Process for oligomerization of ethylene

Abstract

The present invention relates to a process for the oligomerization of ethylene, comprising: a) oligomerization of ethylene in a reactor in the presence of solvent and catalyst; b) transferring reactor overhead effluent to an externally located cooling device and recycling condensed effluent into the reactor; c) transferring the reactor bottom effluent to a series of fractionation columns and, in the following order, i) optionally separating a C4 fraction, ii) separating a C6 fraction, iii) simultaneously separating C8 and C10 fractions and recycling thereof into the reactor , and iv) separating residues comprising C12 fractions, spent catalyst polymer material and quench media, from the process, wherein the solvent is separated in any of the steps i)-iv)and/or in an additional step.

Claims

1. A process for oligomerizing ethylene, comprising: a) oligomerizing ethylene in a reactor in the presence of a solvent and a catalyst; b) transferring a reactor overhead effluent from the reactor to an externally located cooling device to condense a portion of the reactor overhead effluent and recycling the condensed portion of the reactor overhead effluent into the reactor; c) recovering a reactor bottom effluent from the reactor, wherein the reactor bottom effluent comprises C4 hydrocarbons, C6 hydrocarbons, C8 hydrocarbons, C10 hydrocarbons, residual C12+ hydrocarbons, residual spent catalyst, and residual polymer material; d) transferring the reactor bottom effluent to a quenching unit, wherein quench media is added to the reactor bottom effluent, to produce a quenched reactor bottom effluent; e) transferring the quenched reactor bottom effluent to a series of fractionation columns and, in the following order, i) optionally separating a fraction comprising the C4 hydrocarbons from the quenched reactor bottom effluent; ii) separating a fraction comprising the C6 hydrocarbons from the quenched reactor bottom effluent; iii) separating a fraction comprising both the C8 hydrocarbons and C10 hydrocarbons from the quenched reactor bottom effluent and recycling said fraction comprising both the C8 hydrocarbons and C10 hydrocarbons into the reactor, and iv) separating the residual C12+ hydrocarbons, the residual spent catalyst, the residual polymer material, and residual quench media from the quenched reactor bottom effluent, wherein the solvent is separated from the quenched reactor bottom effluent in any of steps i)-iv) and/or in an additional step.

2. The process according to claim 1, wherein the catalyst comprise (1) a chromium compound,(2) a lingand of the general structure (A) R.sub.1R.sub.2PN(R.sub.3)P(R.sub.4)N(R.sub.5)H or (B) R.sub.1R.sub.2PN(R.sub.3)P(R.sub.4)N(R.sub.5)PR.sub.6R.sub.7, wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6 and R.sub.7 are independently selected from halogen groups, amino groups, a trimethylsilyl group, C.sub.1-C.sub.10 alkyl groups, C.sub.6-C.sub.20 aryl groups, and substituted C.sub.6-C.sub.20 aryl groups, and (3) an activator or co-catalyst.

3. The process according to claim 2, wherein the chromium compound is selected from the group consisting of CrCl.sub.3(THF).sub.3, Cr(III) acetyl acetonate, Cr(III) octanoate, chromium hexacarbonyl, Cr(III)-2-ethyl hexanoate, benzene(tricarbonyl)-chormium, and Cr(III) chloride.

4. The process according to claim 2, wherein the activator or co-catalyst is selected from trimethyl aluminum, triethyl aluminum, triisopropyl aluminum, triisobutyl aluminum, ethylaluminum sesquichloride, diethyl aluminum chloride, ethyl aluminum dichloride, methyl aluminoxane (MAO) or mixtures thereof.

5. The process according to claim 1, wherein oligomerizing ethylene comprises trimerizing ethylene.

6. The process according to claim 1, wherein the condensed portion of the reactor overhead effluent recycled to the reactor comprises unreacted ethylene.

7. The process according to claim 1, wherein the condensed portion of the reactor overhead effluent is at a temperature of 30 C. to +10 C. prior to being recycled into the reactor.

8. The process according to claim 1, wherein make-up ethylene is added to the condensed portion of the reactor overhead effluent to be recycled into the reactor.

9. The process according to claim 1, wherein the fraction comprising both the C8 hydrocarbons and C10 hydrocarbons obtained in step iii) is recycled into the reactor at a temperature of about 10-20 C.

