Recovery of isobutylene from commercial butane-butylene fractions

Article abstract of DOI:10.1023/A:1012799724474

A possibility of recovery of isobutylene with high concentration and purity from abgases of petroleum production and oil refining, e.g., from gases released in pyrolysis or catalytic cracking, by reversible reaction of isobutylene with isobutanol was studied.

Full text of DOI:10.1023/A:1012799724474

Russian Journal of Applied Chemistry, Vol. 74, No. 4, 2001, pp. 691 695. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 4, 2001,
pp. 670 674.
Original Russian Text Copyright
2001 by Sharonov, Rozhnov, Karaseva, Myshentseva, Barkov, Alenin.
CHEMISTRY
OF FOSSIL FUEL
Recovery of Isobutylene
from Commercial Butane Butylene Fractions
K. G. Sharonov, A. M. Rozhnov, S. Ya. Karaseva, Yu. B. Myshentseva,
V. I. Barkov, and V. I. Alenin
Samara State Technical University, Samara, Russia
Received February 28, 2000; in final form, September 2000
Abstract A possibility of recovery of isobutylene with high concentration and purity from abgases of pe-
troleum production and oil refining, e.g., from gases released in pyrolysis or catalytic cracking, by reversible
reaction of isobutylene with isobutanol was studied.
In recent years, the production of methyl tert-butyl
ether (MTBE) and methyl tert-amyl ether (MTAE) by
alkylation of methanol with isoolefins has increased
in many countries. These compounds are used as ad-
ditives to motor fuel.
These drawbacks are lacking in the case of the re-
action of isobutylene with aliphatic alcohols C C .
The reaction yields tert-alkyl ethers, which are subse-
4
5
quently decomposed.
The procedure for synthesizing MTBE and MTAE
was thoroughly studied and discussed in [1]. As re-
gards synthesis, and especially decomposition of ethers
of higher alcohols, a number of problems still remain
unsolved. It is well known [2, 3] that the reactivity
of alcohols and the equilibrium degree of their con-
version in the reaction with isobutylene decrease with
increasing molecular weight of alcohol (Table 1). In
addition, butyl alcohols do not undergo intermolecular
dehydration on sulfonic cation exchanger (contrary to
methanol and ethanol) and have higher boiling point.
Therefore, the use of butyl alcohols as chemical ex-
tracting agents for recovery of isoolefins is of prac-
tical interest.
The hydrocarbon fractions C C of gases released
4
5
in pyrolysis and catalytic cracking can be used as
low-cost raw materials for production of isoolefins.
A review of procedures for recovery of isoolefins from
hydrocarbon gases was given in [1]. The procedures
are based on the high reactivity of the tertiary carbon
atom at the double bond in reactions of electrophilic
addition. With many reagents (water, alcohols, and
acids), such reactions are reversible, which allows
recovery of concentrated isoolefins by subsequent
decomposition of these products.
Strong acids, such as sulfuric, hydrochloric, organ-
ic sulfonic acids, and Friedel Crafts catalysts can cat-
alyze this reaction. The common drawback of these
acids is their high corrosion activity and the low se-
lectivity of the process. The use of weak acids, e.g.,
phosphoric, is inefficient owing to the low rate of the
process. Of most interest as catalysts are sulfonic cat-
ion exchangers, allowing the reaction to be performed
with high selectivity at low temperatures (85 90 C).
In this work the possibility of recovery of isobutyl-
ene from pyrolysis gases by the reaction with isobu-
tanol was demonstrated by calculations and exper-
iments.
Table 1. Rate constants b and equilibrium constants K for
c
*
alkylation of alcohols with isobutylene at 323 K [2, 3]
+
However, the procedure for hydration recovery of
isobutylene via trimethylcarbinol (TMC), in which
sulfonic cation exchangers are used as catalysts, has
significant drawbacks: (1) the use of aqueous solutions
decreases the catalytic activity of sulfonic cation ex-
changer, and (2) concentrated isobutylene-containing
fractions (with isobutylene content of no less than
Alcohol
b, H -equiv mol 1 h 1
K
c
Methanol
Ethanol
Propanol
Butanol
Pentanol
0.28
1.58
2.63
3.53
5.92
12.8 2.0
76.1 2.0
137.6 1.8
150.3 1.8
160.6 1.8
*
5
0 wt %) are used.
For stoichiometric ratio of the initial components.
1
070-4272/01/7404-0691 $25.00 2001 MAIK Nauka/Interperiodica

