Field of the Invention

The present invention is directed to a process for converting polymeric waste to an oil feedstock. More particularly, the present invention is directed to a process for treating polymeric waste wherein the polymeric scrap is broken down into liquid hydrocarbon materials having a boiling point below about 1,000° F.

Background of the Invention Polymeric materials, referred to hereinafter by the generic term "plastics", account for about 7% of municipal solid waste and up to about 20% of the waste by volume. This amounts to about 10 to about 12 million tons per year in the United States. Although plastics recycling is increasing, reprocessing and recycling generally requires segregation by type of plastic. Consumers, in general, and reprocessors often have no idea as to the composition of individual plastic articles. Consequently, processes for utilization of mixed plastic waste, particularly polystyrene, polypropylene and polyethylene, are urgently needed. The present invention provides a process for conversion of mixed plastic waste materials to a high quality synthetic crude oil which can be separated by fractionation into gasoline, diesel fuel and gas-oil components suitable as a feedstock to a catalytic cracker without additional treatment. As used herein, the term "plastic waste" includes all forms of polymeric materials which require or will benefit from recycling, including processing scrap, municipal waste and recovered or recycled polymeric materials.

United States Patent No. 4,724,068 to Stapp describes a process for hydrotreating hydrocarbon- containing feed streams, especially heavy oils. The process of the Stapp patent utilizes a polymeric treating

agent for upgrading the composition of heavy oils. In accordance with the process, an upgrading process is provided comprising the step of contacting (a) a substantially liquid hydrocarbon-containing feed stream substantially simultaneously with (b) free hydrogen, (c) hydrogen sulfide and (d) at least one polymer selected from the group consisting of homopolymers and copolymers of olefinic monomers, in the substantial absence of a solid, inorganic cracking catalyst and a solid inorganic hydroconversion catalyst. The process is performed under conditions so as to obtain a product stream having higher API _gQ gravity and having a lower content of hydrocarbons boiling above 1000° F. than the feed stream.

In accordance with the process of the Stapp patent, impurities contained in the hydrocarbon- containing feed stream are at least partially converted to a "sludge", i.e., a precipitate of metals and coke, which is dispersed in the liquid portion of the hydrocarbon-containing product stream. The sludge and the dispersed olefin polymers are then separated from the liquid portion of the hydrocarbon-containing product stream by any suitable separation means, such as distillation, filtration, centrifugation or settling and subsequent draining of the liquid phase. The hydrocarbon-containing product stream has an increased AP _gg gravity and lower content of heavy fractions. The weight ratio of olefin polymer to hydrocarbon-containing feed is described as being generally in the range of from about 0.01:1 to about 5:1, preferably from about 0.02:1 to about 1:1 and more preferably from about 0.05:1 to about 0.5:1. The Stapp patent generally describes a procedure for hydrovisbreaking a heavy oil with a mixture of hydrogen and hydrogen sulfide in the presence of olefin polymers followed by recovery of an improved hydrocarbon oil product after separation from the olefin polymers.

Summary of the Invention It has now been found that waste plastics can be directly converted to a high quality synthetic crude oil which can be separated by fractionation into gasoline, diesel fuel and gas oils suitable as a feedstock to a catalytic cracker. The process generally includes the steps of heating the plastic waste in a hydrogen atmosphere at moderate temperatures and pressures. It has also been discovered that it is important to the process of the invention that under certain conditions of operation that the proportion of high density polyethylene in the plastic scrap feed mixture be kept below a minimum level of about 25% by weight to achieve complete conversion of the mixture to liquid hydrocarbon materials boiling below 1000° F. Detailed Description of the Invention The present invention is directed to a process for converting polymeric waste to an oil feedstock. In the method, a reaction mixture of polymeric scrap particles is provided in a pressurized reaction vessel provided with stirring means, such as a stirred, pressurized autoclave. The polymeric scrap particles are contacted in the reaction vessel with a gas atmosphere selected from hydrogen and mixtures of hydrogen and hydrogen sulfide. The polymeric scrap particles are heated in the reaction vessel to a temperature in the range of from about 350" C. to about 450° C. at a pressure of from about 500 psig to about 5,000 psig, preferably from about 750 psig to about 3,000 psig. for a time sufficient to convert the plastic scrap to liquid hydrocarbon materials having a boiling point below about 1000" F. , which time is generally in the range of from about 15 minutes to about 8 hours, preferably from about 30 minutes to about 4 hours. The process of the present invention is suitable for conversion of a wide range of plastic waste

feedstocks. Suitable plastic materials include polystyrene, polypropylene, medium density polyethylene, high density polyethylene, polyisoprene, styrene- butadiene copolymer, styrene-ethylene-butylene copolymer, polyethylene terephthalate, polyvinyl chloride and polyamides with the proviso that the high density polyethylene content should be limited to no more than about 25% by weight of the mixture of plastic waste materials at operating temperatures of less than about 400° C. and operating times of less than about 2 hours. It is estimated that municipal waste contains about 8% halogenated polymers on average. Accordingly, if it is known that the polymeric waste includes a halogenated polymer, such as polyvinyl chloride, it is desirable to include a basic material, such as calcium carbonate to neutralize any halogen acids that are formed.

The polymeric waste materials may be comminuted to provide particles of polymeric waste prior to introduction into the reaction vessel. Alternatively, the plastic waste may be melted prior to introduction into the reaction vessel. After polymeric waste particles or melted polymeric waste is charged into the reaction vessel, the reaction vessel is closed, stirring is initiated and the reaction vessel is pressurized with a reaction gas selected from hydrogen and mixtures of hydrogen and hydrogen sulfide. The ratio of hydrogen sulfide to hydrogen for the reaction gas of the present invention is from 0:1 to about 1:1, based on pressure. For some applications, it is desirable to include from about 15% to about 75% of crude oil or used lubricating oil in the charge. The oil serves as a carrier for the polymeric waste, particularly melted polymeric waste. The oil is also substantially upgraded in the reaction vessel to provide an oil stock having a boiling point of less than about 1000" F.

