JPS5817658B2 - Recovery method of tungstic acid catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering a transition metal compound catalyst used in the oxidation of an organic compound with hydrogen peroxide.

. It is well known to oxidize compounds having ethylenically unsaturated bonds with hydrogen peroxide to produce useful oxidation products such as the corresponding epoxy compounds and hydroxyl compounds obtained by further reaction with water or the like.

Hydrogen peroxide is used as an aqueous solution of various concentrations to give an aqueous reaction mixture, and it is also known to be epoxidized with azeotropic dehydration in an organic medium such as ethyl acetate.

For example, glycerin can be obtained from allyl alcohol via glycidol, and epoxysuccinic acid or tartaric acid can be obtained from maleic acid or maleic anhydride.

Furthermore, many oxidation reactions are known, such as those in which corresponding epoxy compounds are obtained from olefinically unsaturated organic compounds such as propylene, dodecene, styrene, and soybean oil.

Transition metal compounds such as tungsten, molybdenum, and vanadium are used as catalysts in these oxidation reactions.

These transition metal compounds are expensive and require high rates of recovery.

In addition, when purifying oxidation products such as glycerin by distillation,
The presence of these compounds promotes side reactions and deteriorates the quality of the product, and from this point of view as well, a high degree of separation is required.

The present invention will be described below regarding the recovery of tungstic acid catalyst, which is the most commonly used among transition metal compound catalysts, but the recovery of other transition metal compound catalysts such as molybdic acid and vanadate can also be carried out in the same manner.

Tungstic acid changes to pertungstic acid in a reaction system in the presence of hydrogen peroxide, and epoxidizes organic compounds having ethylenically unsaturated bonds in a dissolved state.

When the purpose is to produce a hydroxyl compound, such as in the case of glycerin production, the water utilization reaction of Evokind is subsequently carried out, but the tungstic acid catalyst may be separated and recovered before or after the water utilization reaction.

That is, the oxidation product contained in the reaction mixture according to the present invention may be an epoxy compound or a hydroxyl compound.

As mentioned above, the state of the tungstic acid catalyst is related to the hydrogen peroxide present in the reaction system.

Therefore, what is referred to as a tungstic acid catalyst in the present invention includes not only tungstic acid in a chemical sense but also pertungstic acid.

Among tungstic acid catalysts, pertungstic acid and sodium tungstate are soluble compounds, but tungstic acid itself is insoluble, and when organic compounds are oxidized with hydrogen peroxide, hydrogen peroxide is released at the end of the reaction. When most of it disappears, it precipitates out as solid fine particles under acidic conditions.

The reaction mixture targeted by the present invention is such an acidic oxidation reaction mixture, and its pH is usually 5 or less, for example, p
It is around H2.

However, the solid tungstic acid catalyst precipitated in the reaction mixture has extremely small particles and is colloidally dispersed. Efficiency was extremely difficult to achieve and was rarely practical.

Therefore, a large number of techniques have been studied and proposed so far regarding the recovery of tungstic acid catalysts used in the oxidation of organic compounds with hydrogen peroxide.

One of them is an adsorption method, in which, for example, the material is adsorbed onto an anion exchange resin and eluted with an alkaline aqueous solution.

Use of activated alumina as an adsorbent (US Pat. No. 28,699)
86), there are alternative methods such as using an aqueous alkali halide solution as an eluent (West German Patent No. 1114468), but this requires large capacity adsorption equipment and its regeneration life, the need for reprecipitation separation from the eluate, and the need for an alkaline elution catalyst. Many problems remain, such as decreased activity (see JP-A-53-80383).

A method is also known in which the stannic acid is adsorbed on stannic acid and separated by sedimentation or mud separation. There are other problems.

German Patent No. 1,230,000 is also known in which calcium chloride is added to precipitate insoluble calcium tungstate, but this, along with other methods using flocculants such as aluminum sulfate, contaminates the reaction mixture and is problematic.

A method in which tungstic acid is precipitated by acidification using a cation exchange resin and heating (Japanese Patent Publication No. 39-1580)
2) also has problems such as resin regeneration and filterability of lifetime sediment.

