WO2026003178A1

WO2026003178A1 - Process for increasing the yield of a steam cracker by using off-gas from hydroprocessing

Info

Publication number: WO2026003178A1
Application number: PCT/EP2025/068084
Authority: WO
Inventors: Christian Ejersbo STREBEL; Ashwin Singh TENSINGH
Original assignee: Haldor Topsoe AS
Current assignee: Topsoe AS
Priority date: 2024-06-27
Filing date: 2025-06-26
Publication date: 2026-01-02
Anticipated expiration: 2026-12-27

Abstract

A process for converting a hydrocarbonaceous feed into a hydrocarbon product is described. The process comprises subjecting the hydrocarbonaceous feed to hydroprocessing stages, thereby producing a hydroprocessed liquid stream and an off-gas stream. The off-gas stream is separated into a first off-gas stream mainly comprising H2 and C1 and a second off-gas stream mainly comprising C2-C3 or C2-C4. The second off-gas stream and the hydroprocessed liquid stream are subjected to a steam cracking process.

Description

TITLE

Process for increasing the yield of a steam cracker by using off-gas from hydroprocessing.

FIELD OF THE INVENTION

The present disclosure relates to the field of hydroprocessing and steam cracking. More specifically, it discloses a cost-effective way to use off-gas produced during hydroprocessing to increase the yield of a steam cracker while reducing greenhouse gas emissions.

BACKGROUND

Steam crackers play a pivotal role in the petrochemical industry, particularly in the production of olefins such as ethylene and propylene, which are key building blocks for a variety of chemical products. In a steam cracker, hydrocarbon feedstocks like naphtha, ethane, propane, or butane are heated to temperatures above 800 degrees Celsius in the presence of steam, causing the hydrocarbon molecules to break apart in a process known as thermal cracking. The resulting olefins are then separated and purified for further use.

Hydrocarbon feedstocks suitable for steam crackers can be obtained from renewable feedstocks. The process for hydroprocessing fatty acid-based feedstocks, such as vegetable oils and animal fats, is well understood. Newer developments include solid waste items like tires, plastic and biomass. These have previously proven too difficult to process due to the many more complex contaminants and impurities within the feeds. Today, solid waste can be processed via a liquefaction process (pyrolysis or hydrothermal liquefaction) that converts the waste to an oil, which is then purified and upgraded via hydroprocessing so it can be used as a feedstock for a steam cracker. Most liquid feed steam crackers use liquid feedstock with a boiling range between 29 and 650 degrees Celsius. Typically, the liquid feedstock is naphtha with a boiling range between 29 and 200 degrees Celsius.

Most renewable and circular feedstock derived from biomass or waste plastic have a wide boiling range with high end boiling point. Hydrotreatment and hydrocracking are therefore necessary to fully convert renewable and circular feedstocks into naphtha boiling range material suitable for steam crackers. Hydrocracking into naphtha requires a high degree of hydrocracking and there will be a high propensity to produce high yields of off-gas containing LPG (Ci- 04) and hydrogen (H2) in the hydrocracking section.

Off-gas, in the context of hydroprocessing, refers to the gaseous by-products that are generated during hydroprocessing stages such as hydrotreatment and hydrocracking. These gases typically contain a mixture of unreacted/excess hydrogen, light hydrocarbons, and impurities such as hydrogen sulfide, ammonia, and other sulfur and nitrogen compounds. The composition of the offgas is largely dependent on the type of feedstock and the specific refining process used.

Releasing the off-gas produced during hydroprocessing into the atmosphere increases greenhouse gas (GHG) emissions. Different solutions are known in the art to clean and process this off-gas.

For example, it is known to use amine wash or caustic wash to scrub the off-gas streams, helping to remove contaminants such as hydrogen sulfide, ammonia, and particulates. Although this aids in reducing the environmental impact of the refining operation, the clean off-gas would still increase GHG emissions if released into the atmosphere.

It is also known to separate the H2 from the C1-C4 in the off-gas and recycle the H2 into the hydroprocessing stages. The stream of C1-C4 can be used as fuel in a steam cracker. However, separating H2 from C1-C4 is costly. This separation would normally be done within the hydroprocessing unit and would require additional compressors and separation units such as cryogenic, membrane and pressure swing adsorption (PSA) units. In addition, burning Ci-C4 as a fuel in a steam cracker would still result in carbon emissions.

