Feed flexible recycling

Abstract

A method for continuously producing a mixed hydrocarbon stream of predefined composition by recycling a mixed carbonaceous feedstock in an indirect gasification process, wherein the method comprises the steps of a) feeding a mixed carbonaceous feedstock to a fluidized bed reactor, b) gasifying said mixed carbonaceous feedstock in said fluidized bed reactor, c) continuously monitoring the composition of a hydrocarbon product stream obtained from said step b) via at least one gas analyzer; and d) adjusting the composition of said mixed carbonaceous feedstock comprised in step a) in order to obtain a mixed hydrocarbon stream of predefined composition; wherein said mixed carbonaceous feedstock comprises at least a first carbonaceous feed fraction with known composition and a second carbonaceous feed fraction with unknown and / or varying composition; and a fluidized bed reactor assembly for recycling a mixed carbonaceous feedstock via indirect gasification, comprising a fluidized bed reactor, at least one gas analyser being fluidly connected to a product gas outlet of said fluidized bed gasifier and at least one control unit for adjusting the composition of said mixed carbonaceous feedstock; wherein said fluidized bed gasifier comprises at least one, preferably at least two inlets for introducing said mixed carbonaceous feedstock.

Description

[0001] Feed Flexible Recycling

[0002] Field of the invention

[0003] The present invention relates to the field of polymer recycling, in particular to the recycling of polymers to their monomeric parts. Even more particularly, the present invention relates to the recycling of polymers by steam cracking.

[0004] Background

[0005] Current chemical recycling processes are typically limited either in feedstock specification or product value. Commercial scale pyrolysis processes are under development, but thus far require stringent specifications on waste feedstock composition. This poses limitations on the availability of the feed streams. The resulting sorting of fractions also means that residue fractions lose value and it thus becomes increasingly difficult to improve the circularity of the global material system.

[0006] EP 3 950 889 A1 mentions the option of combining plastic waste with hydrocarbon feedstock in catalytic cracking. However, the catalytic nature of the process indicates stringent feed specifications.

[0007] Partial oxidation gasification processes are able to take in feed of lower quality, but are designed to produce mainly syngas which requires further processing and use of energy to convert to hydrocarbons and, thus, to achieve circularity.

[0008] Mandviwala et al., Biomass Conversion and Biorefinery, https: / / doi.org / 10.1007 / s13399-022-02925-z, published online on June 14, 2022, outlines the thermochemical conversion of biogenic feedstock, in particular rapeseed oil, into basic building blocks of the chemical industry as a means to introduce fossil free feeds. This idea, while arguably lowering the global environmental impact of polymer production, does not contribute to solving the issue of accumulating plastic waste unless plastic is either incinerated forming CO2 or materially recycled in some manner.

[0009] Object of the invention

[0010] It is an object of the present invention to develop a method of thermal conversion for chemical recycling of plastic waste that is able to process mixed feedstock streams with negligible mixing effects on product distribution; is designed to achieve single step conversion to high value chemicals, for instance ethylene, propylene and benzene, and is aimed at balancing production by varying feed distribution to compensate for changes in feed quality or product demand over time.

[0011] Summary of the invention

[0012] It has surprisingly been found that the above-mentioned object can be achieved by a method for continuously producing a mixed hydrocarbon stream of predefined composition by recycling a mixed carbonaceous feedstock, i.e. , feedstock rich in carbon, comprising but not limited to cellulosic, aliphatic and aromatic structure, in an indirect gasification process, wherein the method comprises the steps of a) feeding a mixed carbonaceous feedstock to a fluidized bed reactor, b) gasifying said mixed carbonaceous feedstock in said fluidized bed reactor, c) continuously monitoring the composition of a hydrocarbon product stream obtained from said step b) via at least one gas analyzer; and d) adjusting the composition of said mixed carbonaceous feedstock comprised in step a) in order to obtain a mixed hydrocarbon stream of predefined composition.

