CN111072440A - Method for improving comprehensive utilization rate of isobutene - Google Patents
Method for improving comprehensive utilization rate of isobutene Download PDFInfo
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Abstract
The invention provides a method for improving the comprehensive utilization rate of isobutene, which adopts the measures of optimizing process parameters, reforming process flow, exploring recycling mode, selecting feeding points and the like on the basis of fully utilizing equipment facilities of a ready-made butyl rubber device and a polymerization-grade isobutene device, improves the purity of the isobutene to the purity requirement of the polymerization-grade isobutene through three times of rectification, extraction, heavy component removal, secondary extraction and light component removal processes, improves the utilization rate of isobutene raw materials from 90-92% to 94-98% within a control range, completes the conversion of crude isobutene to isobutene while completing impurity removal and purification of waste isobutene, has high efficiency, can realize mass production of isobutene, saves equipment cost and simultaneously increases economic benefits.
Description
Technical Field
The invention belongs to the field of chemical rubber, and particularly relates to a method for improving the comprehensive utilization rate of isobutene.
Background
Butyl rubber is one of synthetic rubbers, is synthesized from isobutene and a small amount of isoprene, and is generally applied to the fields of manufacturing automobile tires, automobile sound insulation products and building waterproofing. Isobutene is used as a main raw material for synthesizing butyl rubber, the using amount accounts for more than 98%, but in a butyl rubber production device, 8% -12% of monomer isobutene cannot participate in the reaction, and the consumption is large for butyl rubber production enterprises.
As shown in FIG. 2, unreacted isobutylene is conventionally treated by entering into a recovery system together with a solvent (such as methyl chloride) and isoprene monomer, and performing a rectification separation operation to obtain methyl chloride solvent, waste isobutylene and waste isoprene, respectively. However, the recovered waste isobutylene cannot be directly used as a raw material for the butyl rubber reaction for the following reasons: (1) the purity of isobutene in the waste isobutene is about 98 percent and can not meet the purity requirement of 99.7 percent of polymerization-grade isobutene. (2) The content of isoprene which is one of impurities in the waste isobutene is 0-1 percent, and the direct recycling can generate polymerization reaction in a pipeline to block the pipeline. (3) The high content of alkane impurities in the waste isobutene (such as 0-1000ppm of isobutane, 0-5000ppm of n-butane and the like) causes the purity of the waste isobutene to be reduced on one hand, and causes the abnormal pressure of a butyl rubber reaction kettle although the waste isobutene does not participate in the polymerization reaction on the other hand. (4) The olefins (such as 1, 3 butadiene, maleic, etc.) in the waste isobutylene can affect the polymerization reaction of the butyl rubber, and the product performance is reduced. (5) The waste isobutene contains solvent (chloromethane about 2000 ppm), and is easy to generate hydrolysis reaction to generate acid, so that equipment is corroded. If polymer-grade isobutene meeting the requirements is obtained, the polymer-grade isobutene needs to be reprocessed to remove impurities, energy consumption and equipment investment are large, and butyl rubber enterprises generally take waste isobutene out as a byproduct rather than recycle the waste isobutene.
The Chinese patent application with the application number of 201610861081.3 discloses a process for recovering a solvent and monomers from butyl rubber, wherein methyl chloride, isobutene and isoprene are separated by adopting a three-tower rectification mode, but the separation of methyl chloride is emphasized, so that high-purity methyl chloride can be obtained, and the quality of the separated isobutene is difficult to judge by rectifying the separated isobutene only through one rectifying tower. Application number is 201720561299.7's chinese utility model patent, a recycle system of recovery isobutene in butyl rubber is disclosed, continue to react as polymerization monomer after mixing unreacted isobutene and raw materials isobutene and realize recycling, the flow through the unreacted isobutene of accurate control makes the normal production that does not influence butyl rubber after the mixing, the utilization ratio of isobutene has been improved to a certain extent to this kind of method, but only be equivalent to diluting unreacted isobutene to the reduction of impurity proportion and available, but its impurity does not reduce in essence, consequently, unable massive processing, low efficiency. In conclusion, the method which is low in cost, high in efficiency and capable of effectively removing impurities is provided to improve the utilization rate of isobutene in the butyl rubber device, and the method is significant.
