Technology tapped to get more from coal

Press, 16 December 1981, Page 14

Technology tapped to get more from coal

From the “Economist, London

Today’s largely uneconomic synthetic-fuels processes rely mostly on the brute strength of heat and pressure to turn coal into oil and gas. ReSearchers now hope that they can develop more scientific, and perhaps more efficient, processes by studying ■the chemistry of coal. Exxon is already enthusiastic about the economic benefits of studying coal chemistry. Researchers there recently devised a technique that can predict which types of coal will give best results in which synthetic-fuels process.

This technique is based solely on an analysis of the chemical make-up of a particular coal. This make-up varies significantly from one mine to another. The analysis can be done in the laboratory, side-stepping the need to test potential coal feedstocks under actual working conditions.

Exxon's work has aroused the interest of researchers elsewhere. How well a coal will burn can roughly be

predicted, from its carbon content alone. But the Exxon results prove that if you want to use coal in chemical reactions you must take into account the amounts of all the elements in coal, including, for example,-oxygen and sulphur. This knowledge gives fresh impetus to scientists who are struggling to find out exactly how all the different types ol atoms that make up coal are linked together into the molecules that give the material its chemical properties. Detailed molecular knowledge, say these scientists, may- help in creating improved processes for making synthetic fuels. Unfortunately, this research is a hard slog. The blame lies in the coal itself, which is impossible to analyse with conventional laboratory techniques. New, computerised techniques provide a glimpse ol coal's molecular structure. Drawn on paper, coal’s collection of atomic loops and chains looks like a surrealist's version of chicken wire. But looking at its molecular structure in more detail shows that bonds between oxygen and carbon atoms play a bigger part in holding coal molecules together than had previously been thought. Generally speaking, bonds between oxygen and carbon are easier to break than those between one carbon

atom and another. Today's synthetic-fuels processes concentrate on this difficult business of breaking carbon-to-carbon bonds. The processes of tomorrow may concentrate more on links beetween oxygen and carbon. With luck, these links and other molecular bonds in coal could be broken with clever chemical processes rather than the energy-inten-' sive heat and pressure which is now used.

Although this is mere hope at present, scientists can point to two other syntheticfuels innovations that have stemmed from advances in basic chemistry during the last 10 years. These are Mobil's discovery that socalled zeolite catalysts can transform methanol into liquid fuels and Exxon’s discovery of how potassium carbonate can help turn coal into gas.

Potassium carbonate speeds up the gasification of coal under pressure and ensures that a certain percentage will be converted to methane (one of the constituents of natural gas). This discovery enabled Exxon to design a process that combines the three steps of conventional gasification into a single, energy-saving process. A $5OO million pilot plant is planned to be built in Rotterdam • by 1985. Mobil may build a‘plant in New

Zealand, based on its process for making petrol from methanol. Innovations are also afoot for getting the oil out of oil shale. The most immediate task is how to reduce the enormous energy needed to separate oil from' the useless rock that comprises more than 80 per cent of most oil shale. This is done today by heat and pressure but researchers are turning to high technology to find ways of separating at least some of the, rock from the oil before this stage of the process. Among the possible separation techniques are: • Ultrasound. In theory, very high-frequency waves of sound could pulverise the oilcontaining rock and help separate oil from it. • Magnets. Rock and oil supposedly respond differently, though very weakly, in a magnetic field. The idea here is to use powerful elec-tro-magnetic fields to push pulverised oil and rock away from one another.

Sceptics of these methods take solace from the fact that the separation technique farthest along the development road is also the simplest: water. Oil-containing rock particles and those without oil sink at different rates. By, for example, floating the particles down a stream, the oil-rock and the ordinary rock could be made to sink in different places.