Conversion of Motor Fuel Range Naphtha to Light Olefins in a Multiriser Fluid Catalytic Cracking (FCC) Unit

Abstract

A process and system for fluid catalytic cracking (FCC) of hydrocarbon feeds using a multi-riser FCC reactor are described. The conditions in each riser can be adjusted to process various feeds. For example, one riser may be configured to crack heavy hydrocarbons such as vacuum gas oil (VGO) to produce intermediate and light products. Other risers may be configured to crack low and / or intermediate hydrocarbons to produce light olefins. Embodiments of the disclosed process and system may be used to provide a product spectrum having a greater amount of light olefins.

Description

Detailed Description of the Invention

[0001] [Cross - Reference to Related Applications] This application claims priority to U.S. Non - Provisional Patent Application No. 17 / 843,586, filed on June 17, 2022, which is incorporated herein by reference.

[0002] [Field of the Invention] This application relates to a reactor system used in a fluid catalytic cracking (FCC) system, and more particularly, to a method and system for selectively shifting the product profile from an FCC process to lighter olefin products based on the feedstock using a plurality of risers optimized respectively based on the feedstock.

[0003] [Introduction] Fluid catalytic cracking (FCC) is a process commonly used in refineries to increase the yields of transportation fuels and fractions such as gasoline. The FCC process uses a reactor called a riser, which is essentially a pipe, where hydrocarbon feedstock is contacted with catalyst particles to convert the feedstock into more valuable products. The FCC unit converts gas oil or residual oil feedstock by "cracking" hydrocarbons into smaller molecules. The resulting hydrocarbon gas and catalyst mixture both flow within the riser, which is the origin of the term fluid catalytic cracking.

[0004] As employed in current refineries, an FCC unit can, first, convert heavy feedstocks (e.g., vacuum gas oil, reduced crudes, bottoms of atmospheric column, bottoms of vacuum column, etc.) into transportation fuel products (e.g., gasoline, diesel, kerosene, and liquefied natural gas, etc.). With the continuous growth of the demand for petrochemical products, the worldwide demand for transportation fuels such as diesel, for example, is on a decreasing trend. The decrease in the demand for transportation fuels can be attributed to the improvement in the efficiency of automotive fuels and the use of alternative sources of supply such as hydrogen and chemically stored electricity (batteries and fuel cells). As a result of this decline in the demand for transportation fuels, the supply of such transportation fuels in the market will be in excess. On the other hand, the demand for petrochemical products will increase due to the increase in population and consumer demand. Propylene is an important raw material in the manufacture of polypropylene, acrylonitrile, propylene oxide, oxo alcohols, and a wide range of industrial products. The demand for propylene is increasing across regions worldwide, which is mainly caused by the demand for polypropylene and accounts for more than 60% of the total demand for all propylene. The propylene market is expected to grow at an average annual rate of 4% in the next few years.

[0005] In recent years, FCC has played an increasing role in the production of propylene as a useful by-product. Therefore, for example, it is envisioned to use FCC to upgrade surplus transportation fuels such as naphtha, kerosene, diesel, and oxygenates to light olefins such as propylene and ethylene. However, in a conventional single riser FCC, it is very difficult to co-process diesel, kerosene, and / or naphtha with vacuum gas oil (VGO) or residue oil. The reason is that the conditions required to crack the low-boiling fraction into propylene and ethylene are very different from those required for VGO and / or residue oil. When diesel is co-processed with VGO or residue oil in a single riser, most of the diesel will be converted into light cycle oil (LCO), which is of lower quality than diesel, without producing a significant amount of propylene. Similarly, when kerosene is co-processed with VGO or residue oil in a single riser, gasoline and (LCO) are mainly produced.

[0006] Therefore, in the art, it is necessary to shift the product spectrum of the FCC process to more light olefins such as propylene and ethylene.

