Classifications

• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P7/00—Preparation of oxygen-containing organic compounds
  • C12P7/40—Preparation of oxygen-containing organic compounds containing a carboxyl group including Peroxycarboxylic acids
  • C12P7/42—Hydroxy-carboxylic acids
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/347—Preparation of carboxylic acids or their salts, halides or anhydrides by reactions not involving formation of carboxyl groups
  • C07C51/377—Preparation of carboxylic acids or their salts, halides or anhydrides by reactions not involving formation of carboxyl groups by splitting-off hydrogen or functional groups; by hydrogenolysis of functional groups
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/42—Separation; Purification; Stabilisation; Use of additives
• • 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
• • 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
• • 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
  • C07C51/487—Separation; Purification; Stabilisation; Use of additives by treatment giving rise to chemical modification
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C57/00—Unsaturated compounds having carboxyl groups bound to acyclic carbon atoms
  • C07C57/02—Unsaturated compounds having carboxyl groups bound to acyclic carbon atoms with only carbon-to-carbon double bonds as unsaturation
  • C07C57/03—Monocarboxylic acids
  • C07C57/04—Acrylic acid; Methacrylic acid
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P7/00—Preparation of oxygen-containing organic compounds
  • C12P7/40—Preparation of oxygen-containing organic compounds containing a carboxyl group including Peroxycarboxylic acids

Definitions

• the invention relates to a process for the dehydration of aqueous 3-hydroxypropionic acid to acrylic acid, wherein the 3-hydroxypropionic acid is produced by fermentation, the 3-hydroxypropionic acid is separated from the fermentation broth, the content of aldehydes in the aqueous 3-hydroxypropionic under 0.02 wt .-% is lowered, the dehydration is carried out in the liquid phase and aqueous acrylic acid is distilled off continuously from the liquid phase.
• Acrylic acid because of its very reactive double bond as well as its carboxylic acid group, is a valuable monomer for making polymers, e.g. water-absorbent polymer particles, binders for aqueous emulsion paints and adhesives dispersed in aqueous solvent.
• Water-absorbing polymer particles are used for the production of diapers, tampons,
• the water-absorbing polymer particles are also referred to as superabsorbers.
• Acrylic acid is produced industrially exclusively from fossil raw materials. This is considered to be disadvantageous by the consumers of the hygiene articles. There is therefore a need for the water-absorbent polymer particles used in the hygiene articles
• One possible route is the fermentative production of 3-hydroxypropionic acid and its conversion to acrylic acid.
• the production of 3-hydroxypropionic acid by fermentation is described, for example, in WO 2012/074818 A2.
• EP 2 565 212 A1 The object of the present invention was to provide an improved process for the production of acrylic acid based on renewable raw materials.
• the object was achieved by a process for the dehydration of aqueous 3-hydroxypropionic acid to acrylic acid in the liquid phase, wherein aqueous acrylic acid is continuously distilled off from the liquid phase, characterized in that the 3-hydroxypropionic acid is produced by fermentation, the 3 -Hydroxypropionic acid from the
• the total amount of 2-furfural, glyoxal, benzaldehyde and crotonaldehyde in the aqueous 3-hydroxypropionic acid is preferably before the dehydration below 0.015 wt .-%, more preferably below 0.01 wt .-%, most preferably below 0.005 wt .-% , lowered.
• the total amount of 2-furfural, glyoxal, benzaldehyde and crotonaldehyde in the aqueous 3-hydroxypropionic acid is lowered by preferably at least 25%, more preferably at least 50%, most preferably at least 75%.
• the content of 2-furfural in the aqueous 3-hydroxypropionic acid is preferably reduced before the dehydration under 0.015 wt .-%, more preferably below 0.01 wt .-%, most preferably below 0.005 wt .-%.
• the content of glyoxal in the aqueous 3-hydroxypropionic acid is preferably reduced before the dehydration below 0.01 wt .-%, more preferably below 0.005 wt .-%, most preferably below 0.001 wt .-%.
• Dehydration preferably below 0.01 wt .-%, more preferably below 0.005 wt .-%, most preferably below 0.001 wt .-%, lowered.
• Dehydration preferably below 0.01 wt .-%, more preferably below 0.005 wt .-%, most preferably below 0.001 wt .-%, lowered.
• the method of lowering the content of aldehydes in the aqueous 3-hydroxypropionic acid is not limited.
• the aqueous 3-hydroxypropionic acid can be purified, for example, by crystallization, distillation or stripping with an inert gas.
• Reagents are, for example, 2,4,6-trihydroxypyrimidine (barbituric acid),
• Adipic dihydrazide, phenylenediamine and aminoguanidine dihydrazide The chemical treatment is carried out at a temperature of preferably at least 30 ° C., more preferably at least 40 ° C., most preferably at least 50 ° C.
• the duration of the chemical treatment is preferably 5 to 120 minutes, more preferably 10 to 90 minutes, most preferably 20 to 60 minutes.
• the present invention is based on the finding that the aqueous 3-hydroxypropionic acid obtained and prepared by fermentation surprisingly
• aldehydic impurities especially 2-furfural and glyoxal.
• the aldehydic impurities may also arise during the treatment of the aqueous 3-hydroxypropionic acid from the fermentation broth. It has also been found that these aldehyde impurities are the cause of the formation of polymeric deposits in the dehydration of the aqueous 3-hydroxypropionic acid. Furthermore, it has been found that the aldehydic impurities can easily be separated by a chemical treatment prior to dehydration.
• the liquid phase preferably contains from 5 to 95 wt .-%, particularly preferably from 10 to 90 wt .-%, most preferably from 20 to 80 wt .-% of an organic solvent
• the boiling point of the organic solvent is 1013 mbar in the range of preferably 200 to 350 ° C, more preferably from 250 to 320 ° C, most preferably from 280 to 300 ° C.
• Suitable organic solvents are, for example
• Phthalic acid esters such as dimethyl phthalate and diethyl phthalate, isophthalic acid esters such as
• Dimethyl isophthalate and diethyl isophthalate terephthalic acid esters such as dimethyl terephthalate and diethyl terephthalate, alkanoic acids such as nonanoic acid and decanoic acid, biphenyl and / or diphenyl ether.
• an aprotic-polar solvent is used.
• Aprotic-polar solvents contain no ionizable proton in the molecule and are generally known, for example, ionizable protons contain molecules with OH, SH and NH groups.
• the preferred apoptotic-polar solvents contain exclusively hydrogen atoms bonded to carbon atoms.
• the dipole moment of the aprotic-polar solvents is preferably from 10 to
• Suitable aprotic-polar solvents are ketones, lactones, lactams, nitro compounds, tertiary carboxylic acid amides, urea derivatives, sulfoxides and sulfones.
