WO2024141214A1 - Pyrolysis oil and/ or fossil naphtha as a feedstock for indirect gasification - Google Patents

Abstract

A process for producing olefins by indirect gasification, wherein the process comprises the steps of feeding a feedstock comprising fluid aliphatic and/ or naphthenic hydrocarbons into a fluidized bed gasifier; feeding a stream of steam to said fluidized bed gasifier; and gasifying said feedstock in said fluidized bed gasifier; wherein said step of gasifying said feedstock in said fluidized bed gasifier is carried out at a temperature in a range of from 600 to 900 °C. Use of a feedstock comprising fluid aliphatic and/ or naphthenic hydrocarbons for the production of olefins.

Description

Pyrolysis oil and/ or fossil naphtha as a feedstock for indirect gasification

Field of the invention

The present invention relates to the field of polymer recycling, in particular to the recycling of pyrolysis products obtained from plastic waste. Even more particularly, the present invention relates to the conversion of such pyrolysis products to olefins by indirect gasification.

Background

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.

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.

GB 2 601 570 A discloses a process for obtaining solid recovered fuel from a waste-based feedstock and converting it into synthesis gas which may - after purification - serve as a feedstock in downstream processes such as for example Fischer-Tropsch synthesis, ammonia synthesis or methanol synthesis.

WO 2021/105327 A1 relates to a method of producing high quality components, in particular hydrocarbons, from liquefied waste plastics and involves co-feeding a highly paraffinic material and, preferably pre-treated, liquefied waste plastics in a steam cracking process. However, a disadvantage of the process is its low tolerance with respect to the content of impurities, in particular chlorine, and olefinic compounds in the mixed feedstock.

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. 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.

Moreover, according to Kusenberg et al., Waste Management, vol.148, pages 83-115 (2022), a typical steam cracker feedstock for base chemical production tolerates only low amounts of contaminants. In particular, a typical steam cracker feedstock may include no more than 3 ppm chlorine, 100 ppm nitrogen and 100 ppm oxygen.

Object of the invention

It is an object of the present invention to provide a one-step conversion process for producing olefins from a feedstock comprising fluid aliphatic and/or naphthenic hydrocarbons, such as pyrolysis products and/or fossil naphtha, without the need for hydrotreatment of the feedstock prior to gasification. Thus, it is an object of the present invention to provide a process which allows for a higher tolerance of contaminants, in particular chlorine.

Summary of the invention

It has surprisingly been found that the above-mentioned object can be achieved by a process for producing olefins by indirect gasification, wherein the process comprises the steps of feeding a feedstock comprising fluid aliphatic and/ or naphthenic hydrocarbons into a fluidized bed gasifier; feeding a stream of steam to said fluidized bed gasifier; and gasifying said feedstock in said fluidized bed gasifier; wherein said step of gasifying said feedstock in said fluidized bed gasifier is carried out at a temperature in a range of from 600 to 900 °C.

Brief description of the figures

Figure 1 is a schematic drawing of the experimental set-up used at industrial scale experiments; Detailed description of the Invention

The present invention relates to a gasification process suitable to convert plastic wastes to olefins.

As already indicated above, Mandviwala et al. discloses a process for producing methane from biomass. However, further developments of said process now allow for the processing a wider range of feeds and products. The technology has shown good yields for ethylene and propylene when using a variety of aliphatic materials as feed.

Unlike partial oxidation gasification, the absence of atmospheric oxygen in the gasifier during an indirect gasification process creates a chemical environment with remarkable similarity to conventional steam cracking of hydrocarbons. This is achieved by transferring solid bed material to a separate vessel for regeneration of heat and incineration of heavy end by-products. Indirect gasification of e.g., polyethylene yields ethylene and propylene comparable to steam cracking of virgin naphtha indicating the commercial potential of the process. However, due to the differing C-H ratios of virgin naphtha and polyethylene, the heavy end of the product distribution exhibits a greater variation for indirect gasification and conventional steam cracking.

In the context of the present invention the expression “indirect gasification” relates to a process where the heat required for the endothermic conversion of the feedstock has been generated outside the chamber where such conversion takes place.

It has now been found that the gasification process developed (Mandviwala et al.) can also accept liquid oil feedstock, like fossil naphtha and pyrolysis oils, thereby obtaining ethylene and propylene yields comparable to industrial steam crackers. The gasification process is robust and can accept extremely poor-quality feedstock, and pyrolysis oils can be fed without any pretreatments steps making it possible to skip the complex and costly upgrading processes of pyrolysis oils.

