Chemical Equilibrium and Reaction Kinetics of the Heterogeneously Catalyzed Formation of Poly(oxymethylene) Dimethyl Ethers from Methylal and Trioxane

Poly­(oxymethylene) dimethyl ethers (OMEs) are attractive components for tailoring diesel fuels. They belong to the group of oxygenates that reduce soot formation in the combustion when added to diesel fuels and can be produced on a large scale based on gas-to-liquid technology. This work deals with a particularly favorable route for their large scale production in which they are formed from methylal and trioxane. Reaction kinetics and chemical equilibrium of the OME formation via this route were studied in a batch reactor using the ion-exchange resin Amberlyst 46 as heterogeneous catalyst at temperatures between 323 and 363 K and for a wide range of feed compositions. An adsorption-based kinetic model is presented that represents both reaction kinetics and equilibrium well

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

Poly­(oxymethylene) dimethyl ethers (OME) are attractive oxygenated fuel additives and physical solvents for the absorption of carbon dioxide. This works studies the synthesis of OME from formaldehyde and methanol in aqueous solutions. The reaction kinetics of OME formation is studied experimentally in a stirred batch reactor on a laboratory scale using the heterogeneous catalyst Amberlyst 46. The influences of the ratio of formaldehyde to methanol, the amount of water, and the temperature (303.15–363.15 K) are investigated. A model of the reaction kinetics is developed that differentiates two competing reaction mechanisms. The model explicitly accounts for the intermediates poly­(oxymethylene) hemiformals and poly­(oxymethylene) glycols

Method for Estimating Activity Coefficients of Target Components in Poorly Specified Mixtures

Mixtures that contain a known target component but are otherwise poorly specified are important in many fields. Previously, the activity of the target component, which is needed, e.g., to design separation processes, could not be predicted in such mixtures. A method was developed to solve this problem. It combines a thermodynamic group contribution method for the activity coefficient with NMR spectroscopy, which is used for estimating the nature and amount of the different chemical groups in the mixture. The knowledge of the component speciation of the mixture is not required. Test cases that are inspired by bioprocess engineering applications show that the new method gives surprisingly good results

Conceptual Design of a Novel Process for the Production of Poly(oxymethylene) Dimethyl Ethers from Formaldehyde and Methanol

Poly­(oxymethylene) dimethyl ethers (OME) are environmentally benign alternative fuels. This work presents the conceptual design of a novel OME process which employs aqueous solutions of formaldehyde and methanol as feedstock. In this process, OME of the desired chain lengths <i>n</i> = 3–5 and water are separated from the reactive mixture (formaldehyde + water + methanol + methylal + OME). Thermodynamic limits are identified by studying distillation boundaries and chemical equilibria. By that it is shown that OME of chain lengths <i>n</i> = 3–5 can be separated from the reactor outlet by distillation. The separation of water is carried out using either an adsorption or a membrane process. Adsorption isotherms of water on Zeolite 3A are determined experimentally. The OME process is simulated and optimized using a reduced process model accounting for the mass balances and the thermodynamic limits. Favorable operating points of the process are identified using multi-objective optimization

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

Poly­(oxymethylene) dimethyl ethers (OME) reduce soot formation during the combustion process when added to diesel fuels. OME are a gas-to-liquid 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, poly­(oxymethylene) glycols and poly­(oxymethylene) hemiformals), in addition to OME are present. The chemical equilibrium of OME formation is studied in a stirred batch reactor in which the educts’ overall ratio of formaldehyde to methanol, the amount of water, and the temperature (333.15 and 378.15 K) varies. A mole fraction-based and 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 the literature are confirmed by NMR experiments in the present work

Solubility of Carbon Dioxide in Poly(oxymethylene) Dimethyl Ethers

Experimental data on the solubility of carbon dioxide (CO₂) in poly­(oxymethylene) dimethyl ethers (CH₃O­(CH₂O)_<i>n</i>CH₃, OME_<i>n</i>) are presented for OME₂, OME₃, and OME₄. The total pressure was measured as a function of the liquid phase composition at 313.15 and 353.15 K for pressures up to 4.3 MPa in a high-pressure view-cell. Henry’s law constants of CO₂ in OME₂, OME₃, and OME₄ are determined. They are similar for all studied OME and depend strongly on the temperature. The experimental data are modeled by the original perturbed-chain statistical associating fluid theory equation of state. As a basis, pure component models for OME were developed based on literature data on the liquid density and vapor pressure. The solubility of CO₂ in OME is successfully described using a group contribution scheme. The results show that OME are interesting candidates as physical absorbents for CO₂

Biocatalytic Production of 1,2,4-Butanetriol beyond a Titer of 100 g/L: Boosting by Intermediates

Many platform chemicals such as 1,2,4-butanetriol (BTO) are still derived from petrochemicals. BTO as a versatile compound with applications ranging from pharmaceutical synthons to plasticizers is of great interest to be manufactured from renewable resources. Albeit biosynthetic pathways to produce BTO from pentoses were proposed two decades ago, no studies have reported production at high yields and titers typically demanded by chemical industries. In this work, we aimed to tackle this challenge by combining several strategies. Selection of suitable enzymes and reaction optimization in a 500 μL lab scale allowed us to achieve a titer of 1.2 M (125 g/L) (S)-BTO from 180 g/L d-xylose with a yield >97%. By the addition of an intermediate of the cascade, we could reduce up to 90% of the original redox cofactor used while still maintaining a space-time yield (STY) of 3.7 g/L/h. By applying the same approach, which we term “intermediate boosting”, we could push the STY to 9.4 g/L/h. After having identified byproduct formation as a possible bottleneck, we increased production of (S)-BTO further to 1.6 M (170 g/L), approaching the toxicity level of BTO at 200 g/L that microorganisms can handle. We demonstrated, however, that our enzymes were still functional at 300 g/L BTO. Finally, we proposed several strategies to further increase the titer and yield of BTO as a feasible alternative to the petroleum-based synthetic route. This work highlights the importance of a combinatorial approach to boost the enzymatic biosynthesis of chemicals