JPWO2018003289A1 - Method of producing acrylic acid - Google Patents

Abstract

An object of the present invention is to reduce propionic acid in acrylic acid which does not require a large amount of capital investment in the production of acrylic acid by gas phase catalytic oxidation of propane and which reduces the decrease in acrylic acid yield due to combustion. It is to provide a method.
The process for producing acrylic acid of the present invention comprises the step of vapor phase catalytic oxidation of propane using propane, oxygen, steam and an inert gas as raw materials in the presence of a metal oxide catalyst represented by the following composition formula In the gas phase catalytic oxidation, a reactor having a two-stage reaction zone is used to supply a part of the oxygen-containing gas to be reacted to the inlet of the second stage reaction zone.
Compositional formula: MoV _a A _b B _c Si _d O _e
In the formula, A is Te or Sb, B is Nb or Ta, a and b are each 0.01 to 1.5, and b / a = 0.3 to 1.0, c is It is 0.001 to 3.0, d is 0.002 to 0.5, and e is a number determined by the oxidation state of other elements.

Description

  The present invention relates to a method for reducing propionic acid in acrylic acid in the production of acrylic acid by gas phase catalytic oxidation of propane.

Acrylic acid is widely used as a raw material for fibers, synthetic resins, flocculants and the like. In general, acrylic acid is subjected to catalytic oxidation reaction of propylene and oxygen at about 400 ° C. in the presence of a Mo-Bi catalyst to produce acrolein, and then at about 300 ° C. in the presence of a Mo-V catalyst. It is produced by catalytic oxidation reaction of acrolein and oxygen.
The above production method is a two-stage oxidation reaction and requires a fixed bed reactor having two reaction zones. As a reactor, for example, a separate reactor in which two reactors are connected in series, a first-stage reaction is performed in the first-stage reactor, and a second-stage reaction is performed in the second-stage reactor, and A tandem-type reactor is used which is equipped with a temperature control device in the upper and lower stages, and performs the first stage reaction in the upper stage and the second stage in the lower stage.

On the other hand, a method of producing acrylic acid by a one-step oxidation reaction in which propane, which is inexpensive compared to propylene, is brought into catalytic reaction with oxygen as a raw material has been studied.
A large number of catalysts used in the method have been proposed, and representative examples include metal oxides based on [Mo, V, Te or Sb, Nb or Ta].
In addition, as a reactor, a reactor similar to gas phase catalytic oxidation of propylene is disclosed (Patent Document 1).

In the vapor-phase catalytic oxidation of propylene and propane, propionic acid is by-produced as acrylic acid is formed, and propionic acid, if contained in acrylic acid, adversely affects the quality of acrylic acid-based products. It is known.
In general, the concentration of propionic acid in crude acrylic acid (acrylic acid immediately after being obtained by oxidation reaction) obtained by gas phase catalytic oxidation of propylene is about several hundred ppm, and this value is within the allowable range.
However, since the concentration of propionic acid in gas phase catalytic oxidation of propane is about several thousand ppm, it is required to reduce propionic acid in order to put gas phase catalytic oxidation of propane into practical use.

  However, since propionic acid has a boiling point close to that of acrylic acid, it is difficult to remove propionic acid by distillation. As a method of reducing propionic acid, there is, for example, a crystallization method, but since a large amount of equipment investment is required, there is a problem that the production cost of acrylic acid increases.

  Patent Document 2 discloses a method of reducing the amount of by-product propionic acid by reducing the amount of steam supplied with propane and oxygen in the vapor phase catalytic oxidation of propane.

Patent Document 3, the gas after the gas-phase catalytic oxidation reaction of propane, are reacted in the presence of a mixed metal oxide catalyst having an iron phosphate catalyst or _CsMo 12 _PAsV 0.2 _Cu 0.2 _{Sb 0.1} Thus, methods of reducing propionic acid are disclosed.

  In Patent Document 4, the gas after the gas phase catalytic oxidation reaction of propane is allowed to flow through a complex oxide (Mo, Bi, Fe, Co, Ni, Na, B, K, Si) heated to 450 ° C. A method of reducing acid is disclosed.

JP 2007-31400 A International Publication No. 2012/091869 Patent No. 5460759 JP 10-21883

However, in the invention described in Patent Document 2, as disclosed in the example of Patent Document 2, when the amount of steam is reduced, the composition of the raw material mixed gas may fall within the explosion range, and the safety aspect There are concerns of
Moreover, in the invention described in Patent Document 3, the concentration of propionic acid after treatment is high, which is not a practical level.
Furthermore, in the invention described in Patent Document 4, there is a problem that acrylic acid burns after processing, and additionally, when using the above complex oxide for reduction of propionic acid, the gas phase of propane is used. There is a problem that a new reaction apparatus is required separately from the reaction apparatus used for the catalytic oxidation, which increases the production cost of acrylic acid.

