The method of producing paraformaldehyde


C08G2/08 - Polymerisation of formaldehyde

 

(57) Abstract:

The method of producing paraformaldehyde with purity of 80 to 89 wt.%, includes the following stages: receiving formaldehyde solution concentration 80 - 89%, heating the solution to 80 - 100oWith, pouring the hot solution over the heated zones of the metal belt conveyor, moving from the heated zone to another, the cooled zone. Formaldehyde solution is preferably pre-mixed with the catalyst. The technical result consists in the fact that the target product is quite solid for processing and transportation, and has the same concentration, which was set initially. The clumping received paraformaldehyde does not occur in the manufacturing process or after its completion and requires no further drying and processing. 10 C.p. f-crystals, 1 Il.

The invention relates to a method for production of paraformaldehyde, in particular to the conditions get of paraformaldehyde with a degree of purity in the range from 80 to 89 wt.%.

Paraformaldehyde is a polymer of formaldehyde with a degree of polymerization of from 8 to 100 and with a degree of purity in the range from 80 to 90 wt.%. The most common on the market types formald the th products special type.

Paraformaldehyde is a product that allows you to use the concentrated formaldehyde for General use, providing its simplicity, especially in the requirement of ease of dissolution. It is known that products with a higher degree of purity of less soluble than those whose degree of purity is less, but even the latter is present in the proportion of high molecular weight polymers that are insoluble or slightly soluble under normal conditions of use, as for example, in the manufacture of resins.

On the other hand, although products with a low degree of purity, less than 89 wt.%, more soluble, they are too soft, and adhesion that occurs during storage, transportation and work with them, creates certain difficulties.

Paraformaldehyde is always obtained from concentrated solutions of formaldehyde. They are obtained by distillation at low pressure of dilute solutions of formaldehyde obtained in conventional apparatus for the production of formaldehyde. Paraformaldehyde is obtained from the concentrated solution with 80-89% wt. formaldehyde one of the following ways:

The first and earliest way is periodic curing concentrated RA is h him, while the reactor must be equipped with a paddle stirrer for grinding the formed mass, or pouring out the contents of the reactor over a cooled surface, equipped with suppen machine. In another method, the concentrated solution is poured over the heated roller device, which evaporates a portion of the concentrated solution, which leads to the production of formaldehyde product of very high purity (FR-p-2 067 169). In the patent US-P-992 277) disclosed the use of twin screw snidero and even the use of the extruder (CN-1 050 201). Depending on the device the product is obtained in the form of a powder, pieces or flakes (US-P-2 992 277 twin screw mixer). These latter processes can also be maintained continuously, but in all cases, the final product should be subjected to the subsequent stage drying to obtain a solid product that will not Kotkovets during storage and transportation. Typically, reactors of this type produce high molecular weight, strongly acidic, membrane not easily soluble products, if only they do not impose alkaline substances, promoting depolymerization when dissolved in water.

In another type of generalised utrirovanny solution of formaldehyde. Splashing, falling through the column, cooled air stream. This continuous method has great advantages in comparison with the previous one. Get the product in the form of spherical particles, which is very advantageous for further processing. However, their material is still too soft and should then be squared away or in a fluidized layer, or on conveyor belts. In another embodiment, a method (US-P-3 772 392) disclosed the addition reaction products of formaldehyde and amine as regulators of molecular weight Performa. This agent must be obtained in a separate process, which lasts for 20 hours at 100oC. After it is received, it is added to a concentrated solution of formaldehyde that is already shredded in the tower for spraying. But in this case, the resulting product must be brought in the fluidized layer or on conveyor belts for some period of time. Similarly, products with a low degree of purity, less 87-89 wt.%, particles stick together and form clumps that can't Peresypkina, and eventually form unsuitable pasty blocks. Method of using a column of spray, 966).

