MXPA00006871A - Method of producing substantially spherical lyogels in water insoluble silylating agents - Google Patents

Abstract

A method of producing substantially spherical lyogels in water insoluble silylating agents. The present invention refers to a method of producing substantially spherical lyogels in which a) a lyogel is provided, b) the lyosol obtained in step a) is transferred to at least one silylating agent in which the lyosol is insoluble, and c) the spherical lyosol formed in step b) is gelatinised in at least one silylating agent in which the lyosol is likewise insoluble, to produce the lyogel.

Description

Method for producing considerably spherical lyogels in water-insoluble silylating agents The aim of the present invention is a method for producing considerably spherical lyogels in water-insoluble silylating agents. Aerogels, particularly those that have a porosity of more than 60% and densities less than 0.6 g / cu.cm, have an extremely low thermal conductivity and are therefore used as a heat insulating material, as described for example in the application EP-A-0 171 722. Aerogels in the broadest sense, for example in the sense of "gel with air as the dispersing agent", are produced by drying an appropriate gel. The term "airgel" in this sense includes angels in the most limited sense, xerogels and cryogels. In relation to this, a dry gel is described as an airgel in the most limited sense, when the fluid in the gel is removed at temperatures above the critical temperature and with effects of pressure above the critical pressure. On the other hand, if the fluid is removed from the gel subcritically, that is, with the formation of a fluid-vapor interface, then the gel produced is usually referred to as a xerogel as well. Where the use of the term aerogels in the present Application concerns, these are aerogels in the broadest sense, for example, in the sense of "gel with air as a dispersing agent". In addition, aerogels can, in accordance with the gel structure class, be basically subdivided into inorganic and organic aerogels. Inorganic aerogels have been known since 1931 (S. Kistler, Nature 1931, 127, 741). These first aerogels were produced from water glass and an acid as the initiating materials. In this case, the water in the resulting wet gels was exchanged for an organic solvent and this lyogel was then dried supercritically. In this way, hydrophilic aerogels were obtained (US-A-2 093 454). To date, a complete series of the broadest diversity of inorganic aerogels has been produced. For example, aerogels Si02_, Al203-, Ti02-, Zr02-, Sn02. -, Li02-, Ce02- and V205-, as well as mixtures of these have been produced (H.D. Gesser, P.C. Goswami, Quim.Rev. 1989, 89, 765 and subsequent). For some years, organic aerogels have also been known. In the literature, for example, we find organic aerogels based on resorcin / formaldehyde, melamine / formaldehyde or resorcin / furfural (RW Pekala, J. Mater, Sci. 1989, 24, 3221, US-A-5 508 341, RD 388047 , WO 94/22943 and US-A-5 556 892). In addition, organic aerogels produced from polyoscyanate are also known (WO 95/03358) and from polyurethanes (US-A-5 484 818). As described for example in the application US-A-5 508 341, the initiating materials are those such as formaldehyde and melamine dissolved in water, which are combined and reacted by appropriate catalysts, the water in the stops of the formed gel is exchanged by an appropriate organic solvent and follow supercritical drying. Inorganic aerogels can be produced in several ways. On the one hand, Si02 aerogels can be produced, for example, by acid hydrolysis and the condensation of tetraethyl orthosilicate in ethanol. The result is a gel that can be dried by supercritical drying to retain the structure. Production methods based on this drying technique are known, for example, from applications EP-A-0 396 076, WO 92/03378 and WO 95/06617. An alternative for top drying is given by a method for the subcritical drying of Si02 gels, in which the latter, before drying, is reacted with a silylating agent containing chlorine. In addition to the tetra-alkoxy silanes used as initiator materials in the methods described above, in any case, it is also possible to use water glasses as initiator materials, with competitive pricing for the production of Si02 aerogels. If the glass of water is used as the initiator material, then the lyogel will always be formed predominantly in an aqueous phase.

