Technical Field
The present invention relates to a fixed bed shell-and-tube heat exchanger-type
reactor used for producing unsaturated acids from olefins via fixed bed partial oxidation.
Background Art
A process of producing unsaturated acids from vapor phase C3 ~ C4 olefins by
using a catalyst is a typical process of catalytic vapor phase oxidation.
Particular examples of such catalytic vapor phase oxidation include a process of
producing acrolein and/or acrylic acid by the oxidation of propylene or propane, a
process of producing methacrolein and/or methacrylic acid by the oxidation of
isobutylene, t-butyl alcohol or methyl-t-butyl ether, a process of producing phthalic
anhydride by the oxidation of naphthalene or orthoxylene, and a process of producing
maleic anhydride by the partial oxidation of benzene, butylene or butadiene.
Generally, catalytic vapor phase oxidation is carried out by charging one or more
kinds of granular catalysts into a reactor tube, supplying feed gas into a reactor through
a reaction tube, and contacting the feed gas with the catalyst in the reactor tube.
Reaction heat generated during the reaction is removed by heat exchange with a heat
transfer medium, whose temperature is maintained at a predetermined temperature.
The heat transfer medium for such heat exchange is provided on the outer surface of
the reaction tube so as to perform heat transfer. The reaction mixture containing a
desired product is collected and recovered through a duct, and men sent to a pu-
rification step. Since the catalytic vapor phase oxidation is a highly exothermic
reaction, it is very important to control the reaction temperature in a certain range and
to reduce the size of the temperature peaks at hot spots generated in reaction zones. It
is also important to accomplish heat dispersion at a point to be subjected to heat ac-
cumulation due to the structure of the reactor or that of the catalyst layer.
The catalysts that may be used to perform partial oxidation of olefins include
composite oxides containing molybdenum and bismuth, molybdenum and vanadium,
or mixtures thereof.
Generally, (meth)acrylic acid, a finalprodnct, is produced from propylene,
propane, isoboryleaie, t-butyl alcohol or methyl-t-butyl ether (referred to as 'propylene
or the like', hereinafter) by a two-step process of vapor phase catalytic partial
oxidation. More particularly, in the first step, propylene or the like is oxidized by
oxygen, inert gas for dilution, steam and a certain amount of a catalyst, so as to
produce (meth)acrolein as a main product Then, in the second step, the (meth)acrolein
is oxidized by oxygen, inert gas for dilution, steam and a certain amount of a catalyst,
so as to produce (meth)acrylic acid. The catalyst used in the first step is a Mo-Bi-based
oxidation catalyst, which oxidizes propylene or the like to produce (meth)acrolein as a
main product Also, some acrolein is continuously oxidized on the same catalyst to
partially produce (meth)acrylic acid. The catalyst used in the second step is a Mo-
V-based oxidation catalyst, which mainly oxidizes (meth)acrolern in the mixed gas
containing the (meth)acrolein produced from the first step to produce (meth)acrylic
acid as a main product.
A reactor for performing the aforementioned process is provided either in such a
manner that both the two-steps can be performed in one catalytic tube, or in such a
manner that the two steps can be performed in different catalytic tubes, respectively.
US patent No. 4,256,783 discloses such a reactor.
Meanwhile, (meth)acrylic acid producers have made diversified efforts to improve
the structure of the above reactor so as to increase the production yield of (meth)acrylic
acid obtained from the reactor; to propose the most suitable catalyst to induce
. oxidation; or to improve operating conditions of the process.
As a part of such prior efforts, the high space velocity or the high concentration of
propylene or the like supplied into the reactor is used.. In this case, there is a problem
in that oxidation occurs rapidly in the reactor, making it difficult to control the
resultant reaction temperature. There is another problem in that hot spots are generated
in the catalyst layers of the reactor and heat accumulation occurs in the vicinities of the
hot spots, so mat the production of byproducts, such as carbon monoxide, carbon
dioxide and acetic acid increases at high temperature, thereby reducing the yield of
(meth)acrylic acid. .
