High-Performance Lining Structure with Controlled Lateral Clearances

Abstract

Container having a lining structure, comprising a crystalline phase containing 55 to 97 wt % of xonotlite crystallites and 3 to 45 wt % of tobermorite crystallites and comprising less than 15 wt % of intermediates of formula CaxSiyOz.wH2O where 1

Description

The present invention relates to containers having novel filler structures and to their method of fabrication, characterized in that the cooling step after the hydrothermal synthesis is carried out by spraying water at a temperature of 15 to 25° C. on at least part of the periphery of the container, in order to arrange a discontinuous or continuous side clearance between the inner surface of the metal shell of the container and the outer surface of the filler mass.

It is known how to use pressurized containers containing gases, such as acetylene, dissolved in a solvent, such as acetone, in various medical and crafts applications, and in particular to perform welding, brazing and heating operations in combination with an oxygen cylinder.

These containers are commonly filled with solid filler materials, designed to stabilize the gases they contain, which are thermodynamically unstable under the effect of pressure and temperature variations and therefore liable to decompose during their storage, transport and/or distribution.

These materials must have sufficient porosity to facilitate the adsorption and release of the gases present in the container. They must also be incombustible, inert to these gases, and have good mechanical strength. These materials conventionally consist of porous silica lime ceramic masses, obtained for example from a homogenous mixture in water of quicklime and milk of lime and silica (particularly in the form of silica flour), as described in documents WO-A-93/16011, WO-A-98/29682, EP-A-262031, to form a paste which is then subjected to hydrothermal synthesis. More precisely, the paste is introduced under partial vacuum into the container to be filled, which is then subjected to autoclaving at pressure and temperature, followed by firing in a furnace to completely remove the water and to form a solid monolithic mass having the composition Ca_xSi_yO_z.wH₂O, having crystalline structures of the tobermorite and xonotlite type, with an optional residual presence of quartz. Various additives can be added to these prior art mixtures to improve the dispersion of the lime and silica and thereby prevent the formation of structural inhomogeneities and of shrinkage observed during the hardening of the porous mass. The filler materials obtained must in fact have a uniform porosity, without voids in which gas pockets could accumulate, incurring the risk of explosion.

Document EP-A-264550 further indicates that a porous mass containing at least 50%, or even at least 65%, or even at least 75% by weight of crystalline phase (compared to the weight of calcium silicate) serves to meet the dual requirement of compressive strength and shrinkage resistance at the hydrothermal synthesis and firing temperatures.

While the known porous masses are generally satisfactory in terms of mechanical strength, the properties of withdrawal of the gases trapped in these porous masses are insufficient and/or completely haphazard today. This haphazard aspect is associated with the lack of control/understanding of the process and in particular of the hydrothermal synthesis step by control of the operating parameters.

In fact, depending on the operating conditions (service temperature, working flow rate, quantity of gas present in the cylinder, etc.), they do not always allow continuous withdrawal of the gas they contain at a high flow rate, throughout the time required for certain applications, particularly welding, with a maximum gas restitution rate, corresponding to the ratio of the quantity of usable gas to the quantity of gas initially stored. In fact, it would be advantageous to be able to provide a flow rate of 200 l/h continuously for 15 minutes and a peak rate of 400 l/h for four minutes, for a gas content equal to or greater than 50% at the start of the test (defined as the ratio of the quantity of gas present at this time to the quantity of gas initially charged in the container), the container having a diameter/length ratio between 0.2 and 0.7, preferably between 0.35 and 0.5, for a minimum water capacity of one liter and preferably between 3 and 10 liters.

This insufficiency is due in particular to the heat loss associated with the extraction of the gas from the solvent, which may prove to be highly detrimental to the withdrawal of the gas. This heat loss is not chiefly associated with the intrinsic conductivity of the silica lime material (for information, the void fraction is 87-92%) but with the size of the needles (dimensions) constituting the porous mass. In fact, the smaller the needles, the higher the number of contact points between them. This harms the conductive heat transfer, giving rise to a more or less long “cylinder unavailability” time. This effect must be correlated with the pore distribution. In the case of an acetylene cylinder, for example, the energy consumption is about 600 joules per gram of acetylene extracted from the solvent. In practice, this results in substantial cooling of the cylinder during the withdrawal, causing greater solubilization of the acetylene in the solvent and thereby a drop in pressure, which affects the withdrawal rate. The flow rate ultimately declines when the cylinder outlet pressure falls before the atmospheric pressure.

