C4 light hydrocarbon pretreatment method

Abstract

The invention relates to a C4 light hydrocarbon pretreatment method, and belongs to the technical field of light hydrocarbon pretreatment. The problems that in the prior art, when catalytic C4 is processed and utilized, impurities, non-condensable steam and light hydrocarbon in hydrogenation products need to be treated independently, the process is long, and raw materials are poor in applicability are solved. The method comprises the following steps: firstly, removing heavy components in the mixed C4 by using a prefractionator, then carrying out selective hydrotreatment in a hydrogenation reactor to remove dialkene and alkyne, separating the hydrogenated material in a dehydrogenation tower, reacting residual hydrogen and C2 and C3 light hydrocarbons, and separating the residual hydrogen and C2 and C3 light hydrocarbons in the hydrogenation reactor. Oxygen-containing compounds such as dimethyl ether, methanol and water in the etherified C4 are extracted and separated from the tower top; and purified C4 materials which are free of hydrogen, low in light hydrocarbon and low in oxygen-containing compound residue are extracted from the tower bottom and are sent to a downstream device. The method not only can be used for removing dialkene and alkyne through hydrogenation, but also can be used for removing residual hydrogen and light hydrocarbon, can also be used for reducing the content of impurities in the raw materials, and has the characteristics of high operability, good raw material adaptability and optimized energy consumption.

Description

Technical Field

[0001] The present invention belongs to the technical field of light hydrocarbon pretreatment, and specifically relates to a method for pretreatment of C4 light hydrocarbons. The method is mainly applicable to the pretreatment process of C4 light hydrocarbon fractions produced by processes such as petrochemical refining catalytic cracking, steam cracking and coal chemical industry, and can also be applicable to the pretreatment process of C5 light hydrocarbon fractions. Background Art

[0002] C4 light hydrocarbons are important petrochemical resources. The main industrial sources are catalytic cracking units in refineries, steam cracking ethylene units, and coal chemical MTO units. Olefins in the fraction are important chemical raw materials and can produce a variety of chemical products. The C4 fraction mainly contains alkanes - isobutane and n-butane, and olefins - isobutylene, butene-1, trans-butene and cis-butene. These olefins can be used to produce a variety of chemical derivatives such as methyl tert-butyl ether, butyl rubber, polybutene, butadiene, methyl ethyl ketone, isooctane, etc. In addition, the material also contains a small amount of dienes and alkynes. Usually, C3 contains propadiene and propyne, C4 contains 1,3-butadiene and butyne, and C5 contains pentadiene. When used downstream, dienes and alkynes will not only polymerize to form colloids, but in severe cases, they will even affect the operation cycle of the unit. Therefore, before the light hydrocarbon raw materials enter the subsequent processing units, the dienes and alkynes in the raw materials must be removed. The catalytic C4 in the refinery is affected by crude oil, and C4 contains more sulfides. Although it has been treated by desulfurization and desulfurization devices, the material still contains a small amount of sulfides and residues of these treatment devices. These sulfides and residues are impurities of the hydrogenation catalyst. When accumulated to a certain extent, it will cause the catalyst to deactivate and affect the operation of the device. At the same time, the downstream process will have certain requirements for the non-C4 light hydrocarbon components in the material. For example, if the downstream device is MTBE, if the dissolved hydrogen content in C4 after hydrogenation is too high, it will cause phase separation of materials in the etherification reactor, resulting in bias flow. After the reaction, the materials enter the catalytic distillation tower, and too much non-condensable steam will cause the tower pressure of the catalytic distillation tower to be too high, which will affect the operation; some C4 formylation and other device processes have proposed process index requirements such as diene content <5ppm, hydrogen content <1ppm, and C3 content in C4 fraction <0.05%, while conventional designs usually have flash tanks to remove excess hydrogen, but the flash process cannot completely remove the dissolved hydrogen in the C4 material, and it has no effect on the content of light components such as C3, and excessive emissions will also cause increased losses of C4. Therefore, in order to solve the above problems, the design and development of light hydrocarbon hydrogenation pretreatment and other process flows have been re-conducted to meet various requirements.

[0003] Patent CN 105152840 A discloses a refining process for C4 hydrocarbon flow, and its preparation equipment includes a methanol removal tower, a first-stage hydrogenation reactor, a second-stage hydrogenation isomerization reactor, a depropanizer, a deethanizer and an adsorption tower. It is mainly aimed at the purification process of alkylation raw materials. Mixed C4 hydrocarbons are used as raw materials. First, methanol is extracted with water to remove methanol, so that the methanol content in C4 hydrocarbons is reduced to 50ppm, and then selective hydrogenation and isomerization are performed to make the butadiene content in C4 lower than 50ppm, and more than 70% of 1-butene is converted into 2-butene. Finally, dimethyl ether and C3 are removed by distillation to obtain refined C4 as alkylation raw materials, and the by-product refined C3 is used as propane dehydrogenation to produce propylene raw materials. This process is long and has high energy consumption. It is only applicable to the process of alkylation unit using etherified C4 as raw materials.

