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Overview: Methanol is one of the simplest chemicals; it is an important basic raw material in the chemical industry as well as a clean liquid fuel. It is widely used in industries such as organic synthesis, dyes, pharmaceuticals, pesticides, coatings, automobiles, and defense. Methanol was first produced by the dry distillation of wood and lignin, which is why it is commonly known as wood alcohol. During the long-term heating and carbonization process of wood, condensable and non-condensable volatile substances are produced. The condensable liquid, known as pyrolic acid, contains methanol, acetic acid, and tar. Pyrogallic acid, free from tar, can be used to separate natural methanol and acetic acid through distillation. Approximately 60–80 kg of wood is needed to produce 1 kg of methanol. This is the oldest method for producing methanol. The United States did not completely abandon this process until the early 1970s. In 1923, based on the industrialization of ammonia synthesis, Germany’s BASF company was the first to achieve industrial production of methanol from carbon monoxide and hydrogen using zinc-aluminum catalysts under high temperature and pressure conditions, thus paving the way for the industrial synthesis of methanol. The low cost and high output of industrially synthesized methanol have driven the rapid development of the methanol industry. The expansion of the methanol consumption market has further driven continuous improvements in methanol production processes, resulting in lower production costs and an increasing scale of production. In 1966, the British company ICI successfully developed a low-pressure methanol synthesis process using copper-based catalysts, and later introduced a more economical medium-pressure methanol synthesis process. Meanwhile, the German company Lurgi also successfully developed a medium and low-pressure methanol synthesis process. As the methanol synthesis process matures and scales up, the methanol industry, which encompasses both methanol production and its applications, has become an important branch of the chemical industry, playing an increasingly significant role in economic development. Physical properties: Methanol is the simplest saturated fatty acid, with the molecular formula CH3OH and a relative molecular mass of 32.04. The bonding orbitals of the carbon and oxygen atoms in a methanol molecule are sp3 hybridized orbitals with a tetrahedral structure, which overlap with each other to form a C—O bond. The O–H bond is formed by the overlap of an sp3 hybridized orbital of the oxygen atom with the 1s orbital of the hydrogen atom, while the two pairs of unshared electron pairs of the oxygen atom occupy the other two sp3 hybridized orbitals. The bonding orbitals of the methanol molecule and the tetrahedral structure of the oxygen atom are shown in Figure 1-1 ； The bond lengths and bond angles of methanol molecules are shown in Table 1-1. (a) (b) Figure 1-1: The bonding orbitals of methanol (a) and the tetrahedral structure of the oxygen atom in the methanol molecule (b). Table 1-1: Bond lengths and bond angles of the methanol molecule. Bond length / 0.1 nm; Bond angles: C—H 1.10, O—H 0.96, C—O 1.43; H—C—H 109°, H—C—O 110°, C—O—H 108°. At normal temperature and pressure, pure methanol is a colorless and transparent, volatile, flammable liquid with a slight alcoholic odor; it is also toxic. Methanol is infinitely miscible with water as well as many organic liquids such as ethanol and ether, but it is not miscible with aliphatic hydrocarbon compounds. A mixture of methanol vapor and air can form an explosive mixture, with an explosion limit of 6.0% to 36.5% (by volume). The general physical properties of methanol are shown in Table 1-2. The boiling points of methanol at different pressures and its vapor pressures at various temperatures are shown in Tables 1-3 and Table 1-4. Table 1-2 General Physical Properties of Methanol
Property Data Property Data
Density (0°C)/(g/mL) 0.8100 Autoignition point/°C 473
Relative density (d20) 0.7913 Boiling point/°C 64.5–64.7
Air 461 Melting point/°C -97.8
Critical temperature/°C 240 Flash point/°C 16
Critical pressure/Pa 79.54×105 Closed system: 12
Critical volume/(mL/mol) 117.8 Open system: 16
Critical compressibility factor 0.224 Vapor pressure at 20°C/Pa 1.2879×104
Heat of combustion/(kJ/mol) 727.038 Heat capacity of liquid (20–25°C)/2.51–2.53
Heat capacity of gas at 25°C 742.738 Viscosity at 20°C/Pa·s 5.945×10-4
Enthalpy of formation/(kJ/mol) 238.798 Heat conductivity 2.09×10-3
Surface tension at 20°C/(N/cm) 22.55×10-5 Liquid at 25°C: 201.385
Refractive index at 20°C 1.3287 Gas at 25°C: 22.55×10-5
Coefficient of expansion at 20°C 0.00119
Latent heat of vaporization at 64.7°C/(kJ/mol) 35.295
Corrosivity: Non-corrosive at room temperature, except for lead and aluminum
Heat of fusion/(kJ/mol) 3.169 Explosiveness in air/% (by volume): 6.0–36.5

Table 1-3 Boiling Point of Methanol
Pressure/mmHg Temperature/°C Pressure/mmHg Temperature/°C Pressure/atm Temperature/°C Pressure/atm Temperature/°C
1 10 20 40 -44.0 -16.2 -6.0 5.0
100 200 400 760 21.2 34.8 49.9 64.0
2 5 10 20 84 112.5 138.0 167.0
30 40 50 60 186.5 203.5 214.0 224.0
1 mmHg = 133.322 Pa, 1 atm = 101325 Pa

Table 1-4 Vapor Pressure of Methanol
Temperature/°C Vapor pressure/mmHg
-67.4 0.102
-60.4 0.212
-54.5 0.378
-48.1 0.702
-44.4 0.982
-44.0 1
-40 2
-30 4
-20 8
-10 15.5
0 29.6
10 54.7
20 100
30 200
40 300
50 400
60 500
64.7 625
70 760
80 927
90 1341
100 1897
110 2621
120 3561
130 4751
140 6242
150 8071
160 10336
170 13027
180 16292
190 20089
200 24615
210 29787
220 35770
230 42573
240 50414
250 59660
1 mmHg = 133.322 Pa

Methanol and water are completely miscible with each other. The properties of methanol-water solutions are important physical characteristics of methanol, and they play a significant role in the application of methanol, its purification, and environmental protection. Table 1-5 shows the relationship between the density of methanol aqueous solutions and the methanol concentration as well as temperature; Table 1-6 gives the boiling points of methanol aqueous solutions; Table 1-7 provides the flash points of methanol aqueous solutions. Table 1-5: Relationship between the density of methanol aqueous solutions and methanol concentration and temperature