For this purpose, it is possible to produce, for example, an aqueous glass water solution and by mechanisms of an ion-forming resin, a silicic acid which can be polycondensed by adding a base to produce a SiO2 gel. After the medium exchange aqueous to an appropriate organic solvent, it can then be dried supercritically or subcritically. For subcritical drying, in another step, the gel obtained is reacted, for example, with a silylating agent containing chlorine. By virtue of the other reactivity, methylchlorosilanes are preferably used (Me4_I1SiCla: 1 in which n = 1 to 3) as silylating agents. The resulting Si02 gel, modified on the surface with methylsilyl groups, can then be dried in the air outside of an organic solvent. The production method based on this technique is disclosed, for example, in the application EP-A-0 658 513. Other special methods for producing aerogels in an aqueous lyogel base are described in the applications WO 05/06617, DE-A-195 41 279, WO 96/22942, and DE-A-195 25 021, as well as the unpublished German Patent Applications 196 31 267, 196 48 797 and 196 48 798. In the case of wet gels, xerogels and also aerogels, the form plays a decisive role according to the subsequent use. For example, if a macroscopic form defined especially for aerogels is to be given, for example, then this must be carried out during the course of airgel production and in fact before, during and / or immediately after the formation of the airgel. hydrogel or lyogel. While producing the airgel, the macroscopic fiormas present as hydrogel, lyogel or airgel can only be pulverized by methods such as grinding, which is known to a person skilled in the art. Either way, in general the result is that there are no clearly defined forms. Another set of problems occurs in the case of all products in a hydrogel or lyogel base and that must have a defined macroscopic shape. In the case of aerogels dried subcritically, the form acquires another special role. During the course of subríctico drying of organically modified lyogels, there is a considerable shrinkage of up to 90% by volume. Just before finishing the drying, the shrinked lyogels then return to a volume approaching their initial volume, according to the kind of gel and surface modification. This is known to a person skilled in the art as "returning to its original volume". Where said process is related, so that the network of gel particles is retained and there is no splintering or breaking, the gel particles as many as possible are ideally and alternately symmetrical. Again, this must take place in the pervious formation stage a, during and / or immediately after the formation of the hydrogel or lyogel.

In this Application, it is understood that the lyogels mean any gel in the gel pores of which there is at least one solvent. Within the meaning of this Application, hydrogels have more than 50% by volume of water relative to the solvent phase in the pores. Initially, to produce a lyogel, a liosol must be gelatinized to build the lyogel network. The reaction times linked by this vary between a few seconds and a few hours. Since the formation stage must take place at this time to guarantee the macroscopic form clearly defined and mentioned above, it must be adapted to the respective gelatinization time. Because the properties of the lyogel are almost dependent on the time of gelatinization, the formation process is very important for the subsequent properties. The literature describes methods for forming lyogels. In this regard, distinction is made between the methods in which the liosol is carried within a vapor and / or gas atmosphere or within a water-soluble fluid. In the application DE-C-21 03 243 a method is described in which, by means of a special mixing nozzle, a hydrosol of an acid solution and a raw material containing suicide acid is formed and, by droplet formation, it is sprayed into a gaseous medium, for example, air. Either way, the drawback with that method is that where the relatively large particles are being produced, the drip distance must be of a corresponding length, .. depending on the gelatinization time. Consequently, even with extremely short gelatinization times, only a few seconds, this method is limited to very small particles. In addition, there is no homogeneous distribution of the lyogel particles. In the unpublished German Patent Applications 197 22 737 and 197 22 738, a method is disclosed wherein the liosol is sprayed into a vapor atmosphere. In relation to this, the result of this are disadvantages similar to those described above. Somehow larger and more uniform particles can be achieved using water insoluble fluids as the formation medium. It is known, for example, from DE-C-896189 that spherical hydrogels can be produced in that silica hydrosol which forms the gel, from a raw material containing silicic acid, by reaction with an acid, and then this can be passed off in the form of individual drops through a fluid medium, for example a mineral oil, which is not miscible with water, and hydrosol. The hydrosol drops thereby acquire a more or less spherical shape and remain in the oil layer until the time when the conversion of the sol to the solid hydrogel has taken place. The hydrogel spheres produced by this method in any way comprise impurities of mineral oil which can not be completely removed, even by means of costly washing. In the applications DD-C-253242 and DD-C-253243 a method is described in which the residues in the gel particles are adequately removed by an expensive process. In application DD-C-253242, the hydrosol is sprayed into an oil column in which the water forms a layer below. The gel particles formed in the oil column are released from any attached oil residue in a CC14 phase and / or a water phase. Then, with certainty, these cleaning phases must be recycled once more by distillation. In application DD-C-253243, the gel particles are formed in a CC14 phase with an upper water layer. The hydrosol is introduced into the CC14 phase from below and the gel particles that are formed are cleaned from the attached CCl4 residues, by transferring them into the water phase. In any case, due to the reason of its chemical composition, since gel particles have a greater density than water, they are placed directly on the boundary of the phase which makes easy separation difficult. On the other hand, in this case also, the water phase must have a costly cleaning. Therefore, the object of the present invention is to provide a method for producing practically spherical lyogels in which no residue of the formation medium has to be removed from the gel particles before they are subjected to silylation and / or subsequent drying. Surprisingly, this problem is solved by a method to produce practically spherical lyogels in which a) a liosol is provided, b) the liosol obtained in step a) is transferred to at least one silylating agent in which the liosol is insoluble or is not notoriously soluble, and c) the spherical liosol formed in step b) is coagulated in at least one silylating agent in which the lyosol is either insoluble or notoriously soluble.

