WO1991000142A1

WO1991000142A1 - Process and apparatus for producing modified cellulose pearls with microporous structure and high adsorptive surface

Info

Publication number: WO1991000142A1
Application number: PCT/HU1989/000033
Authority: WO
Inventors: László BUNDSCHUH; Jeno^' FARAGÓ; István GIMESI; Szilveszter Hermann; Györgyné KOVÁCS; Mónika LEGÁNYI; László MEISZEL; Nándor MERGENTHALER; René SZABÓ
Original assignee: Magyar Viscosagyár
Priority date: 1989-06-30
Filing date: 1989-06-30
Publication date: 1991-01-10
Also published as: EP0430952A1

Abstract

The invention relates to a process and apparatus for producing cellulose pearls with microporous structure and high adsorptive capacity. The essence of the process is that during the pearl formation gas-forming material and one or more appropriately selected fillers are added to the cellulose derivative, drops are formed and coagulated to give pearls with hollow structure, the time of mixing, pre-coagulation, secondary coagulation, aftertreatment and drying is chosen in accordance with the half-life of the decomposition speed of the applied foam-forming agents. The apparatus is characterized by containing a drop-forming die with special plastic pins and a static stirrer (A) for mixing the solid and liquid additives; has a tilting edge for controlling the coagulation time, a net separator of special space curve form and consisting of the combination of plastic nets for separating the product and the acid; disposes of a jet injector (F) operated with the treating solution for transporting the product and of a fluid reactor (B) for the aftertreatment, the angle of inclination of the reactor is variable between 0-90°.

Description

PROCESS AND APPARATUS FOR PRODUCING MODIFIED CELLULOSE PEARLS WITH MICROPOROUS STRUCTURE AND HIGH ADSORPT I VE SURFACE

Technical field

The object of the invention is to provide a process and apparatus for producing from cellulose solution pearls with microporous structure and high adsorptive surface.

Background Art

It is well-known from practical experiences that the ideal adsorbent is spherical. There are many possibilities for applying the cellulose pearl adsorbent, however, it is applicable first of all as microcapsule. With appropriate. fillers the field of application of cellulose pearl is extended. The product has excellent properties: e.g. it is acid-proof, alkali-proof and solvent-resistant. As a result of its advantageous properties it may be used for cleaning antibiotics in case of fermentation, cleaning nucleic acids, extracting natural dyestuffs, recovering valuable components of waste waters, purifying sewages, removing organic impurities, blotting off plant protectives and plant nutritives.

The multiple applicability explains why so many processes have been elaborated in the recent years for the production of cellulose pearls.

Thus, for example, according to the Japanese patent s pec i f ica t ion s Nos. 73-21738 and 73-60753 the pearl is formed from viscous solution by passing the latter through a bore with high speed, the coagulation is carried out in spinning bath. Usually traditional apparatus is used for realizing the process.

According to the patent specification No. US- 3 579 350 the starting material is cellulose solution, organic solvent is used for preparing a suspension which is precipitated in an acid solution.

According to the patent specifications Nos.

CS-2 858-74, DE-2 523 893 and US-4 055 510 a suspension is prepared from viscous solution in non-aqueous medium.

Epichlorohydrin is used for modifying the final product and the precipitation is carried out with an acid solution.

The patent specification No. US-3 737 337 discloses a process which comprises making microganulates from the

aqueous solution of organic polymers by using an organic soIvent.

It is also known that adsorptive powders are also used as additives for improving the adsorptive characteristics of the cellulose pearl or for developing the selective adsorptive capacity. Such a process is described in patent specifications Nos. CH-625 716 and IT-50-20381. In order to increase the water-absorbing, as well as water-retaining capacity of the cellulose pearl, hydrophilic polymers are used as mixing component according to the patent specification No. DD-206 679. In case of the solutions of the said specifications the process is regarded as important and usually existing machinery is used: only in one case is the pearl forming bore system combined with vibration.

The cellulose pearls formed in the known way have a structure where there is an outer layer and within a filling of cellulose gel and adsorptive powder.

Disclosure of the Invention

According to our tests, this structure reduces the adsorptive capacity. Therefore it is an aim of the invention to produce such cellulose pearls which have, owing to their structure, higher adsorptive capacity than the products known at present.