• Sulfolane, ethylene carbonate, propylene carbonate and gamma-valerolactone are advantageously used. Sulfolane is particularly preferred.
• Aprotic polar solvents additionally prevent unwanted wall deposits in the reactor and heat exchanger.
• the aqueous acrylic acid is advantageously removed by means of a rectification column 2 from
• the aqueous acrylic acid is preferably separated by means of a rectification column 3 into a high-acrylic phase and a water-rich phase.
• an entraining agent is used in the rectification column 3.
• the separation of the aqueous acrylic acid and the separation of the aqueous acrylic acid in a high-acrylic phase and a high-water phase in a rectification column 4 is carried out, wherein the separation of the aqueous acrylic acid from the liquid phase below a
• Rectification column 4 a dividing wall column, wherein the feed to
• Rectification 4 and the side of the rectification rectification column 4 are located on different sides of the partition.
• the obtained acrylic acid-rich phase is preferably purified by crystallization.
• the mother liquor of the crystallization is recycled below the side draw into the rectification column 4.
• aqueous 3-hydroxypropionic acid produced by fermentation is preferably used.
• Such a method is disclosed, for example, in WO 02/090312 A1.
• Oligomeric 3-hydroxypropionic acid is the product of at least two molecules
• 3-hydroxy propionic acid The molecules are interconnected by esterification of the carboxyl group of one molecule with the hydroxyl group of the other molecule.
• Oligomeric acrylic acid is the product of at least two molecules of acrylic acid.
• the molecules are interconnected by Michael addition of the carboxyl group of one molecule with the ethylenic double bond of the other molecule.
• the temperature in the reaction is preferably less than 100 ° C, more preferably less than 90 ° C, most preferably less than 80 ° C performed. Too high temperatures favor the undesirable in step i) dehydration of
• the pressure in the reaction is preferably from 5 to 300 mbar, particularly preferably from 15 to 200 mbar, very particularly preferably from 30 to 150 mbar. Lower pressures in step i) allow gentle removal of the water from the liquid phase. Too low pressures are uneconomical.
• the pressure is the pressure in the reactor or in a distillation, the pressure in the distillation bottoms.
• the heat can be supplied via internal and / or external heat exchanger of conventional design and / or double wall heating (as a heat carrier is advantageous
• the aqueous mixture of monomeric 3-hydroxypropionic acid and oligomeric 3-hydroxypropionic acid obtained in step i) preferably contains from 5 to 50% by weight of water, particularly preferably from 10 to 40% by weight of water, very particularly preferably from 15 to 35% by weight .-% Water.
• the aqueous mixture of monomeric 3-hydroxypropionic acid and oligomeric 3-hydroxypropionic acid obtained in step i) contains more preferably from 10 to 60% by weight of monomeric 3-hydroxypropionic acid, more preferably from 20 to 50% by weight of monomeric 3-hydroxypropionic acid preferably from 25 to 45% by weight of monomeric 3-hydroxypropionic acid.
• the water content in step i) is preferably reduced by at least 5% by weight, more preferably by at least 10% by weight, most preferably by at least 15% by weight.
• the value by which the water content was lowered is the difference from the
• the water content can be determined by the usual methods, for example by Karl Fischer titration.
• the content of monomeric 3-hydroxypropionic acid is preferably in step i) to
• the value by which the content of monomeric 3-hydroxypropionic acid was lowered is the difference between the content of monomeric 3-hydroxypropionic acid of the aqueous 3-hydroxypropionic acid used (educt) and the content of monomeric 3-hydroxypropionic acid of the obtained aqueous mixture of monomeric 3-hydroxypropionic acid and oligomeric 3-hydroxypropionic acid (product).
• the content of monomeric 3-hydroxypropionic acid and oligomeric 3-hydroxypropionic acid can be determined by means of HPLC.
• Monomeric acrylic acid and oligomeric acrylic acid can be determined analogously.
• the water is advantageously separated off in step i) by means of a rectification column 1.
• the rectification column 1 is of a known type and has the usual installations. In principle, all standard installations are suitable as column internals, for example trays, packings and / or fillings. Among the soils, bubble-cap trays, sieve trays, valve trays, Thormann trays and / or dual-flow trays are preferred among the trays those with rings, coils, calipers, Raschig, Intos or Pall rings, Berl or Intalox saddles or braids are preferred.
• the feed into the rectification column 1 is expediently carried out in its lower region.
• the feed temperature is preferably from 20 to 100 ° C, more preferably from 30 to 80 ° C, most preferably from 40 to 60 ° C.
• Particularly preferred are dual-flow trays below the inlet (stripping section) and Thormannböden above the inlet
• a part of the bottom liquid can be conveyed together with the feed into the lower region of the rectification column 1.
• part of the sump liquid is conveyed in a circle via the trays below the inlet (stripping section).
• the rectification column 1 is usually made of austenitic steel, preferably of the material 1.4571 (according to DIN EN 10020).
• the cooling of the water separated off at the top of the rectification column 1 can be effected indirectly, for example by heat exchangers which are known per se to the person skilled in the art and are not subject to any particular restriction, or directly, for example by a quench.
• heat exchangers which are known per se to the person skilled in the art and are not subject to any particular restriction, or directly, for example by a quench.
• already condensed water is cooled by means of a suitable heat exchanger and sprayed the cooled liquid above the sampling point in the vapor. This spraying may be done in a separate apparatus or in the rectification unit itself.
• spraying in the rectification unit is the extraction point of the water
• Bubble-cap trays, sieve trays, valve trays, Thormann trays and / or dual-flow trays are preferred.
• those with rings, coils, calipers, Raschig, Intos or Pall rings, Berl or Intalox saddles or braids are preferred.
• Particularly preferred are dual-flow trays. As a rule, here are 2 to 5 theoretical plates
• step i) The direct condensation of the water can also be carried out in several stages, with upward decreasing temperature. Preferably, however, the cooling takes place by indirect cooling.
• the aqueous mixture of monomeric 3-hydroxypropionic acid and oligomeric 3-hydroxypropionic acid thus obtained in step i) is withdrawn continuously from the bottom of the distillation and converted into acrylic acid in step ii).
• the reaction of the aqueous 3-hydroxypropionic acid or aqueous mixture of monomeric 3-hydroxypropionic acid and oligomeric 3-hydroxypropionic acid from step i) to acrylic acid is carried out in step ii) in the liquid phase at a temperature of preferably from 140 to 240 ° C., more preferably from 160 to 230 ° C, most preferably from 180 to 220 ° C carried out.
