WO2025233470A1

WO2025233470A1 - Method of manufacturing an insulated storage container

Info

Publication number: WO2025233470A1
Application number: PCT/EP2025/062650
Authority: WO
Inventors: Oras ABDUL-KADER
Original assignee: Prtc Nv
Current assignee: Prtc Nv
Priority date: 2024-05-08
Filing date: 2025-05-08
Publication date: 2025-11-13
Anticipated expiration: 2026-11-08

Abstract

The method of manufacturing an insulated storage container for storage of pressurized and/or liquiﬁed ﬂuids, comprises the steps of: (1) providing a storage container having a ﬁrst and a second end surface and at least one container surface extending between the ﬁrst and the second end surface; (2) applying insulaon to at least one surface of said at least one container surface and the ﬁrst and the second end surface Herein the insulaon is applied as a composite insulaon composion comprising a microporous powder mixed into a gelled carrier material. The microporous powder comprises at least an opaciﬁer, inorganic ﬁber and parculate silica material from the group of pyrogenic silica and precipitated silica, said parculate silica material oponally further comprising alumina, wherein said microporous powder and/or at least part of said parculate silica material is hydrophobic. The gelled carrier material is adhered to said at least one surface of the storage container.

Description

Method of manufacturing an insulated storage container

FIELD OF THE INVENTION

The invention relates to a method of manufacturing an insulated storage container for storage of pressurized and/or liquified fluids, comprising the steps of: providing a storage container having a first and a second end surface and at least one container surface extending between the first and the second end surface, which storage container comprises polymer, and applying insulation to at least one surface of said at least one container surface and the first and the second end surface.

The invention further relates to an insulated storage container comprising a multilayer structure of which a first layer comprises a fiber reinforced polymer layer shaped as a storage container having a first and a second end surface and at least one container surface extending between the first and the second end surface; wherein insulation is arranged to at least one surface of said at least one container surface and the first and the second end surface.

The invention further relates to the use of such an insulated storage container for storage of pressurized and/or liquified fluids, especially at cryogenic conditions.

BACKGROUND OF THE INVENTION

Cryogenic storage containers - also referred to as cryogenic tanks - of polymer material have been under development for a significant period of time. Such storage containers are preferably predominantly made of polymer material, for instance as a multilayer structure, of which a first layer is a fiber reinforced polymer layer. The preferred fibers are carbon fibers. A further polymer layer is usually provided at an inner side of said first layer, as a liner inhibiting diffusion of material from the inside to the outside or vice versa. However, further development of storage containers with different and/or additional materials cannot be excluded.

There is clearly a considerable commercial interest in such cryogenic tanks, for instance for storage of liquid nitrogen, hydrogen and other materials of which the boiling point is well below 0°C. However, such storage requires that the container wall is well-closed, that that no material therein can leak out of the cryogenic tank, which is anyhow not desired, but could moreover easily lead to an explosion. Furthermore, properties of polymers depend on the temperature. At cryogenic temperatures, most if not all polymer materials are in the semi-crystalline glassy state and tend to become brittle. Some of the engineering materials widely used at ambient temperature, turn out less suitable for cryogenic temperatures. Certain fluoropolymers, so-called Ultrahigh molecular weight polyethylene (UHWPE) and epoxy are examples among the polymer materials considered useable at cryogenic temperatures. Particulate fillers and fibers may be added to the polymer material to improve or modify its properties. However, such particulate fillers may have an effect on viscosity and other processing properties.

Such cryogenic tanks are known from a variety of patent applications. WO2022189470A1 discloses a tank comprising a fibrous preform, which is impregnated at its outside with polymer and having an internal layer. W02023048073A1 proposes a cryogenic tank with a middle layer of ethylene vinyl alcohol copolymer. USS2023/0122936A1 proposes the incorporation of hollow fibers through which a liquid could run for insulation purposes. EP3984734 discloses a cryogenic tank comprising 1st and 2nd carbon fiber layers. WO2022/112694A1 discloses a cryogenic tank with a sealing layer, preferably a fluoropolymer, and a composite reinforcing layer comprising continuous fibres impregnated with a polymer. Herein, it is indicated that there may be an insulating layer, for instance on the basis of mineral wool, and possibly using a metal layer.

The insulating layer foreseen in WO2022/112694A1 however is arranged externally to the cryogenic tank. Although this has the advantage that the insulation layer can be pure rather than a composite, it is deemed disadvantageous that such layer is arranged separately. This is typically done during or after installation, which requires extra labour force. Moreover, an external assembly has the implicit risk that gaps may remain. Heat can enter the cryogenic tank via such gaps, leading to local differences in temperature and the possibility of tensions and local weakening of the tank. It is therefore desired to provide a cryogenic tank that comprises some insulation as a part of the container wall. More in general, it appears desired to provide a storage container - also referred to as tank - that comprises some insulation as part of the container wall. Such storage container may also be applied at other conditions than at cryogenic conditions.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an improved method of manufacturing an insulated storage container, wherein the insulation may be applied so as to become part of the storage container rather than being separately thereof.

It is a further object of the present invention to provide an improved insulated storage container. It is again a further object of the invention to provide the use of the improved storage container for storage of pressurized and/or liquefied fluids, especially under cryogenic conditions.

