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process to manufacture 1000kg/h of methyl ethyl ketone from dehydrogenation of 2-butanol
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1.0 INTRODUCTION
Design is a creative process whereby an innovative solution to a problem is conceived.
In this modern age of industrial competition, a successful chemical engineer needs more than a
knowledge and understanding of the fundamental sciences and the related engineering
subjects such as thermodynamics, reaction kinetics, and computer technology. The engineer
must also have the ability to apply this knowledge to practical situations for the purpose of
accomplishing something that will be beneficial to society. However, in making these
applications, the chemical engineer must recognize the economic implications which are
involved and proceed accordingly.
All design starts with a perceived need. In the design of a chemical process, the need is the
public need for the product, creating a commercial opportunity, as foreseen by the sales and
marketing organization. Within this overall objective, the designer will recognize sub-objectives,
the requirements of the various units that make up the overall process.
Before starting work, the designer should obtain as complete, and as unambiguous, a
statement of the requirements as possible. If the requirement (need) arises from outside the
design group, from a customer or from another department, then the designer will have to
elucidate the real requirements through discussion. When writing specifications for others,
such as for the mechanical design or purchase of a piece of equipment, the design engineer
should be aware of the restrictions (constraints) that are being placed on other designers. A
well-thought-out, comprehensive specification of the requirements for a piece of equipment
defines the external constraints within which the other designers must work.
Page | 1
2.0 PROBLEM STATEMENT
Pursuant to instruction from our lecturer we proceeded to come up with a preliminary design
of a process to manufacture 1000kg/h of methyl ethyl ketone from dehydrogenation of 2-
butanol. The design work included coming up with a block diagram, a detailed mass and energy
balance, a flow sheet diagram and a detailed design of a distillation column.
Page | 2
3.0 LITERATURE REVIEW
3.1 BACKGROUND
3.1.1 Nature of methyl ethyl ketone (product description)
Methyl ethyl ketone, also known as 2-butanone, is a colorless organic liquid with an acetone-
like odor and a low boiling point. It is partially miscible with water and many conventional
organic solvents and forms azeotropes with a number of organic liquids. MEK is distinguished
by its exceptional solvency, which enables it to formulate higher-solids protective coatings.
The molecular formula of methyl ethyl ketone is CH3COCH2CH3; its molecular structure is
represented as:
Some physical and chemical properties of MEK are presented in Table 1 below. Because of
MEK’s high reactivity, it is estimated to have a short atmospheric lifetime of approximately
eleven hours.
Atmospheric lifetime is defined as the time required for the concentration to decay to 1/e
(37percent) of its original value.
3.1.2 Overview of production and use
Generally, Methyl ethyl ketone production is accomplished by one of two processes:
(1) Dehydrogenation of secondary butyl alcohol or
Page | 3
Fig. 1 2D and 3D dimensional molecular structures of MEK
(2) As a by-product of butane oxidation.
Property Value
Structural formula: CH3COCH2CH3
Synonyms: 2-butanone, ethyl methyl ketone, MEK, methyl acetone
Molecular weight (grams) 72.1
Melting point, °C -86.3
Boiling point, °C 79.6
Density at 20°C, g/L 804.5
Vapor density (air at 101 kPa, 0°C = 1) 2.41
Critical temperature, °C 260
Critical pressure, MPa 4.4
Surface tension at 20°C, dyne/cm 24.6
Dielectic constant at 20°C 15.45
Heat of combustion at 25°C, kJ/mol 2435
Heat of fusion, kJ/(kg*K) 103.3
Heat of formulation at constant pressure, kJ/mol 279.5
Specific heat:
vapor at 137°C, J/(kg*K)liquid at 20°C, J/(kg*K
1732 2084
Latent heat of vaporization at 101.3 kPa, kJ/mol 32.8
Flashpoint (closed cup), °C -6.6
Ignition temperature, °C 515.5
Explosive limits, volume % MEK in air
lowerupper
2 12
Vapor pressure at 20°C, mm Hg 77.5
Viscosity, MPa*s (=cP)
at 0°Cat 20°Cat 40°C
0.54 0.41 0.34
Solubility at 90°C, g/L of water 190
Figure 2 illustrates the production and use of MEK. Major end-users of MEK include protective
coating solvents (61 percent), adhesives (13 percent), and magnetic tapes (10 percent).
Page | 4
Table 1: Physical and chemical properties of MEK
Vinyls are the primary resins that employ MEK as a solvent. Methyl ethyl ketone is commonly
used as a solvent in rubber cements, as well as in natural and synthetic resins for adhesive use.
It is also the preferred extraction solvent for dewaxing lube oil and is used in printing inks.
Overall, the projected use of MEK is expected to gradually decline. The growing trend towards
water-based, higher-solids, and solvent-less protective coatings, inks and adhesives is reducing
the demand for MEK. The installation of solvent recycling facilities will also reduce
requirements for fresh solvent production. Although MEK is favored as a solvent due to its low
density, low viscosity, and high solvency, its addition on the EPA’s hazardous air pollutants list
will likely cause potential users to consider other comparative solvents such as ethyl acetate.
Page | 5
PRODUCTION
Dehydrogenation of secondary butyl alcohol
By-product of Butane oxidation
END USE
Protective coating solvent
Adhesive solvent
Magnetic tapes
Lube oil dewaxing
Chemical intermediate
Printing ink
Miscellaneous
Fig. 2 production and uses of MEK
3.2 APPLICATIONS
3.2.1 as a solvent
Butanone is an effective and common solvent and is used in processes involving gums, resins,
cellulose acetate and nitrocellulose coatings and in vinyl films. For this reason it finds use in the
manufacture of plastics, textiles, in the production of paraffin wax, and in household products
such as lacquer, varnishes, paint remover, a denaturing agent for denatured alcohol, glues, and
as a cleaning agent. It has similar solvent properties to acetone but has a significantly slower
evaporation rate. Butanone is also used in dry erase markers as the solvent of the erasable dye.
3.2.2 as a welding agent
As butanone dissolves polystyrene, it is sold as "polystyrene cement" for use in connecting
together parts of scale model kits. Though often considered an adhesive, it is actually
functioning as a welding agent in this context.
