c© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim10.1002/14356007.a16 465

Methanol 1

Methanol

Eckhard Fiedler, BASF Aktiengesellschaft, Ludwigshafen, Federal Republic of Germany

Georg Grossmann, BASF Aktiengesellschaft, Ludwigshafen, Federal Republic of Germany

D. Burkhard Kersebohm, BASF Aktiengesellschaft, Ludwigshafen, Federal Republic of Germany

Gunther Weiss, BASF Aktiengesellschaft, Ludwigshafen, Federal Republic of Germany

Claus Witte, BASF Aktiengesellschaft, Ludwigshafen, Federal Republic of Germany

1. Introduction . . . . . . . . . . . . . . . 12. Physical Properties . . . . . . . . . . . 23. Chemical Properties . . . . . . . . . . 34. Production . . . . . . . . . . . . . . . . 34.1. Principles . . . . . . . . . . . . . . . . . 34.1.1. Thermodynamics . . . . . . . . . . . . . 34.1.2. Kinetics and Mechanism . . . . . . . . 54.1.3. Byproducts . . . . . . . . . . . . . . . . . 64.2. Catalysts . . . . . . . . . . . . . . . . . . 64.2.1. Catalysts for High-Pressure Synthesis 64.2.2. Catalysts for Low-Pressure Synthesis 64.2.3. Production of Low-Pressure Catalysts 74.2.4. Catalyst Deactivation . . . . . . . . . . 74.2.5. Other Catalyst Systems . . . . . . . . . 85. Process Technology . . . . . . . . . . . 95.1. Production of Synthesis Gas . . . . . 95.2. Synthesis . . . . . . . . . . . . . . . . . . 105.3. Reactor Design . . . . . . . . . . . . . . 11

5.4. Distillation of Crude Methanol . . . 135.5. Construction Materials . . . . . . . . 136. Handling, Storage, and Transporta-

tion . . . . . . . . . . . . . . . . . . . . . 136.1. Explosion and Fire Control . . . . . 136.2. Storage and Transportation . . . . . 147. Quality Specifications and Analysis 158. Environmental Protection . . . . . . 169. Uses . . . . . . . . . . . . . . . . . . . . . 169.1. Use as Feedstock for Chemical Syn-

theses . . . . . . . . . . . . . . . . . . . . 169.2. Use as Energy Source . . . . . . . . . 179.3. Other Uses . . . . . . . . . . . . . . . . 1910. Economic Aspects . . . . . . . . . . . . 2011. Toxicology and Occupational Health 2011.1. Toxicology . . . . . . . . . . . . . . . . . 2011.2. Occupational Health . . . . . . . . . . 2212. References . . . . . . . . . . . . . . . . . 22

1. Introduction

Methanol [67-56-1], CH3OH, Mr 32.042, alsotermed methyl alcohol or carbinol, is one ofthe most important chemical raw materials.Worldwide production capacity in 1989 was ca.21×106 t/a. About 85% of the methanol pro-duced is used in the chemical industry as a start-ing material or solvent for synthesis. The re-mainder is used in the fuel and energy sector;this use is increasing. In 1993 world wide pro-duction capacity was 22.4×106t/a.

Historical Aspects. Methanol was first ob-tained in 1661 by Sir Robert Boyle throughthe rectification of crude wood vinegar overmilk of lime. He named the new compound adi-aphorus spiritus lignorum. Justus von Liebig(1803 – 1873) and J. B. A.Dumas (1800 – 1884)independently determined the composition of

methanol. The term “methyl” was introducedinto chemistry in 1835 on the basis of their work.

From ca. 1830 – 1923, “wood alcohol”, ob-tained by the dry distillation of wood, remainedthe only important source of methanol. As earlyas 1913, A.Mittasch and coworkers at BASFsuccessfully produced organic compounds con-taining oxygen, including methanol, from car-bon monoxide and hydrogen in the presence ofiron oxide catalysts during developmental workon the synthesis of ammonia. The decisive stepin the large-scale industrial production of meth-anol was made byM.Pier and coworkers in theearly 1920s with the development of a sulfur-resistant zinc oxide – chromium oxide catalyst.By the end of 1923 the process had been con-verted from the developmental to the productionstage at the BASF Leuna Works.

Processes based on the above work wereperformed at high pressure (25 – 35MPa) and320 – 450 C. They dictated the industrial pro-

2 Methanol

duction of methanol for more than 40 years. Inthe 1960s, however, ICI developed a route formethanol synthesis in which sulfur-free synthe-sis gas containing a high proportion of carbondioxide was reacted on highly selective copperoxide catalysts. This and other related low-pres-sure processes are characterized by fairly mildreaction conditions (5 – 10MPa, 200 – 300 C).Methanol can now be produced much moreeconomically worldwide by these low-pressuremethods.

2. Physical Properties

Methanol is a colorless, neutral, polar liquid thatis miscible withwater, alcohols, esters, andmostother organic solvents [1], [2]; it is only slightlysoluble in fat and oil. Because of its polarity,methanol dissolves many inorganic substances,particularly salts.

The most important physical data for metha-nol follow [3], [4]:

Density (101.3 kPa), liquidat 0 C 0.8100 g/cm3

at 25 C 0.78664 g/cm3

at 50 C 0.7637 g/cm3

Critical pressure 8.097MPaCritical temperature 239.49 CCritical density 0.2715 g/cm3

Critical volume 117.9 cm3/molCritical compressibility 0.224mp − 97.68 CHeat of fusion (101.3 kPa) 100.3 kJ/kgTriple-point temperature − 97.56 CTriple-point pressure 0.10768 Pabp (101.3 kPa) 64.70 CHeat of vaporization (101.3 kPa) 1128.8 kJ/kgStandard enthalpy of formationat 25 C (101.3 kPa), gas − 200.94 kJ/molat 25 C (101.3 kPa), liquid − 238.91 kJ/mol

Free enthalpy of formationat 25 C (101.3 kPa), gas − 162.24 kJ/molat 25 C (101.3 kPa), liquid − 166.64 kJ/mol

Standard entropyat 25 C (101.3 kPa), gas 239.88 Jmol−1 K−1

at 25 C (101.3 kPa), liquid 127.27 Jmol−1 K−1

Specific heat, cpat 25 C (101.3 kPa), gas 44.06 Jmol−1 K−1

at 25 C (101.3 kPa), liquid 81.08 Jmol−1 K−1

Viscosity (25 C)Liquid 0.5513mPa · sVapor 9.68×10−3 mPa · s

Thermal conductivity (25 C)Liquid 190.16mWm−1 K−1

Vapor 14.07mWm−1 K−1

Electrical conductivity (25 C) (2 – 7)×10−9 Ω−1 cm−1

Dielectric constant (25 C) 32.65Dipole moment 5.6706×10−30 C ·mRefractive index n20D 1.32840

n25D 1.32652Surface tension in air (25 C) 22.10mN/mFlash point (DIN 51 755) 6.5 COpen vessel 15.6 CClosed vessel 12.2 C

Explosion limits in air 5.5 – 44 vol%Ignition temperature 470 C(DIN 51 794)

The temperature dependence of selectedphysical properties is given in [5]; thermody-namic data can be found in [6] and the heat ca-pacity and enthalpy of the liquid in [7].

The vapor pressure ofmethanol is determinedaccording to [8] by a Wagner equation of theform

lnp=8.999+512.64T(

−8.63571q+1.17982q3/2−2.4790q5/2−1.024q5)

where q = 1−T /512.64; T is the absolute tem-perature, and p the pressure in kilopascals. Fur-ther vapor pressure correlation data in the tem-perature range 206 – 512K are given in [9],and critical data in [10]. A selection of binaryazeotropes is shown in Table 1, and a compre-hensive summary is given in [11].

Viscosity data of the pure components havebeen published in [5], [12], [13] for the liq-uid phase, and in [13] for the vapor. The vis-cosity and density of aqueous methanol solu-tions at 25 C are shown in Table 2. Temper-ature-dependent densities of the binary mix-ture are given in [15] and [16]; viscosities aredocumented in [15] and [17]. The pressure de-pendence of viscosity has been measured [18],and isothermal compressibilities, coefficients ofthermal expansion, partial molar volumes, andexcess factors accounting for the difference bet-ween real and ideal behavior can be found in[19]. Information on the liquid – solid phaseequilibrium in the methanol –water system isgiven in [20].

Data on the thermal conductivity of liquidmethanol appear in [21]; the electrical conduc-tivity of the pure liquid and dielectric propertiesare given in [22] and [23], respectively. Safetyaspects have also been discussed [24], [25].

