Description:FIELD OF THE INVENTION:
The present disclosure relates to the field of catalysts. Particularly, the present invention relates to a catalyst composition for a selective dimerization of ethene to 1- butene comprising: a titanium alkoxide compound, an alkyl aluminium compound and an isohexide based diester as Electron donor.

BACKGROUND OF THE INVENTION:
1-Butene and 1-hexene are important petrochemicals, especially for the production of polyethylene. The reaction of ethylene and other alpha-olefins, especially 1-butene and 1-hexene, forms various grades of linear low density polyethylene (LLDPE), a useful commercial polymer. A source of 1-butene is the butene fraction from the effluent of a hydrocarbon cracker, such as a steam cracker or fluidized catalytic cracker. However, the process for isolating 1-butene from such an effluent requires several difficult process steps that may make the process undesirable. Dimerization of ethylene is considered as the most selective and economical route for polymerization grade butene-1. Several commercial processes selectively oligomerize ethylene into alpha-olefins such as 1-butene. A commercially successful dimerization process is the Alphabutol™ Process, developed by the Institute Francais du Petrole (IFP), described in A. Forestiere, et al., "Oligomerization of Monoolefins by Homogenous Catalysts", Oil & Science and Technology-Review de l’Institute Francais du Petrole, pages 663-664 (Volume 64, Number 6, November 2009). This process uses a bubble-point reactor that contains 1-butene as a process fluid to oligomerize ethylene selectively into 1-butene.

US4,532,370B2 discloses a process for synthesizing 1-butene by dimerization of ethylene, in the presence of a catalyst formed by reacting, in a hydrocarbon medium, a trialkylaluminum with a mixture of an alkyl titanate with an ether. The activity and the selectivity are improved when adding the ether to a pre-formed mixture of alkyl titanate with trialkylaluminum.

US006121502A1 discloses a process for oligomerizing an unsaturated aliphatic hydrocarbon to linear alpha-olefins, a catalyst mixture comprising titanium aryl and/or titanium alkoxide, organoaluminum halide and optionally one or more additives selected from a group containing phosphorus, oxygen and sulphur compounds.

US9309167B2 discloses The invention describes a process for oligomerization of olefins into compounds or into a mixture of compounds of general formula CpH2p with 4p80 that employs a catalytic composition that comprises at least one organometallic complex of an element of group IV that is selected from titanium, zirconium, and hafnium, wherein the organometallic complex contains at least one alkoxy-type ligand that is functionalized by a heteroatom selected from nitrogen, oxygen, phosphorus and sulfur, or by an aromatic group. |

Titanium-based compounds have been found to be ideally suited out of all the metals studied for dimerization of ethylene giving high yields of 1-butene. However, 1-butene formation is invariably accompanied by formation of higher oligomers of ethylene and polymer. Formation of these byproducts which complicate the efficacy of an industrial process is believed to be a function of catalyst type and reaction conditions. To minimize the formation of byproducts there is a need to develop catalyst system with improved selectivity for 1-butene and low isomerization, so that 1-butene yield can be increased.

OBJECTIVES OF THE INVENTION:
The main objective of the present invention is to design and synthesize a catalyst composition for selective dimerization of ethylene.

Another objective of the present invention is to synthesize and characterize diesters based on isohexides as electron donors for the ethylene oligomerization.

One more objective of the present invention is to synthesize and characterize diesters based on isohexides as electron donors for the dimerization of ethylene to 1-butene.

Another objective of the present invention is to provide a catalyst composition with high ethylene to 1-butene dimerization activity.

A yet another objective of the present invention is to provide a process for producing 1-butene from ethylene with high selectivity and conversion using a catalyst composition.

SUMMARY OF THE INVENTION:
The present invention relates to a catalyst composition for a selective dimerisation of ethene to 1-butene comprising:
a) a titanium alkoxide compound;
b) an alkyl aluminum compound; and
c) an isohexide based diester,
wherein isohexide based diester acts as an electron donor.

In an aspect, the present invention provides a process for the selective dimerization of ethylene to 1-butene using catalyst composition as defined in claim 1, wherein conversion of ethylene is in a range of 50 to 90 % and wherein the selectivity for 1-butene is at least 99%.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The following figures form part of the present specification and are included to further illustrate aspects of the present disclosure. The disclosure may be better understood by reference to the figures in combination with the detailed description of the specific embodiments presented herein.

