US2098232A - Coating coal - Google Patents

Description

Patented Nov. 9, 1937 2,098,232 COATING COAL Harvey It. Fife, Pittsburgh, Pa.

No Drawing. Application March 2, 1934, Serial No. 713,694. Renewed December 19, 1936 9 Claims.

This invention relates to the protective coating of coal.

It has long been desired to protect coal both from the degradation occurring because of slow oxidation, and from the degradation which occurs by abrasion of the lumps or particles of the coal. This latter may be considered as a physical, rather than a chemical degradation, although it is a fact that oxidation expedites physical degradation, and that physical degradation, by exposing new surfaces, expedites the action of oxidation.

We are here chiefly concerned with the physical degradation in coal which is caused by blows and abrasion in handling the coal. To a great extent, the physical degradation of coal iscaused by blows and rubbing between lumps of coal when the coal is loaded and unloaded, and also during its transportation.

It is a well demonstrated fact that moist coal is highly resistant to physical degradation, the moisture appearing to prevent crumbling, and also serving to some extent as a lubricant. The lubricating efiect of moisture on coal is particularly marked in the presence of coal dust, since the dust tending to adhere to the coal acts as an efficient lubricant, to cause sliding of the coal lumps, and to lessen abrasion. It is, however, a practical impossibility to maintain coal in an adequately moist condition by the application of water. Hygroscopic materials, such as calcium chloride, have been applied to coal, to keep the surface of the lumps or particles of coal moist. Such materials have served successfully, or at least very favorably, during short periods of time. Gradually, however, the calcium chloride entering into solution penetrates into the bodies of coal, and its effect is thus lost. When crude petroleum, or any of the other oils 40 used for the treatmentof coal are first applied to the coal, the effect is to prevent physical degradation due to blows and abrasion. The oils, however, rapidly penetrate the coal lumps, leaving the surface unprotected and unlubricated. It is 5 necexary for the adequate protection of coal, during relatively long periods of time, that there be and remain on the surface of the coal lumps a coating of adherent,non-penetrating material. My prior Patent No. 1,912,697; dated June 6, 1933, 50 discloses a coating consisting primarily of paraifin wax, which possesses to a great extent the noted desirable characteristics. The coating of parafiin wax, or of paraffin wax I and another neutral hydrocarbon, such as a neu- 55 tral pitch or a neutral asphalt, provides a film which remains on the surface of each individual lump of coal, without becoming lost by penetration into the body of the lump. It is viscous and adherent, without being tacky, and. does not rub off by contact between lumps of coal, or contact 5 of the coal lumps with the surface of handling instruments or containers. At temperatures appreciably higher than 0 C., the coating material does not tend to flake from the surface of a coal lump. At low temperatures, such as 0 C. and 10 lower, however, a refined parafiin wax or a paraifin wax unassociated with a plasticizer containing bodies serving to retard crystallization tends to crystallization and brittleness.

According to this invention, I use as my start- 15 ing material for the coating of coal that product of petroleum oil distillation known as petroleum jelly or petrolatum. This I take initially in crude state. 1

Crude petrolatum may be roughly defined as 20 the mother liquor from which paraffin is obtained. The paraifin is present in the petrolatum dissolved in oil. If the crude petrolatum be fractionated, either by distillation, or by solvent precipitation, a certain proportion of paraffin is 25 removed with the lower viscosity cut of the oil, and a certain proportion of the paraflin remains with the heavier oil of higher viscosity. The value-0f crude petrolatum in coal-coating compositions is positive. Being non-crystalline and 30 compatible with the various cuts of hydrocarbon oil, its addition in substantial quantity to a hydrocarbon oil tends to some extent to modify the fugitive quality of a film of the oil as applied to C03,].

I have found crude petrolatum as, such relatively impermanent as a film in the protective coating of coal. This is for the reason that the presence of a large proportion of oil separable as the lighter or low viscosity fraction renders the 40 crude petrolatum greasy, so that it is rubbed from the surface of the coal. Further, the penetration of the oil into the body of the coal tends to leave the paraffin unplasticized and present in isolated areas on the surface of the coal, rather than as a uniform coating.

Taking, therefore, crude petrolatum as my starting material, I- so subtract from and add to the ingredients of the petrolatum that a coating material wholly satisfactory for coal ofall grades and for long continued use under all normal atmospheric temperatures is obtained.

It should-be noted that, as present in the mother liquor, paraffin is without tendency to I cry tallization, there being present bodies capable of maintaining the amorphous nature of the wax even under low temperature conditions. It is refined parafiin wax in itself which exhibits the tendency to become crystalline and brittle at low temperatures.

