Improved method for treating liquefied waste plastic

Abstract

The present invention relates to an improved method for treating liquefied waste plastics. The method comprises: providing a liquefied waste plastic (LWP) feedstock for heat treatment (HT treatment) with an aqueous solution containing an alkaline substance; thermally treating the LWP feedstock with an aqueous solution followed by phase separation to produce at least a treated LWP material and an aqueous phase; determining the mass of the LWP feedstock by measuring at least one property of the LWP feedstock, the at least one property including at least the total acid number (TAN) of the LWP feedstock; and based on at least one property of the LWP feedstock and the water-to-oil ratio, calculating an amount of alkaline species that need to be added in the HT treatment to achieve the target pH level of the aqueous phase, and adding the calculated amount of alkaline species in the form of an aqueous solution to contact the LWP feedstock.

Description

Technical Field

[0001] The present invention relates to an improved method for treating liquefied waste plastics, and more particularly to improvements in purification efficiency and process efficiency of a purification process for (crude) liquefied waste plastics. Background Art

[0002] Purification of liquefied waste plastic (LWP) to produce more valuable (pure) substances, as well as conversion of liquefied waste plastic into more valuable materials, have been studied over the years.

[0003] LWP is usually produced by pyrolysis or hydrothermal liquefaction (HTL) of waste plastics. Depending on the source of the waste plastics, LWP has variable levels of impurities. Typical impurity components are chlorine, nitrogen, sulfur and oxygen, with corrosive chlorine being particularly problematic for refinery / petrochemical processes. These impurities originate from waste plastic materials, such as post-consumer waste plastics (recycled consumer plastics), which have been identified as the most potential large-scale source of plastic waste. Likewise, bromine-containing impurities may be primarily contained in waste plastics of industrial origin (e.g., from flame retardants).

[0004] Whether LWP is subjected to ordinary refinery treatment (e.g. fractionation) or is forwarded to typical petrochemical conversion processes (e.g. steam cracking), the LWP feed needs to meet the impurity levels of these processes to avoid facility degradation such as reactor corrosion or catalyst poisoning.

[0005] In addition to refining, chemical recycling of LWP into plastics (or monomers) is an interesting option that has generated a lot of interest in the petrochemical industry over the past few years. The new Waste Directive and the EU Plastics Strategy, which set ambitious targets for the recycling of waste plastics, have further increased interest.

[0006] Given the growing interest in adding LWP to the value chain, a variety of options have been developed for purifying LWP to make it more suitable for traditional refining processing.

[0007] WO 2018 / 10443 A1 discloses a steam cracking process comprising pre-treating a predominantly paraffinic feedstock such as hydrowax, hydrotreated vacuum gas oil, pyrolysis oil from waste plastics, gas oil or slackwax. Pre-treatment is performed using solvent extraction to reduce contaminating components such as polycyclic aromatic hydrocarbons and resins. This solvent extraction technique may have poor removal efficiency for certain contaminants in LWP and furthermore may result in large amounts of contaminated extracted material that requires post-treatment or disposal.

[0008] US 2016 / 0264874 A1 discloses a method for upgrading waste plastics, which comprises a pyrolysis step, a hydrotreatment step, a polishing step and a steam cracking step in sequence. The process consumes a large amount of hydrogen (usually produced from fossil sources). Therefore, from a sustainability perspective, the process is not favorable.

[0009] FI 128848 B discloses a method for converting LWP into a steam cracker feed by thermally treating the LWP with an aqueous medium having a pH of at least 7 and then subjecting the treated LWP to a hydrotreatment. Purification using an aqueous medium results in large amounts of contaminated water. The contaminated water has a high content of organic contaminants and therefore requires further treatment (e.g. purification) before it can be diverted to conventional wastewater treatment. Purification can be achieved in a variety of ways.

[0010] US 2014 / 0303421 A1 discloses a method for conditioning synthetic crude oil with a caustic process solution. US 2014 / 0303421 A1 uses a slightly elevated temperature and a caustic solution with a pH of about 8 to 10. The conditioning treatment of US 2014 / 0303421 A1 is a washing treatment and is not considered to be the HT treatment of the present invention.

[0011] FI 128069 B relates to a method for purifying, for example, recycled materials such as LWP, which method comprises a purification step and a hydrotreatment step, wherein the purification step may be carried out in the presence of an aqueous alkali metal hydroxide solution. This procedure achieves good removal efficiency of the chlorine impurity, but still produces a large amount of wastewater. Summary of the invention

[0012] The above-mentioned prior art methods employ various purification procedures for LWP, each of which has certain disadvantages with respect to efficiency, in particular with respect to purification efficiency, efficient use of chemicals and treatment of contaminated water (wastewater).

[0013] The present invention is made in view of the above problems, and an object of the present invention is to provide an improvement in the LWP upgrading process, in particular, to improve the purification efficiency of the aqueous solution and the alkaline substance contained therein in the heat treatment process for purifying the LWP raw material. More specifically, an object of the present invention is to optimize the amount of the alkaline substance in the aqueous solution used relative to the amount of the LWP raw material and its impurity content, thereby improving the efficiency of removing impurities from LWP, especially from LWP with high acidity.

[0014] The problem of providing an improved process for upgrading LWP is solved by a method as set forth in any one of the claims.

