Classifications

• • 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
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
  • C07C29/74—Separation; Purification; Use of additives, e.g. for stabilisation
  • C07C29/76—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment
  • C07C29/80—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment by distillation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
  • C07C29/74—Separation; Purification; Use of additives, e.g. for stabilisation
  • C07C29/88—Separation; Purification; Use of additives, e.g. for stabilisation by treatment giving rise to a chemical modification of at least one compound
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C31/00—Saturated compounds having hydroxy or O-metal groups bound to acyclic carbon atoms
  • C07C31/18—Polyhydroxylic acyclic alcohols
  • C07C31/20—Dihydroxylic alcohols
  • C07C31/207—1,4-Butanediol; 1,3-Butanediol; 1,2-Butanediol; 2,3-Butanediol
• • 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
  • C08G63/88—Post-polymerisation treatment
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J11/00—Recovery or working-up of waste materials
  • C08J11/02—Recovery or working-up of waste materials of solvents, plasticisers or unreacted monomers

Definitions

• the present invention relates to a process for working up residues containing dihydroxy compounds which are obtained in the production of polyesters, wherein
• a dicarboxylic acid or its ester or ester-forming derivative is esterified or transesterified with a molar excess of a dihydroxy compound
• polyesters in particular polyalkylene be terephthalates executed so-called large-scale transesterification / lykondensations Kunststoff Po, wherein in a first stage of a esterification or transesterification, and in at least one white ⁇ more advanced stage, the actual polycondensation is carried out (see FIG. Man-made fibers ( Textilindustrie 40 (1992), 1058-1062 and Ulimann's Encyclopedia of Industrial Chemistry, 4th ed. Volume 19, pp. 61-88).
• terephthalic acid is esterified with a mo ⁇ stellar excess, preferably 50-120 mol%, in particular 70-100 mol%, 1,4-butanediol, wherein the esterified Ver ⁇ bond is subjected to further steps in the actual polycondensation .
• the esterification product is then polycondensed, the polycondensation in continuous processes advantageously being carried out in at least two stages, a so-called precondensation and postcondensation.
• DE-A 43 33 929 discloses a process for recovering the starting materials, a distillation residue from dihydroxy-containing compounds (so-called "hex") being metered into the column for easier handling of the usually very highly viscous bottom products.
• the vapors also contain oligomeric and polymeric polyesters in addition to the starting materials and by-products, the pH of the vapors is below 7 owing to the content of carboxyl end groups. In addition, when they are recovered, they are fragmented again, which means that new carboxyl end groups are present
• THF forms to a considerable extent as a by-product (with 1,4-butanediol as a starting material). Since these side reaction is catalyzed by acids, is also in the Destillations Wegge ⁇ winnung 1.4 butanediol to a considerable extent by THF formation be lost.
• the present invention was therefore based on the object of improving the disadvantages described above and improving the work-up of the vapors in such a way that the largest proportion of the dihydroxy compounds contained therein is as economical as possible. lent can be recovered. At the same time, the product quality of the polyester should be maintained.
• this object can be achieved by treating the treatment for recovering the starting materials in the presence of an alkali or alkaline earth compound in an amount of 0.5 to 10% by weight, calculated as alkali metal or alkaline earth metal based on the solids content of the vapors.
• the evaporation device following the distillative preparation can further e.g. Butanediol can be recovered, this workup being independent of the availability of the residue containing dihydroxy compounds (HEX).
• Butanediol can be recovered, this workup being independent of the availability of the residue containing dihydroxy compounds (HEX).
• 0.5 to 10, preferably 1 to 8 and in particular 2.5 to 6% by weight, preferably calculated as alkali metal or alkaline earth metal, is preferably in the bottom of columns A, B or C during the preparation of the vapors based on the solids content of the vapors added.
• inorganic and organic compounds of the alkali metals are suitable.
• suitable inorganic compounds of the (earth) alkali metals, preferably sodium are the corresponding silicates, phosphates, phosphites, sulfates or preferably carbonates, hydrogen carbonates and hydroxides.
• the organic compounds of the (earth) alkali metals include the corresponding salts of (cyclo) aliphatic, araliphatic or aromatic carboxylic acids with preferably up to 30 carbon atoms and preferably 1 to 4 carboxyl groups.
• Alkali aryl sulfonates or also phenolates and alcoholates, such as e.g. Methanolates, ethanolates, glycolates can be used according to the invention.
