Properties and Characteristics
The solvent toluene is produced due to its suitable structural characteristics in the process of making gasoline and other fuels from crude oil and making coke from coal. It is also found naturally in crude oil and the tolu tree.
Some important properties of this product and its structure are as follows:
| Chemical formula | C6H5CH3 |
| Molar mass | 92.141 g/mol |
| Appearance | Clear, colorless liquid with a characteristic aromatic odor |
| Boiling point | 110.6 °C |
| Melting point | -94.9°C |
| Solubility in water | Almost insoluble ( ,526mg/L @ 25 °C,) |
| Other names | Methylbenzene and Phenylmethane |
As is clear from the structure of toluene, this compound consists only of carbon and hydrogen, and although it is an organic solvent, it can dissolve minerals such as phosphorus, sulfur, iodine, bromine and other non-polar covalent substances.
Reactivity:
In free radical conditions, this substance undergoes halogenation reactions
For example, N-Bromo succinimide (NBS) is converted to benzyl bromide when heated with this substance in the presence of AIBN. In addition, toluene can be brominated in the presence of light and by reaction with H2O2 and HBr.
Hydrogenation of this substance leads to the production of methylcyclohexane (this reaction requires high hydrogen pressure and a catalyst)
Oxidation of this substance:
Like other aromatics, this substance has a higher resistance to oxidation. However, the methyl group in this compound can be converted to carboxylic acid against strong oxidations. The methyl group in the structure of this substance is susceptible to oxidation. This substance reacts with potassium permanganate to produce benzoic acid and reacts with chromyl chloride to obtain benzaldehyde. (This reaction is known as the Étard reaction).
Toluene production method:
This organic solvent can be produced by various methods, which we will discuss below:
Production from naphtha
Perhaps the main method of producing toluene can be considered naphtha, in addition, the production of benzene and xylene is also carried out through the catalytic reforming of naphtha. One of the methods of producing TOLUENE from naphtha that has recently received a lot of attention is the use of the continuous catalyst recovery (CCR) method.
This process is usually carried out in 4 reactors arranged in series, to increase efficiency and improve the conversion rate between the reactors, a heater is defined and a return flow is defined for each. Finally, the product from the last reactor includes gasoline and aromatic compounds that are separated from each other.
Fractional distillation:
Crude oil has various components and also contains some toluene. Distillation is used for separation, which separates the substances based on the difference in boiling point.
Azeotropic distillation:
Azeotrope is a mixture of two or more liquids that cannot be separated by conventional distillation. Currently, there are two processes for separating toluene, which are the use of an aqueous solution of methyl ketone and water or the use of methanol.
Solvent extraction:
In this method, a solvent with high selectivity to the above product is used. It is added to the solution and then the solvent and toluene are separated from each other using common methods such as distillation. Among these solvents are sulfur dioxide or an aqueous solution of diethylene glycol.
Steam cracking of liquid hydrocarbons:
This method is based on the cracking of naphtha hydrocarbons, which produces products such as gasoline and toluene
Also, industrial alkylation of benzene and methanol can be used to produce this material. In some cases, this material is also obtained from the reaction of benzene and methyl chloride in the presence of an acid such as aluminum chloride, which reaction is as follows.
Preparation of dry toluene:
Methylbenzene has a very low solubility in water, but about 0.05% water can dissolve in this substance. In some cases, when the presence of water is harmful or pure methylbenzene is required, the water is separated and dry toluene (free of water) is obtained. There are different methods for doing this, and distillation seems to be the easiest way to separate the water if you have the right equipment. Other methods, which include the use of benzophenone and sodium, unlike distillation, add side substances to the solution and the risks of the work (using sodium) are also much greater.
Is this substance polar?
In answer to the question of whether toluene is polar or not, it must be said no, because of the small difference between the electronegativities of carbon and hydrogen, all the bonds in this substance are non-polar, which makes the entire molecule non-polar. be.
Uses of Toluene
The main chemical uses of this substance are the production of benzene, xylene and other solvents. This compound is also used to manufacture substances such as phenol, nitrobenzene, benzoic acid and benzyl chloride. Perhaps the most important uses of this product can be considered as follows:
Production of TNT
The nitration of this substance with the help of a mixture of nitric acid and sulfuric acid leads to the production of 2,4,6 trinitrotoluene or TNT. During this process, substances such as tetranitromethane, nitrobenzoic acid and… are also produced.
Use in aerosols
In general, aerosol refers to the combination of solid particles or liquids with gas, and toluene plays the role of a propellant in these products. Aerosols can be found in insecticides, deodorants, paint sprays, dust from construction activities, smoke from burning fuel, etc., which are called artificial aerosols (created by human activity). In contrast, natural types of aerosols can be fog, or even sandstorms in deserts. It is interesting to know that when you shake a soda bottle or spray paint, or even sneeze, you actually create an artificial aerosol.
Use as a solvent
As a solvent, toluene can be used in paints, paint thinners, adhesives, inks, resins, detergents, and leather tanning agents. This compound can also be used in the manufacture of polymers used in the production of nylon, plastic soda bottles, and medicines, paints, and cosmetics.
Its specific applications include its use in nuclear reactor rings as a coolant.
One of the famous uses of this substance is its use as a solvent in nail polish. Because this compound has a high ability to remove resins and plasticizers. These substances are used in nail polish formulations as a polisher and hardener.
Toluene in gasoline
As mentioned, the above product does not dissolve in water, but it mixes well with organic solvents. This substance is used as an additive along with benzene and xylene to make gasoline.
Toluene increases the octane number in fuels used in racing cars or other vehicles. The higher the octane number, the greater the fuel’s resistance to impact and noise during combustion. The above product is a good option for increasing octane number and improving vehicle power due to its suitable density and significant energy per unit volume.
Grades:
There are generally 3 grades of toluene available in the market
- TDI grade with a purity of 99%
- Nitration grade: with 98.5-100% purity (the reason for naming this grade is because of its history of use in the preparation of nitrotoluene. However, today this material is used as a solvent in TDP and HDA devices.)
- Commercial grade: with a purity of 96% for mixing with gasoline and use as feed in HDA devices
Global toluene sales and purchases market:
Amidst the COVID-19 crisis, the global toluene market is expected to be valued at $18.4 billion in 2020, which will reach a revised size of $23.4 billion by 2027, growing at a CAGR of 3.5% during the analysis period 2020-2027. Also, toluene and xylene, one of the reported segments, is expected to register a CAGR of 3.8% by the end of the period, i.e. 2027, reaching $14 billion.
The increasing use of toluene in the manufacturing of pharmaceuticals and blending of gasoline due to rapid industrialization and expansion of oil and gas industries offers maximum market potential in the global toluene sales and purchase market. On the other hand, the demand for it as an octane booster in gasoline is increasing its global market.
The toluene market is segmented based on type, technology, application, and geography. The benzene and xylene derivatives segment dominated the global market in 2016 and is expected to maintain its dominance during the forecast period. Based on application, the market is categorized into pharmaceuticals, paints, nail cosmetics, and others (TNT, pesticides, and fertilizers). The pharmaceuticals segment is estimated to grow at a significant CAGR of 4.9%.
The toluene sales and purchase market volume in the United States was valued at $5 billion in 2020. China, the world’s second largest economy, is expected to reach $4.9 billion by 2027, growing at a CAGR of 6.4%. Other notable geographic markets include Japan and Canada, each expected to grow by 1% and 2.6%, respectively, over the period 2020-2027. In Europe, Germany is expected to grow at a CAGR of approximately 1.7%.
