Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C7/00—Purification; Separation; Use of additives
  • C07C7/04—Purification; Separation; Use of additives by distillation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
  • B01D3/14—Fractional distillation or use of a fractionation or rectification column
  • B01D3/141—Fractional distillation or use of a fractionation or rectification column where at least one distillation column contains at least one dividing wall
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C2/00—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms
  • C07C2/02—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by addition between unsaturated hydrocarbons
  • C07C2/04—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by addition between unsaturated hydrocarbons by oligomerisation of well-defined unsaturated hydrocarbons without ring formation
  • C07C2/06—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by addition between unsaturated hydrocarbons by oligomerisation of well-defined unsaturated hydrocarbons without ring formation of alkenes, i.e. acyclic hydrocarbons having only one carbon-to-carbon double bond
  • C07C2/08—Catalytic processes

Definitions

• the invention relates to a method for separating a mixed hydrocarbon stream comprising n-butenes and a method for making n-butenes.
• Butenes are the four isomeric substances
• n-butenes obtained during ethylene dimerization are a mixed stream including
• 1 -butene and 2-butenes may have considerably different reactivities in several of the downstream reactions. For example, essentially only the
• 2-butenes react in a metathesis reaction, while 1 -butene is essentially inert. Ethylene dimerization is accompanied by the generation of heavier olefins. Hence, the effluent from an ethylene dimerization is separated by distillation.
• the conventional distillation of the dimerization mixture can be carried out with two distillation columns. In a first column, light components including ethylene, 1 -butene, and 2-butenes are separated as overhead and the heavy components including pentenes, hexenes, octenes are recovered from the bottom of the first distillation column.
• the light components are further distilled in a second column to separate the 1 -butene stream (which may contain unreacted ethylene) from a 2-butenes stream.
• US 2012/095275 discloses a process for producing propylene and 1 -butene. The process comprises dimerizing ethylene in the presence of a dimerization catalyst to produce a dimerization mixture comprising 1 -butene and 2-butenes. The dimerization mixture is distilled to produce a 1 -butene stream containing 1 -butene and ethylene, a 2-butenes stream, and a heavy stream.
• the 2-butenes stream is reacted with ethylene in the presence of a metathesis catalyst to produce a metathesis mixture comprising propylene, ethylene, and 2-butenes.
• a metathesis catalyst to produce a metathesis mixture comprising propylene, ethylene, and 2-butenes.
• US 2012/095275 describes that distillation of the dimerization mixture may be carried in a single column distillation or a dividing wall column.
• the heat requirements in the sump of a column must satisfy, in general, three requirements, i.e., heating up the liquid to sump temperature, supplying energy for separation of feed components, and generating stripping vapor.
• a dividing wall column offers the advantages of both lower investment costs and reduced energy demand during operation. Since however, the dividing wall column is a single column that has only one common sump - as opposed to a two column separation train - the energy must be input at a temperature level corresponding to the higher of the two sump temperatures in a conventional two-column separation train. This is due to the fact that in the single column design of the dividing wall column, high boilers are invariably present in the sump causing a high boiling temperature of the bottom liquid located in the sump.
• the technical problem on which the invention is based is the provision of a process for the separation of 1 -butene and 2-butenes using a dividing wall column that maximizes the proportion of thermal energy provided at a relatively lower temperature level while still minimizing the overall energy demand of the process.
• a dividing wall column with the lowest possible number of theoretical stages should be used.
• a method for separating a mixed hydrocarbon stream comprising 1 -butene, 2-butene, heavier olefins and unconverted ethylene comprising: introducing the mixed hydrocarbon stream into the feed section of a dividing wall distillation column, the dividing wall distillation column having a shell defining a middle vapor-liquid contacting area, an upper vapor-liquid contacting area being above and in communication with the middle vapor-liquid contacting area, and a lower vapor-liquid contacting area being below and in communication with the middle vapor-liquid contacting area, the middle vapor-liquid contacting area containing at least one vertically oriented partition dividing the middle vapor-liquid contacting area into at least the feed section defined by the shell and the partition and a sidedraw section defined by the shell and the partition, providing thermal energy to the dividing wall distillation column via a bottom reboiler which is in communication with the lower vapor-liquid contacting area, at least partially condensing vapors emerging
• the invention maximizes the proportion of thermal energy provided at a relatively lower temperature level while still minimizing the overall energy demand of the process. With all other variables constant, the invention further allows for a reduction of the number of plates in the feed section of the middle vapor-liquid contacting area.
