A process for the catalytic dehydrogenation to olefins

Abstract

The application discloses a method for preparing olefins by catalytic dehydrogenation, which comprises the following steps: T1. introducing mono-olefins into an alkane raw material stream to obtain a dehydrogenation raw material stream mixed with mono-olefins; and T2. contacting the dehydrogenation raw material stream with a catalyst in a dehydrogenation reaction unit under dehydrogenation conditions to perform a catalytic dehydrogenation reaction. The method for preparing olefins by catalytic dehydrogenation is particularly suitable for preparing olefins by catalytic dehydrogenation of low-carbon alkane with 2-4 carbon atoms. The method for preparing olefins by catalytic dehydrogenation introduces a small amount of mono-olefins into the alkane raw material, and the low-carbon mono-olefins have lower high-temperature cracking activity than the corresponding alkane, thereby inhibiting the high-temperature cracking of the raw material alkane in the hot zone of the reactor, and the phenomenon of decreased olefin selectivity and increased carbon deposition caused by the increase of the reaction temperature can be inhibited, so that the yield of olefins and the selectivity of olefins are improved.

Description

Technical Field

[0001] This invention relates to the field of low-carbon alkane dehydrogenation technology, specifically to a method for catalytic dehydrogenation to produce olefins. Background Technology

[0002] Low-carbon olefins are important basic organic synthesis feedstocks, especially ethylene and propylene. Driven by the increasing demand for downstream olefin derivatives, the global market demand for ethylene and propylene continues to rise, and the market outlook remains optimistic. However, with the rapid development of shale gas, the feedstocks for steam cracking to produce olefins are becoming lighter, leading to a continuous decline in propylene production via steam cracking. This directly results in traditional processes, represented by steam cracking, being unable to meet the growing propylene market demand. Against this backdrop, low-carbon alkane dehydrogenation technology, with its advantages of high selectivity and high yield, has emerged as a crucial method for current propylene production.

[0003] Dehydrogenation of low-carbon alkanes is a reversible endothermic reaction constrained by thermodynamic equilibrium. In the Oleflex propane dehydrogenation process, the single-pass conversion rate of alkane is only about 35%, and a large amount of unconverted propane needs to be recycled to the dehydrogenation reactor, significantly increasing the energy consumption of the unit. Although increasing the reaction temperature can increase the conversion rate of alkane, excessively high reaction temperatures not only intensify alkane cracking and deep dehydrogenation reactions, causing a decrease in selectivity, but also accelerate coking on the catalyst surface, leading to rapid catalyst deactivation. Against this backdrop, researchers have been committed to adjusting the relationship between olefin selectivity and alkane conversion rate to obtain higher olefin yields. For example, Zhang Guoliang et al. found that the main reason for the decrease in olefin selectivity under dehydrogenation reaction conditions is the occurrence of high-temperature cracking reactions, generating byproducts such as methane, ethane, and ethylene.

[0004] Patent CN111433174A discloses a method for catalytic dehydrogenation of low-carbon alkanes. A feed stream containing hydrogen and alkanes is fed into a dehydrogenation zone. Utilizing a highly selective platinum-based catalyst system, it can operate at a lower H2 / HC ratio and lower reaction temperature, while maintaining catalyst coking at levels comparable to higher H2 / HC ratios and higher reactor inlet temperatures, thereby improving propane conversion and propylene yield. Patent CN103998403A discloses a method for catalytic dehydrogenation of low-carbon alkanes. This method includes mixing a mixed feedstock with at least one hydrocarbon component selected from light-chain alkanes, heavy-chain alkanes, or combinations thereof. Furthermore, it includes introducing an inert diluent into the mixed feedstock, allowing the mixed feedstock and inert diluent to contact the dehydrogenation catalyst in the reactor to obtain reaction products. The light-chain alkanes include at least one selected from propane, butane, and pentane; the inert diluent is methane, nitrogen, helium, argon, or combinations thereof; and the heavy-chain alkanes are at least one C6-C20 alkanes. US Patent 6756515B2 discloses a method for producing olefins using a layered dehydrogenation catalyst. The catalyst comprises an inner core of α-alumina and an outer layer of γ-alumina; simultaneously, platinum and tin are uniformly dispersed on the outer layer. This dehydrogenation catalyst exhibits excellent durability and olefin selectivity under dehydrogenation conditions with low water concentrations. US Patent 5321192A discloses a method for producing olefins from the dehydrogenation of low-carbon alkanes, which improves the selectivity and yield of low-carbon olefins by introducing 10–300 mol ppm of water at the reactor inlet.

[0005] While the above technologies have made some progress in optimizing dehydrogenation catalysts and processes for low-carbon alkanes, how to suppress the decrease in olefin selectivity and the increase in coking caused by the increase in reaction temperature, thereby effectively improving the olefin yield, is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] The purpose of this invention is to provide a method for catalytic dehydrogenation to olefins, which can suppress the decrease in olefin selectivity and the increase in coking caused by the increase in reaction temperature, thereby effectively improving the olefin yield.