10. The process according to claim 1, wherein the content of C4 hydrocarbons in the reactor is from 5 to 30 weight percent, the content of C8 hydrocarbons in the reactor is from 1 to 2 weight percent, and/or the content of C10 hydrocarbons in the reactor is from 5 to 30 weight percent, where all weight percentages are based on the total weight of liquids contained in the reactor.

11. The process according to claim 1, wherein the total content of linear alpha-olefins in the reactor is from 30 to 75 weight percent based on the total weight of liquids contained in the reactor.

12. The process according to claim 1, wherein the reactor is a multi tubular reactor and/or a bubble column reactor.

Description

(1) Additional advantages and features of the inventive process can be taken from the following detailed description of a preferred embodiment, together with the drawings, wherein

(2) FIG. 1 discloses a schematic illustration of a state of the art commercial process for oligomerization; and

(3) FIG. 2 is a schematic illustration of the process of the present invention.

(4) As for the process illustrated in FIG. 1, also in FIG. 2 solvent 20 (optionally with fresh make-up solvent), catalyst 30 and ethylene 40 (optionally with fresh make-up ethylene 60) are entered into a reactor 10 for oligomerization. Reactor overhead effluent, preferably containing ethylene and butenes, is transferred to an externally located cooling device 50 and is recycled, either with fresh make-up ethylene or directly, into the reactor 10. Reactor bottom effluent is discharged from the reactor 10 and transferred to a quenching unit 70 where quenching medium is added. The quenched reactor bottom effluent is then transferred to a series of fractionation columns 80-110, wherein in the first fractionation column 80 ethylene dissolved in the solvent and butenes are separated jointly and transferred to the cooling device 50 to be finally recycled into the reactor 10. In fractionation column 90, hexenes are separated and discharged for further processing. If, for example, toluene is used as solvent, this can be removed and separated in fractionation column 100. Finally, C8 and C10 fractions are removed and separated simultaneously (jointly) in fractionation column 110. C8 and C10 fractions are recycled into the reactor 10, while any further residues can be then transferred for further processing.

(5) Illustrative Embodiments

(6) A multi compartment reactor model was developed to account for detailed hydrodynamics, thermodynamics and the variable gas flow-rate resulting from chemical/physical contraction, and gas/liquid re-circulation in a bubble-column reactor. The reactor model was coupled to a mechanistic kinetic model developed specifically for the novel ethylene trimerization catalyst system described by US 20120029258. The model was used to analyze one embodiment of the present invention. The performance of a pilot-scale bubble-column reactor for ethylene trimerization process for this embodiment of the present invention was verified with the developed rigorous reactor model.

(7) Further, a comparative example is provided illustrating a process for oligomerization known in the art, however utilizing an externally located condenser with a total reflux to separate unconverted ethylene from reactor top effluents. The separated ethylene is combined with make-up ethylene and ethylene from C2 column, which is recycled back to the reactor. Hence, in this comparative example, the feed gas composition is mostly ethylene, i.e., 98-99 wt. % C2. 1-butene is not present in the ethylene recycle stream, nor is there any recycling of C8 and C10 fractions into the reactor.

COMPARATIVE EXAMPLE

(8) TABLE-US-00001 TABLE 1 Stream analysis for the comparative example with an overhead condenser having total reflux and without C.sub.4 recycle Source_Gas Source_Liquid Sink-Liquid Sink_Gas Condenser Condenser (Feed gas) (Liq_in) (Liq products) (gas_products) (Flow_in) (Liq_out) Molare flowrate 4.19 0.09 0.41 3.70 5.19 1.49 (kmol/hr) Temperature (K) 308.15 294.15 323.15 271.15 323.09 271.15 Pressure (bar) 30.00 30.00 29.97 29.97 29.97 29.97 TOLUENE 0.00 1.00 0.21 0.00 0.00 0.01 (mol/mol) ETHYLENE 0.98 0.00 0.47 0.99 0.95 0.85 (mol/mol) 1-BUTENE 0.02 0.00 0.12 0.01 0.04 0.12 (mol/mol) 1-HEXENE 0.00 0.00 0.20 0.00 0.01 0.02 (mol/mol) 1-OCTENE 0.00 0.00 0.00 0.00 0.00 0.00 (mol/mol) DECENES 0.00 0.00 0.00 0.00 0.00 0.00 (mol/mol) DODECENES 0.00 0.00 0.00 0.00 0.00 0.00 (mol/mol)

(9) The stream analysis from the comparative example 1 is presented in Table 1. Process key performance indicators (KPIS) are shown in Table 2.

