Abstract: A method for purifying raw methanol containing sulfur compounds, wherein the method comprises the step of washing raw methanol with a non-polar organic solvent.

Abstract: The invention relates to a method and apparatus to recover and purify methanol from gases produced in the digester during the kraft pulping process. The gas is typically recovered as a foul gas (called stripper off gas or SOG) comprising methanol, water and various other contaminants. The gas is then treated with successive decanting and distillation steps to remove impurities, thereby producing highly purified methanol.

Abstract: The invention relates to method for deacidification of fats and oils comprising: feeding stream (1) to a stripping section; condensing the volatile phase in a high temperature condensing zone, sending the condensed phase to distillation A; distillating the condensed phase, obtaining a volatile stream; passing the volatile stream along with the vapour phase from the condensation zone to a cold condensation zone obtaining a condensate and a stream (4); allowing stream (4) to continue to vacuum system and subjecting the cold condensate to distillation B; and producing a stream of fatty acids (5) and a stream of micronutrients (6).

Abstract: A method of dehydrating tolylenediamine which includes subjecting tolylenediamine having a water content of 5-40 wt. % to first-stage distillation at a vacuum of 13-101.3 kPa and subjecting the bottoms from the first-stage distillation to second-stage distillation at a vacuum lower than 13kPa.

Abstract: Methods and apparatuses for extractive distillation using internal addition of steam to an extractive distillation column from a reboiler are described herein. The apparatuses include an extractive distillation column, a reboiler (for example, a kettle reboiler) coupled to the extractive distillation column, and a steam input line. The steam input line is coupled to an internal steam sparger device of the reboiler. Methods utilizing the apparatuses to perform extractive distillation of a hydrocarbon feed stream are also described herein.

Abstract: The invention relates to improved systems for recovery of alkylene oxide from feed streams containing the same in an alkylene oxide recovery column. The invention also relates to improved processes for recovery of alkylene oxide from feed streams containing the same in an alkylene oxide recovery column.

Abstract: Systems and processes for recovering alkylene oxide, including an alkylene oxide recovery column including a stripping section located in the column to convert a portion of a feed stream to a gas phase including alkylene oxide; a reabsorption section in the column above the stripping section including a water stream to reabsorb the alkylene oxide in the gas phase portion and to produce an aqueous solution, a first stripping gas to strip carbon dioxide and oxygen from the aqueous solution by converting a portion of the aqueous solution to a gaseous portion, producing an alkylene oxide stream, and a side take-off located at a bottom portion of the reabsorption section for removal of the alkylene oxide stream; a condenser to partially condense the gas phase portion; and a top take-off for removal of a light impurity fraction.

Abstract: A multi-stage process for the treatment of organic waste comprising: (a) drying the sewage sludge waste to reduce the water content to below 15%; (b) mixing of dried sewage sludge with solvent medium for slurry preparation; (c) subjecting slurry from step (b) to a the?no-chemical liquefaction process in the presence of a solvent medium at a temperature of about 275° C.

Abstract: A process of separating a purified propylene oxide from a crude epoxidation product produced, preferably, in an epoxidation reaction of propylene with hydrogen peroxide. The process involves removing bulk water, bulk methanol, and unreacted propylene from the crude epoxidation product and thereafter subjecting the resulting propylene oxide product to extractive distillation with water as an extraction solvent. Under distillation conditions, including a bottoms temperature of greater than about 55° C. and less than about 75° C., an overhead or side-cut distillate stream containing a purified propylene oxide is obtained with low yield loss of propylene oxide to propylene glycols and other glycol heavies. The purified propylene oxide can be further purified in a finishing distillation to obtain propylene oxide meeting commercial grade purity requirements.

Abstract: The present invention relates to methods and systems for processing an exhaust stream containing a recyclable component mixed with other components and impurities to produce a high purity product that contains all of the recyclable component. One or more waste streams containing none of the recyclable component are also produced. The present invention particularly relates to the recovery of valuable recyclable components used in the manufacture of semiconductor devices.

Abstract: The present invention provides new highly-efficient separation processes and systems for separating polymerization-grade ethylene and propylene from an initial effluent stream comprising ethane, ethylene, propylene, dimethyl ether, and one or more of propane, acetylene, methyl acetylene, propadiene, methane, hydrogen, carbon monoxide, carbon dioxide and C4+ components. In one embodiment, the initial effluent stream is provided from a methanol-to-olefin reaction system. It has been discovered that the best separation of these components is realized when DME is selectively removed in a first separation step, followed by separation of the remaining components in additional separation steps.