In an acetylene cylinder and during its discharge, wide heterogeneities are therefore observed locally in (a) temperature, (b) pressure and (c) charging ratio, which is defined as the quantity of acetylene dissolved per gram of solvent. These heterogeneities are the major drawback of present-day acetylene cylinders, and are detrimental to their optimal use.

In practice, and from the general standpoint, the harmful mechanisms observed on a prior art cylinder are the following:

• • The cylinder cools more during a long withdrawal. The relative temperature differences can reach −40° C. from the initial temperature of the cylinder, which is ambient temperature. This incurs the risk of appearance of liquid acetylene.
  • The flow rate declines faster with a lower ambient service temperature, the pressure of the solvent/acetylene solution itself being lower. The capacity of the cylinder to deliver over a long period can therefore be particularly limited in winter or in cold climates.
  • The flow rate declines faster if the regulated working rate is high compared to the volume of the cylinder.
  • The pressure and temperature properties deteriorate primarily near the shoulder, that is at the location of the cylinder where the migration of acetylene from the solvent is the highest.
  • A pressure difference of up to 4 bar is observed between the top and bottom of the cylinder during withdrawal. These pressure differences occur over large sections generating mechanical stresses that could cause damage to the filler material over time.
  • The bottom cools more slowly (with a lag of up to 3-4 h).

These mechanisms are illustrated in FIGS. 1 and 2, for a cylinder “A” having a water volume of 5.8 liters, suitable for containing 800 liters of acetylene but charged to only 38% and used at 20° C., filled with a coherent silica lime filler of which the D50 is 0.36 μm and the D95 is 0.42 μm, and for which the flow rate is regulated at 400 liters/h. The flow curve in FIG. 1 shows that the flow rate declines after 6.5 minutes of use, or after only 15% of the gas initially present has been withdrawn. The pressure Ph is the pressure at the regulator inlet and the pressure Pb is the pressure after expansion, for example before the torch. The variation in Ph, the pressure measured at the cylinder outlet before the regulator (FIG. 3), indicates that it drives the acetylene withdrawal: to within the pressure drops in the circuit, when Ph equals Pb, the acetylene flow rate drops. The temperature monitoring on the cylinder wall indicates that the temperature first drops at the top of the cylinder before the bottom. Moreover, it is confirmed that the drop in pressure accompanies the drop in temperature of the cylinder during the test.

Furthermore, the temperature and pressure variations are not uniform in the container, which could lead to the appearance of mechanical stresses liable to damage the porous mass over time.

Hence added to the withdrawal difficulties are problems of mechanical strength, liable to have safety repercussions.

Accordingly, a problem that arises is to provide a container having a filler structure with satisfactory withdrawal properties and mechanical properties, serving to meet the concern for safety, and a method for fabricating such a container.

One solution of the invention is a filler structure comprising a crystalline phase having 55 to 97% by weight of xonotlite crystallites and 3 to 45% by weight of tobermorite crystallites, characterized in that it comprises less than 15% by weight of intermediates having the formula Ca_xSi_yO_z.wH₂O where 1<x<16, 1<y<24, 4<z<60 and 1<w<18 including less than 5% by weight of CaCO₃ and less than 5% by weight of SiO₂, and in that said filler structure is homogenous.

In the context of the present invention “homogeneous” means that various samples taken locally at various points of the filler structure (for example at the top center, the bottom center, the core of the mass, at the center along the metal wall, etc.) yield uniform analytical results (X-ray diffraction, porosity, pore size distribution), that is that each quantitative datum measured does not differ by more than 10% from one zone to another.

This “uniform” character is important because it conditions the homogeneity of the solvent-acetylene solution in the case of an acetylene cylinder, and in consequence the uniformity of the local charging rates throughout the volume of the container comprising the filler structure. If the microstructure is not homogenous in the mass, pressure excesses are locally created in zones where the charging rate is higher than the nominal charging rate of the cylinder. For example, simulations have shown that at 35° C., the pressure of a cylinder could shift from 22.3 bar to 24 bar assuming a charging rate that is 30% higher than the nominal charging rate for ⅓ of the volume of the mass.

