Method for thermal cracking of hydrocarbons

Abstract

A method for thermal cracking of hydrocarbons comprises A-1) providing electrically conductive support particles having a particle density of 1.2 g / cm3 or more, A-2) allowing the support particles to flow downwardly under gravity flow as a particle bed through a cracking zone; A- 3) heating the support particles in the cracking zone to a temperature of at least 700 °C by applying a voltage across the particle bed in the cracking zone; A-4) feeding a hydrocarbon-containing cracker feed gas stream through the cracking zone in counter current to the support particles flow, whereby thermal cracking of the cracker feed gas stream to form olefins, and concomitant deposition of carbon on the support particles occurs; A-5) recovering an olefin-containing gas stream from the cracking zone; A-6) withdrawing the support particles having carbon deposited thereon and directing them to a regeneration zone. The method further comprises B-1) allowing the support particles having carbon deposited thereon to flow downwardly under gravity flow as a particle bed through the regeneration zone; B-2) heating the support particles having carbon deposited thereon in the reaction zone to a temperature of at least 900 °C by applying a voltage across the particle bed in the regeneration zone; B-3) feeding a gaseous regeneration stream comprising a species selected from carbon dioxide and steam through the regeneration zone in counter current to the support particles flow, whereby regenerated particles are obtained; B-4) withdrawing a regeneration product stream from the regeneration zone; and B-5) withdrawing the regenerated particles from the regeneration zone and at least partially directing them as electrically conductive support particles to the cracking zone. In the method, a thermal cracking operation can be combined with a regeneration step comprising regenerating the support particles having carbon deposited thereon in a regeneration zone.

Description

[0001] 240579W001 1

[0002] Method for Thermal Cracking of Hydrocarbons

[0003] The present invention relates to a method for thermal cracking of hydrocarbons.

[0004] Ethylene and propylene are important feedstocks used in the production of numerous petrochemical intermediate products and end products. They are made by cracking ethane, propane, or sometimes heavier paraffins or naphthas at high temperature. The gas mixture leaving the cracker is typically a mixture of hydrogen and hydrocarbons, of which 10 to 80% of the gas may be ethylene produced by reactions that can be represented by simplified net reaction equations such as

[0005] C2H6C2H4+ H2

[0006] and

[0007] C3H8 ^ C2H4+ CH4

[0008] In recent years, it has also been suggested to perform cracking in a fluidized bed or moving bed reactor with electrical heating. Generally, in a moving bed reactor, a feed gas and solid material particles flow in counter current throughout the reactor while a reaction occurs to produce a gaseous product mixture. Typically, by operating the moving bed reactor in counter current mode, the feed gas entering the reactor is preheated by hot solid material particles, and the gaseous product mixture leaving the reactor is cooled by cold solid material particles.

[0009] The required energy of the system can be supplied via electrodes within the reaction zone. The application of moving bed reactors with a direct electrical heating concept via electrodes enables an efficient heat integration within the reactor as well as an efficient energy supply for the reactions taking place in the reactor. Therefore, such concepts are well suited for endothermic reactions, such as the cracking of hydrocarbons to obtain olefins (an olefin-containing gas stream) as described above.

[0010] To achieve a desired composition of the olefin-containing gas stream, defined reaction conditions have to be set. These reaction conditions include, for example, temperature, pressure and residence time. The residence time depends on the gas flow through the reactor as well as on the length of the reaction zone (hereinafter also referred to as "cracking zone”).

[0011] Often, electrically conductive support particles such as carbonaceous particles are used as solid material particles. The benefit of using electrically conductive support particles such as carbonaceous particles is that carbon formed in the cracking reaction, e.g. in the form of coke, can directly be withdrawn from the reactor on240579W001 2

[0012] the solid material particles and no separation step to remove carbon from the solid material particles is to be carried out after the solid material particles are withdrawn from the reactor.

[0013] However, using electrically conductive support particles such as carbonaceous particles as solid material particles can limit the production capacity of the reactor. The production capacity of the reactor depends on the diameter of the reactor, limited by manufacturing capabilities, as well as on the flow velocity through the reactor and the electric energy input.

[0014] The flow velocity is limited by the fluidization velocity, which is a function of the particle size, shape and density.