Disclosure of Invention
In order to solve the problems, the invention provides a method for improving the comprehensive utilization rate of isobutene, which adopts measures such as process parameter optimization, process flow transformation, retrieval and utilization mode exploration, feeding point selection and the like on the basis of fully utilizing equipment facilities of the existing butyl rubber device and polymerization-grade isobutene device to improve the purity of waste isobutene to the purity requirement of polymerization-grade isobutene, wherein the content of key impurities is in a control range, so that the cost of an enterprise is reduced, and the economic benefit is increased.
In order to achieve the purpose, the invention adopts the following specific technical scheme:
a method for improving the comprehensive utilization rate of isobutene adopts equipment comprising a recovery system and a polymerization-grade isobutene device, wherein the recovery system comprises a first rectifying tower, a second rectifying tower and a third rectifying tower, and the polymerization-grade isobutene device comprises a storage tank, a first extraction tower, a heavy component removal tower, a second extraction tower and a light component removal tower;
the method comprises the following specific steps:
s1: the mixed material of methyl chloride, isobutene and isoprene enters a first rectifying tower for rectification and separation, and the methyl chloride is discharged from the top of the tower;
s2: the distillate at the bottom of the first rectifying tower enters a second rectifying tower for rectification and separation, and methyl chloride containing isobutene returns to the first rectifying tower from the top of the tower;
s3: the distillate at the bottom of the second rectifying tower enters a third rectifying tower for rectification separation, waste isobutene is obtained at the top of the tower, and the content of methyl chloride and isoprene in the waste isobutene does not exceed 200 ppm;
s4: and (2) conveying the waste isobutene obtained in the step S3 to a storage tank, mixing the waste isobutene with crude isobutene produced by a polymerization-grade isobutene device, then feeding the mixture into a first extraction tower, adding an extracting agent to remove soluble impurities, feeding the crude isobutene obtained at the top of the tower into a de-heavy tower, performing pressurized rectification to enrich impurities with a boiling point higher than that of the isobutene to a tower bottom to remove the impurities, feeding a mixture at the top of the de-heavy tower into a second extraction tower, performing secondary extraction to completely remove the soluble impurities, conveying a mixture at the top of the second extraction tower to a de-light tower, performing pressurized rectification to enrich impurities with a boiling point lower than that of the isobutene to the top of the tower to.
Preferably, the ratio of the feeding flow of the second rectifying tower to the feeding flow of the first rectifying tower is 0.15-0.5. Increase second rectifying column feed flow, be equivalent to the reflux volume that increases the rectifying column, theoretically can improve the separation effect, but on the other hand increases the feed volume and still need consider the throughput of rectifying column, because solvent methyl chloride content is higher in the second rectifying column feeding, excessively increases its flow, can lead to the separation effect to descend on the contrary for tower cauldron methyl chloride content increases, consequently needs to select suitable feed flow. The feeding flow rate is related to the design productivity of the device, the specific flow rates of different production devices are different, but the proportion range of the feeding flow rate of the second rectifying tower and the feeding flow rate of the first rectifying tower can be determined, and the proportion range of 0.15-0.5 is proper, so that the separation effect of the methyl chloride and the mixture of the two monomers can be effectively improved.
Preferably, the temperature of the sensitive plate of the second rectifying tower is 73-80 ℃, and the temperature of the tower kettle is 80-85 ℃. On the basis of adjusting the feeding flow of the second rectifying tower, the temperature of the sensitive plate and the temperature of the tower kettle are improved, and the content of methyl chloride in the tower kettle of the second rectifying tower can be reduced to 0-200 ppm.
More preferably, the temperature of the sensitive plate of the second rectifying tower is 75-78 ℃, and the temperature of the tower kettle is 82-85 ℃; the content of methyl chloride in the tower bottom of the second rectifying tower can be further reduced to 0-50 ppm.
Preferably, the ratio of the feeding flow of the second rectifying tower to the feeding flow of the first rectifying tower is 0.3-0.35.
