Method for catalyzing light hydrocarbon cracking reaction and application

Abstract

The invention provides a method for catalyzing cracking reaction of light dydrocarbon and application, the method adopts light dydrocarbon raw materials with high olefin concentration, fluoroalkane is added into a fixed bed reactor at an inlet of the fixed bed reactor, and the fluoroalkane is contacted on a catalyst and is subjected to catalytic cracking reaction. The method has the characteristics of high raw material conversion rate, low equipment investment and simple process.

Description

Technical Field

[0001] The invention belongs to the technical field of olefin production, and specifically relates to a method for catalyzing light hydrocarbon cracking reaction and application thereof. Background Art

[0002] Propylene is one of the important basic organic chemical raw materials, mainly used to produce polypropylene, cumene, acrylonitrile, acrylic acid and many other products. In recent years, the demand for propylene has grown strongly, and the market demand for propylene has exceeded the demand for ethylene. Among them, polypropylene is the fastest growing propylene derivative.

[0003] At present, propylene production is mainly based on the co-product of ethylene plant and refinery by-product route. About 70% of the world's propylene comes from the co-product of steam cracking unit and the conventional catalytic cracking unit (FCC unit) of the refinery. The ratio of propylene to ethylene in the steam cracking unit is about 0.6, and the investment cost of increasing the propylene yield of the refinery FCC unit is high. There is limited room for increasing propylene production through these two processes. In order to increase propylene production, various countries have developed a variety of other methods for producing propylene. The new processes for increasing propylene production mainly include propane dehydrogenation, olefin disproportionation, olefin cracking, methanol to olefins, methanol to propylene and other technologies.

[0004] Whether it is steam cracking, catalytic cracking, or methanol to olefins production, a certain amount of C4+ fraction will be produced as a by-product. The different utilization methods of this part of C4+ resources have a significant impact on the economic benefits of the device.

[0005] Traditional C4 hydrocarbon utilization includes fuel utilization and chemical utilization. Fuel utilization is mainly used for liquefied gas, MTBE and alkylate. Chemical utilization mainly uses the separable components in the C4 fraction to produce various related derivatives. In addition, in order to increase the added value of the C4 fraction, some new technologies have emerged, such as olefin cracking, olefin disproportionation and other technologies for increasing the production of propylene and ethylene. These technologies not only increase the added value of the C4 fraction, but also meet the market's growing demand for propylene.

[0006] The basic principle of olefin catalytic cracking technology to produce propylene is to use the ZSM-5 catalyst with unique shape selectivity and acidity to selectively convert low-carbon olefins into propylene and ethylene. Olefin catalytic cracking technology uses C4-C6 olefins produced as by-products of ethylene plants, refineries or MTO to produce propylene and ethylene with high selectivity. It is a new technology route for producing low-carbon olefins. Due to its wide source of raw materials and simple process, it has developed rapidly in recent years.

[0007] Chinese patent CN1490287A discloses an alkane-olefin co-cracking catalyst and an alkane-olefin mixed catalytic cracking method, wherein the catalyst is obtained by hydrothermal aging treatment of modified γ-Al2O3, a binder and a composite auxiliary agent at 500-1000°C; the modified γ-Al2O3 is obtained by impregnating and modifying γ-Al2O3 with at least two non-metallic elements and at least four metal elements in sequence; the composite auxiliary agent includes at least inorganic acid and cellulose. The alkane-olefin co-cracking catalyst uses γ-Al2O3 as a carrier, and uses a combination of multiple metal elements to prepare active components and non-metallic elements to modify the γ-Al2O3 carrier. It has different types of acid centers such as superacid, strong acid and weak acid, and is used for catalytic cracking of alkane-olefin mixed raw materials to improve the alkane-olefin conversion rate and propylene yield. However, the patent adopts a fluidized bed reactor, the equipment construction cost is high, the preparation process of the catalyst is lengthy, and the production cost is high.

