JPH082823B2 - Method for stable oxidation of methylal - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for stably producing formaldehyde by an oxidation reaction of methylal. For more information,
The present invention relates to a method for producing formaldehyde by oxidizing methylal in a gas phase in a gas phase containing oxygen in the presence of an oxidation catalyst containing iron and molybdenum oxide as main components.

(Prior Art) Formaldehyde is conventionally produced by oxidizing methanol in the presence of a silver or iron-molybdenum catalyst. However, the formalin concentration obtained by this method is at most 63% by weight even if it reacts stoichiometrically.
Is. On the other hand, the concentration of formalin obtained by the oxidation reaction of methylal is 83% by weight if it reacts stoichiometrically.
It has a feature that the amount of water in the produced gas is much smaller than that of the oxidation of methanol, As a catalyst effective for the oxidation reaction of methylal, a catalyst in which iron, manganese, magnesium, cadmium, calcium, etc. are added based on silver, copper oxide, and molybdenum is known. However, with these catalysts, carbon monoxide, dimethyl ether, and methyl formate are large by-products, and it is difficult to obtain formaldehyde with high selectivity. The Applicant has previously been selected from iron, molybdenum, and alkali metals, bismuth, chromium, tungsten, nickel, cobalt1.
The inventors have found that a catalyst containing one or more metals as an active ingredient has a high selectivity with less by-products as described above, and filed a patent application (JP-A-57-134432). Further, a patent of an improved invention in which the content ratio of these metal elements is 0.001 to 0.1 in total of molybdenum 1.5-3.0, alkali metal, bismuth, chromium, tungsten, cobalt, nickel in terms of metal atomic ratio of iron to iron 1. (Japanese Patent Application Laid-Open No. 59-107442) (Problems to be solved by the present invention) In the oxidation of methylal, in a catalyst containing iron and molybdenum as main components, by-products of carbon monoxide are generated with time. An increasing phenomenon was observed. It has been found that this is mainly due to the fact that the valence of molybdenum shifts from hexavalent to tetravalent in the iron-molybdenum oxide catalyst and the state of reduction remains, that is, the by-product of molybdenum dioxide. As a result of intensive studies on the production of formaldehyde by the oxidation of methylal, the present inventors have found a method for producing formaldehyde in a stable manner, and completed the present invention. The present invention provides a method for producing formaldehyde by oxidation of methylal, which not only has high conversion and selectivity in the initial stage of reaction but also provides high productivity without lowering the selectivity of the reaction for a long period of time. is there.

(Means for Solving the Problems) The present invention relates to iron and molybdenum, or in addition thereto, alkali metal, bismuth, chromium, tungsten,
When formaldehyde is produced by oxidation of methylal in a gas phase containing oxygen using an oxide containing one or more metal elements selected from cobalt and nickel as an active ingredient, it is used as a catalyst. It is characterized in that the oxidation reaction of methylal in (1) is operated in a range satisfying the following relational expression.

[Oxygen consumption rate per unit catalyst weight] / [Oxygen partial pressure] ≦ 1.0 mol / hr. [G-catalyst]. [Atm] (1) However, in formula (1), [oxygen per unit catalyst weight] The "consumption rate" is the number of moles of oxygen consumed by the reaction per 1 g of the catalyst in 1 hour, and the "oxygen partial pressure" is a numerical value indicating the partial pressure of oxygen in the reaction gas in atm unit. A high oxygen consumption rate means a high reaction rate in the oxidation reaction. Although it is difficult to directly obtain the oxygen consumption rate during the gas phase reaction, the reaction temperature rises due to the heat of reaction in the oxidation reaction, the specific heat of the reaction product, the flow rate of the reaction product, and the reaction system (usually a catalyst is packed in the tube, It can be calculated from the heat balance between methylal, oxygen, nitrogen, water, and reaction products flowing in it) and outside the system (usually a heat medium such as molten inorganic salt or heat-resistant organic catalyst). . The oxygen partial pressure can also be calculated from the initial oxygen partial pressure before contacting the catalyst layer, the oxygen consumption rate, and the mass balance of the reaction products.

