The present invention relates to a process allowing the tuning of the gasoline/diesel balance by converting an initial feedstock containing olefins from 4 to 20 carbon atoms, more particularly from 4 to 15 carbon atoms, preferably from 4 to 9 carbon atoms with or without addition of aromatics, using a crystalline catalyst, preferably a zeolite-based catalyst, with reduced diffusional limitations.

Refineries of today have to adapt to a continuously evolving and fluctuating market, requiring always more flexibility. It is especially the case with the gasoline/ middle distillates markets, which have largely evolved during the years: in the current and future European market demands, a shift in product focus from gasoline to middle distillates is being observed.

To respond to the above-mentioned disequilibrium, a nice way of readjusting the gasoline/diesel balance according to the market needs consists in upgrading at least part of the gasoline into middle distillates (jet, diesel).

In a typical refinery today, most of the C4-C8 molecules end up in the gasoline-pool. It is important to note that only around 5% of these molecules were initially present in the crude oil as delivered, while cracking during refinery processing creates the rest. About 50% of the C4's and 40% of the C5's that are produced during Fluidized

Catalytic Cracking (FCC) are olefinic in nature. Currently the C4 olefins are used as feed for the alkylation and etherification units to create gasoline components with high octane number, and the higher olefins are generally directly blended into the gasoline pool.

In that context, a convenient solution that allows a renewed equilibrium between gasoline and distillates would be to convert unsaturated molecules (olefins and/ or aromatics) contained in the gasoline feed into heavier molecules lying in the middle distillate range

(i.e; diesel and kerosene) by selective oligomerization and/or alkylation of these unsaturated molecules.

This invention relates to a process for the manufacture of higher molecular weight organic molecules from a stream of lower molecular weight molecules using a catalyst, preferably a zeolite based catalyst, with reduced diffusional limitations.

Today, different technologies are already commercially available to convert olefins through oligomerization.

Typically known oligomerization processes involve contacting an initial feedstock containing 4 to 10 carbon atoms with a solid acid catalyst, such as Solid Phosphoric Acid (SPA) catalyst, crystalline molecular sieve or amorphous silica-alumina.

With SPA catalyst, the pressure drop over the catalytic bed(s) increases gradually due to coking, swelling of the catalyst, and is therefore the limiting factor of a run duration, the unit being shutdown once the maximum allowable pressure drop has been reached. The amorphous silica-alumina catalysts present the advantage of operating at quite low temperatures (140- 160°C), thus allowing a larger range of operating temperature before being limited by secondary reactions (cracking....). However, such catalytic systems are not shape selective, and the diesel cut produced exhibits bad cetane number.

The use of crystalline molecular sieves is to be found in the MOGD process (Mobil Olefins to Gasoline and Distillate), proposed by Mobil (US-4, 150,062; US-4,227,992; US-4482772; US-4506106; US- 4543435) and developed between the seventies' and eighties' using ZSM-5 zeolite as catalyst.

In a similar manner, Lurgi AG, Germany (WO2006/076942), has developed the Methanol to Synfuels (MTS) process, which is in principle similar to the MOGD process. The Lurgi route is a combination of simplified Lurgi MTP technology with COD technology from Slid Chemie (US5063187). This process produces gasoline (RON 80) and diesel

(Cetane Number ~ 55) in the ratio of approximately 1 :4.

On the contrary to amorphous silica-alumina catalysts, zeolitic catalysts do have shape selectivity induced by the microporosity of the zeolitic structure, thus leading to diesel cut with good cetane number.

However, the micropores may also have a negative impact, which is often illustrated by the low rate access of molecules into the zeolitic crystals, on unwanted adsorption effects of reactants and/or products during the catalytic reaction.

These steric constraints are supposed to cause the decrease of the accessibility of the zeolite micropore volume during the catalytic action, and it can be stated that the zeolite crystals have not always been used effectively.

At a macroscopic scale, this is illustrated by the need for higher operating temperatures (generally at least 200°C) to limit pore blocking and enhance oligomer diffusion, thus limiting considerably the operating window as high operating temperatures favor secondary reactions (secondary reactions such as cracking/ isomerization/ coking become predominant at temperatures higher than 300°C).

One of the constraints concerning the oligomerization/ alkylation is the competition between oligomerization / alkylation on one hand and cracking. To avoid these undesired reactions and enhance the selectivity of the catalyst towards heavies formation, the design of an optimally accessible catalyst is required. Shape selective zeolites appear to be the most promising catalysts, since by proper materials choice, the isomerization reaction could be limited. For light olefins conversion, typically 10 membered ring zeolites are highly suitable in their micropore size range.

