CS269415B1 - A process for preparing a water-soluble binder based on polymethyl-phenenol compounds - Google Patents

Abstract

The preparation method consists in the reaction of phenol with formaldehyde catalyzed by amino oxides of the general formula R^ R2 R3 N = 0, where Ri and R2 are alkyls with a number of carbon atoms of 1 to 4. R3 is alkyl with a number of carbon atoms of 1 to 18, in an amount of 2 to 10% by weight based on the phenol charged to the reaction.

Description

The invention relates to a method for preparing a water-soluble binder based on polymethylolphenol compounds, free of inorganic electrolytes and with a low ash content, by reacting phenol with formaldehyde.

It is known that binders based on phenol-formaldehyde resins, suitable especially for bonding and impregnation of organic and inorganic fibrous materials, are prepared in a wide range of β with various properties. They differ from each other, for example, in the type of solvent, concentration, viscosity, content of free components - phenol and formaldehyde, type and content of catalyst, reactivity, etc. For some special purposes of using binders, other properties important from the point of view of application are required, for example, high compatibility with water, absence of electrolytes, minimum ash content, etc.

The synthesis of phenol-formaldehyde resins used as binders essentially consists of the reaction of phenol with formaldehyde in a molar ratio of 1:1 to 1:3 in the presence of an alkaline catalyst, most often HaOH, Ba(OH) ₂ ^or Ca(OH) ₂ . Depending on the sol ratio of phenol to formaldehyde used and on other reaction conditions - the amount of catalyst, reaction time and reaction temperature - products with different structural and chemical compositions and therefore with different technical properties are obtained. If a high molar excess of formaldehyde over phenol, a high content of alkaline catalyst and a low reaction temperature are used, the reaction product has a low average molecular weight, a high content of methylol groups and good compatibility with water. In the optimal case, if the reaction product consists only of mononuclear and dinuclear methylated compounds - polymethylolphenols - it is infinitely dilutable with water. In such a case, the high content of alkali in of the reaction mixture, which is necessary because it acts as a stabilizer of the reactions of the resulting methylol and polymethylol phenols and prevents their condensation into higher molecular weight products, must usually be removed after the reaction is complete, because in most cases, when alkalis are applied, they corrode or otherwise damage the bonded fibrous material and often also because they increase the reaction rate during thermal curing to an undesirable extent.

The removal of the alkaline catalyst from the product is most simply carried out by neutralization with a suitable acid, organic or inorganic. The salt formed is either soluble and remains dissolved in the binding solution, or is insoluble and remains in solution as a suspension, or is removed by filtration, sedimentation or centrifugation.

Soluble salts, if left in the resin solution, deteriorate - for example, in the case of insulating materials - the thermal insulation properties of the product due to their hygroscopicity. If a suspension of insoluble catalyst salts is left in the binder solution, it often causes problems due to the formation of sediments in pipes, in tanks, in nozzles, etc. Removing insoluble salts from the solution by filtration or centrifugation is difficult, since a large residue of binder remains in the filter cake and, if necessary, washing creates a large amount of diluted binder solution. β This is a difficult problem to solve, such as recycling or disposal, which in any case represents economic losses.

A number of patents describe various processes for neutralizing or removing the catalyst. For example, DE patent No. 2,434,401 uses acidic ammonium lignosulfonate to neutralize the alkaline catalyst, US patent No. 3,704,199 proposes to neutralize the catalyst (Ba(0H) ₂ with sulfuric acid and the precipitated fine suspension of barium sulfate with a size of 1 μm to 1 μm is left in the binder. Czech patent No. 112,703 describes a procedure consisting in neutralizing the catalyst Ba(0H) ₂ with ammonium sulfate, the precipitated suspension of barium sulfate remains in solution and the released ammonia reacts with the formaldehyde present to form hexamethylenetetramine, which binds free phenol during curing. PR patent No. 2,130,02? proposes to remove Ca ⁴⁴ ions from the binder by the action of an alkaline solution of ammonium salt, Czech patent No. 149,787 proposes to remove calcium hydroxide or barium hydroxide by the action of carbonate, respectively ammonium bicarbonate. BE Pat. No. 819 777 protects a process for producing a binder based on phenol-formaldehyde resins, catalyzed by calcium hydroxide or oxide, by neutralization with a mixture of phosphoric acid and sulfuric acid. In GB Pat. No. 1 439 027, ica-.a

CS 269 415 Bl lyser Ca(OH) ₂ or Ba(OH) ₂ is neutralized with ammonium, magnesium or sodium lignosulphate and finally the pH is adjusted with phosphoric, formic or acetic acid. GB pní. No. 1 382 963 leaves barium sulphate precipitated by sulphuric acid in the binder with the addition of a dispersant based on fatty acid amines from coconut oil.

As can be seen, none of these proposed procedures solve the problems mentioned above.

Pat. SU 2. 537 058 protects a method for producing insulating materials based on mineral fibers and proposes to remove the alkaline catalyst from a phenol-formaldehyde binder containing 50% phenol alcohols and 0.5 to 1.5% H2O by filtration through an ion exchange resin (sulfonated copolymer of styrene), thereby reducing the original pH of 8.7 to 8.9 to 5.0 to 5.5. The filter is washed with distilled water and then regenerated with 3% hydrochloric acid and washed again with distilled water. An obvious disadvantage of this method is the relatively low capacity of the strongly acidic cation exchange resin used and hence the need for a large amount of it or, conversely, the need to use a small amount of catalyst in the preparation of the binder. Another disadvantage is the high acidity of the ion exchange resin, because the resulting pH value of 5.0 to 5.5 of the neutralized binder greatly reduces its stability. Another economic disadvantage is the difficult and expensive filter regeneration procedure. On the one hand, a large excess of acid is required due to the high affinity of the ion exchanger for Na+ ions, and on the other hand, distilled water must be used to wash away the binder residues and acid residues after filter regeneration.

