. . . gatheredby Harold Wittcoff
An Economic Anomaly One 01 rhr ''l~u'i"181 indu..tr~~l chvmi:rry i j thnt pn,p?.lcne
is nlua). chwpvr rnnn t.1 h\.lc.nr. Sor 5,) in 1.Jh2 u , l i ~ n rhe priuv of propylene reached 21.5 cents per pound and the price of ethylene fell to 17.7 cents per pound. Why the reversal? When petroleum feedstocks such as ethane, propane, and higher hydrocarbons are steam cracked to make ethylene, propylene is always a co-product. Furthermore propylene unlike ethylene is a co-product in catalytic cracking. Thus, large quantities of it are available. Of the roughly 30 billion pounds which come from these sources about 13 billion pounds go to the chemical industry whereas 17 billion pounds are reacted with isohutane in a Friedel-Crafts reaction to give hranched chain hydrocarbons known as alkylates which enhance the octane number of gasoline. The switch in pricing shows the vagaries of modern industrial chemical economics and is not easy to explain. One explanation is that the need for ethylene decreased because of the recession in 1982. Coupled with this decreased need were huge stockpiles of ethylene. Thus, refineries reduced their steam cracking activities in order not to add to the ethylene glut. In so doing they did not produce propylene which had not been stockpiled hecause the demand for propylene derivatives was not depressed. This created a shortage of propylene and the price went up. The fact that the stockpiles of ethylene only slowly dissipated depressed its price. But this is only one explanation. The major use of propylene, as stated above, is for alkylate for casoline. Less alkylate is needed now because the consumption of gasoline has decreased. This
plained.
Cost-Factors in Choosing an Alkylate for Unleaded Gas Alkylate is a term applied to a mixture of hranched chain hydrocarbons included in gasoline in order to enhance octane number. Alkylate has become very important for nun-leaded gasoline since its content has been increased to compensate in part for the absence of lead tetraethyl. There are two sources of alkylate: the reaction of propylene with isohutane and the reaction of hutene-l or butene-2 with isohutane in the presence of a Friedel-Crafts catalvst. Of course in each case s lsrre ~iurnbvroi i;mier, r c s ~ ~ Alkvlnte lt. ir.m rht 1,urrlw; is normally ~~rriPrred 1,) n k y l t ~ t In8111 ~. ~ r .. ~ ~ u d \Vhy m c .i. 1hk" . An obvio;; answer is that the former are more highly hranched and accordingly have higher octane numbers. This is correct. However, there is still another reason which the academic chemist would he hard pressed to find. The reaction of the two C4 molecules takes less catalyst than does the reaction of propylene with isobutane simply because the molecular weight of the Cq unsaturate is greater than that of the CS unsaturate. This lesser use of catalyst is an economic advantage and thus an important consideration to the industrial chemist.
Decreased Oil Imports How much oil does the United States import? In 1982 the average was about 4.5 million barrels per day. Five years earlier, in 1977, the United States imported 9.2 million barrels per day. Why the difference? Depressed business conditions and decreased gasoline consumption certainly comprise one answer. But another is conservation. Here is a dramatic example of how profligacy can be curbed when economic considerations demand it.
Volume 60 Number 7 July 1983
579
