A method and system for isobutene oligomerization with self-circulating heat extraction of raw materials

Abstract

The present invention particularly relates to a method and system for isobutene oligomerization with self-circulating heat extraction of raw materials, belonging to the technical field of petrochemical industry. The method comprises the following steps: splitting the C4 raw material to obtain a reaction raw material and a circulating raw material; mixing the reaction raw material with tert-butanol to obtain a premixed raw material; heating the premixed raw material to a first temperature and subjecting it to a first oligomerization reaction to obtain a first oligomer; using the circulating raw material to absorb the reaction heat of the first oligomerization reaction so that the final reaction temperature of the first oligomerization reaction is a second temperature; evaporating the circulating raw material that has absorbed the reaction heat of the first oligomerization reaction at a third temperature, and then condensing it to the bubble point temperature and mixing it with the premixed raw material. This method can effectively solve the technical problem of generating a large number of side reaction products when dealing with the reaction heat generated by isobutene oligomerization.

Description

Technical Field

[0001] The present invention belongs to the chemical industry field, and particularly relates to a method and system for isobutene oligomerization with self-circulating heat extraction of raw materials. Background Art

[0002] The isobutene selective oligomerization process uses isobutene in mixed C4 to carry out a polymerization reaction under the action of an acidic catalyst. Isobutene adsorbs on the active center of the catalyst, dissociates, forms a C4 carbocation, and then combines with another isobutene molecule to generate a C8 carbocation. The C8 carbocation can desorb at the active center to generate isooctene, or continue to combine with other isobutene molecules to form a C12 carbocation, making the carbon chain longer. A large amount of reaction heat is released during the oligomerization process, and the overall temperature rise of the reactor exceeds the temperature limit, resulting in high-temperature deactivation of the catalyst. Currently, the widely adopted measure to control the temperature rise of the reactor is the external circulation cooling method. In this method, part of the reacted material is cooled by an external cooler and then recycled back into the reactor. The disadvantage is that a large amount of dimers in the recycled reaction products are backmixed to the reactor inlet, which not only reduces the driving force of the isobutene dimerization reaction, but also correspondingly increases the yields of side reaction products such as the reaction of dimers with isobutene to form trimers and the reaction of trimers with isobutene to form tetramers, resulting in a decrease in the yield of the target product.

[0003] CN107827694A discloses an apparatus and method for producing isooctane using indirect alkylation technology, including a fixed-bed reactor I, a catalytic distillation column, an extraction column, and a recovery column connected in sequence: mixed C4 and a polymerization inhibitor react in reactor I, and a part of the product enters the catalytic distillation column, and the other part returns after removing the reaction heat through a heat exchanger, that is, the mixed C4 raw material enters the catalyst bed from the reactor inlet, and under the action of the catalyst, an isobutene oligomerization reaction occurs, releasing reaction heat, the bed temperature rises, and the generated oligomer is discharged from the reactor outlet. A part of it is separated as recycled material, pressurized by a recycle pump and cooled by a cooler, and then returned to the reactor inlet, entering the catalyst bed together with the fresh raw material to control the adiabatic temperature rise of the entire bed from not exceeding a certain value. However, the main disadvantages of setting a recycle heat removal device in the fixed-bed reactor are as follows: ① A large amount of dimers are contained in the recycled material, causing backmixing when returning to the reactor inlet, not only reducing the driving force of the isobutene dimerization reaction, but also increasing the amount of trimers formed by the reaction of dimers with isobutene and the amount of tetramers formed by the reaction of trimers with isobutene, resulting in a decrease in the selectivity of dimers. Seriously, it will cause the final boiling point temperature of the oligomer to exceed the maximum final boiling point temperature of 205°C required by the vehicle gasoline standard (GB 17930-2016); ② Under the same scale and the same raw materials, more catalysts are used than other reactors, and the catalyst utilization rate is low; in addition, although catalytic distillation can directly use the isobutene oligomerization reaction heat for the separation process, there are also the following problems: the structure of the catalytic distillation column is complex, the price of the catalytic distillation module is high; it is difficult to load and unload the catalyst; when the height of the catalytic distillation column exceeds 70m due to the loading of the catalyst, in order to reduce the wind load, it is generally divided into an upper tower and a lower tower, resulting in an increase in equipment investment and floor area, etc. Summary of the Invention

[0004] The purpose of this application is to provide a method and system for isobutene oligomerization with self-circulation heat removal of raw materials, to solve the technical problem of generating a large number of side reaction products when dealing with the reaction heat generated by isobutene oligomerization in the prior art.

[0005] To solve the above technical problem, an embodiment of the present invention provides a method for isobutene oligomerization with self-circulation heat removal of raw materials, including the following steps:

[0006] Shunt the C4 raw material to obtain a reaction raw material and a recycled raw material;

[0007] Mix the reaction raw material with tert-butanol to obtain a premixed raw material;

[0008] Heat the premixed raw material to a first temperature and perform a first oligomerization reaction to obtain a first oligomer;

[0009] Use the recycled raw material to absorb the reaction heat of the first oligomerization reaction so that the final reaction temperature of the first oligomerization reaction is a second temperature;

[0010] The recycled feedstock that absorbs the reaction heat of the first polymerization reaction is evaporated at a third temperature, then condensed to the bubble point temperature, and mixed with the premixed feedstock;

[0011] Wherein:

[0012] The first temperature is 55 - 75 °C;

[0013] The second temperature is 60 - 95 °C;

[0014] The third temperature is 44 - 79 °C;

[0015] The bubble point temperature is 39 - 74 °C.

