PRODUCT AND PROCESS DEVELOPMENT earlier workers, who obtained a sealed tube melting point of 343" (6). The oxidation was usually terminated when roughly 40 to 50% of the hydrocarbon had been converted to acid. It was observed that the oxidation rate often tended to decrease a t about this conversion level and was not accelerated by the addition of more catalyst. I n order to obtain complete oxidation of the alkylaromatic hydrocarbon, it was, therefore, necessary to remove the acidic oxidation products and recycle the remainder. I n the case of high-melting crystalline acids, this can be done by crystallization a8 well as by alkaline extraction. The crystallization-recycle system was employed for the oxidation of p-tert-butyltoluene in order to obtain information as to the ultimate yield of products. The hydrocarbon was treated with oxygen a t atmospheric pressure in the stirred flask reactor for 18 hours a t 135' C. in the presence of 0.25 weight yo cobalt naphthenate. Six cycles were completed in which the crystalline acids were removed by filtration and washed with make-up tert-butyltoluene. The filtrate was recycled without adding more catalyst. The crystals were washed with petroleum ether and dried in vacuo. The tert-butylbenzoic acid prepared in this manner melted sharply a t 164.5' C., but was found to contain a small amount of terephthalic acid (less than o.570). This could have been removed by filtration of the hot solution before crystallization of the major product. The acid was recovered from the final filtrate by alkaline extraction, which also saponified any ester present. This acid was recrystallized from isooctane. Approximately 75% was recovered in the first crystallization and melted substantially a t the melting paint of p-tertbutylbenzoic acid. The balance melted considerably lower (110' and 89' C.) and was assumed to be a mixture of m- and ptertbutylbenzoic acids. This experiment showed that the yield of p-tert-butylbenzoic acid under these conditions was 86 mole yo,while an additional 3% was indicated to be m-tert-butylbenzoic and 0.57, terephthalic acid. Other products present in small quantities were formaldehyde, formic acid, acetaldehyde, acetone, twl-butyl alcohol, and p-tert-butylbenzaldehyde.
c.
fert-Alkylaromatic acids have many potential applications
A wide variety of tert-alkglaromatic acids can be made available by the techniques of alkylation followed by catalytic oxidation. p-tert-Butylbenzoic acid, which has been studied more intensively than the other members of the series, has established a place for itself in the field of plastics and resins. It is used as a modifier and regulator of air drying and baking alkyd resins, for the preparation of mono- and polyesters having properties ranging from liquids to brittle resinous solids, for the preparation of metal salts, and as a means of preparing derivatives previously not readily obtainable via the currently available commercial acids. I n general, the derivatives of p-tert-butylbenzoic acid are characteristically higher in melting point, and have bett,er hydrocarbon solubility and improved resin and oil compatibility, greater color stability, increased hardness, and less thermoplasticity as compared to derivatives of benzoic and rosin acids (9). Acids containing a larger tertiary alkyl group or a tertiary alkyl group in the meta position form derivatives which are in general more soluble in hydrocarbons. The sodium salts of acids of higher molecular weight, such as dodecylbenzoic acid, have detergent properties similar to the aliphatic carboxylates, but these are subject to the same limitation as to calcium tolerance (9). Still another group of chemical intermediates may be made by aromatic ring reactions of tert-alkylbenzoic acids. The principal factors governing these reactions will be the deactivating effect of the carboxyl group and the steric hindrance of the tertiary alkyl group. Further potentialities of industrial application of tert-alkylbenzoic acids are still in the developmental stage. Literature cited
Baur-Thurgau, A., Ber., 33, 2569 (1900). Hearne, G. W., Evans, T. W., and Ruls, V. W.(to Shell Development C o . ) , U. s. Patent 2,578,654 (Dee. 18, 1951). Kreysler, E., Ber., 18, 1709 (1885). Rlittan. R.. U. S. Deut. Commerce. O.P.B. 565 (1945). Nightingale, D., Ridford, H. D., and Shanholtzer, J . Am. Chem. Soc., 64, 1664 (1942).
Palmer, R. C., and Bibb, C . H., U. S. Patent 2,302,462 (Nov. 17, 1942).
Senseman, C. E., and Stubbs, J. J., IND.ENG.CHEX.,24, 1184 (1932).
