INDUSTRY & BUSINESS
Ethylene makers take new look at butane Prospects for continued low prices for butane and the added quantities of increasingly valuable propylene that comes through as a coproduct, tempt ethylene makers to use butane as a feedstock
ery in September at Mont Belvieu, near Houston, Tex. Butane can compete with propane in some uses. By far the largest use is as the raw material for butadiene made by catalytic dehydrogenation. The other is in making acetic acid by oxidation. Butane can be stored in salt dome caverns similar to the way propane is stored. And, changes in the price of butane can have a psy chological impact on the price of pro pane. But as is the case for nearly every economic decision in making chemi cals, the possibilities of using n-butane as a raw material for ethylene are com plex. Each ethylene manufacturer's plant differs at least slightly from any other. Each manufacturer has some what different profitability criteria, market need, and current feedstock situation. Therefore, some producers of olefins might use butane at 5 cents per gallon and others might not use it at 2 cents per gallon. The 2 centper gallon price floor is roughly bu tane's fuel value at point of produc tion. This 2-cent floor comes from two factors—heating value of n-butane at 103,000 B.t.u. per gallon of liquid, and cost of heat assumed at 20 cents per million B.t.u. on the Gulf Coast, which is equivalent to natural gas at
Ethylene producers are attempting to take advantage of a small bonanza in current low spot prices for butane by using it as a feedstock. They also are taking another hard look at the eco nomics and technology of using more butane to make ethylene because of the prospects for continued low prices for butane and because of the added quantities of increasingly valuable pro pylene that come through as coprod u i s of ethylene. A large part of the ethylene made in the U.S. is produced from propane or ethane, or a mixture of the two. Prices could bottom out this sum mer at under 3.5 cents per gallon for field butane ( that produced from proc essing natural gas) on a spot basis in southern Louisiana and in west Texas. A little over a year ago the price was 6 cents a gallon. Prices should firm in the fall and climb 1 or 2 cents per gallon, depending on how cold the weather is next winter. Prices in the summer of 1969 could match those of the summer of 1968 if the winter should be average or less cold than normal. As butane prices have declined, so have propane prices. According to the relatively new propane futures market, propane prices are in the 2.5 to 3 cent-per-gallon range for deliv
High-severity hydrocarbon pyrolysis yields high ethylene percentage Product
Feedstock (Weight %) Ethane
Hydrogen Methane Ethylene
3.6% 3.4 48.2
Ethane
40.0
η-Butane
1.5% 24.2 34.9
1.0% 21.7 31.6
Light naphtha
0.9% 16.0 28.0
Field condensate
0.7% 9.5 19.5
Naphtha /300°to650°\ V F . /
0.6% 10.0 20.8
5.0
6.5
3.9
5.0
3.7
Propylene Propane C4 cut total
1.85 0.15 1.4
14.3 10.0 4.2
20.0 1.6 9.0
13.1 1.1 9.0
15.1 1.3 11.1
13.8 1.2 8.7
Butadiene Aromatic distillate cut total Benzene Toluene
0.7 0.9 0.4 0.02
2.1 4.9 2.0 0.4
2.0 7.2 3.6 1.2
4.5 23.7 7.6 4.8
3.8 20.0 4.5 4.0
4.0 20-0 4.5 4.0
650+° F. cut
0.5
1.0
1.4
4.3
15.0
15.0
Note: Totals do not equal 100. to fuel. Source: C&EN estimates
38
Propane
C&EN JUNE 10, 1968
Once-through basis; not all products identified; ethane and heavier paraffins may be recycled; some products
Typical light olefin yields from pyrolysis (Recycled to extinction)
Source: C&EN estimates
a price of 20 cents per 1000 cu. ft. This new interest in butanes for olefins is limited to η-butane. Isobutane sells at about half a cent per gallon below η-butane in distress sit uations on a spot basis. (A distress situation is one in which a producer has an oversupply with no place to store it and, hence, sells the isobutane for whatever he can get.) This con trasts with the situation a year ago when it sold for more than n-butane. Isobutane, however, holds little appeal to a producer as a feedstock for ethyl ene because of very low conversion to ethylene under typical pyrolysis con ditions. The current price situation for bu tanes comes largely from changes in oil refining, particularly the rapid growth in hydrocracking. Hydrocracking, more catalytic reforming, wide use of molecular sieve catalysts, increased crude oil throughputs, and efforts to reduce air pollution are all tending toward slower gains in needs for butanes by refiners. At the same time, increased natural gas processing accelerates output of field butanes. The result is roughly a 50% gain in the size of available stocks of n-bu tane. Hydrocracking reduces refiners' needs for isobutane more than for nbutane. This is because hydrocrack ing produces much more isobutane than does catalytic cracking and very few, if any, olefins which could be alkylated with isobutane. Dehydrogenation of isobutane to isobutylene in refineries for subsequent alkylation isn't likely to occur. The reasons are that isobutane is highly refractive and other gasoline ingredients with high-