[0007] To solve the above-mentioned technical problems, the present invention provides a method for catalytic dehydrogenation to olefins, comprising the following steps:

[0008] T1. Introducing a monoolefin into an alkane feedstock yields a dehydrogenation feedstock mixed with a monoolefin;

[0009] T2. The dehydrogenation feedstock stream is brought into contact with the catalyst in the dehydrogenation reaction unit under dehydrogenation conditions to carry out a catalytic dehydrogenation reaction.

[0010] Optionally, the dehydrogenation feedstock stream is obtained through the following steps:

[0011] S1. Mix the alkane feed stream with the recycled stream to obtain a mixed feed stream, wherein the recycled stream contains dienes and / or alkynes;

[0012] S2. The mixed feedstock stream is passed through a selective hydrogenation reaction unit.

[0013] Optionally, the dehydrogenation feedstock stream further comprises hydrogen, wherein the molar ratio of hydrogen to alkanes is 0.1 to 10.

[0014] Optionally, the dehydrogenation conditions include: an inlet temperature of 550–700°C for the dehydrogenation reaction unit, an inlet pressure of 0.01–1.0 MPa for the dehydrogenation reaction unit, and a weight hourly space velocity of 1–12 h⁻¹. -1 .

[0015] Optionally, the alkane feedstock stream includes one or more low-carbon alkanes with 2-4 carbon atoms, and the monoolefin is a monoolefin having the same number of carbon atoms as the low-carbon alkanes; preferably, the low-carbon alkanes are propane and / or butane.

[0016] Optionally, in step T2, the dehydrogenation reaction unit includes 2 to 6 dehydrogenation reactors connected in series, and a heating furnace is provided between two adjacent dehydrogenation reactors; the dehydrogenation reactor is a combination of one or more reactors selected from moving bed, fixed bed and fluidized bed.

[0017] Optionally, the alkane feedstock stream includes propane. If the monoolefin content in the dehydrogenation feedstock stream is 500–1000 ppm, the inlet temperature of the first dehydrogenation reactor is 600–630 °C based on the total mass of the dehydrogenation feedstock stream; if the monoolefin content in the dehydrogenation feedstock stream is 1000–3000 ppm, the inlet temperature of the first dehydrogenation reactor is 600–633 °C based on the total mass of the dehydrogenation feedstock stream; if the monoolefin content in the dehydrogenation feedstock stream is 3000–10000 ppm, the inlet temperature of the first dehydrogenation reactor is 600–635 °C based on the total mass of the dehydrogenation feedstock stream.

[0018] Optionally, before performing step S1, which involves mixing the alkane feedstock stream with the recycled stream to obtain a mixed feedstock stream, the following steps are further included:

[0019] The alkane feedstock stream is fed into the feedstock pretreatment unit for dehydration and impurity removal to obtain a pretreated feedstock. The pretreated feedstock is then mixed with the circulating feedstock to obtain the mixed feedstock stream.

[0020] Optionally, in step T2, the dehydrogenation feedstock stream undergoes a catalytic dehydrogenation reaction to obtain a reaction effluent stream containing at least hydrogen, alkanes, and olefins.

[0021] Optionally, the method for catalytic dehydrogenation to olefins further includes the following steps after step T2:

[0022] T3. Pass the reaction effluent stream through a cooling and separation unit to obtain a hydrogen stream and a liquefied component stream;

[0023] T4. Pass the liquefied component stream through a light component removal unit to obtain a light component stream and a light component removed stream;

[0024] T5. Pass at least a portion of the light component removal stream as a feed stream through an alkane / olefin separation unit to obtain an olefin product stream and a de-olefin removal stream;

[0025] The circulating stream includes a deolefins stream and, optionally, a delighted component stream.

[0026] Optionally, the monoolefin content in the dehydrogenation feedstock stream is 500–10,000 ppm, based on the total mass of the dehydrogenation feedstock stream.

[0027] Beneficial effects:

[0028] The present invention provides a method for catalytic dehydrogenation to olefins by introducing a small amount of monoolefins into alkane feedstocks. The low-carbon monoolefins have lower high-temperature cracking activity than the corresponding alkanes, thereby inhibiting the high-temperature cracking of the feedstock alkanes in the reactor hot zone. This can suppress the phenomenon of decreased olefin selectivity and increased coking caused by increased reaction temperature, thereby effectively improving olefin yield and olefin selectivity. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the process flow of one embodiment of the catalytic dehydrogenation to olefins method of the present invention;

[0030] Figure 2 This is a schematic diagram of the process flow for catalytic dehydrogenation to olefins in Comparative Examples 1-3 of the present invention.

[0031] The components are as follows: 1-Raw material pretreatment unit, 2-Selective hydrogenation reaction unit, 3-De-heavy component removal unit, 4-Dehydrogenation reaction unit, 5-Cooling separation unit, 6-Light component removal unit, 7-Alkane / olefin separation unit, 10-Alkane feedstock stream, 11-Pre-treated stream, 12-Mixed feedstock stream, 13-Selective hydrogenation treated stream, 14-Dehydrogenated feedstock stream, 15-Heavy component stream, 16-Reaction effluent stream, 17-Hydrogen stream, 18-Liquefied component stream, 19-Light component stream, 20-De-light component removal stream, 21-Feed stream, 22-Olefin product stream, 23-Partially de-light component removal stream, 24-De-olefin removal stream, 25-Recycle stream. Detailed Implementation

[0032] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. Through these descriptions, the features and advantages of the present application will become clearer and more apparent.

