MULTIPLE CATALYSTS PRODUCE A SYNTHETIC FUEL FROM COAL

A recent government study indicates that oil prices will be substantially higher within the next few years. Thus liquid fuels from coal, will be required. The study concludes, however, that the considerable effort, time and money spent to date in trying to make gasoline from coal will be of no help in reducing in the 1990's our almost entire dependence on foreign oil.

Any grade of coal may be gasified with oxygen. The syngas is separated and adjusted, to give substantially a mixture of hydrogen, carbon monoxide, carbon dioxide after sulfur removal, and adjustment of the carbon to hydrogen ratio for methanol. It is then passed at an elevated temperature and pressure through a catalyst bed. A small percentage is converted to methanol with the evolution of a large amount of heat. This heat is removed to prevent overheating the catalyst and, in the past, has been wasted to a large extent. The gas has been recycled to build up a maximum concentration of 3 to 4% methanol containing on condensation 10 to 20% water, which must be separated.

For the American (Wentworth) process, a second catalyst has been developed whose optimum reaction temperature is above that of the gas stream leaving the first catalyst. The gas stream is passed through this second bed of catalyst without cooling, and on through a third bed of previously developed catalyst, whose optimum reacting temperature is still higher. The accumulated heat of the gas stream leaving this third catalyst bed is at a high enough temperature to allow the recovery, along with waste heat from the gasifier steps of most of the reaction heat in a waste heat boiler together with that from subsequent passage of the gas through additional beds of the first two catalysts. This recovered heat supplies energy for the complete operation of the plant including coal handling and oxygen preparation, as well as, for some electric power for sale outside.

Flow sheets with temperatures and material and heat balances show the reasons of the advantages of the multiple catalyst process, including the considerable saving of energy accomplished in the much lower compression needs for recycle of the much lower amount of gas through the beds of catalysts.