Experimental findings indicate that heteroatoms tend to exit the carbon matrix and form smaller molecular compounds when processed by indirect gasification. Thus, they become available for removal by simpler methods than hydroprocessing e.g., adsorption, filtration, or even other separation methods. The presence of olefins in the pyrolysis oil is no cause for issue since unlike conventional steam cracking continuous regeneration of the solid bed material in indirect gasification prevents coke build-up by design thus avoiding unit downtime due to de-coking. Furthermore, contaminants that remain solid under the process conditions, such as for example certain metals, will become entrapped in the solid flow and can thus be removed via solids purging.

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 by means of a heated solid medium transferring between the reactor and a regenerator.

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”.

Feedstock

In general, the feedstock used in the process of the present invention comprises aliphatic and/ or naphthenic hydrocarbons, preferably in an amount of at least 50 wt.% based on the total feedstock.

In general, the feedstock comprising aliphatic and/ or naphthenic hydrocarbons comprises hydrocarbons having more than 4 carbon atoms.

Preferably, the feedstock comprising aliphatic and/ or naphthenic hydrocarbons comprises at least 30 wt.% of fluid hydrocarbons, more preferably at least 30 wt.% of liquid hydrocarbons.

In the context of the present application, the expression “fluid hydrocarbons” refers to hydrocarbons being in a liquid or gaseous state at ambient temperature and pressure (298 K, 1013 hPa). Likewise, the expression “liquid hydrocarbons” refers to hydrocarbons being in a liquid state at ambient temperature and pressure (298 K; 1013 hPa).

Preferably, the liquid hydrocarbons comprised in the feedstock have a dynamic viscosity in the range of from 0.1 to 100 mPa • s as determined by ASTM D7042, for example using Viscometer SVM3000 and a density of about 1 g/ml (1000 kg/m³).

Preferably, the liquid hydrocarbons comprised in the feedstock have a density at ambient temperature in a range of from 0.6 to 1 .3 g/ml.

Preferably, the feedstock comprises pyrolysis products, such as pyrolysis oils and gases. More preferably said pyrolysis product(s) is/ are obtained from plastic waste, such as post-consumer waste plastics/ recycled consumer plastics. An alternative expression for describing the above is “liquefied waste plastics”.

Specifically, it is preferred that the feedstock comprises one or more fluid pyrolysis product(s), more preferably one or more fluid pyrolysis product(s) obtained from plastic waste and even more preferably one or more fluid pyrolysis product(s) obtained from plastic waste that has not been subject to hydrotreatment.

In the context of the present invention, the term "pyrolysis oil" is understood to mean any oil at least partially originating from the pyrolysis of plastic waste, including (i) any crude pyrolysis oil fully originating from the pyrolysis of plastic waste (herein referred to as “plastic waste pyrolysis oil”), (ii) any crude pyrolysis oil originating from the pyrolysis of a mixture of plastic waste and biomass, or (iii) any crude pyrolysis oil comprising a mixture of crude plastic waste pyrolysis oil and crude biomass pyrolysis oil.

As used herein, “(crude) plastic waste pyrolysis oil” means pyrolysis oil derived from pyrolysis of a feedstock consisting of plastic waste.

The term "pyrolysis" includes slow pyrolysis, fast pyrolysis, flash catalysis and catalytic pyrolysis. These type of pyrolysis differ in the process temperature, heating rate, residence time, feed particle size, etc. resulting in different product quality. Sharuddin et al, “A review of pyrolysis of plastic waste”, Energy Conversion and Management, vol 115, pages 308-326 (May 2016) describes typical process conditions for pyrolysis of plastic waste.

