Description:FIELD
The present disclosure relates to a process for the preparation of a purified chromium 2-ethylhexanoate. Particularly, the present disclosure relates to a process for the preparation and purification of the aquated chromium 2-ethylhexanoate for its use in olefin oligomerization.
BACKGROUND
The background information herein below relates to the present disclosure but is not necessarily prior art.
Chromium (III) carboxylates are used commercially in a variety of applications including catalytic and materials applications. Among chromium carboxylates, chromium (III) tris(2-ethylhexanoate) [Cr(EH)3] is of interest as it is the main component of catalysts for ethylene oligomerization. Chromium (III) tris(2-ethylhexanoate) is used in the industrial process of ethylene trimerization to obtain 1-hexene and in the reaction of ethylene tetramerization to obtain 1-octene.
Chromium 2-ethylhexanoate is generally prepared by metathesis reaction of chromium salt and sodium 2-ethylhexanoate. Chromium 2-ethylhexanoate salts in which the coordination sites are occupied by water, are referred to as "aquated' chromium 2-ethylhexanoate compounds. The “aquated' chromium 2-ethylhexanoate is prepared by reaction of chromium nitrate nonahydrate and sodium 2-ethylhexanaote in water. The aquated chromium 2-ethylhexanoates are trimeric compounds whereas anhydrous chromium 2-ethylhexanoate is generally mononuclear in nature. Both are denoted with general structure of Cr(2-EH)3 (2-EH=2-ethylhexanoate). The aquated chromium 2-ethylhexanoate compounds often contain coordinated or residual water and carboxylic acid molecules. These protic sources are incompatible with many catalyst activators. Structurally characterized aquated chromium (III) 2-ethylhexanoate form clusters with a variety of bridging groups introduced from aqueous reaction conditions and usually insoluble in aliphatic hydrocarbon solvent.
The use of impure aquated chromium 2-ethylhexanoate in ethylene trimerization leads to the formation of polymer by-product which gets coated on the inner surfaces of the reactor as well as in the piping of the reactor. Moreover, major amount of the polymer formed are flown out of the reactor as a suspended solid in the reactor effluent. Thus, the polymer continued to flow to downstream part of the reaction system and thereby choked the Thin Film Evaporator (TFE) and filters. The build-up of polymeric by-product which remained within the oligomerization reactor itself and associated with reactor piping can be troublesome. Over time, the accumulated polymeric by-products completely foul the internal surfaces of the reactor and the associated piping. Hence, it becomes necessary to shut down the plant to clean the reactor and piping with a suitable solvent which can dissolve the built-up polymeric by-products. However, frequent shutting down of the reactor for cleaning and maintenance is economically disadvantageous as production of the desired oligomerization product gets interrupted.
Further, the conventional methods for the preparation and purification of the aquated chromium 2-ethylhexanoate employs multiple purification procedures such as washing with sodium hydroxide and sodium carbonate solution, drying with anhydrous magnesium sulfate and removing solvent by vacuum. These purification procedures are tedious and hence, not economical at a commercial scale.
Therefore, there is, felt a need to provide a process for the preparation of chromium 2-ethylhexanoate that mitigates the drawbacks mentioned herein above or at least provides a useful alternative.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems given in the background or to at least provide a useful alternative.
An object of the present disclosure is to provide a process for the preparation of a purified chromium 2-ethylhexanoate.
Another object of the present disclosure is to provide a single pot process for the preparation and purification of chromium 2-ethylhexanoate.
Still another object of the present disclosure is to provide a simple, economical and efficient process for the preparation of a purified chromium 2-ethylhexanoate.
Yet another object of the present disclosure is to provide a process for the preparation of a purified chromium 2-ethylhexanoate that is feasible at commercial scale.
Still another object of the present disclosure is to provide a less viscous and pumpable precursor catalyst mixture comprising the purified chromium 2-ethylhexanoate.
Yet another object of the present disclosure is to provide a catalyst composition comprising the precursor catalyst mixture for olefin oligomerization.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure relates to a process for the preparation of a purified chromium 2-ethylhexanoate. The process comprises adding a first organic fluid medium to an aqueous sodium 2-ethylhexanoate solution to obtain a mixture followed by adding an aqueous solution of a chromium precursor to the mixture and heating at a first predetermined temperature for a first predetermined time period to obtain a product mixture. The product mixture is cooled to a temperature in the range of 20 °C to 40 °C to obtain a biphasic product mixture comprising an aqueous phase and an organic phase and separating the aqueous phase from the biphasic product mixture to obtain the organic phase. A second organic fluid medium is added to the organic phase under stirring at a speed in the range of 400 rpm to 600 rpm for a time period in the range of 1 minute to 5 minutes to obtain solids of chromium 2-ethylhexanoate. The solids of chromium 2-ethylhexanoate is dried under vacuum for a second predetermined time period at a second predetermined temperature to obtain vacuum dried solids of chromium 2-ethylhexanoate. The vacuum dried solids of chromium 2-ethylhexanoate are washed with a third organic fluid medium to obtain a purified chromium 2-ethylhexanoate.
