Abstract: A method of and system for recovering a solvent from a mixture of solvent and hydrocarbons, the system comprising at least two evaporation flasks successively fed with a charge consisting of said mixture to be separated, at least one steam generator performing the condensation of the solvent, a circuit for conveying the evaporated solvent and connecting the flasks to the generator and a circuit of an intermediate fluid in gaseous phase including a compressor for raising the condensation temperature of this fluid, the latter circuit connecting the generator to heat exchangers arranged upstream of each flask.

Abstract: A caustic alkali solution is concentrated to high density or high caustic alkali concentration by evaporation under high pressure at elevated temperature and expansion of the thus obtained concentrated caustic alkali solution to low pressure, preferably below atmospheric pressure. The pressure difference between the high pressure evaporator and the low pressure expansion vessel is absorbed gradually by a pressure difference absorber, preferably comprising a liquid column in a U-shaped siphon tube, so that corrosion and erosion are reduced considerably.

Abstract: Alkylidene diesters such as ethylidene diacetate are selectively produced in high yields by reacting an ether and/or an ester under substantially anhydrous conditions with carbon monoxide and hydrogen in contact with a catalyst system comprising a rhodium compound, a halogen component, a palladium cocatalyst and a promoter component which is an agent for liberation of carboxylic acid anions. The process is carried out in the liquid phase in a solvent comprising a carboxylic acid at a temperature in the range of 150.degree. to 190.degree. C. and at a carbon monoxide partial pressure in the range from about 1.0 to 1100 kg/cm.sup.2 and a carbon monoxide/hydrogen mole ratio of 6:1 to 1:2 for the ester reaction and 10:1 to 1:2 for the ether reaction. When ethylidene diacetate is the product, it can then be decomposed to produce vinyl acetate and acetic acid by well-known techniques.

Abstract: A method and apparatus for devolatilizing high viscosity polymer solutions are provided wherein high viscosity polymer solutions are heated along a short zone of indirect heat exchange. The residence time within the zone of indirect heat exchange ranges from approximately 5 seconds to 120 seconds.

Abstract: Ammonia which is present in fuel cell power plant water in free form, in ionic form, and in forms combined with carbon dioxide, is removed from the power plant water by steam stripping. Water which has been used to cool the fuel reformer effluent, and thus has become contaminated with ammonia, is fed to a first steam stripper wherein a first portion of the ammonia contaminant is removed. The partially stripped water is then fed to a second steam stripper wherein further amounts of ammonia are removed from the water with steam. The ammonia laden steam from the two strippers is combined and vented through a single vent thus conserving the amount of water lost from the system.

Abstract: The invention relates to a method for evaporation of spent liquor by heat from a blow condenser where blow steam from a pulp cooker is condensed in a direct condenser connected with a hot water accumulator. Spent liquor heated indirectly by hot water from the accumulator is brought to expand and released expansion vapor is used as a heat medium in a following evaporation stage. The apparatus comprises a heat exchanger, at least one flash tank and at least one evaporation unit, the heat exchanger being disposed to receive hot water from the upper part of the accumulator and to return it to its lower part and thus heat the spent liquor, and the flash tank being disposed to receive spent liquor heated in the heat exchanger and to release liquor vapor and spent liquor to the evaporation unit.

Abstract: A distillation system and process for removing vaporizable components from an aqueous medium including a distillation column for receiving an aqueous medium containing vaporizable components and passing steam through the column such that the steam directly contacts the aqueous medium to vaporize at least a portion of the components, a condenser in a communication with the column to condense at least a portion of the vapor in the column, a separator in communication with the condenser to separate flash vapor from liquid condensate in the separator and a thermal compressor in communication with the separator and the column to remove vapor from the separator and to inject exhaust steam from the thermal compressor into the column.

Abstract: An inlet horn for reducing liquid entrainment of liquid in vapor products in distillation towers. The inlet horn has a tangential entry for the vapor-liquid feed which opens into a peripheral open bottomed horn with a number of deflector vanes angularly disposed horizontally and vertically along the length of the horn to deflect liquid components of the feed radially outwards and vapor components downwards so as to improve their separation. The horn may be used in atmospheric and vacuum crude distillation and other vapor-liquid separation units.

Abstract: Color properties of crude phenolic esters of aromatic dicarboxylic acids are improved by comminuting the ester to a finely divided particle size in the presence of an aqueous or alcoholic alkali solution and thereafter distilling the esters to obtain phenolic esters of reduced color.

