Vapor-Phase Clay Treatment of Cracked Gasoline H. M. STEININGER, Standard Oil Company (Indiana), Sugar Creek, Mo.
T
HE decade prior to 1920 High yields from clay can be obtained when a manner specific to each parsaw the experimental deticular case. using initial color as a criterion. Yields of velopment, and early comThe major objects, then, for 5000 to 6000 barrels of stock of acceptable color mercial application of the art of which a pressure distillate was stability per ton of clay can be obtained when cracking hydrocarbon oils. The treated were initial color, and to treating distillates of the type used in this work decade 1920 to 1930 saw this art some degree, color stability, in progress and further develop in and under the conditions employed. Higher addition to a certain amount of very rapid fashion. This new art oxidation stability as measured pressures and temperatures with increased concarried with it many new probby the copper-dish teat. tact time seem, on the basis of the data presented, lems, of which a major one was Existent l i t e r a t u r e reveals to result in improved color stability properties the chemical treatment of the little, if any, quantitative data of the product. pressure distillate produced by relating to the properties of the cracking. As is often the case, The oxidation stability is materially affected pressure distillate treated by coni n d u s t r y t u r n e d to a known tacting in the vapor phase with by clay treating, and a definite relation exists method of treating this product clay. It is the purpose of this belween yield f r o m clay and the oxidation charwhich would produce a product paper to present such data, deacteristics of the treated product. The induction of satisfactory properties without rived from several experimental period is favorably affected u p to a yield of considering whether or not the installations, together with a disprocess employed was the most cussion of some factors which 4000 to 5000 barrels per ton of clay. desirable when taking into conhave a bearing on this type of Since initial color can be obtained u p to high sideration all factors. Thus the treatment with respect to the yields from clay, at which yield the color stability conventional acid t r e a t m e n t , properties of the treatedmaterial. may not be of as high a n order as desirable, the with subsequent rerunning, was CLAY-TREATING EQUIPMENT use of butyl or amyl amines offers a means of resorted to almost universally for Clay treating can be carried securing improvement in color stability even at the purpose of producing marketout by rerunning the pressure able gasoline from the pressure high yields f r o m clay. distillate in a seDarate unit and distillate. passing the vapors through a Treatment with acid has always been open to numerous objections. Events of the last vessel filled with clay. However, it is usually, and with much few years have brought these objections more sharply to the greater economy, carried out by conducting the vapors difore. The more prominent are the cost of treating and rerun- rectly from a cracking still through a vessel containing 30-60 ning, loss of octane number, losses due to polymerization, etc. or 60-90 mesh clay, after which the treated vapors pass to an The new problems created by cracking, and inadequately afterfractionator for complete separation of entrained polymet by the use of acid treatment, called for methods of re- merized material and fractionation of the desired product fining this cracked gasoline in a more economical manner. prior to condensation. The clay in the clay-treating chamber One of the new methods (and by far the most widely used of rests on a screen supported by a false bottom, the lower porthe processes other than acid treatment) for the chemical tion of the tower forming a polymer chamber wherein the treatment for cracked distillate was found in the vapor- major portion of the polymerized and liquefied material sepaphase treatment with clay. This process was originally de- rates from the vapors. In the early installations no afterveloped and promoted by the late T. T. Gray and is widely fractionator was employed to rectify the vapors subsequent known ( 2 ) . to clay contacting, but now the use of the afterfractionator The rapidity with which this form of treating has grown in has become virtually universal. favor with the refiners is shown by the fact that in 1924, the Various arrangements of the clay-containing towers are first year in which commercial clay treating was carried out, used-namely, single and double towers, both in parallel and the total daily average capacity for this method of treatment in series; in one installation four towers are used in parallel. was 300 barrels' per day. In 1933 the total daily vapor- In the case of the series flow through towers it is customary, phase clay-treating capacity was upwards of 100,000 barrelsand highly desirable, t o separate the polymer fraction which a 330 fold increase in nine years. is intermediate between the two towers. The towers can be The objects of any type of treating pressure distillate were so manifolded as t o produce a semi-countercurrent treatment. initially restricted largely to color and, to some degree, color The applicability of series flow is dependent, in a large measstability. In the early development of clay treating, oxidation ure, on the pressure drop allowable in any particular instance, stability was not a major item since little was known a t that since this type of flow will give greater pressure drops through time concerning this property. But it has, in the last few the towers than will parallel flow. In recent years the matter years, assumed a much higher degree of importance, because of pressure drop has become more important owing to the of the more severe cracking conditions than formerly pre- fact that stabilization often follows clay treatment, and as vailed, as well as the higher ratio of cracked to straight-run much of the original pressure of the cracking unit as possible gasoline that is produced a t the present time. Other minor is desirable in connection with the stabilizing process.2 objects of treating pressure distillate are odor removal, copper The installation mentioned above, which utilizes four towers in parallel. corrosion, sulfur content, etc., all of which must be handled in is of particular interest in t h a t it is perhaps the only installation of its kind f
1
All barrels mentioned i n this paper consist of 42 gsllons (U. 5.) each
in existence.
