SMC

Methanol

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Methanol Manufacturing Process

Methanol is the simplest alcohol compound, comprised of one carbon atom, one oxygen atom and four hydrogen atoms (CH3OH). It is also referred to as wood alcohol, carbinol and methyl alcohol. It is flammable and has no taste (but do not drink it - is poisonous), or color, but it does have a slight scent.

Methanol is a basic ‘building block’ for the production of other chemical products such as Plastics, Paints and Man-Made Fibers. It has also found a large use in the production of Gasoline Fuel additives. (See below Methanol applications). Many millions of tons of Methanol are produced by the Chemical Industry every year.

Step 1: Feed Purification
Before the Natural Gas is sent for steam reforming, the gas is desulphurised by passing it through a bed of catalyst which converts the sulphur compounds in the natural gas to hydrogen sulphide and then through beds of zinc oxide which adsorb the hydrogen sulphide. The outlet Sulphur content is less than 0.1 ppm. Sulphur is a catalyst poison for both reforming and methanol catalysts.
Step 2: Steam Reforming
Reforming is the process which transforms the methane (CH4)/higher hydrocarbons present in natural gas when mixed with steam (H2O) to intermediate reactants of hydrogen (H2), carbon dioxide (CO2), carbon monoxide (CO).

A great deal of heat is necessary to make this reforming reaction proceed. The reason that such a large fuel consumption is necessary is because the Steam Reforming reaction is ‘endothermic’ this means it is heat demanding.
The feedstock gas passes through hundreds of catalyst-filled tubes in the reforming furnace and is heated and maintained at about 850-875 ºC.

After the Steam Reforming process, most of this heat is not wasted but recovered by use of heat exchangers that transfer this heat energy to other parts of the process that requires it.

The reformed gas that has passed through a cooling process must now have its pressure boosted in order for the Methanol Synthesis reaction to occur at an economic rate.
Step 3: Synthesis and Compression
Compression is achieved through a centrifugal compressor which is driven by one large and powerful steam turbine. Synthesis takes place at a pressure of about 80 bar. This compressor has as much power as about 400 cars running together.

Methanol Synthesis also requires the use of a (different) Catalyst and the reaction takes place at a temperature that allows the best conditions for optimum production.

The methanol produced at this stage is in vapor form and is too hot to become a liquid, it is therefore cooled so that it changes to liquid Crude Methanol.

In liquid form, it can then be separated from other gases that are circulating around and through the Methanol Converter.

Circulation of un-reacted synthesis gases is essential to ensure these reactants get as many opportunities as necessary to convert to methanol as quickly as possible.
Step 4: Purification of Crude Methanol by Distillation
Crude Methanol contains approximately 18% of water at this stage (along with other impurities). It is transferred to the Crude Methanol storage tank where it will become the feed to the next part of the operation i.e. Purification by distillation

Purification of Crude Methanol to the required methanol product quality (IMPCA or US Federal Grade AA spec) is achieved in two separate distillation columns.

The first column is designed to remove low boiling impurities, also called ‘Light Ends’. These ‘light ends’ are simply materials that will boil at a lower temperature than the boiling point of Methanol. Traditionally, this process is called ‘topping’ and the equipment is called a ‘Topping Column’ or ‘Light Ends Column’.

After the ‘topping’ process, the crude is transferred to the ‘Refining Column or Heavy Ends Column’. It is in this next step of purification that the liquid is again constantly boiled until the water (which boils at a higher temperature) is separated from product methanol (which leaves the top of the column).

Good quality methanol vapor separates and rises to the top of this column. From here it is changed back to liquid, (condensed). Part of this condensed liquid methanol, (called distillate) is taken to the storage tanks called Check Tanks.

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Use of Methanol

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