Methanol (CH3OH) can be used as a transportation fuel, either pure (M100) or as an 85% blend (M85), or transformed to diesel, ethanol, or gasoline. But currently, its major use is as a key building block (intermediate) chemical that is used to produce other industrial organic chemicals such as formaldehyde (35% of global methanol production), methyl tert-butyl ether (MTBE) (25% of production), acetic acid (9% of production), and the remainder for other chemicals such as dimethyl ether, methyl amines, methyl halides.
Methanol synthesis is a well-developed commercial process with high activity and very high selectivity (>99%). Today, world methanol production is almost exclusively (90%) produced from syngas, a gaseous mixture consisting of primarily carbon monoxide (CO) and hydrogen (H2). Syngas is produced from the gasification of feedstocks in excess of 1100°F under conditions where the amounts of oxygen (from air, pure oxygen, or steam) are less than what is needed for complete combustion. In principle, syngas can be produced from any hydrocarbon (chemical composed of hydrogen and carbon molecules) feedstock, including natural gas, petroleum products, coal, and biomass.
Formaldehyde
Formaldehyde is combined with phenol, urea, or melamine to make resins used in the manufacture of various construction board products, and its demand is driven by the construction industry. Formaldehyde is produced by dehydrogenating and partially oxidating methanol.
Commercial production of formaldehyde uses one of three industrial processes: (1) the BASF process (uses air in the presence of a silver crystals, steam, and excess methanol; 1280-1354°F; conversion rate of methanol to formaldehyde of 97-98%), (2) a variation of the BASF process (uses crystalline silver; 1138-1228°F; the unreacted methanol is recycled; conversion rate of 77-87%), and (3) the Formox process (oxidation with a lean methanol-air mixture; iron/molybdenum/vanadium oxide catalyst; conversion rate of 98-99%).
The estimated costs of production for each process are $378, $407, and $387/tonne respectively ($0.17/lb, $0.19/lb and $0.18/lb respectively). The price of formaldehyde (January, 2003) was $463/tonne ($0.21/lb).
Methyl tertiary-butyl ether (MTBE)
MTBE is used primarily (95%) as an oxygenate in gasoline, with North America consuming about 65% of global production. U.S. consumption of MTBE increased substantially following the Clean Air Act Amendments of 1990 but recent environmental concerns are leading states to phase out use of the additive. MTBE is also used in the petrochemical industry to produce isobutene, methacrolein, methycrylic acid, isoprene, and industrial solvents.
MTBE is produced by reacting isobutene with methanol in the presence of an acidic catalyst. Conversion yields of up to 90% can be achieved at optimum reaction conditions. Most commercial reactors are similar and consist of a reaction and a refining section.
MTBE is produced by refinery/petrochemical plants, by merchant plants, and by tertiary butyl alcohol (TBA) plants. Capital costs for MTBE facilities range from $6,000 to $28,000/BPD of capacity depending on process. Currently, there are over 140 MTBE plants with a total installed capacity of about 20 million tonnes/year (44 billion pounds/year). From 1980 to 2001, the average price for MTBE fluctuated between $0.63/gallon (1998) and $1.27/gallon (1981).
Acetic Acid
The third most abundant chemical synthesized from methanol is acetic acid. Acetic acid is used to produce a number of other chemicals such as vinyl acetate (used to make latex emulsion resins for paints, adhesives, paper coatings, and textile finishing agents), acetic anhydride (used to make cellulose acetate fibers and cellulosic plastics), and terephthalic acid (used to make polyester). In 1999, the world demand for acetic acid was 6.17 billion lb and the price was $0.45/lb (in January 2003).
Nearly one-half of the global production of acetic acid is produced from methanol and that share is expected to increase in the future. Two commercial processes are used: (1) the BASF process (cobalt-iodine catalyst, 250°C, 500-700 atm; 90% selectivity), and (2) the Monsanto process (rhodium-iodine catalyst; 382°F; 30-40 atm; 99% selectivity). The Monsanto process has displaced the BASF process and since 1973, all new installed capacity has used it. However, the high cost of the rhodium catalyst has lead to the search for other, lower cost, catalysts.
Synthetic fuels
Methanol can be used to produce synthetic gasoline, synthetic diesel fuel, and olefins (alkenes;CnH2n).
The Methanol to Gasoline (MTG) process was developed by Mobil Oil and involves the conversion of methanol to hydrocarbons using zeolite catalysts. Crude methanol is first super-heated, partially dehydrated, mixed with heated recycled syngas, and then introduced into a reactor containing a ZSM-5 zeolite catalyst (688-716°F; 19-23 atm) to produce hydrocarbons (44%) and water (56%). The process usually involves multiple gasoline conversion reactors in parallel because the zeolites have to be frequently regenerated. The selectivity to gasoline is greater than 85% with the remainder of the product being primarily liquid petroleum gas (LPG). The process results in a high quality gasoline with a high octane number, but it also contains significant quantities (~ 40%) of aromatics (cyclic unsaturated hydrocarbons) consisting of benzene compounds (20%), toluene (26%), xylene (43%), and other (12%)) which are limited under the 1990 Clean Air Act Amendments. A commercial facility was built in New Zealand in 1985, using natural gas, but currently produces methanol rather than gasoline. The estimated capital cost (14,450 BPD capacity) was $767 million dollars (mid-1980) with a total project cost of $1,475 million dollars (1985). Production cost (including a return on investment) was estimated to be $0.96/gallon. The MTG product has nearly the same automobile exhaust emissions as gasoline from petroleum.
