. .
A NEW CHEMICAL STRUCTURE FOR
COAL
HETEROCYCLIC GROUPS
Typiwl Cross-bonded Sfrueturn for High Volatile Coals RON Alicyclic rings of N carbons RN
Alkyl side chain of N carbons
R'N Unsahmhd alkyl side chain of N carbon CB Cross-bonding by 0 or S to new heterocyclic groups with side chains T T.kahdra1 Sdimensional G C bonds, G O bonds, and W bonds
GEORGE R. H I L L
L L O Y D B. L Y O N
Q
This new concept ofers a Possible structure f o r coal thut may change the direction of coal utilization. Positioning and signgcance of various chemical groups represent a compilation of the best thinking around the world
hemical structure of coal is a riddle that has long defied solving. But in the last several years much excellent work has been done which contributes to a better understanding of the basic structure of coal. An impressive array of chemical and physical methods has been applied in this work, building up useful data bit by bit. From this compilation, a molecular model for high volatile bituminous coal evolved. The model suggests that coal consists of large heterocyclic nuclei monomers with alkyl side chains held together by three dimensional C-C groups, and includes functional oxygen groups, and ether bonds. Sulfur is interchangeable with oxygen in some structures. The close relationship between the chemical properties of similar fractions suggests that sulfur and oxygen may be present in linking units. Nitrogen occurs mainly in the heterocyclic ring structures. Paraffins seem to be more important than was originally thought. The model does not suggest that there are a large number of isomers as one might expect. Large condensed nuclei have the same simple aliphatic side chains. Consideration of the large number of possible isomers may have been the cause of confusion in past research. The present model seeks to clarify some of this confusion by offering a simplified explanation for some of the observed reactions. Although coals from different sources may vary, it appears that long-chain, simple aliphatic and alicyclic hydrocarbon groups predominate in many high volatile bituminous coals. Multiple polynuclear ring structures are apparently absent. Although coals were once thought to be a chicken-wire of 50 to 60 of these ring structures tied together, it now seems more logical to assume that only five or six combine for each aggregate.
C
u
(I
Functional Groups
Oxygen groups in coal are best presented by a functional oxygen group diagram (2). Van Krevelen's method of calculating these groups by the amount of water, carbon dioxide, and carbon monoxide derived from primary carbonization was applied to the gases obtained from low temperature carbonization of a Utah semicoking coal. The results agree with the proposed model. Evaluation of the work of Frolich and Fulton on coals heated to temperatures of 750' to l l O O o F. is in part the basis for concluding that long chain, simple, aliphatic, and alicyclic hydrocarbons groups predominate in the coal structure. Other evidence is found in work citing high yields of olefins and paraffins in low temperature carbonization distillates. Olefins found in low temperature tars may be as high as 50% of the neutral oil yield. Olefins and paraffins combined in a typical sample of distillate from a high volatile bituminous B coal from Spring Canyon, Utah, totaled 64%. The normal and isoparaffin content of low temperature tars is reported by Lewis. He identified C9 to C Z Z normal paraffins and Cl0 to C17 isoparaffins in the products of low temperature distillation ( 7 3 ) . Friedel and Queiser, using ultraviolet and visible spectra studies, concluded that aliphatic groups rather than polynuclear condensed aromatics predominate in the coal structure ( 9 ) . Evidence has been presented for polycondensed aromatics (4, 5, 70). It may be that coals can vary in the relative amounts of hydrocarbon class constituents as do different crude oils. Polycondensed aromatic rings are not common below SS%, but from 88 to 93'% carbon, a great increase occurs (76). The structures tying together the components conVOL. 5 4
NO. 6
JUNE 1 9 6 2
37
COAL PROCESSING DIAGRAM Sulfur Rocovary
"I,
1
Hydrogen-rich aiiwcllc, olkyhlod oromatic poly-cyclic produch and gases
1
..I.._.., ..,".