Furthermore, when (meth)acrylic acid is produced by using propylene or the like to
a high space velocity and high concentration, reaction temperature increases
abnormally in the reactor, thereby causing various problems., such as the loss of active
ingredients from the catalyst layer, or a reduction in the number of active sites caused
by the sintering of metal components, resulting in degradation in the quality of the
catalyst layer.
Accordingly, in the production of (meth)acrylic acid, control of the reaction heat in
the relevant reactor is the most important to ensure high productivity. Particularly, both
the formation of hot spots in the catalyst layers and the heat accumulation in the
vicinities of the hot spots should be inhibited, and the reactor should be effectively
controlled so that the hot spots do not cause the so-called runaway phenomenon of the
reactor (runaway: a state in which the reactor cannot be controlled or the reactor
explodes due to a highly exothermic reaction). Therefore, it is very important to inhibit
the generation of the hot spots and heat accumulation in the vicinities of the hot spots
so as to extend the lifetime of catalysts and to inhibit side reactions, and thus to
increase the yield of (meth)acrylic acid. To achieve these objectives, many attempts
have been steadily made.
Meanwhile, in order to operate the above processes more effectively, the reaction
system should be designed in such a manner that it is suitable for oxidation with
excessive heat generation. Particularly, in order to inhibit the deactivation of a catalyst
caused by excessive heat generation, it is necessary to establish an efficient heat
control system capable of controlling extremely high temperatures at hot spots, heat
accumulation in the vicinities of the hot spots, and a runaway phenomenon. To provide
an efficient heat control system, many studies have been made to establish a circulation
pathway of molten salts by mounting various baffles (e.g., US patent No. 3,871,445),
to design an oxidation reactor integrated with a cooling heat exchanger (e.g., US patent
No. 3,147,084), to provide a multi-stage heat control structure using an improved heat
exchanger system (e.g., Korean patent application No. 10-2002-40043, and PCT/
KR02/02074), and to control the structure of a catalyst layer and the reaction
temperature, so as to be suitable for an improved heat exchange system (e.g., Korean
patent application No. 10-2004-0069117).
Disclosure of Invention
Technical Problem
In view of the above-mentioned problems occurring in the prior art, the present
inventors have made improvements in a fixed-bed shell-and-tube heat exchanger type
reactor of producing unsaturated acids from olefins. An objective of the present
invention is to provide a fixed-bed shell-and-tube heat exchanger-type reactor of
producing unsaturated acids from olefins, which comprises a catalyst layer with no
need for a layer of inactive materials, which has been packed in the reactor prior to a
catalyst layer in a second-step reaction zone, by controlling the activity of an inlet
portion of the catalyst layer of the second-step reaction zone and/or by controlling the
second-step reaction zone in a multi-stage manner.
Technical Solution
According to an aspect of the present invention, there is provided a shell-and-tube
heat exchanger type reactor that can be used for a process of producing unsaturated
acids from olefins via fixed-bed catalytic partial oxidation, which comprises at least
one reaction tube, each including at least one first-step catalyst layer, in which olefins
are oxidized by a first-step catalyst to mainly produce unsaturated aldehydes, and at
least two second-step catalyst layers, in which the unsaturated aldehydes are oxidized
by a second-step catalyst to produce unsaturated acids, wherein a first catalyst layer of
the second-step catalyst layers, disposed right adjacent to the first-step catalyst layer,
has an activity corresponding to 5 ~ 30% of the activity of the catalyst layer having a
highest activity among the second-step catalyst layers. There is also provided a method
of producing unsaturated acids from olefins by using the same reactor.
As used herein, the term 'activity' refers to the percent ratio of the conversion of
unsaturated aldehydes into unsaturated acids in a relevant catalyst layer, divided by the
conversion in the catalyst layer having the highest activity under the same conditions.
Description of Drawings
FIG. 1 is a schematic diagram showing the structure of a pilot reactor having one
reaction tube, and the structure of a catalyst layer inside the reaction tube, wherein both
the first-step reaction and the second-step reaction are carried out in one reactor
according to Example 1 of the present invention.
Mode for Invention
Hereinafter, the present invention will be explained in more detail.
