CN1927780A - Method for preparing propylene by catalytic cracking olefin with four carbon or above - Google Patents

Abstract

The invention relates to a method for producing propylene by catalytic cracking of olefins with carbon four and above, and mainly solves the problems of poor high-temperature hydrothermal stability of the catalyst and deactivation of the catalyst in dealumination in the prior art. The present invention adopts C4-C8 olefins as raw materials and ZSM-5 molecular sieve with silicon-aluminum molar ratio SiO ₂ /Al ₂ O ₃ of 10-180 as the catalyst active body, and reacts at a reaction temperature of 400-600°C. The technical scheme of cracking reaction to generate propylene under the condition of pressure of 0-0.2 MPa and weight space velocity of 1-10 hours ^-1 solves the above problems well, and can be used in the industrial production of propylene cracking of olefins.

Description

Method for producing propylene by catalytic cracking of olefins with carbon four and above

Technical field

The invention relates to a method for producing propylene by catalytic cracking of olefins with carbon four and above, in particular to a method for producing propylene by catalytic cracking of carbon four to carbon eight olefins.

Background technique

Mixed C4 olefins are by-products of FCC units in ethylene plants and refineries, and can only be used as low value-added products such as liquefied gas fuels. It is economically and technically feasible to further process it into propylene and ethylene and make full use of this considerable amount of precious olefin resources.

The active components of catalysts usually used for olefin cracking are molecular sieves such as hydrogen ZSM-5, ZSM-11 or SAPO-34. A large amount of inert gas as a heat carrier and diluent is extremely beneficial to the performance of this reaction, and the most ideal dilution The agent is water. However, the presence of water in the reaction process is extremely unfavorable to the long-term use of the catalyst. Usually acidic molecular sieve catalysts will undergo severe skeleton dealumination under high-temperature hydrothermal conditions, resulting in a rapid decrease in the acid density of the catalyst, resulting in an irreversible loss of catalyst activity; At the same time as ethylene, side reactions such as olefin superposition chain growth, hydrogen transfer, and aromatization can occur, and even coke can be formed in the pores of the molecular sieve catalyst, covering the active center of the reaction, making the catalyst rapidly deactivated.

Previous technology, such as CN1284109A discloses a kind of technology that is used for the above olefin cracking of carbon four to produce propylene, ethylene, and its used catalyst is a kind of hydrothermally modified ZSM-5 molecular sieve with silicon-aluminum molar ratio greater than 200, its embodiment In 3, the cracking conversion rate of etherified C4 is 54%, the yield of propylene is only 29%, and there is only data for 160 hours of operation.

EPA0109059 discloses a method for cracking olefins with carbon four or more to produce propylene and ethylene, using ZSM-5 or ZSM-11 molecular sieves with a silicon-aluminum molar ratio of less than 360 as a catalyst, and the reaction must be carried out at a high space velocity of 50 hours ^-1 to obtain Higher propylene yield, and its examples show that the reaction is only a few hours, so it cannot meet the industrial application of hundreds of hours.

US6307117 discloses a catalyst whose active component is nearly aprotic acid and silver-containing ZSM-5 molecular sieve. The process requires reaction space velocity (16-39 hours ^-1 ) and high temperature (~600°C). The high temperature makes the energy consumption of the product high, and the high space velocity requires high mechanical strength of the catalyst, otherwise it is easy to pulverize, resulting in an increase in the pressure drop of the bed, and the device cannot be operated for a long time.

A kind of small hole phosphorous aluminum molecular sieve catalyst disclosed in US6049017, such as SAPO-34, its embodiment 2 fixed bed evaluation C4 cracking reaction, the result propylene selectivity is lower, only 25～30%, and produces more methane, activity only Can be stable for 4 hours.

US5981819 discloses a process of reacting below 500°C with a water ratio of about 1.5. The catalyst is only described as a type-selective molecular sieve with a silicon-aluminum molar ratio of 10-200 and a specific surface area of 300-600 m2/ ^g .

The HZSM-5 or phosphorus-modified molecular sieve catalysts disclosed in the above-mentioned documents have defects such as poor high-temperature hydrothermal stability, easy coking and deactivation, and inability to meet long-term operation, although the yield of propylene in the reaction is acceptable. Therefore, it is difficult to realize industrialization .