[0016] Optionally, in the step of using the recycled feedstock to absorb the reaction heat of the first polymerization reaction,

[0017] The initial pressure of the recycled feedstock is controlled to be 1.0 - 2.1 MPa;

[0018] The final pressure of the recycled feedstock is controlled to be 0.6 - 0.9 MPa.

[0019] Optionally, the following steps are further included:

[0020] The first polymer is fractionated to obtain light components, azeotrope and polymerized oil;

[0021] The light components are condensed to a fourth temperature to obtain condensate;

[0022] The condensate is pressurized and split to obtain reflux C4, product C4 and recycled C4;

[0023] The recycled C4 is heated to a fifth temperature and undergoes a second polymerization reaction to obtain a second polymer;

[0024] The second polymer is used as the feed for the fractionation;

[0025] Wherein:

[0026] The fourth temperature is 40 - 55 °C;

[0027] The fifth temperature is 45 - 65 °C;

[0028] The mass percentage of isobutene in the recycled C4 is ≤ 20%;

[0029] The components of the azeotrope include 65 - 80% mole fraction of tert-butanol.

[0030] Optionally, the mass flow ratio of the reaction feedstock to the recycled feedstock is (2 - 10):1.

[0031] Optionally, the mass flow ratio of the reflux C4, the recycled C4, and the product C4 is (0.5 - 2.5) : (1.0 - 3.0) : 1.

[0032] Optionally, the following steps are further included:

[0033] Shunt the azeotrope to obtain a first azeotrope and a second azeotrope;

[0034] Mix the first azeotrope with the premixed raw materials;

[0035] Mix the second azeotrope with the recycled C4 heated to the fifth temperature.

[0036] Optionally, the molar ratio of tert-butanol in the first azeotrope to isobutene in the reaction raw materials is (0.05 - 0.10) : 1, and the molar ratio of tert-butanol in the second azeotrope to isobutene in the recycled C4 is (0.05 - 0.10) : 1.

[0037] Optionally, the reaction pressures of the first oligomerization reaction and the second oligomerization reaction are both 0.9 - 2.0 MPa, and the liquid hourly space velocities of the first oligomerization reaction and the second oligomerization reaction are both 0.5 - 5 h -1 .

[0038] Based on the same inventive concept, an embodiment of the present invention further provides an isobutene oligomerization system with self-circulating heat extraction of raw materials applicable to any one of the above methods, including a mixer, a first heater, a first oligomerization reactor, a first condenser, and a fractionating tower; the first oligomerization reactor is provided with a reaction inlet, a reaction outlet, a heat exchange inlet, and a heat exchange outlet; the source of the C4 raw material is connected to the mixer through a first shunt pipe, the outlet of the mixer is connected to the reaction inlet through a first heater, and the reaction outlet is connected to the inlet of the fractionating tower; the source of the C4 raw material is connected to the heat exchange inlet through a second shunt pipe, the heat exchange outlet is connected to the mixer through a first circulation pipe, and the first condenser is arranged on the first circulation pipe; the source of tert-butanol is connected to the mixer.

[0039] Optionally, it further includes a second oligomerization reactor, a second condenser, and a second heater; the fractionating tower is provided with a top outlet, a side outlet, and a bottom outlet; the top outlet is connected to the inlet of the second oligomerization reactor through a second condenser and a second heater, and the outlet of the second oligomerization reactor is connected to the fractionating tower; the side outlet is connected to the mixer through a second circulation pipe; the side outlet is connected to the inlet of the second oligomerization reactor through a third circulation pipe.

[0040] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0041] A method for isobutene oligomerization with self-circulating heat extraction of raw materials provided by an embodiment of the present invention includes the following steps: splitting a C4 raw material to obtain a reaction raw material and a circulating raw material; mixing the reaction raw material with tert-butanol to obtain a premixed raw material; heating the premixed raw material to a first temperature and subjecting it to a first oligomerization reaction to obtain a first oligomer; using the circulating raw material to absorb the reaction heat of the first oligomerization reaction so that the final reaction temperature of the first oligomerization reaction is a second temperature; evaporating the circulating raw material that has absorbed the reaction heat of the first oligomerization reaction at a third temperature, then condensing it to the bubble point temperature, and mixing it with the premixed raw material; wherein: the first temperature is 55-75 °C; the second temperature is 60-95 °C; the third temperature is 44-79 °C; the bubble point temperature is 39-74 °C. This method splits the C4 raw material into a reaction raw material and a circulating raw material, uses the reaction raw material to carry out the oligomerization reaction first, and reaction heat is released during the oligomerization process. At the same time, the circulating raw material is used to absorb the reaction heat. Specifically, the reaction heat is absorbed by the evaporation and gasification of the circulating raw material. Since the gasification temperature of the circulating raw material is lower than the reaction temperature of the reaction raw material, the circulating raw material can quickly evaporate and absorb heat, so that the final reaction temperature of the first oligomerization reaction can be effectively maintained at an appropriate second temperature. The circulating raw material after absorbing heat is evaporated at the third temperature and then condensed to the bubble point temperature, and is mixed with the newly introduced premixed raw material as a raw material. On the one hand, since the reaction raw material and the circulating raw material are of the same origin, and the heat absorption and condensation processes are both non-chemical changes, no unnecessary other reactants will be introduced, completely avoiding the generation of side reaction products. On the other hand, the circulating raw material as a saturated liquid has a relatively high bubble point temperature, which can preheat the newly introduced reaction raw material, thereby reducing the heat consumed for heating to the first temperature and effectively utilizing the reaction heat. Relying on the boiling heat transfer rate of the C4 raw material, which is much higher than that of cooling media such as circulating water, the reaction heat can be quickly removed, and the reaction temperature rise can be more effectively controlled to ensure that the first oligomerization reaction proceeds under stable conditions.

