Improved method for treating liquefied waste plastics

Abstract

The present invention relates to an improved method for treating liquefied waste plastic. The method includes providing a liquefied waste plastic (LWP) raw material for heat treatment (HT treatment) using an aqueous solution containing a basic substance, heat-treating the LWP raw material with the aqueous solution and subsequently phase-separating to result in at least a treated LWP material and an aqueous phase, determining the quality of the LWP raw material by measuring at least one characteristic of the LWP raw material, wherein the at least one characteristic includes the total acid number (TAN) of the LWP raw material, calculating the amount of basic substance that needs to be added in the HT treatment to reach a target pH level of the aqueous phase based on at least one characteristic of the LWP raw material and the water-oil ratio, and adding the calculated amount of basic substance in the form of an aqueous solution to contact the LWP raw material.

Description

Technical Field

[0001] The present invention relates to an improved method for treating liquefied waste plastic, and more specifically, to improving the purification efficiency and process efficiency of the purification process of (crude) liquefied waste plastic.

Background Art

[0002] The purification of liquefied waste plastic (LWP) to obtain more valuable (pure) substances and the conversion of liquefied waste plastic (LWP) into more valuable materials have been studied for several years.

[0003] LWP is typically produced by thermal decomposition or hydrothermal liquefaction (HTL) of waste plastic. Depending on the source of the waste plastic, LWP has various levels of impurities. Typical impurity components are chlorine, nitrogen, sulfur, and oxygen, and its corrosive chlorine is particularly problematic for refineries / petrochemical processes. These impurities are derived from waste plastic materials such as post-consumer waste plastic (recycled consumer plastics), which are identified as the most potential large-scale sources of plastic waste. Similarly, bromine-containing impurities can be contained mainly in industrial waste plastics (e.g., from flame retardants).

[0004] Regardless of whether LWP undergoes simply a general purification process (e.g., fractional distillation) or is sent to a typical petrochemical conversion process (e.g., steam cracking), to avoid facility degradation such as reactor corrosion or catalyst poisoning, the LWP feedstock needs to meet the impurity levels for these processes.

[0005] In addition to purification, chemical recycling of LWP back to plastic (or monomer) is also an interesting option that has attracted great attention in the petrochemical industry in recent years. The new waste directive and EU plastic strategy, which set ambitious goals for waste plastic recycling, have further increased the attention.

[0006] Considering the increasing interest in adding LWP to the value chain, several options have been developed to purify LWP to make it more suitable for conventional oil refining processes.

[0007] Patent Document 1 discloses a steam cracking process that includes pretreatment of mainly paraffinic hydrocarbon raw materials such as hydro wax, hydrotreated vacuum gas oil, pyrolysis oil from waste plastics, gas oil, or slack wax. Pretreatment is performed using solvent extraction to reduce contaminating components such as polycyclic aromatics and resins. Such solvent extraction technology can result in low removal efficiency for specific contaminants in LWP and can further generate large amounts of contaminated extraction substances, which require workup or disposal.

[0008] Patent Document 2 discloses a process for improving waste plastics that includes a pyrolysis step, a hydrotreating step, a polishing step, and a steam cracking step in this order. A large amount of hydrogen is consumed in this process, and hydrogen is usually produced from fossil resources. Therefore, this process is not suitable from the perspective of sustainability.

[0009] Patent Document 3 discloses a process for converting LWP into a steam cracker feedstock by heat-treating LWP in an aqueous medium having a pH of at least 7 and subsequently hydrotreating the treated LWP. Purification using an aqueous medium results in the generation of large amounts of contaminated water. Since the contaminated water contains a large amount of organic contaminants, it needs to be further treated (e.g., purified) before being sent to conventional wastewater treatment. Purification can be achieved through several routes.

[0010] Patent Document 4 discloses a method for preparing synthetic crude oil using a caustic treatment solution. Patent Document 4 utilizes a slightly elevated temperature together with a caustic solution having a pH of about 8 - 10. The adjustment treatment of Patent Document 4 is a washing treatment and does not correspond to the HT treatment of the present invention.

[0011] Patent Document 5 relates to a method for purifying recycled materials such as LWP, including a purification step and a hydrogenation treatment step. The purification step can be carried out in the presence of an aqueous solution of an alkali metal hydroxide. In this procedure, the removal efficiency of chlorine impurities is achieved well, but as a result, a large amount of wastewater is still generated.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0013] In the above prior art approaches, various purification procedures are adopted for LWP, but each of them has specific drawbacks in terms of efficiency, particularly with respect to purification efficiency, efficient use of chemicals, and handling of contaminated water (wastewater).

[0014] The present invention has been made in view of the above problems, and the object of the present invention is to improve the process for improving LWP, particularly to improve the purification efficiency and usage amount of the aqueous solution and the basic substance contained therein in the heat treatment process for purifying LWP raw materials. More specifically, the present invention aims to improve the efficiency of impurity removal from LWP, particularly from highly acidic LWP, by optimizing the amount of the basic substance in the aqueous solution used relative to the amount of LWP raw materials and its impurity content.

Means for Solving the Problem

[0015] This problem of providing an improved process for improving LWP is solved by the method specified in any one of the claims.

