Oxymethylene Ethers Research Articles

Unraveling the structure-activity relationships of Cu/H-BEA bifunctional catalyst for selective synthesis of dimethoxymethane by non-oxidative dehydrogenation of methanol

Oxymethylene ethers (OMEs) are synthetic fuels with excellent ability in reducing soot formation and good compatibility for diesel engines. Among OMEs, dimethoxymethane (DMM) is the simplest compound and its conventional production relies on an oxidative route leading to low H2 efficiency. Hence, recently, our group presented a H2 efficient gas-phase DMM synthesis route via nonoxidative dehydrogenation of methanol over Cu/Hβ. Herein, the role of Cu and Hβ are investigated by preparing Cu/Hβ catalysts with tailored properties. Highest DMM selectivity (81.5 %) was obtained over 1% Cu/Hβ-DeAl8 (Si/Al: 520). Besides, both calcined (consisting of Cu+) and reduced (consisting of Cu0) 1% Cu/Hβ-DeAl8 catalysts were active for DMM formation. Initial DMM selectivity reached 49 and 41 % for the calcined and in situ reduced catalysts, respectively, increasing to 75 % (calcined) and 81.5 % (reduced) after 1500 min TOS. The increased DMM selectivity relates to evolution of Cu species and changes with the amount of Lewis acidic sites.

Synthesis of tailored oxymethylene ether (OME) fuels via transacetalization reactions

Oxymethylene ethers (OME) as environmentally benign fuels: progress in the design of compounds with tailored properties.

Selective catalytic synthesis of short chain oxymethylene ethers by a heteropoly acid – a reaction parameter and kinetic study

Oxymethylene ethers (OME) are considered as a low-emission additive or replacement to diesel fuel. They can by efficiently produced in a catalytic process using heteropoly acids as catalyst.

Inhibiting and promoting effects of NO on dimethyl ether and dimethoxymethane oxidation in a plug-flow reactor

The effects of NO addition (1000, 2000 ppm) on the low-temperature oxidation of dimethyl ether (DME) and dimethoxymethane (DMM), as particular cases of oxymethylene ethers (OMEn) with n = 0 and 1, have been investigated in a plug-flow reactor at near-atmospheric pressure in a temperature range of 400–1000 K. An in-situ electron ionization molecular-beam mass spectrometer (EI-MBMS) was used to measure the reactants, intermediates, and products, with particular attention on nitrogenous species that were scarcely detected previously. Explorative modeling with published mechanisms was performed, indicating the necessity of further model development. Potential kinetic fuel/NO interactions are discussed based on the experimental observations. The results reveal an overall inhibiting effect of NO addition on DME reactivity in the low-temperature regime, but a pronounced promoting effect at higher temperatures. For DMM, a similar temperature-dependent effect of NO was observed, but only for high NO concentration (2000 ppm). NO addition significantly suppresses the formation of hydrocarbon intermediates for both DME and DMM, but remarkably promotes the formation of methyl formate and methanol for DME. Several nitrogenous species were detected upon NO addition. The interactions of NO + HO2 and NO + OH, together with the regeneration routes of NO, are thought to be influential for both DME and DMM oxidation, while the significance of the NO + RO2 (R, fuel radical) reaction depends on the reactivity of the respective RO2 radical of DME and DMM. These results contribute to the understanding of OMEn/NO interactions and serve as a basis for further model development by providing new and detailed speciation data for DME/NO and DMM/NO oxidation.

Particle Size Distribution Measurements of Neat and Water-Emulsified Oxymethylene Ethers in a Heavy-Duty Diesel Engine

Diesel-fueled compression ignition engines display a distinct trade-off in particulate matter (PM) and nitrogen oxide (NOX) emissions due to the nature of diffusive combustion. The modification of fuel properties has drawn much attention since these methods offer additional potential to reduce emissions. Oxygenated fuels are reported to greatly diminish particle emissions while water emulsification of regular diesel causes a significant decrease in NOX. However, recent studies indicate that these fuel-based approaches may lead to an increase in nanoparticle emissions, which are known to be more dangerous to human health than large particles. This has raised the question about whether current engine technology is prone to nanoparticle formation.In this work, the authors present a detailed study on combustion and emission performance of the oxygenate fuel Oxymethylene Ether (OMEn, the mixture contains neat OME with chain length n = 2 − 6). In a novel approach, a single-cylinder heavy-duty diesel engine was fueled with both neat and water-emulsified OME to combine the two fuel-based methods in order to simultaneously reduce both NOX and particle emissions to a great extent. Particular emphasis was put on the particle size distribution (PSD) of emitted PM to elaborate a potentially severe drawback of these fuel-based approaches. In the process, hydrogenated vegetable oil (HVO) was used as the diesel reference fuel. The findings are summarized as such: PSD measurements of OME2-6 reveal similar particle diameters in mid-load operation and a shift to smaller particles at unfavorable engine operations compared to HVO. Water-emulsified OME2-6 reduces NOX by roughly 2-3% with a one percent increase in water concentration while maintaining a nearly constant combustion efficiency. Adverse effects on nanoparticle formation by water emulsification were not observed.