Another solution to minimize the unwanted C1-C4 in a hydrocracking process involves operating the hydrocracker in a more selective way with a lower per pass conversion, increasing the hydrocracker section feed rate. However, such adjustments increase capital and operational costs.

Therefore, there is a need for a cost-efficient solution for processing the off-gas produced during hydroprocessing without increasing GHG emissions. SUMMARY OF THE INVENTION

The present invention describes using off-gas produced during hydroprocessing stages as a feed in a steam cracker along with the hydroprocessed liquid feed. This solution not only decreases costs and reduces GHG emissions, but also contributes to increasing the yield of the steam cracker. The off-gas is neither lost nor does it involve any costly optimization of the steam cracker.

Preferably, the present invention describes routing the off-gas to an existing separation section of the steam cracker and using this section to separate C1-C4 and H2. H2 and Ci can be recycled back to hydroprocessing stages or used as fuel in the steam cracker. C2-C4 will be fed into the steam cracker along with the hydroprocessed liquid feed. The advantage is that the cost of separating H2 from C1-C4 is minimized by using the existing separation section of the steam cracker.

Such a solution implies lower cost and higher product yield, as well as less demand for selectivity in the hydrocracking section. C2 and C3 are excellent feedstocks to a steam cracker and will improve ethylene and propylene yields of the steam cracker. In addition, no carbon is released into the atmosphere and all carbon apart from Ci is used as raw material for ethylene and propylene in the process. Reducing GHG emissions provides significant economic value to a company. Circular ethylene and propylene production, with a minimal GHG emission, has a value beyond the savings in operational cost.

Preferably, the present invention describes cleaning the off-gas produced during hydroprocessing stages using a water wash. The advantage of the water wash in combination with the process described is that it reduces the H2S, NH3 and HCI amounts in the off-gas to the required levels for a steam cracker without using amine and/or caustic wash. Feedstocks coming from solid waste possess high levels of contaminants. In particular, high amounts of ammonia may be present in the off-gas. Since ammonia is soluble in water, a water wash is very efficient in getting the ammonia content of the off-gas to the required levels. The advantage is that cost and handling of caustic and amine substances is avoided. A further advantage over amine and caustic washes is that, by using high wash water to off-gas ratios, the water used in the water wash will contain sufficiently low amounts of impurities, such that it can be recycled as wash water into hydroprocessing stages. Preferably, the hydrogen that is separated in the steam cracker is recycled into the hydroprocessing stages. Such an integration between hydroprocessing and steam cracking enhances the efficiency and profitability of the overall process.

In the following, ‘a hydrocarbonaceous feed’ shall be used to signify a feedstock rich in molecules comprising hydrogen and carbon, but possibly also heteroatoms, i.e. other elements, such as oxygen, sulfur and nitrogen.

Commonly, hydrocarbonaceous feedstock derived from a thermochemical decomposition of a solid renewable material, comprises 40-85 wt% C and 3-50 wt% 0 and an atomic ratio between H and C of less than 1 .8 or

1.6. Hydrocarbonaceous feedstock originating from thermal decomposition of artificial polymers may involve 0.5-5 wt% or 0.5-10 wt% of conjugated di-olefins and as much as 30-90 wt% such as 65 wt% olefins. The atomic oxygen content may typically be below 1 wt% such as from 500 ppmwt, but it may be up to 15 wt%.

In the following, ‘a hydroprocessing stage’ shall be used to signify any process treating a hydrocarbonaceous feedstock or intermediate product in the presence of a catalytically active material and hydrogen. In particular, a hydroprocessing stage can refer to hydrotreatment, hydrocracking or hydroisomerisation. It would be understood that a hydroprocessing stage is conducted in a hydroprocessing reactor or in a catalytic bed of the hydroprocessing reactor. A hydroprocessing reactor may comprise one or more catalytic beds.

