US-12617689-B2 - Separation and recovery method for boron trifluoride and complex thereof in olefin polymerization reaction

US12617689B2US 12617689 B2US12617689 B2US 12617689B2US-12617689-B2

Abstract

The present invention provides a method for separation and recovery of boron trifluoride and complexes thereof in an olefin polymerization reaction. The method for separation and recovery of boron trifluoride and complexes thereof in an olefin polymerization reaction, comprising: 1) subjecting a mixture obtained after an olefin polymerization reaction to flash distillation separation to separate part of gaseous boron trifluoride; 2) subjecting the liquid phase obtained from the flash distillation separation to membrane separation to obtain complexes of boron trifluoride and a crude product of the olefin polymerization reaction; and 3) subjecting the crude product of the olefin polymerization reaction obtained in step 2) to gas stripping separation to separate the remaining gaseous boron trifluoride, so as to obtain a pure product of the olefin polymerization reaction The present invention designs a matching process based on the polymorphic characteristics of boron trifluoride and complexes thereof to achieve efficient separation of boron trifluoride and complexes thereof from polymerization intermediates.

Inventors

Tong Liu
Han Gao
Hongling CHU
Yongjun Zhang
Yonggang Ji
Kecun MA
Yan Jiang
Qian Chen
Hongliang HUO
Qi Yu
Yuanyuan Cao
Yulong WANG
Libo Wang
Xianming Xu
Hongping Li
Enhao SUN
Xiuhui Wang
Wei Sun

Assignees

PETROCHINA COMPANY LIMITED

Dates

Publication Date: 20260505
Application Date: 20211027
Priority Date: 20201204

Claims (11)

1 . A method for separation and recovery of boron trifluoride and complexes thereof in an olefin polymerization reaction, comprising: 1) subjecting a mixture obtained after an olefin polymerization reaction to flash distillation separation to separate part of gaseous boron trifluoride; 2) subjecting a liquid phase obtained from the flash distillation separation to membrane separation to obtain complexes of boron trifluoride and a crude product of the olefin polymerization reaction; and 3) subjecting the crude product of the olefin polymerization reaction obtained in step 2) to gas stripping separation to separate the remaining gaseous boron trifluoride, so as to obtain a pure product of the olefin polymerization reaction.
2 . The method for separation and recovery according to claim 1 , wherein an organic membrane of a fluorine-containing polymer is used in the membrane separation.
3 . The method for separation and recovery according to claim 2 , wherein the organic membrane of a fluorine-containing polymer is an organic membrane of polyvinylidene fluoride or polytetrafluoroethylene.
4 . The method for separation and recovery according to claim 1 , wherein the membrane separation is carried out at a separation pressure of 0.1 to 1 MPa and a separation temperature of 5 to 50° C.
5 . The method for separation and recovery according to claim 1 , further comprising: passing the gaseous boron trifluoride separated in step 1) through a gas booster to pressurize it to a desired pressure for recovery and reuse.
6 . The method for separation and recovery according to claim 5 , wherein the gaseous boron trifluoride is subjected to a purification treatment prior to the pressurization, wherein the purification treatment comprises cooling the gaseous boron trifluoride down to 0 to 30° C.
7 . The method for separation and recovery according to claim 1 , further comprising: further subjecting the complexes of boron trifluoride separated in step 2) to solvent extraction before recovery and reuse, wherein the extractant for the solvent extraction is a saturated hydrocarbon with a carbon number of 10 to 18 having an electron-donating group; and the volume ratio of the extractant to the complexes of boron trifluoride is 1:1 to 10:1.
8 . The method for separation and recovery according to claim 1 , further comprising: subjecting the gaseous boron trifluoride separated in step 3) to complexation and absorption by a complexing agent before reuse.
9 . The method for separation and recovery according to claim 8 , wherein the complexing agent is water or an alcohol-based complexing agent; and the complexation and absorption is carried out at a temperature of −10° C. to 30° C.
10 . The method for separation and recovery according to claim 1 , wherein the flash distillation separation is carried out at a flash distillation pressure of 1 to 101 kPa, and a flash distillation temperature of 5 to 120° C. for a flash distillation duration of 1 to 60 min.
11 . The method for separation and recovery according to claim 10 , wherein the gas stripping separation is carried out at a gas stripping temperature of 5 to 120° C. for a duration of 10 to 60 min, a volume ratio of the gas used for gas stripping to the crude product of the olefin polymerization reaction is 1:1 to 50:1, and a gas stripping medium is one or a combination of two or more of nitrogen, helium, argon, krypton and xenon.

