CN115990506A - Catalyst for co-cracking of carbon-four mixed hydrocarbon, and preparation method and application thereof - Google Patents

Abstract

The invention discloses a catalyst for co-cracking of carbon-four mixed hydrocarbon, a preparation method and application thereof. The catalyst comprises the following components by taking the total weight of the catalyst as a reference: i) 58 to 84 percent of ZSM-5 molecular sieve; II) 10% -41% of a binder component; III) 0.5 to 6 percent of alkaline earth metal element; the acid quantity ratio of the B acid to the L acid of the catalyst is 0.5-2:1, and the apparent skeleton density is 1.0-2.3 g/ml. The catalyst is used in propylene ethylene production reaction by co-cracking of carbon-four mixed hydrocarbon, and the carbon-four olefin and the carbon-four alkane in the carbon-four mixed hydrocarbon can be subjected to co-cracking to produce propylene ethylene, and has the characteristics of high conversion rate of cracking raw materials, high propylene ethylene yield of products and good catalyst stability.

Description

Catalyst for co-cracking of C4 mixed hydrocarbons and its preparation method and application

Technical Field

The invention relates to the field of catalytic cracking, and in particular to a catalyst for co-cracking of C4 mixed hydrocarbons, and a preparation method and application thereof.

Background Art

Propylene and ethylene are important basic raw materials for the petrochemical industry. Driven by the rapid growth in demand for polyolefins and their derivatives, the demand for propylene and ethylene has continued to be strong and has grown at a relatively fast rate in recent years. Therefore, it is considered to be a product with great market potential. With the annual increase in refining capacity, the output of by-product mixed C4 hydrocarbons has increased accordingly. The utilization of C4 hydrocarbons produced by refineries is mainly concentrated in the etherification of isobutylene to produce methyl tert-butyl ether as a fuel additive or for the preparation of isobutylene and other products. The rest is mostly used as fuel in the form of liquefied petroleum gas. At present, the comprehensive utilization rate of mixed C4 hydrocarbons in refineries is very low. It is urgent to find effective ways to utilize a large amount of by-product mixed C4 hydrocarbons. Petrochemical researchers in various countries have paid great attention to this. In order to realize the high added value utilization of C4 and above light hydrocarbons in FCC units or cracking units, Universal Oil Products and Atofina jointly developed the olefin cracking (OCP) process, Lummus developed the olefin conversion technology (OCT), Mobil developed the olefin interconversion (MOI) process, Lurgi and Schume developed the Propylur process, Asahi Kasei developed the Omega olefin conversion process, and Shanghai Petrochemical Research Institute developed the catalytic cracking olefin (OCC) process. The above processes can produce propylene and ethylene from olefins in C4 and above light hydrocarbons through catalytic cracking or olefin disproportionation. However, in addition to olefins, there are also a large number of alkanes in mixed C4. The chemical properties of C4 alkanes are very stable. Research on mixed C4 hydrocarbons focuses on the utilization of olefins in C4 hydrocarbons. Some scholars have also conducted special research on the production of propylene and ethylene by butane cracking. Further research on catalysts for co-cracking of olefins and alkanes in C4 mixed hydrocarbons remains to be explored.

The active components of the catalyst used for olefin cracking are generally hydrogen-type ZSM-5, ZSM-11 or SAPO-34 molecular sieves. Inert gas as a heat carrier and diluent is of great benefit to the improvement of various indicators of olefin cracking reaction. Usually, acidic molecular sieve catalysts will undergo serious skeleton dealumination under high-temperature hydrothermal conditions, which will cause the catalyst acid density to drop rapidly and cause irreversible loss of catalyst activity. At the same time, due to the strong acidity of molecular sieves, while olefin cracking to produce propylene and ethylene, side reactions such as olefin superposition chain growth, hydrogen transfer and aromatization will occur, and even coking will occur in the pores of the molecular sieve catalyst, covering the reaction active center and causing the catalyst to deactivate quickly.

CN200410029871.2 discloses a catalyst for producing propylene by cracking C4-C7 olefins, comprising 1-20 mass% of a VIB group metal oxide and a zirconium oxide carrier, wherein the average crystal grain size of the zirconium oxide is 10-100 nanometers. The catalyst is used for the reaction of producing propylene by cracking olefins, and under the conditions of 440-470°C, 0.3MPa, and a raw material volume space velocity of 3.0h ^-1 , the C4 olefin conversion rate is 79-91%, and the propylene single-pass yield is 48-50%. US6307117 discloses a method for producing propylene and ethylene by cracking C4-C12 olefins, wherein the active component of the catalyst used is a protonic acid-free, IB group-containing ZSM-5 molecular sieve.

The above-mentioned olefin cracking processes all have defects such as poor product selectivity, low yield, low olefin feed conversion rate, poor catalyst stability, etc. The olefin cracking catalysts in the prior art are used in the reaction of co-cracking of mixed hydrocarbons to produce propylene and ethylene, and the catalytic performance needs to be further improved.

Summary of the invention

In view of the problems of the prior art in the mixed hydrocarbon cracking process being complicated, the mixed hydrocarbon conversion rate being low and the product selectivity being low, the present invention provides a catalyst for co-cracking of C4 mixed hydrocarbons to produce propylene and ethylene, and its preparation method and application. The catalyst is used in the reaction of co-cracking of C4 mixed hydrocarbons to produce propylene and ethylene, and the C4 olefins and C4 alkanes in the C4 mixed hydrocarbons can be co-cracking to produce propylene and ethylene, and has the characteristics of high conversion rate of the cracked raw C4 olefins and C4 alkanes, high yield of product propylene and ethylene, and good catalyst stability.