Contents of Invention

The technical problem to be solved by the present invention is to overcome the problem of poor catalyst stability in previous literatures, and provide a new method for producing propylene by catalytic cracking of olefins with carbon four and above. The method has the advantages of enabling the catalyst to have good hydrothermal stability and long service life while maintaining high reactivity and high yields of propylene and ethylene.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is as follows: a method for producing propylene by catalytic cracking of olefins with carbon four and above, using ZSM molecular sieve as a catalyst, and the reaction temperature of olefins with carbon four and above is 400-600 ℃, the reaction pressure is 0-0.2MPa, and the weight space velocity is 1-10 hours ^-1 , the pyrolysis reaction occurs to generate propylene, and the silicon-aluminum molar ratio SiO ₂ /Al ₂ O ₃ of the ZSM molecular sieve used is 10-180 .

The C4 and above olefin raw materials in the above technical scheme can come from the mixed C4 of the catalytic cracking unit of the refinery or the C4 fraction of the steam cracking unit in the ethylene plant. The preferred range of reaction temperature is 500-550°C, the preferred range of weight space velocity is 1.5-3 hours ^-1 , the preferred range of silicon-aluminum molar ratio SiO ₂ /Al ₂ O ₃ is 20-100, more preferably 30-80; ZSM The preferred solution of type molecular sieve is selected from ZSM-5 molecular sieve or ZSM-11 molecular sieve, and the more preferred solution is selected from ZSM-5 molecular sieve; the preferred solution of catalyst is to use steam at a temperature of 400-800°C for 0.5-100 hours, and the more preferred solution is to use Steam treatment at a temperature of 450-600°C for 2-30 hours.

The catalyst used in the inventive method is prepared according to the following method:

1. The synthesis of ZSM-5 molecular sieve, the synthesis method of ZSM-5 molecular sieve is a commonly used method, that is, tetrapropylammonium bromide is used as template agent, aluminum sulfate is used as aluminum source, and water glass is used as silicon source. The colloid is then transferred to a stainless steel autoclave, and crystallized at 100-200°C for 30-100 hours under appropriate salinity, alkalinity, and hydrothermal conditions to obtain a molecular sieve with a grain size of 0.1-5 microns, and then pass through Roasting demoulding, hydrochloric acid exchange, washing, to obtain HZSM-5 molecular sieve with required silicon-aluminum ratio.

2. Hydrothermal aging treatment. The catalyst is treated with water vapor at 400-800°C for 0.5-100 hours to remove the skeleton aluminum atoms that are easy to fall off and have poor hydrothermal stability, so as to stabilize the activity of the catalyst.

The catalyst used in the method of the present invention can be used for cracking to produce lower olefins (such as C ₂ -C ₃ ), especially suitable for producing propylene. The raw materials used are: C4-C8 branched, linear and cyclic alkenes.

The calculation of conversion rate, selectivity and propylene yield in the present invention is based on the sum of carbon tetraolefins in the raw material, and materials such as alkanes basically do not participate in the reaction.

Water vapor is used as a diluent in the raw material gas to reduce the partial pressure of olefins in the reactant stream and shorten the residence time of olefins on the catalyst, which can reduce hydrogen transfer reactions, propane, oligomerization products and coking, and is beneficial to increase propylene , The selectivity of ethylene. Using water vapor as the diluent gas for the reaction has the advantages of being cheap and easy to separate from gas and organic matter. However, water vapor has an inhibitory effect on this reaction, and different water/olefin ratios can be used to adjust and control the conversion rate of the reaction and the selectivity of propylene to achieve the best product yield.

The cracking reaction is a molecular increase reaction, and it has better propylene and ethylene selectivity at low pressure, while increasing the pressure will increase the contact time and increase the formation of propane and oligomerization products.

The invention improves the stability of the catalyst by adopting the method of controlling and reducing the silicon-aluminum molar ratio of the ZSM molecular sieve. Because the hydrothermal stability of similar ZSM type catalysts is similar, the molecular sieve material with low silicon-alumina ratio contains more active centers with high hydrothermal stability. After artificial dealumination of the catalyst by steam pretreatment with set conditions to remove the active centers with low hydrothermal stability in the molecular sieve, the remaining acid centers have high hydrothermal stability. It is precisely because of ^the above reasons that the low-silicon-aluminum-ratio molecular sieve after steam treatment has better carbon deposition resistance and stability. The rate reaches 41%, the selectivity exceeds 55%, and a good technical effect has been obtained.

