Abstract: A method for recovering base oil from waste lubricating oil by separating base oil range constituents from a waste lubricating oil mixture, thereafter separating higher quality base oil constituents and lower quality base oil constituents from the base oil recovered from the waste lubricating oil mixture and thereafter treating the lower quality base oil constituents to produce marketable base oil. The total base oil produced from a waste lubricating oil mixture by this process is greater than the quantity producible by previous processes using only base oil separation from the waste lubricating oil mixture or processes which use only treatment of the base oil recovered from the waste lubricating oil mixture to produce the product base oil.

Abstract: A modular distillation apparatus including at least one heat exchanger that preheats contaminated liquids: a heater that heats the contaminated liquid from the heat exchanger; an evaporator condenser adapted o boil the contaminated liquid coming out of the heater to produce water vapor and contaminant concentrate, and condenser the water vapor into distilled water; a vacuum chamber capable of operating at below atmospheric pressure, the vacuum chamber housing the evaporator condenser and including at least one partition to separate the distilled water from the contaminate concentrate; a vapor compressor operably associated with the vacuum chamber to receive water vapor from the evaporator condenser in the vacuum chamber and pump the water vapor at pressure back through the evaporator condenser, wherein the heat exchanger recovers sensible heat from outgoing condensed distilled water and contaminant concentrate recycled from the vacuum chamber.

Abstract: In one embodiment, the invention is to a process for purifying acetic anhydride. The process includes the steps of feeding a liquid crude acetic anhydride stream directly to a distillation column and separating the liquid crude acetic anhydride stream to produce a light ends stream, a sidedraw and a residue stream. The sidedraw comprises substantially pure acetic anhydride product. The distillation column is operated at a pressure less than 101 kPa. The substantially pure acetic anhydride product comprises greater than 98 wt. % acetic anhydride, has a permanganate time of greater than 10 minutes, and has an APHA color of less than 10.

Abstract: The present invention is directed to an enhanced process for separating dissolved and suspended solids from valuable or harmful liquids and more particularly to improving the operational aspects and separation efficiency of treating certain water miscible fluids including those used for oil and gas processing such as glycols, as well as automobile and aircraft fluids, that have become contaminated with dissolved and/or suspended solid matter.

Abstract: Process for the recovery of ethylene oxide (EO) from fat absorbent (FA) which comprises providing a feed of elevated temperature FA to an EO Stripper, providing a stripping gas feed and contacting the stripping gas feed at elevated temperature with the elevated temperature FA feed, obtaining stripped lean absorbent (LA) and an EO-containing gas, and providing one or more external process stream feeds to the EO Stripper at a location above the elevated temperature FA feed and at a lower temperature with respect to the elevated temperature FA feed thereby concentrating EO in the EO-containing gas. The process can also include one or more impurity removal stages in the form of one or more side draws from the EO Stripper or an EO Stripper Concentrator. The invention also includes an apparatus for performing the process.

Abstract: A process and system for removing bound water from bio-oil by azeotropic distillation. The process includes combining a bound-water-containing bio-oil with an azeotrope agent and subjecting the resulting treated bio-oil to azeotropic distillation under reduced pressure. The azeotropic distillation removes a substantial portion of the bound water from the bio-oil, thus producing a water-depleted bio-oil that is less corrosive, more stable, and more readily miscible with hydrocarbons.

Abstract: The invention disclosed and claimed herein relates to treatment of water contaminated with glycol to be recycled for further effective use of the cleaned water resulting therefrom, especially at airports. More specifically, this invention relates to improved techniques for efficiently and reliably generating continuous flows of cleaned water as well as a continuous flow of recyclable glycol water of controlled concentration.

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: A process comprising: continuously distilling a crude xylylenediamine in a column to form a pure xylylenediamine and a bottom product, wherein the column comprises a distillation column having a side draw and the distillation column is operated under a reduced pressure and a bottom temperature of 185° C. or less; drawing off the pure xylylenediamine from the side draw; evaporatively concentrating the bottom product of the distillation column in an additional evaporation stage to form a condensate; and returning the condensate into the distillation column.

