Preparation method and application of a PNP ligand synthesis solution for ethylene selective oligomerization chromium complex catalyst

Abstract

The present application belongs to the technical field of homogeneous catalysis in petroleum chemical industry, and relates to a process for the selective oligomerization of ethylene, in particular to a preparation method and application of a PNP ligand synthesis solution for a chromium complex catalyst for the selective oligomerization of ethylene. The preparation method provided by the present application can greatly simplify the catalyst preparation process, reduce equipment investment and production cost under the premise of ensuring the synthesis yield of the PNP ligand, and can provide favorable conditions for the continuous, automatic preparation of the chromium complex catalyst for the selective oligomerization of ethylene and the digitalization and intelligentization of the complete technology for the selective oligomerization of ethylene.

Description

Technical Field

[0001] This invention belongs to the field of homogeneous catalysis technology in petrochemicals, and relates to a method for preparing and applying a PNP ligand synthesis solution for a selective oligochromium complex catalyst for ethylene. Background Technology

[0002] Selective oligomerization of ethylene is mainly used to produce 1-hexene and 1-octene. 1-Hexene copolymerized PE is currently the fastest-growing polyethylene variety. Adding 1-hexene significantly increases the branching degree of PE during the production of high-density polyethylene (HDPE) or linear low-density polyethylene (LLDPE), resulting in copolymers with lower crystallinity, melting point, and density, thus improving polymer flexibility and tear resistance. Linear low-density polyethylene copolymerized from 1-hexene can be used as a high-grade specialty PE resin to produce high-toughness, high-strength, and thinner LLDPE, particularly suitable for large hollow blow-molded containers, pipes, packaging films, and agricultural covering films.

[0003] 1-Octene is a superior comonomer. Polyethylene produced using 1-octene as a comonomer has better mechanical and optical properties than polyethylene produced using 1-hexene as a comonomer, and its tear strength and impact strength are twice that of polymer products using 1-butene as a comonomer.

[0004] In the early 1990s, Union Carbide reported a chromium-based selective oligomerization catalytic system for ethylene, consisting of four components: chromium salt, pyrrole, alkyl aluminum, and an electron pair donor. This catalytic system achieved high selectivity for 1-hexene, reaching a selectivity of 70%. In 1995, Phillips disclosed its patent for a selective oligomerization process for ethylene, achieving a 1-hexene selectivity of 90-95% and a catalyst activity of 1.7 × 10⁻⁶. 5g / (gCr·h). Phillips' ethylene oligomerization process includes three parts: catalyst preparation, oligomerization, and product separation. Catalyst preparation is carried out in a batch manner, as follows: First, chromium isooctanoate (i.e., chromium 2-ethylhexanoate) is dissolved in toluene, and then 2,5-dimethylpyrrole is added to it under stirring to generate a chromium pyrrole complex; (2) a mixture of triethylaluminum and electron pair donor is added to the chromium pyrrole complex and reacted for 2 hours to generate an active ethylene selective oligomerization catalyst composition. The ethylene oligomerization reaction is carried out in a batch reactor equipped with a cooling coil. The ethylene trimerization reaction is carried out at a reaction temperature of 115°C, a reaction pressure of 4.8 MPa, and a catalyst composition of chromium isooctanoate / 2,5-dimethylpyrrole / dichloroethylaluminum / triethylaluminum in a ratio of 1:4:5:15 (molar ratio) and cyclohexane as solvent (a small amount of hydrogen is injected into the reactor). The ethylene conversion rate is 68%-84%, and the 1-hexene selectivity is 89-93%. The aforementioned selective oligomerization process for ethylene is simple, with relatively mild reaction conditions, high catalyst activity, and few byproducts. The product, 1-hexene, contains at least 96% hexene-1 and can be directly used as a comonomer for LLDPE without special refining. Furthermore, the production cost of 1-hexene is low. In 1997, Phillips completed a pilot-scale study with an annual production capacity of 90 tons of 1-hexene using a loop reactor. In 2000, Phillips built an industrial plant in Qatar with an annual production capacity of 50,000 tons of 1-hexene and in the United States with an annual production capacity of 90,000 tons of 1-hexene.

[0005] Subsequently, Mitsubishi Corporation of Japan also announced the successful development of a chromium-based catalyst process for the preparation of 1-hexene. Mitsubishi improved the electron pair donor in Phillips' patent and changed the catalyst pre-preparation to in-situ preparation. The catalyst composition exhibited an ethylene oligomerization activity of 2 × 10⁻⁶. 5 g / (gCr·h), with a 1-hexene selectivity of approximately 90%. Mitsubishi Corporation of Japan has industrialized its ethylene selective oligomerization process for producing 1-hexene in Chiba, Japan.

[0006] Compared to the selective oligomerization of ethylene to produce 1-hexene, the process for directly producing 1-octene using selective oligomerization of ethylene is not yet mature. Those familiar with the field know that the main catalyst system for selective oligomerization of ethylene is chromium-based. The main ligands in chromium-based catalysts are tridentate ligands containing phosphine, nitrogen, and sulfur coordinating atoms, and bisphosphineamine (PNP) ligands. Among these, tridentate ligands containing phosphine, nitrogen, and sulfur are mainly used for the selective oligomerization of ethylene to synthesize 1-hexene, while bisphosphineamine (PNP) ligands are mainly used for the selective oligomerization of ethylene to synthesize 1-octene.

[0007] In 2004, the first published paper, J. Am. Chem. Soc. 2004, 126, 45, 14712-14713, reported a Cr catalyst system for the selective synthesis of 1-octene from ethylene tetramerization. This catalyst system used toluene as a solvent and chromium acetylacetone as the Cr source. The main catalyst ligand was N-methylbis(diphenylphosphine) (PNP) ligand, and two co-catalysts were used: trimethylaluminum and ethylaluminoxane. The molar ratio of the catalyst composition was Cr(acac)3:((Ph)2P)2NMe:EAO:TMA = 1:1.35:1000:250. The ethylene oligomerization reaction was carried out at a temperature of 45℃, a pressure of 4.5 MPa, and a reaction time of 30 min. The activity of the ethylene oligomerization reaction was 5 × 10⁻⁶. 5 g / (gCr·h), with a selectivity of up to 70% for 1-octene.

[0008] To date, numerous Chinese invention patents have been filed concerning the selective oligomerization of ethylene into 1-octene. For example:

[0009] Chinese invention patent CN102451759A (applied on October 22, 2010) discloses an ethylene tetramerization catalyst, its preparation method, and its application. The ethylene tetramerization catalyst is a two-component catalytic system comprising a transition metal complex (I) and a co-catalyst (II). The transition metal complex (I) conforms to the general formula [AMB]. n[C], where A is a PNP ligand, B is a CO ligand, M is a transition metal Cr, Mo, or W, and C is a fluorine-containing group. The co-catalyst (II) is an organoaluminum compound, preferably a mixture of one or more of triethylaluminum, diethylaluminum chloride, diethylaluminum chloride, sesquiethylaluminum, trimethylaluminum, and triisobutylaluminum, with triethylaluminum being the most preferred. The preparation method of its metal complex (I) is as follows: In an organic solvent, the metal source compound is mixed with compound A (PNP ligand), heated to reflux, and then the reaction solution is cooled to room temperature. The solvent is removed, and the residue is recrystallized to obtain a solid product. Then, the solid product is dissolved in an organic solvent, and the compound containing group C is added. The reaction is stirred at room temperature. After the reaction is complete, the reaction solution is filtered, and the filtrate is dried under vacuum to obtain the transition metal complex (I). In Example 1 of this patent, a method for preparing a metal complex (I) is specifically described: A measured amount of hexacarbonyl chromium and a PNP ligand ((phenyl)2phosphine-nitrogen(isopropyl)-phosphine(phenyl)2) are added to a round-bottom flask, followed by diethylene glycol dimethyl ether. The mixture is heated to 160°C and refluxed for 2 hours. The mixture is cooled to room temperature, and the solvent is removed under reduced pressure (10 mmHg). The residue is recrystallized with a certain amount of mixed solvent (methanol / dichloromethane, volume ratio 1:1), filtered, and the crystals are dried at room temperature to obtain a yellow crystalline product. Then, the yellow crystalline product is dissolved in a certain amount of dichloromethane solvent, and an organic compound containing a C group, AgAl[OC(CF3)3]4, is added. The mixture is stirred overnight at room temperature. Finally, the mixture is filtered, and the filtrate is dried under vacuum (10 mmHg) to obtain the chromium complex (I). The method for using the chromium complex (I) in the ethylene oligomerization reaction is as follows: the reactor is a 300 ml stainless steel polymerization kettle. The autoclave was heated, evacuated, and purged several times with nitrogen. Then, ethylene was introduced at a pressure of 0.5 MPa, and the temperature was lowered to 40°C. The vent valve was opened, and 50 ml of dehydrated toluene was quickly added, along with 5 μmol of metal complex (I) and 0.5 mmol of triethylaluminum to achieve an Al / Cr molar ratio of 100. Dehydrated toluene was then added until the total volume of the mixture was 100 ml. The vent valve was closed, and the reaction pressure was controlled at 4.0 MPa. Ethylene was introduced to initiate the polymerization reaction for 30 minutes. After the reaction was complete, the system was cooled to room temperature. The gaseous product was collected in a gas metering vessel, and the liquid product was collected in an Erlenmeyer flask. Ethanol was added as a terminator to terminate the ethylene oligomerization reaction. Chromatographic analysis of the metered gas and liquid products yielded a catalytic activity of 9.62 × 10⁻⁶. 4 The C8 olefin selectivity is 72.6%, the 1-octene content is 98.9%, the C6 olefin selectivity is 20.1%, and the 1-hexene content is 77.3%. The preparation method of the PNP ligand is not mentioned in this invention, but it is clear that the PNP ligand used is a solid powder obtained through separation and recrystallization, and the preparation process of the complex catalyst is complex.

[0010] Chinese invention patent CN 108017673 A (applied November 4, 2016) discloses a ligand compound, its preparation method, and its application. The ligand compound belongs to the PNP type, and its synthesis method generally involves two steps: First, an amine with the general formula R-NH2 is dissolved in an organic solvent, and then R'2PCl is added. After the reaction, a PN-type intermediate compound with the general formula R-NH-PR'2 is obtained. Wherein, R is an unsubstituted or substituted alkyl, cycloalkyl, or aryl group; R' is an unsubstituted or substituted aryl group. Second, the above PN-type intermediate is dissolved in an organic solvent, an alkyllithium catalyst is added, and then a phosphine chloride compound derived from diphenyl ether is added to catalyze the reaction, finally obtaining the PNP-type ligand. Example 1 of this invention patent provides a specific ligand preparation method: a certain amount of isopropylamine is dissolved in diethyl ether solvent, and then a certain amount of Ph2PCl is added. The mixture is stirred at room temperature for 4 hours. After filtration, the solvent is removed from the filtrate by rotary evaporation to obtain the intermediate compound. Then, the intermediate compound was dissolved in an appropriate amount of toluene solvent, and a small amount of hexane solution of butyllithium catalyst was added dropwise under ice bath conditions, with the addition completed within half an hour. A certain amount of phosphine chloride compound derived from diphenyl ether was then added, and the reaction was stirred for 3 hours. After the reaction was complete, the solvent was removed by rotary evaporation, and the PNP-type ligand compound was obtained by column chromatography with a yield of 55.7%. Example 5 of this invention patent provides a catalyst composition based on the prepared PNP-type ligand and its catalytic performance in the selective oligomerization of ethylene. Specifically, the ethylene oligomerization reaction was carried out in a stainless steel polymerization reactor. The autoclave was heated to 80°C, evacuated, and purged several times with nitrogen. Then, methylcyclohexane was added at 60°C, along with 2.5 μmol of tetrahydrofuran chromium chloride, 5 μmol of the PNP ligand compound, and 500 μmol of triethylaluminum. The total volume of the mixture was 100 mL, with a molar ratio of chromium, ligand compound, and co-catalyst of 1:2:200. The reaction pressure was controlled at 2 MPa, and ethylene was introduced to carry out the ethylene oligomerization reaction. After the reaction was complete, the system was cooled to room temperature. The gaseous product was collected in a gas metering vessel, and the liquid product was collected in an Erlenmeyer flask. 1 mL of ethanol was added as a terminator to terminate the ethylene oligomerization reaction. The gas and liquid products were then analyzed by gas chromatography. The reaction results were as follows: the catalytic activity was 2.3 × 10⁻⁶. 7 g / (molCr·h) (equivalent to 4.42×10) 5 The selectivity of C6 component was 29.8%, the selectivity of C8 component was 63.3%, and the total selectivity of C6 and C8 components was 93.1%. 1-Octenene accounted for 99.6% of C8.

