Note: Descriptions are shown in the official language in which they were submitted.
~229~
PROCESS FOR HYDROGENOLYSIS_OF CARBOXYLIC ACID~ESTERS
J
This invention relates to the hydrogenolysis of
carboxylic acid esters.
Hydroaenolysis of carboxylic acid esters has been
described on numerous occasions in the literature. Typically
in such a reaction the -CO-O- linkage of the ester group is
cleaved so that the acid moiety of the ester group i5 reduced
to an alcohol whilst the alcohol moiety is released as free
alcohol acco~ding to the following equation:
RlCR2 ~ 2H2 = RlCH2OH ~ HOR2 (I)
where Rl and R2 are each alkyl radicals, for example.
According to page 129 et seq of the book "Catalytic
Hydrogenation in Organic Synthesis" by M. Freifelder,
published by John Wiley and Sons Inc (1978), the catalyst of
choice for t~is reaction is said to be barium promoted cop~er
chromite. Typical reaction condit.ions include use of
temperatures in the region of 250C and pressures in the
range of 225-250 atmospheres (about 22.81 MPa to about 25.35
MPa). Although a good yield of alcohol is often obtained
using this technique for hy~3rogenolysis of an ester, the
temperature necessary or conversion of the ester to alcohol
is also conducive to side reactions. For example, the
resulting alcohol may undergo further hydrogenolysis to
hydrocarbon or may react with s~arting material to produce a
higher molecular weig~-t ester that is more difficult to
hydroye~olyse.
Besides these side reactions copper chromite
catalysts have other disadvantages for commercial scale
operation. In particular, the use of copper chromite
catalysts is environmentally hazardous and necessitates the
adoption of special and costly handling techniques on account
of the toxicity of chromium. Moreover it is difficult to
produce successive batches of copper chromite w.ith
reproduci~le catalyst ac~ivity.
J
United States Patent Specification No. 2079414
describes a process for catalytic hydrogenation of esters
using catalys-ts such as fused copper oxide, either wholly or
partially r~duced, which may be promoted with oxide promoters
such as manganese oxide, zinc oxide, magnesium oxide or
chromium oxide. Particularly recommended catalysts are those
comprising copper oxide promoted by chromium oxide, e.g.
copper chromite. According to page 3, right-hand column line
57 et seq.: "In operating in the vapour phase it is preferred
to use temperatures within the range of 300C to 400C". It
is also stated that: "The best conversions to alcohols are
obtained at the highest pressures obtainable in the available
equipment and at the lowest temperatures consistent with
obtaining a practical rate of reaction" (page 4, right hand
column, line 2 et seq.~. The Examples describe batch
reactions and in all cases the pressure is 2500 psia or
higher (17250 kPa or higher), whilst in all cases the
temperature is 250C or higher; in most cases i-t exceeds
300~C. A limitation to the process is that methyl esters
cannot be used because methanol, which would be a
hydrogenation product from a methyl ester, is subject to
gaseous decomposition (see page 5, right hand column, line 58
et ~). Similar considerat:ions would appear to prevent the
application of the process to esters of formic acid since the
formic acid moiety would also be likely to yield methanol.
Further teaching of the use of chromites as
catalysts for hydrogenation of esters will be found in United
States Paten~ Specification ~o. 2109844.
Example 4 of Vnited States Patent Specification No.
3197418 discloses the preparation of a copper-~inc catalyst
which can be used in the liquid phase hydrogenation of oils
and fats at pressures in excess of 120 kg/cm2 (11776 kPa)
and at a temperature of 3~0~C.
Vnited States Patent 5pecification No. 2241417
teaches the produc~ion of higher aliphatic alcohols by liquid
~3L2~9~3~6
--3--
phase hydrogenation of glycerides in the presence of
copper-containing catalysts at temperature of 200C to 400C
and at pressures of 60 to 500 atmospheres (5884 to 49033
kPa).
Hydrogenolysis of esters to saturated hydrocarbons
using catalysts having as essential ingredients an indium or
rhodium component and a halogen component is described in
United States Paten-t Specification No. 4067900.
Catalytic hydrogenolysis of formate esters present
in oxo reaction products using Ni catalysts is described in
East German Patent Specification No. 92440 (see Chem. Abs.,
124069j, Vol 78 (1973), page 439). O-ther references to
hydrogenation of formates include a paper by E. Lederle,
Anales Real Soc. Espan. Fis. y Quim. (Madrid) 57B, pages
473-S (1961). Also West German Patent Specification No.
