ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT (19) Mills, G. A., Heinemann, H., and associates, IND.ENQ.CHEM., 45, 134 (1953). (20) Minachev, Xh. M., and associates, Izvest. A k a d . Na'auk S.S.S.R., OtdeE. Khim. iVauk, 1952, No. 4, pp. 603-15. (21) Murphree, E. V., Petroleum Refiner, 30, No. 12, 97 (1951). (22) Nelson, E. F., presented at the 37th Annual hIeeting of the Western Petroleum Refiners Assoc., San Antonio, Tex., March 1949; Petroleum Processing, 4, No. 5, 553 (1949). (23) Oblad, A. G., Llarschner, R. F., and Hear, L., J. Am. Chem. SOC., 62, 2066 (1940).
(24) Payne, J. W., Evans, L. P., and associates, Petroleum Refiner, 31, No. 5, 117 (1952). (25) Teter, J. W., and associates, Oil Gas J., 52, No. 23, 118 (1953). (26) Zelinski:, N. D., and Shuikin, N. I., Compt. rend. acad. sci. U.R.S.S., 3 , 255 (1934). RECEIvED for review January 4, 1954. Acomr5n hfay 28, 1054. Presented before the Divisions of Petroleum Chemistry and Industrial and Engineering Chemistry a t the Southwest Regional Conclave of the AMERICAN CHEMICAL SOCIETY, S e w Orleans, La., December 1953.
Fuels and Chemicals from Coal Hydrogenation E.
E. DONATH
Kopperr Co., Inc., Pitfsburgh, Pa.
I
N A previous paper ( 1 ) a projected coal hydrogenation plant was described with capacity to produce about 30,000 barrels
per day of chemicals and fuels. I n this plant Illinois coal is processed in two hydrogenation stages by liquid and vapor phase hydrogenation. The other main processing units include plants for coal preparation, residue coking combined with liquid phase hydrogenation, tar acids recovery from liquid phase oil, vapor phase gasoline fractionation combined with aromatics extraction, and Platforming and hydroforming. The main products, as shown in Table I, are tar acids from phenol to xylenols, aromatics from benzene to naphthalene, liquefied petroleum gas (LPG) and gasoline, predominantly motor gasoline.
Table I. Chemicals and Fuels from 30,000 Barrel-per-Day Coal Hydrogenation Plant
Broinatios Benzene Toluene Xylenes Mixed aromatics Ethylbenzene S a p hthalene
316,000
Liquefied petroleum gas
Gasoline Motor Aviation Total Ammonium sulfate, t o n s i d a s Sulfuric acid, tons/day
2,210 3,770 4,190 1,780 750 --790 13,490
8 2 13.9 15 4 6 8 2 8 3 7 50 8
-
7,300
16.4
5,260 3,660 8,920
11.1 __
v
31,090 450 89
15.6
26.7
100.0
Forecasts for the demand for chemicals in the United States indicate that most of the chemicals produced in such a plant would find a ready market. This is especially true for benzene, phenol, ammonia, and sulfuric acid. However, the higher boiling aromatics and tar acids would be produced in amounts which constitute a major proportion of the anticipated future production. It can be assumed that the sale of these chemicals could be in-
2032
creased if they were produced on a large scale and in constant quality or if they were offered at somewhat reduced prices. Another approach t o the utilization of these higher boiling aromatics and tar acide is the conversion within the coal hydrogenation plant into chemicals for which a large market already exists. The inherent flexibility of the coal hydrogenation process can be used to effect the desired change in the product distribution pattern. This paper discusses such possibilities, particularly with regard to increased production of phenol and benzene. If such an increase can be achieved at low expense, it will markedly improve the economics of the process. Rehydrogenation of Higher Boiling Tar Acids Is Proposed to Increase Phenol Production
Increased production of phenol by the further hydrogcnntion The product of the liquid phase hydrogenation is the main source of tar acids. It contains about 20Y0 total tar acids of n-hich one third are phenol, cresols, and xylenole. I n the proposed plant ( I ) , only the latter were recovered. The higher boiling tar acids remained in the liquid phase product and Fere converted in the vapor phase into gasoline and aromatics. Perhaps in the future, satisfactory methods for the separation of the components of these higher tar acids can be developed and attractive markets found. I n this case these tar acids would be extracted and separated into marketable products. The lack of the necessary technical and market information makes an economic evaluation of