[0008] Chinese patent CN113070099A discloses a phosphorus-modified deactivated titanium silicon molecular sieve catalyst, which is prepared by mixing a phosphorus-containing compound solution with a deactivated titanium silicon molecular sieve having an MFI structure by an impregnation method. As an active component of a solid acid catalyst, the phosphorus-modified deactivated titanium silicon molecular sieve shows a higher product propylene / ethylene ratio and lower by-product alkane and aromatic selectivity than the unmodified deactivated titanium silicon molecular sieve in the reaction process of olefin cracking reaction to produce propylene and methanol catalytic conversion to produce propylene, which is conducive to the efficient utilization of raw materials. However, the butene conversion rate described in the patent is less than 50%, which is difficult to meet the requirements of large-scale production for high conversion rate. Summary of the invention

[0009] The technical problem to be solved by the present invention is the low raw material conversion rate in the reaction of catalytic cracking of C4 and above olefins to produce propylene in the prior art, and a method for catalytic cracking of light hydrocarbons is provided, which has the characteristics of high raw material conversion rate, low equipment investment and simple process.

[0010] One of the objects of the present invention is to provide a method for catalyzing light hydrocarbon cracking reaction, comprising the step of adding fluoroalkane feed to the feed inlet of a fixed bed reactor.

[0011] According to the present invention, the fluoroalkane is selected from at least one of C2-C8 polyfluoroalkanes, preferably difluoroethane, tetrafluoroethane, pentafluoroethane or at least one of the isomers of the above fluoroalkanes. Specifically, at least one of 1,1-difluoroethane, 1,1,1-trifluoroethane, 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane, pentafluoroethane and perfluoroethane can be used.

[0012] According to the present invention, the method for catalyzing the cracking reaction of light hydrocarbons provided by the present invention comprises: introducing fluoroalkane and light hydrocarbon raw material into a reactor from a feed port of a fixed bed reactor, contacting with a catalyst to undergo a catalytic cracking reaction to obtain light olefins. Specifically, the fluoroalkane and light hydrocarbon raw material are mixed and then introduced into a fixed bed reactor from a feed port, or the fluoroalkane and light hydrocarbon raw material are introduced into a fixed bed reactor from a feed port in sequence, and then the fluoroalkane and light hydrocarbon raw material are contacted with a catalyst in the reactor to undergo a catalytic cracking reaction to obtain light olefins including ethylene, propylene, butene, pentene, hexene, etc.

[0013] According to the present invention, the fluoroalkane added in an appropriate amount can improve the activity of the catalyst in the catalytic cracking reaction. According to an embodiment of the present invention, the volume ratio of the fluoroalkane to the light hydrocarbon feedstock is (0.000001-0.001):1, for example, any value among 0.000001:1, 0.000005:1, 0.00001:1, 0.00005:1, 0.0001:1, 0.0005:1, 0.001:1, 0.0005:1, 0.001:1, etc., or a value between any two of the above value ranges; preferably, the volume ratio of the fluoroalkane to the light hydrocarbon feedstock is (0.00001-0.0001):1.

[0014] According to the present invention, the light hydrocarbon feedstock can be a common light hydrocarbon fraction in the art. Preferably, the light hydrocarbon feedstock is a fraction with an olefin concentration of not less than 20wt%, preferably a fraction with an olefin concentration of not less than 40wt%, wherein the olefins include 1-butene, 2-butene, isobutylene, 1-pentene, etc. Specifically, the light hydrocarbon feedstock is a fraction containing C4 and above, preferably at least one of the C4 and above fractions from the FCC unit, the C4 and above fractions produced as byproducts of the MTO unit, and the C4 and above fractions produced by the ethylene unit.

[0015] According to the present invention, the catalyst is a catalyst comprising a ZSM-5 molecular sieve, wherein the ZSM-5 molecular sieve is not particularly limited, and can be a ZSM-5 molecular sieve commonly used in the art, can be any commercially available ZSM-5 molecular sieve, or can be a ZSM-5 molecular sieve prepared by a preparation method commonly used in the prior art. According to the present invention, the silicon-aluminum ratio of the ZSM-5 molecular sieve is 20 to 300, preferably 60 to 240.

