JP4776081B2 - Synthesis method of trioxane - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to obtaining trioxane which is an important raw material monomer for polyacetal resin as an engineering resin. More specifically, the present invention relates to a method for efficiently obtaining trioxane from formalin using a heteropolyacid as a catalyst.
[0002]
[Prior art]
So far, sulfuric acid that is corrosive to metal materials has been used as a catalyst to synthesize trioxane from formalin.
In the case of a sulfuric acid catalyst, for example, a special metal or non-metallic glass fiber reinforced plastic (FRP) has been used as a reaction vessel.
However, in FRP, there remains anxiety about stress loading on a material having a boiling point of formalin of 100 ° C. or higher. Moreover, anxiety remains in the joint between FRP and a metal material.
From this point of view, use of a cross-linked ion exchange resin as a trioxane synthesis catalyst as a non-corrosive catalyst (Japanese Patent Publication No. 1-11025), and use of a heteropolyacid as a synthesis catalyst of trioxane from formalin. (Japanese Patent Publication No. 63-37109) was proposed by the present applicants.
These non-corrosive catalysts have been found to have excellent effects in several respects with respect to conventionally used sulfuric acid catalysts.
For example, heteropolyacids have a very high selectivity for trioxane compared to sulfuric acid catalysts when synthesizing trioxane from formalin, and also have high conversion of reaction because high concentrations of formalin can be dissolved even at low temperatures. It has excellent characteristics such as.
[0003]
[Problems to be solved by the invention]
However, when synthesizing trioxane from formalin using a cross-linked ion exchange resin or heteropolyacid as a catalyst, there is a problem that the activity of the catalyst is not maintained.
[0004]
[Means for Solving the Problems]
As a result of intensive investigations to solve the above problems, the present inventors have completed a method for maintaining the activity of the heteropolyacid catalyst when synthesizing trioxane from formalin by the following method.
That is, the present invention provides: A method of synthesizing trioxane, comprising using a titanium-based material that is corrosion resistant to formic acid as a material for a reactor, a connecting portion, and a distillation column in synthesizing trioxane by bringing a formalin aqueous solution into contact with a heteropolyacid catalyst. , it is.
[0005]
The present invention will be described in detail below.
The formalin used in the present invention is obtained by oxidizing methanol.
As a method for oxidizing methanol, there are a methanol excess method using silver as a catalyst and an air excess method using an iron oxide-molybdenum oxide composite compound as a catalyst.
As another most preferable method, there is a method of obtaining a high concentration formalin obtained by oxidizing methylal. This method is shown in Japanese Patent Publication No. 4-15213 by the present applicants.
Usually, the formalin concentration is 55% to 70%. A higher formalin concentration is advantageous in the synthesis of trioxane.
[0006]
Examples of the heteropolyacid used in the present invention include silicotungstic acid and phosphotungstic acid. Examples of desirable catalysts are described in detail in Japanese Patent Publication No. 63-37109 proposed by the present applicant. In other words, this heteropolyacid has a heterogeneous element (central element) at the center as shown in “Catalyst” Vol. Is a heteronuclear condensed acid having a mononuclear or binuclear complex ion, and is generally represented by the following chemical formula.
Hn [MxM'yOz] · mH ₂ O
[0007]
Here, M is a central element, M ′ is a coordination element, generally one or more elements selected from W, Mo, V, and Nb, x is 0.1 to 10, y is 6-30, z is a number in the range of about 10-80 indicating the number of oxygen in the heteropolyacid, n is the number of acidic hydrogens in the heteropolyacid, and is greater than 1. , M is the number of moles of crystal water and is a number in the range of 0 to about 40. In addition, so-called mixed heteropolyacids containing two or more coordination elements are also included in the heteropolyacid of the present invention.
The central element M in the above composition formula is generally selected from P, B, Si, Ge, Sn, As, Sb, U, Mn, Re, Cu, Ni, Co, Fe, Ce, Th, and Cr. Consists of two or more elements. Particularly preferably used is the case where the central element M is P, Si, B, Ge, Cu, or Sn. Among these, the case of Si or P is preferable, and silicotungstic acid, silicomolybdic acid, phosphotungsten are particularly preferable. The use of acids and phosphomolybdic acid or mixtures thereof is particularly effective.
[0008]
The coordination element M ′ in the above composition formula is composed of one or more elements selected from W, Mo, V, and Nb. Particularly preferably, the coordination element M ′ is W, Mo, or This is the case of any one of V or a mixture thereof.
The heteropolyacid catalyst used is suitably 10 to 600 parts by weight per 100 parts by weight of formalin.
