EP0456655A1 - Procede de production hydrothermique de solutions de silicate de sodium - Google Patents

Procede de production hydrothermique de solutions de silicate de sodium

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Publication number
EP0456655A1
EP0456655A1 EP90901810A EP90901810A EP0456655A1 EP 0456655 A1 EP0456655 A1 EP 0456655A1 EP 90901810 A EP90901810 A EP 90901810A EP 90901810 A EP90901810 A EP 90901810A EP 0456655 A1 EP0456655 A1 EP 0456655A1
Authority
EP
European Patent Office
Prior art keywords
sodium silicate
quartz
sio
temperatures
reaction step
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP90901810A
Other languages
German (de)
English (en)
Inventor
Rudolf Novotny
Alfred Hoff
Jost SCHÜRTZ
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Henkel AG and Co KGaA
Original Assignee
Henkel AG and Co KGaA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Henkel AG and Co KGaA filed Critical Henkel AG and Co KGaA
Publication of EP0456655A1 publication Critical patent/EP0456655A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/20—Silicates
    • C01B33/32—Alkali metal silicates

Definitions

  • the present invention relates to a process for the hydrothermal production of sodium silicate solutions with a high SiO 2: Na 2 O molar ratio by reaction of quartz sand with aqueous sodium hydroxide solutions and subsequent reaction of this intermediate product with a further crystalline SiO 2 modification.
  • sodium silicate solutions - generally referred to as sodium water glass - are most frequently used for technical purposes.
  • Sodium water glasses of this type predominantly have a solids content of about 30 to 40% by weight and a molar ratio of silicon dioxide to sodium oxide of 3.4 to 3.5: 1.
  • the production of soda water glasses on an industrial scale is generally carried out by melting together quartz sand and soda in suitable ovens at temperatures in the range from 1400 to 1500 ° C. with elimination of carbon dioxide. The melt which solidifies on cooling, the solid glass, is then dissolved in water in a further process step using pressure and elevated temperatures, and the solution obtained — depending on the quality requirement — is optionally filtered.
  • this high-temperature melting process is very expensive both in terms of equipment and in terms of the amounts of energy required and also leads to not inconsiderable emissions such as dust, nitrogen oxides and sulfur oxides.
  • hydrothermal processes for the production of aqueous sodium silicate solutions are also known and are described in a number of patent applications.
  • these processes are based on amorphous silicon dioxide, that is to say essentially on fly dusts and naturally occurring amorphous silicon dioxide modifications.
  • the process products obtained here are of poor quality due to the usual impurities in the fly dusts and the natural amorphous silicon dioxide compounds which are used as input materials and can therefore only be used to a limited extent for technical products.
  • DE-AS 2826432 relates to a process for the preparation of water glass solutions by reacting flue dust, which is obtained when silicon or ferrosilicon alloys are obtained, with aqueous alkali metal hydroxide solutions at elevated temperatures and then filtering the solutions contained, which is characterized in that is that you can fly dust with a 6- to 15-wt. -% aqueous alkali metal hydroxide solution at temperatures from 120 ° C to 190 ° C and a pressure of 2.9 to 18.6 bar treated in an autoclave, the weight ratio of alkali metal hydroxide solution to solid dust is 2: 1 to 5: 1.
  • the process products have a Si ⁇ : a2 ⁇ molar ratio of 2.2 to 4: 1.
  • the dusts used as starting materials have one Silicon content of 89 to 98% by weight, which according to the exemplary embodiments is always 90% by weight; the rest consists of impurities.
  • DE-OS 26 09 831 relates to a process for the treatment of silicon dioxide-containing, environmentally harmful waste dusts from silicon metal and silicon alloy production to give silicic acids or silicates, which is characterized in that the following process steps I to III are combined:
  • the alkali silicate solutions obtained in this way generally have a SiO 2: Na 2 O molar ratio in the range from 3.3 to 5.0: 1.