Xonotlite is a calcium silicate having the formula Ca₆Si₆O₁₇(OH)₂, which has repetitive units consisting of three tetrahedra. Tobermorite is also a calcium silicate, having the formula Ca₅Si₆(0,OH)₁₈.5H₂O, crystallized in orthorhombic form.

The most generally accepted mechanism of formation of xonotlite from the precursors CaO and SiO₂ in the CaO/SiO₂ molar ratio of about 1 with water used as solvent is the following:

CaO/SiO₂/H₂O→Ca(OH)₂/SiO₂/H₂O→Gel C—S—H→tobermorite→xonotlite

The total intermediate phases preferably account for 0 to 10% and more preferably 0 to 5% by weight of the crystalline phase present in the filler structure.

Calcium carbonate and silica each preferably accounts for less than 3% of the total weight of these crystalline phases.

Depending on each case, the filler structure may have one of the following features:

• the crystallites are in the form of interlocking needles,
• it contains at least 70% by weight of crystalline phase,
• the crystallites are bonded to one another so as to arrange between them a pore diameter D95 (diameter at which 95% by volume of the pores have a lower diameter) equal to or higher than 0.4 μm and lower than 5 μm, and a mean pore diameter D50 (diameter at which 50% by volume of the pores have a lower diameter) that is equal to or higher than 0.4 μm and lower than 1.5 μm. The filler structure accordingly advantageously has a total open porosity of 80% to 90%. These values can all be measured by mercury porosimetry;
• said filler structure has a compressive strength higher than 15 kg/cm², or 1.5 MPa. Its strength is preferably higher than 20 kg/cm², or 2 MPa;
• said filler structure has a porosity coefficient k that may be between 0.1×10⁻¹⁴ m² and 0.7×10⁻¹⁴ m², preferably between 0.2×10⁻¹⁴ m² and 0.5×10⁻¹⁴ m².

The mechanical and compressive strength can be measured by taking a sample of a 100×100 mm² cube from the filler structure and applying a pressure force to its surface, while it is pressed against a horizontal metal plate. This force corresponds to the pressure (in kg/cm² or MPa) above which the material begins to crack.

The use of a filler structure according to the invention serves to reach the desired withdrawal rate while meeting the requirements for safety and mechanical strength.

In addition to the crystalline phase described above, the filler structure according to the invention may comprise fibers selected from carbon based synthetic fibers, as described in particular in document U.S. Pat. No. 3,454,362, alkali resistant glass fibers, like those described in particular in document U.S. Pat. No. 4,349,643, partially delignified cellulose fibers, like those described in particular in document EP-A-262031, and mixtures thereof, but this list is nonlimiting. These fibers are useful in particular as reinforcing materials, to improve the impact strength of the filler structure, and also serve to avoid problems of cracking upon drying of the structure. These fibers can be used as such or after surface treatment.

The filler structure may also include dispersants and/or binders, such as cellulose derivatives, particularly carboxymethylcellulose, hydroxypropylcellulose or ethylhydroxyethylcellulose, polyethers, such as polyethylene glycol, synthetic clays such as smectite, amorphous silica advantageously having a specific surface area of 150 to 300 m²/g, and mixtures thereof, but this list is nonlimiting.

Preferably, the filler structure contains fibers, in particular carbon and/or glass and/or cellulose fibers. The quantity of fibers is advantageously lower than 55% by weight, compared to the total solid precursors employed in the fabrication of the filler structure. It is preferably between 3 and 20% by weight.

The invention also relates to a container having a filler structure as described above, said container being suitable for containing and distributing a fluid.

The container is characterized in that it has a discontinuous or continuous side clearance between the inner surface of its metal shell and the outer surface of the filler structure. The continuous or discontinuous side clearance has a width between 0.001 mm and 0.1 mm, preferably between 0.001 and 0.05 mm.

The container commonly has a metal shell enclosing the filler structure described above. The metal shell may consist of a metallic material such as steel, for example a normalized carbon steel P265NB according to standard NF EN10120, whereof the thickness makes it suitable for withstanding at least the hydrothermal synthesis pressure without any risk of accident and capable of withstanding a test pressure of 60 bar (6 MPa), a regulatory standard value for packing acetylene in the abovementioned conditions. The container is also normally cylindrical and generally provided with closure means and a pressure regulator. This container preferably has a diameter/length ratio between 0.2 and 0.7, more preferably between 0.35 and 0.5, and a minimum water capacity of one liter. Such a container normally has a bottle shape.