Methanol 3

Table 1. Binary azeotropic mixtures of methanol [11]

Component bp of component, C bp of azeotrope, C Methanol content ofazeotrope, wt%

Acetonitrile 81.6 63.45 19Acrylonitrile 77.3 61.4 61.3Acetone 56.15 55.5 12Ethyl formate 54.15 50.95 16Methyl acetate 57.1 53.9 17.7Furan 31.7 < 30.5 < 7Thiophene 84 < 59.55 < 55Methyl acrylate 80 62.5 542-Butanone 79.6 64.5 70Tetrahydrofuran 66 60.7 31.0Ethyl acetate 77.1 62.25 44Methyl propionate 79.8 62.45 47.5Methyl methacrylate 99.5 64.2 82Cyclopentane 49.4 38.8 14n-Pentane 36.15 30.85 7Benzene 80.1 57.50 39.1Cyclohexane 80 54 38Cyclohexene 82.75 55.9 40Toluene 110.6 63.5 72.5

Table 2. Viscosity and density of aqueous methanol solutions at 25 C [14]

Mole fraction of methanol Kinematic viscosity, mm2/s Density, kg/m3 Absolute viscosity,mPa · s

0.0 0.893 997.1 0.8900.0507 1.126 983.4 1.1070.1125 1.385 966.9 1.3390.1411 1.480 960.2 1.4210.2276 1.657 941.1 1.5590.2927 1.683 925.7 1.5580.4198 1.593 898.4 1.4310.4856 1.505 884.5 1.3310.5542 1.396 869.9 1.2140.7133 1.149 837.7 0.9630.8040 0.992 821.0 0.8140.8345 0.952 816.0 0.7770.9140 0.825 800.1 0.660

3. Chemical Properties

Methanol is the simplest aliphatic alcohol. As atypical representative of this class of substances,its reactivity is determined by the functional hy-droxyl group [26–28]. Reactions of methanoltake place via cleavage of the C−O or O−Hbond and are characterized by substitution ofthe −H or −OH group (→Alcohols, Aliphatic,Chap. 2.2.) [29]. In contrast to higher aliphaticalcohols, however, β-elimination with the for-mation of a multiple bond cannot occur.

Important industrial reactions ofmethanol in-clude the following (Fig. 1):

1) Dehydrogenation and oxidative dehydroge-nation

2) Carbonylation3) Esterificationwith organic or inorganic acids

and acid derivatives4) Etherification5) Addition to unsaturated bonds6) Replacement of hydroxyl groups

4. Production

4.1. Principles

4.1.1. Thermodynamics

The formation of methanol from synthesis gascan be described by the following equilibriumreactions:

4 Methanol

Figure 1. Industrially important reactions of methanol

CO+ 2H2CH3OH ∆H300 K =− 90.77 kJ/mol (1)

CO2+ 3H2CH3OH+H2O ∆H300 K

= −49.16 kJ/mol (2)

Reaction enthalpies are determined from thestandard enthalpies of the reactants and prod-ucts [30]. Both reactions are exothermic and ac-companied by a decrease in volume. Methanolformation is thus favored by increasing pres-sure and decreasing temperature, the maximumconversion being determined by the equilibriumcomposition.

In addition to the twomethanol-forming reac-tions, the endothermic reaction of carbon diox-ide and hydrogen (Eq. 3, the reverse water-gasshift reaction) must also be taken into account:

CO2+H2CO+H2O ∆H300 K = 41.21 kJ/mol (3)

For the sake of simplicity, Equations (1) and (3)can be discussed as independent reaction path-ways. The conversion of carbon dioxide tometh-anol (2) is then the overall result of Equations(1) and (3), and the equilibrium constant K2 canbe described as K2=K1·K3. When the nonidealbehavior of gases is taken into account, the equi-librium constants are determined as follows:

K1 =

[fCH3OH

fCOf2H2

]

=

[ϕCH3OH

ϕCOϕ2H2

][pCH3OH

pCOp2H2

]

= Kϕ1 ·Kp1 (4)

K3=[fCOfH2O

fCO2 fH2

]=

[ϕCOϕH2O

ϕCO2ϕH2

] [pCOpH2O

pCO2 pH2

]=Kϕ3 ·Kp3 (5)

where fi is the fugacity, ϕi the fugacity co-efficient, and pi the partial pressure of the i-thcomponent.

A number of numerical formulations exist forcalculating the temperature-dependent equilib-riumconstantsK1 [31–38] andK3 [36–39]; theirresults differ widely [40]. The binomial formu-lations of Cherednichenko (Eq. 6) [34] andBisset (Eq. 7) [39] are examples:

K1= 9.740× 10−5exp[21.225+

9143.6T−

7.492lnT+4.076× 10−3T − 7.161× 10−8T 2] (6)

K3= exp[13.148− 5639.5

T− 1.077lnT−

5.44× 10−4T+1.125× 10−7T 2+49170T 2

](7)

The fugacity coefficients can be determined ac-cording to [41] by assuming ideal solubility forthe individual pure components, or they can becalculated from suitable equations of state [42],[43].

The carbon monoxide and carbon dioxideconversions up to attainment of equilibrium areshown as a function of pressure and tempera-ture in Table 3 [35]. A synthesis gas formed by

Methanol 5

Table 3. Temperature and pressure dependence of the carbon monoxide and carbon dioxide equilibrium conversions [35]

Temperature, CO conversion∗ CO2 conversion

C 5 10 30 5 10 30MPa MPa MPa MPa MPa MPa

200 96.3 99.0 99.9 28.6 83.0 99.5250 73.0 90.6 99.0 14.4 45.1 92.4300 25.4 60.7 92.8 14.1 22.3 71.0350 − 2.3 16.7 71.91 9.8 23.1 50.0400 − 12.8 − 7.3 34.1 27.7 29.3 41.0

∗Negative sign denotes CO formation via Equation (3) [44]: CO2 +H2 CO+H2O.

steam reforming was chosen as the starting gas(15 vol% CO, 8 vol% CO2, 74 vol% H2, and3 vol% CH4). Equations (6) and (7) were usedto establish temperature dependence, and the fu-gacity coefficientswere determined according tothe Soave –Redlich –Kwong equation. The neg-ative sign for the carbon monoxide conversiondenotes carbon monoxide formation by back-conversion [44].

4.1.2. Kinetics and Mechanism

The formation of methanol, as a typical hetero-geneously catalyzed reaction, can be describedby an absorption – desorption mechanism(Langmuir –Hinshelwood or Eley –Rideal).The nature of the active centers in thecopper – zinc oxide – alumina catalysts used un-der industrial conditions is still a subject ofdiscussion (see Chap. 5). The active species inlow-pressure methanol synthesis may be a so-lution of copper(I) ions in the zinc oxide phase[45]. On the other hand, evidence can be foundthat copper(0) also catalyzes methanol forma-tion. The feed gas composition ( particularlythe proportions of CO2 and H2O) also plays animportant role in determining the activity andselectivity of catalysts in methanol production.Investigations have shown that various routesmust exist for the formation of methanol viacarbon monoxide or carbon dioxide, and thatdifferent active centers in the catalyst are in-volved [46–50].

According to [51], alumina exists in an X-rayamorphous form. The proposed functions of alu-mina in copper – zinc oxide – alumina catalystsinclude:

1) prevention of sintering of the fine copper par-ticles by the formation of zinc spinel;

2) stabilization of the highly dispersecopper – zinc oxide catalyst system; and

3) formation of surface defects by the incorpo-ration of alumina clusters in the copper lat-tice [46], [51].

Which effect prevails in methanol synthe-sis is still not clear. However, alumina has animportant function as a structural promoter incopper – zinc oxide catalysts by improving theirmechanical stability and long-term activity.

Some kinetic investigations have concen-trated on the role of carbon dioxide in methanolsynthesis, which aroused a great deal of contro-versy during the 1980s [40], [46], [52–54]. Untilthe beginning of the 1980s, mechanistic consid-erations were based almost exclusively on thehydrogenation of carbon monoxide to methanol(Eq. 1, see 4.1.1) [55–59]. The increased yieldachieved by adding carbon dioxide was ascribedto the displacement of the reversewater-gas shiftequilibrium (Eq. 3). In addition, carbon dioxidewas assumed to influence the oxidation state ofthe active centers in the catalyst [45].

In contrast, Kagan et al. [60] proposed thatmethanol was formed solely according to Equa-tion (2) from carbon dioxide. Recent experi-ments with isotope-labeled reactants show thatboth reaction pathways (Eqs. 1 and 2) are pos-sible [61], [62]. Similar results were obtainedin other studies [63–65]. However, according to[62], formation via carbon dioxide predominatesunder conditions of large-scale industrial meth-anol synthesis.

6 Methanol

4.1.3. Byproducts

Commercially availableCu –ZnO–Al2O3 cata-lysts for the low-pressure synthesis of methanolpermit production of the desired product withhigh selectivity, typically above 99% referredto the added COx.