Serijan, K. T., Hipsher, H. F., and Gibbons, L. C . , J . Am. Chem. Soc., 71, 873 (1949).
Shell Development Co., unpublished data. RECEIVED for review April 28, 1955.
ACCEPTED August 17, 1955.
Split-Treatment Softening of Water J.
R. ROSSUM
California W a f e r Service Co., Sun lose, Calif.
T
HE split-treatment modification of lime-soda water softening offers very considerable advantages over conventional treatment. At Ann Arbor, Mich., split treatment is reported by YIcEntee (5) to have produced a satisfactory effluent using only 80% of the amount of lime required for conventional treatment and at Cedar RapidB, Iowa, Cherry ( g ) reports a saving of $14,000 annually. It is the author's belief that the general lack of appreriation of the benefits of split treatment stems, in part, from the absence in the literature of a mathematical analysis of the chemistry involved and, in part, from the fact that it is not applicable to all raw waters. The following development of formulas for split treatment requires the selection of criteria for a satisfactory effluent. Larson (4)has stated that a good effluent should have an alkalinity of a t least 50 p.p.m., a pH of from 8.2 to 8.5, and a slightly positive saturation index ( 3 ) . For the purpose of this paper, this statement may be simplified to specify that the effluent should have a pH, not exceeding 8.4. Split treatment automatically produces a water with a positive saturation index, and establishing an November 1955
upper limit on pH, ensures that the alkalinity will be reasonably high, for otherwise the calcium hardness will be excessive. Other values for pH, may be required, depending upon the quality and temperature of the raw water ( 4 ) . The following formulas are developed so that any pH, value from 8.0 to 9.2 may be selected. All concentrations and chemical dosages are expressed in terms of equivalent calcium carbonate in milligrams per liter (parts per million). The subscripts e, 1, and r refer to the effluent, treated portion, and raw water, respectively, as indicated in the flowsheets (Figure 1). The fraction of raw water bypassed is designated by X , the fractionof the water bypassing zeolite is designated by Y , and the fraction of water treated with zeolite is designated by 2. A and B differentiate the calcium carbonate precipitated before and after mixing with the bypassed portion. Equilibrium constants are the same as those used by Caldwell and Lawrence ( I ) , a t 25' C. and an ionic strength of 0.01. For use a t other temperatures and other values of ionic strengt h, the appropriate values should be substituted.
INDUSTRIAL AND ENGINEERING CHEMISTRY
2313,
PRODUCT AND PROCESS DEVELOPMENT attainable by the split-treatment modification of the lime-soda process is given by Equation 7 when
When lime is used to remove some magnesium
~
~~
F1 [(HC03-), 4 M g +)r
(HCOa-).
~
+ (COd, + (OH-)tl
(8)
+
split-treatment softening offers
Over the range of effluent pH values considered
. . . reduced lime consumption . . . improved water quality
Fz (A1ky)s
(HCOs-),
(9)
where Fz is a function of pH, because ovei this p H range both ( H + ) and (OH-) are negligible. The expression for soda ash required,
compared with conventional limesoda methods
l\;azC03 = (Alky)e - (Alky),
+ (Hard), - (Hardh
(10)
is valid for split treatment as well as conventional treatment. Combined with Equation 9, this equation becomes:
XazCOs = (HCOa-)B/F2 - (Alky),
Development of equations requires selection of criteria for effluent The chemistry of split treatment requires that the hydroxyl ion concentration in the treated portion of the water be large enough to precipitate essentially all the magnesium therein and the development of the equations assumes no further magnesium precipitation after the bypassed portion is combined with the treated portion. The minimum practical hydroxyl ion concentration in the treated flow is about 50 p.p.m., equivalent to a p H of approximately 11.0. If equilibrium at this hydroxyl concentration weie attained, the magnesium concentration would be approximately 5 p.p.m., but in practice it is somewhat greater. Jar tests, as well as plant experience, indicate that the error involved in the assumption of complete magnesium precipitation in the treated portion is satisfactorily compensated by slight magnesium precipitation which occurs after mixing, so that the effluent magnesium is reasonably well expressed by Equation 1.
