Poly(oxymethylene) dimethyl ethers (OME) reduce the soot formation during the combustion process, when added to diesel fuels. OME are a Gas-to-Liquid (GtL) option as they can be produced via methanol from natural gas or renewable feedstocks. This work deals with the synthesis of OME from the educts formaldehyde and methanol in aqueous solutions. The studied mixtures are complex reacting systems in which besides OME, also poly(oxymethylene) glycols and poly(oxymethylene) hemiformals are present. The chemical equilibrium of the OME formation is studied in a stirred batch reactor varying in the educts' overall ratio of formaldehyde to methanol and the amount of water and varying the temperature between 333.15 K and 378.15 K. A mole fraction-based, as well as an activity-based model of the chemical equilibrium of the OME formation are developed, which explicitly account for the formation of poly(oxymethylene) glycols and poly(oxymethylene) hemiformals. Information on the latter reactions from literature are confirmed by NMR experiments in the present work.

Liquid mixtures of formaldehyde, water, and butynediol are complex reacting multicomponent systems in which formaldehyde forms oligomers both with water and butynediol. ‐ and ‐NMR spectra of these mixtures are elucidated. The species distribution of the oligomers is quantitatively determined by ‐NMR spectroscopy. The measurements cover temperatures from 293 to 366 K, overall formaldehyde mass fractions from to , and overall butynediol mass fractions from to . A mole fraction‐based and an activity‐based model of the chemical equilibrium in the studied system are developed and chemical equilibrium constants are reported. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4442–4450, 2017

Formaldehyde reacts with solvents that contain hydroxyl groups (R-OH) in oligomerization reactions to oxymethylene oligomers (R-(OCH 2 ) n -OH). The chemical equilibria of these reactions have been studied in the literature for water, for the mono-alcohols methanol, ethanol, and 1-butanol, as well as for the diols ethylene glycol and 1,4butynediol. In the present work, the collective data were analyzed. It was found that the prolongation of the oxymethylene chains by the addition of formaldehyde can be described very well with a generalized chemical equilibrium constant K R-OHx,n≥2 , which is independent of the substructure (R) of the solvent. This holds for the oligomerization reactions leading to R-(OCH 2 ) n -OH with n ≥ 2. The chemical equilibrium constantof the reaction of formaldehyde with the solvent R-OH depends on the solvent, but simple trends are observed. The hypotheses of the existence of a generalized chemical equilibrium constant K R-OH x,n≥2 was tested for the reactions of formaldehyde with ethanol and 1-propanol, for which neither K R-OHx,1 nor K R-OHx,n were previously available.The corresponding equilibria were studied by 13 C NMR spectroscopy and the equilibrium constants were determined. A novel method was developed and used in these studies to obtain data on K R-OHx,1 by NMR spectroscopy, which is difficult due to the low amount of molecular formaldehyde. It was found that the generalized equilibrium constant is even valid for the acid-catalyzed formation of poly(oxymethylene) dimethyl ethers (OME).

A liquid thermostated microreactor Nuclear Magnetic Resonance (NMR) probe head is presented that facilitates the investigation of kinetics of fast reactions. With this setup, reaction kinetics can be studied in a broad temperature (–20 – 100 °C) and pressure range (0 – 60 bar). The setup and NMR probe head are discussed from a reaction engineering standpoint based on experiments and simulations. The microreactor probe head widens significantly the range of applications of online NMR spectroscopy for reaction and process monitoring.

Formaldehyde reacts with solvents that contain hydroxyl groups (R–OH) in oligomerization reactions to oxymethylene oligomers (R–(OCH2)n–OH). The chemical equilibria of these reactions have been studied in the literature for water, for the mono-alcohols methanol, ethanol, and 1-butanol, as well as for the diols ethylene glycol and 1,4-butynediol. In the present work, the collective data were analyzed. It was found that the prolongation of the oxymethylene chains by the addition of formaldehyde can be described very well with a generalized chemical equilibrium constant Kx,n≥2R–OH, which is independent of the substructure (R) of the solvent. This holds for the oligomerization reactions leading to R–(OCH2)n–OH with n ≥ 2. The chemical equilibrium constant Kx,1R–OH of the reaction of formaldehyde with the solvent R–OH depends on the solvent, but simple trends are observed. The hypotheses of the existence of a generalized chemical equilibrium constant Kx,n≥2R–OH was tested for the reactions of formaldehyde with ethanol and 1-propanol, for which neither Kx,1R–OH nor Kx,nR–OH was previously available. The corresponding equilibria were studied by 13C NMR spectroscopy and the equilibrium constants were determined. A novel method was developed and used in these studies to obtain data on Kx,1R–OH by NMR spectroscopy, which is difficult because of the low amount of molecular formaldehyde. It was found that the generalized equilibrium constant is even valid for the acid-catalyzed formation of poly(oxymethylene) dimethyl ethers (OME).

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Measurements of the vapor-liquid equilibrium in the system formaldehyde þ water þ butynediol were performed at 393 K and 413 K for overall formaldehyde mass fractions between 0:1 g g À1 and 0:2 g g À1 and overall butynediol mass fractions between 0:05 g g À1 and 0:35 g g À1 . The studied system is a complex reactive multicomponent mixture as formaldehyde reacts both with formaldehyde and butynediol. A predictive physico-chemical model of the vapor-liquid equilibrium from the literature [1] is validated by the experiments of the present work. Residue curves are calculated to illustrate the distillation behavior of the studied system.

Measurements of the vapor-liquid equilibrium in the system formaldehyde þ water þ butynediol wereperformed at 393 K and 413 K for overall formaldehyde mass fractions between 0:1gg?1 and 0:2gg?1and overall butynediol mass fractions between 0:05 g g?1 and 0:35 g g?1. The studied system is acomplex reactive multicomponent mixture as formaldehyde reacts both with formaldehyde and buty?nediol. A predictive physico-chemical model of the vapor-liquid equilibrium from the literature [1] isvalidated by the experiments of the present work. Residue curves are calculated to illustrate thedistillation behavior of the studied system.