Other known methods include extraction method (Japanese Patent Publication No. 49-48922) and combustion treatment elution method of distillation residue C (Japanese Patent Publication No. 51-101799), but the steps are complicated.

The present inventor conducted research with the aim of achieving a simpler and higher separation efficiency for the recovery of tungstic acid catalyst, which has been attempted in many techniques and only recovered through complicated steps.

As a result, we unexpectedly went back to the basics and found an excellent solution in the tear separation method of a tungstic acid catalyst dispersed in colloidal fine particles, leading to the present invention.

The present invention differs essentially from conventional recovery methods in which the tungstic acid content is separated as a solid filtrate cake and then processed to return it to a reusable form. The point is that it is concentrated in
This concentrated slurry can be returned to the X reaction system while still in liquid form.

Adoption of the slurry concentration method eliminates the need for handling a colloidal cake of tungstic acid, the use of adsorbents, coprecipitants, flocculants, etc., ion exchange resin treatment, combustion treatment, etc.

Furthermore, this method is suitable for continuous processing and is easy to implement industrially.

Despite these great benefits, the recovery of tungstic acid catalysts by slurry concentration was completely unknown.

Concentration of the catalyst slurry was achieved by membrane filtration while reducing the active oxygen concentration of the reaction mixture to 107% atoms/9 or less.

Membrane filtration is a method of separating particles based on the particle permeability of the pores of a thin filtration membrane itself, and includes ultra filtration (UP) and precision filtration (MP), which are distinguished by pore size.

The membrane filtration method is a cake filtration method commonly used in industry, in which solid particles are removed by a vortex layer consisting of the precipitate itself formed on a support layer such as a cloth or a filtration aid. The principle is different from depth-type filtration methods such as trapping filtration methods and filtration methods using offshore paper, which itself forms a thick vortex layer; There is no need for some p-vortex layer.

As is clear from this, in the membrane offshore filtration method, there is no need for the formation of an offshore vortex layer, and the sediment can be separated from the offshore filtrate in the form of a concentrated slurry.

Since the solid tungstic acid catalyst contained in the aqueous reaction mixture is a colloidal particle too fine to be captured by conventional depth filtration, various separation methods such as those described above have been required. As a result of the study of the present invention, it was found that solid particles of the tungstic acid catalyst can be completely concentrated by membrane filtration.

Both ultrafiltration and precision filtration are applicable, but in the case of precision filtration, the processing flow rate may drop over time depending on the type of membrane or reaction liquid.

An ultrafiltration membrane having an asymmetric structure is preferable since there is no fear of clogging caused by fine tungstic acid particles.

Although any membrane filtration method may be used, generally the solid particulate tungstic acid catalyst is separated as a concentrated slurry.

The slurry containing the tungstic acid catalyst can be directly returned to the reaction system for reuse without requiring any special reprocessing.

At this time, since a part of the reaction product circulates along with the catalyst, it is generally preferable for the concentration ratio to be high in order to prevent sequential side reactions.

However, in the oxidation reaction using a tungstic acid catalyst, the solid content concentration in the raw solution is not very high, so if it is concentrated to a slurry with a concentration of 5 to 30%, it is possible to overcome the disadvantages by circulating the product. It has the advantage that the slurry is easy to handle.

In the membrane filtration method, it is generally known that it is advantageous to increase the flow rate of the liquid passing through the membrane surface and reduce the flow resistance at the membrane surface.

This is also true in the case of the present invention, and it is advantageous to apply a method in which a part of the concentrate is recycled, combined with the reaction mixture, and fed to a membrane filter, that is, a known closed-circuit membrane filtration method. .

Other methods include the so-called Christmas tree type membrane filtration method, which does not have concentrate feedback, but instead reduces the membrane area as the concentration increases and the liquid flow rate decreases to maintain the required liquid flow rate. Can be used.

When concentrating the acidic tungstic acid catalyst slurry by the membrane filtration method as described above, by controlling the active oxygen concentration in the reaction mixture to 10 m9 atoms/kg or less,
For the first time, a concentrated slurry of tungstic acid catalyst can be obtained with a high recovery rate of 95% or more.

