CN106854135B - Method for preparing p-xylene by alkylating benzene and methanol - Google Patents
Method for preparing p-xylene by alkylating benzene and methanol Download PDFInfo
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- C07C2/86—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by condensation between a hydrocarbon and a non-hydrocarbon
- C07C2/862—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by condensation between a hydrocarbon and a non-hydrocarbon the non-hydrocarbon contains only oxygen as hetero-atoms
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- C07C6/08—Preparation of hydrocarbons from hydrocarbons containing a different number of carbon atoms by redistribution reactions by conversion at a saturated carbon-to-carbon bond
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- C07C6/126—Preparation of hydrocarbons from hydrocarbons containing a different number of carbon atoms by redistribution reactions by conversion at a saturated carbon-to-carbon bond of exclusively hydrocarbons containing a six-membered aromatic ring of more than one hydrocarbon
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Abstract
The invention discloses a method for preparing p-xylene by alkylating benzene and methanol on a fixed bed radial reactor with a multi-channel structure, which mainly solves the problems that in the prior art, a unit catalyst has small raw material processing amount in unit time, the catalyst is not fully utilized, the separation energy consumption is high, the production efficiency of the reactor is low and the like. The invention adopts a fixed bed radial reactor, and the separation process of separation and condensation is adopted, which is beneficial to reducing energy consumption; the process of generating water by adopting the reflux part reaction is beneficial to the heat transfer of the catalyst bed layer and the function of inhibiting the carbon deposition of the catalyst.
Description
Technical Field
The invention belongs to the technical field of chemical reaction engineering, and particularly relates to a method for preparing paraxylene by alkylating benzene and methanol on a fixed bed radial reactor.
Background
Benzene is a chemical product with wide application, mainly comes from catalytic reforming, coal tar and ethylene processes, and with the vigorous development of the oil refining industry and the coal tar industry, the benzene capacity in the market is excessive, and the development of a more valuable utilization way of benzene becomes imperative. In recent years, the methanol production capacity in the domestic market is greatly surplus, and the methanol becomes a relatively cheap chemical raw material. Therefore, the mixed xylene produced by alkylating benzene and methanol can be used as a raw material for increasing the yield of p-xylene in an aromatic hydrocarbon combination plant, and has strong social and economic benefits.
The benzene and methanol alkylation reaction refers to a process of adding one or two methyl groups on a benzene ring to generate toluene and xylene by using methanol as an alkylating agent. The reaction follows a carbonium ion reaction mechanism, methanol is firstly activated in a molecular sieve catalyst acid center to form methyl carbonium ions, and then electrophilic substitution reaction is carried out on the methyl carbonium ions and benzene rings to generate toluene, electrophilic substitution reaction is carried out on the methyl carbonium ions and the toluene to generate xylene, a small amount of ethylbenzene and carbon nonaromatic hydrocarbon are generated, and waste water is generated as a byproduct. Due to the presence of methanol, side reactions during alkylation are mainly due to etherification, carbonylation, etc. of methanol.
The alkylation reaction process of benzene or toluene and methanol adopts fixed bed axial reactor process. US4377718 and US4761513 disclose a fixed bed process for the alkylation of toluene, in which the alkylating agent is added in portions at different locations between the fixed beds in order to increase the yield. Using these fixed bed processes during production, the catalyst can be packed separately in distinct and discrete zones. During the reaction, the reaction product from one zone is mixed with additional alkylating reagent and then enters the next zone for alkylation. However, the reaction products from the previous zone inevitably pass through the high temperature catalyst bed again using this process, exacerbating the potential for catalyst fouling and reducing the catalyst treatment efficiency.
Patent CN1326430A discloses a fluidized bed aromatic alkylation process in which an aromatic hydrocarbon is introduced at a first location in a fluidized bed reaction zone and an alkylating agent is introduced into the fluidized bed reaction zone at one or more locations downstream of the first location, which process results in high toluene conversion and high methyl utilization. But the fluidized bed process increases the abrasion of the catalyst and the energy consumption, and has higher requirements on the preparation of the catalyst.
