WO2008005975A2

WO2008005975A2 - Process for making an improved isomerization catalyst

Info

Publication number: WO2008005975A2
Application number: PCT/US2007/072721
Authority: WO
Inventors: David Stephen Brown
Original assignee: Shell Oil Company; Shell Internationale Research Maatschappij B.V.
Priority date: 2006-07-06
Filing date: 2007-07-03
Publication date: 2008-01-10
Also published as: WO2008005975A3

Abstract

The invention relates to an improved catalyst for use in a process of converting alpha olefins to internal olefins while minimizing skeletal isomerization as well as dimerization. The catalyst may be made by impregnating the solid acid silica-alumina catalyst with a nickel salt and then calcining it to produce the final catalyst. The catalyst may comprise from 1 to 20 %wt. of nickel, based upon the weight of contained nickel in the finished catalyst. The isomerized internal olefins may be prepared by isomerizing and olefinic composition comprising at least one alpha olefin in the presence of such a solid nickel supported acid silica-alumina catalyst.

Description

PROCESS FOR MAKING AN IMPROVED ISOMERIZATION CATALYST

Field of the Invention

The invention relates to process for making an improved isomerization catalyst and a process for isomerization using the improved catalyst. Background of the Invention

While alpha olefins have a wide variety of end uses, certain applications, such as paper sizing agents and drilling fluids, additionally require the use of internal olefins. Internal olefins may be produced from the double bond isomerization of alpha olefins. There are a number of catalysts known for the double bond isomerization of alpha olefins to internal olefins. Highly active catalysts are capable of reaching the thermodynamic isomerization limit, thereby giving internal olefins with an equilibrium distribution of double bond isomers. Internal olefins produced in this way are referred to as "fully isomerized." Generally, it is believed that the internal olefins should be fully isomerized in order for them to exhibit a low pour point, low residual alpha olefin content and minimal branching, characteristics which are thought to be important for drilling fluid applications.

Like drilling fluid compositions, paper sizing compositions have been reported to benefit from the incorporation of isomerized olefins. See, for instance, U.S. Patent No. 6,348,132 which describes an internal olefin wherein the double bonds are near the end of the chain, but not in the alpha position, which may be used to make a superior paper sizing composition compared to those made with fully isomerized products wherein the double bonds of the olefins are more equally distributed throughout the carbon chain. These "lightly isomerized" alpha olefins have lower residual alpha content which is desired for use in paper sizing compositions.

U.S. Published patent application No. 2005/0070747 describes a process for converting alpha olefins to internal olefins while minimizing skeletal isomerization as well as dimerization . This process increases the amount of "lightly isomerized" olefins in the isomerized mixture. In this process, an olefinic composition of Ci₆ and/or Ci₈ alpha olefins isomerizes to a mixture of isomers, wherein the amount of residual alpha olefin content in the isomerized olefin mixture is less than 10 weight percent. The isomerized olefin mixture is prepared by isomerizing Ci₆ and/or Ci₈ alpha olefins in the presence of a solid acid silica-alumina catalyst wherein the weight ratio of silica to alumina in the solid acid silica-alumina catalyst is preferably from about 45:55 to about 55:45. This catalyst is very useful in producing lightly isomerized internal olefins but suffers from the disadvantage that it catalyzes the undesirable skeletal isomerization and olefin dimerization reactions. It would be desirable to provide an improved catalyst which exhibits reduced activity for olefin dimerization and skeletal isomerization while exhibiting high activity for olefin double bond isomerization. Summary of the Invention The invention relates to an improved catalyst for use in a process of converting alpha olefins to internal olefins while minimizing skeletal isomerization as well as dimerization. The catalyst may be made by impregnating a solid acid silica-alumina catalyst with a nickel salt and then calcining it to produce the final catalyst. The catalyst may comprise from 1 to 20 %wt . of nickel, preferably from 5 to 10 %wt . , based upon the weight of contained nickel in the finished catalyst. The isomerization process comprises isomerizing an olefinic composition comprising at least one alpha olefin in the presence of a solid nickel supported acid silica-alumina catalyst wherein the weight ratio of silica to alumina in the solid acid silica-alumina catalyst is preferably from 45:55 to 55:45 to produce olefin (s) containing an internal unsaturated bond. Detailed Description of the Preferred Embodiments

