Moderatelytoxic for small animals – Highly toxic to large animals and humans (in high concentrations) – May be fatal/lethal or causeblindness and damage to theliver,kidneys, andheart if swallowed –Toxicity effects from repeated over exposure have an accumulative effect on thecentral nervous system, especially theoptic nerve –Symptoms may be delayed, become severe after 12 to 18 hours, and linger for several days after exposure[9]
Small amounts of methanol are present in normal, healthy human individuals. One study found a mean of 4.5 ppm in the exhaled breath of test subjects.[19] The mean endogenous methanol in humans of 0.45 g/d may be metabolized frompectin found in fruit; one kilogram of apple produces up to 1.4 g of pectin (0.6 g of methanol.)[20]
Methanol is also found in abundant quantities in star-forming regions of space and is used in astronomy as a marker for such regions. It is detected through its spectral emission lines.[23]
In theirembalming process, theancient Egyptians used a mixture of substances, including methanol, which they obtained from thepyrolysis of wood. Pure methanol, however, was first isolated in 1661 byRobert Boyle, when he produced it via the distillation ofbuxus (boxwood).[27] It later became known as "pyroxylic spirit". In 1834, the French chemistsJean-Baptiste Dumas andEugene Peligot determined its elemental composition.[28]
They also introduced the word "methylène" to organic chemistry, forming it fromGreekmethy = "alcoholic liquid" +hȳlē = "forest, wood, timber, material". "Methylène" designated a"radical" that was about 14% hydrogen by weight and contained one carbon atom. This would beCH2, but at the time carbon was thought to have anatomic weight only six times that of hydrogen, so they gave the formula as CH.[28] They then called wood alcohol (l'esprit de bois) "bihydrate de méthylène" (bihydrate because they thought the formula wasC4H8O4 or(CH)4(H2O)2). The term "methyl" was derived in about 1840 byback-formation from "methylene", and was then applied to describe "methyl alcohol". This was shortened to "methanol" in 1892 by theInternational Conference on Chemical Nomenclature.[29] Thesuffix-yl, which, inorganic chemistry, forms names ofcarbon groups, is from the wordmethyl.
French chemistPaul Sabatier presented the firstprocess that could be used to produce methanol synthetically in 1905. This process suggested that carbon dioxide and hydrogen could be reacted to produce methanol.[9] German chemistsAlwin Mittasch and Mathias Pier, working forBadische-Anilin & Soda-Fabrik (BASF), developed a means to convertsynthesis gas (a mixture ofcarbon monoxide,carbon dioxide, andhydrogen) into methanol and received a patent. According to Bozzano and Manenti, BASF's process was first utilized inLeuna, Germany in 1923. Operating conditions consisted of "high" temperatures (between 300 and 400 °C) and pressures (between 250 and 350 atm) with azinc/chromium oxide catalyst.[30]
US patent 1,569,775 was applied for on 4 September 1924 and issued on 12 January 1926 to BASF;[31] the process used achromium andmanganese oxidecatalyst with extremely vigorous conditions: pressures ranging from 50 to 220atm, and temperatures up to 450 °C. Modern methanol production has been made more efficient through use of catalysts (commonly copper) capable of operating at lower pressures. The modern low pressure methanol (LPM) process was developed byICI in the late 1960s with the technology patent long since expired.[32]
DuringWorld War II, methanol was used as a fuel in several German military rocket designs, under the nameM-Stoff, and in a roughly 50/50 mixture withhydrazine, known asC-Stoff.
The use of methanol as a motor fuel received attention during theoil crises of the 1970s. By the mid-1990s, over 20,000 methanolflexible fuel vehicles (FFVs) capable of operating on methanol or gasoline were introduced in the US. In addition, low levels of methanol were blended in gasoline fuels sold in Europe during much of the 1980s and early-1990s. Automakers stopped building methanol FFVs by the late-1990s, switching their attention to ethanol-fueled vehicles. While the methanol FFV program was a technical success, rising methanol pricing in the mid- to late-1990s during a period of slumping gasoline pump prices diminished interest inmethanol fuels.[33]
Condensation of methanol to producehydrocarbons and evenaromatic systems is the basis of several technologies related togas to liquids. These include methanol-to-hydrocarbons (MtH), methanol to gasoline (MtG), methanol to olefins (MtO), and methanol to propylene (MtP). These conversions are catalyzed byzeolites asheterogeneous catalysts. The MtG process was once commercialized atMotunui in New Zealand.[36][37]
TheEuropean Fuel Quality Directive allows fuel producers to blend up to 3% methanol, with an equal amount of cosolvent, with gasoline sold in Europe. In 2019, it is estimated thatChina used as much as 7 million tons of methanol as transportation fuels, representing over 5% of their fuel pool.[38]
Methanol is a promisingenergy carrier because, as a liquid, it is easier to store than hydrogen and natural gas. Itsenergy density is, however, lower thanmethane, per kg. Its combustion energy density is 15.6MJ/L (LHV), whereas that of ethanol is 24 and gasoline is 33 MJ/L.