such processing unreliable. Therefore, it appears of interest to investigate conversion of these high boiling tar acids into phenol, cresols, and xylenols. The highw tar acids from coal hydrogenation products ohtained in a pilot plant have been shown t o consist primarily of polyalkyl phenols (6'). The dealkylation of such higher boiling tar acids by hydrogenolysis is probable ( 3 ) ,and 32.5% conversion of tar acids in the 235O t o 280' C. range into lower boiling tar acids in the phenol to xylenol range has been obtained in a oncethrough operation in autoclaves. Indirect data for the dealkylation of higher boiling tar acids in continuous hydrogenation experiments are also available. Pasting oils containing various amounts of middle oil and tar acids were used in liquid-phase coal hydrogenation and permitted evaluation of the rate of tar acid dealkylation in a continuous process. These data indicate that a 30y0 conversion of tar acids in the boiling range 225" to 275" C. into phenols, cresols, and xylenols is a conservative figure. On this basis a calculation was made of the yields obtainable by methanol evtraction of a middle oil fraction, followed
of higher boiling tar acids is one possibility.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, No. 10
ENGINEERING. DESIGN. AND PROCESS DEVELOPMENT by hydrogenation of the tar acid concentrate. A material balance for the proposed treating of the liquid phase product is shown in Figure 1. The liquid phase product is distilled to produce liquid phase gasoline which is essentially free of tar acids and a naphtha from which phenol, cresols, and xylenols are recovered as described in a previous paper (1). In the present process a middle oil fraction boiling from 225' to 275' C. is separated from the product normally sent to the vapor phase stage. The increase in yield for phenol, cresols, and xylenols by extraction of this 225' to 275' C. middle oil fraction and the rehydrogenation of the extracted tar acids amounts to 34%. It can be expected that the future market for phenol will be larger and more attractive than for cresols and xylenols. I t is possible to increase the phenol production a t the expense of cresols and xylenols by their further hydrogenation. The extent of this operation will be determined by economic considerations. Table I1 shows the tar acid production calculated for a 30,000barrel-per-day plant by such rehydrogenation, compared with the production without rehydrogenation. Yields of salable tar acids that can be obtained by separation and rehydrogenation of tar acids in the 225' to 275' C. boiling range and by the rehydrogenation of part of the cresols and xylenols are shown. Although the total tar acid production is less from the rehydrogenation of the 200' to 275" C. fraction than 225' to 275' C. fraction, the production of phenol is increased. The direct use of the tar acids in the boiling range 225" to 275' C. is the more attractive. However, these higher boiling tar acids cannot readily be separated into pure compounds with methods available a t present. With the trend in the plastics industry to use chemically pure raw materials to obtain welldefined products, it appears desirable to convert these higher boiling tar acids into phenol, cresols, and xylenols which can be readily separated and obtained in pure form. The liquid phase coal hydrogenation of middle oil is not the only source of tar acids. Water separated from the so-called cold catch-pot oil contains dissolved tar acids. This water is partly obtained by reduction of oxygen contained in the coal and partly added as flushing water to dissolve salts like ammonium sulfide and carbonate. Extraction of this aqueous effluent with solvents such as butyl acetate is necessary to avoid stream pollution. The extracted tar acids are rich in phenol, but they also contain higher boiling, dihydric tar acids. The production of phenol, cresols, and xylenols from this source is included in the figures of Table 11. The tar acids from the aqueous effluent from Illinois coal hydrogenation obtained in the U.S. Bureau of Mines Demonstration Plant, a t Louisiana, Mo., contain resorcinol according to recent analyses (2). The expected production of a 30,000-barrel-per-day plant would be 9200 pounds of resorcinol per day.
Table II.