Typically, plastic waste is a mixture of different plastic material, including hydrocarbon plastics, e.g., polyolefins such as polyethylene (HDPE, LDPE) and polypropylene, polystyrene and copolymers thereof, etc., and polymers composed of carbon, hydrogen and other elements such as chlorine, fluorine, oxygen, nitrogen, sulfur, silicone, etc., for example chlorinated plastics, such as polyvinylchloride (PVC), polyvinylidene chloride (PVDC), etc., nitrogencontaining plastics, such as polyamides (PA), polyurethanes (PU), acrylonitrile butadiene styrene (ABS), etc., oxygen-containing plastics such as polyesters, e.g. polyethylene terephthalate (PET), polycarbonate (PC), etc.), silicones and/or sulfur bridges crosslinked rubbers. PET plastic waste is often sorted out before pyrolysis, since PET has a profitable resale value. Accordingly, the plastic waste to be pyrolyzed often contains less than about 10 wt.%, preferably less than about 5 wt.% and most preferably substantially no PET based on the dry weight of the plastic material.

The pyrolysis product(s) may be present in fluid form, preferably the pyrolysis product is present in liquid form (at ambient temperature and pressure; 298 K, 1013 hPa). Liquid pyrolysis products may alternatively be referred to as pyrolysis oil (see above); gaseous pyrolysis products may alternatively be referred to as pyrolysis gas.

Optionally, the pyrolysis product(s) may be subject to pre-treatment operations such as described for example in WO 2020/ 242912 A1 ; WO 2020/242916 A1 ; WO 2020/ 242925 A1 and WO 2021/ 105327 A1.

However, the pyrolysis product(s) comprised in the feedstock are used without being subject to hydrotreatment; viz. no hydrogen and/ or hydrogenation catalyst is present during any optional pre-treatment steps. That is, the pyrolysis product(s) does not undergo hydrogenation and/ or hydrocracking prior to its use as a feedstock in the process as detailed herein.

Preferably, the feedstock comprising aliphatic and/ or naphthenic hydrocarbons may comprise, more preferably consist of, one or more pyrolysis product(s) as defined above.

The feedstock is preferably further characterized by having at least one of:

- a chlorine content of 10 ppm or more,

- a nitrogen content of 10 ppm or more,

- a sulfur content of 10 ppm or more, and

- an oxygen content of 10 ppm or more.

When the density of the feedstock is about 1 g/ml (1000 kg/m³), the above concentrations given in mg/l equals the same concentrations in ppm, i.e. 1 mg/l then equals 1 ppm.

The content of heteroatoms, such as chlorine, sulfur, oxygen and nitrogen in the feedstock may be determined by standard procedures, such as, for example gas chromatography.

Moreover, the feedstock preferably contains less than 10 wt.% of fatty acids.

Fatty acids quantification can be performed, for example, via Gas Chromatography coupled with a Flame Ionization Detector (GC-FID) in accordance with standard procedures. Preferably, the feedstock may be characterized as a mixed carbonaceous feedstock comprising at least a first feedstock fraction as defined herein above and a second feedstock fraction comprising at least one of oils and waxes of synthetic or biogenic origin, sorted plastic waste (solid), biomass and mixed plastic waste (solid).

Process

The present invention is directed to a process for producing olefins by indirect gasification, wherein the process comprises the steps of a) feeding a feedstock comprising fluid aliphatic and/ or naphthenic hydrocarbons into a fluidized bed gasifier; b) feeding a stream of steam to said fluidized bed gasifier; and c) gasifying said feedstock in said fluidized bed gasifier; wherein said step c) is carried out at a temperature in a range of from 600 to 900 °C, preferably in a range of from 700 to 820°C.

Preferably, the process is carried out in an inert or quasi-inert atmosphere in the reactor.

In the context of the present application, an inert atmosphere is characterized by the complete absence of oxygen, a condition achievable using gases like N2, CO2, or any other gas that does not react with the feedstock molecules. A quasi-inert atmosphere consists of a gas with limited interaction with hydrocarbons. Steam, for instance, serves as a quasi-inert environment. It not only functions as a dilution agent in the hydrocarbons mixture, restricting the extent of runaway reactions (e.g. secondary free-radical reactions) and limiting the formation of unwanted complex structures such as polyaromatics and char, but also plays a role in determining the equilibrium of syngas formation.

Preferably, the process is carried out at a steam to fuel (feedstock) ratio in a range of from 1 to 5 (v/v).

The bed material to be used in the above process is not particularly limited and may be selected from inert and catalytically active bed materials. However, preferably the bed material is inert. Silica sand is an exemplary inert bed material that may be used in the above process.

Preferably, the process is a continuous process. Generally speaking, the feedstock used in step a) is a feedstock as detailed herein above.

