January 21, 2024 | UR Gate

Methanol: Comprehensive Study on Its Industry, Reactions, and Impact

Introduction

Methanol, also known as methyl alcohol, wood alcohol, or wood spirit, is considered one of the simplest organic compounds belonging to the group known as alcohols. It is toxic, flammable, and has an odor resembling that of alcohol when pure. Its molecular formula is CH₃-OH , with a molecular weight of 32.04 grams/mol and a density of 0.7866 grams/cm3. It has a melting point of -97.8°C and a boiling point of 64.7°C.
In the past, methanol was produced through the destructive distillation of wood. The modern method of methanol production is based on the direct synthesis of carbon monoxide and hydrogen gas in the presence of a catalyst. Most of the methanol is currently produced from methane gas found in natural gas.

Pure methanol

is a significant substance in chemical industries. Its derivatives are used in large quantities for the production of various compounds such as dyes, resins, pharmaceuticals, and perfumes. Large amounts of methanol are converted into dimethyl aniline for dyes and formaldehyde for synthetic resin production. It is also used in the manufacturing of antifreeze for car engines, rocket fuel, and as a general solvent. [1]

Chemical Reactions of Methanol

Oxidation Reaction: Methanol undergoes oxidation to produce formaldehyde (methanal), a crucial component in the plastics industry, metal corrosion inhibitors, pharmaceutical manufacturing, and more, as shown in the following equation:

2CH₃OH + O₂ → 2H₂CO + 2H₂O

Reaction with Carbon Monoxide: The reaction of methanol with carbon monoxide results in acetic acid, which is used in aspirin production, paper industry auxiliary materials, cellulose acetate production used in fiber manufacturing, and others.

Reaction with Hydrogen Chloride: This reaction produces methyl chloride, used in the silicone industry and the production of butyl rubber, as shown in the following equation:

CH₃OH + HCl → CH₃Cl +H₂O

Reaction with Ammonia: Methanol reacts with ammonia to produce methylamines, utilized in insecticide production and leather tanning.

Reaction with Isobutylene: Methanol reacts with isobutylene to produce methyl tert-butyl ether, used as a solvent in various industries, including petrochemicals.

Reaction with Oxidized Xylenes: The reaction with oxidized xylenes produces dimethyl terephthalate, used in the production of polyester fibers, food and beverage can manufacturing, and more.

These chemical reactions showcase the versatility of methanol as a precursor to various valuable compounds across different industrial applications.[2]

Methanol Production

There are two methods for methanol production:[3]

1- Laboratory Method

Methanol can be prepared in the laboratory by the reaction of methyl chloride with sodium hydroxide, as depicted in the following equation:

CH₃Cl + NaOH → CH₃OH + NaCl

2- Industrial Method

Methanol has been manufactured from synthesis gas (syngas) since 1923 using the same method employed today. The manufacturing process involves the following steps:

a. Natural Gas Purification: The natural gas undergoes desulphurization to eliminate sulfur compounds. Activated carbon is used to remove sulfur compounds present with methane.

b. Chemical Formation of Syngas: Methane is heated and mixed with carbon dioxide and water vapor. The mixture is then passed over a catalyst, such as nickel. The presence of sulfur compounds can poison the catalyst, reducing or eliminating its effectiveness. The reaction occurs at temperatures around 800°C, transforming methane into carbon monoxide and hydrogen (syngas).

c. Syngas: Syngas is a gaseous mixture of carbon monoxide and hydrogen produced by the reaction of natural gas with water vapor through two processes:

i. Steam Reforming Process: This catalytic process utilizes catalysts containing nickel.
ii. Partial Oxidation Process: This process is more recent than steam reforming, but steam reforming is more widely adopted. The partial oxidation process gained popularity as the cost of producing oxides decreased.

d. Crude Methanol Production: Syngas is then used in a methanol production reactor to produce crude methanol.

e. Distillation and Purification Stage: The crude methanol undergoes distillation and purification processes to meet international specifications, resulting in the final product.

