WO1993008217A1 - Process for separating cellulose ether and other cellulose derivates - Google Patents

Process for separating cellulose ether and other cellulose derivates Download PDF

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Publication number
WO1993008217A1
WO1993008217A1 PCT/EP1992/002347 EP9202347W WO9308217A1 WO 1993008217 A1 WO1993008217 A1 WO 1993008217A1 EP 9202347 W EP9202347 W EP 9202347W WO 9308217 A1 WO9308217 A1 WO 9308217A1
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WO
WIPO (PCT)
Prior art keywords
cellulose
stage
membrane filtration
concentrate
flocculation point
Prior art date
Application number
PCT/EP1992/002347
Other languages
German (de)
French (fr)
Inventor
Klaus-Dieter Kothe
Uwe Müller
Reinhold Sedelies
Lutz Jeromin
Wilhelm Johannisbauer
Levent YÜKSEL
Horst Götze
Original Assignee
Henkel Kommanditgesellschaft Auf Aktien
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 Henkel Kommanditgesellschaft Auf Aktien filed Critical Henkel Kommanditgesellschaft Auf Aktien
Publication of WO1993008217A1 publication Critical patent/WO1993008217A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B11/00—Preparation of cellulose ethers
    • C08B11/20—Post-etherification treatments of chemical or physical type, e.g. mixed etherification in two steps, including purification
    • C08B11/22—Isolation

Definitions

  • the invention relates to a process for separating cellulose ether and other cellulose derivatives from an aqueous solution / suspension, in particular from the wash water obtained in the purification of raw cellulose ether.
  • the raw products obtained in the production of cellulose ether contain undesirable by-products such as table salt, methanol, glycols, etc.
  • Cellulose ethers which become insoluble when the temperature rises and flocculate, e.g. B. methyl, hydroxypropyl cellulose ether, are cleaned according to the prior art by washing with hot water from the by-products and washed salt-free. Flakes of cellulose derivative are carried away, some of which dissolve in water.
  • the washed cellulose ethers are centrifuges or filters according to the state of the art in a further step Technology pre-dried (EP 0305898 A2 and EP 0 305 899 A2).
  • the cellulose ethers washed out by the hot water wash represent a significant loss of product.
  • Sedimentation tanks can be used for recovery, in which the cellulose derivative flakes are separated. However, microflakes and dissolved cellulose derivative are not retained, so that the clarified overflow of the settling tank still contains product.
  • the invention is based on the object of providing an effective and economical process of the type mentioned at the outset which allows a considerably larger amount of cellulose derivative to be recovered from the wash water.
  • This object is achieved according to the invention in that in a first stage the flocculated cellulose derivative is separated from the solution heated above the flocculation point, the solution obtained is subjected to membrane filtration in a second stage after cooling below the flocculation point and the concentrate obtained heats up the flocculation point and further constricts it and in particular leads it back to the entrance of the first stage.
  • the amount of recyclable material recovered from the wash water can be doubled according to the invention.
  • a considerable reduction in the wastewater pollution, expressed by the COD value, is achieved.
  • part of the undissolved cellulose derivative is first separated off in a settling tank in the first stage and then the remaining part which is still contained in its overflow is separated off. This can be done by a centrifugal separator or by flotation. A practically complete separation of undissolved cellulose derivative is thus achieved. In terms of process technology, it is advantageous if the remaining part of the undissolved cellulose derivatives separated off in the centrifugal separator or in the flotation is returned to the settling tank.
  • the hot wash water obtained during the cleaning of raw cellulose ether first runs into a settling tank 1, in which the majority of the entrained cellulose ether flakes are separated off and returned to the production process at 2.
  • the overflow of the settling tank 1 is conveyed by means of a pump 3 into a hydrocyclone 4, from which the concentrate is conveyed back into the settling tank via line 5.
  • the still hot cleaned water phase of the hydrocyclone is cooled in a recuperator 6 and a further heat exchanger 7 operated with cooling water below the flocculation temperature of the dissolved cellulose ethers.
  • the liquid is then concentrated in a Querstronimen.branfi1trationsstrom, which consists of a membrane module 8, a circulation pump 9 and a pressure pump 10 used for adjusting the operating pressure. Both organic and inorganic membranes can be used, the separation limit being in the nano, ultra or in the microfiltration range.
  • the permeate 11 free of cellulose ether can be channeled.
  • the concentrate is heated in the recuperator 6 and a further heat exchanger 12 via the flocculation temperature and returned to the settling tank 1.
  • the recovered cellulose ether is withdrawn continuously or batchwise from the settling tank 1, worked up and blended with the product. If the wash water of the individual production lines is processed separately, a direct blending without loss of quality of the product is possible. In a simpler embodiment, the washing water is mixed, and the cellulose ethers recovered are processed into a product with lower quality requirements.
  • Table 1 shows an example of the individual COD concentrations and methyl cellulose ether contents.
  • a hydrocyclone and an ultrafiltration membrane made of polyvinylidene fluoride (PVDF) were used as the separation membrane.
  • the solution was concentrated by a factor of 2 in the membrane system.
  • Methyl cellulose content in% by weight 0.405 0.340 0.016 List of reference symbols

