The Total Recycling Of Carbon Compounds

One of the major sources of pollution is the material discarded by individuals and industry. These materials are commonly called trash, garbage or solid waste. These discarded materials can probably be converted to usable materials by the process that converts coal to petroleum-like chemicals. This has been investigated and has the potential as a method of total recycle of carbon compounds. The Pittsburgh Center of the Bureau of Mines has used hydrogen to treat municipal solid waste and produce a product similar to crude oil. In these investigations, solid waste was placed in a cylindrical chamber lined with a refractory material. A mixed gas consisting of a large excess of hydrogen with a small amount of oxygen was injected into the cylinder and ignited. The excess hydrogen and the waste were heated to a high temperature by the reaction of the hydrogen with the small amount of oxygen. The cylinder was rotated to stir and grind the waste. The hot hydrogen rich gas converted the organic materials to a crude oil-like chemical mixture. The mixture was swept from the cylinder as a vapor by the incoming gas and the steam produced by the combustion of the hydrogen with the oxygen. On exit from the cylinder, the gas was cooled. Cooling will condense most of the crude oil material and water, to a liquid. Physical and chemical processes removed the organic compounds remaining in the gas. Any un-reacted hydrogen was recycled. The sulfuric and hydrochloric acids produced by reacting sulfur or chlorine-containing materials were recovered with the water. 157

There was no atmospheric nitrogen introduced into this process. As a result, there was no waste gas vented to the atmosphere. All gases exiting from the cylindrical reactor were recovered or recycled. The remaining solids consisted of glass, ceramic and metal components of the solid waste. The

197 Corey, R. C., "Pyrolysis, Hydrogénation and Incineration of Municipal Refuse", Proceedings of the second Mineral Waste Utilization Symposium, Illinois Institute of Technology, Chicago, March 1970

hydrogen reduced most common metals, with the exception of aluminum, to the free metal state. Aluminum has a high chemical affinity for oxygen. Hydrogen cannot strip the oxygen form aluminum oxide. As a result, this process will convert the aluminum in the waste to aluminum oxide, a ceramic like material. Iron can be separated from the ceramic materials by magnetic separation. The only product from this process that will not be recovered or recycled is the ceramic ash containing nonmagnetic stainless steel and modest amounts of other metals present in the solid waste.

While not investigated in depth, the un-reacted ash can be subjected to a mixture of hydrogen and oxygen, with sufficient oxygen to raise the temperature above the melting point of the steel. This will melt the ceramic materials to an ash and allow the recovery of the metals as a peculiar mixture of iron, nickel, chromium, lead, tin, copper, zinc and other metals. The properties of this alloy are not known, but it may be useful in applications where a metal is desired but high quality is not essential. It may also be possible to reprocess this alloy to recover the pure metals.

A portion of the slag can be molded into the grinding balls used for the low temperature processing of the waste materials. The remaining material has properties similar to many rocks and can safely be used as fill for construction projects or buried in conventional landfills. Because of its inert rock like nature, it will have no more impact on the environment than do natural rocks.

This process will allow the recycling of solid waste to produce a useful product. High pressure and temperature combined with hydrogen can convert most types of domestic and industrial wastes back into products that are currently obtained from fossil coal and oil. No volatile polluting chemicals will be vented into the atmosphere. The metals can be recovered for further use and the ceramic materials will be converted into a product difficult to distinguish from natural rocks. This type of process will not solve all the solid waste disposal problems, but will provide a potential method for recovery of valuable products from waste. When implemented, it will dramatically reduce the amount of solid waste placed in landfills. This process also has the potential to reduce the amount of oil and coal mined to provide the carbon compounds needed to manufacture all petrochemical derived materials. This waste reduction process is a variation on the Fischer-Tropsch process, mentioned on page 101, in use commercially to produce hydrocarbon materials from coal.

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