The following impurities are important forthe large-scale industrial process:

1) Higher alcohols formed by catalysis withtraces of alkali [66–68]nCO+2 nH2CnH2n+1OH+ (n− 1)H2O

2) Hydrocarbons and waxes formed by catal-ysis with traces of iron, cobalt, and nickelaccording to the Fischer – Tropsch process[67,69,70]CO+ 3H2CH4+H2O

CO2+ 4H2CH4+ 2H2O

nCO+ (2 n− 1)H2CnH2n+2 + nH2O

3) Esters [68], [70], [71](CH2O)ads + (RCHO)ads CH3COOR

4) Dimethyl ether [70], [72]

5) Ketones [73]RCH2CH2OHRCH2CHO+H2

2RCH2CHORCH2COCHRCH3+Oads

The formation of most byproducts from syn-thesis gas, particularly C+

2 species, is thermo-dynamically favored over methanol synthesis.Because methanol constitutes the main prod-uct, however, reactions yielding impurities arecontrolled kinetically rather than thermodynam-ically [40]. In addition to catalyst constituentsand feed gas composition, the residence time atthe catalyst [68], as well as the temperature [69],[70], mainly determine the extent of byproductformation: an increase in these parameters raisesthe proportion of byproducts. A detailed discus-sion of individual byproduct classes is given in[40].

4.2. Catalysts

4.2.1. Catalysts for High-Pressure Synthesis

The first industrial production of methanol fromsynthesis gas by the high-pressure process em-ployed a catalyst system consisting of zinc

oxide and chromium oxide. This catalyst, whichwas used at 25 – 35MPa and 300 – 450 C, washighly stable to the sulfur and chlorine com-pounds present in synthesis gas [44], [54], [74],[75].

Production of methanol with zinc oxide –chromium oxide catalysts by the high-pressureprocess is no longer economical. A new gener-ation of copper-containing catalysts with higheractivity and better selectivity is now used. Thelast methanol plant based on the high-pressureprocess closed in the mid-1980s. For a detaileddiscussion of high-pressure methanol catalysts,see [74].

4.2.2. Catalysts for Low-Pressure Synthesis

Well before the industrial realization of low-pressure methanol synthesis by ICI in the 1960s,copper-containing catalysts were known to besubstantially more active and selective thanzinc oxide – chromium oxide catalysts. Copperoxide – zinc oxide catalysts and their use inthe production of methanol were described byBASF in the early 1920s [76], [77]. These cata-lysts were employed at 15MPa and 300 C.

Their industrial use was prevented, however,by a serious disadvantage: impurities such as hy-drogen sulfide and chlorine compounds in syn-thesis gas rapidly deactivated the catalysts. Nev-ertheless, the copper-containing catalyst sys-tems proved to be themost promising candidatesfor producing methanol industrially at lowertemperature and pressure. A series of publica-tions on this topic appeared between 1925 and1955 [74], [78], [79]. Investigations of coppercatalysts continue to this day [53].

A low-pressure catalyst for methanol synthe-sis was first used industrially in the process de-veloped by ICI in 1966. This copper oxide – zincoxide catalyst was thermally stabilized with alu-mina. It was used to convert extremely pure (i.e.,largely free of sulfur and chlorine compounds,H2S< 0.1 ppm) synthesis gas to methanol [80].Because this copper catalyst was extremely ac-tive, methanol synthesis could be carried out at

Methanol 7

220 – 230 C and 5MPa. Premature aging dueto sintering of copper was thereby avoided. Thehigh selectivity of the new catalyst gave a meth-anol purity > 99.5%. The formation of byprod-ucts (e.g., dimethyl ether, higher alcohols, car-bonyl compounds, andmethane) associatedwiththe old high-pressure catalyst, was drasticallyreduced or, in the case of methane, completelyeliminated.

All currently used low-pressure catalystscontain copper oxide and zinc oxide with one ormore stabilizing additives (Table 4). Alumina,chromium oxide, or mixed oxides of zinc andaluminum have proved suitable for this purpose[81], [82].

4.2.3. Production of Low-Pressure Catalysts

Catalysts now used in low-pressure meth-anol synthesis plants and based oncopper – zinc – aluminum (or chromium) are ob-tained asmetal hydroxycarbonates or nitrates bycoprecipitation of aqueous metal salt solutions(e.g., nitrates) with sodium carbonate solution.Precipitation may occur in one or several stages.The quality of the subsequent catalyst is deter-mined by the optimum composition of the metalcomponents, the precipitation temperature, thepH used for precipitation, the sequence of metalsalt additions, and the duration of precipitation.The stirring rate, stirring energy, and shape ofstirrer also affect catalyst quality.

The precipitated catalyst precursors (largelymetal hydroxycarbonates) are filtered off fromthe mother liquor, washed free of interferingions (e.g., sodium), and dried at ca. 120 C.Examples of such hydroxycarbonates are mala-chite rosasite (Cu, Zn)5(CO3)(OH)2, hydroz-incite (Cu, Zn)5(OH)6(CO3)2, and aurichalcite(Cu0.3Zn0.7)5(OH)6(CO3)2 [40], [47], [82].Aurichalcite derivatives with the composi-tion Cu2.2Zn2.8(OH)6(CO3)2, containing smallamounts of alumina for stabilization, are ob-tained by coprecipitation of metal nitrates [87],[88]. The catalyst precursor is converted to finelydivided metal oxide by subsequent calcinationat ca. 300 – 500 C [80]. The calcined productis then pelleted to commercial catalyst forms.Cylindrical tablets 4 – 6mm in diameter andheight are common [46], [47], [82], [89].

The catalysts still have a total BET sur-face area of 60 – 100m2/g and have to be ac-tivated [47]. They are activated by controlledreduction with 0.5 – 2% hydrogen in nitrogenat 150 –230 C. Particular care must be taken toavoid hot spots, which lead to premature cata-lyst aging. In their reduced (i.e., active) form,the synthesis-active copper surfaces of commer-cial catalysts have a surface area of 20 – 30m2/g[81].

Catalysts for the low-pressure synthesis ofmethanol can also be produced by other meth-ods, e.g., impregnating a carrierwith active com-ponents, kneading metal compounds together,and leaching Raney alloys [17], [82].

Catalysts must be devoid of interfering impu-rities. Alkali compounds reduce the useful lifeand adversely affect the selectivity of catalysts.Even iron or nickel impurities in the parts-per-million range promote the formation of hydro-carbons and waxes. Acidic compounds such assilicon dioxide increase the proportion of di-methyl ether in crude methanol [90].

4.2.4. Catalyst Deactivation

As mentioned in Section 4.1, efficient catalystsfor low-pressure synthesis of methanol shouldhave a highly disperse distribution of activecenters stabilized by structural promoters. Thelonger a catalyst can retain these properties un-der industrial conditions, the more valuable itis for industrial operation: downtimes for cata-lyst replacement are reduced.Catalysts normallyhave useful lives of 2 – 5 years. Many factorscan drastically reduce catalyst activity and, thus,useful life. Detailed review articles on catalystdeactivation and poisoning can be found in [40],[47], [90].

Even during catalyst production,manufactur-ing faults can seriously affect the complex struc-ture of the active centers (see Section 4.2.3). Cat-alyst damage and, consequently, premature de-activation may also occur during reduction. Thetemperature conditions, hydrogen concentrationof the reducing gas, and gas loadmust be strictlycontrolled. Deviations from specified reductionprocedures may lead to hot spots in the pellets,resulting in sintering of the copper constituents;copper becomes mobile at 190 C and can ag-glomerate from its finely divided form into fairly

8 Methanol

Table 4. Summary of typical copper-containing catalysts for low-pressure methanol synthesis

Manufacturer Component Content, Referenceatom%

IFP Cu 25 – 80 [83]Zn 10 – 50Al 4 – 25

Sud Chemie Cu 65 – 75 [84]Zn 18 – 23Al 8 – 12

Shell Cu 71 [85]Zn 24rare-earth oxide 5

ICI Cu 61 [86]Zn 30Al 9

BASF Cu 65 – 75 [87]Zn 20 – 30Al 5 – 10

Du Pont Cu 50 [88]Zn 19Al 31

United Catalysts Cu 62 [88]Zn 21Al 17

Haldor Topsoe Cu 37 [88]Zn 15Cr 48

large crystallites. Reductionmust be complete toobtain the entire active mass from the precursorcompounds (see Section 4.2.3). Deviations fromthe specified reduction conditions may perma-nently decrease the active BET surface area andthus irrevocably damage the catalyst.

Another important point regarding the deac-tivation of copper catalysts is their high sensitiv-ity to impurities in synthesis gas. Chlorine- andsulfur-containing contaminants long preventedthe use of copper-containing catalyst systems inindustrial methanol plants. These catalyst poi-sons must be removed from the feed gas prior tomethanol synthesis. A certain degree of protec-tion against deactivation by sulfur is afforded bycatalysts containing zinc oxide because the sul-fur is bound as zinc sulfide. After deactivation,the catalyst is still able to absorb large quantitiesof sulfur to protect subsequent catalyst layersagainst poisoning. Other synthesis gas impuri-ties (e.g., silicon compounds, nickel carbonyls,or iron carbonyls) also cause catalyst damage[90].

The catalyst can also be deactivated by over-heating during operation. Thermal damage tothe catalyst can occur after use of nonoptimumrecycled gas compositions, incorrect tempera-

ture control, or overloaded catalyst in the startupphase. The active surface area of the catalyst isdecreased and phase transformations occur. Theformation of copper spinels as well as malachiterosasite is observed. In effect, this removes ac-tive centers for methanol synthesis from the cat-alyst [40], [45], [91].