[0015] Briefly, the present invention relates to one or more of the following:

[0016] 1. A method comprising:

[0017] Provide liquefied waste plastic (LWP) raw materials for thermal treatment (HT treatment) and aqueous solutions containing alkaline substances,

[0018] subjecting said LWP feedstock to said heat treatment with said aqueous solution followed by phase separation to produce at least a treated LWP material and an aqueous phase,

[0019] Characterized in that the method comprises

[0020] determining the quality of the LWP feedstock by measuring at least one property of the LWP feedstock, the at least one property comprising at least a total acid number (TAN) of the LWP feedstock, and

[0021] Based on at least one property of the LWP feedstock and the water-oil ratio, the amount of the alkaline substance required to be added in HT treatment to reach the target pH level of the aqueous phase is calculated, and the calculated amount of the alkaline substance is added in the form of an aqueous solution to contact the LWP feedstock.

[0022] 2. The method according to claim 1, wherein the method further comprises monitoring the pH level of the aqueous phase obtained from the phase separation.

[0023] 3. The method according to item 1 or 2, wherein the method further comprises the step of repeatedly readjusting the amount of the alkaline substance in the form of the aqueous solution to reach the target pH level of the aqueous phase.

[0024] 4. The method according to any of the preceding items, wherein the target pH level is above pH 10.0, preferably in the range of 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.

[0025] 5. The method according to any of the preceding items, wherein at least one property of the LWP feedstock comprises both the total acid number (TAN) and the total chlorine content of the LWP feedstock.

[0026] 6. The method according to any one of the preceding items, further comprising measuring the alkalinity of the aqueous phase by titration and using the alkalinity measurement result as a basis for readjusting the amount of the alkaline substance.

[0027] 7. The method according to any one of the preceding items, wherein

[0028] The amount of the alkaline substance is adjusted and / or readjusted by changing the concentration of the alkaline substance in the aqueous solution employed in the HT treatment.

[0029] 8. The method according to any of the preceding items, wherein the LWP feedstock 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 mgKOH / 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 mgKOH / g.

[0030] 9. The method according to any of the preceding items, wherein the LWP feedstock is crude liquefied waste plastic or a fraction thereof.

[0031] 10. The method according to any of the preceding items, wherein the LWP feedstock has an initial boiling point below 50°C, such as having an initial boiling point in the range of 15°C to 50°C, 20°C to 45°C, or 25°C to 40°C.

[0032] 11. The method according to any of the preceding items, wherein the LWP feedstock has a final boiling point 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.

[0033] 12. The method according to any one of the preceding items, wherein the alkaline substance is selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides.

[0034] 13. The method according to any one of the preceding items, wherein the alkaline 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.

[0035] 14. The method according to any one of the preceding items, wherein the alkaline substance is NaOH.

[0036] 15. The method according to any of the preceding items, wherein the LWP feedstock has 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.

[0037] 16. The method according to any of the preceding items, wherein the LWP feedstock has an olefin content of 85 wt% or less, such as 80 wt% or less, 70 wt% or less, or 65 wt% or less.

[0038] 17. The method according to any of the preceding items, wherein the aqueous solution comprises at least 50 wt % water, preferably at least 70 wt % water, more preferably at least 85 wt % water, at least 90 wt % water, or at least 95 wt % water.

[0039] 18. The method according to any of the preceding items, wherein the aqueous solution comprises at least 0.3 wt % of the alkaline substance, more preferably at least 0.5 wt %, at least 1.0 wt % or at least 1.5 wt % of the alkaline substance, such as 0.5 wt % to 10.0 wt %, 1.0 wt % to 6.0 wt %, or 1.5 wt % to 4.0 wt %.

[0040] 19. The method according to any of the preceding items, wherein the aqueous solution comprises at least 0.5 wt %, preferably at least 1.0 wt % or at least 1.5 wt % of a metal hydroxide or alkali metal hydroxide, such as 0.5 wt % to 10.0 wt %, 1.0 wt % to 6.0 wt %, or 1.5 wt % to 4.0 wt %.

[0041] 20. The method according to any of the preceding items, wherein the HT treatment is carried out at a temperature above 150°C, preferably above 190°C.

[0042] 21. The method according to any of the preceding items, wherein the HT treatment is carried out at a temperature above 200°C, such as above 210°C, above 220°C, above 240°C or above 260°C.

[0043] 22. The method according to any of the preceding items, wherein the HT treatment is carried out at a temperature below 450°C, preferably below 400°C, below 350°C, below 320°C, or below 300°C.

[0044] 23. The method according to any of the preceding items, 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.

[0045] 24. The method according to any of the preceding items, wherein the chlorine content of the LWP feedstock is in the range of 1 wt ppm to 4000 wt ppm, such as 100 wt ppm to 4000 wt ppm, or 300 wt ppm to 4000 wt ppm.

[0046] 25. The method according to any of the preceding items, wherein the LWP feedstock is a fraction of liquefied waste plastic.

[0047] 26. The method according to any of the preceding items, wherein the liquefied waste plastic (LWP) feedstock has a 5% boiling point of 25°C or above, preferably 30°C or above, or 35°C or above, such as in the range of 25°C to 120°C, in the range of 25°C to 100°C, in the range of 30°C to 90°C, or in the range of 35°C to 80°C.