Hydrotrwling of hydrogen-. rich portion
Primary
W ~ -U
Primary hydro% ~ e n o l y l i f , hydrolreotina hydrocracking and depdymerirotion; conlrolliw temperatme, presswe, rplrce voiocily,
,
Conlroliad poiymeriralion. condenwion, sakinotion; controliing lempera~ure, -coke PrellYre, flow, re.ction time
Unreaclod Cool, Pitch, ond'Minera1 Refwe
I
-
Thermal Ciocklnp and P~l~~rrr~lion-Cood~rwtion
*
Fuel and M-bfuu
b Liquor
HI, CHI. HIO, COS,CO, H A NH). elc. P a d i n 5 oIeRn5 w a r a t l ~ tar ,
Ca'bonlzation Controlling tempemlure and roto of healing
Irop.arefiin Hydrocracking Aromatic Of liquid 0 ParoRin produch Nophlhsne Hydrocarbow
Peiym~rii~tion-condonMfion roosflorn Cake, Char, prsdeninote wilh secondary themml -Gases, Light cracking. reducing 011 prodush lo Oila, Tar ges101.coke, refractory liquid
Cote, char, pdycondenred pitch
1
Hydracatalytic Processing of Coal
2
Conventional CarbanizaHan of Coal
suggulcd tahnipes for m i g t h slnrcfurol componcnb of high wlatile coals arc compawd with conventionnl carbonization
stituting coal are considered to be principally aliphatic (methylene) bridges (6,7, 70, 74, 19,27). Friedel and Queiser (9) believe that tetrahedral bonds are the crossliking units required to give coal its three dimensional structure. Brown found little evidence for methylene bridge carbons (4,s). The structure proposed here is in agreement with these observations. There seems to be a general belief that the larger the organic molecule the more complex it becomes. This belief is probably a logical consequence of the increase in the number of theoretically possible isomers with increase in molecular weight and the difficulty of separating the large molecules. However, Hood and his associates lind the molecules contain essentially one long carbonatom chain, to one or both ends of which a ring system or short branch may be attached. In paraffin waxes the molecules are predominantly n-alkanes along with some slightly branched~ isoalkanes, cycloalkanes, and even traces of aromatics. In lubricating oils, the isoalkanes have slightly longer branches, and the monocydoalkanes and monoaromatics have several short methyl branches on the ring. Polyammatics generally appear to have all of their aromatic rings in a single condensed nucleus. Similarly, mass spectral evidence for polycyclic saturates suggests molecules with a condensed ring system at one end of a chain, but the interpretations are less clear and cannot yet exclude the possibility of a ring system at both
AUTHOR5 G. R. Hill is Head, Department of Fuels Engi-
ncaing, Uniuersity of Utah. L. B. Lyon is with the Struchwes Diuision of Ih4 State of Utah. Both have been active in coal utiliwtion and research. 38
INDUSTRIAL A N D ENGINEERING CHEMISTRY
ends. Although it is recognized that a small percentage of complex molecules might be present, the new picture is considered to be one which, in general, is representative of the distillate range of petroleum (72). This concept of simplicity and lack of isomers of large molecules is probably true in the basic structure of coal as well. Struch~nand DirHlletion
The yield of liquids from coal distillation is dependent upon the basic structure of the coal, particularly the functional groups, and the process used to convert the coal into liquids and coke (7, 8, 75,ZO). It has been observed that distillation under moderate pressures for hydrogen eliminates the oxygen bridges, increases the liquid yield, and also increases coke quality (8, 75). It hns been dononstrated that total hydrogenation of coal is uneconomical. Howevcr, a distillation process in which the hydrogen-rich portions of the coal are retained as relatircly low molecular weight hydrocarbons by hydrogenation in the pres~nce of suitable catalysts might be worth considming. Most investigators agree that the functional oxygen and sulfur groups control the yield of liquid products from coal. Van Krevelen states that the secondary reactions (polymerization to high molecular weight products) are especially noticeable with phenolic model materials. Cleaving of nonhydmarbon bonds, such as those of nitmgen, oxygen, and sulfur, by hydrogen treating methgds has recently become well established in the petmleum industry (75). Commercial catalytic hydrocracking methods indude the Gulf HDS process, the Union Oil Unicracking process, the Standard O il of California Isocracking process, and the Universal Oil Lomax process,
.