[0013] Brief description of the figures

[0014] Figure 1 is a schematic drawing of the configuration of a typical dual fluidized bed (DFB) system;

[0015] Figure 2 is a schematic drawing of the experimental set-up used at lab scale experiments;

[0016] Figure 3 is a schematic drawing of the experimental set-up used at industrial scale experiments.

[0017] Detailed description of the Invention

[0018] The present invention relates to co-feeding of mixed carbonaceous fractions to an indirect gasification process. The method of indirect gasification has proven potential for chemical recycling of plastic. The current invention strengthens this potential for converting mixed carbonaceous fractions further.

[0019] Indirect gasification provides conditions for a high temperature pyrolysis with limited formation of carbon oxides. Instead of supplying heat through direct oxidation of a fraction of the feed, heat is added to the process indirectly by means of a heated solid medium. Specifically, the solid medium is heated, for example in a fluidized bed reactor serving as a combustor / regenerator, and then transferred to the gasification reactor being a fluidized bed reactor (also denoted as gasifier herein below) wherein the decomposition of the carbonaceous feedstock into high value chemicals occurs.

[0020] The type of the solid medium is not particularly limited. Thus, the solid medium may be either chemically inert or catalytically active. However, it is a requirement that the solid medium is thermally stable at the operating temperature of the method according to the invention. Alternatively, the expression “solid bed material” may be used to describe said “solid medium”.

[0021] The invention further provides a solution to overcoming the stringent feed specifications of current pyrolysis technology while simultaneously achieving a direct conversion of mixed carbonaceous feed fractions into valuable chemicals. Unlike partial oxidation gasification, the absence of added oxygen in the reactor leads to a smaller fraction of syngas (e.g. less than 0.15 kg syngas (CO + H2)Z kg of feedstock) in the product stream and a larger fraction of high valuable chemicals e.g. monomers and monoaromatic compounds. Since an additional step of converting a syngas fraction can be essentially avoided, less energy thus needs to be expended to obtain valuable products from the mixed carbonaceous feedstock. Furthermore, the invention simplifies the design and cost of equipment by providing a single type of reactor for a wide variety of carbonaceous feed streams.

[0022] The method described herein involves combining lesser quality waste fractions, also denoted as carbonaceous feed fractions with unknown composition, with carbonaceous feed streams of stable and known quality, i.e. carbonaceous feed streams which are well-defined and preferable have a constant and stable composition, thus providing a stable load on certain downstream processes for benefits to operation and design of the recycling plant in addition to simplifying the reactor design. Since drawbacks associated with such lesser quality waste streams are compensated for via the addition of at least one carbonaceous feed fraction of known composition, this enables the incorporation of lesser quality waste streams (carbonaceous feed fraction of unknown composition) into current downstream assets without designing multiple processes for various carbonaceous waste feed streams.

[0023] The invention thus enables recovery of smaller fractions of gaseous hydrocarbons, including monomers such as ethylene and propylene, or other high value chemicals, from a mixed carbonaceous feedstock comprising lower quality feed fractions, at a lower energy cost through economies of scale when combined with carbonaceous feed fractions of known composition that provide greater fractions of monomers or other high value chemicals.

[0024] The invention has been demonstrated for several feedstocks of varying chemical complexity: pure polyethylene, a mechanically recycled blend of polyethylene and polypropylene, a plastic waste derived pyrolysis oil of aliphatic character with a high degree of unsaturated substances, vegetable oil, animal fat, a reject fraction of mechanical recycling, a reject fraction of paper recycling constituting among others a fraction of polyolefins and a fraction of cellulose fibres. However, the selection of the carbonaceous feedstock is not particularly limited and may include (pre-)sorted plastic waste, oils and waxes of synthetic or biogenic origin, biomass or possibly even mixed solid waste.

[0025] In general, the mixed carbonaceous feedstock comprises at least a first carbonaceous feed fraction of known composition and a second carbonaceous feed fraction of unknown and / or varying composition and / or lesser quality and being selected from the list of: a vegetable oil, animal fat, a (pre-)sorted plastic waste fraction, a fossil feedstock, oils and waxes of synthetic or biogenic origin, biomass, mixed plastic waste, pyrolysis oil from recycled mixed plastics, a reject fraction obtained after fiber recovery from mixed plastic and cardboard materials or even mixed solid waste.

