Method for purifying a synthetic crude oil stream

Abstract

The present invention relates to a method for purifying a synthetic crude oil stream (1), the method comprising the following steps: - providing the synthetic crude oil stream (1), the synthetic crude oil stream (1) containing diene compounds and having a diene number of at least 0.1g / 100g; - contacting the synthetic crude oil stream (1) with a polysulphide stream (2) containing at least one polysulphide compound in order to form a mixture, thereby converting at least some of the diene compounds into diene-free products; and - separating the diene-free products from the mixture in order to obtain a purified synthetic crude oil stream (3).

Description

[0001] Process for purifying a synthetic crude oil stream

[0002] The present invention relates to processes for purifying a synthetic crude oil stream.

[0003] Synthetic crude oil, sometimes also called syncrude, can be obtained from various processes. For example, synthetic crude oil can be shale oil, which is extracted from oil shale by pyrolysis. Another source is hydrocarbons extracted from oil sands, particularly bitumen, which can be upgraded to produce synthetic crude oil. Furthermore, synthetic crude oil can also be produced from plastic materials, such as plastic waste, through cracking.

[0004] Synthetic crude oils typically contain various impurities that can have adverse effects on refining processes and refinery facilities, or even render the crude oil completely unsuitable for certain refining processes. The type and content of the impurities can vary greatly depending on the source and method used to extract the synthetic crude oil.

[0005] A particularly serious problem in the processing of synthetic crude oils is gum formation. Pyrolysis oils typically contain various chemical compounds that can tend to form deposits. Such deposits can subsequently clog or otherwise damage refinery equipment, increase cleaning requirements, and shorten the service life of the equipment.

[0006] The problem of gum formation in connection with synthetic crude oils has not yet been satisfactorily solved. There continues to be a need for methods to reduce the tendency of synthetic crude oils to gum. It is therefore an object of the present invention to provide processes to reduce gum formation in synthetic crude oils.

[0007] The present invention therefore relates to a process for purifying a synthetic crude oil stream, the process comprising the following steps: - providing the synthetic crude oil stream, wherein the synthetic crude oil stream contains diene compounds and has a diene number of at least 0.1 g / 100 g;

[0008] - contacting the synthetic crude oil stream with a polysulfide stream containing at least one polysulfide compound to form a mixture, whereby at least a portion of the diene compounds is converted into diene-free products; and

[0009] - Separating the diene-free products from the mixture to obtain a purified synthetic crude oil stream.

[0010] In connection with the present invention, it has been found that synthetic crude oils are particularly prone to gum formation when they have a high content of diene compounds. Reactive dienes can therefore act as gum formers and lead to harmful deposits in refinery plants. For example, some dienes can undergo Diels-Alder reactions, thereby leading to cross-linking between molecules and ultimately to deposits. Furthermore, dienes can form stable complexes with catalysts in hydrogenation plants. It has therefore proven advantageous within the scope of the invention to reduce the diene content of synthetic crude oils.

[0011] In the process according to the invention, this is achieved by reacting the synthetic crude oil stream with polysulfide compounds. It has been shown that polysulfide compounds are excellently suited to converting reactive dienes into insoluble products or solids that can be easily separated from the synthetic crude oil stream. Dienes can react with polysulfide compounds in an addition reaction to form a thiol, which can then react with other molecules, for example alkenes. This results in cross-linking of several molecules and thus in targeted precipitation. In the process according to the invention, gum formation is thus induced in a targeted manner, and the "gum" - i.e. the insoluble reaction products of the diene compounds and the polysulfide compounds - is separated.The purified synthetic crude oil stream therefore has a lower diene content and is therefore less prone to gum formation.

[0012] US 5,417,844 A mentions certain polysulfides in a different context, namely in connection with the pretreatment of catalysts.

[0013] The use of sulfur-containing compounds for removing olefins from hydrocarbon products is generally known from the prior art. For example, WO 2021 / 021449 A1 describes processes for removing olefins from light hydrocarbon streams by mercaptanization with hydrogen sulfide in the presence of a catalyst. The process involves converting olefins into mercaptans, which are then oxidized in a so-called MEROX process step and finally separated. However, WO 2021 / 021449 A1 refers neither to the treatment of synthetic crude oils nor to diene compounds, which are particularly problematic in connection with gum formation.