• the pressure is preferably from 25 to 750 mbar, particularly preferably from 50 to 500 mbar, very particularly preferably from 100 to 300 mbar. At lower pressure, the liquid phase contains less monomeric acrylic acid, which reduces the risk of radical polymerization.
• the pressure is the pressure in the reactor or in a distillation, the pressure in the distillation bottoms.
• the aqueous 3-hydroxypropionic acid or aqueous mixture of monomeric 3-hydroxypropionic acid and oligomeric 3-hydroxypropionic acid from step i) used in step ii) preferably contains from 5 to 50% by weight of water, more preferably from 10 to 40% by weight of water , most preferably from 15 to 35 wt .-% water.
• the aqueous 3-hydroxypropionic acid or aqueous mixture of monomeric 3-hydroxypropionic acid and oligomeric 3-hydroxypropionic acid from step i) used in step ii) preferably contains from 10 to 60% by weight of monomeric 3-hydroxypropionic acid, more preferably from 20 to 50% by weight. % of monomeric 3-hydroxypropionic acid, most preferably from 25 to 45% by weight of monomeric 3-hydroxypropionic acid.
• the heat can be supplied via internal and / or external heat exchanger of conventional design and / or double wall heating (as a heat carrier is advantageous
• External circulation evaporator with natural or forced circulation.
• External circulation evaporators with forced circulation are particularly preferably used. Very particularly preferred
• the liquid phase preferably contains a polymerization inhibitor 1.
• Polymerization inhibitors 1 are phenothiazine, hydroquinone, hydroquinone monomethyl ether, copper salts and / or manganese salts. Very particularly preferred are phenothiazine and
• the liquid phase preferably contains from 0.001 to 5% by weight. %, particularly preferably from 0.01 to 2% by weight, very particularly preferably from 0.1 to 1% by weight of the polymerization inhibitor 1.
• an oxygen-containing gas is additionally used for polymerization inhibition.
• Particularly suitable for this purpose are air / nitrogen mixtures having an oxygen content of 6% by volume (lean air). If an oxygen-containing gas is used for polymerization inhibition, this is preferably fed below the evaporator.
• the liquid phase preferably contains from 15 to 90% by weight, more preferably from 20 to 85% by weight, most preferably from 30 to 80% by weight of the aprotic polar solvent.
• the reaction in step ii) is preferably carried out in the absence of a catalyst.
• the reaction in step ii) can also be catalyzed basic or acidic.
• Suitable basic catalysts are high boiling tertiary amines such as pentamethyldiethylenetriamine.
• Suitable acidic catalysts are high boiling inorganic or organic acids such as phosphoric acid and dodecylbenzenesulfonic acid.
• High-boiling means here a boiling point at 1013 mbar of preferably at least 160 ° C, more preferably at least 180 ° C, most preferably at least 190 ° C. If a catalyst is used, the amount of catalyst in the liquid phase is preferably from 1 to 60 wt .-%, particularly preferably from 2 to 40 wt .-%, most preferably from 5 to 20 wt .-%.
• aqueous acrylic acid formed during the reaction in step ii) is advantageously separated off from the reaction mixture by means of a rectification column (rectification column 2).
• Rectification column 2 instead and the aqueous 3-hydroxypropionic acid or the aqueous
• the polymerization inhibitor 1 is at least partially metered via the reflux.
• the rectification column 2 is of a known type and has the usual installations. In principle, all standard installations are suitable as column internals, for example trays, packings and / or fillings. Under the floors are
• Bubble trays, sieve trays, valve trays, Thormann trays and / or dual-flow trays are preferred, among the trays are those with rings, spirals, saddles, Raschig, Intos or Pall rings, Berl or Intalox saddles or braids preferred. Particularly preferred are dual-flow trays.
• the rectification is usually carried out at reduced pressure.
• the top pressure is preferably from 50 to 900 mbar, particularly preferably from 100 to 500 mbar, very particularly preferably from 150 to 300 mbar.
• Acrylic acid unnecessarily thermally stressed and too low head pressure, the process is technically too expensive. In addition, the concentration of acrylic acid is lower at lower pressure. The sump pressure results from the head pressure, the number and the type of
• the rectification column 2 is usually made of austenitic steel, preferably of the material 1.4571 (according to DIN EN 10020).
• the cooling of the aqueous acrylic acid separated off at the top of the rectification column 2 can be effected indirectly, for example by heat exchangers which are known per se to the person skilled in the art and are not subject to any particular restriction, or directly, for example by a quench. Preferably, it is done by direct cooling.
• heat exchangers which are known per se to the person skilled in the art and are not subject to any particular restriction, or directly, for example by a quench.
• it is done by direct cooling.
• already condensed aqueous acrylic acid is cooled by means of a suitable heat exchanger and the cooled liquid is sprayed above the take-off point in the vapor. This spraying may be done in a separate apparatus or in the rectification unit itself.
• the removal point of the aqueous acrylic acid is advantageously designed as a capture bottom.
• Valve bottoms, Thormann floors and / or dual-flow trays preferred.
• those with rings, coils, calipers, Raschig, Intos or Pall rings, Berl or Intalox saddles or braids are preferred.
• Particularly preferred are dual-flow trays.
• 2 to 5 theoretical plates are sufficient here. These soils are not taken into account in the previous information on the number of theoretical plates of the rectification column 2.
• the direct condensation of the aqueous acrylic acid can also be carried out in several stages, with upward decreasing temperature.
• the cooling is carried out by direct cooling.
• the condensed distillate of the rectification column 2 can be separated by means of a phase separator.
• the organic phase can be recycled to the rectification column 2, for example into the bottom of the rectification column 2.
• the aqueous phase can also be partially recycled to the rectification column 2, for example as reflux and for the direct cooling of the vapor.
• Part of the bottom (residue) of the rectification column 2 can be discharged and a distillation 1 (residue distillation) are supplied.
• the residue is preferably passed through a solids separator (cyclone) and optionally supplemented by fresh aprotic-polar solvent.
• the resulting aqueous acrylic acid can be separated by distillation into an acrylic acid-rich phase (crude acrylic acid) and a water-rich phase (acid water) in an optional step iii).
• the heat supply in step iii) can be done via internal and / or external heat exchanger conventional design and / or double wall heating (as a heat carrier is advantageously used water vapor). Preferably, it takes place via external
• Circulation evaporator with natural or forced circulation External circulation evaporators with forced circulation are particularly preferably used. Such evaporators are described in EP 0 854 129 A1. The use of several evaporators, connected in series or in parallel, is possible.
