hydration of propylene to isopropanol - stars
TRANSCRIPT
University of Central Florida University of Central Florida
STARS STARS
Retrospective Theses and Dissertations
1987
Hydration of Propylene to Isopropanol Hydration of Propylene to Isopropanol
Nehemiah Diala University of Central Florida
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HYDRATION OF PROPYLENE TO ISOPROPANOL
BY
Nehemiah Diala B.S., Rust College, 1983
Research Report
Submitted in partial fulfillment of the requirements for the Master of Science degree in Industrial Chemistry
in the Graduate Studies Program of the College of Arts and Sciences University of Central Florida
Orlando, Florida
Spring Term 1987
ABSTRACT
The hydration of propylene to isopropanol was investigated. The
first part of this study concerned the direct hydration reaction in
various liquid phase systems in the presence of sulfuric acid or
p-toluenesulfonic acid. The second part involved a two-stage process in
which propylene was contacted with excess acetic acid to form isopropyl
acetate; the ester was then hydrolyzed to isopropyl alcohol and acetic
acid.
ACKNOWLEDGEMENTS
I would like to express my appreciation to Dr. Guy Mattson for his
excellent contributions. I would also like to express my gratitude to
Imo State Government of Nigeria and to my senior brother, Mr. Samuel
Diala, for their financial assistance during my undergraduate and
graduate studies.
Finally, I would like to thank the Department of Chemistry at the
University of Central Florida for providing me with all the materials
that were used in this study.
i i i
TABLE OF CONTENTS
ACKNOWLEDGEMENTS
TABLE OF CONTENTS
LIST OF TABLES
LIST OF FIGURES
INTRODUCTION
Present technology
Reaction mechanism
Thermodynamic consideration
Kinetic Conversion
EXPERIMENTAL
Direct hydration
Indirect hydration-catalyst screening
Indirect hydration-isopropyl acetate formation
Indirect hydration-hydrolysis reaction
Analytical methods .•......•••
DISCUSSION OF RESULTS
CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . .
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . .
iv
i i i
iv
v
vi
1
1
5
5
9
12
12
14
17
17
20
21
27
28
LI ST OF TABLES
I. Standard free energies of formation 6
I I. Free energy change and equilibrium constants for the reaction •...••.... 7
I I I. Effect of temperature on equilibrium yield 8
IV. Effect of pressure on equilibrium yield 8
v. Effect of molar ratio on equilibrium yield 9
VI. Direct hydration of propylene 13
VI I. Direct hydration of cyclohexene 15
VIII. Reaction conditions for catalyst screening 16
IX. Formation of isopropyl acetate . . . . . . . . . . . . 18
x. Hydrolysis of isopropyl acetate . . . . . . . . . . . 19
v
LIST OF FIGURES
1. Relation of yield and reaction temperature formation of isopropyl acetate • . . • . • • . • . . 24
2. Relation of yield and reaction time formation of isopropyl acetate ...........•
vi
25
INTRODUCTION
Present Technology
The hydration of propylene to isopropanol has been the topic of
many experimental studies. The introduction of the first commercial
process for the manufacture of isopropanol in 1920 is considered to be
the origin of the modern synthetic petrochemical industry.
Berthelot discovered in 1855 that concentrated sulfuric acid
consumes a substantial amount of propylene.1,2 He observed that the
resulting solution when reacted with water produces an alcohol which
distills at 82°C. The configuration of the new compound was not known
until 1882. At that time, Kolbe proposed a structure for the alcohol
produced from reducing acetone over sodium amalgam. He observed that
this alcohol had similar properties to the alcohol Berthelot patented in
1855. Since 1855, many patents have described different processes for
producing isopropanol.3,4
1
~ (2)
H2~ CH3CH(OH)CH3
~) ( 1)
2
The need for isopropanol during and after World War II created a
market demand which increased rapidly. Isopropanol is used as a solvent
and a basic intermediate in the manufacture of other compounds. It can
also be used as a deicing agent, a rubbing agent and in the formulation
of shampoos, detergents and cosmetics. The increase in demand for
isopropanol has stimulated improvement in the technology of production.