among others. The trend of increased hydrogen processing in industry is evidenced by such new techniques as hydrocracking of residual oils, hydrogenation of shale oil and gilsonite, hydrogenation of low gravity, high sulfur crudes, and hydrogenation of aromatics to form superior iet fuels. Some of these methods have been and are being applied to coal and to coal liquids (8)for the removal of the functional crossbonding groups to produce maximum yields of liquids and high quality coke. Van Krevelen worked on model material pyrolysis using the hydrogen donor materials suggested by Orchin and Storch, to increase liquid yields and to m i n i i z e the polymerization-conde&?ation reactions promoted by ,hydroxyl groups (20). The Varga process and the Lozovoi process are two additional w m p l e s of the use of hydrocracking techniques to produce high octane gasoline and other liquids from coal, primary tars, shale oil, and high asphalt crude oil residues. Catalytic methods are also applicable to coal and coal liquids. The high liquid yields made possible by hydrocracking hydrotreating distillation of high volatile coals plus the marketability of the residual coke make it apparent that there will be a smooth and gradual transition from conventional p m l e u m refming to coal refining as the economic picture becomes favorable.
b
;
l&EC's editors obtained the philosophy and plans of the Office of Cool Research in developing a coal refinery. The reader will find the comments on the following two pages of pcrticular interest since the research controcts olreody approved and under considerotion point toward a coal refinery, in the future
COAL REFINING-HYDROCATALYTIC PROCESSING High VdoNl. b w Rank CoaL Refractory uecycia
I -Hydmalol*tlc Uqu.foh--ll.d& Syilnn Primary hydrowivollon. hydrogenel@% trqdrolreding, hydmdealkylalion, ond hydrocracking which mobilirsr lhha 5001 by braoking 0 ond S c l o y bonding. C-C bridgw, oikql fide chains, rmovinp hydroxyl group% .ana opening homo. cyclic rings; controlling tempera~rcpressure, space veio.
PERTINENT REFERENCES (I) Brrkowitz, N.,Fuel ( W m )39,4/-3M (IVOO). (2) Blom, L., Eddhausen, L., Van Krevelcn, D. W.,Ibid., 36, 135-38 (1957).
(3) Brwb, J. D.,Zm.,36, 51-62 (1957). (4) Bmm, J. K., Ibid., 38, 55-63 (1959). ( 5 ) Bmm, J. K., Ladner, W. R., Sheppard, N.,Ibid., 39, 79-86,
_-
L -.17-9'. 119N)) \----I.
(6) Dryden, 1. G. C.,Ibid., 37.444-68 (1958). (7) Fiagerald, D., Van Krcvcien, D. W.,Ibid., 38, 17-37 (1959). (8) FranLe, N. W., h l e y , E. L , Eider, H. S., IND.ENC.b u . 49,140248 (Septernbcr 1957). (9) Fricdel, R. A,, Qudser, J. A,, Fud (London) 38, 369-79 (1959). (10) Given, P. H., Ibid., 39,147-53 (1960). (11) Golumbic, C., Anduson, J. B., Orchin, M., Storch, H. H., U. S. B w a u of Mines, R. I. 4462, March 1960. (12) H o d , A. Clerc, R. J., O'Neal, M. J., J . Iw6. PefroL. 45, No. 426,168-73 (June 1959). (13) Lewis, H. R.,C h . Id.(London) 1049-50 (August 15,1959). (14) Lyon, Lloyd, Hili, George . R., Ed., Univ. of Utah Eng. Bull. 109 (1960). (15) Orebin, M.,Columbic, C., Anderson, J. E., Storch, H. H.,
U.S.BmauofMinaBull.505.1951.
(16) P d g a Symp. Nature df Coal, Central Fuel Re. Inst., Jealgora, India, 1959. (17) Roy, M. M., Fuel (London) 36, 344-54 (1957). (18) Smirnov, R. N., Aduoncas in Clumidq, I w f . of Fossil Fuck (Momw) 28,No. 7 (1959). (19) Van K m d e n , D. W.,Ghumin, H. A. G., Sehuycr, . I , Ful ( W o n ) $6, 313-20 (1957). (20) Van Krevden, D. W.,Waterman, H. I., Wolfs, I?. M. J., Brmwfof Clmnir,Pts. I to VII,40 (1959). (21) Woffi, P. M. J., Van Knvden, D. W.,Waterman, H. I., Fuel (London) 39,25-38 (1960). VOL 5 4 NO. 6 JUNE 1 9 6 2
39
WHY NOT
n COAL REFINERY?