  • DE-OS 26 19604 relates to a process for the production of liquid water glass from amorphous silicon dioxide and alkali metal hydroxide, which is characterized in that silicon dioxide dust in the form of fly ash is separated from the exhaust gases from ferroalloy industries and other industries working with silicon furnaces has been mixed, alkali metal hydroxide and water are mixed in a certain weight ratio and then brought to a temperature between 75 and 100 ° C. with stirring, after which the liquid obtained is cooled.
  • the silicon dioxide dusts used as the starting material for this water glass production have in generally has a silicon dioxide content of 94 to 98 wt .-%, the rest consists of impurities.
  • DE-AS 23 28 542 relates to a process for the preparation of alkali metal silicates by treating perlite with an alkali solution and hydrothermally treating the pulp obtained in an autoclave with subsequent filtration, which is characterized in that an alkali solution is used to treat the perlite with a concentration of 40 to 140 g / 1 Na 2 O in an amount in which the ratio of the liquid phase to the solid phase is 0.7 to 1.5: 1.
  • Perlite is an essentially amorphous, glass-like mountain rock of volcanic origin, which mainly consists of (in% by weight) silicon dioxide 73, aluminum oxide 15 and other oxides 8.
  • the prior art described below relates to processes for the hydrothermal production of sodium silicate solutions from crystalline silicon dioxide, that is to say sand, and sodium hydroxide solution, which according to the processes of the prior art, however, only have an SO2: A2O molar ratio of less than 2. 89: 1 can be implemented.
  • DE-OS 3002857 relates to a process for the hydrothermal production of sodium silicate solutions with a SiÜ2: Na2 ⁇ molar ratio of 1.03 to 2.88: 1 by reaction of sand with aqueous sodium hydroxide solution under pressure and at elevated temperatures and subsequent filtration, which thereby is marked that the aqueous sodium hydroxide solution has a concentration of 10 to 50% by weight with an excess of sand of up to 300%, based on the molar ratios of S1O: a2 ⁇ in the batch, at temperatures in the range from 150 to 250 ° C. and these temperatures corresponding pressures of saturated water vapor and the unreacted excess of sand is used in whole or in part as a filter medium for the sodium silicate solution formed. According to the exemplary embodiments of this published specification, however, a maximum SiO 2: Na 2 O molar ratio of 1.68: 1 is achieved.
  • DE-OS 34 21 158 relates to a process for the hydrothermal production of sodium silicate solutions with a molar ratio of SiO 2: Na 2 O of 1.96 to 2.17 by reacting excess sand with aqueous sodium hydroxide solution, which is characterized in that one has an excess of sand and a reaction mixture containing preheated aqueous sodium hydroxide solution in a rotating, cylindrical, closed pressure reactor until a certain molar ratio SiO 2: Na 2 O is reached and then filtered using the excess sand and, if appropriate, an additional filter aid.
  • aqueous sodium silicate solutions with a molar ratio of SiO 2: Na 2 O of up to 2.27: 1 are disclosed.
  • DE-OS 33 13 814 relates to a process for the preparation of a clear solution of a sodium silicate, the molar ratio silicon dioxide: sodium oxide of which is at most 2.58: 1, by digestion of crystalline silicon dioxide with an average grain size between 0.1 and 2 mm, in which an aqueous solution of sodium hydroxide passes through a bed of silicon dioxide, which is formed in a vertical tubular reactor without mechanical movement and is fed from top to bottom with silicon dioxide and the aqueous solution of sodium hydroxide.
  • Belgian patent specification 649 739 relates to a method and an apparatus for the production of clear sodium silicate bases by dissolving a material containing silicic acid at high temperature and under pressure in aqueous caustic soda solution, which is characterized in that the product is made from the excess material containing silicic acid and / or is separated from the insoluble contaminated substances by means of filter elements which are attached in the vicinity of the reactor bottom, the said filtration advantageously taking place under the temperature and pressure conditions which are very similar to the reaction conditions.
  • the aqueous sodium silicate solutions obtained in this way have a molar ratio SiO 2: Na 2 O of about 2.5: 1.
