NL2016236B1

NL2016236B1 - Process and system for the production of olefins.

Info

Publication number: NL2016236B1
Application number: NL2016236A
Authority: NL
Inventors: Motelica Anatolie; Wilco Dijkstra Jan; Alouisius Zacharias Pieterse Johannis
Original assignee: Stichting Energieonderzoek Centrum Nederland
Priority date: 2016-02-08
Filing date: 2016-02-08
Publication date: 2017-08-14

Abstract

The invention relates to a process and system for the production of olefins via cracking of a feedstock comprising saturated hydrocarbons, wherein hydrogen gas separated from the cracking product stream is used in combination with CO2, which may or may not originate as by-product from the process itself, for the production of further olefins via a CO2 hydrogenation reaction. The secondary product stream of the CO2 hydrogenation reaction is conveniently combined with the main product stream of the cracker, as such enabling isolation of all olefins in a single step. The process according to the invention affords an improved yield of olefins from the same amount of naphtha, compared to conventional cracking processes.

Description

Process and system for the production of olefins [0001] The present invention relates to an improved process for the production of olefins from a feedstock typically comprising naphtha. In other words, the process according to the invention is an improved cracking process. The invention also relates to a system for executing the process according to the invention.

Background [0002] Steam cracking is the present-day standard for the production of light olefins such as ethene and propene from mainly naphtha, although other feedstocks may also be used. Naphtha is a mixture of mainly C5-10 hydrocarbons which are largely saturated although traces of unsaturated hydrocarbons may also be present. It is obtained from the distillation of crude oil. Gas oil, a heavier fraction of crude oil distillation mainly containing C14-20 hydrocarbons, may also be used in the formation of olefins by steam cracking, although its use as feedstock is less frequent in view of its lower olefin yield and increased formation of aromatic compounds. Moreover, gas oil is less readily available and more expensive to use, compared to naphtha. The use of ethane and propane, obtained from e.g. shale gas, in olefins production has increased over the last years given the increase in shale gas exploration. Depending on the feedstock, the composition of the product stream may vary (see Table 1). Although pure ethane as feedstock provides the highest yield of olefins, in particular ethane, ethane is only marginally available as feedstock. Mostly, naphtha or gas oil is used.

[0003] Table 1: Typical product composition (in wt%) for various cracking feedstocks.

Source = Petroleum processes Volume 1, A. Chauvel and G. Lefebrve, Institut Franqais du Petrole Publications, 1989 * diene = buta-1,3-diene; RPG = raw pyrolysis gasoline.

[0004] Light olefins such as ethene and propene are of huge industrial importance as they are the monomers used in for the production of plastics (polyethylene (PE) and polypropylene (PP)). While the demand for light olefins is continuously increasing, the availability of feedstocks like naphtha and gas oil (both obtained from crude oil) is gradually decreasing. The availability of olefins obtained from renewable source is still very limited, and mankind will remain dependent on non-renewable feedstocks to fulfil the demand of olefins. So, there is an urgent need in the art to increase the efficiency of conventional cracking processes in order to increase the yield of the olefins obtainable from non-renewable feedstocks such as naphtha. The present invention provides in this need.

Summary of the invention [0005] The invention relates to an improved process for the production of olefins by cracking a feedstock typically comprising naphtha. In the improved cracking process according to the invention, the yield of olefins is increased compared to prior art processes. The invention resides in the conversion of CO and/or CO2 with H2, obtained as by-products in conventional cracking processes, to olefins. CO and/or CO2 is used as source of carbon, which preferably originates from the off-gas of the furnace which is used to heat the feedstock during cracking thereof. The H2 that is used herein originates from the cracking product mixture itself. As such, compounds that are usually discharged from the process and/or merely used as fuel, are now converted to useful olefins. In case imported CO2 is used, the hydrogen feed, which is normally for a large part combusted, is used for manufacturing additional quantities of the primary products, rather than used for lower-value heating purposes, for which it can easily be replaced with more abundant and inexpensive alternative fuels such as natural gas. The invention also relates to a system for executing the process according to the invention.

[0006] The process according to the invention affords the same amount of olefins from a reduced amount of feedstock, in particular from naphtha, compared to conventional cracking process. The inventors have shown that the amount of naphtha needed in order to obtain the same amount of olefins could be reduced by 13 wt%. Advantageously, the inventive concept of the process according to the present invention, i.e. the conversion of H2 and carbon oxides species into additional olefins, is readily implemented in existing cracking process, which thus enables easy improvement of existing cracking plants.

Preferred embodiments 1. A process for the production of olefins from a feedstock comprising saturated hydrocarbons, comprising: (a) subjecting the feedstock to cracking to obtain a main product stream comprising olefins and H2; (b) separating H2 from the main product stream; (c) contacting the H2 obtained in step (b) and a carbon oxide species selected from CO2, CO and a mixture thereof, to a catalyst capable of converting H2 and CO and/or CO2 into olefins, to obtain a secondary product stream comprising olefins; (d) combining the main product stream obtained in step (a) or in step (b) and the secondary product stream obtained in step (c); and (e) isolating olefins from the main product stream obtained in step (d). 2. The process according to embodiment 1, further comprising a step (vi) of converting CO2 to CO by a reverse water gas shift reaction, wherein the carbon oxide species used in step (c) comprises CO obtained in step (vi). 3. The process according to embodiment 1 or 2, wherein the carbon oxide species used in step (c) and/or in step (vi) comprises CO2 at least partly originating as a by-product from the process according the embodiment 1, preferably from step (a). 4. The process according to embodiment 3, further comprising a step (vii) of separating CO2 from an off-gas comprising CO2 originating from burning of fuel during step (a), wherein at least part of the CO2 obtained in step (vii) is used in step (c) and/or in step (vi), optionally supplemented with carbon oxide species from an external source. 5. The process according to any of the preceding embodiments, wherein at least part of the carbon oxide species used in step (c) and/or in step (vi) originates from an external source. 6. The process according to any one of the preceding embodiments, wherein step (d) occurs upstream of step (b). 7. The process according to any one of the preceding embodiments, wherein the feedstock comprises naphtha, gas oil, ethane and/or propane, preferably naphtha. 8. The process according to any one of the preceding embodiments, wherein the secondary product stream obtained in step (c) is subjected to one or more steps selected from an acid gas removal step, a primary fractionation to remove a heavy fraction from the secondary product stream, a water quench to remove a heavy fraction from the secondary product stream, a compression step, a H2 removal step and a water removal step before it is used in step (d). 9. The process according to embodiment 8, wherein the secondary product stream obtained in step (c) is subjected to a CO2 removal step (viii), wherein CO2 is separated from the secondary product stream prior to being subjected to step (d). 10. The process according to any one of the preceding embodiments, further comprising: (i) subjecting the main product stream obtained in (a) to primary fractionation to obtain a first heavy fraction and a main product stream from which a first heavy fraction is removed; (ii) subjecting the main product stream obtained in step (i) to a water quench to obtain a second heavy fraction and a main product stream from which a second heavy fraction is removed; (iii) subjecting the main product stream obtained in step (ii) to a first compression step to obtain a compressed main product stream; (iv) subjecting the main product stream obtained in step (iii) to an acid gas removal step to obtain a main product stream from which acid gas is removed; (iii’) subjecting the main product stream obtained in step (iv) to a second compression step to obtain a compressed main product stream; and (v) subjecting the main product stream originating from step (iii’) to a water removal step to obtain a dried main product stream; wherein the main product stream obtained in step (v) is used in step (b). 11. The process according to embodiment 10, wherein step (d) occurs in between step (iii’) and step (v) and wherein the main product stream obtained in step (iii’) is subjected to step (d) and the main product stream obtained in step (d) is used in step (v). 12. The process according to any one of the preceding embodiments, wherein the catalyst is selected from the group consisting of Fischer-Tropsch type of catalysts, CO2 hydrogenation catalysts and reverse water gas shift/Fischer-Tropsch catalysts, preferably the catalyst is an Fe-based Fischer-Tropsch catalyst or Fe-based CO2 hydrogenation catalyst. 13. The process according to any one of the preceding embodiments, further comprising, between steps (b) and (e), a step (ix) of removing methane from the main product stream. 14. The process according to any one of the preceding embodiments, wherein step (e) involves a series of steps comprising deethanisation coupled to a C2-splitter, depropanisation coupled to a C3-splitter and debutanisation. 15. A modular system suitable for carrying out the process according to any one of embodiments 1-14, comprising: (a) a cracking reactor, comprising (al) an inlet for receiving a feedstock comprising saturated hydrocarbons, (a2) an outlet for discharging a main product stream and (a3) a furnace designed to combust fuel to heat the cracking reactor, wherein the furnace comprises (a4) an inlet for receiving fuel and (a5) an outlet for discharging an off-gas; (b) an H2 separation module, comprising (bl) an inlet for receiving the main product stream, (b2) means for separating H2 from the main product stream, (b3) a first outlet for discharging H2 and (b4) a second outlet for discharging a main product stream from which H2 is removed; (c) a CO2 hydrogenation reactor, comprising (cl) one or more inlets for receiving the H2 originating from module (b) and carbon oxide species selected from CO2, CO and a mixture thereof, (c2) a catalyst capable of converting H2 and CO and/or CO2 into olefins, and (c3) an outlet for discharging a secondary product stream comprising olefins; (d) a combining module, comprising (dl) a first inlet for receiving the main product stream, (d2) a second inlet for receiving the secondary product stream and (d3) an outlet for discharging a main product stream; (e) an olefin isolation module, comprising (el) an inlet for receiving the main product stream, (e2) means for isolating olefins from the main product stream, and (e3) one or more outlets for discharging olefins.

Detailed description [0007] The present invention relates to an improved process for the production of olefins by cracking of a feedstock comprising saturated hydrocarbons, typically naphtha. The inventors surprisingly found that the efficiency of the cracking process can be significantly increased by conversion of H2 and preferably CO2, formed as by-products of the cracking process, to olefins in order to increase the total yield of olefins from the saturated hydrocarbon feedstock. In a second aspect, the invention relates to a system for executing the process according to the invention. According to the invention, H2 that is typically separated from the cracking product stream, is fed to a catalyst which is capable of converting the H2 and CO and/or CO2 to olefins.