Abstract: A mixture of propylene oxide and methanol is separated by liquid/liquid extraction using water and a hydrocarbon such as n-octane as extractive solvents.

Abstract: An aqueous solution of free hydroxylamine is prepared by treating a hydroxylammonium salt with ammonia by the countercurrent method in a stripping column by a process in which hydroxylamine is liberated and at the same time the solution obtained is separated by distillation into an aqueous hydroxylamine solution and a salt fraction. The novel process can be carried out in a simple and gentle manner and on a large scale. The danger of decomposition is minimized owing to the low thermal load, the low concentration of hydroxylamine and the short residence time in the process.

Abstract: In a process for the preparation of methylglyoxal dimethyl acetal from methylglyoxal and methanol in the presence of an acidic ion exchanger, water is introduced in an amount sufficient to form an acidic reaction mixture in which the acetal product and water form an azeotropic mixture, with or without the retention of some methanol reactant. After subjecting a single phase acidic reaction mixture to an azeotropic distillation, it will separate into two distinct liquid phases with a simple recovery of the acetal product from the aqueous phase.

Abstract: A process for pre-treating a spent caustic stream prior to oxidation which includes countercurrent multi-stage elevated temperature solvent extraction of dissolved organic material from the spent caustic using a solvent to yield a spent caustic raffinate containing only residual amounts of organic solute and steam distilling the spent caustic raffinate to remove the residual organic solutes, yielding a pretreated spent caustic stream substantially free of organic material which is then subjected to wet air oxidation and thereafter to ozonolysis to yield a wastewater stream having a low COD and BOD, which is neutralized to a pH of 8.5 to 9.0.

Abstract: A process for pretreating a spent caustic stream prior to oxidation includes countercurrent multi-stage elevated temperature solvent extraction of dissolved organic material from the spent caustic using a solvent to yield a spent caustic raffinate containing only residual amounts of organic solute. The raffinate is steam distilled to remove the residual organic solutes, yielding a pretreated spent caustic stream substantially free of organic material. The pretreated spent caustic is suitable for use in a Kraft paper process or for oxidation prior to recycle or disposal. Solvent extract from the extractor is regenerated in a solvent regenerator having an overhead stream for purging light ends, a bottom stream for purging heavy ends, and a heart-cut side stream for recycling solvent to the extractor.

Abstract: A process for separating the product gas mixture from the catalytic synthesis of methyl mercaptan. Because of improved separation of the product gas mixture into its components, less hydrogen sulfide and methyl mercaptan are lost in discharging the inert gases than in the known process. The inert gases can be burned without after-treatment of the exhaust gas. Likewise, the process water that is discharged is less contaminated with polysulfides.

Abstract: An apparatus and method for treating chemical production plant process condensate and low pressure purge gas such that a contaminant-rich stream is recoverable from the condensate and purge gas, wherein the contaminants are substantially removed from the condensate by steam stripping and subsequent rectification in a relatively low pressure stripping/rectification tower. The tower overhead is then condensed, and any non-condensed gases are subjected to water scrubbing, along with the low pressure purge gas to further recover contaminates from the non-condensed gas. A portion of the condensed overhead and scrubbing water containing contaminates is returned to the top of the rectification section of the tower as reflux and the balance being withdrawn as a concentrated stream for reuse in the plant. The apparatus may be used in conjunction with existing low pressure equipment, avoiding costly major modifications, and is particularly adapted to use in conjunction with ammonia and methanol plants.

Abstract: A method for recovering methanol from sulfur-based wood pulping process vapors, which contain at least methanol and dimethyl disulfide. The method involves three steps. The first step consists of introducing the vapors into a first distillation tower at a vapor introduction point. The second step consists of introducing water into the first tower at a point above the vapor introduction point. The third step consists of heating liquid which is in the first tower below the vapor introduction point so that a liquid stream flows from the bottom of the first tower and a gas stream flows from the top of the first tower. The liquid stream contains most of the methanol originally in the vapors. The gas stream contains most of the dimethyl disulfide originally in the vapors. The liquid stream can then be distilled in a second distillation tower by conventional distillation to produce dry methanol. The first and third steps can be combined by introducing sufficiently heated vapors.