In the following, ‘a hydrotreatment stage’ shall be used to signify any process treating a hydrocarbonaceous feedstock or intermediate product in the presence of a catalytically active material and hydrogen, in which the objective and dominant reaction is conversion by addition of hydrogen in the existing hydrocarbon structure, typically while either removing heteroatoms such as sulfur, oxygen or nitrogen or while saturating olefinic bonds. Hydrotreatment may have the effect of rearranging the structure of some hydrocarbons, but it is not the primary objective or effect of hydrotreatment.

In the following, ‘a hydrocracking stage’ shall be used to signify any process treating a hydrocarbonaceous feedstock or intermediate product in the presence of a catalytically active material and hydrogen, in which the objective and dominant reaction is breaking carbon-carbon bonds, such that the size of molecules is reduced, or rings are opened. In the following, ‘a hydroisomerisation stage’ shall be used to signify any process treating a hydrocarbonaceous feedstock or intermediate product in the presence of a catalytically active material and hydrogen, in which the objective and dominant reaction is to convert straight-chain hydrocarbons into branched isomers. This process involves the rearrangement of the carbon atoms within the hydrocarbon molecules to create a more compact and branched structure with the objective of lowering freezing point.

In the present context, the terms ‘stage’ and ‘unit’ shall only imply a process step, and not additional features of gas/l iquid separation or whether the step is carried out in separate vessels, unless expressed otherwise.

In the following, ‘a material catalytically active’ in a chemical reaction such as hydrotreatment or hydrocracking shall be understood as a material having significant catalytic activity and preference for said chemical reaction under the conditions used. As it will be realised by the skilled person, most reactions will show an amount of side reactions, but unless otherwise specified the term ‘a material catalytically active’ in a chemical reaction shall be understood as a combination of a material and conditions under which a commercially relevant amount of conversion takes place with higher selectivity than any other chemical reaction.

In the following, ‘a material catalytically active in hydrotreatment’ shall be understood as a material typically comprising an active metal (sulfided base metals such as nickel, cobalt, tungsten and/or molybdenum, but possibly also either elemental noble metals such as platinum and/or palladium) and a refractory support (such as alumina, silica or titania, or combinations thereof).

In the following, ‘a material catalytically active in hydroisomerisation’ typically comprises an active metal (either elemental noble metals such as platinum and/or palladium or sulfided base metals such as nickel, cobalt, tungsten and/or molybdenum), an acidic support (typically a molecular sieve showing high shape selectivity, and having a topology such as MOR, FER, MRE, MWW, AEL, TON and MTT) and a refractory support (such as alumina, silica or titania, or combinations thereof).

In the following, ‘a material catalytically active in hydrocracking’ shall be understood as of similar nature to the material catalytically active in hydroisomerisation, and it typically comprises an active metal (either elemental noble metals such as platinum and/or palladium or sulfided base metals such as nickel, cobalt, tungsten and/or molybdenum ), an acidic support (typically a molecular sieve showing high cracking activity, and having a topology such as MFI, BEA and FAU) and a refractory support (such as alumina, silica or titania, or combinations thereof). The difference to a material catalytically active in hydroisomerisation is typically the nature of the acidic support, which may be of a different structure (even amorphous silica-alumina) or have a different acidity e.g. due to silica:alumina ratio.

In the following, ‘hydrotreatment conditions’ shall be understood as conditions involving a temperature in the interval 250-400 degrees Celsius, a pressure in the interval 3-15 MPa, and a liquid hourly space velocity (LHSV) in the interval 0.1 -2, optionally together with intermediate cooling by quenching with cold hydrogen, feed or product.

In the following, ‘hydrocracking conditions’ shall be understood as conditions involving a temperature in the interval 250-400 degrees Celsius, a pressure in the interval 3-15 MPa, and a liquid hourly space velocity (LHSV) in the interval 0.5-8, optionally together with intermediate cooling by quenching with cold hydrogen, feed or product.

In the following, ‘hydroisomerisation conditions’ shall be understood as involving a temperature in the interval 250-350 degrees Celsius, a pressure in the interval 2-10 MPa, and a liquid hourly space velocity (LHSV) in the interval 0.5-8.

In the following, the unit “Barg” shall, in compliance with the practice of the field, be used to denote Bar, gauge, i.e. the pressure relative to atmospheric pressure and all pressures reported and compared shall be pressures relative to atmospheric pressure.