r
E Total hydrogenation of coal to fuel products is uneconomical, and according to latest research data, impractical. But techniques developed for the petroleum industry can be used to improve yield and value of coal liqaids and gases. Increased hydrogen processing in the petroleum industry has resulted in well developed techniques for hydrocracking, hydrogenation, and cleavage of nonhydrogen bonds by hydrotreating. More complete knowledge of the chemical structure of coal strongly suggests that these processes can be used to upgrade coal and coal products. Coal needs to be revitalized. It needs fresh thinking and approaches not taken before to solve its problems. Perhaps this is one of the best reasons for establishing the Office of Coal Research as a separate entity within the Department of the Interior, under Section 7 of Public Law 86-599 (74 Stat. 336). OCR does not conduct research on its own-research activity is initiated through proposals submitted. The prime purpose of OCR is to convert into reality the research potential which exists for expanding the uses of coal, reducing costs, and materially improving the economic position of the coal industry. The “coal refinery” concept is evident in the types of research projects under study and those for which contracts have been awarded. About 200 proposals have been received to date by OCR. Si contracts have been awarded. Six additional studies are in the final stages of contract negotiation. Some 20 projects show promise of developing new methods for mining, preparing, and using coal. Another 120 proposals have been rejected because they failed to offer an adequate research program or represented duplication. The refinery concept is not the sole scope of OCR‘s research contract work. But it is the target far getting maximum utilization from coal. OCR envisions three major products from the refinery-low ash coal, a high aromatic hydrocarbon stream, and gases-and “coalby-wire” power. Two basic approaches are suggested. One at the coal mining site for separating the coal into its three most useful components; the other removed from the site employing the latest in solids-carrying techniques to get the coal to its refining area. In either case, the aromatic-rich stream could be bled into an operating petroleum refinery system or worked off in idle equipment. The gases could be stripped for pipeline fuel value, hydrogen for processing, or fuel at the site. Modified petroleum refining techniques could be adapted to processing these “coal” streams. 40
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
I&EC in late 1960.(52, 813) called attention to the real challenge facing the Director of the Office of Coal Research and the responsibility of the rest of government, private industry, labor, and associations to help him meet this challenge. Progress to date is an excellent start toward activating research to improve the health of the coal industry and enhancing the value of coal resources to the nation. The chemical industry will follow with keen interest OCR’s efforts and stand ready to be of service.
OCR PROJECTS UNDER CONTRACT Booz-Allen S Hamilton; $l39,000 Executed August 4, 1961, completed May 1, 1962.
Provides for a comprehensive study of the market potential of coal. It represents an over-all appraisal of the opportunities for coal as well as an analysis of some of the promising uses of coal. It will provide guidelines for future projects, and will examine properties of coal and relate them to specific services which coal can perform, some of which are now being provided by products other than coal. Blhrminour Coal Research, inc.; $142,900 Executed Octobar 4,1961; a two-year contract.
Development of processes and methods to prepare, transport, and use ultrafine coal sizes in the range of 5 to 74 microns. This development will create an entirely new commodity. Since finely ground materials exhibit many properties normally associated with fluids, the material can be pumped and handled in simple equipment. Ease and convenience of handling will introduce coal in many markets which currently are not available to it. Finely ground coal can be used in gasification, liquefaction, ond . . chemical manufacture. An additional potential exists in removal of impurities such as ash and sulfur. Geomio Tech Rereorch Ins$24,000 Executed March 30, 1W2; a one-year contract.
To study reactions of various moterials with coal in a plasma jet. The purpose is to determine the reactions which occur between pulverized coal and various gases at hi$h temperature. Reactions will include those between ultrafine coal and hydrogen, argon, hydrogen and argon, methane ond atgon, steam, and various halogens. This project is part of a larger program designed to identify projects which can be integrated into a coal refinery. Quantitative determinations of desirable productswill be obtained. General Electric Co.; $750,000 Executed March 30, 1962; a M m o n l h contract.
