AU620990B2 - Process for the purification of alkali metal metaborate solutions and alkali metal perborate prepared from these solutions - Google Patents

Description

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AUSTRALIA

Patents Act 620990 COMPLETE SPECIFICATIO1

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority C Cr o oc Cr rIC C Related Art: Ap 5 ,.l.icant(s) Interox (Societe Anonyme) Rue du Prince Albert, 33, B-1050 Brussels, BELGIUM

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Address for Service is: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Complete Specification for the invention entitled: PROCESS FOR THE PURIFICATION OF ALKALI METAL METABORATE SOLUTIONS AND ALKALI METAL PERBORATE PREPARED FROM THESE SOLUTIONS Our Ref 173832 POF Code: 1659/4711 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 600- 1 6006

A

la- The present invention relates to a process for the purification of alkali metal metaborate solutions.

Solutions of alkali metal metaborate make it possible, by reacting with hydrogen peroxide, to prepare perborates which, on account of their active oxygen content, are often employed as bleaching agents in washing products.

00 Unfortunately, alkali metal metaborate solutions i are often characterized by a yellowish colour. Before S°o0 their conversion into perborate and their incorporation in washing products it is therefore desirable to purify o o 0o 1 these solutions, and this is what a simple conventional 00 0 0 filtration cannot effect.

o0o In British Patent 1,020,446 (Laporte Chemicals Ltd.), alkali metal pyrophosphate and metaborate solutions are purified by treatment with sequestering agents 0oO6 in order to form insoluble complexes which, after a 000 period of rest and addition of reducing agents (Na 2 S and Na 2

S

2 04), can be separated off by filtration or by extraction with an organic solvent.

0 0 0 In German Patent 2,608,597 (Treibacher Chem.

Werke), a metaborate solution is produced by treating S colemanite (CazBO0 11 with an aqueous solution of an alkali metal hydroxide at between 100 and 700°C for 10 min to 3 hours, by mixing the solution obtained with a solution of Na 2

CO

3 maintained at a temperature close to 90'C and by then finally filtering the metaborate solution under vacuum.

These known processes demand the use of a numbeof successive operations and generally comprise a chemical or heat treatment which, in addition to the time which it requires and the cost which it entails, can unfavourably affect the composition or the subsequent behaviour of the solution.

lb The present invention consequently relates to a process for the purification of alkali metal metaborate solutions, characterized in that these solutions are clarified by removal of the suspended particles which have a diameter smaller than or equal to lOpm and larger than or equal to 0.2pm and characterized in that the suspended particles are removed by being retained on a microfiltration membrane.

fl 0 a o 5 RB a e 2 4process for the purification of alkali meta orate solutions, according to which t eeo utions are clarified by removal ofe-d'spended particles which have a diame aIffaler than or equal to 10 Am and larger than 00 0 0 0 0 0 0 00 So 00c I t l [C 00 1| 0 0' 0001 test 'sit 1 1 11 O 01 0 Ott I G1 r-9 yR1 aI G W L 4 Through the application of the process according to the invention, the original colour of the solutions, which is perhaps due to a turbidity phenomenon caused by the impurities present in the starting mineral, disapo pears and clarified solutions are obtained without the need to resort to the use of reactants or to a multistage 0 treatment.

The term "to clarify" means to make the metabor- 15 ate solution to be treated clear and colourless.

In most cases the solutions are aqueous solutions. The invention applies particularly to any solution whose weight concentration is at least 10 and not more than 350 g of alkali metal metaborate per kg of solution.

,20 The pH of these solutions is in most cases between 11 and 14. The solutions are generally obtained by the alkaline digestion of a calcioboric (Ca 2

B

6 On 11 or sodioboric S(Na 2

B

4 07) mineral. Various contents of suspended particles may be encountered. In particular in solutions obtained by digesting a sodioboric mineral it is generally possible to find from 10 to 170 mg of solid particles per kg of solution.

Solutions of various alkali metal metaborates can be purified using the process according to the invention.

The alkali metal is often sodium.

Various techniques can be employed to remove very small particles; among these, centrifuging is found to be advantageous. A particularly efficient alternative consists in r.taining the particles on a microfiltration membrane. These processes make it possible to extract a perfectly clarified filtrate by only removing the suspended particles which have a diameter smaller than or equal to 10 pm and larger than or equal to 0.2 Am. The use of the microfiltration technique yields excellent uJ

U\

0 I t a t o 0 C$tT 0! j m 3 results.

During the microfiltration the liquid to be clarified may travel perpendicularly or in parallel to the membrane. In most cases it travels in parallel to the membrane and the filtrate flows perpendicularly to this direction, the microfiltration being then known as "crossflow microfiltration". This relative arrangement reduces the formation of the layer of deposit which introduces a risk of blocking the pores of the membrane.

