OLEFIN ISOMERIZATION WITH SMALL CRYSTALLITE ZEOLITE CATALYST

Abstract

A skeletal isomerization process for isomerizing olefins is described. The process includes the steps of feeding an olefin-containing feed to a reactor having an isomerization catalyst with a small crystalline size that is less than 1 μm in all directions. The small crystalline size increases the life of the catalyst and the yield of skeletal isomer products, as well as reducing the formation of heavy C5+ olefin byproducts, as compared to processes using conventional catalyst with crystalline sizes of 1 μm or more.

Claims

1. A skeletal isomerization process comprising the steps of: a) feeding, at a weight hourly space velocity (WHSV), a hydrocarbon feed comprising at least one olefin to a reactor containing an isomerization zeolite catalyst, wherein said isomerization zeolite catalyst has a crystallite size that is less than 1 μm in diameter in all directions; and b) isomerizing said at least one olefin to at least one skeletal isomer product in said reactor for at least one catalyst cycle, wherein said WHSV is between about 7 to about 30 hr.sup.−1.

2. The skeletal isomerization process of claim 1, further comprising the step of recovering said at least one skeletal isomer product from the reactor.

3. The skeletal isomerization process of claim 1, wherein said isomerization zeolite catalyst has a crystallite size of about 0.2 μm in diameter in all directions.

4. The skeletal isomerization process of claim 1, wherein said isomerization zeolite catalyst has a silica to alumina ratio from 10:1 to 60:1.

5. The skeletal isomerization process of claim 1, wherein said isomerization zeolite catalyst additionally comprises a binder material selected from the group consisting of: silica, silica-alumina, bentonite, kaolin, bentonite with alumina, montmorillonite, attapulgite, titania and zirconia.

6. The skeletal isomerization process of claim 1, wherein a temperature of said reactor is from about 340° C. to about 500° C.

7. The skeletal isomerization process of claim 6, wherein a temperature of said reactor is from 380° C. to 425° C.

8. The skeletal isomerization process of claim 1, wherein said at least one olefin is an iso-olefin.

9. The skeletal isomerization process of claim 1, wherein said at least one olefin is a linear olefin.

10. The skeletal isomerization process of claim 1, wherein said at least one olefin is isobutylene and said at least one skeletal isomer product is 1-butene and 2-butene.

11. The skeletal isomerization process of claim 1, wherein said at least one olefin comprises 1-butene and 2-butene, and said at least one skeletal isomer product is isobutylene.

12. The skeletal isomerization process of claim 1, wherein said hydrocarbon feed further comprises alkanes, aromatics, hydrogen and other gases.

13. The skeletal isomerization process of claim 1, wherein said hydrocarbon feed comprises at least 40 wt. % isobutylene.

14. A skeletal isomerization process comprising the steps of: a) feeding, at a weight hourly space velocity (WHSV) from about 7 to about 30 hr.sup.−1, a hydrocarbon feed comprising at least one olefin to a reactor containing an isomerization zeolite catalyst, wherein said isomerization zeolite catalyst has a crystallite size that is less than 1 μm in diameter in all directions; and b) isomerizing said at least one olefin to at least one skeletal isomer product in said reactor for at least one catalyst cycle, wherein said catalyst cycle is at least twenty-one days.

15. The skeletal isomerization process of claim 14, wherein said hydrocarbon feed has a weight hourly speed velocity of about 14 hr.sup.−1.

16. The skeletal isomerization process of claim 14, wherein said hydrocarbon feed comprises 1-butene and 2-butene, and said at least one skeletal isomer product is isobutylene, or wherein said at least one olefin is isobutylene and said at least one skeletal isomer product is 1-butene and 2-butene.

17. The skeletal isomerization process of claim 14, wherein said catalyst cycle is at least twenty-five days.

18. The skeletal isomerization process of claim 14, wherein said hydrocarbon feed further comprises alkanes, aromatics, hydrogen and other gases.

19. The skeletal isomerization process of claim 14, wherein said hydrocarbon feed comprises at least 40 wt. % isobutylene.

20. A skeletal isomerization process comprising the steps of: a) feeding, at a weight hourly space velocity (WHSV) from about 7 to about 30 hr.sup.−1, a hydrocarbon feed comprising at least one olefin to a reactor at a known temperature and containing an isomerization zeolite catalyst, wherein said isomerization zeolite catalyst has a crystallite size that is less than 1 μm in diameter in all directions; and b) isomerizing said at least one olefin to at least one skeletal isomer product in said reactor for at least one catalyst cycle, wherein said catalyst cycle is at least seventeen days; wherein said known temperature is between about 380° C. and 425° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0076] FIG. 1A. The conversion rate of isobutylene to normal butene of one embodiment of the present disclosure.