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  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Biochemistry (AREA)
  • Materials Engineering (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

A process is disclosed for removing cellulose ether and other cellulose derivates from an aqueous solution/suspension. An effective and economical process that allows a considerably higher amount of cellulose derivate to be recovered from the wash water as in the state of the art, is characterized in that the flocculated cellulose derivates are removed in a first step from the solution heated over the flocculation point, the solution is subjected in a second step to a membrane filtration, after cooling down below the flocculation point, and the concentrate thus obtained is heated over the flocculation point and further concentrated.

Description

Verfahren zum Abtrennen von Celluloseether und anderen Cellulosederivaten Process for the separation of cellulose ether and other cellulose derivatives
Die Erfindung betrifft ein Verfahren zum Abtrennen von Cellulose¬ ether und anderen Cellulosederivaten aus einer wäßrigen Lösung/Sus¬ pension, insbesondere aus dem bei der Reinigung von Rohcellulose- ether anfallenden Waschwasser.The invention relates to a process for separating cellulose ether and other cellulose derivatives from an aqueous solution / suspension, in particular from the wash water obtained in the purification of raw cellulose ether.
Die bei der Herstellung von Celluloseether erhaltenen Rohprodukte enthalten unerwünschte Nebenprodukte wie Kochsalz, Methanol, Gly- cole, usw.. Celluloseether, die bei Temperaturerhöhungen unlöslich werden und ausflocken, z. B. Methyl-, Hydroxypropylcelluloseether, werden nach dem Stand der Technik durch Wäsche mit Heißwasser von den Nebenprodukten gereinigt und salzfrei gewaschen. Dabei werden Flocken von Cellulosederivat mitgerissen, die sich teilweise im Wasser lösen. Die gewaschenen Celluloseether werden in einem wei¬ teren Schritt mittels Zentrifugen oder Filtern nach dem Stand der Technik vorgetrocknet (EP 0305898 A2 und EP 0 305 899 A2). Die durch die Heißwasserwäsche herausgewaschenen Celluloseether stellen einen deutlichen Produktverlust dar. Zur Rückgewinnung können zwar Absetzbecken eingesetzt werden, in denen die Cellulosederivatflocken abgetrennt werden. Mikroflocken und gelöstes Cellulosederivat werden jedoch nicht zurückgehalten, so daß der geklärte Überlauf des Absetz¬ beckens noch Produkt enthält.The raw products obtained in the production of cellulose ether contain undesirable by-products such as table salt, methanol, glycols, etc. Cellulose ethers, which become insoluble when the temperature rises and flocculate, e.g. B. methyl, hydroxypropyl cellulose ether, are cleaned according to the prior art by washing with hot water from the by-products and washed salt-free. Flakes of cellulose derivative are carried away, some of which dissolve in water. The washed cellulose ethers are centrifuges or filters according to the state of the art in a further step Technology pre-dried (EP 0305898 A2 and EP 0 305 899 A2). The cellulose ethers washed out by the hot water wash represent a significant loss of product. Sedimentation tanks can be used for recovery, in which the cellulose derivative flakes are separated. However, microflakes and dissolved cellulose derivative are not retained, so that the clarified overflow of the settling tank still contains product.
Der Erfindung liegt die Aufgabe zugrunde, ein effektives und wirt¬ schaftliches Verfahren der eingangs genannten Art bereitzustellen, das eine erheblich größere Menge an Cellulosederivat aus dem Wasch¬ wasser zurückzugewinnen erlaubt.The invention is based on the object of providing an effective and economical process of the type mentioned at the outset which allows a considerably larger amount of cellulose derivative to be recovered from the wash water.