More specifically, it is preferred that the feedstock used in step a) comprises one or more fluid pyrolysis products, preferably one or more fluid pyrolysis products obtained from plastic waste that has not been subject to hydrotreatment.

Further, it is preferred that said feedstock comprising fluid aliphatic and/ or naphthenic hydrocarbons contains less than 10 wt.% of fatty acids based on the total weight of said feedstock.

Preferably, in the above process at least part of said feedstock comprising fluid aliphatic and/ or naphthenic hydrocarbons is in a liquid state at ambient temperature and pressure (298 K; 1013 hPa).

Preferably, in the above process at least part of said feedstock comprising aliphatic and/ or naphthenic hydrocarbons and being in a liquid state at ambient temperature and pressure is fed to the reactor as a spray.

Preferably, in the above process at least part of said feedstock comprising fluid aliphatic and/ or naphthenic hydrocarbons is in a gaseous state at ambient temperature and pressure.

Preferably, in the above process the feedstock used in step a) comprises from 30 to 100 wt.%, preferably from 40 to 100 wt.% and more preferably from 50 to 100 wt.% of fluid aliphatic and/ or naphthenic hydrocarbons based on the total weight of said feedstock.

Preferably, said feedstock used in step a) is a mixed feedstock further comprising at least one of oils and waxes of synthetic or biogenic origin, sorted plastic waste, biomass and mixed plastic waste.

It is further preferred that said feedstock comprising fluid aliphatic and/ or naphthenic hydrocarbons has at least one of:

- a chlorine content of 10 ppm or more; and/ or

- a sulfur content of 10 ppm or more; and/ or

- an oxygen content of 10 ppm or more; and/ or

- a nitrogen content of 10 ppm or more.

Preferably, said step c) is carried out at a temperature in a range of from 650 to 850°C, preferably from 700 to 820°C. Preferably, said process further comprises the steps of d) continuously monitoring the composition of a hydrocarbon product stream obtained from said step c) via at least one gas analyzer; and e) adjusting the composition of said feedstock comprised in step a) in order to obtain a mixed hydrocarbon stream of predefined composition.

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.

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 a fluidized bed gasifier.

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

Preferably, the combined amount of ethylene and propylene recovered via the method described herein above is at least 30 wt.%, more preferably at least 40 wt.% based on the total amount of the aliphatic and/ or naphthenic content of the feedstock comprising liquid aliphatic and/ or naphthenic hydrocarbons. Preferably, the combined amount of ethylene and propylene recovered via the method described herein above is in a range of from 30 to 50 wt.% based on the total amount of the aliphatic and/ or naphthenic content of the feedstock.

Fluidized bed reactor assembly

The process according to the present invention is preferably carried out in a fluidized bed reactor system (or assembly). According to a particularly preferred embodiment, said fluidized bed reactor system 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 may be fed with a single feedstock comprising liquid aliphatic and/ or naphthenic hydrocarbons. Alternatively, the reactor can be fed with two or more compositionally different feedstock fractions simultaneously under the provision that at least one feedstock fraction is a feedstock comprising liquid aliphatic and/ or naphthenic hydrocarbons. Preferably, a fluidized bed reactor system suitable for carrying out the process of the present invention comprises a fluidized bed gasifier, 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 feedstock; wherein said fluidized bed gasifier comprises at least one, preferably at least two inlets for introducing said mixed carbonaceous feedstock.

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

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.

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.

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.

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. 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.

In a DFB system, a solid bed material is continuously circulated between two interconnected fluidized beds. 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. 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 gases. Usually, these loop seals are fluidized to avoid agglomeration of hot bed material.

A schematic drawing of an exemplary DFB system is depicted in Figure 1 , wherein said DFB system comprises (1 ) a combustor (or regenerator); (2) fuel feed for the combustor; (3) a cyclone; (4) a particle distributor; (5) a first loop seal to the gasifier; (6) a gasifier; (7) a second loop seal to the combustor; (8) fuel feed for the gasifier. Moreover, a sampling point (X) as well as return points of the second loop seal (crossed circle) are included in Figure 1.

Moreover, details regarding a reactor set-up for conventional steam cracking can be found, for example, in Ullmann’s Encyclopedia of Industrial Chemistry (DOI: 10.1002/14356007).

Moreover, a reactor set-up as described in “Kusenberg, et al., Waste Management, 141 (2022), 104-114” (DOI: 10.1016/j.wasman.2022.01.033) was used to carry out the comparative examples.

