Method for reducing tar content in isopropyl benzene preparation process

Abstract

The invention provides a method for reducing tar content in a cumene preparation process. According to the method, isopropylbenzene crude tar generated by an isopropylbenzene device is used as a raw material, alkane light tar in the isopropylbenzene crude tar is separated from the tower top through a crude tar tower, and the remaining isopropylbenzene tar is separated from the tower bottom; cumene tar is mixed with alkane, an acid solution is added, and the mixture enters a cracking unit after being preheated; the product tower separates materials at the outlet of the cracking unit, and propylene is separated from the top part of the product tower; the gas-phase propylene directly returns to an isopropylbenzene device; the liquid-phase mixture is separated into a water phase and an oil phase through a coalescer, the acid aqueous solution is returned to the front of the cumene tar preheating unit, and the benzene and the cumene organic phase are returned to the cumene device; the alkane solution comprises hexane and nonane in a ratio of (5: 1)-(1: 5). According to the invention, the tar generated by cumene is recovered by the cracking device and then can be directly reused to the cumene device, so that the overall discharge capacity of the tar of the cumene device is reduced, no new waste gas or waste liquid is added, and efficient utilization of resources is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of cumene preparation, and specifically to a method for reducing the tar content during the cumene preparation process. Background Art

[0002] Cumene is an important organic chemical raw material and is the main intermediate compound for the production of phenol, acetone, and α-methylstyrene.

[0003] Currently, the mainstream production process is the reaction of benzene and propylene. The produced cumene and impurities are purified through 3 to 5 distillation columns to obtain the cumene product, and the generated tar is directly discharged, resulting in low raw material utilization rate.

[0004] In industry, the production methods of cumene include various alkylation processes using solid phosphoric acid as a catalyst, zeolite molecular sieve catalysts, and the aluminum trichloride method, etc. The existing methods either have low conversion rates, serious pollution, or have not been industrialized yet. At the same time, for the production method of zeolite molecular sieve catalysts, the main problems are that during the alkylation reaction process, there are a series of side reactions such as catalyst poisoning and raw material self-polymerization, generating impurities such as propylene polymers and cumene dimers, and the irreversible reaction produces cumene, ultimately leading to a high tar content.

[0005] Therefore, the existing technology still needs to be improved and developed, and there is an urgent need for a process to reduce the tar production during the cumene device preparation process. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for reducing the tar content during the cumene preparation process, which can significantly reduce the tar content during the cumene preparation process.

[0007] To achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0008] A method for reducing the tar content during the cumene preparation process, the method comprising the following steps:

[0009] S1. Using the crude cumene tar produced by the cumene device as a raw material, separating the alkane light tar from the top of the crude tar column, and separating the remaining cumene tar from the bottom of the column;

[0010] S2. Mixing the cumene tar with alkanes, adding an acid solution, and after preheating, entering the cracking unit to obtain propylene, benzene, cumene, and heavy aromatics;

[0011] S3. Separating the material at the outlet of the cracking unit in the product column, separating the gaseous propylene from the top of the product column, and separating the mixture of liquid water, benzene, and cumene from the top of the product column;

[0012] S4. The gaseous propylene is directly returned to the cumene unit; the liquid-phase mixture is separated into water and oil phases by a coalescer. The acidic aqueous solution is returned to the front of the cumene tar preheating unit, and the organic phases of benzene and cumene are returned to the cumene unit;

[0013] S5. The heavy aromatic tar from the S3 product column and the light alkane tar from S1 are sent to an incinerator for treatment;

[0014] Among them, the composition of the alkanes in S2 is hexane and nonane with a molar ratio of (5:1)-(1:5).

[0015] In the present invention, in the cracking unit, cumene tar is mixed with a specific alkane solution, then mixed with an acid solution, and finally enters the cracking reactor after preheating, and the following hydrogen transfer and acid cracking reactions can occur directionally to obtain the target products propylene, benzene, cumene, and heavy aromatic tar. The reactions involved are as follows:

[0016]

[0017]

[0018] In one embodiment of the present invention, the proportion of diphenylpropane and its isomers in the S1 crude cumene tar > 80 wt%.

