TECHNOLOGY
Unleaded gasoline: anxiety for the refiner Restricting lead alkyls as an antipollution measure would result in higher capital investment for refineries Petroleum refiners across the country are taking a hard look at their processing technology and refinery economics. They are spurred by a dismaying thought—possible restrictions that might end or radically reduce use of lead alkyls as additives to improve antiknock qualities of gasolines. Such restrictions could result from the clamor about lead as a pollutant in the atmosphere, though no scientific evidence yet shows that lead or its compounds exists in amounts large enough to present a public health problem (C&EN, Dec. 20, 1965, page 17). The impact of any restrictions or of
even a voluntary reduction in the amount of lead alkyls used could be significant to motorists, to oil and chemical companies, and to engineering and equipment companies. Much of this impact would be economic. But it could also affect the petroleum industry's ability to meet emergency needs for products and for conservation of crude oil. If restrictions should come about, refiners needn't look beyond their own gates for help in keeping performance of gasolines in engines at current levels. At least for the short term, the burden will be theirs.
Octane ratings define antiknock qualities Several types of octane ratings define antiknock qualities of gasolines and gasoline components. Research, motor, and road octane ratings are generally considered important by most refiners and others concerned with gasoline and engine performance. In addition, clear defines the octane rating of a material without antiknock additives. Usually determined as a research octane number, the clear rating is used to specify intermediates and some refinery products. Research and motor octane ratings are determined in the laboratory using a specially designed single-cylinder engine that has a variable compression ratio. Laboratory tests for motor gasolines follow procedures developed by the American Society for Testing and Materials. In testing, a gasoline or other hydrocarbon is compared with standard reference fuels blended from n-heptane and isooctane (2,2,4-trimethylpentane). n-Heptane is given a clear rating of zero, and isooctane a clear rating of 100. Research octane rating is determined with the test engine running at 600 r.p.m., and the motor octane rating at 900 r.p.m. The research rating is a higher octane number. Road octane rating is measured either in a car on the road or on a chassis dynamometer, or it is calculated from research and motor octane numbers. Many factors can influence the relationship of one octane number to another. Also, octane ratings of various hydrocarbons are not necessarily additive for calculating octane ratings of a blend. The difference between research and motor octanes, called sensitivity varies with different hydrocarbons. For example, alkylate contributes less sensitivity to gasoline than does reformate. Composition of a gasoline also determines the effect lead alkyls will have in improving antiknock qualities. Generally, lead alkyls increase antiknock ratings most for saturated hydrocarbons and least for olefinic and aromatic stocks. Also, as concentration of lead alkyls increases, the effectiveness of the alkyls in raising antiknock ratings diminishes. Sulfur radically reduces the effectiveness of lead alkyls, so refiners place limits on sulfur content. For example, the average sulfur contents of gasolines sold in the U.S. during 1964 were 0.025% for premium gasoline and 0.045% for regular gasoline.
62 C&EN MAY 2, 1966
Excluding an unlikely reduction of engine compression ratios, some minor compensation—one to four octane numbers—could come from relatively simple mechanical modifications of engines. These would be in the combustion chamber or intake manifold. Minor help could also come from improved lubrication oils. But, according to John M. Clark, Jr., of Southwest Research Institute, important mechanical changes in engines—ones which might reduce antiknock requirements—are probably five years away. Currently, the only domestic marketer of an unleaded gasoline is American Oil, a Standard Oil (Ind.) subsidiary. Its gasoline, called a super premium, generally sells at retail for 1 cent per gallon more than other companies' premiums. American Oil has begun a major expansion program at its refinery at Texas City, Tex., including a 50,000 bbl.-per-day extraction unit to produce aromatics, most of which will go into more unleaded gasoline. Technology adequate. Oil companies won't need to develop new refining technology to make unleaded gasolines that give antiknock performance equal to present levels. Currently available commercial processes can make gasolines required for any volume-produced automobile in the world—but at a price. The capacity needed to make higher octane components would be more than that required to keep up with normal expansion in leaded-gasoline sales. Industry estimates of costs for such new capacity vary. The head of Ethyl Corp.'s refinery technology division, William W. Sabin, has said that the U.S. refining industry would have to invest about $3 billion in new processing facilities to meet demands for gasolines without lead antiknock additives. This is roughly a third of the industry's current total investment in refinery process facilities. On the other hand, M. J. Sterba, assistant to the senior vice president of Universal Oil Products, puts additional capital investment at $1.5 to $2 billion. Both Mr. Sabin and Mr. Sterba estimate that the industry currently spends about $500 million annually for refinery expansion and modernization.
