Process integration for cracking light paraffinic hydrocarbons

Abstract

Systems and methods for the catalytic cracking of light hydrocarbons, such as naphtha, to form light olefins and aromatics is disclosed. The systems and methods may include a catalytic cracking process that involves mixing catalyst with a gas and then this mixture is used to contact a hydrocarbon feed, e.g., light straight run naphtha or heavy straight run naphtha. The hydrocarbon feed may be mixed with dry gas such as methane and/or hydrogen to dilute the hydrocarbon feed, before the hydrocarbon feed is contacted with the catalyst/gas mixture.

Claims

1. A method of producing olefins, the method comprising: preheating a hydrocarbon feed comprising C.sub.5 to C.sub.7 hydrocarbons to at least a temperature of 400° C. to form a preheated hydrocarbon feed; mixing a catalyst with a gas comprising at least one member selected from the group consisting of methane and hydrogen to form a gas/catalyst mixture; contacting the gas/catalyst mixture with the preheated hydrocarbon feed at reaction conditions sufficient to produce C.sub.2 to C.sub.4 olefins; and mixing a hydrocarbon feedstock with a dry gas member selected from the group consisting of methane and hydrogen to dilute the hydrocarbon feedstock and form the hydrocarbon feed; wherein the hydrocarbon feedstock is one member selected from the group consisting of light straight run naphtha and heavy straight run naphtha; wherein the catalyst comprises a solid acid based zeolite catalyst selected from the group consisting of one or more medium pore zeolites, one or more large pore zeolites and combinations thereof; wherein the zeolite catalyst is only modified by at least one member selected from the group consisting of desilication and steaming; wherein the reaction conditions comprise a temperature in a range of 500 to 750° C. and pressure in a range of 0.5 to 5 bars; wherein a weight ratio of dry gas/hydrocarbon feedstock in the hydrocarbon feed ranges from 20 to 100; and wherein the catalyst is fresh.

2. The method of claim 1, wherein the weight ratio of dry gas/hydrocarbon feedstock in the hydrocarbon feed ranges from 30 to 100.

3. The method of claim 1, wherein the weight ratio of dry gas/hydrocarbon feedstock in the hydrocarbon feed ranges from 50 to 100.

4. The method of claim 1, wherein the zeolite catalyst is modified by desilication.

5. The method of claim 1, wherein the mixing occurs at a first point in a riser of a fluid catalytic cracking reactor and the method further comprises: allowing the gas/catalyst mixture to rise to a second point in the riser; and injecting the preheated hydrocarbon feed comprising C5 to C7 hydrocarbons at the second point in the riser, wherein the contacting the gas/catalyst mixture with the preheated hydrocarbon feed causes cracking of at least some of the C5 to C7 hydrocarbons to produce the light olefins, wherein effluent from the fluid catalytic cracking reactor comprises methane, ethane, ethylene and propylene, or LPG(C.sub.3+C.sub.4).

6. The method of claim 1, wherein the mixing occurs at a first point in a riser of a vertical fluid catalytic cracking reactor and the method further comprises: allowing the gas/catalyst mixture to rise to a second point in the riser; and injecting the preheated hydrocarbon feed comprising C5 to C7 hydrocarbons at the second point in the riser, wherein the contacting the gas/catalyst mixture with the preheated hydrocarbon feed causes cracking of at least some of the C5 to C7 hydrocarbons to produce the light olefins; and wherein the preheated hydrocarbon feed enters the riser at an elevated location relative the catalyst entrance and meets an upwardly flowing gas/catalyst mixture.

7. The method of claim 1, wherein the catalyst is fresh.

8. The method of claim 1, wherein the zeolite catalyst is modified by steaming.

9. A method of producing olefins, the method comprising: preheating a hydrocarbon feed comprising C.sub.5 to C.sub.7 hydrocarbons to at least a temperature of 400° C. to form a preheated hydrocarbon feed; mixing a catalyst with a gas comprising at least one member selected from the group consisting of methane and hydrogen to form a gas/catalyst mixture; contacting the gas/catalyst mixture with the preheated hydrocarbon feed at reaction conditions sufficient to produce C.sub.2 to C.sub.4 olefins; and mixing a hydrocarbon feedstock with a dry gas selected from the group consisting of methane and hydrogen to dilute the hydrocarbon feedstock and form the hydrocarbon feed; wherein a weight ratio of dry gas/hydrocarbon feedstock in the hydrocarbon feed is 100; and wherein the catalyst is fresh.