Use

The present invention is further directed to the use of a feedstock as defined herein above for the production of olefins.

Thus, the invention is directed to the use of a feedstock comprising fluid aliphatic and/ or naphthenic hydrocarbons for the production of olefins.

Preferably, said feedstock comprising fluid aliphatic and/ or naphthenic hydrocarbons comprises one or more pyrolysis products as defined herein above.

Preferably, the use involves a feedstock containing less than 10 wt.% of fatty acids based on total weight of said feedstock.

Examples

Materials

Different feedstocks were used to demonstrate the versatility of a DFB system in comparison to a conventional steam cracking set-up. The feedstocks studied were: • Fossil Naphtha - Batch A (obtained from Borealis AG);

• Fossil Naphtha - Batch B (obtained from Preem Petroleum AB);

• Pyrolysis oil from Renasci - Batch C (obtained from Renasci);

• Pyrolysis oil from Renasci - Batch D (obtained from Renasci).

The different feedstocks used were analyzed for PIONA (paraffin, isoparaffin, olefin, naphthene, aromatics), the results of the analyses are given in Table 3 below. As usual, fossil naphtha is very low in olefins. Batches A and C were analyzed via GCxGC-FID/TOF-MS. Batches B and D were analyzed using GC- VUV method.

Detailed characterization using GC-VLIV

To determine the mass composition of the feedstock batches B and D, GC- VUV (Type Thermo Scientific TRACE 1310) analysis was performed. Detailed information about the analytical methods employed on the GC-VLIV for batches B and D is provided in the table 1. The results of these analyses relating to feedstock batches B and D are given in table 3 (PIONA analyses).

Table 1 : GC-VLIV conditions and settings

Following this approach, the GC-VLIV system has the capability to detect and quantify all hydrocarbon species within the boiling point range of C5 to C18.

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.

Detailed characterization using GCxGC-FID/TOF-MS

All experiments were carried out using three Thermo Scientific TRACE GCxGC’s (Interscience, Belgium). For both FID and MS analyses the GCxGC conditions are shown in Table 2 for the selected normal phase column combination (PONAxBPX-50). Quantification procedure is performed based on the methods developed by Dijkmans et al. published, for example, in:

Industrial & Engineering Chemistry Research, 53(40), 15436-15446 (DQI: 10.1021/ie5000888), and

Fuel, 140(0), 398-406 (DOI: 10.1016/j. fuel.2014.09.055).

The results of these analyses relating to feedstock batches A and C are given in table 3 (PIONA analyses).

Table 2: GCxGC settings for off-line analysis using FID and TOF-MS detectors

^adimethyl polysiloxane (Restek);^b50% phenyl polysilphenylene-siloxane (SGE); PTV: programmable temperature vaporizing injector

A quantitative analysis of the samples is carried out with the use of a GCxGC- FID. This analysis is based on the peak surface volumes. The peak surface volumes in a chromatogram is proportional to the quantity of the corresponding component. Hence, integration of the peaks observed in the chromatogram makes it possible to obtain a quantitative analysis of the sample.

Internal standards (3-chlorothiophene and 2-chloropyridine) were added in known amounts to the samples for the FID analyses. The internal standards for each of the chromatograms were chosen in such a way that they were properly separated from all other peaks (Dijkmans et al. (DOI: 10.1016/j.fuel.2014.09.055). The amount of internal standard that is added is chosen in such a way that the internal standard would have a similar peak height as the components quantified by the internal standard.

The mass fraction of each compound on the FID can be calculated using the mass fraction (wi) of the internal standard (3-chlorothiophene or 2- chloropyridine) w_st:

where fi is the relative response factor for compound i, Vi is the peak volume (corresponding to sum of peak areas recorded in two-dimensional mode) of compound i, fst is the relative response factor of the internal standard and Vst is the peak volume of the internal standard. It has been demonstrated that various isomeric hydrocarbons, produce only slightly different relative FID responses, and hence that a fair approximation of the relative response factor (in respect to methane) may be written as: f _ Mi

^MCH4^{x N}C.i (2) where Mi is the molar mass of compound i, Nc is the carbon number of compound i and MCH4 is the molar mass of methane. This approximation removes the need to calibrate for each compound present in the mixture. Calibration was however carried out for 3-chlorothiophene and 2- chloropyridine. Using the internal standard method, it has been observed that the total weight fraction that could be measured using GCxGC-FID for this feed is around 100 wt.% (±5 wt.%). Therefore, internal standard is only used to check if the analyses were performed regularly, while the weight fraction of single compounds were calculated using internal normalization to 100 wt.%. All of these calculations are handled by in in-house written excel macro.

