EP3253818A1

EP3253818A1 - Method for producing an aerogel material

Info

Publication number: EP3253818A1
Application number: EP16703515.3A
Authority: EP
Inventors: Matthias Koebel; Lukas Huber
Original assignee: Eidgenoessische Materialprufungs und Forschungsanstalt EMPA
Current assignee: Eidgenoessische Materialprufungs und Forschungsanstalt EMPA
Priority date: 2015-02-04
Filing date: 2016-02-04
Publication date: 2017-12-13
Also published as: JP2018511663A; CN107428545B; AU2016214370A1; US20180001576A1; KR20170113606A; CN107428545A; AU2016214370B2; JP6936147B2; WO2016124680A1; EP3053952A1

Abstract

The invention relates to a method for producing an aerogel material with a porosity of at least 0.55 and an average pore size of 10 nm to 500 nm, having the following steps: • a) preparing and optionally activating a sol; • b) filling the sol into a casting mold (10); • c) gelling the sol, whereby a gel is produced, and subsequently aging the gel; at least one of the following steps d) and e), • d) substituting the pore liquid with a solvent; • e) chemically modifying the aged and optionally solvent-substituted gel (6) using a reaction agent; followed by • f) drying the gel, whereby the aerogel material is formed. The casting mold used in step b) is provided with a plurality of channel-forming elements (2) which are designed such that the sol filled into the casting mold lies overall at a maximum distance X from a channel-forming element over a specified minimum length L defined in the channel direction of the elements, with the proviso that X < 15 mm and L/X > 3.

Description

Process for producing an airgel material Technical field

The invention relates to a method for the simplified production of an airgel material according to the preamble of claim 1, depending on a precursor product according to the preamble of claim 13 or 14, and an airgel plate according to the preamble of claim 15th

State of the art

Aerogels are increasingly being used in highly specialized niche markets, such as in building technology as high-insulation materials or in the aerospace and marine industries, as well as in high-tech applications. Aerogels are available in various designs and materials. The industrialization of aerogels and xerogels has been experiencing a significant boom since the turn of the millennium. Today, silicate-based aerosols (Si0 ₂ ) are available in particular. The best-known forms include granules and monolithic plates. In addition, airgel based on at least partially crosslinked polymers are well known, such as the resin-based resorcinol-Formalhedyd [Pekala et. al, J. Mater. Sei, 1989, 24, 3221-3227] and related systems which have not attained industrial significance until today. The industrial process scaling of alternative polymer-based aerogels, in particular polyisocyanate-based aerogels such as PU and PUR, is currently in full swing, with several new launches expected in the coming years. In the future, silicate and polymer-based aerogels as well as carbon aerogels obtained from pyrolysis in building and energy technology as well as in the areas of mobility and high-tech applications will become increasingly important.

A critical step in the production of airgel materials is the drying of a wet gel. For this purpose, previously used for silicate-based gels only supercritical drying, ie drying from a supercritical fluid (typically lower alcohols or later C0 ₂ ). In the case of silicate aerogels, by solvent drying (subcritical drying) of hydrophobic gels materials with quasi-identical properties as the supercritically dried aerogels can be produced. These were in the beginning according to the classical definition Xeroge- called le, a term that is still used today for solvent-dried aerogels. In the following, however, the definition based on material properties (density <0.15 g / cm ³ , porosity> 85%, pore size 20 to 80 nm) is also used for subcritically dried materials, which are thus also referred to as aerogels. The development of solvent-drying processes for organic gels (eg polyurethane and polyurea) is currently in full swing.

The main costs of today's comparatively expensive aerogels are the complex process control, solvents, solvent losses and associated VOC charges as well as raw materials and water repellents. The development of the production processes aims at savings at all mentioned points, whereby to date the following history of development was passed. Increasingly important today is the simplified drying at atmospheric pressure from solvent-containing gels, which for Si0 ₂ aerogels for the first time by Anderson, Scherer and their collaborators [J. Non. Cryst. Solids, 1995, 186, 104-1 12]. The process quickly became known and inspired new manufacturing processes for silicate aerogels. The patent US 5,565,142 describes such a method for the production. The solvent exchange times and hydrophobing times total about 120 hours, with the dimension or the shape of the gel body not being further described.