4.2.5. Other Catalyst Systems

A number of modified copper – zincoxide – alumina catalysts have been prepared bydoping with boron, manganese, cerium, chromi-um, vanadium, magnesium, or other elements[92–100]. Other basic types of catalyst systemshave also been investigated: Raney copper cat-alysts, copper alloys with thorium or rare-earthoxides, and supported precious-metal catalysts[101–106]. Only copper alloy catalysts are re-ported to have a higher activity than conven-tional copper – zinc oxide – alumina catalysts[107]. Until now, however, exclusively copper-containing zinc oxide – alumina catalysts havebeen used in industrial methanol plants. Thesecatalysts have high activity, very good selectiv-ity, long-term stability, and favorable production

Methanol 9

costs. They are still the most cost effective cat-alysts.

5. Process Technology

The oldest process for the industrial produc-tion of methanol is the dry distillation ofwood, but this no longer has practical im-portance (→Biomass Chemicals, Chap. 4.9.).Other processes, such as the oxidation of hy-drocarbons and production as a byproduct ofthe Fischer – Tropsch synthesis according to theSynthol process, have no importance today.

Methanol is currently produced on an indus-trial scale exclusively by catalytic conversion ofsynthesis gas. Processes are classified accordingto the pressure used:

1) High-pressure process 25 – 30MPa2) Medium-pressure process 10 – 25MPa3) Low-pressure process 5 – 10MPa

The main advantages of the low-pressure pro-cess are lower investment and production costs,improved operational reliability, and greaterflexibility in the choice of plant size.

Industrial methanol production can be subdi-vided into three main steps:

1) Production of synthesis gas2) Synthesis of methanol3) Processing of crude methanol

5.1. Production of Synthesis Gas

All carbonaceous materials such as coal, coke,natural gas, petroleum, and fractions obtainedfrompetroleum (asphalt, gasoline, gaseous com-pounds) can be used as starting materials forsynthesis gas production. Economy is of pri-mary importance with regard to choice of rawmaterials. Long-term availability, energy con-sumption, and environmental aspects must alsobe considered.

Natural gas is generally used in the large-scale production of synthesis gas for methanolsynthesis. In a fewprocesses (e.g., acetylenepro-duction), residual gases are formed which haveroughly the composition of the synthesis gas re-quired for methanol synthesis.

Synthesis gases are characterized by the sto-ichiometry number S:

S=[H2] − [CO2][CO] + [CO2]

where the concentrations of relevant compo-nents are expressed in volume percent. The sto-ichiometry number should be at least 2.0 for thesynthesis gas mixture. Values above 2.0 indicatean excess of hydrogen,whereas values below2.0mean a hydrogen deficiency relative to the stoi-chiometry of the methanol formation reaction.

Natural Gas. Most methanol producedworldwide is derived from natural gas. Naturalgas can be cracked by steam reforming and bypartial oxidation (Fig. 2, see also→Ammonia).

In steam reforming the feedstock is catalyti-cally cracked in the absence of oxygen with theaddition of water and possibly carbon dioxide(→Gas Production, Chap. 2.→Gas Production,Chap. 7.1.). The reaction heat required is sup-plied externally. In partial oxidation, crackingtakes place without a catalyst (→Gas Produc-tion, Chap. 3.2.). Reaction heat is generated bydirect oxidation of part of the feedstock withoxygen. In a combination of the two processes,only part of the natural gas stream is subjectedto steam reforming [108]. The remainder passeswith the reformed gas to an autothermal re-formerwhere the natural gas is partially oxidizedby oxygen.

Only the production of synthesis gas by steamreforming is discussed here in some detail.

The catalysts used in steam reforming are ex-tremely sulfur sensitive; sulfur concentrations< 0.5 ppm quickly poison the catalyst. A gas pu-rification stage therefore precedes the reformerstage. If sulfur occurs primarily in the form ofhigher boiling compounds (e.g., mercaptans),batchwise adsorption on a regenerable activatedcharcoal bed is recommended. In the case of hy-drogen sulfide, zinc oxide is used as adsorbentto remove sulfur as zinc sulfide at 340 – 370 C.Hydrogenating desulfurization becomes neces-sary if organic sulfur compounds (e.g., COS) arepresent that cannot be removed with charcoal.Hydrogen (e.g., in the form of purge gas frommethanol synthesis) ismixedwith the gas streamto be desulfurized and passed over a cobalt ornickel –molybdenum catalyst at 290 – 370 C.

10 Methanol

Figure 2. Processes for producing synthesis gases

The sulfur compounds are converted into hydro-gen sulfide, which can be removed in a subse-quent zinc oxide column.

In the reformer, natural gas is catalyticallycracked in the presence of steam:

CH4+H2OCO+3H2 ∆H300 K = 206.3 kJ/mol

CO+H2OCO2+H2 ∆H300 K =− 41.2 kJ/mol

The first of these reactions is endothermic andleads to an increase in volume, whereas the sec-ond is exothermic and proceeds without changein volume. The degree of conversion of methaneincreases with increasing temperature, increas-ing partial pressure of steam, and decreasing ab-solute pressure.

The interfering Boudouard equilibrium

2COCO2+C ∆H300 K =− 172.6 kJ/mol

whichwould lead to carbon deposits on the cata-lyst or on thewalls of reformer tubes, can largelybe prevented by using excess steam and avoidinglong residence times in the critical temperaturerange above 700 C.

To reach the stoichiometry necessary formethanol synthesis, carbon dioxide, if available,is mixed with exit gas from the steam reformer.If carbon dioxide is not available, the conversionmust be performed with an excess of hydrogen.Hydrogen accumulates in the synthesis recyclegas and must be removed.

Other Raw Materials. Natural gas is not theonly raw material for synthesis gas used inmethanol production plants. Higher hydrocar-bons (e.g., liquefied petroleum gas, refinery off-gases, and particularly naphtha) are also used(→Gas Production, Chap. 2.1.); they are pro-cessed mainly by steam reforming. Crude oil,heavy oil, tar, and asphalt products (→Gas Pro-duction, Chap. 3.1.) can also be converted intosynthesis gas, but this is more difficult than withnatural gas. Their sulfur content is considerablyhigher (0.7 – 1.5% H2S and COS) and must beremoved. Synthesis gas also contains excess car-bon monoxide and must, therefore, be subjectedto shift conversion.

Coal can be converted into synthesis gaswith steam and oxygen by a variety of pro-cesses at different pressures (0.5 – 8MPa) andtemperature (400 – 1500 C); see also →Coal,Chap. 9.4.; →Gas Production, Chap. 4. Syn-thesis gas must be desulfurized and subjectedto shift conversion to obtain the required stoi-chiometry for methanol synthesis.

5.2. Synthesis

Important reactions (Eqs. 1 – 3) for the forma-tion of methanol from synthesis gas are dis-cussed in Section 4.1. In one pass only about50% of the synthesis gas is converted becausethermodynamic equilibrium is reached; there-fore, aftermethanol andwater are condensed out

Methanol 11

and removed, the remaining synthesis gas mustbe recycled to the reactor. A simplified flow di-agram for methanol synthesis is shown in Fig-ure 3. The make-up synthesis gas is brought tothe desired pressure (5 – 10MPa) in amultistagecompressor (f ). The unreacted recycle is addedbefore the recycle stage. A heat exchanger (b)transfers energy from the hot gas leaving the re-actor to the gas entering the reactor. The exother-mic formation of methanol takes place in thereactor (a) at 200 – 300 C. The heat of reactioncan be dissipated in one ormore stages. Themix-ture is cooled further (c) after passing throughthe heat exchanger (b); the heat of condensationof methanol and water can be utilized at anotherpoint in the process.

Figure 3.Methanol synthesisa) Reactor; b) Heat exchanger; c) Cooler; d) Separator;e) Recycle compressor; f ) Fresh gas compressor

Crude methanol is separated from the gasphase in a separator (d) and flashed before beingdistilled. Gas from the separator is recycled tothe suction side of the recycle compressor (e).The quantity of purge gas from the loop is gov-erned by the concentration and absolute amountof inert substances and the stoichiometry num-ber. If hydrogen is used to adjust the compositionof the fresh gas to give the required stoichiom-etry number it can be recovered from the purgegas by various methods (e.g., pressure swing ab-sorption). The purge gas is normally used forreformer heating.

5.3. Reactor Design

Current industrial processes for producingmeth-anol differ primarily in reactor design.Many dif-ferent reactors are available [109]; they may be

either adiabatic (e.g., ICI) or quasi-isothermal(e.g., Lurgi). The ICI process (Fig. 4) accountsfor 60%, and the Lurgi process (Fig. 5) for 30%of worldwide methanol production.

Adiabatic Reactors. The ICI process(Fig. 4) uses an adiabatic reactor with a sin-gle catalyst bed [110]. The reaction is quenchedby adding cold gas at several points. Thus, thetemperature profile along the axis of the reactorhas a sawtooth shape.

In the Kellogg process, synthesis gas flowsthrough several reactor beds that are arrangedaxially in series [111]. In contrast to the ICIquench reactor, the heat of reaction is removedby intermediate coolers. The Haldor Topsoe re-actor operates on a similar principle, but synthe-sis gas flows radially through the catalyst beds[112].

