KR100527015B1 - Improved Process for the Preparation of Linear Alpha-olefins - Google Patents

Abstract

It is an object of the present invention to increase the ethylene oligomer purity in an oligomerization process catalyzed by a transition metal catalyst system dissolved in a polar organic solvent. In one embodiment, water is added to the polar organic solvent in an amount of 1 to 10% by weight of the solvent. In another embodiment, the polar solvent contains 2 to 5 weight percent water. In another embodiment, the transition metal catalyst system comprises a transition metal compound, an organophosphorus sulfonate ligand, and optionally (but quite preferably) a catalyst activator. In another embodiment, the polar organic solvent is sulfolane.

Description

Improved Method of Making Linear Alpha-olefins

Linear olefins are one of the most useful hydrocarbons used as raw materials in the petrochemical industry, of which linear alpha-olefin-unbranched olefins whose double bonds are placed at the chain ends constitute an important subclass. Linear alpha-olefins can be converted to linear primary alcohols by hydroformylation (oxo synthesis); Alcohols with less than 11 carbon atoms are used for plasticizer synthesis, while alcohols with more than 11 carbon atoms are used for detergent synthesis. Hydroformylation can also be used to prepare aldehydes as main products, which can also be oxidized to provide synthetic fatty acids, particularly synthetic fatty acids having an odd carbon number, which are useful in lubricant production. Linear alpha-olefins are also used in the most important class of detergents for household use, namely linear alkylbenzenesulfonates, which are prepared by reacting benzene with Friedel-Crafts and then sulfonating it.

Another important use of alpha-olefins is radical hydrobromination for obtaining primary bromoalkanes, which are important intermediates in the preparation of thiols, amines, amine oxides and ammonium compounds. Direct sulfonation of the alpha-olefins affords a mixture of alpha-olefin sulfonates, isomer alkensulfonic acids and alkanesulfones, which are effective detergents in hard water and even at low concentrations. Linear alpha-olefins, in particular linear alpha-olefins having 8 or less carbon atoms, are also used as comonomers in the production of high density polyethylene and low density linear polyethylene.

Although linear olefins are the hydrogen removal products of linear alkanes, the main part of such products is internal olefins. The preparation of alpha-olefins is mainly based on ethylene oligomerization and as a result, the carbon number of the prepared alpha-olefins is even. Ethylene oligomerization methods are mainly based on organoaluminum compounds or transition metals as catalysts. For example, using triethylaluminum as the catalytic amount, ethylene oligomerization proceeds under 200 ° C. to obtain an alpha-olefin mixture whose carbon number conforms to the Schulz-Flory distribution. Branched alpha-olefins in the C _6-10 range are present at less than 4%, but the degree of branching increases by about 8% when the chain length extends to 18. Although the conversion of ethylene to alpha-olefins is higher and the distribution is more controlled by a so-called modified method called ethyl method, the quality of the product is dramatically reduced, especially in the branched olefin content. For example, only about 76% of the products in the C _14-16 range represent linear alpha-olefins.

An advantage notable in the art is the use of transition metals as catalysts for ethylene oligomerization. For example, the process using nickel, cobalt, titanium or zirconium catalysts actually provided 100% monoolefins of more than 95% as alpha-olefins, 3% or less as branched olefins and 3% or less as internal olefins. . Since the catalyst is insoluble in hydrocarbons, oligomerization by the catalyst system based on transition metals is typically carried out in polar solvents to dissolve the catalyst. Ethylene and its oligomers have limited solubility in the polar solvents used. Thus, this type of oligomerization process involves three phase systems: a polar solvent liquid phase containing the catalyst, a second hydrocarbon liquid phase (comprising the prepared oligomer) which is incompatible with the polar liquid phase, and ethylene in the gas phase. Such a system allows for a continuous oligomerization process because ethylene can be introduced into the polar phase and the oligomerization product can be recovered as a hydrocarbon phase.

