CIEC Promoting Science at the University of York, York, UK

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Basic chemicals Methanol
Methanol

Methanol is produced from synthesis gas (carbon monoxide and hydrogen), itself derived from oil,coal or, increasingly, biomass.  It may become central to the development of biorefineries as an intermediate in the conversion of biomass to useful products.

 

Uses of methanol

The largest use for methanol is as a feedstock for the plastics industry.  It is used to make methanal and hence a variety of plastics, based on reactions with phenol, carbamide (urea) and melamine.

Polymers such as the polyesters (e.g. Terylene) and poly(methyl-2-methylpropenoate) (e.g. Perspex) use methanol as the original feedstock.  Methanol is now the principal source for the manufacture of ethanoic acid.

 

Figure 1  Uses of methanol.

Data from Methanol Market Services Asia, 2014.  Data (estimated) for 2013

 

The uses shown above correspond to the World demand but they vary proportionately from country to country.  For example, more ethanoic acid (25%) is produced from methanol in the US whereas less is used to make methanal (29%).

Whereas a few years ago, only a small amount of methanol was used directly as a fuel in cars, this use is now increasing rapidly.  In China petrol is mixed with methanol (15%) without the need for engines to be redesigned.  With some redesigning, more methanol (up to 85%) can be used.  The advantage for China is that the methanol can be produced from both coal and biomass via synthesis gas.  This emphasis of using methanol as a fuel is reflected in the global production figures for methanol.  Thus worldwide, use of methanol as a fuel now accounts for 14% (about 9 million tonnes a year) but is expected to increase to 16% of an increased total production of 92 million tonnes (about 15 million tonnes) by 2016.

Figure 2  M-85 is a mixture of methanol (85%) and petrol used in many cars in China.
By kind permission of The Methanol Institute.
A photograph of a fuel pump in a garage in China on which M-85 is displayed, indicating that the fuel is a mixture of methanol (85%) and petrol, used in many cars in that country
A photograph of two buses in China with diesel engines, refuelling with pure methanol Figure 3  Pure methanol is used in diesel engines in some buses in China.
By kind permission of The Methanol Institute.
Figure 4  Stena Line is converting its fleet of ships to run on methanol in order to reduce the pollution that occurs when burning fuel oil which is of particular concern in the Baltic.  The Stella Germanica, here in Gothenburg, Sweden, getting ready to sail to Kiel in Germany, underwent extensive sea trials using methanol before the decision was made to convert over 20 other ships.
By kind permission of Marcusroos (Wikimedia Commons).

An even more remarkable increase is the use of methanol to produce alkenes by the MTO and MTP processes, from 6.6 million tonnes in 2013  to an expected 20 million tonnes in 2016, which will mean that a large proportion of plastics such as poly(ethene) and poly(propene) will be derived from synthesis gas.

Annual production of methanol

World 65 million tonnes
Europe 2.6 million tonnes
US 2.8 million tonnes
Middle East 14 million tonnes
S E Asia 4.8 million tonnes
China 35 million tonnes
South America 10 million tonnes

Data from Methanol Market Services Asia, 2014.  Data (estimated) for 2013

 

Manufacture of methanol

Methanol is manufactured from synthesis gas which is a mixture of carbon monoxide and hydrogen.

The feedstock, over the last 40 or more years, has been oil or natural gas.

However, two developments have occurred over recent years.  In one, particularly in China, coal, rather than natural gas or oil is being used.

In the second, there have been major developments to produce methanol which is largely ‘green’.  Any solid biomass including for example agricultural, city and industrial waste can be used to make synthesis gas using techniques similar to its production from coal.   More recent developments include a plant in the Netherlands, which is using liquid propane-1,2,3-triol (glycerol), a by-product from the production of biodiesel, from animal fats and vegetable oils , to produce the gas.

Another ‘green’ route is to use waste carbon dioxide.  Although the first such plant is linked to geothermal energy, it could be used to convert carbon dioxide waste from, for example, lime kilns and steel manufacture, to methanol.

Synthesis gas is catalytically converted to methanol at elevated temperatures and pressures in a fixed bed reactor. The catalyst is an alumina pellet coated with copper and zinc oxides.

The main methanol synthesis reaction may be written:

From considering the energetics of the reactions, it can be seen that the yield of methanol is favoured by high pressures and low temperatures. A low pressure process came about by the discovery of a copper-based catalyst which was active at 475-575 K, thus allowing economical conversions to occur at 40-100 atm.  One plant, for example, operates at 525- 575 K and 100 atmospheres. It eventually achieves a 97% conversion of the reactants.

The actual mechanism for the formation of methanol has been an active area of research.  By using radioactive 14CO2 it is believed that the majority, if not all, of the methanol is derived via CO2.

A photograph of a converter in which methanol is being produced from synthesis gas, a mixture of carbon monoxide and hydrogen

Figure 4  The converter in which methanol is being produced from synthesis gas.
By kind permission of Johnson Matthey.

Future outlook

A large proportion of methanol is used to make methyl t-butyl ether (MTBE), which is added to petrol in many countries.   It reduces 'knock' and also the proportion of carbon monoxide and hydrocarbon in the exhaust.  However it is a serious pollutant and, when spilled, gets into water-courses.  Its use is being phased out in the US.

Methanol is destined to be a major fuel for cars, either a liquid fuel, mixed with petrol, or in fuel cells. It is also a route by which synthesis gas can be converted into liquid fuels.  One way is by using the Mobil MTG (methanol to gasoline) process.

Methanol is converted into alkanes and aromatic hydrocarbons suitable for petrol (hydrocarbons with 5 to 8 carbon atoms), by passing the vapour over alumina at ca 600 K.  An equilibrium mixture of methanol, dimethyl ether and steam is produced, containing about 25% methanol:

This mixture of gases is then passed over a bed of a zeolite in its acid form, HZSM-5, heated to ca 650 K, to produce the mixture of hydrocarbons (with 5-10 carbon atoms) for use as petrol.

Although dimethyl ether is a gas at ambient temperatures, it can be readily liquefied under pressure and is considered to be an attractive alternative fuel to diesel oil.  It is also mixed with liquid petroleum gas (LPG) as a fuel for use in homes.

The first MTG plant was built in New Zealand and new plants are being built that will also respond to demand for methanol and ammonia, both of which need synthesis gas.  Recent work in China and Japan has led to the development of the direct synthesis of dimethyl ether from the mixture of carbon monoxide and hydrogen, instead of a two stage process via methanol.  Also by changing the catalyst slightly, (a silicoaluminate with phosphate ions), the main products are ethene and propene.  Furthermore there is the possibility of altering the rate depending on which alkene is in greater demand.

It is thought that the reactants produce methanol which is dehydrated over the catalyst to produce CH2 species which, in turn, combine to form the two alkenes.

These processes are of particular interest as it could provide a route to produce chemicals from biomass.

 

 

Date last amended: 6th April 2014

 

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