  The object of the present invention is to eliminate the need for large capital investment in the production of acrylic acid by gas phase catalytic oxidation of propane, and to reduce the decrease in acrylic acid yield due to combustion, thereby reducing propionic acid in acrylic acid. It is to provide a method.

  As a result of intensive studies to solve the above problems, the present inventors have studied acrylic acid by gas phase catalytic oxidation of propane using propane, oxygen, steam and an inert gas as raw materials using a catalyst of a specific composition. By carrying out this gas phase catalytic oxidation under specific conditions in the production of propionic acid, it is possible to reduce propionic acid in acrylic acid under conditions that there is no need for large capital investment and that acrylic acid yield by combustion does not decrease. It has been found that it is possible to complete the present invention.

That is, the first invention in the present invention comprises the step of vapor phase catalytic oxidation of propane using propane, oxygen, steam and an inert gas as raw materials in the presence of a metal oxide catalyst represented by the following composition formula A method for producing acrylic acid, wherein a portion of the gas containing oxygen to be subjected to reaction is supplied to the inlet of the second reaction zone using a reactor having a two-stage reaction zone, the gas phase catalytic oxidation being performed. .
Compositional formula: MoV _a A _b B _c Si _d O _e
(Wherein, A is Te or Sb, B is Nb or Ta, a and b are each 0.01 to 1.5, and b / a = 0.3 to 1.0, c Is 0.001 to 3.0, d is 0.002 to 0.5, and e is a number determined by the oxidation state of other elements.)

  According to a second aspect of the present invention, the ratio of the raw material gas supplied to the first reaction zone is propane / oxygen / steam / inert gas = 1.0 / 0.5-2.5 / 2.0-8. When the ratio of the gas containing oxygen supplied to the second stage reaction zone is 0 / 2.4 to 14.0 (molar ratio) and the ratio of propane supplied to the first stage reaction zone is 1.0, It is a manufacturing method of the acrylic acid as described in 1st invention which is oxygen / inert gas = 0.8-1.8 / 3.8-8.6 (molar ratio).

The third invention in the present invention comprises the step of vapor phase catalytic oxidation of propane using propane, oxygen, steam and an inert gas as raw materials in the presence of a metal oxide catalyst represented by the following composition formula, This is a method for producing acrylic acid in which the reaction temperature in the second reaction zone is made higher than the reaction temperature in the first reaction zone using a reactor having a two-stage reaction zone in gas phase catalytic oxidation.
Compositional formula: MoV _a A _b B _c Si _d O _e
(Wherein, A is Te or Sb, B is Nb or Ta, a and b are each 0.01 to 1.5, and b / a = 0.3 to 1.0, c Is 0.001 to 3.0, d is 0.002 to 0.5, and e is a number determined by the oxidation state of other elements.)

  The fourth invention of the present invention is the method for producing acrylic acid according to the third invention, wherein the reaction temperature in the second reaction zone is 1 to 15 ° C. higher than the reaction temperature in the first reaction zone.

  A fifth invention according to the present invention is the acrylic acid according to the third or fourth invention, wherein in the gas phase catalytic oxidation, a part of the gas containing oxygen to be reacted is supplied to the inlet of the second reaction zone. It is a manufacturing method.

A sixth invention of the present invention relates to the method for producing acrylic acid according to any one of the first invention to the fifth invention, wherein the gas phase catalytic oxidation is performed using a separate type reactor in which two fixed bed reactors are connected in series. It is.

Further, to summarize the first and third inventions of the present invention, the present invention uses propane, oxygen, steam and an inert gas as raw materials in the presence of a metal oxide catalyst represented by the following composition formula, A step of vapor phase catalytic oxidation of propane, wherein the vapor phase catalytic oxidation is carried out using a reactor having a two-stage reaction zone, and a part of an oxygen-containing gas to be subjected to reaction is an inlet of a second stage reaction zone Or supply a part of the oxygen-containing gas to be supplied to the inlet of the second stage reaction zone using a reactor having a two-stage reaction zone. A method for producing acrylic acid, which comprises carrying out either or both of
Compositional formula: MoV _a A _b B _c Si _d O _e
(Wherein, A is Te or Sb, B is Nb or Ta, a and b are each 0.01 to 1.5, and b / a = 0.3 to 1.0, c Is 0.001 to 3.0, d is 0.002 to 0.5, and e is a number determined by the oxidation state of other elements.)

  According to the production method of the present invention, in the production of acrylic acid by gas phase catalytic oxidation of propane, there is no need for a large investment in equipment, and the decrease in yield of acrylic acid due to combustion is small, and propionic acid in acrylic acid Can be reduced.

