JPH0686399B2 - Method for producing acrylic acid - Google Patents

Description

TECHNICAL FIELD The present invention relates to a process for producing acrylic acid by catalytic vapor-phase oxidation of propylene. More specifically, the present invention relates to a process for producing acrylic acid with high productivity by using a raw material gas having a specific composition.

[Conventional technology]

Propylene over two stages (first stage reaction is a reaction that mainly converts propylene to acrolein, second stage oxidation reaction is a reaction that mainly converts acrolein to acrylic acid, a combination of both reactions) Processes for producing acrylic acid by phase oxidation are known. The following problems are pointed out when attempting to increase the productivity of acrylic acid in this process. (1) Increasing space velocity It is impossible to raise the space velocity unnecessarily in relation to the performance (yield and life) of the catalyst. (2) When the propylene conversion rate is increased, there arises a problem that the selectivity to an effective product becomes low. (3) When the amount of propylene as a raw material is increased, there is a limit due to problems such as heat removal of reaction heat and avoidance from the explosion range.

Against this background, various processes have been studied as a method for increasing the productivity of acrylic acid. For example, a method of recycling unreacted propylene for reuse is disclosed in British Patent Publication No. 996898. In addition, there are many known documents regarding the reuse of reaction waste gas. For example, according to Japanese Patent Publication No. 47-10614, the activity of the catalyst is changed in two steps so that the activity is constantly or stepwise from the inlet of the reaction tube toward the reaction tube.
%, And the reaction waste gas from which the condensable gas obtained at the outlet of the second-stage reaction has been largely removed is replaced by first or second steam instead of part or all of steam as an inert diluent gas.
Resupplying the stage is disclosed. According to this method, it is necessary to dilute the catalyst, which is disadvantageous for implementation. Also, since the propylene concentration is low, the productivity is low and the level is unsatisfactory.

According to the specification of JP-A-51-36415, a process for suppressing the late stage reaction is performed by utilizing the returned waste gas, but the returned gas is essentially nitrogen and other small amount of unreacted gas. The reaction consists of propylene, oxygen, propane and carbon oxide.

JP-A-49-134618 discloses the use of carbon dioxide produced in the reaction as a circulating carrier gas. It is said that the advantage of using carbon dioxide as a carrier gas is that it is easy to avoid the explosive range and to remove the reaction heat without reaction, which contributes to the improvement of the yield.
There is no specific disclosure regarding a method for producing acrylic acid by oxidizing propylene.

According to the specification of JP-A-49-70913, molybdenum and bismuth containing small amounts of indium and / or aluminum and / or lanthanum and / or gallium as oxides and / or mixed oxides and According to the use of a catalyst further containing other elements as oxides or mixed oxides at temperatures of 280-450 ° C., optionally in the vapor phase in the presence of steam and / or ammonia, α-
A method of oxidizing or ammoxidating an olefin with molecular oxygen to obtain the corresponding α-β olefinically unsaturated aldehyde or nitrile is disclosed.
Further, in this specification, the content of α-olefin such as propylene or isobutylene in the synthesis raw material gas is generally
Gaseous mixture of 0.5 to 15% by volume, especially 2 to 6% by volume if oxygen is supplied instead of air, using pure oxygen and part of the reaction gas after separating acrylic acid for oxidation. When adding (circulation method), it is 6 to 15% by volume.
The concentration of oxygen is often 2 to 20% by volume, preferably 5 to
It is 15% by volume. Other mixtures contain inert gases such as carbon monoxide, carbon dioxide and nitrogen and often small amounts of noble gases, hydrogen, ethylene and propane. Further, the synthesis raw material gas may contain steam. The proportion of water vapor is generally about 40% by volume or less, but 20% by volume or less,
In particular, it is disclosed that a ratio of 10% by volume or less, particularly 2 to 8% by volume is preferable. However, there is no specific description in this publication regarding the production of acrylic acid by propylene oxidation by oxygen oxidation.

According to Japanese Patent Publication No. 39-3670, pure oxygen is used as an oxygen source, a circulating gas consisting of unreacted propylene is taken out, propylene, oxygen and steam are newly added, and the mixture is sent again to the reactor as a diluent gas. CO ₂ generated during the reaction
And a process using CO and steam is disclosed.

According to the specification of JP-A-47-17711, when pure oxygen is used as an oxidant, the product mixture remaining after taking out the carbonyl compound and the carboxylic acid compound is treated to remove carbon dioxide and leave the rest. A process of circulating a mixture containing unreacted olefin and oxygen and water to a reactor is disclosed.

According to German patent DE 1 733 302, pure oxygen is used as oxidant. A second stage waste gas is used as a diluent for propylene and oxygen after separating acrylic acid, which contains carbon oxides and water vapor as inert components. However, the embodiment disclosed in the specification essentially has an oxygen: propylene ratio of less than 1.5: 1, which facilitates reduction of the catalyst due to oxygen deficiency, selectivity to acrolein and acrylic acid, conversion of propylene, and even catalyst. There is a risk of shortening the life.