THE PROCESS

[0008] The process according to the invention comprises: (a) subjecting the feedstock to cracking to obtain a main product stream comprising olefins and H2; (b) separating H2 from the main product stream; (c) contacting the H2 obtained in step (b) and carbon oxide species selected from CO2, CO and a mixture thereof, to a catalyst capable of converting H2 and CO and/or CO2 into olefins, to obtain a secondary product stream comprising olefins; (d) combining the secondary product stream with the main product stream prior to or after step (b); and (e) isolating olefins from the main product stream originating from step (d).

[0009] The process according to the invention results in the production of olefins from a feedstock comprising saturated hydrocarbons. In the art, the entire process from the actual cracking of the feedstock to the isolation of the olefins is referred to as a cracking process. The process according to the invention may this also be referred to as a “cracking process” or a process for “cracking the feedstock”. Typically, the present process is a steam cracking process. The olefins produced by the process according to the invention are the olefins that are obtained from a conventional cracking process. In the context of the present invention, the term “olefins” refers to unsaturated hydrocarbons, typically C1-6 alkenes, preferably Cm alkenes. The olefins typically include ethene and propene, although higher olefins such as isomers of butene and butadiene may also be formed. Preferably, the process according to the invention is for the production of ethene and/or propene, most preferably ethene and propene.

[0010] In the context of the present invention, the “main product stream” designates the product stream which comprises the olefins formed during the cracking of step (a) and optionally (downstream of step (d)) the olefins formed during the contacting of step (c), while the “secondary product stream” designates the product stream which comprises the olefins formed during the contacting of step (c), but not the olefins formed during the cracking of step (a). The designation of the product stream is irrespective of any separation of by-products, i.e. products not being olefins. Thus, upon the combining of step (d), the combined stream, comprising both the olefins formed during the cracking of step (a) and the olefins formed during the contacting of step (c), is referred to as the main product stream. In the context of the present invention, “downstream” and “upstream” are used to define the location of a certain step compared to another step with respect to the main product stream. Thus in case step (d) occurs upstream of step (b), the main product stream is first subjected to step (d) and then to step (b). Likewise, whenever a product stream is mentioned to “originate from” a certain step, it may indicate that the product stream is directly obtained by said step, or that the product stream is subjected to one or more further steps after said step.

[0011] Preferably, the process according to the invention is a continuous process. Thus, a main product stream is generated in step (a) as a continuous stream. Downstream of the cracking step (a) H2 is separated from the main product stream in step (b), and downstream of the H2 separation step (b) olefins are isolated from the main product stream in step (e). In between step (a) and (e), i.e. downstream of step (a) and upstream of step (e), the main product stream is combined in step (d) with a secondary product stream, which comprises olefins that are formed in step (c) with the H2 which is separated in step (b). The combining of step (d) may occur either downstream of step (b) or upstream of step (b), preferably it occurs upstream of step (b), such that the main product stream comprising both the olefins formed during the cracking of step (a) and the olefins formed during the contacting of step (c) is subjected to hydrogen separation step (b). As such, the conventional cracking process, which involves steps (a), (b) and (e) is optimized by inclusion of a loop comprising steps (c) and (d). This improvement in the cracking process may be referred to as a loop, since a component, H2, is taken from the product stream and, after conversion into valuable olefins, recycled back to the product stream. As such, the step (e) of olefin isolation effectively isolates both the olefins formed during the cracking of step (a) and during the contacting of step (c).

[0012] In the process according to the invention, the order of steps (b) and (d) is reversible, although it is preferred that step (d) occurs upstream of step (b). Thus, in one embodiment, step (d) occurs downstream of step (b) and the process according to the invention comprises the steps of: (a) subjecting the feedstock to cracking to obtain a main product stream comprising olefins and H2; (b) separating H2 from the main product stream; (c) contacting the H2 obtained in step (b) and carbon oxide species selected from CO2, CO and a mixture thereof, to a catalyst capable of converting H2 and CO and/or CO2 into olefins, to obtain a secondary product stream comprising olefins; (d) combining the secondary product stream with the main product stream originating from step (b); and (e) isolating olefins from the main product stream originating from step (d).

[0013] Thus, in a more preferred embodiment, step (d) occurs upstream of step (b) and the process according to the invention comprises the steps of: (a) subjecting the feedstock to cracking to obtain a main product stream comprising olefins and H2; (b) separating H2 from the main product stream originating from step (d); (c) contacting the H2 obtained in step (b) and carbon oxide species selected from CO2, CO and a mixture thereof, to a catalyst capable of converting H2 and CO and/or CO2 into olefins, to obtain a secondary product stream comprising olefins; (d) combining the secondary product stream with the main product stream originating from step (a); and (e) isolating olefins from the main product stream originating from step (b).

[0014] Although any feedstock known to be suitable in a cracking process may be used, the feedstock is preferably comprises one or more selected from the group consisting of naphtha, liquefied petroleum gas (LPG), gasoline, natural gas, fuel oil, pyrolysis oil or pyrolysis gas from e.g. biomass pyrolysis or coal pyrolysis, associated gas from natural gas production or shale gas production and saturated hydrocarbons originating as byproduct from a cracking process. Most preferably, the feedstock comprises naphtha. Typically, the feedstock includes an external feedstock, such as naphtha, to which saturated hydrocarbons formed as by-product in the cracking process itself and isolated from the main product stream (i.e. an internal feedstock) are added. The recycle of such saturated hydrocarbons to the cracking reactor is common in the art and improves the yield of olefins obtainable from the external feedstock. The saturated hydrocarbons comprised in the feedstock typically are C1-10 hydrocarbons. The preferred external feedstock naphtha mainly contains C5-10 hydrocarbons, while the internal feedstock mainly contains Cm hydrocarbons, such as ethane, propane and butane.

Step (a) [0015] During step (a), a conventional cracking process is performed, wherein a feedstock comprising saturated hydrocarbons is subjected to cracking. Step (a) may also be referred to as steam cracking. Such a cracking process is well-known in the art, and the present invention covers all known variants and alternatives thereof. Any cracking reactor known in the art may be used. Cracking is typically performed at a temperature of 500 - 1000 °C, preferably 600 - 850 °C, and at a pressure of 0.2 - 10 bar, preferably 1-3 bar. Such elevated temperatures are typically provided and maintained by furnaces wherein fuel is burned. The fuel typically comprises methane (e.g. natural gas or pure methane), although other fuels may be equally effective in maintaining the temperature. It is preferred that the fuel used in the furnace during step (a) is not mixed with Fb or, in other words, does not comprise an added source of Fb, since the Fb which may mixed with the fuel in conventional cracking processes typically originates from the cracking process as a by-product, while the present invention relates to the use of that H2 byproduct for enhancing the olefin yield. The off-gas of the furnace typically contains CO2 and H2O. At such temperatures and pressures the splitting of large hydrocarbons into smaller ones is favoured. Typically, steam is present to decrease the partial pressure of reactor products and prevent deposition of solid carbon (coke) on the walls. Reaction times are typically very short. Feedstock fluids usually reside in the cracking reactor for 0.01-1 s, preferably 0.1 - 0.5 s, after which the product mixture is discharged from the cracking reactor as the main product stream.

[0016] The cracking of step (a) results in a main product stream, which is the typical product mixture as directly obtained from a cracking step. It comprises olefins and H2 and usually further components such as heavy fractions comprising RPG (raw pyrolysis gasoline) and/or FO (fuel oil), acid gases such as CO2 and/or H2S, methane and saturated hydrocarbons (e.g. methane, ethane, propane, etc.). The olefins comprised in the main product stream are the olefins that are obtained from a conventional cracking process, preferably ethene and/or propene.

[0017] Preferably, the main product stream that is discharged from the cracker reactor is cooled rapidly from the cracking temperature as defined above to a temperature of below 350 °C, preferably to a temperature of 200 - 300 °C. Such rapid cooling avoids further reaction of the formed products to e.g. solid carbon (quenching) and is typically accomplished by subjecting the main product stream to a transfer line heat exchanger and/or a quenching header using quenching oil. The main product stream may preferably undergo one or more further treatment steps prior to being subjected to step (b). Such optional further treatment steps are common for cracker product streams, and preferably at least one further treatment step selected from a primary fractionation, a water quench, one or more compression steps, acid gas removal and water removal is performed prior to step (b). Primary fractionation (step (i)) usually involves an oil quench wherein a first heavy fraction which typically includes fuel oil is separated from the main product stream.

[0018] The main product stream when leaving the primary fractionation usually has a temperature of 80 - 125 °C, preferably about 100 °C, which is further lowered to typically 30 - 50 °C, preferably about 40 °C, during a water quench (step (ii)). In step (ii), the gaseous main product stream is mixed with liquid water to separate a second heavy fraction, typically including RPG, from the main product stream. Usually, the main product stream, from which the first and second heavy fractions are removed, is compressed in a first compression step (step (iii)). During compression the temperature preferably does not exceed 75 °C, as higher temperatures promote the oligomerisation of double unsaturated olefins such as butadiene. The process according to the invention preferably comprises two compression steps, between which a further step, preferably an acid gas removal step, may be performed. The one or more compression step(s) (iii) typically compress the main product stream to a pressure of 20 - 50 bar, preferably 30 -40 bar.

[0019] After the compression step(s) or between the first and second compression step, acid gases are typically removed from the main product stream (step (iv)). Acid gas removal may be accomplished by a caustic wash or by amine scrubbing, preferably by a caustic wash. Acid gases that are removed typically include CO2 and H2S. Water is typically removed from the main product stream in a drying step (v), usually after the acid gas removal, more preferably after a second compression step (iii’). Water removal may be accomplished by any means known in art, such as cooling down the stream resulting in water condensation, followed by water-knockout, and subsequently contacting the main product stream with a water-selective adsorbent, preferably with molecular sieves. Water removal step (v) is especially preferred in case step (b) of the process according to the invention is performed by chilling, wherein the main product stream is chilled to temperatures below -150 °C, such as between -200 °C and -160 °C, as otherwise ice formation would hamper the separation of step (b). In a preferred embodiment of the process according to the invention, step (d) is performed upstream of step (b), more preferably upstream of step (v). Herein, the main product stream subjected to water removal in step (v) is the main product stream originating from step (d). Using this preferred order of steps, any water molecules that may be present in the secondary product stream are, after being combined with the main product stream in step (d), also removed in step (v).