[0015] The electric energy input depends on the available voltage, which can be limited due to safety concerns, and the resistivity of the bed, which in turn is a function of the length of the reaction zone and the carrier material properties.

[0016] Thus, both the flow velocity and the electric energy input are influenced by the properties of the electrically conductive support particles such as carbonaceous particles. While the size of the electrically conductive support particles such as carbonaceous particles is an adjustable parameter, the size has an inverse effect on the fluidization velocity and the resistivity of the bed. Large electrically conductive support particles such as carbonaceous particles increase the fluidization velocity, but at the same time increase the resistivity due to the lower amount of contact points between the particles.

[0017] US 2 982 622 describes subjecting a hydrocarbon feedstock to a high temperature conversion to convert the hydrocarbon(s) into light products and high-grade coke by contact with an electrically heated, dense mass of solid particles.

[0018] WO 2013 / 004391 describes a process for the production of synthesis gas in which methane and carbon dioxide are introduced into a reaction space, e.g. of a moving bed reactor or a fluidized bed reactor, and reacted in the presence of a solid at elevated temperatures to give hydrogen and carbon monoxide, wherein methane and carbon dioxide are passed through a carbon-containing granular material, e.g. carbonaceous granules having at least 80 wt.-% carbon and a grain size of 0.1 to 100 mm, and reacted in a high-temperature zone.

[0019] WO 2014 / 095661 describes a process for utilizing a hydrocarbon-containing and / or carbon dioxide-containing blast furnace gas. The hydrocarbon-containing and / or carbon dioxide-containing blast furnace gas is introduced into a reaction chamber, e.g. of a moving bed reactor or a fluidized bed reactor, and converted into a high-temperature zone at temperatures of above 1000°C and in the presence of a support. A hydrogen and carbon monoxide enriched product-gas mixture is obtained. Furthermore, a carbon-containing solid is obtained of which more than 75 wt.-%, based on the total mass of the carbon-containing solid, is deposited onto the support.240579W001 3

[0020] DE 102016005 188 describes a process for producing synthesis gas comprising passing a hydrocarbon fluid through a bed of carbonaceous granules in a reaction space to split the hydrocarbon fluid to carbon and hydrogen with the addition of heat. The method further comprises mixing the carbon and hydrogen with CO2from an external source and converting the mixture to CO in a CO2converter.

[0021] There is an ongoing need to provide improved concepts for carrying out endothermic reactions such as thermal cracking of hydrocarbons to obtain olefins in moving bed reactors which overcome the above-mentioned shortcomings.

[0022] This object is solved by the inventive method for thermal cracking of hydrocarbons, comprising

[0023] A-1) providing electrically conductive support particles having a particle density of 1.2 g / cm3or more, A-2) allowing the support particles to flow downwardly under gravity flow as a particle bed through a cracking zone;

[0024] A-3) heating the support particles in the cracking zone to a temperature of at least 700 °C, preferably 700 to 1600 °C, by applying a voltage across the particle bed in the cracking zone;

[0025] A-4) feeding a hydrocarbon-containing cracker feed gas stream through the cracking zone in counter current to the support particles flow, whereby thermal cracking of the cracker feed gas stream to form olefins, and concomitant deposition of carbon on the support particles occurs;

[0026] A-5) recovering an olefin-containing gas stream from the cracking zone;

[0027] A-6) withdrawing the support particles having carbon deposited thereon and directing them to a regeneration zone;

[0028] B-1 ) allowing the support particles having carbon deposited thereon to flow downwardly under gravity flow as a particle bed through the regeneration zone;

[0029] B-2) heating the support particles having carbon deposited thereon in the reaction zone to a temperature of at least 900 °C, preferably in the range of 900 to 1400 °C by applying a voltage across the particle bed in the regeneration zone;

[0030] B-3) feeding a gaseous regeneration stream comprising a species selected from carbon dioxide and steam through the regeneration zone in counter current to the support particles flow, whereby regenerated particles are obtained;

[0031] B-4) withdrawing a regeneration product stream from the regeneration zone; and

[0032] B-5) withdrawing the regenerated particles from the regeneration zone and at least partially directing them as electrically conductive support particles to the cracking zone.