In order to maximize the effectiveness of the zeolitic crystal, one solution to reduce the diffusional limitations consists in using small crystal size zeolite. Although this concept has been explored for several zeolites (A.Corma, Nature, 396 ( 1998), 353), in industrial practice the application of small dealuminated zeolite crystals may not always be feasible.

A more generally applied strategy to obtain materials with reduced diffusional limitations is the creation of a secondary pore system consisting of mesopores (2-50 nm) inside the microporous zeolite crystals

In recent years, several alternative techniques have been developed that allow obtaining a structured mesoporosity next to the zeolite microporosity, such as : Recrystallization of the walls of a mesoporous material into zeolite material ;

Mesoscale cationic polymer templating ;

Building a mesoporous material by using amphiphilic organosilica zeolite ;

Direct zeolite seed assembly using a template to shape the mesopores.

For some of these approaches, it has already been shown that catalysts with improved performances in various reactions can be obtained. As for example, WO 2009/ 153421 discloses the synthesis of a crystallized material with hierarchised and organized porosity and its application in the oligomerization of light olefins.

Despite of the considerable developments over the last years in the domains of the synthesis, characterization and comprehension of the formation mechanisms of these structured mesoporous materials, their effective application in industry is still highly limited because of their cost, which is partially related to the high cost of the organic template.

Therefore, from a cost perspective, the classical hydrothermal and acid leaching routes remain the most attractive techniques, today largely used in industry. However, the introduction of mesopores by these ways is not easily controlled and often materials exhibit a random and non-optimized mesoporosity. In a paper by Janssen et al (A.H. Janssen, Angew.Chem.Int.Ed., 40 (2001), 1 102), it was demonstrated using three-dimensional electron microscopy that a large part of the mesopores in a commercially available steamed and acid leached zeolite Y were cavities, not optimally connected to the outer surface of the zeolite crystal. Obviously, for catalysis, a system of interconnected cylindrical mesopores is expected to enhance the accessibility for reactants and the diffusion of reaction products much more than mesoporous cavities inside the crystal.

Recently, another route has emerged, being an alternative to the above-discussed routes. It consists in a careful desilication of the as- synthesized zeolite by a treatment in an alkaline medium (Ogura M., Chem.Lett. (2000), 82 ; Ogura M., Appl.Catal.A Gen. 219 (2001), 33). Extraction of silicon atoms leads to a significant amount of extra- porosity inside the zeolite crystals. There is an optimum of the Si/Al ratio for this method, which in the case of ZSM-5 was proven to be in the range of 25-50 (Groen J.C., J.Phys.Chem.B, 108 (2004) 13062, Groen J.C., JACS 127 (2005), 10792). Other publications deal with the alkaline treatment of BEA, FER, MOR (Groen JC.et al., Microporous Mesoporous Materials, 69 (2004), 29)

Improved catalytic performances were demonstrated for the liquid-phase alkylation of benzene with ethylene when using such hierarchical zeolites combining micro and mesoporosity prepared by the desilication of ZSM-5 using aqueous solutions of organic bases : the combination in a single material of the catalytic power of micropores and the improved transport consequence of a complementary mesopore network allows to alleviate at least partly diffusional limitations (Perez-Ramirez J.etaL, Appl.Catal.A, 364 (2009), 191- 198). Same conclusions were reported by Christensen C.H. et al., JACS, (2003), 125, 13370- 13371. The applicant has discovered that catalysts obtained by this process and thus exhibiting optimized accessibility of the active sites leads to enhanced catalyst performances towards the conversion of gasoline to distillates, hereby facilitating process design : broader range of operating conditions (lower temperature and/ or higher LHSV), while preserving higher or at least similar yields and selectivities towards middle distillates.

A first object of the invention relates to a process allowing to upgrade gasoline into middle distillate by conversion a feedstock containing olefins from 4 to 20 carbon atoms in the presence or absence of aromatics, over a catalyst containing a crystalline compound with combined micro/ mesoporous structure allowing to reduce significantly the diffusional limitations.

The invention thus concerns a process for the manufacture of middle distillates from a gasoline stream, said process comprising: - processing a feedstock stream containing olefins Cn from 4 to 20 carbon atoms, with or without the presence of an aromatic containing stream,

- contacting said stream(s) with a catalyst at conditions effective to oligomerize a least a portion of the olefins and eventually alkylate at least a portion of the aromatics,

wherein the catalyst is a crystalline compound with micro / mesoporous structure chosen among crystalline aluminosilicates, crystalline aluminophosphates, crystalline silico-aluminophosphates, crystalline zeolites, or the catalyst is a composite material comprising at least

20%wt of at least one of the above mentioned crystalline compounds, and wherein the mesoporous volume of the crystalline compound is at least 0.22 ml/g, preferably at least 0.25 ml/g, and most preferably at least 0.30 ml/g.

