Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
  • C07C45/78—Separation; Purification; Stabilisation; Use of additives
  • C07C45/81—Separation; Purification; Stabilisation; Use of additives by change in the physical state, e.g. crystallisation
  • C07C45/82—Separation; Purification; Stabilisation; Use of additives by change in the physical state, e.g. crystallisation by distillation
  • C07C45/83—Separation; Purification; Stabilisation; Use of additives by change in the physical state, e.g. crystallisation by distillation by extractive distillation
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/02—Treatment of water, waste water, or sewage by heating
  • C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
  • B01D3/14—Fractional distillation or use of a fractionation or rectification column
  • B01D3/141—Fractional distillation or use of a fractionation or rectification column where at least one distillation column contains at least one dividing wall
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
  • B01D3/34—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping with one or more auxiliary substances
  • B01D3/40—Extractive distillation
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/02—Treatment of water, waste water, or sewage by heating
  • C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
  • C02F1/048—Purification of waste water by evaporation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
  • C07C45/27—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation
  • C07C45/32—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen
  • C07C45/33—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of CHx-moieties
  • C07C45/34—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of CHx-moieties in unsaturated compounds
  • C07C45/35—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of CHx-moieties in unsaturated compounds in propene or isobutene
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C47/00—Compounds having —CHO groups
  • C07C47/02—Saturated compounds having —CHO groups bound to acyclic carbon atoms or to hydrogen
  • C07C47/04—Formaldehyde
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
  • C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
  • C07C51/215—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of saturated hydrocarbyl groups
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
  • C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
  • C07C51/23—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of oxygen-containing groups to carboxyl groups
  • C07C51/235—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of oxygen-containing groups to carboxyl groups of —CHO groups or primary alcohol groups
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
  • C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
  • C07C51/25—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of unsaturated compounds containing no six-membered aromatic ring
  • C07C51/252—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of unsaturated compounds containing no six-membered aromatic ring of propene, butenes, acrolein or methacrolein
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/42—Separation; Purification; Stabilisation; Use of additives
  • C07C51/43—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation
  • C07C51/44—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation by distillation
  • C07C51/46—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation by distillation by azeotropic distillation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/42—Separation; Purification; Stabilisation; Use of additives
  • C07C51/48—Separation; Purification; Stabilisation; Use of additives by liquid-liquid treatment
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C53/00—Saturated compounds having only one carboxyl group bound to an acyclic carbon atom or hydrogen
  • C07C53/08—Acetic acid
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2/00—Processes of polymerisation
  • C08F2/04—Polymerisation in solution
  • C08F2/10—Aqueous solvent
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F20/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride, ester, amide, imide or nitrile thereof
  • C08F20/02—Monocarboxylic acids having less than ten carbon atoms, Derivatives thereof
  • C08F20/04—Acids, Metal salts or ammonium salts thereof
  • C08F20/06—Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/30—Organic compounds
  • C02F2101/34—Organic compounds containing oxygen
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/10—Process efficiency

Definitions

• the present invention relates to a method for treating aqueous effluents containing formaldehyde, in particular a method for treating aqueous solutions resulting from the synthesis of acrylic acid.
• the invention also relates to the use of the purified aqueous solution in a process for the production of acrylic acid by catalytic oxidation of propylene and / or propane in vapor dilution.
• Formaldehyde is used as a raw material in the chemical industry, which generally requires the treatment of wastewater containing residual formaldehyde, before discharge.
• Other industrial processes generate formaldehyde as a by-product, for example during the synthesis of acrylic acid by oxidation of propylene, producing aqueous phases containing formaldehyde which it is desirable to purify before rejection or for recycling within the process.
• Formaldehyde also known as formaldehyde, methanal or formaldehyde
• formaldehyde is a gas at room temperature which is very soluble in water by forming hydrates, which makes it difficult to separate during the treatment of aqueous effluents containing formaldehyde as an impurity. .