WO 1998/005591 A1 relates to a production process for organically modified, permanently hydrophobic aerogels. As in the case of WO 1995/006617 A1, the SiO ₂ gel is formed starting from a waterglass solution by means of neutralization by acid or after the formation of a silica sol by ion exchange and subsequent base additions. The pH during gelation is typically in the range between 4 and 8. The wet gel is washed in an organic solvent until the water content is below 5% and then hydrophobed. Drying under atmospheric pressure by evaporation of the solvent leaves the airgel material as granules back. The dimension or shape of the gel bodies are not further described in this publication. Also not further described are the washing and hydrophobing times wherein the grinding of the solidified gel is mentioned by name.

As examples of organic aerogels, US 5,484,818 A and US 2006/021 1840 A1 describe the preparation of polyisocyanate-based aerogels. isocyanate Precursor compounds are dissolved in an organic solvent mixture and reacted with polyols, polyamines or water, gelled and dried supercritically after the solvent has been exchanged for C0 ₂ . The two patents mentioned are typical of the majority of the technical documents on polymer aerogels in that they do not describe the chemistry but process-specific process steps: The type of gel bodies and their shape or exact topology is generally poorly documented. No. 5,962,539 A describes a process for the supercritical drying of organic gels. Again, no information about the gel form or shape can be found.

It is known that solvent-exchange processes are diffusion-limited in nanoporous systems, which in some situations leads to undesirably long exchange times. As a simple measure, diffusion processes can be accelerated by raising the temperature. This is already exploited today in airgel production by frequently carrying out exchange processes in organic solvents as close as possible to their boiling point.

Alternatively, aerogels are prepared either as granules or thin mats or plates having a shortest dimension or thickness of less than 2 cm and then glued in one or more refining steps. Thus, thicker insulation boards or other, partly functional composite materials can be produced. US 2014/0004290 A1 and US 2014/0287641 A1 describe such production methods of composite materials starting from airgel as a base material by means of adhesive technology, the main focus being on improved mechanical properties and processability. WO 2012/062370 A1 describes a similar process, wherein the adhesive component used is a resorcinol-formaldehyde resin system in xerogel form.

In the industrial production of airgel granules, the dimensionality of the gel is caused by fragmentation before the solvent exchange by mechanical processes or by gelling in drop form in the drop tower. The first method has become established in the industry, as it allows a significantly better space utilization in the system. The state of the art is the gelation of a gel carpet on a moving belt and dismemberment of the aged gel carpet over a rather. However, the shearing forces occurring there have the consequence that in addition to the desired granules in the size range of 1 to 5 mm, a considerable amount of the gel remains as fine fraction <1 mm. This fine fraction can amount to up to 30% of the total yield and is produced in the production as an inferior product.

In all of the above examples, it would be desirable to improve the manufacturing processes to achieve, inter alia, increased throughput. A possible improvement of the process may be due to the process efficiency over the prior art, i. at the maximum throughput of the desired end product which is technically feasible in a given plant.

Presentation of the invention

The object of the invention is to provide an improved process for the production of airgel materials. Further objects are to provide precursor products for the production of an airgel plate as well as a new airgel plate.

These objects are achieved according to the invention by the production method according to claim 1 and by the precursor products according to claim 13 or 14 and by the airgel plate according to claim 15.

Advantageous embodiments are defined in the dependent claims.

The process according to the invention for producing an airgel material having a porosity of at least 0.55 and an average pore size of 10 nm to 500 nm comprises the following steps:

a) preparation and optionally activation of a sol;

b) filling the sol into a mold;

c) gelation of the sol to form a gel, followed by aging of the gel;

at least one of the following steps d) and e)

d) replacement of pore fluid by a solvent;

e) chemical modification of the aged and optionally solvent-exchanged gel by a reactant; followed by

f) drying the gel, wherein the airgel material is formed.