(10) TABLE-US-00002 TABLE 2 Ethylene conversion 0.0627512 Selectivity (1-BUTENE) 0.0248341 Selectivity (1-HEXENE) 0.941373 Selectivity (1-OCTENE) 1.61962E11 Selectivity (1-DECENE) 0.0337925 Selectivity (1-DODECENE) 3.78892E11 Heat of reaction (kW) 5.02985 Condenser duty (kW) 7.54554 Catalyst mole fraction in liquid feed 0.000200259 Condenser temperature 271.150

(11) As shown in Table 2, ethylene per pass conversion of 6 wt % was obtained with the condenser duty of 7.5 kW operated at 2 C.

INVENTIVE EXAMPLE

(12) Ethylene and 1-butene are sent directly to the externally located condenser after passing through an heat exchanger to reduce temperature to about 35 C. The condensed ethylene/1-butene enters the reactor as liquid streams preferably from the top of a disengagement zone, even more preferably from the side towards the reaction zone for effective cooling. The ethylene/1-butene content in the reactor can be maintained between 5-30 wt % via a purge stream.

(13) Similarly, decenes/1-octene from the top of 1-C.sub.8/C.sub.10 fractionation column are routed back to the reactor after been cooled from 170 C. to 1020 C. The decenes content in the reactor can be maintained between 5-10% via a purge stream. Additional duty to cool the recycled 1-C.sub.8/C.sub.10 to lower temperatures may have to be considered. Notwithstanding, the extra benefits provided by the recycled heavy fraction for polymer mobilization and reactor cooling in form of sensible heats may offset this duty.

(14) Table 3 shows the stream analysis, while Table 4 illustrates the key process indicators for this inventive process.

(15) TABLE-US-00003 TABLE 3 Stream analysis for the preferred embodiment of present invention with C.sub.2/C.sub.4 as recycled as liquid streams and 1-octene/decenes recycled Source_Gas Source_Liquid Sink-Liquid Sink_Gas Condenser Condenser (Feed gas) (Liq_in) (Liq products) (gas_products) (Flow_in) (Liq_out) Molare flowrate 1.77 0.09 0.47 3.02 1.52 0.27 (kmol/hr) Temperature (K) 308.15 294.15 323.15 314.34 274.15 308.15 Pressure (bar) 30.00 30.00 29.96 29.96 29.96 30.00 TOLUENE 0.00 0.93 0.17 0.00 0.00 0.00 (mol/mol) ETHYLENE 0.99 0.00 0.46 0.90 0.81 0.59 (mol/mol) 1-BUTENE 0.01 0.00 0.19 0.10 0.17 0.40 (mol/mol) 1-HEXENE 0.00 0.00 0.17 0.01 0.01 0.02 (mol/mol) 1-OCTENE 0.00 0.00 0.00 0.00 0.00 0.00 (mol/mol) DECENES 0.00 0.07 0.02 0.00 0.00 0.00 (mol/mol) DODECENES 0.00 0.00 0.00 0.00 0.00 0.00 (mol/mol)

(16) TABLE-US-00004 TABLE 4 Ethylene conversion 0.0773188 Selectivity (1-BUTENE) 0.0251504 Selectivity (1-HEXENE) 0.946202 Selectivity (1-OCTENE) 3.85301E12 Selectivity (1-DECENE) 0.0286475 Selectivity (1-DODECENE) 3.35246E12 Heat of reaction (kW) 4.52678 Condenser duty (kW) 5.26443 Catalyst mole fraction in liquid feed 0.000170544 Condenser temperature 274.150

(17) As shown in the illustrative example, ethylene per pass conversion is 8% with condenser duty of 5 kW operated at 1 C. This embodiment typify the lower ethylene feed rate at 50 kg/hr.

(18) The features of the invention disclosed in the above description and in the claims can be essential to implementing the invention in its various embodiments both individually and in any combination.