In the following, the term ‘Cn’ represents hydrocarbons or hydrocarbonaceous compounds comprising n carbon atoms. The range Cn-Cm represents a mixture of hydrocarbons comprising n to m carbon atoms. For example, C2-C4 represents a range of hydrocarbons comprising 2, 3 or 4 carbon atoms.

In a first aspect, the present invention discloses:

A process for converting a hydrocarbonaceous feed into a hydrocarbon product, wherein the process comprises: a. subjecting said hydrocarbonaceous feed to one or more hydroprocessing stages, thereby producing a hydroprocessed liquid stream and an off-gas stream; wherein said one or more hydroprocessing stages comprise at least one hydrotreatment stage; wherein said at least one hydrotreatment stage is conducted under effective hydrotreatment conditions in the presence of a material catalytically active in hydrotreatment and an amount of hydrogen; b. separating the off-gas stream produced during said one or more hydroprocessing stages into a first off-gas stream mainly comprising H2 and Ci and a second off-gas stream mainly comprising C2-C3 or C2-C4; c. subjecting the second off-gas stream and the liquid hydroprocessed stream to a steam cracking process, thereby producing the hydrocarbon product.

The technical advantage is that the yield of the steam cracking process is increased while carbon emissions are reduced.

In a further embodiment, the present invention discloses:

Said one or more hydroprocessing stages comprise at least one hydrocracking stage, wherein said at least one hydrocracking stage is conducted under effective hydrocracking conditions in the presence of a material catalytically active in hydrocracking and an amount of hydrogen.

In a further embodiment, the present invention discloses:

Said one or more hydroprocessing stages comprise at least one hydroisomerisation stage, wherein said at least one hydroisomerisation stage is conducted under effective hydroisomerisation conditions in the presence of a material catalytically active in hydroisomerisation and an amount of hydrogen.

In a further embodiment, the present invention discloses:

At least a first fraction of the first off-gas stream is recycled into at least one of said one or more hydroprocessing stages.

The technical advantage is that the amount of hydrogen used in the process is reduced.

In a further embodiment, the present invention discloses: The steam cracking process is heated, at least in part, by combustion of at least a second fraction of the first off-gas stream.

The technical advantage is that the amount of energy used in the process is reduced.

In a further embodiment, the present invention discloses:

Separating the off-gas stream produced during said one or more hydroprocessing stages comprises directing the off-gas stream to a separation unit of a steam cracker.

The technical advantage is that, by using the existing separation unit of the steam cracker, no additional separating units are required for processing the offgas. Therefore, as mentioned for claim 1 , the yield of the steam cracking process is increased and the carbon emissions are reduced without increasing the complexity and cost of the existing system.

In a further embodiment, the present invention discloses:

The separation unit of the steam cracker comprises a cryogenic separator.

In a further embodiment, the present invention discloses:

Cleaning the off-gas stream produced during said one or more hydroprocessing stages before separating the off-gas stream into the first off-gas stream and the second off-gas stream.

The technical advantage is that the potential contaminants present in the offgas are removed to meet the specifications of a steam cracker.

In a further embodiment, the present invention discloses:

Cleaning the off-gas stream produced during said one or more hydroprocessing stages comprises cleaning the off-gas stream with wash water and separating the cleaned off-gas from the wash water.

The technical advantage is that the off-gas is cleaned without the need to handle amine or caustic substances.

In a further embodiment, the present invention discloses: The cleaned off-gas is separated from the wash water using a knockout drum.

In a further embodiment, the present invention discloses:

At least a fraction of the wash water is recycled into at least one of said one or more hydroprocessing stages.

The technical advantage is that the amount of water used in the process is reduced.

In a further embodiment, the present invention discloses:

Said fraction of the wash water is purified before being recycled into said one or more hydroprocessing stages.

In a further embodiment, the present invention discloses:

Cleaning the off-gas stream produced during said one or more hydroprocessing stages comprises choosing a pressure, a temperature, a wash water to off-gas mass fraction ratio and a mixing efficiency so that the H2S content of the off-gas stream is reduced to less than 5 ppmw, the NH3 content of the off-gas stream is reduced to less than 5 ppmw and the HCI content of the off-gas stream is reduced to less than 1 ppmw.