According to the invention, the mold used in step b) is provided with a plurality of channel-forming elements, which are designed so that the sol filled in the mold over a predetermined, defined in channel direction of the elements minimum length L everywhere a maximum of a distance X of one Channel-forming element is removed, with the proviso that X <15 mm and L / X> 3. The sol filled in the mold is - over a predetermined, defined in channel direction of the elements minimum length L - anywhere a maximum of a distance X from a channel-forming Element removed. Considering a cross-section perpendicular to the channel direction, this means that no point in the sol is further than X from the nearest channel-forming element. This ensures that even the innermost regions in the sol are not too far away, namely at most by a maximum distance X, from the interface defined by the channel-forming element. By having X at most 15 mm, any location in the gel is efficiently accessible to a solvent or reagent supplied through said interface. However, this advantageous geometric situation must not be given only to individual constrictions in the channel direction, but must be formed over a distance L which is at least 3 times the maximum distance X.

It should be noted that the term "maximum distance" should not be misunderstood as absolute maximum distance. Rather, it is the maximum of all shortest distances. Stated another way, the "maximum distance" in the sense of the present invention is the shortest distance between the innermost point of a cross-sectional area and the interface defined by the channel-forming element.

It is understood that the maximum distance X depends on the shape and in certain cases also on the mutual spacing of the channel-forming elements. The corresponding relations result from known relationships of planar geometry. For complicated and / or irregular shapes, the maximum distance must be determined numerically, if necessary. The formation of an airgel starting from a sol is basically known and includes in particular a step of solvent exchange and / or a step of chemical modification. The inventive arrangement a much better accessibility of the gel is ensured for supplied solvent and / or reagent. This results in a shortening of the process duration and, consequently, an improvement of the process economy. These advantages arise not only for already known airgel production processes, but also for later processes still to be developed, provided that these likewise rely on the introduction of a liquid or possibly gaseous species into the gel.

By deliberately selecting the geometry, ie by limiting the dimension in at least one spatial direction, the diffusion-limited solvent exchange processes can be greatly accelerated. In this way, for example, it is possible to exchange large-area, monolithic gel slabs with a thickness of a few millimeters within one solvent mixture in a reasonable time from the point of view of an industrial production process. A silicate-based gel slab of 50 nm average pore size and 5 mm thickness can be mixed in one Alcohol-based solvent mixture at room temperature within a few hours completely (ie to the depth of the plate) replace. The diffusion rate is given by the solution of the 2nd Fick's Law: In the case of a gel plate, the time required for solvent replacement (concentrations of all solvent components in equilibrium) approximates the square of the plate thickness, that is, the shortest dimension. This means that a doubling of the plate thickness results in a quadrupling of the exchange time. This has profound consequences for industrial production processes of airgel and xerogel materials: depending on the system, in practice airgel plates of 2 to 3 cm can still be produced with reasonable expenditure of time. A plate thickness of 10 cm, which is desirable, for example, in insulation technology, can not be economically produced as a solid material according to current technology. The inventive method allows a much simpler and faster production of airgel materials compared to the previously known methods by controlled structuring of the gel body, whereby process efficiency and throughput can be significantly increased. In principle, various materials come into question for the production of the casting mold, ie for the outer housing as well as for any pipe or rod elements that may be used. These include, for example, polyolefins, in particular polypropylene or polyethylene, but also glass or ceramic and metals such as stainless steel. In any case, the choice of materials will require compatibility with the media used (acids, bases, solvents).

According to one embodiment (claim 2), the channel-forming elements are configured as a bundle of mutually parallel tubes, wherein the mold for the sol is formed by the interiors of the tubes, and wherein the solvent exchange d) and / or the chemical modification of the gel e) by a gap formed between the gel and the channel-forming element as a result of shrinkage during the aging of the gel c) is carried out directly in the casting mold, preferably by forced convection of supplied solvent or reaction agent. It is understood that in this type of arrangement, the maximum distance X is to be determined by considering the distance of a point located inside the tube from the inner surface of the respective tube element.

In principle, different shapes of the pipe cross-section can be used. Advantageously, these are tubes with a circular or quadrangular, in particular square inner profile. Furthermore, it is advantageous to handle, if in each case a certain number of tubes is held together to form a tube bundle.

In an advantageous embodiment (claim 3), all tubes have an identical cross section, which is preferably hexagonal. This makes it possible to build compact tube bundles with little dead volume between the individual tubes.