[0077] FIG. 1B. Yield of isobutylene of one embodiment of the present disclosure.

[0078] FIG. 1C. Yield of C5+ heavies of one embodiment of the present disclosure.

[0079] FIG. 2A. Conversion rate of isobutylene to normal butene between embodiments of the present disclosure utilizing different space velocities.

[0080] FIG. 2B. Comparison of yield of isobutylene for embodiments of the present disclosure utilizing different space velocities.

[0081] FIG. 2C. Comparison of yield C5+ heavies for embodiments of the present disclosure utilizing different space velocities.

DETAILED DESCRIPTION

[0082] The disclosure provides a skeletal isomerization method for isomerizing olefins using a zeolite catalyst with a small crystallite size, and a faster feed flow and/or lower reactor temperature, to increase the lifetime of the catalyst before regeneration is needed. In some embodiments of the presently disclose method, a reduction in the formation of the heavy C5+ olefins occur while increasing the formation of the skeletal isomer products. In some embodiments of the presently disclose method, the smaller zeolite catalyst is more active than conventional sized catalysts, resulting in less catalyst material being needed for the same feed flow rate.

[0083] Conventional skeletal isomerization processes, both forward isomerization of linear olefins to branch olefins and reverse isomerization of branched olefins to linear olefins, employ catalysts, such as zeolites, with large crystallites that have a diameter of 1 μm or greater. These zeolite catalysts can be used with or without a refractory oxide binder material such as silica or alumina, and many are commercially available. However, these zeolite catalysts are susceptible to quick coking and subsequent blocking of pores, which lead to low cycle times before the catalyst must be de-coked and regenerated. Further, processes using zeolite catalysts with conventional crystallite sizes can also result in an undesired by-product formation of heavy C5+ olefins, particularly in the beginning of the cycle for reverse isomerization.

[0084] The presently disclosed methods overcome the issues in the conventional isomerization process by using a zeolite catalyst with a “small” crystallite size that is defined as being less 1 μm in diameter in all directions. This is a smaller crystallite size than what is conventionally used, and is more active. This results in the need for less catalyst material that a conventionally sized catalyst for the same feed rate. Further, increase in activity also results in a longer catalyst cycle. However, in some methods, it may not improve the reaction product yield or selectively of reaction product formation. Thus, the presently disclosed method further includes using a faster hydrocarbon feed flow through the reactor than the conventional isomerization methods and/or decreasing the reactor temperature compared to conventional isomerization methods. These changes to the zeolite catalyst and the process conditions not only increase the yield of reaction productions while reducing the formation of C5+ olefins, but also increase the catalyst cycle compared to methods using a catalyst with conventional crystallite sizes. In some embodiments, the increase in the length of the catalyst cycle and the use of less catalyst material is retained even with the changes to the feed or reactor temperatures.

[0085] Without being bound by theory, it is thought that the smaller zeolite crystallite size catalyst is utilized in a different way than the conventional larger crystallite zeolites. Contrary to conventional belief that catalyst of smaller crystallite sizes might have diffusion limitation due to their sizes, the results shown in this disclosure indicate the opposite is true. It is proposed that the smaller size provides less surface area for an unselective transformation to coke, therefore possibly increasing the life of the catalyst. It is also proposed that the smaller crystallites provide an increase in active site density affording a higher activity. Additionally, it is proposed that a preferential coking could occur at specific locations in the zeolite catalyst, such that once the preferential coking occurs, further coking is reduced.

[0086] The rate of isomerization is also increased with the use of the smaller zeolite crystallite size of this disclosure. In some embodiments, the rate of isomerization is increased by 5 to 20% as compared to conventionally sized zeolite catalysts. In some embodiments, the rate of isomerization is increased by at least 10% as compared to conventionally sized zeolite catalysts.

[0087] The life cycle of the catalyst, also called the catalyst cycle, of this disclosure can also be increased as compared to conventionally sized catalyst in the isomerization process. In some embodiments, the life cycle of the catalyst is at least 50% longer than a conventionally sized catalyst. In some embodiments, the life cycle of the catalyst is at least 75% longer than a conventionally sized catalyst. In some embodiments, the life cycle of the catalyst is at least 100% longer than a conventionally sized catalyst.