octane values, such as toluene, are in good supply at low costs. Coincident with a fresh look at the present low prices for η-butane is the associated question of how long these low prices, in terms of 1968 dollars, will continue. The answer depends on numerous factors, including the politics of the oil import control pro gram and the trend toward lower con centrations of ethane and heavier hy drocarbons in the natural gas pro duced in the U.S. Opinion on the Gulf Coast is that butane prices will be low for about three more years. After 1970, the growth in demand for all of the liquefied petroleum gases for fuel and chemical uses could de plete the inventories of butane and propane, which can now be considered excessive according to current prices. Some chance exists that butane will still be in excess in 1971 and later if fuel and chemicals do not grow as fast as would be expected from low prices. Besides the price of butane as a raw material, the physical facilities of a given olefin plant can influence how much butane, if any, will be used. Under conditions of high-severity cracking—temperatures of 1500° to 1600° F. are used in most modern ole fins plants—yields of heavier coproducts from butane increase rapidly. This means that the plant must have the recovery facilities downstream from the furnaces to produce the coproducts economically. Butane feed can add a unique cost to recovery of products from cracking. The unreacted part of the feed shows up in the C 4 stream and dilutes the more valuable butadiene and butènes
ETHYLENE PLANT. This Humble Oil plant makes ethylene from ethane and propane. But with low spot prices for butane, producers are considering a switch to butane as a feedstock
present. A larger debutanizer would be needed and operating costs would be increased because of the separation of large quantities of C 4 , s. Yields of ethylene drop precipitously as butane is substituted for propane. As a result, a much greater amount of butane must be used to produce the same amount of ethylene with the attendant even greater increase in the quantities of coproducts than occurs if just equal amounts of butane or propane are fed to the furnaces. Usually, the capacity limit of one or more of the recovery units downstream quickly becomes the bottleneck as the fraction of butane is increased in the feed. Sometimes, these bottlenecks are not serious and can be handled with minor changes in mechanical equipment. Some reduction in ethylene output can be accepted sometimes and compensated for by the larger amounts of propylene produced, if a recovery unit can't handle JUNE 10, 1968 C&EN 39
IBM needs 6 types of technicians to help advance the art of microcircuitry· (You may be one and not know it·) If you're a technician in the field of electronics, electro-mechanical design, chemistry, metallurgy, materials or physics, your background and experience may be more valuable than you ever imagined. With training, you could help IBM scientists and engineers advance the art of microcircuitry. Here at the IBM Components Division, we are working at the state-of-the-art level in the development and fabrication of microcircuits. And the smaller the circuits become, the larger the industry (and your opportunity) grows. Microcircuitry has stepped beyond electronics alone. It now encompasses electro-mechanical design, chemistry, metallurgy, materials and physics. If you have experience in any of these fields, and are otherwise qualified, we will train you in any other area you need. At IBM you'll find a wide range of company-paid benefits and a variety of educational opportunities, including a Tuition Refund Program. We're located in East Fishkill, N. Y, just 65 miles north of Manhattan. You and your family can enjoy the pleasant combination of living in the country while being near enough to the city to enjoy it. If you want more information, please send a letter or resume, briefly describing your background and experience to Don Carmichael, IBM Components Division, Dept. BF4002, East Fishkill Facility, Route 52, Hopewell Junction, New York 12533.
IBM.
An Equal Opportunity Employer
40 C&EN JUNE 10, 1968
all of the heavier coproducts which result from using butane as a feedstock Plants which are designed to handle feedstocks heavier than ethane and propane, such as Mobil's plant at Beaumont, Tex., Union Carbide's plant near Taft, La., and Shell's plane being built at Deer Park, Tex., could handle increased butane in the feed with little trouble. (Carbide's plant is designed for naphtha in part, but is not using it yet. ) Butane feed apparently would most seriously affect plants which were designed to operate on ethane or ethanepropane mixtures with high (75%) ethane fractions. Typical of a new ethane-feed plant is the one which Continental Oil recently put on stream at Lake Charles, La. The size of downstream recovery facilities, and, in some cases the existence of them, would limit use of butane to very low levels. The severity of cracking conditions used with ethane in modern plants is greater than for other feedstocks. Butane would be overcracked under these conditions. And if the conditions were made less severe, recycle of increased quantities of unreacted ethane would increase operating costs. Prospects for any big reduction in the cost of making ethylene using nbutane are slim, even if moderately optimistic values are given to the additional coproducts. If butane were used in large enough amounts to give a significant—up to 300%—increase in coproducts, prices of these would fall or at least not continue to rise as propylene has done. On balance, the economic gain from lower raw material costs may be more than offset by the lower values the producer gets for the products. This situation of product selling prices declining faster than costs drop may last while overcapacity exists in the ethylene industry. Today the U.S. ethylene manufacturing industry has a demand for about 70% of its installed capacity. Some improvement might occur in 1969 and high use of in-place capacity should be reached in 1971, judging by announced additions of producing and consuming capacity. Possibly the present look at economics and technology of making olefins using butane will go beyond the near-term objective of cutting costs. Decisions might be made on future olefins capacity which will be designed with flexibility to use raw materials ranging from ethane to naphtha, depending on price and availability of these materials at any given time. Part of the final answer includes what the demand for propylene will be.
