Process for producing .alpha.-phenylethyl alcohol

A process for producing .alpha.-phenylethyl alcohol, which comprises hydrogenating acetophenone by a fixed bed flow reaction in the presence of a catalyst, wherein the reaction is conducted in the state where the liquid hold up ratio in a reactor is in the range of from 30% to 90%.

BACKGROUND OF THE INVENTION 
The present invention relates to a process for producing 
.alpha.-phenylethyl alcohol. More particularly, the present invention 
relates to a process for producing .alpha.-phenylethyl alcohol in which 
acetophenone is hydrogenated by a fixed bed flow reaction in the presence 
of a catalyst, wherein the amount of ethylbenzene produced as a by-product 
is controlled at a sufficiently low level, and hence the selectivity for 
.alpha.-phenylethyl alcohol is high, thus the process being extremely 
excellent in an industrial production. 
The .alpha.-phenylethyl alcohol is useful as, for example, a starting 
material for producing styrene, and materials for producing various kinds 
of perfumes. It is known that .alpha.-phenylethyl alcohol can be produced 
by the hydrogenation of acetophenone. For example, in Japanese Patent 
Publication No.59-27216, there is disclosed a process for hydrogenating 
acetophenone by using copper-chromite catalyst containing barium, zinc, 
and magnesium. However, there had not been previously known that a process 
for producing .alpha.-phenylethyl alcohol by hydrogenating acetophenone in 
a fixed bed with high selectivity and efficiency. 
SUMMARY OF THE INVENTION 
Under these circumstances, an object of the present invention is to provide 
a process for producing .alpha.-phenylethyl alcohol in which acetophenone 
is hydrogenated by a fixed bed flow reaction in the presence of a 
catalyst, i.e., a process for producing .alpha.-phenylethyl alcohol 
extremely excellent in an industrial production, wherein productivity per 
unit volume of a reactor is high even under low pressure (the reaction 
efficiency is high), and the amount of ethylbenzene produced as a 
by-product is controlled at a sufficiently low level, resulting in high 
selectivity for .alpha.-phenylethyl alcohol 
That is, the present invention is to provide a process for producing 
.alpha.-phenylethyl alcohol, which comprises hydrogenating acetophenone by 
a fixed bed flow reaction in the presence of a catalyst, wherein the 
reaction is conducted in the state where the liquid hold up ratio in a 
reactor is in the range of from 30% to 90%. 
It is difficult to proceed the reaction of the hydrogenation of 
acetophenone in general because the reaction rate of the hydrogenation of 
acetophenone is slower than that of the other hydrogenation reaction such 
as olefin. Accordingly, the hydrogenation reaction of acetophenone has 
been conducted industrially under high pressure and a large amount of 
hydrogen. The liquid feed must be also diluted by the other solvent that 
enables hydrogen gas to dissolve in liquid phase. In these cases, the 
running and equipment cost are high due to an increase in equipment for 
recycling excess hydrogen and the solvent for the dilution of feed. The 
applicants have found that the reaction rate strongly depends on the ratio 
of a reaction liquid (containing acetophenone) to a reaction gas in a 
reactor (catalyst charged layer) by an analysis of the acetophenone 
hydrogenation rate in detail. 
With respect to the hydrogenation reaction, the acetophenone in a liquid is 
allowed to react with dissolved hydrogen on a catalyst, wherein the 
hydrogen consumed in the liquid is supplied from a gas phase. In the 
present invention, the reaction is carried out under the conditions of 
holding larger liquid hold up than that of the conventional process, 
resulting in longer liquid residence time in the catalyst bed and the 
larger amount of dissolved hydrogen. Consequently, high reaction 
efficiency can be achieved, resulting in high acetophenone conversion 
ratio and small yield of by-product ethylbenzene even under lower pressure 
than the conventional process. When the liquid hold up is too low, the 
reaction efficiency decreases. On the other hand, when it is too large, 
the gas hold up extremely decreases and it is impossible to supply 
hydrogen gas from the gas phase effectively to become the reaction 
efficiency worse. It has been found that running at most suitable liquid 
hold up ratio can maintain the reaction efficiency at high level, 
completing the present invention. 
