Chemistry of hydrocarbon compounds – Production of hydrocarbon mixture from refuse or vegetation – From synthetic resin or rubber
Reexamination Certificate
2002-04-18
2004-11-23
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Production of hydrocarbon mixture from refuse or vegetation
From synthetic resin or rubber
C208S018000, C208S027000, C208S950000
Reexamination Certificate
active
06822126
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for transforming waste polymeric materials into useful products and more particularly to an improved process for manufacturing lubricating oils from waste plastics and Fischer-Tropsch waxes.
2. Description of Related Art
There is a steadily increasing demand for technology capable of converting discarded and waste plastic materials into useful products. This is due in large measure to public concerns over potential environmental damage caused by the presence of these waste materials. According to a recent report from the Office of Solid Waste, about 62% of plastic packaging in the United States is made of polyethylene, the preferred feed for processing waste plastics. Plastics waste is the fastest growing waste product, with about 18 million tons per year in 1995 compared to only four million tons per year in 1970, and this amount is growing by approximately 10% per year. Transforming plastic waste material and particularly polyethylene into useful products presents a unique opportunity to address a growing environmental problem.
Because of environmental concerns, the specifications for fuels, lubricants and other petroleum products have become more stringent. This in turn has lead to a greater demand for lighter and cleaner petroleum feedstocks with the result that supplies of these feedstocks have been dwindling. In response to this, the production of synthetic lubricating oils from Fischer-Tropsch synthesized hydrocarbons has received increased attention, particularly in view of the relatively large amounts of natural gas reserves and the desire to convert these into more valuable products such as paraffinic lubricating oils. Accordingly, it would be advantageous to devise an economical process which converts waste plastic such as polyethylene into high viscosity index (VI) lube oils.
Processes are known which convert waste plastic into hydrocarbon lubricants. For example, U.S. Pat. No. 3,845,157 discloses cracking of waste or virgin polyolefins to form gaseous products such as ethylene/olefin copolymers which are further processed to produce synthetic hydrocarbon lubricants. U.S. Pat. No. 4,642,401 discloses the production of liquid hydrocarbons by heating pulverized polyolefin waste at temperatures of 150-500° C. and pressures of 20-300 bars. U.S. Pat. No. 5,849,964 discloses a process in which waste plastic materials are depolymerized into a volatile phase and a liquid phase. The volatile phase is separated into a gaseous phase and a condensate. The liquid phase, the condensate and the gaseous phase are refined into liquid fuel components using standard refining techniques. U.S. Pat. No. 6,143,940 discloses a procedure for converting waste plastics into heavy wax compositions. U.S. Pat. No. 6,150,577 discloses a process of converting waste plastics into lubricating oils. EP0620264 discloses a process for producing lubricating oils from waste or virgin polyolefins by thermally cracking the waste in a fluidized bed to form a waxy product, optionally using a hydrotreatment, then catalytically isomerizing and fractionating to recover a lubricating oil.
One drawback to any process which converts plastic waste into useful products is the fact that, as with any recycle feed, the quality and consistency of the starting material is an important factor in obtaining quality end products. Recycled waste plastic not only is quite variable in consistency but its quality varies from one extreme to the other due to the many grades and types of plastics on the market. Another key factor is the importance of having a constant and continuous supply to make the process economical particularly when using off-specification waste obtained from polyolefin processing plants (so-called “virgin” polyolefin). A process which economically and efficiently converts plastic waste into high VI lube oils while maintaining control over the quality and quantity of the waste plastic supply and insuring the quality of the end products would be highly desirable.
Therefore, an object of the present invention is to provide an economic and efficient process for converting plastic waste into high VI lube oils.
Another object of the invention is to improve the quality of waste plastic pyrolysis feeds and the quality of the end product.
Still another objective of the invention is to develop an improved process which pyrolyzes plastic waste in combination with Fischer-Tropsch waxy feeds to upgrade the quality of the resultant products.
These and other objects of the present invention will become apparent to the skilled artisan upon a review of the following description, the claims appended thereto and the Figures of the drawings.
SUMMARY OF THE INVENTION
The objects and advantages of the invention are attained by a process which includes the steps of:
passing a waste and/or virgin polyolefin into a heating unit maintained at a temperature below the decomposition point of the polyolefin to provide a molten feed;
continuously passing the molten feed through a flow-through pyrolysis reactor maintained at a temperature sufficient to depolymerize at least a portion of the polyolefin and at an absolute pressure of at least one bar to produce a pyrolyzed effluent;
passing at least a portion of the effluent from the pyrolysis reactor to a catalytic isomerization dewaxing unit;
fractionating the product from the isomerization dewaxing unit; and
recovering a lubricating oil base stock.
In a separate embodiment, at least a portion of the pyrolyzed effluent of step (b) is passed to a hydrotreating unit to remove a significant portion of any nitrogen-containing, sulfur-containing and/or oxygenated contaminants. At least a portion of the effluent from the hydrotreating unit is passed to the catalytic isomerization dewaxing unit of step (c).
The process of the invention provides several advantages over previously known techniques. The use of a heating unit enables the practitioner to provide a continuous supply of liquified, heated feedstock readily available for pumping to the pyrolysis reactor. Advantageously, the feedstock is blanketed with inert gas thereby minimizing the formation of oxygenated compounds which could cause downstream catalyst deactivation and could lower the quality of the end products. Continuously passing the polyolefin feed through the pyrolysis reactor allows the practitioner to maintain a low residence time in the reactor which contributes to overall efficiency and economy since a larger volume of feed can be processed. It also enables one to use smaller capacity reactors which likewise provides an economical benefit. Although a hydrotreatment is preferred in the process of the invention to eliminate virtually all nitrogen, sulfur, and oxygen-containing contaminants, such is not necessary if an inert gas has been used to blanket the feed in the heating unit since it has been observed that lube oil stocks lighter in color are obtained by using an inert gas to minimize formation of oxygenated compounds. The use of an intermediate pore size molecule sieve SAPO in the isomerization dewaxing unit minimizes the cracking associated with other known dewaxing techniques.
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Burns Doane Swecker & Mathis L.L.P.
Chevron U.S.A. Inc.
Dang Thuan D.
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