[0033] The inventive method involves thermal cracking of a cracker feed gas stream in a cracking zone comprising a moving bed of electrically conductive support particles. In the above idealized equations, no elemental carbon is produced in the cracking operation. However, during thermal cracking, carbon, e.g. coke, is almost inevitably formed and deposited on the support particles. In order to maintain performance of the thermal cracking operation, it may become necessary to remove the carbon deposited on the support particles. It has been found240579W001 4

[0034] that the thermal cracking operation can be combined with a regeneration step comprising regenerating the support particles having carbon deposited thereon in a regeneration zone. The regeneration step may involve a the Boudouard reaction or the reverse Bosch reaction for selectively removing the carbon deposited on the support particles, e.g. by converting the carbon to carbon monoxide or carbon dioxide, respectively.

[0035] The inventive method involves support particles which are electrically conductive. Therefore, heating the support particles can be carried out by applying a voltage across the particle bed which allows for an especially advantageous supply of energy for the inventive method as well as for a highly efficient heat integration.

[0036] Step A-1)

[0037] Step A-1) involves providing electrically conductive support particles having a particle density of 1.2 g / cm3or more, preferably 2.5 g / cm3or more. The support particles with a higher density have a higher fluidization velocity and enable a higher flow velocity of the cracker feed gas stream through the cracking zone, thereby enabling a higher production capacity.

[0038] The nature of the electrically conductive support particles is not particularly limited as long as the electrically conductive support particles are constituted from a material which is electrically conductive and have a particle density of 1.2 g / cm3or more. In an embodiment, the electrically conductive support particles are constituted from a material selected from carbon, aluminum oxide, titanium oxide, silicon carbide, and zirconium carbide, preferably aluminum oxide, titanium oxide, silicon carbide, and zirconium carbide.

[0039] The electrically conductive support particles may also comprise a material with no or limited electrical conductivity which is doped with an electrically conductive material. Suitable electrically conductive doping materials are selected from carbon, aluminum, iron, nickel, copper, palladium and platinum.

[0040] In an embodiment, the electrically conductive support particles comprise a core, and a shell surrounding the core. The material constituting the core may comprise a ceramic material, silicon carbide, a metallic material or composites thereof, and the material constituting the shell may comprise carbon.

[0041] Metallic materials may be metallic throughout or have a metallic coating over a non-metallic core. Metallic particles include conductive pre-reduced oxidic particles. An especially preferred metallic material is aluminum oxide.

[0042] As outlined above, the electrically conductive support particles of step A-1) have a particle density of 1.2 g / cm3or more. Herein, the term "particle density” is defined as the relationship between the mass and volume of the material, including closed intraparticle spaces but excluding open intraparticle spaces. The particle density can240579W001 5

[0043] be determined by water pycnometry without comminution of the particles. Determining particle density by water pycnometry can be carried out as follows:

[0044] a) weighing a glass container having a graduation up to 500 mL,

[0045] b) filling the glass container with 130 mL of distilled water,

[0046] c) weighing the filled glass container,

[0047] d) determining the weight difference between the filled and empty glass container to obtain the weight of the filled water,

[0048] e) calculating the density of the filled water from the weight of the filled water divided by the volume of the filled water,

[0049] f) adding 80 g of electrically conductive support particles,

[0050] g) determining the weight gain and volume gain in the glass container,

[0051] h) calculating the particle density of the electrically conductive support particles from the determined weight gain divided by the determined volume gain.

[0052] In step f), make sure that the electrically conductive support particles are completely covered with the water added in step b). If not, the determination must be repeated with a larger amount of water to be added in step b).

[0053] In an embodiment, the electrically conductive support particles have a particle size D5o in the range of 1 to 50 mm, preferably 4 to 40 mm, more preferably 5 to 30 mm. Herein, D5o refers to the D5o (by volume) which corresponds to the 50thpercentile of the particle size distribution, meaning that 50% of the particles have a size of the D5O or smaller and 50% have a size larger than the D5o. The D5o can be determined using a Camsizer X2 device (available from Retsch Technology GmbH; Haan; Germany), according to, e.g. ISO 13322-2_2021.

