Styrene-assisted polyolefin depolymerization.

Abstract

Described herein is a method for depolymerizing polyolefin-based materials into useful petrochemical products using styrene oligomers or polymers and heat, which improves depolymerization by shortening the depolymerization half-life, resulting in higher depolymerization rates and shorter residence times in the depolymerization unit, thereby allowing for predictable depolymerization and reducing branched or aromatized formations in the product.

Description

Technical Field

[0001] The present disclosure relates to a method of depolymerizing polyolefin-based materials using styrene oligomers or polymers and heating them to form useful petrochemical products.

Background Art

[0002] With the improvement of living standards and the progress of urbanization, the demand for polymer products, especially polyolefin plastics, is increasing. Polyolefins are widely used in commercial plastic applications due to their outstanding performance and cost characteristics. For example, polyethylene (PE) is one of the most widely used and recognized polyolefins because of its high strength, very toughness, and excellent durability. This enables it to be highly designed for various applications. Similarly, polypropylene (PP) is mechanically strong but flexible, heat-resistant, and resistant to many chemical solvents such as bases and acids. Therefore, polypropylene is ideal for various end-use industries and is mainly used in packaging and labeling, textiles, plastic parts, and various types of reusable containers.

[0003] The disadvantage of the demand for polyolefin plastics is the increase in waste. Post-consumer plastic waste usually ends up in landfill, about 12% is incinerated, and about 9% is recycled. In landfill, most plastics do not decompose rapidly and are the main source of waste causing excessive burden on landfill. Also, incineration is not an ideal solution for treating plastic waste because it causes the formation of carbon dioxide and the emission of other greenhouse gases. Therefore, in order to reduce the burden on landfill while considering the environment, great attention has been paid to the development of recycling methods for plastic waste.

[0004] A drawback of plastic waste recycling is the difficulty in successfully manufacturing commercially usable or desired products. Plastic waste recovery currently involves washing the materials and their mechanical reprocessing. However, the resulting particles are still contaminated with impurities such as food residues, dyes, and fragrances. From a performance and appearance standpoint, these impurities make the materials unsuitable for most applications.

[0005] Recent advances have focused on converting plastic waste into useful products such as fuel sources or commercially important raw materials. Methods have been developed to thermally decompose a stream of plastic waste followed by catalytic depolymerization to produce a variety of products including gas, gasoline fractions, kerosene fractions, diesel fractions, and waxes.

[0006] Unfortunately, these methods are expensive and time-consuming because they require a large amount of energy to completely decompose polyolefin waste into useful classifications of products. Furthermore, the reaction products themselves are unpredictable because side reactions occur under thermal decomposition conditions, resulting in the formation of branched and aromatic products. The catalysts themselves also tend to be poisoned by impurities in the polymer feed.

[0007] While polymer recycling is progressing, there remains a need to develop robust processes for converting plastics into useful petrochemicals while minimizing the formation of branched and / or aromatic products. [Overview of the project] [Problems that the invention aims to solve]

[0008] This disclosure provides an improved method for the thermal depolymerization of polyolefin materials. The improved method relies on the thermal depolymerization of a feed stream with one or more polyolefins in the presence of a styrene oligomer or polymer. Specifically, a styrene oligomer or polymer, such as oligostyrene and polystyrene, is mixed with the polyolefin material in a depolymerization unit and heated in the absence of oxygen. The styrene oligomer or polymer initiates a radical depolymerization reaction at a faster depolymerization rate (with a shorter depolymerization half-life) than the depolymerization of polyolefin materials without the styrene oligomer or polymer. This radical depolymerization results in the formation of a liquid product that is minimally branched or aromatic. The liquid product is then used as is, or may be further processed, such as olefin cracking, to improve the feed material.

[0009] The methods described herein can be used to process any polyolefin materials, including post-industrial and post-consumer waste. Processing post-consumer polyolefin waste is particularly important given the excessive burden on landfills and the potential for generating raw materials from the waste. The methods described herein relate to processing post-consumer waste after the processing center has separated it, either in a landfill or other recycling center, to separate polyolefin materials from other recyclable materials such as glass, cellulose (paper), and polyethylene polymers. [Means for solving the problem]

[0010] This disclosure includes any combination of the following embodiments.