[0042] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly, it can be implemented according to the content of the description. And in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention are specifically given below. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0044] Figure 1 It is a flowchart of a method for isobutene oligomerization with self-circulating heat extraction of raw materials provided by an embodiment of the present invention;

[0045] Figure 2 It is a schematic diagram of an isobutene oligomerization system with self-circulating heat extraction from raw materials provided by an embodiment of the present invention.

[0046] Reference numerals:

[0047] 10 - mixer; 11 - first heater; 12 - first oligomerization reactor; 121 - reaction inlet; 122 - reaction outlet; 123 - heat exchange inlet; 124 - heat exchange outlet; 13 - first condenser; 14 - fractionating tower; 15 - second oligomerization reactor; 16 - second condenser; 17 - second heater; 20 - first shunt pipe; 21 - second shunt pipe; 22 - first circulation pipe; 23 - second circulation pipe; 24 - third circulation pipe. Detailed implementation manners

[0048] The following will specifically elaborate on the present invention in combination with the detailed implementation manners and embodiments, and the advantages and various effects of the present invention will be presented more clearly therefrom. Those skilled in the art should understand that these detailed implementation manners and embodiments are used to illustrate the present invention rather than limit the present invention.

[0049] Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as having the meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as the general understanding of those skilled in the art to which the present invention pertains. In case of contradiction, this specification shall prevail. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. For example, room temperature may refer to the temperature within the range of 10 - 35 °C.

[0050] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0051] The technical solution of the embodiment of the present application is to solve the above technical problems, and the general idea is as follows:

[0052] First of all, it should be noted that the C4 raw materials mentioned in the present invention specifically refer to: FCC by - product C4 fraction and ethylene steam cracking C4 fraction. Among them, the mass percentage of isobutene in the FCC by - product C4 fraction is 10 - 25%, and the content of isobutene in the ethylene steam cracking C4 fraction is 15 - 45%; in addition, the products of isobutane dehydrogenation and the by - product C4 components in the co - oxidation method for producing propylene oxide using isobutane and propylene as raw materials can also be used as C4 raw materials.

[0053] According to a typical embodiment of the present invention, an isobutene oligomerization method with self - circulating heat extraction from raw materials is provided, including the following steps:

[0054] S1. Split the C4 raw material to obtain a reaction raw material and a recycled raw material;

[0055] S2. Mix the reaction raw material with tert-butanol to obtain a premixed raw material;

[0056] S3. Heat the premixed raw material to a first temperature and carry out a first oligomerization reaction to obtain a first oligomer;

[0057] S4. Use the recycled raw material to absorb the reaction heat of the first oligomerization reaction so that the final reaction temperature of the first oligomerization reaction is a second temperature;

[0058] S5. Evaporate the recycled raw material that has absorbed the reaction heat of the first oligomerization reaction at a third temperature, then condense it to the bubble point temperature, and mix it with the premixed raw material;

[0059] Wherein: the first temperature is 55 - 75 °C; the second temperature is 60 - 95 °C; the third temperature is 44 - 79 °C; the bubble point temperature is 39 - 74 °C.

[0060] The mechanism of catalyst deactivation caused by the reactor temperature rise is as follows: The standard reaction heat of isobutene dimerization to form isooctene is -82.8 kJ / mol, which is more than twice the standard reaction heat of -39.7 kJ / mol for the etherification reaction of isobutene with methanol to form MTBE. Therefore, the isobutene oligomerization reaction is more likely to cause the catalyst bed temperature to exceed the limit due to the stronger reaction heat release, resulting in high-temperature deactivation of the catalyst. In the oligomerization reaction, the relationship between the reaction heat and the reactor temperature rise with the change of the isobutene mass fraction in the raw material is shown in Table 1.

[0061] Table 1 Relationship between reaction heat and reactor temperature rise with the change of isobutene mass fraction in the raw material

[0062]

[0063] As can be seen from Table 1, as the isobutene content in the mixed C4 raw material continuously increases, the reaction heat and the temperature rise of the reactor increase correspondingly. When the mass fractions of isobutene in the feed are 20%, 25%, 30%, and 40% respectively, the temperature rises of the reactor are 44.11°C, 54.62°C, 64.93°C, and 76.88°C respectively, and the outlet temperatures of the reactor are 99.11°C, 109.62°C, 119.93°C, and 131.88°C respectively. Since the acidic cation exchange resin catalyst commonly used in the oligomerization reaction is severely deactivated due to the breaking of the polymerization chain when the temperature exceeds 120°C, the maximum heat-resistant temperature of acidic cation exchange resin catalysts such as D-005, D-006, QRE-01 and their equivalent oligomerization catalysts is 120°C. The above 109.62°C is close to the maximum heat-resistant temperature of the catalyst and is the limit temperature at which the reactor can operate without taking any cooling measures. 119.93°C has reached the maximum heat-resistant temperature of the catalyst, and operating at this temperature will cause the catalyst to quickly deactivate. 131.88°C has exceeded the maximum heat-resistant temperature of the catalyst and 15.84% of the liquid reaction material has vaporized at this time. In addition, too high a reactor temperature will also lead to an increase in by-products such as trimers and tetramers in the oligomerization oil product.