The process of the invention relates thus to the production of cellulose pearls of porous structure and of high adsorptive capacity and differs from the previously described processes in that bubbling and foam-forming agents are used for the pearl formation and for the aftertreatment. It has been found that pearls of fundamentally different structure may be formed as compared to the known processes. This new structure ensures unexpected surplus actions of which good use may be made when applying the product. According to the invention, the foam-forming agent is mixed into a solution of cellulose or of a cellulose derivative, such as cellulose xanthogenate, which solution is dropped in the precipitating bath through an opening of preferably 1-10 mm diameter. The viscosity of the cellulose solution is preferably 200-10.000 mPs. The employed foamforming agents are gases, such as N₂, O₂, NH₃, air,N₂O, hydrogen, acetylene, etc., carbonates, preferably Na₂CO_3, ZnCO₃ or (NH₄)₂CO_3, calcium and magnesium carbonate. If desired, the viscous solution may contain fillers as well. On dropping, the CO₂, SO₂, CS_2, O₂, H₂ , C₂H₂, N₂ , N₂O, NH₃ gases formed on the surface and in the interior of the drops bring about "hollows" in the pearl. The structure of the pearl obtained in this way differs from that of the usual pearl, since its surface is faveolate and porous and its cross-section contains hollows and channels. This difference in structure may be observed on electron microscopic pictures. The acidic precipitating bath can be e.g. 2-6 N acid solution (preferably sulfuric acid) containing 50-200 g/cm³ of sodium sulfate as well.

In the formation of the porous structure the influencing of the cellulose xanthogenate decomposition, the releasing speed of developing carbon bisulfide steams, as well as the bubbling agents charged in the viscous solution play an important part. The decomposition products of materials of different half-life appear with a time-lag during the production, thus the gaseous products of the simultaneous reactions facilitate the development of channels. The decomposition products of the gas-forming materials quicken the formation of the cellulose skeleton.

The process of the invention aiming at producing cellulose pearls gives the positive results of the known processes and shows surplus action as compared to them, which manifest themselves first of all in the modification of the structure of the pearls. On the pearl formed in the known way, an outer layer is developed within which a filling of cellulose gel or adsorptive powder can be found. The foamed pearl produced according to the process of the invention has, however, a spongy structure on the large surface of which the adsorbents are set easily. These phenomena can be seen on electron microscopic pictures.

The foam-forming material has no detrimental effect on the properties of the additives, it even increases their action. Usual fillers, such as active carbon, silica-gel, zeolite, bentonite, ion-exchange resin, bone coal, alumina silica gel, polymer powders (CMG, sodium alginate, hydroxyethyl cellulose, poly/vinyl alcohol/, poly/acryl nitrile/), etc., can be used also in case of the process of the invention.

The process for producing the foamed pearls of the in vention enables a very advantageous version of the silica gel pearls to be formed. According to the original solution silica gel powder is mixed in the viscous solution to give the pearl. In this case the grain size of silica gel, the homogeneity of the viscous solution and the conditions of precipitation determine the arrangement of silica gel in the interior of the pearl.

It has been found, however, that if the silica gel is not mixed in the viscous solution but it is formed simultaneously with the formation of the pearl, it covers the wall of the pearl's spaces in a very fine layer. This may be achieved by precipitating silica gel on the pearl's wall.

Pearls with new properties may be produced furthermore by utilizing humic acids. Humic acid is formed in the system by charging humates. Chilorophyll and cyclodextrin may also be incorporated into the pearl. Advantageous pearl of good practical value may be obtained by using magnetic iron oxide (magne t i t e ) a s f i l le r wh ich keep s it s ac t iv i t y in t he ce l lu los e pearls, too. Activated red mud may also be used. Polymer powder additives may be besides the known ones: polyamide, polypropylene, polyethylene. Also incorporated may be sulfur, solid or liquid plant protectives which are water-insoluble.

In case of the processes known until now the task is generally solved in a number of technological steps and insufficient attention is paid to rentability which should be a further advantage.

The influencing of the new s t ruc t ur e may be well observed on electron microscopic pictures. Best Mode of Carrying out the Invention

The invention may be better understood by means of the drawings where Figures 1-6 are electron microscopic pictures and serve to illustrate the structure, and Figure 7 is a sketch of the apparatus of the invention.

Figures 1 and 2 show that without foaming a relatively smooth surface, glass free from pores and channels is formed.

Figures 3 and 4 show that the surface of the product manufactured by the process and apparatus of the invention is broken, faveolate and contains numerous pores.

On the cross-sectional picture of Fig. 5 inner hollows and small channels leading to the surface may be seen, while in case of the filled type of Fig. 6 a more solid structure with smaller pores may be observed.

This structure may be changed according to the aim of the application, by influencing the technology.

This kind of pearl absorbs solutions from its environment and releases them in unchanged condition. Thereby it ensures an ideal component transport.

The novelty of the solution of the invention consists in that the desired result is achieved by the technological steps ensuring the new properties together with special machinery. Thus special static stirrer is used for mixing the additives. The bearing pressure of the drop-forming die is preferably 1-10 bars.

