Background Art Generally, polyalphaolefins have excellent fluidity in the wide range of temperature due to their high viscosity index and low-temperature fluidity, as well as narrow molecular weight distribution resulting in a low loss on heating, and high stability for long-term use, and are useful as a base stock for automotive or industrial oils.

As such, many studies have been made on the preparation of polyalphaolefins with the industrial development.

References of interest are: U. S. Patent No. 4,532,061 describes a method for preparing high-viscosity polyalphaolefins that comprises providing (a) an aluminum compound having the formula R3AI2X3 or R,, AIX3. n, wherein R is C)-C, 8 alkyi, Cy-Cg arylalkyi, Cy-C9 alkaryl or C6-Cio aryl; X is Cl, Br or I ; and n is an integer from 1 to 3, and (b) a polyhalogenated hydrocarbon catalyst having the formula (--CH2CR'RZ)", Yp, wherein R'is hydrogen or Cl-C3 alkyl ; R2 is linear or branched Cl-C30 alkyl ; Y is Cl, Br or I ; m is an integer from 3 to 3000 ; and p is an integer of at least 3 ; diluting above (a) and (b) with an alphaolefin having at least three carbon atoms ; and bringing into contact the diluted (a) and (b) by mixing at a temperature of 0 to 60 °C.

U. S. Patent 4, 469,910 also discloses a method for preparing high-viscosity polyalphaolefins that comprises diluting an alkyl aluminum and an alkylhalide catalyst having at least one halogen group with an alphaolefin having at least three carbon atoms,

and bringing into contact the diluted alkyl aluminum and alkylhalide catalyst by mixing at a temperature of 422 °C.

U. S. Patent 4,594,469 describes a method for preparing high-viscosity polyalphaolefins having a kinetic viscosity of at least 300 cSt at 40 °C that comprises bringing an alphaolefin having at least three carbon atoms into contact with a catalyst composition composed of an alkyl aluminum bromide or iodine compound and a cocatalyst (selected from the group consisting of iodoalkyl and bromoalkyl).

The above-described methods use various catalysts and one alphaolefin, especially 1-decene, which is expensive and hardly available due to increasing demand, in the preparation of polyalphaolefins. To overcome this problem, many attempts have been tried to prepare polyalphaolefins from 1-hexene or 1-octene that is less expensive than 1-decene. However, the polyalphaolefins prepared from 1-hexene or 1-octene have lower viscosity index, which is a measure of stability, than those from 1-decene.

More specifically, the polyalphaolefins obtained from 1-decene typically have a viscosity index of about 140, but those from 1-octene have a lower viscosity index in the range from 125 to 130.

Disclosure of Invention Thus the inventors have studied on the method for preparing polyalphaolefins from a much smaller amount of 1-decene to have almost the same viscosity index as those prepared from 1-decene, and contrived the present invention based on the fact that preparation of polyalphaolefins having a kinetic viscosity of at least 90 cSt at 40 °C and a viscosity index of at least 135 involves prepolymerizing a small amount of 1-decene using a catalyst system composed of ethyl aluminum dichloride (EADC) and t-butyl chloride (TBC) and bringing the prepolymerization product into contact with 1-octane, less expensive and more available than 1-decene, under conditions of high temperature and high pressure.

It is therefore an object of the present invention to provide a method for preparing high-viscosity polyalphaolefins having a viscosity index by far greater than that of the prior art polyalphaolefins obtained from 1-octene and at least equal to that of the prior art polyalphaolefins from 1-decene.

To achieve the object of the present invention, provided is a method for preparing a polyalphaolefin including: prepolymerizing a small amount of 1-decene or 1-dodecene using a catalyst composed of ethyl aluminum dichloride (EADC) and t-butyl chloride (TBC) to obtain a prepolymer; and bringing 1-octene into contact with the prepolymer used as a catalyst to obtain a polyalphaolefin having a viscosity index of at least 135.