Study the possibility of extracting gas and chemicals from coal through use of electrical corona created by exceptionally high voltages and frequencies. Corona, a phenomenon characterized by ionization or breakdown of’air around conductors, is avoided in commercial transmission of electricity. But the effect may hove useful applications in capturing valuable products from coal when created purposely and used under precisely controlled conditions.
c-
GE has already studied the use of high voltage, high frequency electricity for promoting chemical reactions. In the case of coal, one possibility l a the reaction of hydrogen, methone;or similar gases, under corona with powdered coal to make pipeline gas and chemicals. .OCR envisions .the ultimate commerciol plant as on integrated chemical and energy installation using only cool, water, and air as row materials. The contract is in two ports. The first, for $XO,ooO, is to demonstrate the technical feasibility of the corona technique. If successful, the additional funds will be provided.
I
Virginia Polytechnic Instilutq $132,000 Execuhd March 30, 1962; a two-year contract.
To develop scientific engineering methods for determining the most favorable combination of various elements of mining .which can be. controlled by the operator. This will ensure lowest cost production unddr existing physical conditions. VPi will develop formulas, programs, and models which con be solved by computer techniques.
high B.t.u. pipeline gas. Will also include detailed evaluation of various coal matvials as feeds for the p c c s s and novel equipment arrangements. Werhrn Coal Study
Examine the potential market for coal produced in the western part of the U.S. Study is based on a locational analysis of the demand-supply energy balance for this region both in t m n s of energy types and consumption. Export Market
Appraix the foreign market potential of U. S. metallurgical and steam coals and the obstacles to achieving this potential. Development of Induswlal Complexes
Determine the quantity and quality of ores associated with coal and economic feasibility of their recovery and utilization.
Pope, Evans, and Robbinr; $129,185 Executed February 28, 1962; a two-year contract.
PROJECTS UNDER CONSIDERATION
Develop and design a totally new, completely integrated, coal-fired industrial 'heating plant of an intermediate size range-10,CCQ to 60,ooO pounds of steam per hour. Unit is to require minimum attendance, minimum space, maximum efficiency with initial cost and operating costs considerably more favorable than existibig cool-tired equipment. New concepts for coal handling, combustion, ash, and fly ash collection will be develoDed and evaluated.
Jet Fuel
Feasibility study followed by process development and pilot plant teats to develop a jet fuel meeting Air Force and Navy specifications.
Fuel Cell
Development of coal-based fuel cell for generation of central station power. Same preliminary work completed.
PROJECTS FOR WHICH CONTRACT WORK IS LARGELY COMPLETED
Pipeline Reactor
Investigate the use of transportation line to provide chemical reaction time so that materials intmduced in one end will interact and produce at the outlet end an upgraded product.
Project COED (Char-Oil-Energy-Development)
Determine the technical feasibility of extracting from coal the equivalent ofa crude oil suitable as a diluent for a refmery feed stock. Conduct expeimental work on a multiple fluid-bed and a high temperature pyrolysis process, or a combination, to produce a pumpable synthetic crude oil to transport the remaining fuel constituents (char) to a market located some distance away. Only processes not previously investigated will be studied.
Western Cod Study impmved utilization of western coal and fit data into over-all OCR program.
k~w-Temperame carbonisption
Determine wtential for Droducine hieh B.t.u. gas, coke briquets, and liquid products from a variety of typical coals.
Rocket
Evaluate various fu& that can be obtained fmm coal for military mcket applications. Will include consideration of energy levels required, cost of production, and effect on the cast of military hardware.
Pipe
Develop a method for continuous field extrusion of a plastic pipe which can be used to transport coal "spulrions bath within a plant and transcontinentally.
I
I
Project Gasoline
An accelerated pilot plant development program for a process using new process methods and a new catalyst for making gasoline and related chemicals and char from high volatile bituminous coal. Work will include detailed feasibility study, pilot plant design, construction, and operating program to determine over-all process, technology, and economics. This process is not a duplication or repeat of work previously performed, Project G a s
Will include experimental operation of a multiple staged bed gasification process for coal duFted to development of a high quality synthesis gas and/or
Low-ashCoal Develop a coal fractionating
system to
produce a high quality, ash- and sulfurfree coal. V O L 5 4 NO. 6 JUNE 1 9 6 2
41
