CN1176748C - Catalyst for Synthetic Diesel with Molecular Sieve as Carrier - Google Patents

Abstract

The present invention relates to a Fischer-Tropsch reaction catalyst prepared from a molecular sieve and metallic cobalt, wherein the molecular sieve is a Y-type molecular sieve, a Beta molecular sieve or an MOR molecular sieve. The catalyst is prepared from 3 wt% to 10 wt% of cobalt and a surplus quantity of molecular sieve, and the silica alumina ratio n of the molecular sieve is from 5 to 200. The catalyst is prepared with an impregnation method, and the conversion rate of synthetic gas in the reaction process is nearly remained unchanged under appropriate reaction conditions; the selectivity of hydrocarbons from C10 to C20 is higher than 35% under suitable reaction conditions when a molecular sieve with the pore diameter of larger than 0.7 nm is used as a carrier and the cobalt carrying capacity is appropriate; the selectivity of straight chain paraffin from C10 to C20 exceeds 50% when the MOR molecular sieve in a one-dimensional pore canal structure is used as the carrier. In addition, the phenomenon of the carbon deposition of the catalyst is avoided or reduced at a relatively high reaction temperature (higher than 250DEG C) so that the continuous running of the catalyst is guaranteed.

Description

Catalyst for Synthetic Diesel with Molecular Sieve as Carrier

technical field

The invention relates to a Fischer-Tropsch reaction catalyst.

Background technique

The technology of converting natural gas into synthesis gas first and then synthesizing liquid hydrocarbons (GTL) through Fischer-Tropsch reaction provides a feasible way for the conversion and utilization of natural gas. Companies such as Shell, Sasol, Exxon, Syntroleum, and Energe International have developed their own GTL patented technologies and new processes. The liquid products in GTL products are basically composed of straight-chain hydrocarbons and olefins, and have the characteristics of no sulfur, no nitrogen, no metals, no aromatics, etc., and are environmentally friendly fuel oils and chemicals. GTL technology can adapt to a variety of needs through the regulation of catalysts. Products range from clean and high-quality oils (such as aviation kerosene, diesel oil, lubricating oil) to chemicals (such as high-carbon olefins, light olefins and oxygenated compounds), with high Added value is of great significance for the development and utilization of scattered small and medium gas fields in remote areas, especially natural gas with oil and gas coexistence.

The composition of the typical cobalt-based Fischer-Tropsch synthesis catalyst of commercialization reported in recent literature (Scholten J J F, Xu X D, Von Der Decken CB et al.Int J EnergRes, 1994,18,185): cobalt, trace amount of second A metal (usually a noble metal), an oxide additive (alkali metal, rare earth metal and transition metal oxide, such as ZrO ₂ , etc.) and a carrier (Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZSM, etc.). European Patent EP 800 864 discloses that a novel Fischer-Tropsch catalyst supported by Si, Al, Zr, Sn, Mg or rare earth, Ti and other oxides can produce linear mixed saturated hydrocarbons from syngas. CN1052844 discloses a catalyst for converting synthesis gas into hydrocarbons, the components of which mainly include Co and Zn. CN 1084153 discloses a catalyst for preparing higher hydrocarbons, including Co/Al ₂ O ₃ and a second metal that is not sensitive to the loading amount, and the product is mainly a mixture containing alkanes. U.S. Patent No. 5,545,674 sprays the active surface layer of cobalt metal on the outer surface of the inorganic oxide carrier by spraying, and adds additives (such as rhenium, zirconium, hafnium, cerium, thorium, and uranium or their mixtures) at the same time to improve the activity of the catalyst. The ability and selectivity of liquid hydrocarbons, the catalyst deactivation is slow during the reaction, the yield of distillate oil containing linear alkanes and olefins is high, and the basic composition of the products is C ₁₀₊ hydrocarbons. It can be seen from patents and literature reports that although the above-mentioned catalyst can be used to obtain lower selectivity of CH ₄ and higher selectivity of C ₅₊ and the conversion rate of synthesis gas, its product distribution is more in line with the FSA distribution, which makes the product The selectivity of diesel components (C ₁₀ -C ₂₀ ) is generally lower. In addition, the reaction temperature is generally below 250°C, so that the heavy carbon hydrocarbons generated by the reaction tend to stay on the catalyst, block the pores of the catalyst, and change the activity and selectivity of the catalyst.

