SI9111803A - Process for purifying aqueous solutions of N-methylmorpholine-N-oxide - Google Patents

Abstract

To clean aqueous solutions of N-methylmorpholine-N-oxide, especially spinning bath solutions, the solutions according to the invention are brought into contact with adsorbents and then submitted to filtration. Aluminium oxide, silicon oxide or charcoal are used preferentially as adsorbents. A reasonable grain size of adsorbents amounts to less than 0,15 mm. The presence of adsorbents make easy the filtration of substances which cause turbidity, and besides discolouration results in elimination of metallic salts.

Description

LENZING AKTIENGESELLSCHAFT

Process for the purification of aqueous N-methylmorpholine-N-oxide solutions

The invention relates to a process for the purification of an aqueous N-methylmorpholine-Noxide (NMMO) solution, in particular a spinning bath solution, which is formed in the preparation of cellulose products.

Cellulose is known to be introduced into aqueous NMMO solutions and to prepare spinning homogeneous cellulose solutions. By coloring these solutions in water, they obtain foils, fibers or molds based on cellulose, that is, objects that are now largely prepared by the process of viscous fibers. However, in view of the environmental portability of the pulp in aqueous NMMOs, the crucial advantage is that the NMMOs can be recovered from the spinning bath without the addition of sulfur-containing emissions.

In order that NMMOs contained in the used spinning bath can be used for the reconstitution of spinning cellulose solutions, the spinning bath solution must be cleaned and concentrated.

Complete cleaning should include the following steps:

A) discoloration:

By evaporation of water due to the concentration of NMMOs from dilute aqueous NMMO solutions, strong yellow to brown coloration occurs on the basis of NMMO reactions with the cellulosic degradation products.

In particular, pigment compounds are formed from polyhydroxyphenols, from the cellulose degradation products themselves, and from NMMO stabilizers, which are usually added to the solution.

Due to the increasing discoloration of NMMOs, cellulose molders can no longer be whitened to the desired bleaching rate.

B) Transition metal removal:

Transition metals, in particular iron, are introduced into the process cycle, on the one hand, with the amount used, and on the other, by corrosion. The content of transition metal ions, however, is critical in that it lowers the initial temperature for the deflagration of the spinning mass. When used as a galiperic acid propyl ester stabilizer, anionic metal complexes are formed that can be removed by anion exchangers. However, if they use, for example, a stabilizer. routines are formed by iron complexes that are no longer removable by ion exchangers. Therefore, without the purification of NMMOs in the management cycle, the enrichment of iron in the process would inevitably lead to an increase in safety risk. Therefore, the removal of iron and other transition metal ions from the process is absolutely necessary.

C) Nitrosamine removal:

Nitrosamines may be present in fresh NMMOs - subject to its preparation; they can cause a variety of different toxic effects, such as. acute liver damage, genetic toxicity both in vitro and in germs

2) cells, cancers in somatic cells, etc. On the basis of the overall effect of nitrosamines on tumor initiation, insistence on complete removal of these should be insisted on for safety reasons.

D) Removal of opacifiers:

In addition to coloring the spinning bath, a precipitate may be formed, consisting mainly of the finest cellulose matter. In addition, alkali or alkaline earth alkali salts are also present. These opaque substances, which are also enriched by repeated use of the solvent, cannot be filtered without the auxiliary; these affect the quality of the product, leading to disruption eg. in inline color measurement and should therefore be removed.

It should be further noted at the above mentioned cleaning steps that the loss of NMMO should be avoided as far as possible.

The methods of cleaning known so far utilize both of the following methods with basic disadvantages:

a) Anion exchanger cleaning

In this method, the discoloration is limited to ionic color complexes: iron or transition metals can only be removed if they are in ionic form, which depends, among other things, on the stabilization system; nitrosamines cannot be removed; it is also not possible to mention fine cellulose precipitate removal; relatively large amounts of regeneration chemicals are required.

b) Recrystallization from acetone

This method is very time consuming and energy consuming; moreover, NMMO recoveries are only a maximum of 85%.