As the amount of heteropolyacid catalyst used increases, the concentration of formalin used can be increased, and the amount of conversion of formalin to trioxane per unit time can be increased. In some cases, the reaction temperature can be lowered for the same formalin concentration.
[0009]
The reaction temperature for obtaining a trioxane by bringing a formalin aqueous solution into contact with a heteropolyacid catalyst can usually be carried out in the range of 70 ° C to 120 ° C.
When the reaction temperature is higher than 100 ° C., the reaction is performed under pressure, and when the reaction temperature is 100 ° C. or lower, the reaction is performed under reduced pressure.
When the temperature is increased, a high concentration of formalin is used, the yield to trioxane can be increased, and the amount of conversion to trioxane per unit time can be increased, but the selectivity is lowered.
[0010]
On the other hand, when the reaction temperature is lowered, the selectivity is increased, but the concentration of formalin that can be used is lowered. As a result, the yield of trioxane is lowered, and the conversion amount to trioxane per unit time is also lowered.
The reaction temperature is optimized by the amount of trioxane required, taking these points into account. Usually, the reaction is carried out under normal pressure.
Examples of the material having corrosion resistance to formic acid used in the present invention include glass, glass fiber reinforced plastic (FRP), carbon material, and titanium-based material.
[0011]
When synthesizing trioxane from formalin, formalin is oxidized as a side reaction to produce formic acid.
When the material of the system is a material that is not resistant to formic acid, for example, when SUS is used, metal ions (Fe, Ni, Cr, etc.) in the SUS attack the heteropolyacid catalyst, Deactivate the acid catalyst.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The gist of the present invention will be described below with reference to examples, but this does not limit the scope of the present invention.
( Reference example )
For the distillation column that is a concentration system of trioxane from the reactor and formalin, a glass material that is corrosion resistant to formic acid was used. Under normal pressure, 100 g of 70% formalin and 500 g of silicotungstic acid catalyst were charged into a 1000 mL glass reactor and the reactor was immersed in a heated oil bath to boil the contents. The reactor was continuously fed with 100 g of formalin per hour.
[0013]
The product vapor was continuously extracted from the reactor and supplied to the bottom of a glass distillation column (column height: 3 m).
A reflux apparatus was attached to the top of the distillation tower to extract a condensed liquid of trioxane and dilute formalin at a reflux ratio of 5.
The remainder of the condensate was returned to the top of the distillation column, and the condensate was extracted from the bottom of the distillation column and continuously returned to the reactor.
[0014]
A level gauge is installed in the reactor, and the level gauge is used as a sequence linked to the heating temperature of the oil bath, and the temperature of the oil bath is set to control the amount of evaporation so that the liquid level of the reactor becomes constant. Controlled.
57 g of trioxane was extracted from the top of the distillation column every hour. The selectivity of the reaction was 99%.
This reaction was continuously carried out for 1 month, but no change was observed in the yield and selectivity of trioxane.
[0015]
( Example 1 )
The same operation as in the reference example was performed, except that the material of the reactor, the connecting portion, and the distillation column in the reference example was a titanium material that was corrosion resistant to formic acid. 57 g of trioxane was extracted from the top of the distillation column every hour. The selectivity of the reaction was 99%. This reaction was continuously carried out for 1 month, but no change was observed in the yield and selectivity of trioxane.
[0016]
(Comparative Example 1)
The same operation as in the reference example was performed except that the material of Example 1 was stainless steel SUS306, which was not excellent in corrosion resistance against formic acid. 57 g of trioxane was extracted from the top of the distillation column every hour. The selectivity of the reaction was 99%. When this reaction was continuously carried out for 1 month, the produced trioxane decreased to 45 g per hour and the selectivity also decreased to 97%.
[0017]
(Comparative Example 2)
The same operation as in the reference example was performed except that the material of Example 1 was stainless steel SUS304, which has poor corrosion resistance against formic acid. 57 g of trioxane was extracted from the top of the distillation column every hour. The selectivity of the reaction was 99%. When this reaction was carried out continuously for one week, the produced trioxane was reduced to 40 g per hour and the selectivity was also reduced to 97%.
[0018]
【The invention's effect】
The present invention provides an excellent method for producing trioxane, which is a raw material monomer for polyacetal resin. This method is useful as a method for producing trioxane.

Claims (1)

  A method of synthesizing trioxane, comprising using a titanium-based material that is corrosion resistant to formic acid as a material for a reactor, a connecting portion, and a distillation column in synthesizing trioxane by bringing a formalin aqueous solution into contact with a heteropolyacid catalyst. .