WO 2005/061414 PCT/KR2004/003373
METHOD OF PRODUCING UNSATURATED ACID IN FIXED-BED CATALYTIC
PARTIAL OXIDATION REACTOR WITH ENHAHCED HEAT CONTROL SYSTEM
Technical Field
5 The present invention relates to a process of producing
unsatutated acids from unsaturated aldehydes, particularly a
process of producing acrylic acid from acrolein, by the
catalytic vapor phase oxidation, as well as a fixed bed
shell-and-tube heat exchanger-type reactor for use in this
10 process.
Background art
A process of producing unsaturated aldehydes and
unsaturated acids from olefins corresponds to typical
15 catalytic vapor phase oxidation.
Generally, catalytic vapor phase oxidation is carried
a reactor tube (catalytic tuae), supplying feed gas into a
reactor through a pipe, 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
mediumwhose temperature is maintained at a predetermined
temperature. The heat transfer medium for heat exchange is
provided on the outer surface of the catalytic tube so as to
25 perform heat transfer. The mixture containing the desired
product is collected, recovered and sent to a purification
step through a pipe. Since the catalytic vapor phase
oxidation is a highly exothermic reaction, it is vary
important to control the reaction temperature in a certain
30 range and to reduce the size of the temperature peak at a hot
1

WO 2005/061414 PCT/KR2004/003373
spot occurring in a reaction zone.
The partial, oxidation of olefin uses a mltimetal oxide
containing molybdenum and bismuth or vanadimn or a mixture
thereof, as a catalyst. Typical examples thereof include a
5 process for the production of acrolein or acrylic acid by the
oxidation of propylene, a process for the production of
phthalic anhydride by the partial oxidation of naphthalene of
orthoxylene, and a process for the production of maleic
anhydride by the partial oxidation of benzene, butylene or
10 putadiene.
Generally, acrylic acid, a final product, is produced
from propylene by a two-stage process of vapor phase
catalytic partial oxidation. In a first stage, propylene is
oxidized by oxygen, dilution insert gas, steam and a certain
15 amount of a catalyst, so as to mainly produce acrolein, and
in a second stage, the produced acrolein is oxidized by
oxygen, inert dilution gas, steam and a certain amount of a
catalyst, so as to produce acrylic acid. The catalyst, used in
the first stage is a Mo-Bi-based oxidation catalyst which
20 oxidizes propylene to mainly produce acrolein. Also, some
acrolein is continuously oxidized on such a catalyst to
produce acrolic acid. The catalyst used in the second stage
is a Mo-V-based oxidation catalyst, which oxidizes mainly
acrolein in acrolein-containing gas mixture produced in the
25 first-stage, thus mainly producing acrylic acid.
A reactor for performing such a process is provided
either in such a manner that both the two-stages can be
performed in one catalytic tube or in such a manner that the
two stages can be performed in different catalytic tubes (see
30 US patent No. 4,256,783).
2

WO 2005/061414 PCT/KR2004/003373
Meanwhile, acrylic acid, manufacturers now conduct
diversified efforts to improve the structure of such a
oxidation, or to inprove process operations, so as to
5 increase the production of acrylic acid by the reactor.
In part of such prior efforts, propylene which is
supplied into the reactor is used at high space velocity or
high concentration. In this case, there are problems in that
10 control the resulting reaction temperature, and also a high
temperature at hot spot in the catalyst layer of the reactor
and a heat accumulation around the hot spot are produced,
resulting in an increase in the production of byproducts,
such as carbon monoxide, carbon dioxide and acetic acid, thus
15 reducing the yield of acrylic acid.
Furthermore, in the case of producing acrylic acid
using a high space velocity and high concentration of
propylene, as an abnormal increase in temperature occurs in
the reactor, various problems, such as the loss of active
20 ingredients from the catalyst Layer, a reduction in the
number of active sites caused by the sintering of metal
components, are caused, thus deteriorating the function of
the catalyst layer.
Accordingly, in the production of acrylic acid, the
25 control of the heat of reaction in the relevant reactor is
important of all things. Particularly, not only the formation
of hot spots in the catalytic layer but also the accumulation
of heat around the hot spot must be inhibited, and the
reactor must be effectively controlled such that the hot
30 spots do not lead to reactor runaway (a state where the
3

WO 2005/061414 PCT/KR2004/003373
reactor is not controlled or explodes by a highly exothermic
reaction).
Thus, it is very important to inhibit hot spots and
heat accumulation around the hot spot so as to extend the
5 life cycle of a catalyst and inhibit side reactions, thus
increasing the yield of a product such as acrylic acid. To
achieve this inhibition, various attempts have been steadily
made.
A fundamental method is to form several catalyse layers
direction"). Namely, at a reactor inlet side where hot spots
generate, a catalytic layer with low activity is formed, and
catalyst layers whose activities increase slowly toward a
15 reactor outlet side are formed. Typical methods for
catalytic particles by mixing a catalytic material with
inactive materials (e.g., US patent No, 3,801,634, Japanese
patent No, 53-30688B, and Japanese patent No. 63-38831); a
20 method of controlling activity and selectivity by either
changing the kind of alkali, metals and controlling the amount
thereof (e.g., US patent No. 6,563,000); a method of
controlling activity by adjusting the occupied volume of
catalytic particles (e.g., US patent No. 5,719,318); and a
25 method for controlling activity by controlling sintering
temperature in the preparation of a catalyst (e.g., US patent
No. 6,028,220). However, such methods have some effects but
still need to be iuproved.
Furthermore, in order to more effectively use the
30 above-mentioned technologies, a reactor system needs to be
4

WO 2005/061414 PCT/KR2004/003373
designed such that, it is suitable for oxidation with
5 control system capable of controlling excessively high peak
temperature at hot spots, thermal accumulation around the hot
spot and runaway. For the establishment of the efficient heat
introduction of a perforated shield plate (e.g., US patent
10 No. 4,256,783, European patent No, 293224A, and Japanese
pathway of molten salts by the placement of various baffles
(e.g., US patent No. 3,871,445), the design of an oxidation
reactor integrated with a cooling heat exchanger (e. g., US
using an inproved heat exchanger system [e.g,, Korean patent
application No. 10-2002-40043, and PCT/KR02/02074), etc.
Brief Description, of the Drawdngs
20 FIG. 1 is a schematic diagram showing the structure of
catalyst layers and the location of a partition in a pilot
reactor in which first-stage reaction and second-stage
reaction are successively performed in one catalytic cube. A
partition is placed at a boundary between the catalyst layers
25 in the second-stage reaction zone.
FIG. 2 is a schematic diagram showing the structure of
a pilot reactor consisting of two catalytic tubes, and the
structure of catalyst layers and the location of a partition
in each of the catalytic tubes. First-stage reaction and
30 second- stays reaction are conducted in the two catalytic
5

