WO2024218178A1 - Method for extracting a wax from a pyrolysis residue - Google Patents

Abstract

The invention relates to a method for extracting a wax from a pyrolysis residue, comprising the steps of (a) providing the pyrolysis residue, wherein the pyrolysis residue comprises the wax, (b) mixing the pyrolysis residue with a solvent at at least 30°C to obtain a mixture, wherein the wax is at least partially dissolved in the solvent, (c) cooling the mixture to crystallise at least one portion of the dissolved wax, (d) separating at least one portion of the crystallised wax from the mixture.

Description

Process for obtaining a wax from a

pyrolysis residue

The invention relates to a process for obtaining a wax from a pyrolysis residue.

It is known from the prior art to separate a wax from a starting product by crystallization. For example, US 2002/0096451 A1 describes a process for purifying a petroleum product. A solvent is added to the petroleum product at room temperature. The resulting mixture is then cooled in order to crystallize and separate a wax contained in the petroleum product.

A similar process for dewaxing is disclosed in WO 2021/115982 Al, where a solvent is added at room temperature to a pyrolysis residue obtained from the pyrolysis of a plastic. The resulting mixture is then cooled to separate a wax contained therein by crystallization.

Further processes related to the separation of waxes are known from US 3,720,599 A, US 5,006,222 A, US 2, 614,065 A, WO 2017/168165 Al and WO 2021/115982 Al.

In the processes known in the prior art, the separation of the wax serves primarily to purify the starting product. The separated wax can have a relatively low purity. However, for numerous applications it may be necessary to use a wax with a high purity, which may require further, complex purification of the separated wax. There is a need for inexpensive, simple processes for producing a wax with a high purity. One object of the invention is to provide such a process.

The process according to the invention for obtaining a wax from a pyrolysis residue comprises the steps

(a) providing the pyrolysis residue, wherein the pyrolysis residue comprises the wax,

(b) Mixing the pyrolysis residue with a Solvent at at least 30 °C to obtain a mixture wherein the wax is at least partially dissolved in the solvent,

(c) cooling the mixture to crystallize at least a portion of the dissolved wax,

(d) separating at least a portion of the crystallized wax from the mixture.

The invention is based on the finding that a pyrolysis residue, in particular a pyrolysis residue obtained by plastic pyrolysis, represents a valuable source of wax. By mixing the pyrolysis residue with the solvent at at least 30 °C, the wax can dissolve largely or even completely in the solvent and can subsequently be separated from the pyrolysis residue with a high degree of purity. The wax obtained can represent a sustainable alternative to wax obtained directly from petroleum.

The pyrolysis residue can be obtained by pyrolyzing a plastic, in particular a waste plastic. The pyrolysis can take place in a pyrolysis reactor, preferably at a temperature of 300 to 500 °C, in particular 350 to 450 °C. This makes it possible to achieve a good balance between economic viability and process efficiency.

The pyrolysis may be thermal pyrolysis (i.e. thermal cracking without the addition of a catalyst) and/or catalytic pyrolysis (i.e. catalytic cracking). Thermal pyrolysis is preferred to avoid any contamination of the wax and/or the solid due to catalyst components.

Pyrolysis can be carried out largely in the absence of oxygen, particularly in an inert atmosphere, for example under nitrogen. A lack of oxygen or the absence of oxygen can prevent complete combustion and a polymer contained in the plastic can be split or depolymerized.

Within the scope of the invention, it has proven advantageous if a fraction, preferably a heavy fraction, of the pyrolyzed plastic is used as pyrolysis residue. In a preferred embodiment, the pyrolysis residue is therefore obtained by pyrolyzing a plastic and separating at least one fraction, preferably a gaseous fraction, from the pyrolyzed plastic. The separated fraction preferably has a lower boiling temperature (or a lower boiling range) than the pyrolysis residue.

In a particularly preferred embodiment, the pyrolysis residue has a boiling point (or a lower end of a boiling range) of at least 100 °C, preferably at least 150 °C, more preferably at least 200 °C, more preferably at least 240 °C, more preferably at least 270 °C, more preferably at least 300 °C. Preferably, the pyrolysis residue has a boiling point (or a lower end of a boiling range) in the range from 100 °C to 700 °C, preferably from 150 °C to 600 °C, more preferably from 200 °C to 500 °C, more preferably from 240 °C to 460 °C, more preferably from 270 °C to 430 °C, more preferably from 300 °C to 400 °C. It has been found that fractions with such a boiling temperature can have particularly high wax contents and are therefore particularly well suited to the process according to the invention. It has been found to be particularly advantageous if the pyrolysis residue is a spindle oil, preferably with a boiling temperature (or a lower end of a boiling range) in the range from 300 °C to 400 °C. In this case, the wax content of the pyrolysis residue can be, for example, approximately 50% by weight.

The boiling temperature (or boiling range) can preferably be determined using the standard ASTM D7500-15: 2019. Alternatively, the standard ASTM D2887-22: 2022 can be used.

