DE4112849A1 - Purification of cellulose ether(s) from suspension - by sepn. and purification on sequential pressure filter - Google Patents

Abstract

A process for sepg. cellulose ethers (I) from suspensions of (I) and purifying the sepd. (I) is carried out with the aid of a sequential pressure filter. The suspension is an aq. suspension or a suspension contg. organic solvent (II); (I) is purified with an aq. or solvent-contg. wash liq. (opt with a solvent other than (II)), pref. in several stages; purificn. is carried out with a liq. from previous purificn. of another batch of prod., which contains, but is not satd. with salts or by-prods.; the filter cake is treated with steam after each sepn. or purificn. stage; sepn. and purificn. are carried out at 10-150 (pref. 60-120) deg.C under pressure; moisture is removed from the filter cake by passing in air or nitrogen; the pressure filter has several chambers in which the direction of filtration is constantly reversed every time the chamber is loaded with the next batch of prod. on the moving belt. USE/ADVANTAGE - Provides a process for the sepn. and purificn. of (I) obtd. in suspension by etherification of cellulose with, e.g. MeCl, EtCl, ethylene oxide, etc.; it enables sepn. and purificn. of (I) with a high coagulation pt. without blocking the filter medium and without high prod. losses due to cleaning the filter medium or to prod. coming through the filter.

Description

The invention relates to a method for separating Cellulose ethers from a cellulose ether suspension with subsequent cleaning using a pressure filter.

Cellulose ethers are usually water-soluble polymers, by the reaction of pulp with a Etherification reagent under the influence of alkali hydroxide in Presence of a humidifier or suspending agent or an excess of the etherification reagent as Humidifying or suspending agents are manufactured. On an industrial scale, preference is given to methyl chloride, Ethyl chloride, ethylene oxide, propylene oxide, chloroacetic acid used as etherification reagent.

Cellulose ethers are used as thickeners, water retention agents, Film formers, viscosity generators in a large number of contain different products and have despite low use concentration has a decisive influence on their application properties. In Depending on the area of application, some become high Requirements for the purity of cellulose ethers. An essential step in cellulose ether production is therefore their cleaning of the during Manufacturing process by hydrolysis of the reagents and by Neutralization of the alkali hydroxide formed By-products and salts or from those already in the pulp contained natural accompanying substances of cellulose.

Depending on the type of etherification and the amount of Degrees of substitution are products with a different temperature dependence of the dissolving behavior  obtained in aqueous media, whereupon the implementation of the Cleaning must be coordinated. On cellulose ethers that any temperature are soluble in water, cleaning will with a solvent / water mixture in which they are not solve, accomplished. Made from cellulose ethers, which are used for increased Have a flocculation point, as is the case with Methyl celluloses and methyl cellulose mixed ethers the case is, by-products are conveniently with hot water at a temperature above the flocculation point carried out.

The cleaning process is usually technically complete Preparing a suspension of the raw cellulose ether in hot water and subsequent separation of the suspension in Solid and decantate carried out. By repeated Apply hot water and separate again liquid phase, the desired purity of the Reach cellulose ether. Technically, the separation of the Suspension generally running continuously Screen centrifuges or solid bowl centrifuges carried out, including a post-wash step in the centrifuge itself is possible, such as in the US patent 33 72 810 is described.

The ones that often occur during suspension separation Problems have different causes.

So thermoplastic cellulose ethers in the Separating units mechanically stressed and form under the Exposure to shear forces on the high-speed machine parts, which makes it Deterioration of the separation performance, due to bearing damage Unbalance and in the event of insufficient rinsing for thermal Product damage is coming.

One has these disadvantages by using one trying to overcome batch filter  as in European patent application 01 94 877 is described. Here, through repeated use the washing liquid from previous batches Washout losses kept low. The separation of the liquid and solid phase as well as the washing process can in a vertical cylindrical filter apparatus or a horizontal cylinder, in the latter case the pressure difference acting as the driving force Centrifugal forces can be generated.