3.2.3 Other uses
Butanone is the precursor to methyl ethyl ketone peroxide, a catalyst for some polymerization
reactions. It can also initiate crosslinking of unsaturated polyester resins.
3.3 SAFETY
3.3.1 Flammability
Butanone can react with most oxidizing materials, and can produce fires. It is moderately
explosive; it requires only a small flame or spark to cause a vigorous reaction. Butanone fires
should be extinguished with carbon dioxide, dry chemicals or alcohol foam. Concentrations in
the air high enough to be flammable are also intolerable to humans due to the irritating nature
of the vapor.
Page | 6
3.3.2 Health effects
Butanone is an irritant, causing irritation to the eyes and nose of humans, but serious health
effects in animals have been seen only at very high levels. When inhaled, these effects included
birth defects.
Butanone is listed as a Table II precursor under the United Nations Convention against Illicit
Traffic in Narcotic Drugs and Psychotropic Substances.
On December 19, 2005, the U. S. Environmental Protection Agency removed butanone from the
list of hazardous air pollutants (HAPs). After technical review and consideration of public
comments, EPA concluded that potential exposures to butanone emitted from industrial
processes may not reasonably be anticipated to cause human health or environmental
problems. Emissions of butanone will continue to be regulated as a volatile organic compound
because of its contribution to the formation of tropospheric (ground-level) ozone.
Page | 7
Aqueous
OH
H2SO4
OH Zn or Brass
400-550°C
Butene
4.0 METHYL ETHYL KETONE PRODUCTION
This section discusses the methods which are used for production of methyl ethyl ketone.
4.1 SECONDARY-BUTYL ALCOHOL DEHYDROGENATION
The majority of MEK manufactured is produced by dehydrogenation of secondary-butyl alcohol.
This subsection discusses the 2-butanol dehydrogenation process.
4.1.1 Dehydrogenation Process Description
Methyl ethyl ketone manufacture by secondary-butyl alcohol dehydrogenation is a two-step
process where the first step involves the hydration of butenes to produce secondary-butyl
alcohol. The second step consists of the dehydrogenation of secondary-butyl alcohol yielding
MEK and hydrogen gas. These steps are illustrated by the following reactions:
(1) CH3CH=CHCH3 CH3CH2CH3
(2)
CH3CHCH2CH3
Since the first reaction (1) does not involve MEK as a product, this discussion will focus on the
second step of the reaction. Figure 3 illustrates the process of secondary-butyl alcohol
dehydrogenation. Initially, preheated vapours of secondary-butyl alcohol are passed through a
reactor (Step 1) containing a catalytic bed of zinc oxide or brass (zinc-copper alloy) which is
maintained between 400° and 550°C (750° and 1,025°F). A mean residence time of two to eight
Page | 8
Sec-butyl alcohol
Sec-butyl alcohol
MEK
CH3CCH2CH3 + H2
Hydrogen gas
Solvent Hydrogen
Alcohol to recovery
seconds at normal atmospheric pressures is required for conversion from secondary-butyl
alcohol to MEK.
Product gases from the reaction vessel are then condensed via a brine-cooled condenser (Step
2) and sent to a distillation column for fractioning (Step 3). The main fraction (methyl ethyl
ketone) is typically obtained at an 85 to 90 percent yield based on the mass of secondary butyl
alcohol charged. The uncondensed gas may be scrubbed with water or a non-aqueous solvent
to remove any entrained ketone or alcohol from the hydrogen-containing gas (Step 4).The
hydrogen may then be re-used, burned in a furnace, or flared.
A liquid-phase process for converting secondary-butyl alcohol to methyl ethyl ketone has been
developed and is used sometimes. In this process, secondary-butyl alcohol is mixed with a high-
boiling solvent containing suspended finely divided Raney or copper chromite catalyst. The
reaction occurs at a temperature of 150°C (300°F) and at atmospheric pressure allowing MEK
and hydrogen to be driven off in vapour form and separated as soon as each is formed. The
Page | 9
Preheater Reactor
Product storage and
loading
Condenser Scru
bber
Colu
mn
Fig. 3 methyl ethyl ketone from secondary butyl alcohol by dehydrogenation
1 24
3
∥ ∥
n-butane Oxygen or air
Acetic acid MEK Water
advantages of this process include a better yield (typically 3 percent better), longer catalyst life,
simpler product separation, and lower energy consumption.
4.2 N-BUTANE OXIDATION
Another method of manufacturing Methyl ethyl ketone is by liquid-phase oxidation of n-
butane. However, MEK has occasionally been commercially available in significant quantities
from the liquid-phase oxidation of butane to acetic acid. Depending on the demand for acetic
acid, this by-product methyl ethyl ketone can be marketed or recycled. This subsection
discusses MEK production via n-butane oxidation.
4.2.1 N-butane oxidation description process
Figure 4 illustrates the liquid-phase oxidation of n-butane. Initially, n-butane and compressed
air or oxygen are fed into a reactor (Step 1) along with a catalyst, typically cobalt, manganese or
chromium acetate to produce acetic acid, MEK and other by-products such as ethanol, ethyl
acetate, formic acid, and propionic acid. This process produces the following chemical reaction:
O O
CH3CH2CH2CH3 + O2 CH3COH + CH3CCH2CH3 + + H2O
Page | 10
Other by-products
Air is bubbled through the reactant solution at 150° to 225°C (300° to 440°F) with pressures of
about 5.5 MPa (800 psi). Conditions must be carefully controlled to facilitate MEK production
and prevent competing reactions that form acetic acid and other by-products. Process
conditions can be varied producing different ratios of product components through the choice
of raw material, reaction conditions, and recovery methods.
Vapors containing crude acetic acid and the various by-products including MEK are separated
from unreacted n-butane and inert gases (Step 2), then stripped or flashed to remove dissolved
butane and inert gases (Step 3), and sent to the purification section (Step 4). Unreacted
nitrogen leaving the reactor carries various oxidation products (formic, acetic, and propionic
acids; acetone, MEK, methanol, etc.) and some unreacted butane and is sent to a separator
(condenser) for removal/recycling of unreacted hydrocarbons (Step 5).