6
92
SHARONOV et al.
Table 2. Data on the equilibrium of reaction (1) in the liquid phase in the presence of sulfonic cation exchanger KU-23
at molar ratio alcohol : isobutylene = 4 : 1
Composition of equilibrium
mixture, mole fraction
Activity coefficient
Num-
ber
of
Catalyst
content,
mol %
i
T,
K
Kc
=
Ka
=
, h
*
eth/ al ol
KcK
iso-
C4H8
iso-
C H OH
iso-
tests
BTBE
0.2330
BTBE olefin
C H OH
4
9
4 9
3
3
3
4
4
43 10 15
63 10 15
83 10 12
13
14
12
12
13
9 23 0.01360
9 15 0.02439
10 17 0.04251
0.7534
0.7561
0.7606
0.7661
0.7724
2270 0.36
1.079
1.073
1.066
1.058
1.049
2.087 1.551
2.033 1.544
1.995 1.546
1.965 1.555
1.941 1.568
28.46
14.64
7.37
4.10
2.36
0.2195 11.90 0.31
0.1968
0.1693
0.1382
6.09 0.18
3.42 0.21
2.00 0.13
03
23
8 10
8 10
1.5 5
0.75 5
0.06459
0.08946
*
K = eth/ al ol
.
Table 3. Concentration equilibrium constants Kc of reaction (1) at various iso-C H OH : iso-C H molar ratios
4
9
4 8
Molar ratio iso-C H OH : iso-C H
4
9
4
8
T, K
Ka
1 : 1
2 : 1
5 : 1
10 : 1
20 : 1
Kc
Kc
Kc
Kc
Kc
Kc
Kc
Kc
Kc
Kc
343
363
383
403
423
27.66
13.73
7.33
4.17
2.50
114.18 140.42
57.46
26.72
13.38
7.16
59.44
27.91
14.00
7.48
28.65
14.27
7.62
4.32
2.59
28.65
14.28
7.63
4.41
2.59
21.56
10.89
5.90
3.41
2.07
21.53
10.88
5.90
3.40
2.07
18.46
9.38
5.11
2.97
1.81
18.45
9.37
5.11
2.97
1.81
47.34
21.75
1 .97
6.00
57.21
25.64
12.54
6.65
4.09
4.98
It has been shown in a number of studies concerned
with synthesis of MTBE and MTAB [4, 5] that the
The reaction products were analyzed by gas-liquid
chromatography on a KhROM-3.1 device equipped
with a flame-ionization detector and temperature pro-
gramming unit on a 6-m-long column packed with
15% PEG-20M on silanized Chromaton AW-HDMS.
The results of the experiments are given in Table 2
concentration equilibrium constant K does not cor-
c
respond to the thermodynamic constant K owing
a
to deviation of the system alcohol ether isobutylene
from ideality. At the same time, at the molar ratio
alcohol : isobutylene equal to 3 : 1 and higher the con-
centration equilibrium constant becomes stable. The
equilibrium of the reaction
listing the activity coefficients of the mixture com-
i
ponents and the thermodynamic equilibrium constants
K . The values of were calculated by the UNIFAC
a
i
technique [6], using the quantitative data for molec-
ular fragments given in [7]. The resulting equilibrium
CH CH CH OH + CH =C(CH )
3 2
3
2
2
CH CH CH O C(CH )
(1)
constants K are described by the equation
3
2
3 3
a
log Ka
=
4.08 + 1894/T.
(2)
was studied in the liquid phase in the range 343
4
23 K. The experiments were carried out in her-
With the use of K values, we calculated the equi-
librium composition of the products of reaction (1) by
the scheme
a
metically sealed glass ampules in the presence of
KU-23 sulfonic cation exchanger as catalyst. For
the study, we used isobutylene (99.8 wt %), isobuta-
nol (99.8 wt %), and isobutyl tert-butyl ether (ITBE)
Ka
(composition)
UIFAC
K
K = K /K . (3)
c a
(98.5 wt %).
In doing so, the butane-butylene fraction with iso-
Isobutyl tert-butyl ether was produced by the re-
action of isobutylene with isobutanol, with subsequent
rectification. The equilibrium for each temperature
butylene content of 20 mol % was used as isobutyl-
ene-containing fraction. The calculations were carried
out for the range 343 423 K and iso-C H : iso-
4
8
was reached for both direct and reverse reactions. C H OH molar ratios of 1 : 1, 1 : 2, 1 : 5, 1 : 10, and
4
9
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 4 2001