Processes for the manufacture of isopropanol are based upon direct
or indirect hydration of propylene. Standard Oil of New Jersey
commercialized the first indirect, liquid phase hydration
process.1,5,6 Propylene was reacted with concentrated sulfuric acid to
form a sulfate ester which was then hydrolized with water to isopropanol
and dilute sulfuric acid. This process is still in use today, but it
has the disadvantages of high energy costs, very corrosive conditions
and pollution problems. The hydrolysis step yields a dilute aqueous
sulfuric acid solution, which is regenerated by submerged combustion.
The high temperatures involved in this process result in high energy
costs as well as corrosive damage. Materials such as silicon, iron,
teflon and graphite have been used for plant construction to minimize
damage. During the regeneration of the sulfuric acid, large amounts of
so2 are given off. This compound is an environmental nuisance from the
standpoint of air pollution. Also, large amounts of waste water are
generated which must be treated before disposal. These factors add to
the capital and operating costs. Despite these problems this process is
still being used by a number of producers because it gives a reasonable
conversion and efficiency and because it can utilize a rather low purity
propylene feed.
3
In 1947 the Shell Development Company developed the first direct
hydration process. 1 Propylene gas was contacted with steam to produce
isopropanol. Phosphoric acid catalyst on an inert support was used.
This is an equilibrium reaction. Improved equilibrium yields are
favored by low temperatures, high pressures and high water
concentration. However, there are a number of other factors which
determine the process conditions. The catalyst is not sufficiently
active to give useful reaction rates at low temperatures. Increases in
the water/propylene feed ratio decrease the formation of the two major
by-products, isopropyl ether and propylene polymers, as well as having a
favorable effect upon the equilibrium. Increasing the operating
pressure increases the equilibrium yield but increases polymer formation
and increases the capital cost of the plant. Large excesses of water,
combined with high pressures lead to catalyst deactivation by
accelerated depletion of the phosphoric acid from the catalyst support.
Other vapor phase processes include the ICI process. 6 This process
uses acidic oxide catalysts such as tungsten oxides which allow high
water/propylene feed ratios. These catalysts however are not
impressively active, so conversion rates are low and the high
temperatures required lead to decreased equilibrium yields.
More recently, a direct hydration process using a gas/liquid phase
in a trickle bed reactor was developed by Deutsche Texaco. It utilizes
a strong acid ion exchange resin as the catalyst.7 It allows high water
concentrations which favor higher equilibrium yields and suppress by
product formation. High pressures are necessary to increase the
solubility of the gaseous propylene in the liquid water.
In 1978, Tokyuama Soda announced the development of a liquid phase
direct hydration process. 7 The acidic catalyst system was described as
containing an "inorganic polyacid anion" and was said to resist
hydrolytic degradation. The principal advantages claimed are - high
conversions; improved catalyst life; and the elimination of corrosion
and pollution problems.
Direct hydration processes utilizing H3Po3, H2so4 and HCl at high
pressures and temperatures have also been reported.8,9 Although the
direct hydration processes generally require high pressures and a high
purity propylene feed, a number of commercial plants utilize direct
hydration.
4
This study concerns a search for alternate schemes to affect the
hydration of propylene. The first part of the work is based upon direct
hydration and is an investigation of various liquid phase systems
containing a strong acid catalyst and an agent to dissolve sufficient
propylene to achieve acceptable reaction rates at modest temperatures
and pressures. The second part of the work concerns the investigation
of an indirect process in which propylene is first reacted, in the
liquid phase, with acetic acid to form isopropyl acetate. The ester is
then hydrolyzed to isopropanol and acetic acid. After separation, the
dilute acetic acid would be concentrated and recycled. Such a process
could avoid the severe corrosion and pollution problems of the sulfuric
acid based indirect process. It could offer advantages over the vapor
phase processes in terms of conversion rates and over the direct
processes in propylene purity requirements.
