Advancements and Challenges in the Synthesis of Oxymethylene Ethers (OMEs) as Sustainable Transportation Fuels

The urgent need for sustainable alternatives to fossil fuels in the transportation sector is driving research into novel energy carriers that can meet the high energy density requirements of heavy-duty vehicles without exacerbating the climate change. This concept article examines the synthesis, mechanisms, and challenges associated with oxymethylene ethers (OMEs), a promising class of synthetic fuels potentially derived from carbon dioxide and hydrogen. We highlight the importance of OMEs in the transition towards non-fossil energy sources due to their compatibility with the existing Diesel infrastructure and their cleaner combustion profile. The synthesis mechanisms, including the Schulz-Flory distribution and its implications for OME chain length specificity, and the role of various catalysts and starting materials are discussed in depth. Despite advancements in the field, significant challenges remain, such as overcoming the Schulz-Flory distribution, efficiently managing water as an undesirable byproduct, and improving the overall energy efficiency of the OME synthesis. Addressing these challenges is crucial for OMEs to become a viable alternative fuel, contributing to the reduction of greenhouse gas emissions and the transition to a sustainable energy future in the transportation sector.

Stability and Reactivity of a Polyoxymethylene Dimethyl Ether over Typical Catalysts for Diesel Emission Control

Polyoxymethylene dimethyl ethers (OME) produced from methanol are considered as potential substitutes of Diesel fuel. Emissions of formaldehyde and other components have been observed, particularly under cold-start conditions in engine test-bench experiments with OME fuel. In this study, the reactivity of OME3 (CH3O(CH2O)3CH3) and its decomposition products was studied in the temperature range 80–450 °C in a model gas test bench over V2O5/WO3/TiO2 and Cu-CHA SCR catalysts, a platinum-coated V2O5/WO3/TiO2 ammonia slip catalyst (ASC) and two diesel oxidation catalysts (DOC), based on platinum and platinum-palladium. Already at 80 °C, OME3 was largely hydrolyzed to methanol and formaldehyde over all catalysts. At temperatures above 150 °C, V2O5/WO3/TiO2 oxidized methanol and formaldehyde to CO via formic acid as intermediate. The platinum ASC showed a similar behavior but oxidized the decomposition products to CO2. Whereas Cu-CHA hydrolyzed OME3 quantitatively to methanol and formaldehyde, it did not show oxidation activity in the studied temperature range. The data indicate that the release of significant amounts of OME from a catalytic converter can be virtually ruled out under cold start conditions, but also that low temperature hydrolysis produces formaldehyde and methanol emissions.

Selective oxidation conversion of methanol/dimethyl ether

As important platform compounds, methanol and dimethyl ether (DME) are vital bridges between the coal chemical, petrochemical and fine chemical industries. At present, the synthesis of methanol/DME has been industrialized, and the production capacity is much larger than the market demand. Therefore, the conversion of methanol/DME into more valuable chemicals is an important and significant topic. The synthesis of high value-added oxygenated chemicals and diesel oil additives from methanol/DME by an oxidation method has attracted substantial attention due to it being green and environmentally friendly and having good atom economy. In this feature article, we have summarized the recent advances in the synthesis of formaldehyde, methyl formate, dimethoxymethane, and polyoxymethylene dimethyl ethers, from the selective oxidation of methanol/DME, and further discussed the adsorption and activation of reactant molecules, selective cleavage of C-O, C-H or O-H bonds in methanol/DME molecules and the C-O chain growth in the target products. In the end, major challenges and future prospects are proposed from the viewpoint of catalyst design and application. It is expected that this feature article will provide theoretical guidance for the activation and cleavage of C-O, C-H, or O-H bonds in other small molecules of alcohol/ether as well as low-carbon alkanes, so as to synthesize high value-added chemicals.

Catalytic Reductive Alcohol Etherifications with Carbonyl-Based Compounds or CO2 and Related Transformations for the Synthesis of Ether Derivatives

Ether derivatives have myriad applications in several areas of chemical industry and academia. Hence, the development of more effective and sustainable protocols for their production is highly desired. Among the different methodologies reported for ether synthesis, catalytic reductive alcohol etherifications with carbonyl-based moieties (aldehydes/ketones and carboxylic acid derivatives) have emerged in the last years as a potential tool. These processes constitute appealing routes for the selective production of both symmetrical and asymmetrical ethers (including O-heterocycles) with an increased molecular complexity. Likewise, ester-to-ether catalytic reductions and hydrogenative alcohol etherifications with CO2 to dialkoxymethanes and other acetals, albeit in less extent, have undergone important advances, too. In this Review, an update of the recent progresses in the area of catalytic reductive alcohol etherifications using carbonyl-based compounds and CO2 have been described with a special focus on organic synthetic applications and catalyst design. Complementarily, recent progress made in catalytic acetal/ketal-to-ether or ester-to-ether reductions and other related transformations have been also summarized.

Oxygenated Transport Fuels from Carbon Dioxide : Driving towards Net Zero

The restructuring of the economy post-COVID-19 coupled to the drive towards Net Zero carbon dioxide emissions means we must rethink the way we use transport fuels. Fossil-carbon based fuels are ubiquitous in the transport sector, however there are alternative synthetic fuels that could be used as drop-in or replacement fuels. The main hurdles to achieving a transition to synthetic fuels are the limited availability of low-cost carbon dioxide at an appropriate purity, the availability of renewable hydrogen and, in the case of hydrocarbons, catalysts that are selective for small and particular chain lengths. In this paper we will consider some of the alternative fuels and methods that could reduce cost, both economically and environmentally. We recommend that increased effort in the rapid development of these fuels should be a priority in order to accelerate the possibility of achieving Net Zero without costly infrastructure changes. As ground transportation offers a more straightforward approach legislatively, we will look at oxygenated organic fuels as an alternative drop-in replacement for hydrocarbons.

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.