Ethylene oligomerization provides alpha-olefins having a Schulz-Florie distribution that is catalyst dependent and at least to a lesser extent temperature dependent for catalysts, which is an important object of the present application. Catalyst types with transition metal components of particular interest when used in oligomerization catalysts are described in US-A-4,689,437, US-A-4,716,138 and US-A-4,822,915. See also US-A-4,668,823. Such catalysts are used under conditions of the Schulz-Florie distribution constant of 0.55 to 0.65 to obtain oligomerization products whose C _6-16 alpha-olefin distribution is particularly preferred from an economic point of view. The oligomerization under such conditions also produces about 10% oligomers having 20 or more carbon atoms (C20 +), which are waxy solids at ambient temperatures with limited solubility in the hydrocarbon phase of the oligomerization process described above, and also waxy solids. There is a tendency to separate as water and block the secondary reactor. A solution to the above annoying problem is described in US-A-5,523,508.

Linear alpha-olefin formation by ethylene oligomerization as catalyzed by transition metal salts such as Ni (II) includes the Schultz-Flori distribution constant (α) as its most significant commercial variable. The distribution of oligomers formed for this purpose is determined. Since the necessary oligomer distribution changes from market to market, it is clear that demand in the market will determine α of the most economical oligomerization method. The Schultz-Florie distribution constants vary depending on the ligand used, but the method of varying the ligand to change α is quite promising because only a limited number of ligands are commercially viable due to their usefulness, cost, and purity of the ligand itself. This is possible. The Schultz-Florie distribution constant also varies slightly with temperature, but the temperature dependence of α is usually quite small. Thus, the variables that can be used to control α are quite limited under the commercial background and there is a need to introduce additional control means into the oligomerization method.

The oligomeric olefins formed in the linear alpha-olefin process are mainly terminal olefins, but significant amounts of branched olefins and internal olefins are also formed as undesirable by-products that degrade the value of the product. Linear alpha-olefins are used in the preparation of detergents by obtaining linear alkylbenzenesulfonates by direct sulfonation with alkylsulfonates or by sulfonation following alkylation of aromatics. In either case, the linearity of the alkyl chains is crucial for biodegradability. For example, when oligomers are used to form polyethylene, the presence of internal oligomers leads to reactivity problems with respect to polyethylene formation; The presence of branched or internal olefins also leads to undesirable subtle differences in the properties of the resulting polyethylenes. Thus, the method of minimizing the internal and branched olefins formed through ethylene oligomerization is preferentially chosen in any method.

Thus, we surprisingly found that when oligomerizing ethylene in a process using a transition metal compound as catalyst in sulfolane as a solvent, the presence of water affects this process in several ways that could be used to improve the production of linear alpha-olefins. I found out. The findings of the inventors were not predictable because, in the prior art, the presence of water was disadvantageous and it was necessary to work with dry sulfolane as possible. The inventors' findings are also surprising because such effects were not previously known. The inventors have observed that the concentration of water in the sulfolane solvent increases the purity of the olefinic oligomers, providing a greater amount of alpha-olefins, clearly, with fairly desirable results while lowering the internal and branched olefins. It has also been found that the concentration of water present affects the Schultz-Florie distribution so that, if necessary, if the temperature increment shifts α , the shift could be hindered by increasing the water concentration. Therefore, the concentration of water in the polar organic solvent acted as a means of controlling the ethylene oligomerization method. The above findings are significant because the number and nature of the methods of controlling the above methods are limited.

The inventors also observed that the method of increasing the water concentration has an adverse effect on oligomer productivity. However, in systems where the catalysts are transition metal salts and ligands, and when activators are also used in conjunction with the catalysts, the inventors believe that such productivity degradation can be offset, at least in part, by increasing the catalyst concentration or activator concentration. Incidentally discovered the facts. Thus, the overall effect of the method of adding water to the reaction system is advantageous.

