Enhanced light olefin yield via steam catalytic downer pyrolysis of hydrocarbon feedstock

Abstract

Systems and methods for steam and catalytic cracking of a hydrocarbon inlet stream comprising hydrocarbons. Systems and methods can include a catalyst feed stream, where the catalyst feed stream comprises a fluid and a heterogeneous catalyst, the heterogeneous catalyst operable to catalyze cracking of the hydrocarbons on surfaces of the heterogeneous catalyst a steam feed stream, where the steam feed stream is operable to effect steam cracking of the hydrocarbons, and where the steam feed stream decreases coking of the heterogeneous catalyst; and a downflow reactor, where the downflow reactor is operable to accept and mix the hydrocarbon inlet stream, the catalyst feed stream, and the steam feed stream, where the downflow reactor is operable to produce light olefins by steam cracking and catalytic cracking, and where the downflow reactor is operable to allow the heterogeneous catalyst to flow downwardly by gravity.

Claims

1. A system for steam and catalytic cracking of a hydrocarbon inlet stream comprising hydrocarbons, the system comprising: a catalyst feed stream, where the catalyst feed stream comprises a fluid and a heterogeneous catalyst, the heterogeneous catalyst operable to catalyze cracking of the hydrocarbons on surfaces of the heterogeneous catalyst, and the hydrocarbons comprising a crude oil feed; a steam feed stream, where the steam feed stream is operable to effect steam cracking of the hydrocarbons, where the steam feed stream decreases coking of the heterogeneous catalyst, and where the steam feed stream comprises a recycle steam stream; a mixing zone for atomization of the hydrocarbon inlet stream with the steam feed stream, where a catalyst feed stream inlet to the mixing zone precedes a steam feed stream inlet to the mixing zone, and where the steam feed stream inlet to the mixing zone precedes a hydrocarbon inlet stream to the mixing zone, and where the steam feed stream can be injected directly and separately to the mixing zone before, simultaneous with, or before and simultaneous with the hydrocarbon inlet stream and the catalyst feed stream; and a downflow reactor, where the downflow reactor is operable to accept and mix the hydrocarbon inlet stream, the catalyst feed stream, and the steam feed stream, where the downflow reactor is operable to produce light olefins by steam cracking and catalytic cracking, where the total amount of steam supplied to the downflow reactor enhances light olefin yield from the hydrocarbon inlet stream effecting steam catalytic cracking resulting in a product stream comprising ethylene and propylene with a total yield of ethylene and propylene together at about at least 20% from the crude oil feed, and where the downflow reactor is operable to allow the heterogeneous catalyst to flow downwardly by gravity.

2. The system according to claim 1, where the downflow reactor operates in a temperature range between about 500° C. to about 700° C.

3. The system according to claim 1, further comprising a catalyst hydrocarbon stripper with structured packing, where the catalyst hydrocarbon stripper is operable to remove hydrocarbons adsorbed to the heterogeneous catalyst by applying steam.

4. The system according to claim 3, where the recycle steam stream comprises steam used in the catalyst hydrocarbon stripper with structured packing to remove hydrocarbons adsorbed to the heterogeneous catalyst.

5. The system according to claim 4, further comprising a catalyst regenerator operable to regenerate spent heterogeneous catalyst through combustion of coke disposed on the heterogeneous catalyst.

6. The system according to claim 5, where the catalyst feed stream comprises new, unused heterogeneous catalyst and regenerated catalyst from the catalyst regenerator.

7. The system according to claim 1, where a yield of light olefins from the hydrocarbon inlet stream is at least about 30%.

8. The system according to claim 1, where the system is operable to accept the steam feed stream when the steam feed stream is greater than about 3% by weight of the hydrocarbon inlet stream.

9. The system according to claim 1, where the system is operable to accept the steam feed stream when the steam feed stream is between about 5% by weight and about 15% by weight of the hydrocarbon inlet stream.

10. The system according to claim 1, where the system is operable to accept the steam feed stream when the steam feed stream is about 10% by weight of the hydrocarbon inlet stream.

11. The system according to claim 1, where the residence time of the downflow reactor prevents secondary reactions responsible for the consumption of the light olefins.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following descriptions, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the disclosure and are therefore not to be considered limiting of the disclosure's scope as it can admit to other equally effective embodiments.