Abstract: An apparatus and method for treating chemical production plant process condensate such that a contaminant-rich stream and a relatively pure aqueous stream is separately recoverable from the condensate, wherein the contaminants are substantially removed from the condensate by steam stripping and subsequent rectification in a relatively low pressure stripping/rectification tower. The tower overhead is then condensed, and any non-condensed gases are subjected to water scrubbing to further recover contaminates from the non-condensed gas. A portion of the condensed overhead and scrubbing water containing contaminates is returned to the top of the rectification section of the tower as reflux and the balance being withdrawn as a concentrated stream for reuse in the plant. The apparatus may be used in conjunction with existing low pressure equipment, avoiding costly major modifications, and is particularly adapted to use in conjunction with ammonia and methanol plants.

Abstract: In a process for the recovery of N-ethylpiperazine by distillation from mixtures with N,N'-diethylpiperazine, piperazine, ethanol, water and accompanying substances, water is added in a manner such that, at the location of the addition of the water, the piperazine concentration is greater than the N-ethylpiperazine concentration. The water may be added to the reflux to the top of the column.

Abstract: A method for separating boric acid from a liquid, especially liquid waste obtained from a nuclear power plant. In the method, the waste solution containing the boric acid is contacted with steam in a reactor so that the boric acid evaporates from the liquid and passes into the steam vapor phase. Consequently, the radioactive wastes which are not evaporated with the steam remain in the waste water while the boric acid is removed from the waste water when it passes into the vapor or steam phase. The boric acid can then be separated and recovered from the steam by means of a distillation and fractionating column or a wash column. By removing the boric acid from the liquid waste, it is possible to obtain concentrated radioactive waste having a reduced volume due to the absence of boric acid in the waste.

Abstract: In an improved process for recovering ethylene oxide from an aqueous ethylene oxide solution further containing formaldehyde is provided wherein the impure aqueous ethylene oxide solution is introduced into a distillation zone as a feed stream and undergoes distillation therein to form an ethylene oxide product sidestream and an aqueous bottoms product, water is added to the distillation zone to absorb formaldehyde vapor into a liquid phase and combines with the formaldehyde vapor to form an apparent azeotrope, and removing the apparent azeotrope from the column, the improvement is that all or part of the water is a recycled aqueous stream originating from the aqueous bottoms product and introduced to the distillation zone above the feed stream.

Abstract: The present invention provides a method for separating boric acid from a liquid, especially liquid waste obtained from a nuclear power plant. In the process, the waste solution containing the boric acid is contacted with steam in a reactor so that the boric acid evaporates from the liquid and passes into the steam vapor phase. Consequently, the radioactive wastes which are not evaporated with the steam remain in the waste water while the boric acid is removed from the waste water when it passes into the vapor or steam phase. The boric acid can then be separated and recovered from the steam by means of a distillation and fractionating column or a wash column. By removing the boric acid from the liquid waste, it is possible to obtain concentrated radioactive waste having a reduced volume due to the absence of boric acid in the waste.

Abstract: An apparatus and method for treating chemical production plant process condensate such that a contaminant-rich stream and a relatively pure aqueous stream is separately recoverable from the condensate, wherein the contaminants are substantially removed from the condensate by steam stripping and subsequent rectification in a relatively low pressure stripping/rectification tower. The tower overhead is then condensed with a portion of the condensed overhead being returned to the top of the rectification section of the tower as reflux and the balance being withdrawn as a concentrated stream for reuse in the plant. In a second embodiment, separate stripping and rectification towers operate in series whereby the overhead of the stripping tower is delivered to the lower section of the rectification tower and the rectification bottoms are returned to the top of the stripping tower.

Abstract: For separating ETBE and ethanol the following principal stages are employed:(1) Extraction of ethanol by water, the raffinate being ETBE saturated in water and the extract an ethanol/water mixture containing a small proportion of ETBE;(2) Concentration of the above mixture, the distillate being a mixture close to the ethanol/water azeotrope in composition and containing a very small proportion of ETBE;(3) Heteroazeotropic distillation of this distillate in two coupled columns with an overhead decanter, this distillation using ETBE as azeotroping agent; the residue of the first column being ethanol which is ca. 99% by mole and the residue of the second column being practically pure water, this water and the water recovered during the concentration stage being used as extraction solvent in stage (1).Stage (3) may be an ethanol dehydration unit using ETBE as dehydrating agent.