A disadvantage of a filter arrangement, however, is that it easily glued, because fine product particles get into the Place gaps between the filter cake and adhere there, see above that the filtration process in the following Filtration steps comes to a standstill. That can only be done by intensive backwashing and blowing free of the filter fabric be met. In the European patent application 03 26 939 becomes a rotary pressure filter for this purpose used, the filter medium consisting of four layers owns. Its cleaning is done with steam, Compressed air or pressurized water.

The one in the European patent application 03 05 899 described process for cleaning cellulose ethers an inverted centrifuge. It is stated that the Filter cloth by spinning the filter cake without Residues of the adhering product remain, but that is Unit can only be used for cellulose ethers whose Flock point is below 95 ° C.

That in the European patent application 03 05 898 In contrast, described candle filters can be up to Temperatures of 130 ° C are operated, and is therefore for the cleaning of cellulose ethers with high flock points suitable. But this device also has technical features Disadvantage. So is the formation of an even one Filter cake problematic. To achieve this, the must  filtering suspension are often pumped in a circle, which results in unnecessarily increased batch times. Furthermore, neither the suspension to be filtered, still the washing liquid completely through the filter medium be pressed. Since this is in the upper part of the Filter housing must always have liquid residues over complicated interconnections of the pipelines will. Furthermore, in this apparatus, too Backwashing the filter medium with nitrogen, air, steam or water necessary.

There is therefore still a need for one Process that does not have the disadvantages mentioned above and the separation and purification of cellulose ethers with high flocculation point without the filter medium sticking and without high product losses by cleaning the filter medium or penetration of the product allowed.

The invention thus relates to a method for Separation and purification of cellulose ethers from one Cellulose ether suspension, the separation and Cleaning with the help of a cyclical Pressure filter is made.

A pressure press filter suitable for carrying out the method is shown in FIGS. 1 to 3, with FIG. 1 showing an overall diagram, FIGS. 2 and 3 showing enlarged detailed representations. Such a pressure filter or a filter chamber of such a pressure filter consists of two plates ( 1 ) and ( 2 ), which can be moved vertically against each other with a suitable device (not shown here). Each of these two plates contains a box-shaped recess ( 3 ) or ( 4 ) on its top or bottom. The depressions ( 4 ) are divided by movable membranes ( 5 ) which are anchored in the walls which delimit these depressions.

Both plates ( 1, 2 ) of such a pressure filter are arranged so that the recess ( 3 ) of one plate ( 1 ) connects to the recess ( 4 ) of the other plate ( 2 ) and thus form a filter chamber. These abutting parts are designed so that there is a movable filter cloth ( 6 ) between them. In addition, the plates each have a channel ( 7 ) following the recess ( 3 ) for draining off the filtrate and a channel ( 8 ) or ( 9 ) each on the underside or top of the membrane ( 5 ) following the recess ( 4 ). Channel ( 8 ) is used to supply the cellulose ether suspension and channel ( 9 ) is used to supply a medium (e.g. air or water) to generate the pressure on the membrane.

In practice, one works with units that not only contain a filter chamber, but one combines a larger number of plates ( 1, 2 ) according to FIG. 1, the plates always being arranged in such a way that the respective depressions ( 3 ) and ( 4 ) the plates form a filter chamber which is divided into three parts by the filter cloth ( 6 ) and the membrane ( 5 ). In such a pressure filter, the filter cloth ( 6 ) is designed as an endless circulating belt and is routed through the filter chambers in cycles. At the beginning and at the end of each filter chamber there are deflection elements ( 10 ) for the filter cloth outside the plates ( 1, 2 ) from which the filter chamber is formed. At these points, wipers ( 11 ) are attached, which wipe the filter cake ( 12 ) from the filter cloth ( 6 ). The fact that the filtering direction on the filter cloth reverses when the filter cloth runs into the next filter chamber results in a self-cleaning effect and counteracts the risk of the filter cloth sticking together. In this way, one and the other side of the filter cloth ( 6 ) carries the filter cake ( 12 ) alternately. The revolving filter cloth can be rinsed off after leaving the last filter chamber at ( 20 ), so that for many filtrations and washing cycles there is only one cleaning step of the filter medium before it is led again into the first filter chamber.

