United States Patent This invention relates to porous masses for use in vessels for the storage and handling of acetylene in solution.
When acetylene is stored or transported it is necessary to use a cylinder or other pressure vessel containing an inert porous mass and a solvent for acetylene which is usually acetone. The cylinder is charged with acetylene up to a maximum pressure which is governed by otficial regulations in each country; in Great Britain the maximum pressure allowed is 225 pounds per square inch gauge at 60 F.
The porous mass is needed for a variety of safety and practical considerations. Its function is to absorb the acetylene solution and to sub-divide the entire interior of the cylinder into small cells. This sub-division prevents an acetylene decomposition, which may be initiated for instance by backfire from external equipment attached to the cylinder or in some other way, from spreading throughout the cylinder. Frequently the porous mass is formed in situ in the cylinder, and is a homogeneous medium with interconnected pores known as a monolithic mass. Alternatively a granular porous mass may be compacted into a cylinder, the cells then being constituted partly by the intergranular spaces, i.e. the porosity due to the interstices between the granules, and partly by the porosity inherent in the porous granular material itself. Since the cell size of the intergranular porosity is normally markedly greater than that of the porosity inherent in the porous material, it is desirable that the inter-granular porosity be kept as low as possible, bearing in mind the need for reasonable ease of charging the cylinder with acetylene. Other advantages obtained by the use of a porous mass are an increased acetylene charging rate resulting from the very :great surface area presented by the mass, and a reduced loss of solvent during discharge through entrainment.
The chief requirements of a satisfactory porous mass for filling acetylene cylinders may be summarised as follows:
(1) Chemical stability: the mass must not react with acetylene or with the solvent or with the material of construction of the cylinder itself, nor must it catalyse any decomposition of the acetylene, or of the solvent, or any reaction between them; also, of course, it must be chemically stable itself over prolonged periods of time.
(2) High porosity: for economic reasons the porous mass must not detract any more than is necessary from the capacity of the cylinder to hold solvent and acetylene; it must not add unduly to the total weight of the cylin der or in particular to the ratio of this total weight to the quantity of acetylene carried in a full charge.
(3) Mechanical stability: during the course of handling in transport and use of the cylinders, the mass must not be liable to subsidence or the production of cracks, fissures, cavities, or regions of abnormally low density, whereby the efficiency of the mass from the safety point of view might become impaired in time.
(4) Safety efficiency: the mass must resist the propagation of acetylene decomposition either passed into the cylinder from equipment attached thereto, or initiated "ice from the walls of the cylinder by external heating whether of a localised or general character.
It has previously been proposed to use kieseiguhr as a porous mass. Kieselgnhr offers many advantages as a porous mass but by itself is difficult to compact into cylinders and in use tends to settle, leaving an empty space at the top of the cylinder. This propensity may be reduced by mixing the kieselguhr with a fibrous material such as asbestos, but this complicates filling still further and does not give a complete cure. Heat treatment of the kieselguhr is not suitable; if sufiicien-t heat is applied to modify the settling properties, some fritting of the kieselg-u-hr takes place and the porosity is reduced.
It has also been suggested to bond kieselguhr with an inorganic material, such as cement. This procedure is not, however, satisfactory because (a) large amounts of bonding material are necessary owing to the low bulk density of the kieselguhr, thus increasing the weight of the charge and decreasing its absorptive powers; and (b) an excessive amount of fine material is obtained on crushing the bonded material to suitable size for use as a granular filling.
According to the present invention, a granular porous mass for filling cylinders or other pressure vessels for the storage or transport of acetylene dissolved under pressure in a solvent comprises kiesel-guhr bonded with a melamine-formaldehyde resin.
The melamine-formaldehyde resin is not affected by acetylene or acetone and does not affect the porosity of the kieselguhr. Moreover, only comparatively small amounts are required to bond the kieselghur and when the bonded kieselghur is crushed to form the granular material, there is no tendency to crumbling or to the formation of excessive quantities of fine material. The melamine-formaldehyde resin is not affected by moisture or by most other solvents.
