JP4103416B2 - How to start up the reactor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reactor start-up method, and more specifically, for example, a reactor suitably used as an oxidation reactor when producing (meth) acrylic acid and / or (meth) acrolein by a catalytic gas phase oxidation reaction. Is related to the startup method.
[0002]
[Prior art]
In a shell-tube reactor that circulates a solid heat medium at room temperature, it is necessary to maintain fluidity by maintaining the heat medium at a temperature above the freezing point in order to circulate the heat medium in the reactor. is there.
[0003]
Japanese Patent Application Laid-Open No. 2001-310123 discloses a multi-tube reactor having a reaction tube and an inlet and an outlet for a fluid outside the reaction tube for removing heat generated in the reaction tube. There is provided a reactor start-up method characterized by introducing a gas at ˜400 ° C. to raise the temperature, and then circulating the heated heat medium outside the reaction tube. As the gas introduced to the reaction tube side, a gas (for example, air) that is not affected even when mixed with a catalyst or a raw material gas built in the reaction tube is selected.
[0004]
However, in the method as described above, since a large amount of high temperature gas is introduced into the reaction tube side, the oxidation state of the catalyst changes. Therefore, the activity and selectivity of the catalyst are affected, and as a result, the yield and catalyst life may be reduced.
[0005]
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned circumstances, and its purpose is to efficiently perform a shell-tube reactor in which a solid heat medium is circulated at room temperature without adversely affecting the activity of the catalyst. Is to provide a way to start up the reactor.
[0006]
[Means for Solving the Problems]
That is, the gist of the present invention is a shell-tube reactor that circulates a solid heat medium at room temperature, and introduces a reaction tube and a reaction tube outer fluid for removing heat generated in the reaction tube. In a shell-tube reactor having a mouth and an outlet, a gas having a temperature of 100 to 400 ° C. is introduced to the outside of the reaction tube to raise the temperature, and then the heated heating medium is circulated to the outside of the reaction tube. Reactor start-up method characterized by this.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described with reference to the accompanying drawings. FIG. 1 is a process explanatory diagram showing an example of a preferred embodiment of a reactor start-up method according to the present invention.
[0008]
The present invention is a shell-tube reactor of a system in which a solid heat medium is circulated at room temperature, and is an inlet and outlet for a reaction tube and a fluid outside the reaction tube for removing heat generated in the reaction tube. Is a start-up method of a shell-tube reactor having
[0009]
First, the shell-tube reactor used in the present invention will be described. As the shell-tube type reactor, any known reactor may be used as long as it has a reaction tube and an introduction port and a discharge port for fluid outside the reaction tube for removing heat generated in the reaction tube. Among these, a multi-tube reactor is preferable because of high reaction efficiency per volume of the reactor. The multitubular reactor that can be used in the present invention generally has the following structure. That is, a tube plate is provided above and below the reactor shell, and both ends are held by the tube plate, and a plurality of reaction tubes are built in, and the reaction tube of the reactor shell is used to remove heat generated in the reaction tube. It has an inlet and outlet for external fluid. In the present invention, a blocking plate for partitioning the inside of the reactor shell into a plurality of chambers may be further incorporated.
[0010]
Next, the heat medium used as the fluid outside the reaction tube in the present invention will be described. The freezing point of the heat medium is usually 50 to 250 ° C, preferably 130 to 180 ° C. As such a heat medium, there is typically a nighter. The nighter is particularly preferable in that it has excellent thermal stability among the heating media used for temperature control of chemical reaction, and particularly has the most excellent stability for heat exchange at a high temperature of 350 to 550 ° C. The nighter is a so-called molten salt, which has various compositions and different freezing points. In the present invention, any type of nighter can be suitably used as long as it has the above freezing point. As compounds used in such nighters, there are sodium nitrate, sodium nitrite, and potassium nitrate, and these can be used alone or in admixture of two or more.
[0011]
Next, features of the reactor start-up method according to the present invention will be described. In the present invention, in order to make the temperature in the reactor higher than the freezing point of the heat medium in advance, the temperature is raised by introducing a gas having a temperature of 100 to 400 ° C. outside the reaction tube. That is, in the case of the method described in the above-mentioned publication, the temperature raising gas of the reactor is introduced to the reaction tube side filled with the catalyst, but in the present invention, it is introduced to the outside of the reaction tube. This is a feature of the present invention, and the reactor start-up method according to the present invention does not adversely affect the catalyst. Air is preferably used as the temperature raising gas.
[0012]
Next, the above temperature raising method for the process shown in FIG. 1 will be described. In FIG. 1, a reactor (reactor) denoted by reference numeral (50) has a first chamber and a second chamber. In the illustrated example, the process gas is supplied by down flow and the heat medium is supplied by up flow. The Lines (L1), (L2), (L3), and (L4) constitute a process line, and lines (L6), (L7), (L8), (L9), (L10), (L12), (L13) ) And (L14) constitute a heating medium line, and lines (L15) and (L16) are discharge lines used for raising the temperature. In the figure, symbols ●-and ○-represent spectacle blinds (SB), so-called partition plates, in which SB is inserted into the piping to open and close the flow paths. The former symbol represents an open state, and the latter symbol represents a closed state.