1039
This installation treats the cracked vapors produced b y the
1040
INDUSTRIAL AND ENGIISEERING CHEMISTRY
The liquid, polymer-bearing fraction from the base of the clay chamber and the bottoms from the afterfractionator, both containing material boiling in the gasoline range, are disposed of by pumping them to various points within the cracking system. I n the case of the polymer-bearing fraction from the base of the clay tower, it is customary, particularly in a clean oil unit, to pump this stock to the evaporator tower so 22s
.
FIGUBE1. HYPOTHETICAL SET-UP
that the heavy polymerized material will eliminate itself from the system with the fuel oil, In the case of a reduced crude unit or other dirty oil system, it can be disposed of by pumping either to the evaporator tower or to the bubble tower of the cracking still. It is customary in most installations to pump the material from the bottom of the afterfractionator to the cracking-still bubble tower for the redistillation of the gasoline content.
TREATISG RATES Until recently the rate a t which vapor-phase clay treatment is carried out has usually been expressed as the barrels of final product per hour per ton of clay. As long as relatively low pressures are used, this method of expression is probably satisfactory. Within the past few years, however, the application of high-pressure clay treating has made this method of expressing treating rates seem somewhat inadequate. Owing to the wide differences in conditions under which vapor-phase clay treating is carried out, it has seemed preferable to calculate the contact time and utilize this figure as a measure of the rate of treatment. This method takes into account the fixed gases present with the gasoline vapors, the temperature of treatment, and the pressure a t which treatment is carried out. Therefore, the contact time, expressed as seconds, is the actual time that any average particle is in contact with the clay in passing through the treating zone. In making these calculations, the perfect gas laws have been assumed and a void space of GO per cent assumed for the clay. In order to demonstrate the reasonableness of this method for expression of treating rates, the data in Table I have been assembled, showing treating rates expressed by both methods. In these instances all items except pressure and temperature were held constant. In all four cases the treating rate, expressed as new combination cracking unit recently put into operation at the Texas City (Texas) refinery of the Pan American Refining Corporation. Some recent test data with respect to pressure drops through clay beds are of interest. During a period when 410 barrela of cracked material and gas produced were being treated per hour, the number of clay towers was varied from four to two, each tower being charged with 25 tons of 30-60 mesh clay. With four towers in parallel the pressure drop was observed t o be 8 pounds per square inch. Under this flow the treating rate was 4.10 barrels per hour per ton. When three towers were used in parallel, the presa w e drop inrreased t o 10.5 pounds per square inch. Under this flow the treating rate was 5.5 barrels per hour per ton. When two towers were used in parallel, the pressure drop rose to 17 pounds per square inch. Under this Bow the treating rate was 8.2 barrels per hour per ton. In all caaea the pressure at the clay tower outlet was 190 pounds.