• the term “heavier olefins” denotes olefins having more than four carbon atoms.
• the mixed hydrocarbon stream comprises 4 to 10% by weight, preferably 5 to 8% by weight, of 1 -butene; 60 to 95% by weight, preferably 75 to 90% by weight, of 2-butene; 1 to 27% by weight, preferably 2 to 15% by weight, of heavier olefins and 0 to 3% by weight, preferably 0 to 2% by weight, of ethylene.
• the heavier olefins mainly encompass olefins with a carbon number that is a multiple of two, in particular hexenes.
• the mixed hydrocarbon stream may comprise minor concentrations of olefins with an odd number of carbon atoms such as propylene and pentene.
• the mixed hydrocarbon stream may be an effluent stream of an ethylene dimerization process.
• the invention also relates to a method for making n-butenes, the method comprising: introducing an ethylene stream into a dimerization zone containing a dimerization catalyst and into contact with the dimerization catalyst, operating the dimerization zone at conditions effective to produce a mixed hydrocarbon stream comprising 1 -butene, 2-butenes, heavier olefins and unconverted ethylene, if any, and separating the mixed hydrocarbon stream by the method described above.
• the dividing wall distillation column has at least one inlet port.
• the inlet port is for introducing the mixed hydrocarbon stream into the feed section of the dividing wall distillation column.
• the 2-butenes stream is withdrawn from the dividing wall distillation column as a sidedraw from the sidedraw section.
• the dividing wall distillation column also produces an overhead stream comprising the 1 -butene and any unconverted ethylene.
• the dividing wall distillation column also produces a bottom stream comprising the heavier olefins.
• the dividing wall distillation column usually is a vertically oriented cylindrical column having a shell with a cylindrical inner surface.
• the phrase "vertically oriented” means forming an angle with the horizontal of generally between about 85 and about 95°, and preferably between about 87.5 and 92.5°.
• the dividing wall distillation column has three distillation vapor-liquid contacting areas - an upper area, a middle area, and a lower area.
• the middle vapor-liquid contacting area contains at least one partition or dividing wall, a plane which is usually vertically oriented.
• the longitudinal axis of the middle vapor-liquid contacting area is also vertically oriented, similar to the longitudinal axes of the upper and lower vapor-liquid contacting areas.
• the dividing wall divides the middle vapor-liquid contacting area into two sections, a feed-side section and a sidedraw-side section.
• the area of any horizontal cross-section of the middle area of the column is divided between the feed-side section and the sidedraw-side section.
• the division of the column's horizontal cross-section between these two sections is not necessarily equal. The division depends in part on the composition of the feed stream entering the middle vaporliquid contacting area and on the proportion of that feed that is in the vapor phase.
• the area of the feed-side section may be from about 30% to about 60% of the area of any horizontal cross-section.
• the area of the sidedraw-side section is generally from about 40% to about 70% of the area of any horizontal cross-section.
• Each partition or dividing wall is generally a baffle that is preferably imperforate.
• Each dividing wall may be a single piece or may consist of multiple sectional pieces that are affixed together, such as by welding or bolting.
• the baffle is generally rectangular having two faces and four edges. One face of the baffle faces the feed-side section of the middle vapor-liquid contacting area, and the other face faces the sidedraw-side section.
• the pair of opposing side edges of the dividing wall is usually affixed to the inside surface of the column wall of the middle vapor-liquid contacting area, and preferably, each edge of this pair is sealingly engaged to the inside surface wall in a manner, such as by seal welding, so that with respect to passing between the attached edge and the column wall, fluids in one section of the middle vapor-liquid contacting area are not in communication with fluids in any other section of the middle vapor-liquid contacting area.
• the top edge of the dividing wall delineates the top of the middle vapor-liquid contacting area and the bottom of the upper vapor-liquid contacting area.
• the bottom edge of the dividing wall delineates the bottom of the middle vapor-liquid contacting area and the top of the lower vapor-liquid contacting area.
• the side edges may be shaped or rounded in order to facilitate attachment of the dividing wall to the column wall.
