Kinetics of Initiated Ethanediol Formation from Methanol–Formaldehyde Solutions
Abstract
The mechanism and kinetics are developed for the initiated non branched-chain formation of ethanediol in methanol– formaldehyde solutions at formaldehyde concentrations of 0.1–3.1 mol dm–3 and temperatures of 373–473 K. The experimental concentrations of the free insolated form of formaldehyde are given at the different temperatures and total concentrations of formaldehyde in methanol. The experimental dependence of the radiation-chemical yields of ethanediol on formaldehyde concentration in γ-radiolysis of methanol–formaldehyde solutions at 373–473 K is shown. At a formaldehyde concentration of 1.4 mol dm–3 and T = 473 K, the radiationchemical yield of ethanediol is 139 molecules per 100 eV. The effective activation energy of ethanediol formation is 25 ± 3 kJ mol–1 . The quasi-steady-state treatment of the reaction network suggested here led to a rate equation accounting for the non monotonic dependence of the ethanediol formation rate on the concentration of the free (unsolvated) form of dissolved formaldehyde. It is demonstrated that the peak in this dependence is due to the competition between methanol and CH2=O for reacting with the adduct radical HOCH2CH2O • .
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Introduction
Ethanediol is widely used in the production of polyester fibers and films, antifreezes, hydraulic and quench liquids, alkyds, polyurethanes, etc. The main commercial method of ethanediol synthesis is ethylene oxide hydration. The annual world ethanediol output is over 20 million tons.
These facts stimulate development of new, energetically efficient ethanediol synthesis technologies. A possible one is radiation-chemical synthesis using a dual-purpose heterogeneous nuclear reactor in which the graphite moderator is replaced with a methanol–formaldehyde mixture and the heat carrier is steam flowing past fuel elements. A technological analysis of this system demonstrated that, at a reactor thermal power of 2.5 GW, it is possible to profitably manufacture 80 thousand tons of ethanediol per year along with producing 677 MW electric powers.
Here, we report the experimental dependences of the radiation-chemical yield of ethanediol on the total formaldehyde concentration at different temperatures and present the reaction network deduced for the process examined. By applying quasi-steady-state treatment to this network, we obtain a rate equation for ethanediol formation.
Conclusion
The mechanism and kinetics are developed for the initiated non branched-chain formation of ethanediol in methanol– formaldehyde solutions. The quasi-steady-state treatment of the reaction network suggested here yielded a rate equation describing the non monotonic (peaking) dependence of the ethanediol formation rate on the concentration of the free (unsolvated) form of dissolved formaldehyde.