[0013]
First, SB (61) is inserted into the line (L3) (that is, the flow path is closed), and the supply line to the reaction tube side (catalyst layer) of the reactor (50) used during normal operation is closed. SB (62) and SB (63) of line (L5) are removed (that is, the flow path is opened), line (L1) → blower (10) → line (L2) → line (L5) → line ( Establish a shell-side line of reactor (50) consisting of L6) → heater (21) → line (L7) and line (L8) → tank (30) → line (L9). At this time, the valve (71) of the line (L5) is closed. Further, the introduced gas is released by opening the SB (64) of the line (L15) and the valve (72) of the line (L16).
[0014]
Next, the blower (10) is started, and the gas heated to a temperature of 100 to 400 ° C. by the heater (21) is introduced outside the reaction tube of the reactor (50). This gas raises the temperature of the reactor (50). The temperature in the reactor (50) is preferably equal to or higher than the freezing point of the heat medium circulated thereafter, and can be appropriately selected depending on the heat medium used. Generally, the temperature may be increased until the shell side of the reactor (50) reaches 150 to 250 ° C. This is because, if the temperature on the shell side is within the above range, even if a heating medium is supplied thereafter, the freezing point of the heating medium does not occur because the freezing point of the heating medium is 50 to 250 ° C. It is. At this time, the reaction tube side (catalyst side) is preferably maintained in an air atmosphere.
[0015]
Next, the blower (10) is stopped, the SB (62) of the line (L5), the SB (63) of the line (L15) are closed, the valve (72) of the line (L16) is opened, and the pump (41) and (42) are started, a heating medium is introduced into each of the first chamber (51) and the second chamber (52) of the reactor (50), and the attached pump (43) is used in each chamber. Then, the heat medium is circulated to increase the temperature in each chamber.
[0016]
Each of the above operations is preferably performed quickly. Preferably it is performed within 1 hour. If it takes too much time, the temperature on the shell side decreases due to heat dissipation, and thus the heat medium may be solidified again when the heat medium is introduced.
[0017]
When heat exchange is performed using a solid heat medium at room temperature, the heat medium is often recovered in the tank (30) after the use of the reactor (50). It does not remain in the vessel (50) but is stored in the tank (30). Accordingly, the heating medium in the tank (30) is heated by the heaters (22) and (23) to such an extent that fluidity can be secured, and then introduced into the reactor (50).
[0018]
The introduction of the heat medium into the reactor (50) is performed through the following two routes. That is, the heat medium is supplied to the first chamber (51) via the lines (L13), (L14), (L6), and (L7) by the heat medium pump (41) of the tank (30). The heat medium pump (42) of (30) supplies the second chamber (52) via the lines (L12) and (L10).
[0019]
Next, the heat medium introduced into the reactor (50) is circulated in each chamber by an attached pump (43). This is because it may not be possible to raise the temperature in the reactor (50) to the target temperature simply by introducing and circulating the heat medium initially heated. Therefore, the heating medium is circulated, heated by the heater (21), and then introduced again into the reactor (50). For example, the heat medium is led out from the chamber 1 (51) and the line (L8), and introduced into the reactor (50) via the heater (21) and the line (L7) by the pump (41).
[0020]
As described above, when the required temperature of the reactor (50) can be secured by circulating the heat medium, the raw material gas is supplied to the reaction tube side (catalyst side) and the production of the target product is started. I can do it.
[0021]
The reactor start-up method according to the present invention is particularly preferable as a reactor start-up method used for production of, for example, acrylic acid, methacrylic acid, acrolein, and methacrolein. The reason is as follows. That is, acrylic acid or the like is a compound that is produced and used in large quantities, and the reactor size is increased accordingly. Therefore, it is particularly difficult to raise the temperature of the reactor. According to the present invention, it is particularly suitable for raising the temperature at the start-up of the reactor when using a large reactor.
[0022]
Acrylic acid is produced by supplying propylene, propane, acrolein or the like as a raw material gas to a known reactor filled with an oxidation catalyst, and performing a catalytic gas phase oxidation reaction. In general, the catalytic gas phase oxidation reaction is carried out in the presence of a predetermined amount of molecular oxygen-containing gas and inert gas in the raw material gas. For example, when propylene is used as the raw material gas, acrolein is produced, and then acrylic acid is obtained by further catalytic vapor phase oxidation.
[0023]
A publicly known oxidation catalyst can be used as the pre-stage and post-stage catalyst in the above two-stage catalytic gas phase oxidation reaction. Further, the shape of the catalyst is not particularly limited, and may be a ball field, a columnar shape, a cylindrical shape, or the like. Further, at the time of filling, the catalyst may be diluted and filled with a solid inert material. Examples of the solid inert material include α-alumina, alundum, mullite, carborundum, stainless steel, copper, aluminum, ceramic and the like.
[0024]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to a following example, unless the summary is exceeded.
