A method for preparing a premium steam cracking feedstock

Abstract

This invention discloses a method for preparing high-quality steam cracking feedstock, comprising the following steps: under a hydrogen atmosphere, contacting naphtha fraction with a catalyst in a reactor to react and obtain high-quality steam cracking feedstock; wherein the naphtha fraction is selected from at least one of C5 and C6 alkanes; the high-quality steam cracking feedstock is selected from at least one of ethane, propane, and n-butane; the catalyst is composed of an acidic support and a metal active element and an auxiliary element supported on the surface of the acidic support; the metal active element includes tungsten and nickel, wherein the mass ratio of nickel to tungsten is 1 to 4:1; the auxiliary element is selected from at least one of boron and phosphorus; in the catalyst, the loading of the metal active element is 2 to 15 wt%, and the loading of the auxiliary element is 0.1 to 1 wt%.

Description

Technical Field

[0001] This invention relates to a method for preparing high-quality steam pyrolysis feedstock, belonging to the field of chemical engineering. Background Technology

[0002] The trienes (ethylene, propylene, and butadiene) produced by steam cracking are fundamental raw materials for the petrochemical industry and are widely used in the production of synthetic materials such as plastics, rubber, and fibers. These chemicals play a vital role in industrial production, providing modern society with a large number of basic chemical products and advanced functional materials.

[0003] Ethylene is the most demanded basic chemical feedstock among olefins. Globally, 95% of ethylene production is achieved through steam cracking, and domestic steam cracking capacity accounts for over 80% of total ethylene production. Steam cracking is a non-catalytic thermal process, and the ethylene yield is determined by the overall composition of the feedstock. In China, naphtha is the primary feedstock for steam cracking units, but the ethylene yield from naphtha cracking is typically only around 30%, far lower than that of ethane (approximately 80%), propane (approximately 40%), and n-butane (approximately 40%). Converting naphtha fractions into ethane, propane, and n-butane before feeding them into the steam cracking unit can significantly improve the ethylene yield. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing high-efficiency steam cracking feedstocks such as ethane, propane, and n-butane by pre-catalytic conversion of naphtha fractions.

[0005] According to one aspect of the present invention, a method for preparing high-quality steam cracking feedstock is provided. The method uses naphtha fraction as feedstock and, under hydrogen-containing conditions, achieves highly selective preparation of high-quality steam cracking feedstocks such as ethane, propane, and n-butane through the action of a catalyst in a reactor.

[0006] According to one aspect of the present invention, a method for preparing high-quality steam cracking feedstock is provided, comprising at least the following steps:

[0007] In a hydrogen atmosphere, naphtha fraction is contacted with a catalyst in a reactor to react and obtain high-quality steam cracking feedstock.

[0008] The naphtha fraction is selected from at least one of C5 and C6 hydrocarbons;

[0009] The high-quality steam cracking feedstock is selected from at least one of ethane, propane, and n-butane;

[0010] The catalyst is composed of an acidic support and metal active elements and auxiliary elements supported on the surface of the acidic support;

[0011] The active metal elements include tungsten and nickel, wherein the mass ratio of nickel to tungsten is 1 to 4:1;

[0012] The auxiliary element is selected from at least one of boron and phosphorus;

[0013] In the catalyst, the loading of the active metal element is 2-15 wt%, and the loading of the auxiliary element is 0.1-1 wt%.

[0014] The catalyst is obtained through the following steps:

[0015] An acidic support is impregnated in an aqueous solution containing a precursor of a metal active element and a precursor of an auxiliary element, then dried (I), calcined (I), and reduced with hydrogen to obtain the catalyst.

[0016] The metal active element precursor is selected from at least one of nickel acetate, nickel acetate, ammonium metatungstate, sodium tungstate, and ammonium tungstate;

[0017] The precursor of the auxiliary element is selected from at least one of boric acid, sodium borate, phosphoric acid, and sodium phosphate;

[0018] The temperature of the drying process I is 100–130°C;

[0019] The drying time for step I is 2–30 hours;

[0020] The temperature of the calcination I is 500–600°C;

[0021] The roasting time for I is 1 to 8 hours;

[0022] The temperature for hydrogen reduction is 500–600°C;

[0023] The hydrogen reduction time is 1 to 10 hours.

[0024] The acidic carrier is obtained through the following steps:

[0025] (1) Mix the molecular sieve with a hydrocarbon solution containing silicon compounds, process it, dry it (II), calcine it (II), and treat it with steam to obtain the modified molecular sieve.

[0026] (2) The modified molecular sieve is mixed with matrix, molding aid and water, kneaded, extruded into strips, dried (III), and calcined (III) to obtain the acidic carrier.