[Problems to be solved by the invention]

As mentioned above, the method of increasing the productivity of acrylic acid is to increase the supply amount of propylene, which is a raw material, as a load on the catalyst.
The contact time on the catalyst should be as short as possible.
Increasing the amount of propylene used for the reaction (at the same time increasing the space velocity) increases the amount of heat generated by the oxidation reaction. Further, if the conversion rate of propylene is to be increased, it is necessary to increase the oxygen concentration, but it is difficult to avoid propylene from the explosion range. Conventionally, these measures have been taken, that is, for the purpose of removing a large amount of heat generation and avoiding from the explosive range, measures for entraining water vapor or diluting a portion having a large reaction amount of the catalyst with an inert carrier or the like. Alternatively, a method of reusing waste gas to reduce the oxygen concentration has been taken. To deal with these problems, the concentration of recovered acrylic acid decreases due to the labor for diluting the catalyst and the addition of water vapor, and the energy loss due to the division of acrylic acid cannot be avoided. Further, even in the conventional waste gas, the removal of a large amount of reaction heat is insufficient, and the high-concentration propylene oxidation reaction is limited.

Therefore, the present invention solves such problems,
It is an object of the invention to provide a wrestling with high productivity, which is capable of producing acrylic acid in a safe and high yield over a long period of time even if a high load reaction condition for a catalyst is adopted.

[Means for solving problems]

According to the invention, the object is, according to the invention, to convert propylene with molecular oxygen by oxidising propylene in the first stage to produce acrolein and in the second stage by oxidizing acrolein to produce mainly acrylic acid. In the method for producing acrylic acid by catalytic vapor-phase oxidation in a step, the number of carbon atoms is 1
5 to 70% by volume of saturated aliphatic hydrocarbon, 3 to 50% by volume of carbon dioxide, and 20 to 80% by volume of total of the aliphatic hydrocarbon and carbon dioxide, and 1 mol of water vapor of propylene. In the range of 0.5 to 8 mol,
Furthermore, the propylene concentration in the raw material gas is in the range of 5 to 20% by volume, and the molecular oxygen concentration is 1.4 in molar ratio with respect to propylene.
It is achieved by a method for producing acrylic acid, which comprises subjecting a raw material gas contained in a range of to 4.0 to the first stage reaction.

[Action]

In the catalytic gas-phase oxidation of propylene in the presence of molecular oxygen, the present invention uses a diluent gas having 1 to 5 carbon atoms as described above.
5 to 70% by volume of saturated aliphatic hydrocarbon, 3 to 50% by volume of carbon dioxide and 20 to 80% by volume of the total amount of the aliphatic hydrocarbon and carbon dioxide, and 0.5% of steam per mol of propylene. The content of propylene in the raw material gas is in the range of 5 to 20% by volume, and the molecular oxygen concentration is 1.4 to 4.0 in molar ratio with respect to propylene.
It was found that high productivity can be maintained even under a reaction condition of high load on the catalyst by using the raw material gas contained in the above range.

In adjusting the source gas of the above composition, the second
It is industrially advantageous to reuse the waste gas obtained by mainly recovering acrylic acid from the reaction mixed gas obtained in the first-step reaction as a component of the raw material gas in the first-step reaction. It is preferable to adjust the reaction raw material gas in conformity with the above composition by reusing 50% by volume or more of the waste gas.

Regarding the mechanism of action of the effect obtained by adopting the reaction conditions of the present invention, since the heat capacity of the raw material gas of the specific composition is larger than that of steam, nitrogen, etc. which are conventionally used as diluents, It is estimated that the large heat removal effect is also a factor. That is, the constant pressure specific heat (Kcal / kg mol · deg) at about 300 ℃ is 12.5 for methane and 2 for ethane.
1.3, propane 30.9, butane 40.3, carbon dioxide 11.5, water vapor 8.8, oxygen 7.9, carbon monoxide 7.3, nitrogen 7.1, argon
5.0 and 5.0.

To summarize the advantages in carrying out the present invention, by increasing the heat capacity of the reaction gas itself, the gas itself absorbs the amount of heat generated by the oxidation reaction, so that the heat removal effect is remarkably improved. Since the heat rise of the catalyst itself is suppressed, the heat load of the catalyst is greatly relaxed. Also, since carbon oxide in the reaction raw material gas coexists in a high concentration, the explosion risk of propylene can be mitigated, so that high-concentration propylene can be reacted at a high space velocity to achieve high productivity and high productivity. Since a high concentration of acrylic acid can be obtained, the energy consumption in the separation and purification of acrylic acid is reduced. Next, under the temperature of the catalyst layer and the reaction temperature (external heating medium) (△
Since T) is lowered, the selectivity to acrolein and / or acrylic acid is improved, which leads to an improvement in yield. Further, ΔT is further lowered, so that the catalyst component is stably maintained in the catalyst and the catalyst is deteriorated. Is reduced and catalyst life is improved. In addition, the use of the supported catalyst becomes possible by adopting this process. Usually, as a catalyst for propylene oxidation, for example, a catalyst coated or attached to an inert carrier is used, but the activity is maintained in the very initial stage, but the activity tends to decrease with time. This is thought to be due to the deterioration of the catalyst itself due to the heat of reaction, but the adoption of this process facilitates removal of the heat of reaction, resulting in a decrease in ΔT and suppression of thermal deterioration of the catalyst. It will be possible. Further, since the circulation amount of the waste gas is as large as 50% or more excluding the condensed components in the reactor outlet gas, the propylene for reaction can be effectively used.