Vol. 26, No. 10
barrels per hour per ton, is the same, since this is determined only by the amount of material treated per hour and the weight of the clay. However, owing to the different conditions under which clay treating is carried out, the calculated contact time varies quite widely. These data were prepared without taking into account fixed gases, since the relative effect would be virtually the same. On a number of calculated installations it has been found that usually about one mole of gas is found associated with each two moles of gasoline; hence the result, when taking into account these fixed gases, is a contact time of about two-thirds that calculated when neglecting the fixed gases. The concept of contact time is of two kinds-vis., once through contact time, calculated and based on the total material entering the clay chamber per unit time, and the total or integrated contact time, which takes into account the recycling of material through the clay bed. Figure 1 illustrates this situation for a hypothetical set-up. For 100 gallons of gasoline as vapors entering bubble tower A from the cracking still, 25 gallons are returned as reflux material from gas separator D , and an additional 25 gallons from clay tower B and afterfractionator C, which results in 150 gallons leaving bubble tower A and entering clay chamber B. The net gasoline production from the system consists of 100 gallons. Thus, a contact time calculated on the basis of 150 gallons entering clay tower B would be two-thirds of that obtained if the calculation were based on the net make of 100 gallons, gas being momentarily neglected for the sake of simplicity in illustration. However, since 100 gallons of material is the net production per unit time, and 150 gallons of material enter clay tower B per unit time, it appears that the number of passes through B is one and one-half. Therefore, a total or integrated contact time can be calculated which takes into account this recycling. Thus the once-through contact time multiplied by the number of passes is equal to the total contact time. Similar reasoning will show that, in order to arrive a t the total contact time (which takes into account all recycling), it is necessary only to take into account the volume of the fixed gas and the volume of the net distillate product a t the conditions of temperature and pressure existing in the clay tower. If, however, it is desired to know the once-through contact time, then it is necessary only to take into account the total amount of material entering the clay chamber per unit time. TABLEI. TREATIXG RATES [Basis: ( a ) 100 barrels distillate per hour, 130' A.,P. I . ; ( b ) 25 tons clay (50 pounds per cublc foot). 6 0 per cent void; ( e ) no gas] CONTACT CASE G A G E PRESSURE TEMP. RATE TIM^ Lb / s q . in. F. B bl. / hr ./ton Second8 285 4.0 14.2 1 0 2 3 4
45 160 392
420 430 460
4.0 4.0 4.0
48.9 141.8 320.0
The perfect gas laws have been assumed for the purposes of this calculation. It is realized, however, that the corrected gas laws would perhaps give more valid calculation than the assumption mentioned. DATA The data presented below were derived from two sources and represent two radically different rates of treatment expressed as contact time but of virtually the same treating rate expressed as barrels per hour per ton. The B data were taken on distillate derived from cracking reduced (60 per cent) Pine Island crude in a Cross unit and treating the distillate in the vapor phase with clay in a 15-ton, single clay tower, operating a t 45 pounds per square inch pressure, followed by afterfractionation in a seven-tray bubble tower prior to condensation. The B data were taken on distillate derived from cracking 28" to 30" A. P. I. Midcontinent gas
I N D U S T R I A L A N D E N G I N E E R I K G C H E h!l I S T R Y
October, 1934
oil in a Holmes-Manley unit operating under conditions of low liquid level and from treating a portion of the distillate from the cracking unit in the vapor phase with clay in a 100-pound experimental clay tower, the clay treatment being carried out a t full still pressure of 350 pounds per square inch. The treated vapors were passed through a small eight-tray bubble tower after contacting with the clay. From the foregoing it should not be concluded that the contact time is the only item of difference in conditions between these two sets of data. Other factors which must be considered are kind of stock charged to the cracking unit, whether reduced crude or gas oil, type of cracking unit with respect t o pressure employed, transfer line temperature, cracking per pass, etc. Pertinent data bearing on some of these conditions are as follows: A
Data Type of cracking unit
Cross
Pressure, l b . gage Stock charged r r a n s f e r line temp. O F. Treating rate, bbl.;hr./ton Contact time Bec. Temp. in cla; bed, ' F.
