DD155779A3 - METHOD FOR REMOVING HARDENED AMINO LOAD FROM PRODUCTION PLANT - Google Patents

Abstract

1. A process for the removal of hardened aminoplasts from plants or plant parts, which serve the production of aminoplasts, characterized in that the cured aminoplasts with aqueous, 1 to 70 wt .-% ammonium, alkali or Erdalkalisulfitlösungen or ammonium , Alkali or Erdalkalihydrogensulfitlösungen or mixtures of these solutions at temperatures of 20 to 100 degrees C dissolves and the dissolution process, a weight ratio of dissolving Plast to solvent of 1 to 1 to 1 to 10 complies. 2. The method according to claim 1, characterized in that one uses 10 to 20 wt .-% tige ammonium and / or Natriumhydrogensulfitlösungen as a solvent.

Description

VBB Leuna-Werke ''. Merseburg, 10.02.197 £

"Walter Ulbricht" DC.Hi / Tri

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LP 7570

Process for removing hardened aminoplasts from production plants

The invention relates to a process for the dissolution and removal of hardened aminoplasts from plants or plant components, which serve the production of aminoplasts. Aminoplasts are condensation products of urea, melamine, Dizyandiamid, guanidine or thiourea with aldehydes, especially formaldehyde.

The production of aminoplasts, especially urea-formaldehyde resins, has gained great economic importance in recent years. Liquid urea-formaldehyde condensation products are needed in large quantities for wood processing, especially for particleboard production. In accordance with these large production quantities, the plant capacities for producing these resins have also been constantly increased. D13 The effectiveness of large production facilities depends crucially on cleaning and repair-related downtimes.

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Aminoplate mining equipment must be periodically shut down to remove thermoset and deposited resins. Deposits of hardened resins occur especially in the process stage for the concentration of aminoplasts and in the cooling of the finished products'in appearance.

The cleaning is currently carried out so that the resin residues and encrustations are mechanically removed with high manual effort and heavy physical labor after drying the corresponding equipment parts. Particularly heavily contaminated plant components (tube bundles, cooling and heating segments) must even be replaced by new apparatuses. Occasionally, a long-term pretreatment with boiling sodium hydroxide solution is made to facilitate the subsequent mechanical work. (There is no evidence in the literature).

All mechanical cleaning processes require a high level of maintenance and cause long downtimes and production downtime. Solvents for aminoplasts in the cured state are not yet known. According to Bachmann / Bertz, Aminoplaste, VEB German publishing house for primary industry, 1970, page 65 »hardened aminoplasts are insoluble and unquellbar in all solvents. According to H. Petersen, KunststoffJahrbuch '10th episode, melamine resins are particularly appreciated for their good water resistance and insensitivity to organic solvents, dilute acids and alkalis. It is known that strong acids such as sulfuric acid, hydrochloric acid and phosphoric acid, in concentrated form hardened aminoplasts destroy slowly by hydrolytic degradation. However, these agents do not cause dissolution

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and are useless because of their corrosive behavior towards the equipment to be cleaned (Bachmann / Bertz, Aminoplaste, page 161).

Purpose of the invention is to reduce the high maintenance costs and caused by long downtime production loss and to eliminate heavy physical work.

The object was to develop a process which allows ea to remove hardened aminoplasts from plants or plant components in a simple, non-mechanical manner.

This object is achieved in that the cured aminoplastics with aqueous, 1 to 70 G-ew .-% strength ammonium, alkali or Erdalkalisulfitlösungen or ammonium, alkali or Erdalkalihydrogensulfit solutions or mixtures of these solutions at temperatures of 20 to 100 ⁰ C dissolves and the dissolution process, a weight ratio of dissolving Plast to solvent of 1 to 1 to 1 to 10 complies.

It has proven particularly expedient to use 10 to 20% strength by weight aqueous ammonium and / or sodium hydrogen sulfite solutions whose pH values are between 4.5 and 5.5 as the solvent.

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In the presence of the cured aminoplast resin to be dissolved, the pH rises within 2 hrs. At 90 ⁰ C to ca..6,0 (measured at 20 ⁰ G). Parallel to this, the sulfur dioxide odor occurring in a minor form during the storage period disappears, and the viscosity of the sodium bisulfite solution increases

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with progressive dissolution of the cured resin to 1 cP. ^ hen during Lösungsνorgangeθ viscosities of 40 cP achieved / v ground, the dissolution rate is so low that no further resin can be more added to the solution. In this palle fresh solvent must be used. The dissolution rate of the cured aminoplasts in sodium hydrogen sulfite solution is largely dependent on the surface shape of the resin to be dissolved, the solvent flow rate and the temperature. In general, about 120 hours at 90 ⁰ C for the dissolution of aminoplasts in a large-scale plant sufficient.