[0026] The introduction of certain carbonaceous feed fractions of lesser quality in the feedstock lowers the relative amount of monomers, in particular ethylene and propylene, in the product stream. For example, increasing the weight fraction of biomass in a mixed carbonaceous feedstock would increase syngas generation at the detriment of monomer yield. However, it has been found that the feed ratio between a carbonaceous feed fraction of lesser quality and / or unknown composition, for example a waste fraction of increased biomass content, and a further carbonaceous feed fraction of higher quality and / or known composition, for example a feed rich in aliphatic carbon, can be adjusted to maintain a constant production of monomers.

[0027] This is to say, the invention enables control of the process through varying feed composition, either by co-feeding a mixed carbonaceous feedstock into the same reactor volume, or by feeding at least two different carbonaceous feed fractions to different areas of the reactor.

[0028] Even though prior art (Hofbauer et al., Fuel, 107 (2013) 787-799) had concluded that there are synergies or mixing effects in contradiction to this invention, scaling up the process has clearly refuted this earlier assumption. The present invention is therefore directed to a method for continuously producing a mixed hydrocarbon stream of predefined composition by recycling a mixed carbonaceous feedstock in an indirect gasification process, wherein the method comprises the steps of a) feeding a mixed carbonaceous feedstock to a fluidized bed reactor, b) gasifying said mixed carbonaceous feedstock in said fluidized bed reactor, c) continuously monitoring the composition of a hydrocarbon product stream obtained from said step b) via at least one gas analyzer; and d) adjusting the composition of said mixed carbonaceous feedstock comprised in step a) in order to obtain a mixed hydrocarbon stream of predefined composition; wherein said mixed carbonaceous feedstock comprises at least a first carbonaceous feed fraction with known composition and a second carbonaceous feed fraction with unknown and / or varying composition.

[0029] Preferably, said step a) comprises feeding said first carbonaceous feed fraction and said second carbonaceous feed fraction to the fluidized bed reactor via at least two separate inlets.

[0030] Preferably, wherein said step a) comprises mixing said first carbonaceous feed fraction and said second carbonaceous feed fraction prior to feeding them - as a mixed carbonaceous feedstock - to the fluidized bed reactor via at least one inlet.

[0031] Preferably, wherein said step d) comprises adjusting a feed ratio of said at least first carbonaceous feed fraction and said at least second carbonaceous feed fraction.

[0032] Preferably, said gasification step c) is carried out at a temperature in a range of from 400 to 800°C, more preferably from 700 to 800°C.

[0033] Preferably, said first carbonaceous feed fraction of known composition comprises at least one of a vegetable oil, animal fat, a pre-sorted plastic waste fraction or a fossil feedstock.

[0034] Preferably, said second carbonaceous feed fraction of unknown composition comprises at least one of mixed plastic waste, pyrolysis oil from recycled mixed plastics, a reject fraction obtained after fiber recovery from mixed plastic and cardboard materials.

[0035] Preferably, the method further comprises a step of regenerating a solid bed material used in said fluidized bed reactor. More preferably, said step of regenerating the bed material is carried out in a fluidized bed combustor being fluidly connected to the fluidized bed gasifier.

[0036] More preferably, said step of regenerating said solid bed material is carried out at a temperature of 800 to 1100 °C.

[0037] Preferably, the combined amount of ethylene and propylene recovered via the method described herein above is at least 15 wt.%, more preferably at least 20 wt.% based on the total amount of the mixed carbonaceous feedstock.

[0038] Fluidized bed reactor assembly

[0039] The invention comprises a fluidized bed reactor assembly. According to a particularly preferred embodiment, said fluidized bed reactor assembly comprises a dual fluidized bed reactor system comprising a reactor / gasifier and a regenerator / combustor wherein heating is provided to a solid bed material which transfers to the reactor / gasifier bed. The reactor can be fed with a mixed carbonaceous feedstock and / or the reactor can be fed with two or more carbonaceous feed fractions simultaneously.

