JP2014058517A - SYSTEM AND PROCESS FOR PRODUCING STRAIGHT CHAIN α-OLEFIN - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system and process for producing straight chain α-olefin that can cut down the energy consumption amount.SOLUTION: A system and a process for producing straight chain α-olefin are as follows. A hydrocarbon mixture comprising a first hydrocarbon, a second hydrocarbon and a higher-boiling point hydrocarbon is divided into a first feed stream and a second feed stream, and the first feed stream is fed into a first intermediate stage of a first distillation column and the second feed stream is fed into a second intermediate stage of a second distillation column; a first distillate comprising most of the first hydrocarbon is extracted from an overhead of the first distillation column and is partially condensed to be fed into a third intermediate stage of the second distillation column; the higher-boiling point hydrocarbon is extracted from a bottom of the first distillation column; and the first hydrocarbon is extracted from an overhead of the second distillation column and the second hydrocarbon is extracted from a bottom of the second distillation column, and a part thereof is heated by using the first distillate and returned back to the second distillation column.

Description

  This application claims priority from US Provisional Patent Application No. 61 / 072,993 (filing date, April 4, 2008).

  Embodiments described herein relate to the production of linear alpha olefins, and more particularly to linear alpha olefin production processes with reduced energy consumption.

  Linear alpha olefins can be produced by selective oligomerization of ethylene. In general, the oligomerization is carried out in the presence of a catalyst such as an alkylated metal catalyst. Long residence times are used to produce hydrocarbon chains of varying lengths. Each time an ethylene molecule is added, an olefinic double bond remains in the alpha position. Ethylene oligomerization produces linear alpha olefin products with a broad spectral range. Large scale rectification is required to separate alpha olefins having different carbon numbers.

  US Pat. No. 3,776,974 discloses a detergent range by disproportionating linear alpha olefins using 2-butene to produce both low and high carbon number linear beta olefins. The purpose of this process is to produce a linear monoolefin. The resulting lower beta olefin fraction is subjected to disproportionation to produce 2-butene and a linear internal monoolefin.

  US Pat. No. 6,727,396, assigned to Lummus Technology Inc., describes a process for producing linear alpha olefins in which Linear alpha olefins having the number of carbon atoms are subjected to metathesis reactions in the presence of conditions and catalysts that minimize or eliminate skeletal and / or double bond isomerization. The reaction product includes ethylene and a linear internal olefin (LIO) having a number of carbon atoms greater than the first number of carbon atoms. Specifically, when a feed linear alpha olefin having n carbons is metathesized using a second feed linear alpha olefin, ethylene and a linear internal olefin having 2n-2 carbon atoms are obtained. It is formed. The linear internal olefin so obtained may then be isomerized to produce a linear alpha olefin. In one embodiment described therein, 1-butene is subjected to an automated metathesis reaction in the presence of a metathesis catalyst and conditions that minimize or eliminate skeletal and / or double bond isomerization. To produce a reaction product comprising ethylene and 3-hexene. The 3-hexene is then isomerized to 1-hexene. In the automated metathesis reaction, the catalyst and reaction conditions are such that the isomerization of the 1-butene starting material is minimized. The catalyst used in the automatic metathesis reaction may be a supported catalyst or an unsupported catalyst, and the catalyst as a whole has both an acidic site and a basic site in a minimum amount. Typical isomerization catalysts include basic metal oxides or promoted zeolites.

  It is known to use superfractionation to separate two components having similar boiling points. In general, ultra rectification involves a very high number of theoretical plates and a high reflux ratio in the distillation column, so a large amount of energy input is required to provide reboiling and condensation loads. Is needed.

US Pat. No. 3,776,974 US Pat. No. 6,727,396

  It would be useful to have a system and method for reducing energy consumption in the production of linear alpha olefins including ultra rectification.

One embodiment is a process that includes the following steps:
(A) A mixed butene stream containing 1-butene and 2-butene is separated into a 1-butene stream at the top of the column and a 2-butene stream at the bottom of the column in a butene distillation column. Separating a portion to form a butene reboiler stream, heating it in a reboiler and evaporating it back to the butene distillation column;
(B) subjecting at least a portion of the top 1-butene stream from (a) to catalytic metathesis to produce an effluent comprising 3-hexene;
(C) isomerizing 3-hexene from (b) to produce a mixed hexene stream comprising 1-hexene, 2-hexene and 3-hexene;
(D) separating the mixed hexene stream in a hexene rectification column to a top stream of 1-hexene vapor (which is condensed in a condenser) and a bottom stream comprising 2-hexene and 3-hexene. And (e) heating the butene reboiler stream of (a) using the heat obtained by condensing the overhead stream of 1-hexene vapor of (d).

  Another embodiment is a system for producing 1-hexene from butene comprising a butene distillation column, a metathesis reactor, a metathesis recovery zone, a hexene isomerization reactor, a hexene rectification column, and a condenser including. The butene distillation column is configured to separate 1-butene from 2-butene, which is accompanied by a butene reboiler containing a first heat source. The metathesis reactor converts 1-butene to 3-hexene and ethylene. The metathesis recovery zone separates 3-hexene from ethylene. The hexene isomerization reactor is configured to isomerize 3-hexene into 1-hexene and 2-hexene, and the hexene distillation column converts 1-hexene vapor to 2-hexene and 3-hexene. Is configured to be separated from The condenser condenses 1-hexene vapor. The first heat source for the butene reboiler is at least part of the condensation heat of 1-hexene vapor.

  A further embodiment is a separation process comprising obtaining a hydrocarbon mixture comprising a first hydrocarbon, a second hydrocarbon, and a higher boiling hydrocarbon, wherein the second hydrocarbon is It has an atmospheric pressure boiling point that is 0.3 to 10 ° C. higher than the atmospheric pressure boiling point of the hydrocarbon. The hydrocarbon mixture is divided into a first feed stream and a second feed stream. The first feed stream is fed to the first intermediate stage of the first distillation column and the second feed stream is fed to the second intermediate stage of the second distillation column. . The first distillation column is operated at a higher overhead pressure than the second distillation column. The first distillate containing most of the first hydrocarbon is withdrawn from the top of the first distillation column and is at least partially condensed from the second intermediate stage of the second distillation column. Is also fed to the third intermediate stage above. Higher boiling hydrocarbons are withdrawn from the bottom of the first distillation column. The first hydrocarbon is withdrawn from the top of the second distillation column, and the second hydrocarbon is withdrawn from the bottom of the second distillation column. At least a portion of the second hydrocarbon extracted from the bottom of the second distillation column is heated using the first distillate and returned to the second distillation column.