The present invention provides a shell-and-tube heat exchanger type reactor that
can be used for a process of producing unsaturated acids from olefins via fixed-bed
catalytic partial oxidation, the reactor being an integrated reactor, in which a first-step
reaction of mainly producing unsaturated aldehydes from olefins and a second-step
reaction of producing unsaturated acids from the unsaturated aldehydes are carried out
sequentially in one reaction tube. The present invention makes an improvement in the
second-step reaction zone.
(1) Catalyst Layer in Second-Step Reaction Zone
The present invention is characterized in that the first catalyst layer of at least two
second-step catalyst layers, disposed right adjacent to the first-step catalyst layer, has
an activity corresponding to 5 ~ 30% of the activity of the catalyst layer having the
highest activity among the second-step catalyst layers.
In general, the inlet portion (herein, the second catalyst layer of the second-step
catalyst layers) of the second-step reaction zone has a high concentration of un-
saturated aldehydes and oxygen, thereby causing a severe reaction. Thus, the inlet
portion contributes to the total conversion of the unsaturated aldehydes to a degree of
40% or higher. Therefore, it is preferable to control the reaction in the inlet portion of
the second-step reaction zone in such a manner that the peak temperature of the
catalyst is significantly lower than the calcination temperature of the catalyst
The temperature of unsaturated aldehyde-containing gas produced from the first-
step reaction generally ranges from 300 °C to 380 °C, which is the same as the
temperature of the first-step catalyst layer. The temperature of the second-step catalyst
layer suitably ranges from 250 °C to 350 °C. Therefore, the unsaturated aldehyde-
containing gas produced from the first-step reaction should be cooled so that the
temperature of the gas is adjusted to the reaction temperature of the second-step
reaction zone. For this, an inactive layer formed of inactive materials has been
introduced between the first-step reaction zone and the second-step reaction zone
according to the prior art. However, according to the present invention, a catalyst layer,
which has the activity of the second-step catalyst but a significantly lower catalytic
activity, for example by mixing inactive materials with the second-step catalyst, is
introduced into a reactor. By doing so, it is possible to reduce the temperature of the
unsaturated aldehyde-containing gas produced from the first-step reaction, while
decreasing the load of conversion of the unsaturated aldehydes in the second catalyst
layer of the second-step catalyst layers, in which unsaturated acids are produced to a
full scale.
In other words, according to the present invention, at least two second-step catalyst
layers are disposed right adjacent to the first-step catalyst layer with no use of an
inactive layer, wherein the first catalyst layer of the second-step catalyst layers
performs pre-reaction of a part of the unsaturated aldehydes into unsaturated acids, so
that the second catalyst layer of the second-step catalyst layers can perform the
reaction of producing unsaturated acids from unsaturated aldehydes to a full scale
under mild conditions with a reduced load of conversion of unsaturated aldehydes. Par-
ticularly, the first catalyst layer of the second-step catalyst layers causes the un-
saturated aldehyde-containing gas produced from the first-step reaction to have a
temperature and a pressure, suitable for the reaction conditions of the second catalyst
layer of the second-step catalyst layers. For example, the unsaturated aldehyde-
containing gas (reaction product of the first-step reaction) present at about 300 °C can
be adapted to the reaction temperature of the second-step reaction zone, which is lower
than the above temperature by about 30 ~ 50 °C, by virtue of the first catalyst layer of
the second-step catalyst layers. Therefore, it is possible to prevent excessive heat
generation in the second-step reaction zone and to extend the lifetime of the second-
step catalyst
Additionally, when the load of conversion of the unsaturated aldehydes in the
second catalyst layer of the second-step catalyst layers decreases, it is possible to suf-
ficiently increase the temperature of a heat transfer medium in the shell space cor-
responding to the second catalyst layer of the second-step catalyst layers, resulting in
an increase in the conversion, and thus an increase in the yield of unsaturated acids.
. Herein, it is preferable that the first catalyst layer of the second-step catalyst layers
shows a drop of the load of conversion of unsaturated aldehydes (i.e., conversion of
unsaturated aldehydes into unsaturated acids, caused by the first layer of the second-
step catalyst layers) of 5 ~ 30%.