CH3OH concentration /% Density/(g/cm3) 30℃ 0℃ 20℃ 30℃ 40℃ 60℃
10 0.9595 0.9434 0.9250 0.9873 0.8870 0.8640
20 0.9842 0.9725 0.9604 0.9459 0.9287 0.9090
30 0.8869 0.8634 0.9794 0.9625 0.9442 0.9250
40 0.9050 0.8835 0.8610 0.8361 0.8090 0.9750
50 0.9287 0.9090 0.8869 0.8634 0.8202 0.9635
60 0.9459 0.9287 0.9090 0.8869 0.8634 0.9450
70 0.9604 0.9459 0.9287 0.9090 0.8869 0.9260
80 0.9725 0.9604 0.9459 0.9287 0.9090 0.9061
90 0.9842 0.9725 0.9604 0.9459 0.9287 0.8844
100 0.9873 0.9842 0.9725 0.9604 0.9459 0.8609

Table 1-6: Boiling points of methanol aqueous solutions
Pressure (760 mmHg) Pressure (500 mmHg) Pressure (350 mmHg)
Methanol concentration/% Boiling point/℃ Methanol concentration/% Boiling point/℃ Methanol concentration/% Boiling point/℃
Liquid phase Gas phase Liquid phase Gas phase Liquid phase Gas phase
0 27.97 42.77 52.33 58.70 63.52 67.23
5 0 42.77 52.33 58.70 63.52 67.23
10 0 52.33 58.70 63.52 67.23 70.36
15 0 58.70 63.52 67.23 70.36 73.17
20 0 63.52 67.23 70.36 73.17 75.92
25 0 67.23 70.36 73.17 75.92 78.34
30 0 70.36 73.17 75.92 78.34 80.65
35 0 73.17 75.92 78.34 80.65 82.87
40 0 75.92 78.34 80.65 82.87 84.96
45 0 78.34 80.65 82.87 84.96 87.18
50 0 80.65 82.87 84.96 87.18 89.46
55 0 82.87 84.96 87.18 89.46 91.67
60 0 84.96 87.18 89.46 91.67 93.87
65 0 87.18 89.46 91.67 93.87 95.97
70 0 89.46 91.67 93.87 95.97 98.06
75 0 91.67 93.87 95.97 98.06 100.00
80 0 93.87 95.97 98.06 100.00 92.39
85 0 95.97 98.06 100.00 92.39 87.53
90 0 98.06 100.00 92.39 87.53 84.01
95 0 100.00 92.39 87.53 84.01 81.48
100 0 92.39 87.53 84.01 81.48 79.48

Note: 1 mmHg = 133.322 Pa. Table 1-7 Flash point of methanol-water solutions at a pressure of 9.6×104 Pa (720 mmHg) Methanol concentration/%(volume) Flash point/°C Methanol concentration/%(volume) Flash point/°C Methanol concentration/%(volume) Flash point/°C 7.5 10 20 30 65.25 58.75 44.25 36 40 50 60 70 30 26 22.75 20.28 80 90 100 16.75 13.25 9.50 As can be seen from these tables, the density of methanol-water solutions decreases as the methanol concentration and temperature increase ； The boiling point of a methanol aqueous solution decreases as the methanol concentration in the liquid phase increases ； At the same temperature and pressure, the methanol concentration in the gas phase is higher than that in the liquid phase, especially when the concentration of methanol in the liquid phase is low. Methanol has a low flash point; the flash point of pure methanol is 16°C. The flash point of methanol aqueous solutions remains low, which requires special attention. Methanol is a highly polar organic compound with strong solvating power; it is miscible with various organic solvents and can form azeotropic mixtures. The formation of azeotropes affects the removal of organic impurities from methanol as well as the purification of other downstream products synthesized using methanol as a raw material. Table 1-8 shows the compositions of azeotropes formed by methanol and certain organic compounds, as well as the boiling points of these azeotropes. Methanol also has a strong ability to dissolve gases, especially carbon dioxide and hydrogen sulfide; it can be used as a detergent in industrial processes to remove excess harmful gases such as carbon dioxide and hydrogen sulfide from syngas. The strong adsorption of methanol on carbon monoxide gas provides a favorable factor for the reaction system between methanol and carbon monoxide. Tables 1-9 and 1-10 show the solubilities of carbon monoxide and carbon dioxide in methanol, respectively. Table 1-8 Substances that form azeotropes with methanol and the boiling points of these azeotropes
Compound | Boiling point/°C | Azeotrope boiling point/°C | Methanol concentration/%
CH3COCH3 | 56.4 | 55.7 | 12.0
CH3COOCH3 | 57.0 | 54.0 | 19.0
HCOOC2H6 | 54.1 | 50.9 | 16.0
(CH3)2O | 42.3 | 41.8 | 8.2
CH3CH(OCH3)2 | 79.6 | 63.5 | 70.0
CH2=CHCOOC2H5 | 79.8 | 62.4 | 4.7
CH3COC2H5 | 80.9 | 61.9 | 50.2
C2H5COOCH3 | 38.9 | 38.8 | 10.0
HCOOC3H7 | 64.3 | 57.5 | 24.2
CH2(OCH3)2 | 43.1 | 64.5 | 84.4
C6H12 | 97.9 | 64.6 | 95.0
HCOOC4H9 | 80.8 | 54.2 | 61.0
C3H7)2O | 90.4 | 63.3 | 72.0
HCOOC6H12 | 90.5 | 80 | 70.0

Table 1-9 Solubility of carbon monoxide in methanol/(cm3/g CH3OH)
Pressure/(kgf/cm2) | Temperature/°C
25 | 90 | 140
25 | 90 | 140
55 | 75 | 100
150 | 10.5 | 17.4 | 23.2
34.1 | 15.9 | 28.5 | 38.9
23.0 | 32.9 | 47.2
200 | 250 | 300 | 46.4 | 60.0 | 48.2 | 55.8 | 62.1 | 57.0 | 64.7 | 71.2
1 kgf/cm2 = 9.80665×10^4 Pa

Table 1-10 Solubility of carbon dioxide in methanol/(cm3/g CH3OH)
Pressure/(kgf/cm2) | Temperature/°C
0 | 25 | 49.8
75 | 0 | 25 | 49.8
6.8 | 10.7 | 16.5 | 22.3
59.5 | 174 | 270 | 29.9 | 49.3 | 82.5 | 118 | 19.5 | 32.1 | 51.8 | 71.9
12.8 | 22.3 | 35.5 | 48.6 | 30.3 | 39.7 | 49.4 | 55.2
197 | 287 | 112 | 161 | 228 | 269 | 71.5 | 103 | 104

Methanol is a highly toxic compound; ingesting 5–10 mL can cause severe poisoning, more than 10 mL can lead to blindness, and 60–250 mL can be fatal. Methanol can enter the human body through the digestive tract, respiratory tract, skin, and other pathways. Mild poisoning may cause headache, dizziness, insomnia, fatigue, dry throat, chest tightness, abdominal pain, nausea, vomiting, and decreased vision ； Moderate poisoning is characterized by confusion and eye pain, as well as blindness due to optic atrophy ； In cases of severe poisoning, severe headaches, dizziness, nausea, confusion, and blindness can occur, along with epileptic seizures and coma; ultimately, death results from respiratory failure. Methanol is generally considered a potent neurotoxin and vasotoxin. Once methanol enters the body, it is converted into formaldehyde due to the action of methanol dehydrogenase; further, under the action of formaldehyde dehydrogenase, it is oxidized to formic acid. Formic acid inhibits the process of oxidative phosphorylation, disrupts mitochondrial electron transfer, limits the synthesis of adenosine triphosphate (ATP), leading to degenerative changes in cells, which in turn results in cellular necrosis, tissue hypoxia, and pathological alterations. Table 1-11 shows the permitted concentration of methanol in air. Table 1-11 Permitted concentrations of