1. Field of the Invention
The present invention is of a process for degrading long chain hydrocarbon-containing compositions to produce simpler hydrocarbons suitable for use as a fuel. More specifically, waste plastics (organic polymers) are heated in an oxygen-free atmosphere and subjected to intense light of a wave length that will excite and break chemical bonds causing degradation of the plastic into simpler hydrocarbons suitable for use as fuel. Further, the process may also be applied to tar sands and oil shale to produce simpler hydrocarbons.
2. Description of the Related Art
Recent studies reveal that some of the primary concerns of Americans in the 90's are the continuing pollution of the environment, the availability of sources of environmentally-friendly fuel, and landfill space for disposal of wastes. Ironically, one of the prime constituents of waste is "plastics"--a range of durable organic polymeric components largely made from petroleumderived hydrocarbons that now pose environmental issues as declining U.S. reserves and political needs dictate a shift to production in environmentally sensitive geographic areas in the United States.
Since plastics are produced from hydrocarbons, the reduction of used or waste plastics back to gaseous hydrocarbons would be desirable thereby reducing the need for hydrocarbon fuels and pressures to exploit reserves in environmentally sensitive areas.
The primary method used to decompose plastic materials, either alone or in combination with other solid waste, is by incineration or oxidation with direct heat. Unfortunately, the burning of plastic materials in their solid state results in the formation of corrosive and toxic products. Decomposition of plastics may also be accomplished by direct pyrolysis. Depending on the materials being processed, this requires temperatures from about 450.degree. C. to 700.degree. C. As such, the considerable amount of energy required with direct pyrolysis makes it cost-prohibitive. In the present invention, the process of breaking the molecular bonds of plastic materials to produce simpler hydrocarbons utilizes pyrolysis in conjunction with radiation without the need for the high energy requirement of conventional pyrolysis and without significant production of corrosive products.
It is well-known that solar ultraviolet radiation causes decomposition of plastic materials. Plastic manufacturers add UV blockers to their products to inhibit this degradation. Earlier studies have suggested the use of sunlight's ultraviolet rays for the purposeful decomposition of plastic materials. M. Day and D. M. Wiles in "Photochemical Degradation of Polyethylene Terephthalate. Irradiation Experiments with the Xenon and Carbon Arc," Journal of Applied Polymer Science, vol. 16, pp. 175-89 (1972) suggested the use of 200 to 400 nm wavelength range of sunlight and durations of 1,000 hours of arc lamp exposure. Tests performed with large lamps, however, gave unsatisfactory results. Similarly, Bennington et al. in U.S. Pat. No. 4,432,344 disclosed a method and apparatus for solar destruction of toxic and hazardous materials. The patent described the use of a solar collector to concentrate and focus the sun's energy into a reaction vessel containing a mixture of solids, liquids, or gases to break chemical bonds and then to further oxidize the resulting hazardous and toxic wastes to complete the destruction process.
The excimer laser has been utilized as an ultraviolet wave source for ablative photodecomposition associated with etching or fabricating of polymer materials. Unlike pyrolysis, photo ablation is not a chemical process. Portney et al. in U.S. Pat. No. 4,842,782 disclosed the precision machining of ophthalmic lenses using an excimer laser radiating ultraviolet light. Blum et al. described a technique for the fabrication of devices and circuits composed of multiple layers of materials in U.S. Pat. No. 4,414,059. The Blum process utilized ablative photodecomposition for the selective removal of portions of the resist layer to produce a patterned layer as required in lithography. Photoetching of polyesters, such as polyethylene terephthalate, by ultraviolet radiation was disclosed by Mayne-Banton et al. in U.S. Pat. No. 4,417,948. Both Blum and Mayne-Banton disclosed the use of an ArF excimer laser emitting wavelengths of 193 nm for their etching techniques. The presence of atmospheric oxygen or air was described to enhance the etching process.
More recent studies of the ablation process include a report by R. Srinivasan and Bodel Braren in Chemical Review, vol. 89, no. 6, pp. 1303-16 (1989). The article gives an overview of the ablative etching process for numerous polymers. Another comprehensive report titled "Ultraviolet Laser Photo Ablation of Polymers: A Review in Recent Results" was reported by S. Laser and V. Granier of the Photo Physics Laboratory for Molecular Photo Chemistry in Talence, France. This report, published in Laser Chemistry, vol. 10, pp. 25-40 (1989) gives a comprehensive review and theoretical analysis of the ablation process.
Recycling of plastics waste through physical methods such as compression and melting was described by McDonald in U.S. Pat. No. 4,413,969. The recovery and reuse of volatile blowing agents used in the production of thermoplastic foams can be found in Burt's U.S. Pat. No. 4,531,950 which discloses a method and apparatus for recovering the gaseous blowing agents which are contained within the cellular structure of foam. In the process, both the blowing agent and the thermoplastic resin are recovered in a form suitable for reuse. Vreenegoor in U.S. Pat. No. 4,601,864 also described a method of drawing off noxious gases during the production of polymeric foam products for recycling purposes.
None of the processes described above, however, suggest the recovery of simple hydrocarbon gases during the pyrolysis of plastics. Nor have they addressed the problems of recovering simple hydrocarbons from oil shale or tar sands.