(Mg++), = X (Mg++),
+ X (C0z)r - (1 - X) (OH-)t
(11)
If treatment without soda ash is contemplated] the righthand side of Equation 11 is equal to 0 and the resulting equation can be solved simultaneously with Equation 7 to give an expression for the hardness obtained b y treatment with lime only. (Hard), =
B
+ d B 2 + 4 AC
(12)
2A
where
(1)
The effluent quality standards previously discussed require that .the effluent contain appreciable bicarbonate ion concentration, .as even at p H 9.2 the ratio of carbonates to bicarbonates is less khan 1. It follows, then, that the sum of the carbon dioxide and fhe bicarbonates in the bypassed portion must be greater than khat required to neutralize the hydroxyl ion in the treated porfion : ((HC03-), = X (HCOg-),
+ (Hard), - (Hard),
(2)
Values of F 1 and F z for various p H values are given in Table I. Lime dosage can be computed as in conventional treatment
Ca(OH)t = (HC03-),
+ (Cod, - (HC03-). + (1
- X ) (Mg++)i
(13)
or it can be computed in terms of the hydroxyl ion in the treated portion.
o r rearranging: (3)
It has been shown (5)that a t equilibrium
The calcium concentration of the effluent can also be computed by considering the material balances.
+ CaC03.4 + C a C 0 3 ~(15) + 2(1 - x)(HCOa-)r ( I - X ) (COS--)' (16) CaCOas = X(COz), + 2X(HCOa-), + (1 - X ) (COa--)t 2(HC03-), - (co3--)e + N a ~ C 0 3 (17) (Ca++),
CaCOsa
(5) where F1 is a function of the pH. As hardness is the sum of calcium and magnesium, it follows Erom Equations 1 and 5 that
+ Ca(OH), (1
=
(Ca++):
- x) (coz),
The solubility product of calcium carbonate is (Ca++),
= 100
(18)
Combining Equations 15, 16, 17, and 18 and solving for calcium:
If lime-soda treatment is contemplated, the right-hand sides of :Equations 3 and 6 aan be equated t o give:
(Ca++), where D = (Ca
By making th fiwt derivative of (Hard), with respect to ((HCOZ-)~ equal to 0, it &anbe shown that the minimum hardness
,2314
+ +)?
d D2 a
+ 400
+ Ca( OH)z - ( COZ)?2(HC03-), + 2(HC03-), - NazCOa
Equation 19 can be used in calculations where prior computation of the pH of the effluent is inconvenient.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 41, No. 11
PRODUCT AND PROCESS DEVELOPMENT using the water-conditioning diagram of C a l d w e l l a n d Lawrence (1). The formulas a p p l y e q u a l l y well t o under- or s u p e r s a t u r a t e d waters. For lime softening, the (Ca+ +h (Ma' "1, (HCOT), (CO2)r
bo,co,] t
(Ca++)e (Mg++Ie
(Caf')
(c03*).
(Mg++) (HCOa-)
(Hc 03-)e
fraction
-
(Ca+ +I (OH-)
The equations for the lime-zeolite process are derived in a manner similar to those for the lime and lime-soda processes. The equations developed for lime apply t o the flowsheet shown in Figure 1, c, provided only that (Ca++),, (Mg++)r,and (Hard), are multiplied by the factor Y . Equations 1, 4, 5 , 9, and 18 apply to the flowsheet shown in Figure 1, d. Equation 2 then becomes (HCOs-1,
=
(X
+ Z ) (HCO,-)r +
(X
+ 2 ) (COz), - (1 - X
-
2 ) (OH-),
p
250
hardness attainable by split t r e a t m e n t , t h e minimum value of 50 p.p.m. is selected for (OH-)$. Assuming that the pH. required for the effluent is 8.4, it is
(cl Lime-zeolite softening
(Co(0H)d
= 150 = 100
(20)
t -
stituting t h e s e v a l u e s i n Equation 12, it is found that the minimum effluent hard-
CO++lS .t?ig++,. (HCO-Ic 4COV1,
t h e c a l c i u m 39:5 f r o m Equation 5, the magnesium 34.4 by subtracting calcium from hardness, the fraction to be bypassed 0.344 from Equation I, and the lime required 297 p.p.m. from Equation 13 or 14. If the value of (OH-), is increased to 100, it will be found upon repeating the above calculations that (Hard), = 80.4, (Allcy)d = 80.4, (HCOa-), = 77.6, (Ca++), = 36.3, (Mg++), = 44.1, X = 0.441, and Ca(OH)2 = 281. Although the hardness has increased only 6.5 p.p.m., the lime required has decreased 16 p.p.m. Calcium soaps are more insoluble than magnesium soaps, so that the harder water might appear to be softer and hence more satisfactory to the domestic consumer.