[0019] In one embodiment of the present invention, the temperature of the crude tar column in S1 is 250 - 270 °C.

[0020] In one embodiment of the present invention, the mass ratio of cumene tar to alkane in S2 is (5:1)-

[0021] (1:5).

[0022] In one embodiment of the present invention, the acid solution in S2 is a sulfuric acid solution; preferably, after adding the acid solution to the mixture, the concentration of the acid is 0.5 - 2 wt%.

[0023] In one embodiment of the present invention, the cracking temperature in S2 is 320 - 380 °C, and the pressure is 5.2 - 5.8 MPaG.

[0024] In one embodiment of the present invention, the temperature of the product column in S3 is 200 - 220 °C.

[0025] In one embodiment of the present invention, the water content in the oil phase in S4 is less than 11 ppm.

[0026] In one embodiment of the present invention, the recovery rates of benzene and cumene in the medium tar are greater than 70 wt%.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] In the method of the present invention, the heavy components are reduced from 2.4 kg / t cumene in the existing process to 0.24 kg / t. The recovery rates of benzene and cumene can reach over 70%. Moreover, the catalytic cracking produces propylene, benzene, and cumene, all of which are materials within the original cumene plant system, without introducing new substances and having no impact on the operation of the original system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic process flow diagram of a solution adopted by the method of the present invention; the marks in the figure are as follows: 1 cumene crude tar, 2 alkane light tar, 3 cumene tar, 4 circulating acid solution, 5 tar after cracking, 6 cumene / benzene / water mixture, 7 heavy aromatic tar, 8 crude tar column, 9 reflux drum of the crude tar column, 10 cracking reactor, 11 product column, 12 reflux drum of the product column, 13 static mixer, 14 high-efficiency coalescer, 15 acid solution, 16 cumene / benzene mixture, 17 recovered propylene, 18 reactor pressure control valve, 19 alkane solution. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] The present invention will be further described in detail below in conjunction with embodiments. The following embodiments are only used to explain the present invention and do not constitute a limitation to the protection scope of the present invention.

[0031] The main raw materials and equipment sources are as follows:

[0032] The cumene crude tar comes from tar A produced by the cumene unit of the bisphenol A unit of Wanhua Chemical. The content of diphenylpropane and its isomers in this batch of raw materials is 93 wt%, and the remaining benzene ring organic substances are 7 wt%; tar B, the content of diphenylpropane and its isomers in this batch of raw materials is 85 wt%, and the remaining benzene ring organic substances are 15 wt%.

[0033] The high-efficiency coalescer comes from Shandong Puchuang Fluid Technology Co., Ltd., with an inner diameter of 0.5 m, a length of 3 m, horizontal, and the filter element model is LCS4H1AH;

[0034] The crude tar column comes from Beijing Zehua Chemical Engineering Co., Ltd., with a tower inner diameter of 1 m, a tower height of 22 m, and a total of 40 trays in the rectifying section and stripping section;

[0035] The product column comes from Beijing Zehua Chemical Engineering Co., Ltd., with a tower inner diameter of 0.9 m, a tower height of 18 m, and a total of 35 trays in the rectifying section and stripping section;

[0036] The cracking reactor comes from Jiangnan Boiler Pressure Vessel Priority Co., Ltd., with an internal coil length of 170 m, a design pressure of 7 MPa, and a design temperature of 400 °C.

[0037] The present invention provides a recovery system for cumene crude tar as shown in the attached Figure 1 figure, including:

[0038] The first separation unit is used to receive cumene crude tar from the cumene plant and simultaneously separate light alkane tar and cumene tar;

[0039] The batching and mixing / preheating unit is used to mix the cumene tar obtained from the first separation unit with a certain proportion of alkane solution and acid solution, and after heat exchange between substances, obtain the raw material for the cracking unit;

[0040] The cracking unit is used to receive the material after the static mixer, and under high temperature and high pressure conditions, ensure a certain residence time to carry out cracking reaction to obtain propylene, benzene and cumene;

[0041] The second separation unit is used to separate the cracked material to obtain water, and the target products propylene, benzene and cumene, and simultaneously separate heavy aromatic tar;

[0042] The phase separation unit is used to receive the water, benzene and cumene separated by the second separation unit. The obtained aqueous phase is returned before the preheating unit, and the obtained organic phase is returned to the cumene plant.