  Another embodiment is a super rectification system comprising a first distillation zone and a second distillation zone. The first distillation zone includes a first distillation column, a first condenser using a first coolant source, and a first reboiler using a first heat source. The first distillation column has a first feed inlet configured to receive a first portion of a fresh feed, a first distillate outlet, and a first bottom outlet. The second distillation zone includes a second distillation column configured to operate at a lower pressure than the first distillation column, a second condenser, and a second recycle using a second heat source. A boiler is included. The second distillation column is positioned above the second feed inlet configured to receive a second portion of the fresh feed, above the second feed inlet, and at least distillate from the first distillation zone. A third feed inlet configured to receive a portion, a second distillate outlet, and a second bottom outlet. The second heat source for the second reboiler includes a first coolant source for the first condenser.

1 is a schematic diagram of a portion of a system for producing 1-hexene, according to one embodiment. FIG. 1 is a schematic diagram of a conventional dual pressure super rectification system. FIG. FIG. 6 is a graph illustrating energy consumption of some embodiments disclosed herein as compared to conventional systems. 1 is a schematic diagram of a pressure differential ultra rectification system of an embodiment described herein. FIG. FIG. 5 illustrates a variation of the system of FIG. 4 employing an open loop heat pump. 1 is a schematic diagram showing a conventional rectification-isomerization system for obtaining linear alpha olefins. FIG. 1 is a schematic diagram illustrating a novel rectification-isomerization system for obtaining linear alpha olefins. FIG. 2 is a process flow diagram illustrating the overall process for producing 1-hexene, according to certain embodiments.

  Embodiments described herein provide a process for producing linear alpha olefins that results in reduced energy usage in production. In one embodiment, the overhead condenser from the hexene separation column is used as a reboiler for the butene separation column. This reduces the overall heat requirement in the system. In another embodiment, which may be used in connection with or separately from the first embodiment, in another embodiment, a two tower refinery for either or both of the butene and hexene purification towers. Use the retention system. The feed is split and fed to two separate but integrated towers operating at two different pressures to allow heat exchange, further reducing production costs.

  As used herein, the term “super rectification” refers to the separation of two or more components having a boiling point difference between 0.3 and 10 ° C. by distillation. As used herein, the term “catalytic metathesis” refers to a disproportionation reaction between two olefins to produce two other olefins.

In the production of hexene in metathesis reactions including butene automatic metathesis, there are three general processes. In the first stage, the production of 1-butene from C ₄ streams such as raffinate 2 stream. In the next step, the 1-butene is subjected to self-disproportionation or automatic metathesis to form ethylene and 3-hexene. In the last step, 3-hexene is isomerized to 1-hexene, which is then purified. Each of these processing steps will be described in detail below.

In the production of 1-butene, raffinate 2 is fed to a combined distillation / butene isomerization system. Raffinate 2 is a C ₄ stream that contains butane, butene-1 and butene-2, but contains only very small amounts of both isobutylene and butadiene. The product from the distillation typically includes an overhead stream comprising at least 90% by weight of 1-butene. Due to the low relative volatility between the isomers of normal butene, very multi-stage distillation trays and very high reflux ratios are required to achieve separation. With these requirements, the distillation column requires enormous energy for the reboiling and condensation loads.

In self-disproportionation or automatic metathesis where ethylene and 3-hexene are produced from 1-butene, 1-butene is reacted over a metathesis catalyst and the product of the reaction is separated in a rectification system. Since the reaction product includes products having C ₂ to C ₇ carbon numbers, there are a number of rectification options associated with the rectification column arrangement. The requirements for the rectification system are as follows:
(1) Separation for recovering the C ₂ / C ₃ reaction product as a useful olefin,
(2) Recycling C ₄ / C ₅ olefins to achieve high process yields, and (3) Separation of 3-hexene-based streams as feed to the final process steps. Examples of suitable automated metathesis catalysts include, but are not limited to, Group VIB or Group VIIB metal oxides such as tungsten oxide, molybdenum oxide, or rhenium oxide.

  In the final step of 1-hexene production, ie isomerization of 3-hexene to 1-hexene and purification of the 1-hexene, the purification is carried out in a second “super rectification column”. This distillation is even more difficult than in the case of 1-butene rectification. Multiple trays and a very high reflux ratio are required, resulting in considerable energy consumption. For the entire process, in addition to the energy required for butene separation, hexene separation also results in significant energy consumption. Some processes and systems described herein reduce energy usage in the production of linear alpha olefins such as 1-hexene.

  One process for reducing energy consumption in the production of 1-hexene from butene is to use the hexene-splitter top tray vapor to heat the butene-splitter bottom tray liquid. is there. This eliminates both the heating energy consumption of the n-butene separation system and the overhead cooling requirement for the hexene tower separation system.

  Both the butene-splitter and the hexene-splitter need to have a high concentration of alpha-olefin in the product overhead condenser liquid. Butene splitters often require more than 90%, sometimes more than 95% of 1-butene in the product stream. Hexene splitters often require more than 98% 1-hexene in the product stream. The relative volatility of internal olefins (2-butene, 2-hexene and 3-hexene) and alpha olefins (1-butene and 1-hexene) in butene and hexene towers is very low. In rectification, a remarkable number of plates and reflux are required in any column. Specific volatility is the ratio of vapor pressures of individual components at the same temperature and represents the relative tendency of separation by rectification. The higher the relative volatility, the easier it is to separate.

