EP0944418A1 - Procede de cristallisation en suspension - Google Patents

Procede de cristallisation en suspension

Info

Publication number
EP0944418A1
EP0944418A1 EP97952811A EP97952811A EP0944418A1 EP 0944418 A1 EP0944418 A1 EP 0944418A1 EP 97952811 A EP97952811 A EP 97952811A EP 97952811 A EP97952811 A EP 97952811A EP 0944418 A1 EP0944418 A1 EP 0944418A1
Authority
EP
European Patent Office
Prior art keywords
stage
mother liquor
mixture
crystallization
exchange
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP97952811A
Other languages
German (de)
English (en)
Inventor
Rüdiger DROPE
Dieter Grenner
Hartmut Hetzel
Hans-Peter Schal
Gerhard Wegener
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Bayer AG
Original Assignee
Bayer AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Bayer AG filed Critical Bayer AG
Publication of EP0944418A1 publication Critical patent/EP0944418A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C263/00—Preparation of derivatives of isocyanic acid
    • C07C263/18—Separation; Purification; Stabilisation; Use of additives
    • C07C263/20—Separation; Purification
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D9/00—Crystallisation
    • B01D9/0004—Crystallisation cooling by heat exchange
    • B01D9/0013—Crystallisation cooling by heat exchange by indirect heat exchange
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D9/00—Crystallisation
    • B01D9/004—Fractional crystallisation; Fractionating or rectifying columns
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D9/00—Crystallisation
    • B01D9/004—Fractional crystallisation; Fractionating or rectifying columns
    • B01D9/0045—Washing of crystals, e.g. in wash columns
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D9/00—Crystallisation
    • B01D9/0059—General arrangements of crystallisation plant, e.g. flow sheets