Aminoplasts are usually converted to the cured, insoluble state at pHs between 2.0 and 5jO. It is therefore surprising that cured resins can be dissolved with an agent having a pH of 4 »5. It was to be assumed that the application of a compound with such a low pH accelerates the hardening and thus the insoluble state even further.

example 1

A liquid urea-formaldehyde resin in the molar ratio 1: 1.55 with 70 % pesticide content was cured by addition of 10 % of a 15% ammonium chloride solution for 15 hours at 100 ⁰ O in a drying oven and dried.

200 g of this cured resin were crushed into pieces of about 20 mm in diameter and mixed in a 2-liter round bottom flask with 1000 g of a 10% sodium hydrogen sulfite solution. With stirring, the mixture was heated to 90 ⁰ G and 3 hours at this temperature

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held. Except for a Re3t of about 1 g, the entire resin was dissolved.

The viscosity of the solution rose from about 1 cP to 4.3 cP (at 20 ⁰ C), the pH, which was 4.5 at the beginning of the experiment, rose to 6.3. The resulting resin solution was miscible with water.

Example 2

250 g of a urea-formaldehyde resin according to Example 1 were added ulfitlösung 1 000 g of a 50 follow ammonium Hydrogens and heated with stirring to 70 ⁰ G. This mixture was kept at this temperature for 5 hours. Except for a remainder of 5 g, all of the resin was dissolved. The solution was miscible with water.

Example 3

230 g of a urea-formaldehyde resin according to Example i were admixed with 1 900 g of a 5 $ calcium hydrogen sulfite solution and heated to 90 ^° C. with stirring. The mixture was held at this ν temperature for 3 hours. After that, the resin was down to one

Remainder of 3 g dissolved. The solution was miscible with water.

Example 4 . *

A liquid urea-formaldehyde resin in a molar ratio 1: 2.0 with 60% solids content was determined by - transferred to the addition of 10% of a 15 followed by ammonium chloride solution within 1 hour at 20 ⁰ C in the cured, insoluble state.. After 2 days drying in air, 200 g of approximately 20 mm pieces of resin,

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treated as described in Example 1, with 500 g of a 20% sodium hydrogen sulfite solution. After 5 hours of treatment at 90 ⁰ O, the resin was completely dissolved, the pH Y / ert of the obtained solution was increased to 6.4, the viscosity was 6.5 cP.

Example 5

600 g of a liquid melamine-formaldehyde resin in the molar ratio 1: 3 »3 with 70% solids content were stirred well with 2 g Ämmoniumchlorid and cured for 24 hours at 110. ⁰ C 'and dried. 200 g of the hardened and comminuted to 20 χ 20 mm pieces of resin were treated with 2000 g of 20% igeu Natriuinhydrogensulfitlösung according to Example 1. After 24 hours, a milky cloudy solution was formed, which dissolved clearly in water.

Example 6

In a 20 m stirred vessel equipped with cooling coils, approximately 8 tons of hardened, insoluble urea resin had settled between the container wall and the cooling coil. The stirred vessel was charged with 15 m of 20% sodium bisulfite solution and treated for 120 hours at 90 ⁰ G with this solution at a stirring speed of 35 U / min. During this time, the entire cured resin, which had settled in a layer thickness of 400 to 500 mm between the vessel wall and the cooling segment dissolved.

Claims (2)

- 7 - · 19125 7 LP 7570 claims 1 »A process for the removal of cured aminoplasts from plants or plant components, which serve the production of aminoplasts, characterized in that the cured aminoplasts with aqueous, 1 bi 70 wt .-% ammonium, alkali metal or Brdalkalisulfit solutions or ammonium , Alkali or Erdalkalihydrogensulfitlösungen or mixtures of these solutions at temperatures of 20 to 100 ⁰ C dissolves and the dissolution process, a weight ratio of aufzulösendem. Plast to solvent from 1 to 1 to 1 to 10 complies 2. The method according to claim 1, characterized in that one uses 10 to 20 wt .- ^ ige ammonium and / or Hatriumhydrogensulfitlösungen as a solvent.