[0025]
Example 1
Using the process shown in FIG. 1, a nighter having a composition of 40% by weight of sodium nitrite, 7% by weight of sodium nitrate and 53% by weight of potassium nitrate is used as a heating medium, and air is used as a temperature raising gas introduced outside the reaction tube. The multi-tube reactor was started up. The nighter is stored in the tank before startup and does not remain in the reactor. The used multitubular reactor is an oxidation reactor having an inner diameter of 4500 mm, and has a structure in which 13,000 reaction tubes having a length of 4000 mm are supported by an upper tube plate and a lower tube plate. Further, a blocking plate for partitioning the inside of the reactor into two chambers is provided at a position 300 mm below.
[0026]
First, the SBs (61) and (62) of the lines (L3) and (L5) are switched, and the line introduced from the blower (10) to the reactor (50) is changed from the blower (10) to the heater (21). Switched to the line to be sent. Then, the blower (10) is started, air is supplied to the heater (21) at a rate of 6 t / hr to preheat up to 250 ° C., and the tank (30) and the line from the line (L7) and / or the line (L8) It was supplied to the oxidation reactor (50) via (L9).
[0027]
When the temperature of the reactor (50) reached 230 ° C., the blower (10) was stopped and the above SBs were switched. And the heat medium heated beforehand at the temperature of 200 degreeC with the heaters (22) and (23) was supplied from the tank (30) with the pumps (41) and (42). A heat medium is supplied to the first chamber (51) from the pump (41) via the lines (L13), (L14), (L6), and (L7), and the second chamber (52) The heat medium was supplied from the pump (42) via the lines (L12) and (L10).
[0028]
Next, after the heat medium was introduced into the reactor (50), the pump (43) was started to circulate the heat medium in the first chamber (51). The temperature of the first chamber (51) is adjusted by supplying the heating medium from the reactor (50) to the heater (21) via the lines (L8), (L13), (L14), and (L6). This was done by circulating to reactor (50) via (L7). The temperature of the second chamber (52) was adjusted with the heater (23) attached to the tank (30).
[0029]
Since the heat medium temperature of the first chamber (51) was 330 ° C. and the heat medium temperature of the second chamber (52) was 230 ° C. and reached a predetermined reaction temperature, the operation of the heater (21) was stopped and the start-up was completed. . The startup took 40 hours.
[0030]
Example 2
A shell-tube reactor having the following structure was used. That is, it is a stainless steel double tube structure, an inner tube having an inner diameter of 24 mm and a length of 3.5 m, and Mo (12) Bi (5) Ni (3) as a catalyst in the inner tube. Packed with a catalyst of the composition Co (2) Fe (0.4) Na (0.2) B (0.4) K (0.1) Si (24) O (x) (the oxygen composition x is a value determined by the oxidation state of each metal. In other words, the inner tube and the outer tube are filled with a nighter as a heat medium so that a uniform temperature can be maintained by stirring.
[0031]
Instrument air is supplied to the reaction tube at a rate of 1 NL / hr, the temperature on the shell side is 250 ° C. and held for 40 hours, a night gas at 330 ° C. is circulated, and a raw material gas containing 9% by volume of propylene is used as a raw material. Supplied. The propylene conversion was 97%, and the total yield of acrolein and acrylic acid was 92%.
[0032]
Comparative Example 1
In Example 2, the reaction was performed under the same conditions as in Example 2 except that nitrogen heated to 250 ° C. was supplied to the inner tube (catalyst layer) at a rate of 20 L / hr for 40 hours. In this case, the temperature of the nighter had to be raised to 340 ° C. in order to achieve a propylene conversion of 97%.
[0033]
Comparative Example 2
In Example 2, the reaction was performed under the same conditions as in Example 2 except that air heated to 250 ° C. was supplied to the inner tube (catalyst layer) at a rate of 20 NL / hr for 40 hours. In this case, the activity of the catalyst changed, a runaway reaction occurred, and the reaction had to be stopped.
[0034]
【The invention's effect】
According to the present invention described above, there is provided a method for efficiently starting up a reactor without adversely affecting the activity of the catalyst in a shell-tube reactor that circulates a solid heat medium at room temperature. Therefore, the industrial value of the present invention is remarkable.
[Brief description of the drawings]
FIG. 1 is a process explanatory diagram showing an example of a preferred embodiment of a reactor start-up method according to the present invention.
10: Blower 21, 22, 23: Heater 30: Tank 41, 42, 43: Pump 50: Reactor 51: First chamber 52: Second chamber L1, L2, L3, L4: Process lines L6, L7, L8, L9, L10, L12, L13, L14: Heat medium lines L15, L16: Release lines used for raising the temperature

Claims (3)

A shell-tube reactor that circulates a solid heat medium at room temperature, and has a reaction tube and an inlet and a discharge port for a fluid outside the reaction tube for removing heat generated in the reaction tube -In a tube reactor, a gas having a temperature of 100 to 400 ° C is introduced to the outside of the reaction tube to raise the temperature, and then the heated heating medium is circulated to the outside of the reaction tube. Startup method. The method according to claim 1, wherein the heating medium solid at normal temperature is a heating medium having a freezing point of 50 to 250 ° C. The process according to claim 1 or 2, wherein the shell-tube reactor is a multi-tube reactor.

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