  In conventional systems, the butene splitter operates at the lowest possible pressure to increase the relative volatility between 1-butene and 2-butene, thereby facilitating the required separation. Designed to be. Increasing the specific volatility reduces the amount of reflux required and the heating / cooling load level. However, the temperature required to cool the condenser liquid limits the pressure in the butene tower. If the pressure in the butene tower is very low, the tower top temperature will be out of the temperature range of the cooling water, resulting in the need for refrigeration and additional process energy to provide that refrigeration. In this application, the butene tower (s) will typically be designed at 70 gauge pounds per square inch (70 psig) at approximately gauge pressure.

  The hexene splitter in conventional systems is also designed in the same way as the butene splitter (s) for the same reason as explained above, i.e. using low column pressure to increase relative volatility. This promotes separation. Because hexenes boil at higher temperatures than butenes, the hexene column can be operated at atmospheric pressure or lower and water can still be used in the condenser. This column is typically operated at a pressure in the range of -10 to 5 psig.

  In one of the embodiments described herein, the hexene splitter is operated at a higher pressure, thereby utilizing the overhead vapor stream to heat the butene splitter reboiler stream. Is possible. If the hexene splitter (s) is operated at a higher pressure, the higher the absolute pressure, the lower the relative volatility, so more constant theoretical plates are required if the reflux ratio is constant. As can be seen from the computer simulation shown in Table 1 below, when the top pressure of the hexene splitter is increased from 0 psig to 15 psig, the theoretical separation stage increases from 103 to 125. This corresponds to an increase rate of 21%. Thus, higher pressure towers will have higher construction costs due to the increased number of stages.

  Alternatively, if the same number of stages was used at a top pressure of 15 psig, a higher reflux ratio would be required for higher pressure columns to achieve the same resolution. This increases the tower diameter and construction costs, and also increases the amount of energy used due to higher reboiling and condensation loads.

In processes where the hexene column is operated to provide a reboiler load for the butene column, the butene column pressure is preferably above 70 psig to avoid the use of refrigeration in the condenser, Alternatively, it should be about 70 psig to about 100 psig. As a result, the reboiler temperature of the C ₄ column is approximately 139 ° F. (about 59 ° C.). By operating the hexene column at high pressure, it is possible to use the top condenser temperature (the lowest temperature in the hexene column) and the hexene column condenser as a reboiler for the C ₄ column. Can be raised to temperature. This increases the rectification requirement (number of stages, reflux, or both) in the hexene column, so the hexene column pressure is increased and the condenser is used to reduce the reboiling load of the butene column. It was not anticipated that this would give a net energy-saving result.

  In order to allow heat exchange between the 1-butene / 2-butene splitter bottom tray liquid and the 1-hexene / 2-hexene and 3-hexene top tray vapors, at a minimum, The pressure must be increased to the “high pressure” range (15 psig) listed in Table 1. Operating at lower pressures in the hexene tower reduces the minimum approach of the heat exchanger, as seen in Table 2 below.

  Operating this hexene tower at atmospheric pressure, which is optimal for hexene rectification, does not effectively heat the butene bottom tray liquid at the top tray vapor temperature. Will. The use of high pressure in the hexene tower is counterintuitive because trying to achieve the required separation requires more trays. However, by using high pressure in the hexene column, the hexene vapor can be used to heat the butene reboiler stream. This saves energy for the entire system.

  FIG. 1 shows a system having the heat integration described above. The whole system is called 100. The system includes a 1-butene / 2-butene splitter 102 having a reboiler 104 and 1-hexene / 2- and 3-hexene splitter 106 having a reflux drum 108. The 1-hexene vapor stream 110 is withdrawn from the top of the hexene splitter 106 and used as a heating stream in the reboiler 104 so that the temperature of the stream 110 is passed through the reboiler 104. Typically, some condensation of the stream 110 occurs. Stream 112 is withdrawn from the bottom of butene splitter 102 and split into reboiling stream 114 and butene bottom stream 116. Stream 114 is heated in reboiler 104 and then returned to the lower end of butene splitter 102.

  After application of heat in heat exchanger 104, if necessary, 1-hexene vapor stream 110 is further cooled in heat exchanger 118 using cooling water stream 120 to fully condense. . The cooled 1-hexene stream 110 is sent to the reflux drum 108. A portion of the effluent from drum 108 is returned to splitter 106 as reflux stream 122 and the remainder is withdrawn as 1-hexene product stream 124. In the case described above, the condenser load required for the hexene column 106 is greater than the reboiler load for the butene column 102. In other designs where the butene composition is more dilute or otherwise draws the 1-butene stream of the product in addition to the 1-butene stream that will go to metathesis, the butene splitter reboiler The load will be greater than the load on the hexene splitter condenser. In such a case, instead of an additional cooler for stream 110, an additional reboiler would be present in stream 114 to balance the reboiler load for the butene splitter. .

  The degree of cooling water / steam reduction in the hexene and butene splitters depends on the tower specifications and production capacity. The heat integration that has been described in connection with FIG. 1 can significantly reduce both cooling water (CW) and steam for heating (LPS). Tables 3 and 4 below compare the energy for the process before and after integrating the hexene tower and the butene tower for a 1-hexene production capacity of 50 KMTA.

  As can be seen from these tables, by exchanging heat between the butene reboiler and the hexene condenser, the CW requirement is reduced from 76231 KW to 48771 KW (ie 36%) and the heating load of the low pressure steam ( LPS) is reduced from 68301 KW to 39901 KW (ie 42%).

  In order to increase the production capacity, a plurality of 1-butene / 2-butene splitters and a plurality of 1-hexene / 2- & 3-hexene splitters may be employed. Under this scenario, the flow as shown in the butene-splitter stream 112 may be combined and heat exchanged with the combination of flows as shown in the hexene-splitter stream 110. In some cases, a trim cooling water exchanger may be required.

  Another way to improve process efficiency is to divide the feed to the butene splitter and / or the feed to the hexene splitter into two separate columns, and the two columns are at different pressures in the ultra-rectification process. It is a method to drive with. When used in hexene separation, the functionality of the embodiments disclosed herein reduces the energy consumption of the hexene tower system by approximately 33% at equivalent tray numbers and operating pressures. These saving methods are generally applicable to ultra rectification systems that separate hydrocarbons with low relative volatility. In the case of a hexene system, the benefits achieved by this embodiment are added to the benefits achievable with the integrated heat exchange system described above.

