阅读说明：本技术 连续超临界干燥气凝胶颗粒的方法 (Method for continuous supercritical drying of aerogel particles ) 是由 S·莫瓦海德 W·勒尔斯贝格 D·温里克 M·弗力可 R·苏布拉马尼亚姆 I·斯米尔诺瓦 于 2019-09-12 设计创作，主要内容包括：本发明涉及用于干燥凝胶颗粒的方法,特别是用于制备气凝胶的方法,所述方法包括：提供包含凝胶颗粒(P1)和溶剂(LM)的悬浮液；将所述悬浮液注入二氧化碳以逆流方式流过的塔中；并将干燥的气凝胶颗粒从塔中分离出,将所述悬浮液在塔的顶部区域中注入,并将干燥的气凝胶颗粒在塔的下部区域中分离出,并且其中设定塔中的压力和温度以使二氧化碳和溶剂的混合物为几乎超临界或超临界。所述气凝胶颗粒既可以通过排放容器又可以通过连续膨胀而排出。本发明还涉及根据所述方法可获得或获得的气凝胶颗粒,以及根据本发明的气凝胶颗粒的用途,用于医学和药物应用,作为添加剂或载体材料用于食品添加剂,作为催化剂载体,用于化妆品、卫生、洗涤和清洁应用,用于生产传感器,用于隔热或作为芯材用于VIP。(The present invention relates to a method for drying gel particles, in particular for preparing aerogels, comprising: providing a suspension comprising gel particles (P1) and a solvent (LM); injecting the suspension into a column through which carbon dioxide flows in countercurrent; and separating the dried aerogel particles from the tower, injecting the suspension in a top region of the tower, and separating the dried aerogel particles in a lower region of the tower, and wherein the pressure and temperature in the tower are set such that the mixture of carbon dioxide and solvent is nearly supercritical or supercritical. The aerogel particles can be discharged both through the discharge vessel and through successive expansions. The invention also relates to aerogel particles obtainable or obtained according to the method, and to the use of the aerogel particles according to the invention, for medical and pharmaceutical applications, as an additive or carrier material for food additives, as a catalyst carrier, in cosmetic, hygiene, washing and cleaning applications, for producing sensors, for thermal insulation or as a core material for VIP.)

1. A method for drying gel particles, in particular for preparing aerogels, comprising the steps of:

(i) providing a suspension comprising gel particles (P1) and a solvent (LM),

(ii) the suspension is introduced into a column in which carbon dioxide flows in countercurrent,

(iii) the dried aerogel particles are removed from the tower,

wherein the suspension is introduced in the top region of the column and the dried aerogel particles are removed in the lower region of the column,

wherein the pressure and temperature in the column are set such that the mixture of carbon dioxide and solvent is almost supercritical or supercritical.

2. The method of claim 1, wherein the gel particles are deposited in a counter current manner.

3. The method of any one of claims 1 and 2, wherein the resulting aerogel particles are continuously removed in a valveless manner.

4. The method of any one of claims 1 to 3, wherein CO₂The mass flow rate is set to obtain dry aerogel particles.

5. The method of any one of claims 1 to 4, wherein the gel particles have an average diameter of 20 μm to 1000 μm.

6. The method of any one of claims 1 to 5, wherein the gel particles have an average pore size of 2 to 100 nm.

7. The process according to any one of claims 1 to 6, wherein the solvent (LM) is selected from methanol, ethanol, propanol, butanol, pentanol and hexanol.

8. Aerogel particles obtainable or obtained by the method of any one of claims 1 to 7.

9. Use of aerogel particles according to claim 8 or obtained or obtainable by the method of any of claims 1 to 7, for medical and pharmaceutical applications, as additive or carrier material for food additives, as catalyst carrier, for cosmetic, hygiene, washing and cleaning applications, for producing sensors, for thermal insulation or as core material for VIP.

The methods known from the prior art have the disadvantage that they are associated with high plant outlay and/or involve long residence times and high material consumption.

Starting from the prior art, it is an object of the present invention to provide a process for drying mesoporous and macroporous gel particles which can be operated economically and at low equipment costs.

According to the invention, this object is achieved by a method for drying gel particles, in particular for preparing aerogels, comprising the steps of:

(i) providing a suspension comprising gel particles (P1) and a solvent (LM),

(ii) the suspension is introduced into a column through which carbon dioxide flows in countercurrent,

(iii) the dried aerogel particles are removed from the tower,

wherein the suspension is introduced in the top region of the column and the dried aerogel particles are removed in the lower region of the column,

wherein the pressure and temperature in the column are set such that the mixture of carbon dioxide and solvent is supercritical or almost supercritical.