Diese Aufgabe wird erfindungsgemäß dadurch gelöst, daß man in einer ersten Stufe aus der über dem Flockungspunkt erwärmten Lösung das ausgeflockte Cellulosederivat abtrennt, die erhaltene Lösung in ei¬ ner zweiten Stufe nach Abkühlen unter den Flockungspunkt einer Mem¬ branf ltration unterwirft und das erhaltene Konzentrat über den Flockungspunkt aufheizt und weiter einengt und insbesondere zum Ein¬ gang der ersten Stufe zurückführt.This object is achieved according to the invention in that in a first stage the flocculated cellulose derivative is separated from the solution heated above the flocculation point, the solution obtained is subjected to membrane filtration in a second stage after cooling below the flocculation point and the concentrate obtained heats up the flocculation point and further constricts it and in particular leads it back to the entrance of the first stage.
Gegenüber dem Einsatz eines einfachen Absetzbeckens kann erfindungs¬ gemäß die aus dem Waschwasser zurückgewonnene Wertstoffmenge verdop¬ pelt werden. Außerdem wird eine erhebliche Reduzierung der Abwasser¬ belastung, ausgedrückt durch den CSB-Wert, erreicht.Compared to the use of a simple sedimentation basin, the amount of recyclable material recovered from the wash water can be doubled according to the invention. In addition, a considerable reduction in the wastewater pollution, expressed by the COD value, is achieved.
In einer besonders wichtigen vorteilhaften Ausgestaltung trennt man in der ersten Stufe zunächst einen Teil des ungelösten Cellulose- derivats in einem Absetzbehälter und dann den restlichen, in dessen Überlauf noch enthaltenen Teil ab. Dies kann durch einen Fliehkraft¬ abscheider oder durch eine Flotation erfolgen. Damit wird eine prak¬ tisch vollständige Abtrennung von ungelöstem Cellulosederivat er¬ reicht. Verfahrenstechnisch ist es vorteilhaft, wenn der im Fliehkraftab¬ scheider oder in der Flotation abgetrennte restliche Teil der unge¬ lösten Cellulosederivate zum Absetzbehälter zurückgeführt wird.In a particularly important advantageous embodiment, part of the undissolved cellulose derivative is first separated off in a settling tank in the first stage and then the remaining part which is still contained in its overflow is separated off. This can be done by a centrifugal separator or by flotation. A practically complete separation of undissolved cellulose derivative is thus achieved. In terms of process technology, it is advantageous if the remaining part of the undissolved cellulose derivatives separated off in the centrifugal separator or in the flotation is returned to the settling tank.
Um den Energieaufwand beim Abkühlen und Erwärmen in der zweiten Ver¬ fahrensstufe gering zu halten, wird vorgeschlagen, daß der Zulauf und das Konzentrat der Membranfiltration über einen Rekuperator ge¬ führt werden. Weitere vorteilhafte Ausgestaltungen des Verfahrens sind in den übrigen Unteransprüchen genannt.In order to keep the energy expenditure during cooling and heating low in the second process stage, it is proposed that the feed and the concentrate of the membrane filtration be passed through a recuperator. Further advantageous embodiments of the method are mentioned in the remaining subclaims.
Ein Ausführungsbeispiel des Verfahrens wird im folgenden anhand des schematischen Verfahrensfließbildes in Figur 1 beschrieben. Das bei der Reinigung von Rohcelluloseether anfallende heiße Waschwasser läuft zunächst in ein Absetzbecken 1, in dem der größte Teil der mitgerissenen Celluloseetherflocken abgetrennt und bei 2 wieder in den Produktionsprozeß zurückgeführt wird. Der Überlauf des Absetz¬ beckens 1 wird mittels einer Pumpe 3 in einen Hydrozyklon 4 geför¬ dert, aus dem das Konzentrat über Leitung 5 zurück in das Absetz¬ becken gefördert wird. Die noch heiße gereinigte Wasserphase des Hydrozyklons wird in einem Rekuperator 6 und einem weiteren, mit Kühlwasser betriebenen Wärmeaustauscher 7 unter die Flockungstem- peratur der gelösten Celluloseether abgekühlt. Die Flüssigkeit wird dann in einer Querstronimen.branfi1trationsanläge aufkonzentriert, die aus einem Membranmodul 8, einer Umwälzpumpe 9 und einer zum Einstel¬ len des Betriebsdrucks dienenden Druckpumpe 10 besteht. Es können sowohl organische als anorganische Membranen eingesetzt werden, wo¬ bei die Trenngrenze in Nano-, Ultra- oder im Mikrofiltrationsbereich liegen kann. Das von Celluloseether freie Permeat 11 kann kanali¬ siert werden. Das Konzentrat wird zur Energieeinsparung