When the pressure filter is loaded in cycles, all of the plates are first pressed against one another and the filter chambers are thus formed. The possibly hot suspension of the cellulose ether is then pumped into each filter chamber through the channel or line ( 8 ) and filtered through the filter cloth ( 6 ) until an optimal layer thickness (filter cake 12 ) of cellulose ether has formed on the filter cloth. Then in a second step through the channel or line ( 9 ) an optionally preheated medium such. B. hot water, wherein the movable membrane ( 5 ) compresses the cellulose ether on the filter cloth ( 6 ). Surprisingly, despite the high contact pressure, the product does not stick to the filter cloth. The pressing process dehumidifies the cake ( 12 ) and thus a large part of the by-products to be removed are discharged with the filtrate through the channels or lines ( 7 ), so that only a small amount of washing liquid has to be used in the subsequent washing process.

For this purpose, the pressing of water through the channel ( 9 ) is ended and washing water is passed through the channel or lines ( 8 ) onto the filter cake ( 12 ). The filter cake ( 12 ) with the membrane ( 5 ) is then pressed again. If necessary, the washing and pressing process can be repeated.

The filtrate during pressing in the first stage and the washing water from the subsequent cleaning stages are removed from the filter chambers through the channel or lines ( 7 ) and fed to a container ( 21 ) with a pressure control valve ( 22 ).

If several washing cycles are planned, it is recommended that to start the washouts with washing liquid that from the previous cleaning of another batch of product already loaded with salts and by-products, but not is saturated, and only then pure washing liquid  to be used, which in turn is used for pre-washing the subsequent product batch is used.

For cleaning cellulose ethers that do not Have a flocculation point in water Solvent / water mixture used, whose Composition on the dissolving properties of each Cellulose ether is matched. So for Carboxymethyl cellulose as the organic component is preferred Methanol, ethanol or isopropanol are used. For Hydroxyethyl cellulose has acetone, isopropanol and tert-butanol or mixtures of the aforementioned components proven.

A solvent / water mixture can also be used for washing out are used, whose organic component differs from the solvent that differs in the manufacture of the Cellulose ether was used. By pressing well and an intermediate application of water vapor becomes a Mixing the different solvents on one Minimum reduced.

Methyl cellulose, methyl hydroxyethyl cellulose, Methyl hydroxypropyl cellulose, hydroxypropyl cellulose, Hydroxypropyl hydroxyethyl cellulose, Ethyl hydroxyethyl cellulose, ethyl cellulose have one Flock point in water, the height of which depends on the degree of etherification and ratio of degrees of substitution with different substituents is determined and also at Temperatures can be above 100 ° C.

The washing out of such cellulose ethers takes place on cheapest in hot water at temperatures that are clear lie above the flocculation point of the cellulose ether instead. With the washout temperature approaching the flocculation point of the Cellulose ether increases the risk of dissolving and Gluing the product. It is therefore advisable to work as high as possible.  

This is used in the method according to the invention a pressure filter. Except that the device can be heated as such and through the press membranes Loading with a heated pressure build-up Liquid can be kept at a high temperature Products that tend to stick or paste, before the washing process by steam application (condition) in the filter chamber of the cake be heated.

If the flocculation point of the cellulose ether is above 90 ° C, it is advisable to carry out cleaning at temperatures above 100 ° C. In such a case, work is carried out above a pressure predetermined by the vapor pressure of the water. This can be accomplished in a simple manner by means of a corresponding pressure holding device ( 22 ) in the filtrate collecting line behind the filtrate collecting vessel ( 21 ).

When loading the filter medium under pressure, through the Apply hot water to the filter cake and through the membrane pressure will then overcome pressure maintenance and the mother liquor or the washing liquid from the Cake removed. Depending on the pressure specification of the pressure maintenance can be used in commercially available devices Achieve temperatures up to 200 ° C.