[0088] Alternatively, the life cycle of the catalyst is extended by at least 3 days, 4 days, 5 days, 6 days, 7 days, or 8 days, compared to methods using zeolites with bigger, conventionally sized crystallites. In some aspects of the present method, the catalyst cycle is at least seventeen days (˜2.5 weeks), at least twenty-one days (3 weeks), or at least twenty-five days (˜3.5 weeks), when the WHSV is at least 7 hr.sup.−1.

[0089] The yield of linear olefins by using the catalyst of this disclosure is increased due to the longer life cycle and higher reaction rate. In some embodiments, the yield of linear olefin by using the catalyst of this disclosure can be 5 to 20% higher than using a conventionally sized catalyst. In some embodiment, the yield of linear olefin using the catalyst of this disclosure is at least 10% higher than using a conventionally sized catalyst.

[0090] The amount of catalyst material when using the small crystallite sized catalyst of this disclosure is reduced compared to a conventional sized catalyst, for the same feed flow. In some embodiments, the amount of the catalyst of this disclosure needed for a given feed flow can be 5 to 67% less than using a conventionally sized catalyst. In other embodiment, the amount of the catalyst of this disclosure needed for a given feed flow is at least 33% less than using a conventionally sized catalyst. In some embodiments, the skeletal isomerization process uses about one-third to about two-thirds less of the small crystallite size zeolite catalyst than the amount of conventionally sized catalyst, for the same process conditions.

[0091] In some embodiments, the novel method presently disclosed comprises the steps of feeding a hydrocarbon feed that has at least one olefin into to a reactor having an isomerization zeolite catalyst with a small crystallite size that is less than 1 μm in diameter in all directions at a hydrocarbon weight hour space velocity (WHSV) in the range of from 1 to 30 hr.sup.−1, wherein the reactor is maintained at a first temperature and a first pressure, and collecting one or more skeletal isomer olefin product. The at least one olefin in the feed can have two to ten carbons, and, during the feeding steps, a portion of the at least one olefin is isomerized into the at least one skeletal isomer olefin product. For example, if the at least one olefin is an iso-olefin such as isobutylene, then the skeletal isomer olefin product will be a linear olefin such as 1- or 2-butene. If the at least one olefin is a linear olefin such as 2-butene, then the skeletal isomer olefin product will be an iso-olefin such as isobutylene.

[0092] In some embodiments, the novel method presently disclosed comprises the steps of feeding a hydrocarbon feed that has at least one olefin into to a reactor having an isomerization zeolite catalyst with a small crystallite size that is <0.2 μm in diameter in all directions at a first hydrocarbon weight hour space velocity, wherein the reactor is maintained at a first temperature and a first pressure, and collecting one or more skeletal isomer olefin product. The at least one olefin in the feed can have two to ten carbons, and, during the feeding steps, a portion of the at least one olefin is isomerized into the at least one skeletal isomer olefin product.

[0093] In some embodiments, the novel method presently disclosed comprises the steps of feeding a hydrocarbon feed that has at least one olefin into to a reactor having an isomerization zeolite catalyst with a small crystallite size that is less than 1 μm in diameter in all directions at a hydrocarbon weight hour space velocity (WHSV) in the range of from 1 to 30 hr.sup.−1, wherein the reactor is maintained at a temperature between 340° C. and 500° C. and a pressure between zero to about 1034 kPa (150 psig), and collecting one or more skeletal isomer olefin product. The at least one olefin in the feed can have two to ten carbons, and, during the feeding steps, a portion of the at least one olefin is isomerized into the at least one skeletal isomer olefin product.

[0094] In some embodiments, the novel method presently disclosed comprises the steps of feeding a hydrocarbon feed that has at least one olefin into to a reactor having an isomerization zeolite catalyst with a small crystallite size that is less than 1 μm in diameter in all directions at a first hydrocarbon weight hour space velocity, wherein the reactor is maintained at a first temperature and a first pressure, and collecting one or more skeletal isomer olefin product, wherein the catalyst cycle is at least 50% longer than a method that does not use the small crystallite size. The at least one olefin in the feed can have two to ten carbons, and, during the feeding steps, a portion of the at least one olefin is isomerized into the at least one skeletal isomer olefin product.

[0095] In some embodiments, the novel method presently disclosed comprises the steps of feeding a hydrocarbon feed that has at least one olefin into to a reactor having an isomerization zeolite catalyst with a small crystallite size that is less than 1 μm in diameter in all directions at a first hydrocarbon weight hour space velocity, wherein the reactor is maintained at a first temperature and a first pressure, and collecting one or more skeletal isomer olefin product, wherein the catalyst cycle is at least 50% longer than a method that does not use the small crystallite size and the first hydrocarbon weight hour space velocity is at least 3 times as fast as a method that does not use the small crystallite size. The at least one olefin in the feed can have two to ten carbons, and, during the feeding steps, a portion of the at least one olefin is isomerized into the at least one skeletal isomer olefin product.