Also, it is preferable that the first catalyst layer of the second-step catalyst layers
has a catalytic activity corresponding to 5 ~ 30% of the catalytic activity of the catalyst
layer having the highest activity among the second-step catalyst layers, so that the
aldehyde-containing mixed reaction gas introduced into the second catalyst layer of the
second-step catalyst layers can be cooled to a temperature suitable for oxidation.
The unsaturated aldehyde-containing gas, which is a reaction product obtained
from the first-step reaction zone (i.e., gas containing unsaturated aldehydes, oxygen,
nitrogen, steam, unsaturated acids, acetic acid, carbon dioxide, carbon monoxide and a
small amount of byproducts), has a temperature higher than the HTS (heat transfer salt)
present at the inlet of the second-step reaction zone by 20 °C or more. Hence, the first
catalyst layer of the second-step catalyst layers should be designed so as to inhibit an
excessive exothermic reaction. For this reason, it is preferable for the first catalyst
layer of the second-step catalyst layers to have a catalytic activity corresponding to 5 ~
30% of the catalytic activity of the catalyst layer having the highest activity among the
second-step catalyst layer.
For example, when mixing catalyst particles with inactive material particles to
provide the first catalyst layer of the second-step catalyst layers, it is possible to use the
catalyst particles to an amount of 5 ~ 30 wt%.
Methods of reducing the activity of the first catalyst layer of the second-step
catalyst layers include: a method of mixing the same catalytically active component as
used in another catalyst layer of the second-step catalyst layers with inactive materials
and packing the resultant mixture into the first catalyst layer; a method of forming the
first catalyst layer by using a catalyst having a catalytically active component or a
composition, different from the active component or the composition used in another
catalyst layer of the second-step catalyst layers; a method of forming the first catalyst
layer by using a catalytically active material having different particle sizes or volumes,
or catalyst pellets having different particle sizes or volumes; or a method of modifying
catalyst calcination temperatures. When the first catalyst layer of the second-step
catalyst layers is mixed with inactive materials, the catalytically active component may
be mixed with inactive material powder before pelletizing the catalyst Otherwise, the
pellets of inactive materials may be mixed with catalyst pellets. In the latter case, the
catalyst pellets include not only catalysts comprising catafytically active components
alone but also supported catalysts comprising catalytically active components
supported on some carriers. The shapes of such catalyst pellets include a spherical
shape, hollow cylindrical shape, cylindrical shape or other particle shapes.
The inactive materials that may be used in the first catalyst layer of the second-step
catalyst layers include alumina, silica alumina, stainless steel, iron, steatite, porcelain
and various ceramic products. The pellets of such inactive materials may take the form
of spheres, cylinders, rings, rods, plates, iron nets and agglomerates with a suitable
size. If desired, inactive materials having different forms may be used in combination
at an adequate mixing ratio.
Meanwhile, the first catalyst layer of the second-step catalyst layers preferably has
a length corresponding to 5 ~ 50% of the length of the reaction tube of the second-step
reaction zone.
The first catalyst layer of the second-step catalyst layers is the layer having a
reduced catalytic activity so as to prevent degradation in the thermal stability caused
by an excessive reaction heat, which is generated by chemical reactions in the catalyst
layer. However, it is preferable for the first catalyst layer to provide a conversion ratio
of reactants to a degree of 5% or more, in order to ensure the effect of stabilizing the
temperature in the second catalyst layer of the second-step catalyst layers. The length
of the first catalyst layer depends on the activity of the corresponding catalyst In order
to provide a conversion ratio of about 5% by the first catalyst layer, based on the total
conversion ratio of the second-step reaction, the first catalyst layer should have a
length corresponding to at least 5% of the length of the reaction tube of the second-step
reaction zone, with the proviso that the first catalyst layer has an activity as disclosed
herein. However, when the length of the first catalyst layer is too long relative to the
total length of the second-step catalyst layer, the overall activity of the total catalyst
layer decreases, which may result in a significant decrease in conversion ratio.