[0011] This method for depolymerizing polyolefins comprises adding a polyolefin-based feed stream and a styrene oligomer or styrene polymer to a depolymerization unit heated to a predetermined temperature, and reacting the polyolefin-based feed stream with the styrene oligomer or styrene polymer to depolymerize the polyolefin-based feed stream.

[0012] This method for depolymerizing polyolefins includes adding a polyolefin-based feed stream and a styrene oligomer to a depolymerization unit heated to a predetermined temperature, and reacting the polyolefin-based feed stream with the styrene oligomer to depolymerize the polyolefin-based feed stream.

[0013] This method for depolymerizing polyolefins includes adding a polyolefin-based feed stream and a styrene polymer to a depolymerization unit heated to a predetermined temperature, and reacting the polyolefin-based feed stream with the styrene polymer to depolymerize the polyolefin-based feed stream.

[0014] In any one of the methods described herein, the depolymerization rate of the polyolefin feed stream is at least 10% higher than the depolymerization rate of the polyolefin feed stream that does not contain a styrene oligomer or styrene polymer.

[0015] In any one of the methods described herein, the depolymerization onset temperature of the polyolefin feed stream is at least 5% lower than the depolymerization onset temperature of the polyolefin feed stream that does not contain a styrene oligomer or styrene polymer.

[0016] In any of the methods described herein, the depolymerization half-life of the polyolefin feed stream is at least 30% lower than the depolymerization half-life of the polyolefin feed stream that does not contain a styrene oligomer or styrene polymer.

[0017] In any one of the methods described herein, the styrene oligomer is oligostyrene.

[0018] In any one of the methods described herein, the styrene polymer is polystyrene.

[0019] In any one of the methods described herein, the styrene oligomer and polymer have an average molecular weight of 500 Da to 20 kDa.

[0020] In any one of the methods described herein, the polyolefin feed stream is low density polyethylene, high density polyethylene, polypropylene, or a combination thereof.

[0021] In any one of the methods described herein, the polyolefin feed stream is post-consumer waste.

[0022] In any one of the methods described herein, the polyolefin feed stream is post-industrial waste.

[0023] In any one of the methods described herein, the polyolefin feed stream includes both post-industrial waste and post-consumer waste.

[0024] In any one of the methods described herein, the styrene polymer is post-consumer waste, post-industrial waste, or a combination thereof.

[0025] In any one of the methods described herein, the styrene oligomer is post-consumer waste, post-industrial waste, or a combination thereof.

[0026] In any one of the methods described herein, the concentration of the styrene oligomer or styrene polymer is greater than 0 wt% to about 20 wt%.

[0027] In any one of the methods described herein, the concentration of the styrene oligomer or styrene polymer is about 2.5 wt% to about 5 wt%.

[0028] In any one of the methods described herein, the predetermined temperature is about 200 °C to about 600 °C.

[0029] A method for depolymerizing a polyolefin includes adding a polyolefin-based feed stream and a styrene oligomer or a styrene polymer to a depolymerization unit heated to a temperature of about 200°C to about 600°C, and reacting the polyolefin-based feed stream with the styrene oligomer or the styrene polymer to depolymerize the polyolefin-based feed stream. In some embodiments, the depolymerization rate of the polyolefin-based feed stream is at least 10% higher than the depolymerization rate of a polyolefin-based feed stream that does not contain a styrene oligomer or a styrene polymer. Further, or alternatively, the depolymerization start temperature of the polyolefin-based feed stream is 5% lower than the start temperature of a polyolefin-based feed stream that does not contain a styrene oligomer or a styrene polymer.

[0030] The summary of the present invention is provided to introduce some concepts that are further described in the following detailed description of the invention. The summary of the present invention is not intended to identify the key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0031] Definitions As used herein, the term "depolymerization half time" or "half time of depolymerization" refers to the time required to achieve a 50% mass loss of a sample at a specific temperature during a TGA pyrolysis reaction.

[0032] As used herein, "residence time" refers to the time required to depolymerize one batch of polymer waste in a depolymerization unit.

[0033] As used herein, "pyrolysis" refers to a pyrolytic polymerization reaction that occurs in the absence of oxygen.

[0034] As used herein, "post-consumer waste" refers to waste generated by the end consumer of a material stream.

[0035] As used herein, “post-industrial waste” refers to waste generated during the manufacturing process of a product.