According to a first aspect, the invention provides a method of manufacturing an insulated storage container for storage of pressurized and/or liquified fluids, comprising the steps of: Providing a storage container having a first and a second end surface and at least one container surface extending between the first and the second end surface; applying insulation to at least one surface of said at least one container surface and the first and the second end surface,

Wherein the insulation is applied as a composite insulation composition comprising a microporous powder mixed into a gelled carrier material,

Wherein said microporous powder comprises at least an opacifier, inorganic fiber and particulate silica material from the group of pyrogenic silica and precipitated silica, said particulate silica material optionally further comprising alumina, wherein said microporous powder and/or at least part of said particulate silica material is hydrophobic. wherein the gelled carrier material is adhered to said at least one surface of the storage container.

According to a second aspect, the invention provides an Insulated storage container and shaped as a storage container having a first and a second end surface and at least one container surface extending between the first and the second end surface. Composite microporous insulation is arranged and adhered to at least one surface of said at least one container surface and the first and the second end surface, said composite microporous insulation comprising a microporous powder mixed into a gelled carrier material, wherein the microporous powder comprises at least an opacifier, inorganic fiber and particulate silica material from the group of pyrogenic silica and precipitated silica, said particulate silica material optionally further comprising alumina, wherein said microporous powder and/or at least part of said particulate silica material is hydrophobic.

According to a third aspect, the invention provides the use of the insulated storage container of the invention for storage of a fluid under cryogenic conditions and/or high-pressure conditions.

As is well known in the art, microporous insulation material comprising a microporous powder provides insulation with a very low thermal conductivity that can remain stable to a very high temperature of more than 1000°C, and even higher. It is used in many industrial and specialty applications such as heating systems, fuel cells, piping for oil and gas and aerospace applications. Usually, microporous insulation is provided in the form of a blanket or panel, wherein a textile material encapsulates the - compacted - microporous powder. In investigations leading to the present invention, it was however understood that such panels or blankets have limitations for storage containers, and especially those under high pressure and/or cryogenic conditions. A first limitation is that the material remains separate and needs to be attached with strips around the container. Furthermore, the blanket or panel shape, even when flexible, must be cut out and shaped for appropriate arrangement around a container. This is not highly practical, and the insulation remains separate from the container. A second limitation is that the textile material may give rise to scratches on the container wall in case of any displacement or due to ageing. At the extreme conditions of high pressure and cryogenic temperatures, such scratches might lead to crack initiation and/or microcracks. This evidently should be avoided.

In accordance with the invention, the microporous insulation is provided as a composite material that comprises a gelled carrier material into which the microporous powder is loaded and mixed. The gelled material is preferably a hydrogel material or a silica gel material or a combination thereof. It was found that this composite insulation material can have thermal conductivity values that approach those of pure microporous insulation. Furthermore, due to the gelled carrier material, the composite insulation material is flexible, even after moulding into predefined shapes. The material furthermore is sticky resulting in adhesion to a surface to which it is applied. Flexibility may be reduced by drying, which can bring humidity levels down to less than 2%. Hence, it is feasible to apply microporous insulation without risk of scratches, as a part of an insulated storage container and allowing use of the insulated storage container under high-pressure and/or cryogenic conditions.

Furthermore, in accordance with the invention, the composite insulation composition is applied to at least one surface of the container, which at least one surface may be an end surface or a container surface, such as a cylindrical surface. As compared to a conventional blanket or panel, the composite insulation composition of the invention can be brought into a desired shape. This facilitates application to end surfaces, but also application around an inlet and/or outlet of the container. This is deemed beneficial, such curved shapes and inlets areas and outlet areas are generally considered to be comparatively vulnerable for temperature variations. While it is deemed preferable that the composite insulation composition is applied to the entire container surface, it is not excluded that application occurs onto merely one or two surfaces, such as one or more end surfaces. This is a matter for an ultimate container design. Moreover, even when the composite insulation composition is applied to several or all surfaces of the container, it is not necessary that the composite insulation composition is applied with the same thickness everywhere. Rather, the composite insulation may be applied in a first thickness on a first surface area of the container and in a second thickness on a second surface area of the container, wherein the first thickness and the second thickness are mutually different. The first surface area may for instance be an area with a high risk of microcrack formation, such as an area with increased curvature.

Preferably, the container comprises a multilayer structure comprising polymer material. Storage containers for cryogenic applications based on polymer material have been investigated and are deemed advantageous. The composite microporous material serves here even more profoundly than for other container materials, such as metals, in order to prevent any damage in the form of cracks. In a further implementation, the storage container comprises a multilayer structure, of which a first layer is a fiber reinforced polymer layer, especially reinforced with carbon fibers. While the construction of the storage container may change as a consequence of further developments, further regulations and in dependence of the specific use, the use of fiber reinforced polymer layers is deemed preferred, with the carbon fibers especially preferred.

Furthermore, in one further implementation, an intermediate layer may be present between the container surface and the composite insulation on one or more of the said surfaces. One example of such an intermediate layer may be a resin comprising microporous powder as a filler. The exact implementation may depend on the shape of the container, the application conditions including temperature and pressure and any sources of heat or comparatively high temperature in the vicinity of the storage container. Hence, it is typically a matter of the ultimate container design.