In a further embodiment (claim 4), the optionally solvent-exchanged and optionally chemically modified gel is removed in the form of gel bars from the mold and then the drying f) is carried out by means of subcritical drying. In this process, the individual tie rods disintegrate into smaller fragments, advantageously an airgel or xerogel granules with minimal fines. According to a further embodiment (claim 5), the channel-forming elements are configured as a bundle of mutually parallel rod elements, wherein the mold for the sol is formed by a space located between the rod elements, and wherein the rod elements after gelation and aging in the channel direction from the The mold can be pulled out in such a way that a plate-shaped gel body with continuous channels is formed. The solvent exchange d) and / or the chemical modification of the gel e) is carried out by applying solvent or reagent. It is understood that in this type of arrangement, the rod elements act as placeholders for subsequently formed channels in the aged gel. Accordingly, the maximum distance X is to be determined by considering the distance of a point lying between the rod elements from the outer surface of the nearest rod element.

In principle, different cross-sectional shapes can be used for the rod elements. Advantageously, these are rods with a circular or quadrangular, in particular square or hexagonal outer profile.

In one embodiment, the application of solvent or reagent to a previously formed plate-shaped gel body after removal of the same is carried out of the mold.

Advantageously, the rod elements are attached to one end of a removable bottom surface or top surface of the mold and can be easily pulled out of the gel body after aging of the gel.

It is particularly advantageous (claim 6), if the application of solvent or reagent by forced convection by the gel body is placed on an at least partially permeable suction plate, on the underside of a negative pressure for removing the solvent or reagent is applied means and wherein from above the gel body new solvent or reagent is supplied. Such methods are basically known in particular from papermaking.

As advantageous, a method has been found (claim 7), in which as Sol a silica sol is prepared in an alcoholic solvent mixture containing at least one acid-catalytically activatable hydrophobing agent, wherein the volume fraction of the hydrophobing agent in the sol is 5 to 60%,

- The gelation of the sol is triggered by base addition;

a chemical modification of the aged gel is performed, wherein the chemical modification is a hydrophobing initiated by the release or addition of at least one hydrophobizing catalyst co-operating with the hydrophobizing agent; and

- The drying of the gel is carried out by subcritical drying.

Activation of the hydrophobing agent in this case can be triggered by the addition of a small amount, typically of the order of 10-20% of the gel volume, of an acidic hydrophobing catalyst dissolved in a compatible solvent mixture. In order to ensure a homogeneous hydrophobization in the gel material, however, the hydrophobizing agent must also diffuse into the depth of the gel material, wherein the shape and shape of the gel body affect the time required for the hydrophobing step sensitively. According to the invention, the introduction of small amounts of hydrophobing catalyst, measured on the gel volume, is significantly easier and more economical to implement by targeted structuring of the gel.

Characterized in that the hydrophobicization is an acid-catalyzed process, ie by H ⁺ and H ₃ 0 ⁺ ions is catalyzed, the process running under slightly basic conditions gelling process and the process running under acidic conditions hydrophobicity can approximately process clean time in one and the same organogel be carried out separately from each other. As a further advantage, the process is characterized by a significantly reduced solvent consumption. In particular, it is possible to limit the amount of solvent used to produce an airgel to 1.1 to 1.2 times the volume of the gel. The prior art typically requires more than 2 times the gel volume of solvents.

Alcoholic solvent mixture is understood in the present context to mean a mixture which consists essentially of one or optionally several their alcohols (especially ethanol, methanol, n-propanol, isopropanol, butanols) and a suitable proportion of water repellents. It is understood that the mixture may also contain a small amount of water, unavoidable impurities, and optionally, as explained elsewhere, certain additives.

A hydrophobizing agent is understood in a manner known per se to mean a component which makes a surface hydrophobic, ie. gives water-repellent properties. In the present context, the hydrophobing agent or the hydrophobing process refers primarily to the silicate gel and the modifications of its properties.

The advantageous embodiment comprises the gelling of an alkoxide-based silicate sol in an alcoholic solvent mixture which contains at least one catalytically activatable hydrophobizing agent.

