Field of the invention

The invention relates to a process of ethylene valorization from diluted streams of varied origin at low pressure in order to reduce a waste of ethylene containing gas. This ethylene is directed to the production of more valuable liquids.

Background of the invention

Refinery off-gases, e.g., Fluid Catalytic Cracking (FCC) off-gas and Delayed Cocker Unit (DCU) off-gas, contain significant amount of ethylene (5-50 wt% as based on the total weight of the feedstream) and nowadays are burned as fuel gas. From both economical and environmental point of view, it could be interesting to recover this wasted ethylene. Moreover, development of Oxidative Coupling of Methane (OCM) technology gives even more ethylene on the market, which needs to be valorized into easier transportable liquid products. From these ethylene streams, others types of products than polyethylene can be considered to be formed, such as aromatic hydrocarbons.

Few industrial technologies including heterogeneous catalysis of ethylene transformation into liquids exists, the aromatic hydrocarbons content being of at least 30 wt% as based of the total weight the total products. The end products of all these processes are hydrocarbons of at least 5 carbons atoms (C5+), liquid, applied as motor fuels. Most of the technologies are using metal exchanged (typically Zn or Ga) ZSM-5 as a catalyst and low pressure (0.1 to 1 MPa). The product composition can account for up to 30 wt% of Liquefied Petroleum Gas (LPG) as based on the total weight of the production composition, reducing the carbon efficiency of the process. The content of aromatic hydrocarbons in the product mixture can be tuned depending on the choice of the operating conditions and of the catalyst. Higher carbon efficiency (less than 9 wt% of LPG) can be achieved with the use of Ni-Si02 Al203 catalyst, but the process require high pressure which severely increases the costs.

In "Heterogeneous oligomerization of ethylene over highly active and stable Ni-AI-SBA-15 mesoporous catalysts" by Andrei, R. D. et al., Journal of Catalysis, 323 (2015) 76-84; Ni-AI- SBA-15 catalyst has been shown to have superior performance in terms of activity and stability compared to known catalysts (Ni-zeolites, Ni-Si02 Al203, Ni-MCM-41 ) for oligomerization of concentrated ethylene (at least 99.9 wt%) at high pressure (> 29 barg).

In "Nickel and molybdenum containing mesoporous catalysts for ethylene oligomerization and metathesis" by Andrei, R. D. et al., New J. Chem 40 (2016) 4146-4152; Ni-Al-Si0 ₂ (where Si0 ₂ is a non-ordered mesoporous silica) catalyst was evaluated for oligomerization of concentrated ethylene (at least 99.9 wt%) at high pressure 3.0 MPa and showed a conversion of 80% of ethylene with a selectivity of about 50 % to C4.

CN 103752346 discloses a process of aromatization of Fischer-Tropsch tail gas using a catalyst comprising a platinum-supported inorganic refractory oxide and a transition metal acid modified ZSM-5 molecular sieve at a temperature of at least 550°C.

WO 98/05738 describes a multi-step process for converting non-aromatic hydrocarbons to lower olefins and aromatic hydrocarbons via a two step process.

Thus there is still a need for a process to convert the refinery off-gases, such as fluid catalytic cracking (FCC) off gases, into valuable products without the need of purification of the stream to concentrate it. There is a need for a process to convert refinery off-gases comprising ethylene to aromatic hydrocarbons with high carbon efficiency and which is cost efficient.

It is an object of the invention to provide a new process and a new use of a catalyst for the conversion of diluted stream of ethylene into aromatic hydrocarbons that is cost effective and have high carbon efficiency. It is also an objective of the invention to provide a new process and a new use of a catalyst that further shows an improved selectivity toward aromatic hydrocarbons.

Summary of the invention

According to a first aspect, the invention provides a process for the conversion of ethylene into aromatic hydrocarbons wherein the process comprises: a) providing a feedstream comprising from 0.5 to 50 wt% of ethylene as based on the total weight of the feedstream;

b) putting the feedstream in contact with a first and a second catalyst at a temperature ranging from 80 to 500°C and under a pressure ranging from 0.1 to 2.9 MPa; wherein the feedstream is put in contact with the first and the second catalysts together in a single reactor as a catalyst composition or wherein the feedstream is put in contact with the first and the second catalysts subsequently in reactors arranged in series;

c) recovering the aromatic hydrocarbons; further wherein in step b) the first catalyst consists of one or more metals of group VIIIB and/or of group VIB deposited on a support being a mesoporous material, and the second catalyst is a zeolite or is Pt/CI/AI ₂ 0 ₃ .

Reference to metals of group VIIIB and of group VIB is made according to the CAS classification. It has been found by the inventors that, surprisingly, said catalysts can be used in aromatization process to convert ethylene from diluted stream at low reaction pressure with high carbon efficiency of more than 80 % and with a high selectivity to aromatic hydrocarbons up to 85 %. The invention permits using FCC off gases as fuel gases in order to upgrade them into valuable products without the need of high cost compression and without the need of any purification of the stream.

In a preferred embodiment the invention provides a process for the conversion of ethylene into aromatic hydrocarbons wherein the process comprises: a) providing feedstream comprising from 0.5 to 50 wt% of ethylene as based on total weight of the feedstream;

b) putting the feedstream in contact with a first and a second catalyst at a temperature ranging from 80 to 500°C, under a pressure ranging from 0.1 to 2.9 MPa and at a weight hourly space velocity (WHSV) of the feedstream ranging from 0.1 to 10.0 h ^"1 ; wherein the feedstream is put in contact with the first and the second catalysts together in a single reactor as a catalyst composition or wherein the feedstream is put in contact with the first and the second catalysts subsequently in reactors arranged in series;

c) recovering the aromatic hydrocarbons; further wherein in step b) the first catalyst consists of one or more metals of group VIIIB and/or of group VIB deposited on a support being a mesoporous material, and the second catalyst is a zeolite or is Pt/CI/AI ₂ 0 ₃ .

The WHSV is determined on the total feed.

Indeed, it has also been found by the inventors that conducting the reaction at low WHSV of 10.0 h ^"1 or less combined with a diluted stream of ethylene increases the contribution of olefins having 4 carbon atoms in the product distribution of the oligomerization reaction, thus further improves the aromatization results.

With preference, one or more of the following features can be used to better define the first catalyst of step b):

The mesoporous material is an ordered mesoporous material or any type of mesoporous material based on silica.

The mesoporous material is an Al-containing material, preferably Al modified silica type.

The mesoporous material of the first catalyst of step b) is a mesopourous material of SBA-15 topology or is a mesopourous material of Al-modified silica type. The one or more metals of group VI 11 B and/or of group VI B of the first catalyst of step b) are selected from nickel, cobalt, chromium, molybdenum, tungsten, palladium and any mixture thereof.

The one or more metals of group VI 11 B and/or of group VIB is a mixture of nickel with one or more metals selected from cobalt, chromium, tungsten, palladium, molybdenum and any mixture thereof, preferably the mixture comprises more than 50 wt% of nickel as based on the total weight of the mixture, more preferably more than 70 wt% of nickel. The first catalyst of step b) consists of nickel deposited on a support being a mesoporous material, preferably on a support being an aluminated ordered mesoporous material.