For the purposes of the present invention, gels are crosslinked systems based on polymers which are brought into contact with liquids, known as solvent gels (solvogels) or liquid gels (lyogels), or with water as liquid (hydrogels (aquagels)). Here, the polymer phase forms a continuous three-dimensional network.

In the context of the present invention, the term "supercritical" is understood to mean when the operating pressure is higher than CO₂And solvent at the critical pressure of the respective operating temperature, the mixture is in a supercritical state.

In the context of the present invention, when solvent and CO₂The state of the mixture is said to be "almost supercritical" when the pressure and/or temperature of the mixture is lower than the critical pressure and/or critical temperature of the mixture, but the interfacial tensions generated between the phases have been reduced so that they do not cause the destruction of the pore structure.

Suitable pressure and temperature ranges may vary within wide ranges. For example, if ethanol is used as solvent, the process is carried out, for example, at a temperature of from 30 to 260 ℃ and a pressure of from 70 to 160 bar.

According to the invention, CO₂The feeding and removal can be for example by lateral suction, for example by partial cross-flow. This mode of operation has proven particularly advantageous for longer drying times and/or larger particle sizes.

In the context of the present invention, the particles may be removed semi-continuously through two or more alternating discharge vessels. Advantageously, the tower may be mounted above the discharge vessel so that the particles fall into the vessel due to gravity.

In the context of an alternative embodiment, it is also possible to proceed continuously through a capillary in a valveless mannerThe row is removed. In this case, the tower is preferably mounted above an intermediate collection vessel into which the particles fall due to gravity. To prevent clogging of the capillary inlet, it is preferred to pass CO with a fluidization aid₂The stream discharges the particles from the intermediate vessel.

Thus, according to another embodiment, the present invention relates to a method of drying gel particles as described above, wherein the resulting aerogel particles are continuously removed in a valveless manner.

In the process, for example, aerogel particles are continuously depressurized through a capillary tube from a pressurized storage vessel (e.g., a countercurrent extraction column) to ambient pressure in a valveless manner. In the context of the present invention, the pressure may in this case be, for example, from 80 to 200 bar, preferably from 100 to 150 bar. Depending on the gas mass flow rate, the pressure drop over the entire pipe length due to fluid-wall friction, particle-wall friction and particle-particle friction/collisions must preferably be precisely large enough to overcome the pressure difference between the storage vessel and the environment. Thus, no valve is required to create an additional pressure drop. Finally, the particles depressurized to ambient pressure (or nearly ambient pressure) are separated from the gas stream by a cyclone or filter and collected.

According to the invention, the drying is carried out under supercritical conditions. Such drying methods are known per se to the person skilled in the art. Supercritical conditions mean CO₂Or the temperature and pressure at which any particular solvent mixture used to remove the gelling solvent is in a supercritical state. In this way, shrinkage of the gel upon removal of the solvent can be reduced. Carbon dioxide is particularly well suited for heat-sensitive substances, since it has a favorable critical temperature of 31 ℃. Generally, the choice of drying fluid depends on various aspects. The thermal stability of the particles to be dried or of the end product, in particular, determines the choice of the drying fluid and therefore also limits the critical temperature of the drying fluid if it is desired to set "near" critical conditions.

Continuous pressure reduction is preferably performed with small diameter tubing/capillaries to maintain a large pressure drop. However, a certain diameter must be maintained in order to transport the particles without clogging. Suitable internal diameters of the tubes are from 1.5mm to 50mm, preferably from 1.6mm to 20 mm. The inner diameter of the tube, the proportion of solids by volume, the length of the tube and the type and number of internals and the gas mass flow rate determine the pressure drop across the tube.

The length of the conduit may be 30m to 400m and the gas mass flow rate may be 3kg/h to 20 t/h.

The discharge of the particles from the storage vessel, for example from the bottom of the column for continuous drying, into the capillary is preferably carried out using fluidization aids and metering devices, but can also be carried out without the use of fluidization aids and metering devices, depending on the material properties of the aerogel. Decompression by externally heated capillary to prevent CO in the pores of the aerogel₂Condensation or CO of₂Freezing of (2). For heating, the tubes/capillaries can be guided with a single tube, as in a tube bundle heat exchanger, and many tubes pass through a housing with a heat transfer fluid. Various internal components, such as pipe constriction and pipe expansion, may be added to the capillary to increase the pressure drop.