[0033] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0034] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0035] This invention provides a method for catalytic dehydrogenation to olefins, such as... Figure 1 Or as shown in Figure 2, it includes the following steps:

[0036] T1. A monoolefin can be introduced into the alkane feedstock 10 to obtain a dehydrogenation feedstock 14 mixed with a monoolefin;

[0037] T2. The dehydrogenation feedstock stream 14 can be brought into contact with the catalyst in the dehydrogenation reaction unit 4 under dehydrogenation conditions to carry out a catalytic dehydrogenation reaction.

[0038] It should be noted that the catalytic dehydrogenation method for producing olefins of the present invention is particularly applicable to low-carbon alkanes with 2-4 carbon atoms. The monoolefin introduced in step T1 is a monoolefin having the same number of carbon atoms as the low-carbon alkane; for example, in the catalytic dehydrogenation of propane to produce olefins, propylene is introduced into the fresh propane feedstock. Low-carbon olefins have lower high-temperature cracking activity than the corresponding alkanes. By introducing a small amount of monoolefin into the alkane feedstock stream 10, the presence of the monoolefin can effectively suppress the high-temperature cracking reaction of the alkane feedstock during the catalytic dehydrogenation reaction in the dehydrogenation reaction unit 4, thereby improving olefin selectivity.

[0039] In another embodiment of the method for catalytic dehydrogenation to olefins according to the present invention, the alkane feedstock stream 10 may include one or more low-carbon alkanes having 2-4 carbon atoms, and the monoolefin may be a monoolefin having the same number of carbon atoms as the low-carbon alkanes; preferably, the low-carbon alkanes may be propane and / or butane.

[0040] In another embodiment of the method for catalytic dehydrogenation to olefins according to the present invention, the content of mono-olefins in the dehydrogenation feedstock stream 14 can be 500 to 10,000 ppm, based on the total mass of the dehydrogenation feedstock stream 14. It should be noted that the content of mono-olefins in the dehydrogenation feedstock stream 14 is preferably 1,500 to 6,000 ppm, and more preferably 1,500 to 3,000 ppm, based on the total mass of the dehydrogenation feedstock stream 14.

[0041] In another embodiment of the method for catalytic dehydrogenation to olefins according to the present invention, the dehydrogenation feedstock stream 14 may further contain hydrogen, wherein the molar ratio of hydrogen to alkanes is 0.1 to 10. It should be noted that in the entire dehydrogenation to olefins method or process, a certain amount of hydrogen can be obtained through cooling separation. The hydrogen separated by cooling in the process can be introduced as recycled hydrogen into the dehydrogenation feedstock stream 14, and then the hydrogen-containing dehydrogenation feedstock stream 14 enters the dehydrogenation reaction unit 4 to carry out the dehydrogenation reaction.

[0042] In another embodiment of the method for catalytic dehydrogenation to olefins according to the present invention, in step T2, the dehydrogenation reaction unit 4 may include 2 to 6 dehydrogenation reactors connected in series, and a heating furnace may be provided between two adjacent dehydrogenation reactors; the dehydrogenation reactor may be a combination of one or more reactors selected from moving bed, fixed bed and fluidized bed.

[0043] In one embodiment, the dehydrogenation conditions include: the inlet temperature of the dehydrogenation reaction unit 4 can be 550–700°C, the inlet pressure of the dehydrogenation reaction unit 4 can be 0.01–1.0 MPa, and the weight hourly space velocity can be 1–12 h⁻¹. -1 .

[0044] In another embodiment of the method for catalytic dehydrogenation to olefins according to the present invention, the alkane feed stream comprises propane. If the monoolefin content in the dehydrogenation feed stream 14 is 500–1000 ppm, the inlet temperature of the first dehydrogenation reactor can be 600–630 °C based on the total mass of the dehydrogenation feed stream 14; if the monoolefin content in the dehydrogenation feed stream 14 is 1000–3000 ppm, the inlet temperature of the first dehydrogenation reactor can be 600–633 °C based on the total mass of the dehydrogenation feed stream 14; if the monoolefin content in the dehydrogenation feed stream 14 is 3000–10000 ppm, the inlet temperature of the first dehydrogenation reactor can be 600–635 °C based on the total mass of the dehydrogenation feed stream 14.

[0045] It should be noted that in the above implementation scheme, firstly, by introducing a small amount of mono-olefins into the alkane feedstock, the high-temperature cracking of alkanes in the reactor hot zone is suppressed; secondly, for different mono-olefin contents, the optimal olefin product yield can be obtained by optimizing the reaction temperature distribution. Taking propane dehydrogenation as an example, after increasing the inlet temperature of the first dehydrogenation reactor, an optimization scheme can be selected based on propylene production and unit operation: firstly, the inlet temperature of the final reactor can be moderately reduced to improve olefin selectivity; secondly, the inlet temperature of the final reactor can be maintained or increased to obtain a higher olefin yield. Finally, regardless of the optimization scheme chosen, the olefin product yield can be improved, which is beneficial to enhancing the competitiveness of the unit.