The gelation process is initiated by adding a dilute base such as ammonia. Optionally, the gel thus formed, which may also be referred to as "organogel", is subjected to an aging process. The optionally aged gel now contains all the components required for hydrophobicization and subcritical drying according to WO 2013/053951 A1 or, more precisely, a pore liquid with the main components alcohol and activatable hydrophobizing agent, with the exception of the hydrophobizing catalyst. As a consequence, it is necessary to introduce the hydrophobization catalyst into the gel in a controlled manner entirely without additional solvent input or with minimal solvent input. According to a preferred embodiment (claim 8), hexamethyldisiloxane (HMDSO) is used as acid-catalytically activatable hydrophobizing agent.

It is particularly advantageous (claim 9) if the volume fraction of the hydrophobizing agent in the sol is from 20 to 50%, in particular from 25% to 40% and in particular from 34% to 38%. According to a further embodiment (claim 10) is used as the hydrophobing catalyst trimethylchlorosilane (TMCS) and / or HCl in alcoholic solution or a mixture of these two components, which is dissolved in a dilute solvent mixture consisting of a similar or identical composition as the pore liquid and in the Liquid phase is brought into contact with the gel. The amount of catalyst-loaded solution measured in terms of gel volume should be kept as small as possible in order to maintain the advantage of the lowest possible solvent balance. Preferably, the catalyst-containing solution in a batch process or continuous process makes up a volume fraction or volume flow rate fraction of not more than 30%, in particular not more than 10%. Instead of HCl, other mineral acids can be used, with nitric acid (HN0 ₃ ) has proved to be particularly advantageous.

According to another embodiment of the method (claim 1 1), the gel is a polymer-based gel, preferably a polyisocyanate-based gel.

For certain applications with increased structural stability requirements, it has proven advantageous to add the optionally activated sol prior to gelation into a fiber-based matrix. This makes it possible to produce fiber-reinforced airgel plates.

According to a further aspect of the invention, a first precursor product for producing an airgel plate is provided which consists of an airgel plate provided with slots according to the invention. The elongated holes can as perpendicular through the plane of the plate extending through channels or as corresponding blind holes with only one-sided opening. The elongated holes can in particular be produced by a method described above (claim 5), wherein the hole dimension is essentially defined by the external dimensions of the rod elements used. However, the shrinkage during aging of the gel should be taken into account.

According to another aspect of the invention, a second precursor product is provided for producing an airgel plate which consists of a plurality of airgel rods. These rods can be produced in particular by a method described above (claim 2), wherein the outer mass of the airgel rods in the way is significantly defined by the internal dimensions of the pipe elements used. However, the shrinkage during aging of the gel must also be taken into account here.

According to yet a further aspect of the invention, an airgel plate is provided, which comprises a first precursor product in the form of an airgel plate, in the slots of which appropriately shaped airgel rods of a second precursor product are inserted or pressed. In principle, the same material can be used for the airgel plate and for the airgel rods. In this way, the plate element with the advantages of the method according to the invention can first be produced. The ultimately undesirable in the produced airgel plate slots, which would result in a significant reduction in heat insulation capacity, can be eliminated by the airgel rods used. But there are also applications conceivable in which the airgel rods used are made of a different material, which in particular allows an improvement of the mechanical and thermal properties of the final product. For example, formed from a silicate-based gel, provided with continuous slots airgel plate with airgel rods are made of a Polyurethanangel.

Brief description of the drawings

Exemplary embodiments of the invention will be described in greater detail below with reference to the drawings, in which:

Fig. 1 is a schematic representation of distance relations in different

Arrangements: (a) square tube profile, (b) circular tube profile, (c) arrangement with several circular tube profiles (d), hexagonal tube profile, (e) arrangement with several hexagonal tube profiles, (f) orthogonal arrangement of circular bars and (g hexagonal arrangement of circular rods; Fig. 2 (a) to (d) the sequence of a first embodiment of the method; and

Fig. 3 (a) to (e) the flow of a second embodiment of the method. Ways to carry out the invention

Fig. 1 illustrates some basic geometric shapes and relations. Therein, the innermost point furthest from the next channel-forming element is represented by a cross. The maximum distance X defined in the sense explained above, ie the shortest distance of the innermost point from the next channel-forming element, is also shown.