In an embodiment of the present disclosure, the purified chromium 2-ethylhexanoate is treated with an organic sulfonic acid in a fourth organic fluid medium at a temperature in the range of 120 °C to 250 °C for a time period in the range of 1 hour to 5 hours to obtain chromium 2-ethylhexanoate solution having a viscosity in the range of 1x10-6 m2/s to 100x10-6 m2/s (1 cSt to 100 cSt).
The organic sulfonic acid is selected from the group consisting of p-toluene sulfonic acid, methane sulfonic acid, benzene sulfonic acid, dodecyl benzene sulfonic acid and C10 – C14 mixture of dodecyl benzene sulfonic acid.
The step of preparing the product mixture comprises the following sub-steps:
i) adding 2-ethylhexanoic acid to an aqueous sodium hydroxide solution in a predetermined molar ratio under stirring to obtain the aqueous sodium 2-ethylhexanoate solution;
ii) adding the first organic fluid medium to the solution to obtain the mixture; and
iii) gradually, adding the aqueous solution of the chromium precursor to the mixture followed by heating at the first predetermined temperature for the first predetermined time period to obtain the product mixture.
In an embodiment of the present disclosure, the predetermined molar ratio of 2-ethylhexanoic acid to sodium hydroxide is in the range of 1:0.5 to 1:1.5.
The first organic fluid medium and the fourth organic fluid medium are independently selected from the group consisting of toluene, hexane, cyclohexane, ethylbenzene, heptane, benzene, mesitylene, diethylbenzene and xylenes.
The chromium precursor is selected from the group consisting of chromium nitrate nonahydrate, chromium chloride hexahydrate, chromium sulphate, chromium bromide and chromium fluoride.
The first predetermined temperature is in the range of 70 °C to 110 °C and the first predetermined time period is in the range of 1 hour to 5 hours.
The second organic fluid medium is selected from the group consisting of acetone, methanol, ethanol, propanol, butanol and 2-ethyl hexanol.
The second predetermined time period is in the range of 10 minutes to 180 minutes.
The third organic fluid medium is selected from the group consisting of n-hexane, n-heptane, n-pentane and cyclohexane.
The second predetermined temperature is in the range of 25 °C to 100 °C.
The present disclosure further relates to a precursor catalyst mixture comprising:
i. the purified chromium 2-ethylhexanoate prepared in accordance with the present disclosure;
ii. an organic sulfonic acid; and
iii. a first non-polar solvent.
A molar ratio of chromium 2-ethylhexanoate to the organic sulfonic acid is in the range of 1: 0.1 to 1:5.
The organic sulfonic acid is selected from the group consisting of p-toluene sulfonic acid, methane sulfonic acid, benzene sulfonic acid, dodecyl benzene sulfonic acid and C10 – C14 mixture of dodecyl benzene sulfonic acid.
The first non-polar solvent is selected from the group consisting of toluene, hexane, cyclohexane, ethylbenzene, heptane, benzene, mesitylene, diethylbenzene and xylenes.
Still further, the present disclosure relates to a catalyst composition for olefin oligomerization. The catalyst composition comprises:
(i) the precursor catalyst mixture prepared in accordance with the present disclosure;
(ii) at least one organic ligand;
(iii) a first co-catalyst;
(iv) a second co-catalyst; and
(v) at least one second non-polar solvent.
The organic ligand is selected from the group consisting of 2, 5 dimethylpyrrole, tris(4-methoxyphenyl) phosphine, 2,5-dimethylthiophene and cis-2,6-dimethylpiperidine.
The first co-catalyst is selected from the group consisting of triethylaluminium, tridecylaluminum, tri-n-butylaluminum, tri-isopropylaluminum, triisoprenylaluminum, tri-isobutylaluminum, triphenylaluminum and tri-n-octylaluminum.
The second co-catalyst is selected from the group consisting of diethyl aluminium chloride, di-isobutyl aluminum chloride and ethyl aluminum dichloride.
The second non-polar solvent is selected from the group consisting of toluene, hexane, cyclohexane, ethylbenzene, heptane, benzene, mesitylene, diethylbenzene and xylenes.
A molar ratio of chromium 2-ethylhexanoate to the organic ligand to the first co-catalyst to the second co-catalyst is in the range of 1:2:8:4 to 1:6:15:12.
DETAILED DESCRIPTION
The present disclosure relates to a process for the preparation of purified chromium 2-ethylhexanoate. Particularly, the present disclosure relates to a process for the preparation and purification of the aquated chromium 2-ethylhexanoate for its use in olefin oligomerization.
Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components, and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.
The terminology used, in the present disclosure, is only for the purpose of explaining a particular embodiment and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.
The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third etc., when used herein do not imply a specific sequence or order unless clearly suggested by the present disclosure.