The purification section of the plant is complex and highly specialized utilizing three phase
distillation in conjunction with straight extraction. The low-boiling organics such as MEK are
separated from the crude acetic acid by conventional distillation. Azeotropic distillation is used
Page | 11
Fig. 4 Methyl ethyl ketone from n-butane by liquid phase oxidation
to dry and purify the crude acetic acid. Recovery and purification of the various by-products
require several distillation columns and involve extractive distillation or azeotrope breakers or
both. Liquid organic wastes are typically burned in boilers to recover their heat value.
4.3 N-BUTENE OXIDATION
A new one-step process that converts olefins to ketones called OK technology was developed.
Specifically, MEK is produced via direct oxidation of n-butenes at about 85°C (185°F) and 690
kPa (100 psi), using a proprietary, and homogenous non-chloride catalyst. Advantages of this
process are that it is noncorrosive, environmentally clean, and economical because of low
capital investment and low energy needs. The process is currently in lab-scale operation;
however, plans are underway to design a facility for large scale production.
4.4 JUSTIFICATION OF THE PROCESS USED
The justification of the method used was based on the problem statement given to the group
by the supervisor.
Page | 12
4.5 DISTILLATION
Distillation as a separation process is indispensable in the production of methyl ethyl ketone
from dehydrogenation of 2-butanol.
The separation of liquid mixtures by distillation depends on differences in volatility between the
components. In distillation, the greater the relative volatilities, the easier the separation.
The basic equipment required for continuous distillation consists of column, a re-boiler and a
condenser system.
Vapor flows up the column and liquid counter-currently down the column. The vapor and liquid
are brought into contact on plates, or packing. Part of the condensate from the condenser is
returned to the top of the column to provide liquid flow above the feed point (reflux), and part
of the liquid from the base of the column is vaporized in the re-boiler and returned to provide
the vapor flow.
In the section below the feed, the more volatile components are stripped from the liquid and
this is known as the stripping section. Above the feed, the concentration of the more volatile
components is increased and this is called the enrichment, or more commonly, the rectifying
section.
If the process requirement is to strip a volatile component from a relatively non-volatile
solvent, the rectifying section may be omitted, and the column would then be called a stripping
column.
In some operations, where the top product is required as a vapor, only sufficient liquid is
condensed to provide the reflux flow to the column, and the condenser is referred to as a
partial condenser. When the liquid is totally condensed, the liquid returned to the column will
have the same composition as the top product. In a partial condenser the reflux will be in
equilibrium with the vapor leaving the condenser. Virtually pure top and bottom products can
be obtained in a single column from a binary feed, but where the feed contains more than two
Page | 13
components; only a single “pure” product can be produced, either from the top or bottom of
the column.
In engineering terms, distillation columns have to be designed with a larger range in capacity
than any other types of processing equipment, with single columns 0.3–10 m in diameter and
3–75 m in height. Designers are required to achieve the desired product quality at minimum
cost and also to provide constant purity of product even though there may be variations in feed
composition.
A distillation unit should be considered together with its associated control system, and it is
often operated in association with several other separate units.
The vertical cylindrical column provides, in a compact form and with the minimum of ground
requirements, a large number of separate stages of vaporization and condensation.
A complete unit will normally consist of a feed tank, a feed heater, a column with boiler, a
condenser, an arrangement for returning part of the condensed liquid as reflux, and coolers to
cool the two products before passing them to storage.
The reflux liquor may be allowed to flow back by gravity to the top plate of the column or, as in
larger units, it is run back to a drum from which it is pumped to the top of the column. The
control of the reflux on very small units is conveniently effected by hand-operated valves and
with the larger units by adjusting the delivery from a pump.
In many cases the reflux is divided by means of an electromagnetically operated device which
diverts the top product either to the product line or to the reflux line for controlled time
intervals.
Page | 14
2-butanol MEK Hydrogen
5.0 PROCESS DESCRIPTION
5.1 DEHYDROGENATION OF 2-BUTANOL
Methyl ethyl ketone (MEK) is manufactured by the dehydrogenation of 2-butanol. A description
of the processes listing the various units used is given below:
5.1.1 Reactor
A reactor in which the butanol is dehydrated to produce MEK and hydrogen, according to the
reaction:
CH3CH2CH3CHOH CH3CH2CH3CO + H2
The conversion of alcohol to MEK is 88 per cent and the yield is taken as 100 per cent. Initially,
preheated vapours of secondary-butyl alcohol are passed through a reactor (Step 1) containing
a catalytic bed of zinc oxide or brass (zinc-copper alloy) which is maintained between 400°C and
550°C (750°F and 1,025°F). A mean residence time of two to eight seconds at normal
atmospheric pressures is required for conversion from secondary-butyl alcohol to MEK.
5.1.2 Cooler-condenser
In the cooler-condenser the reactor off-gases (i.e. product gases) are cooled and most of the
MEK and unreacted alcohol are condensed. Two exchangers are used but they are modeled as
one unit. Of the MEK entering the unit 84 per cent is condensed, together with 92 per cent of
the alcohol. The hydrogen is non-condensable. The condensate is fed forward to the second
distillation column which is the final purification stage. The MEK is cooled to a temperature of
32 °C. The water is fed to the cooler at a temperature of 24 °C.
Page | 15
5.1.3 Absorption column
In the absorption column the uncondensed MEK and alcohol are absorbed in water. Around 98
per cent of the MEK and alcohol can be considered to be absorbed in this unit, giving a 10 per
cent w/w solution of MEK. The water feed to the absorber is recycled from the next unit, the
extractor. The vent stream from the absorber, containing mainly hydrogen, is sent to a flare
stack.
5.1.4 Extraction column
In the extraction column the MEK and alcohol in the solution from the absorber are extracted
into trichloroethylane (TCE). The raffinate, water containing around 0.5 per cent w/w MEK, is
recycled to the absorption column. The extract, which contains around 20 per cent w/w MEK,
and a small amount of butanol and water, is fed to the first distillation column.