Abstract: Calcium containing sulphate spent liquor is deactivated by means of heating. Spent liquor is heated by means of direct condensing in a flash-steam-system. Liquor vapors generated during expansion of the already deactivated spent liquor are used for heating the spent liquor. Spent liquor is led to a retention tank through n+1 in series connected direct condensers (DK I-DK V) and from the retention tank through n in series connected flash tanks (FT I-FT IV) disposed counter-currently to the direct condensers. In the last one of the direct condensers (DK V) the liquor is heated by means of externally supplied steam; in all others (DK I-DK IV) by means of expansion vapor.

Abstract: An apparatus for vaporizing a liquid and condensing the vapor includes at least one chamber in which the liquid is vaporized and in which the vaporized liquid is condensed. The vaporizing chamber contains a heat emitting device providing a surface temperature above the vapor temperature for substantially instantaneously vaporizing the liquid condensate maintaining a predetermined vapor level in the vaporizing chamber, and a heat absorbing device for condensing the vaporized liquid.

Abstract: A multi-flash evaporator having modular vertical cyclone chambers designed to generate a paraboloid of revolution providing an extended surface area for release of flashed vapors and attaining equilibrium. With multiple stages, the system incorporates deep loop seals to prevent blowby between stages at all levels of capacity and employs a vapor lift system to permit low pressure differentials between stages at high vacuum. The cyclone chambers employ an intermediate tangential inlet whereby the flashing vapors propel the liquid at higher velocities to generate a deeper paraboloid of revolution and centrifugally separate the heavier liquid from the flashing vapor. An anti-creep ring is interdisposed at the top of the cyclone to prevent the liquid from entering a mesh so only vapor impinges on the mesh and passes to the heat recovery condensers embodying a bayonet augmented tube heat exchanger.

Abstract: Volatile matter especially solvents is recovered from waste material using a hot granular material such as sand, as a heat carrier to drive off the solvents, and as a carrier for the non-volatile resin content of the waste; the resins are thermally decomposed in reactions which provide heat to maintain the granular material hot and the granular material is continuously circulated; the exhaust gases from the thermal decomposition of the resins can be used as a source of heat outside the system.

Abstract: An atomizer with a capillary passage to a tip surface which is vibrated by a directly coupled ultrasonic device to disperse droplets of liquid fed to the passage. The tip is associated with a heated vaporization chamber, and a cooling chamber between the tip and the ultrasonic device protects the device from the heat of the chamber.

Abstract: A process of recovering elemental phosphorus from sludge is disclosed wherein the sludge is flash evaporated utilizing a heat transfer means and then separated from the solid impurities contained therein.

Abstract: A beneficiated kaolin clay slurry is concentrated from a solids content of about 50% to 60% by weight to a solids content of at least 65% by weight by evaporating water therefrom by passing the aqueous clay slurry through one or more non-contact evaporated heat exchangers. The kaolin clay slurry is passed in indirect heat exchange relationship with a heating vapor, with the heating vapor comprising water vapor previously evaporated from the aqueous clay slurry.

Abstract: A method and apparatus for converting a long tube vertical evaporator to a falling film evaporator in a manner which permits salvaging most of the long tube vertical evaporator structure. The bottom chamber of the existing evaporator is extended to define a flash chamber intermediate the existing heat exchanger chamber and the bottom chamber. A vapor riser conduit is provided for directing vapor from the flash chamber to the vapor separation chamber positioned above the heat exchanger chamber. A recirculation conduit is provided for directing liquid from the bottom chamber therethrough into a distribution chamber which is provided above and in communication with the upper ends of the heat exchange tubes positioned in the heat exchanger chamber. The distribution chamber is preferably provided with a plurality of spray nozzles which communicate with the recirculation conduit to evenly distribute a film of liquid downwardly through the heat exchange tubes.

Abstract: A method of recovering light organic solvent from a liquid mixture containing the solvent and a process material, such as asphaltenes or coal liquefaction products. The solvent-process material mixture is treated in a solvent separation zone to separate a first vapor phase rich in solvent and a first liquid phase rich in process material. At least a portion of the liquid in the solvent separation zone is transferred to a mixing zone, where the liquid is intimately contacted with steam, under shearing conditions. The steam-liquid phase mixture thus produced is returned to the solvent separation zone and treated to separate a second vapor phase, rich in steam and solvent, and a second liquid phase, rich in process material and substantially depleted of solvent. Solvent is recovered from the first and second vapor phases.