10. The method of claim 9, wherein the hydrocarbon feedstock comprises light straight run naphtha and heavy straight run naphtha.

11. The method of claim 9, wherein the mixing and contacting occur in a fluid catalytic cracking reactor, wherein effluent from the fluid catalytic cracking reactor contains cracked hydrocarbon products, wherein the cracked hydrocarbon products consist of at least one member selected from the group consisting of methane, ethane, ethylene, propylene and LPG (C.sub.3+C.sub.4).

12. The method of claim 9, wherein the preheating is conducted in a heat exchanger.

13. The method of claim 9, wherein the gas comprises methane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 shows a schematic of a system for cracking a hydrocarbon feedstock to form light olefins, according to embodiments of the invention;

(3) FIG. 2 shows a vertical fluid catalytic cracking riser reactor for cracking a hydrocarbon feedstock to form light olefins, according to embodiments of the invention;

(4) FIG. 3 shows a method for cracking a hydrocarbon feedstock to form light olefins, according to embodiments of the invention; and

(5) FIG. 4 shows a graph of methane equilibrium conversion as a function of temperature.

DETAILED DESCRIPTION OF THE INVENTION

(6) A method has been discovered for catalytically cracking hydrocarbon mixtures into light olefins. In embodiments of the invention, the catalyst used in the catalytic cracking process is a solid and is mixed with a gas (fluidizing solid catalyst particles) and then this mixture is used to contact a hydrocarbon feed, e.g., light straight run naphtha or heavy straight run naphtha. Further, in embodiments of the invention, instead of using steam as a diluent, as conventional cracking methods do, the hydrocarbon feed may be mixed with methane to dilute the hydrocarbon feed, before the hydrocarbon feed is contacted with the gas/catalyst mixture (fluidized solid catalyst). In embodiments of the invention, the hydrocarbon mixture that is cracked includes components with a boiling point of less than 350° C.

(7) Embodiments of the invention involve a catalytic cracking process that uses dry gas (e.g., methane and/or hydrogen) to dilute the hydrocarbon feed and to fluidize the catalyst. The catalytic cracking may be implemented in a vertical fluid catalytic cracking reactor. According to embodiments of the invention, the dry gas is mixed with the solid catalyst particles and the gas/catalyst mixture (fluidized solid catalyst) formed is fed into a riser of the vertical fluid catalytic cracking reactor at a location upstream and below the hydrocarbon feed entrance into the riser. Thus, in embodiments of the invention, the hydrocarbon feed enters the riser at an elevated location relative the catalyst entrance and meets an upwardly flowing gas/catalyst mixture. In embodiments of the invention, spent catalyst is removed from the reactor, regenerated and returned to the reactor.

(8) FIG. 1 shows system 10 for cracking a hydrocarbon feedstock to form light olefins, according to embodiments of the invention. FIG. 2 shows vertical fluid catalytic cracking riser reactor 20 for cracking a hydrocarbon feedstock, according to embodiments of the invention. Vertical fluid catalytic cracking riser reactor 20 may be used as a reactor in system 10. FIG. 3 shows method 30 for cracking a hydrocarbon feedstock, according to embodiments of the invention. Method 30 may be implemented, at least in part, by system 10 and/or vertical fluid catalytic cracking riser reactor 20.