In another embodiment of the invention, less compressible supercritical CO may be added before or during depressurization₂A miscible inert gas, such as nitrogen. Thus, the pressure-dependent variation in volume of the gas mixture becomes smaller and the rate of depressurization produced can be reduced in the case of a gas flow which has been partly separated beforehand in a cyclone at the same total gas mass flow rate.

In another embodiment of the invention, the depressurization can also be carried out in stages: the staged depressurization consists of 2 or more capillary elements (e.g., the heat exchanger described above). The capillary element/heat exchanger may be operated at different temperature levels, for example in order to reduce the energy requirement for compensation of the Joule-Thomson effect (Joule-Thomson effect) or in order to utilize the Joule-Thomson effect for cooling of the sol at low pressure.

For example, in a stepwise depressurization with different temperature levels, the first stage may be operated at 50 ℃ at a pressure of 60 to 120 bar, the further stage at 25 ℃ at a pressure of 40 to 60 bar and the third stage at 5 ℃ at a pressure of 1 to 40 bar.

Another embodiment of staged depressurization is the interconnection of cyclones between stages. Between the various pressure reduction stages, the aerogel particles can be separated from a portion of the gas stream in a cyclone or filter. The particle-free gas stream can then be recirculated. The remaining gas stream with particles enters the next pressure reduction stage. In this way, the compression work required to depressurize the gas stream can be reduced.

Of course, a combination of the two embodiments of the staged pressure reduction is also possible.

According to the invention, for example, staged depressurization and CO with different temperature levels₂May be combined with the separation in the cyclone. For example, a first stage at 50 ℃ at a pressure of 80 to 120 bar, a separation in a cyclone, another separation stage at 40 ℃ at a pressure of 55 to 80 bar, another stage at 25 ℃ at a pressure of 40 to 55 bar, and optionally another stage at 5 ℃ at a pressure of 1 to 40 bar are possible.

The person skilled in the art can determine suitable proportions or suitable settings of the material streams and flow rates for establishing and maintaining the counter-current flow of drying fluid and particles to be dried within the scope of routine experimentation in the art. The setting depends inter alia on the height of the column, the internal mass and heat transfer in the particles to be dried and the fluidization point, i.e. on the density and particle size/particle size distribution of the porous particles to be dried.

In the context of the present invention, the process is preferably carried out continuously. According to another preferred embodiment, the carbon dioxide stream is recycled.

It has surprisingly been found that with the method according to the invention gel particles can be dried quickly and gently. According to the invention, drying can be carried out in particular at low temperatures so that even sensitive materials can be sufficiently dried.

According to the invention, the process is carried out herein so that the gel particles are preferably deposited in the carbon dioxide stream.

Thus, according to another embodiment, the present invention relates to a method of drying gel particles as described above, wherein the gel particles are deposited in a counter-current manner.

Dependent on CO₂Mass flow rate and column height, solvent in CO₂Suitable ranges for the mass ratio at the outlet can vary within wide ranges. In the context of the present invention, the solvent (e.g. in CO)₂Ethanol in (b) may vary in the range of about 30% to 98%.

In the context of the present invention, the mass flow rate is set according to the diameter of the column, according to principles known per se to the person skilled in the art, so that the particles remain deposited.

Thus, according to another embodiment, the present invention relates to a method for drying gel particles as described above, wherein CO₂The mass flow rate is set to obtain dry aerogel particles.

In the context of the present invention, CO₂The mass flow rate is set, for example, to 0.75kg/h to 25 t/h.

Thus, according to another embodiment, the present invention relates to a method for drying gel particles as described above, wherein CO₂The mass flow rate is set to 0.75kg/h to 25 t/h.

In the context of the present invention, gel particles having, for example, an average diameter of from 20 μm to 1000 μm, preferably from 20 μm to 500 μm, more preferably from 50 μm to 250 μm, may be dried.

Thus, according to another embodiment, the present invention relates to a method for drying gel particles as described above, wherein the average diameter of the gel particles is between 20 μm and 1000 μm.

The particles are preferably mixed with supercritical CO₂Guided through the tower in a counter-current, free-falling manner. Surprisingly, it can be shown that a significantly reduced residence time in free fall compared to a moving bed meets the requirements for drying the particles and does not require transport or other internals in connection with it.

The process shown is particularly suitable for continuous countercurrent drying of relatively small particles of 20 μm to 500 μm and has the advantage that no screw conveyors or moving internals are required in the drying vessel.