5
Reaction Mechanism
All of the direct hydration processes utilize acidic catalysts.
Based upon fundamental studies on the reaction of other alkenes, such as
isobutylene, 10 it is commonly accepted that the mechanism involves a
carbocation intermediate and the overall reaction rate is proportional
to the acidity factor of the system.
With the exception of the work reported by Onoue et al. at Tokyuama
Soda, 7 there is no indication that the anion of the acidic catalyst
plays a direct role in the kinetics of the reaction.
Thermodynamic Considerations
(2)
Free energy calculations are a powerful tool that can be employed
to predict the equilibrium yield of a reaction. By definition the free
energy of a reaction is the energy change occurring when the reactants,
in their standard states, are converted to the products in their
standard states.11
tiGreaction = EtiGproducts - EtiGreactants (3)
6
Table I Standard free energies of formation
TemEerature OK 298 400 500 700 1000
CH3-CH=CH2 14.99 17.62 22.45 30.60 43.43
H2o -54.64 -53.52 -52.36 -49.92 -46.04
CH3-yH-CH3 -41.49 -33.17 -24.66 -7.07 19.93 OH
Using equation (3) and the values in Table I, it is possible to
calculate the free energy change for the following reaction:
(4)
Using these values for the free energy change of the reaction, and the
following relation:
6G reaction = -RT ln Kp (5)
the equilibrium constants can be calculated. For example, at 298°K
G ( 6GC3HgO)-( 6GH20 + 6 reaction =
= (-41,49)-(-54.64 + 14.99)
= -1.84 Kcal/mole
6Greaction = -RT ln Kp (6)
log KP = 6Greaction
2.303·1.987 cal/mole/°K·298°K
Kp = 22.36
7
Table II Free energy change and equilibrium constants for the reaction
Tem~erature °K 298 400 500 700
~GreactionKCal -1.84 +1.73 +5.25 +12.25
Kp 22.36 0.113 0.005 0.0015
It is noted in Table II that the equilibrium constant Kp decreases
rapidly as the temperature increases. These values of KP can be used to
calculate the equilibrium yield of isopropanol at various temperatures
as follows:
(7)
(8)
K = K P to ta 1 ~v p n ntota 1
at P total = 1 atm
nc3H80 ( 1 )
-1 KP = .
n -n ntota 1 c3H8 · H20
assuming an initial charge of 1 mole C3H5 and 1 mole H20 forming X moles
of C3H80 at 298°K -
22.36 x =~-~-~ (1-X)(l-X)
2-X -1-
X = 0.793 (79.3% yield)
In a similar manner the theoretical equilibrium yields at other
temperatures can be calculated. Also the effects of changes in total
pressure and the mole ratio of water and propylene can be determined.
The results are presented in Tables III, IV and V.
Table III Effect of temperature on equilibrium yield
(1 atmosphere, 1:1 mole ratio)
TEMPERATURE EQUILIBRIUM YIELD %
298
373
400 500
25
100
127 227
Effect
PRESSURE Atm PSIA
1 14.7
2 29.4
5 73.5
Table IV
79.3
13.8 5.2 0.2
of pressure on equilibrium yield (25°c, 1:1 mole ratio)
EQUILIBRIUM YIELD
79.3 85.2 90.6
%
8
Table V Effect of molar ratio on equilibrium yield
(loo0 c, 1 atm)
MOL RATIO C3H5/H20
1/1 1/10
1/100
EQUILIBRIUM YIELD %
13.8
24.0 25.6
These calculations, which do not consider reaction rates, by-product
formation or the problems of achieving the required concentrations of
reactants in the same phase with the catalyst, indicate the benefits of
a reaction system which has reasonable conversion rates at low
temperatures.
Kinetic Conversion
This approach to a consideration of the kinetics of this reaction
is based upon the following mechanism:
kl ___::::.....
