Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C67/00—Preparation of carboxylic acid esters
  • C07C67/48—Separation; Purification; Stabilisation; Use of additives
  • C07C67/52—Separation; Purification; Stabilisation; Use of additives by change in the physical state, e.g. crystallisation
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D47/00—Separating dispersed particles from gases, air or vapours by liquid as separating agent
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/50—Improvements relating to the production of bulk chemicals
  • Y02P20/582—Recycling of unreacted starting or intermediate materials

Definitions

• the invention relates to an improved process for cleaning and cooling a dialkyl ester A) of a gas stream containing aromatic carboxylic acid.
• Aromatic dialkyl esters are technically important starting materials, for example for the production of all kinds of polyesters.
• Dimethyl terephthalate in particular is an important intermediate for the production of various technically important polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT).
• DMT is this implemented in molten form with the corresponding alcohols, ethylene glycol and 1, 4-butanediol catalytically and the thus obtained monomeric intermediates (subsequently converted by polycondensation in the polyester Ullmann's Encyclopedia of industrialization al Chemistry, th edition 6, 2000 Electronic Release , Wiley-VCH, Weinheim 2000).
• dialkyl esters hydrolyze very quickly when they come into contact with water; an equilibrium reaction forms the corresponding acid, which has a negative impact on the product quality of the polyester.
• DMT is usually stored in molten form at temperatures of 165 ° C - 170 ° C in an inert atmosphere (nitrogen) to prevent oxidation or hydrolysis of the DMT and to facilitate metering during the transesterification. With continuous nitrogen replenishment, DMT-laden, hot gas streams are released from the tank storage.
• DMT When cooling, DMT tends to desublimation from the gas phase. This can lead to the formation of solid DMT particles, which make the cleaning and cooling of DMT-laden gas streams considerably more difficult. If the solid DMT particles are not separated, the permissible emission limit values with regard to DMT can be exceeded.
• DD-A 160829 describes the gas scrubbing of gas streams containing DMT from a PBT reactor with 1,4-butanediol.
• the low-boiling reac- stripped by-product methanol which is separated by distillation.
• DMT is separated from the methanol carrier gas stream by 4-butanediol as entrainer with an inlet temperature of 100-150 ° C. and returned to the reaction zone. Simultaneous gas cooling is not described.
• DD-A 145540 claims the separation and recovery of DMT during PET production in a DMT sublimate separator provided with a glycol cap.
• the gas streams loaded with DMT originate from the intermediate storage or melting of DMT.
• the DMT-containing gas with fresh glycol at a temperature of 70 - 120 ° C is led in cocurrent in the middle of 3 chambers and is then pressed into an outlet chamber of the gas by overpressure with inert gas via a glycol seal (20 - 160 ° C) , The DMT dissolved in the glycol can thus be returned to PET synthesis. Additional gas cooling is not mentioned in this process.
• the washing of DMT-laden gas streams from the DMT synthesis in a countercurrent apparatus with methanol is described in CS 134835.
• the DMT can be returned to the process after a solid-liquid separation. Due to the volatility of the methanol, a second separator is required, in which the methanol is separated from the clean gas stream by gas washing with water. The present temperatures are not described in detail.
• DMT washing with methanol is also claimed in EP-A 0741124.
• Xylene (DE-A 2105017) and liquid DMT (US 3227743) can also be used to recover the DMT from gas streams.
• a process for the simultaneous purification and cooling of gas streams from the PET synthesis in a two-stage countercurrent wash with ethylene glycol is described in US 6312503.
• the hot gas stream (175 ° C.) from a polymerization reactor for PET production contains unspecified by-products and unreacted starting materials, in particular ethylene glycol, acetaldehyde and water.
• a two-stage scrubbing is claimed, in which the gas is cooled in the lower section of the apparatus at cooling rates of less than 5.4 ° C./ft 2 (based on the surface of the internals) by direct contact with a liquid. With the same liquid, however, the foreign matter is washed out of the inert gas stream in the upper section of the apparatus at lower temperatures.
• DE-A 103 16466.9 proposes a two-stage procedure in which the first stage is carried out above the melting point of the dialkyl ester.
• the object of the present invention was therefore to provide an improved process for cooling and purifying a dialkyl ester A) of an aromatic dicarboxylic acid-containing gas stream, which is characterized in that in a first stage the gas stream is mixed with an aliphatic dihydroxy compound B) treated at a temperature less than / equal to the melting point of the dialkyl ester A) and in at least a second stage the gas stream was treated with an aliphatic dihydroxy compound B) above the melting point of the dihydroxy compound B).
