Abstract: A method and a plant are disclosed for purifying lactams, particularly lactams obtained by cyclizing hydrolysis of aminonitrile. The purification of ?-caprolactam obtained by cyclizing hydrolysis of aminocapronitrile is described which includes eliminating the ammonia from the reaction medium of the hydrolysis, then recovering the lactam from the medium in purified form. The recovery is carried out by performing at least a distillation of the lactam in the presence of a base producing optionally a fronts fraction having compounds more volatile than the lactam, a fraction having the lactam to be recovered to the degree of desired purity and a distillation tails having the lactam and compounds less volatile than the lactam. The distillation tails are treated by various processes such as evaporation in thin layers to recover the major part of the caprolactam and recycling the latter in the purification process.

Abstract: Process for devolatilization of a polymer of an aromatic alkylene, such as styrene and, in particular, an improved process using water as a stripping agent (i) in which the total amount of water to be disposed of can be reduced, (ii) which allows at least a portion of the water to be recycled as stripping agent, reducing make-up requirements for the stripping agent, and (iii) which allows at least a portion of the aromatic alkylene monomer in the water to be recycled to the polymerization process (via the devolatilization steps) rather than being disposed.

Abstract: Process for the continuous fractional distillation of mixtures including morpholine (MO), monoaminodiglycol (ADG), ammonia and water obtained by reaction of diethylene glycol (DEG) with ammonia, which includes separating off ammonia at the top of a first distillation column K10, feeding the bottoms from K10 to a second distillation column K20 in which water and organic products are separated off at the top at a temperature at the top in the range from 45 to 198° C. and a pressure in the range from 0.1 to 15 bar, feeding the bottoms from K20 to a third distillation column K30 in which MO and organic products having a boiling point of <140° C. (1.013 bar) are separated off at the top or at a side offtake and ADG and organic products having a boiling point of >190° C. (1.013 bar) are separated off at the bottom, feeding the MO including stream which is separated off at the top or at a side offtake of the column K30 to a fourth column K40 in which organic products having a boiling point of ?128° C. (1.

Abstract: Water is removed from oily water produced during operation of a separation column by withdrawing the oily water from the column during separation into an external separator where the oily water is separated into a water phase and an oily phase. The oily phase is then heated to a temperature effective to produce a density differential that drives the oily phase back into the operating column.

Abstract: A process for reducing the energy consumption of a distillation column is disclosed. The process includes drawing off an intermediate vapor stream from the rectification section of the distillation column. The vapor stream is compressed and the heat in the vapor stream is exchanged with a portion of the liquid bottoms stream. The heat transfer condenses a portion of the vapor stream, while vaporizing the liquid bottoms stream.

Abstract: Processes and apparatuses for separating diisopropylbenzene (DIPB) and triisopropylbenzene (TIPB) from a feed including DIPB, TIPB, and polyalkylate heavies are disclosed. The disclosed processes include introducing the feed into a distillation column having a column top pressure of less than 5 psia, a column bottoms pressure of less than 3 psi, and preferably 2 psi or less above the column top pressure with a bottoms temperature ranging from about 435° F. to about 465° F. The processes also include taking off a side draw including at least 99.8 wt % of the DIPB and at least 50 wt % of the TIPB present in the feed and a bottoms stream including at least 95 wt % of the heavies contained in the distillation feed. The low temperature bottoms temperature enables high pressure steam to be used as the bottoms reboiler heat source.

Abstract: A process for treatment of an aqueous stream to produce a low solute containing distillate stream and a high solute/solids containing blowdown stream utilizing a method to increase the efficiency of an evaporator while providing an essentially scale free environment for the heat transfer surface. Multi-valent ions and non-hydroxide alkalinity are removed from aqueous feed streams to very low levels and then the pH is increased preferably to about 9 or higher to increase the ionization of low ionizable constituents in the aqueous solution. In this manner, species such as silica and boron become highly ionized, and their solubility in the concentrated solution that is present in the evaporation equipment is significantly increased. The result of this is high allowable concentration factors and a corresponding increase in the recovery of high quality reusable water with essentially no scaling.