According to a preferred embodiment, the gelled carrier material is selected from the group of polymer-based hydrogels and silica gels or a combination thereof. It has been found that both polymer-based hydrogels and silica gels can be used as gelled carrier material. A polymer-based hydrogel is for instance obtainable by crosslinking a hydrophilic polymer such as a polyalkylene oxide (and preferably polyethylene oxide) or a polyacrylamide with an oligomeric or polymeric crosslinker. Suitable crosslinkers for polyalkylene oxide are polyacids, such as polyacrylic acids. Alternative hydrophilic polymers for hydrogel formation such as cellulose-based materials (for instance hyarulonic acid) are not excluded. Molecular weights can be chosen broadly. Good results have been achieved with hydrogels of which both the hydrophilic polymer and the crosslinker had an (mass)- average molecular weight in the range of 1.10⁵ to 6.10^s g/mol, such as 5.10⁵ to 5.10^s g/mol. Silica gel may for instance be formed from colloidal silica that is destabilized via a pH change and preferably activated by means of a setting agent. One feasible combination is an acid stabilized colloidal silica with a base stabilized colloidal silica as setting agent or vice versa. The use of a polymer-based hydrogel is deemed preferred, as low thermal conductivities have been obtained therewith. Furthermore, the formation of the polymer-based hydrogel seems somewhat better controllable than the formation of the silica gel.

In a further embodiment, the polyalkylene oxide, preferably polyethylene oxide, is crosslinked with a polymeric or oligomeric polyacid. While hydrogels may be formed by way of physical crosslinking (i.e. hydrogen bonding), the formation of a hydrogel with chemical crosslinks is preferred, so as to ensure the stability of the hydrogel during any mixing with further ingredients. A variety of polyacids may be used, provided that these are oligomeric or polymeric so as to enable that the resulting polymer network has sufficient flexibility. It will be understood that a combination of polyacids may be used alternatively. Good results have been achieved with the use of polyacrylic acid as a crosslinker. The polyacrylic acid may herein be partially esterified for stabilization and to obtain a sufficient distance between (carboxylic) acid groups along the chain. The polyacrylic acid is suitably used in powder form, for instance as a spray-dried polyacrylic acid. It may be a copolymer of acrylic acid, acrylate and further monomers. Examples of spray-dried acrylic polymers, which are redispersible powders are BASF ACRONAL S430P, BASF ACRONAL S629P, DOW DRYCRYL 2903, ELOTEX FLEX 8300, ELOTEX FLEX 8310, ELOTEX FLEX 8320, ELOTEX FX 7000, ELOTEX TITAN 8100 or a mixture thereof. One way of preparing such redispersible powder is known from W02008059034, which is included herein by reference. It is herein disclosed to form a polyacrylic acid (or acrylate) in the form of a dispersion, emulsion or microemulsion (low viscous) in the presence of a stabilization colloid. The dispersion is then formulated into a powder by addition of a water-soluble polymer and subsequent drying, such as by spray-drying, freeze-drying, fluidized bed drying, drum drying and/or flash drying. Hence, it is preferred to provide the acrylic polymer as a dispersible powder, and more preferably as a dried (such as spray-dried) formulation of a particulate, acrylic polymer or copolymer (latex) with a water-soluble polymer. Examples of such water-soluble polymers include one or several polyvinyl pyrrolidones and/or polyvinyl acetals with a molecular weight of 2,000 to 400,000, fully or partially saponified and/or modified fully or partially saponified polyvinyl alcohols with a degree of hydrolysis of preferably about 70 to 100 mol. %, in particular of about 80 to 98 mol. %, and a Hbppler viscosity in 4% aqueous solution of preferably 1 to 100 mPas, in particular of about 3 to 50 mPas (measured at 20° C. in accordance with DIN 53015), as well as melamine formaldehyde sulfonates, naphthaline formaldehyde sulfonates, block copolymerisates of propylene oxide and ethylene oxide, styrene-maleic acid and/or vinyl ether-maleic acid copolymerisates.

In a further implementation, the gelled carrier material comprises a polymer-based hydrogel, and comprises colloidal silica or a precursor thereof. Such a precursor is for instance waterglass. The precursor is expected to be converted into colloidal silica upon formation of the hydrogel, when mixing ingredients together and diluting with water. While experiments were performed successfully, the exact underlying mechanism is not known. The colloidal silica is herein preferably chosen to have high stability, for instance by means of the (mean) particle size and/or by functionalization of the particle surface. Before loading of the microporous powder, such colloidal silica may It is believed that such colloidal silica may be transformed into silica gel at a later stage, such as during drying, which occurs after loading of the carrier material with microporous powder. It therewith believed o contribute to stability of the gel during temperature changes. For sake of clarity, it is observed that the term "carrier material" should not be interpreted as a solid carrier on top of which the powder is applied. Rather, the microporous powder is mixed and dispersed into the gelled carrier material.

