This is going to be a simple story of how you take one kind of gas from over here, and another kind from over there, and add a touch of this and a dash of that—and get aviation gasoline.
It’s the story of the Arabian American Oil company’s new $7,000.000 alkylation plant at Ras Tanura, "on stream" since June, 1959.
The new plant makes it possible to manufacture in Saudi Arabia the aviation gasoline that formerly had to be imported. It provides a local supply for Saudi Arabian Airlines, Aramco’s aircraft and the several foreign carriers, like SAS, TWA, KLM and Middle East Airlines.
As an added gain, it uses, as part of its raw material, gases previously usable only as feul for the refinery power plant or processing furnaces.
It’s well worth a look-see, especially if you can find a couple of patient engineers like C. V. Copeland and John Santos, and start asking childlike questions. When you’re through, you still won't really understand, but you'll have a fair layman's idea.
Copeland, district engineer, lived with the plant from its pre-blueprint days, and helped build it. Santos operates it.
They assume you know that aviation gasoline must burn smoothly in a very high-compression engine. Ordinary gasoline would explode, or "knock." But, take a very high quality gasoline, mix with alkylate, add a touch of tetra-ethyl lead, and you're in business.
So ... what's alkylate? You get the answers from first one and then the other, so let's make it a composite response:
"Petroleum is a mixture of hydrocarbons—molecules consisting of hydrogen and carbon. Some molecules are called 'normal'; others, 'iso.' For example: (and Santos begins sketching a diagram) hydrogen is 'H;' carbon, C
"This is normal butane, a gas at atmospheric pressure. Liquefied, it's sold as 'bottled gas' in rural areas everywhere. But, refiners can change the molecule so it has the same number of each atom, but arranged differently. Do this to normal butane and it becomes isobutane, also a gas at atmospheric pressure." Santos sketches . . .
"O.K.? Well, there's another difference: molecules like butane and isobutane are called paraffins, and are 'saturated:' each of the four 'hands' of each carbon atom is linked with another atom. (Hydrogen atoms have only one "hand.') Notice in the diagram? But, other molecules, called 'olefins,' are 'unsaturated,' like butylene . . .
"In olefins, one or more carbon 'hand' has nothing to hold: it's restless—never satisfied until it finds a free atom to grab."
So, now we know—in a way— what Santos means when he says:
"Alkylation is the combining—an iso-paraffin molecule and an olefin molecule. The product is called alkylate."
And, there's a ray of meaning when Copeland tells you:
"Alkylate is made here by taking butylene and isobutane, liquefying them, and bringing them together in a reaction chamber in the presence of sulfuric acid catalyst at 35° to 40° F."
The butylene comes as a by-product of the two thermal reformers, whose purpose, being very general and skipping a lot of details, is to make a higher-octane gasoline than you get by distillation.
Part of the isobutane comes from the hydroformer, which has the same purpose as the thermal reformers, except it's a newer process, using a fluid catalyst and making a very high-octane gasoline, known to the technologists as hydroformate.
The rest of the isobutane comes from the light straight-run stabilizers, which strip light gases from naphthas, the part of crude oil used in making gasoline.
So, let's wander around the plant and see how they put things together. We'll start in the control room, where they automatically control and record everything—temperatures, pressures, flow rates, etc.—from the big instrument panel.
With admirable tolerance, Santos relates what's happening, and, happily, we can look out the window and see the equipment he's talking about . . .
"When the "feed streams' reach here, they go first to the surge drums to give us added flexibility in controlling flow rate.
"Now, at this point, the streams contain certain gases that mustn't be in the feed. So, the isobutane goes first to the depropanizer, then to the de-isobutanizer—the tallest column out there: 160 feet high. It has 60 perforated trays, and isobutane is separated out at about 85 per cent concentration.
"The olefin stream is sent to the olefin splitter column that separates out the desired butylene."
Now, the streams are caustic-washed to take out hydrogen sulfide and vile-smelling mercaptans . . . cooled . . . and now:
Isobutane and acid enter at the end of the horizontal reactor drum, butylene at the top—and then there's action. Out of the turbulence comes what you were after—alky-late—plus excess isobutane, which is separated out and re-cycled through the reactor.
The alkylate, after a water wash, goes to the debutanizer, and then to its final stage: the re-run tower, where the light part is separated from the heavy. The former goes into aviation gasoline; the latter is blended into automotive fuel.
So ... that's the story of the alkylation plant. It's designed to make 1,210 barrels daily, using the M. W. Kellogg process.
And, now we're ready to get finished aviation gasoline. Remember that very high-octane gasoline from the hydroformer: the hydroformate? Well, we take the very choicest "cut" of this, and we take the alkylate, and pump them both, in the desired proportions, to a mixing tank described by Copeland as "sort of like a Waring blender."
Here, tetraethyl lead is added—about 4.5 cubic centimeters per gallon; and, when the mixing's over, it's aviation gasoline. Two grades are made: one for engines with high requirements; the other for those that are less demanding.
But, making the aviation gasoline is only part of the job: the rest is checking it. Samples of each batch are put through an elaborate test engine to make certain it will yield the specified power.
All in all, you might say it's a bit more involved than whipping up a batch of hollandaise sauce.