methanol in air. Continuous exposure time, Permitted concentration/(mg/L); Continuous exposure time, Permitted concentration/(mg/L): 1 hour, 8 hours, 24 hours, 5×8 hours. Values: 1000, 500, 200, 200. For exposure periods of 168 hours, 30 days, 60 days, and 90 days, the values are 50, 10, 5, and 3 respectively. Chemical properties: Methanol is the simplest saturated fatty alcohol and possesses the chemical properties typical of fatty alcohols; it can undergo reactions such as oxidation, esterification, carbonylation, amination, and dehydration. Methanol cracking produces CO and H2, and it is an important chemical method for preparing CO and H2. (1) Oxidation reaction: Methanol can be oxidized to formaldehyde by air over an electrolytic silver catalyst, which is an important industrial method for producing formaldehyde. CH3OH+0.5O2→HCHO+H2O Formaldehyde is further oxidized to formic acid: HCHO+0.5O2→HCOOH Methanol undergoes partial oxidation in a Cu-Zn/Al2O3 catalyst: CH3OH+0.5O2→2H2+CO2 When methanol burns completely, it is oxidized to CO2 and H2O, releasing a large amount of heat: CH3OH+O2→CO2+H2O (2) Esterification reaction Methanol can undergo esterification reactions with various inorganic and organic acids. Methanol reacts with sulfuric acid in an esterification reaction to produce methyl hydrogen sulfate, which is then converted into dimethyl sulfate, an important methylation reagent, through distillation under heating and reduced pressure: CH3OH+H2SO4→CH3OSO2OH+H2O; CH3OSO2OH→CH3OSO2OCH3+H2SO4. Methanol reacts with nitric acid to yield methyl nitrate: CH3OH+HNO3→CH3NO3+H2O. It also reacts with formic acid to produce methyl formate: CH3OH+HCOOH→HCOOCH3+H2O. (3) Carbonylation reactions: Methanol reacts with phosgene in a carbonylation reaction to form methyl chloroformate, which further reacts to produce dimethyl carbonate: CH3OH+COCl2→CH3OCOCl+HCl; CH3OCOCl+CH3OH→(CH3O)2CO+HCl. At a pressure of 65 MPa and a temperature of 250°C, using cobalt iodide as a catalyst, or at a pressure of 3 MPa and a temperature of 160°C using rhodium iodide as a catalyst, methanol reacts with CO in a carbonylation reaction to produce acetic acid or acetic anhydride: CH3OH+CO→CH3COOH; CH3OH+CO→(CH3CO2)O+H2O. At a pressure of 3 MPa and a temperature of 130°C, using CuCl as a catalyst, methanol reacts with CO and oxygen in an oxidative carbonylation reaction to produce dimethyl carbonate: CH3OH+CO+0.5O2→(CH3O)2CO+H2O. Under the action of a basic catalyst, methanol reacts with CO2 in a carbonylation reaction to produce dimethyl carbonate: 2CH3OH+CO2→(CH3O)2CO. At a pressure of 5–6 MPa and a temperature of 80–100°C, using sodium methoxide as a catalyst, methanol reacts with CO to produce methyl formate: CH3OH+CO→HCOOCH3. (4) Amination reactions: At a pressure of 5–20 MPa and a temperature of 370–420°C, using activated alumina or molecular sieves as catalysts, methanol reacts with ammonia to produce a mixture of monomethylamine, dimethylamine, and trimethylamine, which can be separated by distillation to yield these products. CH3OH + NH3 → CH3NH2 + H2O
2CH3OH + NH3 → (CH3)2NH + 2H2O
3CH3OH + NH3 → (CH3)3N + 3H2O

(5) Dehydration reaction: Under high temperature and in the presence of acidic catalysts such as ZSM-5 or γ-Al2O3, methanol undergoes intermolecular dehydration to form dimethyl ether:
2CH3OH → (CH3)2O + H2O

(6) Cracking reaction: On copper catalysts, methanol can be cracked into CO and H2:
CH3OH → CO + 2H2
If water vapor is present during this cracking process, a steam reforming reaction occurs:
CO + H2O → H2 + CO2
That is, it’s a methanol steam reforming reaction:
CH3OH + H2O → 3H2 + CO2

(7) Chlorination reaction: Methanol and hydrogen chloride react on ZnO/ZrO catalysts to produce chloromethane:
CH3OH + HCl → CH3Cl + H2O
Chloromethane and hydrogen chloride further undergo oxychlorination reactions on CuCl2/ZrO2 catalysts to yield dichloromethane and trichloromethane. CH3OH + HCl + 0.5O2 → CH2Cl2 + H2O
CH3Cl2 + HCl + 0.5O2 → CHCl3 + H2O
(8) Other reactions: Methanol and isobutylene react under the catalysis of acidic ion exchange resin to form methyl tert-butyl ether (MTBE): CH3OH + CH2=CH(CH3)2 → CH3—O—C(CH3)3. Methanol and benzene can react at 3.5 MPa and temperatures between 350–380°C, with the help of a catalyst, to produce toluene: CH3OH + C6H6 → C6H5CH3 + H2O. Methanol and carbon disulfide react under the catalysis of γ-Al2O3 to form dimethyl sulfide, which can further be oxidized to dimethyl sulfoxide: 4CH3OH + CS2 → 2(CH3)2S + CO2 + 2H2O; 3(CH3)2S + 2HNO3 → 3(CH3)2SO + 2NO + H2O. Under conditions of 0.1–0.5 MPa and temperatures between 350–500°C, methanol reacts under the catalysis of silicoaluminophosphate molecular sieves (SAPO-34) to produce lower hydrocarbons: CH3OH → CH2=CH2 + H2O; CH3OH → CH2=CH2–CH3 + H2O + H2. At 750°C, methanol reacts under the catalysis of Ag/ZSM-5 to produce aromatics: CH3OH → C6H6 + H2O + H2. At temperatures between 240–300°C and pressures of 0.1–1.8 MPa, methanol and ethanol react under the catalysis of Cu/Zn/Al/Zr to produce methyl acetate: CH3OH + CH3CH2OH → CH3COOCH3 + H2. At 220°C and 20 MPa, methanol undergoes a homologation reaction under the catalysis of cobalt to produce ethanol: CH3OH + CO + H2 → CH3CH2OH + H2O. As methanol synthesis technologies become more advanced, production scales expand, and the raw materials used in synthesis become more diverse, new chemical reactions involving methanol continue to be discovered and studied, thereby enriching the field of methanol chemistry. Methanol synthesis: In 1661, Robert Boyle in Germany discovered a \"neutral substance\" in pyroguic acid, which he named \"wood alcohol\". In 1934, Damds and P’eligr isolated methanol from pyrogallic acid and determined its relative molecular mass. In 1857, Berthelot synthesized methanol chemically for the first time by hydrolyzing chloromethane in an alkaline solution. The large-scale industrial production of methanol began in the 1920s with the industrial implementation of the high-pressure method for methanol synthesis. In 1913, the German company BASF conducted research on the synthesis of oxygen-containing compounds from carbon monoxide and hydrogen using its high-pressure ammonia synthesis test plant. In 1923, the world’s first production