[0027] The molecular sieve has a 10-membered ring pore structure and / or an 8-membered ring pore structure, and is selected from at least one of ZSM-5, MOR, ZSM-35 and ZSM-22;

[0028] The silicon-containing compound is selected from at least one of 3-aminopropyltriethoxysilane, tetramethoxysilane, and trimethoxychlorosilane;

[0029] The hydrocarbons are selected from at least one of cyclohexane, n-octane, and toluene;

[0030] The processing temperature of the hydrocarbon solution is 60–90°C;

[0031] The processing time for the hydrocarbon solution is 1 to 5 hours;

[0032] The temperature of the drying II process is 100–120°C;

[0033] The drying time for step II is 4–20 hours;

[0034] The temperature of the second calcination is 500–600°C;

[0035] The roasting time for II is 2–8 hours;

[0036] The temperature for steam treatment is 500–600°C;

[0037] The steam treatment time is 1 to 5 hours.

[0038] The matrix is ​​selected from at least one of boehmite, kaolin, alumina, chlorite, alumina sol, and silica sol.

[0039] The molding aid is selected from at least one of polyethylene glycol, polyvinyl alcohol, acetic acid, citric acid and tartaric acid;

[0040] The temperature of the drying III process is 100–120°C;

[0041] The drying time for the third stage is 5 to 30 hours;

[0042] The temperature of calcination III is 500–600°C;

[0043] The roasting time for the third stage is 2 to 8 hours.

[0044] The mass hourly space velocity (MSV) of the naphtha fraction is 0.2–10 h⁻¹. -1 ;

[0045] The molar ratio of hydrogen to naphtha fraction is 0.5 to 10:1.

[0046] The reaction temperature is 300–500°C;

[0047] The reaction pressure is 0.1–6 MPa.

[0048] The beneficial effects that this invention can produce include:

[0049] (1) This invention provides a method for preparing high-quality steam cracking feedstock capable of producing more ethylene from naphtha fraction;

[0050] (2) The acidic support in the catalyst provided by the present invention contains modified molecular sieves, which makes the catalyst have suitable pore acidity and effectively eliminates the acidity of the outer surface. While effectively catalyzing the cracking and decomposition conversion of naphtha, it inhibits the occurrence of side reactions such as hydrogen transfer and polymerization.

[0051] (3) The catalyst provided by the present invention can stabilize the reaction intermediate and promote the synergistic catalytic effect between the metal active site and the acidic site in the support, which improves the raw material conversion rate and effectively inhibits the occurrence of side reactions.

[0052] (4) The catalyst preparation method provided by the present invention is simple, easy to operate, and has good repeatability, making it suitable for large-scale industrial production.

[0053] (5) The catalyst provided by the present invention can catalyze the efficient conversion of naphtha fractions, especially C5 and C6 hydrocarbons in naphtha fractions, into high-quality steam cracking feedstocks. It has the characteristics of good catalytic activity, good selectivity and not easy to deactivate. Detailed Implementation

[0054] The present invention will be described in detail below with reference to the embodiments, but the present invention is not limited to these embodiments.

[0055] Unless otherwise specified, all raw materials used in the examples are commercially available, and the instruments and equipment are configured with parameters recommended by the manufacturer.

[0056] Example 1: Preparation of modified molecular sieves Z1-Z7

[0057] The hydrogen-type molecular sieve to be modified was added to a hydrocarbon solution containing silicon compounds with a mass concentration of 5 wt%. The solution was refluxed at a liquid-to-solid ratio of 10:1 mL / g, then dried in an oven and calcined in a muffle furnace. The calcined sample was then loaded into a quartz tube reactor and heated at a water vapor hourly space velocity (WHSV) of 2 h⁻¹. -1 Under the specified conditions, the molecular sieves Z1 to Z7 were modified by steam treatment for 2 hours.

[0058] The preparation conditions for the hydrogen-type molecular sieves used in the preparation of the above-mentioned modified molecular sieves, including the types of silicon-containing compounds, the types of hydrocarbon solvents, the treatment time of the silicon-containing compound hydrocarbon solution, the treatment temperature of the silicon-containing compound hydrocarbon solution, the steam treatment temperature and time, the drying temperature and time, and the calcination temperature and time, are shown in Table 1.

[0059] Table 1 Preparation conditions of modified molecular sieves Z1 to Z7

[0060]

[0061]

[0062] Example 2: Preparation of acidic carriers S1 to S8

[0063] The modified molecular sieve prepared in Example 1, the aluminum-containing acidic metal component, the molding aid and water are mixed in a certain proportion, then kneaded, extruded into strips, dried in an oven and calcined in a muffle furnace to prepare acidic carriers S1 to S8.