It is known that alkaline salts of tungstic acid are water-soluble, and in the present invention, in which solid particles are concentrated and separated as a slurry by membrane separation, it is easy to use a tungstic acid catalyst in an acidic reaction mixture. I can understand it.

On the other hand, there is little to be learned from the prior art regarding active oxygen concentration, especially its permissible limit value.

The prior art sought adsorption, flocculants, and other methods based on the recognition that direct overseparation of the reaction mixture was difficult, and therefore only when the direct overseparation method of the reaction mixture was used would it be possible to avoid recovery. It is natural that no attention was paid to the amount of soluble tungstic acid catalyst, which is a problem.

However, the present inventor found that even if fine solid particles were completely separated by membrane filtration, a significant amount of tungstic acid catalyst may leak into the acidic furnace liquid, and this phenomenon has been investigated. As a result, it was found that there was a soluble tungstic acid catalyst that was proportional to the active oxygen concentration in the reaction mixture, and that this leaked out from the membrane filtration.

According to experiments, the amount was about 35-40 g of tungsten per gram of active oxygen atom.

Based on this discovery, the method of the present invention was created, which requires low active oxygen in order to reduce the amount of soluble tungstic acid contained in the reaction mixture during slurry concentration by membrane filtration.

From only the recovery rate of the tungstic acid catalyst, the lower the amount of active oxygen contained in the reaction mixture, the better.

The amount of active oxygen in the reaction mixture largely depends on the reaction rate of hydrogen peroxide, and therefore it is generally preferable to use an unsaturated compound as a raw material in a slightly excess amount relative to hydrogen peroxide.

The amount of active oxygen in the reaction mixture can also be reduced by increasing the reaction temperature and reaction time in addition to the molar ratio of raw materials.

However, such conditions must be selected within a range in which disadvantages due to side reactions do not increase.

The hydrogen peroxide can also be destroyed by the addition of reducing agents such as iron salts or sodium bisulfite, but this is not a preferred method as it contaminates the reaction mixture.

In this way, regulating the amount of active oxygen to reduce soluble tungstic acid is related to other factors, and it was difficult to predict whether there was a range that could be achieved. As a result of the study, the concentration of active oxygen in the reaction mixture was set at a value of 10 atoms or less per 1kp of the oxidation reaction mixture, which can be achieved without significant side reactions or other adverse effects, and which also suppresses the amount of soluble tungstic acid. The present invention was completed by discovering that it is sufficient to take the following steps.

Since the amount of active oxygen can be determined by a known analytical method, reaction conditions can be easily selected with reference to this analytical value.

Of course, it is desirable to use as low an amount of active oxygen as the quality of the product and other factors permit.

If the reaction conditions are appropriately selected, it is often possible to obtain a value of 1 to 5 atoms of active oxygen per kg of the oxidation reaction mixture.

According to the present invention, a high recovery rate can be achieved by directly overseparating the reaction mixture without the disadvantages of complicated operations using adsorbents, contamination of oxidation products using flocculants, etc.

The recovered tungstic acid catalyst is an easy-to-handle slurry that can be directly reused in the reaction system, and the Oki filtrate containing the reaction products is a high boiling point in processes such as distillation and purification as a result of the catalyst being removed to a high degree. Generation, decomposition, etc. are prevented.

As shown in the Examples below, in the present invention, the residual amount of tungstic acid catalyst in the offshore filtrate can be reduced to 100 ppm or less without adding any special flocculant or precipitant.

This means that when using conventional oxidation reaction conditions with about 0.5% tungstic acid catalyst in the reaction mixture, catalyst recoveries reaching greater than 98% can be obtained.

Even in the actual case of prior art precipitation by addition of calcium chloride, 200-800 ppm of tungstic acid remains in P[, and in the case of stannic acid adsorption, the adsorption rate is 90%.
It will be understood that a very high degree of separation and recovery can be achieved compared to the conventional method.

The present invention will be explained below with reference to Examples.