In this process, it is indispensable for water vapor to coexist with carbon dioxide in the first stage reaction gas. First, water vapor is the main product produced in the catalytic gas phase oxidation reaction of propylene, acrolein, and other useful compounds, acrylic acid, and the elimination or reaction of particularly high-boiling products. It is effective because there is a direct involvement in This effect cannot be achieved only by the presence of other coexisting gases, carbon dioxide and saturated hydrocarbons. When steam is not contained in an amount of 0.5 mol or more per 1 mol of propylene, the desorption effect of by-products is not particularly remarkable, so that the reaction temperature rises quickly (and therefore the catalyst life becomes short), which is inconvenient for an industrial catalyst. Further, the influence of the water vapor on the catalyst life also greatly affects the catalyst for acrolein oxidation mainly composed of polybutene oxide and vanadium oxide. Further, as a steam coexisting effect, carbon dioxide is acidified by steam to improve the production / selectivity of propylene to acrolein. Although the reason is unknown, it is considered that it is involved in the control of the acid-base of the catalyst due to the acidic gas.

However, on the contrary, if too much water vapor is added, a high-concentration acrylic acid aqueous solution cannot be obtained, and when water vapor is recycled to the reaction system based on the method of one embodiment of the present invention, an acrylic acid collector is used. In some cases, it is necessary to raise the temperature at the top of the column, and a large amount of impurities are recycled to the reaction system, which causes inconvenience.

As for the purity of the raw material propylene used in the present invention, it is preferable that propane contains propane because the heat capacity is larger and the effect of removing reaction heat is large. Preferred propylene purity is 97% by volume
Below (the balance is propane). The use of propane-rich propylene obtained, for example, by the oxidative dehydrogenation of propane, is convenient. However, if the content of propane is too large, the amount of waste gas recycled and used will be small, and the effective utilization of unreacted propylene will be reduced, which is disadvantageous.

Mo for the first stage reaction as the catalyst used in the present invention,
Oxide catalysts containing Fe and Bi are preferable, but the following general formulas are particularly preferable. MoaWbBicFedAeBfCgDhOx
(Here, Mo is molybdenum, Bi is bismuth, W is tungsten, Fe is iron, O is oxygen, A is at least one element selected from the group consisting of nickel and cobalt, B is an alkali metal, an alkaline earth metal and At least one element selected from the group consisting of thallium, C is at least one element selected from phosphorus, arsenic, boron and niobium, and D is at least one element selected from the group consisting of silicon, aluminum and titanium. Represents an element.
The subscripts a, b, c, d, e, f, g, h and x respectively represent the numbers of atoms of Mo, W, Bi, Fe, A, B, C, D and O, and a = 2 to 10 , B = 0 to 10 and a + b = 12, c = 0.1 to 10.0, d = 0.1 to 10, e = 2 to 20, f = 0.
005 to 3.0, g = 0 to 4, h = 0.5 to 15, and x is a value determined by the valence of each element. ) Here, the oxide catalyst may be in the form of, for example, a pellet formed by a tablet molding machine or an extrusion molding machine, a spherical shape, or a ring shape having a through-hole. It is also useful to support the above.

The catalyst used for the second stage reaction is preferably an oxide catalyst containing molybdenum and vanadium, and particularly preferably one represented by the following general formula.

MomVnQqRrSsTtOy (where Mo is molybdenum, V is vanadium, Q is at least one element selected from the group consisting of tungsten and niobium, and R is at least one element selected from the group consisting of iron, copper, bismuth, chromium and antimony. The element, S is at least one element selected from the group consisting of alkali metals and alkaline earths, T is at least one element selected from the group consisting of silicon, aluminum and titanium, and O represents oxygen, and m, n, q, r, s,
t and y respectively represent the number of atoms, m = 12s, t and y respectively represent the number of atoms, and when m = 12, n = 2 to 14,
q = 0 to 12, r = 0 to 6, s = 0 to 6, t = 0 to 30 and y are numerical values determined by the oxidation state of each element. ) Of course, this catalyst substance can also be used by holding it on a refractory carrier.

The reaction conditions include a reaction temperature of 250 to 450 in the first stage reaction.
C., preferably 270 to 370.degree. Propylene as a reaction gas composition is 5 to 20% by volume, more preferably 7 to 15% by volume, oxygen is 8 to 40% by volume, preferably 12 to 30% by volume, and saturated fat having 1 to 5 carbon atoms, preferably 1 to 3 carbon atoms. Group hydrocarbon 5
70% by volume, preferably 10-60% by volume, carbon dioxide 3-50
%, Preferably 5 to 40% by volume (however, the sum of the hydrocarbon and carbon dioxide is 30 to 80% by volume, preferably 30 to 70% by volume), and water vapor is 3 to 50% by volume, preferably 5
-40% by volume (however, the molar ratio of steam to propylene is 0.5 to 8, preferably 0.6 to 5), the molar ratio of oxygen and propylene is 1.4 to 4.0, preferably 1.6 to 3.0, and the contact time is 1.0. -7.2 seconds, preferably 1.8-6 seconds. And as a catalyst, the propylene conversion rate is 70 mol% or more,
A catalyst that can achieve 80 mol% or more is preferably used.
As the second stage oxidation reaction conditions, the reaction temperature is 180 to 350 ° C., preferably 200 to 320 ° C., the contact time is 1.0 to 7.2 seconds, and preferably 1.
6 to 6 seconds. A catalyst capable of achieving a single-flow yield of propylene to acrylic acid of 70 mol% or more, preferably 80 mol% or more in total from the first-stage oxidation reaction is used for the second-stage catalyst.

In adjusting the source gas of the above composition, the second
It is industrially advantageous to reuse the waste gas obtained by mainly recovering acrylic acid from the reaction mixed gas obtained in the first-step reaction as a component of the raw material gas in the first-step reaction. It is preferable to adjust the reaction raw material gas in conformity with the above composition by reusing 50% by volume or more of the waste gas.

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. The conversion rate, single-flow yield, and recycle yield in the present invention are defined as follows.