facility for synthetic methanol, with an annual capacity of 3,000 tons, was built in Leuna, Germany, and brought into operation successfully. This device uses Zn-Cr oxide as a catalyst, with carbon monoxide and hydrogen as raw materials; the reaction takes place at pressures of 30–35 MPa and temperatures of 300–400°C. This method is known as the high-pressure synthesis of methanol. In 1965, 2.988 million tons of methanol were produced using this method. The successful commissioning of high-pressure methanol production plants has attracted widespread attention from countries around the world, which have subsequently embarked on research and development for the laboratory synthesis and industrial production of methanol. In 1927, the American company Commerical Solvent built the world’s first industrial plant for synthesizing methanol from carbon dioxide and hydrogen, which was put into commercial operation. The device uses Zn-Cr oxide or Cu-Zn-Cr oxide as a catalyst, with a reaction pressure of 31.6 MPa; the product composition is 68% methanol and 32% water. Due to economic reasons, the device was discontinued in 1951. The industrial production of methanol by high-pressure methods requires large investment and results in high production costs. To this end, countries around the world are seeking industrial production methods that can reduce synthetic pressure. The British company ICI and the German company Lurgi successfully developed medium- and low-pressure methanol synthesis catalysts, which reduced the reaction pressure and facilitated rapid growth in methanol production. In 1966, ICI successfully developed a process for synthesizing methanol from CO and H2 at an operating pressure of 5 MPa, using a Cu-Zn-Al oxide catalyst; this process was known as the ICI low-pressure process. In 1972, ICI successfully developed a medium-pressure methanol synthesis process at 10 MPa. In 1970, the German company Lurgi used Cu-Zn-Mn or Cu-Zn-Mn-V, Cu-Zn-Al-V oxide-based copper catalysts to successfully build a low-pressure production facility with an annual capacity of 4,000 tons of methanol; this process is known as the Lurgi low-pressure process. Meanwhile, other chemical companies around the world also competed to develop their own medium- and low-pressure methanol synthesis processes and build methanol production facilities, but ICI’s and Lurgi’s medium- and low-pressure processes are the commonly used synthesis technologies. By 1982, the total annual production capacity of methanol worldwide using the ICI medium and low-pressure processes reached 10.28 million tons, accounting for 50% of the world’s total methanol production capacity; the scale of these plants ranged from 50,000 to 825,000 tons per year ； The total production capacity of methanol plants that have been built or are under construction using the Lurgi low-pressure process amounts to 6.06 million tons, accounting for 30% of the world’s total methanol production capacity. The scale of these plants ranges from 45,000 to 810,000 tons per year. With the continuous advancement of methanol synthesis technology and the expansion of its scale, the raw material pathways used have also undergone significant changes. They have evolved from the original approach of using coal and coke gasification to produce syngas, to the current approach in which natural gas is the primary source, with coal, naphtha, heavy oil, and other materials also being utilized. Before the 1950s, the syngas used for synthesizing methanol was produced by gasifying coal and coke at atmospheric or elevated pressure, using steam and air as gasification agents. Water gas was generated, and then through the reverse water-gas shift reaction and the removal of some carbon dioxide, methanol synthesis syngas was obtained, in a manner similar to that used in ammonia production to create semi-water gas. Since the 1950s, oil and gas resources have been exploited on a large scale. In particular, the development of steam reforming technology for natural gas, which is abundant and inexpensive, has reduced the cost of the feed gas used in methanol production, making it the main route for methanol synthesis. Currently, the natural gas route accounts for about 80% of methanol production capacity, with the Middle East and Latin America being the regions where methanol production capacity has grown fastest in recent years, thanks to their inexpensive and abundant natural gas. The development of naphtha steam reforming technology and the partial oxidation of heavy oil to produce syngas will also gradually make naphtha and heavy oil the main raw materials for methanol production, especially in those regions that lack natural gas resources. As a traditional raw material for producing methanol synthesis gas, coal has relatively high costs due to issues related to environmental protection and gas purification; however, it remains the primary raw material option in regions that lack oil and gas but are rich in coal. From the perspective of long-term development trends, coal is the energy source with the largest reserves of fossil fuels in the world, far exceeding the reserves of natural gas and oil. Moreover, with the advancement of gasification and purification technologies, as well as the use of methanol as a clean fuel for vehicles and a raw material for methanol fuel cells, it will once again become the main raw material route for synthesizing methanol. China’s methanol industry began in the 1950s. After the founding of the People’s Republic of China, the country utilized technology from the former Soviet Union to build high-pressure methanol synthesis plants in Lanzhou, Taiyuan, and Jilin, using zinc-chromium catalysts. In the 1960s and 1970s, the Wujing Chemical Plant in Shanghai built methanol synthesis units using coke and naphtha as raw materials. The Research Institute of Nanjing Chemical Industry Company developed medium-pressure copper-based catalysts for the simultaneous production of ammonia and methanol, which promoted the industrial development of ammonia synthesis coupled with methanol production. In the 1970s, the Sichuan Vinylon Plant introduced China’s first low-pressure methanol synthesis unit, which used acetylene off-gases as raw material