[0016] Briefly, the present invention relates to one or more of the following items: 1. A step of providing a liquefied waste plastic (LWP) raw material for heat treatment (HT treatment) in an aqueous solution containing a basic substance; A method comprising: heat-treating the LWP raw material with an aqueous solution and subsequently performing phase separation to obtain at least a treated LWP material and an aqueous phase as a result, wherein the method includes a step of determining the quality of the LWP raw material by measuring at least one characteristic of the LWP raw material, wherein the at least one characteristic includes the total acid number (TAN) of the LWP raw material; and a step of calculating the amount of the basic substance that needs to be added in the HT treatment to reach the target pH level of the aqueous phase based on at least one characteristic of the LWP raw material and the water-oil ratio, and adding the calculated amount of the basic substance in the form of an aqueous solution to contact the LWP raw material. 2. The method according to item 1, wherein the method further includes a step of monitoring the pH level of the aqueous phase obtained from the phase separation. 3. The method according to item 1 or 2, wherein the method further includes a step of repeatedly readjusting the amount of the basic substance in the form of an aqueous solution to reach the target pH level of the aqueous phase. 4. The method according to any one of items 1 to 3, wherein the target pH level is in the range of pH 10.0 or higher, preferably 10.2 to 13.9, 10.3 to 13.8, 10.4 to 13.6, 10.5 to 13.5, 10.6 to 13.4, 10.7 to 13.3, 10.8 to 13.2, 10.9 to 13.1, or 11.0 to 13.0. 5. The method according to any one of items 1 to 4, wherein at least one characteristic of the LWP raw material includes both the total acid number (TAN) and the total chlorine content of the LWP raw material. 6. The method according to any one of items 1 to 5, further comprising a step of measuring the alkalinity of the aqueous phase by titration and readjusting the amount of the basic substance based on the result of the measurement of the alkalinity. 7. The method according to any one of items 1 to 6, wherein the amount of the basic substance is adjusted and / or readjusted by changing the concentration of the basic substance in the aqueous solution used in the HT treatment. 8. The method according to any one of items 1 to 7, wherein the LWP raw material has a total acid number (TAN) in the range of 0.1 to 100.0 mg KOH / g, such as 0.2 to 95.0 mg KOH / g, 0.3 to 90 mg KOH / g or more, 1.0 to 80 mg KOH / g, 3.0 to 60 mg KOH / g, 5.0 to 50.0 mg KOH / g, 7.0 to 30.0 mg KOH / g, or 9.0 to 20.0 mg KOH / g. 9. The method according to any one of items 1 to 8, wherein the LWP raw material is crude liquefied waste plastic or a fraction thereof. 10. The method according to any one of items 1 to 9, wherein the LWP raw material has an initial boiling point of 50°C or lower, such as an initial boiling point in the range of 15°C to 50°C, 20°C to 45°C, or 25°C to 40°C. 11. The method according to any one of items 1 to 10, wherein the LWP raw material has a final boiling point of 400°C or higher, such as in the range of 400°C to 700°C, 450°C to 650°C, 500°C to 650°C, or 550°C to 650°C. 12. The method according to any one of items 1 to 11, wherein the basic substance is selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides. 13. The method according to any one of items 1 to 12, wherein the basic substance is selected from the group consisting of KOH, NaOH, LiOH, Ca(OH)2, Mg(OH)2, RbOH, Sr(OH)2, and Ba(OH)2. 14. The method according to any one of items 1 to 13, wherein the basic substance is NaOH. 15. The method according to any one of items 1 to 14, wherein the LWP raw material has an olefin content of 5% by weight or more, such as 10% by weight or more, 15% by weight or more, 20% by weight or more, 30% by weight or more, 40% by weight or more, or 50% by weight or more. 16. The method according to any one of items 1 to 15, wherein the LWP raw material has an olefin content of 85% by weight or less, such as 80% by weight or less, 70% by weight or less, or 65% by weight or less. 17. The method according to any one of items 1 to 16, wherein the aqueous solution contains at least 50% by weight of water, preferably at least 70% by weight of water, more preferably at least 85% by weight of water, at least 90% by weight of water or at least 95% by weight of water. 18. The method according to any one of items 1 to 17, wherein the aqueous solution contains at least 0.3% by weight of a basic substance, such as 0.5% by weight to 10.0% by weight, 1.0% by weight to 6.0% by weight, or 1.5% by weight to 4.0% by weight, more preferably at least 0.5% by weight, at least 1.0% by weight, or at least 1.5% by weight of a basic substance. 19. The method according to any one of items 1 to 18, wherein the aqueous solution contains at least 0.5% by weight, preferably at least 1.0% by weight, or at least 1.5% by weight of a metal hydroxide or an alkali metal hydroxide, such as 0.5% by weight to 10.0% by weight, 1.0% by weight to 6.0% by weight, or 1.5% by weight to 4.0% by weight. 20. The method according to any one of items 1 to 19, wherein the HT treatment is carried out at a temperature of 150°C or higher, preferably 190°C or higher. 21. The method according to any one of items 1 to 20, wherein the HT treatment is carried out at a temperature of 200°C or higher, such as 210°C or higher, 220°C or higher, 240°C or higher, or 260°C or higher. 22. The method according to any one of items 1 to 21, wherein the HT treatment is carried out at a temperature of 450°C or lower, preferably 400°C or lower, 350°C or lower, 320°C or lower, or 300°C or lower. 23. The method according to any one of items 1 to 22, wherein the HT treatment is carried out at a temperature in the range of 200°C to 350°C, preferably 220°C to 330°C, 240°C to 320°C, or 260°C to 300°C. 24. The method according to any one of items 1 to 23, wherein the chlorine content of the LWP raw material is in the range of 1 ppm to 4000 ppm by weight, such as 100 ppm to 4000 ppm by weight or 300 ppm to 4000 ppm by weight. 25. The method according to any one of items 1 to 24, wherein the LWP raw material is a fraction of liquefied waste plastic. 26. The method according to any one of items 1 to 25, wherein the liquefied waste plastic (LWP) raw material has a 5% boiling point in the range of 25°C or higher, preferably 30°C or higher, or 35°C or higher, such as in the range of 25°C to 120°C, 25°C to 100°C, 30°C to 90°C, or 35°C to 80°C. 27. The method according to any one of items 1 to 26, wherein the liquefied waste plastic (LWP) raw material has a 95% boiling point in the range of 700°C or lower, preferably 650°C or lower, 600°C or lower, or 550°C or lower, such as in the range of 180°C to 700°C, 250°C to 700°C, 300°C to 650°C, 350°C to 600°C, 380°C to 500°C, or 400°C to 500°C. 28. The method according to any one of items 1 to 27, wherein the step of providing the LWP raw material preferably includes a step of liquefying waste plastic by thermal degradation of waste plastic, such as a pyrolysis or hydrothermal liquefaction or similar process step. 29. The method according to any one of items 1 to 28, wherein the step of providing the LWP raw material includes a step of liquefying the selected waste plastic, and the method further includes a step of sorting waste plastic to provide the selected waste plastic, preferably removing at least 50% by weight, more preferably at least 55% by weight, at least 60% by weight, at least 65% by weight, at least 70% by weight, at least 75% by weight, at least 80% by weight, or at least 85% by weight of chlorine-containing waste plastic, such as polyvinyl chloride (PVC) (relative to the original content of chlorine-containing waste plastic such as PVC in the waste plastic). 30. The method according to any one of items 1 to 29, wherein no hydrogen is added to the HT treatment and / or no hydrogenation treatment catalyst is present. 31. The method according to any one of items 1 to 30, wherein the ratio of the bromine number (BN2) of the treated LWP material to the bromine number (BN1) of the LWP raw material, BN2 / BN1, is in the range of 0.90 or higher, preferably 0.95 or higher, such as in the range of 0.90 to 1.10, 0.90 to 1.02, or 0.95 to 1.00. 32. The method according to any one of items 1 to 31, wherein the LWP raw material has a density measured at 15 °C in the range of 0.780 to 0.950 kg / l, such as in the range of 0.780 to 0.900 kg / l or in the range of 0.780 to 0.850 kg / l. 33. The method according to any one of items 1 to 32, wherein the mixing ratio (water-oil ratio) of the aqueous solution and the LWP raw material in the heat treatment step is in the range of 0.1 to 1.4, such as in the range of 0.2 to 0.7, preferably in the range of 0.2 to 1.0, by weight.