Example-1 Preparation of first-stage catalyst Ammonium molybdate 10.62K while heating water 15
g, ammonium paratungstate (3.24 Kg) and stirred vigorously (this is referred to as liquid A) Separately, 7.00 Kg of cobalt nitrate was added to 2 of water, and ferric nitrate 2.43 was added.
Kg was dissolved in 2 of water and 2.92 Kg of bismuth nitrate was dissolved in 3 of acidified acid by adding 0.6 of concentrated nitric acid.
A liquid obtained by mixing the nitrate solution of the seed was added dropwise to the liquid A. Then, silica sol containing 20% by weight in terms of silicon dioxide.
A solution prepared by dissolving 2.44 Kg and 20.2 g of potassium hydroxide in 1.5 of water was added, and the suspension thus formed was heated and evaporated, and then molded and calcined at 450 ° C for 6 hours under air flow to prepare a catalyst. .

The composition of this catalyst with elements other than oxygen was Co ₄ Fe ₁ Bi ₁ W ₂ Mo ₁₀ Si _1.35 K _0.06 in atomic ratio.

Preparation of second-stage catalyst Ammonium paratungstate 1.25Kg, ammonium metavanadate 1.03K
g, ammonium molybdate 4.06 Kg, and then ammonium dichromate 0.14 Kg were mixed and dissolved, and 103 Kg of copper nitrate was dissolved in 0.72 of water to prepare an aqueous solution, and both solutions were mixed. The mixed solution thus obtained was placed in a stainless steel evaporator equipped with a steam heater, and the carrier substrate consisted of α-alumina, and had a surface area of 1 m ² / g or less, a porosity of 42%, and a fine pore size of 75 to 250 microns. The volume occupied by pores is
Granular carrier 12 having a diameter of 3 to 5 mm occupying 92% was added and evaporated to dryness with stirring to adhere to the carrier.
The catalyst was prepared by calcination for an hour. The composition of elements other than oxygen excluding the carrier of this catalyst was Mo ₁₂ V _4.6 Cu _2.2 Cr _0.6 W _2.4 in atomic ratio.

Reaction and collection of acrylic acid The pre-catalyst 12.0 consists of 10 steel reaction tubes with an inner diameter of 25 mm and a length of 3,000 mm, and the shell side is a multi-tube reactor capable of heat exchange by circulating molten salt. Fill evenly, 32
Heated to 5 ° C.

Separately, the latter catalyst 9.0 is composed of 10 steel reaction tubes having an inner diameter of 25 mm and a length of 3,000 mm, and the shell side is uniformly filled in a multi-tubular reactor capable of heat exchange by circulating a molten salt,
Heated to 260 ° C.

The two reactors were connected by a conduit equipped with a heat exchanger so that the reaction product gas leaving the reactor containing the pre-catalyst was introduced into the reactor containing the front and rear catalysts. The reaction product gas emitted from the reactor containing the pre-catalyst is a stainless steel column having an inner diameter of 200 mm, equipped with 20 stages of bubble cap racks having a hot water jacket on the outer wall, and equipped with a multitubular cooler at the bottom thereof. Waste gas containing acrylic acid as an aqueous solution of acrylic acid by flowing down water containing a polymerization inhibitor (mainly composed of hydroquinone) from the top of the column and further containing water vapor at a concentration determined by the column top temperature. Was introduced into an acrylic acid collector that was designed to be discharged. The gas containing water vapor discharged from the acrylic acid collector is returned to the inlet of the reactor containing the pre-catalyst by a blower except that a part of it is not concentrated and purged, and the purity is newly 95.0%.
Propylene and purity (the balance is mainly propane)
95.7% oxygen (the balance was mainly argon) was added and mixed, and introduced into the reactor containing the pre-catalyst.

Propylene 7.0% by volume, oxygen 12.6% by volume,
Water vapor 7.0% by volume, carbon dioxide 26.0% by volume, carbon monoxide 1
A mixed gas consisting of 3.0% by volume, 14.0% by volume of propane, and the balance of argon was introduced at 16.2 m ³ / Hr (NTP conversion). At this time, the yield of acrylic acid was highest when the propylene conversion rate was 95.0%.

At this time, the circulation rate of the waste gas to the former reactor was 97.6%. As a result, the difference ΔT between the maximum temperature of the catalyst layer of the first stage reactor and the reaction temperature (the temperature of the molten salt as the heating medium) was 43 ° C.
The yield of acrylic acid based on the supplied propylene is 9
It was 2.0% and the space-time yield was 159.8 g acrylic acid / hr.catalyst.

The reaction was continued for 8000 hours. At 8000 hours, the temperature of the first stage reaction night bath was 330 ° C and the temperature of the second stage reaction night bath was 266 ° C. It can be seen that the propylene conversion rate and the acrylic acid yield are 95.0% and 91.7%, respectively, and are stable.

Comparative Example-1-1 In Example-1, air was used as the oxygen source. At this time, the circulation rate of the waste gas to the former reactor was zero.

First-stage inlet gas composition is propylene 7.0 vol%, oxygen 12.6
% By volume, 7.0% by volume of water vapor, and the balance was nitrogen and a small amount of argon and propane. Further, the steam was supplied after being sufficiently mixed with the raw material propylene and air. The propylene conversion yielding the highest yield of acrylic acid was 95.5%, and the molten salt temperatures of the first and second stages were 320 ° C and 260 ° C, respectively.

