simple process, well known reaction, and
moderately exothermic where the heat or reaction, H is -0.0114kJ/mole with no
danger of decomposition reaction. The optimum temperature for this reaction is
in the range of 363 K – 400 K while the optimum pressure is in the range of 20
bar – 40 bar.
CH3CH2OH + CH3COOH
↔CH3COOCH2CH3 + H2O
Ethanoic Acid +Acetic Acid → Ethyl Acetate + Water
The reaction
between acetic acid and ethanol to produce ethyl acetate in the presence of
concentrated sulphuric acid .This process is released a few amount of heat to
the surrounding and classified as exothermic reaction. This reaction is called
a homogeneous liquid phase. Water is formed in the reaction is removed
continuously to ensure maximum conversion of acetic acid. The catalyst can be
heterogeneous and homogeneous. There are two categories of catalyst that can be
used in this reaction, mineral acid catalyst and para toluene sulphuric acid or
ion exchange resins can serve as heterogeneous catalyst.
1. Esterification (The Selected
Pathway)
2. Tischenko Reaction
3. Addition of Ethylene and Acetic Acid
4. Dehydrogenation of Ethanol
5. Oxidation of Ethanol
1.Esterification
• CH3CH2OH + CH3COOH
↔CH3COOCH2CH3 + H2O
• Reversible reaction
• Remove water by-product to drive reaction to
the right
Table 2.1- Advantages and
Disadvantages of Esterification Process.
Advantages
|
Disadvantages
|
Ease of raw material
availability
|
Ethanol conventional air
pollutant
|
Non-toxic, less harmful raw
materials
|
Water as waste product impeding
reaction eventually
|
Less cost of catalyst
|
Two equivalents of acetaldehydes
Table 2.2.-Advantages and
Disadvantages of Tishchenko Reaction Process.
Advantages
|
Disadvantages
|
• Raw material acetaldehyde is
not costly
|
• Acetaldehyde is a very toxic
substance
|
Table 2.3-Advantages and
Disadvantages of Avada Process.
Advantages
|
Disadvantages
|
• Energy efficient,
environmentally friendly
|
• Ethylene requires special
safety and firefighting facilities
|
4. Oxidation of Ethanol
Table 2.4-Advantages and
Disadvantages of Oxidation of Ethanol.
Advantages
|
Disadvantages
|
• Availability of raw material ethanol
|
• Weak metal support interaction
|
• High risk of explosion requires larger reactor size and
costs
|
5. Dehydrogenation of
Ethanol
• Carried out in four process stages
Table 2.5- Advantages and
Disadvantages of Dehydrogenation of Ethanol.
Advantages
|
Disadvantages
|
Ethanol is easily available
|
Complicated Unit
Operations
|
Acetaldehyde has high toxicity
|
Physical state and appearance: Liquid.
Odour: Ethereal. fruity. (Slight.)
Taste: Bittersweet, wine-like burning taste
Molecular Weight: 88.11 g/mole
Colour: Colourless.
pH (1% soln/water): Not available.
Boiling Point: 77°C (170.6°F)
Melting Point: -83°C (-117.4°F)
Critical Temperature: 250°C (482°F)
Specific Gravity: 0.902 (Water = 1)
Vapour Pressure: 12.4 kPa (@ 20°C)
Vapour Density: 3.04 (Air = 1)
Volatility: Not available.
Odour Threshold: 3.9 ppm
Water/Oil Dist. Coeff. The product is more
soluble in oil; log(oil/water) = 0.7
lonicity (in Water): Not available.
Dispersion Properties: See solubility in
water, diethyl ether, acetone.
Solubility: Soluble in cold water, hot water,
diethyl ether, acetone, alcohol, benzene.
Why
Esterification is Chosen?
• Raw Material
• Safety, Health and Environment
• Utilities
• Simplicity of the Process
• Operating Conditions
• Conversion and Selectivity
• Raw Materials for Tishchenko Reaction
cannot be found in Saudi Arabia
• Technology of dehydrogenation of
ethanol is still developing
• Catalysts used in oxidation of
ethanol are expensive despite the reaction gives highest profit
• Avada process has short reaction rate
and depends highly on the performance of catalysts
• Avoid usage of Acetaldehyde as raw
material as it is toxic and very harmful
Drawbacks
and Improvements of Esterification Reaction
• Heterogeneous catalyst replaces
homogeneous catalyst
• Reactive Distillation is suggested for
Esterification Reaction
• Heuristic studies are conducted to
avoid repeating the same mistakes in the future
Reactive
Distillation
• Shifting chemical equilibrium and
thus results in an increase of conversion of raw material by simultaneous
reaction and separation product.
