Comparison of carbon dioxide reduction methods

1. THE CARBON DIOXIDE PROBLEM

The concentration of carbon dioxide in Earth’s atmosphere is approximately 400 ppm in this year and rose by 2.0 ppm/yr during 2000-2009. This current concentration is substantially higher than the 280 ppm concentration present in pre-industrial times, with the increase largely attributed to anthropogenic sources. Carbon dioxide is a prominent greenhouse gas. The present level is higher than at any time during the last 800 thousand years, and likely higher than in the past 20 million years (Wikipedia).

2. THEORETICAL AND CLASSICAL REDUCTION METHODS

2.1. The thermal decomposition

The thermal decomposition of carbon dioxide to carbon monoxide begins at 1500oC, around 20 % at 2500oC and 90 % at 3500oC. The recomposition should be prevented so that the temperature must be suddenly reduced below 700oC. This method is not applied due to technical difficulties.

2.2. Reduction with metal

The reduction to carbon can be carried out with magnesium at 600oC.

The method is impractical because of the cost of the regeneration of magnesium oxide.

2.3. Reduction with hydrogen

These methods are common in many different versions. Methods differ in the hydrogen source, catalyst and products. Hydrogen can be produced from water with electrolysis, from natural gas. Products are formic acid, oxalic acid, methanol, methane, carbon monoxide etc.
The source of the energy is electrical energy or fossil fuel.

3. OTHER CARBON DIOXIDE REDUCTION METHODS

3.1. Sandia method

Sandia’s Sunshine to Petrol (S2P) technology uses the high temperatures generated by concentrating sunlight along with a zirconia/ferrite catalyst to break down atmospheric carbon dioxide into oxygen and carbon monoxide. The carbon monoxide can then be used to synthesize conventional fuels such as methanol, gasoline and jet fuel.

3.2. Stanford method

A combination thermal/photochemical cell has also been proposed. The Stanford PETE process uses solar thermal energy to raise the temperature of a thermionic metal to about 800oC to increase the rate of production of electricity to electrolyse atmospheric carbon dioxide down to carbon or carbon monoxide which can then be used for fuel production, and the waste heat can be used as well.

3.3. The problem of these methods

They are reducing the carbon dioxide with solar energy therefore they can do the reduction only when there is enough sunshine.

In the temperate zone, the annual dispersion of the energy is not adequate either. Most of the energy is needed in the winter, however the sunbeams are the least effective in the winter. In the summer the number of sunbeams is too much, in the winter it is too few. The situation is the same at the named energy producing areas too.

4. AND THE SIMONYI’S METHOD

This method does not use solar energy for the reduction. This energy comes from the reagent therefore the reduction can be carried out in the winter, too. The regeneration of the reagent can be done in the summer because it can be stored for a long time.

And this method does not use fossil fuel for the reduction.

Professor, Dr Laszlo de Nagy