The technical advantage is that the specifications of a steam cracker are met without using amine or caustic washes.

In a further embodiment, the present invention discloses:

Cleaning the off-gas stream with wash water comprises injecting the wash water into the off-gas stream, and wherein the wash water to off-gas mass fraction ratio is comprised between 3:1 and 15:1.

The technical advantage is that the wash water can be recycled without further processing, e.g. to an upstream position in the hydroprocessing unit.

In a further embodiment, the present invention discloses:

The cleaning is conducted at a temperature of between 35 and 55 degrees Celsius. In a further embodiment, the present invention discloses:

The cleaning is conducted at a pressure of between 5 and 25 Barg.

In a further embodiment, the present invention discloses:

Cleaning the off-gas stream produced during said one or more hydroprocessing stages comprises cleaning the off-gas stream with an amine wash and/or a caustic wash.

In a second aspect, the present invention discloses:

A process plant for carrying any of the process above.

In a third aspect, the present invention discloses:

A process for revamping a steam cracker comprising a heater unit and a separation unit, the process comprising: a. configuring the separation unit of the steam cracker to receive an additional stream being an off-gas stream produced during one or more hydroprocessing stages; b. directing an off-gas stream mainly comprising C2-C3 or C2-C4 into the heater unit of the steam cracker.

The technical advantage is that the yield of the steam cracker is increased and the carbon emissions are reduced without increasing the complexity and cost of the existing system.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a process for converting a hydrocarbonaceous feed into a hydrocarbon product according to an embodiment of the invention.

Fig. 2 shows an example of an integration between a hydroprocessing unit and a cleaning unit according to some aspects of the invention. DETAILED DESCRIPTION

Figure 1 depicts an embodiment of the present invention. The elements indicated by dashed lines are optional and depict preferred embodiments of the invention.

A hydrocarbonaceous feed 1 is fed into a hydroprocessing unit 100. The hydrocarbonaceous feed 1 can come from various sources such as biological feeds, municipal waste and plastic waste having undergone liquefaction processes.

The hydroprocessing unit 100 can contain various units such as hydrotreatment units, hydrocracking units, hydroisomerisation units, gas/liquid separation units, cryogenic separation units, membrane and pressure swing adsorption (PSA) units. The hydrocarbonaceous feed 1 is subjected to one or more hydroprocessing stages within the hydroprocessing unit 100. The hydroprocessing unit 100 outputs a liquid hydroprocessed stream 2 and an offgas stream 8. The liquid hydroprocessed stream 2 typically consists of hydrocarbon with a boiling range comprised between 29 and 650 degrees Celsius, such as naphtha boiling between 29 and 200 degrees Celsius. The offgas stream 8 typically consists of H2 and C1-C4 with contaminants such as NH3, H2S and HCI.

The liquid hydroprocessed stream 2 is directed to a steam cracker unit and more specifically to a steam cracker heater unit 300. The steam cracker heater unit 300 can comprise elements such as: ethane furnaces, butane furnaces, naphtha furnaces (boiling point between 29 and 210 degrees Celsius), heavy liquids furnaces (boiling point between 180 and 650 degrees Celsius) as well as other elements known in the art.

The off-gas stream 8 is optionally sent to a cleaning unit 200 to produce a clean off-gas stream 9. The clean off-gas stream 9 is then sent to a separator, preferably to the separation unit 400 of the steam cracker. The steam cracker separation unit 400 can comprise elements such as: quench units, distillation columns, cryogenic separators, compressors, dryers as well as other elements known in the art. If no cleaning unit 200 is present, the off-gas stream 8 is sent directly to a separator, such as separation unit 400 (not shown on the figure).

Hydrotreated feedstocks coming from solid waste typically possess high levels of contaminants such as H2S, NH3 and HCI that will be left in the off-gas. The amounts of these contaminants often need to be to reduced to the required levels for a steam cracker. Known methods to clean off-gas include amine wash and caustic wash.