[0096] More details on the skeletal isomerization process conditions and feeds are provided below.

[0097] Hydrocarbon Feedstream:

[0098] The presently described methods are for the skeletal isomerization (both forward and reverse) of olefins, also known as alkenes. Thus, the hydrocarbon feedstream, or feed, used herein may comprises at least one olefin that will be isomerized into a skeletal isomer thereof. For example, an iso-olefin is a skeletal isomer of a linear olefin, and vice versa. In some embodiments, the at least one olefin in the hydrocarbon feed has two to ten carbon atoms.

[0099] In some embodiments, the hydrocarbon feed comprises unbranched linear, or normal, olefins having two to ten carbons, as well as other hydrocarbons such as alkanes, di-olefins, aromatics, hydrogen, and inert gases. In other embodiments, the feed comprises at least 40 wt. % of linear C4 olefins, as well as other hydrocarbons such as alkanes, other olefins, aromatics, hydrogen, and inert gases. Alternatively, the feed comprises at least 55 wt. % of linear C4 olefins, at least 70 wt. % of linear C4 olefins, at least 85 wt. % of linear C4 olefins, at least 95 wt. % of linear C4 olefins, or at least 99 wt. % of linear C4 olefins.

[0100] In other embodiments, the hydrocarbon feed used herein comprises branched olefins, also known as “iso-olefins”. In this disclosure, the branched olefins can have four to ten carbon atoms. In some embodiments, the feed used herein comprises a methyl-branched iso-olefin. In some embodiments of the disclosure, the feed contains isobutylene. As before, the hydrocarbon feed used in some embodiments of the disclosure may also include other hydrocarbons such as alkanes, di-olefins, and aromatics, as well as hydrogen and other gases.

[0101] In some embodiments of the disclosure, the feed comprises at least 40 wt. % isobutylene, at least 55 wt. % isobutylene, at least 70 wt. % isobutylene, at least 85 wt. % isobutylene, at least 95 wt. % isobutylene, or at least 99 wt. % isobutylene. The isobutylene can be from any source. In some embodiments, the isobutylene comes from a Raffinate 1 stream derived from a cracker/fluid catalytic cracking unit and has had its C4 alkanes removed. Alternatively, the isobutylene can come from a stream derived from a propylene oxide/t-butyl alcohol (PO/TBA) plant. The dehydration of the t-butyl alcohol can result in a more purified isobutylene stream than a stream sourced from a cracker.

[0102] Isomerization Catalyst:

[0103] Conventional skeletal isomerization zeolite catalysts have large crystallite sizes that are 1 μm or greater (≥1 μm) in all directions. However, the isomerization catalysts used in the presently disclosed process differ from conventional isomerization catalysts in that the present process utilizes an isomerization catalyst with a smaller crystallite size (less than 1 μm in diameter in all directions) than the conventional catalyst.

[0104] The crystallite size for the catalyst used in the presently disclosed methods has a diameter less than 1 μm, less than 0.5 μm, less than 0.3 μm, or less than 0.2 micron. In addition to the smaller crystallite, the catalyst used in the presently disclosed methods may also have a silica to alumina ratio (SAR) of about 10:1 to about 60:1. In some embodiments, the SAR of the catalyst used in the presently described methods is about 10, about 20, about 40 or about 50. In other embodiments, the SAR is limited to 10 to 50 due to the small crystallite size of the catalyst.

[0105] In some embodiments of the presently disclosed process, the catalyst has a crystallite size that is about 0.2 μm in diameter and a SAR of about 20. Alternatively, the catalyst has a crystallite size that is about 0.2 μm in diameter, a SAR of about 20, a surface area ranging from about 300 m.sup.2/g to about 450 m.sup.2/g and a micropore volume ranging from about 0.10 cc/g to about 0.20 cc/g. In some embodiments of the present disclosure, the H-FER catalyst has a Na.sub.2O content in the range of 0 to 0.10 wt. %. In some embodiments of the present disclosure, the H-FER catalyst has a Na.sub.2O content in the range of 0 to 0.05 wt. %. In some embodiments of the present disclosure, the H-FER catalyst has a Na.sub.2O content in the range of 0.05 to 0.10 wt. %. In some embodiments of the present disclosure, the H-FER catalyst has a Na.sub.2O content of 0 wt. %. In some embodiments of the present disclosure, the H-FER catalyst has a Na.sub.2O content less than 0.04 wt. %, a SAR of about 25, an XRD crystallinity of 96%, a BET surface area of 421 m.sup.2/g, a crystal size (SEM) less than 200 nm, and a loss on ignition of about 9 wt. %. All relative amounts defined within this paragraph are based upon the total weight of the H-FER catalyst.