[0016] According to the present invention, the catalyst can only use ZSM-5 molecular sieve, or ZSM-5 molecular sieve can be blended with other components, for example, a binder is added. The catalyst optionally includes a binder, specifically, the ZSM-5 molecular sieve and the binder are mixed evenly, molded, dried, and calcined for use as a catalyst. Wherein, the binder can be an aluminum-containing or silicon-containing component commonly used in the art, for example, the binder is selected from at least one of silica sol, aluminum sol, and pseudo-boehmite; based on the total weight of the catalyst as 100%, the binder is 0-80%, preferably 0-65%. The catalyst containing a binder can be prepared by the following method: ZSM-5 molecular sieve and the binder are mixed evenly and ground, water is added to the grinding process until it is muddy, and then the molded catalyst is dried and calcined to obtain the catalyst, wherein the equipment and process conditions used for molding, drying and calcining are not particularly limited, and the equipment and process conditions commonly used in the art can be used, for example, the drying temperature is preferably 70-120°C, and the calcination temperature is preferably 400-600°C.

[0017] According to the present invention, the catalytic cracking reaction is carried out in a fixed bed reactor. The fixed bed reactor is not particularly limited and can be a fixed bed reaction device commonly used in the art. The catalytic cracking reaction conditions are also not particularly limited and can adopt catalytic cracking reaction conditions commonly used in the art. For example, the catalytic cracking reaction conditions are: reaction temperature of 400-650°C and reaction pressure of 0-0.2MPa; preferably, the reaction temperature is 450-600°C and the reaction pressure is 0.01-0.15MPa.

[0018] A second object of the present invention is to provide a method for catalyzing the cracking reaction of light hydrocarbons, and its application in the catalytic cracking of C4 fractions.

[0019] In order to solve the problem of low conversion rate of light hydrocarbon feedstock in the prior art, the present invention provides a method for catalyzing light hydrocarbon cracking reaction, which includes adding a step of feeding fluoroalkane to the feed port of a fixed bed reactor. In the technical solution provided by the present invention, under high temperature reaction conditions, the fluoroalkane will contact and react with the molecular sieve catalyst, continuously changing the skeleton structure of the molecular sieve, thereby improving the activity of the catalyst and thus improving the olefin conversion rate.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] First, the present invention can effectively improve the conversion rate of the catalytic reaction, has the characteristics of flexible adjustment of the P / E ratio (ratio of propylene to ethylene) and simple process, and better solves the problem of low conversion rate of catalytic cracking reaction.

[0022] Secondly, the present invention utilizes fluoroalkanes as co-feed raw materials, providing an effective solution for the recycling of fluorine-containing refrigerants. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The butene conversion curves in Examples 1 to 2 and Comparative Example 1 are shown in FIG. 1 , wherein the abscissa represents the reaction time (h) and the ordinate represents the butene conversion (%). DETAILED DESCRIPTION

[0024] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the contents of the present invention still fall within the scope of protection of the present invention.

[0025] The present invention aims at the problem of low raw material conversion rate and proposes a method for catalyzing light hydrocarbon cracking reaction. The reaction conditions used in the present invention can adopt the existing technology, and the implementation of the present invention is not limited by the technical points disclosed or not disclosed in the present invention. Those skilled in the art can select appropriately according to the situation. However, the present invention is by no means a simple combination of these existing technologies, but solves the problems that do exist in current practical applications and has quite significant application value.