  In the ultra rectification column, a huge amount of energy is consumed in both the reboiling utility and the condensation utility. Studies on various options for reducing energy costs in ultra rectification columns have been published. Known systems include the following.

(A) Pressure difference tower. There, the tower is divided into two separate towers. The first column is operated at a higher pressure than the second column, and the first column condenser is used to reboiler the second column.

(B) Use of a heat pump. In this case, the top vapor is compressed to a higher pressure. The compression energy heats the vapor and raises it to a higher temperature. The higher pressure / higher temperature vapor is then condensed (at a higher temperature) to obtain a reboiling load for the column. This option does not save energy by itself, but allows operation under conditions that would save energy. By reducing the tower pressure, the relative volatility of the hydrocarbons increases. This makes it possible to reduce the number of stages and reduce the reflux to achieve a predetermined separation. However, operation at lower pressures will lower the tower temperature and may require refrigeration rather than cooling water due to the condenser load. This will increase energy consumption. By operating the heat pump, it is possible to supply both cooler and reboiling loads with compressed power, which does not lead to an increase in energy due to additional refrigeration.

  The two-column system of system (a) has been used in various separation column arrangements, such as when lower olefins are separated from their paraffin analogs. If a single column is designed for utility, its condenser load is 100% at the top and its reboiling load is 100% at the bottom. This represents the maximum temperature difference across the tower. By rectifying at two different pressures using two towers, each tower can be operated at different reflux ratios, and the load can be optimized both in terms of total energy and energy level. it can. The term “energy level” can often be defined as the cooler level of refrigeration temperature, which requires more energy in the refrigeration system. This integration is not for adjusting the reflux and temperature distribution in order to optimize service in a single column, unlike when using a side distiller or side distiller. Absent.

  In the embodiment described herein, when 1-hexene is separated from 2-hexene and 3-hexene in a two-column system with split feed, the difference in pressure at the top of each of the two distillation columns. Is usually 4 to 40 psi, or 6 to 20 psi, or 8 to 15 psi. When using the two-column system described herein to separate other boiling or close components, the pressure difference at the top of each of the two distillation columns is typically 4-40 psi, or 6 It is in the range of ~ 20 psi, or 8-15 psi. The optimum choice of differential pressure depends on the desired temperature difference for heat exchange and the resulting heat exchanger size (and cost).

  The key to efficient use of system (a) is to balance the operation of each of the two towers so that the condensation load in the first tower matches the reboiling load required in the second tower. Is to do. In some cases, the presence of imbalance is also acceptable, but a small external heated reboiler, or a small cooling condenser instead, to compensate for the difference, is compensated for. This is often used to adjust the system. Another possibility is to adjust and balance the rectification load in each column. Traditionally practiced to balance operation either allows some of the steam from the first column to be bypassed to the second column or, alternatively, the second A method of shifting the load from one tower to another by either allowing some of the liquid from the tower to pass through the first tower. In the first of the conventional options, the tower feed is sent to the first or higher pressure column. The amount of condensation load in the first column is adjusted by bypassing steam from the first column to the second column. This bypass shifts the load from the condensing portion of one tower to the reboiling load of the other tower, thereby matching the condenser of tower 1 with the reboiler load of tower 2. It becomes possible. The savings realized with this type of system are primarily at energy levels (temperature) rather than overall energy savings. Furthermore, in the case of a tower having a large number of stages, dividing the tower into two separate towers reduces costs compared to a single very high tower.

  In the following, a comparison is made between a conventional single tower system and a conventional two tower system with a steam bypass from the first tower to the second tower. Case A and Case B represent single tower systems with different capacities and tray stages. Case E uses a lower pressure drop tray (column dP = 20 kPa versus 35 kPa for case A and case B). Case C and Case D are representative of a two tower system with equivalent capacity but different number of trays. A single column hexene system is a conventional distillation unit, typically having 100 or more (usually 150 or more) stages. These stages are numbered from the top. The feed enters column number 75. The product 1-hexene is extracted as distillate. The bottom 2-hexene and 3-hexene are recycled to a hexene isomerization reactor (not shown), where it is isomerized to a mixture of 1-, 2- and 3-hexene, the effluent Is returned to the tower. In this way, 3-hexene is converted to 1-hexene. A small amount of purge is withdrawn from the system. The specifications for the tower are shown in Table 5. Case A and Case B are operated at different flows and pressures and different stages to obtain 1-hexene of slightly different purity.

Conventional pressure-distillation separation of 1-hexene is carried out in two towers each having 100 plates (total of 200 plates). A schematic diagram of the two tower system is shown in FIG. The system includes a first distillation column 202 and a second distillation column 204. Feed containing approximately 8% 1-hexene in stream 206 (most of which is 2-hexene and 3-hexene and a small amount of C ₇₊ (carbon number 7 or higher) material) is fed to the first column Enter the 40th stage of 202. The bottom product of this tower in stream 211 is primarily C ₇₊ , which is purged into stream 213 and the remainder is returned to the bottom of tower 202 in stream 215. The distillate product from the first column is 35% 1-hexene in stream 212. A steam side distillate is withdrawn from the 81st stage of the first column 202 into stream 217 to balance the interchange load. If the first column 202 is integrated with an isomerization reaction system, a liquid side distillate is withdrawn from stage 87 into stream 214 and fed to the isomerization reaction system. This recycle stream, consisting mostly of 2-hexene and 3-hexene, is mixed with a fresh 3-hexene feed (not shown) and passed through an isomerization reactor (not shown) to give 2-hexene and 3 -Make some 1-hexene from hexene and feed it back to the first column as feed 206.