902375 describes the production of methanol by hydrogenation
of alkyl formates at pressures of 20 to 50 atmospheres (1961
to 4903 kPa) using copper chromite catalysts; there is a
passing suggestion to incorporate zinc oxide in the catalyst.
Catalytic cleavage of formic acid esters is
described in British Patent Specification No. 1277077.
According to this proposal a hydrogenation catalyst
containing copper and nickel is used but the formyl radical
is reported to he dehydrogenated in the course of the
reaction and appears as carbon monoxid
Production of ethylene glycol by hydrogenolysis is
suggested by some references including United States Patent
Specification No. 4113662 which teaches hydrogenation of
esters to alcohols at temperatures of 150VC to 450C and
pressures of 500-10,000 psig (3450-69000 kPa) using catalysts
comprising cobalt, zinc and copper. Examples IV, V and VIII
describe comparative experiments using polyglycolide and
~ethyl glycolate with Cu-Zn oxides as catalyst at 250~C and
at pressures of at least 2800 psig tl9421 kPa~, i.e.
conditions under which the ester (polyglycolide or methyl
~Z~909~;
-4-
glycolate) is in the liquid phase. United States Patent
Specification ~o. 2305104 describes hydrogenation of alkyl
glycolates using catalysts containing Zn, Cr, and Cu to
produce ethylene glycol. Vapour phase hydrogenation oE
oxalate esters at temperatures of 150~C to 300C for the
production of ethylene glycol has been described in United
States Patent Specification No. 4112245; this process uses
a copper chromite or copper zinc chromite catalyst and
re~uires that the oxalate ester has a sulphur content of
less than 0.4 ppm.
It would be desirable to provide a process for
effectirlg hydrogenolysis of esters with negligible
formation of by-products or of "heavies" which can be
effected under mild conditions.
It would further be desirable to provide a
process for effecting hydrogenolysis of methyl esters of
aliphatic C2+ monocarboxylic acids without significant
decomposition of product methanol in the course of the
reaction.
It would also be desirable to provide a
hydrogenolysis process which utilises a simple catalyst
that can be prepared with reproducible catalyst activity.
The present invention accordin~ly seeks to
provide an improved process for effectinc3 hydrogenolysis
of alkyl esters of aliphatic C2+ monocarboxylic acid
esters which can be effected under mild conditions.
It also seeks to provide a process for the
production of ethanol by eEfecting hydrogenolysis of alkyl
acetates in high yield and at high conversions under mild
conditions.
According to the present invention there is
provided a continuous process for the production of an
optionally substituted C2+ alkyl alcohol which comprises:
vaporising an alkyl ester of a C2+
aliphatic monocarboxylic acid in a stream of a hydrogen-
5 2;~9~
containing gas to form vaporous mixture containing the
ester in vapour form and hydrogen, the partial pressure of
the ester in the vaporous mixture being at least about
0.05 kg/cm2 (about 4.9 kPa);
supplying the vaporous mixture to a catalytic
reaction zone containing a charge of a eatalyst consisting
essentially of a reduced mixture of copper oxide and zine
oxide;
contacting the vaporous mixture with the
eatalyst at a temperature of from 150C to 240C and at a
pressure in the range of from 5 kg/em2 absolute (491 kPa)
up to 50 kg/em2 absolute (4906 kPa); and
reeovering from the catalytic reaction zone a
reaction product comprising at least one optionally
substituted C2+ alkyl alcohol.
The ester may be essentially any vaporisable
alkyl ester of a C2+ aliphatic monocarboxylic acid.
Amongst esters that may be mentioned are those of the
general ~ormula:
R COOR'
in whieh R represents a substituted or unsubstituted
monovalent hydrocarbon radical and R' represents an alkyl
radical. Preferably the ester of formula RCOOR' has a
boiling point at atmospheric pressure of not more than
about 300C. Examples of possible substituents on the
radical R inelude oxygen atoms as well as hydroxy and
alkoxy groups. Preferably R and R' eaeh contain from 1 to
12 earbon atoms. Typically R is seleeted from alkyl,
alkenyl, alkoxyalkyl, and hydroxyalkyl radieals.