The use of such catalysts in olefin conversion has demonstrated enhanced activity and efficiency due to higher accessibility of the active sites.

Preferably, the mesoporous volume of the crystalline compound is at least 0.2 ml/g, most preferably at least 0.3 ml/g.

Preferably, the microporous volume of the crystalline compound is inferior or equal to 0.20 ml/g, more preferably inferior or equal to 0.17 ml/g, most preferably inferior or equal to 0.15 ml/g.

The ratio mesoporous volume/ microporous volume of the crystalline compound may be superior or equal to 1 , more preferably superior or equal to 2, most preferably superior or equal to 2.5.

As regards the catalyst :

Before use in the process of the invention, the catalyst, particularly the micro-mesoporous crystalline silicates of zeolite structure, may be subjected to one or several of the following treatments :

Optionally, a dealumination treatment (either via hydro thermal route and/ or an acid leaching), so as to (i) decrease the acidity of the material (ii) increase, though slightly, the mesoporosity of the initial material. Such treatments are described in US 5601798. A careful desilication of the material by a treatment in an alkaline medium containing at least a strong inorganic base (NaOH, KOH) and/or an organic base (such as TMAOH, TPAOH...), the concentration of which ranges from 0.1 to 2M, preferably from 0.15 to 1M. The alkaline treatment is performed under stirring, at a temperature ranging from ambient temperature to 100°C, preferably up to 85°C.

By ambient temperature is to be understood a temperature ranging from 18°C to 25°C, more preferably 20°C.

The duration of the alkaline treatment may be comprised between 5 to 120min, preferably from 10 to 60min, advantageously from 15 to 30min. The obtained material is then filtered and may be subsequently washed with large amounts of a polar solvent (by way of example, pure demineralized water).

Optionally, the neutralization of the alkaline solution may be performed before the filtration step so as to stop the desilication reaction. Indeed, if the desilication is becoming too important, this may lead to the significant loss of the crystallinity of the zeolite structure, which may induce a decrease of the intrinsic activity of the material.

- If during the preparation of the catalyst, alkaline or alkaline rare earth metals have been used, the material might be subjected to an ion-exchange step, typically using ammonium salts, or inorganic acids.

The catalyst is then generally calcined for example at a temperature of from 400 to 800°C at atmospheric pressure for a period of from 1 to 10 hours.

Optionally, the material can be subjected to a final mild hydrothermal treatment, aiming at healing the crystalline defects generated by the alkaline treatment.

As already mentioned, the catalyst used in the process of the invention may be a composite material comprising at least 20%wt of at least one crystalline compound with micro/ mesoporous structure chosen among crystalline aluminosilicates, crystalline aluminophosphates, crystalline silico-aluminophosphates, crystalline zeolites, or mixture thereof.

The crystalline compound(s), eventually modified as previously mentioned, may be mixed with a binder, preferably an inorganic binder, and shaped to a desired shape, e.g. pellets. The binder is selected so as to be resistant to the temperature and other conditions employed in the reaction of the invention. The binder is preferably an inorganic material selected from clays, silica, metal silicates, metal oxides such as ZrO2 and/ or metals, gels including mixtures of silica and metal oxides. If the binder which is used in conjunction with the crystalline compound is itself catalytically active, this may alter the conversion and/ or the selectivity of the catalyst. Inactive materials for the binder may suitably serve as diluents to control the amount of conversion so that products can be obtained economically and orderly without employing other means for controlling the reaction rate. It is desirable to provide a catalyst having good crush strength. This is because in commercial use, it is desirable to prevent the catalyst from breaking down into powder-like materials. Such clay or oxide binders have been employed normally only for the purpose of improving the crush strength of the catalyst.

The crystalline compound used in the process of the invention presents preferably a structure of the zeolite type.

The atomic ratio Si/Al of the zeolite structure, before alkaline treatment, is preferably at least 15, preferably at least 25, most preferably at least 30.

The atomic ratio Si/Al of the zeolite structure, before alkaline treatment, is preferably lower than 60, preferably below 50. Preferably, the mesoporous volume of the crystalline compound used in the present invention is at least 0.2 ml/g, most preferably at least 0.3 ml/g.