The composition of the microporous powder can be chosen relatively broadly. The opacifier can be present in an amount of lwt% up to 50wt% of the (weight of the) microporous powder. Preferably, the amount of opacifier is at least 10wt%, preferably at least 15wt% and more preferably at least 20wt%. Good results have been achieved with amounts of above 30wt%, such as 35-45wt%. The opacifier is for instance one of silicon carbide, titanium oxide (rutile), magnesium oxide, zirconium silicate. A preferred opacifier for use in combination with pyrogenic silica or precipitated silica or a combination hereof is silicon carbide or titanium oxide (rutile). Good results have been obtained with titanium oxide. The particulate silica material is for instance present in an amount of 25wt% to 70wt%, preferably 30wt% to 60wt%. When a filler is present, the amount of particulate silica material is in the lower part of the range, for instance 30-45wt%. The amount of inorganic fiber is suitably in the range of 0.1-20% by weight, preferably 0.1-10% by weight. Good results have been achieved with microporous powders comprising less than 7 wt% inorganic fiber, and even less than 5wt%. One example of fibers is so-called alkaline earth silicate, also known as AES and/or wool, such as for instance Superwool™ 607 obtainable from Thermal Ceramics, which is a calcium magnesium silicate, with a diameter of 3 microns. Another example of fibers is a silica-based fiber, such as based on at least 80wt% SiO2 and 5-20w% AI2O3. These fibers may have a diameter of 4-8 micron, such as 6 micron. Fiber mixtures comprising one or more of these fibers are also feasible. Preferably any of the fibers have a content of at least 70wt% of silica, preferably at least 80wt%. it is believed that the silica of the fibers helps to ensure cohesion of the microporous powder and its mixing into the carrier material.

Most preferred is an implementation, wherein the fibers comprise silica-based fibers, as based on at least 80wt% SiO2 and 5-20w% AI2O3, with a diameter of 4-8 micron, in an amount of up to 10wt% of the microporous powder, or even up to 7wt%. This implementation may be advantageously combined with titania opacifier, such as in an amount of 30wt% or more, and with particulate silica in an amount of 30-60wt%. A filler is optionally present.

The particulate silica material may be hydrophobic or the microporous powder has been treated to become hydrophobic. Preferably, the particulate silica is hydrophobic. Hydrophobic pyrogenic silica can be purchased from suppliers, such as Evonik, Wacker etc. Alternatively hydrophobic agents, typically in the form of optionally halogenated alkylsilanes or alkylsilanols or silicones may be used and added to the microporous powder or be applied to the particulate silica. It is not deemed necessary that all particulate silica is hydrophobic. A mixture of hydrophilic (i.e. not treated) and hydrophobic particulate silica may be used instead. In such a case, the relative amount of hydrophobic silica is preferably at least 50wt%, preferably at least 60%, more preferably at least 75wt%, based on the total amount of particulate silica.

According to an advantageous embodiment, wherein said at least one surface of the storage container is not water-repellent, and more preferably hydrophilic. The structure of this embodiment facilitates adhesion of the composite insulation to at least one surface of the container. However, when using composite microporous insulation comprising hydrophobic particulate silica or microporous powder, the adhesion to a resin may be sufficient even without modification or tuning of the surface properties.

One preferred implementation onto a surface resides in the functionalization of the surface with silanol or hydroxyl groups. This is deemed particularly useful when the surface of the container is provided with a resin, such as a polyolefin or halogenated polymer. Rather than rendering the at least one surface of the storage container more hydrophilic, the surface of the composite insulation may be rendered more hydrophobic, such as by using a hydrophobic agent or functionalization of the surface. This is deemed easily feasible when applying the composite insulation composition in the form of a molded body. One further option is the application of a primer prior to the application of the composite microporous insulation material.

In one embodiment, the composite insulation composition is dried. Drying typically occurs after application of the composite insulation composition to the at least one surface of the container. However, it is not excluded that a drying step is performed before application, for instance during or after molding of the composite insulation composition to a predetermined shape. Drying may be performed using one or more known drying methods. A first method is drying in a chamber above room temperature, such as in an oven. Preferably the oven temperature does not exceed 150°C, or 100°C to avoid unforeseen destabilization. A second method is drying by means of radiation, such as infrared. A third method resides in the circulation of dry (and heated) air or gas over the insulation. A fourth method is the use of freeze-drying. Preferably, the composite insulation composition is dried to a humidity level to at most 5% by weight, preferably at most 3% by weight or even at most 2% by weight. The humidity level may be tuned so as to ensure sufficient flexibility when decreasing the temperature down to cryogenic temperatures of -100°C or less. The level of flexibility may also depend on the type of gelled carrier material and any further silica present.

The composite insulation material is applied, according to one embodiment, as one or more molded bodies. Herein, the composite insulation material is put into a mould of predefined shape and formed into a molded body. It has turned out that the molding does not diminish the flexibility of the material. The molded body can then be applied and adhered to the at least one surface of the container. Advantage over conventional moulded parts.

In a preferred implementation, said one or more molded bodies comprise a first body and a second body each comprising a fixation element for mutual assembly. This enables to apply an encapsulation, and facilitates the application of the moulded bodies around the container. One example of fixation elements include tongues and grooves parts. Another example resides in two overlapping thinned areas. Again a further example is the provision of a channel and a corresponding protrusion, preferably across the entire thickness of the moulded body. Such channel and protrusion may include a curve or hook so as to ensure fixation in two dimensions. It will be understood that a single molded body may be provided with more than one fixation element, for fixation to one further molded body and/or for fixation to a plurality of further molded bodies.