' We shall assume initially that the petrolatum taken as the starting material is a petrolatum derived from Pennsylvania crude petroleum, which has, as is well known, a totally parafl'in base. I then remove from the crude petrolatum a proportion or cut of lower boiling point. Desirably I remove that cut, which will distil at a temperature no higher than 500 F. While distillation temperature gives a convenient definition to the removed cut, it is to be understood that the removal may be made by any of the well known solvent precipitation processes, as well as by fractional distillation.

In this topped petrolatum, the heavier cut of oil then providing the total oil content is of body suitable to serve as a plasticizer for the paraflin wax, and is of sufiiciently high viscosity to prevent its penetration into the body of the coal. Even as so constituted, however, the petrolatum is greasy, and does not fulfill all of the requirements desirable in a coal-coating material. I have found that in several ways I may render this material wholly suitable.

One mode of improving the qualities of the topped crude petrolatum is to add to it a suitable proportion of unrefined paraflin wax. By unrefined paraffin wax I mean the paraflin wax content of crude petrolatum, from which all or almost all of the oil has been expressed. This material should be added in substantial quantity, and I have found it desirable to restore to the crude petrolatum a quantity of unrefined paraffin wax at least equal to that which has been removed with the lighter cut of oil.

Another material which has proven satisfactory, when added to-the topped crude petrolatum, is refined paraffin'wax, which is the well known paraffin wax-of. commerce. This refined paraffin wax possesses in itself the tendency to crystallize at low temperatures, but as added to the unrefined wax and oil, constituting the topped crude j petrolatum, the presence of crude bodies in the unrefined content entirely or substantially negative s the tendency to crystallization. If relatively large quantities of the refined paraflin wax are added to the topped crudematerial, I have found it desirable to add a small quantity of asphalt or a tar acid, to counteract that tendency. Plasticity, generally considered, is provided by the heavy oil content of the coating material. Another manner of increasing the proportional content of paraflin wax in the crude topped petrolatum is to remove some of the heavier oil, so that the percentage content of wax inthe material is substantially increased. It is to be understood that, while the oil content of the coating material is lessened by the addition of solid wax, or by removal of a portion of the oil, I have found it of relatively great importance to retain a substantial content of the heavier oil,

distilling at a temperature higher than 500 F.

While a lessening in the oilcontent avoids greasiness in the coating material, the oil itself performs a highly useful function, in that it plasticizes the paramn wax, and gives a coating maintains the adherence of the coating 1.50 the coal at extremely low temperatures. Even though paraflin wax, applied alone to coal, be unrefined and thus lacks a tendency to crystallize, it does not present adequate flexibility and adherence at the lower atmospheric temperatures.

. Another procedure by which the topped crude petrolatum may be rendered wholly suitable as a coating material for the enduring protection of coal is to add to this topped crudepet'rolatum a proportion of pitch or asphalt, either by itself or as combined with a paraflln wax. The quan tity of the pitch or asphalt added, or the quantity of a mixed quantity of pitch or asphalt with parafiin wax as added, may likewise desirably equal the quantity of wax initially removed from the crude petrolatum in removing the lighter oil content from it.

The above has dealt with a petrolatum derived from Pennsylvania crude oil, which is an unmixed paraflin base oil. found that I may successfully use a petrolatum derived from the mid-continent crude petroleums, which have a mixed paraflin and asphalt base, and that the crude petrolatum derived from these petroleums requires a somewhat lesser adjustment than the crude petrolatum derived from Pennsylvania crude petroleum. Taking the crude petrolatum resulting from the distillation of the mixed base petroleums, I remove a cut of,.

the-lighter oils, desirably such cut as distils at a temperature no higher than 500 F., by a suitable process such as a solvent precipitation process.

It is possible that, with this mixed base petroleum, the proper amount of semi-solid may exist.

in the topped petrolatum. This is for the reason that there is a lesser tendency in such petrolatum for a large' proportion of the semi-solid content of the petrolatum to be removed with the lighter oil content. 01' the petrolatum. In

I have, however,

general, however, it is necessary to increase the that the flexibility and adherence of the coating may be preserved at'thelower atmospheric temperatures.

