Urea–formaldehyde reaction system. An experimental investigation

Abstract

SynopsisBatch production of urea-formaldehyde resins at temperatures up to 100°C takes several hours for completion. Reduction of the batch time may be possible with the higher reaction rates obtained at higher temperatures and increased pressures. In order to investigate this possibility, an experimental technique to obtain the necessary kinetic data, without loss of formaldehyde by evaporation, was developed. The results are compared with earlier low-temperature data extrapolated to the present range of interest. The results were interpreted on the basis of the successive reaction of two or three molecules of formaldehyde with a molecule of urea. Rate EquationsIn order to carry out the chemical engineering design procedure for a reactor producing UF (urea-formaldehyde) resins, appropriate rate equations would be required of the formwhere r = rate of appearance or disappearance of a chemical, c = concentration of that chemical, and t = time elapsed from start of reaction.It has been established1 that the combination of urea and formaldehyde begins with a series of addition reactions2 followed by condensation reactions3; that the speed and extent of reaction are dependent on temperature, pH, and U:F ratio, although the reaction rate is essentially constant in the pH range 4-9 at constant temperature4 and that UF3 is produced in significant quantities only at low U:F ratio^.^ Therefore, since the commercial process usually involves U:F molar ratios between 1:1.33 and 1:2.2, within the pH range 4-9, it is reasonable to assume initially that the reactions taking place are UF1+F+UF2so that the rate equations become

Modeling of polymerization of urea and formaldehyde using functional group approach

“…A careful examination of the experimental data reported in ref. 31 reveals that the concentrations of free formaldehyde in the reaction mass falls very rapidly for short times. However, for large times, depending upon the temperature of the reaction mass, it attains an equilibrium.…”

A very simple empirical kinetic model of the acid‐catalyzed cure of urea–formaldehyde resins

“…Kumar and Sood 21 have put forward a FSSE model for the early stage of the UF condensation process and have been able to fit the data of Price et al 18 assuming the hydrolysis reactions to be bimolecular. Both de Jong and de Jong 16 and Price et al 18 have considered them to be unimolecular.…”

“…Both de Jong and de Jong 16 and Price et al 18 have considered them to be unimolecular. However, available experimental data could not clarify this question, since water concentrations were always the same.…”

“…Besides these older results, the only contributions, which might be used for establishing a kinetic model of the curing reaction were: (a) a few higher temperature experiments by Price et al 18 who followed the formaldehyde concentration decrease in closed batch reactors; (b) a more recent study by Mejdell and Schønsby 19 with three kinetic runs including GPC measurements.…”

Comparison of Concentration Profiles for Boundary Layers in Absorption with Chemical Reaction Processes

“…The absorption process may be affected by diffusion, convection, and chemical reaction on the gas and liquid sides of the interface. The gas-liquid reaction can only proceed at the rate at which the liquid absorbs the gas, and the gas can only be absorbed by diffusing into the bulk liquid from the interface [1][2][3][4][5][6][7][8][9][10][11][12][13][14].…”