[0048] 27. A method according to any preceding claim, wherein the liquefied waste plastic (LWP) feedstock has a 95% boiling point of 700°C or less, preferably 650°C or less, 600°C or less, or 550°C or less, 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.

[0049] 28. The method according to any of the preceding items, wherein the step of providing the LWP feedstock comprises a step of liquefying the waste plastic, preferably by thermal degradation of the waste plastic, such as pyrolysis or hydrothermal liquefaction or similar process steps.

[0050] 29. A method according to any one of the preceding items, wherein the step of providing the LWP feedstock comprises the step of liquefying the sorted waste plastic, and the method further comprises the step of sorting the waste plastic to provide sorted waste plastic, thereby 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 chlorinated waste plastics, such as polyvinyl chloride, PVC (relative to the original content of chlorinated waste plastics, such as PVC in the waste plastic).

[0051] 30. The method according to any of the preceding items, wherein no hydrogen is added and / or no hydrotreating catalyst is present in the HT treatment.

[0052] 31. The method according to any of the preceding items, wherein the ratio BN2 / BN1 of the bromine number (BN2) of the treated LWP material to the bromine number (BN1) of the LWP raw material is 0.90 or more, preferably 0.95 or more, such as in the range of 0.90 to 1.10, 0.90 to 1.02, or 0.95 to 1.00.

[0053] 32. A method according to any preceding claim, wherein the LWP feedstock has a density as 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 0.750 to 0.850 kg / l.

[0054] 33. The method according to any one of the preceding items, wherein in the heat treatment step, the mixing ratio of the aqueous solution to the LWP raw material (water-oil ratio) is in the range of 0.1 to 1.4 by weight, preferably in the range of 0.2 to 1.0, such as 0.2 to 0.7. DETAILED DESCRIPTION

[0055] The present invention relates to improvements in methods for upgrading liquefied waste plastics.

[0056] LWP feeds, such as pyrolysis products of collected consumer plastics, contain large and varying amounts of contaminants that can be detrimental to downstream processes. Among these contaminants are halogens (mainly chlorine) from halogenated plastics such as PVC and PTFE, sulfur from cross-linking agents in rubber polymers such as scrap tires, and metal (e.g. Si, Al) contaminants from composite materials and additives such as films coated with metals or metal compounds, scrap tires, or plastic processing aids. These contaminants may be present in elemental form, in ionic form, or as part of organic or inorganic compounds.

[0057] These impurities should be removed before further processing of LWP. The present invention focuses on a method for removing such impurities (or contaminants) by treating LWP feedstock with an aqueous solution containing an alkaline substance (also referred to as an alkaline aqueous solution) at high temperature (also referred to as HT treatment). HT treatment may also be referred to as "reactive extraction". HT treatment produces a large amount of wastewater (emerging from the aqueous phase obtained by phase separation). The present invention provides improvements to the HT process for LWP feedstock, especially LWP feedstock with high acidity, and post-treatment that enables more efficient use of alkaline substances and improved purification efficiency.

[0058] The present invention specifically focuses on the case of LWP feedstocks containing a certain amount of acidic substances other than halogen compounds. That is, even in the theoretical case of treating an LWP feedstock containing an extremely high content of chlorine (elemental content, organic and inorganic) of 2000 wt ppm with 2 wt % aqueous NaOH (having a pH of about 13.7) at a weight ratio of aqueous NaOH to LWP of 0.4 (flow ratio by weight), and assuming that the chlorine is completely removed in the form of NaCl, the calculated pH value will only be reduced to 13.2. Such a pH change is not problematic. However, the LWP feedstock may contain additional acidic substances, in particular organic acids derived from oxygen-containing waste plastics (such as PET) that are subjected to liquefaction. In this case, the presence of organic acids may lead to a further reduction in the pH value to pH 7 or even lower after the reaction in the HT treatment. Such a large pH reduction may have a significant negative impact on the HT treatment efficiency, for example by reducing the Si removal efficiency. In addition, the aqueous phase thus neutralized may be difficult to post-process. For example, if the pH is too high, the efficiency of membrane filtration used to separate organic contaminants from the aqueous phase may be reduced.

[0059] In the prior art, the presence of organic acids and other acidic substances in HT treatments and the problems that arise in the case of partial or complete neutralization with alkaline aqueous solutions have not been recognized or considered.

[0060] The present invention provides a method involving adjusting the amount of alkaline substance added in the form of an aqueous solution based on the water-oil ratio, i.e. the relative amounts of aqueous solution ("water") and LWP feedstock ("oil") in the HT treatment, and based on at least one property measured from the LWP feedstock. In particular, the present invention relates to a method for optimizing the amount of alkaline substance (in the form of an aqueous solution) added to the LWP feedstock. In particular, the quality of the LWP feedstock is determined by measuring at least one property of the LWP feedstock. The at least one property includes (reflects) at least the total acid value of the LWP feedstock. Based on the measurement result, the amount of alkaline substance added (relative to the LWP feedstock taking into account the water-oil ratio) is adjusted (calculated and added) so that the pH value of the aqueous phase (which is obtained from the phase separation after the HT treatment and contains contaminated substances) reaches a target pH level after all acidic components of the LWP (as determined by the total acid value) have been neutralized by the alkaline substance. Even in continuous processes (continuous flow processes), such adjustments are preferably made only when the raw material composition has changed or is expected to change (e.g. at the beginning of the process or every time the raw material source or batch is changed) and / or when relevant (e.g. at certain intervals).