[0020] In a particularly preferred embodiment, the following steps are performed between step (a) and step (b): (i) subjecting the main product stream to primary fractionation to obtain a first heavy fraction and a main product stream from which a first heavy fraction is removed; (ii) subjecting the main product stream originating from step (i) to a water quench to obtain a second heavy fraction and a main product stream from which a second heavy fraction is removed; (iii) subjecting the main product stream originating from step (ii) to a first compression step to obtain a compressed main product stream; and (iv) subjecting the compressed main product stream originating from step (iii) to an acid gas removal step to obtain a main product stream from which CO2 and H2S are removed. (iii’) subjecting the main product stream originating from step (iv) to a second compression step to obtain a compressed main product stream; and (v) subjecting the main product stream originating from step (iii’), preferably from step (d), to a water removal step to obtain a dried main product stream.

Herein, the dried main product stream originating from step (v) is the main product stream to be used in step (b) or (d), preferably in step (b). It is especially preferred that the main product stream originating from step (iii’) is the main product stream to be used in step (d), and the main product stream originating from step (d) which is combined with the secondary product stream is the main product stream to be used in step (v).

Step (b) [0021] During step (b), H2 is separated from the main product stream. The separation of H2 from a cracker reaction product stream is well-known in the art, and any means suitable to separate H2 may be used in step (b). Most preferably, step (b) is performed by chilling the main product gas. Conveniently, the main product stream has a pressure of 20-50 bar, preferably 30-40 bar when subjected to step (b). At such pressure, chilling the main product gas to a temperature of below -150 °C, such as between -200 °C and -160 °C, results in condensation of all species present in the main product gas except H2, which remains gaseous. Such chilling typically occurs in a cold box, wherein external refrigeration loops enable such low temperatures. Alternative methods, such as hydrogen selective membranes or electrochemical hydrogen compression, may also be used. Hydrogen selective membranes could be of any type known in the art, including polymeric membranes, porous nanofiltration membranes, metallic membranes or metal-ceramic membranes such as supported Pd-alloy membranes. Electrochemical hydrogen compression combines selective separation of hydrogen with compression (see e.g. Bouwman, in PEM Electrolysis for hydrogen production (Ed. Bessarabov et al.), Ch. 13: Fundamentals of Electrochemical Elydrogen Compression).

[0022] Step (b) is thus performed downstream of step (a) and upstream of step (e). The main product stream obtained in step (b), from which H2 is removed, is thus fed to step (e). Step (d) may be performed in between step (a) and step (b), or between step (b) and step (e). In case step (d) is performed in between step (a) and step (b), the main product stream originating from step (d), which is combined with the secondary product stream, is used as feed stream of step (b) and the main product stream from which H2 is removed, originating from step (b), is used as a feed stream for step (e). In case step (d) is performed between step (b) and step (e), the main product stream originating from step (a), is used as a feed stream of step (b) and the main product stream from which H2 is removed, originating from step (b), is used as main product feed stream for step (d). Preferably, step (d) is performed between step (a) and step (b), and the main product stream used as feed stream in step (b) is the main product stream originating from step (d), which is combined with the secondary product stream. Using this preferred order of steps, any remaining H2 in the secondary stream is removed in step (b), after combining the secondary stream with the main product stream in step (d).

[0023] Step (b) affords gaseous hydrogen and a main product stream from which hydrogen has been removed. Typically, at least 80 wt% of the H2 present in the main product gas as obtained in step (a), preferably at least 90 wt%, more preferably at least 95 wt%, most preferably substantially all H2, is removed during step (b). The hydrogen obtained in step (b) is typically at least 90 wt% pure (i.e. less than 10 wt% impurities), or at least 99 wt% pure or even at least 99.9 wt% pure. The hydrogen is led to step (c), while the main product stream from which hydrogen is removed is led to step (d) or (e). Minor amounts of CO may be present in the main product stream originating from step (a). Depending on the conditions at which step (b) is performed, the CO may also be separated together with the H2, and is thus comprised in the gaseous hydrogen stream originating from step (b) that is led to step (c), which slightly reduces the amount of the carbon oxide species that needs to be added to the feed gas of step (c). This is especially the case when chilling is used in step (b).

Step (c) [0024] The implementation of step (c) is a major improvement over prior art cracking processes. Herein, the H2 obtained in step (b) is used to prepare further olefins, instead of using the H2 as fuel for the cracking process or collecting the hydrogen as a by-product of the cracking process. In step (c), H2 and CO2 and/or CO are converted into monounsaturated olefins, by catalytic CO2 hydrogenation. The overall reaction is as follows:

(1)

Herein, n = 2 for ethene as olefin, n = 3 for propene as olefin and n = 4 for butane as olefin. Likewise, x = 1 for CO as carbon species, x = 2 for CO2 as carbon species, while x is between 1 and 2 for mixtures of CO and CO2. Generally, x = [CO] + 2[C02]. Herein, [CO] is the molar fraction of CO in the mixture and [CO2] is the molar fraction of CO2 in the mixture. For pure CO as carbon species (x = 1), the overall reaction is given in reaction (2) , and for pure CO2 as carbon species (x = 2), the overall reaction is given in reaction

(3) : (2) (3) [0025] In the feed gas of step (c), the molar ratio of H2 to carbon oxide species is typically in the range of 1:1 to 5:1. For CO as carbon oxide species, the ideal H2 to carbon oxide species molar ratio is 2:1, while for CO2 as carbon oxide species, the ideal H2 to carbon oxide species molar ratio is 3:1. For mixtures of CO and CO2, an intermediate ratio is ideal. For a given value of x, the ideal H2 to carbon oxide species molar ratio is (1 + x). It should be noted that some deviation from this ideal ratio is allowable without significantly affected the effectiveness of the process according to the invention. Thus, the H2 to carbon oxide species molar ratio is preferably in the range of (0.5 + x) to (2 + x), more preferably in the range of (0.8 + x) to (1.5 + x), most preferably about (1 + x). Since the feed gas for step (c) is conveniently prepared by mixing the H2 originating from step (b) with an appropriate source of carbon oxide species, the molar ratio between H2 and carbon oxide species easily set to the desired value by adjusting the amount of each of the two reactant streams that are mixed. Thus, in a preferred embodiment, step (c) includes the mixing of the H2 originating from step (b) (first reactant stream) and a composition comprising the carbon oxide species (second reactant stream). Typically both reactant streams are gases. Preferably, the mixing is performed such that the ratio of H2 to carbon oxide species is as defined above. The second reactant stream may be an external source of CO and/or CO2, or originate from the process according to the invention, or a combination thereof, as defined below. According to a preferred embodiment, the H2 originating from step (b) is mixed with an external source of CO and/or CO2 in the appropriate ratio, prior to the contacting of step (c).

[0026] Although it is preferred that the feed gas for step (c) consists essentially of H2 and carbon oxide species, further components may also be present, such as components that also originate from step (b) and that are separated together with H2 from the main product stream and/or components that are present in the source of the carbon oxide species. Such optionally present further components may include H2O, inert gases such as N2, hydrocarbons, etc. Although minor amounts of H2O may be present, its content is preferably kept low. The reaction to olefins generates H2O and the since equilibria play a role within the general reactions presented above, the presence of significant amounts of H2O in the feed gas may push such equilibria towards the reactants. Preferably, the H2O content of the feed gas of step (c) is below 1 %, more preferably below 1000 ppm. Preferably, at least 50 % of the feed gas of step (c) contains H2 and carbon oxide species, more preferably at least 80 %, most preferably at least 95 %. If needed, the feed gas of step (c) and/or the hydrogen originating from step (b) is dried prior to being subjected to step (c). Such drying may be accomplished by any means known in the art, such as cooling with water condensation and separation, glycol removal or sorbent processes including those using molecular sieves. The H2 and the carbon oxide species, either separately or the mixed feed gas, may be pressurized prior to being subjected to step (c). Such pressurization may be accomplished by any means known in the art, e.g. using a compressor. Another option is an electrochemical hydrogen compressor in which the separation of hydrogen and compression can be combined.

[0027] In a preferred embodiment, heat is removed from the reaction during step (c). The overall reaction (1) to form olefins is highly exothermic. As a result the temperature of the stream passing through the reactor increases with increasing progression of the reaction. The conversion of the reaction could be positively affected if this temperature increase is inhibited or reduced, since the chemical equilibrium composition contains less olefins at higher temperature. Heat removal can be accomplished by any means known in the art, preferably by an external cooling medium such as the generation of steam, heat exchange with streams in the underlying process (steps (a), (b) and (d)), by means of a cold utility stream such as cooling water, or by integration in a heat pump or mechanical vapour recompression system.

[0028] Alternatively or additionally, the olefin yield can be increased by splitting the reactor in which step (c) is performed. Thus, preferably the reactor is split in multiple reactors (i.e. at least two reactors, preferably 2-5 reactors) in series, with intermediate cooling steps (e.g. by heat exchange). Preferably, part of the product stream of any of the outlet streams of any of the multiple reactor may be split of and subsequently cooled (e.g. by any of the means described for the heat removal above), followed by mixing the split of and cooled stream with any of the feed streams of any of the multiple reactors in series. Such means for increasing the olefin yield of olefins by overall reaction (1) are known in the art, and are preferably included in the step (c) of the process according to the invention. In one embodiment, part of the product stream of step (a) or part of the product stream of (one of) the reactor(s) of step (c) is split off and mixed with the feed stream of the first reactor of step (c) or mixed with the feed stream of one of the upstream reactors in series of step (c), if present.

[0029] In step (c), the hydrogen originating from step (b) and a carbon oxide species selected from CO2 and/or CO are contacted with a catalyst. The contacting of step (c) typically occurs at a temperature of 150 - 400 °C, preferably 250 - 350 °C, and at a pressure of 1 - 30 bar, preferably 15-22 bar.