[0011] CN 108017674 A (application filed November 4, 2016) also discloses a ligand compound, its preparation method, and its application. The ligand compound belongs to the PNP type, and its synthesis method is relatively simple, as follows: First, a phosphonic chloride compound derived from diphenyl ether is added to an organic solvent. Then, an acid-binding agent and an amine with the general formula R-NH2 are added to the solution for reaction. After the reaction is complete, the PNP ligand is obtained. The acid-binding agent is selected from at least one of organic amines and inorganic bases. The organic solvent is selected from at least one of aromatic compounds and aliphatic hydrocarbons, preferably at least one of toluene, diethyl ether, tetrahydrofuran, hexane, and dichloromethane. The molar ratio of the raw materials is phosphonic chloride compound: acid-binding agent: R-NH2 = 1:(1-3):(0.2-1), the reaction temperature is 0-100℃, preferably 20-30℃, and the reaction time is 1-10 hours, preferably 2-4 hours. Example 1 of this invention patent provides a specific method for ligand preparation: Under nitrogen protection, 4.1 mmol of a phosphonic chloride compound derived from diphenyl ether is dissolved in 10 mL of dichloromethane solvent. Then, 11 mmol of triethylamine is slowly added dropwise to the solution under ice bath and stirring. After the addition is complete, 2 mmol of R-NH2 (R = iPr) is added, and the reaction is carried out for 4 hours. After the reaction is completed, the ammonium salt precipitate is first filtered off, and then separated by column chromatography to obtain the desired PNP ligand in 85.0% yield. Example 7 of this invention patent provides a catalyst composition based on the prepared PNP-type ligand and its catalytic performance in the selective oligomerization reaction of ethylene. Specifically, the ethylene oligomerization reaction is carried out in a stainless steel polymerization reactor. The autoclave was heated to 80°C, evacuated, and purged several times with nitrogen. Then, methylcyclohexane was added at 60°C, along with 2.5 μmol of tetrahydrofuran chromium chloride, 5 μmol of PNP ligand compound, and 500 μmol of triethylaluminum. The total volume of the mixture was 100 mL, with a molar ratio of chromium, ligand compound, and co-catalyst of 1:2:200. The reaction pressure was controlled at 2 MPa, and ethylene was introduced to initiate the ethylene oligomerization reaction. After the reaction was complete, the system was cooled to room temperature. The gaseous product was collected in a gas metering vessel, and the liquid product was collected in an Erlenmeyer flask. 1 mL of ethanol was added as a terminator to terminate the ethylene oligomerization reaction. The gas and liquid products were metered and analyzed by gas chromatography. The reaction results were as follows: the catalytic activity was 2.5 × 10⁻⁶. 7 g / (molCr·h) (equivalent to 4.81×10) 5 g / (gCr·h)), the selectivity of C6 component was 29.0%, the selectivity of C8 component was 66.5%, and the total selectivity of C6 and C8 components was 95.5%. 1-Octenene accounted for 99.6% of C8. 10 4.0% of the above components.

[0012] Chinese invention patents CN 111434669 A, CN 111434668 A, CN 11143 4670 A, CN 111434667 (all filed January 15, 2019), Chinese invention patents CN 113583052 A, CN 113583053 A (all filed April 30, 2020), as well as Chinese invention patents CN 114054095 A (filed August 10, 2020) and CN115724883A (filed August 25, 2021), all relate to the preparation of chromium complex catalysts using PC=CP type ligands or PCCP type ligands. In these ligands, the benzene ring of the diphenylphosphine moiety is attached to various hydrocarbon groups and fluorine or other halogen atoms, and various alkyl, cycloalkyl, and aryl groups can be attached to the carbon atoms of the bridging groups -C=C- and -CC-. The bridging group -C=C- is provided by acetylene, acetylene derivatives, or a benzene ring. The complex catalyst formed using the above ligands and transition metal chromium compounds is characterized by its ability to be used for the trimerization or tetramerization of ethylene under certain conditions. Furthermore, the complex catalyst is characterized by its high activity in the oligomerization of ethylene. In addition, the C6 product of the complex catalyst contains approximately 98% 1-hexene (significantly reducing byproducts such as cyclic olefins and cyclizations); simultaneously, the C8 product contains over 98% 1-octene. Among these, CN 111434669 A discloses a PC(R)=CP type fluorinated ligand, which is prepared according to the methods reported in J.Am.Chem.Soc, 2007, 129, 4009-4104 and ACS Catalysis, 2013, 3, 2311-2317. This involves a chemical reaction between acetylene with an R-group at one end and difluorophenylphosphine chloride in the presence of an organolithium compound. The R-group is C1-C. 12 Alkyl chain, C3-C 12 cycloalkyl or C6-C 20Aryl. The above-mentioned PC(R)=CP type fluorinated ligand can be used in combination with transition metal compounds and co-catalysts commonly used in ethylene oligomerization for ethylene oligomerization reactions (reaction temperature 30-90℃, ethylene pressure 2-8MPa). The transition metal compound is selected from at least one of chromium compounds, molybdenum compounds, iron compounds, titanium compounds, zirconium compounds, and nickel compounds. The transition metal compound can be selected from at least one of transition metal salts of acetylacetone, transition metal salts of carboxylic acids, and tetrahydrofuran transition metal complexes. The transition metal compound is preferably selected from at least one of chromium acetylacetone, chromium isooctanoate, chromium tri(tetrahydrofuran)trichloride, and chromium di(tetrahydrofuran)dichloride. More preferably, the transition metal compound is chromium acetylacetone. The molar ratio of the ligand to the transition metal compound is 1:0.5-0.8. The co-catalyst is preferably an organoaluminum compound. More preferably, the co-catalyst is selected from at least one of alkylaluminum, alkoxyaluminum, and alkylhalide aluminum. More preferably, the co-catalyst is at least one selected from methylaluminoxane, trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, diethylaluminum chloride, diethylaluminum chloride, ethylaluminoxane, and modified methylaluminoxane. Modified methylaluminoxane is preferred.

[0013] Under specific conditions, a catalyst system based on a transition metal compound catalyst with a PC(R)=CP type fluorine-containing ligand and a co-catalyst can be used for ethylene trimerization and ethylene tetramerization. The ethylene trimerization reaction is carried out at 60-90°C and an ethylene pressure of 2-3 MPa. The ethylene tetramerization reaction is carried out at 30-50°C and an ethylene pressure of 4-5 MPa. The ethylene oligomerization reaction is carried out in an organic solvent capable of dissolving the oligomerization product, and can be at least one selected from alkanes, cycloalkanes, and aromatics, preferably selected from C6-C4 hydrocarbons. 12 Alkanes, C6-C 12 Cycloalkanes and C6-C 12 At least one of the aromatic hydrocarbons. Wherein, C6-C 12 Cycloalkanes primarily refer to hydrocarbon molecules containing a six-membered ring. Cycloalkanes containing a five-membered ring are only mentioned in the context of methylcyclopentane. (C6-C) 12The aromatic hydrocarbons mainly refer to toluene, ethylbenzene, and xylene (including o-xylene, m-xylene, and p-xylene). The organic solvent is more preferably selected from at least one of methylcyclohexane, heptane, cyclohexane, toluene, and xylene. Example 1 of this patent describes a specific method for preparing a PC(R)=CP type fluorinated ligand: Under nitrogen protection, 11 mmol of tert-butylacetylene and 15 mL of dry tetrahydrofuran are added to a 50 mL reaction flask, followed by the dropwise addition of 11 mmol of n-butyllithium (6.6 mL of a hexane solution of n-butyllithium, with a concentration of 1.6 M) at 0 °C. After the addition is complete, stirring is continued at 0 °C for 30 min, followed by the dropwise addition of 2.2 g (10 mmol) of difluorophenylphosphine chloride. After the addition is complete, the temperature is raised to room temperature (25 °C) and stirring is continued for 2 h. A catalytic amount of CuI and cesium carbonate was added, followed by 2.2 g (10 mmol) of difluorophenylphosphine chloride. The temperature was raised to 90 °C and stirred at 90 °C for 4 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filtrate was dried under reduced pressure. The residue was passed through a silica gel column (petroleum ether (PE) / ethyl acetate (EA) = 20:1) to obtain PC(R)=CP type fluorinated ligands. Example 1 of this patent provides a specific procedure and reaction results for selective tetramerization of ethylene: a 300 mL stainless steel polymerization autoclave was heated to 80 °C, evacuated, and then purged with nitrogen. Ethylene was then introduced for further purging, and the temperature inside the autoclave was lowered to 40 °C. Methylcyclohexane, 0.5 μmol of chromium acetylacetone, a PC(R)=CP type fluorinated ligand, and modified methylaluminoxane (MMAO, purchased from AkzoNobel) as a co-catalyst were added to an autoclave and mixed thoroughly. The total volume of the mixture was 100 mL, and the molar ratio of chromium acetylacetone:fluorinated compound:co-catalyst was 1:2:400, i.e., the amount of PC(R)=CP type fluorinated ligand added was 1 μmol, and the amount of MMAO added was 200 μmol. Ethylene was introduced and the pressure of ethylene was controlled at 3 MPa. The ethylene oligomerization reaction was carried out at 40 °C. After 30 minutes, 1 mL of ethanol was added as a terminator to terminate the reaction. The temperature of the autoclave was lowered to room temperature (25 °C). The gas phase product was collected in a gas metering vessel, and the liquid phase product was collected in an Erlenmeyer flask. The gas and liquid phase products were separately metered and analyzed by gas chromatography to calculate the catalyst activity and product composition. The results showed that the catalyst activity was 2.36 × 10⁻⁶. 8 g / (molCr·h), equivalent to 4.5×10 6The total selectivity for 1-hexene and 1-octene exceeds 94.3 wt% (g / (gCr·h)), with a 1-hexene selectivity of 33.0% and a 1-octene selectivity of 62.4%. Specifically, the 1-hexene content reaches approximately 97.8% in the C6 product and 99.5% in the C8 product. Example 10 of this patent provides a specific method and reaction results for selective trimerization of ethylene: According to Example 10, the ethylene trimerization method is the same as in Example 1, except that the reaction temperature is 90°C. The results show a catalyst activity of 2.52 × 10⁻⁶. 8 g / (molCr·h), equivalent to 4.8×10 6 The total selectivity for 1-hexene and 1-octene exceeds 92.4 wt% (g / (gCr·h)), with a 1-hexene selectivity of 75.8% and a 1-octene selectivity of 17.9%. Specifically, the 1-hexene content reaches approximately 98.6% in the C6 product and 98.6% in the C8 product. Example 5 of this patent provides a specific procedure and reaction results for selective oligomerization of ethylene: According to Example 5, the procedure for selective oligomerization of ethylene is the same as in Example 1, except that the modified methylaluminoxane used as a co-catalyst is replaced with triethylaluminum (purchased from Beijing Bailingwei Chemical Reagent Co., Ltd.). The result is: catalyst activity 0.97 × 10⁻⁶. 8 g / (molCr·h), equivalent to 1.9×10 6 The total selectivity for 1-hexene and 1-octene exceeds 93.7 wt% (g / (gCr·h)), with a selectivity of 42.0% for 1-hexene and 52.8% for 1-octene. In particular, the 1-hexene content reaches approximately 98.4% in the C6 product and 99.1% in the C8 product.