It is an object of the present invention to increase the ethylene oligomer purity in an oligomerization process catalyzed by a transition metal catalyst system dissolved in a polar organic solvent. In one embodiment, water is added to the polar organic solvent in an amount of 1 to 10% by weight of the solvent. In another embodiment, the polar solvent contains 2 to 5 weight percent water. In another embodiment, the transition metal catalyst system comprises a transition metal compound, an organophosphorus sulfonate ligand, and optionally (but quite preferably) a catalyst activator. In another embodiment, the polar organic solvent is sulfolane.

The present invention is based on the discovery that the method of adding water to a polar organic liquid which functions as a solvent for the transition metal catalyst system in the ethylene oligomerization process provides a higher purity linear alpha-olefin oligomer than those formed in the absence of water. It has also been found that the water concentration in such polar organic solvents affects the Schultz-Flori distribution of olefinic oligomers resulting from ethylene oligomerization. Therefore, the water concentration in the polar organic liquid functioning as a solvent provides a control measure for the olefinic oligomer distribution. When water is added to the polar organic solvent, the productivity, i.e., the productivity per conversion of ethylene into the oligomeric olefin, decreases, but this decrease is offset by an increase in the concentration of the catalyst system and / or an increase in the concentration of the activator.

The process of the invention relates to ethylene oligomerization as catalyzed by a transition metal catalyst system. See, eg, Ullman's Encyclopedia of Industrial Chemistry, 5th Ed., V. A13, pp. 245, below, VCH (1989). Particularly preferred transition metal catalyst systems are those described in US Pat. No. 4,689,437, which is incorporated herein in its entirety. In the transition metal catalyst systems described there are reaction products of three components: transition metal compounds, catalyst activators and organophosphorus sulfonate ligands. Other transition metal catalyst systems are described, for example, in US-A-3,635,937, US-A-3,637,636, US-A-3,644,563, US-A-3,644,564, US-A-3,647,915, US-A-3,661,803 and US-A-3,686,159 Is described. Since transition metal catalyst systems for ethylene oligomerization are well known in the art, these need not be discussed further herein.

Typical catalyst concentrations are 10 to 1,000 ppm by weight of transition metal in solvent. Some of the more active catalysts provide significantly higher reaction rates at 40 ppm, with a wider range of catalyst concentrations of 0.1 to 1,000 ppm. In a preferred embodiment of the present invention, the catalyst concentration is 15 to 300 ppm by weight. We prefer a method using the catalyst system described in US-A-4,689,437, which is the reaction product of a transition metal compound, a catalyst activator and an organophosphorus ligand. Nickel is the preferred transition metal and we have found that borohydrides, such as sodium borohydride, are particularly preferred activators. However, the inventors generally believe that the present invention can be applied to ethylene oligomerization by transition metal catalyst systems. Since they are widely described in the prior art, they need not be discussed in detail herein.

Ethylene oligomerization is a liquid phase reaction and the catalyst can be dissolved in a solvent or suspended in a liquid medium. In a variant of particular interest herein, the catalyst is dissolved in a solvent which is a polar organic liquid. Solvents need to be inactivated to advance the components and apparatus under process conditions. Examples of polar organic liquids suitable as solvents, which are intended to be representative but not limited to, include sulfolane (tetramethylenesulfone), ethylene glycol, 1,4-butanediol and ethylene carbonate, as well as mixtures thereof. . In order to obtain a polar solvent phase and a hydrocarbon phase in the variants discussed herein, solvents that allow easy phase separation from the oligomeric product are preferred. The most preferred polar organic liquid as the solvent for ethylene oligomerization is sulfolane, wherein the catalyst of the invention is quite soluble but the oligomer is insoluble.