Patent CN102372588A discloses a moving bed method for preparing paraxylene by alkylation of aromatic hydrocarbons, which adopts a moving bed reactor to carry out alkylation reaction, wherein the catalyst to be regenerated coming out from the bottom of the moving bed enters a catalyst regenerator, and the regenerated catalyst returns to the moving bed reactor for recycling. The method requires large investment in design and construction of part of the reactor, and is not easy to run stably in the production operation process.
The fixed bed radial reactor has short process fluid flowing distance, large flow passage sectional area and small fluid pressure drop, is an effective method for solving the problem of insufficient catalyst treatment capacity, and is not applied to the field of preparing mixed aromatic hydrocarbon by alkylating benzene and methanol at present.
The invention relates to a method for preparing mixed aromatic hydrocarbon by alkylating benzene or toluene and methanol on a radial reactor of a fixed bed, which adopts a unique process that reaction products directly enter a rectifying tower after heat exchange in a separation part to separate tail gas, benzene and reaction water tower top components and mixed aromatic hydrocarbon tower kettle components rich in toluene, xylene and the like, and benzene and part of reaction water are obtained after separation and are circulated back to a reaction system.
Disclosure of Invention
The invention discloses a method for preparing p-xylene by alkylating benzene and methanol on a fixed bed radial reactor with a multi-channel structure, which mainly solves the problems that in the prior art, a unit catalyst has small raw material processing amount in unit time, the catalyst is not fully utilized, the separation energy consumption is high, the production efficiency of the reactor is low and the like. Compared with a fixed bed axial reactor, the fixed bed axial reactor is adopted, the distance of a reactant flow channel is shortened, the flow cross section is increased, the xylene yield of the catalyst in unit time is improved on the premise that the loading amount of the catalyst is the same and the conversion rate of alkylation reaction and the selectivity of products are ensured, the axial temperature distribution of the reactor is uniform, and the inactivation period of the catalyst is ensured to be consistent; the method adopts a separation process of separation and condensation, which is beneficial to reducing energy consumption; the method adopts the process of producing water by the reflux part reaction, which is beneficial to the heat transfer of the catalyst bed layer and the function of inhibiting the carbon deposition of the catalyst.
The invention aims to solve the problems of lower catalyst unit time yield, difficult temperature control of hot spots of a catalyst bed layer, low utilization rate in an activity period and the like in the conventional benzene and methanol alkylation fixed bed axial reactor technology, and provides a novel fixed bed radial reactor method for preparing mixed aromatic hydrocarbon by alkylation of benzene and methanol.
The invention provides a method for preparing paraxylene by alkylating benzene and methanol, which comprises the following steps:
a) vaporizing the benzene feed to obtain gas phase benzene;
b) vaporizing the methanol feed to obtain an alkylating agent vapor phase methanol;
c) combining the gas-phase benzene, the gas-phase methanol and a carrier gas to obtain a reaction mixture;
d) the reaction mixture and a reaction product exchange heat through a heat exchanger, the reaction mixture is preheated to the reaction temperature and then introduced into a central pipe of a fixed bed radial reactor, gas-phase radial flow distribution is realized through the central pipe and enters a catalyst bed layer to carry out alkylation reaction, the reaction product forms a reaction product after heat exchange, the reaction product after heat exchange is fractionated through a rectifying tower to obtain a mixture of tower top tail gas, unreacted benzene and reaction generated water, and an oil phase reaction effluent rich in toluene and xylene is obtained at a tower kettle;
e) condensing a mixture of the tail gas at the top of the tower, unreacted benzene and reaction generated water by a condenser and then dividing the mixture into a gas phase and a liquid phase, wherein 70-99% of the volume of the gas phase reaction effluent is refluxed and combined with hydrogen carrier gas, the rest part of the gas phase reaction effluent is discharged as tail gas, the liquid phase effluent comprises unreacted benzene and reaction generated water, all the unreacted benzene and part of the reaction generated water are combined with the gas phase benzene in the step a) and enter a fixed bed radial reactor to carry out alkylation reaction to generate xylene, and the other part of the reaction generated water is discharged;
f) separating oil phase reaction effluent rich in toluene and xylene obtained at the bottom of the tower by a toluene tower; the distillate at the top of the toluene tower is toluene, the distillate at the bottom of the toluene tower is mixed xylene fraction and carbon nonaromatic hydrocarbon fraction, and then the distillate at the bottom of the toluene tower enters a xylene tower;
the distillate at the top of the xylene column is mixed xylene, the mixed xylene enters an adsorption separation unit to obtain p-xylene and o-xylene and m-xylene, the o-xylene and the m-xylene enter an isomerization unit to produce p-xylene, and the distillate at the bottom of the xylene column is carbon nonaarene;
g) toluene as the top distillate of the toluene tower and carbon nonaromatic hydrocarbon as the bottom distillate of the xylene tower enter a disproportionation unit to produce xylene.