• the concentration of formaldehyde in its CH2O form in an aqueous solution is very low, generally less than 0.1%; formaldehyde is in the form of methylene glycol HO (CH 2 0) H and its oligomers HO (CH 2 0) n H (with n generally ranging from 1 to 8).
• the formation of polyoxymethylene glycols in the aqueous solution depends on the temperature and the presence of other impurities such as acids which can catalyze the formation of polymers. These reactions considerably limit the volatility of formaldehyde and therefore its separation by distillation, the vapor pressure of formaldehyde during distillation being determined by the kinetics of the associated reactions.
• third-party compounds are generally used in order to form adducts with formaldehyde which are more easily separable from the aqueous medium, by distillation or by absorption on resins.
• the inventors have discovered that the presence of acetic acid in an aqueous solution containing formaldehyde facilitates the separation of formaldehyde from the aqueous solution and allows its elimination by simple distillation.
• the invention thus provides a new process for treating aqueous effluents containing formaldehyde by distillation in the presence of acetic acid.
• the document FR 2152849 describes a process for extracting acetic acid from a mixture comprising 0.5-10% formaldehyde, 0.5-15% water and the additional acetic acid.
• the process consists of an extractive distillation with water as an exhausting agent, by carrying out a reactive distillation by injection at the top of the water column. which will selectively capture formaldehyde and allow recovery at the bottom of the column of pure acetic acid (see example 1 and figure of the process).
• water manages to selectively separate formaldehyde from acetic acid despite a very high content of the latter in the medium.
• the invention is particularly advantageous for treating aqueous phases generated in a process for the synthesis of acrylic acid.
• the synthesis of acrylic acid by catalytic oxidation of propylene and / or propane in the gas phase generates water and the formation of light condensable by-products, in particular the formation of formaldehyde and acetic acid.
• the complexity of the gaseous mixture obtained in this process requires the use of a set of operations to recover the acrylic acid and transform it into a grade of purified acrylic acid compatible with its end use.
• the aqueous streams originating from the purification steps of acrylic acid can contain formaldehyde and / or acetic acid.
• the reagent is introduced in the diluted state in the gas phase, generally at a volume concentration of 4% to 15%.
• part of the dilution gas is supplied by the nitrogen accompanying the oxygen introduced in the form of air, and the complement is advantageously constituted either by partial recycling of a mixture of inert compounds and residual light products from the 'stage of condensation of the reaction flow of acrylic acid, either by steam, which advantageously comes from an aqueous flow obtained downstream of the process.
• a recycled aqueous stream is generally used coming from the recovery and purification stages of the process, so as to limit the consumption of external water.
• An objective of the present invention is to provide a simple technical solution for removing formaldehyde to meet this need and improve the productivity and the service life of the propylene and / or propane oxidation catalyst.
• the invention relates to a process for removing formaldehyde by distillation of an aqueous solution containing formaldehyde, characterized in that the distillation is carried out in the presence of acetic acid.
• the aqueous solution contains from 0.1 to 5% by mass, preferably from 1 to 3% by mass of formaldehyde.
• the aqueous solution contains from 1 to 10% by mass, preferably from 2 to 6% by mass of acetic acid.
• the mass ratio between acetic acid and formaldehyde in the aqueous solution is between 1 and 5, preferably between 1 and 4.
• the distillation is carried out using a distillation column, surmounted by an overhead condenser.
• the distillation is carried out using a distillation column, surmounted by a mechanical steam compressor.
• the aqueous solution containing formaldehyde comes from a process for the synthesis of acrylic acid by catalytic oxidation of propylene and / or propane.
• the acetic acid can be present in the aqueous solution subjected to the treatment, or the acetic acid is added via a stream comprising acetic acid generated in said process for the synthesis of acrylic acid.
• the method for synthesizing acrylic acid includes a method for purifying acrylic acid comprising separation of the water by liquid extraction using a solvent.
