I
OSCAR A. COLTEN Shell Chemical Corp., 380 Madison Ave., New York 16, N. Y.
Basic Raw Materials in the Petrochemical Industry Availability, location, and processes determine which raw material will be used on a new venture N r \ m T R r \ L GAS AND CRUDE o n are estimated to be the origin of perhaps three fourths of all the tonnage of synrheric organic chemicals produced in this country today. \Vhen a company enters upon a new manufacturing venture. there are many factors to consider in selecting the most economical raw material. If only the cost per pound were to be considered, ethylene-the cheapest raw material-Lvould be a n easy choice; however, the total overall economics must be the guide. Therefore, each possible source of raw material should be checked as to availability, location. a n d manufacturing process.
Availability United States’ consumption of liquified petroleum gases for 1958 increased again, despite the recession, a n d totalled nearly 7.6 billion gallons ( I ) . Of this sum? about 2.3 billion gallons went to chemical uses, including raw material for synthetic rubber production. These statistics include both natural gas a n d refining streams. Another unmeasured flow of raw material from petroleum is the use of natural gas itself or, more generally, the methane residue after absorption of the heavier hydrocarbons, as a reforming (pyrolysis) or oxidation process feed for producing hydrogen and carbon monoxide synthesis gas, or for acetylene manufacture. There has also grown in recent years a new trend toward recovery of hydrogen from catalytic reforming units-the hydrogen employed as is that made from methane-in ammonia synthesis, for methanol manufacture, or for miscellaneous hydrogenation services. Here the alternate disposition is to the plant fuel system, a n d the hydrogen may be charged to purification operation a t essentially equivalent fuel value. Thus, where gas is available a t 20 cents per 1000 cubic feet, the platformer hydrogen becomes available a t 6 to 7 cents per 1000 cubic feet, before purification. Sulfur removal and, for some uses, carbon monoxide removal \vi11 of course be necessary. At large refineries, this is a n interesting source of petrochemical raw material. Although a large share of the total liquified petroleum gas consumption
moves into chemicals, the value is still controlled by alternate use valuei.e., as a highly demanded fuel. Similarly, use of natural gas methane to produce acetylene and synthesis gas is subject to the predominant markets for gas as a fuel-for industrial. commercial, and domestic use. Location
T h e petroleum-derived raw materials, on the aliphatic side-this does not apply to the aromatics-are gases, and, because they are plentiful where they are, they have favorable low unit values. However, they cannot be transported economically for very great distances. T h e economical pipeline distribution systems around the Gulf Coast and the Delaware River Valley extend less than 200 miles and are basically dependent on numerous users and very large producing units. Hence, the choice of feed stock is further influenced by where the processor is or chooses to be-adjacent to or satellite to a large refinery installation, or along the course of one of the merchant ethylene pipelines. Alternatively, acetylene is desirable if locating near a source of cheap power such as the TVA-based Calvert City acetylene complex a n d the Siagara Falls hydroelectric complex, Fvhich are the principal areas for acetylene-based synthetics not perrochemical in origin. T h e petrochemical acetylene, on the other hand, is captive in large multiproduct plants and located mainly in the Gulf area, where natural gas feed is cheapest. Many things are happening in the way of new developments which, as a n d if they prove economically sound, may alter the balance of relative costs and availabilities. S o t only liquefied petroleum gas for heating use, but even ethylene is now handled in underground storageso-called “jugs,” naturally occurring caverns or volumes dissolved out of salt domes-so that the smoothing out of seasonal fluctuations in storage much less costly than above-ground pressure vessels, may come more widely into use. There is also the recent and interesting development-still to be clarified as to economics-by which water-going transport of natural gas has become a reality (7). This may conceivably lead
the \vay to use of marine transportation for ethylene. for instance, and remove part of the difference between locations. Another type of adjustment to location is exemplified by two mid-b7estern ventures, Xational Petro-Chemicals a t Tuscola, Ill.? a n d Olin hfathie:on a t Doe R u n , Ky. Here the operators chose to locate their plants--respectively producing ethyl alcohol, ethyl chloride, polyethylene for Sational, a n d ethylene glycol in the case of Mathieson--asrride large natural gas pipelines, carrying fuel to the north and east. Extraction plants remove the propane and ethane from the natural gas, the remaining dry gas being perfectly suitable for domestic and commercial use; pyrolysis of the ethane yields ethylene for the synthesis mentioned. \Vhat advantages accrue? T h e manufacturer now finds his product shipping costs are lower than if he had to move the same quantities from the gas and oil locations, and his raw material is delivered to him in a n economical fashion-though certainly not logically as a “free-ride.” O n the other hand, there are limitations, particularly as the pipeline capacity is reached and further expansion may be hindered. Processes
O n e important raw material, acetylene, was examined as to the elements of cost that are involved in its manufacture, first by the Sachsse process (,5). Five tons of oxygen are required per ton of finished acetylene. i\cetylene yields 2670 by weight on methane converted, with a n off-gas of some 90y0 hydrogen and carbon monoxide in about a 2 to 1 ratio. Process unit investment, a t today’s construction cost level, would come to about $lO,000,000, including the oxygen unir, but excluding the necessary utilities a n d general plant facilities. Manufacturing cost data given in this article (5), adjusted for today’s price levels, would appear as follows, when fuel value credit is taken for the off-gas. These data show the dominating influence of the capital investment and the consequent importance of considering location and layout in influencing economies in that capital cost. Raw material is a fair portion of the direct production expense, a n d here, too, the site as it affects gas prices paid for charge VOL. 5 1 , NO. 9
SEPTEMBER 1959
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Acetylene cost, $/Lb.