According to another embodiment, the composite insulation composition is applied as a paste present on a foil. The foil will be arranged at a side facing away from the at least one surface of the container. This foil may be removed after application and drying of the composite insulation composition. Alternatively, the foil may remain present and acts as a protective foil.

In again a further embodiment, the storage container comprises at least at least one surface a resin layer that is filled with particulate microporous powder, for instance in the form of granules. The provision of a resin layer filled with particulate microporous powder as a surface layer on the storage container is deemed beneficial for the case that the storage container is foreseen to be used to contain liquids at high pressure. The resin layer provides extra stability combined with a relatively low thermal conductivity. The composite insulation material of the present invention provides lower thermal conductivity combined with the option to provide layers of larger thickness. As will be understood in the context of the present invention, the particulate microporous powder incorporated in the resin layer preferably comprises a particulate silica material and an opacifier. Examples of each of them are given hereinabove.

In one implementation, the particulate microporous powder is present in the resin layer in the form of a granulate. This is beneficial to enable sufficient loading of the microporous powder into the resin without too much increase in viscosity. A storage container comprising such a resin layer comprising granules of microporous powder material is described in the non-prepublished application EP24156702.3 in the name of Applicant and filed on 8 February 2024, which is included herein by reference. The amount of microporous material is for instance at least 5wt%, preferably at least 10wt% based on the total weight of the filled polymer material. The amount may be as high at 25wt%. The granules are typically free of any fiber material. In one specific implementation, the microporous material may further comprise a microsphere additive in amounts up to 30wt%. An example of such microspheres are perlite microspheres. A granular microporous composition comprising particulate silica material, opacifier and microspheres may be rendered hydrophobic by application of a hydrophobic agent and especially an agent in polymeric form, such as a silicone material. This granular material is described in the non-prepublished application PCT/EP2024/058701 in the name of Applicant and filed on 28 March 2024, which is included herein by reference. According to again a further embodiment, the method comprises the further step of applying a blanket or panel of insulation material onto and preferably around said - composite microporous - insulation. It is deemed that the risk of formation of microcracks is reduced when a conventional blanket or panel is applied onto the composite insulation. The effective temperature at the outside of the composite insulation will be higher than at the container surface, reducing risk of formation of microcracks due to brittleness. Additionally, the relative flexibility of the composite insulation will reduce risk of cracking and will reduce impact of any strips bound around the panel. Furthermore, the composite insulation may have an outer shape that is made fit for the application of a blanket. For instance, the composite insulation may be present at end surfaces and is covered by a panel or blanket in such a manner, that the blanket or panel covers not only the - cylindrical - container surface, but also the composite insulation arranged at the end surface. In this manner, an edge of the blanket or panel is not aligned with an end surface of the container, which is deemed beneficial to thermally protect such end surface.

In one implementation, such blanket or panel comprises microporous insulation. In a further implementation, such blanket or panel comprises fire-resistance material, Use of fire-resistance material is deemed relevant for storage containers, even when using low operating temperatures. In the event that a fire would occur outside of the storage container, the stability of the storage container is to be protected so as to minimize risk of explosion of the contents of the storage container. Fire resistance materials are known per se and for instance include calcium silicate materials sold by Promat International NV. One option resides in the use of a blanket or panel comprising both microporous insulation and fire resistance material, especially in different layers. This option has been described in the non-prepublished application EP24156703 filed on 8 February 2024 in the name of Applicant, which is included herein by reference.

In one implementation, the composite microporous insulation composition is applied in a thickness of at least 5 mm, preferably at least 1 cm. This is deemed a useful thickness. Hence, the resulting composite insulation may have a thickness well going beyond the thickness of a conventional layer applied by spraying or coating.

For sake of clarity, it is added that the microporous powder is a powder material as specified in ASTM C-1676. It is referred to as microporous in view of the porosity of the pyrogenic or precipitated silica, and especially pyrogenic silica. Especially, such materials have a lattice structure in which the average interstitial dimension is less than the mean free path of the molecules of air or other gas in which the material is used. The lattice structure is created by very fine silica particles, such as pyrogenic silica and precipitated silica, which adhere to each other in a chain-like formation. Additives, such as rheology modifiers, biocides, water retention agents such as cellulose ethers, dyes and pigments and the like may be added into the composite insulation composition.

It is observed for sake of clarity that any of the embodiments and implementations discussed hereinabove and in the discussion of illustrated embodiments and examples hereinafter, are deemed applicable to any of the aspects of the invention, i.e. the manufacturing method, the resulting insulated storage container and the use thereof, even when this is not explicitly mentioned.

BRIEF INTRODUCTION OF FIGURES

These and other aspects of the invention will hereinafter be elucidated with reference to the figures, which are not drawn to scale and in which equal reference numerals refer to equal or corresponding parts, and wherein:

Fig. 1 shows schematically a storage container in a bird's eye perspective;

Fig. 2 shows a cross-sectional view of the storage container through the container wall;

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

Fig. 1 shows a schematical view of a storage container 30. The storage container 30 is provided with a first end part 18 and a second end part 19 (each having a surface), in between of which a container wall 10 extends. The container wall 10 is cylindrical in the illustrated example. This is deemed preferred but not essential, and other shapes are not excluded. The container wall 10 is composed of polymer material in one or more layers, as further shown in Fig. 2. The container wall 10 typically is continuous and extends onto the first end surface 18 and the second end surface 19, as known to the skilled person. On the first end surface 18, an opening 20 is arranged, through which the storage container 30 may be filled and unfilled. While not shown, it is not excluded that more than one opening is present, for instance on the second end surface 19.