5.1.5 Distillation column I
In the distillation column the unit separates the MEK and alcohol from the solvent TCE. The
solvent containing a trace of MEK and water is recycled to the extraction column. The recovery
is 99.99%.
5.1.6 Distillation column II
In the second distillation column, also known as the final the purification stage which produces
a 99.9% pure MEK product from the crude product from the first column. The residue from this
column, which contains the bulk of the unreacted 2-butanol, is recycled to the reactor. The
steam generated by the re-boiler in this unit is at a temperature of 140 °C.
The following is the block diagram for the production process of methyl ethyl ketone.
Page | 16
2-butanol
Unreacted alcohol and MEK
Gaseous products
Uncondensed MEK & alcohol
To flame stack
Water 0.5% w/w MEK
MEK and alcohol
Extract
TCE (trichloroethyl
ane)
Crude product
H2
Pure MEK (99.9%)
Unreacted 2-butanol
Page | 17
Fig. 5 Block diagram for the production of methyl ethyl ketone
Reactor (dehydrogenation)
Cooler- condenser
Absorption column
Extractor
Distillation column 1
Distillation column 2
5.2 MATERIAL BALANCES
Material balances are the basis of process design. A material balance taken over the complete
process will determine the quantities of raw materials required and products produced.
Balances over individual process units set the process stream flows and compositions.
Material balances are also useful tools for the study of plant operation and trouble shooting.
They can be used to check performance against design; to extend the often limited data
available from the plant instrumentation; to check instrument calibrations; and to locate
sources of material loss.
All mass/material balances are based on the principle of conservation of mass that is massr can
neither be created nor destroyed with an exception of nuclear processes according to Einstein’s
equation; E=mc2.
The general conservation equation for any process system can be written as:
Material out−Material∈+Generation−Consumption=Accumulation
For a steady state process the accumulation term is zero and thus for a continuous steady state
process, the general balance equation for any substance involved in the process can be written
as:
Material∈+Generation=Material Out+Consumption
If no chemical reaction takes place, material balance is computed on the basis of chemical
compounds mass basis that are used whereas if a chemical reaction occurs molar units are
used.
Also it is worthwhile to note that when a reaction occurs an overall balance is not appropriate
but a reactant balance (a compound balance) is.
Page | 18
5.2.1 Choosing a Basis
The correct choice of the basis for a calculation will often determine whether the calculation
proves to be simple or complex.
A time basis was chosen in which the results will be presented. The basis for calculations was
chosen as 1 hour and thus results will be presented in kg/h.
Page | 19
YieldsCH3CH2CH3CHOH CH3CH2CH3CO + H2
X (kg)
XR
2-butanol XF
X (kg)
5.2.2 MATERIAL BALANCE FOR THE PRODUCTION METHYLETHYLKETONE (MEK) FROM 2-
BUTANOL
Basis used: 1 hour
The material balance was done around the following units:
(1) Reactor
RMM of 2-butanol =74
Moles of 2-butanol =X (kg)
74=0.01335 x
Moles of the2-Butanol that reacted 0.88 × 0.01369 x = 0.01188 x
From the equation:
Mole ratio for the reaction is 1:1
Hence moles of the MEK reacting is 0.01188X
Mass of MEK then is 0.01188x×72=0.8554x
Mass of 2-butanol is 12
100× x=012 x
Mass of then H2 is 0.01188×2=0.0276x
Page | 20
Reactor
Reactor
MEK
2-butanol
H2
MEK = 0.8554x
2-Butanol=012 x
H2 =0.02376x
MEK¿0.01369 x
2-Butanol¿0.0096 x(Non-condensable)MEK = 0.8554x
2-Butanol=012 x
All the components leaving the reactor are discharged directly into the cooler condenser for the
next operation.
(2) Cooler-condenser
Condensate (which is then directly sent to the final purification column) comprises:
84% MEK= 0.8×0.8554x=0.7185 x
92% 2-Butanol=0.92× 012 x=0.1104 x
Incondensable stream comprises:
H2=0.02376 x
2-Butanol¿0.0096 x
MEK¿0.01369 x
(Condensate) MEK¿0.7185 x
2-butanol¿0.1104 x
Page | 21
Cooler-condenser
H2=0.02376 xH2=0.02376 x
MEK¿0.5 %=0.005 K
H2OK
2-Butanol¿0.0096 x
JJ
MEK ¿0.98 (0.1369 x )+0.005 K=0.1 J
K
2-Butanol
MEK
(3) MEK balance around the absorption column
0.1369 x+0.005 K=0.02 (0.1369 X )+0.1 J
01369 x+0.005 K=0.002738+0.1 J
J=1.342 x+0.05 K
Overall balance
(0.02376 x+0.0096 x+0.1369 x )+ K=1.342 x+0.05k+(0.02376 x+0.005 k+0.002738 x)
k=1.262033 x
Performing a new balance around the absorption column to express the k -value in terms of x
in the above equations gives the following values:
2
Page | 22
Absorption column
Absorption column
MEK=0.02(0.1369 x)2-Butanol¿0.02(0.0096 x )H2=0.02376 x
(non-condensable)MEK¿0.01369 x
H2=0.02376 x
2-Butanol¿0.98(0.0096 x)H2O=?
MEK
H2O¿1.256 xMEK¿0.1369 x
H2¿0.02376 x
MEK¿0.02 (0.1369 x )Butanol¿0.02(0.0096 x )
H2=0.02376 x
MEK¿0.1342 x+0.00631 x=0.14051 x
H2O¿10256 x and
2−butanol=0.009408x
ϑ
R- Recycle from next operation (TCE)
: MEK ¿0.00631 x H2O¿1.256 x
2-butanol =0.009408 x
Raffinate: MEK¿0.005 K=0.005 (1.262033684 x )=0.00635 x
H2O¿0.995 K=0.995 (1.262033 x )=1.256 x
Stream J: MEK¿0.1 J=0.1 {1.3426 x+0.005 (1.26033684 x ) }=0.1404 x
H2O¿1.262033684 x
2-butanol ¿0.009408 x
(4) Extraction column
Raffinate B
Q
R ¿TC
MEK Balance around the extractor
0.1404 x=0.00631 x+0.2 ϑ
ϑ¿0.6704 x
Overall balance
R+Q=ϑ+B
Page | 23
Extractor
MEK¿0.1404 x
H2O¿1.256 x
MEK¿0.13409 x
2-butanol¿0.009408 x
TCE¿0.527 x
2-Butanol ¿0.009408 x
1000kg/hr (flow rate as given)
1.399 x+R=1.2623 x+0.67045 x
R=0.533 x
TCE=0.6704 x−(0.13409 x+0.009408 x )
¿0.527 x (Which is approximately =R)
(5) Distillation column 1
For this unit operation, the balances were obtained from the previous unit operation i.e. the
extraction column and are indicated in the block diagram below.
