Evaluation of Zr–Alumina in Production of Polyoxymethylene Dimethyl Ethers from Methanol and Formaldehyde: Performance Tests and Kinetic Investigations

Abstract

Polyoxymethylene dimethyl ethers (PODE n ) converted from methanol and formaldehyde were investigated with alumina supported ZrO2 catalyst in a stainless steel tube fixed-bed reactor within the temperature range from 333 to 433 K and the pressure range from 0.1 to 2.5 MPa. First, results from catalytic performance tests showed that the catalyst γ-Al2O3 containing 4 mol % ZrO2 exhibited the highest activity for PODE n synthesis. The stoichiometry analysis of raw material indicated that ZrO2 modified catalyst had the optimum activity at methanol/formaldehyde = 3 (mol/mol). An increase of the reaction pressure resulted in a significant increase in methanol conversion from 13.18 to 48.64%, and selectivity to PODE3–8 was enhanced to 24.82%. The temperature experiment analysis confirmed the optimization of the reaction temperature to be 393 K. Second, SEM and TEM showed the relationship between the catalytic activity and the catalyst-crystal alignment. Incorporation of ZrO2 in the framework of γ-Al2O3 was noticed and confirmed by X-ray diffraction (XRD) and BET analysis. The NH3-TPD tests indicated the relationship between catalytic activity and acidity. Finally, an elimination mechanism was proposed to explain the PODE n synthesis reaction rate and kinetic model. The contributions of intraparticle and external diffusion were eliminated by changing the size of catalyst particles and space velocity. The proposed model can reasonably predict the observed behaviors of PODE n synthesis from methanol and formaldehyde.

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

“…• Activity-based model of the chemical equilibrium: Parameters and correlations for the calcu- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 17 Zhao et al 12 Methanol Aqueous formaldehyde solution Zhang et al, 10,11 This work Table 2: Parameters for the calculation of the mole fraction-based chemical equilibrium constant K x ...…”

“…2 There is large number of articles (e.g. [7][8][9][10][11][12][13][14][15][16][17][18] ) and patents from China concerning OME, as China is the largest coal producer in the world and is seeking for an option to produce liquid fuels from coal. Synthesis gas may however also be produced from renewable feedstocks.…”

“…10,11 In this system the selectivity of formaldehyde towards OME is limited by the competing reactions of formaldehyde with methanol and water towards poly(oxymethylene) glycols and poly(oxymethylene) hemiformals. [25][26][27] Zhang et al did not mention these competing reactions.…”

Kinetics of synthesis of polyoxymethylene dimethyl ethers from paraformaldehyde and dimethoxymethane catalyzed by ion-exchange resin

“…Recent papers on synthesis of PODE n have focused on catalyst preparation and characterization, and process optimization. Various acidic catalysts, including acidic ionexchange resins Zheng et al, 2013Zheng et al, , 2014Burger et al, 2012), ionic liquids , molecule sieves (Zhao et al, 2011), and solid superacids (Li et al, 2015;Zhang et al, 2014), have been employed in synthesis of PODE n . Burger et al (2012) proposed that water reacts with ethers and form alcohols during the synthesis of PODE n from DMM and trioxane in the acidcatalyzed system.…”

“…Burger et al (2012) reported the reaction kinetics of the heterogeneously catalytic formation of PODE n from DMM and trioxane, and proposed an adsorptionbased kinetic model to describe the results. Zhang et al (2014) synthesized PODE n from methanol and formaldehyde solution and proposed a kinetic model based on an elimination mechanism. In our previous work (Zheng et al, 2014), we reported the synthesis of PODE n from DMM and PF over acidic ion-exchange resins and proposed an equilibrium molecular size distribution model based on a sequential reaction mechanism, but did not study the kinetics in detail.…”