The fluids stored in the filler structure according to the invention may be gases or liquids.

As a gas, mention can be made of compressed gases, pure or in mixtures, in gaseous or liquid form, such as hydrogen, gaseous hydrocarbons (alkanes, alkynes, alkenes), nitrogen and acetylene, and gases dissolved in a solvent such as acetylene and acetylene-ethylene or acetylene-ethylene-propylene mixtures, dissolved in a solvent such as acetone or dimethylformamide (DMF).

As liquids, mention can be made of metalorganic precursors such as Ga and In precursors, used in particular in electronics, and also nitroglycerin.

In particular, the container according to the invention contains acetylene dissolved in DMF or in acetone.

In this context, and to obtain the method described above, the present invention relates to a method for fabricating a container, characterized in that it comprises the following steps:

• a) a step of hydrothermal synthesis of the filler mass carried out with a mixture of quicklime and silica,
• b) a step of introducing the filler mass issuing from step a) into a container having a metal shell,
• c) a step of cooling the filler mass issuing from step b) by spraying a liquid (for example water) or a gas (for example compressed air), taken at a temperature between 15 and 25° C., on at least part of the periphery of the container, during a period between 30 seconds and 10 minutes, in order to arrange a discontinuous or continuous side clearance between the inner surface of the metal shell and the outer surface of the filler mass,
• d) a step of drying the filler mass issuing from step c).

Depending on each case, the fabrication method may have one of the following features:

• in step c), the water is sprayed on the whole periphery of the container in order to arrange a continuous side clearance between the whole inner surface of the metal shell and the whole outer surface of the filler mass,
• before step b) of introducing the filler mass, a degradable lining product is applied during the drying step on the whole inner surface of the metal shell of the container in order to facilitate the arrangement of the side clearance,
• step a) of hydrothermal synthesis comprises:
• (i) a sub-step of temperature rise, over a period shorter than 10 h, of an initial mixture of quicklime and silica at a temperature T1 between 150 and 300° C.,
• (ii) a sub-step of fabrication of the filler mass carried out:
  • using the mixture of quicklime and silica issuing from step (i),
  • at a temperature T1 between 150 and 300° C.,
  • at a pressure P1 between 5×10⁵ Pa and 25×10⁵ Pa, and
  • during a period between 10 h and 70 h;
• the quicklime is obtained by calcination, at a temperature of at least 850° C. for at least one hour, of limestone fragments such that at least 90% by weight have a size of 1 to 15 mm, said limestone having a purity of at least 92% by weight and an open porosity of 0 to 25%,
• the drying step is carried out at a temperature of 300 to 450° C.

In the context of the present invention, “purity” means the percentage by weight of calcium carbonate in the limestone.

A person skilled in the art will know how to identify the quarries or seams mined to obtain the abovementioned limestone fragments.

The type of filler structure according to the invention is primarily the consequence of the preparation of a quicklime having a satisfactory reactivity and capable, after hydrothermal synthesis, of forming the desired acicular material. The second step of the method consists in mixing the quicklime with silica, which may be amorphous or crystalline, in a CaO:SiO₂ molar ratio of 0.8 to 1. Furthermore, the water/solid precursor (lime+silica) ratio is preferably between 2 and 60, more preferably between 3 and 25.

The mixture is then introduced into the containers to be filled and subjected to hydrothermal synthesis. To be complete, the hydrothermal synthesis must be carried out:

• at a hydrothermal synthesis temperature T1 that may be between 150 and 300° C., preferably between 180 and 250° C.,
• at a pressure between 5×10⁵ Pa and 25×10⁵ Pa (5 and 25 bar), preferably between 7×10⁵ Pa and 15×10⁵ Pa (7 and 15 bar). According to a first embodiment, the synthesis can be carried out by introducing the mixture into the open container that it is intended to fill, and then placing said container in an autoclave subject to the pressure described above. According to a second embodiment, the hydrothermal synthesis can be carried out by placing the mixture in the container that it is intended to fill, closing said container with a plug equipped with a pressure regulation system (such as a valve), pressurizing the container to a pressure between atmospheric pressure and the pressure as previously described, and then placing the container in an unpressurized furnace,
• during a period, depending on the volume of the container to be filled, of 10 h to 70 h, for example close to 40 hours for a container having a water volume of 6 liters.
• The temperature rise to T₁ must take place over a period shorter than 10 h, preferably shorter than 2 h. When a plurality of containers filled with filler material are charged in the same furnace, this parameter actually defines the positioning of the cylinders with regard to one another, because the air flow between the cylinders depends strongly on the number and position of the charged cylinders in accordance with the heated air flow inside the synthesis furnace. It is necessary to limit these variations over the temperature rise time, because this parameter also has a direct impact on the crystallization rate of the needles of the Ca_xSi_yO_z.wH₂O type compounds formed.