[0014] In the catalyst composition disclosed in Chinese invention patent CN 116020558 A (application dated October 27, 2021), the ligand of the main catalyst is a pyrrole-bridged PNP ligand, which can be denoted as P(CNC). 吡咯环 P. In this type of ligand, the four benzene rings bonded to the two P atoms may have fluorine atoms at their adjacent positions. The metal center of the main catalyst is selected from at least one compound of chromium, molybdenum, iron, titanium, zirconium, and nickel; preferably at least one of chromium acetylacetonate, chromium isooctanoate, chromium tri(tetrahydrofuran)trichloride, and chromium di(tetrahydrofuran)dichloride. The catalyst composition also includes an aluminum-containing co-catalyst. The aluminum-containing co-catalyst is an organoaluminum compound, preferably at least one of methylaluminoxane, trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, diethylaluminum chloride, dichloroethylaluminum, ethylaluminoxane, and modified methylaluminoxane. In Preparation Example 1 of this patent, a P(CNC) is specifically described.吡咯环 The preparation process of the P ligand. In this ligand, the four benzene rings bonded to the two P atoms are surrounded by fluorine atoms at their ortho positions. The preparation process is as follows: Under nitrogen protection, N-Boc-2,5-dibromopyrrole (15 mmol) and tetrahydrofuran (200 mL) were added to a three-necked flask, cooled to -78 °C, and n-butyllithium (30 mmol) was added dropwise. The mixture was stirred for 1 hour, and then di-(2-bromophenyl)phosphine chloride (30 mmol) was added dropwise. After the addition was complete, the mixture was allowed to stand at room temperature for 18 hours. After the reaction was complete, the solvent was removed under reduced pressure. The residue was dissolved in toluene (50 mL) under nitrogen protection and heated to 155 °C for 18 hours. After the reaction was complete, the solvent was removed under vacuum to obtain a yellow solid. Recrystallization from toluene yielded a white solid product, namely P(CNC). 吡咯环 P-ligand. The embodiments of this patent specifically describe the reaction method for ethylene oligomerization: a 300mL stainless steel polymerization reactor is used. The polymerization reactor is heated to 80°C, evacuated, and purged several times with nitrogen. Then, ethylene is introduced for purging, and the temperature is lowered to the set temperature. Methylcyclohexane is then added at 40°C, along with 0.5μmol of chromium acetylacetone, catalyst ligand, and co-catalyst modified methylaluminoxane (MMAO). The total volume of the mixture is 100mL, where the molar ratio of chromium acetylacetone (calculated as chromium), ligand, and co-catalyst is 1:2:500, i.e., the amount of ligand added (calculated as Cr) is 1.0μmol / L, and the amount of MMAO added is 250μmol. The reaction pressure is controlled at 3MPa, the temperature at 40°C, and ethylene is introduced to carry out the ethylene oligomerization reaction. After half an hour, the reaction is complete. The system is cooled to room temperature, the gaseous product is collected in a gas metering vessel, and the liquid product is collected in an Erlenmeyer flask. 1mL of ethanol is added as a terminator to terminate the reaction. After metering, the gas and liquid phase products were analyzed by gas chromatography (using a HP 5890 chromatograph). From Table 1 provided in this patent, based on P(CNC)... 吡咯环 The chromium complex catalyst system with P-ligands is characterized by its ease of carrying out selective oligomerization of ethylene, producing comparable amounts of 1-hexene and 1-octene. For example, in Example 1, the catalyst activity for the ethylene oligomerization reaction was 1.87 × 10⁻⁶. 8 g / (molCr·h), equivalent to 3.6×10 6 The total selectivity for 1-hexene and 1-octene exceeds 95.0 wt% (g / (gCr·h)), with a selectivity of 41.2% for 1-hexene and 55.0% for 1-octene. Specifically, the 1-hexene content reaches approximately 98.5% in the C6 product and 99.0% in the C8 product. However, under specific conditions, based on P(CNC)... 吡咯环Chromium complex catalyst systems with P ligands can also be used for selective oligomerization of ethylene with predominantly trimerizing or tetramerizing activity. For example, in Example 4, the catalyst activity for the ethylene oligomerization reaction was 1.15 × 10⁻⁶. 8 g / (molCr·h), equivalent to 2.2×10 6 The total selectivity for 1-hexene and 1-octene exceeded 94.2 wt% (g / (gCr·h)), with a 1-hexene selectivity of 32.0% and a 1-octene selectivity of 64.3%. In particular, the 1-hexene content reached approximately 95.3% in the C6 product and 99.0% in the C8 product; in Example 7, the catalyst activity for the ethylene oligomerization reaction was 0.82 × 10⁻⁶. 8 g / (molCr·h), equivalent to 1.6×10 6 The total selectivity for 1-hexene and 1-octene exceeds 96.1 wt% (g / (gCr·h)), with a selectivity of 60.6% for 1-hexene and 35.9% for 1-octene. In particular, the content of 1-hexene can reach about 99.8% in the C6 product and 99.2% in the C8 product.

[0015] Chinese Invention Patent CN 116328837 A (filed December 24, 2021) discloses a catalyst composition in which the main catalyst is a metal complex with the general formula AMBn, and the co-catalyst is an organoaluminum compound. In the main catalyst, A is an organic ligand with the general formula PNP; M is a metal center selected from transition metals chromium, molybdenum, or tungsten; and B is selected from acetylacetone, tetrahydrofuran, and isooctanoic acid. The organoaluminum compound is selected from at least one of alkylaluminum compounds, alkoxyaluminum compounds, and alkylaluminum chloride compounds, more preferably at least one of methylaluminoxane, trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, diethylaluminum chloride, dichloroethylaluminum, ethylaluminoxane, and modified methylaluminoxane. In the catalyst composition, the molar ratio of the main catalyst to the co-catalyst is 1:1-3000, preferably 1:10-2000, and more preferably 1:100-1000. The catalyst composition is characterized by the PNP ligand in the main catalyst. Specifically, the four phenyl groups attached to the two P atoms on the PNP ligand are each an independent phenyl group or a halogen-substituted phenyl group, particularly phenyl groups having one or more fluorine atoms or fluorinated substituents at the ortho position. The method for using the above catalyst composition for ethylene oligomerization is as follows: the concentration of the catalyst composition, calculated based on the volume of the organic solvent, is 0.1-10 μmol / L (metallic); the reaction temperature is 0-75°C, preferably 30-75°C, more preferably 40-65°C; and the reaction pressure is 0.1-20.0 MPa, preferably 0.5-5.0 MPa, more preferably 2.0-5.0 MPa. It is noteworthy that this invention confirms that the catalyst composition based on the described PNP ligand can also achieve ethylene trimerization or ethylene tetramerization under specific conditions. In Preparation Example 1 of this invention, a method for synthesizing the PNP-type ligand (Ph)2PN(iPr)P(Ph)(2-F-Ph) is described in detail: (o-fluorophenyl)phenylphosphine chloride (10 mmol) was added dropwise to a solution of isopropylamine (12.5 mmol) and triethylamine (5 mL) in dichloromethane (10 mL) at 0 °C and stirred for 30 minutes. The mixture was then heated to room temperature and stirred overnight. The solvent was removed from the mixture, and anhydrous diethyl ether (20 mL) was added to form a suspension. The suspension was filtered, and the filtrate was dried under reduced pressure to obtain an oily substance. The oily substance (2.0 g) was dissolved in dichloromethane (10 mL), and triethylamine (0.5 mL) was added. Then, diphenylphosphine chloride (3.3 g, 15.2 mmol) was added dropwise. After the addition was complete, the mixture was heated to room temperature and stirred overnight. The solvent was removed from the mixture, and the mixture was purified by alkaline alumina column chromatography to obtain a white solid powder of the PNP ligand. The preparation method of the main catalyst AMBn is as follows: under nitrogen protection, 5 mmol of organic ligand and 5 mmol of metallic chromium compound (chromium acetylacetone or chromium isooctanoate, chromium tetrahydrofuran chloride) are transferred to a Schlenk tube, 50 mL of toluene solution is added, and then the mixture is heated to 80 °C and stirred for 8 hours.The reaction solution was cooled to room temperature and filtered. The obtained solid was washed with toluene and n-hexane, respectively, and dried under vacuum to obtain the corresponding metal complex AMBn. Example 1 of this invention specifically illustrates the method of ethylene oligomerization: a 300 mL stainless steel polymerization reactor was used. First, the polymerization reactor was heated to 80°C, evacuated, and purged several times with nitrogen. Then, ethylene was introduced for purging, and the temperature was lowered to the set temperature. Then, methylcyclohexane solvent was added at 40°C, along with 0.1 μmol of the main catalyst and the co-catalyst modified methylaluminoxane (MMAO). The total volume of the mixture was 100 mL, with a molar ratio of main catalyst to co-catalyst of 1:2000. The reaction pressure was controlled at 3 MPa, and ethylene was introduced. The ethylene oligomerization reaction was carried out at 40°C. After half an hour, the reaction was complete. The system was cooled to room temperature, and the gaseous product was collected in a gas metering vessel, while the liquid product was collected in an Erlenmeyer flask. 1 mL of ethanol was added as a terminator to terminate the reaction. The gas and liquid products were metered and analyzed by gas chromatography (using a HP 5890 chromatograph). As can be seen from Table 1 provided by this invention, the catalyst system based on PNP-type ligands mainly undergoes ethylene tetramerization with 1-octene as the predominant product. However, under certain conditions, selective oligomerization of ethylene occurs, producing equal amounts of 1-hexene and 1-octene. For example, ethylene tetramerization was carried out in Example 14. The catalyst activity was 5.9 × 10⁻⁶. 8 g / (molCr·h), equivalent to 1.1×10 7 The total selectivity for 1-hexene and 1-octene exceeded 95.4 wt% (g / (gCr·h)), with a 1-hexene selectivity of 23.7% and a 1-octene selectivity of 72.3%. Specifically, the 1-hexene content reached approximately 99.5% in the C6 product and 99.3% in the C8 product; the ethylene-selective oligomerization reaction in Example 18 produced comparable amounts of 1-hexene and 1-octene. The catalyst activity was 1.8 × 10⁻⁶. 8 g / (molCr·h), equivalent to 3.5×10 6 The total selectivity for 1-hexene and 1-octene exceeds 96.9 wt% (g / (gCr·h)), with a selectivity of 43.0% for 1-hexene and 55.7% for 1-octene. In particular, the content of 1-hexene can reach about 99.6% in the C6 product and 97.0% in the C8 product.

[0016] Literature review revealed that the ligand type of chromium complexes significantly influences the oligomerization activity and product distribution in ethylene selective oligomerization catalyst systems. Therefore, structural innovation of ligands has received considerable attention from researchers in this field. However, known ligand synthesis processes for chromium complex catalysts still involve cumbersome, time-consuming, and energy-intensive post-purification steps, including separation, crystallization, and recrystallization, which inevitably lead to reduced ligand yields and the generation of large amounts of organic waste. Furthermore, the ligand crystals obtained after this lengthy post-processing must be redissolved in organic matter before being used to formulate chromium complex catalysts. This traditional approach makes continuous operation of the catalyst preparation unit difficult and hinders the digitalization and intelligent development of the overall ethylene selective oligomerization process. Summary of the Invention

[0017] The purpose of this invention is to provide a method for preparing and applying a PNP ligand synthesis solution for a selective oligochromium complex catalyst for ethylene.

[0018] Specifically, this invention provides a method for preparing a PNP ligand synthesis solution that can be directly used to formulate a chromium complex catalyst (PNP-Cr) for the selective tetramerization of ethylene into 1-octene. More specifically, this invention provides a method for preparing a synthesis solution of a bis(diphenylphosphine)isopropylamine type PNP ligand.

[0019] Studies have found that the synthesis of bis(diphenylphosphine)-isopropylamine PNP ligands from diphenylphosphine chloride and isopropylamine is solvent-sensitive. Dichloromethane is known to be a commonly used solvent for this reaction. On the other hand, the selective tetramerization of ethylene using a chromium complex of bis(diphenylphosphine)-isopropylamine as the main catalyst is also a solvent-sensitive reaction. Cyclohexane, methylcyclohexane, and toluene are known to be commonly used solvents for this reaction. In order to eliminate the cumbersome post-processing steps of separation, crystallization, and recrystallization in known PNP ligand synthesis processes, and to directly prepare PNP-Cr complex catalysts from the PNP ligand synthesis solution, thereby constructing a highly continuous ethylene selective oligomerization process, the inventors attempted to use cyclohexane instead of dichloromethane to react diphenylphosphine chloride with isopropylamine to synthesize bis(diphenylphosphine)-isopropylamine PNP ligands. However, this resulted in a synthesis solution with a yield of less than 40% for the bis(diphenylphosphine)-isopropylamine PNP ligand. The synthesized solution has a low content of the active ingredient (bis(diphenylphosphine) isopropylamine). When used directly to prepare PNP-Cr complex catalysts, the catalyst composition (mainly composed of PNP-Cr complex and methylaluminoxane co-catalyst) exhibits very low catalytic activity in the selective oligomerization reaction of ethylene. The inventors also attempted to use a mixed solvent of cyclohexane and dichloromethane instead of pure dichloromethane to react chlorodiphenylphosphine with isopropylamine to synthesize bis(diphenylphosphine) isopropylamine-type PNP ligands. By utilizing a mixed solvent containing an appropriate amount of dichloromethane, the synthesis yield of bis(diphenylphosphine) isopropylamine-type PNP ligands is increased to approximately 80%, thus significantly increasing the content of the active ingredient (bis(diphenylphosphine) isopropylamine) in the obtained PNP ligand synthesis solution. However, when this synthesis solution is directly used to prepare PNP-Cr complex catalysts, the catalytic activity of the catalyst composition remains low due to the large presence of dichloromethane solvent.