In a preferred embodiment, the off-gas stream 8 can be cleaned with wash water 10 in the cleaning unit 200. The wash water 10 can be injected into the off-gas stream 8 using, for example, a water wash injector 40 (see figure 2). The off-gas can then be separated from the wash water to produce a clean off-gas stream 9 using, for example, a knockout drum 43 (see figure 2). The advantage of the water wash in combination with the process described is that it reduces the H2S, NH3 and HCI amounts in the off-gas stream to the required levels for a steam cracker without using amine and/or caustic wash. In the field, amine and caustic washes are used due to their higher capture efficiency. However, since ammonia is soluble in water, a water wash is very efficient in getting the ammonia content of the off-gas stream to the required levels for a steam cracker. The advantage is that handling and cost of caustic and amine solutions are avoided.

By selecting the appropriate pressure, temperature, wash water to off-gas ratio and mixing efficiency, it has been found that the values shown in the following table can be achieved through a water wash. These values meet the required specifications of a steam cracker.

In particular, the water wash can be conducted at a temperature of between 35 and 55 degrees Celsius, a pressure of between 5 and 25 Barg and a wash water to off-gas ratio of between 3:1 and 15:1 by mass fraction. The wash water 11 exiting from the cleaning unit 200 can be recycled into the hydroprocessing unit 100. In a preferred embodiment, the wash water to off-gas ratio used during cleaning is high enough to allow the wash water 11 to be directly reinjected into the hydroprocessing stages. The wash water 11 can also be purified before being reinjected into the hydroprocessing stages using, for example, a sour water stripper and/or a degasser (not shown). The wash water stream 11 can be combined with another wash water stream 12 used in the hydroprocessing stages (see for example stream 28 in figure 2).

In the separation unit 400, the off-gas stream 8, 9 is separated into a first offgas stream 5 comprising Ci and H2 and a second off-gas stream 4 comprising C2-C3 or C2-C4. It is noted that H2, Ci , C2, C3 and C4 are standard products exiting a steam cracker separation unit when processing a liquid stream such as a naphtha stream. Therefore, the separation unit 400 does not need any adjustments when processing the off-gas stream 8, 9 to separate H2, Ci , C2, C3 and C4.

A first fraction of the first off-gas stream 7 can be recycled back to the hydroprocessing unit 100. For example, a fraction of the first off-gas stream 7 can be routed to a recycle gas compressor of a hydroprocessing stage (not shown). Additionally, or alternatively, a second fraction of the first off-gas stream 6 can be fed to the steam cracker heater unit 300 as fuel. In other words, the steam cracking process can be heated by combustion of at least a fraction of the first off-gas stream 6. The second off-gas stream 4 is fed to the steam cracker heater unit 300 along with the liquid hydroprocessed stream 2 as raw material. If only C2-C3 are fed into the steam cracker, C4 can be directed to a further unit downstream of the steam cracker (not shown).

It is emphasized that the off-gas stream 8,9 and the second off-gas stream 4 form a path between the hydroprocessing unit 100 and the steam cracker heater unit 300. This path is physically distinct from the path followed by the liquid hydroprocessed stream 2 that goes directly from the hydroprocessing unit 100 to the steam cracker heater unit 300. These distinct paths allow for phasespecific processing, such as cleaning the off-gas, for example, as described above.

The hydrocarbon product 3 exiting from the steam cracker separation unit 400 can comprise ethylene, propylene, butane, pyrolysis gasoline (boiling point between 29 and 210 degrees Celsius) and pyrolysis oil (boiling point above 180 degrees Celsius). The hydrocarbon product 3 can be routed to a downstream unit for further refinement (not shown).

Figure 2 shows an example of an integration between a hydroprocessing unit 100’ and a cleaning unit 200’.

The elements represented inside hydroprocessing unit 100’ are standard elements known in the art, namely stripper 20, stripper overhead cooler 21 , stripper receiver 22, stripper overhead pump 23 and stripper feed bottoms exchanger 24. Streams of hot separator liquid 25, steam 26, cold separator liquid 27, wash water 28 and sour water 29 are also represented. The product streams coming out from hydroprocessing unit 100’ are hydroprocessed liquid stream 2’ and off-gas stream 8’. These correspond, for example, to streams 2 and 8 of figure 1 . Wash water stream 28 can correspond to wash water stream 12 of figure 1 . Additionally or alternatively, wash water stream 12 of figure 1 can be injected into other parts of hydroprocessing unit 100’ (not represented).