• Examples of particularly preferred representatives are sodium acetate, sodium propionate, sodium butyrate, sodium oxalate, sodium malonate, sodium succinate, sodium methoxide, sodium ethanolate, sodium glycolate.
• Sodium methoxide is very particularly preferred, which is used particularly advantageously in an amount of 2.5 to 6% by weight, calculated as Na, based on the solids content of the vapors. Mixtures of different (earth) alkali metal compounds can also be used.
• the (earth) alkali metal or the (earth) alkali metal compound can, depending on the work-up method, be added to at least one column A, B or C. Of course, the addition can also be distributed over all columns, preference being given to metering the same amounts into each column.
• terephthalic acid and 1,4-butanediol (the latter in 5 150 to 220 mol%, preferably 70 to 100 mol% excess) in a manner known per se at temperatures in the range from 150 to 220 ° C., and pressures in the range from 0.7 to 2.0 bar for a period of from 150 to 300, preferably from 200 to 280 minutes, reacted with one another, an esterification taking place and ent
• THF tetrahydrofuran
• BD butanediol
• small amounts of oligomeric and polymeric compounds as well as residual amounts of terephthalic acid are transferred into a column A with the vapors (a).
• the place of addition is preferably in the middle or in the lower part of the column.
• Step (1) of the process is shown in the figures as a process step.
• Step (1) is preferably divided into at least four process steps, these consisting of a mixing reactor for solvent, catalyst, etc. and at least
• the esterification product of stage (1) of the process is polycondensed in at least one second stage (2). This polycondensation is carried out in a manner known per se at temperatures of
• stage (2) is divided into two process steps, firstly a so-called precondensation and then one
• Fig. 1 shows a preferred embodiment for recovering the starting materials, the vapors (a) obtained in stage (1) being transferred to at least one column A and the
• Fig.2 shows a further preferred process for working up the vapors, the vapors (a) 45 and part of the vapors (bi) from stage (2) of the process obtained in stage (1) being combined in at least one column A and the low-boiling components of the vapors in column A are removed overhead and the bottom product, which predominantly contains the excess dihydroxy compounds and oligomeric and polymeric reaction products, is returned to stage (1) and the other part of the vapors (b 2 ) of stage (2) of the process is passed into at least one column B. transferred and the low-boiling constituents of the vapors removed overhead and the bottom product discharged from column B and then subjected to at least one column C for a further treatment to recover the dihydroxy compound.
• the excess diol can be recycled in a technically simple manner the esterification take place. As a result, the process is more economical and less expensive, while the product quality of the polyester is retained.
• Fig. 3 shows a further preferred embodiment of the process, the vapors (a) and (b) obtained in stages (1) and (2) being transferred to at least one column A and the low-boiling constituents being removed overhead and then discharging the bottom product from column A and subjecting it in at least one column C to a further treatment for the recovery of the dihydroxy compound.
• the low-boiling THF / water is removed overhead and these low-boiling constituents are then subjected to recovery of the starting materials (separation of THF from water).
• the low-boiling components consist essentially of water or methanol with acetaldehyde; in the production of PBT based on methyl terephthalate from methanol and THF. Then the bottom product, which predominantly contains the excess dihydroxy compounds, is returned to stage (1).
• columns A to C can be divided into several columns Ai, A 2 to A n or B 1 ( B 2 to B n and Ci, C 2 to C n .
• the vapors are worked up in such a way that the vapors of stage (2), which are predominantly THF, water, excess butanediol and somewhat larger amounts than in the vapors from Stu ⁇ fe (1) of oligomeric and polymeric compounds and residual amounts of terephthalic acid are either proportionally A and B or all of them are transferred to a column A, the vapors from stage (1) of the process already being present in column A.
• the workup is carried out separately and the vapors (b) are transferred to a column B.
• the place of addition is preferably in the middle or in the lower part of the columns. How to divide these proportions goes without saying, since the division depends on the filling quantity of the columns and the quality of the required starting materials in the esterification.
• the low-boiling constituents of the vapors are separated off overhead and the bottom product is removed from column A and / or B depending on the procedure. Subsequently, the bottom product is subjected to a further treatment for the recovery of the dihydroxy compound. For this purpose, the bottom product from column A or B is discharged into a column C, depending on the procedure, if appropriate with removal of the solids.
• a liquid residue containing dihydroxy compounds (“hex”) such as is obtained, for example, from the distillation of 1,4-butanediol or 1,6-hexanediol, is preferably introduced in column C in parallel.