(2) FIG. 1 is a schematic showing one layout for an apparatus and method applying fluidized catalytic pyrolysis (FCP).

DETAILED DESCRIPTION

(3) So that the manner in which the features and advantages of the embodiments of apparatus, systems, and methods for fluidized catalytic pyrolysis, as well as others, which will become apparent, may be understood in more detail, a more particular description of the embodiments of the present disclosure briefly summarized previously may be had by reference to the various embodiments, which are illustrated in the appended drawings, which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the disclosure and are therefore not to be considered limiting of the present disclosure's scope, as it may include other effective embodiments as well.

(4) Referring now to FIG. 1, a schematic is pictured showing one layout for an apparatus and method applying fluidized catalytic pyrolysis (FCP). FCP system 100 includes a catalyst regenerator 102, a downflow reactor 104, and a catalyst stripper with structured packing 106. FCP system 100 further includes a steam supply line 108, a steam outlet line 110, a steam recycle line 112, which is optional, and a steam inlet line 114, which combines steam from steam supply line 108 and steam from optional steam recycle line 112. Hydrocarbon feedstock, such as for example crude oil in addition to or alternative to other hydrocarbons, is fed to FCP system 100 by feed injection line 116, and products, such as for example light olefins including ethylene and propylene, exit FCP system 100 by product outlet line 118.

(5) FCP system 100 further includes a gas-solid separator 120, such as for example a cyclone separator, to separate gaseous components, such as for example gaseous products including light olefins such as ethylene and propylene, from solid catalyst. Catalyst and products are separated using one or more cyclone separators, or similar separators, with solid catalyst particles being sent to the catalyst regenerator 102, while products consisting of hydrocarbons pass from the system 100 and are sent downstream for separation and collection. A combined downflow reactor inlet line 122 provides steam, catalyst, and hydrocarbon feedstock to downflow reactor 104. In downflow reactor 104, catalytic cracking and steam cracking (pyrolysis) proceed synergistically and in unison to produce light olefins from hydrocarbon feedstock. Light olefins (gases) exit via gaseous outflow lines 124 and product outlet line 118.

(6) Hydrocarbon feedstock from feed injection line 116 is charged to a mixing zone (for atomization of the feed) where it is mixed with high pressure steam from steam inlet line 114 and hot regenerated catalyst from the catalyst regenerator 102. High pressure steam disperses the feedstock, and a mixture of steam, hydrocarbons, and catalyst (either or both regenerated catalyst and new catalyst) moves downwards through a reaction zone in downflow reactor 104 where hydrocarbon cracking reactions take place. A mixture of steam, spent catalyst, and hydrocarbon products from the reaction zone enters a gas solid separation zone in gas-solid separator 120. Spent solid catalyst is separated from gases by centrifugal forces, and the catalyst flows downwardly by gravity to an upper section of the catalyst stripper with structured packing 106.

(7) Hydrocarbon product gases, such as ethylene and propylene, are recovered in a product recovery section from gas-solid separator 120. For the spent catalyst, high pressure steam is injected into catalyst stripper with structured packing 106 to strip heavy hydrocarbons adsorbed on catalyst particles. Vapors of heavy hydrocarbons and unreacted feed from the spent catalyst are withdrawn from the catalyst stripper with structured packing 106 and sent to product recovery. Spent catalyst is then transferred to the catalyst regenerator 102 from the catalyst stripper with structured packing 106.

(8) The downward arrow labeled “catalyst down flow” pointing downwardly from catalyst regenerator 102 to catalyst stripper with structured packing 106 shows the general flow of activated catalyst (optionally new or regenerated or both) downwardly, with gravity, through the system. The upward pointing arrow labeled “catalyst up flow” shows the general flow of deactivated, coked catalyst in catalyst return line 126 from catalyst stripper bottoms line 128 to catalyst regenerator 102. Upward gas flow, such as for example air, through catalyst return line 126 carries deactivated, coked catalyst particles from catalyst stripper bottoms line 128 to catalyst regenerator 102.