[0064] The oligomerization method provided by the present invention uses part of the raw material as the heat-taking medium for the oligomerization reaction. Specifically, through steps S1-S3, the C4 raw material is split into reaction raw material and recycled raw material. The reaction raw material is first used for the oligomerization reaction, and reaction heat is released during the oligomerization process. At the same time, through step S4, the recycled raw material is used to absorb the reaction heat. Specifically, the reaction heat is absorbed by the evaporation and gasification of the recycled raw material. Since the gasification temperature of the recycled raw material is lower than the reaction temperature of the reaction raw material, the recycled raw material can quickly evaporate and absorb heat, so that the final reaction temperature of the first oligomerization reaction can be effectively maintained at an appropriate second temperature. Through step S5, the recycled raw material after absorbing heat is evaporated at a third temperature and then condensed to the bubble point temperature, and is mixed with the newly introduced premixed raw material as raw material. On the one hand, since the reaction raw material and the recycled raw material are of the same source, and the heat absorption and condensation processes are both non-chemical changes, no unnecessary other reactants will be introduced, and the generation of side reaction products is completely avoided. On the other hand, the recycled raw material as a saturated liquid has a relatively high bubble point temperature, which can preheat the newly introduced reaction raw material, thereby reducing the heat consumed for heating to the first temperature and effectively utilizing the reaction heat. Relying on the boiling heat transfer rate of the C4 raw material, which is much higher than that of cooling media such as circulating water, the reaction heat can be quickly removed, and the reaction temperature rise can be controlled more effectively to ensure that the first oligomerization reaction proceeds under stable conditions.

[0065] It should be noted that the above gasification expansion heat absorption is boiling heat transfer, and the boiling heat transfer coefficient and heat transfer rate are much higher than those of conventional methods such as using circulating water for cooling, which can effectively control the temperature rise of the oligomerization reaction in the tube side and ensure that the oligomerization reaction operates at a stable operating temperature.

[0066] The reason for controlling the first temperature (the temperature after heating) at 55 - 75°C in step S3 is as follows: within this temperature range, the reaction rate of isobutene under the action of the cation exchange resin catalyst is moderate, the selectivity of the target product dimer is high, and the side reaction products such as trimers and tetramers are few, which is conducive to improving the product quality. At the initial stage of the plant startup, the catalyst activity is relatively high, and the reaction is controlled at a lower initial temperature; at the end stage of the plant startup, the catalyst activity is relatively low, and the reaction is controlled at a higher initial temperature.

[0067] The reason for controlling the second temperature (the final reaction temperature of the first oligomerization reaction) at 60 - 95°C in step S4 is as follows: within this temperature range, the over-temperature of the catalyst bed layer caused by the isobutene oligomerization reaction is 5 - 40°C. Within this temperature rise range, it is possible to avoid catalyst deactivation caused by over-temperature of the catalyst bed layer and shedding of the sulfonic acid groups of the catalyst, and there are few side reactions, which is conducive to extending the catalyst life and maintaining a high product quality.

[0068] The reason for controlling the third temperature (the evaporation temperature of the recycled C4) at 44 - 79°C in step S5 is as follows: it can ensure that the difference between the reaction temperature of the first oligomerization reaction and the vaporization temperature of the recycled C4 is ≥15°C, so that heat transfer can proceed smoothly.

[0069] The reason for adding tert-butanol in step S2 is as follows: under the action of acidic catalysts such as sulfonic acid type cation exchange resin, the oligomerization reaction between isobutenes occurs and the reaction rate is relatively fast. If the reaction is not controlled, a large number of side reaction products such as trimers (TIB) and tetramers (TEB) will be generated. To avoid a decrease or unqualified product quality caused by too high content of these polymers, certain measures must be taken to reduce the generation amount of polymers during the oligomerization reaction. And tert-butanol, as a polar component, can effectively reduce the generation of polymers. Therefore, the present invention uses tert-butanol as an inhibitor for the oligomerization reaction. It is easily adsorbed on the active center of the catalyst and reacts with the sulfonic acid group as follows:

[0070]

[0071] Since the acidity of SO3 - MeOH2 + is weaker than that of H + it reduces the activity of the resin catalyst and the polymerization reaction rate, which is conducive to inhibiting the formation of trimers and tetramers. The main advantages of using tert-butanol as an inhibitor include: (1) the oligomerized oil produced by the reaction does not contain oxides such as ethers and can be used as a blending component oil for vehicle ethanol gasoline; (2) the amount of inhibitor used is small, and when the molar ratio of tert-butanol to isobutene in the C4 raw material is (0.05 - 0.10):1, it can meet the requirements of conversion rate and selectivity.

[0072] It should be noted that tert-butanol can be fed continuously or intermittently to make up for the loss of tert-butanol discharged by the product obtained in the subsequent process.

[0073] As an optional embodiment, the use of the circulating raw material to absorb the reaction heat of the first superposition reaction,

[0074] Controlling the initial pressure of the circulating raw material to be 1.0-2.1 MPa;

[0075] The terminal pressure of the circulating raw material is controlled to be 0.6-0.9 MPa.

[0076] The mechanism for controlling the above pressure range is: using the SRK physical property model of Aspen Plus, a large-scale chemical process simulation software, the bubble point temperatures of isobutane, isobutylene, 1-butene, n-butane, trans-2-butene, and cis-2-butene under different operating pressures are simulated and calculated, and the results are shown in Table 2. As can be seen from Table 2, when the operating pressure is 0.6MPa, the bubble point temperature of isobutane among the C4 components is the lowest, which is 44.36°C; when the operating pressure is 0.9MPa, the bubble point temperature of cis-2-butene among the C4 components is the highest, which is 78.05°C. It can be seen that when the shell side operating pressure of the first superposition reactor is set in the range of 0.6-0.9MPa, the corresponding bubble point temperature range of the C4 raw material is 44.36-78.05℃, and the superposition reaction temperature in the tube side is 60-95℃. Therefore, setting the second temperature to 60-95℃ and the third temperature to 44-79℃ can ensure that the difference between the reaction temperature of the first superposition reaction and the vaporization temperature of the circulating C4 is ≥15℃, so that the heat transfer can proceed smoothly.