Embodiments for Carrying Out the Invention

[0017] The present invention relates to an improvement in a method for improving liquefied waste plastic.

[0018] LWP raw materials, such as pyrolysis products of recovered consumer plastics, contain a large amount of various contaminants that may have an adverse effect on downstream processes. Such contaminants include, in particular, halogens (mainly chlorine) derived from halogenated plastics (such as PVC and PTFE), sulfur derived from crosslinking agents of rubbery polymers (such as in used tires), and metal (such as Si, Al) contaminants (such as films coated with metals or metal compounds, used tires, or plastic processing aids) derived from composite materials and additives. These contaminants can exist in elemental form, ionic form, or as part of organic or inorganic compounds.

[0019] These impurities should be removed before subjecting the LWP to further processing. The present invention focuses on a method for removing such impurities (or contaminants) by treating the LWP raw material with an aqueous solution containing a basic substance at a high temperature (also called an alkaline aqueous solution, or HT treatment). HT treatment can also be referred to as "reactive extraction". In HT treatment, a large amount of wastewater (generated from the aqueous phase obtained from phase separation) results. The present invention provides a workup that enables not only improvement of the HT treatment of LWP raw materials, particularly those with a high acidity, and more efficient use of the basic substance, but also an improvement in purification efficiency.

[0020] Specifically, the present invention focuses on the case of LWP raw materials containing a certain amount of acidic substances other than halogen compounds. That is, even in the theoretical case of an LWP raw material containing 2000 weight ppm of extremely high chlorine content (element content, organic + inorganic) treated with a 2 weight% NaOH aqueous solution having a pH of about 13.7 at a weight ratio (flow rate ratio by weight) of the NaOH aqueous solution to 0.4 of the LWP, assuming complete removal of chlorine as NaCl, the calculated pH only drops to 13.2. Such a pH shift is not a problem. However, the LWP raw material may contain additional acidic substances, particularly organic acids derived from oxygen-containing waste plastics (such as PET) that have been subjected to liquefaction. In this case, the presence of the organic acid can result in a further decrease in the pH to 7 or lower after the reaction in the HT treatment. As a result of such a large pH decrease, for example, due to a decrease in Si removal efficiency, it has a significant adverse effect on the HT treatment efficiency. Furthermore, the thus-neutralized aqueous phase can make post-treatment difficult. For example, if the pH is too high, the efficiency of membrane filtration for separating organic contaminants from the aqueous phase can decrease.

[0021] The problems caused by the presence of organic acids and other acidic substances and the partial or complete neutralization of the alkaline aqueous solution in the HT treatment have not been recognized or considered in the prior art.

[0022] The present invention provides a method including adjustment of the amount of a basic substance added in the form of an aqueous solution based on the water-oil ratio in the HT treatment, i.e., the relative amounts of the aqueous solution ("water") and the LWP raw material ("oil"), and at least one property measured from the LWP raw material. Specifically, the present invention relates to a method for optimizing the amount of the basic substance added to the LWP raw material (in the form of an aqueous solution). In particular, the quality of the LWP raw material is determined by measuring at least one property of the LWP raw material. The at least one property at least includes (reflects) the total acid value of the LWP raw material. Based on this measurement result, the amount of the basic substance added (relative to the LWP raw material considering the water-oil ratio) is adjusted (calculated and added) such that after all the acidic components in the LWP determined by the total acid value are neutralized by the basic substance, the pH level of the aqueous phase (obtained by phase separation after the HT treatment and containing contaminants) reaches the target pH level. Even in a continuous process (continuous flow process), such adjustment is preferably performed only when the raw material composition changes or is predicted to change (e.g., at the very start of the process, or whenever the raw material source or batch is changed), and / or relatedly (e.g., at regular intervals).

[0023] Accordingly, the present invention provides a rapid and efficient method for setting the appropriate amount of the basic substance added in the HT treatment step, thereby enabling efficient use of the basic substance by very simple means (without the need for very excessive utilization).

[0024] In an embodiment, the pH level of the aqueous phase is monitored (and / or the alkalinity of the aqueous phase is determined). Preferably, the amount of the basic substance added is repeatedly readjusted to maintain the pH at the target pH level (or to reach the target pH level) when, for example, the pH level falls below the target level or decreases. This readjustment can be repeated throughout the process and / or at least at the start of the process (or when the LWP raw material is changed). Accordingly, the readjustment is suitable for "fine-tuning" the amount of the basic substance added.