Preferably, the tower bottom temperature of the third rectifying tower is 56-65 ℃. The temperature of the tower bottom of the third rectifying tower is properly reduced, so that isoprene can be prevented from rising to the tower top, and the separation effect of waste isobutene and waste isoprene is improved.
Preferably, the ratio of the extracted amount of the waste isoprene at the tower bottom of the third rectifying tower to the content of the isoprene fed into the first rectifying tower is 1.82-2.22. Increasing the tower bottom output of the third rectifying tower can also reduce isoprene rising to the tower top, but increasing the tower bottom output also increases the isobutene content in the tower bottom, resulting in loss. According to the invention, the proper tower bottom material extraction amount and tower bottom temperature are selected, so that the isoprene content in the tower top waste isobutene is reduced to 0-200ppm, and the loss of the tower bottom isobutene is not increased obviously. The extraction amount is generally determined according to the content proportion of the isoprene component in the tower bottom of the third rectifying tower. After the improvement, the content ratio of the isoprene is changed from 0.5-0.7 to 0.45-0.55. Examples are: if the isoprene content of the feeding material of the first rectifying tower is calculated by 100kg/h, the tower flow of the third rectifying tower is 200kg/h before the improvement, and the tower flow of the third rectifying tower is 222 kg/h after the improvement, the extraction amount is increased by about 10-28% compared with the prior art, and the extraction amount is increased by about 10-28% compared with the prior art.
Preferably, the reflux ratio of the de-heavy tower is 1.0-2.0, all isoprene possibly contained in the waste isobutene and part of n-butane can be enriched to the bottom of the tower to be removed, and crude isobutene without isoprene is obtained at the top of the tower.
Preferably, the reflux ratio of the light component removal tower is 30-50, most of isobutane in the waste isobutene can be enriched to the top of the tower for removal, and polymerization-grade isobutene is obtained at the bottom of the tower.
Preferably, the recycling proportion of the waste isobutene obtained by the third rectifying tower is 0-8% of the unit time yield of the crude isobutene produced by the polymerization-grade isobutene device. The recycling proportion can be flexibly determined according to the impurity content change of the waste isobutene. On one hand, the waste isobutene contains 1, 3-butadiene, maleic and other impurities with boiling points very close to that of isobutene and cannot be removed, and on the other hand, the boiling points of the n-butane, isobutane and other impurities are also relatively close to that of isobutene, so that the process flow cannot be completely removed. If the waste isobutene is recycled completely, the impurities are accumulated, the product quality of polymerization-grade isobutene is affected, and subsequent polymerization reaction is abnormal, so that the waste isobutene is recycled according to a certain proportion. The reuse proportion selection principle needs to be determined by combining the factors of the raw material quality of a polymerization grade isobutene generating device, the unit time yield of crude isobutene generated by the polymerization grade isobutene generating device and the quality of a final polymerization grade isobutene product.
Preferably, the polymerization grade isobutylene plant does not comprise a second extraction column; in step S4, the top mixture of the heavy component removal column is sent to the light component removal column.
Generally, butyl rubber production enterprises are provided with a butyl rubber device and a polymerization grade isobutene device, and the recovery system is an inherent part of the butyl rubber device, so that the recovery system and the polymerization grade isobutene production device are independent equipment and are not necessarily connected. The waste isobutene recovered by the recovery system cannot be directly utilized and is generally sold as a byproduct. The main reason why the product cannot be directly used is that the product contains other impurities and the purity of the product does not meet the requirement, and the details are described in the background of the invention.
The invention utilizes the recovery system and adjusts the control parameters to reduce the content of methyl chloride and isoprene in the waste isobutene to 0-200ppm, even below 50 ppm. If the isobutene is intended to be used, such a purity is clearly insufficient. The method comprises the steps of mixing the waste isobutene with the crude isobutene produced by the polymerization-grade isobutene device, and then removing all isoprene and part of alkane impurities in the mixed isobutene by utilizing impurity removing equipment of the polymerization-grade isobutene device through adjustment of various control parameters to obtain the polymerization-grade isobutene.