A detailed qualitative characterization is obtained using information obtained by GCxGC-TOF-MS analysis, the available library of mass spectra (NIST) and the Kovats retention indices (Kovats, Helvetica Chimica Acta, 41 (7), 1915- 1932; DOI: 10.1002/hlca.19580410703). In addition, the structured chromatogram obtained by orthogonal GC*GC separation was used to aid in the identification of the components.

Operation of the GCxGC-TOF-MS is computer controlled, with GC peaks automatically detected as they emerge from the column. Each individual mass spectrum is directly recorded onto the hard disk for subsequent analysis. This technique provides information on the identity of every individual component obtained by chromatographic separation by taking advantage of the common fragmentation pathways for individual substance classes. The interpretation of the mass spectra was carried out using XCalibur and/ or Hyperchrom software.

Table 3: Results of PIONA analyses of exemplary feedstocks (results are presented in wt.% of feedstock)

Reactor setup

Comparative Examples - Conventional Steam Cracking Set-up

Steam cracking pilot testing of pyrolysis oil was carried out in the pilot plant set-up for steam cracking of hydrocarbons at the “Laboratorium voor Chemische Technologie” of Ghent University. Fossil naphtha (Batch A) was used as feedstock in CE1 a and CE1 b. Details regarding the reactor set-up can be found in Kusenberg, et al., Waste Management, 141 (2022), 104-114. Pyrolysis oil (Batch C; 40%) was blended with fossil naphtha (Batch A; 60%) to obtain a feedstock for CE2a and CE2b. The respective feedstocks were processed in the steam cracker pilot at a coil outlet temperature (COT) of 840 and 860 °C in order to determine product yields and coking tendency. The Coil Outlet Pressure (COP) of 1.7 bara, hydrocarbon mass flow of 3.5 kg/h and a dilution of 0.5 kg steam/kg hydrocarbons were kept fixed throughout the tests. DMDS (dimethyl disulfide) was continuously added to keep the sulfur content at 120 ppmw (ppmw = parts per million weight).

An on-line product analysis of the reactor effluent was performed and allowed the characterization and quantification of the different product fractions. The C2-analysis of the quenched effluent gases was performed simultaneously on two gas chromatography (GC) devices. Hydrogen was only detected on one GC. The use of two devices for the same analysis allows checking the consistency of the results. The first system was an Interscience Trace GC Ultra called Refinery Gas Analyzer (RGA). Hydrogen, carbon dioxide, carbon monoxide, nitrogen, methane, ethane, ethylene and acetylene were all detected by a thermal conductivity detector (TCD). The second system was an Interscience Fisons GC 8340 called the Permanent Gas Analyzer (PGA) with a TCD which detects the same compounds except hydrogen.

The C1 to C4 compounds were also analyzed with the Interscience Trace GC Ultra using a flame ionization detector (FID). Comprehensive two-dimensional GC, known as GCxGC, was also used to detect C5+ compounds (hydrocarbons comprising 5 or more carbon atoms) in general and, in particular, the total content of benzene, toluene, styrene and xylenes (BTSX). The GCxGC apparatus was combined with an FID for quantitative analysis and a TOF-MS (time-of-flight mass spectrometer) for qualitative analysis. It can be used both for on-line analysis as it is used for off-line analysis as already described herein above in the context of feedstock analysis.

Coke formation in the radiant sections was measured after 6 hours of cracking in the radiant and convection sections of the pilot of the three different feeds at COT of 840 and 860 °C.

Results of the product analyses (presented in wt.% of feedstock) for the comparative examples are given in table 4.

Inventive Examples - Dual Fluidized Bed (DFB) System

The indirect gasification experiments were performed in the Chalmers pilot unit 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 160 kg/h of steam was used in the gasifier as fluidization media. The liquid feedstock was pumped and fed directly into the gasifier like a spray. For all experiments the bed material used was silica sand.

For a better view of the system, the schematic of the set-up is provided in Figure 1 .

