Classifications

• • 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

Definitions

• the invention relates to a process for the continuous dehydration of aqueous 3-hydroxypropionic acid to acrylic acid in the liquid phase, wherein the liquid phase from 5 to
• water-absorbent polymer particles binders for aqueous emulsion paints and adhesives dispersed in aqueous solvent.
• Water-absorbing polymer particles are used in the manufacture of diapers, tampons, sanitary napkins and other sanitary articles, but also as water-retaining agents in agricultural horticulture.
• the water-absorbing polymer particles are also referred to as superabsorbers.
• the preparation of water-absorbing polymer particles is described in the monograph "Modern Superabsorbent Polymer Technology", F.L. Buchholz and AT. Graham, Wiley-VCH, 1998, pages 71-103.
• 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 to produce the water-absorbing polymer particles used in the hygiene articles from renewable raw materials.
• One possible route is the fermentative production of 3-hydroxypropionic acid and its conversion into acrylic acid.
• the production of 3-hydroxypropionic acid by fermentation is described, for example, in WO 2012/074818 A2.
• 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 has been achieved by a process for the continuous dehydration of aqueous 3-hydroxypropionic acid to acrylic acid in the liquid phase, the liquid phase containing from 5 to 95% by weight of an aprotic polar solvent and distilling off aqueous acrylic acid continuously from the liquid phase is characterized in that a portion of the liquid phase is discharged as a liquid residue and a distillation 1, the distilled liquid residue in the distillation 1 and the distillate of the distillation 1 is recycled to the continuous dehydration, wherein the average molar mass of in the liquid residue contained oligomers in the feed of the distillation 1 less than
• the average molar mass of the oligomers contained in the liquid residue in the feed of distillation 1 is preferably from 10,000 to 60,000 g / mol, particularly preferably from 20,000 to 50,000 g / mol, very particularly preferably from 30,000 to 40,000 g / mol.
• the mean molar mass of the oligomers can be determined by GPC. In the measurement, all oligomers are detected, i. also oligomers of the by-products.
• the present invention is based on the finding that with increasing average molar mass of the oligomers, the yield in the distillation 1 decreases, i. the losses of aprotic polar solvent increase.
• the dipole moment of the present invention to be used aprotic polar solvent is preferably from 10 to 30 x 10 "30 cm, more preferably from 12 to 25 x 10" 30 cm, most preferably from 14 to 20 x 10 "30 cm.
• 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 aprotic polar solvents have a boiling point at 1013 mbar of preferably 200 to 350 ° C, more preferably from 250 to 320 ° C, most preferably from 280 to 300 ° C, on.
• 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.
• the residence time of the liquid phase in the continuous dehydration is preferably less than 100 hours, more preferably less than 90 hours, most preferably less than 85 hours.
• the residence time is the volume of liquid phase in the continuous dehydration divided by the volume of liquid residue discharged per hour. As the liquid phase and the liquid residue are identical to the composition, the residence time can alternatively be calculated by means of the amounts instead of the volumes.
• the residue is at least 10 hours, preferably at least 15 hours, preferably at least 20 hours, more preferably at least 25 hours, most preferably at least 30 hours, at a temperature of at least 100 ° C, preferably at least 120 ° C, preferably at least 140 ° C, more preferably at least 160 ° C, most preferably min. at least 180 ° C, stored. After storage, the liquid residue is distilled in the distillation 1.
• the high molecular weight oligomers are slowly degraded during storage.
• the residue is treated with a base and filtered.
• the high molecular weight oligomers can be precipitated by means of a base and depleted by subsequent filtration.
• the filtrate is distilled in the distillation 1.
• Suitable bases are alkali metal hydroxides, alkali metal oxides, alkali metal carbonates or alkali metal bicarbonates 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 bottom temperature of distillation 1 is preferably from 100 to 350.degree. C., more preferably from 150 to 250.degree. C., most preferably from 180 to 220.degree.
• the top pressure of the distillation 1 is preferably from 1 to 250 mbar, particularly preferably from 5 to 100 mbar, very particularly preferably from 10 to 50 mbar.
• the distillation 1 can be carried out continuously and discontinuously.