The method for preparing p-xylene by alkylating benzene and methanol, disclosed by the invention, is characterized in that the molar ratio of benzene in the step a) to methanol in the step b) is preferably 8: 1-0.1: 1.
The method for preparing the p-xylene by alkylating benzene and methanol, disclosed by the invention, comprises the step of combining all unreacted benzene and part of water generated by reaction in the step e) with the gas-phase benzene in the step a) and then feeding the combined gas-phase benzene into a fixed bed radial reactor to carry out alkylation reaction to produce the xylene, wherein the mass fraction of the part of water generated by reaction accounts for preferably 10-100%.
The method for preparing p-xylene by alkylating benzene and methanol, disclosed by the invention, is characterized in that the molar ratio of benzene in the step a) to methanol in the step b) is preferably 4: 1-0.5: 1.
The method for preparing p-xylene by alkylating benzene and methanol according to the invention is characterized in that, the alkylation reaction conditions in step d) are as follows: the reaction temperature is 350-550 ℃, the reaction pressure is 0.1-5.0 MPa, the molar ratio of hydrogen to benzene in the step a) is 1-10, and the weight space velocity of benzene in the step a) is 0.1-10.0 h-1。
In the method for preparing p-xylene by alkylating benzene and methanol, the carrier gas is preferably nitrogen, hydrogen or other inert gases.
The invention discloses a method for preparing paraxylene by alkylating benzene and methanol on a fixed bed radial reactor with a multi-channel structure. Compared with the alkylation of benzene and methanol in an axial reactor of a fixed bed, the method shortens the distance of a reactant flow channel, increases the flow cross section, slows down the carbon deposition speed of the catalyst by refluxing part of reaction water, improves the yield of the xylene in unit time of the catalyst on the premise of ensuring the conversion rate of alkylation reaction and the selectivity of products due to the same loading amount of the catalyst, has uniform axial temperature distribution of the reactor, and improves the one-way service life of the catalyst.
Drawings
FIG. 1: process diagram for preparing paraxylene by alkylation of benzene and methanol on fixed bed radial reactor
Wherein the reference numerals
Gas phase benzene 1
Gas phase methanol 2
Reaction mixture 4
Reaction product 5
Fixed bed radial reactor 6
Reaction product 7 after heat exchange
Mixture 8 of off-gases, unreacted benzene and water of reaction
Unreacted benzene and part of the reaction to water 10
The other part of the reaction product water is discharged out 11
Oil phase reaction effluent 12 of toluene and xylene
Toluene 13
Mixed xylenes and carbon nonaaromatics 14
Mixed xylene 15
O-and m-xylene 16
Para-xylene 17
Carbon nonaarene 18
Rectifying column 21
Xylene column 23
An adsorption separation unit 24.
Detailed Description
The following examples illustrate the invention in detail: the present example is carried out on the premise of the technical scheme of the present invention, and detailed embodiments and processes are given, but the scope of the present invention is not limited to the following examples, and the experimental methods without specific conditions noted in the following examples are generally performed according to conventional conditions.