• the aqueous acrylic acid preferably contains a polymerization inhibitor 2. Suitable polymerization inhibitors 2 are phenothiazine, hydroquinone and / or
• the liquid phase preferably contains from 0.001 to 5% by weight, particularly preferably from 0.01 to 2% by weight, very particularly preferably from 0.1 to 1% by weight, of the polymerization inhibitor 2. containing gas to
• Polymerization inhibition used are air / nitrogen mixtures having an oxygen content of 6% by volume (lean air). If an oxygen-containing gas is used for polymerization inhibition, this is preferably fed below the evaporator.
• the separated acrylic acid-rich phase (crude acrylic acid) a
• Polymerization inhibitor 3 added.
• Suitable polymerization inhibitors 3 are phenothiazine, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, hydroquinone and / or
• Suitable entraining agents are low boiling hydrophobic organic solvents having a solubility in water at 23 ° C of preferably less than 5 grams per 100 milliliters of water, more preferably less than 1 gram per 100 milliliters of water, most preferably less than 0.2 grams per gram 100 ml of water, and a boiling point at 1013 mbar in the range of preferably 60 to 160 ° C, more preferably from 70 to 130 ° C, most preferably from 75 to 1 15 ° C.
• Suitable hydrophobic organic solvents are, for example, aliphatic hydrocarbons, such as hexane, heptane, dodecane, cyclohexane, methylcyclohexane, isooctane and hydrogenated triisobutylene, aromatic hydrocarbons, such as benzene, toluene, xylene and ethylbenzene, ketones, such as methyl isobutyl ketone, ethers, such as methyl tert-butyl ether , or mixtures thereof.
• aliphatic hydrocarbons such as hexane, heptane, dodecane, cyclohexane, methylcyclohexane, isooctane and hydrogenated triisobutylene
• aromatic hydrocarbons such as benzene, toluene, xylene and ethylbenzene
• ketones such as methyl isobutyl ket
• a rectification column 3 is preferably used.
• the polymerization inhibitor 2 is at least partially metered via the reflux.
• the rectification column 3 is of a known type and has the usual installations. In principle, all standard installations are suitable as column internals, for example trays, packings and / or fillings. Under the floors are
• Bell bottoms, sieve trays, valve trays, Thormann trays and / or dual-flow trays are preferred, among the trays are those with rings, spirals, caliper bodies, Raschig, Intos or Pall rings, Berl or Intalox saddles or braids preferred. Particularly preferred are dual-flow trays.
• the rectification is usually carried out at reduced pressure.
• the top pressure is preferably from 50 to 600 mbar, more preferably from 150 to 400 mbar, most preferably from 200 to 300 mbar. If the top pressure is too high, the aqueous acrylic acid is unnecessarily thermally stressed, and if the top pressure is too low, the process becomes technically too expensive. In addition, the concentration of acrylic acid is lower at lower pressure.
• the sump pressure results from the head pressure, the number and the type of
• the rectification column 3 is usually made of austenitic steel, preferably of the material 1 .4571 (according to DIN EN 10020).
• the cooling of the water-rich phase (acid water) separated off at the top of the rectification column 3 can be effected indirectly, for example by means of heat exchangers, known per se to the person skilled in the art are known and are not subject to any particular restriction, or directly, for example by a quench done. Preferably, it is done by direct cooling.
• heat exchangers known per se to the person skilled in the art are known and are not subject to any particular restriction, or directly, for example by a quench done.
• it is done by direct cooling.
• already condensed water-rich phase (acid water) by means of a suitable
• Cooled heat exchanger and sprayed the cooled liquid above the sampling point in the vapor can be done in a separate apparatus or in the
• Rectification unit itself.
• the removal point of the water-rich phase (sour water) is advantageously designed as a catch bottom.
• internals which improve the mixing of the cooled water-rich phase (sour water) with the vapor, the effect of direct cooling can be increased.
• all common installations are suitable for this, for example floors, packings and / or fillings. Under the floors are bubble trays, sieve trays,
• Valve bottoms, Thormann floors and / or dual-flow trays preferred.
• those with rings, coils, calipers, Raschig, Intos or Pall rings, Berl or Intalox saddles or braids are preferred.
• 2 to 5 theoretical plates are sufficient here. These soils are not taken into account in the previous information on the number of theoretical plates of the rectification column 3.
• the direct condensation of the water-rich phase can also be carried out in several stages, with upward decreasing temperature.
• the cooling is carried out by direct cooling.
• Acid water extraction can be supplied.
• the condensed distillate of the rectification column 3 is separated by means of a phase separator.
• the organic phase can be recycled to the rectification column 3, for example as reflux.
• the acrylic acid-rich phase taken from the bottom of the rectification column 3
• the acrylic acid-rich phase (crude acrylic acid) is further purified by crystallization.
• the resulting in the crystallization mother liquor can in the
• Rectification column 3 are recycled, preferably below the take-off point for the acrylic acid-rich phase (crude acrylic acid).
• the acrylic acid-rich phase (crude acrylic acid) can by layer crystallization, such as
• the rectification column 4 combines the tasks of the rectification columns 2 and 3 in a single rectification column.
• the reaction of the aqueous mixture of monomeric 3-hydroxypropionic acid and oligomeric 3-hydroxypropionic acid to acrylic acid takes place in the bottom of the rectification column 4 and the aqueous mixture of monomeric 3-hydroxypropionic acid and oligomeric 3-hydroxypropionic acid is the feed of the
• the heat in the bottom of the rectification column 4 via internal and / or external heat exchanger (heat transfer is again preferably water vapor) of conventional design and / or double wall heating.
• heat transfer is again preferably water vapor
• external circulation evaporator with forced circulation are particularly preferred.
• Forced circulation flash evaporators are very particularly preferably used.
• the feed into the rectification column 4 is expediently carried out in its lower region.
• the feed temperature is preferably at least 50 ° C, more preferably at least 100 ° C, most preferably at least 150 ° C.
• an oxygen-containing gas is used for polymerization inhibition, this is preferably supplied below the lowest soil.
• the bottom residue of the rectification column 4 can be discharged and a
• Residual distillation or a residue cleavage can be supplied.
• the bottom residue is preferably passed through a solids separator (cyclone) and optionally supplemented by fresh high-boiling organic solvent.
• the withdrawn acrylic acid-rich phase (Rohacrylsaure) is cooled by means of a heat exchanger (for example, surface waters are suitable as a coolant).
• a heat exchanger for example, surface waters are suitable as a coolant.
• Heat exchanger connected in series or in parallel, is possible.
• the heat exchangers are known per se to the person skilled in the art and are not subject to any particular restriction.
• the withdrawn acrylic acid-rich phase (crude acrylic acid) is discharged and partially used as a solvent for the polymerization inhibitor 2.