[0054] Suitably, the electrically conductive support particles have a high value of sphericity. "Sphericity” is a measure of how closely the shape of an object, e.g. a particle, resembles that of a perfect sphere. Sphericity is defined as the ratio of surface area of a sphere that has the same volume as the particle or object to the surface area of the particle itself. Average sphericity can be measured, for example, using the Camsizer® image analysis system (Retsch Technology GmbH; Haan; Germany). The average sphericity is the volume average sphericity. In an embodiment, the electrically conductive support particles have a sphericity value of at least 0.6, preferably a sphericity value in the range of 0.6 to 1 , more preferably 0.7 to 1.

[0055] Step A-2)

[0056] Step A-2) involves allowing the support particles to flow downwardly under gravity flow as a particle bed through a cracking zone.

[0057] Suitably, the cracking zone is part of a reactor such as a moving-bed reactor. Thus, preferably, the inventive process is carried out in a moving-bed reactor. Generally, in a moving-bed reactor, a feed gas and solid material240579W001 6

[0058] particles flow in counter current throughout the reactor. Typically, the process comprises feeding solid material particles (herein, the electrically conductive support particles) to the cracking zone, preferably to the top of the cracking zone, and allowing the particles to flow downwardly under gravity flow as a compact column, which means that the movement of the moving bed is gravity driven.

[0059] For this purpose, the reactor is preferably a vertical elongated reactor. The particles are withdrawn from the reactor at the bottom of the reactor. Flow through the moving bed advantageously takes place homogeneously and uniformly (see for example WO 2013 / 004398, WO 2019 / 145279 and WO 2020 / 200522).

[0060] Suitably, the support particles are introduced via the top of the cracking zone, preferably having a temperature in the range of 10 to 200 °C.

[0061] The flow velocity of the support particles is advantageously in the range of 0.005 to 1.2 cm / s.

[0062] Step A-3)

[0063] Generally, thermal cracking is an endothermic reaction. The energy required to run the thermal cracking operation is provided by heat. Thus, step A-3) involves heating the support particles in the cracking zone to a temperature of at least 700 °C, preferably 700 to 1600 °C, by applying a voltage across the particle bed in the cracking zone.

[0064] In other words, the thermal energy provided to thermal cracking is provided by electrical heating. The use of electric energy as a heat source instead of heating by combustion of natural gas allows considerable advantages, in particular with regard to the ease of control. When the electricity comes from a non-fossil resource, the endothermic reaction can be implemented with negative emission of carbon dioxide.

[0065] Heating the support particles by resistive heating (Joule heating) is described in, e.g., US 2,982,622, WO 2019 / 145279 and WO 2020 / 200522. Step A-3) requires providing electrical power used for applying a voltage across the particle bed in the cracking zone for heating the electrically conductive support particles by direct electric resistance heating. In an embodiment, the voltage is applied through a plurality of electrodes that are in an electrically conductive relationship with the particle bed, e.g., immersed in the particle bed. Suitably, the electrodes are spaced apart along the axis of the reactor, wherein the spacing between the electrodes defines the cracking zone. Preferably, electrodes are employed that are spaced apart along the longitudinal axis of the reactor. The longitudinal axis of the reactor is preferably orientated vertically. Suitable electrode assemblies are described in, e.g., WO 2019 / 145279 A1.

[0066] The resistive thermal energy generated by passing a current through the particles may be supplemented by other heat sources. In embodiments, additional heat can be provided by preheating the feed gas to be flowed240579W001 7

[0067] through the particle bed (herein referred to as "cracker feed gas stream”; see step A-4) below). In still other embodiments, additional heat can be provided by inductive heating. Optionally, additional resistive heating elements may be used.

[0068] Generally, a refractory lining electrically and thermally insulates the moving particles from the reactor shell surrounding the cracking zone. Typically, refractory rocks advantageously comprising aluminum oxide, zirconium oxide and mixed oxides of aluminum, magnesium, chromium, silicon are used for the refractory lining.

[0069] The reactor may include an outer pressure jacket. For ease of assembly and disassembly, the pressure jacket is preferably split in sections with flanged ends that may be secured by bolts or the like to the flange of an adjacent section of the pressure jacket or the flange of the terminal hoods of the reactor.