~
k -~ ~ 4
(a)
It is assumed that the cation C3H7+ is very reactive; its concentration
is indeterminate but very small. The net rate of formation is assumed
to be zero.
9
(10)
The rate of formation of product is
(11)
This expression relates to a homogeneous reaction system. In a
heterogeneous system, where the reaction takes place on the surface of
a solid catalyst, the effective concentrations are not equal to the
concentrations in the bulk liquid or vapor. In such systems [H20J,
[C3H6] and [C3H70H] may be replaced by aw[H20J, ap[C 3H6] and aa[C 3H70H]
where the a represents a suitable distribution coefficient.
10
11
In a liquid phase system the problems of achieving effective
reaction rates at low temperatures and pressures involve the vastly
different solubility characteristics of propylene and water. In the
first part of this work, we have evaluated several unique solvent
systems such as toluenesulfonic acid/water, toluene/sulfuric acid/water,
toluene/sulfuric acid/water/surfactant and toluene/sulfuric
acid/water/phase transfer catalyst.
EXPERIMENTAL
The experimental work described in this section includes fourteen
runs to evaluate various catalysts for the direct hydration of propylene
in liquid phase systems. In order to more easily quantify the extent of
reaction four runs were made using cyclohexene as the alkene. Five
candidate catalysts for the acylation step of the indirect hydration
were screened using cyclohexene. Thirteen runs were made reacting
propylene with acetic acid and eight runs were made hydrolyzing
isopropyl acetate.
Direct hydration-catalyst screening
A preliminary series of runs were made at atmospheric pressure,
passing propylene gas through a p-toluenesulfonic acid/water (2/1)
system at 110° and 150°. No propylene was absorbed under these
conditions and these runs are not discussed further.
The runs made at pressures above atmospheric recorded in Table VI
were carried out in a Parr Model 4521 stirred Reactor. This stainless
steel reactor is equipped with three inlet valves, a rupture disc, a
pressure gage, two 6-blade impellers on the stirrer shaft and a Type J
thermocouple in a thermocouple well. The temperature was controlled by
a Parr Model 4831 automatic temperature controller. At the start of
each run the reactor was .charged with the water, candidate catalyst and
any solvent or surfactant. The reactor was then sealed, evacuated under
house vacuum and purged with propylene three times to displace air. The
reactor was then raised to the designated temperature and propylene
Tabl
e VI
D
irec
t hy
drat
ion
of p
ropy
lene
Res
iden
ce
Pres
sure
W
ater
C
atal
lst
Prop
ylen
e Te
mpe
ratu
re
IPA
Run
(gra
ms}
T~
~e
Amou
nt {g
ram
s}
Tim
e {H
rs)
{oq
~Si
form
ed
1 20
0 to
luen
e-su
lfon
ic a
cid
200
30.6
30
25
0-
50
no
2 20
0 to
luen
e-su
lfon
ic a
cid
200
30.8
6 30
.5
75-8
5 10
-50
yes
3 20
0 to
luen
e-su
lfon
ic a
cid
200
30.1
18
.5
100
60-1
00
yes
4 32
0 to
luen
e-su
lfon
ic a
cid
80
1.76
5
150
90-1
00
no
5 20
0 to
luen
e-su
lfon
ic a
cid
200
9.2
37
150
90-1
00
no
6 20
0 do
decy
lben
zene
-20
0 2.