[0030] The catalysts used in step (c) is capable of converting H2 and CO and/or CO2 into olefins. Any such catalyst known in the art is suitable in this respect. In this context, the catalyst may also refer to a catalyst system comprising two or more distinct catalysts that together are active in the conversion of H2 and CO and/or CO2 into olefins. More specifically, any Fischer-Tropsch type of catalyst that is known to form lower olefins is suitable to be used in step (c), especially when CO is comprised in the feed. In case CO2 is comprised in the feed of step (c), a CO2 hydrogenation catalyst or a (combination of) catalyst(s) that is known to have reverse water gas shift activity and Fischer-Tropsch activity may also be used. Such catalysts or catalyst systems are herein referred to as RWGS/FT catalysts. The skilled person knowns how to select a suitable catalyst or catalyst system based on the composition of the feed. The catalyst may thus also be referred to as Fischer-Tropsch catalyst or as a CO2 hydrogenation catalyst. Thus, in one embodiment, the catalyst is selected from the group consisting of Fischer-Tropsch type of catalysts, CO2 hydrogenation catalysts and RWGS/FT catalysts. Such catalysts are known to the skilled person, and further guidance may be found in Wang et al., Chern. Soc. Rev., 2011, 40, 3703-3727 and Saedi et al., J. CO2 Util., 2014, 5, 66-81. Preferred Fischer-Tropsch catalysts are catalysts based on Fe, Cu, Co and/or Al, as those are known for the high olefin content of the product mixture. Preferably, the catalyst is Fe-based, as Fe-based catalysts are especially capable to convert CO2 in situ to CO and are capable of forming olefins in high yield. Fe(II), preferably iron oxides, and most preferably in combination with γ-alumina, are particularly suitable in this respect. In one embodiment, the catalyst comprises Fe in the form of nanoparticles. Fe-based nanoparticles are known for their high yield of lower olefins (see Torres Galvis et al., Science, 2012, 335, 835-838 and WO2011049456A1). An alternative approach to tailor the product mixture of step (c) towards olefins is the incorporation of promoters. Preferably, the catalyst is promoted with alkali metal and/or a group 7 metal, more preferably the catalyst comprises a promoter selected from K, Na, Li, Cs, Mn and mixtures thereof. The presence of such promoters is known to promote olefin formation. The catalyst preferably comprises K and/or Mn as promoter, The presence of K may lead to a 4-fold increase in olefin yield, while Mn was found to suppress the formation of methane and subsequently increase the olefin yield. Most preferably, a Fe-based, K- and/or Μη-promoted catalysts is used. Such catalysts are known in the art, e.g. from J. CO2 Util. 2013, 3-4, 56-64. The catalyst is typically immobilized on a solid support, typically of alumina (e.g. gamma and/or alpha, preferably alpha-alumina), silica, zinc oxide, titania, zeolites (molecular sieve) material, ceria, carbon nano fibre or carbon nanotubes.

[0031] The typical substrates for a Fischer-Tropsch catalyst are FL and CO, although using CO2 as a substrate has also been found effective in Fischer-Tropsch catalysis, especially when RWGS/FT catalysts are used. Fischer-Tropsch catalysts that are active towards CO2 are typically also active in the conversion of CO2 to CO by the reverse water gas shift reaction (WGSR), as such forming CO in situ, which is then converted into olefins by the Fischer-Tropsch activity of the catalyst. Step (c) should thus be performed with CO, CO2 or a mixture thereof as carbon oxide species. In one embodiment, the carbon oxide species comprises CO, i.e. consists of CO and optionally CO2. In one embodiment, the carbon oxide species comprises CO2, i.e. consists of CO2 and optionally CO. Although CO may in some instances be preferred in view of the increased activity in the formation of olefins, CO2 is more readily available in cracking plants. The skilled person knows how to determine the activity of a catalyst towards CO and CO2, and thus is able to select the appropriate carbon oxide species to be reacted with H2 in step (c). In view of its abundant availability, the use of CO2 as carbon oxide species in step (c) is preferred. Alternatively, CO2 is converted to CO prior to step (c), as such enabling the use of the abundantly available CO2 and at the same time employing the increased olefin formation associated with CO. Such a step (vi) is described further below. In the context of this preferred embodiment, step (c) is performed with CO as carbon oxide species. It is thus preferred that CO2 is used, which is converted into CO either prior to step (c), i.e. in step (vi), or in situ during the contacting of step (c).

[0032] In case the catalyst is not or insufficiently reactive towards CO2, e.g. in terms of olefin yield, it may thus be desirable to include a separate step (vi), wherein CO2 is converted into CO by the reverse water gas shift reaction. In the water gas shift reaction (WGSR), CO and H2O are in equilibrium with CO2 and H2. Specific catalysts are designed to catalyse the reverse reaction wherein CO2 is converted into CO upon consumption of H2 and formation of H2O. In step (vi), a feed gas comprising CO2 and H2 is contacted with a reverse WGSR catalyst to obtain a gaseous mixture comprising CO, H2O and optionally remaining H2. Preferably, the H2 in the feed gas of step (vi) originates from step (b), wherein the feed gas is prepared by mixing the H2 originating from step (b) with an appropriate amount of CO2. Preferably, H2 originating from step (b) is used in step (vi) and the amount of CO2 added to the feed gas is set as such that the optimal H2 to CO ratio for performing step (c) is obtained after step (vi). The use of the reverse WGSR and subsequent Fischer-Tropsch for the formation of olefins from CO2 has been suggested by Centi et al. (ChemSusChem, 2011, 4, 1265-1273). The present inventors for the first time have used this process for increasing the yield of olefins from naphtha cracking. Thus, in a preferred embodiment, the process according to the invention further comprises a step (vi) of converting CO2, preferably CO2 at least partly originating from the furnace off-gas, more preferably CO2 at least partly originating from step (vii) as defined below, into CO by a reverse water gas shift reaction, and the carbon oxide species used in step (c) comprises CO obtained in step (vi). It is especially preferred that H2 and CO2 are contacted in step (vi) in a weight ratio of H2 to CO2 is in the range of 2:1 - 5:1, more preferably 2.5:1-4:1, most preferably about 3:1. In step (vi), typically a molecule of CO2 is converted together with one molecule of H2 into one molecule of CO (and one H2O). Using the H2 to CO2 weight ratios as defined above, the product mixture of step (vi), which is used as feed gas for step (c), thus comprises H2 to CO in a weight ratio in the range o f 1:1 - 4:1, more preferably 1.5:1 - 3:1, most preferably about 2:1. fh and CO in such a ratio are ideally suited to be converted into olefins in step (c).

[0033] The reverse WGSR is known to the skilled person, and typically employs a temperature in the range of 500 - 100 °C, preferably 800 - 900 °C. Any reverse WGSR catalysts known in the art is suitable to be used in step (vi). Preferably, a Cu-based catalyst is used as reverse WGSR catalyst. Typically, the reverse WGSR catalysts is immobilized on a support, preferably alumina.

[0034] In a preferred embodiment, step (c) operates using more than one, preferably at least two, most preferably two CO2 hydrogenation reactors. As such, the first reactor may be used for the contacting of step (c), while the second reactor is being regenerated, which enables continuous operation. Regeneration is typically performed by solvent extraction of the catalyst, to remove wax and contaminants from the catalyst. The wax-free catalyst is then subjected to controlled oxidation to convert the reduced catalyst to its initial oxidized state, e.g. for iron-based catalysts to Fe203. Reactivation of the oxide catalyst precursor is carried out by contacting with synthesis gas.

[0035] The CO2 used in step (c) and/or the CO2 subjected the reverse WGSR in step (vi) may originate from an external source or from the process according to the invention as by-product, or a combination thereof. In one embodiment, the CO2 used in step (c) and/or step (vi) at least partly originates from an external source. In an alternative embodiment, the CO2 used in step (c) and/or step (vi) at least partly originates from an the process according to the invention. In a most preferred embodiment, the CO2 used in step (c) and/or step (vi) partly originates from an the process according to the invention and partly from an external source.

[0036] The CO2 originating from an external source conveniently is a gas stream containing at least 50 % CO2, preferably at least 90 % CO2. Such streams may originate from chemical or petrochemical processes, power generation or from natural gas production requiring the removal of CO2. Also concentrated CO2 streams resulting from processes for biomass conversion by means of digestion, fermentation, gasification or pyrolysis processes for the production of synthetic natural gas, fuels, chemicals or power can be used as a source of CO2. Suitable processes that could serve as an external source include but are not restricted to methanol production, ammonia production, ethylene oxide production, hydrogen production, power production with CO2 capture from coal, oil and/or gas, gasification of coal, oil, oil fractions and/or biomass, substitute natural gas production and CO2 removal in natural gas processing or a combination thereof

Alternatively or additionally, imported streams containing significant amounts of CO could be used. Those streams are readily available from e.g. the steel industry and more specifically a basic oxy furnace gas, blast furnace gas and/or cokes oven gas could be used, preferably basic oxy fuel gas is used. These streams may be beneficially pre-treated, such as removal of N2, hydrocarbons and sulphur-containing components such as H2S, by means known in the art.

[0037] The CO2 as by-product from the process of the invention, also referred to as “internal CO2”, may originate from an off-gas that is discharged from a furnace used during the cracking of step (a) and/or from the acid gas removal step (iv) and/or (viii), or mixtures thereof. Preferred sources of internal CO2 are acid gas removal step (viii) and furnace off-gas of step (a), most preferably the furnace off-gas. CO2 is typically formed during step (a) in the furnace where fuel preferably comprising methane (e.g. natural gas, methane) is burned, and ends up in the off-gas. Such an off-gas typically comprises CO2, H2O and optionally other species depending on the type and purity of the fuel used. Preferably, CO2 is removed in step (vii) from the off-gas (e.g. before it is emitted as flue gas), which is not only beneficial for the environment but also enables the use of the removed CO2 in step (c). CO2 removal may be accomplished by any means known in the art, such as physical or chemical adsorption of CO2. Typically, amine scrubbing is used to remove CO2 from the furnace off-gas, but other techniques may be used.

[0038] A second source of by-product from the process is from the CO2 removal step (vii), wherein CO2 is removed from the secondary product stream prior to step (d). Thus, in one embodiment, the process according to the invention comprises a step (vii) of removing CO2 from the off-gas of the fuel burning during step (a) and wherein at least part, preferably all, of the CO2 originating from step (vii) is used in step (c) or in step (vi). It should be noted that potentially the amount of H2 separated from the main product stream in step (b) requires a greater amount of CO2 to establish the ideal ratio for steps (c) and/or (vi) than the amount of CO2 available from step (vii). Thus, according to one embodiment, the CO2 used in the contacting of step (c) and/or (vi) originates partly from the process itself, as described hereinabove, and partly from an external source of CO2, as defined further above. In this embodiment, the CO2 originating from an external source and the CO2 as by-product from the process according to the invention, preferably originating from step (vii), are mixed prior to step (vi) or prior to step (c).

