MXPA98004316A - Use of airbrushes as rell materials - Google Patents

Abstract

Use of silica aerogels having an amorphous structure, density comprised between 0.6 g / cm and 0.003 g / cm as filler materials for transport and / or storage of fluids, especially acetylene. Aerogels have the property of transforming a fluid into a solid that includes it and subdividing it into small portions. This property is a very important feature when it comes to highly dangerous fluids. The severe conditions required for the transport or storage of fluids are reduced when the transport or storage of said fluids is carried out in a silica airgel.

Description

USING AEROGELS AS FILLING MATERIALS DESCRIPTION OF THE INVENTION The present invention relates to the use of aerogels as filling materials. The aerogels referred to in the present invention have application as fillers for the transport and / or storage of fluids, in particular for the transport of acetylene. Aerogels are the lightest solid materials known. Its lightness lies in its high porosity so that they behave like open cell foams with a large surface area. The pores have a wide distribution of sizes although their typical diameter is usually 15-20 nm, occupying about 95% of the total volume. Its density goes from 0.6 g / cm3 (only three times denser than air). Its structure is derived from the gel that formed it and is, therefore, amorphous. The most widely used procedure for obtaining silica aerogels comprises the synthesis of silicon gels and subsequent supercritical drying. A typical reaction for obtaining silicon gels, starting from tetramethoxysilane (TMOS), is the one outlined below: catalyst nSi OCH, + 4nH, 0 = • nSi (OH), + 4nCH, 0H (hydrolysis) nSi ( OCH,) < - s nSiO, * 2nH, 0 < condensation) tiS WCH.h + 2nH, 0 > nSiO, + 4nCH, 0H (net reaction) where the starting silicon alkoxide, the solvent, methanol or acetone, and the catalyst, potassium hydroxide or ammonia with acetic acid, are variables with which it can be played to obtain an airgel made to measure according to the desired properties. Then, in order to obtain the airgel, the extraction in supercritical conditions of the solvent occupying the pores of the gel is necessary. However, the current application of aerogels has been, in particular, as a thermal insulator, for example, silica airgel which is a colloidal silica powder is used as a low temperature insulator. Other applications of aerogels are, for example, in satellites where they facilitate the capture of meteorites, or as high quality gas filters or autofocus cameras for televisions. The present invention relates to the use of aerogels as filling materials for the transport and / or storage of fluids. More especially, the present invention relates to the use of silica aerogels as fillers for transport and storage of fluids, especially for acetylene. It is important to highlight the current problems of the transport of some fluids, which due to their dangerous nature, for example, are flammable or toxic they require very special conditions for their transport or storage. The present invention relates to the use of aerogels for the transport or storage of said fluids, especially for acetylene. Acetylene is a flammable gas in the presence of air or high temperature. It is used in a variety of industrial applications such as chemical synthesis, autogenous welding, metal cutting, thermal treatment of materials and even lighting in buoys. Being a flammable gas it must be transported in steel cylinders subject to very strict regulations. These regulations require, among others, that the steel used in the cylinder meet certain physical-chemical requirements and that the cylinder's filling has a maximum of 92% porosity when it is filled with a certain amount of solvent, in addition it must carry the Adequate safety escape. The filling material of the cylinders must be porous in order to avoid the characteristic of fine decomposition and thus eliminate the possibility of the formation of even small bags of gaseous acetylene. Normally, the porous filling mass of the acetylene cylinders is saturated with acetone or another solvent in which the Acetylene dissolves. Still and dissolved in acetone, acetylene reacts chemically giving rise to polymer chains. This reaction is also very exothermic although, fortunately, it is also slow. To prevent this polymerization, the cylinders must contain a porous material that occupies practically all of the interior volume, this material is soaked in a suitable solvent, usually acetone, where the acetylene is dissolved under pressure. To prevent the exothermic polymerization of the gas and the subsequent explosion of the same, the filling material of the cylinders must be porous with cellular spaces of very small dimensions so that no bags are produced. The appearance of bags where acetylene can accumulate initiates the polymerization reaction increasing the temperature of its immediate environment. This increases the speed of reaction, with which the phenomenon extends to other areas of the cylinder. This heats up becoming red. Then it is usually submerged in water or carried to where it can explode safely. This process, once triggered, takes about 24 hours. It is for this reason that the operators who handle these bottles touch them periodically to observe if any of them get hot. In the past, the cylinders were filled with a fine sand of calcium silicate reinforced with asbestos fibers to prevent their compaction, otherwise it would be a large bag in the upper part of the cylinder with the consequent danger already mentioned. Due to the fact that the use of asbestos fibers did not solve the problem of the bags and that their use is also restricted due to their carcinogenic effects, the filling material of