im Rekupera¬ tor 6 und einem weiteren Wärmeaustauscher 12 über die Flockungstem- peratur aufgeheizt und zum Absetzbecken 1 zurückgeführt. Aus dem Absetzbecken 1 wird der zurückgewonnene Celluloseether kontinuierlich oder absatzweise abgezogen, aufgearbeitet und mit dem Produkt verschnitten. Werden die Waschwässer der einzelnen Produk¬ tionsstränge getrennt aufgearbeitet, ist eine direkte Verschneidung ohne Qualtitätseinbußen des Produkts möglich. In einer einfacheren Ausführungsform werden die Waschwässer vermischt, und die zurück¬ gewonnenen Celluloseether werden zu einem Produkt mit geringeren Qualitätsanforderungen verarbeitet.An exemplary embodiment of the method is described below with reference to the schematic process flow diagram in FIG. 1. The hot wash water obtained during the cleaning of raw cellulose ether first runs into a settling tank 1, in which the majority of the entrained cellulose ether flakes are separated off and returned to the production process at 2. The overflow of the settling tank 1 is conveyed by means of a pump 3 into a hydrocyclone 4, from which the concentrate is conveyed back into the settling tank via line 5. The still hot cleaned water phase of the hydrocyclone is cooled in a recuperator 6 and a further heat exchanger 7 operated with cooling water below the flocculation temperature of the dissolved cellulose ethers. The liquid is then concentrated in a Querstronimen.branfi1trationsanlage, which consists of a membrane module 8, a circulation pump 9 and a pressure pump 10 used for adjusting the operating pressure. Both organic and inorganic membranes can be used, the separation limit being in the nano, ultra or in the microfiltration range. The permeate 11 free of cellulose ether can be channeled. To save energy, the concentrate is heated in the recuperator 6 and a further heat exchanger 12 via the flocculation temperature and returned to the settling tank 1. The recovered cellulose ether is withdrawn continuously or batchwise from the settling tank 1, worked up and blended with the product. If the wash water of the individual production lines is processed separately, a direct blending without loss of quality of the product is possible. In a simpler embodiment, the washing water is mixed, and the cellulose ethers recovered are processed into a product with lower quality requirements.
Die nachfolgende Tabelle 1 zeigt beispielhaft die einzelnen CSB- Koπzentrationen und Gehalte an Methylcelluloseether. Bei diesem Ver¬ such wurde ein Hydrozyklon und als Trennmembran eine Ultra-Filtra¬ tionsmembran aus Polyvinylidenfluorid (PVDF) eingesetzt. Die Lösung wurde in der Membrananlage um den Faktor 2 aufkonzentriert. Die an¬ gegebenen Permeatwerte zeigen deutlich, daß erfindungsgemäß nahezu der gesamte Celluloseether aus dem Waschwasser zurückgewonnen werden können.Table 1 below shows an example of the individual COD concentrations and methyl cellulose ether contents. In this experiment, a hydrocyclone and an ultrafiltration membrane made of polyvinylidene fluoride (PVDF) were used as the separation membrane. The solution was concentrated by a factor of 2 in the membrane system. The permeate values indicated clearly show that, according to the invention, almost all of the cellulose ether can be recovered from the wash water.
Tabelle 1: Waschwasserbelastung nach den einzelnen TrenπstufenTable 1: Wash water load after the individual separation stages
Überlauf des Oberlauf des Permeat Absetzbeckens ZyklonsOverflow of the upper reaches of the cyclone permeate sedimentation basin
Ort der Probenahme 13 14 15 (Fig. 1)Sampling location 13 14 15 (Fig. 1)
CSB in mg/1 13200 10820 6700COD in mg / 1 13200 10820 6700
Gehalt an Methyl- cellulose in Gew.-% 0,405 0,340 0,016 B e z u g s z e i c h e n l i s t eMethyl cellulose content in% by weight 0.405 0.340 0.016 List of reference symbols
AbsetzbeckenSedimentation tanks
Pfeilarrow
Pumpepump
HydrozyklonHydrocyclone
Leitungmanagement
RekuperatorRecuperator
WärmeaustauscherHeat exchanger
MembranmodulMembrane module
UmwälzpumpeCirculation pump
DruckpumpePressure pump
PermeatPermeate
weiterer Wärmeaustauscherfurther heat exchanger
Probenahmesampling
Probenahmesampling
Probenahme sampling

