CN1292824C - Selective absorption method for reducing propylene in catalytic cracking dry gas - Google Patents

Abstract

A process for absorbing propylene from dry gas produced by a refinery catalytic cracking unit. The method is to remove propylene through an absorption device that selectively absorbs olefins without any purification and refining of catalytic cracking dry gas. The contact mode of dry gas and absorbent is convective. The absorbent includes one or a mixture of benzene, ethylbenzene, diethylbenzene, triethylbenzene, three or more ethylbenzenes (polyethylbenzenes), diesel oil, gasoline, etc. Absorption conditions of absorbent for propylene in dry gas: operating temperature is -10-40°C, pressure is 0.1-3.5MPa, absorbent/dry gas volume ratio (ml/L): 3-25. Absorbent desorption conditions after gas adsorption: temperature 20-300°C, pressure 0.1-3.5MPa, purge gas/absorbent volume ratio: 1-15, purge time 1-10 hours. The purge gas includes one or a mixture of N ₂ , H ₂ , methane, ethane, etc. The desorbed absorbent can be recycled.

Description

A method for selectively absorbing and reducing propylene in catalytic cracking dry gas

technical field

The invention relates to the field of separation and purification of mixed gas, in particular to a method for reducing propylene in catalytic cracking dry gas through selective absorption.

Background technique

In the past ten years, my country's ethylene industry has developed relatively rapidly, and 18 sets of large and medium-sized ethylene production units have been built so far. After 2000, a number of ethylene plants began to be transformed and expanded. By 2005, the national ethylene production capacity will reach 8.4 million tons. There is still a big gap between our country and foreign ethylene industry. Many factors make the cost of ethylene higher than that of foreign countries, thus affecting the development of domestic ethylene. Industry Many oil refineries in my country still use a large amount of catalytic cracking dry gas containing 12% to 25% (volume fraction) of ethylene as gas or burn it with a torch, resulting in waste of resources and pollution of the environment. At present, the scale of catalytic cracking units in my country ranks second in the world, with a dry gas output of 112MtPa to 315MtPa, and a considerable amount of ethylene in the dry gas. If it can be recovered, it can improve the competitiveness of oil refining enterprises and ease the contradiction between supply and demand of domestic ethylene. It is of great significance to extract ethylene from catalytic cracking dry gas.

At present, the technologies for extracting ethylene and separating propylene from mixed gas such as catalytic cracking dry gas mainly include cryogenic separation, absorption separation, hydrate separation, membrane separation and adsorption separation. Among them, hydrate separation method is a new separation method. Membrane separation method and adsorption separation method are in the stage of laboratory research or industrial experiment, while cryogenic separation method and absorption separation method are quite mature, and have achieved industrialization, and achieved great achievements. Good economic benefits. The cryogenic separation method can obtain polymer grade ethylene, but due to the low concentration of ethylene in the dry gas, it is generally suitable for dealing with a large amount of dry gas, especially suitable for areas where refineries are concentrated. If the refinery scale is small, it is not economical.

The absorption separation method mainly uses the different solubility of each component of the catalytic cracking dry gas in the absorbent to separate. The intercooler oil absorption process generally uses oils such as C3, C4 and aromatics as absorbents, first removes methane and hydrogen, and then separates the absorbed components one by one by rectification. The lowest operating temperature is -70°C, generally -20-40°C, the purity of ethylene is about 90%, and the yield is 85% [Wu Ciping, Sun Li. Separation, recovery and comprehensive utilization of refinery dry gas, Modern Chemical Industry, 2001, 21(5): 20-23]. The Mehra process was developed by AET in Houston, USA. The process uses Mehrsolr solvent, and the cracked gas can be separated into hydrogen-rich, methane-rich and ethylene-rich gases on a conventional gas processing device for conventional fractionation downstream. The process can obtain hydrogen and methane fuel gas with a purity of 90%, and the hydrogen can be further purified in a pressure swing adsorption device to reach a purity of 99%. Mehrsol solvents are typically special mixtures of polyalkylene glycol dialkyl ethers, N-methylpyrrolidone, dimethylcresylamine, propylene carbonate, sulfolane and ethylene glycol triacetate. In addition, C ₈ -C ₁₀ aromatic compounds can also be used as solvents in this process. The operating temperature is generally around -37°C, and the pressure is 1.7MPa [1. Mehra Y R. Using Extraction to treat hydrocarbongases, Chem. Eng. 1986, 93(20): 53-55; 2. Savage P., Brooks K. , Refinery gases: a quick source of ethylene, Chem. Week, 1988, 142(19): 16].