Sueh esters may be derived from the following
aeids:
aeetie aeid;
propionie acid;
n- and iso-butyric acids;
n- and iso-valeric aeids;
.: ;
- 6 - 1229~96
caproic acid;
caprylic acid;
capric acid;
2-ethylhexanoic acid;
glycolic acid;
pyruvic acid;
acrylic acid;
methacrylic acid;
alpha- or beta-crotonic acid;
methoxyacetic acid;
lactic acid;
and the like.
Preferably the acid contains from 2 to 12 carbon atoms.
The ester is further derived from an alkyl
alcohol. Suitable alkyl alcohols may be selected from:
methanol;
ethanol;
n- or lso-propanol;
n-, iso-, sec- or t-butanol;
pentan-l- or -2-ol;
2-methyl-butan-2-, -3- or -4- ol;
hexanols;
heptanols;
octanols (e.g. 2-ethyl-hexanol~;
cetyl alcohol;
lauryl alcohol;
I and the like.
Preferably the alkyl alcohol contains not more than 12
carbon atoms.
As examples of specific esters there may be
mentioned:
alkyl acetates te.g. methyl, ethyl, n- and
so-propyl, and n-, iso-, sec-
and t-butyl acetates);
alkyl propionates (e.g. n-propyl propionate);
,,~ r~;.
~,', `` ~
.
~2~ 6
-- 7
alkyl n-butyrates (e.g. n-butyl n
-butyrate);
alkyl iso~butyrates (e.g. iso-butyl
lso-butyrate);
alkyl n-valerates te.g. n-amyl valerate);
alkyl iso-valerates (e.g. methyl lso_
valerate);
alkyl caproates (e.g. ethyl caproate);
alkyl caprylates (e.g. methyl caprylate);
alkyl caprates (e.g. ethyl caprate);
alkyl 2-ethylhexanoates (e.g. 2-ethylhexyl 2-
ethylhexanoate);
alkyl alkoxyacetates (e.g. methyl
methoxyacetate); alkyl glycolates (e.g. methyl
and ethyl glycolates);
alkyl lactates (e.g. ethyl lactate);
alkyl pyruvates (e.g. ethyl pyruvate);
and the like.
In the process of the invention the vaporous
mixture to be contacted with the catalyst contains, in
addition to the ester, hydrogen either alone or in
admixture with other gases tdesirably gases inert to the
ester and the catalyst). The gaseous mixtures containing
hydrogen include inert gases such as nitrogen, or carbon
monoxide.
The term "hydrogen-containing gas" as us~d
herein includes both substantially pure hydrogen gas as
well as gaseous mixtures containing hydrogen.
~ The hydrogenolysis process o the present
; 30 invention is conducted at a temperature of between 150~C
and 240C~ Typically the temperature is between l~O~C and
240C. The total pressure is between 5 kg/cm2 a~solute
(491 kPa) and 50 kg/cm2 absolute (4906 kP~, and even more
preferably between 5 kg~cm2 absolute t491 kPa~ and 25
kg/cm~ absolute (2453 kPa).
The catalyst is a mixed metal oxide catalyst that
consists essentially of a reduced mixture of copper oxide
and zinc oxide. By the term "consists essentially of" we
mean that the catalyst includes as essential ingredients
in the mixture before reduction copper oxide and zinc
oxide, but may also include amounts of other metal oxides
that do not materially alter the basic characteristics of
the catalyst as well as inert fillers or supports, such as
carhon.
The catalyst may be der~ved from a mixture which
contains only copper oxide and zinc oxide. Alternatively
it may include one or more other materials, such as an
inert support or other material that is effectively
catalytically inactive in the ester hydrogenolysis
15 reactionO
The mixture of CuO and Zn0, before reduction,
preferably contains from about S to about 95 percent by weight,
typically from about 10 to about 70 percent by weight, of CuO
and from about 95 to about 5 percent by weight, typically from
about 90 to about 30 percent by weight, of ZnO. Hence the
mixture may contain, for example, from about 20 to about 40
percent by weigllt of CuO and from about 60 to about 80 percent
by weight of ZnO. A preferred mixture, for example, comprises
from about 30 to about 36 percent by weiqht of CuO and from
about 62 to about 68 percent by weight of ZnO. Other
particularly preferred mixtures comprise from about 65 to about
85 percent by weight of CuO and from about 35 to about 15
percent by weiqht of ZnO, for example mixtures comprising from
about 68 to about 75 percent by weight of CuO and from about 32
to about 25 percent by weight of ZnO. As already mentioned, the
hydrogenolysis catalyst may contain minor amounts of other
materials such as carbon, sodium, titanium, r~irconium,
manqanese, silica, diatomaceous earth, kieselquhr, and aluminium
oxide. Such other materials do not usually comprise more than
about 20 percent by weiqht calcula~ed (except in the case of
carbon) as oxide. In the case of sodium it is best not to
~2~
g
exceed about 0.5 percent by weight, calculated as oxide.