Ammonia – Casale S. A. has developed a re-actor that employs a combination of axial andradial flow (mixed flow). This type of reactorinitially developed for ammonia plants is offeredby Davy McKee in ICI license [113].

Quasi-Isothermal Reactors. The Lurgiprocess (Fig. 5) employs a tubular reactor (f )with cooling by boiling water [114]. The cata-lyst is located in tubes over which water flows.The temperature of the cooling medium is ad-justed by a preset pressure.

The Variobar reactor developed by Linde[115] consists of a shell-and-tube reactor coiledin several tiers, whose cooling tubes are embed-ded in the catalyst packing. The reactor temper-ature is adjusted by water cooling. As in otherprocesses, the heat of reaction is utilized to pro-duce steam, which can be used, for example, todrive a turbine for the compressor or as an energysource for subsequent methanol distillation.

Whereas synthesis gas flows axially throughthe two above-mentioned reactors, Toyo offersa reactor through which it flows radially [116].The advantages, as in the Variobar reactor, lie ina high heat transfer rate with only slight pressureloss.

The Mitsubishi Gas Chemical (MGC) pro-cess uses a reactor with double-walled tubes thatare filled in the annular spacewith catalyst [117].The synthesis gas first flows through the innertube to heat it up and then, in countercurrent,through the catalyst between the two tubes. The

12 Methanol

Figure 4. The ICI low-pressure methanol processa) Pure methanol column; b) Light ends column; c) Heat exchanger; d) Cooler; e) Separator; f ) Reactor; g) Compressor;h) Compressor recycle stage

Figure 5. Lurgi low-pressure methanol processa) Pure methanol columns; b) Light ends column; c) Heat exchanger; d) Cooler; e) Separator; f ) Reactor; g) Compressorrecycle stage

Methanol 13

outer tubes are cooled by water, Mitsubishi con-siders the main advantage of this process to bethe high conversion rate (ca. 14% methanol inthe reactor outlet).

5.4. Distillation of Crude Methanol

Crudemethanol leaving the reactor contains wa-ter and other impurities (see Section 4.1). Theamount and composition of these impurities de-pend on reaction conditions, feed gas, and typeand lifetime of the catalyst. Crude methanol ismade slightly alkaline by the addition of smallamounts of aqueous caustic soda to neutralizelower carboxylic acids and partially hydrolyzeesters.

The methanol contains low-boiling and high-boiling components (light and heavy ends). Thelight ends include dissolved gases, dimethylether, methyl formate, and acetone. The heavyends include higher alcohols, long-chain hydro-carbons, higher ketones, and esters of lower al-cohols with formic, acetic, and propionic acids.Higher waxy hydrocarbons consisting of a mix-ture of mostly straight-chain >C8–C40 com-pounds are also formed in small amounts. Theyhave low volatility and thus remain in the dis-tillation bottoms, from which they can easily beremoved because of their low solubility in waterand low density.

The impurities in crude methanol are gen-erally separated in two stages. First, all com-ponents boiling at a lower temperature thanmethanol are removed in a light ends col-umn (Fig. 4 b, Fig. 5 b). Pure methanol is thendistilled overhead in one or more distillationcolumns (Fig. 4 a, Fig. 5 a). If the columns op-erate at different pressures, the heat of conden-sation of the vapors of the column operating athigher pressure can be used to heat the columnat lower pressure.

5.5. Construction Materials

Low-molybdenum steels are normally used asconstruction materials in methanol synthesis.Because organic acids are especially likely to beencountered in themethanol condensation stage,stainless steels are generally used then. Damagedue to acids can also be prevented by the additionof small amounts of dilute caustic soda.

Stainless steels are normally employed inequipment operating at temperatures in whichthe formation of iron pentacarbonyl is likely(i.e., 100 – 150 C). This applies, for example, toheat exchangers and compressors. Contamina-tion with iron pentacarbonyl should be avoidedbecause it decomposes at the temperatures usedfor methanol synthesis. Iron deposited on thecatalyst poisons it and promotes the formationof higher hydrocarbons (waxy products).

6. Handling, Storage, andTransportation

6.1. Explosion and Fire Control

The flammability of methanol and its vapors re-presents a potential safety problem. The flashpoint is 12.2 C (closed cup) and the ignitiontemperature 470 C; in the Federal Republic ofGermany methanol is thus included in ignitiongroup B of the VbF [119].

Methanol vapor is flammable at concentra-tions of 5.5 – 44 vol%. The saturated vapor pres-sure at 20 C is 128 kPa; a saturated methanol –air mixture is thus flammable over a wide tem-perature range. Methanol is included in ignitiongroup G1, explosion class 1 (ExRL).

In premises andworkshops inwhich the pres-enceofmethanol vapor is likely, electrical equip-ment must be designed in accordance with therelevant regulations:

Guidelines for explosion protection (ExRL)Regulations governing electrical equipmentin explosionhazard areas (ElE×V)DIN VDE 0165DIN EN 50 014 – 50 020

For international guidelines on the handlingof methanol publications of the Manufactur-ing Chemists’ Association should be consulted[118].

Pure, anhydrous methanol has a very lowelectrical conductivity. Measures to preventelectrostatic charging must therefore be adoptedwhen transferring and handling methanol.

Fire Prevention. TheVbF restrictions on theamount of methanol that can be stored in labo-ratory premises should be observed. When largeamounts of methanol are stored in enclosed

14 Methanol

spaces, monitoring bymeans of lower explosionlimit monitors is desirable.

Permanently installed fire-extinguishingequipment should be provided in large storagefacilities. Water cannons are generally installedin storage tank farms to cool steel constructionsand neighboring tanks in the event of fire. Largetanks should have permanently installed pipingsystems for alcohol-resistant fire-extinguishingfoams.

Fire Fighting. Conventional fire-extingui-shing agents such as powder, carbon dioxide,or Halon can be used for small fires. Water isunsuitable as an extinguishing agent for firesinvolving large amounts of methanol because itis miscible with the compound; mixtures con-taining small amounts of methanol may alsoburn. Protein-based alcohol-resistant foams aresuitable.

A methanol flame is practically invisible indaylight, which complicates fire fighting. Themethanol flame does not produce soot, althoughformaldehyde and carbon monoxide form dur-ing combustion when oxygen is lacking. Respi-ratorsmust therefore bewornwhen fighting firesin enclosed areas.

6.2. Storage and Transportation

Small-Scale Storage. Fairly small amounts(≤ 10 L) of methanol for laboratory and indus-trial use are stored in glass bottles or sheet-metalcans; amounts up to 200 L are stored and trans-ported in steel drums. Some plastic bottles andcontainers cannot be used because of their per-meability and the danger of dissolution of plasti-cizers. High-density polyethylene and polypro-pylene are suitable, whereas poly(vinyl chlo-ride) and polyamides are unsuitable.

Large-Scale Storage. Large amounts ofmethanol are stored in tanks that correspondin design and construction to those used forpetroleum products; cylindrical tanks with ca-pacities from a few hundred cubic meters tomore than 100 000m3 are normally used. Withfixed-roof tanks, specialmeasures (e.g., nitrogenblanketing) should be adopted to prevent the for-mation of an ignitable atmosphere in the spaceabove the liquid surface. Emission of methanol

may occur if the level fluctuates. To avoid theseproblems, large tanks are often equipped withfloating roofs; attention should therefore be paidto guard against entry of rainwater.

For anhydrous and carbon dioxide-freemeth-anol tanks, pipelines and pumps can be con-structed from normal-grade steel; seals can bemade from mineral fiber, graphite, and metal.Styrene – butadiene rubber, chlorine – butadienerubber, and butyl – chlorobutyl rubber can beused for shaft seals.

Table 5.Federal specifications for puremethanol in theUnited States

Property Grade A Grade AA

Ethanol content, mg/kg < 10Acetone content, mg/kg < 20Total acetone and aldehydecontent, mg/kg < 30 < 30

Acid content (as acetic acid),mg/kg < 30 < 30

Color index (APHA) < 5 < 5Sulfuric acid test (APHA) < 30 < 30Boiling point range(101.3 kPa), must include < 1 < 164.6± 0.1 C

Dry residue, mg/L < 10 < 10Density (20 C), g/cm3 0.7928 0.7928Permanganate number > 30 > 30Methanol content, wt% > 99.85 > 99.85Water content, wt% < 0.15 < 0.10Odor typical,

non-persistent

Large-Scale Transportation. Methanol istraded worldwide. The recent trend toward re-locating production to sites that are remote fromindustrial centers where inexpensive natural gasis available, has meant that ca. 30% of meth-anol produced worldwide must be transportedby sea to consumer countries (Japan, Europe,United States). Specially built tankers with ca-pacities up to 40 000 t are available for this pur-pose; ships built to transport petroleum productsare also used.