(6) Distillation column 2
The material balance for the second distillation column is given as follows;
Balancing around this gives:
MEK:
0.8526 x=1000
Page | 24
Distillation column 1
Distillation column 2
TCE¿0.533 x
MEK¿0.13409 x
TCE¿0.527 x
MEK¿0.13409 x2-Butanol¿0.009408 x
MEK¿(0.13409 x+0.71912 x)¿0.8526 x
2-Butanol
¿0.1198 x
2-Butanol (recycled back to the reactor)
x= 10000.8526
=1172.882 kg
2-Butanol:
0.1198 x
x=0.1198 (1172.882)¿140.51 kg (Returning to the reactor)
4.2.3 CALCULATION OF ACTUAL MASS OF THE COMPONENTS IN ALL THE STREAMS
The streams are indicated in the diagrams above.
1) Reactor
From the balances carried out in the previous exercise the value of X was obtained as 1172.883
kg based on the 1 hour basis.
In = out
Entering stream:
XF + XR= X where: XF = feed and XR = feed as recycle
Leaving streams:
MEK = 0.8554 x=0.8554 ×1172.883=1003.24 kg
2-butanol ¿0.12 x=0.12 ×1172.883=140.74 kg
H2¿0.02376 x=0.02376 × 1172.883=27.87 kg
2) Cooler condenser
In = out
MEK ¿0.7185 x=0.7185 ×1172.883=842.716 kg
2-butanol¿0.1104 x=0.1104 ×1172.883=128.486 kg
Non-condensable
Page | 25
MEK¿0.1369 x=0.1369 ×1172.883=160.568 kg
2-Butanol ¿0.0096 x=0.0096 × 1172.883=11.260kg
H2¿27.87 kg
3) Absorption column
Entering stream:
MEK¿0.1369 x=0.1369 ×1172.883=160.568 kg
2-Butanol ¿0.0096 x=0.0096 × 1172.883=11.260kg
H2¿27.87 kg
Raffinate stream:
MEK 0.00631 x=0.00631 ×1172.883=7.401 kg
H2O:1.256 x=1.256 ×1172.883=1473.141 kg
Leaving stream:
MEK 0.14051 x=0.14051 ×1172.883=164.881 kg
H2O 1.256 x=1.256 ×1172.883=1473.141 kg
2-butanol ¿0.009408 x=0.009488 ×1172.883=11.034 kg
4) Extractor
Entering stream:
MEK 0.14051 x=0.14051 ×1172.883=164.881 kg
H2O 1.256 x=1.256 ×1172.883=1473.141 kg
2-butanol ¿0.009408 x=0.009488 ×1172.883=11.034 kg
Page | 26
Recycle stream = TCE (Tri chloro ethylane)
TCE: 0.527 x=0.527 × 1172.883=618.109 kg
Leaving stream:
MEK:0.13409 x=0.13409 ×1172.883=157.272 kg
2-butanol0.009408 x=0.009408 ×1172.883=11.0334 kg
5) Distillation column 1
Entering stream:
MEK: 0.13409 x=0.13409 ×1172.883=157.272 kg
2-butanol0.009408 x=0.009408 ×1172.883=11.0334 kg
Leaving stream:
MEK:0.13409 x=0.13409 ×1172.883=157.272 kg
2-butanol0.009408 x=0.009408 ×1172.883=11.0334 kg
TCE: 0.527 x=0.527 × 1172.883=618.109 kg (This is recycled back into the extractor)
6) Distillation column 2
In = out
Entering stream:
MEK: 0.13409 x+0.71912 x=0.8526 x
2-butanol: 0.009408 x+0.1104 x=0.1199 x (this is recycled back to the reactor)
Leaving stream
Page | 27
99.99% pure MEK at 1000kg/hr
5.3 ENERGY BALANCES
As with mass, energy can be considered to be separately conserved in all but nuclear processes.
The conservation of energy, however, differs from that of mass in that energy can be generated
(or consumed) in a chemical process. Material can change form, new molecular species can be
formed by chemical reaction, but the total mass flow into a process unit must be equal to the
flow out at the steady state. The same is not true of energy. The total enthalpy of the outlet
streams will not equal that of the inlet streams if energy is generated or consumed in the
processes; such as that due to heat of reaction.
Energy can exist in several forms: heat, mechanical energy, electrical energy, and are the total
energy that is conserved.
In process design, energy balances are made to determine the energy requirements of the
process: the heating, cooling and power required. In plant operation, an energy balance (energy
audit) on the plant will show the pattern of energy usage, and suggest areas for conservation
and savings.
A general equation can be written for the conservation of energy:
Accumulation=Energy∈+Generation−Consumption−Energy out
This is a statement of the first law of thermodynamics. An energy balance can be written for
any process step. Chemical reaction will evolve energy (exothermic) or consume energy
(endothermic). For steady-state processes the accumulation of both mass and energy will be
zero.
The energy balance was carried out around cooler condenser and the second distillation
column. In chemical processes the kinetic and potential energy terms are usually small
compared with heat and work terms, and can normally be neglected.
Page | 28
If the kinetic and potential energy terms are neglected the energy equation reduces to
H 2−H 1=Q−W
For many processes the work term will be zero, or negligibly small, and equation above reduces
to the simple heat balance equation:
Q=H 2−H 1
Where heat is generated in the system; for example in a chemical reactor:
Q=QP+Q S
QS=¿ heat generated in the system. If heat is evolved (exothermic processes) QS is taken as
positive, and if heat is absorbed (endothermic processes) it is taken as negative.