In these patents collected many existing variants of the method of producing paraformaldehyde. In their examination it appears that the problem is always the same, namely, adhesion of particles, which makes it difficult to carry out the subsequent processing. Even in DE-P-3 925 966, which discloses an improved method, it is necessary to use concentrations higher than 83 wt.%, to obtain particles that do not stick together, and that, despite working with recycle product, is the fact that make it difficult to install and more expensive its manufacture.

For many applications, i.e. obtain urea-formaldehyde, melamine-formaldehyde or phenol-formaldehyde resins and adhesives for the manufacture of individual products, there is no need to paraformaldehyde high purity, such that reach using columns with spray. Usually it is sufficient that the degree of purity was more than 80 wt.%, that is enough for manufacturers of resins, which do not need to pay for the transportation of water in a normal 40 wt.% commercial solutions of formaldehyde and do not need to ward off excess water from the reaction solution.

As mentioned earlier, these formaldehyde products with a low degree of h is E. Similarly, products with a low degree of purity obtained in the periodic and semi-continuous methods, for example, using suppen device, may be subjected to additional processing. In order to make them suitable for further processing, or it is necessary to add a catalyst, or they need a long time to stay in the reactor, or both simultaneously. The result is a product that has a sufficient degree of polymerization, but at the same time soft enough to provide flakes, which are subjected to drying to obtain a solid product suitable for further processing.

Similarly, the ways in which they use the device with heated rollers or extruders, also require further processing, for example, an auxiliary drying, to obtain the desired product concentration, and hardness. And in General, all these processes are periodic.

And finally a way that does not allow for a continuous process with less concentrated solutions of formaldehyde, disclosed in U.S. patent US-P-3 001 235. It hot concentrated solution of formaldehyde is in the reactor-type Tun, which is partially immersed relevant to auth with a knife for cutting on rolls, resulting gain is still soft flakes. Then these flakes are dried in the dryer with a perforated tape by passing through it a hot dry inert gas.

This method has several disadvantages.

First, a concentrated formaldehyde solution you need to keep the hot reactor, and the vapours of formaldehyde that is necessary to collect, and it also increases the acidity. Secondly, to achieve low concentration of solid parts, that is 80 wt.%, the drum must be cooled to very low temperature, namely, -10oC, and that required the use of expensive cooling baths and refrigeration equipment. Thirdly, it is necessary to use air or inert gas (N2if you want to achieve a significant reduction of acidity.

The present invention overcomes the above limitations. His goal is to create a process of the above type, which includes the following stages: obtaining a solution of formaldehyde concentration is almost equal to the purity of formaldehyde that is to be obtained; heating the specified solution to a temperature in the range from 80oo heated zones in the second heated zone, and loading is carried out on one of these first zones.

In accordance with a preferred variant of the invention the formaldehyde solution is placed in a mixer, then add the catalyst; formaldehyde solution and catalyst are mixed together at a temperature in the range from 80oC and up to 100oC to obtain a homogeneous mixture; maintaining the temperature within the specified interval, gomogenizirovannogo mixture was poured into one of the first areas of the metal belt. The use of catalyst is particularly preferable if you want to get paraformaldehyde purity below 87 wt.%.

In accordance with the present invention, the catalyst is a strongly basic hydroxide or amine with a pKa in the range between 10.4 to 11.3.

In accordance with the present invention the preferred primary amines are methylamine, ethylamine, n-Propylamine, n-butylamine, ISO-butylamine and tert. - butylamine; preferred secondary amines are dimethylamine, diethylamine, di-n-Propylamine, di-ISO-Propylamine and dibutylamine; the most preferred tertiary amines are triethylamine and triethanolamine.

In accordance with another predpochtitel is from 6.0 to 20.0 mEq/kg and more preferably about 9.5 mEq/kg

The present invention also contemplates that the first heated zone should be maintained at a temperature in the range from 70 to 90oC and that the temperature of the second zone must be maintained in the range from 25 to 35oC.

