Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D5/00—Condensation of vapours; Recovering volatile solvents by condensation
  • B01D5/0057—Condensation of vapours; Recovering volatile solvents by condensation in combination with other processes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
  • B01D53/1487—Removing organic compounds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
  • B01D53/1493—Selection of liquid materials for use as absorbents
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D319/00—Heterocyclic compounds containing six-membered rings having two oxygen atoms as the only ring hetero atoms
  • C07D319/10—1,4-Dioxanes; Hydrogenated 1,4-dioxanes
  • C07D319/12—1,4-Dioxanes; Hydrogenated 1,4-dioxanes not condensed with other rings
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/78—Preparation processes
  • C08G63/785—Preparation processes characterised by the apparatus used
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
  • C08G63/06—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from hydroxycarboxylic acids
  • C08G63/08—Lactones or lactides

Definitions

• the present invention relates to a condensation and washing device with which in particular the process vapors obtained in Polylactidher ein can be worked up and purified. Furthermore, the present invention relates to a polymerization sationsvorraum for the production of polylactide and a process for the processing of resulting in Polylactidher ein process vapors; also uses of both the condensation and washing devices and the method are called.
• US 5,266,706 describes a process for obtaining a cyclic ester such as lactide from a gas stream containing the lactide and hydroxyl-containing impurities such as water and hydroxycarboxylic acids by washing the gas stream with a water-immiscible solvent such as non-polar hydrocarbons, cycloaliphatic hydrocarbons or halogenated hydrocarbons.
• a water-immiscible solvent such as non-polar hydrocarbons, cycloaliphatic hydrocarbons or halogenated hydrocarbons.
• the temperature in the wash is adjusted so that the cyclic ester and the hydroxycarboxylic acid is removed from the gas stream, while water remains in the gas stream and is discharged therewith.
• the crude mixture of cyclic ester and acid is separated from the solvent and purified by extracting the acid therefrom.
• the condensation and washing liquid should entrain no foreign substances in the condensate, which would be separated again before returning to the polylactide.
• washing device provided, comprising
• condensation and washing liquid is an aqueous solution of an alpha-hydroxycarboxylic acid of the formula I,
• R is selected from hydrogen or linear or branched aliphatic radicals having 1 to 6 carbon atoms, preferably lactic acid.
• concentration of the alpha-hydroxycarboxylic acid is in particular between 50 and 100 wt .-%, preferably between 70 and 95 wt .-%.
• the concentration of the diester of the formula II in the condensation and washing liquid is preferably between 0 and 6% by weight, preferably between 1 and 4% by weight.
• the mass transfer packing contained in the condensation and washing device comprises in principle all packaging possibilities for columns known from the prior art, but in particular the mass transfer pack is selected from the group consisting of rings, such as Raschig and / or Pall rings, saddles such as Berl saddles, balls, hackles, NOR-PAC, BIO-NET, HeI-X, top-packs, Mellapak, Montz-Pak, Ralu-Pak, Raschig-Super-Pak and / or tissue packs.
• the surface of the used mass transfer packs is between 20 m 2 / m 3 and 500 m 2 / m 3 .
• the at least one column has at least one liquid distributor for distributing the condensation and washing liquid supplied via the pipeline, which is arranged above the at least one mass transfer package.
• the liquid distributor is a sprinkler or a spray device, a spray condenser or a sprinkler.
• the at least one column and / or the sump container have means for controlling the temperature of the condensation and washing liquid.
• the pipeline for the condensation liquid has a heat exchanger.
• a polymerization device for the polymerization of the diester of the formula II which comprises a condensation device described above.
• the Kondensationsvorrich- device for example, at least one cleaning device for dilactide, which is operated under vacuum, is connected upstream. It is likewise possible for the condensation device to be preceded by at least one de-polymerisation reactor which is operated under vacuum.
