Process and integrated reactor system for gasifying a carbonaceous feedstock

Abstract

A process for producing a mixture of hydrocarbons from a carbonaceous feedstock, the process comprising the steps of a) providing a gaseous stream comprising a mixture of hydrogen, oxygen and steam via at least one gas inlet to a bottom section of a fluidized bed reactor; b) allowing at least part of the oxygen and hydrogen comprised in said gaseous stream to react at the bottom section of said fluidized bed reactor to produce a superheated stream of steam; c) contacting said superheated stream of steam with a solid bed material thereby transferring heat from said superheated stream of steam to said bed material such that a gaseous stream comprising steam and a heated bed material are obtained; d) feeding a carbonaceous feedstock into said fluidized bed reactor; e) contacting said carbonaceous feedstock with said gaseous stream comprising steam thereby forming a mixture of gaseous hydrocarbons and a mixture of condensed hydrocarbons, and f1) withdrawing a gaseous product mixture comprising said mixture of gaseous hydrocarbons from said fluidized bed reactor; and an integrated reactor system for gasifying a carbonaceous feedstock, comprising an electrolyser and at least one fluidized bed reactor, wherein said electrolyser comprises at least a first gas outlet and wherein said first gas outlet of said electrolyser is fluidly connected to at least one gas inlet of said at least one fluidized bed reactor.

Description

[0001] Process and integrated reactor system for gasifying a carbonaceous feedstock

[0002] Field of the invention

[0003] The present invention relates to a process for producing a mixture of hydrocarbons from a carbonaceous feedstock and an integrated reactor system for gasifying a carbonaceous feedstock.

[0004] Background

[0005] The production of hydrocarbons, in particular monomers such as ethylene and propylene for polymer synthesis, from non-fossil carbonaceous feedstocks is gaining more and more importance in view of global developments. Simultaneously, there is a strong need to reduce the overall amount of waste generated. In this regard, research activities with respect to chemical recycling of plastic waste and other potentially valuable sources of carbonaceous feedstock are continuously increasing.

[0006] However, at present, the chemical recycling of plastic waste is expected to generate large amounts of CO and CO2, especially when processing lower quality waste streams. Straightforward separation of syngas (hydrogen + carbon monoxide) and CO2 from the product stream is expected to provide a source of carbon for the production of chemicals by synthesis reactions (e.g. , methanol synthesis). However, processing a low quality feedstock will lead to a hydrogen deficiency. Synthesis reactions require the ratio (H2 - CO2) / (CO + CO2) = 2. This ratio is known as the R ratio. The hydrogen make-up, to achieve R ratio = 2, will have to be derived of renewable sources to avoid atmospheric emission of carbon.

[0007] Indirect gasification of carbonaceous feedstocks, such as plastic waste, in fluidized bed reactor systems is considered a promising technology.

[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.

[0009] 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.

[0010] 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.

[0011] Hofbauer et al., Fuel, 107 (2013) 787-799, studied steam gasification of plastic materials in a dual fluidized bed gasification pilot plant (DFB).

[0012] These processes rely on steam (water vapor) as a fluidization gas.

[0013] On the other hand, the production of hydrogen for the purposes of being a feedstock - in addition to being an energy carrier - is expected to rise in the coming years. Electrolysis of water is the most common process when it comes to the production of renewable hydrogen. However, in order to utilize hydrogen from electrolysis for synthesis reactions, the water vapor comprised in the product streams at the outlet(s) of an electrolyser must be condensed out. Obviously, this reduces the overall energy efficiency of the electrolysis process.

[0014] Object of the invention

[0015] It is an object of the present invention to provide a process for producing a mixture of hydrocarbons from a carbonaceous feedstock - in particular from carbonaceous waste streams - that overcomes the problem of excessive syngas production due to hydrogen deficiency.

[0016] Moreover, it is an object of the present invention to overcome the drawbacks of current chemical recycling processes and the electrolysis of water by providing an integrated reactor system for gasifying a carbonaceous feedstock. Summary of the invention