[0040] A fluidized bed reactor assembly for recycling a mixed carbonaceous feedstock via indirect gasification, comprising a fluidized bed reactor, at least one gas analyzer being fluidly connected to a product gas outlet of said fluidized bed gasifier and at least one control unit for adjusting the composition of said mixed carbonaceous feedstock; wherein said fluidized bed gasifier comprises at least one, preferably at least two inlets for introducing said mixed carbonaceous feedstock.

[0041] Preferably, said at least one inlet for introducing said mixed carbonaceous feedstock to the fluidized bed reactor assembly comprises an extruder.

[0042] Preferably, said at least one inlet for introducing said mixed carbonaceous feedstock to the fluidized bed reactor assembly is adapted for introducing said mixed carbonaceous feedstock in a liquid state, more preferably as a melt, into said gasifier.

[0043] Optionally, said at least one inlet for introducing said mixed carbonaceous feedstock in a liquid state to the fluidized bed reactor assembly comprises a nozzle for spraying said mixed carbonaceous feedstock into said gasifier.

[0044] According to a particularly preferred embodiment, the fluidized bed reactor assembly comprises a dual fluidized bed reactor comprising a first fluidized bed reactor, serving as a gasifier, and a second fluidized bed reactor, serving as a combustor / regenerator. Said first and said second fluidized bed reactor being fluidly connected to one another.

[0045] The configuration of a dual fluidized bed (DFB) system can be compared to more extensively studied fluid catalytic cracking (FCC) units. In a DFB system, hot fluidized bed material recirculates between two interconnected fluidized beds: a combustor (or regenerator) and a gasifier (Figure 1 ). The overall reaction on the combustor side is exothermic whereas on the gasifier side the reaction is endothermic. The heat generated on the combustor side is transported by the solid fluidized bed material to the gasifier side to meet its endothermic heat demand. This type of configuration allows production of two separate gas streams: flue gas from the combustor and product gas from the gasifier.

[0046] In a DFB system, a solid bed material is continuously circulated between two interconnected fluidized beds (Figure 1 ). The solid bed material is completely oxidized in the combustor (in presence of air) and partially reduced in the gasifier (in the presence of hydrocarbon feed). Partially reduced bed material leaves the gasifier along with unconverted solids and enters the combustor. Unconverted solids along with the bed material are oxidized in the combustor.

[0047] Also in a DFB system, the two fluidized beds are preferably interconnected through non mechanical valves called loop seals (LS). Loop seals allow for the transport of bed material between two reactors without exchange of any gasses. Usually, these loop seals are fluidized to avoid agglomeration of hot bed material.

[0048] Examples

[0049] Measurement methods

[0050] Devolatization gas analysis

[0051] The sampled gas is analysed for its H2, CO, CO2 and CH4 concentration (%vol) by a SICK GMS 820 permanent gas analyser. These gases are monitored continuously to determine the total time of devolatization and to make sure that no volatile gases are left after the sampling time of 120 s.

[0052] Comprehensive gas analysis

[0053] For a comprehensive analysis of other devolatilized species, the remaining part of the sampled gas is passed through a coil condenser, maintained at -5 °C. Gases leaving the coil condenser are collected in a 0.5 I Tedlar gas bag. The gas bags collected during each experiment are analysed with an Agilent 490 Micro GC system to measure the composition. The Agilent micro-GC is equipped with four different columns with a TCD detector for each column. A summary of gases measured by the micro-GC system is shown in Table 1.

[0054] Table 1 : Conditions of micro GC system

[0055] Materials

[0056] Different feedstocks were used to exemplify the flexible feeding to a DFB system. The feedstocks studied were:

[0057] • Pure polyethylene pellets (PE)

[0058] • Pellets of a mixture of polyethylene and polypropylene (PE + PP)

[0059] • Pyrolysis oil from recycled mixed plastics (PO)

[0060] • A mixed plastic waste stream (MPW)

[0061] • Rapeseed oil (RO)

[0062] • Animal fat (AF)

[0063] • A reject fraction obtained after fiber recovery from mixed plastic and carboard materials (MPC)

[0064] A brief description of the different feedstocks used, comprising the elemental composition thereof, is given in Table 2 below. The feedstocks evaluated at laboratory scale and at industrial scale are shown separately.