Contents of the invention

The object of the present invention is to provide a cobalt-based catalyst that uses molecular sieve as a catalyst carrier, has higher selectivity for C ₁₀ -C ₂₀ hydrocarbons and can avoid or reduce carbon deposition on the catalyst, and can produce high-grade diesel from syngas.

Said catalyzer of the present invention is made up of molecular sieve and metal cobalt, and the chemical composition of catalyzer is

xCo/Na ₂ O Al ₂ O ₃ nSiO ₂

Where x is the weight percentage of Co in the catalyst, Na ₂ O·Al ₂ O ₃ ·nSiO ₂ is the chemical expression of the molecular sieve, and n is the molar ratio of SiO ₂ and Al ₂ O ₃ in the molecular sieve. Said molecular sieves are sodium faujasite molecular sieve Y, sodium mordenite molecular sieve (MOR) and sodium β molecular sieve (Beta). The ratio of each component of the catalyst is 3% to 10% of cobalt (weight percentage), preferably 5%, and the balance is molecular sieve. The molar ratio n of SiO ₂ and Al ₂ O ₃ in the molecular sieve is 5-200.

The preparation of catalyst is prepared by impregnation method, and its steps are as follows:

1) Weigh the cobalt salt according to the distribution ratio of the catalyst components, add deionized water to prepare a solution with a concentration of 2% to 5% by weight, and said cobalt salt is cobalt nitrate, cobalt acetate or cobalt acetylacetonate;

2) Weigh the molecular sieve according to the distribution ratio of the catalyst components, add it into the prepared cobalt solution, stir evenly (2h), and place it for 24h;

3) Evaporate the above mixed solution to dryness in a water bath at 50-80°C, and then vacuum-dry at 40-100°C for 24 hours;

4) After fully grinding the dried solid, calcining at 300-800°C for 4-10 hours;

5) molding the calcined solid powder, and sieving components of 30 to 60 meshes as catalyst precursors;

6) The catalyst precursor is reduced in a hydrogen atmosphere at 400-500° C. for 12-20 hours to obtain a Fischer-Tropsch synthesis catalyst.

Catalyst evaluation was carried out in a fixed-bed stainless steel high-pressure microreactor (reaction tube inner diameter 8mm). The reaction conditions are raw material gas composition H ₂ /CO/Ar=64:32:4, reaction temperature 250-260°C, reaction pressure 2.0MPa, space velocity 1.5-6.0Lg ^-1 h ^-1 . The gas phase products generated by the reaction were analyzed by GC-950 gas chromatograph 5A molecular sieve column (analyzing Ar, CH ₄ , CO), Porapak-Q column (analyzing CO+CH ₄ , CO ₂ , C ₂ H ₄ , C ₂ H ₆ , C ₃ H ₆ , C ₃ H ₈ , etc.), TCD online analysis. The liquid phase product was collected by a cold trap and then analyzed by a GC-112 gas chromatograph AT PONA quartz capillary column and FID. Catalyst of the present invention is under suitable reaction conditions _, and the syngas conversion ratio remains almost unchanged in the reaction process; The selectivity of ~C ₂₀ hydrocarbons is more than 35%; when the MOR molecular sieve with a one-dimensional pore structure is used as a carrier, the selectivity of C ₁₀ ~C ₂₀ linear alkanes exceeds 50%. In addition, the present invention uses a relatively high reaction temperature (above 250° C.) to avoid or reduce carbon deposition on the catalyst, thereby ensuring continuous operation of the catalyst.

Description of drawings

Fig. 1 is the relationship diagram of the conversion rate of CO with time in Example 1.

Fig. 2 is the relationship diagram of the conversion rate of CO with time in Example 2.

Fig. 3 is the relationship graph of the conversion rate of CO with time in Example 3.

Detailed ways

The present invention will be further described below by embodiment.

Example 1: Weigh 5.20 g of Co(NO ₃ ) ₂ 6H ₂ O and add 200 g of deionized water to dissolve it, weigh 20 g of MOR whose molar ratio n of SiO ₂ to Al ₂ O ₃ is 18.5, and add it to the above solution, Stir for 2 hours and then stand for 24 hours; evaporate the above mixed solution to dryness in a water bath at 70-80°C, then vacuum-dry at 60°C for one day, grind the dried solid thoroughly, and roast at 550°C for 6 hours, and shape the roasted solid powder , sieving 30-60 mesh components as a catalyst precursor, and reducing the catalyst precursor in a hydrogen atmosphere at 400°C for 16 hours to obtain a 5wt% Co/MOR Fischer-Tropsch synthesis catalyst. Mordenite molecular sieve MOR is prepared by hydrothermal synthesis method, Table 1 shows its chemical composition and some physical and chemical properties.