It is to be understood that, with both the Pennsylvania base petrolatum and the corre-- sponding material produced from a mixed base petroleum, which I also herein term petrolatum", the quantity of paraflin wax or other semi-solid material which is ,added after the petrolatum has been topped will vary somewhat with the character of the particular petroleum from which the petrolatum is obtained. Starting with the general proposition that I prefer to add to the topped petrolatum a semisolid content at least equal to that which has been.

removed by topping, the quantity so added may bevaried above and below the quantity generally so defined. The exact quantity of semi-solid material to be added is subject to determination in each instance by trial, without extended experimentation. It may be stated generally that if the heavier oil'remaining in the petrolatum be of particularlyhigh viscosity, or if the percentage of wax or asphalt remaining be particularly high, the quantity of added paraflin asphalt or paraffin asphalt mixture may be lessened.

In applying the coating material to the coal, it is desirable to follow a procedure such as disclosed in my above-noted Patent-No. 1,912,697.

According to one method of application as noted in that patent, the coal may be passed through a fused bath of the coating material, drained, and the adherent coating allowed to solidify. The most economical method of procedure is that disclosed in the above-noted patent, in which the coating material is deposited on the coal from heated liquid suspension.

If the last-noted method of application is to be followed, care should be taken that any asphalt or pitch included in the coating material does not bring the acidity of the material to such point that it will tend to emulsify in a bath of heated liquid. It should be noted that, as my coating material is applied by either of the modes mentioned, as distinguished particularly from a method which involves spraying the coal with an emulsified bath of coating material, the coating is continuous, and acts to wholly cover and protect each lump or body of coal.

When my improved coating material has been applied to lumps or particles of coal, it not rrily protects the coal from chemical degradation due to oxidation, but also prevents dusting and degradation of the coal due to shocks and abrasion resulting from handling and storage. i The coating acts both as an intervening film, to prevent abrasion of the coal, and as a lubricant, lessening the effect of blows to which the coal is subjected. Thus when coal having my protective coating on the individual lumps or particles is dumped, the lubricating quality of the coating causes the lumps to slide over each other, thus lessening the force of what would otherwise be direct blows, and preventing breakage of the coal.

Because of the content of heavy oil, the lubricating effect is greater than is obtainable by parafiin wax alone, whether the paraffin wax be refined or unrefined. Because of its resistance to crystallizing tendencies at all atmospheric temperatures, the coating serves to protect the coal at lower atmospheric temperatures, as well as at higher atmospheric temperatures. It may be noted that at high atmospheric temperature the coating does not tend to become tacky.

An additional use of my coating material re-' sides in the fact that it may cause fine coal dust to adhere to the substantial lumps or particles of coal. Thus by applying coal dust to the coal, when freshly coated, the coal dust becomes embedded in the coating in such manner as to form an integral part of the coating. Lumps of coal so coated are additionally protected, in that the coal dust itself serves as a lubricant and as an additional protective armor for the lumps or particles of coal. A further advantage rising from the addition of the coal dust is one of economy, since the coal dust thus forming a component of the coating on the lumps of coal is not lost, but increases the effective fuel value of the lumps.

My improved coating material is economical, in that crude materials of relatively low cost are used, advantage being taken of the peculiar qualities of the crude, as compared with the refined, material. The coating difiers widely from crude petroleum as a treating material for coal, in that it is highly viscous, non-penetrating, and forms a coherent coating on the coal. It differs also in a marked degree from crude petrolatum, although the advantageous qualities of crude petrolatum are preserved in it. It is, as explained, notably to the lubricating quality provided by" the heavier component oil of the crude petrolatum, and to the plasticizing effect of that oil on the paraflin wax or asphalt included in the coating mixture.

As previously explained, the plasticizing effect-is such that the coating remains flexible and adherent at extremely low atmospheric temperatures.

It is to be understood that my coating material may be applied to the exterior of briquettes composed of divided fuel particles. bonded together. In this connection, the coating material may, or may not, be used as the bondingmaterial, my purpose being to form a protective and lubricating coating on the surface of the briquette in the same manner as on a lump of solid coal. In fact, for my purpose, each briquette may be considered the full equivalent of a lump of solid coal.

It has been noted above that coal dust will adhere to my coated coal lumps, and it should be explained that sawdust and other finely divided solid fuels may similarly be caused to adhere to the lumps, to provide an outer coating. If sawdust is used, the lubricating efiect of adherent coal dust is lacking, but an increasedcushioning effect is obtained.

As used throughout the specification and claims, the term heavy out" of petrolatum, or heavy cu of mineral'oil, and likewise "high viscosity mineral oil, each defines the petrolatum of the mineral oil which does not distil at a temperature substantially lower than 500 F. Similarly, the lighter cut of petrolatum, and the lighter oil designates the cut of petrolatum or oil which distils at a temperature approximating 500 F.

