Aromatic alkylation process

Abstract

The invention relates to an aromatic hydrocarbon alkylation method. The method comprises the following steps: sequentially carrying out at least two alkylation reactions on an aromatic hydrocarbon raw material, and separating the obtained material to obtain a first component rich in unreacted aromatic hydrocarbons, a second component rich in intermediate products and a third component rich in products; wherein at least part of the first component and at least part of the second component are circulated back to the alkylation reaction system, and the second component is circulated back to the alkylation reaction system at the downstream of the alkylation reaction system where the first component is circulated back. The method can reduce the total residence time of the aromatic hydrocarbon, prevent the deep alkylation of the aromatic hydrocarbon from generating by-products with heavier components compared with the product, maximally convert the aromatic hydrocarbon into xylene, improve the conversion rate of the aromatic hydrocarbon, reduce the problems of coking and inactivation of the catalyst, prolong the service life of the catalyst, and reduce the production cost. And moreover, the equipment investment for recycling the subsequent aromatic hydrocarbon intermediate product is reduced, and the method has relatively good economic and social benefits and can be applied to industrial production.

Description

Technical Field

[0001] The present invention relates to a method for alkylation of aromatic hydrocarbons. Background Art

[0002] The products in the alkylation reaction process of benzene, toluene, etc. include water, unreacted benzene / toluene, xylene, and heavy aromatic components, among which the yield of xylene is low. At present, through distillation separation technology, the unreacted aromatic raw materials are separated and recycled to the reaction system for continuous reaction to improve the yield of xylene; or through the modification of the catalyst, the yield of xylene in the alkylation product is significantly improved, but there are still problems such as low single-pass conversion rate of aromatic raw materials during the reaction. So far, the research has mainly focused on the improvement of process technology.

[0003] CN104169242A discloses a method for preparing xylene by methylation of aromatic compounds. In this technology, a fixed-bed reactor is used, and no hydrogenation operation is required during the operation. The reaction products are obtained through a separator and distillation operation. The unreacted raw materials, methanol, water, etc. are recycled to the fixed-bed reactor system. In this process scheme, there is no distinction between benzene and toluene in the reaction products, and toluene is recycled together with the aromatic raw materials as the reactor feed.

[0004] CN105732293A discloses a separation device and separation method for the alkylation reaction products of benzene and toluene. The reaction is carried out through a toluene removal tower and a xylene separation tower to separate the materials of benzene, toluene, and xylene. Benzene is recycled to the reaction system as an alkylation raw material for continuous reaction, toluene participates in the reaction of the combined device as a toluene disproportionation raw material, xylene is taken out as a raw material, and the benzene separated from toluene disproportionation is recycled to the alkylation reactor.

[0005] CN102731243A discloses a method for separating the alkylation reaction products of benzene / toluene and methanol. In this design, a single benzene / toluene tower is used to separate the alkylated products. The mixture of benzene / toluene is taken out from the top of the tower, part of which is used for reflux, and part of which is returned to the alkylation reactor to be mixed with the raw materials for continuous reaction. Summary of the Invention

[0006] The inventors have found through research that in the technical solutions for alkylation of aromatic hydrocarbons pointed out in the background art, either the residence time of the recycled materials (intermediate products toluene and benzene) is relatively long, which will cause deep alkylation of aromatic hydrocarbons, reduce the yield of xylene, and cause problems such as carbon deposition deactivation of the catalyst, or there are problems that the process involves more operating units and requires more equipment investment.

[0007] The object of the present invention is to overcome the problems existing in the prior art of aromatic alkylation, such as the excessive selectivity of heavier components than the product, low aromatic conversion rate, easy deactivation of the catalyst, and complex process, and to provide a method for aromatic alkylation, which has a lower selectivity of heavier components than the product and a higher aromatic conversion rate.

[0008] To achieve the above object, the present invention provides a method for aromatic alkylation, which includes: separating the materials after the aromatic raw material undergoes at least two alkylation reactions in sequence to obtain a first component rich in unreacted aromatics, a second component rich in intermediate products, and a third component rich in products;

[0009] Wherein, at least a part of the first component and the second component are each recycled back to the alkylation reaction system, and the second component is recycled back to the alkylation reaction system downstream of the alkylation reaction system to which the first component is recycled.