[0017] It has now been found that the above objectives can be achieved by a process for producing a mixture of hydrocarbons from a carbonaceous feedstock, the process comprising the steps of a) providing a gaseous stream comprising a mixture of hydrogen, oxygen and steam via at least one gas inlet to a bottom section of a fluidized bed reactor; b) allowing at least part of the oxygen and hydrogen comprised in said gaseous stream to react at the bottom section of said fluidized bed reactor to produce a super-heated stream of steam; c) contacting said superheated stream of steam with a solid bed material thereby transferring heat from said superheated stream of steam to said bed material such that a gaseous stream comprising steam and a heated bed material are obtained; d) feeding a carbonaceous feedstock into said fluidized bed reactor; e) contacting said carbonaceous feedstock with said gaseous stream comprising steam thereby forming a mixture of gaseous hydrocarbons and a mixture of condensed hydrocarbons, f1 ) withdrawing a gaseous product mixture comprising said mixture of gaseous hydrocarbons from said fluidized bed reactor; and providing an integrated reactor system for gasifying a carbonaceous feedstock, comprising an electrolyser and at least one fluidized bed reactor, wherein said electrolyser comprises at least a first gas outlet and wherein said first gas outlet of said electrolyser is fluidly connected to at least one gas inlet of said at least one fluidized bed reactor.

[0018] Short description of the Figures

[0019] Figure 1 is a schematic drawing of the experimental set-up used for the exemplified experiments;

[0020] Figure 2 is a comparison of the molar yield of hydrogen produced by the gasification process with / without added hydrogen.

[0021] Detailed description of the invention

[0022] Process

[0023] A process for producing a mixture of hydrocarbons from a carbonaceous feedstock, the process comprising the steps of: a) providing a gaseous stream comprising a mixture of hydrogen, oxygen and steam via at least one gas inlet to a bottom section of a fluidized bed reactor; b) allowing at least part of the oxygen and hydrogen comprised in said gaseous stream to react at the bottom section of said fluidized bed reactor to produce a superheated stream of steam; c) contacting said superheated stream of steam with a solid bed material thereby transferring heat from said superheated stream of steam to said bed material such that a gaseous stream comprising steam and a heated bed material are obtained; d) feeding a carbonaceous feedstock into said fluidized bed reactor; e) contacting said carbonaceous feedstock with said gaseous stream comprising steam thereby forming a mixture of gaseous hydrocarbons and a mixture of condensed hydrocarbons, f1 ) withdrawing a gaseous product mixture comprising said mixture of gaseous hydrocarbons from said fluidized bed reactor.

[0024] The process according to the invention involves indirect gasification of a carbonaceous feedstock.

[0025] Generally speaking, 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.

[0026] Importantly, unlike partial oxidation gasification, an indirect gasification process leads to a smaller fraction of syngas in the product stream and a larger fraction of valuable chemicals, e.g. gaseous hydrocarbons. Since an additional step of converting a syngas fraction can be essentially avoided, less energy needs to be expended to obtain valuable products (in particular gaseous hydrocarbons) from the carbonaceous feedstock.

[0027] The expressions “solid medium” and “(solid) bed material” as used herein aim at describing the same component used in the process and / or comprised in the reactor system; hence, the expressions may be used synonymously throughout the description and the claims.

[0028] The type of the solid medium / bed material 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”.

[0029] The type of said carbonaceous feedstocks is not particularly limited and may be selected from, for example: 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, (pre-)sorted plastic waste, oils and waxes of synthetic or biogenic origin, biomass or possibly even mixed solid waste.

[0030] Preferably, the carbonaceous feedstock is a mixed carbonaceous feedstock, i.e. , a feedstock rich in carbon, comprising but not limited to cellulosic, aliphatic and aromatic structure, and 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.

[0031] In practice, said step c) of contacting said superheated stream of steam with a solid bed material thereby transferring heat from said superheated stream of steam to said bed material such that a gaseous stream comprising steam and a heated bed material are obtained corresponds to an internal heating step. The step of transferring heat may also be described as an internal heating step. It is believed that the requirement of heating the gasifier via an external heat source may be reduced or even overcome in case the process comprises said step c). Moreover, it is believed that the heat transfer between said superheated steam and the bed material is suitable to assure a constant temperature level of the bed material which may be beneficial for the overall efficiency of the process.

[0032] Said step e) may be carried out at a temperature suitable to achieve gasification of the carbonaceous feedstock. Preferably step e) is carried out at a temperature in a range of from 400 to 900°C, more preferably of 600 to 850°C, and even more preferably of 700 to 800°C.

[0033] Preferably, said step a) comprises providing a mixture of a first gaseous stream comprising hydrogen and steam, and a second gaseous stream comprising oxygen and steam to said bottom section of said fluidized bed reactor. More preferably, said first gaseous stream comprising hydrogen and steam and said second gaseous stream comprising oxygen and steam are combined at the entry point / inlet located at the bottom section of said fluidized bed reactor at the time of entering. Optionally, said first gaseous stream and / or said second gaseous stream may be preheated prior to entering the entry point / inlet of said fluidized bed reactor.