[0036] Unless otherwise specified, all concentrations in this specification are expressed in weight percentage ("wt%").

[0037] As used herein, “oligomer” refers to a molecule consisting of a few (≤100) repeating units. As used herein, “polymer” refers to a molecule consisting of a large (>100) repeating units. Both oligomers and polymers can be synthesized from one or more monomers.

[0038] The term "oligostyrene" refers to an oligomer containing repeating units derived solely from styrene monomer. The term "polystyrene" refers to a polymer containing repeating units derived solely from styrene monomer.

[0039] In the claims or specification, the words "one" or "one" mean one or more unless otherwise indicated by the context, when used in combination with the term "including".

[0040] The term "approximately" refers to the value obtained by adding or subtracting the measurement error limit from the displayed value, or by adding or subtracting 10%.

[0041] The term “or” in a claim is used to mean “and / or” unless it is explicitly stated that it refers only to the alternatives or that the alternatives are mutually exclusive.

[0042] The terms “to have,” “to possess,” “to include,” and “to contain” (and their variations) are open linking verbs and, when used in claims, allow for the addition of other elements.

[0043] The phrase "composed of" is closed, and all additional elements are excluded.

[0044] The phrase "essentially composed of..." allows for the inclusion of non-material elements that exclude additional material elements but do not substantially alter the essence of the invention.

[0045] The following abbreviations are used in this specification. [Table 1] [Modes for carrying out the invention]

[0046] This disclosure provides an improved method for recycling polyolefin materials into commercially important raw materials using styrene oligomers or polymers. Specifically, in a depolymerization unit, the styrene oligomer or polymer is mixed with a polyolefin feed stream containing at least one polyolefin material. When this mixture is heated, a thermal decomposition reaction occurs, in which the styrene oligomer or polymer causes the depolymerization of the polyolefin material to produce a useful liquid product having minimally branched or aromatic forms.

[0047] There are many advantages to improving the thermal depolymerization of polyolefins using styrene oligomers or polymers. As mentioned above, styrene oligomers or polymers are not catalysts in the recycling process. Rather, they act as initiators. More specifically, the double bond (C=C) in the main chain of the styrene oligomer or polymer undergoes homolysis cleavage at low temperatures, thereby generating a radical stabilized by the aromatic ring. This radical then triggers a chain reaction with the polyolefin, thereby promoting the radical depolymerization of the polyolefin in the feed stream. This limits isomerization reactions during depolymerization and results in a simpler mixture of reaction products similar to those produced from the same feed stream depolymerized in the absence of styrene oligomers and polymers. Thus, the reaction products of a given feed stream composition with polymers are easily predictable.

[0048] Another advantage of using styrene oligomers and polymers is that they are readily available as post-consumer and post-industrial waste, particularly in the form of expanded polystyrene foam (EPS). Over the past 15 years, the global EPS industry has managed to recover an average of 19% post-consumer EPS and 25% post-industrial EPS, with the remaining waste being landfilled. The method of the present invention makes it possible to easily combine landfill-bound polystyrene with post-consumer and post-industrial polyolefin waste. As an example, polyolefin materials separated by a processing center at a landfill or other recycling center can be combined with styrofoam cups and other polystyrene food containers in a depolymerization unit. Thus, not only are polyolefin materials depolymerized and recycled, but less polystyrene foam ends up in landfills. Alternatively, "new" polystyrene, or other styrene oligomers and polymers, can be specially manufactured for use in this method.

[0049] Finally, styrene oligomers and polymers are robust because they are less affected by "toxins" in the polymer feed stream than other conventional depolymerization catalysts. This allows for a wider range of polyolefin feed compositions than other depolymerization methods.

[0050] The addition of styrene oligomers and polymers in a wide range of weights can improve the depolymerization rate of polyolefins. In some examples, styrene oligomers and polymers are present at concentrations of over 0 wt% to about 50 wt% of the feed stream. Alternatively, styrene oligomers and polymers are present at concentrations of over 0 wt% to about 30 wt%, about 2.5 wt% to about 10 wt%, about 5 wt% to about 20 wt%, about 15 wt% to about 30 wt%, about 25 wt% to about 50 wt%, or about 35 wt% to about 50 wt%. In other examples, styrene oligomers and polymers are present at concentrations of 2.5 wt%, 5 wt%, 10 wt%, 15 wt%, or 20 wt%.

