1. Technical Field
The present invention relates to a method of upgrading low-value linear alpha olefins (LAOS) of C18 or more. More particularly, the present invention relates to a method of manufacturing high-quality lube base oil by converting a low-value LAO having a C18 or more hydrocarbon chain into a linear internal-olefin (LIO) having a controlled double bond position distribution, which then undergoes oligomerization.
2. Description of the Related Art
Ethylene is a raw material used in the chemical industry to the extent that the production and consumption thereof are considered as indicators of the chemical industry scale of a country. Typically, ethylene is employed as a monomer for preparing a polymer such as polyethylene. In some cases, LAOs having a C4-C40 carbon length (or chain) are prepared by adjusting the degree of polymerization of ethylene, and thus utilized to manufacture a variety of chemicals. In this regard, as used herein, the term “full range LAO” refers to a C4-C40 LAO mixture resulting from ethylene polymerization or oligomerization.
The reason why LAO production techniques are important is that LAO is a chemical without sulfur and nitrogen derived from crude oil. Generally, since crude oil contains impurities such as sulfur and nitrogen components in amounts of ones of wt %, it is difficult to directly prepare chemicals composed of pure hydrocarbons without such impurities. However, ethylene resulting from catalytic cracking of crude oil is converted into LAO, which is then converted again into a desired chemical, thereby obtaining chemicals composed of pure hydrocarbons without impurities.
Ethylene polymerization is mainly carried out using a batch reactor under air-sensitive conditions in the presence of a metallocene catalyst. Since a metallocene catalyst has a very strong single acid site, ethylene is selectively polymerized at the single acid site of the catalyst, and is thus linearly grown at the acid site of the catalyst. Ultimately, the olefin produced by the LAO preparation reaction possesses a linear alpha-olefin structure having an even number of carbon atoms because of the use of an ethylene monomer.
When operating conditions for the LAO preparation reaction are controlled, the LAO composition distribution may be altered. For example, when the reaction temperature or the polymerization time is increased, the proportion of LAO having a relatively high molecular weight may become high. In contrast, when the reaction temperature or the polymerization time is decreased, the proportion of LAO having a relatively low molecular weight may increase. Taking into consideration the industry scale for LAO-derived chemicals by LAO manufacturers, the LAO composition is changed in such a manner that the reaction conditions are appropriately controlled, thereby ensuring optimal profitability for individual projects.
Alpha-olefins produced by the LAO preparation processes exhibit properties varying depending on the number of carbon atoms thereof, and the properties of the resulting chemicals may become different depending on the type of LAO feed. For example, C4 LAOs obtained by polymerizing two ethylene monomers are present in a gas phase, and polymers resulting from the polymerization thereof have an excess of intramolecular branches, making it difficult to apply to a specific product, for example, lube base oil. Also, even when C6 LAOs obtained by polymerizing three ethylene monomers are converted into polymers, such polymers are unlikely to be applied to lube base oil and so on due to many intramolecular branches thereof. As such, copolymerization of ethylene with a C6 LAO may result in an ethylene-1-hexene copolymer having properties different from those of conventional polyethylene. Also, C8 LAOs obtained by polymerizing four ethylene monomers may be applied to Group IV lube base oil via polymerization, and may be used to produce a copolymer with ethylene, as in the C6 LAOs. Also, C10-C12 LAOs are polymerized and thus mainly used as Group IV base oil, and C14-C16 LAOs are reacted with amine or succinic acid, so that the resulting products may be applied to various functional chemicals, or mixed and thus used for cheap drilling oil.
The aforementioned LAOs have certain end-uses, and the markets adapted for the demand thereof are established. Furthermore, the related techniques have been already developed to some extent. The most expensive LAO is a C8-C12 LAO for preparing high-quality lube base oil (e.g. Group IV lube base oil), and C6 and C8 LAOs may be mainly utilized because the demand thereof is high for producing copolymers. Also, although C14-C16 LAOs are relatively less used due to limited end-uses thereof compared to the C6-C12 LAOS, C14-C16 LAOs may be used to prepare specialty chemicals and may thus be formed into products by increasing purity thereof. However, C18 or more LAOs are problematic because the end-uses thereof are limited, and the purity thereof has to be increased to obtain desired products. In this regard, C18 or more LAOs have been employed as an additive for lube oil or in wax form, but are not general-purpose chemical products, and thus the demand thereof is undesirably low. Also, C20 or more LAOs are limited in serving as feeds because they exist as a solid at room temperature. Like this, the market prices of C18 or more LAOs are maintained very low compared to the other LAOS, on account of low demands, tendencies to exist as a solid, and restrictions where such feeds may be prepared into products only when the purity thereof is increased.
Owing to the limitations of end-uses as above, the yield of high-value C8-C12 LAOs is intended to be selectively increased while decreasing the yield of C18 or more LAOs, by LAO manufacturers. However, the LAO products have a composition of the normal distribution due to characteristics of the polymerization catalyst, making it impossible to attain operating conditions for preparing only C8-C12 LAOs and for drastically lowering the yield of C18 or more LAOS.
Hence, LAO preparation under reaction conditions able to lower the yield of C18 or more LAOs as much possible is chosen by LAO manufacturers, and is advantageous because only LAOS, the demand of which is high and the value of which is also high, may be selectively prepared while decreasing the yield of C18 or more LAOs regarded as byproducts. However, since the composition of products resulting from ethylene polymerization has the normal distribution as mentioned above, the yield of C8-C12 LAOS, corresponding to feeds for end-uses (especially Group IV lube base oil) which have the highest price and a future market of which is expected to grow, is relatively low, which is undesirable.
Alternatively, the reaction conditions may be set so as to maximize the yield of the most expensive C8-C12 LAOs without taking into account the yield of C18 or more LAOS. As such, the yield of C18 or more LAOs is 10 wt % or more, but the yield of relatively high-value C8-C12 LAOs may be increased. Therefore, if C18 or more LAOs obtained by full range LAO techniques can be simply converted into general-purpose high-value products, the effect of such technology is expected to be very significant. Accordingly, methods of converting C18 or more LAOs into high-value chemicals are required.
Meanwhile, techniques for preparing chemicals (e.g. drilling oil) having improved properties in such a manner that a double bond present at the alpha position of the LAO is shifted to the inside of the carbon chain to form a linear internal-olefin (LIO) (olefin shift reaction) are also known (e.g. U.S. Pat. No. 6,281,404). However, the above techniques are not regarded as the application of low-value C18 or more LAOs because a wide range of C4-C50 LAOs are utilized, and also because the double bond shift reaction for 1-pentene is mainly disclosed. In addition, there are known techniques for manufacturing lube base oil (e.g. EP 0 136 377 B1) by oligomerizing internal olefins (especially, internal olefin produced from dehydrogenation of paraffin so that a double bond is randomly distributed in the molecule) in the presence of a boron trifluoride catalyst and a promoter, and for manufacturing lube base oil (Japanese Patent Application Publication NO. 1993-306241) by oligomerizing a C10-C24 LAO/LIO mixture. However, these techniques are limited in improving properties of the lube base oil because the position of the double bond in the olefin is not controlled. In particular, such techniques are unlikely to become technology for increasing the value of low-value C18 or more LAOS produced inevitably as byproducts in full range LAO preparation.