[0007] [Summary] Disclosed herein is a process for cracking hydrocarbons using a multiraiser fluid catalytic cracking (FCC) reactor. The method comprises cracking a heavy hydrocarbon feedstock using first FCC conditions in a first riser to form a first effluent rich in intermediate and / or light hydrocarbons, and cracking one or more light and / or intermediate hydrocarbon feedstocks under FCC conditions different from the first FCC conditions in one or more risers different from the first riser to form one or more effluents rich in light olefins. According to some embodiments, the heavy feedstock comprises one or more hydrocarbons having an average carbon number of 18 or more. According to some embodiments, the heavy feedstock comprises one or more components selected from the group consisting of vacuum gas oil (VGO), atmospheric residue, atmospheric column bottoms, vacuum column bottoms, residue, and deasphalted oil (DAO). According to some embodiments, the first effluent is rich in hydrocarbons having 3 to 18 carbon atoms. According to some embodiments, the one or more light and / or intermediate hydrocarbon feedstocks comprise fractions. According to some embodiments, the one or more light and / or intermediate hydrocarbon feedstocks comprise one or more hydrocarbons having an average carbon number of 1 to 18. According to some embodiments, the one or more light and / or intermediate hydrocarbon feedstocks comprise one or more components selected from the group consisting of jet fuel, diesel, naphtha, kerosene, C4s, and oxygenate. According to some embodiments, the first FCC conditions comprise maintaining the outlet temperature of the first riser at 510 °C to 575 °C. According to some embodiments, the first FCC conditions comprise mixing steam and the heavy hydrocarbon feedstock at a concentration of 1 wt% to 6 wt% in the first riser. According to some embodiments, the FCC conditions different from the first FCC conditions comprise maintaining the outlet temperature of one or more risers different from the first riser at 550 °C to 675 °C. According to some embodiments, the FCC conditions different from the first FCC conditions comprise mixing steam with the one or more light and / or intermediate hydrocarbon feedstocks at a concentration of 5 wt% to 20 wt%. According to some embodiments, the process further comprises feeding at least a portion of the first effluent to one or more risers different from the first riser.According to some embodiments, supplying at least a portion of the first effluent to one or more risers different from the first riser includes separating the first effluent using a separation system to produce a separated stream enriched in one or more components of the first effluent and recycling the separated stream from the separation system to one or more risers different from the first riser. According to some embodiments, the separated stream is enriched in one or more of naphtha and C4s. According to some embodiments, cracking one or more light and / or intermediate hydrocarbon feeds in one or more risers different from the first riser includes cracking an intermediate feed under second FCC conditions in a second riser and cracking a light feed under third FCC conditions different from the second FCC conditions in a third riser. According to some embodiments, the intermediate feed includes one or more of gasoline, kerosene, jet fuel, and diesel fuel. According to some embodiments, the second FCC conditions include maintaining the outlet temperature of the first riser at 550°C to 675°C. According to some embodiments, the light feed includes one or more of naphtha, C4s, and oxygenate. According to some embodiments, the FCC reaction in each of the risers includes cracking using a catalyst mixture including Y-type zeolite and a shape-selective zeolite. According to some embodiments, the shape-selective zeolite is ZSM-5.