[0034] Preferably, said gaseous stream comprising a mixture of hydrogen, oxygen and steam or said first gaseous stream and / or said second gaseous stream are at least partially, more preferably completely, produced in an electrolyser and transferred directly to said bottom section of said fluidized bed reactor via at least one fluid connection between at least one outlet of said electrolyser and at least one gas inlet of said fluidized bed reactor.

[0035] Preferably, step a) further comprises preheating said gaseous stream comprising a mixture of hydrogen, oxygen and steam. Preferably, said gaseous stream provided in step a) comprises excess hydrogen.

[0036] Preferably, the process according to the invention further comprises a step f2) of transferring at least part of a solid bed material and at least part of said mixture of hydrocarbons produced in step e) to a second fluidized bed reactor being fluidly connected to said first fluidized bed reactor.

[0037] Preferably, the process according to the invention further comprises the step of: g) oxidizing said mixture of condensed hydrocarbons in the presence of a solid bed material thereby forming a flue gas and a heated solid bed material.

[0038] More preferably, said step f2) is carried out prior to said step g) and said step g) takes places in said second fluidized bed reactor.

[0039] Said step g) may be carried out at a temperature suitable to achieve full oxidation / combustion of said mixture of condensed hydrocarbons. Usually, said step g) is carried out at a higher temperature than said step e). Preferably, step g) is carried out at a temperature in a range of from 800 to 1200°C; more preferably of from 850 to 1100°C and even more preferably of from to 900 to 1100°C.

[0040] More preferably, a gaseous stream comprising steam and oxygen used as an oxidizing agent in step g) is at least partially, even more preferably completely, produced in an electrolyser.

[0041] Preferably, the process according to the invention further comprises the steps of: h) continuously monitoring the composition of said gaseous product mixture via at least one gas analyser; and i) adjusting the composition of the gaseous stream comprising a mixture of hydrogen, oxygen and steam in step a). Preferably, the process of the invention is carried out in an integrated reactor system as described herein below.

[0042] Even more preferably, the process of the invention is carried out in a particularly preferred embodiment of the integrated reactor system, wherein the reactor system comprises an electrolyser being fluidly connected to a dual fluidized bed (DFB) system; and wherein each one of said mixed gaseous streams comprising steam and oxygen and / or steam and hydrogen and / or steam, oxygen and hydrogen is produced in the electrolyser via the electrolysis of water and directly transferred to the DFB system via at least one fluid connection without any intermediate steps of drying / reducing the moisture content of said mixed gaseous stream. This particularly preferred embodiment of the invention may also be described as process for the indirect gasification of a carbonaceous feedstock via indirect electric heating.

[0043] Integrated reactor system

[0044] The integrated reactor system according to the present invention is an integrated reactor system for gasifying a carbonaceous feedstock, and comprises an electrolyser and at least one fluidized bed reactor, wherein said electrolyser comprises at least a first gas outlet and wherein said first gas outlet of said electrolyser is fluidly connected to at least one gas inlet of said at least one fluidized bed reactor.

[0045] Preferably, in the integrated reactor system as described herein, said electrolyser further comprises a second gas outlet and wherein said second gas outlet is fluidly connected to at least one gas inlet of said at least one fluidized bed reactor.

[0046] Said at least one gas inlet of said at least one fluidized bed reactor being fluidly connected to said second gas outlet of the electrolyser may be the same as, or different from, the at least one gas inlet of said at least one fluidized bed reactor being fluidly connected to said first gas outlet of the electrolyser.

[0047] Preferably, the integrated reactor system as described herein, is an integrated reactor system and said integrated reactor system comprises a dual fluidized bed reactor assembly comprising a fluidized bed gasifier and a fluidized bed combustor. More preferably, said gasifier and said combustor are fluidly connected via loop seals.

[0048] Preferably, in the integrated reactor system as described herein, said first gas outlet of said electrolyser is fluidly connected to at least one gas inlet of said fluidized bed gasifier and / or wherein said second gas outlet of said electrolyser is fluidly connected to at least one gas inlet of said fluidized bed gasifier.

[0049] Preferably, in the integrated reactor system as described herein, said second gas outlet of said electrolyser is fluidly connected to at least one gas inlet of said fluidized bed combustor.

[0050] Preferably, the integrated system as described herein, further comprises at least one gas analyser being fluidly connected to a product gas outlet of said recycling unit and at least one control unit for adjusting the composition of said mixed carbonaceous feedstock.

[0051] Examples

[0052] Measurement methods

[0053] Devolatization gas analysis

[0054] 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.