It is noted that other elements well-known in the art may form part of hydroprocessing unit 100’. Those elements are not the focus of the present invention and are therefore not represented.

The off-gas stream 8’ coming out of the hydroprocessing unit 100’ can be routed to an off-gas water wash injector 40 within cleaning unit 200’, where it is cleaned with wash water 10’. Wash water stream 10’ corresponds, for example, to the wash water stream 10 of figure 1 . The wash water can be separated from the cleaned off-gas in an off-gas knockout drum 43. The clean off-gas 9’ can then be routed to a steam cracker separation unit. This corresponds, for example, to off-gas stream 9 being routed to steam cracker separation unit 400 of figure 1 . The wash water 1T can be recycled into hydroprocessing stages, with or without prior purification. This corresponds, for example, to wash water stream 11 of figure 1. The wash water 1T can be reinjected at different location within hydroprocessing unit 100’, for example at stream 28. The wash water 1T can be reinjected at other locations within hydroprocessing unit 100’ (not shown). Optionally, an off-gas cooler 42 can be used to inject cooling water 41 into the mixed gas/water stream.

In this proposed scheme, the stringent specifications of a steam cracker are met without amine and caustic treatment.

The present invention also discloses a process for revamping an existing steam cracker comprising a heater unit and a separation unit. In addition to receiving a liquid stream, for example a naphtha liquid stream, the separation unit of the steam cracker is configured to receive an additional stream of off-gas produced during one or more hydroprocessing stages. The off-gas stream can be separated into a first off-gas stream comprising Ci and H2 and a second off-gas stream comprising C2-C3 or C2-C4 by the separation unit of the steam cracker. The second off-gas stream is fed into the heater unit of the steam cracker along with the liquid stream.

Along with hydrocarbon products comprising ethylene, propylene, butane, pyrolysis gasoline (boiling point between 29 and 210 degrees Celsius) and pyrolysis oil (boiling point above 180 degrees Celsius), a steam cracker also produces H2, Ci , C2, C3 and C4. Therefore, the separation unit of the steam cracker does not need any adjustments when processing the off-gas stream to separate H2, Ci , C2, C3 and C4. However, as these streams are normally not desired, a standard steam cracker is optimized to minimize their production. The purpose of the revamping process is to make use of the streams of C2, C3 and optionally C4 by feeding them back into the steam cracker heater unit. This ultimately increases the amount of ethylene, propylene, butane, pyrolysis gasoline and pyrolysis oil produced by the steam cracker and reduces lost carbon streams which would have contributed to GHG emissions.

Any feature disclosed in previous embodiments in relation to figures 1 and 2 can be included in the revamping process.

REFERENCE SIGNS

1 hydrocarbonaceous feed

2, 2’ hydroprocessed liquid stream

3 hydrocarbon product

4 second off-gas stream

5 first off-gas stream

6 second fraction of first off-gas stream

7 first fraction of first off-gas stream

8, 8’ off-gas stream , 9 off-gas stream 0, 10’ wash water 1 , 11’ recycled fraction of wash water2 wash water 0 stripper 1 stripper overhead cooler2 stripper receiver 3 stripper overhead pump 4 stripper feed bottoms exchanger5 hot separator liquid 6 steam 7 cold separator liquid 8 wash water 9 sour water 0 off-gas water wash injector1 cooling water 2 off-gas cooler 3 off-gas knockout drum 00, 100’ hydroprocessing unit 00, 200’ cleaning unit 00 steam cracker heater unit00 steam cracker separation unit

Claims

1 . A process for converting a hydrocarbonaceous feed (1 ) into a hydrocarbon product (3), wherein the process comprises: a. subjecting said hydrocarbonaceous feed (1 ) to one or more hydroprocessing stages, thereby producing a hydroprocessed liquid stream (2) and an off-gas stream (8, 8’, 9, 9’); wherein said one or more hydroprocessing stages comprise at least one hydrotreatment stage; wherein said at least one hydrotreatment stage is conducted under effective hydrotreatment conditions in the presence of a material catalytically active in hydrotreatment and an amount of hydrogen; b. separating the off-gas stream (8, 8’, 9, 9’) produced during said one or more hydroprocessing stages into a first off-gas stream (5) mainly comprising H2 and Ci and a second off-gas stream (4) mainly comprising C2-C3 or C2-C4; c. subjecting the second off-gas stream (4) and the liquid hydroprocessed stream (2) to a steam cracking process, thereby producing the hydrocarbon product (3).