The first aspect of the present invention provides a catalyst for co-cracking of C4 mixed hydrocarbons, wherein the catalyst, based on the total weight of the catalyst, comprises the following components:

I) 58% to 84% ZSM-5 molecular sieve;

II) 10% to 41% of a binder component;

III) 0.5% to 6% of alkaline earth metal elements;

The acid amount ratio of B acid to L acid of the catalyst is 0.5-2:1, and the apparent skeleton density is 1.0-2.3 g/ml.

In the above technical solution, preferably, the acid amount ratio of B acid to L acid in the catalyst is 0.8 to 1.5:1.

In the above technical solution, preferably, the apparent skeleton density of the catalyst is 1.0 to 1.8 g/ml.

In the above technical solution, the SiO ₂ /Al ₂ O ₃ molar ratio of the ZSM-5 molecular sieve in the catalyst component I) is 50-1000, preferably 100-1000.

In the above technical solution, the alkaline earth metal element in the catalyst component III) is selected from at least one of Mg, Ca, Sr and Ba.

The second aspect of the present invention provides a method for preparing the above catalyst, comprising the following steps:

a) preparing ZSM-5 molecular sieve raw powder;

b) kneading the raw powder obtained in step a) and a binder into a mold, drying, and first calcining to obtain a molded product;

c) exchanging the formed product obtained in step b) with ammonium, and performing a second calcination to obtain an ammonium exchange product;

d) treating the ammonium exchange product obtained in step c) in an acid solution, performing a third calcination, loading an alkaline earth metal and performing a fourth calcination to obtain the catalyst.

In the above technical scheme, step a) of preparing ZSM-5 molecular sieve raw powder includes: uniformly mixing the template, aluminum source, silicon source, alkali source and water, hydrothermally crystallizing and drying to obtain ZSM-5 molecular sieve raw powder.

In the above technical solution, in the step of preparing the raw powder in step a), the template includes at least one of tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide and tetrapropylammonium hydroxide. The aluminum source includes at least one of aluminum nitrate, aluminum sulfate, aluminum phosphate and sodium aluminate. The silicon source includes at least one of water glass, silica sol and tetraethyl orthosilicate. The alkali source includes at least one of sodium hydroxide and potassium hydroxide.

In the above technical scheme, in the raw materials used for preparing the original powder in step a), the template is calculated as _NH4 ⁺ , the aluminum source is _calculated as _Al2O3 , the silicon source is calculated as _SiO2 , the alkali source is calculated as ^OH- , and the molar ratio of water is: _NH4 ⁺ : _Al2O3 : _SiO2 : _OH- ^: _H2O = 0.1-0.5: 0.001-0.02: 1: 0.1-0.4: 5-10.

In the above technical solution, in the step of preparing the raw powder in step a), the device is preferably an autoclave. The pressure is autogenous pressure, generally less than or equal to 2 MPa. The conditions for the hydrothermal crystallization are: crystallization at 120-180°C for 10-60 hours. The product obtained after hydrothermal crystallization can be washed and dried. The drying conditions are: drying at 80-120°C for 10-30 hours.

In the above technical solution, in step b), the binder is selected from one or more of alumina, aluminum sol and silica sol. When aluminum sol is used as the binder, the binder component is Al ₂ O ₃ ; when silica sol is used as the binder, the binder component is SiO ₂ .

In the above technical solution, the drying condition in step b) is: drying at 80-120° C. for 5-10 hours. The first calcination condition is: calcining at 500-600° C. for 4-8 hours.

In the above technical scheme, the conditions of ammonium exchange in step c) are: temperature of 80-90°C and time of 1-3h. The number of ammonium exchanges is 2-5 times. The concentration of the ammonium salt aqueous solution in the ammonium exchange is 5wt%-10wt%. The ammonium salt is at least one selected from ammonium chloride, ammonium nitrate and ammonium sulfate. After the ammonium exchange, washing and drying can be performed. The drying conditions are: drying temperature of 80-120°C and drying time of 6-20 hours. The second roasting condition is roasting at 500-600°C for 4-8 hours.

In the above technical scheme, the acid content in the acid solution in step d) is 2wt% to 5wt%; the acid is an organic acid; the organic acid includes at least one selected from citric acid, oxalic acid, acetic acid, and oxalic acid. The treatment can be soaking, and the treatment conditions are as follows: the volume ratio of the acid solution to the ammonium exchange product is 2:1 to 5:1, the treatment temperature is 70 to 80°C, and the treatment time is 4 to 8 hours. The treatment is carried out under stirring conditions. After treatment in the acid solution, washing and drying can be carried out. The drying conditions are: temperature 80 to 120°C, time 6 to 20 hours. The conditions for the third roasting are roasting at 500 to 600°C for 4 to 8 hours.

In the above technical scheme, the loading of alkaline earth metal in step d) is an equal volume impregnation method. The impregnation liquid is an alkaline earth metal salt solution. The alkaline earth metal salt is a soluble salt of an alkaline earth metal, preferably a nitrate. The mass concentration of the alkaline earth metal salt solution is 0.5% to 5% in terms of metal ions. The impregnation time is 5 to 15 hours. Drying can be performed after impregnation. The drying is performed at 80 to 120° C. for 6 to 20 hours. The fourth calcination condition is calcination at 500 to 600° C. for 4 to 8 hours.

