SU540576A3 - Method for continuous production of urea-formaldehyde resins - Google Patents

Description

(54) METHOD FOR CONTINUOUS RECEIVING

UREA FORMALDEHYDE

1 Pitch 1: 0.8 and before entering into the first stage of mixing with an aqueous solution of formaldehyde, continuously proceed with a molar ratio of 1 and 1.8 to 1 to 2.5. To dissolve urine in order to obtain 1 solution of urea and formaldehyde, 30-45% by weight formaldehyde solution can be used, which contains less than 2.5% by weight stabilization with 1% of methanol. As other compounds forming a-ollollaces that can be transferred to fsYoipoii cycles, 1grg1Sh melamine divdsandiamide,. alkylamine, polyamche and the like. Thus, different ones can be obtained. Modification of urea formaldehyde It is advisable to carry out a condensation reaction in the first and second cycles, which consist of a reactor, a heat exchanger and a circulating pump. A special advantage of the method is that such reactions, which have appeared during condensation of MOSCOW and formaldehyde can be used completely. Used to achieve a high condensation rate in the first cycle, heat can be used to release water (the end of the green product) in the second cycle. Another advantage of the method is the possibility of varying the production capacity of a given installation over a wide range, as well as the quality of the desired final product, and the ratio of the dimensions of the installation to the production capacity can be very favorable. Upon vacuum distillation of a solution from urea and formaldehyde with a molar ratio of urea and formaldehyde with a molar ratio of urea to a dehydrate of from 1: 1.8 to 1: 2.5 and distillate there is usually more than 2% formaldehyde, which can later apply only at high cost. Unexpectedly, LB distillate was found with additional condensation of less than 1% formaldehyde. Example 1. In the first reactor, a urea-formaldehyde solution is metered through the pipeline at a rate of 10 fractions per hour, which contains 28 fractions of 28 fractions of urea and 72 fractions of 37% formaldehyde per 100 fractions. In the cycle of the reactor is circulated at a temperature of 130 ° C and a pressure of 2.7 atm 8 shares of the reaction mixture at a speed of 360 shares per hour. The contents of the first reactor in an amount of 8 fractions are kept constant by adjusting the constant Level, and 10 parts of the reaction mixture are etched into the second reactor through the pipeline. The reaction mixture directed to the next reactor has, under these conditions, a viscosity from 29 to 31 cf. measured at 20 ° C. At the same time, 1.28 parts of a 50% aqueous solution of urea are added through the pipeline to the second reactor, and the same amount of 10% sodium alkali is added via another pipeline so that the reaction product reaches a pH of 7.2-7.5. in the second reactor, the amount of product obtained in the course of the reaction was kept in 10 fractions constant, DIR.) by a constant level control aid. In the reactor cycle, at a temperature of SpC and Leshga of about 300 Torr, 10 fractions of the reaction product circulate at a rate of 320 fractions per hour, and at the same time, so much water is removed through the pipeline, so that the urea-formaldehyde resin with a solid resin content of 67% and 700–720 ° C is measured at 20 ° C, flows into the receiver. Example 2. In the first reactor through the pipeline at a rate of 10 fractions per hour, the solution is metered, containing 100 fractions, 23.0 fractions of urea, 66.0 fractions of 37% formaldehyde, 9.5 fractions of a 31% aqueous solution of monomethylamine and 1 , 5 Fractions of concentrated hydrochloric acid. In the cycle of the first reactor is stirred at a temperature of 105 ° C and a pressure of about 1.0 atmu 12h the reaction mixture with a speed of 360 shares per hour. The content of the first reactor in the amount of 12 fractions is constantly maintained by adjusting the level, so that 10 fractions of the reaction mixture flow through the pipeline to the second reactor. At the same time, the overflow product has a viscosity of about 70-80 centipoise, measured at 20 ° C. At the same time, 10% sodium hydroxide is metered through the pipeline in such an amount that the reaction product in the second reactor reaches a pH of about 7.2 -7.5. The amount of 8 fractions contained in this reactor is also kept constant by level control. The reactor cycle is stirred at a temperature of 50 ° C and a pressure of 300 Torr of 8 fractions of the reaction mixture at a rate of 300 fractions per hour, and the pipeline simultaneously drains so much water that the resin solution flows into the receiver at 48-50% of solid resin and A viscosity of 850-900 spz measured at. The resulting modified urea-formaldehyde resin contains 2% free formaldehyde and is suitable mainly for the manufacture of wet papers. Example 3. A solution containing 100 fractions 26.9 hours of urea to 73.1 hours of 37% formaldehyde and set with formic acid to a pH value of 6 is docked at the rate of 10 fractions per hour into the first reactor at a rate of 6. In the first reactor cycle stirred at a temperature of 110 ° C and a pressure of 1.5 ata 8 h of the reaction mixture at a speed of 360 parts per hour. The contents of the reactor in an amount of 8 fractions are kept constant by adjusting the level so that 10 fractions of the reaction mixture flow through line 5 to the second reactor. The reaction mixture passed through the pipeline to this reactor has, under these conditions, a viscosity on the order of 25-28 CPS measured at 20 ° C. At the same time, 1.46 hours are added to the reactor via the pipeline