Abstract: A method and apparatus are provided for distillation of hydrocarbon oil subject to coking threshold temperature limits. A hydrocarbon oil is heated to a first predetermined maximum temperature above which coking is likely to occur. The heated hydrocarbon oil is introduced into a first distillation zone, wherein the heated hydrocarbon oil is separated into a liquid portion and a vapor portion. The descending liquid portion is withdrawn from the bottom region of the first distillation zone, and the withdrawn liquid is reheated to a second predetermined maximum temperature, above which coking is likely to occur in the return heater line. Finally, the heated withdrawn liquid is returned to a second distillation zone, wherein a second separation occurs to achieve increased valuable products recovery. A divider arrangement maintains the first and second distillation zones physically separate from each other.

Abstract: A method of vaporizing a multicomponent liquid, such as a hydrogen peroxide and water solution, for injection into a vacuum chamber including the steps of metering successive predetermined increments of the liquid at a predetermined rate onto a heated surface in a vaporization chamber. Upon exposure to the heated surface, each liquid increment is substantially instantaneously vaporized before the next succeeding liquid increment is metered onto the heated surface to produce a multicomponent vapor increment having substantially the same weight percent composition as the multicomponent liquid increment. Each vapor increment is passed into the vacuum chamber.

Abstract: A process for producing sorbic acid is described, by first reacting crotonaldehyde with ketene to prepare a polyester, then decomposing the polyester with hydrochloric acid, separating the crude sorbic acid from the reaction solution, and purifying the separated sorbic acid, said purifying step comprising the following steps:(a) continuously dissolving the crude sorbic acid in petroleum at a temperature in the range of from 100.degree. to 140.degree. C. while evaporating the residual water and hydrochloric acid from the solution of the sorbic acid in petroleum;(b) separating the tar content from the petroleum solution in a separation column at a temperature in the range of from 100.degree. to 140.degree. C.; and(c) subjecting the mixture of sorbic acid and petroleum to flash evaporation in a film-type evaporator at a reduced pressure in the range of from 20 to 60 mmHg, with the evaporation residue being withdrawn from the bottom of the evaporator and recycled to step (a).

Abstract: In the distillation of fresh water from sea water, the sea water is passed ownwardly in a falling film evaporator through a multiplicity of vertical tube evaporator (VTE) stages and multiple stage flash (MSF) evaporators. After the sea water passes through the first VTE stage where it forms a liquid component and a steam component, the liquid component is distributed evenly into the next VTE stage while the steam component enters an adjoining MSF stage. Condensed fresh water flows downwardly from one MSF stage to the next and experiences flash evaporation. The sea water or brine component and the fresh water distillate flow downwardly through the VTE and MSF stages so that the brine component can be removed from the final VTE stage and the fresh water distillate from the final MSF stage.

Abstract: In a continuous alkoxidation-phosphorylation process for producing tributyl phosphate having low color utilizing excess butanol in the alkoxidation reaction which is heated by an alcohol flasher wherein the excess butanol is recovered after phosphorylation by two stage flash distillation, the bottoms product from the first stage going to the second stage, the overhead product from the second stage returning to the first stage flash distillation, and the bottoms from the second stage distillation going to final product washing and drying process while the overhead from the first stage flash distillation is fed to the process alkoxidation alcohol flasher, the improvement which comprises distilling in a distillation column the overhead product from the first stage flash distillation and then feeding the overhead from the distillation column to the alkoxidation alcohol flasher.

Abstract: An apparatus for concentrating aqueous solutions of hygroscopic organic liquid having boiling points higher than the normal boiling point of water is disclosed. The apparatus includes an airtight evacuated chamber, means for injecting a preheated temperature adjusted solution into the chamber to vaporize water from the solution and produce a concentrated aerosol of organic liquid, and means for coalescing the concentrated aerosol. Also included is a system for recovery of organic vapor leaving the chamber along with the vaporized water.

Abstract: An improved distillation apparatus is disclosed containing expansion means and vapor draw means surrounded by heating means to provide vapor/liquid phase separation entirely within the heating bath. The apparatus is especially useful for determining phenol content in refinery waste streams.

