PROCESS AND APPARATUS FOR PRODUCING MODIFIED CELLULOSE PEARLS WITH MICROPOROUS STRUCTURE AND HIGH ADSORPTIVE SURFACE

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 DEG .

Description: -. - PROCESS AND APPARATUS FOR PRODUCING MODIFIED CELLULOSE PEARLS WITH ICROPOROUS STRUCTURE AND HIGH ADSORPTI VE SURFACE Techni ca I field The object of the invention is to provide a process and apparatus for producing from cel lulose solution pearls with microporous structure and high αdsorptive surface. Background Art It is wel l-known from practical experiences that the ideal adsorbent is spherical . There are many possibi l ities for applying the cel lulose pearl adsorbent, however, it is appl icable first of al l as mi crocapsu I e . With appropriate- fi l lers the field of appl ication of cel lulose pearl is extended. The product has excel lent properties: e.g. it is acid-proof, alkal i-proof and solvent-resistant. As a result of its advantageous properties it may be used for cleaning antibiotics in case of ermentation, cleaning nucleic acids, extracting natural dyestuffs, recovering valuable components of waste waters, purifying sewages, removing organic impurities, blotting off plant protec- tives and plant nutritives. The multiple appl icabi l ity explains why so many pro¬ cesses have been elaborated in the recent years for the production of cel lulose pearls. Thus, for example, according to the Japanese patent specifications 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. Usual ly traditional apparatus is used for real izing the process. According to the patent specification No. US- 3 579 350 the starting material is cel lulose solution, or¬ ganic 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. Epi chI orohydr in 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 pro- cess which comprises making mi croganu l ates from the aqueous solution of organic polymers by using an organic so I vent . It is also known that adsorptive powders are also used as additives for improving the adsorptive charac- teristics of the cel lulose 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 wel l as water-retaining capacity of the cel lulose pearl , hydro- phi lie 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 re¬ garded as important and usual ly existing machinery is used: only in one case is the pearl forming bore system combined with vibration. The cel lulose pearls formed in the known way have a structure where there is an outer layer and within a fi l l ing of cel lulose 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 inven¬ tion to produce such cel lulose pearls which have, owing to their structure, higher adsorptive capacity than the pro¬ ducts known at present. The process of the invention relates thus to the pro¬ duction of cel lulose pearls of porous structure and of high adsorptive capacity and differs from the previously described processes in that bubbl ing and foam-forming agents are used for the pearl formation and for the after- treatment. It has been found that pearls of fundamental ly 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 cel lulose or of a cel lulose derivative, such as cel lulose xanthogenate , which solution is dropped in the precipitating bath through an opening of preferably 1-10 nπm diameter. The viscosity of the cel lulose solution is preferably 200-10.000 Ps . The employed foam- forming agents are gases, such as N ? , 0 ? , NH , air,N ? 0, hydrogen, acetylene, etc., carbonates, preferably Na ? CO,,. ZnCO„ or (NH, ) ? C0,,, calcium and magnesium carbonate. If desired, the viscous solution may contain fi l lers as wel l . On dropping, the C0 2 , S0 2 , CS 2> 0 2 , - , C^, N 2 , N 2 0, NHg gases formed on the surface and in the interior of the drops bring about "hol lows" 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 hol lows and channels. This dif- ference in structure may be observed on electron micro¬ scopic pictures. The acidic precipitating bath can be e.g. 2-6 N acid solution (preferably sulfuric acid) containing 3 50-200 g/cm of sodium sulfate as wel l . In the formation of the porous structure the influ¬ encing of the cel lulose xanthogenate decomposition, the releasing speed of developing carbon bisulfide steams, as wel l as the bubbl ing agents charged in the viscous solu¬ tion play an important part. The decomposition products of materials of different half-l ife appear with a time-lag during the production, thus the gaseous products of the simultaneous reactions faci l itate the development of chan¬ nels. The decomposition products of the gas-forming mate¬ rials quicken the formation of the cel lulose skeleton. The process of the invention aiming at producing cel lulose pearls gives the positive results of the known processes and shows surplus action as compared to them, which manifest themselves first of al l 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 fi l¬ l ing of cel lulose 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 easi ly. 