Dimethyl ether (DME) as an alternative fuel

doi:10.1016/j.jpowsour.2005.05.082

Journal of Power Sources

Volume 156, Issue 2, 1 June 2006, Pages 497-511

https://doi.org/10.1016/j.jpowsour.2005.05.082 Get rights and content

Abstract

With ever growing concerns on environmental pollution, energy security, and future oil supplies, the global community is seeking non-petroleum based alternative fuels, along with more advanced energy technologies (e.g., fuel cells) to increase the efficiency of energy use. The most promising alternative fuel will be the fuel that has the greatest impact on society. The major impact areas include well-to-wheel greenhouse gas emissions, non-petroleum feed stocks, well-to-wheel efficiencies, fuel versatility, infrastructure, availability, economics, and safety. Compared to some of the other leading alternative fuel candidates (i.e., methane, methanol, ethanol, and Fischer–Tropsch fuels), dimethyl ether appears to have the largest potential impact on society, and should be considered as the fuel of choice for eliminating the dependency on petroleum.

DME can be used as a clean high-efficiency compression ignition fuel with reduced NO_x, SO_x, and particulate matter, it can be efficiently reformed to hydrogen at low temperatures, and does not have large issues with toxicity, production, infrastructure, and transportation as do various other fuels. The literature relevant to DME use is reviewed and summarized to demonstrate the viability of DME as an alternative fuel.

Introduction

At the turn of the 19th century, petroleum was plentiful, and the US built its society around this fuel. Petroleum was the fuel that supplied much of the energy needs of our society and the industrial revolution. It is estimated that the world has peaked in petroleum production, and world petroleum consumption has outpaced new-found reserves. A century later, our generation is faced with reverse engineering a society based on petroleum to a new society based on an alternative fuel that will maintain economic, political, and environmental security for future generations.

In 1997, the US transportation sector consumed 13 million barrels day⁻¹ (accounting for 66% of the US petroleum consumption) and is forecasted to reach 21 million barrels day⁻¹ by 2025 [1]. As developing countries such as China, India, and Russia increase consumption, the petroleum demand could increase by as much as 75%. In China, the vehicle population was 16.56 million in 2000, and is forecasted to reach 65.38 million by 2010.

A means of reducing or eliminating the dependency on petroleum is to use fuels derived from natural gas, biomass, or coal. For this reason, methanol, ethanol, Fischer–Tropsch fuels, biodiesel and biogasoline are being researched as alternative fuels. Whatever fuel is to replace petroleum, it must address the following criteria:

•
Availability
- ∘
  Are there production facilities? What are their capacities?
- ∘
  Is there a pre-existing infrastructure?
- ∘
  What natural resource is used as the raw material?
  - -
    fossil fuels (natural gas, coal);
  - -
    renewable (timber, switchgrass, corn, sugar beets, etc.).
•
Economics
- ∘
  What are the fuel production and fuel distribution costs?
- ∘
  What are the costs of constructing new production facilities?
- ∘
  What is the cost of the raw material used for fuel production?
- ∘
  What are the costs of retrofitting old equipment to process the new fuel (if possible) or to replace them with new technology?
•
Acceptability
- ∘
  Is the new generation fuel inherently safe in handling and refueling?
- ∘
  Are there inherent health risks to humans or animal life?
•
Environmental and emissions
- ∘
  How does the new generation fuel affect global warming?
- ∘
  In the event of a large scale release, how does it affect the environment?
•
National security
- ∘
  Are the raw material(s) readily available and processed without reliance on foreign materials?
•
Technology
- ∘
  Are there commercially available or emerging technologies that can process the fuel?
- ∘
  Are they more efficient?
•
Versatility
- ∘
  Is the new generation fuel versatile in application (e.g., can the fuel be used as a residential fuel for heating and cooking, as a transportation fuel, as a power generation fuel, as a fuel that can produce hydrogen-rich fuel-cell feeds)?
- ∘
  Can the new generation fuel be manufactured using various feedstocks (e.g., coal, natural gas, and biomass)?

This report details dimethyl ether as an alternative fuel that could potentially replace petroleum-based fuels. Dimethyl ether is compared to the leading alternative fuel candidates; namely, hydrogen, methane, methanol, ethanol, biofuels, and Fischer–Tropsch fuels. As a benchmark, comparison is also made to conventional diesel and gasoline. A list of acronyms and abbreviations used in the text appear under ‘Abbreviations’.

Section snippets

Physical and thermo-physical properties

Dimethyl ether is the simplest ether, with a chemical formula of CH₃OCH₃. The physical properties of dimethyl ether are similar to those of liquefied petroleum gases (i.e., propane and butane). Dimethyl ether burns with a visible blue flame and is non-peroxide forming in the pure state or in aerosol formulations.

Unlike methane, dimethyl ether does not require an odorant because it has a sweet ether-like odor. The physical properties of dimethyl ether compared to the other fuels are detailed in

DME production

Traditionally, dimethyl ether has been produced in a two step process (a.k.a. the conventional route) where syngas (typically generated from the steam reforming of methane) is first converted to methanol—followed by methanol dehydration to dimethyl ether.