[0039] Step (c) affords a secondary product stream comprising (lower) olefins, typically together with alkanes such as methane, ethane and propane. Also remaining carbon oxide species and/or H2 may be present in the secondary product stream. The exact composition of the secondary product stream may vary depending on the specific process conditions employed in step (c), the composition of the feed stream of step (c), in particular regarding the H2 to carbon oxide species and the catalysts used. The possible presence of CO2 in the secondary product stream is undesirable when said stream is combined with the main product stream, while possible alkanes and H2 molecules are easily separated from the olefins. The main product stream typically undergoes separation of methane prior to step (e) and separation of ethane and propane during step (e), as described below. Also hydrogen is readily removed from the main product stream, in case the combining of step (d) occurs prior to hydrogen separation of step (c), as described below. The secondary product stream obtained in step (c), prior to being subjected to step (d), may be subjected to one or more separation steps as known in the art. Preferably, such one or more separation steps are selected from a CO2 removal step, removal of a heavy fraction (i.e. having 5 or more carbon atoms) from the secondary product stream, e.g. by primary fractionation and/or a water quench, a compression step, an acid gas removal step, a H2 removal step and a water removal step. The H2 removal step is preferably implemented when step (d) is performed downstream of step (b). The H2O removal step is preferably implemented when step (d) is performed downstream of step (v) or in case no step (v) is performed. In case step (d) is performed upstream of step (v) and of step (b), the separation steps are preferably selected from a CO2 removal step, removal of a heavy fraction from the secondary product stream, a compression step and an acid gas removal step.

[0040] In this respect, it is preferred that the process according to the invention comprises an acid gas removal step (viii), wherein acid gases, typically mainly CO2, are removed from the secondary product stream prior to step (d). As CO2 is typically the only acid gas removed in step (viii), this step may also be referred to as a CO2 removal step. CO2 removal may be accomplished by any means known in the art, such as physical or chemical absorption of CO2. Preferably, physical sorption is used to remove CO2 in step (viii), as such a means for CO2 removal is highly compatible with step (c), as the desired process conditions (in terms of temperature and pressure) are very similar. Alternatively, CO2 is not removed from the secondary product stream, i.e. the process according to the invention does not comprise a step (viii) as defined herein, and the combining of step (d) of the secondary product stream occurs with the main product stream prior to it being subjected to acid gas removal in step (iv). Before being subjected to step (d), higher hydrocarbons and olefins (such as having 5 carbon atoms or more), if present, may be removed from the secondary product stream by any means known by the skilled person, such as but not restricted to quenching with water or oil, cooling, adsorption by solid sorbents, or absorption by liquid solvents. As such, the separation of olefins in step (e) may be performed optimally.

Step (d) [0041 ] The secondary product stream from which preferably CO2 is removed is combined with the main product stream in step (d). Although the combining of step (d) may occur with the main product stream after hydrogen is isolated in step (b), it is preferred that the combining of step (d) occurs with the main product stream downstream of step (b), especially downstream of step (v). As such, any remaining hydrogen that is present in the secondary product stream is removed in step (b) and subsequently utilized in step (c). In case step (d) occurs downstream of step (v), any water that may be present in the secondary product stream is removed prior to subjecting the main product stream which is combined with the secondary product stream to removal of hydrogen in step (b).

[0042] It should be noted that the process according to the invention advantageously runs in continuous mode, so that it is possible to isolate hydrogen from the main product stream at a certain point in the work-up sequence and reintroduce the product of step (c) performed with said isolated hydrogen earlier in the work-up sequence, such that the combined stream is subjected to hydrogen isolation. Thus, the secondary product stream may be combined with the main product stream at any point in the process between step (a) and (e) (downstream of step (a) and upstream of step (e)), i.e. between step (a) and (b) or between step (b) and (e), preferably between step (a) and (ix), i.e. between step (a) and (b) or between step (b) and (ix), even more preferably between step (a) and (b), most preferably between step (a) and (v). In case the combining of step (d) occurs in between step (a) and (b), step (d) preferably is performed between step (ii) and (iii), between step (iii) and (iv), between step (iv) and (v) or between step (v) and (b), most preferably between step (iv) and (v). The main product stream that is subjected to the combining of step (d) thus originates from step (a) or (b), preferably it originates from step (a), most preferably it originates from step (a) via steps (i) - (iv). Using this preferred order of steps, any remaining water in the secondary stream is removed in step (v) and any remaining H2 in the secondary stream is removed in step (b), after combining the secondary stream with the main product stream in step (d).

[0043] Combining the main product stream and the secondary product stream may be accomplished by any means known in the art, such as in-line or “in pipe” (i.e. by the joining of two incoming pipes into one single outgoing pipe), in a (balance) tank or vessel, in an agitated vessel or by any industrial mixer or blender.

[0044] The combining of step (d) affords a main product stream, which is combined with the secondary product stream. Such a combined product stream is referred to as the main product stream in the context of the present invention, since it comprises olefins formed during the cracking of step (a). The main product stream originating from step (d) comprises mainly olefins and optionally some further components originating from the main and secondary product streams, such as hydrogen, alkanes (e.g. methane, ethane, propane), alkynes (e.g. ethyne, propyne) and higher hydrocarbons. Typically, the main product stream originating from step (d) consists essentially of hydrocarbons (i.e. olefins, alkanes and alkynes).

Step (e) [0045] The main product stream, which is combined with the secondary product stream, originating from step (b) or (d), preferably from step (b), is subsequently subjected to step (e), the isolation of olefins. In the context of the present invention, step (e) may also be referred to as separation of olefins. Such olefin isolation or separation is common in the art and is usually performed on the product stream from a cracking process, typically after removal of the heavy fractions, acid gases and fh as described above for the main product stream. The effectiveness of the process according to the invention in part resides in that the olefin mixture obtained in step (c) is separated together with the conventional olefin separation as conventionally performed in a cracking plant. Isolation or separation of olefins may be accomplished in any manner known in the art. Typically, step (e) involves a series of steps comprising deethanisation, depropanisation and hydrogenation (for conversion of e.g. acetylene to ethylene). The skilled person finds further guidance in Zimmerman and Walzl, Chapter “Ethylene” in Ullmann’s Encyclopedia of Industrial Chemistry, 2009.

[0046] In one embodiment, step (e) involves a series of steps comprising deethanisation coupled to a C2-splitter, depropanisation coupled to a C3-splitter and debutanisation. Herein, the main product stream, preferably after demethanisation as described below, is typically first subjected to deethanisation in a deethaniser which separates the C2-ffaction from the remaining main product stream. The C2-fraction is then led to a C2-splitter, preferably via a C2-acetylene converter wherein possibly formed acetylene (ethyne) molecules are converted to ethene. The C2-splitter then separates ethene from ethane, after which the ethane is conveniently recycled to the cracker reactor and used as part of the feedstock in step (a). Ethene is obtained as isolated olefin as one of the primary products of the process according to the invention. The main product stream from which the C2-fraction is removed is then subjected to depropanisation in a depropaniser which separates the C3-fraction from the remaining main product stream. The C3-fraction is then led to a C3-splitter, preferably via a C3-acetylene converter wherein possibly formed propyne molecules are converted to propene. The C3-splitterthen separates propene from propane, after which the propane is conveniently recycled to the cracker reactor and used as part of the feedstock in step (a). Propene is obtained as isolated olefin as one of the primary products of the process according to the invention. The main product stream from which the C2- and C3-fractions are removed is then subjected to debutanisation in a debutaniser which separates the C^fraction from C5 and higher hydrocarbons. The mixture of butene and butadiene isomers are thus obtained as isolated olefin as one of the primary products of the process of the invention. The residue of the debutanisation comprising C5 and higher hydrocarbons is typically combined with the RPG obtained in the water quench of step (ii). Such isolation or separation of olefins is known to the skilled person, who is aware how to perform these steps most efficiently.

[0047] Typically, methane is also removed from the main product stream in step (ix), e.g. using demethanisation. Being the most volatile component, methane is preferably removed prior to step (e). As methane is typically also present in the secondary product stream, step (ix) is preferably performed after step (d), i.e. between step (d) and step (e), more preferably after step (b), i.e. between step (b) and (e). Methane removal is conveniently performed using a demethaniser as known in the art. The main product stream is subjected to demethanisation in a demethaniser which separates the Ci-fraction (methane) from the remaining main product stream. The main product stream from which methane is removed is then used as main product stream in step (e).

[0048] According to an especially preferred embodiment, the process of the invention comprises: (a) subjecting the feedstock to cracking to obtain a main product stream comprising olefins and H2; (i) subjecting the main product stream to primary fractionation to obtain a first heavy fraction and a main product stream from which a first heavy fraction is removed; (ii) subjecting the main product stream originating from step (i) to a water quench to obtain a second heavy fraction and a main product stream from which a second heavy fraction is removed; (iii) subjecting the main product stream originating from step (ii) to a first compression step to obtain a compressed main product stream; (iv) subjecting the compressed main product stream originating from step (iii) to an acid gas removal step to obtain a main product stream from which acid gas is removed; (iii’) subjecting the main product stream originating from step (iv) to a second compression step to obtain a compressed main product stream; (v) subjecting the main product stream originating from step (d) to a water removal step to obtain a dried main product stream; (b) separating H2 from the dried main product stream originating from step (v); (vii) optionally removing CO2 from an off-gas comprising CO2 originating from burning fuel in a furnace during step (a); (vi) optionally converting CO2 originating from step (vii) and/or from an external source, to CO by a reverse water gas shift reaction, to obtain a mixture comprising CO; (c) contacting the H2 obtained in step (b) and carbon oxide species selected from CO2, CO and a mixture thereof, optionally wherein the CO2 originates from step (vii) and/or wherein the CO originates from step (vi), to a catalyst capable of converting H2 and CO and/or CO2 into olefins, to obtain a secondary product stream comprising olefins; (viii) preferably removing CO2 from the secondary product stream originating from step (c); (d) combining the secondary product stream originating from step (c), preferably from step (viii), with the main product stream originating from step (iii’); (ix) preferably removing methane from the main product stream originating from step (b); and (e) isolating olefins from the main product stream originating from step (d), preferably from step (ix), wherein step (e) preferably comprises deethanisation coupled to a C2-splitter, depropanisation coupled to a C3-splitter and debutanisation.