Abstract: Where side stream distillate strippers are used in the distillation of hydrocarbons, the required size of the distillation column and the amount of stripping gas or vapor required are reduced by passing components stripped from the distillates through a plurality of strippers in series, rather than directly back to the distillation zone.

Abstract: The separation of ethyl tertiobutyl ether from mixtures with ethanol is based on heteroazeotropic distillation with water as the entrainer using two distillation columns, coupled with an overhead decanter. Purified ethanol is collected from the bottom of the first column and purified ETBE from the bottom of the second column. The separation method may be incorporated into an ETBE production unit in which isobutene (contained in a C.sub.4 -cut from steam cracking, catalytic cracking, or dehydrogenation of isobutane) is etherified by ethanol. Ethanol separated from the ETBE is then recycled to the etherification zone.

Abstract: A distillation tower (1) has a plurality of liquid sidestream lines (5, 6, 7) and a multi-stage sidestream stripper (13) which includes a respective stripping section (14, 15, 16) for each sidestream line housed in a common, upright, cylindrical shell (28) which allows vapor to pass freely from each stage to the one above. Partial vaporization of each sidestream is achieved by applying a vacuum to the top of the stripper shell (point 21) and/or introducing strip gas at the bottom (point 20). Because the vapor passes serially through the stripping sections from the bottom of the stripper (13) to the top, the need to supply strip gas separately to the stripping sections and/or apply vacuum individually is avoided. The separation between the sidestream products is improved by including, in each stage, a rectification zone (22, 23, 24) positioned above the stripping section.

Abstract: The process for rectification of phenol prepared from crude phenol being the product of decomposition of cumene hydroperoxide and having previously been distilled to remove large portions of acetone, cumene and alpha methylstyrene which includes:feeding the column overhead vapors to a condenser, thereby condensing a major portion of the overhead vapors;withdrawing a small portion of the overhead vapors from the condenser while still in a vapor state, the small portion being relatively enriched in lights and laden with light acids;returning the condensate from the condenser to the phenol distillation column as reflux; andwithdrawing product phenol from at least one-theoretical stage below the top of the phenol distillation column, the product phenol having improved clarity when dispersed in water, clarity being at least 93 percent light transmission as measured by an electrophotometer in a water light test.

Abstract: A purification process for methyl methacrylate (MMA) and a recovery process for methanol are disclosed. A mixture, which contains water, methanol and methyl methacrylate (MMA) as principal components along with at least one of methyl acrylate, methyl propionate and methacrylic acid, is azeotropically distilled together with hexane to obtain MMA in a form substantially free of water, methanol methyl acrylate, methyl propionate and hexane and a low boiling-point fraction. The low boiling-point fraction is cooled and separated into a water phase and an oil phase. Methanol can be recovered from the water phase by adding an alkaline substance to it and then distilling the resultant mixture. A preparation process of MMA is also disclosed. MMA can be prepared by esterifying methacrylic acid or methacrylamide with methanol and then applying the above purification process.

Abstract: An improved process for separating ethylene-oxide from formaldehyde and acetaldehyde in contaminated ethylene oxide, the process involves introducing the contaminated ethylene oxide into a reflux column and distilling the contaminated ethylene oxide under conditions such that the fluid stream leaving the bottom of the reflux column contains the water present in the contaminated ethylene oxide and the ethylene oxide in amounts corresponding, on a weight basis, to 0.15 to 3 times the weight of the water, and the ethylene oxide resulting from the separation of the formaldehyde and acetaldehyde leaves the column at its top.

Abstract: The separation of homozeotropic mixtures of a paraffin or paraffins of 6-14 carbon atoms and an alcohol or alcohols of 4-8 carbon atoms is conducted in two rectification steps. In a first step, rectification is carried out in the presence of water as the azeotropic agent, and the resultant distillate, after condensation, is separated into two liquid phases. The thus-obtained organic phase is rectified in a further step without the addition of water, and the head product consisting of an alcohol/paraffin mixture is recycled into the first step. The paraffin or paraffins and the alcohol or alcohols are obtained in the lower section of the individual rectifying step or steps. The water which may be present in the starting mixture is removed from the cycle. Low-boiling paraffins and/or low-boiling alcohols are suitable as additional azeotropic agents.