Experimental Study of the Effect of Hydrotreated Vegetable Oil and Oxymethylene Ethers on Main Spray and Combustion Characteristics under Engine Combustion Network Spray A Conditions

The stringent emission regulations have motivated the development of cleaner fuels as diesel surrogates. However, their different physical-chemical properties make the study of their behavior in compression ignition engines essential. In this sense, optical techniques are a very effective tool for determining the spray evolution and combustion characteristics occurring in the combustion chamber. In this work, quantitative parameters describing the evolution of diesel-like sprays such as liquid length, spray penetration, ignition delay, lift-off length and flame penetration as well as the soot formation were tested in a constant high pressure and high temperature installation using schlieren, OH∗ chemiluminescence and diffused back-illumination extinction imaging techniques. Boundary conditions such as rail pressure, chamber density and temperature were defined using guidelines from the Engine Combustion Network (ECN). Two paraffinic fuels (dodecane and a renewable hydrotreated vegetable oil (HVO)) and two oxygenated fuels (methylal identified as OME1 and a blend of oxymethylene ethers, identified as OMEx) were tested and compared to a conventional diesel fuel used as reference. Results showed that paraffinic fuels and OMEx sprays have similar behavior in terms of global combustion metrics. In the case of OME1, a shorter liquid length, but longer ignition delay time and flame lift-off length were observed. However, in terms of soot formation, a big difference between paraffinic and oxygenated fuels could be appreciated. While paraffinic fuels did not show any significant decrease of soot formation when compared to diesel fuel, soot formed by OME1 and OMEx was below the detection threshold in all tested conditions.

Optimal Integrated Facility for Oxymethylene Ethers Production from Methanol

In this work, we use a mathematical optimization approach for the evaluation of the production of oxymethylene ethers (OMEs) from methanol. OME1, methylal, and the mixture of OME3–5 are the targete...

Carbon Supported Phosphoric Acid Catalysts for Gas-Phase Synthesis of Diesel Additives

Carbon supported phosphoric acid (H3PO4/C) was found to be a more productive catalyst for the gas-phase synthesis of the diesel fuel additive/substitute oxymethylene ethers (OME) as compared to benchmark zeolite catalysts. In this contribution, the performance of catalysts H3PO4/C and related H2PO4−/C and HPO42−/C materials in OME synthesis from methanol and formaldehyde is described.Graphic

Facile Two‐Phase Catalysis: From Dimethoxymethane and Monomeric Formaldehyde towards Oxymethylene Ethers (OMEs)

AbstractAn efficient, biphasic route towards oxymethylene dimethyl ethers (OMEs) allowing for catalyst recycling and reuse is presented (OMEs=CH3(−OCH2−)nO−CH3, n=3–5). OMEs are an interesting novel class of non‐toxic, diesel‐like synthetic fuels with soot‐free combustion properties. A solution of commercial OMe3+BF4− in the ionic liquid (IL) 1‐ethyl‐3‐methylimadazolium tetrafluoroborate acts as the immobilized catalyst. Upon addition of dimethoxymethane (OME1) and anhydrous formaldehyde (FA) very pure OMEs form in the upper phase of the biphasic mixture. In the lower IL‐phase, the catalyst remains immobilized. After phase separation and removal of the top OME layer, the catalytically active IL‐phase is reusable for at least ten times without loss of activity and selectivity.

Challenges and Opportunities in the Production of Oxymethylene Dimethylether

AbstractTo reduce the NOx and soot emissions of conventional diesel fuels, different renewable alternatives are investigated. One example are oxymethylene ethers (OMEx) of different chain lengths, which are intended to be used as diesel blends. Especially OME3–5 show properties comparable to diesel. The key to producing longer chain OMEs is OME1 as feedstock, which can react with formaldehyde to afford larger molecules. This article reviews different synthesis routes for OME1, in order to elucidate energy‐efficient methods.

Temperature- and pressure-dependent kinetics of the competing C-O bond fission reactions of dimethoxymethane.