[0026] The present invention provides a method for catalyzing light hydrocarbon cracking reaction. A light hydrocarbon raw material with a high olefin concentration is used, and a fluoroalkane is added at the inlet of a fixed bed reactor to enter the reactor together with the raw material, so that the fluoroalkane contacts with the catalyst and a catalytic cracking reaction occurs. The present invention adopts a method of feeding the light hydrocarbon raw material and the fluoroalkane together, so that the fluoroalkane and the light hydrocarbon raw material are mixed and then enter the fixed bed reactor, or the fluoroalkane and the light hydrocarbon raw material are separately fed into the fixed bed reactor.

[0027] In the above technical solution, the fluoroalkane is selected from at least one of C2-C8 polyfluoroalkanes, preferably difluoroethane, tetrafluoroethane, pentafluoroethane or at least one of the above fluoroalkane isomers.

[0028] In the above technical solution, the fluoroalkane and light hydrocarbon raw materials are mixed and then enter the fixed bed reactor from the feed port, or the fluoroalkane and light hydrocarbon raw materials are respectively and sequentially enter the fixed bed reactor from the feed port.

[0029] In the above technical solution, the volume ratio of the fluoroalkane and the light hydrocarbon raw material is (0.000001-0.001):1, preferably (0.00001-0.0001):1.

[0030] In the above technical solution, the light hydrocarbon feedstock is a fraction with an olefin concentration of not less than 20 wt%, preferably a fraction with an olefin concentration of not less than 40 wt%.

[0031] In the above technical scheme, the light hydrocarbon feedstock is selected from at least one of the C4 and above fractions of the FCC unit, the C4 and above fractions produced as by-products of the MTO unit, and the C4 and above fractions produced by the ethylene unit.

[0032] In the above technical scheme, the catalyst is a catalyst containing ZSM-5 molecular sieve; the catalyst optionally includes a binder, wherein the silicon-aluminum ratio of the ZSM-5 molecular sieve is 20 to 300, preferably 60 to 240; the binder is selected from at least one of silica sol, aluminum sol, and pseudo-boehmite; based on the total weight of the catalyst as 100%, the binder is 0 to 80%, preferably 0 to 65%.

[0033] In the above technical solution, the conditions of the catalytic cracking reaction are: reaction temperature is 400-650°C, and reaction pressure is 0-0.2MPa; preferably, the reaction temperature is 450-600°C, and the reaction pressure is 0.01-0.15MPa.

[0034] The test instruments and test conditions used in the examples are as follows:

[0035] The catalytic performance evaluation experiment of the catalyst was carried out on a fixed-bed microreactor evaluation device.

[0036] The olefin concentration in the raw material was measured using a gas chromatograph.

[0037] The raw materials used in the examples and comparative examples, unless otherwise specified, are disclosed in the prior art, for example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0038] Embodiment 1:

[0039] The raw material is MTO by-product C4, in which the olefin concentration is 60%, the fluoroalkane is 1,1,1,2-tetrafluoroethane, the volume ratio of fluoroalkane to light hydrocarbon raw material is 0.00005:1, the catalyst is ZSM-5 molecular sieve catalyst, and the silicon-aluminum ratio is 180. The catalytic cracking reaction activity is evaluated on a fixed bed micro-reactor evaluation device. Fluoroalkane and MTO by-product C4 are added to the fixed bed micro-reactor evaluation device in sequence. The evaluation conditions are reaction temperature of 550°C and pressure of 0.1MPa. The evaluation results are listed in Table 1. The relationship between butene conversion rate and reaction time is shown in Table 1. Figure 1 shown.

[0040] The calculation formula for butene conversion is:

[0041]

[0042] from Figure 1 It can be seen that the butene conversion rate can reach 70%, the conversion rate has been significantly improved, and the P / E ratio has also increased.