Rehydrogenation of Tar Acids
(30,000-Barrel-per-day coal hydrogenation plant) Recovery of T a r Acids, Bbl./Day Rehydrogenation 225-275O C. 200-275O C. genation
No rehydro-
Recovery of higher tar acids from liquid phase middle oil and their rehydrogenation permits an increase in the production of the low boiling tar acids, phenol, cresols and xylenols. Similarly, the destructive rehydrogenation of high boiling gasoline fractions permits an increase in the production of aromatics like benzene. The process can be described as production of gasoline in the aviation gasoline boiling range in vapor phase hydrogenation
October 1954
instead of the production of motor gasoline. Vapor phase gasoline is the raw material for the separation of aromatic hydrocarbons. In the previously described plant (1) motor gasoline was produced which was then distilled and its fractions subjected to Platforming or hydroforming treatment to increase the aromatic content. These aromatics were separated by extraction with selective solvents or, in the case of mixed aromatics and naphthalene, by distillation. Recycle operation is necessary for B complete conversion of the liquid phase middle oil into motor gasoline, and the recycle feed amounts to 80% of the fresh feed.
l,W Ibs.Liquld Phase Product
202 I bs. M. O., 225-275'C
!
'
I I b a r Ph%b~~d&ktlon-
i 132 Iba to Vapor Phase Hydrogenotion
59 !bs Product Containin 19 Ibs Phenol, !resols, and Xylenols
30 8 Ibs. > 275% to
Vapor Phase Hydrogenation Figure 1.
Tar Acid Separation
An increase in the recycle ratio from 80 to about 90% of the fresh. feed is sufficient to permit conversion of the middle oil into vapm phase gasoline of aviation gasoline boiling range. Such gasoline, in comparison with motor gasoline, has a higher content of low boiling fractions and a considerably higher content of benzene and of naphthenic hydrocarbons which can be converted into benaene. Conversion into aviation gasoline is accompanied by increased formation of gaseous hydrocarbons. Conversely, the yield of aviation gasoline is about 3% lower than that of motor gasoline. The increase in total hydrogen consumption amounts to about 2% in comparison to the previously described plant. The decrease in gasoline space time yield or the increase in catalyst volume is small and can be made practically negligible by a slight increase in reaction temperature. Table I11 shows the production of aromatics that can be obtained by Platforming of fractions from aviation gasoline operation, in comparison to the aromatics obtained from motor gasoline. (The benzene production from motor gasoline operation is higher than that indicated in Table I, in which part of the benzene was used for the manufacture of ethylbenzene.) The increase in benzene production is considerable. The production of toluene and xylene decrease somewhat and mixed aromatics and naphthalene are not produced. However, withdrawal of a suitable fraction from the products distillation would permit production of naphthalene, whereby the production of the lower boiling aromatics would correspondingly decrease. Recently (6) new vapor phase hydrogenation catalysts have been described which produce gasolines with a higher content of aromatic and isoparaffinic hydrocarbons. The use of such cata-
INDUSTRIAL A N D ENG INEERING CHEMISTRY
2033
ENGINEERING, DESIGN, AND PROCESS DEVELOPMENT U. S. Production
8001 1950 1955
rCresols
Figure 2. Aromatics Production
Figure 3. 1. 2.
3.
Tar Acids Production
Without rehydrogenation of tar acids Rehydrogenation of tar acids, 22.5-275' Rehydrogenation of tar acids, 200-275'
C. C.
lysts in this plant x-ould increase the yield of aromatic hydrocarbons and improve the octane number of the gasoline. I t would furthermore reduce hydrogen consumption and thereby decrease capital investment and operating cost of such a plant.
Table 111.
Destructive Rehydrogenation of Gasoline Fractions
(30,000-Barrel-per-day coal hydrogenation p!ant) Aromatics Production, Bb!./Das, from Motor Aviation gasoline gasoline 2,710 4,570 Benzene 3,310 3,610 Toluene 3,670 4,000 Xrienes 0 1,700 Nixed mn 0 Naphthalene __ 11,550 12,810 Total
The liquid fuels production of this plant is shown in Table IT'. The production of motor gasoline has decreased. Aviatiori gasoline is obtained in a larger amount, and the liquefied petroleum gas production has also increased. Table 4 shows also the overall change in production and product distribution obtained by additional recovery of rehydrogenation of tar acids boiling above the xylenols, as well as the change in aromatic production that is achieved by vapor phase operation to obtain aviation gasoline instead of motor gasoline.