Further advantages for methanol is its ready biodegradability and low environmental toxicity. It does not persist in either aerobic (oxygen-present) or anaerobic (oxygen-absent) environments. The half-life for methanol in groundwater is just one to seven days, while many common gasoline components have half-lives in the hundreds of days (such asbenzene at 10–730 days). Since methanol ismiscible with water and biodegradable, it is unlikely to accumulate in groundwater, surface water, air or soil.[41]
Methanol is occasionally used to fuelinternal combustion engines. It burns forming carbon dioxide and water:
2 CH3OH + 3 O2 → 2 CO2 + 4 H2O
Methanol fuel has been proposed for ground transportation. The chief advantage of a methanol economy is that it could be adapted to gasoline internal combustion engines with minimum modification to the engines and to the infrastructure that delivers and stores liquid fuel. Its energy density, however, is less than gasoline, meaning more frequent fill ups would be required. However, it is equivalent to super high-octane gasoline in horsepower, and most modern computer-controlled fuel injection systems can already use it.[42]
Methanol is an alternative fuel for ships that helps the shipping industry meet increasingly strict emissions regulations. It significantly reduces emissions ofsulfur oxides (SOx),nitrogen oxides (NOx) and particulate matter. Methanol can be used with high efficiency in marine diesel engines after minor modifications using a small amount of pilot fuel (dual fuel).[43][44]
In China, methanol fuels industrial boilers, which are used extensively to generate heat and steam for various industrial applications and residential heating. Its use is displacing coal, which is under pressure from increasingly stringent environmental regulations.[45]
Direct-methanol fuel cells are unique in their low temperature, atmospheric pressure operation, which lets them be greatly miniaturized.[46][47] This, combined with the relatively easy and safe storage and handling of methanol, may open the possibility of fuel cell-poweredconsumer electronics, such as laptop computers and mobile phones.[48]
Methanol is also a widely used fuel in camping and boating stoves. Methanol burns well in an unpressurized burner, so alcohol stoves are often very simple, sometimes little more than a cup to hold fuel. This lack of complexity makes them a favorite of hikers who spend extended time in the wilderness. Similarly, the alcohol can be gelled to reduce risk of leaking or spilling, as with the brand "Sterno".
Methanol is mixed with water and injected into high performance diesel and gasoline engines for an increase of power and a decrease in intake air temperature in a process known aswater methanol injection.
Methanol is used as adenaturant for ethanol, the product being known asdenatured alcohol ormethylated spirit. This was commonly used during theUS prohibition to discourage consumption ofbootlegged liquor, and ended up causing several deaths.[49]
It is sometimes used as a fuel in alcohol lamps, portable fire pits and camping stoves.
Carbon monoxide and hydrogen react over a catalyst to produce methanol. Today, the most widely used catalyst is a mixture of copper andzinc oxides,supported onalumina, as first used byICI in 1966. At 5–10 MPa (50–100 atm) and 250 °C (482 °F), the reaction
CO + 2 H2 → CH3OH
is characterized by high selectivity (>99.8%). The production ofsynthesis gas from methane produces threemoles of hydrogen for every mole of carbon monoxide, whereas the synthesis consumes only two moles of hydrogen gas per mole of carbon monoxide. One way of dealing with the excess hydrogen is to injectcarbon dioxide into the methanol synthesis reactor, where it, too, reacts to form methanol according to the equation
CO2 + 3 H2 → CH3OH + H2O
In terms of mechanism, the process occurs via initial conversion of CO intoCO2, which is thenhydrogenated:[54]
which is the same as listed above. In a process closely related to methanol production from synthesis gas, a feed of hydrogen andCO2 can be used directly.[55] The main advantage of this process is thatcapturedCO2 and hydrogen sourced fromelectrolysis could be used, removing the dependence on fossil fuels.