Oligomerization conditions include temperatures of 5 to 200 ° C., with 20 to 140 ° C. being preferred and 40 to 100 ° C. even more preferred. The method can be carried out at a pressure of 101.3 kPa to 34.6 mPa (atmospheric pressure up to about 5,000 psig), but the preferred pressure is 2.86 to 13.89 mPa (400 to 2,000 psig). These pressures are the pressure at which ethylene is introduced into the reactor and the pressure at which the reactor is maintained. When ethylene is oligomerized at a temperature of 40 to 100 ° C. using the catalyst of the invention, the optimum water concentration in the polar organic solvent is 1 to 6% by weight.

The oligomerization method is a predominantly linear alpha-olefin having more than 4 to 20 carbon atoms, and particularly forms oligomers with low solubility in polar solvents used when sulfolane is the transition metal catalyst solvent of the present invention. Thus, oligomer formation is carried out by the formation of separate hydrocarbon phases whose constituents are ethylene oligomers having a relative proportion closely following the Schultz-Florie distribution. Practices prior to the present invention included a method of maintaining the water concentration in the polar organic liquid solvent as low as possible, preferably as close as ppm, but reliably below one tenth of 1% of water. The present invention is in contrast to the prior art practice and is in fact polar as a solvent containing 1 to 10% by weight or less of water, more preferably 2 to 5% by weight or less of water and most preferably 3 to 4% by weight of water. Construct a method of using organic liquids. The inventors have found that sulfolanes containing these amounts of water are particularly preferred and preferred variants. When ethylene is oligomerized at 40 to 100 ° C. using the catalyst of the invention, the optimum water concentration is 1 to 6% by weight or less.

<Example>

<Example 1>

Effect of Water on Linear Alpha-olefin Purity

The continuous phase reactor system consisted of a stirred autoclave containing a solution of sulfolane and catalyst, and a separator. Ethylene was fed into the reactor at a rate of 160 g / hr at 10.44 mPa (1,500 psig). A mixture of sulfolane solution, oligomeric product and unreacted ethylene was passed from the reactor through a second tube to the separator; The sulfolane solution of the catalyst was recycled to the reactor and the product / ethylene mixture was withdrawn.

The catalyst solution was prepared by adding 1 mole portion of sodium salt of 2-diphenylphosphino-1-naphthalene sulfonic acid and 2 parts nickel tetrafluoroborate in sulfolane at a total nickel concentration of 25 ppm Ni. An activator solution of NaBH ₄ was then added in a ratio of 1 part borohydride to 4 parts nickel. Additional ligands, nickel salts and activators were added in anhydrous sulfolane at a ratio of 2: 4: 1 per mole to give an ethylene conversion of 10 to 50% by weight. The reaction was carried out at 60 ° C.

2 parts of nickel tetrafluoroborate and 1 mole of sodium salt of 2-diphenylphosphino-1-naphthalene sulfonic acid in a solution of 1% by weight of water in sulfolane together with a solution of an activator of NaBH _{4 in} 1 part in anhydrous sulfolane A similar reaction was carried out except that the catalyst solution was prepared by addition in ppm total nickel concentration. Ligands, nickel salts and activators were added at a molar ratio of 1: 2: 1 in sulfolane containing 1% by weight of water to bring the ethylene conversion to 10-50% by weight.

The purity of the linear alpha-olefins formed by oligomerization was evaluated by careful analysis of the C ₁₀ olefin fraction. The decene fraction without water was 95.05 wt.% Decene-1; The decene fraction in the presence of about 1.0% by weight of water in sulfolane was 95.99% by weight of decene-1. The main impurities are in the table below.

TABLE 1

These results clearly show the effect of water on the olefin purity. This is confirmed by the following data using similar catalyst systems at the 3.5 wt% level of water. The continuous phase reactor system consisted of a stirred autoclave containing a solution of sulfolane and catalyst, and a separator. Ethylene was fed to the reactor at a rate of 405 g / hr at 10.44 mPa (1,500 psig). The temperature of the reactor was maintained at about 93 ° C. A mixture of sulfolane solution, oligomeric product and unreacted ethylene was passed from the reactor through a second tube to a heated separator; The sulfolane solution of the catalyst was recycled to the reactor and the product / ethylene mixture was withdrawn. LAO product and ethylene were separated in series and unreacted ethylene was recycled to the reactor.