[0010] By the above technical solution, the present invention has the following advantages:

[0011] The present invention conducts multiple reactions in stages, which can effectively increase the feed ratio of aromatics (such as toluene) and alkylating reagents, effectively reduce the alcohol concentration in the material, prevent its self-reaction to generate light olefins, and secondly effectively reduce the adiabatic temperature rise of a single-stage reactor; in addition, recycling the aromatic reaction raw materials and reaction intermediate products to different reaction stages, wherein the reaction intermediate products (such as toluene) are recycled to the middle and later parts of the reaction, can reduce the total residence time of aromatics, prevent the deep alkylation of aromatics to generate heavier by-products than the product, and can maximize the conversion of aromatics such as toluene into xylene, improve the aromatic conversion rate, and at the same time can reduce the occurrence of problems such as coking and deactivation of the catalyst, improve the service life of the catalyst, and reduce the equipment investment for the subsequent reuse of aromatic intermediate products, having good economic and social benefits and can be applied to industrial production. Description of the Drawings

[0012] Figure 1 is a process flow diagram of the method process device according to a preferred embodiment of the present invention.

[0013] Description of the Reference Numerals

[0014] Figure 1 is a process diagram for aromatic alkylation of the present invention:

[0015] E-101 is a heat exchanger, R-101 / 102 are alkylation reactors, T-101 is a distillation column, and V-101 is an oil-water-gas separator;

[0016] 1 is the aromatic hydrocarbon raw material, 2 and 11 are the alkylating agents, 3 is the feed to the alkylation reactor R-101, 4 is the effluent from the alkylation reactor R-101, 5 is the outlet material of the alkylation reactor R-102, 6 is the material after heat exchange, 7 is the oil phase, 8 is the overhead product of the distillation column, 9 is the side stream of the distillation column, 10 is the product, 12 is the aqueous phase, and 13 is the non-condensable gas. Detailed implementation manners

[0017] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0018] The present invention provides a method for aromatic hydrocarbon alkylation, which includes: separating the material after the aromatic hydrocarbon raw material undergoes at least two alkylation reactions in sequence to obtain a first component rich in unreacted aromatic hydrocarbons, a second component rich in intermediate products, and a third component rich in products; wherein, at least part of each of the first component and the second component is recycled back to the alkylation reaction system, and the second component is recycled back to the alkylation reaction system downstream of the alkylation reaction system to which the first component is recycled.

[0019] The present invention conducts multiple reactions in stages, which can effectively increase the feed ratio of aromatic hydrocarbons (such as toluene) and alkylating agents, effectively reduce the alcohol concentration in the material, prevent its self-reaction to generate light olefins, and secondly effectively reduce the adiabatic temperature rise of a single-stage reactor; in addition, recycling the aromatic hydrocarbon reaction raw materials and reaction intermediate products to different reaction stages, wherein the reaction intermediate products (such as toluene) are recycled to the middle and later part of the reaction, can reduce the total residence time of aromatic hydrocarbons, prevent the deep alkylation of aromatic hydrocarbons to generate by-products with a higher molecular weight than the product, enable the maximum conversion of aromatic hydrocarbons into xylene, improve the conversion rate of aromatic hydrocarbons, and at the same time can reduce the problems such as coking deactivation of the catalyst, improve the service life of the catalyst, and reduce the equipment investment for the subsequent reuse of aromatic hydrocarbon intermediate products, having good economic and social benefits, and can be applied to industrial production.

[0020] According to a preferred embodiment of the present invention, at least 50 wt%, preferably at least 80 wt%, more preferably at least 95 wt%, and most preferably all of the first component and the second component are recycled back to the alkylation reaction system.

[0021] According to a preferred embodiment of the present invention, the method is carried out under non-hydrogen and / or non-inert gas and / or non-water conditions.

[0022] According to a preferred embodiment of the present invention, the alkylation reaction is carried out 2-8 times, preferably 2-6 times. By adopting the foregoing preferred scheme, the autocatalytic reaction of methanol to produce light olefins can be further prevented, the selectivity of heavy components can be further reduced, and the conversion rate of aromatics can be increased.

[0023] According to a preferred embodiment of the present invention, the temperature of each alkylation reaction increases along the material flow direction, and the temperature difference between adjacent alkylation reactions is 5-15 °C. By adopting the foregoing preferred scheme, the autocatalytic reaction of methanol to produce light olefins can be further prevented, the selectivity of heavy components can be further reduced, and the conversion rate of aromatics can be increased.

[0024] According to a preferred embodiment of the present invention, the alkylation reagent for the alkylation reaction is fed in segments, preferably evenly divided and then fed in segments, so that the conditions of the first alkylation reaction independently include: the molar ratio of the aromatic raw material to the alkylation reagent based on aromatics is 1:1-12:1, preferably 4:1-10:1. By adopting the foregoing preferred scheme, the selectivity of heavy components can be further reduced, and the conversion rate of aromatics can be increased.