Table 1 Chemical composition and physical and chemical properties of MOR Name Na-Mordenite Exterior powdery chemical components SiO ₂ wt% 87.0 Al ₂ O ₃ wt% 7.99 Na ₂ O wt% 5.03 Fe wt% 0.03 Ig. Loss wt% 8.9 SiO ₂ /Al ₂ O ₃ ratio 18.5 physical properties particle size μm 0.1～0.5 proportion g/cc 0.29 specific surface area m ² /g 340

The catalytic reaction is carried out in a fixed-bed stainless steel high-pressure microreactor (the inner diameter of the reaction tube is 8mm), and 0.8g of the precursor (30-60 mesh) of 5wt% Co/MOR is weighed, put into the reaction tube, and hydrogen is passed under normal pressure. Raise the temperature (heating rate 4°/min) to 400°C for reduction for 16 hours, and the hydrogen flow rate is 30ml/min; after reducing the precursor, cool down to below 40°C, according to the raw material gas composition H ₂ /CO/Ar=64:32:4, The reaction temperature is 250°C, the reaction pressure is 2.0MPa, and the reaction conditions are 1.5Lg ^-1 h ^-1 space velocity. Switch the synthesis gas, adjust the synthesis gas pressure to 2.0MPa, and the flow rate to 20ml/min. After the pressure and flow rate of the system are stable, The temperature was programmed (heating rate 4°/min) to 250°C for the reaction, and the reaction was run for 12 hours. The gas phase product generated by the reaction was collected by the 5A molecular sieve column (analyzing Ar, CH ₄ , CO) and the Porapak-Q column of the GC-950 gas chromatograph. (Analysis of CO+CH ₄ , CO ₂ , C ₂ H ₄ , C ₂ H ₆ , C ₃ H ₆ , C ₃ H ₈ , etc.), TCD online analysis. The liquid phase product was collected by a cold trap and then analyzed by a GC-112 gas chromatograph AT PONA quartz capillary column and FID.

The performance evaluation of the catalytic reaction is listed in Table 2. It can be seen from Table 2 that the selectivity of gas products in the products of 5wt% Co/MOR catalyst does not exceed 30%, while the liquid products are mainly high-grade diesel oil and light wax. The diesel component (C ₁₀ -C ₂₀ ) in the liquid product is about 75% by weight, and the product is mainly normal hydrocarbons, and the olefins and isomeric hydrocarbons are only about 10% by weight. The catalyst can run continuously for thousands of hours without activity change.

Table 2 Reaction performance of 5wt% Co/MOR catalyst CO conversion rate (%) 42.8 CH ₄ selectivity (%) 17.6 Selectivity of gaseous hydrocarbons (C ₂ ～C ₄ ) (%) 4.3 Selectivity of liquid light hydrocarbons (C ₅ ～C ₉ ) (%) 8.6 Selectivity of diesel components (C ₁₀ ~C ₂₀ ) (%) 57.1 Selectivity of normal hydrocarbons in diesel components (%) 50.3 Selectivity of wax phase (C ₂₁₊ ) (%) 9.7

Figure 1 shows the relationship of the conversion rate of CO with time. It can be seen from the figure that the conversion rate of the synthesis gas remains almost unchanged during the reaction process under suitable reaction conditions for the 5wt% Co/MOR catalyst.

Example 2: Weigh 5.20 g of Co(No ₃ ) ₂ 6H ₂ O and add 200 g of deionized water to dissolve it, weigh 20 g of NaY whose molar ratio n of SiO ₂ to Al ₂ O ₃ is 5.6, and add it to the above solution, After stirring for 2 hours, let it stand for 24 hours. Evaporate the above mixed solution to dryness in a water bath at 70-80°C, then dry it under vacuum at 60°C for one day, grind the dried solid thoroughly, and then calcinate at 550°C for 6 hours, and shape the calcined solid powder , 30-60 mesh components were sieved as catalytic precursors, and the catalyst precursors were reduced in a hydrogen atmosphere at 400°C for 16 hours to obtain a 5wt% Co/NaY Fischer-Tropsch synthesis catalyst. NaY molecular sieves were prepared by hydrothermal synthesis in the experiment, and Table 3 shows their chemical composition and some physical and chemical properties.