6 10
10
0 90
-100
no
su
lfon
ic a
cid
7 20
0 to
luen
e 97
11
.5
21
100
80-1
00
yes
sulf
uric
aci
d 10
3 8
200
tolu
ene
297
41.3
3 5
90
70-1
00
no
sulf
uric
aci
d 10
3
9 70
to
luen
e 30
0 15
.25
8 10
0 70
-100
no
su
lfur
ic a
cid
30
10
70
tolu
ene
250
11.5
34
10
0 14
0 ye
s to
luen
e su
lfon
ic a
cid
95.5
11
70
tolu
ene
250
45.8
26
.5
25
140
no
tolu
ene
sulf
onic
aci
d 95
.5
12
70
tolu
ene
250
13.2
24
10
0 14
0 no
su
lfur
ic a
cid
95.5
13
200
tolu
ene
97
11.5
24
10
0 14
0 ye
s te
trap
heny
l bo
ron
sodi
um
2 su
lfur
ic a
cid
103
14
140
tolu
ene
160
32.2
48
10
0 13
5 ye
s ph
osph
oric
aci
d 20
0 (4
8% y
ield
) te
trap
hylb
oron
sod
ium
2
.....,
w
4
passed into t e reactor at the designated press re.. Pro ylene
absorption or reaction was indicated by a drop ·n press~ e. Under t ese
condit"ons tbe v lu e of propylene re ated to a pressu e d o o SI
to PSIG as asured y wet tes eter to e 2.35 • H e e , se
of t e d "ff ·c lt ·es and "nhererot errors in m1eas11Jr • g pro yle e act a.illl y
fed to t e reactor,, these rn.ms were co s "dered to be qual "tativ1e a:t 1e
ua t· a ive. t thte end of the 11react i o pe i od the e.ac
c o]e to o um t erat re and t e co te ts t sfe ed .o a
d"stil]iatiion set p. Dist"llatilll11 was. ieontimJ1ed u 1rt"l thie head
t erat re reac e 10 °c. T e d"sti ate ~s t e a al zecl y Jas
r at ra y as esc e le 0 . I 0 1 r1 :ns ere a e si g eye 0 1exet111e as thie a ke :e ii I a · a:1 e.1pt
t 1'. antiify t ie f o 1at i oni of alcoiho 21 I1 t ese 1r1 I S t 'E: li
a:s c a e the eaicto ith t 1e ()I er co o e· "ts. e ·a'....
·e sea e "
e ac ate a ro g t to t 1e 1es g ate t e
es . g1 ·. ated ti :0 e c. it iio s fo·ir t ese r s a. e s 0 i a le \fII. I 'I
a se es o Ul ~S
off a a · .e , · c ac 1 d to fio1 m a · 1Gy1 .ace·tates
Cj ""1 o 1ex.ene ic I i s ore corrvi 1en1 · e1 ·t1:y easure t a ga'Seo. s
e a .. 5> a 1 e· ""' , cat.a yst a d so · e e ] I ifi.
las fitte it a ef l a 1
i1]ij .1 ; s: .as ifi, :i::.i · b , Q. g t to t e d.e~ i g ated temper·"@.tur e f t e
es i g a·terl e.a'"'··t i. o i 1e. e.a·-·t 1 I co itio· ii e
. e a .... t e: i s.o 1 a .. e fi e- ti
fr ·a t.10. .aJ ati m ~· i 8 I g of ice,
ex·tra:ct i i0 n t. ·~ e:e t.; I 1 es \11.dt. 51 I m1 0 ti on o·f e ·afll1e .. A.I aljsies 0 t e
Tabl
e V
II
Dir
ect
hydr
atio
n of
cyc
lohe
xene
Run
Wate
r Te
mpe
ratu
re
Res
iden
ce
Cyc
lohe
xene
A
lcoh
ol
Num
ber
{gra
ms)
Ca
tal~
st
Solv
ent
(oq
Tim
e {H
rs}
{gra
ms}
fo
rmed
1
7 ph
osph
oric
aci
d,
tolu
ene,
8 g
10
0 4
5 no
10
g
2 25
ph
osph
omol
ybdi
c 18
0 4
10
no
acid
, 0.
25 g
3 20
0 ph
osph
omol
ybdi
c 18
0 3
80
no
acid
, 1.
52 g
C
r(N03
)3,
0.56
g
4 7
phos
phor
ic a
cid,
to
luen
e, 8
g
180
4 5
no
10 g
Do
w Ex
peim
enta
l Su
rfac
tant
XDS
839
0,
0.35
g
Tabl
e V
III
Rea
ctio
n co
nditi
ons
for
cata
lyst
scr
eeni
ng
Ace
tic A
cid
Ace
tic A
nhyd
ride
Cat
alys
t C
yclo
hene
Te
mp.