[0004] Patent CN107417500 A discloses a mixed C4 raw material pretreatment method, including: desulfurization, light removal, and heavy removal of the mixed C4 raw material; and hydrogenation isomerization reaction of the treated C4 raw material. However, the process flow is long and lacks specific process indicators.

[0005] Patent CN 110256209A discloses a method and device for pretreating C4 raw materials after etherification, including: dehydrating and deoxygenating the C4 raw materials after etherification; regenerating the dehydrating agent and deoxidizing agent. This method can remove impurities such as trace water, ethers, alcohols, etc. in C4 after etherification, and various indicators meet the limit requirements of the impurity content of raw materials in the n-butene isomerization unit and the selective hydrogenation unit. However, this process does not involve the separation of residual hydrogen and light hydrocarbons, and does not include hydrogenation reaction. The process is long, the regeneration process is cumbersome, and the energy consumption is high. It is only for the process of using C4 after etherification as raw materials.

[0006] Patent CN110407660A provides a pretreatment process for raw material C4, including the following steps: first, the raw material C4 is washed and dehydrated, then subjected to adsorption treatment, then subjected to hydrogenation operation, then light hydrocarbons and oxygen-containing compounds are removed, then subjected to comprehensive adsorption treatment, and dehydrated again to obtain the pretreated raw material C4. The method provides a comprehensive pretreatment process for raw material post-ether C4 for solid acid alkylation, which can effectively reduce and remove harmful impurities and meet the requirements of solid acid catalysts for raw material components. However, the process does not separate the remaining hydrogen and light hydrocarbons, has a long process, a cumbersome adsorbent regeneration process, and high energy consumption, and is only applicable to the treatment process of raw material post-ether C4 of solid acid alkylation units.

[0007] Patent CN 115253430A provides a pretreatment device in a carbon four production process, including a water washing tower, a first agglomerator, a dehydration dryer, an adsorber, a hydrogenation reactor, a raw material light removal tower, a comprehensive adsorber and a second agglomerator. Its essence is an improvement on the agglomerator and does not involve the separation of residual hydrogen and light hydrocarbons.

[0008] Patent CN116178093A discloses a method for optimizing the feed of alkyne hydrogenation, which changes the feed mode of the second-stage hydrogenation reactor, adds an external circulation process of the second-stage hydrogenation reactor, increases the mass space velocity of the second-stage hydrogenation reactor, and reduces the reaction of hydrogen and butene to form butane. This method greatly reduces the amount of hydrogen used and reduces the overall material loss. However, it does not involve the separation of light components such as hydrogen and non-condensable steam.

[0009] In summary, in the methods disclosed in the prior art, the treatment of light hydrocarbon C4 is only applicable to C4 after etherification, and oxygen-containing compounds such as alcohols and ethers in C4 after etherification are separated, and sulfides are treated. The methods adopted are water washing or adsorbent adsorption, and the residual hydrogen in the hydrogenation process and the light hydrocarbons in the raw materials are not treated. Moreover, the treatment process of the method is only for source materials for specific purposes, the process is relatively complicated, and the energy consumption is high. Summary of the invention

[0010] The present invention aims to solve the technical problems in the prior art that when catalytic carbon four is processed and utilized, there are high impurities in the raw materials, the hydrogenation catalyst is easy to deactivate, the impurities and non-condensable steam and light hydrocarbons in the hydrogenation product need to be treated separately, the process is long, and the applicability of the raw materials is poor. The present invention provides a method for obtaining purified carbon four by first performing precise fractionation, then performing selective hydrogenation, and then performing fractionation. The method can not only remove dienes and alkynes by hydrogenation, but also remove residual hydrogen and light hydrocarbons, and at the same time can reduce the impurity content in the raw materials, and has the characteristics of strong operability, good raw material adaptability, and optimized energy consumption.

[0011] The present invention adopts the following technical solutions to solve the above technical problems.