Figure 1 illustrates 1H-NMR spectra of D-Glucitol, 1,4:3,6-dianhydro-2,5-dibenzoate.
Figure 2 illustrates 13C-NMR spectra of D-Glucitol, 1,4:3,6-dianhydro-2,5-dibenzoate.
Figure 3 illustrates 1H-NMR spectra of D-Glucitol, 1,4:3,6-dianhydro-2,5-diacetate.
Figure 4 illustrates 13C-NMR spectra of D-Glucitol, 1,4:3,6-dianhydro-2,5-diacetate.

DETAILED DESCRIPTION OF THE INVENTION:
For convenience, before further description of the present disclosure, certain terms employed in the specification, and examples are delineated here. These definitions should be read in light of the remainder of the disclosure and understood as by a person of skill in the art.

The terms used herein have the meanings recognized and known to those of skill in the art, however, for convenience and completeness, particular terms and their meanings are set forth below. The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

The terms “comprise” and “comprising” are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as “consists of only”. The term "at least one" is used to mean one or more and thus includes individual components as well as mixtures/combinations. Throughout this specification, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of element or steps but not the exclusion of any other element or step or group of element or steps. The term “including” is used to mean “including but not limited to”. “including” and “including but not limited to” are used interchangeably.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods and materials are now described.

The present disclosure is not to be limited in scope by the specific embodiments described herein, which are intended for the purposes of exemplification only. Functionally equivalent products, compositions, and methods are clearly within the scope of the disclosure, as described herein.

In the present invention a systematic study of the role of catalyst composition and reaction parameters has been carried out for dimerization of ethylene based on conversion and selectivity of the reaction. The novel catalyst composition developed has the advantages of showing high selectivity to 1-butene and having a very low isomerization activity.

In an aspect, the present invention provides a catalyst composition for a selective dimerization of ethylene to 1-butene comprising:
a) a titanium alkoxide compound;
b) an alkyl aluminum compound; and
c) an isohexide based diester,
wherein isohexide based diester acts as an electron donor.

In an embodiment of the present invention, the titanium alkoxide compound to alkyl aluminum compound is present in a molar ratio in the range of 1: 2-10.

In an embodiment of the present invention, the titanium alkoxide compound to isohexide based diester is present in a molar ratio in the range of 1: 0.1-1.

In another embodiment of the present invention, the titanium alkoxide compound is selected from a group consisting of titanium (IV) methoxide Ti(OMe)4, Titanium (IV) ethoxide Ti(OEt)4 , Titanium(IV) i-propoxide Ti(i-OPr)4 , Titanium (IV) Butoxide Ti(OBu)4 or combination of thereof.

In another embodiment of the present invention, the alkyl aluminium compound is selected from a group consisting of tri-ethyl aluminium (TEAL), tri-isobutyl aluminium (TIBA), tri-isopropyl aluminium (TIPRA), tri-n-hexyl aluminium (TnHA), and diethyl aluminium chloride (DEAC) or combination of thereof.

In another embodiment of the present invention, the isohexide based diester is a compound of formula I, and an isomer of formula I or combination thereof;

Formula I
wherein R is independently selected from a group consisting of CH3, C2H5, C3H7 and Ph or a combination thereof.

Further, the present invention provides a process for the selective dimerization of ethylene to 1-butene using catalyst composition as defined in claim 1, wherein conversion of ethylene is in a range of 50 to 90 % and wherein the selectivity for 1-butene is at least 99%.

Chemicals used in the synthesis of the catalyst composition as described in the present invention include Isosorbide, acetic acid, benzoic acid, dicyclohexylcarbodiimide (DCC), DCM, di-isopropyl amine (DIPA), water, anhydrous MgCl2, Ti(OBu)4, hexane, toluene, heptane, methanol, hydrochloric acid, ethylene gas, triethylaluminum.

The electron donors are prone to coordinate with catalyst Titanium alkoxide and cocatalyst alkyl Aluminium compound which effects the conversion of ethylene to 1-butene and selectivity for 1-butene.

All the reactions were carried out using standard Schlenk technique and Glove box. The chemicals used for the catalyst preparations were stored under glove box having argon atmosphere. Dimerization reactions were performed using high pressure reactor. Hexane, heptane, toluene, cyclohexane was distilled over a sodium benzophenone system and freshly distilled solvents were used throughout experiment.