The third aspect of the present invention provides the use of the above catalyst in the co-cracking reaction of C4 mixed hydrocarbons to produce propylene and ethylene.

In the above technical solution, the C4 mixed hydrocarbons are derived from the C4 mixed hydrocarbons of the refinery; the C4 mixed hydrocarbons include at least one of isobutane, normal butane, 1-butene, isobutene, trans-2-butene, and 1,3-butadiene; preferably, the C4 mixed hydrocarbons are at least one alkane and at least one olefin. Further preferably, in the C4 mixed hydrocarbons, the mass ratio of alkane to olefin is 0.1 to 10, exemplified but not limited to: 0.3, 0.4, 0.5, 0.8, 1.0, 1.5, 2.0, 3.0, etc.

In the above technical solution, the reaction of cracking and co-cracking of C4 mixed hydrocarbons to produce propylene and ethylene can adopt a fixed bed reactor.

In the above technical solution, the reaction conditions are: reaction temperature is 500-700°C, reaction pressure is 0-1.0 MPa, and weight space velocity of the mixed hydrocarbon feedstock is 1-40 h ^-1 .

At present, in the reaction of preparing propylene and ethylene by catalytic cracking of mixed C4 hydrocarbons, there are problems such as low raw material conversion rate and low propylene and ethylene yield. This is mainly because butene and butane have different stability and different cracking mechanisms. Butene cracking can occur at a lower temperature, while butane cracking requires a higher reaction temperature. Therefore, under the reaction conditions of butene catalytic cracking, butane hardly reacts. Under the catalyst and reaction conditions of butane cracking, butene cracking produces too many by-products, and the yield of product propylene and ethylene is lower than the effect of cracking a single raw material.

Compared with the prior art, the present invention has significant advantages and outstanding effects, as follows:

(1) In the present invention, the catalyst for the co-cracking of C4 mixed hydrocarbons comprises the following components based on the total weight of the catalyst: I) 58% to 84% of ZSM-5 molecular sieve; II) 10% to 41% of a binder component; III) 0.5% to 6% of an alkaline earth metal element; the acid amount ratio of B acid to L acid of the catalyst is 0.5 to 2:1, and the apparent skeleton density is 1.0 to 2.3 g/ml. The catalyst of the present invention has a specific acid amount B/L ratio and a special apparent skeleton density. By optimizing the reaction process conditions, the C4 olefins and C4 alkanes in the C4 mixed hydrocarbons can be simultaneously converted into propylene and ethylene under common process conditions. The catalyst of the present invention is used in the co-cracking reaction of C4 mixed hydrocarbons to produce propylene and ethylene, and has the characteristics of high cracking raw material conversion rate, high product propylene and ethylene yield, and good catalyst stability.

(2) In the present invention, the catalyst preparation method adopts the method of first preparing ZSM-5 molecular sieve raw powder, and then forming, ammonium exchanging and acid-modifying the raw powder to obtain the catalyst. The preparation method of the present invention modifies the synthesized ZSM-5 molecular sieve raw powder, and the catalyst prepared has a specific acid amount B/L ratio and a special apparent skeleton density, produces a richer pore structure, and accelerates the diffusion of reaction intermediates and products. The catalyst prepared by this method can convert C4 olefins and C4 alkanes in C4 mixed hydrocarbons into propylene and ethylene under common process conditions under optimized reaction process conditions, and has the characteristics of high cracking raw material conversion rate, high product propylene ethylene yield, and good catalyst stability.

(3) In the present invention, the catalyst is used in the reaction of co-cracking of C4 mixed hydrocarbons to produce propylene and ethylene. Under the optimized reaction process conditions, the C4 olefins and C4 alkanes in the C4 mixed hydrocarbons can be simultaneously converted into propylene and ethylene under common process conditions, and have the characteristics of high cracking raw material conversion rate, high product propylene and ethylene yield, and good catalyst stability. After 2 hours of reaction, the C4 olefin conversion rate in the raw material mixed hydrocarbon can reach more than 75%, the C4 alkanes conversion rate can reach more than 41%, and the product propylene and ethylene yield can reach more than 66%. The reaction was run for 75 hours, the catalyst stability was good, the catalytic activity did not change significantly, and a good technical effect was achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a pyridine adsorption infrared spectrum of the catalyst obtained in Example 1;

FIG2 is an XRD pattern of the molecular sieve raw powder obtained in Example 1;

FIG3 is an XRD pattern of the molecular sieve raw powder obtained in Comparative Example 1;

FIG. 4 is a pyridine adsorption infrared spectrum of the catalyst obtained in Comparative Example 1.

DETAILED DESCRIPTION

The present invention will be further described below by way of examples.

In the context of this specification, XRD analysis was performed on a Rigaku D/MAX-1400X polycrystalline X-ray diffractometer, with a graphite monochromator, Cu Kα radiation, tube voltage 40 kV, tube current 40 mA, scanning speed 15°·min ^-1 , and scanning range 2θ 5-50°.