[0014] The present invention is based on a completely different approach. It specifically targets the removal of dienes in synthetic crude oils and uses polysulfide compounds to selectively precipitate the diene compounds as diene-free products and thus remove them.

[0015] Treatment with polysulfide compounds also has other positive effects on the quality of the synthetic crude oil stream. Neutral compounds such as esters, aldehydes, ketones, organohalogen compounds, amides, and nitriles can be converted and subsequently removed. Such compounds can, for example, be hydrolyzed using base, producing polar or charged compounds that can be removed in a wash with an aqueous phase.

[0016] The diene compounds present in the synthetic crude oil stream are preferably compounds containing conjugated or cumulated carbon-carbon double bonds, especially conjugated carbon-carbon double bonds. Such compounds are particularly prone to gum formation, for example through Diels-Alder reactions, and can be removed particularly effectively using the process according to the invention.

[0017] The person skilled in the art is familiar with methods for determining the diene number. Preferably, the diene number is determined according to ASTM UOP326-07. The synthetic crude oil stream has a diene number of at least 0.1 g / 100g, preferably at least 0.2 g / 100g, more preferably at least 0.3 g / 100g, more preferably at least 0.4 g / 100g, more preferably at least 0.5 g / 100g, more preferably at least 0.6 g / 100g, more preferably at least 0.7 g / 100g, more preferably at least 0.8 g / 100g, more preferably at least 0.9 g / 100g, more preferably at least 1.0 g / 100g, more preferably at least 1.1 g / 100g, more preferably at least 1.2 g / 100g, more preferably at least 1.3 g / 100g, more preferably at least 1.4 g / 100g, more preferably at least 1.5 g / 100g, more preferably at least 1.6 g / 100g, more preferably at least 1.7 g / 100g, more preferably at least 1.8 g / 100g, more preferably at least 1.9 g / 100g, more preferably at least 2.0 g / 100g.Preferably, the synthetic crude oil stream has a diene number in the range from 0.1 g / 100g to 15 g / 100g, more preferably from 1.0 g / 100g to 12 g / 100g, in particular from 1.5 g / 100g to 10 g / 100g.

[0018] The purified synthetic crude oil stream preferably has a lower diene number than the synthetic crude oil stream. Preferably, the purified synthetic crude oil stream has a diene number of less than 5 g / 100 g, more preferably less than 4 g / 100 g, more preferably less than 3 g / 100 g, more preferably less than 2 g / 100 g, more preferably less than 1.5 g / 100 g, more preferably less than 1 g / 100 g, more preferably less than 0.9 g / 100 g, more preferably less than 0.8 g / 100 g, more preferably less than 0.7 g / 100 g, more preferably less than 0.6 g / 100 g, more preferably less than 0.5 g / 100 g. Preferably, the purified synthetic crude oil stream has a diene number in the range of 0.01 g / 100g to 5 g / 100g, more preferably from 0.1 g / 100g to 2 g / 100g, in particular from 0.2 g / 100g to 1 g / 100g.

[0019] It has proven advantageous if the synthetic crude oil stream is brought into contact with the polysulfide stream at a temperature of at least 80 °C, preferably at least 100 °C, more preferably at least 120 °C, more preferably at least 140 °C, more preferably at least 160 °C, more preferably at least 180 °C. In particular, it is preferred if the synthetic crude oil stream is brought into contact with the polysulfide stream at a temperature in the range from 80 to 450 °C, preferably from 100 to 400 °C, more preferably from 120 to 350 °C, more preferably from 140 to 300 °C, more preferably from 160 to 260 °C, more preferably from 180 to 220 °C. A higher temperature may favor the reaction between the diene compounds and the polysulfide compounds and therefore lead to an even greater reduction in the diene content.