Below by embodiment the present invention will be further elaborated.

Detailed ways

[Embodiments 1-3]

Molecular sieve silicon aluminum ratio has a significant impact on the stability of the catalyst. ZSM-5 molecular sieves with three silicon-aluminum ratios of A, B, and C were synthesized according to the ratio and crystallization conditions in Table 1.

Table 1 Molecular sieve Proportion Crystallization conditions SiO ₂ /Al ₂ O ₃ molar ratio A 40SiO ₂ : Al ₂ O ₃ : 30TPABr : 26OH ^-1 : 7600H ₂ O 140℃, 24h 40 B 80SiO ₂ : Al ₂ O ₃ : 30TPABr : 80NaCl : 26OH ^{-1 :} 7600H ₂ O 140℃, 48h 80 C 160SiO ₂ : Al ₂ O ₃ : 30TPABr : 80NaCl : 26OH ^{-1 :} 7600H ₂ O 140℃, 60h 160

5 grams of ZSM-5 molecular sieve A was calcined at 600° C. for 10 hours in an air atmosphere. Then place it in 200 ml of 5% by weight NH ₄ NO ₃ solution, exchange at 85-90° C. for 2 hours, repeat 3 times. After the exchange, the hydrogen-type ZSM-5 molecular sieve was obtained by washing and drying at 120°C, and the catalyst A-1 was obtained. Catalyst B-1 and catalyst C-1 were prepared using molecular sieves B and C in the same manner.

[Embodiments 4-5]

The _C4 feedstock used in the experiments comes from raffinate mixed C4 in ethylene plants. The raw material composition is shown in Table 2.

Table 2 Composition of mixed carbon four in ethylene plant raffinate project Raw material composition (weight%) Isobutane 1.81 n-butane 5.05 Propylene 0.12 Acetylene 0.08 Anti-butene 11.25 Butene-1 32.07 Isobutylene 43.39 Butene 6.20 C ₄ or above 0.04

Get 2 grams of A-1 catalyst, the pre-reaction catalyst is activated at 500°C under a nitrogen atmosphere for 2 hours, then use the raffinate mixed carbon four as raw material, at 500°C, the weight space velocity is 3 hours ^-1 to react, During the reaction process, water is added to the raw material as a diluent gas, and the water/olefin weight ratio is 1.5. Another 2 grams of B-1 catalyst was taken, and before the reaction, it was processed for 24 hours in a water vapor atmosphere at 500° C. and a space velocity of 3.0 hours ⁻¹ to obtain B-2 catalyst. The specific reaction conditions were the same as those of B-1. The results are compared in Table 1. It can be seen from Table 1 that the steam pretreated molecular sieve has higher propylene yield and selectivity.

Table 1 Effect of steam pretreatment on catalyst performance Product distribution (%) selectivity (%) Yield (%) A-1 A-2 A-1 A-2 methane 0.23 0 0.16 0 ethane 0.18 0.19 0.13 0.14 propane 2.77 2.99 1.95 2.21 butane 6.17 5.55 4.35 4.1 Vinyl 12.52 17.09 8.83 12.62 Propylene 53.82 55.59 37.98 41.05 C5 13.74 10.88 9.69 8.04 _C6 + 10.57 7.71 7.46 5.7 Butene conversion (%) 70.56 73.86

[Embodiments 7-9]

Take 2 grams of catalysts A-1, B-1, and C-1 respectively, and treat them for 24 hours at 500°C under a water vapor atmosphere with a space velocity of 3.0 hours ^-1 before the reaction to obtain A-2, B-2 , C-2 catalyst. Before the reaction, the catalyst was activated at 500°C under a nitrogen atmosphere for 2 hours, and then the residual mixed carbon four was used as the raw material, and the reaction was carried out at 500°C and the weight space velocity was 3 hours ^-1 , and water was added to the raw material during the reaction. As diluent, the water/olefin weight ratio was 1.5. The initial butene conversions of A-2, B-2, and C-2 after steam treatment were all greater than 75%. After a reaction time of 500 hours, the performance of the catalysts was compared.