[0008] Also disclosed herein is a fluid catalytic cracking (FCC) reactor comprising a first riser configured to decompose a heavy hydrocarbon feedstock using first FCC conditions to form a first effluent rich in intermediate and / or light hydrocarbons, and one or more additional risers configured to decompose one or more light and / or intermediate hydrocarbon feedstocks under FCC conditions different from the first FCC conditions to form one or more effluents rich in light olefins. According to some embodiments, the heavy feedstock comprises one or more hydrocarbons having an average carbon number of 18 or more. According to some embodiments, the heavy feedstock comprises one or more components selected from the group consisting of vacuum gas oil (VGO), atmospheric residue, atmospheric column bottoms, vacuum column bottoms, residue, and deasphalted oil (DAO). According to some embodiments, the first effluent is rich in hydrocarbons having 3 to 18 carbon atoms. According to some embodiments, the one or more light and / or intermediate hydrocarbon feedstocks comprise fractions. According to some embodiments, the one or more light and / or intermediate hydrocarbon feedstocks comprise one or more hydrocarbons having an average carbon number of 1 to 18. According to some embodiments, the one or more light and / or intermediate hydrocarbon feedstocks comprise one or more components selected from the group consisting of jet fuel, diesel, naphtha, kerosene, C4s, and oxygenates. According to some embodiments, the first FCC conditions include maintaining the outlet temperature of the first riser at 510°C to 575°C. According to some embodiments, the first FCC conditions include mixing steam and the heavy hydrocarbon feedstock at a concentration of 1 wt% to 6 wt% in the first riser. According to some embodiments, the FCC conditions different from the first FCC conditions include maintaining the outlet temperature of one or more risers different from the first riser at 550°C to 675°C. According to some embodiments, the FCC conditions different from the first FCC conditions include mixing steam and the one or more light and / or intermediate hydrocarbon feedstocks at a concentration of 5 wt% to 20 wt%. According to some embodiments, the reactor is configured to supply at least a portion of the first effluent to one or more risers different from the first riser.According to some embodiments, supplying at least a portion of the first effluent to one or more risers different from the first riser includes separating the first effluent using a separation system to produce a separated stream enriched in one or more components of the first effluent and recycling the separated stream from the separation system to one or more risers different from the first riser. According to some embodiments, the separated stream is enriched in one or more of naphtha and C4s. According to some embodiments, cracking one or more light and / or intermediate hydrocarbon feeds in one or more risers different from the first riser includes cracking an intermediate feed under second FCC conditions in a second riser and cracking a light feed under third FCC conditions different from the second FCC conditions in a third riser. According to some embodiments, the intermediate feed includes one or more of gasoline, kerosene, jet fuel, and diesel fuel. According to some embodiments, the second FCC conditions include maintaining the outlet temperature of the first riser at 550°C to 675°C. According to some embodiments, the light feed includes one or more of naphtha, C4s, and oxygenate. According to some embodiments, the FCC reaction in each of the risers includes cracking using a catalyst mixture including Y-type zeolite and a shape-selective zeolite. According to some embodiments, the shape-selective zeolite is ZSM-5.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0010] [Detailed Description] Figure 1 shows one embodiment of a multi-riser FCC reactor 100 as disclosed herein. The general functionality of an FCC reactor is well known in the art and will only be briefly described herein. Reactor 100 includes three risers 102, 104, and 106. However, other embodiments may include more or fewer risers, such as, for example, two, four, five risers, etc. As will be described in more detail below, each of the risers may be configured for different feeds. The feed is supplied to the first riser 102 at the first feed nozzle 114. According to some embodiments, any of the risers may have more than one nozzle. The catalyst is supplied to the first riser at the first valve 116. Valve 116 may be, for example, a slide valve. The feed is supplied to the second riser 104 at the second feed nozzle 118, and the catalyst is supplied via the second valve 120. The feed is supplied to the third riser 106 at the third feed nozzle 122, and the catalyst is supplied via the third valve 124. Each of the first, second, and third risers is respectively connected to dedicated cyclones 126, 128, and 130, which separate most of the catalyst from each of the hydrocarbon riser effluents. The reactor includes a plenum system 132 and one or more upper riser cyclones 134. While the illustrated embodiment includes a common upper cyclone, other embodiments may include dedicated first and second stage cyclone systems for each riser. The plenum system 132 and one or more upper riser cyclones 134 are configured to remove residual catalyst from the hydrocarbon product before the product is discharged as reactor effluent. According to some embodiments, there may be separate lines instead of a single reactor effluent line as shown in the drawings. The reactor includes a disengaging section 108, a stripper section 110, and a regeneration section 112. As is well known in the art, the spent catalyst separated using cyclones (e.g., 126, 128, 130, and 134) is supplied to the stripper section 110, where hydrocarbons are stripped from the catalyst, for example, using steam. The stripped catalyst is then supplied to the regeneration section 112, where the catalyst is heated to burn off coke.The hydrocarbons recovered from the catalyst during stripping exit the reactor through the discharge section 132 together with the hydrocarbons separated through the cyclone. On the other hand, the coke supported on the catalyst is burned off in the regeneration section 112, and the flue gas produced by the combustion of the coke is released through the discharge section 136. The regenerated catalyst can be recycled to the riser.

[0011] As described above, the conditions of each riser may be adjusted based on the raw materials reacting in that riser. The conditions that can be controlled within each riser include temperature, the residence time of the raw materials within the riser, the partial pressure of the raw materials, and the ratio of the catalyst to the raw materials. The partial pressure of the raw materials is controlled by controlling the amount of steam injected into the riser. Generally, lighter reactants require more steam for decomposition than heavier components, and paraffinic raw materials require more steam than olefinic raw materials.