As is clearly seen in Fig. 1, a storage container 30 has a first and second end surface 18, 19. In order to obtain adequate insulation of the storage container 30, it is not sufficient to apply an external roll, blanket or batten of insulation material around the storage container 30. The first and second end surfaces 18, 19 need to be insulated as well. This applies to storage containers 30 in general, since the first end surfaces 18, 19 may be the mechanically weaker areas due to their changing curvature. Moreover, the opening 20 is a sensitive part for variations in temperature and any resulting risk of evaporation, leakage or clogging. The risk of evaporation would exist at low temperatures, such as cryogenic conditions, due to - uncontrolled - heating up. The risk of clogging would occur at higher temperatures, for instance due to cooling down and resulting effects on viscosity and on homogeneity of a dispersion and/or adhesion to the surface of some ingredients. Fig. 2 shows in cross-sectional view the storage container of the invention, and more particularly the container wall 10 surrounding an interior 40 of the storage container 30. The container wall 10 is provided with an inner side 11 and an outer side or container surface 12. Such a container wall preferably comprises polymer material, and typically comprises a main layer, and an inner liner 16. The main layer 15 may be a laminate of several sublayers. It seems generally preferable that the main layer 15 is provided with reinforcement, typically by addition of fibers. For cryogenic tanks, the use of carbon fibers as reinforcement of the main layer 15 seems preferable. The inner liner 16 is for instance a fluoropolymer. Specific examples and embodiments are disclosed in the patent documents cited in the background section, such as WO2022/112691A1, which is herein included by reference.

In accordance with the invention, the container wall 10 comprises a further layer 50 at its container surface 12. This further layer 50 comprises a composite microporous insulation composition according to the invention, also referred to as composite insulation composition. The resulting layer is referred to as composite insulation or composite microporous insulation and preferably has a thickness of at least 5 mm or even at least 1 cm. The thickness does not need to be equal everywhere, and could for instance be larger on one or more of the end surfaces 18, 19 than on the container surface 12. It is an advantage of the composite insulation composition that it is free of a textile encapsulation, such as an encapsulation of fiber glass. Therewith, it is prevented that the textile encapsulation could result in microcracks on the container surface 12 and/or the end surface(s) 18, 19 on which it is applied. The composite microporous insulation composition comprises a gelled carrier material that is loaded with a microporous powder. As has been described hereinabove and will be further elucidated in the Examples, the gelled carrier material comprises a polymer-based hydrogel and/or a silica gel. In a preferred embodiment, the gelled carrier material is a polymer-based hydrogel. The composite insulation composition as applied to at least one said surfaces 12, 18, 19 preferably comprises a source of colloidal silica, such as a stabilized colloidal silica or waterglass. This source of colloidal silica may be transformed into a silica gel during processing of the composite insulation composition, such as by means of pH changes and/or by drying. The microporous powder typically comprises an opacifier, a particulate silica and an inorganic fiber. By application of the said composite insulation composition onto said at least one surface 12, 18 19 of the storage container 30, the composite insulation composition gets adhered to the said surface 12, 18, 19, rather than merely being adjacent to it, as would be the case with a conventional panel, blanket or even moulded microporous part. Therewith a storage container 30 is obtained that comprises the further layer 50 of composite insulation composition. This is advantageous, since no separate fixation means such as strips will be necessary. Moreover, the storage container 30 with said further layer 50 may be manufactured by a container manufacturer, rather than that the insulation needs to be applied on-site, i.e. after transport. This may be cost-effective. Evidently, it is not excluded that the further layer would be applied during installation.

In one implementation, the composite insulation composition is applied in the form of molded bodies. In another implementation, the composite insulation composition is applied as a paste present on a foil.

It is not excluded that an intermediate layer - not shown in Fig. 2 - would be present at the at least one surface 12, 18, 19 of the storage container 30 and the (further layer 50 of) composite insulation. This may be particularly advantage in case that the storage container 30 would be operated under high pressure. In a preferred embodiment, such intermediate layer is a resin layer comprising a microporous granulate as a filler. The intermediate layer may additionally comprise further granulates, such as a calcium silicate granulate and especially a granulate of synthetic forms of calcium silicate such as synthetic xonotlite. This material is commercially available from Promat International under the trade name Promaxon®. The presence in the form of a granulate is preferred in order to obtain adequate mixing with the microporous granulate and within the further layer 50. The microporous granulate and any other granulate preferably is treated to be hydrophobic, for instance by using hydrophobic ingredients, and especially hydrophobic pyrogenic silica such as commercially available from Evonik under the tradename Aerosil R974. Alternatively, the microporous granulate may be rendered hydrophobic by adding a hydrophobic agent to the composition of the microporous material, and/or by performing a hydrophobation treatment after preparation of the granules. Alternatively or additionally, the granules may be coated with an organic coating, such as a silicone coating. This however is a more complicated treatment. Such subsequent hydrophobation is facilitated in that the granules further comprise an inorganic microsphere as a filler. An example is a perlite microsphere. The polymer may be chosen in dependence of processing properties at the application temperature, for instance at ambient temperature or even above ambient temperature, and in dependence of the operation temperature of the storage container. The choice of the polymer material may further depend on the polymer layer used for the main layer 15. If the polymer of the main layer 15 would be an epoxy material, an epoxy may be used for the intermediate layer 50. If the polymer of the main layer 15 would be a polyolefin or a fluoropolymer, then the intermediate layer 50 may comprise such polyolefin, a fluoropolymer or any other material compatible therewith. However, use of thermoplastics such as polyurethane or polyimide is not excluded. It is not excluded that the material of the intermediate layer 50 would contain further fillers, which are preferably inorganic insulating particulate fillers. In fact, it is an advantage of the invention that the microporous insulation can be added in a form, which will have less impact on the processing properties of the polymer material due to its significantly reduced external surface area as compared to particulate fillers.