• the distillation 1 can be carried out both single-stage and multi-stage, for example as a cascade of thin-film evaporators.
• the aqueous 3-hydroxypropionic acid used 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 of water.
• the aqueous acrylic acid is advantageously separated off from the reaction mixture by means of a rectification column 2.
• a rectification column 2 By selecting the separation stages and the reflux ratio, the content of 3-hydroxypropionic acid and aprotic polar solvent in the distillate can be kept low.
• the aqueous acrylic acid is preferably separated by means of a rectification column 3 into an acrylic-acid-rich 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 an acrylic-rich phase and a water-rich phase in a rectification column 4 is carried out, wherein the separation of the aqueous acrylic acid from the liquid phase below a side draw in the rectification column 4 takes place, the separation of the aqueous acrylic acid in a high acrylic acid phase and a high-water phase above the side take off and the acrylic acid-rich phase is removed liquid at the side offtake.
• an entraining agent is used in the rectification column 4.
• the rectification column 4 is a dividing wall column, wherein the feed to the rectification column 4 and the side draw of the rectification column 4 are located on different sides of the dividing wall.
• 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.
• the process according to the invention preferably uses aqueous 3-hydroxypropionic acid produced by fermentation. Such a method is described, for example, in
• WO 02/090312 A1 discloses.
• part of the water can be distilled off in an optional step i), with part of the monomeric 3-hydroxypropionic acid reacting with elimination of water to give oligomeric 3-hydroxypropionic acid.
• Oligomeric 3-hydroxypropionic acid is the product of at least two molecules
• 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 monomeric 3-hydroxypropionic acid to acrylic acid.
• 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 water vapor is advantageously used). 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 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, more preferably from 10 to 40% by weight of water, most preferably from 15 to 35% by weight of water.
• the aqueous mixture of monomeric 3-hydroxypropionic acid and oligomeric 3-hydroxypropionic acid obtained in step i) 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 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 between the water content of the aqueous 3-hydroxypropionic acid used (educt) and the water content of the resulting aqueous mixture of monomeric 3-hydroxypropionic acid and oligomeric 3-hydroxypropionic acid (product).
• the water content can be determined by the usual methods, for example by Karl Fischer titration.
• the content of monomeric 3-hydroxypropionic acid in step i) is preferably reduced by at least 5% by weight, more preferably by at least 15% by weight, most preferably by at least 25% by weight.
• the value by which the content of monomeric 3-hydroxypropionic acid was reduced 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.
• the signals of the first four oligomers, i. to the pentamer, using the calibration factor of the monomeric 3-hydroxypropionic acid and the sum formed 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 are those with rings, spirals, calipers, Raschig, Intos or Pall rings, Berl or Intalox saddles or Braided 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.
• Dual-flow trays below the feed (output part) and Thormann trays above the feed (enrichment part) are particularly preferred.
• 2 to 5 theoretical plates below the feed and 2 to 15 theoretical plates above the feed of the rectification column 1 are sufficient.
• the rectification is usually carried out in such a way that the bottom pressure required for the reaction sets in.
• the top pressure results from the sump pressure, the number and type of column internals and the fluid dynamic requirements of the rectification.
• 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.
• the extraction point of the water is advantageously designed as a catch bottom. Built-in components that improve the mixing of the cooled water with the vapor can increase the effect of direct cooling.
• step i) 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 reacted in step ii) to give acrylic acid.
• 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 holds from 5 to 50% by weight of water, more preferably from 10 to 40% by weight of water, most preferably from 15 to 35% by weight of 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 water vapor is advantageously used). Preferably, it takes place via external circulation evaporator with natural or forced circulation. External circulation evaporators with forced circulation are particularly preferably used.
• Forced circulation expansion evaporators are very particularly preferably used. In a forced circulation flash evaporator evaporation does not take place on a hot surface, but by pressure release. Such evaporators are described in EP 0 854 129 A1. The use of several evaporators, connected in series or in parallel, is possible.
• the liquid phase preferably contains a polymerization inhibitor 1. Suitable polymerization inhibitors 1 are phenothiazine, hydroquinone, hydroquinone monomethyl ether, copper salts and / or manganese salts. Very particular preference is given to phenothiazine and hydroquinone monomethyl ether.