[0106] The small crystallite sized isomerization catalyst used in embodiments of this disclosure includes catalysts suitable to skeletally isomerize olefins. This includes isomerizing iso-olefins to linear, or normal, olefins (unbranched) and vice versa.

[0107] In some embodiments of the present disclosure, the isomerization catalyst is a smaller version of FER called “small ferrierite” or s-FER. The s-FER has the same crystal structure as the conventionally sized ferrierite but with a crystallite size that is less than 1 μm. The s-FER can also be in the hydrogen form. Conversion of ferrierite to its hydrogen form, H-FER, replaces sodium cations with hydrogen ions in the crystal structure, making it more acidic.

[0108] In some embodiments, the isomerization catalyst is a H-FER with a small crystallite size of about 0.2 μm or less in diameter and a silica to alumina ratio of about 10 to about 60. Alternatively, the isomerization catalyst is a H-FER with a small crystallite size of about 0.2 μm or less in diameter and a silica to alumina ratio of about 20.

[0109] Various ferrierite zeolites (“FER”), including the hydrogen form of ferrierite, are described in U.S. Pat. Nos. 3,933,974, 4,000,248, and 4,942,027 and patents cited therein. Various methods are provided which teach procedures for preparing H-ferrierite, including U.S. Pat. Nos. 4,251,499, 4,795,623 and 4,942,027, incorporated herein by reference in their entirety. In some embodiments of the present disclosure, the zeolite catalyst may be a H-FER catalyst prepared in accordance with U.S. Pat. No. 9,827,560 B2, incorporated herein by reference in its entirety. In other embodiments of the present disclosure, the zeolite catalyst is a commercially available catalyst including, but not limited to, ZD18018TL from Zeolyst International.

[0110] The small crystallite size zeolite catalyst used in embodiments of the present disclosure may be used alone or suitable combined with a refractory oxide that serves as a binder material. Suitable refractory oxides include, but are not limited to, natural clays, such as bentonite, montmorillonite, attapulgite, and kaolin; alumina; silica; silica-alumina; hydrated alumina; titania; zirconia and mixtures thereof. The weight ratio of binder material and zeolite suitably ranges from 1:10 to 10:1. In some embodiments of the disclosure, the weight ratio of binder to zeolite is in the range of 1:10 to 5:1, the range of 3:5 to 10:1, or the range of 3:5 to 8:5. In some embodiments of the present disclosure, the binder comprises from 10 wt. % to 20 wt. % of the catalyst-binder combination. In some embodiments of the present disclosure, the binder comprises from 10 wt. % to 15 wt. % of the catalyst-binder combination. In some embodiments of the present disclosure, the binder comprises from 15 wt. % to 20 wt. % of the catalyst-binder combination. In some embodiments of the present disclosure, the binder comprises from 13 wt. % to 17 wt. % of the catalyst-binder combination.

[0111] Despite the difference in the crystallite size, the isomerization catalyst in the presently disclosed methods, when combined with at least one binder, can be any shape used with conventional isomerization catalysts. This includes, but is not limited to, spheres, pellets, tablets, platelets, cylinders, helical lobed extrudate, trilobes, quadralobes, multilobed (5 or more lobes), and combinations thereof. In some embodiments, the isomerization catalyst is a trilobed, quadralobe, or multilobed extrudate.

[0112] Operating Conditions for Skeletal Isomerization Process:

[0113] In some embodiments of the disclosure, the hydrocarbon feed may be contacted with the isomerization catalyst under reaction conditions effective to skeletally isomerize the olefins therein. This contacting step may be conducted in the vapor phase by bringing a vaporized feed into contact with the solid isomerization catalyst. The hydrocarbon feed and/or catalyst can be preheated as desired.

[0114] The isomerization process of the disclosure may be carried out in a variety of reactor types. In some embodiments of the disclosure, the reactor is a packed bed reactor. In some embodiments of the disclosure, the reactor is a fixed bed reactor. In some embodiments of the disclosure, the reactor is a fluidized bed reactor. In some embodiments of the disclosure, the reactor is a moving bed reactor. In embodiments of the disclosure using a moving bed reactor, the catalyst bed may move upwards or downwards.