CO above critical point of mixture in counter-current extraction tower₂The aerogel particles were continuously dried in a counter-current manner. The top of the column is supplied with a pump with a suspension of gel particles consisting of gel particles suspended in an organic solvent that is readily soluble in CO₂. The gel particles are in contact with the upward flowing CO₂Depositing in the opposite gravitational field to the bottom of the column. Supercritical CO₂Flows through the column from bottom to top and extracts the solvent from the gel particles in the process. Thus, completely dry (solvent-free), preferably mesoporous, aerogel particles are obtained at the bottom of the column, while a high loading of solvent/CO is obtained at the top of the column₂And (4) logistics.

Particle size is a determining factor for continuous countercurrent extraction. At constant CO₂The particle size determines the drying time and the residence time in the column at the mass flow rate. Under constant process conditions, the drying time/residence time ratio increases with increasing particle size, since the first required drying time increases and at the same time the residence time decreases.

Likewise, in the case of a constant particle size, the drying time/residence time ratio can be set in particular by varying the residence time by means of process parameters. Residence time under CO₂Density and upwards oriented CO₂The effect of mass flow rate. CO directed upwards opposite to the falling direction of the particles, with constant relative velocity₂An increase in the mass flow rate leads to a decrease in the absolute velocity of the particles and thus to an increase in the residence time. The desired drying time/residence time ratio should preferably be < 1.

Suitable methods for preparing gel particles are known per se. In the context of the present invention, the gel may for example be an organic or inorganic gel.

In principle, gels can be prepared by hydrolysis and subsequent condensation (gelling) of suitable precursors.

Suitable gel material precursors for inorganic or hybrid materials may be inorganic components or mixtures of organic and inorganic components. The sol can be catalyzed to induce gelation by various methods. Examples include setting the pH and/or temperature of the diluted metal oxide sol to a point at which gelation occurs. Suitable materials for forming inorganic aerogels are oxides of metals, transition metals, and semimetals capable of forming oxides, such as silicon, aluminum, titanium, zirconium, hafnium, yttrium, vanadium, and the like.

The primary synthetic route for forming inorganic aerogels can be the hydrolysis and condensation of suitable metal alkoxides.

Suitable precursors for the gelling of organogels are likewise known to the person skilled in the art.

Suitable gels are, for example, those based on polysaccharide-containing materials, such as alginates. For example, alkali metal alginates such as sodium alginate are known to be water soluble, whereas alkaline earth metal alginates such as calcium alginate are insoluble in water. Gels can thus be prepared from water-soluble polysaccharides, in particular natural polysaccharides such as alginates. According to the present invention, water-soluble polysaccharides can be preferably used for forming a gel. Among them, the use of natural polysaccharides and/or their derivatives is particularly attractive due to their stability, availability, reproducibility and low toxicity.

With respect to the present invention, "water soluble" means having a solubility in water sufficient to form a solution that can be used to prepare a gel. According to the invention, a gel is formed from a water-soluble polysaccharide and a suitable cross-linking agent. The polysaccharide used in the process of the invention must be suitable for forming a gel together with the crosslinking agent, and in particular must have suitable functional groups. Particularly preferred are natural polysaccharides such as agar, alginate, carrageenan (carrageenan), cellulose, hyaluronic acid, pectin, starch and xanthan gum; and semi-synthetic polysaccharides such as modified cellulose, chitin and chitosan.

According to the invention, a hydrogel is formed, which is then subjected to a solvent exchange. According to the invention, the water-soluble polysaccharide is preferably selected from agar, alginates, carrageenans, cellulose, hyaluronic acid, pectin, starch, xanthan gum, modified cellulose, chitin and chitosan.

Other natural or synthetic hydrocolloid-forming polymers include (partially) water-soluble natural or synthetic polymers which form gels or viscous solutions in aqueous systems. They are carefully selected from other natural polysaccharides, synthetically modified derivatives thereof or synthetic polymers. Other polysaccharides include, for example, carrageenan, pectin, tragacanth, guar gum, carob flour, agar, acacia, xanthan gum, natural and modified starches, dextran, dextrin, maltodextrin, chitosan, dextrans, such as beta-carboxymethylcellulose, 1, 3-dextran, beta-1, 4-dextran, cellulose, mucopolysaccharides (mucopolysaccharides), such as, in particular, hyaluronic acid. Synthetic polymers include cellulose ethers, polyvinyl alcohol, polyvinyl pyrrolidone, synthetic cellulose derivatives (e.g., methylcellulose, carboxymethylcellulose (especially sodium carboxymethylcellulose), cellulose esters, cellulose ethers (e.g., hydroxypropyl cellulose)), polyacrylic acid, polymethacrylic acid, poly (methyl methacrylate) (PMMA), Polymethacrylate (PMA), polyethylene glycol, and the like. Mixtures of these polymers may also be used.