The gas phase catalytic oxidation of propane in the present invention will be described.
In the production method of the present invention, a reactor having a two-stage reaction zone is used, and vapor phase catalytic oxidation is continuously performed in the first stage reaction zone and then in the second stage reaction zone.
As a reactor, there is a separate type reactor in which two reactors used in gas phase catalytic oxidation of propylene are connected in series, and a tandem type reactor provided with temperature control devices in the upper and lower stages in one reactor. It is preferable to use a fixed bed reactor as a reactor.
It is preferable to use a separate type reactor in which two reactors are connected in series, since it is easy to supply a source gas containing oxygen to the inlet portion of the second stage reaction zone.

Acrylic acid is obtained by vapor phase catalytic oxidation of propane by introducing the above raw materials into a reactor maintained at high temperature with propane, oxygen, steam and an inert gas as raw materials and being charged with the following metal oxide catalyst Is manufactured.
The raw materials may be separately introduced into the reactor, and they may be mixed in the reactor, or may be introduced into the reactor in a state where they are mixed in advance.
As oxygen, it is supplied in the state of pure oxygen and air, but it is economically preferable to use air.
In addition, as the inert gas, nitrogen, helium, argon, carbon dioxide gas and the like can be mentioned, but nitrogen is preferable for economic reasons, and when air is used as an oxygen source, nitrogen can be supplied simultaneously.

(1) When using a separate-type reactor in which two fixed bed reactors are connected in series A separate-type reaction in which the raw material is supplied to the first-stage reactor and the reaction is performed also continuously in the second-stage reactor It is an apparatus. 0.3-3.0 are preferable at a molar ratio with respect to propane, and, as for the ratio of the oxygen supplied to a 1st-stage reactor, 0.5-2.5 are more preferable. When it is 0.3 or more, the amount of oxygen is sufficient and the acrylic acid yield is improved, and when it is 3.0 or less, it is economically excellent.
The ratio of steam supplied to the first stage reactor is preferably 1.0 to 10.0, and more preferably 2.0 to 8.0 in molar ratio to propane. When it is 1.0 or more, the sequential combustion reaction is suppressed and the acrylic acid yield is improved, and when it is 10.0 or less, the rectification process and the waste water treatment process do not require an extra load and the economy Excellent.
The ratio of the inert gas supplied to the first stage reactor to propane is preferably 1.5 to 18.0, and more preferably 2.4 to 14.0. Within the above range, the composition of the mixed gas does not fall within the explosion range, which is preferable from the viewpoint of safety.

By supplying a gas containing oxygen to the second stage reactor, byproduct of propionic acid is suppressed. By setting the ratio of oxygen supplied to the first stage reactor to a molar ratio of 0.8 to 1.8, propionic acid can be effectively reduced. When it is 0.8 or more, the reduction effect of propionic acid is excellent, and when it is 1.8 or less, cost load is small and it is economically excellent.
The ratio of the inert gas supplied to the second stage reactor is preferably 3.8 to 8.6 for propane. Within the above range, the composition of the mixed gas does not fall within the explosion range, which is preferable from the viewpoint of safety.

  The reaction temperature is preferably 300 ° C. to 460 ° C., and more preferably 350 ° C. to 420 ° C. in both the first stage reactor and the second stage reactor. In addition, propionic acid can be effectively reduced by setting the reaction temperature of the second stage reactor higher than the temperature of the first stage reactor. At that time, a preferable temperature difference is 1 ° C. to 15 ° C. When the reaction temperature of the second stage reactor is higher than the reaction temperature of the first stage reactor, the formation of propionic acid is suppressed. In addition, reaction temperature means the highest temperature in the packed bed area | region of the metal oxide catalyst at the time of reaction.

The space velocity of the raw material mixed gas is suitably 500 to 4,000 hr.sup.- ¹ . When it is 500 hr ⁻¹ or more, the space-time yield of acrylic acid is high, and when it is 4,000 hr ⁻¹ or less, the reaction rate of propane is improved.
In addition, although unreacted propane contained in the reaction gas discharged from the reactor outlet and propylene as an intermediate product can be used as it is as fuel, it is separated from the other components in the reaction gas and sent to the reactor. It can be returned and reused. As a method for separating the unreacted propane gas from the other products and the inert gas, for example, known pressure swing adsorption (PSA), organic solvent adsorption and the like can be used.

(2) When using a tandem-type reactor equipped with temperature control devices in the upper and lower stages in one fixed bed reactor, the ratio of oxygen supplied to the upper stage (the first reaction zone) is the molar ratio to propane Is preferably 0.3 to 3.0, and more preferably 0.5 to 2.5. When it is 0.3 or more, oxygen is sufficiently supplied by the reaction to improve the acrylic acid yield, and when it is 3.0 or less, it is economically excellent.
The ratio of steam supplied to the upper stage is preferably 1.0 to 10.0, and more preferably 2.0 to 8.0 in molar ratio to propane. If it is 1.0 or more, the sequential combustion reaction is suppressed and the acrylic acid yield is improved, and if it is 10.0 or less, the rectification process and the wastewater treatment process do not require an extra load and it is economical Excellent.
The ratio of the inert gas supplied to the upper stage to propane is preferably 1.5 to 18.0, and more preferably 2.4 to 14.0. Within the above range, the composition of the mixed gas does not fall within the explosion range, which is preferable from the viewpoint of safety.