• the diols also have a high solubility for the esters, so that no solid precipitation occurs and the solvent can be operated in a cycle.
• dialkyl esters A are understood to mean those compounds which are composed of an aromatic dicarboxylic acid with aliphatic ester radicals.
• Preferred dicarboxylic acids are 2,6-naphthalenedicarboxylic acid, terephthalic acid and isophthalic acid or mixtures thereof.
• Up to 30 mol%, preferably not more than 10 mol%, of the aromatic dicarboxylic acids can be replaced by aliphatic or cycloaliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, dodecanedioic acids and cyclohexanedicarboxylic acids.
• Terephthalic acid may be mentioned as a particularly preferred dicarboxylic acid.
• Preferred alkyl radicals have 1 to 4 carbon atoms, in particular 1 to 2 carbon atoms.
• Preferred dialkyl esters are those which are derived from 2,6-naphthalenedicarboxylic acid, terephthalic acid and isophthalic acid or mixtures thereof, the dimethyl esters being preferred.
• Dimethyl terephthalate is particularly preferred.
• the aliphatic dihydroxy compound B) used is preferably diols having 2 to 6 carbon atoms, in particular 1,2-ethanediol, 1,3-propanediol, 1,2-butanediol, 1,6-hexanediol, 1,4-hexanediol, 1,4 -Butanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol and neopentyl glycol or mixtures thereof, 1,4-butanediol being particularly preferred.
• DMT is generally kept in the molten state at temperatures of 140 to 286 ° C., preferably 165 to 170 ° C. and overlaid with a dry gas stream, preferably an inert gas stream, in particular a nitrogen stream.
• a dry gas stream preferably an inert gas stream, in particular a nitrogen stream.
• a DMT-laden gas stream is created.
• Such a gas stream also arises as a so-called exhaust gas stream after the precondensation or postcondensation of the polyesters, which can be cleaned and cooled in a corresponding manner by the process according to the invention.
• the DMT-containing gas stream is treated in a first stage with the above dihydroxy compounds B) at temperatures less than / equal to the melting point of the dialkyl ester A).
• the melting point is 140 ° C
• the temperatures of the gas stream are usually from 140 to 286 ° C, preferably from 150 to 170 ° C.
• Suitable devices are generally those which can bring the gas stream into contact both in cocurrent and in countercurrent. These are, in particular, falling film apparatus, packing, packing columns, apparatus with disperse liquid and continuous gas phase / spray apparatus, apparatus with gas and continuous liquid phase, such as bubble columns or tray columns.
• the corresponding apparatus is equipped with internals such as trays, packing elements, structured packings and other column internals which are effective in terms of separation and correspond to the prior art.
• the apparatus can also be installed without an atomization of the liquid. leads.
• Component B) is introduced into the gas stream via conventional distribution devices or nozzles.
• the gas volume flow during tank storage is usually from 5 to 75 m 3 / h, preferably from 25 to 50 m 3 / h.
• the proportion of DMT in the gas stream is limited by the respective saturation vapor pressure in the corresponding inert gas stream. This is a maximum of 23% by weight in N 2 , and cleaning is effectively possible up to a concentration of 0.0001 ppm by weight of DMT in the N 2 stream.
• the concentration of the DMT is usually from 0.001 to 16 ppm by weight in the N 2 stream.
• the degree of saturation of the gas flow is a measure of the concentration of the DMT in the gas phase and is defined by
• Component B) is simultaneously or subsequently e.g. via distribution devices e.g. Nozzles or preferably added at the end of the 1st stage in the case of countercurrent operation.
• distribution devices e.g. Nozzles or preferably added at the end of the 1st stage in the case of countercurrent operation.
• the temperature in the 1st stage of component B) is limited by the melting point of component A). For a procedure with DMT as ester, this is less than / equal to 140 ° C, preferably 140-50 ° C, and in particular 136-60 ° C, and very particularly preferably 124-110 ° C.
• the upper value of the temperature is limited by the boiling point of the diol used in each case.
• the temperature of the purification stage is preferably below 237 ° C, preferably below 227 ° C.
• the temperature is below 198 ° C, preferred wise 190 ° C, with propanediol temperatures below 213 ° C, preferably 200 ° C are recommended.
• 1,4-butanediol as well as 1,4-butanediol loaded with DMT
• the 1, 4-butanediol can be brought into contact with the gas both in a single pass and in a recirculation mode.
• Gas and liquid phases can be applied at any point in the apparatus which corresponds to the principle described above.
• the principle of the method can simultaneously be extended to a three-stage and multi-stage mode of operation.
• the pressure in the 1st stage is usually from 1013 mbar (ambient pressure, normal pressure) to 1113 mbar, preferably from 1013 to 1083 mbar (for tank storage).
• DMT is converted from the gas phase into the liquid detergent (dihydroxy compound) by the treatment.
• the gas stream When leaving the 1st stage, the gas stream contains 0.01 to 1000 ppm by weight of DMT, preferably from 1 to 50 ppm by weight of DMT.