• the method for synthesizing acrylic acid includes a method for purifying acrylic acid comprising separation of the water by azeotropic distillation using a solvent.
• the process for the synthesis of acrylic acid is a process for the catalytic oxidation of propylene and / or propane in vapor dilution, that is to say fed by a flow of raw materials diluted in steam of water.
• the aqueous phase after treatment is recycled in the acrylic acid synthesis process, preferably as a source of vapor in the reaction section.
• the invention also relates to a process for the synthesis of acrylic acid by catalytic oxidation of propylene and / or propane comprising the treatment by distillation of an aqueous phase containing formaldehyde and acetic acid in a mass ratio of acetic acid / formaldehyde ranging from 1 to 4, and recycling the purified aqueous phase as a source of vapor in the reaction section of the process, said aqueous phase being recovered at the bottom of the distillation column, while formaldehyde is recovered at the head of the column.
• the treatment by distillation is carried out using a distillation column with a separating wall, making it possible to remove formaldehyde, and the residual solvents dissolved in the aqueous phase which can be recycled.
• the inventors have discovered that the joint presence of acetic acid and formaldehyde in the aqueous stream supplying a distillation column makes it possible to remove a larger part of the formaldehyde present at the top of the distillation column.
• the treatment process according to the invention is thus particularly advantageous for removing the formaldehyde present in aqueous streams containing acetic acid generated in a process for the synthesis of acrylic acid; acetic acid may be present in the flow to be treated directly because of its favored training under certain operating conditions of the purification process of acrylic acid. Alternatively, the acetic acid is added through a concentrated flux of acetic acid produced in the purification process of acrylic acid.
• These two alternatives have the advantage of not introducing external phases or products liable to pollute the flow to be treated, and lead to an aqueous phase essentially free of formaldehyde suitable for being used as a vapor source to dilute the gases entering the reaction section of the acrylic acid synthesis process. This results in a gain in terms of water consumption within the process.
• the energy balance of the acrylic acid synthesis process can also be optimized by combining mechanical recompression of the distilled steam at the top of the distillation column, enabling this steam to be used as heat transfer fluid.
• FIG. 1 schematically represents an installation for producing acrylic acid with separation of water by liquid extraction and purification according to the invention of the recycled aqueous stream as a source of vapor.
• FIG. 2 schematically represents an installation for producing acrylic acid with separation of water by azeotropic distillation and purification according to the invention of the recycled aqueous stream as a source of vapor.
• FIG. 3 represents a variant of the purification process according to the invention usable in the installation of FIG. 1 and of FIG. 2.
• FIG. 4 visualizes the effect of the presence of acetic acid on the elimination of formaldehyde by distillation.
• the treatment process according to the invention is carried out by distillation using a conventional distillation column which may comprise at least one packing, such as for example a loose packing and / or a structured packing, and / or trays such as for example perforated trays, trays with fixed flaps, trays with movable flaps, domed trays, or combinations thereof.
• a conventional distillation column which may comprise at least one packing, such as for example a loose packing and / or a structured packing, and / or trays such as for example perforated trays, trays with fixed flaps, trays with movable flaps, domed trays, or combinations thereof.
• the distillation column preferably has a number of theoretical stages between 1 and 15, and operates at atmospheric pressure.
• the distillation column is surmounted by an overhead condenser which condenses the vapors generated.
• the condensed product can be recycled at least in part as reflux from the distillation column, the rest being advantageously withdrawn and recycled in whole or in part in the process, for example in a step of absorption of acrylic acid in the gas mixture from the reaction section, or sent to a treatment station for further treatment before rejection.
• the distillation column is surmounted by a mechanical steam compressor, bringing the steam to a pressure such that the temperature reached is higher than the temperature at the bottom of the column. The vapors thus compressed can be used as a heat transfer fluid providing part of the necessary heat flow at the level of the boiler associated with the distillation column, to ensure distillation.