Abstract: A process for the nondegenerative distillation of C.sub.6 -C.sub.24 -fatty acids, of the type obtained by splitting natural fats and oils or by synthetic processes, such as for example the oxidation of paraffins, the crude product is thermally dried under reduced pressure, the dried and heated crude product is subjected to fractional evaporation in falling-film evaporators, optionally in the presence of superheated steam, and the various vapor fractions are deposited in condensers. The thermal drying process is conducted at a temperature of 60.degree.-80.degree. C. and a pressure of 90-100 mbars. The de-watered crude product is fractionated in a film-forming evaporator and, after distillation, passes to a rectification column which condenses the low boiling constituents as the main runnings.

Abstract: A two-stage distillation method for separating a mixed liquid such as a dimethylformamide-containing aqueous liquid or a methanol-containing aqueous liquid, into light and heavy fractions. The mixed liquid is first subjected to a distillation treatment in a first distillation zone of a vapor recompression type. When the boiling point of the mixed liquid is close to that of the desired light fraction, the top product from the first distillation zone is recovered as the light fraction, while the bottom product is subjected to a further distillation treatment to obtain the heavy fraction as its bottom product. When the boiling point of the mixed liquid is close to that of the heavy fraction, the bottom product from the first distillation zone is recovered as the heavy fraction, while the top product from the first distillation zone is subjected to a further distillation treatment to obtain the light fraction as its top product.

Abstract: A flow of fermenting liquor from a fermentor is separated into a yeast concentrate flow, which is recirculated to the fermentor, and a yeast-free flow which is separated in a simple evaporator unit into a first ethanol-enriched vapor flow and a first liquid bottom flow. The first vapor flow is treated to produce the desired ethanol while a major part of the first liquid bottom flow is recirculated to the fermentor. A minor, residual part of the latter flow is fed to a stripping unit where it is separated into a second ethanol-enriched vapor flow and a second liquid bottom flow exhausted of ethanol.

Abstract: Method of adding water and a hydroxide of an alkali metal or alkaline earth metal to a washing solvent such as an alkylamide and/or alkylsulfoxide when washing and removing high molecular substances stuck on the interior of a production apparatus or molding machine for an aromatic vinyl-acrylonitrile copolymer. A method for regenerating and recovering the washing solvent used for the above-mentioned washing and removal by means of an evaporator and distillation tower.

Abstract: This invention relates to a process for purifying crude ethanol, whether produced by fermentation or by the synthetic route, to produce a pure ethanol-water azeotrope. The process uses only two distillation columns for fermentation ethanol or synthetic ethanol eventhough the latter has diethyl ether as impurity. The inventive concept lies in the design and specification of the columns and the specific high pressure and low reflux ratio distillation conditions which enable each of the impurities in ethanol to be reduced below ppm. Ethanol of such purity is most desirable when used for potable or pharmaceutical purposes.

Abstract: A liquid containing a contaminant such as water or polymeric solids is purified. Purification of a liquid containing a contaminant is enhanced by the use of second fractionating column in conjunction with a first fractionating column to recover a portion of the liquid to be purified from the kettle product of the first column. Vapor from a second fractionating column is used to control the total energy input to a first fractionating column.

Abstract: Provided is a process for preparing tertiary butyl alcohol from isobutylene comprising reacting isobutylene or a hydrocarbon mixture containing isobutylene with an aqueous solution of an aliphatic carboxylic acid having from 1 to 6 carbon atoms in the presence of a solid, acidic ion-exchange resin as catalyst, to produce an aqueous reaction mixture of a major amount of tertiary butyl alcohol and a minor amount of the tertiary butyl ester of the carboxylic acid comprising the improved steps of:(1) subjecting said reaction mixture to distillation to remove unreacted isobutylene or hydrocarbon mixture therefrom;(2) supplying the treated reaction mixture of step (1) to a distillation column and passing water from the top to the bottom of said distillation column to remove said tertiary butyl ester of the carboxylic acid, wherein the amount of water used for removing the ester in step (2) is less than the sum of the amount of water used for converting said isobutylene into tertiary butyl alcohol and the amount of

Abstract: A flow of fermenting liquor from a fermentor is separated into a yeast concentrate flow, which is recirculated to the fermentor, and a yeast-free flow which is separated in a simple evaporator unit into a first ethanol-enriched vapor flow and a first liquid bottom flow. The first vapor flow is treated to produce the desired ethanol while a major part of the first liquid bottom flow is recirculated to the fermentor. A minor, residual part of the latter flow is fed to a stripping unit where it is separated into a second ethanol-enriched vapor flow and a second liquid bottom flow exhausted of ethanol.