[0043] Embodiment 2:

[0044] The raw material is MTO by-product C4, in which the olefin concentration is 60%, the fluoroalkane is 1,1,1,2-tetrafluoroethane, the volume ratio of fluoroalkane to light hydrocarbon raw material is 0.0001:1, and the catalyst is ZSM-5 molecular sieve catalyst (silicon-aluminum ratio is 180). The catalytic cracking reaction activity is evaluated on a fixed bed micro-reactor evaluation device. Fluoroalkane and MTO by-product C4 are added to the fixed bed micro-reactor evaluation device in sequence. The evaluation conditions are reaction temperature of 550°C and pressure of 0.1MPa. The evaluation results are listed in Table 1. The relationship between butene conversion rate and reaction time is shown in Table 1. Figure 1 shown.

[0045] It can be seen from the figure that the butene conversion rate can reach 75%, the conversion rate has been significantly improved, and the P / E ratio has also increased. This shows that the method of catalyzing light hydrocarbon cracking reaction mentioned in the present invention can improve the olefin conversion rate and effectively adjust the P / E ratio.

[0046] Embodiment 3:

[0047] The raw material is MTO byproduct C4, the olefin concentration in its composition is 40%, the fluoroalkane is 1,1,1,2-tetrafluoroethane, the volume ratio of fluoroalkane to light hydrocarbon raw material is 0.0001:1, and the catalyst is ZSM-5 molecular sieve catalyst (silicon aluminum ratio is 180). The catalytic cracking reaction activity is evaluated on a fixed bed micro-reactor evaluation device. The fluoroalkane and MTO byproduct C4 are mixed and added to the fixed bed micro-reactor evaluation device. The evaluation conditions are reaction temperature 550℃, pressure 0.1MPa, and the evaluation results are listed in Table 1. The butene conversion rate can reach 68% during the reaction evaluation period, the conversion rate has been improved, and the P / E ratio has also increased.

[0048] Embodiment 4:

[0049] The raw material is MTO byproduct C4, the olefin concentration in its composition is 60%, the fluoroalkane is pentafluoroethane, the volume ratio of fluoroalkane to light hydrocarbon raw material is 0.0001:1, the catalyst is ZSM-5 molecular sieve catalyst (silicon aluminum ratio is 180), and the catalytic cracking reaction activity is evaluated on a fixed bed micro-reactor evaluation device. Fluoroalkane and MTO byproduct C4 are added to the fixed bed micro-reactor evaluation device in sequence. The evaluation conditions are reaction temperature 550℃, pressure 0.1MPa, and the evaluation results are listed in Table 1. The butene conversion rate can reach 73% during the reaction evaluation period, the conversion rate has been improved, and the P / E ratio has also increased.

[0050] Embodiment 5:

[0051] The raw material is C4, a byproduct of MTO, in which the olefin concentration is 60%, the fluoroalkane is 1,1,1,2-tetrafluoroethane, the volume ratio of the fluoroalkane to the light hydrocarbon raw material is 0.0001:1, and the catalyst composition is 85% by weight of ZSM-5 molecular sieve (silicon-aluminum ratio is 180) and 15% of silica sol. The catalyst preparation process is: ZSM-5 molecular sieve and silica sol are uniformly ground, water is added to the grinding process until it is muddy, and then formed. The formed catalyst is dried at 80°C and calcined at 550°C, and the catalytic cracking reaction activity is evaluated on a fixed bed micro-reaction evaluation device. Fluoroalkane and C4, a byproduct of MTO, are added to the fixed bed micro-reaction evaluation device in sequence. The evaluation conditions are a reaction temperature of 550°C and a pressure of 0.1MPa. The evaluation results are listed in Table 1. The butene conversion rate can reach 72% during the reaction evaluation period, the conversion rate is improved, and the P / E ratio is also increased.

[0052] Embodiment 6:

[0053] The raw material is C4 produced as a byproduct of the FCC unit, and the olefin concentration in its composition is 45%. The fluoroalkane is 1,1,1,2-tetrafluoroethane. The volume ratio of fluoroalkane to light hydrocarbon raw material is 0.0001:1. The catalyst is ZSM-5 molecular sieve catalyst (silicon-aluminum ratio is 180). The catalytic cracking reaction activity is evaluated on a fixed bed micro-reactor evaluation device. The fluoroalkane and the byproduct C4 of the FCC unit are mixed and added to the fixed bed micro-reactor evaluation device. The evaluation conditions are a reaction temperature of 550°C and a pressure of 0.1MPa. The evaluation results are listed in Table 1. The butene conversion rate can reach 69% during the reaction evaluation period. The conversion rate has been improved and the P / E ratio has also increased.

