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INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
to allow a coniparisori n-iib graphical results. Among thost: suitable for use are a report of laboratory work by Hartung ( 3 ) and a report of plant scale tests by Sheen and Woodruff ( I O ) . Hartung treated a series of water samples with increasing quantities of 92% calcium oxide. After a reaction period, each sample was filtered and equilibrated with calcium carbonate. Results of tests for total, calcium, and magnesium hardness, and pH (where available) are given in Table I11 for two different waters. The table also gives values of total, calcium, and magnesium hardness, pH, and alkalinity as determined graphically from the 25' C. diagram. Agreement between the experimental and computed hardness values is reasonably good. In geiieral, the computed values of calcium hardness are higher than thc experimental, indicating incomplete stability a t larger lime dosages. This may be duetoincompletesolutionof thelimeduringtho experiments. Magnesium started to precipitate before the theoretical solubility product for magnesium hydroxide was exceeded. This resulted in less lime being used for calciuni precipitation than is indicated by the diagram. The computed total hardness values, however, agree well with the experimental except for large lime dosages. Sheen and Woodruff (IO) reported upon the results of a series of tests of Softening Plant No. 2 a t the Wright Aeronautical Corp., Cincinnati, Ohio. This plant employs an Accelator and analytical determinations during the test periods were exceptionally complete. Table IV presents significant analytical
Vol. 45, No. 3
results of the raw water itiid of tho Accelator effluunt for two typical tests. The table also gives tho corresponding graphical results determined from tho conditioning diagram. Both of these tests were aimed a t removing its much calcium as possible without reduction in magn~sium. As pointed out by the authors, t,he Accelator effluent is not completely stable but is supcwaturated with calcium carbona,tc,. It is apparent from Table I\' that t,hn artual Cxoess of calcium carhonatc in solution is 23 p,p.ni. in t h o first t,est and 43 p p m . in t>lirsrcond. IJTER,YILlR
C [TED
( I ) Arbatsky, J. W., Gas- i i . WasserSnch, 8 3 , 9 0 , 116 (1940). ( 2 ) H a r t u n g , H. O., Water W o r k s & Sewerage, 8 8 , 5 3 9 (1941). (3) Langelier, W.F., J . Am. Water W o r k s Aseoc., 28, 1500 (1936). (4) Ibid., 38, 169 (1946). (5) Ibid., p. 179. (6) Langelier, W.F., a n d Ludwig, lr. F.,Ibid., 34, 335 (1942). (7) Lawrence, W. B., paper presented a t a m . W a t e r Works Assoc. convention, San Francisco, Calif. (July 1947). (8) McKinney, D. S., IND. EKG.CHEX.,ANAL.ED.,3, 192 (1931). (9) N&s&nen,R., 2. p h y s i k . Chem., A188, 272 (1941). (IO) Sheen, R. T., a n d Woodruff, E. R . , IND.ENG.CHEM..36, 971 (1944).
(11) Travers, A., a n d Kouvel, C o m p t . rend., 1 8 8 , 4 9 9 (1929) RECEIVED for review June 2Z, 1S5l. ACCEPTEDNovember 7, 1933. Presented.before the Division of Water, Sewage, and Sanitation Chemistry a t t h e 114th Meeting of the AMZRICAX C H E M I CSOCIETY, ~L St. Louis, Mo.
Elements in Coal Ash an Industrial Signi A. J. W. HEADLEE ANI) RICHARD G . HUKTER West Virginia Geological S u r v e y , 'Morgantown, W . V a .