An olefinic composition of alpha olefins may be double bond isomerized to olefin (s) containing internal unsaturated bonds by contacting the olefinic composition with a solid nickel acid silica-alumina catalyst made by first making a solid acid silica-alumina catalyst having a weight ratio of silica to alumina from 45:55 to 55:45, preferably about 50:50. Decreasing the amount of silica typically leads to a decrease in catalyst activity. The olefinic composition may be comprised of Ci₄_₂4 alpha olefins or mixtures thereof. The solid acid silica-alumina catalyst may then be impregnated with a nickel salt. In one embodiment, this may be carried out by pore volume impregnation of the solid acid silica-alumina catalyst with a solution of a nickel salt in water. A wide variety of nickel salts may be used for the impregnation including carbonates, nitrates, and acetates. The impregnation is carried out such that the amount of nickel deposited on the solid acid silica-alumina catalyst may range from 1 to 20 wt%, preferably from 5 to 10 wt%, based upon the weight of contained nickel in the finished catalyst .

After impregnation of the nickel, the catalyst may be calcined at a temperature of 400 to 600⁰C for a period of 1 to 24 hours. The calcination may be carried out in a gas atmosphere such as air or nitrogen or other appropriate gas. Preferably, the calcination may be conducted at 450 to 500⁰C for from 1 to 3 hours. Most preferably, the conditions are from 480 to 485°C for 2 hours to produce the finished catalyst .

The solid acid silica-alumina catalyst may be prepared by precipitating alumina in a silica slurry, followed by firing. In a preferred mode, the catalyst may be prepared by reducing the pH of sodium silicate from its relatively high pH of over 11 to 3.0 by the addition of a strong mineral acid, such as sulfuric acid. This results in the formation of a thick, pasty gel. Once the silica gel has been generated, the pH may be adjusted upward to approximately 8.1 by the addition of an aluminate, such as sodium aluminate. Once the pH of 8.1 is reached, precipitation begins. At this point, both the aluminate and aluminum sulfate may be added at a rate sufficient to maintain the pH at about 8.1. Once all of the aluminum sulfate has been added, more aluminate may be added to bring the pH up to approximately 10.3. The high pH is required in order that the sulfate may be washed out of the slurry. The material at this point is a thick slurry. The sulfate and the sodium, introduced with the alumina precursors and sulfuric acid, may then be washed out of the slurry by treatment of the slurry with deionized water. The washings preferably occur in stages, with the first taking place at pH 10.3 (sulfate removal) . For the second wash, the pH may be decreased to approximately 6.0 to facilitate the removal of sodium. Finally, the pH may be reduced to 3.7 to allow removal of the last traces of sodium. After this wash, the pH may be increased to 5.0 by the addition of a strong base, such as ammonia. The pH may be raised to enable filtering of the slurry. After the washings are completed, the material may be spray dried to yield, as a final powder, amorphous silica-alumina. The BET surface area of the catalyst may typically be greater than 400 m²/g with a total pore volume of 0.7 to 0.8 g/ml . Especially preferred as the solid acid silica-alumina catalyst is the X-600 catalyst, a product of Criterion Catalyst Co. This catalyst is capable of lightly isomerizing either the alpha olefins, such as C14-24, Ci₆, Ci₈ or a blend of Ci₆/Ci₈ isomers to render linear internal olefins having minimal residual alpha olefin content and an enhanced C₂-C₅ isomer content as described in U.S. Published patent application No. 2005/0070747, which is herein incorporated by reference . In a preferred mode, prior to being contacted with the solid acid silica-alumina catalyst, the olefinic composition feedstream may be passed over a water adsorption bed which, preferably contains a molecular sieve. The adsorbent in this adsorption unit may be a molecular sieve, either a 3A, 4A or 13X.