[0020] In a preferred embodiment, the synthetic crude oil stream is contacted with the polysulfide stream for a period of at least 0.5 minutes, preferably at least 1 minute, more preferably at least 2 minutes, even more preferably at least 5 minutes, most preferably at least 12 minutes. Providing a longer period allows the reactions between the diene compounds and the polysulfide compounds to proceed more completely, so that the diene content can be reduced even further. In particular, it is therefore preferred if the period is between 0.5 and 180 minutes, preferably between 1 and 120 minutes, more preferably between 2 and 60 minutes, even more preferably between 5 and 30 minutes, most preferably between 12 and 20 minutes.The duration is preferably the average time between the initial contact of the synthetic crude oil stream with the polysulfide stream and the separation of the diene-free products from the mixture to obtain the purified synthetic crude oil stream. If the process is carried out as a continuous operation, the duration preferably corresponds to the average residence time in a scrubbing device used, e.g., in a mixer-settler.

[0021] In a preferred embodiment, the synthetic crude oil stream is contacted with the polysulfide stream in a pressure vessel. The provision of a pressure vessel enables treatment at higher pressures and temperatures and can promote the removal of diene compounds.

[0022] Preferably, the washing of the synthetic crude oil stream with the first aqueous washing solution takes place at a pressure of more than 2 bar, preferably more than 3 bar, more preferably more than 5 bar, even more preferably more than 7 bar, most preferably more than 10 bar. Providing such a high pressure enables, as mentioned, a high temperature. It is particularly preferred if the washing of the synthetic crude oil stream with the first aqueous washing solution takes place at a pressure in the range from 2 bar to 50 bar, preferably from 3 bar to 35 bar, more preferably from 5 bar to 25 bar, even more preferably from 7 bar to 20 bar, most preferably from 10 bar to 18 bar.

[0023] The polysulfide stream can be an anhydrous stream, for example, it can be obtained from sulfur dissolved in an amine. However, it is preferred if the polysulfide stream is an aqueous solution. This has the advantage, among other things, that other impurities, such as certain salts and polar compounds, can be removed particularly efficiently. Furthermore, the use of an aqueous solution favors the removal of neutral compounds such as esters, aldehydes, ketones, organohalogen compounds, amides, and nitriles by basic hydrolysis. The impurities can then be easily removed with the aqueous phase.

[0024] The concentration of polysulfide compounds in the polysulfide stream is preferably at least 1 wt.%, more preferably at least 5 wt.%, more preferably at least 10 wt.%, more preferably at least 15 wt.%, more preferably at least 20 wt.%, more preferably at least 25 wt.%. Preferably, the concentration is between 1 wt.% and 80 wt.%, more preferably between 5 wt.% and 60 wt.%, more preferably between 10 wt.% and 50 wt.%, more preferably between 15 wt.% and 40 wt.%. The use of such high polysulfide concentrations promotes the reaction with the diene compounds present in the synthetic crude oil stream and can thus lead to an even greater reduction in the diene content.

[0025] In a preferred embodiment, the polysulfide stream has a pH of more than 8, preferably more than 9, more preferably more than 10, more preferably more than 11, more preferably more than 12, more preferably more than 13. The pH is preferably in the range from 8 to 14, preferably from 10 to 13. An advantage of such a basic pH is that the polysulfide compounds are deprotonated to a greater extent and are therefore more nucleophilic. This favors the basic hydrolysis of neutral compounds such as esters, aldehydes, ketones, organohalogen compounds, amides, and nitriles.

[0026] Any type of polysulfide compound can be used in connection with the process according to the invention. The polysulfide compound is preferably an inorganic or organic polysulfide, in particular an inorganic polysulfide. Preferably, the at least one polysulfide compound is an amine polysulfide, an alkali metal polysulfide, or an alkaline earth metal polysulfide. Calcium polysulfide, sodium polysulfide, and potassium polysulfide, in particular sodium or potassium polysulfide, have proven particularly suitable. A sodium or potassium polysulfide can be prepared, for example, by dissolving sulfur in NaOH or KOH solution. Amine polysulfides can be prepared, for example, by dissolving sulfur in amines, e.g., ethanolamine or diethanolamine.