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 IN/min). A raw gas stream was continuously sampled and was 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, C3H8 and N2.

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. 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 BRLIKER 430 GC-FID. 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.

BTSX and aromatics species in general are quantified following a solid phase adsorption (SPA) method. In this method, a sample from the producer gas line is sucked by a 100ml syringe at a constant rate, forcing it to pass through an adsorbent column (Supelclean ENVI-Carb/NH2 SPE columns) consisting of an amine adsorbent layer (500mg) followed by an activated carbon layer (500mg). A mixture of dichloromethane, isopropanol, and acetonitrile (8:1 :1 ) is used to elute into a vial the adsorbed species from the column. Hexylbenzene or 4-ethoxyphenol are added as internal standards with concentrations suitable for the species quantification (~12000 mg/L and ~250mg/L respectively). The vial is characterized in a Gas Chromatograph Broker GC430 coupled with a Flame Ionization Detector (FID), equipped with a midpolar column BR-17 MS (BR85877) using H2 as carrier gas. Twentyeight different aromatic species are measured with boiling points ranging from C6 until C18 which include monoaromatics such as BTSX, and polyaromatics as naphthalene, anthracene until triphenylene (C18). Results of the product analyses (presented in wt.% of feedstock) for the inventive examples are given in table 5.

Comparison of experimental results from comparative and inventive examples

The product distribution and yields obtained for the pyrolysis oil feedstocks both from the comparative conventional steam cracker set-up and DFB gasification process are presented in tables 4 and 5. The results are presented in wt.% of feedstock.

The results of the comparative and inventive experiments are grouped according to feedstock:

CE1 a and CE1 b: Batch A using two different temperatures (COT);

CE2a and CE2b: Blend of Batch C (40 wt.%) and Batch A (60 wt.%) using two different temperatures (COT);

IE1 a to IE1 c: Batch D using three feedstock mass flow to heating ratios;

IE2a to IE2c: Batch B using two different cracking temperatures.

From tables 4 and 5 it is evident that the ethylene and propylene yields are similar for both the comparative examples using a conventional steam cracking set-up and the inventive examples using the DFB gasification process. This result shows that the DFB gasification process may be used instead of a conventional steam cracking process to produce comparable amounts of ethylene and propylene from pyrolysis oil.

In conventional steam crackers, olefins are known to cause coking in the cracking coils, increasing the steam cracker downtime. In table 4, total amounts of coke formed in the comparative examples are shown. In the inventive examples involving DFB gasification, coking is not seen as a production limitation. This is due to the fact that continuous regeneration of the bed material in the DFB gasification process prevents the production unit downtime associated with de-coking of steam cracker furnaces.

Furthermore contaminants present containing heteroatoms such as oxygen, chloride, cyanide, sulfur and nitrogen, during thermal conversion, above elements will be converted into stable products, such as CO2, HCI, H2S, HCN, and NH3, under tailored operating conditions that enable their recovery and avoid operational problems. (Energy Fuel 23 (5), (2009), 2743-2749 and Additives in Polymers, Modification of Polymer Properties, William Andrew Publishing, 2017, pp. 87-108.) In fact, the inventive examples exhibit increased ethylene yields compared to the comparative examples. Overall, gasification yields of the inventive examples in the range of C1 -C5 match or exceed the results obtained in comparative examples despite occurring at a lower temperature. While the coil outlet temperature (COT) in the comparative examples is not directly comparable to the cracking temperature of the DFB process (inventive examples), the results clearly indicate that higher severity cracking is possible in the DFB process at lower process temperatures.

The continuous regeneration of the heat carrying solid phase in the inventive examples provides additional benefits by removing coke during production, thus minimizing or even avoiding altogether interruption of production for decoking the equipment.

Furthermore, the DFB process (inventive examples) resulted in much lower yield of aromatics as compared to the conventional steam cracking set-up (comparative examples). The total yield of aromatics in the DFB process was 6 wt.% at 780°C (IE2b). On the other hand, the conventional steam cracker yielded 17.34 wt.% at 840°C (CE1 a). This indicates that a higher cracking severity at a lower temperature, as in the inventive DFB process, is beneficial since it lowers the yield of aromatics which are economically less valuable than olefins. In addition, a decreased tendency of aromatization is indicative of decreased tendency of coking.