The technical scheme adopted by the invention comprises the following steps:
a) vaporizing the benzene feed to obtain gas phase benzene 1;
b) vaporizing the methanol feed to obtain alkylating agent gas phase methanol 2;
c) mixing gas-phase benzene 1, gas-phase methanol 2 and hydrogen carrier gas 3 to obtain a reaction mixture 4;
d) the reaction mixture 4 and the reaction product 5 exchange heat through a heat exchanger 19, then are preheated to the reaction temperature, and are introduced into a central pipe of a fixed bed radial reactor 6, the gas phase radial flow distribution is realized through the central pipe, the gas phase radial flow enters a catalyst bed layer for alkylation reaction, the reaction product 5 forms a reaction product 7 after heat exchange, the reaction product 7 after heat exchange is fractionated through a rectifying tower 21 to obtain a mixture 8 of the tail gas at the top of the rectifying tower, unreacted benzene and reaction generated water, and an oil phase reaction effluent 12 rich in toluene and xylene is obtained at the bottom of the rectifying tower;
e) condensing a mixture 8 of the tail gas at the top of the tower, unreacted benzene and reaction generated water to separate into a gas phase and a liquid phase, wherein 70-99% of the volume of the gas phase reaction effluent is refluxed and combined with hydrogen carrier gas, the rest part of the tail gas is discharged 9, the liquid phase effluent comprises unreacted benzene and reaction generated water, all the unreacted benzene and part of the reaction generated water 10 are combined with the gas phase benzene in the step a) and enter a fixed bed radial reactor to carry out alkylation reaction to generate xylene, and the other part of the reaction generated water is discharged 11;
f) separating the oil phase reaction effluent 12 rich in toluene and xylene obtained at the bottom of the tower through a toluene tower 22; the distillate 13 at the top of the toluene tower is toluene, and the distillate at the bottom of the toluene tower is mixed xylene and carbon nonaromatic hydrocarbon fraction 14;
g) the mixed xylene and the carbon nonaromatic hydrocarbon fraction 14 enter a xylene tower 23 to separate mixed xylene 15 and carbon nonaromatic hydrocarbon 18, the mixed xylene 15 enters an adsorption separation unit 24 to obtain a p-xylene product 17, and m-xylene and o-xylene 16 enter an isomerization unit to produce p-xylene;
h) the separated toluene 13 and carbon nonaromatic hydrocarbon 18 enter a disproportionation unit to produce xylene;
in the technical scheme, the molar ratio range of benzene to the alkylating reagent methanol is 8: 1-0.1: 1, preferably 4: 1-0.5: 1; the mass fraction of the reflux water in the total reaction water is 10-100%; the reaction conditions for benzene and methanol alkylation are as follows: the reaction temperature is 350-550 ℃, the reaction pressure is 0.1-5.0 MPa, the carrier gas/benzene molar ratio is 1-10, and the weight space velocity of the aromatic hydrocarbon is 0.1-10.0 h-1。
Combining all unreacted benzene and part of water generated by reaction in the step e) with the gas-phase benzene in the step a) and introducing the combined gas-phase benzene into a fixed bed radial reactor for alkylation reaction to produce dimethylbenzene, wherein the mass fraction of the part of water generated by reaction accounts for 10-100% of the water generated by reaction; if the mass fraction of the water generated by the reaction of the reflux part accounts for less than 10 percent of the water generated by the reaction, the carbon deposition speed of the catalyst is not obviously slowed down, namely, the effect of inhibiting the carbon deposition of the catalyst cannot be achieved due to the too small amount of the reflux water.
Example 1
As shown in the attached figure 1, a fixed bed radial reactor process is selected for carrying out an alkylation reaction experiment, the loading amount of a catalyst is 1000 g, the molar ratio of benzene to methanol as a reaction raw material is 1:1, and the reaction process conditions are as follows: the reaction temperature is 470 ℃, the reaction pressure is 1.0MPa, and the mass space velocity of the fed benzene is 5.0h-1The molar ratio of hydrogen to the feed benzene is 2; the volume fraction of the backflow tail gas in the whole tail gas is 90%; the mass fraction of the reflux water in the total reaction generated water is 50%.