The first catalyst of step b) consists of nickel deposited on a support being a mesoporous material, and the catalyst comprises from 0.5 to 10.0 wt% of nickel based on the total weight of the catalyst as determined according to UOP961 -12, preferably from 1 .0 to 5.0 wt% and more preferably from 2.0 to 3.0 wt%.

The first catalyst of step b) consists of nickel deposited on a support being a mesoporous material of SBA-15 topology, preferably the catalyst is Ni-AI-SBA-15. The first catalyst of step b) consists of nickel deposited on a support being a mesopourous material of Al-modified silica type, preferably the catalyst is Ni-AI-SiC>2. The first catalyst of step b) comprises a mesoporous material with mesoporous pores having an average diameter ranging from 2 to 50 nm as determined according to ASTM D 4641 - 94 (reapproved 2006), preferably ranging from 5 to 40 nm.

The first catalyst of step b) comprises a mesoporous material with mesoporous pores having an average diameter of at least 2nm, preferably of at least 5 nm, more preferably of at least 7 nm as determined according to ASTM D 4641 - 94 (reapproved 2006), and even more preferably of at least 7.5 nm.

The mesoporous material of the catalyst comprises mesoporous pores having an average diameter of at least 2 nm as determined according to ASTM D 4641 - 94 (reapproved 2006) and a mesoporous pore volume of at least 0.1 mL/g as determined according to ASTM D 4641 - 94 (reapproved 2006).

The first catalyst of step b) comprises an ordered mesoporous silica material, or any other silica exhibiting a type IV isotherm.

The first catalyst of step b) has a total surface area ranging from 100 m ² /g to 1000 m ² /g, preferably from 120 m ² /g to 700 m ² /g, more preferably from 150 m ² /g to about 500 m ² /g, as determined by N2 sorption analysis according to ASTM D 4365 - 95 (reapproved 2008).

The first catalyst of step b) has a bulk Si/AI ratio ranging from 5 to 10, preferably from 6 to 8, as determined according to UOP961 -12. With preference, one or more of the following features can be used to better define the second catalyst of step b):

The second catalyst is a zeolite selected from ZSM-5, Pt-Y and Pt-BETA and mixtures thereof.

- The second catalyst is a zeolite of the MFI group, preferably ZSM-5.

The second catalyst is a zeolite selected from H-ZSM-5, Ga-ZSM-5 and Zn-ZSM-5.

With preference, one or more of the following features can be used to better define the process of the invention:

The reactions of step b) are performed at a weight hourly space velocity (WHSV) of the feedstream of from 0.1 to 10.0 h ^"1 , preferably from 0.5 to 8.0 h ^"1 , more preferably from

1 to 5.0 h ^"1 .

The feedstream comprises at least 2 wt% of ethylene based on the total weight of the feedstream, preferably at least 3 wt% of ethylene, more preferably at least 5 wt% of ethylene, even more preferably at least 10 wt% of ethylene, most preferably at least 15 wt% of ethylene.

The feedstream comprises at most 45 wt% of ethylene based on the total weight of the feedstream, more preferably at most 40 wt%, even more preferably at most 35 wt% and most preferably at most 30 wt%.

The process is carried out without replacement or reactivation of the catalysts during more than 40 hours, preferably more than 50 hours, more preferably more than 60 hours, and even more preferably more than 70 hours.

The feedstream comprises from 0.1 to 5.0 wt% of CO as based on the total weight of the feedstream, preferably less than 2.0 wt%, more preferably less than 1.0 wt%. The feedstream comprises from 2.0 to 20.0 wt% of hydrogen as based on the total weight of the feedstream, preferably less than 4.0 wt%.

The feedstream comprises less than 90 wt ppm of CO and less than 1 .0 wt% of hydrogen as based on the total weight of the feedstream.

The feedstream comprises from 0.1 to 5.0 wt% of CO2 as based on the total weight of the feedstream, preferably less than 3.0 wt%, and more preferably less than 1.0 wt%. - The feedstream comprises at most 10000 wt ppm of water based on the total weight of the feedstream, preferably at most 1000 wt ppm, more preferably at most 500 wt ppm. The feedstream comprises less than 0.01 wt% of H2S and N H3 as based on the total weight of the feedstream.

In a preferred embodiment, in step b) the feedstream is put into contact with a first and a second catalyst together in a single reactor as a catalyst composition wherein the first and second catalysts are present in the catalyst composition in a weight ratio ranging from 10:1 to 1 :1 , preferably ranging from 5:1 to 1 :1 , more preferably ranging from 2:1 to 1 :1 respectively.

In a preferred embodiment, in step b) the feedstream is put into contact with a first and a second catalyst together in a single reactor as a catalyst composition wherein:

the feedstream is put into contact with a first and a second catalyst at a temperature ranging from 150 to 450°C, more preferably at a temperature ranging from 200 to 400°C, and/or

the feedstream is put into contact with a first and a second catalyst under a pressure ranging from 0.2 to 1 MPa, and most preferably from 0.3 to 0.7 MPa.

the feedstream is put into contact with a first and a second catalyst at an ethylene partial pressure of at most 1 .0 MPa, preferably of at most 0.8 MPa, more preferably of at most 0.5 MPa and even more preferably of at most 0.4 MPa.

In another embodiment, in step b), the feedstream is put into contact with a first and a second catalyst subsequently in reactors arranged in series and the feedstream is put in contact with the first catalyst in a first reactor under a pressure ranging from 0.1 to 2.9 MPa, preferably ranging from 0.5 to 2.0 MPa, and most preferably from 1 ,0 to 1 ,5 MPa.

In an embodiment, in step b), the feedstream is put into contact with a first and a second catalyst subsequently in reactors arranged in series and the feedstream is put in contact with the first catalyst in a first reactor under an ethylene partial pressure of at most 1 .45 MPa, preferably of at most 1 .0 MPa, more preferably of at most 0.8 MPa, and even more preferably of at most 0.5 MPa and even more preferably of at most 0.4 MPa.

In another embodiment, in step b), the feedstream in contact with a first and a second catalyst subsequently in reactors arranged in series and the feedstream is put in contact with the first catalyst in a first reactor at a temperature ranging from 150 to 350°C, more preferably at a temperature ranging from 180 to 280°C.

In an embodiment, in step b) the feedstream in contact with a first and a second catalyst subsequently in reactors arranged in series and the feedstream is put in contact with the second catalyst in a second reactor under a pressure ranging from 0.2 to 1 MPa, and preferably from 0.3 to 0.7 MPa.

