Article No : a08_541

Dimethyl Ether
MANFRED MÜLLER, DEA Mineraloel AG, Wesseling, Federal Republic of Germany
UTE HÜBSCH, DEA Mineraloel AG, Wesseling, Federal Republic of Germany

1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . 305 4. Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

2. Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 5. Toxicology . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
3. Production . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 308

Critical density 269.9 kg/m3 [1]

1. Introduction Heat of combustion (gas) 31.75 MJ/kg
Heat of formation
183 kJ/mol
Dimethyl ether [115-10-6], C2H6O, is the sim- Specific heat capacity (at
24  C) 2.26 kJ kg
1 K
1
plest aliphatic ether. Heat of vaporization (at
20  C) 410.2 kJ/kg
Autoignition temperature 235  C [2]
CH3

O

CH3 Explosive limits 3.0 – 17 vol % in air
Flash point
41  C
Relative density (gaseous, air ¼ 1) 1.59
For a long time it was obtained on an industrial Density
scale as a byproduct in the high-pressure produc- (at 20  C) 668.3 kg/m3 [2]
tion of methanol. Recently the high-pressure (at 50  C) 615.0 kg/m3 [2]
methanol plants have been almost completely Solubility in water
(at 20  C, 1 bar) 5.7 wt % [2]
replaced by low-pressure plants; this has led to (at 20  C, 4.8 bar) 36 wt % [2]
the erection of special plants for the synthesis of Surface tension (liquid) 0.0125 N/m [2]
dimethyl ether. The production of dimethyl ether Viscosity
in Western Europe is approx. 50 000 t per year. gaseous 0.0091 mPa  s [2]
liquid 0.11 mPa  s
Dimethyl ether is industrially important as the
starting material in the production of the meth-
ylating agent dimethyl sulfate and is used as an
aerosol propellant.
Density of liquid dimethyl ether [2]:

t,  C 10 20 30 40 50 60 70 80
2. Properties r, kg/m3 682 666 649 631 612 593 573 552

Dimethyl ether (DME, methoxymethane), Mr

46.07, is a colorless, almost odorless gas at room
temperature and atmospheric pressure and has Vapor pressure [2]:
the following physical properties:
t,  C
20
10 0 10 20 50
p, MPa
measured 0.124 0.184 0.266 0.375 0.512 1.149
Mr 46.07 calculated 0.114 0.185 0.267 0.374 0.512 1.152
bp at 0.1 MPa
24.8  C
mp
141  C
Critical pressure 5.28 MPa
Dimethyl ether is miscible with most polar
(52.84 bar) [1]
Critical temperature 400.29 K [1] and nonpolar organic solvents. It is also partly
(127.1  C) miscible with water (76 g in 1 L of water at

2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI: 10.1002/14356007.a08_541
306 Dimethyl Ether Vol. 11

18  C). In addition, numerous polar and nonpolar resulted in the almost complete replacement of all
substances readily dissolve in dimethyl ether. high-pressure plants by 1980. The low-pressure
processes, which require less severe conditions,
Chemical Properties. Unlike most other produce only very small amounts of dimethyl ether
aliphatic ethers, dimethyl ether is not susceptible (! Methanol). As a result, special catalytic pro-
to autoxidation. This is of considerable impor- cesses have been developed for the production of
tance for industrial applications. Numerous stud- dimethyl ether.
ies have confirmed that dimethyl ether is stable to The preparation of dimethyl ether from
atmospheric oxygen and does not form peroxides methanol in the presence of acidic catalysts on
[3]. a laboratory scale has been known for many
Dimethyl ether is converted to dimethyl sul- years [11]. Numerous methods have been dis-
fate [77-78-1] by sulfur trioxide (! Dialkyl cussed in the patent literature. For instance,
Sulfates and Alkylsulfuric Acids). aliphatic ethers can be prepared by heating
alcohols in the presence of zinc chloride [12].
SO3 þCH3

