CENG0013 Design Project
Design of a process for the production of
ethylbenzene
Professor Eric S Fraga
10th February 2022
1. The Process
The majority of ethylbenzene (EB) processes produce EB for internal consumption within a
coupled process that produces styrene monomer. We wish to design the process for the production
of ethylbenzene. The production of EB takes place via the direct addition reaction between
ethylene and benzene:
C6H6 + C2H4 −−→ C6H5C2H5 . (R1a)
The reaction between EB and ethylene to produce diethylbenzene (DEB) also takes place:
C6H5C2H5 + C2H4 −−→ C6H4(C2H5)2 . (R1b)
The competition between these two reactions limits the selectivity towards the desired EB prod-
uct. The chemists have done a number of experiments in their lab. Using their data, they have
come up with models for the single pass conversion of benzene, x, and the selectivity of EB to
DEB production, S, as functions of the residence time, t, in seconds:
x =
0.7
ρ
(
1− e−t/100
)
(1)
S = ρ1.3
(
30e−t/20 + 2
)
(2)
for t ∈ [5, 1000] s in both cases and ρ ∈ [1, 8] is the molar ratio of benzene to ethylene fed to the
reactor. The chemists have determined that the ratio, ρ, has a significant effect on the selectivity.
Reaction R1a is an exothermic reaction. Therefore, the reaction takes place in the vapour phase.
Since the moles of reactants are more than the moles of products, any reactor used will need
to be run at high pressure (20 bar), according to Le Chatelier’s principle. The usually adopted
temperature range for this reaction is T ∈ [350, 440] ◦C.
2. The design task
The process needs to be designed to meet a production requirement of (20+ d10) mol s
-1 of ethyl-
benzene with molar purity 0.98. d is the last digit of your student ID number. Please state the
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value of d at the start of your submission. This ethylbenzene will be subsequently fed into a
process (not considered here) for the production of styrene. To meet this requirement, separate
feeds of benzene and ethylene are available. Both of the feed streams are available at T = 25 ◦C
and P = 20 bar.
The benzene feed has a 2% by mole impurity of toluene (C6H5CH3). The chemists have deter-
mined that this small amount of toluene also reacts with ethylene:
C6H5CH3 + 2 C2H4 −−→ C6H5C2H5 + C3H6 (R1c)
The toluene reacts completely in a few seconds (t < 5 s).
The design of the process flowsheet will be based on the application of the full Douglas approach,
levels 1 through 5. You will be expected to identify and to model all the main processing units,
along with sizing information, and their interconnections including possible heat exchanges.
3. Market information and cost models
The accountants have given you a detailed report of the market prices of reactants and products
as well as models for estimating processing unit costs. Table 1 summarises the costs or values
for particular streams. Table 2 presents the cost models for various types of units. The costs of
the different utilities available, for heating, cooling, and electricity, are given in Table 3.
Table 1: Market prices for feeds and products.
Species Price Minimum purity
[€ mol-1] (molar percentage)
Ethylene 0.03
Benzene (with toluene) 0.12
Ethylbenzene 0.30 98.00
Di-ethylbenzene 0.05 95.00
Table 2: Cost models for processing units for estimating the total annualised cost, TAC, in mil-
lions of €, of buying, installing, and maintaining the equipment.
Unit type TAC Notes
Distillation 1100(1−r)
1.0
αlh−1
√
Fd Fd flow of feed to the column in mol s−1, αlh relative
volatilities of light to heavy keys, r recovery of keys
∈ [0.9, 0.998].
Reactors 0.001tFr Fr flow of feed to the reactor in mol s−1, t residence
time ∈ [5, 1000] s.
Heat exchangers 0.09A0.65 A = heat exchanger area [m2].
Flash vessels 0.001Fv Fv = flow rate to the vessel [mol s−1].
Compressors 0.02Fc Fc = vapour flow rate to the compressor [mol s−1].
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