Definitions

  • the present invention relates to a method for separating crystallizable organic compounds from a liquid compound mixture by suspension crystallization
  • organic compounds are generally obtained in the form of a compound mixture which, in addition to the desired organic compounds, has significant or predominant proportions of other compounds such as solvents, starting compounds, by-products and / or isomers of the organic
  • the desired organic compound can be separated from the mixture by crystallization.
  • a characteristic of many crystallizable organic compounds is the low solubility of foreign substances, so that crystallization is often the means of choice for the separation.
  • suspension crystallization processes are in particular for water-based systems, such as the removal of water from food liquids from US Pat. Nos. 4,004,886, 4,316,368, 4,430,104 and 4,459 144
  • Known suspension systems for cleaning chemicals in several stages have also been proposed according to US Pat. No. 4,787,985
  • the washing column has the task of completely separating the resulting pure crystal phase from the mother liquor.
  • the crystal slurry is introduced into the column from below, compacted by a tamper designed as a sieve plate, the mother liquor flowing through the sieve plate below and a compacted one above the sieve plate Crystal block forms Above the block, crystals freed from the mother liquor are scraped off, melted and discharged from the block by means of a scraper. A liquid pressure of the melted crystals is maintained above the block that a small amount of the liquid is washed out by the crystal block adhering mother liquor is printed.
  • the purity of the separated crystal phase depends to a large extent on the temperature difference between the melting temperature of the crystals and the temperature of the pulp fed to the washing column
  • Such washing columns can advantageously only be operated up to temperature differences of 5 to max. 10 ° C. between the Kstastaususpension supplied and the melted pure phase
  • Organic compounds generally have very low solubility in one another, so that single-stage suspension crystallization processes are suitable for the separation.
  • the object of the present invention is to provide a method in which the required number of crystallization stages in the suspension crystallization can be reduced.
  • the present invention relates to a process for the separation of organic compounds by single-stage or multi-stage suspension crystallization, each stage consisting of a crystallizer, optionally a recrystallization container and a filter for separating liquid phase from the crystal slurry, the liquid phase separated off in the filter in the respective crystallization Stage is recycled, the crystal slurry is transferred to the subsequent stage or from the last stage to the washing column for complete separation of the mother liquor, and the liquid phase depleted in the compound to be crystallized is discharged from the first stage, the starting compound mixture being behind the last crystallization stage is supplied, which is characterized in that the mother liquor of the crystal slurry from the last crystallization stage is at least partially gradually replaced by the starting compound mixture.
  • the exchange can take place in stages in at least two stages.
  • the exchange is preferably carried out gradually continuously, ie continuously in infinitesimal steps. This can be done in a flow channel with sieves on both sides. Designed walls take place, with the starting compound mixture flowing in through one sieve and, on the other side, mother liquor being drawn off through the other sieve.
  • the flow channel has an annular flow channel which is formed by concentric sieve tubes.
  • a preferred exchange element consists of three concentric tubes, the two inner tubes being designed as sieves. The crystal slurry emerging from the last crystallization stage flows through the middle one Tube, the starting compound mixture is introduced into the outer tube and from the innermost tube
  • the feed of the starting compound mixture and the drain of mother liquor can be exchanged via changeover valves. In this way, the direction of flow through the sieve bores can be reversed and any blockages can be effectively prevented
  • the exchange is preferably carried out in such a way that the mother liquor demanding the crystal slurry is undersaturated with the crystallized compound, ie part of the crystal phase in the mother liquor disappears.
  • the undersaturation is preferably chosen so that 2 to 5% of the crystal phase is dissolved again. This prevents it that caking of crystals occurs in the exchange organ
  • the mother liquor drawn off by the exchange is fed back to the crystallizer in single-stage crystallization processes.
  • the exchange mother liquor is preferably returned to the previous crystallization stage. It is particularly preferably used for the corresponding exchange of mother liquor in the previous stage
  • the process according to the invention is preferably carried out with only one crystallization stage
  • the process according to the invention is particularly preferably used for the isomer separation of isocyanates, in particular for the isomerically pure recovery of 2,4-tolylene diisocyanate or 4,4'-diphenylmethane diisocyanate from the isomer mixtures with 2,6-tolylene diisocyanate or 2,4'-diphenylmethane diisocyanate
  • Toluene diisocyanate is obtained as an isomer mixture containing 80% 2,4-TDI and 20% 2,6-TDI.
  • the liquidus temperature of the mixture is 13.5 ° C.
  • the melting point of the pure 2,4-TDI is 22 ° C. Due to the different reaction behavior when using TDI in the polyaddition reaction for the production of polyurethanes, isomerically pure 2,4-TDI becomes on the one hand and on the other
  • FIG. 1 schematically shows a crystallizer 1, in which heat is removed from the crystal suspension therein via the cooling jacket 2.
  • the cooling jacket 2 is cooled via the cow unit 3.
  • the crystal suspension is fed via line 4 to an exchange container 5, which functions as the first exchange stage for the mother liquor.
  • Via line 6a part of the starting compound mixture, preferably about 40-60%, is fed to the exchange container 5.
  • Filter 7 is used to exchange exchange mother liquor via line 8 returned to the crystallizer 1.
  • a crystal suspension is withdrawn via line 9 from the exchange container 5, the mother liquor of which has a higher concentration ah of the compound to be crystallized than that Crystal suspension emerging from crystallization vessel 1 via line 4
  • the mass flow through line 8 is controlled in such a way that a crystal suspension with good pumpability is present in line 9, ie that the crystal suspension in line 9 has a solids content of 25-35%
  • Starting substance mixture is supplied at a temperature such that after mixing with the crystal suspension supplied via line 4, the mixture is slightly undersaturated.
  • the remaining part of the starting compound mixture is introduced via line 6b into the mixing container 10, into which the crystal suspension from the Exchange container 5 is introduced.
  • the mixing container 10 serves as a second stage for the gradual mother liquor exchange.
  • a filter can be provided at the outlet of the mixing container 10, through which excess mother liquor is separated and returned to the crystallizer 1.
  • the function of the filter is taken over by the washing column 20.
  • the crystal suspension is transferred via line 11 and the hollow axis of the reciprocating piston pump 12 Introduced into the washing column 20 above the sieve plate 13.
  • the reciprocating pump 12 periodically moves the sieve plate 13 upwards, the mother liquor flowing down through the sieve plate 13.
  • Above the sieve plate 13, a compact crystal block is formed due to the movement of the sieve plate the scraper 14 scraped off pure crystals from the crystal block, at least partially melted in the heat exchanger 15 and discharged via the valve 16 in the direction of arrow 17 as a pure crystallizable compound.
  • a part of the melted pure crystallizable compound is returned to the head of the washing column 20 via the pump 18 as a transport medium for the scraped-off crystals.
  • Appropriate adjustment of the valve 16 maintains a pressure in the head of the washing column such that a part of the pure crystallizable compound is used as Washing liquid is printed against the compacted crystal block
  • the mother liquor separated in the washing column is returned to the crystallizer 1 via line 19.
  • Mother liquor depleted in the crystallizable compound is discharged from the crystallizer via filter 22 and line 21.
  • the device according to FIG. 1 is designed to separate 2,4-TDI from an 80% 2,4-TDI. holding starting isomer mixture to obtain a depleted isomer mixture still containing 69% 2,4-TDI, as described above.
  • the exchange container 5 is replaced by the exchange column 5 for continuously gradual mother liquor exchange compared to FIG. 1.
  • the exchange column 5 is described in more detail below.
  • 2 is suitable for the recovery of 2,4-TDI from a starting isomer mixture containing 80% 2,4-TDI with simultaneous recovery of a depleted isomer mixture with 65% 2,4-TDI (discharge via line 21).
  • the entire starting isomer mixture is preferably introduced into the exchange column via line 6a
  • the exchanged mother liquor flowing out of the exchange column 5 is returned to the first stage (I) via line 8 and mixed in the mixing container 40 with the crystal suspensions emerging from the crystallizer 31 in the first stage.
  • Container 40 exiting mother liquor through line 41 becomes excess 47 in the filter
  • the method according to FIG. 3 is particularly suitable for the separation of isomers of diphenylmethane diisocyanate (MDI). Due to the manufacturing process, MDI is obtained as a starting isomer mixture with 90% 4,4'-MDI and 10% 2,4'-MDI, although minor amounts of 2,2'-MDI may still be present. The liquidus temperature of the starting isomer mixture is approx. 36 ° C . The pure 4,4'-MDI has one
  • the isomer mixture to be discharged which is depleted in 4,4'-MDI, still has 55% by weight 4,4'-MDI with a liquidus temperature of 18 ° C. Accordingly, the crystal suspension leaving crystallizer 31 has a temperature of 18 ° C
  • the second crystallization stage 1 is operated at a temperature of 27 ° C. This corresponds to a mother liquor which contains 72% 4,4'-MDI.
  • the mother liquor is introduced into the exchange column 5 via line 4.
  • the starting isomer mixture is added via line 6 90% 4,4'-MDI with one Temperature of 40 ° C initiated in the exchange column 5.
  • An exchanged mother liquor with 76% 4,4'-MDI flows out via line 8.
  • the crystal suspension emerging from exchange column 5 via line 9 has a mother liquor with 80% 4,4'-MDI corresponding to a liquidus temperature of 32 ° C. For every 100 parts of starting isomer mixture fed via line 6, 77.8 parts of pure 4,4'-MDI corresponding to a liquidus temperature of 32 ° C.
  • FIG. 5 shows a mother liquor exchange tube 5 which can be used according to the invention and which consists of three concentric tubes 61, 62 and 63, the inner tubes 61 and 62 being designed as sieve tubes.
  • the crystal suspension coming from the crystallizer flows through the ring channel 64 between the two sieve tubes 61 and 62
  • the starting isomer mixture is introduced into the outer ring channel 65, which enters the ring channel 64 through the sieve tube 62.
  • mother liquor is displaced into the inner sieve tube 61, and is discharged via line 8, which can be switched via the simultaneously switchable valves 66 and 67
  • Direction of flow through the sieve tubes 61 and 62 are reversed, so that a blockage of the sieve openings by periodic switching or by a change in pressure detected in the lines 6 or 8 " triggered switching of a blockage of the Screen openings are counteracted.
  • the mother liquor concentration change in the ring channel 64 caused by the changeover is made more uniform in the mixing container 10 which is connected downstream.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Abstract