SYSTEM

[0049] The invention also relates to an apparatus or system which is specifically designed to implement or execute the process according to the invention. The system according to the invention is modular system comprising at least five modules, wherein the modules are in fluid connection with each other. Herein, each module may be a separate unit or two or more modules may be integrated as a single unit. Preferably, at least modules (a), (c) and (e) are separate units distinguishable as such in the system, and modules (b) and (d) may be integrated as one module or may be separate modules. The modular system for performing the process according to the invention may also be referred to as a cracking plant, preferably a steam cracking plant.

[0050] The modular system according to the invention is a cracking plant which comprises a CO2 hydrogenation reactor (c) and a combining module (d). In the cracking plant according to the invention, reactor (c) comprises (cl) one or more inlet designed to receive H2 separated from a cracking product stream and carbon oxide species selected from CO2, CO and a mixture thereof, (c2) a catalyst capable of converting H2 and CO and/or CO2 into olefins, and (c3) an outlet for discharging a secondary product stream comprising olefins, and module (d) comprises (dl) a first inlet designed to receiving a cracking product stream, (d2) a second inlet for receiving the secondary product stream originating from reactor (c) and (d3) an outlet for discharging a main product stream to an olefin isolation module.

[0051] In other words, the modular system according to the invention comprises: (a) a cracking reactor, comprising (al) an inlet for receiving a feedstock comprising saturated hydrocarbons, (a2) an outlet for discharging a main product stream and (a3) a furnace designed to combust fuel to heat the cracking reactor, wherein the furnace comprises (a4) an inlet for receiving fuel and (a5) an outlet for discharging an offgas; (b) an H2 separation module, comprising (bl) an inlet for receiving the main product stream originating from cracking reactor (a) or the main product stream originating from combining module (d), (b2) means for separating H2 from the main product stream, (b3) a first outlet for discharging H2 and (b4) a second outlet for discharging a main product stream from which H2 is removed; (c) a CO2 hydrogenation reactor, comprising (cl) one or more inlets for receiving the H2 originating from module (b) and carbon oxide species selected from CO2, CO and a mixture thereof, (c2) a catalyst capable of converting H2 and CO and/or CO2 into olefins, and (c3) an outlet for discharging a secondary product stream comprising olefins; (d) a combining module, comprising (dl) a first inlet for receiving the main product stream originating from module (a) or (b), (d2) a second inlet for receiving the secondary product stream originating from reactor (c) and (d3) an outlet for discharging a main product stream; (e) an olefin isolation module, comprising (el) an inlet for receiving the main product stream originating from module (b) or (d), (e2) means for isolating olefins from the main product stream, and (e3) one or more outlets for discharging olefins.

[0052] In the system of the invention, the different modules are interconnected, i.e. the outlet of one module is in fluid connectivity with the inlet of another module, preferably by means of a conduit. As such, the constant flow of streams through the system is enabled. Thus, outlet (a2) is in fluid connection with inlet (bl), outlet (b3) is in fluid connection with inlet (cl), outlet (b4) is in fluid connection with inlet (el), outlet (c3) is in fluid connection with inlet (d2), outlet (d3) is in fluid connection with inlet (el). Such fluid connectivity allows for the incorporation of further modules, e.g. the fluid connectivity between outlet (a2) and inlet (bl) may contain one or more additional modules such as module (d). In the context of the present invention, “downstream” and “upstream” are used to define the location of a certain module compared to another module with respect to the main product stream. Thus in case module (d) is located upstream of module (b), the main product stream is first led through module (d) and then through module (b). Likewise, whenever a product stream is mentioned to “originate from” a certain module, it may indicate that the product stream is directly obtained from said module, or that the product stream is led through one or more further modules after said module.

[0053] In the system of the invention, the order of modules (b) and (d) is reversible, although it is preferred that module (d) is located upstream of module (b) or that module (b) and (d) are integrated as defined below. Thus, in one embodiment, module (d) is located downstream of module (b) and the system according to the invention comprises: (a) a cracking reactor, comprising (al) an inlet for receiving a feedstock comprising saturated hydrocarbons, (a2) an outlet for discharging a main product stream and (a3) a furnace designed to combust fuel to heat the cracking reactor, wherein the furnace comprises (a4) an inlet for receiving fuel and (a5) an outlet for discharging an offgas; (b) an H2 separation module, comprising (bl) an inlet for receiving the main product stream originating from cracking reactor (a), (b2) means for separating H2, (b3) a first outlet for discharging H2 and (b4) a second outlet for discharging a main product stream from which H2 is removed; (c) a CO2 hydrogenation reactor, comprising (cl) one or more inlets for receiving the H2 originating from module (b) and carbon oxide species selected from CO2, CO and a mixture thereof, (c2) a catalyst capable of converting H2 and CO and/or CO2 into olefins, (c3) an outlet for discharging a secondary product stream comprising olefins; (d) a combining module, comprising (dl) a first inlet for receiving the main product stream originating from module (b), (d2) a second inlet for receiving the secondary product stream originating from module (c) and (d3) an outlet for discharging a main product stream; (e) an olefin isolation module, comprising (el) an inlet for receiving the main product stream originating from module (d), (e2) means for isolating olefins from the main product stream, and (e3) one or more outlets for discharging olefins.

[0054] Alternatively, in a more preferred embodiment, module (d) is located upstream of module (b) and the system of the invention comprises: (a) a cracking reactor, comprising (al) an inlet for receiving a feedstock comprising saturated hydrocarbons, (a2) an outlet for discharging a main product stream and (a3) a furnace designed to combust fuel to heat the cracking reactor, wherein the furnace comprises (a4) an inlet for receiving fuel and (a5) an outlet for discharging an offgas; (b) an H2 separation module, comprising (bl) an inlet for receiving the main product stream originating from combining module (d), (b2) means for separating H2, (b3) a first outlet for discharging H2 and (b4) a second outlet for discharging a main product stream from which H2 is removed; (c) a CO2 hydrogenation reactor, comprising (cl) one or more inlets for receiving the H2 originating from module (b) and carbon oxide species selected from CO2, CO and a mixture thereof, (c2) a catalyst capable of converting H2 and CO and/or CO2 into olefins, (c3) an outlet for discharging a secondary product stream comprising olefins; (d) a combining module, comprising (dl) a first inlet for receiving the main product stream originating from module (a), (d2) a second inlet for receiving the secondary product stream originating from module (c) and (d3) an outlet for discharging a main product stream; (e) an olefin isolation module, comprising (el) an inlet for receiving the main product stream originating from module (b), (e2) means for isolating olefins from the main product stream, and (e3) one or more outlets for discharging olefins.

[0055] The system of the invention comprises a cracker reactor (a). Cracker reactor (a) comprises an inlet (al) for receiving the feedstock comprising saturated hydrocarbons, an outlet (a2) for discharging the main product stream and a furnace (a3). Any type of cracker reactor as known in the art may be used as cracker reactor (a). Typically, reactor (a) is a tubular reactor. Furnace (a3) is designed to combust fuel in order to heat the cracking reactor and comprises an inlet (a4) for receiving fuel and an outlet (a5) for discharging an off-gas. Typically, the furnace comprises means to ignite the fuel and an inlet for receiving a gas comprising O2. Such cracking reactors are common in the art. Outlet (a2) is in fluid connection with inlet (bl) of module (b), preferably via at least module (d), most preferably via modules (i) - (v) and (d).

[0056] The system according to the invention comprises an H2 separation module (b). Such H2 separation modules are known in the art, and any known type or design of the H2 separation module is suitable in the system according to the invention. Most preferably, module (b) is a cold box. Module (b) comprises an inlet (bl) for receiving the main product stream. Said main product stream may originate from cracking reactor (a) or from combining module (d), preferably it originate from combining module (d). The main product stream is received to means (b2) for separating H2. Means (b2) may be any means known in the art to be suitable to separate H2 from a main product stream of a cracker reactor. Preferably, means (b2) include a chilling means, capable of lowering the temperature of the main product stream to below -150 °C, such as between -200 °C and -160 °C. Furthermore, it is preferred that module (b) is designed such that the main product stream has a pressure of 20 - 50 bar, preferably 30-40 bar, when residing within module (b). Such pressure may be maintained in case the main product stream is received by module (b) at such pressure, or means (b2) further include a compression means to capable compress the main product stream to a pressure of 20 - 50 bar, preferably 30 -40 bar. Under such conditions, the H2 present in the main product stream remains gaseous, while all other species present in the main product condense. Means (b2) are thus preferably capable of separating the incoming main product stream into a gaseous H2 stream and a liquid main product stream from which H2 is removed. Module (b) further comprises a first outlet (b3) for discharging H2 and (b4) a second outlet for discharging a main product stream from which Fb is removed. Preferably, outlet (b3) is capable of discharging a gaseous stream and outlet (b4) is capable of discharging a liquid stream. Outlet (b3) is in fluid connection with inlet (cl) of module (c), preferably via module (vi). The fluid connection between outlet (b3) and inlet (cl) may contain pressurizing means, such as a compressor, such that the H2 may be brought to the optimal pressure for performing CO2 hydrogenation. The fluid connection between outlet (b3) and inlet (cl) may also contain means for mixing the gaseous stream comprising H2 with an carbon oxide species, which may originate from an external source and/or from the system according to the invention, e.g. from module (vii). Outlet (b4) is in fluid connection with inlet (el) of module (e), optionally via module (d) and preferably via module (ix).

[0057] In a preferred embodiment, module (b) and (d) are integrated. Herein, module (b) comprises a further inlet (b5) for receiving the secondary product stream, such that combining of the main product stream and the second product stream is feasible within module (b). In the present embodiment, the combining module (d) is part of the H2 separation module (b). Herein, inlets (dl) and (bl) are the same inlet, inlets (d2) and (b5) are the same inlet, and outlets (d3) and (b4) are the same outlet.