Table 2 Effect of Si-Al ratio on catalyst stability Product distribution (%) selectivity (%) Yield (%) A-2 B-2 C-2 A-2 B-2 C-2 methane 0 0 0 0 0 0 ethane 0.1 0.1 0 0.07 0.06 0 propane 2.78 1.45 0.65 1.94 0.88 0.28 butane 7.1 5.55 3.68 4.95 3.36 1.57 Vinyl 12.46 8.1 4.71 8.69 4.9 2.01 Propylene 55.91 55.36 49.49 39.01 33.49 21.18 C ₅ 14.37 21.68 31.44 10.02 13.12 13.45 _C6 + 7.27 7.76 10.03 5.07 4.69 4.29 P/E value: 4.49 6.83 10.53 Butene conversion (%) 69.75 60.5 42.78

It can be clearly seen from Table 2 that after the same time of reaction, the A-2 catalyst with the lowest silicon-aluminum ratio has the highest conversion rate, while the C-2 catalyst with the highest silicon-aluminum ratio has the lowest butene conversion rate, thus indicating a low Si-alumina catalysts have higher hydrothermal stability than ZSM catalysts. Wherein P is propylene and E is ethylene.

[Example 10-14]

Taking catalyst A-2 as an example, the effect of temperature on catalyst performance was studied. The same reaction conditions as in Examples 7-9 were adopted, except that different reaction temperatures were used. After reacting for 4 hours, the comparative reaction results are shown in Table 3.

Table 3 Effect of temperature on the catalytic performance of A-2 Product distribution (%) selectivity (%) Yield (%) 450°C 500℃ 550°C 600°C 450°C 500℃ 550°C 600°C methane 0.00 0.16 0.56 1.68 0.00 0.12 0.41 1.21 ethane 0.21 0.33 0.69 1.56 0.15 0.24 0.50 1.12 propane 4.18 4.46 4.77 5.20 2.97 3.25 3.48 3.74 butane 8.04 5.10 3.68 1.45 5.71 3.72 2.68 1.04 Vinyl 11.20 18.49 20.84 25.31 7.96 13.48 15.20 18.21 Propylene 48.21 54.48 51.91 49.15 34.26 39.73 37.85 35.36 C ₅ 17.80 9.76 7.87 4.98 12.65 7.12 5.74 3.58 _C6 + 10.36 8.94 9.68 10.68 7.36 6.52 7.06 7.68 Butene conversion (%) 71.06 74.18 72.92 71.94

It can be seen from Table 3 that when the reaction temperature is 500°C, the best butene conversion and propylene yield can be obtained.

[Examples 15-17]

Taking catalyst A-2 as an example, the effect of feed gas space velocity on catalyst performance was studied. The same reaction conditions as in Examples 7-9 were adopted, except that different raw material feeding space velocities were used. After reacting for 4 hours, the comparative reaction results are shown in Table 4.

Table 4 Effect of feed gas space velocity on the performance of A-2 catalyst Product distribution (%) selectivity (%) Yield (%) 1.5 hours ^-1 3 hours ^{- 1} 9 hours ^-1 1.5 hours ^-1 3 hours ^{- 1} 9 hours ^-1 methane 0.00 0.00 0.00 0.00 0.00 0.00 ethane 1.22 0.32 0.12 0.97 0.24 0.08 propane 11.98 4.39 2.43 9.49 3.25 1.62 butane 8.47 5.02 5.83 6.71 3.72 3.88 Vinyl 20.73 18.20 11.21 16.42 13.48 7.46 Propylene 37.97 53.65 57.95 30.07 39.73 38.58 C ₅ 9.31 9.61 15.91 7.37 7.12 10.59 _C6 + 10.30 8.80 6.55 8.16 6.52 4.36 P/E value 1.83 2.95 5.17 Conversion rate(%) 79.19 74.06 66.57

It can be seen from Table 4 that with the increase of feed gas space velocity, the conversion of butene tends to decrease, but the selectivity of propylene shows a tendency to increase.

[Embodiments 18-20]

Taking catalyst A-2 as an example, the effect of the ratio of diluent gas and feed gas on the reaction performance was studied. The same reaction conditions as in Examples 7-9 were adopted, except that the ratio of water vapor and raw material gas was adjusted. After 4 hours of reaction, the comparative reaction results are shown in Table 5, and W/C is the weight ratio of water vapor to feed gas.