[0025] In connection with the present invention, liquefied waste plastic (LWP) means a product stream from a liquefaction process that includes at least depolymerized waste plastic. LWP is a material obtained by depolymerizing waste plastic. LWP may also be referred to as polymer waste-based oil.

[0026] Waste plastic can originate from any source, such as consumer plastics (recycled or recovered), industrial plastics (recycled or recovered), or end-of-life tires (ELT) (recycled or recovered). In particular, the term waste plastic refers to organic polymer materials that have become unsuitable for their intended use or have been disposed of for other reasons. More specifically, waste plastic can refer to end-of-life tires, recovered consumer plastics (consumer plastics refer to any organic polymer material included in consumer goods, even if the consumer plastic itself does not have "plastic" properties), and recovered industrial polymer waste. In the context of the present invention, the term waste plastic or "polymer" generally does not include purely inorganic materials (otherwise this might be called an inorganic polymer). The polymers in waste plastic can be of natural and / or synthetic origin and can be based on renewable and / or fossil raw materials.

[0027] The liquefaction process is typically carried out at high temperature, preferably under non-oxidizing conditions. The liquefaction process may be carried out at high pressure. The liquefaction process may be carried out in the presence of a catalyst. The product stream from the liquefaction process can be used directly as a liquefied waste plastic feedstock, or it can be subjected to fractional distillation (or separation) to provide a fraction (or separated liquid) of the product stream as a liquefied waste plastic feedstock. For example, the LWP feedstock can be hydrothermal liquefied oil or a fraction thereof. Similarly, multiple fractional distillations can be carried out. In addition, the product streams and / or fractions thereof from two or more liquefaction processes can be combined to produce an LWP feedstock. These product streams and / or fractions can have the same or similar boiling point ranges or different boiling point ranges.

[0028] Typical product effluents from the liquefaction process include gaseous (NTP) hydrocarbons, in addition to liquid (NTP) hydrocarbons, i.e., hydrocarbons that are liquid at normal temperature and pressure (NTP; absolute values of 20 °C and 101.325 kPa), and hydrocarbons that are waxy or solid at NTP but become liquid when heated, for example, when heated up to 80 °C.

[0029] In the context of the present disclosure, the depolymerization of waste plastics means decomposing or degrading the polymer backbone of waste plastics, typically at least thermally, to produce polymer and / or oligomer species that have a lower molecular weight compared to the starting waste plastics but still contain at least liquid (NTP) hydrocarbons. In other words, as used herein, liquefied waste plastics do not include liquid plastics obtained simply by melting or dissolving in a solvent without sufficient cleavage of the polymer backbone, nor waste plastics that have been completely depolymerized to the monomer level and thus are in gaseous (NTP) form. The depolymerization of waste plastics may optionally also involve cleavage of covalently bonded heteroatoms such as O, S, and N from any heteroatom-containing compounds present.

[0030] Initially, each waste plastic species in the waste plastics or mixed waste plastics to be liquefied is usually in a solid state and typically has a melting point in the range of 100 °C or higher as measured by DSC, as described by Larsen et al. (“Determining the PE fraction in recycled PP”, Polymer testing, vol.96, April 2021, 107058). However, the waste plastics or each waste plastic species may be melted before and / or during depolymerization.

[0031] Solid waste plastics may contain various additional components such as fillers, pigments, printing inks, flame retardants, stabilizers, antioxidants, plasticizers, lubricants, labels, metals, paper, cardboard, cellulose fibers, glass fibers, and even sand or other contaminants. Some of the additional components can be removed from the solid waste plastics, molten waste plastics, and / or liquefied waste plastics using generally known methods if desired.

[0032] Preferably, the (solid) waste plastics that are subjected to the liquefaction process (depolymerization) and thus serve as the base material for the LWP feedstock have an oxygen content of 15 wt% or less, preferably 10 wt% or less, more preferably 5 wt% or less of the total weight of the (solid) waste plastics. The oxygen content may be 0 wt%, and preferably may be in the range of 0 wt% to 15 wt% or 0 wt% to 10 wt%. The oxygen content in wt% can be determined by difference using the formula 100 wt% - (CHN content + ash content), where the CHN content refers to the combined content of carbon, hydrogen, and nitrogen determined according to ASTM D5291, and the ash content refers to the ash content determined according to ASTM D482 / EN15403.

[0033] In this disclosure, when referring to a standard, unless otherwise specified, it shall mean the latest revised version available as of January 31, 2022. Further, all embodiments of the present invention (such as all preferred values and / or ranges within the embodiments) may be combined with each other to provide new (preferred) embodiments as long as they are not explicitly specified otherwise or their combination does not result in a contradiction.

[0034] The LWP is preferably mainly composed of hydrocarbons in an amount exceeding 50% by weight, typically based on the total weight of the LWP. Typically, the LWP is composed of two or more hydrocarbon species selected from paraffins, olefins, naphthenes, and aromatics. The composition of the LWP can vary, for example, depending on the composition of the waste plastics, the type and conditions of the liquefaction process, and additional treatment. Furthermore, due to the classification of various types of waste plastics and impurities associated with the recovered waste, impurities including silicon, sulfur, nitrogen, halogens, and oxygen-related substances will be present in varying amounts in the resulting LWP.

[0035] The LWP raw material of the present invention is derived from (crude) LWP and can be, for example, crude LWP (i.e., the liquid fraction directly resulting from the liquefaction process), pre-purified LWP, or a fraction of one of the foregoing.

[0036] Furthermore, in the present invention, the term "pH" refers to the pH value of a solution measured at 20°C (or converted to a value corresponding to measurement at 20°C). The pH can be measured according to the Finnish standard SFS 3021.

[0037] The term "mechanical filtration" (also called macrofiltration) relates to filtration with a pore size of 0.5 to 40 μm, preferably 1 to 20 μm, such as 2 to 20 μm. The term "reverse osmosis" refers to filtration with a membrane having a small pore size capable of separating at least water from organic components of a specific size. Such membranes are generally specified by molecular weight cut-off (rejection size) rather than pore size. For example, a membrane with a cut-off of 200 Daltons is usually related to filtration with a pore size of 0.05 to 0.1 nanometers.