700
B Holmes-hlanley, low liquid level 350
Reduced crude
Midcontinent gaa oil
875 6.4 23 415
900 6.3 150 494
The character of the material undergoing clay treatment and also that of the treated stock are illustrated by the following typical data: Data
Sp. gr. atO6O0 F. Gravity, A. P. I. A. S.T. hl. 100-cc. distn.. Initial B. P. yo distilled orer: 20 50 90
E n d point Sulfur % Color b a y b o l t )
-.Feed *- t o ' F.:
IXITI.4L COLOR
The data given in Tables I1 and I11 show that an initial color of 30 can be obtained for all yields from clay covered by the data. In the case of the commercial tower operating under conditions of the A data, a yield of 23,000 barrels per ton has been attained with an initial color of 28. From the results of numerous installations it appears that, as far as initial color is concerned, very high yields from clay can be attained. T.4BLE
clay tower
Claytreated stock
0.7616 54.3
0.7443 58.6
0.7531 56.4
0.7245 63.8
Sour ) Sweet Blend ( Sour /
98
90
88
86
158 282 386 400
182 272 392 440
150 220 342
396
0.055 12
0.040
0 070 5
0.055 30
30
Sunlight color stahilit'y is determined by completely filling carefully cleaned quart bottles (French type) with the gasoline to be treated. Just before placing in direct sunlight, a 4-ounce sample is withdrawn for initial color determination, the bottle is stoppered, and successive 4-ounce samples are withdrawn for color determinnt'ion at the end of each\ hour of exposure. All exposures were made by placing the k,ottle on an aluminum-
11. D.4RK-STORAGE
COLOR STABILITY
SAMPLE YIBLDF R O M CLAY Initial Bbl.,'ton Sour 30+ Sweet 30 30+ Blend (SO+
,----B-Feed t o clay tower
It should be understood that the data given above on "feed to clay tower" consist of tests of the normally liquid portion of the feed to the clay towers. The feed to the clay towers consists of a mixture of hydrocarbons which are normally gases and of hydrocarbons which are normally liquid. The principal data presented below relate to (a) initial color, ( b ) color stability, and ( c ) oxidation stability. These data were taken a t various times throughout the use of the clay so that the effect of clay usage on these various properties of the treated material becomes possible. The data herewith submitted clearly demonstrate this effect. Tests include in all cases both the sour stock and the same inaterial after being sweetened in the laboratory by the use of doctor solution with carefully controlled addition of free sulfur in solution. It has been an almost universal experience that laboratory sweetening can readily have a deleterious effect on some of the properties of the sweetened stock. Furthermore, it has also been observed that plant sweetening is usually less severe in adverse effect on a stock than is laboratory sweetening. For this reason more reliance is placed in the oxidat,ion stability data obtained on sour stocks than those obtained on laboratory-sweetened ones. The methods used for evaluating co1o.r stability rind oxidation stability follow:
painted board.
Several methods were employed for testing color stability in dark storage. Gallon samples were stored in glass bottles with air present at about 75" F. in the case of the A data. In both sets of data a n additional test was employed at 125' F. using 4-ounce bottles filled to within 0.25 inch of the neck, stoppers being firmly tied in. Eight or ten such samples were prepared, and one was removed at the end of each of various intervals up to 12 weeks. Oxidation stability was determined by the method of Voorhees and Eisinger, recently described by Rogers, Bussies, and Ward (3). The samples set away as noted above for color stability were also tested periodically for gum content by method A as published for information in 1932 by the American Society for Testing Materials (1).
Claytreated stock
176 330 410 425
104 1
5
( A DATA)
COLOR(SAYBOLT)-
1 month
3 months
---.
6 months
30+
30+
30+
2+
28 30 27
30 30 30+
28 28 30
30+ 30 30
29 30
1500
30f 30 30
29 26 30f
27 25 30
27 28 30
Sour I Sweet > Blend \
2400
30 29 30
28 22 28
23 19 24
23 21 26
Sour Sweet i Blend \
3250
30 30 30
23 22 27
21 20 26
22 22 27
Sour Sweet Blend
4650
30 30 30
19 18 22
19 15 91
19 20 22
8903
30 29 30
24 17
..
18 7 22
16 11 19
26
21
17
13
30
20
18
16
E:$]
Sweet Blend Sweet Blend
1
1000
1130J
++
++
..
+
+
+
30
..
+
+ +
..