[0070] Step A-4)

[0071] Step A-4) involves feeding a hydrocarbon-containing cracker feed gas stream through the cracking zone in counter current to the support particles flow, whereby thermal cracking of the cracker feed gas stream to form olefins, and concomitant deposition of carbon on the support particles occurs.

[0072] The hydrocarbon-containing cracker feed gas stream may originate from upstream refinery processes such as an atmospheric distillation tower, hydrocracker, coker etc. and typically contains naphtha, liquefied petroleum gas (LPG), ethane, propane and / or butane etc. In an embodiment, the hydrocarbon-containing cracker feed gas stream comprises natural gas, recyclate, bio-based gas, C2+-paraffins, naphtha, bio-naphtha, liquefied petroleum gas (LPG), or bio-liquefied petroleum gas (bio-LPG).

[0073] The term "natural gas” encompasses a naturally occurring mixture of gaseous hydrocarbons which primarily consists of methane in addition to small amounts of other higher alkanes such as ethane, propane etc.

[0074] The term "recyclate” encompasses pyrolysis oils obtained by pyrolysis of recycled plastic waste materials.

[0075] The term "bio-based gas” encompasses a mixture of gases, primarily consisting of methane besides carbon dioxide and hydrogen sulfide which is produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, food waste etc.

[0076] The term "C2+-paraffins” encompasses a mixture of saturated hydrocarbons containing two or more carbon atoms such as ethane, propane, butane etc.240579W001 8

[0077] The term "naphtha” encompasses liquid hydrocarbon mixtures produced from natural gas condensates, petroleum distillates, and the distillation of coal tar and peat. Naphtha typically comprises aliphatic and / or aromatic C5+-hydrocarbons.

[0078] The term "bio-naphtha” encompasses naphtha produced from complex mixtures of naturally occurring fats and oils.

[0079] The term "liquefied petroleum gas (LPG)” encompasses a fuel gas containing a flammable mixture of hydrocarbon gases, in particular propane and butane. Liquefied petroleum gas is prepared by refining petroleum or "wet” natural gas.

[0080] The term "bio-liquefied petroleum gas (bio-LPG)” encompasses liquefied petroleum gas produced from complex mixtures of naturally occurring fats and oils. Thus, bio-naphtha is a renewable source of energy.

[0081] Herein, the designator "Cx” refers to a hydrocarbon including x carbon atoms, "Cx+” refers to a hydrocarbon or mixture of hydrocarbons including x or greater carbon atoms, and "Cxminus” refers to a hydrocarbon of mixture of hydrocarbons including x or fewer carbon atoms.

[0082] Suitably, the cracker feed gas stream is introduced via the bottom of the cracking zone, preferably having a temperature in the range of 10 to 350 °C.

[0083] The support particles are maintained at the reaction temperature in the cracking zone. This heat is released and transferred to the cracker feed gas stream. Consequently, thermal cracking of the cracker feed gas stream to form olefins occurs. Concomitantly, carbon, e.g. in the form of coke, is formed. The formed carbon deposits on the support particles. Thus, during thermal cracking, an olefin-containing gas stream and support particles having carbon deposited thereon are formed.

[0084] The olefin-containing gas stream travels towards the top of the cracking zone, while being cooled down upon contact with cold fresh support particles.

[0085] In an embodiment, the method additionally comprises

[0086] successively guiding the electrically conductive support particles through a first heat integration zone located above the cracking zone, the cracking zone, and a second heat integration zone located below the cracking zone;

[0087] transferring heat from the product gas leaving the cracking zone to the particles in the first heat integration zone by direct heat transfer; and

[0088] transferring heat from electrically conductive support particles leaving the cracking zone to the hydrocarbon-containing cracker feed gas stream in the second heat integration zone.240579W001 9

[0089] Heat exchange in the heat integration zones can be optimized by varying the downward flow velocity of the support particles and / or the volume flow of the cracker feed gas stream to the reactor. The mass flow of solid and gas are adjusted to have the same heat capacity. With this measure heat is recovered and loss through hot gas / solid streams leaving the reactor are minimized.