WO 2005/061414 PCT/KR2004/003373
tubes, respectively, and a partition is placed at a boundary
between the catalyst layers in the second-stage reactor.
FIG. 3 is a schematic diagram showing the structure of
a pilot reactor consisting of two catalytic tubes, and the
5 structure of catalyst layers and the location of a partition,
in each of the catalytic tubes. First-stage reaction and
second-stage reaction are conducted in the two catalytic
tubes, respectively, and a partition is not placed at a
boundary between the catalyst layers in the second-stage
10 reactor.
FIG. 4 is a schematic diagram showing the structure of
a pilot reactor consisting of two catalytic tubes, and the
stage reaction and second-stage reaction are conducted in the
15 two catalytic tubes, respectively, and a partition is not
Disclosure of the Invention
As described above, since the catalytic vapor phase
20 oxidation not only progresses at high temperature but also is
an exothermic reaction which has excessiue heat generation,
it can cause a reduction in selectivity due to the generation
of a hot spot with very high temperature around a reactor
inlet or the heat accumulation around the hot spot, and also
25 can result in a significant- reduction in the performance of a
catalyst in a long-term viewpoint. Particularly, if the
temperature of the hot spot is higher than the calcination
temperature of the catalyst, the life cycle of the catalyst
will be reduced to shorten the replacement time of the entire
30 catalyst layers, resulting in an economical loss. In
6

WO 2005/061414 PCT/KR2004/003373
addition, if the activity of the filled catalyst layers is
reduced and the temperature of a heat transfer Medium (molten
salt) is elevated in order to compensare for the reduction in
activity, the temperature of a hot spot and the heat
result, a solution to solve this problem is required.
A catalyst for use in the second-stage reaction zone of
mainly producing unsaturated acids from unsaturated aldehydes
is generally calcinated in a temperature of 300-500 °C. For
10 this reason, when the maximum peak temperature of the
catalyst layer is higher than the calcination temperature in
the preparation thereof, the deterioration of the catalyst
layer will occur, resulting in a reduction in yield.
Accordingly, there is a need for a production process and
plurality of reaction spaces so that the peak, temperature of
each of the reaction zones can be controlled.
In addition, in the results of experiments conducted by
the present inventors over several years, if a second-stage
20 reactor filled with a highly active catalyst having an
independent temperature control along the axial direction, a
hot spot close to the calcination tamperature of the catalyst
25 The present inventors have made improvements in a
fixed-bed shell-and-tube heat exchanger-type reactor of
producing unsaturated aldehydes and unsaturated acids from
olefins. In the inprovements, a second-stage reaction zone of
performing the catalytic vapor phase oxidation of an
30 acrolein-containing gas mixture produced in a first-stage
7

WO 2005/061414 PCT/KR2004/003373
reaction zone was divided into two or more zones in an axial
direction by at least one partition, and the temperature of a
heat transfer medium filled in each of the divided shell
spaces of the second-stage reaction zone was independently
and the degree of reaction, As a result of such improvements,
the present inventors have found that a hot spot and heat
accumulation around the hot spot could be inhibited. The
present invention has been perfected based on this finding.
10 An object of the present invention is to provide a
production process in which the temperature difference
between the peak, temperature of a catalyst layer is each of
the divided reaction zones and the temperature of a heat
transfer medium filled in the shell space corresponding to
15 that zone is controlled, so that the process is not only
thermally stable but also can be operated without a reduction
in yield, even in the presence of a catalyst with very high
activity, as well as an improved beat exchange-type reactor
for use in this process.
20 Another object of the present invention is to provide a
production process in which a reaction inhibition, layer is
inserted, in order to facilitate the removal of heat
generation at a location where the partition is placed, as
well as a shell-and-tube heat exchanger-type reactor for use
25 in this process.
In one aspect, the present invention provides a process
of producing unsaturated acids from unsatutated aldehydes,
particularly a process of producing acrylic acid from
acrolein, by fixed-bed catalytic partial oxidation in a
30 shell-and-tube heat exchanger-type reactor, the reactor
8

WO 2005/061414 PCT/KR2004/003373
comprising one or more catalytic tubes each including a
reaction zone of producing the unsaturated acids, the
improvement therein: the reaction zone is divided into two or
more shell spaces by at least one partition, each of the
5 divided shell spaces being filled with a heat transfer
medium, the heat transfer medium being maintained at
isothermal temperature or a temperature difference of 0-5 oC,
in which the temperature difference, between the temperature
of the heat transfer medium and the temperature of a hot spot
10 is limited, and/or a reaction inhibition layer is inserted
into a location where the partition is placed.
shell-and-tube heat exchanger-type reactor which can be used
in a process of producing unsaturated aldehydes and
25 unsaturated acids ftom clefins by fixed-bed catalytic partial
each including a first-stage reaction zone of mainly
producing the unsaturated aldehydes, a second-stage reaction
zone of mainly producing the unsaturated acids, or both the
zone is divided into two or more shell spaces by at least one
partition, each of the divided shell spaces being filled with
a heat transfer medium, the heat transfer medium being
maintained at isothermal temperature or at a temperature
25 difference of 0-5 °C, in which, the temperature difference
between the temperature of the heat transfer medium and the
temperature of a hot spot is limited, and/or a reaction
inhibition layer is inserted into a location where the
partition is disposed.
30 As used herein, the tern "divided shell spaces"
9

WO 2005/061414 PCT/KR2004/003373
indicates internal spaces surrounded by a catalytic tube, a
shell, a partition, a tube sheet, etc.
1. Placement of partition
Only with uniform circulation of a heat transfer medium
5 in a reactor, the heat of catalytic vapor phase reaction
cannot be satisfactorily controlled, and a great heat spot
underisable combustion reactions, thus reducing the yield of
10 the desired product. Furthermore, a catalyst, is always
exposed to high temperature caused by the hot spot sa that
the life cycle of the catalyst reduced.
Also, if the temperature of the heat transfer medium is
changed continuously in the axial direction without a
15 partition, excessive efforts will be required in order to
inhibit heat accumulation, and it will be very difficult to
exactly set the desired temperature profile. Moreover, the
magnitude and location of the hot spot will vary depending on
20 the kind and activity of a catalyst used.
Accordingly, considering the characteristic and
reactivity of the catalyst, the present invention utilizes a
heat control system in which, a partition is used such that a
hot spot and heat accumulation around the heat spot can be
25 controlled and the generation of heat can be structurally
controlled.
The location of the partition is preferably established
based on the exact prediction of a position where a hot spot
30 In the present invention, the location of the partition
10