[0051] Styrene oligomers and polymers can have an average molecular weight of 500 Da to 20 kDa. In some examples, the added styrene component has only styrene repeating units, such as oligostyrene and polystyrene. In some examples, the added styrene component has one or more other repeating units besides styrene. In other examples, the added styrene component is oligostyrene having 10 to about 80 repeating units. Alternatively, the oligostyrene has 10 to about 50 repeating units. Alternatively, the oligostyrene has 40 to about 80 repeating units.

[0052] The method described herein is applicable to feedstreams containing materials having a single polyolefin component or a mixture of any amount of polyolefin components. A broad range of polyolefins, including but not limited to polyethylene (high-density and low-density), polypropylene, ethylene-propylene copolymer, polybutene-1, polyisobutene, and their copolymers, may be present in the feedstream. Furthermore, the waste is not limited to any particular form, and films, foams, textiles, or other molding materials can be processed in this manner. The feedstream may include post-consumer polyolefin waste, post-industrial polyolefin waste, or both post-industrial and post-consumer polyolefin waste.

[0053] Polyolefin materials combined with styrene oligomers and polymers are processed in a depolymerization unit having an operating temperature of approximately 200°C to 600°C. Alternatively, the operating temperature of the depolymerization unit is approximately 225°C to 500°C. Yet another alternative is that the operating temperature of the depolymerization unit is approximately 250°C to 450°C, or approximately 400°C.

[0054] In the depolymerization unit, the polyolefin feed stream is batched, taking into account the residence time required for complete depolymerization. Depending on the thermal conductivity of the depolymerization unit and the amount of styrene oligomer or polymer, the estimated residence time per batch is approximately 30 minutes to 180 minutes. Alternatively, the estimated residence time is approximately 60 minutes.

[0055] Under the reaction conditions described above, batches containing even small amounts (less than 5 wt%) of styrene oligomers and polymers are expected to have a depolymerization half-life at least 30% lower than polyolefin batches without added styrene oligomers and polymers. In some examples, the depolymerization half-life is reduced by at least 40%. With larger amounts of styrene oligomers and polymers (approximately 10 wt% to 20 wt%), the depolymerization half-life is reduced by at least 59%, depending on the polyolefin content.

[0056] Therefore, the depolymerization methods of this disclosure enable the rapid depolymerization of polyolefin materials into predictable liquid products having minimally branched or aromatic forms. The liquid products can then be used as is or further processed to improve the quality of the product flow. These methods also reduce the amount of styrene oligomer and polymer waste in landfills.

[0057] Examples To illustrate embodiments of the appended claims using the polyolefin depolymerization method described above, the following examples are included. These examples are for illustrative purposes only and are not intended to unduly limit the scope of the appended claims. Those skilled in the art will understand that similar or comparable results can be obtained by making various modifications to the specific embodiments disclosed without departing from the spirit and scope disclosed herein. The following examples should not be understood in any way as limiting or defining the scope of the appended claims.

[0058] TGA depolymerization The effect of polystyrene as a depolymerization initiator was investigated by processing a series of single-component polyolefin feed streams using thermogravimetric analysis (TGA) as the depolymerization unit. The feed consisted of high-density polyethylene (grade ACP9255, LyondellBasell) or polypropylene (grade Moplen HP522H, LyondellBasell). Homogeneous samples were prepared by melt-mixing 10 g of polyolefin raw material with various amounts of polystyrene (PS 3010-01, Sigma-Aldrich) in a HAAK MiniCTW mixer at 200°C and 200 RPM for 5 minutes.

[0059] In the case of the TGA pyrolysis reaction, the prepared sample was heated under nitrogen in Mettler Toledo TGA / DSC 3+ (Mettler Toledo, Columbus, OH) at 10 K / min to the desired depolymerization temperature and held for 1 hour. In these examples, a depolymerization temperature of 400 °C was used. The depolymerization half-life at a specific temperature (defined as the time required for a 50% reduction in mass) was directly recorded if this value was less than 60 minutes, or, if this value was greater than 60 minutes, determined according to t1 / 2 = 0.693 / k under the assumption of first-order decomposition dynamics, where k is the first-order rate constant and is determined graphically using a plot of Ln(C0 / C) versus time.