Abstract: Sulfur compounds are separated from aqueous mixtures containing same by employing a stripper having at least two stripping sections with at least a portion of the stripper kettle product being recycled to the lower stripping section. The process is particularly effective in recovering mercaptans from steam condensate. In the production of mercaptans by reacting hydrogen sulfide with olefins, steam condensate contaminated with mercaptans is obtained from the steam ejector employed in the product fractionation column.

Abstract: A process for the production of alcohol from a fermented feed wherein insoluble organic matter is separated prior to entry into a first distillation column. The insoluble organic matter is dried under pressure to produce dried distillers grain and wherein excess vapor is removed from the drying zone to provide heat to the distillation system. The present process also includes removing excess water vapor from the evaporation zone, obtained from supplemental heating supplied by the overhead from said first distillation column, compressing said water vapor, and recycling it to the distillation columns and the evaporation zone.

Abstract: Process for purifying crude ethanol, whether produced by fermentation or by the synthetic route, to produce a pure ethanol-water azeotrope. The process uses only two distillation columns for fermentation ethanol and only three columns for synthetic ethanol because the latter has diethyl ether as impurity. The inventive concept lies in the design and specification of the columns and the specific distillation conditions which enable each of the impurities in ethanol to be reduced below 1 ppm. Ethanol of such purity is most desirable when used for potable or pharmaceutical purposes. The crude ethanol is fed into a first column and water is separately fed there as well, a side stream of purified aqueous ethanol is withdrawn from the first column and fed to a rectification column where a substantially pure ethanol-water azeotrope is withdrawn as a side stream. The points of introduction and removal of the respective streams to and from the columns are critical for a successful operation and product recovery.

Abstract: Process for isolating methyl tert-butyl ether contained in the reaction product of methanol with a C.sub.4 hydrocarbon cut containing isobutene, comprising fractionating said reaction product by introducing it at an intermediate point of a distillation zone, recovering methyl tert-butyl ether at the bottom thereof and, at the top thereof, a mixture of C.sub.4 hydrocarbons with methanol which is washed with water and condensed and wherefrom is separated a condensed C.sub.4 hydrocarbon fraction, a portion of which is fed back as reflux to the top of the distillation zone and another portion discharged, and separating the remaining water-methanol mixture by distillation.

Abstract: A method for purifying acrylonitrile resulting in capital and operating cost savings consists of distilling a solution of acrylonitrile and impurities in a distillation column under vacuum, and removing the purified acrylonitrile as a vaporous sidestream from the column.

Abstract: Anhydrous hydrogen fluoride of high purity can be recovered from metallic fluoride salts containing phosphate values by digesting the metallic salts in an aqueous solution in a humid atmosphere at a sufficiently high temperature to release a gas containing hydrogen fluoride and negligible amount of P.sub.2 O.sub.5. The released gas is rectified in a rectification operation which includes a rectification zone in which the rectification occurs in the presence of sulfuric acid.

Abstract: Oil or fat is deodorized by contacting with steam. The oil or fat is finely distributed in a vacuum contact zone by spray means whereupon it contacts a steam vapor. The contacted oil or fat is then recycled in the same contact zone, finely distributed, and once again contacted with the steam vapor. The steam efficiently removes flavoring and scenting components and free fatty acids normally present in natural fats and oils.

Abstract: A process for the recovery of methylglyoxal acetal from a reaction mixture which has been obtained in the reaction of acetone with an alcohol and a nitrosation agent or oxidizing agent in the presence of an acid catalyst followed by neutralization which comprises diluting the neutralized reaction mixture with such an amount of water that a homogeneous solution is formed, subsequent distillation in a first column in which a mixture of acetone, alcohol and solvent is removed overhead and returned direct to the synthesis and an azeotrope of methylglyoxal acetal, water and high-boilers is withdrawn as a side stream, condensation of the azeotrope thus obtained and separation of the phase rich in methylglyoxal acetal, subsequent distillation of the phase rich in methylglyoxal acetal thus obtained in a second column in which purified methylglyoxal acetal is withdrawn as a side stream and the overhead and bottoms products are returned with the feed to the first column, pure methylglyoxal acetal being obtained as the