Quantitative NMR Spectroscopy of Complex Liquid Mixtures:  Methods and Results for Chemical Equilibria in Formaldehyde−Water−Methanol at Temperatures up to 383 K

Abstract

Quantitative 13 C NMR spectroscopy was used to investigate the complex chemical equilibria in ternary liquid mixtures of formaldehyde-water-methanol at temperatures between 298 and 383 K. In these mixtures, formaldehyde is predominantly bound in methylene glycol, poly-(oxymethylene) glycols, hemiformal, and poly(oxymethylene) hemiformals, which are formed by a series of oligomerization reactions. The present study is the first in which data on the species distribution in the studied technically important ternary system is reported. It complements previous work in which the focus was on the binary systems formaldehyde-water and formaldehyde-methanol. It also extends the temperature range in which data are available, which was previously limited by the fact that all experiments were carried out in batch cells under ambient pressure. In the present experimental study, a pressurized NMR flow cell was used for the first time. The results from the present study were obtained independently in two different laboratories with different NMR techniques and instruments. Details on the experimental procedures are presented. A comparison of the two data sets shows excellent agreement. The experimental results are compared to predictions from a recently published physicochemical model that aims at the description of vapor-liquid equilibria in the studied mixtures. The results suggest that some model parameters should be revised if the model is to be applied to quantitatively predict liquid-phase compositions (e.g., the distribution of formaldehyde to different species) in the studied ternary system.

Quantitative on-line high-resolution NMR spectroscopy in process engineering applications

“…For effective shimming deuterium-free probes, proton shim maps can be acquired prior to the experiment with the PFGtechnique. 1 H field mapping [19,20] was shown to work well even under flow conditions [21].…”

“…The complex 1 H and 13 C NMR spectra of these solutions were successfully interpreted and evaluated quantitatively [21]. The example demonstrates that this is possible although the pure components are not available.…”

“…4 Reaction kinetics after 1:1 dilution (by mass) of a formaldehyde-methanol mixture (w FA = 0.420 g g -1 ) with pure methanol at T = 323 K. For nomenclature, see ref. [21] changing CO 2 loading, two-dimensional heteronuclear correlation spectroscopy ( 13 C-1 H) becomes an important technique for peak assignment in this application.…”

Application of NMR in Online Monitoring of Catalyst Performance

“…Reliable reaction kinetic data are the key to success in the design and scale-up of these integrated processes. Reactive distillation is interesting for equilibrium-limited reactions such as those in the production of esters [46,47] The common quantitative analysis with, for example, gas chromatography (GC) suffers from long analysis runs. As a result, the monitoring of rapidly changing compositions is difficult, for example, shortly after starting the kinetic experiment, and valuable information is lost.…”

Phase equilibria in chemical reactive fluid mixtures

“…The research covered, e.g., the dimerisation of carboxylic acids [1][2][3][4][5], the association of alcohols in organic liquids [6][7][8], the solubility of sour gases in aqueous solutions of ammonia [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] or amines (as well as amine blends) [24][25][26][27][28][29][30][31][32][33][34][35][36][37], the phase equilibrium in aqueous and methanolic solutions of formaldehyde [38][39][40][41][42][43][44][45][46][47][48][49][50]…”