1 a to 1 e show a situation in which the tube components 2 used as channel-forming elements as well as a sol or a gel 4 formed therefrom, still unaged, can be seen. For better illustration, these figures also show a solvent or a reaction agent 5 for the steps d) or e) described at the outset, which after penetration of the pipe components is to penetrate into the previously aged gel. Figures 1f and 1g show another situation in which channeling in an aged gel material 6 has already been accomplished by rod members; the rod elements were removed and circular channels 7 were formed into which the reagent 5 was filled.

In the case of the square tube profile with inner edge length a shown in FIG. 1a, the maximum distance X = a / 2. As already mentioned, this is the shortest distance from the innermost point within the profile. In the circular tube profile with the inner diameter d shown in FIG. 1 b, the maximum distance X = d / 2. In the regular hexagonal tube profile shown in FIG. 1 d with the inner side length b, the maximum distance X = b / 2 V3. Arrangements of densely packed circular or hexagonal tube profiles are shown in FIGS. 1 c and 1 e.

. In the direction indicated in Fig 1f orthonormal grid, in which the lattice points each channel-forming circular rods are arranged and there is a quadratic from louder tables elementary cells of the side length A, the maximum distance is given by X = ^_1/2 (AV2 - ds).

In the hexagonal lattice network indicated in FIG. 1 g, in the lattice points of which channel-forming circular rods are respectively arranged and which consists of nothing but hexagonal lattice rods. gonal unit cells of side length B, the maximum distance is given by X = B - 14 ds.

The process sequence shown in FIGS. 2a to 2d initially shows in FIG. 2a a bundle of circular cylindrical tubes 2, which initially is still empty and in particular stands on the bottom of a boundary shell (not shown). In Fig. 2b, the tube bundle is filled with a sol or an unaged gel 4 formed therefrom. In Fig. 2c, aging of the gel has occurred with concomitant shrinkage, whereby between the cylindrical rods 6 of aged gel and the tubes 2 a filled with Synereseflüssigkeit gap-like gap 8 has arisen. In Fig. 2d, the tie rods 6 are shown with partially pulled up tubes 2. These are now ready for further processing.

The process sequence shown in FIGS. 3 a to 3 e initially shows in FIG. 3 a a cuboid boundary shell 10 with a bottom plate 12 which is provided with a nail rod arrangement with an arrangement of cylindrical rods 14. In the example shown, all rods are about the same length. In FIG. 3 b, the boundary shell contains a filled sol or a gel 4 which is still unaged, and whose level is just below the rod tips. In Fig. 3c, an aging of the gel with concomitant shrinkage has occurred, whereby between the cylindrical rods 14 and the plate-shaped body 16 of aged gel each have a gap 8 is formed. In FIG. 3d, a cover part 18 of the boundary shell has been lifted up, whereby a bottom part 20 of the boundary shell with the gelatinous gel body 16 located therein is exposed. In FIG. 3e, the aged gel body 16 provided with through-holes 22 has been lifted out of the bottom part 20 provided with the rods 14 and is ready for further processing.

Preparation of an Inorganic Organic Hybrid Airgel Granules

A silica sol in alcohol is activated by adding dilute ethanolic ammonia solution at room temperature. The sol contains as secondary component 2% aminopropyltnethoxysilane (APTES) which is added together with the ammonia. This sol is now filled in an open vessel, which, as shown in FIG. 2, is provided with a tube bundle core insert of d = 13 mm internal pipe diameter, h _w = 1 mm wall thickness and L = 90 cm length. This insert fills the entire Vessel volume off. After gelation, the gel packet is aged for 12 h. Thereafter, the tube bundle insert is removed and decanted excess liquid. Thereafter, a dilute solution containing an amine crosslinking polymer crosslinker and a hydrophobing agent is added. The mixture is allowed to enter the gel in the vessel for a further 12 h and react, whereupon excess liquid is removed again. The resulting loops are now placed in an autoclave, exchanged for C0 ₂ and then dried supercritically. As a product remain X airgel rods with a density of 0.14 g / cm ³ and a compressive strength> 10 MPa back.