The olefinic composition feedstream may then be passed over an absorption unit or guardbed for a time sufficient to remove catalyst poisons, including Lewis bases such as phosphines, from the linear alpha olefin feedstream. The absorption unit or guardbed may contain an alumina, most preferably an alumina containing only negligible amounts of calcium or magnesium and do not exhibit microrods in their surface morphology.

In a preferred mode, a 0.8 mm alumina trilobe extrudate may be employed which is fairly pure alumina made by combining aqueous solutions of sodium aluminate and aluminum sulfate in ratios sufficient to give a pH of approximately 8.0, at which point precipitation of the alumina occurs. The resulting slurry may be then washed to remove undesired ions, primarily sulfate and sodium. The pH may be then increased to approximately 10.0 by the addition of sodium aluminate. Sulfate may be then removed by washing. The pH may be then reduced to approximately 7.0 by the addition of a strong mineral acid, such as nitric acid, and the sodium may be then removed in the wash. The material may be then spray-dried to give the finished powder. The preparation may be done in a batch process; the precipitation requiring one hour. Such products may have a BET surface area of 210-230 m²/g an average length of 1.5 to 3.0 mm, an average diameter of 0.77 to 0.94 mm and a median pore diameter of 115 to 130 A.

Alternatively, the alumina in the absorption unit may be an alumina trilobe shaped aluminum support, such as KL-5715, available from KataLeuna GmBH Catalysts, Germany. Such products may have a BET surface area of 200 m²/g, an average length of 1.5 to 3.0 mm, an average diameter of 0.77 to 0.94 mm and a median pore diameter of 138 A.

The impregnation may be carried out using an aqueous solution of the nickel salt at ambient temperature. Especially preferred is the method of pore-volume impregnation. The impregnation solution may be contacted with the silica-alumina solid acid for a period of 5 minutes to 24 hours. After impregnation, the catalyst may be aged for 1 to 6 hours prior to calcination.

The catalyst made by the process of the invention may also be used to make the lightly isomerized internal olefins described in U.S. Published patent application No. 2005/0070747, which is herein incorporated by reference. As described therein, that olefinic composition contains less than about 40 weight percent of the Ci and C₆-C₈ isomers and, when the olefinic composition contains a Ci₈ isomer, the C₉ isomer. Sixty weight percent or greater of the resulting olefinic composition contains the C₂-C₅ olefinic isomers. Preferably, the isomerized olefinic composition comprises less than 25 weight percent of the Ci and C₆-C₈ isomers, more preferably, less than about 13 weight percent of the Ci and C₆-C₈ isomers and, optionally, the C₉ isomer and, most preferably, less than 6 weight percent of the Ci and C₆-C₈ isomers and, optionally, the C₉ isomer. Typically less than 3 percent, more typically less than 1 percent, by weight of olefins are branched during the isomerization . The catalyst made by the process of this invention has the additional advantage that it can be used to make internal olefin compositions that are more than "lightly isomerized, up to and including those compositions that are "fully isomerized". The olefinic composition to be isomerized may contain a feedstream of Ci₄_₂₄ alpha olefins or a mixture thereof .

The double-bond isomerization of the alpha olefin containing olefinic composition may be carried out by first passing the composition over an adsorption bed containing a molecular sieve adsorbent to remove water. The mixture may then be passed over a guardbed or absorption unit containing an alumina-based absorbent to remove certain catalyst poisons. This partially purified feed may then be double- bond isomerized over the nickel-containing solid acid silica- alumina catalyst . The operating temperature of the isomerization bed may be from 70° to 140° C. This heating step may either be a batch or continuous flow reaction.

The olefinic composition feedstream may then be contacted with the nickel-containing solid acid silica- alumina catalyst. The catalyst may be activated by heating it to a temperature between from 25° to 500° C in flowing nitrogen at atmospheric pressure. The isomerization may be carried out in a reactor operated from between 70° to 140° C and from 30 to 1800 kPa (5 to 250 psig) to produce the linear internal olefin mixture. No post treatment is required to be conducted.