[0065] Table 2: elemental composition of feedstocks used For all the experiments (at lab scale and at industrial scale) the bed material used was silica sand.

[0066] The gasification temperature (measured in the bed) was 750°C + / - 10°C for all feedstocks analyzed.

[0067] Reactor setup

[0068] Laboratory scale

[0069] A bubbling fluidized bed (BFB) reactor was used for the lab-scale experiments (Figure 2). It consists of a stainless-steel tube with 88.9 mm of internal diameter and 1305 mm of height. The reactor is electrically heated and the temperature is controlled by three thermocouples that are installed along the height of the reactor. The thermocouple located in the bottom of the reactor was used to determine the reaction temperature in the bed. The fluidization gases were introduced from the bottom of the reactor through a windbox that allows a proper premixing of the gases before entering in the reactor through a distributor plate. Mass flow controllers regulate the volumetric flows of the different gases used. If batch experiments are to be done, the BFB configuration can mimic the DFB reactor operation by switching the fluidization gases used. For a better view, a schematic of this experimental set-up can be seen in Figure 1.

[0070] For the steam gasification tests at lab scale, batch experiments were done. The samples were dropped from the top of the reactor. Approximately 2 g of the selected fuels (RO, AF, MPC and PE + MPC) were used in each test. Four repetitions were considered to ensure a good repeatability of the experiments. To conduct the experiments mimicking a DFB operation, where the bed materials enters the gasifier after being fully oxidized in a combustor, the following steps were performed for each test (Table 3). Table 3: reaction conditions and fluidization gases used during laboratory scale experiments

[0071] *For the experi ments with M PC and PE + M PC, this ti me was set at 120 s because of the feedstock com position and structure.

[0072] Helium was used as a tracer gas to be able to determine the volume of gases produced both in the devolatilization and the char combustion stages. The time selected for the cracking and combustion stages was determined using the permanent analyzer, where the process is continuously monitored to measure the total time needed for the reaction, making sure that not volatiles are left after 90 or 120 s of sampling, depending on the feedstock.

[0073] Gas measurement

[0074] The produced gas when the reaction takes place is sampled through a gas probe that is kept at 350 °C via electrical heating to avoid steam and hydrocarbons condensation. Then, the gas is split into two streams. One of them is passed through a solid-phase extraction amine (SPA) to capture the condensable species for further analysis allowing to obtain a clean gas that is collected in a 0.5 L Tedlar gas bag that is further analyzed. The SPA used is a Supelclean™ ENVI-CarbTM / NH2 tube from Sigma-Aldrich. The second stream is passed through a conditioning system consisting of scrubbing, cooling and drying steps. This dry cold gas is sent to a SICK GMS 820 permanent gas analyzer which is used to monitor the different steps in the process.

[0075] The collected gases from both the gasification and the combustion stages were analyzed as detailed above (comprehensive gas analysis); while a Broker GC-FID GC-430 was used for the quantification of the aromatic hydrocarbons captured in the solid-phase adsorption method (SPA). Industrial scale

[0076] The industrial scale experiments were performed in the Chalmers DFB system, which consists of a 12 MWth circulated fluidized bed (CFB) combustor coupled to a 2-4 MWth bubbling fluidized bed (BFB) gasifier. This configuration allows to obtain the heat needed in the gasification side by the recirculation of the bed material that comes from the combustor. To perform the steam gasification experiments, a flow of 150 kg / h of steam was used in the gasifier as fluidization media. In this case, the feeding was done in a continuous way through an extruder that has to functions: (1 ) to melt the feedstock allowing a more steady and homogeneous feeding to the gasifier; and (2) act as sealing preventing air to enter in the gasifier. Steam was also added to the extruder (80 kg / h). The temperature in the gasifier was set at ca. 750 °C during the tests with the different fuels (PE, PE + PP and MPW). For the PO a different feeding system was used. The liquid feedstock was pumped and fed directly into the gasifier like a spray. For a better view of the system, the schematic of the set-up is provided in Figure 3.