COLORSTABILITY I N DARKSTORAGE Dark-storage color stability in glass bottles with air present and a t atmospheric temperature is shown only for the A data in Table If. The data cover the sour stock, laboratorysweetened stock, and a blend of equal parts of aweet-cracked clay-treated material with sweet-virgin, since the claytreated product is marketed in such a blend. The data in general show that the color stability decreases with clay usage. The stability is greatest during the first 1500 barrels put through the clay. After the first 1500 or 2000 barrels the stability remains somewhat more constant. While these data do not show the effect, similar sets of data tend to show that sweetening increases the color stability in dark storage. The blend of virgin with the clay-treated cracked material is more stable than the straight-cracked material. Table I11 gives data on dark-storage color stability taken by the 125" F. test. In the case of the B data, no blends were included. Both the A and B data again show the effect of yield from clay on dark-storage color stability. It appears, however, that the B data show the product from treatment at high pressure and temperature, and consequently longer contact time, to be more stable than the products of the A data. It will be recalled that under conditions of the A data,
INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 26, No. 10 TABLE111. DARK-STORAGE COLOR STABILITY AT 125' F. TABLEIV. SUNLIGHTCOLORSTABILITY
1042
SAMPLB YIELDFROM CLAY Initial
COLOR(SAYBOLT) 4 weeka 8 weeka 12 weeks
BbE./ton A DATA Sweet Blend
75
Sweet Blend
1000
30 30 30
Sour Sweet Blend )
1500
30 30 30
1
+++
++ +
Sweet Blend
\
I
2400
30 29 30
Sweet sour Blend
I
3250
30 30 30
I\
4650
30+ 30
Sour
SOW
Sweet Blend
Sour I sweet
i
Sour I Sweet
i
30+ B DATA 105
680
Sour ) Sweet
1
1 Sweet ( sour
1860
2400
4100
3
Sweet sour
F i
6100
30 20 25
28 15 20
26 9 18
1000
30 17 18
27 15 15
25 14 14
17 16
20 17 18
20 20 16
2400
25 14 17
24 16 16
21 15 12
I
3250
1
22 16 23
21 16 20
21 15 20
4650
25 10 16
22
16
22 15 15
30+ 30 2s
30 28 26
28 29 27
I
Sour Sweet Blend
1\
22 26 25
25
22 30 11
Sour
1
26 22 27
24 22 20
19 15
..
E3$
22 23 28
22 23 23
16 20 18
Sour Sweet Blend \
22 23 24
15 19 21
17 19
..
25
27
27
27
27
27
30
25
22
28
30
26
26
23
29
25
22
23
130
26
26
28
1 30
27
27
25
130
26
25
24
27
26
27
25
23
23
23
25
25
25
26
27
25
30
28
25
22
330
27
24
22
4800
75
Sweet Sour Blend
26
30
{
3 hours
28
30+
the contact time was only 23 seconds, the shortest contact time of any known commercial installation, whereas under conditions of the B data, the contact time was 151 seconds. These data, however, become more significant when it is recalled that the rpaterial treated in the B data was cracked a t a higher temperature, and presumably would he more difficult to treat than the Cross-cracked product of the A data. These conditions indicate quite strongly that, while rate of treatment and clay usage are important items affecting the character of the treated product, the type of stock and cracking conditions under which it is produced also play an important role in determining the character of the treated materials.
; : 2 i' /
Sour
Sour Sweet Blend
680
Sweet
f
Sour
1860
2400
Sweet
Sour Sweet
1500
105
Sweet
Sour Sweet
i/
Sweet!
COLOR(SAYBOLT) 2 houri
27 30 30
30
Initial
1 hour -
29 26 30
30
Sweet
Sour Sweet
++
SAMPLE YISLDFROM CLAY BbUton
4100
6100
18
+
9
27
27
28
25
24
28
27
23
29
29
27
28
25
22
28
21
21
27
23
22
27
23
22
27
27
22
26
23
21
20
28+
26
26
30
26
24
are of about the same order of stability as the sweet-cracked stock. This is in line with other findings that a virgin stock of a given degree of stability, when blended with a cracked stock of a given stability, yields a product, the stability of which in sunlight is of a lower order than either component tested individually. The interpretation of the sunlight stability data is facilitated when the correlation between the quart-bottle test and visible bowl is known. This correlation has been firmly established. By means of numerous tests it has been found that about 8 hours of exposure in a visible bowl are required to obtain the same color degradation as is obtained in 1hour of exposure in the quart bottle when conducted as described above.