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: The present invention relates to a process for distilling an aqueous polymethylol mixture which comprises a polymethylol of the formula (I) (HOCH2)2—C—R2??(I) in which each R is independently a further methylol group or an alkyl group having 1 to 22 carbon atoms or an aryl or aralkyl group having 6 to 22 carbon atoms, a tertiary amine, water and the adduct of tertiary amine and formic acid (amine formate), which comprises performing the distillation in a distillation column which is connected at the bottom to an evaporator, the bottom temperature being above the evaporation temperature of the monoester of formic acid and polymethylol (polymethylol formate) which forms during distillation. The present invention further relates to a composition comprising polymethylol and 1 to 10 000 ppm by weight of polymethylol formate, and to the use thereof.

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: Disclosed is process for the recovery of HFC-43-10mee from a mixture comprising hydrogen fluoride and HFC-43-10mee, comprising feeding the composition comprising hydrogen fluoride and HFC-43-10mee to a distillation column, subjecting said mixture to a distillation step from which is formed a column distillate composition comprising an azeotrope or azeotrope-like composition of hydrogen fluoride and HFC-43-10mee, and a column-bottoms composition comprising HFC-43-10mee, condensing said column distillate composition to form two liquid phases, being i) an HFC-43-10mee-rich phase and ii) an HF-rich phase; and separating said two liquid phases.

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 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 top temperature T1 of a distillation tower 1 is held below a liquefying temperature of a light fraction by returning a part of an exhaust gas W, which is cooled by a condenser 5, to the upper zone of the distillation tower 1. A bottom temperature T2 is raised up to 300° C. at highest by returning a part of a liquid product P from a re-boiler 3 to a lower zone of the distillation tower 1. When a liquid hydrocarbon L comes in countercurrent contact with a stripping gas G inside the distillation tower 1 with the temperature profile that an inner temperature gradually falls down along an upward direction, mercury is efficiently transferred from the liquid L to a vapor phase without effusion of the light fraction in accompaniment with the exhaust gas W.

Abstract: A process comprising: continuously distilling a crude xylylenediamine in a column to form a pure xylylenediamine and a bottom product, wherein the column comprises a distillation column having a side draw and the distillation column is operated under a reduced pressure and a bottom temperature of 185° C.

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 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: 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 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: Disclosed is a process for removing DME from a stream containing C4 olefins. The process includes providing a first stream comprising C4 olefins, C5+ hydrocarbons, DME, and methanol. The first stream is separated into a second stream comprising the C4 olefins and the DME and a third stream comprising the C5+ hydrocarbons and the methanol. The second stream is directed to a DME absorption unit, wherein the second stream contacts water under conditions effective to separate the C4 olefins from the DME. Also disclosed is a process including contacting the first stream with water in a methanol removal unit under conditions effective to separate remove the methanol therefrom; distilling the methanol-depleted stream to remove C5+ hydrocarbon components, and contacting the stream with water in a DME removal unit under conditions effective to form an overhead stream comprising the C4 olefins and a bottoms stream comprising the DME.

Abstract: A process for purifying grafted polyolefins by extraction is disclosed. The purified grafted polyolefins have improved color and adhesion properties. The extraction is performed with an azeotropic solvent that is strong enough to extract impurities but does not cause sticking of the grafted polyolefin. The azeotropic solvent can be easily recycled.

Abstract: Disclosed herein are methods for the recovery of at least one of an organic acid or an organic acid amide, such as a heat stable lactic acid or lactamide, from a feed stream which contains the organic acid and/or organic acid amide. The feed stream is mixed with at least one azeotroping agent. The azeotroping agent is a hydrocarbon capable of forming at least one heteroazeotrope with the organic acid or the organic acid amide in the feed stream. The mixture of the feed stream and the azeotroping agent is heated to produce a vapor stream. The heteroazeotrope is a component of that vapor stream. The vapor stream can be heated further to separate components or it can be condensed into a liquid stream. The liquid stream is capable of being separated into a first phase and a second phase. The first phase contains the highest concentration of the organic acid and/or the organic acid amide and the azeotroping agent is part of the second phase.