• 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 supplied 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).
• the reaction of the aqueous 3-hydroxypropionic acid or the aqueous mixture of monomeric 3-hydroxypropionic acid and oligomeric 3-hydroxypropionic from step i) to acrylic acid in the bottom of the rectification column 2 takes place and the aqueous 3-hydroxypropionic acid or the aqueous Mixture of monomeric 3-hydroxypropionic acid and oligomeric 3-hydroxypropionic acid from step i) is the feed of the rectification column 2.
• 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. Among the soils, bubble-cap trays, sieve trays, valve trays, Thormann trays and / or dual-flow trays are preferred, among the trays are those with rings, spirals, calipers, Raschig, Intos or Pall rings, Berl or Intalox saddles or Braided 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. 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 bottom pressure results from the top pressure, the number and type of column internals and the fluid dynamic requirements of the rectification.
• 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, done. 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, done.
• 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.
• the effect of direct cooling can be increased.
• all common installations are suitable for this, for example floors, packings and / or fillings.
• the trays bubble-cap trays, sieve trays, valve trays, Thormann trays and / or dual-flow trays are preferred.
• the beds 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.
• a portion of the bottom (residue) of the rectification column 2 is discharged and the distillation 1 (residue distillation) are fed.
• 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 take place via internal and / or external heat exchangers of conventional design and / or via double wall heating (water vapor is advantageously used as the heat carrier).
• water vapor is advantageously used as the heat carrier.
• 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 aqueous acrylic acid preferably contains a polymerization inhibitor 2.
• Suitable polymerization inhibitors 2 are phenothiazine, hydroquinone and / or hydroquinone monomethyl ether.
• 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 used for polymerization inhibition 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) is advantageously added to a polymerization inhibitor 3.
• Suitable polymerization inhibitors 3 are phenothiazine, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, hydroquinone and / or hydroquinone monomethyl ether. Very particular preference is given to phenothiazine and hydroquinone monomethyl ether.
• an entraining agent may be added. Suitable entraining agents are low-boiling hydrophobic organic solvents having a solubility in water at 23 ° 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 For distillative separation of the aqueous acrylic acid, a phase rich in acrylic acid (crude acrylic acid) and a water-rich phase (acid water) in step iii), a rectification column 3 is preferably used.
• 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. Among the trays, bubble-cap trays, sieve trays, valve trays, Thormann trays and / or dual-flow trays are preferred.
• the trays include those with rings, spirals, saddles, Raschig, Intos or Pall rings, Berl or Intalox rings. Saddling or braiding 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 bottom pressure results from the top pressure, the number and type of column internals as well as the fluid dynamic requirements of the rectification.
• the rectification column 3 is usually made of austenitic steel, preferably of the material 1.4571 (according to DIN EN 10020).
• Acid water can indirectly, for example by heat exchangers, which are known in the art and are not subject to any particular restriction, or directly, for example by a quench occur. Preferably, it is done by direct cooling.
• already condensed water-rich phase sour water
• sour water is cooled by means of a suitable heat exchanger and the cooled liquid is sprayed in the vapor above the take-off point. This spraying may be done in a separate apparatus or in the rectification unit itself.
• the removal point of the water-rich phase is advantageously designed as a catch bottom.
• 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.
• a portion of the condensed at the top of the rectification column 3 water-rich phase (sour water) can be used as reflux, the remainder of the water-rich phase (acid water) is discharged and fed to the recovery of acrylic acid sour water extraction.
• 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-rich phase (crude acrylic acid) withdrawn from the bottom of the rectification column 3 can be used directly for the preparation of water-absorbing polymer particles.
• the acrylic acid-rich phase (Rohacrylsaure) is further purified by crystallization.
• the mother liquor obtained in the crystallization can be recycled to the rectification column 3, preferably below the take-off point for the acrylic-acid-rich phase (crude acrylic acid).
• the acrylic acid-rich phase (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 combination of a suspension crystallization with a washing column, as described in WO 2003/041832 A1, is particularly preferred.