OXIDATIONSTABILITY COLORSTABILITY IN SUNLIGHT Table N gives the data showing the effect of yield from clay on the sunlight color Stability on both sour and sweet materials. It will be noted for the A data that sweetening has a deleterious effect on sunlight stability for very low clay yields, as noted above. It has been rather general experience that laboratory sweetening must be carried out with extreme caution, and that even then the sweetened product is often of lower stability than the same material sweetened on plantscale equipment. I n general these two sets of data when compared again seem to indicate the beneficial effects of treating a t higher pressures with higher resulting temperatures and longer contact time. With regard to the sunlight color stability of the blends, it will be recalled from data on dark-storage stability that the blends were more stable than the straight-cracked product. However. in the case of sunlight stability the blends (A data)
The data on relation of induction period to clay yield or usage are shown graphically in Figure 2. As indicated earlier in this paper, these data were all secured on sour stocks. In each case the induction period is quite high during the early life of the clay when, it will be recalled, color stability is also a t its maximum, Associated with these effects and decreasing with clay usage are found: (a) temperature rise of the vapors passing through the clay (being as much as 30" to 40" F. during the very early life of the clay); (a) quantity of material in the polymer fraction boiling above a certain temperature-i. e., 600' F.; and (c) iodine number of this heavy material. As the amount of distillate treated.per ton of clay increases, the i:nduction period decreases until a t a yield of 5000 to 6000 lbarrels per ton of clay the induction period of the product i s virtually the same as the untreated material. I n other vords, the clay ceases to affect the induction period of the matcyial undergoing treatment, even though
October, 1934
INDUSTRIAL AND ENGINEERIKG CHEMISTRY
the product is still of 30+ color and the polymer fraction continues to show that polymerization is still taking place. In the case of the A data numerous samples were taken by bypassing the clay tower so as to produce an untreated material identical in distillation properties, etc., except for the claytreating step. The average induction period of this material was found to be 253 minutes. This point is noted in Figure 2 by a horizontal line appropriately marked for comparison with its respective curve based on the relation of induction period to clay usage Samples taken a t various times during the life of the clay were set aside to obtain data relating to gum formation with time of storage. Dissolved gum was determined by method A of the American Society for Testing Materials (Table V). TABLEV. GUM STABILITY ON S T O R ~ G E SAhiPLE
E
!
DP
ss
(Air present; average temperature, 75' F.) --GUM CONTENT (mg./100 cc.@)--CLAY Initial 3 months 6 months 9 months BbZ./ton I N QLASS BOTTLES
A.
1.8
Sour / Sweet h Blend \
1.0 0.0
c
samples in Table VB are over 10 mg. per 100 cc., and these values were obtained after 6 months of storage. The unclayed stock required only slightly over 2 months for the formation of 10 mg. of gum per 100 cc. under identical conditions of storage.
Y I E L D FROM
Sour ) Sweet Blend (
-Sour Sweet Blend
1043
0.4
1274
Sour / Sweet Blend \
2000
Sour sweet Blend )
1
3730
Sour 1 dweet Blend (
3900
1.0 0.2 0.0
1.0
0.6
0.0
0.2 0.0
1.0 0.4
0.2
0.2
0.2 0.2
0.6 0.2 0.2
0.6 1.6 0.6
7.4
0.0 0.0 0.0
0.8
0.6 1 .o
2.6
1.4
1.2 0.6 0.0
6.8
5.6 6.0 0.8
2.6 0.8
1.6 5.6 5.0
0.6 0.0
1.0 0.4 0.0 B.
?.O (1.4 0,0
0.2
--
... ...
0.6
0.6
82!f
...
0.4 0.0
1.2
(I . 2
1.2
(1.4
2.0 6.0
2.2 2.0
10.0 4.2 2.8
IN T I N CANS
GUM CONTENT (mg./100 C C . ~ ) 2 months 4 months 6 mont,hs 12 months
YIELDFROM CLAYInitial Bbl./fon 2.0 3.: 0.8 2.8 90 9.8 7 .I: 789 0.8 4.0 4.0 11.4 ' 1284 1.0 2.8 3.0 6.6 2020 0.8 0.4 4.E. 1.6 1.4 3.6 3441 6.0 10.0 4852 1.0 3.6 50.0 22.0 Unolayed stock 2.0 8.0 a 1 mg. per 100 cc. = 1.34 ounces per 1000 gallons.