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 distillation system is provided for recovering water from sea water and other polluted water source. The system has a heat engine embodying Carnot cycle and a Rankine cycle formed by heat exchangers, flash evaporator and condenser. Burnt gases from the engine such as a jet engine no longer fit for flying are directed into a duct where the exchangers are located. Sea water is pumped into the heat exchanger for preheating by residue heat in the duct and then into the exchanger for further heating. A recirculating pump raises water pressure in the exchanger for increasing boiling point to about 165° C. The heated water is fed into the evaporator where it changes into vapour and condensed into water by the condenser. The jet air stream is used to create Venturi effect for maintaining sub-atmospheric pressure in the evaporator. Any solid left in the evaporator is removed by a transfer mechanism.

Abstract: Disclosed herein are methods for the recovery of an organic acid, such as a heat stable lactic acid, from a feed stream which contains at least one of an organic acid amide, an organic acid ammonium salt, or an alkylamine-organic acid complex. The feed stream is mixed with at least one azeotroping agent. The azeotroping agent is a hydrocarbon capable of forming at least one azeotrope with the organic acid that is produced by the thermal decomposition of the amide, ammonium salt, or complex in the feed stream. Preferably the azeotrope is a heteroazeotrope. The mixture of the feed stream and the azeotroping agent is heated to produce a vapor stream. The azeotrope is a component of the vapor stream. The vapor stream can be condensed to a liquid stream, and the organic acid is recovered in the liquid stream that is produced. When the azeotrope is a heteroazeotrope, the vapor stream can be condensed into a liquid stream, which can be separated into a first phase and a second phase.

Abstract: A process for distillative removal of ammonia from solutions (I) which include a lactam and ammonia comprises effecting said removal in a distillation apparatus (a) at an absolute pressure of less than 10 bar.

Abstract: A process is provided for the distillative separation of pentene nitrile isomers which have a relative volatility alpha ranging from 1.0 to 1.3 in the pressure range from 1 to 500 kPa, wherein the distillation is carried out in the presence of a liquid diluent which forms with the pentene nitrile isomers, under the same pressure conditions, azeotropes whose relative volatility alpha is higher than that of the pentene nitrile isomers to be separated.

Abstract: A process of treating waste solvent acetonitrile streams which contain at least one water extractable impurity such as isopropyl acetate to remove substantially all of the impurity by distilling the waste solvent acetonitrile in the presence of water for a time sufficient to allow the water extractable impurity to be extractively distilled from the acetonitrile. In preferred embodiments of the present invention the feed may contain either a mixture of waste solvent acetonitrile and crude acetonitrile or crude acetonitrile free of hydrogen cyanide by itself.

Abstract: A process for working up hydroxylamine-containing solutions as obtained in particular in the electronics industry during the cleaning of electronic components is described. According to the invention, the hydroxylamine is stripped from the wastewater with steam. The products obtained are aqueous hydroxylamine and an aqueous solution of the amines. Both product streams can be purified in further process steps to give a saleable product.

Abstract: A process for pretreating a very acid natural gas containing a substantial amount of hydrogen sulfide (H2S), possibly combined with carbon dioxide (CO2), includes at least a stage wherein the initial natural gas is contacted in a distillation column with a liquid condensate itself resulting from cooling of the gaseous fraction obtained during the contacting stage. This solution allows to eventually recover at a lower cost a gas enriched in methane, depleted in hydrogen sulfide and freed from substantially all of the water it contains, and a liquid phase containing most of the hydrogen sulfide, substantially all of the water and depleted in hydrocarbon. Control of the thermodynamic conditions during the stages that characterize the process, according to the water content of the gas during treatment, allows progressive exhaustion of the water contained in the gas while preventing hydrates formation.