The plastic preferably comprises a polyolefin and/or a polystyrene (PS), whereby the polyolefin can comprise a polyethylene (PE) and/or a polypropylene (PP). The plastic preferably comprises the polyolefin and/or the polystyrene in an amount of at least 65% by weight, more preferably at least 70% by weight, in particular at least 90% by weight, based on the total weight of the plastic. This makes it possible to obtain a pyrolysis residue which comprises a significant proportion of an aliphatic hydrocarbon (or a mixture of several aliphatic hydrocarbons), ie a significant proportion of the wax. Preferably, the plastic comprises at least 20% by weight of the polyolefin, more preferably at least 50% by weight, even more preferably at least 70% by weight, in particular at least 90% by weight, based on the total weight of the plastic. With increasing polyolefin content, the amount of wax obtained with the process according to the invention can be increased, which can improve the economic efficiency of the process.

In the course of the invention, it has been found that a high polyethylene (PE) content is particularly advantageous, since a particularly high wax content can be obtained when plastic with a high PE content is pyrolyzed. In a particularly preferred embodiment, the plastic therefore has a PE content of at least 10% by weight, preferably at least 20% by weight, more preferably at least 30% by weight, more preferably at least 40% by weight, more preferably at least 50% by weight, more preferably at least 60% by weight, even more preferably at least 70% by weight.

The plastic can comprise another polymer from the group consisting of thermoplastics, thermosets and/or elastomers, in particular an acrylonitrile-butadiene-styrene copolymer (ABS), a polyvinyl chloride (PVC), a polyamide (PA) and/or a polyester.

Before pyrolysis, the plastic can be plasticized, for example in a mixer, in particular in an extruder. The plastic is preferably heated to a temperature of at least 120 °C in order to plasticize it, more preferably to a temperature of 200 to 500 °C, even more preferably 400 to 470 °C. The subsequent pyrolysis can then be carried out more energy efficiently and in a shorter time. The plastic can also be degassed in the extruder in order to produce a uniform mass without gas inclusions, so that a homogeneous pyrolysis product can be obtained by the subsequent pyrolysis.

Before pyrolysis, a diluent can be added to the plastic, in particular the plasticized plastic, to reduce viscosity. The diluent is preferably added to the plastic in an amount of at least 5% by weight, more preferably at least 9% by weight, based on the total weight of the plastic. The ratio of Plastic to diluent ratio of at least 1:4, preferably at least 1:9. By adding the diluent to the plastic, the mobility of polymer chains can be increased at a given temperature, so that the heat input into the plastic can be improved during pyrolysis. Furthermore, due to the reduction in viscosity, the risk of overheating of plastic in wall areas of the pyrolysis reactor can be reduced, since it is usually heated by a heating device arranged near an outer wall of the pyrolysis reactor. The risk of coking of the plastic during pyrolysis can also be reduced by reducing the viscosity.

By adding the diluent to the plastic, its viscosity can preferably be reduced by at least 30%, more preferably by at least 50%, particularly preferably by at least 80%, based on the viscosity of the plastic without diluent under the same measuring conditions, in particular at a temperature in the range of 180 to 240 °C. This can improve the pumpability of the plastic, which can facilitate its processing.

When the diluent is added, the plastic preferably has a temperature of at least 120 °C, more preferably a temperature of 150 to 300 °C, in particular of 200 to 300 °C. Alternatively or additionally, the diluent can be heated to a temperature of preferably at least 120 °C, more preferably at least 150 °C, in particular to a temperature of 200 to 300 °C before being added to the plastic. By increasing the temperature of the plastic and/or the diluent, the diluent can be mixed into the plastic more quickly and efficiently. The subsequent pyrolysis can also be carried out more energy-efficiently and more quickly.

The addition of the diluent to the plastic can be carried out by means of an addition device. The addition device can have a metering device, such as a metering pump. For example, the plastic, in particular the plasticized plastic, can be fed to a mixer, e.g. a static mixer, and mixed there with the diluent. If the plastic is plasticized in an extruder, the The diluent can be added directly in the extruder. For this purpose, the addition device can be arranged, for example, in the compression zone or mixing zone of the extruder.

The diluent can comprise a hydrocarbon selected from an alkane, a cycloalkane and/or an aromatic. By means of pyrolysis, such a diluent can be converted into a gaseous and/or liquid product which can be at least partially separated from the pyrolysis residue and further utilized. In particular, the diluent can comprise a fraction obtained from crude oil, preferably a heavy oil. The heavy oil can be an oil obtained from crude oil in a petroleum refinery, e.g. a residual oil from a pyrolysis plant. The diluent preferably comprises at least part of a liquid fraction of the pyrolysis residue. This can be separated, for example, in a hydrocyclone.

The diluent preferably has a boiling point (or a lower end of a boiling range) of at least 300 °C, in particular at least 350 °C. This makes it possible to avoid the diluent evaporating immediately after a mixture of plastic and diluent is introduced into the pyrolysis reactor, but rather evaporation, splitting and/or depolymerization of the diluent can only take place as the mixture spends longer in the pyrolysis reactor and the mixture is heated up as a result. This makes it possible to obtain a homogeneous pyrolysis product.

The pyrolysis residue provided in step (a) of the process can comprise a liquid fraction in addition to the wax and the solid. The proportion of the liquid fraction is preferably a maximum of 95% by weight, more preferably 30 to 95% by weight, in particular 50 to 70% by weight, based on the total weight of the pyrolysis residue. As the proportion of the liquid fraction decreases, the speed at which at least part of the wax dissolves in the solvent can increase, or a smaller amount of solvent can be added to the pyrolysis residue in order to dissolve the wax at least partially in the solvent. This can subsequently also make it easier to separate at least part of the wax from the solid-free mixture. The use of solvent can also be reduced as a result. can be reduced. This makes the process more efficient.