•
Methanol synthesis: $CO + 2 H_{2} ⇌ C H_{3} OH, Δ H_{rxn} ° = - 90.3 kJ mo l^{- 1}$
•
Methanol dehydration: $2 C H_{3} OH ⇌ C H_{3} OC H_{3} + H_{2} O, Δ H_{rxn} ° = 23.4 kJ mo l^{- 1}$
•
Water–gas shift: $H_{2} O + CO ⇌ H_{2} + C O_{2}, Δ H_{rxn} ° = 40.9 kJ mo l^{- 1}$
•
Net reaction: $3 H_{2} + 3 CO ⇌ C H_{3} OC H_{3} + C O_{2}, Δ H_{rxn} ° = 258.6 kJ mo l^{- 1}$

Natural gas is not the

Infrastructure

The infrastructure needed to supply an alternative fuel to the end user may include ocean transport, land transport and refueling stations. In the US, the most extensive infrastructures are those of natural gas and gasoline/diesel, followed by the infrastructure for LPG fuels. Depending on the alternative fuel, existing infrastructures may be modified or used as is. For example, the gasoline/diesel infrastructure can be used for ethanol. In the absence of a suitable infrastructure (as is the

Dimethyl ether as a diesel substitute

Since the mid 1990s dimethyl ether (cetane: #55–60) has been promoted as a diesel substitute (cetane: #55) [7], [8], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40]. With the concerns of diminishing petroleum reserves, dimethyl ether is garnering more attention as a viable alternative to diesel. The advantages of dimethyl ether over conventional diesel include decreased emissions of NO_x, hydrocarbons and carbon monoxide. Dimethyl ether combustion does not produce soot.

A comparison of transportation fuels

Because the US transportation sector accounts for 66% of total petroleum consumption, the alternative fuel that addresses this market will have the largest impact on reducing petroleum consumption.

The GREET model, developed at Argonne National Laboratory [1] is a widely used model that performs life cycle analyses (a.k.a. cradle-to-grave or well-to-wheel) for alternative transportation fuels. This model calculates relative performances of various transportation fuels (e.g., Fischer–Tropsch

Residential Fuel

Liquefied petroleum gas (i.e., propane and butane) is primarily used as a residential fuel for heating and cooking. In 2000, Australia exported 1.4 million tonnes of liquefied petroleum gas, with the largest markets being China and Japan. The LPG market in 2000 was 180 million tonnes per annum, and is expected to grow to 260 million tonnes. By 2010, the potential demand for DME as a residential fuel in Asia is forecasted to be 25 million tonnes per annum [34].

Dimethyl ether, having similar methods of

Conclusions

Current transportation fuels are based on petroleum, a resource that is being depleted, and whose importation has political and societal ramifications. Hydrogen is viewed by many as the ultimate ‘end-game’ fuel. A transition from petroleum to DME to hydrogen may be more cost effective than a step change to hydrogen. DME can be introduced and exploited with existing technologies, and enable the eventual implementation of advanced technologies, such as fuel cells.

Because dimethyl ether is

Acknowledgements

This work was partially supported by the US Department of Energy, Hydrogen, Fuel Cells and Infrastructure Program, and by Los Alamos Laboratory Directed Research and Development. The authors gratefully acknowledge Catherine G. Padró for her comments and suggestions.