[0043] In a specific embodiment, the feeding position of the cumene crude tar is relatively high, which can better remove the irreversible light alkane tar in the tar and ensure more stable pressure in the subsequent cracking unit;

[0044] In a specific embodiment, hexane / nonane is selected as the alkane solution for the cracking reaction;

[0045] In a specific embodiment, after the three streams of materials are mixed, it further includes a static mixer for fully mixing the materials, in which the organic phase and water are fully mixed to reduce the risk of poor cracking effect caused by too high local material concentration;

[0046] In a specific embodiment, the phase separation unit adopts a coalescer to fully separate the aqueous phase and the organic phase, remove the possible residual metal ions in the organic phase, and the obtained second organic phase enters the solvent removal unit; the obtained aqueous phase can enter before the preheating unit as recycled material, reducing the external discharge amount of wastewater.

[0047] In a specific embodiment, the coalescer filter element adopts a Pall coalescing filter element made of polyvinylidene fluoride, with a quantity of 8 pieces, and the water content in the outlet organic phase is less than 11 ppm, so as to ensure that as little water as possible is entrained into the subsequent cumene plant, leading to the occurrence of corrosion problems due to the introduction of acidic substances.

[0048] Example 1

[0049] A method for reducing the tar yield during the cumene preparation process includes the following steps:

[0050] Such as Figure 1As shown, 300 kg / h of crude cumene tar 1 (tar A) produced by the cumene unit is fed into the upper part of the crude tar column 8. The tower pressure is controlled at 65 kpaA, and the bottom temperature of the tower is 260 °C. 10 kg / h of lighter alkanes in the crude cumene tar 1 are separated. In the above process, the total organic matter of C10 and below in the tower bottom is 0.8 ppm. The non-recoverable light components are separated, and at the same time, the operating parameters of the subsequent cracking process are ensured to be stable. The alkanes separated from the top of the tower are treated as waste liquid, and the aromatic hydrocarbons at the tower bottom are used as the feed for the subsequent cracking unit.

[0051] The cumene tar 3 in the bottom material of the crude tar column 8 is mixed with an alkane solution with a mass ratio of 1:1.1. The composition of the alkane solution 19 is a hexane / nonane solution with a molar ratio of 1:1. Then it is mixed with the circulating sulfuric acid solution 4 in a mass ratio of 1:1, and is mixed evenly through the static mixer 13. The addition amount of the sulfuric acid solution is adjusted in a timely manner according to the composition of the inlet and outlet materials of the cracking reactor 10, and the sulfuric acid content in the mixed solution is controlled at 1 wt%. After heat exchange with the outlet material of the cracking reactor 10 to 285 °C, it enters the cracking reactor 10.

[0052] In the cracking reactor 10, the inlet material is heated to 350 °C through multi-stage electric heating, and the pressure in the cracking reactor is controlled at 5.5 MPaG through the outlet valve to ensure a residence time of 20 min for the material.

[0053] The product tower 11 controls the tower pressure at 35 KPaA and the bottom temperature at 220 °C. The cracked tar 5 exchanges heat with the inlet material to 265 °C and enters the product tower 11. The material entering the tower is vaporized and quickly separated. 180 kg / h of propylene 17 is separated from the top of the tower in the form of gas phase. Cumene / benzene / water 6 is separated from the top of the tower, and after being mixed with the intermittently added sulfuric acid solution 15, it enters the high-efficiency coalescer 14 to separate the circulating sulfuric acid solution 4 from cumene / benzene / water 6. 231 kg / h of cumene / benzene mixture 16 is separated, with a water content of 3 ppm. The circulating sulfuric acid solution 4 returns to the front of the static mixer 13 to be mixed with the cumene tar and continues to enter the cracking reactor, and the cumene / benzene mixture returns to the original cumene unit for recycling.