Various membrane configurations can be adopted.

In particular, microfiltration on a tubular membrane 00 0 Soo gives very good results.

o o0 The microfiltration operation in accordance with the process according to the invention can be performed o 0 continuously or noncontinuously, in one or more stages.

In the type of application in question, in view of the low sludge content of the solution, the microfiltration can be performed in a single stage (single stage recirculation) operating at the desired final concentration and with an input of solution and an extraction of °filtrate which are continuous.

o oo oo° o According to the invention the purification may be carried out at various temperatures. The latter are not critical. However, in practice the choice of an elevated working temperature results in a reduction in tsolution viscosity and makes it possible to increase the t filtrate flow in the case of a given plant. In general, -the operating temperature tolerated by the membrane makes it possible to operate at from 20 to 65 0

C.

Similarly, the output efficiency of the process, expressed in 1/h m 2 can be improved by an increase in the driving pressure, characterized by the pressure difference across the membrane. Assuming microfiltration of solutions with a high concentration of insoluble particles, when the driving pressure is greatly increased, blocking of the pores of the membrane is produced and the output efficiency is not improved in proportion. In the present case, in view of the low content of suspended particles, the limit of the driving pressure is imposed 4 essentially by the mechanical strength of the plant. In general, the driving pressure can range from 0.1 to 3 bars. In practice, values from 1.2 to 3 bars are advantageous.

In this operation at elevated driving pressure the speed of travel of the solution inside the membrane has only a small effect when it does not exceed 5 m/s.

In the process according to the invention it is particularly advantageous to wash the membrane countercurrentwise by reversing at regular intervals the flow of the filtrate passing through it in order to extract from the pores the particles which block them (backflushing).

These flushings can be carried out according to various 0 0 periodicities and durations. They are generally performed from 1 to 70 times an hour. Each flushing has the same S o o° duration, in most cases from 0.5 to 10 seconds.

SIt may also be fruitful to regenerate the microfiltration membrane using a chemical treatment at regular intervals. In general, this treatment is carried out after an operating period of 3 to 250 hours.

In a particular embodiment of this regeneration i to the succession of two treatments with caustic soda (NaOH) and with hydrochloric acid (HC1) is found to be highly ¢iI teffective. In practice, the use of solutions of 5 to 15 g of HC1/100 g of solution and of 3 to 25 g of NaOH/100 g of solution gives excellent results.

The invention also relates to the alkali metal perborate prepared by using a hydrogen peroxide solution and an alkali metal metaborate solution obtained by a process in accordance with that described above. The examples given below illustrate the invention without restricting its scope.

Example 1R (reference, not in accordance with the invention) A sodium metaborate solution, cloudy and yellowish, is fractionated into 6 samples of 250 to 300 ml which are filtered successively at room temperature under a pressure varying from 0.33 to 0.97 bar, through a Durieux paper.

During the first test the average permeability of the filter is 6740 kg/h m 2 bar. The filtrate obtained remains cloudy and yellowish.

During the successive filtration of the various samples the filter paper acquires a brown colour. Correspondingly, the average permeability decreases to reach 92 kg/h m 2 bar with the 6th sample.

The filtrate obtained during this 6th test is much clearer than that resulting from the first test, but it still contains suspended particles.

o 0 This experiment shows the major influence of the formation of a deposit on the filter, this deposit S affecting the result of the filtration progressively in o the direction of an improvement.

a o 5 Be that as it may, conventional filtration does 000 0 o oo not guarantee the removal of all the suspended particles from the sodium metaborate solution.

Example 2R (reference, not in accordance with the invention) A sodioboric pentahydrate mineral Na 2

B

4

O

7 .5H 2 0 (3 .o kg) is digested, in aqueous medium (8.5 1 of water) at 45°C, with a solution of caustic soda NaOH (2.8 1 at o° strength). The sodium metaborate solution obtained is yellowish in colour and contains 83 mg of solid matter per kg of solution.

I Analysis of this solid matter shows the preponderant presence of iron cations, but also of sodium, 0° 0 silicon, aluminium, magnesium, etc.

Particle size analysis of the sludge present in the solution shows that 90 of this sludge consists of particles with a diameter of between 3 and 20 pm and that their average diameter lies between 6 and 7 Am.

A settling test was carried out with this solution in a 500-ml test tube at 45 0

C.

After settling for 2 h, the upper 1/3 of the liquid was removed; it still contained 22 of the initial quantity of solid matter.

Example 3 (in accordance with the invention) The treated metaborate solution is comparable to 6 the solution in Example 2R; prepared according to the same reaction as under 2R, but starting with another sample of sodioboric mineral. It has an initial solid matter content of 133 mg/kg of solution. It is microfiltered in a pilot unit which has the following characteristics: the membranes are made of polypropylene, tubular in form, with an internal diameter of 5.5 mm, an external diameter of 8.6 mm, each tube being 1.5 m in length, each unit comprising 43 tubes, the total exchange surface area being one square meter. The average diameter 0o 0 of the pores of the membrane is 0.22 Mm (Enka trademark o 00 membrane of Accurel MD 080 TP 2N type).