Run
(gra
ms)
(g
ram
s)
Type
(g
ram
s)
(gra
ms)
(O
C)
Yie
ld
1 12
0 2
sulf
uric
aci
d 10
8.
2 25
no
ne
2 12
0 2
poly
phos
phor
ic
acid
10
0 8.
2 25
no
ne
3 12
0 2
SnCl
4 15
8.
2 55
6%
4
120
2 su
lfur
ic a
cid
10
8.2
55
12%
5 12
0 2
poly
phos
phor
ic
acid
10
0 8.
2 55
49
% 6
120
2 Sn
C14
15
8.2
55
42%
7 12
0 2
tolu
enes
ulfo
nic
acid
20
8.
2 55
7.8
%
8 12
0 2
sulf
uric
aci
d 10
8.
2 55
96
% 9
120
2 P2
05
(66.
43 g
) an
d 85
% H 3
Po4
8.2
55
none
extract, after washing with water, 10% NaHC03 solution and saturated
NaCl solution, and drying over anhydrous calcium sulfate is described
below.
Indirect hydration-isopropyl acetate formation
17
Gaseous propylene was reacted with acetic acid with a sulfuric acid
catalyst in a Parr Model 3911 shaker type reactor, equipped with a
heater. The 500 ml pressure bottle was charged with 120 g of glacial
acetic acid, 2 g of acetic anhydride and 10 g of sulfuric acid. The
bottle was connected to the gas inlet tube. The bottle was then
evacuated and purged with propylene three times. The pressure was then
adjusted to the designated amount, the shaker started and the
temperature adjusted to the designated value. Shaking was continued for
the designated reaction time with periodic recording of the drop in
propylene pressure and readjustment of the bottle pressure from the gas
reservoir. At the end of the reaction period the pressure was released
and the contents of the bottle transferred to a simple distillation
setup. The reaction was distilled to a head temperature of 98°c. The
isopropyl acetate content of the distillate was measured as described
below. The reaction conditions are recorded in Table IX.
Indirect hydration-hydrolysis reaction
The hydrolysis of isopropyl acetate or the reaction mixture to
isopropyl alcohol and acetic acid was carried out by refluxing the ester
and water for the designated time. The hydrolysis product was then
distilled to a head temperature of 100°c, the distillate weighed and
analyzed as described below. Conditions for the hydrolysis are recorded
in Table X.
Table IX
Formation of isopropyl acetate
Temperature Pressure Reaction Run {oC} {~si} Time {Hrs} Yield
1 25 25 4 none
2 25 50 4 none
3 25 100 4 none
4 55 50 4 1.04 g
5 40 100 4 2.36
6 55 100 4 10%
7 75 100 4 25%
8 75 100 1 41.5%
9 75 100 2 64%
10 75 100 3 66%
11 75 100 4 67%
12 85 100 2 71%
13 82 55 4 80%
Note: 17.6 grams of propylene was used in runs 1-12. 8.4 grams of propylene was used in run 13.
g
18
distillate
distillate
Isopropyl Run Acetate*
1 10.2
2 10.2
3 10.2
4 10.2
5 10.2
6 7.8
7 28.1
8 29.l
*grams
Table X Hydrolysis of isopropyl acetate
Sulfuric Water* Acid*
100 1
30 1
100 5
30 1
30 1
200 5
600
600
Acetic Acid*
60
30
30
60
Reaction Time-hrs
3
3
3
3
5
3
2
2
19
Yield 19%
19.8%
64%
47%
47%
63%
61%
75%
Note - In run 7, the isopropyl acetate was the reaction product from run 12 in Table IX. Similary, in run 8, the reaction product from run 13 in Table IX was used.