drogenation plant with the U.S.production of these materials in 1950 and the projected production in 1955. Figure 2 shows t,he comparison for phenol and other tar acids. The increase in phenol and total tar acids by rehydrogenation of the 225" t o 275" C. fraction and the increase in phenol production by rehydrogenation of the 200" to 275' C. tar acid fraction are indicat'ed. Figure 3 shows the comparison for benzene and other aromatics and the increase in benzene production that can be obtained by adjusting the operation of the vapor phase hydrogenation unit to the production of aviation gasoline instead of motor gasoline. The product' of coal hydrogenation especially the primary liquid phase product, is a source of a wide variety of chemical components. However, the products are extremely complex. There are many examples in the history of technology of the liniited extent to which high boiling complex mixtures can be separated economically into components of commercially useful purity. The liquid phase coal hydrogenation product resembles coal t'ar in many respects and probably contains an even greater variety of substances. Pure chemicals separated from tmheproducts of coal carbonizat'ion form only a small portion of the total liquid products t,hat are obtained. The bulk of the production is used as creosote oil and pitch. However, it' would be advantageous if cheap and simple processes were available which would make possible a high yield of pure compounds. -4s raw materials or intermediat,es for the preparation of plastics, dyed u f s , and pharmaceuticals, the chemical industry prefers pure compounds rather than mixtures. The technique of coal hydrogenation makes it possible to change production distribution from complex mixtures to simpler, lower molecular weight compounds. This paper has outlined the operating conditions in the coal hydrogenation process that permit recovery of a high yield of pure substances, with attention to product8 for which markets exist and for which lit.tle, if any, product development work is needed. However, it can be expected that some products for which commercial separation methods are not known at present, or which are not marketed in subst'antial quantities, will materially improve the economy of a commercial coal hydrogenation plant. The flexibility of the coal hydrogenation process can be utilized to advantage to change the product distribution. Changes are described in this paper which would result in large increases in the product'ion of benzene and phenol, primarily a t the expense of fractions for which a large future demand is less certain or from which separation of commercial grade chemicals is difficult. The more favorable product distribution justifies the increased cost of such processing.
Table IV.
Total Production from Recycle of Liquid and Vapor Phase Hydrogenation (30,000-Barrel-per-day coal hydrogenation plant) Production, Bbl./Day, from ~Aviation Motor g a s o l i n c ga5oline S o rehydro- Rehydrogenation of tar genation acids (225-275' C . ) _I_____
Tar acids Phenol Cresols, xylenols Resorcinol
Total Aromatics Benzene Other Total Gasoline Notor
Aviation
Economically Favorable Product Distribution Balances Increased Processing Costs
Recently published data ( 4 ) are used to compare the tar acid and aromatics production of a 30,000-barrel-per-day coal h) 2034
Total Liqiiefied petroleum gas Total
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
428 9 52 25
i,29n
1,290
1,402
1.895
1,805
550 22
580
23
10,530 ___
___
2,710 10,100
4,370 6,080
13,m
12,810
11,550
5,260 3,660
5,310 3,060
8,920 7,300
8,970 7,230
0,750
30,970
30,880
30,870
2,840
2,710 7,040 ---
7,700
Vol. 46, No. 10
ENGINEERING. DESIGN, AND PROCESS DEVELOPMENT Literature Cited
(1) Donath, E. E., Trans. Am. Inst. Min. Engrs., 193, 381-5 (1952). (2) Lombardi, A. D., and Nickels, J. E., Mellon Institute and Koppers Co., Pittsburgh, Pa., investigations under terms of cooperative agreement between U. S.Bur. Mines, Demonstration Branch, Louisiana, N o . , and Koppers Co., unpublished data. (3) Orchin, Milton, and Storch, H.H., J . Soc. Chem. Ind. (London), 69, 121-2 (1950).