the cylinders has been evolving in recent years. Due to the conditions that the acetylene cylinder fillers must fulfill such as porosity, absence of voids, little or no space between the internal wall of the cylinder and the external one of the filler, adequate strength and stability as well as other considerations in its manufacture and in safety requirements, attempts to find new fillers have not given the desired success. Thus, for example, the use of fiberglass gives rise to cracks and, over time, the filler shrinks slightly. On the other hand, a filler based on cotton fiber has given rise to elongated holes. Polyester and rayon fibers have a tendency to settle during preparation, making it difficult to fill the cylinder. The use of supplementary ingredients tends to decrease the strength and porosity of the filler and adversely affects the acetylene discharge. The limitations of filling materials used to date both in the transport of acetylene and in that of other similar gases are evident taking into account the properties that are required of said filling materials, which are summarized below: - elevated porosity; -Great mechanical resistance; -that do not suffer degradation or aging over time; -that occupy all the interior volume of the cylinder without leaving empty spaces. It is therefore evident that there is still a need to find new fillers that meet the required conditions, that do not contain asbestos fibers, that maintain a high porosity, and that are at the same time inert, stable and light. The invention provides a solution to the drawbacks cited in the prior art by the use of silica aerogels as fillers that have application in the transport and / or storage of fluids, especially acetylene. Aerogels have the property of transforming a fluid into a solid that includes it and subdividing it into small portions. This property is a very important feature when it comes to highly dangerous fluids. The severe conditions required for transportation or Storage of said fluids are reduced when the transport or storage of said fluids is carried out in a silica airgel. On the other hand, the necessary safety conditions for the transport of said fluids in conventional filling materials must be taken into account since an accident during said transport would entail the loss of almost all of the fluid. Advantageously, the use of silica aerogels as fillers has the advantage that in case of an accident the loss of the fluid would be minimal since the fluid in question is dissolved in the airgel forming a solid. The silica aerogels fulfill the characteristics mentioned above that the filling materials must comply with. Reference is now made to the physical characteristics of the silica gels and aerogels used as filling materials of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows the diffractogram of an air-dried gel. Figures 2, 3 and 4 are the diffractograms of different aerogels. Figures 5, 6, 7 and 8 show the distribution of the pore size for different aerogels. Visual inspection Aerogels are monolithic and not monolithic with few cracks or defects. Structural Characterization: X-Rays X-ray results confirm a completely amorphous structure of the material, with only one very broad peak around 2? = 23 ° (see figures 1-4). There is no difference between the X-ray results for the air-dried gel (Fig. 1) and the supercritical dried monolithic aerogels (Fig. 2 and 3), nor between the monolithic aerogels and the pulverulent type (Fig. 4) . Characterization of the porous structure According to the IUPAC nomenclature the pores have a size with D = pore diameter of: micropores of D <; 2 nm, mesoporos of 2 nm < D < 50 nm and macropores D > 50 nm. Silica aerogels contain pores of the three types, with most pores being the size of the mesopores and the minority of the pores. Density The density was calculated by weighing the monolithic pieces of the different aerogels with a precision balance and calculating their volume. All the samples made are collected in the following table. The densities and porosities (P = (l- Paeroei / Psio2) porosity by weight, for a density of silica of 2.19 g / cm3) are referred to the resulting airgel. In acetone gels, V refers to the ratio between the volumes of the TMOS and the dissolution of TMOS and acetone. Table 1 BET The BET method (gas absorption), is used to measure the surface area of a material, the total volume occupied by the pores and the distribution of their sizes. The results of BET of some aerogels are shown in Table 2 (see Figures 5, 6, 7 and 8). Table 2 Properties of the porous structure of some aerogels.

Considerations of the results obtained from these measures. The surface areas of all aerogels are quite similar, between approximately 400 and approximately 600 m2 / g. The total pore volume is double for the gels obtained with methanol compared with those obtained with acetone. The average diameter of the pores is lower for aerogels obtained with acetone compared to those obtained with methanol.

Claims (6)

1. CLAIMS 1. Use of silica aerogels with an amorphous structure, density between 0.6 g / cm3 and 0.003 g / cm3 as filling materials for transport and / or storage of fluids.
2. 2. Use according to claim 1, characterized in that the micropores have a diameter size of less than about 2 nm.
3. 3. Use according to claim 1, characterized in that the micropores have a diameter size of less than about 2 nm.
4. 4. Use according to claim 1, characterized in that the mesopores have a diameter size between approximately 2 nm and approximately 50 nm.
5. 5. Use according to claim 1, characterized in that the macropores have a diameter size greater than about 50 nm.
6. 6. Use according to claim 1, characterized in that the surface area is greater than about 400 m2 / g.