The reaction temperature may be from 0 ℃ to 100 ℃, preferably from 5 ℃ to 75 ℃, in particular from 10 ℃ to 50 ℃. The sol concentration, i.e. the concentration of the agent in the solvent, may be from 0.25 to 65% by weight, preferably from 0.5 to 60% by weight, in particular from 1 to 10% by weight.

In principle, any solvent (LM) may be used, provided that it is miscible with carbon dioxide or has a sufficient boiling point to allow removal of the solvent from the resulting gel. Typically, the solvent is a low molecular weight organic compound, i.e., an alcohol having 1 to 6 carbon atoms, preferably 2 to 4 carbon atoms, although other liquids known in the art may also be used. Examples of possible solvents include ketones, aldehydes, alkyl alkanoates, amides (e.g., formamide), N-methylpyrrolidone, N-ethylpyrrolidone, sulfoxides (e.g., dimethyl sulfoxide), aliphatic and alicyclic halohydrocarbons, halogenated aromatics, and fluoroethers. Mixtures of two or more of the above compounds are also possible.

Examples of other useful liquids include, but are not limited to: ethyl acetate, ethyl acetoacetate, acetone, methylene chloride, isopropanol, methyl ethyl ketone, tetrahydrofuran, propylene carbonate, and the like.

Other possibilities for the solvent are acetals, in particular diethoxymethane, dimethoxymethane and 1, 3-dioxolane.

Dialkyl ethers and cyclic ethers are also suitable as solvents. Preferred dialkyl ethers are in particular those having from 2 to 6 carbon atoms, in particular methyl ethyl ether, diethyl ether, methyl propyl ether, methyl isopropyl ether, propyl ethyl ether, ethyl isopropyl ether, dipropyl ether, propyl isopropyl ether, diisopropyl ether, methyl butyl ether, methyl isobutyl ether, methyl tert-butyl ether, ethyl n-butyl ether, ethyl isobutyl ether and ethyl tert-butyl ether. Preferred cyclic ethers are in particular tetrahydrofuran, dioxane and tetrahydropyran. Aldehydes and/or ketones are particularly preferred as solvents. Aldehydes or ketones suitable as solvents are in particular those corresponding to the general formula R2- (CO) -R1, where R1 and R2 are each hydrogen or alkyl having 1, 2, 3, 4, 5,6 or 7 carbon atoms. Suitable aldehydes or ketones are, in particular, acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, 2-ethylbutyraldehyde, valeraldehyde, isovaleraldehyde, 2-methylpentanaldehyde, 2-ethylhexanal, acrolein, methacrolein, crotonaldehyde, furfural, acrolein dimer, methacrolein dimer B, 1, 2, 3, 6-tetrahydrobenzaldehyde, 6-methyl-3-cyclohexenal, cyanoacetaldehyde, ethyl glyoxylate, benzaldehyde, acetone, diethyl ketone, methyl ethyl ketone, methyl isobutyl ketone, methyl n-butyl ketone, methyl amyl ketone, dipropyl ketone, ethyl isopropyl ketone, ethyl butyl ketone, diisobutyl ketone, 5-methyl-2-acetylfuran, 2-methoxy-4-methylpent-2-one, 5-methylhept-3-one, 2-heptanone, octanone, cyclohexanone, cyclopentanone, and acetophenone.

The abovementioned aldehydes and ketones can also be used in the form of mixtures. In many cases, particularly suitable solvents are obtained by using two or more completely miscible compounds selected from the abovementioned solvents.

Thus, according to another embodiment, the present invention relates to a method for drying gel particles as described above, wherein the solvent (LM) is selected from the group consisting of methanol, ethanol, propanol, butanol, pentanol and hexanol.

Furthermore, one or more auxiliary substances may be present in the suspension of the invention. The auxiliary substances comprise: fillers, pH adjusting agents such as buffer substances, stabilizers, co-solvents, pharmaceutically and cosmeceutically conventional or other dyes and pigments, preservatives, food supplements, vitamins, active agents, plasticizers, lubricants and lubricants.