  • the present invention is based on the object of a method for the hydrothermal production of To provide sodium silicate solutions by reacting crystalline silicon dioxide with aqueous sodium hydroxide solution, in which, among other things, quartz, ie
  • the object of the invention is achieved by hydrothermal conversion of quartz, i.e. Sand, with aqueous sodium hydroxide solutions and subsequent hydrothermal conversion of the sodium silicate solutions obtained as an intermediate product with a specially tempered quartz.
  • the present invention thus relates to a process for the hydro-thermal production of sodium silicate solutions with high SiO 2: Na 2 O molar ratios by reacting quartz sand with aqueous sodium hydroxide solutions at temperatures in the range from 150 to 300 ° C and the pressures corresponding to these temperatures saturated water vapor in a pressure reactor, which is characterized in that the sodium silicate solutions obtained in this way, which have SiO 2: Na 2 O molar ratios of less than 2.9: 1, then with a temperature at Implemented in the range from over 1100 ° C to quartz tempered to the melting point, temperatures and pressures also being maintained in the ranges mentioned.
  • the process according to the invention is technically more straightforward to use due to its simple process control and is therefore more cost-effective than the technically complex, large amounts of energy which are required and which are extremely harmful to the environment, ie the high-temperature melting process with the subsequent solution step .
  • the process according to the invention has the advantage that, through the use of the specially tempered quartz as crystalline silicon dioxide component, sodium silicate solutions with an SiO 2: Na 2 O molar ratio of more than 2.9 are also used in the subsequent process step : 1 can be obtained, which, as discussed above, has not hitherto been possible according to the prior art hydro-thermal processes using quartz, ie sand.
  • tempered quartz as the silicon dioxide component and a sodium silicate solution as part of a hydrothermal synthesis under the conditions specified above enables the direct manufacture of aqueous sodium silicate solutions as end product with short reaction times, which has a molar ratio of SiO 2 : Na2 ⁇ of more than 2.9: 1.
  • sodium silicate solutions with high silicon dioxide-sodium oxide molar ratios are obtained in a technically simple and very economical manner by carrying out the basic reaction, ie the conversion of quartz (sand) and aqueous sodium hydroxide solution can initially use the less expensive silicon dioxide component, ie sand, and only uses the more expensive crystalline silicon dioxide component obtained by quartz annealing only for a "silicification reaction".
  • sodium silicate solutions with an S 2 Establish a Na2 ⁇ -ol ratio of 2.9 to 3.6: 1.
  • the sodium silicate solutions thus obtained preferably have SiÜ2: Na2 ⁇ molar ratios from 3.0 to 3.5: 1 and particularly preferably from 3.3 to 3.5: 1.
  • quartz, i.e. Sand, sodium silicate solutions initially obtained as an intermediate with sodium hydroxide solutions can be obtained in a manner known per se by any corresponding prior art method.
  • quartz sand with aqueous sodium hydroxide solution in a concentration range from 10 to 50% by weight, in particular from 15 to 30% by weight, in a pressure reactor, temperatures in the range from 150 to 300 ° C., in particular in the range from 200 to 250 ° C., and the pressures of saturated water vapor corresponding to these temperatures are observed.
  • the sodium silicate solutions obtained in this way have SiO 2: Na 2 O mol ratios of less than 2.9: 1 and in general solids concentrations in the range from 20 to 55%.
  • sodium silicate solutions are preferred as the intermediate product which have solid concentrations in the range from 25 to 40%, in particular from 30 to 38%.
  • the sodium silicate solutions obtained as an intermediate, as described above are subsequently quartz-annealed at temperatures in the range from 1200 to 1700 ° C. with the addition of catalytic amounts of alkali essentially converted into cristobalite under these tempering conditions, reacted as part of the hydrothermal synthesis under the conditions specified above.