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 ac¬ tion. Usual fi l lers, such as active carbon, si l ica-gel , zeol ite, bentonite, ion-exchange resin, bone coal , alumina si l ica gel , polymer powders (CMG, sodium alginate, hydroxy- ethyl cel lulose, poly/vinyl alcohol/, poly/acryl nitri le/), etc., can be used also in case of the process of the inven¬ tion. The process for producing the foamed pearls of the in- vention enables a very advantageous version of the si l ica gel pearls to be formed. According to the original solution si l ica gel powder is mixed in the viscous solution to give the pearl . In this case the grain size of si l ica gel , the homogeneity of the viscous solution and the conditions of precipitation determine the arrangement of si l ica gel in the interior of the pearl . It has been found, however, that if the si l ica gel is not mixed in the viscous solution but it is formed simul- taneously with the formation of the pearl , it covers the wal l of the pearl 's spaces in a very fine layer. This may be achieved by precipitating si l ica gel on the pearl 's wa I I . Pearls with new properties may be produced further- more by uti l izing humic acids. Humic acid is formed in the system by charging humates. Ch.lorophyl I and cyclodextrin may also be incorporated into the pearl . Advantageous pearl of good practical value may be obtained by using magnetic iron oxide (magnetite) as fi l ler which keeps its activity in the cel lulose 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, sol id or l iquid plant protectives which are water- inso I ub I e. In case of the processes known unti l now the task is general ly solved in a number of technological steps and insufficient attention is paid to rentabi l ity which should be a further advantage. The influencing of the new structure may be wel l ob- served on electron microscopic pictures. Best Mode of Carrying out the I nvent i on The invention may be better understood by means of the drawings where Figures 1-6 are electron microscopic pictures and serve to i l lustrate the structure, and Figure 7 is a sketch of the apparatus of the invention. Figures 1 and 2 show that without foaming a relative¬ ly smooth surface, glass free from pores and channels is formed. Figures 3 and 4 show that the surface of the product manufactured by t'he process and apparatus of the invention is broken, faveolate and contains numerous pores. On the cross-sectional picture of Fig. 5 inner hol lows and smal l channels leading to the surface may be seen, whi le in case of the fi l led type of Fig. 6 a more sol id structure with smal ler pores may be observed. This structure may be changed according to the aim of the appl ication, by influencing the technology. This kind of pearl absorbs solutions from its environ¬ ment 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 technolo¬ gical 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 ti lting edge from plastic and the coagulate is separated from the acid for instance by a net separator. The raw product may be forwarded by l iquid injector, a secondary coagulation bath may serve to operate the injector. The secondary co¬ agulation is carried out preferably under reduced pres¬ sure . For carrying out the el imination of acid and desul- furating it is preferred to employ a contact fluid equip¬ ment the angle of incl ination 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 uni f 1 ow 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 for¬ mation of a favourable structure. The novelty of the invention l ies furthermore in that a production l ine of industrial scale has been created from apparatuses which have not yet been used for simi lar purposes, thus an extremely economic solution is provided. The fol lowing explanation serves to clarify Fig. 7: The cel lulose solution (preferably viscous) intended for use is fi l led in A stirring recipient, then the bubbl ing material prepared in 9 anterior recipient is added. The bubbl ing material may be a real solution or suspension, but may contain gas bubbles as wel l . After mixing the 1 viscous solution and 2 additives (sol id powders, solutions, crossl inking agents, etc-.) , as wel l as the bubbl ing material , the viscous solution passes through B static stirrer (intensive homogeni zat ion) and reaches the drop-forming die. The C drop-forming die con¬ tains elastic drop-forming elements of low friction co- efficient 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-coagu- lation takes place and the formation of the porous struc¬ ture begins. From the drops pearly coagulate is formed, the continuous transport of which must be ensured, other¬ wise the col l ision 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 obl ique ti lting 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 cel lulose pearl being in the stage of pre-coagu I at i on gets in the E secon¬ dary coagulation apparatus by gravity. The net separator inserted between the D and E apparatuses is intended for separating the cel lulose pearl from the coagulating fluid, which fluid is returned into the circulation system. The net separator is a so-cal led reinforced plastic grate formed by hyperbo I a-type tracing, which gr_at_e_ is - seen from the side of the product's flow - a diamond shaped plastic riet including an angle of 60 and having an edge distance of 2 nrm and is reinforced on the back side by a hexagon supporting grate having an edge distance of 25 rrm. The two types of grates are fastened together by heat treatment. It is in the E secondary coagulation apparatus that the cel lulose 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 aftertreat ing reactor by jet injector. Here take place the removal by hot-water washing of the re¬ mainders of the coagulation bath and the decomposition pro- ducts of the foaming process, the washing-out by alkal i solution of sulfur compounds formed in the secondary reac¬ tions, as wel l as the bleaching of the product, if neces¬ sary. This process