Or
(OH-)t = Table 1.
Values of Constants F1 and FZ for Various Values
of PH, Equation 10 becomes (Hard), - (AlkylL - (1 - 2)(Hard),
+ (Alky), = 0
(22)
pHa
FI = KsKi/(H+)
8.0 8.2 8.4 8.6 8.8 9.0 9.2
7080 4467 2818 1778 1122 708 447
Fz
=
1/[1
+
(H+)/KII
0.9861 0.9781 0.9657 0.9468 0.9106 0,8762 0.8171
FI/Fz 7180 4567 2918 1878
1232
808 647
Equations 13 and 14 become, respectively,
+
Ca(OH)z = (HCO,-), (COZ), (HC0,-), (1
+
-
X - 2 ) (Mg"),
(24)
and Ca(OH)2 = (1
-
X
- 2) [(HCO3-),
+ +
i- (CO,), (Mg++I7 (OH-)tl
(25)
Equations were tested with hypothetical raw waters
To illustrate the use of the foregoing equations, hypothetical raw waters saturated with respect to calcium carbonate have been chosen to simplify comparison of the results with thobe obtained
November 1955
The water-conditioning diagram of Caldwell and Lawrence ( I ) has been used t o determine the chemicals necessary to produce the same quality of effluent by conventional treatment. It is found that a lime dose of 369 p.p.m., followed by recarbonation with 89 p.p.m. of carbon dioxide, is required to produce a water having a hardness of 80 p.p.m. a t a pH, of 8.4. Split treatment represents a savings of almost 25% in lime and completely avoids recarbonation. It is interesting to observe the changes in composition of the effluent a t a constant lime dosage while the fraction bypassed is varied. To do this, (OH-), is computed for different values of X from Equation 14, (HCOI-), from Equation 2, (Caf+). from Equation 19, (Mg++)dfrom Equation 1, and pH, from Equation
INDUSTRIAL AND ENGINEERING CHEMISTRY
2315
PRODUCT AND PROCESS DEVELOPMENT ~
I
I
I
0.1
0.2
I
I
,
0.4
0,5
*'Or
00.0
0.3
Fraction
Figure 2.
0.6
0.7
08
0.9
1.0
bypassed
Relation of composition of effluent to fraction bypassed
4. The results of these calculations for the above water with a lime dosage of 281 p.p.m. are plotted in Figure 2 as dashed lines. The solid lines in Figure 2 are plotted for the same conditions as the dashed lines, except that the points were obtained graphically from the water-conditioning diagram of Caldwell and Lawrence ( I ) . The composition of the treated portion of the water was determined according to the directions given (1). The composition of effluent was found to lie on the straight line connecting the points representing the composition of the treated portion and the point representing the raw water. The ratio of the distance between points representing the effluent and the treated portion to the total length of the line is the fraction bypassed. The locus of the effluent composition is a straight line in the Mg++ direction from the point of 0% bypass. The shape of the solid curves indicates that identical results could be obtained a t two different values of fraction bypassed. This would be true if equilibrium were attained, but on the left of the calcium maximum, equilibrium conditions are more difficult to reach than on the right-hand side. I n operating to the right of the calcium maximum, the higher pH values result in better magnesium floc and a smaller fraction of the water is treated, so that appieciably smaller treatment facilities are needed. The dashed lines are practically coincidental with the solid lines over the range where split treatment is useful. I n general, the results obtained with the equations developed herein are in good agreement with those obtained by the graphical method of Caldwell and Lawrence ( I ). To illustrate the use of the equations for lime-soda treatment, the following raw water analysis may be considered:
-
C a + + = 200 M ++ 200 H8Ot = 250 COz = 70 pH 7.16
2316
~~
If the required effluent pH, is 8.4,the softest water that can be obtained from lime alone by split treatment will be 172 from Equation 12, by setting (OH-) equal to 50. Using lime-soda treatment, it is found from Equation 8 that minimum hardness will occur when the bicarbonate is 72 p.p.m. Substituting this value in Equation 7, the minimum obtainable hardness is found to be 105 p.p.m. The alkalinity from Equation 9 is found to be 75 p.p.m., and the soda ash dose from Equation 10 is 120 p.p.m. Calcium, magnesium, lime dose, and fraction bypassed are found, as for lime-only treatment, to be 39, 66, 382, and 0.330, respectively. Using this same raw water analysis to illustrate the use of the equations for lime-zeolite treatment as shown in Figure 1, d, the effluent may be assumed to be required to have a hardness of 80 p.p.m., an alkalinity of 80 p.p.ni., and a pH, of 