[0061] The present invention thus provides a fast and efficient method for setting the appropriate amount of alkaline substance to be added to the HT treatment step, which allows the efficient use of alkaline substance in a very simple manner (without the need to employ very high excesses).

[0062] In one embodiment, the pH level of the aqueous phase is monitored (and / or the alkalinity of the aqueous phase is determined). Preferably, the amount of alkaline substance added is repeatedly readjusted, e.g. if the pH level is below a target level / drops below a target level, so that the pH is maintained at the target pH level (or reaches the target pH level). This readjustment may be repeated throughout the process and / or at least at the beginning of the process (or when the LWP feedstock is changed). Thus, the readjustment is suitable for "fine tuning" the amount of alkaline substance added.

[0063] In the context of the present invention, liquefied waste plastic (LWP) means the product effluent from a liquefaction process which comprises at least depolymerizing waste plastic. Thus, LWP is a material obtainable by depolymerizing waste plastic. LWP may also be referred to as polymer waste base oil.

[0064] Waste plastics may be obtained from any source, such as (recycled or collected) consumer plastics, (recycled or collected) industrial plastics or (recycled or collected) end-of-life tyres (ELTs). In particular, the term waste plastics refers to organic polymeric materials that are no longer suitable for their use or are disposed of for any other reason. Waste plastics may more specifically refer to end-of-life tyres, collected consumer plastics (consumer plastics refers to any organic polymeric material in consumer products (even if not having such "plastic" characteristics)), collected industrial polymer waste. In the sense of the present invention, the term waste plastics or "polymers" generally does not cover purely inorganic materials (sometimes otherwise referred to as inorganic polymers). The polymers in the waste plastics may be of natural and / or synthetic origin and may be based on renewable and / or fossil raw materials.

[0065] The liquefaction process is usually carried out at high temperature, and preferably under non-oxidative conditions. The liquefaction process can be carried out under high pressure. The liquefaction process can be carried out in the presence of a catalyst. The effluent of the liquefaction process can be directly used as a liquefied waste plastic raw material, or can be fractionated (or separated) to provide a fraction of the effluent (or separated liquid) as a liquefied waste plastic raw material. For example, the LWP raw material can be a hydrothermal liquefied oil or a fraction thereof. Similarly, multiple fractionations can be performed. In addition, two or more liquefaction process effluents and / or their fractions can be combined to give a LWP raw material. These effluents and / or fractions can have the same or similar boiling ranges, or can have different boiling ranges.

[0066] In addition to liquid (NTP) hydrocarbons, i.e. hydrocarbons that are liquid at normal temperature and pressure (NTP; 20°C, 101.325 kPa absolute), a typical product effluent from a liquefaction process also contains gaseous (NTP) hydrocarbons, as well as hydrocarbons that are waxy or solid at NTP but become liquid upon heating, e.g. upon heating to 80°C.

[0067] In the context of the present disclosure, depolymerizing waste plastics means decomposing or degrading the polymer backbone of the waste plastics, usually at least thermally decomposing or degrading, to the extent of producing polymers and / or oligomers of smaller molecular weight than the starting waste plastics, but still at least containing liquid (NTP) hydrocarbons. In other words, as used herein, liquefied waste plastics do not encompass plastics in liquid form obtained only by melting or dissolving in a solvent, as these do not involve sufficient cracking of the polymer backbone, nor do they encompass waste plastics that are completely depolymerized to the monomer level and are therefore in gaseous (NTP) form. Depolymerization of waste plastics may also involve cleavage of covalently bound heteroatoms, such as O, S and N, from optionally present heteroatom-containing compounds.

[0068] Initially, the waste plastic or each of the mixed waste plastics to be liquefied is generally solid, generally having a melting point in the range above 100°C, as described by Larsen et al. (“Determining the PE fraction in recycled PP”, Polymer testing, vol. 96, April 2021, 107058). However, the waste plastic or each of the waste plastic substances may melt before and / or during depolymerization.

[0069] Solid waste plastics may contain various additional components, such as additives, reinforcing materials, etc., including fillers, pigments, printing inks, flame retardants, stabilizers, antioxidants, plasticizers, lubricants, tracers, metals, paper, cardboard, cellulose fibers, glass fibers, and even sand or other dirt. If necessary, some additional components can be removed from solid waste plastics, molten waste plastics and / or liquefied waste plastics using known methods.

[0070] Preferably, the (solid) waste plastic to be subjected to the liquefaction process (depolymerization), and therefore the base material of the LWP feedstock, has an oxygen content of less than 15 wt %, preferably less than 10 wt %, more preferably less than 5 wt %, based on the total weight of the (solid) waste plastic. The oxygen content may be 0 wt %, and may preferably be in the range of 0 wt % to 15 wt %, or 0 wt % to 10 wt %. The oxygen content (in wt %) may be determined by using the difference of the formula 100 wt % - (CHN content + ash content), wherein CHN content refers to the combined content of carbon, hydrogen and nitrogen as determined according to ASTM D5291, and ash content refers to the ash content as determined according to ASTM D482 / EN15403.