Oxymethylene ethers are often considered as promising fuel additives to reduce the emissions of soot and NOx from diesel engines. Dimethoxymethane (DMM) is the smallest member of this class of compounds and therefore particularly suitable to study the reactivity of the characteristic methylenedioxy group (O-CH2-O). In this context, we investigated the pyrolysis of DMM behind reflected shock waves at temperatures between 1100 and 1600 K and nominal pressures of 0.4 and 4.7 bar by monitoring the formation of H atoms with time-resolved atom resonance absorption spectroscopy. Rate coefficients for the C-O bond fission reactions of DMM were inferred from the recorded [H](t) profiles, and a pronounced temperature and pressure dependence of the rate coefficients was found. To rationalize this finding, we characterized the relevant parts of the potential energy surface of DMM by performing quantum chemical calculations at the CCSD(F12*)(T*)/cc-pVQZ-F12//B2PLYP-D3/def2-TZVPP level of theory. On the basis of the results, a two-channel master equation accounting for the two different C-O bond-fission reactions of DMM was set up and solved. Specific rate coefficients were calculated from the simplified Statistical Adiabatic Channel Model. The branching between the two reaction channels was modeled, and the CH3OCH2O + CH3 product channel was found to be clearly dominating. A Troe parameterization for the pressure dependence of this channel was derived. To enable implementation of both channels into kinetic mechanisms for combustion modeling, 'log p' parameterizations of the rate coefficients for both reaction channels are also given and were implemented into a literature mechanism for DMM oxidation. With this slightly modified mechanism, the results of our experiments could be adequately modeled. The role of competing molecular (i.e. nonradical) decomposition channels of DMM was also quantum-chemically checked, but no indications for such channels could be found.

Auto-ignition of oxymethylene ethers (OMEn, n = 2–4) as promising synthetic e-fuels from renewable electricity: shock tube experiments and automatic mechanism generation

Carbon-neutral synthetic fuels can be produced from renewable electricity by the hydrogenation of carbon dioxide captured from air or exhaust gas. A promising class of these synthetic fuels are long-chain oxymethylene ethers (OMEs), which exhibit good auto-ignition characteristics for compression-ignition engine application. This study aims to investigate the auto-ignition of three oxymethylene ethers (OMEn, n = 2–4) numerically and experimentally. A shock tube is applied to measure ignition delay times over a range of initial conditions and the obtained results serve as the validation and optimization targets for a chemical mechanism of OME2-4 developed in this work. This model is derived first using an automatic reaction class-based mechanism generator. To ensure the chemical validity of the mechanism, the automatic generator applies reaction classes and rate rules consistently for OME2-4, which are adopted from a recently published OME1 mechanism. For improved model prediction accuracy of ignition delay times, the mechanism is then optimized automatically by calibrating these rate rules within their uncertainties using data for all OMEn fuels. It is shown that this highly automated model development process is able to provide accurate chemical mechanisms for large fuel components in a very efficient manner, if accurate prior kinetic knowledge exists for their short-chain counterparts.

Laminar premixed and non-premixed flame investigation on the influence of dimethyl ether addition on n-heptane combustion

Several different ether components have been proposed as renewable replacements for diesel fuel in compression ignition engines. From a fundamental point of view, blends of n-heptane and dimethyl ether (DME) have been considered in this study, where n-heptane is a single-component diesel surrogate and DME acts as a representative for oxymethylene ethers. n-Heptane and n-heptane / DME blends have been investigated experimentally under laminar premixed low-pressure and non-premixed atmospheric-pressure counterflow flame conditions. For the premixed case, a series of three fuel-rich flames was studied with oxygen as the oxidizer, at a constant C/O ratio of 0.47, pressure of 4 kPa, with 50% argon dilution, and an equivalence ratio ϕ near 1.5, burning pure n-heptane and mixtures of n-heptane with DME in the ratios 1:1 and 1:4. In the non-premixed counterflow configuration, two fuel/oxygen/argon flames were studied with pure n-heptane and a 1:1 DME–n-heptane mixture as the fuel. Electron ionization molecular-beam mass spectrometry was used for both flame configurations to investigate the flame structure and determine quantitative mole fraction profiles of stable and reactive species formed in the combustion process. Particular attention was given to the changes caused by partial replacement of n-heptane by DME.Notwithstanding the experimental focus of this work, the experimental results were compared with predictions from a model suitable for both n-heptane and DME that was combined for this case from recent mechanisms available in the literature for these fuels. While the overall flame structure was not significantly altered upon DME addition, with some smaller differences mainly due to temperature effects, more prominent changes and interactive effects were found for a number of primary decomposition products, oxygenated species, and higher-molecular hydrocarbon compounds. In most cases, experimentally observed trends, but not always quantitative changes, could be satisfactorily reproduced and explained by the model.