In an embodiment, in step b) the feedstream in contact with a first and a second catalyst subsequently in reactors arranged in series and the feedstream is put in contact with the second catalyst in a second reactor at a temperature ranging from 150 to 450°C, more preferably at a temperature ranging from 200 to 400°C. According to a second aspect the invention provides the use of a catalyst consisting of one or more transition metals deposited on a support being a mesoporous material as first catalyst in a process to convert ethylene into aromatics hydrocarbons as defined in the first aspect, wherein the process comprises a step wherein:

- the feedstream is put in contact with a first and a second catalyst at a temperature ranging from 80 to 500°C and under a pressure ranging from 0.1 to 2.9 MPa;

the feedstream is put in contact with the first and the second catalysts together in a single reactor as a catalyst composition or the feedstream is put in contact with the first and the second catalysts subsequently in reactors arranged in series;

- the second catalyst is a zeolite or Pt/CI/A Os, and

the feedstream comprises from 0.5 to 50 wt% of ethylene as based on the total weight of the feedstream.

The invention provides the use of a catalyst consisting of one or more metals of group VI 11 B and/or of group VIB deposited on a support being a mesoporous material, in a process to convert ethylene into aromatics hydrocarbons, wherein said catalyst is the first catalyst is as defined in the first aspect. Thus, preferably the mesoporous material is an ordered mesoporous material or any type of mesoporous material based on silica and more preferably the mesopourous material of the first catalyst is a mesoporous material of SBA-15 topology, or is a mesopourous material of Al-modified silica type. More preferably, the first catalysts consists of nickel deposited on a support being a mesoporous material of SBA-15 topology, preferably the first catalyst is Ni-AI-SBA-15; or consists of nickel deposited on a support being a mesopourous material of Al-modified silica type, preferably the first catalyst is Ni-AI-SiC>2.

With preference the second catalyst is selected a zeolite selected from ZSM-5, Pt-Y and Pt- BETA and mixtures thereof. More preferably the second catalyst is a zeolite selected from H- ZSM5, Zn-ZSM-5, Ga-ZSM-5 and any mixture thereof.

With preference the use is performed in a process conducted at a weight hourly space velocity (WHSV) of the feedstream ranging from 0.1 to 10.0 h ^~1 .

Preferably, the feedstream comprises at most 45 wt% of ethylene based on the total weight of the feedstream, more preferably at most 40 wt%, even more preferably at most 35 wt% and most preferably at most 30 wt%.

With preference, the feedstream comprising ethylene is an effluent of a process selected from methanol to Olefin process (MTO), ethane/naphta cracker process, bio-ethanol process or oxidative coupling of methane process (OCM), or is a fluid catalytic cracking (FCC) off gases. Description of the figures:

Figure 1 illustrates, for Ni-AI-SBA-15 catalyst, the conversion and selectivity of ethylene oligomerisation from diluted streams at P = 1 .5 MPa, T = 250 °C, 17 wt% C2- in N ₂ stream as based on the total weight of the stream, WHSV (feed) = 0.75 h ^"1 .

- Figure 2 illustrates, for Ni-AI-SBA-15 catalyst, the influence of WHSV on conversion and selectivity of ethylene oligomerisation from diluted streams at WHSV (feed) of 1 .75 and 3.5 IT ¹ after 10 hours TOS at T = 250 °C, P = 1 .5 MPa, 17 wt% C ₂ - in N ₂ stream as based on the total weight of the stream.

Figure 3 illustrates, for Ni-AI-SBA-15 catalyst, the space time yield of ethylene oligomerisation from diluted streams at WHSV (feed) 0.75, 1.75 and 3.5 h ^"1 after 10 hours TOS at T = 250 °C, P = 1 .5 MPa, 17 wt% C2- in N ₂ stream as based on the total weight of the stream.

Figure 4 illustrates the conversion and selectivity of ethylene oligomerisation and aromatisation from diluted streams at WHSV (feed) 0.75 h ^"1 (oligomerisation), 1 .5 h ^"1 (aromatisation), after 40 hours TOS. T = 350 °C, P = 4 MPa

Detailed description of the invention

As used herein the term "catalyst" refers to a "supported catalyst" which is a catalyst comprising an active phase and a support.

As used herein the term "aromatics hydrocarbons" refers to hydrocarbons with sigma bonds and delocalized pi electrons between carbon atoms forming rings.

The invention relates to the conversion of ethylene from a diluted stream having at most 50 wt% of ethylene, into aromatic hydrocarbons via succession of oligomerization and aromatization reactions in presence of a first catalyst consisting of one or more metals of group VIIIB and/or of group VIB deposited on a support being a mesoporous material. Preferably, the first catalyst consists of nickel deposited on a support being a mesoporous material. The first catalyst is the catalyst of the oligomerization reaction. The second catalyst is the catalyst of the aromatization reaction. Both reactions are conducted on a diluted ethylene stream, under low pressure and with preference at a low weight hourly space velocity (WHSV).

The invention relates to a process for the conversion of ethylene into aromatic hydrocarbons wherein the process comprises: a) providing afeedstream comprising from 0.5 to 50 wt% of ethylene as based on the total weight of the feedstream;

b) putting the feedstream in contact with a first and a second catalyst at a temperature ranging from 80 to 500°C and under a pressure ranging from 0.1 to 2.9 MPa; wherein the feedstream is put in contact with the first and the second catalysts together in a single reactor as a catalyst composition or the feedstream is put in contact with the first and the second catalysts subsequently in reactors arranged in series;

c) recovering the aromatic hydrocarbons ; wherein in step b) the first catalyst consists of one or more metals of group VII IB and/or of group VI B deposited on a support being a mesoporous material, and the second catalyst is a zeolite or Pt/CI/AI ₂ 0 ₃ .

In a preferred embodiment the process is carried out at a weight hourly space velocity (WHSV) of the feedstream ranging from 0.1 to 10.0 h ^"1 . The WHSV is determined on the total feed. The invention provides a process to convert a diluted stream of ethylene into aromatic hydrocarbons, wherein the diluted feedstream comprises at least 5 wt% of ethylene as based on the total weight of the feedstream, preferably at least 10 wt%, more preferably at least 15 wt%. In an embodiment of the invention the feedstream comprises at most 50 wt% of ethylene as based on the total weight of the feedstream, preferably at most 45 wt%, more preferably at most 40 wt%, even more preferably at most 35 wt% and most preferably at most 30 wt%.

According to the invention, the feedstream comprises ethylene diluted into inert components such as a mixture of ChU, C2H6, C3H8, N2. The feedstream can have a typical composition of an FCC off gases i.e. the feedstream can comprise ethylene diluted into a mixture of CH4, C ₂ H ₆ , C ₃ H ₈ , N ₂ together with C3 and C4 olefins. However, the feedstream may also comprise some contaminants such as carbon oxide (CO), carbon dioxide (CO2), hydrogen (H2) and H2O. In such a case, the feedstream preferably comprises from 0.1 to 5.0 wt% of CO, preferably less than 2.0 wt% more preferably less than 1 .0 wt% CO. Preferably, the feedstream comprises from 0.1 to 5.0 wt% of CO2, preferably less than 3.0 wt% CO2. Preferably, the feedstream comprises from 2.0 to 20.0 wt% of hydrogen, preferably less than 4.0 wt% H2. All wt% are based on the total weight of the feedstream. Preferably the feedstream comprises less than 1 .0 wt% of H2 based on the total weight of the feedstream.

