Selective dimerization of ethylene to but-1-ene under the conditions of industrial process. I. Influence of temperature and pressure on the rate of the process in a bubbling type reactor

Article abstract of DOI:10.1134/S1070427207070385

Analysis of mass and heat balance in the reaction node of the process of ethylene dimerization into but-1-ene under the industrial conditions is performed. It is found that ethylene concentration in the reactor liquid phase by a complex way depends on the reactor temperature, pressure and but-1-ene concentration in the liquid phase. Optimal process temperature is 80-90°C, operating pressure in the reactor is 0.6-0.8 MPa. Increase in pressure above 1 MPa practically excludes heat withdraw via but-1-ene evaporation and makes the system of heat withdrawing ineffective.

Full text of DOI:10.1134/S1070427207070385

ISSN 1070-4280, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 7, pp. 1195–1200. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © V.I. Zhukov, G.V. Val’kovich, B.N. Skorik, Yu.M. Petrov, G.P. Belov, 2005, published in Khimicheskaya Promyshlennost’, 2005,
Vol. 82, No. 8, pp. 382–388.
TECHNOLOGY OF ORGANIC
AND INORGANIC SUBSTANCES
Selective Dimerization of Ethylene to But-1-ene under
the Conditions of Industrial Process.
I. Influence of Temperature and Pressure on the Rate
of the Process in a Bubbling Type Reactor
V. I. Zhukova, G. V. Val’kovicha, B. N. Skorika, Yu. M. Petrova, and G. P. Belovb
aLukoil-Neftekhim Group, Stavrolen Co., Budenovsk, Russia
bInstitute of Probems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Russia
e-mail: gbelov@cat.icp.ac.ru
Received April 19, 2005
Abstract—Analysis of mass and heat balance in the reaction node of the process of ethylene dimerization into but-
1-ene under the industrial conditions is performed. It is found that ethylene concentration in the reactor liquid
phase by a complex way depends on the reactor temperature, pressure and but-1-ene concentration in the liquid
phase. Optimal process temperature is 80−90°C, operating pressure in the reactor is 0.6−0.8 MPa. Increase in pres-
sure above 1 MPa practically excludes heat withdraw via but-1-ene evaporation and makes the system of heat
withdrawing ineffective.
DOI: 10.1134/S1070427207070385
But-1-ene is the most widespread, after ethylene
and propylene, monomer of olefin series and it is more
and more used in the plastics industry for the synthesis
of linear medium and low density polyethylene, isotac-
tic polybutene, polybutylene oils and copolymers with
propylene. For the solving a problem of obtaining but-
1-ene of polymerization purity grade, a new technol-
ogy of high-selective catalytic dimerization of ethyl-
ene into but-1-ene has been developed.
Now in the world industrial practice two variants
of technology for manufacturing but-1-ene of polym-
erization purity are in application:
—The variant “Alfa-okhtol” [1–3] developed in the
Institute of Probems of Chemical Physics, Russian
Academy of Sciences in cooperation with industrial
branch institutions and applied in the beginning of 80th
of 20th century in the biggest plants in Kazan and
Budenovsk for manufacturing polyethylene; its princi-
pal scheme is shown in Fig. 1.
dimerization is perrgformed in liqid phase with the ho-
mogenous catalytic system tetrabutoxytitan–
tralkylaluminum–modificator. As a solvent basically
is applied a mixture of isohexenes (hereinafter in the
text hexenes) formed as by-products in the process of
ethylene dimerization, or a mixture of but-1-ene and
hexenes. In the process of dimerization a mixture of
but-1-ene and hexenes of the following composition is
formed: hex-1-ene 10 wt %, 2-ethylbut-1-ene 60 wt %,
3-methylpent-1-ene 30 wt %. Besides hexenes, as a
side product in a small amount are formed octenes and
a polymer, which in the further consideration are not
accounted for.
Mathematic model of the reaction of ethylene
dimerization into but-1-ene on the Ti(OR)4–AlR'3 cata-
lytic system has been considered in [5].
The technology of dimerization in the “Alfa-
okhtol” variant (Fig. 1) assumes heat withdrawing by
circulation of evaporating liquid phase from the reactor
I as a vapor-gas mixture (g3 flow) through condenser II
with further returning of the gas phase (g6 flow) and a
part of liquid phase (g9 flow) from the condenser II
into reactor I. The material flows by this scheme are
shown in Fig. 2.
—The variant “Alfa-butol” of the French Oil Insti-
tute, applied in 80th of 20th century [4], based on the
investigations of the Institute of Probems of Chemical
Physics, Russian Academy of Science.
In both these variants the process of ethylene
1195