[0025] According to a preferred embodiment of the present invention, the conditions of each alkylation reaction independently include: the reaction temperature is 360-500 °C; and / or the reaction pressure is 0.1-1.0 MPa.

[0026] According to a preferred embodiment of the present invention, the separation method is rectification treatment, and the conditions of the rectification treatment include: the temperature for the third component to be withdrawn from the bottom of the tower is 140-240 °C; and / or the temperature for the first component to be withdrawn from the top of the tower is 70-140 °C; and / or the temperature for the second component to be withdrawn from the side line is 100-180 °C.

[0027] According to a preferred embodiment of the present invention, the rectification treatment is carried out under atmospheric pressure and a single rectification tower is used.

[0028] According to a preferred embodiment of the present invention, the catalyst for the alkylation reaction is a modified molecular sieve with a ten-membered ring pore structure. By adopting the foregoing preferred scheme, the selectivity of heavy components can be further reduced, and the conversion rate of aromatics can be increased.

[0029] According to a preferred embodiment of the present invention, the elements for modification include at least one of P, Mg, B, Ca, Al, Zn, and La, preferably including P and La, and more preferably the mass ratio of P to La is 0.5-0.8∶1.6-3.0. By adopting the foregoing preferred scheme, the selectivity of heavy components can be further reduced, and the conversion rate of aromatics can be increased.

[0030] According to a preferred embodiment of the present invention, the molecular sieve is selected from at least one of ZSM-5, MCM-56, MCM-22, and ZSM-11.

[0031] According to a preferred embodiment of the present invention, the method further includes heat-exchanging the material after at least two consecutive alkylation reactions with an aromatic hydrocarbon-containing raw material and then performing oil-water-gas separation, and sending the oil phase for rectification treatment.

[0032] According to a preferred embodiment of the present invention, the alkylation reaction is carried out in at least one of a fixed-bed reactor, a moving bed, and a fluidized bed.

[0033] According to a preferred embodiment of the present invention, the alkylation reagent used in the alkylation reaction is selected from at least one of methanol and / or ethanol.

[0034] According to a preferred embodiment of the present invention, the aromatic hydrocarbon is selected from at least one of benzene, toluene, biphenyl, and naphthalene.

[0035] As Figure 1 , the present invention provides a device of a preferred embodiment by taking the setting of two-stage alkylation reaction as an example. The device includes: an alkylation reactor R101, an alkylation reactor R102, an oil-water-gas separator V-101, and a rectification tower T-101 connected in series in sequence; the top discharge port of the rectification tower T-101 is communicated with the feed port of the alkylation reactor R102, the side-line discharge port of the rectification tower T-101 is communicated with the feed port of the alkylation reactor R102, the top discharge port of the rectification tower T-101 is communicated with the feed port of the alkylation reactor R101, and the oil-phase discharge port of the oil-water-gas separator V-101 is communicated with the feed port of the rectification tower T-101; the device is further provided with a heat exchanger E-101 for heat-exchanging the discharge of the alkylation reactor R102 with the feed of the alkylation reactor R101.

[0036] The aromatic hydrocarbon alkylation reaction is carried out in the device, and the process includes:

[0037] An aromatic hydrocarbon raw material 1 is mixed with a part of an alkylation reagent 2 to obtain a mixed material. The mixed material is heat-exchanged through the heat exchanger E-101 to obtain an alkylation reactor R-101 feed 3, which enters the alkylation reactor R101. The discharge 4 of the alkylation reactor R-101 is mixed with another part of the alkylation reagent 11 and then enters the alkylation reactor R102 to obtain an alkylation reactor R-102 outlet material 5. The alkylation reactor R-102 outlet material 5 is heat-exchanged with the mixed material in the heat exchanger E-101. The heat-exchanged material 6 obtained enters the oil-water-gas separator V-101. The bottom water phase 12 is drawn out, the upper non-condensable gas 13 is discharged, and the middle oil phase 7 is drawn out and enters the rectification tower T-101. The top discharge 8 of the rectification tower rich in unreacted aromatic hydrocarbons is recycled to the alkylation reactor R101, the side-line discharge 9 of the rectification tower rich in intermediate products is recycled to the alkylation reactor R102, and the product 10 is drawn out from the bottom of the rectification tower.