QP=¿ process heat added to the system to maintain required system temperature.
Hence:
QP=H 2−H 1−QS
H 1=¿ enthalpy of the exit stream
H 2=¿ enthalpy of the outlet stream.
For a practical reactor, the heat added (or removed) Qp to maintain the design reactor
temperature will be given by:
QP=¿ H products−Hreactants−Qr¿
Where
H products is the total enthalpy of the product streams, including unreacted materials and by-
products, evaluated from a datum temperature of 25°C;
Page | 29
H reactants is the is the total enthalpy of the feed streams, including excess reagent and inerts,
evaluated from a datum of 25°C;
Qr is the total heat generated by the reactions taking place, evaluated from the standard heats
of reaction at 25°C (298 K).
This equation can be written in the form:
QP=∑ ∫T ref
Tout
ni c pidT−¿∑ ∫T ref
Tout
ni c pidT−¿∑ [−∆ H °rxn ] × mol of product formed ¿¿
C p=A+BT+C T2+D T3
Page | 30
MEK=160.568 kg
2-Butanol¿11.260 kg(Non-condensable)
MEK = 0.8554x
2-Butanol=012 x
MEK =842.716 kg
2-butanol¿128.486 kg
CondensateQR
5.3.1 ENERGY BALANCE FOR THE PRODUCTION METHYLETHYLKETONE (MEK) FROM 2-
BUTANOL
The energy balance was carried around the cooler condenser and the second distillation
column (final purification stage). The balances are as indicated below.
4.3.1.1 Cooler condenser
The temperature at which the products of the reactor leave is 400 °C. The condenser cooler
lowers cools the products to a temperature of 32 °C. The energy balance is given as shown in
the calculations below.
Energy balance for MEK
Sensible heat to lower the temperature of the condensate MEK from 400 °C to 79.6 °C,
¿mC p ∆ T
¿842.716 ×1732 × (400−79.6 )
¿467.65 × 106 J
Sensible heat to lower the temperature of the incondensable MEK from 400 °C to 80 °C,
¿mC p ∆ T
Page | 31
Cooler-condenser
H2=27.87 kgH2=0.02376 x
MEK¿1003.24 kg
2-butanol 140.74 kg H2 27.87 kg
¿160.568 ×1732 × ( 400−80.0 )
¿88.99 ×106 J
Sensible heat to lower the temperature of the condensate MEK from 79.6 °C to 32 °C,
¿mC p ∆ T
¿842.716 × 2084 × (79.6−32 )
¿83.60×106 J
No of moles of MEK condensed
842.716 kg72 kg/kmol
=11.704 kmol
Latent heat of vaporization of MEK,
¿11.704 ×32.8
¿383.89 ×106 J
Total energy required for MEK cooling and condensation,
¿ (467.65+88.99+83.60+383.89 )106
¿1024.13 MJ /h
Energy balance for 2-butanol
Sensible heat to be removed to lower the temperature of 2-butamol from 400 °C to 99 °C is
determined as follows,
Q=mC p ΔT
Q=140.7474
×197.1J
mol . K× ( 400−99 )× 103=112.83× 106 J /h
To condense the 2-butanol,
Page | 32
Q=5.95 × 105 Jkg
×128.486 kg=764.5 ×106 j /hTotal heat to be removed from 2-butanol,
¿Q1+Q2
¿ (112.83+764.49 )× 106 Jh
¿877.32 ×106 J /hTotal heat to be removed from the cooler condenser,
QR=(877.32+1024.13)× 106 j /h
QR=1901.45 MJ /h
5.3.1.2 Distillation column 2
Page | 33
R
QR
QC
D=1000kg/hXD=0.999
F=1140.52kg/hXF=0.88
Taking reflux ratio (R.R) = 1.94
Total energy balance equation is:
HF+QB=QC+HD+HB
QC is obtained by a balance around the condenser
Page | 34
B=140.52kg/hXB=0.0088
QC
DHD
RHR
VHV
An energy balance at steady state is:
HV = QC + HR + HD
Values of enthalpy of product (distillate) and reflux are zero as they are both at the reference
temperature. Both are liquid and the reflux will be at the same temperatures as the distillate.
Enthalpy of vapour:
Hv= latent heat + sensible heat
For methyl ethyl ketone, latent heat is given as:
Ln = 4.56 × 105 J /kg
Latent heat of the vapor stream:
L=mn Ln
L=(2940 ) ( 4.56 ×105 )
L=1340.6 × 106 J /K
Page | 35
Sensible heat
=∑∫ niC pidT
Boiling point of methyl ethyl ketone
=79.6 ℃ (352.6 K)
Sensible heat of MEK,
=0.026362×106 ∫298
352.6
(24.643+33.557¿× 10−2 T−2.057 ×10−4T 2+63.781 ×10−9T 3)dT ¿
¿167.575 ×106 J¿1340.6 ×106+167.575 × 106
H v=1508.18× 106 kJ
H D=(mols of stream)(value of intergral)
¿(0.105488× 106)(2100.98)+(0.026372 ×106)(2203.23)
¿27.9710 6kJ
H R=(molsof stream)(value of intergral)
¿(0.316465× 106)(2100.98)+(0.079116 ×106)(2203.23)
¿111.884 ×106 J
A balance around the condenser yields:
QC=H v−(H R+H D)
¿ [1508.18−(27.97106+111.884 )]× 106 J
Q c=1368.32 ×106 J
The quantity of heat that needs to be extracted from the condenser by the cooling fluid is
obtained as follows.
Page | 36
QR is obtained by an overall energy balance around the column.
QR=QC+H D+HB−H F
H F=41.8 ×103 ×1140.6 J
¿15.884 × 106 J
HB=140.6 × 41.8 ×1000
¿5.852 ×106 J
QR=(1368.32+111.884+5.852−15.884 )×106
QR=1470.2 ×106 J
Page | 37
6.0 DESIGN OF DISTILLATION COLUMN 2
6.1 DISTILLATION PRINCIPLES
Separation of components from a liquid mixture via distillation depends on the differences in
boiling points of the individual components. Also, depending on the concentrations of the
components present, the liquid mixture will have different boiling point characteristics.