• the top edge may be shaped or segmented in a manner that facilitates attachment or fit-up between the dividing wall and plates or other column internals in the top of the middle vapor-liquid contacting area and/or the bottom of the upper vapor-liquid contacting area.
• the bottom edge may be shaped to enhance the fit between the dividing wall and plates or internals at the bottom of the middle vapor-liquid contacting area and/or the top of the lower vapor-liquid contacting area.
• the thickness of the dividing wall may be any suitable thickness, subject to mechanical requirements of the structural strength of the dividing wall, attachment to the column wall, or attachment to other column internals including other dividing walls in the column.
• the dividing wall may comprise two walls with a gas space in between.
• the dividing wall may be constructed from any suitable material, and it is believed preferable that the dividing wall and the column wall shell are of the same material.
• the dividing wall material is usually carbon steel.
• the surfaces of the faces of the dividing wall are generally smooth.
• Vapor-liquid contacting devices are in the upper, middle, and lower vapor-liquid contacting areas of the dividing wall distillation column. Any suitable vapor-liquid contacting device may be used. Suitable vapor-liquid contacting devices include plates and packing. As used herein, the term "plate" includes tray. The trays generally consist of a solid tray or deck having a plurality of apertures and are installed on support rings within the tower. Suitable trays include cross-flow trays like sieve trays, fixed valve trays or bubble cap trays. Packing is used in a vapor-liquid contacting area, either in addition to or instead of plates. A vapor-liquid contacting area is usually designed based on the hydraulic performance (e.g., pressure drop, flooding, and loading) and mass transfer performance (e.g., height equivalent to a theoretical plate, or HETP).
• hydraulic performance e.g., pressure drop, flooding, and loading
• mass transfer performance e.g., height equivalent to a theoretical plate, or HETP
• one or more plates are usually located above the elevation of the inlet port to the feed-side section and below the elevation of the top edge of the dividing wall, and one or more plates are usually located between that inlet port and the bottom of the dividing wall.
• One or more plates are usually in the sidedraw section, and one or more plates usually are in the lower vapor-liquid contacting area. Any of the plate spacings in any of these areas or sections may be the same as or different from not only plate spacings in other areas or sections but also spacings in the same area or section. Generally, the spacings for the plates at the elevation at which the feed streams are introduced into the column are generally greater than the spacings for other plates.
• Plates usually have a plate efficiency of 80%, but plates having a higher or lower efficiency may be used.
• plate efficiency is the approach to equilibrium defined as the ratio of the actual change in vapor composition as the vapor passes through the plate to the change that would have occurred if the vapor had reached a state of equilibrium with the liquid leaving the plate.
• the plates below the mixed hydrocarbon steam inlet in the feed-side section act as a stripping section to decrease the concentrations of 1 -butene without significantly decreasing the concentrations of 2-butenes and heavier olefins in the downflowing liquid.
• the V/L in the feed-side section below the mixed hydrocarbon stream inlet, as well as the temperature at the bottom of the dividing wall in the feed-side section, are important parameters for controlling the concentration of 1 -butene in the sidedraw stream.
• the plates in the lower vapor-liquid contacting area act as a stripping zone not only to further decrease the concentration of 1 -butene but also to decrease the concentration of 2-butenes in the downflowing liquid in order to attain a highly concentrated bottom stream comprising heavier olefins and a minimal amount, if any, of 2-butenes.
• the plates above the sidedraw outlet in the sidedraw-side section act as a stripping section to decrease the concentrations of 1 -butene in the descending liquid.
• the plates below the sidedraw outlet in the sidedraw-side section act as a rectification section to decrease the concentrations of heavier olefins in the ascending vapor.
• V/L ratio is the ratio of moles of upflowing vapor (V) to moles of downflowing liquid (L).
• V upflowing vapor
• L downflowing liquid
• the dividing wall distillation column including the upper vapor-liquid contacting area, the middle vapor-liquid contacting area and the lower vapor-liquid contacting area, comprises 80 to 200, preferably 130 to 170 theoretical stages, with the 1 st theoretical stage being the lowermost theoretical stage in the dividing wall distillation column.