[0012] Since the cracking reaction is an endothermic reaction, that is, heat must be supplied to the reactor process to heat the raw materials and maintain the reaction temperature, it is important to control the temperature in each riser. The required temperature is determined by the individual raw materials, and generally, lighter molecules require a higher temperature than heavier molecules for the duration of the reaction. The heat to sustain the reaction in the riser is provided by the heat generated during catalyst regeneration. Coke is formed during the conversion process using heavy raw materials. The coke is deposited on the catalyst and is ultimately burned in the regeneration section 112 with an oxygen source such as air. The combustion of coke is an exothermic process that can supply the heat required for the cracking reaction. The heat of combustion generated by regeneration raises the temperature of the catalyst, and the hot catalyst is recycled to contact the raw materials in the riser, thereby maintaining the overall heat balance within the system. The amount of heat provided to the riser can be controlled by adjusting the amount of catalyst supplied to the riser, for example, by controlling valves (e.g., valves 116, 120, and 124 in FIG. 1). In a balanced operation, no external heat source or fuel is required to complement the heat from coke combustion. A balanced operation can be achieved when a sufficient amount of heavy material is processed, thereby forming a sufficient amount of coke to supply the heat required for the heat balance in all risers. Oxygenates are usually exothermic, so a balance can be achieved with an appropriate selection of raw materials, even if coke formation is low. If additional heat is required to maintain the heat balance, a coke former can be added to the raw materials to increase the amount of coke formed and then burned. Alternatively, fuel can be added to the regeneration process. U.S. Patent No. 8,383,052, the entire contents of which are incorporated herein by reference, describes a method for maintaining the heat balance within an FCC reactor.

[0013] Figure 2 shows an embodiment of process 200 incorporating a multi-riser FCC reactor 202. The multi-riser FCC reactor 202 may be, for example, a three-riser reactor such as reactor 100 (FIG. 1), or may comprise more or fewer risers. Figure 2 shows some examples of the assumed feed streams to reactor 202. It should be noted that the illustrated feeds are merely examples and are not exhaustive. Reactor 202 generally comprises at least one riser (referred to herein as a "heavy riser") configured for heavy feeds such as, for example, vacuum gas oil (VGO), atmospheric residue, bottoms of the atmospheric column, bottoms of the vacuum column, residue, and / or deasphalted oil (DAO). Generally, as used herein, a "heavy riser" refers to a feedstock having an average carbon number greater than 18. According to some embodiments, the heavy riser may be configured to crack the heavy feed into fuel products (e.g., gasoline, diesel, kerosene, liquefied natural gas, etc.) and / or naphtha-rich streams.

[0014] Reactor 202 can also be composed of one or more risers configured to decompose intermediate and / or light feeds into a stream rich in light olefins such as, for example, ethylene and / or propylene. Generally, "intermediate feed" refers to a feedstock having an average carbon number of about 8 to 18, and "light feed" refers to a feedstock having an average carbon number of about 1 to 8. Examples of these intermediate and / or light feeds include paraffinic, cycloparaffinic, monoolefinic, diolefinic, cycloolefinic, naphthenic, and aromatic hydrocarbons, as well as hydrocarbon oxygenates. Further representative examples include light paraffinic naphtha, heavy paraffinic naphtha, light olefinic naphtha, heavy olefinic naphtha, mixed paraffinic C4s, mixed olefinic C4s (such as raffinate), mixed paraffinic C5s, mixed olefinic C5s (such as raffinate), mixed paraffinic and cycloparaffinic C6s, non-aromatic fractions from aromatic extraction units, products containing oxygenates from Fischer-Tropsch units, etc., or any combination thereof. Hydrocarbon oxygenates can include alcohols having a carbon number in the range of 1 to 4, ethers having a carbon number of 2 to 8, etc. Examples include methanol, ethanol, dimethyl ether, methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether, tertiary amyl methyl ether (TAME), tertiary amyl ethyl ether, etc.