In the context of this specification, the pyridine adsorption infrared spectrum is analyzed and measured by Bruker's IFS-88IR infrared spectrometer. Specifically: the sample is ground and pressed into a tablet with a diameter of 2 cm and a total weight of 11-14 mg. Then it is placed in a sample tube and desorbed at 300°C for 4 hours under a vacuum of ^10-2 Pa to remove impurities such as water in the sample. After cooling, the sample is placed in pyridine saturated vapor for adsorption, and then heated to different temperatures of 150°C, 200°C, 250°C, 300°C, and 350°C for 10 minutes and then the spectrum is taken. After 300°C, the spectrum tends to be stable. In the obtained spectrum, the peak near the wave number 1452cm ^-1 corresponds to the L acid center of the catalyst, and the peak near the wave number 1542cm ^-1 corresponds to the B acid center of the catalyst. The acid ratio of B acid to L acid (B acid/L acid) is the ratio of the infrared absorption peak areas near 1542cm ^-1 and 1452cm ^-1 .

In the context of this specification, the silicon-aluminum molar ratio SiO ₂ /Al ₂ O ₃ is calculated by analyzing the elemental composition of the solid sample using a MagixX fluorescence spectrometer from Philips, the Netherlands, with an operating voltage of 40 kV and an operating current of 40 mA.

In the context of this specification, the apparent skeleton density is measured using an AutoPoreV 9600 fully automatic mercury intrusion instrument from Micromeritics Instruments, Inc., USA. The maximum pressure of the high-pressure analysis is 60,000 psia (413,685 kPa), and the minimum diameter of the high-pressure pore size analysis is 4 nm.

In the context of this specification, the following formula is used for calculation:

C4 olefin conversion rate (%) = (1-C4 olefin mass in product/C4 olefin mass in raw material) × 100%;

C4 alkane conversion rate (%) = (1-C4 alkane mass in product/C4 alkane mass in raw material) × 100%;

Yield of propylene, ethylene and diene (%) = mass of propylene and ethylene generated in the product/mass of C4 mixed hydrocarbons in the raw material × 100%.

In the examples and comparative examples of this specification, the C4 mixed hydrocarbons used are from refineries. The specific composition is shown in Table 1.

[Example 1]

a) Preparation of ZSM-5 molecular sieve raw powder

Tetramethylammonium bromide is used as a template, aluminum nitrate is used as an aluminum source, silica sol is used as a silicon source, and sodium hydroxide is used as an alkali source. The molar ratio of tetramethylammonium bromide, aluminum nitrate, silica sol, alkali, and water is: NH ₄ ⁺ :Al ₂ O ₃ :SiO ₂ :OH ^- :H ₂ O=0.2:0.001:1:0.2:5. After being fully mixed and stirred, the mixture is transferred into an autoclave, crystallized at 180°C for 10 hours under autogenous pressure, and then cooled. The synthesized product is filtered, washed with water, and dried at 80°C for 30 hours to obtain ZSM-5 molecular sieve raw powder.

b) 70 g of the above ZSM-5 molecular sieve raw powder, 40 g of binder alumina and 30 g of 5% dilute nitric acid were kneaded, extruded into strips, dried at 80° C. for 10 hours, and then calcined at 500° C. for 8 hours to obtain a molded product.

c) The obtained molded product was ammonium exchanged in a 5 wt% aqueous solution of ammonium nitrate at 90°C for 1 hour. The number of ammonium exchanges was 5. After washing and drying at 120°C for 6 hours, it was calcined at 500°C for 8 hours.

d) The obtained ammonium exchange product is placed in a 2wt% citric acid solution at 70°C and stirred for 4 hours, with the volume ratio of the acid solution to the ammonium exchange product being 3:1, washed, dried at 80°C for 120 hours, and then calcined at 500°C for 8 hours. By adopting an equal volume impregnation method, the above catalyst is impregnated in a 2wt% magnesium nitrate solution for 5 hours, dried at 120°C for 6 hours, and then calcined at 500°C for 8 hours, thereby obtaining the desired catalyst for catalytic cracking of C4 mixed hydrocarbons to produce propylene and ethylene.

Figure 1 is a pyridine adsorption infrared spectrum of the catalyst obtained in Example 1. The acid ratio of B acid to L acid in the catalyst is 1.06:1, and the apparent skeleton density is 1.0 g/ml.

The catalyst comprises: a) 60% of ZSM-5 molecular sieve; b) 38% of binder component; and c) 2% of metal element Mg.

The silicon-aluminum molar ratio SiO ₂ /Al ₂ O ₃ of the ZSM-5 molecular sieve in the catalyst component is 1000.

The XRD pattern of the obtained ZSM-5 molecular sieve raw powder is shown in Figure 2.

The fixed bed catalytic reaction device was used to evaluate the catalytic cracking activity of C4 mixed hydrocarbons to produce propylene and ethylene. The process conditions used were: 0.6 g catalyst, 500°C reaction temperature, 0.2 MPa reaction pressure, and 10 h ^-1 weight space velocity.

The results of the reaction at 2 h and 75 h are listed in Table 2.