• the invention likewise provides a process for the condensation and / or scrubbing of a vaporous, biodegradable, intermolecular cyclic diester of an alpha-hydroxycarboxylic acid of the formula II
• R is selected from hydrogen or linear or branched aliphatic radicals having 1 to 6 Kohlenstoffatoraen, from a vapor mixture containing the diester of formula II, the diester of formula II corresponding alpha-hydroxycarboxylic acid of formula I and water provided, wherein at least one Contacting a stream of a condensation and washing liquid, comprising an aqueous solution of the diester of the formula II corresponding alpha-hydroxycarboxylic acid of the formula I. OH ⁇ .
• Formula IR COOH is carried out with the vapor mixture, so that the diester of the formula II contained in the vapor mixture is dissolved in the condensation and washing liquid.
• the contacting of the vapor mixture with the liquid can be carried out in any desired manner.
• the vapor mixture is introduced into the condensation and washing liquid, for example by blowing or passing, but alternatively it is also possible if the condensation and washing liquid is contacted by sprinkling, spraying or sprinkling of the vapor mixture.
• condensation and washing liquid is circulated.
• Washing liquid with the vapor prior to contacting - mixture are between 10 0 C and 80 0 C, preferably between 15 0 C and 60 0 C.
• the condensation and washing liquid is added in portions or continuously a mixture of water and hydroxycarboxylic acid of formula I.
• the amount of the aqueous solution of the hydroxycarboxylic acid of the formula I to be added must be such that the crystallization of the diester of the formula II does not occur.
• the added amount should be such that the viscosity of the condensation and washing liquid remains approximately constant.
• the amount or rate of the solution to be added thus depends on various parameters, for example the temperature of the condensation and washing liquid and the amount of the diester of the formula II in the vapor mixture, so that the amount or rate of the solution to be added to reduce the concentration of the diester of formula II in the washing and condensation liquid can be determined by the person skilled in the respective case by means of simple experiments.
• the concentration of the diester of the formula II in the condensation and washing liquid is always kept below 5 wt .-%.
• a further preferred embodiment provides that the contacting of the washing liquid with the vapor mixture takes place at reduced pressures, in particular between 5 mbar and 900 mbar, preferably between 10 mbar and 200 mbar.
• the diester of formula II is dilactide and the alpha-hydroxycarboxylic acid of formula I is lactic acid.
• the invention is applicable to the two enantiomeric forms L, L-dilactide and D, D-dilactide and L-lactic acid and D-lactic acid. It is also applicable when the diester is £, L-dilactide or mesolactide. Furthermore, it is possible that at least part of the diester of the formula II originates from an upstream purification device.
• dilactide is understood as meaning L, L-dilactide, D, D-dilactide, mesolactide and mixtures thereof.
• the vapor mixture from different process stages in the polymerization of lactide namely from a process stage of the production of polylactide, the polycondensation of lactic acid, the thermal depolymerization of oligomers of lactic acid with an average molecular weight between 500 g / mol and 5000 g / mol, the rectification of dilactide, the ring-opening polymerization of a dilactide-containing reaction mixture, the vacuum demonomerization of polylactide or its copolymers and / or of several of the abovementioned process stages at the same time.
• the method described above can be carried out with a device also described in the foregoing.
• the contacting of the vapor mixture with the washing or condensation liquid preferably takes place in the region of the mass transfer packet.
• the process of the present invention is designed not to recover the cyclic ester - the lactide - but to purify the vapor stream of any condensable and abrasive or corrosive impurities before entering a vacuum pump or a series of vacuum pumps connected in series.
• the temperature during the washing is chosen so low that, on the one hand, the largest possible proportion of the components contained in the vapor stream condenses, including water. On the other hand, it is chosen so high that the viscosity of the washing liquid is not too high, so that even a good distribution over a packed bed or a mass transfer packing is possible.
• the inventive method does not work with non-process solvents, but essentially with the condensed out liquid itself, which is recycled.
• the temperature of the washing liquid is adjusted by circulating cooler and kept constant.
• the dilactide reacts with the water in the liquid by ring opening to Lactoylmilchklare.
• the viscosity of the liquid increases and the distribution over the bed or packing is made more difficult and the condensation and washing effect decreases. It is therefore advantageous to supply continuously or in portions a mixture of water and lactic acid to the circulating condensing and washing liquid, whose composition and mass flow are chosen such that the solubility limit of the dilactide in the circulation is not reached and the viscous sity of the liquid mixture does not increase.