Therefore, it is preferable that the first catalyst layer of the second-step catalyst layers
is less than 50% of the length of the second-step reaction zone. In other words, high-
activity catalyst layers of the second-step catalyst layers, except the first catalyst layer,
should be provided to a proportion of at least 50%, so as to obtain a conversion ratio of
at least 95%.
As described above, the catalyst layer according to the present invention avoids a
need for an inactive layer for cooling between the first-step reaction zone and the
second-step reaction zone, and makes it possible to reduce the length of the catalytic
reaction tube. Therefore, the reactor according to the present invention is very cost-
efficient
(2) Partition for Dividing First-Step Reaction Zone from Second-Step Reaction
Zone, and Placement of First Catalyst Layer of Second-Step Catalyst Layers
The composition, temperature and pressure of feed mixture to the second-step
reaction zone, namely, those of a resultant product in the first-step reaction zone in
which unsaturated aldehydes are mainly produced from olefins, depend on those of
feed mixture to the first-step reaction zone. Hence, it is preferable to change the
temperature condition of a heat transfer medium in the second-step reaction zone in
order to establish new optimal process conditions flexibly depending on variations in
the external environment and feed mixture conditions.
According to another aspect of the present invention, the shell space of the reactor
is divided axially by using a partition into two shell spaces, wherein one of the shell
spaces mainly comprises the first-step reaction zone and the other of the shell spaces
comprises the second-step reaction zone. Herein, the first catalyst layer of the second-
step catalyst layers, corresponding to the inlet portion of the second-step reaction zone,
is packed into the reaction tube in such a manner that it includes the whole sections of
the partition, by which the shell space of the first-step reaction zone is divided from
that of the second-step reaction zone. Considering the cost needed for the construction
of the reactor, it is preferable for the first catalyst layer of the second-step catalyst
layers to occupy the first-step reaction zone by at most 500 mm. Retention time cor-
responding to about 500 mm may reduce the load of conversion of unsaturated
aldehydes to about 10%. When the first catalyst layer of the second-step catalyst
layers, which has a low catalytic activity according to the present invention, is
disposed in the reaction tube at a position corresponding to the portion having the
partition, by which the shell space of the first-step reaction zone is divided from that of
the second-step reaction zone, it is possible to prevent a local temperature increase
caused by an incomplete heat transfer at the portion having the partition.
(3) Multi-stage Heat Control for Second-Step Reaction Zone
According to the present invention, the catalyst layer is formed with no use of a
cooling layer that has been packed into the reactor prior to the catalyst layer of the
second-step reaction zone. For this reason, it is preferable to perform the heat control
of the second-step reaction zone in a multi-stage manner, besides controlling the
catalytic activity of the first catalyst layer of the second-step reaction zone.
To perform such multi-stage heat control, it is preferable to further divide the shell
corresponding to the second-step reaction zone into at least two shell spaces by using
partitions, and to set the temperature of the heat transfer medium supplied to each shell
space in an independent manner.
By doing so, it is possible to set an optimal temperature depending on the activity
of the catalyst packed into the reaction tube of the relevant shell, and thus to increase
the yield. Also, it is possible to inhibit heat accumulation at a hot spot and to prevent a
so-called runaway phenomenon by virtue of the aforementioned multi-stage heat
control.
It is preferable to set the temperature of the heat transfer medium in such a manner
that the temperature of the reaction mixture at the beginning of the first catalyst layer
of the second-step catalyst layers is higher than the temperature of the heat transfer
medium circulating in the first shell space of the second-step reaction zone by 20~ 70
°C . This makes it possible to inhibit an excessive exothermic reaction and to provide a
sufficient catalytic activity. On the other hand, it is preferable to set the temperature of
the heat transfer media of the subsequent shell spaces high enough to increase the
conversion of the unsaturated aldehyde as high as possible.
Reference will now be made in detail to the preferred embodiments of the present
invention. It is to be understood that the following examples are illustrative only and
the present invention is not limited thereto.
Example 1. Use of Mixed Catalyst Layer and Multi-stage Heat Control
The following experiment was carried out in a pilot reactor having one reaction
tube, in which both the first-step reaction and the second-step reaction are performed.