Abstract: The present disclosure is generally directed to a solar distillation system capable of recovering potable water from non-potable water. In certain embodiments, the system includes a substantially air tight solar still having a roof top composed of a solar light-transmitting material. The solar still includes a tube positioned below and running underneath the roof top, the tube having an exit end. Additionally, the solar still includes a heating surface positioned below the roof top and adapted for receiving at least a portion of the non-potable water exiting the tube at the exit end. Non-potable water on the heating surface is solar heated and a portion of the non-potable water evaporates and condenses on the outside of the tube to be collected as potable water.

Abstract: A process recovers of pyridine and/or its derivatives from their aqueous mass and/or manufacturing reaction mass by liquid-liquid extraction employing an alkyl acetate. The process further involves effective recovering and recycling of solvents from the aqueous phase and other waste obtained during the process.

Abstract: A system and method for removing water from a liquid desiccant such as a glycol used to dry cooled air in order to restore the desiccant to a purity up to around 97% in a closed continuous flow process. Liquid desiccant can be sprayed into cooled air in a conditioner where it gains moisture. The wet or gained desiccant can be optionally preheated in an economizing heat exchanger and then routed into a concentrator. Desiccant pure to around 97% can be removed from the concentrator, passed through an economizing heat exchanger to provide the preheating and returned to the conditioner holding area. The concentrator can be heated by steam or other means such as natural gas to boil the wet desiccant causing mixed vapor to enter a vertical distillation column where most of the glycol condenses out on the column packing or plates and returns to the concentrator.

Abstract: A system for distilling sea or brackish water includes a feed water arrangement for supplying feed water from a feed water source to one or more flashing stages. Each flashing stage has a water flash evaporator for vaporizing at least part of the water therein, and a condenser for receiving the vapour and converting at least a part of the vapour into distilled water. A heat storage arrangement provided with a heat generating source for storing heat energy is used to heat a fluid medium flowing through it. A heat exchange arrangement receives the hot fluid medium and transfers heat to a stream of vapour flowing under pressure from each flashing stage. The vapour leaving the heat exchange arrangement being at a raised temperature is arranged to be condensed into water at the condenser and to transfer some of its latent heat to the evaporator.

Abstract: A glycerol preparation method for preparation of medical grade glycerol from a by-product of a bio-diesel process includes a first stage phosphoric acid chemical reaction process and a posterior by-product centrifugal separation process to have the phosphoric acid chemical reaction by-product be separated into free fatty acid, potassium phosphoric acid, and a crude glycerol and methanol mixture. The crude glycerol and methanol mixture is further processed through a first step of thin film evaporation process where methanol is reclaimed, a second step of thin film evaporation process where the mixture is dehydrated, a third step of molecular distillation process where an industrial grade glycerol of purity over 95% is extracted, and a fourth step of molecular distillation process where a medical grade glycerol of purity in exceed of 99.75% that meets USP/BP standards is extracted.

Abstract: A splitter system is disclosed that produces a product stream from a mixed stream of two materials with similar boiling points. A multi-stage heat pump compressor is used in combination with a bottoms reboiler and an intermediate reboiler resulting in reduced utility consumption. The appropriately placed intermediate reboiler enables use of a lower temperature heat source relative to the bottoms reboiler heat source. As a result, a lower pressure overhead vapor stream can be used to deliver heat to both the intermediate and bottoms reboilers, thereby conserving energy. The first stage of the multi-stage heat pump compressor delivers pressurized overhead vapor to the intermediate reboiler and the second stage provides pressurized overhead vapor to the bottoms reboiler. The disclosed design and method lessens the heat pump compressor power consumption and trim condenser duty for a propylene/propane splitter system by over 20%.

Abstract: A process for treating produced water to generate high pressure steam. Produced water from heavy oil recovery operations is treated by de-oiling the produced water to provide a de-oiled evaporator feedwater that is fed to an evaporator. The pretreated produced water stream is evaporated to produce (1) a distillate having a trace amount of residual solutes therein, and (2) evaporator blowdown containing substantially all solutes from the de-oiled produced water feed. The distillate may be directly used, or polished to remove the residual solutes therein, before being fed to a steam generator. Steam generation in a once-through steam generator, or in a packaged boiler such as a water tube boiler having a steam drum and a mud drum with water cooled combustion chamber walls, produces high pressure steam for down-hole use.