• a theoretical stage in distillation processes is a hypothetical zone or stage in which the liquid and vapor phases of the substance to be distilled establish a thermodynamic equilibrium with each other. The greater the number of theoretical stages, the greater the efficacy of the separation process. The concept, as well as the calculation, of theoretical stages is well known to the skilled person.
• the dividing wall is configured such that the bottom edge of the dividing wall is located at an elevation from the 2 nd to the 50 th , preferably from the 4 th to the 30 th , more preferably from the 5 th to the 15 th theoretical stage, with the 1 st theoretical stage being the lowermost theoretical stage in the dividing wall distillation column.
• the vertical extent of the dividing wall may be from 10 to 150, preferably from 80 to 120, theoretical stages.
• the inlet port is at a position at an elevation from 1 theoretical stage above the bottom edge of the dividing wall to 1 theoretical stage underneath the top edge of the dividing wall, preferably from 50 theoretical stages above the bottom edge of the dividing wall to 1 theoretical stage underneath the top edge of the dividing wall.
• the 2-butene withdrawal port is at a position at an elevation from 1 theoretical stage above the bottom edge of the dividing wall to 1 theoretical stage underneath the top edge of the dividing wall, preferably from 1 theoretical stage above the bottom edge of the dividing wall to 50 theoretical stages underneath the top edge of the dividing wall.
• the liquid fraction to be directed to the sidedraw evaporator is withdrawn from the dividing wall distillation column via a sidedraw.
• a sidedraw there is an accumulator plate and a downcomer from which downflowing liquid may be withdrawn from the column.
• the liquid that collects on the accumulator plate preferably flows to the downcomer from which the liquid is withdrawn from the dividing wall distillation column.
• the liquid fraction is withdrawn from the lower vapor-liquid contacting area, e.g., at an elevation from the 2 nd to 40 th , more preferably from the 3 rd to the 6 th theoretical stage, with the 1 st theoretical stage being the lowermost theoretical stage in the dividing wall distillation column.
• the heated, partially evaporated fraction is directed back to the lower vapor-liquid contacting area, in particular within 20, in particular 2, in particular 1 theoretical stage(s) below or above the sidedraw from which the liquid fraction is withdrawn.
• a condenser is in communication with the upper vapor-liquid contacting area.
• the condenser is capable of condensing vapor to liquid, either as a total condenser or a partial condenser of the entering vapor, and such condensers are known to the skilled person.
• the condenser may be external to the column or located within the column.
• An internal condenser may be located within the column directly above the upper vaporliquid contacting area, and so there is communication between the condenser and the upper vapor-liquid contacting area.
• communication with the upper vapor-liquid contacting area may be via one or more ports, conduits, and/or accumulators.
• a nozzle attached to the shell of the dividing wall distillation column vessel may be connected to the condenser to permit vapor to flow from the upper vaporliquid contacting area to the condenser.
• a nozzle attached to the shell of the column vessel may be connected to the condenser to allow liquid flow from the condenser to the upper vapor-liquid contacting area.
• An accumulator may be located between the condenser and the upper vapor-liquid contacting area, to collect condensed liquids and separate the liquids from uncondensed vapor, and this accumulator may be in communication via ports or conduits with the condenser and the upper vapor-liquid contacting area.
• a pump may be used to pump liquid from the accumulator to the upper vapor-liquid contacting area, and the liquid flow may be regulated by a control valve.
• the outlet port for vapors from the dividing wall distillation column and the inlet port for liquid to the dividing wall distillation column are preferably separate ports, they may be the same port, with relatively less-dense vapor rising and relatively more-dense liquid falling through the same port.
• At least a part of the condensate is recycled as a reflux to the upper vapor-liquid contacting area, with the remainder being drawn off as a top stream from the diving wall distillation column.
• the reflux ratio is in the range of 20 to 90, preferably 30 to 70.
• the reflux ratio is defined as the ratio of reflux flow rate to the rate of the top stream draw-off.
• the top stream comprises a majority of 1 -butene with the remainder being ethylene, such as 60 to 99% by weight, preferably 80 to 99% by weight, of 1 -butene.
• a bottom reboiler is in communication with the lower vapor-liquid contacting area.
• the reboiler is capable of evaporating liquid to vapor, usually as a partial reboiler of the entering liquid, and such reboilers are known to the skilled person.
• the reboiler may be an external reboiler or an internal reboiler located within the column.