As a result, ΔT was as high as 65 ° C., the acrylic acid yield to the supplied propylene was 84.5 mol%, and the space-time yield was 146.8 g acrylic acid / hr · catalyst. The unreacted propylene was lost as it was.

Comparative Example-1-2 In Comparative Example-1-1, the first stage inlet gas composition was propylene.
It was 7.0% by volume, 12.6% by volume of oxygen, 7.0% by volume of water vapor, 10.0% by volume of carbon dioxide, and the balance was nitrogen and a small amount of argon and propane. Other than that, the reaction was performed under the same conditions as in Comparative Example-1-1.

As a result, ΔT was as high as 63 ° C., but the acrylic acid yield to the supplied propylene was 86.6 mol%, and it was the effect of carbon dioxide addition that the yield was improved compared to Comparative Example-1-1.
It is due to the effect of carbon dioxide as an acid gas, rather than due to the larger heat capacity of carbon dioxide.

Comparative Example-1-3 In Example-1, propylene 7.0% by volume, oxygen 12.6% by volume, water vapor 2.0% by volume, carbon dioxide 31.
A mixed gas consisting of 5% by volume, 19.7% by volume of carbon monoxide, 10.9% by volume of propane, and the balance of argon at 16.2 m ³ / hr (NTP
(Conversion) was introduced. However, the amount of water vapor is adjusted at the exhaust gas outlet temperature of the acrylic acid trap, the reaction temperature of the first stage reactor is 325 ° C, and the reaction temperature of the second stage reactor is 260 ° C. The yield of acrylic acid was highest when the propylene conversion was 94.0%.

At this time, the circulation rate of the waste gas to the front-stage reactor was 96.9%. As a result, the ΔT of the first-stage reactor was 45 ° C., the yield of acrylic acid with respect to the propylene fed was 85.7%, and the space-time yield was 148.9 g acrylic acid / hr · catalyst.

The reaction was continued for 4000 hours. It was necessary to raise the temperature of the first-stage reaction night bath to 335 ° C and the second-stage reaction night bath temperature of 270 ° C at 4000 hours. At that time, the conversion of propylene and the yield of acrylic acid were 93.8% and 84.8%, respectively, and the reaction conditions were constantly changing due to the large deterioration of the catalyst activity, making it difficult to control the reaction. It is considered that this is because the amount of the added steam is too small and the desorption of by-products from the surface of the catalyst does not proceed easily, resulting in overreaction and reduction of the catalyst.

Comparative Example-2 In Example-1, air was used as the oxygen source. The water vapor source at the inlet of the first stage was secured by adjusting the column top temperature of the acrylic acid collector. The molten salt temperature in the first and second stages is 320 each
℃ and 260 ℃. At that time, the waste gas circulation rate was 36.7%. The carbon dioxide concentration at the front inlet was 0.57% by volume, propane 0.59% by volume, carbon monoxide 0.28% by volume, argon 0.9% by volume, and the balance nitrogen.

As a result, ΔT was 64 ° C. The recycled acrylic acid yield based on the propylene fed was 85.6%, and the space-time yield was 148.7 g acrylic acid / hr.catalyst.

Comparative Example-3 Oxygen 80.0 instead of 95.7 purity oxygen in Example-1
%, An oxygen source consisting of 20.0% nitrogen was used. The composition of gas used for the first-stage oxidation reaction is 7.0% by volume of propylene and 1% of oxygen.
2.6% by volume, carbon dioxide 14.0% by volume, carbon monoxide 7.0% by volume, water vapor 7.0% by volume, propane 0.6% by volume, and the balance being nitrogen. The reaction temperature giving the highest yield was 325 ° C. in the first stage oxidation reaction and 265 ° C. in the second stage oxidation reaction, and the propylene conversion rate at that time was 95.0%.

As a result, ΔT was 60 ° C, the circulation rate of waste gas was 94.2%, the yield of acrylic acid was 89.2% with respect to the supplied propylene,
The space-time yield was 155.0 g / acrylic acid / hr.catalyst.

Example-2 In Example-1, the pre-stage catalyst 12 was changed to 8.1 and the post-stage catalyst 9 was used.
Were reduced to 8.1 respectively. In order to maximize the acrylic acid yield, the propylene conversion was 95.0% and the molten salt temperatures of the first and second stages were 330 ° C and 270 ° C, respectively.

The composition of the first-stage reaction gas is 11.0% by volume of propylene and 1 for oxygen.
9.8% by volume, 7.0% by volume of water vapor, 22.5% by volume of carbon dioxide,
A mixed gas consisting of 13.0% by volume of carbon monoxide, 11.0% by volume of propane, and the balance of argon was introduced at 16.2 m ³ / Hr (NTP conversion).

As a result, △ T was 51 ℃ and the circulation rate of waste gas was 95.1%.
And the acrylic acid yield based on propylene supply is 90.3%.
The space-time yield was 323.5 g acrylic acid / hr.catalyst.

Example-3 Preparation of pre-catalyst In the same manner as in Example-1, except that thallium nitrate and barium nitrate were used instead of potassium hydroxide in Example-1, the elemental composition excluding oxygen Co ₄ Bi ₁ Fe ₁ W ₂ Mo was prepared. ₁₀ Si _1.35 Tl _0.04 Ba _0.05
Got

Preparation of second-stage catalyst While stirring water 60 under heating, ammonium metavanadate 897 g was dissolved therein, ammonium molybdate 4060 g was dissolved, silica sol 575 g containing 20 wt% in terms of silicon dioxide was added, and copper nitrate 926 g and nitric acid were added separately. 155g ferric iron in water
The solution dissolved in 3.8 was mixed. The mixed solution thus obtained was placed in a stainless steel evaporator equipped with a steam heater, and the granular carrier 12 used in Example 1 was added as a carrier substrate, and the mixture was evaporated to dryness with stirring to adhere to the carrier. A catalyst was prepared by calcining at ℃ for 6 hours. The composition of elements other than oxygen excluding the carrier of this catalyst was Mo ₁₂ V ₄ Cu ₂ Fe _0.2 Si ₁ in atomic ratio.