( 4 ) Petroleum Processing, 7, 1154-60 (1952). (5) Pier, bl., Wissel, K., and Oettinger, W., Erdol u. Kohle, 6, 693, 696 (1953). (6) Woolfolk, E. O., and associates, U. S. Bur. Mines, BUZZ. 487,
3, 1950.
ACCEPTEDJ u l y 9 , 1954. RECEIVED for review April 23, 1954. Presented as p a r t of the Symposium on Synthetic Liquid Fuels and Chemicals before the Division of Gas and Fuels Chemistry, a t the 125th Meeting, ACS, Kansas City, Mo.
Digital Computer Solution for Heat Transfer to Temperature Probes H. F. KRAEMERI
AND
J. W. WESTWATER
University o f Illinois, Urbana, 111.
W
HENEVER possible, scientists develop exact analytical solu-
tions for problems that arise, but when equations of unusual mathematical complexity are faced, some other attack may be needed. Graphical methods or numerical methods may be used, although the drudgery involved is sometimes discouraging. The digital computer is a powerful tool for attacking problems by numerical techniques. Its value is a result of the high speed with which it can perform. A typical problem that cannot be solved analytically is thnt of a fin or a probe that is undergoing heat transfer by simultaneous convection, conduction, and radiation. The temperature probe is of particular interest. With a probe, a reading of the probe-tip temperature is obtained, but the measurement desired is the temperature of the fluid into which the probe is inserted. This paper is concerned with obtaining exact solutions to the heat transfer equation that can be set up for a simple probe. The exact solutions are compared with approximate solutions presented in a prior paper ( 4 ) .
Equation 1 can be generalized to obtain dimensionless limits of 0 and 1for positions on the probe and dimensionless groups for the other variables. The appropriate substitutions in Equation 1 yield Equation 2.
Equation 2 contains five dimensionless variables. It is a secondorder differential expression and contains the fourth power of the dependent variable, as does Equation 1. Although Equation 1 contains 10 variables, the five variables of Equation 2 are sufficient to describe the problem. I t is possible to reduce the order of the equation by the common technique of letting a new variable be defined, say p = de/dl. A substitution yields a first-order equation which is formidable, because it is not linear. No exact analytical method is available for integrating the new equation, but if a digital computer is available, it can handle the two simultaneous equations de ;fi = P
Digital Computer Handles Differential Equations Relating Fluid and Probe Temperatures
(3)
and
Consider a temperature probe inserted through a duct wall into a fluid. The probe is undergoing heat transfer by conduction, convection, and radiation. The temperature-sensitive element is assumed to give a true reading of the temperature of the tip of the probe. The problem is to calculate the temperature of the fluid. For liquids the problem is often trivial, but for gases the gas temperature may be very different from the probe temperature and the problem becomes important. A short element of the probe, a t distance 1: from the tip, may be considered. A heat balance for the length, dx, gives
and thus it is not necessary to deal with one highly complex expression. "eat Transfer at Tip. The heat transfer a t the tip of the probe is important for thick probes and negligible for slender probes. I n any case, it is easy to include this factor in the problem to be handled by a computer. A heat balance for the tip area gives
Equation 1 states that the heat received by convection is equal to that lost by conduction and radiation. The equation is general and holds even if the gas is colder than the probe. The fluid is treated as if it were transparent; the base of the probe is assumed to be at the temperature of the durt \Tall, 5°F. The equation cannot be integrated directly. An approximate solution is available ( 4 ) . Bn exact solution can be obtained by using numerical methods with a digital computer. This attack was used.
where ( d T / d x ) z is the temperature gradient a t the tip. Various writers have simplified the tip area problem by assuminga value of zero for ( d T / d x ) ~ .This will not be done in the present treatment. -4much more reasonable assumption is made-namely, that the temperature gradient a t the tip is the same for all positions on the tip. Changing Equation 5 to the generalized, dimensionless variables gives Equation 6, which represents the boundary conditions that a t e = BE, p = p ~ .
1
Present address, E t h y l Corp., Baton Rouge, La.
October 1954
(4)
pE
=
Orl*(@E4
- 1) - P I * ( e G - B E )
INDUSTRIAL AND ENGINEERING CHEMISTRY
(6)
2035,
