CN-116194553-B - Styrene-assisted polyolefin depolymerization

Abstract

Described herein are methods for depolymerizing polyolefin-based materials into useful petrochemical products using styrene oligomers or polymers and heat. Styrene oligomers or polymers improve the depolymerization reaction by reducing the half-life of the depolymerization, which results in higher depolymerization rates and shorter residence times in the depolymerization unit, allowing for predictable depolymerization reactions and reducing branched or aromatic formation in the product.

Inventors

• S. Naji
• D.F. White
• SMITH CHRISTOPHER DENNIS
• D.L. Ramachi

Assignees

• 巴塞尔聚烯烃意大利有限公司

Dates

Publication Date

20260512

Application Date

20211007

Priority Date

20201009

Claims (9)

1. 1. A method of depolymerizing a polyolefin, comprising: a) Adding a polyolefin-based feed stream and a styrene polymer to a depolymerization unit heated to a temperature between 200 ℃ and 600 ℃, wherein the concentration of the styrene polymer is from 2.5 to 5 weight percent, and B) Reacting the polyolefin-based feed stream with the styrene polymer to depolymerize the polyolefin-based feed stream, Wherein the styrene polymer acts as a depolymerization initiator.
2. 2. The method of claim 1, wherein the polyolefin-based feed stream is combined with styrene oligomer.
3. 3. The method of claim 2, wherein the styrene oligomer is an oligostyrene.
4. 4. The method of claim 1, wherein the styrene polymer is polystyrene.
5. 5. The method of claim 1, wherein the polyolefin-based feed stream is a low density polyethylene, a high density polyethylene, a polypropylene, or a combination thereof.
6. 6. The method of claim 1, wherein the polyolefin-based feed stream is post-consumer waste.
7. 7. The method of claim 1, wherein the polyolefin-based feed stream is post-industrial waste.
8. 8. The method of claim 1, wherein the polyolefin-based feed stream comprises both post-industrial waste and post-consumer waste.
9. 9. The method of claim 4, wherein the polystyrene is post-consumer waste, post-industrial waste, or a combination thereof.

Description

Styrene-assisted polyolefin depolymerization Prior related application The present application is filed according to the patent cooperation treaty, claiming the benefit of priority from U.S. provisional patent application No. 63/089,706 filed on 9, 10/2020, which is incorporated herein by reference in its entirety. Statement of federally sponsored research Is not applicable. Reference microfilm annex Is not applicable. Technical Field The present disclosure relates to methods of depolymerizing polyolefin-based materials using styrene oligomers or polymers and heating to form useful petrochemical products. Background Increasing the level of living and increasing the urbanization has led to an increasing demand for polymer products, in particular polyolefin plastics. Polyolefins are often used in commercial plastic applications due to their outstanding performance and cost characteristics. For example, polyethylene (PE) has become one of the most widely used and accepted polyolefins because it is strong, extremely tough, and very durable. This allows it to be highly engineered for a variety of applications. Similarly, polypropylene (PP) is mechanically strong but flexible, is heat resistant, and is resistant to many chemical solvents, such as bases and acids. Polypropylene is therefore ideal for various end use industries, mainly for packaging and labeling, textiles, plastic components, and various types of reusable containers. A disadvantageous aspect of the demand for polyolefin plastics is the increase in waste. Post-consumer plastic waste is typically terminated in landfills, with about 12% burned and about 9% diverted to recycling. In landfill sites, most plastics do not degrade rapidly, becoming a major source of waste overload for landfill sites. Incineration is also not an ideal solution for disposal of plastic waste, as incineration leads to the formation of carbon dioxide and other greenhouse gas emissions. Therefore, there is great interest in developing a method of recycling plastic waste to reduce the burden on landfills while being environmentally friendly. The disadvantage of recycling plastic waste is that it is difficult to successfully produce commercially available or desirable products. Plastic waste recycling currently involves washing the material and mechanically reprocessing it, however, the resulting particles remain contaminated with impurities such as food residues, dyes and fragrances. These impurities render the pellets unsuitable for most uses, based on properties and appearance. Recent developments have focused on converting plastic waste into usable products, such as fuel sources or commercially important raw materials. Methods have been developed to carry out pyrolysis followed by catalytic depolymerization of plastic waste streams to produce various products, gases, gasoline fractions, kerosene fractions, diesel fractions and waxes. Unfortunately, these methods are expensive and time consuming because they require a large amount of energy to completely decompose the polyolefin waste into useful classes of products. Furthermore, the reaction products themselves are unpredictable, as side reactions occur under pyrolysis conditions, leading to the formation of branched and aromatic products. The catalyst itself is also prone to poisoning by impurities in the polymer feed. Despite advances in the recovery of polymers, there remains a need to develop a robust process for converting plastics into useful petrochemical products that minimizes the formation of branched and/or aromatic products. Disclosure of Invention The present disclosure provides improved methods for thermally depolymerizing polyolefin-based materials. The improved process relies on thermally depolymerizing the feed stream with one or more polyolefins in the presence of styrene oligomer or polymer. In particular, styrene oligomers or polymers, such as oligostyrenes and polystyrenes, are mixed with polyolefin-based materials in depolymerization units and heated in the absence of oxygen. The styrene oligomer or polymer initiates a free radical depolymerization reaction that can proceed at a faster depolymerization rate (less depolymerization half-life of the reaction) than the depolymerization reaction of the polyolefin-based material without the styrene oligomer or polymer. This radical depolymerization results in the formation of liquid products with minimal branching or aromatic formation. The liquid product may then be used as is or subjected to further processing such as an olefin cracker to upgrade the feedstock. The methods described herein can be used to treat any polyolefin-based material, including post-industrial waste and post-consumer use. Disposal of post-consumer polyolefin waste is particularly important due to the overload of landfills and the possibility of raw materials being produced from the waste. The methods described herein involve treating post-consumer waste after it is classified by a proce