• the aqueous solution subjected to the distillation treatment according to the invention generally contains 0.1 to 5% by mass of formaldehyde.
• a content ranging from 1 to 10% by mass of acetic acid in the aqueous solution promotes the removal by distillation of formaldehyde.
• a mass ratio between acetic acid and formaldehyde of between 1 and 4 makes it possible to achieve a formaldehyde elimination rate greater than 60%, or even greater than 70%.
• the aqueous solution subjected to the process according to the invention is generated by a process of purification of acrylic acid implemented in a process of production of acrylic acid by catalytic oxidation of propylene and / or propane in gas phase.
• aqueous solution is represented for example by the flow (9) in FIGS. 1 and 2.
• an installation for the production of acrylic acid comprises a first reactor 1 supplied with a mixture (1) of propylene and / or propane and oxygen in which a mixture rich in acrolein is produced, and sent in a second reactor 2 where the selective oxidation of acrolein to acrylic acid is carried out.
• the gaseous mixture (2) resulting from the second stage consists, apart from acrylic acid, of non-transformed compounds derived from the reactants involved or from impurities generated during at least one of the 2 reaction stages, to know
• - light compounds which cannot be condensed under the temperature and pressure conditions usually used, essentially: propylene, propane, nitrogen, unconverted oxygen, carbon monoxide and dioxide formed in small quantities by ultimate oxidation;
• - light condensable compounds essentially: water, light aldehydes such as unconverted acrolein, formaldehyde and acetaldehyde, formic acid, acetic acid, propionic acid;
• the complexity of the gaseous mixture (2) obtained in this process requires carrying out a set of operations to recover the acrylic acid contained in this gaseous effluent and transform it into a grade of acrylic acid compatible with its end use.
• the gas mixture (2) is sent to an absorption column 3 where acrylic acid and other oxidation products are condensed by absorption with water, a flow (4) of noncondensable compounds being eliminated.
• the liquid stream (3) leaving the absorption column 3 is subjected to a dehydration step which is carried out in the presence of a solvent (7) of acrylic acid immiscible with water in a unit 4.
• the dehydration step is carried out by liquid-liquid extraction of acrylic acid in the presence of the solvent (7) in a liquid extraction column 4, generating a bottom flow ( 5) containing water and impurities including formaldehyde, and a head stream (14) rich in acrylic acid in a solvent medium.
• solvents which can be used mention may, for example, be made of ethyl acrylate or isopropyl acetate.
• the stream (14) is then subjected to a distillation 8 to recover the solvent (16) which is recycled via the stream (6) in the extraction column 4, the stream (15) at the bottom being subjected to a purification in a distillation column 9 leading at the bottom to obtaining an acrylic acid of technical grade (18), and at the top a stream concentrated in light impurities.
• the dehydration step is carried out by azeotropic distillation with a solvent (7) in a distillation column 4, generating a two-phase medium (6) at the head of the column: an organic phase (16 ) essentially consisting of the solvent, which is recycled to reflux in the column 4, and an aqueous phase (5) containing impurities including formaldehyde.
• solvents which can be used mention may, for example, be made of methyl isobutyl ketone (MIBK) or toluene.
• the stream (15) is subjected to a purification in a distillation column 9 leading at the bottom to obtaining a technical grade acrylic acid (18), and at the head at a stream (17) concentrated in light impurities.
• the aqueous stream (5) containing a small amount of dissolved solvent is advantageously sent to a step of recovering solvent by distillation in a column 5; the solvent is recovered at the top (8) and recycled in the stream (6) supplying the unit 4, and an aqueous phase containing most of the formaldehyde is obtained at the bottom (9).
• the process according to the invention consists in treating the aqueous phase (9) by distillation in a distillation column 6, so as to eliminate in the overhead stream (11) most of the formaldehyde present, and to obtain a purified aqueous phase ( 12).