O

CH3 !ðCH3 Þ2 SO4
Other suitable catalysts are iron chloride, copper
Addition of boron trifluoride to dimethyl ether sulfate, copper chloride, manganese chloride,
results in the formation of BF3 CH3OCH3 [353- aluminum chloride, aluminum sulfate, chromi-
42-4], mp
14  C, bp 127  C, a distillable liquid um sulfate, alums, thorium compounds, alumi-
which fumes when exposed to moist air. This num oxide, titanium oxide, barium oxide, silica
addition compound is easier to handle than gas- gel, and aluminum phosphate [13]. Aluminum
eous boron trifluoride. oxide and aluminum silicate, with or without
In the presence of CoI2, dimethyl ether reacts doping, are the most important catalysts for
with carbon monoxide and water to form acetic industrial use [14]. Figure 1 illustrates the pro-
acid [64-19-7] (! Acetic Acid, Section 4.1.) [4]. cess developed by Union Rheinische Braunkoh-
len Kraftstoff AG (now DEA Mineraloel AG,
CH3

O

CH3 þH 2 Oþ2 CO!2 CH3 COOH
Wesseling) for the production of high-purity
The reaction of dimethyl ether with hydrogen dimethyl ether (purity > 99.99). This quality
sulfide in the presence of a catalyst, e.g., tungsten is virtually odorless.
sulfide (WS2), gives dimethyl sulfide [75-18-3] The catalytic dehydration of pure, gaseous
[5]. methanol is carried out in a pipe reactor. The
product is cooled in two stages and subsequently
CH3

O

CH3 þH 2 S!CH3

S

CH3 þH 2 O distilled to yield pure dimethyl ether. Small
The reaction of dimethyl ether to give unsat- amounts of dimethyl ether are recovered from
urated and saturated hydrocarbons proceeds in the off-gas in a scrubber and recycled to the
the presence of zeolitic catalysts [6]. reactor. Unreacted methanol is separated from
water in a second column and also recycled.
CH3

O

CH3 !H 2 C ¼ CH2 þH 2 O Very pure dimethyl ether which is suitable as
The catalytic conversion of dimethyl ether to an aerosol propellant is obtained by special rec-
formaldehyde has also been observed [7]. tification processes.
Direct synthesis of dimethyl ether from syn-
CH3

O

CH3 þO2 !2 CH2 OþH 2 O thesis gas (CO þ H2) has also been described
[15].

3. Production Safety and Environmental Aspects. Di-

methyl ether is a flammable gas. Water, foam,
Until about 1975 dimethyl ether was obtained as a carbon dioxide, and dry chemical powders can be
byproduct in the high-pressure production of meth- employed to control dimethyl ether fires. Fire
anol [8]. In this process up to 3 – 5 wt % dimethyl extinguishers suitable for class C (Europe) or
ether is formed. Dimethyl ether can be recovered in class B (United States) can be used. Endangered
pure form by distillation of crude methanol. The vessels must be cooled.
development of the low-pressure methanol synthe- Although dimethyl ether is soluble in water
sis, particularly by Lurgi [9] and ICI [10], has and biologically easily degradable, large
Vol. 11 Dimethyl Ether 307

Figure 1. Dimethyl ether production by dehydration of methanol

a) Vaporizer; b) Reactor; c) Dimethyl ether column; d) Scrubber; e) Methanol column

amounts of this compound should not enter the Suppliers are DEA Mineraloel AG in
wastewater system because evaporation can Germany, Akzo Nobel Chemicals B.V. in the
cause the formation of explosive mixtures over Netherlands, and DuPont & Nemours in
the surface of the water. Switzerland.
Available data do not indicate a danger for the
environment [2].
4. Uses
Quality Specifications and Analysis. Di-
methyl ether is available in two commercial Up to the 1980s, the main industrial use for dimethyl
qualities: ether was its conversion to dimethyl sulfate by
treatment with sulfur trioxide. Dimethyl sulfate is
. Technical grade contains up to 0.05 % metha- used as a methylating agent. Of the 50 000 t of
nol and contaminations with a strong odor. dimethyl ether produced in Western Europe in 1998,
. High-purity dimethyl ether, practically free of about 15 000 t was used in the production of di-
sulfur-containing and other substances with an methyl sulfate. The remaining 35 000 t of DME
unpleasant odor, can be used in the aerosol were used in the aerosol industry as a propellant.
industry; the methanol content should not ex- Owing to its high solubility coefficient, it also acts
ceed 10 mg/kg for this quality. as a solvent in aerosol formulations. This property is
of particular value in aerosol formulations which
The purity of dimethyl ether is determined by contain substances that are difficult to dissolve.
GC analysis. Oil and ash content are measured by The reaction of dimethyl ether with carbon
special methods of evaporation and combustion. monoxide and water can be used in large-scale
production of acetic acid instead of the metha-
Storage and Transportation. Dimethyl nol – carbon monoxide reaction. Future industri-
ether is usually stored as a liquid under pressure. al uses of dimethyl ether could include the pro-
It is transported in railway pressure tanks, tank duction of olefins, especially ethylene, propene,
trucks, and other pressure containers. Overseas and butenes in the presence of zeolitic catalysts.
transport is carried out in ISO tankers (Interna- DME is also considered an alternative fuel for
tional Shipping Organization). diesel engines (compression ignition) [16]:
Transportation is subject to the following . It has a low autoignition temperature
regulations: GGVS/ADR GGVE/RID class 2, . It is an oxygenated fuel, and as a gas it helps
no. 2 F; ADN/ADNR class 2, no. 2 F; UN no. establishing a good air – fuel mixture and
1033; IMDG Code (Amendment 20–82), consequently prevents soot formation
class 2.1, p. 2052. . It enables NOx reduction.
308 Dimethyl Ether Vol. 11