  The reaction temperature is preferably 300 ° C. to 460 ° C., and more preferably 350 ° C. to 420 ° C. in both the upper stage (the first reaction zone) and the lower stage (the second reaction zone). In addition, propionic acid can be effectively reduced by setting the reaction temperature in the lower stage higher than that in the upper stage. At that time, a preferable temperature difference is 1 ° C. to 15 ° C. If the lower reaction temperature is lower than the upper reaction temperature, propionic acid may increase. In addition, reaction temperature means the highest temperature in the packed bed area | region of the metal oxide catalyst at the time of oxidation reaction.

The space velocity of the raw material mixed gas is suitably 500 to 4,000 hr.sup.- ¹ . If it is 500 hr ^-1 or more, excellent yield of acrylic acid, if it is 4,000 hr ^-1 or less, thereby improving the reaction rate of propane. In addition, although unreacted propane contained in the reaction gas discharged from the reactor outlet and propylene as an intermediate product can be used as it is as fuel, it is separated from the other components in the reaction gas and sent to the reactor. It can be returned and reused. As a method for separating the unreacted propane gas from the other products and the inert gas, for example, known pressure swing adsorption (PSA), organic solvent adsorption and the like can be used.

Next, used in the present invention, the composition _formula: MoV _a in _{A b B c Si d O e} ( wherein, A is Te or Sb, B is Nb or Ta, a and b each 0.01 ~ 1.5 and b / a = 0.3 to 1.0, c is 0.001 to 3.0, d is 0.002 to 0.5, e is another element The method for producing a metal oxide catalyst, which is a number determined by the oxidation state of
An aqueous liquid containing Mo, V and metal A is produced by the following method, and a metal B compound is added to the obtained aqueous liquid to obtain an aqueous liquid containing Mo, V, metal A and metal B.

In the preparation of an aqueous liquid containing Mo, V and metal A, the Mo compound and the V compound are mixed in an aqueous medium, and the resulting mixture is heated with stirring. Thereafter, metal A is added to obtain an aqueous solution containing Mo, V and metal A.
The preferable temperature of the said liquid mixture by heating is 40 degreeC or more, More preferably, it is 40 degreeC-100 degreeC. The heating time is preferably 1 to 10 hours, more preferably 2 to 5 hours.

Examples of the Mo compound include ammonium molybdate, molybdenum oxide and molybdic acid. Among these compounds, ammonium molybdate is preferred in view of water solubility.
As the V compound, ammonium metavanadate, vanadium pentoxide and the like are preferable.
The addition amounts of Mo compound, V compound and metal A compound are such that the atomic ratio of V and metal A to Mo (a and b) is 0.01 to 1.5, and the atomic ratio of metal A to V (b / A) is 0.3 to 1.0. When the blending ratio of Mo, V and metal A is out of the above range, a metal oxide catalyst having high catalytic performance can not be obtained.

  The metal A is Te or Sb, and examples of the Te compound include metal tellurium, tellurium dioxide, orthotelluric acid, metatelluric acid and ammonium tellurite. The metal tellurium is preferably one previously wet-ground and particles having a particle size of 5.0 μm or less obtained by reducing tellurium dioxide and telluric acid with a reducing agent in an aqueous medium. Further, as the Sb compound, metal antimony and antimony trioxide are preferable.

It is preferable to add ammonia water at the time of addition of the metal A in view of the performance of the obtained metal oxide catalyst. There is no particular limitation on the temperature of ammonia water and metal A.
As for the addition amount of ammonia water, the molar ratio of ammonia to metal A is preferably 0.4 or more, and more preferably 0.8 to 4.0. An effect is fully acquired as it is 0.4 or more, and the cost of waste gas treatment is suppressed as it is 4.0 or less.

By adding the metal B compound to the reaction liquid obtained by the above operation, an aqueous liquid containing Mo, V, metal A and metal B is obtained.
The metal B is Nb or Ta. Examples of the metal B compound include oxides, nitrates, carboxylates, oxoacids, borates and the like. The insoluble metal B compound may be dispersed in water for use, but in this case, it can be dissolved in water by using boric acid and the like in combination. In addition, it is preferable to add hydrogen peroxide to the aqueous solution containing the metal B obtained.