The pyrolysis residue provided in step (a) of the process can be obtained by pyrolyzing the plastic in a pyrolysis reactor and then increasing a solids concentration of the pyrolysis residue. As a result, the proportion of the liquid fraction of the resulting pyrolysis residue can be reduced to preferably a maximum of 95% by weight, more preferably to 30 to 95% by weight, in particular to 50 to 70% by weight, based on the total weight of the pyrolysis residue. In order to increase the solids concentration, a hydrocyclone can be used, which can be connected downstream of the pyrolysis reactor.

If the pyrolysis residue is obtained by pyrolyzing a plastic, a gaseous fraction can be separated from the pyrolysis residue following pyrolysis and before step (a) of the process. The gaseous fraction can be separated by means of evaporation, for example in a hydrocyclone, which can be connected downstream of the pyrolysis reactor.

The separation of the gaseous fraction from the pyrolysis residue and the increase in the solid concentration of the pyrolysis residue can be carried out, for example, with one separation device or with several separation devices connected in series. Advantageously, both the separation of the gaseous fraction from the pyrolysis residue and the increase in the solid concentration of the pyrolysis residue are carried out in just one process step by means of a hydrocyclone, which can be connected downstream of the pyrolysis reactor. Such a hydrocyclone is described in WO 2023/036751 A1. By introducing a mixture comprising the pyrolysis residue and the gaseous fraction via an inlet arranged in an upper region of a shell of the hydrocyclone, a vortex flow can be generated in the hydrocyclone, whereby the gaseous fraction can be separated from the pyrolysis residue and discharged via an outlet arranged in the upper region of the hydrocyclone (e.g. on its ceiling). The pyrolysis residue can then be discharged due to gravity in the direction of a bottom of the hydrocyclone, whereby a tangential speed of a developing vortex flow can continuously increase. As a result, at least part of the pyrolysis residue, in particular at least a part of the pyrolysis residue which at least partially comprises the wax and the solid can be discharged via an outlet arranged in the bottom of the hydrocyclone, while at least a part of the liquid fraction of the pyrolysis residue can pass into an inner container arranged in the hydrocyclone and from there be discharged via an outlet, e.g. for further use as a diluent. The pyrolysis residue discharged via the outlet arranged in the bottom of the hydrocyclone can then be provided according to step (a) of the process. The hydrocyclone is preferably operated at a temperature in the range of 300 to 450 °C, more preferably from 320 to 420 °C, particularly preferably from 360 to 400 °C.

The pyrolysis residue can be cooled before the addition of the solvent, either before step (a) of the process, or between steps (a) and (b). The cooling can be carried out by means of a cooling unit. The pyrolysis residue is preferably cooled to a temperature of not more than 220 ° C, more preferably not more than 200 ° C, particularly preferably not more than 180 ° C. The cooling of the pyrolysis residue can be necessary in particular if the pyrolysis residue is obtained by immediately preceding processing of a plastic (by pyrolyzing and optionally subsequently separating a gaseous fraction from the pyrolysis residue and/or increasing the solids concentration of the pyrolysis residue). By cooling the pyrolysis residue, undesirable evaporation and/or decomposition of the solvent when it is added to the pyrolysis residue can be reduced or completely prevented. The pyrolysis residue is preferably cooled to a temperature of not less than 30 ° C, more preferably not less than 80 ° C, even more preferably not less than 100 ° C, particularly preferably not less than 120 ° C. Further cooling below the said temperature may impair the solubility of the wax in the solvent.

The solvent can be added to the pyrolysis residue by means of an introduction device. The introduction device can comprise a metering device, such as a metering pump. In order to mix the pyrolysis residue with the solvent in step (b) of the process, the pyrolysis residue can be fed to a container with which the The container can be heated so that the wax can be dissolved in the solvent at a certain temperature.

The mixing in step (b) of the process is preferably carried out at at least 50 °C (i.e. at 50 °C or above), more preferably at at least 80 °C (i.e. at 80 °C or above).

Then a fraction of the wax with a melting point above room temperature (i.e. above 20 to 25 °C) can be dissolved in the solvent. The mixing in step (b) preferably takes place at a temperature in the range from 50 to 200 °C, more preferably from 100 to 200 °C, even more preferably from 80 to 200 °C, particularly preferably from 80 to 120 °C. This not only allows the wax to be dissolved to a large extent or in its entirety in the solvent, but it can also be ensured that the solvent does not evaporate due to a temperature that is too high. The wax can dissolve particularly well in the solvent at a temperature of 100 to 120 °C, while a temperature of 120 to 140 °C can be optimal in terms of process technology.

Mixing in step (b) of the process is preferably carried out at a pressure in the range from 1 to 25 bar, in particular from 5 to 16 bar. This can further improve the process control and achieve rapid dissolution of the wax in the solvent.

The solvent preferably has a boiling temperature (or boiling range) in the range of 20 to 250 °C, more preferably 50 to 150 °C, even more preferably 35 to 130 °C. The lower the boiling temperature of the solvent, the lower the temperature at which the wax can be brought into a liquid state. Furthermore, as the boiling temperature of the solvent decreases, the ability of the wax to crystallize during subsequent cooling of the mixture in step (c) of the process may increase, thereby increasing the yield of wax obtained. The boiling temperature (or boiling range) of the solvent can be determined using ASTM D5399-09:2017 or ASTM D2887-22:2022.