  The distillate from first column 202 in stream 212 is condensed in condenser 216 and then divided into reflux stream 218 entering the top of first column 202 and distillate stream 220. To do. Distillate stream 220 is placed in the 54th stage of the second column 204. The steam side distillate in stream 217 is placed in the 90th stage of the second column 204. Stream 217 is placed in a lower stage than stream 220 because it contains less 1-hexene because it was extracted at a lower stage. Product 1-hexene is withdrawn as distillate from the second column 204 into stream 222, condensed and split into 1-hexene product stream 223 and reflux stream 225. The bottom product from the second column 204 in the stream 224 is reboiled in the reboiler 228, a portion of which is returned from the stream 226 to the second column 204. The remaining portion is mixed with the liquid side distillate from the first column in stream 214 to form stream 232 which is recycled to the hexene isomerization reactor. If necessary, a small amount of purge can be withdrawn into stream 234.

  The second column 204 operates at a lower pressure than the first column 202. This allows the condenser 216 of the first column 202 to operate at a higher temperature than the reboiler 228 of the second column 204 and allows heat exchange between them. . Thereby, heat integration is achieved by connecting the condenser of the first column 202 with the reboiler of the second column 204. The specifications for the tower are shown in Table 6. Two different designs with different total number of rectification stages are shown. In the first case, each of the two towers uses 100 (total 200) trays, whereas in the second case, each of the two towers uses 150 (total 300) trays.

  The energy consumption in single tower cases A to B and E and two tower cases C to D are shown in Tables 7 and 8 below.

  The results are summarized in a table from the perspective of energy usage, and it is clear that the total energy usage in these two systems is similar where the number of distillation stages is similar. This also appears in the graph of FIG. In the case of a single tower and in the case of a double tower steam bypass, the energy usage is on a similar curve. There is a slight difference depending on the operating pressure, and in the case of a single column with lower pressure, the specific energy is about 10% lower. As can be seen, Case A has a higher recovery rate (stricter standards) than Case B. This does not have a dramatic impact on energy. However, Case B and Case E have similar recovery rates, but Case E has a much lower tray dP. This affects the relative volatility.

  The advantage of a two-column system with a steam bypass is in the ability to raise the reboiler temperature of the first column, rather than in energy per tonne of product. In this case, the reboiler temperature rises from 99 ° C. in the single tower case to 124 ° C. in the two tower case. The dual tower steam bypass system is most applicable for refrigeration systems where the reboiler requires refrigeration. In many cases, this increase can either reduce refrigeration from a lower temperature that requires refrigeration compression, or possibly be reboiled by steam or a lower cost energy source. The load can be shifted to higher temperature levels. The case given does not use refrigeration, but a shift in the temperature of the reboiler explains the principle. Note that in many cases when using a very large number of trays (greater than 100), the tower is designed as two towers in series, reducing costs by reducing base and structure costs. . When the tower is constructed as two columns in series, it is preferable to adjust the pressure difference.

  Another embodiment disclosed herein is a differential pressure two-column system using feed splitting and heat integration, which also includes a corresponding method. These systems have reduced energy consumption compared to the conventional double pressure tower systems listed above. The system and method is schematically illustrated in FIG. The entire system is called 250. The drawings and description are intended to separate 1-hexene from 2-hexene and 3-hexene, but the scope of that embodiment includes the production of other components with near boiling points. It is.

  Distillation of 1-hexene from 2-hexene and 3-hexene is carried out in columns 252 and 254. In the illustrated embodiment, column 252 has 80 stages and column 254 has 70 stages. Therefore, the total number of stages (150) is the same as in one of the single towers described above. Note that in actual cases, other numbers of stages can also be used.

The feed to the separation system is split and a portion of the feed stream 256 is placed in the 25th stage of the first column 252 as stream 258. The remaining portion enters the 60th stage of the second column 254 as stream 260. The bottom product of column 252 in stream 261 is primarily C ₇ , most of which is purged into stream 263. Heat in reboiler 259 to return reboiler stream 265 to first column 252. The distillate from the first column 252 in stream 262 is 40% 1-hexene. A side distillate withdrawal of liquid containing 2-hexene and 3-hexene is withdrawn as stream 264 from stage 74 of the first column 252 and fed to an isomerization reaction system (not shown). This recycle stream, consisting mostly of 2-hexene and 3-hexene, is mixed with a fresh 3-hexene feed (not shown) and passed through an isomerization reactor (not shown) to give 2-hexene and Some 1-hexene is produced from 3-hexene and fed back to the first column as feed 256.

  The distillate 262 from the first column 252 is condensed in the condenser 266 and the condensate is returned to the reflux stream 268 back to the top of the first column 252 and the feed stream 270 to the second column. The feed stream enters the 40th stage of the second column 254, which is above the feed point of the second part of the fresh feed entering the 60th stage. It should be noted that the side distillate and feed locations can use other locations than those described herein.

Product 1-hexene is withdrawn from the second column 254 as distillate in stream 272. Distillate 272 is condensed in condenser 274 and separated into reflux stream 273 and 1-hexene product stream 275. The bottom product from the second column 254 in the stream 274 is partially reboiled in the reboiler 278. The reboiled stream is separated into a stream 276 that returns to the bottom of the second column 254 and a remaining bottom stream 280. The bottom stream 280 is mixed with the side distillate of liquid in the stream 264 from the first tower to form a stream 282. A portion of stream 282 is separated into a C ₆ purge stream 284 and the remaining stream 286 is recycled to a hexene isomerization reactor (not shown).

  The second column 254 operates at a lower pressure compared to the first column 252. This allows the first tower condenser to be at a higher temperature than the second tower reboiler, allowing heat exchange between them. These loads are balanced by splitting the feed to their towers. By increasing or decreasing the amount of fresh feed sent to column 2, the relative loads of reboiler 278 and condenser 266 can be balanced. Thereby, heat integration is achieved by connecting the condenser of the first column with the reboiler of the second column.