[0012] The present invention provides a method for pretreating C4 light hydrocarbons, the steps of which are as follows:

[0013] S1. The mixed C4 enters a pre-fractionation tower, the de-heavy C4 is obtained at the top of the tower, and the heavy component is obtained at the bottom of the tower;

[0014] S2. The de-heavy carbon tetrachloride enters the agglomerator to remove free water to obtain the de-heavy carbon tetrachloride after dehydration;

[0015] S3. The dehydrated deheaved carbon four is combined with the hydrogen in one path and enters a hydrogenation reactor to obtain hydrogenated carbon four;

[0016] Alternatively, the dehydrated deheavy C4 is combined with one path of hydrogen to enter a first-stage hydrogenation reactor, and the first-stage hydrogenated C4 is combined with another path of hydrogen to enter a second-stage hydrogenation reactor to obtain hydrogenated C4;

[0017] S4. After hydrogenation, C4 enters the dehydrogenation tower, and purified C4 is extracted from the bottom of the tower. Mixed light hydrocarbons are extracted from the top of the tower and sent to the condenser for condensation before entering the reflux tank. The gas and liquid are separated in the reflux tank, and the settled water is discharged from the bottom of the tank. Non-condensable steam is extracted from the top of the tank. Part of the liquefied C4 is refluxed to the top of the dehydrogenation tower, and the other part is transported to the product tank area.

[0018] Preferably, in step S1, the number of plates of the pre-fractionation tower is 35-102, and the working conditions of the pre-fractionation tower are: pressure 0.4-2.0 MPa, temperature 40-110° C., and reflux ratio 0.1-10.

[0019] Preferably, in step S3, one or both of the first-stage hydrogenation reactor and the second-stage hydrogenation reactor contain two upper and lower catalyst beds, and when the first-stage hydrogenation reactor contains two upper and lower catalyst beds, one path of the hydrogen is connected to the middle of the first-stage hydrogenation reactor, and when the second-stage hydrogenation reactor contains two upper and lower catalyst beds, one path of the hydrogen is connected to the middle of the second-stage hydrogenation reactor.

[0020] Preferably, in step S3, the reaction conditions of the first stage hydrogenation reactor and the second stage hydrogenation reactor are: pressure 1.5-2.5 MPa, temperature 40-80°C, hydrogen to diene ratio 1-4 mol / mol, liquid phase space velocity 3-20h -1 .

[0021] Preferably, in step S3, the selective hydrogenation catalysts used in the first-stage hydrogenation reactor and the second-stage hydrogenation reactor respectively include a carrier and an active component, the carrier is alumina or silicon oxide, and the active component consists of a main active component, an auxiliary active component and an auxiliary active component; the main active component is a metal element of Group VIII, the auxiliary active component is a metal element of Group IA, and the auxiliary active component is a metal element of Group IB;

[0022] More preferably, the Group VIII metal element is one of Pt, Pd, Ni, Ru, Rh and Co.

[0023] Preferably, in step S3, the first-stage hydrogenation reactor and the second-stage hydrogenation reactor respectively use a catalyst for 1-butene isomerization.

[0024] Preferably, in step S3, a water cooler is provided between the first stage hydrogenation reactor and the second stage hydrogenation reactor to ensure that the temperature of the material entering the second stage hydrogenation reactor is 40-80°C.

[0025] Preferably, in step S3, the hydrogenated C4 brings heat into a dehydrogenation tower for heat recovery.

[0026] Preferably, in step S4, the dehydrogenation tower has 75 plates, the tower operating pressure is 0.4-2.0 MPa, and the reflux ratio is 1-50.

[0027] Preferably, in step S4, the sedimentation water is discharged from the bottom of the tank to the sewage treatment device, and the non-condensable steam is extracted from the top of the tank to the flare or gas pipe network.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The method of the present invention can remove butadiene and alkynes in mixed C4 from different sources such as catalytic cracking and post-etherification, and at the same time separate and remove impurities such as sulfides, oxides and light components brought therein to a certain extent, and control the content of residual hydrogen after hydrogenation, ultimately obtaining purified C4 with higher purity and less impurities to meet the requirements for downstream utilization of C4.

[0030] The method of the present invention can carry out economical and effective hydrogenation to remove impurities from C4 and other light hydrocarbon fractions including the oil refining catalytic cracking process, can remove dienes and alkynes in C4 and light hydrocarbons under mild conditions, and has a high regulation capacity for dienes and alkynes in the raw materials, and maintains a high yield of C4 light hydrocarbons. Moreover, based on the selection of different selective hydrogenation catalysts, a higher purity isobutane product can also be obtained. The reaction heat of hydrogenation can also be utilized, the process is simple, easy to implement, the raw material applicability is good, and the production cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the specific implementation modes of the present invention, the drawings required for use in the specific implementation modes will be briefly introduced below. Obviously, the drawings described below are only some specific implementation modes of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 The process flow chart of the C4 light hydrocarbon pretreatment method of the present invention;

[0033] Figure 2 The process flow chart of the C4 light hydrocarbon pretreatment method of the present invention;