[0090] As a consequence, the support particles are preheated by the outlet gas before entering the cracking zone and being heated. Likewise, the cracker feed gas stream is preheated by contact of the support particles having carbon deposited thereon leaving the cracking zone. Thus, the thermal energy may advantageously be stored in the particle bed to a high degree. Heat recovery rates of more than 95% of the sensible heat may be accomplished.

[0091] The gas residence time in the cracking zone is typically in the range of 0.05 to 10 s, preferably 0.1 to 5 s. The residence time of the support particles is typically in the range of 0.1 to 15 h, preferably 0.2 to 10 hours, more preferably 0.25 to 8 h.

[0092] As outlined above, the reaction is carried out at temperatures of at least 700 °C, preferably 700 to 1600 °C. The reaction is preferably carried out at pressures in the range of 1 to 20 bara, more preferably 1 to 15 bara.

[0093] The flow velocity of the cracker feed gas stream may be in the range of 0.025 to 2 m / s.

[0094] The cracking zone, e.g. in the moving-bed reactor, provides a very good heat transfer between the cracker feed gas stream and the support particles. In addition, there is no back-mixing, and the residence time can be controlled for both phases. The counter flow operation allows the energy integration of the reactor, and the excellent heat transfer between the cracker feed gas stream and the support particles guarantees a thermally efficient process.

[0095] Step A-5)

[0096] Step A-5) involves recovering the olefin-containing gas stream from the cracking zone. The olefin-containing gas stream is preferably recovered via the top of the cracking zone, preferably having a temperature in the range of 10 to 200 °C.

[0097] Step A-6)

[0098] Step A-6) involves withdrawing the support particles having carbon deposited thereon and directing them to a regeneration zone.240579W001 10

[0099] The support particles having carbon deposited thereon are preferably recovered via the bottom of the cracking zone, preferably having a temperature in the range of 10 to 200 °C. Withdrawing the support particles having carbon deposited thereon may be accomplished by conventional discharge means, e.g., by a cellular wheel sluice.

[0100] The withdrawn support particles having carbon deposited thereon are subsequently directed to a regeneration zone. The regeneration zone and the cracking zone may be located in the same reactor. Alternatively and preferably, the regeneration zone and the cracking zone are configured as separate reactors.

[0101] Suitably, the regeneration zone is part of a reactor, preferably of a moving-bed reactor, as analogously described above for step A-2).

[0102] Step B-1)

[0103] Step B-1) involves allowing the support particles having carbon deposited thereon to flow downwardly under gravity flow as a particle bed through the regeneration zone.

[0104] Suitably, the regeneration zone is part of a reactor such as a moving-bed reactor. Thus, preferably, regeneration is carried out in a moving-bed reactor. Generally, in a moving-bed reactor, a feed gas and solid material particles flow in counter current throughout the reactor. Typically, the process comprises feeding solid material particles (herein, the support particles having carbon deposited thereon) to the regeneration zone, preferably to the top of the regeneration zone, and allowing the particles to flow downwardly under gravity flow as a compact column, which means that the movement of the moving bed is gravity driven.

[0105] For this purpose, the reactor is preferably a vertical elongated reactor. The particles are withdrawn from the reactor at the bottom of the reactor. Flow through the moving bed advantageously takes place homogeneously and uniformly (see for example WO 2013 / 004398, WO 2019 / 145279 and WO 2020 / 200522).

[0106] Suitably, the support particles having carbon deposited thereon are introduced via the top of the regeneration zone, preferably having a temperature in the range of 10 to 200 °C.

[0107] The flow velocity of the support particles having carbon deposited thereon is advantageously in the range of 0.005 to 1.2 cm / s.240579W001 11

[0108] Step B-2)

[0109] Step B-2) involves heating the support particles having carbon deposited thereon in the reaction zone to a temperature of at least 900 °C, preferably in the range of 900 to 1400 °C by applying a voltage across the particle bed in the regeneration zone.

[0110] "Applying a voltage across the particle bed in the regeneration zone” can be realized by providing direct electric resistance heating, as described in detail above regarding step A- 3). The embodiments outlined in step A- 3) apply analogously.

[0111] Step B-3)

[0112] Step B-3) involves feeding a gaseous regeneration stream comprising a species selected from carbon dioxide and steam through the regeneration zone in counter current to the support particles flow, whereby regenerated particles are obtained.