Highly efficient production of a silicate-based airgel granulate

A silica sol is produced in a continuous process and diluted with HMDSO from a 10% Si0 ₂ content to 6.6%. At a filling station, this sol is activated at a temperature of 35 ° C. by admixing dilute ammonia solution. At the filling station are 200 I container already, which are provided with a cavity fully filling, honeycomb-like insert. The honeycomb shape has a wall thickness of 0.5 mm and a cell diameter of 8mm. The containers are now filled individually and hermetically sealed by means of a lid, after which they are stored for 18 h at 70 ° C. During this time, the mixture gels and gel bodies formed in the honeycomb channels age, shrinking slightly. Due to the shrinkage, gaps are created in which the liquid can circulate (analogous to FIG. 2c). After aging, the containers are opened and the Synereseflüssigkeit drained. Thereafter, 20 l of dilute mineral acid are added as a catalyst per container, which is evenly distributed in the spaces between gel and honeycomb wall. The containers are resealed and stored for 8 hours at 90 ° C, whereby the gels are rendered hydrophobic. The containers are then emptied and the hydrophobic gel bars are dried in an oven at 150 ° C. During drying, the lashing bars break themselves into an airgel granulate with a particle size between 4 and 7 mm. The density of the aerogranular granules thus obtained is 0.096 g / cm ³ and the heat conductivity of the bed 17.8 mW / m K. By the processing according to the invention, the gel bodies remain unchanged in the mold until the drying step which leads to a granule yield of at least 95% , Compared to mechanically comminuted gels arises like this significantly less airgel dust, which must be considered as an inferior product.

In an alternative embodiment, the inserts are used in a large-scale process not in individual containers but in an elongated process tunnel, and thus pass through the entire production process on a conveyor belt drive with the gel, whereby the syneresis liquid is removed from the bottom in a certain area and shortly thereafter the hydrophobizing catalyst is metered from the ceiling through an injection system.

Production of a structured polyurethane airgel plate

Two freshly prepared solutions in an organic solvent mixture consisting of an isocyanate mixture (component 1) and a polyol with a catalyst (component 2) are mixed together and placed in a shell mold in which a uniform, area-wide arrangement of cylindrical rods according to FIG. 3a) is. The individual rods have a diameter d _s = 20 mm, a length Ls = 331 mm and a shortest center distance A = 35 mm. The filling level of the sol mixture consisting of components 1 and 2 is H = 315 mm. On the top, the sol is covered with a matching perforated plate that fits into the bars. After gelation and aging of the gel, the perforated plate is removed and the individual rods pulled out. The gel body is then removed from the mold and transferred to an autoclave. The pore liquid contained in the gel body is then extracted in this autoclave by means of supercritical C0 ₂ and the gel is then dried supercritically. At the end, a polyurethane orogel perforated plate of 273 mm thickness remains.

In an alternative embodiment, mixtures 1 and 2 consist of a solution of resorcinol with a small addition of acid catalyst and a dilute, aqueous formaldehyde solution. In this case, however, it is necessary to convert the aqueous pore liquid by means of solvent exchange into a suitable solvent medium such as acetone or ethanol before the supercritical drying.

Industrial production of an airgel plate A prepared in a continuous flow reactor silica sol is adjusted to a silicate content of 5.7% (measured as Si0 ₂ ). The sol is provided with ammonia as a gelation catalyst and placed in a dish form containing a nail-board-like insert. The insert consists of a base plate on which a regular hexagonal arrangement of normal to the surface standing needle-like rods analogous to Figure 1 g with a diameter ds = 1 .5 mm and a length Ls = 70 mm and a shortest center distance B = 10 mm, which Side length of the hexagon corresponds, are applied. The filling height H of the mixed solution is also 70 mm so that the tips of the bars are barely covered. Now the sol is covered with a second plate (cover plate, not shown). After gelation and aging of the gel, the cover plate is removed, the gel plate removed from the mold and the insert carefully dissolved out. The through holeed gel plate is transferred to a slow speed (7.3 m / h) conveyor belt. This gel body is sprayed from above with a mixture of fresh hydrophobing agent mixture consisting of 85% HMDSO and 15% hydrochloric acid dilute ethanol, wherein the build-up on the plate excess liquid sucked continuously through the gas and liquid permeable conveyor belt membrane material by means of pump at low vacuum becomes. After 6 hours of exchange and hydrophobization time at 75 ° C., the plate is dried by means of solvent drying at 150 ° C.