According to the invention, these disadvantages can be avoided by contacting the solution with adsorption agents and then filtration. Particularly preferably aluminum oxide, silica and / or charcoal can be used as the adsorbing agent.

h

By the process of the invention, at least 70% solution discoloration, practically quantitative removal of the transition metals, complete removal of nitrosamines as well as removal of fine cellulose precipitate are possible;

further, the purified solution is completely free of any opacities;

a further substantial advantage of the process of the invention is that there is virtually no loss of amino acid.

The following warnings are used to explain the process:

i) We use A1 ₂ O ₃ types C of the Degussa factory. The amount used is calculated on a 20% spinning bath of about 1%. The retention time is a few minutes. The adsorption agent can be decided together with the substances which cause turbidity by simple filtration. The subsequent rinsing of the NMMO filter cake completely reverses.

ii) The silica of the Degussa plant with the designation FK 700 is used. The amount used is 1% calculated on 20% aqueous NMMO. The retention time is a few minutes and the separation of SiO ₂ together with the opacifiers is carried out by filtration.

iii) Use powdered charcoal (brown or black coal) with an average grain size of 0.15 mm. The decisive factor in this case is the grain size of the charcoal used and thus the surface available for cleaning.

The use of charcoal is between 0.1% and 1% depending on the amount of spinning bath, depending on the degree of contamination of the spinning bath, the desired cleaning effect and the size of the activated carbon surface. The retention time takes an average of several minutes.

Normal filtration for the separation of coated charcoal is heavily influenced by, for the first time, smaller traces of the cellulose precipitate present, since they greatly increase the pressure loss on the filter even after the shortest filtration time and, second, in the spinning bath, which cause opacities. We therefore propose the following methods for the separation of charcoal:

- cell filtration

- leachate filtration, or

- overnight microfiltration.

F

In addition, the following must be observed individually:

Cell filtration as a filter aid.

Since even the smallest traces of the finest charcoal particles drastically reduce the whiteness of the pulp molds, the separation of the coated charcoal must be complete. This is also a guarantee that the substances that cause turbidity are largely removed.

Both the fine-cellulose precipitate in the NMMO spinning bath and the finest charcoal particles lead, after the shortest filtration time, to a severe loss of pressure on the filter. For this reason, we need to find a porous filter layer that is permeable to aqueous NMMO but retains the fine substances described above.

This task is solved by breaking the leaf cell with a mixer in water (to obtain fibers) and then floating on a moderately coarse metal sieve. When a thick cellulose layer is obtained, the charcoal can be completely removed from the suspension. Subsequent rinsing with VE water (i.e. completely demineralised water) allows NMMO to be washed out without loss from the filter bed.

Flood filtration

A porous filter layer is also obtained if the charcoal in the form of a thick charcoal / water suspension is floated directly to e.g. standing filter candle. The solution of the spinning bath to be cleaned can then be led to the wear of the charcoal through this layer, taking care not to cause turbidity caused by the finest charcoal particles in this guiding method. Once the charcoal cleaning effect is exhausted, the amino acid can be completely washed out of the charcoal layer by subsequent rinsing with VE water. A standing filter candle also offers the advantage that, in order to minimize the amount of rinse water, the amine oxide can be discharged before the rinse cycle, thereby preventing the formation of a mixed zone when flushing the charcoal. Before drying the charcoal blower to raise the heating value, the flushing water is drained again. If the discharge of the respective liquids retains the pressure difference between the carbon layer outside and the filter candle inside, this allows the carbon layer to be retained even when the media is exchanged.

Precision microfiltration

First, the suspension of the carbon spinning bath is placed in a cross-section microfiltration (QMF) presentation container. Thereafter, a continuous determination of the purified spinning bath as the QMF permeate takes place. The charcoal slurry with a strongly concentrated volume (retentate) is then dried through chamber filter presses. We then rinse the charcoal with VE water in a chamber filter press to make it NMMO free. By blowing air, the charcoal can be further drained to increase its heating value. The charcoal can either be heated or regenerated for new use.

For example, they are suitable for regeneration. the following regenerating chemicals: sodium hydroxide, sodium hydroxide / ethanol, ammonia / methanol, ammonia / propanol-2 and / or ammonia / acetone.

The charcoal to be regenerated was suspended in the regeneration solution after complete elution of NMMO and then filtered off. After neutral rinsing, it can then be used again to purify the aqueous NMMO solution.