Transportation and Distribution

At every stage of transportation and distribution, methanol should be stored safely to handle it securely, minimizing risks to both humans and the environment. This is crucial for preserving the integrity of transportation modes, whether on land or sea, for the most commonly transported methanol worldwide.[4]

Uses of Methanol

Methanol finds applications in various industries, including:

Chemical Industry: It serves as a raw material in many chemical industries, such as the production of formaldehyde and acetic acid.
Medical Preparations: Methanol is utilized in the pharmaceutical industry.
Plastics Industry: It is a key component in the plastics industry.
Fuel Cells: Methanol is used in fuel cells where it undergoes dissociation to generate energy.
Solvent: It acts as a good solvent for certain organic substances.
High-Purity Fuel: Methanol is employed as a high-purity fuel for some machines, automobiles, and in household applications.
Deicing Aircraft Surfaces: Used in deicing external surfaces of aircraft, where methanol dissolves in ice (water), lowering the freezing point of the solution (melting the ice).

These diverse applications highlight the versatility of methanol across different industries and functions.

Impact on Humans

Methanol itself is not toxic; however, its toxic effects result from metabolic byproducts. Methanol is metabolized into the highly toxic formaldehyde, which is 33 times more toxic than methanol. Formaldehyde rapidly converts into formic acid within 3 minutes. Methanol is quickly absorbed in the digestive system, reaching its peak concentration in the blood after half an hour to an hour, depending on the presence or absence of food in the stomach. Poisoning usually occurs within a period ranging from 6 hours to three days, during which the person may not exhibit any toxic symptoms.

The toxic effect of methanol is attributed to its conversion in the human body to formaldehyde and formic acid by the alcohol dehydrogenase enzyme in the liver. The accumulation of these toxic metabolites is responsible for the appearance of symptoms and signs of methanol poisoning. The most important of these metabolites is formaldehyde, which has a destructive effect on many body cells, particularly the retinal cells and optic nerves, leading to acidosis due to formic acid formation. Symptoms of methanol poisoning typically appear 12 to 14 hours after ingestion, presenting as headache, dizziness, nausea, vomiting, severe abdominal and back pain associated with pancreatitis. Symptoms of central nervous system depression and respiratory failure may also occur. Visual disturbances are a consistent sign of methanol poisoning.

Impact on the Environment

Methanol is considered an environmental pollutant as it readily degrades in water and soil, leading to high concentrations that can pollute both fresh and saltwater, adversely affecting aquatic life, especially in areas near discharges. Methanol typically evaporates when exposed to air, reacting with air to form formaldehyde, contributing to air pollution. It can also react with various chemicals in the atmosphere or be absorbed in rainwater. Methanol is easily disposed of in soil and water through organisms that feed on it.

Conclusion

The process of methanol manufacturing remains costly, and current research is underway to discover a catalyst that allows the direct conversion of methane to methanol without the reaction reversing. Hope is still pinned on achieving progress in this field. Methanol, a toxic and flammable compound, known as alcohol with the chemical formula CH3OH, is primarily produced from methane gas found in natural gas.

It undergoes various reactions, such as methylation reactions, reaction with carbon monoxide, hydrogen chloride, ammonia, and isobutylene. Additionally, it reacts with oxidized xylenes, producing dimethyl terephthalate, used in the production of polyester fibers for food and beverage packaging industries. There are two methods of production: laboratory synthesis and industrial production.

When handling and distributing methanol, caution must be taken to avoid environmental and human risks. Its significant uses include being a raw material in chemical industries, pharmaceuticals, and plastic manufacturing. It is crucial in fuel cells that rely on breaking down methanol for energy generation. It also serves as a good solvent for organic materials and can be used as a high-purity fuel for certain machines and vehicles.

Methanol poses a significant risk to humans, possibly containing formaldehyde, highly toxic. It is rapidly absorbed in the digestive system, reaching peak blood levels within half an hour to an hour, causing toxicity in some cases between 6 hours to three days. Interestingly, during this period, individuals may not exhibit any symptoms of toxicity.

Moreover, methanol is a pollutant in the environment, contributing to air pollution, but it can be decomposed by organisms that feed on it.