The process not only completes the impurity removal and purification of the waste isobutene, but also completes the conversion of the crude isobutene to the isobutene, can realize the mass production of polymerization-grade isobutene, and increases the economic benefit. Crude isobutene produced by the polymerization-grade isobutene device is obtained by cracking MTBE in an upstream reaction, and the waste isobutene is recycled before entering a storage tank, namely the waste isobutene and the waste isobutene are mixed and then need to be subjected to extraction, heavy component removal, secondary extraction and light component removal (wherein the secondary extraction determines whether the secondary extraction can be saved according to the primary extraction effect) so as to ensure the quality of the polymerization-grade isobutene product.
In the process, a series of problems need to be solved, firstly, a recovery system is utilized and parameters are controlled to adjust, for example, the ratio of the feeding flow of the second rectifying tower to the feeding flow of the first rectifying tower is controlled to be 0.15-0.5, the temperature of a sensitive plate of the second rectifying tower is adjusted to be 73-80 ℃, the temperature of a tower kettle is adjusted to be 80-85 ℃, the ratio of the feeding flow of the second rectifying tower to the feeding flow of the first rectifying tower is adjusted to be 0.3-0.35, the temperature of a tower kettle of the third rectifying tower is controlled to be 56-65 ℃, the ratio of the extracted amount of the waste isoprene in the tower kettle of the third rectifying tower to the content of the isoprene in the feeding of the first rectifying tower is controlled to be 1.82-2.22, and the content of methyl chloride and isoprene in the waste isobutylene is controlled to be 0-200ppm, even below 50 ppm; compared with the isoprene content within 1 percent recorded in the background technology, the isoprene content is obviously reduced, so that the problem of pipeline blockage caused by polymerization of isoprene and isobutene carried in the waste isobutene in a pipeline or a tower kettle is avoided as much as possible; however, since isoprene cannot be removed completely, a small amount of polymer is produced, such as during long-term operation and without cleaning, and blockage is caused by accumulation, we have solved the problem by increasing the amount of produced appropriately. After the problem of blockage is solved, the problem that the recycled waste isobutene is increased in a certain proportion, namely the feeding of a subsequent tower kettle is increased, and if the treatment efficiency is not improved, the phenomenon that the tower kettle is overloaded can also be solved by adjusting the parameters of the subsequent tower kettle, wherein the reflux ratio of a heavy component removal tower is controlled to be 1.0-2.0, and the reflux ratio of a light component removal tower is controlled to be 30-50; therefore, the separation effect is improved, and the separation efficiency is also improved, so that the series of problems are solved.
More specifically, the impurity content is reduced to a controllable range by optimizing the purification process, and the influence on the reuse is reduced as much as possible: adjusting the feeding flow of the second rectifying tower and increasing the temperature of a sensitive plate and a tower kettle of the second rectifying tower, so that the content of methyl chloride in the waste isobutene is reduced to 0-200ppm, and the high-concentration methyl chloride is prevented from corroding equipment; the isoprene content in the tower top waste isobutene is reduced to 0-200ppm by properly increasing the material extraction amount of the tower kettle and reducing the temperature of the tower kettle in the third rectifying tower, the loss amount of the isobutene in the tower kettle is not obviously increased, and pipeline blockage caused by polymerization of isoprene and isobutene is avoided as much as possible; the method is characterized in that the reflux ratio of the de-heavy tower is increased to remove all isoprene and part of normal butane in the waste isobutene, and the reflux ratio of the de-light tower is increased to remove most isobutane in the waste isobutene, so that the influence of alkane impurities is reduced. The recycling point of the waste isobutene is selected before the waste isobutene enters a storage tank to ensure the quality of a polymerization-grade isobutene product, and the accumulation of impurities which are difficult to remove is prevented by controlling the recycling proportion of the waste isobutene.
The invention has the following beneficial effects:
the ready-made butyl rubber device and polymerization grade isobutene device are adopted, investment is not required to be increased, and cost is saved. The waste isobutene is obtained by the treatment of the butyl rubber device, and is mixed with the crude isobutene and then treated by the polymerization grade isobutene device, so that impurities are effectively removed, and the polymerization grade isobutene is obtained. The invention improves the utilization rate of the isobutene raw material from 90-92% to 94-98%, completes the impurity removal and purification of the waste isobutene, and simultaneously completes the conversion of the crude isobutene to the isobutene, has high efficiency, can realize the mass production of the isobutene, and increases the economic benefit.