The following analytical methods are used to test the cleaning effect of individual process variants:

discoloration: by extinction measurement at 470 nm with a Perkin-Elmer photometer iron content: by atomic absorption and X-ray fluorescence measurements opacity (induced by fine-cellulose precipitate): by the ophthalmic meter of the TRM-L factory Drott nitrosamines: by gas chromatographic determination evidence by TEA of the Thermo Electron factory. The test is performed with N-nitrosomorpholine and dimethylnitrosamine.

The following embodiments show further details of the process of the invention.

EXAMPLE 1:

Using aluminum oxide as an adsorbing agent ml of the NMMO spinning bath was mixed with 0.5 g aluminum oxide (i.e. 0.1% relative to the spinning bath) in a glass beaker and then allowed to stand for 30 minutes. The filter was then filtered through a blue strip filter and the filtrate analyzed.

The discoloration effect is 98%, the removal rate is 94%. The opacity reduction is 98%.

EXAMPLE 2:

Using silica as an adsorbing agent, ml of the spinning bath was mixed with 0.5 g of silica and filtered through a blue tape filter after half an hour. The filtrate is completely clear, up to 72% discolored and the iron content reduced by about 70%.

EXAMPLE 3 TO 8:

Use of coal as adsorption agent

EXAMPLE 3:

g of brown coal coke powder are suspended for 2 minutes in a 100 ml spinning bath. The suspension was filtered through a glass fitt. 3 (15 cm ^{2 of the} filter surface) to which the blue ribbon filter is placed and measure the extinction of the filtrate at 470 nm.

Extinction: Spin bath outlet: 0.608 Spin bath cleaned: 0.095

Discoloration effect: 85%

Turbidity: Spin bath outlet 16.3 FTU Spin bath purified 0.2 FTU diminutive opacity 98.8% (FTU = formazine unit of opacity; formazine is a calibration substance)

EXAMPLE 4:

Filter over 100 g of coke powder each time with 100 ml of spinning bath (extinction)

0.413) and determine the filtrate extinction.

The table shows the relationship between the amount of coal used and its discoloration effect.

Coal / spinning ratio Extinction 470 nm Discoloration % 1:40 0.042 90 1:80 0,092 78 1: 120 0,138 67 1: 160 0.175 57 1: 200 .208 49 1: 240 0.255 38 1: 280 0.283 31 1: 320 0.318 22

The turbidity reduction is in all cases over 95%, but the filtration duration in the test series increases 10-fold.

EXAMPLE 5:

200 ml of spinning bath (20.6% NMMO) was filtered through 27.37 g (= 50 ml) of dry coke powder. 48.52 g of a wet coke powder are obtained; this corresponds to a quantity of NMMO of 4.45 g.

The wet coal is subsequently washed 4 times with 50 ml of VE water each time and the NMMO content of the individual wash water fractions determined.

NMMO (%) NMMO (g) 1. Flushing water fraction 6,8 3,40 2. Flushing water fraction 1.6 0.80 3. Flushing water fraction 0.4 0.20 4. Flushing water fraction 0.1 0.05 Sum 4,45

EXAMPLE 6:

FeCl ₃ .6H ₂ O was added to the aqueous NMMO solution and the iron removal was then measured at different coal quantities. The extinction of the starting material at 470 nm is 0.682, the iron content is 33.5 ppm, the opacity is 20.3 FTU.

Amount of coal Extinction Discoloration Fe Removal Fe Clarity % 470 nm % ppm % % 0.2 0.081 88 3.1 90.7 96.3 0.5 0.031 95 1.5 95,5 97.1 1.0 0.020 97 1,2 96.4 97.8 2.0 0.009 98 1.1 96.7 98.0

EXAMPLE 7:

kg of coke powder was dispersed in 200 ml of 1 times used spinning bath (20.7% NMMO) for 5 minutes. A 5 μ GAF filter (5 1) is used to decide coal. The first filtrate is black in color because of the finest coal particles, but with increasing filtration duration it is always brighter until it is finally as clear as water.