• the invention consists in operating the distillation in column 6 in the presence of acetic acid, either by adding this compound via a stream (10), external or generated within the process, preferably via of a recycled stream, either by operating the purification / recovery process of acrylic acid so as to promote the entrainment of acetic acid impurity in the stream (9).
• the distillation is preferably carried out at atmospheric pressure in column 6 by introducing this stream 9 at the lower third of this column.
• An advantageous way of introducing acetic acid into the stream (9) before the distillation of formaldehyde is to use as stream (10) a stream concentrated in acetic acid obtained at the head of a column for separating this impurity.
• such a stream concentrated in acetic acid is represented by the stream (17) obtained during the distillation of the acrylic acid (18) recovered at the bottom of the distillation column 9.
• the aqueous phase (12), freed of most of the formaldehyde, is advantageously sent to a steam generator 7 and the generated water vapor (13) is sent to the reaction section of the process to dilute the propylene / propane at the inlet. of the first reactor, and obtain a volume concentration of propylene / propane of between 5% and 10% in reactor 1.
• the stream (11) distilled at the top of column 6 containing the formaldehyde can be eliminated, or at least partly recycled in the process.
• the stream (11) is recycled at the top of the absorption column 3 of acrylic acid.
• the formaldehyde is then entrained with the inert gases and light compounds not condensed in the stream (4) at the head of the column, the stream (4) being able to be eliminated by incineration.
• a third variant consists in combining the step of recovering the solvent present in the aqueous phase containing formaldehyde with the removal of formaldehyde by distillation in the presence of acetic acid.
• the combination of these two stages is carried out using a single distillation column with a separating wall as shown for example in FIG. 3.
• a column 6B with a separating wall is supplied directly with an aqueous phase (9) containing formaldehyde and a small amount of dissolved solvent, obtained from the dehydration step of the reaction mixture.
• An addition of a flux (10) comprising acetic acid can be carried out under the conditions described above.
• Column 6B performs the same function as distillation columns 5 and 6 placed in series in the diagrams shown in FIGS. 1 and 2.
• a configuration of column 6B can be as follows:
• the distillation column 6B has a separating wall joined with the upper dome of the column at the top and not joined with the bottom of the column at the bottom, the wall thus separates the column in two sections, the lower space of which communicates with the column bottom space, and the head space of which is separated into two hermetic zones.
• the column 6B is fed at the upper plate of the feed section 50.
• a head stream (8) comprising the solvent is distilled and can be recycled.
• a stream (11) rich in formaldehyde is distilled at the top and a stream (12) corresponding to the aqueous phase free of most of the formaldehyde is recovered at the bottom, this stream (12 ) can advantageously be recycled as a source of steam.
• the invention also relates to a process for the synthesis of acrylic acid by catalytic oxidation of propylene and / or propane comprising at least one step generating an aqueous phase containing from 0.1 to 5% of formaldehyde, in which the elimination of formaldehyde in said aqueous phase at the head of a distillation column, characterized in that the distillation is carried out in the presence of acetic acid, in an acetic acid / formaldehyde mass ratio ranging from 1 to 5, the purified aqueous phase obtained at the bottom of the column being recycled as a source of vapor in the reaction section of the process.
• the column was fed at a point located in the lower part (third) by an aqueous stream comprising formaldehyde subjected to distillation at atmospheric pressure five degrees below the bubble point of the feed plate.
• the column is topped with a pin condenser.
• the gaseous phase is sent to a vent and the liquid phase drawn off and sent to a tank placed on a scale.
• the reflux rate is ensured by the positioning time of an automatic 3-way valve towards the reflux of the column or towards the withdrawal line.
• a formaldehyde separation rate could thus be determined, expressed by the mass percentage between the flow rate of formaldehyde at the top of the column and the flow rate of feed formaldehyde.
• the formaldehyde removal rate remains below 50% in the absence of acetic acid, which confirms that the distillation of formaldehyde is difficult.

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• 2018
  • 2018-11-29 FR FR1872059A patent/FR3089222A1/fr active Pending
• 2019
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