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HE ash produced by combustion of the coal mined in West Virginia amounts to some 10,000,000tons of ash each year. Since West Virginia produces some 28y0 of the bituminous coal consumed in the United States, a large tonnage of coal ash is available. This paper is a resume of the analyses of 596 spot saniples for 38 elements from 16 coal seams, representing the major coal producing area in West Virginia. The study was undertaken t o supply fundamental data on the composition of coal ash. These data have an industrial significance indicated below. Coal ash is made up of the elements sodium, potassium, calcium, aluminum, silicon, iron, and titanium in concentrations greater than 1y0when calculated as the oxide; lithium, rubidium, strontium, barium, magnesium, arsenic, beryllium, boron, chromium, cobalt, copper, gallium, germanium, mercury, lanthanum, manganese, molybdenum, nickel, phosphorus, lead, tin, vanadium, tungsten, zinc, and zirconium in concentrations between 1 and 0.01% calculated as oxide; silver, bismuth, and antimony in concentrations between 0.01 and O.OOl7, as oxide; and a number of other elements not reported in this paper, such as sulfur, halogens, nitrogen, and rare earths. Gibson and Selvig ( 1 ) give a review of the minor elements in coal ash. The minerals that make up coal ash are either inherent in the organic matter which makes up the coal or are in joints and partings, extraneous from or outside of the organic matter. The over-all composition of the two types is similar; however, spot samples may be quite unlike because of the presence of localized concentrations of calcite or pyrite. The compounds making up these two types of ash, however, may not be the same.
SAMPLING AND TESTISG SOLID COLUNINS O F COAL
Samples were obtained by sawing a 3-inch square column of coal from the full height of the seam and bringing this column intact into the laboratory for further sampling. One-inch cubes were cut from the column every 3 inches beginning a t the top. Apparent specific gravity and porosity of these cubes were determined. The cube was then ground to 60-mesh. The pvritic, sulfate, organic and total sulfur, and ash content were determined on each sample. The ash determination was made by spreading the coal in a flat porcelain dish, placing in a cold muffle furnace, and heating to 740" C. maximum. One-gram samples of coals having more than 5% ash were burned; if the coals had less than 5 % ash, 2 grams TSere ashed. The ash from these determinations was ground t o 200 mesh and analyzed quantitatively for 38 elements with a large Littrow spectrograph (4). T h e quantity of the element reported in these ash analyses is not necessarily the total amount present in the raw coal sample. The burning operation mag volatilize some of these elements similar to the manner in which sulfur is removed. Analyses of coal and its ash indicate that considerable beryllium and possibly aluminum are volatilized in t h e laboratory ashing process. Most of the halogens probably volatilize in the ashing process as volatile metal halides. ANALYTICAL PROCEDURE
The basic method was proposed by Slavin (6) and f u r t l i c ~ developed in this laboratory ( 4 ) for thc analysis of coal and coal ash. Only the major improvements since that report was written are presented here. The standard employed for these analyses was the ash of a West Virginia coal identified as C-5 ( 4 ) . T o this ash was added a mixture of 20 oxides of elements, six of which were not in the
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INDUSTRIAL AND ENGINEERING CHEMISTRY