The most important European transshipmentpoint for methanol is Rotterdam. Methanol isdistributed to inland industrial regionsmainly byinland waterways on vessels with capacities upto 3000 t. Boats specialized for methanol trans-port are the exception; impurities can thereforebe introduced into the methanol due to frequentchange of cargo. Analysis prior to delivery isgenerally essential.

Methanol is also transported by road and railtank cars. Permanently coupled trains consisting

Methanol 15

of several large tank cars with common filling,discharge, and ventilation lines are used to sup-ply large customers.

Transportation via pipeline is only of impor-tance for supplying individual users within en-closed, self-contained chemical complexes.

Safety Regulations Governing Trans-portation. The transportation of methanol asless-than-carload freight in appropriate vessels,containers, and bulk, is governed by specific reg-ulations that differ from country to country. Aneffort is being made, and is already well ad-vanced, to coordinate these regulations withinthe EC. Relevant legal regulations governingless-than-carload and bulk transportation by sea,on inland waterways, and by rail, road, and airare as follows [120]:

IMDG Code (D-GGVSee) D 3328/E-F 3087,Class 3.2, UN No. 1230

RID (D-GGVE) Class 3, Rn 301, Item 5ADR (D-GGVS) Class 3, Rn 2301, Item 5ADNR Class 3, Rn 6301, Item 5,

Category KxEuropean Yellow Book No. 603-001-00-XEC Guideline/D VgAst No. 603-001-00-XFRG (Land, VbF) BGreat Britain Blue Book: flammable liquid

and IMDG Code E 3087United States CRF 49, Paragraph 172.1.1,

flammable liquidIATA RAR, Art. No. 1121/43,

flammable liquid

7. Quality Specifications andAnalysis

Methanol for Laboratory Use. Methanolis available commercially in various puritygrades for fine chemicals:

1) “Synthesis” quality (corresponding to nor-mal commercial methanol)

2) Certified analytical quality3) Extremely pure qualities for semiconductor

manufacture

Commercial Methanol. In addition to labo-ratory grades, commercial methanol is generallyclassified according to ASTM purity grades Aand AA (Table 5). Methanol for chemical usenormally corresponds to Grade AA.

In addition to water, typical impurities in-clude acetone (which is very difficult to separateby distillation) and ethanol. When methanol isdelivered by ships or tankers used to transportother substances, contamination by the previouscargo must be expected.

Comparative ultraviolet spectroscopy hasproved a convenient, quick test method for de-ciding whether a batch can be accepted andloaded. Traces of all chemicals derived fromaro-matic parent substances, as well as a large num-ber of other compounds, can be detected.

Further tests for establishing the quality ofmethanol includemeasurements of boiling pointrange, density, permanganate number, turbidity,color index, and acid number. More comprehen-sive tests include water determination accordingto the Karl Fischer method and gas chromato-graphic determination of byproducts. However,the latter is relatively expensive and time con-suming because several injections using differ-ent columns and detectors must be made due tothe variety of byproducts present.

The most important standardized test meth-ods for methanol are

DIN 51 757 densityASTM D 941 densityASTM D 1078 boiling rangeASTM D 1209 color indexASTM D 1353 dry residueASTM D 1363 permanganate numberASTM D 1364 water contentASTM D 1612 acetone contentASTM D 1613 acid content

Apart from pure methanol, methanol ob-tained directly from synthesis without any pu-rification, or with only partial purification, issometimes used. This crude methanol can beused for energy (fuel methanol), for the manu-facture of synthetic fuels, and for specific chem-ical and technical purposes; it is not normallyavailable commercially. Composition varies ac-cording to synthesis conditions; principal im-purities include, 5 – 20 vol% water, higher al-cohols, methyl formate, and higher esters. Thepresence of water and esters can cause corrosionduring storage due to the formation of organicacids (see Section 6.2); remedies include alka-line adjustment with sodium hydroxide and, ifnecessary, the use of corrosion-resistant materi-als.

16 Methanol

8. Environmental Protection

Methanol is readily biodegraded; most microor-ganisms possess the enzyme alcohol dehydro-genase, which is necessary for methanol oxida-tion. Therefore, no danger exists of accumula-tion in the atmosphere, water, or ground; the bi-ological stages of sewage treatment plants breakdown methanol almost completely. In the Fed-eral Republic of Germany methanol has beenclassified as a weakly hazardous compound inwater hazard Class 1 (WGK I, § 19 Wasser-haushaltsgesetz). In accidents involving trans-port, large amounts of methanol must be pre-vented from penetrating into the groundwateror surface waters to avoid contaminating drink-ing water. Little is known about the behaviorof methanol in the atmosphere. Emissions oc-curring during industrial use are so small thatharmful influences can be ignored. That situa-tion could alter, however, if methanol were usedon a large scale as an alternative to petroleum-based fuels.

In methanol production, residues that presentserious environmental problems are not gener-ally formed. All byproducts are used when pos-sible; for example, the condensate can be pro-cessed into boiler feedwater, and residual gasesor low-boiling byproducts can be used for en-ergy production. The only regularly occurringwaste product that presents some difficulties isthe bottoms residue obtained after distillation ofpure methanol; it contains water, methanol, eth-anol, higher alcohols, other oxygen-containingorganic compounds, and variable amounts ofparaffins. The water-soluble organic substancesreadily undergo biological degradation; the in-soluble substances can be incinerated safely ina normal waste incineration unit. In some casesthis residual water is also subjected to furtherdistillative purification; the resultant mixture ofalcohols, esters, ketones, and aliphatics can beadded in small amounts to carburetor fuel.

The spent catalysts contain auxiliary agentsand supports, as well as copper (synthesis),nickel (gas generation), and cobalt and molyb-denum (desulfurization) as active components.These metals are generally recovered or other-wise utilized.

Modern steam reformers can be fired so thatemission of nitrogen oxides (NOx) in theflue gas

is maintained below 200mg/m3 without havingto use secondary measures.

9. Uses

9.1. Use as Feedstock for ChemicalSyntheses

Approximately 70% of the methanol producedworldwide is used in chemical syntheses: in or-der of importance formaldehyde, methyl tert-butyl ether (MTBE), acetic acid,methylmethac-rylate, and dimethyl terephthalate. Only a smallproportion is utilized for energy production, al-though this use has great potential.

Formaldehyde. Formaldehyde is the mostimportant product synthesized from methanol(→Formaldehyde, Chap. 4.); in 1988, 40%; in1996 35%, of themethanol producedworldwidewas used to synthesize this product. The annualestimated increase in formaldehyde productionfrommethanol is ca. 3%, but because other bulkproducts have higher growth rates its share as aproportion of methanol use will decrease.

The processes employed are all based on theoxidation ofmethanolwith atmospheric oxygen.They differ mainly with regard to temperatureand nature of the catalyst used.

Methyl tert-butyl ether is produced by re-acting methanol with isobutene on acid ion ex-changers (→Methyl tert-Butyl Ether). Increas-ing amounts of methanol are used in this formin the fuel sector. The ether is an ideal octanebooster and has become extremely importantdue to the introduction of unleaded grades ofgasoline and awareness of the possible harm-fulness of aromatic high-octane components. In1988, 20%; in 1996 27%, of worldwide meth-anol production was used for MTBE synthesis;annual increase rates of up to 12% are expected.The availability of isobutene is becoming an in-creasing problem in MTBE synthesis, althoughthe situation has recently been improved bythe construction of plants for the isomerizationof butane and subsequent dehydrogenation ofisobutane.

Methanol 17

Acetic Acid. Another 9% of the methanolproduced is used to synthesize acetic acid,and annual growth rates of 6% are esti-mated. Acetic acid is produced by carbon-ylation of methanol with carbon monoxidein the liquid phase with cobalt – iodine, rho-dium – iodine, or nickel – iodine homogeneouscatalysts (→Acetic Acid, Chap. 4.1.). The olderBASF process operates at 65MPa, whereasmoremodern processes (e.g., theMonsanto pro-cess) operate at 5MPa. By varying operatingconditions the synthesis can also be modifiedto produce acetic anhydride or methyl acetate.

Other Synthesis Products. In the intensivesearch after the oil crisis for routes to alter-native fuels, processes were developed that al-lowed fuels to be produced from synthesis gaswith methanol as an intermediate. Mobil in theUnited States has contributed decisively to thedevelopment of such processes, which involvemainly the reaction of methanol on zeolite cat-alysts. The most important and, up to now, theonly industrially implemented process is meth-anol to gasoline (MTG) synthesis. A plant forproducing and converting 4500 t/d of methanolfrom natural gas into 1700 t/d of gasoline hasbeen built and operated as a joint venture bet-ween the New Zealand government and Mobil.Since the prices of petroleum products have notrisen as expected, ways are now being sought toprocess the methanol from this plant into puremethanol and to market it as such.

Further synthesis routes that could becomeimportant in the event of a scarcity of petroleumproducts are the methanol to olefins (MTO) andmethanol to aromatic compounds (MTA) pro-cesses [121].

A product that received great attention as aresult of the discussion of environmental dam-age caused by chlorofluorocarbons is dimethylether (→Dimethyl Ether). It can be used as analternative propellant for sprays. Compared topropane – butane mixtures also used as propel-lants, its most important feature is its higher po-larity and, thus, its better solubilizing power forthe products used in sprays. Dimethyl ether isalso used as a solvent, organic intermediate, andin adhesives.