1196
ZHUKOV et al.
When liquid phase presents in the reactor and con-
denser, all abovementioned hydrocarbons are in equi-
librium. The ethylene, but-1-ene and hexenes concen-
trations in gas and liquid phases depend on several
factors:
The process temperature,
Pressure in the reactor I,
The process selectivity,
Values of the flows g2, g5 and g6, (Fig. 2),
Ratio of the flows g3/g4 and g9/g7.
Taking into account a large number of variables
defining composition of liquid and gas phases, it was
attempted to develop algorithms of mass and heat bal-
ances proceeding from the suggestion that gas and liq-
uid phase are in equilibrium and the relations below
are fulfilled.
For the reactor I:
Ypc2 + Ypc4 + Ypc6 = 1,
Xpc2 + Xpc4 + Xpc6 = 1,
Kp = Yp / Xp .
(1)
(2)
(3)
(4)
Fig. 1. Principal technological scheme of reaction node for
ethlene to but-1-ene dimerizationaccording in “Alfa-okhtol”
process. (I) reactor, (II, IV) condensers, (III) circulation
compressor.
i
i
i
g4 = g3 (I − Ep) / Ep,
where g3, g4 denote amount of gas and liquid, respec-
tively, leaving reactor I, kgmol/h; Yp , Yp , Yp ,
c2
c4
c6
Xp , Xp , Xp are molar fractions of ethylene, but-1-
c2
c4
c6
Such a technology is used in the processes of po-
lymerization of low molecular weight olefins [6] and
ene and hexenes in gas (Y) and liquid (X) phases of
the reactor, Kp are the constants of phase equilibrium
i
in suspension
merization [7].
ethylene and propylene copoly-
for ethylene, but-1-ene and hexenes at the temperature
and pressure that occurred in the reactor (elucidated by
Fig. 2. Scheme of material flows in the reaction node for ethylene to but-1-ene dimerization by “Alfa-okhtol” process.
(I) reactor, (II) condenser. Flows: (g1) ethylene, (g2, g5) hexenes, (g3) vapor-gas mixture from the reactor to condenser, (g4)
liquid phase from the reactor bottom, (g6) gas phase from condenser to the reactor, (g7) liquid phase from condenser, (g8)
liquid phase from condenser to rectification, (g9) liquid phase from condenser to reactor, (g10) the sum of flows g1, g2, g6,
and g7.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 7 2007