WO 2005/061414 PCT/KR2004/003373
is established by the characteristic analysis of temperature
profile such that it includes at least one temperature peak.
5 controlled in an independent heat control space, and even the
case where the characteristic of temperature profile is
changed can be overcome with flexibility.
The hot spot where the highest temperature peak occurs
is produced by the generation of reaction heat resulting from
10 catalytic vapor phase oxidation, and determined by factors,
such as the composition of reactants, the flow rate (L/min)
of reactants, the temperature of a heat transfer medium,
etc, and has a certain position and size in a certain
process condition. However, when the activity of a catalyst
15 changes with time, the location and temperature magnitude of
the hot spot can change.
Each of catalyst layers generally has at least one hot
spot. Portions of the second-stage, reaction zone, which have
the problem of heat control, are hot spots which are
20 generated in the front portion of the second-stage oxidation
catalyst layer, in which unsaturated aldehyde (acrolein), a
main reactant, and molecular oxygen, are present at high
concentrations. Also, if two or more catalyst layers are
filled in the second-stage reaction zone, a hot spot can be
25 generated around the boundary between the adjacent catalyst
layers.
The partition is preferably located at either a
position where a hot spot and heat accumulation caused by the
hot spot beccme problems, or a position allowing the largest
30 possible removal of heat generation in each zone.
11

WO 2005/061414 PCT/KR2004/003373
2. Heat transfer medium
In the inventive production process and heat exchanger-
type reactor, che temperatures of the heat transfer medium in
each of the divided shell spaces are set as nearly as
5 possible to isothermal conditions. The difference between the
temperatures of the heat transfer medium at both the ends of
a catalyst layer in each of the divided shall spaces
preferably has a temperature difference of 0-5 oC and more
preferably 0-3 °C, depending on the amount of heat generation
10 and the heat transfer capacity of the heat transfer madium.
The temperature difference between the heat transfer
media in the adjacent shell spaces of the second-stage
5-15 °C, in an asial direction.
15 Examples of the heat transfer medium include very
highly viscous media, for example a molten salt which
nitrite. Other examples of the heat transfer medium include
phenyl other media (e.g., "Dowtherm"), polyphenyl media
20 (e.g., "Therm S"), hot oil, naphthalene derivatives (S.K.
oil) and mercury.
By controlling the flow rate of the heat transfer
medium, a reaction in each of the shell spaces of the reactor
can be carried out at substantially the same temperature of
25 the heat transfer-medium.
If the temperatures of the heat transfar medium filled
each of the divided shall spaces are set to change in the
moving direction of reactants (hereafter, referred to as the
"axial direction"), the reactivity of the catalyst layer will
30 change in proportion to temperature magnitude.
12

WO 2005/061414 PCT/KR2004/003373
By applying the multi-stage heat control system in
which the partition is used and the temperature of the heat
transfer medium is controlled, the present invention can
provide a process of producing acrylic acid in an efficient
5 and stable manner even in catalyst layers with the same size,
shape and activity, as well as a reactor for use in this
process.
The temperatures of the heat transfer medium (molten
salt) in each of the divided shall spaces are preferably so
10 set that a catalyst has the optimum activity.
In the present invention, in order to inhibit a hot
spot and heat accumulation around the hot spot either in a
catalytic tube for each, reaction stage or in each reaction
stage in one catalytic tube under high reactant concentration
15 or high reactant space velocity, the temperatures of the heat.
transfer medium are changed in the axial direction so as to
reduce catalyst damage caused by a highly exothermic reaction
20 The temperature control of the heat transfer medium in
the axial direction is preferably performed in the following
manner. The temperature profile of a catalyst layer is
analyzed so as to quantitatively determine the location and
peak magnitude of a hot spot. As a result of the analysis, in
25 a divided reaction region where the hot spot occurs, the
temperature of the. heat transfer medium is set close to the
lowest possible temperature for catalyst activation, and in
other regions where thermal accumulation at the hot spot
would not become a great problem, the temperature of the heat
30 transfer medium is increased to the maximum temperature
13

WO 2005/061414 PCT/KR2004/003373
acceptable in the present invention so as to obtain the
highest yield. Also, continuous feedback of the temperature
profile analysis is performed so as to set process conditions
to the optimum conditions.
5 Since a reactor front—portion with high unsaturated
aldehyde concentration and high unsaturated aldehyde space
velocity shows the highest activity, a hot spot of the
highest temperature peak is formed in the reactor front-
portion. It is preferable that the temperature of the heat
10 transfer medium within a portion of the shell space, which
corresponds to a location where this hot spot is formed,
should be lowered to the lowest possible temperature for
catalyst activation, such that the magnitude of the hot spot
can be reduced and heat accumulation around the hot spot can
15 be prevented while preventing significant reduction in
catalyst reactivity.
According to one embodiment of the present invention,
improvements are made in a process of producing unsaturated
acid by reacting unsaturated aldehyde in the presence of a
20 catalyst with molecular oxygen, dilute inert gas, steam, and
optionally recycled off-gas which has not been absorbed into
an absorbing column. In the improvements, the second-stage
reaction zone of producing unsaturated acid from unsaturated
aldehyde-containing gas is divided into two or more separate
25 shell spaces in an axial direction, and the temperatures of a
heat transfer medium filled in each of the shell spaces are
set within the temperature difference range proposed in the
present invention, so that the activity and reactivity of
catalyst layers are suitably controlled.
30 In the second-stage reaction zone where acrylic acid is
14

WO 2005/061414 PCT/KR2004/003373
mainly produced from acrolein, the temperature of the
catalyst layer with activity is about 260-360 °C and the
temperature of the heat transfer medium is set to about 260-
330 °C. Here, in addition to acrylic acid, unreaction
5 acrolein, carbon monoxide, carbon dioxide, steam, acetic
acid, unreacted propylene and small amounts of byproducts are
discharged through an outlet. Since the second-stage reaction
is a reaction which progresses at high temperature and is
highly exothermic, a heat of 60 kcal per g-mol of acrolein is
10 generated and the temperature at a hot spot reaches 310-350
°C.
for example, when a shell space corresponding to the
second-stage reaction zone is divided into three independent
spaces, two partitions will be disposed within the shell
15 space in a perpendicular direction to the axis of the
catalytic tube so as to provide a structure with three
divided shell spaces where the temperatures of the heat
transfer medium are independently controlled. In this case,
ths temperatures of the heat transfer medium filled in each
20 of the divided shell spaces may be set to, for example, 310
oC, 305 °C and 315 oC, respectively, in a direction from an
inlet to an outlet.
3- Control of temperature of heat transfer medium
The present invention is characterized in that the
25 temperatures of the heat transfer medium in a plurality of
the divided shell spaces are set in such a way that the
temperatures are suited to the activity and reactivity of a
catalyst. Namely, the temperatures of the heat transfer
medium are so set that, when the shell spaces divided by the
30 partitions in the second-stage- reaction zone are named, such
15