8.4. The bicarbonate and calcium concentrations are found to be 77.3 and 36.5, respectively, from Equations 9 and 5 . Magnesium is found to be 43.5 by subtracting the calcium from the hardness. The fraction bypassed from Equation 1 is found to be 0.218. The fraction treated with zeolite is found from Equation 23 to be 0.375, and (OH-), from Equation 21 is found to be 276. If this value were less than 50, split treatment could not produce the required water and calculations would have to be repeated with a higher effluent hardness or a higher alkalinity. The lime dosage from either Equation 24 or 25 is found to be 325 p.p.m. Table I1 shows the effect of varying the selected alkalinity on the above calculations. From left to right, the cost of treating the water would increase because less hardness is removed by lime and more by the relatively expensive zeolite process. The quality improves from left to right from the standpoint of red water because of the increase of alkalinity, and from the consumer's standpoint because of the lower Ca + +/Mg + + ratio. Smaller facilities for lime treatment are required for effluents on the right-hand side of the table, but this is more than offset by the increased size of the zeolite unit required. It is evident from the chemistry of split treatment that it is applicable only when lime is used to remove part of the magnesium. If the concentration of magnesium in the raw water R i small enough, removal of magnesium will be unnecessary. In that event, it will be found from the above equations that all the water should be bypassed, so that the result is identical with conventional treatment removing calcium only. On the other hand, if the concentration of magnesium in the raw water is extremely large, it may be found that split treatment cannot produce a satisfactory effluent without resorting to the lime-soda or limezeolite modifications, when conventional treatment may produce a satisfactory effluent using lime only.
Table II. Comparison o f Effluent Analyses with Variations in Lime-Zeolite Process to Produce Water o f Constant Hardness and pH, with Varying Alkalinity Hardneas Alkalinity PHI Calcium Magnesium (HCOa-) e
X
Z
(OH -)r Ca(0H)z
80
80 80 80 60 80 90 70 8.4 8.4 8.4 8.4 36.6 32.4 48.6 41.6 43.5 47.6 31.4 38.4 77.3 86.9 57.9 67.6 0.035 0.108 0.157 0.192 0.218 0.238 0.375 0.400 0.325 0.350 0,275 0.300 276 324 186 231 87.8 139 324 305 344 390 366 419 80 40 8.4 73.0 7.0 38.6
80 50 8.4 58.4 21.6 48.3
Composition of effluent may differ from that computed
I n practice, the composition of the effluent will usually differ from that computed by the foregoing equations. The major causes of difference are reactions of ions other than those considered, and failure of the water to reach equilibrium. Many of the ions normally present in water or added as coagu-
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47,No. 11
PRODUCT AND PROCESS DEVELOPMENT lants will react with lime. Some of these, such as iron, will react stoichiometrically and the equations may be modified to include these ions. For example, iron(I1) in the raw water will normally be oxidized and mill precipitate as ferric hydroxide. This reaction will be essentially complete, and the equations may be changed to provide for the reactions of iron in those waters where its concentration is great enough to require this refinement. Aluminum and manganese can be handled in the same manner. It is not practical to produce a lime-softened water in equilibrium with calcium carbonate, nor, indeed, is it desirable to do so. As in conventional lime softening without recarbonation, split treatment will produce a water supersaturated with calcium carbonate, so that both the calcium and the alkalinity will be greater than the concentrations computed from the equations. Unlike conventional treatment, split treatment will produce a mater undersaturated with magnesium hydroxide. The mixture of raw water and overtreated water produces a metastable water highly supersaturated m-ith calcium carbonate. Very little precipitate will settle from this solution in conventional settling basins, but in solids contact units, the water rapidly reaches a reasonable degree of stability. Unless prior contact with calcium carbonate is provided, most of the supersaturated calcium carbonate will be removed by precipitation on the filter sands, causing a significant increase in effective size. According t o Myers ( 6 ) ,this should not cause operating difficulties.
