METHOD FOR OL IGOMERI ZATI ON OF ETHYLENE AND REACTOR SYSTEM THEREFOR WITH REMOVAL OF HEAVY MOLECULAR WEIGHT OLIGOMERS

Descπption

The present invention relates to a method for ohgomenzation of ethylene to form linear alpha- olefins in an ohgomenzation reactor m the presence of solvent and catalyst, wherein a reaction product contaimng heavy molecular weight oligomers (HMWO) is discharged from the ohgomenzation reactor and is passed to and filtrated in a filtration unit, and to a reactor system therefore

Methods for ohgomenzation of ethylene are widely known in the art For example, DE 43 38 414 Cl discloses a process for the preparation of linear alpha-olefins by ohgomenzation of ethylene, wherein ohgomenzation takes place m the presence of an organic solvent and a homogenous liquid catalyst Usually, a catalyst is utilized m that process comprising a zirconium component and an organoalummum component which acts as a cocatalyst From the ohgomenzation reactor gaseous and liquid reaction products are discharged and further processed The liquid reaction product may, amongst solvent, catalyst, dissolved ethylene and liquid linear alpha-olefins, also compnse heavy linear alpha-olefins havmg more than 20 carbon atoms which are more or less solid These undesired by-product have to be removed from the liquid reaction product pnor to further processing thereof Usually, the solid heavy molecular weight oligomers are separated from the liquid reaction product by filtration in a filtration unit The filtration residue of HMWO has to be removed from the filtration unit, i e a specific amount of HMWO shall be removed per unit of time According to the prior art, this amount has been so far removed continuously via a small valve having a very small opening and employing a high differential pressure

Such small valve openings have, however, a high tendency for plugging and result in significant maintenance efforts and reduced availability of the reactor system

It is an object of the present invention to provide a method for ohgomeπsation of ethylene which overcomes the drawbacks of the pnor art Especially plugging of the discharge valve of

the filtration unit for separating the heavy molecular weight oligomers from the liquid reaction product shall be avoided to reduce maintenance efforts and increase reactor availability Additionally, it is an object to provide a reactor system which may be utilized m the inventive method.

The first object is achieved in that the filtration residue of HMWO is removed from the filtration unit discontmuously via a discharge valve

Preferably, opening and closing of the discharge valve is controlled by a timer, preferably periodically

In one embodiment the discharge valve has a diameter of about 1 to 2 men, preferably 1 inch, each with full-size internals

Preferably, arestπction oπfice is installed downstreams of the discharge valve.

The differential pressure between both sides of the discharge valve is adjusted at a certain level at about 1 to 20 bar, preferably 1 to 5 bar, more preferably 1 to 2 bar.

Preferably, heavy molecular weight oligomers (HMWO) are oligomers of ethylene with a carbon number of C20+.

The object is also achieved by a reactor system for oligomeπzation of ethylene to form linear alpha-olefins, preferably utilizing an inventive method, comprising a reactor and a filtration unit to remove heavy molecular weight oligomers from reaction product, the filtration unit comprising a discharge valve which is openable and closeable discontinuously.

Surprisingly, it was found that utilizing the inventive method a specific amount of heavy molecular weight oligomers per unit of time may be emptied from the filtration unit which is identical to the amount being so far removed continuously by prior art methods. However, in

contrast to the prior art, the filtration residue of HMWO is now removed discontmuously via a much larger discharge valve with a larger opening, the opening and closing thereof is preferably controlled by a timer, more preferably periodically The filtration residue is removed discontmuously, the differential pressure between both sides of the discharge valve may be reduced and controlled at a certain level, also allowing enlargement of the valve diameter and / or valve opemng Thus, plugging of the discharge valve may be successfully excluded, maintenance efforts may be reduced and reactor availability may be increased

Additional features and advantages of the inventive method are further illustrated with reference to the accompanying drawing, wherein figure 1 illustrates a filtration unit which may be utilized in the inventive method

Figure 1 illustrates a filtration unit 1 which may be utilized in a reactor system for the ob- gomerization of ethylene From an ohgomeπzation reactor (not shown) a liquid reaction product comprising solvent, dissolved monomers, catalyst, cocatalyst and liquid linear alpha- olefins as well as a solid heavy molecular weight olefins (HMWO) is transferred to the filtration unit 1 via line 2 Via line 3 the liquid components (solvent, dissolved monomer, catalyst, cocatalyst and liquid linear alpha-olefms) are removed and can be passed to a further processing unit (not shown) From the filtration unit 1 the filtration residue of HMWO has to be removed Especially, a specific and constant amount per unit of time shall be removed Removal of the filtration residue is accomplished in a discontinuous manner by opening and closing a discharge valve 4 opemng and closing thereof is controlled by a timer 5 The timer 5 may be m communication with a pressure control device 6 The discharge valve 4 is opened discontmuously, the differential pressure between both sides of the discharge valve 4 may be significantly reduced and controlled, also allowing an enlarged valve diameter and / or valve opening. Since the valve diameter and / or valve opening is enlarged, plugging thereof can be successfully excluded

The features disclosed in the foregoing description, m the claims and in the drawing may, both separately and in any combination thereof, be material for realizing the invention in diverse forms thereof