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Three methods used in industrial production of toluene

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Three methods used in industrial production of toluene

Post  bejoy on Tue Feb 11, 2014 2:01 am

Toluene is an aromatic hydrocarbon that is widely used as an industrial feedstock and as a solvent. Toluene occurs naturally at low levels in pine oil and is usually produced in the processes of gasoline via a catalytic reformer, in an ethylene cracker or making coke from coal. Final separation, either via distillation or solvent extraction, takes place in one of the many available processes for extraction of benzene, toluene and xylene isomers.

Previously Toluene was produced commercially from
From Coal Gas and Light Oil

Toluene is obtained from light oil by fractional distillation. The light oil from coal carbonization is recovered by cooling and scrubbing the by- product coke oven gas. The light oil which condenses with the tars contains 12 to 20 per cent of toluene. This is scrubbed from coke oven gas and distilled from tar, are combined and fractionally distilled in continuous or semi continuous units. Between 0.1 to 0.2 gal of toluene is obtained per gal of combined light oil distilled.

Chemical properties of Toulene From
Petroleum by Hydroforming

Toluene is produced from specially selected fractions of petroleum, rich in naphthenes, by catalytic reforming (also known as hydroforming). This involves catalytic dehydrogenation in the presence of hydrogen (which reduces coke formation) to yield a mixture of aromatic hydrocarbons, chiefly toluene. The feed stock (a selected naphtha fraction) is preheated in heat exchangers and is then totally vapourized in a furnace. Here it is joined with a hydrogen rich recycle gas and a mixture is passed through a reactor with a constant time.

The reactor contains a dehydrogenated catalyst consisting of 10 per cent molybdenum dioxide on alumina. The reaction gas passed through heat exchangers (preheating the feed stock) to a gad – liquid condenser and separator. Here a large portion of a separated wet gas is compressed and is recirculated to the furnace and reactor to increase the hydrogen concentration. The hydrogen tends to reduce coke formation and thus maintain catalytic activity. The remaining gas and liquid passed to conventional absorption and stabilizing columns, which produce fuel gas gasoline and hydroformate. The latter contains about 20 per cent of toluene and may be recirculated through the reactor for maximum conversion to obtain a two pass hydroformate containing 38 per cent toluene.

Find here toluene manufacturers, toluene suppliers

Alternate Catalytic Reforming Processes.

Several catalytic reforming processes have been developed by various organizations.
The processes differ in details, operating conditions, and type of catalyst used. Some of these processes are listed below.
Fluid Hydroforming Process uses a fluidized solids technique in the reactor and continuous regeneration of the molybdenum on alumina catalyst in a separate vessel.
Platforming is a fixed bed process using several reactors in series with intermediate reheating. Catforming is also a fixed process using a platinum catalyst.

Present day the method used to produce Toluene is by separating the aromatic Mixture.

The methods used to separating benzene, toluene and xylene are grouped as -

a. Fractional distillation - The various components of crude oil have different sizes, weights and boiling temperatures; so, the first step is to separate these components. Because they have different boiling temperatures, they can be separated easily by a process called fractional distillation. Hence, toluene is separated by boiling components at different boiling points.

b. Azeotropic distillation - Azeotropic distillation can be defined as distillation in which the added substance forms an azeotrope. Two commercial processes have been developed for the separation of toluene using azeotropic distillation. One using an aqueous solution of methyl ethyl ketone and water and the other using methanol. Both processes operate on a narrow boiling range concentration gradient.

c. Extractive distillation – Extractive distillation can be defined as distillation in the presence of a substance which is relatively non-volatile compared to the components to be separated, and which, therefore, is charged continuously near the top of the fractionating tower, so that an appreciable concentration is maintained on all plates in the tower below its entry.

The extractive distillation involves the use of a solvent for liquid-liquid extraction. Many different solvents are suitable, including sulfolane (C4H8O2S), furfural (C5H4O2), tetraethylene glycol (C8H18O5), dimethylsulfoxide (C2H6OS), and N-methyl-2-pyrrolidone (C5H9NO).

d. Solvent extraction - The most important requirement for a solvent in a solvent extraction process are that it should have a high selectivity for aromatics against non- aromatics, that a two- phase system is obtained in a reasonable range of temperature, and that the phases should separate within a reasonable range of temperature; of course it must also be non- corrosive, non- reactive and thermally stable.


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