[0071] In the present disclosure, when a standard is mentioned, the latest version available on January 31, 2022 shall be meant unless otherwise specified. In addition, all embodiments of the present invention (such as all preferred values ​​and / or ranges in the embodiments) can be combined with each other to give new (preferred) embodiments, unless explicitly stated otherwise or unless such combination leads to a conflict.

[0072] The LWP preferably comprises predominantly hydrocarbons, typically in excess of 50 wt %, based on the total weight of the LWP. Typically, the LWP comprises two or more hydrocarbon species selected from alkanes, olefins, cycloalkanes and aromatics. The composition of the LWP may vary, for example, depending on the composition of the waste plastic, the type and conditions of the liquefaction process, and any additional processing. In addition, the sorting of various waste plastics and impurities associated with the collected waste may result in the presence of varying amounts of impurities in the LWP, including silicon, sulfur, nitrogen, halogens and oxygen-related species.

[0073] The LWP feedstock of the present invention is obtained from (crude) LWP and may be, for example, crude LWP (ie the liquid fraction directly from a liquefaction process), pre-purified LWP or a fraction of one of the above.

[0074] 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 the measurement at 20° C.). The pH can be measured according to Finnish Standard SFS 3021.

[0075] 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 smaller pore size, so that it can separate water from at least organic components of a certain size. Such membranes are usually specified by their molecular weight cut-off (rejection size) rather than by pore size. For example, a membrane with a cut-off value of 200 Daltons usually refers to filtration with a pore size of 0.05 nm to 0.1 nm.

[0076] The term "addition" or "adjustment" or "re-adjustment" (hence used in the HT treatment) of "the amount of alkaline substance" refers to the total amount of alkaline substance employed in the HT treatment. The amount can be (re)adjusted by changing the content (concentration) of the alkaline substance in the aqueous solution containing the alkaline substance.

[0077] The present invention relates to a method comprising subjecting a LWP raw material to HT treatment together with an aqueous solution comprising an alkaline substance, and characterized in that the amount of alkaline substance added is adjusted based on the determination of the quality of the LWP raw material, and optionally readjusted based on the results of monitoring the pH level of the aqueous phase (obtained from phase separation after HT treatment). The method of the present invention produces a treated LWP material (after heat treatment and phase separation).

[0078] Specifically, the present invention relates to a method comprising providing a liquefied waste plastic (LWP) feedstock for thermal treatment (HT treatment) with an aqueous solution containing an alkaline substance, determining the quality of the LWP feedstock by measuring at least one property of the LWP feedstock, calculating the amount of alkaline 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 property of the LWP feedstock and a water-oil ratio, and thermally treating the LWP feedstock with the aqueous solution containing the calculated amount of alkaline substance in the form of an aqueous solution, followed by phase separation to produce at least a treated LWP material and an aqueous phase. Specifically, the phase separation produces an oil phase (containing the treated LWP) and an aqueous phase.

[0079] 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 comprises at least the total acid number (TAN) of the LWP raw material. This single value can be easily determined and already provides a high accuracy for predicting the amount of alkaline material required for maintaining (or adjusting) the pH value of the aqueous phase (i.e. after heat treatment and subsequent phase separation) at a target level. The TAN can be determined, for example, according to method ASTM D664.

[0080] The at least one property is preferably measured from the LWP feedstock after providing the LWP feedstock, which allows for simple integration of the measurements.

[0081] The amount of alkaline substance to be added to the LWP feed can be easily calculated based on the TAN of the LWP feed. The TAN itself describes how much of a specific alkaline substance (KOH) is needed to neutralize all the acids present in a given oil sample. If the LWP is contacted with an aqueous solution containing a stoichiometric amount of KOH to neutralize the acids, the pH of the resulting solution is expected to be 7. However, if the target has a pH of, for example, 10 (or more), a higher amount of alkaline substance is required. Therefore, the target pH is taken into account when calculating the amount of alkaline substance required. Furthermore, the water-oil ratio is taken into account, since the pH of the aqueous phase (after phase separation) depends of course on the amount of water and the amount of unneutralized alkaline substance.

[0082] At least one property may include both the total acid number (TAN) and the total chlorine content of the LWP feedstock. When based on these two properties, the amount of alkaline material to be added may be even more accurate. In the case of chlorine, the calculation may be based on the assumption that all chlorine present in the LWP will be released in the form of hydrogen chloride (HCl) during the HT treatment. The released HCl will then react with the alkaline material, thereby lowering the pH value. The total chlorine content may be determined, for example, according to method ASTM D7359.

[0083] Furthermore, the method of the invention may comprise repeatedly (re)adjusting the amount of alkaline substance added. The readjustment may be based on the results of monitoring the pH of the aqueous phase (e.g. based on the results of pH measurements) and / or based on the results of determining the alkalinity of the aqueous phase. Thus, possible inaccuracies in the determination (calculation) of the amount of addition based solely on the mass of the LWP may be compensated. However, since the determination based solely on the mass of the LWP is already quite accurate, only minor adjustments are required, so that the efficiency of the HT treatment can be maintained at a near-optimal level throughout the process.