[0055] Comprehensive gas analysis

[0056] 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.

[0057] Table 1 : Conditions of micro GC system Materials

[0058] The PE pellets used in this work, with bulk density of 945 kg / m3and 2.5 mm pellet size are provided by Borealis AB. Bauxite was used as the bed material. Composition of the bed material used in this work are detailed in Table 2.

[0059] Table 2: Composition of the used material

[0060] Reactor setup

[0061] The experimental setup used for the comparative and the inventive examples is shown in Figure 1 . The main reactor is a stainless-steel tube of 88.9 mm in internal diameter (ID) and 1305 mm in height. It is a bubbling fluidized bed reactor, which resembles the cracker of a DFB (dual fluidized bed) system Fluidization gases are fed from the bottom of the reactor via a windbox and a distributor plate. The fluidization gases are fed separately and mixed homogeneously in the windbox before entering the reactor through the gas distributor plate. The flow of the fluidization gases is controlled by a mass flow controller (MFC).

[0062] The reactor is heated externally with an electric oven. Temperature along the height of the reactor is measured and logged continuously by the thermocouples on the back side of the reactor. Bed material is loaded from the top of the reactor before turning on the reactor oven. A split stream of the gases leaving the reactor is sampled through one of the gas sampling port: hi to h3.

[0063] A gas sampling probe is inserted into the reactor through one of the ports while the rest of the ports are sealed to avoid bed material entering the port. The height of the port is selected depending on the height of the fluidized bed. The probe is heated up to 350 °C with electrical heating band to avoid condensation of hydrocarbons and steam. The sampled gas is then split into two parts, one part is passed through a gas conditioning system and the other is passed through the SPA amine.

[0064] The gas conditioning system involves scrubbing of the sampled gas with isopropanol followed by drying with silica gel beads and glass wool. The gas conditioning system is immersed in a water bath. The cold and dry gas is then analysed by a SICK GMS 820 permanent gas analyser. Gas sampled through the SPA amine is collected in a 0.5 I Tedlar gas bag.

[0065] PE pellets weighing 1 g per batch are dropped directly on the top of the hot fluidized bed. The experimental conditions and the procedure for each set of experiment are summarized in Table 4 and Table 5, respectively.

[0066] During devolatilization and char combustion stages of each experiment, helium is used as one of fluidization gases. A known volume of helium is used a tracer gas to determine the volume of gases produces during devolatilization and char combustion. Before dropping each batch of PE pellets, the bed material is subjected to an oxidizing environment at the same reaction temperature. Oxidation of bed material is achieved by fluidizing the bed material with air, as mentioned in the previous section. A slipstream of gases leaving the reactor is sampled through the sampling port h2 and continuously analysed for its O2 concentration (%vol). Complete oxidation is assumed when the O2 concentration leaving the fluidized bed matches the ambient O2 concentration of 20.9 %vol. Bed materials are fully oxidized before each batch of experiments so as to simulate the conditions of a DFB system, where the bed material enters the cracker after being fully oxidized in the regenerator.

[0067] The condition used in the comparative examples are shown in tables 3 and 4.

[0068] Table 3: Reaction conditions for comparative and inventive examples Table 4: Fluidization gas flows during comparative example

[0069] During steam cracking of polyethylene, one part of the sampled gas is analysed for its H2, CO, CO2 and CPU concentration (%vol) by the continuous gas analyser. These gases are monitored continuously to determine the total time of devolatilization and to make sure that no volatile gases are left after the sampling time of 120 s.

[0070] To analyse the full spectrum of products in the created output gas, micro-GC was undertaken.

[0071] Inventive Examples

[0072] The invention described here involves integration of electrolysers with chemical polymer recycling unit. Integrating an electrolyser with a fluidized bed gasifier will lead to induction of hydrogen gas as one of the potential reactants in the gasifier.

[0073] The reactivity of hydrogen gas was experimentally validated by using hydrogen gas as one of the fluidization agents during the devolatilization stage of the experiments. Other reaction conditions, and sampling and analytical procedures were kept same as the comparative example to evaluate the exclusive impact of hydrogen gas on the gasification products.

[0074] The conditions used for the inventive example are shown in Table 5.

[0075] Table 5: Fluidization gas conditions during inventive example.