  By incorporating a heat pump that circulates heating and cooling fluid between the reboiler 259 of the second column 252 and the condenser 274 of the first column 254, further advantages of the process of FIG. 4 can be realized. . In one embodiment, as seen in FIG. 5, an open loop heat pump employing distillate from the first column 254 is used. In this embodiment, many of the system components are identical and the entire system is designated 250 ', but the feed 256' is split and the first tower 252 'enters the first tower. Feed 258 'and second tower feed 260' entering the second tower 254 '. Distillate 262 'is withdrawn from first column 252', condensed in condenser 266 ', and separated into reflux stream 268' and second column feed stream 270 '. The difference is that distillate 272 'from second column 254' is compressed in compressor 290 and used as the heated fluid in reboiler 259 '. Stream 272 'is then separated in separator 292 into a vapor stream 275' that is withdrawn as product and a liquid stream 273 'that is used as a reflux stream to rectification column 254'. In this embodiment, the compressor pressurizes hot steam to a pressure that results in the desired reboiling temperature.

  Table 9 shows the tower specifications for computer simulation. In the table, Case F represents a two-column feed splitting column. In this example, the pressure in the first split feed column has been increased to a level that is fairly comparable to a single column system. The top pressure of the second column is almost equal to the top pressure of the single column. This allows an equivalent exchange between the hexene condenser and the butene column reboiler as described above (if used in combination with this embodiment).

  Table 10 summarizes the simulation results. The energy usage of the two-column feed splitting system dropped to 1.44 KW / (KTA product, hexene-1). This is also shown in FIG. 3 as “two tower feed split”. This number can be contrasted with 2.13 for a single tower system with the same number of tray stages and equivalent specifications for tray pressure loss. This is a 32% reduction. In a single column operating with the same number of low pressure drop trays (high cost trays) and low 1-hexene recovery, the energy is 23% higher (1.91 vs. 1.44). In addition, the energy can be comparable to a conventional double pressure tower system that requires twice as many trays. This represents that the system of the embodiment disclosed herein is substantially advantageous in terms of construction costs. The first tower of the two tower system operates at a higher pressure than the single tower system (or the second tower). Therefore, most of the rectification occurs at higher pressures, reducing the diameter of the tower in that part, which also saves construction costs.

  It was unexpected that the arrangement shown in FIG. 4 would significantly reduce the energy usage in a two-column system used to separate a mixture containing materials with very close boiling points. is there. Split feed columns have been used previously in some applications using a single column, where each portion of the split feed is of a different composition. For example, split feed towers are known for use after vapor-liquid separation. In this case, the vapor is fed to the high part of the tower and the liquid is fed to the low part of the tower to obtain the advantages of equilibrium flash separation. Feed the same feed composition and a similar phase (vapor phase or liquid phase), separated by 25 rectification trays, located in two different columns and operating at different pressures Doing this is the opposite of previous rectification methods that seek to find the optimum feed position. The optimum feed position is typically defined as the point at which the composition is similar within the column. However, significant energy savings can be achieved by using the concept of the embodiments disclosed herein as a means of balancing the operation of a two-column, two-pressure system.

  In the described split feed embodiment, the column pressure level can be increased or decreased to optimize energy usage. This makes it possible not only to achieve further energy savings in the refrigeration system, as in the case of the conventional two-column system, but also to achieve the ultimate energy saving of rectification.

  In a further embodiment, minimizing the 1-hexene content of the stream by selecting the side distillation position of stream 264 from the first column 252 in FIG. 4 for a particular system design. You can also. As explained earlier, the relative volatility between 1-hexene and 2-hexene and 3-hexene is close to separating high purity (> 99 mol%) 1-hexene. The number of stages and the reflux of the tower are required. As a result, the hexene rectification process consumes a great deal of energy. In the hexene rectification column, 1-hexene is extracted from the top, and 2-hexene and 3-hexene are extracted from the bottom. The 2-hexene and 3-hexene bottoms are recycled to the hexene isomerization reactor where they are enriched with 1-hexene. The effluent from the hexene isomerization reactor is combined with a fresh 3-hexene feed and returned to the hexene rectification column. Whatever the exit temperature of the isomerization reactor, the concentration of 1-hexene is limited by equilibrium. Operation at high temperatures is limited by fouling, and operation at lower temperatures has the limitation that equilibrium is undesirable. The conversion per pass in the isomerization reactor is determined by the inlet concentration of 1-hexene in the recycle stream and the outlet concentration determined by the equilibrium in the reactor outlet.

  A person constructing a system for producing a linear alpha olefin such as 1-hexene can reduce the concentration of 1-hexene at the bottom of the rectifying column (an example in the case of 1 mol% is shown in the following mode It is believed that the rectification system would be designed to increase the conversion per pass of the downstream hexene isomerization reactor. The lowest possible concentration of 1-hexene in the column system is at the bottom of the column. The single column system is most plausible because the amount of 1-hexene at the bottom of the rectification column is low, reducing the amount of hexene tower recycling. FIG. 6 shows a conventional rectification column 290. A portion of the bottom stream 291 is recycled to the hexene isomerization reactor 292 and then returned to the rectification column 290. Further, the design of FIG. 6 (mode 1, shown below, 1-hexene at the bottom of the column has a low concentration), 1-hexene is hardly lost during the purge, so that a high 1-hexene recovery rate (1 produced) -The ratio of hexene to the total hexene in the fresh feed is also possible.

  The scheme of FIG. 7 can be used in connection with the embodiment of FIG. 4 or can be incorporated into the embodiment of FIG. In the embodiment shown in FIG. 7 (mode 2), the hexene side distillation is withdrawn at a higher 1-hexene composition than at the bottom and fed to the hexene isomerization reactor. . More specifically, the rectification column 294 has a side distillation draw 295 that is sent to the isomerization reactor 296. A non-limiting example of 1-hexene concentration in the side distillation is 2.5 mole% 1-hexene. The higher the concentration of 1-hexene in the reactor feed, the lower the conversion rate of the hexene reactor per pass and the higher the hexene isomerization reactor recycling rate by 2.7%. As this rises, the energy requirements for the isomerization reactor will increase. The hexene purge (column bottom) in FIG. 7 (mode 2) is again extracted from the column bottom with the same 1-hexene column bottom standard. In mode 2, the hexene isomerization reactor recycle rate is increased by 25%, thereby increasing the utility of the isomerization system, including evaporation and preheating, and therefore the internal reflux flow of the hexene column is an absolute reference. It is not clear whether it will decrease in large quantities. As a result, at the same 1-hexene recovery, using mode 2 will netly reduce isomerization energy consumption and reflux ratio over the tower. This net reduction in the reflux flow of the column occurs because the required amount of energy is reduced because the hexene isomerization recycling standards to be adapted have been slightly relaxed.