• the separation of the aqueous acrylic acid from the liquid phase and the separation of the aqueous acrylic acid in an acrylic acid-rich phase (crude acrylic acid) and a water-rich phase (acid water) by means of a rectification column with a side draw (rectification column 4) are performed.
• the rectification column 4 combines the tasks of the rectification columns 2 and 3 in a single rectification column. In this case, the section below the side take-off of the rectification column 2 and the section above the side take-off of the rectification column 3.
• 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 Particularly preferred are external circulation evaporator with forced circulation.
• Forced circulation expansion evaporators are very particularly preferably used. In a forced circulation flash evaporator evaporation does not take place on a hot surface, but by pressure release.
• Such evaporators are described in EP 0 854 129 A1.
• the use of several evaporators, connected in series or in parallel, is possible.
• 2 to 4 evaporators are operated in parallel.
• the feed into the rectification column 4 is expediently carried out in its lower region. Preferably, it takes place below the first bottom of the rectification column 4 and / or into the circulation of the heat exchanger.
• 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 fed to a residue distillation or a residue splitting.
• the bottom residue is preferably passed through a solids separator (cyclone) and optionally supplemented by fresh high-boiling organic solvent.
• the acrylic acid-rich phase (crude acrylic acid) is taken off via the side draw of the rectification column 4.
• the extraction of the acrylic acid-rich phase (crude acrylic acid) is carried out in the usual manner and is not subject to any restriction. Suitable is the removal of a catch bottom, the entire return is collected and a part discharged and the other part is used as return below the catch bottom, or a floor with integrated deduction, preferably a dual-flow floor with integrated deduction option.
• the withdrawn acrylic acid-rich phase (crude acrylic acid) is cooled by means of a heat exchanger (for example, surface waters are suitable as the coolant).
• the use of several heat exchangers, 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 through a quench. Preferably, it is done by direct cooling.
• already condensed water-rich phase (sour 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.
• the removal point of the water-rich phase (sour water) is advantageously designed as a catch bottom.
• the effect of direct cooling can be increased.
• all common installations are suitable for this, for example floors, packings and / or fillings. Above the floors, 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.
• 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 (sour water) can also be carried out in several stages, with upward decreasing temperature.
• the cooling is carried out by direct cooling.
• a portion of the water-rich phase (acid water) condensed at the top of the rectification column 4 can be used as reflux, the remainder of the water-rich phase (acid water) is discharged and fed to the extraction of acrylic acid for extraction with acid water.
• 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 the 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 production of water-absorbing polymer particles.
• the crude acrylic acid is 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 combination of a suspension crystallization with a wash column, as described in WO 2003/041832 A1, is particularly 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 acid / methacrylic acid.
• Copolymers but also for the preparation of water-absorbing polymer particles and acrylic acid esters, e.g. Methyl acrylate, ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate, as well as the homo- and copolymers thereof.
• acrylic acid esters e.g. Methyl acrylate, ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate, as well as the homo- and copolymers thereof.
• Water-absorbing polymer particles are obtained by polymerization of a monomer solution or suspension comprising a) at least one ethylenically unsaturated, acid group-carrying monomer which may be at least partially neutralized, in particular partially neutralized acrylic acid
• 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, for example, ethylenically unsaturated sulfonic acids, such as styrenesulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid (AMPS).
• 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).
• 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, polyethylene glycol diacrylate, allyl methacrylate, trimethylolpropane triacrylate, triallylamine, tetraallylammonium chloride, tetraallyloxyethane, as described in EP 0 530 438 A1, di- and triacrylates, as in EP 0 547 847 A1, EP 0 559 476 A1, EP 0 632 068 A1, WO 93/21237 A1, WO 2003/104299 A1, WO 2003/104300 A1, WO 2003/104301 A1 and DE 103 31 450 A1, mixed acrylates which, in addition to acrylate groups, contain further ethylenically unsaturated Groups, as described in DE 103 31 456
• Preferred crosslinkers b) are pentaerythritol triallyl ether, tetraallyloxyethane, methylenebismethacrylamide, 15-tuply ethoxylated trimethylolpropane triacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate and triallylamine.
• Very 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.
