418061 Reaction Kinetics of the Formation of Poly(oxymethylene) Dimethyl Ethers from Formaldehyde and Methanol in Aqueous Solutions

Sunday, November 8, 2015: 4:10 PM
355F (Salt Palace Convention Center)
Niklas Schmitz, Jakob Burger and Hans Hasse, Laboratory of Engineering Thermodynamics, University of Kaiserslautern, Kaiserslautern, Germany

Poly(oxymethylene) dimethyl ethers (OMEs) are oxygenates of the chemical structure H3C-O-(CH2O)n-CH3 with n ≥ 2. OMEs are environmentally benign diesel fuel additives, which drastically reduce the soot formation during the combustion process. [1] In addition, OMEs can be beneficially employed as physical solvents for the absorption of carbon dioxide. [2] All the synthesis routes for the production of the OMEs start from methanol, which in turn is produced from synthesis gas. Hence, they open a route for the production of liquid fuel on the basis of alternative feedstocks, such as shale gas or biogas. The educts for the state-of-the-art process for the production of OMEs are trioxane and methylal, [3] which are produced in additional steps from methanol via the formaldehyde route. A direct synthesis of the OMEs from formaldehyde and methanol is a short-cut on the value added chain and is thus highly desirable. Liquid mixtures of formaldehyde and methanol/water are complex reacting systems in which formaldehyde is almost entirely bound in the oligomers poly(oxymethylene) hemiformals (structure: HO-(CH2O)n-CH3) and poly(oxymethylene) glycols (structure: HO-(CH2O)n-H). The formation of OMEs in these mixtures occurs only under acidic conditions. [4] In the present work, the reaction kinetics of this formation is studied employing the ion exchange resin Amberlyst 46 as heterogeneous acidic catalyst. The experiments are conducted in a stirred batch reactor at different temperatures (303.15 K, 333.15 K, 363.15 K) and varying ratios of formaldehyde to methanol and varying water-contents. The measurements indicate that the OMEs of various chain lengths are formed rather by an etherification of poly(oxymethylene) hemiformals (n ≥ 2) and methanol than by the sequential addition of monomeric formaldehyde into OMEs of shorter length. Based on this assumption, a Langmuir-Hinshelwood-Hougen-Watson model is adjusted to the experimental data. The model is consistent to the model of the chemical equilibrium [5] and describes the experimental composition profiles with good accuracy. The results of this work enable a reliable reactor design for the OME synthesis from formaldehyde and methanol in the presence of water.


[1] Lumpp, B.; Rothe, D.; Pastötter, C.; Lämmermann, R.; Jacob, E. Oxymethylene ethers as diesel fuel additives of the future. MTZ 2011, 72, 34–38.                                  

[2] Burger, J.; Papaioannou, V.; Gopinath, S.; Jackson, G.; Galindo, A.; Adjiman, C.S. A hierarchical method to integrated solvent and process design of physical CO2 absorption using the SAFT-γ mie approach. AIChE J. In press.(2015) doi:10.1002/aic.14838

[3] Burger, J.; Ströfer, E.; Hasse, H. Production process for diesel fuel components poly(oxymethylene) dimethyl ethers from methane-based products by hierarchical optimization with varying model depth. Chem. Eng. Res. Des. 91(2013) 2648–2662.

[4] Drunsel, J.-O.; Renner, M.; Hasse, H. Experimental study and model of reaction kinetics of heterogeneously catalyzed methylal synthesis. Chem. Eng. Res. Des. 2012, 90, 696–703.

[5] Schmitz, N.; Homberg, F.; Berje, J.; Burger, J., Hasse, H.: Chemical Equilibrium of the Synthesis of Poly(oxymethylene) Dimethyl Ethers from Formaldehyde and Methanol in Aqueous Solutions. Ind. Eng. Chem. Res. submitted (2015).

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