RECOVERY OF HYDROCARBONS FROM A HYDROCARBON RECYCLE

Abstract

The invention relates to a process for the polymerization of olefins comprising the comprising the steps of a. Polymerizing olefins in a reaction mixture comprising monomers, diluent, processing as aids to prepare a product stream comprising polyolefins, monomers and diluent; b. Removing the polyolefins from the product stream to obtain a purge stream; c. Removing gaseous components from the purge stream to obtain a liquid fraction; d. Treating the liquid fraction with at least one ionic liquid to obtain a fraction containing unsaturated hydrocarbons; e. Recycling the fraction containing unsaturated hydrocarbons to the reaction mixture, optionally after purification of said fraction containing unsaturated hydrocarbons. The invention also relates to an olefin polymerization system comprising a polymerization reactor, a purge vessel, a vent gas recovery and an ionic liquid separator for separating liquid alkenes from liquid alkanes, wherein the liquid alkenes which are separated from the alkanes in the ionic liquid separator can be recycled to the polymerization reactor.

Claims

1. A process for the polymerization of olefins comprising the steps of a. Polymerizing olefins in a reaction mixture comprising monomers, diluent, processing aids to prepare a product stream comprising polyolefins, monomers and diluent; b. Removing the polyolefins from the product stream to obtain a purge stream; c. Removing gaseous components from the purge stream to obtain a liquid fraction; d. Treating the liquid fraction with at least one ionic liquid to obtain a fraction containing unsaturated hydrocarbons; e. Recycling the fraction containing unsaturated hydrocarbons to the reaction mixture, optionally after purification of said fraction containing unsaturated hydrocarbons.

2. The process according to claim 1, wherein the monomers are chosen from the group of ethylene, propylene, 1-butene, 1-hexene, 1-octene and mixtures of these monomers.

3. The process according to claim 1, wherein the monomers comprise ethylene and 1-hexene.

4. The process according to claim 1, wherein the polymerization is carried out with the aid of metallocene catalysts or Ziegler-Natta catalysts.

5. The process according to claim 1, wherein the polymerization is carried in the gas phase in a fluid bed.

6. A polymerization system for the polymerization of olefins, comprising a. a polymerization reactor (1) for polymerizing olefins in a reaction mixture comprising monomers, diluent, processing aids to prepare a product stream comprising polyolefins, monomers and diluent, b. a purge vessel (2) for removing the polyolefins from the product stream to obtain a purge stream, c. a vent gas recovery unit (4) for removing gaseous components from the purge stream to obtain a liquid fraction and d. an ionic liquid separator (5) for treating the liquid fraction with at least one ionic liquid to obtain a fraction containing unsaturated hydrocarbons, wherein the system is arranged to recycle the fraction containing unsaturated hydrocarbons to the polymerization reactor (1), optionally after purification of said fraction containing unsaturated hydrocarbons in an optional purification unit (6).

7. The polymerization system according to claim 6, wherein the system is suitable for carrying out polymerization with at least two incompatible catalyst systems, which can be used alternately.

8. The polymerization system according to claim 7, wherein the system is suitable for polymerization with alternately metallocene and Ziegler-Natta catalysts.

Description

[0045] An example of a process for the polymerization of olefins according to the invention is shown in FIG. 1.

[0046] FIG. 1 illustrates a polymerization system for the polymerization of ethylene and 1-hexene comprising a polymerization reactor 1 operated as a continuously stirred reactor or fluidized bed reactor, purge vessel 2, vent gas recovery 4, an ionic liquid separator 5, and optional purification vessel 6.

[0047] The product stream comprising polyolefin is formed in the polymerization reactor and sent to purge vessel 2. The polyolefin is separated as a product stream 3 from the purge vessel 2 and the purge stream is sent to the gas-liquid separator 4. In the gas-liquid separator the lighter, gaseous components (like nitrogen and ethylene) are separated as a gas and the liquid stream is sent to the ionic liquid separator 5. In the ionic liquid separator 5 liquid mixtures like n-hexane and 1-hexene are separated. Hexene is recycled to the polymerization reactor after optional purification in the purification vessel 6. In the purification vessel 6 hexene can be purified from catalyst residues and other polar components.

[0048] Although the invention has been described in detail for purposes of illustration, it is understood that such detail is solely for that purpose and variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the claims.

[0049] The invention also relates to a polymerization system for the polymerization of olefins, comprising [0050] a. a polymerization reactor 1 for polymerizing olefins in a reaction mixture comprising monomers, diluent, processing aids to prepare a product stream comprising polyolefins, monomers and diluent, [0051] b. a purge vessel 2 for removing the polyolefins from the product stream to obtain a purge stream, [0052] c. a vent gas recovery unit 4 for removing gaseous components from the purge stream to obtain a liquid fraction and [0053] d. an ionic liquid separator 5 for treating the liquid fraction with at least one ionic liquid to obtain a fraction containing unsaturated hydrocarbons, wherein the system is arranged to recycle the fraction containing unsaturated hydrocarbons to the polymerization reactor 1, optionally after purification of said fraction containing unsaturated hydrocarbons in an optional purification unit 6.

[0054] The polymerization system is preferably suitable for carrying out polymerization with at least two incompatible catalyst systems, which can be used alternately. For example the system can be suitable for polymerization with metallocene and Ziegler-Natta catalysts. In conventional polymerization systems, only one of these types of catalysts is being used, and the polymerization system is optimized for either Ziegler Natta catalysts or metallocene catalysts. It is known that these types of catalysts have a different conversion of monomers relative to each other, and also contain catalytic components that will deactivate the other class of catalysts. Changing from one catalyst system to another is therefore cumbersome with a view on the type of catalysts used, but also on the different reactivity towards monomers. In the polymerization system according to the invention, the liquid monomers (like for example 1-hexene) are separated from the liquid fraction from the purge stream and can be recycled back to the polymerization reactor, independently from the catalyst system used. This increases the flexibility of the polymerization system, reduces waist, and increases efficiency.

[0055] It is further noted that the invention relates to all possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims.

[0056] It is further noted that the term ‘comprising’ does not exclude the presence of other elements. However, it is also to be understood that a description on a product comprising certain components also discloses a product consisting of these components. Similarly, it is also to be understood that a description on a process comprising certain steps also discloses a process consisting of these steps.