  • cristobalite is a crystal modification of silicon dioxide. This is practically exclusively produced synthetically by calcining quartz, by continuously converting quartz sand at temperatures of approximately 1500 ° C. with the addition of catalysts (alkali compounds).
  • quartz tempered at temperatures in the range from 1300 to 1600 ° C. with the addition of catalytic amounts of alkali, which quartz essentially converts to cristobalite under these tempering conditions. It is also particularly advantageous to use a freshly tempered, yet warm cristobalite material for the process according to the invention.
  • the stoichiometrically required amount of cristobalite based on the desired SiO 2: Na 2 O molar ratio, can be used as the end product desired sodium silicate solution.
  • excesses of up to 100% of cristobalite again based on the desired ratio SiO 2: Na 2 O in the target end product, can be used.
  • the implementation can also be carried out with excesses greater than 100% of cristobalite; however, this is generally not technically sensible.
  • the hydrothermal reaction with an excess of 1 to 10% of tempered quartz, ie in particular cristobalite, based on the desired SiO 2: Na 2 O mol ratio in the end product.
  • the hydrothermal preparation of the end product sodium silicate solutions with a high SiO 2: Na ⁇ molar ratio is carried out in the following manner: First, quartz sand and aqueous sodium hydroxide solution (sodium hydroxide solution) are carried out on one Temperature and pressure level implemented in the pressure reactor.
  • the annealed quartz, in particular the cristobalite, which is to be added to the sodium silicate solution formed as an intermediate, is brought to the same temperature and pressure level and is thus combined in the pressure reactor with the sodium silicate solution present therein.
  • the hydrothermal synthesis is then continued under the same temperature and pressure conditions until the target molar ratio SiÜ2 • • Na2 ⁇ in the range from 2.9 to 3.6: 1 of the end product is reached.
  • the pressure vessel can first be relaxed and allowed to cool to a practical working temperature, then the cristobalite, which may also have been preheated, can be fed into the pressure vessel and - after the desired temperature and pressure conditions have been restored - hydrothermal synthesis End lead.
  • the preferred procedure described above which can be described as practically one-stage in view of the constant temperature and pressure conditions in hydrothermal synthesis, has particular economic advantages with regard to high space / time yields with minimal energy consumption .
  • reactors customary for the hydrothermal synthesis of sodium silicate can be used to carry out the process according to the invention.
  • These include, for example, rotating solvers, standing solver arrangements, reactors with agitators, Jet loop reactors, tubular reactors and, in principle, all reactors which are suitable for reacting solids with liquids under pressure.
  • Such reactors are described in detail, for example, in DE-OS 30 02857, DE-OS 34 21 158, DE-AS 28 26 432, BE-PS 649 739, DE-OS 33 13814 and in DE-PS 968034.
  • a suitable separate pressure vessel in which the cristobalite to be added to the sodium silicate solution formed as an intermediate product can be brought to the desired temperature and pressure level.
  • This separate pressure vessel is either directly connected to the actual reactor by corresponding lines provided with shut-off elements, or it is connected to the actual reactor via appropriate lines, for example in the case of rotating reactors, if necessary.
  • the devices and equipment required here are also familiar to the person skilled in the art.
  • the finished end product - the sodium silicate solution with a high SiO 2: Na 2 O molar ratio - is released from the pressure reactor after it has been let down and, if desired, can also be subjected to filtration for cleaning. All filter devices known to those skilled in the art for the filtration of water glass solutions can be used for this purpose.
  • sodium silicate solutions sodium silicate solutions prepared in the manner according to the invention can be used for all common uses which are known to the person skilled in the art and are described in the relevant literature, for example for the production of fillers (precipitated silicas) as adhesives , as a binder in paints, foundry auxiliaries, Catalyst carriers, as a component in detergents and cleaning agents, and as a component for refractory materials.