Methanol is used to synthesize a large num-ber of other organic compounds:

Formic acid preservatives, pickling agentsMethyl esters of organicacids

solvents, monomers

Methyl esters of inorganicacids

methylation reagents, explosives,

insecticidesMethylamines pharmaceutical precursors,

auxiliaries,absorption liquids for gas washingand scrubbing

Trimethylphosphine pharmaceuticals, vitamins,fragrances,fine chemicals

Sodium methoxide organic intermediates, catalystMethyl halides organic intermediates, solvents,

propellantsEthylene organic intermediates, polymers,

auxiliaries (→Ethylene)

9.2. Use as Energy Source

Methanol is a promising substitute for petro-leum products if they become too expensive foruse as fuels. As a result of the oil crisis in theearly 1970s, a number of projects were startedbased on the assumption that the use of meth-anol produced from coal would be more eco-nomical in the medium term than the use of pe-troleum products. The estimates made at the be-ginning of the 1980s proved to be too optimistic,however, with regard to costs and to overcomingtechnical or environmental problems involved inproducing synthesis gas from coal, and too pes-simistic with regard to the price and availabilityof crude oil (Table 6). Nearly all the large-scaleprojects for coal utilization have been discontin-ued. Large-scale operational plants (e.g., CoolWater, United States and Rheinbraun, Wessel-ing, FRG) are being shut down or modified foruse with other feedstocks [122].

Methanol as a Fuel for Otto Engines. Theuse of methanol as a motor fuel has been dis-cussed repeatedly since the 1920s. Use has so farbeen restricted to high-performance engines forracing cars and aeroplanes. The combustion ofmethanol in four-stroke engines has been inves-tigated for a long time.Methanol has been foundto be an ideal fuel in many respects. Because ofits high heat of vaporization and relatively lowcalorific value, a substantially lower combus-tion chamber temperature is achieved than withconventional motor fuels. Emissions of nitrogenoxides, hydrocarbons, and carbon monoxide arelower.This is offset, however, by increased emis-sion of formaldehyde.

18 Methanol

Table 6. Comparison of the efficiencies of natural gas conversion in liquid fuels

Energy carrier Higher heatingvalue, Gcal/t

Yield, t/t CH4 Higher heatingvalue, Gcal/t CH4

Theoreticalefficiency

Stoichiometricfactor,[H] – [20]/[C]

Technicalefficiency∗∗

Methane 13.2 1 13.28 100 4Synthesis gas, partialoxidation 6.36 2 12.70 95.7 2 85 – 90

Synthesis gas, steamreforming 7.96 2.12∗ 16.91∗ 6

Methanol 5.36 2 10.72 80.7 2 68 – 72Ethanol 7.14 1.43 10.25 77.2 2Kerosene 11.00 0.87 9.57 72.1 ca. 2.05Diesel fuel 10.70 0.87 9.34 70.4 ca. 2 55 – 60 FTGasoline (average) 10.50 0.86 9.06 68.2 ca. 1.8 58 – 63 MTG

55 – 60 FTBenzene 10.02 0.81 8.13 61.2 1

∗With extra heat energy for reformer.∗∗ FT=Fischer – Tropsch; MTG=methanol to gasoline.

Table 7. Comparison of methanol and a typical fuel (gasoline) foruse in Otto engines

Property Gasoline Methanol

Density, kg/L 0.739 0.793Calorific value, kJ/kg 44 300 21 528Air consumption, kg/kg 14.55 6.5Research octane number 97.7 108.7Motor octane number 89 88.6Mixed research octanenumber 120 – 130

Mixed motor octane number 91 – 94Reid vapor pressure, kPa 64 32Boiling point range, C 30 – 190 65Heat of vaporization, kJ/kg 335 1174Cooling under vaporizationwith stoichiometricamount of air, C 20 122

The important properties of methanol for useas a fuel are compared with those of a conven-tional fuel (gasoline) in Table 7. Consumption ishigher because of the lower calorific values.

Methanol can be used in various mixing ra-tios with conventional petroleum products:

M3 Mixture of 3% methanol with 2 – 3% solubilizers (e.g.,isopropyl alcohol) in commercially available motor fuel.This system is already widely used because modificationof motor vehicles and fuel distribution systems is notrequired.

M15 Mixture of 15% methanol and a solubilizer with motorfuel; alterations to the motor vehicles are necessary in thiscase. The proposed use of M15 to increase the octanenumber in unleaded gasoline has been supplanted by thelarge increase in the use of MTBE.

M85 Methanol containing 15% C4–C5 hydrocarbons toimprove cold-start properties. Modified vehicles and fueldistribution systems are necessary.

M100 Pure methanol–vehicles must be substantially modifiedand fully adapted to methanol operation.

The necessary modifications for methanoloperation involve the replacement of plasticsused in the fuel system (see Section 6.2). Theignition system and carburetor or fuel injectionunit also have to be adapted. With M85 andM100 the fuel mixture must be preheated be-cause vaporization of the stoichiometric amountof methanol in the carburetor results in a coolingof 120K.

In mixtures with a low methanol content(M3, M15) phase separation in the presenceof traces of water must be avoided. Absolutelydry storage, transportation, and distribution sys-temsmust be available formixed fuels to preventseparation of water –methanol and hydrocarbonphases.

A further restriction on the use ofmethanol ingasoline is imposed by the increase in gasolinevapor pressure (Reid vapor pressure, RVP). Insome warm regions of the United States, legalrestrictions on the RVP have already been intro-duced to reduce hydrocarbon emissions, whichare an important factor in the formation of photo-chemical smog and increased ozone concentra-tion in the lower atmosphere. As a result, meth-anol can not longer be added to motor fuel be-cause it increases the vapor pressure of the bu-tane used as a cheap octane booster.

Widespread use of methanol as an exclusivefuel for cars is inhibited by its high cost and thelack of a suitable distribution system. Possiblesolutions to the latter problem include the con-struction of dual-purpose vehicles (flexible fuelvehicles), which can use either methanol or nor-

Methanol 19

mal fuel. Another solution is to use methanol forcompany or government car fleets, which refilltheir tanks at a few specific filling stations. Tri-als based on this concept are underway in severalcountries; the largest is taking place in Califor-nia [123].

Methanol as Diesel Fuel. Exclusive opera-tion with methanol is not possible in diesel en-gines because methanol has a cetane number of3 and will therefore not ignite reliably. To en-sure ignition the engine must have an additionalinjector for normal diesel fuel; methanol is in-jected into the cylinder after ignition of the dieselfuel [124]. Additives are being developed to im-prove ignition performance.

Other Uses ofMethanol in the Fuel Sector.In contrast to pure methanol, the use of MTBEin Otto engine fuels is not limited by considera-tions of miscibility or vapor pressure. The use ofmethanol for MTBE synthesis could soon quan-titatively overtake its conventional uses. Arco,the world’s largest producer of MTBE, is alsopromoting the use of oxinol, a mixture of meth-anol and tert-butanol.

An additional development in the use ofmethanol is the Lurgi Octamix process. Use ofan alkali-doped catalyst andmodified conditions(higher temperature, lower CO2 concentration,higher CO concentration) in methanol synthesisyields amixture ofmethanol, ethanol, andhigheralcohols [125]. Thismixture can be used directlyin the engine fuel. The presence of higher alco-hols is desirable not only because of the increasein octane number, but also because they act assolubilizers for methanol. However, this processis not yet used on an industrial scale.

Other Energy Uses of Methanol. A usethat has been discussed particularly in theUnitedStates and implemented in pilot projects is thefiring of peak-load gas turbines in power stations( peak shaving). Benefits include simple storageand environmentally friendly combustion in thegas turbine. The use of methanol as a fuel inconventionally fired boilers obviates the needfor costly flue gas treatment plants but is not yeteconomically viable.

The gasification of methanol to obtain syn-thesis gas or fuel gas has often been proposed.Apart from exceptions such as the production of

town gas in Berlin, here too, economic problemshave prevented technical implementation.

9.3. Other Uses

Methanol’s low freezing point and its miscibil-ity with water allow it to be used in refrigerationsystems, either in pure form (e.g., in ethyleneplants) or mixed with water and glycols. It isalso used as an antifreeze in heating and coolingcircuits; compared to other commonly used an-tifreezes (ethylene glycol, propylene glycol, andglycerol), it has the advantage of lower viscos-ity at low temperature. It is, however, no longerused as an engine antifreeze; glycol-based prod-ucts are employed instead.

Large amounts of methanol are used to pro-tect natural gas pipelines against the formationof gas hydrates at low temperature. Methanol isadded to natural gas at the pumping station, con-veyed in liquid form in the pipeline, and reco-vered at the end of the pipeline. Methanol canbe recycled after removal of water taken up fromnatural gas by distillation.