[0077] Table 2 Bubble point temperature of each C4 component under different operating pressures

[0078]

[0079] As an optional implementation, the method further includes the following steps:

[0080] S6, fractionating the first stack to obtain a light component, an azeotrope and a stack oil;

[0081] S7, condensing the light component to a fourth temperature to obtain a condensate;

[0082] S8, pressurizing and splitting the condensate to obtain reflux C4, product C4 and circulating C4;

[0083] S9, heating the cyclic C4 to a fifth temperature and performing a second polymerization reaction to obtain a second polymerization product;

[0084] S10, using the second stack as feed for the fractionation;

[0085] Wherein: the fourth temperature is 40 - 55 °C; the fifth temperature is 45 - 65 °C;

[0086] The mass percentage of isobutene in the recycled C4 is ≤ 20%;

[0087] The components of the azeotrope include 65 - 80% mole fraction of tert-butanol.

[0088] Through step S6, the first polymer obtained in step S3 is fractionated into light components, an azeotrope, and polymerized oil. Further, through steps S7 - S8, the light components are split into reflux C4, product C4, and recycled C4. Among them, the product C4 is discharged as a product, the reflux C4 is returned to the fractionating tower for mass transfer and heat transfer of the internal medium, and the recycled C4 undergoes a second polymerization reaction through step S9 to obtain a second polymer. Then, through step S10, the second polymer is used as the feed for fractionation in the same way as the first polymer for fractionation.

[0089] The significance of carrying out the second polymerization reaction is as follows: After the first polymerization reaction, the conversion rate of isobutene is generally between 75 - 90%. To increase the total conversion rate of isobutene, the recycled C4 is introduced into the second polymerization reaction to enable the isobutene therein to further undergo a polymerization reaction, so as to further increase the total conversion rate of isobutene to 90 - 99%. In addition, there are no heavy components such as dimers in the recycled C4, and the content of side reaction products such as trimers and tetramers in the polymer obtained by the second polymerization reaction is small, which is beneficial to improving the product quality.

[0090] The reason for controlling the fourth temperature (condensation temperature) at 40 - 55 °C in step S7 is that: using a conventional circulating water condenser or air cooler can condense the light components to this temperature, which is beneficial to reducing the operating cost.

[0091] The reason for controlling the fifth temperature (heating temperature) at 45 - 65 °C in step S9 is that: this temperature is the initial temperature of the second polymerization reaction. After the first polymerization reaction, the mass fraction of isobutene in the recycled C4 is less than or equal to 20%. Since the mass fraction of isobutene in the feed of the second polymerization reaction is relatively low, the reaction temperature rise is not greater than 25 °C. Without measures such as external circulation to reduce the reactor temperature rise, the outlet temperature of the second polymerization reaction is not greater than 90 °C. At this outlet temperature, the content of side reaction products such as trimers and tetramers is small, and the product quality is high. In the initial stage of plant startup, the catalyst activity is relatively high, and the reaction is controlled at a lower initial temperature; in the final stage of plant startup, the catalyst activity is relatively low, and the reaction is controlled at a higher initial temperature.

[0092] It should be noted that during the fractionation process, tert-butanol forms an azeotrope with the oligomerization oil. The azeotropic composition, azeotropic temperature of the azeotrope formed by tert-butanol and the oligomerization oil (represented by 2,4,4-trimethylpentene) under different operating pressures, as well as the boiling points of diisobutene, isobutene, and n-butane, were calculated. The results are shown in Table 3.

[0093] Table 3 Azeotropic Composition and Component Boiling Points of the Azeotrope of Tert-Butanol and Diisobutene under Different Pressures

[0094]

[0095] As can be seen from Table 3, the composition of the azeotrope formed by tert-butanol and the oligomerization oil is different under different pressures. Among them, the components of the azeotrope include 65 - 80% mole fraction of tert-butanol. At the same pressure, the azeotropic temperature of the azeotrope is lower than the bubble point temperature of the oligomerization oil but higher than the bubble point temperature of the light components. Therefore, the azeotrope can be obtained by fractionation, and the mole fraction of tert-butanol in this azeotrope is as high as 65 - 80%. It can be refluxed as a cycle inhibitor, and the molar ratio of the components other than tert-butanol in it to isobutene in the C4 raw material < 0.04:1. Therefore, when used as an inhibitor, it hardly affects the oligomerization reaction. It supplements the inhibitor (tert-butanol) for the first oligomerization reaction as a cycle inhibitor, thereby effectively reducing the input amount of tert-butanol, improving the utilization rate of tert-butanol, and reducing production costs.

[0096] As an alternative embodiment, the mass flow ratio of the reaction raw material to the recycle raw material is (2 - 10):1.

[0097] The reason for controlling the above ratio range is that the latent heat of vaporization per unit mass of the C4 raw material is much higher than the sensible heat required per unit mass and per unit temperature rise. For example, for a C4 raw material with a temperature of 55.0 °C, a pressure of 1.7 MPa, a flow rate of 5000.0 kg / h, and an isobutene mass fraction of 21.01% undergoing the first oligomerization reaction, if the isobutene conversion rate is 95% and the reactor outlet temperature is controlled at 80.0 °C, the reaction heat to be removed is 83.43 kW, which only requires 525.6 kg / h of the C4 raw material with the same components and a pressure of 0.75 MPa to vaporize to absorb this reaction heat; setting the mass flow ratio of the reaction raw material to the recycle raw material to (2 - 10):1 enables the recycle raw material to be discharged in a gas-liquid two-phase state, ensuring heat transfer of the recycle raw material in a bubble point boiling state, which is conducive to better controlling the reaction temperature rise of the reaction raw material.