[0054] A small amount of heavy aromatics 7 at the tower bottom is discharged at 10 kg / h and incinerated as waste liquid, with a calorific value 40 kJ / kg higher than that of the crude cumene tar.

[0055] The conversion rate of the crude cumene tar in this process is 93%, and the recovery rates of benzene / cumene are 80%. It is calculated that the tar unit consumption of the original device is 2.4 kg / t of cumene, which is now reduced to 0.24 kg / t of cumene. The benzene unit consumption is reduced from 0.640 t / t of cumene to 0.635 t / t of cumene, and the waste liquid generation amount is reduced from 0.2 kg / t of cumene to 0.02 kg / t of cumene. The generated waste liquid is incinerated as high-calorific value tar.

[0056] Example 2

[0057] As Figure 1 shown, 300 kg / h of crude cumene tar 1 (tar A) produced by the cumene unit is fed into the upper part of the crude tar column 8. The tower pressure is controlled at 65 kpaA, and the bottom temperature of the tower is 250 °C. 10 kg / h of lighter alkanes in the crude cumene tar 1 are separated out. In the above process, the total organic matter in the tower bottom with C10 and below is 0.9 ppm, and the non-recoverable light components are separated out, while ensuring the stable operation parameters of the subsequent cracking process. The alkanes separated from the top of the tower are treated as waste liquid, and the aromatic hydrocarbons in the tower bottom are used as the feed for the subsequent cracking unit.

[0058] The cumene tar 3 in the bottom material of the crude tar column 8 is mixed with an alkane solution with a mass ratio of 1:1.1. The composition of the alkane solution 19 is a nonane and hexane solution with a molar ratio of 5:1. Then it is mixed with the circulating sulfuric acid solution 4 in a mass ratio of 1:1, and is mixed evenly through the static mixer 13. The addition amount of the sulfuric acid solution is adjusted in time according to the composition of the inlet and outlet materials of the cracking reactor 10, and the sulfuric acid content in the mixed solution is controlled at 2 wt%; after heat exchange with the outlet material of the cracking reactor 10 to 285 °C, it enters the cracking reactor 10.

[0059] In the cracking reactor 10, the inlet material is heated to 340 °C through multi-stage electric heating. The pressure in the cracking reactor is controlled at 5.6 MPaG through the outlet valve to ensure a residence time of 15 min for the material. When the residence time is short, the cracking rate of the cumene tar 3 cannot be guaranteed. When the residence time is long, self-polymers will be generated in the cumene tar 3, resulting in a decrease in the recovery rate of the target product.

[0060] The product column 11 controls the tower pressure at 35 KPaA and the bottom temperature at 200 °C. The cracked tar 5 exchanges heat with the inlet material to 265 °C and enters the product column 11. The material entering the tower is vaporized and quickly separated. Propylene 17 is separated from the top of the tower in a gaseous state, and cumene / benzene / water 6 is separated from the top of the tower. After mixing with the intermittently added sulfuric acid solution 15, it enters the high-efficiency coalescer 14 to separate the circulating sulfuric acid solution 4 from the cumene / benzene / water 6, and separate out 16 the cumene / benzene mixture, in which the water content is 10 ppm. The circulating sulfuric acid solution 4 returns to the front of the static mixer 13 to be mixed with the cumene tar and continues to enter the cracking reactor, and the cumene / benzene mixture returns to the original cumene unit for recycling.

[0061] A small amount of heavy aromatic hydrocarbons 7 in the tower bottom are discharged as waste liquid for incineration treatment, and the calorific value is 40 kJ / kg higher than that of the crude cumene tar.