[0015] The raffinate is an example of an intermediate / light feedstock that can be cracked in the riser of reactor 202 to produce light olefins. As used herein, the term raffinate may refer to one or more of naphtha, diesel, kerosene, and jet fuel. The raffinate may be a light raffinate or an intermediate raffinate, as commonly used terms in the art. According to some embodiments, reactor 202 may comprise separate risers for various intermediate / light components. For example, the reactor may comprise risers for diesel range material, further for jet fuel, and still further for naphtha. According to some embodiments, feedstocks having very similar boiling points or properties may be fed to a common riser. Ideally, the reaction conditions within each riser can be optimized to convert that particular feedstock to light olefins. Also, reactor 202 may comprise risers configured to process feedstocks from different processes within an oil refinery. For example, one embodiment of reactor 202 may comprise one riser configured to receive raffinate from a crude oil distillation column, which raffinate may include straight run naphtha and / or straight run diesel as components. The reactor may also comprise another riser capable of receiving naphtha from other processes such as, for example, from a coker and / or from a visbreaker, etc.

[0016] As shown in FIG. 1, hydrocarbon products from each riser are typically discharged from the reactor as a single, mixed reactor effluent. Thus, the reactor effluent includes effluents from each of the risers and includes a stream rich in fuel / naphtha products from the heavy riser and a stream rich in lighter products (e.g., light olefins) obtained from one or more light / intermediate feedstock risers. Alternatively, each riser may be provided with a dedicated discharge line. Referring again to FIG. 2, the reactor effluent may be fed to a separation system 204. Separation is generally well known in the art and the individual configurations are environment-dependent, so the separation system will not be described in detail here. Generally, the separation system may comprise one or more distillation columns configured to separate the reactor effluent into its components to produce a product spectrum, as shown. Embodiments of process 200 are configured to shift the product spectrum towards a greater amount of light olefins, such as ethylene and / or propylene, etc. According to some embodiments, one or more streams from separation system 204 may be returned to and recycled in FCC reactor 202. For example, a stream rich in naphtha and / or C4+ species may be recycled as feedstock to one of the risers of reactor 202. Some embodiments of process 200 include cracking a heavy stream in a heavy riser to produce a first effluent stream rich in light components such as fuel products, C4s, and / or naphtha, feeding the first effluent stream to a separation system, separating the first effluent stream to produce one or more second streams, and returning and recycling one or more second streams to one or more light / intermediate risers of the FCC reactor for further cracking to produce light olefins.

[0017] In conventional FCC processes configured to produce gasoline and the like, Y-type zeolite catalysts are typically used, which are configured to break down larger (C9+) molecules. Other examples of catalysts useful in fluid catalytic cracking include USY, REY, RE-USY, faujasite, and other synthetic and naturally-derived zeolites, and mixtures thereof. As an embodiment of the disclosed dual riser process described herein, such catalysts may be used in combination with a catalyst that is better configured to break down light feedstocks to produce light olefins. Examples of light feedstock catalysts include shape-selective zeolites configured to break down naphthalene range molecules. Examples of catalysts suitable for use in the breakdown of light feedstocks include ZSM-5 and similar catalysts. Other catalysts include ZSM-11, ZSM-12, ZSM-23, ZSM-35, ZSM-38, and ZSM-48. The ratio of Y-type zeolite catalyst to shape-selective zeolite is optimized based on the relevant feedstock and product targets.

[0018] As an example of how a multi-riser FCC reactor can be used in a process to produce light olefins, consider reactor 100 (FIG. 1). Assume that riser 102 is a heavy riser (i.e., a riser configured to crack heavy feedstocks). The conditions in riser 102 may be optimized to crack the heavy feedstock to produce an effluent rich in intermediate-range products such as naphtha or fuel products. Assume that riser 104 is configured to crack intermediate-range feedstocks and riser 106 is configured to crack light feedstocks, each producing an effluent rich in light olefins. In this example, assume that the heavy feedstock is VGO, the intermediate feedstock is straight-run diesel, and the light feedstock is light naphtha recycle. Table 1 below describes exemplary ranges for temperature, residence time, partial pressure control (i.e., amount of steam), and catalyst / oil ratio for each of the risers. As described herein, each riser can be individually adjusted for its particular feedstock. Note that the lightest component, light naphtha (riser 106), has the highest temperature and the most steam, the intermediate-weight feedstock, diesel (riser 104), has intermediate temperature and intermediate steam, and the heaviest feedstock, VGO (riser 102), has the lowest temperature and the least steam.