The solvent preferably comprises an aliphatic hydrocarbon, or a mixture of two or more aliphatic hydrocarbons. An impurity that dissolves in the solvent can then remain dissolved while the wax is already crystallizing. Thus, the wax can be separated in a high purity and the impurity can remain in the mixture. The impurity can contain an organic impurity comprising nitrogen, oxygen, sulfur, silicon, chlorine, bromine and/or iodine, for example a heteropolymer (e.g. a polyamide, a polyethylene terephthalate, a polyvinyl chloride and/or an acrylonitrile-butadiene-styrene copolymer) and/or an additive (e.g. an anti-aging agent, a plasticizer, a color pigment and/or a flame retardant).

The solvent preferably comprises at least 10% by weight, preferably at least 20% by weight, more preferably at least 50% by weight, of the aliphatic hydrocarbon or a mixture of two or more aliphatic hydrocarbons, based on the total weight of the solvent. As the proportion of aliphatic hydrocarbon increases, not only can the ability of the solvent to dissolve the wax improve, but the solubility of the solid in the solvent can also be reduced. If the proportion of an aromatic in the solvent is high, however, the solid, in particular an asphaltene or a tar, can dissolve well in the solvent, which can make the subsequent separation of the wax more difficult or can contaminate the separated wax. If the proportion of a cycloalkane in the solvent is high, the wax can dissolve well, but the yield can be comparatively low.

The aliphatic hydrocarbon is preferably selected from the group of aliphatic hydrocarbons with up to 15 carbon atoms per molecule, in particular from 4 to 12 carbon atoms per molecule. This enables the process to be carried out efficiently and enables good separation of the wax from the solid mixture.

The aliphatic hydrocarbon is preferably selected from n-pentane, n-hexane, n-heptane, n-octane, an isomer thereof, or a mixture of the foregoing (ie a mixture comprising n-pentane, n-hexane, n-heptane, n-octane, an isomer of these alkanes, and/or several isomers of these alkanes). the boiling point of these aliphatic hydrocarbons is in the range of 35 to 130 °C, the process can be carried out efficiently and economically. Mixing in step (b) of the process can then preferably be carried out at 120 °C or below, more preferably at 100 °C or below, in order to avoid evaporation of the solvent. Furthermore, due to the low molecular weight of these solvents, the wax can not only dissolve well in them, but can also have a good tendency to crystallize during subsequent cooling in step (c) of the process.

The solvent preferably comprises at least 10% by weight of an alcohol, more preferably at least 20% by weight, based on the total weight of the solvent. This allows a polar impurity to be dissolved in the solvent and thereby separated from the wax, which crystallizes when the mixture cools. This can further increase the purity of the wax obtained. The solvent preferably comprises 10 to 30% by weight of the alcohol, more preferably 10 to 20% by weight of the alcohol, based on the total weight of the solvent. Particularly preferably, the solvent comprises at least 50% by weight of the aliphatic hydrocarbon and 10 to 30% by weight of the alcohol. This allows both the non-polar wax and a polar impurity to be easily dissolved in the solvent and easily separated from one another during the subsequent cooling of the mixture. Overall, a wax with a high level of purity can then be obtained.

The alcohol can preferably be selected from methanol, ethanol, propanol or a mixture thereof. Propanol is particularly preferred because it can reduce adhesions between wax crystals. This can enable easier separation of the wax from the solvent in step (d) of the process. Furthermore, solvent remaining in the wax after washing can subsequently be easily separated from the wax during drying of the wax.

The ratio of pyrolysis residue to solvent in the mixture obtained in step (b) of the process may depend on the melting temperature of the wax. The higher the melting temperature of the wax, the more solvent may be required to dissolve the wax. It is preferred if the ratio of pyrolysis residue to solvent is in the range of 5:1 to 1:5, preferably 2:1 to 3:1, especially 1:1. The wax can then dissolve largely or even completely in the solvent.

If the pyrolysis residue contains a solid, this can be at least partially separated from the mixture before step (c). Separating the solid can involve filtration, adsorption and/or centrifugation. Preferably, the solid is separated by means of adsorption. An adsorbent can be added to the pyrolysis residue, which can include activated carbon and/or bleaching earth. This allows the solid to be separated efficiently and as completely as possible from the mixture.

The solid can comprise an inorganic salt, a ceramic raw material, an asphaltene, a tar and/or a coke. In particular, the solid can comprise talc, an iron oxide (e.g. iron (III) oxide), aluminum oxide, titanium dioxide, magnesium oxide and/or calcium carbonate. If the pyrolysis residue provided is obtained by pyrolyzing a plastic, the solid can comprise an additive contained in the plastic. For example, the additive can comprise a filler, a color pigment and/or an additive. A person skilled in the art knows which additives are used depending on the respective plastic and field of application.

The solid can be dried after it has been separated from the mixture, for example in an oven. This makes the solid free-flowing and thus easier to process. The solid is preferably dried at a temperature in the range from 50 to 250 °C, more preferably from 100 to 200 °C, even more preferably from 130 to 160 °C. The drying time is preferably up to 120 minutes, in particular from 5 to 60 minutes.

One or more components can be separated from the solid, particularly from the dried solid, e.g. by means of filtration and/or centrifugation. Separated components can then be reused, e.g. as an additive for a plastic.