The method of the invention may also comprise other steps, such as suitable processing steps.

At the end of the supercritical extraction, the pressure is released at a rate that enables optimum material properties and proper time consumption, and the particles are removed from the column.

It has been found that the process according to the invention makes it possible to obtain aerogel particles having improved particle size and porosity. In particular, stable, dry and highly porous aerogel particles having high surface area and high pore volume are obtained.

At present, there is no continuous depressurization of the temperature-sensitive substances after drying by the LTSCD method via a valve, since the aerogel particles-CO must be heated intensively before depressurization₂The stream is fed to compensate for the joule-thomson effect. The process shown makes it possible to reduce the maximum temperature experienced by the aerogel product, since heating is carried out at moderate temperatures over longer distances.

Continuous valveless pressure reduction is known, but has not heretofore been used in porous materials. Particularly with aerogels, continuous depressurization does not appear to be possible due to the low depressurization rates required to obtain the pore structure specified in the prior art. By valveless continuous depressurization of the aerogel, a truly continuous process for preparing aerogel by the LTSCD process was first achieved. This means that a separate large volume discharge vessel is not required. The result of the valveless depressurization also avoids the wear and clogging problems associated with the use of valves to depressurize the particles.

The product obtained in the process of the invention is a micron-sized powder formed from a porous aerogel having a porosity of at least 70% by volume. The size of the particles can generally vary, with particle sizes ranging from 20 μm to 1000 μm. The aerogels obtained according to the invention can be inorganic or organic aerogels.

In other embodiments, the aerogel comprises an average pore size of about 2nm to about 100nm, such as 5 to 55nm or 10 to 50 nm. In further embodiments, the average pore size of the dried gel material may be about 4nm, about 6nm, about 8nm, about 10nm, about 12nm, about 14nm, about 16nm, about 18nm, about 20nm, about 25nm, about 30nm, about 35nm, about 40nm or about 45nm, about 50nm or about 55 nm. In the context of the present invention, unless otherwise indicated, the surface area, pore size and pore volume are according to ISO 9277: 2010 measured by BET. The international standard defines the determination of the total specific external and internal surface area of a dispersed solid (e.g. a nanopowder) or porous solid by measuring the amount of physisorbed gases by the Brunauer-Emmett-teller (bet) method. It takes into account the recommendations of the International Union of Pure and Applied Chemistry (IUPAC) in 1984 and 1994.

Thus, according to another embodiment, the present invention relates to a method for drying gel particles as described above, wherein the average pore size of the gel particles is between 2 and 100 nm.

According to another aspect, the invention also relates to aerogel particles obtainable or obtained by the method of drying gel particles as described above.

The aerogel particles obtained or obtainable by the process of the present invention are suitable for use in various applications.

The invention also relates to a building material and a vacuum insulation panel comprising the powdered nanoporous material, and to the use of the powdered nanoporous material for thermal insulation. The material obtained according to the invention is preferably used for thermal insulation, in particular in buildings, or for cold insulation, in particular in mobile transport applications or stationary applications, for example in refrigerators for mobile applications. The fibers may be used as an additive for mechanical reinforcement.

According to another aspect, the invention also relates to the use of aerogel particles obtainable or obtained by the method of drying gel particles as described above, for medical and pharmaceutical applications, as additive or carrier material for food additives, as catalyst carrier, for cosmetic, hygiene, washing and cleaning applications, for producing sensors, for thermal insulation or as core material for VIP.

Other embodiments of the invention can be found in the claims and in the examples. It is to be understood that the features of the subject matter/method of the invention or the features of the use of the invention which are described above and illustrated below can be used not only in the combination specified in each case but also in other combinations without leaving the scope of the invention. Thus, for example, even if such a combination is not explicitly mentioned, a combination of preferred features with particularly preferred features, or a combination of features not further characterized with particularly preferred features, etc. is implicitly included.

Illustrative embodiments of the invention are described in detail below, but the invention is not limited thereto. The invention also includes in particular those embodiments which result from the dependent references and combinations which are thus specified in detail hereinafter.

1. A method of drying gel particles comprising the steps of:

(i) providing a suspension comprising gel particles (P1) and a solvent (LM),

(ii) the suspension is introduced into a column through which carbon dioxide flows in countercurrent,

(iii) the dried aerogel particles are removed from the tower,

wherein the suspension is introduced in the top region of the column and the dried aerogel particles are removed in the lower region of the column,

wherein the pressure and temperature in the column are set such that the mixture of carbon dioxide and solvent is almost supercritical or supercritical.