[0064] The preparation conditions for the above-mentioned acidic carrier preparation, including the modified molecular sieve, silicon or aluminum-containing matrix, type and quantity of molding aids, drying temperature and time, and calcination temperature and time, are shown in Table 2.

[0065] Table 2 Preparation conditions of acidic carriers S1 to S8*

[0066]

[0067]

[0068] *Soluble calculations are based on a dry basis.

[0069] Example 3: Preparation of catalysts Cat.1 to Cat.10

[0070] The saturated water absorption of the acidic support in Example 2 was determined using the saturated water absorption method. Then, based on the saturated water absorption, the target loading of the metal active component, and the auxiliary component, the concentrations of the metal active component precursor and the auxiliary component precursor in the modified solution were calculated. Based on the above calculation results, a modified solution containing the metal active component precursor and the auxiliary component precursor was prepared.

[0071] The modified solution was uniformly added to the acidic support prepared in Example 2 until adsorption saturation, then allowed to stand at room temperature for 24 hours, dried in an oven, calcined in a muffle furnace, and then reduced in a hydrogen atmosphere to obtain catalysts Cat.1 to Cat.10.

[0072] The preparation conditions for the above catalysts, including the type of acidic support, the type and loading of the metal active component precursor (based on metal element), the type and loading of the auxiliary component precursor (based on boron or phosphorus element), the drying temperature and time, the calcination temperature and time, and the reduction temperature and time, are shown in Table 3.

[0073] Table 3. Preparation conditions of catalysts Cat.1 to Cat.10

[0074]

[0075]

[0076] Comparative Example 1

[0077] A comparative acidic support was prepared by mixing 70 parts by weight of unmodified hydrogen-type ZSM-5 molecular sieve, 15 parts by weight of pseudoboehmite, 5 parts by weight of alumina sol, 10 parts by weight of silica sol, 6 parts by weight of polyethylene glycol, 3 parts by weight of citric acid, and deionized water. The mixture was then kneaded, extruded into strips, dried in an oven at 110°C for 10 hours, and calcined in a muffle furnace at 550°C for 4 hours. Then, using the above-mentioned comparative acidic support as the matrix, the comparative example catalyst 1 was prepared according to the preparation method of Cat.5 in Example 3.

[0078] Comparative Example 2

[0079] Using the acidic support S5 from Example 2 as the support, and following the preparation method of Cat.5 in Example 3, the loading of the metal active component was omitted to prepare the catalyst of Comparative Example 2.

[0080] Comparative Example 3

[0081] Using the acidic support S5 from Example 2 as the support, and following the preparation method of Cat.5 in Example 3, the loading of the auxiliary components was omitted to prepare the catalyst of Comparative Example 3.

[0082] Example 4: Evaluation of the catalytic activity of the catalyst prepared from high-quality steam cracking feedstock

[0083] The catalytic activity of catalysts Cat.1–Cat.10 prepared in Example 3 and the comparative catalysts was evaluated using high-quality steam cracking feedstocks. A fixed-bed reactor with an inner diameter of 9 mm and a catalyst loading of 2 mL was used. Feedstocks containing C5 and / or C6 hydrocarbons and hydrogen were introduced for the reaction. The C5 and / or C6 hydrocarbon compositions of feedstocks YL1–YL4 used for the activity evaluation are shown in Table 4.

[0084] Table 4 Composition of raw materials YL1 to YL4

[0085]

[0086] *The table only lists the C5 and / or C6 alkanes in the raw materials. The composition content is the mass composition of each component in the C5 and / or C6 alkanes. In addition to the listed C5 and / or C6 alkanes, the raw materials may contain olefins, aromatics and alkanes with more than six carbons, with a total amount not exceeding 10 wt%.

[0087] The products were analyzed online using an Agilent 7890A chromatograph. The catalyst activity was evaluated based on indicators such as the conversion rate of C5 and / or C6 alkanes in the feedstock and the selectivity for high-quality steam cracking feedstocks (ethane, propane, and n-butane). The calculation methods for each indicator are as follows:

[0088]

[0089]

[0090] [Raw Material Alkanes] 进 The mass flow rate (g / h) of the C5 and / or C6 alkane feedstock at the reactor inlet. [Feedstock Alkanes] 出 The mass flow rate (g / h) of unconverted C5 and / or C6 alkane feedstock at the reactor outlet, [ethane]. 出 [Propane] 出 [n-Butane] 出 and [hydrocarbon products] 出 The values ​​represent the mass flow rates (g / h) of ethane, propane, n-butane, and all hydrocarbon products at the reactor outlet, respectively. The catalysts used in experiments exp1–exp15, along with the reaction conditions and catalyst activities, are shown in Table 5.