The synthesized isohexide based diesters was characterized using the following techniques:
a) Fourier Transform Infrared Spectroscopy (FTIR): FTIR spectra were recorded with Perkin Elmer Spectrum GX equipment (Waltham, Massachusetts, USA). Samples were scanned with a resolution of 2 cm-1 in the scan range of 4000-400 cm-1.
b) NMR analysis: 1H and 13C-NMR spectra were recorded on Bruker Avance 500 MHz spectrometer. Deuterated solvents for NMR experiments were obtained from Aldrich Chemical Co.
Gas Chromatography: Gas samples were analyzed by using Perkin Elmer Clarus 690 with elite alumina column having 0.53 ID and 30-meter length. For liquid samples, GC-VUV, Rxi-1ms column having 30-meter length and 0.25 mm ID was used.

EXAMPLES:
The present disclosure is further illustrated by reference to the following examples which is for illustrative purposes only and does not limit the scope of the disclosure in any way. These examples are not intended to be inclusive of all aspects of the subject matter disclosed herein, but rather to illustrate representative features, methods, compositions, and results. These examples are not intended to exclude equivalents and variations of the present disclosure, which are apparent to one skilled in the art.

Example 1: Synthesis of isohexides based diesters as electron donors.

Example 1a: Synthetic protocol of D-Glucitol, 1,4:3,6-dianhydro-2,5-dibenzoate.
In a clean and dried 250 ml Schlenk RBF, benzoic acid (8.35 g, 0.0684 mol) and DCC (15.51 g, 0.0752 mol) was mixed under nitrogen. To this, 70 ml of DCM (dichloromethane) was added followed by DIPA (Di-isopropyl amine) (11.77 mL, 0.1163 mol). The above reaction was stirred at RT (23 °C) for 30 minutes and 5 g, 0.0341 mol Isosorbide (isohexide) was added under inert atmosphere. The color of the reaction mixture changed to pale yellow. The reaction mixture was stirred for 48 hours at RT. Workup of the reaction was carried out by adding 950 mL water. The organic layer was extracted and dried over sodium sulphate. Solvent was evaporated under rota evaporator and obtained solid was again diluted with DCM to remove insoluble dicyclohexyl urea by filtration. The obtained product purified by recrystallization method.

The structure of the resultant molecule was established using 1H, 13C-NMR and FTIR analysis. Melting point of D-Glucitol, 1,4:3,6-dianhydro-2,5-dibenzoate = 165-168 °C.

Example 1b: Synthetic protocol of D-Glucitol, 1,4:3,6-dianhydro-2,5-diacetate.
In a clean 250 ml Schlenk RBF, acetic acid (3.91 mL, 0.0684 mol) and DCC (15.51 g, 0.0752 mol) was mixed under nitrogen. To this, 70 ml of DCM (dichloromethane) was added followed by DIPA (Di-isopropyl amine) (11.77 mL, 0.1163 mol). Reaction mixture was stirred at RT (23 °C) for 30 minutes. Isosorbide (5 g, 0.0342 mol) was added under nitrogen atmosphere to reaction mixture. The change in the reaction color was noted as yellow. The above reaction mixture was stirred at RT for 48 hours. Reaction was quenched with 950 mL water. The organic layer was extracted and dried on sodium sulfate. Solvent was evaporated and solid was diluted with DCM. Insoluble solid was found to be dicyclohexyl urea which was filtered. Soluble fraction was evaporated, dried and characterized. Isosorbide acetic ester (D-Glucitol, 1,4:3,6-dianhydro-2,5-diacetate) obtained in ~ 94% yield. The structure of the resultant molecule was established using 1H, 13C-NMR and FTIR analysis. Melting point of D-Glucitol, 1,4:3,6-dianhydro-2,5-diacetate = 110-112 °C.

Example 2: Evaluation of the catalyst composition.
To evaluate the effect of Electron Donor diester of isohexides on the catalyst composition as described in the present invention, ethylene oligomerization reactions were carried out and evaluated. The control sample which had THF as Electron Donor is listed as “Comparative Example” in Table 1. For the experiments, catalyst mixtures were used that contained titanium tetrabutoxide, D-Glucitol, 1,4:3,6-dianhydro-2,5-diacetate, triethyl aluminum (referred to as “TEAL”).

Example 2a: Preparation of comparative catalyst composition.
To a clean dried Schlenk flask, 5-10 mL heptane was added, 0.2 g Titanium tetrabutoxide (5.876 × 10-4 mol) and THF (36 µL, 4.7×10-4 mol) were added and stirred for 5 min. the reaction mixture was directly used in the dimerization reaction.

Example 2b: Preparation of catalyst composition 1.
To a clean dried Schlenk flask, 5-10 mL heptane was added, 0.2 g Titanium tetrabutoxide (5.876 × 10-4 mol) and D-Glucitol, 1,4:3,6-dianhydro-2,5-diacetate (0.108 g, 4.7×10-4 mol) were added and stirred for 5 min. the reaction mixture was directly used in the dimerization reaction.

