JPS5856368B2 - Manufacturing method of urea formaldehyde adhesive or resin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for producing urea formaldehyde adhesives or resins, and to the products obtained by this process.

More particularly, the present invention relates to a method for making urea-formaldehyde adhesives or resins by preparing a concentrated aqueous solution of formaldehyde from methanol and reacting it with urea.

The present invention also relates to a method for producing concentrated aqueous solutions of formaldehyde that can be run off from equipment for other applications such as the production of paraformaldehyde.

Various processes are already known for producing formaldehyde from methanol, generally by passing methanol vapor and air in appropriate proportions over a catalyst in the gas phase and at elevated temperatures.

In one of these known methods, the oxidation products obtained are condensed to obtain condensable products on the one hand and uncondensed gases on the other hand.

The uncondensed gas is washed with water to form a formaldehyde solution and unreacted methanol is recovered.

The solution thus obtained is combined with the condensation product,
Form a crude formaldehyde aqueous solution.

The concentration of formaldehyde in this solution depends on the amount of water used to scrub the gas.

The crude solution obtained contains, in addition to formaldehyde, methanol in an amount that varies according to both the type of catalyst used and the air to methanol ratio used.

This solution can be used directly or the methanol present therein can be partially or completely separated.

Although this method is generally satisfactory, it nevertheless has the following drawbacks.

Due to the fact that the uncondensed gas is washed with a sufficient amount of water to remove the formaldehyde and methanol present in it, which would otherwise be lost from the system, the concentration of the resulting aqueous formaldehyde solution is necessarily limited.

The aqueous formaldehyde solution thus obtained, with a concentration of 30-50%, can then be processed to give a dilute solution of urea-formaldehyde adhesive, which can be concentrated by vacuum distillation to a standard industrial grade. of adhesive, i.e. with a solids content of 65%.

This final distillation step has the following steps.

(a) It is necessary to use equipment operating in vacuum, which is always expensive in both continuous and batch operations.

The discharged resin has to be heated, in which case a local temperature increase occurs in the walls of the device, with the result that secondary reactions occur which have an adverse effect on the quality of the resin.

(e) It is also difficult to control the amount of resin produced due to viscosity changes that occur during distillation, and in addition, the heated surface will form a crust as a result of polymerization of the resin.

and (d) the distillate contains relatively large amounts of formaldehyde, which must be constantly removed, which creates contamination problems.

The present invention eliminates these drawbacks by providing a method.

This method prepares a solution containing formaldehyde at a concentration of 68-70% and reacts it directly with urea to produce a urea-formaldehyde adhesive with a solids content of, for example, 65%, without the need for a final distillation step. It consists of generating.

According to the invention, (a) methanol is catalytically oxidized with air; (b)
(e) condensing the gas resulting from the catalytic oxidation of step [a), thereby condensing the condensable gas in the gas in the form of a solution; (d)
Cooling the uncondensed gas from step (e), washing the cooled gas with a low temperature aqueous polymerized formaldehyde solution in a washing tower to absorb methanol and formaldehyde present in the uncondensed gas, and step (e) Distilling the solution obtained in step (e) to separately recover the concentrated formaldehyde aqueous solution and methanol; (f) distilling the solution obtained in step (d) to remove the methanol absorbed in the solution. recovering and isolating the formaldehyde in the form of its solution; (g) combining a portion of the formaldehyde solution obtained in step (f) with the condensed, distilled formaldehyde solution obtained in step (e); and (h) A urea-formaldehyde adhesive characterized in that a urea-formaldehyde adhesive or resin is obtained by mixing the concentrated aqueous formaldehyde solution obtained in step (e) and urea at a predetermined pH and temperature. Alternatively, a method for producing a resin is provided.

If desired, all or part of the concentrated aqueous solution of formaldehyde can be drained off after step (e) for other uses, for example for the production of paraformaldehyde.

According to another aspect of the invention, in step (b) the gas is condensed by scrubbing with a condensate product circulated by a pump from the bottom of the scrubber, which condensate product is outside the scrubber. Cooled by a cooler.