L'invention concerne un procédé de séparation de composés organiques par cristallisation en suspension à un ou plusieurs étages, chaque étage consistant en un cristallisoir, éventuellement en une cuve de cristallisation et en un filtre (7) pour séparer la phase liquide de la pâte cristalline. La phase liquide (8) séparée dans le filtre (7) est renvoyée dans chaque étage de cristallisation. La pâte cristalline (9, 11) est transportée jusqu'à l'étage suivant ou est acheminée du dernier étage de traitement jusqu'à la colonne de lavage (20) en vue de la séparation complète de la lessive-mère. Le liquide appauvri en isomère à cristalliser (21) est extrait par éclusage de l'étage, le mélange de composés initial (6a, 6b) étant acheminé derrière le dernier étage de cristallisation. Ce procédé se caractérise en ce que la lessive-mère de la pâte cristalline extraite du dernier étage de cristallisation est remplacée au moins en partie progressivement par le mélange de composés initial.
EP97952811A 1996-12-10 1997-11-27 Procede de cristallisation en suspension Withdrawn EP0944418A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DE19651215A DE19651215C1 (de) 1996-12-10 1996-12-10 Verfahren zur Trennung von kristallisierbaren Isomerenmischungen organischer Verbindungen
DE19651215 1996-12-10
PCT/EP1997/006611 WO1998025680A1 (fr) 1996-12-10 1997-11-27 Procede de cristallisation en suspension