Analytical methods
Isopropyl alcohol and isopropyl acetate samples were analyzed on a
Barber-Coleman gas chromatograph equipped with a thermal conductivity
detector. Conditions were as follows. A 30 meter column was packed
with Porr Pack Q with inlet temperature at 15o0 c and 1aooc for the
detector. The column temperature was held isothermal at 19ooc. Helium
was used as a carrier gas at a flow rate of 20 ml/min. The internal
standard used was n-butanol. A 1.0 µl syringe was used. Pure samples
of isopropyl alcohol, n-butanol, water and toluene were injected
separately into the gas chromatograph and each elution time was
observed. To quantify the product, a mixture of isopropyl alcohol and
n-butanol was injected into the gas chromatograph and each response was
observed. A quantity (O.l g) of the internal standard was dissolved in
2 g of sample and 0.2 µl of the mixture was injected into the gas
chromatograph. The amount of isopropyl alcohol present in the 2 g of
sample was determined by dividing 0.1 g by the calculated area of the
internal standard signal multiplying the result by the area of the
isopropanol signal.
Analysis of the cyclohexylacetate samples was performed on a Sigma
300 Perkin Elmer gas chromatograph equipped with flame ionization
detector, a laboratory data system (Sigma 3600) and an auto sampler. A
Durabond 5 capillary column was used. Durabond 5 is a non-polar
stationery phase consisting of 95% dimethyl-(5%) diphenyl polysiloxane,
with a temperature range of -60° to 3500c. The capillary column was 30
meters long with an inner diameter of 0.25 mm and a standard film
thickness of 0.25 µm. The inlet temperature was kept at 325°C and the
detector at 2so0 c. Column temperature was held isothermal at so 0 c for
21
one minute, then programmed at 8°C/minute to 16o0 c for one minute, then
30°C/minute to 270°C for 30 minutes. Hydrogen and breathing air were
used for flame ignition. Helium was used as carrier gas.
A stock standard solution was prepared by transferring exactly 50
mg of pure cyclohexyl acetate to a 50 ml volumetric flask and diluting
with hexane. One ml of this solution was further diluted to 50 ml in
hexane to give 20 g/ml concentration. About 0.5 ml of this solution
was placed into an auto sampler vial and injected into the gas
chromatograph. The calculated area of the standard peak was observed.
About 50 mg of each sample was treated the same way. The auto sampler
tray was loaded with sample vials in the even number position while odd-
numbered vials were loaded with hexane. The auto sampler was set such
that it sampled even numbered vials and flushed the syringe with odd
numbered vials. The syringe assembly had a nominal volume of 5 µl. The
syringe barrel was graduated and the distance travelled by the syringe
was adjusted to 2 µl by means of a knurled stop screw. The amount of
cyclohexyl acetate was calculated as follows:
1 standard x cone. standard standard response
x sample response x 1 sample injected
final volume sample size
DISCUSSION OF RESULTS
Direct Hydration
The initial runs (runs 1-5) evaluated the reaction of propylene gas
with one phase toluene/sulfonic acid/water systems at pressures from o
to 100 PSIG and temperatures from 25 to 150°c. At 25°c no product was
formed. At temperatures from 75 to 100°c traces of isopropyl alcohol
were formed. There was no evidence of product formation at 15o0 c. It
appears that, with this system, the reaction rate increases with
temperature but passes through an optimum. At high temperatures (150°C)
the solubility of propylene is too low for reaction to occur. In run
6, the toluene sulfonic acid was replaced with a long chain alkyl aryl
sulfonic acid to increase the solubility of the propylene, but no
isopropyl alcohol was formed.
In runs 7-12 the one phase system was replaced with a two phase
toluene/water/acid system. This increased the solubility of propylene,
but did not have a significant effect on the rate of reaction. At low
temperature (25°C) a large amount of propylene was absorbed but no
product was formed. At 100°c and 140 PSI the propylene absorption was
lower but a small amount of product was formed. In runs 13 and 14
tetraphenyl boron sodium was added as a proton phase transfer
catalyst. The yield of product increased significantly.
