CN102126908B - A method for selective hydrogenation of carbon distillates - Google Patents

Abstract

A method for selective hydrogenation of carbon distillates, in which the carbon distillates from the deethanizer in the ethylene plant are hydrogenated and then entered into a fixed-bed catalytic hydrogenation reactor for selective hydrogenation to remove acetylene and fix The bed catalytic hydrogenation reactor is a multi-stage fixed-bed catalytic hydrogenation reactor, which is characterized in that between the multi-stage fixed-bed catalytic hydrogenation reactors, besides the selective hydrogenation reaction process, the carbon distillate also has a polymerization reaction process. A polymerization catalyst, the polymerization catalyst is preferably a ZSM-5/Al ₂ O ₃ catalyst. Using the method of the invention, after increasing the polymerization reaction, the amount of carbon tetraolefins is greatly reduced, and the degree of pollution of the second-stage or third-stage hydrogenation catalyst is greatly reduced.

Description

A method for selective hydrogenation of carbon distillates

technical field

The invention relates to a method for selective hydrogenation, in particular to a method for selective hydrogenation of carbon distillates to remove acetylene.

Background technique

The production of polymer grade ethylene is the leader in the petrochemical industry. Polymer grade ethylene and propylene are the most basic raw materials for downstream polymerization units. In addition to ensuring that the acetylene content at the outlet of the hydrogenation reactor is up to standard, the catalyst has excellent selectivity and can minimize ethylene. The formation of ethane is of great significance for improving the ethylene yield of the whole process and improving the economic benefits of the device.

The cracked carbon distillate contains acetylene with a mole fraction of 0.5% to 2.5% (v/v). When producing polyethylene, a small amount of acetylene in ethylene will reduce the activity of the polymerization catalyst and deteriorate the physical properties of the polymer. Therefore The acetylene content in ethylene must be reduced to a certain limit before it can be used as a monomer for the synthesis of high polymers. Therefore, the separation and conversion of acetylene is one of the important processes in the flow of ethylene plants. At present, two types of processes are mainly used to remove acetylene from cracked gas in ethylene units, namely extractive distillation and catalytic selective hydrogenation conversion.

Solvent extraction and rectification separation of acetylene is the use of solvents (such as dimethylformamide, N-methylpyrrolidone, acetone, etc.) to extract and separate acetylene, which not only removes acetylene in cracked gas, but also utilizes acetylene as a useful product. This process has good co-production economic benefits, but this process requires strict operation, complex process, and pollutes the environment, so there are few industrial devices using this process. Compared with solvent extraction and rectification, catalytic selective hydrogenation to convert acetylene into ethylene and increase ethylene content is currently the most economical process route and has been widely used at home and abroad.

Catalytic selective hydrogenation in the ethylene plant is divided into pre-hydrogenation and post-hydrogenation according to the position of the acetylene hydrogenation reactor relative to the demethanizer. The hydrogenation reactor is located before the demethanizer. After the methane tower is post-hydrogenation. The advantage of the post-hydrogenation process is that there are many control methods in the hydrogenation process, it is not easy to overheat, and it is easy to operate. The disadvantage is that the catalyst is easy to coke and the regeneration of the catalyst is relatively frequent. The reason is that in the hydrogenation process, due to the small amount of hydrogen added, the hydrogenation dimerization of acetylene is prone to occur, and 1,3-butadiene is generated, and oligomers with a wider molecular weight distribution are further generated, commonly known as "green" Oil". The green oil is adsorbed on the surface of the catalyst, and further forms coke, blocks the pores of the catalyst, and reduces the activity and selectivity of the catalyst.

At present, the post-hydrogenation of carbon dioxide mainly adopts two-stage or three-stage reactors in series to remove alkynes. For devices with low space velocity or low alkyne content, two-stage reactors in series can be used. At present, industrial installations are mainly based on the process of removing alkyne with three-stage reactors connected in series.

The general composition of the post-hydrogenation material is: 1.0-2.5% (v/v) of acetylene, 65-85% (v/v) of ethylene, and the rest is ethane. Hydrogen is added after metering.