From table 3 it is clear that the naphtha used in the inventive examples was of superior quality when compared to the one used in the comparative examples, considering the naphthenic and aromatic fractions. However, even though the quality of naphtha may contribute to the superior yield in the inventive examples to some extent, it is obvious that the overall difference in product yields outcompetes the difference in the quality of the feedstocks.

A further advantage of the inventive process can be seen from the examples using pyrolysis oil as feedstock (IE1 a to IE1 c) where conventional steam cracking is limited by coking due to a high prevalence of unsaturated C-C bonds in the feed. Unsaturated C-C bonds are well known drivers of coking in steam cracking and there are limitations on how much can be allowed in a steam cracking furnace feed. The inventive process is able to process this material due to the aforementioned continuous regeneration/decoking. The pyrolysis oil examples (IE1 a to IE1 c) are indicative of yields from olefinic naphtha and show no losses in ethylene yield. Table 4: Comparative examples; conventional steam cracking set-up

*BTSX = total of benzene, toluene, styrene and xylenes; measured via GCxGC as detailed above with respect to comparative examples.

Table 5: Inventive examples; DFB system

*BTSX = total of benzene, toluene, styrene and xylenes; measured as detailed above with respect to inventive examples.

Claims

1. A process for producing olefins by indirect gasification, wherein the process comprises the steps of a) feeding a feedstock comprising fluid aliphatic and/ or naphthenic hydrocarbons into a fluidized bed gasifier; b) feeding a stream of steam to said fluidized bed gasifier; and c) gasifying said feedstock in said fluidized bed gasifier; wherein said step c) is carried out at a temperature in a range of from 600 to 900 °C.

2. The process according to claim 1 , wherein the process is a continuous process.

3. The process according to any one of the preceding claims, wherein the feedstock comprises one or more fluid pyrolysis products, preferably one or more fluid pyrolysis products obtained from plastic waste and more preferably one or more fluid pyrolysis products obtained from plastic waste that has not been subject to hydrotreatment.

4. The process according to any one of the preceding claims, wherein said feedstock comprising fluid aliphatic and/ or naphthenic hydrocarbons contains less than 10 wt.% of fatty acids based on the total weight of said feedstock.

5. The process according to any one of the preceding claims, wherein said feedstock comprising fluid aliphatic and/ or naphthenic hydrocarbons has a chlorine content of 10 ppm or more; and/ or a sulfur content of 10 ppm or more; and/ or an oxygen content of 10 ppm or more; and/ or a nitrogen content of 10 ppm or more.

6. The process according to any one of the preceding claims, wherein said step c) is carried out at a temperature in a range of from 650 to 850 °C, preferably from 700 to 820 °C.

7. The process according to any one of the preceding claims, wherein at least part of said feedstock comprising fluid aliphatic and/ or naphthenic hydrocarbons is in a liquid state at ambient temperature and pressure.

8. The process according to claim 7 wherein at least part of said feedstock comprising aliphatic and/ or naphthenic hydrocarbons and being in a liquid state at ambient temperature and pressure is fed to the reactor as a spray.

9. The process according to any one of the preceding claims, wherein at least part of said feedstock comprising fluid aliphatic and/ or naphthenic hydrocarbons is in a gaseous state at ambient temperature and pressure.

10. The process according to any one of the preceding claims, wherein the feedstock used in step a) comprises from 50 to 100 wt.% of fluid aliphatic and/ or naphthenic hydrocarbons based on the total weight of said feedstock.

11. The process according to any one of the preceding claims, wherein said feedstock used in step a) is a mixed feedstock further comprising at least one of oils and waxes of synthetic or biogenic origin, sorted plastic waste, biomass and mixed plastic waste.

12. The process according to claim 1 1 , further comprising the steps of d) continuously monitoring the composition of a hydrocarbon product stream obtained from said step c) via at least one gas analyzer; and e) adjusting the composition of said feedstock comprised in step a) in order to obtain a mixed hydrocarbon stream of predefined composition.

13. Use of a feedstock comprising fluid aliphatic and/ or naphthenic hydrocarbons for the production of olefins.

14. Use according to claim 13, wherein said feedstock comprising fluid aliphatic and/ or naphthenic hydrocarbons comprises one or more pyrolysis products obtained from plastic waste.

15. Use according to claim 13 or 14, wherein said feedstock contains less than 10 wt. % of fatty acids based on the total weight of said feedstock.