[0046] It should be noted that, as a specific implementation, the dehydrogenation reaction unit 4 may include four dehydrogenation reactors connected in series, namely a first dehydrogenation reactor, a second dehydrogenation reactor, a third dehydrogenation reactor, and a fourth dehydrogenation reactor. This invention introduces a small amount of monoolefin into the dehydrogenation feedstock; for example, a small amount of propylene is introduced into the propane dehydrogenation reaction feedstock. Propylene has lower high-temperature cracking activity than propane, thus allowing for optimization of the temperatures of the first and fourth dehydrogenation reactors. Specifically, the reaction temperatures of the first and fourth dehydrogenation reactors can be increased, thereby improving the yield of olefin products.

[0047] The dehydrogenation reaction is carried out in the presence of a catalyst. This catalyst can include various catalysts used in the art, such as the catalyst disclosed in CN105363443A for the dehydrogenation of low-carbon alkanes to low-carbon olefins.

[0048] In another embodiment of the method for catalytic dehydrogenation to olefins according to the present invention, such as Figure 1 As shown, the dehydrogenation feedstock stream 14 can be obtained through the following steps:

[0049] S1. Mix the alkane feedstock stream 10 with the recycled stream 25 to obtain a mixed feedstock stream 12, wherein the recycled stream 25 contains dienes and / or alkynes;

[0050] S2. The mixed raw material stream 12 is passed through the selective hydrogenation reaction unit 2.

[0051] It should be noted that the selectively hydrogenated feedstock 13 obtained after step S2 is, in some embodiments, the selectively hydrogenated feedstock 13 is the dehydrogenated feedstock 14.

[0052] In one embodiment, the low-carbon alkane is propane, the introduced monoolefin is propylene, and the diene and alkyne in the circulating stream 25 are propadiene and propyne, respectively.

[0053] It should be noted that in S1, the recycled stream 25 can be a stream containing dienes and / or alkynes from outside the entire reaction, or it can be a recycled feedstock stream from the entire reaction.

[0054] In step S2, after selective hydrogenation, the dienes and alkynes in the mixed feed stream 12 are converted into monoolefins. In one embodiment, the selectively hydrogenated feed stream 13 obtained in step S2 can be used as the dehydrogenation feed stream 14.

[0055] In one embodiment, the conditions for selective hydrogenation include: a reaction temperature of 20–100°C, a reaction pressure of 3.0–4.5 MPa, and a volume hourly space velocity of 1–20 h⁻¹. -1 .

[0056] Preferably, the recycled feed stream 25 can be derived from the recycled feed stream of the entire reaction. In this embodiment, the recycled feed stream 25 may also contain alkanes, mono-olefins, and heavy components. Therefore, the mixed feed stream 12 may contain alkanes, mono-olefins, dienes, alkynes, and heavy components. Therefore, the method further includes the following steps after step S2:

[0057] S3. Pass the selective hydrogenation treatment post-stream 13 through the de-recombination component unit 3 to obtain the dehydrogenated feedstock stream 14.

[0058] As described above, in S2, after selective hydrogenation, the dienes and alkynes in the mixed feed stream 12 are converted into monoolefins. Therefore, the feed stream 13 after selective hydrogenation contains alkanes and monoolefins, and may also contain heavy components. S3 allows the heavy components to be separated to obtain the heavy component feed stream 15, while the dehydrogenated feed stream 14 mainly contains alkanes and monoolefins.

[0059] In this application, the term "heavy component" can refer to a hydrocarbon component with a higher number of carbon atoms than the target product olefin. For example, when propane dehydrogenation is carried out to produce propylene, the heavy component can be a C4 or higher component. The heavy component removal unit 3 can remove this heavy component by methods such as distillation or membrane separation. For example, during the propane dehydrogenation reaction, C1-C2 light components, C4 or higher heavy components, hydrogen, and the target product propylene are generated.

[0060] In one embodiment, the dehydrogenated feedstock stream 14 can be obtained by directly introducing a stream containing olefins (e.g., a pure olefin stream) into the alkane feedstock stream 10.

[0061] In another embodiment of the method for catalytic dehydrogenation to olefins according to the present invention, the following steps may be included before step S1, which involves mixing the alkane feed stream 10 with the recycled stream 25 to obtain the mixed feed stream 12:

[0062] The alkane feedstock stream 10 is fed into the feedstock pretreatment unit 1 for dehydration and impurity removal to obtain the pretreated feedstock 11. The pretreated feedstock 11 can be mixed with the circulating feedstock 25 to obtain the mixed feedstock stream 12.

[0063] It should be noted that the raw material pretreatment unit 1 can remove water and impurities contained in the alkane raw material stream 10, preventing water and impurities from interfering with subsequent reactions.