The reaction is an exothermic reaction, but the temperature rise is relatively low. According to the space velocity, the maximum temperature rise of a single reactor ranges from 30 to 60°C, so an adiabatic reactor is basically used.

For two-stage hydrogenation reactors, the first-stage hydrogenation reactor is required to convert more than 70% of acetylene, and the second-stage hydrogenation reactor converts the remaining acetylene to a content of less than 5 μl/l.

For devices with high space velocity or high acetylene content, a three-stage hydrogenation reactor process is generally used. The first stage converts about 50% of acetylene, and the remaining two stages convert the remaining acetylene. The content of acetylene at the outlet of the three-stage hydrogenation reactor Less than 5μl/l.

The amount of hydrogen added is related to the content of acetylene and the process used. For the three-stage hydrogenation reactor process, generally the hydrogen/acetylene ratio of the first-stage hydrogenation reactor is 0.8-1.2, the hydrogen/acetylene ratio of the second-stage hydrogenation reactor is 1-1.5, and the hydrogen/acetylene ratio of the third-stage hydrogenation reactor is (v/v) is 1.5-3.

For the two-stage hydrogenation reactor process, the hydrogen/acetylene ratio of the first-stage hydrogenation reactor is generally 1-1.5, and the hydrogen/acetylene ratio of the second-stage hydrogenation reactor is 1.5-4.

Generally speaking, green oil is most likely to be produced in the first stage of the reactor. Part of the green oil will continue to polymerize and eventually coke on the catalyst in the first stage. The coking or enrichment of the reactor will lead to the decline of the catalyst performance of the second-stage hydrogenation reactor. In order to avoid this situation, the industrial device has set up a green oil separation tank after the first-stage hydrogenation reactor. After the exchanger, the green oil is deposited at the bottom of the green oil tank due to the reduction of the material temperature, and the green oil is released intermittently through the bottom of the green oil tank to avoid its pollution to the second-stage hydrogenation reactor.

The inventors have found that this technique is effective for the heavier green oil components, but less effective for the lighter components generated in the reaction, especially the carbon four cuts, and these lighter components enter the second stage of processing. After the hydrogen reactor, it will still have a serious impact on the performance of the catalyst, and even reduce the performance of the catalyst by more than 80%, which will lead to a shortened operation period of the catalyst and a decrease in the purity of the ethylene product.

Contents of the invention

The inventors have proposed a solution to the degradation of catalyst performance in the C2 hydrogenation process, which is especially suitable for sequential separation processes.

A method for selective hydrogenation of carbon distillates, in which the carbon distillates from the deethanizer in the ethylene plant are hydrogenated and then entered into a fixed-bed catalytic hydrogenation reactor for selective hydrogenation to remove acetylene and fix The bed catalytic hydrogenation reactor is a multi-stage fixed-bed catalytic hydrogenation reactor, which is characterized in that between the multi-stage fixed-bed catalytic hydrogenation reactors, besides the selective hydrogenation reaction process, the carbon distillate also has a polymerization reaction process. A polymerization catalyst, the polymerization catalyst is preferably a ZSM-5/Al ₂ O ₃ catalyst.

In the present invention, a polymerization catalyst is used to polymerize the C4-olefins produced by the hydrogenation reaction in the previous stage to generate oligomers with C8 or even higher carbon numbers, so as to better remove the C4 fraction from the material at the outlet of the front-stage reactor Separation to reduce the impact of the C4 fraction on the subsequent hydrogenation reactor.

The ZSM-5/Al ₂ O ₃ catalyst described in the present invention is prepared by conventional methods in the prior art, as shown in CN200510008986, obtained by kneading molecular sieves, alumina, binders with water, molding and roasting. The silicon-aluminum molar ratio of the molecular sieve is preferably 5-200, and the specific surface area is 200-500m ² /g.

ZSM-5 molecular sieve is preferably used in the polymerization catalyst of the present invention, and its usage is preferably 10-90%, more preferably 30-80%.

The preferred Al ₂ O ₃ specific surface area in the polymerization catalyst of the present invention is 50-300 m ² /g, and the amount thereof is preferably 10-90%. More preferably, it is 20 to 70%.

The binder is a general binder in the prior art, such as cellulose, aluminum sol and the like.