Since the flock temperature of cellulose ethers other than that of Substitution criteria listed above also from Electrolyte content of the surrounding aqueous medium in the Way that the flock temperature increases with increasing Electrolyte concentration drops, it is often the case that the separation of the saline mother liquor from the Reaction of cellulose ether production at normal pressure and Temperatures below 100 ° C can be carried out during the subsequent cleaning steps for higher ones Temperatures and must be carried out under pressure.  

If the filter cake ( 12 ) is cleaned sufficiently, compressed air can optionally be injected through the channel ( 8 ) in order to dry the filter cake ( 12 ). Subsequently, the closing device for the plates ( 1, 2 ), which form the filter chambers, is released and by further movement of the filter cake ( 6 ) the filter cake is guided onto the deflection members ( 10 ) and stripped there ( 11 ). Fig. 3 shows a filter chamber in the open state. The filter cloth length required for opening is taken from a reservoir ( 18 ) with a dancer roller ( 19 ). Due to the opposite movement of the filter cake ( 6 ), the filter cake ( 12 ) is discharged from filter chamber to filter chamber alternately to the left or right.

The following examples illustrate this marked the use of a pressure filter Process for separating and cleaning cellulose ethers, without the invention being limited to these examples.

It is clear that even with cellulose ethers, the due to their low viscosity or high Flock point difficult to clean by other methods through the use of little washing liquid excellent cleaning effects can be achieved.

Example 1

According to the known method, a Methyl hydroxypropyl cellulose - MHPC - manufactured according to Removal of the used for the reaction Suspending agent had the following values:

Water humidity 31%
Saline content 38%

The salt-containing product was first suspended in hot water at 95 to 100 ° C. (impact ratio 2.7: 1 based on the raw material) and stored in a container ( 23 ) to be operated under pressure. The pulsed pressure filter is charged by means of a pump ( 24 ). The filter cloth of the pressure filter consisted of polypropylene monofilament with an air permeability of 2 m³ / m² min at 1500 Pa.

The following cycle took place on the pressure filter:

• 1. Conditioning the filter chambers with steam (supply line 25 ) for 30 s
• 2. Fill the filter chambers with cellulose ether suspension
• 3. Press the filter cake with the membrane for 3 min at 16 bar
• 4. Condition the filter chambers with steam for 30 s
• 5. Add wash water (supply line 26 ) at 98 ° C in a ratio of 0.55: 1 based on the raw material
• 6. Press the filter cake with the membrane for 3 min at 16 bar
• 7. Open the filter chambers and discharge the filter cake ( 12 )

A residual moisture of 48% was determined for the product discharged at ( 7 ). The residual table salt content was 0.4%. The MHPC had the following product features:
Höppler viscosity (20 ° C, 1.9% solution) 150 mPa · s

Degree of substitution
a) methoxyl 25.8%
b) hydroxypropyl 8.5%

The saline content can be selected by choosing the amount of wash water, the residual moisture by choosing the pressure in a wide range Limits are regulated.  

Example 2

According to known methods Methylhydroxyethylcellulose - MHEC - manufactured according to Removal of the used for the reaction Suspending agent had the following values:

Water humidity 33%
Saline content 36%

The saline product was initially in 95 to 100 ° C. hot water suspended (impact ratio 3.1: 1 based on raw goods) and in one under pressure operating container stocked. The loading of the intermittent pressure filter works as in Example 1. The same filter cloth was used.

The following cycle took place on the pressure filter:

• 1. Condition the filter chamber with steam for 30 s
• 2. Fill the filter chambers with cellulose ether suspension
• 3. Press the filter cake with the membrane for 3 min at 16 bar
• 4. Condition the filter chamber with steam for 30 s
• 5. Add wash water at 98 ° C in a ratio of 2.25: 1 based on raw goods
• 6. Press the filter cake with the membrane for 3 min at 16 bar
• 7. Open the filter chambers and discharge the filter cake

A residual moisture of 39% was determined for the discharged product. After the product had dried, a residual salt content of <0.1% was determined. The MHEC had the following product features:
Höppler viscosity (20 ° C, 1.9% solution) 24 600 mPa · s

Degree of substitution
a) methoxyl 29%
b) hydroxyethyl 2.6%

Example 3

According to the known method, a Methylhydroxyethylcellulose - MHEC - manufactured according to Removal of the used for the reaction Suspending agent had the following values:

Water humidity 40%
Saline content 27%

The saline product was first heated to 110 ° C Suspended water (impact ratio 2.9: 1 based on Raw goods) and in a pressure of 1.4 bar operating container stocked. The loading of the intermittent pressure filter works like in Example 1 (filter cloth as in Example 1).