According to yet another aspect of the invention, a formaldehyde solution is discharged from the bottom of the washing column, heated, and partially distilled to recover the methanol present therein and isolate the formaldehyde. , and after cooling, remove a portion of the solution and add that portion to the condensate product coming out of step (e) to obtain the formaldehyde cleaning solution used in d).

Therefore, according to the present invention, due to the fact that the formaldehyde solution only contains water produced during the catalytic oxidation of methanol, this method uses a highly concentrated formaldehyde solution, thus carrying out the final distillation step. Without urea formaldehyde adhesive or resin can be obtained directly.

This process also has the advantage that all the methanol present in the uncondensed gas can be recovered, since the amount of cleaning agent is limited only by the increased heat consumption resulting from the use of the methanol content of the cleaning solution.

Washing columns using polymerized formaldehyde must be operated at low temperatures, and the plates of this column can be cooled by liquid cooling medium or by air-cooled methanol in the catalytic reaction front-washer.

Distillation of formaldehyde solution to recover methanol
It can be carried out in a conventional manner, ie in a suitable column at atmospheric pressure or lower pressure.

However, in view of the fact that high temperatures are required to completely remove the formaldehyde present in concentrated formaldehyde solutions, if a heat exchanger is present,
The heat of the gases generated during the catalytic reaction at 00°C can be used directly.

In step (h), the hot formaldehyde solution is mixed with urea at pH 7.5-8.5, and if you want to obtain a storable solution of urea-formaldehyde adhesive, add acidic substance to keep the pH at 5-6.5. .

Alternatively, maintaining a pH value of around 8-9 throughout the step (h) and maintaining a lower proportion of urea than formaldehyde results in a highly stable concentrated urea-formaldehyde solution, which is especially useful for solid resins, molding powders, etc. Alternatively, it can be commercially available as a base material for adhesives.

The method according to the invention has inter alia the following advantages.

Firstly, there is no need to concentrate the resin obtained, so there is no need for vacuum operations and the use of expensive equipment in both continuous and batch processes.

Second, the resulting resin does not need to be heated, thus avoiding local temperature increases on the equipment walls due to secondary reactions that could adversely affect the quality of the resin, and preventing deposits on the equipment wall soil. generation can be avoided.

Thirdly, the fact that once the reaction is complete, the resin is viable and only needs to be cooled makes it possible to control the different properties of the resin produced even more effectively.

Therefore, there is no viscosity change or other change with subsequent concentration.

Fourthly, due to the fact that it is possible to work in batches of 30 tons and there is no crust formation that has to be removed, even during cleaning there is no effluent formation, so the ultimate problem of contamination is eliminated. , completely excluded.

Furthermore, the gas remaining after formaldehyde formation is burned in the boiler, so there is no air pollution.

It should be noted that although this method can be carried out continuously, it also offers the particular advantage of being able to produce individual adhesive or resin batches.

This is important for the following reasons.

In order to meet the requirements, it is often necessary to produce adhesives of different quality, as specific adjustments are made to each different adhesive required.

Having to carry out adjustments of this type is a disadvantage in continuous processes, and it is therefore preferable to work batchwise using separate vessels in which specific adjustments can be made.

According to the invention, it is possible to work effectively with this type of tank, which is simple and lightweight.

This was not possible with conventional methods requiring a final distillation step with associated equipment.

A specific embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a diagram of an apparatus for producing urea formaldehyde adhesives or resins.

FIG. 2 is a diagram of one embodiment of an apparatus for continuous production of urea-formaldehyde adhesive from a concentrated solution of formaldehyde.

When using the apparatus shown in FIG.
0 and introduced into the saturator 12 where valve 1
50.5℃ by steam heating unit adjusted by 4
Whisk in methanol held in water.

Methanol is supplied to the saturator 12 from the reservoir 16, and its constant introduction amount is regulated by a valve 58.
6 to the saturator 12.