The use of impure aquated chromium 2-ethylhexanoate in ethylene trimerization leads to the formation of polymer by-product which gets coated on the inner surfaces of the reactor as well as in the piping of the reactor. Moreover, major amount of the polymer formed are flown out of the reactor as a suspended solids in the reactor effluent. Thus, the polymer continued to flow to downstream part of the reaction system and thereby choked the Thin Film Evaporator (TFE) and filters. The build-up of polymeric by-product which remained within the oligomerization reactor itself and associated with reactor piping can be troublesome. Over time, the accumulated polymeric by-products completely foul the internal surfaces of the reactor and the associated piping. Hence, it becomes necessary to shut down the plant to clean the reactor and piping with a suitable solvent which can dissolve the built-up polymeric by-products. However, frequent shutting down of the reactor for cleaning and maintenance is economically disadvantageous as production of the desired oligomerization product gets interrupted.
Further, the conventional methods for the preparation and purification of the aquated chromium 2-ethylhexanoate employs multiple purification procedures such as washing with sodium hydroxide and sodium carbonate solution, drying with anhydrous magnesium sulfate and removing solvent by vacuum. These purification procedures are tedious and hence, not economical at a commercial scale.
The present disclosure relates to a process for the preparation of a purified chromium 2-ethylhexanoate. Particularly, the present disclosure relates to a process for the preparation and purification of the aquated chromium 2-ethylhexanoate for its use in olefin oligomerization.
In an aspect, the present disclosure relates to a process for the preparation of a purified chromium 2-ethylhexanoate. The process comprises the following steps:
(a) adding a first organic fluid medium to an aqueous sodium 2-ethylhexanoate solution to obtain a mixture followed by adding an aqueous solution of a chromium precursor to the mixture and heating at a first predetermined temperature for a first predetermined time period to obtain a product mixture;
(b) cooling the product mixture to a temperature in the range of 20 °C to 40 °C to obtain a biphasic product mixture comprising an aqueous phase and an organic phase and separating the aqueous phase from the biphasic product mixture to obtain the organic phase;
(c) adding a second organic fluid medium to the organic phase under stirring at a speed in the range of 400 rpm to 600 rpm for a time period in the range of 1 minute to 5 minutes to obtain solids of chromium 2-ethylhexanoate;
(d) drying the solids of chromium 2-ethylhexanoate under vacuum for a second predetermined time period at a second predetermined temperature to obtain vacuum dried solids of chromium 2-ethylhexanoate;
(e) washing the vacuum dried solids of chromium 2-ethylhexanoate with a third organic fluid medium to obtain a purified chromium 2-ethylhexanoate.
In an embodiment of the present disclosure, the purified chromium 2-ethylhexanoate is treated with an organic sulfonic acid in a fourth organic fluid medium at a temperature in the range of 120 °C to 250 °C for a time period in the range of 1 hour to 5 hours to obtain chromium 2-ethylhexanoate solution having a viscosity in the range of 1x10-6 m2/s to 100x10-6 m2/s (1 cSt to 100 cSt).
In an embodiment of the present disclosure, the organic sulfonic acid is selected from the group consisting of p-toluene sulfonic acid, methane sulfonic acid, benzene sulfonic acid, dodecyl benzene sulfonic acid and C10 – C14 mixture of dodecyl benzene sulfonic acid.
The step-(a) of preparing the product mixture comprises the following sub-steps:
i) adding 2-ethylhexanoic acid to an aqueous sodium hydroxide solution in a predetermined molar ratio under stirring to obtain the aqueous sodium 2-ethylhexanoate solution;
ii) adding the first organic fluid medium to the solution to obtain the mixture; and
iii) gradually, adding the aqueous solution of the chromium precursor to the mixture followed by heating at the first predetermined temperature for the first predetermined time period to obtain the product mixture.
In an embodiment of the present disclosure, the predetermined molar ratio of 2-ethylhexanoic acid to sodium hydroxide is in the range of 1:0.5 to 1:1.5. In an exemplary embodiment of the present disclosure, the predetermined molar ratio of 2-ethylhexanoic acid to sodium hydroxide is 1:1.
The first organic fluid medium and the fourth organic fluid medium are independently selected from the group consisting of toluene, hexane, cyclohexane, ethylbenzene, heptane, benzene, mesitylene, diethylbenzene and xylenes. In an exemplary embodiment of the present disclosure, the first organic fluid medium and the fourth organic fluid medium is toluene.
The chromium precursor is selected from the group consisting of chromium nitrate nonahydrate, chromium chloride hexahydrate, chromium sulphate, chromium bromide and chromium fluoride. In an exemplary embodiment of the present disclosure, the chromium precursor is chromium nitrate nonahydrate.
The first predetermined temperature is in the range of 70 °C to 110 °C. In an exemplary embodiment of the present disclosure, the first predetermined temperature is 85 °C.
The first predetermined time period is in the range of 1 hour to 5 hours. In an exemplary embodiment of the present disclosure, the first predetermined time period is 2 hours.
The second organic fluid medium is selected from the group consisting of acetone, methanol, ethanol, propanol, butanol and 2-ethyl hexanol. In an exemplary embodiment of the present disclosure, the second organic fluid medium is acetone.
The second predetermined time period is in the range of 10 minute to 180 minutes. In an exemplary embodiment of the present disclosure, the second predetermined time period is 60 minutes.
The third organic fluid medium is selected from the group consisting of n-hexane, n-heptane, n-pentane and cyclohexane. In an exemplary embodiment of the present disclosure, the third organic fluid medium is n-hexane.