also contributes to the formation of the channel structure. The G apparatus is a contact fluid reactor, the angle of incl ination of which is variable between 0-90°, further¬ more, 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 hol lows is the final step in the formation of the porous channel system. The fol lowing examples serve to i l lustrate the pearl forming process. Example 1 3 1600 dm of viscous solution containing 8 % by mass of cel lulose (arrmon i urn chloride number = 7,9) and 100 kgs of Na^CO n are mixed to give a homogeneous solution which is 3 dropped into 4000 dm of 20 % sulfuric acid solution by a special dropping apparatus. The pearls formed after coagula- t i on are washed with water, hypo and again with water to el iminate sulfur, then they are dried. The obtained pearls have diameter of 1-5 mm, depending on the parameters app I i ed . Examp I e 2 To the viscous solution, the composition and quantity of which is given in Example 1, 50 kgs of ZnCO,, are mixed; the pearl is formed from this solution. Precipitation and aftertreatment are the same as in Example 1. Examp Ie 3 3 To 2000 dm of viscous solution of fibre industry 120 kgs of Na„CO and 140 kgs of active carbon are mixed, with a static stirrer. The formation of pearl is carried out according to Example 1. Cel lulose pearls are obtained- which are f ϊ I led up with active carbon and have a good ad¬ sorptive capacity. The dropping apparatus operates at a pressure of 2 bars, the coagulating acid level is ensured by means of a t i I t i ng -edge , the constant removal of the pearls formed continuously is also arranged. Example 4 3 To 1000 dm of viscous solution 60 kgs of Na ? C0 o and 100 I of sodium sil icate are mixed. Finely dispersed, si lica gel-fi l led pearls are obtained if the solution is dropped in 15 % sulfuric acid. Through the ti lting 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 re¬ turns it into the circulation system. Example 5 3 To 2000 dm of viscous solution according to Example 3 Na CO,, and 700 kgs of bentonite are mixed with a static stirrer. The pearl formation is the same as in the previous Example. Cel lulose pearls containing more than 80 % by mass of bentonite are obtained, for the aftertreatment of which obl ique 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 (NH. )„C0 4 _ o and 25 kgs of chlorophyl l are added. The solution is homo¬ genized and pearls are formed according to the process of Example 5. The chlorophyl I content of the pearl amounts to about 15 % by mass . Example 7 3 To 2000 dm of homogeneous viscous solution contain¬ ing 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 ob¬ tained. 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 re¬ gulating apparatus with ti lting edge is appl ied, the l iquid is separated from the solid product by a net separator of hyperbola tracing. The aftertreatment is carried out in a contact fluid aftertreat ing reactor.

Claims: C I a ims 1. Process for producing cel lulose pearls of micro- porous structure and of high adsorptive capacity, c h a r a c t e r i z e d in that during the pearl forma- 5 t i on gas-forming foaming material and one or more appro¬ priately selected fi l lers are added to the cel lulose deri¬ vative, drops are formed and coagulated to give pearls with hol low structure, the time of mixing, pre-coagu I at i on, secondary coagulation, aftertreatment and drying is chosen 10 in accordance with the half-l ife of the decomposition speed of the appl ied 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, SO ? , CS„, N ? 0 or acetylene or NH, , Zn , Na, 15 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 solu¬ tion of cel lulose derivatives, preferably from viscous solu- 20 t i on or from waste viscose. 4. Process according to claims 1-3, c h a r a c t e r¬ i z e d in that si l ica gel is used as fi l ler which is pre¬ pared from soda or potassium water glass during the pearl formation; the quantity of water glass is 10-80 % by mass, 25 preferably 40-50 % by mass with respect to cel lulose. 5. Process according to claims 1-4, c h a r a c t e r¬ i z e d in that during the pearl formation magnetic iron oxide, activated red mud, chlorophyl l , polymer powders, humic acids, powders with high adsorptive activity, plant protect- ' 30 i ve or plant nutritive materials are used as fi l ler. 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 nrn 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 coagula- 3 tion of cel lulose, which solution contains 50-200 g/dm of 3 sodium sulfate and preferably 10 g/dm of formaldehyde. 8. Process according to claims 1-7, c h a r a c t e r¬ i z e d in that cel lulose solutions with a viscosity of 200-10.000 mPs are used. 9. Process according to the previous claims, c h a ¬ 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 un i f I ow 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 sol id and l iquid additives; has a ti lting edge for control l ing 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 i nc I i nat i on -of the reactor is variable between 0-90 .

Inventors: BUNDSCHUH LASZLO, FARAGO JENOE, GIMESI ISTVAN, HERMANN SZILVESZTER, KOVACS GYOERGYNE, LEGANYI MONIKA, MEISZEL LASZLO, MERGENTHALER NANDOR, SZABO RENE, BUNDSCHUH, LASZLO, FARAGO, JENOE, GIMESI, ISTVAN, HERMANN, SZILVESZTER, KOVACS, GYOERGYNE, LEGANYI, MONIKA, MEISZEL, LASZLO, MERGENTHALER, NANDOR, SZABO, RENE
Applicants: MAGYAR VISCOSAGYAR
Application year: 1989
Main classification: B01J20
IPC codes: B01J20, C08B16, C08J3