• a partial flow of the circular flow corresponding to this flow rate Running fluid is discharged in addition to the flow rate of the condensate, preferably together with this, from the circulation and returned to the polylactide process at a suitable location.
• FIG. 2 shows an embodiment of a polymerization device according to the invention with reference to a flow chart of a typical procedure for the preparation of polylactide, starting from lactic acid.
• a condensation device 1 whose principle is shown in Fig. 1, contains a column shot 6 with a nominal diameter of 200 mm. In this shot, a packed bed 7 of PaIl rings is arranged with the dimension 15 mm. The height of the bed is 500 mm.
• 60 1 commercial lactic acid (Purae HS88) are filled with a water content of 12% as condensation and washing liquid 3.
• the lactic acid is withdrawn with a pump 15 from the bottom, conveyed back through a heat exchanger 12 via a pipe 10 in the column shot 6 and there distributed with a liquid distributor 11 evenly over the packed bed 7.
• the liquid distributor 11 in the form of a sprinkler be designed.
• the heat exchanger 12 tempered the liquid with a cooling medium 13 or 14, here ethylene glycol, to 30 0 C.
• a pipe socket 9 is arranged above the packing 7 and the liquid distribution 11, which pipe serves to discharge the non-condensable gases and vapors. He is about a (not shown in Fig. 1) cold trap, the z. B. is cooled with dry ice to about -50 0 C, connected to a vacuum pump.
• the device 1 is placed under a vacuum or reduced pressure of 10 mbar for dewatering. Thereafter, the sump is drained to the overflow located at the level of the drain 4.
• the condensation device 1 is part of a continuous plant for the production of polylactide by ring-opening polymerization. The procedure described above is part of the start-up procedure of this appendix. After the other process stages of the plant have been put into operation, the condensing device 1 is continuously fed a vapor stream via port 8, which comes from the thermal depolymerization of a lactic acid oligomer having an average molecular weight M n of 1,500 g / mol and from the Main amount of dilactide has already been condensed out by a surface condenser.
• the Dampfström contains nitrogen, water, lactic acid and residual Dilac- tid and has a temperature of 140 0 C. After entry into the condensation device 1 it flows corresponding to the pressure gradient in countercurrent to the temperature-controlled at 30 0 C liquid 3 through the Greier-üt- tung 7 In doing so, most of the entrained components are either condensed or washed out.
• the non-condensable radicals leave together with the nitrogen contained through the gas outlet 9, the condensation device 1 and are completely deposited in the following cold trap, wherein the nitrogen is withdrawn by the vacuum pump.
• the liquid level in the sump 2 is allowed to rise over 24 hours. Afterwards, the sump is emptied to the level before the start of the steam injection (overflow). The amount of collected condensate is 5.9 kg, the water content is determined by Karl Fischer titration with 2 wt -.%. At the same time, the cold trap in front of the vacuum pump is replaced and the contents weighed. It has deposited 0.9 kg, the water content is determined at 90%. Dilactide could not be detected by HPLC analysis. The vacuum pump does not show any loss of performance that would indicate wear or corrosion.
• fresh aqueous lactic acid can be introduced into the circulation via the feed 16.
• FIG. 2 shows the continuous overall process of the production of polylactide (PLA process) starting from lactic acid.
• the process is subdivided into the following sub-steps, which are carried out with the individual components integrated in the polymerization apparatus 100, which are explained in more detail below.
• the polymerization apparatus 100 in this case comprises a condensation apparatus 1 according to the invention. 1. Concentration of lactic acid
• the starting material for the process is lactic acid.
• the content of lactic acid must be higher than 80 wt .-%.
• the lactic acid concentration is more than 90%, because the water must be removed before the polymerization.
• the separation of water and lactic acid is carried out in a rectification column 101. In this case, a vacuum 103 is applied via a suction, the vapor arising water is condensed and removed via a further nozzle 104 on the head side.
• the supply of lactic acid is carried out continuously via another nozzle 102.
• the distillate is pure water, the product on the swamp side is lactic acid with a concentration of more than 99 wt .-%.