The second predetermined temperature is in the range of 25 °C to 100 °C. In an exemplary embodiment of the present disclosure, the second predetermined temperature is 80 °C.
The present disclosure provides a purified aquated chromium 2-ethylhexanoate that is used in the catalyst composition for olefin oligomerization.
In another aspect, the present disclosure relates to a precursor catalyst mixture comprising:
i. the purified chromium 2-ethylhexanoate prepared in accordance with the present disclosure;
ii. an organic sulfonic acid; and
iii. a first non-polar solvent.
A molar ratio the chromium 2-ethylhexanoate to p-toluene sulfonic acid is in the range of 1: 0.1 to 1:1. In an exemplary embodiment of the present disclosure, the molar ratio of chromium 2-ethylhexanoate to p-toluene sulfonic acid is 1:0.3.
The organic sulfonic acid is selected from the group consisting of p-toluene sulfonic acid, methane sulfonic acid, benzene sulfonic acid, dodecyl benzene sulfonic acid and C10 – C14 mixture of dodecyl benzene sulfonic acid. In an exemplary embodiment of the present disclosure, the organic sulfonic acid is p-toluene sulfonic acid.
The first non-polar solvent is selected from the group consisting of toluene, hexane, cyclohexane, ethylbenzene, heptane, benzene, mesitylene, diethylbenzene and xylenes. In an exemplary embodiment of the present disclosure, the first non-polar solvent is toluene.
The use of purified chromium 2-ethylhexanoate as a catalyst precursor in ethylene trimerization reaction is crucial. The purified chromium 2-ethylhexanoate produces lower amount of polyethylene by-product compared to that of impure chromium 2-ethylhexanoate.
The aquated chromium 2-ethylhexanoate in toluene at concentration higher than 20 wt% is found to be highly viscous in nature. It is difficult to pump and prepare catalyst solution from highly viscous chromium 2-ethylhexanoate solution. Conventionally, the aquated chromium 2-ethylhexanoate is treated with excess of 2-ethylhexanoic acid at high temperature to produce non-viscous chromium 2-ethylhexanoate. The removal of excess of 2-ethylhexanoic acid is a challenging task and presence of traces of 2-ethylhexanoic acid affects the catalyst activity.
Therefore, the inventors of the present disclosure found that the use of p-toluene sulfonic acid reduces the viscosity of the aquated chromium-2-ethylhexanoate.
In an exemplary embodiment of the present disclosure, 1 equivalent of the aquated chromium-2-ethylhexanoate is heated with 0.3 equivalents of p-toluene sulfonic acid in toluene at 150 °C for 2 hours to obtain a less viscous and easily pumpable chromium 2-ethylhexanoate solution having a viscosity in the range of 1x10-6 m2/s to 100x10-6 m2/s (1 cSt to 100 cSt).
In still another aspect, the present disclosure relates to a catalyst composition for olefin oligomerization. The catalyst composition comprises:
(i) the precursor catalyst mixture prepared in accordance with the present disclosure;
(ii) at least one organic ligand;
(iii) a first co-catalyst;
(iv) a second co-catalyst; and
(v) at least one second non-polar solvent.
The organic ligand is selected from the group consisting of 2, 5 dimethylpyrrole, tris(4-methoxyphenyl) phosphine, 2,5-dimethylthiophene and cis-2,6-dimethylpiperidine. In an exemplary embodiment of the present disclosure, the organic ligand is 2, 5 dimethylpyrrole.
The first co-catalyst is selected from the group consisting of triethylaluminium (TEAL), tridecylaluminum, tri-n-butylaluminum, tri-isopropylaluminum, triisoprenylaluminum, tri-isobutylaluminum, triphenylaluminum and tri-n-octylaluminum. In an exemplary embodiment of the present disclosure, the first co-catalyst is triethylaluminium (TEAL).
The second co-catalyst is selected from the group consisting of diethyl aluminium chloride (DEAC), di-isobutyl aluminum chloride and ethyl aluminum dichloride. In an exemplary embodiment of the present disclosure, the second co-catalyst is diethyl aluminium chloride (DEAC).
The second non-polar solvent is selected from the group consisting of toluene, hexane, cyclohexane, ethylbenzene, heptane, benzene, mesitylene, diethylbenzene and xylenes. In an exemplary embodiment of the present disclosure, the second non-polar solvent is toluene.
A molar ratio of chromium 2-ethylhexanoate to the organic ligand to the first co-catalyst to the second co-catalyst is in the range of 1:2:8:4 to 1:6:15:12. In an exemplary embodiment of the present disclosure, the molar ratio of the chromium 2-ethylhexanoate to DMP: TEAL: DEAC is 1:4:11:8.