[0060] The depolymerization half-life is a relation to the residence time required in a large-scale depolymerization unit. A shorter half-life results in a shorter residence time for the polymer feed batch in the depolymerization unit and a higher depolymerization rate.

[0061] Table 1 shows the catalytic activity of polystyrene on HDPE. Comparative Example 1 underwent depolymerization in the absence of polystyrene. The depolymerization half-life of Comparative Example 1 was 347 minutes at 400°C. The addition of polystyrene reduced the half-life of this HDPE feed. A significant reduction in depolymerization half-life was observed even at low polystyrene concentrations (≤5%). A 40% reduction in half-life was observed at a low polystyrene concentration of 2.5%. At a polystyrene concentration of 20%, the half-life was reduced by approximately 82%. This indicates that even the addition of small amounts of polystyrene can reduce the residence time required to completely depolymerize HDPE into useful petrochemical products. [Table 2]

[0062] When polyolefins are converted to PP, a similar decrease in the depolymerization half-life is observed (the depolymerization rate increases accordingly). As shown in Table 2, a significant decrease in the depolymerization half-life of PP was observed even at low polystyrene concentrations (≤5%). At a polystyrene concentration of 20%, the depolymerization half-life decreased by approximately 62%. This is lower than the decrease observed in the HDPE stream, but the decrease in the half-life of the PP stream with 20 wt% polystyrene is faster than in Comparative Example 2. [Table 3]

[0063] Polystyrene can improve the depolymerization rate of various polyolefins at concentrations ranging from 2.5% to 20%, which means reducing the time required to depolymerize these compounds in larger reactors.

[0064] Polystyrene concentrations exceeding 20% ​​also reduce the depolymerization rates of HDPE and PP. However, this benefit is offset by the generation of more aromatic products, namely styrene, in the resulting reaction product. The presence of aromatic products affects the quality of the resulting feedstock. Therefore, depending on the end use of the reaction product, an additional step to hydrogenate the reaction product may be required.

[0065] Although the examples are described using polystyrene, other styrene polymers can also be used. Furthermore, styrene oligomers having several to 100 repeating units, such as oligostyrene, can also reduce the depolymerization rate of the polyolefin feedstock.

[0066] Compared to methods that do not use styrene oligomers or polymers, the currently described method using styrene oligomers or polymers for the depolymerization of polyolefin streams can offer lower energy efficiency (i.e., better cost-effectiveness).

[0067] This application claims priority to U.S. Provisional Patent Application No. 63 / 089,706, filed under the Patent Cooperation Treaty on 9 October 2020, the entirety of which is incorporated herein by reference.

[0068] Federal government-funded research report Not applicable.

[0069] See the microfiche appendix. Not applicable.

Claims

1. A method of producing a depolymerization process comprising: a) adding a polyolefin-based feed stream and a styrene oligomer or polymer to a depolymerization unit heated to a temperature of about 200°C to about 600°C; b) reacting said polyolefin-based feed stream with said styrene oligomer or said styrene polymer to depolymerize said polyolefin-based feed stream.

2. 10. The method of claim 1, wherein the polyolefin-based feedstream is combined with the styrene oligomers.

3. The method of claim 2 wherein the styrene oligomer is an oligostyrene.

4. 10. The method of claim 1, wherein the polyolefin-based feedstream is combined with the styrenic polymer.

5. The method of claim 4 wherein the styrene polymer is polystyrene.

6. 10. The method of claim 1, wherein the polyolefin-based feed stream is low density polyethylene, high density polyethylene, polypropylene, or a combination thereof.

7. 10. The method of claim 1, wherein the polyolefin-based feedstream is a post-consumer waste stream.

8. 10. The method of claim 1, wherein the polyolefin-based feedstream is a post-industrial waste stream.

9. 10. The method of claim 1, wherein the polyolefin-based feedstream comprises both post-industrial and post-consumer waste streams.

10. 10. The method of claim 1, wherein the polystyrene is post-consumer waste, post-industrial waste, or a combination thereof.

11. 2. The method of claim 1, wherein the concentration of the styrene oligomer or the styrene polymer is from greater than 0 wt % to about 20 wt %.

12. 12. The method of claim 11, wherein the concentration of the styrene oligomer or the styrene polymer is from about 2.5 wt % to about 5 wt %.