The author has had the opportunity of comparing split treatment with conventional treatment in the South Basin Treatment Plant operated by the California Water and Telephone Co. as a supply for its San Diego Bay Division. Substantial savings in lime resulted from using split treatment, as well as a noticeable improvement in effluent quality. Acknowledgment
The author gratefully acknowledges the assistance of Primo Villarruz, California Water Service Co., in checking the accuracy of the manuscript and helpful suggestions from W. F. Langelier, University of California, T. E. Larson, Illinois State Water Survey, and Richard Pomeroy, Pomeroy and Associates. literature cited (1) Caldwell, D. H., and Lawrence, W B., IND. ENG.CHEM., 45, 535 (1953). (2) Cherry, A. K., J . Am. Water Worlcs Assoc., 47, 393 (1955). (3) Langelier, W. F., Ibid., 38, 169 (1946). (4) Larson, T. E., I b i d . , 43, 664 (1951). (5) RfcEntee, H. E., Ibid., 32, 1600 (1940). (6) Myers, H. C.,I b i d . , 31, 1045 (1939). RECEIVED for review February 28, 1955.
ACCEPTEDJune 11, 1955.
Fractional Carbonization of Wyoming Noneoking Coals EDWARD PROSTEL
AND
NEAL RICE
Nafural Resources Research Inrfitufe, University o f W y o m i n g , l a r o m i e , W y o .
I
NVESTIGATIONS pertaining to the carbonization of coal have been motivated overwhelmingly, at least in the United States, by the requirements of the coke oven industry. The reactions taking place in the coke oven are complicated by the fact that products of decomposition are heated beyond the temperature of formation, and altered before they are extracted ( 1 ) . I n most low-temperature carbonization, the coal is heated gradually, and the products of decomposition are removed without, or with little, further heating. The difference is one of degree, and the extremes may be characterized by slowly carhonizing a coal in a stream of nitrogen, or by using the Bureau of MinesAmerican Gas Association method (9). If the BM-AGA method is used, carbonization a t a comparatively low temperature yields a maximum of tar, and a t a comparatively high temperature yields a maximum of gas. For any method of carbonization, where the coal is heated gradually and products of decomposition are removed before secondary reactions can take place, the yield of tar will increase with increasing temperature, until all tars are removed; with further rise in temperature products will be gas exclusively. It may be worth while to consider the historical development of carbonization ( 2 ) . The coking industry was developed primarily for the production of coke and gas, and processed only coking coal. Independently, a charring industry was developed in Europe processing noncoking coals mostly for the production of primary tars (6),and employing processes radically different from those of the coking industry and operated a t much lower carbonization temperatures. For this reason, the charring procNovember 1955
esses were referred t o as low-temperature carbonization and the coking processes as high-temperature carbonization. In recent years a number of charring processes have been modified for the production of low-volatile char. They employ a comparatively high retort temperature ( 7 , 9), in some cases higher maximum temperatures than are customary in the coking industry. It may be desirable to avoid the terms “high-temperature carbonization” and “low-temperature carbonization” to refer t o the coking processes as coking, and to designate as charring the process whereby volatile matter gradually evolves with a minimum of secondary reactions. Fractional carbonization gives information on products from coal
The University of Wyoming is confronted with the task of furthering the utilization of noncoking coals which are available in abundance within the state. There exists a certain demand for char, for tar, and for gas, but it is not easy to reconcile the processing costs with the revenue obtainable. Present knowledge of carbonization does not give enough information on the combination of products obtainable from various coals. Volatile matter and tars vary with retort temperature and operating conditions. With lower carbonization temperature less of the volatile matter is evolved than with higher carbonization temperature, and the more gently the heat is applied to induce the carbonizing process, the less secondary reactions may be brought about.
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
2317