Application of Hetero-Triphos Ligands in the Selective Ruthenium-Catalyzed Transformation of Carbon Dioxide to the Formaldehyde Oxidation State

Due to the increasing demand for formaldehyde as a building block in the chemical industry as well as its emerging potential as feedstock for biofuels in the form of dimethoxymethane and the oxymethylene ethers produced therefrom, the catalytic transformation of carbon dioxide to the formaldehyde oxidation state has become a focus of interest. In this work, we present novel ruthenium complexes with hetero-triphos ligands, which show high activity in the selective transformation of carbon dioxide to dimethoxymethane. We substituted the apical carbon atom in the backbone of the triphos ligand platform with silicon or phosphorus and optimized the reaction conditions to achieve turnover numbers as high as 685 for dimethoxymethane. The catalytic systems could also be tuned to preferably yield methyl formate with turnover numbers of up to 1370, which in turn can be converted into dimethoxymethane under moderate conditions.

Dimethoxymethane as a Cleaner Synthetic Fuel: Synthetic Methods, Catalysts, and Reaction Mechanism

The increasing concerns regarding exhaust and CO2 emissions from fossil-based transportation fuels have propelled intensive research aimed at finding alternative fuel candidates to realize a clean and renewable fuel system. In this context, dimethoxymethane and its derivatives oxymethylene ethers, a class of oxygenated synthetic fuel, have recently attracted increasing interest because of their fascinating characteristics as a diesel blend compound to significantly reduce soot and nitrogen oxide formation. At present, dimethoxymethane production primarily relies on an established two-step process comprising methanol oxidation and methanol condensation with formaldehyde. Several new synthetic routes based on methanol or CO2/H2 have been proposed by adopting a reaction coupling strategy, which enables the production of dimethoxymethane in one step. A large variety of bi- and multifunctional catalysts have been developed for each synthetic route. This Review comprehensively summarizes the latest advances in ...

Coupled Production of Steel and Chemicals

AbstractWithin Carbon2Chem® the presented subproject focused on oxymethylene ethers (OME) as possible diesel fuel components. Six different scenarios for CO2emission reduction in steel mills were calculated, in four of which methanol is generated as an OME intermediate from steel mill gases. Potential synergies in raw material and energy streams of the coupled processes were identified. Shared process streams and equipment could lead to savings in capital and operational expenditure. CO2reduction volumes and avoidance costs were calculated for the six scenarios. If coupled with methanol production, natural gas‐based direct reduced iron processes offer the chance for quantitative CO2emission reduction at the lowest CO2avoidance costs. Energy required for this process could be co‐fed, e.g., as renewable electricity.

Recent Progress in the Production, Application and Evaluation of Oxymethylene Ethers

AbstractTo counteract greenhouse gas and other harmful emissions, ambitious regulatory measures with respect to energy generation, supply and consumption have been set. In the fuel sector, successive substitution of common fossil fuels by non‐fossil ones is a promising option to meet the respective demands. Regarding diesel fuels, the use of oxymethylene ethers (OMEs) has been proposed. Especially OMEs of the type CH3O(CH2O)nCH3 (n = 3 – 5) exhibit properties that are similar to common diesel fuel and formation of soot and NOx is drastically reduced during combustion. Within this work, recent progress regarding production, application and evaluation of OMEs is summarized and discussed.

Biogenous ethers: production and operation in a diesel engine

Fuels from lignocellulosic biomass have the potential to contribute to sustainable future mobility targets by reducing the fossil CO2 emissions of the transport sector. Of special interest for the diesel engine are oxygenated fuels, since they can help to solve traditional conflicts of objectives like the soot–NOx trade-off or the efficiency–NOx compromise. Dibutyl ether (DBE) and oxymethylene ethers (OME) are among the most promising fuel candidates. The suitability of these compounds for diesel engines is investigated in this study. The fuels are injected in pure form as well as a diesel–biofuel blend with 20% volumetric biogenic share. During the course of these investigations special attention is given to soot and particle emissions, and also to measured engine efficiency. The combustion tests are combined with an analysis of suitable production paths of the evaluated bio-ethers as second generation biofuels. Production simulation shows high greenhouse gas savings potential, but also high investment costs.

Heterogeneously catalyzed synthesis of oxymethylene dimethyl ethers (OME) from dimethyl ether and trioxane

Oligomeric oxymethylene ethers (OMEs) are promising fuels for internal combustion engines with self-ignition. A tremendous reduction of soot, nitrogen oxide and hydrocarbon emissions can be realized by employing OMEs. This work describes the synthesis of OMEs from dimethyl ether (DME) and trioxane. Zeolite H-BEA 25 was found to be a suitable catalyst for this reaction and a study on reaction parameters (e.g. temperature, reactant feed ratio and reaction time) has been carried out. A maximum DME conversion of 13.9 wt% could be obtained and the maximum reactant-related product yield for OME3–5 was 8.2 wt%. An OME formation mechanism is proposed which explains the observed product spectrum.

Gas-phase synthesis of oxymethylene ethers over Si-rich zeolites

A new approach for production of potential diesel substitutes oxymethylene ethers via continuous gas-phase synthesis from methanol and formaldehyde over zeolite catalysts.