(9) In FCP system 100, an amount of steam is applied in downflow reactor 104 to enhance light olefin yield from hydrocarbon feedstock and to reduce the coking rate of solid catalyst. The catalyst system applies a suitable high olefinic catalyst containing zeolite, such as for example zeolite socony mobil-5™ (ZSM-5). ZSM-5 is an aluminosilicate zeolite belonging to the pentasil family of zeolites, Na.sub.nAl.sub.nSi.sub.96-nO192.16H.sub.2O (0<n<27), used in the petroleum industry as a heterogeneous catalyst. Other suitable catalysts include faujasite, such as faujasite-Na, faujasite-Mg and faujasite-Ca which share the same basic formula: (Na.sub.2,Ca,Mg).sub.3.5[Al.sub.7Si.sub.17O.sub.48].32(H.sub.2O) by varying the amounts of sodium, magnesium and calcium, and BEA zeolites (zeolite beta) supported on refractory oxides such as alumina.

(10) One problem associated with the use of steam is hydrothermal stability of the catalyst, and catalysts used in embodiments of the present disclosure are suitable or operable to withstand hydrothermal conditions which facilitate catalyst degradation in prior art systems. Catalysts used in embodiments of the present disclosure are utilized in fluidized, rather than packed, beds enabling greater conversion to light olefins. Steam in embodiments of the present invention is used not only for atomization of the hydrocarbon feed, fluidization of catalysts, and stripping of hydrocarbons from spent catalyst, but is also advantageously used in an amount operable to effect steam cracking of hydrocarbons simultaneous with catalytic cracking on a catalyst surface. Steam can be injected to downflow reactor 104 before, simultaneous with, or before and simultaneous with a hydrocarbon feed and catalyst. Steam in embodiments of the present disclosure is not used merely for stripping spent catalyst, but instead positively impacts the product distribution toward light olefins by causing steam cracking reactions in the downflow reactor 104.

(11) Steam is used for pyrolysis as well as to reduce coke formation on the catalyst. Fresh steam can be introduced to downflow reactor 104 with fresh catalyst injection from catalyst regenerator 102. In addition, steam used in the catalyst stripper with structured packing 106 to clean the catalyst of remaining hydrocarbons adsorbed on the catalyst can be recycled to the downflow reactor 104 by steam recycle line 112. In some embodiments, the preferred operation temperature of FCP system 100 is in the range of about 500° C. to about 700° C. The temperature range used in prior art steam cracking is about 750° C. to about 900° C., but in in embodiments of the present disclosure, the temperature is about 50° C. to about 400° C. less than what is used in steam cracking.

(12) In FCP system 100, hydrocarbon feedstock, such as for example petroleum feedstock, is preheated and mixed with steam and then fed to downflow reactor 104, where it intimately mixes with and contacts hot catalyst from catalyst regenerator 102. Preheating steam is used to atomize the hydrocarbon feedstock and reduce the viscosity of the feed before being sent to the reactor. Prior to entering downflow reactor 104, additional steam is injected to make up the total quantity of steam required for steam cracking (pyrolysis) reactions, in addition to catalytic cracking. In embodiments of the present disclosure, the amount of steam fed to downflow reactor 104 is greater than about 3 weight % of the hydrocarbon feed, in some embodiments the amount of steam fed to downflow reactor 104 is greater than about 5 weight % of the hydrocarbon feed, in some embodiments the amount of steam fed to downflow reactor 104 is greater than about 10 weight % of the hydrocarbon feed, and in some embodiments the amount of steam fed to downflow reactor 104 is between about 5 weight % and about 15 weight %, for example about 10 weight %, of the hydrocarbon feed.

(13) The hydrocarbon feedstock is catalytically cracked in the presence of steam while steam cracking also simultaneously takes place, and spent catalyst containing coke is transferred by gravity to catalyst stripper with structured packing 106. Deposited hydrocarbons on the catalyst particles (other than coke) are stripped with steam, and the partially-clean, but still-coked catalyst is transferred to the catalyst regenerator 102 where air, in addition to or alternative to pure oxygen, is introduced to combust coke on the catalyst particles. Hot, regenerated catalyst, optionally with or without fresh catalyst makeup, is sent to downflow reactor 104 via a controlled circulation rate to achieve heat balance of the system. In some embodiments, additional steam can be injected into the catalyst stripper with structured packing 106 by way of stripper steam inlet 107.

(14) In FCC operations, ideally at steady state only the amount of coke necessary to meet the reactor energy demands is produced, and then the coke is combusted in a regenerator. Each FCC unit has a certain coke burning capability which can be used as a basis to either increase or decrease the severity to the desired level based on the feedstock. One goal is to produce enough coke to sustain feed conversion and subsequent downstream processes such as fractionation. Adjusting the catalyst circulation rate, the feed and product circulation rates, as well as other parameters, allows for suitable conversion of the hydrocarbon feedstock to olefins.