[0027] In a preferred embodiment, the volumetric mixing ratio between the synthetic crude oil stream and the polysulfide stream is from 10:1 to 1:5, more preferably from 5:1 to 1:2.5, more preferably from 1.5:1 to 1:1.5. Such mixing ratios have proven particularly good for treating the synthetic crude oil stream.

[0028] In a preferred embodiment, the mixture formed from the synthetic crude oil stream and the polysulfide stream has a polar phase and an apolar phase, with the diene-free products predominantly present in the polar phase. The separation of the diene-free products from the mixture is preferably achieved by separating the polar phase. If the polysulfide stream is an aqueous solution, the polar phase can be an aqueous phase. The diene-free products can thus be separated in a particularly simple manner.

[0029] It has proven particularly advantageous if the contacting with the polysulfide stream and the subsequent separation of the polar phase are carried out in a mixer-settler. Mixer-settlers typically comprise a continuously operated mixing zone and a continuously operated settling zone, thus allowing the mixing of the synthetic crude oil stream with the polysulfide stream, as well as the subsequent settling process for phase separation and separation of the purified synthetic crude oil stream, to be carried out in a continuous process.

[0030] In an advantageous embodiment, the separated polar phase is at least partially recycled and reused as at least part of the polysulfide stream. It has been found that the separated polar phase often still contains a significant proportion of unused polysulfide compounds. If the wastewater stream is partially recycled, the polysulfide compound can therefore be better utilized. For example, the recycling can comprise from 1 to 25 cycles. This recycling can have energetic advantages and lead to lower costs and also enables a smaller plant design. The proportion of used chemicals can also be compensated by dosing fresh medium into the circuit.

[0031] In a preferred embodiment of the process according to the invention, the purified synthetic crude oil stream is washed with an aqueous wash solution to obtain a second purified synthetic crude oil stream. Such an additional wash step allows impurities present in the synthetic crude oil stream to be removed even more thoroughly.

[0032] The aqueous wash solution is preferably an acidic aqueous wash solution. It is particularly preferred if the pH of the aqueous wash solution is less than 6, preferably less than 5, more preferably less than 4, more preferably less than 3.5. Such a pH is particularly preferred if the polysulfide stream has a basic pH. Thus, a basic wash in the form of treatment with the polysulfide stream can be followed by an acidic wash.

[0033] Washing the purified synthetic crude oil stream with an acidic wash solution can improve the removal of basic compounds such as amines, pyridines and other basic impurities. If basic hydrolysis of neutral compounds has taken place during treatment with the polysulfide stream, basic hydrolysis products, e.g. amines, can also be removed. In particular, polycyclic amines can also be efficiently removed by this step. Polycyclic amines can be present in large quantities in synthetic crude oils, especially in pyrolysis oils. They can form, for example, in cracking processes in the presence of a nitrogen source, for example additives or polymers such as polyamide (PA), polyacrylonitrile (PAN) or acrylonitrile-butadiene-styrene copolymer (ABS).Polycyclic amines, for example, can be polycondensed, saturated, mono- and polyunsaturated or aromatic ring systems. They can be partially dissolved in synthetic crude oil or suspended in the colloidal region and often result in undesirable deposits and thus make cleaning of the system more difficult. They can also block the active surfaces of catalysts in subsequent applications. In addition, they can dissolve undesirable compounds such as salts, chlorides, heavy metals or sulfides in the organic product phase. It has been shown that polycyclic amines can be removed efficiently by an acidic wash step. For the removal of polycyclic amines, it has proven advantageous if the acidic wash step is carried out at a temperature of at least 20 °C. Removal is particularly efficient when the temperature is at least 50 °C.

[0034] However, in the course of the invention, it has surprisingly proven advantageous if the temperature in the acidic wash step is not too high, in particular lower than the temperature of contact with the polysulfide stream. It has been shown that high temperatures in the acidic wash step can lead to a reduction in the product yield and to the formation of impurities. It has therefore proven advantageous to carry out the acidic wash step at a temperature of less than 120 °C. In particular, these adverse effects can be minimized if the temperature is less than 100 °C, even more preferably less than 95 °C.