Drawings
FIG. 1: the process of the method of the invention is schematically illustrated.
FIG. 2: schematic diagram of a conventional treatment process for unreacted isobutylene in a butyl rubber unit.
In the figure: 1-a first rectifying tower, 2-a second rectifying tower, 3-a third rectifying tower, 4-a storage tank, 5-a first extraction tower, 6-a heavy component removal tower, 7-a second extraction tower and 8-a light component removal tower.
Detailed Description
The present invention will be further described with reference to the following specific examples.
A method for improving the comprehensive utilization rate of isobutene adopts a recovery system and a polymerization-grade isobutene device, as shown in figure 1, wherein the recovery system is an inherent part of a butyl rubber device and comprises a first rectifying tower 1, a second rectifying tower 2 and a third rectifying tower 3, and the polymerization-grade isobutene device comprises a storage tank 4, a first extraction tower 5, a heavy component removal tower 6, a second extraction tower 7 and a light component removal tower 8.
Example 1
The mixed material of methyl chloride, isobutene and isoprene enters a first rectifying tower 1, the feeding flow of the first rectifying tower 1 is 1t/h, wherein the content of isoprene is 50kg/h, the methyl chloride is discharged from the top of the tower after rectification and separation, and the distillate in the tower bottom enters a second rectifying tower 2; the feeding flow of the second rectifying tower 2 is 300kg/h, the temperature of a sensitive plate of the rectifying tower is 75 ℃, the temperature of a tower bottom is 80 ℃, methyl chloride containing isobutene returns to the first rectifying tower 1 from the top of the tower after rectification and separation, and the distillate of the tower bottom enters a third rectifying tower 3; the temperature of a tower kettle of a third rectifying tower 3 is 56 ℃, waste isobutene is obtained at the top of the tower, waste isoprene is obtained at the tower kettle, and the recovery amount of the waste isoprene in the tower kettle is 98 kg/h. Conveying the waste isobutene obtained by the third rectifying tower 3 to a storage tank 4 for recycling, wherein the recycling proportion is 3% of the unit time yield of the crude isobutene produced by the polymerization-grade isobutene device, and mixing the waste isobutene with the crude isobutene in the storage tank 4 and then feeding the mixture into a first extraction tower 5; adding an extracting agent to remove soluble impurities, discharging the soluble impurities at the tower bottom, and feeding the crude isobutene obtained at the tower top into a de-weighting tower 6; performing pressure rectification in a de-heavy column 6 with a reflux ratio of 1.0, enriching impurities with a boiling point higher than that of isobutene in a column kettle for removal by the pressure rectification, and feeding a mixture at the top of the column into a second extraction column 7; the soluble impurities are completely removed by secondary extraction, and the mixture at the top of the tower is conveyed to a light component removal tower 8; performing pressure rectification in a light component removal tower 8 at a reflux ratio of 30, enriching impurities with a boiling point lower than that of isobutene to the top of the tower for removal, obtaining polymerization-grade isobutene at the bottom of the tower, and supplying the polymerization-grade isobutene to a butyl rubber device to produce butyl rubber.