SELECTIVE DIMERIZATION OF ETHYLENE TO BUT-1-ENE. I.
1197
calculation or from published data); Ep is mole fraction
of distillate of the g10 flow feeding into the reactor
take it equal to 0.1; 0.5; 0.9.
Relations between the concentrations of compo-
nents in the reactor gas phase and condenser liquid
phase are expressed as follows:
g10 = g3 / Ep.
(5)
XxC2 = YpC2/(I+A)[Ex(KxC2 − 1) + 1],
XxC4 = YpC4/(I+A)[Ex(KxC4 −1) + 1],
(14)
(15)
For the determination of olefins (ethylene, but-1-
ene and hexenes) concentrations in the reactor liquid or
gas phase it should be defined concentration of one of
them and operating conditions in the reactor, e.g.:
Xpc4 = 0.1; 0.25; 0.5; 0.75
XxC6 = YpC6 +A/(I+A)[Ex(KxC6 −1) + 1]. (16)
The reactor mass balance of dimerization on the
but-1-ene is expressed as:
Temperature 50, 60, 70, 80, 90°C
Pressure 0.6, 0.8, 1.0 MPa
For condenser II:
g3 ·YpC4 + g4 · XpC4 = g6 · YxC4 +g9 · XxC4 +GC4 (17)
Yxc2 + Yxc4 + Yxc6 = 1,
Xxc2 + Xxc4 + Xxc6 = 1,
Kx = Yx / Xx ,
(6)
(7)
(8)
(9)
where GC4 is amount of the formed but-1-ene in
kgmol/h, other flows are shown in Fig. 2 and by rela-
tions (1, 2, 6, 7).
Using above relations (1)–(16) we transform rela-
tion (17) to otain the following dependence:
i
i
i
g7 = g6 (I − Ex) / Ex ,
where g6, g7 denote amount of gas and liquid, respec-
tively, leaving condenser II, kgmol/h; Yx , Yx , Yx ,
GC4 = g3XpC4 · [Ep(KpC4−1) + 1/Ep
c2
c4
c6
Xx , Xx , Xx are molar fractions of ethylene, but-1-
− KpC4 · Ex(KxC4 − B) + B/Ex(KxC4 − 1) + 1]
(18)
c2
c4
c6
ene and hexenes in gas (Y) and liquid (X) phases of
the condenser, Kx are the constants of phase equilib-
The amount of ethylene gC4C2 consumed for the forma-
tion of but-1-ene in kgmol/h equals:
i
rium for ethylene, but-1-ene and hexenes at the given
temperature and pressure 0.6, 0.8, 1.0 MPa; Ex is mole
fraction of distillate of the g11 flow (under the condi-
tions occurred in the condenser), hence
gC4C2 = 2GC4
(19)
The total amount of ethylene used for the forma-
g11 = g6 / Ex,
11 = g3 + g5 ,
g5 = g3·A.
(10)
(11)
(12)
tion of but-1-ene and hexenes gC4+C6 is expressed by
C2
g
the relation:
gC4+C6C2 = 2GC4
(20)
The A value can vary in the range 0–1.0, optimally
0–0.1.
The liquid phase from the condenser (g7 flow) is
devided into two flows:
1. The flow g8 is directed to rectification.
where S is the process selectivity of dimerization on
but-1-ene.
The mass balance on ethylene is expressed as:
g1 = gэтС4+С6 + g4XpC2+g8Xx
(21)
C2
2. The flow g9 is returned to the reactor for heat with-
drawing
The mass balance on hexenes is expressed by the
relations below:
g9 = B·g7.
(13)
Amount of the formed hexenes
The B value can vary from 0 to 1, and further we
GC6 = 2GC4(1−S)/3S.
(22)
____________
⎛
⎜
P
⎞
⎟
KCP 1-B 1-EX
⎡
⎢
⎢
⎤
2XCP
(
)
(
1-EP
⎡
⎢
⎤
⎥
E
KP -1 +1 KP EX KX -B + B
(
)
(
)
)
C4
C4
C4
P
2
4
⎥
⎥
g1 = g3
-
+ XC
+
EX KX -1 +1
EX KX -1 +1
S
EP
EP
2
⎜
⎜
⎝
⎟
⎟
⎠
⎢
⎥
(
)
C4
(
)
C2
⎣
⎦
⎢
⎣
⎥
⎦
,
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 7 2007