• Suppression of side reaction and thus
higher purity of desired product can be obtained.
• Utilization of heat of reaction
(esterification is an exothermic reaction) for mass transfer operation.
• These features on the process can
further lead to economic benefits which are shown below:
• Lower capital investment (reactive
distillation combined both the function of reactor and distillation column)
• Lower energy cost (heat generated
from the process in used as the mass transfer purpose)
• Higher product yield (Suppression of
water by-Product )
CHAPTER No-3
Types of Catalyst Used
Manufacture Ethyl acetate is produced by the esterification
reaction of ethyl alcohol and acetic acid using catalysts such as sulphuric
acid, para toluene sulphonic acid or ion exchange resins. Most of the production in India is based on
sulphuric acid catalysis; very little acid is required, though corrosion is a
problem if material of construction is not appropriate. There is small
producers manufacture but the larger ones use continuous columns with a
reboiler for the reaction. The water formed in the reaction (and also from the
95% alcohol used as raw material) is removed continuously. Conditions are such
as to ensure maximum conversion of acetic acid, which is costlier than ethyl
alcohol.
TABLE.3-SPECIFICATIONS OF
ETHYL ACETATE USED IN INDIA
Property
|
Value
|
Clarity
|
Clear, colourless liquid
|
Ester Contents
|
99.0(% by mass, min)
|
Acidity
|
as acetic acid 0.01 (% by mass, Max)
|
Water content
|
0.1 (% by mass, Max)
|
Residue on evaporation
|
0.01(% by mass, Max)
|
Relative density
|
2/27°C 0.894 -0.898
|
Distillation range
Shall distil within the (at 760 mm Hg), not less range of 76-78°C
|
Than 95 % by volume
|
Raw Material:
Ø Ethanol(C2H6)
Ø Acetic
Acid(CH3COOH)
Catalyst Used:-
Ø Para-Toluene
Sulfonic Acid (CH7H8O3S.H2O)
Ø Sulfuric
Acid (H2SO4)
Reaction :-
CH3COOH + C2H5OH ⇔CH3COOC2H5
+ H2O
The
Manufacturing Process is divided into four section.
1. Reaction
Section
2. Crude
Distillation section
3. Main
Distillation Section
4. Recovery
Section
5. Propyl
Distillation Unit
REACTION
SECTION UNIT
Figure 3.1-Reaction section of Ethyl acetate
Process
Description of Reaction Section :- This is the first section for the manufacturing of ethyl
acetate. The raw materials (ethyl alcohol and acetic acid) are first fed to the
CSTR-1 and then to the CSTR-2. Both these reactors are connected in series for
increasing the conversion of ethyl acetate. The conversion in these reactors .generally
achieved by the recirculation pumps connected at the bottom of reactor. The
esterification reaction is carried out in the reactors, the catalyst (sulfuric
acid/ PTSA) is charged in some little quantity to the reactor-1. This catalyst
enhances the rate of production/ conversion of Ethyl acetate. The charging of
catalyst is done by mixing it with some alcohol because PTSA normally found in
powdery solid state. A special type of kettle called Dump Kettle is used in
this section to separate the exhaust catalyst. This is a steam heated system provided with the jacket around the
kettle. The effluent from the CSTR-2 is further send to the crude distillation
unit.