Some special aspects of the invention comprise the application of a metal conveyor belt that transfers the concentrated solution of formaldehyde with one end, and temperature control along the specified tape. It is established that if the first zone of the tape is in a hot condition, and in subsequent zones is cooled, the solid product formed on the ribbon itself is loosened upon reaching the other end of the tape, and the usual chipper enough to reduce the particle size of the product to the desired value. On the contrary, if the tape is cooled along the length, the final product is soft and it must then be dried, as in other processes. In this way clumping received paraformaldehyde does not occur in the manufacturing process or after its completion and requires no drying or processing.

If the concentration of the formaldehyde solution is less than 87 wt.%, it is desirable to add any cargo introduction leads to the acceleration process. Moreover, as mentioned earlier, to achieve the solidification is necessary to support the first part of the tape in a hot condition, which causes an increase in the degree of polymerization, facilitating subsequent processing. Not require any further processing or drying with inert gases, as the product falling from the tape, hard enough for processing and transportation, and has the same concentration, which was set initially.

The tape can be cooled process water or water cooled to 5-10oC.

In order to avoid small amounts of vapors of formaldehyde, it is advisable to set up a cap for the absorption of gases. These gases are sequentially cleaned in an appropriate scrubber or refer to an existing unit for the production of formaldehyde.

The drawing shows a diagram of the process of the present invention.

Prepare a concentrated solution of formaldehyde with purity of 80 to 89 wt.%, preferably 84 wt.%, with temperatures in the range from 80 to 100oC by any known method, in particular, in this case by distillation at low pressure dilute solution of formaldehyde.

Along the line of the other operating parameters, set forth below, in the mixer 2, which is also served with a dilute aqueous solution of the catalyst in line 3. The mixer 2 is designed so that its internal volume is 100 to 150 ml, where at specified flow rates of formaldehyde stay in the mixture is from 0.5 to 2.5 seconds, which is sufficient to create a homogeneous absolutely homogeneous mixture, but without precipitation of the polymer. Both products can also be mixed, sending them on one line.

As catalysts it is possible to use a strongly basic hydroxides or some amines with pKa /pKa=14-pKa/ in the interval between 10.4 to 11.3. Is preferred to use amines have already been listed earlier, and it was emphasized that are most suitable secondary amines, which are used in the form of aqueous solutions with concentrations in the range from 10 to 25 weight. %, in such quantity that the resulting concentration of amine in the mixed product is in the range from 6.0 to 20 mEq/kg, preferably 9.5 mEq/kg, depending on the type of amine and purity formaldehyde.

Gomogenizirovannogo mixture solutions of formaldehyde and catalyst is evenly distributed through the distributor over 4 len is positive, from distillers low pressure dilute solution of formaldehyde, and its temperature maintained within the range from 80 to 100oC in order to avoid curing before it is poured on the metal strip 5. This tape has first sections 6, where the temperature of the support in the range of 70-90oC, preferably 80oC.

The cooling and consequent solidification of the product to the final temperature in the range from 25 to 35oC, preferably 30oC, carried out on the second site 7 tape 5.

The tape dimensions are specified as a function of the desired performance. Tape a length of 10 m and a width of 1 m is sufficient for the above mentioned performance. Depending on these dimensions, the number of sections, which are divided tape for heating or cooling, varies from 3 to 6.

As the belt speed is adjustable and the number of sites used for heating/cooling, you can change the duration of the reaction and cooling can also be changed depending on changes in the hardness and temperature of the obtained paraformaldehyde. The residence time of the product on the belt varies from 3 to 6 minutes, and from 1/3 to 2/3 of this time uh implement process water, supplied through line 8 at a temperature in the range from 25 to 30oC, or water, cooled to 5-10oC, depending on the required cooling rate.

As soon as paraformaldehyde sufficiently polymerized and it starts cooling, the product is starting to crack as long as he does not pull away from the tape, and it can easily be removed. Thus the product is removed from the end of the tape without difficulty with the aid of a surgical knife 9 and easily Packed.

Get paraformaldehyde has the form of a solid square plates 1-10 cm2and thickness 1-4 mm the temperature of the product at the end of the stainless steel belt 25 to 35oC.