The chemical composition and physicochemical properties of Table 3NaY Name NaY Exterior powdery chemical components SiO ₂ wt% 67.3 Al ₂ O ₃ wt% 20.3 Na ₂ O wt% 12.4 Ig. Loss wt% 20.7 SiO ₂ /Al ₂ O ₃ ratio 5.6 physical properties particle size μm 0.2～0.6 proportion g/cc 0.33 specific surface area m ² /g 660

The catalytic reaction was carried out in a fixed-bed stainless steel high-pressure microreactor (the inner diameter of the reaction tube was 8mm), and 0.8g of the precursor (30-60 mesh) of 5wt% Co/NaY was weighed and loaded into the reaction tube. The reaction conditions and product analysis were the same as the implementation example 1.

The reaction properties of 5wt% Co/NaY are listed in Table 4. It can be seen from Table 4 that the selectivity of gas products in the products of 5wt% Co/NaY catalyst is not more than 30%, while the liquid products are mainly diesel oil and light wax. The diesel component (C ₁₀ -C ₂₀ ) in the liquid product is about 66wt%, and the product is mixed hydrocarbon, and the normal hydrocarbon is about 66wt%. It can be seen from Figure 2 that under the reaction conditions of the 5wt% Co/NaY catalyst, the conversion rate of syngas increases with the reaction time during the reaction process, reaches the maximum value after 3 hours and then gradually decreases, and remains almost unchanged after 8 hours.

Table 4 Reaction performance of 5wt% Co/NaY catalyst CO conversion rate (%) 47.0 CH ₄ selectivity (%) 21.4 Selectivity of gaseous hydrocarbons (C ₂ ～C ₄ ) (%) 6.5 Selectivity of liquid light hydrocarbons (C ₅ ～C ₉ ) (%) 17.9 Selectivity of diesel components (C ₁₀ ~C ₂₀ ) (%) 46.9 Selectivity of normal hydrocarbons in diesel components (%) 31.3 Selectivity of wax phase (C ₂₁₊ ) (%) 5.6

Example 3: Weigh 5.20 g of Co(NO ₃ ) ₂ 6H ₂ O and add 200 g of deionized water to dissolve it, weigh 20 g of Beta with a molar ratio n of SiO ₂ and Al ₂ O ₃ of 25, and add it to the above solution, After stirring for 2 hours, let it stand for 24 hours. Evaporate the above mixed solution to dryness in a water bath at 70-80°C, then dry it under vacuum at 60°C for one day, grind the dried solid thoroughly, and then calcinate at 550°C for 6 hours, and shape the calcined solid powder , 30-60 mesh components were sieved as catalytic precursors, and the catalyst precursors were reduced in a hydrogen atmosphere at 400°C for 16 hours to obtain a 5wt% Co/Beta Fischer-Tropsch synthesis catalyst. Beta molecular sieves were prepared by hydrothermal synthesis in the experiment, and Table 5 shows their chemical composition and some physical and chemical properties.

Chemical composition and physicochemical properties of Table 5Beta Name Beta Exterior powdery chemical components SiO ₂ wt% 93.54 Al ₂ O ₃ wt% 6.28 Na wt% 0.15 Fe wt% 0.03 Ig. Loss wt% 10 SiO ₂ /Al ₂ O ₃ ratio 25 physical properties specific surface area m ² /g 500

The catalytic reaction was carried out in a fixed-bed stainless steel high-pressure microreactor (the inner diameter of the reaction tube was 8mm), and 0.8g of the precursor (30-60 mesh) of 5wt% Co/Beta was weighed and loaded into the reaction tube. The reaction conditions and product analysis were the same as the implementation example 1.

The reactivity of 5 wt% Co/Beta is listed in Table 6. It can be seen from Table 6 that the selectivity of gas products in the products of 5wt% Co/Beta catalyst does not exceed 35%, while the liquid products are mainly diesel oil. The diesel component (C ₁₀ -C ₂₀ ) in the liquid product is about 72wt%, and the product is mixed hydrocarbon, and the normal hydrocarbon is only about 20wt%. It can be seen from Figure 3 that under the reaction conditions of the 5wt% Co/Beta catalyst, the conversion rate of the synthesis gas began to increase with time during the reaction process, reached the maximum after 3 hours and then gradually decreased, and remained almost unchanged after 8 hours.