[0064] In another embodiment of the method for catalytic dehydrogenation to olefins according to the present invention, in step T2, the dehydrogenation feedstock stream 14 undergoes a catalytic dehydrogenation reaction to obtain a reaction effluent stream 16 whose components may contain at least hydrogen, alkanes and olefins.

[0065] It should be noted that the dehydrogenation feedstock stream 14 entering dehydrogenation reaction unit 4 contains alkanes, mono-olefins, and hydrogen. In dehydrogenation reaction unit 4, the alkanes in dehydrogenation feedstock stream 14 undergo a dehydrogenation reaction under certain dehydrogenation reaction conditions and with the aid of a catalyst. Some alkanes are dehydrogenated to form olefins, while others remain alkanes. Therefore, the reaction effluent stream 16 contains alkanes, olefins, and hydrogen. The olefins in reaction effluent stream 16 are partly dehydrogenation products of alkanes and partly introduced mono-olefins.

[0066] In another embodiment of the method for catalytic dehydrogenation to olefins according to the present invention, the method may further include the following steps after step T2:

[0067] T3. The reaction effluent stream 16 can be passed through the cooling and separation unit 5 to obtain hydrogen stream 17 and liquefied component stream 18;

[0068] T4. The liquefied component stream 18 can be passed through the light component removal unit 6 to obtain light component stream 19 and light component removed stream 20;

[0069] T5. At least a portion of the light component removal stream 20 can be used as feed stream 21 to pass through the alkane / olefin separation unit 7 to obtain olefin product stream 22 and deolefin removal stream 24.

[0070] In one embodiment, the recycle stream 25 may include a deolefin stream 24 and optionally a light component deolefin stream 20.

[0071] In this application, the term "light component" refers to hydrogen and hydrocarbon components with a carbon number lower than that of the target product olefin. For example, when propane is dehydrogenated to produce propylene, the light component can be hydrogen and C1-C2 components. The light component removal unit 6 can typically remove the light component by means of distillation, rectification, membrane separation, etc., to obtain light component stream 19 and light component removed stream 20.

[0072] It should be noted that, as a preferred embodiment, the light component removal stream 20 may contain alkanes and olefins. The light component removal stream 20 can be divided into two parts. The first part, the light component removal stream 20, is fed into the alkane / olefin separation unit 7 as feed stream 21 for alkane and olefin separation, yielding an olefin product stream 22 and a de-olefin stream 24. The de-olefin stream 24 mainly consists of alkanes and may also contain small amounts of dienes, alkynes, and heavy components. The second part, the light component removal stream 20, is mixed with the de-olefin stream 24 as a partial light component removal stream 23 to obtain a recycled stream 25. The recycled stream 25 may contain alkanes, monoolefins, dienes, alkynes, and heavy components. Thus, by mixing the alkane feed stream with the recycled stream 25, and after selective hydrogenation and removal of heavy components, a dehydrogenated feed stream 14, mainly composed of alkanes and monoolefins, can be obtained, and the product can be recycled. The hydrogen stream 17 can be further fed into the PSA unit to obtain high-purity hydrogen.

[0073] To provide a more complete understanding of the present invention, the following embodiments are provided. These embodiments are for illustrating implementation of the present invention and should not be construed in any way as limiting the scope of the present invention.

[0074] The following examples are illustrative, and as those skilled in the art will recognize, the specific reagents and reaction conditions used for particular compounds can be modified. The raw materials used in the following schemes are either commercially available or readily prepared by those skilled in the art from commercially available raw materials.

[0075] The following examples illustrate the raw materials, reactor, catalyst, and reaction conditions:

[0076] The raw materials used were purchased gas sources, of which propane had a purity of 99.8 vol%, butane was isobutane reagent with a purity of 99.5 wt%, and ethane had a purity of 99.9 vol%.

[0077] Raw material pretreatment unit 1 includes a raw material protector, a mercury remover, a raw material dryer, etc.

[0078] The selective hydrogenation reaction unit 2 includes a hydrogenation mixer and a fixed-bed reactor;

[0079] The heavy component removal unit 3 is a heavy component removal tower unit, including a distillation tower and a stripping tower (when the feed alkane is ethane, it is a C3+ removal tower unit; when the feed alkane is propane, it is a C4+ removal tower unit; when the feed alkane is butane, it is a C5+ removal tower unit).

[0080] The dehydrogenation reaction unit 4 includes one feed heat exchanger, four to five moving bed reactors, and a heating furnace in front of each reactor;

[0081] The cooling separation unit 5 is a cold box, which includes several flash tanks, a refrigerator, an expander, etc.

[0082] Unit 6, which removes light components, is a light component removal tower unit, including a distillation tower (when the feed alkane is ethane, it is a demethanizer tower unit; when the feed alkane is propane, it is a C2 and C1 hydrocarbon removal tower unit; when the feed alkane is butane, it is a C3, C2 and C1 hydrocarbon removal tower unit).

[0083] Alkane / olefin separation unit 7 is a propane / propylene separation tower or a propylene distillation tower (when the feedstock is propane), including 1 to 2 distillation towers and a compressor. When the feedstock is ethane, alkane / olefin separation unit 7 is an ethane / ethylene separation tower or an ethylene distillation tower; when the feedstock is butane, alkane / olefin separation unit 7 is a butane / butene separation tower or a butene distillation tower.