The product from the conveyor belt 10 is fed into the hopper for the storage 11, from which it directly Packed in a packaging machine 12 and is directed to the sale, or if necessary paraformaldehyde different quality with particles of different size, it may be directed into a suitable shredder 13.

Example 1

480 kg/h formaldehyde solution concentration 80,4% at a temperature of 83oC and 1.5 l/h of a 10% aqueous solution of sodium hydroxide serves to direct flow mixer with a volume of 150 ml Overlooking the mixture of the soap the hour. Working conditions are such that at the end of the first 3 m of the section length of the tape temperature not lower than 72oC /2oC/ a; at the end of the second 2 m section length temperature 55oC /2oC/, and the remaining 5 m length of the third section is cooled with water at room temperature, so that the product flows from the end of the tape at a temperature of 28oC. Hence the product arrives on the conveyor belt 10 and the container for storage, where it can directly packing or submit to the mill for grinding to the desired particle size.

Example 2

320 kg/h of a solution of formaldehyde to 83.5% at 85oC and 2.2 l/h of an aqueous solution containing 124 g/l n-Propylamine, served in a once-through mixer with a volume of 120 ml Overlooking the mixture is spread on top of a moving stainless steel belt, the velocity of which 120 m/h. Working conditions are such that at the end of the first section of the tape length 5 m temperature not lower than 84oC /2oC/, and the second long section in the remaining 5 m cool water at room temperature, so that the product flows from the end of the tape at a temperature of 26oC. Hence the product is delivered to the conveyor belt 10 and the container for storage, where it can be directly packaged or served in melnicoe 85oC and 1.8 l/h 22% aqueous solution of Diisopropylamine served in the flow mixer with a volume of 150 ml Overlooking the mixture is spread on top of a moving stainless steel belt, the speed is 120 m/h. Working conditions are such that at the end of the first section of the tape 5 m long temperature not less than 78oC /2oC/, and the rest of the line is 5 m in length is cooled with water at room temperature, so that the product flows from the end of the tape at a temperature of 26oC. Hence, the product is fed through the conveyor belt 10 in the storage container, where it can be directly packaged or delivered to the mill for grinding to the desired particle size.

1. Method for continuous receipt of paraformaldehyde with purity of 80 - 89 weight. %, characterized in that the method comprises the following stages: preparation of a solution of formaldehyde is almost the same concentration as the purity of the target paraformaldehyde; heating the solution to 80 - 100oC; pouring the heated solution over the metal conveyor belt moving in the direction from the first heated zone to a second cooling zone, and filling is carried out on one of these first zones.

2. The way the formaldehyde solution and the catalyst are mixed together at 80 - 100oTo obtain a homogeneous mixture, and then, maintaining the temperature within the specified interval, pour gomogenizirovannogo the mixture on top of the first areas of the metal belt.

3. The method according to p. 2, characterized in that the catalyst used is a strong base.

4. The method according to p. 2, characterized in that the catalyst used amine with a pKa in the range between 10.4 to 11.3.

5. The method according to p. 4, characterized in that the amine is a primary amine selected from the group consisting of methylamine, ethylamine, n-Propylamine, n-butylamine, ISO-butylamine and tert.-of butylamine.

6. The method according to p. 4, characterized in that the amine is a secondary amine selected from the group consisting of dimethylamine, diethylamine, di-n-Propylamine, di-ISO-Propylamine and dibutylamine.

7. The method according to p. 4, characterized in that the amine is a tertiary amine selected from the group consisting of triethylamine, and triethanolamine.

8. The method according to any of paragraphs.4 to 7, characterized in that the concentration of the specified amine in the homogenized mixture is in the range from 6.0 to 20.0 mEq/kg

9. The method according to p. 8, characterized in that the PP.1 - 9, wherein the temperature above the first zone support in the interval from 70 to 90oC.

11. The method according to any of paragraphs.1 to 10, characterized in that the temperature of the second support zones in the interval from 25 to 35oC.

 

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