Water gas

Water gas is a synthesis gas, containing carbon monoxide and hydrogen. It is a useful product but requires careful handling because of the risk of carbon monoxide poisoning. The gas is made by passing steam over a red-hot carbon fuel such as coke:

H₂O + C → H₂ + CO (ΔH = +131 kJ/mol)

The reaction is endothermic so the fuel must be continually re-heated to keep the reaction going. In order to do this, an air stream, which alternates with the vapor stream, is introduced for the combustion of carbon to take place.

O₂ + C → CO₂ (ΔH = −393.5 kJ/mol)

Theoretically to make 6 L of water gas, 5 L of air is required.

Or alternatively to prevent contamination with nitrogen, energy can be provided by using pure oxygen to burn carbon into carbon monoxide.

O₂ + 2 C → 2 CO (ΔH = −221 kJ/mol)

In this case 1 L of oxygen will create 5.3 L of pure water gas

History

The water gas shift reaction was discovered by Italian physicist Felice Fontana in 1780. Water gas had been made in England since 1828 by blowing steam through white-hot coke, this water gas was carburized by petrol according to a process invented by Lewis Thompson and Hind (Singer 119). Charles Singer also states in his "A History of Technology" that, in the United States, natural gases were often used for carburizing (Singer 119).

Lowe's gas process

In 1873, Thaddeus S. C. Lowe developed and patented the water gas process by which large amounts of hydrogen gas could be generated for residential and commercial use in heating and lighting. Unlike the common coal gas, or coke gas which was used in municipal service, this gas provided a more efficient heating fuel. The process used the water gas shift reaction:

CO + H₂O → CO₂ + H₂

The process was discovered by passing high-pressure steam over hot coal, the major source of coke gas. Lowe's process improved upon the chimney systems by which the coal could remain superheated thereby maintaining a consistently high supply of the gas. This process created a thermo-chemical reaction of applying hydrogen, in the steam, to carbon monoxide, in the coke gas. The reaction produced carbon dioxide and pure hydrogen which after a process of cooling and "scrubbing," passing through water vapor, produced pure hydrogen gas.

The process spurred on the industry of gas manufacturing, and gasification plants were established quickly along the Eastern seaboard of the United States. Similar processes, like the Haber Process, led to the manufacture of ammonia (NH₃) by the combining of nitrogen, found in air, with high volumes of hydrogen. This spurred on the refrigeration industry which long used ammonia as its refrigerant. Prof. Lowe also held several patents on artificial ice making machines, and was able to run successful businesses in cold storage as well as products which operated on hydrogen gas.

Variations

Carburetted water gas

Water gas had a lower calorific value than coal gas so the calorific value was often boosted by passing the gas through a heated retort into which oil was sprayed. The resulting mixed gas was called carburetted water gas.

Semi-water gas

Semi-water gas is a mixture of water gas and producer gas made by passing a mixture of air and steam through heated coke. The heat generated when producer gas is formed keeps the temperature of the coke high enough to allow water gas to be formed.

Water gas shift reaction

Pure hydrogen can be obtained from water gas by using the water gas shift reaction, after subsequent removal of the carbon dioxide formed when carbon monoxide reacts with water.

See also

• Coal gasification
• Fluidized bed
• Fluidized bed combustion
• Gasification
• Gasifier
• History of manufactured gas
• Isle of Wight gasification facility
• Lane hydrogen producer
• Linde-Frank-Caro process
• List of solid waste treatment technologies
• Mond gas
• Plasma arc waste disposal
• Pyrolysis
• Renewable natural gas
• Town gas
• Wood gas

References

• Mellor, J.W., Intermediate Inorganic Chemistry, Longmans, Green and Co., 1941, pp 210–211
• Adlam, G.H.J. and Price, L.S., A Higher School Certificate Inorganic Chemistry, John Murray, 1944, page 309
• Singer, Charles Joseph; Raper, Richard. A history of technology : edited by Charles Singer ... [et al.]. Clarendon Press, 1954-1978. History e-book project.. ACLS Humanities E-book. Vol 5. "The use of mineral oil" p. 119ar:غاز الماء