[0038] The term "amount of basic substance" "added", "adjusted", or "readjusted" (and thus utilized in the HT treatment) refers to the total amount of basic substance utilized in the HT treatment. The amount can be (re)adjusted by changing the content (concentration) of the basic substance in an aqueous solution containing the basic substance.

[0039] The present invention relates to a method comprising a step of subjecting a liquefied waste plastic (LWP) raw material to HT treatment together with an aqueous solution containing a basic substance, adjusting the addition amount of the basic substance based on the determination of the quality of the LWP raw material, and optionally readjusting the addition amount of the basic substance based on the result of monitoring, for example, the pH level of the aqueous phase (obtained from phase separation after HT treatment). In the method of the present invention, a treated LWP material is produced (after heat treatment and phase separation).

[0040] Specifically, the present invention provides a step of providing a liquefied waste plastic (LWP) raw material for heat treatment (HT treatment) using an aqueous solution containing a basic substance, a step of determining the quality of the LWP raw material by measuring at least one property of the LWP raw material, a step of calculating the amount of the basic substance that needs to be added in the HT treatment to reach the target pH level of the aqueous phase based on at least one property of the LWP raw material and the water-oil ratio, and a step of subjecting the LWP raw material to heat treatment using an aqueous solution containing the calculated amount of the basic substance in the form of an aqueous solution, followed by subjecting it to phase separation, resulting in obtaining at least a treated LWP material and an aqueous phase. Specifically, as a result of phase separation, an oil phase (including treated LWP) and an aqueous phase are obtained.

[0041] The quality of the LWP raw material is determined by measuring at least one property of the LWP raw material. The at least one property at least includes the total acid number (TAN) of the LWP raw material. This single value can be determined quite easily and already provides a high accuracy for predicting the amount of the basic substance required to maintain (or adjust) the pH of the aqueous phase at the target level (i.e., after heat treatment and subsequent phase separation). TAN can be measured, for example, according to the ASTM D664 method.

[0042] The at least one property is preferably measured from the LWP raw material after providing the LWP raw material, thereby enabling simple integration of the measurements.

[0043] The amount of basic substance added to the LWP feedstock can be easily calculated based on the TAN of the LWP feedstock. TAN itself describes how much of a specific basic substance (KOH) is required to neutralize all the acids present in a given oil sample. When LWP is contacted with an aqueous solution containing a stoichiometric amount of KOH for acid neutralization, the resulting pH value of the solution is predicted to be 7. However, if a target pH value of, for example, 10 (or higher) is aimed for, a larger amount of basic substance is required. Thus, the target pH is taken into account when calculating the amount of basic substance required. In addition, since the pH of the aqueous phase (after phase separation) depends on both the amount of water and the amount of unneutralized basic substance, the water-oil ratio is also considered.

[0044] At least one characteristic can include both the total acid number (TAN) and the total chlorine content of the LWP feedstock. The amount of basic substance added can be made even more accurate based on both of these characteristics. In the case of chlorine, it can be based on a calculation assuming that all the chlorine present in the LWP is released in the form of hydrogen chloride (HCl) during the HT treatment. The released HCl then reacts with the basic substance and thus reduces the pH value. The total chlorine content can be determined, for example, according to the ASTM D7359 method.

[0045] In addition, the method of the present invention can include a step of repeatedly (re)adjusting the amount of basic substance added. The readjustment can be carried out based on the result of monitoring the pH of the aqueous phase (e.g., based on the pH measurement result) and / or based on the result of determining the alkalinity of the aqueous phase. Thus, it is possible to compensate for the possible inaccuracies in the determination (calculation) of the addition amount based only on the quality of the LWP. However, since the determination based only on the quality of the LWP is already quite accurate, only a slight readjustment is required, and therefore, the efficiency of the HT treatment can be maintained in an optimally close state throughout the process.

[0046] The method preferably includes a step of monitoring the pH of the aqueous phase (obtained from phase separation), for example, a step of (repeatedly) measuring its pH. Measuring the pH of the aqueous phase (also referred to as the separated aqueous phase or contaminated aqueous substance) is easy to perform. The measurement can be carried out continuously or discontinuously (e.g., in a batch manner from a sample taken from the aqueous phase).

[0047] It is preferred that the pH measurement can be carried out directly after phase separation. In this regard, "directly after" means that no further process (or work-up) is provided in between, and does not necessarily mean "immediately after" (or "soon after") phase separation.

[0048] Monitoring of the pH can be achieved by simple and rapid measurements. Based on the measured pH (based on the monitoring results), the amount of basic substance added can be easily (re)adjusted. For example, if the pH is below the target pH level, the amount of basic substance is increased. For determining the necessary adjustment, for example, tabulated values or calculated values can be used.

[0049] In addition to (or instead of) monitoring the pH of the aqueous phase, the alkalinity of the aqueous phase can be (repeatedly) determined and used as a (further) criterion for (re)adjusting the amount of basic substance added (to reach / maintain the target pH of the aqueous phase). Alkalinity is a measure of resistance to acid addition and can be measured by titration. Thus, in this embodiment, if the alkalinity is too low, the basic substance is consumed excessively and further added in the process of readjustment, i.e., its amount is adjusted to a larger amount (in the next batch or continuous process). Alkalinity can be easily measured by titration, which may be suitable because titration is very robust against (e.g., organic) impurities and / or contaminants in the aqueous phase (obtained from phase separation).