A soluble catalyst can also be added to polymeric waste in the reaction vessel. Suitable catalysts include molybdenum octoate, molybdenum acetyl acetonate, molybdenum hexacarbonyl and molybdenum napthenate. When used, the catalyst is preferably added at a level sufficient to provide from about 10 ppm to about 5,000 ppm of molybdenum.

For oxygenated polymers, it is preferred to use a catalyst and a hydrogen/hydrogen sulfide atmosphere. While not wishing to be bound by any theory, it is believed that sulfur replaces the oxygen in the oxygenated polymers and that the sulfur is hydrogenated to form the hydrocarbon.

A range of plastic waste material feedstocks were tested utilizing temperatures in the range of 385° C. to 415° C. The plastic scrap materials were first converted to particles by use of suitable comminuting apparatus. The polymeric scrap particles were introduced into a stirred autoclave, the autoclave was sealed and hydrogen pressures were developed in the range of 1400/1500 psig. Table 1 summarizes the results of heating the various combinations of plastic scrap materials and synthetic rubber materials under hydrogen atmospheres in the stirred autoclave. Table 1

Oil Yield API

Experiment Feedstock

Composition* t % Gravit

Remarks

A560-81 49.0% PS, 42.6% PP, 8.4% MDPE

415° C, lh Hr

A560-95 46.5% PS, 44.9% PP, 8.6% MDPE

400° C, 2 Hr A560-97 47.5% Ps, 42.1% PP, 10.5% MDPE

385° C, 2 Hr

A560-99 51.1% PS, 48.9% MDPE

24.8 400° C, 2 Hr

A560-107 75.0% PS, 25.0% MDPE 97.2

Hr

- 6 -

A560-109 33.9% PS,

66.1% SBR 98.3 17.5400° C. , 2

Hr

A560-111 100 SBR 96.4 17.8 400° C. , 2 Hr

A560-117 75.6% PS,

24.4% HDPE 97.4 21.5415° C. , 2

Hr

A560-119 SEB Copolymer 98.0 21.0 400° C, 2 Hr

* PS = Polystyrene PP = Polypropylene MDPE = Medium density polyethylene SBR = Styrene-butadiene rubber HDPE = High density polyethylene

SEB = Styrene-ethylene-butylene copolymer

Analysis of the product oils produced by the above treatment of the plastic scrap materials provided the composition shown in Table 2. Table 2

Resid

F650-

932 866

949

Polyethylene terephthalate and nylon 6/6 were also converted in the stirred autoclave in admixture with polystyrene. The product oils can be used, but they are contaminated with the corresponding organic acids, terephthalic acid and adipic acid and either filtration or some additional processing would be required.

Results of comparison experiments involving liquification of mixtures of polystyrene (50%) , polypropylene (30%) and medium density polyethylene (20%) with hydrogen sulfide-hydrogen combinations and hydrogen alone are shown in Tables 3 and 4. These experiments were conducted at 415° C. for 1.25 hours at an identical initial total pressure of 1400/1500 psig.

Table 3

Oil Yield Coke Yield API Sulfur

Experiment Gas Used Wt % Wt % Gravity Content

A560-77 H ₂ S-H ₂ 90.1 3.4 31.9 1.4 A560-81 H ₂ 92.9 0.5 32.0 The liquid product distributions (by simulated distillation) are shown in Table 4.

Table 4

Gasoline Diesel Gas Oil End

Experiment IBP-400° F 400-650° F650- 1000° F Point ° F

A560-77 68.0% 16.0 16.0 861 A560-81 58.5% 22.5 19.0 932

Both experiments provided very high quality oils from a refinery viewpoint. There is no liquid material boiling above 1000° F. and the major constituents are hydrocarbons boiling in the gasoline range. The runs with hydrogen sulfide-hydrogen mixtures provided a lighter oil containing more gasoline, but also produced significantly more coke and contained enough sulfur so that catalytic hydrotreating would be required before the oil product could be used. The hydrocarbon products produced using hydrogen alone are of extremely high quality, contain no sulfur and essentially no coke is produced.

It is also within the scope of this invention to recycle any gas oils (b.p. 650-1000° F.) and resids

(b.p. > 1000° F.) back into the reaction vessel and reprocess them with additional polymeric waste to provide gasoline and diesel range hydrocarbon materials.

The present invention describes a simple process to convert mixed waste scrap plastics and to a synthetic crude oil which would be highly useful as a feedstock for a refinery. Only a small amount of coke is produced and the coke produced contains no heteroatoms. The coke could therefore be used as a fuel to supply process heat. The hydrocarbon products contain no sulfur, oxygen, nitrogen or metals and would be suitable refinery feedstocks, when hydrogen alone is used. Sulfur is introduced when mixtures of hydrogen and hydrogen sulfide are used. The presence of sulfur poses no problem to refiners and existing refinery equipment can be used to handle sulfur containing feedstocks. If, for example, the octane number of the gasoline is too low, it could be reformed or isomerized without the hydrotreating that is normally required for petroleum napthas. Similarly, diesel oil obtained from the process would be expected to have a high cetane number, particularly diesel oil produced from polyethylene. Such diesel oil would not require hydrotreating for sulfur removal. Gas oils and residues contain no heteroatoms and would be suitable cat cracker feedstocks without prior hydrotreating or demetalization. The process of the present invention could readily use a mixed plastic separated by gravity segregation from municipal solid waste.