[Example 2]

a) Preparation of ZSM-5 molecular sieve raw powder

Tetrapropylammonium bromide is used as a template, aluminum sulfate is used as an aluminum source, water glass is used as a silicon source, and potassium hydroxide is used as an alkali source. The molar ratio of tetrapropylammonium bromide, aluminum sulfate, water glass, alkali, and water is: NH ₄ ⁺ :Al ₂ O ₃ :SiO ₂ :OH ^- :H ₂ O=0.5:0.01:1:0.4:10. After being fully mixed and stirred, the mixture is transferred into an autoclave, crystallized at 120°C for 60 hours under autogenous pressure, and then cooled. The synthesized product is filtered, washed with water, and dried at 120°C for 10 hours to obtain ZSM-5 molecular sieve raw powder.

b) 70 g of the above ZSM-5 molecular sieve powder and 75 g of silica sol ( _SiO2 weight content 40%) as a binder were kneaded, extruded into strips, dried at 120°C for 5 hours, and then calcined at 600°C for 4 hours to obtain a molded product.

c) The obtained molded product was subjected to ammonium exchange in a 10 wt% aqueous solution of ammonium sulfate at 80°C for 2 hours, the ammonium exchange was performed twice in total, and the molded product was washed and dried at 80°C for 20 hours, and then calcined at 600°C for 4 hours.

d) The obtained ammonium exchange product is placed in a 5% by weight oxalic acid solution at 80°C and stirred for 8 hours, the volume ratio of the acid solution to the ammonium exchange product is 5:1, washed, dried at 120°C for 6 hours, and then calcined at 600°C for 4 hours. By adopting an equal volume impregnation method, the above catalyst is impregnated in a 5% calcium nitrate solution for 15 hours, dried at 80°C for 20 hours, and then calcined at 600°C for 4 hours to obtain the desired catalyst for catalytic cracking of C4 mixed hydrocarbons to produce propylene and ethylene.

The acid ratio of B acid to L acid in the catalyst is 0.8:1, and the apparent skeleton density is 1.2 g/ml.

The catalyst comprises: a) 64% of ZSM-5 molecular sieve; b) 31% of binder component; and c) 5% of metal element Ca.

The silicon-aluminum molar ratio SiO ₂ /Al ₂ O ₃ of the ZSM-5 molecular sieve in the catalyst component is 100. The XRD pattern of the obtained ZSM-5 molecular sieve raw powder is similar to FIG2 .

The fixed bed catalytic reaction device was used to evaluate the catalytic cracking activity of the prepared catalyst in producing propylene and ethylene from mixed C4 residues extracted from ethylene plants. The process conditions used were: 0.6 g catalyst, 600°C reaction temperature, 0.5 MPa reaction pressure, and 20 h ^-1 weight space velocity of olefin feedstock.

The results of the reaction at 2 h and 75 h are listed in Table 2.

[Example 3]

a) Preparation of ZSM-5 molecular sieve raw powder

Tetrapropylammonium hydroxide is used as a template, sodium aluminate is used as an aluminum source, tetraethyl orthosilicate is used as a silicon source, and sodium hydroxide is used as an alkali source. The molar ratio of tetrapropylammonium hydroxide, sodium aluminate, tetraethyl orthosilicate, alkali, and water is: NH ₄ ⁺ :Al ₂ O ₃ :SiO ₂ :OH ^- :H ₂ O=0.1:0.00125:1:0.1:8. After being fully mixed and stirred, the mixture is transferred into an autoclave, crystallized at 150°C for 30 hours under autogenous pressure, and then cooled. The synthesized product is filtered, washed with water, and dried at 100°C for 20 hours to obtain ZSM-5 molecular sieve raw powder.

b) 80 g of the ZSM-5 molecular sieve powder and 80 g of aluminum sol (Al ₂ O ₃ weight content 25%) as a binder were kneaded, extruded into strips, dried at 100° C. for 8 hours, and then calcined at 550° C. for 6 hours to obtain a molded product.

c) The obtained molded product was subjected to ammonium exchange in a 10 wt% aqueous solution of ammonium chloride at 85°C for 1.5 hours, the ammonium exchange was performed 4 times in total, and then washed, dried at 120°C for 6 hours, and calcined at 550°C for 6 hours.

d) The obtained ammonium exchange product is placed in a 3% by weight oxalic acid solution at 75°C and stirred for 6 hours, with the volume ratio of the acid solution to the ammonium exchange product being 2:1. After washing and drying at 120°C for 6 hours, it is calcined at 550°C for 7 hours. By adopting an equal volume impregnation method, the above catalyst is impregnated in a 3% strontium nitrate solution for 10 hours, dried at 100°C for 10 hours, and then calcined at 550°C for 6 hours, thereby obtaining the desired catalyst for catalytic cracking of C4 mixed hydrocarbons to produce propylene and ethylene.

The acid ratio of B acid to L acid in the catalyst is 1.5:1, and the apparent skeleton density is 2.02 g/ml.

The catalyst comprises: a) 77.6% of ZSM-5 molecular sieve; b) 19.4% of binder component; and c) 3% of metal element Sr.

The silicon-aluminum molar ratio SiO ₂ /Al ₂ O ₃ of the ZSM-5 molecular sieve in the catalyst component is 800. The XRD pattern of the obtained ZSM-5 molecular sieve raw powder is similar to FIG2 .

The fixed bed catalytic reaction device was used to evaluate the catalytic cracking activity of C4 mixed hydrocarbons to produce propylene and ethylene. The process conditions used were: 0.6 g catalyst, 700℃ reaction temperature, 0.1 MPa reaction pressure, and 1 h ^-1 weight space velocity of olefin feedstock.

The results of the reaction at 2 h and 75 h are listed in Table 2.