original a s h i n d e t e c t a b l e quantities, Seventeen of these T A B L E I. OBIP POSITION OF COATI ASH were added to the extent OS EnriohO.Olyo of the ash niatiix. inent Cube Analysis Ratio oi Earth’s These were zinc, silver, tin, VariVariCoal Ash Crust (8). lead, antimony, arsenic, bisMaxiMinirnum, MaxiMinirniim, ance ance Average, to Earth’s Yo as muth, m e r c u r y , c a d m i u m , satio Crust Oxide mum, % Oxide iatio mum, % % % % cerium, cobalt, molybdenum, 2 10 Liz0 0.27 0.37 0.17 0.68 0.07 19 0.014 1.78 4 0.30 30 3.81 3.66 0.96 9.13 0.47 NazO tellurium, tungsten, zirconium, 3 13 3.11 2.44 0.51 IC20 1.60 0.38 0.89 4.86 gallium, a n d I a n t h a n u i n . 6 0.030 0.117 Germanium, phosphorus, and 11.9 15 0.12 0.53 CaO 0 81 35.8 300 2.70 5.07 beryllium were. added to the 4 25 11 0.050 SrO 0.54 0.90 0.21 1.89 0.08 extent of 0.1% of the ash BaO 0.08 81 0.043 0.31 0.70 2.45 0.03 9 7 24 3 1.46 0.28 0.10 3.48 0.58 0.99 2.36 MgO matrix. This standard was 38.1 21.9 2 52.3 5.3 16.7 10 1.85 30.0 Alios checked against a synthetic 2 59 0 3.35 25 0.75 44.0 54.9 30.4 82.5 Si02 mixture and functioned well 134 33.6 9 0.66 1.94 7.26 14.1 3.6 88.4 Fez08 for practically all the samples 1.03 1.51 2.30 1.00 5.73 1.47 2 0.17 34 TiOz 0,003 150 0.00001 with the exception of those 42 AgzO 1 0 . 0 1 < 0 . 0 1 0.060 0.29 26 0.0007 0.018 >6 >29 As203 containing iron oxide in the 196 Be0 0.008 0.002 15 0.030 0.098 0.0019 concentr8ion range 50.0 to 0,007 10 80.0%. 39 0.66 108 11 0,309 0.027 0.017 0.0009 0.097 &Os 5 The major problem in the 2 0,029 0.010 0,053 0.62 0.018 0.016 0.029 CraOs 2.4 19 0.0050 5 290 0,004 0.38 0.120 0,234 MnO 0.016 1.16 15 0.046 which flies out in mass or in part shortly after ignition of 0,010 Moos 0.016 0.040 4 0.140 10.001 > 140 6 0.0025 NiO 0.046 0.016 0.006 3.6 0.104 95 0.0127 7 0.57 the arc. A change in electrode 258 0.0017 PbO 0,019 8 28 0.048 y separations of the bottom 3 inches have given coal whose ash contains 0.3y0 of germanium dioxide. This ash contains germanium dioxide valued as a finished product a t $900 per ton and the value of the ash as a germanium ore is $57.50 per ton. Coal samples are
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already available which will yield ash with 1% germanium dioxide. Although very extensive reserves are available, however, it's production will be dependent on the rate of coal production, with germanium a by-product in most cases. The germanium in used in very small quantities in the manufacture of photocells, diodes, triodes, and transistors. When the technique of manufacturing transistors in quantity is perfected, the demand for germanium will increase so that coal will be its probable source of supply. The germanium can be commercially recolrered by keeping the bottom 3 inches of undercutting separate from the rest of the coal, washing the cuttings, and separating the germanium from the ash after burning the coal. Eight of the 38 element's determined are present in the coal ash to a lesser extent than their average presence in the earth's crust (2): sodium, potassium, rubidium, calcium, magnesium, silicon, chromium, and manganese. Magnesium i s the lowest in this respect with only 0.28 times as much in the ash as in the earth's crust. Silver, boron, bismuth, and mercury are 100 or more times as concentrated in the ash as in the earth's cwst, with mercury showing the highest enrichment-namely, I85 times. The authors have analyzed t'he ash from small thin lenees of coal, which had more than 1% of vanadium pentoxide and 18y0 of titanium dioside. They are of academic interest only and it, is not likely that they represent an economic resource. Based on a n enrichment ratio of 10 or more, lithium, strontium, silver, arsenic, bismuth, boron, gallium, germanium, lanthanum, mercury, lead, antimony, tin, zinc, and zirconium might lie wcoverable from coal ash. A comparison of the cube variance ratio with the enrichment, ratio is of interest. Sevent,een of the 35 elements have high cube variance ratios and relatively low enrichment ratios. They are sodium, potassium, rubidium, calcium, barium, magnesium, silicon, iron, titanium, beryllium, copper, gallium, germanium, manganese, molybdenum, nickel, and phosphorus. These elements would occur in localized high concentrations. Lithiuni, strontium, bismuth, boron, and mercury have relatively low cube variance Kith high enrichment ratios. Coal ash in g e n e ~ d would be enriched with these elements. Silver, arsenic, and 1e;ttl have high cube variance and enrichment ratios. IAanthanuiii, tin, and zinc h a w medium high cube variance and enrichinelit ratios. Aluminum, cobalt, chromium. vanadium, tungnten, and zirconium have low cube variance and enrichment ratios. Their doncentration