Next, the mixture containing 1950 kg/hour of methanol and exiting from the saturator 12 is heated to a catalyst 1 maintained at about 500°C.
8, 1160 kg/h of methanol is converted into formaldehyde by the usual reaction with liberation of the corresponding hydrogen, a part of which is oxidized to water due to the oxygen present in the air.

A small amount of carbon dioxide is simultaneously produced and virtually all the oxygen present in the air is converted during the reaction.

The gas mixture exiting the contactifier then enters the bottom of the washer 20, which at its head is connected to a pump 2.
2 receives the condensation product from the bottom of the washer, which is circulated by the condenser 24 and cooled by the condenser 24.

The mixture thus collected is drawn off by pump 28 under the control of valve 30 to a distillation column 32 which removes the methanol present in the introduced mixture.

This methanol is condensed in the condenser 34 and then
It is returned to the saturator 12 under the regulation of 6.

The formaldehyde aqueous solution remaining in the column 32 has a concentration of 65% and does not substantially contain methanol.

This solution is removed from the bottom of distillation column 32 and reactor 60
In this reactor 60, formaldehyde and urea are reacted.

The gas exiting the scrubber 20 is introduced into a scrubbing tower 26 where it is cooled and washed with a low temperature 50% aqueous solution of polymerized formaldehyde introduced from a column 40 (lower) into the top of the scrubbing tower 26 .

A liquid mixture of the following components is thus collected at the bottom of washer 26:

Total formaldehyde 1410kg water
1400kg methanol
130ky total condensate
At 2940, the liquid from the second scrubbing of the gas in column 26 is introduced into column 40 to remove methanol;
Fix formaldehyde.

The methanol is collected in condenser 42 and from there passed through valve 44.
is extracted to the saturator 12 under the control of

The liquid coming out of the bottom of the column 40 is transferred to the cooler 4 by a pump 46.
8 and then recycled to the head of the washing tower 26.

In order to maintain a constant amount of liquid circulating between columns 26 and 40, this excess liquid is removed from the discharge end of pump 46 by valve 50 and added to the concentrated formaldehyde in distillation column 32.

Meanwhile, 100 kg/h of concentrated partially polymerized formaldehyde are removed from column 32 and drawn off under control of valve 52 into column 40 .

Distillation column 40 is heated by a steam coil regulated by valve 54, while distillation column 32 is heated by a steam coil regulated by valve 56.

Many modifications can be made to the method of producing the concentrated aqueous formaldehyde solution described above without departing from the scope of the invention.

For example, to accelerate the polymerization of the formaldehyde used for cleaning, trace amounts of suitable products, such as trace amounts of acids or alkalis, can be added to it.

Also, by increasing the diameter of column 32 and performing two corresponding distillation operations within this single column, distillation column 40
can be omitted.

By modification, a portion of the formaldehyde can be drained from the last two plates at the bottom of the column 32 to obtain, for example, 50% formaldehyde and 85% formaldehyde on the other hand.

The resulting 1420 ky of 68% formaldehyde is introduced into the reactor 60 along with varying amounts of urea depending on the quality of the adhesive to be obtained.

For example, 2,620 kg of adhesive can be replaced using 1,200 kg of urea.

The concentrated formaldehyde can be drained through line 38 for other applications, such as the production of paraformaldehyde.

Referring now to FIG. 2, the apparatus shown diagrammatically here is used for the 68% formaldehyde solution obtained in the manner described above.

This device is connected to the plate tower 60, and this plate tower 6
0 is equipped with a stirrer 62 rotated by a motor 64 and powered by a plurality of blades, e.g. 66, designed to stir the reaction mixture at each plate level.

Urea is fed from the reservoir 70 in a continuous feed by an endless screw 72 to an inlet 68 formed at the top of the column.

This hot 68% formaldehyde is introduced into the upper part of the column in controlled amounts through the lateral inlet lower 4.

The pH of this mixture is adjusted at the top of the column and maintained at pH 7.5 to 8.5, depending on the amount of adhesive to be obtained.

A product that is sufficiently acidic to maintain the pH between 5 and 6.5 is introduced through pipe 76 towards the center of the column.

