Part I Overview of Methanol I. Definition and Classification of Methanol Methanol, also known as xylol or methyl alcohol, with the chemical formula CH3-OH, is a colorless, slightly mellow volatile liquid, soluble in water, highly soluble in gasoline, toxic and flammable, and its vapor and air can form an explosive mixture. Methanol is one of the important chemicals produced from syngas. It is not only an important chemical raw material, but also a fuel.
In general, methanol can be divided into industrial methanol, fuel methanol and denatured methanol. At present, industrial methanol is mainly used. All products synthesized with coal, tar, natural gas, light oil, heavy oil, etc. as raw materials, whose quality indicators meet the requirements of the national standard GB 338-2004, are industrial methanol. With the development and utilization of renewable resources, methanol can also be synthesized by gasification of crop straw, fast-growing trees and forest waste, urban organic waste, etc. The anhydrous methanol used as fuel after dehydration and refining of crude methanol is called fuel methanol. As fuel methanol is only required to be combustible and anhydrous, it is generally not added with denaturant, and the cost is often lower than industrial methanol. Denatured methanol refers to fuel methanol or industrial methanol added with methanol denaturant. Because methanol is not miscible with gasoline and diesel oil, and stratification (phase separation) occurs especially in low temperature and humid environment, the engine cannot work normally. Therefore, fuel methanol (or industrial methanol) can be added to gasoline and diesel oil for use after denaturation. The denatured fuel methanol is a methanol specially used for blending methanol gasoline for vehicles after adding a certain proportion of methanol gasoline additive for vehicles to industrial methanol. 2、 Physical and chemical properties of methanol Alcohol is composed of hydrocarbon group and hydroxyl group. According to the type of hydrocarbon group, alcohols can be divided into saturated alcohols, unsaturated alcohols, alicyclic alcohols and aromatic alcohols. According to the number of hydroxyl groups in alcohol molecule, it can be divided into monohydric alcohol, binary alcohol and ternary alcohol. Diols and above are collectively referred to as polyols. Methanol is the simplest monobasic saturated alcohol among organic alcohols.
Methanol is a colorless, transparent, flammable and volatile toxic liquid with a slight alcohol smell. The molecular weight is 32.04, the relative density is 0.792 (20/4 ℃), the melting point is - 97.8 ℃, the boiling point is 64.5 ℃, the flash point is 12.22 ℃, the spontaneous ignition point is 463.89 ℃, the vapor density is 1.11, the vapor pressure is 13.33KPa (100mmHg 21.2 ℃), and the explosion limit of the vapor and air mixture is 6.0% - 36.5% (volume). It is miscible with water, ethanol, ether, benzene, ketone, halogenated hydrocarbon and many other organic solvents, and easy to burn when exposed to heat, open flame or oxidant. The combustion reaction formula is:. Methanol is smokeless and the flame is blue.
Methanol has a relatively active chemical property and has the general property of aliphatic primary alcohol. It can undergo chemical reactions such as oxidation, esterification, carbonylation, etc. The three hydrogen atoms on the carbon atom connected with hydroxyl can be oxidized one by one, or dehydrogenated to generate formaldehyde, and then oxidized to formic acid. The final products of formic acid oxidation are carbon dioxide and water. Methanol is not acidic, and its molecular composition is not alkaline, although it has hydroxyl groups that can be used as alkaline characteristics. It is neutral to phenolphthalein and litmus. The reagent methanol is usually sealed and stored in a brown bottle in a cooler place.
Methanol can cause poisoning when absorbed through respiratory tract, gastrointestinal tract and skin. The main health hazard of methanol is its anesthetic effect on the central nervous system; It has special selective effect on optic nerve and retina, causing pathological changes; It may cause metabolic acidosis. The normal allowable concentration in the air is 5mg/m3. Methanol industrial wastewater can only be discharged after treatment, and the allowable content of methanol after treatment shall not be greater than 200mg/L. When working on the site with methanol steam for a short time, wear gas masks, rubber gloves, protective glasses and other safety equipment. The packaging containers shall be marked with "flammable liquid", "with drugs" and other dangerous goods. 3、 Methanol production process The main raw materials for methanol production are carbon monoxide and hydrogen. The conversion process does not produce any by-products, and there is no pollutant emission.
Since the industrial production began in 1923, the raw material route of methanol synthesis has undergone great changes. Before the 1950s, coal and coke were mostly used as raw materials; After 1950s, methanol production process with natural gas as raw material was widely used; Since the 1960s, methanol plants with heavy oil as raw material have developed. At present, countries in Europe, the United States and the Middle East mainly use natural gas as raw material to produce methanol. This process has the advantages of low investment and pollution-free, and it does not need to consider the sales of by-products too much. As China's primary energy structure is characterized by "rich coal, poor oil and little gas", it lacks cheap natural gas resources. At the same time, with the shortage of oil resources and the continuous rise of oil prices, under the background of vigorously developing clean coal utilization technology, coal is still the most important raw material for methanol production in China at present and for a long time to come. In addition, some enterprises in China use coke oven gas as raw material to produce methanol, which is also a unique methanol production technology in China.
In 2010, the capacity of methanol plants with coal as raw material accounted for 63% of the total domestic capacity, 21.2% with natural gas as raw material, and 15.8% with coke oven gas as raw material.
In the coal to methanol process, coal and oxygen from the air are used to produce raw gas with high CO content in the gasifier. The raw gas is added according to a certain hydrocarbon ratio, and the excess and sulfide are removed by the purification process to obtain methanol syngas. Then, the water containing crude methanol is produced through compression, synthesis and other processes, and the product methanol is refined through the rectification process.
The production process of methanol from natural gas mainly consists of pre conversion, conversion, compression, synthesis and rectification units. After the natural gas is pre converted and desulfurized, it is only necessary to adjust the appropriate water carbon ratio, and the converted syngas will meet the requirements of methanol synthesis. Therefore, the natural gas to methanol process has reliable technology, short process, few equipment and simple operation, which is suitable for the construction of large or ultra large methanol plants.
At present, China is the only country in the world that uses coke oven gas to produce methanol on a large scale. The key technology of methanol production from coke oven gas is to convert methane and a small amount of multi carbon hydrocarbons in coke oven gas into carbon monoxide and hydrogen. The basic process is that the coke oven gas is first compressed under low pressure, and then the organic sulfur is added and converted into inorganic sulfur. After fine desulfurization, the hydrocarbon in the coke oven gas is pressurized and catalysed for partial oxidation, so that it can be converted into CO and crude methanol is synthesized under pressure, and the product methanol is produced through rectification.
4、 Methanol use Methanol is an important organic chemical raw material, which is widely used to produce formaldehyde, dimethyl ether, acetic acid, methyl tert butyl ether (MTBE), dimethyl formamide (DMF), methylamine, methyl chloride, dimethyl terephthalate, methyl methacrylate, and synthesis rubber And a series of organic chemical products; Methanol is not only an important chemical raw material, but also an excellent energy and vehicle fuel. It can be blended with gasoline or used as a power fuel instead of gasoline; In recent years, the technology of methanol to olefin has been paid more and more attention; Methanol is also the raw material for producing trichlorfon, parathion methyl, carbendazim and other pesticides; Methanol protein can be produced by biological fermentation of methanol and used as feed additive. In addition, in recent years, with the development of C1 chemistry, the process routes such as the synthesis of ethylene glycol, acetaldehyde, and ethanol from methanol (now mostly from ethylene) are getting more and more attention.