Example 2
The mixed material of methyl chloride, isobutene and isoprene enters a first rectifying tower 1, the feeding flow of the first rectifying tower 1 is 2t/h, wherein the content of isoprene is 100kg/h, the methyl chloride is discharged from the top of the tower after rectification and separation, and the distillate in the bottom of the tower enters a second rectifying tower 2; the feeding flow of the second rectifying tower 2 is 600kg/h, the temperature of a sensitive plate of the rectifying tower is 78 ℃, the temperature of a tower bottom is 83 ℃, methyl chloride containing isobutene returns to the first rectifying tower 1 from the tower top after rectification separation, and the distillate of the tower bottom enters a third rectifying tower 3; the temperature of a tower kettle of the third rectifying tower 3 is 60 ℃, waste isobutene is obtained at the top of the tower, waste isoprene is obtained at the tower kettle, and the output of the waste isoprene is 165 kg/h. Conveying the waste isobutene obtained by the third rectifying tower 3 to a storage tank 4 for recycling, wherein the recycling proportion is 6% of the unit time yield of the crude isobutene produced by the polymerization-grade isobutene device, and the waste isobutene and the crude isobutene are mixed in the storage tank 4 and then enter a first extraction tower 5; adding an extracting agent to remove soluble impurities, discharging the soluble impurities at the tower bottom, and feeding the crude isobutene obtained at the tower top into a de-weighting tower 6; performing pressure rectification in a de-heavy column 6 with a reflux ratio of 1.5, enriching impurities with a boiling point higher than that of isobutene in a column kettle for removal by the pressure rectification, and feeding a mixture at the top of the column into a second extraction column 7; the soluble impurities are completely removed by secondary extraction, and the mixture at the top of the tower is conveyed to a light component removal tower 8; and (3) performing pressure rectification in a light component removal tower 8 at a reflux ratio of 40, enriching impurities with a boiling point lower than that of isobutene to the top of the tower for removal, obtaining polymerization-grade isobutene at the bottom of the tower, and supplying the polymerization-grade isobutene to a butyl rubber device for producing butyl rubber.
Example 3
The mixed material of methyl chloride, isobutene and isoprene enters a first rectifying tower 1, the feeding flow of the first rectifying tower 1 is 8t/h, wherein the isoprene content is 160kg/h, the methyl chloride is discharged from the top of the tower after rectification and separation, and the distillate in the tower bottom enters a second rectifying tower 2; the feeding flow of the second rectifying tower 2 is 1.5t/h, the temperature of a sensitive plate of the rectifying tower is 80 ℃, the temperature of a tower kettle is 85 ℃, methyl chloride containing isobutene returns to the first rectifying tower 1 from the top of the tower after rectification and separation, and distillate at the tower kettle enters a third rectifying tower 3; the temperature of a tower kettle of a third rectifying tower 3 is 65 ℃, waste isobutene is obtained at the top of the tower, waste isoprene is obtained at the tower kettle, and the recovery amount of the waste isoprene in the tower kettle is 323 kg/h. Conveying the waste isobutene obtained by the third rectifying tower 3 to a storage tank 4 for recycling, wherein the recycling proportion is 8% of the unit time yield of the crude isobutene produced by the polymerization-grade isobutene device, and the waste isobutene and the crude isobutene are mixed in the storage tank 4 and then enter a first extraction tower 5; adding an extracting agent to remove soluble impurities, discharging the soluble impurities at the tower bottom, and feeding the crude isobutene obtained at the tower top into a de-weighting tower 6; performing pressure rectification in a de-heavy column 6 with a reflux ratio of 2.0, enriching impurities with a boiling point higher than that of isobutene in a column kettle for removal by the pressure rectification, and feeding a mixture at the top of the column into a second extraction column 7; the soluble impurities are completely removed by secondary extraction, and the mixture at the top of the tower is conveyed to a light component removal tower 8; performing pressure rectification in a light component removal tower 8 at a reflux ratio of 50, enriching impurities with a boiling point lower than that of isobutene to the top of the tower for removal, obtaining polymerization-grade isobutene at the bottom of the tower, and supplying the polymerization-grade isobutene to a butyl rubber device to produce butyl rubber.
The above embodiments can achieve the following effects: the recovery system reduces the content of methyl chloride and isoprene in the unreacted isobutene monomer to below 200ppm respectively, wherein in the first embodiment, the content of methyl chloride and isoprene can be reduced to below 10ppm, in the second embodiment, the content of methyl chloride and isoprene can be reduced to below 50ppm, and in the third embodiment, the content of methyl chloride and isoprene can be reduced to below 200 ppm; the polymerization grade isobutene device removes alkane impurities such as normal butane, isobutane and the like and all isoprene, and obtains polymerization grade isobutene, wherein the comprehensive utilization rate of isobutene at least reaches 94%; wherein, the comprehensive utilization rate of the isobutene in the first embodiment can reach 94 percent, the isobutene in the second embodiment can reach 96 percent, and the isobutene in the third embodiment can reach 98 percent.