Parameter s :-
CSTR-1:- Temperature = 104-106°C
Pressure = 0.228 -0.248 kg/cm2
CSTR:-2 - Temperature. = 100- 102°C
Pressure= 0.03-0-035 Kg/cm2
Dump Kettle :- Temperature :- 120-125
CRUDE DISTILLATION SECTION UNIT
Figure 3.2-Crude distillation unit of Ethyl acetate
Process Description of Crude
distillation Section :- Here the crude from the
CSTR-2 is further processed, to increase the conversion and purity of ethyl
acetate, in two distillation column's arranged in parallel .The vapours from
both the columns are either sent to the PHE (plate type heat exchanger) or to compa block (special type of Heat
exchangers) where condensation of vapours takes place with the help of
either cooling water or with some other sources for achieving desired cooling
of vapours. The condensate is collected in a receiver and sent to the decanter
where separation based on density difference of different constituent present
is achieved. The top layer of decanter contains 60-63% converted
ethyl acetate which is refluxed to both the column's for
increasing more purity. The bottom layer of Decanter contains water, and some
little amount of alcohol, which is sent to the column-3 Some part of top layer
is sent to the Extractor column and
then to the main distillation section. The bottoms from both the column's is
fed back to the CSTR-I. The bottoms are normally acetic acid
Parameters :
Column 1A :- Top temperature =
75-78
Top Pressure:-0 0.2-0.3
kg/cm2
Bottom temperature =
120-123°C
Bottom pressure =05-0.6kg/cm2
Column 1B :- Top Temperature =
78-80°C
Top Pressure=0:35-0.5 kg /cm2
Bottom temperature=120-122
Bottom Pressure=0.5-0.6kg/cm2
Decanter : Temperature = 118-123
Pressure = 1.75-1.77 kg/cm2
MAIN DISTILLATION SECTION UNIT.
Figure 3.3-Main distillation unit of Ethyl acetate
Process
Description of Main distillation section: - Crude from the top of
decanter is sent for washing in Extractor column where washing is achieved with
Demineralised water. This DM water absorbs the water content present in the
feed and removed from the bottom and sent to the recovery section. The top of
the extractor column is fed to the tray type distillation column (Column-2)
where vacuum distillation is achieved with the help of vacuum pump. The top of
this column is used as a reflux to the extractor column. The side draw is taken
from column-2 and fed to the auxiliary column. Where pungent smell of product
is removed by further treating with distillation column . The bottoms from the
column-2 normally carried propyl acetate which is separately sent to the propyl
column for achieving the separation of ethyl acetate from it. The product from
auxiliary column is taken as a final product(Ethyl-acetate) with the purity of
97-98% of ethyl acetate and 0.002% water content and is stored in the Daily
Storage Tank(DST)
Parameter:-
Column-2:- Top Temperature= 46-48
Top Pressure= 460-470 mm Hg
Bottom Temperature=62-64
Pressure = 260-290mm Hg
Auxiliary Column :- Top Temperature = 58-60
Main Vacuum Supply :-600-620mm Hg
RECOVERY
SECTION UNIT
Figure.3.4-Recovery section of Ethyl acetate
Process
Description of Recovery Section:
The decanter bottom and Extractor bottom (mainly contain water) is fed to the
column-3 where recovery of water generally take place and other chemicals
(without water) are sent to the CSTR-1 for further purification. Column-3
operates under vacuum pressure. The top product of the column-3 goes to the PHE
for condensation and the draw goes to Reactor-1.The bottom products normally
Contains water which is sent to the drain tank with the help of centrifugal
pump. The water from the drain tank is commonly used to generate Vacuum.
Parameter:-
Top Temperature= 71-73
Bottom Temperature=100-103
Middle
Top Temperature=81-83
Middle Bottom Temperature=98-100
PROPYL COLUMN UNIT
Figure 3.5-Propyl Distillation Unit of Ethyl acetate
Process Description of Propyl
Distillation Unit
The bottoms from the column-2 and
bottoms from the auxiliary column normally carries propyl acetate which is
separately sent to the propyl column for achieving the separation of ethyl
acetate from it. The vapour from the top of the column is condensed by plate
type heat exchanger (PHE) which is collected in a receiver. The vapour contains
ethyl acetate. The some part of the condensate is send to the receiver and some
part is reflux to the column. The bottom product of the propyl distillation
unit is re-heated by heat-exchanger to improve the purity of product and
contain propyl acetate in separate storage tank as a by-product.
Parameters affecting the yield and
conversion of ethyl acetate:-
Crude distillation column middle –top
temperature:- The middle- top temperature in both
the column should maintained in between 78-82
. By doing so, conversion as well as yield of ethyl acetate increases because,
at this temperature high boiling point components condense and goes to the
bottom and thus increases the quantity of low boiling point component in the
top product.