Solvent separated during drying of the solid can be reused in step (b) of the process Before being returned to the process, the solvent can be purified, preferably by evaporation, in particular by rotary evaporation.

In step (c) of the process, the mixture is cooled to crystallize at least a portion of the wax dissolved in the solvent. The mixture is preferably cooled at a rate of no more than 25 °C/min, more preferably no more than 15 °C/min, more preferably no more than 10 °C/min, more preferably no more than 5 °C/min, more preferably no more than 2 °C/min. Preferably, the cooling is carried out at a rate in the range of 0.05 to 25 °C/min, more preferably 0.1 to 15 °C/min, more preferably 0.2 to 10 °C/min, more preferably 0.4 to 5 °C/min, more preferably 0.5 to 2 °C/min. Wax crystals can form well at a slow cooling rate in this range, which can enable better mechanical separation. It has also been shown that slow cooling can lead to a clean product. Faster cooling, on the other hand, can lead to an increased formation of microcrystals, which are more difficult to separate mechanically and which can also carry more impurities.

It is therefore preferred if the cooling in step (c) of the process takes place over a period of at least 5 minutes, more preferably at least 10 minutes, more preferably at least 30 minutes, more preferably at least 60 minutes. Preferably, the cooling takes place over a period of 5 to 240 minutes, more preferably from 10 to 180 minutes, more preferably from 30 to 150 minutes, more preferably from 60 to 120 minutes. The wax crystals which form in this process can have a flaky shape which is characteristic of these process parameters.

In step (c) of the process, the mixture is preferably cooled to 10 °C or below, more preferably to 0 °C or below, even more preferably to -10 °C or below. Although the wax can in principle crystallize from e.g. 100 to just 50 °C when cooled at a slow cooling rate, in particular a maximum of 5 °C/min, a relatively large amount of solvent can be enclosed in the wax crystals, which can reduce the purity of the wax, especially since the solvent can also contain a contaminant dissolved in it, which can then also be present in the wax crystals. can be enclosed. By cooling to a lower temperature (e.g. to 10 °C or below), the inclusion of solvent can be reduced or completely prevented, so that the purity of the wax obtained can be significantly increased.

In step (d) of the process, at least part of the crystallized wax can be separated from the mixture. The separation can comprise filtration and/or centrifugation. The temperature during separation is preferably 80°C or below, more preferably 30°C or below. The temperature is preferably in the range from -10 to 80°C, in particular from 0 to 30°C. This can prevent the wax from dissolving again in the solvent. Furthermore, the separation can preferably be carried out at a pressure of up to 10 bar, more preferably at 5 to 10 bar. This can improve the process efficiency.

After separating the wax from the mixture in step (d) of the process, solvent contained in the mixture can be at least partially separated from the mixture. The separation can be carried out by evaporation or distillation. Separated solvent can be reused in step (b) of the process. Before being returned to the process, the solvent can be additionally purified, preferably by evaporation, in particular by rotary evaporation.

The wax separated in step (d) of the process may have a boiling temperature (or a lower end of a boiling range) of preferably at least 270 °C, more preferably at least 300 °C, even more preferably a boiling temperature (or a boiling range) in the range from 340 to 700 °C. The boiling temperature (or boiling range) of the wax can be determined by means of the standard ASTM D7500-15: 2019 (preferably for a wax with a boiling temperature or a boiling range of 100 to 850 °C, in particular from 100 to 735 °C) or by means of the standard ASTM D2887-22: 2022 (preferably for a wax with a boiling temperature or a boiling range of 55 to 538 °C).

The separated wax preferably has at least 15 carbon atoms per molecule, more preferably at least 20, in particular at least 40 . Preferably the wax has 20 to 80 carbon atoms per molecule , in particular 20 to 65 . Such waxes are well suited for further use .

The separated wax can be fed to a processing plant in a refinery, in particular a fluid catalytic cracking (FCC) plant, a thermal gasoil unit (TGU plant), a hydrogenation plant and/or a coker. The separated wax can also be used in other technical areas, for example as a lubricant and/or additive. The separated wax can be processed before further use. For example, the wax can be cleaned and/or separated into different carbon fractions.

The separated wax preferably has a proportion of one (or more) carbon fractions of at least 60% by weight, more preferably at least 70% by weight, even more preferably at least 80% by weight, in particular at least 85% by weight, based on the total weight of the separated wax. This proportion provides information about the purity of the separated wax, with a high proportion of the carbon fraction corresponding to a high purity of the separated wax. By means of the process according to the invention, a wax with a high purity can thus be obtained, which can be increased even further by subsequently washing the wax. The proportion of the carbon fraction can be determined by means of a gravimetric analysis, wherein the gravimetric analysis can comprise a determination of the masses of the pyrolysis residue, the added solvent and the separated wax.

The separated wax may be washed after step (d) of the process. In particular, the wax may be washed one to three times. This may further increase the purity of the separated wax.

When washing, the temperature of the wax is preferably 80 ° C or below, more preferably 30 ° C or below, even more preferably in the range of - 10 to 80 ° C, especially 0 to 30 ° C. This can prevent the wax from dissolving again in the solvent. When washing the wax, a similar or the same temperature can be chosen as when separating the wax in step (d) of the process. The wax is preferably washed with an alcohol. This allows any remaining polar impurities to be washed out, thereby producing a wax with a particularly high level of purity. The alcohol used for washing is preferably selected from methanol, ethanol, propanol or a mixture thereof. This not only allows any remaining polar impurities to be washed out effectively, but any solvent remaining in the wax after washing can subsequently be easily separated from the wax during drying.