The present embodiments are to be considered in all respects as illustrative and not restrictive. Any changes that may be made by one of ordinary skill in the art after reading this description of the invention, which are within the purview of the patent laws, are intended to be covered by the scope of the claims.
Claims (10)
1. A method for improving the comprehensive utilization rate of isobutene is characterized by comprising the following steps: the equipment adopted by the method comprises a recovery system and a polymerization-grade isobutene device, wherein the recovery system comprises a first rectifying tower (1), a second rectifying tower (2) and a third rectifying tower (3), and the polymerization-grade isobutene device comprises a storage tank (4), a first extraction tower (5), a heavy component removal tower (6), a second extraction tower (7) and a light component removal tower (8);
the method comprises the following specific steps:
s1: the mixed material of methyl chloride, isobutene and isoprene enters a first rectifying tower (1) for rectification and separation, and the methyl chloride is discharged from the top of the tower;
s2: the distillate at the bottom of the first rectifying tower (1) enters a second rectifying tower (2) for rectification separation, and methyl chloride containing isobutene returns to the first rectifying tower (1) from the top of the tower;
s3: the tower bottom distillate of the second rectifying tower (2) enters a third rectifying tower (3) for rectification separation, waste isobutene is obtained at the tower top, and the content of methyl chloride and isoprene in the waste isobutene is not more than 200 ppm;
s4: and (2) conveying the waste isobutene obtained in the step S3 to a storage tank (4), mixing the waste isobutene with crude isobutene produced by a polymerization-grade isobutene device, then feeding the mixture into a first extraction tower (5), adding an extracting agent to remove soluble impurities, feeding the crude isobutene obtained at the top of the tower into a de-heavy tower (6), performing pressurized rectification to enrich impurities with a boiling point higher than that of the isobutene to a tower bottom to remove the impurities, feeding a mixture at the top of the de-heavy tower (6) into a second extraction tower (7), completely removing the soluble impurities through secondary extraction, conveying the mixture at the top of the second extraction tower (7) to a de-light tower (8), performing pressurized rectification to enrich impurities with a boiling point lower than that of the isobutene to the top of the tower to remove.
2. The method for improving the comprehensive utilization rate of isobutene according to claim 1, characterized by comprising the following steps: the ratio of the feeding flow of the second rectifying tower (2) to the feeding flow of the first rectifying tower (1) is 0.15-0.5.
3. The method for improving the comprehensive utilization rate of isobutene according to claim 1 or 2, characterized by comprising the following steps: the temperature of the sensitive plate of the second rectifying tower (2) is 73-80 ℃, and the temperature of the tower kettle is 80-85 ℃.
4. The method for improving the comprehensive utilization rate of isobutene according to claim 2, characterized in that: the ratio of the feeding flow of the second rectifying tower (2) to the feeding flow of the first rectifying tower (1) is 0.3-0.35.
5. The method for improving the comprehensive utilization rate of isobutene according to claim 1, characterized by comprising the following steps: the tower kettle temperature of the third rectifying tower (3) is 56-65 ℃.
6. The method for improving the comprehensive utilization rate of isobutene according to claim 1 or 5, characterized by comprising the following steps: the ratio of the extracted amount of the waste isoprene at the tower bottom of the third rectifying tower (3) to the content of the isoprene fed into the first rectifying tower (1) is 1.82-2.22.
7. The method for improving the comprehensive utilization rate of isobutene according to claim 1, characterized by comprising the following steps: the reflux ratio of the de-heavy tower (6) is 1.0-2.0.
8. The method for improving the comprehensive utilization rate of isobutene according to claim 1, characterized by comprising the following steps: the reflux ratio of the light component removal tower (8) is 30-50.
9. The method for improving the comprehensive utilization rate of isobutene according to claim 1, characterized by comprising the following steps: the recycling proportion of the waste isobutene obtained by the third rectifying tower (3) is 0-8% of the unit time yield of the crude isobutene produced by the polymerization-grade isobutene device.
10. The method for improving the comprehensive utilization rate of isobutene according to claim 1, characterized by comprising the following steps: the polymerization grade isobutylene plant does not comprise a second extraction column (7); in step S4, the top mixture of the heavy component removal column (6) is sent to the light component removal column (8).
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