Example 2
As shown in the attached figure 1, a fixed bed radial reactor process is selected for carrying out an alkylation reaction experiment, the loading amount of a catalyst is 1000 g, the molar ratio of benzene to methanol as a reaction raw material is 1:1, and the reaction process conditions are as follows: the reaction temperature is 450 ℃, the reaction pressure is 0.5MPa, and the mass space velocity of the fed benzene is 3.0h-1The molar ratio of nitrogen to the fed benzene is 2; the volume fraction of the backflow tail gas in the whole tail gas is 80%; the mass fraction of the reflux water in the total reaction generated water is 10%.
Example 3
Referring to figure 1, fixed bed radial reactor process was selected for alkylation reaction experiments, catalystThe loading is 1000 g, the molar ratio of the reaction raw material benzene to the methanol is 4:1, and the reaction process conditions are as follows: the reaction temperature is 470 ℃, the reaction pressure is 1.0MPa, and the mass space velocity of the fed benzene is 5.0h-1The molar ratio of hydrogen to the feed benzene is 2; the volume fraction of the backflow tail gas in the whole tail gas is 90%; the mass fraction of the reflux water in the total reaction generated water is 50%.
Example 4
As shown in the attached figure 1, a fixed bed radial reactor process is selected for carrying out an alkylation reaction experiment, the loading amount of a catalyst is 1000 g, the molar ratio of reaction raw materials, namely benzene to methanol is 0.5:1, and the reaction process conditions are as follows: the reaction temperature is 350 ℃, the reaction pressure is 0.1MPa, and the mass space velocity of the fed benzene is 0.1h-1The molar ratio of nitrogen to the feed benzene was 10; the volume fraction of the backflow tail gas in the whole tail gas is 70%; the mass fraction of the reflux water in the total reaction generated water is 50%.
Example 5
As shown in the attached figure 1, a fixed bed radial reactor process is selected for carrying out an alkylation reaction experiment, the loading amount of a catalyst is 1000 g, the molar ratio of benzene to methanol as a reaction raw material is 4:1, and the reaction process conditions are as follows: the reaction temperature is 550 ℃, the reaction pressure is 5.0MPa, and the mass space velocity of the fed benzene is 10.0h-1The molar ratio of hydrogen to the feed benzene is 1; the volume fraction of the backflow tail gas in the whole tail gas is 70%; the mass fraction of the reflux water in the total reaction generated water is 30%.
Example 6
As shown in the attached figure 1, a fixed bed radial reactor process is selected for carrying out an alkylation reaction experiment, the loading amount of a catalyst is 1000 g, the molar ratio of reaction raw materials, namely benzene to methanol is 0.5:1, and the reaction process conditions are as follows: the reaction temperature is 550 ℃, the reaction pressure is 1.0MPa, and the mass space velocity of the fed benzene is 2.0h-1The molar ratio of hydrogen to the feed benzene is 1; the volume fraction of the return tail gas in the total tail gas is 95 percent; the mass fraction of the reflux water in the total reaction generated water is 100%.
Comparative example 1
Other reaction conditions were the same as in example 1 except that: condensing a mixture of the tail gas at the top of the rectifying tower, unreacted benzene and reaction generated water by a condenser and then dividing the mixture into a gas phase and a liquid phase, wherein 90% of the mass of a gas phase reaction effluent is combined with hydrogen carrier gas, the rest part of the gas phase reaction effluent is discharged as tail gas, a liquid phase effluent comprises unreacted benzene and reaction generated water, all the unreacted benzene and the reaction generated water are separated by an oil-water separator, all the unreacted benzene and the gas phase benzene are combined and enter a fixed bed radial reactor for alkylation reaction to produce xylene, and all the reaction generated water is treated and then discharged after reaching the standard; that is, all the water produced by the reaction was discharged outside the system, no reflux water was present, and the process conditions and technical effects are shown in Table 1. The reaction process conditions and the reaction results of examples 1 to 6 and comparative example 1 are shown in Table 1.