2. The method of embodiment 1, wherein the gel particles are deposited in a counter current manner.

3. The method according to any one of embodiments 1 and 2, wherein the resulting aerogel particles are continuously removed in a valveless manner.

4. The process according to any one of embodiments 1 to 3, wherein CO₂The mass flow rate is set to obtain dry aerogel particles.

5. The process according to any one of embodiments 1 to 4, wherein the CO₂The mass flow rate is set to 0.75kg/h to 25 t/h.

6. The method according to any one of embodiments 1 to 5, wherein the average diameter of the gel particles is from 20 μm to 1000 μm.

7. The method according to any one of embodiments 1 to 6, wherein the average pore size of the gel particles is from 2 to 100 nm.

8. The process according to any one of embodiments 1 to 7, wherein the solvent (LM) is selected from methanol, ethanol, propanol, butanol, pentanol and hexanol.

9. Aerogel particles obtainable or obtained by the method of any one of embodiments 1 to 8.

10. Aerogel particles obtainable or obtained by a method of drying gel particles, the method comprising the steps of:

(i) providing a suspension comprising gel particles (P1) and a solvent (LM),

(ii) the suspension is introduced into a column in which carbon dioxide flows in countercurrent,

(iii) the dried aerogel particles are removed from the tower,

wherein the suspension is introduced in the top region of the column and the dried aerogel particles are removed in the lower region of the column,

wherein the pressure and temperature in the column are set such that the mixture of carbon dioxide and solvent is almost supercritical or supercritical.

11. The aerogel particles of embodiment 10, wherein the gel particles are deposited in a counter-current manner.

12. The aerogel particles of any of embodiments 10 and 11, wherein the resulting aerogel particles are continuously removed in a valveless manner.

13. The aerogel particles of any of embodiments 10-12, wherein CO₂The mass flow rate is set to obtain dry aerogel particles.

14. The aerogel particles of any of embodiments 10-13, wherein the CO₂The mass flow rate is set to 0.75kg/h to 25 t/h.

15. The aerogel particles of any of embodiments 10-14, wherein the average diameter of the gel particles is from 20 μ ι η to 1000 μ ι η.

16. The aerogel particles of any of embodiments 10-15, wherein the average pore size of the gel particles is from 2 to 100 nm.

17. The aerogel particles according to any of embodiments 10-16, wherein the solvent (LM) is selected from methanol, ethanol, propanol, butanol, pentanol, and hexanol.

18. Use of aerogel particles according to any of embodiments 10 to 17 or obtained or obtainable by the method of any of embodiments 1 to 8, for medical and pharmaceutical applications, as additive or carrier material for food additives, as catalyst carrier, for cosmetic, hygiene, washing and cleaning applications, for producing sensors, for thermal insulation or as core material for VIP.

The invention is illustrated in more detail below by means of examples.

Examples

I.Configuration example

Some rough calculations and one configuration example are given below. In the following configuration, the operating conditions (120 bar, 50 ℃) and the particle properties (particle porosity ∈ 0.93 and curvature τ 2.5) were assumed to be constant. In the following, it is also assumed that the flux is initially very low, which means that pure CO is used₂The fluid phase is approximately described.

1.Calculation of drying time

The drying times for particles of various diameters were simulated under the assumption of one-dimensional mass transfer. Fluid (CO) using Peng-Robinson equation of state and appropriate mixing rules₂And ethanol) were modeled. By particle porosity of 0.93 ∈ (corresponding to V)_{Pores of}＝8cm³The curvature of/g) and τ 2.5 describes the particle.

1.1 diffusion in particles

The following drying times were calculated assuming that the rate determination step was intragranular diffusion (table 1). It is assumed that the mass transfer from the particles to the surrounding fluid phase is very large. The drying time of 5 μm large particles is only a few milliseconds and less than one second in the range up to 100 μm.

Table 1: calculated drying time of alginate aerogel particles at 120 bar and 50 ℃

1.2 consider mass transfer

The drying times of the arrangement in table 2 take into account the mass transfer from the particles to the surrounding fluid phase. The average mass transfer coefficient was calculated from the Sh correlation of the individual spheres. Interestingly, the mass transfer coefficient is a function of particle size only, not flow rate, since the relative velocity and hence Re is constant and only changes when particles are discharged.