.
8.8
9.4 21.8 6.6
11.4 17.6
283.0
In the case of the A data no figures are available on unclayed material comparable to the clayed stock, since facilities for by-passing the clay tower were not available a t the time these data were obtained. I n general, Table VA shows that the tendency to form gum increases as the yield from clay increases. The sweetened samples, in general, appear to be more gum stable than do the sour samples. The effect of the virgin stock is c1earl.y shown by the blends, the rate of gum formation being much lower in the case of the blends. The data in Table VB include no figures on sweetened stocks for reasons noted above. Data for the uriclayed stock show quite a rapid rate of gum formation in storage. However, in comparison to the unclayed stock, the clay-treated samples all exhibited a much lower rate of gum formation. While such gum formation was more pronounced in the case of these samples than those in Table VA, i t must again be recalled that the distillate used in the B data was more severely cracked than the Cross distillate used in the A data and hence would presumably be a more unstable, gumforming material. Furthermore, it is well known that can storage is more severe than glass storage. While these data are somewhat more erratic, the tendency for gum formation on storage is shown. Somewhat less pronounced is the relation between the tendency to form gum on storage and yield from clay. It should be pointed out, however, that only four
rmouwur
BBLS ~ P J N
FIGURE2. RELATION OF INDUCTION PERIODTO CLAYYIELD
In connection with oxidation stability of clay-treated stocks, it should be pointed out that these stocks respond very well to the use of oxidation inhibitors. Using one of the most effective ones known, p-benzylaminophenol (commercially available and known as B. A. P.), results,are obtained of which the following is typical: A sample of cracked gasoline used in the A data, having an original induction period of 215 minutes, was sweetened and treated with 0,001 per cent by weight of B. A. P. The resulting induction period was 520 minutes. This indicates an excellent response to the use of this inhibitor. No data were secured on either set of samples to show the effect of clay treating on copper-dish gums. Data on other installations where copper-dish gums were secured show that, in general, clay treating gives a product of low gum values by this test.
EFFECTO F COLOR STABILIZERS I N CLAY-TREATED STOCKS Table IVA showed that sweetening, particularly laboratory sweetening, resulted in somewhat decreased sunlight color stability. It has been found by Sorg (4)that butyl and amyl amines in small concentrations are quite effective in improving this property of a gasoline. Since production of a 3O-color gasoline up to a high yield from clay is a n easy matter, the application of these color stabilizers offers a ready means for securing additional color stability. Some typical data are given in Table VI. These data show the effectiveness of these substances in a clay-treated product and indicate the possibility of realizing higher yields from clay while sustaining desired color stability. TABLE VI.
EFFECTOF AMIXESON COLORSTABILITY OF CLAYTREATED CR.4CKED GASOLINE
GASOLINE
YIELD CLAY
FROM
COLORAFTER HOUR EXPOSURE Blank +0.00379 amyl amine
Bbl . / t o n
19 19 19
19 17 Blend of clay-treated cracked and straight-run (sweetened)
COLORAFTER
.. .. ..
20 23
17
28 23 22 22
++
21+ HOUR EXPUWRE 23 26 f 20
COLORAFTER 3 - H o c ~EXPOSURE 18 23 16 25 14 22
INDUSTRIAL AND ENGINEERING CHEMISTRY
1044
ACKNOWLEDGMENT The author wishes to acknowledge the assistance of H. H. Thompson and L. V. Sorg, who aided in the gathering of data herewith presented. Thanks are also due Mr. Sorg for the drawings.