WO 2005/061414 PCT/KR2004/003373
as zone 1, zone 2, zone 3, ... and zone N in the axial
direction, ThI-TsaltI is 130 oC, and preferably oC, and
ThN-TsaltN is  110 °C, and preferably  70 oC, wherein N is an
integer of 2 or more.
5 Here, ThL is the peak temperature of a reaction mixture
(the peak temperature of the catalyst layer) in a catalyst
layer corresponding to the first shell space, and ThN is the
peak temperature of a reaction mixture in a catalyst layer
corresponding to the Nth shell space. And Tsalt is the
10 temperature of a heat transfer medium (molten salt) filled in
the first shell space, and TsaltN is the temperature of a heat
transfer medium filled in the Nth shell space.
If the temperatures of the heat transfer medium in each
of the shell spaces divided by the partition are set within
15 the temperature difference range given as described above,
the activity and reactivity of a catalyst can be suitably
controlled so as to inhibit a hot spot and heat accumulation
around the hot spot.
In the first shell space, the concentration and
20 pressure of reactants are high, so that the temperature
difference between the peak temperature of the catalyst layer
and the temperature of the molten salt is higher than that in
the next shell space. For this reason, the temperature
difference range in the first shell space will be surely
25 wider than that in the next shell space. However, the
inventive method is a method by which the magnitude of peak
temperature in the first shell space is minimized while a
temperature difference in the next shell space is also
limited to a certain range, so as to prevent local excessive
30 heat generation, thus making the shape of temperature profile
16

WO 2005/061414 PCT/KR2004/003373
smooth. The limited temperature difference range is based on
the result of various experiments conducted over several
years by the present inventors.
If operations are done without this limited temperature
5 difference range, the sintering of a catalyst in a hot spot,
the loss of important metal components, an increase in
byproducts, etc., can be caused, and particularly accidents
when introducing raw materials into a reactor. For these
10 reasons, the inventive method is technologically necessary
for safe start-ups and stable operations.
4. Reaction inhibition layer
The number of catalytic tubes in a commercial shell-
and-tube reactor of producing unsaturated acid such as
15 acrylic acid reaches several thousands to several tens of
thousands, and a partition disposed in the reactor has a very
large thickness of 50-100 mm. Thus, if the second-stage
reaction zone is divided into two or mare shell spaces, the
removal of heat generation caused by a reaction in the
20 position where the partition is disposed will not be easy,
thus causing a problem in heat transfer.
To eliminate such a problem, the present invention has
another characteristic in that a layer made of an inactive
material alone or a mixture of an inactive material and a
25 catalytic material, i.e., a reaction inhibition layer is
provided within a portion of the catalytic tube, which
corresponds to a position where the partition is disposed.
Such a reaction inhibition layer is a layer with
different characters from an inactive layer which is filled
30 between the first-stage reaction zone and the second-stage
17

WO 2005/061414 PCT/KR2004/003373
reaction zone to a height of about 400-1,000 mm so as to
induce cooling to a reaction temperature suitable for the
second—stage reaction, This reaction inhibition layer is a
filling layer for minimizing heat generation in a position
5 with the problem of heat transfer.
The volume ratio of an inactive meterial to a catalytic
material in this reaction inhibition layer is preferably 20-
100%, and more preferably 80-100%. The filling height of the
reaction inhibition layer is 20-500%, and preferably 120-
10 150%, relative to the thickness of the partition, indicating
that the reaction inhibition layer completely overlaps the
thickness of the partition.. However, if the height of the
reaction inhibition layer must be made smaller than the
thickness of the partition, the reaction inhibition layer
15 will preferably be filled in such a manner that the largest
possible area overlaps.
The inactive material used in the reaction inhibition
layer is designated as a material which is inactive to a
reaction, of producing unsaturatsd acids from olefins or
20 unsaturated aldehydes, for example, a catalytic oxidation
sphere, cylinder, ring, rod, plate or wire mesh shape, or a
mass shape with suitable size, or a suitable combination
thereof. Widely Known examples of the inactive material
25 include alumina, silica alumina, stainless steel, iron,
steatite, porcelain, various ceramics, and mixtures thereof.
5. Structure of catalyst layer
The catalyst tubes in the reactor include at least one
catalyst layer made of oxidation catalyst particles for each
30 of the two reaction zones.
18

WO 2005/061414 PCT/KR2004/003373
The catalyst layer in the second-stage reaction zone
may be made of either one layer whose activity is uniform in
the axial direction, or made of at least two layers stacked
in a direction along which the catalyst activity increases.
This is likewise applied to the catalyst layer in the first-
stage reaction zone.
6. Reactor structure and reaction procedure
Regarding the structure of a reactor according to the
present invention, the shell space in the second-stage
10 reaction zone is divided into at least two shell spaces by
the partition, such that the temperatures of the heat
transfer medium filled in each of the divided shell spaces
can be independently controlled. The temperatures of the heat
transfer medium filled in each of the divided shell spaces
reactivity of a catalyst.
FIGS, 1 to 3 show a pilot structure designed to
transfer the idea of the present invention, and the scope of
the present invention is not limited only to details shown in
20 the drawings.
It is well known that an actual shell-and-tube heat
exchanger-type reactor can be represented by one catalytic
tube reactor with respect to reactor behavior
characteristics, such as temperature, yield, etc. Thus, the
25 effects of the present invention will now be described by a
pilot experiment where one catalytic tube is disposed in each
reaction stage.
For the description below, a catalyst layer for a
second-stage reaction is named as follows, and the following
30 sequence coincides with a reaction pathway:
19

WO 2005/061414 PCT/KR2004/003373
The first catalyst layer in the second-stage reaction:
a second stage-layer A;
The second catalyst layer in the second-stage reaction:
a second stage-layer B;
5 The third catalyst layer in the second-stage reaction:
a second stage-layer C;
If necessary, the catalyst layers may be disposed in
such a manner that their catalytic activity gradually
10 increases toward the Layers A, B, C,
EIG. I shows the structure of a pilot reactor
structured such that two-stage reaction occurs in one
catalytic tube. As shown in FIG. 1, a first-stage reaction
zone 10 and a second-stage reaction zone 20 are connected in
15 series with each other, such that reactants fed into a
reactor inlet are subjected to first-stage reaction and then
to second-stage reaction, thus producing acrylic acid. If
necessary, two or more catalyst layers with different
activities (excluding an inactive material layer and a
20 reaction inhibition layer) can be included in each of the
reaction zone.
Hereinafter, a reaction system in which two catalyst
layers with different activities are placed in each reaction
stage will be described by way of example.
25 In FIG. 1, reference numerals 11, 21 and 22 denote
shell spaces (jackets) into which heat transfer media with
different temperatures are filled. FIG. 1 shows the structure
of the catalyst layers in the catalytic tube, and the
following layers are filled in the catalytic tube in an order
30 from the lower level to the upper level;
20