• An internal reboiler may be located within the column directly below the lower vapor-liquid contacting area, and so there is communication between the reboiler and the lower vapor-liquid contacting area.
• communication with the lower vapor-liquid contacting area may be via one or more ports and/or conduits.
• a nozzle attached to the shell of the dividing wall distillation column vessel may be connected to the reboiler to permit liquid to flow from the lower vapor-liquid contacting area to the reboiler.
• a pump may be used to pump liquid from the column to the reboiler, and the liquid flow may be regulated by a control valve.
• the reboiler may be a so-called thermal siphon reboiler, in which reboiling changes the density of the material being reboiled and that density change, in turn, induces flow through the reboiler.
• a nozzle attached to the shell of the column vessel may be connected to the reboiler to allow vapor, or perhaps a vapor-liquid two-phase mixture, to flow from the reboiler to the lower vapor-liquid contacting area.
• the outlet liquid for liquid from the dividing wall distillation column and the inlet port for vapor to the dividing wall distillation column are preferably separate ports, they may be the same port, with relatively more-dense liquid falling and relatively less-dense vapor rising and through the same port.
• the evaporation rate in the bottom reboiler is in the range of 2 to 15% by weight, more preferably 5 to 12% by weight.
• the distillation is typically carried out at a pressure (at the top of the dividing wall distillation column) of 3 to 8 bara, preferably 3.6 to 6.7 bara.
• the sump temperature is generally in the range of 100 to 150 °C, preferably 110 to 130 °C, with the temperature at the top of the dividing wall distillation column being in the range of 30 to 70 °C, preferably 30 to 50 °C.
• Heating in the bottom reboiler is supplied by a heat transfer medium at a temperature of 130 to 250 °C, preferably 135 to 160 °C, such as heating steam with 3 to 40 bara.
• the temperature differential between the heat transfer medium and the bottom liquid is suitably within 5 to 25 K.
• additional thermal energy is provided to the dividing wall distillation column by the use of a sidedraw evaporator.
• a liquid fraction is withdrawn from the dividing wall distillation column via a sidedraw, and the liquid fraction is heated and partially evaporated the in the sidedraw evaporator.
• the heated, partially evaporated fraction is directed back to the dividing wall distillation column.
• a pump may be used to pump the liquid fraction from the column to the sidedraw evaporator, and the flow of liquid fraction sidedraw evaporator may be regulated by a control valve.
• Heating in the sidedraw evaporator is preferably effected against a heat transfer medium at a temperature of 65 to 125 °C, preferably 65 to 99 °C, more preferably 70 to 90 °C, such as hot water.
• the temperature differential between the heat transfer medium and the liquid fraction is suitably within 5 to 25 K.
• a significant proportion of the total thermal energy provided to the dividing wall distillation column can be provided via the sidedraw evaporator at a comparatively lower temperature level, i.e., a temperature lower than the temperature required for the bottom reboiler. This may allow heat recovery from low grade waste heat generated by a wide variety of industrial and commercial processes and operations. When waste heat is low grade, such as waste heat having a temperature of heat below 100 °C, for example, conventional heat recovery systems do not operate with sufficient efficiency to make recovery of energy cost-effective.
• the sidedraw evaporator By using the sidedraw evaporator, it is possible to drive up 2-butenes in the sidedraw section of the dividing wall column even with reduced energy input via the bottom reboiler. This is particularly true if a high evaporation rate of the liquid fraction is achieved in the sidedraw evaporator.
• the sidedraw evaporator is not especially limited and may be selected from a falling film evaporator, a rising film evaporator and a forced or natural circulation evaporator or combinations thereof.
• High evaporation rates can be achieved, for example, by using a circulating evaporator with additional internal circulation such as a Robert evaporator.
• a simple circulating evaporator may be sufficient.
• the ratio of thermal energy provided by the bottom reboiler to thermal energy provided by the sidedraw evaporator may be in the range of 10 to 90%.
• a stream essentially consisting of 2-butene is drawn off as a sidedraw from the sidedraw section.
• the 2-butene stream comprises at least 98% by weight, preferably at least 99% by weight, of 2-butene.
• the dimerization catalyst can be a homogeneous catalyst or a heterogeneous catalyst. Examples of suitable homogeneous catalysts are taught in US 3,321 ,546, US 4,242,531 , US 4,476,341 , US 5,260,499 and US 5,414,178.