[0098] As an alternative embodiment, the mass flow ratio of the reflux C4, the recycle raw material, and the product C4 is (0.5 - 2.5):(1.0 - 3.0):1.

[0099] The reason for controlling the above ratio range is as follows: The reason for setting the mass flow ratio of the reflux C4 to the product C4 to (0.5 - 2.5):1 is that the reflux C4 returns to the fractionating tower for mass transfer and heat transfer of the medium in the tower. When this ratio is too low, the product quality is not easily qualified or too many trays are required to obtain the required product purity; when this ratio is too high, the energy consumption of the device will increase. The reason for setting the mass flow ratio of the recycle feedstock to the product C4 to (1.0 - 3.0):1 is that when this ratio is too small, the isobutene conversion rate is not easily satisfied; when this ratio is too high, the energy consumption of the device will also increase.

[0100] As an alternative embodiment, the following steps are further included:

[0101] S11: Split the azeotrope to obtain a first azeotrope and a second azeotrope;

[0102] S12: Mix the first azeotrope with the premixed feedstock;

[0103] S13: Mix the second azeotrope with the recycle feedstock heated to the fifth temperature.

[0104] As can be seen from the above, the azeotrope contains a high content of tert-butanol, which can be used as an inhibitor to inhibit the formation of polymerization by-products. Therefore, through steps S11 - S13, the azeotrope is split into a first azeotrope and a second azeotrope, and the first azeotrope and the second azeotrope are used as inhibitors for the first polymerization reaction and the second polymerization reaction respectively.

[0105] As an alternative embodiment, the components of the azeotrope include 65 - 80% of tert-butanol in terms of mole fraction.

[0106] As an alternative embodiment, the molar ratio of tert-butanol in the first azeotrope to isobutene in the reaction feedstock is (0.05 - 0.10):1, and the molar ratio of tert-butanol in the second azeotrope to isobutene in the recycle feedstock is (0.05 - 0.10):1.

[0107] The reason for controlling the above ratio range is as follows: When the dosage of the recycle inhibitor is too low, the formation amounts of trimers and tetramers cannot be effectively reduced. When the dosage of the recycle inhibitor is too high, not only will the energy consumption for separation increase, but also a large amount of inhibitor will enter the bottom of the fractionating tower, and a qualified polymerization oil product cannot be obtained at the bottom.

[0108] As an alternative embodiment, the reaction pressures of both the first polymerization reaction and the second polymerization reaction are 0.9 - 2.0 MPa, and the liquid hourly space velocities of both the first polymerization reaction and the second polymerization reaction are 0.5 - 5 h -1 。

[0109] The reason for controlling the above numerical range is as follows: The isobutene oligomerization reaction is a liquid-phase reaction carried out under the action of a catalyst. Within this pressure range, it can ensure that the first oligomerization reaction and the second oligomerization reaction proceed in the liquid phase;

[0110] The reason for controlling the above liquid hourly space velocity range is as follows: When the liquid hourly space velocity is too high, the amount of catalyst used is small, the reaction is incomplete, and the catalyst in the reactor needs to be frequently replaced due to catalyst deactivation; when the liquid hourly space velocity is too low, the amount of catalyst used is large, resulting in an increase in side reactions and the largest reactor size.

[0111] Please refer to Figure 2 , according to another typical embodiment of the present invention, there is provided an isobutene oligomerization system with self-circulation heat extraction of raw materials applicable to any one of the above methods, including a mixer 10, a first heater 11, a first oligomerization reactor 12, a first condenser 13 and a fractionating tower 14; the first oligomerization reactor 12 is provided with a reaction inlet 121, a reaction outlet 122, a heat exchange inlet 123 and a heat exchange outlet 124; the source of the C4 raw material is connected to the mixer 10 through a first shunt pipe 20, the outlet of the mixer 10 is connected to the reaction inlet 121 through the first heater 11, and the reaction outlet 122 is connected to the inlet of the fractionating tower 14; the source of the C4 raw material is connected to the heat exchange inlet 123 through a second shunt pipe 21, the heat exchange outlet 124 is connected to the mixer 10 through a first circulation pipe 22, and the first condenser 13 is arranged on the first circulation pipe 22; the source of tert-butanol is connected to the mixer 10.

[0112] By providing a mixer 10, it is used to prepare a premixed raw material in step S2. By providing a first heater 11, it is used to heat the premixed raw material to a first temperature. By providing a first oligomerization reactor 12, it is used to carry out the first oligomerization reaction. By providing a first condenser 13, it is used to condense the recycled raw material to the bubble point temperature. By providing a fractionating tower 14, it is used to fractionate the first oligomer and the subsequent second oligomer.

[0113] By providing a first shunt pipe 20 and a second shunt pipe 21, the C4 raw material is respectively shunted into reaction raw material and recycled raw material.

[0114] By providing a first circulation pipe 22, the heat-absorbed recycled raw material is circulated into the mixer 10 to be mixed with the premixed raw material.

[0115] It should be noted that in this embodiment, the first superposition reactor 12 is any one of the existing tubular reactors. The advantages of using this type of reactor are as follows: (1) Compared with the external circulation type reactor, less catalyst is used; (2) Under the action of the rising fluid, the catalyst particles in the tubes have irregular self-rotation and slight disturbance, and the pressure drop of the whole bed is small; (3) The temperature distribution of the whole reactor is relatively uniform, and the catalyst bed can be controlled to operate within a more suitable temperature range, which is beneficial to inhibiting the formation of trimers and tetramers. Under optimized operating conditions, the mass fractions of the generated trimers and tetramers are not greater than 10% and 0.1% respectively.