The reaction and collection method of acrylic acid were in accordance with Example-2.
The results are shown in Table-1. The reaction temperature was selected such that the acrylic acid yield was the highest.

Example-4 Preparation of pre-catalyst Prepared in the same manner as in Example-1 except that cesium nitrate was added in place of potassium hydroxide in Example-1 and titanium dioxide was added simultaneously with the 20 wt% silica sol. , Elemental composition excluding oxygen Co ₄ Bi ₁ Fe ₁ W ₂ Mo ₁₀ Si _1.35 C
I got s _0.02 Ti ₁ .

Preparation of second-stage catalyst 10.00 Kg of ammonium molybdate was dissolved in 75 water by heating. Ammonium metavanadate 1.38K in this solution
g, niobium hydroxide 7.058 Kg, ferrous oxalate 1.02 Kg, cuprous chloride 0.56 Kg, and potassium sulfate 0.28 Kg were sequentially added while sufficiently stirring. After heating and stirring, add 4.25Kg of SiO ₂ powder, evaporate to dryness, and then pulverize to outer diameter 6.0mm, length 6.6mm, through hole inner diameter 2.0m.
It was molded into m and baked at 420 ° C. for 5 hours. The composition of this catalyst oxide was Mo ₁₂ V _2.5 Nb _8.4 Cu _1.2 Fe _1.2 K _0.6 Si ₁₅ in atomic ratio.

The reaction and collection method of acrylic acid were in accordance with Example-2.
The reaction results are shown in Table 1.

Example-5 Preparation of pre-catalyst Prepared in the same manner as in Example-1 except that potassium hydroxide was used instead of potassium hydroxide in Example-1, and the elemental composition except oxygen was Co ₄ Bi ₁ Fe in atomic ratio. ₁ Mo ₁₀ W ₂ Si
_A catalyst oxide of _1.35 Sr _0.06 was molded into an outer diameter of 6.0 mm, a length of 6.6 mm, and a through hole inner diameter of 2.0 mm to obtain a ring-shaped catalyst.

Preparation of second-stage catalyst Ammonium paratungstate in Example-1
Instead of ammonium dichromate and copper nitrate, antimony pentoxide was used as an antimony source, magnesium nitrate was used as a magnesium source, and its oxide was used as aluminum.
The elemental composition excluding oxygen was Mo ₁₂ V ₄ Sb _0.5 Mg ₂ Al ₅ .

The reaction and collection method of acrylic acid were in accordance with Example-2.
The reaction results are shown in Table 1.

Example-6 Preparation of First Stage Catalyst Except for using calcium nitrate in place of potassium hydroxide in Example-1, and adding niobium pentoxide after adding silica sol and calcium nitrate.
Prepared in the same manner as in No. 1, and the elemental composition except oxygen is Co ₄ B in atomic ratio.
i ₁ Fe ₁ Mo ₁₀ W ₂ Si _1.35 Ca _0.06 Nb _0.5 catalyst oxide with outer diameter 6.
It was molded into a ring shape with a length of 0 mm, a length of 6.6 mm, and an inner diameter of a through hole of 2.0 mm.

Preparation of second-stage catalyst While stirring water 75 under heating, ammonium paratungstate 2.55 and ammonium metavanadate 2.2 were added.
1. Ammonium molybdate 10.00Kg, mixed and dissolved separately, strontium nitrate 2.68Kg and copper nitrate 2.28Kg in water
Prepare an aqueous solution dissolved in 13, mix both solutions, heat and stir, add 0.38 Kg of titanium oxide powder and evaporate to dryness, then powder down outer diameter 6.0 mm, length 6.6 mm, through hole inner diameter 2.0 mm Molded into 400
Calcination was carried out for 5 hours. The composition of this catalyst oxide is atomic ratio
It was Mo ₁₂ V ₄ W ₂ Cu ₂ Sr ₂ Ti ₁ .

The reaction and collection method of acrylic acid were in accordance with Example-2.
The reaction results are shown in Table 1.

Example-7 Preparation of pre-catalyst Example 5 except that nickel nitrate was added simultaneously with cobalt nitrate, rubidium nitrate was used instead of strontium nitrate, and phosphoric acid was added instead of ammonium paratungstate. By the same method as above, a catalyst oxide having an elemental composition of Co ₃ Ni ₁ Bi ₁ Fe ₂ Mo ₁₂ Si _4.7 P ₁ Rb _0.1 was molded into an outer diameter of 6.0 mm, a length of 6.6 mm, and a through hole inner diameter of 2.0 mm, and air was passed through 500 It was calcined at ℃ for 6 hours.

Preparation of second-stage catalyst In Example 6, strontium nitrate and titanium oxide were replaced with ferric nitrate as an iron source, sodium nitrate as a sodium source, and aluminum oxide as an aluminum source. The elemental composition of the catalyst oxide is Mo ₁₂ V ₆ W ₄ Cu ₁ Fe ₁ Na _0.5 Al ₅ with an outer diameter of 6.
Molded to 0mm, length 6.6mm, through hole inner diameter 2.0mm, 5 at 400 ℃
Burned for hours.