1198
ZHUKOV et al.
⎛
⎜
⎞
⎟
1 - E P
E X
⎡
⎤
⎥
⎡
⎤
P
P
X
g2 = g3 X C KCP
+
- K P X C + A B 1 - E
1 + A +
-
⎢
(
)
)
(
)
(
⎢
⎥
⎦
C6
E P
6
6
6
E X K X -1 +1
⎜
⎟
⎠
⎢
⎥
⎣
(
)
C6
⎣
⎦
⎝
P
P
K P -1 +1
E X K X - B + B
C4
⎡
⎤
⎥
E
2 X C 1 - S
(
)
(
)
)
(
3S
)
C4
4
⎢
-g3
- KCP
E P
4
E X K X -1 +1
⎢
⎥
(
C4
.
⎣
⎦
____________
g3+g4
Amount of hexenes GC6
the flows g3 and g4:
leaving reactor with
ing certain relations it is necessary:
define flow g3 = 1 kgmol/h
define molar concentration Xpc4 = 0.1, 0.25, 0.5
define A = 0, 0.1
gC6g3+g4 = g3 YpC6 + g4 Xp
.
C6
(23)
.
define B = 0.1, 0.5, 0.9
Amount of hexenes formed in the dimerization
process and incoming with the flows g6 and g9
At the given dimerization conditions on tempera-
ture and pressure, the values of all flow can be calcu-
lated. These values will be true when the reactor heat
balance is fulfilled.
Income of heat into the reactor is expressed by the
relation
gC6g6+g9+Gc6 = g9 XxC6 + g6YxC6 + GC6.
(24)
and
g6+g9+Gc6
g2 = gC6g3+g4 − gC6
.
(25)
Qincome = Q1 + Q6 + Q9 + Q2 + Qreaction
,
(26)
Transforming relations 21 and 25 and using (1) to
where Qincome, Q1, Q6, Q9, Q2 and Qreaction , are the
amount of heat incoming to the reactor totally, of the
flows g1, g2, g6, g9, and of the reaction heat, respec-
tively.
The heat outcome from the reactor is expressed by
the relation:
(20) we obtain expressions for g1 and g2 showing (see
Fig. 2) that they are functions of the flow g3, but-1-ene
concentration in the liquid phase of the reactor Xp ,
c4
phase equilibrium constants Ki at the temperatures in
the reactor and in condenser, and of B value:
The flow value g1 will be shown to depend also on eth-
Qoutcome = Q3 + Q4 + Qloss
,
(27)
ylene concentration in the reactor liquid phse Xpc2 and
flow g2 on the hexenes concentration Xp , A value and
c6
where Qoutcome, Q3, Q4, and Qloss are respectively total
outcoming heat, the heat of flows g3, and g4 and the
the process selectivity.
Such a system has many solutions, and for obtain-
Fig. 3. Plots of ethylene concentration in the reactor liquid phase on but-1-ene concentration in the reactor liquid phase at
different temperature and pressure. Pressure, MPa: (a) 0.6, (b) 0.8, (c) 1.0. Temperature, ºC: (1) 50, (2) 60, (3) 70, (4) 80,
(5) 90.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 7 2007

SELECTIVE DIMERIZATION OF ETHYLENE TO BUT-1-ENE. I.
1199
Fig. 4. Plots of ethylene amount gC2 consumed for the
Fig. 5. Dependence of maximum productivity of reaction
formation of but-1-ene and hexenes, on the process pressure,
node G on the pressure; (1) A = 0; (2) A = 0.1.
at Xp = 0.1; B= 0.1, 0.5, 0.9; (a) at the temperature 80ºC,
C4
(b) at the temperature 90ºC.
losses of heat to environment.
ethylene.
Despite the increase of ethylene concentration in
the reactor liquid phase, the amount of ethylene con-
sumed for the formation of but-1-ene and hexenes falls
down. The plots obtained are shown in Fig. 4.
The reaction node productivity as a dependence on
the pressure is defined by the expression:
Q
income = Q3 + Q4 + Qoutcome
.
(28)
Join solution of the above relations allows to ana-
lyze influence of temperature and pressure on the proc-
ess rete in the bubble type reactor.
The rate and selectivity of the dimerization proc-
ess an hence the values of g1, g2 flows are affected by
the concentration of ethylene in the recator liquid
phase which in turn, as seen from Fig. 3, depends on
the following factors: pressure, temperature and but-1-
ene concentration in the reactor liquid phase.
Analysis of the data obtained shows that increase
in pressure from 0.6 to 1.0 MPa increases ethylene
concentration by the factor 1.5 to 2; increase in the
process temperature from 50°C to 90°C decreases eth-
ylene concentration in the reactor liquid phase by the
factor 1.5 to 3, increase in but-1-ene concentration in
the reactor liquid phase leads to decrease in ethylene
concentration by the factor 1.5 to 2. Hence, maximum
ethylene concentration occurs at the pressure 1.0 MPa,
∆t = 50°C, and at mimimum concentration of but-1-
ene in the reactor liquid phase.
g6 · gc2 · P
work
G =
kgmol/h,
E 1+ A
(
)
x
where g6 is is circulation compressor discharge (flow
g6), Ex is the distillate fraction in condenser, g2 is
amount of ethylene consumed in the process of ethyl-
ene dimerization at the value of flow g3 = 1 kgmol/h,
Pwork is working pressure.
The calculations show that maximum output of the
reaction node falls by factor more than 3 in the pres-
sure range 0.6 to 1.0 MPa (Fig. 5). Hence, it can be
said that increase in pressure over 1.0 MPa practically
excludes heat withdraw in account of evaporation of
but-1-ene and makes this system of heat withdraw in-
effective.
The dependence of ethylene amount on the tem-
perature in the reactor or on the temperature difference
between reactor and condenser ∆t (tcondenser = 40ºC),
which can be consumed for the dimerization reaction
Further analysis shows that temperature and pres-
sure affect oppositely the ethylene concentration in the
reactor liquid phase and on the amount of consumed
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 7 2007