In the hydrogenation reaction of the fixed bed reaction system of the 
present invention, effective removal of heat of reaction is particularly 
important in maintaining the reaction selectivity at high level. In the 
hydrogenation reaction of acetophenone, excessive hydrogenation reaction 
results in the formation of ethylbenzene. Accordingly, it has great 
industrial significance to produce .alpha.-phenylethyl alcohol by limiting 
the amount of ethylbenzene as small as possible. The analysis of the 
reaction results indicate that the formation of ethylbenzene greatly 
depends on the reaction temperature, and significantly increases at a 
temperature of over 150.degree. C. The reaction heat of the hydrogenation 
of acetophenone to .alpha.-phenylethyl alcohol is about 50 KJ per 1 mol of 
acetophenone. When the liquid hold up ratio in a reactor is too small, 
insufficient removal of reaction heat in the reactor results in the 
formation of heat spots to produce much amount of ethylbenzene as a 
by-product, and the reaction selectivity becomes worse. Under these 
circumstances, the inventors has found that the amount of ethylbenzene 
produced as a by-product can be controlled by setting the liquid hold up 
ratio in a reactor at a prescribed amount resulting in maintaining high 
conversion ratio of acetophenone. The liquid hold up ratio in a reactor is 
determined depending upon the amount of liquid and the amount of gas per 
sectional area of the reactor. The liquid hold up ratio in a reactor is in 
the range of from 30% to 90%, preferably in the range of from 40% to 70% 
so as to control the amount of ethylbenzene produced as a by-product. 
The terms "liquid hold up" and "liquid hold up ratio" in the present 
invention are defined as follows: 
The amount of liquid capable of filling the inside of a reactor after 
charging a catalyst into the reactor is taken as 100. The amount of liquid 
staying in the reactor at the time when a material gas and material liquid 
are actually flown therein to reach the steady state is defined as liquid 
hold up. The value expressed as the ratio to the above described 100 is 
defined as liquid hold up ratio. For example, the liquid hold up and 
liquid hold up ratio can be determined as follows: a prescribed gas and 
liquid are supplied into a reactor to ensure the steady state, after which 
the valves each provided at the inlet and outlet of the reactor, 
respectively, are stopped at the same time. Then, the amount of liquid 
remaining in the reactor is drawn to be measured. However, the measuring 
method is not limited thereto. The liquid hold up can be changed into the 
desired amount by appropriately selecting the amounts of gas and liquid to 
be fed into the reactor, and the size of the reactor. 
The catalyst usable in the present invention is the one which allows 
acetophenone to be hydrogenated to produce .alpha.-phenylethyl alcohol. 
Examples of which said catalyst include copper-based catalysts, and noble 
metal catalysts. Examples of the copper-based catalyst include catalysts 
disclosed in Japanese Patent Publication No. 59-27216, EPO No. 714877, and 
DE No.3933661, but do not limit to these catalyst. These catalysts mean 
the catalysts containing CuO as a main component. The content of CuO in a 
catalyst is generally in the range of from 10% to 90 wt %, preferably in 
the range of from 20% to 80 wt %. Even if the content is too high or too 
low, hydrogenation activity may become low. Examples of components other 
than CuO in a catalyst include various kinds of metal oxides such as 
Cr.sub.2 O.sub.3, ZnO, FeO.sub.3, Al.sub.2 O.sub.3, La.sub.2 O.sub.3, 
Sm.sub.2 O.sub.3, CeO.sub.2, Zro.sub.2, TiO.sub.2, MnO.sub.2, Co.sub.2 
O.sub.3, NiO, SiO.sub.2, BaO, CaO, and MgO. Specifically, catalysts of the 
mixed oxides with silica are preferable. Further, an alkali metal compound 
may be contained as a component other than the above-described ones. 
Examples of the noble metal type catalysts include catalysts containing 
Pd, Rh, Pt, and Ru. Examples of these include catalysts disclosed in U.S. 
Pat. No. 4,996,374, Japanese Patent Publication No. 1-272540, and Japanese 
Patent Publication No. 2-78639, but do not limit to these catalysts. 
The catalyst of the present invention may be supported on a carrier. 
Examples of the carrier include metal oxides such as silica, alumina, 
titania, zirconia, magnesia, and silica-alumina, and mixed oxides thereof; 
bentonite, monmorillonite, diatomaceous earth, and acid clay. Among them, 
silica and diatomaceous earth are preferable. Binders such as graphite, 
silica sol, and aluminamaybe added in molding a catalyst. 