In an embodiment, the feedstream comprises less than 0.01 wt% of H2S and NH3 as based on the total weight of the feedstream. In an embodiment, the feedstream comprises at most 10000 wt ppm of water based on the total weight of the feedstream, preferably at most 1000 wt ppm, more preferably at most 500 wt ppm. When the feedstream comprises more than 1000 wt ppm it is preferable to dry the feedstream In a preferred embodiment the reaction is carried out in a single reactor and the feedstream in contact with a catalyst composition being a mixture comprising the first and the second catalysts. The process is carried out in an installation comprising:

an optional purification section consisting of amine absorber, water wash unit, guard bed and drying section;

a batch (CSTR), fixed or fluidized bed oligomerisation reactor, preferably in a fixed catalyst bed mode preferably equipped with an heat exchange system;

lines to introduce the feedstream to the reactor and remove products from the reactor; an oligomerisation separation device to separate gas and liquid products;

- a temperature sensor and controller for detecting and controlling the temperature of the reactor at a reaction temperature ranging from 80 to 500°C;

flow controllers to control the weight hourly space velocity (WHSV) of the feedstream to the reactors, preferably of from 0.1 to 10.0 h ^"1 ; and

a pressure controller to control the reactor pressure to a pressure ranging from 0.1 to 2.9 MPa.

The installation according to the invention can further comprise a separation device to recover unreacted ethylene and lines to recycle said unreacted ethylene into the reactor.

With preference, the first and second catalysts are present in the catalyst composition in a weight ratio ranging from 10:1 to 1 :1 , preferably ranging from 5:1 to 1 :1 , more preferably ranging from 2:1 to 1 :1 respectively. The ratio of 1 :1 is preferred. If the ratio is not 1 :1 it is preferable to have the first catalyst being predominant in the catalyst composition.

The above catalyst composition is useful for the conversion of ethylene into aromatic hydrocarbons by oligomerization and aromatization reactions.

With preference, the process according to all embodiments wherein the feedstream is put into contact with the first and the second catalysts together in a single reactor as a catalyst composition, the reaction is carried out at a reaction temperature of at least 100°C, preferably of at least 150°C, more preferably of at least 180°C and even more preferably of at least 200°C. In an embodiment, the temperature is kept below 500°C, preferably below 450°C, more preferably below 400°C and even more preferably below 350°C. With preference, the process according to all embodiments wherein the feedstream is put into contact with a first and a second catalyst together in a single reactor as a catalyst composition, the reaction is carried out at a pressure of at least 0.1 MPa, preferably of at least 0.15 MPa, more preferably of at least 0.2 MPa and even more preferably of at least 0.28 MPa. Preferably the pressure is at most 1 .0 MPa, preferably at most 0.7 MPa, more preferably at most 0.65 MPa, even more preferably at most 0.6 MPa and most preferably at most 0.5 MPa. In another embodiment, the reaction is carried out in two reactors arranged in series and the feedstream in contact in a first step with the first catalyst and subsequently in a second step with the second catalyst. The process is carried out in an installation comprising:

an optional purification section consisting of amine absorber, water wash unit, guard bed and drying section;

two reactors arranged in series; wherein the first one is an oligomerisation reactor, preferably in a fixed catalyst bed mode ;

lines to introduce the feedstream within the first reactor, to remove intermediate products from the first reactor, to direct intermediate products to the second reactor and to remove final products from the second reactor ;

an oligomerisation separation device to separate gas and liquid products;

temperature sensors and controllers for detecting and controlling the temperature of the reactors at a reaction temperature ranging from 80 to 500°C;

flow controllers to control the weight hourly space velocity (WHSV) of the feedstream to the reactors preferably of from 0.1 to 10.0 h ^"1 ; and

pressure controllers to control the reactors pressure to a pressure ranging from 0.1 to

2.9 MPa.

The installation according to the invention can further comprises a separation device to recover unreacted ethylene and lines to recycle said unreacted ethylene into the first reactor. With preference, when in step b) the feedstream in contact with the first and the second catalysts subsequently in reactors arranged in series and the feedstream is put in contact with the first catalyst in a first reactor at a temperature ranging from 100 to 500°C, preferably 150 to 350°C, more preferably at a temperature ranging from 180 to 280°C.

Preferably, when in step b) the feedstream in contact with the first and the second catalysts subsequently in reactors arranged in series and the feedstream is put in contact with the first catalyst in a first reactor under a pressure ranging from 0.1 to 2.9 MPa, preferably ranging from 0.5 to 2.0 MPa, and most preferably from 1 .0 to 1.5 MPa.

With preference, in step b) the feedstream in contact with the first and the second catalysts subsequently in reactors arranged in series and the feedstream is put in contact with the second catalyst in a second reactor under a pressure ranging from 0.2 to 1 MPa, and most preferably from 0.3 to 0.7 MPa.

With preference, in step b) the feedstream in contact with the first and the second catalysts subsequently in reactors arranged in series and the feedstream is put in contact with the second catalyst in a second reactor at a temperature ranging from 150 to 450°C, more preferably at a temperature ranging from 200 to 400°C. In a preferred embodiment of the invention the process is carried out at an ethylene partial pressure of at most 1 .0 MPa, preferably of at most 0.8 MPa, more preferably of at most 0.5 MPa and even more preferably of at most 0.4 MPa.

In a mixture of gases, each gas has a partial pressure which is the hypothetical pressure of that gas if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal gas mixture is the sum of the partial pressures of each individual gas in the mixture.

It relies on the following isotherm relation:

px nx

ptot ntot

• px is the partial pressure of gas X

• tot is the total pressure of the gas mixture

• n _x is the amount of substance of gas (X)

• ntot is the total amount of substance in gas mixture

The weight hourly space velocity (WHSV) is the quotient of the mass flow rate of the reactants divided by the mass of the catalyst(s) in the reactor. In a preferred embodiment, the reactions are performed at a WHSV of at most 10.0 h ^"1 , preferably ranging from 0.1 to 9.0 h ^-1, more preferably ranging from 0.5 to 8.0 h ^"1 , and even more preferably ranging from 1 to 5.0 h ^"1 . The low WHSV combined with the dilution of ethylene and the use of the Ni-AI-SBA-15 catalyst has been shown to have an effect on the product distribution of olefins having 4 atoms of carbon (C ₄ ) and olefins having 6 atoms of carbon (Ce). Indeed, it has been shown that low WHSV increases the contribution of C ₄ over C6 (see examples).

In a preferred embodiment the process can be carried out with a stable performance with respect to activity and selectivity during more than 40 hours, preferably more than 50 hours, more preferably more than 60 hours, and even more preferably more than 70 hours without the need of reactivation or replacement of the catalysts.

In an embodiment, the process is carried out in a fixed bed or in a fluidized bed reactor comprising at least one catalytic bed. Such reactors are well-known from the person skilled in the art and for instance described in EP2257366 or in US7279138.