[0020] After extensive research and exploration, this invention has found a simple and easy method for preparing PNP ligand synthesis solution that can meet both the needs of upstream PNP ligand synthesis reaction and downstream ethylene selective oligomerization reaction.

[0021] In summary, the method for preparing the PNP ligand synthesis solution for ethylene selective oligomerization chromium complex catalyst provided by this invention includes two steps: The first step involves synthesizing a bis(diphenylphosphine)-isopropylamine type PNP ligand using dichloromethane, a commonly used solvent for synthesizing PNP ligands, under optimal reaction conditions using dichlorophosphine and isopropylamine as raw materials, to obtain a first synthesis solution of the PNP ligand. The second step involves adding a commonly used solvent for ethylene selective oligomerization to the first synthesis solution of the PNP ligand, and then distilling off the dichloromethane solvent used for synthesizing the PNP ligand using a conventional distillation method, thereby obtaining a second synthesis solution of the PNP ligand. The second synthesis solution is a ligand synthesis solution using a commonly used solvent for ethylene oligomerization as the dispersion medium. This solution does not require further purification and can be directly used to prepare highly active ethylene selective oligomerization PNP-Cr complex catalysts.

[0022] The technical solution of the present invention:

[0023] A method for preparing a PNP ligand synthesis solution for an ethylene-selective oligomeric chromium complex catalyst includes the following steps:

[0024] Step 1: In dichloromethane solvent, which is commonly used for synthesizing PNP ligands, dichlorodiphenylphosphine and isopropylamine are reacted under optimal reaction conditions to synthesize bis(diphenylphosphine)-isopropylamine type PNP ligands, thus obtaining the first synthesis solution of PNP ligands.

[0025] The synthesis of bis(diphenylphosphine)isopropylamine from dichlorodiphenylphosphine and isopropylamine in dichloromethane solvent is a non-catalytic reaction. In addition to the solvent and the two reactants, a suitable amount of triethylamine is added to the reaction system. Triethylamine acts as an acid-binding agent in this reaction, responsible for converting the hydrogen chloride produced during PNP ligand synthesis into triethylamine hydrochloride precipitate, thereby promoting the conversion of reactants and the formation of PNP ligands.

[0026] The optimal range of conditions for the synthesis of bis(diphenylphosphine)-isopropylamine type PNP ligands by reacting chlorodiphenylphosphine with isopropylamine in dichloromethane solvent is:

[0027] Reaction pressure: atmospheric pressure

[0028] Reaction temperature: 5-30℃

[0029] Reaction time: 2-12 hours

[0030] The molar ratio of dichlorophenylphosphine to isopropylamine is 1:(0.55-0.60).

[0031] The molar ratio of diphenylphosphine chloride to triethylamine is 1:(2-3).

[0032] Dichloromethane solvent volume (expressed as molar concentration of dichlorodiphenylphosphine): 0.2 mol / L - 1.0 mol / L

[0033] It should be noted that, according to the stoichiometric reaction requirements for the synthesis of diphenylphosphine-isopropylamine, the stoichiometric ratio of diphenylphosphine chloride and isopropylamine, i.e., the theoretical molar ratio, is 1:0.5. However, this invention requires that the amount of isopropylamine reactant added is at least 10% in excess (at this point, it is equivalent to a molar ratio of diphenylphosphine chloride to isopropylamine of 1:0.55) and at most 20% in excess (at this point, it is equivalent to a molar ratio of diphenylphosphine chloride to isopropylamine of 1:0.60). That is, when the actual molar ratio is 1:0.55, the excess portion of isopropylamine is 0.05, accounting for 10% of 0.5; when the actual molar ratio is 1:0.60, the excess portion of isopropylamine is 0.10, accounting for 20% of 0.5.

[0034] The reason this invention requires the amount of isopropylamine to be slightly higher than the theoretical amount is to ensure that the chlorodiphenylphosphine is converted as completely as possible. The benefits are twofold: firstly, more complete conversion of the chlorodiphenylphosphine improves the synthesis yield of the PNP ligand (based on chlorodiphenylphosphine); secondly, more complete conversion also reduces the residual amount of high-boiling-point chlorodiphenylphosphine (boiling point 320℃) in the first and second synthesis solutions of the PNP ligand. Isopropylamine (boiling point 33-34℃) is a low-boiling-point organic amine, and its excess can be removed by distillation during the preparation of the second synthesis solution from the first synthesis solution.

[0035] However, research has found that if the amount of isopropylamine added is too large, triethylamine will lose its acid-binding agent effect. This is because isopropylamine is more basic than triethylamine. Therefore, when isopropylamine is in large excess, the hydrogen chloride released during the reaction of dichlorodiphenylphosphine and isopropylamine to synthesize bis(diphenylphosphine)isopropylamine will preferentially undergo an acid-base neutralization reaction with the more basic isopropylamine, resulting in the formation of isopropylamine hydrochloride. Therefore, if isopropylamine is in large excess, it is neither conducive to the timely removal of hydrogen chloride released from the reaction nor to obtaining the ideal PNP ligand synthesis yield.

[0036] Engineers skilled in the art can synthesize bis(diphenylphosphine) isopropylamine (PNP) ligands by reacting chlorodiphenylphosphine with isopropylamine in a dichloromethane solvent based on their own experience. Alternatively, they can follow the methods described in the literature, such as those described in Chinese invention patents CN108017673A (November 4, 2016), CN108017674A (November 4, 2016), and CN116328837 A (application dated December 24, 2021), to synthesize bis(diphenylphosphine) isopropylamine PNP ligands by reacting chlorodiphenylphosphine with isopropylamine in a dichloromethane solvent.

[0037] Although engineers skilled in the art can synthesize bis(diphenylphosphine)-isopropylamine PNP ligands in dichloromethane solvent using their experience or by following the procedures described in the literature, it is still necessary to provide the following supplementary explanation of the specific synthesis method for the PNP ligands: First, since this invention requires an overall excess of 10-20% in the amount of isopropylamine reactant, in order to facilitate the reaction of two molecules of diphenylphosphine with one molecule of isopropylamine to generate one molecule of PNP ligand, this invention requires the isopropylamine solution to react with diphenylphosphine chloro via slow dropwise addition. This ensures... The synthesis reaction of PNP ligands is carried out under the condition of relative excess of diphenyl chlorophosphine; secondly, because it was found in the study that diphenyl chlorophosphine and organic amines are easily degraded when exposed to moisture and oxygen in the air, resulting in a decrease in ligand yield, the present invention requires the following preventive measures to be taken when synthesizing bis(diphenylphosphine) isopropylamine type PNP ligands in dichloromethane solvent: (1) Diphenyl chlorophosphine and isopropylamine are dissolved separately in purified dichloromethane solvent that has been dehydrated and deoxygenated to prepare raw material solutions for use, so that the two come into contact with moisture and oxygen as little as possible during the feeding process; (2) The reaction is carried out under the protection of high-purity nitrogen.

[0038] Engineers skilled in the art can flexibly choose the purification method for dehydration and deoxygenation of dichloromethane solvent based on their experience and production conditions. For example, in industrial production, a 4A molecular sieve drying and dehydrating agent can be used first to remove trace amounts of moisture from the dichloromethane, and then a commercially available deoxidizer can be used to remove trace amounts of dissolved oxygen from the dichloromethane. This invention does not limit the purification method for dichloromethane solvent.

[0039] The following are typical operating methods for the laboratory synthesis of PNP ligands provided by this invention, for reference by engineers in the field: (1) A three-necked flask is used as the reactor. First, a magnetic stir bar is placed in the reactor, and then the three-necked flask reactor, purified dichloromethane solvent, dichlorophosphine, isopropylamine, triethylamine, a single-necked flask, and a constant pressure funnel are placed in a glove box purged with nitrogen; (2) Purified dichloromethane solvent is added to the three-necked flask, and then dichlorophosphine and triethylamine are added in sequence to prepare a dichlorophosphine solution containing triethylamine. In addition, purified dichloromethane solvent is added to the single-necked flask to prepare an isopropylamine solution. Then, the isopropylamine solution is transferred to the constant pressure funnel; (3) The three-necked flask reactor is connected to a double-row tube, and then the constant pressure funnel is installed on top of the three-necked flask. Before the synthesis begins, the reactor is protected by high-purity nitrogen, then the stirring is turned on, the heating temperature is set, and the reactor is heated by a water bath. After the reactor temperature stabilizes, open the constant pressure funnel and begin to slowly and uniformly add isopropylamine solution to the reactor, timing the reaction. The time taken to add isopropylamine solution should be the same as the reaction time for synthesizing PNP ligands (2-12h); (4) After the reaction is complete, stop heating and stirring, and cool the reactor to room temperature under nitrogen protection. Then filter the material in the reactor to remove triethylamine hydrochloride precipitate, and collect the filtrate as the first synthesis solution of PNP ligands.

[0040] To determine the synthesis yield of PNP ligands and the concentration of PNP ligands in the first synthesis solution, a suitable sample of the solution was taken and rotary evaporated in a rotary evaporator until a viscous solid appeared. The evaporation was then stopped, and the solid was dissolved in an appropriate amount of methanol, poured off, and placed in a -18°C refrigerator overnight for crystallization. The PNP ligand crystals were collected by filtration. Then, the crude PNP product was washed with an appropriate amount of methanol, and the solid product was collected and dried to obtain the PNP product. The filtrate from the first filtration and the washings from washing the crude PNP product with methanol were combined and concentrated by rotary evaporation, followed by low-temperature crystallization to recover the PNP ligands. Finally, all PNP products were dried at 80°C for 8 hours and weighed. The data were used to calculate the concentration of PNP ligands in the first synthesis solution and the synthesis yield of PNP ligands based on diphenylphosphine chloride.

[0041] Step 2: Add the commonly used solvent for the selective oligomerization reaction of ethylene to the first synthesis solution of PNP ligands, and use conventional distillation methods, namely atmospheric distillation and vacuum distillation, to distill off the dichloromethane solvent used to synthesize PNP ligands, to obtain the second synthesis solution of PNP ligands with the solvent for the selective oligomerization reaction of ethylene as the dispersion medium.

[0042] The commonly used solvents for the selective oligomerization of ethylene are cyclohexane, methylcyclohexane, n-heptane, toluene, p-xylene, m-xylene, or o-xylene; preferably n-heptane, toluene, or p-xylene; more preferably toluene. The commonly used solvents for the selective oligomerization of ethylene must undergo dehydration and deoxygenation purification treatment before use.

[0043] The amount of solvent commonly used in the selective oligomerization reaction of ethylene is given by calculation. The calculation should ensure that the content of PNP ligand in the solvent of the selective oligomerization reaction of ethylene falls within the range of 2 mmol / L-10 mmol / L; preferably between 3 mmol / L-9 mmol / L; more preferably between 4 mmol / L-8 mmol / L.

[0044] In the preparation of the second synthesis solution for PNP ligands, dichloromethane distilled from the first synthesis solution using conventional distillation is purified and returned to the first step as a circulating solvent. The purification of the dichloromethane circulating solvent primarily involves removing organic amines (isopropylamine and triethylamine). Although isopropylamine can theoretically be used as a reactant and triethylamine as an acid-binding agent after the circulating solvent is returned to the first step, given that isopropylamine and triethylamine in the circulating solvent are easily oxidized and deteriorated after the reaction and separation processes, this invention recommends removing them before using the circulating solvent to synthesize PNP ligands; otherwise, the synthesis yield of PNP ligands will be reduced. Many methods exist for removing small amounts of organic amines from the circulating solvent, including dry removal (e.g., adsorption with activated carbon or clay) and wet removal (e.g., acid washing-water washing-dehydration and drying). Engineers skilled in the art can flexibly choose the purification method for the dichloromethane circulating solvent based on common sense and practical conditions and needs. Furthermore, engineers skilled in the art can flexibly select appropriate purification methods based on their experience and production conditions to dehydrate and deoxygenate the commonly used solvents for the selective oligomerization of ethylene. For example, in industrial production, a 4A molecular sieve drying and dehydrating agent can be used to remove trace amounts of water from the commonly used solvents for the selective oligomerization of ethylene, and then a commercially available deoxygenating agent can be used to remove trace amounts of dissolved oxygen. This invention does not limit the purification methods for recycled solvents or the refining methods for fresh solvents.