Abstract: A process for extractively removing homogeneously dissolved catalysts from a reaction effluent of a hydrocyanation of unsaturated mononitriles to dinitriles with a hydrocarbon H, including performing the steps of a) concentrating the reaction effluent before step b) by distillation at pressures of from 0.1 to 5000 mbar and temperatures of from 10 to 150° C., b) adding a hydrocarbon H to the concentrated reaction effluent to obtain a stream I, and c) feeding stream I, without prior separation of the liquid phases, into an extraction apparatus and extracting it at a temperature T with the hydrocarbon H to obtain a stream II comprising the hydrocarbon H enriched with the catalyst and a stream III having a low catalyst content.

Abstract: A method of recovering a liquid medium from a mixture containing the liquid medium, the method including: (a) blowing a first gas into the mixture containing the liquid medium to vaporize the liquid medium, in a first vaporizing means, thereby to form a second gas containing which is a mixture of the first gas and vaporized liquid medium; (b) continuously dropwise feeding the mixture containing the liquid medium into a second vaporizing means and counter-flowingly contacting the mixture containing the liquid medium, with the second gas to vaporize additional liquid medium to form a third gas which is a mixture of the second gas and additional vaporized liquid medium; and (c) feeding the third gas into a condensing means to condense the vaporized liquid medium into a liquid and separate the first gas, which is then blown into the first vaporizing means in step (a).

Abstract: A dehydration method of a water-containing substance using a liquefied matter, including a step (1) of contacting a liquefied matter of a substance which is in a gas phase under a condition at ambient temperature and atmospheric pressure with the water-containing substance, to dissolve contained water in the water-containing substance into the liquefied matter, for obtaining the liquefied matter containing a large amount of water; and a step (2) of vaporizing the substance out of the liquefied matter containing a large amount of water, to thereby separate the substance as the gas from water.

Abstract: The invention relates to a process for the distillation of ionic liquids, in which a pressure not higher than ambient pressure is set in a first step and the ionic liquid is heated to a temperature in the range from 60° C. to 350° C. in a second step. The process is employed, in particular, for the purification of ionic liquids.

Abstract: Systems and methods for producing gas-to-liquids products using reactive distillation are provided. The method for producing gas-to-liquids products can include reacting a feedstock in a column having a distillation zone and a reaction zone to provide a bottoms stream and an overhead stream. A first portion of the overhead stream can be recycled to the column at the top of the reaction zone and second portion of the overhead stream can be recycled to the column at the bottom of the reaction zone.

Abstract: A distillation process for separating a target component from a mixture containing a solvent and the target includes the steps of flashing off a vapor mixture of said solvent and said target in an evaporator, separating said target from said vapor mixture, and providing additional solvent to said evaporator to maintain the temperature of said evaporator substantially below the boiling point of said target. The process also includes the step of removing accumulated non-volatile components from said evaporator by allowing the non-volatile components to precipitate from a mixture of the target and the solvent.

Abstract: A process for conditioning of wastewater treatment brines for deep well injection during recovery of heavy hydrocarbon oils in situ. High pressure steam is used to mobilize oil, which is recovered in a mixture of oil and produced water. The produced water is pre-treated by removing residual oil. The remaining water is acidified and steam stripped to remove non-hydroxide alkalinity and non-condensable gases, and is then fed to a crystallizing evaporator, where it is evaporated from a circulating brine slurry to produce (1) a distillate stream having a trace amount of residual solutes, and (2) evaporator blowdown stream containing, as dissolved or suspended solids, substantially all of the solutes from the produced water feed. The distillate stream is used as boiler feedwater, either directly or after polishing. The evaporator blowdown is conditioned to remove substantially all suspended solids and to produce a clear brine solution for deep well injection.

Abstract: A sub-atmospheric pressure desalinating still employs a closed top, open bottom pipe filled with source water to be distilled, such as seawater, having a height greater than the height of a column of seawater that can be supported by the pressure at the bottom of the tank so that a subatmospheric pressure volume is formed at the top. Water from the source is also pumped into the subatmospheric volume and passed through an evaporator which enlarges its surface volume. A small percentage of the water is vaporized and the balance is cooled to provide the heat of vaporization and falls into the top of the seawater column, creating a downward flow. The vapor is drawn from the vacuum and condensed, preferably in a second subatmospheric volume above a column of fresh water.

Abstract: A method of recovering and recycling solvents, comprising, during printing or coating of solvent-recoverable and recyclable printing ink composition comprising solvents, a step of recovering the solvents vaporized in a solvent recovery apparatus, a step of separating the solvents obtained into one or more single solvents and/or one or more azeotropic compositions of two or more solvents by multi-stage distillation, and a step of recycling them as a printing ink raw material and/or dilution solvent raw material.