2. The process according to claim 1 , wherein said one or more hydroprocessing stages comprise at least one hydrocracking stage, wherein said at least one hydrocracking stage is conducted under effective hydrocracking conditions in the presence of a material catalytically active in hydrocracking and an amount of hydrogen.

3. The process according to claims 1 or 2, wherein said one or more hydroprocessing stages comprise at least one hydroisomerisation stage, wherein said at least one hydroisomerisation stage is conducted under effective hydroisomerisation conditions in the presence of a material catalytically active in hydroisomerisation and an amount of hydrogen.

4. The process according to any one of claims 1 to 3, wherein at least a first fraction (7) of the first off-gas stream (5) is recycled into at least one of said one or more hydroprocessing stages.

5. The process according to any one of claims 1 to 4, wherein the steam cracking process is heated, at least in part, by combustion of at least a second fraction (6) of the first off-gas stream (5).

6. The process according to any one of claims 1 to 5, wherein separating the off-gas stream (8, 8’, 9, 9’) produced during said one or more hydroprocessing stages comprises directing the off-gas stream (8, 8’, 9, 9’) to a separation unit (400) of a steam cracker.

7. The process according to claim 6, wherein the separation unit (400) of the steam cracker comprises a cryogenic separator.

8. The process according to any one of claims 1 to 7, further comprising cleaning the off-gas stream (8, 8’) produced during said one or more hydroprocessing stages before separating the off-gas stream (9, 9’) into the first off-gas stream (5) and the second off-gas stream (4).

9. The process according to claim 8, wherein cleaning the off-gas stream (8, 8’) produced during said one or more hydroprocessing stages comprises cleaning the off-gas stream (8, 8’) with wash water (10, 10’) and separating the cleaned off-gas from the wash water.

10. The process according to claim 9, wherein the cleaned off-gas is separated from the wash water using a knockout drum (43).

11 . The process according to claims 9 or 10, wherein at least a fraction (11 , 1 T) of the wash water (10, 10’) is recycled into at least one of said one or more hydroprocessing stages.

12. The process according to claim 11 , wherein said fraction (11 , 1T) of the wash water (10, 10’) is purified before being recycled into said one or more hydroprocessing stages.

13. The process according to any one of claims 9 to 12, wherein cleaning the off-gas stream (8, 8’) produced during said one or more hydroprocessing stages comprises choosing a pressure, a temperature, a wash water to off-gas mass fraction ratio and a mixing efficiency so that the H2S content of the off-gas stream is reduced to less than 5 ppmw, the NH3 content of the off-gas stream is reduced to less than 5 ppmw and the HCI content of the off-gas stream is reduced to less than 1 ppmw.

14. The process according to any one of claims 9 or 13, wherein cleaning the off-gas stream (8, 8’) with wash water (10, 10’) comprises injecting the wash water (10, 10’) into the off-gas stream (8, 8’), and wherein the wash water to off-gas mass fraction ratio is comprised between 3:1 and 15:1 .

15. The process according to claims 9-14, wherein the cleaning is conducted at a temperature of between 35 and 55 degrees Celsius.

16. The process according to claims 9-15, wherein the cleaning is conducted at a pressure of between 5 and 25 Barg.

17. The process according to claim 8, wherein cleaning the off-gas stream (8, 8’) produced during said one or more hydroprocessing stages comprises cleaning the off-gas stream (8, 8’) with an amine wash and/or a caustic wash.

18. A process plant for carrying the process of any preceding claim.

19. A process for revamping a steam cracker comprising a heater unit (300) and a separation unit (400), the process comprising: a. configuring the separation unit (400) of the steam cracker to receive an additional stream (8, 8’, 9, 9’) being an off-gas stream produced during one or more hydroprocessing stages; b. directing an off-gas stream (4) mainly comprising C2-C3 or C2- C4 into the heater unit (300) of the steam cracker.