1200
ZHUKOV et al.
Fig. 6. Plots of ethylene amount gC2 consumed for the formation of but-1-ene and hexenes, on the difference in the reactor
and condenser temperatures ∆t. Pressure, MPa: (a) 0.6, (b) 0.8, (c) 1.0; parameters: Xp = 0.1; A = 0; B: (1) 0.1, (2) 0.5,
C4
(3) 0.9.
without disturbance of heat and mass balances, is
shown in Fig. 6. As seen, at ∆t = 10ºC the reaction
node maximum output is minimal, while at ∆t = 40 to
50ºC it increases sharply. Depending on the pressure
and B value the output at ∆t = 40ºC grows by the fac-
tor 10 to 20, at ∆t = 50ºC by factor 20 to 70. It should
be noted that B value does not affect output at the ∆t =
10ºC, while at ∆t = 50ºC increase in B from 0.1 to 0.9
leads to increase in output by factor 1.5 to 2.
Thus, considering two characteristics of the indus-
trial process of ethylene to but-1-ene dimerization in
the bubble type reactor, the reactor productivity
(amount of ethylene consumed g1) and ethylene con-
centration in the reactor liquid phase it possible to con-
clude:
ture, pressure and but-1-ene concentration in liquid
phase.
Hence, for the considered scheme of technological
process the optimum temperature in the reactor is 80 to
90ºC, the optimum pressure is 0.6 to 0.8 MPa.
REFERENCES
1. Ivanchev, S.S., Zhukov, V.I., Belov, G.P., Ivolgina, S.R.,
Germashev, A.I., Gabutdinov, M.S., and Shestak, N.P.,
Plasticheskie Massy, 1990, vol. 10, p. 82.
2. Zhukov, V.I., Belov, G.P., Germashev, A.I., and Saush-
kin, Yu.I., Plasticheskie Massy, 1996, no. 5, p. 6.
3. Belov, G.P., Borodin, A.M., Val’kovich, G.V., Zhu-
kov, V.I., Polevshchikov, N.P., Petrov, Yu.M., and
Skorik, I.N., Summa tekhnologii (Review of Russian
Technologies), 2001, no. 1, p. 79.
4. Neftegazovye Tekhnologii, 1995, no. 5, p. 39.
5. Belov, G.P., Psikha, B.L., Furman, G.A., Davtyan, S.P.,
and Agasaryan, A.V., Neftekhimiya, 1990, vol. 30,
no. 5, p. 609.
6. Zhukov, V.I., Sergienko, G.S., and Frid, M.M., Plas-
ticheskie Massy, 1986, no. 2, p. 15.
–Increase in the process temperature to 90ºC leads
to grow in amount of consumed ethylene.
–Increase in pressure is not reasonable because grow
in the reaction node productivity is much lower than
increase in ethylene concentration in the reactor liq-
uid phase and besides is restricted by the conditions
of heat withdraw.
7. Arutyunov, I.A., Zhuravlev, V.P., Markosov, P.I., Dan-
nik, V.P., and Rezumenko, Z.Ya., Promyshlennost’ Sin-
teticheskogo Kauchuka, 1971, no. 2, p. 10.
–Ethylene concentration in the reactor liquid phase
by complicate way depends on the reactor tempera-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 80 No. 7 2007