In addition to 10-25% ethylene, there is a certain amount of propylene and butene in the catalytic cracking dry gas of the refinery. Fast, in addition to generating ethylbenzene and diethylbenzene, there are also the following side reactions: propylene+benzene=propylbenzene (1); butene+benzene=butylbenzene (2). Reaction (1) and (2) all need to consume benzene, make the benzene consumption rate of process increase, influence ethylbenzene production cost, for this reason, Wang Qingya et al. 4:32] Using modified ZSM-5 zeolite catalyst can convert propylene and butene in catalytic cracking dry gas into hydrocarbons, and 95% of ethylene is retained.

Contents of the invention

The purpose of the present invention is to provide a method for reducing propylene in catalytic cracking dry gas by selective absorption on the basis of the above prior art. When the method provided by the invention is used to produce ethylbenzene by catalytic cracking dry gas, the consumption of benzene can be obviously reduced and the utilization rate of ethylene can be improved.

In order to achieve the above object, the present invention provides a method for absorbing propylene in catalytic cracking dry gas through an absorbent to improve the purity of ethylene in the dry gas, absorbing propylene with an absorbent, and then desorbing the absorbent that has absorbed propylene with a purge gas , The absorbent after desorption with purge gas is recycled. in:

Conditions for absorbent to absorb propylene in dry gas:

The dry gas is introduced from the lower end of the absorption device, and the absorbent is fed from the upper end, and the contact mode between the dry gas and the absorbent in the absorption tower equipped with packing is convective;

The temperature is -10-40°C, the pressure is 0.1-3.5MPa, the absorbent/dry gas volume ratio (ml/L): 3-25;

Absorbents include one or more mixtures of benzene, ethylbenzene, diethylbenzene, triethylbenzene, more than three ethylbenzenes (polyethylbenzenes), diesel oil and gasoline;

The desorption condition of absorbent after adsorbing gas is:

The temperature is 20-300°C, the pressure is 0.1-3.5MPa, the purge gas/absorbent volume ratio is 1-15, and the purge time is 1-10 hours;

The purge gas includes one or a mixture of N ₂ , H ₂ , methane and ethane.

The dry gas is the dry gas produced from the catalytic cracking unit of the refinery, the propylene in the dry gas is more than 50ppm, and the remaining gases are hydrogen, methane, ethane, ethylene, carbon monoxide and carbon dioxide.

When the method of the invention is used to selectively absorb propylene in the catalytic cracking dry gas, the raw material of the catalytic cracking dry gas does not need any purification and refining.

Detailed ways

The present invention will be further described below in conjunction with the examples, but the present invention is not limited in any way.

Example 1-7

Under the conditions that the absorption tower is 110 cm high, the absorption device with an inner diameter of 32 mm is filled with inert Φ3 spherical packing with a height of about 90 cm, the dry gas enters from the bottom, and the absorbent enters from the top, the following results of Examples 1-7 are obtained. It can be seen from the results of the examples that the larger the adsorbent/dry gas volume ratio, the less propylene in the absorbed dry gas, and the higher the adsorption temperature, the more propylene in the absorbed dry gas.

Example 1 Absorption result of benzene at 17°C Adsorbent/Benzene Absorption pressure/0.8MPa Experimental results Absorption rate(%) temperature(℃) Adsorbent flow(ml/h) Dry gas flow(L/h) Volume ratio (ml/L) N2 CH4 CO2 C2= C2 C3＝ C3 C2 C2= C3＝ 17 120 20 6 17.63 39.12 3.47 24.01 15.58 0.19 0.07 12.57 2.70 83.19 17 150 20 7.5 18.14 40.65 3.33 23.10 14.68 0.08 0.02 17.62 6.39 92.92 17 180 20 9 19.04 40.89 3.27 22.61 14.15 0.04 0 20.59 8.37 96.46 Feedstock Composition of Catalytic Cracking Dry Gas 16.32 36.16 3.65 24.68 17.82 1.13 0.22