and employed the ICI low-pressure cold-quenching synthesis process. In the mid-1980s, Qilu No. 2 Chemical Plant introduced a low-pressure methanol synthesis unit from the German company Lurgi, using residue oil as raw material. Entering the 1990s, with the rapid growth in demand for methanol, dozens of methanol and dimethyl ether production facilities were built using both imported and domestic technologies, enabling the rapid development of methanol production in China on an unprecedented scale. The methanol synthesis process: Characteristics of the methanol synthesis process. Methanol production is carried out at a pressure of 13×106 Pa, using copper-based catalysts, and it is integrated into the ammonia synthesis process; CO, CO2, and H2 present in the ammonia synthesis feed gas are used to produce methanol. Therefore, compared with traditional high-pressure or low-pressure methods, the hydroformylation method for methanol production has the following characteristics: (1) It is integrated into the ammonia synthesis process, so it must meet both the requirements of that process and those for methanol synthesis. Any change in the process conditions of either party will affect the production and operation of synthetic methanol and synthetic ammonia; therefore, necessary supplementary adjustment measures must be implemented during production to ensure that both synthesis processes can proceed simultaneously. (2) Since it is connected in series in the ammonia synthesis process, the process gas after methanol synthesis must also be purified before being used in the ammonia synthesis reaction. Therefore. The composition of the feed gas, after methanol synthesis, must meet the requirements for ammonia synthesis. Methanol synthesis gas is produced through partial recycling, and methanol synthesis is not the end stage of the entire production process. (3) Compared with the ammonia synthesis process, since hydrazine uses a copper-based catalyst and its resistance to poisoning is lower, special purification measures must be taken. It maintains the CO and CO2 necessary for synthesizing methanol, while preventing gases such as H2S from entering the system. Requirements of the co-ethanol process: The co-ethanol process differs from traditional methanol synthesis processes as mentioned above; therefore, in addition to the general requirements for methanol production, there are also specific requirements associated with the co-ethanol process. (1) General requirements for methanol production: (1) Before the feed gas enters the synthesis tower, its main components must be adjusted to certain proportions, and any substances that are harmful to the catalyst must be removed. This includes carbonyl iron Fe(CO)5 and carbonyl nickel Ni(CO)4 formed by iron and nickel present in the equipment and pipelines, as well as soluble iron and nickel compounds. It is also necessary to prevent basic oxides and alkali metals from being carried into the catalyst bed along with the gas. Because the introduction of trace amounts of iron and nickel compounds increases the reaction that converts CO and H2 into alkanes ； The introduction of alkali metals leads to an increase in the production of higher alcohols, which raises the impurity content in the synthesized crude methanol and increases the consumption of useful gases. (2) The synthetic catalyst begins to react at temperatures above 200°C; in order to ensure that the entire catalyst bed reaches the activation temperature uniformly, the gas entering the reactor must be preheated. At the same time, to prevent hydrogen corrosion of carbon steel equipment at high temperatures, the gas exiting the tower must be cooled. To meet the temperature requirements of the gas entering and exiting the tower, heat exchange is carried out within the tower, which increases the temperature of the gas entering the catalyst bed while reducing the temperature of the gas exiting the tower. (3) The methanol produced through the synthesis reaction must be separated promptly from unreacted gases such as H2, N2, CO, and CO2, in order to reduce the concentration of reaction products and thereby increase the equilibrium rate of the synthesis reaction. (4) To improve the catalyst utilization efficiency, a portion of the gas is synthesized and separated, then sent to copper washing for purification; after removing the remaining CO and CO2, it is used as feed gas for ammonia synthesis. Meanwhile, most of the gas is circulated using a recycler to continue methanol synthesis. (II) Special requirements for syngas alcohol production (1) Since the syngas alcohol production process is carried out in series with ammonia synthesis, the production capacity is represented by the sum of the ammonia synthesis output and the methanol output, namely the so-called \"total ammonia\" output. With the production capacity of \"total ammonia\" remaining unchanged, the methanol production capacity is expressed as the alcohol-ammonia ratio (methanol output/total ammonia output). This ratio can be adjusted within a certain range, and the method of adjustment generally involves changing the H2/CO ratio in the feed gas; more precisely, it involves adjusting the ratio of (H2—CO2): (CO+CO2) = f. Therefore, in the hydroformylation process, in addition to means to adjust the hydrogen-to-nitrogen ratio during ammonia synthesis, there must also be control mechanisms capable of adjusting the f-value. Generally, in the production of alcohols, the CO content in the feed gas is adjusted by changing the conversion rate of CO in the shift reaction, or by creating a shortcut between the inlet and outlet of the shift reactor, thereby enabling the alcohol-to-ammonia ratio to be controlled within a certain range. (2) As part of the ammonia synthesis process, methanol production can affect ammonia synthesis and the overall operation of the system. Factors such as catalyst deactivation, the start-up and shutdown of methanol synthesis towers, and changes in operating conditions can lead to variations in the CO+CO2 content in the gas going through the copper washing process, thereby causing fluctuations in the load on the copper washing unit and even impacting the normal operation of the ammonia synthesis tower ； The gas-liquid separation condition after the methanol synthesis tower affects the composition of the copper melt ； In cases of abnormal operation or accidents in methanol production, it is necessary to maintain ammonia synthesis and other processes. Synthesis process: Methanol synthesis is a reversible exothermic reaction, governed by thermodynamics and kinetics. Typically, in a single-pass reactor, the single-pass conversion rates of CO and CO2 do not reach 100%. In the gas exiting the reactor, the methanol content is only 3% to 6%; the unreacted CO, CO2, and H2 need to be separated from methanol and then further compressed before being recycled back into the reactor. The zinc-chromium catalysts developed earlier had low activity, and only at a reaction temperature of 300°C did they achieve sufficient activity. To ensure a high methanol content in the gas exiting the reactor, a reaction pressure of 30 MPa or higher is generally used. Copper-based catalysts exhibit high catalytic activity, showing good performance at a reaction temperature of 270°C; medium or low pressure conditions are generally used for synthesis. A comparison of the two catalysts is shown in Table 1-12. Table 1-12 Comparison of zinc-chromium and copper-based catalysts. Operating pressure/MPa; Percentage of methanol at the exit of the synthesis tower/%. Exit temperature of the zinc-chromium catalyst: 648 K; Exit temperature of the copper-based catalyst: 543 K. Values: 33, 20, 10, 5, 5.5, 2.4, 0.6, 0.2; 18.2, 12.4, 5.8, 2.5. The high-pressure method for methanol synthesis is being phased out due to its disadvantages such as high operating pressures, high energy consumption, complex equipment, and poor product quality. The medium-low pressure process uses copper-based catalysts, with an operating pressure of around 5–10 MPa. Due to the low operating pressure in the low-pressure method, the equipment required is large in size, and the yield of methanol synthesis is also low; therefore, it is less favorable from an investment and economic evaluation perspective compared to the medium-pressure method. Currently, about 70% of the world’s methanol production is carried out using the medium and low pressure processes developed by the British company ICI, with capacities ranging from 50 t/d to 2500 t/d. In addition, there are also production processes from German companies such as Lurgi, American company UCI, and Danish company Topsoe. The process flow diagram for the synthesis of methanol by high-pressure method is shown in Figure 1-2. After pentacarbonyl carbon is removed from the compressed syngas in an activated carbon adsorber, it is sent together with the recycle gas into a tubular reactor, where carbon monoxide and hydrogen react across a catalyst layer at 350°C and 30.4 MPa (300 atm) to produce crude methanol. The gas containing crude methanol is cooled by a cooler and then quickly sent to a crude methanol separator to cause the crude methanol to condense, while the unreacted carbon monoxide and hydrogen are recycled back to the reactor. The condensed crude methanol enters the distillation unit, where dimethyl ether, methyl formate, and other low-boiling impurities are separated out in the first distillation column ； Water and fusel oils are removed in the second distillation column to obtain pure methanol. The process flow diagram for methanol synthesis by the medium-pressure method is shown in Figure 1-3. The feedstock starts as natural gas or naphtha, and is converted into syngas through reforming. Raw materials, fuel natural gas, and flare gas are burned for heating inside the conversion furnace, which is filled with nickel catalysts in its tubes. The gas coming out of the converter undergoes heat exchange before being sent to the syngas compressor, where it is compressed and preheated together with the recycled gas in the recycle compressor. It then enters the synthesis tower, where the pressure is 8.106 MPa (80 atm) and the temperature is 220°C. In the synthesis tower, syngas is converted into crude methanol through a catalyst. The tower is of the quench type, recovering the heat from the synthesis reaction to generate medium-pressure steam. The gas exiting the tower preheats the gas entering the tower, which is then cooled to condense the crude methanol in the condenser. Most of the gas is recycled, while the remaining off-gas is used as fuel for the converter. In the stripping tower and purification tower, crude methanol is distilled to separate impurities such as dimethyl ether, methyl formate, and fusel oils, thereby yielding purified methanol product. Fig. 1-2 Process flow diagram for methanol synthesis by high-pressure method 1 — Activated carbon adsorbent ； 2—Tubular reactor ； 3—Coarse methanol separator ； 4—Crude methanol storage tank ； 5—Coarse separation tower ； 6—Fine separation tower Figure 1-3 Process flow diagram for methanol synthesis by medium-pressure method 1—Converter ； 2, 3, 7—Heat exchanger ； 4—Compressor ； 5—Recirculation compressor ； 6—Methanol condenser ； 8—Synthesis Tower ； 9—Coarse separation tower ； 10—Refining tower. The process flow diagram for low-pressure methanol synthesis by German Lurgi is shown in Figure 1-4. Syngas is produced by steam reforming of natural gas. The natural gas is desulfurized to below 0.1 mg/L and then fed into a steam reformer, where the methane contained in the natural gas is converted, under the action of a nickel catalyst, into syngas containing carbon monoxide, carbon dioxide, and inert gases. After being cooled, the syngas is fed into a centrifugal turbine compressor, where it is compressed to 4.053–5.066 MPa (40–50 atm) before being sent to the synthesis tower. Syngas reacts to form methanol in the presence of a copper catalyst. The reaction heat of methanol synthesis is used to generate high-pressure steam, which serves as power for the turbine compressor. The gas containing methanol at the outlet of the synthesis tower is cooled by heat exchange with the mixture gas, and then cooled further with air or water to cause the crude methanol to condense, which is subsequently separated in a separator. The condensed crude methanol is sent to a flash tank for flashing, and then to a distillation unit for purification. Crude methanol is first decontaminated of dimethyl ether, methyl formate, and other low-boiling-point impurities in a primary distillation tower. The tower bottom product enters the first distillation column. After distillation, 50% of the methanol comes out from the top of the tower; the gaseous pure methanol is used as a heat source to heat the reboiler in the second distillation column ； Methanol containing heavy components, coming from the bottom of the first distillation tower, is distilled in the second distillation tower; pure methanol is obtained from the top of the tower, while the residue remains at the bottom ； The purified methanol from the second distillation tower is cooled to room temperature and then sent to a storage tank, where it becomes the final product in the form of pure methanol. Figures 1-4: Process flow diagram for methanol synthesis using Lurgi’s low-pressure method. 