An intermediate step at this stage of the method may consist in suddenly cooling the cylinders by a quench.

This intermediate step is followed by a step of “redescent” of the filler structure to ambient temperature.

Finally, the drying step has the function not only of removing the residual water, but also giving the treated mass a mainly crystalline structure. This operation is performed in a conventional electric furnace (possibly the same as the one used for the hydrothermal synthesis), at atmospheric pressure, that is after the plugs and valves have been removed from the top of the containers after hydrothermal synthesis in the second hydrothermal synthesis example described above.

The extraction of the gas from the solvent in which it is dissolved in the ceramic structure that fills the container is governed by three determining factors which depend directly on the following characteristics of the cylinder:

• • (a) the intrinsic permeability of the ceramic filler, which defines a resistance to the flow of gas molecules desorbed from the solvent to reach the neck of the cylinder where the gas is released. This first parameter is controlled by the microstructure of the filler (type of porosity and size of the filler particles);
  • (b) the total permeability of the gas container;
  • (c) the chemical formulation of the main material constituting the filler and in particular its thermal conductivity when charged with solvent, which defines its capacity to convey the quantity of negative calories generated at the time when the gas is extracted from the solvent.

In fact, the total permeability of the gas container depends partly on the intrinsic permeability of the ceramic filler, and partly on the existence of side clearances between the inner surface of the metal shell of the container and the outer surface of the porous ceramic mass.

Accordingly, an essential step of the method for preparing a container according to the invention is to effect a thermal shock on the container, such as a shower or a quench between the hydrothermal synthesis step and the drying step. This may also involve a step of lining the inside walls of the cylinder with a degradable lining during the drying operation that would create this shrinkage.

It may also involve a step which consists in performing a mechanical treatment on the cylinder (impact or vibration imposed on the container by striking the bottom part thereof on the ground, this operation being feasible “by hand” and individually per cylinder, or even collectively on a group of containers using mechanized handling means) to detach the porous material from the metal wall.

This step serves to create side clearances (delaminations) between the inside walls of the container and the outer surfaces of the ceramic filler mass, thereby offsetting a possible lack of intrinsic permeability of the mass to favor the gas restitution performance. In other words, the proposed solution serves to counterbalance the fact that a filler mass has a restricted pore size, conventionally hindering the gas filling/extraction process.

The invention resides in the fact that the intermediate step of cooling by shower or quench (or lining, or thermal or mechanical shock) to be performed between the hydrothermal synthesis step and the drying step allows a change of the filtration mode, by changing from an axial filtration mode (without shower) to a radial filtration mode (according to the invention). This principle is illustrated in FIG. 4 which shows the pressure gradients modeled for two extreme cylinders, the first according to the prior art (without intermediate step) and the second according to the invention (with intermediate step) to represent the two corresponding filtration modes, axial and radial, in both cases for a cylinder having a volume of 3.35 liters, whereof the porous mass has an intrinsic permeability coefficient k of 0.8×10⁻¹⁴ m². These differences were experimentally confirmed by nitrogen permeability tests, which consist in measuring the semi-drainage time t₅₀ of nitrogen previously introduced into these cylinders. In the first case, in which no side clearance existed (h=0 mm), this characteristic time was 130 seconds, whereas it was only 3.7 seconds in the second case (continuous side clearance of 0.1 mm).