[0077] To quantify the total dry gas produced during the experiments a small flow of helium was added in the gasifier as a tracer gas (35 lN / min), similar to what is done at lab scale. In this case, a raw gas stream is continuously sampled, that is used for both the permanent gases and the condensable hydrocarbons (tars). To analyze the raw gas composition, a slipstream of the dragged raw gas sampled was passed through a hot ceramic filter, cooled down and scrubbed in isopropanol to remove the condensable hydrocarbons. This cold and dry stream was then analyzed in a micro-GC (Varian CP-4900). This micro-GC has two channels and uses Poraplot Q and MS5A columns, with He and Ar as carrier gases, respectively. The micro-GC takes a point-injection (10-30 ms injection time) of the dry and tar-free raw gas every 3 minutes, generating a new chromatogram from each injection. The micro-GC is calibrated every week with five concentration levels that cover the range of the expected concentrations. The species analyzed are: H2, He, CO, CO2, CH4, C2H2, C2H4, C2H6, C3H6, CsHs and N2.

[0078] The results of the gas composition are the average of the chromatograms taken over a period of stable operation (i.e., when the gasification temperature and the fuel flow were stable). During this stable measurement the temperature in the gasifier varied in a range of ±3 °C.

[0079] Further, there is a sequential arrangement consisting of a single layered SPA, a pump, and a 0.5L Tedlar gas bag, to draw product gas. GC-VUV (Type Thermo Scientific TRACE 1310) analysis is used to determine the content of hydrocarbon species comprising 3 or more carbon atoms in the gas bag.

[0080] Detailed regarding GC-VUV conditions and settings are provided in table 4.

[0081] Table 4: GC-VUV conditions and settings

[0082] Following this approach, the GC-VUV system has the capability to detect and quantify all hydrocarbon species within the boiling point range of C3 to C8.

[0083] To determine the mass composition of the samples, the VUV Analyze software (version 1.8.1 ) developed by VUV Analytics, Inc. in Texas, United States, was utilized. This software takes into consideration the relative response factors (RRF) for each of the species present in the gas sample to determine the mass composition of the sample.

[0084] To measure the tar species, the solid-phase adsorption method was used in the same way that was presented in the previous section. In this case, a set of 4 amines was taken during the stable operation. After elution, the resulting liquid was analyzed in a BRUKER GC-FID GC-430. Each sample was analyzed 3 times, and the results presented are the average of the values obtained in the three-repeat analysis for the 4 different samples.

[0085] The feeding rates to the industrial-scale DFB gasifier were different due to the feedstock variability in terms of density, shape and composition. In Table 5, these values are indicated. Table 5: feeding rates for industrial scale experiments

[0086] The product distribution obtained for the different feedstocks (both at lab and industrial scale) is presented in Table 6. Each of the materials denoted as “PE”, “RO”, “AF”, “PE+PP” corresponds to a first fraction of known composition, whereas each of the materials denoted as “MPW”, “MPC”, “PO” corresponds to a second fraction of unknown composition. In addition, a mixture of PE + MPC (mixing ratio 1 :1 ) was tested. The results are presented in kg / kg of feedstock.

[0087] Table 6: Product distribution obtained for the different feedstocks used

[0088] *numerical val ues extrapolated from GC-VUV measurements

[0089] As can be seen from Table 6, the yield of lighter olefins, especially ethylene and propylene, recovered from mixed and / or low quality feedstocks is not significantly different from the yield obtained from feedstock streams with a known composition such as pure polyolefins (e.g. PE, PE+PP, RO, AF). Thus, it is evident that all the evaluated materials are suitable to recover valuable products therefrom. Overall, experimental findings confirm that streams comprising multiple types of materials do not exhibit significant mixing effects with regard to the decomposition products. For example, the presence of cellulose in the feedstock (MPC fraction) appears to have limited impact on the decomposition of e.g. synthetic polymers. Similar results are observed from the test involving a mixture of PE + MPC.