Abstract: A distillation system is provided having an evaporation conduit and a condensing conduit connected by a transfer system for transferring distillate vapour from the evaporation conduit to the condensing conduit to condense the distillate. The evaporation and condensing conduits operate under vacuum pressure. An intake conduit and a return conduit communicate in an unrestricted manner between a source of solution and the evaporation conduit. A distillate conduit communicates with the condensing conduit for dispensing condensed distillate therefrom. A radiant heat capturing system is provided for capturing and using heat radiated from the distillate conduit to generate power.

Abstract: A process for distillative removal of ammonia from solutions (I) which include a lactam and ammonia comprises effecting said removal in a distillation apparatus (a) at an absolute pressure of less than 10 bar.

Abstract: A material contaminated with a solvent is treated with a hydrofluorocarbon to remove the contaminant. The hydrofluorocarbon can be tetrafluoroethane.

Abstract: A process for the purification of a mixture of aromatic polyamines obtained by hydrogenation of the corresponding aromatic polynitro compounds, said mixture including the various isomers of the said amines as well as reaction by-products, including the steps of carrying out a distillation of the mixture in a distillation column, wherein a first stream, corresponding to a fraction or to all of the stream recovered at the bottom of the distillation column, is separated and is used in a chemical reaction and a second stream is separated corresponding (i) to a stream drawn off from the side in the gas phase, in the lower third of the said column, this stream representing at most 20% or more than 80% of the total volume (first and second stream); or (ii) to a fraction of the first stream, this fraction representing 2 to 50% of the volume of the first stream; in order to treat it subsequently.

Abstract: A closed tunnel system for distilling fresh water from ocean salt water is provided with an elongated evaporation plate adapted to hold ocean water for evaporation therefrom. During the distillation process, a vacuum is drawn in the tunnel, and sunlight is focused onto the evaporation plate with a concave lens-structure roof. External concave mirrors automatically track the sun and focus additional sunlight onto the lens-structure roof. An agitator-wiper unit agitates the ocean water on the evaporation plate to maintain a homogeneous liquid mixture, and to present additional water surface area for evaporation of fresh water. The fresh water vapor then condenses under pressure in heat exchangers that simultaneously pre-heat the ocean water prior to entry onto the evaporation plate.

Abstract: A process for separating hydrogen chloride from a mixture including an N-(C1-C18)-alkyl-2-pyrrolidone and hydrogen chloride by distilling the mixture including an N-(C1-C18)-alkyl-2-pyrrolidone and hydrogen chloride at from 100 to 220° C. and from 50 to 850 hPa in the presence of water in a distillation column, condensing the water as water-hydrogen chloride azeotrope at the top by cooling, returning the water-hydrogen chloride azeotrope to the distillation column, separating off gaseous hydrogen chloride at the top and taking off the N-(C1-C18)-alkyl-2-pyrrolidone from the bottom.

Abstract: Disclosed herein are methods for the recovery of an organic acid, such as a heat stable lactic acid, from a feed stream comprising at least one of an organic acid amide, an organic acid ammonium salt, or an alkylamine-organic acid complex. The feed stream that comprises the organic acid amide, organic acid ammonium salt, or alkylamine-organic acid complex is mixed with at least one azeotroping agent. The azeotroping agent is a hydrocarbon capable of forming at least one azeotrope with the organic acid that is produced by the thermal decomposition of the amide, ammonium salt, or complex in the feed stream. Preferably the azeotrope is a heteroazeotrope. The mixture comprising the feed stream and the azeotroping agent is heated to produce a vapor stream that comprises the azeotrope. The vapor stream can be condensed to a liquid stream, and the organic acid is recovered in the liquid stream that is produced.