The porous masses of the prewnt invention may be prepared by first forming an aqueous dispersion of the melamine-formaldehyde resin by any suitable method, for example, by direct reaction of melamine with aqueous formaldehyde. The required amount of kieselguhr may then be added and incorporated in a mixer. When the mass is completely homogeneous, it is removed and dried, preferably in a vacuum oven or other device which prevents the production of a temperature in excess of ISO-200 C. The dried mass is then reduced in size by suitable means such as a grinding mill and is screened to obtain a fraction of the desired mesh size. This fraction may then be charged into an empty acetylene cylinder in the normal manner.
In general, the amount of melamine-formaldehyde resin used will be such as to form 515% of the weight of the final product, the preferred amount being about 10%. The size of the granules to be charged into the cylinder will depend somewhat on the kieselguhr used on the porosity properties required. The preferred range of particle size for the porous masses of the present invention is 8 mesh to 72 mesh B.S.S., but the invention is not limited to this range.
The invention is illustrated by the following example:
492 g. of 40% aqueous formaldehyde solution was adjusted to pH 8.0 with N sodium hydroxide solution. The solution was then heated to 85 C. in a stirred vessel and 252 g. of melamine were added. Stirring was continued until all the melamine had dissolved. The product was then poured into a solution of ml. of concentrated hydrochloric acid in 2720 ml. of water. The total volume of the resultant colloidal solution was 3384 ml. Its solids content was 11.8%.
After standing for 3 hours, 2100 ml. of the above solution (containing 156 g. of the original melamine) was compounded with 900 ml. of water and 1200 g. of kieselguhr in a mixer. The resultant paste was then dried in a steam-heated vacuum oven at 120 C. for 15 hours. The dried material was crushed and sieved', the fraction 10-72 mesh being collected. When charged into a small acetylene cylinder, it had thefollowing properties:
Bulk density g. per l 466' Apparent density g. per l 545 True density g. per l 2270 Total porosity percent 79.5
Intergranular porosity do 14.5
We claim:
1. The method of manufacturing a granular porous mass for filling pressure vessels for the storage of acetylene dissolved under pressure in a solvent, which comprises the steps of mixing kieselguhr with an aqueous dispersion of a melamine-formaldehyde resin to form a homogeneous mass, drying saidmass at a temperature below 200 C. and granulating the dried mass, theamount of melamine-formaldehyde resin being from 515% by weight of the dried mass.
2.. The method of manufacturing a granular porous mass for filling pressure vessels for the storage of acetylene dissolved under pressure in a solvent, which comprises the steps of mixing kieselgnhr with an aqueous dispersion of a melamine-formaldehyde resin to form a homogeneous mass, drying said mass at a temperature below 200 C.,, granulating the dried mass and sieving the granulated mass to separate a granular product having a size range of 8-72 mesh B.S.S.,. the amount of melamine-formaldehyde resin being from 515% by weight of the dried mass.
3. A porous mass for filling pressure vessels for the storage of acetylene dissolved iunder pressure in a solvent, comprising granules formed of kieselguhr bonded with 5-15 by weight of the mass of a melamine-formaldehyde resin.
4. A porous mass for filling pressure vessels for the storage of acetylene dissolved under pressure in a solvent, comprising granules formed of kieselguhr bonded with about 10% by weight of the mass of a melamine-formaldehyde resin. 1
5. A porous mass for filling pressure vessels for the storage of acetylene dissolved under pressure in a solvent, comprising granules having a size range of 8-72 mesh B85. and formed of kieselgnhr bonded with 5-15 by weight of the mass of a melamine-formaldehyde resin.
6. A porous mass for filling pressure vessels for the storage of acetylene dissolved under pressure in a solvent,.
comprisingygranules having a size range of 8-72 mesh -B.S.S. and formed of kieselguhr bonded with about 10% by weight of the mass of a melamine-formaldehyde resin.
References Cited in the file of this patent UNITED STATES PATENTS 1,623,169 Dalen Apr. 5, 1927 2,540,599 Segura Feb. 6, 1951 2,751,650 Froberger June 26, 1956 2,933,455 Doying Apr. 19, 1960