[0116] It should be noted that the structure of the first superposition reactor 12 is in the form of a shell covering the tube body. The tube body is used for carrying out the first superposition reaction, and the shell is used for introducing the circulating raw materials. The shell and the tube body are not connected, but heat exchange can be carried out.

[0117] As an alternative embodiment, it further includes a second superposition reactor 15, a second condenser 16 and a second heater 17; the fractionating tower 14 is provided with a top outlet, a side outlet and a bottom outlet; the top outlet is connected to the inlet of the second superposition reactor 15 through the second condenser 16 and the second heater 17, and the outlet of the second superposition reactor 15 is connected to the fractionating tower 14; the side outlet is connected to the mixer 10 through the second circulation pipe 23; the side outlet is connected to the inlet of the second superposition reactor 15 through the third circulation pipe 24.

[0118] By providing the second superposition reactor 15 for carrying out the second superposition reaction, by providing the second condenser 16 for condensing the light components to the fourth temperature, and by providing the second heater 17 for heating the circulating C4 to the fifth temperature.

[0119] By providing the second circulation pipe 23, the first azeotrope is mixed with the premixed raw materials.

[0120] By providing the third circulation pipe 24, the second azeotrope is mixed with the circulating raw materials.

[0121] In summary, in this application, the C4 raw materials are first divided into reaction raw materials and circulating raw materials; the reaction raw materials are mixed with tert-butanol and other substances and then enter the tube side of the first superposition reactor for the superposition reaction, and the reaction heat is absorbed by the vaporization of the circulating raw materials entering the shell side of the first superposition reactor; the vaporized shell side C4 is then condensed, pressurized and returned to the inlet of the first superposition reactor; the reaction products generated by the reaction of the reaction raw materials on the tube side enter the fractionating tower. The remaining C4 at the top of the fractionating tower is divided into three parts, which are used as reflux, product and feed for the second superposition reactor respectively; the tert-butanol azeotrope drawn from the side line is divided into two parts, which are used as inhibitors for the first and second superposition reactions respectively; the products of the first and second superposition reactions share the fractionating tower. Compared with the conventional process, this process has the following characteristics:

[0122] (1) Using part of the C4 raw material as the heat removal medium for the oligomerization reaction can more effectively control the temperature rise of the oligomerization reactor, reduce the production of trimers and tetramers, and improve the utilization rate of the oligomerization reaction catalyst;

[0123] (2) Withdrawing the inhibitor from the side stream of the fractionation tower and recycling it can eliminate one azeotropic tower;

[0124] (3) Using two-stage reaction to replace catalytic distillation and sharing the fractionation tower for the reaction products reduces the equipment cost and no longer uses expensive catalyst modules, reducing the overall catalyst cost by more than 50%. The optimized process features flexible operation, low equipment and operation costs, and high product quality.

[0125] The present application will be described in detail below in conjunction with examples, comparative examples and experimental data.

[0126] Example 1

[0127] This example provides a method for isobutene oligomerization with self-circulating heat removal of raw materials, including the following steps:

[0128] S1. The C4 raw material with a temperature of 30°C, a pressure of 1.6 MPa, a flow rate of 5000 kg / h, and an isobutene mole fraction of 25.45% is split into reaction raw materials and recycled raw materials.

[0129] Among them: the flow rate of the reaction raw materials is 4000 kg / h, and the flow rate of the recycled raw materials is 1000 kg / h.

[0130] S2. Mix the reaction raw materials with tert-butanol to obtain premixed raw materials.

[0131] S3. Heat the premixed raw materials to 60°C and conduct the first oligomerization reaction to obtain the first oligomer.

[0132] Among them: the initial pressure of the recycled raw materials entering the reaction zone of the first oligomerization reactor 12 is 1.5 MPa; the pressure of the recycled raw materials entering the heat exchange zone of the first oligomerization reactor 12 is 0.7 MPa.

[0133] S4. Use the recycled raw materials to absorb the reaction heat of the first oligomerization reaction so that the final reaction temperature of the first oligomerization reaction (i.e., the outlet temperature of the reaction zone of the first oligomerization reactor 12) is 80°C.

[0134] S5. Evaporate the recycled raw materials that have absorbed the reaction heat of the first oligomerization reaction at 63.7°C, then condense them to the bubble point temperature and boost the pressure to 1.5 MPa, and mix them with the premixed raw materials.

[0135] S6. Fractionate the first stack to obtain a light component, an azeotrope and a stack oil.

[0136] Among them: the mass flow rate of the azeotrope is 265.8 kg / h, the mass fraction of tert-butyl alcohol is 0.6836, and the mass fraction of the superposition oil is 0.3164.

[0137] S7. Condensing the light component to 45° C. to obtain a condensate.

[0138] S8. The condensate is pressurized and split to obtain reflux C4, product C4 and circulating C4.

[0139] Wherein: the mass percentage of isobutylene in the circulating C4 is ≤20%.

[0140] S9, heating the circulating C4 to 45°C and subjecting it to a second polymerization reaction to obtain a second polymerization product.

[0141] S10, using the second stack as feed for the fractionation.

[0142] S11, splitting the azeotrope to obtain a first azeotrope and a second azeotrope.

[0143] Wherein: the mass flow rate of the first azeotrope is 216.9 kg / h, and the mass flow rate of the second azeotrope is 48.9 kg / h.

[0144] S12, mixing the first azeotrope with the premixed raw material.

[0145] S13, mixing the second azeotrope with the circulating feedstock heated to the fifth temperature.

[0146] The data of feed and discharge are shown in Table 4, and the reaction parameters of each device are shown in Table 5.