It is an advantage of the invention that the container surface 12, the first end surface 18 and/or the second end surface 19 herewith are provided with insulation. In comparison to blankets or panels, the composite insulation can be brought into a desired shape, thus following the shape of the surfaces 12, 18, 19 of the storage container 30, and enabling the application in a desired thickness. Any area that is covered less easily with such conventional external insulation material is still insulated. Furthermore, this provides additional safety. In case that by errors during assembly or any unexpected changes during the lifetime of the storage container, part of the external insulation material would be moved or damaged to locally reduce the insulation performance of the external insulation material, the insulation material of this further layer 50 remains.

EXAMPLES

Measurement methods

Thermal conductivity at 10°C is measured using a heatflow meter according to ASTM C518, wherein the lower plate is at 0 °C and the higher plate is at 20°C. Thermal conductivity at 400°C is obtained by extrapolation from the value at 10°C, using a model for the development of thermal conductivity for microporous materials, such as indicated on page 17 of the product brochure "High temperature microporous insulation" of Promat International NV, dated 052014. The relevant graph is that of the Microtherm 1000 Grade.

Shrinkage is defined by weight loss (Wt%), change in length of width (W+L%) and change in thickness (Thx%). The reported change is change after a heat treatment during 12 hours at 600°C. The total shrinkage may be calculated on the basis of a disc-volume on the basis of the changes in length and width (W+L%) and thickness (Thk%) as A(7tr² x t ) = A(7t/4d² x t ) = K/4 - [K/4*(1-(W+L))² X (1-Thk)]. Herein r refers to radius, t to thickness, d to the diameter. The W+L and Thx are specified in %.

Density is measured after initial drying of the samples.

Example 1

Microporous powder mixtures were prepared as specified in Table 1. Use was made of a hydrophobic pyrogenic silica with a surface area of 200 m²/g as commercially available from Evonik under the trade name Aerosil™. The mineral fiber is a silica based fiber comprising 81-94% SiO2 and 6-19% AI2O3 with the remainder being ZrO2 and/or TiO2 and maximum 3% of Na2O and maximum 1.5% of further components, as available from Belchem Fiber Materials, Germany. Its average diameter is 6 pm. The AES Bio soluble fiber is an Alkaline Earth Silicate fiber containing silica as a main component. It is also referred to as a wool, due to its small average diameter (2-3 pm) and consist of a mix of amorphous fibers, which are melted and then rapidly solidified using a combination of silica (SiO2) and calcium oxide (CaO) with or without magnesium oxide (MgO). When inhaled into the human body, it readily dissolves, and hence is referred to as a bio soluble fiber (BSF). Such fibers are for instance produced by Unifrax. Glass fibers were conventional E-glass fibers with a length of 15 mm.

Table 1 - composition of microporous powder mixtures. Values in weight per cent

Gelation mixtures were prepared in accordance with table 2. The mixtures were in powder form. The polyethylene oxide was a water-soluble nonionic polymer with an average molecular mass of 4.0.10⁶, available from Dow Chemicals under the tradename Polyox™ WSR-301. The polyacrylic acid was obtained from Celanese under the tradename ElotexTM Flex 8320. It is a spray-dried redispersible polymer powder based on acrylic monomers. The methylcellulose is a medium molecular weight (approximate weight 88,000 g/mol) methylcellulose thickener with methoxy substitution between 27.5 and 31.5% by weight as commercially available under the trade name Methocel. The fumed silica is a hydrophilic fumed silica with a surface area of 200 m²/g available from Evonik under the trade name Aerosil™ and known for use as a dispersant.

Table 2 - gelation powder mixtures. All values in weight% of the gelation powder mixture

Liquid mixtures were prepared in accordance with Table 3. The colloidal silica was a neutral, aqueous dispersion of colloidal silica with approximately 40% solids by weight. The silica dispersion is sterically stabilized and the amorphous silica particles carry a negative surface charge and have been surface modified with an epoxy silane. The silicone binder is a methoxy functional terminated silicone resin emulsion (43% by weight resin content in water) containing methyl phenyl groups commercially available from Wacker under the trade name SILRES™ MPF. Water was tap water.