Abstract: Deodorizing and/or physical refining of cocoa butter and cocoa butter substitutes is carried out in accordance with the principle of continuous counter-current falling film stripping steam distillation in at least two different zones, where different flow and current conditions prevail for the liquid film and the vapors, respectively. In the initial zone 10 the vapors pass through trickle passages having a hydraulic equivalent diameter greater than the hydraulic equivalent diameter in the final zone 22.The working pressure in the top of the falling film column 10 is maintained below 2.0 mbar, and in the bottom of the falling film column 22 it is maintained by at most 1.6 mbar in excess of that in the falling film column 10. The accumulation of any significant liquid content in the bottoms of the serially operating zones is avoided. Stripping steam is supplied in an amount of 2 to 10 kg of steam per 100 kg of charged liquid.

Abstract: The deodorization and/or physical refining of high-boiling organic edible oils, fats and esters is carried out according to the principle of continuous counter-current falling film stripping steam distillation in an internally imposed temperature field in at least two different zones having different flow conditions for the liquid film and the vapors, respectively, prevailing therein. In the initial zone 10 directly adjacent the liquid charge and ensuring at least two separation stages the vapors flow through trickle passages having a hydraulic equivalent diameter of 73 to 150 mm. If necessary, this initial zone may be subdivided, wherein in the first sub-zone the trickle passages are provided with hydraulic equivalent diameters of 120 to 150 mm and in the second sub-zone the trickle passages are provided with hydraulic equivalent diameters of 73 to 120 mm.

Abstract: A conventional cross-flow or paired-stage multi-stage flash evaporator plant is provided with duct means for collecting distillate from collection trays in the successive evaporator units in the plant. Distillate from individual units is diverted to a bypass flow path from the duct means when it is detected to be contaminated with brine.

Abstract: A continuous process for reducing the arsenic content of phosphorus is described in which the impure phosphorus is continually passed through a heat exchanger and heated to vaporize a portion of the phosphorus at a temperature not above 200.degree. C., separating the vaporized phosphorus in a disengaging zone under subatmospheric pressure and introducing it into a fractionating zone under subatmospheric pressure, fractionating the phosphorus from the less volatile arsenic, condensing under subatmospheric pressure low-arsenic phosphorus rising from the fractionating zone, returning a portion of the low-arsenic phosphorus condensate as reflux to the column, removing high-arsenic liquid phosphorus as bottoms from the fractionating zone, and recovering the remaining portion of low-arsenic phosphorus condensate as product.

Abstract: The disclosure relates to a process for separating the catalyst system from reaction mixtures which are obtained by reacting methyl acetate and/or dimethylether with carbon monoxide and optionally hydrogen at elevated temperatures to acetic anhydride and optionally ethylidene diacetate in the presence of a catalyst system consisting of carbonyl complexes of noble metals belonging to group VIII of the Periodic System, acetic acid, an organophosphorus or organonitrogen compound, methyl iodide and optionally compounds of carbonyl-yielding common metals, and which issue from the reaction zone under a pressure of 25 to 150 bars at a temperature of 100.degree. to 250.degree. C. More particularly, the reaction mixture coming from the reaction zone is introduced into a separator heated to 60.degree. to 140.degree. C. and released to a pressure of 0.5 to 3.

Abstract: An improved distillation apparatus is disclosed containing expansion means and vapor draw means surrounded by heating means to provide vapor/liquid phase separation entirely within the heating bath. The apparatus is especially useful for determining phenol content in refinery waste streams.

Abstract: Ethylene glycol is purified, particularly for fiber-grade applications, by removal of the residual ethylene carbonate from which the glycol was derived. The effluent from a reactor in which ethylene carbonate is hydrolyzed to ethylene glycol is distilled to produce a lower-boiling fraction comprising substantially ethylene glycol and water and a higher-boiling fraction comprising substantially ethylene glycol, higher glycols, and concentrated in hydrolysis catalyst. The higher-boiling fraction is recirculated to reflux against the lower-boiling product, thereby essentially completing the hydrolysis of unreacted ethylene carbonate thereby reducing the ethylene carbonate content of the ethylene glycol to very low levels suitable for fiber-grade applications.