Raw materials Natural gas at 20 #/MCF Chemicals, solvents, etc.
1.93 0.31 2.24
Conversion costs Utilities (net) Operation (incl. supervision) Maintenance Royalty and plant overhead Depreciation at 870 Total factory cost
0.44 0.50 1.04
1.98 0.90 1.33 6.45
kwital, battery liuiith. 810,000,000. (.'apacity, conrerted t o 80 toll\ per day, 60,000, 000 pounds per year. Unit in.r-estriierit, Igroceas only, 16.7 cents per annual pound.
and utilities \vi11 be important. Size of plant has considerable significance on product cost at lower volumes, but beyond the 80-ton-per-day level, the curve appears rather flat-presumably the multiplicity of burners and preheat furnaces precludes much further savings from size alone. Most of the large U. S. installations of acetylene from natural gas are of the Sachsse type. Published data are also available 011 another process for converting methane b y partial oxidation to acetylene--the SBA-Kellogg process (8). The direct cost, including oxygen, is shown to be somewhat higher than the Sachsse figures--namely? 4.9 cents per pound, including the oxygen costs; where 20cent natural gas was the feed stock. 'This process is able to produce 9 9 . 8 7 , dcetylene purity very easily, using a two.olvent purification train, which has certain safety advantages (8). As a consequence, rather higher capital of 5ome $12,000,000 for the 60,000,000pound-per-year plant, battery limits, including oxygen unit, was encountered. 'The resultant 7','s-cent-per-pound manufacturing cost cited by Patton and others excludes royalty and is on a dightly different financial basis than the Forbath costs, but with 20 cents per annual pound invested, it will show a somewhat higher total cost, including yield on invested capital. Cost Comparison of Methane- and Carbide-Based Acetylene
Starting with purchased carbide at 4 cents per pound and using nearly 3 pounds per pound of finished acetylene. the raw material input alone-12 cents per pound-exceeds the total manufactured cost of natural gas acetylene. Shipping the carbide any distance a t all hccomes a major consideration in the price structure. However, starting from ihe basic materials coke and limestone, on [he yield structure given in Faith, Keyes, and Clark ( d ) , and using 5 kw. per pound of ultimate acetylene, the direct cost based on $20 per ton of coke and $14 per ton of lime, using j-rnil
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pobver. ivould run about 8 cents per pound of acetylene a t the site. Total plant investment> however, is believed to amount to only half of that for a methane-origin petrochemical unit -i.e., about $j,OOO,OOO to $6,000,000 for a 60,000,000-pound installation. Therefore, locating near mineral raw materials and cheap electric power becomes of paramount importance. and all the considerations affecting location cconornies of plant construction have less eff'ecr on the product cost. Similariv. the profit or earning on the investment, \vith un1)- 10 cents per annual pound invested in the entire 1,rocr.js; takes a lesser share of merchant acetylene prices, and the reported value (I)of 12 to 14 cents per pound in the pipeline a t Calvert City: Ky. should represent ii fair rrturn on capital.