Formic acid is commonly used for this purpose. The hot urea formaldehyde adhesive is collected at the bottom of the tower, cooled in cooler 78, and then stored.

The column 60 is equipped with means for adjusting the pH 1 temperature and the viscosity in certain plates, these adjustments being made according to the quality of the adhesive to be obtained.

For this purpose, certain parts of the column are heated or cooled independently and separately by means of suitable equipment.

Instead of working continuously with the equipment shown in FIG.
For example, it is possible to work in a batch process using a tank with a capacity of 30 cubic meters.

The invention is not limited to the embodiments described above, and various modifications can be made without going beyond the scope of the invention.

[Brief explanation of the drawing]

FIG. 1 is a diagram of an apparatus for producing urea formaldehyde adhesives or resins. FIG. 2 is a diagram of an apparatus for continuously producing urea-formaldehyde adhesive from a concentrated solution of formaldehyde. 10...Gas floor 12...Saturator, 14゜30.36, 44, 50, 52, 54, 56゜58...Valve, 16,70... ...Tame, 1
8...Catalyst, 20...Cleaning device, 22,
28,46...Pabongpu, 24.48,78...
...Cooler, 26...Cleaning tower, 32.40.
...-distillation column, 34,42--condenser, 3
8... Line, 60...-Reactor or plate column, 62... Stirrer, 64...
...Motor, 66...Blade, 68...
...Population, 72... Endless screw
74...Inlet, 76...Pipe.

Claims (1)

[Claims] 1(a) catalytically oxidizing methanol with air; (b)
condensing the gas resulting from the catalytic oxidation of methanol, thereby condensing the condensable gas in the gas in the form of a solution; (e) remaining with the condensed product-containing solution obtained in step (b) after the condensation step; Separate the uncondensed gas (
d) cooling the uncondensed gas from step (c) and washing the cooled gas with a cold polymerized formaldehyde aqueous solution in a washing tower to absorb methanol and formaldehyde present in the uncondensed gas; (e) Distilling the solution obtained in step (e) to separately recover the concentrated formaldehyde aqueous solution and methanol; (f) distilling the solution obtained in step (d) to collect the concentrated formaldehyde aqueous solution and methanol; The methanol is recovered and the formaldehyde is isolated in the form of its solution, (gl) a portion of the formaldehyde solution obtained in step (f) is combined with the condensed, distilled formaldehyde solution obtained in step e, and ( h) A urea-formaldehyde adhesive or resin, characterized in that the concentrated aqueous formaldehyde solution obtained in step (e) and urea are mixed at a predetermined pH and temperature to obtain a urea-formaldehyde adhesive or resin. Process for producing resins. 2. In step (b), the gas is condensed by washing with a condensate product circulated by a pump from the bottom of the washer, which condensate product is cooled by a cooler outside the washer. The method according to claim 1. 3. Letting the formaldehyde solution flow out from the bottom of the washing tower,
This is heated, the solution is partially distilled to recover the methanol present therein and the formaldehyde is isolated, and after cooling a portion of the solution is removed and the condensate product leaving step (e) is removed. 2. A method according to claim 1, wherein in addition to the liquid, the remainder of the solution is used as a cleaning solution in Md). 4. The method according to claim 1, wherein the methanol recovered in steps (e) and (f) is returned to step (a). 5. The method according to claim 1, wherein the distillation in step (e) and the distillation in step (f) are carried out in two separate columns. 6. The method according to claim 1, wherein the distillation in step (e) and the distillation in step (f) are carried out in a single column. 7. In step (h), if you want to mix the hot formaldehyde solution with urea at pH 7.5-8.5 and obtain a storable solution of urea-formaldehyde adhesive,
The method according to claim 1, wherein the pH is maintained at 5 to 6.5 by adding an acidic substance. 8. The method according to claim 1, wherein in step (h), if a highly stable concentrated solution of urea-formaldehyde is desired, the hot formaldehyde solution is mixed with urea at pH 8-9. 9. The method according to any one of claims 1 to 8, which is carried out continuously. 10. The method according to any one of claims 1 to 8, which is carried out by a batch method.