[0045] Furthermore, this invention does not limit the specific conditions of the conventional distillation methods, namely atmospheric distillation and vacuum distillation. However, it requires that the conventional distillation methods, namely atmospheric distillation and vacuum distillation, be used when preparing the second synthetic solution of the PNP ligand to achieve the following separation indicators:

[0046] (1) The amount of ethylene selective oligomerization solvent contained in the dichloromethane solvent distilled from the distillation vessel for the synthesis of PNP ligands is less than 1.0 wt%, preferably less than 0.5 wt%, and more preferably less than 0.1 wt%.

[0047] (2) The liquid at the bottom of the distillation vessel is the second synthesis liquid; the amount of dichloromethane solvent used for synthesizing PNP ligands in the obtained second synthesis liquid is less than 1.0 wt%, and the content of total organic amines (in terms of nitrogen content) is less than 1000 ppm; preferably, the amount of dichloromethane solvent used for synthesizing PNP ligands in the obtained second synthesis liquid is less than 0.5 wt%, and the content of total organic amines (in terms of nitrogen content) is less than 100 ppm; more preferably, the amount of dichloromethane solvent used for synthesizing PNP ligands in the obtained second synthesis liquid is less than 0.1 wt%, and the content of total organic amines (in terms of nitrogen content) is less than 10 ppm.

[0048] The second synthesis solution of the PNP ligand prepared by the above method is used to directly prepare an ethylene selective oligomeric chromium (PNP-Cr) complex catalyst for the selective oligomerization reaction of ethylene.

[0049] Compared to the conventional method of preparing PNP-Cr complex catalysts using recrystallized PNP ligands, the only difference in directly preparing PNP-Cr complex catalysts using a second synthesis solution is that the second synthesis solution is measured according to the amount of PNP ligand used and the concentration of PNP ligands in the second synthesis solution, and the PNP ligands are added to the container for preparing the complex catalyst by adding the second synthesis solution. All other procedures for carrying out the selective oligomerization reaction of ethylene are the same as the conventional method. Therefore, apart from this, the present invention does not limit the method for carrying out the selective oligomerization reaction of ethylene. Engineers skilled in the art can conveniently carry out the selective oligomerization reaction of ethylene using the PNP ligand synthesis solution (second synthesis solution) provided by the present invention, based on experience or relevant literature on the selective oligomerization methods of ethylene.

[0050] The beneficial effects of this invention are:

[0051] This invention provides a method for preparing a PNP ligand synthesis solution, which, while ensuring high-yield synthesis of PNP ligands, offers favorable conditions for the continuous and automated preparation of ethylene selective oligomeric chromium complex catalysts and the digitalization and intelligentization of ethylene selective oligomerization technology. Simultaneously, it significantly simplifies the process flow and reduces equipment investment and production costs. The concept and method of this invention can be used to prepare synthesis solutions for various PNP ligands, thereby enabling the continuous preparation of the corresponding ethylene selective oligomeric metal complex catalysts. The concept and method of this invention can also be used to prepare synthesis solutions for non-PNP ligands, thereby enabling the continuous preparation of the corresponding ethylene oligomeric metal complex catalysts. Detailed Implementation

[0052] The effectiveness of this invention can be evaluated primarily using the following methods:

[0053] (1) Preparation effect of PNP ligand synthesis solution:

[0054] The formula for calculating the yield of bis(diphenylphosphine)isopropylamine (PNP) ligand synthesis is as follows:

[0055]

[0056] In the formula, m 实际 For the actual yield of bis(diphenylphosphine)isopropylamine ligand, m 理论 This represents the theoretical yield of bis(diphenylphosphine)isopropylamine ligands. Wherein, m 理论 The calculation is performed by multiplying the molar mass of diphenylphosphine isopropylamine by half the molar mass of diphenylchlorophosphine fed. 实际 Determined by crystallization.

[0057] In addition, the content of solvents for the selective oligomerization of ethylene (such as toluene, n-heptane, and xylene) in the dichloroethane circulating solvent was determined by gas chromatography.

[0058] Similarly, the content of dichloroethane solvent in the second synthesis solution of PNP was determined by gas chromatography.

[0059] The concentration of PNP ligands in the second synthesis solution was determined by crystallization, and the total organic amine content was analyzed according to GB / T23961-2009 "Determination of Low-Carbon Fatty Amine Content: Gas Chromatography".

[0060] (2) Catalytic effect of PNP ligand synthesis solution:

[0061] A PNP-Cr complex catalyst was prepared directly using a second synthesis solution of PNP ligands, and then a commercially available methylaluminoxane (MAO) was used to form a catalyst composition. The ethylene oligomerization activity and product distribution of the catalyst composition were evaluated in the laboratory using a high-pressure reactor.

[0062] The composition of linear α-olefin products in the liquid products of ethylene oligomerization was analyzed using a Shimadzu GC2014C gas chromatograph. The gas chromatograph was equipped with an FID detector and a PONA column (50m × 0.2mm × 0.2μm). The detector temperature was 330℃, the injection port temperature was 330℃, and the initial column temperature was 50℃. The column temperature program was as follows: after injection, the column was held at 50℃ for 5 min, then increased to 330℃ at a rate of 10℃ / min, held at that temperature for 10 min, and then cooled to 50℃, awaiting the next injection.

[0063] The content of α-olefins with different carbon numbers was quantitatively calculated using the internal standard method, and the total catalyst activity and linear α-olefin selectivity were calculated by weighing the solid product ethylene wax.

[0064] The present invention will be further described below through specific embodiments, but the present invention is not limited to these embodiments.

[0065] Example 1:

[0066] This embodiment illustrates the process of synthesizing bis(diphenylphosphine)-isopropylamine PNP ligands using dichloromethane, a common solvent for PNP ligand synthesis, under optimal reaction conditions via the reaction of dichlorodiphenylphosphine and isopropylamine, yielding a first synthesis solution of PNP ligands. Then, a solvent commonly used in ethylene selective oligomerization is added to the first synthesis solution of PNP ligands, and the dichloromethane solvent used for ligand synthesis is distilled off using conventional distillation, yielding a second synthesis solution of PNP ligands. This second synthesis solution of PNP ligands, using a solvent commonly used in ethylene selective oligomerization as the dispersion medium, is a ligand synthesis solution that requires no further purification and can be directly used to prepare highly active ethylene selective oligomerization PNP-Cr complex catalysts.

[0067] Step 1: In dichloromethane solvent, which is commonly used for synthesizing PNP ligands, dichlorodiphenylphosphine and isopropylamine are reacted under optimal reaction conditions to synthesize bis(diphenylphosphine)-isopropylamine type PNP ligands, thus obtaining the first synthesis solution of PNP ligands.

[0068] First, the reactor (three-necked flask with a magnetic stir bar), the purified dichloromethane solvent that has been dehydrated and deoxygenated, the reactants dichlorophenylphosphine (320℃) and isopropylamine (33-34℃), the acid-binding agent triethylamine (89.5℃), the single-necked flask and the constant pressure funnel, etc., are placed in a glove box that has been purged with nitrogen.

[0069] Next, 50 mL of purified dichloromethane solvent was added to the reactor. While stirring, 6.64 mL (37 mmol) of dichlorophosphine and 12.86 mL (92.5 mmol) of triethylamine were added to the reactor to prepare a dichlorophosphine solution containing triethylamine. Separately, 50 mL of purified dichloromethane solvent was added to a single-necked flask, and then 1.80 mL (21 mmol) of isopropylamine was added and shaken well to prepare an isopropylamine solution. After shaking, the resulting isopropylamine solution was transferred to a constant pressure funnel.

[0070] Next, the reactor was connected to the high-purity nitrogen port of the double-row pipe, and a constant-pressure funnel was installed on the reactor. Before the synthesis began, the reactor was protected with high-purity nitrogen, then the stirring was started, the heating temperature was set, and the reactor was heated in a water bath. After the reactor temperature stabilized, the constant-pressure funnel was opened, and isopropylamine solution was slowly added dropwise to the reactor, with the reaction timed. The dropwise addition time of the isopropylamine solution was approximately 6 hours. The main reaction conditions were:

[0071] Reaction pressure, MPa: 0.1

[0072] Reaction temperature, °C: 25

[0073] Reaction time, h: 6

[0074] Diphenylphosphine chloride / isopropylamine, mol / mol: 1:0.57

[0075] Chlorodiphenylphosphine / triethylamine, mol / mol: 1:2.5

[0076] Solvent volume (expressed as concentration of diphenylphosphine chloride, mol / L): 0.37

[0077] After the reaction is complete, heating and stirring are stopped, and the reactor is cooled to room temperature under nitrogen protection. The material in the reactor is then filtered to remove the triethylamine hydrochloride precipitate. The collected filtrate is the first synthesis solution of PNP ligands, which is stored in a sealed container for later use.

[0078] To determine the synthesis yield of bis(diphenylphosphine) isopropylamine-type PNP ligands and the concentration of PNP ligands in the first synthesis solution, a suitable sample (50 mL) was taken from the first synthesis solution and rotary evaporated until a viscous solid appeared. Evaporation was then stopped, and the solid was dissolved in methanol. The sample was then placed in a -18°C refrigerator overnight for crystallization. The PNP ligand crystals were collected by filtration. The crude PNP product was then washed with 10 mL of methanol, and the solid product was collected and dried to obtain the PNP product. The filtrate from the first filtration and the washings from washing the crude PNP product with methanol were combined and concentrated by rotary evaporation, followed by low-temperature crystallization to recover the PNP ligands. Finally, all PNP products were dried at 80°C for 8 hours and weighed. The data were used to calculate the concentration of PNP ligands in the first synthesis solution, which was approximately 165 mmol / L. The calculated synthesis yield of PNP ligands based on diphenylphosphine chloride was approximately 97%.

[0079] Step 2: Add the commonly used solvent for the selective oligomerization reaction of ethylene to the first synthesis solution of PNP ligands, and distill off the dichloromethane solvent used to synthesize PNP ligands by conventional distillation to obtain the second synthesis solution of PNP ligands.

[0080] In this example, the commonly used solvent for the selective oligomerization of ethylene is toluene (boiling point 110.6℃), which has been purified by dehydration and deoxygenation before use. Take 40 ml of the first synthesis solution of PNP ligands. The concentration of PNP ligands in this solution is known to be approximately 165 mmol / L. According to calculations, adding 1000 ml of purified toluene solvent to the 40 ml first synthesis solution of PNP ligands will bring the content of PNP ligands in the solvent (toluene) for the selective oligomerization of ethylene into a more preferred range (4 mmol / L-8 mmol / L). Therefore, add 1000 ml of purified toluene solvent to the 40 ml first synthesis solution of PNP ligands, shake well, and then remove the dichloromethane solvent used for ligand synthesis by atmospheric distillation. During the distillation of the dichloromethane solvent, unconverted isopropylamine (33-34℃) can be distilled off simultaneously. Finally, the gas phase temperature of the distillation flask was controlled at around 90°C and maintained for 2 hours to distill off excess triethylamine (89.5°C).

[0081] Gas chromatography analysis revealed that the toluene solvent (solvent for the selective oligomerization of ethylene) content in the dichloromethane recycled solvent was 0.1 wt%. This dichloromethane recycled solvent was then treated with a 20 wt% acidic aqueous solution of sodium dihydrogen phosphate to remove organic amines, followed by water washing, dehydration and drying using 4A molecular sieves, and ultrasonic degassing. The purified dichloromethane recycled solvent was reserved for use in the first step.

[0082] The second PNP synthesis solution obtained by atmospheric distillation is a solution of PNP ligand synthesis with toluene as the dispersion medium. The PNP ligand content was determined to be approximately 6.6 mmol / L by crystallization. The dichloromethane solvent (ligand synthesis solvent) content was determined to be approximately 0.06 wt% and the total organic amine content was approximately 9 ppm by gas chromatography. This solution was stored in a glove box to prevent air exposure for later use.