Table 3 - liquid mixtures, all data as added amounts. The water was added into the mixtures separately

Test compositions were prepared on the basis of the microporous mixtures, the gelation mixture and the liquid mixtures as specified hereinabove in Tables 1-3. Thereto the gelation mixture was mixed with the liquid mixture, without the specified amounts of water. The water was added subsequently as a diluent. Thereafter, mixing took place, which resulting in gelation of ingredients to form a gel. The microporous mixture is thereafter added to the gel in the mixer. The entire mixture is then mixed and blended until a homogeneous mixture is obtained. Table 4 shows the compositions 1-6 based on dry weight, wherein the liquid mixture is based on either colloidal silica or water only. Table 5 shows comparative compositions based on dry weight. Gelation phase quality and paste quality were reviewed visually by the formulators.

Table 4, experiments according to the invention. Al data in weight% based on dry weight only. In experiment 3 amount adds up to 80% only.

Table 5, experiments according to the invention. All data in weight% based on dry weight o

Characterization tests were performed on the experiments of the invention, forming an appropriate paste. Each time small tiles of 20 x 20 cm were made by casting in a mold, following by drying in an oven at temperature below 100°C for 2-3 hours. After this drying, measurement of density, thermal conductivity was performed. Shrinkage was measured by mass and dimensional determination before and after a 12-hour heat treatment at 600°C. Results are presented in Table 7

Table 6 - characterization data for the experiments 1-6 Table 6 - characterization data for the experiments 7-9

Review of experiments

In experiment 1, the gelation mixture G1 was used, comprising both a polyethylene oxide and a polyacrylic acid. Upon addition of water, a gel was formed. In experiment 3, the colloidal silica was left out, and just water was added. The result thereof was a good polymer-based hydrogel, into which the microporous powder mixture could be inserted. Comparison with experiment 4 demonstrates that the colloidal silica does not lead to any change in the thermal conductivity. However, the density increases and the weight loss upon heating decreases. Addition of colloidal silica therefore turns out beneficial for the temperature stability of the microporous paste. The shrinkage observed when heating to higher temperatures is considered an indication for the behaviour at lower temperatures, such as cryogenic temperatures. Particularly, less shrinkage will occur when going down in temperature. Furthermore, when operating at low and/or cryogenic temperatures, it may happen that the temperature rises suddenly. Then it is important that the material remains safe and performs to optimum.

Experiments 7-9 demonstrate that the addition of waterglass is feasible as well.

Claims

1. Method of manufacturing an insulated storage container for storage of pressurized and/or liquified fluids, comprising the steps of:

Providing a storage container having a first and a second end surface and at least one container surface extending between the first and the second end surface;

Applying insulation to at least one surface of said at least one container surface and the first and the second end surface, wherein the insulation is applied as a composite insulation composition comprising a microporous powder mixed into a gelled carrier material,

2. Method as claimed in claim 1, wherein the gelled carrier material is selected from the group of polymer-based hydrogels and silica gels or combinations thereof.

3. Method as claimed in any of the claims 1-2, wherein said composite insulation composition is applied as one or more molded bodies.

4. Method as claimed in claim 3, wherein said one or more molded bodies comprise a first body and a second body each comprising a fixation element for mutual assembly.

5. Method as claimed in any of the claims 1-4, wherein said composite insulation composition is applied as a paste present on a foil.

6. Method as claimed in any of the claims 1-5, wherein the composite insulation composition is in the form of an aqueous paste and is dried after application to said at least one surface of the storage container.

7. Method as claimed in any of the claims 1-6, wherein the storage container comprises at least at least one surface a resin layer that is filled with particulate microporous powder, for instance in the form of granules.

8. Method as claimed in any of the claims 1-7, further comprising the step of applying a blanket or panel of insulation material onto and preferably around said - composite microporous - insulation.

9. Method as claimed in claim 8, wherein said composite material is applied to the first end surface and/or to the second end surface, and wherein said blanket or panel of insulation material covers the container surface and extends on said composite material applied to the first and/or second end surfaces.

10. Method as claimed in any of the claims 1-9, wherein the composite microporous insulation composition is applied in a thickness of at least 5 mm, preferably at least 1 cm.

11. Method as claimed in any of the claims 1-10, wherein the storage container comprises polymer material.

12. Method as claimed in claim 11, wherein the storage container comprises a multilayer structure of polymer material, of which a first layer is a fiber reinforced polymer layer, especially reinforced with carbon fibers.

13. Insulated storage container comprising:

A multilayer structure shaped as a storage container having a first and a second end surface and at least one container surface extending between the first and the second end surface; composite microporous insulation arranged and adhered to at least one surface of said at least one container surface and the first and the second end surface, said composite microporous insulation comprising a microporous powder mixed into a gelled carrier material, wherein the microporous powder comprises at least an opacifier, inorganic fiber and particulate silica material from the group of pyrogenic silica and precipitated silica, said particulate silica material optionally further comprising alumina, wherein said microporous powder and/or at least part of said particulate silica material is hydrophobic.

14. Insulated storage container as claimed in claim 13, obtained by the method as claimed in any of the claims 1-12.

15. Use of the insulated storage container as claimed in claim 13 or 14 or as obtained in accordance with any of the claims 1-12 for storage of a fluid under cryogenic conditions and/or high-pressure conditions.