The foregoing description of the embodiments has been provided for purposes of illustration and not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment, but, are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
Experimental details:
Experiment 1: Process for the preparation of a purified chromium 2-ethylhexanoate in accordance with the present disclosure
In a 3-litre reactor, 90 g (2.25 mole) of sodium hydroxide was dissolved in 375 ml of distilled water to obtain an aqueous sodium hydroxide solution. To this solution, 2-ethylhexanoic acid (327g, 2.27 mole) was added under stirring to obtain a resultant solution comprising sodium 2-ethylhexanoate (pH was neutral). 600 ml of toluene was added to the resultant solution to obtain a mixture. In a separate container, 150 g (0.375 mol) of chromium nitrate nonahydrate was dissolved in 375 ml of distilled water to obtain an aqueous solution of chromium nitrate nonahydrate. The aqueous chromium nitrate solution was slowly added to the mixture at 25 °C followed by heating at 85 °C for 2 hours to obtain a product mixture.
The product mixture was cooled to 25 °C to obtain a biphasic product mixture comprising an aqueous phase and an organic phase and the aqueous phase was separated from the biphasic product mixture to obtain the organic phase. 700 ml of acetone was added to reactor containing the organic phase under stirring at 500 rpm for 2 minutes to obtain blue granular solids of chromium 2-ethylhexanoate in the reactor.
The liquid mixture was drained from bottom of the reactor and the blue solids of chromium 2-ethylhexanoate was dried under flow of nitrogen for 15 minutes followed by vacuum drying (100mBar) at 80 °C for 1 hour to remove the traces of acetone from the solids of chromium 2-ethylhexanoate to obtain vacuum dried solids. Further, the vacuum dried solids of chromium 2-ethylhexanoate were washed with 250 ml of n-hexane to ensure the complete removal of acetone to obtain a purified aquated chromium 2-ethylhexanoate. 130g of the aquated chromium-2-ethylhexanoate (yield = 70%) was found in reactor.
A sample of the aquated chromium-2-ethylhexanoate was dissolved in toluene and tested for the presence of acetone by GC method. The acetone content was found to be less than 0.01wt% in the final batch of the aquated chromium-2-ethylhexanoate.
Experiment 2: To study the effect of vacuum drying and addition of n-hexane on the purity of chromium 2-ethylhexanoate in accordance with the present disclosure
The same procedure of experiment 1 was repeated to obtain the blue granular solids of chromium 2-ethylhexanoate in the reactor.
The liquid mixture was drained from bottom of the reactor and the blue solids of chromium 2-ethylhexanoate was dried under flow of nitrogen for 15 minutes followed by vacuum drying (100 mBar) at 30 °C for 2 hours to remove the traces of acetone from the solids of aquated chromium 2-ethylhexanoate (yield = 75%),
A sample of the aquated chromium-2-ethylhexanoate was dissolved in 10 ml of toluene and tested for presence of acetone by GC method.
Further, the solids, aquated chromium 2-ethylhexanoate was dissolved in toluene and poured into methanol solution. The solid was separated in the solution and the clear solution was injected into GC. The peaks of acetone, methanol and toluene were seen in GC spectrum. The ratio of acetone to toluene was measured from these spectrums. The acetone/toluene ratio gives the information on amount of acetone present in the toluene solution of chromium 2-ethylhexanoate.
The samples of the aquated chromium 2-ethylhexanoate were collected before vacuum drying and at different time intervals of vacuum drying and subjected to GC analysis to measure the amount of acetone present in the sample. The results are summarized in Table 1.
Table 1: Acetone content in the solid aquated chromium-2-ethylhexanoate measured by GC
Samples of aquated chromium 2-ethylhexanoate Acetone (wt%)
Sample 1(without vacuum drying) 2.51
Sample 2 (1 hour vacuum drying at 30 oC) 0.48
Sample 3 (2 hour vacuum drying at 30 oC) 0.17
Sample of Experiment 1 (1 hour vaccum drying at 80 oC + washing with n-hexane) 0.01

From the results as given in Table 1, it is observed that the vacuum could not remove the traces of acetone completely even after drying under vacuum for a long period. The presence of the traces of acetone in the purified toluene solution of the aquated chromium 2-ethylhexanoate will affect the productivity and selectivity of the reaction.
Further, by employing the step of washing with acetone, the step of washing the aquated chromium-2-ethylhexanoate solution by using sodium bicarbonate or sodium hydroxide solution can be avoided. The washing of the aquated chromium-2-ethylhexanoate with acetone completely removes the excess of 2-ethyl hexanoic acid and other chromium impurities. However, the removal of acetone by applying vacuum at room temperature for a longer period is not economical. Additionally, the transfer of the aquated chromium-2-ethylhexanoate solution from one vessel to a vessel containing acetone is tedious process because of the high viscosity of concentrated the aquated chromium-2-ethylhexanoate solution.
Thus, the process in accordance with the present disclosure is an improved process as the process is economical and easy to handle the aquated chromium-2-ethylhexanoate at a commercial scale. In the commercial production of the aquated chromium-2-ethylhexanoate, it is difficult to transfer toluene solution of the aquated chromium-2-ethylhexanoate from one reactor to another reactor containing acetone. Therefore, acetone is added to the reactor itself in which the aquated chromium-2-ethylhexanoate is prepared. Further, in the process of the present disclosure, the solid aquated chromium-2-ethylhexanoate is dried at 80 °C to remove traces of acetone. In addition to this, the solid aquated chromium-2-ethylhexanoate is washed with minimum amount of n-hexane to completely remove the traces of acetone.