[0034] In the figure, 1. mixed C4, 2. deheaved C4, 3. pre-fractionation tower, 4. coalescer, 5. hydrogen, 6. deheaved C4 after dehydration, 7. one-stage hydrogenation reactor, 8. one-stage hydrogenation C4, 9. two-stage hydrogenation reactor, 10. C4 after hydrogenation, 11. dehydrogenation tower, 12. mixed light hydrocarbons, 13. condenser, 14. reflux tank, 15. non-condensable steam, 16. sedimentation water, 17. purified C4, 18. heavy components. DETAILED DESCRIPTION

[0035] In order to further understand the present invention, preferred embodiments of the present invention are described below. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0036] Under the condition of mixed C4 from different sources, the present invention proposes a process of first precise fractionation, then selective hydrogenation, and then fractionation to obtain purified C4. The present invention first uses a pre-fractionation tower to remove the heavy components in the mixed C4, and then performs selective hydrogenation in a hydrogenation reactor to remove diolefins and alkynes. The hydrogenated materials then enter a dehydrogenation tower for separation, and the remaining hydrogen and C2 and C3 light hydrocarbons, as well as dimethyl ether, methanol, water and other oxygen-containing compounds in the C4 after etherification are extracted and separated from the top of the tower; the purified C4 with no hydrogen, low light hydrocarbons, and low oxygen-containing compounds remaining is extracted from the bottom of the tower and sent to the downstream device.

[0037] like Figure 1 and Figure 2 As shown, the method for pretreating C4 light hydrocarbons of the present invention comprises the following steps:

[0038] S1. The mixed C4 1 enters the pre-fractionation tower 3 for precise fractionation. The pre-fractionation tower 3 removes the heavy component C5 and impurities such as heavy sulfides in the mixed C4 1, and obtains the deheavy C4 2 at the top of the tower, and obtains the heavy component 18 (mainly C5 and heavy C4) in the bottom of the tower;

[0039] S2. The dehydrated carbon tetrachloride 2 enters the agglomerator 4 to remove free water to obtain the dehydrated carbon tetrachloride 6;

[0040] S3. selectively hydrogenating the dehydrated carbon four 6 to obtain hydrogenated carbon four 10;

[0041] S4. After hydrogenation, the C4 10 enters the dehydrogenation tower 11 for precise distillation, and the purified C4 17 is taken out from the bottom of the tower, and the mixed light hydrocarbons 12 (residual hydrogen and C2 and C3 light hydrocarbons, as well as dimethyl ether, methanol, water and other oxygen-containing compounds in the C4 after etherification) are taken out from the top of the tower, sent to the condenser 13 for condensation, and then enter the reflux tank 14, where the gas and liquid are separated, and the methanol, water and the like are precipitated and separated, and the precipitated water 16 is discharged from the bottom of the tank and goes to the sewage treatment device, and the non-condensable steam 15 is taken out from the top of the tank, and a part of the liquefied C4 is refluxed to the top of the dehydrogenation tower 11, and the other part is transported to the product tank area.

[0042] In the above technical solution, in step S1, the number of plates of the pre-fractionation tower 3 is preferably 35-102, and the working conditions of the pre-fractionation tower 3 are: pressure 0.4-2.0 MPa, temperature 40-110° C., and reflux ratio 0.1-10.

[0043] In the above technical solution, in step S3, the process of selective hydrogenation of the dehydrated heavy carbon four 6 is:

[0044] For the feedstock with low diene content (≤0.8wt%), the dehydrated deheavy C4 6 is combined with one of the hydrogen 5 to enter the first stage hydrogenation reactor 7 to obtain hydrogenated C4 10;

[0045] For raw materials with high diene content (>0.8wt%), a one-stage hydrogenation reactor 7 containing two upper and lower catalyst beds is used, and the hydrogen 5 is divided into two paths. After being controlled by flow meters, one path merges with the dehydrated heavy carbon four 6 and enters the one-stage hydrogenation reactor 7, and the other path enters the middle part of the one-stage hydrogenation reactor 7. In the one-stage hydrogenation reactor 7, dienes and alkynes react with hydrogen to generate olefins, butadiene and alkynes are removed to obtain hydrogenated carbon four 10; the hydrogen 5 in the middle part of the one-stage hydrogenation reactor 7 can be cold hydrogen to ensure that the temperature of the two catalyst beds is maintained in a reasonable range, preferably 40-80°C; the total amount of hydrogen prepared in the one-stage hydrogenation reactor 7 is calculated according to the hydrogen ratio (1-2mol / mol) required by the content of butadiene in the raw material, wherein the feed in the middle part of the one-stage hydrogenation reactor 7 (the second path) preferably accounts for 0%-50%, usually greater than 0% and less than or equal to 50%, and can also be adjusted as needed;