[Example 4]

a) Preparation of ZSM-5 molecular sieve raw powder

Tetraethylammonium bromide is used as a template, aluminum phosphate is used as an aluminum source, water glass is used as a silicon source, and potassium hydroxide is used as an alkali source. The molar ratio of tetraethylammonium bromide, aluminum phosphate, water glass, alkali, and water is: NH ₄ ⁺ :Al ₂ O ₃ :SiO ₂ :OH ^- :H ₂ O=0.2:0.002:1:0.2:10. After being fully mixed and stirred, the mixture is transferred into an autoclave, crystallized at 160°C for 15 hours under autogenous pressure, and then cooled. The synthesized product is filtered, washed with water, and dried at 90°C for 25 hours to obtain ZSM-5 molecular sieve raw powder.

b) 80 g of the above ZSM-5 molecular sieve powder and 50 g of silica sol ( _SiO2 weight content 40%) as a binder were kneaded, extruded into strips, dried at 80°C for 10 hours, and then calcined at 500°C for 8 hours to obtain a molded product.

c) The obtained molded product was ammonium exchanged in a 5 wt% aqueous solution of ammonium nitrate at 80°C for 2 hours, the ammonium exchange was performed 3 times in total, and then washed and dried at 100°C for 10 hours, and then calcined at 600°C for 4 hours.

d) The obtained ammonium exchange product is placed in a 5% by weight citric acid solution at 70°C and stirred for 4 hours, with the volume ratio of the acid solution to the ammonium exchange product being 2:1. After washing and drying at 100°C for 10 hours, it is calcined at 500°C for 6 hours. By adopting an equal volume impregnation method, the above catalyst is impregnated in a 2% magnesium nitrate solution for 10 hours, dried at 100°C for 10 hours, and then calcined at 550°C for 6 hours, thereby obtaining the desired catalyst for catalytic cracking of C4 mixed hydrocarbons to produce propylene and ethylene.

The acid ratio of B acid to L acid in the catalyst is 0.8:1, and the apparent skeleton density is 2.3 g/ml.

The catalyst comprises: a) 76.9% of ZSM-5 molecular sieve; b) 21.1% of binder component; and c) 2% of metal element Mg.

The silicon-aluminum molar ratio SiO ₂ /Al ₂ O ₃ of the ZSM-5 molecular sieve in the catalyst component is 500. The XRD pattern of the obtained ZSM-5 molecular sieve raw powder is similar to FIG2 .

The prepared catalyst was evaluated for its catalytic cracking activity in producing propylene and ethylene by using a fixed-bed catalytic reaction apparatus and mixed C4 residues extracted from ethylene plants as raw materials. The process conditions used were: 0.6 g catalyst loading, 550°C reaction temperature, 1.0 MPa reaction pressure, and 40 h ^-1 weight space velocity of olefin feedstock.

The results of the reaction at 2 h and 75 h are listed in Table 2.

[Example 5]

a) Preparation of ZSM-5 molecular sieve raw powder

Tetrapropylammonium hydroxide is used as a template, aluminum nitrate is used as an aluminum source, silica sol is used as a silicon source, and sodium hydroxide is used as an alkali source. The molar ratio of tetrapropylammonium hydroxide, aluminum nitrate, silica sol, alkali, and water is: NH ₄ ⁺ :Al ₂ O ₃ :SiO ₂ :OH ^- :H ₂ O=0.1:0.005:1:0.2:6. After being fully mixed and stirred, the mixture is transferred into an autoclave, crystallized at 180°C for 10 hours under autogenous pressure, and then cooled. The synthesized product is filtered, washed with water, and dried at 120°C for 10 hours to obtain ZSM-5 molecular sieve raw powder.

b) 85 g of the above ZSM-5 molecular sieve raw powder, 25 g of binder alumina and 32 g of 5% dilute nitric acid were kneaded and extruded into strips, dried at 80° C. for 10 hours, and then calcined at 600° C. for 4 hours to obtain a molded product.

c) The obtained molded product was subjected to ammonium exchange in a 10 wt% aqueous solution of ammonium sulfate at 90°C for 1.5 hours, the ammonium exchange was performed 3 times in total, and then washed, dried at 120°C for 6 hours, and calcined at 500°C for 8 hours.

d) The obtained ammonium exchange product is placed in a 5% by weight acetic acid solution at 70°C and stirred for 6 hours, with the volume ratio of the acid solution to the ammonium exchange product being 5:1. After washing and drying at 120°C for 6 hours, it is calcined at 500°C for 8 hours. By adopting an equal volume impregnation method, the above catalyst is impregnated in a 2% calcium nitrate solution for 8 hours, dried at 120°C for 6 hours, and then calcined at 550°C for 8 hours, thereby obtaining the desired catalyst for catalytic cracking of C4 mixed hydrocarbons to produce propylene and ethylene.

The acid ratio of B acid to L acid in the catalyst is 1:1, and the apparent skeleton density is 1.5 g/ml.

The catalyst comprises: a) 74% of ZSM-5 molecular sieve; b) 24% of binder component; and c) 2% of metal element Ca.

The silicon-aluminum molar ratio SiO ₂ /Al ₂ O ₃ of the ZSM-5 molecular sieve in the catalyst component is 200. The XRD pattern of the obtained ZSM-5 molecular sieve raw powder is similar to FIG2 .