The reaction tube had an inner diameter of 26 mm. The first-step catalyst layer and the
second-step catalyst layer were packed into the reaction tube to a height of about 3570
mm and about 3125 mm, respectively. The catalyst packed into the first-step reaction
zone was a first-step oxidation catalyst based on molybdenum (Mo) and bismuth (bi).
Preparation of the catalyst is disclosed in Korean Patent No. 0349602 (Korean Patent
Application No; 10-1997-0045132). Each of the three catalyst layers packed into the
second-step reaction zone was comprised of a second-step oxidation catalyst based on
molybdenum (Mo) and vanadium (V). Preparation of the catalyst is disclosed in
Korean Patent No. 0204728 or 0204729.
The second-step catalyst layers were formed by using three catalyst layers that
have different activities, increasing when viewed from the inlet to the outlet (see US
Patent Nos. 3801634 and 4837360: Control of Catalytic Activity). The first catalyst
layer of the second-step catalyst layers, which was the inlet portion of the second-step
reaction zone, was comprised of amixture of 20 wt% of the same catalytic substance
as used in the third catalyst layer of the second-step catalyst layers and 80 wt% of an
inactive material. Therefore, the first catalyst layer had an activity corresponding to
about 20% of the activity of the third catalyst layer. The second catalyst layer of the
second-step catalyst layers had an activity corresponding to about 87% based on the
activity of the third catalyst layer.
The three catalyst layers of the second-step reaction zone had a height of 500 mm,
700 mm and 1925 mm, respectively, along the axial direction. The mixed layer as the
first catalyst layer of the second-step catalyst layers was packed into the reaction tube
corresponding to the shell space of the second-step reaction zone to a height of 250
mm, and the remaining height (250 mm) of the first catalyst layer was packed in such a
manner that the remaining part covered the partition (partition for dividing the first-
step reaction zone from the second-step reaction zone) and some part of the shell space
of the first-step reaction zone.
The second-step reaction zone was divided into two independent shell spaces by a
partition disposed at the border between the second catalyst layer and the third catalyst
layer. Each of the molten salts filled into each of the shell spaces was individually set
at a temperature of 275 °C and 270 °C.
Starting materials injected into the second-step reaction zone (at the position of the
partition for dividing the first-step reaction zone from the second-step reaction zone)
included acrolein, acrylic acid, oxygen, steam and nitrogen gas. More particularly, the
starting materials included 5.5% of acrolein, 0.9% of acrylic acid, 5.0% of oxygen,
1.0% of byproducts including CO and acetic acid, and the remaining amount of
nitrogen gas. The space velocity in the second-step reaction zone was 1500 hr-1
(standard temperature and pressure, STP). Herein, the space velocity of acrolein as a
hydrocarbon reactant supplied to the second-step reaction zone had a space velocity of
81 hr" (STP) and the mixed feed gas had a pressure of 0.4 kgf7cm2 G,
In the second-step reaction zone, two catalyst layers except the first catalyst layer
(mixed layer) showed temperature peaks at a temperature of 309.4 °C and 321.7 °C
along the axial direction. When propylene was introduced into the first-step reaction
zone to an amount of 7.0%, yield of acrylic acid was 86.2%. Yields of byproducts, i.e.,
CO (carbon monoxide and carbon dioxide) and acetic acid were 8.51 % and 1.80%, re-
spectively.
The reaction mixture that reached the first catalyst layer of the second-step catalyst
layers along the axial direction showed a temperature of 316 °C, which was different
from the temperature of the first heat transfer medium of the second-step reaction zone
by41°C.