• the dimerization catalyst comprises a nickel compound and an organo aluminum compound.
• Suitable nickel compounds include nickel salts of a mono- or dicarboxylic acid, preferably an acid having from 5 to 20 carbon atoms, such as nickel oleate, nickel dodecanoate, and nickel octanoate.
• Other nickel compounds include coordination complexes of organic phosphines with nickel salts. Examples of such complexes are nickel bis(triethylphosphine) chloride [N EtsP ⁇ Cfe], nickel bis(triphenylphosphine) octanoate, nickel bis(triphenylphosphine) chloride, and nickel bis(tricyclohexylphosphine) chloride.
• Suitable organo aluminum compounds include those having 1 to 2 alkyl groups and 1 to 2 halogen atoms per aluminum atom. The alkyl groups preferably have 1 to 5 carbon atoms. The halogen is preferably chlorine.
• One particularly preferred dimerization catalyst comprises nickel bis(triphenylphosphine) octanoate and ethyl aluminum dichloride.
• the molar ratio Ni:AI is generally from 0.9:1 to 1 :0.9.
• Another preferred dimerization catalyst comprises (1 ) an organo aluminum compound of the formula R n AIX3- n where R is an alkyl, X is a halogen, n is 1 or 2; (2) a complex of a nickel salt of an organic or inorganic acid with tertiary phosphine or tertiary phosphite, the atomic ratio Al/Ni being varied within the range of 1 :1 to 100:1.
• the dimerization reaction is typically performed at a temperature within a range of 10 to 100 °C, preferably 20 to 80 °C.
• the dimerization reaction can be carried out in a liquid or gas phase by contacting ethylene with the catalyst, depending on the reaction temperature and pressure employed.
• the pressure of the dimerization reaction is generally from 1 to 40 bara.
• the dimerization reaction produces a dimerization mixture that comprises ethylene, 1 -butene, and 2-butenes.
• Other olefins such as hexenes and octenes may be present in the dimerization mixture. It is preferable to minimize the amount of hexenes, octenes, and other higher olefins produced. Generally, this can be achieved by selecting the appropriate catalyst and controlling ethylene conversion. Higher butenes selectivities can be achieved by running at lower ethylene conversions.
• reactors in which the reaction can be carried out are a stirred tank reactor, stirred tank cascade, flow tube and loop reactor.
• the active catalyst is inactivated by treatment of the reaction effluent with an aqueous solution of alkali such as sodium hydroxide.
• the effluent from the dimerization zone is subjected to a caustic wash and drying before being introduced into the feed section of the dividing wall distillation column.
• Fig. 1 shows a plant for the separation of mixed hydrocarbons comprising n-butenes by a process according to the invention, using a dividing wall distillation column with a sidedraw evaporator.
• Fig. 2 shows a plant for separation of mixed hydrocarbons comprising n-butenes according to the prior art, using a dividing wall distillation column.
• Fig. 3 shows a plant for separation of mixed hydrocarbons comprising n-butenes by a process according to the prior art, using a conventional two column distillation train.
• a dividing wall distillation column 101 with a sidedraw evaporator 104 is shown.
• the dividing wall distillation column 101 comprises a feed section, a middle vapor-liquid contacting area, an upper vapor-liquid contacting area above the middle vapor-liquid contacting area, and a lower vapor-liquid contacting area below the middle vapor-liquid contacting area.
• the middle vapor-liquid contacting area is divided by a vertically oriented partition into a feed section and a sidedraw section.
• a mixed hydrocarbon stream 1 comprising 1 -butene, 2-butenes and heavier olefins is introduced into the feed section of the dividing wall distillation column 101 via a side inlet.
• Thermal energy is provided to said dividing wall distillation column 101 via a bottom reboiler 103.
• Vapors emerging from the upper vapor-liquid contacting area of the dividing wall distillation column 101 are condensed via a condenser 102.
• a part of the condensate is recycled to the upper vapor-liquid contacting area as a reflux, and another part of the condensate is drawn off as stream 2 comprising 1 -butene.