• the cooling of the water-rich phase (acid water) separated off at the top of the rectification column 4 can be effected indirectly, for example by heat exchangers which are known per se to the person skilled in the art and are not subject to any particular restriction, or directly, for example by a quench. Preferably, it is done by direct cooling.
• already condensed water-rich phase (acid water) by means of a suitable
• Cooled heat exchanger and sprayed the cooled liquid above the sampling point in the vapor can be done in a separate apparatus or in the
• Rectification unit itself.
• the removal point of the water-rich phase (sour water) is advantageously designed as a catch bottom.
• internals which improve the mixing of the cooled water-rich phase (sour water) with the vapor, the effect of direct cooling can be increased.
• all common installations are suitable for this, for example floors, packings and / or fillings. Under the floors are bubble trays, sieve trays,
• Valve bottoms, Thormann floors and / or dual-flow trays preferred.
• those with rings, coils, satellites, Raschig, Intos or Pall rings, Berl or Intalox saddles or braids are preferred.
• Particularly preferred are dual-flow trays.
• 2 to 5 theoretical plates are sufficient here. These soils are not taken into account in the previous information on the number of theoretical plates of the rectification column 4.
• the direct condensation of the water-rich phase can also be carried out in several stages, with upward decreasing temperature.
• the cooling is carried out by direct cooling.
• Acid water extraction can be supplied.
• the condensed distillate of the rectification column 4 is separated by means of a phase separator.
• the organic phase can be recycled to the rectification column 4, for example as reflux.
• a dividing wall column is used as the rectification column 4.
• a dividing wall column has a vertical dividing wall which divides the cross section of a part of the column into two sections. The reflux is distributed to the two column sections. The inlet and the side outlet of
• Dividing wall column are located on different sides of the partition wall.
• the crude acrylic acid withdrawn from the rectification column 4 can be used directly for the preparation of water-absorbing polymer particles.
• the crude acrylic acid withdrawn from the rectification column 4 can be used directly for the preparation of water-absorbing polymer particles.
• the crude acrylic acid withdrawn from the rectification column 4 can be used directly for the preparation of water-absorbing polymer particles.
• Rohacryl Textre further purified by crystallization.
• the mother liquor obtained in the crystallization can be recycled to the rectification column 4, preferably below the take-off point for the crude acrylic acid.
• the recycled mother liquor for cooling the crude acrylic acid and the crude acrylic acid discharged from the rectification column 4 are preferably used for heating the mother liquor (thermal bond).
• the crude acrylic acid can be purified by layer crystallization, as described, for example, in EP 0 616 998 A1, or by suspension crystallization, as described in DE 100 39 025 A1.
• the suspension crystallization is preferred.
• the acrylic acid thus prepared can be used directly as a monomer for the preparation of homopolymers or copolymers, in particular acrylic acid homopolymers, acrylic acid / maleic anhydride copolymers, acrylic acid / maleic acid copolymers and acrylic / methacrylic acid copolymers, but also for the preparation of water-absorbing polymer particles and acrylic esters, e.g. Methyl acrylate, ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate, as well as the homo- and copolymers thereof.
• Water-Absorbent Polymer particles are prepared by polymerizing a monomer solution or suspension containing a) at least one ethylenically unsaturated, acid group-carrying monomer
• At least one initiator optionally one or more ethylenically unsaturated monomers copolymerizable with the monomers mentioned under a) and
• water soluble polymers optionally one or more water soluble polymers, and are usually water insoluble.
• the monomers a) are preferably water-soluble, i. the solubility in water at 23 ° C. is typically at least 1 g / 100 g of water, preferably at least 5 g / 100 g of water, more preferably at least 25 g / 100 g of water, most preferably at least 35 g / 100 g of water.
• Suitable monomers a) are, for example, ethylenically unsaturated carboxylic acids, such as acrylic acid, methacrylic acid, and itaconic acid. Further suitable monomers a) are
• ethylenically unsaturated sulfonic acids such as styrenesulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid (AMPS).
• styrenesulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid (AMPS).
• AMPS 2-acrylamido-2-methylpropanesulfonic acid
• the proportion of acrylic acid and / or salts thereof in the total amount of monomers a) is preferably at least 50 mol%, particularly preferably at least 90 mol%, very particularly preferably at least 95 mol%.
• Suitable crosslinkers b) are compounds having at least two groups suitable for crosslinking. Such groups are, for example, ethylenically unsaturated groups which can be radically copolymerized into the polymer chain, and functional groups which can form covalent bonds with the acid groups of the monomer a). Furthermore, polyvalent metal salts which can form coordinative bonds with at least two acid groups of the monomer a) are also suitable as crosslinking agents b).
• Crosslinkers b) are preferably compounds having at least two polymerizable groups which can be incorporated in the polymer network in free-radically polymerized form.
• Suitable crosslinkers b) are, for example, ethylene glycol dimethacrylate, diethylene glycol diacrylate,
• Crosslinker mixtures such as in DE 195 43 368 A1, DE 196 46 484 A1, WO
• Preferred crosslinkers b) are pentaerythritol triallyl ether, tetraallyloxyethane,
• Polyethylene glycol diacrylate, trimethylolpropane triacrylate and triallylamine are particularly preferred crosslinkers b) are the polyethyleneglyoxylated and / or propoxylated glycerols esterified with acrylic acid or methacrylic acid to form diioder triacrylates, as described, for example, in WO 2003/104301 A1. Particularly advantageous are di- and / or triacrylates of 3- to 10-fold ethoxylated glycerol. Very particular preference is given to diacrylates or triacrylates of 1 to 5 times ethoxylated and / or propoxylated glycerol.
• the amount of crosslinker b) is preferably from 0.05 to 1, 5 wt .-%, particularly preferably 0.1 to 1 wt .-%, most preferably 0.2 to 0.5 wt .-%, each based on
• generating compounds are used, for example thermal initiators, redox initiators, photoinitiators. Suitable redox initiators are
• Sodium peroxodisulfate / sodium bisulfite and hydrogen peroxide / sodium bisulfite are used, such as
• the reducing component used is preferably a mixture of the sodium salt of 2-hydroxy-2-sulfinatoacetic acid, the disodium salt of 2-hydroxy-2-sulfonatoacetic acid and sodium bisulfite.
• acid group-carrying monomers a) copolymerizable ethylenically unsaturated monomers d) are, for example, acrylamide, methacrylamide,
• water-soluble polymers e) can polyvinyl alcohol, polyvinylpyrrolidone, starch,
• Starch derivatives modified cellulose, such as methylcellulose or hydroxyethylcellulose, gelatin, polyglycols or polyacrylic acids, preferably starch, starch derivatives and modified
• an aqueous monomer solution is used.