The method may comprise a further step(s): drying the separated wax. This allows solvent separated together with the wax crystals to be removed. Drying may be carried out thermally at an elevated temperature, or alternatively at a low temperature under vacuum. The type of drying may depend on the further use of the wax. In order to retain the structure of the wax crystals, drying under vacuum is preferred. If the wax is subsequently used in liquid form, it can also be dried at an elevated temperature and possibly melted in the process. Thermal drying is preferably carried out at a temperature of 150 °C or below and at ambient pressure (0.7 to 1.1 bar). Drying under vacuum is preferably carried out at a temperature of 30 °C or below and at a pressure of 750 mbar or below, in particular at 500 mbar or below. Solvent separated during drying of the wax can be reused in step (b) of the process. Before being returned to the process, the solvent can be additionally purified, preferably by evaporation, in particular by rotary evaporation.

The invention particularly relates to the following embodiments:

1 . A process for obtaining a wax from a pyrolysis residue, comprising the steps

( a ) providing the pyrolysis residue , wherein the pyrolysis residue comprises the wax ,

(b) Mixing the pyrolysis residue with a Solvent at at least 30 °C to obtain a mixture wherein the wax is at least partially dissolved in the solvent,

(c) cooling the mixture to crystallize at least a portion of the dissolved wax,

(d) separating at least a portion of the crystallized wax from the mixture.

2. Process according to embodiment 1, wherein the pyrolysis residue is obtained by pyrolyzing a plastic, in particular a waste plastic.

3. Process according to one of the preceding embodiments, wherein the pyrolysis residue is obtained by pyrolyzing a plastic and separating at least one fraction, preferably a gaseous fraction, from the pyrolyzed plastic.

4. Process according to one of the preceding embodiments, wherein the pyrolysis residue has a boiling temperature of at least 100 °C, preferably at least 150 °C, more preferably at least 200 °C, more preferably at least 240 °C, more preferably at least 270 °C, more preferably at least 300 °C.

5. Process according to one of the preceding embodiments, wherein the pyrolysis residue has a boiling point in the range from 100 °C to 700 °C, preferably from 150 °C to 600 °C, more preferably from 200 °C to 500 °C, more preferably from 240 °C to 460 °C, more preferably from 270 °C to 430 °C, more preferably from 300 °C to 400 °C.

6. Method according to one of the preceding embodiments, wherein the plastic comprises a polyolefin and/or a polystyrene (PS), wherein the polyolefin may comprise a polyethylene (PE) and/or a polypropylene (PP).

7. Process according to embodiment 6, wherein the plastic comprises the polyolefin and/or the polystyrene in an amount of at least 65% by weight, more preferably at least 70% by weight, in particular at least 90% by weight, based on the total weight of the plastic.

8. Method according to one of the preceding embodiments, wherein the plastic has a PE content of at least 10 wt.%, preferably at least 20 wt.%, more preferably at least 30 wt.%, more preferably at least 40 wt.%, more preferably at least 50 wt%, more preferably at least 60 wt%, even more preferably at least 70 wt%.

9. Process according to one of the preceding embodiments, wherein the pyrolysis residue is cooled to a temperature of not more than 220 °C, more preferably not more than 200 °C, particularly preferably not more than 180 °C, before the addition of the solvent.

10. Process according to one of the preceding embodiments, wherein the pyrolysis residue is cooled to a temperature of not less than 30 °C, more preferably not less than 80 °C, even more preferably not less than 100 °C, particularly preferably not less than 120 °C, before the addition of the solvent.

11. Process according to one of the preceding embodiments, wherein the mixing in step (b) takes place at at least 50 °C, more preferably at at least 80 °C, in particular in the range from 50 to 200 °C, preferably from 100 to 200 °C, more preferably from 80 to 200 °C, in particular from 80 to 120 °C.

12. Process according to one of the preceding embodiments, wherein the mixing in step (b) takes place at a pressure of 1 to 25 bar, preferably 5 to 16 bar.

13. Process according to one of the preceding embodiments, wherein the solvent has a boiling temperature in the range from 20 to 250 °C, preferably from 50 to 150 °C, more preferably from 35 to 130 °C.

14. The process of any preceding embodiment, wherein the solvent comprises an aliphatic hydrocarbon.

15. A process according to any preceding embodiment, wherein the solvent comprises at least 10 wt%, preferably at least 20 wt%, more preferably at least 50 wt%, of the aliphatic hydrocarbon, based on the total weight of the solvent.

16. Process according to embodiment 14 or 15, wherein the aliphatic hydrocarbon is selected from the group of aliphatic hydrocarbons having up to 15 carbon atoms per molecule, preferably from 4 to 12 carbon atoms per molecule.

17. Method according to one of the embodiments 14 to 16, wherein the aliphatic hydrocarbon is selected from n-pentane, n-hexane, n-heptane, n-octane, an isomer thereof, or a mixture of the foregoing.

18. Process according to one of the preceding embodiments, wherein the solvent comprises at least 10% by weight of an alcohol, preferably at least 20% by weight, based on the total weight of the solvent.

19. The process of embodiment 18, wherein the solvent comprises 10 to 30 wt% of the alcohol, preferably 10 to 20 wt% of the alcohol, based on the total weight of the solvent.

