THE METHANOL PROCESS, A BASIC INTRODUCTION

1

What is Methanol ?

Many millions of tons of Methanol are produced by the Chemical Industry every year.

Methanol is the lowest member of a group of organic chemicals that belong to the Alcohol “family”.

This material must never be confused with Ethanol, (note the different spelling) which is another, (next highest) member of that family group.

This is because Ethanol is a natural product of fermentation, and when produced that way becomes the active ingredient of alcoholic drinks.

However Methanol is extremely poisonous to humans, even when ingested in very small quantities.

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.

How Is Methanol commercially produced?

Although some is still produced from old and inefficient coal gasification plants, Methanol is mainly produced in areas of the world where a large supply of Natural Gas is available at an economical supply cost.

By creating the necessary chemical reactions within the process, natural gas is converted into a valuable liquid product that is easily transported to markets in Europe, Asia and America by ship.

The two main essential ingredients, (feedstock) to produce Methanol here at “Ampco” are basically Natural Gas and Water.

However it is simply not enough to mix gas and water, (as steam) together. A lot of other conditions are also necessary.

These extra conditions include a lot of heat and pressure, in addition to another necessary material.

This other material is called a Catalyst. This is something that promotes, (encourages) the ingredients in this particular process to “crack” and “reform” into something entirely different from the original feedstock.

This is the first major step in the production of Methanol, and the process is given the general name of “Steam Reforming”

In order to understand the Steam Reforming process, a little knowledge of chemistry is helpful.

First, most people will know what H₂O is. It is of course water, but it is still H₂O even if it is in solid form, (ice), or as a vapor(steam).

2

Now if we can “crack” H₂O into its basic elements of H₂ and O we get two types of gas: Hydrogen and Oxygen.

This is what is done in a Steam Reformer, some of that H₂O, (as steam) “cracks” to go back to the elements that originally formed it.

However, not only is H₂O ‘cracked’, something similar happens to the Natural gas. Natural gas is composed of Hydrocarbons and the major part of this gas that feeds Ampco is the simplest type of Hydrocarbon, Methane, (CH₄ )

The formula CH₄ shows that there is one piece, (atom), of Carbon (C), and four pieces, (atoms), of Hydrogen, (H) in this molecule. When this Methane molecule also cracks into its basic parts, we now have a situation where these elements can be reformed into something else.

And if controlled correctly, the result is exactly the correct mixture of gases to make Methanol.

HOW THE STEAM REFORMING REACTION TAKES PLACE

3

The gases required to make Methanol later in the process leaves the Steam Reformer and the mixture is simply called Reformed Gas.

The reformed gas contains a lot of unreformed steam at this stage, however this will be cooled, condensed into water and removed. The necessary ingredients are:

75% Hydrogen, (H₂)                    all very approximate

10% Carbon Dioxide, (CO₂)               -- ------- ‘’-------- ---

10% Carbon Monoxide,(CO)               -- ------- ‘’-------- ---

A few percent of unreformed Methane, (CH₄) remains. This will be removed, (purged) from the downstream synthesis area and burned as another source of reformer fuel.

As mentioned, a great deal of heat is necessary to make this reforming reaction proceed.

A Steam Reformer is a huge gas fuelled ‘hot-box’ furnace that consumes about 30 million cubic feet of new fuel gas every day, it also burns other waste gases from the

process.

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 feed gases that pass through hundreds of catalyst filled tubes in the reforming furnace need to be heated, and maintained at about 1540ºF, (840 ºC).

It is at these conditions, and in contact with the necessary catalyst, that the reaction takes place.

This is an extreme temperature for most metals and if you are to look inside a reformer furnace you would see that these metal tubes are “white hot”. Because of this, special high temperature resisting metallic alloys are used to construct these catalyst tubes.

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

4

 A  SIMPLIFIED OVERVIEW OF THE “FRONT END” PRODUCTION OF REFORMED GAS

As was also mentioned earlier, the methanol production process requires a lot of pressure energy.

The reformed gas that has passed through a cooling process of the plant must now have its pressure boosted in order for the Methanol Synthesis reaction to occur.

Compression is achieved in 3 stages, Low, Medium and High. All these compression stages are driven by one large and powerful gas fired Gas Turbine, that itself consumes about 10 million cubic feet of gas every day.

Synthesis takes place at a pressure of about 1400 pounds per square inch, about 95 times atmospheric pressure.

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

Unlike the Steam Reforming Reaction, Methanol Synthesis creates heat and this type of heat of reaction is called “Exothermic”.

Consequently outlet gases from this reaction vessel, (called a Methanol Converter) are significantly hotter than they entered. For example, 440ºF inlet, 540ºF outlet, (226ºC / 280ºC), these temperatures vary during the life of the catalyst.

As is normal in process plant design, the exothermic reaction is made use of by heat

exchange to preheat the incoming reaction gas.

5

Again some knowledge of basic chemical reactions is helpful to get an understanding of the process of Synthesizing Methanol.

As the product methanol has the formula CH 3 OH, one molecule of methanol has:

1 part, (atom), of Carbon, (C)

1 part, (atom), of Oxygen, (O)

4 parts, (atoms), of Hydrogen, (H)

Two separate reactions can produce methanol from the above gases that were first  made in the steam reformer:

a) 2 H₂ + CO → CH₃OH

b) 3 H₂ + CO₂ → CH₃OH +H₂O

The methanol produced at this stage is in vapor form and is too hot to become a liquid, it is cooled by air fans and water cooled condensers 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. This is done in special separation vessels. Constant circulation of the unreacted synthesis gases is maintained by a separate steam turbine driven compressor, simply called the “Circulator”

Circulation, of unreacted synthesis gases is essential to ensure these reactants get as many opportunities as necessary to convert to methanol as quickly as possible.

THE SYNTHESIS OF METHANOL: THE SYNTHESIS “LOOP”

6

Purification of Methanol by Distillation

Crude Methanol contains approximately 18% of water at this stage, (along with other impurities). It is transferred to specially assigned Crude Methanol storage tanks where it will become the feed to the next part of the operation, Purification.

Purification of crude methanol to the required product quality 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. Therefore by careful control, these unwanted impurities are stripped out of the top of the column, leaving methanol and water remaining inside the column as a liquid..

Traditionally, this process is called ‘topping’ and the equipment is called a “Topping Column”

After the “topping” process, the crude is transferred to the “Refining Column”