[0083] Step 3: PNP-Cr complex catalyst is directly prepared using the second synthesis solution of PNP ligand (with toluene as solvent). Based on this, the catalyst composition is prepared in situ in an ethylene oligomerization high-pressure reactor to carry out the selective oligomerization reaction of ethylene.

[0084] First, the high-pressure reactor is heated to 110°C. Then, the reactor and its auxiliary piping system are repeatedly purged and evacuated five times using high-purity nitrogen. Finally, the reactor and its auxiliary piping system are purged with high-purity ethylene that has passed through a dehydration and deoxygenation tube, so that the reaction system is in an ethylene environment (0.3 MPa), and the reactor temperature is lowered to 40°C (the ethylene oligomerization reaction temperature) and kept at a constant temperature for later use.

[0085] Then, in a glove box, add 3.7 mg (10.5 μmol) of chromium acetylacetone to a Shrek bottle, followed by 3.18 mL of the second synthesis solution of PNP ligands prepared in step two (PNP ligand concentration 6.6 mmol / L). Next, add 30 mL of purified cyclohexane solvent and shake well. Add more cyclohexane solvent until the total solution volume is 50 mL, shake well, and this is the PNP-Cr complex catalyst solution (Cr:PNP = 1:2) prepared directly using the second synthesis solution of PNP ligands, for later use.

[0086] In a glove box, following the requirement of an Al / Cr molar ratio of 400, add 2.795 mL of a commercially available toluene solution of methylaluminoxane (MAO) to another Shrek flask, followed by 30 mL of purified cyclohexane solvent, and shake well. Then add cyclohexane solvent until the total solution volume is 50 mL, shake well, and this is the methylaluminoxane (MAO) co-catalyst solution, ready for use.

[0087] Next, under air-isolated conditions, 50 mL of the prepared PNP-Cr complex catalyst solution and 50 mL of methylaluminoxane (MAO) solution were sequentially drawn into a high-pressure reactor under stirring, thereby preparing an in-situ catalyst composition for the selective oligomerization of ethylene.

[0088] Finally, ethylene was introduced into the reactor, and the pressure was increased to 3 MPa. The reaction was started and timed for 30 minutes. After the reaction, the ethylene feed, reactor heating, and stirring were sequentially shut off, and then the high-pressure reactor was depressurized. When the actual temperature inside the reactor was below 30°C, the reactor was carefully opened under normal pressure, and all reaction products were removed. 2 mL of acidified ethanol was added to the reaction products to terminate the reaction. The reaction products were then centrifuged to obtain two fractions: a solid product and a liquid product. The solid product was dried overnight in an 80°C oven and then measured; the liquid product was measured and sampled for gas chromatography analysis. Based on the chromatographic analysis data, the reaction results were calculated as follows: the activity of the catalyst composition is approximately 5.15 × 10⁻⁶. 6 g / (molCr·h). Liquid products account for approximately 95% of the total solid and liquid products, of which C6 accounts for 13.50%, C8 82.41%, and C 10 0.95%, C 12 0.34%, C 14+ 2.80%. The selectivity of 1-hexene in hexene (C6) was 75.52%, and the selectivity of 1-octene in octene (C8) was 99.74%.

[0089] Comparative Example 1:

[0090] This embodiment illustrates the synthesis of bis(diphenylphosphine)-isopropylamine PNP ligands using dichloromethane, a common solvent for synthesizing PNP ligands, under optimal reaction conditions via the reaction of dichlorodiphenylphosphine and isopropylamine, yielding a first synthesis solution of the PNP ligands. Then, the PNP ligands are crystallized from the first synthesis solution using conventional methods. The crystalline PNP ligand powder is then used to prepare a PNP-Cr complex catalyst for the selective oligomerization of ethylene, achieving highly active selective oligomerization of ethylene. However, the conventional method is cumbersome and not conducive to the continuous preparation of catalysts.

[0091] Example 1 was repeated, but after obtaining the first synthesis solution of PNP ligands (a dichloromethane solution of PNP ligands) in the first step, the entire first synthesis solution was rotary evaporated using a rotary evaporator until a viscous solid appeared. The rotary evaporation was then stopped, and an appropriate amount of methanol was added to dissolve the solid. The solid was then placed in a -18°C refrigerator overnight for crystallization, and the PNP ligand crystals were collected by filtration. Then, the crude PNP product was washed with 20 mL of methanol, and the solid product was collected and dried to obtain the PNP product. The filtrate from the first filtration and the washing liquid generated during the methanol washing of the crude PNP product were combined and concentrated by a second rotary evaporation, followed by low-temperature crystallization to recover the PNP ligands. Finally, all the PNP crystal products were dried at 80°C for 8 hours to obtain a PNP crystalline powder product for later use. The PNP ligand synthesis yield, based on diphenylphosphine chloride, was approximately 97%. The PNP ligand crystalline powder product was used in the third step to prepare a PNP-Cr complex catalyst, and based on this, a catalyst composition was prepared in situ in an ethylene oligomerization high-pressure reactor for the selective oligomerization reaction of ethylene. The specific procedure for preparing the PNP-Cr complex catalyst using the crystalline powder product of PNP ligand is as follows: In a glove box, add 3.7 mg of chromium acetylacetone (10.5 μmol) to a Shrek flask, then weigh approximately 9 mg of the crystalline powder product of PNP ligand (21.18 μmol) and add it to the flask. Next, add 30 mL of purified methylcyclohexane solvent and shake well. Then, add methylcyclohexane solvent until the total solution volume is 50 mL, shake well, and you will obtain the PNP-Cr complex catalyst solution (Cr:PNP = 1:2) prepared using the crystalline powder product of PNP. The results of the selective oligomerization reaction of ethylene are as follows: the activity of the catalyst composition is approximately 5.32 × 10⁻⁶. 6 g / (molCr·h). Liquid products account for approximately 96% of the total solid and liquid products, of which C6 accounts for 13.43%, C8 82.67%, and C 10 0.90%, C 12 0.32%, C 14+ 2.68%. The selectivity of 1-hexene in hexene (C6) was 77.45%, and the selectivity of 1-octene in octene (C8) was 99.60%.

[0092] Comparative Example 2:

[0093] This embodiment illustrates the synthesis of bis(diphenylphosphine)-isopropylamine PNP ligands using dichloromethane, a common solvent for synthesizing PNP ligands, under optimal reaction conditions via the reaction of dichlorodiphenylphosphine and isopropylamine, yielding a first synthetic solution of the PNP ligands. This first synthetic solution of the PNP ligands was then directly used to prepare a PNP-Cr complex catalyst. Due to the adverse effects of dichloromethane on the complex catalyst, the ethylene selective oligomerization reactivity of the catalyst composition was low.

[0094] Example 1 was repeated, but after obtaining the first synthesis solution of the PNP ligand (a dichloromethane solution of the PNP ligand) in the first step, the second step was skipped, and the first synthesis solution of the PNP ligand was directly used in the third step. That is, the PNP-Cr complex catalyst was directly prepared using the first synthesis solution (approximately 127 μl), and then the catalyst composition was prepared in situ in an ethylene oligomerization high-pressure reactor for selective oligomerization of ethylene. In the catalyst composition, the molar ratios of dichloromethane and triethylamine (excess acid-binding agent) introduced with the first synthesis solution to chromium were 0.19 and 6, respectively, and the amount of isopropylamine (excess reactant) introduced with the first synthesis solution was negligible. Therefore, the evaluation result of the ethylene oligomerization reaction was: the activity of the catalyst composition decreased to 4.0 × 10⁻⁶. 5 g / (molCr·h).

[0095] Comparative Example 3:

[0096] This embodiment illustrates that if dichloromethane is not used as a solvent for synthesizing PNP ligands, but instead the commonly used solvent for the selective oligomerization of ethylene is used as the solvent for the reaction of diphenylphosphine chloride and isopropylamine to synthesize bis(diphenylphosphine)-isopropylamine type PNP ligands, the first synthesis solution of PNP ligands in this case is a ligand synthesis solution with the commonly used solvent for the selective oligomerization of ethylene as the dispersion medium. This solution can be directly used to prepare ethylene selective oligomerization PNP-Cr complex catalysts, making the process simpler. However, because the yield of PNP ligands synthesized in the commonly used solvent for the selective oligomerization of ethylene is low, the content of the active component (bis(diphenylphosphine)-isopropylamine type PNP ligand) in the first synthesis solution of PNP ligands is low. This also leads to low reactivity of the catalyst composition in the selective oligomerization of ethylene, and the main reaction product is ethylene wax.

[0097] Example 1 was repeated, but in the first step of preparing the first synthesis solution of the PNP ligand, cyclohexane that had undergone dehydration and deoxygenation treatment was used as the solvent. The concentration of the PNP ligand in the first synthesis solution was measured to be approximately 64 mmol / L using crystallization. The calculated yield of the PNP ligand, based on diphenylphosphine chloride, was approximately 40%. After preparing the first synthesis solution (cyclohexane solution of the PNP ligand) in the first step, the second step was skipped, and the first synthesis solution of the PNP ligand was directly used in the third step. That is, the PNP-Cr complex catalyst was directly prepared using the first synthesis solution of the PNP ligand (approximately 328 μl), and then the catalyst composition was prepared in situ in an ethylene oligomerization high-pressure reactor for the selective oligomerization reaction of ethylene. In the catalyst composition, the amount of unconverted diphenylphosphine chloride carried in with the first synthesis solution is approximately 6 (molar ratio of diphenylphosphine chloride to chromium), the amount of unconverted isopropylamine is approximately 4 (molar ratio of isopropylamine to chromium), and the amount of unconverted triethylamine is approximately 21 (molar ratio of triethylamine to chromium). Therefore, the evaluation result for the ethylene oligomerization reaction is: the activity of the catalyst composition decreases by 2.43 × 10⁻⁶. 6 g / (molCr·h), of which liquid products account for only about 14%.

[0098] Comparative Example 4:

[0099] This example further illustrates that if the PNP ligand is synthesized via the reaction of dichlorophosphine and isopropylamine in a mixed solvent containing dichloromethane and commonly used solvents for selective oligomerization of ethylene instead of using dichloromethane as a solvent, the yield of PNP ligand synthesis will also be negatively affected. If the resulting PNP ligand synthesis solution is directly used to prepare a PNP-Cr complex catalyst, the low content of the active ingredient (bis-diphenylphosphine-isopropylamine type PNP ligand) in the synthesis solution, coupled with the adverse effects of the dichloromethane solvent, results in poor ethylene selective oligomerization reaction performance of the catalyst composition.

[0100] Example 1 was repeated, but in the first step of preparing the PNP ligand's first synthesis solution, a mixed solvent of dehydrated and deoxygenated cyclohexane and dichloromethane (volume ratio 7:3) was used as the solvent for synthesizing PNP (dual solvent). The concentration of PNP ligand in the first synthesis solution was measured to be approximately 139 mmol / L using crystallization. The calculated yield of PNP ligand, based on dichlorodiphenylphosphine, was approximately 83%. After preparing the first synthesis solution (dichloromethane-cyclohexane solution of PNP ligand) in the first step, the second step was skipped, and the first synthesis solution of PNP ligand was directly used in the third step. That is, the PNP-Cr complex catalyst was directly prepared using the first synthesis solution (approximately 151 μl), and then the catalyst composition was prepared in situ in an ethylene oligomerization high-pressure reactor for the selective oligomerization reaction of ethylene. In the catalyst composition, the molar ratio of dichloromethane to chromium introduced with the first synthesis solution is 0.07, the amount of unconverted dichlorophenylphosphine is approximately 0.8 (molar ratio of dichlorophenylphosphine to chromium), the amount of unconverted isopropylamine is approximately 0.7 (molar ratio of isopropylamine to chromium), and the amount of unconverted triethylamine is approximately 8 (molar ratio of triethylamine to chromium). Therefore, the evaluation result for the ethylene oligomerization reaction is: the activity of the catalyst composition decreases to 4.0 × 10⁻⁶. 5 g / (molCr·h), of which liquid products account for only about 30%.