20. The process of any one of embodiments 14 to 19, wherein the solvent comprises at least 50 wt% of the aliphatic hydrocarbon and 10 to 30 wt% of the alcohol, based on the total weight of the solvent.

21. Process according to one of embodiments 18 to 20, wherein the alcohol is selected from methanol, ethanol, propanol or a mixture thereof, in particular propanol.

22. Process according to one of the preceding embodiments, wherein the ratio of the pyrolysis residue to the solvent in the mixture obtained in step (b) is in the range from 5:1 to 1:5, preferably from 2:1 to 3:1, in particular 1:1.

23. Process according to one of the preceding embodiments, wherein a solid contained in the pyrolysis residue before step

(c) is at least partially separated from the mixture.

24. The method of embodiment 23, wherein the solid comprises an inorganic salt, a ceramic raw material, an asphaltene, a tar and/or a coke.

25. The method according to embodiment 23 or 24, wherein the separation of the solid comprises filtration, adsorption and/or centrifugation.

26. The method according to embodiment 25, wherein the separation of the solid comprises an adsorption, wherein an adsorbent is added to the pyrolysis residue, and wherein the adsorbent preferably comprises an activated carbon and/or a bleaching earth.

27. Process according to one of embodiments 23 to 26, wherein the separated solid is dried, preferably at a temperature of 50 to 250 °C, more preferably 100 to 200 °C, and/or for a period of up to 120 min, preferably 5 to 60 min.

28. A process according to any preceding embodiment, wherein the mixture in step (c) is cooled to 10°C or below, preferably to 0°C or below, more preferably to -10°C or below.

29. Process according to any one of the preceding embodiments, wherein the mixture in step (c) is cooled at a rate of maximum 25 °C/min, preferably maximum 15 °C/min, more preferably maximum 10 °C/min, more preferably maximum 5 °C/min, more preferably maximum 2 °C/min, preferably in the range of 0.05 to 25 °C/min, more preferably from 0.1 to 15 °C/min, more preferably from 0.2 to 10 °C/min, more preferably from 0.4 to 5 °C/min, more preferably from 0.5 to 2 °C/min.

30. Process according to one of the preceding embodiments, wherein the cooling in step (c) takes place over a period of at least 5 minutes, more preferably at least 10 minutes, more preferably at least 30 minutes, more preferably at least 60 minutes, preferably over a period of from 5 to 240 minutes, more preferably from 10 to 180 minutes, more preferably from 30 to 150 minutes, more preferably from 60 to 120 minutes.

31. Process according to one of the preceding embodiments, wherein the separation of the crystallized wax in step (d) comprises filtration and/or centrifugation.

32. Process according to any one of the preceding embodiments, wherein the temperature in step (d) is 80 °C or below, preferably 30 °C or below, more preferably in the range from -10 to 80 °C, in particular from 0 to 30 °C.

33. Process according to one of the preceding embodiments, wherein the solvent is at least partially separated from the mixture after step (d), wherein separated solvent is preferably reused in step (b).

34. Process according to one of the preceding embodiments, wherein the separated wax has a boiling temperature of at least 270 °C, preferably at least 300 °C, more preferably a boiling temperature in the range of 340 to 700 °C. 35. The method according to any of the preceding embodiments, wherein the wax has at least 15 carbon atoms per molecule, preferably at least 20, in particular at least 40.

36. The method of embodiment 35, wherein the wax has 20 to 80 carbon atoms per molecule, preferably 20 to 65.

37. Process according to one of the preceding embodiments, wherein the separated wax has a proportion of a carbon fraction of at least 60 wt.%, preferably at least 70 wt.%, more preferably at least 80 wt.%, in particular at least 85 wt.%, based on the total weight of the separated wax.

38. Process according to one of the preceding embodiments, wherein the separated wax is washed after step (d), preferably with an alcohol, in particular selected from methanol, ethanol, propanol or a mixture thereof.

39. Process according to one of the preceding embodiments, wherein the temperature during washing of the separated wax is 80 °C or below, preferably 30 °C or below, more preferably in the range from -10 to 80 °C, in particular from 0 to 30 °C.

40. Process according to one of the preceding embodiments, further comprising step (e): drying the separated wax.

41. The process of embodiment 40, wherein the wax in step (e) is dried at a temperature of 150°C or below and a pressure of 0.7 to 1.1 bar.

42. Process according to embodiment 40 or 41, wherein the wax is dried in step (e) at a temperature of 30 °C or below and a pressure of 750 mbar or below, preferably 500 bar or below.

43. A process according to any one of embodiments 40 to 42, wherein solvent separated during drying of the wax in step (e) is reused in step (b).

Fig. 1 shows a flow diagram of a pyrolysis process in which wax is recovered from a pyrolysis residue.