Preferably, in step b) and also in step c), only one silylating agent is used. It is particularly preferred to carry out the formation in step b) and the coagulation in one step, and therefore also only in a silylating agent. In the present Application, it is intended that the term liosol means a Sun, the molecules or particles that form it are dissolved, suspended and / or dispersed in at least one solvent. Preferably, the liososl used is a hydrosol. The hydrosol, according to the present Application, means that the solvent contains at least 50% by weight and preferably at least 80% by weight and particularly preferably at least 90% by weight and in particular at least 98% by weight. % by weight of water. In the present Application, the term coagulation means that the liosol exceeds the gel point. The lyogel network formed in step c) may be present in any desired organic and / or inorganic basic composition. Any system known to a person skilled in the prior art technique is possible as a basic organic composition. A basic inorganic composition based on compounds of silicon oxide, tin, aluminum, gallium, indium, titanium and / or zirconium is preferred. More particularly, a silicone hydrogel which may contain fractions of zirconium, aluminum, titanium, vanadium and / or iron compounds, particularly a purely silicic hydrogel, is preferred. Where basic organic and / or inorganic compositions are related, the various components do not necessarily have to be homogenously distributed and / or form a continuous network. It is also possible for the individual components to be present in whole or in part in the form of inclusions, cores and / or deposits in the network. Hereinafter, two preferred embodiments are described for the production of a liosol without in any way restricting the invention. In a first preferred embodiment, in step a), a silicate liososl is produced in that aqueous glass water solution which is transferred by means of an exchange resin from the acid ion to a silica sol having a pH value of < 3. Preferably, the glass of sodium and / or potassium water is used as water glass. As an ion exchange resin, an acid is preferably used, particularly that which contains sulfonic acid groups is appropriate. Prior to step b), the pH value of the liosol can possibly be increased by means of a base to achieve a more rapid formation of the gel in step c). By this, the pH value is generally between 2 and 8, preferably between 4 and 6 and particularly preferably between 4 and 5. Generally, the bases used are NH408, NaOH, KOH, Al (OH) 3 and / or colloidal silicic acid. The liosol produced preferably from the silicone starting compounds described above may additionally contain zirconium, aluminum, tin and / or titanium compounds which are capable of producing condensation. In addition, before and / or during the production of Sol, opacifiers can be added as additives, particularly infrared opacifiers to produce the contribution of radiation to the heat conductivity, such as carbon black, titanium oxides, iron oxides and / or zirconium oxides. In addition, fibers can be added to the Sun to increase its mechanical stability. Inorganic fibers, such as glass fibers or mineral fibers, organic fibers such as polyester fibers, aramid fibers, nylon fibers or fibers of vegetable origin, as well as mixtures thereof, can be used as the fiber materials. Fibers can also be covered, for example, polyester fibers metallized with a metal such as aluminum for example. In a second preferred embodiment, step a) provides a silicotic liosol which is produced in a silica sol which is obtained from an aqueous glass water solution with the aid of at least one organic and / or inorganic acid . Thus, in general, 6 to 25% by weight (based on the SiO2 content) of glass water solution of sodium and / or potassium is used. Preferably, 10 to 25% by weight of glass water solution and in particular 10 to 18% by weight of water glass solution is used. In addition, the water glass solution can also contain up to 90% by weight (relative to SiO2) of zirconium, aluminum, tin and / or titanium compounds capable of producing condenization. As acids, in general 1 to 50% by weight and preferably 1 to 10% by weight of acids are used. The preferred acids are sulfuric, phosphoric, fluoric, oxalic and hydrochloric acids. Particular preference is given to hydrochloric acid.