Hereinafter, the present invention will be described in more detail as follows.

Normal polyalphaolefins are useful as automobile lubricants or industrial oils, but those prepared according to the present invention method have a high viscosity (for example, kinetic viscosity of at least 90 cSt at 40 °C and viscosity index of at least 135) and are very useful as industrial oils.

More specifically, in the method for preparing a polyalphaolefin according to the present invention, a catalyst system composed of EADC and TBC is used in the prepolymerization reaction of 1-decene or 1-dodecene.

The prepolymer thus obtained is used as a catalyst and brought into contact with 1-octene to produce a high-viscosity polyalphaolefin according to the present invention.

Preferably, the mole ratio of 1-octene to 1-decene or 1-dodecene is in the range from 10 to 50. If the mole ratio is less than 10, the method is inefficient in the economical aspect due to the excess of I-decene or 1-dodecene. Otherwise, if the mole ratio is greater than 50, the added amount of 1-decene or 1-dodecene is too small to provide increased viscosity index.

The reaction conditions, i. e., temperature and pressure during the reaction of the prepolymer and 1-octene are desirably defined as room temperature (i. e., in the range of 20 to 40 °C) and atmospheric pressure (i. e., about 760 mmHg).

If the reaction temperature is lower than 20 °C, energy consumption is required to cool the stock material. Otherwise, if the reaction temperature is higher than 40 °C, the stock material has to be heated.

Best Mode for Carrying out the Invention Hereinafter, the present invention will be described in further detail by way of the following examples, which are not intended to limit the scope of the present invention.

Example 1

300 ml of 1-octane was added to a 1L reactor, which is equipped with a stirrer, a cooling coil and a thermometer and kept under the nitrogen atmosphere at 30 °C.

In addition, 1-decene was separately added to 5.4 ml of 3.4M ethyl aluminum dichloride (EADC) and 2.1 ml of 8. 99M t-butyl chloride (TBC) to have the total volume of 21 ml and a mole ratio of EADC to TBC being 1: 1. The mixture was then charged in an injector. Here, the mole ratio of 1-octene to 1-decene was 10: 1.

A 500ml four-necked flask equipped with a stirrer, a condenser having a cooling coil, and a thermometer was kept under the nitrogen atmosphere at 30 °C. The mixture of EADC and TBC diluted with 1-decene was injected into the flask using a microinjector with stirring for 5 minutes, and stirred for more 5 minutes to obtain a prepolymer. The prepolymer was then immediately added to the injector.

Subsequently, the prepolymer was added to the 1L reactor containing 1-octene using a microinjector for 20 minutes. After the completion of injection and 30 minutes of stirring, the catalyst residue was removed with 200 ml of 0. 1M NaOH. The product removed of the residue was vacuum distilled at 180 °C under 1 torr to remove products having a low boiling point and monomers unturned, followed by filtering out the distillation residue to obtain the final product (77. 3 wt% yield).

The polyalphaolefin thus obtained was then measured in regard to kinetic viscosity and viscosity index according to the regulations of the KSM 2014. The measurement results are presented in Table 1.

Example 2 The procedures as described in Example 1 were performed to cause the prepolymerization reaction and prepare a reactor. The subsequent procedures were performed in the same manner as described in Example 1, excepting that the prepolymer obtained was added to the 1L reactor with a microinjector for 10 minutes in order to obtain a polyalphaolefin having a lower kinetic viscosity (76.8 wt. % yield) through removal of catalyst residue, distillation and filtration.

The polyalphaolefin thus obtained was also measured in regard to kinetic viscosity and viscosity index as described in Example 1. The measurement results are presented in Table 1.

Example 3 300 ml of 1-octane was added to a 1L reactor in the same manner as described in Example 1. In addition, 1-decene was separately added to 5.4 ml of 3. 4M EADC and 2.1 ml of 8.99M TBC to have the total volume of 12.4 ml and a mole ratio of EADC to TBC being 1: 1. The mixture was then charged in an injector. Here, the mole ratio of 1-octene to 1-decene was 20: 1.