WO 2005/061414 PCT/KR2004/003373
Inactive particle-layer A 16
First-stage faction zone-.
First stage-layer A 14
First stage-layet B 15
5 Inactive particle-layer B 31
Second-stage reaction zone:
Second stage-layer A 24
Second stage-reaction inhibition layer 21
Second stage-layer B 25
10 The first stage-layer A and the first stage-layer B can
be filled with catalyst layers with the same or different
activities. The second stage-layer A and the second stage-
layer B can be filled with catalyst layers with the same or
different activities. Between the first-stage reaction zone
15 and the second-stage reaction zone, inactive particles
(inactive particle-layer B) are suitably filled such that the
temperature of a reaction mixture entering the second stage
is in the range of activation temperature of second stage-
layer A. The shell space in the second-stage reactor is
20 divided into two heat control spaces which are heat-
controlled independently. As shown in FIG. 1, a partition 23
in the second-stage reaction zone is located at a boundary
between the catalyst layers. Reference numeral 30 in FIG. 1
denotes a partition of providing a division between the
25 first-stage and second-stage reaction zones, and the inactive
material layer 31 is a filling layer of bring the temperature
of reactants to a temperature suitable for the catalyst layer
24 in the second-stage reactrion zone.
Reference numeral 1 in FIG. 1 denotes the flow of
30 reactants consisting of propylene, molecular oxygen, dilute
21

WO 2005/061414 PCT/KR2004/003373
gas, and steam. Reference numeral 3 in FIG. 1 denotes the
flow of products consisting of main product acrylic acid,
dilute gas, molecular oxygen, unreacted propylene, unreacted
acrolein, and small amounts of byproducts, etc. Into the
5 second-stage reaction zone according to the present
invention, acrolein-containing gas mixture passed through the
first-stage reaction zone (gas mixture just after the first
stage-layer B) is fed which consists of acrolein as a main
feed material, dilute gas, molecular oxygen, unreacted
10 propylene, acrylic acid, carbon monoxide, carbon dioxide, and
small amounts of byproducts.
Reference numerals 21 and 22 in FIG. 1 denote two
divided shell spaces (jackets) in the second-stage reaction
gone, and refscenes numeral 11 in FIG. 1 denotes a shell
1 5 space (jacket) in the first-stage reaction zone.
FIG. 2 shows the structure of a pilot reactor in which
a first-stage reaction zone and a second-stage reaction zone
are separated in two catalytic tubes, respectively, In FIG.
2, the fundamental structure of the reactor, and the
20 structure of the catalyst layers, are the same as those in
FIG. 1.
FIG. 3 shows a structure where two or more catalyst
layers with different activities are filled in each of the
reaction zones. In this structure, a partition is placed away
25 from a boundary between the catalyst layers. Also, this
structure can be used when the first heat control zone is
defined by a section, ranging from a second-stage reactor
inlet to the peak temperature zone of the second stage-layer
B, and the second heat control zone is defined by the
30 remaining section. Also, this structure can be applied when
22

WO 2005/061414 PCT/KR2004/003373
two or more adjacent temperature peaks are present in the
catalyst layer so that such temperature peaks need to be
controlled at the same time using one shell space (jacket) .
For example, peak temperatures occurring in the second
5 (stage-layer A and the second stage-layer B can be controlled
below a pre-determined peak temperature of catalyse layers to
be managed, by controlling the temperatures of heat transfer
medium filled of the first heat control zone. In FIG. 3, a
method of positioning the partition, and a method of filling
10 the catalyst and the inactive material , are the same as those
in FIG. I.
In the location of the partition, a first partition can
be disposed between the preceding catalyst layer and the
relevant catalyst layer in the filling order, and a second
15 partition can be disposed following the peak, position of the
relevant catalyst layer. If the relevant catalyst layer is a
first catalyst layer either, at a reactot inlet or at the
partition will be disposed following the peak position of the
20 relevant catalyst layer. The shell spaces divided by the
partition may include the position of one or more peak
temperatures occurring in a plurality of the catalyst layers.
The inventive heat control system can be applied in the
oxidation of olefins, and also in a reaction system where the
25 kind of reaction varies in the axial direction so that it is
reaction temperature must be changed according to each
reaction zone so that it is controlled at the optimal
temperature.
30
23

WO 2005/061414 PCT/KR2004/003373
Mode for Carrying Out the Invention
Hereinafter, the present invention will be illustrated
by way of the following examples which are not construed to
limit the scope of the present invention.
5 Example 1 (improved heat control system) : changes in
yield and magnitudes of temperature peaks at hot spots with
change in setting temperature of molten salt
As shown in FIG. 1, a pilot reactor was provided in
which first-stage reaction and second-stage reaction are
10 conducted in a catalytic tube. The catalytic tubes was 26 mm
in inner diameter, and the catalytic tube corresponding the
second-stage reaction zone was filled with catalyst layers
with a height of about 2670 mm. Reference numerals 21 and 22
in FIG. 1 denote the divided shell spaces of the second-stage
15 reaction zone. The temperatures of molten salts filled in the
shell spaces were set to 285 oC and 270 oC, respectively. The
two catalyst layers filled in the first-stage reaction zone
10 as shown in FIG. 1 were made of a catalyst based on
polybdenum (Mo) and bismuth (Bi), the preparation of which is
20 described in Korean patent No. 0349602 (application No. 10-
1997-0045132). The two catalyst layers filled in the sacond-
stage reaction zone 20 were made of a catslyst based on
molybdenum and vanadium (V), the preparation of which is
described in Korean patent No. 0204728 or Korean patent No.
25 0204729.
The second-stags reaction zone was filled with two
catalyst layers whose activity increases from an inlet to an
outlet, according to a method for controlling catalytic
activity as disclosed in US patent Nos. 3801634 and 4837360.
30 The activity of the first catalyst layer is about 87% of the
24

WO 2005/061414 PCT/KR2004/003373
second catalyst.
The second-stage reaction zone was filled with two
catalyst layers having heights of 700 mm and 1970 mm
respectively, in an axial direction. The location of a
5 partition in the second-stage reaction zone was 700 mm away
front the initiation point of the catalyst layers. This
partition was disposed based on the results of experimental
studies conducted by the present inventors over several
years, which revealed that a hot spot was generally generated
10 before locations 1000 mm away from the initiation point of
the catalyst layers, and 700 mm away from the initiation
portion under the experimental conditions of Example 1. In a
portion inside the catalytic tube corresponding to the
15 filled to a thickness corresponding 120% of the thickness of
the partition. An acrolein-containing gas mixture including
acrolein, acrylic acid, oxygen, steam, inert gas, carbon
monoxide, carbon dioxide and other byproducts, which has been
produced from the first-stage reaction zone, was fed into the
20 second-stage reaction region, passed through a reaction
pathway and then discharged through an outlet 3. The starting
materials fed into the second-stage reaction zone was
conprised of 5.5% of acrolein, 0.9% of acrylic acid, 5.0% of
oxygen, 1.0% of byproducts such as cox and acetic acid, and
25 the remaining amount of nitrogen gas. Space velocity in the
second-stage reaction zone was 1500 hr-I (STP) [standard
temperature and pressure) . Also, the space velocity of
acrolein (reaction hydrocarbon) entering the second-stage
reaction zone was 81 hr-1 (STP), and the pressure of the fed
30 gas mixture was 0.6 kgf/cm2G.
25