The prepared catalyst was evaluated for its catalytic cracking activity in producing propylene and ethylene from C4 mixed hydrocarbons using a fixed bed catalytic reaction apparatus and mixed C4 residues from ethylene plants as raw materials. The process conditions used were: 0.6 g catalyst loading, 650°C reaction temperature, 0.05 MPa reaction pressure, and 30 h ^-1 weight space velocity of olefin feedstock.

The results of the reaction at 2 h and 75 h are listed in Table 2.

[Comparative Example 1]

a) Preparation of ZSM-5 molecular sieve raw powder

Tetrapropylammonium hydroxide is used as a template, sodium aluminate is used as an aluminum source, tetraethyl orthosilicate is used as a silicon source, and sodium hydroxide is used as an alkali source. The molar ratio of tetrapropylammonium hydroxide, sodium aluminate, tetraethyl orthosilicate, alkali, and water is: NH ₄ ⁺ :Al ₂ O ₃ :SiO ₂ :OH ^- :H ₂ O=0.1:0.00125:1:0.1:8. After being fully mixed and stirred, the mixture is transferred into an autoclave, crystallized at 150°C for 30 hours under autogenous pressure, and then cooled. The synthesized product is filtered, washed with water, and dried at 100°C for 20 hours to obtain ZSM-5 molecular sieve raw powder.

b) 80 g of the ZSM-5 molecular sieve powder and 80 g of aluminum sol (Al ₂ O ₃ weight content 25%) as a binder were kneaded, extruded into strips, dried at 100° C. for 8 hours, and then calcined at 550° C. for 6 hours to obtain a molded product.

c) The obtained molded product was subjected to ammonium exchange in a 10 wt% aqueous solution of ammonium chloride at 85°C for 1.5 hours, the ammonium exchange was performed 4 times in total, and then washed, dried at 120°C for 6 hours, and calcined at 550°C for 6 hours.

d) The ammonium exchange product was immersed in a 3% strontium nitrate solution for 10 hours by an equal volume impregnation method, dried at 100°C for 10 hours, and then calcined at 550°C for 6 hours to obtain the desired catalyst for catalytic cracking of C4 mixed hydrocarbons to produce propylene and ethylene.

FIG4 is a pyridine adsorption infrared spectrum of the catalyst obtained in Comparative Example 1. The ratio of B acid to L acid in the catalyst is 0.13:1, and the apparent skeleton density is 2.4 g/ml.

The catalyst comprises: a) 77.6% of ZSM-5 molecular sieve; b) 19.4% of binder component; and c) 3% of metal element Sr.

The silicon-aluminum molar ratio SiO ₂ /Al ₂ O ₃ of the ZSM-5 molecular sieve in the catalyst component is 800.

The XRD pattern of the obtained ZSM-5 molecular sieve raw powder is shown in Figure 3.

The catalyst evaluation method is the same as in Example 3, and the reaction results are listed in Table 2.

[Comparative Example 2]

a) Preparation of ZSM-5 molecular sieve raw powder

Tetrapropylammonium hydroxide is used as a template, sodium aluminate is used as an aluminum source, tetraethyl orthosilicate is used as a silicon source, and sodium hydroxide is used as an alkali source. The molar ratio of tetrapropylammonium hydroxide, sodium aluminate, tetraethyl orthosilicate, alkali, and water is: NH ₄ ⁺ :Al ₂ O ₃ :SiO ₂ :OH ^- :H ₂ O=0.1:0.00125:1:0.1:8. After being fully mixed and stirred, the mixture is transferred into an autoclave, crystallized at 150°C for 30 hours under autogenous pressure, and then cooled. The synthesized product is filtered, washed with water, and dried at 100°C for 20 hours to obtain ZSM-5 molecular sieve raw powder.

b) 80 g of the ZSM-5 molecular sieve powder and 80 g of aluminum sol (Al ₂ O ₃ weight content 25%) as a binder were kneaded, extruded into strips, dried at 100° C. for 8 hours, and then calcined at 550° C. for 6 hours to obtain a molded product.

c) The obtained molded product was subjected to ammonium exchange in a 10 wt% aqueous solution of ammonium chloride at 85°C for 1.5 hours, the ammonium exchange was performed 4 times in total, and then washed, dried at 120°C for 6 hours, and calcined at 550°C for 6 hours.

d) The obtained ammonium exchange product is placed in a 3 wt% oxalic acid solution at 75°C and stirred for 6 hours, with the volume ratio of the acid solution to the ammonium exchange product being 2:1. After washing and drying at 120°C for 6 hours, it is calcined at 550°C for 7 hours. The desired catalyst for catalytic cracking of C4 mixed hydrocarbons to produce propylene and ethylene is obtained.

The acid ratio of B acid to L acid in the catalyst is 2.1:1, and the apparent skeleton density is 2.0 g/ml.

The catalyst comprises: a) 78.3% of ZSM-5 molecular sieve; and b) 21.7% of a binder component.

The silicon-aluminum molar ratio SiO ₂ /Al ₂ O ₃ of the ZSM-5 molecular sieve in the catalyst component is 800. The catalyst evaluation method is the same as that in Example 3. The reaction results are listed in Table 2.