Main distillation column vacuum:- The
top vacuum of the main distillation column should be kept at 459-470 mm Hg .
Because at this vacuum, proper cooling and heating requirement are archived.
Increase in vacuum will create the problem on cooling vapour. Better conversion
is achieved at this vacuum
Level and Residence time in the Reactor :- Normally
CSTR should be filled 70-75% of its
total Volume . It can be increased up to ±5% to increase the yield. The residence
time in these reactors can be taken as 6-8 seconds. The conversion can also be
increased by employing the agitator in the reactor along with circulating pump.
Cooling water and Chilled water temperature :- The cooling water temperature must be around
25-28
in summer for the efficient cooling of the vapours
in the heat exchangers. With increase in cooling water temperature, the cooling
problem occurs in the heat exchangers and system starts venting. High capacity
cooling water pump should be used. If proper cooling temperature is maintained,
yield will definitely increase to a great extent.
Quantity of catalyst :- For 150 tone/day production required 90 kg of p-toulene sulfonic
acid as a catalyst to promote the esterification of reaction . The quantity of
catalyst can be increased or decreased
to effect more better conversion and yield of ethyl acetate. Proper
removal of traces of catalyst from drum kettle increased the purity of the
product. The p-toluene sulfonic acid is better than sulfuric acid because it
will promote better conversion of H+ ions
.
CHAPTER No-4
DESIGNING OF DISTILLATION COLUMN
There are two basic approaches used in
distillation column design, namely, design and rating. The former approach
involves the design of a new column to determine the column diameter and height
required to achieve a specified separation. This approach utilizes
stage-to-stage calculations for determining the number of equilibrium stages.
The rating approach involves the retrofit of an existing column in which the
column diameter and height are fixed and the flow capacity and separation are
to be determined. Since the rating approach has convergence advantages, it is
most often used in computer algorithms which do stage-to-stage calculations.
In the design of a new column or rating of an existing one,
many design engineers obtain final designs and price quotes from equipment
vendors. However, to evaluate such vendor responses, a preliminary design
should be made. Accordingly, the procedures involved in the design of a
distillation column are summarized in and briefly outlined with supporting
equations in this section of the chapter.
·
Designation of
Design Bases The first step in the design procedure is to establish the
composition and physical properties of the feed and products, the feed rate,
and any special limitations placed on the separation. The latter could include
maximum temperature and pressure drop restrictions, presence of toxic materials
or reactive components, etc.
·
Selection of
Design Variables The second step involves selecting adequate design
variables. The operating pressure is generally the first variable to be
addressed. An increase in operating pressure is often reflected by an increase
in separation difficulty, an increase in reboiler and condenser temperatures,
an increase in vapour density, and a decrease in the latent heat of
vaporization. As the pressure is lowered, these effects are reversed. The lower
limit is often set by the desire to avoid vacuum operation and use of external
refrigeration for the condenser because of capital and operating cost
penalties. It is usually adequate, if process constraints permit, to fix the
operating pressure at as low a pressure above ambient that permits cooling water
or air cooling to be used in the condenser. In other words, the operating
pressure should be selected so that the bubble point of the overhead product is
at least 5 to 10°C above the summer cooling water temperature , or to
atmospheric pressure if the latter would introduce vacuum operation.
|
Select operating condition
|
|
Obtain or develop equilibrium data
|
|
Calculate equilibrium stage or transfer
units
|
|
Select column internals
|
|
Establish separation basis
s
|
|
Calculate column height
|
|
Calculate column diameter
|
Random Packing Standard Packing
Tray type
|
Calculate column height
|
|
Calculate column diameter
|
|
Calculate column diameter
|
|
Calculate column height
|
Procedure step involve in
the design of a distillation column
Determination of Number of Equilibrium Stages Even though
shortcut and stage-by-stage methods for calculating the number of equilibrium
stages are available in many commercial computer software programs, it is
necessary to understand the fundamentals involved to determine whether the
computer results are realistic. Of the shortcut methods, the
Fenske-Underwood-Gilliland method is the most widely used. To determine the
number of equilibrium stages, first the minimum number of stages and the
minimum reflux must be evaluated. The minimum number of stages N min is obtained from the Fenske
relations
In[(xLK/xHK)p(xHK/XLK)
B]
N min = ------------------------------------------------
In(ά LK/HK) av
Where:- xLk is the mole fraction of the light key
Xux the mole fraction of the
heavy key
(ά LK/HK)av the average geometric
relative volatility of the light key to the heavy key,
while the subscripts D and B refer to the
distillate and bottom products, respectively
·
Selection of Column Internals At this point the
designer must make a selection based on performance and cost whether a tray,
random packing, or structural packing is best for the separation process being
considered. Typically, trays are favored when the operating pressure and liquid
flow rate are high and when the column diameter is large. Random packings are
more often recommended when the column diameter is small, corrosion and foaming
are present, or batch columns are to be used. Structural packings, on the other
hand, are considered for low-pressure and vacuum operation. Additionally, they
are often selected when low pressure drop across the column is required or low
liquid holdup is desired.