Abstract: A process for fractionating a starting mixture of two or more components by extractive distillation using a selective solvent in a dividing wall column aligned in the longitudinal direction of the column and extending to the upper end of the column and dividing the column interior into a first region, a second region, and a lower combined column region. The starting mixture is fed into the first region, a first top stream is taken off from the first region, and a second top stream is taken off from the second region, each stream having a prescribed specification. The selective solvent is introduced in the upper part of the first region and/or in the upper part of the second region, and solvent flow into the first region and/or solvent flow into the second region are set so that each of the prescribed specifications for the top streams are met.

Abstract: A process for purifying an aqueous solution to obtain purified gaseous acrolein by introducing the aqueous solution into a distillation column equipped at its base with at least one boiler and at its top with at least one condenser, withdrawing a liquid mixture essentially containing water at the base of the distillation column, withdrawing a gas essentially containing acrolein and water at the top of the distillation column, cooling the gas mixture withdrawn at the top of the distillation column in the condenser, to a temperature which makes it possible to obtain, on the one hand, an aqueous condensate and, on the other hand, an acrolein-rich gas mixture, and withdrawing the acrolein-rich gas mixture.

Abstract: A distillation column is disclosed with a folded design. The column includes a plurality of rectification zones and corresponding stripping zones Each rectification zone is linked to a heat pump or a stage of a heat pump. Overhead vapor from the top rectification zone is compressed and used to heat bottoms liquid from the bottom stripping zone Similarly, overhead vapor from the middle rectification zone is compressed and used to heat liquid from a middle stripping zone and overhead from a lower rectification zone is compressed and used to heat liquid taken from the uppermost or top stripping zone. A single multiple stage heat pump compressor may be utilized as opposed to a plurality of heat pumps Because the heat exchanger from each rectification-stripping zone pair has a lower duty, economical stab-in heat exchangers may be utilized.

Abstract: The present invention relates to a process for the manufacture and separation of dinitrile compounds. It relates more particularly to a process for the manufacture and separation of dinitrile compounds from a medium originating from the hydrocyanation of unsaturated mononitriles. The invention consists in feeding the medium comprising the dinitriles to a distillation column and then recovering the purified dinitriles as intermediate fraction, the heavy products being removed as column tail fraction and the light products, including the unsaturated mononitriles, being recovered as top fraction.

Abstract: An energy efficient process scheme for a highly exothermic reaction-distillation system in which the reactor is external to the distillation column and the feed to the reactor is a mixture of at least one liquid product stream from the distillation column with or without other liquid/vapor reactants. The reactor is operated under adiabatic and boiling point conditions and at a pressure that results in vaporizing a portion of the liquid flow through the reactor due to the heat of reaction. Under these conditions, reaction temperature is controlled by reactor pressure. The pressure (and hence the temperature) is maintained at a sufficiently high level such that the reactor effluent can be efficiently used to provide reboil heat for the distillation column.

Abstract: The invention relates to a semibatchwise process for the mild distillative separation of mixtures, in a first stage a column being supplied continuously with a feed and the feed being separated at least into different fractions, one of the fractions being removed continuously into a container, and, in a second step, the fraction removed into the container being recycled to the column and being separated again batchwise into different fractions.

Abstract: A process for separating carbon dioxide from a fluid containing carbon dioxide, NO2, and at least one of oxygen, argon, and nitrogen comprises the steps of separating at least part of the fluid into a carbon dioxide enriched stream, a carbon dioxide depleted stream comprising CO2 and at least one of oxygen, argon, and nitrogen and a NO2 enriched stream and recycling said NO2 enriched stream upstream of the separation step.

Abstract: A decomposition reaction apparatus or distillation apparatus for acrylic acid in which a column bottom liquid heated in a reboiler (5) is supplied from a supply port (1a) provided on a side wall of a column body (1) having: a top plate (12a) above the supply port (1a); and an impingement plate (12b) provided vertically to the top plate (12a), for preventing scattering of the column bottom liquid to a supply direction. The top plate (12a) is provided such that the top face of the top plate (12a) is inclined downward from a base end to a tip end. The present invention allows: suppression of formation of a polymerized product due to flowing of a liquid or gas heated in a reboiler into a column with a simple structure; and a stable continuous operation of column equipment over a long period of time.