  The reduction in energy consumption when using mode 2 instead of mode 1 is shown in Table 11 below.

  As seen in Table 11, using mode 2 reduces the total energy usage from 93.59 MM Kcal / hr to 88.58 MM Kcal / hr, which is an energy reduction of about 5%.

  Certain embodiments of the automated metathesis process described in US Pat. No. 6,727,396 include a butene isomerization reaction used to convert internal butene and internal hexene olefins to external alpha olefins, respectively. And a hexene isomerization reactor are included. In addition, the process employs an automatic metathesis reactor system. Each of these three reaction systems is a vapor phase fixed bed reaction system. In each, it is necessary to first evaporate the feed to the reactor (because the feed is a liquid at the feed point to the unit). Further, in each reactor, the temperature of the effluent is significantly higher than the feed temperature and / or the temperature of the rectification column following the reactor. In the isomerization process, higher temperatures are advantageous for the desired alpha olefin, and automatic metathesis requires higher temperatures from the viewpoint of reaction kinetics, so these higher temperatures are required. In conventional systems, the effluent from the reactor is used to evaporate the feed to some extent and preheat, with the remainder required for preheating being supplied by a combustion heater. It will be.

FIG. 8 shows a process flow scheme for producing 1-hexene, with the addition of additional heat exchangers 330, 332, and 334 to reduce the construction costs of furnaces 342, 344, and 346. The system shown in FIG. 8 includes a hexene isomerization and purification zone 302, a butene isomerization and purification zone 304, and an automatic metathesis zone 306. The butene feed stream 305 is combined with the recycle stream 311 to form a stream 307. Stream 307 is heated in heat exchanger 330, further heated in heat exchanger 336, sent to furnace 342, and then isomerized in reactor 331. Reactor effluent stream 308 is rectified in rectification column 309 and the overhead stream 310 is split into reflux stream 341 and metathesis feed stream 313, the latter being sent to metathesis zone 306. Although the bottom stream 331 is recycled, it can also be partially purged into the stream 337. In metathesis zone 306, stream 313 is combined with metathesis recycle stream 312 to form stream 314. Stream 314 is heated in heat exchanger 334, further heated in heat exchanger 340, sent to furnace 346, and subjected to metathesis in reactor 335. The reactor effluent (in stream 316) is rectified in rectification section 318. Byproduct is withdrawn into stream 320 and purge stream 322 is withdrawn. C _{4 ′} and C _{5 ′} are recycled to stream 312. The metathesis reaction product stream 324 is sent to the hexene isomerization and purification zone 302.

In zone 302, stream 324 is heated in heat exchanger 332, heated in heat exchanger 338, sent to furnace 344, and then isomerized in reactor 333. The reactor effluent (in stream 325) is rectified in rectification section 326 to form 1-hexene product stream 328, C ₆ purge stream 329, and C ₇₊ purge stream 339. By adding separate heat exchangers 330, 332, 334 to preheat the reactor feed upstream of butene isomerization reactor 331, hexene isomerization reactor 333, and automatic metathesis reactor 335, respectively, these reactions. The energy consumption in the furnaces upstream of each unit is reduced. Most of the required heat load occurs in the evaporators 330, 332 and 334, but they are upstream of the process / process heat exchangers 336, 338 and 340, which are further in furnaces 342, 344, respectively. And directly upstream of 346. The flow scheme shown in FIG. 8 results in a furnace construction cost savings of over 80% compared to known prior art systems that do not include heat exchangers 330, 332 and 334.

  The heat exchangers 330, 332 and 334 are often evaporators. In these heat exchangers, in some cases, waste heat from other heat sources can be used (if available). For example, in an ethylene system, this can be quench water. In addition, in various integrated steam systems, the overall efficiency of the steam system will be increased by making the best use of “pass-out” steam. Combustion heaters require additional heat recovery (after process load preheating) to prevent energy waste. As the combustion load in the heater increases, a greater amount of heat is required, resulting in higher construction costs for the system. Adding devices to achieve device cost savings is counterintuitive. However, in this case, a low-cost evaporator is added to reduce the size of the high-cost combustion heater, thus saving construction costs and reducing energy consumption.

  It can be appreciated that various of the above and other features and functions, or alternatives, are also desirable to be incorporated into many other systems or applications. In addition, alternatives, modifications, variations or improvements thereto may be made by those skilled in the art that are not foreseeable or foreseeable at this time, which are also encompassed by the following claims. It is also intended to wax.

Embodiments described herein provide a process for producing linear alpha olefins that results in reduced energy usage in production. In one embodiment, the overhead condenser from the hexene separation column is used as a reboiler for the butene separation column. This reduces the overall heat requirement in the system. In another embodiment, which may be used in conjunction with or separately from this one embodiment, in another embodiment, a two tower refinery for either or both of the butene and hexene purification towers. Use the retention system. The feed is split and fed to two separate but integrated towers operating at two different pressures to allow heat exchange, further reducing production costs.

In conventional systems, the butene splitter operates at the lowest possible pressure to increase the relative volatility between 1-butene and 2-butene, thereby facilitating the required separation. Designed to be. Increasing the specific volatility reduces the amount of reflux required and the heating / cooling load level. However, the temperature required to cool the condenser liquid limits the pressure in the butene tower. If the pressure in the butene tower is very low, the tower top temperature will be out of the temperature range of the cooling water, resulting in the need for refrigeration and additional process energy to provide that refrigeration. In this application, the butene tower (s) will typically be designed at 70 gauge pounds per square inch (70 psig) at approximately gauge pressure. Here, 1 psig = 6.895 kPa. In the following, the pressure is expressed in psig, but is converted into SI unit kPa at the above conversion rate.