Description

TECHNICAL FIELD The present invention relates to the field of olefin polymerization, and specifically to a method for separating and recovering boron trifluoride and complexes thereof in an olefin polymerization reaction. BACKGROUND Boron trifluoride is a typical representative of Lewis acid catalysts, and the boron trifluoride complexes formed from it and an initiator are widely used as catalysts in various reactions such as olefin polymerization, oligomerization, alkylation and isomerization, with characteristics of high selectivity and catalytic activity, high product yield and narrow relative molecular mass distribution. However, boron trifluoride is highly corrosive, which tends to cause corrosion to equipments and reduce product quality. Therefore, when the reaction is finished, boron trifluoride and its complex need to be separated from the polymerization reaction system. The separation of boron trifluoride and its complex is usually carried out by neutralizing the reaction intermediate with an aqueous solution of alkaline such as ammonia, sodium hydroxide or lime, and then washing the reaction intermediate with water to neutral. However, in the above method, wastewater containing high concentration of boron trifluoride hydrate or neutralized boron trifluoride is discharged, which can bring serious issues of environmental pollution. Since it is difficult to remove the boron element in a simple and convenient manner by using the current drainage treatment technology, complete removal of the boron element is very costly. Moreover, due to the high price of boron trifluoride, researchers intend to recycle and reuse the removed boron trifluoride or boron trifluoride complex. Thus, there is a need to seek for a simple and easy industrial method to directly separate boron trifluoride and its complex from reaction intermediate products and recover them for recycling, allowing a fundamental change of the recycling process and substantial reduction of the production cost, and avoiding the generation of a large amount of waste water and waste alkali, which is of a great significance for environmental protection. A number of methods for the separation and recovery of boron trifluoride have been previously reported and disclosed. For example, a fluid of a reaction intermediate product containing boron trifluoride or boron trifluoride complex is contacted with calcium fluoride (CaF2) at a temperature of 200° C. or below and the resulting calcium tetrafluoroborate (Ca(BF4)2) is heated at a temperature of 100-600° C. to obtain boron trifluoride and calcium fluoride, so as to recover boron trifluoride. As another example, fluorides such as lithium fluoride and barium fluoride are contacted with a fluid of a reaction intermediate product containing boron trifluoride or boron trifluoride complex to generate tetrafluoroborate, which is heated at a temperature of 100-600° C., so as to recover boron trifluoride. Further, a common method used in industry to separate boron trifluoride complexes is a cracking process. However, in a reaction where boron trifluoride or boron trifluoride complex is used as a catalyst, in many cases the reaction needs to be carried out at a temperature at or below room temperature. After the reaction is completed, if the temperature rises to 100° C. or above, there may be the following adverse effects: (1) a high temperature favors side reactions such as the generation of tetrafluoroboric acid, causing a decrease in the yield or quality of the target reaction product; (2) a heating decomposition reaction at a high temperature is not preferable in terms of energy conservation; (3) when the fluid of the reaction intermediate product containing boron trifluoride or boron trifluoride complex is viscous, its separation from borates such as calcium tetrafluoroborate becomes more difficult. There is also a technology in which the reaction intermediate product is contacted with silica. Due to the much stronger adsorption on silica of boron trifluoride than that of a complexing agent, boron trifluoride in the intermediate product of the reaction is removed by adsorption, and then recovered for reuse upon desorption under heating. The advantage is that no new impurity is introduced during the separation process and the operation is simple. However, functional groups such as siloxane and silanol groups present within the silica molecules tend to decompose boron trifluoride during the removal of boron trifluoride, resulting in lower separation and recovery efficiency, and thus it is not suitable for large-scale separation. Both the method of removing boron trifluoride from oligomer reaction products by extraction with water and the method of separating boron trifluoride catalyst dispersed in the intermediate products of polymerization reaction with an electrostatic agglomerator are simple and easy to operate, with good separation results. However, the former consumes a large amount of extractant and require