Table 2: drying time of alginate aerogel particles at 120 bar and 50 ℃ calculated taking into account the average mass transfer coefficient

When mass transfer is considered, the relative change in drying time is greatest for small particle sizes and becomes smaller as the particle size increases, compared to the assumption of infinite mass transfer coefficients. However, the variation in absolute drying time is relatively small and the drying time remains within the same order of magnitude.

2. ₂Discharging of particles: mass flow rate and particle size of CO

In addition to drying time, another key aspect of continuous supercritical drying in a countercurrent column is the particle hydrodynamics and associated residence time. The descending speed of the particles can be described by the relationship between the archimedes number and the reynolds number. For the transition region between the stokes region and the newton region, the following conditions apply according to MARTIN:

the (drop) velocity calculated from the Re number represents the relative velocity between the particle and the surrounding fluid and depends on the particle size. Thus, depending on the CO oriented upwards₂The amount of flow, the absolute rate of descent of the particles or the passage of the particles through the top of the column with the CO₂And discharging the material flow.

For an internal diameter of d_i20.57mm and therefore a free cross-section a 3.32E-04m²And a column height of 500mm, summarized in Table 3 for the various COs₂Mass flow rate, calculated residence time of alginate aerogel particles of various diameters. This is based on the average apparent density of the granules consisting of wet and completely dry granules.

Table 3: calculated residence time of alginate aerogel particles with epsilon 0.93

Porosity of aerogel particles versus particle in CO₂The theoretical rate of descent and residence time in the stream have a great influence. As can be seen from Table 4, for relatively low porosity, smaller particles may also be excluded and/or higher CO₂Drying at flow rate, so a higher particle flux can be selected for the same column height.

Table 4: calculated residence time of alginate aerogel particles,. epsilon. 0.85

3.Effect of Mass flow Rate on the desired drying time/residence time ratio

For the configuration of the column length, the ratio of residence time to drying time is understood to be > 1. Table 5 reports the residence time/drying time of a column having a height of 500mmAnd (4) the ratio. For CO shown to be 0.5kg/h to 3kg/h₂The particles having a diameter of 500 μm were not completely dried at the mass flow rate. This may be by CO₂Further increases in mass flow rate counteract this, but this results in smaller particles being discharged. Alternatively, an increase in the height of the column results in a proportional increase in the residence time and hence in the residence time/drying time ratio. Doubling the column height to, for example, 1m would lead to doubling the residence time/drying time ratio and thus also to drying of particles having a diameter d of 500 μm without discharging smaller particles.

Table 5: residence time/drying time ratio for a column height of 0.5m at infinite mass transfer coefficient

Table 6: residence time/drying time ratio for a column height of 1m at infinite mass transfer coefficient

4.Effect of particle loading on drying

In the previous rough calculation, it was assumed that almost pure CO was also present at the outlet₂In other words, operation is only performed at very low particle loadings. In industrial applications, the purpose of the countercurrent operation is to discharge CO with the highest possible loading of ethanol (EtOH) at the top of the column₂Logistics to reduce CO used per kg aerogel₂. For this reason, the extended drying time must be compensated by a corresponding increase in the tower height. For example, 1L/h of 500 μm particles in a 1m tall column as shown in Table 6 were dried in CO₂The mass flow rate of 1kg/h or less cannot be achieved. (see Table 7) however, as the column increases to 3m, C at 1kg/h is driedO₂The same is true and a high outlet mass ratio of 64% (w/w) of EtOH can be maintained.

Table 7: in a column with a height of 1m at different CO₂Countercurrent drying of 1L/h 500 μm aerogel particles at mass flow rate

II.Examples

The principle feasibility of the drying process can be demonstrated in a pilot plant.

A suspension (14% (v/v)) of alginate gel particles having a diameter of 50-300 μm in ethanol was removed from the storage vessel at 23mL/min and delivered to a length of 0.5m and an internal diameter d_i20.6mm top of the column. Supercritical CO is introduced at an operating pressure of 120 bar and an operating temperature of 50 DEG C₂The feed was fed to the particle stream in a countercurrent of 40 g/min. After the experiment the collection vessel was depressurized.

Gel particles with CO₂The stream instead settles, while the free ethanol (despite ethanol-CO)₂The density of the mixture is the same as the ratio of CO₂High) with CO₂-the ethanol mixture stream is discharged through the top. The relatively short residence time of the particles compared to a moving bed surprisingly results in complete drying of the aerogel particles. The pore volume of the particles that had fallen into the collection vessel was 9.4cm³Per g and a BET surface area of 500m²In g, similar to the properties of aerogel particles prepared by the same gelling process and dried in batches.