[0046] Alternatively, a first-stage hydrogenation reactor 7 and a second-stage hydrogenation reactor 9 are connected in series, and the hydrogen 5 is divided into three paths. After being controlled by flow meters, one path is merged with the dehydrated deheavy C4 6 to enter the first-stage hydrogenation reactor 7, and the other path enters the middle part of the first-stage hydrogenation reactor 7. The first-stage hydrogenated C4 8 obtained by the first-stage hydrogenation reactor 7 is merged with the third path of hydrogen 5 to enter the second-stage hydrogenation reactor 9 to obtain hydrogenated C4 10. A water cooler can be arranged between the first-stage hydrogenation reactor 7 and the second-stage hydrogenation reactor 9 to ensure that the temperature of the material entering the second-stage hydrogenation reactor 9 is within a reasonable range, preferably 40-80° C.; the total amount of hydrogen prepared by the first-stage hydrogenation reactor 7 is calculated according to the hydrogen ratio (1-2 mol / mol) required by the content of butadiene in the raw material, wherein the feed (second path) of the middle part of the first-stage hydrogenation reactor 7 preferably accounts for 0%-50%, usually greater than 0% and less than or equal to 50%, and the feed (third path) of the second-stage hydrogenation reactor 9 is 20%-100% of the feed of the first-stage hydrogenation reactor 7;

[0047] Alternatively, a two-stage hydrogenation reactor 9 containing two upper and lower catalyst beds can be used, and the hydrogen is divided into four paths. After being controlled by flow meters, one path merges with the dehydrated heavy carbon four 6 to enter the first hydrogenation reactor 7, and the other path enters the middle of the first hydrogenation reactor 7. The first hydrogenated carbon four 8 obtained by the first hydrogenation reactor 7 merges with the third path of hydrogen 5 and enters the second hydrogenation reactor 9, and the hydrogen 5 enters the middle of the second hydrogenation reactor 9; a water cooler can be set between the first hydrogenation reactor 7 and the second hydrogenation reactor 9 to ensure that the temperature of the material entering the second hydrogenation reactor 9 is within a reasonable range, preferably 40-80°C, and the hydrogen 5 in the middle of the first hydrogenation reactor 7 and the second hydrogenation reactor 9 can be cold hydrogen to ensure that the temperature of the two catalyst beds is maintained within a reasonable range, preferably 40-80°C. The total amount of hydrogen added to the first-stage hydrogenation reactor 7 is calculated according to the hydrogen ratio (1-2 mol / mol) required by the content of butadiene in the raw material. The middle feed (second route) of the first-stage hydrogenation reactor 7 preferably accounts for 0%-50%, usually greater than 0% and less than or equal to 50%, and the feed (third route) of the second-stage hydrogenation reactor 9 is 20%-100% of the feed of the first-stage hydrogenation reactor 7; the middle feed (fourth route) of the second-stage hydrogenation reactor 9 preferably accounts for 0%-50% of the hydrogen feed of the second-stage hydrogenation reactor 9, usually greater than 0% and less than or equal to 50%.

[0048] In the above technical scheme, in step S3, the reaction conditions of the first stage hydrogenation reactor 7 and the second stage hydrogenation reactor 9 are preferably: pressure 1.5-2.5 MPa, temperature 40-80°C, hydrogen to diene ratio 1-4 mol / mol, liquid phase space velocity 3-20h -1 .

[0049] In the above technical solution, in step S3, the hydrogenated C4 10 brings heat into the dehydrogenation tower 11 for heat recovery and utilization.

[0050] In the prior art, since C4 light hydrocarbons contain a small amount of butadiene and alkynes, it is difficult to remove them by conventional distillation. In downstream applications, strict index requirements are put forward for the butadiene content. Therefore, a butadiene removal process must be added to control its content within its quality standards. The best way to remove butadiene is selective hydrogenation. Although the existing C4 selective hydrogenation catalyst has good hydrogenation activity in industrial applications, it cannot meet the requirements due to different requirements of downstream devices. Therefore, different catalysts need to be selected to meet the needs of downstream processes. In the above technical scheme, in step S3, different types of hydrogenation catalysts are selected according to the process objectives, and different process objectives can be achieved in combination with the pretreatment process:

[0051] (1) For the process targeting butene-1, under mild conditions, dienes (butadiene and alkynes) react with H2 to produce butene, and the hydrogenation catalyst is, for example, a catalyst prepared by the method of patent CN104549247A;

[0052] (2) For processes such as alkylation that target butene-2, a catalyst for 1-butene isomerization can also be selected. The selected catalyst can remove butadiene while isomerizing butene-1 to butene-2 ​​in large quantities. The hydrogenation catalyst can be prepared using the method of patent ZL98110280.8.