[0084] The method preferably comprises monitoring the pH value of the aqueous phase (obtained from the phase separation), for example (repeatedly) measuring its pH. The measurement of the pH of the aqueous phase (which may also be referred to as the separated aqueous phase or the contaminated aqueous material) is easy to implement. The measurement can be performed continuously or discontinuously (e.g., batchwise by sampling from the aqueous phase).

[0085] The measurement of pH is preferably carried out directly after phase separation. In this respect, "directly after" means that no further processing (or work-up) is provided in between - it does not necessarily mean that the phase separation is carried out "immediately after" (or shortly after).

[0086] Monitoring the pH value can be achieved by simple and quick measurement. Based on the measured pH (based on the monitoring results), the amount of alkaline substance added can be easily (re)adjusted. For example, if the pH value is below the target pH value, the amount of alkaline substance is increased. For example, tabulated values ​​or calculated values ​​can be used to determine the necessary adjustments.

[0087] In addition to (or alternatively to) monitoring the pH of the aqueous phase, the alkalinity of the aqueous phase may also be (repeatedly) determined and used as a (further) basis for (re)adjusting the amount of alkaline substance added (for reaching / maintaining a target pH of the aqueous phase). Alkalinity is a measure for resistance to acid addition and may be determined by titration. Thus, in this embodiment, if the alkalinity is too low, too much alkaline substance has been consumed and more is added during readjustment, i.e. the amount is adjusted to a higher amount (in the next batch or in a continuous process). The alkalinity can be easily determined by titration, which may be advantageous because titrations are very robust to (e.g. organic) impurities and / or contaminants in the aqueous phase (obtained from the phase separation).

[0088] In the method of the present invention, the target pH value is preferably above 10.0. In the case of this minimum target pH level, a good HT treatment efficiency can be ensured. Although the HT treatment efficiency will be high as long as the target pH (more preferably the actual pH of the aqueous phase) is above 10.0, even if the target pH has no actual upper limit, it is also advantageous to avoid excessive addition of the alkaline substance in order to effectively utilize the alkaline substance. In view of this, the target pH level (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. However, using the method of the present invention, the pH value can be (almost completely) set or even maintained at a constant level, thereby providing well-defined conditions. Such well-defined conditions cannot be achieved by prior art methods of simply adding an (estimated) excess of alkaline substances, which leads to strong variations and thus inhomogeneous conditions.

[0089] The amount of alkaline substance (added in the form of aqueous solution to the HT treatment) can be (re)adjusted by changing the concentration of the alkaline substance in the aqueous solution employed in the HT treatment. The readjustment may comprise (re)calculating the (new / modified) amount to be added and adding the calculated (modified) amount in the HT treatment. Adjusting the concentration of the alkaline substance in the aqueous solution may be easily accomplished, for example, by mixing different amounts of a highly concentrated aqueous solution (stock solution) comprising the alkaline substance with other aqueous feeds, such as fresh water and / or recycle water. The mixing may be accomplished prior to the HT treatment or during the HT treatment (e.g. by co-feeding the stock solution and the other aqueous feeds).

[0090] The method of the present invention may also include post-treatment of the aqueous phase, which post-treatment includes at least membrane filtration (reverse osmosis). Membrane filtration provides a TOC (total organic carbon)-depleted permeate and a TOC-enriched retentate. The inventors were surprised to find that an aqueous phase with a high pH shows good responsiveness to membrane filtration. That is, in the case of such an aqueous phase, a good filtration efficiency can be achieved. In the present invention, the reverse osmosis membrane preferably has a retention rate in the range of 50 to 400 Daltons, preferably 100 to 300 Daltons, for example 150 to 250 Daltons. The post-treatment may also include mechanical filtration. Mechanical filtration can be performed in particular before membrane filtration, which can then extend the service life of the membrane (e.g., by protecting the membrane from coarse impurities and / or by preventing rapid clogging).

[0091] The method may further comprise recycling (at least a portion of) the TOC-depleted permeate back to the HT treatment (e.g. as part of the aqueous solution used in the HT treatment). Thus, alkaline substances (e.g. sodium hydroxide) that have not been consumed in the HT treatment may be reused. Furthermore, the necessity for adding fresh water may be reduced.

[0092] The LWP feedstock employed in the present invention may, for example, 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 process of the present invention is particularly useful for LWP having a wide range of TAN values, and even for continuous processes employing LWP feedstocks in which the TAN values ​​vary.

[0093] The LWP feedstock is preferably a crude liquefied waste plastic or a fraction thereof. For example, the LWP feedstock has an initial boiling point below 50°C, 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 (ASTM D86), 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 LWP feedstock that has been subjected to little pre-purification (such as fractionation).

[0094] The alkaline 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 and therefore allow simple adjustment of the amount added and good control of the target pH level. In particular, the alkaline 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 alkaline substance can especially be NaOH, as this is a readily available strong base.

[0095] The LWP feedstock may 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 may be, for example, 85 wt % or less, 80 wt % or less, 70 wt % or less, or 65 wt % or less.

[0096] The aqueous solution preferably comprises at least 50 wt% water, preferably at least 70 wt% water, more preferably at least 85 wt% or at least 90 wt% water. Mainly containing water makes the process easier to carry out.