Example 1 A solution prepared by adding 0.5% tungstic acid to a 5.92% aqueous hydrogen peroxide solution was dissolved at a rate of 179.1 g/hour.
Complete mixing tank 3 with 21.6g of allyl alcohol per hour
It was charged into the first tank of a continuous oxidation reactor with tanks connected in series.

60°C for 3 hours in the first reactor and 70°C for 1 hour in the second reactor.
The reaction was carried out at 80° C. for 0.5 hour in the third reactor, and then passed through a cooler to obtain a reaction mixture at 40° C.

This reaction mixture was PE (approximately 2), and the active oxygen concentration was 7
The tungstic acid catalyst was dispersed in colloidal fine particles.

The amount of active oxygen was determined by collecting a portion of the reaction solution and measuring the acidity of sulfuric acid from 0 to 10.
0°C in the presence of ferroin reagent. It was determined by titration with IN cerium sulfate solution.

The above reaction mixture was continuously membrane-filtered using a closed-circuit ultrafiltration device using a polyacrylonitrile/polyvinylpyrrolidone copolymer-based ultrafiltration membrane (molecular weight cut off: 40,000).

The operating pressure is 1.2 m'/3ky/ml gauge at the outlet.
The flux of m Day was obtained.

The residual catalyst concentration in the aqueous solution of filtrate glycerin was 1105 pp as tungsten.

The tungstic acid was recovered as a 10% slurry and recycled to the first reactor for reuse without any problems.

The recovery rate of the tungstic acid catalyst was 97%.

Example 2 179.5 g/hour of an aqueous solution containing 0.5% tungstic acid and 5.92% hydrogen peroxide, 21.5 g/hour of allyl alcohol.
9 g was charged into the first reactor of the same reactor as Example-1.

60°C for 3 hours in the first reactor, 80°C for 1 hour in the second reactor
The third reactor was operated under conditions of 1000 CO05 hours, and cooled to 60° C. with a cooler to obtain a reaction mixture with a pH of about 2 and an active oxygen concentration of 1.5 m9 atoms per 1 kg of reaction liquid.

The membrane was filtered using a closed-circuit ultrafiltration device using a polysulfone-based ultrafiltration membrane (molecular weight cut off: 50,000), and the flux was 1.
．． A filtrate was obtained at a ratio of Om3/m Day.

The amount of catalyst remaining in the F liquid is 45 ppm as tungsten.
Met.

Tungstic acid was recovered as a 10% slurry (recovery rate 98.8%) and reused by helicycle in the reaction system.

Reference example Hydrogen peroxide, allyl alcohol (molar ratio 1:1.5),
An aqueous solution containing a tungstic acid catalyst (0.5%) (water was 30 times the mole of hydrogen peroxide) was reacted at 60°C.

The reaction rate of hydrogen peroxide reached 98.0% after 3 hours, and remained at 98.3% even after a further 2 hours.

The reaction mixture thus obtained (active oxygen concentration 29
．． 4 to 4 atoms/ky) was separated using the same ultrafiltration membrane used in Example 1, and the amount of catalyst in the reactor fluid (glycerin aqueous solution) was 1250 ppm as tungsten.
Met.

This is 0.17% as tungstic acid, which corresponds to 34% of the amount of catalyst used.

Acidic reaction mixtures (PH 1.7 to 2.4) obtained from many experiments with different molar ratios, catalyst amounts, reaction temperatures, times, etc. were subjected to ultraviolet filtration to determine the active oxygen concentration (N and Table 1 shows some of the results of comparing the relationship between tungsten concentration (W) and tungsten concentration (W).

(Units are the same as above)

Claims (1)

[Claims] 1. A method for recovering a tungstic acid catalyst from an acidic reaction mixture obtained by epoxidizing or hydroxylating a compound having an ethylenically unsaturated bond with hydrogen peroxide in the presence of a tungstic acid catalyst. Recovery of a tungstic acid catalyst, characterized in that the tungstic acid content is recovered as a concentrated slurry that can be reused in the reaction by membrane flooding while keeping the active oxygen concentration at 10 atoms per kg of reaction mixture or less. Law. 2. The recovery method according to claim 1, wherein the concentration of the concentrated slurry is 5 to 30%.