·
Sieve, valve, and bubble-cap trays are examples of
traditional crossflow trays. The development of newer trays over the past
decade to provide improved performance has been significant. Descriptions of
some of these newer trays, including the Nye,TM Max-Frac,TM some of the
improved multiple-down-comer trays, such as ECMB and EEMD, as well as the
Ultra-Frac, TM P-K,TM and Trutna trays, are presented by Humphrey and Keller.
·
Figure provides a cross-sectional view of a traditional
distillation column in operation showing an example of a sieve, valve, and
bubble-cap tray. Of these tray types, the sieve tray is the choice in many
distillation separations since its tray fundamentals
.
Figure 4.1-cross-sectional
view of a finite-stage contactor column in operation sieve tray, a valve tray
bubble cap tray
·
Random Packing
Figure 4.2-Various type of Packing
Table.4.1-Geometry and
efficiency of several random packing
Types of packing
|
Void fraction
|
Surface area per volume,m²/m³
|
Approx. HETP,m
|
25-mm Ceramic Raschig rings
|
0.73
|
190
|
0.6-0.12
|
25-mm Ceramic Intalox saddles
|
0.78
|
256
|
0.5-0.9
|
25-mm Ceramic Berl saddles
|
0.69
|
259
|
0.6-0.9
|
25-mm Plastic Pall rings
|
0.90
|
267
|
0.4-0.5
|
25-mm Metal Pall rings
|
0.94
|
207
|
0.25-0.3
|
50-mm Norpac
|
0.94
|
102
|
0.45-0.6
|
50-mm Highflow® rings
|
0.93
|
108
|
0.4-0.6
|
Table.4.2-Geometry
and HETP of several structured packings
Types of packing
|
Void fraction
|
Surface area per volume,m²/m³
|
Approx. HETP,m
|
Intalox 2T
(Norton)
|
0.96
|
213
|
0.2-0.3
|
Flexipac® 1 (Koch)
|
0.91
|
558
|
0.2-0.3
|
Flexipac® 2 (Koch)
|
0.93
|
249
|
0.3-0.4
|
Gempak 4A (Glitsch)
|
0.91
|
525
|
0.2-0.4
|
Gempak 2A (Glitsch)
|
0.93
|
262
|
0.3-0.4
|
·
Diameter Evaluation
for Columns with Sieve Trays
Determination of the column diameter first requires calculation of the net vapour
(gas) velocity at flood conditions Vf in the column from
Vnf=Csb(σ/20)áµ’·²(pL-pV/pv)áµ’·Æ½
The initial procedures for designing a new
distillation column are similar when either a tray column or a packed column is
selected for the separation process. Differences in the design calculations
become apparent when the column diameter and height need to be established.
Accordingly, the following will describe the design procedures associated with
the diameter and height aspects of those columns utilizing random packing.
·
Diameter Evaluation for Columns with Random Packing; In contrast to
distillation columns with trays, performance in packed columns is strongly
affected by both liquid and vapour rates in the column. Not only is flow
limited, but at high throughputs the gas flow impedes the liquid flow, which
can eventually lead to flooding of the column. Thus, packed columns also
operate at a vapour velocity that is 70 to 90 percent of the flooding velocity.
A simplified shortcut method that has been the standard of the industry for
several decades utilizes the generalized pressure drop correlation chart
originally developed by Sherwood and improved by several other investigators.