If the feed contains higher content of impurities, purification section can be added optionally to remove CO, CO2, H2 or H2O. Optionally, the following units can be introduced: amine absorber to remove H2S, water wash unit to remove amine from amine adsorber and decrease content of NH3 and CO2. Optionally, a guard bed can be implemented to remove impurities such as CO, CO2, H2S and/or NH3. Optionally, a drying section can be added to remove H2O, which can have a negative effect on catalyst performance.

Catalysts:

The present invention contemplates the use of two catalysts as a mixture in a catalyst composition or separately in different reactors arranged in series.

The first and second catalysts being supported catalysts, any reference to a catalyst includes a reference to a calcined supported catalyst.

The first catalyst

The catalyst consists of one or more metals of group VI MB and/or of group VI B deposited on a support being a mesoporous material. The one or more metals of group VIIIB and/or of group VIB are preferably selected from nickel, cobalt, chromium, tungsten, palladium, molybdenum and any mixture thereof. In a preferred embodiment, the active phase is a mixture of nickel with one or more metals of group VIIIB and/or of group VIB selected from cobalt, chromium, tungsten, palladium, molybdenum and any mixture thereof; preferably wherein the mixture comprises more than 50 wt% of nickel as based on the total weight of the mixture, more preferably more than 70 wt% of nickel. In another preferred embodiment nickel is the active phase of the catalyst.

According to an embodiment, the mesoporous material is obtained from a zeolitic material of the FAU, MFI, MOR or FER type framework by various post-treatment procedures. The mesoporized zeolites possesses a residual network of micropores (ie pores < 2 nm in diameter) and contains mesopores (pores with diameter in the range 2-50 nm) connected to the micropores, and a ratio of the volume of the mesopores to the volume of the micropores in the range 0.2 to 3. Further the said materials may be shaped with a binder. The preferred zeolite is FAU (zeolite Y). The mesoporization may include steaming followed by a leaching procedure to remove the extra framework aluminum.

The mesoporisation of zeolite porosity may include the following steps:

- suspending a zeolite or a composite material comprising it in a basic aqueous solution comprising at least one strong base, e.g NaOH or KOH, and/or a weak base, in particular, sodium carbonate, sodium citrate, ammonium hydroxide etc., for example, at a concentration ranging from 0.001 to 2 M, at room or elevated temperature (25-200 °C), optionally an organic base may be present together with inorganic,

- neutralizing the medium by addition of at least one acid solution with pH<5, for example, at a concentration ranging from 0.005 to 2 M, at room temperature, - separating the zeolite obtained from the solution and washing it with a solvent, especially a polar solvent, for example, water,

- optionally drying the washed zeolite,

- placing the washed and optionally dried zeolite in contact with a solution to exchange back the alkaline cations, especially an aqueous solution, of NH4N03, especially at a concentration ranging from 0.01 to 0.5 M; this step can be performed several times, for example 2 to 3 times,

- washing the zeolite with water,

- calcining the zeolite obtained, and recovering the zeolite.

Preferably, the mesoporous material is an ordered mesoporous material or any type of mesoporous material based on silica. Indeed, among the solids which can be used, the mesoporous silicas or silica-alumina have a large specific surface area (preferably above 600 m ² /g) and a mesoporous structure with pores of uniform size which would overcome the constraints related to the diffusion of coarse particles molecules. The mesoporous silicas with ordered structures are obtained by synthesis from a silicic precursor in the presence of structuring agents which are micelles of surface-active agents. An amorphous silica is obtained having a porous structure ordered on the scale of a few nanometers. There are currently a number of structured mesoporous silicas developed by the different surfactant crosslinks / silica precursors. Among the mesostructured porous materials, it can be distinguished : the mesoporous silicas of the M41 S family, which comprise MCM-41 type materials with hexagonal 2D crystallographic structure (p6mm group), MCM-48 type materials having a cubic structure (Ia3d) and MCM-50 materials having a lamellar structure; the mesoporous silicas of type SBA (Santa Barbara Amorphous). Among this type of materials are: SBA-1 (cubic), SBA-15 (hexagonal) SBA-16 (cubic), SBA-14 (lamellar)

SBA-12 (hexagonal):

the mesoporous silicas of the MCF type (Mesostructured Cellular Foam), which are obtained by adding swelling agents such as TMB (1 ,3,5-trimethylbenzene) to the synthesis of SBA-15, which leads to enlargement of the micelles. This makes it possible to obtain a structure consisting of uniform large pores. These materials have high thermal stability.

the MSU-type mesoporous silicas (Michigan State University), these materials are obtained from non-ionic surfactants or from tri-block copolymers. Since the mesoporous silica matrices are not acidic, it is necessary to provide them with acidity and a metallic function (Ni) for use in ethylene ^' s oligomerization. The acidity can be provided either by inserting aluminum dispersed in the silica network by direct synthesis [C.T. Kresge, M. E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 1992, 359, 710; A. Corma, V. Fornes, T. Navarro, J. Perez-Pariente, Journal of Catalysis 1994, 148, 569], or by post- synthesis grafts (alumination) with reagents such as AICI3 [ Mokaya, Journal of Catalysis 2000, 193, 103], AI(N0 ₃ ) ₃ [S. C. Shen, S. Kawi, Chemistry Letters 1999, 28, 1293], Al (0-i-Pr) ₃ [R. Mokaya, W. Jones, Chemical Communications 1997, 2185] ], sodium aluminate [Z. Luan, M. Hartmann, D. Zhao, W. Zhou, L. Kevan, Chemistry of materials, 1999, 1 1 , 1621].

The presence of aluminum confers on the solids ion exchange sites as well as acidic sites of Bransted type and Lewis type. Several studies have addressed the characterization of acidity by TPD of H3 or by adsorption of pyridine followed by infrared (FTIR) [A. Jentys, N.H. Pham, H. Vinek, Journal of the Chemical Society, Faraday Transaction 1996, 62, 3287]. These studies demonstrate an increase in the density of acid sites with the reduction of the bulk Si/Ai ratio and a lower acidity strength than the zeolites. Alumination can be done by the following process:

(A) directly by adding an aluminum precursor in the synthesis of the mesoporous material or indirectly by deposition of alumina on a mesoporous material by treating with at least one aluminum reagent, for example selected from AICI3, NaAIC , Al (NC AI(OR)3 where R is Chosen from linear or branched C1 - C6 alkyl groups, in order to obtain a compound whose bulk Si/AI ratio is comprised between 0.1 and 1000.

(B) adding at least one catalytically active species selected from the group consisting of Group VI 11 B and/or VIB metals preferably by ionic exchange or impregnation.

(C) drying, followed by heat and / or chemical treatment (reduction, sulfurization, etc.) Optionally, step (B) may also comprise the addition of one or more doping metals selected from the group of rare earths or group IVB or IB and/or the addition of one or more other doping elements, for example chosen from chlorine, fluorine, boron or phosphorus. In particular, the addition of chlorine can increase the acidity of the material.

Preferably, the preferred metals of groups IVB and IB are Ti and Cu.