The following cycle took place on the pressure filter:

• 1. Condition the filter chambers with steam for 30 s
• 2. Fill the filter chambers with cellulose ether suspension
• 3. Press the filter cake with the membrane for 3 min at 16 bar
• 4. Condition the filter chambers with steam for 30 s
• 5. Add wash water at 120 ° C and 2 bar in the ratio 0.9: 1 based on raw goods
• 6. Press the filter cake with the membrane for 3 min at 16 bar
• 7. Open the filter chambers and discharge the filter cake

A residual moisture of 50% was determined for the discharged product. The residual table salt content was 0.3%. The MHEC had the following product features:
Höppler viscosity (20 ° C, 1.0% solution) 13,000 mPa · s

Degree of substitution
a) methoxyl 23.1%
b) hydroxyethyl 9.6%

Example 4

A sodium carboxymethyl cellulose - CMC - was produced by a known method. The suspension obtained after the reaction and addition of water had the following composition:
CMC 7%, table salt 2%, isopropanol 52%, water 38% and was pumped directly into the intermittent pressure filter. The following cycle took place:

• 1. Fill the filter chambers with cellulose ether suspension
• 2. Press the filter cake with the membrane for 4 min at 14 bar
• 3. Add an isopropanol / water mixture, which at Squeeze one after the second washing step previous product batch was obtained in Ratio 7: 1 (based on the product)
• 4. Press the filter cake with the membrane for 4 min at 14 bar
• 5. Add an isopropanol / water mixture, which at Squeeze one after the third washing step previous product batch was obtained in Ratio 7: 1
• 6. Press the filter cake with the membrane for 4 min at 14 bar
• 7. Add an isopropanol / water mixture (60:40) in a ratio of 7: 1
• 8. Press the filter cake with the membrane for 4 min at 14 bar  
• 9. Feeding water vapor for 4 min
• 10. Open the filter chambers and discharge the filter cake

A residual moisture of 41% was used for the discharged product certainly. The residual table salt content was 0.4%.

The CMC had the following characteristics:
Höppler viscosity (20 ° C, 2% solution) 26 mPa · s
Degree of substitution 0.76

Claims (10)

1. A process for the separation of cellulose ethers from a cellulose ether suspension and purification of the separated cellulose ethers, characterized in that the separation and purification is carried out with the aid of a pressure filter which operates in cycles. 2. The method according to claim 1, characterized in that the separation from an aqueous or a suspension containing organic solvent. 3. The method according to claim 1, characterized in that cleaning with the help of an aqueous or washing liquid containing organic solvents is made, the solvents differ from those in the suspension separated in the previous step can distinguish. 4. The method according to claim 1, characterized in that the cleaning is carried out in several stages. 5. The method according to claim 1, characterized in that when cleaning one from a previous one Cleaning step obtained with another batch of product Salts or by-products loaded but not saturated Liquid is used. 6. The method according to claim 1, characterized in that the filter cake after the separation or Steam is applied to cleaning steps. 7. The method according to claim 1, characterized in that the separation or cleaning at a temperature between 10 and 150 ° C, preferably between 60 and 120 ° C.   8. The method according to claim 1, characterized in that the separation or cleaning is carried out under pressure becomes. 9. The method according to claim 1, characterized in that the filter cake by adding air or nitrogen is dehumidified. 10. The method according to claim 1, characterized in that a pressure chamber consisting of several chambers is used in which the Filtration direction with the following loading reverses the next batch of product.