Hence other preferred catalysts include mixtures
comprising from about 40 to about 50 weight peroent each of CuO and
ZnO and from 0 to about 20 weight percent of alumlna. The
catalyst is, however, preferably essentially free from
other metals, particularly from metals of Group VIII of
the Periodic Table, such as Fe, Co, Ni, Ru, Rh, Pd, Os,
Ir, and Pt, as well as from Group VI8 metals, such as Cr,
Mo, and W, from the metals Tc, Ag, Re, Au and Cd, and also
fro~ elements of atomic number 80 and above, e.g. Hg and
Pb. By the term "essentially free" we mean that the
catalyst contains not more than about 0.1 wt~ (i.e. not
more than about 1000 ppm~, and preferably not more than
about 250 ppm, of the element in question. The catalyst
lS may be prepared by any of the methods known in the art of
forming a composite of copper oxide and ~inc oxide. The
catalyst may be prepared by fixing the separate oxides, by
coprecipitation of the oxalates, nitrates, carbonates, or
acetates, followed by calcination. The coprecipitation
method is preferred. Generally, the mixture of CuO and
ZnO is reduced by hydrogen or carbon monoxide at a
temperature in the range of between about 160C anclabout 250C
for several hours, preferably for 8 to 29 hours, prior to
contact with the vaporous mixture containing ester and
hydrogen. If the catalyst is charged in a pre-reduced
form the period required for reduction can be reduced
accordingly.
The mixture of CuO and ~nO is reduced prior to its
use as catalyst in the hydrogenolysis step. ~ydrogen or
CO, or mixtures thereof, are generally mixed with a
diluent gas such as steam, nitrogen, or combustion gas, to
maintain the catalyst bed temperature and to carry away
the heat of reduction.
Reduction of the mixture of CuG and'~nO is
complete when no more hydro~en or carbon monoxide is being
f`
96
_ 1 0
reacted as shown by analysis of the inlet and outlet gas.
Whe~ using hydrogen complete reduction of the mixture
occurs when the total amount of water produced ~n the
reduction i~ equal to the stoichiometric value of water
which should be produced when a given amount of copper
oxide is reduced to copper. This value is about 0.079 kg
of water per kg of catalyst for a mixture containing 35
weight percent of CuO.
An inert carrier material may be included in the
hydrogenolysis catalyst composition. The catalyst is
generally formed into pellets, tablets, or any other
suitable shape prior to use, by conventional techniques.
It is advantageous that the mixture oE CuO and ZnO
have an internal surface area of from about 25 to about 50 sq.~.
per gram. The internal surface area may be determined by the
well-known BET method.
The process of the present invention is carried
out in a continuous manner. In the preferred method of
continuous operation, an ester, or a mixture of esters, a
hydrogen containing gas, and optionally, a carrier gas
such as nitrogen, may be brought together and, under the
desired pressure contacted in the vaporous state with the
catalyst. The reaction zone advantageously is an
elongated tubular reactor wherein the catalyst is
~5 positioned.
In the hydrogenolysis process of the invention
the primary reaction observed is that of equation ~I)
above. Hence a monocarboxylic ester yields a mixture of
alcohols, one derived fxom the carboxylic acid moiety and
one derived from ~he alcohol moiety. Some esters, for
example ethyl acetate, may produce a single alcohol as the
alcohol derived from the carboxylic acid moiety in this
case is the same as that derived from the alkyl moiety.
The alcohol product or products from the hydrogenolysis
reaction may be separated from the hydrogen by
. ~
9~6
condensation and the excess hydrogen can be compressed and
recycled to the reaction zone. The crude alcohol product
may be used in this form or it can be further purified in
a conventional manner such as by fractional distillation.
s If desired, any unconverted portion of the ester or ester
mixture may be separated from the reaction product and
recycled to the reaction zone and, preferably, admixed
with fresh feed gases priox to entering the reaction zone.