The subsequent procedures were performed in the same manner as described in Example 1, excepting that the prepolymer was added to the IL reactor with a microinjector for 20 minutes to obtain a polyalphaolefin (80.4 wt. % yield) through removal of catalyst residue, distillation and filtration.

The polyalphaolefin thus obtained was also measured in regard to kinetic viscosity and viscosity index as described in Example 1. The measurement results are presented in Table 1.

Example 4 The procedures were performed in the same manner as described in Example 1, excepting that the catalyst and 1-decene added to an injector were injected into the IL reactor for 5 minutes and, after 5 minutes, 300 ml of 1-octene was injected to the prepolymer using a microinjector with stirring for 20 minutes to obtain a polyalphaolefin (75.4 wt. % yield) through removal of catalyst residue, distillation and filtration.

The polyalphaolefin thus obtained was also measured in regard to kinetic viscosity and viscosity index as described in Example 1. The measurement results are presented in Table 1.

Example 5 In the same manner as described in Example 1,1-octane was added to a 1L reactor and 1-decene was separately added to 5.4 ml of 3. 4M EADC and 2.1 ml of 8.99M TBC to have the total volume of 20 I111 and a mole ratio of EADC to TBC being 1: 1. The mixture was then charged in an injector. Here, the mole ratio of 1-octene to 1-decene was 10: 1.

A 500ml four-necked flask equipped with a stirrer, a condenser having a cooling coil. and a thermometer was kept under the nitrogen atmosphere at 30 °C. The mixture of

EADC and TBC diluted with 1-decene was injected into the flask using a microinjector with stirring for 5 minutes, and stirred for more 5 minutes to obtain a prepolymer. The prepolymer was then immediately added to the injector. The subsequent procedures were performed in the same manner as described in Example 1 to obtain a polyalphaolefin (79.7 wt. % yield).

The polyalphaolefin thus obtained was also measured in regard to kinetic viscosity and viscosity index as described in Example 1. The measurement results are presented in Table 1.

Example 6 In the same manner as described in Example 1, 1-octane was added to a 1L reactor and 1-decene was separately added to 5.4 ml of 3. 4M EADC and 2.1 ml of 8. 99M TBC to have the total volume of 12.2 ml and a mole ratio of EADC to TBC being 1 : 1.

The mixture was then charged in an injector. Here, the mole ratio of 1-octene to 1-decene was 20: 1.

The subsequent procedures were performed in the same manner as described in Example 5 to obtain a polyalphaolefin (82.1 wt. % yield).

The polyalphaolefin thus obtained was also measured in regard to kinetic viscosity and viscosity index as described in Example 1. The measurement results are presented in Table 1.

Comparative Example 1 300 ml of 1-octane was added to a 1L reactor, which is equipped with a stirrer, a cooling coil and a thermometer and kept under the nitrogen atmosphere at 30 °C.

In addition, 1-octene was separately added to 5.4 ml of 3. 4M EADC and 2.1 ml of 8.99M TBC to have the total volume of 21 ml and a mole ratio of EADC to TBC being 1 : 1. The mixture was then charged in an injector.

The mixture of EADC and TBC diluted with 1-octene was injected into the IL reactor using a microinjector with stirring for 20 minutes. After the completion of injection and 30 minutes of stirring, the catalyst residue was removed with 200 ml of 0. 1M NaOH. The subsequent procedures were performed in the same manner as described in Example 1 to obtain a polyalphaolefin (80.4 wt. % yield) through removal of

catalyst residue, distillation and filtration.

The polyalphaolefin thus obtained was also measured in regard to kinetic viscosity and viscosity index as described in Example 1. The measurement results are presented in Table 1.

Comparative Example 2 300 ml of 1-octane and 34.4 ml of 1-decene were added to a 1L reactor, which is equipped with a stirrer, a cooling coil and a thermometer and kept under the nitrogen atmosphere at 30 °C. Here, the mole ratio of 1-octene to 1-decene was 10: 1.