The addition amount of the metal B compound is an amount such that the metal B becomes 0.001 to 3.0 when Mo is 1 in the atomic ratio of the metal in the obtained metal oxide catalyst. In the same catalyst, when the ratio of metal B when Mo is 1 is less than 0.001, deterioration of the obtained catalyst is likely to occur, while when it exceeds 3.0, the activity of the obtained catalyst is lowered, The conversion of propane is reduced.
As for the addition amount of ammonia water, the molar ratio of ammonia to metal B is preferably 0.4 or more, and more preferably 0.8 to 3.0. An effect is fully acquired as it is 0.4 or more, and the cost of the process of waste gas is suppressed as it is 3.0 or less.

  It is preferable to further add nitric acid or ammonium nitrate to the dispersion of fine precipitates obtained by adding aqueous ammonia and metal B compound. The addition amount of nitric acid or ammonium nitrate is preferably such an amount that the nitrate ion is at a molar ratio of 2.0 to 6.0 with respect to the metal B, more preferably 2.2 to 4.0. The addition effect is fully acquired as it is the said range.

  The resulting aqueous slurry, usually in the form of a slurry, is heated to evaporate the water and dried. For drying, a tray dryer and spray drying can be used.

The obtained dried product is preferably crushed to 500 μm or less, and preferably in the presence of oxygen, at a heating temperature of 250 ° C. to 380 ° C., more preferably 280 ° C. to 360 ° C., preferably 0.5 to 10 hours. More preferably, baking of the first stage is performed with a heating time of 1 to 3 hours.
The solid obtained by the first-stage baking is preferably 480 ° C. to 640 ° C., more preferably 570 ° C. to 620 ° C., for a baking temperature of 0.1 to 5 hours under nitrogen flow, More preferably, the second stage of baking is performed with a baking time of 0.2 to 1.5 hours. For firing, a shuttle kiln, a roller husky kiln and a rotary kiln can be used.

  The metal oxide catalyst obtained by the above operation is preferably pulverized to a median diameter of 0.2 to 0.4 μm. For grinding, a wet / dry ball mill, jet mill or the like can be used. As a dispersion medium of the wet ball mill, one obtained by adding oxalic acid to various alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol and the like can be used. After ball milling, the metal oxide catalyst is separated and washed and then dried. For separation or washing, filtration, centrifugation or the like can be used, and for drying, a tray dryer, a rotary kiln, or the like can be used.

  Then, the metal oxide catalyst after grinding is washed with an aqueous solution of oxalic acid. Specifically, an aqueous solution of oxalic acid and a metal oxide catalyst are added to a container and stirred. The concentration of the oxalic acid aqueous solution is preferably 0.5 to 5.0% by mass, and the liquid amount is preferably 1.0 to 5.0 times the weight of the metal oxide catalyst. The stirring time is preferably 0.5 to 5.0 hours. The metal oxide catalyst is separated from the aqueous solution, washed with water and dried. For separation or washing, filtration, centrifugation or the like can be used, and for drying, a tray dryer, a rotary kiln, or the like can be used.

The Si compound is attached to the metal oxide catalyst obtained by the above operation in an atmosphere without water. For deposition, the Si compound may be vaporized and the vapor thereof may be brought into contact with the metal oxide catalyst, or the Si oxide may be immersed in an anhydrous organic solvent in which the Si compound is dissolved and then the organic solvent may be evaporated. .
The form of the metal oxide catalyst used for the deposition of the Si compound may be a powder or a supported product supported on a carrier. In the case of powder, particles having a particle diameter of 500 μm or less are preferable. In the case of a supported product, particles having a particle size of 1.0 to 6.0 mm are preferred.

  As a Si compound, silicon tetrachloride, tetramethoxysilane, tetraethoxysilane, trimethoxysilane, triethoxysilane, trimethylsilane, triethylsilane, hexamethyldisilane, hexamethyldisilane, hexamethyldisilazane, hexamethylsiloxane, methyl silicate 51 (tetramethoxy) Examples include tetramer of silane) and ethyl silicate 40 (pentamer of tetraethoxysilane).

  When depositing the Si compound, it is preferable to carry out a dehydration treatment of the metal oxide catalyst in advance. The temperature for dehydration is preferably 50 ° C to 300 ° C, more preferably 70 ° C to 250 ° C. Dehydration effect is fully acquired as dehydration temperature is 50 ° C or more, change of the surface property of a metal oxide catalyst is suppressed as it is 300 ° C or less, and adhesion nature of Si compound is excellent.

  In the case where the vapor of the Si compound is attached to the metal oxide, any conventionally known method can be adopted as long as the attachment can be performed in an atmosphere without water. As a convenient method, a gas stream containing a vapor of the Si compound having a vapor pressure is produced by passing a dehydrated inert gas (hereinafter sometimes referred to as a carrier gas) through a liquid Si compound, which is then subjected to the metal oxidation. It is a method of contacting with an object.