Czechoslovak patent No. 222 478 protects a method of preparing a water-soluble binder based on polymethylolphenolic compounds without electrolytes and with a low ash content, where the alkaline catalyst is removed after the reaction by a carboxyl ion exchanger based on acrylate copolymers, which have a high exchange capacity, so that ionic reactions take place mainly on the surface of the ion exchanger and the diffusion of phenolic compounds into the pores of the ion exchanger is limited.

All these additional operations when removing the catalyst from the reaction mixture (neutralization, precipitation, filtration, blasting, dispersion, deionization, etc.) complicate production, even with waste treatment or ion exchange regeneration, and are therefore technologically and economically disadvantageous.

The above problems are solved by the invention, the subject of which is a method of preparing a water-dilutable binder based on polymethylolphenol compounds without inorganic electrolytes and with a low ash content by reacting phenol with formaldehyde in the presence of amino oxides as basic reaction catalysts. The essence of the invention lies in the fact that the reaction of phenol with formaldehyde takes place under the catalysis of amino oxides of the general formula Rg R^ N = 0, where s 2? are alkyls with a number of carbon atoms of 1 to 4 and Rj is alkyl with a number of carbon atoms of 1 to 18, in an amount of 2 to 10% by weight, based on the phenol charged into the reaction.

The advantages of the present invention are substantially influenced by the use of amino oxides which have a higher basicity than the corresponding amines, so that they catalyze the above reaction much more effectively by forming a larger amount of Xenolate ions. Furthermore, during the heat treatment of the impregnated mats, the amino oxides present in the binder rearrange to hydroxylamine derivatives and are thus incorporated into the binder and become an integral part thereof.

The technical effect of this invention lies in several advantages that are manifested both in the preparation of the binder itself and in the preparation of insulating mats from fibrous materials. Thus, in the actual reaction of phenol with formaldehyde under the catalysis of amino oxides, the reaction time is shortened by 20 to 30% compared to tertiary amines, the need for further treatment of the resulting low-molecular resol is eliminated, and its stability during storage is significantly increased. In the actual impregnation of fibrous materials, the nozzles of the impregnation machine do not clog, because the impregnating agent is completely homogeneous, clear and low-viscosity. When curing the mats in a tunnel oven, the amino oxides accelerate the curing reaction, while they rearrange to hydroxylamine derivatives and incorporate the binders. The final products have -.-high

CS 269 415 Bl thermal insulation ability because they do not contain any hydrophilic compounds of ionic nature.

The subject matter of the invention is further illustrated by examples.

Example 1

564 g of molten phenol are placed in a 2.5 l reaction flask equipped with a stirrer, reflux condenser, thermometer and separatory funnel, 1,315 g of 37% formaldehyde and 50 g of 40% aqueous trimethylamine oxide solution are added with stirring. The reaction mixture is heated to 60 °C and stirred at this temperature for 7 hours. It is then cooled below 25 °C. 1,929 g of an aqueous solution of polymethylolphenol compounds are obtained. Analysis of the product provides the following results:

ky: dry matter content (2 h at 150 °C) 42.3% by weight free phenol content 2.2% by weight free formaldehyde content 4.3% by weight pH 8.82 reactivity on the block at 130 °G 2 min 50 sec miscibility with water infinite

The content of mononuclear and dinuclear compounds and only trinuclear compounds was determined by gel chromatography. At 20 °C, the product can be stored for 5 weeks until miscible with water 1:5.

Example 2

565 g of molten phenol are placed in a 2.5 l reaction flask equipped with a stirrer, reflux condenser, thermometer and separatory funnel, 1,340 g of 37% formaldehyde and 65 g of 38% triethylamine oxide solution are added with stirring. The reaction mixture is heated to 60 °C and stirred at this temperature for 8 hours. It is then cooled below 25 °C. 1,969 g of an aqueous solution of polymethylolphenol compounds are obtained. Analysis of the product gives the following results:

dry matter content (2 h/150 °C) 41.9% by weight free phenol content 2.7% by weight free formaldehyde content - 4.2% by weight PH 8.76 reactivity on the block at 130 °C 2 min 42 sec miscibility with water infinite

At 20 °C, the product can be stored for 5 weeks until miscible with water 1:5.

Example 3

564 g of molten phenol are placed in a 2.5 l reaction flask equipped with a stirrer, reflux condenser, thermometer and separating funnel, 1,360 g of 37% formaldehyde and 75 g of 35% aqueous octadeoyldimethylamine oxide solution are added while stirring. The reaction mixture is heated to 60 °C and stirred at this temperature for 8.5 hours. It is then cooled below 25 °C. 1,999 g of an aqueous solution of polymethylolphenol compounds are obtained. Analysis of the product provides the following results: Dry matter content (2 h/150 °C) 42.1% by weight, free phenol content 2.8% by weight, free formaldehyde content 4.6% by weight.

pH ⁸ >52 reactivity on block at 130 °C 3 min 5 s miscibility with water infinite

At 20 °C, the product can be stored for 4 weeks up to a miscibility of 1:5.

Claims (1)

SUBJECT OF THE INVENTION A method for preparing a water-dilutable binder based on polymethylolphenol compounds without inorganic electrolytes and with a slight ash content by the reaction of phenol with formaldehydes:, characterized in that the said reaction is catalyzed by amino oxides of the general formula Ej K = 0, where a is alkyl b with a number of carbon atoms of 1 to 4 and alkyl a with a number of carbon atoms of 1 to 18, in an amount of 2 to 10% by weight, based on the phenol charged to the reaction.