Generally, the steps of the above process are carried out in the order (A), (B), (C). However, it is possible to envisage a simultaneous implementation of steps (A) and (B), or even an implementation of step (B) before step (A). In one embodiment of the present invention, deposition of alumina in step (A) is accomplished by grafting. According to a preferred embodiment, the deposition of alumina in the silica is carried out by grafting according to the following steps:

(i) reacting the mesostructured silica with an aluminum-containing compound of the formula AI(OR)3, wherein R is selected from linear or branched C1 -C6 alkyi groups in the presence of an activating agent of the protons of the silanol groups of silica in a solvent whose water content is less than or equal to 0.005% by weight, preferably less than or equal to 0.0002%;

(ii) separating of the solid by filtration and then optionally washing the solid at least once with the same solvent as used in the previous step;

(iii) hydrolyzing of the AI(OR) groups grafted onto the silica by mixing the washed solid in a solution containing at least one alcohol of formula R1OH, Ri being chosen from linear or branched C1 - C6 alkyl groups and a stoichiometric amount of water.

(iv) Filtrating, washing of the solid obtained in an alcohol and drying

(v) Calcining of the washed and dried product.

Step (i) corresponds to the reaction (1 ):

— S-OH + Λ(ΟΚ¾ — Si-O-AI + ROH (1)

' OR

The stirring for step (i) is carried out for a period of 1 to 4 hours at a temperature of 20 to 95 °C, preferably 45 to 90 °C.

The solvent of step (i) can be chosen from hydrophobic solvents (i.e. apolar solvents), such as one or more selected from benzene, toluene, xylene, cyclohexane, n-hexane, pentane, isopropyl benzene, or any mixture thereof. With preference the solvent is toluene. Preferably the solvent is dehydrated by drying on a molecular sieve before use.

Advantageously, the deposition of alumina on the mesoporous solid will be carried out using aluminum tri-sec-butoxide as a source of aluminum and toluene containing triethylamine as solvent. There are grafting methods in which aluminum tri-isopropoxide is used as the aluminum source [P. lengo, M. Di Serio, A. Sorrentino, V. Solinas, E. Santacesaria, Appl. Catal. A, 167 (1998) 85]. For step (i), the silanol group-activation agent of the silica will be chosen from organic basic compounds, for example amines, preferably triethylamine, nitriles, etc. The role of this agent consists in activating the protons of the surface silanol groups and thus accelerating the reaction (1 ). It is thus possible to reduce the reaction temperature, which may be 85 °C. Step (iii) corresponds to the reaction:

OR ^' OH

The hydrolysis step (iii) will preferably be carried out at ambient temperature for a period of from 0.1 to 48 hours, preferably from 1 to 36 hours. By "ambient temperature" is meant a temperature ranging from 18 to 25 °C, and in particular a temperature of 20 °C. The quantity of water required in step (iii) can for example be calculated by considering that AI(OC4Hg)3 completely adsorbs on the solid, taking into account an amount of stoichiometric water (duration less than 2 h). The drying of step (iv) can be carried out at a temperature of 80 to 130 °C. for 1 to 25 hours, optionally under air or nitrogen flow or even under vacuum. The calcination step (v) can be carried out at a temperature of 400 to 600 °C, preferably 400 to 550 °C, for a period of 0.5 to 8 hours, for example 1 to 6 hours, under a flow of gas. The step (A) for depositing alumina, for example by grafting according to steps (i) to (iv), can be repeated several times, generally from 2 to 10 times, in order to obtain a layer of alumina on the surface of the mesoporous solid.

In another embodiment, the grafting method consists in sodium aluminate. In a preferred embodiment, silica is suspended under stirring in an aqueous solution containing sodium aluminate (with a concentration calculated to have the required Si/AI ratio after graphting) for 15h, at room temperature. The sample which results in the sodium form (Na-AI-SBA-15) is filtered, washed with water, dried at 80°C, and calcined for 6h under air at 550°C.

In an embodiment, the mesoporous material is an Al-containing material, preferably Al modified silica type.

Advantageously, the mesoporous material of the first catalyst of step b) is a mesopourous material of SBA-15 topology or is a mesopourous material of Al-modified silica type, preferably of a IV isotherm type. Preferably the first catalyst is selected from Ni-AI-SBA-15 or Ni-AI-SiC>2.

In an embodiment, the mesoporous material of the first catalyst is a mesoporous material is COK-12. In an embodiment, the catalyst consists of nickel deposited on a support being a mesoporous material, and the nickel content of the catalyst is at least 0.5 wt%, preferably at least 1.0 wt%, more preferably at least 1.5 wt%, and even more preferably at least 2.0 wt% based to the total weight of the catalyst. The nickel content is determined according to UOP961 -12. In an embodiment, the catalyst consists of nickel deposited on a support being a mesoporous material, and the nickel content of the catalyst is at most 10.0 wt%, preferably at most 5.0 wt%, more preferably at most 4.0 wt%, preferably of at most 3.5 wt%, and even more preferably of at most 3.0 wt% based to the total weight of the catalyst. The nickel content is determined according to UOP961 -12. In an embodiment, the first catalyst shows large mesoporous pore of at least 2.0 nm, preferably at least 5.0nm, more preferably of at least 7.0 nm, even more preferably of at least 7.5 nm. As known by the person skilled in the art, the size of the pore is determined by the surfactant used during the synthesis. A pore size of at least 7.0 nm can be obtained using (EO)2o(PO)7o(EO)2o triblock copolymer (Pluronic P123, Aldrich) as surfactant during the synthesis of the catalyst. The pore size can be determined according to ASTM D 4641 - 94 (reapproved 2006).

In an embodiment, the catalyst shows mesoporous pores having a mesoporous pore volume of at least 0.1 mL/g as determined according to ASTM D 4641 - 94 (reapproved 2006), preferably at least 0.2 mL/g.

In an embodiment, the first catalyst has a bulk Si/AI ratio ranging from 5 to 10 preferably from 6 to 8, as determined according to UOP961 -12.

The first catalyst has preferably a total surface area (i.e. BET surface area) in the range of about 100 m ² /g to about 1000 m ² /g preferably from 120 m ² /g to 700 m ² /g, more preferably from 150 m ² /g to about 500 m ² /g as determined by N2 sorption analysis according to ASTM D 4365 - 95 (reapproved 2008). The above catalyst is useful for the conversion of ethylene from a diluted feedstream into olefins having at least 4 carbon atoms by oligomerization reaction.

The solids of the present invention can be used as itself as a catalyst. In another embodiment it can be formulated into a catalyst by combining with other materials that provide additional hardness or catalytic activity to the finished catalyst product. Materials which can be blended with can be various inert or catalytically active materials, or various binder materials. These materials include compositions such as kaolin and other clays, various forms of rare earth metals, phosphates, alumina or alumina sol, titania, zirconia, quartz, silica or silica sol, and mixtures thereof. These components are effective in densifying the catalyst and increasing the strength of the formulated catalyst. The catalyst may be formulated into pellets, spheres, extruded into other shapes, or formed into a spray-dried particles. The amount of mesoporous material which is contained in the final catalyst product ranges from 10 to 90 weight percent of the total catalyst, preferably 20 to 70 weight percent of the total catalyst.