The coagulation time is set preferably by a tilting edge from plastic and the coagulate is separated from the acid for instance by a net separator. The raw product may be forwarded by liquid injector, a secondary coagulation bath may serve to operate the injector. The secondary coagulation is carried out preferably under reduced pressure.

For carrying out the elimination of acid and desulfurating it is preferred to employ a contact fluid equipment the angle of inclination of which may usual ly change between 0 and 90 and in which the flow direction of the individual cycles is variable: the treating fluid may be circulated alternately in un if low or in counterflow.

Drying is performed preferably at 60-150 C for 1-20 hours. The drying rate and the speed of releasing the steam from the inner structure contribute also to the formation of a favourable structure.

The novelty of the invention lies furthermore in that a production line of industrial scale has been created from apparatuses which have not yet been used for similar purposes, thus an extremely economic solution is provided.

The following explanation serves to clarify Fig. 7:

The cellulose solution (preferably viscous) intended for use is filled in A stirring recipient, then the bubbling material prepared in 9 anterior recipient is added. The bubbling material may be a real solution or suspension, but may contain gas bubbles as well.

After mixing the 1 viscous solution and 2 additives (solid powders, solutions, crosslinking agents, etc.), as well as the bubbling material, the viscous solution passes through B static stirrer (intensive homogenization) and reaches the drop-forming die. The C drop-forming die contains elastic drop-forming elements of low friction coefficient produced by special plastic shaping technique; this solution makes it possible to produce 1.000-100.000 drops/sec.

From the C drop-forming die (which may be operated at a pressure of 1-10 bars) the viscous solution gets to the coagulation bath in the form of drops. Here the pre-coagulation takes place and the formation of the porous structure begins. From the drops pearly coagulate is formed, the continuous transport of which must be ensured, otherwise the collision of the many thousands of drops and pearls formed in one second would result in undesirable adhesion leading to distorted formations. The continuous transport is achieved by adjusting the flow rate and flow direction of the coagulation bath, the level control and continuous taking away of the product are ensured by the suitably developed oblique tilting edge. In the interest of a favourable general effect, the distance between the drop-forming die and coagulation bath - i.e. the free path length of drops - is adustable.

From the D precipitation tank the cellulose pearl being in the stage of pre-coagulation gets in the E secondary coagulation apparatus by gravity. The net separator inserted between the D and E apparatuses is intended for separating the cellulose pearl from the coagulating fluid, which fluid is returned into the circulation system.

The net separator is a so-called reinforced plastic grate formed by hyperbola-type tracing, which grate is - s een from the side of the product's flow - a diamond shaped plastic net including an angle of 60 and having an edge distance of 2 mm and is reinforced on the back side by a hexagon supporting grate having an edge distance of 25 mm. The two types of grates are fastened together by heat treatment. It is in the E secondary coagulation apparatus that the cellulose skeleton is developed, the foaming reaction and the formation of the porous structure are continued.

This apparatus may be barometric, preferably it is operated, however, at a reduced pressure.

From the E secondary coagulation apparatus the product is passed in the G aftertreating reactor by jet injector. Here take place the removal by hot-water washing of the remainders of the coagulation bath and the decomposition products of the foaming process, the washing-out by alkali solution of sulfur compounds formed in the secondary reactions, as well as the bleaching of the product, if necessary. This process also contributes to the formation of the channel structure.

The G apparatus is a contact fluid reactor, the angle of inclination of which is variable between 0-90°, furthermore, the flow direction of the treating solutions may be changed in the individual cycles. The product obtained by the aftertreatment passes from the G apparatus in the H drier. This dier ensures a very intensive mixing which makes possible a quick release of water. The quick removal of water from the inner hollows is the final step in the formation of the porous channel system.

The following examples serve to illustrate the pearl forming process.

Example 1

1600 dm³ of viscous solution containing 8 % by mass of cellulose ( arrmoniurn chloride number = 7,9) and 100 kgs of

Na₂CO₃ are mixed to give a homogeneous solution which is dropped into 4000 dm³ of 20 % sulfuric acid solution by a special dropping apparatus. The pearls formed after coagula tion are washed with water, hypo and again with water to eliminate sulfur, then they are dried. The obtained pearls have diameter of 1-5 mm, depending on the parameters

applied.

Example 2

To the viscous solution, the composition and quantity of which is given in Example 1, 50 kgs of ZnCO₃ are mixed; the pearl is formed from this solution. Precipitation and aftertreatment are the same as in Example 1. Example 3

To 2000 dm³ of viscous solution of fibre industry

120 kgs of Na₂CO₃ and 140 kgs of active carbon are mixed, with a static stirrer. The formation of pearl is carried out according to Example 1. Cellulose pearls are obtainedwhich are filled up with active carbon and have a good adsorptive capacity. The dropping apparatus operates at a pressure of 2 bars, the coagulating acid level is ensured by means of a tilting edge, the constant removal of the pearls formed continuously is also arranged. Example 4

To 1000 dm³ of viscous solution 60 kgs of Na₂CO₃ and

100 I of sodium silicate are mixed. Finely dispersed, silica gel-filled pearls are obtained if the solution is dropped in 15 % sulfuric acid. Through the tilting edge the product gets to the net separator together with the acid and then to the secondary coagulation apparatus. The net separator separates the acid from the products and returns it into the circulation system.