The calcining condition of the polymerization catalyst is preferably 400-600° C. for 2-8 hours.

According to the scheme described in the present invention, the carbon distillate from the deethanizer in the ethylene unit enters the fixed-bed catalytic reactor for selective hydrogenation after hydrogenation to remove acetylene, and the fixed-bed catalytic hydrogenation reaction The reactor is preferably a multi-stage hydrogenation reactor, such as a two-stage hydrogenation reactor, a three-stage hydrogenation reactor or more hydrogenation reactors, and a polymerization reactor is used between the hydrogenation reactors or the polymerization catalyst is loaded In the hydrogenation reactor or the first two ways are used at the same time.

The specific scheme described in the present invention can be that there is a polymerization reactor between the first stage hydrogenation reactor and the heat exchanger, if it is the situation of the three-stage hydrogenation reactor process, it can also be the first stage or the second stage Set up a polymerization reactor separately after the hydrogenation reactor or install a polymerization reactor after the first stage hydrogenation reactor and the second stage hydrogenation reactor at the same time, or do not set a polymerization reactor, but fill the polymerization catalyst in the first stage In the first stage or/and the second hydrogenation reactor, the polymerization catalyst is preferably packed at the end of the reaction bed of the hydrogenation reactor.

In the present invention, when the polymerization catalyst is packed in the polymerization reactor behind the hydrogenation reactor, the polymerization reactor is generally located between the hydrogenation reactor and the heat exchanger behind the reactor, so that the C4 fraction reacts at a higher temperature , The reacted mixture is separated through a green oil tank to remove the heavier fractions generated.

The hydrogen-alkyne ratio entering the front-stage hydrogenation reactor should not be too high, a large amount of excess hydrogen can cause the selectivity of the hydrogenation reaction to decrease, and can also accelerate the polymerization reaction. The amount of hydrogen in the polymerization reaction is preferably lower than 0.6% (volume).

Other specific reaction conditions for the selective hydrogenation of carbon distillates are not particularly limited in the present invention, usually: fixed-bed catalytic hydrogenation reactor inlet temperature 20-80°C, reaction pressure 1.5-2.5MPa, gas volume space velocity 2000- 10000h ^-1 , C ₂ H ₂ accounts for 1.0-2.5% in the inlet material of the first stage reactor.

The general conditions of the polymerization reactor or polymerization reaction are: reaction temperature 65°C-130°C, reaction pressure 1.5-2.5MPa, gas volume space velocity 5000-40000h ^-1 , the present invention is not particularly limited, and can be determined according to the polymerization catalyst used Adjust for the difference.

The present inventors found that when adopting the method of the present invention, the olefins of the carbon four cuts undergo polymerization reactions, because the carbon four cuts are more likely to be adsorbed by the ZSM-5 molecular sieve, and the carbon two components are difficult to be adsorbed by the polymerization catalyst. Under certain conditions (>2000/h), the polymerization of the carbon two components can be avoided, and a substance with a larger molecular weight can be generated. Moreover, after the polymerization reaction, the amount of carbon tetraolefins is greatly reduced, and the degree of pollution of the second-stage or third-stage hydrogenation catalyst is greatly reduced.

Description of drawings

Fig. 1 is a kind of C2 post-hydrogenation process flow chart of applying the present invention. Among them: 1——oil washing tower; 2——water washing tower; 3——alkali washing tower; 4——dryer; 5——demethanizer; 6——deethanizer; Hydrogen reactor; 8—polymerization reactor; 9—two-stage hydrogenation reactor; 10—three-stage hydrogenation reactor.

Detailed ways

Catalyst source and main physical properties:

The G-58C catalyst of German Südchem Co., Ltd., the appearance of the catalyst is light gray spherical ball, the particle size is φ2～5mm, the active component is Pd, the bulk density is 0.75±0.01g/ml, the BET specific surface is 35±5m ² /g, and the BET pores Capacity 0.32±0.02cm ³ /g, strength ≥60N/grain.