Table 1 examples 1-6, comparative example 1 reaction process conditions and reaction results
From table 1, it can be seen that: the method for preparing p-xylene by alkylating benzene and methanol can obtain high xylene space-time yield and lower catalyst carbon deposition speed; particularly, the comparative example shows that when the process of the invention is adopted, the carbon deposition speed of the catalyst can be obviously slowed down and the service life of the catalyst can be prolonged when the reflux is more than 10 percent of the mass fraction of water generated by the reaction.
Claims (5)
1. A method for preparing paraxylene by alkylating benzene and methanol comprises the following steps:
a) vaporizing the benzene feed to obtain gas phase benzene;
b) vaporizing the methanol feed to obtain an alkylating agent vapor phase methanol;
c) combining the gas-phase benzene, the gas-phase methanol and a carrier gas to obtain a reaction mixture;
d) the reaction mixture and a reaction product exchange heat through a heat exchanger, the reaction mixture is preheated to the reaction temperature and then introduced into a central pipe of a fixed bed radial reactor, gas-phase radial flow distribution is realized through the central pipe and enters a catalyst bed layer to carry out alkylation reaction, the reaction product forms a reaction product after heat exchange, the reaction product after heat exchange is fractionated through a rectifying tower to obtain a mixture of tower top tail gas, unreacted benzene and reaction generated water, and an oil phase reaction effluent rich in toluene and xylene is obtained at a tower kettle;
e) condensing a mixture of the tail gas at the top of the tower, unreacted benzene and reaction generated water by a condenser and then dividing the mixture into a gas phase and a liquid phase, wherein 70-99% of the volume of the gas phase reaction effluent is refluxed and combined with hydrogen carrier gas, the rest part of the gas phase reaction effluent is discharged as tail gas, the liquid phase effluent comprises unreacted benzene and reaction generated water, all the unreacted benzene and part of the reaction generated water are combined with the gas phase benzene in the step a) and enter a fixed bed radial reactor to carry out alkylation reaction to generate xylene, and the other part of the reaction generated water is discharged;
all unreacted benzene and part of water generated by reaction in the step e) are combined with the gas-phase benzene in the step a) and enter a fixed bed radial reactor to carry out alkylation reaction to produce dimethylbenzene, and the mass fraction of the part of water generated by reaction accounts for 10-100% of the water generated by reaction;
f) separating oil phase reaction effluent rich in toluene and xylene obtained at the bottom of the tower by a toluene tower; the distillate at the top of the toluene tower is toluene, the distillate at the bottom of the toluene tower is mixed xylene fraction and carbon nonaromatic hydrocarbon fraction, and then the distillate at the bottom of the toluene tower enters a xylene tower;
the distillate at the top of the xylene column is mixed xylene, the mixed xylene enters an adsorption separation unit to obtain p-xylene and o-xylene and m-xylene, the o-xylene and the m-xylene enter an isomerization unit to produce p-xylene, and the distillate at the bottom of the xylene column is carbon nonaarene;
g) toluene as the top distillate of the toluene tower and carbon nonaromatic hydrocarbon as the bottom distillate of the xylene tower enter a disproportionation unit to produce xylene.
2. The process for alkylation of benzene with methanol to produce para-xylene according to claim 1, wherein the molar ratio of benzene in step a) to methanol in step b) is 8: 1-0.1: 1.
3. The process for alkylation of benzene with methanol to produce para-xylene according to claim 2, wherein the molar ratio of benzene in step a) to methanol in step b) is 4: 1-0.5: 1.
4. The process for alkylation of benzene with methanol to produce para-xylene according to claim 1, wherein the alkylation reaction conditions in step d): the reaction temperature is 350-550 ℃, the reaction pressure is 0.1-5.0 MPa, the molar ratio of hydrogen to benzene in the step a) is 1-10, and the weight space velocity of benzene in the step a) is 0.1-10.0 h-1。
5. The process for alkylation of benzene with methanol to produce para-xylene according to claim 1, wherein the carrier gas is nitrogen or hydrogen.
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| CN203944357U (en) * | 2014-05-21 | 2014-11-19 | 上海寰球工程有限公司 | Be applicable to the reactor of alcohol, benzene or benzene derivative alkylated reaction |
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