[0115] The temperature of the reactor can vary from about 250° C. to about 600° C., or from about 380° C. to about 425° C. Alternatively, the reactor temperature for the isomerization is between about 250° C. to about 420° C., about 400 and 600° C., or about 340° and 500° C. In yet another alternative, the reactor temperature is about 418° C.

[0116] In other embodiments, the temperature of the reactor is at least 20° C. less than the temperature used in conventional isomerization processes. In other embodiments, the temperature of the reactor is at least 40° C. less than the temperature used in conventional isomerization processes. Alternatively, the temperature of the reactor is at least 25° C., at least 35° C., at least 45° C., or at least 55° C. less than the reactor temperature used in conventional isomerization processes.

[0117] The reaction pressure conditions can vary from about zero to about 1034 kPa (150 psig), or from about zero to about 345 kPa (50 psig). Alternatively, the reaction pressure for the isomerization is between about 34 kPa (5 psig) to about 345 kPa (50 psig), about 34 kPa (5 psig) to about 83 kPa (12 psig), 55 kPa (8 psig) to about 138 kPa (20 psig), or 55 kPa (8 psig) to about 97 kPa (14 psig). In yet another alternative, the pressure is about 69 kPa (10 psig).

[0118] In some embodiments of the present disclosure, the smaller crystallite catalyst can be combined with a faster weight hourly space velocity (WHSV) of the hydrocarbon feed rate to improve the yield while prolonging the life of catalyst. The weight hourly space velocity feed rates of the olefin feed can range from about 1 to about 200 hr.sup.−1, with or without a conventional diluent. In some embodiments, the weight hourly space velocity feed rates are from about 1 to about 30 hr.sup.−1. In some embodiments, the weight hourly space velocity feed rates are from about 7 to about 14 hr.sup.−1, or about 14 hr.sup.−1.

[0119] In other embodiments, the weight hourly space velocity feed rates are at least 3 times the feed rates used in conventional isomerization processes. In other embodiments, the weight hourly space velocity feed rates are at least 3 to 8 times the feed rates used in conventional isomerization processes. Alternatively, the weight hourly space velocity feed rates are at least 3.5 times, at least 4 times, at least 7 times, or at least 8 times the feed rates used in conventional isomerization processes.

[0120] By performing a skeletal isomerization using the steps above and a catalyst with a small crystallite size, the catalyst cycle and yield of the skeletal isomer product increases compared to an isomerization process that uses catalysts with conventionally sized crystallites. The catalyst cycle can be increased by at least 50%, 75%, or 100%, compared to an isomerization process that uses catalysts with conventionally sized crystallites. The yield of skeletal isomer product olefins obtained using embodiments of the disclosure may be at least 5 to 20% greater compared to an isomerization process with a conventional catalyst. In some embodiments of the disclosure, the yield of skeletal isomer product olefins obtained may be at least 10% greater than a similar isomerization process that does not include a catalyst with the small crystallite size described in this disclosure.

[0121] In some embodiments of the present disclosure, the use of the smaller crystallite catalyst can increase the life of catalyst to at least seventeen days (˜2.5 weeks), at least twenty-one days (3 weeks), or at least twenty-five days (˜3.5 weeks), when the WHSV is at least 7 hr.sup.−1.

[0122] Using the above described methods, the skeletal isomerization process is improved because the catalyst cycle is longer, allowing for a greater amount of structurally isomerized product, also called skeletal isomer olefin product, to be formed. In some embodiments, when the feed comprises C4 olefins, a greater amount of the desired structurally isomerized product can be formed while forming less heavy C5+ olefins. This leads to a more cost-effective isomerization process for generating greater amounts of structurally isomerized C4 olefins.

EXAMPLES

[0123] The following examples are included to demonstrate embodiments of the appended claims using the above described system and methods of increasing the yield of isomerization products for an isobutylene feed and the catalyst cycle. The example is intended to be illustrative, and not to unduly limit the scope of the appended claims. Those of skill in the art should appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the disclosure herein. In no way should the following examples be read to limit, or to define, the scope of the appended claims.

[0124] Hydrocarbon Feed.

[0125] For each of the Examples below, the feed comprised 99.95 wt. % of isobutylene. The skeletal isomer product olefins for such a feed composition include 1-butene and 2-butene (including both trans-2-butene and cis-2-butene).

[0126] Calculations.