in coal ash is similar to t,hat of the earth's crust. The data indicate that a wide range of fusion temperaturer fov ash from different lump8 of coal would be anticipakd. A 1 1 1 0 1 ~ ~ practical index of clinker formation would be the fusioii teinperature range of spot, samples, rather than one average fusion point for the coal concerned. The sizable quantit,ies of lit,hiuin, strontium, and barium, and 25 other elements totaling 195 on t.li(I average, will require that they and several other elemcnts he considered in efforts to calculate fusion temperatures from cheniical analyses. Variability in the concentration of the compounds in the aqli will have an effect on the catalytic gasification and hydrogenat>ionof coal. 9 few of these elements such as arsenic and antimony will probably act as catalyst poisons while others mill act as catalysts. The effect of catalysts in some work already completed should he reviewed in the light of the presence of seveml of the catalytic elements already in the coal. Problems of atmoPpheric pollut,ion are suggested by the finding of appreciable quantities of stront,ium, barium, silver, arsenic, beryllium, mercury, lead, antimony, and tin in coal ash. .Idditional quantities of some of these elements escape into the air in the combustion process by evaporat,ion. Beryllium, for example, appears to be as high in some coals as it' is in the a,sh aft'er burning. It is a well-known fact that in the combustion of coal, boron compounds condense out on boiler tubes and lower the efficiency
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INDUSTRIAL AND ENGINEERING CHEMISTRY
of the boiler. These data suggest that other elements may also condense out in boiler flues. The recovery of compounds from coal ash is dependent on the development of suitable methods. Although it is not the purpose of this paper to present such methods, certain directions which recovery might take have been indicated from time, to time during the course of this investigation. It would be advisable t o wash the coal to remove most of the extraneous mineral matter (shale, pyrite, and calcite for the most part) prior t o burning. The extraneous shale, however, has a composition similar t o the inherent ash. Coals which have been through a floatsink operation at 1.30 specific gravity contain only about 3% ash, practically all of which is inherent ash. This ash is fine and fluffy. If the coal is not washed prior t o burning, then most of the fine inherent ash can be floated from the heavier, coarser extraneous ash. Gravity separation of the ash effects concentation of certain compounds; for example, barium and strontium can be concentrated in this way. Germanium can be concentrated by selective mining of the bottom 3 inches and washing the coal to an equivalent specific gravity of 3.3. ,4 luxurious growth of plants over a considerable period of years is to be expected in order to produce sufficient vegetation to make a coal seam 3 feet thick. The soil in which they grow
55 1
must have had adequate mineral nutrients t o promote maximum growth. If the present inherent coal ash is representative of the original living plant ash, then these analyses indicate the optimum concentration for maximum plant growth. The enrichment of such a large number of elements by coal-forming plants suggests t h a t each element had some important function in plant nutrition. The fertilization of soils, so t h a t the equivalent of the concentrations of the elements in coal ash is available to the plants, might materially increase the production of farm crops. ACKNOWLEDGMENT
The authors gratefully acknowledge the aid of the staff of the West Virginia Geological Survey, and particularly Paul H. Price, for permission to publish this paper. LITERATURE CITED
(1) Gibson, F. H., and Selvig, W. A,, U. S. Bur. Mines, Tech. Paper 669 (1944). (2) Goldschmidt, V. M., J . Chem. Soc., 1937, 656. (3) Headlee, A. J. W., and Hunter, R. G., West. Va. Geol. Survey, Morgantown, R. Va.,Repts. Invest. 8 (1951). (4) Hunter, R.G.,and Headlee,A. J. W.,AnaZ.Chem., 22,441-5(1950). (5) Slavin, Morris, IND.ENQ.CHEM., ANAL.ED., 10,407-11 (1938). R E C E I V ~for D review May 12, 1952.