·
Height Evaluation for Columns with Random
Packing :-
Determination of the height of packing required in a
column to achieve a specific separation involves use of either the height of a
transfer unit (HTU) or the height equivalent to a theoretical plate (HETP)
approach. To obtain the total height using the first approach also requires one
to evaluate the number of transfer units (NTU) to satisfy the relation
Z = (HTU)(NTU)
where Z is the total height of the mass-transfer zone.
HTU and NTU are defined as
HTU =
NTU=
Where
is the molar flow rate of vapour
KG the overall mass-transfer coefficient
ac the area of interfacial contact between the liquid and vapour phase per
unit volume of contactor.
Ac
the cross-sectional area of the column,
y the mole fraction of the component in the
vapour phase
y* the mole fraction of the component in the
vapour phase that would be in equilibrium with that component in the liquid phase.
·
Diameter
Evaluation for Columns with Structured Packing :- A procedure
similar to that used for determining the diameter of a column with random
packing may be used to obtain the column diameter with structured packing. If
is used to obtain the cross-sectional area of the column, the designer will
need to obtain a suitable packing factor from the vendor for the structured
packing selected. Another procedure,
developed by Kister and Gill, involves calculating the pressure drop over a
unit length of the column under flood conditions. A correlation, similar in
format to, is used to determine the flood velocity in columns with structured
packing. The operating velocity in the column is designated as a fraction of
the flood velocity. The cross-sectional area of the column is then obtained by
dividing the volumetric flow rate of the vapour by the operating velocity.
Column diameter is obtained from D =
(4Ac/T)1/2.
·
Height Evaluation for Columns with Structured Packing:- The total height of packing required to achieve a specific
separation again necessitates determination of HTU and HETP. Several options
are available. A rule of thumb for quick estimation of HETP for structured
packing has been presented by Harrison and Frances
HETP
=
+0.10
As noted earlier, rating a distillation column can
entail either examining performance under new operating conditions or
determining whether a retrofit of an existing column with perhaps improved
column internals could prove to be economically attractive For example,
Humphrey and Seibert have shown that in vacuum distillation, the re. placement
of sieve trays with structured packing with its increased capacity is a good
return on the investment. The steps involved in the rating of a distillation column are not unlike those
used in the design of a new distillation column. The first step must carefully
detail the objective of the rating study and provide precise information about
the column including existing internal hardware. Accurate information must also
be available about feed composition, rates, and physical properties.
Equilibrium data must be obtained from experimental or literature sources. If
none are available, such data will have to be developed by using commercially
available software programs.
If the internal configuration of the column is not to
be modified, the next step is to calculate the number of equilibrium stages
required for the new design specifications. However, if the objective is to
increase the capacity or the purity of the product, the internal configuration
will probably have to be changed. For example, improved purity could be
achieved by removing sieve trays and replacing them with commercial structured
packing with smaller spacing’s between packing elements. Calculation of the
equilibrium stages can be initiated once the column modifications have been
finalized.
Next, the designer must establish if the diameter of
the existing column is adequate to handle the new vapour and liquid rates. The
procedures for evaluating the required diameter of the column are similar to
those described for the design of a new column. Likewise, the procedures for
evaluating the required height of the column are similar to those discussed
earlier. If the resulting values of column diameter and height match those for
the existing column, the proposed separation can be achieved. Obviously, if the
required diameter and height are larger than those available for the existing
column, modifications will have to be made either in the separation objectives
or in the column configuration and operation.
Batch
Distillation:- Most distillation processes operate in a continuous
fashion, but there is a growing interest in batch distillation, particularly in
the food, pharmaceutical, and biotechnology industries. The advantage of this
separation process is that the distillation unit can be used repeatedly, after
cleaning, to separate a variety of products. The unit generally is quite simple,
but because concentration are continually changing, the process is more
difficult to control single-stage distillation, like that shown in Fig. it is
assumed that the vapour and liquid are in equilibrium. If L' is the number of
moles of liquid in the column at any given time and dL' is the differential
amount vaporized, a material balance on component i yields L’X; = (L’ - dL) (X; - dx;) + (Yi + dyi)dL’
Neglecting
products of differentials and integrating over the change in L' from the
initial to the final condition and from the initial to the final concentration
of liquid establishes the Rayleigh equation for batch distillation, given as
Figure 5-Simple Distillation
where L and L, are the initial and final moles of
liquid in the column, respectively: xil and Xi2 are the initial and final mole
fractions of component i in the column, respectively: and x, and y, are the mole
fractions of component i in the liquid and vapour, respectively, during the
batch distillation process. If the mixture to be separated is a binary one and
equilibrium data are available, the vapour mole fraction can be expressed in
terms of x; and dij, the relative volatility between components i and j.