[0127] For each of the Examples below, the conversion of reactants to products is calculated. Without being bound by theory, it is believed that during the isomerization reaction, equilibrium is achieved between, for example, the isobutylene, 1-butene and trans- and cis-2-butene. Therefore, the calculation of conversion reflects the feed (FD) and effluent (EFF) concentrations of 1-butene (B1), 2-butene (B2), and isobutylene (IB1). Conversion is calculated as:

[00001]$\%\mathrm{isobutylene}\mathrm{Conversion}=\frac{\left(\mathrm{wt}\%\mathrm{IB}1\right)\mathrm{FD}-\left(\mathrm{wt}\%\mathrm{IB}1\right)\mathrm{EFF}}{\left(\mathrm{wt}\%\mathrm{IB}1\right)\mathrm{FD}}\times 100$

[0128] Yield is calculated as

[00002]$\%\mathrm{linear}\mathrm{butene}\mathrm{Yield}=\frac{\left(\mathrm{wt}\%B1+\mathrm{wt}\%B2\right)\mathrm{EFF}-\left(\mathrm{wt}\%B1+\mathrm{wt}\%B2\right)\mathrm{FD}}{\left(\mathrm{wt}\%\mathrm{IB}1\right)\mathrm{FD}}\times 100$

[0129] Development of equivalent equations for other olefin reactants and skeletal isomer products are well within the abilities of one with skill in the art.

[0130] For the catalyst cycle determination, a 30% conversion rate was used as a practical economic cut-off before decoking is required. This percentage was based on equipment that was used in the present examples. However, other cutoffs or means for measuring when a catalyst needs to be regenerated are possible, depending on the equipment being used and the amount of hydrocarbon feed that is being recycled.

Example 1: Catalyst with Small Crystallite Size

[0131] A series of skeletal isomerization reactions were performed using isomerization catalysts with different crystallite sizes. The operational conditions for both reactions were exactly the same, with the only difference being the crystallite size.

[0132] Comparative Example 1 used a commercially available H-FER catalyst with a conventional crystallite size that is greater the 1 μm. In contrast, Example 1 used a H-FER catalyst with a small crystallite size that was about 0.2 μm. Both catalysts had a trilobed extrudate shape. The H-FER catalyst in Example 1 had silica:alumina ratio of 20. The H-FER catalyst in Comparative Example 1 had silica:alumina ratio of 90. No catalyst pretreatment was performed for either reaction.

[0133] For both reactions, the isobutylene feed was fed through a fixed bed reactor held at a temperature of approximately 418° C. The isobutylene feed was maintained at a WHSV of 7 hr.sup.−1 (7 g isobutylene/g catalyst/hr) for both reactions. The results for both reactions are displayed in FIGS. 1A-C.

[0134] The conversion rate of isobutylene to linear butenes and the catalyst cycle for each catalyst is displayed in FIG. 1A. The isobutylene conversion for Example 1 is about 10% higher during its catalyst cycle than that in Comparative Example 1. However, the catalyst cycle is much longer. Using 30% conversion rate as a practical economic cut-off for minimum of acceptable catalyst before decoking is required, the catalyst of Example 1 lasted about 336 hours, whereas the conventional catalyst of Comparative Example 1 lasted about 144 hours. The difference is 192 hours, or 8 days. In other words, the life cycle of the catalyst with the small crystallite size is able to more than double the life of a conventional catalyst ((336-144)/144*100%=133%). The doubling of life cycle translates into cost saving in both the amount of catalyst and the fewer interruption on operation.

[0135] The yield of reaction products is shown in FIGS. 1B and 1C. The yield of linear butenes in the reaction for Example 1 is much higher than that in the Comparative Example 1, as shown in FIG. 1B. The conventional catalyst in Comparative Example 1 reaches the highest yield of linear butenes sooner than the small crystallite catalyst of this disclosure, but the yield for Comparative Catalyst 1 quickly drops thereafter. In contrast, the yield of linear butenes for Example 1 slowly increases, before reaching a maximum well after the catalyst cycle for Comparative Example 1 ends. Thus, the yield of linear butenes for Example 1 is much larger than that of Comparative Example 1.

[0136] As seen in FIG. 1C, the production of the undesired heavy C5+ olefins also increased for Example 1. Heavy C5+ olefins are byproducts that have to be separated by other processes downstream for use in low value gasoline or other products. The amount of C5+ olefins producing using the small crystallite catalyst is about 10% higher than the conventionally sized catalyst. It is believed that this increase is due to the lower SAR ratio. The small crystallite size limits the SARs, thus other modifications to the process would be needed to address the increase in heavy C5+ olefins. One potential modification is described below in Example 2.