Methanol is also used as an absorption agentin gas scrubbers. The removal of carbon dioxideand hydrogen sulfide with methanol at low tem-perature (Rectisol process, Linde and Lurgi) hasthe advantage that traces of methanol in the pu-rified gas do not generally interfere with furtherprocessing [126].

The use of pure methanol as a solvent is lim-ited, although it is often included in solvent mix-tures.

Figure 6.Worldwide methanol productionThe estimate for 1989 – 1992 is based on a utilization of80% capacity [126], [127].

20 Methanol

10. Economic Aspects

Economics of Methanol Production. Thecosts of methanol production depend on manyfactors, the most important being direct feed-stock costs, investment costs, and costs involvedin logistics and infrastructure.

Natural gas, naphtha, heavy heating oil, coal,and lignite are all used as feedstocks in metha-nol plants. In heavy oil-based plants and to anincreasing extent in coal-based plants the princi-pal cost burden is accounted for by capital costs.This means that, given the currently prevailinglow energy prices, such plants have high fixedcosts and are, therefore, uneconomical or eco-nomical only under special conditions. Underpresent conditions the balance between invest-ment and operating costs clearly favors naturalgas-based plants. All large plants currently be-ing planned are designed for usewith natural gasand some plants built for operation with naph-tha have been converted. Less than 2×106 t ofthe currently installed worldwide capacity of ca.21×106 t is based on raw materials other thannatural gas.

Methanol on the World Market. Afterammonia, methanol is quantitatively the largestproduct from synthesis gas. Worldwide capacityat the beginning of 1989 was 21×106 t. In 1988,19×106 t of methanol was produced worldwide.The mean annual production growth rate is ca.10%. The production curve for methanol since1965 is illustrated in Figure 6. Worldwide ca-pacity in 1996 was 29.1×106 t/a, 24.3×106 t/aof methanol was produced.

The methanol industry underwent radicalstructural changes during the 1980s. Previously,companies that consumed large quantities ofmethanol produced the compound themselvesfrom the most readily accessible raw materialsat the site of use (i.e., highly industrialized coun-tries with expensive energy sources). Since thenthe number of plants that produce methanol atremote sites exclusively for sale to processorshas risen dramatically.

After the energy crisis of the 1970s, intensiveoil prospecting led to the discovery of large nat-ural gas fields in many remote regions. Becauselittle demand for natural gas existed in these re-gions, the relevant countries in South America,Asia, and the Caribbean were interested in sell-

ing natural gas as such or in another form toindustrialized countries.

Another, hitherto little-used energy source isthe associated gas, which is often flared off.In addition to the transportation of liquefiedmethane and its use as a startingmaterial for am-monia production, methanol production is oftenthe most suitable alternative for marketing suchgases. The technology of methanol productionis relatively simple, and transport and storageinvolve inexpensive technology. On the basis ofthese considerations, 14 new natural gas-basedplants producing methanol for export were builtfrom 1974 to 1985 [128]. The largest single trainplant based on this concept is located at PuntaArenas in southern Chile; it came on streamin 1988 and has an output of 750 000 t/a. As aconsequence of this development, older metha-nol plants in industrialized countries such as theUnited States, Japan, and the Federal Republicof Germany have been shut down. The shift incapacities is illustrated in Figure 7.

Since a close relationship between supply anddemand no longer exists, large price fluctuationsoccur, which are hardly justified by actual mar-ket conditions. This makes long-term price fore-casts impossible and increases economic risksfor new projects.

Figure 7. Distribution of existing and planned productioncapacity for methanol according to region [127]

11. Toxicology and OccupationalHealth

11.1. Toxicology

Human Toxicology. Thefirst accounts of thepoisonous action of “methylated spirits” were

Methanol 21

published in 1855 [129]. However, the numberof cases of poisoning increased only after theproduction of a low-odor methanol. In 1901, DeSchweinitz reported the first cases of industrialpoisoning [130].

Liquidmethanol is fully absorbed via the gas-trointestinal tract [131] and the skin [132] (ab-sorption rate, 0.19mg cm−2min−1). Methanolvapor is taken up in an amount of 70 – 80% bythe lungs [133]. The compound is distributedthroughout body fluids and is largely oxidized toformaldehyde and then to formic acid [134]. Itis eliminated unchanged through the lungs [132]and in the urine. Elimination half-life is ca. 2 –3 h.

The metabolism of methanol to formic acidin humans and primates is catalyzed by the en-zyme alcohol dehydrogenase in the liver. Thisenzyme can be inhibited competitively by etha-nol. Formic acid is oxidized to carbon dioxideand water in the presence of folic acid. Becausefolic acid is not available in sufficient amountin primates, formic acid may accumulate in thebody. This leads to hyperacidity of the blood(acidosis), which is ultimately responsible formethanol poisoning [134].

The symptoms of methanol poisoning do notdepend on the uptake route ( percutaneous, in-halational, oral) and develop in three stages. Aninitial narcotic effect is followed by a symptom-free interval lasting 10 – 48 h. The third stagebegins with nonspecific symptoms such as ab-dominal pain, nausea, headache, vomiting, andlassitude, followed by characteristic symptomssuch as blurred vision, ophthalmalgia, photo-phobia, and possibly xanthopsia. Depending onthe amount of methanol, individual sensitivity,and the time when treatment is initiated, vi-sual disturbances can either improve or progresswithin a few days to severe, often irreversibleimpairment of sight or even to blindness [136–139]. The symptoms are accompanied by in-creasing hyperacidity of the blood due to theaccumulation of formic acid, with disturbancesin consciousness, possibly deep coma, and in se-vere cases, death within a few days. The lethaldosage is between 30 and 100mL per kilo-gram of body weight. Sensitivity to methanolvaries widely, however. Cases have been re-ported in which no permanent damage occurredafter drinking relatively large amounts of meth-anol (200 or 500mL) [135], [140]; in another

case, however, irreversible blindness resulted af-ter consumption of 4mL [141].

The treatment of acute oral methanol poison-ing [137] should be initiated as quickly as pos-sible with the following measures:

1) Administration of ethanol: In suspectedcases of methanol poisoning, 30 – 40mL ofethanol (e.g., 90 – 120mL of whiskey) is ad-ministered immediately as a prophylactic be-fore the patient is referred to a hospital. Be-cause ethanol has a greater affinity for alco-hol dehydrogenase than methanol, oxidationof methanol is inhibited; the production offormaldehyde and formic acid from metha-nol is thus suppressed.

2) Gastric lavage3) Hemodialysis4) Treatment with alkali: sodium bicarbonate is

infused to control blood hyperacidity.5) Administration of CNS stimulants (analep-

tics)6) Drinking larger volumes of fluid7) Eye bandage: the eyes should be protected

against light8) The patient should be kept warm

Methanol has a slight irritant action on theeyes, skin, and mucous membranes in humans.Concentrations between 1500 and 5900 ppm areregarded as the threshold value of detectableodor.

Chronic methanol poisoning is characterizedby damage to the visual and central nervoussystems. Case histories [142], [143] have notbeen sufficiently documented; whether poison-ing is caused by chronic ingestion of low dosesor ingestion of intermittently high (subtoxic)amounts is uncertain.

Animal Toxicology. Experiments on ani-mals have shown that methanol does not causeacidosis or eyedamage innonprimates (e.g., rats,mice); it generally has a narcotic, possibly lethal,effect. Investigations on laboratory animals can-not, therefore, be extrapolated to humans, at leastin the higher dosage range.

In a study on reproductive toxicology, metha-nolwas administered to rats by inhalation duringpregnancy. No embryotoxic effects were foundafter exposure to 5000 ppm [144]. The authorsconclude that observance of the recommended

22 Methanol

concentrations (MAKor TLV values) offers suf-ficient protection against fetal abnormalities inhumans.

In the Ames test, the sex-linked lethal test onDrosophila melanogaster and the micronucleustest in mice, methanol was not mutagenic [145],[146].

11.2. Occupational Health

No special precautions need be taken when han-dling methanol because it is not caustic, corro-sive, or particularly harmful environmentally. Ifmethanol is released under normal conditions,no danger exists of buildup of acutely toxic con-centrations in the atmosphere. (Chronic poison-ing via the respiratory tract or oral ingestion isdescribed in Section 1.) However, absorptionthrough the skin does constitute a danger, andmethanol should be prevented from coming indirect contact with skin.

Appropriate workplace hygiene measuresshould be adopted if methanol is handled con-stantly. Rooms in which methanol is storedor handled must be ventilated adequately.The TLV–TWA value (skin) is 200 ppm(262mg/m3), and the TLV–STEL value is250 ppm (328mg/m3). The MAK value is200 ppm (270mg/m3). Gas testing tubes can beused to measure the concentration in air. Thepeak limit should correspond to category II,1: i.e., the MAK value may be exceeded by amaximum of 100% for 30min, four times pershift [146]. Respirators must be worn if sub-stantially higher concentrations are present. Fil-ter masks (filter A, identification color brown)can be used only for escape or life-saving pur-poses because they are exhausted very quickly.Respirators with a self-contained air supply andheavy-duty chemical protective clothing shouldbe used for longer exposures to high methanolconcentrations (> 0.5 vol%).

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