Claims

P ate n ta n s pr ü c h e P ate n ta ns speeches
1. Verfahren zum Abtrennen von Celluloseether und anderen Cellulo- sederivaten aus einer wäßrigen Lösung/Suspension, insbesondere aus. dem bei der Reinigung von Rohcelluloseether anfallenden Waschwasser, d a d u r c h g e k e n n z e i c h n e t, daß man in einer ersten Stufe aus der über dem Flockungspunkt erwärmten Lösung das ausgeflockte Cellulosederivat abtrennt, die erhaltene Lösung in einer zweiten Stufe nach Abkühlen unter den Flockungspunkt einer Membranfiltration unterwirft und das erhal¬ tene Konzentrat über den Flockungspunkt aufheizt und weiter ein¬ engt und insbesondere zum Eingang der ersten Stufe zurückführt.1. Process for separating cellulose ether and other cellulose derivatives from an aqueous solution / suspension, in particular from. the washing water obtained in the purification of raw cellulose ether, characterized in that in a first stage the flocculated cellulose derivative is separated from the solution heated above the flocculation point, the solution obtained is subjected to membrane filtration in a second stage after cooling below the flocculation point and the concentrate obtained heated above the flocculation point and further concentrated and in particular leads back to the entrance of the first stage.
2. Verfahren nach Anspruch 1, d a d u r c h g e k e n n z e i c h n e t, daß man in der ersten Stufe zunächst einen Teil des ungelösten Cellulosederivats in einem Absetzbehälter und dann den rest¬ lichen, in dessen Überlauf noch enthaltenen Teil abtrennt.2. The method of claim 1, d a d u r c h g e k e n n z e i c h n e t that in the first stage, part of the undissolved cellulose derivative in a settling tank and then the rest, the part still contained in its overflow is separated.
3. Verfahren nach Anspruch 2, d a d u r c h g e k e n n z e i c h n e t, daß der restliche Teil des ungelösten Cellulosederivats zum Absetzbehälter zurückgeführt wird.3. The method according to claim 2, so that the remaining part of the undissolved cellulose derivative is returned to the settling tank.
4. Verfahren nach einem der Ansprüche 1 bis 3, d a d u r c h g e k e n n z e i c h n e t, daß der Zulauf und das Konzentrat der Membranfiltration über einen Rekuperator jgeführt werden.4. The method according to any one of claims 1 to 3, that the feed and the concentrate of the membrane filtration are carried out through a recuperator.
5. Verfahren nach einem der Ansprüche 2 bis 4, d a d u r c h g e k e n n z e i c h n e t, daß man als Fliehkraftabscheider einen Hydrozyklon einsetzt. 5. The method according to any one of claims 2 to 4, characterized in that a hydrocyclone is used as a centrifugal separator.
6. Verfahren nach einem der Ansprüche 1 bis 5, d a d u r c h g e k e n n z e i c h n e t, daß bei der Membranfiltration das Volumenverhältnis von Konzen¬ trat zu Permeat im Bereich von 0,5 bis 5, insbesondere bei etwa 1 liegt.6. The method according to any one of claims 1 to 5, so that the volume ratio of concentrate to permeate is in the range from 0.5 to 5, in particular approximately 1, in membrane filtration.
7. Verfahren nach einem der Ansprüche 1 bis 6, d a d u r c h g e k e n n z e i c h n e t, daß eine Querstrom-Membranf ltra ion vorgenommen wird.7. The method according to any one of claims 1 to 6, d a d u r c h g e k e n n z e i c h n e t that a cross-flow membrane filtration is carried out.
8. Verfahren nach Anspruch 7, d a d u r c h g e k e n n z e i c h n e t, daß eine Ultrafiltrationsmembran aus Polyvinylidenfluorid eingesetzt wird. 8. The method according to claim 7, d a d u r c h g e k e n n z e i c h n e t that an ultrafiltration membrane made of polyvinylidene fluoride is used.
PCT/EP1992/002347 1991-10-19 1992-10-12 Process for separating cellulose ether and other cellulose derivates WO1993008217A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DEP4134662.9 1991-10-19
DE19914134662 DE4134662A1 (en) 1991-10-19 1991-10-19 METHOD FOR SEPARATING CELLULOSE ETHER AND OTHER CELLULOSE DERIVATIVES