In one reference embodiment described herein, the hexene splitter is operated at a higher pressure, thereby utilizing the overhead vapor stream to heat the butene splitter reboiler stream. It becomes possible. If the hexene splitter (s) is operated at a higher pressure, the higher the absolute pressure, the lower the relative volatility, so more constant theoretical plates are required if the reflux ratio is constant. As can be seen from the computer simulation shown in Table 1 below, when the top pressure of the hexene splitter is increased from 0 psig to 15 psig, the theoretical separation stage increases from 103 to 125. This corresponds to an increase rate of 21%. Thus, higher pressure towers will have higher construction costs due to the increased number of stages.

In the embodiment described herein, when 1-hexene is separated from 2-hexene and 3-hexene in a two-column system with split feed, the difference in pressure at the top of each of the two distillation columns. is usually, 4~40psi g or 6~20psi g or 8~15psi g,,. Using a two column system described herein, when separating components other boiling points close to each other, the difference in pressure in each of the top of the distillation column of the two is usually, 4～40Psi g or, in the range of 6～20Psi g or 8~15psi g,. The optimum choice of differential pressure depends on the desired temperature difference for heat exchange and the resulting heat exchanger size (and cost).

The scheme of FIG. 7 can be used in connection with the embodiment of FIG. 4 or can be incorporated into the conventional embodiment of FIG. In the embodiment shown in FIG. 7 (mode 2), the hexene side distillation is withdrawn at a higher 1-hexene composition than at the bottom and fed to the hexene isomerization reactor. . More specifically, the rectification column 294 has a side distillation draw 295 that is sent to the isomerization reactor 296. A non-limiting example of 1-hexene concentration in the side distillate is 2.5 mol % 1-hexene. The higher the concentration of 1-hexene in the reactor feed, the lower the conversion rate of the hexene reactor per pass and the higher the hexene isomerization reactor recycling rate by 2.7%. As this rises, the energy requirements for the isomerization reactor will increase. The hexene purge (column bottom) in FIG. 7 (mode 2) is again extracted from the column bottom with the same 1-hexene column bottom standard. In mode 2, the hexene isomerization reactor recycle rate is increased by 25%, thereby increasing the utility of the isomerization system, including evaporation and preheating, and therefore the internal reflux flow of the hexene column is an absolute reference. It is not clear whether it will decrease in large quantities. As a result, at the same 1-hexene recovery, using mode 2 will netly reduce isomerization energy consumption and reflux ratio over the tower. This net reduction in the reflux flow of the column occurs because the required amount of energy is reduced because the hexene isomerization recycling standards to be adapted have been slightly relaxed.

Claims (15)

A separation process,
(A) obtaining a hydrocarbon mixture comprising a first hydrocarbon, a second hydrocarbon, and a hydrocarbon having a higher boiling point, wherein the second hydrocarbon is a large amount of the first hydrocarbon; Having an atmospheric pressure boiling point 0.3-10 ° C. higher than the atmospheric boiling point;
(B) dividing the hydrocarbon mixture into a first feed stream and a second feed stream;
(C) feeding the first feed stream to a first intermediate stage of a first distillation column operating at a first overhead pressure;
(D) feeding the second feed stream to a second intermediate stage of a second distillation column operated at a second overhead pressure lower than the first overhead pressure;
(E) withdrawing a first distillate comprising most of the first hydrocarbon from the top of the first distillation column, condensing the first distillate at least partially, Feeding the condensed first distillate to the second distillation column in a third intermediate stage above the second intermediate stage;
(F) extracting higher boiling hydrocarbons from the bottom of the first distillation column;
(G) extracting the first hydrocarbon from the top of the second distillation column;
(H) extracting the second hydrocarbon from the bottom of the second distillation column;
(I) Using the first distillate, heating at least a part of the second hydrocarbon extracted from the bottom of the second distillation column, and heating the heated part to the second Returning to the distillation column of
Including processes.   The process of claim 1, wherein the second distillation column is operated at an average pressure that is at least 7 psi less than the average operating pressure of the first distillation column.   The process according to claim 1, further comprising the step of: (j) extracting a side distillate of the first liquid from the first distillation column in a fourth intermediate stage below the first intermediate stage. .   The process of claim 3 wherein the first portion of the first liquid side distillate is purged.   The process according to claim 1, wherein the first hydrocarbon is 1-hexene and the second hydrocarbon is at least one member selected from the group consisting of 2-hexene and 3-hexene. .   The process of claim 1, wherein the first hydrocarbon is 1-butene and the second hydrocarbon is 2-butene.   The process of claim 1 wherein the first portion of the first liquid side distillate is purged and the second portion is isomerized.   The process of claim 3, wherein the energy usage in the isomerization reactor can be adjusted by adjusting the flow rate of the side distillation of the first liquid.   The process of claim 1, wherein a third intermediate stage of the second distillation column is above the second intermediate stage.   The process of claim 1, wherein the process saves at least about 10% energy compared to a single column distillation column system used at the same 1-hexene production rate.   The process of claim 1, wherein the process saves at least about 20% energy compared to a single column distillation column system used at the same 1-hexene production rate. A super rectification system,
A first distillation zone comprising a first distillation column, a first condenser having a first coolant source, and a first reboiler having a first heat source, said first distillation column A first distillation zone having a first feed inlet configured to receive a first portion of a fresh feed, a first distillate outlet, and a first bottom outlet; ,
A second distillation comprising a second distillation column configured to operate at a lower pressure than the first distillation column, a second condenser, and a second reboiler having a second heat source. A second distillation inlet, wherein the second distillation column is configured to receive a second portion of a fresh feed, disposed above the second feed inlet, and A second distillation zone having a third feed inlet, a second distillate outlet, and a second bottom outlet, configured to receive at least a portion of the distillate from the distillation zone of ,
Including
The super rectification system, wherein the second heat source for the second reboiler is the first coolant source for the first condenser.   The ultra-rectification system of claim 12, wherein the first and second distillation zones are configured to separate 1-hexene from 2-hexene and 3-hexene.   13. The ultra rectification system of claim 12, wherein the first and second distillation zones are configured to separate 1-butene from 2-butene.   13. The ultra rectification system of claim 12, further comprising a first side distillation outlet configured to withdraw a side distillation stream for feeding to the isomerization reactor above the first distillation column.

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