LITERATURE CITED (1) Am. SOC. Testing Materials, Proceedings, 32, 407 (19.32) (2) Gray, T . T . , U. S. Patents 1.340,889 (1920); 1,759,812, 1,759,813,
Vol. 26, No. 10
1 , 7 5 9 , 8 1 4 (1930); 1,853,671 (1932) ; 1,908,599 (1933); Mandelbaum, M. R., paper presented before World Petroleum Congress, July, 1933; Cooke, M. B., and Hayford, A. W., Refiner & Natural Gasoline M f r . , 13, 83 (March, 1934). (3) Rogers, Bussies, and Ward, IND.ENQ.CHEM.,25, 397 (1933). (4) Sorg, L. V., paper presented before Division of Petroleum Chemistry a t Twelfth Midwest Regional Meeting of Am. Chem. SOC., Kansas City, Mo., May 3 t o 5, 1934. RECEIVEDMay 25, 1934. Presented before the Division of Petroleum Chemistry at the Twelfth Midwest Regional Meeting of the American Chemical Society, Kansas City, Mo., May 3 to 5 . 1934.
Liquid Film Heat-Transfer Coefficients in a Vertical-Tube Forced-Circulation Evaporator L. A. LOGAN,'N. FRAGEN, AND W. L. BIDGER,University of Michigan, Ann Arbor, Mich. Film heat-transfer coeficients f o r liquids in forced convection through 8-foot, 0.75-inch i. d., vertical copper tubes hare been measured directly in a semi-commercial evaporator and correlated within *10 per cent by means of the following dimensionless equation:
hD/k
=
properties of the liquid, and an equation for liquid film coefficients based on the physical properties has been found to have wide application. Consequently this investigation was conducted for the purpose of obtaining a correlation of the liquid film coefficients in evaporators by means of an equation involving the physical properties of the liquid being evaporated.
0.0205 (Dup/p)O (C,u/k)O
This equation applies with the aboiie accuracy between the following limits: Reynolds' number, 7500 to 250,000; Prandtl's number, 2 to 50; liquor inlet velocity, 7 to 17 feet per second: riscosity, 1 to 20 pound-7 per hour per foot.
T
HE available data on heat transfer through liquid
films deal almost entirely with nonboiling liquids. Some information may be found in the literature concerning liquid film coefficients for boiling liquids. The latest contributions in this field were made in 1931 by Jacob and Fritz (5) and in 1932 by Cryder and Gilliland ( 3 ) . Linden and hlontillon ( 7 ) also measured the individual film coefficients in an inclined-tube natural-circulation evaporator. Both of these investigations showed that with natural circulation the values of the liquid film coefficients increase with increases in temperature drop. There is also considerable information available on over-all coefficients in evaporators. Badger and Shepard (1) and Linden and Montillon (7') found that over-all coefficients increased with increased boiling temperatures. Claassen ( 2 ) and Kerr (6) studied the effect of the concentration of boiling sugar solutions on the over-all coefficients and found that an increase in the percentage solids caused a decrease in the coefficient. It is probable that the changes in over-all coefficients with changes in boiling point and concentration are due mostly to the effect of these variables on the liquid film coefficient. The earlier investigations of heat-transfer coefficients in evaporators expressed the changes in the coefficient in terms of the previously mentioned variables-namely, temperature drop, boiling point, and concentration. Expressions involving these variables limit the application of the results obtained to the particular liquid being evaporated. A change in the variables causes a change in the physical 1 Present address, Union Carblde and Carbon Research Laboratories, Inc , Long Island City, New York.
TO STORACE
FIGURE 1. E V A P O ~ A AND T O RFLOWSHEET 110-gallon feed tank with heating cojl 2. Belt-driven centrifugal feed pump 3. Kinney positive pressure circulatinn DumD 4. Main bo& of evaporator 5. Surface condenser 6. Jet condenser 7. Wet vacuum pump 8. Upper section of heating element 9. Lower section of heating element 10. Asbestos insulation 1.
11.
12. 13. 14. 15.
16.
A.
B. C.
Twelve capper tubes 8 feet long. eleven tubes '(8 inch 0.d.,'16 B.W. G . (Birmingham wire gage) wall: one tube 1 incho. d . , 11 B. W. G. wall, Steelshell around upper casting Steam baffle Sampling tube Steam drip tanks Overhead drip tanka Vacuum manometer with arrangementa for automatic oontrol Pressure drop manometer Steam pressure manometer