[0097] The aqueous solution preferably contains at least 0.3 wt % of alkaline substances, more preferably at least 0.5 wt %, at least 1.0 wt % or at least 1.5 wt % of acidic substances. Although not particularly limited, the content of alkaline substances is preferably 10.0 wt % or less, such as 6.0 wt % or less or 4.0 wt % or less.

[0098] In one embodiment, the aqueous solution comprises at least 0.5 wt %, preferably at least 1.0 wt % or at least 1.5 wt % of a metal hydroxide or alkali metal hydroxide as an alkaline substance. Although not particularly limited, the content is preferably 10.0 wt % or less, such as 6.0 wt % or less or 4.0 wt % or less.

[0099] The HT treatment is preferably carried out at a temperature of 150°C or more, preferably 190°C or more, such as 200°C or more, 220°C or more, 240°C or more or 260°C or more. The HT treatment is preferably carried out at a temperature of 450°C or less, preferably 400°C or less, 350°C or less, or 300°C or less. For example, 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. Such high temperatures during the HT treatment as well as the high pH value improve the impurity removal efficiency, since it allows even organically bound impurities, such as organochlorine compounds or organosilicon compounds, to be removed.

[0100] The chlorine content of the LWP feedstock may be in the range of 1 wt ppm to 4000 wt ppm, such as 100 wt ppm to 4000 ppm, or 300 wt ppm to 4000 ppm. That is, the method of the present invention is applicable to treating LWP feedstock having a wide range of chlorine impurities.

[0101] The LWP feedstock may be a fraction of liquefied waste plastic or crude liquefied waste plastic. In particular, the LWP feedstock may have a 5% boiling point of 25°C, preferably above 30°C, above 35°C, such as in the range of 25°C to 120°C, in the range of 25°C to 100°C, in the range of 30°C to 90°C, or in the range of 35°C to 80°C. The liquefied waste plastic (LWP) feedstock may have a 95% boiling point of 700°C or less, preferably below 650°C, below 600°C, or below 550°C, 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. The 5% boiling point and 95% boiling point of the LWP raw material can be determined according to ASTM D2887-16.

[0102] The step of providing LWP feedstock may include a step of liquefying the waste plastic (preferably by thermal degradation of the waste plastic, such as pyrolysis or hydrothermal liquefaction) or a similar process step. Liquefaction may be performed by any known method, such as pyrolysis (including fast pyrolysis, hydropyrolysis and hydrothermal liquefaction).

[0103] The step of providing the LWP feedstock may include the step of liquefying the sorted waste plastic, wherein the method further includes the step of sorting the waste plastic to provide sorted waste plastic. In the step of sorting the 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%, at least 75%, at least 80%, or at least 85% 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.

[0104] The LWP feedstock preferably has a relative humidity as measured at 15°C of between 0.780 and 0.950 kg / l (kg / dm 3 ), such as a density in the range of 0.780 to 0.900 kg / l, or in the range of 0.780 to 0.850 kg / l.

[0105] Preferably, no hydrogen is added and / or no hydrotreating catalyst is present during the HT treatment. That is, although hydrotreating, in particular hydrogenation, may be advantageous, such procedures are less sustainable because of the consumption of considerable amounts of hydrogen (usually produced from fossil sources and / or with considerable amounts of energy). More preferably, no hydrogen (including dissolved hydrogen) is present during the HT treatment. In other words, the HT treatment is preferably a simple process of thermally treating the LWP feedstock with an aqueous solution at high temperature.

[0106] In the present invention, preferably, 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 0.90 or more, preferably 0.95 or more, such as in the range of 0.90 to 1.10, 0.90 to 1.02 or 0.95 to 1.00. In the present invention, the bromine number can be determined according to ASTM D1159-07 (2017).

[0107] In the thermal treatment step, the mixing ratio between the aqueous solution and the LWP raw material (water-oil ratio) is preferably in the range of 0.1 to 1.4 by weight, preferably in the range of 0.2 to 1.0, such as 0.2 to 0.7. Within these mixing ratios, an efficient treatment can be ensured, i.e. providing a good purification without excessive generation of waste water. In this regard, the mixing ratio "by weight" (weight / weight) 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 ratio (by weight) of the respective compositions.

[0108] Example

[0109] The present invention is described by way of examples to better help understand the present invention. Although the examples provide embodiments of the present invention, the examples should not be used to narrow the interpretation of the claims.

[0110] Example 1

[0111] Three LWP feedstocks with different total acid numbers (TAN) were simulated titrated under the assumption that the LWP feedstock was HT treated with aqueous NaOH solutions with different concentrations (as shown in Table 1) at an aqueous solution / LWP feedstock mixing ratio (water-oil ratio) of 0.67 (by weight) and assuming that all components contributing to TAN were completely reacted. Table 1 shows the calculated pH values ​​of the aqueous phase (after phase separation).

[0112] Table 1:

[0113]

[0114] In Table 1, “<7” means that the (simulated) pH value dropped below pH 7.

[0115] It can be seen that by varying the NaOH concentration depending on the feed TAN, i.e., using 0.8 wt% aqueous solution for LWP feedstock with 5 mg KOH / g TAN, 1.3 wt% aqueous solution for LWP feedstock with 10 mg KOH / g TAN, and 1.8 wt% aqueous solution for LWP feedstock with 15 mg KOH / g TAN, a pH level of, for example, 12.8 can be maintained. Thus, the pH conditions can be kept fairly constant even in processes using different feeds.