  In the above method, the vapor pressure of the Si compound depends on the temperature and pressure of the atmosphere. The temperature of the Si compound may be raised to increase the vapor pressure. The flow rate of the carrier gas is preferably 1.0 to 1,000 ml / min. By adjusting the carrier gas flow rate and the vapor pressure of the Si compound, it is preferable to form a mixed gas in which the vapor concentration of the Si compound is preferably 0.1 to 10,000 ppm, more preferably 1 to 1,000 ppm. By contacting a metal oxide catalyst with a carrier gas containing a Si compound in the above concentration, 0.002 to 0.5 mol of Si can be deposited per 1 mol of Mo.

  The adhesion of the Si compound to the metal oxide catalyst is carried out in a container isolated from the atmosphere, and is preferably carried out by a fixed bed, a fluidized bed or the like. Furthermore, as for the temperature of the metal oxide catalyst at the time of Si compound adhesion, room temperature-350 degreeC is preferable. When the vapor of the Si compound comes in contact with the metal oxide catalyst maintained at this temperature, the Si compound adsorbed on the surface is rapidly converted to the metal oxide, and is surely fixed to the surface of the metal oxide catalyst.

When attaching a Si compound by impregnating a solution containing a Si compound with a metal oxide catalyst, the organic solvent used is not particularly limited, and toluene, hexane, acetone, ethyl acetate, etc. can be used, and toluene and hexane are preferable. .
The water content in the organic solvent is preferably 500 ppm or less, more preferably 300 ppm or less. When the water content in the organic solvent exceeds 2,000 ppm, it is preferable to apply a dehydration method according to a known method, preferably a molecular sieve adsorption method.

The amount of the organic solvent used in the impregnation is preferably 0.5 to 100 times, more preferably 1 to 20 times by volume ratio of the catalyst. The concentration of the Si compound contained in the organic solvent is preferably in the range of 0.01 to 300 μmol / ml, more preferably 0.1 to 150 μmol / ml.
Moreover, in order to improve the contact with Si compound and a metal oxide catalyst in the case of an impregnation, it is preferable to stir. The stirring time is preferably 0.5 to 24 hours.

  After impregnating with an organic solvent containing a Si compound, the metal oxide catalyst is separated from the solvent and the organic solvent is evaporated. It may be evaporated immediately after separation, or may be evaporated after washing the metal oxide catalyst with a dehydrated organic solvent. The removal method of an organic solvent can employ | adopt well-known methods, such as distillation, centrifugation, and filtration. Thereafter, by heating the metal oxide catalyst to, for example, 50 ° C. to 300 ° C., the deposited Si compound can be converted to an oxide and fixed on the surface of the metal oxide catalyst. The content of each metal component in the metal oxide catalyst of the present invention obtained by fixing Si oxide can be measured by fluorescent X-ray analysis.

The metal oxide catalyst obtained by the above operation may be used as a powder particle as it is or may be used by being supported on a carrier. Silica, alumina, silica alumina, silicon carbide and the like can be used as the type of support in the case of supporting.
The particle size of the carrier is preferably 0.5 to 5.0 mm. Although there is no restriction | limiting in particular in the load amount, 20-70 mass% is preferable. A rolling granulator etc. can be used in the case of support | carrier. Water, methanol, ethanol, ethylene glycol, glycerin, silica sol and the like can be used as a binder used for loading, and aqueous solutions of polyvinyl alcohol, starch, polyacrylic acid and the like can also be used. The particle size of the supported product is preferably 1.0 to 6.0 mm.

Example 1
<Manufacture of metal oxide catalyst>
In a flask, 370.8 g of ammonium molybdate, 65.4 g of ammonium metavanadate and 900 g of distilled water were added and dissolved at a temperature of 80 ° C. with stirring. After dissolution was completed, 25.2 g of metal tellurium particles (rods having an average major axis of 0.3 μm and an average minor axis of 0.1 μm) obtained by reducing tellurium dioxide with hydrazine was added to the solution which was not heated. 276 g of the aqueous dispersion was added, and 576 g of 2.0% ammonia water was further dropped. The reaction solution reached 50 ° C. after several minutes under stirring. In an aqueous solution obtained by dissolving 167 g of oxalic acid and 60.1 g of niobic acid hydrate (containing 73.2 mass% of niobic acid) in 1,719 g of distilled water, 17.4 g of 30 mass% hydrogen peroxide water The mixture obtained by adding and mixing was added to the above reaction solution. After stirring for 5 minutes, 96.0 g of ammonium nitrate was added to the reaction solution and stirred.
Thereafter, the reaction solution was spray dried by spray drying. The resulting dried product was calcined at 320 ° C. for 1.5 hours in an air atmosphere. The solid particles thus obtained were calcined at 600 ° C. for 1.5 hours under nitrogen flow to obtain 350 g of a metal oxide. In addition, the atomic ratio was Mo / V / Te / Nb = 1.0 / 0.28 / 0.14 / 0.16 (molar ratio) according to fluorescent X-ray composition analysis.