The catalytic conversion of methane to methanol is effected by enzymes includingmethane monooxygenases. These enzymes are mixed-function oxygenases, i.e. oxygenation is coupled with production of water[56] andNAD+:[57]
CH4 + O2 + NADPH + H+ → CH3OH + H2O + NAD+
Both Fe- and Cu-dependent enzymes have been characterized.[57] Intense but largely fruitless efforts have been undertaken to emulate this reactivity.[58][59] Methanol is more easily oxidized than is the feedstock methane, so the reactions tend not to be selective. Some strategies exist to circumvent this problem. Examples includeShilov systems and Fe- and Cu-containing zeolites.[60] These systems do not necessarily mimic the mechanisms employed bymetalloenzymes, but draw some inspiration from them. Active sites can vary substantially from those known in the enzymes. For example, a dinuclear active site is proposed in thesMMO enzyme, whereas a mononuclear iron (alpha-oxygen) is proposed in the Fe-zeolite.[61]
Global emissions of methanol by plants are estimated at between 180 and 250 million tons per year.[62] This is between two and three times larger than man-made industrial production of methanol.
As of 2023, 0.2% of global methanol production is produced in ways that have relatively low greenhouse gas emissions; this is known as "green" methanol.[63] Most green methanol is produced from gasification ofbiomass.[63]Syngas is produced from biomassgasification and further converted into green methanol.[64]
Another method of producing green methanol involves combining hydrogen, carbon dioxide, and a catalyst under high heat and pressure.[63] To be classified as green methanol, the hydrogen must beproduced using renewable electricity,[63] and the carbon dioxide must be fromcarbon capture and storage,direct air capture or biomass of recent origin.[63] Some definitions of green methanol specify that the carbon dioxide must be captured during the burning ofbioenergy.[65]
Methanol is available commercially in various purity grades. Commercial methanol is generally classified according to ASTM purity grades A and AA. Both grade A and grade AA purity are 99.85% methanol by weight. Grade "AA" methanol contains trace amounts of ethanol as well.[30]
Methanol for chemical use normally corresponds to Grade AA. In addition to water, typical impurities includeacetone and ethanol (which are very difficult to separate by distillation). UV-vis spectroscopy is a convenient method for detecting aromatic impurities. Water content can be determined by theKarl-Fischer titration.
Methanol is highly flammable. Its vapours are slightly denser than air and can travel to a distant ignition source and ignite. Methanol fires should be extinguished withdry chemical,carbon dioxide, water spray or alcohol-resistant foam.[12] Methanol flames are invisible in daylight.
Ingesting as little as 10 mL (0.34 US fl oz) of pure methanol can cause permanent blindness by destruction of theoptic nerve. 30 mL (1.0 US fl oz) is potentially fatal.[66] The median lethal dose is 100 mL (3.4 US fl oz),i.e., 1–2 mL/kg body weight of pure methanol.[67][contradictory] Thereference dose for methanol is 0.5 mg/kg in a day.[68][69] Toxic effects begin hours after ingestion, and antidotes can often prevent permanent damage.[66] Because of its similarities in both appearance and odor toethanol (the alcohol in beverages) orisopropyl alcohol, it is difficult to differentiate between the three.[70]
Outbreaks of methanol poisoning have occurred primarily due to contamination ofdrinking alcohol. It is also worth noting that ethanol is a natural antidote to methanol poisoning.[74] Contaminated batches of alcohol contained a much higher concentration of methanol than ethanol, which did not provide a sufficient dose of the antidote and caused it to be ineffective. This is more common in thedeveloping world.[75] In 2013 more than 1700 cases nonetheless occurred in the United States. Those affected are often adult men.[76] Outcomes may be good with early treatment.[77] Toxicity to methanol was described as early as 1856.[78]
Because of its toxic properties, methanol is frequently used as a denaturant additive for ethanol manufactured for industrial uses. This addition of methanol exempts industrial ethanol (commonly known as "denatured alcohol" or "methylated spirit") from liquorexcise taxation in the US and other countries.
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