[0053] In the above technical solution, in step S4, the dehydrogenation tower 11 preferably has 75 plates, a tower operating pressure of 0.4-2.0 MPa, and a reflux ratio of 1-50.

[0054] In the above technical solution, in step S4, preferably, the sedimentation water 16 is discharged from the bottom of the tank to the sewage treatment device, and the non-condensable steam 15 is extracted from the top of the tank to the flare or gas pipe network.

[0055] In the above technical solution, in step S4, mixed light hydrocarbons 12 are extracted from the top of the dehydrogenation tower 11 and enter the condenser 13 to exchange heat with water and condense into liquid.

[0056] The terms used in the present invention generally have the meanings commonly understood by those of ordinary skill in the art, unless otherwise specified.

[0057] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below in conjunction with embodiments.

[0058] In the following examples, various processes and methods not described in detail are conventional methods known in the art. Unless otherwise specified, the materials, reagents, devices, instruments, equipment, etc. used in the following examples can be obtained from commercial sources.

[0059] Example 1

[0060] The C4 component from catalytic cracking in the refinery is used as raw material for raw material pretreatment to remove heavy impurities and diolefins, as well as light components such as C2 and C3 light hydrocarbons, to prepare raw materials for C4 formylation.

[0061] The specific process flow for purifying C4 is as follows: Figure 1 As shown, the process includes a pre-fractionation tower 3, a coalescer 4, a first hydrogenation reactor 7 and a dehydrogenation tower 11, and the steps are as follows:

[0062] S1. Mixed C4 1 (C4 from catalytic cracking in refinery or C4 after etherification) enters pre-fractionation tower 3, and heavy components C5 and impurities such as heavy sulfides are removed by distillation. The number of tower plates is 45, and the working conditions of the pre-fractionation tower are controlled as follows: pressure 0.5MPa, temperature 45°C at the top of the tower, 58°C at the bottom of the tower, reflux ratio 1-4, deheavy C4 2 is obtained at the top of the tower, and heavy components 18 are obtained in the bottom of the tower.

[0063] S2. Remove the heavy carbon tetrachloride 2 to the agglomerator 4 to obtain the dehydrated heavy carbon tetrachloride 6.

[0064] S3. After dehydration, the deheavy C4 6 is mixed with hydrogen 5 in one way and enters the first hydrogenation reactor 7, and the other way is adjusted to flow into the middle part of the first hydrogenation reactor 7 according to the content of butadiene in the raw material mixed C4 1 (when the butadiene content is greater than 0.8%) (the total amount of hydrogen in the first stage hydrogenation reactor 7 is calculated according to the hydrogen ratio (1-2 mol / mol) required by the content of butadiene in the raw material, and the feed in the middle part of the first stage hydrogenation reactor 7 preferably accounts for 0%-50%, which is adjusted as needed). In the first hydrogenation reactor 7, dienes and alkynes react with hydrogen 5 to generate olefins, and the heat generated by the reaction increases with the increase of the diene content in the raw material. The reaction conditions are: pressure 1.5-2.5MPa, temperature 40-80°C, hydrogen-to-dienes ratio 1-4mol / mol, liquid phase space velocity 3-20h -1 After hydrogenation, the carbon four 10 goes to the dehydrogenation tower 11.

[0065] Preparation of selective hydrogenation catalyst: The method described in patent ZL98110280.8 is used for preparation. The content of active metal Pd on the carrier is 0.2% (m / m), and the amount of auxiliary agent is trace (less than 0.1wt%, usually 0.05wt% or lower).

[0066] S4. After hydrogenation, C4 10 enters dehydrogenation tower 11, with 75 plates, tower operating pressure of 1.0-2.0MPa, reflux ratio of 10-40, tower top temperature of 42-86℃, mixed light hydrocarbons 12 are extracted from the tower top, sent to condenser 13 for condensation and then enter reflux tank 14, gas-liquid phase separation in the tank, methanol and water in C4 after etherification are precipitated and separated in the tank, and the precipitated water 16 is sent to the sewage treatment device, and the condensed gas 15 (hydrogen, dimethyl ether, light hydrocarbons) in the tank is extracted from the tank top to the flare network, and part of the liquefied C4 is returned to the top of the dehydrogenation tower 11 as reflux, and the other part is sent to the product tank area as discharge. The purified C4 17 without hydrogen and C3 light hydrocarbons is extracted from the bottom of the tower and sent to the downstream device.

[0067] The process operation results of this method are shown in Table 1.