Comparative example

According to a standard method which is customary today without channel-forming elements, the replacement and hydrophobicization time to be expected under otherwise identical conditions is approximately 25 times longer, ie. 150 h, which is unsustainable for an industrial process.

In a further embodiment, the airgel plate produced in the above example and produced according to the method according to the invention is filled with aerosol cylinders suitable for the holes. The gel cylinders required for this purpose were previously prepared specifically from a suitably selected polyurethane gel formulation and then dried overcored from C0 ₂ .

Claims

claims

1 . A process for producing an airgel material having a porosity of at least 0.55 and an average pore size of 10 nm to 500 nm, comprising the following steps:

a) preparation and optionally activation of a sol;

b) filling the sol into a mold (10);

c) gelation of the sol to give a gel (4) followed by aging of the gel;

at least one of the following steps d) and e)

d) replacement of pore fluid by a solvent;

e) chemical modification of the aged and optionally solvent-exchanged gel (6) by a reagent;

followed by

f) drying the gel to form the airgel material;

characterized in that the mold used in step b) is provided with a plurality of channel-forming elements (2; 14) which are designed such that the sol filled in the mold reaches a maximum everywhere over a predetermined minimum length L defined in the channel direction of the elements is a distance X from a channel-forming element, with the proviso that X

<15 mm and L / X> 3.

2. The method of claim 1, wherein the channel-forming elements is configured as a bundle of mutually parallel tubes, wherein the mold for the sol is formed by the interiors of the tubes, and wherein the solvent exchange d) and / or the chemical modification of the gel e) by a gap formed between the gel and the channel-forming element as a result of shrinkage during the aging of the gel c) directly in the mold, preferably by forced convection of supplied solvent or reaction medium.

3. The method of claim 2, wherein all the tubes have an identical, preferably hexagonal cross-section.

A process according to claim 2 or 3, wherein the optionally solvent-exchanged and optionally chemically modified gel is removed from the mold as lashing rods and thereafter the drying f) is carried out by means of subcritical drying.

The method of claim 1, wherein the channel-forming elements are configured as a bundle of mutually parallel rod elements, wherein the mold for the sol is formed by a space located between the rod elements, and wherein the rod elements after gelation and aging in Kanalrichtung pulled out of the mold are such that a plate-shaped gel body is formed with continuous channels, wherein the solvent exchange d) and / or the chemical modification of the gel e) is carried out by applying solvent or reagent.

The method of claim 5, wherein the application of solvent or reaction agent by forced convection by the gel body is placed on an at least partially permeable suction plate on the underside of a vacuum for removing the solvent or reagent is applied and wherein from above the gel body new solvent or reactant is supplied.

Method according to one of claims 1 to 6, wherein

as Sol a silica sol is prepared in an alcoholic solvent mixture containing at least one acid-catalytically activatable hydrophobing agent, wherein the volume fraction of the hydrophobing agent in the sol is 5 to 60%,

gelation of the sol is initiated by base addition;

a chemical modification of the aged gel is performed, wherein the chemical modification is a hydrophobing initiated by the release or addition of at least one hydrophobizing catalyst co-operating with the hydrophobizing agent; and the drying of the gel is carried out by subcritical drying;

The method of claim 7, wherein the catalytically activatable hydrophobing agent is hexamethyldisiloxane (HMDSO).

A method according to claim 7 or 8, wherein the volume fraction of the hydrophobizing agent in the sol 20 to 50%, in particular 25% to 40% and especially 34% to 38%.

A process according to any one of claims 7 to 9, wherein the hydrophobizing catalyst is trimethylchlorosilane (TMCS) and / or HCl in alcoholic solution.

A method according to any one of claims 1 to 6, wherein the gel is a polymer-based gel, preferably a polyisocyanate-based gel.

The method of claim 1 to 1 1, wherein the optionally activated sol is added prior to gelation in a fiber-based matrix.

First precursor product for producing an airgel plate, consisting of an airgel plate which can be produced according to claim 5 and provided with oblong holes.

Second precursor product for producing an airgel plate, consisting of a plurality of airgel rods which can be produced according to claim 2.

15. Airgel plate consisting of a first precursor product according to claim 13, in the slots correspondingly shaped airgel rods of a second precursor product according to claim 14 are used.