[0101] Example 2:

[0102] This embodiment illustrates that, using dichloromethane, a common solvent for synthesizing PNP ligands, under optimal reaction conditions, the synthesis of bis(diphenylphosphine)isopropylamine (PNP) ligands via the reaction of dichlorophosphine and isopropylamine can be achieved by using different temperatures, times, and feed ratios within the optimal conditions provided in this invention, yielding a first synthesis solution of PNP ligands. Then, a common solvent for ethylene selective oligomerization is added to the first synthesis solution of PNP ligands, and the dichloromethane solvent is distilled off using conventional distillation, yielding a second synthesis solution of PNP ligands. This second synthesis solution of PNP ligands can also be used directly to prepare highly active ethylene selective oligomerization PNP-Cr complex catalysts without further purification.

[0103] Example 1 was repeated, but in the first step, using dichloromethane solvent commonly used for synthesizing PNP ligands, and under optimal reaction conditions, dichlorodiphenylphosphine and isopropylamine were used to synthesize bis(diphenylphosphine)-isopropylamine type PNP ligands. The reaction conditions were changed to:

[0104] Reaction pressure, MPa: 0.1

[0105] Reaction temperature, °C: 5

[0106] Reaction time, h: 12

[0107] Diphenylphosphine chloride / isopropylamine, mol / mol: 1:0.60

[0108] Chlorodiphenylphosphine / triethylamine, mol / mol: 1:2.5

[0109] Solvent volume (expressed as concentration of diphenylphosphine chloride, mol / L): 0.50

[0110] The reactor feed for the synthesis of PNP ligands was as follows: 37 mL of purified dichloromethane solvent was added to the reactor. While stirring, 6.64 mL (37 mmol) of dichlorophosphine and 12.86 mL (92.5 mmol) of triethylamine were added to the reactor to prepare a dichlorophosphine solution containing triethylamine. Another 37 mL of purified dichloromethane solvent was added to a single-necked flask, followed by the addition of 1.9 mL (22.2 mmol) of isopropylamine. The mixture was shaken well to prepare an isopropylamine solution. The resulting isopropylamine solution was transferred to a constant-pressure funnel. The isopropylamine solution was added dropwise to react with the dichlorophosphine at a uniform rate over approximately 12 hours. The concentration of PNP ligands in the first synthesis solution (using dichloromethane as solvent) was approximately 213 mmol / L, and the yield of PNP ligands based on dichlorophosphine was approximately 95%. Based on this, 30 ml of the first synthesis solution of PNP ligand was used in the second step to prepare the second synthesis solution of PNP ligand. According to the calculation results, adding 1500 ml of purified toluene solvent to the 30 ml of the first synthesis solution of PNP ligand could make the content of PNP ligand in the solvent (toluene) for the selective oligomerization reaction of ethylene fall within a more preferred range (4 mmol / L-8 mmol / L). Therefore, 1500 ml of purified toluene solvent was added to the 30 ml of the first synthesis solution of PNP ligand, shaken well, and then the dichloromethane solvent used for ligand synthesis was removed by atmospheric distillation. The obtained second synthesis solution of PNP ligand, with toluene as the dispersion medium, showed a PNP ligand content of approximately 4.25 mmol / L by crystallization. The content of dichloromethane solvent (ligand synthesis solvent) was approximately 0.03 wt% and the total organic amine content was approximately 8 ppm by gas chromatography; the content of toluene solvent (ethylene selective oligomerization reaction solvent) in the distilled dichloromethane recycled solvent was 0.09 wt%. The second synthetic solution of the PNP ligand was used in the third step, namely, the direct preparation of the PNP-Cr complex catalyst. Based on this, the catalyst composition was prepared in situ in a high-pressure reactor for ethylene oligomerization to carry out the selective oligomerization reaction of ethylene. Specifically, in the step of directly preparing the PNP-Cr complex catalyst solution using the second synthetic solution of the PNP ligand, 3.7 mg (10.5 μmol) of chromium acetylacetone was added to a Shrek flask in a glove box. Then, 4.94 mL of the second synthetic solution of the PNP ligand (PNP ligand concentration 4.25 mmol / L) was added, followed by 30 mL of purified cyclohexane solvent, and the mixture was shaken well. Cyclohexane solvent was then added to bring the total solution volume to 50 mL, and the mixture was shaken well. This was the PNP-Cr complex catalyst solution (Cr:PNP = 1:2) prepared directly using the second synthetic solution of the PNP ligand, and it was ready for use. The reaction result showed that the activity of the catalyst composition was approximately 4.92 × 10⁻⁶. 6 g / (molCr·h), liquid products accounted for 94%. The distribution of α-olefin products remained basically unchanged.

[0111] Example 3:

[0112] This embodiment further illustrates that when synthesizing bis(diphenylphosphine)-isopropylamine (PNP) ligands using dichloromethane, a commonly used solvent for synthesizing PNP ligands, under optimal reaction conditions via the reaction of dichlorophosphine and isopropylamine, PNP ligands can be synthesized using different temperatures, times, and feed ratios within the optimal conditions given in this invention, yielding a first synthesis solution of PNP ligands. Then, a commonly used solvent for ethylene selective oligomerization is added to the first synthesis solution of PNP ligands, and the dichloromethane solvent is distilled off through conventional distillation to obtain a second synthesis solution of PNP ligands. The resulting second synthesis solution of PNP ligands can also be used directly to prepare highly active ethylene selective oligomerization PNP-Cr complex catalysts without further purification.

[0113] Example 1 was repeated, but in the first step, using dichloromethane solvent commonly used for synthesizing PNP ligands, and under optimal reaction conditions, dichlorodiphenylphosphine and isopropylamine were used to synthesize bis(diphenylphosphine)-isopropylamine (PNP) ligands. The reaction conditions were changed to:

[0114] Reaction pressure, MPa: 0.1

[0115] Reaction temperature, °C: 30

[0116] Reaction time, h: 2

[0117] Chlorodiphenylphosphine / isopropylamine, mol / mol: 1:0.55

[0118] Chlorodiphenylphosphine / triethylamine, mol / mol: 1:2

[0119] Solvent volume (expressed as concentration of diphenylphosphine chloride, mol / L): 0.2

[0120] The reactor feed for the synthesis of PNP ligands was as follows: 95 mL of purified dichloromethane solvent was added to the reactor. While stirring, 6.63 mL (37 mmol) of dichlorophosphine and 10.29 mL (74 mmol) of triethylamine were added to the reactor to prepare a dichlorophosphine solution containing triethylamine. Separately, 90 mL of purified dichloromethane solvent was added to a single-necked flask, and 1.74 mL (20.35 mmol) of isopropylamine was added and shaken to prepare an isopropylamine solution. After shaking, the resulting isopropylamine solution was transferred to a constant-pressure funnel; the isopropylamine solution was added dropwise at a uniform rate to react with the dichlorophosphine, with a dropping time of approximately 2 hours. The concentration of PNP ligands in the first synthesis solution (using dichloromethane as solvent) was approximately 87.90 mmol / L, and the PNP ligand synthesis yield based on dichlorophosphine was approximately 91%. Based on this, 70 ml of the first synthesis solution of PNP ligand was used in the second step to prepare the second synthesis solution of PNP ligand. According to the calculation results, adding 770 ml of purified toluene solvent to the 70 ml of the first synthesis solution of PNP ligand could make the content of PNP ligand in the ethylene selective oligomerization reaction solvent (toluene) fall within a more preferred range (4 mmol / L-8 mmol / L). Therefore, 760 ml of purified toluene solvent was added to the 70 ml of the first synthesis solution of PNP ligand, shaken well, and then the dichloromethane solvent used for ligand synthesis was removed by atmospheric distillation. The obtained second synthesis solution of PNP ligand, with toluene as the dispersion medium, was found to contain approximately 8 mmol / L of PNP ligand by crystallization. The content of dichloromethane solvent (ligand synthesis solvent) in the second synthesis solution of PNP ligand was approximately 0.90 wt% and the total organic amine content was approximately 42 ppm, as determined by gas chromatography; the content of toluene solvent (ethylene selective oligomerization reaction solvent) in the distilled dichloromethane recycled solvent was 0.24 wt%. The second synthetic solution of the PNP ligand was used in the third step, namely, the direct preparation of the PNP-Cr complex catalyst. Based on this, the catalyst composition was prepared in situ in a high-pressure reactor for ethylene oligomerization to carry out the selective oligomerization reaction of ethylene. Specifically, in the step of directly preparing the PNP-Cr complex catalyst solution using the second synthetic solution of the PNP ligand, 3.7 mg (10.5 μmol) of chromium acetylacetone was added to a Shrek flask in a glove box. Then, 2.63 mL of the second synthetic solution of the PNP ligand (PNP ligand concentration 8 mmol / L) was added, followed by 30 mL of purified cyclohexane solvent, and the mixture was shaken well. Cyclohexane solvent was then added to bring the total solution volume to 50 mL, and the mixture was shaken well. This was the PNP-Cr complex catalyst solution (Cr:PNP = 1:2) prepared directly using the second synthetic solution of the PNP ligand, and was set aside for later use. The reaction results showed that the activity of the catalyst composition was approximately 4.40 × 10⁻⁶. 6g / (molCr·h), liquid products account for approximately 92% of the total solid and liquid products. The distribution of α-olefin products remains essentially unchanged.

[0121] Example 4:

[0122] This embodiment further illustrates that when synthesizing bis(diphenylphosphine) isopropylamine (PNP) ligands using dichloromethane, a common solvent for synthesizing PNP ligands, under optimal reaction conditions via the reaction of dichlorophenylphosphine and isopropylamine, PNP ligands can be synthesized using different temperatures, times, and feed ratios within the optimal conditions given in this invention, yielding a first synthesis solution of PNP ligands. Then, a common solvent for ethylene selective oligomerization is added to the first synthesis solution of PNP ligands, and the dichloromethane solvent is distilled off through conventional distillation to obtain a second synthesis solution of PNP ligands. The common solvent for ethylene selective oligomerization can be n-heptane. In this case, the second synthesis solution is a ligand synthesis solution with n-heptane as the dispersion medium. This ligand solution does not require further purification and can be directly used to prepare highly active ethylene selective oligomerization PNP-Cr complex catalysts.

[0123] Repeat Example 1, but in the first step, using dichloromethane solvent commonly used for synthesizing PNP ligands, and under optimal reaction conditions, synthesize bis(diphenylphosphine)-isopropylamine (PNP) ligands with dichlorodiphenylphosphine and isopropylamine. When preparing the first synthesis solution of the PNP ligand, change the reaction conditions as follows:

[0124] Reaction pressure, MPa: 0.1

[0125] Reaction temperature, °C: 20

[0126] Reaction time, h: 8

[0127] Chlorodiphenylphosphine / isopropylamine, mol / mol: 1:0.55

[0128] Chlorodiphenylphosphine / triethylamine, mol / mol: 1:3

[0129] Solvent volume (expressed as concentration of diphenylphosphine chloride, mol / L): 1.0

[0130] The reactor feed for the synthesis of PNP ligands was as follows: 18 mL of purified dichloromethane solvent was added to the reactor. While stirring, 6.63 mL (37 mmol) of dichlorophosphine and 15.43 mL (111 mmol) of triethylamine were added to the reactor to prepare a dichlorophosphine solution containing triethylamine. Separately, 19 mL of purified dichloromethane solvent was added to a single-necked flask, followed by 1.74 mL (20.35 mmol) of isopropylamine. The mixture was shaken well to prepare an isopropylamine solution. After shaking, the resulting isopropylamine solution was transferred to a constant-pressure funnel. The isopropylamine solution was added dropwise to react with the dichlorophosphine at a uniform rate over approximately 8 hours. The concentration of PNP ligands in the first synthesis solution (using dichloromethane as solvent) was approximately 370 mmol / L, and the yield of PNP ligands based on dichlorophosphine was approximately 96%.