[0084] In raw material pretreatment unit 1, moisture and impurities are removed, including metals, chlorine, nitrogen, water, and oxygen-containing compounds; heavy metal content <20wt ppb, Hg <0.1wt ppb, H2O content <1wt ppm, Cl <1wt ppm, N <0.2wt ppm, etc.

[0085] The reaction conditions for selective hydrogenation reaction unit 2 include: temperature 20–100 °C, pressure 3.0–4.0 MPa, and weight hourly space velocity 1–20 h⁻¹. -1 The hydrogenation catalyst is a Pd-containing catalyst;

[0086] The removal conditions for de-recombining component unit 3 include: removing C4 and higher-order components, and obtaining nC4+C4 in the C3 component. ＝ The content should be <100 mol ppm (when the raw material is propane); when the raw material is ethane, the deweighting unit should remove C3 and higher C3 components, and the nC3+C3 in the obtained C2 component should be removed. ＝ The content should be <100 mol ppm; when the raw material is butane, the deweighting unit should remove C5 and above components to obtain nC5+C5 in the C4 component. ＝ The content should be <100 mol ppm;

[0087] The reaction conditions for dehydrogenation reaction unit 4 include: inlet temperature 560–700℃, inlet pressure 0.03–0.5 MPa, and weight hourly space velocity 1–10 h⁻¹. -1 The dehydrogenation catalyst is a Pt- or Cr-containing catalyst;

[0088] The separation conditions of the cooling separation unit 5 include: liquefying all C3+ components, and obtaining circulating hydrogen with a purity >92.5% (when the feed is propane); liquefying all C2+ components when the feed is ethane, and liquefying all C4+ components when the feed is butane.

[0089] The light component removal unit 6 removes H2, C1 and C2 components (when the feedstock is propane); when the feedstock is ethane, the light component removal unit removes H2 and C1 components; when the feedstock is butane, the light component removal unit removes H2 and C1 to C3 components.

[0090] The olefin product obtained from alkane / olefin separation unit 7 has a purity >99.5 mol%.

[0091] Example 1

[0092] Example 1 according to Figure 1 Process proceeding as follows:

[0093] (1) Propane feedstock is fed into feedstock pretreatment unit 1 to remove moisture and impurities, resulting in pretreated feedstock 11. Pretreated feedstock 11 is then mixed with recycled feedstock 25 at a mass ratio of 1:2 to obtain mixed feedstock 12. Mixed feedstock 12 is then fed into selective hydrogenation reaction unit 2 to convert propadiene and propyne into propylene, resulting in selectively hydrogenated feedstock 13. Selectively hydrogenated feedstock 13 is then fed into de-heavy component unit 3 to remove heavy components such as C4, resulting in heavy component feedstock 15 and dehydrogenated feedstock 14. The propylene content in dehydrogenated feedstock 14 is 1500 ppm, based on the total mass of dehydrogenated feedstock 14. The hydrogenation catalyst used in selective hydrogenation reaction unit 2 is commercially available catalyst HP-4. The hydrogenation conditions in selective hydrogenation reaction unit 2 include: reactor inlet temperature 40°C, pressure 3.7 MPa, and weight hourly space velocity 16 h⁻¹. -1 ;

[0094] (2) The dehydrogenation feedstock stream 14 is fed into the dehydrogenation reaction unit 4 for catalytic dehydrogenation to obtain the reaction effluent stream 16. The dehydrogenation reaction unit 4 includes four dehydrogenation reactors connected in series, with a heating furnace between adjacent dehydrogenation reactors. The inlet temperature of the first dehydrogenation reactor is 630 ℃, the inlet temperature of the second dehydrogenation reactor is 650 ℃, the inlet temperature of the third dehydrogenation reactor is 650 ℃, and the inlet temperature of the fourth dehydrogenation reactor is 635 ℃. The dehydrogenation catalyst used in the dehydrogenation reaction unit 4 is the commercially available catalyst PST-100. The inlet pressure of the first dehydrogenation reactor is 0.1 MPa, and the weight hourly space velocity is 2.5 h⁻¹. -1 ;

[0095] (3) The reaction effluent stream 16 is fed into the cooling separation unit 5 to obtain hydrogen stream 17 and liquefied component stream 18; the liquefied component stream 18 is passed through the light component removal unit 6 to obtain light component stream 19 and light component removal stream 20; 99.5 wt% of the light component removal stream 20 is fed into the alkane / olefin separation unit 7 as feed stream 21 to obtain olefin product stream 22 and olefin removal stream 24; 0.5 wt% of the light component removal stream 20 is mixed with the olefin removal stream 24 as part of the light component removal stream 23 to obtain the recycling stream 25.

[0096] Example 2

[0097] Example 2 according to Figure 1 The process was carried out in Example 2 according to steps (1)-(3) of Example 1, except that the inlet temperature of the first dehydrogenation reactor was 633°C.