In any case, it is also possible to use mixtures of the appropriate acids. In addition to the actual mixture of the water glass solution and the acid, it is also possible, before the actual mixing, to introduce a part of the acid into the glass water solution and / or a part of the glass solution of water. water in the acid. In this way, it is possible to vary the proportion of the water / acid glass solution flows over a very broad index. After the two solutions have been mixed, preferably 5 to 12% by weight of SiO2 Sol is obtained. Particularly 6 to 9% by weight of SiO2 Sol is preferred. In addition, it is convenient that the pH value of liosol is between 2 and 8, preferably between 4 and 5. If necessary, also the pH value can be increased by means of a base to achieve a more rapid formation of the gel in step c). The base used is generally NH408, NaOH, KOH, Al (OH) 3 and / or colloidal silicic acid. To achieve the most complete possible mixture of the water glass solution and the acid, it is desirable that both solutions, preferably independently of one another, be at a temperature between 0 and 30 ° C, particularly preferably between 5 and 30 ° C. 25 ° C and in particular between 10 and 20 ° C. The complete rapid mixing of the two solutions is carried out in the apparatus with which a person skilled in the art is familiar, such as mixing vats, jet mixers and static mixers. Semi-continuous or continuous methods such as jet mixers are preferred. In addition, it is possible to add to the water glass, the acid and / or the sun opacifying agents as additives, particularly the IR opacifiers to reduce the contribution made by the readiation to the heat conductivity, as for example, carbon black, oxides of titanium, ion oxides and / or zirconium oxides. In addition, fibers can be added to the glass of water, acid and / or Sol to increase mechanical stability. As fiber materials, inorganic fibers such as for example glass fibers or mineral fibers, organic fibers such as polyester fibers, aramid fibers, nylon fibers or fibers of vegetable origin, as well as fibers can be used. mixtures of these. The fibers can also be covered, for example, polyester fibers metallized with a metal such as aluminum. In step b), the liosol obtained in step a) is transferred to at least one insoluble silylating agent. In this case, the silylating agent appears as a fluid. For the formula (I) the disiloxanes are used as silylating agents in steps b) and e). R3Si-0-SiR3 (I) in which the radicals R, independently of one another, are the same or different, each representing a hydrogen atom or a saturated or unsaturated aromatic or heteroaromatic radical, non-reactive, organic, linear , branched and cyclic, preferably C1-C18-alkyl or C6-C14-aryl and particularly preferably CL-Cg-alkyl, cyclohexyl or phenyl and in particular methyl or ethyl. A symmetrical disiloxane is preferred, this term meaning a disiloxane in which both Si atoms have the same radicals R. Particularly preferably disiloxanes are used in which all radicals R are the same. Particularly hexamethyl disiloxane is used. In addition, any silylating agent known to a person skilled in the art, which is not miscible with water, can be used. The temperature of the silylating agent in step b) can be between 0 ° C and the boiling point of the liquid phase in the liosol. Preferred temperatures are between 20 ° C and 120 ° C, particularly preferably between 40 ° C and 120 ° C and more particularly preferably between 40 ° C and 100 ° C. It is also possible to work under pressure at higher temperatures. By means of this the liosol can be incorporated into the silylating agent by any method known to a person skilled in the art., as for example, using jet mixers or distribution media. The silylating agent thus forms a phase in which the liosol forms substantially spherical droplets by virtue of the interfacial tension. The size of the droplet can be adjusted by this, - for example, according to the form of introduction, the mass flows and the distance from the liquid surface. Surprisingly, it has been found that, once formed, the droplets are mutually repellent as long as they are completely enclosed by the fluid medium. Consequently, a more limited distribution of the droplet sizes is guaranteed. In step c), the spherical liosol formed in step b) coagulates in the silylating agent to produce the lyogel. The temperature of the silylating agent in step c) can hereby be between 0 ° C and the boiling point of the liquid phase in the liosol. Preferred temperatures are between 20 ° C and 120 ° C, particularly preferably between 40 ° C and 120 ° C, very special preference is given at temperatures between 40 ° C and 100 ° C. It is also possible to work at higher temperatures under pressure. The temperature can be used to influence the gelatinized index. Generally, liosol is gelatinized more rapidly at a higher temperature. The water-insoluble silylating agent can thereby be present in any kind of container, in any case a column placement is preferred. Where the column placement is related, preferably the lyosol is transferred from above (if the density of the agent or silylating agents is less than the density of the lyosol) or from below in or within the agent or silylating agents. In this regard, the method described above known to a person skilled in the art can be used. The drying time of the lyosol droplets or lyogeTL particles can be adjusted by the height of the column filled with the silylating agent. The gelatinized index can also be adjusted by these means. Furthermore, according to the nature and / or temperature of the silylating agent, a different density and / or viscosity of the fluid will be present, so that the drying time of the liosol droplets or lyogel particles can be adjusted in this way. In addition, practically the size of the liosol droplets or lyogel particles is determined by this. The silylating agent can basically be present in a stationary or moving form, and preferably in any form is still. Possibly an aqueous phase may be present under the silylating agent. If the liosol droplets are coagulated during the drying time in the silylating agent, then the gel particles formed will fall through the phase boundary of the two fluids and the silylating agent is removed from the gel particles with virtually no residues. To achieve greater stability of the gel particles, they can remain in the silylating agent or in a little more aqueous phase. This produces a maturation of the gel. In addition, a longer drying time in the silylating agent can cause silylation of the outer surface. As a result, the particles may be better suspended in an organic solvent for another subsequent treatment. In addition, the particles obtained in this manner can also be processed by known methods to produce aerogels. In relation to this, the hydrophobic aerogels that last are preferred, which are modified by silylating agents.