In operating the process of the invention the
partial pr,essure of the ester may vary within wide limits,
e.~. from about 0.05 kg/cm '(4.9 kPa) or less up to about 10 kq/~2
(981 kPa) or more. Care must however be taken to ensure
that at all times the temperature of the vaporous mixture
in contact with the catalyst is above the dew point of the
ester and of any other condensible component present under
the prevailing pressure conditions.
The vaporous mix.ture preferably contains at
least an amount of hydrogen corresponding to the
stoichiometric quantity of hydrogen required for
hydrogenolysis. Usually an excess of hydrogen over the
.~
.~ , .
-12- ~2~9~
stoichiometric quantity will be present. In this case
the excess hydrogen remaining after product recovery can
be recycled to the catalytic reaction zone. As will be
apparent from equation (I) above, 2 moles of hydrogen
are required for hydrogenolysis of each carboxylic acid
ester group present in the ester molecule. If the ester
contains non-aromatic unsaturation (i.e. carbon-carbon
double or triple bonds) such unsaturated linkages may
also undergo hydrogenation under the hydrogenolysis
conditions employed. Hence the stoichiometric quantity
of hydrogen required for reduction of 1 mole of an
unsaturated mono-ester may correspond to 3, 4 or more
moles of hydrogen.
The hydrogen:ester molar ratio within the
vaporous mixture may vary within wide limits, e.g. from
about 2:1 to about 100:1 or more. This ratio will
depend, at least to some extent, on the volatility of
the ester used. Typically the hydrogen:ester molar
ratio is at least about 25:1.
Although the process of the invention is
generally applicable to alkyl esters of aliphatic
C2+ monocarboxylic acids, best results will usually
be obtained with esters boiling at temperatures of not
more than about 300C at atmospheric pressure. Whilst
it is possibl~ to utilise esters having still higher
boiling points, the use of higher boiling point
materials limits the partial pressure of the ester that
can be used in the vaporous mixture and hence limits the
rate of hydrogenol~sis~ If extremely high boiling
esters are used then rates of reaction will be
correspondingly reduced.
Certain alkyl esters of aliphatic C2~
monocarboxylic acids may undergo ~hermal decomposition
at temperatures approaching 300C and possibly at
temperatures b~low their boiling point at atmospheric
B
229096
pressure. When using such esters the temperature during
hydroqenolysis should not be so high that significant
thermal decomposition of the ester ~ccurs. ?
In general it is preferred to use alkyl esters
of C2+ aliphatic monocarboxylic acids containing from 3 to
20 car~on atoms.
According to a further aspect of the present
invention there is pro~ided a continuous process for the
production of ethanol in which a vaporous mixture
containing (1) an alkyl ester of acetic acid and (2)
hydrogen, in which vaporous mixture the partial pressure
of the ester is at least about 0~05 kg/cm2 (about 4.9
kPa), is continuously fed into contact with a catalyst
consisting essentially of a reduced mixture of copper
oxide and zinc oxide at a temperature in the range of from
150C up to 240C and at a pressure in the ranqe of from 5
kg/cm2 absolute (491 kPa) up to 50 kg/cm2 absolute (4906
kPa), and resulting ethanol is recovered.
2Q In the hydrogenolysis of acetic acid esters to
produce ethanol the temperature preferably ranges from
180C to 240C and the pressure from 5 kg/cm2 absolute
(491 kPaJ to 35 kg/cm2 absolute (3435 kPa).
In all cases recovery of the hydrogenolysis
products can be effected in conventional manner, e.q. by
condensation followed, if desired, by fractional
distillation under normal, reduced or ele~ated pressure.
The invention is further illustxated in the
follvwinq Examples.
~ ~ ~2~9~
Example 1
n-butyl butyrate was pumped at a rate of 3.8
ml/hr to an electrically heated gas/liquid mixing device
to which hydrogen was also supplied at a controlled rate
and pressure. The resulting vaporous mixture was passed
through a lagged, electrically heated line t~ a pre-
heating coil prior to passage through a tubular reactor
packed with 146 ml of a powdered catalyst. Both the
tubular reactor and the pre-heating coil were immersed in
a molten salt bath which was heated to 174C. The vaporous
mixture exiting the reactor was passed through a water
cooled condenser and the resulting condensate was
collected in a water-cooled knock out pot. The exit gas
pressure was controlled to 10.55 kg/cm2 absolute (1035
kPa). The non-condensed gases were then passed through a
let-down valve, the gas flow xate being monitored
downstream from this valve in a wet gas meter. A gas flow
rate of 46.4 litres/hr (measured at atmospheric pressure)
was maintained throughout the experiment. The ester
partial pressure in this experiment was 0.12 kg/cm2 (12
kPa) and the hydrogen:ester molar ratio was 84.3:1. The
liquid hourly space velocity was 0.025 hr~l.