[0113] Suitably, the gaseous regeneration stream comprising a species selected from carbon dioxide and steam is introduced via the bottom of the regeneration zone, preferably having a temperature in the range of 10 to 200 °C.

[0114] By feeding a gaseous regeneration stream comprising carbon dioxide, regeneration occurs via the Boudouard reaction:

[0115] C + CO2^ 2CO

[0116] In the Boudouard reaction, two equivalents of carbon monoxide are formed from one equivalent of carbon dioxide (gas) and one equivalent of carbon (solid). Solid carbon is consumed in the Boudouard reaction. The Boudouard reaction is endothermic with a reaction enthalpy of AH0= +172.5 kJ / mol. The Boudouard reaction is typically carried out with little or no oxygen present. Advantageously, the Boudouard reaction serves as a CO2sink, thus allowing for reducing the carbon footprint of the technology. The formed CO can be utilized as a starting material for various reactions.

[0117] Additionally or alternatively, by feeding a gaseous regeneration stream comprising steam, regeneration occurs via the reverse Bosch reaction:

[0118] C + 2H2O — > C02+2H2240579W001 12

[0119] In the reverse Bosch reaction, carbon and two equivalents of steam are converted to carbon dioxide and hydrogen. Solid carbon is consumed in the reverse Bosch reaction. The reverse Bosch reaction is endothermic with a reaction enthalpy of AH0= +90.1 kJ / mol. The reverse Bosch reaction is typically carried out with little or no oxygen present. The mixture of carbon dioxide and hydrogen may be separated. In this case, hydrogen can be used as, e.g., source of energy. The mixture of carbon dioxide and hydrogen may also be subjected to a water-gas shift reaction:

[0120] CO2+ H2-+ CO + H2O

[0121] The formed CO can be utilized as a starting material for various reactions.

[0122] As shown above, both the Boudouard reaction and the reverse Bosch reaction consume carbon, in the present case carbon deposited on the support particles obtained as described above. As a result, regenerated particles are obtained. In other words, in comparison to the support particles having carbon deposited thereon, the regenerated particles are carbon-depleted. Additionally, a regeneration product stream comprising carbon monoxide if the gaseous regeneration stream comprises carbon dioxide (from the Boudouard reaction) or carbon dioxide if the gaseous regeneration stream comprises steam (from the reverse Bosch reaction) is obtained.

[0123] Generally, the gas residence time in the regeneration zone is typically in the range of 0.5 to 50 s, preferably 1 to 10 s. The residence time of the support particles is typically in the range of 0.2 to 15 h, preferably 0.2 to 10 hours, more preferably 0.2 to 8 h.

[0124] As outlined above, the reaction is carried out at temperatures of at least 900 °C, preferably 900 to 1400 °C. The reaction is preferably carried out at pressures in the range of 1 to 20 bara, more preferably 1 to 15 bara.

[0125] The flow velocity of the gaseous regeneration stream may be in the range of 0.025 to 10 m / s.

[0126] Step B-4)

[0127] Step B-4) involves withdrawing a regeneration product stream from the regeneration zone. The regeneration product stream is preferably recovered via the top of the regeneration zone, preferably having a temperature in the range of 10 to 200 °C.

[0128] Step B-5)

[0129] Step B-5) involves withdrawing the regenerated particles from the regeneration zone and at least partially directing them as electrically conductive support particles to the cracking zone.240579W001 13

[0130] The regenerated particles are preferably recovered via the bottom of the regeneration zone, preferably having a temperature in the range of 10 to 200 °C. Withdrawing the regenerated particles may be accomplished by conventional discharge means, e.g., by a cellular wheel sluice.

[0131] The withdrawn regenerated particles are subsequently at least partially directed as electrically conductive support particles to the cracking zone (recycling), i.e. to step A-2) as described above.

[0132] In an embodiment, the hydrocarbon-containing cracker feed gas stream comprises a diluent gas. A diluent gas is a gas that is inert under the conditions encountered in the reactor, in particular does not take part in thermal cracking and / or the Boudouard reaction and / or the reverse Bosch reaction and does not give rise to side reactions. A suitable diluent gas is selected from hydrogen, methane and nitrogen. Incorporation of a diluent gas allows for further variation of the heat capacity of the gas stream.