[0050] In the method of the present invention, the target pH level is preferably 10.0 or higher. At this minimum target pH level, good HT treatment efficiency can be guaranteed. As long as the target pH (and more preferably the actual pH of the aqueous phase) is 10.0 or higher, the HT treatment efficiency is high. However, even if there is no actual upper limit to the target pH, in order to efficiently utilize the basic substance, it is preferable to avoid excessive addition of the basic substance. From this point, the target pH level (and preferably the actual pH level) is preferably in the range of 10.0 to 14.0, such as 10.2 to 13.9, 10.3 to 13.8, 10.4 to 13.6, 10.5 to 13.5, 10.6 to 13.4, 10.7 to 13.3, 10.8 to 13.2, 10.9 to 13.1, or 11.0 to 13.0. Nevertheless, by using the method of the present invention, it is possible to set (almost completely) the pH at a constant level and further maintain it, and thus it is possible to provide clearly defined conditions. Such clearly defined conditions cannot be achieved by the prior art approach of simply adding (presumed) excessive basic substances, which results in large fluctuations and thus leads to non-uniform conditions.

[0051] The amount of the basic substance (added in the form of an aqueous solution in the HT treatment) can be (re)adjusted by changing the concentration of the basic substance in the aqueous solution used in the HT treatment. The readjustment includes (re)calculating the (new / changed) addition amount and adding the (changed) amount calculated in the HT treatment. The adjustment of the concentration of the basic substance in the aqueous solution can be easily achieved, for example, by mixing various amounts of high-concentration aqueous solutions (stock solutions) containing the basic substance with one or more other aqueous raw materials such as fresh water and / or recycled water. The mixing can be achieved before the HT treatment or during the HT treatment (for example, by supplying the stock solution and one or more other aqueous raw materials together).

[0052] The method of the present invention may further include a step of subjecting the aqueous phase to a work-up including at least membrane filtration (reverse osmosis). Membrane filtration provides a permeate depleted in TOC (total organic carbon) and a retentate enriched in TOC. The inventors have surprisingly discovered that an aqueous phase having a high pH exhibits good responsiveness to membrane filtration. That is, in such an aqueous phase, good filtration efficiency can be achieved. In the present invention, the reverse osmosis membrane preferably has a cut-off in the range of 50 to 400 Daltons, preferably 100 to 300 Daltons, such as 150 to 250 Daltons. The work-up may further include mechanical filtration. Mechanical filtration can be carried out particularly before membrane filtration, which then makes it possible to extend the service life of the membrane (for example, by protecting the membrane from coarse impurities and / or by preventing rapid clogging).

[0053] The method may further include a step of recycling at least a part of the permeate depleted in TOC (for example, as part of the aqueous solution used in the HT treatment) back to the HT treatment. Therefore, it is possible to reuse the basic substance (for example, NaOH) not consumed in the HT treatment. It is also possible to reduce the need for fresh water addition.

[0054] The LWP raw material used in the present invention may have a total acid number (TAN) of 0.1 to 100.0 mg KOH / g, such as 0.2 to 95.0 mg KOH / g, 0.3 to 90 mg KOH / g or more, 1.0 to 80 mg KOH / g, 3.0 to 60 mg KOH / g, 5.0 to 50.0 mg KOH / g, 7.0 to 30.0 mg KOH / g, or 9.0 to 20.0 mg KOH / g. The method of the present invention is particularly useful for LWPs having a wide range of TAN values and is also useful for continuous processes using LWP raw materials with varying TAN values.

[0055] The LWP feedstock is preferably crude liquefied waste plastic or a fraction thereof. For example, the LWP feedstock has an initial boiling point (ASTM D86) below 50°C, such as in the range of 15°C to 50°C, 20°C to 45°C, or 25°C to 40°C, and / or a final boiling point (ASTM D86) above 400°C, such as in the range of 400°C to 700°C, 450°C to 650°C, 500°C to 650°C, or 550°C to 650°C. The method of the present invention is particularly suitable for such LWP feedstocks that have undergone little pre-purification such as fractional distillation.

[0056] The basic substance contained in the aqueous solution used in the HT treatment is preferably selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides. These hydroxides are strong bases, thus enabling simple adjustment of the addition amount and good control of the target pH level. Specifically, the basic substance is preferably selected from the group consisting of KOH, NaOH, LiOH, Ca(OH)2, Mg(OH)2, RbOH, Sr(OH)2, and Ba(OH)2. The basic substance can particularly be NaOH because it is an easily available strong base.

[0057] The LWP feedstock can have an olefin content of 5 wt% or more, such as 10 wt% or more, 15 wt% or more, 20 wt% or more, 30 wt% or more, 40 wt% or more, or 50 wt% or more. The olefin content can be, for example, 85 wt% or less, 80 wt% or less, 70 wt% or less, or 65 wt% or less.

[0058] The aqueous solution preferably contains at least 50 wt% water, preferably at least 70 wt% water, more preferably at least 85 wt% water, or at least 90 wt% water. By mainly containing water, the implementation of the process becomes easier.

[0059] The aqueous solution preferably contains at least 0.3% by weight of a basic substance, more preferably at least 0.5% by weight, at least 1.0% by weight, or at least 1.5% by weight of the basic substance. The content of the basic substance is not particularly limited, but is preferably 10.0% by weight or less, such as 6.0% by weight or less or 4.0% by weight or less.

[0060] In an embodiment, the aqueous solution contains at least 0.5% by weight, preferably at least 1.0% by weight, or at least 1.5% by weight of a metal hydroxide or an alkali metal hydroxide as the basic substance. The content is not particularly limited, but is preferably 10.0% by weight or less, such as 6.0% by weight or less or 4.0% by weight or less.

[0061] The HT treatment is preferably carried out at a temperature of 150°C or higher, preferably 190°C or higher, such as 200°C or higher, 220°C or higher, 240°C or higher, or 260°C or higher. The HT treatment is preferably carried out at a temperature of 450°C or lower, preferably 400°C or lower, 350°C or lower, or 300°C or lower. For example, the HT treatment is carried out at a temperature of 200°C to 350°C, preferably 220°C to 330°C, 240°C to 320°C, or 260°C to 300°C. Such a high temperature during the HT treatment, combined with a high pH, can even remove organic-bound impurities such as organic chlorine compounds and organic silicon compounds uniformly, thus improving the impurity removal efficiency.