For a non-extreme case not shown, in which a continuous side clearance over the whole periphery of the container of 0.025 mm is obtained, and for which the coefficient k of the filler mass is 0.8×10^{−14 m2}, the value of t₅₀ is 73 seconds. This case accordingly corresponds to a gas restitution rate, for a cylinder having a volume of 5.8 liters and for a normal value of the charging rate, about 60%, as shown in FIG. 5. For another case, in which a side clearance of 0.025 mm on the walls only is obtained and for a value of k of 0.8×10⁻¹⁴ m², the value of t₅₀ is 102 seconds. In this case, the gas restitution rate is only about 45%, as shown in FIG. 5. These results and more generally the representation in FIG. 5 serve to demonstrate that the gas restitution rate of a container filled according to the invention depends on the total permeability of the gas container, which depends on the intrinsic permeability of the ceramic filler, but also on the existence of side clearances between the inner surface of the metal shell and the outer surface of the porous ceramic mass. For example, FIG. 5 shows that the same gas restitution rate can be obtained with several containers having different semi-drainage times t₅₀ and porosity coefficients k. Thus, various gas restitution rates can be obtained with various containers having various k and side clearances, although their total permeabilities are identical (same t₅₀).

The invention proposed there therefore serves to obtain:

a longer self-contained operation or a higher restitution rate (defined by the quantity of usable gas compared to the quantity of gas initially stored at the beginning of withdrawal) with a given cylinder volume;

in addition to easier use of the cylinder in withdrawal, faster filling at the packaging center, thanks to an easier passage of the acetone and filling gas into the filler; and

a guarantee of safe performance (standard ignition test).

Claims

1-9. (canceled)

10. A container having a filler structure comprising a crystalline phase having 55 to 97% by weight of xonotlite crystallites, 3 to 45% by weight of tobermorite crystallites, less than 15% by weight of intermediates having the formula CaxSiyOz.wH2O where 1<x<16, 1<y<24, 4<z<60 and 1<w<18, including less than 5% by weight of CaCO3, and less than 5% by weight of SiO2, said filler structure being homogenous and said container having a continuous or discontinuous side clearance between the inner surface of its metal shell and the outer surface of the lining structure.

11. The container as claimed in claim 10, characterized in that the continuous or discontinuous side clearance has a width between 0.001 mm and 0.1 mm, preferably between 0.001 and 0.05 mm.

12. A method for fabricating a container having a filler structure comprising a crystalline phase having 55 to 97% by weight of xonotlite crystallites, 3 to 45% by weight of tobermorite crystallites, less than 15% by weight of intermediates having the formula CaxSiyOz.wH2O where 1<x<16, 1<y<24, 4<z<60 and 1<w<18, including less than 5% by weight of CaCO3, and less than 5% by weight of SiO2, said filler structure being homogenous and said container having a continuous or discontinuous side clearance between the inner surface of its metal shell and the outer surface of the lining structure comprising the following steps: a) a step of hydrothermal synthesis of a filler mass carried out with a mixture of quicklime and silica,b) a step of introducing the filler mass of step a) into a container having a metal shell,c) a step of cooling the filler mass in the container of step b) by spraying a liquid or a gas, having a temperature between 15 and 25° C., on at least part of the periphery of the container for a period of between 30 seconds and 10 minutes, thereby forming a discontinuous or continuous side clearance between the inner surface of the metal shell and the outer surface of the filler mass,d) a step of drying the filler mass in the container after step c).

13. The method as claimed in claim 12, characterized in that in step c), the water is sprayed on the whole periphery of the container in order to arrange a continuous side clearance between the whole inner surface of the metal shell and the whole outer surface of the filler mass.

14. The method of claim 12, characterized in that before step b) of introducing the filler mass, a degradable lining product is applied during the drying step on the whole inner surface of the metal shell of the container wherein the presence of the degradable lining product contributes to the arrangement of the side clearance.

15. The method of claim 12, characterized in that step a) of hydrothermal synthesis comprises: (i) a sub-step of a temperature rise, over a period shorter than 10 h, of an initial mixture of quicklime and silica to a temperature T1 between 150 and 300° C.,(ii) a sub-step of fabrication of the filler mass carried out: using the mixture of quicklime and silica from sub-step (a)(i),at a temperature T1 between 150 and 300° C.,at a pressure P1 between 5×105 Pa and 25×105 Pa, andfor a period between 10 h and 70 h.

16. The method of claim 12, characterized in that the quicklime is obtained by calcination, at a temperature of at least 850° C. for at least one hour, of limestone fragments wherein at least 90% by weight of the limestone fragments are have a size of 1 to 15 mm, a purity of at least 92% by weight, and an open porosity of 0 to 25%.

17. The method of claim 12, characterized in that the drying step d) is carried out at a temperature of 300 to 450° C.

18. The container of claim 10, further comprising an acetylene stored therein.

19. The method of claim 12, further comprising a step e) of filling the container with an acetylene.