WO 2005/061414 PCT/KR2004/003373
Tht-Tsalt1 was 46.2 oC, and Tr2-Tsalt2 was 39.9 oC.
In the second-stage reaction zone, the peak temperature
84.82%. The yields of COx (carbon monoxide and carbon
6 dioxide) and acetic acid as byproducts were 9.73% and 2.13%,
(inactive material layer) did not occur, an abnormal increase
in temperature by a reduction in heat transfer efficiency was
not observed.
Example 2 (improved heat control system) : changes in
yield and magnitudes of temperature peaks at hot spots with
change in setting temperature of molten salt
This example was performed in the same manner as in
15 Example 1 except for the setting temperatures of a molten
salt in the second-stage reaction zone. The temperatures of
280 °C and 270 °C, respectively, in an axial direction.
In the second-stage reaction zone, the temperature at a
20 hot spot was 325.5 °C, and the yield of acrylic acid was
84.40%. The yields of COx avid acetic acid as byproducts were
9.90% and 1.95%, respectively.
Th1-Tsalt1, was 38.1 °C, and Th2-Tsalt2 was 55.5 °C.
Since a reaction in a reaction inhibition layer
25 (inactive material layer) did not occur, an abnormal increase
in temperature by a reduction in heat transfer efficiency was
not observed.
Example 3 (Improved heat control system): changes in
30 change in setting temperature of molten salt
25

WO 2005/061414 PCT/KR2004/003373
This example was performed in the same manner as in
Example 1 except for the setting temperatures of a molten
The temperatures of the molten salt in the second-stage
5 reaction zone were set to 280 "C and 270 °C, respectively, in
an axial direction, and the sheat pressure was abour 0.3
kgf/cm2G.
In the second-stage reaction zone, the temperature at a
hot spot was 335.2 °C and the yield of acrylic acid was
10 84.13%. The yields of COx and acetic acid as byproducts were
8.46% and 1.91%, respectively.
Th1-Tsalt1 was 27.2 °C, and Th2-Tsalt2 was 68.2 oC.
(inactive naterial layer) did not occur, an abnormal increase
15 in temperature by a reduction in heat transfer efficiency was
not observed.
Example 4 (a case of the use of catalyst layers with
slightly different activities
This Example was performed in the same manner as in
20 Example 1 except for the filling structure of the catalysts
and the setting temperature of molten salt.
The catalyst layers filled in the first-stage reaction
zone were the same as in Example 1. In the second-stage
reaction zone, different kinds of catalysts with slightly
25 different activities were filled to heights of 700 mm at a
first shell space and 1970 mm at a second shell space. The
activities of the two catalysts were about 5% higher in the
second shell space than in the first shell space. The
temperatures of molten salt in the two shell spaces of the
30 second-stage reaction zone were set to 275 °C and 270 °C,
27

WO 2005/061414 PCT/KR2004/003373
respectively, in an axial direction.
In the second-stage reaction zone, the yield of acrylic
acid was 83.38%. The yields of COx and acetic acid as
byproducts were 10.8% and 2.17%, respectively.
5 In the second-stage reaction zone,, the temperature of a
hot spot in the catalytic layer corresponding the first shell
space was 321.9 oC, and the temperature of a hot spot, in the
catalytic layer corresponding the second shell space was
313.5oC. Th1-Tsalt1 was 46.9 oC, and Th2-Tsalt2 was 43.5 °C.
10 Example 5 (a case of the use of catalyst layers with
the same activity)
The first-stage reaction zone was filled with a
catalyst layer of about 1200 mm and the second-stage
reaction zone was filled with catalyst layers of about 1100
15 mm. The catalysts filled in the second-stage reaction zone
had the same activity, size and shape. The composition of a
reaction mixture fed into the second-stage reaction zone was
the same as in Example 1. The temperatures of molten salt in
the two shell spaces of the second-stage reaction zone were
20 set to 260 °C and 265 °C, respectively, in an axial direction.
In the second-stage reaction zone, the yield of acrylic
acid was 84.16%, The yields of COx and acetic acid as
byproducts were 8.11% and 1.80%, respectively.
In the aecood-stage reaction zone, the temperature of a
25 hot spot in the catalytic layer corresponding the first shell
space was 311.8 °C, and the temperature of a hot spot in the
catalytic layer corresponding the second shell space was
230.5 °C. Th1-Tsalt1 was 51.8 oC and Th2-Tsalt2 was 15.5 °C.
Example 6 (a case ol the use of catalyst layers with
30 the same activity)
28

WO 2005/061414 PCT/KR2004/003373
Acrylic acid was produced in the same reaction
conditions as in Example 5 except that the activity of
catalysts in the second-stage reaction zone was 130% of the
acid was 83.17%. The yields of COx and acetic acid as
byproducts were 9.11% and 2.00%, respectively.
In the second-stage reaction zone, the temperature of a
hot spot in che catalytic layer corresponding the first shell
10 space was 333.1 °C, and the temperature of a hot spot in the
catalytic layer corresponding the second shell space was
329.5 oC. Th1-Tsalt1 was 73.1 °C, and Th2-Tsalt2 was 64.5 °C.
Comparative Example 1 (the case of operations under
isothermal conditions without the application of a multi-
15 stage heat control system) : Changgs in hot spot temperature
and yield with change in setting temperature of moltem salt
Comparative Example 1 was performed in the same manner
as in Example 1 except that the temperature of molten salt in
the second-stage reaction zone was set to an isothermal
20 temperature of 275 °C.
In the second-stage reaction zone, the yield of acrylic
byproducts were 9.07% and 2.16%, respectively.
In the second-stage reaction zone which had been
25 operated at isothermal conditions, the temperature of a hot
spot was 353.9 °C, and Th1-Tsalt1 was about 79 oC.
Comparative Example 2 (the case of operations under
isothermal conditions without the application of a multi-
stage heat control system) : the use of highly active
30 catalysts with the same activity and size
29