Preferably, the microporous volume of the crystalline compound is inferior or equal to 0.20 ml/g, more preferably inferior or equal to 0.17 ml/g, most preferably inferior or equal to 0.15 ml/g. The ratio mesoporous volume/ microporous volume of the crystalline compound may be superior or equal to 1 , more preferably superior or equal to 2, most preferably superior or equal to 2.5.

This crystalline compound may be selected from the MFI (ZSM-5, silicalite- 1 , boralite C, TS- 1), MEL (ZSM- 1 1 , silicalite-2, boralite D, TS- 2 , SSZ-46), FER (Ferrierite, FU-9, ZSM-35), MTT (ZSM-23), MWW (MCM-22, PSH-3, ITQ- 1 , MCM-49), TON (ZSM-22, Theta- 1 , NU- 10), EUO (ZSM-50, EU- 1), MTW (ZSM- 12), MAZ, SAPO- 1 1 , SAPO-5, FAU, LTL, BETA MOR, SAPO-40, SAPO-37, SAPO-41.

Preferably, the catalyst presents a structure of the ZSM-5 type.

As regards the operating conditions:

The reaction will preferably be conducted under the following conditions :

temperature from 125 to 300°C, preferably from 130 to 280°C, most preferably at 150°C,

with a weight hour space velocity (WHSV) from 0.5 h ¹ to 5 h ¹ , more preferably from 0.5 h ¹ to 3 h ¹ , most preferably from 0.5 h ¹ to 2 h- ¹ .

pressure from atmospheric pressure to 200barg, preferably from 15 to lOObarg, most preferably from 15 to 60barg.

As regards the feedstock:

The feed of the present invention is typically obtained from petroleum refining or petrochemicals operations. In particular, it may be obtained from steam of thermal cracking or catalytic cracking.

Olefin containing feed can also be obtained alternatively from the dehydrogenation of hydrocarbon streams obtained from the processing of crude oils, natural gas, or field condensates. They can also be obtained by dehydrogenation of alcohols.

The composition of the feed (amounts of olefins, aromatics, type of olefins and aromatics) depend upon the feed to the process and the conditions that are employed ; the process may be operated either with the entire gasoline fraction obtained from a catalytic or thermal cracking step or alternatively part of it. Mixture of streams can also be considered : by way of example, a reformate and a LCN gasoline fraction can also be considered.

Preferably, the feedstock is chosen among gasolines containing olefins such as LCCS with boiling points in the range of 30 to 100°C or a mixture of olefins and aromatics such as LCN with boiling points in the range of 30 to 170°C.

Typical feed composition can be found below in table 1 for LCCS (Light Catalytic Cracked Spirit) and in table 2 For LCN (Light Cracked naphta) .

Table 1 : typical composition of LCCS

Density at 15°C 0.6518 g/ml

Diene value USP 326 0.1 1 g 12/1 OOg

Bromine Number ASTM D l 159 140.8 g Br/1 OOg

Reid Vapor Pressure ASTM D5191 125.5 kPa

ASTM D86

T° at IBP 27.6 °C

T° at 5% vol 31 °C

T° at 50% vol 38 °C

T° at 95% vol 0 °C

T° at FBP 63.6 °C

Olefin distribution

C4= 6.80 %wt

C5= 45.44 %wt

C6= 10.65 %wt

Total olefins 62.89 %wt

Table 2 : typical composition of LC N

Density at 15°C 0.7178 g/ml

ASTM D86

T° at 5% vol 52.5 °C

T° at 95% vol 159.3 °C

T° at FBP 171 .9 °C

PIONA

Total olefins 41 .7 %wt

Aromatics 13.4 %wt

As regards the reactor:

A plural reactor system may be employed with inter-reactor cooling, whereby the reaction exotherm can be carefully controlled to prevent excessive temperature above the normal moderate range.

It can be an isothermal or an adiabatic type of fixed bed or a series of such reactors o r a m o v i n g b e d r e a c t o r . T h e oligomerization/ alkylation may be performed continuously in a fixed bed reactor configuration using a series of parallel "swing" reactors. The various preferred catalysts of the present invention have been found to exhibit sufficiently high stability. This enables the oligomerization and/or alkylatio n proce s s to b e pe rformed continuously in two parallel "swing" reactors wherein when one or two reactors are in operating, the other reactor is undergoing catalyst regeneration. The catalyst of the present invention also can be regenerated several times.