Publications (1)

Publication Number Publication Date
EP0944418A1 true EP0944418A1 (fr) 1999-09-29

Family

ID=7814190

Family Applications (1)

Application Number Title Priority Date Filing Date
EP97952811A Withdrawn EP0944418A1 (fr) 1996-12-10 1997-11-27 Procede de cristallisation en suspension

Country Status (7)

Country Link
EP (1) EP0944418A1 (fr)
JP (1) JP2001506539A (fr)
AU (1) AU5655798A (fr)
BR (1) BR9714138A (fr)
DE (1) DE19651215C1 (fr)
TW (1) TW386987B (fr)
WO (1) WO1998025680A1 (fr)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ES2366729T3 (es) * 2008-10-06 2016-06-09 Huntsman International Llc Procedimiento para la producción simultánea de mezclas diferentes de isómeros de diisocianato de la serie del difenilmetano
EP2398767B1 (fr) * 2009-02-23 2015-05-13 GEA Niro PT B.V. Procédé pour cristalliser et séparer différents isomères de diisocyanate
CN109970604B (zh) * 2019-04-25 2021-03-19 青岛科技大学 一种提纯2,4-甲苯二异氰酸酯的工艺
CN112321560A (zh) * 2020-09-18 2021-02-05 江苏科富恺机械设备有限公司 悬浮结晶连续提纯l-丙交酯的方法及系统

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3777892A (en) * 1971-01-27 1973-12-11 H Thijssen Apparatus for the separation and treatment of solid particles from a liquid suspension
US3872009A (en) * 1971-06-25 1975-03-18 Henricus Alexis Corne Thijssen Apparatus for the separation and treatment of solid particles from a liquid suspension
US4314368A (en) * 1978-10-12 1982-02-02 Decoursey Calvin H Receiver for pulse code multiplexed signals
US4781899A (en) * 1984-07-27 1988-11-01 Intermountain Research & Development Corporation Purification of crystallized solids made via continuous crystallization
DE3703646C2 (de) * 1987-02-06 1995-02-09 Krupp Koppers Gmbh Verfahren zur Gewinnung von p-Xylol mit einer Reinheit von mindestens 99,5 %
US4787985A (en) * 1987-08-25 1988-11-29 Grenco Process Technology B.V. Multi-stage purification unit process
EP0730893B1 (fr) * 1995-03-07 1999-12-08 Waterworks International, Inc. Procédé et appareil de concentration par congélation

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9825680A1 *

Also Published As

Publication number Publication date
TW386987B (en) 2000-04-11
WO1998025680A1 (fr) 1998-06-18
DE19651215C1 (de) 1998-07-09
BR9714138A (pt) 2000-02-29
AU5655798A (en) 1998-07-03
JP2001506539A (ja) 2001-05-22

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