  • a cristobalite obtained by tempering at 1300 to 1600 ° C. and alkali catalysis was used as the annealed quartz.
  • a horizontally arranged cylindrical pressure vessel made of steel with a nickel lining with a volume of approximately 0.5 1 served as the reactor for carrying out the tests.
  • the pressure vessel rotated about its horizontal axis at a speed of approximately 60 revolutions per minute. Heating was carried out from the outside via a heat transfer medium heated to the reaction temperature.
  • Sodium silicate solutions with a SiO2: Na2O molar ratio of 2.0: 1 and 2.5: 1 were prepared from sand and sodium hydroxide solution, added to the pressure reactor with the addition of cristobalite and at 215 or 225 ° C and reaction times between 20 and 60 min converted to sodium silicate solutions with a S1O2: Na2 ⁇ molar ratio of 3.33 to 3.50: 1.
  • Example 1 relates to the preparation of a sodium silicate solution with a molar ratio SiO 2: a 2 O of 2.0: 1;
  • Examples 2 to 7 relate to the reaction of such a “base” sodium silicate solution, ie one with a molar ratio of SiO 2 J Na 2 O ⁇ 2.9: 1, with cristobalite.
  • the process for producing the basic sodium silicate solution with a molar ratio ⁇ 2.9: 1 can be directly combined with the subsequent reaction of the reaction of this sodium silicate solution with the addition of cristobalite to the desired sodium silicate solution with a SiO: Na2 ⁇ molar ratio of 2 , 9 to 3.6: 1. This process flow is described below:
  • the quantities of material are recorded using weighing devices.
  • the raw materials sand and caustic soda are filled into the reactor, which is then sealed and set in rotation.
  • the reaction mixture is then heated to a reaction temperature of approximately 215 ° C. and left at this temperature. After a reaction time of 30 minutes at this temperature, the reactor is brought to a standstill.
  • the required amount of cristobalite is transferred from a pressure vessel flanged to the reactor and filled with cristobalite, which is brought to the same pressure as the reaction vessel, and which reacts the previously formed sodium silicate solution with a molar ratio SiO 2: Na 2 O of contains about 2.5: 1, dosed. Then the pressurized reservoir is closed again, decompressed and separated from the reactor. The amount of cristobalite added corresponds to the additional SiO 2 fraction which is required to achieve a SiO 2 '• Na 2 O 3 molar ratio of 3.46: 1 in the sodium silicate solution aimed for as the final product. The reactor is then left at the reaction temperature for a further 20 to 60 min.
  • the soda-water glass solution can then be worked up either via a sedimentation tank for the rough separation of solids or - in the case of higher requirements for the clarity of the solution - via a filter.
  • a sedimentation tank for the rough separation of solids or - in the case of higher requirements for the clarity of the solution - via a filter.
  • the hydrothermal process can also take place in the reactor at relatively high solids concentrations, since under reaction conditions, for example 215 ° C./20 bar, the sodium silicate solution in the reactor has a viscosity range which is sufficient for the process.
  • water can then be added either
  • This example relates to the preparation of a "base” sodium silicate solution, which served as the starting material for the further reaction with cristobalite.
  • This sodium silicate solution was further reacted with cristobalite, as described in Example 2.
  • the sodium silicate solutions, which served as starting materials for the further reactions according to Examples 3 to 7, were obtained analogously to Example 1 with appropriately changed batch ratios (SiO 2: Na 2 O 2.5: 1) and extended reaction times (90 min).
  • Examples 3, 4 and in particular 5 show that the reaction of sodium silicate solutions with a molar ratio SiO 2: Na 2 O ⁇ 2.9: 1 with the crystalline SiO 2 component cristobalite increases even with short reaction times ( ⁇ 30 min) and relatively low reaction temperatures Sodium silicate solutions with molar ratios SiO2: Na2O between 3.33 and 3.43: 1 leads.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Silicates, Zeolites, And Molecular Sieves (AREA)
  • Silicon Compounds (AREA)

