August, 1926
IhTDUSTRI.4L A N D ENGINEERING CHEMISTRY
After 20 or 30 seconds the bulbs have a frosting suitable for light diffusion. Bulbs frosted for 60 seconds in the foregoing test were used in making a strengthening test. These bulbs were treated with a solution containing water, barium sulfate, dextrin, and 7.44 per cent by weight of hydrofluoric acid, the mixture being sprayed over the inner frosted surface in the same manner as used for frosting (Table 111). T a b l e 111-Average S t r e n g t h of Treated Bulbs Seconds 0 1.0 20 30 40 50 80 180 Strength 3.2 5.6 8 . 2 39.6 45.2 43.6 42.4 44.8
775
acid solution does not give uniform strength. Besides giving strength this treatment must produce a surface that can be washed clean. This strengthening process always loosens up a thin layer of material so that it can be washed out. Frosting and treating mixtures containing large amounts of ammonium salts are especially recommended, because the waste products are much more soluble in mater than the potassium or sodium salts and the chances of leaving any volatile fluorides in the bulbs are much less. Where a frosting and treating mixture contains a large amount of ammonium bifluoride, the inside-frosted bulbs show no more volatile gases when heated than do clear bulbs, but if some such compound as potassium fl'llosilicateis left on the inside-frosted surface, a volatile gas such as silicon fluoride would be expelled during sealing and exhausting and might give lamps of poor quality. Comparison of Exterior and Interior Frosting
I n order to obtain accurate comparative information regarding the effect of exterior and interior frosting, a lot of S-19 Pitney lime glass bulbs was divided into two portionsone portion mas frosted inside in the regular manner but varying the treating time. Inside-frosted and clear bulbs were made into lamps, using special care to get them as uniform as possible. Part of the clear lamps were acid-frosted outside, some only once, others twice. (Table IV) Table IV-Comparative
Figure 2-Photomicrograph of Inside-Frosted Treatment
Bulb
before
From this it appears that, whereas the frosting machine causes the strength of the bulbs to drop from 44.8 to 3.2, or about 92.8 per cent, subsequent treating for 30 seconds raises the strength from 3.2 to 39.6, or about 1137 per cent. These strengthened bulbs are usually slightly less opaque than those not so treated. Frosting and Strengthening Mixtures
The most economical frosting mixture is one that will produce good frosting quickly. Commercially it has been found that if 48 to 60 per cent hydrofluoric acid is saturated with ammonium bifluoride and enough water and sodium carbonate are added to bring the acidity down to about 25 per cent hydrofluoric acid, the mixture is well suited for the process in which the surface of the bulb is covered and allowed to set for 25 to 50 seconds at from 30" to 50" C. A frosting mixture containing 42 per cent of ammonium bifluoride, 7 per cent dextrin, 20 per cent barium sulfate, 3.5per cent sodium bisulfate, 27.5 per cent hydrofluoric acid, and water, showing an acidity of from 18 to 25 per cent hydrofluoric acid, will give finely grained and uniform etching when the time and temperature are kept constant. The most efficient method of frosting is to wet the bulb surface with the frosting mixture and allow it to set in air for a few seconds. This gives the chemicals in the mixture time to become partially crystallized. Any frosting mixture becomes better after using, because i t takes up calcium, sodium fluorides, and fluosilicates from the glass. The best system of frosting, Lherefore, is one in which just enough new frosting material is added to replace losses and maintain the proper chemical equilibrium. The treatment for strengthening the bulb can be carried out with any mixture that will dissolve glass. It may be the same as the frosting mixture, provided that either the time in contact or the temperature is different from that used for frosting. Commercially this solution is weaker in acid than the one used for frosting. The use of a very strongly
Effect of Exterior a n d Interior Frosting Max. Abbrightsorption ness Lumens/ of light Candles/ Finish Strength Ampere Lumens watt Per cent sq. cm. Clear 4 4 . 8 0.3434 409.2 10.24 0.00 201.8 9.12 Frosted outside once 4 4 . 8 0.3472 386.2 5.13 5.36 Frostedoutsidetwice 44 S 0.3474 393 9.80 3.96 5.40 Frosted inside, not 6 . 8 0.3476 400 treated 10.0 2.25 3.02 Frosted inside, treated 3 0 . 4 0.3476 404.2 10 seconds 10.08 1.22 4.5 Frosted inside, treated 20 seconds 4 2 . 0 0.3476 404 10.1 1.27 5.G Frosted inside, treated 40 seconds 44.8 0.347 404.8 10.14 1.07 6.92
I n calculating the loss in light, 409.2, the average lumen as shown for the clear lamp is assumed to be the correct
Figure 3-Photomicrograph of Inside-Frosted Bulb after T r e a t m e n t
total light output, and the average as shown for each lot of lamps has been assumed to be correct for that particular type of frosting. I n arriving a t the figure for per cent loss in light due to absorption, the average lumen has been deducted from the average for clear lamps and the loss calculated as per cent. The brightness should be a very good measure of diffusion or dispersion of light. The data show
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INDUSTRIAL AND ENGINEERING CHEMISTRY
776
that the diffusion is about the same, but that there is a great saving in light for the inside-frosted lamps. A Of the brightness in per square centimeter between clear and inside-frosted lamps was made by having a series of lamps made, employing special care to obtain as good uniformity as possible, so that the only differencewould be due to the frosting. Included in this series of lamps are clear and inside-frosted 100-watt daylight or blue glass lamps. As will be noted, the inside-frosted daylight lamps show a much greater loss in light than the clear daylight lamps. This is perhaps explained by the fact that when light rays are dispersed they have to travel farther to get through the glass, resulting in a higher loss.