(15) HS-FCC processes have specific process conditions including downflow, high reaction temperature, short contact time, and high catalyst/oil ratio. In embodiments of the present disclosure, regenerator combustion gases provide lift for the upward flow of regenerated catalyst. Combustion gases lift regenerated catalyst in the upper section of a turbulent-phase fluidized bed to an acceleration zone and then to a riser-type lift line. Regenerated catalyst can then be carried to a catalyst hopper located at the end of the lift line.

(16) In embodiments of the present disclosure, a down-flow reactor system is applied in an HS-FCC process to minimize back-mixing in the reactor in order to narrow the residence time distribution. Thus, light olefin production is maximized with minimum dry gas yield (such as for example methane). Addition of steam to the reaction in downflow reactor 104 enhances light olefin production via cracking middle-distillate and saturated paraffins. The use of a downflow reactor prevents back mixing and over cracking of reaction products, while the use of a high catalyst/oil ratio ensures catalytic cracking is predominant. While high temperature favors the formation of useful reaction intermediates such as light olefins, short contact time prevents secondary reactions which are responsible for the consumption of the useful intermediates.

(17) The expected ethylene-plus-propylene yield in some embodiments is at least about 40% or at least about 30%, with a reduction in the production of dry gas, for example hydrogen, methane, and ethane. The steam-to-hydrocarbon weight ratio is a function of the feedstock as well as a compromise between the yield structure (olefin selectivity) and type of catalyst used. For a downflow reactor in some embodiments of the present disclosure, the residence time is expected to be between about 0.5 seconds to about 1.5 seconds. The amount of steam used is also a function of the type of feedstock hydrocarbon as well as a compromise between the yield structure (olefin selectivity) and type of catalyst used.

(18) In embodiments of the present disclosure, FCP units are operated at temperatures in the range of between about 500° C. to about 700° C. Under these reaction temperatures, steam assists in the catalytic cracking, while minimizing the formation of coke on the catalyst particles. As noted, when applying downer technology in embodiments of the present disclosure, the residence time in the downflow reactor is short, for example about between about 0.5 to about 1.5 seconds, and this will prevent over cracking and dry gas formation, which are often encountered with other riser technologies due to longer residence times.

(19) Embodiments of systems and methods of the present disclosure operate at high catalyst to oil ratios (C/O), for example in the range of about 15 to about 25 to recompense for the decrease in conversions due to the short contact time. An advantage of operation at high C/O ratios is the enhanced contribution of catalytic cracking over thermal cracking and to maintain the heat balance.

(20) Micro-activity tests have been conducted to show the effect of steam on conversion and product distribution. The results of Table 1 show that the catalyst is stable and active even after 100 hours of operation. This is indicative of the catalyst performance in fluidized beds in which reaction time is in seconds. According to Table 1, a suitable catalyst can undergo several operations before it deactivates.

(21) TABLE-US-00001 TABLE 1 Dodecane conversion at 350° C. and 10% steam over Catalyst. Selectivity Conversion, Naphthenes Paraffins I-Parraffins Aromatics Olefins Hours vol % Vol % Vol % Vol % Vol % Vol % 1 79.9 3.37 32.98 21.83 6.36 38.01 2 76.0 3.45 31.10 23.24 8.08 33.23 3 72.9 3.30 33.01 24.14 7.46 34.89 4 68.1 3.34 32.24 24.06 8.20 35.15 5 70.6 3.16 32.62 24.54 6.88 35.68 25 66.1 3.10 32.64 22.67 5.76 38.91 56 61.5 2.86 33.02 20.79 4.78 41.86 101 41.3 3.60 31.54 23.35 3.10 43.35

(22) The singular forms “a,” “an,” and “the” include plural referents, unless the context clearly dictates otherwise.

(23) In the drawings and specification, there have been disclosed embodiments of apparatus, systems, and methods for fluidized catalytic pyrolysis, as well as others, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The embodiments of the present disclosure have been described in considerable detail with specific reference to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the disclosure as described in the foregoing specification, and such modifications and changes are to be considered equivalents and part of this disclosure.