The sample 3, the aquated chromium-2-ethylhexanoate with traces of acetone (0.17 wt%), was used for preparing the catalyst and was prepared by mixing 2,5-dimethylpyrrole, triethyl aluminium and chlorodiethyl aluminium in an appropriate ratio. A slight amount of turbidity was observed in the catalyst solution due to the reaction of acetone and alkyl aluminium. This catalyst solution was tested for ethylene trimerization under the reported conditions. Due to the contamination of acetone, a low productivity of n-hexane and formation of high content of polymer was observed in ethylene trimerization reaction. The sample of Experiment 1 which is free from acetone, showed excellent productivity of n-hexane and low polymer formation under similar reaction conditions.
One of the issues of the aforesaid prepared aquated chromium-2-ethylhexanoate is that it is highly viscous when it is dissolved in toluene. It was difficult to pump the highly viscous solution in the plant. The viscosity of 6 wt % aquated chromium-2-ethylhexanoate in toluene solution was measured at 25 °C by using Ostwald viscometer and was found to be 85 cSt to 95 cSt. On the other hand, 40 wt% aquated chromium-2-ethylhexanoate in toluene solution was found to be highly viscous and was difficult to pump in plant for preparing the catalyst solutions.
Traditionally, the aquated chromium-2-ethylhexanoate is treated with excess of 2-ethyl hexanoic acid to convert into anhydrous aquated chromium-2-ethylhexanoate. During the process, the viscosity of chromium salt reduces drastically depending on their concentration. One of the key issues in this process is removal of excess of 2-ethylhexanoic acid. The presence of acid in chromium 2-ethylhexanoate reduces the performance of the catalyst solution in ethylene trimerization reaction.
Therefore, in the present disclosure, p-toluene sulfonic acid is used to reduce the viscosity of the aquated chromium-2-ethylhexanoate. The aquated chromium-2-ethylhexanoate was heated with minimum quantity of sulfonic acid.
Experiment 3: Preparation of a precursor catalyst mixture comprising chromium 2-ethylhexanoate of a desired viscosity
1 equivalent of the aquated chromium-2-ethylhexanoate was heated with 0.3 equivalents of p-toluene sulfonic acid at 150 °C for 2 hours.
Particularly, 14.8 g (0.078 mole) of p-toluene sulfonic acid was added to the reactor containing the aquated chromium-2-ethylhexanoate (experiment 1) followed by adding 338 g of toluene. The reactor was heated to 150 °C for 2 hours to obtain a solution of aquated chromium-2-ethylhexanoate. 30 wt% solution of the aquated chromium-2-ethylhexanoate in toluene was filtered through celite to obtain the less viscous chromium sample. Similarly, different concentrations of the aquated chromium-2-ethylhexanoate were prepared and their viscosities were measured.
The viscosity of different concentrations of the aquated chromium-2-ethylhexanoate samples treated with p-toluene sulfonic acid (PTSA) and 2-ethyl hexanoic acid (2-EHA) were recorded and tabulated in table 2.
Table 2: Viscosity of different concentrations of the aquated chromium-2-ethylhexanoate samples treated with PTSA and 2-ethyl hexanoic acid
Sr. No. Conc (wt%) Equivalents of PTSA Viscosity (centistokes)
1. 30 0.3 12 - 15
2. 40 0.3 19 - 24
3. 50 0.3 150 - 160
4. 50 0.6 7 - 9
5. 6 0.7 0.9
6. 10 0.7 1.0
7. 15 0.7 1.2

Sr. No. Conc. (wt%) Equivalents of 2-EHA Viscosity (centistokes)
1 6 0 85 - 95
2 6 0.7 2 - 3
3 10 0.7 3 - 4
4 15 0.7 28 - 30
5 40 0.7 >300

One of the advantages of using p-toluenesulfonic acid is that it is cheaper than the 2-ethylhexanoic acid. The equivalents of p-toluenesulfonic acid used are less than that of 2-ethyl hexanoic used in the traditional methods. Traditionally, excess of organic acid was used whereas in the present disclosure at least 0.3 equivalents of organic acid were used. The use of 0.3 equivalent of 2-ethylhexanoic acid could not decrease the viscosity of the aquated chromium-2-ethylhexanoate as viscosity reduced by p-toluene sulfonic acid. p-Toluenesulfonic acid was found to be effective in reducing the viscosity of the aquated chromium-2-ethylhexanoate in comparison to 2-ethylhexanoic acid.
All the operations including preparing the aquated chromium-2-ethylhexanoate, its purification and treatment with p-toluenesulfonic acid in toluene were carried out in a single reactor. This avoids the issue of the product loss, pumping issue due to viscosity and contamination thereby, making the production of the catalyst precursor mixture comprising chromium-2-ethylhexanoate easy and clean.
Experiment 4: Preparation of a catalyst composition comprising the precursor mixture in accordance with the present disclosure
Example (i): 30 wt% chromium tri-2-ethylhexanoate sample (0.3 equiv of PTSA) was tested for ethylene oligomerization. The catalysts were prepared by the following method.