25% aqueous solution of dicyandiamide and the pipeline dispense such amount of sodium liquor that; the reaction product in the reactor reaches a pH of 7.2-7.5. The reaction product contained in the second reactor in an amount of 10 hours is also kept constant. In the reactor cycle, at a temperature of 50 ° C and a pressure of about 300 Torr, the reaction product is stirred for 10 hours at a speed of 300 fractions per hour, and at the same time

the pipeline drains out so much water that the solution

the resin flows to a receiver with a solid resin content of 65% and a viscosity of about 850-900 cps, measured at 20 ° C.

The resulting modified urea. The formaldehyde resin contains 1% free formaldehyde and is preferably suitable as an adhesive for gluing massive chipboard, in particular for gluing on cold cijacofbi Example 4. In the first reactor of the pipeline, a solution containing 100.5 parts of 24.5 parts of urea is fed to the first reactor. , 3.5 hours of melamine and 72.0 hours of 37% formaldehyde, at a rate of 10 fractions per hour. In the cycle of the first reactor at a temperature of 115 ° C and a pressure of 1.7 atm, they are stirred for 5 hours of the reaction mixture at a speed of 360 fractions per hour. The contents of the first reactor are kept constant by adjusting the level, so that 10 hours flow through the pipeline to the second reactor. the reaction mixture. Flowed into the second reactor through the pipeline, this mixture has a viscosity in the order of 33-35 spz, from MefTeHHyH} at 20 ° C. At the same time, 0.88 parts of an aqueous 50% urea solution are added to the second reactor through the pipeline and the 10% sodium hydroxide liquor is metered through the pipeline so that the reaction product reaches a pH of 7.2-7.5 . The amount of the reaction product contained in this reactor is also maintained continuously by adjusting the level. In a loop reactor at a temperature

50 ° C and a pressure of about 300 Torr at a rate of 300h. per hour stirred 8h. of the reaction product, at the same time so much water is being drained that urea-melamine-formaldehyde resin 6 is contained in the receiver with a solid resin content of about 65% and in the order of 900-1000 sps, measured at 20 ° C.

The urea-melamine-formaldehyde resin obtained contains 1.5% free formaldehyde and is suitable for gluing flat surfaces, in particular for heat-resistant gluing.

Claims (2)

1. A method for the continuous preparation of urea-formaldehyde resins by condensation of the initial mixture obtained by dissolving crystalline urea in a 30-45% formaldehyde solution at a molar ratio of 1: 1.8-2.5, temperature 100-140 ° and pressure 1-4 atm with subsequent condensation while concentrating the solution, characterized in that, in order to reduce the content of free formaldehyde in the finished resin, both stages are carried out using a flow-circulation method with an average time of reaction in the first stage, 10-60 minutes and the ratio The quality and output of the reagents to the circulation mass of 1: 10-50, then the reaction products of the first stage are continuously fed to the second stage, the molar ratio of urea to formaldehyde is adjusted to 1: 1, 5-1 9 for the addition 50-80 / s and continue to condense at a temperature of 30-90 ° C, a pH of 7-8 and a pressure of 40-600 Torr until the resin concentration reaches 50-70 v. 2. Method II. 1, of which is t i p h a lO Sch i and s with I; M. T- if necessary, the initial solution mchzhet to contain other aminonlast-forming additives and / or they can be added - p ;: :: ;, a swarm of the stage with the addition of the ratio of the reagents;,: yy-fused value.