The metals can be introduced either in the power form or to the extruded form. The second catalyst

The second catalyst is or comprises a zeolite or Pt/CI/A Os.

When the second catalyst is or comprises a zeolite, the zeolite is preferably of the MFI group.

With preference, the second catalyst comprises or is a zeolite selected from ZSM-5, Pt-Y and Pt-BETA and mixtures thereof. The second catalyst is a zeolite of the MFI group and is selected from H-ZSM-5 Ga-ZSM-5 and Zn-ZSM-5, more preferably the second catalyst is H-ZSM-5.

It is indeed preferred according to the invention to use molecular sieves in the hydrogen form, such as H-ZSM5. Preferably, at least 50 wt%, more preferably at least 90 wt% and most preferably 100 wt% as based on the total weight of the molecular sieve used as second catalyst is in the hydrogen form. It is well known in the art how to produce such molecular sieves in hydrogen form. Such catalysts are commercially available from ZEOLYST International for example.

With preference, the second catalyst has a bulk Si/AI ratio in the range of 1 1.5 to 140, more preferred is of 15 as according to UOP961 -12.

Test methods and definitions Total surface area was determined by N2 sorption analysis according to ASTM D 4365 - 95 (reapproved 2008).

Pore diameter and pore volume were determined according to D4641 -94 (reapproved 2006).

Bulk Si/AI ratio and Ni content were determined according to UOP961 -12.

Gas chromatography was performed on Columns: DB1 (40 m, 0.1 mm, 0.4 μηη) and A O3 (50 m, 0.32 mm, 5 μηη) using Agilent operated by ChemStation software.

Examples

The advantages of the present invention are illustrated by the following examples. However, it is understood that the invention is by no means limited to the specific examples.

Example 1 : synthesis of a Ni-AI-SBA-15 catalyst Preparation of the catalyst The catalyst can be prepared according to the procedure described in "Heterogeneous oligomerization of ethylene over highly active and stable Ni-AI-SBA-15 mesoporous catalysts" by Andrei, R. D. et al, Journal of catalysis, 323 (2015) 76-84.

According to this procedure, pure siliceous SBA-15 was synthetized according to conventional method. Synthesis is performed in water using (EO)2o(PO)7o(EO)2o triblock copolymer (Pluronic P123, Aldrich), Tetraethyl orthosilicate (TEOS, Aldrich) and HCI 2 M (Aldrich) with a molar ratio of 1 TEOS/0.016 P123/ 4.9 HCI/40.5 H ₂ 0. The mixture is stirred for 24 hours at 40°C, and then it is maintained for 48 hours at 100°C in a Teflon line autoclave under static conditions. The solid product is filtered, washed with water and dried in an oven at 80°C overnight. The material is calcined in air flow at 550°C for 8 hours to obtain a white SBA-15 powder.

Al-containing material (AI-SBA-15) is obtained from SBA-15 silica by grafting with sodium aluminate. For this, 3.8 g of SBA-15 is suspended under stirring in 400 mL of aqueous solution containing 1 .03 g of sodium aluminate for 15 h, at room temperature. The sample which results in sodium form (NaAI-SBA-15) is filtered, washed with water, dried at 80°C in air and calcined for 6 hours in air at 550°C. 2g of Na-AI-SBA-15 is contacted three times, for 2 hours at 30°C, under constant agitation, with 100 cm ³ of 0.5 M aqueous solution of NH4NO3 to obtain the ammonium form, NH4-AI-SBA-I 5. The sample in ammonium form is subjected to successive nickel-ion exchanges with a 0.5 M aqueous solution of nickel nitrate, following the same procedure as above. The exchanged sample is dried and then calcined for 5 hours at 550°C to obtain the catalyst Ni-AI-SBA-15 of the invention.

Characterization of the catalyst is conducted on calcined samples

The bulk Si/AI ratio in AI-SBA-15 samples is in the range 6-8. The amount of nickel in Ni-AI- SBA-15 is 2.6 wt% based on the total weight of the catalyst. This concentration corresponds to an exchange level of NH ₄ ⁺ ions with Ni ²⁺ of about 50%. The catalyst produced exhibits a type IV isotherm. The total surface area is 460 m ² /g. The pore diameter D is 7.9 nm.

Example 2: Ethylene oligomerization

The ethylene oligomerization reaction was performed in a stainless fixed bed reactor using 2 g of catalyst. The pressure was regulated via a back pressure regulator. Thermocouple was placed on the top of the catalyst bed. Gas chromatography was connected on-line with the outlet of the reactor.

Prior to the reaction, the catalyst Ni-AI-SBA-15, was activated in a reactor either in N2 flows (5 NL/h), at 550°C for 8 hours, applying 60°C/h heating rate. After the activation the catalyst was cooled down to 150°C. The temperature was then increase gradiently up to a final reaction temperature of 200 or 250°C for the oligomerization reaction. For all oligomerisation tests, the reaction was conducted at a pressure of 1.5 MPa.

In the following tests, the feedstream comprised C2H4 and N2 at a ratio 17-29 wt% (C2H4): 83- 71 wt% (N2) as based on the total weight of the feedstream. Conversion and selectivity was calculated based on the results of gas chromatography, making sure that all the peaks were integrated.

Regeneration of Ni-AI-SBA-15 was carried out after every test. The catalyst was regenerated in a reactor in air flows (5 NL/h), at 550°C for 2 hours, applying 60°C/h heating rate and then in N2 flows (5 NL/h) during 8 hours. Conditions: Pressure P = 1 .5 MPa, Temperature T = 250 °C, 17 wt% C2- in N2 stream as based on the total weight of the feedstream, WHSV (total feed) = 0.75 h ^"1 , TOS: 65 hours.

It can be seen that in accordance with the invention the ethylene partial pressure is about 0.3 MPa.

Example 3: Ethylene oligomerization: Conversion and selectivity with Ni-AI-SBA-15 catalyst

The conversion and selectivity with TOS for the test of example 2 are presented in Fig. 1 . The catalyst is active, showing the conversion of more than 90% after a time of 40 hours on stream. The catalyst is stable for at least 70 hours. Product composition consists of about 90 wt% of butene (C4-) - octene (C8-) fraction, about 5 wt% of ethane and about 5 wt% of C5+ paraffins including traces of uneven olefins. As it is seen in the Table 1 , butene- fraction is prevailing (about 60 wt%), where mainly internal olefins are formed.

Table 1 : Product of ethylene oligomerization

Conditions: Pressure P = 1 .5 MPa, Temperature T = 250 °C, 17 wt% C2- in N ₂ stream as based on the total weight of the feedstream, WHSV (total feed) = 0.75 h ^"1 , TOS: 65 hours.

Example 4: Ethylene oligomerization: Influence of the WHSV with Ni-AI-SBA-15 catalyst

The WHSV of the feed was increased from 1 .75 up to 3.5 h ^"1 , which gives WHSV of ethylene equal to 0.5 and 1 h ^"1 , respectively. The results are presented in Fig. 2.