Abstract: Disclosed herein are methods for the recovery of at least one of an organic acid or an organic acid amide, such as a heat stable lactic acid or lactamide, from a feed stream comprising the organic acid and/or organic acid amide. The feed stream that comprises the organic acid and/or organic acid amide is mixed with at least one azeotroping agent. The azeotroping agent is a hydrocarbon capable of forming at least one heteroazeotrope with the organic acid or the organic acid amide. The mixture comprising the feed stream and the azeotroping agent is heated to produce a vapor stream that comprises the heteroazeotrope. The vapor stream can be heated further to separate components or it can be condensed into a liquid stream. The liquid stream is capable of being separated into a first phase and a second phase. The first phase contains the highest concentration of the organic acid and/or the organic acid amide and the second phase comprises the azeotroping agent.

Abstract: A process for separating water from methanol in an aqueous methanol initial mixture, comprising subjecting said mixture to azeotropic distillation in the presence of sufficient added methyl acrylate to form an azeotrope with most of the methanol in said initial mixture such that a substantial proportion of methanol in the initial mixture is removed as an azeotrope of methanol and methyl acrylate in the overhead vapors resulting from said distillation and a major proportion of water in said initial mixture is removed in the liquid residue of said distillation.

Abstract: Method and apparatus for concentrating slurries by removing liquid in a single effect unit maintained under vacuum to effect low temperature flashing of the liquid. The single effect unit is a single flash column with separate recirculation loops, one to preheat incoming slurry for concentration and a separate loop for withdrawal of concentrated slurry Vapor from the flash column can be treated to separate liquid from other components in the vapor.

Abstract: Pertaining mainly to the field of the petrochemical industry the method essentially includes delivery of a motive liquid into a liquid-gas ejector from a separator by a pump, feeding a liquid-gas mixture obtained in the ejector into the separator, cooling of the motive liquid with simultaneous heating of a circulating portion of a distillation residual while the motive liquid is pumped through a heat-exchanger/heater by the pump, and maintaining such an operational mode while the temperature of mediums in the separator is higher than the temperature of the motive liquid at the nozzle inlet of the ejector, where the latter is higher than the temperature of the distillation residual at the point of discharge from a rectification column and the temperature of a gas-vapor phase at the gas inlet of the ejector is lower than the temperature of the distillation residual at the point of discharge from the column.

Abstract: A process for producing methylal that involves feeding a liquid containing methanol, formaldehyde and water to an uppermost reactor of at least four solid acid catalyst-filled reactors which are each externally connected to an intermediate portion of a distillation column; and forcibly circulating a liquid containing methanol, formaldehyde, water and produced methylal in a temperature range of 80° C. to 100° C.

Abstract: The present invention relates to a process for separating hydrogen chloride from a mixture comprising an N-(C1-C18)-alkyl-2-pyrrolidone and hydrogen chloride by distilling the mixture comprising an N-(C1-C18)-alkyl-2-pyrrolidone and hydrogen chloride at from 100 to 220° C. and from 50 to 850 hPa in the presence of water by means of a distillation column, condensing the water as water-hydrogen chloride azeotrope at the top by cooling, returning the water-hydrogen chloride azeotrope to the distillation column, separating off gaseous hydrogen chloride at the top and taking off the N-(C1-C18)-alkyl-2-pyrrolidone from the bottom.

Abstract: Process for the recovery of fluorinated sulphonic acid including the step of subjecting the spent acid to heat treatment with stepwise or continuously increasing temperature, withdrawing at least two fractions during the heat treatment; and recovering the fluorinated sulphonic acid from each fraction.

Abstract: A distillation procedure is provided for the separation of impurities from organic materials such as glycols and glycol ethers whereby a liquid stripping component is interfaced into a distillation column with or below the organic material introduction, heat being provided by a reboiler, the stripping component and impurities being removed overhead.

Abstract: A process for concentrating spent sulphuric acids particularly sulphuric acids which arise during the nitration of hydrocarbons with nitric acid in the presence of sulphuric acid, wherein single- or multi-stage concentration is effected under vacuum.