(9) FIG. 3 shows that method 30 may begin at block 300, which may involve, with respect to system 10 as shown in FIG. 1, mixing hydrocarbon feedstock 100 with dry gas 101 to form hydrocarbon feed 102. Hydrocarbon feedstock 100 may include a mixture of hydrocarbons having a boiling point less than 350° C. For example, hydrocarbon feedstock 100 may include light naphtha having C.sub.5 to C.sub.7 hydrocarbons and/or heavier hydrocarbon with boiling point of less than 350° C. In embodiments of the invention, hydrocarbon feedstock 100 may include one or more of N—C.sub.5, I—C.sub.5, cycl-C.sub.5, N—C.sub.6, I—C.sub.6, cycl-C.sub.6, hydrocarbons, benzene, or C.sub.7 hydrocarbons. Dry gas 101 may include methane (CH.sub.4) and/or hydrogen (H.sub.2).

(10) Mixing hydrocarbon feedstock 100 with dry gas 101 dilutes hydrocarbon feedstock 100 so that, in embodiments of the invention, the dry gas/feed weight ratio in hydrocarbon feed 102 is 0.1 to 100 to reduce the hydrocarbon partial pressure and to ensure proper fluidization flow. When dry gas 101 dilutes hydrocarbon feedstock 100 and thereby reduces the partial pressure of the reactive hydrocarbons in hydrocarbon feed 102, in the cracking process, this reduction in partial pressure reduces side reactions and minimizes catalyst dealumination.

(11) As noted above, methane and/or hydrogen are examples of diluents that may be used in embodiments of the invention. Methane is a very stable molecule that has very limited reactivity at the reaction temperature of the catalytic cracking process described herein. FIG. 4 shows a graph of methane equilibrium conversion as a function of temperature. As the graph of FIG. 4 shows, a temperature of 650° C. is required for the equilibrium conversion of methane to reach only 8%. Given the expected residence time in vertical fluid catalytic cracking riser reactor 20, which would be very low, the conversion of methane will be less than the equilibrium conversion. Therefore, methane is reasonably considered as a diluent in the catalytic cracking process described herein to dilute and reduce the partial pressure of the reactive hydrocarbons.

(12) After mixing to form hydrocarbon feed 102 or otherwise providing hydrocarbon feed 102, method 30 may include, at block 301, with respect to system 10 as shown in FIG. 1, flowing hydrocarbon feed 102 to heat exchanger 103. And at block 302, according to embodiments of the invention, heat exchanger 103 preheats hydrocarbon feed 102 to, for example, a temperature in the range from 400° C. to 600° C. to form preheated hydrocarbon feed 104. This temperature, in embodiments of the invention, may be effective in minimizing thermal cracking. Block 302 further includes flowing preheated hydrocarbon feed to reactor 105, as shown in FIG. 1.

(13) Reactor 105 of FIG. 1 is adapted to carry out the catalytic cracking of preheated hydrocarbon feed 104 to form light olefins (C.sub.2-C.sub.4 olefins). In embodiments of the invention, reactor 105 contacts preheated hydrocarbon feed 104 with regenerated catalyst 106 and dry gas 107 under reaction conditions sufficient to form the light olefins.

(14) In embodiments of the invention, reactor 105 is a riser reactor such as vertical fluid catalytic cracking riser reactor 20, as shown in FIG. 1. FIG. 2 shows vertical fluid catalytic cracking riser reactor 20 may include dry gas nozzles 200 for injecting dry gas, e.g., dry gas 107 (FIG. 1), into riser 201 at lower point A of riser 201. Vertical fluid catalytic cracking riser reactor 20 may also include catalyst feed section 202. Catalyst feed section 202 is in fluid communication with riser 201, as shown in FIG. 2, in a manner so that catalyst (e.g., regenerated catalyst 106, FIG. 1) flows down towards dry gas nozzles 200, while dry gas nozzles 200 are injecting dry gas 107 (FIG. 1) into riser 201. The effect of this is that dry gas 107 flowing upwards is mixed with regenerated catalyst 106 flowing tangentially into the path of dry gas 107 to form a catalyst gas/mixture (fluidized solid catalyst) such as gas/catalyst mixture 108 (FIG. 1).