The liquid condensate was analysed by gas
chromatography using a 2 metre stainless steel column t6
mm outside diameter) packed with polyethylene glycol
(nominal molecular weight 20,000) on Chromosorb PAW, a
helium gas flow rate of 30 ml/minute and a flame
ionisation detectorO (The word "Chromosorb~' is a
Registered Trade Mark). Th~ instrument was fitted with a
chart recorder having a peak integrator and was calibrated
using a mixture of n-butanol and n-butyl butyrate of known
composition. The condensate was shown to contain a
mixture of 99.62 wt ~ butanol and 0.28 wt % n-butyl
butyrate, corresponding to a 99.7% conversion
-15- ~29096
with essentially 100% selectivity.
The catalyst used in this Example was charged
to the reactor as a co-precipitated mixture of CuO and
ZnO containing 33+3% Cuo and 65+3% ZnO having a
particle size in the range of 1.2 mm to 2.4 mm and an
internal surface area of about 45 sq. m. per gram. This
was pre-reduced in the reactor using a 5 vol % H2 in
N2 gas mixture at 200C for 17 hours followed by pure
hydrogen at 200C for 8 hours, the gas flow rate in each
case being about 20 Iitres/hr (measured at atm~spheric
pressure using the wet gas meter) and the gas pressure
being 10.55 kg/cm2 absolute (1035 kPa). After this
pre-reduction stage the catalyst was at all times
maintained in a hydrogen-containing atmosphere.
Example 2
The procedure of Example 1 was repeated using
ethyl acetate in place of n-butyl butyrate at a feed
rate of 7.4 mls/hr and a hydrogen flow rate of 41.9
litres/hr (measured at atmospheric pressure by means of
the wet gas meter). In this experiment the liquid
hourly space velocity was 0.05 hr~l, the salt bath
temperature was 185C and the exit gas pressure was
10.55 kg/cm2 absolute (1035 kPa). The hydrogen:ester
molar ratio was 23.3:1 and the ester partial pressure
25 was 0.43 kg/cm2 (42 kPa). The liquid condensate was
shown to contain a minor amount of ethyl acetate, a
major amount of ethanol and a trace of n-butanol. The
observed conversion to ethanol was 97.1~ and the
selectivity to ethanol was about 95~.
Exam~e 3
When the procedure of Example 2 was repeated
at a salt bath temperature of 203C, with a gas flow
rate of 160.4 litres/hr and a liquid feed flow rate (of
ethyl acetate) of 34~8 ml/hr (i.e. a liguid hourly space
~ t
~2~9~g6
-16-
velocity of 0.24 hr-l), both ethyl acetate and
ethanol were identified in the liquid condensate but
essentially no n-butanol was formed. The hydrogen:ester
molar ratio was 19.0:1 and the ester partial pressure
was 0.53 kg/cm2 (52 kPa). The conversion of ester was
82~6% and the selectivity to ethanol was approximately
1 00% .
Example 4
The procedure of Example 1 was repeated using
methyl acetate in place of n-butyl butyrate at a feed
rate of 75 mls/hr (i.e. a liquid hourly space velocity
of 0.51 hr~l) and a hydrogen flow rate of 115.2
litres/hr (measured at atmospheric pressure). In this
experiment the salt bath temperature was 194C and the
15 exit gas pressure was 9.49 kg/cm2 absolute (935 kPa).
The hydrogen:ester molar ratio was 5.06:1 and the ester
partial pressure was 1.57 kg/cm2 (154 kPa). The
liquid condensate was shown to contain 55.7 wt~ methyl
I acetate, 10.02 wt% ethyl acetate, 15.24 wt% ethanol, and
¦ 20 18095 wt~ methanol. The observed conversion to ethanol
~ was 52.4 mol%.
¦ Example 5
! The procedure ~f Example 4 was repeated at a
' salt bath temperature of ~17C with an exit gas pressure
] 25 of 8.86 kg/cm2 absolute (868 kPa), with a gas flow
rate of ~25 litres/hr, and with a liquid feed flow rate
(of methyl acetate) of 75 ml/hr. In this Example the
partial pressure of methyl acetate was 0,81 kg/cm2 (79
kPa), whilst the hydrogen:ester molar ratio was 9.9:1.