Then, the obtained metal oxide was ground by a dry jet mill. The median diameter after grinding was 0.28 μm. The metal oxide after grinding was added to a 1.0% aqueous solution of oxalic acid and stirred for 1 hour, then filtered and washed with water, and dried at 120 ° C. for 3 hours.
After 200 g of the metal oxide obtained by the above operation was crushed to 250 μm or less, it was placed in a flask, mounted on a rotary evaporator, and dried under reduced pressure at 80 ° C. for 0.5 hours. Thereafter, the pressure was returned to normal pressure, a nitrogen gas line was introduced into the flask, and the evaporator was rotated. Nitrogen at a flow rate of 21.0 ml / min was passed through to 8.0 g of tetramethoxysilane, and the vapor was introduced into a flask through a nitrogen gas line to bring the metal oxide into contact with the vapor for 53 hours.
Using a rolling granulator, 200 g of the metal oxide obtained by the above operation was supported on 200 g of 2.6 mm alumina balls using a 7.5% aqueous starch solution as a binder. Thereafter, the product was dried at 120 ° C. for 1 hour to obtain a supported product of metal oxide having a particle size of 4.0 mm.
400 g of the metal oxide-supported product obtained by the above operation was charged in a reaction kettle, 740 g of toluene was added thereto, and 8.1 g of tetraethoxysilane was further added, followed by stirring for 60 hours. After stirring, it was filtered and dried at 120 ° C. for 1 hour. The atomic ratio of the final metal oxide catalyst is Mo / V / Te / Nb / Si = 1.0 / 0.28 / 0.14 / 0.16 / 0.06 (molar) by fluorescent X-ray composition analysis. Ratio).
The metal oxide catalyst obtained above was used in Examples and Comparative Examples.

<Production method of acrylic acid>
Two 18 mm diameter Pyrex (registered trademark) reaction tubes were connected, and a separate type reactor in which an electric furnace was attached to each reaction tube was produced. Moreover, piping was connected so that gas could be introduced between the first stage and the second stage reaction tube of the separate reactor. Into the first and second stage reaction tubes, 5.4 g (filling volume: 4.6 ml) of the metal oxide catalyst support prepared above was loaded.
The reaction temperature (peak temperature of the sensor inserted in the longitudinal direction of the loaded product packed bed) is set to a temperature of 370 ° C. for both the first and second stages, and propane / oxygen / steam from the inlet of the first stage reaction tube A mixed gas of nitrogen / 1.0 = 1.2 / 2.3 / 7.1 / 11.0 (molar ratio) was supplied at a space velocity of 1,200 / hr ⁻¹ . In the second stage, a mixed gas of oxygen / nitrogen = 0.2 / 1.0 (molar ratio) was supplied together with the first stage reaction gas to produce acrylic acid. The space velocity of the second stage was 1,265 / hr ⁻¹ (= ^1, 200 + 65).
The gas after reaction was compositionally analyzed by gas chromatography (GC), and the propane conversion and acrylic acid yield were calculated on a molar basis by the following equation. The concentration of propionic acid was quantified by FID-GC.
The propane conversion was 75.5%, the acrylic acid yield was 59.2%, and the propionic acid concentration was 1,600 ppm. The results are shown in Table 1.
Propane conversion rate (%) = 100 × [(feed propane-unreacted propane) / feed propane]
Acrylic acid selectivity (%) = 100 × [formed acrylic acid / (supplied propane-unreacted propane)]
Acrylic acid yield (%) = (propane conversion × acrylic acid selectivity) / 100

Comparative Example 1
The reaction was performed under the same conditions as in Example 1 except that the mixed gas of oxygen and nitrogen was not supplied to the second stage.
The propane conversion was 76.3%, and the acrylic acid yield was 59.2%. Also, the propionic acid concentration was 2,050 ppm, which exceeded 2,000 ppm, which is an indication of the tolerance range of propionic acid.

Example 2
The reaction was performed under the same conditions as in Example 1 except that the reaction temperature, the molar ratio of the source gas, and the space velocity were as described below. The reaction temperature is set to first stage / second stage = 365 ° C./365° C., and from the inlet of the first stage reaction tube, propane / oxygen / steam / nitrogen = 1.0 / 1.6 / 4.7 / 7 .6 (molar ratio) mixed gas is supplied at a space velocity of 840 / hr.sup.- ¹ , and in the second stage, oxygen / nitrogen = 0.7 / 3.2 (molar) with the gas after the first stage reaction. Mixed gas was supplied to produce acrylic acid. The space velocity of the second stage was 1,041 / hr- ¹ (= 840 + 201).
The propane conversion was 77.7%, the acrylic acid yield was 59.3%, and the propionic acid concentration was 1676 ppm.