Another advantage of the present invention is that in other processing of the lyogels produced to obtain hydrophobic aerogels permanently by silylation and subsequent drying preferably subcritical, expensive washing steps should not be carried out. The present invention is explained in greater detail hereinafter, with reference to an example of the embodiment, without being thereby restricted. Example Production of gel articles in HMDSO fluid: - column height: 4 m - column diameter: 25 cm - temperature: 80 to 90 ° C 2 liters of a glass solution of sodium water (Si02 content 6% by weight ) and Na20: Si02 (ratio of 1: 3.3) are passed over a lined glass column (length 100 cnm diameter 8 cm) filled with an acid ion exchange resin (benzene copolymer of divinylstyrene with sulfonic acid groups, commercially available under the name of ®Dolite C 20) (approximately 70 ml / min). The column is placed at a temperature of about 7 ° C. The solution of silicic acid spilling on the lower end of the column has a pH value of 2.3. The sol of the ion exchanger is adjusted to a pH value of 4.6 to 4.9 by NaOH (0.5 to 1 molar) in a mixer. Then it is cooled (7 ° C) and by means of a pump it is passed through a hose (internal diameter of 4 mm, distance from the surface of the HMDSO approximately 5 to 10 cm) and on top of the hot HMDSO surface. The resulting hydrosol droplets slowly fall down into the HMDSO fluid and can be removed while the hydrogel spheres are suspended directly from the hot HMDSO or, by means of a second water phase (below the HMDSO phase in the column) in the water and remove from the column. The gel particles have an average diameter of 2 mm.

Claims (1)

1. CLAIMS A method for producing considerably spherical lyogels in which a) a lyogel is available b) the liosol obtained in step a) is transferred to at least one silylating agent in which the liosol is insoluble, and c) the spherical liosol formed in step b) is gelatinized in at least one silylating agent in which the liosol is likewise insoluble, to produce the lyogel. A method according to claim 1, characterized in that in each case only a silylating agent is used in step b) and in step c). A method according to claim 1 or 2, characterized in that the liosol obtained in step a) is transferred to a silylating agent and gelatinized therein to produce the lyogel. A method according to at least one of the preceding claims, characterized in that a liosol is provided as silicate. A method according to at least one of the preceding claims, characterized in that in step a) a lyogel as silicate is presented, which is produced in that aqueous glass water solution which is transferred by means of an exchange resin from acid ion to a silica sol with a pH value < . 3. A method according to at least one of claims 1 to 4, characterized in that in step a) a liosol such as silicate is presented, which is produced in that silica sol obtained from an aqueous glass solution of water by means of at least one organic and / or inorganic acid. A method according to at least one of the preceding claims, characterized in that a hydrosol is presented in step a). A method according to at least one of the preceding claims, characterized in that the silylating agent in steps b) and c) is presented as fluid. A method according to at least one of the preceding claims, characterized in that the liosol is introduced into the silylating agent of step b) by means of mixing nozzles or distributing mechanisms. A method according to at least one of the preceding claims, characterized in that in steps b) and e), disiloxanes are used for the formula (I) as the silylating agent R3Si-0-SiR3 (I) the radicals R are independently of each other identically or differently, each denoting a hydrogen atom or an aromatic or heteroaromatic radical saturated or unsaturated, non-reactive, organic, linear, branched, cyclic. 11. A method according to claim 10, characterized in that a symmetrical disiloxane such as disiloxane is used. 12. A method according to claim 10 or 11, characterized in that a disiloxane is used in which all the radicals R are the same. 13. A method according to claim 10 or 11, characterized in that a hexamethyl disiloxane is used as the disiloxane. 14. A method according to at least one of claims 10 to 12, characterized in that the silylating agent in step c) is placed in one. column. 15. A method according to at least one of the preceding claims, characterized in that the obtained lyogel is modified and then dried. 16. A method according to claim 15, characterized in that the modified lyogel is dried subcritically.