WO 2005/061414 PCT/KR2004/003373
Comparative Example 2 was performed in the same manner
as in Example 5 except that the temperature of molten salt in
the second-stage reaction zone was set to an isothermal
temperature of 275 °C.
5 In the second-stage reaction zone, the yield of acrylic
acid was 82.83%. The yields of COx and acetic acid as
byproducts were 9-35% and 2.40%, respectively.
In the second-stage reaction, zone which had been
operated at isothermal conditions, the temperature of a hot
10 spot was 410.1 °C, and Th1-Tsalt1 was 135.1 oC.
Comparative Examples 3 (the case where a multi-stage
heat control system was applied but operation was performed
at temperatures out of the limited temperature range):
Changes in hot spot temperature and yield with change in
15 setting temperature of moltem salt
This Comparative Example was performed in the same
manner as in Example 6 except that the second-stage reaction
zone was divided into two shell spaces and the temperatures
of molten salt in the divided shell spaces were set to 275 °C
20 and 280 °C, respectively, in an axial direction.
In the second-stage reaction zone, the yield of acrylic
acid was 81.87%. The yields of COx and acetic acid as
byproducts were 10.2% and 2.42%, respectively.
In a portion corresponding to the first shell space in
25 the second-stage reaction zone, the peak temperature (the
temperature at a hot spot) was 407.3 °C, and in a portion
corresponding to the second shell space, the peak temperature
was 391.3 °C. Th1-Tsalt1 was 132.3 °C, and Th2-Tsalt2 was about
111.3 °C.
30 Comperative Example 4 (a case where a multi-stage heat
30

WO 2005/061414 PCT/KR2004/003373
control system was applied but the thickness of a reaction
inhibition layer was 10% of the thickness of a partition);
Change in hot spot temperature and yield with change in
setting temperature of molten salt
5 The filling structure of the catalyst layers was the
same as in Example 4, but the reaction inhibition layer used
considering heat transfer in the location of the partition
was inserted to a thickness corresponding to only about 10%
10 in the second-stage reaction zone were set to 275 oC and 270
oC in an axial direction. The results of Example 4 and
Comparative Example 4 are shown in Table 1 below for
comparison.
Comparative Example 5 (a case where a multi-stage heat
15 control system was applied but a reaction, inhibition layer
was not used): Changes in hot spot tamperature and yield with
change in setting temperature of molten salt)
Example 4 was repeated except that the reaction
inhibition layer was not used. Heat transfer rate can be
20 cantrolled by, for example, a method of controlling the
salt in the second-stage reaction zone were set to 275 °C and
270 oC in an axial direction. The results of Example 4 and
Comparative Examples 4 and 5 are shown in Table 1 for
25 comparison.
(Table 1)

31

WO 2005/061414 PCT/KR2004/003373

Title: The temperature of a catalyst layer at the position, of a
partition.
It could be found that Th1-Tsalt1 and Th2-Tsalt2 in Examples
5 1 to 4 were within limits of 130 °C and 110 °C, and preferably
75 °C and 70 °C, respectively, as proposed in the present
invention. When Examples where the reaction inhibition layer
had been introduced in the multi-stage heat control system
and two or more catalyst layers had been used in the second—
10 stage reaction region, were compared to Comparative Examples,
it could be found that the yield in Examples was always
higher than that in Comparative Examples.
Particularly Example 1 conducted without the improved heat
15 control system, the yield of acrylic acid, a final prcduct,
was about 1.5% higher in Exanple 1 than in Comparative
Example 1.
And in Comparative Example 1, it could be found that T
(Th-Tsalt) exceeded 75 oC, a preferred value proposed in the
20 present invention, and the yield of acrylic acid, a final
product, was about 1.5% lower than that in Example 1 due to
increases in unreacted scrolein and byproducts, such as
carbon dioxide and acetic acid.
In addition, in Cornparative Example 2 using the highly
25 active catalyst with, reduced size, it could be found that T
32

WO 2005/061414 PCT/KR2004/003373
(Th-Tsalt) exceeded 130 °C, a limit proposed in the present
invention and the yield of acrylic acid was significantly
reduced as compared to Example 6.
In Comparative Example 3 where the second-stage
5 reactioin zone had been divided into two reaction zones whose
temperature setting had been changed in an axial direction,
it could be found that Th1-Tsalt1 and Th2-Tsalt2 were not within
Limits of 130 °C and 110 oC respectively, as proposed-in the
present invention. Also, the yield of acrylic acid was
10 reduced and the amount of byproduct COx was 1% increased, as
compared to Example 6.
Table 1 above shows the results of experiments
conducted in order to solve the problem that heat transfer
does not easily occur due to the insertion of the partition.
15 In Example 4, the reaction inhibition layer was inserted into
a location into which the partition has been placed.
Comparative Example 4 was the same as in Example 4 except
that the thickness of the reaction inhibition layer was 10%
of the partition, thickness. Comparative Example 5 was the
20 same except that the reaction inhibition layer was not
Table 1 since it was not easy to control temperature at the
partition location with the problem of heat transfer,
Comparative Examples 4 and 5 showed temperature increases of
25 37.7 °C and 51.3 oC, respectively, compared to the
temperatures of molten salt, which are significantly
different from that of Example 4. Particularly in Comparative
Example 5, it could be found that Time (the temperature of the
catalyst layer at the partition location) was close to the
30 peak tamperature of the catalyst layer. It is believed that
33

WO 2005/061414 PCT/KR2004/003373
this is mainly attributed to heat accumulation by an
the partition is not easy. If the reaction inhibition layer
is not used, heat accumulation will not be the only problem,
5 As apparent from Comparative Examples 4 and 5 where the
reaction inhibition layer was not sufficiently ensured, the
yield of acrylic acid, a final product, was also reduced as
compared to Example 4. This indicates that reaction, heat at
the partition location did not easily flow out, so as to
10 cause an abnormal increase in temperature and finally a
reduction in selectivity, thus leading to an increase in the
amount of byproducts.
In addition, the results of Example 5 where catalysts
with the same catalyst activity had been used in the divided
15 shell spaces also showed no problems of a hot spot and heat
accumulation around the hot spot.
Industrial Applicability
As described above, the present invention provides the
20 improved heat control system for use in the two-stage process
or producing unsaturated acids by the oxidation of olefins.
This heat control system allows the design of a reactor
system to which the advantages of the prior art can be
sufficiently applied even under reaction conditions with high
25 load. If this heat control system is used, the formation of a
hot spot or heat accumulation in the hot spot can be
inhibited, and as a result, unsaturated acids can be produced
at high productivity and also the life cycle of a catalyst
can be extended.
30 According to the present invention, the temperature
34

WO2005/061414 PCT/KR2004/003373
difference between the peak temperature of the catalyst layer
and the temperature of the heat transfer medium (molten salt)
in each of the divided reaction zones is controlled, so that
the catalyst can show relatively uniform activity in an axial
5 direction. This can inhibit not only heat accumulation at a
hot spot but also side reactions, thus preventing a reduction
in yield.
Accordingly, the present invention can be stably
performed at high reactant concentration or high reactant
10. space velocity without controlling the activity of a catalyst
filled in the second-stage reactor.
35