CONCLUSION
This project report presents an
overview of recent developments in the production of ethyl acetate, including
the suitable preparation methods and their potential applications in various
fields. We have gone through the study of esterification reaction used for the
production of ethyl-acetate and the possible methods for the proper utilization
of the ester thus formed. We have also studied the other possible reactions by
which it can be manufactured, but as a result it has been concluded that
esterification is the most promising pathway for the effective production of
ethyl acetate. Two commonly used catalysts are used. Para-toluene sulfonic acid
(PTSA) and Sulfuric acid.
According to the
researcher’s by R&D departments, PTSA is the best type of catalyst used for
increasing the reaction rate without much losses. Industrial as well as lab
scale production is discussed but we have mainly focused on its industrial
production. While studying its industrial production process, we have studied
the various mass transfer equipment (such as distillation column, extractors), Heat
transfer equipments (such as shell and tube heat exchangers, Plate heat
exchangers, reboiler), fluid machinery (like centrifugal pump, vacuum pumps,
pneumatic control-valves), Instruments (such as temperature indicators,
pressure transmitters, level recorder) . and the unit for chemical reaction b/w
acid and alcohol in continuous stirred tank reactor (CSTR).
Different kinds of distillation column
are used for its production including vacuum distillation, atmospheric pressure
distillation and steam distillation. The various parameters affecting the yield
and purity of ethyl acetate are discussed in brief in this report such as temperature of
reactors should be maintained between 100
to 105
, crude distillation
main top temperature must be 78
and the cooling water
temperatures should be as low as possible.
A brief study on the designing of
distillation column used for the production of ethyl acetate, have also been studied
which mainly includes the designing of various types of distillation columns
(such as batch column, sieve tray column, packed columns) by using different
designing relations and formula's.
- This project shows the core
application of chemical engineering as it involves the study of subject’s like
heat transfer, mass transfer, chemical reaction engineering, process
instrumentation, fluid mechanics and plant utilities.
1. NIOSH
Pocket Guide to Chemical Hazards. "#0260". National
Institute for Occupational Safety and Health (NIOSH).
3. "Ethyl
acetate". Immediately
Dangerous to Life and Health Concentrations (IDLH). National
Institute for Occupational Safety and Health (NIOSH).
4. Riemenschneider, Wilhelm; Bolt, Hermann
M., "Esters, Organic", Ullmann's
Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a09_565.pub2
5. Dutia,
Pankaj (August 10, 2004). "Ethyl
Acetate: A Techno-Commercial Profile" (PDF). Chemical Weekly: 184. Retrieved 2009-03-21.
6. Misono,
Makoto (2009). "Recent progress in the practical applications of
heteropolyacid and perovskite catalysts: Catalytic technology for the
sustainable society". Catalysis Today. 144 (3–4):
285–291. doi:10.1016/j.cattod.2008.10.054.
9. Mackison,
F. W.; Stricoff, R. S.; Partridge, L. J., Jr., eds. (Jan 1981). NIOSH/OSHA
– Occupational Health Guidelines for Chemical Hazards. DHHS (NIOSH) Publication
No. 81–123. Washington, DC: U.S. Government Printing Office.
10. Clayton,
G.D.; Clayton, F.E., eds. (1993–94). Patty's Industrial Hygiene and
Toxicology. Volumes 2A, 2B, 2C, 2D, 2E, 2F: Toxicology (4th ed.). New
York, NY: John Wiley & Sons. p. 2981.
11. Encyclopedia of Occupational Health and
Safety, Geneva, Switzerland: International Labour Office, 1983, p. 782
Book’s:- Unit Operation in Chemical engineering by McCabe
smith,
Plant Design and economics for chemical
engineer by-McGraw hills
Mass Transfer Operations by Treybal.
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