• the composition of the residue is not subject to any particular restriction as long as the liquid form is present and there are no compounds which interfere with the separation in the column. This is usually the case with residues from butanediol or hexanediol distillation.
• the point of addition is preferably in the middle or in the lower part of the column, and the amount added is generally 0.03 to 5 kg per kg of bottom products transferred into the column, preferably from 0.04 to 0, 1 kg / kg.
• the bottom product remains liquid or conveyable in column C, and the dihydroxy compound can therefore be obtained at the bottom of this column in a process-technically simple manner overhead and in turn a liquid or conveyable bottom product which can be easily incinerated.
• the dihydroxy compound is then returned from column C to the esterification (stage 1).
• the bottom product is discharged from column C into an evaporation device D and the dihydroxy compound is separated off and returned to column C and the remaining residue is discharged from D.
• This preferred embodiment further e.g. 1,4-butanediol is recovered and the residue can be worked up in a simple and economical way without adding a distillation residue.
• Another advantage of this procedure is that the removal of the dihydroxy compound does not have to be carried out completely in column C, the residue is not as viscous and thus remains manageable.
• the place where the recovered butanediol is added is preferably in the lower part of column C, in particular above the vapor space of the column bottom of column C.
• Suitable evaporation devices D are, for example, special columns, stirred evaporators, extruders, self-cleaning evaporators or disk evaporators.
• the temperature of the evaporation device is preferably above the melting point of the remaining residue. This depends on the solids content and the type of residue.
• the temperature is usually 180 to 250 ° C., preferably 190 to 230 ° C., for residues from the production of polyethylene terephthalate generally from 180 to 280 ° C., preferably 190 to 265 ° C.
• bottom product in the device D is only concentrated to a solids content of 30 to 70%, based on the bottom discharge, lower temperatures of 150 to 220 ° C. in the device D are also suitable.
• the starting materials such as butanediol can be recovered to a considerable extent simply and inexpensively by the process according to the invention. At the same time, the proportion of by-products such as THF is drastically reduced.
• terephthalic acid TPA
• BD 1,4-butanediol
• reaction product was transferred to stage 2 with at least 95% conversion.
• 50 ppm of Ti were added. added on PBT as TBOT:
• stage 2 After the precondensation in stage 2, the product was converted into the post-condensation of stage 2 with at least 98.5% conversion. At the beginning of the post-condensation 30 ppm Ti were. added on PBT as TBOT.
• stage (1) The vapors from stage (1) were transferred to column A in vapor form as stream (a) (see table for Fig. 2) at 210-220 ° C and 2 bar abs . Water and THF were separated off at the top.
• the butanediol was returned to stage (1).
• the butanediol contained in the vapors of stage (2) (stream b + b 2 ) was fed into the columns A and B in liquid form with the entire vapors of this stage.
• the streams of the precondensation and postcondensation were divided up such that the vapors of the postcondensation of stage (2) and part of the vapors of the precondensation of stage (2) were added to column B while the other part of the vapors was added the precondensation of stage (2) was added to column A.
• Table 1 for Fig. 2 shows the BD losses for the various processing variants according to Example 1.
• the processing variants are 1.1. until 1.5. was carried out as follows:
• the reaction product was transferred to stage 2 with at least 95% conversion.
• the precondensation was carried out:
• the product was then melted out with a viscosity ⁇ (intrinsic) of 0.9-1.3 and granulated.
• Example 2 In a departure from the work-up in Example 1, the entire vapors from stage 2 were added to column B. In contrast to Example 1, MeOH and THF are separated off at the tops of columns A and B.
• V a: BD fully recovered in vapors a

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Life Sciences & Earth Sciences (AREA)
• Sustainable Development (AREA)
• Polyesters Or Polycarbonates (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Priority Applications (4)

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• 1996
  • 1996-03-06 DE DE19608614A patent/DE19608614A1/de not_active Withdrawn
• 1997
  • 1997-03-04 US US09/125,064 patent/US6174970B1/en not_active Expired - Fee Related
  • 1997-03-04 WO PCT/EP1997/001081 patent/WO1997032915A2/de not_active Ceased
  • 1997-03-04 AU AU20951/97A patent/AU2095197A/en not_active Abandoned
  • 1997-03-04 EP EP97906160A patent/EP0885252A2/de not_active Withdrawn
  • 1997-03-04 KR KR1019980707008A patent/KR19990087569A/ko not_active Ceased
  • 1997-03-04 CN CNB971928096A patent/CN1140561C/zh not_active Expired - Fee Related
  • 1997-03-04 JP JP9531454A patent/JP2000506203A/ja not_active Ceased

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