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To uncover the microscopic reaction mechanisms of dimethyl ether (DME) pyrolysis and oxidation, reactive molecular dynamics simulations were employed to investigate the reaction processes under various O₂/DME ratios and impurity environments at 2200 K–3200 K. The results show that DME pyrolysis begins with a decomposition reaction of CH₃OCH₃ → CH₃O + CH₃, ultimately leading to the formation of CO, H₂ and PAHs. The reaction pathways of DME oxidation contain light gas conversion and combustion. In fuel rich conditions, the oxidation produces mainly H₂ and CO, while in fuel lean conditions, the oxidation products tend to be H₂O and CO₂. The carbon components of DME are completely converted into CO₂ and CO regardless of O₂ content. In the presence of impurities H₂O or CO₂, the oxidation reaction pathway is altered, causing consumption and transformation of these impurities into active radicals such as OH, further promoting the progress of the reaction. The top three light gases produced are hydrogen, methanol and methane, and increasing H₂ production in the DME oxidation process can be achieved through both oxygen subtraction and water addition. The rate of formaldehyde generation during pyrolysis is higher than that during oxidation. However, a higher oxygen content leads to increased formaldehyde production.
Multichannel kinetics of methoxymethyl + O<inf>2</inf> in combustion
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Organic peroxy radicals (RȮ₂), formed by association reaction of Ṙ + O₂, are important intermediates in low-temperature combustion of hydrocarbon fuels. A fate of RȮ₂ is isomerize to QOOH, and the downstream reactions of QOOH are known to profoundly fuel reactivity. However, both experimental measurements and high-level theoretical calculations of RȮ₂ kinetics are scarce, leading to a large gap in our understanding of RȮ₂ fate. In this study, methoxy-methyl-peroxy radical (CH₃OCH₂OȮ) is investigated as a model compound to elucidate the fate of RȮ₂. Based on a high-level quantum chemical calculation and RRKM/master equation calculation, we report a detailed RȮ₂ unimolecular reaction surface, as well as the corresponding temperature- and pressure-dependent rate coefficients. All the calculated results can be used to estimate the corresponding rate coefficients of larger oxygen-centered fuels and to construct the chemical kinetic model of dimethyl ether in combustion science.
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The addition of dimethyl ether (DME) to hydrocarbons is proposed to be a feasible strategy to reduce carbon dioxide emissions in engines. In order to unravel the interaction between hydrocarbons and oxygenated fuels, the co-pyrolysis of benzene, acetylene, and dimethyl ether (DME) is investigated in a flow reactor at 880–1250 K and 1 atm using gas chromatography in this work. Additionally, pyrolysis of pure benzene and co-pyrolysis of benzene and acetylene are also performed. It is observed that the pyrolysis of pure hydrocarbon components and co-pyrolysis of benzene and acetylene can hardly happen in the investigated temperature region, while the addition of DME to the pyrolysis of benzene and acetylene significantly accelerate their decompositions and enhance the formation of key aromatics, such as toluene and indene, showing remarkable synergistic effects on pyrolysis reactivity and aromatics growth. A kinetic model describing the combustion of the three components is developed and used to perform numerical investigation on fuel decomposition and PAH formation. Modeling analysis shows that the addition of DME can effectively activate the pyrolysis system through fast C-O bond dissociation reactions, thereby reducing the decomposition temperatures of benzene and acetylene. The phenyl radical produced from the H-abstraction of benzene can react with acetylene to produce phenylacetylene, while phenylacetylene can further combine with another phenyl radical to form b-phenyl-a-styryl radical which can readily convert to phenanthrene. The addition of DME also generates abundant methyl radical, which further reacts with benzene or other aromatics to form large aromatics such as toluene and methylated PAHs.
Efficient post-HCl treatment for promoting DTO performance of SAPO-18 and Ni-substituted SAPO-18
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Silicoaluminophosphate-18 (SAPO-18) may be a potential catalyst with relatively enhanced stability in dimethyl ether to olefins (DTO) process. In this work, the effect of post-treatment with hydrochloric acid (1 ∼ 5 h with 0.01 ∼ 0.2 M HCl) was investigated to improve the catalytic performance of hydrothermally synthesized SAPO-18 (S-0). The physicochemical and catalytic performances of DTO were compared with those of S-0 and Ni-0 (Ni-substituted SAPO-18), and the effect of the post-treatment of Ni-0 was also identified. The microporous surface areas of S-0.1-3 (S-0 treated with 0.1 M HCl for 3 h) and NiS-0.1-3 (NiS-0 treated with 0.1 M HCl for 3 h) were 645 m²·g⁻¹ and 642 m²·g⁻¹, respectively, and the pore channel entrance of crystal surface was extended compared to S-0 (590 m²·g⁻¹). Due to the moderate acidity (Brønsted/Lewis ratios of 0.96 and 0.98, respectively) of S-0.1-3 and NiS-0.1-3, the single-run lifetime in DTO was prolonged by 1.5–1.7 times that of S-0, while the light olefins selectivity was elevated by about 11 %. Therefore, the modification of S-0 and NiS-0 by HCl treatment was evidenced to be a facile method to promote its performance.
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Dimethyl ether (DME) as an alternative fuel

Abstract

Introduction

Section snippets

Physical and thermo-physical properties

DME production

Infrastructure

Dimethyl ether as a diesel substitute

A comparison of transportation fuels

Residential Fuel

Conclusions

Acknowledgements

Stud. Surf. Sci. Catal.

Catal. Today

Appl. Catal. A: Gen.

Appl. Catal. A: Gen.

Energy Convers. Manage.

Int. J. Hydrogen Energy

Catal. Today

Int. J. Hydrogen Energy

J. Power Sources

Int. J. Hydrogen Energy

Fuel Process. Technol.

J. Power Sources

J. of Power Sources

J. Power Sources

J. Catal.

J. Power Sources

Int. J. Hydrogen Energy

Int. J. Hydrogen Energy

Catal. Today

Appl. Catal. A: Gen.

Chem. Eng. J.

J. Power Sources

Catal. Commun.

Appl. Catal. B: Environ.

Int. J. Hydrogen Energy

Appl. Catal. A: Gen.

Catal. Today

Appl. Catal. B: Environ.

Appl. Catal. A: Gen.

Int. J. Hydrogen Energy

Appl. Catal. A: Gen.

Appl. Catal. A: Gen.

Appl. Catal. A: Gen.

Appl. Catal. A: Gen.

Appl. Catal. A: Gen.

Appl. Catal. A: Gen.

Int. J. Hydrogen Energy

Perry's Standard Tables and Formulas for Chemical Engineers

J. Geophys. Res.

J. Phys. Chem. A

Chem. Eng. News

Pet. Sci. Technol.

Chem. Eng. News

Catal. Lett.