Soo The test is carried out at a temperature of 0 o o at a driving pressure of 0.75 bar, at a speed of travel 0 015 of 3.5 m/s, with an average permeability of 250 1/h m 2 0ao o bar. Backflushing of the membrane is carried out at a frequency of 6 h 1 for 5 s, with a driving pressure of 2 bars.

After this microfiltration 0 mg of solid matter was measured in the filtrate and the solution was i completely clear and colourless.

Example 4 (in accordance with the invention) C The treated metaborate solution is comparable to same reaction as under 2R, but starting with another sample of sodioboric mineral. It has an initial solid matter content of 115 mg/kg of solution. It is microfiltered in a pilot unit which has the same characteristics as that in Example 2, but with an exchange surface area of two square meters.

The test is carried out at a temperature of at a driving pressure of 0.7 to 1.7 bars, at a speed of travel of 3.6 m/s, with an average permeability of 120 to 175 1/h m 2 bar. Backflushing of the membrane is carried out at a frequency of 6 h 1 for 5 s, with a driving pressure of 1 to 1.9 bars.

After this microfiltration 0 mg of solid matter was measured in the filtrate and the solution was completely clear and colourless.

7 At the end of this test, which lasted 3 hours, the water permeability of the membrane, which was initially 1050 1/h m 2 bar had fallen to 495 1/h m 2 bar. A regeneration was then performed, according to the scheme: washing of the tubular membranes with water at 45 0 C and for 15 minutes, with permeation of this water "in the normal direction" (from the inside concentrate side, to the outside filtrate side) under a driving pressure of 0.1 to 0.3 bar and with a concentrate-side travel speed of 1.5 to 3.5 m/s, washing of the tubular membranes with 10 HC1 at V t, and for 15 minutes, with permeation of this HC1 solution "in the normal direction" under a driving pressure of 0.1 t to 0.3 bar and with a concentrate-side travel speed of 1.5 to 3.5 m/s, washing of the tubular membranes with water at 45°C and for 15 minutes, with permeation of this water "in the normal direction" under a driving pressure of 0.1 to 0.3 bar and with a concentrate-side travel speed of 1.5 to 3.5 m/s, t- washing of the membranes with 5 NaOH at 45 0 C and for i t t 30 minutes, with permeation of this water "countercurrentwise" (from the outside filtrate side to the inside concentrate side) under a driving pressure of 0.5 to 1.5 bars; during this permeation the speed of travel of the NaOH solution was nil (frontal filtration), t washing of the tubular membranes with water at 45°C and for 15 minutes, with permeation of this water "in the normal direction" under a driving pressure of 0.1 to 0.3 bar and with a concentrate-side travel speed of 1.5 to m/s.

At the end of this treatment a water permeability of 843 1/h m 2 bar was regained.

Claims (9)

1. Process for the purification of alkali metal metaborate solutions, characterized in that these solutions are clarified by removal of the suspended particles which have a diameter smaller than or equal to 10 pm and larger than or equal to 0.2 pm and characterized in that the suspended particles are removed by being retained on a microfiltration membrane.

2. Process according to claim 1, characterized in that the alkali metal is sodium. °o

3. Process according to either of claims 1 and 2, characterized in that the microfiltration is carried out by crossflow microfiltration, in a single stage and continuously.

4. Process according to any one of claims 1 to 3 0"88 characterized in that the microfiltration is carried out at a temperature which can range from 20 to 65°C and at a SO' driving pressure which can range from 0.1 to 3 bars.

5. Process according to any one of claims 1 to 4, characterized in that the membrane is washed countercurrentwise, from 1 to 70 times an hour, for 0.5 to I 10 seconds.

6. Process according to any one of claims 1 to characterized in that the membrane is regenerated chemically V after an operating period of 3 to 250 hours.

7. Process according to claim 6, characterized in that the chemical regeneration of the membrane is carried out by two successive treatments with caustic soda (NaOH) and with hydrochloric acid (HC1).

8. Alkali metal perborate prepared from an alkali metal metaborate solution obtained by a process according to one of claims 1 to 7.

9. A process substantially as hereinbefore described with reference to either of Examples 3 and 4. RB 9 An alkali metal perborate substantially as hereinbefore described with reference to either of Examples 3 and 4. o o e a o 9 o e e t i t 0a i 1 oesert at i 0 oi e 3 63 aoo0 DATED: 5 December, 1991 PHILLIPS ORMONDE FITZPATRICK Attorneys for:- INTEROX (SOCIETE ANONYME) RB Q -ki~ imp