 Below, the aspect of this invention is described in detail.

The reaction takes place in the tube. Industrially, inner diameter 15
A ~ 25mm tube is used. The length of the tube is normal
It is 60 cm to 200 cm. These tubes range from 5,000 to 50,000
This gathering connects industrial reactors.

The shape of the catalyst packed and fixed in the tube is cylindrical, Raschig ring-shaped, spoke ring-shaped, or granular.

Specific examples of the catalyst here include iron molybdate, a mixture of iron molybdate and molybdenum trioxide, and further,
In addition to the mixture, a catalyst containing one or more metal oxides selected from alkali metals, bismuth, chromium, tungsten, cobalt, nickel and the like is included. Atomic ratio of molybdenum and iron of the catalyst used at this time
Mo / Fe is usually in the range of 1.5-4.5. Preferably 1.5-3.
0, more preferably 1.6 to 2.3, particularly preferably 1.6 to 1.9
Is in the range.

During the reaction, heat is exchanged between the inside and outside of the tube. The temperature of the heat medium circulating outside the tube is usually in the range of 240 to 300 ° C.

The methylal concentration supplied to the reaction system is 2 to 7% by volume,
Preferably 3-6% by volume, more preferably 4-5% by volume
Is. These concentrations are determined by productivity and operation stability.

In the present invention, the oxidation reaction of methylal is usually 250 to 4
It is performed in the range of 00 ℃. The conversion yield of methylalyl to formaldehyde in this reaction is usually 85 to 95%, although it depends on the reaction conditions. If the reaction temperature is too low, the reaction yield will decrease, and if the reaction temperature is too high, by-products to carbon monoxide will increase. The value of oxygen consumption rate] / [oxygen partial pressure] increases,
Not preferred. A preferable reaction temperature is 250 to 380 ° C., a particularly preferable reaction temperature is 360 ° C. as a maximum temperature, and a preferable reaction yield is 88% or more, more preferably 91% or more.

Usually, the linear velocity in the reactor is used in the range of 1.0 to 2.5 Nm ³ / m ² .sec.

[Oxygen consumption rate per unit catalyst weight] / [Oxygen partial pressure]
Is 1.0 or less, more preferably 0.7 or less, and particularly preferably 0.5 or less.

The value of [oxygen consumption rate per unit weight of catalyst] / [oxygen partial pressure] in the tube filled with the catalyst shows a behavior corresponding to the reaction temperature rising curve. That is, it rises as the reaction temperature rises, takes a maximum value immediately before the reaction temperature reaches its maximum, and then falls as the reaction temperature falls. The highest value of [oxygen consumption rate per unit weight of catalyst] / [oxygen partial pressure] is important.
It is affected by the methylal concentration, the degree of catalyst dilution (the degree of dilution of the catalyst with an inert substance), the linear velocity of the reaction product, and the like.

When the value of [oxygen consumption rate per unit amount of catalyst] / [oxygen partial pressure] exceeds 1.0, reduction of molybdenum occurs, black molybdenum dioxide is produced as a by-product, and oxidation reaction for a long time may be continued. Have difficulty.

The gas containing formaldehyde, which is the reaction product obtained in the present invention, is supplied to an absorption tower and taken out of the system as a formalin aqueous solution.

(Example) Hereinafter, the gist of the present invention will be described in detail with reference to Examples.

Example 1 An iron tube having an inner diameter of 21 mm and a length of 100 cm is filled with a spoke-shaped iron molybdate to molybdenum trioxide (Mo / Fe atomic ratio 2.3). At this time, the first half 50 cm of the catalyst layer is filled with 75% by volume of the catalyst and 25% by volume of Raschig rings made of ceramics. In the latter half 50 cm, only the catalyst is filled. Circulate organic heat-resistant oil (brand name SK oil) at 260 ° C outside the tube. 4% by volume of methylal and oxygen in this catalyst layer
8.3% by volume, 2% water, balance nitrogen gas linear velocity 1.3Nm ³ /
Supplied in m ² · sec. In addition, a thin hollow injection needle with an inner diameter of 1 mm and an outer diameter of 1.5 mm is passed from the top to the bottom of the tube catalyst layer, and the inside temperature is measured by passing a thermocouple through the needle. It is said. From these heat balance and reaction analysis, [oxygen consumption rate per unit catalyst weight] / [oxygen partial pressure] in the reaction layer can be determined. The maximum value was 0.42 mol / hr. [G-catalyst] [atm].

