Methanol is emitted into the atmosphere from a number of natural sources, including volcanoes, vegetation, microbes, insects, animals and decomposing organic matter . The anthropogenic (human-caused) release of methanol into the environment is presently mainly due to its use as a solvent through evaporation. Releases to the water and ground are less significant. In the environment, methanol is readily degraded by photooxidation and biodegradation processes. This is, beside other reasons, why methanol is widely used for example in windshield washer fluids. Methanol is rapidly degraded under both aerobic (in the presence of air) and anaerobic conditions (in the absence of air) in fresh and salt water, groundwater, sediments and soils with no evidence of bioaccumulation. It is a regular growth substrate (source of carbon and energy) for many microorganisms which are found in the ground and are able to degrade methanol to CO2 and water. Methanol is of low toxicity to aquatic and terrestrial organisms, and effects due to environmental exposure to methanol are unlikely to be of consequence under normal conditions . In fact, methanol is used for the deni-trification of wastewater in sewage treatment plants. The addition of methanol in this process accelerates the conversion of nitrates to harmless nitrogen gas by anaerobic bacteria. If discharged in large quantities, nitrates can accumulate in rivers, lakes, oceans and have devastating effects on the water ecosystem. Excess nitrogen from nitrates causes an overgrowth of algae, and this prevents oxygen and sunlight from penetrating deeply into the water; the result is often suf focation of the fish and all aquatic life below. Currently, more than 100 wastewater treatment plants across the United States use methanol in their denitrification process. The Blue Plains Wastewater Treatment Facility, which serves the Washington D.C. area, is one of the largest such treatment plants in the country, and by using methanol denitrification avoids the release each day of some 10 tonnes of nitrogen into the Potomac River .
The accidental release of methanol into the environment during its production, transportation and storage - although possible - would cause much less damage than a corresponding crude oil or gasoline spill, due to the above-mentioned favorable chemical and physical properties of methanol. A large accidental methanol spill into surface water would have some immediate impact on the ecosystem in close proximity to the spill. However, since the methanol is totally miscible with water it would rapidly be diluted and dissipated into the environment by wave action, winds or tides to non-toxic levels. It has been calculated that the release of 10 000 tonnes of methanol into the open sea would result in a concentration of only 0.36% within the first hour of the spill, and this would be much less during the following hours . At this point, biodegradation through microorganisms would take care of the dilute methanol in a matter of days. A similar accident involving petroleum oil, which is not miscible with water, covers large surfaces and does not easily dissipate into the environment, would most likely lead to an ecological disaster. Methanol, in leaving no residues, also avoids the long and fastidious cleaning of beaches, shorelines, birds and wild life needed after a crude oil spill. On land, the accidental release from a tank truck or rail car transporting methanol, or from an underground storage tank, are possible scenarios. Depending on the size and location of the spill, different situations might be encountered, but in most cases the miscibility of methanol with water should allow it to be diluted and the effects to be dispersed rapidly, allowing also rapid biodegradation by microorganisms present in the ground. It should also be pointed out that the behavior of methanol in the environment is very different from that of MTBE, which is not easily degraded, and explains the reason for its ban as an oxygenated additive for transportation fuels . Methanol leaks are also less hazardous than gasoline leaks because the latter contains many toxic and carcinogenic compounds (e.g., benzene) which biodegrade slowly and persist for a longer time in the environment. To further minimize the risk of leaks in underground storage, the use of double-walled storage tanks and leak detectors are preferable for all fuels.
Compared to gasoline or diesel fuel, methanol is clearly environmentally much safer and less toxic.
208 | Chapter 11 Methanol as a Fuel and Energy Carrier Methanol and Issues of Climate Change
Today, methanol is manufactured almost exclusively from syn-gas produced by catalytic reforming of natural gas or coal (i.e., from fossil fuel sources). In contrast to natural gas, our coal reserves are extensive. However, because of coal's deficiency in hydrogen, its conversion to methanol produces the most CO2 compared to all other fossil fuels, and especially natural gas. Currently, on a large scale the cleanest, most efficient and most economical way to produce methanol is from natural gas-generated syn-gas. In the area of ongoing research and development, however, much progress has been made in the direct oxidative conversion of methane to methanol (see Chapter 12). As long as natural gas is still quite abundant, it would seem inevitable that it will be used to produce methanol. It is, however, feasible to develop technologies to convert it directly to methanol without passing first through the generation of syn-gas. It should also be recognized that (as discussed in Chapter 4) there are large resources of methane hydrates tied up in vast areas of the subarctic tundras and under the seas in the areas of the continental shelves. All of these resources will eventually be utilized, but they will only extend the inevitable exhaustion of our natural hydrocarbon resources.
Using methanol produced from natural gas in traditional ICE vehicles will only moderately - if at all - reduce the CO2 emissions compared to their gasoline and diesel equivalents. Real benefits in terms of greenhouse gas emissions will be obtained only with more efficient FCVs powered by hydrogen produced from methanol reforming or the direct use of methanol in DMFC.
In order to further reduce CO2 emissions and to provide a sustainable alternative source for the long term, methanol will have to be produced from feedstocks other than fossil fuels. Production from biomass is one possibility, but this could provide only a minor portion of our growing energy needs. Methanol, however can also be obtained from CO2 by catalytic reduction with hydrogen or by electrochemical reduction in water (see Chapter 12). The flue gases of coal- and other fossil fuel-burning power plants, as well as from facilities such as cement and steel factories, contain high concentrations of CO2, and these will increasingly need to be captured and disposed of. Instead of sequestration, the chemical recycling of CO2 into methanol, besides providing useful fuels and a source for synthetic hydrocarbons will also mitigate human-caused climate changes. Eventually, the CO2 content of the atmosphere itself will be similarly recycled, freeing humankind from its dependence on fossil fuels, assuming that we will be able to produce the required energy from non-fossil fuel sources (renewable energy sources and safe atomic energy) for the production of hydrogen and conversion to methanol.
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Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.