[0058] The system of the invention comprises a CO2 hydrogenation reactor (c), comprising one or more inlets (cl) for receiving the H2 originating from module (b) and carbon oxide species selected from CO2, CO and a mixture thereof. Reactor (c) further comprises a catalyst (c2) capable of converting H2 and CO and/or CO2 into olefins, as further defined above. Said catalyst is typically comprised in a bed, e.g. a packed bed or a fluidized bed. Reactor (c) further comprises an outlet (c3) for discharging a secondary product stream comprising olefins. Reactor (c) is designed such that the incoming main product stream from inlet (cl) are led through or over the catalyst bed towards outlet (c3). Outlet (c3) is in fluid connectivity with inlet (d2) of module (d), preferably via module (viii). The CO2 hydrogenation reactor (c) may also be referred to as a Fischer-Tropsch reactor. Module (c) preferably comprises means for pressurizing the incoming gaseous stream(s) via inlet(s) (cl). Typically, the H2 and the carbon oxide species, either separately or in a mixed feed gas, may be pressurized by any means known in the art, e.g. using a compressor or electrochemical hydrogen compressor. In a preferred embodiment, module (c) comprises means for removing heat from the reaction that occurs within module (c). Heat removal could positively affect the conversion of the CO2 hydrogenation reaction. Heat removal is preferably accomplished by an external cooling medium such as the generation of steam, heat exchange with streams in the underlying process (e.g. in modules (a), (b) and (d)), integration with a mechanical vapour recompression cycle or heat pump, or by means of a cold utility stream such as cooling water.

[0059] In a preferred embodiment, the system according to the invention comprises a module (c) comprising more than one, preferably at least two, most preferably two CO2 hydrogenation reactors. Each of the CO2 hydrogenation reactors is designed as described above. In case two reactors are used, the system is capable of using the first reactor for the contacting of step (c) of the process according to the invention, while the second reactor is being regenerated. Regeneration is typically performed by solvent extraction of the catalyst, to remove wax and contaminants from the catalyst. The wax-free catalyst is then subjected to controlled oxidation to convert the reduced catalyst to its initial oxidized state, e.g. for iron-based catalysts to Fe(II). Reactivation of the oxide catalyst precursor may be carried out by contacting with synthesis gas. Downstream the hydrogenation reactor, i.e. in the fluid connection between outlet (c3) and inlet (d2), higher hydrocarbons and olefins (such as having 5 carbon atoms or more) may be removed by any means known by the skilled person, such as but not restricted to quenching with water or oil, cooling, adsorption by solid sorbents, or absorption by liquid solvents.

[0060] Module (c) may also contain two or more CO2 hydrogenation reactors that operate in series. Thus, preferably module (c) is split in multiple reactors (i.e. at least two reactors, preferably 2-5 reactors) in series, with intermediate means for cooling (e.g. by heat exchange). Preferably, part of the product stream of any of the outlet streams of any of the multiple reactor may be split of and subsequently led to the cooling means (e.g. by external cooling medium such as the steam generation, heat exchange with streams in the underlying process (e.g. in modules (a), (b) and (d)), or by means of a cold utility stream such as cooling water), followed by mixing the split of and cooled stream with any of the feed streams of any of the multiple reactors in series. In one embodiment, the system according to the invention contains one or more recycles. In case module (c) contains two or more reactors operating in series, part of the product stream of one or more of these reactors may be recycled to the first or further reactors within module (c). Thus, one or more of the reactors of module (c), preferably at least the last one, preferably contains an outlet for discharging part of the secondary product stream, or part of an intermediate stream that exists between two reactors within module (c), and one or more of the reactors of module (c), preferably at least the first one, preferably contains an inlet for receiving this part. Additionally or alternatively, cracking reactor (a) or the fluid connectivity between reactor (a) and module (b) or (d) contains an outlet for discharging part of the main product stream one of the reactors of module (c), preferably the first one, preferably contains an inlet for receiving this part. As will be appreciated by the skilled person, the outlets and the inlets defined herein are in fluid connection.

[0061] The system according to the invention comprises a combining module (d). Module (d) comprises two inlets, a first inlet (dl) for receiving the main product stream originating from module (a), optionally via module (b), and a second inlet (d2) for receiving the secondary product stream originating from module (c). Module (d) further comprises an outlet (d3) for discharging a main product stream which is combined with the secondary product stream. Module (d) is designed such that the main product stream originating from module (a) is mixed with the secondary product stream originating from module (c). Any means for mixing or combining as known in the art can be used in module (d), such as “in line” or “in pipe” mixing. In a preferred embodiment, module (b) and (d) are integrated and module (d) is part of module (b), as described above. Herein, inlets (dl) and (bl) are the same inlet, inlets (d2) and (b5) are the same inlet, and outlets (d3) and (b4) are the same outlet.

[0062] The system according to the invention comprises an olefin isolation module (e). Modules for the isolation of olefins are known in the art, and the system according to the invention may comprise such a module of any type and design. Module (e) comprises an inlet (el) for receiving the main product stream originating from module (b) or (d), preferably from module (d), means (e2) for isolating olefins from the main product stream and one or more outlets (e3) for discharging olefins and optionally further products isolated from the main product stream. Any means known in the art to isolate olefins may be used as means (e2). The one or more outlets (e3) preferably comprise at least three outlets, one for discharging ethene, one for discharging propene and one for discharging a C4-olefin mixture (mixture of butene en butadiene isomers). It is especially preferred that the one or more outlets (e3) comprise at least six outlets, one for discharging each of ethane, ethene, propane, propene, a C4-olefin mixture, a third heavy fraction. The outlets for discharging ethane and propane are preferably in fluid connection with inlet (al) or a further inlet of module (a). The outlets for discharging ethene, propene and the C4-olefm mixture are preferably designed to discharge an end-product.

[0063] Typically, module (e), especially means (e2), comprises five to seven, preferably seven, distinct units selected from a deethaniser (e2-i), a C2-acetylene converter (e2-ii), a C2-splitter (e2-iii), depropaniser (e2-iv), a C3-acetylene converter (e2-v), a C3-splitter (e2-vi) and a debutaniser (e2-vii). The entire module (e) comprises an inlet (el) for receiving the main product stream originating from module (d), preferably via modules (b) and (ix). Inlet (el) preferably receives the main product stream to the deethaniser (e2), which is capable of removing the c2-fraction (ethene and optionally ethane and ethyne). The deethaniser is designed to discharge the C2-fraction via a first outlet to the c2-acetylene converter, which converts any possibly present ethyne molecules into ethene molecules, and the main product stream from which the C2-ffaction is removed via a second outlet to be led to the depropaniser. The mixture of ethene and ethane as discharged from the C2-acetylene converter is led to the C2-splitter, which is capable of splitting this mixture in ethane and ethene, after which the ethane is preferably led to module (a) to be used as internal feedstock in the cracking reactor. The depropaniser is capable of removing the C3-fraction (propene and optionally propane and propyne). The depropaniser is designed to discharge the C3-fraction via a first outlet to the C3-acetylene converter, which converts any possibly present propyne molecules into propene molecules, and the main product stream from which the C3-fraction is removed via a second outlet to be led to the debutaniser. The mixture of propene and propane as discharged from the C3-acetylene converter is led to the C3-splitter, which is capable of splitting this mixture in propane and propene, after which the propane is preferably led to module (a) to be used as internal feedstock in the cracking reactor. The debutaniser is designed to discharge the C4-fraction, typically comprising a mixture of butene and butadiene isomers (C4-olefin mixture), via a first outlet and a third heavy fraction via a second outlet. The third heavy fraction may be discharged as such from the system, or may be combined with the second heavy fraction which is discharged from module (ii), as described below.

[0064] The system according to the invention may comprise further modules. Preferably, the system comprises one or more further modules selected from: (i) a primary fractionation module, (ii) a secondary fractionation module, (iii) a compression module, (iv) an acid gas removal module, (v) a water removal module; (vi) a reverse water gas shift module; (vii) a first CO2 removal module; (viii) a second CO2 removal module; and (ix) a methane removal module, more preferably the system according to the invention comprises at least modules (i) - (v) and (ix), most preferably the system according to the invention comprises all of modules (i) - (ix).

[0065] Primary fractionation module (i) typically comprises an inlet for receiving the main product stream originating from module (a), means for primary fractionation, a first outlet for discharging a main product stream from which a first heavy fraction is removed and second outlet for discharging a first heavy fraction. Such a primary fractionation module is common in the art, and usually includes an oil quench as means for primary fractionation. Outlet (a2) of module (a) is in fluid connection with the inlet of module (i), and the first outlet of module (i) is in fluid connection with the inlet of module (ii).

[0066] Secondary fractionation module (ii) typically comprises an inlet for receiving the main product stream originating from module (i), means for secondary fractionation, a first outlet for discharging a main product stream from which a second heavy fraction is removed and second outlet for discharging a second heavy fraction. Such a secondary fractionation module is common in the art, and usually includes a water quench as means for secondary fractionation. The first outlet of module (i) is in fluid connection with the inlet of module (ii), and the first outlet of module (ii) is in fluid connection with the inlet of module (iii).

[0067] Compression module (iii) typically comprises an inlet for receiving the main product stream originating from module (ii), means for compression, an outlet for discharging a compressed main product stream. Such a compression module is common in the art, and may include any means for compression as known in the art, such as any gas compressors. The first outlet of module (ii) is in fluid connection with the inlet of module (iii), and the outlet of module (iii) is in fluid connection with the inlet of module (iv) .

[0068] Acid gas removal module (iv) typically comprises an inlet for receiving the main product stream originating from module (iii), means for acid gas removal, a first outlet for discharging a main product stream from which acid gas is removed and second outlet for discharging acid gases. Such an acid gas removal module is common in the art, and usually includes chemical or physical sorption (e.g. amine scrubbing) as means for acid gas removal. The outlet of module (iii) is in fluid connection with the inlet of module (iv), and the first outlet of module (iv) is in fluid connection with the inlet of module (v) or (d), preferably of module (d), optionally via a second compression module (iii’).

[0069] Water removal module (v) typically comprises an inlet for receiving the main product stream originating from module (iv) or (d), means for water removal, a first outlet for discharging a dried main product stream and optionally second outlet for discharging water. Such a water removal module is common in the art, and may include any means for water removal as known in the art. The outlet of module (iv) or outlet (d3) of module (d), preferably outlet (d3) of module (d), is in fluid connection with the inlet of module (v) , and the first outlet of module (v) is in fluid connection with the inlet of module (b), [0070] The reverse water gas shift module (vi) typically comprises an inlet for receiving a feed gas comprising CO2, which may originate from module (vii) and/or from an external source (E), and H2 originating from module (b), a reverse water gas shift catalyst, typically comprised in a bed (e.g. packed or fluidized bed), an outlet for discharging a gas comprising CO. Module (vi) may comprise one inlet, for receiving the mixture of the feed gas, or two or inlets for receiving the separate streams that are combined within module (vi) to form the feed of module (vi). Module (vi) is designed such that the incoming feed gas from the inlet is led through or over the catalyst bed towards the outlet. The outlet of module (vi) is in fluid connection with inlet (cl) of module (c). Preferably, the outlet of module (vii) and outlet (b3) of module (b) are in fluid connection, preferably via means for mixing the product streams of module (vii) and (b), with the inlet of module (vi).