[0133] When a diluent gas is used, the mass ratio of the diluent gas to the cracker feed gas stream may be in the range of 0 to 0.8.

[0134] In an embodiment, the volume flow of the cracker feed gas stream, the proportion of diluent gas and / or the support particle mass flow are selected such that the olefin-containing gas stream leaves the first heat integration zone at a temperature below 200 °C, such as below 40 °C, and / or the particles leave the second heat integration zone at a temperature of below 200 °C, such as below 100 °C.

Claims

240579W001 14Claims1. A method for thermal cracking of hydrocarbons, comprisingA-1) providing electrically conductive support particles having a particle density of 1.2 g / cm3or more, A-2) allowing the support particles to flow downwardly under gravity flow as a particle bed as a compact column through a cracking zone;A- 3) heating the support particles in the cracking zone to a temperature of at least 700 °C, preferably 700 to 1600 °C, by applying a voltage across the particle bed in the cracking zone; A-4) feeding a hydrocarbon-containing cracker feed gas stream through the cracking zone in counter current to the support particles flow, whereby thermal cracking of the cracker feed gas stream to form olefins, and concomitant deposition of carbon on the support particles occurs; A- 5) recovering an olefin-containing gas stream from the cracking zone;A-6) withdrawing the support particles having carbon deposited thereon and directing them to a regeneration zone;B-1) allowing the support particles having carbon deposited thereon to flow downwardly under gravity flow as a particle bed through the regeneration zone;B-2) heating the support particles having carbon deposited thereon in the reaction zone to a temperature of at least 900 °C, preferably in the range of from 900 to 1400 °C by applying a voltage across the particle bed in the regeneration zone;B-3) feeding a gaseous regeneration stream comprising a species selected from carbon dioxide and steam through the regeneration zone in counter current to the support particles flow, whereby regenerated particles are obtained;B-4) withdrawing a regeneration product stream from the regeneration zone; andB-5) withdrawing the regenerated particles from the regeneration zone and at least partially directing them as electrically conductive support particles to the cracking zone.

2. The method according to claim 1 , wherein the voltage is applied through a plurality of electrodes that are in an electrically conductive relationship with the particle bed.

3. The method according to claim 1 or 2, wherein the electrically conductive support particles have a particle size D5o in the range of from 1 to 50 mm, preferably 4 to 40 mm, more preferably 5 to 30 mm.

4. The method according to any one of the preceding claims, wherein the electrically conductive support particles have a sphericity value of at least 0.6.

5. The method according to any one of the preceding claims, wherein the electrically conductive support particles are constituted from a material selected from carbon, aluminum oxide, titanium oxide, silicon carbide, and zirconium carbide.240579W001 156. The method according to any one of the preceding claims, wherein the electrically conductive support particles comprise a material with no or limited electrical conductivity which is doped with an electrically conductive material.

7. The method according to claim 6, wherein the electrically conductive material is selected from carbon, aluminum, iron, nickel, copper, palladium and platinum.

8. The method according to any one of the preceding claims, wherein the electrically conductive support particles comprise a core, and a shell surrounding the core.

9. The method according to claim 8, wherein the material constituting the core comprises aluminum oxide, and the material constituting the shell comprises carbon.

10. The method according to any one of the preceding claims, wherein the hydrocarbon-containing cracker feed gas stream comprises natural gas, recyclate, bio-based gas, C2+-paraffins, naphtha, bio-naphtha, liquefied petroleum gas (LPG), or bio-liquefied petroleum gas (bio-LPG).

11. The method according to any one of the preceding claims, wherein the hydrocarbon-containing cracker feed gas stream comprises a diluent gas.

12. The method according to any one of the preceding claims, additionally comprisingsuccessively guiding the electrically conductive support particles through a first heat integration zone located above the cracking zone, the cracking zone, and a second heat integration zone located below the cracking zone;transferring heat from the product gas leaving the cracking zone to the particles in the first heat integration zone by direct heat transfer; andtransferring heat from electrically conductive support particles leaving the cracking zone to the hydrocarbon-containing cracker feed gas stream in the second heat integration zone.