Therefore, distillation processes depends on the vapor pressure characteristics of liquid
mixtures.
6.2 VAPOUR PRESSURE AND BOILING
The vapor pressure of a liquid at a particular temperature is the equilibrium pressure exerted
by molecules leaving and entering the liquid surface. Here are some important points
regarding vapor pressure:
energy input raises vapor pressure
vapor pressure is related to boiling
a liquid is said to ‘boil’ when its vapor pressure equals the surrounding
pressure
the ease with which a liquid boils depends on its volatility
liquids with high vapor pressures (volatile liquids) will boil at lower
temperatures
the vapor pressure and hence the boiling point of a liquid mixture depends
on the relative amounts of the components in the mixture
distillation occurs because of the differences in the volatility of the
components in the liquid mixture
6.3 DESIGN OF DISTILLATION COLUMN
Page | 38
Distillation columns are designed using the vapor-liquid equilibrium data for the mixtures to be
separated.
The vapor liquid equilibrium characteristics of the mixture will determine the number of stages
and hence the number of trays required for the separation.
Most distillation columns are designed by use of the McCabe Thiele method.
6.4 McCabe THIELE DESIGN METHOD
The McCabe Thiele approach is a graphical one and use the VLE plot to determine the
theoretical number of stages required to effect the separation of the mixture (binary in our
case).
The method assumes constant molar overflow and this implies that:
Molar heats of vaporization of the components are roughly the same.
Heat effects (heats of solution, heat losses to and from the column etc.) are
negligible.
For every mole of vapor condensed one mole of liquid is vaporized.
The design process is simple. Given the VLE data/relationship for the more volatile component,
operating lines are drawn first.
Operating lines define the mass balance relationships between the liquid and
vapor phases in the column.
There is one operating line for the bottom (stripping) section of the column and
one for the top (rectifying) section of the column.
Use of the constant molar overflow assumption also ensures that the operating
lines are straight.
In the design done for the distillation column 2 the following criteria was followed.
Page | 39
QC
F=1140.52kg/hXF=0.88
1. Specification of degree of separation required
2. Selection of the operating conditions
3. Selection of the type of contacting device e.g. plates , pickings
4. Determining the stage and reflux requirements.
5. Sizing the column e.g diameter and height.
Assumptions made in the design of the distillation column:
Equimolar overflow
Total condenser
Partial reboiler
Density does not vary with temperature
Theoretical plates i.e perfect phase equilibrium exists between both phases
leaving the plate.
1. Degree of separation required
The feed to the distillation column contains 88 mol % of the less volatile component (methyl
ethyl ketone) and 12 mol % of the more volatile component (2-butanol).
An overhead purity of 99.9 mol percent is desired while a bottoms purity of 0.1 mol % is
obtained thus the following mole fraction value relate to the more volatile component:
X F=0.8768
X B=0.0088
X D=0.999
A reflux ratio of 16 was used as calculated based on the minimum reflux ratio.
Page | 40
The following vapour liquid equilibrium data was used to draw the VLE curve.
X 0.088 0.278 0.383 0.467 0.478 0.582 0.702 0.803 0.855 0.900
Y 0.192 0.468 0.583 0.644 0.655 0.737 0.823 0.885 0.905 0.940
Page | 41
0 0.2 0.4 0.6 0.8 1 1.20
0.2
0.4
0.6
0.8
1
1.2
X
Y
y'
xF
The value of y’ is read from the graph as shown above.
Page | 42
0 0.2 0.4 0.6 0.8 1 1.20
0.2
0.4
0.6
0.8
1
1.2
X
Y
y'
2. Determination of stages and reflux requirements
The theoretical number of stages was determined by the McCabe Thiele method. This is a
graphical method for the determination of the ideal number of stages. This was procedure was
carried as follows.
Determining the minimum reflux ratio
The minimum reflux rate can be determined mathematically from the endpoints of the
rectifying line at minimum reflux – the overhead product composition point (xD, yD) and the
point of intersection of the feed line and equilibrium curve(x’, y’).
RDmin=
xD− y '
y '−x '
xD=0.99 y’=0.92 x’=0.8768
RDmin= 0.99−0.92
0.92−0.8768=1.62
Rreal=1.2 RD min=1.2× 1.62=1.94
Rreal=RD
R=R real × D=1.94 ×1000=1940 kg/h
The equation for the rectifying section is given as follows,
yn=RR
1+RRxn+1+
1RR+1
xD
yn=1.94
1+1.94xn+1+
11.94+1
0.999
yn=0.66 xn+1+0.34
The above equation is plotted in the curve as shown below, and the McCabe Thiele method is used to determine the number of stages.
Page | 43
From the above analysis using the McCabe Thiele method, the theoretical number of stages was obtained as 12 stages.
Ideal number of stages obtained= 12
i.e. Rectifying section= 3 stages
Stripping section = 9 stages
Page | 44
0 0.2 0.4 0.6 0.8 1 1.20
0.2
0.4
0.6
0.8
1
1.2
X
Y
q-line
VLE curve
45° line
stripping operat-ing line
rectifying operating line
xDxB
3. Sizing of the column
The sizing of the column was carried out using Carrillo, Martin and Roselle’s correlation (2000).
HETP=P √ ρL
(2712+82.0P )¿¿
Where Fv is defined by the following expression
FV=uGs √ ρL
uGs is the vapor phase superficial velocity
ρL is the liquid phase specific mass
ρGis the vapor phase specific mass
X=¿
y=e−4 x (2)
y=ug
2 a ρg
g ε3 ∆ ρ¿
Where
a=surfacearea
ε=voidage area
V g=velcity of gas∈the column
mL=mass flowrate of the liquid
mg=mass flowrate of the gas
At 760mmHg, data for MEK is as given below
ρg=2.5 ×1=2.5 kgm−3 , ρL=0.806 ×1000=806 kg m−3 ,a=364 m2
m3 , ε=0.63 , g
¿9.80 m / s2
Page | 45
F
VR
VSLS
R=LR
To obtain the mass flow rate of the gas and the liquid the following balance is carried out as below.