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0632056A1 (en) * 1993-06-14 1995-01-04 The Dow Chemical Company Purification of aqueous reaction or washing medium containing cellulose ethers
WO1995025127A1 (en) * 1994-03-14 1995-09-21 The Dow Chemical Company Process for recovering cellulose ethers from an aqueous medium containing such cellulose ethers

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ATE336515T1 (en) * 2001-02-28 2006-09-15 Hercules Inc METHOD FOR SEPARATING CELLULOSE ETHER FROM AQUEOUS SOLUTIONS USING ULTRAFILTRATION WITH ENHANCED SHEAR EFFECT

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0136518A2 (en) * 1983-09-05 1985-04-10 Hoechst Aktiengesellschaft Process for the purification of aqueous distillation residues obtained during the treatment of liquids in the preparation of cellulose ethers
EP0305898A2 (en) * 1987-09-02 1989-03-08 Henkel Kommanditgesellschaft auf Aktien Process for the isolation and purification of cellulose ethers and other derivatives of cellulose

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0136518A2 (en) * 1983-09-05 1985-04-10 Hoechst Aktiengesellschaft Process for the purification of aqueous distillation residues obtained during the treatment of liquids in the preparation of cellulose ethers
EP0305898A2 (en) * 1987-09-02 1989-03-08 Henkel Kommanditgesellschaft auf Aktien Process for the isolation and purification of cellulose ethers and other derivatives of cellulose

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
ULLMANNS ENZYCLOP[DIE DER TECHNISCHEN CHEMIE, 4. AUFLAGE Bd. 9, 1975, Seiten 192 - 212 K. BALSER & M. ISERINGHAUSEN 'Cellulose{ther' *

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0632056A1 (en) * 1993-06-14 1995-01-04 The Dow Chemical Company Purification of aqueous reaction or washing medium containing cellulose ethers
US5482634A (en) * 1993-06-14 1996-01-09 The Dow Chemical Company Purification of aqueous reaction or washing medium containing cellulose ethers
WO1995025127A1 (en) * 1994-03-14 1995-09-21 The Dow Chemical Company Process for recovering cellulose ethers from an aqueous medium containing such cellulose ethers

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