Chemical Equilibrium of the Synthesis of Poly(oxymethylene) Dimethyl Ethers from Formaldehyde and Methanol in Aqueous Solutions

Abstract

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.

Poly(oxymethylene) dimethyl ether synthesis – a combined chemical equilibrium investigation towards an increasingly efficient and potentially sustainable synthetic route

“…OME 5 was calibrated based on extrapolation and relating the chromatogram area per mass fraction as a linear function of carbon number in the OME molecule. 30 As a complimentary qualitative analysis, an Agilent 6890A GC was also employed equipped with a CP-SIL5 (30 m x 8 µm) column and a Thermal Conductivity Detector (TCD). Samples were analysed using He as the carrier gas, an oven temperature ramp of 40 to 280 °C, and a column pressure ramp of 35 -60 psi.…”

“…In a previous report, Burger et al explained the formation of poly(oxymethylene) hemiformals (denoted as HF n ) HO-(CH 2 O) n -CH 3 and poly(oxymethylene) glycols (denoted as MG n ) HO-(CH 2 O) n -H in aqueous and methanolic FA solutions at values across the entire pH scale. 30 In the absence of a catalyst, the majority of monomeric FA is considered bound as either HF n or MG n , with the equilibrium lying strongly in favour of the products for Equations 1 to 4 ( Figure 2). However, HF n and MG n are known to be unstable (intermediates in this context) and can be expected to decompose relatively easily towards the reactants.…”

“…As comparative datasets, two previously published works performed at similar reaction conditions were selected; A) Burger et al investigated the equilibrium experimentally under almost identical conditions, using Amberlyst ® -46 as the catalyst (T = 75 °C, catalyst loading = 0.6 % g/g mix ). 30 …”

“…28,29 Likewise Burger et al studied the thermodynamics and kinetics of this OME synthetic system over a Amberlyst®-46 catalyst in a batch reactor. 30,31 Complimentarily to these works, the following report describes a multiphase chemical equilibrium thermodynamic model for OME synthesis, that includes all components for a complex aqueous reaction system ( Figure 2). To assess and validate this developed model, batch autoclave experiments were also performed with results compared to those of previous reports.…”

Nature of Synergy between Brønsted and Lewis Acid Sites in Sn–Beta Zeolites for Polyoxymethylene Dimethyl Ethers Synthesis

“…[2,3] Upon blending with Diesel fuel they reducet he level of soot emission with ac oncomitanti ncrease in combustion efficiency. Acidity is essential for OME synthesis, and various solida cids have already been used as catalysts: acidic resins, [9,10] zeolites, [11][12][13] or other aluminosilicate-based materials. [4] Finally,t hey can be produced from methanol (MeOH), which could be af uture platform molecule synthesized from CO 2 or biomass.…”