Ls=F+LR
¿ F+R
¿1140.5208+1940=3080.52 kg /h
V s=V R=R+D=1940+1000=2940 kg /h
M l=Ls=3080.52 kg/h
M g=V s=2940 kg/h
∆ ρ=(80.6−2.5 )=803.5
μL=0.426 cP , μH 2 O=1.005 cP
x=(3080.522940 )
14 ( 2.5
803.5 )18
x=1.0117 ×0.486=0.492
Using the value of x in equation (1),
y=e−4 (0.492)=0.1399
From equation (3),
Page | 46
υg2= y . g . ε3 Δ ρ
a ρg( μl
μH2 O )0.16
μl
μH 2 O
=0.4261.005
=0.4239
υg=( 0.1399 ×9.81 ×0.633× 803.5364 × 2.5 ×0.42391.6 )
12=( 275.74
793.24 )12=√0.3476=0.5896 m / s
V g=υg . A
volumetric flowrate=flowrate× areaV g=υg × A=υg .π D 2
4
Dc=√ 4 V g
π × υg
V g=υρ=1000 kg /h
2.5 kg /m3=400 m3/hr
¿0.1111m3
s
Dc=√ 4×0.1111π × 0.5896
Dc=0.4898 m
DD=DC
0.75=0.4898
0.75=0.6531 m
Therefore the diameter of the column is,
DD=0.65m
Determining the height of the column using the following procedure,
HETP=P √ ρL
(2712+82.0P )¿¿
FV=uGs √ ρL
¿0.5896 ×√2.5=0.9322 m /s
Page | 47
760 mmHg=101325.024 Pa(N / M 2)
101.325× 103× √ 806 ×0.93220.42
(2712+82.0 P ) ¿¿
Numerator=0.97094 ×28.39 ×101.325 ×103=2793045.141
Denominator=18.365 × 8311.362=15263816.31
¿ 2793045.14115263816.31
=0.18298
HOP=N op× HETP
Nop=number of stages∈theupper section
H op=height of upper part of the column
H ETP=height of equivalent theretical plate
HOL=NOL × HETP
NOL=number of stages∈the lower section
Stages in the upper section= 3
Stages in the lower section = 9
HOP=3 × 0.18298=0.54894
HOL=9 ×0.18298=1.64682
HTotal=HOP+HOL
¿0.54894+1.64684
¿2.19576
HTotal≅ 2.2m
The active part of the distillation column is 2.2 m
4. Selection of the type of contacting device to be used
Raschig rings will be used as the contacting device in the distillation column. They are ceramic
in nature are 1/3 mm in size.
Page | 48
Raschig rings are pieces of tube (approximately equal in length and diameter) used in large numbers as
a packed bed within columns for distillations and other chemical engineering processes. They are usually
ceramic or metal and provide a large surface area within the volume of the column for interaction
between liquid and gas or vapour.
They form what is now known as random packing, and enable distillations of much greater
efficiency than the use of fractional distillation columns with trays.
In a distillation column, the reflux or condensed vapour runs down the column, covering the
surfaces of the rings, while vapour from the re-boiler goes up the column. As the vapour and
liquid pass each other counter-currently in a small space, they tend towards equilibrium. Thus
less volatile material tends to go downwards, more volatile material upwards.
Raschig rings made from borosilicate glass are sometimes employed in the handling of nuclear
materials, where they are used inside vessels and tanks containing solutions of fissile material,
for example solutions of enriched uranyl nitrate, acting as neutron absorbers and preventing a
potential criticality accident.
Page | 49
Fig. 7 Raschig rings used for the operation
7.0 CONCLUSION
Distillation column design requires the selection of the right various packing and tower sizing to
meet the process, hydraulic, efficiency, and mechanical requirements of the service. Process
considerations include operating conditions, flexibility, and solid handling requirements.
Hydraulic and efficiency criteria involve selection of a suitable packing material that allows for
cost-effective optimization of vessel height vs. diameter.
Determining the number of stages required for the desired degree of separation and the
location of the feed tray is merely the first steps in producing an overall distillation column
design.
Other things that need to be considered are tray spacing; column diameter; internal
configurations; heating and cooling duties. All of these can lead to conflicting design
parameters. Thus, distillation column design is often an iterative procedure. If the conflicts are
not resolved at the design stage, then the column will not perform well in practice.
It can be deduced from the previous section on distillation column design that the number of
trays will influence the degree of separation.
As the feed stage is moved lower down the column, the top composition becomes less rich in
the more volatile component while the bottoms contains more of the more volatile component.
However, the changes in top composition are not as marked as the bottoms composition.
Page | 50
8.0 REFERENCES
1. Chemical Engineering Design, 4th Edition by R.K Sinnot.
2. Unit Operations of Chemical Engineering, 5th Edition by McCabe and Smith.
3. Li, Y.L., “Production technology and market analysis of methyl ethyl ketone”, Fine and
Specialty Chemicals, 12(18), 22—25(2004). (in Chinese)
4. Zhang, Y.X., “Production technology and application status of methyl ethyl ketone”,
Journal of Henan Chemical Industry, 11(1), 51—55(2003). (in Chinese)
5. Distillation: An Introduction by M. T Tham.
6. Qi, J., Gao, N., “Market analysis of methyl ethyl ketone”, Petrochemical Industry
Technology, 10(3), 61 — 64(2003). (in Chinese)
7. Ma, Y.S., Su, J., Wang, C.M., “A process of ketone from secondary alcohol by
dehydrogenation”, C.N Pat., 1289753(2001).
8. Perry’s Chemical Engineering Handbook.
9. Coulson and Richardson’s Chemical Engineering, Volume 2, Fifth Edition.
10. Lecture notes from CHP 461 (Chemical Engineering Design I) and CHP 372 (Mass
Transfer I)
11. www.wikipedia.org .
12. www.basf.com
Page | 51