WO2005/061414 PCT/KR2004/003373
Claims
1. In a process of producing ausatutated acids from
unsaturated aldehydes by fixed-bed catalytic partial
ox idation in a she l1- and- tube heat exchanger —type reactor
5 the reactor comprising one or more cataytic tubes each
includeing a reaction zone of producing the urisaturated acids,
the improvement wherein:
the reaction zons is divided into two or more shell
spaces by at least one parition,
10 each of the divided shell spaces being filled with a
heat transfer medium, the heat transfer medium being
maintained at isothermal temperture or a temperture
difference of 0-5 °C, and
when the shell spaces divided by the partition in the
15 reaction zone are named, such as zone 1, zone 2. zone 3,
and zone N in an axial direction, Tn-Tsalt is  130 °C and Tw-
Tsalt is ºC wherein N is an ioteger of 2 or more Tm is
the peak temperature of a reaction mixture in a catalyst
layer corresponding to the first shell space, Tm is the peaK
20 temperature of a reaction mixture in a catalyst layer
corresponding to the Nth shell space, Tsalt is the temperature
of a heat transfer medium filled in the first shell space,
and Tsalt is the temperature of a heat transfer medium filled
in the Nth shell space.
25
2. In a process of producing insaturated acids from
unsaturated aldehydes by fixed-bed. catalytic partial
oxidation in a shell-and-tube heat exchanger-type reactor,
the reactor coapirising one or moxe catalytic tuoes each
30 including a reaction zone of producing the unsaturated acids,
36

WO2005/061414 PCT/KR2004/003373
the improvement wherein;
the reaction zone is divided into two or more shell
spaces by at least one partition.
each of the divided shell spaces being filled with a
5. heat transfer medium, the heat transfer medium being
maintained at isothemal temperature or a temperature
difference of 0-5 ºC,
in which a reaction inhibition layer made of an
inactive material alone or a mixture of the inactive material
10 and a catalyst material is placed in a position within the
catalytic tube, which corresponds to a position where the
partition is disposed.
3. The process of Claim 1 or 7, which is a process of
15 producing acrylic acid from an acrolein-containing gas
mixture.
4. The process of claim 1 or 2 wherein the temperture
difference between the heat transfer media filled in the
20 adjacent shell spaces is in a range of 0 ºC-50 ºC.
5. The process of Claim 1 ot 2, wherein the partition
is disposed in such a manner that it covers at least one

tamperature peak.
25
6. The process of Claim 5, wherein the tenperature peak
occurs at the inlet of the reactor, the front portion of the
reaction zones, or a boundary between the adjacent catalyst
layers with different activities.
30
37

WO2005/061414 PCT/KR2004/003373
7. The process of Claim 1, wherein 5 reaction
inhibition layer made of an inactive material alone or a
mixture of the inactive material and a catalyst material is
placed in a position within the catalytic tube, which
5 corresponds to a position where the partition is disposed.
8. The process of Claim 2 or 7, wherein the volume
ratio of the inactive material to the catayst material in
the reaction inhibition layer is 20-100%.
10
9. The process of claims 2 or 7, wherein the filling
beight of the reaction inhibit ion layer is 20-500% of the
thickness of the partition.
15 10, The process of Claim 1 or 2, wherein the
temperatutes of the heat transfer medium filled in each of
the shell spaces can be controlled independently.
11. The process of Claim 1 or 2, wherein the space
20 velocity of the unsaturcated aldehydes introduced into the
reactor inlet is in a range of 50-130 hr-1
12. In a shell-and-tube heat exchanger-type reactor
which can be used in a process of producing unsaturated acids
25 from olefins by fixed-bed catalytic partial oxidation, the
reactor consprising one or more catalytic tubes each including
a first-stage reaction zone of mainly producing unsaturated
aldehydes, a second- stage reaction zone of mainly producing
unsatmated acids, ot both. the two reaction zones, the
30 improvement wherein: the second-stage reaction zona is
38

WO2005/061414 PCT/KR2004/003373
divided into two or more shell spaces by at least one
partition, each of the divided shell spaces being filled with
a heat transfer medium, the heat transfer medium in each of
the shell spaces being maintained at isothermal temperature
5 or a temperature difference of 0-5 °C, and when the shell
spaces divided by the partition in the second-stage reaction
zone are named, such as zone 1, zone 2, zone 3, and zone N
in an axial direction ThI-TsaIrl is ºC and ThN-TsaItN is 
110ºC wherein N is an integer of 2 or more, Tm is the peak
10 temperature of a reaction mixture in a catalyst layer
corresponding to the first shell space , TnN is the peak
temperature of a reaction mixture in a catalyst layer
corresponding to the Nth shell space, Tsaltl is the temperature
of a heat transfer medium filled in the first shell space,
15 and Tsaltn is the temperature of a heat transfer medium filled
in the Nth shell space.
13. In a shell-and-tube heat- exchanger-type reactor
which can be used in a process of producing unsaturated acids
20 from, olefins by fixed-bed catalytic partial oxidation, the
reactor comprising one or more cacalycic tubes each including
a first-stage reaction zone of mainly producing unsaturated
aldehydes, a second-stage, reaction. zone of mainly producing
imsarurated acids, or both the two reaction zones, the
25 improvement wherein: the second-stage reaction zone is
divided into two or more shell spaces by at least- one
partition, each of the divided shell spaces being filled with
a heat transfer medium, the heat transfer media being
maintained at isothermal temperature or a temperature
30 difference of 0-5 °C, in which a reaction inhibition layer
39

WO2005/061414 PCT/KR2004/003373
made of an inactive material alone or a mixture of the
inactive material and a catalyst is placed within a portion
of the catalytic tube, which corresponds to a Location where
the partition is disposed.
5
40

(54) Title: METHOD OF PRODUCING UNSATURATED ACID IN FIXED-BED CATALYTIC PARTIAL OXIDATION REAO
TOR WITH ENHANCED HEAT CONTROL SYSTEM

(57) Abstract: The present invention provides a process of producing onsatu-
rated acids form unsaioraicd aldehydes by fixed-bed cataytic patial oxidation
in a shell and the heat exchanger-type reactor, as well as a shell and hide heat
exchangar type reactor for use in the process. In the invention, second-stage
reaction zone of mainly producing unsaturated acids by the calalytic vapor
phase oxidation of an unsaturated aklehyde containing gas mixture prodeced
in a first stage relation zone with molecular oxygen is divided into two or more
shell spaces by at least one partition . Each of the divided shell spaccs is filled
with a heat transfer medium and the heat transfer medium in each shell space
is mainlined at isothnnal temperature on a temperature difference of 0-5 °C.
Also. in order to prolect catalyst layers from a highly exothemic rcaction, the
process is performed at a limited temperature difference between the temper
ature at a hot spot and the temperture of the heat transfer medium. Also, in
order to faciliare the removal of hear generation as a location where the par-
tition is placed a reaction inhibition layer is disposed in that location. The
improved heat control system for reactors providesd according to the present
invention can secure the heat statrility of the calatyst layer, reduce the amount
of byproducls, and increase the yield of a final product.
41