[0071] The first CO2 removal module (vii) typically comprises an inlet for receiving an off-gas from of the fuel burning in the furnace (a3) of module (a), means for CO2 removal, a first outlet for discharging a gas comprising CO2 and optionally a second outlet for discharging a flue gas depleted in CO2 compared to the off-gas. Such a CO2 removal module is common in the art, and usually includes chemical or physical sorption (e.g. caustic wash or amine scrubbing, preferably amine scrubbing) as means for CO2 removal. Outlet (a5) of furnace (a3) of module (a) is in fluid connection with the inlet of the first CO2 removal module (vii), and the first outlet of the first CO2 removal module (vii) is in fluid connection with an inlet of reverse water gas shift module (vi) or with an inlet of module (c).

[0072] The second CO2 removal module (viii) typically comprises an inlet for receiving the secondary product mixture from module (c), means for CO2 removal, a first outlet for discharging a secondary product stream from which CO2 is removed and optionally a second outlet for CO2. Such a CO2 removal module is common in the art, and usually includes chemical or physical sorption (e.g. caustic wash or amine scrubbing, preferably amine scrubbing) as means for CO2 removal. Outlet (c3) of module (c) is in fluid connection with the inlet of the second CO2 removal module (viii), and the first outlet of the second CO2 removal module (viii) is in fluid connection with inlet (d2) of module (d).

[0073] Methane removal module (ix) typically comprises an inlet for receiving the main product stream from module (b) or (d), preferably form module (b), means for methane removal, a first outlet for discharging a main product stream from which methane is removed and a second outlet for methane. Such a methane removal module is common in the art, and is usually referred to as a demethaniser. Outlet (b4) of module (b) or outlet (d3) of module (d), preferably outlet (b4) of module (b), is in fluid connection with the inlet of methane removal module (ix). The outlet of methane removal module (ix) is in fluid connection with inlet (el) of module (e).

Figure [0074] A preferred embodiment of the system according to the invention is depicted in the figure, with reference to the reference numbers used in the description above. Herein, F = feedstock, E = CO2 from an external source, RPG = raw pyrolysis gasoline, FO = fuel oil.

Example [0075] The beneficial effect of the process according to the invention, compared to conventional naphtha cracking for producing olefins is outlined here for ethylene production. Similar effects are present for the other olefins. Scenario 1 represents a conventional cracking process, wherein 2200 kton/yr naphtha is used as feedstock. Typically, the mass yield in olefins is 30% and in hydrogen 1%, mass balance (see Ren et. al., Energy 31, 2006, 425-451), thus giving an annual yield of 660 kton ethylene and 22 kton hydrogen.

[0076] Scenarios 2 and 3 are according to the present invention. In scenario 2, the same amount of naphtha feed as in scenario 1 is used, and the cracking process itself (step (a) according to the invention), thus produces the same amounts of hydrogen and ethylene. Thus, 22 kton hydrogen gas is combined with 161 kton CO2 (i.e. a stoichiometric ratio of 3:1; MW(CC>2) = 44; MW(H2) = 2) and fed to the CO2 hydrogenation reactor (c). In the present example, all carbon of the CO2 is converted into ethylene. With one mole of ethylene (MW(C2H4) = 28) being formed per mole of consumed CO2, 103 kton of additional ethylene is formed. These olefins are combined in step (d) with the main stream of 660 kton ethylene, thus providing a 16 % increase in yield. In scenario 3, only 1904 kton/yr naphtha is used as feed. With a mass balance of 30 % ethylene and 1 % hydrogen, 571 kton ethylene and 19 kton hydrogen is produced. The hydrogen is combined with 140 kton CO2 and converted into 89 kton ethylene in the CO2 hydrogenation reactor (c). After combining with the original 571 kton ethylene in step (d), a total of 660 kton ethylene is thus produced. Compared to scenario 1, the same amount of ethylene is produced , while the amount of naphtha feedstock could be reduced with 13 %.

[0077] Table 2: Process streams in kton/yr for scenarios 1, 2 and 3

a] producing during naphtha cracking (Ren et. al.); [b] produced by CO2 hydrogenation; [c] combined C2H4 yield.

[0078] This example demonstrates that the yield of ethylene from the same amount of naphtha is dramatically increased, by as much as than 16 %. Likewise, a 13 % reduction in naphtha feedstock can be employed to produce the same amount of ethylene. Typically, the yield of ethylene in step (c) is not 100 %, but carbon atoms from CO2 may also end up in higher olefins such as propylene and C4-isomers. As these are also valuable products of the process according to the present invention, this would not constitute a lowering in efficiency but merely a slight shift in product distribution. Importantly, any remaining CO2 present in the product mixture of step (c) is readily recycled to the CO2 hydrogenation reactor (c), thus enabling such high conversions.

Claims

A method for producing olefins from a feed comprising saturated hydrocarbons, comprising: (a) subjecting the feed to cracking to obtain a main product stream comprising olefins and H 2; (b) separating H 2 from the main product stream; (c) contacting H 2 obtained in step (b) and a carbon oxide selected from CO 2, CO and mixtures thereof, with a catalyst capable of converting H 2 and CO and / or CO 2 into olefins, to produce a secondary obtain a product stream comprising olefins; (d) combining the main product stream obtained in step (a) or in step (b) and the secondary product stream obtained in step (c); and (e) isolating olefins from the main product stream obtained in step (d).

The method of claim 1, further comprising a step (vi) wherein CO2 is converted to CO by a reverse water gas shift reaction, wherein the carbon oxide used in step (c) is the CO obtained in step (vi) includes.

A method according to claim 1 or 2, wherein the carbon oxide used in step (c) and / or step (vi) comprises CO2 which is derived at least in part as a by-product from the method according to claim 1, preferably from step (a) ).

The method of claim 3, further comprising a step (vii) wherein CO2 is separated from an exhaust gas comprising CO2 from burning fuel during step (a), wherein at least a portion of the CO2 obtained in step (vii) is used in step (c) and / or in step (vi), optionally supplemented with carbon oxide from an external source.

The method of any preceding claim, wherein at least a portion of the carbon oxide used in step (c) and / or in step (vi) is from an external source.

The method of any one of the preceding claims, wherein step (d) is upstream of step (b).

Method according to any one of the preceding claims, wherein the feed comprises naphtha, gas oil, ethane and / or propane, preferably naphtha.

A method according to any preceding claim, wherein the secondary product stream obtained in step (c) is subjected to one or more steps selected from an acid gas removal step, a primary fractionation to remove a heavy fraction from the secondary product stream, a water quench to remove a heavy fraction from the secondary product stream, a compression step, an Fb removal step, and a water removal step, before the secondary product stream is used in step (d).

The method of claim 8, wherein the secondary product stream obtained in step (c) is subjected to a CCk removal step (viii), wherein CO2 is separated from the secondary product stream before being subjected to step (d).

The method of any preceding claim, further comprising: (i) subjecting the main product stream obtained in step (a) to primary fractionation to obtain a first heavy fraction and a main product stream from which a first heavy fraction has been removed; (ii) subjecting the main product stream obtained in step (i) to a water quench to obtain a second heavy fraction and a main product stream from which a second heavy fraction has been removed; (iii) subjecting the main product stream obtained in step (ii) to a first compression step to obtain a compressed main product stream; (iv) subjecting the main product stream obtained in step (iii) to an acid gas removal step to obtain a main product stream from which acid gas has been removed; (iii ’) subjecting the main product stream obtained in step (iv) to a second compression step to obtain a compressed main product stream; and (v) subjecting the main product stream obtained in step (iii) to a water removal step to obtain a dried main product stream; wherein the main product stream obtained in step (v) is used in step (b).

The method of claim 10, wherein step (d) occurs between step (iii ') and step (v) and wherein the main product stream obtained in step (iii') is subjected to step (d) and the main product stream obtained in step (d) ) is used in step (v).

A method according to any one of the preceding claims, wherein the catalyst is selected from the group consisting of Fischer-Tropsch type catalysts, CO2 hydrogenation catalysts and reverse water gas shift / Fischer-Tropsch catalysts, preferably the catalyst is an Fe-based Fischer-Tropsch catalyst or an Fe-based CCb hydrogenation catalyst.

A method according to any one of the preceding claims, further comprising, between step (b) and step (e), a step (ix) wherein methane is removed from the main product stream.

A method according to any preceding claim, wherein step (e) is a series of steppes comprising deethanization coupled to a C2 splitter, depropanization coupled to a C3 splitter and debutanization.

A modular system suitable for performing the method according to any of claims 1-14, comprising: (a) a cracker, comprising (a1) an inlet for receiving a feed comprising saturated hydrocarbons, (a1) an outlet for ejecting a main product stream and (a3) an oven designed to burn fuel to heat the cracker, the oven (a4) including an inlet for receiving fuel and (a5) an outlet for ejecting an exhaust gas; (b) an Fb separation module, comprising (b1) an inlet for receiving the main product stream, (b2) means for separating Fb from the main product stream, (b3) a first outlet for ejecting Fb and (b4) a second outlet for ejecting a main product stream from which Fb is removed; (c) a CCb hydrogenation reactor comprising (c1) one or more inlets for receiving the Fb from module (b) and a carbon oxide selected from CO2, CO and a mixture thereof, (c2) a catalyst capable of Converting Fb and CO and / or CO2 to olefins, and (c3) an outlet for ejecting a secondary product stream comprising olefins; (d) a combination module comprising (d1) a first inlet for receiving the main product stream, (d2) a second inlet for receiving the secondary product stream and (d3) an outlet for ejecting a main product stream; (e) an olefin isolation module, comprising (el) an inlet for receiving the main product stream, (e2) means for isolating olefins from the main product stream, and (e3) one or more outlets for ejecting olefins.