Table 6 Reaction performance of 5wt% Co/Beta catalyst CO conversion rate (%) 46.9 CH ₄ selectivity (%) 28.1 Selectivity of gaseous hydrocarbons (C ₂ ～C ₄ ) (%) 6.6 Selectivity of liquid light hydrocarbons (C ₅ ～C ₉ ) (%) 24.4 Selectivity of diesel components (C ₁₀ ~C ₂₀ ) (%) 39.1 Selectivity of normal hydrocarbons in diesel components (%) 8.0 Selectivity of wax phase (C ₂₁₊ ) (%) Trace

Example 4: Weigh 4.58 g of Co(NO ₃ ) ₂ ·6H ₂ O and add 300 g of deionized water to dissolve. Weigh 30 g of MOR, add it to the above solution, stir for 2 hours and then place it for 24 hours. The rest of the operation steps are the same as in Example 1 to obtain a 3wt% Co/MOR Fischer-Tropsch synthesis catalyst. The performance evaluation of the catalyst is the same as in Example 1, and the results are listed in Table 7.

Table 7 Reactivity of 3wt% Co/MOR catalyst CO conversion rate (%) 26.0 CH ₄ selectivity (%) 23.0 Selectivity of gaseous hydrocarbons (C ₂ ～C ₄ ) (%) 5.0 Selectivity of liquid light hydrocarbons (C ₅ ～C ₉ ) (%) 12.6 Selectivity of diesel components (C ₁₀ ~C ₂₀ ) (%) 49.1 Selectivity of normal hydrocarbons in diesel components (%) 43.7 Selectivity of wax phase (C ₂₁₊ ) (%) 10.4

Example 5: Weigh 16.5 g of Co(NO ₃ ) ₂ ·6H ₂ O and add 200 g of deionized water to dissolve it. Weigh 30 g of MOR, add it to the above solution, stir for 2 hours and then place it for 24 hours. The rest of the operation steps are the same as in Example 1 to obtain a 10 wt% Co/MOR Fischer-Tropsch synthesis catalyst. The performance evaluation of the catalyst is the same as in Example 1, and the results are listed in Table 8.

Table 8 Reaction performance of 10wt% Co/MOR catalyst CO conversion rate (%) 64.3 CH ₄ selectivity (%) 10.5 Selectivity of gaseous hydrocarbons (C ₂ ～C ₄ ) (%) 3.0 Selectivity of liquid light hydrocarbons (C ₅ ～C ₉ ) (%) 9.8 Selectivity of diesel components (C ₁₀ ~C ₂₀ ) (%) 43.0 Selectivity of normal hydrocarbons in diesel components (%) 37.0 Selectivity of wax phase (C ₂₁₊ ) (%) 30.3

Claims (2)

1. Molecular sieve is the catalyst of the synthetic diesel oil of carrier, it is characterized in that described catalyst is made up of molecular sieve and metallic cobalt, and the chemical composition of catalyst is xCo/[M ¹ ]O·Al ₂ O ₃ ·nSiO ₂ , wherein x is Co The weight percent content in the catalyst, [M ^I ]O Al ₂ O ₃ nSiO ₂ is the chemical expression of the molecular sieve, M ^I is Na, n is the molar ratio of SiO ₂ and Al ₂ O ₃ of the molecular sieve, the catalyst The proportion by weight of each component is 3% to 10% of cobalt, and the balance is molecular sieve, the molar ratio n of _SiO2 and _Al2O3 of the molecular sieve is 5 to 25, and _the molecular sieve is sodium faujasite molecular sieve Y, sodium mordenite molecular sieve MOR or sodium β molecular sieve Beta; The preparation of catalyst is prepared by impregnation method, and its steps are as follows: 1) Weigh the cobalt salt according to the distribution ratio of the catalyst components, add deionized water to prepare a solution with a concentration of 2% to 5% by weight, and the cobalt salt is cobalt nitrate, cobalt acetate or cobalt acetylacetonate; 2) Weigh the molecular sieve according to the distribution ratio of the catalyst components, add it into the prepared cobalt solution, stir it evenly, and place it for 24 hours; 3) Evaporate the above mixed solution to dryness in a water bath at 50-80°C, and then vacuum-dry at 40-100°C for 24 hours; 4) After fully grinding the dried solid, calcining at 300-800°C for 4-10 hours; 5) molding the calcined solid powder, and sieving components of 30 to 60 meshes as catalyst precursors; 6) The catalyst precursor is reduced in a hydrogen atmosphere at 400-500° C. for 12-20 hours to obtain a Fischer-Tropsch synthesis catalyst. 2. molecular sieve as claimed in claim 1 is the catalyst of the synthetic diesel oil of carrier, it is characterized in that the weight percentage content of cobalt is 5% in the described catalyst.

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