The catalyst is preferably a molded pellet with a diameter of 3 mm or less, 
preferably of 2 mm or less. When the catalyst is too large, the reaction 
may not proceed to a sufficient degree, or the amount of ethylbenzene 
produced as a by-product may increase. The lower limit of the diameter of 
the catalyst is not specifically limited. However, it is preferable that 
the diameter of the catalyst is 1 mm or more in terms of controlling the 
pressure drop in the catalyst bed. Examples of the shape of the catalyst 
include spheroidal or cylindrical shape and the like. In the case of 
cylindrical shape, said diameter represents the diameter of the sectional 
circle. In the cases of other shapes, said diameter means the maximum 
diameter of the section In the case of the cylindrical shape, the height 
of the cylindrical shape is not specifically limited, however it is 
generally in the range of from 1 mm to 10 mm 
The catalyst of the present invention can be produced by a coprecipitation 
method, precipitation method, mixing method, and the like. For example, 
paste obtained by the coprecipitation method is heated to obtain catalyst 
powder. The aforementioned binder and the like are added to said catalyst 
powder to obtain a molded pellet by tabletting molding or extrusion 
molding. The commercially available catalysts can be also employed. 
The hydrogenation reaction of acetophenone is carried out by the use of a 
fixed bed flow reactor charged with the above-mentioned catalyst. This 
method requires no filtration of catalyst powder from a reaction liquid 
and hence it is more excellent method in terms of industrial production as 
compared with a slurry reaction method using powder catalyst. The reaction 
temperature is generally in the range of from 40.degree. C. to 200.degree. 
C., preferably in the range of from 60.degree. C. to 150.degree. C. The 
reaction pressure is generally in the range of from 1 MPa to 20 MPa. It 
becomes possible to react under lower pressure of from 1 MPa to 5 MPa in 
the present invention. The reaction under lower pressure becomes possible, 
so the method of the present invention has great industrial significance 
in terms of a reduction in equipment cost and improvement in safety. 
Excessive low temperature or low pressure may inhibit the proceeding of 
the reaction to a sufficient degree. On the other hand, excessive high 
temperature or high pressure may cause not only increase of equipment cost 
and maintenance cost, but also increase of the amount of ethylbenzene 
produced as a by-product. The amount of catalyst to be used is generally 
in the range of from 0.01 hr.sup.-1 to 50 hr.sup.-1, preferably in the 
range of from 0.1 hr.sup.-1 to 20 hr.sup.-1 as space velocity of a 
material liquid to a catalyst bed. The amount of hydrogen to be supplied 
is generally in the range of from 1.0 to 3 times as much as the amount of 
acetophenone in the material liquid to be fed on a mole basis. 
The hydrogen and material liquid may be supplied by up flow or down flow if 
the liquid hold up ratio is in the range of from 30% to 90%. In the case 
of up flow, the liquid phase becomes continuous phase in a catalyst bed by 
its own weight of the material liquid, and hydrogen gas flows therein as 
bubbles. Accordingly, there is no danger of entailing the following 
situation as in the case of down flow: the dispersion of the liquid 
becomes uneven, resulting in an increase of the amount of ethylbenzene 
produced as a by-product, runaway of the reaction, and a decrease of 
catalyst activity due to a local temperature rise. In the case of down 
flow, the liquid hold up ratio in a reactor changes depending on the 
liquid space velocity and gas space velocity, resulting in variations in 
reaction results. On the other hand, in the case of up flow, the liquid is 
a continuous phase in the reactor, and hence it is difficult for the 
variations as described above to arise. 
As a raw material for the reaction, only acetophenone may be used, however, 
mixed liquid containing impurities and the like other than acetophenone 
may be also used. A solution with an adequate solvent being added therein 
may be used. Examples of the solvent include alcohols such as methanol, 
ethanol, propanol, ethylene glycol monomethyl ether, and 
.alpha.-phenylethyl alcohol; ethers such as diethyl ether, tetrahydrofran, 
dioxane, and ethylene glycol dimethyl ether; hydrocarbons such as hexane, 
heptane, toluene, and ethylbenzene; and mixed solvent thereof. The amount 
of solvent to be used is generally in the range of from 0.5 to 10 times 
that of acetophenone on a weight basis. Such dilution of acetophenone 
material is effective in maintaining the selectivity of the reaction at 
high level. 