The reaction and collection method of acrylic acid were in accordance with Example-2.
The reaction results are shown in Table 1.

Example-8 Preparation of pre-catalyst Example-5 except that nickel nitrate and aluminum nitrate were added simultaneously with cobalt nitrate, potassium nitrate was used instead of ammonium paratungstate, and boric acid was used instead of strontium nitrate. In the same way as in the above, the elemental composition excluding oxygen Mo ₁₂ Bi ₁ Fe ₂ Ni ₁ Co ₃ Si _4.7 B ₂ K
_A catalyst oxide of _0.2 Al ₁ was molded into an outer diameter of 6.0 mm, a length of 6.6 mm, and an opening inner diameter of 2.0 mm, and was calcined at 500 ° C. for 6 hours under air flow.

Preparation of Second Stage Catalyst In Example-7, bismuth nitrate was used instead of ferric nitrate, rubidium nitrate was used instead of sodium nitrate, and silicon oxide was used instead of aluminum oxide. Elemental composition is Mo ₁₂ V ₈ W ₄ Cu
₁ Bi _0.05 Rb _0.05 Si ₅ catalyst oxide with an outer diameter of 6.0 mm and a length of 6.6
mm, through hole inner diameter 2.0 mm, and baked at 400 ° C. for 5 hours.

The reaction and collection method of acrylic acid were in accordance with Example-2.
The reaction results are shown in Table 1.

Example-9 Preparation of first-stage catalyst In Example-7, arsenous acid was used instead of phosphoric acid, and thallium nitrate was used instead of rubidium nitrate. The elemental composition is Co ₃ Ni ₁ Bi ₁ Fe ₂ Mo ₁₂ Si _4.7 As _0.5 Tl
_0.05, the catalyst oxide outer diameter 6.0 mm, length 6.6 mm.
A through hole having an inner diameter of 2.0 mm was formed and fired at 500 ° C. for 6 hours while circulating air.

Preparation of second-stage catalyst In Example 6, bismuth nitrate was used instead of copper nitrate, cesium nitrate was used instead of strontium nitrate, and silicon dioxide was used instead of titanium oxide. The oxide composition of this catalyst was Mo ₁₂ V ₈ W ₁ Bi ₁ Cs _0.05 Si ₅ in terms of atomic ratio excluding oxygen.

The reaction and acrylic acid collection follow Example-2. The reaction results are shown in Table 1.

Example-10 A demister is installed as a flame propagation blocking device on the inlet side of the pre-reactor, and the space between the device and the pre-reactor inlet is filled with a packing so as to reduce the space density, or the pre-reactor is used. Use the equipment designed to avoid the combustion range of propylene or acrolein by using the equipment designed to select the reaction temperature in a single reactor without separating the first-stage reactor. went.

Preparation of First Stage Catalyst and Second Stage Catalyst A catalyst similar to that prepared in Example-1 was prepared.

Reaction and Collection Method of Acrylic Acid In Example 2, in order to maximize the acrylic acid yield, the propylene conversion was 95.0%, and the molten salt temperatures of the first and second stages were 335 ° C. and 275 ° C., respectively. The composition of the first-stage reaction gas is propylene 15% by volume, oxygen 27.0% by volume, water vapor 10.0% by volume, carbon dioxide 17.7% by volume, carbon monoxide 10.1% by volume, propane 8.
A mixed gas consisting of 4% by volume and the balance of argon was introduced at 16.2 m ³ Hr (NTP conversion). The results are shown in Table-1.

Example-11 In Example-1, propylene 5 was used as a propylene raw material.
It carried out according to Example-1 except that 5.0% by volume and 45.0% by volume of propane were used. To the 1st stage reactor 7.0% by volume propylene, 12.6% by volume oxygen, 7% by volume steam, 58.8% by volume propane, 5.6% by volume carbon dioxide, carbon monoxide
A mixed gas consisting of 3.6% by volume and the balance of argon was 16.2 m ³ / Hr.
(NTP conversion) was introduced. The acrylic acid yield was optimum when the propylene conversion rate was 95.0%. The results are shown in Table-1.

Example-12 In Example-10, propylene 5 was used as the propylene raw material.
Example 10 was repeated except that 5.0% by volume of propane and 45.0% by volume of propane were used. To the first-stage reactor, propylene 15.0% by volume, oxygen 27.0% by volume, steam 10.0% by volume,
A mixed gas consisting of propane 37.4% by volume, carbon dioxide 5.2% by volume, carbon monoxide 3.0% by volume, and the balance argon 16.2 m ³ /
It was introduced by Hr (NTP conversion). The yield of acrylic acid was highest when the propylene conversion was 95.0%. Table of the results
Shown in 1.

Example-13 The preparation of the pre-stage catalyst of Example-1 was changed as follows.

Ammonium molybdate 10.62K while heating water 15.
g and ammonium paratungstate (3.24 Kg) were added and the mixture was vigorously stirred (this is referred to as liquid A).