Example 2 Absorption results of transhydrocarbonated materials (diethylbenzene 30w%, triethylbenzene 30w%, polyethylbenzene 40w%) at 15°C Adsorbent/antihydrocarbon feed Absorption pressure/0.8MPa Experimental results Absorption rate(%) temperature(℃) Adsorbent flow(ml/h) Dry gas flow(L/h) Volume ratio (ml/L) N2 CH4 CO2 C2= C2 C3＝ C3 C2 C2= C3＝ 15 200 20 10 18.89 40.92 3.79 22.64 13.72 0.03 0 20.37 10.27 97.41 15 250 20 12.5 18.97 42.11 3.83 22.11 12.98 0 0 24.67 12.37 100 Feedstock Composition of Catalytic Cracking Dry Gas 15.90 36.43 3.83 25.23 17.23 1.16 0.20

Example 3 Absorption results of ethylbenzene at 17°C Adsorbent/Ethylbenzene Absorption pressure/0.8MPa Experimental results Absorption rate(%) temperature(℃) Adsorbent flow(ml/h) Dry gas flow(L/h) Volume ratio (ml/L) N2 CH4 CO2 C2= C2 C3＝ C3 C2 C2= C3＝ 17 150 20 7.5 18.04 40.06 3.72 23.38 14.63 0.13 0.03 10.25 3.43 88.07 17 200 20 10 18.22 40.21 3.72 23.20 14.59 0.05 0 10.49 4.17 95.41 17 250 20 12.5 18.88 41.42 3.60 22.44 13.64 0.03 0 16.32 7.31 97.25 Feedstock Composition of Catalytic Cracking Dry Gas 19.71 34.92 3.57 24.21 16.30 1.09 0.20

Example 4 The absorption result of diesel oil at 17°C Adsorbent/diesel Absorption pressure/0.8MPa Experimental results Absorption rate(%) temperature(℃) Adsorbent flow(ml/h) Dry gas flow(L/h) Volume ratio (ml/L) N2 CH4 CO2 C2= C2 C3＝ C3 C2 C2= C3＝ 17 150 20 7.5 18.05 40.29 3.67 23.85 14.04 0.10 0 17.19 5.07 91.30 17 200 20 10 18.65 40.89 3.96 23.19 13.28 0.04 0 21.68 7.70 96.52 17 250 20 12.5 21.55 45.14 3.88 21.07 8.34 0.02 0 50.81 16.14 98.26 Feedstock Composition of Catalytic Cracking Dry Gas 15.99 36.71 3.89 25.13 16.96 1.15 0.19

Table 5 Absorption results of ethylbenzene/transhydrocarbon feedstock (weight ratio 1/1) at 10°C Adsorbent/ethylbenzene/transhydrocarbonate=1/1(w/w) Absorption pressure/0.8MPa Experimental results Absorption rate(%) temperature(℃) Adsorbent flow(ml/h) Dry gas flow(L/h) Volume ratio (ml/L) N2 CH4 CO2 C2= C2 C3＝ C3 C2 C2= C3＝ 10 100 20 5 17.43 40.39 3.93 23.78 14.22 0.21 0.04 9.60 5.30 75.58 10 142 19.5 7.3 18.27 40.91 3.93 23.21 13.58 0.10 0 13.67 7.57 88.37 10 190 20 9.5 18.68 42.20 3.89 22.43 12.75 0.04 0 18.94 10.67 95.35 10 230 20.4 11.3 19.08 42.72 3.90 22.01 12.29 0 0 21.87 12.35 100 Feedstock Composition of Catalytic Cracking Dry Gas 16.15 38.11 3.94 25.11 15.73 0.86 0.10

Example 6 Absorption results of ethylbenzene/transhydrocarbonated material (weight ratio 1/1) at 20°C Adsorbent/ethylbenzene/transhydrocarbonate=1/1(w/w) Absorption pressure/0.8MPa Experimental results Absorption rate(%) temperature(℃) Adsorbent flow(ml/h) Dry gas flow(L/h) Volume ratio (ml/L) N2 CH4 CO2 C2= C2 C3＝ C3 C2 C2= C3＝ 20 193 18.9 10.2 18.39 42.32 3.92 22.48 12.83 0.10 0 18.64 10.26 87.95 20 253 18 14.1 19.53 43.48 3.88 21.38 11.72 0.02 0 25.68 14.65 97.59 Feedstock Composition of Catalytic Cracking Dry Gas 15.91 38.26 4.06 25.05 15.77 0.83 0.12

