Chemistry of hydrocarbon compounds – Production of hydrocarbon mixture from refuse or vegetation – From synthetic resin or rubber
Reexamination Certificate
2001-10-04
2004-04-13
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Production of hydrocarbon mixture from refuse or vegetation
From synthetic resin or rubber
C585S435000, C585S436000
Reexamination Certificate
active
06720467
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This application concerns a process and apparatus for the reclamation of polystyrene-type waste materials and a reclaimed polystyrene product. Due to the choice of dissolution solvent and the use of lower temperatures in the recovery section, the reclaimed polystyrene product will not be subject to degradation. Accordingly, the reclaimed polystyrene product will be within the specification ranges of the input polystyrene-type material.
The process and apparatus include dissolution of the waste polystyrene-type materials in a dissolve section utilizing a reusable solvent having a low boiling point and high vaporization rate, removal of solid contaminants in one or more filter sections, devolatilization of the dissolved polystyrene and recovery of the polystyrene-type material in a solid form in a recovery section. Preferably the process and apparatus include recycling and reuse in the process of the vaporized solvent from the recovery section. The process and apparatus may also include reduction of the polystyrene-type material to be reclaimed in a reduction section prior to its entry into the dissolve section. The maximum temperature in the recovery section is 190° C. The reusable solvent is preferably environmentally safe and has a low boiling point and high vaporization rate. n-Propyl bromide, or environmentally safe mixtures thereof, is the preferred reusable solvent.
The recovery of plastic materials has been a focus of many organizations, governments, and individuals for some time. Some plastic materials, such as polyethylene-terephthalate and polyethylene, have found extensive use in the recycling industry. However, recycling of polystyrene-type resins has not met with the same technical or economical success, and the disposal of polystyrene-type materials continues to present unresolved environmental problems. No simple means for recovery of polystyrene-type material is presently available, especially when the polystyrene-type material are fabricated into foam material. Polystyrene foam is much less dense than non-foamed polystyrene because it contains considerable volume of air encapsulated by the solid polystyrene construction. This increases the storage, transportation and disposal costs, including the use of mechanical and chemical means of reducing the size of such waste material. Waste toner, for example, as used in copying and printing machines, is another polystyrene based product which is in need of an environmentally safe means of recovery.
Due to the lack of efficient and environmentally safe recycling means, most of the products made of polystyrene-type materials are disposed of in landfills or incinerated. However, the polystyrene resin in such landfills does not decompose and may be dissolved by leachate from decomposition of other organic matter. The resulting leachate material contaminates the methane gas generated in landfills, which is finding use as a fuel source by energy generating companies. Thus, the removal of polystyrene-type materials from solid landfill materials is desirable even though their presence could add to the fuel value. Similarly, when the polystyrene resin is incinerated, the resulting gases are toxic and heavy carbon deposits tend to cause clogging of the stacks.
Current methods for recycling polystyrene have the additional drawback of degrading the material so that it is not reusable for the same grade or quality of polystyrene-type product as the waste material. This further devalues the recovered polystyrene-type material. The present process, on the other hand, will provide a reclaimed polystyrene product within the specification ranges of the input polystyrene-type material, where the input material comprised of a single polystyrene or closely related polystyrenes. Even when reclaimed from diverse waste polystyrenes, the reclaimed polystyrene product of the invention exhibits a surprisingly high quality when compared to a similar product made from virgin polystyrene.
2. Prior Art
U.S. Pat. No. 4,517,312, to Kumasaka et al., describes a process for regenerating a resin based on dissolving the waste plastic in an organic solvent and the solution mixed with an immiscible solvent, scarcely dissolving the resin, which will then precipitate the resin. Organic solvents having specific gravities larger than water, such as methylene chloride, trichloroethylene or carbon tetrachloride are preferably used. In the examples wherein waste foam polystyrene foam is recovered, it is dissolved in methylene chloride and then mixed with water resulting in the resin separating out at the interface of the liquids. Such solvents are not considered environmentally safe.
U.S. Pat. No. 5,198,471, to Nauman et al., describes a process for selectively separating various plastic materials found in a typical waste stream from a household. The process utilizes specific solvents to separate each type of plastic of the commingled stream, then separates the resulting solution from the remaining materials and removes the solvent to recover the specific resin. Tetrahyrofuran, toluene, and xylene are used to dissolve mixtures of polystyrene (PS) materials with other plastic materials, resulting in a mixture of PS and one or more other plastic materials in solution. The other plastic materials may be present individually or in combination and include polyvinyl chloride (PVC), low and high density polyethylene (LDPE and HDPE), polypropylene (PP), and polyethylene terephthalate (PET). However, for efficient operation of the process, the dissolved solids concentration must be either very little <20% or concentrated to >80%, preferably <10% or concentrate to >80%, to be effective. For a PVC/PS mixture first dissolved in tetrahydrofuran, methylene chloride may be used to separate out the PS. The flash evaporation (devolatilization) temperature is between 200° C. and 400° C. and takes the solution to a concentration of 50-95% by weight of polymer solids.
U.S. Pat. No. 5,223,543, to Iovino, describes a process for reducing the volume of polystyrene foam using d-limonene as a solvent.
U.S. Pat. No. 5,269,948, to Krutchen, describes decontamination of polystyrene using styrene monomer to dissolve the contaminated polystyrene. The resultant solution is then used in the polymerization of polystyrene.
U.S. Pat. No. 5,300,267, to Moore, describes process and apparatus to reclaim solid polystyrene type waste materials. It includes a dissolve unit and a recovery unit that is based on thin film evaporation and higher temperatures for processing with the solvent, the specific solvent being perchloroethylene.
U.S. Pat. No. 5,629,352, to Shiino et al., describes a process for reduction of polystyrene foam and the recycling of such using solvents consisting of a mixture of a glycol ether and dialkyl ester. The solvent comprises at least one member selected from the group consisting of such a glycol ether compound as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, or dipropylene glycol dimethyl ether and such a fatty acid dialkyl ester compound as dimethyl succinate, dimethyl glutarate or dimethyl adipate. These solvents have flash points of 100° C. or greater and need the addition of water to be made non-flammable.
U.S. Pat. No. 5,824,709, to Suka, discloses a process wherein a waste plastic containing a polymer such as polystyrene, polypropylene or ABS resin is dissolved in a solvent to forma solution of waste plastic at elevated temperature. The solution is filtered to remove labels or adhered foreign debris. The filtrate is heated to a temperature of 200° C. to 300° C. under a pressure of 1-75 torrs to remove the solvent by evaporation, and the resulting plastic melt is extruded into pellet whereby the waste plastic is recovered. If the plastic material to be recovered is polystyrene, toluene and ethylbenzene are the most preferred solvents.
U.S. Pat. No. 5,891,403, to Badger et al., describes a portable waste disposal unit for treating waste polystyrene, especially foamed polystyrene, using per
Carreras Edmond J.
Cistone David R.
Moore L. Steven
Dang Thuan D.
Resource Recovery Technologies, Inc.
Seifert Arthur G
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