Example 5

To 2000 dm³ of viscous solution according to Example 3 Na₂CO₃ and 700 kgs of bentonite are mixed with a static stirrer. The pearl formation is the same as in the previous Example. Cellulose pearls containing more than 80 % by mass of bentonite are obtained, for the aftertreatment of which oblique contact fluid washer is used. The obtained product has the superficial and cross-sectional picture shown on the attached photos.

Example 6

To 1500 dm of viscous solution 100 kgs of (NH₄)₂CO₃ and 25 kgs of chlorophyll are added. The solution is homogenized and pearls are formed according to the process of Example 5. The chlorophyll content of the pearl amounts to about 15 % by mass.

Example 7

To 2000 dm³ of homogeneous viscous solution containing 120 kgs of calcium magnesium carbonate 75 kgs magnetite are mixed and pearls are formed as described above. 270 kgs of magnetic pearls of high adsorptive capacity are obtained. Dropping is carried out on a die comprising special plastic pins, where 1.000-100.000 drops may be formed in one second. In the interest of the good coagulation and in order to avoid the harmful adhesion of drops a flow regulating apparatus with tilting edge is applied, the liquid is separated from the solid product by a net separator of hyperbola tracing. The aftertreatment is carried out in a contact fluid after treating reactor.

Claims

1. Process for producing cellulose pearls of microporous structure and of high adsorptive capacity,

c h a r r i z e d in that during the pearl formation gas m foaming material and one or more appropriately cted fillers are added to the cellulose derivative, drops are formed and coagulated to give pearls with hollow structure, the time of mixing, pre-coagulation, secondary coagulation, aftertreatment and drying is chosen in accordance with the half-life of the decomposition speed of the applied foam-forming agents.

2. Process according to claim 1, c h a r a c t e r i z e d in that a gas, preferably nitrogen, carbon dioxide, air, oxygen, hydrogen, SO₂, CS₂, N₂O or acetylene or NH₄, Zn, Na, Ca, magnesium carbonate or several of these are used as foam- forming material.

3. Process according to claim 1 or 2, c h a r a c t e r i z e d in that the pearls are formed from the solution of cellulose derivatives, preferably from viscous solution or from waste viscose.

4. Process according to claims 1-3, c h a r a c t e ri z e d in that silica gel is used as filler which is prepared from soda or potassium water glass during the pearl formation; the quantity of water glass is 10-80 % by mass, preferably 40-50 % by mass with respect to cellulose.

5. Process according to claims 1-4, c h a r a c t e ri z e d in that during the pearl formation magnetic iron oxide, activated red mud, chlorophyll, polymer powders, humic acids, powders with high adsorptive activity, plant protective or plant nutritive materials are used as filler.

6. Process according to claims 1-5, c h a r a c t e r- i z e d in that the pearls are formed through an opening of 1-10 mm diameter, at a pressure of 1-10 bars.

7. Process according to claims 1-6, c h a r a c t e r i z e d in that 2-6 N acid solution is used for the coagulation of cellulose, which solution contains 50-200 g/dm₃ of sodium sulfate and preferably 10 g/dm₃ of formaldehyde.

8. Process according to claims 1-7, c h a r a c t e ri z e d in that cellulose solutions with a viscosity of 200-10.000 mPs are used.

9. Process according to the previous claims, c h a r a c t e r i z e d in that the secondary coagulation is carried out at a reduced pressure.

10. Process according to any of the previous claims, c h a r a c t e r i z e d in that during the aftertreatment the fluid is circulated in uniflow or counterflow by turns.

11. Process according to any of the previous claims, c h a r a c t e r i z e d in that the drying is carried out at a temperature of 60-150 C, for 1-10 hours.

12. Apparatus for carrying out the process of claims 1-11, c h a r a c t e r i z e d in that it contains a drop-forming die with special plastic pins and a static stirrer (A) for mixing the solid and liquid additives; has a tilting edge for controlling the coagulation time, a net separator of special space curve form and consisting of the combination of plastic nets for separating the products and the acid; disposes of a jet injector (F) operated with the treating solution for transporting the product and of a fluid reactor (G) for the aftertreatment, the angle of inclination of the reactor is variable between 0-90 .