1 – Waste heat boiler ； 2—Converting furnace ； 3—Cooler ； 4—Turbine compressor ； 5—Synthesis tower ； 6—Separator ； 7—Flash tower ； 8—Distillation tower ； 9—First Distillation Tower ； 10—Second Distillation Tower. Uses of Methanol. In recent years, demand for methanol has been growing steadily; part of this demand comes from traditional applications such as the production of formaldehyde, while new applications such as acetic acid and MTBE contribute to the increase in demand for methanol. The main application area of methanol is in the production of formaldehyde, which is used to manufacture adhesives, primarily in the wood processing industry ； Secondly, it is used as a treatment agent for molding compounds, coatings, textiles, and paper, among others; adhesives used in wood processing account for about 80% of its total consumption. The growth rate of demand for formaldehyde is closely related to the growth rate of GDP. Formaldehyde is also used in the production of acetal resins and 1,4-butanediol, a specialty chemical, and its demand is growing rapidly; however, this will not significantly change the overall demand for formaldehyde. Acetic acid accounts for about 7% of global methanol demand; it is used to produce vinyl acetate, acetate fiber, and acetic acid, among other products. Its demand is closely linked to the needs in industries such as coatings, adhesives, and textiles. Methyl methacrylate accounts for about 2% to 3% of global methanol demand, and is primarily used in the production of acrylic sheets, surface coatings, and molding resins. It is expected that growth rates will be moderate in developed countries, while they will be higher in Asia. With the development of C1 chemicals, processes for synthesizing ethylene glycol, acetaldehyde, ethanol, and others from methanol as a raw material are receiving increasing attention. Methanol, as an important raw material, plays a crucial role in the production of pesticides such as trichlorfon, methyl parathion, and carbendazim, as well as in industries such as pharmaceuticals, dyes, plastics, and synthetic fibers. Methanol can also be used to produce methanoprotein through biological fermentation, which serves as a feed additive and holds broad application prospects. Methanol is not only an important chemical raw material but also an energy source and vehicle fuel with excellent properties. Methanol reacts with isobutylene to produce MTBE, which is an additive for high-octane lead-free gasoline and can also be used as a solvent. Since the first 100 kt/a plant was built and put into operation in 1973, it has become the world’s second-largest consumer of methanol, after formaldehyde. Methyl tert-butyl ether (TAME) is also an important oxygenate additive for gasoline; due to historical reasons, its total production volume remains low. Market conditions and development trends: Based on the global consumption structure and forecasts for methanol, its consumption pattern is expected to remain similar to what it is today; formaldehyde will continue to be the most widely used form, accounting for around 35%–36% of total consumption ； Next is methyl tert-butyl ether (MTBE), accounting for about 27% ； Acetic acid again, accounting for about 7% to 9%. Overall, the global supply and demand for methanol are currently in balance, but the situation varies across different regions. Based on the current situation and future projections, there will be a surplus of methanol produced in regions such as Canada, Latin America, Eastern Europe, the Middle East, Africa, and Oceania, making them the world’s major exporting countries or regions. The United States, Western Europe, Asia and other regions suffer from a shortage of methanol produced there, making them major importing countries or regions. In the search for alternatives to gasoline, alcohol-ether fuels hold great potential and prospects for application. Alkyl ether fuels refer to new types of liquid fuels made by mixing methanol and dimethyl ether in certain proportions; they exhibit higher combustion efficiency and thermal efficiency than liquefied gas. Due to its good volatility, dimethyl ether effectively overcomes the disadvantages of methanol fuel, such as its difficulty in ignition, the need for air compression, the requirement for an external preheater, and challenges related to safe transportation. Methanol can also be used directly as a fuel for automotive internal combustion engines. Methanol is a hydrogen-rich liquid that can be used to produce hydrogen via steam reforming as a hydrogen source for fuel cells, or it can be used directly as a fuel for fuel cells, making it the most promising candidate as a fuel for fuel cell electric vehicles. Methanol fuel cell vehicles represent a potential major area for methanol consumption. The development of the methanol industry has the potential to be integrated into the development of the entire energy system, particularly that based on fossil coal energy. Methanol is synthesized from CO and H2; in coal, electricity, and chemical industry co-production systems centered on coal-to-syngas conversion, methanol synthesis can be used to regulate peak power generation demands. When the electrical load is low, methanol can be synthesized using syngas; whereas when the load is high, CO and H2 generated from the pyrolysis of methanol can