The liquid hourly space velocity was 0.51 hr~l. The
liquid condensate was shown to contain l9r31 wt% methyl
acetate, 11.19 wt~ ethyl acetate, 35.64 wt~ ethanol, and
31.96 wt~ methanoi. The observed conversion to ethanol
was 72.40 mol%~
Example 6
~.
-17-
The procedure of Example 1 was repeated using
~ec-butyl acetate in place of n-butyl butyrate at a feed
rate of 118 mls/hr (i.e. a liquid hourly space velocity
of 0.81 hr~l) and a hydrogen flow rate of 193.9
litres/hr (measured at atmospheric pressure). In this
experiment the salt bath temperature was 203C and the
exit gas pressure was 10.55 kg/cm2 absolute tlO35
kPa). This corresponded to an ester partial pressure of
1.37 kg/cm2 1134 kPa) and a hydrogen:ester ~olar ratio
of 6.7:1. The liquid condensate was shown to contain
6.0 wt% ethyl acetate, 20.6 wt% ethanol, 40.1 wt%
sec-butyl acetate, and 33.3 wt~ sec-butanol. The
observed conversion to ethanol was 59.9 mol~ and the
selectivity to ethanol and sec-butanol was essentially
100~.
Example 7
t-butyl acetate was pumped at a rate of 18.3
ml/hr to an electrically heated gas/liquid ~ixing device
to which hydrogen was also supplied at a controlled rate
and pressure via an electrically heated line. The
resulting vap~rous mixture was passed through a lagged,
electrically heated line to a pre-heating coil prior to
passage through a tubular stainless steel reactor packed
with 15 ml of a crushed catalyst. Both the tubular
reactor and the pre-heating coil were immersed in a
molten salt bath. The temperature of the salt bath was
adjusted until the temperature of the vaporous mixture,
as detected by a thermoc~uple positioned immediately
upstream from the catalyst bed, was 2Ql~C. The vaporous
mixture exiting the reactor was passed through a water
cooled condenser and then through a second refriger~ted
condenser through which coolant at -15~C was passed.
The resulting condensate was collected in a refrigerated
knock out pot also ~ept at -15C. The exit gas pressure
was controlled t~ 26.7 ky/cm~ absolute ~2622 kPa).
~,,
!36
-18-
The non~condensed yases were then passed through a
let-down valve, the gas flow rate being monitored
downstream from this valve in a wet gas meter. A gas
flow rate of 156.6 litres/hr (measured at atmospheric
pressure) was maintained throughout the experiment. The
liquid hourly space velocity of the t-butyl acetate was
1.22 hr~l, the H2:ester molar ratio was 47.0:1,
and the ester partial pressure was 0.55 kg/cm2 ~54
kPa).
The liquid condensate was analysed by gas
chromatography using a 2 metre stainless steel column
(6mm outside diameter) packed with polyethylene glycol
(nominal molecular weight 20,000) on Chromosorb PAW, a
helium gas flow rate of 30 ml/minute and a thermal
conductivity detector. The instrument was fitted with a
chart recorder having a peak integrator and was
; calibrated using a mixture of ethanol, t-butanol, ethyl
acetate, t-butyl acetate and water of known composition.
¦ ¦ Gas chromatographic analysis showed the
condensate to contain:-
19.87 wt% ethanol
3.18 wt~ t-butanol
0.74 wt~ ethyl acetate,
65.58 wt~ t-butyl acetate
6.51 wt~ water
This corresponds to a 56.5% conversion of
t-butyl acetate. Although the selectivity to ethanol
and t-butanol appears to ~e high, accurate assessment of
selectivity was difficult because some of the t-butanol
underwent dehydration to iso-butene which was detected
as a product but not collected.
The catalyst used in this Example was charged
to the reactor as a co-precipitated mixture o~ CuO and
Zno containing 33+3% CuO and 65+3~ 2nO having a
.. . ..
~L~29~6
--19--
particle size in the range of 1.2 mm to 2.4 mm and an
internal surface area of about 45 sq.m. per gram. This
was pre-reduced in the reactor using a 5 vol % H2 in
N2 gas mixture at 200~C for 16 hours followed by pure
hydrogen at 200C for 16 hours, the gas flow rate in
each case being about 20 litres/hr (measured at
atmospheric pressure) and the gas pressure being 15.5
kg/cm2 absolute (1518 kPa). After this pre-reduction
stage the catalyst was at all times maintained in a
hydrogen-containing atmosphere.