[0062] The chlorine content of the LWP raw material can be in the range of 1 ppm to 4000 ppm by weight, such as 100 ppm to 4000 ppm by weight or 300 ppm to 4000 ppm by weight. That is, the method of the present invention is suitable for treating LWP raw materials having a wide concentration range of chlorine impurities.

[0063] The LWP feedstock can be a fraction of liquefied waste plastic or crude liquefied waste plastic. In particular, the LWP feedstock can have a 5% boiling point in the range of 25°C to 120°C, 25°C to 100°C, 30°C to 90°C, or 35°C to 80°C, etc., preferably 25°C or more, more preferably 30°C or more, 35°C or more. The liquefied waste plastic (LWP) feedstock can have a 95% boiling point in the range of 180°C to 700°C, 250°C to 700°C, 300°C to 650°C, 350°C to 600°C, 380°C to 500°C, or 400°C to 500°C, etc., preferably 700°C or less, more preferably 650°C or less, 600°C or less, or 550°C or less. The 5% boiling point and 95% boiling point of the LWP feedstock can be determined according to ASTM D2887-16.

[0064] The step of providing the LWP feedstock can preferably include a step of liquefying waste plastic by thermal degradation of waste plastic, such as pyrolysis or hydrothermal liquefaction or similar process steps. The liquefaction can be carried out by any known method such as pyrolysis, including fast pyrolysis, hydrothermal decomposition, and hydrothermal liquefaction.

[0065] The step of providing the LWP feedstock can include a step of liquefying the selected waste plastic, and the method further includes a step of sorting waste plastic to provide the selected waste plastic. In the step of sorting waste plastic, preferably, at least 50% by weight, more preferably at least 55% by weight, at least 60% by weight, at least 65% by weight, at least 70% by weight, at least 75% by weight, at least 80% by weight, or at least 85% by weight of chlorine-containing waste plastic, such as polyvinyl chloride, PVC (relative to the original content of chlorine-containing waste plastic such as PVC in the waste plastic), is removed from the waste plastic.

[0066] The LWP feedstock preferably has a density measured at 15°C in the range of 0.780 to 0.950 kg / l (kg / dm 3 ), such as in the range of 0.780 to 0.900 kg / l or 0.780 to 0.850 kg / l.

[0067] Preferably, hydrogen is not added to the HT treatment and / or no hydrotreating catalyst is present. That is, hydrotreating, especially hydrogen addition, may be suitable, but such procedures are not very sustainable as they typically consume large amounts of hydrogen gas produced from fossil resources and / or use large amounts of energy. More preferably, no hydrogen gas (including dissolved hydrogen gas) is present during the HT treatment. In other words, the HT treatment is preferably a simple process of heat-treating the LWP raw material at a high temperature together with an aqueous solution.

[0068] In the present invention, the ratio of the bromine number (BN2) of the treated LWP material to the bromine number (BN1) of the LWP raw material, BN2 / BN1, is preferably in the range of 0.90 or more, preferably 0.95 or more, such as in the range of 0.90 - 1.10, 0.90 - 1.02, or 0.95 - 1.00. In the present invention, the bromine number can be determined according to ASTM D1159 - 07(2017).

[0069] The mixing ratio (water - oil ratio) of the aqueous solution and the LWP raw material in the heat - treatment step is preferably in the range of 0.1 - 1.4, preferably 0.2 - 1.0, such as 0.2 - 0.7, by weight ratio. Within these ranges of the mixing ratio, efficient treatment is guaranteed, that is, good purification is achieved without excessive generation of wastewater. In this regard, the mixing ratio "by weight ratio" (wt / wt) means the total weight of the aqueous solution divided by the total weight of the LWP raw material. In a continuous process, the mixing ratio refers to the flow rate ratio (weight ratio) of each composition.

Examples

[0070] The present invention is described by way of examples to better assist in understanding the invention. The examples provide embodiments of the present invention but should not be used to narrow the interpretation of the claims.

[0071] Example 1 Simulated titrations of three types of LWP raw materials with different total acid numbers (TANs) were performed as shown in Table 1, assuming that the LWP raw materials were subjected to HT treatment together with NaOH aqueous solutions of various concentrations at a mixing ratio (weight ratio) of the aqueous solution / LWP raw material ratio (water-oil ratio) of 0.67, assuming sufficient reaction of all components contributing to TAN. Table 1 shows the calculated pH of the aqueous phase (after phase separation).

[0072]

Table 1

[0073] In Table 1, "<7" indicates that the (simulated) pH is below pH 7.

[0074] By changing the NaOH concentration according to the TAN of the raw material, that is, using a 0.8 wt% aqueous solution for the LWP raw material with a TAN of 5 mg KOH / g, a 1.3 wt% (slightly less than that) aqueous solution for the LWP raw material with a TAN of 10 mg KOH / g, and a 1.8 wt% aqueous solution for the LWP raw material with a TAN of 15 mg KOH / g, it can be seen that a pH level of, for example, 12.8 can be maintained. Therefore, the pH conditions can be kept fairly constant even in processes using various raw materials.

[0075] Example 2 To demonstrate the effect of the pH level of the aqueous phase on the silicon removal efficiency, small-scale experiments were performed using an LWP raw material containing 37 ppm by weight of Si and having a TAN of 15 mg KOH / g at 240 °C (pyrolysis temperature) and a ratio of the aqueous solution to the LWP raw material of 0.67 by weight (water-oil ratio). The basic substance used in these experiments was sodium hydroxide (NaOH).

[0076] (An aqueous solution containing a basic substance) The initial NaOH concentration was set to 2 wt%. By considering the TAN of the LWP raw material, the water-to-oil ratio, and the NaOH concentration, it was calculated that the pH value of the aqueous phase after phase separation would be approximately 13. However, the pH value obtained in the experiment was 8.6. The treated LWP material still contained some residual acidity (TAN 1.0 mgKOH / g), and the silicon removal efficiency was 35%. Based on the calculation of the required amount of the basic substance, it was found that a certain degree of silicon removal was achieved.