[0098] Example 3

[0099] Example 3 according to Figure 1 The process is carried out in Example 3 according to steps (1)-(3) of Example 2. The difference from Example 2 is that the pretreated feed 11 is mixed with the circulating feed 25 to obtain a mixed feed 12. After passing through the selective hydrogenation reaction unit 2 and the de-heavy component unit 3, the propylene content in the dehydrogenated feed 14 is 3000ppm, based on the total mass of the dehydrogenated feed 14.

[0100] Example 4

[0101] Example 4 according to Figure 1 The process is carried out in Example 4 according to steps (1)-(3) of Example 1. The difference from Example 1 is that the pretreated feed 11 is mixed with the circulating feed 25 to obtain a mixed feed 12. After passing through the selective hydrogenation reaction unit 2 and the de-heavy component unit 3, the propylene content in the dehydrogenated feed 14 is 6000ppm. Based on the total mass of the dehydrogenated feed 14, the inlet temperature of the first dehydrogenation reactor is 635℃.

[0102] Example 5

[0103] Example 5 according to Figure 1 The process was carried out in Example 5 according to steps (1)-(3) of Example 1. The difference from Example 1 was that the raw material in Example 1 was replaced with butane, and the inlet temperature of the four dehydrogenation reactors was 560°C.

[0104] Example 6

[0105] Example 6 according to Figure 1The process was carried out in Example 6 according to steps (1)-(3) of Example 1. The difference from Example 1 is that the raw material in Example 1 was replaced with ethane, and the temperature of the inlet of the four dehydrogenation reactors was 700°C.

[0106] Comparative Example 1

[0107] Comparative Example 1 Figure 2 The process is as follows:

[0108] (1) The propane feedstock 10 is fed into the feedstock pretreatment unit 1 to remove moisture and impurities, and dehydrogenated feedstock 14 is obtained, in which the propylene content is 0.

[0109] (2) After the dehydrogenation feedstock stream 14 enters the dehydrogenation reaction unit 4 for catalytic dehydrogenation reaction, the reaction effluent stream 16 is obtained. The dehydrogenation reaction unit 4 includes four dehydrogenation reactors connected in series, and a heating furnace is set between two adjacent dehydrogenation reactors. The inlet temperature of the first dehydrogenation reactor is 630 ℃, the inlet temperature of the second dehydrogenation reactor is 650 ℃, the inlet temperature of the third dehydrogenation reactor is 650 ℃, and the inlet temperature of the fourth dehydrogenation reactor is 635 ℃. The dehydrogenation catalyst, dehydrogenation reaction pressure, and space velocity conditions are the same as in Example 1.

[0110] (3) The reaction effluent stream 16 is fed into the cooling separation unit 5 to obtain hydrogen stream 17 and liquefied component stream 18; the liquefied component stream 18 is fed into the selective hydrogenation reaction unit 2 to convert the propyne and propadiene produced by excessive dehydrogenation into propylene to obtain selectively hydrogenated stream 13; the selectively hydrogenated stream 13 is fed into the light component removal unit 6 to obtain light component stream 19 and light component removal stream 20; the light component removal stream 20 is fed into the alkane / olefin separation unit 7 to obtain olefin product stream 22.

[0111] Comparative Example 2

[0112] Comparative Example 2 Figure 2 The process was carried out according to steps (1)-(3) of Comparative Example 1, except that the inlet temperature of the first dehydrogenation reactor was 633℃.

[0113] Comparative Example 3

[0114] Comparative Example 3 Figure 2 The process was carried out according to steps (1)-(3) of Comparative Example 2, except that propylene was introduced into the dehydrogenation feedstock 14 by direct introduction, so that the propylene content in the dehydrogenation feedstock 14 was 400 ppm, based on the total mass of the dehydrogenation feedstock 14.

[0115] Test Example 1

[0116] The alkane conversion, olefin selectivity, net olefin yield, and coke yield of Examples 1-6 and Comparative Examples 1-3 were detected and calculated. The detection results are shown in Table 1 below.

[0117] The alkane conversion rate is calculated as follows:

[0118]

[0119] olefin selectivity is calculated as follows:

[0120]

[0121] The net yield of olefins is calculated as follows:

[0122] Net olefin yield, m%

[0123] =Alkane conversion rate, m% × Olefin selectivity, m% × 100%

[0124] -Olefin content of raw materials, m%

[0125] The yield of coke deposits is calculated as follows:

[0126]

[0127] Methods for analyzing the composition of raw materials and products: Q / SH 3360 316-2020;

[0128] Catalyst carbon content analysis method: Q / SH 3360 317-2020;

[0129] Table 1

[0130]

[0131] As can be seen from Comparative Example 1 and Example 1, under the conditions of an inlet temperature of 630°C for the first dehydrogenation reactor and an inlet temperature of 635°C for the fourth dehydrogenation reactor, the propylene selectivity and propylene yield increased significantly after the addition of 1500 ppm olefins.

[0132] Comparative Examples 1 and 2 show that as the inlet temperature of the first dehydrogenation reactor increases, both the propylene yield and the coke yield increase, but the propylene selectivity decreases. Comparative Examples 2 and 2 show that, at the same temperature, incorporating olefins into the dehydrogenation feedstock can mitigate the decrease in propylene selectivity caused by the increase in temperature, thereby improving the propylene yield.