Within the same reaction temperature (250 °C) and TOS (1 Oh) deactivation rate decreased proportionally to the increase of WHSV, for WHSV (total feed) 1 .75 and 3.5 h ^"1 . For higher space velocity, the selectivity towards C4- olefins and towards total even olefins is increased. It is worth noticing that there is not a big difference in terms of stability, conversion and selectivity between WHSV of 1.75 and 3.5 h ^"1 . Surprisingly it can be seen that selectivity toward olefins having 4 atoms of carbons is 70 wt% at a WHSV of 1.75 h ^"1 and 65 wt% at a WHSV of 3.5 h ^"1 . Thus, the selectivity increases whereas the WHSV decreases.

The increase of selectivity toward C4- olefins in a diluted stream of ethylene when lowering the WHSV is surprising as the results obtained in "Heterogeneous oligomerization of ethylene over highly active and stable Ni-AI-SBA-15 mesoporous catalysts" by Andrei, R. D. et al., Journal of catalysis, 323 (2015) 76-84 showed a decrease of the selectivity toward C4- olefins in correlation with the decrease of WHSV as shown by the results of table 2 given as comparative example of the inventive process. Without being bound by a theory the inventors found that this might be an effect of the dilution of ethylene in the stream. Table 2: Product of ethylene oligomerization (comparative)

Conditions of comparative tests: Temperature T = 150 °C, 99 wt% C2, TOS: about 1 hour, catalyst Ni-AI-SBA-15.

In the comparative test the ethylene partial pressure is about 3.0 MPa.

Fig. 3 shows space time yield for each case for the highest tested WHSV (3.5 h ^"1 ). The isomers distribution within each olefin's fraction does not change much between the different conditions, i.e., mostly internal C4= olefins are formed. Example 5: synthesis of a Ni-AI-Si02 catalyst

Preparation of the catalyst

The catalyst can be prepared according to the procedure described in "Nickel and molybdenum containing mesoporous catalysts for ethylene oligomerization and metathesis" by Andrei, R. D. et al, New J. Chem 40 (2016) 4146-4152.

According to this procedure, S1O2 was synthetized according to the conventional method, using (EO)2o(PO) ₇ o(EO)2o triblock copolymer (Pluronic P123, Aldrich), Tetraethyl orthosilicate (TEOS, Aldrich) and HCI 2 M (Aldrich) with a molar ratio of 1 TEOS/0.016 P123/ 4.9 HCI/40.5 H2O. The mixture is stirred for 24 hours at 40°C, and then it is maintained for 48 hours at 100°C in a Teflon-lined autoclave under static conditions. The solid product is filtered, washed with water and dried in an oven at 80°C overnight. The material is calcined in air flow at 550°C for 8 hours.

AI-S1-O2 is obtained from S1O2 (commercially available and supplied by Saint Gobain, SS6 ^* 137, 138) by grafting with sodium aluminate (54+/- 1 % AI2O3 Carlo Erba). For this, 4.0 g of silica were suspended under stirring in 400 mL of aqueous solution containing 1.1 g of sodium aluminate for 15 h, at 25 °C, corresponding to a bulk Si/AI ratio of 5. The sample which results in sodium form (Na-AI-SiC>2) was subjected to successive ion exchange with NH4NO3 (99+%, Acros Organics) and Ni(N0 ₃ )2 · 6H ₂ 0 (98%, Alfa Aesar). Typically 2 g of Na-Al-Si0 ₂ were contacted three times, for 2 h at 25°C, under constant agitation, with 100 cm ³ of the 0.5 M aqueous solution of NH4NO3 to obtain the ammonium form NH4-AI-SiC>2. The sample in ammonium form was subjected to successive nickel-ion exchanges with a 0.5 M aqueous solution of nickel nitrate, following the same procedure as above. The exchanged sample is dried and then calcined for 5 hours at 550°C to obtain the catalyst Ni-AI-Si02 of the invention.

The S1O2 used in the catalyst had a pore diameter of 10-12 nm, and total surface area was ranging from 160-250 m ² /g.

Example 6: Ethylene oligomerization: Conversion and selectivity with Ni-AI-Si02 catalyst

The conversion and selectivity was studied with a time on stream of 75 hours. The conversion of ethylene was more than 80 % after a time of 40 hours on stream for both fresh and regenerated catalyst. The catalyst is stable for at least 75 hours. Product composition showed a C4- fraction of about 75 wt% as based on the total weight of the product composition.

The tests were conducted in a flow mode using a fixed-bed reactor with a time on stream (TOS) of 75 hours, at a temperature of 250°C, under a pressure of 1.5 MPa with a feed of 1 L/h of N2 and 0.2 L/h of ethylene (corresponding to 17 wt% C2 in N2 stream as based on the total weight of the feedstream and to a WHSV (feed) of 1.1 h ^"1 ).

This can be compared to the results obtained in ""Nickel and molybdenum containing mesoporous catalysts for ethylene oligomerization and metathesis"by Andrei, R. D. et al., New J. Chem 40 (2016) 4146-4152; wherein the catalytic behavior of the of the Ni-Al-Si0 ₂ catalyst was evaluated for ethylene oligomerization carried out in the flow mode, using a fixed-bed reactor. Initial conversion of ethylene was about 90 wt% and it declined smoothly to reach about 80 wt% after 9 hours (see figure 5 of the document). The product distribution did not change during the catalytic test. The results are given in table 3 as comparative example of the inventive process.

Table 3: Products of ethylene oligomerization (comparative)

Conditions comparative test: Pressure P = 3.0 MPa, Temperature T = 250 °C, 99 wt% C2 as based on the total weight of the feedstream, WHSV (feed) = 10 h ^"1 , Time on stream: 9 hours. Comparison of inventive and comparative examples shows an increase of the selectivity toward C4- products according to the inventive process.

Example 7: Aromatization

The oligomerization catalyst Ni-AI-SBA-15 and well-known aromatization catalyst H-ZSM-5 were combined in one reactor via mixing. The weight ratio was 1 :1 . This approach takes advantage of the high selectivity of the oligomerization catalyst toward C4+ olefins which are much easy activate to aromatics compared to ethylene. The process has showed high carbon efficiency and the catalyst is stable for at least 40 hours. The results are presented in figure 4.

From the results it can be seen that the use of catalytic composition comprising Ni-AI-SBA-15 + H-ZSM-5 compared to traditional Zn-ZSM-5, led to reduced yield of C1 -C4 paraffins, down to 5 wt%. It makes the process more carbon efficient as the total aromatics yield about 85 wt%, where BTX fraction (Benzene - Toluene - Xylene fraction) accounts for about 50 wt%. In the inventive process the LPG fraction is reduced. Detailed results are provided in table 4. Table 4: Products of ethylene aromatization

Zn-ZSM-5 Ni-AI-SBA-15 + H-ZSM-5

Product selectivity wt%

(comparative) (inventive)

Benzene 1 .6 1 .6

Toluene 15.0 17.3

Xylene 18.6 27.6

C9+ Aromatic 15.2 38.8

LPG 48.8 6.0

C5+ non aromatic 0.8 8.7