[0035] An additional advantage of the lower temperature in the acidic scrubbing step is that the requirements for the scrubbing device material are significantly lower. The presence of acidic solutions at high temperatures often requires the use of special materials or coatings, which would lead to a significant increase in costs. In a preferred embodiment, the scrubbing of the purified synthetic crude oil stream with the acidic scrubbing solution therefore takes place at a lower temperature than the contacting of the synthetic crude oil stream with the polysulfide stream.

[0036] In a preferred embodiment, the aqueous wash solution contains sulfuric acid. The concentration of sulfuric acid is preferably between 0.5 and 10 wt.%, in particular between 1 and 5 wt.%.

[0037] It has also proven advantageous if the volumetric mixing ratio between the purified synthetic crude oil stream and the aqueous scrubbing solution is from 10:1 to 1:5, preferably from 5:1 to 1:2.5, even more preferably from 2.5:1 to 1:1.5. Such a mixing ratio enables particularly efficient removal of basic contaminants.

[0038] The process according to the invention can also comprise further washing steps. For example, it is possible for the purified synthetic crude oil stream to undergo further washing or purification steps before washing with the aqueous wash solution. However, it is preferred if no further purification step, in particular no washing step, no filtration step, and / or no hydrotreating step, takes place between the separation of the diene-free products to obtain the purified synthetic crude oil stream and the washing of the purified synthetic crude oil stream with the aqueous wash solution. This has the advantage, among others, that basic products formed by basic hydrolysis of neutral compounds can be removed in the preferably acidic washing step immediately following the basic washing step.

[0039] In a further preferred embodiment of the process according to the invention, the second purified synthetic crude oil stream is washed with a further aqueous wash solution to obtain a third purified synthetic crude oil stream. The provision of such a further wash step enables particularly thorough removal of impurities that may still be present after the acidic wash step.

[0040] In this context, it is particularly preferred if the pH of the further aqueous washing solution is in the range from 3 to 13, preferably from 4 to 12, more preferably from 5 to 11, even more preferably from 6 to 10, even more preferably from 6.5 to 9, most preferably from 7 to 8. A pH in this range is particularly effective for the removal of small polar neutral molecules as well as inorganic and organic salts. It is particularly advantageous if the further aqueous washing solution is basic or essentially neutral, in particular essentially neutral.

[0041] In a preferred embodiment of the process according to the invention, the purified synthetic crude oil stream, the second purified synthetic crude oil stream, or the third purified synthetic crude oil stream is fed to a hydrogenation plant. It has been found that reducing the diene content in the synthetic crude oil stream is particularly advantageous during hydrogenation in a hydrogenation plant, since dienes can form stable complexes with catalysts in such plants. The use of the process according to the invention in combination with hydrogenation can thus significantly improve the service life of the hydrogenation plants and in particular of the catalysts used.

[0042] In connection with the invention, it is preferred if the process for purifying a synthetic crude oil stream is a continuous process. Compared to a batch process, this has the advantage of achieving higher productivity and shorter downtimes.

[0043] Washing the respective crude oil streams with the respective washing solutions as described herein may comprise mixing the crude oil stream with the washing solution, followed by separating the purified crude oil stream from the aqueous washing solution. Preferably, the washing steps of the process according to the invention are carried out in a mechanical mixer, in a static mixer, and / or in a mixer-settler. It has proven particularly advantageous if the washing steps are each carried out in a mixer-settler, as described above for the treatment with the polysulfide stream.

[0044] In the context of the invention, a “synthetic crude oil stream” is preferably understood to mean a material stream comprising a synthetic crude oil or a fraction of a synthetic crude oil. The synthetic crude oil stream preferably consists of synthetic crude oil or a fraction thereof. Within the scope of the invention, it is particularly preferred if the synthetic crude oil stream comprises a pyrolysis oil or a fraction thereof, in particular consists thereof. The pyrolysis oil is preferably a pyrolysis oil obtained from biomass, in particular wood, and / or plastic. The process according to the invention has proven to be particularly suitable if the synthetic crude oil stream is a hydrocarbon mixture obtained from the depolymerization of biomass or plastic material, in particular plastic material.The synthetic crude oil stream is therefore preferably a plastic pyrolysate or a fraction thereof, or a biomass, in particular wood, pyrolysate or a fraction thereof. However, the process according to the invention is also well suited for other synthetic crude oils and fractions thereof. In further preferred embodiments, the synthetic crude oil stream therefore comprises shale oil or upgraded bitumen, preferably consisting thereof.