Example 7 Absorption results of ethylbenzene/transhydrocarbonated material (weight ratio 1/1) at 40°C Adsorbent/ethylbenzene/transhydrocarbonate=1/1(w/w) Absorption pressure/0.8Mpa Experimental results Absorption rate(%) temperature(℃) Adsorbent flow(ml/h) Dry gas flow(L/h) Volume ratio (ml/L) N2 CH4 CO2 C2= C2 C3＝ C3 C2 C2= C3＝ 40 155 twenty two 7.1 18.17 40.12 3.98 23.41 13.85 0.39 0.08 10.53 6.13 54.65 40 180 twenty two 8.2 18.70 40.43 3.93 23.06 13.57 0.25 0.05 12.34 7.54 70.93 40 271 21.7 12.6 19.57 41.65 3.85 22.23 12.59 0.11 0 18.67 10.87 87.21 Feedstock Composition of Catalytic Cracking Dry Gas 16.63 37.98 3.96 24.94 15.48 0.86 0.17

Embodiment 8:

Absorbent ethylbenzene/transhydrocarbon feedstock (weight ratio 1/1) absorbs catalytic cracking dry gas under the conditions of 10°C, 0.8MPa, and adsorbent/dry gas volume ratio (ml/L) of 11.3 (results See Example 5), with _N purge gas, at 30°C, 0.1MPa, the purge gas/absorbent volume ratio is 5 for a continuous purge time of 3 hours, the analysis results show that no methane is detected in the absorbent , ethane, ethylene and propylene gases, indicating that almost all the gases adsorbed by the absorbent are desorbed under this condition. After desorption, the absorbent ethylbenzene/anti-hydrocarbonated material (weight ratio 1/1) has been subjected to 10 consecutive adsorption/desorption cycle operations, and the performance is good.

Embodiment 9:

Absorbent ethylbenzene/transhydrocarbon feedstock (weight ratio 1/1) absorbs catalytic cracking dry gas under the conditions of 10°C, 0.8MPa, and adsorbent/dry gas volume ratio (ml/L) of 11.3 (results See Example 5), with _H purge gas, at 150°C, 1.0MPa, purge gas/absorbent volume ratio is 12 for a continuous purge time of 1 hour, the analysis results show that no methane is detected in the absorbent , ethane, ethylene and propylene gases, indicating that almost all the gases adsorbed by the absorbent are desorbed under this condition. After desorption, the absorbent ethylbenzene/anti-hydrocarbonated material (weight ratio 1/1) has been subjected to 10 consecutive adsorption/desorption cycle operations, and the performance is good.

Claims (3)

1. A method for selectively absorbing and reducing propylene in the catalytic cracking dry gas, absorbing the propylene in the dry gas with an absorbent, and then desorbing the absorbent that absorbs propylene with a purge gas; wherein: Conditions for absorbent to absorb propylene in dry gas: The dry gas is introduced from the lower end of the absorption device, and the absorbent is fed from the upper end, and the contact mode between the dry gas and the absorbent in the absorption tower equipped with packing is convective; The temperature is -10-40°C, the pressure is 0.1-3.5MPa, and the absorbent/dry gas volume ratio is 3-25ml/L; Absorbents include one or more mixtures of benzene, ethylbenzene, diethylbenzene, triethylbenzene, more than three ethylbenzenes, diesel oil and gasoline; The desorption condition of the absorbent after absorption is: The temperature is 20-300°C, the pressure is 0.1-3.5MPa, the purge gas/absorbent volume ratio is 1-15, and the purge time is 1-10 hours; The purge gas includes one or a mixture of N ₂ , H ₂ , methane and ethane. 2. The method according to claim 1, characterized in that, more than 50 ppm of propylene in the dry gas, and the rest of the gases are hydrogen, methane, ethane, ethylene, carbon monoxide and carbon dioxide. 3. The method according to claim 1, characterized in that, the absorbent after desorption with purge gas is recycled.