Other Sources of Raw Materials .\ considerable numbel. o! alternate feed stocks are useful: ranging from ethane and propane. \vith these being the most widely used. rip to heav!hydrocarbon sources. 'I'he possibility of using higher hydrocarbons all the xvay u p to crude oils \\'AS reported by Linden and Reid (6). 'Ihis study shows basic process considerations for a wide [range of feed stocks. Fair, Bolles, and Nisbct ( 3 )give data for d 120,000,000-pound-per-year eth)-kne unit charging refinery gases. with complete iwycle of ethane! propane. and propylene to the pyrolysis unit. 'Thii particular biudy .;how the relati\.e economics of various methods of demethanizing and indicates a slight ad\'antage €or a propane absorption procedure. though man) designers still prefer and show advantages for lo\\ temperature demethanizing. Using the mean values of the Fair article, the authors show capital ranging from $13,000.000 to $15,000,000. and manufacturing cost of some 3.2 cents per pound at this level. I n their comparisons, they bring this up to 5Ii2 cents per pound by adding 20% on return. exclusive of taxes, as a return on [lie involved capital. Scaling this estimate to the 6U>OOO,OOOpound level, the process moves out of the favorable economic range ivith a 910, 000,000 capital or 16 cents per annual pound of capacity. T h e manufacturing cost would go up to 4'/2 or 5 cents per pound, and the value including the samr 2OyGreturn figure used by Fair would be a b u t 7 ' i p cents per pound. As is well known, the Gulf Coast pipelines fed from plants of the 300 ton per day level (200,000,000 pounds per year) offer their ethylene in the pipeline a t 5l,'9 to 6 cents per pound on contract. T h e significant effect of plant size and economies arising from the volume of production has probably led
INDUSTRIAL AND ENGINEERING CHEMISTRY
t o adequate return on the large capital investments which have been made to establish this merchant ethylene process. Propylene is no less important than ethylene as a raw material for chemical operations, although today ir is used in about half as great a volume. However, in the next few years, demand for propylene to go into polypropylene and for synthesis of acrolein and arrylonitrile, will bring renewed attention to this product. Propylene's major source is from refinery cracking gases; in addition large quantities are made as co-product \vith ethylene, as mentioned before. Propylene-propane fractionation, though not requiring the !ow temperatures of the ethylene separation, still is a difficult task because of lower alpha values. Butylenes, in addition to their \videspread use in alkylation, arc used in butadiene or as iso-butylene itself in the synthetic rubber field. I n recent >-ears, as this volume grew, a number of ddditional dehydrogenation units charging butane have been constructed, and particularly interesting is the flexibility and undoubted economy of a combinarion plant where the butylenes may br directed partly to alkylation and partly to butadiene manufacture. I n addition to the aliphatic raw materials: the oil industry has: in receni years, become a n important source lot aromatics, formerly the exclusive pro\-ince of coal and coke chemistry. Benzene is destined in large measure t o chemical conversions; lesser proporrions of toluene and xylene go to cheniicals, the balance being used as solvent.. and other similar applications. O n e innovation in aromatic usiigc. involves the separation of ethyl benzene from a xylene fraction instead of its synthesis from ethylene a n d benzene, as a step on the way to styrene manufacture. For particular crude sources, where the ethyl benzene content so warrants, this is a favorable route io the styrene precursor.
literature Cited , 1 I Bureau of Mines, Mineral Marlwt Siirvey, 1958. $em. Eng. dVews 35, No. 5 , 113 (1958 . -tir, 3.R., Bolles, W. L., Nisbet, W. R.. Chon. Eng. Progr. 54, No. 12, 39 (1958,. '4) Faith, W. L., Keyes, D. B., Clark. R. L., "Industrial Chemicals," p. 34. Wiley, New York, 1956. 15) Forbath, T. P., Gaffney, B. ,J., I + / , V / . K r f n c r 33,160 (1954). 1 6 ) Linden, H. R., Reid, J. M., Chem. I Prop. 55, No. 3, 71 (1959). (7) Oil Gas J . 55, No. 50, 59 (1957,. 18) Patton, J. F., Grubb, G. C., and Stephenson, K. F., Petrol. Refiner 37, 180
(1958).
RECEIVED for review Aprii 17, 195'1 ACCEPTED April 27, 19.50 Division of Industrial and En ineerirg Chemistry, Symposium on Plant 8osts and Economics in the Chemical Process Industry, 135th Meeting. ACS, Boston, M a s s . . . \ p i 1 1959.