Separately, 7.00 kg of cobalt nitrate is added to 2 parts of water, and ferric nitrate 2.43
Kg was dissolved in 2 of water, 2.92 Kg of bismuth nitrate was dissolved in 3 of acidified acid by adding 0.60 of concentrated nitric acid.
A liquid obtained by mixing the nitrate solution of the seed was added dropwise to the liquid A. Then, silica sol containing 20% by weight in terms of silicon dioxide.
A liquid prepared by dissolving 2.44 Kg and 20.2 g of potassium hydroxide in 1.5 of water was added thereto, and the suspension thus formed was heated and evaporated, and then dried at 150 ° C. for 16 hours in a dryer under air flow. Then, the powder was pulverized to a particle size of about 100 mesh. Next, 2.4 kg of this powder and a silica-alumina inert carrier having a diameter of 3 to 5 mm were used, and a rolling granulator was used to fix the catalyst component to the inert carrier. At this time, distilled water was used as a binder. The adhered substance was dried in a dryer at 120 ° C. for 12 hours, and then calcined at 450 ° C. for 6 hours in an air stream to prepare a catalyst.

The reaction method was according to Example-1. However, the molten salt temperature for the pre-stage catalyst (the temperature of the molten salt circulated in the reactor) was heated to 330 ° C. As a result, the difference ΔT between the maximum temperature of the catalyst layer of the first stage reactor and the reaction temperature was 38 ° C. Molten salt temperature for pre-catalyst 33
0 ° C is the temperature at which the yield of acrylic acid gives the highest value,
At that time, the propylene conversion rate was 95.7% and the acrylic acid yield was 9
It was 1.3%.

The reaction was continued for 8000 hours. After 8000 hours, the temperature of the first stage reaction night bath was 343 ° C and the temperature of the second stage reaction night bath was 266 ° C. The propylene conversion rate and acrylic acid yield at that point were 93.1% and 88.8%, respectively.
It was mol%.

Comparative Example-4 The reaction was carried out in the embodiment of Comparative Example-1-1 using the pre-stage catalyst of Example-13 (catalyst in which the catalyst components were fixed to the inert carrier by a tumbling granulator). However, the molten salt (nighter) temperature for the pre-stage catalyst was heated to 330 ° C. As a result, ΔT is 58 ℃
The conversion rate of propylene was 95.3%, and the yield of acrylic acid was 86.0%.

The reaction was continued for 4000 hours. At 4000 hours, the temperature of the first stage reaction night bath was 355 ° C and the temperature of the second stage night bath was 264 ° C. At that time, the propylene conversion rate was 90.
The yield of acrylic acid was 6% and the yield of acrylic acid was 81.8%. It can be seen that the decrease in the activity of the pre-catalyst is particularly remarkable in the ordinary reaction method.

Example-14 In Example-1, propylene 7.0 vol%, oxygen 12.6 vol, steam 35.0 vol%, carbon dioxide 16.8
A mixed gas consisting of vol.%, Carbon monoxide 5.6 vol.%, Propane 9.3 vol.%, And the balance argon was introduced at 16.2 m ³ / hr (NTP conversion). At this time, the amount of water vapor was adjusted at the temperature of the outlet gas from the top of the acrylic acid collector, and the reaction temperature of the first-stage reactor was 325 ° C and the reaction temperature of the second-stage reactor was 260 ° C.
At this time, the conversion of propylene was 94.5%, and the yield of acrylic acid was the highest.

At this time, the circulation rate of the waste gas to the front stage (first stage) reactor is 9
It was 6.4%. As a result, the ΔT of the first stage reactor was 46 ° C. The yield of acrylic acid with respect to the propylene supplied was 91.9%, and the space-time yield was 159.6 g acrylic acid / hr.
It was a catalyst.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Masamitsu Sasaki 1 992, Nishikioki, Kamahama, Aboshi-ku, Himeji-shi, Hyogo 1 Ichira Karaki

Claims (10)

[Claims] 1. Propylene obtained by oxidizing propylene in the first stage to produce acrolein and in the second stage to oxidize acrolein to mainly produce acrylic acid, and catalytic vapor phase oxidation of propylene with molecular oxygen in two stages. In a method for producing acrylic acid at least, 5-70% by volume of a saturated aliphatic hydrocarbon having 1 to 5 carbon atoms and 3 to 50% of carbon dioxide are used.
% By volume and the total of the aliphatic hydrocarbon and carbon dioxide is 20
-80% by volume, water vapor in the range of 0.5-8 mol per 1 mol of propylene, propylene concentration in the raw material gas in the range of 5-20% by volume, and molecular oxygen concentration in molar ratio to propylene. 1. A method for producing acrylic acid, which comprises subjecting a raw material gas contained in the range of 1.4 to 4.0 to the first stage reaction. 2. The method according to claim 1, wherein the propylene conversion in the first stage reaction is at least 70%. 3. The method according to claim 1, wherein the molecular oxygen is supplied as a molecular oxygen-containing gas having a purity of at least 90% by volume. 4. The method according to claim 1, wherein the saturated aliphatic hydrocarbon is at least one selected from the group consisting of methane, ethane and propane. 5. The method according to claim 1, wherein the waste gas obtained by separating acrylic acid from the reaction mixed gas obtained in the second stage reaction is reused as a raw material gas for the first stage reaction. 6. The steam supplied to the first stage reaction is steam contained in a waste gas obtained by separating acrylic acid from the reaction mixed gas obtained in the second stage reaction. the method of. 7. The method according to claim 1, wherein the molar ratio of oxygen to propylene is 1.4 to 4.0. 8. The amount of water vapor is 0.6 per mole of propylene.
The method according to claim 7, which is -5 mol. 9. The reaction temperature in the first step is 250 to 450 ° C.,
The method according to claim 7, wherein the reaction temperature in the second step is 180 to 350 ° C. 10. The first step reaction is carried out in the presence of an oxide catalyst containing molybdenum, bismuth and iron, and the second step reaction is carried out in the presence of an oxide catalyst containing molybdenum and vanadium. The method according to claim 1, wherein