Table 5 Effect of water/olefin ratio on the catalytic performance of A-2 Product distribution (%) selectivity (%) Yield (%) W/C: 0.5 W/C: 1.5 W/C: 3.0 W/C: 0.5 W/C: 1.5 W/C: 3.0 methane 0.42 0.16 0.12 0.34 0.12 0.08 ethane 1.23 0.32 0.12 1.00 0.24 0.08 propane 14.81 4.38 2.05 11.99 3.25 1.35 butane 13.89 5.01 4.13 11.25 3.72 2.72 Vinyl 15.83 18.17 11.84 12.82 13.48 7.80 Propylene 29.71 53.56 58.42 24.06 39.73 38.48 C ₅ 12.67 9.60 15.59 10.26 7.12 10.27 _C6 + 11.43 8.79 7.73 9.26 6.52 5.09 P/E value: 1.88 2.95 4.93 Conversion rate(%) 80.98 74.18 65.87

It can be seen from Table 5 that with the increase of the water-to-hydrocarbon ratio, the conversion of butene tends to decrease, but the selectivity of propylene tends to increase.

[Examples 21-23]

Taking A-2 catalyst as an example, the influence of reaction system pressure on catalyst performance was studied. The same reaction conditions as in Examples 7-9 were adopted, except that the pressure of the reaction system was adjusted. After reacting for 4 hours, the comparative reaction results are shown in Table 6.

Table 6 Effect of pressure on the performance of A-2 catalyst Product distribution (%) selectivity (%) Yield (%) 0.MPa 0.1MPa 0.2MPa 0.MPa 0.1MPa 0.2MPa methane 0.33 0.10 0.56 0.25 0.08 0.47 ethane 0.70 1.24 1.45 0.53 1.04 1.21 propane 6.11 15.36 17.73 4.65 12.84 14.83 butane 6.68 17.84 18.66 5.08 14.91 15.61 Vinyl 22.49 15.86 13.21 17.11 13.26 11.05 Propylene 48.25 30.78 27.38 36.70 25.73 22.90 C5 10.12 11.17 11.05 7.70 9.34 9.24 C6+ 5.32 7.64 9.97 4.05 6.39 8.34 Conversion rate(%) 76.07 83.59 83.65

It can be seen from Table 6 that as the system pressure increases, the conversion of butene increases, but the selectivity of propylene decreases significantly.

Claims (7)

1. A method for producing propylene by catalytic cracking of olefins with carbon four and above, using ZSM molecular sieve as a catalyst, raw material olefins with carbon four and above at a reaction temperature of 400-600°C, a reaction pressure of 0-0.2MPa, and an empty weight Cracking reaction to generate propylene under the condition of 1-10 hours ^-1 , characterized in that the silicon-aluminum molar ratio SiO ₂ /Al ₂ O ₃ of the ZSM molecular sieve used is 10-180. 2. The method for producing propylene by catalytic cracking of carbon four and above olefins according to claim 1, characterized in that the raw material of carbon four and above olefins is from the mixed carbon four of the refinery catalytic cracking unit or the carbon of the steam cracking unit in the ethylene plant. Four fractions. 3. The method for producing propylene by catalytic cracking of C4 and above olefins according to claim 1, characterized in that the reaction temperature is 500-550°C, the weight space velocity is 1.5-3 hours ^-1 , and the silicon-aluminum molar ratio SiO ₂ / Al ₂ O ₃ is 20-100, ZSM type molecular sieve is from ZSM-5 molecular sieve or ZSM-11 molecular sieve. 4. The method for producing propylene by catalytic cracking of C4 and above olefins according to claim 3, characterized in that the ZSM molecular sieve is ZSM-5 molecular sieve. 5. The method for producing propylene by catalytic cracking of C4 and above olefins according to claim 3, characterized in that the silicon-aluminum molar ratio SiO ₂ /Al ₂ O ₃ is 30-80. 6. The method for producing propylene by catalytic cracking of C4 and above olefins according to claim 1, characterized in that the catalyst is treated with steam at a temperature of 400-800°C for 0.5-100 hours. 7. The method for producing propylene by catalytic cracking of C4 and above olefins according to claim 6, characterized in that the catalyst is treated with steam at a temperature of 450-600°C for 2-30 hours.