[0038] The present invention will be described in detail below through examples. In the following examples, the vent tail gas was analyzed by sampling, and the reaction conversion rate and product yield parameters were measured by chromatographic analysis methods; the raw materials were all commercially available products.

[0039] Comparative Example 1

[0040] Four alkylation fixed-bed reactors were set up, filled with 0.5 wt% P-2 wt% La-ZSM-5 catalyst. The benzene feed rate was 1000 kmol / h, and the methanol feed rate was 1000 kmol / h. Benzene was fed into the first reactor in one go, and methanol was fed in four sections, with a single-section feed rate of 250 kmol / h. The reaction temperature in the first reactor was 450 °C, and the temperature of each subsequent reactor was 10 °C higher than that of the previous reactor. The reaction pressure was 0.5 MPaG. After the reaction, the benzene conversion rate was 40%. The reacted material was heat-exchanged with the raw materials and then entered the oil-water separator. The oil phase was taken from the middle and entered the distillation system. The operation was under slightly positive pressure. The top operation temperature was 100 °C, and the top material was taken out as a mixture of benzene and toluene, and all the top materials were recycled to the first reactor and mixed with the raw materials; the bottom operation temperature was 200 °C, and the total content of heavy components in the product after distillation was about 16 wt%.

[0041] Example 1

[0042] The operating conditions of this example were the same as those of Comparative Example 1, except that the reacted material entered the distillation system. When the distillation system was refined, the top operation temperature was controlled at 80 °C, the bottom operation temperature was 220 °C, and a material discharge port with an operation temperature of 120 °C was set on the side line. After the reaction, the benzene conversion rate was comparable. All the benzene taken out from the top was recycled to the first reactor for mixed feeding, and all the toluene taken out from the middle entered the third reactor and was mixed with the feed. The total content of heavy components in the product after distillation was not higher than 12 wt%, and the content of xylene in the reaction product increased by 25%. The catalyst could operate stably for 1000 h, with a longer operation time than that of Comparative Example 1.

[0043] Example 2

[0044] The operating conditions of this example were the same as those of Example 1, except that 2 reactors were selected for the reaction system, methanol was fed in two sections, with a single-section feed rate of 500 kmol / h. The reaction temperature in the first reactor was 360 °C, and the temperature of each subsequent reactor was 15 °C higher than that of the previous reactor. After the reaction material entered the distillation system, all the benzene taken out from the top was recycled to the first reactor for mixed feeding, and all the toluene taken out from the middle entered the second reactor and was mixed with the feed. Analysis of the reaction system showed that the benzene conversion rate was comparable. The methanol concentration in the feed was high, the single-pass conversion rate of the reaction was relatively high, the reaction temperature rise could reach 60 - 80 °C, and the content of xylene in the reaction product was 5% lower, and the total content of heavy components was not higher than 13 wt%.

[0045] Example 3

[0046] The operating conditions of this example are the same as those of Example 1. The difference is that 8 reactors are selected for the reaction system, methanol is fed in 8 segments, the single-segment feed rate is 125 kg / h, the reaction temperature of the first reactor is 420 °C, and the temperature of each subsequent reactor is 5 °C higher than that of the previous reactor. After the reaction materials enter the distillation system, 95 wt% of benzene taken from the top is recycled to the first reactor for mixed feeding, and 95 wt% of toluene taken from the middle is fed into the 3rd reactor for mixing with the feed. After this reaction, the conversion rate of benzene is comparable, the xylene in the reaction product is reduced by 10%, and the total content of heavy components is not higher than 15 wt%.

[0047] Example 4

[0048] The operating conditions of this example are the same as those of Example 1. The difference is that an unmodified ZSM-5 molecular sieve is used as the alkylation catalyst. After the same reaction conditions, the conversion rate of benzene is about 20 wt%, the xylene in the reaction product is comparable, and the total content of heavy components is not higher than 15 wt%.

[0049] Example 5

[0050] The operating conditions of this example are the same as those of Example 1. The difference is that 2.5 wt% Mg-ZSM-5 is used as the alkylation catalyst. After the same reaction conditions, the conversion rate of benzene is about 32 wt%, the xylene in the reaction product is comparable, and the total content of heavy components is not higher than 15 wt%.

[0051] Example 6

[0052] The operating conditions of this example are the same as those of Example 1. The difference is that the temperatures of the four alkylation reactors are the same, which is 450 °C. The conversion rate of benzene is about 35 wt%, the xylene in the reaction product is reduced by 15%, and the total content of heavy components is not higher than 15 wt%.