[0054] Comparative Example 1:

[0055] The raw material is C4 produced by MTO, the olefin concentration in its composition is 60%, and the catalyst is ZSM-5 molecular sieve catalyst (silicon aluminum ratio is 180). The catalytic cracking reaction activity is evaluated on a fixed bed micro-reactor evaluation device. The evaluation conditions are a reaction temperature of 550°C. The evaluation results are listed in Table 1. The relationship between the butene conversion rate and the reaction time is shown in Table 1. Figure 1 shown.

[0056] Table 1

[0057]

[0058] Depend on Figure 1 It can be seen from the results in Table 1 that, compared with Comparative Example 1, a small amount of fluoroalkane was added during the reaction in Examples 1, 2, and 4, and the conversion rate and P / E ratio were significantly improved, indicating that the method for catalyzing light hydrocarbon cracking reaction provided by the present invention can effectively improve the olefin conversion rate and effectively adjust the P / E ratio.

[0059] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, and they should be covered by the protection scope of the present invention.

Claims

1. A method for catalyzing light hydrocarbon cracking reaction, comprising the step of adding fluoroalkane feed to the feed inlet of a fixed bed reactor.

2. The method according to claim 1, characterized in that The fluoroalkane is selected from at least one of C2-C8 polyfluoroalkanes, preferably difluoroethane, tetrafluoroethane, pentafluoroethane or at least one of the isomers of the above fluoroalkanes.

3. The method according to claim 1 or 2, characterized in that: The method comprises: feeding fluoroalkane and light hydrocarbon raw materials into a fixed bed reactor from a feed port, contacting with a catalyst to undergo catalytic cracking reaction to obtain light olefins.

4. The method according to claim 3, characterized in that: The fluoroalkane and light hydrocarbon raw materials are mixed and then fed into the fixed bed reactor from the feed inlet, or the fluoroalkane and light hydrocarbon raw materials are fed into the fixed bed reactor from the feed inlet in sequence.

5. The method according to claim 3, characterized in that: The volume ratio of the fluoroalkane to the light hydrocarbon raw material is (0.000001-0.001):1, preferably (0.00001-0.0001):

1.

6. The method according to claim 3, characterized in that: The light hydrocarbon feedstock is a fraction with an olefin concentration of not less than 20 wt%, preferably a fraction with an olefin concentration of not less than 40 wt%.

7. The method according to claim 6, characterized in that The light hydrocarbon feedstock is selected from at least one of the C4 and above fractions of the FCC unit, the C4 and above fractions produced as by-products of the MTO unit, and the C4 and above fractions produced by the ethylene unit.

8. The method according to claim 3, characterized in that The catalyst is a catalyst comprising ZSM-5 molecular sieve; and / or, The catalyst optionally includes a binder.

9. The method according to claim 8, characterized in that The silicon-aluminum ratio of the ZSM-5 molecular sieve is 20 to 300, preferably 60 to 240; and / or, The binder is selected from at least one of silica sol, alumina sol and pseudo-boehmite; and / or, Based on the total weight of the catalyst being 100%, the binder accounts for 0 to 80%, preferably 0 to 65%.

10. The method according to claim 3, characterized in that: The conditions for the catalytic cracking reaction are: reaction temperature of 400-650° C., reaction pressure of 0-0.2 MPa; preferably, reaction temperature of 450-600° C., reaction pressure of 0.01-0.15 MPa.

11. Use of the method for catalytic cracking of light hydrocarbons according to any one of claims 1 to 10 in catalytic cracking of C4 fractions.

Images