[0090] Optimization of the product output in terms of quantity and constant quality, may be achieved by adjusting the mixing ratio of individual feed fractions as detailed herein above.

Claims

CLAIMS1. A method for continuously producing a mixed hydrocarbon stream of predefined composition by recycling a mixed carbonaceous feedstock in an indirect gasification process, wherein the method comprises the steps of a) feeding a mixed carbonaceous feedstock to a fluidized bed reactor, b) gasifying said mixed carbonaceous feedstock in said fluidized bed reactor, c) continuously monitoring the composition of a hydrocarbon product stream obtained from said step b) via at least one gas analyzer; and d) adjusting the composition of said mixed carbonaceous feedstock comprised in step a) in order to obtain a mixed hydrocarbon stream of predefined composition; wherein said mixed carbonaceous feedstock comprises at least a first carbonaceous feed fraction with known composition and a second carbonaceous feed fraction with unknown and / or varying composition.

2. The method according to claim 1 , wherein said step a) comprises feeding said first carbonaceous feed fraction and said second carbonaceous feed fraction to the fluidized bed reactor via at least two separate inlets.

3. The method according to claim 1 , wherein said step a) comprises mixing said first carbonaceous feed fraction and said second carbonaceous feed fraction prior to feeding them - as a mixed carbonaceous feedstock - to the fluidized bed reactor via at least one inlet.

4. The method according to anyone of the preceding claims, wherein said step d) comprises adjusting a feed ratio of said at least first carbonaceous feed fraction and said at least second carbonaceous feed fraction.

5. The method according to anyone of the preceding claims, wherein said gasification step c) is carried out at a temperature in a range of from 400 to 800°C.

6. The method according to anyone of the preceding claims, wherein said first carbonaceous feed fraction of known composition comprises at least one of a vegetable oil, animal fat, a pre-sorted plastic waste fraction or a fossil feedstock.

7. The method according to anyone of the preceding claims, wherein said second carbonaceous feed fraction of unknown composition comprises at least one of mixed plastic waste, pyrolysis oil from recycled mixed plastics, a reject fraction obtained after fiber recovery from mixed plastic and cardboard materials.

8. The method according to anyone of the preceding claims further comprising a step of regenerating the bed material in a fluidized bed combustor being fluidly connected to the fluidized bed gasifier.

9. The method according to claim 8, wherein the method further comprises a step of regenerating a bed material used in said fluidized bed reactor, preferably, wherein said step of regenerating said bed material is carried out at a temperature of 800 to 1100 °C.

10. The method according to anyone of the preceding claims, wherein the combined amount of ethylene and propylene recovered via the method is at least 15 wt.%, preferably in an amount of at least 20 wt.% based on the total amount of the mixed carbonaceous feedstock.

11. A fluidized bed reactor assembly for recycling a mixed carbonaceous feedstock via indirect gasification, comprising a fluidized bed reactor, at least one gas analyser being fluidly connected to a product gas outlet of said fluidized bed gasifier and at least one control unit for adjusting the composition of said mixed carbonaceous feedstock; wherein said fluidized bed gasifier comprises at least one, preferably at least two inlets for introducing said mixed carbonaceous feedstock.

12. The fluidized bed reactor assembly according to claim 11 , wherein said at least one inlet for introducing said mixed carbonaceous feedstock comprises an extruder.

13. The fluidized bed reactor assembly according to claim 12, wherein said at least one inlet is adapted for introducing said mixed carbonaceous feedstock in a liquid state, preferably as a melt, into said gasifier.

14. The fluidized bed reactor assembly according to claim 13, wherein said at least one inlet for introducing said mixed carbonaceous feedstock in a liquid state comprises a nozzle for spraying said mixed carbonaceous feedstock into said gasifier.

15. The fluidized bed reactor assembly according to any one of claims 11 to 14, comprising a dual fluidized bed reactor comprising a first fluidized bed reactor, serving as a gasifier, and a second fluidized bed reactor, serving as a combustor / regenerator; wherein said first and said second fluidized bed reactor are fluidly connected to one another.

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