Discoloration on average: 93% Reduced opacity: 97.5%

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EXAMPLE 8:

Suspend 200 g of coal in 1800 ml of VE-water and pour on a standing filter candle (filter area 0,012 m ² ) from the factory of Dr. M. Stamps Fundapack. In total, 44 l is purified, the specific flow decreases during this time from 1250 1 / m ² h to 910 1 / m ² h. The discoloration effect is 96.4%. The opacity reduction is 99% and the iron reduction 96%. To rinse NMMOs, use 3 L of VE water, NMMO being completely washed out of coal. By blowing 71 air, a dry coal content of 62% is reached.

EXAMPLE 9:

Use of activated carbon as an adsorption agent

200 l of the spinning bath (20% NMMO) were mixed in the delivery container of the microfiltration device with 0.5% activated carbon of Chemviron Typ BL and preheated to 50 ° C. The Purolator factory Teflon membrane is used to decide the charcoal and cellulosic fines (starting material: 12 FTU).

Diaphragm overflow: 2 m / s

Pressure difference: 0.2 bar

Permeate flow: 1660 l / m ² / h, falling to 1000 l / m ² / h

Permeate opacity: 0.2 FTU

No NMMO concentration occurs (NMMO concentration of starting material is identical to that of permeate and retentate).

The charcoal slurry was evaporated to 91 corresponding to a concentration of 1:22. The thick charcoal slurry is then dried in a chamber filter press (floating pressure towards the end of 10 bar) and the charcoal cake is washed with VE-water to keep it free of NMMO. Then, by blowing air, the dry carbon content is 59.6%.

Flushing

Floating

Pressure Quantity Pressure Quantity NMMO conc. bar 1 bar 1 % 0.1 0 5.0 0 14,48 0.2 2 7.9 3 7.38 0.4 3 7.5 6 1.37 0.5 4 7.4 9, 0.70 0.7 5 6.5 12 0.48 1.0 6 7.4 15 0.00

1.4 7

3.0 8

10,0 9

EXAMPLE 10:

Regeneration in the sense of Example 9 of activated carbon used

Closer explanation is given to the regeneration of activated carbon, preferably by sodium hydroxide in combination with an organic solvent, in particular acetone; In doing so, we manage to keep the capacity loss after regeneration below 2%.

Use a once used spinning bath with a concentration of 19.8% and activated carbon of the Chemviron factory. For each coating, suspend activated charcoal by intensive stirring in a spinning bath. Charcoal filtration is carried out through a membrane filter (type PA or Versapor). The filter cake is washed with VE-water until neutral and treated in small portions with a regeneration solution. After rinsing to neutral, charcoal is scraped from the membrane and used again.

Comparison of carbon capacity after regeneration with different regeneration solutions:

(amount of charcoal by NMMO: 0.5%).

Charcoal capacity (% of zero value)

Regenerating NaOH / H ₂ O NH ₄ OH / MeOH NH ₄ OH / PrOH NH ₄ OH / acetone solution

Regeneration

1 94.4% 97.4% 97.1% 95.8% 2 89.2% 91.7% 93,4% 93,5% 3 84,2% 95.0% 92.1% 89.5% 4 80.8% 88.9% 89.5% 91.2% 5 75.9% 88.5% 90.3% 6 87.7% 90.2% 7 85.5% 90.7% 8 82,2% 87.8% 9 80.7% 83,9% 10 82.9% 84.9% 11 86.6% 12 86.6% 13 87.7% 14 79.2% 15 80.8% 16 81.0% 17 79.7% 18 75.6% 19 78.5%

FOR

Claims (6)

PATENT APPLICATIONS A process for cleaning an aqueous N-methylmorpholine-N-oxide solution, in particular a spinning bath solution, characterized in that the solution is contacted with adsorption agents and then subjected to filtration. Process according to claim 1, characterized in that aluminum oxide is used as the adsorbing agent. Process according to claim 1, characterized in that silicon dioxide is used as the adsorbing agent. Process according to claim 1, characterized in that charcoal is used as the adsorbing agent. Method according to one of Claims 1 to 4, characterized in that the adsorption agent has a grain size of <0.15 mm. A method according to claim 4, characterized in that the filtration is carried out with the cellulose as an auxiliary filtering agent, or that the filtration is a flooding filtration or a transverse microfiltration.