• the liquid stream of the dihydroxy compound B) contains 0.01 ppm by weight to 59% by weight, preferably from 0.1 ppm by weight to 10% by weight of DMT when it leaves the 1st stage.
• the gas stream is cooled in a second stage with an aliphatic dihydroxy compound B), it being essential that work is carried out above the melting point of component B) in this stage.
• the temperature is accordingly for 1,4-butanediol greater than 19 ° C, preferably from 20 to 80 ° C and in particular from 50 to 70 ° C, with ethylene glycol and propanediol the melting points are -10 ° C and -32 ° C, respectively that a way of working with the above Temperature ranges is also recommended.
• the temperature parameters of the method according to the invention are designed such that the actual DMT partial pressure (content in the gas phase) does not exceed the partial pressure of the beginning desublimation.
• the gas flow has a DMT content of 0.001 to 16 ppm by weight, preferably of 0.01 to 1 ppm by weight.
• DMT is kept in a molten state in a tank farm (1) and overlaid with dry inert gas (2) (e.g. nitrogen) to avoid oxidation and water contact.
• dry inert gas (2) e.g. nitrogen
• a DMT-laden gas stream (3) is fed to an absorption column (5) via a heated gas line and a heated gas inlet (4).
• the gas stream is directed towards the gas stream via a distribution device (7), liquid 1,4-butanediol with a temperature of 50 ° C. ⁇ T ⁇ 139 ° C. (depending on degree of saturation).
• DMT is transferred from the gas phase to the liquid detergent.
• the liquid flow (8) is preheated to the inlet temperature via a heat exchanger (9).
• the stream can either be withdrawn from the bottom discharge from column (10) as partial stream (11) with the addition of pure 1,4-butanediol (12) or fed in as pure 1,4-butanediol (12).
• the gas stream depleted in DMT is fed to a second column section (13) which is filled with separating internals and is cooled there by direct contact with a second detergent stream (14) at a temperature of 20 ° C. ⁇ T ⁇ 140 ° C.
• the washing medium stream is fed into the column via a distribution device (15) and temperature-controlled via a heat exchanger (16). Pure 1,4-butanediol (12) and a recycle stream (17) from the bottom discharge (10) of the absorption column can be used as the detergent stream.
• the cleaned carrier gas stream (18) leaves the apparatus overhead.
• the valuable substance DMT is returned to the PBT process in a process solvent and the overall yield based on DMT is improved.
• the return of the DMT can be done without additional Processing steps take place directly in the esterification reactor, in which DMT is catalytically esterified with 1,4-butanediol.
• 1,4-butanediol Compared to the already known absorption processes with low-boiling solvents (e.g. methanol), the two-stage gas scrubbing with high-boiling 1,4-butanediol reduces the loss of solvent through the gas discharge from the scrubber. 1,4-butanediol also has a high solubility for DMT, so that no solid precipitates occur from the liquid phase. A circulatory operation of the solvent is therefore possible. The space-time yield is therefore significantly increased in the subsequent polycondensation process for the production of polyesters, in particular polybutylene terephthalate (PBT), PET or PTT.
• PBT polybutylene terephthalate
• Example DMT is stored in a tank farm at a temperature of 170 ° C.
• the gas atmosphere contains 4.8% by weight of DMT and 95.2% by weight of nitrogen.
• a gas flow of 41 kg / h is typically emitted when the tank is emptied.
• the gas stream is passed on a two-stage scrubber with a diameter of 200 mm and washed in the lower section of the apparatus with 370 kg / h of pure 1,4-butanediol at a temperature of 124 ° C. in countercurrent via separating internals.
• the gas is cooled by the countercurrent flow with 125 kg / h of pure 1,4-buttanediol, which has an inlet temperature of 60 ° C, using internals that separate the gas.
• the pure gas stream cooled to 60.15 ° C. is released with a content of less than 0.1% by weight of butanediol and less than 0.2% by weight of DMT.
• gas and liquid have the following compositions at the transition from the lower (hot BD as detergent) to the upper section of the apparatus (cold BD):
• the gas phase has the following composition when it emerges from the apparatus: Phase value DMT 0.2 ppm by weight

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• General Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Gas Separation By Absorption (AREA)

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• 2004
  • 2004-03-19 DE DE102004013967A patent/DE102004013967A1/de not_active Withdrawn
• 2005
  • 2005-03-17 MX MXPA06010479A patent/MXPA06010479A/es active IP Right Grant
  • 2005-03-17 CN CNB2005800083111A patent/CN100448510C/zh not_active Expired - Fee Related
  • 2005-03-17 US US10/593,333 patent/US7959713B2/en not_active Expired - Fee Related
  • 2005-03-17 JP JP2007503290A patent/JP4488251B2/ja not_active Expired - Fee Related
  • 2005-03-17 EP EP05716152.3A patent/EP1727610B1/de not_active Expired - Lifetime
  • 2005-03-17 WO PCT/EP2005/002847 patent/WO2005089905A1/de not_active Ceased
  • 2005-03-17 KR KR1020067021576A patent/KR20060132001A/ko not_active Ceased
  • 2005-03-18 MY MYPI20051187A patent/MY154874A/en unknown

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