[0045] In a particularly preferred embodiment, the synthetic crude oil stream is therefore produced by depolymerizing plastic material, in particular plastic waste. Those skilled in the art are familiar with the production of a synthetic crude oil stream by depolymerizing plastic material. Such processes are known, for example, from WO 2012 / 149590 A1 and US Pat. No. 6,060,631 A.

[0046] In a preferred embodiment, the plastic material comprises polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyamide (PA), styrene-acrylonitrile (SAN), and / or acrylonitrile-butadiene-styrene (ABS). The process according to the invention has proven particularly suitable for purifying pyrolysis oils from the aforementioned plastic materials.

[0047] It is particularly preferred if the plastic material contains PVC. This typically leads to contaminants in the form of organochlorine compounds in the crude oil stream obtained from the plastic material. Organochlorine compounds can be removed particularly effectively by basic hydrolysis, for example, if the polysulfide stream is a basic aqueous solution.

[0048] It is also preferred if the plastic material contains PET. This typically leads to impurities in the form of ester compounds in the crude oil stream obtained from the plastic material, which can also be removed particularly well by basic hydrolysis. In particular, it is preferred if the plastic material comprises PA, SAN, and / or ABS. These plastic materials typically lead to impurities in the form of amides and nitriles. In the course of the process according to the invention, these compounds can also be hydrolyzed using basic hydrolysis. If the process according to the invention includes an acidic wash, the basic compounds formed from the basic hydrolysis, in particular amines, can also be removed particularly efficiently.PA, SAN, and ABS can also serve as nitrogen sources and contribute to the increased formation of polycyclic amines through rearrangement reactions, condensation reactions, and / or radical reactions with, for example, PE, PP, and PS. These can also be efficiently removed in an acidic wash.

[0049] Unless otherwise indicated, all parameters mentioned herein refer to SATP conditions according to IUPAC ("Standard Ambient Temperature and Pressure"), in particular to a temperature of 25 °C and a pressure of 101,300 Pa.

[0050] All percentages (%) herein refer to percentages by weight unless otherwise indicated.

[0051] Unless otherwise indicated, all mixing ratios given herein refer to volumetric mixing ratios, i.e. volume ratios (volume : volume).

[0052] The present invention is illustrated by the following figure, to which it is of course not limited.

[0053] Figure 1 shows a process flow diagram of a preferred embodiment of the process according to the invention.

[0054] In the embodiment shown in Figure 1, the synthetic crude oil stream 1 is obtained by depolymerizing plastic material. The plastic material is compacted, degassed, and melted in an extruder 12. The plastic melt emerging from the extruder 12 is mixed in a static mixer 13 with an external solvent 14, preferably heavy oil, and / or with already cracked plastic material, which is recycled as a recycling stream 15, in order to reduce the viscosity of the plastic melt. The resulting mixture is introduced into a depolymerization reactor 16, in which the plastic material is depolymerized, preferably at a temperature between 400°C and 440°C. Cracked plastic material is obtained as the overhead product of a column 17.After separation of a gas stream 18 in a further column 19, the synthetic crude oil stream 1 is obtained, wherein the synthetic crude oil stream 1 has a diene number of at least 0.1 g / 100 g.

[0055] In the embodiment shown, the synthetic crude oil stream 1 is mixed with a polysulfide stream 2 in a mixing zone of a first mixer-settler 8, preferably in a volumetric mixing ratio of 1:1. The polysulfide stream 2 is preferably a basic aqueous solution containing sodium or potassium polysulfide. The mixture of the synthetic crude oil stream 1 and the polysulfide stream 2 preferably has a temperature of at least 80°C. The diene compounds contained in the synthetic crude oil stream 1 react at least partially with the polysulfides and form insoluble diene-free products. The oil phase is subsequently separated from the water phase in a settling zone of the mixer-settler 8. The diene-free products are separated out with the water phase. The average residence time in the first mixer-settler 8 is preferably between 5 and 30 minutes.The water phase is removed as part of the wastewater stream 11 and the oil phase is separated as purified synthetic crude oil stream 3 .