Abstract: This process separates less volatile contaminates from thermal power recovery systems utilizing a volatile working fluid in a cyclic closed system; such a system may comprise a reservoir, a pump, a heater, a separator, a throttle device, a turbine and a condenser. The purification can be accomplished during start-up, shut-down or periods of low power generation. The contaminant is separated from the working fluid in the separator in which the temperature and pressure correspond to a dew-point substantially above that of a sample of uncontaminated working fluid. To achieve this condition, the normal flow of liquid from the reservoir to the heater is reduced and the heater and throttle device are correspondingly adjusted. The condensed contaminant is removed from the separator while substantially all of the working fluid which has been vaporized is passed on through the throttle device to the turbine.

Abstract: Apparatus for carrying out thermodynamic processes in which a work medium undergoes mutually opposite phase transitions. The apparatus comprises casings consisting of confining plates and spacers therebetween, the casings being arranged in stacked relationship. Each casing encloses a plurality of phase transition compartments in superposed relationship. There are orifices in the confining plates through which pairs of phase transition compartments open directly into one another so as to form a number of work chambers. These are also passages delimited by the spacers in the casings for connecting the work chambers in series and passages delimited by the spacers in the casings for introducing and drawing work medium into and from the phase transition compartments. Finally, there are passages delimited by the spacers in the casings for supplying and abducting heat to and from the work medium.

Abstract: Apparatus and methods are provided for controlling liquid levels in different vessels, and the blending of different materials in the separation and purification of polymeric materials in solution, such as polyethylene in cyclohexane.

Abstract: A process for the separation of diisopropylether from a hydrocarbon stream containing it, by contacting the stream with ethylene glycol whereby the diisopropylether is absorbed by the glycol and a purified hydrocarbon stream is separated therefrom.

Abstract: In a batch process in which reaction effluent is dumped from the reactor to a flash tank through a dump line which contains both a dump valve and a control valve, the control valve is manipulated in response to a signal which opens the control valve at a desired rate as a function of time or in response to a signal which is representative of the maximum opening of the control valve which can be maintained without exceeding a pressure limit in the flash tank whichever signal is representative of the lower opening of the control valve. In this manner, reaction effluent is withdrawn from the reactor at a substantially maximum rate without causing flashing across the dump valve and without exceeding a pressure limitation for the flash tank.

Abstract: Disclosed is a process for the distillation of readily polymerizable vinyl aromatic compounds and a new polymerization inhibitor therefor. The process comprises subjecting a vinyl aromatic compound to elevated temperatures in a distillation system in the presence of a new polymerization inhibitor comprising 2,6-dinitro-p-cresol. Also disclosed is a distillation method and apparatus for use with this inhibitor.

Abstract: In a multiphase flow tube for drying pumpable suspensions to form solids having low residual moisture contents, the process uses brief increases in the pressure of the gas stream to prevent blockages.

Abstract: A process is provided for the continuous separation of slightly volatile components from a crude phthalic acid anhydride wherein a portion of the crude phthalic acid anhydride is compressed and heated before being reintroduced into a flash evaporator.

Abstract: An improved distillation method and apparatus are provided for recovering anhydrous ethanol from fermentation or synthetic feedstocks. The system includes at least one stripper-rectifier tower, a dehydrating tower, and an azeotropic agent stripping tower. Substantial energy savings are realized by operating the dehydrating tower, and preferably also the azeotropic agent stripping tower, at a higher pressure than the stripper-rectifier tower and by condensing the overhead vapors from the dehydrating tower (or dehydrating tower and azeotropic agent stripping tower) to provide the heat required in the stripper-rectifier tower. In a preferred embodiment, two stripper-rectifier towers are used, one operating at a higher pressure than the other, in which case the higher pressure tower is heated as just described and the overhead vapors from the higher pressure tower are condensed to supply the heat required in the lower pressure tower.

Abstract: A mechanical energy conversion method and system for the restoration of dissipated heat energy, contained in natural or artificial water bodies at or near ambient temperatures, to industrial process heat, mainly in the form of steam up to 200.degree.-400.degree. C. The sensible heat contained in a water body is concentrated as latent heat in low pressure water vapor which is thermo-compressed by steam ejection to an intermediate pressure level, wherefrom mechanical compression takes over, generating highly superheated output steam. The ejecting steam is not generated in a boiler, but is continuously regenerated by the compressor and routed back for repeated ejection. The compressor is driven by a heat engine whose reject heat is collected and upgraded as well. The output of heat energy is essentially equal to the sun of the heating value of the fuel consumed and the intake of latent heat and amounts thus to substantially more than the heating value of the fuel alone.