• diacrylates or triacrylates of 1 to 5 times ethoxylated and / or propoxylated glycerol.
• Most preferred are the triacrylates of 3 to 5 times ethoxylated and / or propoxylated glycerol, in particular the triacrylate of 3-times ethoxylated 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 Monomer a).
• the centrifuge retention capacity CRC
• initiators c) it is possible to use all compounds which generate free radicals under the polymerization conditions, for example thermal initiators, redox initiators, photoinitiators.
• Suitable redox initiators are sodium peroxodisulfate / ascorbic acid, hydrogen peroxide / ascorbic acid, sodium peroxodisulfate, sodium bisulfite and hydrogen peroxide / sodium bisulfite.
• mixtures of thermal initiators and redox initiators are used, such as sodium peroxodisulfate / hydrogen peroxide / ascorbic acid.
• 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.
• Such mixtures are available as Brüggolite® FF6 and Brüggolite® FF7 (Brüggemann Chemicals, Heilbronn, Germany).
• acrylamide, methacrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminopropyl acrylate, diethylaminopropyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate are ethylenically unsaturated monomers d) which are copolymerizable with the ethylenically unsaturated acid group-carrying monomers a).
• water-soluble polymers e it is possible to use polyvinyl alcohol, polyvinylpyrrolidone, starch, starch derivatives, modified cellulose, such as methylcellulose or hydroxyethylcellulose, gelatin, polyglycols or polyacrylic acids, preferably starch, starch derivatives and modified cellulose.
• an aqueous monomer solution is used.
• the water content of the monomer solution is preferably from 40 to 75% by weight, more preferably from 45 to
• 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 polymerization on the belt is described, for example, in DE 38 25 366 A1 and US Pat. No. 6,241,928.
• Polymerization in a belt reactor produces a polymer gel 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. However, it is also possible to drip an aqueous monomer solution and to polymerize the drops produced in a heated carrier gas stream.
• 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%, wherein the customary neutralizing agents can be used, preferably alkali metal hydroxides, alkali metal oxides, alkali metal carbonates or Alkalimetallhydrogenkarbonate and mixtures thereof.
• the customary neutralizing agents can be used, preferably alkali metal hydroxides, alkali metal oxides, alkali metal carbonates or Alkalimetallhydrogenkarbonate and mixtures thereof.
• 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 their mixtures.
• 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. For this purpose, 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 is preferably 0.5 to 15% by weight, particularly preferably 1 to 10% by weight, very particularly preferably 2 to 8% by weight, where Residual moisture content in accordance with the NA Recommended Test Method No. WSP 230.2-05 "Mass Loss Upon Heating". 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. %, particularly preferably from 35 to 70% by weight, very particularly preferably from 40 to 60% by weight. Optionally, however, a fluidized bed dryer or a paddle dryer can also be used for the drying.
• the dried polymer gel is then ground and classified, wherein for grinding usually one- 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 average 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.
• Polymer particles with too small particle size lower the permeability (SFC). Therefore, the proportion of too small polymer particles ("fines") should be low, so too small polymer particles are usually separated and recycled to the process, preferably before, during or immediately after the polymerization, ie before drying the polymer gel
• Polymer particles can be moistened with water and / or aqueous surfactant before or during the recycling process It is also possible to separate small polymer particles in later process steps, for example after surface postcrosslinking or another coating step. 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 polymer particles which are too small are added very late, for example only in an apparatus downstream of the polymerization reactor, for example an extruder, then the polymer particles which are too small can only be incorporated into the resulting polymer gel with difficulty. Insufficiently incorporated too small polymer particles, however, dissolve again during the grinding of the dried polymer gel, are therefore separated again during classification and increase the amount of recycled too small polymer particles.
• 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.
• the polymer particles can be surface-post-crosslinked 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.
• Very particularly preferred surface postcrosslinkers are 2-hydroxyethyl-2-oxazolidinone, 2-oxazolidinone and 1, 3-propanediol.
• the amount of surface postcrosslinker is preferably 0.001 to 5 wt .-%, more preferably 0.02 to 2 wt .-%, most 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.
• polyamines can also be 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. Subsequent to the spraying, the polymer coated with surface postcrosslinker are thermally dried, whereby the surface postcrosslinking reaction can take place both before and during drying.