[0068] Table 1 Material data sheet

[0069]

[0070] As shown in Table 1, after pretreatment, butadiene in the C4 was not detected, C3 was less than 0.01%, dimethyl ether was less than 20 ppm, and the residual hydrogen was not detected, which met the requirements of the downstream device process.

[0071] Example 2

[0072] Using coal chemical MTO carbon four components as raw materials, raw material pretreatment is carried out to remove heavy impurities and diolefins, as well as light components such as non-condensable steam, carbon two and carbon three light hydrocarbons, to prepare raw materials for the downstream 1-butene unit.

[0073] The specific process flow for purifying C4 is as follows: Figure 2 As shown, the process includes a pre-fractionation tower 3, a coalescer 4, a first-stage hydrogenation reactor 7, a second-stage hydrogenation reactor 9 and a dehydrogenation tower 11, and the steps are as follows:

[0074] S1. The mixed C4 1 (MTO C4 component) enters the pre-fractionation tower 3, and the heavy component C5 and heavy impurities are removed by distillation. The number of tower plates is 45. The working conditions of the pre-fractionation tower are controlled as follows: pressure 0.5MPa, temperature 45°C at the top of the tower, 58°C at the bottom of the tower, reflux ratio 0.5-2, and deheavy C4 2 is obtained at the top of the tower, and heavy C4 18 is obtained in the bottom of the tower.

[0075] S2. De-heavy carbon four 2 de-agglomerator 4, to obtain dehydrated de-heavy carbon four 6;

[0076] S3. After dehydration, the deheavy carbon tetrachloride 6 is combined with one of the hydrogen gases 5 and enters the inlet of the first stage hydrogenation reactor 7. The temperature of the other hydrogen gas 5 is raised to 10°C in the first stage hydrogenation reactor 7, and the flow rate is controlled to enter the middle of the first stage hydrogenation reactor 7. In the first stage hydrogenation reactor 7, dienes and alkynes react with hydrogen to generate olefins. The first stage hydrogenated carbon tetrachloride 8 is combined with another hydrogen gas 5 and enters the second stage hydrogenation reactor 9. Under the action of the selective hydrogenation catalyst, dienes and alkynes react almost completely with the hydrogen gas 5 and are removed. The heat generated by the reaction increases according to the increase of the diene content in the raw material. The reaction conditions are: pressure 1.5-2.5MPa, temperature 40-80°C, hydrogen-to-diene ratio 1-4mol / mol, liquid phase space velocity 3-20h -1 After hydrogenation, the C4 10 goes to the dehydrogenation tower 11. The total amount of hydrogen added to the first stage hydrogenation reactor 7 is calculated according to the hydrogen ratio (1-2 mol / mol) required by the content of butadiene in the raw material. The middle feed (second route) of the first stage hydrogenation reactor 7 preferably accounts for 0%-50%, and the feed (third route) of the second stage hydrogenation reactor 9 is 20%-100% of the feed of the first stage hydrogenation reactor 7, which can be adjusted as needed.

[0077] Preparation of the selective hydrogenation catalyst: The catalyst was prepared by the method of patent CN104549247A. The content of active metal Pd on the carrier was 0.3% (m / m).

[0078] S4. After hydrogenation, C4 10 enters dehydrogenation tower 11, with 75 plates, tower operating pressure of 1.0-2.0MPa, reflux ratio of 10-40, tower top temperature of 42-86℃, mixed light hydrocarbons 12 are extracted from the tower top, sent to condenser 13 for condensation and then enter reflux tank 14, gas-liquid phase separation in the tank, methanol and water in C4 after etherification are precipitated and separated in the tank, and the precipitated water 16 is sent to the sewage treatment device, and the condensed gas 15 (hydrogen, dimethyl ether, light hydrocarbons) in the tank is extracted from the tank top to the flare network, and part of the liquefied C4 is returned to the top of the dehydrogenation tower 11 as reflux, and the other part is sent to the product tank area as discharge. The purified C4 17 without hydrogen and C3 light hydrocarbons is extracted from the bottom of the tower and sent to the downstream device.

[0079] The process operation results of this method are shown in Table 2.

[0080] Table 2 Material data sheet

[0081]

[0082]

[0083] As can be seen from Table 2, when MTO C4 is used, butadiene in the C4 after pretreatment is not detected, C3 is less than 0.01%, dimethyl ether is less than 20 ppm, the residual hydrogen is not detected, and the 1-butene yield is 100%, which meets the requirements of the downstream device process.

[0084] Comparative Example 1

[0085] Patent CN 105152840 A, after pretreatment steps such as water washing, hydrogenation to remove diolefins, distillation to remove propane, distillation to remove ethane and adsorption to remove dimethyl ether, the mixed carbon four finally obtains a product with dimethyl ether content reduced to 10ppm.