Abstract: Excess water and color-forming materials present in crude 1,4-butanediol are reduced by subjecting the crude 1,4-butanediol to distillation under conditions wherein substantially all the water present in the crude 1,4-butanediol is first removed and then the 1,4-butanediol with reduced water content is further refined by flash evaporation under vacuum.

Abstract: A method for separating close-boiling chlorosilanes by the procedures of extractive distillation using sulfolane as the extractive solvent is described. An example of close-boiling chlorosilanes which can be separated by this method include dimethyldichlorosilane and methyltrichlorosilane containing mixtures. The invention comprises heating a mixture of the close-boiling chlorosilanes with sulfolane to distill the lower-boiling chlorosilane from the mixture and thereafter separating the sulfolane and the high-boiling chlorosilane.

Abstract: The energy requirements of a solution rubber process are significantly improved by employing solvent which has been removed in subsequent process steps.The invention concerns the separation treatment of the solvents and the polymer solutions produced by solution polymerization. In one embodiment a polymer solution is flashed to remove solvent vapor overhead and a concentrated polymer solution is removed as bottoms. The flashed solvent vapor is divided into at least two streams. A first stream is used as a stripping vapor medium in a zone for stripping a wet solvent to recover a wet solvent vapor overhead from the stripping zone and a dry solvent liquid as bottoms; the second flashed solvent vapor stream is used to preheat the wet solvent feed to the stripping zone by indirect contact heat exchange; a third portion of said solvent vapor can be combined with the second portion downstream of the heat exchange step, and the combined stream can be condensed.

Abstract: A solar desalting method and apparatus includes a storage tank for receiving heated sea water at a first rate from a solar collector during daylight hours and for delivering the same to a flash evaporator a second rate. The flash evaporator is connected for delivery of the evaporated and unevaporated portions of the feed water as the heating vapor and feed liquid, respectively, to a serially connected multi-effect film evaporator. Sea water is used to condense the vapor from the last evaporator effect as the distillate product of the system. The storage tank permits nighttime operation with the brine from the last effect and a portion of the cooling water being fed to the solar collector during the daytime and discharged at night.

Abstract: Apparatus and methods are provided for controlling liquid levels in different vessels, and the blending of different materials in the separation and purification of polymeric materials in solution, such as polyethylene in cyclohexane.

Abstract: Process and apparatus for extracting an organic liquid from an organic liquid solute/solvent mixture. The mixture is contacted with a fluid extractant which is at a temperature and pressure to render the extractant a solvent for the solute but not for the solvent. The resulting fluid extract of the solute is then depressurized to give a still feed which is distilled to form still overhead vapors and liquid still bottoms. The enthalpy required to effect this distillation is provided by compressing the still overhead vapors to heat them and indirectly to heat the still feed. The process is particularly suitable for separating mixtures which form azeotropes, e.g., oxygenated hydrocarbon/water mixtures. The energy required in this process is much less than that required to separate such mixtures by conventional distillation techniques.

Abstract: An apparatus for producing fresh water from sea water in which a vertical accumulator utilizes the sensible heat of sea water so as to evaporate said sea water to a temperature above 100.degree. C. under pressure, a heat-exchanger connecting between the upper and lower portions of said accumulator causes a high temperature liquid to effect heat-exchange with sea water to be evaporated, a fresh sea water feed line connected to the lower portion of said accumulator adjusts the pressure within the accumulator and an evaporator receives higher temperature sea water. The accumulator accumulates heat in such a manner that the upper portion of said accumulator holds higher temperature sea water and the lower portion of the accumulator holds lower temperature sea water so that when heat is accumulated, the amount of said higher temperature sea water increases and when heat is radiated, the amount of higher temperature decreases whereby sea water evaporates at all times.

Abstract: There is disclosed a process and apparatus for the fractionation of close boiling components of a multi-component system and comprised of at least two fractionation columns having a plurality of equilibrium stages wherein the vapor from a down-stream fractionation column is compressed and passed into a lower portion of a preceding fractionation column. In a particularly preferred embodiment, the compressed overhead vapor stream is passed in heat transfer relationship to a liquid stream withdrawn from the preceding fractionation column prior to introduction into the lower portion of such preceding fractionation column.