The selectivity of the reaction of formaldehyde to methylal is
It was 94%. The selectivity after three months was also 94%, showing no change. No molybdenum dioxide was found in the catalyst taken out.

Example 2 The same operation as in Example 1 was carried out with the temperature of the catalyst body set at 270 ° C. The maximum value of [oxygen consumption rate per unit weight of catalyst] / [oxygen partial pressure] is 0.82 mol / hr ・ (g-solvent) [atm]
It was.

The selectivity of the reaction from methylal to formaldehyde is
It was 92%. The selectivity after 3 months was also 92%, but a black deposit of molybdenum dioxide was observed in the catalyst taken out.

Comparative Example 1 The same operation as in Example 1 was performed except that the temperature of the heat medium was 305 ° C. [Oxygen consumption rate per unit weight of catalyst]
The maximum value of / [oxygen partial pressure] is 1.3 mol / hr. [G-catalyst] [a
tm]. The selectivity of the reaction from methylal to formaldehyde was 91%. The selectivity of the reaction for three months is 87.
It was in%. In addition, a black precipitate based on molybdenum dioxide was observed in the catalyst taken out.

Example 3 When the operation of Example 2 was continued for another 6 months, the selectivity of the reaction was 91%.

Comparative Example 2 The same operation as in Example 2 was carried out by completely filling the catalyst layer with the catalyst without diluting it. The maximum value of [oxygen consumption rate per unit catalyst weight] / [oxygen partial pressure] is 1.1 mol / hr.
[G-catalyst] [atm]. The selectivity of the reaction from methylal to formaldehyde was 91%. The selection rate for three months was 88%. In addition, a black precipitate based on molybdenum dioxide was observed in the catalyst taken out.

Example 4 Methylal was 4.5% by volume and oxygen was 8.8% by volume.
Performed the same operation as. The maximum value of [oxygen consumption rate per unit catalyst weight] / [oxygen partial pressure] is 0.49 mol / hr ・ [g-
Catalyst] [atm]. The selectivity of the reaction from methylal to formaldehyde was 94%. The selectivity after 3 months was also 94%, and no change was observed in the catalyst taken out.

Example 5 The reaction product obtained in Example 4 is introduced into an absorption tower which is equipped with a condenser at the top and which is filled with Dickson packing. Water is supplied from the top of the absorption tower, and the formalin concentration at the bottom of the absorption tower is adjusted to 65% by weight. The formalin aqueous solution was taken out of the system.

(Effects of the Invention) As described above, the method of the present invention provides a method for stably producing formaldehyde for a long period of time by producing methylaldehyde by oxidizing methylal, and its industrial significance is Extremely large.

Claims (3)

[Claims] 1. Iron and molybdenum, or in addition to them, an oxide containing, as an active ingredient, one or more metal elements selected from alkali metals, bismuth, chromium, nickel, tungsten, cobalt and nickel. Then, in producing formaldehyde by oxidizing methylal in a gas phase containing oxygen, a method for producing formaldehyde is characterized in that the oxidation reaction of methylal on a catalyst is operated within a range satisfying the following relational expression. [Oxygen consumption rate per unit catalyst weight] / [Oxygen partial pressure] ≦ 1.0 mol / hr. [G-catalyst]
[Atm] Here, the [oxygen consumption rate per unit weight of catalyst] is the number of moles of oxygen consumed by the reaction in 1 hour per 1 g of the catalyst, and the "oxygen partial pressure" is in the reaction gas. The partial pressure of oxygen (atm). 2. The method according to claim 1, wherein the concentration of methylal in the gas phase before contacting the catalyst layer is 2 to 7% by volume. 3. The method according to claim 1, wherein the oxidation reaction is carried out at 250 to 400 ° C., and the yield of the obtained formaldehyde based on methylal is 85% or more.