[0053] Example 7

[0054] The operating conditions of this example are the same as those of Example 1. The difference is that 50 wt% of benzene taken from the top is recycled to the first reactor for mixed feeding, and 50 wt% of toluene taken from the middle is fed into the 3rd reactor for mixing with the feed. The conversion rate of benzene is about 36 wt%, the xylene in the reaction product is comparable, and the total content of heavy components is not higher than 15 wt%.

[0055] Comparative Example 2

[0056] The operating conditions of this embodiment are the same as those of Embodiment 1, except that only one reactor is provided. Since the reaction temperature rise is relatively high during a single pass, it is necessary to add hydrogen and water as heat-carrying components. The molar ratio of benzene: alcohol: hydrogen: water is 1:1:4:4. The reaction temperature rise is about 10 °C, the benzene conversion rate is 32%, the xylene content in the product increases by about 26%, and the total content of heavy components is 12 wt%. The addition of hydrogen can dilute the concentration of methanol and reduce the self-reaction of methanol. However, the equipment material needs to be changed under the hydrogen-containing condition, and the operation of hydrogen recycling requires an additional compressor unit. The addition of water requires an increase in the size of the oil-water separator, the reactor size, etc. Undoubtedly, this increases the equipment investment and is not conducive to industrial application.

[0057] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for alkylation of aromatic hydrocarbons, characterized in that, the method comprises: separating the material after the aromatic hydrocarbon raw material undergoes at least two alkylation reactions in sequence to obtain a first component rich in unreacted aromatic hydrocarbons, a second component rich in intermediate products, and a third component rich in products; wherein, at least a part of each of the first component and the second component is recycled back to the alkylation reaction system, and the second component is recycled back to the alkylation reaction system downstream of the alkylation reaction system to which the first component is recycled.

2. The method according to claim 1, wherein, at least 50 wt%, preferably at least 80 wt%, more preferably at least 95 wt% of each of the first component and the second component is recycled back to the alkylation reaction system; and / or the method is carried out under non-hydrogen and / or non-inert gas and / or non-water conditions.

3. The method according to claim 1 or 2, wherein, the alkylation reaction is carried out 2 - 8 times, preferably 2 - 6 times; preferably, the temperature of each alkylation reaction increases along the material flow direction, and the temperature difference between adjacent alkylation reactions is 5 - 15 °C.

4. The method according to any one of claims 1 - 3, wherein, the alkylation reaction uses the alkylating agent for segmented feeding, so that the conditions of the first alkylation reaction include: the molar ratio of the aromatic hydrocarbon raw material to the alkylating agent based on aromatic hydrocarbons is 1:1 - 12:1, preferably 4:1 - 10:

1.

5. The method according to any one of claims 1 - 4, wherein, the conditions of each alkylation reaction independently include: the reaction temperature is 360 - 500 °C; and / or the reaction pressure is 0.1 - 1.0 MPa.

6. The method according to any one of claims 1 - 5, wherein, the separation method is rectification treatment, and the conditions of the rectification treatment include: the temperature for withdrawing the third component at the bottom of the column is 140 - 240 °C; and / or the temperature for withdrawing the first component at the top of the column is 70 - 140 °C; and / or the temperature for withdrawing the second component from the side line is 100 - 180 °C.

7. The method according to any one of claims 1 - 6, wherein, the catalyst for the alkylation reaction is a modified molecular sieve with a ten - membered ring pore structure, preferably, the modifying elements include at least one of P, Mg, B, Ca, Al, Zn, La, preferably include P and La, and more preferably the mass ratio of P and La is 0.5 - 0.8∶1.6 - 3.0; and / or the molecular sieve is selected from at least one of ZSM - 5, MCM - 56, MCM - 22, ZSM - 11.

8. The method according to any one of claims 1 - 7, wherein, the method further comprises heat - exchanging the material after the aromatic hydrocarbon raw material undergoes at least two alkylation reactions in sequence with the aromatic hydrocarbon raw material and then carrying out oil - water - gas separation, and sending the oil phase for rectification treatment.

9. The method according to any one of claims 1 - 8, wherein, the alkylation reaction is carried out in at least one of a fixed - bed reactor, a fluidized bed, and a moving bed.

10. The method according to any one of claims 1 - 9, wherein, the alkylating agent used in the alkylation reaction is selected from methanol and / or ethanol; and / or The aromatic hydrocarbon is selected from at least one of benzene, toluene, biphenyl and naphthalene.

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