Comparative Example 1; Experiment with No Use of Mixed Layer and Multi-
stage Heat Control
The shell space of the second-step reaction zone was a single non-divided shell
space. Additionally, a cooling layer formed of inactive particles was disposed between
the first-step reaction zone and the second-step reaction zone. The cooling layer was
packed into the reactor to a height of 500 mm. More particularly, the cooling layer was
packed into the second-step reaction zone to a height of 250 mm, and the remaining
part of the cooling layer was packed into the reaction tube ranging from the partition to
the first-step reaction zone. The second-step catalyst layers included two different
kinds of catalysts, which were the same as used in the second catalyst layer and the
third catalyst layer of Example 1, respectively. Both catalyst layers were packed to a
height of 700 mm and 2000 mm along the axial direction. The heat transfer medium
was set at a temperature of 270 °C under an isothermal condition. Except the foregoing,
the experiment was carried out in the same manner as described in Example 1. Ad-
ditionally, the two kinds of catalysts, which were used in Example 1, were used in this
Example to the same total amount
In the second-step reaction zone, two catalyst layers showed temperature peaks at a
temperature of 318.2 °C and 305.2 °C along the axial direction. Yield of acrylic acid
was 84.4%. Yields of byproducts, i.e., CO (carbon monoxide and carbon dioxide) and
acetic acid were 10.4% and 2 03%, respectively.
Comparative Example 2: Experiment with No Use of Mixed Layer and Multi-
stage Heat Control
Comparative Example 1 was repeated, except that the heat transfer medium was set
at a temperature of 275 °C .
In the second-step reaction zone, two catalyst layers showed temperature peaks at a
temperature of 325.1 °C and 324.9 °C along the axial direction. Yield of acrylic acid
was 82.9%. Yields of byproducts, i.e., CO (carbon monoxide and carbon dioxide) and
acetic acid were 11.4% and 2.42%, respectively.

It can be seen from the above results of Example 1 and Comparative Examples 1
and 2 that Example 1 provides a higher yield of acrylic acid, compared to the other
Examples by about 2% or more, and shows the first peak at a significantly stable
temperature. Yield of acrylic acid relates directly to the productivity, and thus is very
important Additionally, the first peak temperature is important because it relates to the
lifetime of the catalyst Reactions carried out in the second catalyst layer of the second-
step reaction zone according to Example 1 and the first catalyst layer of the second-
step reaction zone according to Comparative Examples 1 and 2 contribute the total
acrolein conversion by 50% or more. Although the above catalyst layers are relatively
short, they provide a relatively high conversion. In these layers, the compositions of
acrolein and oxygen are high, resulting in a severe reaction. Thus, in these layers, it is
preferable to control the reactions in such a manner that the peak temperature of the
catalyst is significantly lower than the calcination temperature of the catalyst
According to Example 1, the peak tenmerature is 309.4 °C. This indicates that the
reaction is carried out at a temperature significantly lower than the reaction tem-
peratures in Comparative Examples 1 and 2 (318.2 °C and 325.1 °C). Therefore,
because the reaction is carried out at the inlet portion of the catalyst layers, having a
high conversion load, under a milder condition, it is possible to extend the lifetime of
the catalyst
Additionally, Example 1 uses a mixed layer comprising a diluted catalyst in the
inlet portion, and thus permits a pre-reaction in a catalyst layer having a significantly
lower catalytic activity. Hence, it is possible to reduce the load of conversion of
acrolein into acrylic acid in the second catalyst layer to a certain degree. Because a part
of acrolein is preliminarily converted into acrylic acid under a mild condition provided
by the diluted mixed catalyst layer, the second catalyst layer can have a significantly
lower load of conversion of acrolein, compared to the loads of Comparative Examples
1 and 2 with no use of a mixed layer. Also, it is possible to obtain a higher conversion
by increasing the temperature of the heat transfer medium in the first shell space along
the axial direction, resulting in an increase in the yield of acrylic acid. In Example 1,
the first heat transfer medium has a temperature of 275 °C, which is higher than the
corresponding temperature of Comparative Example 1 by 5 °C. However, the peak
temperature of the catalyst layer according to Example 1 is lower than the cor-
responding temperature of Comparative Example 1 by about 9 °C. This is because the
mixed layer allows the reaction to be performed partially. -
In Comparative Example 2, the temperature of the heat transfer medium in the shell
space of the second-step reaction zone is same as the corresponding temperature of the
first shell space of the second-step reaction zone in Example 1 (275 °C ). However, due
to the lack of the mixed layer in the inlet portion, acrolein reacts severely with oxygen
under a high concentration, so that the peak temperature increases to 325.1 °C. Such
reaction performed at a high temperature may result in a drop in the lifetime of the first
catalyst layer having a high load of conversion.