China Petrochemical Research Institute LY-C ₂ -O2 catalyst, the appearance is a brown-gray ball. The particle size is φ2.5～4mm, the active component is Pd, the bulk density is 0.72±0.01g/ml, the BET specific surface is 50±5m ² /g, the BET pore volume is 0.38±0.02cm ³ /g, and the strength is ≥60N/grain.

Molecular sieve B: ZSM-5, Nankai University Catalyst Factory, silicon-aluminum ratio 90, specific surface area 180m ² /g.

Molecular sieve C: ZSM-5, Qingdao Chuangliheng International Trade Co., Ltd., silicon-aluminum ratio 200, 280m ² /g.

Total selectivity: S=(total ethylene increment at the outlet of each hydrogenation reactor/acetylene content at the hydrogenation reactor inlet)*100% by volume

Example 1

The process flow is shown in Figure 1, the difference is that the two-stage C2 hydrogenation process is adopted, and the reaction conditions are: adiabatic reactor, G-58C hydrogenation catalyst loading capacity 300ml, acetylene content at the inlet of the first stage hydrogenation reactor 2.1% (v/v), space velocity 3000/h, pressure 1.5MPa, first stage hydrogenation reactor outlet temperature 120°C. The polymerization reactor catalyst loading capacity is 100ml, and the polymerization catalyst preparation process is as follows:

1 Synthesis of molecular sieves

Reagents: tetrapropylammonium hydroxide, Alfa Company; ethyl orthosilicate (content 98wt.%, Aldrich Company); triisopropyl aluminum oxide, Aldrich Company.

Dissolve 110g of tetrapropylammonium hydroxide in 900g of deionized water, 59g of triisopropylaluminum oxide, and stir at 0°C for half an hour to obtain a clear solution. Add 218g tetraethyl orthosilicate to the solution, stir at 200°C for 4 hours to completely hydrolyze the tetraethyl orthosilicate, heat at 400°C under vacuum to completely volatilize the generated ethanol, and in the obtained supersaturated solution, in Reflux at 70°C for 100 hours, with a stirring rate of 100rpm, centrifuge the obtained crystals, wash 3 times with deionized water, dry at 120°C overnight, and roast at 550°C for 5 hours to obtain molecular sieve ZSM-5 molecular sieve A, Silicon/aluminum = 32 for molecular sieves.

2 Preparation of polymerization catalyst

Take 180g of molecular sieve A prepared above, 20g of alumina (commercially available, specific surface 180m ² /g), weigh 2g of cellulose, knead with water, extrude into strips, and bake at 450°C for 3 hours. Polymerization catalyst A was obtained.

As shown in accompanying drawing 1, polymerization catalyst A 200mL is filled in the polymerization reactor behind the first stage hydrogenation reactor. The temperature at the inlet of the polymerization reactor is 80°C, the content of acetylene at the inlet is the content of acetylene at the outlet of the first-stage hydrogenation reactor, the pressure is 1.5MPa, and the space velocity is 9000/h.

Comparative Example 1: Except that there is no polymerization reactor, other conditions are the same as in Example 1.

The reaction result of table 1 comparative example 1 and embodiment 1

Example 2

The process flow is shown in Figure 1, using a three-stage C2 hydrogenation process, reaction conditions: three-stage C2 hydrogenation process, adiabatic reactor, hydrogenation catalyst loading 300ml, acetylene content at the inlet of the first stage hydrogenation reactor 1.7 % (molar ratio), pressure 2.0MPa, space velocity 4000/h, first stage hydrogenation reactor outlet temperature 90 ℃. The bottom of the reaction bed of the first-stage hydrogenation reactor is filled with 150 ml of polymerization catalyst. There is also a polymerization reactor with a polymerization catalyst loading capacity of 100ml, which is located after the second-stage hydrogenation reactor and before the third-stage hydrogenation reactor. The polymerization reactor inlet temperature is 100°C, the inlet acetylene content is the outlet acetylene content of the second-stage hydrogenation reactor, the pressure is 2.0 MPa, and the space velocity is 12000/h.

The polymerization catalyst was prepared by the method of this example.

Preparation of polymerization catalyst:

Take 140g of commercially available molecular sieve B, 60g of alumina, weigh 2g of cellulose, knead with water, extrude into strips, and bake at 550°C for 6 hours. Catalyst B is obtained.