Abstract: The invention provides for the removal of impurities from treatment fluid including a base liquid and a variety of impurities contained in the base liquid by conveying the treatment fluid to at least one preheating separating device, including a preheating heat exchanger and a separator unit, before the admixture of a carrier gas to the treatment fluid. The treatment fluid is preheated by the preheating heat exchanger to a temperature below the boiling temperature of a base liquid so that the liquid impurities with lower boiling temperatures than the base liquid are evaporated and expelled thermally, whereby the evaporated and expelled impurities are separated in the separator unit of the preheating separator device. The treatment fluid is then evaporated and separated from impurities having a higher boiling point than the base liquid.

Abstract: A sulfur-bearing residue treatment system is provided for the recovery of valuable organic components and the reduction of capital costs and operating costs. The treatment system involves the use of a stripping vessel in conjunction with a heating apparatus. All elements of the treatment system may be coupled together to form one integral piece of equipment.

Abstract: A process for treating produced water to generate high pressure steam. Produced water from heavy oil recovery operations is treated by first removing oil and grease. Feedwater is then acidified and steam stripped to remove alkalinity and dissolved non-condensable gases. Pretreated produced water is then fed to an evaporator. Up to 95% or more of the pretreated produced water stream is evaporated to produce (1) a distillate having a trace amount of residual solutes therein, and (2) evaporator blowdown containing substantially all solutes from the produced water feed. The distillate may be directly used, or polished to remove the trace residual solutes before being fed to a steam generator. Steam generation in a packaged boiler, such as a water tube boiler having a steam drum and a mud drum with water cooled combustion chamber walls, produces 100% quality high pressure steam for down-hole use.

Abstract: The invention relates to a semibatchwise process for the mild distillative separation of mixtures, in a first stage a column being supplied continuously with a feed and the feed being separated at least into different fractions, one of the fractions being removed continuously into a container, and, in a second step, the fraction removed into the container being recycled to the column and being separated again batchwise into different fractions.

Abstract: A sub-atmospheric pressure desalinating still employs a closed top, open bottom pipe filled with source water to be distilled, such as seawater, having a height greater than the height of a column of seawater that can be supported by the pressure at the bottom of the tank so that a subatmospheric pressure volume is formed at the top. Water from the source is also pumped into the subatmospheric volume and passed through an evaporator which enlarges its surface volume. A small percentage of the water is vaporized and the balance is cooled to provide the heat of vaporization and falls into the top of the seawater column, creating a downward flow. The vapor is drawn from the vacuum and condensed, preferably in a second subatmospheric volume above a column of fresh water.

Abstract: A process for treating produced water to generate high pressure steam. Produced water from heavy oil recovery operations is treated by first removing oil and grease. Pretreated produced water is then fed to an evaporator. Up to 95% or more of the pretreated produced water stream is evaporated to produce (1) a distillate having a trace amount of residual solutes therein, and (2) evaporator blowdown containing substantially all solutes from the produced water feed. The distillate may be directly used, or polished to remove the trace residual solutes before being fed to a steam generator. Steam generation in a packaged boiler, such as a water tube boiler having a steam drum and a mud drum with water cooled combustion chamber walls, produces 100% quality high pressure steam for down-hole use.

Abstract: Naphthenic acid corrosivity of hydrocarbon feedstocks is correlated with the chemical composition of naphthenic acids, and especially with a ratio between an alpha fraction and a beta fraction of naphthenic acids. Contemplated plants, configurations, and methods are directed to reducing naphthenic acid corrosivity of hydrocarbon feedstocks by increasing the beta fraction over the alpha fraction.

Abstract: A thermal separating process for removing a stream containing enriched (meth)acrylic monomers from a mixture containing (meth)acrylic monomers, in which the liquid phases retained in the separating space at high temperature and high (meth)acrylic monomer content are minimized.

Abstract: An energy efficient process scheme for a highly exothermic reaction-distillation system in which the reactor is external to the distillation column and the feed to the reactor is a mixture of at least one liquid product stream from the distillation column with or without other liquid/vapor reactants. The reactor is operated under adiabatic and boiling point conditions and at a pressure that results in vaporizing a portion of the liquid flow through the reactor due to the heat of reaction. Under these conditions, reaction temperature is controlled by reactor pressure. The pressure (and hence the temperature) is maintained at a sufficiently high level such that the reactor effluent can be efficiently used to provide reboil heat for the distillation column.