[0091] Table 5. Reaction conditions and catalyst activity for experiments exp1–exp15

[0092]

[0093] In the experiments shown in Table 5, samples were taken and analyzed every 2 hours. The results in the table are the average values ​​over 50 hours. Experiment exp5 was run continuously for 1000 hours, and no significant decrease in conversion or selectivity was observed, indicating that the catalyst has good stability.

[0094] The above description is merely a few embodiments of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any modifications or alterations made by those skilled in the art without departing from the scope of the technical solution of the present invention using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing high-quality steam pyrolysis feedstock, characterized in that, At least the following steps are included: In a hydrogen atmosphere, naphtha fraction is contacted with a catalyst in a reactor to react and obtain high-quality steam cracking feedstock. The naphtha fraction is selected from at least one of C5 and C6 hydrocarbons; The high-quality steam cracking feedstock is selected from at least one of ethane, propane, and n-butane; The catalyst is composed of an acidic support and metal active elements and auxiliary elements supported on the surface of the acidic support; The active metal elements include tungsten and nickel, wherein the mass ratio of nickel to tungsten is 1 to 4:1; The auxiliary element is selected from at least one of boron and phosphorus; In the catalyst, the loading of the active metal element is 2-15 wt%, and the loading of the auxiliary element is 0.1-1 wt%.

2. The preparation method according to claim 1, characterized in that, The catalyst is obtained through the following steps: The acidic support was impregnated in an aqueous solution containing a precursor of a metal active element and a precursor of an auxiliary element, dried (I), calcined (I), and reduced with hydrogen to obtain the catalyst.

3. The preparation method according to claim 2, characterized in that, The metal active element precursor is selected from at least one of nickel nitrate, nickel acetate, ammonium metatungstate, sodium tungstate, and ammonium tungstate; The precursor of the auxiliary element is selected from at least one of boric acid, sodium borate, phosphoric acid, and sodium phosphate; The temperature of the drying process I is 100–130°C; The drying time for step I is 2–30 hours; The temperature of the calcination I is 500–600°C; The roasting time for I is 1 to 8 hours; The temperature for hydrogen reduction is 500–600°C; The hydrogen reduction time is 1 to 10 hours.

4. The preparation method according to claim 2, characterized in that, The acidic carrier is obtained through the following steps: (1) Mix the molecular sieve with a hydrocarbon solution containing silicon compounds, process it, dry it (II), calcine it (II), and treat it with steam to obtain the modified molecular sieve. (2) The modified molecular sieve is mixed with matrix, molding aid and water, kneaded, extruded into strips, dried (III), and calcined (III) to obtain the acidic carrier.

5. The preparation method according to claim 4, characterized in that, The molecular sieve has a 10-membered ring pore structure and / or an 8-membered ring pore structure, and is selected from at least one of ZSM-5, MOR, ZSM-35 and ZSM-22; The silicon-containing compound is selected from at least one of 3-aminopropyltriethoxysilane, tetramethoxysilane, and trimethoxychlorosilane; The hydrocarbons are selected from at least one of cyclohexane, n-octane, and toluene; The processing temperature of the hydrocarbon solution is 60–90°C; The processing time for the hydrocarbon solution is 1 to 5 hours; The temperature of the drying II process is 100–120°C; The drying time for step II is 4–20 hours; The temperature of the second calcination is 500–600°C; The roasting time for II is 2–8 hours; The temperature for steam treatment is 500–600°C; The steam treatment time is 1 to 5 hours.

6. The preparation method according to claim 4, characterized in that, The matrix is ​​selected from at least one of boehmite, kaolin, alumina, chlorite, alumina sol, and silica sol. The molding aid is selected from at least one of polyethylene glycol, polyvinyl alcohol, acetic acid, citric acid and tartaric acid; The temperature of the drying III process is 100–120°C; The drying time for the third stage is 5 to 30 hours; The temperature of calcination III is 500–600°C; The roasting time for the third stage is 2 to 8 hours.

7. The preparation method according to claim 1, characterized in that, The mass hourly space velocity (MSV) of the naphtha fraction is 0.2–10 h⁻¹. -1 ; The molar ratio of hydrogen to naphtha fraction is 0.5 to 10:

1.

8. The preparation method according to claim 1, characterized in that, The reaction temperature is 300–500°C; The reaction pressure is 0.1–6 MPa.

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