Comparative Example 2: Except that there is no additional polymerization reaction section and polymerization reactor, other conditions are the same as in Example 2.

The reaction result of table 2 comparative example 2 and embodiment 2

Example 3

Reaction conditions: Two-stage C2 hydrogenation process, adiabatic reactor, hydrogenation catalyst loading 500ml, acetylene content at the inlet of the first stage hydrogenation reactor 1.8% (molar ratio), space velocity 2000/h, pressure 2.5MPa, the second The outlet temperature of the first-stage hydrogenation reactor is 105°C. Adopt the technological process shown in accompanying drawing 1, difference is not to set up polymerization reactor in addition, but the bottom of the reaction bed of the first stage hydrogenation reactor is loaded with polymerization catalyst, loading capacity 100ml, polymerization catalyst is obtained by present embodiment method of synthesis.

Preparation of polymerization catalyst

Take 100g of commercially available molecular sieve C, silicon-alumina ratio 200, 280m ² /g, 100g alumina (commercially available, specific surface area 180m ² /g), weigh 2g of cellulose, add appropriate amount of water, knead, and extrude into strips, Baking at 600°C for 2 hours. Polymerization catalyst C was obtained.

Polymerization catalyst C 200g is packed at the bottom of the reaction bed of the first stage hydrogenation reactor.

Comparative Example 3: Except that no polymerization catalyst was added to the first-stage hydrogenation reactor, other conditions were the same as in Example 3.

The reaction result of table 3 comparative example 2 and embodiment 2

As can be seen from the above examples and comparative examples, after adopting the method of the present invention, the attenuation rate of the catalyst performance of the second and third stage reactors is greatly reduced, and the removal effect of acetylene and the total selectivity are obviously improved, and the Economic benefits of the hydrogenation process.

Claims (8)

1. A method for selective hydrogenation of carbon distillates, in which the carbon distillates from the deethanizer in the ethylene plant enter a fixed-bed catalytic hydrogenation reactor for selective hydrogenation after hydrogenation to remove acetylene therein , the fixed-bed catalytic hydrogenation reactor is a multi-stage fixed-bed catalytic hydrogenation reactor, which is characterized in that between the multi-stage fixed-bed catalytic hydrogenation reactors, the carbon distillate has a polymerization reaction process in addition to the selective hydrogenation reaction process, A polymerization catalyst is used, and the conditions of the polymerization reaction are: reaction temperature 65°C-130°C, reaction pressure 1.5-2.5MPa, gas volume space velocity 5000-40000h ^-1 ; the polymerization catalyst is a ZSM-5/Al ₂ O ₃ catalyst. 2. The method according to claim 1, characterized in that between the outlet of the first-stage hydrogenation reactor positioned in the multi-stage fixed-bed catalytic hydrogenation reactor to the heat exchanger and/or the outlet of the second-stage hydrogenation reactor A polymerization reactor is arranged between the heat exchanger and a polymerization catalyst is filled in it. 3. method according to claim 1 is characterized in that being positioned at the reaction bed lower part of the first stage hydrogenation reactor and/or the first stage hydrogenation reactor in the multistage fixed-bed catalytic hydrogenation reactor is loaded with polymerization catalyst. 4. The method according to claim 1, characterized in that the inlet temperature of the fixed-bed catalytic hydrogenation reactor is 20-80°C, the reaction pressure is 1.5-2.5MPa, the gas volume space velocity is 2000-10000h ^-1 , and the first-stage reactor C ₂ H ₂ accounts for 1.0-2.5% in the inlet material. 5. The method according to claim 1, characterized in that ZSM-5 molecular sieves account for 10% to 90% of the polymerization catalyst. 6. The method according to claim 1, characterized in that the polymerization catalyst is obtained by kneading, molding, and roasting ZSM-5 molecular sieve, alumina, and binder with water. 7. The method according to claim 6, characterized in that the molar ratio of silicon to aluminum of the molecular sieve is 5-200, and the specific surface area is 200-500 m ² /g. 8. The method according to claim 6, characterized in that the polymerization catalyst is calcined at 400-600° C. for 2-8 hours.

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