[0062] The conversion rate of cumene crude tar in this process is 85%, and the recovery rate of benzene / cumene is 75%. It is calculated that the tar unit consumption of the original unit is 2.4 kg / t cumene, which is now reduced to 0.36 kg / t cumene. The benzene unit consumption is reduced from 0.640 t / t cumene to 0.638 t / t cumene, and the waste liquid generation amount is reduced from 0.2 kg / t cumene to 0.03 kg / t cumene. The generated waste liquid is incinerated as high-calorie tar.

[0063] Example 3

[0064] As Figure 1 shown, 300 kg / h of cumene crude tar 1 (tar B) produced by the cumene unit is fed into the upper part of the crude tar column 8. The tower pressure is controlled at 65 kpaA, and the bottom temperature of the tower is 270 °C. 10 kg / h of lighter alkanes in the cumene crude tar 1 are separated out. In the above process, the total organic matter below C10 and C10 in the tower bottom is less than 0.9 ppm, and the non-recoverable light components are separated out, while ensuring the stable operation parameters of the subsequent cracking process. The alkanes separated from the top of the tower are treated as waste liquid, and the aromatics at the tower bottom are used as the feed for the subsequent cracking unit.

[0065] The cumene tar 3 in the bottom material of the crude tar column 8 is mixed with an alkane solution with a mass ratio of 1:1.1. The composition of the alkane solution 19 is a solution of nonane and hexane with a molar ratio of 1:5. Then it is mixed with the circulating sulfuric acid solution 4 in a mass ratio of 1:1, and is mixed evenly by the static mixer 13. The addition amount of the sulfuric acid solution is adjusted in time according to the composition of the inlet and outlet materials of the cracking reactor 10, and the sulfuric acid content in the mixed solution is controlled at 1 wt%; after heat exchange with the outlet material of the cracking reactor 10 to 285 °C, it enters the cracking reactor 10.

[0066] In the cracking reactor 10, the inlet material is heated to 360 °C by multi-stage electric heating. The pressure in the cracking reactor is controlled at 5.4 MPaG through the outlet valve to ensure that the residence time of the material is 25 min. When the residence time is short, the cracking rate of cumene tar 3 cannot be guaranteed. When the residence time is long, self-polymers will be generated in cumene tar 3, resulting in a decrease in the recovery rate of the target product.

[0067] The product column 11 controls the column pressure at 35 KPaA and the bottom temperature at 220 °C. The cracked tar 5 exchanges heat with the inlet material to reach 265 °C and then enters the product column 11. The material entering the column vaporizes and separates rapidly. Propylene 17 is recovered and separated from the top of the column in gaseous form, and cumene / benzene / water 6 is separated from the top of the column. After mixing with the intermittently added sulfuric acid solution 15, it enters the high-efficiency coalescer 14 to separate the circulating sulfuric acid solution 4 from cumene / benzene / water 6, and a cumene / benzene mixture 16 is separated, with a water content of 5 ppm. The circulating sulfuric acid solution 4 returns to the static mixer 13 and mixes with cumene tar before continuing to enter the cracking reactor. The cumene / benzene mixture returns to the original cumene unit for recycling.

[0068] A small amount of heavy aromatics 7 at the bottom of the column is discharged as waste liquid for incineration treatment, and its calorific value is 40 kJ / kg higher than that of cumene crude tar.

[0069] In this process, the conversion rate of cumene crude tar is 66%, and the recovery rates of benzene / cumene are 71%. It is calculated that the single consumption of tar in the original unit is 2.4 kg / t cumene, which is now reduced to 0.8 kg / t cumene. The single consumption of benzene is reduced from 0.640 t / t cumene to 0.639 t / t cumene, and the waste liquid generation amount is reduced from 0.2 kg / t cumene to 0.1 kg / t cumene. The generated waste liquid is incinerated as high-calorific value tar.

[0070] Comparative Example 1

[0071] Compared with Example 1, the difference is that hexane and nonane are replaced with liquid-phase cetane and eicosane, and the ratio is still 1 part of cumene tar mixed with 1.1 parts of alkane solution. Then sulfuric acid is mixed in a mass ratio of 1:1 and enters the reactor. The conversion rate of cumene crude tar is only 20%, far lower than 93% in Example 1. The external discharge amount of system tar is reduced by 20%, and there is no obvious improvement in tar single consumption and raw material consumption.