[0116] Example 2

[0117] To demonstrate the effect of aqueous phase pH on silicon removal efficiency, small-scale experiments were conducted with an LWP feedstock containing 37 wt ppm Si and with 15 mg KOH / g TAN at 240°C (pyrolysis temperature) and a weight ratio of aqueous solution to LWP feedstock (water-to-oil ratio) of 0.67. The alkaline substance used in these experiments was sodium hydroxide (NaOH).

[0118] The initial NaOH concentration (aqueous solution containing alkaline substances) was set to 2 wt%. By considering the TAN of the LWP feedstock, the water-to-oil ratio, and the NaOH concentration, it was calculated that the pH of the aqueous phase after phase separation would be about 13. However, the pH value obtained experimentally was 8.6. The treated LWP material still contained some residual acidity (TAN 1.0 mg KOH / g) and the silicon removal efficiency was 35%. It was found that a certain degree of silicon removal was obtained based on the amount of alkaline substances required for the calculation.

[0119] In another test, the alkaline (NaOH) concentration was readjusted to 3 wt% and the test was repeated with a fresh LWP feed sample. By considering only the TAN of the LWP feed, the water-to-oil ratio and the NaOH concentration, it was calculated that the pH of the aqueous phase after phase separation would be approximately 13.5. After readjusting the alkaline concentration, the experimentally obtained pH of the aqueous phase after phase separation was 11.8. The treated LWP material no longer contained any residual acidity (TAN < 0.1 mg KOH / g) and the silicon removal efficiency was 90%. Therefore, it was surprisingly found that the silicon removal efficiency was significantly improved at higher pH levels of the aqueous phase.

[0120] Comparative Example 1

[0121] For comparison, a fresh LWP feed sample (same as in Example 2) was treated with a NaOH solution containing 1 wt% NaOH under otherwise identical conditions (but ignoring TAN when setting the amount of NaOH added). By taking into account the TAN of the LWP feed, the water-oil ratio and the NaOH concentration, it was calculated that all the NaOH would be neutralized and the pH of the aqueous phase after phase separation would be less than 7. The pH value experimentally obtained was 5.3. The treated LWP material still contained significant residual acidity (TAN 7.7 mg KOH / g) and the silicon removal efficiency was 0%. Therefore, by choosing a concentration of alkaline material that would theoretically produce a neutral or acidic solution after HT treatment and phase separation, it was found that no silicon removal was obtained.

[0122] Based on the above findings, it was unexpectedly found that in order to have acceptable levels of silicon removal efficiency of LWP in thermal processing in large scale operations, the preferred (target) pH level of the aqueous phase after phase separation would be at least above 10.

Claims

1. A method comprising: Provide liquefied waste plastic (LWP) raw materials for thermal treatment (HT treatment) and aqueous solutions containing alkaline substances, subjecting said LWP feedstock to said heat treatment with said aqueous solution followed by phase separation to produce at least a treated LWP material and an aqueous phase, Characterized in that the method comprises determining the quality of the LWP feedstock by measuring at least one property of the LWP feedstock, the at least one property comprising at least a total acid number (TAN) of the LWP feedstock, and Based on at least one property of the LWP feedstock and the water-oil ratio, the amount of the alkaline substance required to be added in HT treatment to reach the target pH level of the aqueous phase is calculated, and the calculated amount of the alkaline substance is added in the form of an aqueous solution to contact the LWP feedstock.

2. The method of claim 1, wherein the target pH level is above pH 10.

0.

3. The method according to claim 1 or 2, wherein the method further comprises the step of repeatedly readjusting the amount of the alkaline 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 the preceding claims, wherein the at least one property of the LWP feedstock comprises both the total acid number (TAN) and the total chlorine content of the LWP feedstock.

5. The method according to any one of the preceding claims, wherein the amount of the alkaline substance is adjusted by changing the concentration of the alkaline substance in the aqueous solution employed in the HT treatment.

6. The method according to any one of the preceding claims, wherein the LWP feedstock 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.

7. A method according to any one of the preceding claims, wherein the alkaline substance is selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides; and preferably, the alkaline 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; preferably NaOH.

8. The method according to any one of the preceding claims, wherein the aqueous solution comprises at least 50 wt. % water, preferably at least 70 wt. % water, more preferably at least 85 wt. % water, at least 90 wt. % water, or at least 95 wt. % water.

9. The method according to any one of the preceding claims, wherein the aqueous solution comprises at least 0.3 wt. % of the alkaline substance, more preferably at least 0.5 wt. %, at least 1.0 wt. % or at least 1.5 wt. % of the alkaline substance, such as 0.5 wt. % to 10.0 wt. %, 1.0 wt. % to 6.0 wt. %, or 1.5 wt. % to 4.0 wt. %.

10. The method according to any one of the preceding claims, wherein the method further comprises monitoring the pH value of the aqueous phase obtained from phase separation.

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

12. The method according to any one of the preceding claims, wherein the liquefied waste plastic (LWP) feedstock has a 95% boiling point below 700°C, preferably below 650°C, below 600°C, or below 550°C, 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 of the preceding claims, wherein the LWP feedstock 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 0.750 to 0.850 kg / l.

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

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

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