[0133] In the description of this application, it should be noted that the terms "upper", "lower", "inner", "outer", "front", "rear", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship in the working state of this application. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0134] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0135] The present application has been described above with reference to preferred embodiments; however, these embodiments are merely exemplary and illustrative. Various substitutions and modifications can be made to the present application based on these embodiments, all of which fall within the protection scope of the present application.

Claims

1. A method for catalytic dehydrogenation to olefins, characterized in that, Includes the following steps: T1. Introducing a mono-olefin into the alkane feedstock stream (10) yields a dehydrogenated feedstock stream (14) mixed with a mono-olefin; the dehydrogenated feedstock stream (14) is obtained through the following steps: S1. Mix the alkane feedstock stream (10) with the recycled stream (25) to obtain a mixed feedstock stream (12), wherein the recycled stream (25) contains dienes and / or alkynes; S2. Pass the mixed feedstock stream (12) through the selective hydrogenation reaction unit (2); The alkane feedstock stream (10) includes one or more low-carbon alkanes such as ethane or propane; In the dehydrogenated feedstock stream (14), the monoolefin content is 500~10000ppm, based on the total mass of the dehydrogenated feedstock stream (14); T2. The dehydrogenation feedstock stream (14) is brought into contact with the catalyst in the dehydrogenation reaction unit (4) under dehydrogenation conditions to carry out a catalytic dehydrogenation reaction.

2. The method for catalytic dehydrogenation to olefins according to claim 1, characterized in that, The dehydrogenated feedstock stream (14) further comprises hydrogen, wherein the molar ratio of hydrogen to alkanes is 0.1 to 10.

3. The method for catalytic dehydrogenation to olefins according to claim 2, characterized in that: The dehydrogenation conditions include: an inlet temperature of 550~700℃ for the dehydrogenation reaction unit (4), an inlet pressure of 0.01~1.0MPa for the dehydrogenation reaction unit (4), and a weight hourly space velocity of 1~12h. -1 .

4. The method for catalytic dehydrogenation to olefins according to claim 1, characterized in that, The monoolefin is a monoolefin having the same number of carbon atoms as the low-carbon alkane.

5. The method for catalytic dehydrogenation to olefins according to claim 4, characterized in that, The low-carbon alkane is propane.

6. The method for catalytic dehydrogenation to olefins according to any one of claims 1-5, characterized in that, In step T2, the dehydrogenation reaction unit (4) includes 2 to 6 dehydrogenation reactors connected in series, and a heating furnace is provided between two adjacent dehydrogenation reactors; the dehydrogenation reactor is a combination of one or more reactors selected from moving bed, fixed bed and fluidized bed.

7. The method for catalytic dehydrogenation to olefins according to claim 6, characterized in that: The alkane feedstock stream (10) contains propane. If the monoolefin content in the dehydrogenation feedstock stream (14) is 500~1000ppm, the inlet temperature of the first dehydrogenation reactor is 600~630℃ based on the total mass of the dehydrogenation feedstock stream (14); if the monoolefin content in the dehydrogenation feedstock stream (14) is 1000~3000ppm, the inlet temperature of the first dehydrogenation reactor is 600~633℃ based on the total mass of the dehydrogenation feedstock stream (14); if the monoolefin content in the dehydrogenation feedstock stream (14) is 3000~10000ppm, the inlet temperature of the first dehydrogenation reactor is 600~635℃ based on the total mass of the dehydrogenation feedstock stream (14).

8. The method for catalytic dehydrogenation to olefins according to claim 2, characterized in that, Before performing step S1, which involves mixing the alkane feedstock stream (10) with the recycled stream (25) to obtain the mixed feedstock stream (12), the following steps are also included: The alkane feedstock stream (10) is fed into the feedstock pretreatment unit (1) for dehydration and impurity removal to obtain the pretreated feedstock (11), and the pretreated feedstock (11) is mixed with the circulating feedstock (25) to obtain the mixed feedstock stream (12).

9. The method for catalytic dehydrogenation to olefins according to claim 3, characterized in that, In step T2, the dehydrogenated feedstock stream (14) undergoes a catalytic dehydrogenation reaction to obtain a reaction effluent stream (16) containing at least hydrogen, alkanes and olefins.

10. The method for catalytic dehydrogenation to olefins according to claim 9, characterized in that, The method for catalytic dehydrogenation to olefins further includes the following steps after step T2: T3. Pass the reaction effluent stream (16) through the cooling separation unit (5) to obtain a hydrogen stream (17) and a liquefied component stream (18); T4. Pass the liquefied component stream (18) through the light component removal unit (6) to obtain the light component stream (19) and the light component removal stream (20); T5. Pass at least a portion of the light component removal stream (20) as feed stream (21) through the alkane / olefin separation unit (7) to obtain olefin product stream (22) and deolefin removal stream (24); The circulating stream (25) includes a deolefins stream (24) and optionally a light component de-component stream (20).

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