It's the final consumer, however— the motorist—who will be paying most of the additional cost. Based on UOP and Ethyl Corp. data, refinery-gate cost works out to an additional 1.1 to 2.6 cents per gallon of gasoline. At Ethyl Corp.'s figure of 2.6 cents per gallon, the total annual increase in gasoline cost becomes about $2 billion. A host of qualifying factors influence
the actual cost, however—refinery location, size, and age, and, far from least, expected return on investment. Motorists may be partially compensated by saving on auto maintenance. Spark plugs, valves, and mufflers will last longer. Also, a minor gain in gas mileage might result from higher energy content due to the higher density of unleaded premium gasolines.
Eliminating lead alkyls could have other effects on gasoline performance. Ethyl Corp. suggests that premium gasolines would become less volatile, have poorer warm-up properties, and produce more hydrocarbon emissions during engine warm-up. Regular gasolines without lead alkyls would become more volatile and more likely to cause carburetor icing and vapor lock.
Three routes to high-octane gasoline. Cracking
Specific details of catalytic cracking vary somewhat with the particular process. Generally, however, each has a reactor where cracking takes place at around 900° F. and 10 p.s.i.g. in the presence of catalyst. Coke which deposits on the catalyst is burned off in a regenerator, providing heat for the reaction. Petroleum fractions heavier than gasoline make up the feed. Yield of gasoline is about 45 to 55% of the feed. Small molecules —butane, butylene, propane, propylene, and dry gas—account for about 20%
Standard Oil (Calif.) Richmond refinery
Reforming
Depending on the particular process, reforming reactions are carried out on a variety of naphthas at about 800° to 1000° F. and 200 to 800 p.s.i. The main product is aromatics, resulting from naphthene dehydrogenation and isomerization and paraffin dehydrocyclization. In a typical reforming process, for example, a naphtha feed containing 42.7% paraffins, 0.7% olefins, 37.8% naphthenes, and 18.8% aromatics is reformed into a product containing 39.1% paraffins, 1.1% olefins, 3.4% naphthenes, and 56.4% aromatics
American Oil Texas City refinery
Alkylation
In alkylation processes, butylenes, propylenes, and amylenes are fed along with isobutane and hydrogen fluoride or sulfuric acid catalyst to a reactor. In one process, reaction takes place at 70° to 100° F. Some processes take advantage of autorefrigeration to maintain low temperature by using heat of vaporization to vaporize some of the hydrocarbons. The product alkylate contains high-octane, branched-chain hydrocarbons
Tidewater Oil Delaware refinery
MAY 2, 1966 C&EN" 63
One of a series
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Hydrogen Bonds-•Clean Engines +Dirty Oils
One way to keep an engine clean inside is to keep the oil dirty. Oil additives—dispersants—help to do this. But how? Chemists have postulated that one way is through a dispersant's ability to form hydrogen bonds with polar oxidation products—products such as acids and solids that result from cooking the oil and burning the fuel during engine operation. But experimental evidence has been scarce. Now GM Research has evidence that ashless dispersants of both high and low molecular weight do form hydrogen bonds with polar liquids, tying the polar molecules to the dispersants. Using alcohols as polar molecules—representing oxidation products—one of our chemical engineers studied the effects of adding various concentrations of two ashless dispersants (an aminoalkenylsuccinimide, with low molecular weight, and a high molecular weight methacrylate-pyrrolidone copolymer). He monitored the interactions, using infrared spectroscopy . . . and found that hydrogen bonds did form between the dispersants and the hydroxylic hydrogen atoms of the alcohols. In an engine oil, hydrogen bonding apparently enables the dispersants to form protective shrouds around the polar oxidation products, keeping any sludge in the oil, preventing sludge deposition. We knew that dispersants worked. Now we have a better understanding of how. But that's not the end. From the new understanding may come a better product . . . and even cleaner engines.