The subsequent procedures were performed in the same manner as described in Comparative Example 1 to prepare the catalyst, inject it into the reactor for 20 minutes and obtain a polyalphaolefin (79.4 wt. % yield) through removal of catalyst residue, distillation and filtration.

The polyalphaolefin thus obtained was also measured in regard to kinetic viscosity and viscosity index as described in Example 1. The measurement results are presented in Table 1.

Comparative Example 3 300 ml of l-octane and 34.4 ml of 1-dodecene were added to a 1L reactor, which is equipped with a stirrer, a cooling coil and a thermometer and kept under the nitrogen atmosphere at 30 °C. Here, the mole ratio of 1-octene to 1-dodecene was 10: 1.

The subsequent procedures were performed in the same manner as described in Comparative Example 1 to prepare the catalyst, inject it into the reactor for 20 minutes and obtain a polyalphaolefin (81.1 wt. % yield) through removal of catalyst residue, distillation and filtration.

The polyalphaolefin thus obtained was also measured in regard to kinetic viscosity and viscosity index as described in Example 1. The measurement results are presented in Table 1.

Comparative Example 4 344 ml of 1-decene was added to a 1L reactor, which is equipped with a stirrer, a cooling coil and a thermometer and kept under the nitrogen atmosphere at 30 °C.

In addition, 1-octene was separately added to 5. 4 ml of 3. 4M EADC and 2.1 ml of

8.99M TBC to have the total volume of 21 ml and a mole ratio of EADC to TBC being 1 : 1. The mixture was then charged in an injector.

The mixture of EADC and TBC diluted with 1-octene was injected into the 1L reactor using a microinjector with stirring for 20 minutes. After more 30 minutes, the catalyst residue was removed with 200 ml of 0. 1 M NaOH. The subsequent procedures were performed in the same manner as described in Example 1 to obtain a polyalphaolefin (82.4 wt. % yield) through removal of catalyst residue, distillation and filtration.

The polyalphaolefin thus obtained was also measured in regard to kinetic viscosity and viscosity index as described in Example 1. The measurement results are presented in Table 1.

Table 1 Mole Ratio of 1-Prepolymerization Reaction Kinetic Viscosity Octene/1-Decene or Time (Min) Time Viscosity Index 1-Octene/I-Dodecene (Min) at 40 °C (cSt) 1 10 10 20 124.6 138 2 10 10 10 94. 7 138 A 3 20 20 108.4 136 4 10 5 20 101.5 135 5 10 10 20 128.4 141 6 20 20 114. 2 137 1 oc 0 20 77. 1 130 B'10 0 20 93. 5 132 3 10 0 20 97.5 134 40 0 20 103. 3 139 Note: A-Example B-Comparative Example As described above, the present invention involves prepolymerizing a small amount of 1-decene or l-dodecene using a catalyst system composed of EADC and TBC and bringing the prepolymerization product into contact with 1-octene. According to the present invention, the use of l-octene less expensive than 1-decene as a main stock material and a small amount of 1-decene or 1-dodecene makes it possible to produce a polyalphaolefin with high yield at room temperature and under atmospheric pressure,

wherein the polyalphaolefin thus obtained has a high kinetic viscosity index almost equal to that of the polyalphaolefin obtained from 1-decene as a monomer and much higher than that of the polyalphaolefin from 1-octene. The present invention also allows it to easily control the kinetic viscosity of the polyalphaolefin by regulating the polymerization reaction or the mole ratio of 1-octene to 1-decene or 1-dodecene.

Industrial Applicability So, the polyalphaolefins of the invention have excellent fluidity in the wide range of temperature due to their high viscosity index and low-temperature fluidity, as well as narrow molecular weight distribution resulting in a low loss on heating, and high stability for long-term use, and are useful as a base stock for automotive or industrial oils.