[0147] Table 4 Data of feeding and discharging in Example 1

[0148]

[0149] Table 5 Reaction parameters of each device in Example 1

[0150]

[0151]

[0152] In summary, in this embodiment, the conversion rate of isobutene is 98.2%, and the yield of diisobutene product is 91.0%. There are few by-products in the product C4, effectively solving the technical problem of a large number of side reaction products generated when the prior art treats the reaction heat generated by isobutene oligomerization. Moreover, the first oligomer and the second oligomer are fractionated in the same fractionating column, and the azeotrope is withdrawn from the side line of the fractionating column while realizing the recycling of the inhibitor, featuring high isooctene selectivity, simple process, flexible operation, low equipment and operation costs.

[0153] Finally, it should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0154] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they learn the basic creative concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0155] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for isobutene oligomerization with self-circulating heat extraction of raw materials, characterized in that, It includes the following steps: The C4 raw material is split to obtain reaction raw materials and recycled raw materials; The reaction raw materials and tert-butanol are mixed to obtain premixed raw materials; The premixed raw materials are heated to a first temperature and subjected to a first oligomerization reaction to obtain a first oligomer; The recycled raw materials are used to absorb the reaction heat of the first oligomerization reaction so that the final reaction temperature of the first oligomerization reaction is a second temperature; The recycled raw materials that have absorbed the reaction heat of the first oligomerization reaction are evaporated at a third temperature, then condensed to the bubble point temperature, and mixed with the premixed raw materials; Wherein: The first temperature is 55-75 °C; The second temperature is 60-95 °C; The third temperature is 44-79 °C; The bubble point temperature is 39-74 °C.

2. The method for isobutene oligomerization with self-circulating heat extraction of raw materials according to claim 1, characterized in that, In the step of using the recycled raw materials to absorb the reaction heat of the first oligomerization reaction, The initial pressure of the recycled raw materials is controlled to be 1.0-2.1 MPa; The final pressure of the recycled raw materials is controlled to be 0.6-0.9 MPa.

3. The method for isobutene oligomerization with self-circulating heat extraction of raw materials according to claim 1, characterized in that It further includes the following steps: The first oligomer is fractionated to obtain light components, an azeotrope, and oligomer oil; The light components are condensed to a fourth temperature to obtain condensate; The condensate is pressurized and split to obtain reflux C4, product C4, and recycled C4; The recycled C4 is heated to a fifth temperature and subjected to a second oligomerization reaction to obtain a second oligomer; The second oligomer is used as the feed for the fractionation; Wherein: The fourth temperature is 40-55 °C; The fifth temperature is 45-65 °C; The mass percentage of isobutene in the recycled C4 is ≤20%; The components of the azeotrope include 65-80% mole fraction of tert-butanol.

4. The method for isobutene oligomerization with self-circulating heat extraction of raw materials according to claim 3, characterized in that The mass flow ratio of the reaction raw materials to the recycled raw materials is (2-10):

1.

5. The method for isobutene oligomerization with self-circulating heat extraction of raw materials according to claim 3, characterized in that The mass flow ratio of the reflux C4, the recycled C4, and the product C4 is (0.5-2.5):(1.0-3.0):

1.

6. The method for isobutene oligomerization with self-circulating heat extraction of raw materials according to claim 3, characterized in that It further includes the following steps: The azeotrope is split to obtain a first azeotrope and a second azeotrope; The first azeotrope is mixed with the premixed raw materials; The second azeotrope is mixed with the recycled C4 heated to the fifth temperature.

7. The method for isobutene oligomerization with self-circulating heat extraction of raw materials according to claim 6, characterized in that The molar ratio of tert-butanol to isobutene in the reaction raw materials in the first azeotrope is (0.05-0.10):1, and the molar ratio of tert-butanol to isobutene in the recycled C4 in the second azeotrope is (0.05-0.10):

1.

8. The method for isobutene oligomerization with self-circulating heat extraction of raw materials according to claim 3, characterized in that The reaction pressures of the first oligomerization reaction and the second oligomerization reaction are both 0.9 - 2.0 MPa, and the liquid hourly space velocities of the first oligomerization reaction and the second oligomerization reaction are both 0.5 - 5 h -1 .

9. An isobutene oligomerization system with self-circulating heat extraction of raw materials applicable to the method described in any one of claims 1-8, characterized in that, It includes a mixer (10), a first heater (11), a first oligomerization reactor (12), a first condenser (13), and a fractionating tower (14); The first oligomerization reactor (12) is provided with a reaction inlet (121), a reaction outlet (122), a heat exchange inlet (123), and a heat exchange outlet (124); The source of the C4 raw material is connected to the mixer (10) through a first shunt pipe (20), the outlet of the mixer (10) is connected to the reaction inlet (121) through the first heater (11), and the reaction outlet (122) is connected to the inlet of the fractionating tower (14); The C4 raw material source is communicated with the heat exchange inlet (123) through the second shunt pipe (21), and the heat exchange outlet (124) is communicated with the mixer (10) through the first circulation pipe (22). The first condenser (13) is arranged on the first circulation pipe (22). The source of tert-butanol is communicated with the mixer (10).

10. The isobutene oligomerization system with self-circulating heat extraction of raw materials according to claim 9, wherein It further includes a second polymerization reactor (15), a second condenser (16) and a second heater (17). The fractionating tower (14) is provided with a top outlet, a side outlet and a bottom outlet. The top outlet is communicated with the inlet of the second polymerization reactor (15) through the second condenser (16) and the second heater (17), and the outlet of the second polymerization reactor (15) is communicated with the fractionating tower (14). The side outlet is communicated with the mixer (10) through the second circulation pipe (23). The side outlet is communicated with the inlet of the second polymerization reactor (15) through the third circulation pipe (24).

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