[0019]

Table 1

[0020] While particular embodiments of the invention have been shown and described, it should be understood that the foregoing discussion is not intended to limit the invention to these embodiments. It will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, the invention is intended to cover alternatives, modifications, and equivalents that may fall within the spirit and scope of the invention as defined by the claims.

Claims

**Claim 1** A process for cracking hydrocarbons using a multi-riser fluid catalytic cracking (FCC) reactor, comprising: in a first riser, cracking a heavy hydrocarbon feedstock using first FCC conditions to form a first effluent rich in intermediate and / or light hydrocarbons; in one or more risers different from the first riser, cracking one or more light and / or intermediate hydrocarbon feedstocks under FCC conditions different from the first FCC conditions to form one or more effluents rich in light olefins; A method comprising the steps of: **Claim 2** The process according to claim 1, wherein the heavy feedstock comprises one or more hydrocarbons having an average carbon number of 18 or more. **Claim 3** The process according to claim 1, wherein the heavy feedstock comprises one or more components selected from the group consisting of vacuum gas oil (VGO), atmospheric residue, bottoms of the atmospheric column, bottoms of the vacuum column, residue, and deasphalted oil (DAO). **Claim 4** The process according to claim 1, wherein the first effluent is rich in hydrocarbons having 3 to 18 carbon atoms. **Claim 5** The process according to claim 1, wherein the one or more light and / or intermediate hydrocarbon feedstocks comprise fractions. **Claim 6** The process according to claim 1, wherein the one or more light and / or intermediate hydrocarbon feedstocks comprise one or more hydrocarbons having an average carbon number of 1 to 18. **Claim 7** The process according to claim 1, wherein the one or more light and / or intermediate hydrocarbon feedstocks comprise one or more components selected from the group consisting of jet fuel, diesel, naphtha, kerosene, C4s, and oxygenates. **Claim 8** The process according to claim 1, wherein the first FCC conditions include maintaining the outlet temperature of the first riser at 510°C to 575°C. **Claim 9** The process according to claim 1, wherein the first FCC conditions include mixing steam and the heavy hydrocarbon feedstock in the first riser at a concentration of 1 wt% to 6 wt%. **Claim 10** The FCC conditions different from the first FCC conditions include maintaining the outlet temperature of one or more risers different from the first riser at 550°C to 675°C. **Claim 11** The FCC conditions different from the first FCC conditions include mixing steam with the one or more light and / or intermediate hydrocarbon feedstocks at a concentration of 5 wt% to 20 wt%. **Claim 12** The process according to claim 1, further comprising supplying at least a portion of the first effluent to one or more risers different from the first riser.

13. Supplying at least a portion of the first effluent to one or more risers different from the first riser comprises: separating the first effluent using a separation system to produce a separated stream enriched in one or more components of the first effluent; and recirculating the separated stream from the separation system to one or more risers different from the first riser. The process according to claim 12, comprising:

14. The process according to claim 13, wherein the separated stream is enriched in one or more of naphtha and C4s.

15. Decomposing the one or more light and / or intermediate hydrocarbon feeds in one or more risers different from the first riser comprises: decomposing an intermediate feed in a second riser under second FCC conditions; and decomposing a light feed in a third riser under third FCC conditions different from the second FCC conditions. The process according to claim 1, comprising:

16. The process according to claim 15, wherein the intermediate feed comprises one or more of gasoline, kerosene, jet fuel, and diesel fuel.

17. The process according to claim 15, wherein the second FCC conditions comprise maintaining the outlet temperature of the first riser at 550°C to 675°C.

18. The process according to claim 15, wherein the light feed comprises one or more of naphtha, C4s, and oxygenate.

19. The FCC reaction in each of the risers comprises decomposing using a catalyst mixture comprising Y zeolite and a shape-selective zeolite.

20. The process according to claim 19, wherein the shape-selective zeolite is ZSM-5.

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