The results of these direct hydration runs confirmed that the
inhomogeniety of the reaction system is a major obstacle to reaction.
Reaction was not observed at 25oc. As the temperature is increased
reaction does occur but the rate is limited by the decreased solubility
of propylene.
23
Four runs, recorded in Table VII, were made using cyclohexene as
the alkene. Two runs utilized toluene/water systems with phosphoric
acid as the catalyst. In one of these runs hexadecyl diphenyl oxide
sulfonic acid, a surfactant active in strong acid systems was used. Two
runs were aqueous systems containing phosphomolybdic acid. No cylo
hexanol was detected in this series.
Indirect hydration
In the second phase of the work an indirect hydration process was
evaluated. In this approach the propylene would be reacted with acetic
acid to form isopropyl acetate. This ester would then be hydrolyzed to
isopropyl alcohol and acetic acid which would be dried and recycled. It
was thought that the solubility of the alkene and strong acid catalysts
in the acetic acid would eliminate the problems of inhomogeniety which
hampered the reaction in aqueous systems.
In the first stage of this phase catalysts for the acylation
reaction were evaluated using cyclohexene as the alkene. These runs are
recorded in Table VIII. There were some initial difficulties in the
separation and analysis of the product. The best results were obtained
by dilution of the reaction product with ice water, extraction with
hexane and GC analysis of the extract. This required a gas
chromatograph with a more sensitive detector. The analytical procedure
has been described in the Experimental section. The results indicated
that sulfuric acid is an active and selective catalyst for the acylation
reaction. Toluene sulfonic acid was less active. Stannous chloride and
polyphosphoric acid were less selective. The analysis of runs using
24
these catalysts was marked by peaks of several coproducts which were not
isolated or identified.
Table IX records the runs made evaluating the reaction of propylene
and acetic acid with a sulfuric acid catalyst. Again it was found that
the reaction rate at 25°C was too slow to be practical. The relation of
yield to product to temperature is illustrated in Figure 1. The data
from runs 8 through 11 indicate that at 75°c the reaction is essentially
complete within two hours. This is illustrated in Figure 2.
The runs made to evaluate the acid catalyzed hydration of isopropyl
acetate are recorded in Table X. The results indicate that an increase
in catalyst concentration from 0.01 moles/mole ester to 0.05 moles/mole
of ester increases the reaction rate. The equilibrium is displaced
towards product by a large excess of water. The yield of product is
increased by the presence of acetic acid, probably by increasing the
solubility of the ester in the reaction mixture. Under these conditions
the reaction is essentially complete within three hours.
100
80
60
.,.... 40 >-
20
25 50 75 100
Temperature (0 c)
Figure 1. Relation of yield and reaction temperature formation of isopropyl acetate.
25
100
80 -
60
r-- 40 Q)
•r-
20
0 1 2 3 4
Time (hrs)
igure 2. Relation of yield and reaction time formation of isopropyl cetate at 75°C.
26
CONCLUSIONS
The goal of finding a solvent/catalyst system in which propylene
could be directly hydrated in high conversions at low temperatures and
pressures was not realized. The best results for direct hydration
utilized a toluene/water/sulfuric acid system with tetraphenylboron
anion as a phase transfer catalyst. Since this catalyst is fairly
expensive and is reported to have limited stability in aqueous
solutions, it does not appear to be a practical solution to the
inhomogeniety problem. Any future studies of the direct hydration
process should be conducted in equipment which is capable of operating
at higher pressures and with more efficient mixing of the two phase
liquid system.
The results of the investigation of the two-step, indirect
hydration indicate that it has the potential for an economically
practical route to isopropanol. Sulfuric acid is an active and
selective catalyst for the acylation step at relatively low temperature
and pressures. The results of the investigation of the hydrolysis step
indicate that this reaction takes place at a reasonable rate and in good
yield. Optimum reaction conditions would be determined by economic and
engineering considerations.
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29