be used to generate electricity, thereby increasing the power generation capacity of the plant. For example, Shell’s new concept of a syngas park centers on coal gasification as the core process; using coal to produce syngas, it is then used to manufacture chemical products such as methanol, acetic acid, acetic anhydride, synthetic ammonia, and fertilizers. It also generates electricity through a clean combined cycle system, and produces gases like city gas for use by consumers. Additionally, the waste heat generated during production can be utilized by consumers in the form of hot water. Prospects for the synthetic methanol industry: Compared with zinc-based catalysts, copper-based catalysts are superior. However, many plants still use zinc-based catalysts at present. The reason for this is that copper-based catalysts require strict control over the impurity levels in syngas; impurities such as sulfur and acetylene must be almost completely removed, and the operating temperature also needs to be tightly controlled. Zinc-based catalysts are superior to copper-based catalysts in terms of their resistance to sulfur and unsaturated compounds. Moreover, it can operate with less stringent temperature control, which is why some methanol synthesis plants still use zinc-based catalysts. With the advancement of industrial technology, in modern factories, thanks to the development of steam conversion methods and the use of carbon dioxide in the synthesis of methanol, it is possible to remove impurities from gases and strictly control the operating temperature. Therefore, the application of copper-based catalysts is very promising. The industry for synthesizing methanol has a history of over fifty years. The high-pressure method is highly mature, and the low-pressure method was developed on the basis of the high-pressure method; judging from the situation of plant constructions in various countries, it is also quite mature. The medium-pressure method is a further development of the low-pressure method, and it is also expected to mature relatively quickly. Currently, the following research developments have attracted attention from relevant parties: (1) Catalyst research – aimed at further improving catalyst performance, such as activity, selectivity, and lifespan, in order to determine more appropriate and cost-effective synthesis conditions. (2) Research on automation Improving the level of automation by using electronic computers for control, so as to maintain production under optimal process conditions. (3) Refining aspect: Continue to improve distillation methods, optimize the structure of distillation columns, select high-efficiency trays, enhance product quality, reduce power consumption, and lower costs. (4) Based on the low-pressure method, study the use of the cheap hydrogen and carbon monoxide by-products to supply other chemical production processes. (5) In terms of the new ligand-alcohol process: improve catalyst activity, enhance selectivity, and extend its lifespan. And by studying the process, good economic results will be achieved. Methanol applications in China: In 1997, China’s methanol production capacity was 1,900 kt/year, of which 1,537.3 kt was used regularly. It decreased slightly in 1998, to 1488 kt. The consumption structure of methanol in our country is roughly as follows: formaldehyde production accounts for about 40% of the total consumption, dimethyl terephthalate, methyl methacrylate, and methyl acrylate together account for 20%, pesticide production accounts for 10%, polyvinyl alcohol accounts for 7%, MTBE accounts for 5%, methamine accounts for 6%, dimethyl sulfate accounts for 3%, and other industries account for 9%. In terms of the consumption structure, the proportion of MTBE in China is significantly lower compared to international levels (the world average over the past few years has been 26%~28%). To meet environmental protection requirements, there will be a substantial increase in the demand for MTBE as an additive in high-octane gasoline in China in the future, which in turn will lead to a significant rise in the demand for methanol as well. It is estimated that by 2005, MTBE’s share in the consumption structure of methanol will rise to 21%, while the global average share will drop to 24%. Domestic production of formaldehyde is the main use of methanol, accounting for about 40% of total methanol consumption. In our country, the production process of formaldehyde using refined methanol as raw material and electrolytic silver as a catalyst accounts for over 80%. With the development of China’s national economy, the social demand for formaldehyde is increasing year by year, which has spurred rapid growth in the formaldehyde industry; by the year 2000, China’s demand for formaldehyde was expected to reach 1,350 kt/year. In 1983, China built its first MTBE production plant with a capacity of 5 kt/a at the Qilu Petrochemical Rubber Factory. In 1986, Jihua Company constructed the country’s first MTBE plant with a capacity of 10,000 tons per year; this plant’s production capacity was 27.5 kt/a, and it was later expanded to 55 kt/a. It is currently the largest MTBE production plant in China. As the MTBE plants under construction during China’s Ninth Five-Year Plan period are completed one after another, China’s total MTBE production capacity will reach 647 kt/a, accounting for 2.7% of the world’s total production capacity. In 1995, the demand for MTBE in our country was between 350 and 375 kt; as the use of leaded gasoline is gradually banned in our country, the demand for MTBE will **increase**. Methanol can be used as a clean fuel to partially replace gasoline. The promotion of methanol fuel and the use of new formulations of methanol-based gasoline have led to a significant increase in global demand for methanol. The use of methanol-fueled vehicles is being promoted in the country. It is expected that consumption of methanol as a fuel for automotive internal combustion engines will increase significantly in the near future. Domestically, methanol is also used to produce chemical products such as acetic acid, methylamine, and dimethyl sulfate. The use of methanol in pharmaceuticals, pesticides, and fertilizers is also increasing.