5. Toxicology 7 Shell Oil Company, US 4 439 624, 1982 (R. M. Lewis, R.

V. Ryan, L. H. Slaugh); US 4 442 307, 1982 (R. M.
Lewis, R. C. Ryan, L. H. Slaugh).
Pure dimethyl ether is nontoxic. Inhalation ex-
8 Winnacker-K€ uchler, 4th ed., vol. 5, Carl Hanser Verlag,
periments conducted on rats using concentrations M€unchen–Wien 1981, p. 512.
of up to 20 000 ppm (2 vol % in air) over a 9 E. Supp, Chem. Technol. 3 (1973) 430.
period of 8 months did not lead to any deaths 10 P. L. Rogerson, Chem. Eng. (N.Y.) 80 (1973) no. 19, 112.
[3]. Contact with dimethyl ether is not irritating 11 Houben-Weyl, vol. VI/3, part 3, Georg Thieme Verlag,
to the skin. Stuttgart 1965, pp. 17, 18.
12 Dr. Alexander Wacker, Gesellschaft f€ur elektrochem-
ische Industrie GmbH, DE 680 328, 1934 (P. Halbig,
O. Moldenhauer).
References 13 R. L. Brown, W. W. Odells, US 1 873 537, 1927. N. V. de
Bataafsche Petroleum Maatschappij, FR 701 335, 1930;
1 R. Graviliuc: Dimethylether—Begr€undung f€ur zus€atzliche GB 332 756, 1929;GB 350 010, 1931;GB 403 402, 1932.
thermodynamische Forschung, Institut f€ur Technische 14 Mobil Oil Corp., DE 2 818 831, 1978 (F. G. Dwyer, A. B.
Thermodynamik, Universit€at Karlsruhe 1998. Schwartz); DE-OS 3 201 155, 1982 (W. K. Bell, C.
2 DME Handbook, DEA Mineraloel AG, 1998. Chang). Du Pont, EP-A 99 676, 1983 (D. L. Brake).
3 L. J. M. Bohnenn, Manuf. Chem. Aerosol News 1978, Mitsubishi Chemical Industries, EP-A 124 078, 1984 (N.
August, 39. Murai, K. Nakamichi, M. Otake, T. Ushikubo).
4 Hydrocarbon Process. 50 (1971) no. 11, 115. 15 Snamprogetti, SpA., DE 2 362 944, 1973 (G. Giorgio);
5 Union Rheinische Braunkohlen Kraftstoff AG, Wessel- DE 2 757 788, 1977 (G. Manara, B. Notari, V. Fattore);
ing, DE 1 016 261, 1956 (F. H€ubenett, N. Schnack). DE 3 220 547, 1982 (G. Manara).
6 F. X. Cormerais, G. Perot, M. Guisnet, Zeolites 1 (1981) 16 R. P. Verbeek, A. van Doorn, Global Assessment of
October, 141. W. Lee, J. Mazink, V. W. Weckman Jr., S. Dimethyl Ether as an Automotive Fuel, 2nd ed., TNO-
Yurchak, Biomass Wastes 4 (1980) 721. C. D. Chang, C. report 96.O.VM.029.1/RV, July 1996.
T.-W. Chu, J. Catal. 74 (1982) 203. J. Haggin, Chem.
Eng. News 63 (1985) March 25, 39.