• Monomer solution is preferably from 40 to 75 wt .-%, particularly preferably from 45 to 70 wt .-%, most preferably from 50 to 65 wt .-%. It is also possible
• the monomer solution may be polymerized prior to polymerization by inerting, i. Flow through with an inert gas, preferably nitrogen or carbon dioxide, are freed of dissolved oxygen.
• an inert gas preferably nitrogen or carbon dioxide
• the oxygen content of the monomer solution before polymerization is reduced to less than 1 ppm by weight, more preferably less than 0.5 ppm by weight, most preferably less than 0.1 ppm by weight.
• Suitable reactors are, for example, kneading reactors or belt reactors.
• the polymer gel formed during the polymerization of an aqueous monomer solution or suspension is comminuted continuously by, for example, counter-rotating stirring shafts, as described in WO 2001/038402 A1.
• the polymerization on the belt is described, for example, in DE 38 25 366 A1 and US Pat. No. 6,241,928.
• a polymer gel is formed, which must be comminuted in a further process step, for example in an extruder or kneader.
• the comminuted polymer gel obtained by means of a kneader may additionally be extruded.
• the acid groups of the polymer gels obtained are usually partially neutralized.
• the neutralization is preferably carried out at the stage of the monomers. This is usually done by mixing the neutralizing agent as an aqueous solution or preferably as a solid.
• the degree of neutralization is preferably from 25 to 95 mol%, particularly preferably from 30 to 80 mol%, very particularly preferably from 40 to 75 mol%, the customary neutralizing agents can be used, preferably
• Alkalimetallhydrogenkarbonate and mixtures thereof instead of alkali metal salts and ammonium salts can be used.
• Sodium and potassium are particularly preferred as alkali metals, but most preferred are sodium hydroxide, sodium carbonate or sodium bicarbonate and mixtures thereof.
• the polymer gel is at least partially neutralized after the polymerization
• the polymer gel is preferably comminuted mechanically, for example by means of an extruder, wherein the neutralizing agent can be sprayed, sprinkled or poured on and then thoroughly mixed in.
• the gel mass obtained can be extruded several times for homogenization.
• the polymer gel is then preferably dried with a belt dryer until the
• Residual moisture content preferably 0.5 to 15 wt .-%, particularly preferably 1 to 10 wt .-%, most preferably 2 to 8 wt .-%, wherein the residual moisture content according to the EDANA recommended test method No. WSP 230.2- 05 "Mass Loss Upon Heating" is determined. If the residual moisture content is too high, the dried polymer gel has too low a glass transition temperature T g and is difficult to process further. If the residual moisture content is too low, the dried polymer gel is too brittle and in the subsequent comminution steps undesirably large quantities of polymer particles with too small particle size (“fines”) are produced. , more preferably from 35 to 70% by weight, most preferably from 40 to 60% by weight. Alternatively, a fluidized bed dryer or a paddle dryer can be used for drying.
• the dried polymer gel is then milled and classified, wherein for grinding usually single or multi-stage roller mills, preferably two- or three-stage
• Roller mills, pin mills, hammer mills or vibratory mills can be used.
• the average particle size of the polymer fraction separated as a product fraction is preferably at least 200 ⁇ m, more preferably from 250 to 600 ⁇ m, very particularly from 300 to 500 ⁇ m.
• the mean particle size of the product fraction can be determined by means of the EDANA recommended test method No. WSP 220.2-05 "Particle Size Distribution", in which the mass fractions of the sieve fractions are cumulatively applied and the average particle size is determined graphically.
• the mean particle size here is the value of the mesh size, which results for accumulated 50 wt .-%.
• the proportion of particles having a particle size of greater than 150 ⁇ m is preferably at least 90% by weight, particularly preferably at least 95% by weight, very particularly preferably at least 98% by weight.
• Too small polymer particles are therefore usually separated and recycled to the process. This is preferably done before, during or immediately after Polymerization, ie before the drying of the polymer gel.
• the too small polymer particles can be moistened with water and / or aqueous surfactant before or during the recycling. It is also possible to separate small polymer particles in later process steps, for example after surface postcrosslinking or another coating step. In this case, the recycled too small polymer particles are surface postcrosslinked or otherwise coated, for example with fumed silica. If a kneading reactor is used for the polymerization, the too small polymer particles are preferably added during the last third of the polymerization.
• the proportion of particles having a particle size of at most 850 ⁇ m is preferably at least 90% by weight, particularly preferably at least 95% by weight, very particularly preferably at least 98% by weight.
• the proportion of particles having a particle size of at most 600 ⁇ m is preferably at least 90% by weight, more preferably at least 95% by weight, most preferably at least 98% by weight.
• Polymer particles with too large particle size reduce the swelling rate. Therefore, the proportion of polymer particles too large should also be low.
• Too large polymer particles are therefore usually separated and recycled to the grinding of the dried Polymergeis.
• the polymer particles can be used to further improve the properties
• Suitable surface postcrosslinkers are compounds containing groups that can form covalent bonds with at least two carboxylate groups of the polymer particles. Suitable compounds are, for example, polyfunctional amines, polyfunctional amidoamines, polyfunctional epoxides, as described in EP 0 083 022 A2, EP 0 543 303 A1 and EP 0 937 736 A2, di- or polyfunctional alcohols, as described in DE 33 14 019 A1, DE 35 23 617 A1 and EP 0 450 922 A2, or ⁇ -hydroxyalkylamides, as described in DE 102 04 938 A1 and US Pat. No. 6,239,230.
• Preferred surface postcrosslinkers are ethylene carbonate, ethylene glycol diglycidyl ether, reaction products of polyamides with epichlorohydrin and mixtures of propylene glycol and 1,4-butanediol.
• Very particularly preferred surface postcrosslinkers are 2-hydroxyethyl-2-oxazolidinone, 2-oxazolidinone and 1, 3-propanediol.
• surface postcrosslinkers which contain additional polymerisable ethylenically unsaturated groups, as described in DE 37 13 601 A1.
• the amount of surface postcrosslinker is preferably from 0.001 to 5% by weight, particularly preferably from 0.02 to 2% by weight, completely particularly preferably 0.05 to 1 wt .-%, each based on the polymer particles.
• polyvalent cations are applied to the particle surface in addition to the surface postcrosslinkers before, during or after the surface postcrosslinking.
• the polyvalent cations which can be used in the process according to the invention are, for example, divalent cations, such as the cations of zinc, magnesium, calcium, iron and strontium, trivalent cations, such as the cations of aluminum, iron, chromium, rare earths and
• Manganese, tetravalent cations such as the cations of titanium and zirconium.