• a stream 4 comprising the heavier olefins is drawn off from the lower vapor-liquid contacting area via the reboiler 103, and a stream 3 comprising 2-butenes is drawn off as a sidedraw from the sidedraw section of the dividing wall distillation column 101.
• Additional thermal energy is provided to the dividing wall distillation column 101 via the sidedraw evaporator 104.
• a liquid fraction is withdrawn at a location in the lower vapor-liquid contacting area of the dividing wall distillation column 101 , i.e. below the bottom edge of the dividing wall. Said liquid fraction is then heated and partially evaporated in the sidedraw evaporator 104. The heated, partially evaporated fraction is directed back to the lower vapor-liquid contacting area of the dividing wall distillation column 101.
• Fig. 2 depicts a dividing wall distillation column 201 as shown in Fig. 1. However, no sidedraw evaporator is present.
• Fig. 3 depicts a conventional two column distillation setup with a first distillation column 301 and a second distillation column 304.
• a mixed hydrocarbon stream 1 comprising 1 -butene, 2-butenes and heavier olefins is introduced into the first distillation column 301 .
• Thermal energy is provided to said first distillation column 301 via a bottom reboiler 303.
• Vapors emerging from the top of the first distillation column 301 are condensed via a condenser 302. A part of the condensate is recycled to the first distillation column 301 as a reflux, and another part of the condensate is drawn off as stream 1a comprising 1 -butene and 2-butenes.
• a stream 4 comprising the heavier olefins is drawn off from the first distillation column 301 via the reboiler 303.
• Stream 1a is then introduced into the second distillation column 304 for further fractionation.
• Thermal energy is provided to the second distillation column 304 via a bottom reboiler 306.
• Vapors emerging from the top of the second distillation column 304 are condensed via a condenser 305.
• a part of the condensate is recycled to the second distillation column 304 as a reflux, and another part of the condensate is drawn off as stream 2 comprising 1 -butene.
• a stream 3 comprising 2-butenes is drawn off from the second distillation column 304 via the reboiler 306.
• the bottom temperature in the first distillation column 301 is high (120 °C) due to the heavier olefins present. Due to the high boiling point difference, the heavier olefins can easily be separated and a low reflux ratio is sufficient. Accordingly, the required energy input (60 kW) is significantly lower compared to the downstream second distillation column 304.
• a high reflux ratio is required to achieve the desired purities because the boiling points of 1 -butene and 2-butenes are close to each other.
• a sufficiently large amount of thermal energy 180 kW
• the high boilers are already separated and, therefore, the sump temperature is lower. This energy input can take place at significantly lower temperatures (56 °C).
• the energy input required for using the dividing wall distillation column 201 according to Fig. 2 is 21 % less compared to the conventional two column operation according to Fig. 3.
• a high reflux ratio is required because both the heavier olefins and 2-butenes and 1 -butene are separated simultaneously from each other. Therefore, a high thermal energy input is required (191 kW). Due to the high boiling point of the heavier olefins, the temperature in the sump evaporator is correspondingly high (117 °C).
• the dividing wall distillation column is equipped with a sidedraw evaporator as shown in Fig. 1 , the following advantages result: For the same separation capacity, fewer theoretical separation stages are required than for the dividing wall distillation column without sidedraw evaporator according to Fig. 2 (see table 2: 93 vs. 87 theoretical stages in the feed section). In contrast, the required thermal energy quantity increases slightly by 4 kW. Nevertheless, compared to the conventional two column operation according to Fig. 3, a total of 47 kW can be saved, which corresponds to an energy input reduction of 20%.
• a significant advantage resides in the fact that part of the required heat quantity can be provided via the sidedraw evaporator 104 at a low temperature (58 °C or 56 °C).
• the sidedraw evaporator 104 in Fig. 1 becomes particularly advantageous when operated at a high evaporation rate. This is for the following reasons: At an evaporation rate of 70%, 138 kW can be supplied at a temperature of 58 °C. Accordingly, only 55 kW must be supplied at the high temperature of 123 °C. At an evaporation rate of 10%, most of the heat (173 kW) must be supplied at a temperature of 123 °C. Only a small part (20 kW) can be supplied at 56 °C. By realizing high evaporation rates, the advantages of a conventional two column operation (high energy input at low temperatures) can be combined with the advantages of a dividing wall distillation column (energy savings and lower investment costs).

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• 2023
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