• the rectification column 101 In addition to the separation of water from the source material (lactic acid), the rectification column 101 also serves to separate the vapors from the pre-condensation reactors 105a and 105b.
• the vapor streams consist of lactic acid, Lactoylmilchklare, dilactide and water.
• the water is withdrawn from the top of the head, lactic acid and its derivatives pass into the bottom of the rectification column and from there, together with the concentrated lactic acid, into the first precondensation reactor 105a.
• the concentrated lactic acid is converted into a prepolymer by polycondensation in a series of two reactors 105a and 105b.
• the polycondensation proceeds at two different pressures and temperatures to optimize reaction conversion.
• the first reactor 105a the conditions are selected that the evaporation of lactic acid is minimized and at the same time the removal of water is facilitated.
• the reaction rate is increased by a higher temperature, at the same time the pressure is reduced in order to further reduce the water concentration in the melt.
• the average molecular weight (number average) of the prepolymer is between 500 and 2,000 g / mol.
• the prepolymer is in chemical equilibrium with the cyclic dimer of lactic acid, the dilactide.
• the pressure and temperature in the depolymerization reactor 106 it is ensured that the lactide is formed continuously from the prepolymer and evaporates.
• the vapor stream from the depolymerization reactor 106 consists mainly of lactide. Water, lactic acid and their linear oligomers are only present in minor amounts.
• Vapors are partially condensed in the condensation device 1 according to the invention: water and the largest proportion of lactic acid remain vaporous.
• the condensate primarily contains the lactide, lactoyllactic acid (the linear dimer of lactic acid) and higher linear oligomers.
• lactide is present in two stereoisomeric forms: the optically active L, L-lactide and the mesolactide, from a combination of an L (+) - and D (-) lactic acid unit. Some of the Z (-) units are derived from the starting material and some are formed by racemization of L ⁇ +) units during prepolymerization and depolymerization.] 4. Lactide Purification
• the achievable molecular weight and hence significant mechanical properties of the polylactide depend on the degree of purity of the lactide.
• the hydroxyl groups of the lactic acid and lactoyl lactic acid present as impurities serve as starting point for the polymerization.
• the concentration of hydroxyl groups in Rohlactid is too high after the cyclizing depolymerization.
• the condensed lactide is in a rectification column or a dividing wall column 108 to the required
• Hydroxyl group concentration purified.
• the purified lactide is taken from column 108 as a side product.
• the distillate and the bottom product are returned to the process at different points.
• the D content the amount of structural units having the D configuration.
• the ring-opening polymerization is undertaken in a reactor formed from a combination of a stirred tank 109 and a tubular reactor 110.
• the low-viscosity lactide is polymerized to PLA at a conversion rate of about 50%.
• Catalyst and additives are homogeneously mixed into the melt.
• the polymerization reaction is continued until a chemical equilibrium between polymer and monomer is achieved.
• the maximum conversion of the monomer is about 95%.
• the viscosity increases to about 10,000 pa-sec.
• the melt is removed from the extruder 111 and transferred into a granulate 112.
• both strand granulation or underwater granulation can be carried out.
• the PLA granules must be crystallized before drying and packaging. The crystallization is carried out at elevated temperatures and with stirring until the granules no longer stick together.
• a condensation device 1 described above can be used, for example, to separate dilactide vapors from the individual process stages in a process shown in FIG. 2.
• the condensation device is preferably an integral part of one shown in Fig. 2 Arrangement used.
• a supply of process vapors to the condensation device 1 can take place from one, several or all process stages.
• the arrangement of the condensation device is not limited to the arrangement shown in Fig. 2, the condensation device 1 may also be connected to other process stages after and / or upstream.

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• Chemical & Material Sciences (AREA)
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• General Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
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• Engineering & Computer Science (AREA)
• Health & Medical Sciences (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Polyesters Or Polycarbonates (AREA)
• Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Biological Depolymerization Polymers (AREA)

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• 2007
  • 2007-09-03 AT AT07017233T patent/ATE501778T1/de active
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• 2008
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  • 2008-08-05 CN CN200880111394.0A patent/CN101820970B/zh active Active
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• 2013
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