• hydroxide, chloride, bromide, sulfate, hydrogen sulfate, carbonate, bicarbonate, nitrate, phosphate, hydrogen phosphate, dihydrogen phosphate and carboxylate, such as acetate, citrate and lactate are possible.
• salts with different counterions for example basic aluminum salts, such as aluminum monoacetate or aluminum monolactate.
• Aluminum sulfate, aluminum monoacetate and aluminum lactate are preferred. Except
• Metal salts can also polyamines are used as polyvalent cations.
• the amount of polyvalent cation used is, for example, from 0.001 to 1% by weight, preferably from 0.005 to 0.5% by weight, more preferably from 0.02 to 0.2% by weight. in each case based on the polymer particles.
• the surface postcrosslinking is usually carried out so that a solution of the surface postcrosslinker is sprayed onto the dried polymer particles. in the
• the surface postcrosslinker coated polymer particles are thermally dried, the surface postcrosslinking reaction taking place both before and during drying.
• the spraying of a solution of microwave machines is preferably in mixers with moving mixing tools, such as screw mixers, disk mixers and
• Paddle mixer performed.
• horizontal mixers such as
• Paddle mixers very particularly preferred are vertical mixers.
• the distinction between horizontal mixer and vertical mixer is made by the storage of the mixing shaft, i.
• Horizontal mixers have a horizontally mounted mixing shaft and vertical mixers have a vertically mounted mixing shaft.
• Suitable mixers are, for example, Horizontal Pflugschar® mixers (Gebr. Lödige Maschinenbau GmbH, Paderborn, Germany), Vrieco-Nauta
• solvent mixtures are used, for example isopropanol / water, 1, 3-propanediol / water and propylene glycol / water, wherein the
• the thermal drying is preferably carried out in contact dryers, more preferably paddle dryers, very particularly preferably disk dryers.
• Suitable dryers include Hosokawa Bepex® Horizontal Paddle Dryer (Hosokawa Micron GmbH, Leingart, Germany), Hosokawa Bepex® Disc Dryer (Hosokawa Micron GmbH, Leingart, Germany), Holo-Flite® dryers (Metso Minerals Industries, Inc., Danville, USA ) and Nara Paddle Dryer (NARA Machinery Europe, Frechen, Germany).
• fluidized bed dryers can also be used.
• the drying can take place in the mixer itself, by heating the jacket or blowing hot air.
• a downstream dryer such as a hopper dryer, a rotary kiln or a heatable screw.
• Particularly advantageous is mixed and dried in a fluidized bed dryer.
• Preferred drying temperatures are in the range 100 to 250 ° C, preferably 120 to 220 ° C, more preferably 130 to 210 ° C, most preferably 150 to 200 ° C.
• the preferred residence time at this temperature in the reaction mixer or dryer is preferably at least 10 minutes, more preferably at least 20 minutes, most preferably at least 30 minutes, and usually at most 60 minutes.
• the cooling is preferably carried out in contact coolers, particularly preferably blade coolers, very particularly preferably disk coolers.
• Suitable coolers are, for example, Hosokawa Bepex® Horizontal Paddle Coolers (Hosokawa Micron GmbH, Leingart, Germany), Hosokawa Bepex® Disc Coolers (Hosokawa Micron GmbH, Leingart, Germany), Holo-Flite® coolers (Metso Minerals Industries, Inc., Danville, USA ) and Nara Paddle Cooler (NARA Machinery Europe, Frechen, Germany).
• fluidized bed coolers can also be used.
• the water-absorbing polymer particles to 20 to 150 ° C, preferably 30 to 120 ° C, more preferably 40 to 100 ° C, most preferably 50 to 80 ° C, cooled.
• the surface-postcrosslinked polymer particles can be classified again, wherein too small and / or too large polymer particles are separated and recycled to the process.
• the surface-postcrosslinked polymer particles can be coated or post-moistened for further improvement of the properties.
• the post-wetting is preferably carried out at 30 to 80 ° C, more preferably at 35 to 70 ° C, most preferably at 40 to 60 ° C. At too low temperatures, the water-absorbing polymer particles tend to clump and at higher
• the amount of water used for the rewetting is preferably from 1 to 10 wt .-%, particularly preferably from 2 to 8 wt .-%, most preferably from 3 to 5 wt .-%, each based on the
• the post-humidification is carried out in the cooler after the thermal drying.
• Permeability are, for example, inorganic inert substances, such as water-insoluble metal salts, organic polymers, cationic polymers and di- or polyvalent ones
• Suitable coatings for dust binding are, for example, polyols.
• Suitable coatings against the unwanted caking tendency of the polymer particles are, for example, fumed silica, such as Aerosil® 200, and surfactants, such as Span® 20.
• the mean molar mass of the oligomers is determined by gel permeation chromatography.
• the sample is dissolved in hexafluoro-2-propanol and filtered through a 0.2 ⁇ PTFE syringe tip filter (PTFE syringe filter).
• the concentration of the solution should be about 1, 5 mg / ml.
• hexafluoro-2-propanol As the eluent hexafluoro-2-propanol is used with 0.05 wt .-% potassium trifluoroacetate.
• the flow rate is 1, 00 ml / min.
• the temperature of the separation columns is 35 ° C.
• the volume to be injected is 50 ⁇ .
• the duration is 45 minutes.
• the detector used is a refractive index detector of the DRI Agilent 1 100 Refractive Index Detector type (Agilent Technologies, Waldbronn, Germany).
• the system is calibrated with a commercially available narrow PMMA standard with a molar mass of 800 to 1820000 g / mol (PSS Polymer Standards Service GmbH, Mainz, Germany).
• the average molar mass of the oligomers is the weight average of the oligomers with a molar mass of at least 400 g / mol.
• reagent solution For the reagent solution, weigh 4 g of 2,4-dinitrophenylhydrazine and add 800 ml of water and 200 ml of concentrated hydrochloric acid. The mixture is stirred until a homogeneous solution is obtained.
• sample preparation approx. 100 mg of sample are weighed into a 5 ml volumetric flask, mixed with 2 ml of reagent solution and heated to 60 ° C in a water bath for 5 minutes. After this Cooling is made up with a mixture of 50% by weight of eluent A and 50% by weight of eluent B. Eluent A is water and eluent B is acetonitrile.
• a SymmetryShield RP18 5 ⁇ , 150x2.1 mm column (Waters Corporation, Milford, USA) is used.
• the temperature is 45 ° C
• the injection volume is 5 ⁇
• the flow rate is 0.4 ml / min
• the running time is 45 minutes.
• the UV detector is set to 370 nm.
• Eluent A is a mixture of 1000 ml of water and 1 ml of 0.5 molar sulfuric acid.