[0077] In another test, the concentration of the basic substance (NaOH) was readjusted to 3 wt%, and the test was repeated using a fresh LWP raw material sample. By considering only the TAN of the LWP raw material, the water-to-oil ratio, and the NaOH concentration, it was calculated that the pH value of the aqueous phase after phase separation would be approximately 13.5. After readjusting the concentration of the basic substance, the pH value obtained in the experiment of the aqueous phase after phase separation was 11.8. The treated LWP material no longer contained residual acidity (TAN <0.1 mgKOH / g), and the silicon removal efficiency was 90%. Therefore, surprisingly, it was found that the silicon removal efficiency significantly improved as the pH level of the aqueous phase increased.

[0078] Comparative Example 1 For comparison, a fresh LWP raw material sample (the same as in Example 2) was treated with a NaOH solution containing 1 wt% NaOH under the same conditions (however, TAN was ignored when setting the NaOH addition amount). By considering the TAN of the LWP raw material, the water-to-oil ratio, and the NaOH concentration, it was calculated that all the NaOH would be neutralized and the pH value of the aqueous phase after phase separation would be approximately 7. The pH value obtained in the experiment was 5.3. The treated LWP material still contained a large amount of residual acidity (TAN 7.7 mgKOH / g), and the silicon removal efficiency was 0%. Therefore, it was found that silicon removal could not be obtained by selecting the concentration of the basic substance that would theoretically result in a neutral or acidic solution after HT treatment and phase separation.

[0079] Based on the above findings, it was unexpectedly found that in order to have an acceptable level of silicon removal efficiency of LWP in heat treatment in large-scale operations, the preferred (target) pH level of the aqueous phase after phase separation is at least 10 or more.

Claims

1. A step of providing a liquefied waste plastic (LWP) raw material for heat treatment (HT treatment) using an aqueous solution containing a basic substance, and A step of heat-treating the LWP raw material with the aqueous solution and then performing phase separation to obtain at least a treated LWP material and an aqueous phase as a result, a method comprising: The method is A step of determining the quality of the LWP raw material by measuring at least one characteristic of the LWP raw material, wherein the at least one characteristic includes the total acid number (TAN) of the LWP raw material, the step of Calculating the amount of the basic substance that needs to be added in the HT treatment to reach the target pH level of the aqueous phase based on the at least one characteristic of the LWP raw material and the water-oil ratio, and adding the calculated amount of the basic substance in the form of an aqueous solution to contact the LWP raw material, a method characterized by comprising.

2. The method according to claim 1, wherein the target pH level is pH 10.0 or higher.

3. The method according to claim 1 or 2, further comprising a step of repeatedly readjusting the amount of the basic substance in the form of the aqueous solution to reach the target pH level of the aqueous phase.

4. The method according to any one of claims 1 to 3, wherein the at least one characteristic of the LWP raw material includes both the total acid number (TAN) and the total chlorine content of the LWP raw material.

5. The method according to any one of claims 1 to 4, wherein the amount of the basic substance is adjusted by changing the concentration of the basic substance in the aqueous solution used in the HT treatment.

6. The LWP raw material has a total acid number (TAN) in the range of 0.1 to 100.0 mg KOH / g, such as 0.2 to 95.0 mg KOH / g, 0.3 to 90 mg KOH / g or more, 1.0 to 80 mg KOH / g, 3.0 to 60 mg KOH / g, 5.0 to 50.0 mg KOH / g, 7.0 to 30.0 mg KOH / g, or 9.0 to 20.0 mg KOH / g, the method according to any one of claims 1 to 5.

7. The basic substance is selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides, and preferably, the basic substance is KOH, NaOH, LiOH, Ca(OH) 2 , Mg(OH) 2 , RbOH, Sr(OH) 2 , and Ba(OH) 2 selected from the group consisting of, and preferably NaOH, the method according to any one of claims 1 to 6.

8. The method according to any one of claims 1 to 7, wherein the aqueous solution contains at least 50% by weight of water, preferably at least 70% by weight of water, more preferably at least 85% by weight of water, at least 90% by weight of water or at least 95% by weight of water.

9. The method according to any one of claims 1 to 8, wherein the aqueous solution contains at least 0.3% by weight, more preferably at least 0.5% by weight, at least 1.0% by weight, or at least 1.5% by weight of a basic substance, such as 0.5% by weight to 10.0% by weight, 1.0% by weight to 6.0% by weight, or 1.5% by weight to 4.0% by weight.

10. The method according to any one of claims 1 to 9, further comprising the step of monitoring the pH level of the aqueous phase obtained from phase separation.

11. The method according to any one of claims 1 to 10, wherein the liquefied waste plastic (LWP) raw material has a 5% boiling point in the range of 25°C or higher, preferably 30°C or higher, or 35°C or higher, such as in the range of 25°C to 120°C, 25°C to 100°C, 30°C to 90°C, or 35°C to 80°C.

12. The method according to any one of claims 1 to 11, wherein the liquefied waste plastic (LWP) raw material has a 95% boiling point of 700°C or lower, preferably 650°C or lower, 600°C or lower, or 550°C or lower, such as in the range of 180°C to 700°C, 250°C to 700°C, 300°C to 650°C, 350°C to 600°C, 380°C to 500°C, or 400°C to 500°C.

13. The method according to any one of claims 1 to 12, wherein the LWP raw material has a density measured at 15°C in the range of 0.780 to 0.950 kg / l, such as in the range of 0.780 to 0.900 kg / l or 0.780 to 0.850 kg / l.

14. The method according to any one of claims 1 to 13, wherein the HT treatment is carried out at a temperature of 150°C or higher, 190°C or higher, 200°C or higher, 210°C or higher, 220°C or higher, 240°C or higher, or 260°C or higher.

15. The method according to any one of claims 1 to 14, wherein the mixing ratio (water-oil ratio) of the aqueous solution and the LWP raw material in the heat treatment step is in the range of 0.1 to 1.4, preferably in the range of 0.2 to 1.0, such as in the range of 0.2 to 0.7 by weight ratio.

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