The isomerization may or may not be permitted to proceed to thermodynamic equilibrium. At thermodynamic equilibrium, full isomerization has occurred resulting in an approximately equal distribution of the double bond throughout the internal positions of the carbon chain, with the residual alpha olefin content being less than 5 percent. Operating conditions are varied to prevent full equilibrium from occurring or to allow it to occur, depending upon whether a lightly isomerized or fully isomerized (or in between) internal olefin composition is desired.

The linear internal olefins produced by the isomerization process of the invention are useful as paper sizing compositions as well as drilling fluid compositions.

The following non-limiting examples, and comparative demonstrations, bring out the more salient features of the invention. All parts are given in terms of weight units except as may otherwise be indicated.

EXAMPLES

Example 1 (Comparative) X-600 (27.8g) was loaded into a standard fixed-bed recycle batch reactor. The catalyst was activated at 500⁰C in flowing air for four hours followed by flowing argon for ten hours. The reactor was then cooled to 120⁰C under flowing argon. For the isomerization, the conditions were brought to 120⁰C and 1380 kPa (200 psig) argon. 1-hexadecene feed (253 g) was then started at a flow rate of 500 g/min in recycle mode. The flow was maintained for 6 hours, with samples taken on an hourly basis . The data from the sample taken after 4 hours is shown in Table 1, while the data for the sample taken after one hour is shown in Table 2.

Example 2 (5 wt% Ni) A catalyst with a nickel content of 5 wt% was prepared by pore volume impregnation of the X-600 catalyst with an aqueous solution of nickel nitrate. After impregnation, the catalyst was aged for two hours then calcined at 482°C in air for two hours. The catalyst was then used to isomerize 1- hexadecene according to the procedure of Example 1.

Example 3

The procedure of Example 2 was repeated except that the catalyst prepared had a nickel content of 10 wt% .

Table 1

These results show that both the dimer content and the degree of skeletal isomerization are reduced by the addition of nickel to the catalyst by the process of the invention. In addition, the unique isomerization activity of X-600 described in U.S. patent application 2005/0070747 is maintained. Table 2 summarizes the double bond distribution for samples taken after one hour of reaction time in Examples 1 to 3. All values are given in normalized mole percent . Table 2

Claims

C L A I M S

1. A process for making an improved isomerization catalyst which comprises impregnating a solid acid silica- alumina catalyst with a nickel salt and then calcining it to produce the final catalyst.

2. The process of claim 1 wherein the solid acid silica-alumina catalyst has a weight ratio of silica to alumina from 45:55 to 55:45.

3. The process of claims 1 or 2 wherein the final catalyst contains from 1 to 20 wt . % of nickel, based upon the weight of contained nickel in the finished catalyst.

4. The process of claims 1 to 3 wherein the final catalyst contains from 5 to 10 wt . % of nickel, based upon the weight of contained nickel in the finished catalyst.

5. A process for isomerizing an olefinic composition comprising at least one alpha olefin to olefin (s) containing an internal unsaturated bond which comprising contacting the olefinic composition with the improved isomerization catalyst made by the process of claim 1.

6. A process for isomerizing an olefinic composition comprising at least one alpha olefinto olefin (s) containing an internal unsaturated bond comprising contacting the olefinic composition with the improved isomerization catalyst made by the process of claim 2.

7. A process for isomerizing an olefinic composition comprising at least one alpha olefinto olefin (s) containing an internal unsaturated bond comprising contacting the olefinic composition with the improved isomerization catalyst made by the process of claim 3.

8. A process for isomerizing an olefinic composition comprising at least one alpha olefinto olefin (s) containing an internal unsaturated bond comprising contacting the olefinic composition with the improved isomerization catalyst made by the process of claim 4.

9. The process of Claims 5 to 8 wherein the olefinic composition is passed through a bed containing the improved isomerization catalyst.

10. The process of Claim 9 wherein the operating temperature of the bed is from 70° to 140° C.