• the 3-hydroxypropionic acid For the calibration of the 3-hydroxypropionic acid, four initial weights (about 280 mg, 180 mg, 90 mg and 60 mg) are used, with about 100 ⁇ 25gew.% sulfuric acid to a pH of before filling the 50 ml volumetric flask 3 to 4 is acidified (possibly acidify).
• the calibration range is 0.1 to 280 mg / 50ml.
• At least two initial weights are diluted to at least six concentrations.
• the calibration range is 0.01 to 0.9 mg / 50ml.
• a separation column of the type Prontosil 120-3-C18 AQ 3 ⁇ , 150 ⁇ 4, 6 mm (BISCHOFF Analysentechnik GmbH, Leonberg, Germany) is used.
• the temperature is 25 ° C
• the injection volume is 50 ⁇
• the flow rate is 1, 5 ml / min
• the duration is 15 minutes.
• the UV detector is set to 205 nm. From beginning to 8 minutes, 100% by weight of eluent A, from 8 to 11.5 minutes, a mixture of 40% by weight of eluent A and 60% by weight of eluent B, of 11.5 minutes to the end 100% by weight of eluent A is used.
• Eluent B is acetonitrile. Determination of the content of oligomeric 3-hydroxypropionic acid and oligomeric acrylic acid
• oligomeric 3-hydroxypropionic acid and oligomeric acrylic acid are determined by ion exclusion chromatography with refractive index detection.
• the components to be analyzed are separated from the sample matrix by means of solid phase extraction.
• a bakerband SiOH 6 ml, 1000 mg SPE cartridge J.T.Baker, Avantor Performance Materials, Inc., Center Valley, PA, USA
• the SPE cartridge is activated with 6 ml of methanol and rinsed twice with 6 ml of eluent each time.
• the SPE cartridge should never run dry.
• the sample is then pipetted onto the SPE cartridge and rinsed ten times with 1 ml of eluent in a 10 ml volumetric flask.
• the amount of sample used in sump samples is 65 ⁇ , in head samples 85 ⁇ and in extract samples 75 ⁇ .
• samples do not contain a hydrophobic solvent (high-boiling organic solvent, entraining agent)
• these samples can be sprayed on without extraction by dissolving 85 ⁇ directly in 10 ml of eluent.
• the eluant used is 0.1% by volume aqueous phosphoric acid.
• Example 1 (not according to the invention) The dehydration of aqueous 3-hydroxypropionic acid to acrylic acid was carried out in a forced circulation flash evaporator reactor with rectification column attached.
• the reactor used was a 6 l double-walled glass container.
• the amount of liquid in the reactor was about 2000 g.
• the reactor is at the same time the bottom of the rectification column.
• the forced circulation flash evaporator consisted of a pump, a heat exchanger and a pressure holding valve. The reactor contents were pumped over the
• Heat exchanger and the pressure relief valve in a circle promoted.
• the heat exchanger was heated by means of heat transfer oil.
• the temperature in the reactor was above the temperature of the
• the rectification column had an inner diameter of 50 mm and was heated electrically accompanied.
• the rectification column had expanded metal packages of 50 cm in length (MONTZ Pak type BSH-750, Julius Montz GmbH, Hilden, Germany).
• aqueous 3-hydroxypropionic acid As feed, 250 g / h of aqueous 3-hydroxypropionic acid and 40 g / h of aqueous sulfolane (50% by weight) were fed into the reactor.
• the aqueous 3-hydroxypropionic acid had the following composition:
• the aqueous sulfolane additionally contained 0.1% by weight for polymerization inhibition.
• Phenothiazine and 0.5% by weight hydroquinone monomethyl ether Phenothiazine and 0.5% by weight hydroquinone monomethyl ether.
• the forced circulation flash evaporator conveyed the reactor contents in a circle. Before the pressure relief valve, the pressure was 1, 4 bar. The temperature in the reactor was 180 ° C. The pressure at the top of the rectification column was 150 mbar. The vapor was condensed by means of a cooler and partly recycled as reflux into the rectification column and partially discharged. 296 g / h of condensate were discharged.
• the condensate had the following composition:
• Example 2 (According to the Invention) The aqueous 3-hydroxypropionic acid was chemically treated before dehydration.
• the aqueous 3-hydroxypropionic acid used had the following composition before the chemical treatment:
• the aqueous 3-hydroxypropionic acid was admixed with 0.05% by weight of 2,4,6-trihydroxypyrimidine (barbituric acid) based on 3-hydroxypropionic acid and stirred at 45 ° C. for five hours.
• the aqueous 3-hydroxypropionic acid contained 0.0026% by weight of 2-furfural, less than 0.0005% by weight of glyoxal, less than 0.0005% by weight of benzaldehyde, and less than 0.0005% by weight. -% crotonaldehyde.
• the subsequent dehydration of 3-hydroxypropionic acid to acrylic acid was carried out in a forced circulation flash evaporator reactor with rectification column attached.
• the reactor used was a 6 l double-walled glass container.
• the amount of liquid in the reactor was about 2000 g.
• the reactor is at the same time the bottom of the rectification column.
• the forced circulation flash evaporator consisted of a pump, a heat exchanger and a pressure holding valve. The reactor contents were pumped over the
• Heat exchanger and the pressure relief valve in a circle promoted.
• the heat exchanger was heated by means of heat transfer oil.
• the temperature in the reactor was above the temperature of the
• the rectification column had an inner diameter of 50 mm and was heated electrically accompanied.
• the rectification column had expanded metal packages of 50 cm in length (MONTZ Pak type BSH-750, Julius Montz GmbH, Hilden, Germany).
• aqueous sulfolane As feed, 250 g / h of the chemically treated aqueous 3-hydroxypropionic acid and 40 g / h of aqueous sulfolane (50% by weight) were fed into the reactor.
• the aqueous sulfolane additionally contained 0.1% by weight for polymerization inhibition.
• Phenothiazine and 0.5% by weight hydroquinone monomethyl ether Phenothiazine and 0.5% by weight hydroquinone monomethyl ether.
• the forced circulation flash evaporator conveyed the reactor contents in a circle. Before the pressure relief valve, the pressure was 1, 4 bar. The temperature in the reactor was 180 ° C.
• the pressure at the top of the rectification column was 150 mbar.
• the vapor was condensed by means of a cooler and partly recycled as reflux into the rectification column and partially discharged. 293 g / h of condensate were discharged.
• the condensate had the following composition:
• each 12 g / h of a 5 wt .-% aqueous solution of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl were metered.
• 15 g / h of a solution of phenothiazine and hydroquinone monomethyl ether in acrylic acid were metered into the condensate.
• the solution contained 2% by weight of phenothiazine and 4% by weight of hydroquinone monomethyl ether.

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