It is an object of the present invention to convert a stream containing olefins into heavy hydrocarbons reach in distillate, employing a continuous multi-stage catalytic technique. A plural reactor system may be employed with inter-reactor cooling, whereby the reaction exotherm can be carefully controlled to prevent excessive temperature above the normal moderate range. Advantageously, the maximum temperature differential across only one reactor is not exceeding 75° C.

Optionally, the pressure differential between the two stages can be utilized in an intermediate flashing separation step. The following examples and figure illustrate the invention without limiting its scope.

Figure 1 : sorption -desorption isotherms for desilicated ZSM-5 and parent sample (TPN : standard conditions : 0°C and 760 mmHg).

Examples

Preparation of microporous-mesoporous ZSM-5 A sample of ZSM-5 zeolite (catalyst A) (Si/Al=40) in NH ₄ -form, crystal size of Ο. ΐμπι, supplied by Zeolyst (CBV 8014) has been treated in an alkaline medium as follows : 606 ml of NaOH (0.2M) at 338K (65°C) during 30 minutes under vigorous stirring. The resulting suspension was cooled in an ice bath and the reactive medium was neutralized by adding H2SO ₄ (1M) until the pH was neutral. A gel formation resulting from the precipitation of dissolved silicon atoms is observed and removed by washing with large amounts of demineralized water. The recovered solid is then dried at 383K (1 10°C) overnight. Finally, the alkaline-treated samples is converted into the H-form by ion-exchanges using 200ml NH ₄ C1 (0. 1M) during 18 hours under reflux. The product is then dried at 1 10°C (60°C/h) overnight followed by calcination in air at 823K (550°C) for 6 hours. Catalyst B is obtained. Characteristics of the microporous-mesoporous ZSM-5 prepared

The main characteristics of catalysts A and B are gathered below (Table 3 and figure 1) and characterized by the following methods.

The chemical composition of the samples (molar ratio Si/Al, and Na content) was determined by ICP-AES (Inductive Coupled Plasma -

Atomic Emission Spectroscopy) (Perkin-Elmer 3000 DV).

N2 sorption-desorption isotherms at 77K were measured in an automated porosimeter (Micromeritics Tristar 3000) . Prior to the measurement, the samples were degassed in vacuum at 573K for 12h. The mesopore size distribution was obtained by the BJH model (Barett

E.P., Joyner L.G., Halenda P.P, J.Am.Chem.Soc. 1951 , 73, 373-380. Rouquerol F., Rouquerol J., Sing K., Adsorption by Powders and Porous Solids, Academic Press, San Diego, 1991) applied to the adsorption branch of the isotherm. The t-plot method was used to discriminate between micro and mesoporosity.

Figure 1 shows the nitrogen sorption/desorption isotherms of catalysts A (parent sample) and B (desilicated ZSM-5). The comparison of the two N2-isotherms highlights the enhanced uptake at intermediate pressure, indicative of the formation of a hierarchical porous system combining micro and mesoporosity.

As reported in table 3, the mesoporous volume increases from 0.097 to 0.327 ml/g, while the microporous volume decreases from 0.161 to 0.1 19 ml/g.

Accordingly, the Si/Al ratio decreases from to 46 to 34.

Table 3 - Textural properties of the parent and alkaline-treated zeolite

a: Volume adsorbed at P/Po=0.99

b : V meso =Vtotal - V micro

c : t-plot method

Catalytic performances

The performances of the two catalysts (catalyst A and B) were evaluated on oligomerization of a model feed consisting in a mixture of n-heptane (nC ₇ ) and 1-hexene (1C6 ⁼ ). The following operating conditions were used : 55barg, WHSV (Weight Hourly Space Velocity) of 1 or 2 r ¹ , temperature varying from 150 up to 200°C.

The performances of parent zeolite (catalyst A) and of alkaline treated sample (catalyst B) are presented in table 4.

Table 4 - Yield of different groups of products at 55barg, WHSV of lh ¹ or 2 r ^l , for different temperatures on model feed (nC ₇ / l C6 ⁼ )

Cx represent alkanes with x atom of carbon

Cx ⁼ represent olefins with x atoms of carbon

These results show that by using a catalyst as defined in the invention presenting a particular micro/ mesoporous structure, a significant decrease of the inlet temperature is successfully achieved without impacting the global C6 olefin conversion.

This stresses the improved accessibility to the acid sites of the alkaline treated zeolites compared to the parent one.

At a temperature of 150°C, better olefin conversion is obtained with the alkaline-treated ZSM-5 with a WHSV twice as high (21T ¹ vs lh ¹ ) compared to the parent zeolite.