As can be seen from Fig. 1, a plastic comprising at least 50 wt.% of a polyolefin is fed to an extruder 1 in which the plastic is plasticized and degassed. The plasticized plastic has a temperature of at least 120 ° C and is then added to a static mixer 2 . In the static mixer 2 , a diluent 3 can be added to the plasticized plastic in order to reduce its viscosity . Alternatively or in addition to the diluent 3 , a part of a liquid fraction 4 separated from a pyrolysis residue can be mixed with the plasticized plastic in order to reduce its viscosity . The resulting mixture is then fed to a pyrolysis reactor 5 , in which the plastic is pyrolyzed at a temperature of 350 to 450 ° C. This gives a pyrolysis product 6 comprising a gaseous fraction and a pyrolysis residue, the pyrolysis residue comprising a liquid fraction, a wax and a solid. The pyrolysis product 6 is fed to a hydrocyclone 7 downstream of the pyrolysis reactor 5. First, the gaseous fraction is at least partially separated in the hydrocyclone 7. The separated part of the gaseous fraction 8 can then be further separated into a light oil (e.g. with a boiling range of 35 to 225 °C) and a heavy oil (e.g. with a boiling range of 225 to 410 °C) (not shown). Furthermore, the liquid fraction is at least partially separated in the hydrocyclone 7. The separated part of the liquid fraction 4 can be discharged via an outlet 9 of the hydrocyclone 7 and reused in the process for reducing the viscosity of the plastic, as previously described. At least a part of the pyrolysis residue , which at least partially comprises the wax and the solid , is discharged via an outlet 10 arranged in the bottom of the hydrocyclone 7 .

As can also be seen in Fig. 1, the pyrolysis residue discharged via the outlet 10 is fed to a first cooling unit 11 for cooling to a temperature in the range of 80 to 240 ° C. A solvent 13 comprising at least 20% by weight of an aliphatic hydrocarbon is then added to the pyrolysis residue in a container 12 by means of an introduction device 14 in order to obtain a mixture, wherein the wax is at least partially dissolved in the solvent 13. The aliphatic hydrocarbon is selected from the group of aliphatic hydrocarbons of 4 to 12 carbon atoms per molecule is selected. The resulting mixture has a ratio of pyrolysis residue to solvent in the range from 2:1 to 3:1. The container 12 is heated so that dissolving can take place at a temperature in the range from 80 to 200 °C. In a separation device 15, the solid is at least partially separated from the mixture by means of adsorption on an activated carbon. The separated solid 16 is then dried in an oven 17 at a temperature in the range from 100 to 200 °C. After the separated solid 16 has been dried, individual components can be separated from the solid and reused (not shown). Solvent 13 separated during drying is reused in step (b) of the process by being returned to the container 12 via the introduction device 14. Before being returned, the solvent 13 can be cleaned, e.g. by evaporation (not shown). The mixture is then cooled in a second cooling unit 18 to -10°C or below at a rate of maximum 5°C/min as shown in Fig. 1 in order to crystallize at least a portion of the wax dissolved in the solvent. At least a portion of the crystallized wax is then separated from the mixture by means of a filter 19. Solvent 13 contained in the mixture is separated in an evaporator 20 and also returned to the container 12 via the introduction device 14.

As can also be seen from Fig. 1, the separated wax 21 is washed in a washer 22, wherein an alcohol is used for washing. The washed, separated wax 21 is then fed to a dryer 23 to dry the wax crystals. The wax 24 obtained can then be used for further purposes (not shown). Solvent 13 separated during drying of the separated wax 21 is also returned to the container 12 via the introduction device 14. Before being returned, the solvent 13 can be purified, e.g. by evaporation (not shown).

Claims

Patent claims: 1. A process for obtaining a wax from a pyrolysis residue, comprising the steps (a) providing the pyrolysis residue, wherein the pyrolysis residue comprises the wax, (b) mixing the pyrolysis residue with a solvent at at least 30 °C to obtain a mixture, wherein the wax is at least partially dissolved in the solvent, (c) cooling the mixture to crystallize at least a portion of the dissolved wax, (d) separating at least a portion of the crystallized wax from the mixture. 2. The process of claim 1, wherein the mixing in step (b) is carried out at at least 80°C. 3. The process according to claim 1 or 2, wherein the solvent has a boiling temperature in the range of 35 to 130 °C. 4. A process according to any one of claims 1 to 3, wherein the solvent comprises at least 50% by weight of an aliphatic hydrocarbon. 5. The process of claim 4, wherein the aliphatic hydrocarbon is selected from n-pentane, n-hexane, n-heptane, n-octane, an isomer thereof, or a mixture of the foregoing. 6. A process according to any one of claims 1 to 5, wherein the solvent comprises at least 10% by weight of an alcohol. The process of claim 6, wherein the alcohol is propanol. 8. Process according to one of claims 1 to 7, wherein a solid contained in the pyrolysis residue is at least partially separated from the mixture before step (c), preferably wherein the separation of the solid comprises an adsorption, wherein an adsorbent is added to the pyrolysis residue, and wherein the adsorbent preferably comprises an activated carbon and/or a bleaching earth. 9. A process according to any one of claims 1 to 8, wherein the mixture is cooled in step (c) at a rate of not more than 5 °C/min. 10. A process according to any one of claims 1 to 9, wherein the mixture in step (c) is cooled to -10 C or below. 11. The method according to any one of claims 1 to 10, wherein the separation of the crystallized wax in step (d) comprises filtration and/or centrifugation. 12. The process according to any one of claims 1 to 11, wherein the temperature in step (d) is 80°C or below. 13. Process according to one of claims 1 to 12, wherein the separated wax has a boiling temperature of at least 270 °C. 14. The method according to any one of claims 1 to 13, further comprising step (e): drying the separated wax. 15. A process according to any one of claims 1 to 14, wherein solvent separated during drying of the wax in step (e) is reused in step (b).