Example 3
The reaction was carried out under the same conditions as in Example 2 except that the molar ratio and amount of the second stage feed gas were as follows. In the second stage, a mixed gas of oxygen / nitrogen = 0.9 / 4.4 (molar ratio) was supplied together with the first stage reaction gas to produce acrylic acid. The space velocity of the second stage was 1,120 / hr ⁻¹ (= 840 + 280).
The propane conversion was 77.0%, the acrylic acid yield was 59.7%, and the propionic acid concentration was 1,106 ppm.

Example 4
The reaction was carried out under the same conditions as in Example 2 except that the molar ratio and amount of the second stage feed gas were as follows. In the second stage, a mixed gas of oxygen / nitrogen = 1.2 / 5.6 (molar ratio) was supplied together with the gas after the first stage reaction to produce acrylic acid. The second stage space velocity was 1,192 / hr-1 (= 840 + 352).
The propane conversion was 76.8%, the acrylic acid yield was 59.2%, and the propionic acid concentration was 1,004 ppm.

Example 5
The reaction was carried out under the same conditions as in Example 4 except that the reaction temperature was set to the first step / second step = 360/370 ° C.
The propane conversion was 76.6%, and the acrylic acid yield was 58.9%. Also, the propionic acid concentration was 793 ppm.

Example 6
The reaction was carried out under the same conditions as in Example 4 except that the reaction temperature was set to the first step / second step = 370/360 ° C.
The propane conversion was 76.4%, and the acrylic acid yield was 58.8%. Moreover, the propionic acid concentration was 1,215 ppm.

Example 7
The reaction was carried out under the same conditions as in Example 1 except that the reaction temperature was set to first stage / second stage = 367/374 ° C. and oxygen / nitrogen mixed gas was not supplied to the second stage.
The propane conversion was 76.3%, and the acrylic acid yield was 59.2%. The propionic acid concentration was 1,481 ppm.

Comparative Example 2
The reaction was carried out under the same conditions as in Example 7 except that the reaction temperature was set to the first step / second step = 374/367 ° C.
The propane conversion was 76.2%, and the acrylic acid yield was 59.2%. Also, the propionic acid concentration was 2,222 ppm, which exceeded 2000 ppm, which is an indication of the tolerance range of propionic acid.

  According to the present invention, in the production of acrylic acid by gas phase catalytic oxidation of propane, there is no need for a large investment in equipment, and propionic acid in acrylic acid is reduced under the condition that the decrease in acrylic acid yield due to combustion is small. can do.

Claims (6)

Including a step of vapor phase catalytic oxidation of propane using propane, oxygen, steam and an inert gas as raw materials in the presence of a metal oxide catalyst represented by the following composition formula,
A method for producing acrylic acid, wherein a portion of an oxygen-containing gas to be subjected to reaction is supplied to the inlet of a second reaction zone using a reactor having a two-step reaction zone in the gas phase catalytic oxidation.
Compositional formula: MoV _a A _b B _c Si _d O _e
(Wherein, A is Te or Sb, B is Nb or Ta, a and b are each 0.01 to 1.5, and b / a = 0.3 to 1.0, c Is 0.001 to 3.0, d is 0.002 to 0.5, and e is a number determined by the oxidation state of other elements.)   The ratio of the raw material gas supplied to the first stage reaction zone is propane / oxygen / steam / inert gas = 1.0 / 0.5-2.5 / 2.0-8.0 / 2.4-14. The ratio of the oxygen-containing gas supplied to the second stage reaction zone is 0 (molar ratio), and the ratio of oxygen / inert gas = 0 if the ratio of propane supplied to the first stage reaction zone is 1.0. The manufacturing method of the acrylic acid of Claim 1 which is 8-1.8 / 3.8-8.6 (molar ratio). Including a step of vapor phase catalytic oxidation of propane using propane, oxygen, steam and an inert gas as raw materials in the presence of a metal oxide catalyst represented by the following composition formula,
A method for producing acrylic acid, wherein the reaction temperature in the second reaction zone is made higher than the reaction temperature in the first reaction zone using a reactor having a two-stage reaction zone in the gas phase catalytic oxidation.
Compositional formula: MoV _a A _b B _c Si _d O _e
(Wherein, A is Te or Sb, B is Nb or Ta, a and b are each 0.01 to 1.5, and b / a = 0.3 to 1.0, c Is 0.001 to 3.0, d is 0.002 to 0.5, and e is a number determined by the oxidation state of other elements.)   The method for producing acrylic acid according to claim 3, wherein the reaction temperature in the second stage reaction zone is raised by 1 ° C to 15 ° C higher than the reaction temperature in the first stage reaction zone.   The method for producing acrylic acid according to claim 3 or 4, wherein in the gas phase catalytic oxidation, a part of the gas containing oxygen to be subjected to the reaction is supplied to the inlet of the second reaction zone.   The method for producing acrylic acid according to any one of claims 1 to 5, wherein the gas phase catalytic oxidation is performed using a separate type reactor in which two fixed bed reactors are connected in series.