Abstract

Selon un procédé de production hydrothermique de solutions de silicate de sodium ayant un rapport molaire élevé entre SiO2 et Na2O, on convertit du sable quartzeux avec une solution aqueuse d'hydroxyde de sodium en une solution de silicate de sodium ayant un rapport molaire entre SiO2 et Na2O inférieur à 2,9:1, puis on convertit le produit intermédiaire ainsi obtenu (la solution de silicate de sodium) avec du quartz stabilisé à des températures supérieures à 1100°C jusqu'à son point de fusion.
EP90901810A 1989-01-31 1990-01-22 Procede de production hydrothermique de solutions de silicate de sodium Withdrawn EP0456655A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3902754 1989-01-31
DE3902754A DE3902754A1 (de) 1989-01-31 1989-01-31 Verfahren zur hydrothermalen herstellung von natriumsilikatloesungen

Publications (1)

Publication Number Publication Date
EP0456655A1 true EP0456655A1 (fr) 1991-11-21

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EP90901810A Withdrawn EP0456655A1 (fr) 1989-01-31 1990-01-22 Procede de production hydrothermique de solutions de silicate de sodium
EP90101196A Pending EP0380997A1 (fr) 1989-01-31 1990-01-22 Procédé de préparation hydrothermale de solutions de silicates de sodium

Family Applications After (1)

Application Number Title Priority Date Filing Date
EP90101196A Pending EP0380997A1 (fr) 1989-01-31 1990-01-22 Procédé de préparation hydrothermale de solutions de silicates de sodium

Country Status (16)

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EP (2) EP0456655A1 (fr)
JP (1) JPH04503049A (fr)
KR (1) KR910700202A (fr)
CN (1) CN1044632A (fr)
AU (1) AU623221B2 (fr)
BR (1) BR9007066A (fr)
CS (1) CS276432B6 (fr)
DD (1) DD291535A5 (fr)
DE (1) DE3902754A1 (fr)
DK (1) DK141591A (fr)
HU (1) HUT60697A (fr)
NZ (1) NZ232272A (fr)
TR (1) TR24118A (fr)
WO (1) WO1990008734A1 (fr)
YU (1) YU14390A (fr)
ZA (1) ZA90679B (fr)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE500367C2 (sv) * 1989-11-09 1994-06-13 Eka Nobel Ab Silikasoler och förfarande för framställning av papper
CN101279738B (zh) * 2008-05-12 2011-12-21 崔国强 利用一步法液相反应制备液态硅酸钠的液相反应锅
CN102115092A (zh) * 2011-04-22 2011-07-06 冷水江三A化工有限责任公司 一种液相法生产高模数硅酸钠的方法
CN103964451B (zh) * 2014-04-29 2016-04-06 深圳市国大长兴科技有限公司 利用石英石抛光废粉制备硅酸盐水溶液的方法
BR102020016451B1 (pt) * 2020-08-12 2021-11-03 Pq Silicas Brazil Ltda Solução estável de silicato de sódio e ferro, processo para preparar a referida solução e seus usos

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3002834A1 (de) * 1980-01-26 1981-07-30 Henkel KGaA, 4000 Düsseldorf Verfahren zur hydrothermalen herstellung von natriumsilikatloesungen in einem statischen reaktionsbehaelter
DE3002857A1 (de) * 1980-01-26 1981-07-30 Henkel KGaA, 4000 Düsseldorf Verfahren zur hydrothermalen herstellung von natriumsilikatloesungen
DE3121919A1 (de) * 1980-06-24 1982-04-29 Steirische Magnesit-Industrie AG, 1130 Wien Hydrothermale direktsynthese von alkalisilikaten
FR2541667B2 (fr) * 1982-04-16 1986-07-04 Ugine Kuhlmann Procede de fabrication de solutions de silicate alcalin dans un reacteur statique
FR2525204A1 (fr) * 1982-04-16 1983-10-21 Ugine Kuhlmann Procede de fabrication de solutions de silicate alcalin dans un reacteur statique
DE3421158A1 (de) * 1984-06-07 1985-12-12 Henkel KGaA, 4000 Düsseldorf Verfahren zur hydrothermalen herstellung klarer natriumsilikatloesungen

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9008734A1 *

Also Published As

Publication number Publication date
DK141591D0 (da) 1991-07-30
NZ232272A (en) 1991-02-26
CN1044632A (zh) 1990-08-15
HU912542D0 (en) 1992-07-28
HUT60697A (en) 1992-10-28
CS9000415A2 (en) 1991-01-15
DK141591A (da) 1991-07-30
CS276432B6 (en) 1992-05-13
JPH04503049A (ja) 1992-06-04
TR24118A (tr) 1991-05-01
EP0380997A1 (fr) 1990-08-08
KR910700202A (ko) 1991-03-14
DD291535A5 (de) 1991-07-04
BR9007066A (pt) 1991-10-08
DE3902754A1 (de) 1990-08-02
YU14390A (en) 1991-08-31
AU623221B2 (en) 1992-05-07
AU4957190A (en) 1990-08-24
ZA90679B (en) 1990-11-28
WO1990008734A1 (fr) 1990-08-09

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