Example 2: Faster WHSV

[0137] The results in Example 1 show that decreasing the crystallite size of the catalyst will increase the catalyst cycle, as compared to a similar process using a catalyst with a conventional crystallite size, and subsequently increase the yield of linear butenes. However, the smaller crystallite size also increased the production of the undesirable heavy C5+ olefins. As such, this example is directed to modifying the isomerization conditions to reduce the production of heavy C5+ olefins without sacrificing the benefits of a catalyst with a smaller crystallite size.

[0138] Example 2 is an isomerization reaction of isobutylene that was ran under the same conditions and with the same isomerization catalyst as Example 1, except the WHSV was set at 14 hr.sup.−1 (14 g isobutylene/g catalyst/hr). The reactor temperature was maintained at approximately 406-418° C. The results are shown in FIGS. 2A-C.

[0139] FIG. 2A displays the isobutylene conversion and catalyst cycle for Examples 1 and 2, as well as Comparative Example 1. FIG. 2B displays the yield of linear butene for these examples, and FIG. 2C displays the yield of heavy C5+ olefins for the same examples.

[0140] As can be seen in FIG. 2A, the conversion rate of isobutylene and the catalyst cycle in Example 2, when the WHSV is 14 hr.sup.−1 and is twice as fast as the other examples, is between that of Comparative Example 1 and Example 1. While the catalyst cycle in Example 2 is less than that of Example 1, it is still 83% longer than that of Comparative Example 1 which is a catalyst with a conventional crystallite size ((264-144)/144*100%=83%). Thus, the longer life cycle benefit of the catalyst with a smaller crystallite size was retained even though the feed rate was doubled.

[0141] FIG. 2B shows the yield of normal butene and C5+ heavies with respect to WHSV=7 and WHSV=14. Similar to Example 1, Example 2 had a lower yield than Comparative Example 1 during the early part of the isomerization reaction. However, the longer catalyst cycle allowed for Example 2 to ultimately have a higher yield than Comparative Example 1. Thus, the higher linear butene yield of the catalyst with a smaller crystallite size was retained.

[0142] FIG. 2C displays the yield of heavy C5+ olefins. Unlike Example 1, Example 2 had a much lower yield of C5+ olefins. The amount of C5+ olefins was significantly lower during the beginning of the reaction. Example 1 had an initial value of about 60%, whereas Example 2 was four times lower, with a value of 15%. This lower production of heavy C5+ olefins continued through the catalyst cycles. At the 240-hour mark, Example 2 produced about 191 grams of heavy C5+ olefins. In contrast, Example 1, at the same time in the reaction, produced about 298 grams. By doubling the WHSV, the amount of heavy C5+ olefins was reduced by about 35%. Regarding Comparative Example 1, Example 2 has a lower starting yield, however it should overtake the yield in Comparative Example 1 because of the longer cycle length.

[0143] Thus, the combination of an isomerization catalyst with a small crystallite size and a faster WHSV resulted in an increase in the catalyst cycle length, an increase in the yield of linear butenes, and a decrease in heavy C5+ olefins.

Prophetic Examples

[0144] Experiments can be run under the same conditions as Example 2, except for lowering the reactor temperature to further increase the catalyst cycle while maintaining the higher skeletal isomer product yield and lower C5+ heavies yield.

[0145] Additional experiments can be run using the same conditions as either Example 1 or 2, but with a catalyst with the small crystallite size and a higher SAR. The higher SAR may further lower the C5+ olefin yield.

[0146] Although the examples are described herein in terms of isomerizing an iso-olefin to linear olefin, embodiments of the disclosure are applicable to the isomerization of a linear olefin to an iso-olefin.

[0147] The particular embodiments disclosed above are merely illustrative, as the present disclosure may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended as to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered of modified and such variations are considered within the scope and spirit of the present disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure.

[0148] The following references are incorporated by reference in their entirety for all purposes. [0149] U.S. Pat. No. 3,992,466 [0150] U.S. Pat. No. 5,401,704 [0151] U.S. Pat. No. 5,648,585 [0152] U.S. Pat. No. 6,111,160 [0153] U.S. Pat. No. 6,323,384 [0154] U.S. Pat. No. 6,652,735 [0155] U.S. Pat. No. 9,827,560 [0156] “Atlas of Zeolite Structure Types” by W. M. Meier and D. H. Olson, Butterworths, 2nd Edition, 1987