1.67 g of 30 wt% chromium tri-2-ethylhexanoate sample was mixed with 0.38 g, 2,5-dimethylpyrrole in 10 ml toluene in a first vessel to obtain a first mixture. Similarly, 7.9 ml triethylaluminum (20 wt% in toluene) and 5.4 ml diethylaluminum chloride (20 wt% in toluene) were mixed in a second vessel to obtain a second mixture. The first mixture and the second mixture were mixed at 25 °C to obtain a catalyst. The molar proportion of the aquated chromium (III) 2-ethylhexanoate: DMP: TEAL: DEAC was 1:4:11:8. The catalyst system was tested for activity and polymer formation in ethylene oligomerization reaction.
Oligomerization of ethylene using the catalysts composition prepared from the aquated chromium (III) 2-ethylhexanoate
1 liter Buchi reactor was charged with 400 ml of cyclohexane. The reactor was maintained at 90 °C under ethylene pressure of 3 kg/cm2. This was followed by the addition of the catalyst composition prepared in Example (i) by maintaining the catalyst concentration of 390 ppm. The catalyst composition and cyclohexane present in the reactor were thoroughly mixed by using a stirrer at a speed of 500 rpm. Ethylene gas was fed to the reactor till a pressure of 30 kg/cm2 was attained, while the reactor temperature was maintained at 110 °C. The oligomerization reaction was monitored by an exotherm and the exothermicity of the reaction was controlled by cooling the reactor by a circulating bath containing chilled water. Stirring was continued for 1.5 hours and thereafter ethylene feed was disconnected. The reactor was cooled to 10 °C and degassed carefully by venting out excess ethylene. The contents of the reactor were quenched by injecting 5% acidic methanol, which is used as a terminating agent. The products were collected and weighed separately.
The liquid product was obtained along with some gaseous products. The composition of the gas and the liquid samples were analyzed by Gas chromatography using a Agilent 123-1033: DB-1 30 m * 320 µm * 1 µm GC column and flame ionization detector respectively.
Example (ii): A catalyst composition was prepared by following the same procedure of Example (i) of Experiment 4 except 6 wt% chromium tri-2-ethylhexanoate of Experiment 1 was used. Oligomerization of ethylene was carried out by using the catalyst composition prepared.
Example (iii): A catalyst composition was prepared by following the same procedure of Example (i) of Experiment 4 except 6 wt% chromium tri-2-ethylhexanoate sample 3 of Experiment 2 was used. Oligomerization of ethylene was carried out by using the catalyst composition prepared.
The catalyst performance was evaluated in terms of the catalyst Activity (Kg hexene/g Cr/h), Selectivity of C6, Selectivity of 1-C6 and formation of by-product polyethylene (wt%). The results are summarized in Table 3.
Table 3: Catalyst performance
Catalyst Chromium Sample in the catalyst composition Activity (Kg hexene /g Cr/h) Selectivity of C6 Selectivity of 1-C6 Polyethylene (Wt. %)
Example (i) 30 wt% chromium tri-2-ethylhexanoate sample (0.3 equiv of PTSA) 23.8 91 99.61 0.020
Example (ii) Sample of Experiment 1 25.0 91.1 99.50 0.015
Example (iii) Sample 3 of Experiment 2 18.3 91.2 99.55 0.178
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for the preparation of chromium 2-ethylhexanoate that:
• is a single pot process (wherein both preparation and purification is carried out in the same pot);
• provides a less viscous and pumpable precursor catalyst mixture comprising the chromium 2-ethylhexanoate; and
• is simple, economical and efficient; and
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.
The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the disclosure, unless there is a statement in the specification specific to the contrary.
While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation. , Claims:WE CLAIM:
1. A process for the preparation of a purified chromium 2-ethylhexanoate, said process comprising the following steps:
(a) adding a first organic fluid medium to an aqueous sodium 2-ethylhexanoate solution to obtain a mixture followed by adding an aqueous solution of a chromium precursor to said mixture and heating at a first predetermined temperature for a first predetermined time period to obtain a product mixture;
(b) cooling said product mixture to a temperature in the range of 20 °C to 40 °C to obtain a biphasic product mixture comprising an aqueous phase and an organic phase and separating said aqueous phase from said biphasic product mixture to obtain said organic phase;
(c) adding a second organic fluid medium to said organic phase under stirring at a speed in the range of 400 rpm to 600 rpm for a time period in the range of 1 minute to 5 minutes to obtain solids of chromium 2-ethylhexanoate;
(d) drying said solids of chromium 2-ethylhexanoate under vacuum for a second predetermined time period at a second predetermined temperature to obtain vacuum dried solids of chromium 2-ethylhexanoate; and
(e) washing said vacuum dried solids of chromium 2-ethylhexanoate with a third organic fluid medium to obtain a purified chromium 2-ethylhexanoate.
2. The process as claimed in claim 1, wherein said purified chromium 2-ethylhexanoate is treated with an organic sulfonic acid in a fourth organic fluid medium at a temperature in the range of 120 °C to 250 °C for a time period in the range of 1 hour to 5 hours to obtain chromium 2-ethylhexanoate solution having a viscosity in the range of 1x10-6 m2/s to 100x10-6 m2/s (1 cSt to 100 cSt).