General Motors Research Laboratories Warren, Michigan
48090
UOP suggests that unleaded gasolines generally contain less sulfur and olefins and are clean, stable gasolines which reduce engine maintenance. At any rate, little is known about the potential air pollution characteristics of these gasolines. For low- or unleaded gasolines, these changes in properties, and in clear-octane ratings, would stem from changes in chemical makeup. Generally, composition would shift toward a higher fraction of branched cyclic hydrocarbons. In particular, aromatics would increase, along with highly branched paraffins and naphthenes. There would be a lower content *>f straight-chain paraffins and olefins. Three main processes are used by refiners to make high-octane gasolines—catalytic reforming, catalytic cracking, and alkylation. UOP estimates that 8 5 % of U.S. crude oil is processed in refineries which use all three, and that 9 5 % is handled in refineries having at least catalytic reforming and cracking units. Aromatics made. Mostly, catalytic reforming would get the nod for making more aromatics. In this process, several reactions take place. Dehydrogenation and isomerization of naphthenes along with dehydrocyclization of paraffins give aromatics. More branched-chain paraffins come from paraffin isomerization. And hydrocracking produces small hydrocarbon fragments which have higher octane ratings. All U.S. catalytic reforming processes, such as UOP's Platforming, use platinum as the key ingredient of the catalyst. Ethyl Coip. estimates that completely unleaded gasolines would require double the catalytic reforming capacity along with half a million troy ounces of platinum in the initial catalyst charge for new units. Thus, a strong possibility is worse shortages of platinum and higher costs for the metal. Highly aromatic product streams from reformers can have unleaded octane ratings above 100, as measured by the research method. The bookkeeping value of t h e product varies widely, depending on economic and property factors. The range may b e 10 to 13 cents per gallon. The second major method for rebuilding hydrocarbons—thermal or catalytic cracking—is used in almost every U.S. refinery of any size. In making gasoline, the original thermalcracking process has almost entirely given way to catalytic processes using fluidized or moving catalyst beds. Catalytic cracking of petroleum fractions heavier than gasolines produces light olefins and isobutane in large amounts, along with branchedchain paraffins and cyclics in the gaso-
line range. Temperature during cracking is usually held between 875° and 950° F., depending on the process and operation. Coke deposits on the catalyst and is subsequently burned off in a regenerator. The yield from cracking a highquality feed is a stream that includes 45 to 5 5 % gasoline. Clear researchoctane rating of the gasoline is 92 to 93. Often, gasoline from catalytic cracking is reformed to give a product with still higher octane number. The value of gasoline fractions from cracking is about 10 cents per gallon, before reforming. Alkylation is the third major process for rebuilding hydrocarbons to make high-octane gasoline components. Commercial processes use either sulfuric or hydrofluoric acids as catalyst. Alkylation offers several advantages to refiners. It upgrades olefins and isobutane to gasoline, and it uses one molecule of valuable olefins instead of two as do the older polymerization processes. Also, it makes a product having high motor-octane number. Butylenes are the preferred olefins for alkylation with isobutane, but their supply is limited and more propylene is being used. This trend should continue, since new hydrocracking capacity coming on stream makes even more isobutane available for alkylation. Alkylates have a clear research-octane rating in the 90 to 95 range. Motor-octane ratings are similar. About half of a typical refinery alkylate is C 8 paraffins, including 2,2,4-trimethylpentane (isooctane, which has an assigned octane rating of 100). In value, most alkylates fall between 10 and 14 cents per gallon. Others used. Besides the three majors, many other refining processes are used either to make gasoline fractions or to make feedstocks for reforming and alkylation. Among these are isomerization and hydrocracking. Isomerization is mostly used to convert n-butane to isobutane for alkylation. It is also used to make isopentane. Hydrocracking makes a heavy gasoline fraction of high ring content and a fraction with a high content of branched pentane and hexane in addition to isobutane and other light hydrocarbons. The heavy product from a hydrocracker is fed to a reformer. Most large refineries use all of these processes in one combination or another. Extensive recycling and interchange of streams between units has developed, as refiners try to use every trick available to lower processing costs and to gain higher quality products. This will continue regardless of what happens to the amount of lead alkyls used.
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NEW LARGE PORT VALVES AND FITTINGS TO 60,000 PSI RELIABILITY, COMPACTNESS INTERCHANGEABILITY, EASE OF OPERATION Now, traditional AE dependability in the all-new LP-Line for pipe bores through 1 % " with ratings of 30,000, 4 0 , 0 0 0 , 50,000 and 60,000 p s i . Strong—bodies are alloy steel forcings; connection cone rings, valve stems, seats are stainless steel. Compact—valve block design results in weight savings to 4 0 % . Interchangeable—all valve and fitting connections use identical flanges and cone rings. Easy to use—larger port manual valves have reduction gearing tailored to operating torque . . . hydraulic, air or motor operators, with or without manual override, also available. Send for LP-Line Bulletin. Autoclave Engineers, Inc., Erie, ^ Pa. 16512. ^&~
AUTOCLAVE ENGINEERS Designers and Manufacturers of High Pressure Equipment MAY 2, 1966 C&EN 65