Industrial Applicability
As described above, according to the present invention, there is provided a
structure of catalyst layers, a heat control system and a processing condition, adequate
to an improved reactor for producing unsaturated acids via two-step oxidation of
olefins. Thus, it is possible to obtain a final product in a stable manner even under a
high load reaction conditions. Additionally, use of the heat control system prevents the
generation of a hot spot or inhibits heat accumulation at the hot spot Therefore, it is
possible to obtain a high productivity of unsaturated acids and to extend the lifetime of
a catalyst
We Claim:
1. A shell-and-tube heat exchange reactor for producing unsaturated acids from olefins,
the reactor comprising:
at least one reaction tube;
at least one shell;
at least one first-step catalyst layer disposed in each reaction tube, wherein the first-step
catalyst layer comprises a composite oxide which comprises molybdenum and
bismuth, and which catalyzes the oxidation of olefins to produce unsaturated
aldehydes; and
at least two second-step catalyst layers disposed in each reaction tube, wherein each
second-step catalyst layer comprises a composite oxide which comprises
molybdenum and vanadium, and which catalyzes the oxidation of the unsaturated
aldehydes to produce unsaturated acids,
wherein
a first catalyst layer of the at least two second- step catalyst layers is disposed directly
adjacent to the at least one first-step catalyst layer, and
the first catalyst layer of the at least two second-step catalyst layers has an activity of 5
to 30 percent of an activity among the at least two second-step catalyst layers,
wherein the reactor further comprises a shell space, wherein
the shell space is defined by the at least one reaction tube and the at least one shell,
the shell space is divided axially by a first partition into at least two shells space
portions, wherein
a first shell space portion of the at least two shell space portions comprises a first
portion corresponding to a first-step reaction zone which comprises the at least
one first step catalyst layer, and
a second shell space portion of the at least two shell space portions comprises a
second portion corresponding to a second-step reaction zone which comprises a
second catalyst layer of the at least two second-step catalyst layers, and
the first catalyst layer of the at least two second-step catalyst layers is disposed in a
portion of the at least one reaction tube which overlaps an entirety of a cross-
section of the first partition.
2. The shell-and-tube heat exchange reactor of claim 1, wherein the first catalyst layer of
the at least two second-step catalyst layers provides a drop in a load of conversion of
unsaturated aldehydes of 5 to 30 percent.
3. The shell-and-tube heat exchange reactor of claim 1, wherein the first catalyst layer of
the at least two second-step catalyst layers occupies the first-step reaction zone by at most 500
millimeters.
4. The shell-and-tube heat exchange reactor of claim 1, wherein the second shell space
portion is divided into at least a third shell space portion and a fourth shell space portion by at
least one second partition, wherein each shell space portion comprises a heat transfer medium,
and each heat transfer medium is configured to be independently set at a different
temperature.
5. The shell-and-tube heat exchange reactor of claim 4, wherein a temperature of a
reaction mixture at a beginning of the first catalyst layer of the at least two second-step
catalyst layers is 20 to 70°C. higher than a temperature of a heat transfer medium circulating
in the third shell space of the second-step reaction zone.
6. The shell-and-tube heat exchange reactor of claim 1, wherein the first catalyst layer of
the at least two second-step catalyst layers has a length which is 5 to 50 percent of a length of
the reaction tube of the second-step reaction zone.
7. The shell-and-tube heat exchange reactor of claim 1, wherein the first catalyst layer of
the at least two second-step catalyst layers comprises a catalyst particle and an inactive
material particle.
8. The shell-and-tube heat exchange reactor of claim 1, wherein the first catalyst layer of
the at least two second-step catalyst layers comprises a plurality of pellets, each pellet
comprising a catalyst particle and an inactive material particle.
9. The shell-and-tube heat exchange reactor of claim 1, wherein the second-step reaction
zone is divided by the second partition into at least two shell spaces.