An interesting reactor H2O free approach for the direct synthesis of the wonder fuel DME.

[NNadir]

Regrettably I won't have much time to fully discuss this paper: Kinetics, Mass Transfer, and Reactor Scaling Up in Production of Direct Dimethyl Ether, Kainakhone Pathoumthong, Putong Ratanamalaya, Sunun Limtrakul, Terdthai Vatanatham, and Palghat A. Ramachandran Industrial & Engineering Chemistry Research 2022 61 (46), 17077-17091.

I like it because it has a very nice summary of why DME is the perfect energy currency for the localized distribution of the energy of nuclear heat, since it is a drop in substitute, more or less, for the infrastructure built for the use of dangerous fossil fuels. In short it can replace diesel fuel, gasoline, LPG, methane in all applications without the use of extreme conditions, since its critical temperature is around 150°C, meaning it is easily liquified without the need for refrigeration.

From the text:

Dimethyl ether (DME) is known as a substitute for diesel fuel due to its high cetane number. (1,2) It is easy to store and transport using existing LPG technology because of its similar properties. (3,4) DME fuel is also environmentally benign because the synthesized DME contains no sulfur or nitrogen, leading to no SOX, NOX, or PM emissions when used as a diesel fuel substitute. (5) In addition, DME is nontoxic and nonmetal corrosive. Moreover, DME decomposes in the troposphere, leading to less ozone layer depletion and avoiding contribution to the greenhouse effect. (2,6) DME can be produced from syngas over a bifunctional catalyst. (7,8) DME produced from syngas involves three reaction steps, including a methanol synthesis reaction, a methanol dehydration reaction, and a water–gas shift reaction. (9,10) The most common catalysts for methanol synthesis are metallic function catalysts (Cu/Zn, Cu/Zn/A1, Cu/Zn/Cr, or Cu/Cr/Fe, etc.), while those for methanol dehydration are acidic porous materials (γ-alumina, aluminas, ferrierite, or zeolites, etc.). (10−13)

The authors discuss two reactor approaches commonly used in DME synthesis:

Two popular types of reactors for this gas–solid catalyzed reaction include fixed bed and fluidized bed. A fixed bed reactor is easy to operate, in which gas passing through a catalyst bed displays near-plug flow behavior. A simple flow pattern is easy to identify in the model for a fixed bed reactor. Though a fixed bed reactor is limited by heat transfer, temperature control can be accomplished in a small size operation. With a simple flow pattern, a fixed bed reactor is appropriate for a kinetic parameter study. Many studies on the kinetics of DME synthesis conducted in fixed bed reactors have been reported. (13−18) Since dimethyl ether synthesis is a highly exothermic reaction, a fluidized bed reactor is an ideal reactor for large scale production. Good mixing in a fluidized bed reactor ensures good temperature control in the reactor. However, the flow pattern in a fluidized bed is more complex, leading to difficulty in modeling, especially in a bubbling fluidization mode of operation...

They then note that a problem in direct DME synthesis from syn gas (H2 + CO or H2 + CO2) is that the reaction is highly exothermic, it generates significant heat. The heat can lead to the deactivation of the catalyst, and thus an efficient means of temperature control is required. They then discuss and evaluate a biphasic bubbling reactor, where a liquid phase (typically molten wax) is used to control temperatures, presumably allowing for the recovery and use of the heat in process intensification settings.

Bubbling fluidized bed reactors are characterized by moderate fluidization velocities, and the gas flow behavior is dominated by gas bubbles rising in the fluidized bed. These bubbles are largely responsible for solids mixing. Vigorous mixing of catalyst particles in the bed promotes a high gas–solid mass transfer rate in a fluidized bed reactor and provides excellent temperature control. Bubbling fluidized bed reactors are widely used in chemical and biochemical industries. This type of reactor is applied to carry out many gas–solid catalyzed reactions, such as maleic anhydride production, (19,20) Fischer–Tropsch synthesis, (21) CO2 methanation, (22) and methanol dehydration. (23) Industrial applications of large-scale bubbling fluidized bed reactors have been reviewed, including propylene ammoxidation to acrylonitrile, ethylene polymerization, and butane oxidation to maleic anhydride. (19) Although a circulating fluidized bed has also been proposed for many gas–solid reactions, a bubbling fluidized bed reactor is still in use. The main difference between these two types of fluidized beds is that the fluidization velocity of a bubbling fluidized bed is much lower than that of a circulating fluidized bed. Thus, less catalyst is elutriated from a bubbling fluidized bed reactor. No recycle system is required, leading to a simplified reactor design with a lower cost. In addition, attrition of catalyst is significant in a circulating fluidized bed due to high gas velocity...

The authors discuss issues in scaling these types of reactors to a required industrial scale.

The reactor schematic looks like this:



The caption:

Figure 2. Setup of the bubbling fluidized bed reactor for dimethyl ether synthesis.

What I find interesting, an issue that sometimes troubles me when I think about DME systems is that the water generated is consumed directly, avoiding the somewhat more difficult separation of DME and water for the easier separation of CO2 and DME, whereupon the CO2 can be recycled (perhaps by dry reforming of waste materials) back to CO for reuse.

The reactions in the continuous one step system are given as follows:



Again, I won't have time to go into more detail on this interesting and exciting paper, but this kind of chemistry can save the world, provided the primary energy source is nuclear.

Have a nice day tomorrow.

[Backseat Driver]

1. Question? Would use of the created DME fuel require retooling/different

controls of end user diesel vehicles? If not, working out the kinks in production as well as OSHA stuff for worker safety--seems sort of do-able, and by-products of end-users burning this fuel seem both non-toxic with less wear-and-tear on engine parts while by-products of production could be re-cycled for other uses? Seems a good reason for keeping "nuclear" options open, but I'm totally clueless about industrial chemistry.

[NNadir]

2. Mack/Volvo are adapting diesel engines to run on DME; modifications are required, but are minor.

Mack/Volvo go all in.

Some seals used in diesel engines powered by dangerous fossil fuels are not compatible with DME, as I understand it. DME has lower lubricity than diesel fuel (not surprising) and thus small amounts of lubricant may be required as an additive.

We already have diesel trucks that run on methane, chiefly those associated with waste companies, since landfills often generate methane. (I favor replacing landfills with dry reforming or steam reforming systems driven by nuclear heat. The resulting syn gas might be processed into any of the things now provided by petroleum or into DME.) DME can be used anywhere methane is used, except DME, unlike methane is not a greenhouse gas; it's atmospheric lifetime is about 5 days.

The energy/volume density of DME, although its cetane number is higher than petroleum diesel fuel, is lower. Thus the fuel tank would need to be slightly larger or alternatively, the driving range lower. The storage of the fuel is almost exactly the same as that of LPG, so existing LPG infrastructure would be able to drop in directly to DME.

All existing pipelines can be easily switched to carry DME, preferably in a liquified form.

It is an excellent refrigerant by the way, and it is also a fairly decent thermal fluid, it can be utilized to transfer heat via a system that might allow as a long distance heat pump.

It really is a wonder fuel. It sort of amazes me that the value has not been generally recognized. Mostly today it's used as a propellant in hair spray, having replaced CFCs. It's kind of crazy.