The methanol to olefins (MTO) process optimizes the production of light olefins which are produced as intermediates in the MTG process.
Higher reaction temperatures (~960°F), lower pressures, and lower catalyst (acidity) activity favors light olefin production (compounds with fewer than 4-5 carbons). The rate of olefin production can be modified so that 80% of the product consists of C2 to C5 olefins rich in propylene (32%) and butenes (20%) with an aromatic rich C5+ gasoline fraction (36%). The process can also be modified to produce high yields of ethylene and propylene (>60%).
In the methanol to gasoline and diesel (MOGD) process, olefins produced in the MTO process undergo further reactions to produce a gasoline product consisting of 3 wt% paraffins, 94 wt% olefins, 1 wt% napthenes, and 2 wt% aromatics. The selectivity of gasoline and distillate from olefins is greater than 95%. Neither the MTO nor the MOGD process is currently commercial. The estimated costs of producing olefins via the MTO process, and gasoline via the MTG process are $0.45/gal and $0.59/gal respectively for a natural gas price of $0.47/GJ ($0.50/MBtu).
UOP and HYDRO of Norway license their process to produce ethylene and propylene from methanol-derived olefins. The process uses a fluidized bed reactor at 778–868°F and achieves an 80% carbon selectivity to olefins and nearly complete methanol conversion. The operating parameters can be adjusted so that either more ethylene or more propylene is produced.
The Topsoe Integrated Gasoline Synthesis (TIGAS) process (developed by Haldor Topsoe) seeks to reduce the capital and energy costs of producing gasoline by integrating methanol synthesis with the methanol to gasoline (MTG) step into a single loop without isolating methanol as an intermediate. The TIGAS process involves modified catalysts and conditions so that the same pressure can be used throughout the process, eliminating the need for separate compression steps for syngas production, methanol synthesis, and MTG production.
A 1 MTPD (metric tons per day; tonnes/day) demonstration plant was built in Houston, Texas in 1984 and operated for 3 years with a gasoline yield (amount of gasoline produced divided by the amount of natural gas feed and fuel) of 56.5 wt%. However, the process yields a lower quality gasoline with a lower octane number compared to the MTG product.
Dimethyl ether (DME)
DME is used to produce dimethyl sulfate, an aerosol propellant. DME could also potentially be used as a diesel fuel or as a cooking fuel, a refrigerant, or a chemical feedstock. Commercial production of DME originated as a byproduct of high-pressure methanol production. It is produced by first synthesizing methanol from syngas and then dehydrating it using an acid catalyst at methanol synthesis pressue and temperature conditions. The optimum hydrogen to carbon monoxide ratio for DME synthesis is around one. Recent improvements to the DME synthesis process involve the development of bifunctional catalysts to produce DME in a single step (i.e., one reactor), and the use of a slurry reactor for liquid phase dimethyl ether (LPDME) synthesis. At a natural gas cost of $0.6/MMBTU, the estimated cost of producing DME is $0.67/gallon.
Methanol fuels (M100 and M85)
Neat methanol (M100) can be used as a transportation fuel in place of petroleum gasoline. It has a high heat of vaporization and relatively low heating value (about half of gasoline) that leads to a lower flame temperature compared to gasoline. This results in lower CO, NOx, and hydrocarbons emissions, but higher formaldehyde emissions. Methanol is miscible in water and in low concentration methanol mixtures, phase separation can occur. Methanol is more corrosive than gasoline, but less toxic and is not carcinogenic. Methanol was used as a gasoline blending agent prior to a mid-1980s U.S. EPA prohibition against its use.
Currently, M100 is used as a fuel only in high-performance racing engines and airplanes that have been fully modified and adapted to operate on methanol (i.e., replacement of plastic components in the fuel system, modified carburetor or fuel injection system, and preheating the fuel mixture). The most common use of methanol as a fuel is M85 (a mixture of 85 vol% methanol and 15 vol% gasoline). The addition of gasoline provides color to the flame in case of fire (methanol flames are colorless) and reduces winter cold start problems and summer vapor lock. When used in spark engines, higher methanol/gasoline blend ratios result in lower exhaust emissions of CO, HC, and NOx, and the addition of tertiary butyl alcohol (TBA) and methanol to gasoline may reduce CO emissions by up to 40% and hydrocarbon emissions by up to 20% compared to conventional gasoline. Although automobiles have been manufactured that operate on M85 and some fleets continue to use M85, this fuel has failed to develop on a large-scale. Contributing factors include adverse consumer perceptions coupled with a lack of sufficient infrastructure to handle M85.
M100 is being targeted for use in direct methanol fuel cells (DMFC) which allow the use of methanol as the fuel without requiring a fuel processor to extract hydrogen from the methanol. Significant progress has been made and DaimlerChrysler and Honda both have prototype direct methanol fuel cell vehicles.