Abstract: A system for optimizing operation of an amine regeneration system comprising a flash tank, a rich/lean heat exchanger, a still, a reflux condenser, a reflux accumulator, a pump, a reboiler, and a flash tank pressurization assembly.

Abstract: A system for optimized operation and troubleshooting/diagnosis of an amine regeneration system comprising a flash tank, a rich/lean heat exchanger, a still, a reflux condenser, a reflux accumulator, a pump, a reboiler, and a pump bypass line to the flash tank.

Abstract: A process for rectificatively separating liquids containing (meth)acrylic monomers in a rectification column is provided, in which a stream is withdrawn from the rectification column and recycled into the rectification column as a molecular oxygen-enriched liquid phase.

Abstract: The present invention relates to a vacuum distillation plant and a process for concentrating organic aqueous solutions, especially spissum extracts, using said plant. The vacuum distillation plant of the invention comprises a flash evaporator, a means for vapor concentration and a multi-stage condenser positioned down-stream of said means for vapor concentration, means for recycling at least part of the condensate from a condensation stage into the bottoms product being provided. In addition, the present invention relates to a process for concentrating organic aqueous solutions such as concentrated extracts using said plant.

Abstract: A process for purifying propylene oxide characterized by subjecting a liquid reaction mixture containing propylene oxide, and water, hydrocarbons and oxygen-containing organic compounds as impurities obtained by reacting cumene hydroperoxide with propylene to extractive distillation using an extractant of a hydrocarbon having 7 to 20 carbon atoms with an extractive distillation column, and controlling a concentration of propylene glycol in the extractant supplied to the extractive distillation column to 20% by weight or less.

Abstract: An apparatus for recycling the stripper solutions with higher recycling rate is disclosed. The apparatus includes a stripper condenser; a first buffer tank; a second buffer tank connecting to said stripper condenser by a first pipe and connecting to said first buffer tank by a second pipe; a recycling device connecting to said first buffer tank by a fourth pipe; a first pump mounted on said first pipe; a second pump mounted on said second pipe; a concentration detector mounted in said stripper condenser; and a controller electrically connected to said concentration detector, said flow meter, and said liquid level sensor for receiving the signals therefrom, and electrically connected to said first pump and said second pump for sending on-off messages to said second pump.

Abstract: Method of regenerating a glycol solution containing water, hydrocarbons and salts. The glycol solution is expanded in drum (2), then distilled in column (7). The concentrated glycol collected at the level of reboiler (8) is placed under vacuum to vaporize the water and to precipitate the salts. The salts are separated from the glycol in separation device (13). The concentrated glycol freed of the salts is stored in capacity (16).

Abstract: A process for recovering crude 1,3-butadiene from a C4 fraction by extractive distillation using a selective solvent in a dividing wall column (TK) in which a dividing wall (T) is arranged in the longitudinal direction of the column to form a first subregion (A), a second subregion (B) and a lower common column region (C) and which is preceded by an extractive scrubbing column (K) is proposed.

Abstract: A method for separating difluoromethane from a mixture of difluoromethane and at least one impurity, the method involving extractively distilling the mixture using dichloromethane as an extractive agent to recover a product stream of purified difluoromethane having a concentration of impurity lower than that of the mixture.

Abstract: A process is proposed for the separation of C5+ cuts by distillation into a low-boiler (A), a medium-boiler (B) and a high-boiler fraction (C) in one or more dividing-wall columns (TK), in which a dividing wall (T) is arranged in the longitudinal direction of the column with formation of an upper, common column region (1), a lower, common column region (6), a feed part (2, 4) with rectifying section (2) and stripping section (4), and a withdrawal part (3, 5) with rectifying section (5) and stripping section (3), with feed of the C5+ cut (A, B, C) into the central region of the feed part (2, 4), discharge of the high-boiler fraction (C) from the bottom of the column, discharge of the low-boiler fraction (A) via the top of the column, and discharge of the medium-boiler fraction (B) from the central region of the withdrawal part (3, 5), wherein the dividing ratio of the liquid reflux at the upper end of the dividing wall (T) is set in such a way that the proportion of high-boiling key components in the liquid re