The catalyst solution is about 25 ppm with 2 parts of nickel tosylate and 1 mole of sodium salt of 2-butylphenylphosphino-4-methylbenzene sulfonic acid in a sulfolane solution containing 3.5% by weight of water together with a solution of activator of NaBH ₄ 3 parts. Prepared by adding to the total nickel concentration. Additional ligands, nickel salts and activators were added in a sulfolane containing 3.5% by weight of water at a ratio of 1: 2: 3 molar so that the ethylene conversion was between 10 and 50% by weight. The results are summarized in Table 2.

TABLE 2

Thus there is a much greater advantage of using water at 3.5% by weight.

While clearly showing the effect of the added water advantageous on alpha-olefin purity, a series of experiments were performed to determine the effect of various water contents on ethylene conversion, its maximum conversion and Schultz-Flori distribution constants.

<Examples 2 to 5>

Effect of various water concentrations

The same simulated plant as described in Example 1 (no addition of water) was performed at 95 ° C. Ethylene was fed into the reactor at a rate of 160 g / hr at 10.44 mPa (1,500 psig). The catalyst solution was added to a total concentration of about 15 ppm of nickel tosylate in sulfolane solution and 1 mole of sodium salt of 2-butylphenylphosphino-4-methylbenzene sulfonic acid together with NaBH ₄ 3 parts activator solution. Prepared. The catalyst was added immediately after adding the amount of water that could vary from 0.7 to 5% by weight to sulfolane. The catalyst components were combined over about 1 hour. The reaction proceeded without adding additional catalyst until the reaction rate was reduced to negligible levels. Ethylene conversion was monitored as a function of time after completion of catalyst addition. The purity and α value of the product were also monitored as a function of time. Productivity was calculated by taking the ratio of total LAO product prepared during the run and total ligand added at the start of the run.

TABLE 3

The data indicate that water typically lowers ethylene conversion. As summarized in Table 4, in this case of 4 hours on the stream, a similar conclusion can be reached by comparing the ethylene conversion at a constant reaction time.

TABLE 4

Note that there appears to be little additional adverse water effect on ethylene conversion at water levels above about 2% by weight.

Table 5 shows the productivity (as defined above) at different water levels.

TABLE 5

Once again, there appears to be little adverse effect on productivity at water levels above about 2% by weight.

Table 6 shows the effect of increased water concentration on the Schultz-Florie distribution.

TABLE 6

In contrast to the effect of water on maximum ethylene conversion and productivity, the Schulz-Florie distribution constant appears to decrease over the full range of water concentrations used.

According to the invention, it has been observed that the ethylene oligomer purity is increased in the ethylene oligomerization process catalyzed by a transition metal catalyst system dissolved in a polar organic solvent containing water in a solvent amount of 1 to 10% by weight.

Claims (4)

a. Introducing ethylene into a polar phase comprising as an essential component a solution of a transition metal catalyst system in a polar organic liquid liquid containing 1 to 10% by weight of water, wherein the transition metal catalyst system is a transition metal compound, an organophosphorus sulfo Nate ligand and optionally a catalyst amplifying agent, the polar organic liquid is sulfolane); b. Oligomerizing ethylene in the polar aqueous phase to obtain an oligomer that forms a hydrocarbon phase separate from the polar phase, comprising linear alpha-olefins as an essential component; And c. Continuously recovering the hydrocarbon phase A process for the continuous oligomerization of ethylene to form linear alpha-olefins using a transition metal catalyst system, comprising: The method of claim 1, wherein the polar organic liquid contains 2 to 5 weight percent water. The method of claim 1, wherein the polar organic liquid contains about 3 to about 4 weight percent water. The process of claim 1, wherein ethylene is introduced at an oligomerization temperature of 40 to 100 ° C. 5.