(15) Vertical fluid catalytic cracking riser reactor 20 may have, at point B, feed injector 203, which leads into riser 201 and is adapted to inject hydrocarbon feed, e.g., preheated hydrocarbon feed 104 (FIG. 1), into riser 201, at point B. Point B is at a higher elevation than point A of vertical fluid catalytic cracking riser reactor 20. Thus, after entering riser 201 at point B, in embodiments of the invention, preheated hydrocarbon feed 104 meets and mixes with rising gas/catalyst mixture 108. In this way, vertical fluid catalytic cracking riser reactor 20 is adapted to contact gas/catalyst mixture 108 with preheated hydrocarbon feed 104.

(16) As can be seen from the discussion above, vertical fluid catalytic cracking riser reactor 20 is adapted to and may be used to carry out aspects of method 30. For example, at block 303, method 30, with respect to system 10 of FIG. 1, may involve mixing regenerated catalyst 106 (e.g., a solid zeolite catalyst) with dry gas comprising methane (CH.sub.4) and/or hydrogen (H.sub.2) to form gas/catalyst mixture 108 at a first point in a riser of a fluid catalytic cracking riser reactor. In embodiments of the invention, the catalyst to oil weight ratio as a result of this mixing in the reactor is in the range from 3 to 50, and preferably from 5 to 40.

(17) Block 304 involves, with respect to system 10 as shown in FIG. 1, allowing gas/catalyst mixture 108 to rise from a first point in reactor 105 (e.g., point A in the riser of vertical fluid catalytic cracking riser reactor 20) to a second point in reactor 105 (e.g., point B in the riser of vertical fluid catalytic cracking riser reactor 20). According to embodiments of the invention, as gas/catalyst mixture 108 rises, block 305 involves injecting the preheated hydrocarbon feed of block 302 at point B in the riser of vertical fluid catalytic cracking riser reactor 20. In embodiments of the invention, the hydrocarbon feed comprises C.sub.5 to C.sub.7 hydrocarbons. In this way, block 306 of method 30 may be implemented, which includes contacting gas/catalyst mixture 108 with preheated hydrocarbon feed 104 to cause cracking of at least some of the C.sub.5 to C.sub.7 hydrocarbons to produce the light olefins.

(18) In embodiments of the invention, one or more of the following may also be produced in reactor 105 (e.g., vertical fluid catalytic cracking riser reactor 20): methane, ethane, ethylene and propylene, or LPG (C.sub.3+C.sub.4). The contacting of gas/catalyst mixture 108 with preheated hydrocarbon feed 104 (which may include C.sub.5 to C.sub.7 hydrocarbons) may be at reaction conditions reaction conditions that include a temperature in a range of 500 to 750° C. and pressure in a range of 0.5 to 5 bars. In embodiments of the invention, the residence time in the fluid catalytic cracking is in a range 1 to 10 seconds.

(19) In embodiments of the invention, reactor 105 (e.g., vertical fluid catalytic cracking riser reactor 20) in normal operation, in method 30, is free from steam. For example, in embodiments of the invention, unlike other conventional catalytic cracking processes, steam is not mixed with the hydrogen feed (not used as a diluent) and the amount of water present in the feed to vertical fluid catalytic cracking riser reactor 20 is zero or substantially zero. In embodiments of the invention, only hydrogen and/or methane is used as diluent of the hydrocarbon feed.

(20) After the cracking process of block 306, method 30 may involve separating contents of reactor 105 (e.g., vertical fluid catalytic cracking riser reactor 20) into spent catalyst 110 and reactor vapor effluent 109, at block 307. Reactor vapor effluent 109 may include unreacted hydrocarbon feed, C.sub.2 to C.sub.4 olefins, dry gas 101, and dry gas 107. To recover desired products, block 308 may include, with respect to system 10 of FIG. 1, separating reactor vapor effluent 109 in downstream separation process 112 to produce desired products such as a product stream including ethylene, a product stream including propylene, a product stream including dry gas, and a product stream including other products. The other products may be, for example, unreacted hydrocarbons such as C.sub.4 to C.sub.5 hydrocarbons, which may be recycled and mixed with hydrocarbon feedstock 100, hydrocarbon feed 102, or preheated hydrocarbon feed 104, or combinations thereof, for sending to reactor 105 for further conversion to light olefins, as shown in FIG. 1.