[0076] Results

[0077] The yields of the gaseous products obtained for the comparative and the inventive examples for steam gasification of polyethylene are shown in Table 6. Table 6: Gaseous products produced in comparative and inventive examples

[0078] The yield of methane, ethylene, ethane, propylene, and propane remains more or less the same for the comparative and inventive examples. This proves that the induction of hydrogen gas into the gasifier has very little or no impact on the gasification reactions. Moreover, the difference in the yield of hydrogen gas between the comparative and inventive examples is almost equal to the amount of hydrogen gas input to the gasifier during the experiments (see Fig- ure 2. This, in addition to the previous argument, proves that hydrogen gas inducted into the gasifier, leaves the gasifier unreacted.

Claims

Claims1. A process for producing a mixture of hydrocarbons from a carbonaceous feedstock, the process comprising the steps of: a) providing a gaseous stream comprising a mixture of hydrogen, oxygen and steam via at least one gas inlet to a bottom section of a fluidized bed reactor; b) allowing at least part of the oxygen and hydrogen comprised in said gaseous stream to react at the bottom section of said fluidized bed reactor to produce a superheated stream of steam; c) contacting said superheated stream of steam with a solid bed material thereby transferring heat from said superheated stream of steam to said bed material such that a gaseous stream comprising steam and a heated bed material are obtained; d) feeding a carbonaceous feedstock into said fluidized bed reactor; e) contacting said carbonaceous feedstock with said gaseous stream comprising steam thereby forming a mixture of gaseous hydrocarbons and a mixture of condensed hydrocarbons, f1 ) withdrawing a gaseous product mixture comprising said mixture of gaseous hydrocarbons from said fluidized bed reactor.

2. The process according to claim 1 , wherein said step a) comprises providing a mixture of a first gaseous stream comprising hydrogen and steam, and a second gaseous stream comprising oxygen and steam to said bottom section of said fluidized bed reactor.

3. The process according to anyone of the preceding claims, wherein said gaseous stream comprising a mixture of hydrogen, oxygen and steam or said first gaseous stream and / or said second gaseous stream areat least partially, preferably completely, produced in an electrolyser and transferred directly to said bottom section of said fluidized bed reactor via at least one fluid connection between at least one outlet of said electrolyser and at least one gas inlet of said fluidized bed reactor.

4. The process according to any one of the preceding claims, wherein step a) further comprises preheating said gaseous stream comprising a mixture of hydrogen, oxygen and steam.

5. The process according to any one of the preceding claims, wherein said gaseous stream provided in step a) comprises excess hydrogen.

6. The process according to anyone of the preceding claims, further comprising a step f2) of transferring at least part of a solid bed material and at least part of said mixture of hydrocarbons produced in step e) to a second fluidized bed reactor being fluidly connected to said first fluidized bed reactor.

7. The process according to anyone of the preceding claims, further comprising the step of: g) oxidizing said mixture of condensed hydrocarbons in the presence of a solid bed material thereby forming a flue gas and a heated solid bed material.

8. The process according to claim 7, wherein said step f2) is carried out prior to step g) and step g) takes place in said second fluidized bed reactor.

9. The process according to claim 7 or 8, wherein a gaseous stream comprising steam and oxygen used as an oxidizing agent in step g) is at least partially produced in an electrolyser.

10. The process according to anyone of the preceding claims, further comprising the steps of:h) continuously monitoring the composition of said gaseous product mixture via at least one gas analyser; and i) adjusting the composition of the gaseous stream comprising a mixture of hydrogen, oxygen and steam in step a).

11. An integrated reactor system for gasifying a carbonaceous feedstock, comprising an electrolyser and at least one fluidized bed reactor, wherein said electrolyser comprises at least a first gas outlet and wherein said first gas outlet of said electrolyser is fluidly connected to at least one gas inlet of said at least one fluidized bed reactor.

12. The integrated reactor system according to claim 11 , wherein said electrolyser further comprises a second gas outlet and wherein said second gas outlet is fluidly connected to at least one gas inlet of said at least one fluidized bed reactor.

13. The integrated reactor system according to any one of claims 11 to 12, wherein said integrated reactor system comprises a dual fluidized bed reactor assembly comprising a fluidized bed gasifier and a fluidized bed combustor; and wherein said first gas outlet of said electrolyser is fluidly connected to at least one gas inlet of said fluidized bed gasifier and / or wherein said second gas outlet of said electrolyser is fluidly connected to at least one gas inlet of said fluidized bed gasifier.

14. The integrated reactor system according to claim 13, wherein said second gas outlet of said electrolyser is fluidly connected to at least one gas inlet of said fluidized bed combustor.

15. The integrated system according to anyone of claims 11 to 14, further comprising at least one gas analyser being fluidly connected to a product gas outlet of said at least one fluidized bed reactor and at least one control unit for adjusting the composition of said mixed carbonaceous feedstock.

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