Example 3: Ethylene dimerization to 1-Butene.
Dimerization reaction was performed in high pressure Parr reactor. Before polymerization, precondition the reactor by keeping for baking under nitrogen at 120 °C for 2 hours. The reactor was then cooled down to 40 °C and then kept under nitrogen (1 bar). Freshly distilled heptane (200 mL) was taken into addition vessel under nitrogen and transferred to the reactor under ethylene environment. The solvent was allowed to saturate with ethylene and stirrer is set to the desired RPM. The weighed catalyst composition includes catalyst titanium butoxide, D-Glucitol 1,4:3,6-dianhydro-2,5-diacetate were added to the reactor vessel containing ethylene saturated heptane and kept for 1-2 min stirring. Then, co-catalyst triethyl aluminium was added to the reactor vessel containing ethylene saturated solvent (heptane) and catalyst component to obtain reaction mixture Immediately, stirrer was turned on and reactor was pressured with 12.5 bar to incubate the reaction mixture. Continuous pressure was maintained until the desired reaction time of 20-60 minutes. Afterward, the reactor temperature was brought down to below 25 °C to collect gas samples for analysis. The reaction quenched with acidic methanol, filtered the samplessamples to separate solid particles formed during reaction. The obtained solid precipitate of polymer was filtered off and dried at 60 °C inside the hot air oven. Gas and liquid samples were analyzed by GC and GC-PIONA instruments from Agilent.
Table 1. Ethylene Oligomerization
Run Catalyst Pressure
(bar) Activity (g of ethylene/ hour/millimoles of Ti) % Conversion 1- Butene Yield % C4 Selectivity %1-Butene- Selectivity % C6 Selectivity/% Polymer
1 Comparative catalyst composition 12.5 260 85.95 80.06 97.03 93.14 0.29/ 0.64
2 Catalyst composition 1 12.5 256 89.90 89.30 99.60 99.34 0.41/0.30
3 Catalyst composition 1 23.5 197 51.20 51.17 99.07 99.96 0.33/0.60
4 Catalyst composition 1 10 106 73.92 73.90 98.10 99.97 0.50/1.40

Reaction conditions: Catalyst (titanium butoxide) =200 mg, cocatalyst (10% TEAL), Solvent= heptane, Al:Ti= 8, Electron donor: Al=0.1, T= 60 deg C, RPM=200, time= 30 mins,
The results of table 1 show that the use of D-Glucitol 1,4:3,6-dianhydro-2,5-diacetate as electron donor shows significant improvement in dimerization of ethylene and 1-butene selectivity at 12.5 bar pressure. Also, there is a notable reduction in polymer formation when D-Glucitol 1,4:3,6-dianhydro-2,5-diacetate is used as compared to comparative example, i.e. Run 1. , Claims:1. A catalyst composition for a selective dimerization of ethylene to 1-butene comprising:
a) a titanium alkoxide compound;
b) an alkyl aluminum compound; and
c) an isohexide based diester,
wherein isohexide based diester acts as an electron donor.
2. The composition as claimed in claim 1, wherein the titanium alkoxide compound to alkyl aluminum compound is present in a molar ratio in the range of 1: 2-10.

3. The composition as claimed in claim 1, wherein titanium alkoxide compound to isohexide based diester is present in a molar ratio in the range of 1: 0.1-1.

4. The composition as claimed in claim 1, wherein the titanium alkoxide compound is selected from a group consisting of titanium (IV) methoxide Ti(OMe)4, Titanium (IV) ethoxide Ti(OEt)4 , Titanium(IV) i-propoxide Ti(i-OPr)4 , Titanium (IV) Butoxide Ti(OBu)4 or combination of thereof.

5. The composition as claimed in claim 1, wherein the alkyl aluminium compound is selected from a group consisting of tri-ethyl aluminium (TEAL), tri-isobutyl aluminium (TIBA), tri-isopropyl aluminium (TIPRA), tri-n-hexyl aluminium (TnHA), and diethyl aluminium chloride (DEAC) or combination of thereof.

6. The composition as claimed in claim 1, wherein the isohexide based diester is a compound of formula I, and an isomer of formula I or combination thereof;

Formula I
wherein R is independently selected from a group consisting of CH3, C2H5, C3H7 and Ph or a combination thereof.
7. A process for the selective dimerization of ethylene to 1-butene using catalyst composition as defined in claim 1, wherein conversion of ethylene is in a range of 50 to 90 % and wherein the selectivity for 1-butene is at least 99%.