RECOVERY OF ISOBUTYLENE FROM COMMERCIAL BUTANE BUTYLENE FRACTIONS
693
Table 4. Material balance of IBTBE synthesis at 333 K and molar ratio isobutanol : isobutylene of 2 : 1
Passed
Obtained
Component
liquid phase
gas phase
g h 1
wt %
g h 1
wt %
g h 1
wt %
Isobutane
n-Butane
-Butene
4.1
2.6
2.88
1.83
0.4
0.3
0.44
0.33
5.34
0.22
0.98
1.31
0.01
0.05
38.17
52.47
0.25
0.33
3.7
2.3
7.33
4.56
45.73
15.25
10.50
2.38
0.18
2.87
4.10
6.54
0.20
0.36
1
28.0
7.9
19.69
5.56
4.9
23.1
7.7
trans-2-Butene
cis-2-Butene
Isobutylene
Butadiene
0.2
6.2
4.36
0.9
5.3
1.2
25.2
0.1
17.72
0.07
1.2
0.01
0.05
35.0
48.1
0.23
0.30
0.09
1.45
2.07
3.30
0.10
0.18
C -acetylene
1.5
1.05
4
Isobutanol
66.6
46.84
IBTBE
Isobutene dimers
Trimethylcarbinol
Total
142.2
100.0
91.69
100.0
50.49
100.0
1
: 20. The value of K was determined using approx-
The experimental values of the concentration equi-
c
imation procedure by the scheme
librium constant K for IBTBE synthesis were used
c
to evaluate the equilibrium degree of conversion of
ether in its decomposition. The evaluation was carried
out for the range 353 403 K and isobutanol : IBTBE
molar ratios of 1 : 1, 2 : 1, and 3 : 1. The results of
evaluation are represented by lines in Fig. 2. Also
Ka
(composition, K )
composition, K )
Kc
Kc
Kc .
(
=
(composition, K )
(4)
The approximation was considered acceptable when
the discrepancy in K values did not exceed 10 rel.%.
c
The results of calculations performed by scheme
4), presented in Table 3, suggest that even the first
(
approximation gives K constants coinciding with
c
K within 10 abs.%. A plot of the equilibrium con-
c
version of isobutylene against temperature at various
alcohol : isobutylene ratios is presented in Fig. 1.
The calculations showed that the equilibrium conver-
sion of isobutylene is close to 100% at low tempera-
ture andalcohol : isobutylene molar ratio exceeding
5
: 1. The calculations also confirmed that hydrocar-
Fig. 1. Equilibrium conversion of isobutylene, , vs. tem-
perature T in IBTBE synthesis.
bon gases with isobutylene content of approximately
5
wt % are suitable as feed.
The obtained calculated and experimental data were
verified on a continuous laboratory setup in a temper-
ature-controlled sectional vertical reactor packed with
KU-23 cation exchanger, using butane butylene frac-
1
tion from the catalytic cracking installation and iso-
butanol. The initial isobutanol-containing mixture was
fed from the top of the reactor, and the gaseous bu-
tane-butylene fraction, from the bottom through a bub-
bler. The material balance of the synthesis is pres-
ented in Table 4. The degree of isobutylene recovery
was 90 92%.
Fig. 2. Equilibrium conversion of IBTBE, , vs. temper-
ature T in its decomposition. Isobutanol : IBTBE molar
ratio: (1) 1 : 1, (2) 2 : 1, and (3) 3 : 1. (Line) calculation
and (points) experimental data.
1
Sintezkauchuk (Togliatti).
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 4 2001