Example 8
The procedure of Example 7 was repeated using
ethyl lactate at a feed rate of 15.9 ml/hr. The reactor
pressure was 16.4 kg/cm2 absolute (1608 kPa) and the
inlet temperature was 234C. The gas flow rate was
156.6 litres/hr (measured at atmospheric pressure). The
liquid hourly space velocity was 1.06 hr~l. In this
Example the H2:ester molar ratio was 47.0:1 and the
, ~ ester partial pressure was 0.34 kg/cm2 (33.4 kPa).
I 20 Gas chromatographic analysis showed the
, condensate to contain:-
i 12.62 wt% ethanol
0.25 wt% n-propanol
~i 14.41 wt~ 1,2-propanediol
i 25 64.49 wt% ethyl lactate.
~i This corresponds to a 34.7~ conversion of
ethyl lactate with a selectivity of 97.7% to
1,2-propanedi~l and 2.3% to n-propanol.
Example 9
The procedure of Example 7 was repeated using
methyl methoxyacetate at a feed rate of 17~3 ml~hr. The
reactor pressure was 29 kg/cm2 absolute (2850 kPa) and
the inlet temperature was 217C. The gas flow rate was
157.2 litres/hr (measured at atmospheric pressure). The
liquid hourly space velocity was 1.15 hr~l~ the
~ .
1229~)~6
-20-
H2:ester molar ratio was 37,5:1. and the ester partial
pressure was 0,75 kg/cm2 (73.6 kPa).
Gas chromatographic analysis showed the
condensate to contain--
22.23 wt~ methanol
0.62 wt~ ethanol
46.55 wt% 2-methoxyethanol
23.23 wt% methyl methoxyacetate
4.53 wt~ methoxyethyl methoxyacetate.
This corresponds to a 77.6~ conversion of
methyl methoxyacetate with a selectivity of 2.0% to
ethanol, 93.2~ to methoxyethanol and 4.6~ to
methoxy~thyl methoxyacetate.
Example 10
The procedure of Example 7 was repeated using
a mixture comprising 75 mol % methyl glycolate and 25
mol% methanol at a feed rate of 10.0 ml/hr. The reactor
pressure was 28.1 kg/cm2 absolute (2760 kPa) and the
inlet temperature was 210C. The gas flow rate was
0 155.4 litres/hr (measured at atmospheric pressure). The
liquid hourly space velocity was 0.67 hr~l, the
H2:ester molar ratio was 39:1, and the es~er partial
pressure was 0.7 kg~cm2 ~68.6 kPa).
Gas chromatographîc analysis showed the
condensate to contain a mixture of methanol, methyl
glycolate, and ethylene glycol.
Calculations indicated a 13~7% conversion of
methyl glycolate with a selectivity ~f approximately
~8.0% to ethylene glycol.
Exam~le 11
U~ing a procedure similar to that of Example 7
but
with a catalyst voIume ~ 50 ml, the hydrogenolysis of
ethyl acetate was investigated using a crushed catalyst
35 comprising a reduced mixture of 71.5~ CuO and 18,5~ 2nOr
~L229~9ç;
-21
with a liquid feed rate of 21.7 ml/hr, corresponding to
a liquid hourly space velocity of 0.43 hr~l and a 5
mol~ ethyl acetate in hydrogen feed mixture (i.e. a 19:1
hydrogen:ester molar ratio). The conversion observed at
11.6 kg/cm2 absolute (1138 kPa) and 150C was 65.1%
with essentially quantitative formation of ethanol. The
partial pressure of the ester in this run was 0.55
kg/cm2 (54 kPa). Under the same pressure and flow
conditions at 200C the observed conversion was 90.6~,
also with essentially quantitative producti~n of
ethanol.
Example 12
When Example 11 was repeated using as catalyst
a reduced mixture of 44.3~ CuO, 46.3% ZnO and 9.4%
A12o3, the conversion at 150C was 48.9%. The
partial pressure of the ethyl acetate in this run was
0.55 kg/cm2 (54 kPa), whilst the hydrogen:ester molar
ratio was 19:1. The observed conversion at 200C was
84.2~. In each case essentially quantitative formation
of ethanol was observed.