ACCEPTEDOctober 30, 1952.
Review of Olefin Isomerization H. N. DUNNING‘ 331 Fir St., Park Forest, I l l .
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4
HE subject of olefin isomerization dates back to the turn of the century and the pioneering woilc of Ipatieff (33, 36, 36). From these initial experiments, the expansion of the field has paralleled the advancement of analytical methods for hydrocarbon mixtures. In some cases the necessity for accurate analyses has been overlooked, leading to contradictory reports in the literature. Fortunately, such contradictions are few; many may be resolved in the light of later experimental evidence or of thermodynamic calculations. Twigg (80) points out that analyses of cis- and trans-2-butene mixtures are difficult because of the similarity of the physical properties of these isomers. Further, Rose (699) showed by calculation and Whitmore et al. ( 8 7 ) by experimental evidence that it is impossible to separate many of the isomeric products of n-hexene by present methods of fractional distillation. Literature reports that are based on questionable analytical methods are reviewed in this paper only in the absence of data obtained by more credible methods. The isomerization of olefins t o more highly branched forms results in marked increases in the octane ratings of olefin-containing stocks (6). The considerable olefinic content of most thermall. cracked naphthas has stimulated interest in the isomerization of these stocks. Recent developments in the petroleum industry have added impetus to isomerization studies. Gasolines prepared by the Fischer-Tropsch type synthesis are especially susceptible t o isomerization reactions because of their high olefinic content (68). Octane increases of about twice the amount of those observed with thermally cracked naphthas may be achieved. The outlook for olefin isomerization processes appears even brighter. Shale oil operations are becoming economically more attractive. Naphthas produced from shale oil are exceptionally rich in olefins, containing about 40% to 55% olefins (39). Since over 50% of the total olefins, or 75% of the aliphatic olefins, are unbranched (79), isomerization of these naphthas may be ex’ Present address, U. S. Bureau of iMines, Bartlesville, Okla.
pected to be especially profitable. Another advantage of isomerization processes is their ready adaptability for use in upgrading of gasolines in small refineries where the cost of a catalytic cracking unit necessitates dependence on thermal cracking operations. An olefin isomerization unit may be relatively small and inexpensive because of the extremely high space velocities used, low original cost of catalysts and their easy regenerability, nearly quantitative stock recovery, operation a t atmospheric pressure. THEORETICAL
The isomerization of aliphatic olefins may be classified generally as follows: Double-bond isomerization Movement of the double bond Cis-trans isomerization Chain isomerization Change in number of tertiary carbon atoms Change in position of tertiary carbon atoms in molecule Mechanisms for the double-bond isomerization of olefins on metallic catalysts have been discussed extensively by Twigg (80) and Farkas ( 1 7 ) . The “associative” mechanism of Twigg postulates that the olefin is adsorbed at both ethylenic carbons by the metal catalyst. Then one of these bonds is broken as a hydrogen atom is added t o one of the carbons. This addition correlates with the “proton affinity” calculations of Evans and Polanyi (15). Then a hydrogen atom is expelled from an adjacent carbon atom and the isomerized olefin is desorbed. The “dissociative” mechanism of Farkas ( 17 ) postulates that the C-H bond becomes loosened by catalytic artion, and the hydrogen is expelled. Then a hydrogen atom is added at the remote ethylenic carbon and the molecule is desorbed. Hay, Montgomery, and Coull (28) conclude t h a t the effective catalysts for chain isomerization of olefins are acidic in nature. An extensive survey of the literature on olefin isomerization has produced no contradictory evidence.