• the spraying of a solution of the surface postcrosslinker is preferably carried out in mixers with moving mixing tools, such as screw mixers, disk mixers and paddle mixers.
• horizontal mixers such as paddle mixers
• vertical mixers are particularly preferred.
• the distinction between horizontal mixer and vertical mixer is made by the storage of the mixing shaft, ie 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 Continuous Mixer (Hosokawa Micron BV, Doetinchem, the Netherlands), Processall Mixmill Mixer (Processall Incorporated; Cincinnati, USA) and Schugi Flexomix® (Hosokawa Micron BV, Doetinchem, The Netherlands).
• the surface postcrosslinkers are typically used as an aqueous solution.
• the amount of non-aqueous solvent or total solvent can be used to adjust the penetration depth of the surface postcrosslinker into the polymer particles.
• solvent for example isopropanol / water, 1,3-propanediol / water and propylene glycol / water, the mixing mass ratio preferably being from 20:80 to 40:60.
• the thermal drying is preferably carried out in contact dryers, more preferably paddle dryers, very particularly preferably disk dryers.
• Suitable dryers are, for example, Hosokawa Bepex® Horizontal Paddle Dryer (Hosokawa Micron GmbH;
• 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 water-absorbing polymer particles are cooled after the thermal drying.
• 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). Moreover, 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. Subsequently, 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 rehydrated to further improve 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. If the temperatures are too low, the water-absorbing polymer particles tend to agglomerate and water evaporates appreciably at higher temperatures.
• 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 water-absorbing polymer particles.
• Suitable coatings for improving the swelling rate and the permeability are, for example, inorganic inert substances, such as water-insoluble metal salts, organic polymers, cationic polymers and di- or polyvalent metal cations.
• 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 type DRI Agilent 1 100 Refractive Index Detector (Agilent Technologies, Waldbronn, Germany).
• the system is equipped with a commercially available narrow PMMA standard with a molar mass of 800 to
• the average molar mass of the oligomers is the weight average of the oligomers with a molar mass of at least 400 g / mol.
• Eluent A is a mixture of 1000 ml of water and 1 ml
• 0.5 molar sulfuric acid 0.5 molar sulfuric acid.
• four initial weights about 280 mg, 180 mg, 90 mg and 60 mg
• the calibration range is 0.1 to 280 mg / 50ml.
• To calibrate the acrylic acid 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.
• 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 bacerband SiOH 6 ml, 1000 mg SPE cartridge (J.T.Baker, Avantor Performance Materials, Inc., Center Valley, PA, USA) is used.
• 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, entrainment agent)
• these samples can be sprayed on without extraction by dissolving 85 ⁇ directly in 10 ml eluent.
• the eluant used is 0.1% by volume aqueous phosphoric acid.
• the 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 circulated by the pump via the heat exchanger and the pressure-maintaining valve.
• the heat exchanger was heated by means of heat transfer oil.
• the temperature in the reactor was controlled by the temperature of the heat transfer oil.
• the rectification column had an inner diameter of 50 mm and was electrically accompanied by heating.
• 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:
• aqueous sulfolane additionally contained 0.1% by weight of phenothiazine and 0.5% by weight of hydroquinone monomethyl ether for polymerization inhibition.
• 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. 294 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.
• composition of the residue was:
• the reactor used was a 6 l double-walled glass container.
• the amount of liquid in the reactor was about 5000 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 contents of the reactor were circulated by the pump via the heat exchanger and the pressure-maintaining valve.
• the heat exchanger was heated by means of heat transfer oil.
• the temperature in the reactor was controlled by the temperature of the heat transfer oil.
• 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 had the following composition:
• the aqueous sulfolane additionally contained 0.1% by weight of phenothiazine and 0.5% by weight of hydroquinone monomethyl ether for polymerization inhibition.
• 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. 145 g / h of condensate were discharged.
• the condensate had the following composition:
• the average molar mass of the oligomers was 128000 g / mol.

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  • 2016-02-17 WO PCT/EP2016/053345 patent/WO2016135020A1/de active Application Filing

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