[0086] Obviously, the above embodiments are merely examples for clear explanation, and are not intended to limit the embodiments. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. The obvious changes or modifications derived from them are still within the protection scope of the invention.

Claims

1. A method for pretreating C4 light hydrocarbons, characterized in that: Here are the steps: S1. The mixed C4 (1) enters a pre-fractionation tower (3), the top of the tower obtains the de-heavy C4 (2), and the bottom of the tower obtains the heavy component (18); S2. The dehydrated heavy carbon tetrachloride (2) enters the agglomerator (4) to remove free water to obtain the dehydrated heavy carbon tetrachloride (6); S3. The dehydrated deheaved carbon four (6) and the hydrogen (5) are combined into a hydrogenation reactor (7) to obtain hydrogenated carbon four (10); Alternatively, the dehydrated deheaved C4 (6) is combined with one of the hydrogen (5) and enters a first-stage hydrogenation reactor (7), and the obtained first-stage hydrogenated C4 (8) is combined with another of the hydrogen (5) and enters a second-stage hydrogenation reactor (9) to obtain hydrogenated C4 (10); S4. After hydrogenation, the C4 (10) enters the dehydrogenation tower (11), and the purified C4 (17) is extracted from the bottom of the tower. The mixed light hydrocarbons (12) are extracted from the top of the tower and sent to the condenser (13) for condensation before entering the reflux tank (14). In the reflux tank (14), the gas and liquid phases are separated, and the sedimentation water (16) is discharged from the bottom of the tank. The non-condensable steam (15) is extracted from the top of the tank. A part of the liquefied C4 is refluxed to the top of the dehydrogenation tower (11), and the other part is transported to the product tank area.

2. The method for pretreating C4 light hydrocarbons according to claim 1, characterized in that: In step S1, the number of plates of the pre-fractionation tower (1) is 35-102, and the working conditions of the pre-fractionation tower (1) are: pressure 0.4-2.0 MPa, temperature 40-110° C., and reflux ratio 0.1-10.

3. The method for pretreating C4 light hydrocarbons according to claim 1, characterized in that: In step S3, one or both of the first-stage hydrogenation reactor (7) and the second-stage hydrogenation reactor (9) contain two upper and lower catalyst beds, and when the first-stage hydrogenation reactor (7) contains two upper and lower catalyst beds, one of the hydrogen (5) is connected to the middle of the first-stage hydrogenation reactor (7), and when the second-stage hydrogenation reactor (9) contains two upper and lower catalyst beds, one of the hydrogen (5) is connected to the middle of the second-stage hydrogenation reactor (9).

4. The method for pretreating C4 light hydrocarbons according to claim 1, characterized in that: In step S3, the reaction conditions of the first stage hydrogenation reactor (7) and the second stage hydrogenation reactor (9) are: pressure 1.5-2.5 MPa, temperature 40-80°C, hydrogen to diene ratio 1-4 mol / mol, liquid phase space velocity 3-20h -1 .

5. The method for pretreating C4 light hydrocarbons according to claim 1, characterized in that: In step S3, the selective hydrogenation catalysts used in the first-stage hydrogenation reactor (7) and the second-stage hydrogenation reactor (9) respectively include a carrier and an active component, wherein the carrier is aluminum oxide or silicon oxide, and the active component is composed of a main active component, a co-active component (1) and a co-active component (2); the main active component is a metal element of Group VIII, the co-active component (1) is a metal element of Group IA, and the co-active component (2) is a metal element of Group IB.

6. The method for pretreating C4 light hydrocarbons according to claim 1, characterized in that: In step S3, the first stage hydrogenation reactor (7) and the second stage hydrogenation reactor (9) respectively use a catalyst for 1-butene isomerization.

7. The method for pretreating C4 light hydrocarbons according to claim 1, characterized in that: In step S3, a water cooler is arranged between the first stage hydrogenation reactor (7) and the second stage hydrogenation reactor (9) to ensure that the temperature of the material entering the second stage hydrogenation reactor (9) is between 40°C and 80°C.

8. The method for pretreating C4 light hydrocarbons according to claim 1, characterized in that: In step S3, the hydrogenated C4 (10) brings heat into the dehydrogenation tower (11) for heat recovery.

9. The method for pretreating C4 light hydrocarbons according to claim 1, characterized in that: In step S4, the dehydrogenation tower (11) has 75 plates, an operating pressure of 0.4-2.0 MPa, and a reflux ratio of 1-50.

10. The method for pretreating C4 light hydrocarbons according to claim 1, characterized in that: In step S4, the sedimentation water (16) is discharged from the bottom of the tank to the sewage treatment device, and the non-condensable steam (15) is extracted from the top of the tank to the flare or gas pipe network.

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