(21) In embodiments of the invention, method 30 may further include, in system 10 as shown in FIG. 1, sending spent catalyst 110 to catalyst regeneration system 111 for regenerating spent catalyst 110 by burning off coke formed on spent catalyst 110 during the cracking process of block 306. Thus, block 309 may involve, in system 10 as shown in FIG. 1, catalyst regeneration system 111 regenerating spent catalyst 110 to form regenerated catalyst 106, which, in embodiments of the invention, is returned to reactor 105, at block 310 of method 30.

(22) Catalysts that may be used for the catalytic cracking process, in embodiments of the invention, include a solid acid based catalyst selected from the list consisting of: one or more spray dried medium pore zeolites, including ZSM-5 and modified ZSM-5; one or more large pore zeolites, including zeolite Y and ultra-stable zeolite Y; and combinations thereof. The zeolite may be modified by demetalization such as dealumination or desilication, chemical treatment and steaming. Further, the catalyst may be hydrothermally stabilized by adding phosphorus or rare earth metal to enhance its thermal stability.

EXAMPLES

(23) As part of the disclosure of the present invention, specific examples are included below. The examples are for illustrative purposes only and are not intended to limit the invention. Those of ordinary skill in the art will readily recognize parameters that can be changed or modified to yield essentially the same results.

Example 1

Cracking of Light Naphtha

(24) In Example 1, a catalyst was tested for light naphtha cracking using a fluidized bed reactor without using steam. The catalyst/feed ratio was 12/1 by weight. Inert gas was used to represent (imitate) the use of methane. In this example, fresh catalyst was used and the conversion rate achieved was 64 wt. %. Table 1 shows the composition of the light naphtha feed in wt. %.

(25) TABLE-US-00001 TABLE 1 (Light Naphtha Feed Composition) Feed (LSRN) N-C5 28.8 I-C5 11.8 Cycl-C5 1.9 N-C6 24.5 I-C6 26.9 Cycl-C6 4.6 Benzene 1.3 C7 0.3 sum 100

(26) The product distribution as a result of the catalytic cracking of Example 1 is shown in Table 2.

(27) TABLE-US-00002 TABLE 2 (Light Naphtha Cracking Over Fluidized Reactors Using Fresh Catalyst) Fresh Catalytst Component YIELDS, wt % Methane 6.6 Ethane 8.07 Ethylene + Propylene 33 LPG (C3 + C4) 6.23 C4 Olefins 8.24 heavy product 37.33

Example 2

Comparative Example—Light Naphtha Cracking Over Fluidized Reactors Using Steamed Catalyst

(28) In Example 2, fresh catalyst was first steamed at 750° C. outside the reactor to represent (imitate) the steaming effect when steam is mixed with hydrocarbon feed. The steamed catalyst was mixed with equilibrium catalyst. The reaction is conducted in a fluidized bed reactor. The conversion is 56 wt. % and the product distribution is shown in Table 3.

(29) TABLE-US-00003 TABLE 3 (Light Naphtha cracking over fluidized reactors using steamed catalyst) 90% Steamed Catalyst + 10% Ecat Component YIELDS, wt % Methane 5.19 Ethane 5.87 Ethylene + Propylene 29.98 LPG (C3 + C4) 5.14 C4 Olefins 8.23 heavy product 45.01

Example 3

Published Example of n-Hexane Steam Catalytic Cracking

(30) Example 3 was not carried out by the present inventors; rather, Example 3 is a summary of a publication by Aritomo Yamaguchi et. al., Fuel Processing Technology 126 (2014) 343-349. This publication reported on a study of n-hexane steam catalytic cracking. Yamaguchi et. al. showed that catalyst is deactivated steadily from 100% conversion to 53% over five hours. After the catalyst regeneration under oxidative atmosphere, the initial conversion could not pass 66% indicating that catalyst deactivation by dealumination took place.

(31) Although embodiments of the present application and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the above disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.