1’01. 18, No. 8
Table V-Comparative
Brightness of Clear a n d Inside-Frosted L a m p s . Max. Lumens brightness Lumens/ loss Candles/ Watts Type of lamp Ampere Lumens watt Per cent sq. cm. 15 Flear 0.1256 113.2 7.82 000 176.00 nside-frosted 0.126 111.6 7.7 1.4 2 33 ..
{
0.2252 0.2246 0.3412 0.3408 o0.523 , 5236
253.0 247.2 381.6 371.8 731, 740
Clear 0.8552 Inside-frosted Daylight, clear o.8542 0.8552
1363.8 1369.4 805,2
9.7s 9.54 9.72 9.48 12.3 12, 14 13.86 13.94 8,18
side-frosted Daylight, in-
758,0 3239.6 3140.2 9676.0 9336.0
7.6
5.s7
16.38 15.92 18.9 18.3
3107 000 3.51
%%-frosted
25
fA;ze-frosted
4 0 ( ?%e-frosted 60
{
2oo{ ?Az%e-frosted 5 0 0 ( f%e-frosted
o,856 1.6484 1.643 4.46 4.45
Z:~D 000
2.30 000 1.19 000 ooo 000
261.00 4.1 259.00 5.2 596.00 9.2 632.0 12.3 269.0 6.4 807.0 19.9 925.0 39.0
The Cracking of Petroleum Oils’ By E. H. Leslie and E. H. Potthoff UNIVERSITY OP MICHIGAN, ANN ARBOR,MICH., A N D E. B. BADGER& SONS Co., BOSTON, MASS.
CRACKING apparatus has been developed permitting A study of the individual variables, temperature, pressure, time, effect of nature of oil cracked, and effect of removal or nonremoval of gasoline as formed. Cracking has been shown to be slow a t 700’ F. but rapid a t 800” F. The cracking reaction rate doubles for a n increase of 22” F. Gasoline formation is a straight-line function of time, with two exceptjons t h a t are discussed in detail. With these same two exceptions the formation of gasoline can be regarded and formulated as a reaction of the first order. The over-all process of cracking is extremely complicated and involves reactions both of decomposition and synthesis. Within the limits of error of these experiments, pressure, as such, has been shown to have no effect on the yield of gasoline. Several indirect effects of pressure are discussed. The unsaturation of gasoline is affected by pressure only when pressure indirectly affects the time t h a t the gasoline stays in the reaction vessel. Unsaturation decreases with time of heating. Pressure, as such, has no effect on-the boiling range of the gasoline produced in cracking. . ... . . .
HE cracking of petroleum oils for the production of
T
gasoline is the outstanding development of the last decade in petroleum technology, and is, furthermore] an achievement of such social and economic importance as to rank with the really great industrial advances of all time. Gasoline of superior quality has been made available a t prices well within the reach of all. To this end manufacturers have invested hundreds of millions of dollars in cracking equipment, thereby permitting operations that have exerted a profound stabilizing influence on the entire petroleum industry. I n view of the magnitude of the expenditure involved and the scale on which operations have been conducted] it is odd, indeed, that so little scientific work has been done to establish a foundation of fact on which the engineering superstructure might securely rest. Yet careful review2 of the existent technical literature discloses little dependable definite informa1 Presented under the title “Cracking Liquid Petroleum Oils” before the Division of Petroleum Chemistry a t the 71st Meeting of the American Chemical Society, Tulsa, Okla., April 5 to 9, 1926. * Leslie, “Motor Fuels, Their Production and Technology,” 1923,
p. 270.
Excluding experiments involving limited cracking on y, heavy fuel oil cracks most easily, gas oil nearly as readily, but thetmolized gas oil or “cycle stock” only 0.40 to 0.47 as rapidly. Removal of gasoline as formed has no effect either on the yield or boiling range of the gasoline produced. It does affect the unsaturation of the gasoline somewhat. Rates of pressure rise during cracking of three oils in a bomb, the relationship between specific gravity and extent of cracking, and the boiling ranges of gasolines produced by cracking under various conditions are given. An apparatus for studying the thermal relations in cracking was developed and cracking has been shown to be endothermic to the extent of not over 500 calories per gram of gasoline produced. Cracking is not a process in which a n equilibrium state is reached as is somewhat commonly believed. The apparent state of equilibrium reached in cracking systems using lagged reaction chambers is the result of decreased reaction rate caused by the lowered temperature resulting from heat loss and endothermic cracking reactions.
tion. Much that has been done and described is unreliable because of failure to control the individual variable factors. The purpose of the investigation the results of which are here reported was, in part, to determine quantitatively, or as nearly quantitatively as possible, the effect of the fundamental variables in cracking-namely, temperature, pressure, time, and composition or nature of the oil cracked-and further to ascertain the effect of removal or nonremoval of the gasoline as formed, to determine the quality of the gasoline produced under various conditions, and to measure the heat absorbed or evolved in the over-all process of cracking. These are the most important and fundamental points on which information is necessary for the intelligent layout of a cracking procedure and the design of the equipment for its accomplishment. As is almost invariably true, the more important processes used industrially have been in the main correct in principle. Day-to-day operation is an accurate, if slow, guide to the truth. Yet misconceptions exist and much money has been spent in the construction of ill-designed equipment. Also, the basic ideas of processes in current use are sufficiently