[0056] The purified synthetic crude oil stream 3 obtained in this way is then mixed with an aqueous washing solution 4 in a second mixer-settler 9. The aqueous washing solution 4 is preferably aqueous sulfuric acid having a pH between 0 and 5. The purified oil phase is then separated from the water phase in a settling zone of the mixer-settler 9, the water phase is removed via the wastewater stream 11, and a second purified synthetic crude oil stream 5 is obtained from the oil phase. In the embodiment shown, the second purified synthetic crude oil stream 5 is washed with a further aqueous washing solution 6 in a third mixer-settler 10. The further aqueous washing solution 6 is preferably a neutral washing solution, preferably essentially water.After washing, the water phase is again removed as part of the waste water stream 11 and the third purified synthetic crude oil stream 7 is obtained from the oil phase.

Claims

Patent claims:

1. A process for purifying a synthetic crude oil stream (1), the process comprising the following steps: - providing the synthetic crude oil stream (1), wherein the synthetic crude oil stream (1) contains diene compounds and has a diene number of at least 0.1 g / 100 g; - contacting the synthetic crude oil stream (1) with a polysulfide stream (2) containing at least one polysulfide compound to form a mixture, whereby at least a portion of the diene compounds is converted into diene-free products; and - separating the diene-free products from the mixture to obtain a purified synthetic crude oil stream (3).

2. The process according to claim 1, wherein the contacting of the synthetic crude oil stream (1) with the polysulfide stream (2) takes place at a temperature of at least 80 °C.

3. The process according to claim 1 or 2, wherein the polysulfide stream (2) is an aqueous solution.

4. The process according to any one of claims 1 to 3, wherein the concentration of the polysulfide compounds in the polysulfide stream (2) is at least 1 wt.%.

5. The process according to any one of claims 1 to 4, wherein the polysulfide stream (2) has a pH of more than 8.

6. The process according to any one of claims 1 to 5, wherein the at least one polysulfide compound is an amine polysulfide, an alkali metal polysulfide or an alkaline earth metal polysulfide.

7. The process according to any one of claims 1 to 6, wherein the at least one polysulfide compound is sodium or potassium polysulfide.

8. The process according to any one of claims 1 to 7, wherein the volumetric mixing ratio between the synthetic crude oil stream (1) and the polysulfide stream (2) is from 10:1 to 1:

5.

9. The process according to any one of claims 1 to 8, wherein the mixture formed from the synthetic crude oil stream (1) and the polysulfide stream (2) has a polar phase and an apolar phase, the diene-free products being predominantly present in the polar phase and the separation of the diene-free products from the mixture being achieved by separating the polar phase.

10. The process according to any one of claims 1 to 9, wherein the purified synthetic crude oil stream (3) is washed with an aqueous wash solution (4) to obtain a second purified synthetic crude oil stream (5).

11. The method according to claim 10, wherein the pH of the aqueous washing solution (4) is less than 6.

12. The process according to claim 10 or 11, wherein the second purified synthetic crude oil stream (5) is washed with a further aqueous wash solution (6) to obtain a third purified synthetic crude oil stream (7).

13. The process according to any one of claims 1 to 12, wherein the purified synthetic crude oil stream (3), the second purified synthetic crude oil stream (5) or the third purified synthetic crude oil stream (7) is fed to a hydrogenation plant.

14. The process according to any one of claims 1 to 13, wherein the synthetic crude oil stream (1) is produced by depolymerization of plastic material, in particular plastic waste.

15. The method according to claim 14, wherein the plastic material comprises polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polyamide (PA), styrene-acrylonitrile (SAN) and / or acrylonitrile-butadiene-styrene (ABS).

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