Table 1 Refinery C4 hydrocarbon feedstock composition

Components Composition (wt%) Isobutane 30.64 n-Butane 9.25 1-Butene 10.23 Isobutylene 24.76 Trans-2-Butene 14.52 Cis-2-Butene 10.54 1,3-Butadiene 0.06

Table 2 Catalyst evaluation results for each case

Claims (14)

1. A catalyst for co-cracking of C4 mixed hydrocarbons, the catalyst comprising the following components based on the total weight of the catalyst: I) 58% to 84% ZSM-5 molecular sieve; II) 10% to 41% of a binder component; III) 0.5% to 6% of alkaline earth metal elements; The acid amount ratio of B acid to L acid of the catalyst is 0.5-2:1, and the apparent skeleton density is 1.0-2.3 g/ml. 2. The catalyst according to claim 1, characterized in that the acid amount ratio of B acid to L acid in the catalyst is 0.8-1.5:1, and the apparent skeleton density is 1.0-1.8 g/ml. 3. The catalyst according to claim 1, characterized in that the SiO ₂ /Al ₂ O ₃ molar ratio of the ZSM-5 molecular sieve in component I) is 50 to 1000, preferably 100 to 1000; And/or, the alkaline earth metal element in component III) is at least one selected from Mg, Ca, Sr, and Ba. 4. A method for preparing the catalyst according to any one of claims 1 to 3, characterized in that it comprises the following steps: a) preparing ZSM-5 molecular sieve raw powder; b) kneading the raw powder obtained in step a) and a binder into a mold, drying, and first calcining to obtain a molded product; c) exchanging the formed product obtained in step b) with ammonium, and performing a second calcination to obtain an ammonium exchange product; d) treating the ammonium exchange product obtained in step c) in an acid solution, performing a third calcination, loading an alkaline earth metal and performing a fourth calcination to obtain the catalyst. 5. The preparation method according to claim 4 is characterized in that the process of preparing ZSM-5 molecular sieve raw powder in step a) comprises: uniformly mixing the template, aluminum source, silicon source, alkali source and water, hydrothermally crystallizing, and drying to obtain ZSM-5 molecular sieve raw powder. 6. The preparation method according to claim 5, characterized in that the template comprises at least one of tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide and tetrapropylammonium hydroxide; And/or, the aluminum source includes at least one of aluminum nitrate, aluminum sulfate, aluminum phosphate and sodium aluminate; And/or, the silicon source includes at least one of water glass, silica sol and tetraethyl orthosilicate; And/or, the alkali source includes at least one of sodium hydroxide and potassium hydroxide. 7. The preparation method according to claim 5, characterized in that, in the raw materials used for preparing ZSM-5 molecular sieve raw powder in step a), the molar ratio of the template agent as _NH4 ⁺ , the aluminum source as _{Al2O3 , the} silicon source as _SiO2 , the alkali source as ^OH- , and water is: _NH4 ⁺ : _Al2O3 : _SiO2 : ^OH- : _H2O = 0.1-0.5: 0.001-0.02: 1: 0.1-0.4: 5-10; And/or, the hydrothermal crystallization conditions are: crystallization at 120-180° C. for 10-60 hours. 8. The preparation method according to claim 4, characterized in that in step b), the binder is selected from one or more of alumina, aluminum sol, and silica sol; And/or, the drying conditions in step b) are: drying at 80-120° C. for 5-10 hours; And/or, the first calcination condition is: calcination at 500-600° C. for 4-8 hours. 9. The preparation method according to claim 4, characterized in that the conditions of the ammonium exchange in step c) are: temperature of 80-90°C and time of 1-3h; Preferably, the number of ammonium exchanges is 2 to 5 times; Further preferably, the concentration of the aqueous ammonium salt solution in the ammonium exchange is 5wt% to 10wt%; the ammonium salt is at least one selected from ammonium chloride, ammonium nitrate, and ammonium sulfate; And/or, the second calcination condition is calcination at 500-600° C. for 4-8 hours. 10. The preparation method according to claim 4, characterized in that the acid content in the acid solution in step d) is 2wt% to 5wt%; the acid is an organic acid; the organic acid comprises at least one selected from citric acid, oxalic acid, acetic acid, and oxalic acid; And/or, the treatment in step d) is soaking, and the treatment conditions are as follows: the volume ratio of acid solution to ammonium exchange product is 2:1 to 5:1, the treatment temperature is 70 to 80° C., and the treatment time is 4 to 8 hours; And/or, the third calcination in step d) is carried out at 500-600° C. for 4-8 hours. 11. The preparation method according to claim 4, characterized in that the loading of the alkaline earth metal in step d) is carried out by an equal volume impregnation method; and/or the fourth calcination is carried out at 500-600°C for 4-8 hours. 12. Use of the catalyst according to any one of claims 1 to 3 or the catalyst prepared by the preparation method according to any one of claims 4 to 11 in the co-cracking reaction of C4 mixed hydrocarbons to produce propylene and ethylene. 13. The use according to claim 12, characterized in that the C4 mixed hydrocarbons are derived from C4 mixed hydrocarbons from a refinery; Preferably, the C4 mixed hydrocarbon includes at least one of isobutane, n-butane, 1-butene, isobutene, trans-2-butene, and 1,3-butadiene; More preferably, the C4 mixed hydrocarbon is at least one alkane and at least one olefin. 14. The use according to claim 12, characterized in that the reaction conditions are: reaction temperature is 500-700°C, reaction pressure is 0-1.0 MPa, and weight space velocity of the mixed hydrocarbon feedstock is 1-40 h ^-1 .

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