It is to be understood that the material used in coating the coal may be made up of the heavier cut of crude mineral oil, without its naturally associated semi-solids of the class of parafiin wax and asphalt, and that these semi-solids may be added in appropriate quantity ,to the high viscosity crude mineral oil. In general, such procedure would not be followed, for the reason that it would involve the entire removal of the semisolids, and their replacement. In the event, however, that there should be available a supply of crude mineral oil of suitable viscosity, which has none or a negligible semi-solid content, it is within the contemplation of my invention to utilize such oil in making up my coating material, by adding adequate quantity of the suitable semisolids thereto.

Whereas'it is desirable to have in the coating material a relatively great quantity of semi-solid bonaceous fuel, in whatever condition it may be.

In the case of coal which is in the condition of coke, it is of particular importance that the lighter oil content of the crude petrolatum should not be included in the finished coating material, and that the finished coating material be relatively dense, as well as adequately flexible at low temperatures. This is because of the high adsorptive properties of coke.

I claim as my invention: I

1. The herein describedmethod of preparing a coating material for the protective coating of solid lump fuel of the type subject to degradation by oxidation and to objectionable dusting which comprises removing from crudepetrolatum a cut of the lighter oil content with consequent removal of a portion of the semi-solid content of the crude petrolatum associated with the lighter oil, increasing the relative proportion of semisolid content with respect to the remaining heavier oil content of the crude petrolatum by adding to the heavier end of the crude petrolatum which has been deprived of its lighter associated oil a refined or semi-refined paramn wax, and inhibiting crystallization of the paraffin content of the coating material by including therein a relatively small quantity of a crude hydrocarbon material.

2. A; coating composition for protectively coating solid lump fuel of the type subject to degradation by oxidation and to objectionable dusting comprising a parafiln substance having the approximate composition of a blend of paraffin wax and a petrolatum, said coating composition being substantially non-volatile at temperatures below 500 F., and said coating composition as existing in an applied film on the lump fuel being noncrystalline and tough at low temperatures and having lubricating qualities.

' the paraffin wax content of the composition, said coating composition being substantially nonvolatile at temperatures below 500 F., and said coating composition as existing in an applied film on the lump fuel being non-crystalline and tough at low temperatures and having lubricating qualities. i

5. A coating composition for protectively coating solid lump fuel of the type subject to degradation by oxidation and to objectionable dusting comprising a parafiin substance having the approximate composition of a blend of paramn wax and a heavy petrolatum, and additionally a relatively small quantity of a hydrocarbon material as an inhibitor of crystallization in the paraifin wax content of the composition, said coating composition as existing in an applied film on the lump fuel being non-crystalline and tough at low temperatures and having lubricating qualities.

6. A coating composition for protectively coating solid lump fuel of the type subject to degradation by oxidation and to objectionable dusting comprising a paraffin substance'having the approximate composition of crude paraffin wax and a heavy petrolatum having the property of crude hydrocarbon in tending to inhibit crystallization of the'parafiin wax content of the composition, said coating composition as existing in an applied film on the lump fuel being non-crystalline and tough at low temperatures and having lubri eating qualities.

7. The herein described method of preparing a coating material for the protective coating of solid lump fuel of the type subject to degradation by oxidation and to objectionable dusting which comprises removing from crude petrolatum a cut of the lighter oil content with consequent removal of a portion of the semi-solid content of the crude petrolatum associated with the lighter oil, and increasing the relative proportion of semi-solid content with respect to the remaining heavier oil content of the crude petrolatum.

8. The herein described method of preparing a coating material for the protective coating of solid lump fuel of the type subject to degradation by oxidation and to objectionable dusting which comprises increasing the body and decreasing the penetrability of .crude petrolatum comprising parafin wax and oily hydrocarbon by adding thereto paraffin wax, thereby increasing the semisolid content of the material with respect'to the hydrocarbon oil content thereof.

9. The herein described method ofpreparing a coating material for the protective coating of solid lump fuel of the type subject to degradation by oxidation and to objectionable dusting which comprises removing from crude petrolatum a cut of the lighter oil content with consequent removal of a portion of the semi-solid content of the crude petrolatum associated with the lighter oil, increasing the relative proportion of semisolid content with respect to the remaining heavier oil content of the crude petrolatum by adding to the heavier end of the crude petrolatum which has been deprived of its lighter oils a refined or semi-refined paraflin wax, and inhibiting crystallization of the paraifin content of the material by including therein a relatively small HARVEY R. FIFE.