[0131] Simultaneously, in the second step, the solvent for the ethylene selective oligomerization reaction added to the first synthesis solution was changed to n-heptane (boiling point: 98℃). Before use, the n-heptane solvent underwent routine dehydration and deoxygenation purification. Take 15 ml of the first synthesis solution of PNP ligands and add 2700 ml of purified n-heptane solvent. Then, remove the ligand synthesis solvent (dichloromethane) by atmospheric distillation, obtaining the second synthesis solution, which is a solution of the PNP ligand synthesis compound with n-heptane as the dispersion medium. The PNP ligand content was determined to be approximately 2.06 mmol / L by crystallization. The dichloromethane solvent (ligand synthesis solvent) content was determined to be approximately 0.05 wt% and the total organic amine content was approximately 3 ppm by gas chromatography; the n-heptane solvent (ethylene selective oligomerization reaction solvent) content in the distilled dichloromethane recycled solvent was 0.7 wt%. The second synthetic solution of the PNP ligand was used in the third step, namely, the direct preparation of the PNP-Cr complex catalyst. Based on this, the catalyst composition was prepared in situ in a high-pressure reactor for ethylene oligomerization to carry out the selective oligomerization reaction of ethylene. Specifically, in the step of directly preparing the PNP-Cr complex catalyst solution using the second synthetic solution of the PNP ligand, 3.7 mg (10.5 μmol) of chromium acetylacetone was added to a Shrek flask in a glove box. Then, 10.19 mL of the second synthetic solution of the PNP ligand (PNP ligand concentration 2.06 mmol / L) was added, followed by 30 mL of purified cyclohexane solvent, and the mixture was shaken well. Methylcyclohexane solvent was then added until the total solution volume was 50 mL, and the mixture was shaken well. This was the PNP-Cr complex catalyst solution (Cr:PNP = 1:2) prepared directly using the second synthetic solution of the PNP ligand, and was set aside for later use. The reaction result showed that the activity of the catalyst composition was approximately 4.16 × 10⁻⁶. 6 g / (molCr·h), liquid products account for approximately 93% of the total solid and liquid products. The distribution of α-olefin products remains essentially unchanged.

[0132] Example 5:

[0133] This embodiment further illustrates that when synthesizing bis(diphenylphosphine) isopropylamine (PNP) ligands using dichloromethane, a common solvent for synthesizing PNP ligands, under optimal reaction conditions via the reaction of dichlorophenylphosphine and isopropylamine, PNP ligands can be synthesized using different temperatures, times, and feed ratios within the optimal conditions given in this invention, yielding a first synthesis solution of PNP ligands. Then, a common solvent for ethylene selective oligomerization is added to the first synthesis solution of PNP ligands, and the dichloromethane solvent is distilled off through conventional distillation to obtain a second synthesis solution of PNP ligands. The common solvent for ethylene selective oligomerization can be xylene. In this case, the second synthesis solution is a ligand synthesis solution with xylene as the dispersion medium. This ligand solution does not require further purification and can be directly used to prepare highly active ethylene selective oligomerization PNP-Cr complex catalysts.

[0134] Repeat Example 1, but in the first step, using dichloromethane solvent commonly used for synthesizing PNP ligands, and under optimal reaction conditions, synthesize bis(diphenylphosphine)-isopropylamine (PNP) ligands with dichlorodiphenylphosphine and isopropylamine. When preparing the first synthesis solution of the PNP ligand, change the reaction conditions as follows:

[0135] Reaction pressure, MPa: 0.1

[0136] Reaction temperature, °C: 15

[0137] Reaction time, h: 12

[0138] Chlorodiphenylphosphine / isopropylamine, mol / mol: 1:0.55

[0139] Chlorodiphenylphosphine / triethylamine, mol / mol: 1:3

[0140] Solvent volume (expressed as concentration of diphenylphosphine chloride, mol / L): 0.50

[0141] The reactor feed for the synthesis of PNP ligands was as follows: 37 mL of purified dichloromethane solvent was added to the reactor. While stirring, 6.63 mL (37 mmol) of dichlorophosphine and 15.43 mL (111 mmol) of triethylamine were added to the reactor to prepare a dichlorophosphine solution containing triethylamine. Another 37 mL of purified dichloromethane solvent was added to a single-necked flask, and then 1.74 mL (20.35 mmol) of isopropylamine was added and shaken to prepare an isopropylamine solution. After shaking, the resulting isopropylamine solution was transferred to a constant-pressure funnel; the isopropylamine solution was added dropwise to react with the dichlorophosphine at a uniform rate over approximately 12 hours. The concentration of PNP ligands in the first synthesis solution (using dichloromethane as solvent) was approximately 206 mmol / L, and the PNP ligand synthesis yield based on dichlorophosphine was approximately 95%.

[0142] Simultaneously, in the second step, the solvent for the selective oligomerization of ethylene added to the first synthesis solution was changed to p-xylene (boiling point: 138.37℃). Before use, the p-xylene solvent underwent routine dehydration and deoxygenation purification. Take 30 ml of the first synthesis solution of PNP ligands and add 620 ml of purified p-xylene solvent. Then, remove the ligand synthesis solvent (dichloromethane) by atmospheric distillation, obtaining the second synthesis solution, which is a solution of the PNP ligand synthesis with p-xylene as the dispersion medium. The PNP ligand content was determined to be approximately 10 mmol / L by crystallization. The dichloromethane solvent (ligand synthesis solvent) content was determined to be approximately 0.02 wt% and the total organic amine content was approximately 2 ppm by gas chromatography; the p-xylene solvent (ethylene selective oligomerization solvent) content in the distilled dichloromethane recycled solvent was 0.05 wt%. The second synthetic solution of the PNP ligand was used in the third step, namely, the direct preparation of the PNP-Cr complex catalyst. Based on this, the catalyst composition was prepared in situ in a high-pressure reactor for ethylene oligomerization to carry out the selective oligomerization reaction of ethylene. Specifically, in the step of directly preparing the PNP-Cr complex catalyst solution using the second synthetic solution of the PNP ligand, 3.7 mg (10.5 μmol) of chromium acetylacetone was added to a Shrek flask in a glove box. Then, 2.1 mL of the second synthetic solution of the PNP ligand (PNP ligand concentration 10 mmol / L) was added, followed by 30 mL of purified cyclohexane solvent, and the mixture was shaken well. Cyclohexane solvent was then added to bring the total solution volume to 50 mL, and the mixture was shaken well. This was the PNP-Cr complex catalyst solution (Cr:PNP = 1:2) prepared directly using the second synthetic solution of the PNP ligand, and it was set aside for later use. The reaction results showed that the activity of the catalyst composition was approximately 465 × 10⁻⁶. 6 g / (molCr·h), liquid products account for approximately 96% of the total solid and liquid products. The distribution of α-olefin products remains essentially unchanged.

Claims

1. A method for preparing a PNP ligand synthesis solution for an ethylene selective oligochromium complex catalyst, characterized in that, The steps are as follows: Step 1: In the presence of dichloromethane solvent and triethylamine as an acid binder, bis(diphenylphosphine)-isopropylamine was reacted with chlorodiphenylphosphine to synthesize bis(diphenylphosphine)-isopropylamine PNP ligands, thus obtaining the first synthesis solution of PNP ligands; The conditions for preparing the first synthetic solution of the PNP ligand are as follows: Reaction pressure: atmospheric pressure Reaction temperature: 5-30℃ Reaction time: 2-12 h The molar ratio of dichlorophenylphosphine to isopropylamine is 1:(0.55-0.60). The molar ratio of diphenylphosphine chloride to triethylamine is 1:(2-3). The amount of dichloromethane solvent used is expressed as the molar concentration of dichlorodiphenylphosphine: 0.2 mol / L - 1.0 mol / L in, The procedure for synthesizing bis(diphenylphosphine)isopropylamine type PNP ligands is as follows: First, purified dichloromethane solvent that has undergone dehydration and deoxygenation treatment is added to the reactor. Then, dichlorophosphine and triethylamine are added sequentially to the reactor to prepare a dichlorophosphine solution containing triethylamine. Isopropylamine is added to a container containing purified dichloromethane solvent that has undergone dehydration and deoxygenation treatment to prepare an isopropylamine solution. Before synthesizing the PNP ligand, the reactor is protected by purging with nitrogen. Then, the isopropylamine solution is slowly and uniformly added dropwise to the reactor. After the reaction is completed, the reactor is cooled to room temperature under nitrogen protection. Then, the material in the reactor is filtered to remove the triethylamine hydrochloride precipitate, and the collected filtrate is the first synthesis solution of the PNP ligand. Step 2: Add the solvent for the selective oligomerization reaction of ethylene to the first synthesis solution of PNP ligands, and distill off the dichloromethane solvent used to synthesize PNP ligands, to obtain the second synthesis solution of PNP ligands with the solvent for the selective oligomerization reaction of ethylene as the dispersion medium; the obtained second synthesis solution of PNP ligands is the PNP ligand synthesis solution used for the catalyst of selective oligomerization of chromium complexes of ethylene. The amount of solvent added for the selective oligomerization reaction of ethylene is given by the calculated value, which makes the content of PNP ligand in the solvent of the selective oligomerization reaction of ethylene fall between 2 mmol / L and 10 mmol / L. The solvent for the selective oligomerization reaction of ethylene is cyclohexane, methylcyclohexane, n-heptane, toluene, p-xylene, m-xylene, or o-xylene; the solvent for the selective oligomerization reaction of ethylene must be dehydrated and deoxygenated before use. The specific conditions of the distillation method, namely atmospheric distillation and vacuum distillation, are not limited, but the following separation indicators must be achieved when preparing the second synthetic solution of PNP ligands using the distillation method: (1) The amount of ethylene selective oligomerization solvent contained in the dichloromethane solvent distilled from the distillation vessel for the synthesis of PNP ligands is less than 1.0 wt%; (2) The bottom liquid of the distillation vessel is the second synthesis liquid; the amount of dichloromethane solvent used to synthesize PNP ligands in the obtained second synthesis liquid is less than 1.0 wt%; and the amount of total organic amines contained therein, in terms of nitrogen content, is less than 1000 ppm.

2. The method for preparing a PNP ligand synthesis solution for an ethylene selective oligochromium complex catalyst according to claim 1, characterized in that, The solvent for the selective oligomerization reaction of ethylene is n-heptane, toluene, or p-xylene.

3. The method for preparing a PNP ligand synthesis solution for an ethylene selective oligomeric chromium complex catalyst according to claim 2, characterized in that, The solvent for the selective oligomerization reaction of ethylene is toluene.

4. The method for preparing a PNP ligand synthesis solution for an ethylene selective oligochromium complex catalyst according to claim 1, characterized in that, In the second step, the amount of solvent added for the selective oligomerization reaction of ethylene is given by a calculated value, which makes the content of PNP ligand in the solvent of the selective oligomerization reaction of ethylene fall within the range of 3 mmol / L-9 mmol / L.

5. The method for preparing a PNP ligand synthesis solution for an ethylene selective oligochromium complex catalyst according to claim 4, characterized in that, In the second step, the amount of solvent added for the selective oligomerization reaction of ethylene is given by a calculated value, which makes the content of PNP ligand in the solvent of the selective oligomerization reaction of ethylene fall within the range of 4 mmol / L-8 mmol / L.

6. The method for preparing a PNP ligand synthesis solution for an ethylene selective oligochromium complex catalyst according to claim 1, characterized in that, In step (1), the amount of solvent for the selective oligomerization of ethylene contained in the dichloromethane solvent distilled from the distillation vessel for the synthesis of PNP ligands is less than 0.5 wt%.

7. The method for preparing a PNP ligand synthesis solution for an ethylene selective oligomeric chromium complex catalyst according to claim 6, characterized in that, In step (1), the amount of ethylene selective oligomerization solvent contained in the dichloromethane solvent used for synthesizing PNP ligands distilled from the distillation vessel is less than 0.1 wt%.

8. The method for preparing a PNP ligand synthesis solution for an ethylene selective oligomeric chromium complex catalyst according to claim 1, characterized in that, In step (2), the amount of dichloromethane solvent used for synthesizing PNP ligands in the obtained second synthesis solution is less than 0.5 wt%; the amount of total organic amines, in terms of nitrogen content, is less than 100 ppm.

9. The method for preparing a PNP ligand synthesis solution for an ethylene selective oligomeric chromium complex catalyst according to claim 8, characterized in that, In step (2), the amount of dichloromethane solvent used for synthesizing PNP ligands in the obtained second synthesis solution is less than 0.1 wt%; the amount of total organic amines, in terms of nitrogen content, is less than 10 ppm.

10. The application of the PNP ligand synthesis solution prepared by the method for preparing the PNP ligand synthesis solution for ethylene selective oligochromium complex catalyst according to any one of claims 1-9 in the preparation of the ethylene selective oligochromium complex catalyst.

11. The application according to claim 10, characterized in that, The ethylene-selective oligochromium complex catalyst is used for the selective tetramerization of ethylene into 1-octene.

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