In the fixed bed flow hydrogenation reaction of the present invention, a 
part of the reaction liquid after hydrogenation reaction may be recycled 
in a material liquid for hydrogenation reaction. The recycling of a part 
of the reaction liquid enables the effective removal of reaction heat, and 
hence it is effective in maintaining the selectivity of the reaction at 
high level. 
According to the present invention, it becomes possible to provide a method 
for producing .alpha.-phenylethyl alcohol by a fixed bed flow reaction, 
extremely excellent in terms of industrial production, wherein the amount 
of ethylbenzene produced as a by-product is controlled at sufficiently low 
level, resulting in high selectivity for .alpha.-phenylethyl alcohol.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
EXAMPLES 
The present invention will be described by way of examples, which should 
not be construed as limiting the scope of the invention. 
Example 1 
In a fixed bed adiabatic reactor, which is a tube(inner diameter of 4.1 cm 
and length of catalyst bed of 78 cm) fixed vertically, a copper-silica 
pellet catalyst (1 litter) (containing 63 wt % CuO, 1.5 mm .phi..times.4 
mmL) is charged. Then, a fresh material liquid containing 56 wt % of 
acetophenone (hereinafter, referred to as "ACP"), 16 wt % of 
.alpha.-phenylethyl alcohol (hereinafter, referred to as "MBA"), 0.04 wt % 
of ethylbenzene (hereinafter, referred to as "EB"), and 28 wt % of the 
other compounds at a rate of 11/hr, and mixed gas made of 84 volume % of 
hydrogen and 16 volume % of methane at a rate of 0.3 Nm.sup.3 /hr on a 
normal state basis (the mole ratio of hydrogen to material acetophenone is 
2.4 times on a mole basis) were supplied therein by up flow to conduct a 
hydrogenation reaction at 24 kg/cm.sup.2 G. In this step, a part of the 
hydrogenation reaction liquid at the outlet of the reactor was recycled to 
the inlet of the reactor. In the steady state (after making sure of a 
material balance), the valve provided at the inlet and outlet of the 
reactor were closed at the same time, liquid remaining in the reactor was 
drawn out to be measured. Then, the liquid hold up ratio was calculated 
and the value was 50%. The inlet temperature was controlled at 94.degree. 
C., then the outlet temperature was 116.degree. C. The reaction results 
determined from the composition of the inlet and outlet of the reactor 
were as follows: the ACP conversion ratio was 96%, while the EB 
selectivity ratio was 1.7%. 
Example 2 
The experiment was carried out in the same manner as in example 1, except 
that a fresh material liquid and hydrogen gas were supplied into a reactor 
by down flow, and liquid hold up ratio was adjusted to be set at 35%. The 
temperatures at the reactor inlet and outlet in steady state were found to 
be 109.degree. C. and 118.degree. C., respectively. The reaction results 
determined from the composition of the inlet and outlet of the reactor 
were as follows: the ACP conversion ratio were 94%, and the EB selectivity 
ratio was 1.8%. 
Example 3 
The experiment was carried out in the same manner as in example 1, except 
that the catalyst volume was 21(the height of the catalyst bed was 148 
cm), and that a fresh material liquid containing 46 wt % of ACP, 20 wt % 
of MBA, and 34 wt % of the other compounds at a rate of 21/hr, and mixed 
gas made of 84 volume % of hydrogen and 16 volume % of methane at a rate 
of 1.8 Nm.sup.3 /hr were supplied therein. The inlet temperature was 
controlled at 84.degree. C., then the outlet temperature was 119.degree. 
C. The reaction results determined from the composition of the inlet and 
outlet of the reactor were as follows: the ACP conversion ratio was 96%, 
while the EB selectivity ratio was 1.7%. 
Comparative Example 1 
The experiment was carried out in the same manner as in example 2, except 
that the liquid hold up ratio was set at 25%, and that a fresh material 
liquid containing 52 wt % of ACP, 18 wt % of MBA, 0.04 wt % of EB, and 30 
wt % of the other compounds was supplied. The inlet temperature was 
controlled at 102.degree. C., then the outlet temperature was 115.degree. 
C. The reaction results determined from the composition of the inlet and 
outlet of the reactor were as follows: the ACP conversion ratio was 92% 
while the EB selectivity ratio was 2.6%.