6
94
SHARONOV et al.
Table 5. IBTBE decomposition in a flow-type reactor at 363 K and equimolar ratio of the ether and alcohol
Composition of the reaction mass, wt %
IBTBE
Selectivity with
Relative
error of
v, h 1
conversion respect to isobutylene
isobutylene
dimers
material
balance, %
iso-C H
iso-C H OH
IBTBE
4
8
4 9
mol %
0
0
1
3
5
8
.3
.5
.0
.0
.0
.0
2.38
6.60
2.16
4.09
4.96
6.02
8.23
88.33
82.83
92.70
89.52
86.24
77.76
68.23
8.86
8.48
5.04
6.20
8.57
16.05
23.39
0.43
2.09
0.10
0.19
0.23
0.17
0.15
85.24
85.87
91.60
89.67
85.07
73.27
61.04
99.17
96.11
99.82
99.65
99.55
99.62
99.61
0.35
0.49
1.09
1.50
0.60
0.34
0.72
1
2.0
given are the experimental IBTBE conversions (points)
in IBTBE decomposition at 363 K, isobutanol :
IBTBE molar ratio in the feed of 1 : 1, 2 : 1, and 3 : 1,
butylene fraction of catalytic cracking or pyrolysis
gas: etherification of isobutyle with alcohols C4
blowing off of unreacted hydrocarbons from the ether
1
and volumetric flow rate of feed equal to 1 h .
fraction
decomposition of ether to isobutylene
The results of these experiments showed that removal
of isobutylene from the reaction zone increases the
IBTBE conversion to 91.6%, compared with the equi-
librium value of 21%.
successive washing of isobutylene with alcohol
C4 cooled to 263 K and water. Isobutylene pro-
duced by this scheme was of no less than 99.9 wt %
purity.
The calculations showed that the optimal dilution
is the alcohol : ether ratio of 1 : 1. With increasing
dilution, the conversion of the ether decreases. Al-
though the ether decomposition is a high-tempera-
ture reaction, the temperature should not be raised
above 120 C because of the probable polymerization
of isobutylene and degradation of sulfonic cation ex-
changer.
CONCLUSIONS
(
1) The equilibrium of synthesis and decomposi-
tion of isobutyl tert-butyl ether in the presence of sul-
fonic cation exchanger KU-23 was studied. The equi-
librium conversion of isobutylene in synthesis is close
to 100% at alcohol : isobutylene molar ratios of 5 : 1
and 10 : 1. An experimental verification of the equi-
librium data showed that the isobutylene conversion
is 90 92%.
The experiments on IBTBE decomposition were
carried out in the liquid phase in a temperature-con-
trolled flow-type reactor packed with KU-23 cation
exchanger. A system of traps was mounted at the out-
let of the reactor. The first trap served to collect
the liquid reaction mass, and the second trap con-
tained a 0.5 N solution of bromine in acetic acid to
absorb the released isobutylene. The reaction mass of
the first trap was analyzed on a chromatograph with-
out any pretreatment. The material balance was strick-
en for each run. The maximum error with respect to
material balance was 6.54 rel.%.
(
2) The calculations showed that it is appropriate
to carry out the decomposition of isobutyl tert-butyl
ether in a solution of isobutanol at the optimal alco-
hol : ether molar ratio of 1 : 1. The ether conversion in
a flow-type reactor at 363 K reaches 91% and the se-
lectivity is more than 99% at a volumetric flow rate of
1
feed equal to 1 h .
(3) A scheme for recovery of isobutylene from
dilute gas mixtures was proposed.
The experiments were performed at varied tem-
perature, isobutanol : IBTBE molar ratio, and volu-
metric feed flow rate v. In each run, we determined
the conversion and selectivity of ether decomposition.
The results of one of ether decomposition runs are
presented in Table 5.
ACKNOWLEDGMENTS
The study was financially supported in part by
the Russian Foundation for Basic Research (project
no. 99-03-32312a), the Russian Universities Basic
Research Intercollegiate Program (project no. 991065),
and the Siberian Division of the Russian Academy of
Sciences (Program for Support of Young Scientists).
This study allows us to propose the following
scheme of isobutylene recovery from the butane
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 4 2001

RECOVERY OF ISOBUTYLENE FROM COMMERCIAL BUTANE BUTYLENE FRACTIONS
695
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RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 4 2001