[0072] Comparative Example 2

[0073] Compared with Example 1, the type of alkane solution remains unchanged, and the molar ratio of hexane and nonane is changed to 10:1. The cumene tar in the bottom material of the crude tar column is directly mixed with sulfuric acid in a mass ratio of 1:1 and then enters the reactor. The conversion rate of cumene crude tar is only 65%, far lower than 93% in Example 1. There is almost no change in tar single consumption and raw material consumption, and the un-cracked material is still discharged in the form of tar, resulting in low economic benefits.

[0074] Comparative Example 3

[0075] Compared with Example 1, without changing the type and proportion of the alkane solution, when the type of acid was changed to hydrochloric acid, the conversion rate of cumene crude tar was only 58%, far lower than 93% in Example 1. The unit consumption of tar and raw material consumption hardly changed. The un-cracked materials were still discharged in the form of tar, resulting in low economic benefits. At the same time, the risk of equipment pipeline corrosion was increased.

[0076] Comparative Example 4

[0077] Compared with Example 1, the difference was that hexane and nonane were replaced with liquid-phase cetane and eicosane, and at the same time the type of acid was changed to hydrochloric acid. The conversion rate of cumene crude tar was only 26%, far lower than 93% in Example 1. The unit consumption of tar and raw material consumption hardly changed. The un-cracked materials were still discharged in the form of tar, resulting in low economic benefits. At the same time, the risk of equipment pipeline corrosion was increased.

[0078] As can be seen from the above, in terms of the conversion rate of cumene tar in the examples, the yields of benzene / cumene, the unit consumption of tar production, the amount of waste liquid generated, the unit consumption of raw material benzene, the operation stability of the device, the avoidance of corrosion problems, and the impact on the original device, etc., were all superior to those in the comparative examples, greatly improving the production efficiency of the device.

[0079] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification is only the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection required by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for reducing the tar content in the preparation process of cumene, characterized in that, the method comprises the following steps: S1. Using the cumene crude tar produced by the cumene unit as raw material, separating the alkane light tar from the top of the crude tar column, and separating the remaining cumene tar from the bottom of the column; S2. Mixing the cumene tar with alkanes, adding an acid solution, preheating and then entering a cracking unit to obtain propylene, benzene, cumene and heavy aromatics; S3. Separating the material at the outlet of the cracking unit in a product column, separating gaseous propylene from the top of the product column, and separating a mixture of liquid water, benzene and cumene from the bottom; S4. Directly returning the gaseous propylene to the cumene unit; separating the liquid mixture into an aqueous phase and an oil phase through a coalescer, returning the acid aqueous solution to before the preheating unit of the cumene tar, and returning the organic phase of benzene and cumene to the cumene unit; S5. Sending the heavy aromatic tar from the product column in S3 and the alkane light tar in S1 to an incinerator for treatment; wherein, the composition of the alkanes in S2 is hexane and nonane with a molar ratio of (5:1)-(1:5).

2. The method according to claim 1, characterized in that, the proportion of diphenylpropane and its isomers in the cumene crude tar in S1 > 80 wt%; and / or, the temperature of the crude tar column in S1 is 250 - 270 °C.

3. The method according to claim 1, characterized in that, the mass ratio of the cumene tar to the alkanes in S2 is (5:1)-(1:5); and / or, the acid solution in S2 is a sulfuric acid solution; preferably, after adding the acid solution to the mixture, the concentration of the acid is 0.5 - 2 wt%; and / or, the cracking temperature in S2 is 320 - 380 °C, and the pressure is 5.2 - 5.8 MPaG.

4. The method according to claim 1, characterized in that, the temperature of the product column in S3 is 200 - 220 °C.

5. The method according to claim 1, characterized in that, the water content in the oil phase in S4 is less than 11 ppm.

6. The method according to any one of claims 1 - 5, characterized in that, the recovery rates of benzene and cumene in the tar content are greater than 70 wt%.

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