3. The process as claimed in claim 2, wherein said organic sulfonic acid is selected from the group consisting of p-toluene sulfonic acid, methane sulfonic acid, benzene sulfonic acid, dodecyl benzene sulfonic acid and C10 – C14 mixture of dodecyl benzene sulfonic acid.
4. The process as claimed in claim 1, wherein said step-(a) comprises the following sub-steps:
i) adding 2-ethylhexanoic acid to an aqueous sodium hydroxide solution in a predetermined molar ratio under stirring to obtain said aqueous sodium 2-ethylhexanoate solution;
ii) adding said first organic fluid medium to said solution to obtain said mixture; and
iii) gradually, adding said aqueous solution of said chromium precursor to said mixture followed by heating at said first predetermined temperature for said first predetermined time period to obtain said product mixture.
5. The process as claimed in claim 4, wherein said predetermined molar ratio of 2-ethylhexanoic acid to sodium hydroxide is in the range of 1:0.5 to 1:1.5.
6. The process as claimed in claims 1 and 2, wherein said first organic fluid medium and said fourth organic fluid medium are independently selected from the group consisting of toluene, hexane, cyclohexane, ethylbenzene, heptane, benzene, mesitylene, diethylbenzene and xylenes.
7. The process as claimed in claim 1, wherein said chromium precursor is selected from the group consisting of chromium nitrate nonahydrate, chromium chloride hexahydrate, chromium sulphate, chromium bromide and chromium fluoride.
8. The process as claimed in claim 1, wherein said first predetermined temperature is in the range of 70 °C to 110 °C and said first predetermined time period is in the range of 1 hour to 5 hours.
9. The process as claimed in claim 1, wherein said second organic fluid medium is selected from the group consisting of acetone, methanol, ethanol, propanol, butanol and 2-ethyl hexanol.
10. The process as claimed in claim 1, wherein said second predetermined time period is in the range of 10 minute to 180 minutes.
11. The process as claimed in claim 1, wherein said third organic fluid medium is selected from the group consisting of n-hexane, n-heptane, n-pentane and cyclohexane.
12. The process as claimed in claim 1, wherein said second predetermined temperature is in the range of 25 °C to 100 °C.
13. A precursor catalyst mixture comprising:
i. a purified chromium 2-ethylhexanoate as claimed in claim 1;
ii. an organic sulfonic acid; and
iii. a first non-polar solvent.
14. The precursor catalyst mixture as claimed in claim 13, wherein a molar ratio of chromium 2-ethylhexanoate to said organic sulfonic acid is in the range of 1: 0.1 to 1:5.
15. The precursor catalyst mixture as claimed in claim 13, wherein said organic sulfonic acid is selected from the group consisting of p-toluene sulfonic acid, methane sulfonic acid, benzene sulfonic acid, dodecyl benzene sulfonic acid and C10 – C14 mixture of dodecyl benzene sulfonic acid.
16. The precursor catalyst mixture as claimed in claim 13, wherein said first non-polar solvent is selected from the group consisting of toluene, hexane, cyclohexane, ethylbenzene, heptane, benzene, mesitylene, diethylbenzene and xylenes.
17. A catalyst composition for olefin oligomerization, said catalyst composition comprising:
(i) a precursor catalyst mixture as claimed in claim 13;
(ii) at least one organic ligand;
(iii) a first co-catalyst;
(iv) a second co-catalyst; and
(v) at least one second non-polar solvent.
18. The catalyst composition as claimed in claim 17, wherein said organic ligand is selected from the group consisting of 2, 5 dimethylpyrrole, tris(4-methoxyphenyl) phosphine, 2,5-dimethylthiophene and cis-2,6-dimethylpiperidine.
19. The catalyst composition as claimed in claim 17, wherein said first co-catalyst is selected from the group consisting of triethylaluminium, tridecylaluminum, tri-n-butylaluminum, tri-isopropylaluminum, triisoprenylaluminum, tri-isobutylaluminum, triphenylaluminum and tri-n-octylaluminum.
20. The catalyst composition as claimed in claim 17, wherein said second co-catalyst is selected from the group consisting of diethyl aluminium chloride, di-isobutyl aluminum chloride and ethyl aluminum dichloride.
21. The catalyst composition as claimed in claim 17, wherein said second non-polar solvent is selected from the group consisting of toluene, hexane, cyclohexane, ethylbenzene, heptane, benzene, mesitylene, diethylbenzene and xylenes.
22. The catalyst composition as claimed in claim 17, wherein a molar ratio of chromium 2-ethylhexanoate to said organic ligand to said first co-catalyst to said second co-catalyst is in the range of 1:2:8:4 to 1:6:15:12.
Dated this 16th day of February, 2024

_______________________________
MOHAN RAJKUMAR DEWAN, IN/PA – 25
of R.K.DEWAN & CO.
Authorized Agent of Applicant

TO,
THE CONTROLLER OF PATENTS
THE PATENT OFFICE, AT MUMBAI